EMRP – Earth Magnetism & Rock Physics

EGU22-6157 | Presentations | MAL21 | EMRP Division Outstanding ECS Award

MCADAM: A continuous paleomagnetic dipole moment model for the past 3.5 billion years using the PINT v8.0.0 database 

Richard Bono, Greig Paterson, and Andrew Biggin

Earth’s magnetic field is a long-lived phenomenon generated by dynamo processes occurring in the liquid core. Understanding how the strength of the field changes in time and space is critical to gaining insight into processes in Earth’s core and deep interior. The publication of field strength estimates represents a significant output of the paleomagnetic community, with efforts spanning several decades and dozens of research groups. Recently, the site-mean absolute paleointensity database PINT (www.pintdb.org; Bono et al., GJI, 2022) received a major update to include data published up through 2019 and fully integrates the Quality of Paleointensity (QPI) assessments for 94% of the database. Interpreting the paleointensity record as a continuous record of Earth’s field is challenging because of the non-uniformly spaced, often sparse, data records and the combination of natural variation of field strength due to secular variation and measurement uncertainty. Here, we have used the PINT database to construct a continuous paleomagnetic axial dipole moment model spanning 0.05 to 3500 Ma, MCADAM v1.0 (Monte Carlo Axial Dipole Average Model). The dipole moment model applies three resampling approaches: a non-parametric resampling (akin to a bootstrap) of site-mean records, a Monte Carlo simulation of site-mean estimates using age and paleointensity means and uncertainties, and LOWESS smoothing with an adaptative kernel width. These methods are combined to provide posterior predictions of axial dipole field strength and allow for estimation of the median field with confidence bounds. This approach can reproduce the recent (0-2 Ma) field that matches PADM2M (Ziegler et al., GJI, 2011) as well as salient field intervals (e.g., high fields associated with superchrons) during the Phanerozoic. The model also reveals changes in field strength during the Precambrian which may be used to help constrain dynamo simulations and thermal evolution models of Earth’s core.

How to cite: Bono, R., Paterson, G., and Biggin, A.: MCADAM: A continuous paleomagnetic dipole moment model for the past 3.5 billion years using the PINT v8.0.0 database, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6157, https://doi.org/10.5194/egusphere-egu22-6157, 2022.

EGU22-8972 | Presentations | MAL21 | Louis Néel Medal Lecture

A Laboratory Perspective on Earthquake Nucleation 

David Lockner

Brittle failure of intact rock and frictional sliding on faults are closely related. Much of my early career studying brittle failure using acoustic emission techniques was helpful in providing insight into processes associated with faulting and earthquakes. While I was focusing on failure processes with my colleague and mentor, Jim Byerlee, the basic tenants of what is referred to as rate- and state-dependent friction (RS) were being developed literally next door by Jim Dieterich with Andy Ruina and many others. It was a remarkable period in Menlo Park in the late ‘70s and ‘80s for which I had only limited appreciation at the time. While it is easy to reminisce, it is more useful to take stock of our current understanding of earthquake processes; what we have achieved and how very much farther we have to go. For example, one long-standing goal that remains elusive is earthquake prediction. While long term forecasting is clearly improving, prediction within hours to days remains out of reach. From a laboratory perspective, with tight control of fault roughness, stress, temperature, fluid pressure and other variables, prediction of timing and magnitude are possible, but with notable restrictions.

Rate- and state-dependent friction, for example, has been useful in the analysis of numerous earthquake-related phenomena including earthquake nucleation, earthquake triggering, slow slip, and repeating earthquakes. At the same time, it should be recognized that the RS model was developed using dry, planar laboratory faults at modest normal stress and limited total displacement. Along with the many successes of RS friction, it is useful to consider some of the limitations. Examples include (1) strain hardening- observed in most laboratory experiments as initial fault surfaces undergo rapid and irreversible changes in roughness and fault gouge properties; (2) melt formation or flash heating – where self-heating due to rapid sliding alters surface properties; and (3) hydro-mechanical coupling of low permeability faults where frictional heating increases pore fluid pressure or changes in porosity lead to transient dilatancy-strengthening or compaction-weakening.

I will present laboratory observations of fault strength evolution that are beyond the scope of standard RS formalism. Examples include constant loading rate tests near critical stiffness in which deformation mode spontaneously jumps between sequences of stable slow-slip oscillations and unstable stick-slip. In a second example with a hydraulically isolated, water-saturated fault gouge, incremental increases in slip rate lead to dilatancy, pore pressure decrease and fault stabilization. However, larger jumps in velocity lead to porosity collapse, fluid pressurization and fault instability. Hydrothermal slide-hold-slide tests at 200 °C, 10 MPa deionized water pressure and 30 MPa confining pressure produce the usual log-linear healing rate for hold times less than 5,000 s. Longer hold times, however, show increased weakening. Apparently, an overall time-dependent weakening of the fault surface occurs that dominates instantaneous fault strengthening for long hold periods and requires hundreds of microns of slip to be erased. These examples suggest that extrapolation of R/S models from idealized laboratory conditions to natural fault conditions may lead to erroneous predictions.

How to cite: Lockner, D.: A Laboratory Perspective on Earthquake Nucleation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8972, https://doi.org/10.5194/egusphere-egu22-8972, 2022.

EMRP1 – Rock and Mineral Physics

EGU22-66 | Presentations | ERE5.2

Influence of brittle deformation on the permeability of granite: assessing the geothermal potential of crustal fault zones 

Lucille Carbillet, Michael J. Heap, Hugo Duwiquet, Luke Griffiths, Laurent Guillou-Frottier, Patrick Baud, and Marie Violay

Economically viable geothermal systems rely on the efficiency of fluid circulation and heat transfer. Permeable fault zones are therefore excellent candidates for geothermal exploitation. In crustal fault zones, hot fluids from depths that correspond to the brittle-ductile transition are brought to the surface via crustal-scale permeable fault zones and may therefore constitute a new kind of geothermal system. To assess their geothermal potential, we measured the permeability of reservoir rock during deformation to large strains (up to an axial strain of about 0.1) in the brittle regime - fault formation and sliding on the fault - by performing triaxial experiments on samples of well-characterised Lanhélin granite (France). Prior to deformation, samples were thermally-stressed to 700°C to ensure that their permeability was sufficiently high to measure on reasonable laboratory timescales. All experiments were conducted on water-saturated samples under drained conditions, at a constant pore pressure of 10 MPa and confining pressures of 20, 40, and 60 MPa (corresponding to a maximum depth of about 2 km), and at room temperature. Our data show that permeability decreases by about an order of magnitude prior to macroscopic shear failure. This decrease can be attributed to the closure of pre-existing microcracks which outweigh the formation of new microcracks during loading up to the peak stress. As the macroscopic shear fracture is formed, sample permeability increases by about a factor of two. The permeability of the sample remains almost constant during sliding on the fracture to large strains (corresponding to a fault displacement of ~7 mm), suggesting that the permeability of the fracture does not fall below the permeability of the host-rock. The permeability of the sample at the frictional sliding stress is lower at higher confining pressure (by about an order of magnitude between 20 and 60 MPa) but, overall, the evolution of sample permeability as a function of strain is qualitatively similar for confining pressures of 20−60 MPa. These experimental results will serve to inform numerical modelling designed to explore the influence of macroscopic fractures on fluid flow within a fractured geothermal reservoir.

How to cite: Carbillet, L., Heap, M. J., Duwiquet, H., Griffiths, L., Guillou-Frottier, L., Baud, P., and Violay, M.: Influence of brittle deformation on the permeability of granite: assessing the geothermal potential of crustal fault zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-66, https://doi.org/10.5194/egusphere-egu22-66, 2022.

EGU22-981 | Presentations | ERE5.2

Friction behavior of gabbro under hydrothermal conditions 

Wei Feng, Lu Yao, Rodrigo Gomila, Shengli Ma, and Giulio Di Toro

Fault friction is one of the most significant parameters controlling fault slip behavior and earthquake mechanics. Great success has been achieved in understanding the stability of fault slip, nucleation of earthquake and dynamic weakening mechanism in the past decades by performing low (~1 μm/s, sub-seismic conditions) to high (~1 m/s, seismic conditions) velocity friction experiments. However, extrapolating these experimental results to nature remains limited. In fact, for low velocity experiments, usually performed with tri-axial machines, though the hydrothermal conditions can be imposed, the shear displacement is limited to several millimeters neglecting the effect of cumulative displacement. For high velocity experiments aiming at reproducing coseismic fault slip, the implementation of hydrothermal conditions has been hindered by technical difficulties leaving high-velocity friction property of faults under realistic crustal conditions still ambiguous.

Here we exploited a Low to High Velocity rotary shear apparatus (LHV) equipped with a dedicated hydrothermal pressure vessel installed at the Institute of Geology, China Earthquake Administration, to investigate the frictional behavior of gabbro under realistic hydrothermal conditions. The samples were sheared at effective normal stresses of 10 MPa and 20 MPa, velocities (V) spanning from 1 μm/s to 0.1 m/s, displacement up to 3 m, under temperature conditions (T) up to 400 ℃ and pore pressure (Pf) up to 30 MPa. Our results showed that at T = 300 ℃ and Pf = 10 MPa (pore fluid as liquid), dramatic slip weakening happened at all tested velocities. At slip initiation the friction coefficient increased sharply to a peak value (~0.7±0.05), then decayed toward a residual value of ~0.35. Instead at T = 400 ℃ and Pf =10 MPa (pore fluid as vapor), we observed that friction remained high (~0.7) at V < 10 mm/s and slip weakening only occurred for V ≥ 10 mm/s. For experiments at T = 400 ℃ and Pf =30 MPa (pore fluid in supercritical conditions), slip weakening behavior occurred in most cases. The evolution of friction coefficient with displacement was complex, e.g., two peaks, large variations. Moreover, comparative experiments conducted at relatively low temperature suggested that mechanisms leading to the dramatic weakening under such a wide velocity range could be closely linked with both fluid-rock interactions and the physical state of the fluid. However, what exact fluid-rock reactions are involved is still an open question, which will be investigated by further microstructural and mineralogical analysis. The unique frictional behavior observed in this study challenges the results obtained from small-displacements experiments in many aspects and improves our understanding on friction behavior of faults in geothermal applications.

How to cite: Feng, W., Yao, L., Gomila, R., Ma, S., and Di Toro, G.: Friction behavior of gabbro under hydrothermal conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-981, https://doi.org/10.5194/egusphere-egu22-981, 2022.

Upper Cretaceous (Turonian and Cenomanian) carbonates in the Münsterland Cretaceous Basin, NW Germany, have become a target for geothermal energy production in recent years. These carbonates are present at depths of up to ca. 1,800 m in the region of the city of Münster in the center of the basin (e.g. Münsterland-1 well) and at depths beyond 2,000 m in the so-called Vorosning Depression. They represent the shallowest calcareous strata within the sedimentary succession of the Münsterland Basin and the underlying Rhenish Massif. Previous industrial drilling campaigns mostly focused on potential hydrocarbon gas reservoirs of the Upper Carboniferous. In the context of geothermal reservoir exploration, analog studies in outcrops of the Cretaceous carbonates are a prerequisite for reservoir quality assessment since subsurface/in situ data of these stratigraphic units, and especially petrophysical properties, are very sparse, not accessible or even absent in some areas. Investigations of quarries with Cretaceous carbonates mostly focused on paleontological and facies related research in the past rather than on their petrophysical properties. Three quarries in the Lengerich and Oerlinghausen areas, all at the northern margin of the basin, were now sampled for petrophysical laboratory experiments of Cenomanian and Turonian rocks. Additionally, scanline investigations, which involve collecting information such as length and aperture and others of each fracture along a line intersecting the rock mass, capturing of Unmanned Aerial Vehicle (UAV, commonly called drones) footage and laser scanning was performed at the three Cenomanian outcrops in Lengerich and one Turonian outcrop in Oerlinghausen. Further UAV footage and laser scans were collected for other outcrops within the quarries. The facies of the investigated rocks are expected to be comparable to what can be anticipated in the center of the Münsterland Basin according to the current paleogeographical understanding. Their analysis can thus be helpful in predicting the conditions that may be encountered in the central part of the basin. However, since the data was collected at the northern margin of the basin, the influence of the Osning Fault Zone (Upper Cretaceous inversion tectonics) has to be taken under consideration when further interpreting the data. The drone footage was processed, and Virtual Outcrop Models (VOM) were created using Agisoft Metashape. The point clouds of both, the laser scanning and processed UAV footage, were analyzed using the open-source package CloudCompare with its Facets and Compass plugins. The plugins allowed the detection of differently oriented fracture sets in the point clouds. This allowed to characterize fracture distributions and the comparison between the virtual outcrop data and the scanline data. Subsequently, the parameters of the fracture distributions of these structural features together with the laboratory measurements on bulk petrophysical properties were combined in a discrete fracture network (DFN). This representation of the reservoir, and in particular the 3D distribution of permeability, will be used for reservoir analog modelling to characterize fluid flow in the subsurface.

How to cite: Slama, S., Jüstel, A., Lippert, K., and Kukla, P.: Characterizing fracture networks and petrophysical bulk properties of carbonates from the margin of the Münsterland Cretaceous Basin, NW Germany, from outcrops, virtual outcrop models and laboratory testing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2503, https://doi.org/10.5194/egusphere-egu22-2503, 2022.

EGU22-3309 | Presentations | ERE5.2

CT scan of a small-scale fault network: 3D fault geometries and their interpretation 

Inbar Vaknin and Andy Nicol

Fault surfaces and networks have been shown to have complex geometries. Outcrop observations are typically two-dimensional and limited in size by the exposure dimensions, while three-dimensional (3D) seismic data lack the resolution to characterize and quantify fault complexities on length scales less than a decameter. Defining the geometries of faults and their networks (high-resolution in 3D) is critical for understanding the interactions between faults and fluids. This presentation will examine the geometries of a network of small-scale normal faults displacing (by <1 cm) well bedded sand and silt layers in the Mount Messenger and Mohakatino formations in Taranaki, New Zealand. A 3D model of faulting was produced from high-resolution multi-band CT scanner (MARS Bioimaging Ltd.) imagery of a 10x8x3 cm rock sample. The digitally sectioned rock contains calcified fault rock that is distinguishable from wall rock and mapped throughout the rock volume at sub-millimeter scale. Fault-rock thicknesses vary by in excess of an order of magnitude, with greatest thicknesses at fault steps and fault bends. Fault zones comprise a series of lenses that have strike lengths greater than dip lengths and lens shapes that are often elongate parallel to bedding. The fault network is highly connected with branch lines, fault steps and fault bends most often sub-parallel to bedding. These observations suggest that mechanical heterogeneity of beds may partly control the geometries of both fault zones and the fault network. At the time of formation, the interconnected fault network likely increased bedding-parallel permeability (at scales from sub-millimeter and above) along fault zones.

How to cite: Vaknin, I. and Nicol, A.: CT scan of a small-scale fault network: 3D fault geometries and their interpretation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3309, https://doi.org/10.5194/egusphere-egu22-3309, 2022.

EGU22-3414 | Presentations | ERE5.2

Fluid pressure diffusion in fractured media: insights from harmonic and non-harmonic periodic pumping tests 

Nicolás D. Barbosa, Nima Gholizadeh Doonechaly, and Jörg Renner

Fractures can significantly impact fluid flow and pore pressure distribution in the subsurface. Understanding the mechanisms and conditions influencing their ability to transport fluids and to promote pore pressure diffusion is key for many activities relying on fracture-controlled flow such as, for example, enhanced geothermal systems. In situ characterization of these properties is typically done by performing hydraulic tests in selected intervals of a borehole and their interpretation relies on the solution of a linear pressure diffusion equation. However, it has been shown that the hydraulic behavior of fractures as well as the associated near borehole flow regimes can be largely affected by the coupling between the solid deformation and fluid pressure upon injection/production. In this work, we explore these effects by performing a series of harmonic injection tests (HIT) as well as non-harmonic production tests (NHPT) in a packed-off interval of a borehole containing multiple natural fractures. The borehole is located in the Bedretto Underground Laboratory for Geosciences and Geoenergies in Switzerland and penetrates granitic rock mass. The two kinds of tests consist of a periodic repetition of the same injection or production protocol. Flow rates, interval pressures as well as pressures above and below the double-packer probe are recorded at the surface. An important advantage of periodic testing is that it permits a continuous tracking of hydraulic changes during the test. For our study, we conducted a so-called injectivity analysis, in which the phase-shift (time delay) and amplitude ratio between flow rate and interval pressure are used to infer effective hydraulic properties. We performed over 200 periodic tests including both HIT and NHPT with a large range of periods (7.5 s to 1800 s) as well as varying mean interval pressures (~1300 kPa to 2100 kPa) and flow oscillation amplitudes. As a result, we obtained a robust constraint of the radial flow regime prevailing in the fractures. Overall, we found that results from HIT and NHPT are in very good agreement despite the remarkably different injection protocols. For all cases, a prominent and consistent period dependence of phase shifts and amplitude ratios of flow rates and interval pressure was observed, in which both increase as the oscillatory period decreases. Amplitude ratios showed almost no variation with mean interval pressure regardless of the injection protocol. In contrast, a prominent pressure dependence of the phase shifts is captured by the HIT but not the NHPT data. Using the pressure-independent NHPT results, we reconstruct the general hydraulic response of the tested fractured section, which can be well represented by an analytical solution of the pressure-diffusion equation. This general trend explains the HIT data as well, although evidence of significant variations that are correlated with the amplitude of the pressure oscillations points to the predominant role of hydromechanical coupling effects on the fluid pressure diffusion process.

How to cite: Barbosa, N. D., Gholizadeh Doonechaly, N., and Renner, J.: Fluid pressure diffusion in fractured media: insights from harmonic and non-harmonic periodic pumping tests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3414, https://doi.org/10.5194/egusphere-egu22-3414, 2022.

Flow through faults and fractures has been studied extensively in the context of hydrocarbon exploration and production, to understand charge and migration, hydrocarbon column heights and fault transmissibility. Learnings have typically been captured in pragmatic models, such as the Shale-Gouge-Ratio (SGR) concept, providing dimensionless or relative fault permeability definitions based on limited subsurface data.

The resulting coarse predictions are however not suitable for geoenergy applications, including CO2 sequestration (CCS) or underground hydrogen storage (UHS), where injection into a storage reservoir requires assurance that the injected fluids or gases will not leak out of the storage complex via faults or fractured caprocks. The conventional fault seal analyses do not provide this containment assurance.

A new paradigm is required for characterizing faults and fractures in geoenergy projects, focused on derisking leakage of injected fluids and gases along faults. Such approach is not necessarily about accurately predicting the permeability of a fault or fracture, but rather about understanding what geometric properties and mechanical or chemical mechanisms would contribute to either permeable or sealing behaviour of faults. Improved insights in any of these areas would help in screening fault leakage risks in prospective subsurface geoenergy projects.

Analogue data, both from outcrops for geometric fault attributes and from the lab for mechanical and chemical properties, can help gain those fundamental insights into what controls fault leakage. Properties can be quantified and processes studied at a level of detail that cannot be matched by in-situ subsurface datasets, particularly not in the context of geoenergy systems, where operational subsurface projects are still limited. Outcrop studies can help improve our understanding of vertical connectivity, with focus on lower-permeability ductile rocks analogues to typical reservoir seals. Lab studies and in-situ experiments can provide insights into injected fluids such as CO2 or H2 affect the mechanical and chemical integrity of faults and subsequent flow behaviour. For geoenergy systems in particular, experiments should focus on the impact of rapid pressure or temperature cycling. Induced seismicity is another potential threat to containment integrity and requires further research to understand what fault geometries are most prone to reactivation as well as how reactivation affects the sealing behaviour of a fault.

In recent years, integrated studies such as the multi-scale, multiphysics ACT-DETECT project have started to provide some answers to these questions, resulting in novel insights and workflows that provide a first-order fault leakage risk assessment that can be used to identify ideal storage sites. However, with the envisioned increase in the number of geoenergy projects to meet carbon emission reduction targets, the need for more refined screening criteria will increase too as the flexibility in selecting ideal storage locations will decrease.

How to cite: Bisdom, K.: A new paradigm for flow through faults and fractures in the context of geoenergy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3553, https://doi.org/10.5194/egusphere-egu22-3553, 2022.

At the Äspö hard rock underground laboratory in Sweden, six in situ hydraulic fracturing experiments took place at 410 m depth. A multistage hydraulic fracturing approach is tested with a low environmental impact, e.g., induced seismicity. The idea is to mitigate induced seismicity and preserve the permeability enhancement process under safe conditions. The fractures are initiated by two different injection systems (conventional and progressive). An extensive sensor array is installed at level 410 m, including simultaneous measurements of acoustic emissions, electric self-potential, and electromagnetic radiation sensors. The monitoring catalog includes more than 4300 acoustic emission events with estimated magnitudes from the continuous monitoring setup (in-situ sensors between 1-100 kHz). The experiment borehole F1 is drilled in the direction of Shmin, perpendicular to the expected fracture plane. Two electromagnetic radiation sensors are installed and aligned to (i) Shmin and (ii) the expected fracture plane with a sampling rate of 1 Hz and a frequency range between 35-50 kHz. The self-potential sensors are installed at level 410 with a distance of 50-75 m from the borehole F1, including nine measuring probes and one base probe. A second self-potential setup is deployed at level 280 m in the far-field with a distance of 150-200 m from F1. The self-potential data were measured with a sampling rate of 1 Hz. For the first time (to our knowledge), the results of electric and electromagnetic monitoring of two hydraulic stimulation at meter-scale are presented.

How to cite: Haaf, N. and Schill, E.: Electric self-potential and electro-magnetic monitoring of hydraulic fracturing experiments in the Äspö Hard Rock Laboratoy, Sweden., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3837, https://doi.org/10.5194/egusphere-egu22-3837, 2022.

EGU22-6166 | Presentations | ERE5.2

Assessing damage pattern at depth near the Alpine Fault, New Zealand 

Mai-Linh Doan, Virginia Toy, Rupert Sutherland, and John Townend

 

The Alpine Fault is the principal component of the plate boundary through the South Island of New Zealand, separating the Pacific and Indo-Australian Plates. It is recognised internationally as an important site for studying earthquake physics and tectonic deformation, as it produces large (M7-8) earthquakes approximately every 330 years and last ruptured in 1717. Therefore, the fault is considered to be late in its seismic cycle. It accommodates dextral-slip at a rate of 26 mm/yr with reverse slip at a maximum rate of 10 mm/yr in its central part, thus exhumed a fossil ductile shear zone, that was damaged brittlely during its exhumation.

 

The central Alpine Fault is the focus of the Deep Fault Drilling Project (DFDP), sponsored by the International Continental Drilling Project, which takes advantage of its globally rare tectonic situation to determine what temperatures, fluid pressures, and stresses exist within a plate-boundary fault in advance of an expected large earthquake. During DFDP phase II in 2014, an ~ 900 m drilled well that encountered an exceptionally high geothermal gradient (120 °C/km was measured in the borehole), was extensively characterized by repeated electric and sonic logs. These logs enable detailed study of fracture patterns near a major fault. The more than 19 km of logs run within the borehole gathered datasets covering, among others, thermal resistivity, sonic velocities, acoustic borehole imaging, and electrical resistivity. They show that the hanging wall is extensively fractured, explaining the high geothermal gradient measured in the borehole by lateral flow of hot water deep seated in the mountains.

 

We particularly focus on seven dual laterolog logs that provide a robust and reproducible dataset from which to determine the positions and orientations of conductive fractures. From these, different patterns of damage could be identified within the well. A first pattern consists of an extensive and dense pattern of isolated fractures that could be identified throughout the borehole. A second pattern suggests that decametric  zones of low resistivity localize damage and focus thermal anomalies. This suggests hierarchy of damage zone evolution of the damage zone of the Alpine Fault. A possible explanation is an initial phase of diffuse fracturing (pattern 1) that is followed by subsequent alteration of the major shear zone, which focuses fluid and heat flow (pattern 2).

How to cite: Doan, M.-L., Toy, V., Sutherland, R., and Townend, J.: Assessing damage pattern at depth near the Alpine Fault, New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6166, https://doi.org/10.5194/egusphere-egu22-6166, 2022.

The regionalization of hydraulic properties like specific yield/storativity or permeability in fractured crystalline rock is of utmost importance for a variety of applications, such as geothermal and other resources, waste disposal or underground construction. However, accurate predictions for these properties – particularly for undrilled sites – bear a high degree of uncertainty as already direct observations through hydraulic in-situ tests show a variance of about 2 orders of magnitude at any depth (Achtziger-Zupančič et al., 2017).

Permeability-depth relationships using multiple log-log regressions conducted on an extended version of the worldwide permeability compilation of crystalline rocks (roughly 30000 entries in Achtziger-Zupančič et al., 2017; now consisting of about 50000 single in-situ permeability measurements to depths of 2000 mbgs) indicate that depth is generally the most important geological factor, resulting in a permeability decrease of three to four orders of magnitude in the investigated depth range. Specific yield and storativity show a similar but less pronounced depth trend. Beside depth, most influential factors for permeability in crystalline rock are the long-term tectono-geological history described by geological province which locally is overprinted by current seismotectonic activity as determined by peak ground acceleration (Achtziger-Zupančič et al., 2017). Although petrography might be of local importance, only a low impact has been observed for the global dataset, besides lithologies allowing for karstification. Ongoing vertical movements – particularly resulting from glacial isostatic adjustment – alter the permeability trend with depth.

The latter shows distinct trends starting at about logK -14.5 to -14.8 m² at 100 mbgs and showing diversion of about 1.5 orders of magnitude at 1 km depth between areas without significant uplift and areas with uplift of more than 4 mm/y as determined from a probabilistic interpolation of global geodetic measurements (Husson et al., 2018). The difference is attributed either to glacial loading (normal faulting or reactivation) induced destruction preserved during glacial induced rebound and/or uplift-caused horizontal fracture growth which improved connectivity in the rock mass. Areas undergoing subsidence show similar trends like highly uplifting areas which is attributed to efficient normal faulting induced destruction of the rock mass.

References:

Achtziger-Zupančič, P, Loew, S and Mariéthoz, G (2017). A new global database to improve predictions of permeability distribution in crystalline rocks at site scale. JGR: Solid Earth 122(5): 3513-3539.

Husson, L, Bodin, Th, Spada, G, Choblet, G and Kreemer, C (2018). Bayesian surface reconstruction of geodetic uplift rates: Mapping the global fingerprint of Glacial Isostatic Adjustment. J Geodyn 122: 25-40.

How to cite: Achtziger-Zupancic, P.: The influence of glacial induced adjustment and other geological factors on the depth distribution of permeabilities in crystalline rocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7157, https://doi.org/10.5194/egusphere-egu22-7157, 2022.

EGU22-7835 | Presentations | ERE5.2

Fracture energy variations of rocks: a mechanical investigation 

Antoine Guggisberg, Mathias Lebihain, and Marie Violay

Crack propagation is critical for the assessment of the strength of rocks. Linear Elastic Fracture Mechanics (LEFM) theory is commonly used to describe its propagation. However, the variation of the fracture energy, its key parameter, is generally poorly understood as its experimental measurements are influenced by temperature, stress biaxiality, and rupture velocity. This indicates other dissipative processes may occur in the vicinity of the crack.

We conduct Modified Ring Tests (MRT) on Carrara marble to investigate these mechanisms. MRT provides stable mode I crack propagation under controlled velocity and stress biaxiality conditions. Coupled with a compliance method calibrated through Finite Element Method (FEM), we obtain multiple local measurements of the fracture energy within a single test. FEM also provides estimation of stress biaxiality levels as well as higher order terms of the Williams’ expansion of the stress field.

The method is validated on PMMA through Digital Image Correlation (DIC) techniques. Experiments on Carrara marble show that the stress biaxiality can directly influence the fracture energy measurements. A microscopic investigation on marble is performed to look for micro-mechanisms which may cause observed variations of fracture energy.

How to cite: Guggisberg, A., Lebihain, M., and Violay, M.: Fracture energy variations of rocks: a mechanical investigation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7835, https://doi.org/10.5194/egusphere-egu22-7835, 2022.

Between 2018 and 2021, the STIMTEC and STIMTEC-X hydraulic stimulation experiments were conducted at 130 m depth in the Reiche Zeche underground research laboratory in Freiberg/Germany. The STIMTEC experiment was designed to investigate the rock damage resulting from hydraulic stimulation and to link seismic activity and enhancement of hydraulic properties in anisotropic metamorphic gneiss. The following STIMTEC-X experiment aimed at better constraining the stress field in the rock volume to investigate the mechanisms leading to induced acoustic emission (AE) activity. Here, we present results from focal mechanism analysis of high-frequency (>1 kHz) AE events, associated with brittle deformation at the cm- to dm-scale induced by hydraulic stimulations. Focal mechanisms are calculated using full moment tensor inversion of first P-wave amplitudes using the hybridMT package. We use polarity and amplitude data from a (near) real-time seismic monitoring network, consisting of AE sensors, AE-hydrophones, accelerometers, and one broadband sensor. We observe changes in the predominant type of faulting from reverse faulting focal mechanisms during the frac and refrac cycles to oblique strike-slip focal mechanisms observed during subsequent high-volume fluid-injections performed during periodic pumping test. The observed differences in dominant focal mechanisms are consistent with the activation of less favourably oriented faults at increased pore fluid pressure during extended periodic pumping. We observe a reverse-faulting stress regime from focal mechanism inversion of low-volume injection stages for different boreholes, representative for the rock volume (typically ~5 m radially) surrounding the injection intervals. In contrast, stress field estimates obtained from analysing the instantaneous shut-in pressures of hydraulic stimulations in different boreholes indicate a regime change from thrust to strike-slip faulting in the investigated rock volume. The reservoir complexity seen at the scale of the experiment (30m x 30m x 20m) is large and is reflected by the significant variations in AE event activity in response to stimulation as well as small-scale rock, stress and structural heterogeneities.

How to cite: Boese, C., Kwiatek, G., Renner, J., and Dresen, G.: Stress field observations from hydraulic fracturing and focal mechanism inversion at the STIMTEC underground research lab, Reiche Zeche mine, Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7986, https://doi.org/10.5194/egusphere-egu22-7986, 2022.

Fluid flow in low-porosity/permeability reservoir rocks such as tight carbonates is mostly restricted to structural discontinuities (e.g. faults, fractures, karstified zones). Fault zones, in particular in such rocks, offer both suitable fluid flow pathways, but may also act as impermeable barriers. The heterogeneous permeability structure of fault zones, however, impedes pre-drilling investigations of exploration targets by numerical models. A better understanding of the factors that control the fluid flow and the heterogeneity of permeability distribution along fault zones in tight reservoirs is a pre-requisite for the definition of drilling targets.

In this study, a hydraulic field laboratory with a volume of 30 m x 30 m x 20 m was set up in a quarry in SE Germany to investigate the influence of fault zones on the general permeability structure of tight carbonates. The test field contained three WNW-ESE-striking, repeatedly reactivated normal faults with offsets in the order of <1 m and two roughly perpendicularly oriented NNE-SSW-striking fracture corridors. Fault zones and fracture corridors were targeted by 62 wells. Wells that exhibited a decent hydraulic connection the to the overall conductive fracture network were logged (e.g. borehole image logs, FWS, etcs.) and in selected wells hydraulic tests were conducted. Water levels were measured both during static conditions and during testing. Due to the density of wells we were able to constrain the controlling factors for fluid flow along and across the fault zones. Damage zones were considered as conduits while the fault core was expected to be impermeable. These general assumptions could be confirmed by our tests, however we found some exceptions. While fluid flow in general is restricted to few, well-connected fractures, the majority of the fractures are dead ends, solely serving as storage for fluids. With increasing displacement and complexity of the fault zone, enhanced permeability parallel to the fault zone could be inferred. At larger offsets, where a thicker fault core develops, fhe fault core itself acts as barrier and fractures and fracture corridors do not penetrate the faults. We think that this is related to the presence of the much less competent fault core of a certain thickness which is able to accommodate the brittle deformation. Where the faults offset is less than ~0.4 m, the integrity of the fault seal is breached by fracture corridors, cross cutting the faults. This is clearly shown by the pressure distribution in static and transient conditions. Faulting, hence leads to a compartmentalization of the reservoir, where the compartments do either communicate or interact with significant delay.

The information and data received from the conducted field tests furthermore serve as input parameters and validation for a newly developed numerical approach that aims to simulate fluid flow in this type of geological settings, results of which will be presented in an additional presentation by our project partners.

How to cite: Freitag, S., Bauer, W., Stollhofen, H., and Hähnel, L.: (1)   Transmissivity of fault zones in tight carbonates – results from a reservoir-scale hydraulic field laboratory in the Franconian Alb, SE Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8457, https://doi.org/10.5194/egusphere-egu22-8457, 2022.

In outcrop-based fracture studies, the quantification of fracture intensity is often limited by the limitations of the manual sampling technique, characterized by punctual measurements (e.g. sampling spot, scanline, scanwindow) and moderate biases (e.g. fracture length truncation, technical and personal errors). The proximal remote sensing technologies, as terrestrial or Uncrafted Aerial Vehicle (UAV)-based LiDAR and photogrammetry, can help to overcome these limitations due to the possibility to obtain high-resolution and accurate quantitative data from the digital twin of the outcrop, the so-called Digital Outcrop Model (DOM). The DOMs can be very useful in outcrop-based fracture studies because their analysis allows to obtain several quantitative information with manual and/or automatic methods and with continuity in each position of the outcrop, increasing the accuracy of the fracture intensity estimations. However, due to the novelty of DOM technology and the lack of well-defined DOM-based fracture sampling procedures, these huge fracture datasets are often difficult to study and interpret, and therefore, the benefits of the DOM cannot be fully exploited. 

For this reason we present a complete workflow based on the DICE (Discontinuity Intensity Calculator and Estimator) open-source MATLAB© application that allows to quantitatively characterize the fractures of rocky outcrops from the 3D Digital Outcrop Models (DOMs). The proposed workflow consists in the following steps: (1) fracture mapping onto the 3D DOMs; (2) calculation of the fractures dimension, position and orientation; (iii) determination by DICE algorithm of the discontinuity parameters (persistence/dimension, distribution, spacing and intensity) using different 3D sampling techniques (3D scanline, 3D circular scan window and spherical scan volume). The differences of these sampling techniques and the fracture intensity parameters that can be obtained (p10, p21, p32) are discussed, showing the advantages and limitations of each DICE method.

How to cite: Menegoni, N., Giordan, D., and Perotti, C.: 3D Digital Outcrop Model-based quantification of fracture intensity: the Discontinuity Intensity Calculator and Estimator (DICE) open-source application, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10207, https://doi.org/10.5194/egusphere-egu22-10207, 2022.

EGU22-10259 | Presentations | ERE5.2

CHENILLE: Coupled beHavior undErstaNdIng of fauLts: from the Laboratory to the fiEld 

Audrey Bonnelye, Pierre Dick, Fabrice Cotton, Rüdiger Giese, Yves Guglielmi, Damien Jougnot, Jan Henninges, Grzegorz Kwiatek, and Stefan Lüth

The understanding of the coupled thermo-hydro-mechanical behaviour of fault zones in naturally fractured reservoirs is essential both for fundamental and applied sciences and in particular for the safety assessment of radioactive waste disposal facilities. In this framework, an international research program callled CHENILLE was built to address key questions related to the impact of high temperatures (up to 150°C) on shear zones as well as fault reactivation processes in shale formations. The project includes a thermally controlled in situ fluid injection experiment on a strike-slip fault zone outcropping atIRSN’s Tournemire Underground Research Laboratory (URL) and a series of laboratory experiments to understand the chemical and structural evolution occurring within the fault zones during the thermal and hydraulic loading. The in situ experiment includes a heating system installed around an injection borehole will enable a precise and controlled incremental increase of the thermal load. The injection borehole will be equiped with a Step-Rate Injection Method for Fracture In-Situ Properties (SIMFIP) probe, in order to perform step pressure tests. The probe will not only measure the flow and pressure rate inside the injection borehole but also allow to monitor the borehole’s 3D deformation during the hydraulic and thermal loading steps. In addition, an array of seismicifferent sensors will be implemented around the injection area to measure the seismic and aseismic deformation induced either by thermal or by hydraulic loading. The seismic monitoring system is composed of Acoustic Emission (sensitive between 1kHz and 60kHz) enabling monitoring fracturing processes of sub-decimeter size. Furthermore, a fibre optic network will be installed in the heating boreholes to measure spatially temperature variationsvia Distributed Temperature Sensing technology in the investigation area. Active seismic surveys, using different source types, are scheduled before and after the experiment to determine the structural network but also to detect the appearance of new structures triggered from the hydro-thermal pressurization of the fault by tomography and reflection seismic methods. The overall goal of our work is to present the interaction between the different geophysical methods that we are using as well as some preliminary results. A first part is dedicated to the description of the fault zone through field and core samples observations as well as borehole to borehole correlation, whereas the second is dedicated to preliminary results on the thermal diffusion expected in the fault.

How to cite: Bonnelye, A., Dick, P., Cotton, F., Giese, R., Guglielmi, Y., Jougnot, D., Henninges, J., Kwiatek, G., and Lüth, S.: CHENILLE: Coupled beHavior undErstaNdIng of fauLts: from the Laboratory to the fiEld, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10259, https://doi.org/10.5194/egusphere-egu22-10259, 2022.

EGU22-12748 | Presentations | ERE5.2

Crack healing in salt: time-resolved 3D microtomography 

Yuntao Ji, Christopher Spiers, Suzanne Hangx, Hans de Bresser, and Martyn Drury

Rocksalt caverns are considered or already used as storage for nuclear waste, petroleum, hydrogen, CO2, and compressed air energy because of the low permeability and potential of fracture healing of salt. An important concern is the sealing capacity. Undisturbed rocksalt deposits in nature generally have very low permeability. However, as a result of excavation stress, a network of fractures will be induced within the rocksalt formation, increasing the permeability. At low deviatoric stresses and/or at low effective stresses, a fracture network filled with brine is expected to heal, and the connectivity of the brine-filled network, consisting of grain boundaries, pores, and microcracks, is expected to decrease over time. The driving force for such a healing process is the tendency to reduce the interfacial energy by reducing the total interfacial area. In order to assess the rate of pore reconfiguration and permeability evolution in damaged salt and to capture the key process of crack network evolution during healing, we employ time-resolved 3D microtomography to study the long-term evolution of the fracture network of small-scale polycrystalline rocksalt samples. We found that precipitation prefers to occur in open spaces in the early stage of healing, such as new cracks. As a result, flat cracks evolve into zigzag cracks, which create narrow throats, thereby reducing the permeability of the crack network. Our study also offers a way to testify the thermodynamic models quantitatively.

How to cite: Ji, Y., Spiers, C., Hangx, S., de Bresser, H., and Drury, M.: Crack healing in salt: time-resolved 3D microtomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12748, https://doi.org/10.5194/egusphere-egu22-12748, 2022.

EGU22-12855 | Presentations | ERE5.2

Direct shear experiments to investigate the effect of chemical alteration on fault frictional behaviour in granitic geothermal systems 

Nick Harpers, Nathaniel Forbes Inskip, Michael John Allen, Daniel Faulkner, Hannes Claes, Andreas Busch, and Sabine den Hartog

Enhanced temperature gradients related to locally elevated heat production in granitic plutons offer the potential for low carbon geothermal energy production. Cornwall in SW England hosts several granitic plutons that are the subject of current geothermal projects (United Downs Deep Geothermal Power [UDDGP] Project and Eden Project). These projects target fault zones in crystalline rock that provide pre-existing pathways for fluid flow. Reinjection of cooler fluids into the reservoir after heat extraction may result in chemical disequilibrium with the host rock, potentially driving precipitation or chemical alteration. Such changes could influence the frictional properties of the fault zones, and hence require modifications to numerical risk-based calculations of the likelihood, or not, of induced seismicity.

In order to study the effects of such alterations, we have conducted a series of direct shear experiments under representative in-situ conditions on Cornish Carnmenellis granite samples which have undergone varying degrees of natural chemical alteration. The direct shear experiments were conducted on gouges (grain size < 125 μm) and at effective normal stresses of 80-105 MPa, pore fluid pressures of 25-50 MPa and temperatures of 16-180 °C. These conditions are relevant for the depths where the UDDGP project injection and production boreholes intercept the Porthtowan Fault zone, the assumed main conduit for fluid flow. In each test, load point velocity was stepped between 0.3 μm/s, 1 μm/s and 3 μm/s, and shear resistance of the sample was measured to determine the stability of sliding and thus the likelihood of induced seismicity as a function of degree of alteration. Initial shear tests at room temperature suggest little difference in the frictional response of altered and unaltered samples.

How to cite: Harpers, N., Forbes Inskip, N., Allen, M. J., Faulkner, D., Claes, H., Busch, A., and den Hartog, S.: Direct shear experiments to investigate the effect of chemical alteration on fault frictional behaviour in granitic geothermal systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12855, https://doi.org/10.5194/egusphere-egu22-12855, 2022.

EGU22-12888 | Presentations | ERE5.2

A semi-automatic workflow for structural interpretation of large point-cloud Digital Outcrop Models on complex fractured metamorphic rocks (Aosta Valley, Italy) 

Bruno Monopoli, Andrea Bistacchi, Federico Agliardi, Gloria Arienti, Giovanni Dal Piaz, Davide Bertolo, and Stefano Casiraghi

Characterization of fracture networks, both in fault zones and in the less-fractured background, is essential for the analysis and modelling of mechanical and hydraulic properties of the rock mass (i.e. rock plus fractures). Here we present our experience in characterizing fracture networks and other structural features on large outcrops of different basement and metamorphic cover units in the Penninic, Austroalpine and Helvetic units of the Aosta Valley. These units show a variety of lithological, mechanical, and rheological characteristics and were subjected to different ductile and brittle tectonic evolution, resulting in complex combinations of compositional layering, metamorphic schistosity, and fracture networks.

Our methodology is based on a combination of traditional field surveys and remote-sensing techniques such as ground-based and UAS photogrammetric surveys, and terrestrial or helicopter laser scanning. The first task, whose importance is too often overlooked, is represented by selecting outcrops that are representative in terms of structural and lithological properties of a larger rock volume, based on a thorough knowledge of regional structural geology and tectonics. The field survey is carried out with traditional techniques, paying attention to the kinematics, relative chronology, and mineralization (e.g. veins or mineral coatings) of structures. These features, that are often overlooked in fracture studies, are fundamental to frame the evolution of a complex schistosity and fracture network, to separate tectonic fractures with respect to those related to slope dynamics, and to develop predictive models of fracturing at depth (where slope-related fracture will not be present). At the same time, remote-sensing datasets are collected. The choice of the survey technique (terrestrial vs. aerial, photogrammetry vs. laser scanning) depends on various conditions, but in all cases the output is a point cloud DOM, colorized with RGB values, that should have a density (points/area) sufficient to characterize the smallest relevant structural features. From this, also textured surface DOMs and/or DEM plus orthophotos (for almost flat outcrops) can be obtained.

The first step of DOM analysis is carried out “manually”, selecting facets and traces with suitable software tools (e.g. Compass plugin in CloudCompare). This allows selecting different sets of structures, characterizing their orientation statistics, and assigning them to sets defined in the field (with kinematics, chronology, etc.). This step also allows understanding how well the structural features recognized in the field are represented in the DOM. The second step of DOM analysis consists in an automatic segmentation (in case of a point cloud) or tracing (in case of a DEM of triangulated surface textured with images) with algorithms calibrated with results of the manual interpretation. Overall, this results in a supervised semi-automatic workflow, allowing to extract huge structural datasets in a reasonable time, maintaining the connection with kinematic and chronological observations carried out in the field.

The fracture datasets can be eventually characterized with tools allowing to measure statistical distributions of different parameters of the fracture sets using virtual scanlines and/or scanareas, and these distributions can be used to model different properties of the fracture networks or generate stochastic DFN models.

How to cite: Monopoli, B., Bistacchi, A., Agliardi, F., Arienti, G., Dal Piaz, G., Bertolo, D., and Casiraghi, S.: A semi-automatic workflow for structural interpretation of large point-cloud Digital Outcrop Models on complex fractured metamorphic rocks (Aosta Valley, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12888, https://doi.org/10.5194/egusphere-egu22-12888, 2022.

EGU22-3730 | Presentations | GD9.1

Gravity kernel method for implicit geological modeling 

Zhouji Liang, Miguel De La Varga, and Florian Wellmann

Gravity is one of the most widely used geophysical data types in subsurface exploration. In the recent developments of stochastic geological modeling, gravity data serves as an additional constraint to the modeling construction and can be included in the modeling process as the likelihood function in a Bayesian workflow. A fast but also precise forward gravity simulation is key to the success of the geological modeling inverse problem.

In this study, we present a gravity kernel method, which is based on the widely adopted analytical solution on a discretized grid. As opposed to a globally refined regular mesh, we construct local tensor grids for each sensor, respecting the gravimeter locations and the local sensitivities. The kernel method is efficient in terms of both computing and memory use for meshless implicit geological modeling approaches. This design makes the method well suited for many-query applications like Bayesian machine learning using gradient information calculated from Automatic Differentiation (AD). Optimal grid design without knowing the underlying geometry is not straightforward before evaluating the model. Therefore, we further provide a novel perspective on a refinement strategy for the kernel method based on the sensitivity of the cell to the corresponding receiver. Synthetic results are presented and show superior performance compared to the traditional spatial convolution method.

How to cite: Liang, Z., De La Varga, M., and Wellmann, F.: Gravity kernel method for implicit geological modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3730, https://doi.org/10.5194/egusphere-egu22-3730, 2022.

It is broadly accepted that magmatism plays a key dynamic role in continental and oceanic rifting. However, these dynamics remain poorly studied, largely due to the difficulty of consistently modelling liquid/solid interaction across the lithosphere. The RIFT-O-MAT project seeks to quantify the role of magma in rifting by using models that build upon the two-phase flow theory of magma/rock interaction. A key challenge is to extend the theory to account for the non-linear rheological behaviour of the host rocks, and investigate processes such as diking, faulting and their interaction (Keller et al., 2013). Here we present our progress in consistent numerical modelling of poro-viscoelastic-viscoplastic (VEVP) flow. We show that a VEVP model with a new, hyperbolic yield surface can help to robustly simulate both shear and tensile modes of plastic failure in a two-phase system. 

Failure of rocks (plasticity) is an essential ingredient in geodynamics models because Earth materials cannot sustain unbounded stresses. However, plasticity represents a non-trivial problem even for single-phase flow formulations with shear failure only. In two-phase systems, tensile failure of rocks can also occur due to an overpressured liquid phase. Robustly solving a discretised model that includes this physics presents severe challenges, and many questions remain as to effective solvers for these strongly nonlinear systems.

An appropriate rheological model is required to meet this challenge. The most straightforward choice is a Maxwell visco-elasto-plastic model, but this leads to grid-scale localisation and hence mesh-dependence. To obtain mesh-independent shear localisation, we employ the visco-elasto-viscoplastic model by introducing a viscous dashpot in parallel to the plasticity element. Whilst this formulation has shown promise in regularising shear failures in a single-phase flow model (de Borst and Duretz, 2020), its incorporation within two-phase systems has not been examined. We will show that the linear Griffith criteria for the tensile failure can lead to convergence issues whereas a new, hyperbolic yield surface is proposed to resolve these numerical issues. This yield surface provides a smooth transition between the two modes of failure.

The underlying PDEs are discretised using a conservative, finite-difference, staggered-grid framework implemented with PETSc (FD-PDE) that supports single-/two-phase flow magma dynamics. Here, we present simplified model problems using the FD-PDE framework for poro-viscoelastic-viscoplastic models designed to characterise the solution quality and assess both the discretisation and solver robustness. It has been observed that employing the hyperbolic yield surface improved the robustness in simulating plastic failures in both modes.

 

References

Keller, T., May, D. A., & Kaus, B. J. P., (2013). Numerical modelling of magma dynamics coupled to tectonic deformation of lithosphere and crust, Geophysical Journal International, v195, 1406-1442, https://doi.org/10.1093/gji/ggt306.

de Borst, R., Duretz, T., (2020). On viscoplastic regularisation of strain-softening rocks and soils. International Journal for Numerical and Analytical Methods in Geomechanics, v44, 890-903. https://doi.org/10.1002/nag.3046.

How to cite: Li, Y., Pusok, A., May, D., and Katz, R.: Simulation of partially molten rocks with visco-elasto-viscoplastic rheology and a hyperbolic yield surface for plasticity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5594, https://doi.org/10.5194/egusphere-egu22-5594, 2022.

EGU22-5704 | Presentations | GD9.1 | Highlight

How composable software tools in Julia help developing multi-physics codes in geodynamics 

Boris Kaus, Nicolas Berlie, Valentin Churavy, Matias Cosarinsky, Thibault Duretz, Daniel Kiss, Jeremy Kozdon, Albert de Montserrat, Lucas Moser, Nils Medinger, Samuel Omlin, Ludovic Räss, Patrick Sanan, Arne Spang, Marcel Thielmann, and Ivan Utkin

Julia(https://julialang.org) recently emerged as a very powerful high-level computer language for (parallel) scientific computing, which allows you to “write codes like in MATLAB”, while “achieving the speed of Fortran/C”. A particular strength of Julia is that it is easy to write composable software packages that talk to each other. Here we will discuss our efforts in making Julia a development platform for geodynamic applications that significantly simplifies the process of going from a working solver to a production code which runs on massively parallel (GPU) machines.  We are working on a number of open-source packages that simplify certain steps that many geodynamics codes have in common:

  • GeoParams.jl (https://github.com/JuliaGeodynamics/GeoParams.jl) is a package in which you can specify constitutive relationships (e.g., creeplaws). It automatically handles the (non-)dimensionalization of all input parameters, includes pre-defined creep laws (e.g., dislocation and diffusion creep laws), plotting routine and includes computational routines that can be directly integrated in your code.
  • PETSc.jl (https://github.com/JuliaParallel/PETSc.jl) is the main interface from Julia to PETSc, including MPI support and automatic installations of PETSc (one of the main hurdles that existing users faced). We have recently extended the package to include an interface to DMSTAG, such that you create a staggered finite difference grid and assemble the stiffness matrix in a straightforward manner. You can use automatic differentiation tools in Julia to create the Jacobians for nonlinear equations, which again minimizes the required lines of code (compared to their C counterparts). At the same time, the full range of (nonlinear multigrid) PETSc solvers is available. This is thus very well suited to write implicit solvers.
  • ParallelStencil.jl (https://github.com/omlins/ParallelStencil.jl) and ImplicitGlobalGrid.jl (https://github.com/eth-cscs/ImplicitGlobalGrid.jl) are packages that are devoted to solving stencils in a very efficient manner on (parallel) GPU or CPU machines, which scales to very large GPU-based computers. It is particularly efficient in combination with pseudo-transient iterative solvers and allow running codes on modern architectures.
  • GeophysicalModelGenerator.jl (https://github.com/JuliaGeodynamics/GeophysicalModelGenerator.jl) is a package that gives you a simple way to collect geophysical/geological data of a certain region and combine that to construct a 3D geodynamic input model setup.

Ongoing efforts include the development of a grid generation and a marker and cell advection package that work, seamlessly with both ParallelStencil and PETSc. This will allow developers to apply both direct-iterative and pseudo-transient implicit solvers to the same problem, while only having to make minimal changes to the model setup. Combined, these packages will make the step from developing a new (nonlinear) solver to having an efficient (3D) production code much easier.

How to cite: Kaus, B., Berlie, N., Churavy, V., Cosarinsky, M., Duretz, T., Kiss, D., Kozdon, J., de Montserrat, A., Moser, L., Medinger, N., Omlin, S., Räss, L., Sanan, P., Spang, A., Thielmann, M., and Utkin, I.: How composable software tools in Julia help developing multi-physics codes in geodynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5704, https://doi.org/10.5194/egusphere-egu22-5704, 2022.

One of the great challenges involved in modelling the lithosphere is its plastic behaviour, especially when dealing with compressible materials. Shear fractures are designated as mode 2 and 3 and can be described using a Linear Mohr Coulomb envelope  or a simplification of it like Drucker-Prager. Meanwhile, mode 1 fractures are created when the normal stresses become tensile  and require another yield function, such as the Griffith criterion or a tension cap function.

While the governing equations are well known and widely employed in engineering codes, they are usually expressed with a displacement formulation. Most geodynamic codes, on the other hand, use pressure and velocity as their primary variables. A numerically robust method that takes all plasticity modes into account in a staggered finite difference discretization remains an open task. Here we present a composite yield function implemented with pressure-velocity formulation, capable of producing produce shear and tensile failure.

We have implemented this in a new code that employed PETSc through the recently updated PETSc.jl Julia interface, while utilizing the automatic differentiation tools in julia. We found this workflow to significantly reduce the development time of complex nonlinear coupled codes.  

We will describe the implementation, propose regularization schemes and discuss benchmark cases and simple applications. We demonstrate Newton convergence for most cases and will discuss different methods to combine multiple plastic flow laws.

How to cite: Berlie, N., Kaus, B., Popov, A., Kiss, D., and Riel, N.: How to break the lithosphere: a compressible pressure-velocity formulation for elasto-visco-plastic rheologies that includes shear and tensile failure with dilation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6566, https://doi.org/10.5194/egusphere-egu22-6566, 2022.

EGU22-8816 | Presentations | GD9.1

GPU-based pseudo-transient finite difference solution for 3-D gravity- and shear-driven power-law viscous flow 

Emilie Macherel, Yuri Podladchikov, Ludovic Räss, and Stefan M. Schmalholz

Power-law viscous flow describes the first-order features of long-term lithosphere deformation. Due to the ellipticity of the Earth, the lithosphere is mechanically analogous to a shell, characterized by a double curvature. The mechanical characteristics of a shell are fundamentally different to the characteristics of plates, having no curvature in their undeformed state. The systematic quantification of the magnitude and the spatiotemporal distribution of strain, strain-rate and stress inside a deforming lithospheric shell is thus of major importance: stress is, for example, a key physical quantity that controls geodynamic processes such as metamorphic reactions, decompression melting, lithospheric flexure, subduction initiation or earthquakes. Calculating these stresses in a three-dimensional (3-D), geometrically and mechanically heterogeneous lithosphere requires high-resolution and high-performance computing.

 

Here, we present numerical simulations of 3-D power-law viscous flow. We employ the pseudo-transient finite difference (PTFD) method, which enables efficient simulations of high-resolution 3-D deformation processes by implementing an iterative implicit solution strategy of the governing equations. The main challenges for the PTFD method are to guarantee convergence, minimize the required iteration count and speed-up the iterations. We implemented the PTFD algorithm using the Julia language (julialang.org) to enable optimal parallel execution on multiple CPUs and GPUs using the ParallelStencil.jl module (https://github.com/omlins/ParallelStencil.jl). ParallelStencil.jl enables execution on multi-threaded CPUs and Nvidia GPUs using a single switch.

 

We present PTFD simulations of mechanically heterogeneous (weak and less dense spherical inclusion), incompressible 3-D power-law viscous flow under gravity in cartesian, cylindrical and spherical coordinates systems. The viscous flow is described by a linear combination of a linear viscous and a power-law viscous flow law, representing diffusion and dislocation creep, respectively. The iterative solution strategy builds upon pseudo-viscoelastic behavior to minimize the iteration count by exploiting the fundamental characteristics of viscoelastic wave propagation. We performed systematic numerical simulations to investigate the impact of (i) buoyancy versus shear forces and (ii) linear versus power-law viscous flow on the vertical velocity of the spherical inclusion under bulk strike-slip shearing. We report the systematic results using the controlling dimensionless numbers and compare the numerical results with analytical predictions for buoyancy-driven flow of inclusions in a power-law matrix. We also aim to unveil preliminary results for a vertically and locally loaded power-law viscous lithosphere showing the impact of different lithosphere curvatures on the resulting stress field.

How to cite: Macherel, E., Podladchikov, Y., Räss, L., and Schmalholz, S. M.: GPU-based pseudo-transient finite difference solution for 3-D gravity- and shear-driven power-law viscous flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8816, https://doi.org/10.5194/egusphere-egu22-8816, 2022.

EGU22-8849 | Presentations | GD9.1

Mass-Conserving Thermal Structure for Slabs in Instantaneous Models of Subduction 

Magali Billen, Menno Fraters, and Magalie Babin

Subduction is driven by difference in mass between the sinking plate and the surrounding mantle. The deformation calculated in numerical models of subduction is strongly dependent on the magnitude of the mass difference. The mass difference depends on the temperature of the slab. As the tectonic plate sinks it heats up, but it also cools down the surrounding mantle. The amount of heating and cooling is determined by conservation of thermal energy. Because the temperature also determines the thermal mass, conversing thermal energy also leads to conserving mass. For some studies, models of subduction are made to match the present day structure of a sinking plate. In this case, the temperature is defined to follow the observed geometry. In some previous studies, the temperature structure did not explicitly enforce conservation of energy or mass, and thus the density of the slab was not physically consistent, which is added source of uncertainty when analyzing the resulting flow and sensitivity of model results to mantle and slab rheology. Here we present a mass-conserving thermal structure for slabs that also creates a smoothly varying temperature structure. The thermal structure is based on a 1-D half-space cooling model (bottom) and an infinite space cooling model (top). It uses the age of the plate at the trench to determine the initial mass anomaly of the slab. The sinking velocity modifies the rate of heating and migration of the minimum temperature into the slab interior. The thermal model is calibrated against simple 2D subduction models in which the age and subduction velocity are held fixed. The new thermal structure has been implemented in the Geodynamic WorldBuilder (1), which can be used with different mantle convection software and is distributed as a plugin for ASPECT (2). Comparison of model results with the mass conserving slab thermal structure to the "plate" model from McKenzie (1970) is used to illustrate the differences in modeled results. References: 1. Fraters, M. R. T. et al., Solid earth, 2019. 2. Bangerth, W. et al., https://doi.org/10.5281/ZENODO.5131909, 2021.

How to cite: Billen, M., Fraters, M., and Babin, M.: Mass-Conserving Thermal Structure for Slabs in Instantaneous Models of Subduction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8849, https://doi.org/10.5194/egusphere-egu22-8849, 2022.

Transient superstructures in mantle convection whose life and morphology vary with Rayleigh and Prandtl number have recently been demonstrated. These superstructures appear to be a two-scale phenomenon where smaller scale rolls organize into larger scale convection cells. Simulation of such superstructures requires the ability to model 3D convection in box with very large width/height ratio of order greater than 10, and with resolution to resolve the thermal boundary layer at Rayleigh numbers of 108 to 1010, respectively at least 100 height levels and 200 height levels. We achieve this with an efficient parallel implementation of the Lattice Boltzmann Method using Python which operates with high efficiency and linear speedup on thousands of cores. We present simulations with Rayleigh numbers of up to 1010 and Prandtl numbers from 1 to 100 to illustrate covering regimes from a magma ocean to solid mantle convection. We further present simulations using the LBM to model variable viscosity – specifically, temperature dependent– and illustrate the existence of pulsating plumes. We further demonstrate power law scaling between Nusselt number and Rayleigh number Nu  ~ Rag, which to first order is consistent with the Grossmann and Lohse theory.

How to cite: Mora, P., Morra, G., and Yuen, D.: Simulation of 3D transient superstructures in mantle convection and variable viscosity via the Lattice Boltzmann Method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9069, https://doi.org/10.5194/egusphere-egu22-9069, 2022.

EGU22-9133 | Presentations | GD9.1

Testing a (quasi-)free base for modelling core-mantle boundary topography 

Tobias Rolf, Fabio Crameri, Björn H. Heyn, and Marcel Thielmann

The core-mantle boundary (CMB) is the most prominent compositional boundary inside the Earth. Its topography provides insight on lower mantle flow and the thermochemical structure above the CMB. Yet, CMB topography remains challenging to observe and estimates from seismology vary substantially. Numerical models of mantle convection provide complementary means to estimate CMB topography. Classically, topography is determined from the normal stresses acting on the CMB. However, this is known to face severe complications when applied to the surface boundary of the mantle, leading to non-Earth-like topographic scales and a different style of subduction. A (quasi-)free surface yields more Earth-like predictions, but for the CMB this comparison has never been made.

Here, we compare CMB topography predicted from mantle convection modelling using different treatments of the CMB. Specifically, we test the role of a ‘sticky core’, a quasi-fluid approximation the core. We compare results predicted by different codes (with either sticky core or true free base) and compare to a simple analytical case. Also, we simulate the evolution of subduction and deep thermochemical provinces to compare the topography of the (quasi-)free CMB and the free-slip approach. Initial results indicate that the sticky core approach can reproduce CMB topography reasonably well, but has rather high computational cost (grid resolution, number of particles). In analogy to the sticky air at the surface, the viscosity contrast of the sticky core layer determines the quality of predicted topography, with larger contrasts (≥103) leading to acceptable levels of artificial CMB topography. In dynamic flow cases with vigorous mantle convection, entrainment by plumes further complicates application of the sticky core, but can be tackled with an unmixing procedure. A true free base tends to better accuracy than the sticky core approach and avoids the problem with entrainment, but it also comes with additional computational costs as various forces at the CMB have to be taken into account.

How to cite: Rolf, T., Crameri, F., Heyn, B. H., and Thielmann, M.: Testing a (quasi-)free base for modelling core-mantle boundary topography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9133, https://doi.org/10.5194/egusphere-egu22-9133, 2022.

EGU22-9232 | Presentations | GD9.1

Automatic generation of the adjoint of the StagYY mantle convection model 

Nicolas Coltice, Simon Blessing, Ralf Giering, and Paul Tackley

Motions within the Earth mantle and tectonics constitute a single self-organized system which is cooling the planet over its geological history. Since the end of the XXth century, models of mantle convection self-generating plate tectonic behavior have progressed to a state that makes them applicable to global tectonic problems. The possibility of combining geological and geophysical data with dynamic models to retrieve the recent history of mantle flow and tectonics becomes realistic. Therefore, it is a challenge to build inverse methods to study inverse and sensitivity problems in the Earth's mantle convection. We have automatically generated the tangent-linear and the adjoint source code from the StaggYY code (Tackley, Phys. Earth Planet. Int. 171, 7-18, 2008). The Fortran code of the model was translated to the corresponding derivative codes using TAF (Transformation of Algorithms in Fortran), source-to-source translator. All codes run in parallel mode, using MPI (Message Passing Interface). The economic taping strategy of TAF, including re-computations, and checkpointing, helps to keep the memory footprint of the adjoint code low and the performance high. We highlight some key features of the automatic differentiation, evaluate the performance of the adjoint code, and show first results from 2D and 3D sensitivity fields, focusing on the relationships between temperature in the mantle and tectonics. Ultimately the addjoint code shall be applied to inversion and assimilation problems using a bayesian framework.

How to cite: Coltice, N., Blessing, S., Giering, R., and Tackley, P.: Automatic generation of the adjoint of the StagYY mantle convection model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9232, https://doi.org/10.5194/egusphere-egu22-9232, 2022.

EGU22-9815 | Presentations | GD9.1

Assessing the robustness and scalability of the accelerated pseudo-transient method towards exascale computing 

Ivan Utkin, Ludovic Rass, Thibault Duretz, Samuel Omlin, and Yury Podladchikov

The development of highly efficient, robust, and scalable numerical algorithms lags behind the rapid increase in massive parallelism of modern hardware. In this work, we address this challenge with the accelerated pseudo-transient iterative method. This method is motivated by the physical analogy between numerical iterations and transient processes converging to a steady state.

We analytically determine optimal iteration parameters for a variety of basic physical processes such as diffusion, diffusion-reaction and non-inertial viscous fluid flow featuring Maxwell viscoelastic rheology. We further confirm the validity of theoretical predictions with numerical experiments.

We provide an efficient numerical implementation of various pseudo-transient solvers on graphical processing units (GPUs) using the Julia language. We achieve a parallel efficiency over 96% on 2197 GPUs in distributed memory parallelisation weak scaling benchmarks. 2197 GPUs allow for unprecedented terascale solutions of 3D variable viscosity Stokes flow involving over 1.2 trillion degrees of freedom.

We verify the robustness of the method by handling contrasts up to 9 orders of magnitude in material parameters such as viscosity, and arbitrary distribution of viscous inclusions for different flow configurations. Moreover, we show that this method is well suited to tackle strongly nonlinear problems such as shear-banding in a visco-elasto-plastic medium.

We additionally motivate the accessibility of the method by its conciseness, flexibility, physically motivated derivation, and ease of implementation. This solution strategy has thus a great potential for future high-performance computing applications, and for paving the road to exascale in the geosciences and beyond.

How to cite: Utkin, I., Rass, L., Duretz, T., Omlin, S., and Podladchikov, Y.: Assessing the robustness and scalability of the accelerated pseudo-transient method towards exascale computing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9815, https://doi.org/10.5194/egusphere-egu22-9815, 2022.

EGU22-10412 | Presentations | GD9.1

Rate and state friction on spontaneously evolving faults 

Casper Pranger, Patrick Sanan, Dave May, Laetitia Le Pourhiet, Ludovic Räss, and Alice Gabriel

The rate- and state-dependent friction (RSF) laws (Dieterich, 1979; Ruina, 1983) have been widely successful in capturing the behavior of sliding surfaces in laboratory settings, as well as reproducing a range of natural fault slip phenomena in numerical models.

Studies of exhumed fault zones make it clear that faults are not two-dimensional features at the junction of two distinct bodies of rock, but instead evolve into complex damage zones that show clear signs of multi-scale fracturing, grain diminution, hydro-thermal effects and chemical and petrological changes. Many of these observed factors have been experimentally verified, and several studies have furthered our theoretical understanding of earthquakes and other seismic phenomena as volumetric, bulk-rock processes, including Sleep (1995, 1997), Lyakhovsky and Ben-Zion et al. (2011, 2014a,b, 2016), Niemeijer and Spiers et al. (2007, 2016, 2018), Roubicek (2014), and Barbot (2019).

While the established numerical modeling approach of simulating faults as planar features undergoing friction can be a useful and powerful homogenization of small-scale volumetric processes, there are also cases where this practice falls short -- most notably when studying faults that grow and evolve in response to a changing tectonic environment. This is mainly due to the computational challenges associated with automating the construction of a fault-resolving conformal mesh.

Motivated by this issue, we formulate a generalization of RSF as a plastic or viscous flow law with generation, diffusion, and healing of damage that gives rise to mathematically and numerically well-behaved finite shear bands that closely mimic the behavior of the original laboratory-derived formulation (Pranger et al., submitted). The proposed formulation includes the well-known RSF laws for an infinitely thin fault as a limit case as the damage diffusion length scale tends to zero. We will show the behavior of this new bulk RSF formulation with results of high-resolution 1D and 2D numerical simulations.

Dieterich, J.H. (1979), J. Geophys. Res., 84 (B5), 2161.
Ruina, A. (1983), JGR: Solid Earth, 88 (B12), 10359–10370.
Sleep, N.H. (1995), JGR, 100 (B7), 13065–13080.
Sleep, N.H. (1997), JGR: Solid Earth 102 (B2), 2875–2895.
Roubíček, T. (2014), GJI 199.1, 286–295.
Lyakhovsky, Hamiel and Ben-Zion (2011), J. Mech. Phys. Solids, 59, 1752-1776.
Lyakhovsky and Ben-Zion (2014a), PAGeoph 171.11, 3099–3123.
Lyakhovsky and Ben-Zion (2014b), J. Mech. Phys. Solids 64, 184–197.
Lyakhovsky, Ben-Zion et al. (2016), GJI 206.2, 1126–1143.
Barbot (2019), Tectonophysics 765, 129–145.
Niemeijer and Spiers (2007), JGR 112, B10405,
Chen and Spiers (2016), JGR: Solid Earth 121, 8642–8665.
van den Ende, Chen et al. (2018), Tectonophysics 733, 273-295.
Pranger et al. (202X), ESSOAr (https://www.essoar.org/doi/10.1002/essoar.10508569.1)

How to cite: Pranger, C., Sanan, P., May, D., Le Pourhiet, L., Räss, L., and Gabriel, A.: Rate and state friction on spontaneously evolving faults, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10412, https://doi.org/10.5194/egusphere-egu22-10412, 2022.

EGU22-11131 | Presentations | GD9.1

The Face-Centered Finite Volume method for Geodynamic Modelling 

Thibault Duretz, Ludovic Räss, and Rubén Sevilla

The Face-Centered Finite Volume (FCFV) is a newly developed discretisation technique that has been applied to a variety of engineering problems. This approach is based on the hybridisable discontinuous Galerkin formulation with constant degree approximations. The FCFV is particularly attractive approach since it meets numerous essential criteria for successful geodynamic modelling. It offers full geometric flexibility, natural free surface boundary condition, second order accuracy velocity-field solutions, no oscillatory pressure modes, relatively low computational cost and adequate treatment of jump conditions at material interfaces. Here we present the implementation of Poisson and Stokes solvers in the Julia computing language. Here we present the implementation of Poisson and Stokes solvers using the performant Julia language. We discuss several solving strategies including direct-iterative and iterative pseudo-transient approaches, the latter executing efficiently on Graphical Processing Units. We extend the original FCFV Stokes formulation to account for discontinuous viscosity case and discuss the implementation of complex visco-elasto-plastic rheologies.

How to cite: Duretz, T., Räss, L., and Sevilla, R.: The Face-Centered Finite Volume method for Geodynamic Modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11131, https://doi.org/10.5194/egusphere-egu22-11131, 2022.

EGU22-11469 | Presentations | GD9.1

Strain localization in a visco-elasto-plastic medium using strain-dependent weakening and healing rheology 

Lukas Fuchs, Thibault Duretz, and Thorsten W. Becker

The formation and maintenance of narrow, lithospheric shear zones and their importance in plate-tectonics remain one of the major problems in geodynamics. While the cause and consequence of strain localization and weakening within the lithosphere remain debated, it is clear that these processes play an essential role in lithospheric deformation across a wide range of spatio-temporal scales. Here, we analyze the efficiency of strain localization in a 2-D visco-elasto-plastic medium for a strain-dependent weakening and healing (SDWH) rheology using 2-D numerical, thermo-mechanical experiments with kinematic boundary conditions. Such a parameterized rheology successfully mimics more complex transient weakening and healing processes, akin to a grain-size sensitive composite (diffusion and dislocation creep) rheology. In addition, the SDWH rheology allows for memory of deformation. This enables self-consistent formation and reactivation of inherited weak zones within the lithosphere and sustains those weak zones over an extended period of time. We further analyze the resulting shear zone patterns and seek to answer the questions: What is the typical, effective intensity of strain localization? What are the dimensions of the resulting shear zones? Are such shear zones mesh-dependent in numerical models and, if so, can we exploit existing regularization approaches for the SDWH rheology?

How to cite: Fuchs, L., Duretz, T., and Becker, T. W.: Strain localization in a visco-elasto-plastic medium using strain-dependent weakening and healing rheology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11469, https://doi.org/10.5194/egusphere-egu22-11469, 2022.

EGU22-11494 | Presentations | GD9.1

MAGEMin, a new and efficient Gibbs free energy minimizer: application to igneous systems 

Nicolas Riel, Boris Kaus, Eleanor Green, and Nicolas Berlie

Modelling stable mineral assemblage is crucial to calculate mineral stability relations in the Earth’s lithosphere e.g., to estimate thermobarometric conditions of exposed rocks and to quantify the fraction and composition of magma during partial melting. Accurate prediction models of stable phase are also fundamental to model trace element partitioning and to extract essential physical properties such as, fluid/melt/rock densities, heat capacity and seismic velocities. This thus forms a crucial step in linking geophysical observations with petrological constraints.

Here, we present a new Mineral Assemblage Gibbs free Energy Minimizer (MAGEMin). The package has been developed with the objective to provide a minimization routine that is easily callable and fulfilling several objectives. Firstly, the package aims to consistently compute for single point calculations at given pressure, temperature and bulk-rock composition with no needed a priori knowledge of the system. Secondly, the package has been developed for stability, performance and scalability in complex chemical systems. Finally, the code is fully parallel and we directly translate THERMOCALC formulation of solution models which yields easier and faster updates, less prone to implementation mistakes.

As a proof of concept we apply our new approach to the thermodynamic dataset for igneous systems of Holland et al. (2018). The database works in the NCKFMASHTOCr chemical system and has been updated to account for the new plagioclase model Holland et al. (2021).

How to cite: Riel, N., Kaus, B., Green, E., and Berlie, N.: MAGEMin, a new and efficient Gibbs free energy minimizer: application to igneous systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11494, https://doi.org/10.5194/egusphere-egu22-11494, 2022.

EGU22-12156 | Presentations | GD9.1

Dynamic mesh optimisation for efficient numerical simulation of density-driven flows: Application to the 2- and 3-D Elder problem 

Meissam L. Bahlali, Pablo Salinas, and Matthew D. Jackson

Density-driven flows in porous media are frequently encountered in natural systems and arise from the gravitational instabilities introduced by fluid density gradients. They have significant economic and environmental impacts, and numerical modelling is often used to predict the behaviour of these flows for risk assessment, reservoir characterisation or management. However, modelling density-driven flow in porous media is very challenging due to the nonlinear coupling between flow and transport equations, the large domains of interest and the wide range of time and space scales involved. Solving this type of problem numerically using a fixed mesh can be prohibitively expensive.  Here, we apply a dynamic mesh optimisation (DMO) technique along with a control-volume-finite element method to simulate density-driven flows. DMO allows the mesh resolution and geometry to vary during a simulation to minimize an error metric for one or more solution fields of interest, refining where needed and coarsening elsewhere. We apply DMO to the Elder problem for several Rayleigh numbers. We demonstrate that DMO accurately reproduces the unique two-dimensional (2D) solutions for low Rayleigh number cases at significantly lower computational cost compared to an equivalent fixed mesh, with speedup of order x16. For unstable high Rayleigh number cases, multiple steady-state solutions exist, and we show that they are all captured by our approach with high accuracy and significantly reduced computational cost, with speedup of order x6. The lower computational cost of simulations using DMO allows extension of the high Rayleigh number case to a three-dimensional (3D) configuration and we demonstrate new steady-state solutions that have not been observed previously. Early-time, transient 3D patterns represent combinations of the previously observed, steady-state 2D solutions, but all evolve to a single, steady-state finger in the late time limit.

How to cite: Bahlali, M. L., Salinas, P., and Jackson, M. D.: Dynamic mesh optimisation for efficient numerical simulation of density-driven flows: Application to the 2- and 3-D Elder problem, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12156, https://doi.org/10.5194/egusphere-egu22-12156, 2022.

EGU22-12398 | Presentations | GD9.1

Nonlinear solver acceleration based on machine learning applied to multiphase porous media flow 

Vinicius Silva, Pablo Salinas, Matthew Jackson, and Cristopher Pain

We present a machine learning strategy to accelerate the nonlinear solver convergence for multiphase porous media flow problems. The presented approach dynamically controls an acceleration method based on numerical relaxation. The methodology is implemented and demonstrated in a Picard iterative solver; however, it can also be used with other types of nonlinear solvers. The goal of the machine learning acceleration is to reduce the number of iterations required by the nonlinear solver by adjusting the value of the relaxation factor to the complexity/physics of the system. A set of dimensionless parameters is used to train and control the machine learning. In this way, a simple two-dimensional layered reservoir can be used for training while still exploring a large portion of the dimensionless parameter space. As a result, the training process is simplified, and the machine learning model can be applied to any type of reservoir models.

We demonstrate that the presented technique dramatically reduces the number of nonlinear iterations without sacrificing the quality of the results, even for models that are far more complex than the training case. The average reduction in the number of nonlinear iterations obtained due to the presented method is 24% and the reduction in runtime is 37%. It is worth noting that the optimum value of the relaxation factor is not known a-priori and it is problem specific. Hence, having an acceleration that adapts itself to the complexity/physics of the system throughout the numerical simulation is extremely valuable and has driven several publications in multiple fields.

The method presented here provides an easy way to deal with nonlinear system of equations that does not necessitate as much effort as a custom nonlinear solver while producing outstanding results. We believe that the machine learning acceleration is not limited to the multiphase porous media flow but extendable to any other system that can be studied based on dimensionless numbers, and that a relaxation technique can be used to stabilize the nonlinear solver.

How to cite: Silva, V., Salinas, P., Jackson, M., and Pain, C.: Nonlinear solver acceleration based on machine learning applied to multiphase porous media flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12398, https://doi.org/10.5194/egusphere-egu22-12398, 2022.

EGU22-284 | Presentations | GD6.2

Imprints of Crust- and Mantle-Scale Deformation in Central Anatolide-Tauride Region: Exploiting Receiver Functions 

Derya Keleş, Tuna Eken, Andrea Licciardi, Christian Schiffer, and Tuncay Taymaz

Central Anatolia is a seismically active region with complex tectonic provinces and represents one of the significant regions experiencing active deformation in Turkey. It involves the Anatolide-Tauride Block settled in southern Anatolia that is separated from the Pontides by the İzmir-Ankara-Erzincan Suture Zone (IAESZ). In central Anatolia, the Kırşehir Massif mainly comprises complex crystalline metamorphic and plutonic rocks with obducted ophiolitic fragments. It is detached from the Anatolide-Tauride Block by the Intra-Tauride Suture (ITS). The ITS is thought to represent the footprint of subducted Neo-Tethyan ocean. This region further includes a number of active tectonic features, i.e., the Central Anatolian Fault Zone (CAFZ), the Tuz Gölü Fault (TGZ), the East Anatolian Fault zone (EAFZ), the Dead Sea Fault (DSF), and the Bitlis-Zagros Suture. In order to investigate the style of deformation of the region and its influence on the crustal and lithospheric structure and to better understand the relationship between tectonic features and regional deformation at different depth and tectonic features, we quantify the strength and orientation of seismic anisotropy. To achieve this, we focus on the directional dependence of P-to-S converted teleseismic waves (i.e., receiver functions) through the harmonic decomposition analysis. Our findings indicate that seismic anisotropy is mostly localized in the mid-crust (15-25 km) with an overall NE-SW and NNW-SSE orientation in the west and east portions of the study area which is present in the mid-crust (15-25 km). In the uppermost mantle, we observed NE-SW oriented and relatively strong anisotropy. This is compatible with fast shear wave azimuths inferred from SKS splitting measurements reported in previous studies and likely be associated with a sub-lithospheric origin. Anisotropic orientations found at crustal and upper mantle depths are consistent with a model of the ITS reaching to great depths suggest anisotropic fabrics in frozen related to past deformation events. We further perform a joint inversion of receiver functions with apparent S wave velocities to better constrain crustal thickness estimates derived from the harmonic decomposition analysis. The resulting crustal thicknesses vary from about 25-28 km nearby the EAFZ and DSF, and to ~35 and 40 km beneath the Kırşehir block and the Eastern Tauride Mountains.

How to cite: Keleş, D., Eken, T., Licciardi, A., Schiffer, C., and Taymaz, T.: Imprints of Crust- and Mantle-Scale Deformation in Central Anatolide-Tauride Region: Exploiting Receiver Functions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-284, https://doi.org/10.5194/egusphere-egu22-284, 2022.

EGU22-370 | Presentations | GD6.2

Investigating the response of seismic anisotropy in the crust to the 2014–15 Bárðarbunga-Holuhraun dyke intrusion and eruption 

Conor Bacon, Elisavet Baltas, Jessica Johnson, Robert White, and Nicholas Rawlinson

Existing evidence points towards the evolution of magmatic intrusions being a complex function of both existing structures and the stress state within the crust. Consequently, developing means to make in-situ measurements and effective models of these two factors would provide crucial insight into the dynamics of volcanic systems, feeding forward to volcanic monitoring and crisis response agencies. Seismic anisotropy—the directional dependence of seismic wavespeeds—has been shown to be a direct proxy for the in-situ stress state of the crust, as well as the existing fabric, but its potential for further developing our general understanding of magmatic intrusions has yet to be realised. The wealth of geophysical data recorded during eruptions in the last decade presents a unique opportunity to explore these important natural phenomena in exceptional detail.

We first establish a general model for the bulk properties and structure of upper crust in the central highlands of Iceland by analysing shear-wave splitting (SWS), a common and near-unambiguous indicator of seismic anisotropy. Using this model as a starting point, we subsequently explore the evolution of seismic anisotropy before, during, and after the 2014–15 Bárðarbunga-Holuhraun dyke intrusion and eruption. Seismicity associated with this magmatic intrusion was used to capture the spatial evolution through time of this event in unprecedented detail. Persistent seismicity at “knot points” along the path of the dyke intrusion allow us to negate the effect of changes to source-receiver path on the measured variations in seismic anisotropic properties.

Our preliminary work suggests the far-field response of seismic anisotropy to the intrusion can be explained by existing models relating the stress field to the orientation of the fast direction. It is apparent, however, that this simple model fails to explain sufficiently our observations in the near field. Whether this is due to shortfalls in the stress modelling, the influence of the presence of melt along the raypath, or potentially a breakdown in the established relationship between stress and seismic anisotropy remains unclear.

How to cite: Bacon, C., Baltas, E., Johnson, J., White, R., and Rawlinson, N.: Investigating the response of seismic anisotropy in the crust to the 2014–15 Bárðarbunga-Holuhraun dyke intrusion and eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-370, https://doi.org/10.5194/egusphere-egu22-370, 2022.

EGU22-1166 | Presentations | GD6.2

On singularity point for acoustic orthorhombic model 

Alexey Stovas

The singularity points are very important for elastic waves propagation in low-symmetry anisotropic media (Stovas et al., 2021a). Being converted into the group velocity domain, they result in internal refraction cone with anomalous amplitudes and very complicated polarization fields. I analyze the conditional singularity point in acoustic orthorhombic (ORT) model which is very popular in processing and analysis of 3D seismic data. The elliptic ORT model has one singularity point in one of the symmetry planes (Stovas et al., 2021b). The elastic ORT model has 1 to 6 singularity points. It is shown that for acoustic ORT model the only one S1-S2 wave singularity point (per quadrant) can conditionally be defined in-between the symmetry planes. The required conditions and position of singularity point are computed. The projection of the slowness vector    for singularity point are given by

where are the elements of the stiffness coefficients matrix. I show that the singularity point for this model has the stable conical type of degeneracy (Shuvalov, 1998), which means that the internal refraction cone is always represented by ellipse in 3D space. The slowness surface for acoustic orthorhombic model that consists of three sheets corresponding to P (the inner one) and S1-S2 waves. The image of singularity point in the group domain and its three projections on the symmetry planes can be computed analytically.

 

References

Shuvalov, A.L., 1998, Topological features of the polarization fields of plane acoustic waves in anisotropic media, Proc. R. Soc. Lond., A., 454, 2911–2947.

Stovas, A., Roganov, Yu., and V. Roganov, 2021a, Geometrical characteristics of P and S wave phase and group velocity surfaces in anisotropic media, Geophysical Prospecting, 68(1), 53-69.

Stovas, A., Roganov, Yu., and V. Roganov, 2021b, Wave characteristics in elliptical orthorhombic medium, Geophysics, 86(3), C89-C99.

How to cite: Stovas, A.: On singularity point for acoustic orthorhombic model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1166, https://doi.org/10.5194/egusphere-egu22-1166, 2022.

Presence of the Etendeka continental flood basalts in northwestern Namibia, at the eastern extension of Walvis Ridge toward the African coast, is taken as evidence for the assumption that this region was affected by the Tristan da Cunha mantle plume during the rifting/break-up process between Africa and South America. Investigation of seismic anisotropy can provide further evidence for the cause-and-effect relationship between mantle flow, lithospheric deformation and surface structures. We investigate seismic anisotropy beneath NW Namibia by splitting analysis of core-refracted teleseismic shear waves (SKS family). The waveform data was obtained from two different GEOFON seismic networks in the region. The XC network with 5 stations, which has been operating for two years since 1998 and 6A network with 40 stations including both land and off-shore (OBS) stations, operated for longer than two years in 2010-2012.

The data was analyzed using the SplitRacer software and the results of joint splitting analysis assuming a one-layer of anisotropy are presented here. The less-noisy waveform data from the land stations provide reliable and consistent measurements. We obtained few reliable measurements from the OBS stations due to higher noise level and ambiguity about the sensor orientation. The majority of our fast directions exhibit an NE-SW direction consistent with the regional trend of seismic anisotropy in western Africa compatible with a model of large-scale mantle flow due to the NE-ward motion of the African plate. In the northern part of the study area, we observe an anti-clockwise rotation of the splitting polarization directions that seems to be caused by the Kaoko belt and the Puros shear zone. Based on the short-scale variation of the splitting parameters in this region, we believe that the cause of the lateral variation in SKS-splitting observation is the shallow lithospheric structure rather than a variation of deep mantle flow. Our results does not show any direct plume related observations in the study region.

How to cite: komeazi, A., Rümpker, G., and Kaviani, A.: Investigation of mantle anisotropy in NW Namibia by shear-wave splitting analysis: evidence for large-scale mantle flow and fossil-anisotropy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2576, https://doi.org/10.5194/egusphere-egu22-2576, 2022.

EGU22-3042 | Presentations | GD6.2

3D transversely isotropic shear-wave velocity structure of India and Tibet from joint modeling of Rayleigh and Love waves group velocity dispersion. 

Siddharth Dey, Monumoy Ghosh, Rupak Banerjee, Shubham Sharma, Supriyo Mitra, and Shankar Bhattacharya

We use regional Rayleigh and Love wave data, from 4750 earthquakes (M >= 4.0) recorded at 726 stations across India and Tibet, to compute fundamental mode group velocity dispersion between 10 s and 120 s, using the Multiple Filter Technique (MFA). These result in the dense coverage of 14,706 and 14,898 ray-paths for Rayleigh and Love waves, respectively. The dispersion data at discrete periods have been combined through a ray-theory based tomographic formulation to obtain 2D maps of lateral variation in group velocities, where the best resolution is upto 2.5° and 4° for Rayleigh and Love waves tomographic maps, respectively. The Peninsular Shield, the Himalayan foreland basin, the Himalayan collision-zone and the Tibetan Plateau, have been sampled at unprecedented detail. Rayleigh and Love wave dispersion curves, at each node point of the tomography, have been inverted for 1D isotropic shear-wave velocity structure of Vsv and Vsh, respectively, which are combined to obtain 3D Vsv and Vsh structures across India and Tibet. We jointly invert the two datasets at each node to obtain an isotropic 1D velocity structure. The isotropic inversion fits the two datasets reasonably well, however, the misfit in the dispersion dataset both at high and low periods is high. For this, we incorporate radial anisotropy in the velocity structure and parameterize the crust with three layers and upper mantle with two layers. Assuming this radially anisotropic earth structure, we use Genetic Algorithms (GA) to explore the model space extensively. The synthetic dispersion curves are computed using Thomson-Haskell method with reduced delta matrix. The free parameters used in the inversion are VPH and VSH, layer thickness (h) and Vs anisotropy represented by Xi (ξ=VSH/VSV)2. The non-linear inversion technique converges to a best-fitting model by iteratively minimising the misfit between the observed and the data. The 2D group velocity dispersion heterogeneities, the 3D structures of Vsv and Vsh (both isotropic and transversely isotropic) will be presented with a focus to characterize a) the structure of the Indian plate and it’s extent of underthrusting beneath Tibet, and b) to quantify the low-velocity zone at the base of the Himalayan wedge, across the basal decollement, which ruptures in megathrust earthquakes.

How to cite: Dey, S., Ghosh, M., Banerjee, R., Sharma, S., Mitra, S., and Bhattacharya, S.: 3D transversely isotropic shear-wave velocity structure of India and Tibet from joint modeling of Rayleigh and Love waves group velocity dispersion., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3042, https://doi.org/10.5194/egusphere-egu22-3042, 2022.

EGU22-3339 | Presentations | GD6.2

Evidence for Anisotropy in the Innermost Inner Core from the Earthquake Coda-correlation Wavefield 

Thuany Costa de Lima, Hrvoje Tkalčić, and Lauren Waszek

Progress on seismic imaging of the Earth’s inner core (IC) is fairly limited by the uneven distribution of sources and receivers; large earthquakes are primarily confined to plate margins, and seismic stations are unevenly deployed on the Earth’s surface. Advances in data processing techniques and new methods are required to bridge new opportunities to probe the centre of our planet and provide us with valuable information on the IC seismic structure and its surrounding dynamics. In this study, we present a newly-developed method based on the global earthquake coda-correlation wavefield to investigate the anisotropic structure of the IC. Anisotropy in seismic velocity is the directional dependence of seismic waves. Under IC pressure and temperature conditions, different phases of iron – the core’s main mineral constituent can stabilize and form elastic anisotropy. Thus, improved constraints on its strength and distribution are required to understand the crystallographic structure of iron in the IC, which is linked to the evolution of its solidification and deformation processes. Here, we stack the cross-correlation functions of the late-coda seismic wavefield (the correlation wavefield) that reverberates within the Earth up to 10 hours after large earthquakes. We analyse the travel times of the I2* correlation feature, a mathematical manifestation of similarity among IC seismic phases with the same slowness detected in global correlograms at small interstation distances (<10°). The I2* spatial sampling offers an unprecedented data coverage of the IC’s central portion, also known as the innermost IC (IMIC), which overcomes the shortage of the traditional approach using PKIKP ray paths sampling. By comparing the time residuals of different paths of I2* propagating through the IC, we confirm the presence of a deep IC structure with anisotropy fundamentally different from the IC’s outer layers. Our observations support an IMIC cylindrical anisotropy model with a slow direction oriented 55° from the Earth’s spin axis. This new evidence reinforces previous inferences on the existence of the IMIC, with implications for our understanding of the core’s geodynamical evolution. In the future, a similar approach could be applied to advance our understanding of anisotropy in the Earth’s mantle.

How to cite: Costa de Lima, T., Tkalčić, H., and Waszek, L.: Evidence for Anisotropy in the Innermost Inner Core from the Earthquake Coda-correlation Wavefield, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3339, https://doi.org/10.5194/egusphere-egu22-3339, 2022.

EGU22-5322 | Presentations | GD6.2 | Highlight

Constraining Seismic Anisotropy on Mars: New Challenges and First Detection 

Caroline Beghein, Jiaqi Li, James Wookey, Paul Davis, Philippe Lognonné, Martin Schimmel, Eléonore Stutzmann, Matthew Golombek, Jean-Paul Montagner, and William Banerdt

Seismic anisotropy is now commonly studied on Earth and has been detected at various depths, from the crust to the top of the lower mantle, in the lowermost mantle, and in the inner core. In the mantle, observations of seismic anisotropy are often taken as an indication of past or present deformation resulting in the preferential orientation of anisotropic minerals. In the crust, it can come from stress-induced oriented cracks, compositional layering, or crystallographic preferred orientation of minerals. 

While many questions remain regarding the presence and interpretation of seismic anisotropy on Earth, scientists are now faced with new, exciting challenges in trying to constrain the structure of other planetary bodies. One of the goals of NASA’s InSight mission, which landed on Mars in November 2018 and includes a very broadband seismometer, is to constrain Mars interior structure. Compared to seismic studies of Earth, which benefit from the availability of a wealth of high quality data recorded on many seismic stations, difficulties with InSight stem from having only one seismic instrument and only a few high quality events. 

In this study, we analyzed the horizontally polarized (SH)-wave reflections generated from the shallowest crustal layer (layer 1) detected at 8 ± 2 km beneath the InSight lander site by a previous receiver function (RF) study. From Sol 105, when the first low-frequency marsquake was recorded, to Sol 1094, a total of 83 broadband and low-frequency events were detected, but only nine are rated as quality-A with constraints on both their epicentral distance and back azimuth. Of those nine events, we selected four that did not show any interference with mantle triplications generated by the olivine to the wadsleyite phase transition and that had a clear signal after the direct SH phase. A model space search approach enabled us to obtain a range of acceptable SH-wave velocities and layer thicknesses, which we then compared with the RF models of Knapmeyer-Endrun et al. (2021). We found that the acceptable SH-wave speeds are systematically lower than those from the RF study. Since this RF analysis is sensitive to vertically polarized (SV)-waves, we interpret this difference as the signature of radial anisotropy with an anisotropy coefficient 𝜉=(𝑉𝑆𝐻/𝑉𝑆𝑉)2 between 0.7 and 0.9. Modeling of preferred alignment of inclusions shows that dry or fluid-filled cracks/fractures, and igneous inclusions can reproduce the observed radial anisotropy amplitude with VSV>VSH. 

How to cite: Beghein, C., Li, J., Wookey, J., Davis, P., Lognonné, P., Schimmel, M., Stutzmann, E., Golombek, M., Montagner, J.-P., and Banerdt, W.: Constraining Seismic Anisotropy on Mars: New Challenges and First Detection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5322, https://doi.org/10.5194/egusphere-egu22-5322, 2022.

Teleseismic travel-time tomography remains one of the most popular methods for obtaining images of Earth's upper mantle. However, despite extensive evidence for a seismically anisotropic mantle, assuming an isotropic Earth remains commonplace in such imaging studies. This assumption can result in significant imaging artefacts which in turn may yield misguided inferences regarding mantle dynamics. Using realistic synthetic seismic datasets produced from waveform simulations through elastically anisotropic geodynamic models of subduction, I show how such artefacts manifest in teleseismic P- and S-wave tomography. The anisotropy-induced apparent anomalies are equally problematic in both shear and compressional body wave inversions and the nature of the shear velocity artefacts are dependent on the coordinate system in which the delay times are measured. In general, the isotropic assumption produces distortions in slab geometry and the appearance of large sub- and supra-slab low-velocity zones. I summarise new methods for inverting P- and S-delay times for both isotropic and anisotropic heterogeneity through the introduction of three anisotropic parameters that approximate P and S propagation velocities in arbitrarily orientated hexagonally symmetric elastic media. Through a series of synthetic tomographic inversions, I demonstrate that both teleseismic P- and S-wave delay time data can resolve complex anisotropic heterogeneity likely present in subduction environments. Moreover, including anisotropic parameters into the inversions improves the reconstruction of true isotropic anomalies. Particularly important to the removal of erroneous velocity structure is accounting for dipping fabrics as many imaging artefacts remain when simpler azimuthal anisotropy is assumed. I conclude by highlighting results from recent applications of the anisotropic imaging method to P-wave datasets in the Western US and Mediterranean.

How to cite: VanderBeek, B.: New imaging strategies for constraining upper mantle anisotropy with teleseismic P- and S-wave delay times, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5497, https://doi.org/10.5194/egusphere-egu22-5497, 2022.

Radial seismic anisotropy (RA) designates the difference between the speeds of vertically and horizontally polarized shear waves. RA in the crust can provide information on past tectonic events. Since the amplitude and impact of anisotropic are smaller than the variation of velocity, it is more difficult to distinguish whether radially anisotropic anomalies are driven by the structure or uncertainty. Hence, a lack of considering uncertainty and trade-off here may underestimate radial anisotropy and lead to divergent geodynamical interpretations. The hierarchical transdimensional Bayesian approach is able to provide uncertainty estimates taking fully into account the nonlinearity of the forward problem. Under the Bayesian framework, the mean and the variance of the ensemble containing a large set of models are interpreted as the reference solution and a measure of the model error respectively. 

In our study, we applied a two-step RA inversion of surface wave dispersion and receiver function based on a hierarchical transdimensional Bayesian Monte Carlo search with coupled uncertainty propagation to a temporary broadband array covering all of Sri Lanka. First, we constructed Rayleigh and Love wave phase velocity and errors maps at periods ranging from 0s to 20s. To remove outliers, data uncertainty distribution was expressed as a mixture of a Gaussian and uniform distribution. Next, we inverted local dispersion curves and receiver functions jointly to obtain 1D shear velocity and RA models. The method effectively quantifies the uncertainty of the final crustal shear wave velocity and RA model and shows robust results. The negative RA (Vsv > Vsh) anomalous with low uncertainty found in the mid-lower crust of Central Sri Lanka may show evidence that the charnockite inclusion is associated with the shear zones confined to the cores of some doubly-plunging synforms. In the east Highland Complex, the positive radial anisotropy (Vsh > Vsv) anomalous with low uncertainty may reveal the evidence for sub-horizontal shear zones along the thrust boundary.

How to cite: Ke, K.-Y., Tilmann, F., Ryberg, T., and Dreiling, J.: Radial anisotropy models and their uncertainties beneath Sri Lanka derived from joint inversion of surface wave dispersion and receiver functions using a Bayesian approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5526, https://doi.org/10.5194/egusphere-egu22-5526, 2022.

EGU22-6498 | Presentations | GD6.2

A hybrid computational Framework for 3D anisotropic full-Waveform inversion at a regional scale 

Foivos Karakostas, Andrea Morelli, Irene Molinari, Brandon VanderBeek, and Manuele Faccenda

Seismic anisotropy exists in various depths on Earth. However, computational complexities and limited data coverage often lead many seismic tomographic efforts to neglect it. This isotropic assumption can lead to various misinterpretations, which become more important when the spatial resolution is increased. 

In our project, we aim at constructing, through full-waveform inversion, a 3D seismic model of upper mantle anisotropic structure (approximately 500 km depth) below the Tyrrhenian Sea -- a region of great geodynamic interest mainly because of the Calabro-Ionian subduction zone. 

Here we present the framework and the forward modelling, based on the joint use of SPECFEM3D and AxiSEM software, for the implementation of the so-called "box tomography" [1]. By this, a 3D, anisotropic, model spans the region that we aim to resolve, whereas the rest of the globe is represented by a 1D model with lower resolution. This methodology allows the inclusion of teleseisms -- thus a much larger dataset than allowed by closed-domain modelling, as we can also use numerous seismic events out of the region of interest recorded by the dense network of stations within it. We show that this approach in fact highly improves the coverage of data, that can be used for inversion. 

We use SPECFEM3D for the region of interest and AxiSEM for the global simulation. We process the topography, seismic velocities and anisotropy, in order to construct a realistic 3D input model for the area of interest, that honours the Earth's curvature and transforms the geometry of an a priori model from geographical to Cartesian coordinates, with respect to a point of reference, situated in the middle of the top layer of the constructed mesh. We then process the waveforms, resulting from such forward simulation, with the application of a rotation from the Cartesian coordinates to the geographical ones, in order to perform the inversion with the use of real data of seismic recordings. The forward modelling is then to be used for computation of anisotropic Fréchet kernels and inversion. 

[1] Yder Masson, Barbara Romanowicz, Box tomography: localized imaging of remote targets buried in an unknown medium, a step forward for understanding key structures in the deep Earth, Geophysical Journal International, Volume 211, Issue 1, October 2017, Pages 141–163, https://doi.org/10.1093/gji/ggx141

How to cite: Karakostas, F., Morelli, A., Molinari, I., VanderBeek, B., and Faccenda, M.: A hybrid computational Framework for 3D anisotropic full-Waveform inversion at a regional scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6498, https://doi.org/10.5194/egusphere-egu22-6498, 2022.

EGU22-7184 | Presentations | GD6.2

Patchwork structure of continental lithosphere captured in 3D body-wave images of its anisotropic fabrics 

Jaroslava Plomerová, Helena Žlebčíková, and Luděk Vecsey

Seismic anisotropy, modelled from propagation of teleseismic longitudinal (P) and shear (S/SKS) waves, provides unique constraints on tectonic fabrics and character of past and present-day deformations of the continental lithosphere in different tectonic environments (e.g., Babuška and Plomerová, Solid Earth Sci. 2020). We evaluate body-wave anisotropic parameters (directional variations of velocities or shear-wave splitting) in 3D and invert for three-dimensional structure of the upper mantle (Munzarová et al., GJI 2018) with no limitation imposed on the symmetry axis orientation into the horizontal or vertical directions. Resulting models of the continental lithosphere are based on data from several passive seismic experiments in Archean, Proterozoic and a variety of Phanerozoic provinces of Europe. We emphasize the importance of the three-dimensional approach of modelling anisotropy to be able to detect tilts of symmetry axes in individual domains of the mantle lithosphere. The extent of the domains is delimited by changes in orientation and strength of anisotropy. Assuming only azimuthal anisotropy, similarly to only isotropy, may create artefacts and lead to spurious interpretations (e.g., VanderBeek and Faccenda, GJI 2021). Prevailingly sub-horizontal preferred orientation of olivine, the most abundant mantle mineral, arises from mantle convection in newly formed oceanic lithosphere on both sides of the mid-oceanic ridges. Systematically oriented dipping fabrics in domains of the continental mantle lithosphere reflect series of successive subductions of ancient oceanic plates and their accretions enlarging primordial continent cores. Consequent continental break-ups and assemblages of wandering micro-plates preserve “frozen” anisotropic fabrics and create patchwork structures of the present-day continents.

How to cite: Plomerová, J., Žlebčíková, H., and Vecsey, L.: Patchwork structure of continental lithosphere captured in 3D body-wave images of its anisotropic fabrics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7184, https://doi.org/10.5194/egusphere-egu22-7184, 2022.

EGU22-7201 | Presentations | GD6.2

Olivine texture evolution under simple deformation: Comparing different numerical methods for calculating LPO and anisotropic viscosity 

Yijun Wang, Ágnes Király, Clinton Phillips Conrad, Lars Hansen, and Menno Fraters

The development of olivine texture, or lattice preferred orientation (LPO), has been implemented in many numerical modelling tools to predict seismic anisotropy, which places constraints on mantle dynamics. However, a few recent studies have linked olivine texture development to its mechanical anisotropy, which in turn can affect deformation rates and also the resulting texture. To study the effect of anisotropic viscosity (AV) and LPO evolution in geodynamics processes, it is important to know the role of AV and LPO and the differences between the numerical methods that calculate them.

The modified director method parameterizes the olivine LPO formation as relative rotation rates along the slip systems that participate in the rotation of olivine grains due to finite deformation. When it is coupled with a micromechanical model for olivine AV, it allows the anisotropic texture to modify the viscosity. We compare the olivine textures predicted by the modified director method both with and without a coupled micromechanical model and textures predicted by the D-Rex LPO evolution model. To do this, we recalculate the texture observed in simple 3D models such as a shear box model and two other well-understood models: a corner flow model and a subduction model. 

In general, we observed that the D-Rex models predict a stronger anisotropic texture compared to the texture predicted by the modified director method both with and without the micromechanical model, in agreement with previous studies. When including the micromechanical model, the anisotropic texture changes the observed strain rates, which allows for a slightly faster texture evolution that is more similar to the D-Rex predictions than it is to those produced by the modified director method alone. We found that even for the simplest settings there is an increase of 10~15% in strain rate during deformation until a strain of 2.5. When shearing the asthenosphere over ~10 Myr, such anisotropy could modify the effective viscosity of the mantle,causing an up to 40% increase in plate velocity for the same applied stress. The anisotropy can also induce deformation in planes other than the initial shear plane, which can change the direction of the primary deformation.

Our ultimate goal is to understand the role of AV and LPO evolution in geodynamic processes by looking at deformation paths predicted by geodynamic models in ASPECTWith this initial test, we will gain a basic understanding of olivine AV behavior and LPO evolution under different deformation settings calculated with different numerical methods, which we will carry onto our next step of implementing anisotropic viscosity of olivine in 3D into ASPECT.

How to cite: Wang, Y., Király, Á., Conrad, C. P., Hansen, L., and Fraters, M.: Olivine texture evolution under simple deformation: Comparing different numerical methods for calculating LPO and anisotropic viscosity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7201, https://doi.org/10.5194/egusphere-egu22-7201, 2022.

EGU22-7807 | Presentations | GD6.2

New insights into tomographic image interpretation and upper mantle dynamics by combining geodynamic modelling and seismological methods 

Rosalia Lo Bue, Francesco Rappisi, Brandon Paul Vanderbeek, and Manuele Faccenda

Earth’s crust and upper mantle (above 400 km) exhibit strong anisotropic fabrics which reflect the strain history of the rocks and can provide important constraints on mantle dynamics and tectonics. Although the well-established anisotropic structure of Earth’s upper mantle, the influence of elastic anisotropy on the seismic tomography remains largely ignored. It is in fact commonplace to neglect the effects of seismic anisotropy in the construction of tomographic models assuming an isotropic Earth. This approximation certainly simplifies the computational approach but can introduce notable imaging artefacts hence errors in the interpretation of the tomographic results.

Here, we want to bring new insights into the 3D upper mantle structure and dynamics by combining geodynamic modelling and seismological methods taking into account seismic anisotropy.

An ideal environment for studying seismic anisotropy and related geodynamic processes is the Central-Western Mediterranean, that, in the last 20-30 million years, has experienced a complex tectonic activity characterized by back-arc extension related to slab retreat in the Liguro-Provençal, Alborean, Algerian and Tyrrhenian basins and episodes of slab break-off, lateral tearing and interactions between slabs.

Firstly, we apply the modelling methodology of Lo Bue et al., 2021 to reproduce the geodynamic evolution of the study region over the last ∼20-30 Myr. We validate this geodynamic model by comparing seismological synthetics (e.g., SKS splitting) and major tectonic features (i.e., slab and trench geometry) with observations. Next, we use the elastic tensors of the present-day modelled Mediterranean set-up to performed 3D P-wave anisotropic tomography by inverting synthetics delay times as in VanderBeek and Faccenda, 2021 validated through comparison with the geodynamic reference model.

In this work, we attempt to answer some fundamental questions. Compared to Lo Bue et al., 2021 how does using a more complex initial geometry affect the geodynamic modelling result? How well does P-wave anisotropic tomography recover the isotropic and anisotropic features? By performing purely isotropic inversions, which are the main artefacts introduced in the tomographic image by neglecting seismic anisotropy? How much the vertical smearing effect bias P-wave tomographic models?

 

References

Lo Bue, R., Faccenda, M., & Yang, J. (2021). The role of adria plate lithospheric structures on the recent dynamics of the central mediterranean region. Journal of Geophysical Research: Solid Earth, 126(10), e2021JB022377.

VanderBeek, B. P., & Faccenda, M. (2021). Imaging upper mantle anisotropy with teleseismic p- wave delays: Insights from tomographic reconstructions of subduction simulations. Geophysical Journal International, 225(3), 2097–2119.

How to cite: Lo Bue, R., Rappisi, F., Vanderbeek, B. P., and Faccenda, M.: New insights into tomographic image interpretation and upper mantle dynamics by combining geodynamic modelling and seismological methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7807, https://doi.org/10.5194/egusphere-egu22-7807, 2022.

For the understanding of deformational mechanism and geodynamics of a tectonic set up, the source localization and central depth of anisotropy plays a vital role. Though mantle dynamics and deformation patterns can be understood from studying the shear wave splitting mechanism, the true interpretation of under earth mechanism governing the geodynamics remains little biased and unrealistic without the  proper justification and identification of the source localization and depth of anisotropy. Our present study is focused on the possible central depth determination and source localization of anisotropy beneath the Sikkim Himalayan region based upon the well-established spatial coherency method of Splitting parameters, an improved and dynamic principle of grid search analysis based on the Fresnel zone concept. The principle is based upon the maximum coherency relation between the splitting parameters suggested by a minimization in the variation factor as a function of true depth of the anisotropy. Sikkim Himalaya, sandwiched between the central Nepal Himalaya and the eastern Bhutan Himalaya, demarcates the distinct change in the width of the Himalayan foreland basin and the Main Himalayan Thrust (MHT), which is a part of the active deforming eastern Himalayan fold axis and thrust belt. The Spatial coherency analysis of splitting parameters suggests the central depth of heterogeneity at around 130 km beneath this Sikkim Himalayan region as a consequence of the deformation patterns governed by the complex lithospheric mass at this particular depth.

 

KEYWORDS

Spatial coherency, Shear wave splitting, Sikkim Himalaya, lithosphere.

How to cite: Biswal, S., Dey, G., and Mohanty, D. D.: Implications on source localization and central depth of anisotropy beneath the Sikkim Himalaya: an appraisal on lithospheric deformation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9402, https://doi.org/10.5194/egusphere-egu22-9402, 2022.

EGU22-10088 | Presentations | GD6.2

Quantifying the effective seismic anisotropy produced by a ridge-transform model 

Thomas Bodin, Alexandre Janin, Milena Marjanovic, Cecile Prigent, Yann Capdeville, Sebastien Chevrot, and Stephanie Durand

Global tomographic models depict long-wavelength azimuthal anisotropy in the oceanic upper mantle, with a fast axis direction orthogonal to divergent plate boundaries. This anisotropy is usually attributed to the Lattice Preferred Orientation (LPO) of olivine due to asthenospheric mantle flow away from the ridge axis. In this work, we want to test an alternative hypothesis, whether this observed anisotropic signal could be partially explained by the presence of transform faults and associated fracture zones in the lithosphere. The transform plate boundaries represent sharp structures perpendicular to the ridge-axis with the wavelength (˜10 km), which is much smaller than the wavelength of seismic surface waves used to image the mantle (˜100 km). Therefore, transform faults could potentially result in an effective anisotropy in tomographic images through their Shape Preferred Orientation (SPO). We base our calculations on several thermo-chemical models that follow the observed ridge-transform geometry at different spreading rates. To produce the effective medium as seen by long-period waves, we use a non-periodic homogenization algorithm. The resulting seismic velocity field can be interpreted as the tomographic image that would be obtained after inverting long-period seismic data; it is smooth, fully anisotropic, and comparable to actual tomographic models.

How to cite: Bodin, T., Janin, A., Marjanovic, M., Prigent, C., Capdeville, Y., Chevrot, S., and Durand, S.: Quantifying the effective seismic anisotropy produced by a ridge-transform model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10088, https://doi.org/10.5194/egusphere-egu22-10088, 2022.

EGU22-11315 | Presentations | GD6.2

Differential SKS-SKKS splitting due to lowermost mantle anisotropy beneath North America measured from beamformed SmKS phases 

Jonathan Wolf, Maureen D Long, Daniel A Frost, Adeolu O Aderoju, Neala Creasy, Edward Garnero, and Ebru Bozdag

Differential SKS-SKKS splitting is often interpreted as evidence for lowermost mantle anisotropy, because while SKS and SKKS raypaths are very similar in the upper mantle, they diverge substantially in the lowermost mantle. While discrepant SKS-SKKS splitting is a valuable tool to probe D'' anisotropy, individual measurements are typically noisy and have large scatter, making interpretation challenging. Array techniques are commonly used in observational seismology to enhance signal-to-noise ratios and extract seismic phases that would not be reliably detectable in single seismograms. Such techniques, however, have rarely been applied to resolve seismic anisotropy via shear wave splitting. In this study, we apply stacking and beamforming for different subarrays across the USArray to analyze SKS-SKKS splitting discrepancies measured across the North American continent. A benchmarking exercise demonstrates that the effect of upper mantle anisotropy on the beamformed phases can be understood as a relatively simple average of splitting over different upper mantle volumes, and that discrepant measurements reflect a contribution from the lowermost mantle. We obtain robust differential splitting intensity measurements for beamformed data from a selection of events that occurred in the western Pacific and Scotia subduction zones. This approach yields a robust set of splitting intensity discrepancy values for phases that sample the lowermost mantle beneath North America and the surrounding region, with much less scatter than comparable datasets based on individual seismograms. We find evidence for several distinct regions with strong anisotropy at the base of the mantle beneath our study region, plausibly due to subduction-related lowermost mantle flow and deformation. 

How to cite: Wolf, J., Long, M. D., Frost, D. A., Aderoju, A. O., Creasy, N., Garnero, E., and Bozdag, E.: Differential SKS-SKKS splitting due to lowermost mantle anisotropy beneath North America measured from beamformed SmKS phases, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11315, https://doi.org/10.5194/egusphere-egu22-11315, 2022.

EGU22-11438 | Presentations | GD6.2

Numerical modelling of strain localization by anisotropy evolution during 2D viscous simple shearing 

William Halter, Emilie Macherel, Thibault Duretz, and Stefan M. Schmalholz

Strain localization and associated softening mechanisms in a deforming lithosphere are important for subduction initiation or the generation of tectonic nappes during orogeny. Many strain localization and softening mechanisms have been proposed as being important during the viscous, creeping, deformation of the lithosphere, such as thermal softening, grain size reduction, reaction-induced softening or anisotropy development. However, which localization mechanism is the controlling one and under which deformation conditions is still contentious. In this contribution, we focus on strain localization in viscous material due to the generation of anisotropy, for example due to the development of a foliation. We numerically model the generation and evolution of anisotropy during two-dimensional viscous simple shear in order to quantify the impact of anisotropy development on strain localization and on the effective softening. We calculate the finite strain ellipse during viscous deformation. The aspect ratio of the finite strain ellipse serves as proxy for the magnitude and evolution of anisotropy, which determines the ratio of normal to tangential viscosity. To track the orientation of the anisotropy during deformation we apply a director method. We benchmark our implementation of anisotropy by comparing results of two independently developed numerical algorithms based on the finite difference method: one algorithm employs a direct solver and the other a pseudo-transient iterative solver. We will present results of our numerical simulations and discuss their application to natural shear zones.

How to cite: Halter, W., Macherel, E., Duretz, T., and Schmalholz, S. M.: Numerical modelling of strain localization by anisotropy evolution during 2D viscous simple shearing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11438, https://doi.org/10.5194/egusphere-egu22-11438, 2022.

EGU22-12169 | Presentations | GD6.2

Surface wave detectability of transition zone anisotropy induced by non-Newtonian mantle flow 

John Keith Magali, Sébastien Merkel, and Estelle Ledoux

Large-scale anisotropy inferred from long-period seismic tomography mainly results from the crystallographic preferred orientation (CPO) of olivine aggregates due to mantle deformation. In the 410-km transition zone, the inclusion of wadsleyite CPO diminishes the overall anisotropy. This may predispose the latter below the seismic detection limit.  In this study, we attempt to assess the detectability of the anisotropy in the 410-km transition zone using surface wave dispersion measurements. Proceeding as a purely-forward approach, we consider non-Newtonian mantle flows reminiscent to the deformation by dislocation creep of olivine. A wadsleyite layer is imposed underneath the discontinuity down to a depth of 520 km. We model the CPO development in olivine and in wadsleyite using a visco-plastic self-consistent (VPSC) approach. Finally, we compute local surface wave dispersion curves and its azimuthal variations to study the surface imprint of transition zone anisotropy.  We anticipate the sensitivity kernels to as well provide key insights in evaluating its detectability.

How to cite: Magali, J. K., Merkel, S., and Ledoux, E.: Surface wave detectability of transition zone anisotropy induced by non-Newtonian mantle flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12169, https://doi.org/10.5194/egusphere-egu22-12169, 2022.

EGU22-13364 | Presentations | GD6.2

Seismic anisotropy beneath the western part of the Carpathian-Pannonianregion inferred from combined SKS splitting and mantle xenolith studies 

Nóra Liptai, Zoltán Gráczer, Gyöngyvér Szanyi, Bálint Süle, László Aradi, György Falus, Götz Bokelmann, Máté Timkó, Gábor Timár, Sierd Cloetingh, Csaba Szabó, and István Kovács and the AlpArray Working Group

Information on mantle anisotropy can be obtained from methods such as
studying the lattice-preferred orientation (LPO) in mantle peridotites,
or conducting shear-wave splitting (SKS) analyses which allow to
determine whether it is a single or multi-layered anisotropy and the
delay time of the fast and slow polarized wave can indicate the
thickness. In this study we provide a detailed SKS mapping on the
western part of the Carpathian-Pannonian region (CPR) using an increased
amount of splitting data, and compare the results with seismic
properties reported from mantle xenoliths to characterize the depth,
thickness, and regional differences of the anisotropic layer in the
mantle.
According to the combined SKS and xenolith data, mantle anisotropy is
different in the northern and the central/southern part of the western
CPR. In the northern part, the lack of azimuthal dependence of the fast
split S-wave indicates a single anisotropic layer, which agrees with
xenolith data from the Nógrád-Gömör volcanic field. In the central
areas, multiple anisotropic layers are suggested by systematic azimuthal
variations in several stations, which may be explained by two,
petrographically and LPO-wise different xenolith subgroups described in
the Bakony-Balaton Highland. The shallower layer is suggested to have a
‘fossilized’ lithospheric structure, which could account for the
occasionally detected E-W fast S-orientations, whereas the deeper one
reflects structures responsible for the regional NW-SE orientations
attributed to the present-day convergent tectonics. In the Styrian
Basin, results are ambiguous as SKS splitting data hints at the presence
of multiple anisotropic layers, however, it is not supported clearly by
xenolith data.
Spatial coherency analysis of the splitting parameters put the center of
the anisotropic layer at ~140-150 km depth under the Western
Carpathians, which implies a total thickness of ~220-240 km. Thickness
calculated from seismic properties of the xenoliths resulted in lower
values on average, which may be explained by heterogeneous sampling by
xenoliths, or the different orientation of the mineral deformation
structures (foliation and lineation).

How to cite: Liptai, N., Gráczer, Z., Szanyi, G., Süle, B., Aradi, L., Falus, G., Bokelmann, G., Timkó, M., Timár, G., Cloetingh, S., Szabó, C., and Kovács, I. and the AlpArray Working Group: Seismic anisotropy beneath the western part of the Carpathian-Pannonianregion inferred from combined SKS splitting and mantle xenolith studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13364, https://doi.org/10.5194/egusphere-egu22-13364, 2022.

The Dayi seismic gap of the Longmenshan thrust belt is located between the ruptures of the 2008 Wenchuan Earthquake and the 2013 Lushan Earthquake, with a length of about 40 ~ 60 km. So far, it has been still a heated debate on whether the Dayi seismic gap has the hazard of strong earthquakes in the near future. The occurrence of a strong earthquake in the seismic gap is closely related to the existence of high stress accumulation and the most direct method is to measure the borehole stress in the field. In order to find out the present stress state, in-situ stress measurements were carried out at the hanging wall and footwall of Dachuan-Shuangshi fault zone in Dachuan Town. The results showed that the hanging wall and footwall of Dachuan-Shuangshi fault zone in Dayi seismic gap are in a high-stress state. Based on seismicity parameter b-value, crustal velocity structure, GPS deformation monitoring data and temperature data, etc., it can be learned that there is a positive correlation coupling relationship between near surface shallow stress and deep stress. In this paper, a response model of shallow stress to deep locking was established. It was speculated that Dayi seismic gap has the potential hazard of strong earthquakes. This research result not only deepens the understanding of the relationship between stress and earthquake preparation, but also provides an effective scientific method for identifying seismic hazards in other active fault seismic gaps.

How to cite: li, B., Huang, J., and Xie, F.: In situ stress state and earthquake hazard assessment in Dayi seismic gap of the Longmenshan thrust belt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-648, https://doi.org/10.5194/egusphere-egu22-648, 2022.

EGU22-799 | Presentations | TS1.4

Machine Learning and Underground Geomechanics – data needs, algorithm development, uncertainty, and engineering verification 

Josephine Morgenroth, Usman T. Khan, and Matthew A. Perras

Machine learning algorithms (MLAs) are emerging as a powerful tool for forecasting complex and nuanced rock mass behaviour, particularly when large, multivariate datasets are available. In engineering practice, it is often difficult for geomechanical professionals to investigate all available data in detail, and simplifications are necessary to streamline the engineering design process. An MLA is capable of processing large volumes of data quickly and may uncover relationships that are not immediately evident when manually processing data. This research compares two algorithms developed for two mines representing end member behaviours of rock failure mechanisms: squeezing ground with high radial convergence, and spalling ground with high in situ stresses and seismicity. For the squeezing ground case study, a Convolutional Neural Network is used to forecast the yield of the tunnel liner elements using tunnel mapping images as the input. For the high stress case study, a Long Short Term Memory network is used to forecast the in-situ stresses that takes time series microseismic events and geomechanical properties as inputs. The two case studies are used to compare input data requirements and pre-processing techniques. Ensemble modelling techniques used to quantify MLA uncertainty for both case studies are presented. The development of the two MLAs is discussed in terms of their complexity, generalizability, performance evaluation, verification, and practical applications to underground rock engineering. Finally, best practices for MLA development are proposed based on the two case studies to ensure model interpretability and use in engineering applications.

How to cite: Morgenroth, J., Khan, U. T., and Perras, M. A.: Machine Learning and Underground Geomechanics – data needs, algorithm development, uncertainty, and engineering verification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-799, https://doi.org/10.5194/egusphere-egu22-799, 2022.

EGU22-2742 | Presentations | TS1.4 | Highlight

Assessing the effect of mass withdrawal from a surface quarry on the Mw4.9 Le Teil (France) earthquake triggering 

Julie Maury, Théophile Guillon, Hideo Aochi, Behrooz Bazargan, and André Burnol

On November 11th 2019, the Le Teil, France earthquake occurred in the vicinity of a quarry. Immediately, the question was raised about the potential triggering of this earthquake by the quarry. However, another potential triggering source is a hydraulic effect related to heavy rainfall (Burnol et al, 2021). That’s why it is important to quantify precisely the mechanical effect of mass withdrawal. Results from different studies (Ampuero et al, technical report CNRS, 2019; De Novellis et al, Comm. Earth Env., 2021) agrees to a Coulomb stress variation of 0.15 to 0.2 MPa. However, these studies are based on Boussinesq solution supposing a homogeneous half-space that maximize the effect of the quarry. Here we used the distinct element method code 3DEC @Itasca in 3D to take advantage of an improved geological model and assess the impact of discontinuities as well as lithology. Our results show the maximum Coulomb stress change of 0.27 MPa at 1.4 km depth, a value of the same order as what is obtained with Boussinesq solution. A comparison between the location of the earthquake (Delouis et al, 2021) and the maximum Coulomb stress is realized. The maximum value is located at the intersection of the Rouviere fault with another local fault highlighting the interaction between these structures. However, the in situ stress field is not well-known, fault parameters are difficult to assess and there is some uncertainty on the volume of extracted material in the 19th century estimated by the quarry owner. Additionally, the presence of marl in the Hauterivian layer suggests it could have an elasto-plastic behavior. A parametric study has been realized to assess the effect on Coulomb stress change of these uncertainties taking plausible values for each parameter. We show that the uncertainty associated with our calculations affect the results within a range of less than 10%.

How to cite: Maury, J., Guillon, T., Aochi, H., Bazargan, B., and Burnol, A.: Assessing the effect of mass withdrawal from a surface quarry on the Mw4.9 Le Teil (France) earthquake triggering, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2742, https://doi.org/10.5194/egusphere-egu22-2742, 2022.

EGU22-3272 | Presentations | TS1.4

The stress memory in rocks: insight from the deformation rate analysis (DRA) and acoustic emission (AE) 

Zulfiqar Ali, Murat Karakus, Giang D. Nguyen, and Khalid Amrouch

Deformation rate analysis (DRA) and Acoustic Emission (AE) are popular methods of in-situ stress measurements from oriented cored rocks which take advantage of the rock stress memory also known as the Kaiser effect. These methods rely on the accurate measurement of a point of inflection in the characteristic DRA and AE curves, however, due to the complex geological stress history in rocks, locating point of inflection can be problematic. In order to better understand the stress memory experiments were performed on a combination of six different types of soft, and hard crystalline rocks including concrete with no stress history. The effect of loading modes, strain rates, and time delay were studied on preloaded rock specimens to investigate their influence on the stress memory. A fading effect was observed when the number of the cycles in the test were increased which led to the development of a new method of quantifying the preloads. Results show that the type of loading and the loading rate has little to no influence on the Kaiser effect, however, under faster loading rates the Kaiser effect is more distinct. Likewise, no time dependency was observed for time delays up to seven months.

How to cite: Ali, Z., Karakus, M., Nguyen, G. D., and Amrouch, K.: The stress memory in rocks: insight from the deformation rate analysis (DRA) and acoustic emission (AE), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3272, https://doi.org/10.5194/egusphere-egu22-3272, 2022.

A review of works is presented in which new models of continuum mechanics generalizing the classical theories of elasticity are being intensively developed. These models are used to describe composite and statistically inhomogeneous media, new structural materials, as well as complexly constructed massifs in mine and ground conditions; and in the study of phenomena occurring in permafrost under the influence of heating processes. A characteristic feature of the theory of media with a hierarchical structure is the presence of explicit or implicit scale parameters, i.e. explicit or implicit non-locality of the theory. This work focuses on the study of the non-locality effects and internal degrees of freedom reflected in internal stresses that are not described by the classical theory of elasticity, but can be potential precursors of the development of a catastrophic process in a rock mass.

How to cite: Hachay, O. and Khachay, A.: Geophysical research and monitorind within a block-layered model with inclusions of hierrchical structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4574, https://doi.org/10.5194/egusphere-egu22-4574, 2022.

EGU22-4738 | Presentations | TS1.4

Modeling principal stress orientations in the Arabian plate using plate velocities 

Santiago Pena Clavijo, Thomas Finkbeiner, and Abdulkader M. Afifi

The Arabian Peninsula is part of a small tectonic plate that is characterized by active and appreciable deformations along its boundaries. Knowledge of the present-day in situ stress field in the Arabian plate and its variability is critical for earth science disciplines that require an understanding of geodynamic processes. In addition, it is essential for a range of practical applications that include the production of hydrocarbons and geothermal energy, mine safety, seismic hazard assessment, underground storage of CO2, and more.

This project aims at modeling the stress orientation field in the Arabian Plate using advanced computational tools together with a plate velocity model. We built a three-layer 3D model of the Arabian crust using digital elevation, basement depth, and Moho depth maps. Based on these data, we built a 3D unstructured finite element mesh for the whole Arabian plate, including the offshore area, with finer resolution at critical locations. The latter is a novel approach to this work.  To capture the deformation caused by the water bodies in the Red Sea, Gulf of Aden, and the Arabian Sea areas, we set a hydrostatic boundary condition as a function of bathymetry. Along the Zagros fold and thrust belt, we pinned the plate boundary to capture continental collision. Finally, the partial differential equation of force equilibrium (a linear static analysis) is solved using plate displacements (inferred from plate velocities) as boundary conditions for several displacement conditions.

The modeling results suggest NE-SW SHmax azimuths in northeastern Saudi Arabia and Kuwait while the Dead Sea transform areas show NW-SE to NNW-SSE azimuths, and the rest of the plate is characterized by predominant N-S SHmax azimuth. Due to pinned boundary conditions at the Zagros Mountains, SHmax azimuth changes from N-S at the Red Sea basin to NE-SW at the Zagros fold and thrust belt. We also notice significant stress concentrations in the transition from the Arabian shield to the sedimentary basins in the Eastern parts of the plate. This is in response to associated changes in rock properties. Hence, the simulated stress orientations corroborate the ongoing tectonic process and deepen our understanding of regional and local in situ stress variation drivers as well as the current elastic deformation in the Arabian plate.

How to cite: Pena Clavijo, S., Finkbeiner, T., and Afifi, A. M.: Modeling principal stress orientations in the Arabian plate using plate velocities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4738, https://doi.org/10.5194/egusphere-egu22-4738, 2022.

EGU22-5494 | Presentations | TS1.4 | Highlight

Stress characterization in the Canadian Shield: Complexity in stress rotation 

Wenjing Wang and Douglas Schmitt

NE-SW stress compression in the Western Canadian Sedimentary Basin was discovered in the pioneering borehole breakout observations of Bell and Gough (1979). However, all of these and subsequent stress direction indicators are from the Phanerozoic sediment veneer, while the state of stress in the underlying craton remains unexplored. With the emergent demands on geothermal energy and wastewater and CO2 disposal, however, the state of stress in the cratons can no longer be safely ignored. To address this problem, we analyze various vintages of geophysical logs obtained from a serendipitous wellbore-of-opportunity drilled to 2.4 km in NE Alberta.  The profile of breakout orientations inferred from image and caliper logs exhibits a distinct rotation in breakout orientations changing from N100°E at 1650-2000m to N173°E at 2000-2210m and, finally, to N145°E at the bottom from 2210-2315m. The deepest measurement is consistent with the many observations in the overlying sediments. The heterogeneous breakout orientations at different depth intervals possibly indicate a heterogeneous in-situ stress field in the Precambrian craton. In addition, however, there is a strong correlation between the metamorphic textures and the breakout orientations suggesting that anisotropic strength may play an important role.  Using a recently developed algorithm we show that these observations can indeed be explained by foliation-controlled failure patterns in such anisotropic metamorphic rocks (Wang & Schmitt, accepted).  Models demonstrate that the observed breakout rotations can be produced under uniform stress orientations with failure slip planes controlled by the textured metamorphic rocks with anisotropic strength. This modeled stress field indicates that the stress field in the Canadian Shield where the far-field SH azimuth is at N50°E and the region is under normal/strike-slip faulting regime, is coupled with that in the overlying sedimentary basin.

How to cite: Wang, W. and Schmitt, D.: Stress characterization in the Canadian Shield: Complexity in stress rotation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5494, https://doi.org/10.5194/egusphere-egu22-5494, 2022.

EGU22-6453 | Presentations | TS1.4

Can we afford fracture pressure uncertainty? Limit tests as a key calibration for geomechanical models 

Michał Kępiński, David Wiprut, and Pramit Basu

The Leak-Off Test (LOT) is one of the most common fracture pressure/Shmin calibration measurements conducted in wellbores. Well engineers rely on readings from LOTs to design safe drilling plans. The LOT results indicate the maximum mud weight or equivalent circulating density that can be used to drill the next hole section without causing fluid losses to the formation. Losses are one of the most expensive issues to mitigate in drilling operations. In more severe cases, losses may lead to subsequent drilling challenges such as hole collapse or kicks. Oftentimes, drillers choose not to pressurize the well up to the leak-off pressure due to the risk of weakening the rock beneath the casing shoe by creating a fracture. In these cases, a formation integrity test (FIT) is conducted. However, the FIT is inadequate for properly constraining the fracture gradient or for input to geomechanical models because it is possible for the FIT to terminate at pressures that are either above or below the far-field minimum stress.

Geomechanical modelling from several projects in Poland shows that insufficient LOT measurements introduce a wide range of fracture gradient uncertainty, complicating the analysis of optimal ECD values in narrow margin drilling sections. This leads to difficulty in determining the proper mud weight when a loss event occurs. Additionally, without reliable calibration of the minimum horizontal stress, the geomechanical model used to determine the lower bound of the mud window becomes more uncertain. An inadequately constrained mud window can result in further drilling complications such as tight hole, stuck pipe, poor hole condition, and compromised log quality.

How to cite: Kępiński, M., Wiprut, D., and Basu, P.: Can we afford fracture pressure uncertainty? Limit tests as a key calibration for geomechanical models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6453, https://doi.org/10.5194/egusphere-egu22-6453, 2022.

EGU22-8802 | Presentations | TS1.4

Stress state and patterns at the upper plate of Hikurangi Subduction Margin 

Effat Behboudi, David McNamara, and Ivan Lokmer

Quantifying the contemporary stress state of the Earth’s crust is critical for developing a geomechanical understanding of the behavior of brittle deformation (fractures and faults).In this study we characterize the shallow contemporary stress state of the active Hikurangi Subduction Margin (HSM), New Zealand, to better understand how it affects and responds to variable deformation and slip behavior documented along this plate boundary. The HSM is characterized by along-strike variations in megathrust slip behavior, ranging from shallow slow slip events (SSEs) and creep at the northern and central HSM to interseismic locking and stress accumulation in the southern HSM. We estimate the state of stress across the HSM utilizing rock strength estimates from empirical relationships, leak-off test data, wireline logs and borehole geology, and measurement of borehole wall failures such as borehole breakouts and drilling‐induced tensile fractures from eight boreholes. Stress magnitude constraints at depth intervals where BOs are observed indicate that the maximum principal stress (σ1) is horizontal along the shallow (<3 km) HSM and the stress state is predominantly strike-slip or contractional (barring localized areas where an extensional stress state is determined). Our results reveal a NE-SW (margin-parallel) SHmax orientation in the shallow central HSM, which rotates to a WNW- ESE/NW-SE (margin-perpendicular) SHmax orientation in the shallow southern HSM. The central NE-SW SHmax orientation is inconsistent with active, km-scale, NE-SW striking contractional faults observed across the central HSM. Considering both stress magnitude and orientation patterns at the central HSM, we suggest that long-term clockwise rotation of the Hikurangi forearc, over time, may transform motion on these km-scale central HSM faults from contractional dip-slip to a more contemporary strike/oblique-slip. The southern shallow WNW- ESE/NW-SE SHmax orientation is nearly perpendicular to focal-mechanisms derived NE-SW SHmax orientations within the subducting slab. This, combined with observed strike-slip and contractional faulting in the region and the NW-SE convergence direction, implies the overriding plate in the southern HSM is in a contractional stress state, potentially as deep as the plate interface, which is decoupled from that experienced in the subducting slab. Observed localized extensional stress states across the HSM may occur as a result of local extensions or reflect uncertainties in our estimations of SHmax magnitude which are sensitive to the UCS values used (unconstrained by laboratory testing). This UCS uncertainty and the potential errors it can introduce into a stress model highlights the importance of developing robust empirical relationships for UCS in regions where stress is a critical geological consideration for hazard and resource management.

How to cite: Behboudi, E., McNamara, D., and Lokmer, I.: Stress state and patterns at the upper plate of Hikurangi Subduction Margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8802, https://doi.org/10.5194/egusphere-egu22-8802, 2022.

A series of numerical simulations of mantle convection in 3D spherical-shell geometry were performed to evaluate the intraplate stress regime from numerically obtained velocity and stress fields. The intraplate stress regime was quantitatively classified into nine types by analyzing the principal deviatoric stress axes and the “stress ratio,” which is a continuous parameter accounting for the stress regimes. From the viewpoint of global geodynamics, this study analyzed the depth profile of the stress ratio across the entire depth of the mantle. The results demonstrated that the radial viscosity structure of the mantle interior strongly affected intraplate stress regimes, and the combination of increased viscosity in the lower mantle and the low-viscosity asthenosphere enhanced the pure strike-slip faulting regime within moving plates as indicated using visco-plastic rheology. The temporally averaged toroidal-poloidal ratio (T/P ratio) at the top surface of mantle convection with surface plate-like motion and the mantle’s viscosity stratification may be comparable to the observed T/P ratio of present-day and past Earth. The normal faulting (or strike-slip) regime with a strike-slip (or normal faulting) component, as well as the pure strike-slip faulting regime, were broadly found in the stable parts of the plate interiors. However, the significant dominance of these stress regimes was not observed in the depth profile of the toroidal-poloidal ratio as a remarkable peak magnitude near the top surface of the lithosphere. This result implies that the strike-slip component analyzed in this study does not directly relate to the formation of strike-slip faults that are infinitely narrow plate boundaries compared with the finite low-viscosity boundary obtained from a mantle convection model with visco-plastic rheology. Nonetheless, this first analysis of the stress ratio may contribute to an improved understanding of the intraplate stress reproduced by future numerical studies of mantle convection with further realistic conditions.

How to cite: Yoshida, M.: New analyses of the stress ratio and stress regime in the Earth’s lithosphere from numerical simulation models of global mantle convection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9132, https://doi.org/10.5194/egusphere-egu22-9132, 2022.

EGU22-11827 | Presentations | TS1.4

A kinematic model for observed surface subsidence above a salt cavern gas storage site in Northern Germany 

Henriette Sudhaus, Alison Larissa Seidel, and Noemi Schulze-Glanert

In nation-wide radar satellite time series data of Germany, a linear subsidence motion of several kilometer spatial wavelength shows up south-east of Kiel, northern Germany. The center region of this signal, showing line-of-sight displacement velocities of about 2 mm/a, coincides with the facilities of a gas storage site managing two in-service and one out-of-service caverns in the salt dome beneath. The three caverns have been water-drilled only a few hundred meters apart in 1971, 1996 and 2014 into a large halite salt dome, which has risen up there to depths of around 1000 m. Their sizes range within a couple of 100.000 m³. Above the salt body thick deposits of mainly chalk, silk and claystone below layers of clays, silts, sands and glacial marls in the upper 200 m form a relatively strong roof layer.

We hypothesize that despite a thick and competent cover layer, the long-term ductile behavior of halite, which evidently causes shrinking of the cavern volumes through time, results in the observed continuous surface subsidence across several square kilometers. We present an attempt to test the hypothesis by optimizing a simple kinematic model to fit the surface subsidence signal. Using equivalent body forces to represent an isotropic volume point source embedded in a viscoelastic host medium below a horizontally layered elastic roof medium, we estimate the horizontal position of a single cavern, its depth and the corresponding volume change at the cavern. The medium properties at the cavern sites are well known from borehole geophysical analyses, but likely vary strongly laterally. We use InSAR time series data from two ascending look directions and two descending.

Our results show that a cavern at about 1200 m depth and in very close proximity to above-ground facilities of the storage site can indeed be associated with the observed ground motion. The best-fit models pin the location to the known positions, also in depth. The estimated volume loss is slightly larger than 20.000 m³ per year and is in the same order of volume loss estimated from volume measurements inside the actual caverns.

The model approach we present, a single kinematic point source for three caverns and a one-dimensional medium model, is simple, the signal-to-noise ratio of the satellite data is rather small and furthermore there are considerable spatial gaps in the InSAR time series data in areas of agriculture and forests. However, with a computationally fast forward calculation of surface displacements we can afford to propagate data error statistics that account for spatially correlated errors to model parameter uncertainty estimates in a Bayesian way through model ensembles. We plan to add modeling errors of the medium to better grasp their potential influence on the volume loss estimations. The optimization code we use, Grond, is part of the seismological open-source software toolbox Pyrocko (pyrocko.org). The data is openly available at bodenbewegungsdienst.bgr.de.

How to cite: Sudhaus, H., Seidel, A. L., and Schulze-Glanert, N.: A kinematic model for observed surface subsidence above a salt cavern gas storage site in Northern Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11827, https://doi.org/10.5194/egusphere-egu22-11827, 2022.

EGU22-11830 | Presentations | TS1.4

Geomechanical explanation of the Enguri power tunnel leakage 

Thomas Niederhuber, Birgit Müller, Thomas Röckel, Mirian Kalabegishvili, Frank Schilling, and Bernd Aberle

The Enguri Dam (Georgia) is one of the highest arch dams in the world, located at Enguri river in the Greater Caucasus. A 15 km long pressure tunnel with a slope of 1.1 % connects the reservoir to the power station. The tunnel was initially flooded in 1978 and takes a flow rate of up to 450 m³/s. Annual water level changes in the reservoir reach 100 m and generate variable internal water pressure, which places a considerable and dynamic strain on the structure. Water losses of more than 10 m³/s required extensive rehabilitation work in 2021.

The pressure tunnel is lined by upper and lower concrete parts separated by longitudinal construction joints. During the rehabilitation in spring 2021, an approximately 40 m long section of a construction joint with a gaping fissure and several smaller cracks were located.

To explain why only one of the construction joints was leaking, we combined field observations with numerical modelling of the stress state around the pressure tunnel. To infer the regional tectonic stress field various stress indicators have been used like borehole observations (borehole televiewer data) in the field, hydraulic fracturing and earthquake focal mechanisms. These different methods provide mean values with standard deviations. This enabled the estimation of uncertainties in the model input data (field data).

Our approach is based on a static linear-elastic 2D model of the tunnel at km 13.7 within a limestone of homogeneous material properties. The orientation of the profile section is parallel to the regional maximum horizontal stress (SH), which corresponds to maximum principal stress in a thrust faulting regime. SV is the vertical stress. To account for uncertainties, the model was calculated for different stress state scenarios e.g. variation of SH/SV-ratio from 2 to 6 and internal pressure from 0 to 1.6 MPa.

The results show a symmetrical distribution of tensile and compressive stresses around the tunnel, with the axis of symmetry tilted by ca. 30° clockwise (in flow direction) for all scenarios. This is due to the high topography. Therefore, in some calculations, tangential tensile stresses are observed on the downslope side in the region of the construction joint, while compressive stresses are expected for the upslope construction joint.

Therefore, it can be concluded:

(A) the initial stress state is an important parameter for the positioning of underground installation like pressure tunnels especially in areas of high topography.

(B) geomechanical numerical modelling can help to design and dimension safe constructions.

These kinds of investigations can help to omit leakage which can lead to a reduction of the capacity of the power plant and to prolongate the integrity of the tunnel statics. Further investigations could consider the hydraulic situation of the karst rock in the surrounding of the tunnel.

How to cite: Niederhuber, T., Müller, B., Röckel, T., Kalabegishvili, M., Schilling, F., and Aberle, B.: Geomechanical explanation of the Enguri power tunnel leakage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11830, https://doi.org/10.5194/egusphere-egu22-11830, 2022.

EGU22-11879 | Presentations | TS1.4

Optimizing the use of InSAR observations in data assimilation problems to estimate reservoir compaction 

Samantha S.R. Kim, Femke C. Vossepoel, Marius C. Wouters, Rob Govers, Wietske S. Brouwer, and Ramon F. Hanssen

Hydrocarbon production may cause subsidence as a result of the pressure reduction in the gas-producing layer and reservoir compaction. To analyze the process of subsidence and estimate reservoir parameters, we use a particle method to assimilate Interferometric synthetic-aperture radar (InSAR) observations of surface deformation with a conceptual model of reservoir. As example, we use an analytical model of the Groningen gas reservoir based on a geometry representing the compartmentalized structure of the subsurface at the reservoir depth.

The efficacy of the particle method becomes less when the degree of freedom is large compared to the ensemble size. This degree of freedom, in turn, varies because of spatial correlation in the observed field. The resolution of the InSAR data and the number of observations affect the performance of the particle method.

In this study, we quantify the information in a Sentinel-1 SAR dataset using the concept of Shannon entropy from information theory. We investigate how to best capture the level of detail in model resolved by the InSAR data while maximizing their information content for a data assimilation use. We show that incorrect representation of the existing correlations leads to weight collapse when the number of observation increases, unless the ensemble size growths. However, simulations of mutual information show that we could optimize data reduction by choosing an adequate mesh given the spatial correlation in the observed subsidence. Our approach provides a means to achieve a better information use from available InSAR data reducing weight collapse without additional computational cost.

How to cite: Kim, S. S. R., Vossepoel, F. C., Wouters, M. C., Govers, R., Brouwer, W. S., and Hanssen, R. F.: Optimizing the use of InSAR observations in data assimilation problems to estimate reservoir compaction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11879, https://doi.org/10.5194/egusphere-egu22-11879, 2022.

EGU22-669 | Presentations | TS2.2

Structural analysis of the alpine orogeny in the western High Atlas, Morocco: New insights through a multiscale approach 

Salih Amarir, Mhamed Alaeddine Belfoul, Khalid Amrouch, Yousef Attegue, and Hamza Skikra

The Moroccan Atlas is an intracontinental chain resulted from an aborted rifting during the Mesozoic time, by an uplifting and moderate shortening during the Late Cretaceous-Cenozoic period. Several studies have highlighted the role of tectonic inversion in the evolution of the High Atlas Range, where strike-slip faults are commonly been considered as a main component of the alpine signature within the High Atlas belt. However, more recent works have focused on the geodynamic model of the evolution of the Atlas Range using different approaches. The structural history and chronology of events are still matter of debates. To contribute to the later, a combined meso and microstructural study was conducted in the western part of the chain. It provided an attempt to quantify paleo-stresses from structural analysis of the Permo-Triassic extensional phase to the tectonic reversal phases, acting from Cenozoic to present days.
This work highlighted two major tectonic phases: (1) the first represented by an extensive regime, with a sub-horizontal minimal stress σ3 oriented NE-SW and linked to the Central Atlantic occurrence. This stage is characterized by pull apart basins genesis in horst and graben morphology. (2) the second phase represented by a weakly tilted compression with a maximum stress σ1 oriented in set NNE-SSW to NNW-SSE. This compression began in the Tertiary, contemporary with the Africa and Europe collision. the related inversions are printed at the paleozoic basement/mesozoic cover interface from the Eastern area to the Jurassic-Cretaceous and Cenozoic plateaus in the West, passing through the Triassic detrital formations of the Argana corridor.
Keywords: Paleo-stress, Structural analysis, Tectonic inversion, Western high Atlas, Morocco, Alpine orogeny.

How to cite: Amarir, S., Belfoul, M. A., Amrouch, K., Attegue, Y., and Skikra, H.: Structural analysis of the alpine orogeny in the western High Atlas, Morocco: New insights through a multiscale approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-669, https://doi.org/10.5194/egusphere-egu22-669, 2022.

EGU22-1008 | Presentations | TS2.2

Deciphering the tectonic complexity of the Central High Atlas Mountains using brittle deformation mesostructures and calcite mechanical twinning analysis 

Hamza Skikra, Khalid Amrouch, Abderrahmane Soulaimani, Mustapha Hdoufane, and Salih Amarir

Located in the western segment of the intracontinental Atlas system, the Moroccan Central High Atlas is a NE-SW to ENE-WSW-trending Fold-and-Thrust Belt that is formed during the Cenozoic Alpine orogeny by a positive inversion of Triassic-Jurassic basin. It is structurally distinguished from the other segments of the Moroccan High Atlas orogenic belt by the occurrence of S-shaped ENE-WSW oriented tight anticlinal ridges bounding wider synclines. The elongated ridges core disordered association of plutonic rocks, Liassic carbonate and Late Triassic arigilites, whilst the wider synclines are filled by thick Jurassic series with minor magmatic manifestations expressed by mafic and felsic dikes. The origin of these structures has been ascribed to pre-inversion wrench tectonics with significant compressive component whereas they have been attached to post-rift rift block tilting and or salt tectonics in an alternative view. Characterizing the paleostress history is thereby a crucial matter to unravel the structural evolution of these structures. In order to bring new insights into the actual understanding of the Central High Atlas post-rift structural history, we reconstruct the paleostress tensors preserved in the folded Jurassic series of Anemzi and Tirrhist regions based on brittle deformation structures together with calcite twins stress inversion. The preliminary results highlight the presence of pre-folding layer parallel maximum horizontal stress during three stages: E-W to ENE-WSW, NNE-SSW and NW-SE compressions. Local extensional stress features are observed essentially near diapiric structures and the exhumed magmatic intrusions. The latest structural stage is featured by a post-folding NW-SR compression likely related to the recent phases of the Alpine orogeny.

How to cite: Skikra, H., Amrouch, K., Soulaimani, A., Hdoufane, M., and Amarir, S.: Deciphering the tectonic complexity of the Central High Atlas Mountains using brittle deformation mesostructures and calcite mechanical twinning analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1008, https://doi.org/10.5194/egusphere-egu22-1008, 2022.

EGU22-1324 | Presentations | TS2.2

Stochastic mechanical analysis of the stress field in a 3D thrust fold 

Anthony Adwan, Bertrand Maillot, Pauline Souloumiac, Christophe Barnes, and Pascale Leturmy

Knowledge of the in-situ stress state is a key factor for any subsurface site characterization and for safe underground geotechnical exploitations. Despite the huge progress in estimating the stress field, understanding the state of stress is still a tedious and challenging endeavor due to incomplete data and sparse information. Moreover, the cost of performing stress measurements is quite elevated while the procedure is delicate and time consuming. Thus, the importance of utilizing geomechanical models for a wider stress evaluation.

We conduct a sensitivity analysis of the stress field with respect to rheological parameters in a kilometric scale thrust fold using a 3D numerical implementation of the theory of Limit Analysis (LA). LA searches for the exact loading force at the onset of failure by bounding it through optimization using a kinematic (upper bound) and a static (lower bound) approach. Elastic parameters are not required, and we only adopt the Coulomb failure criterion characterized by a friction angle and a cohesion.

The 3D geological prototype created, is inspired from the north eastern Jura setting, northern Switzerland, and corresponds to the lateral termination of a partially buried fault cored anticline. It is formed by five material layers with different Coulomb parameters and two different décollement levels. We perform a parametric study by varying the friction angle of the bulk materials, the faults and the shallow décollement.

Our simulations, show various stress distribution patterns depending on the uncertainties related to fault and decollement friction angles. This implies different model behaviors and distinct rupture geometries. However, we identify in particular a stress shielded layer presenting low stress values independently of the parametric variations. Comparing our results with a 2D approach consolidates our findings and highlights the importance of 3D modeling. Finally, we perform a stress analysis of several boreholes taken at various locations. We represent each borehole by an average stress profile with its respective standard deviation. In doing so, we are transforming the parametric variations into stress logs reflecting our uncertainties. This process reveals in particular a counter-intuitive vertical stress decrease with depth near activated blind faults. We argue that this observation is related to material uplift in a compression regime and is only possible for a restricted blind fault.

The aim of this study is to evaluate the possibility of performing real stress data inversion in order to both predict stresses away from the measurements, and determine ranges of compatible rock parameters.

How to cite: Adwan, A., Maillot, B., Souloumiac, P., Barnes, C., and Leturmy, P.: Stochastic mechanical analysis of the stress field in a 3D thrust fold, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1324, https://doi.org/10.5194/egusphere-egu22-1324, 2022.

EGU22-1572 | Presentations | TS2.2 | Highlight

Effects of regional and local stresses on fault slip tendency in the southern Taranaki Basin, New Zealand 

Cecile Massiot, Hannu Seebeck, Andrew Nicol, David D. McNamara, Mark J.F. Lawrence, Angela G. Griffin, Glenn P. Thrasher, and G. Paul D. Viskovic

Determining the potential for faults to slip is widely employed for evaluating fault slip potential and associated earthquake hazards, and characterising reservoir properties. Here we use borehole and 3D seismic reflection data to estimate stress orientations and magnitudes, fault geometries and slip tendency in the southern Taranaki Basin, New Zealand. We highlight uncertainties in maximum horizontal stress (SHmax) magnitude calculations from borehole breakout width and rock strength. As in other settings, breakout width is uncertain on resistivity images because one of the breakout edges often lies in-between the resistivity imager pads, so only a subset of borehole breakouts can be used with confidence. The main uncertainty on SHmax magnitude is the rock strength at the borehole depth at which breakouts form. Given the rarity of basin-specific rock mechanical data, we rely on equations used to convert downhole acoustic compressional wave slowness into rock strength defined in sandstone and mudstones. However, lithologies in the southern Taranaki Basin are commonly muddy sandstones and sandy mudstone that can be interlayered. In addition, we show an example where breakouts are confined to moderately cemented carbonate units without change in acoustic compressional wave slowness. Using a range of rock strength equations based on sandstones and mudstones provides a possible SHmax magnitude range. With only one focal mechanism available in the study area, constraints on SHmax magnitudes from borehole data remain valuable and inform on stresses in the shallow crust.

Although the southern Taranaki basin is undergoing active deformation at plate tectonic scales, the stress magnitudes appear insufficiently high to reactivate the faults assuming a classic coefficient of friction. SHmax azimuths and SHmax:Sv magnitude ratios vary locally between boreholes and with depth. A borehole that intersects an inactive seismic-scale fault and borehole-scale faults over a 150-m interval shows SHmax to rotate by up to 30° proximal to the faults, which are favourably orientated for slip in both strike-slip and normal regimes. The small borehole-scale faults may, however, be active within the inactive seismic scale fault's damage zone. We highlight changes of slip tendency along faults resulting from local variations in the stress field and non-planar fault geometries that could not be resolved using only seismic reflection data and regional stress tensor.

How to cite: Massiot, C., Seebeck, H., Nicol, A., McNamara, D. D., Lawrence, M. J. F., Griffin, A. G., Thrasher, G. P., and Viskovic, G. P. D.: Effects of regional and local stresses on fault slip tendency in the southern Taranaki Basin, New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1572, https://doi.org/10.5194/egusphere-egu22-1572, 2022.

EGU22-1823 | Presentations | TS2.2

Tectonic evolution of the northern Verkhoyansk fold-and-thrust belt based on paleostress analysis and U-Pb calcite dating 

Elena A. Pavlovskaia, Andrey K. Khudoley, Jonas B. Ruh, Artem N. Moskalenko, Marcel Guillong, and Sergey V. Malyshev

The formation of the Verkhoyansk fold-and-thrust belt (FTB) is traditionally interpreted as a result of Late Mesozoic subduction and consequent closure of the Oimyakon Ocean, followed by the collision of the Kolyma-Omolon microcontinent with the Siberian Craton. In particular, the northern Verkhoyansk FTB reflects the complex tectonic history and interaction of the Arctic and Verkhoyansk orogens. Although previous studies documented several Cretaceous deformation events, the details of the northern Verkhoyansk evolution are still poorly understood.

A combined structural and geochronological study was carried out to identify the tectonic evolution of the northern Verkhoyansk FTB. Fault and fold geometries and kinematics were used for paleostress reconstruction in the central and western parts of the northern Verkhoyansk FTB. The multiple inverse method was used to separate individual stress fields from heterogeneous fault-slip data and three different stress fields (thrust, normal and strike-slip faulting) were identified. Thrust and normal faulting stress fields were found throughout the study area, whereas a strike-slip faulting stress field was only found in Neoproterozoic rocks in the westernmost part of the northern Verkhoyansk FTB. Furthermore, U-Pb LA-ICP-MS dating of calcite fibers on slickensides was performed to obtain a first-order time constraint on fault activity.

The study reveals the following succession of major deformation events across the northern Verkhoyansk: i) The oldest tectonic event corresponding to the strike-slip faulting stress field with NE-SW-trending compression axis is Early Permian (284±7 Ma) and likely represents a far-field response to the Late Palaeozoic collision of the Kara terrane with the northern margin of the Siberian Craton. ii) A slickenfibrous calcite age of 125±4 Ma is attributed to the most intense Early Cretaceous compression event, when the modern fold and thrust structure developed. Dykes in the eastern part of the northern Verkhoyansk FTB cutting N-S trending folds with 90-85 Ma U-Pb zircon ages mark the end of this event. iii) U-Pb slickenfiber calcite ages of 76-60 Ma estimate the age of a Late Cretaceous–Palaeocene compression event, when thrusts were reactivated. Slickensides related to both (ii) and (iii) compressional tectonic events formed by similar stress fields with W-E trending compression axes. iv) From Palaeocene onwards, extensional tectonics with approximately W-E extension predominated. Within the northern Verkhoyansk FTB, extension settings are supported by the formation of a set of grabens and a clearly recognizable normal faulting stress field.

How to cite: Pavlovskaia, E. A., Khudoley, A. K., Ruh, J. B., Moskalenko, A. N., Guillong, M., and Malyshev, S. V.: Tectonic evolution of the northern Verkhoyansk fold-and-thrust belt based on paleostress analysis and U-Pb calcite dating, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1823, https://doi.org/10.5194/egusphere-egu22-1823, 2022.

In November 2017, an Mw 5.4 earthquake with a shallow (~ 4 km) hypocenter occurred in Pohang, South Korea. Seismotectonics of this region is highlighted by ENE-WSW compression, the dominant stress field in the Korean peninsula, belongs to the Himalayan tectonic domain (HTD), and WNW-ESE or NW-SE compression belongs to the Philippine Sea tectonic domain (PSTD). Here we analyzed the aftershocks, involving focal mechanism of 38 events, to understand the characteristics of the earthquake sequence. Our results show that the mainshock sequence occurred on four ruptures showing a NE-SW trend and in February 2018, one another earthquake (or aftershock) occurred on a NNW-SSE trending rupture at 3.5 km west of the epicenter of the mainshock. Note that aftershocks mainly occurred between two NNE-SSW trending faults: Seonggok Fault and Gokgang Fault.

We analyzed the focal mechanism data as done by fault tectonic analysis. We classified them into several clusters following locations and depths and by whether a population shows a strike-slip faulting type or reverse faulting type. They were classified into several different clusters in the central main area, the northeastern area, and the southwestern area. In the central main area, focal mechanism data of strike-slip faulting type show that the WNW-ESE compression prevails in the depth between 2.0 to 4.0 km and 5.6 to 5.8km, while ENE-WSW compression is dominant between 4.3 and 5.0 km. Those of reverse faulting type display the ENE-WSW compression between 4.7 and 5.7 km deep. This implies that the intermediate depth was affected by the HTD and the upper and lower depths by the PSDT, showing a kind of stress layering.

In the northeastern area, roughly E-W compression prevails between 3.7 and 6.5 km deep, and NW-SE compression between 6.0 and 6.7 km deep. In the southwestern area, roughly E-W compressions were induced in the depth of 4.0 to 5.0 km. E-W compression seems to belong to the combinatory stress state of the HTD and PSTD, and NW-SE compression in the lower part might belong to the stress of PSDT.

The phenomenon of stress layering during the Pohang earthquake reveals that the intervention between the HDT and PSDT resulted in the mainshock and aftershocks of 2017 Pohang earthquake, as in the 2016 Kumamoto, Japan, earthquake.

How to cite: Choi, P., Son, M., and Choi, J. H.: Fault tectonic analysis of focal mechanism data of aftershocks of 2017 Pohang, Korea, earthquake of Mw = 5.4: Stress layering phenomenon between Himalayan and Philippine Sea tectonic domains, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2282, https://doi.org/10.5194/egusphere-egu22-2282, 2022.

EGU22-2969 | Presentations | TS2.2

Determination of the six unknowns of the paleostress tensor from vein data 

Christophe Pascal, Luís Jaques, and Atsushi Yamaji

The quantification of tectonic forces or, alternatively, stresses represents a significant step towards the understanding of the natural processes governing plate tectonics and deformation at all scales. However, paleostress reconstructions based on the observation and measurement of natural fractures are traditionally limited to the determination of four out of the six parameters of the stress tensor. In the present study, we attempt to reconstruct full paleostress tensors by extending the methodologies advanced by previous authors. We selected Panasqueira Mine, Central Portugal, as natural laboratory, and focused on the measurement of sub-horizontal quartz veins, which are favourably exposed in three dimensions in the underground galleries of the mine. Inversion of the vein data allowed for quantifying the respective orientations of the stress axes and the shape ratio of the stress ellipsoid. In order to reconstruct an additional stress parameter, namely pressure, we extensively sampled vein material and combined fluid inclusion analyses on quartz samples with geothermometric analyses on sulphide minerals. Finally, we adjusted the radius of the obtained Mohr circle with the help of mechanical parameters, and obtained the six parameters of the paleostress tensor that prevailed during vein formation. Our results suggests a NW-SE reverse stress regime with a shape ratio equal to ~0.6, lithostatic pore pressure of ~250 MPa and differential stress between ~40 and ~90 MPa.

How to cite: Pascal, C., Jaques, L., and Yamaji, A.: Determination of the six unknowns of the paleostress tensor from vein data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2969, https://doi.org/10.5194/egusphere-egu22-2969, 2022.

Semi-brittle flow occurs when crystal plasticity and cataclastic mechanisms operate concurrently and may be common in the middle Earth’s crust. To better constrain the characteristics of semi-brittle deformation, we performed triaxial tests up to 12% strain on dry samples of Carrara marble, spanning a wide range of temperature (T = 20 - 800°C), confining pressures (PC = 30 – 300 MPa), and strain rates (ε'= 10-3 - 10­-6 s-1). The (differential) stress (Δσ = σ1 - PC) and the hardening coefficient (h = ∂Δσ/∂ε ) depend on the applied conditions. At most conditions, Δσ increases with strain, whereas h decreases with increasing strain. At 5% strain, stress and the hardening coefficient increase as T decreases and PC increases: Remarkably, both are relatively insensitive to temperature and to rate in the range of ≈ 200 < T < 400°C. At T ≲ 400°C, the mechanical behavior of the marble is very similar to that exhibited by high-strength, high-ductility, hexagonal metals that deform by processes called twinning induced plasticity (TWIP). Qualitative microstructural observations show that twinning, dislocation motion, and inter- and intra-crystalline micro-fractures are abundant in the deformed samples over the entire range of conditions. The interplay of these deformation mechanisms leads to complex relationships of Δσ and h with the applied ε'  - T ‑ PC  conditions. Models for TWIP behavior suggest that hardening increases with decreasing twin spacing and increasing dislocation density. The low sensitivity of Δσ and h to T at 200 to 400°C may be explained by the relatively low temperature sensitivity of the critical resolved shear stress for twinning and dislocation slip in calcite in this range. None of the existing models for the brittle-ductile transition or the brittle-plastic transition are able to fully predict our experimental results, and micro mechanism-based constitutive laws for semi-brittle deformation are missing so far. Nevertheless, our observations suggest that peak strengths for calcite rocks deforming by semi-brittle processes will occur at PC ‑ T conditions of the middle crust, but that the strengths are probably more strongly influenced by total strain rather than by strain rate.

How to cite: Rybacki, E., Niu, L., and Evans, B.: Semi-brittle Deformation of Carrara Marble: A Complex Interplay of Strength, Hardening and Deformation Mechanisms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3901, https://doi.org/10.5194/egusphere-egu22-3901, 2022.

Crustal scale low-angle normal faults are typical tectonic features in orogenic post-collisional setting driving the exhumation of deep portions of the orogenic wedge. These extensional structures are commonly active at mid to upper crustal levels within quartz- and feldspar-rich rocks. As deformation localizes along these large-scale shear zones, the understanding of mechanisms controlling their development could provide invaluable insights on the rheology of the continental lithosphere. PT ambient conditions, differential stress, pore fluid pressure and time duration of activity are all factors that could significantly operate on how a shear zones develops in space and time.

We investigated by means of a quantitative approach the evolution of the Simplon Fault Zone (Western Alps, N Italy – Switzerland). We took into account: (i) meso- and microstructures distribution across the shear zone, (ii) its time of activity by 40Ar/39Ar dating of syn-shearing micas, (iii) vorticity distribution across the shear zone and its correlation with mylonite ages, (iv) the estimates of magnitude and variation of differential flow stress and strain rates during shear zone evolution obtained through EBSD-assisted quantitative microstructural analysis. All these data have been combined to reconstruct the structural evolution of the shear zone as the result of the rheological response of involved rocks to changing PT and stress conditions.

The Simplon Fault Zone formed as an extensional detachment accommodating E-W directed lateral extrusion after the collision between Adria and Europe. Several tens of kilometres of extension were accommodated by this structure, allowing the exhumation of the deepest portions of the Central Alps. The shear zone evolved from epidote-amphibolite to greenschist facies and then brittle conditions during shearing. A decrease of simple shear component from c. 90% to c. 40% towards the top of the shear zone is observed, with mylonites displaying ages within the 12-8 Ma time interval. Calculated  differential stress (60-80 MPa) and strain rate (10-11-10-12 s-1) estimates are in agreement with values displayed by several others crustal-scale low-angle normal faults developed at medium to shallow crustal levels.

The quantitative approach used at different scales pointed out that the Simplon Fault Zone experienced a complex evolution, with shear strain that was heterogeneously distributed across the fault zone. Despite this heterogeneity, a general decrease of the simple shear component and increase of the differential flow stress toward the top of the shear zone is clearly defined.

How to cite: Montemagni, C. and Zanchetta, S.: How middle and upper continental crust reacts to prolonged extension: some clues from the Simplon Fault Zone (Central Alps), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5040, https://doi.org/10.5194/egusphere-egu22-5040, 2022.

EGU22-5556 | Presentations | TS2.2

Fast stress-loading and -unloading during faulting and shock indicated by recrystallized grains along quartz cleavage cracks 

Lisa Marie Brückner, Fabian Dellefant, and Claudia A. Trepmann

Recrystallized quartz grains are localized along cleavage cracks in coarse original quartz grains within pseudotachylyte-bearing gneisses from the Silvretta basal thrust, Austria, and in shock-vein-bearing gneisses from the Vredefort meteorite impact structure, South Africa.

In the fault rocks of the Silvretta nappe, the recrystallized grains along two sets of {10-11} cleavage cracks at an angle of about 90° occur in rounded quartz clasts with a diameter of several tens of mm to cm embedded within pseudotachylytes. No evidences of shear offset were found in relation to the cleavage cracks. The fine-grained recrystallized grains have diameters of about 10 ± 6 µm or less and are slightly elongated parallel to the cleavage planes. These new grains have similar but also deviating crystallographic orientations to that of the host. As these quartz microstructures occur exclusively in spatial relation to pseudotachylytes, they are interpreted to result from the associated high stress/high strain-rate deformation. Mechanical (-101) twins in amphibole revealed stresses on the order of 400 MPa during formation of the pseudotachylytes. Yet, the new quartz grains do not show evidence of deformation after their growth, i.e., no internal misorientation, no crystallographic preferred orientation related to dislocation glide. Therefore, we suggest that the secondary quartz grains formed during annealing after the pseudotachylyte-forming event localized at the damage zone surrounding the cleavage cracks at quasi-isostatic stress conditions.

Very similar microstructures are found in Archean gneisses of the Vredefort impact structure, South Africa. There, the recrystallized grains with diameters of few µm along {10-11} and (0001) cleavage planes occur in shocked quartz grains related to mm-sized shock veins, characterized by Schlieren-microstructure of secondary feldspar. Also here, no major shear offset of the cleavage cracks is obvious and the secondary quartz grains do not show evidence of deformation. The observation that quartz shock effects are spatially related to both, the shock veins and secondary quartz grains, suggests that they formed during shock loading and subsequent pressure release with high strain rates (ca. 106 s-1) but minor shearing. Analogous to the Silvretta fault rocks, growth of quartz grains is suggested to occur restricted to the damage zone of the cleavage cracks at quasi-isostatic stresses during post-shock annealing.

In both, the Silvretta fault rocks and shocked gneisses from the Vredefort dome, quartz grains fractured without major shearing at high stresses and subsequently recrystallized localized to the damage zone of cleavage cracks at quasi-isostatic stress conditions. Damage in the process zone surrounding the cleavage cracks must have been large enough for effective grain boundary migration, i.e., growth of grains in orientations weakly controlled by the host orientation. Recrystallization ceased because of the missing driving force during subsequent quasi-isostatic stress conditions. These microstructures indicate quasi-instantaneous loading to high differential stresses of a few hundred MPa and fast unloading to quasi-isostatic stress conditions.

How to cite: Brückner, L. M., Dellefant, F., and Trepmann, C. A.: Fast stress-loading and -unloading during faulting and shock indicated by recrystallized grains along quartz cleavage cracks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5556, https://doi.org/10.5194/egusphere-egu22-5556, 2022.

EGU22-6673 | Presentations | TS2.2

Using surface velocities and subsurface stressing rate tensors to resolve interseismic deep slip distribution on closely spaced faults 

Jack Loveless, Hanna Elston, Michele Cooke, and Scott Marshall

Inversions of interseismic surface velocities alone often struggle to uniquely resolve the 3D fault slip rate distribution along systems with branching or closely spaced faults, such as the southern San Andreas Fault (SAF) in California, USA. Local stress states inferred from microseismic focal mechanisms may provide additional constraints on interseismic deep slip because they contain information about stress at depth and closer to the interseismic deep slip than GPS surface velocities. Here, we invert forward-model generated stressing rate tensors and surface velocities, individually and jointly, to assess how well the inverse approach estimates the distribution of slip rates along both simple and complex fault systems. The inverse approach we present can constrain both the interseismic deep slip rates that reveal fault locking depths and the relative activity of faults. 

We assess the inverse approach by inverting forward model-generated stressing rate tensors and surface velocities to recover fault slip distribution for two models. Forward models that include either a single, planar strike-slip fault or the 3D complex geometry of the southern SAF simulate interseismic loading in a two-step back-slip like approach. The forward models produce surface velocities with a 15 km spacing, which is similar to the GPS station density near the southern SAF, or at GPS station locations in southern California. We utilize the planar fault model to determine the smoothing parameters and stressing rate tensor spacing (>10 km) that minimize the misfit. The 10 km minimum spacing samples crustal volumes that are likely to have >39 focal mechanisms needed to robustly determine a stress tensor. The planar fault model inversions and the availability of focal mechanisms along the southern SAF inform the stressing rate tensor locations that we use to assess the complex model inversion performance. Because focal mechanisms provide normalized deviatoric stress tensors, we invert the full forward-model generated stress tensor as well as the deviatoric and normalized deviatoric stress tensors; this allows us to assess the impact of removing stress magnitude from the inversion.  

The inversions of the forward model-generated stressing rate tensors and surface velocities recover the slip rate distribution well with the exception of the normalized deviatoric stressing rate tensor inversion, which struggles to resolve the fault slip rates in both models. The inversions recover the locking depth with a broader transition zone than prescribed in the forward model due to the smoothing-based regularization within the inversion. The full stressing rate tensor inversion resolves slip rates better than the surface velocity inversions. The deviatoric stressing rate tensor inversion resolves slip rates better than the surface velocity inversion in the complex fault model but not in the planar fault model. Inverting stress and surface velocity information jointly improves the fit to the forward model slip distribution for both models. Joint inversions of both surface velocities and local stress states derived from focal mechanisms may improve constraints on the interseismic deep slip rates and locking depths in regions of complex faulting.

How to cite: Loveless, J., Elston, H., Cooke, M., and Marshall, S.: Using surface velocities and subsurface stressing rate tensors to resolve interseismic deep slip distribution on closely spaced faults, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6673, https://doi.org/10.5194/egusphere-egu22-6673, 2022.

EGU22-6855 | Presentations | TS2.2

Can the crustal strength in the brittle-plastic transition zone be estimated from the flow stress of calcite mylonite? 

Hiroaki Yokoyama, Jun Muto, and Hiroyuki Nagahama

Quantifying crustal strength is essential to understanding lithosphere strengths and tectonic processes, such as long-term fault movements caused by plate motions. In this study, we estimated the strength of granitic upper crust using recrystallized grain size piezometer of calcite mylonite intercalated in the Cretaceous granitic Abukuma Mountains. In addition, Raman carbonaceous material thermometer was used to constrain the deformation temperature. Calcite mylonites are originated from Late Carboniferous Tateishi Formation and locate along Shajigami shear zone at eastern margin of Abukuma Mountains, Northeastern Japan. Shajigami shear zone is a strike-slip shear zone active during the Middle Cretaceous. Along Shajigami shear zone, calcite mylonite and granitic cataclasites expose.

Calcite grains are well recrystallized, and the grain size are determined by electron backscattered diffraction (EBSD) mapping with the step sizes of 2-2.5µm. The mean grain sizes are 17-26 µm. The differential stress estimated by recrystallized grain size piezometer of calcite aggregate (Platt and De Bresser, 2017) is 35-80 MPa. The estimated metamorphic temperature using the Raman carbonaceous material thermometer (Kouketsu et al., 2014) is 340-250 ˚C. The difference in estimated metamorphic temperature is attributed to the thermal effects of the Cretaceous granitoids that penetrated along the calcite mylonite. This is because the estimated metamorphic temperature is higher the closer to the granitoid. Because well dynamically recrystallized calcite grains indicate that the deformation temperature exceeding 200˚C, the estimate by Raman carbonaceous material thermometer is the upper bound for the deformation temperature.

The calcite mylonite and the granitic cataclasite are thought to have formed at the same time in the Shajigami shear zone (Watanuki et al., 2020). Although there is a slight temperature gradient near the granite, widespread deformation has occurred in this area. The deformation temperature obtained in this study is the deformation around the brittle-plastic transition zone of the upper crust. Hence, the collecting flow stress estimated from calcite mylonite intercalated in brittle granitic shear zone may be possible to constrain the stress magnitude of the shear zone data near the brittle-plastic transition at 200-300°C.

 

References

Platt and De Bresser, 2017, J. Struct. Geol., 105, 80-87.

Kouketsu et al., 2014, Island arc, 23, 33-50.

Watanuki et al., 2020, J. Struct. Geol., 137, 104046.

How to cite: Yokoyama, H., Muto, J., and Nagahama, H.: Can the crustal strength in the brittle-plastic transition zone be estimated from the flow stress of calcite mylonite?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6855, https://doi.org/10.5194/egusphere-egu22-6855, 2022.

EGU22-7253 | Presentations | TS2.2

Paleostress and paleoburial history of a post-rift, supra-salt, carbonate reservoir offshore Congo (Atlantic): Insights from calcite twinning and stylolite roughness paleopiezometry. 

Anies Zeboudj, Boubacar Bah, Olivier Lacombe, Nicolas E. Beaudoin, Claude Gout, Nicolas Godeau, and Jean-Pierre Girard

Our understanding of the temporal variation of past stress in the crust is usually pictured in relation to tectonic contexts, where it helps decipher the evolution of deformation of rocks at different scales. The paucity of paleostress reconstructions in passive margins makes the knowledge of the origin of stress and of its evolution very incomplete, especially in poorly accessible offshore parts. Moreover, in salt-rich passive margins like the offshore Congo margin, one may question whether the state of stress in supra-salt formations is mainly controlled by salt tectonics, since the salt usually acts as a decoupling level that prevents the transmission and record of far-field crustal stresses. This study focuses on the analysis of an offshore wellbore core of the Albian, post-rift carbonates of the Sendji Fm that directly overlies the salt of the Aptian Loeme Fm in the Lower Congo Basin. Paleopiezometry based on stylolite roughness and mechanical twins in calcite was combined with fracture analysis, laser U-Pb dating of calcite cement, and burial modeling to unravel the tectonic and burial evolution of the Sendji Fm over time. The results of bedding-parallel stylolite roughness inversion constrain the range of depth over which the Sendji Fm strata deformed under a vertical principal stress s1 to 650-2800 m (median ~1100m). Projection of this depth range onto the Sendji burial model derived from TemisFlow™ basin modelling indicates that pressure solution was active from 105 to 12 Ma. Inversion of calcite mechanical twins measured within the early diagenetic cement (U-Pb age = 100 +/- 1Ma) yields two main states of stress: (1) an extensional stress regime with a horizontal σ3 trending ~E-W associated with sub-perpendicular N-S compression, and (2) a strike-slip stress regime with a horizontal σ1 trending ~E-W (changing from pure E-W compression to N-S extension through stress permutations). We interpret the former state of stress as local and related to the complex geometric interactions between moving halokinetic normal faults, while the latter presumably reflects the push effect of the Atlantic ridge, which prevailed from 12 Ma until present-day. Our results highlight that the stress history of the studied part of the offshore Lower Congo Basin passive margin has first been mainly dominated by burial and local normal faulting related to late Cretaceous to Miocene post-rift salt tectonics, then by a regional stress presumably originated from the far-field ridge push from ~12Ma onwards, which would indicate some mechanical re-coupling between the crust and the sedimentary cover during the Miocene.

Keywords: stress, paleopiezometry, calcite twins, stylolites, passive margin, salt.

How to cite: Zeboudj, A., Bah, B., Lacombe, O., Beaudoin, N. E., Gout, C., Godeau, N., and Girard, J.-P.: Paleostress and paleoburial history of a post-rift, supra-salt, carbonate reservoir offshore Congo (Atlantic): Insights from calcite twinning and stylolite roughness paleopiezometry., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7253, https://doi.org/10.5194/egusphere-egu22-7253, 2022.

EGU22-7305 | Presentations | TS2.2

A new free software to reconstruct stress trajectories: the Atmo-stress service 

Sofia Bressan, Olympia Gounari, Valsamis Ntouskos, Noemi Corti, Fabio Luca Bonali, Konstantinos Karantzalos, and Alessandro Tibaldi

The reconstruction of present-day stress and palaeostress trajectories is of paramount importance to study the tectonic regime and its evolution, in a specific area. Its comprehension is crucial also for seismic and volcanic hazard assessment, especially focusing on the shallow crust.

In the framework of the NEANIAS project (https://www.neanias.eu/), EU H2020 RIA, it has been developed the so called ATMO-Stress service (https://docs.neanias.eu/projects/a2-1-service/en/latest/), an open-source cloud service, currently hosted on the GARR Kubernetes platform, which allows to calculate stress trajectories in plain view, based on the concepts from Lee and Angelier (1994). It is designed to run on modern computers for both academics and non-academics purposes, spanning from research activity to oil and gas industries, natural hazard prevention and management.

The service is freely accessible at https://atmo-stress.neanias.eu/ and is designed to calculate the stress trajectories for a specific area, considering as input the same type of stress (e.g. σHmax or σHmin). Data input can be from different sources (e.g. field data, focal mechanism solutions, in-situ geotechnical measures). They must be listed in a homogeneous ASCII text file or Excel file format, including the geographic coordinates, azimuth of the stress and the angular error. The service is capable of processing data from local to regional scale. Following the principles from Lee and Angelier (1994), the trajectory calculation can be done using different parameters and settings. The outputs can be seen directly on the website and can be downloaded with file formats ready to be imported and analyzed in GIS environment and Google Earth.

How to cite: Bressan, S., Gounari, O., Ntouskos, V., Corti, N., Bonali, F. L., Karantzalos, K., and Tibaldi, A.: A new free software to reconstruct stress trajectories: the Atmo-stress service, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7305, https://doi.org/10.5194/egusphere-egu22-7305, 2022.

Reconstructing the brittle structural history of a complex strike-slip fault system remains a challenging process in paleostress reconstructions. Here, we investigated the small-scale brittle structures such as shear fractures and tension joints which are well developed in the Early Paleozoic Inkisi red sandstones in the “Pool” region of Kinshasa and Brazzaville, along the Congo River. The fracture network affects the horizontally bedded sandstones with alternating cross-bedded, horizontally bedded and massive layers. The fractures are particularly dense and of various orientation in the rapids of the Congo River just downstream Kinshasa and Brazzaville. They control the channels of the Congo River in its connection to the Atlantic Coast.

A total of 1150 factures have been measured and assembled into a single data file, processed using the Win-Tensor Program. They contain only a limited number of kinematic indicators for slip sense (displaced pebbles, irregularities on striated surfaces, slickensides) or extension (plume joints). Before interactive fault-slip data separation into subset and stress inversion, a kinematic data analysis evidenced at least three different phases of brittle deformation, each starting by the formation of plume joints and evolving into a strike-slip fault system. We used the principle of progressive saturation of the rock mass by the apparition of new faults or the reactivation of already existing ones during the successive brittle stages. We combined the stress inversion of fault-slip data, fault-slip tendency analysis and data separation in order to obtain well-separated data subsets, each characterized by its own paleostress tensor. The total data set can be explained by the action of 4 different brittle deformation and related paleostress stages, all of strike-slip type. There possible age is estimated from stratigraphic relations and the known geological history of the area.

The oldest stage developed in intact rock under NW-SE horizontal compression, probably before the Jurassic unconformity that affects the entire Congo Basin. It generated dominantly N-160°E striking left-lateral faults. The second stage generated dominantly new N050°E striking right-lateral faults, at a high angle from the ones of the previous stage, under NE-SW horizontal compression. They are estimated to be related to ridge push forces from the opening of the Atlantic Ocean during the Oligocene. The third stage, which corresponds to N-S horizontal compression, generated additional N030°E and N340°E conjugated fractures and reactivated the preceding fracture networks. A fourth and relatively minor system was also identified with WNE-ESE horizontal compression but its chronological relation with the other ones is not clear. 

How to cite: Delvaux, D., Miyouna, T., Boudzoumou, F., and Nkodia, H.: Using combined paleostress reconstruction and slip tendency for reconstructing the brittle structural history of a complex strike-slip fault system: Fault-controlled origin and evolution of the “Pool” area between Kinshasa and Brazzaville, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7401, https://doi.org/10.5194/egusphere-egu22-7401, 2022.

EGU22-8449 | Presentations | TS2.2 | Highlight

Numerical modelling of current state of stress in the Geneva Basin and adjacent Jura fold-and-thrust belt (Switzerland and France). 

Sandra Borderie, Jon Mosar, Louis Hauvette, Adeline Marro, Anna Sommaruga, and Michel Meyer

The Northern Alpine foreland is divided into two domains: the Molasse Basin and the Jura fold-and-thrust belt (FTB). The Mesozoic and Cenozoic sedimentary cover of this area is deformed by thrust-related folds and strike-slip faults. The main structures root in a basal Triassic décollement. The Geneva Basin, located in western Switzerland, is part of the Plateau Molasse (belonging to the Molasse Basin), and is limited to the NW by the Jura FTB, to the SW by the Vuache fault, and to the SE by the Mont Salève ramp related anticline and the Subalpine Molasse.

If current seismicity indicates that the Geneva Basin is tectonically active, few data regarding the state of stress in the area are currently available. The goal of this study is to densify the knowledge of the state of stress in the Geneva Basin and in the adjacent Jura FTB, by using numerical modelling.

The first part of the study is a regional study. In a 2D section, we study the impact of the friction along the basal décollement, on the localisation of deformation and on the associated stress field. Results indicate that depending on the friction, deformation will localise at the rear of the Mont Salève, in the Geneva Basin or at the frontal part of the Jura FTB. In the range of frictions where deformation localises in the Geneva Basin, the distribution of stress varies. Differential stress is higher and more localised for higher basal frictions.

The second part of the study is more local. The prototype section is based on seismic interpretation of a seismic surveys in the Geneva Basin. We study the impact of friction along the inherited faults on incipient deformation. Results indicate that a decrease in the fault’s friction allows forwards propagation of deformation and allows reactivation of inherited faults. If the friction in the faults is too low, deformation will localise at the first inherited fault (i.e. the Salève thrust in this case study). The stress fields vary depending on the localisation of deformation. Stress magnitudes are lower and more distributed when all faults have the same friction. The more deformation is localised on a structure, the more stress concentration is observed.

These results allow to better constrain the mechanical context of these sections and to populate this part of the Northern Alpine foreland with stress data.

How to cite: Borderie, S., Mosar, J., Hauvette, L., Marro, A., Sommaruga, A., and Meyer, M.: Numerical modelling of current state of stress in the Geneva Basin and adjacent Jura fold-and-thrust belt (Switzerland and France)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8449, https://doi.org/10.5194/egusphere-egu22-8449, 2022.

EGU22-8886 | Presentations | TS2.2

Reconstructing stress magnitude evolution in deformed carbonates: a paleopaleopiezometric study of the Cingoli anticline (North-Central Apennines, Italy) 

Aurélie Labeur, Nicolas E. Beaudoin, Olivier Lacombe, Lorenzo Petraccini, and Jean-Paul Callot

Picturing the distribution of stress, in term of magnitude and orientation, during the development of a fold-and-thrusts belt is key for many fundamental and applied purposes, e.g., crustal rheology, orogen dynamics, fluid dynamics and prediction of reservoir properties. Specific meso- and micro-structures observed in fold-and-thrust belts and related forelands (i.e., faults, stylolites, veins and calcite twins), on top of being good markers of the deformation sequence that affected the rocks before, during and after folding and thrusting, can be used to access the past stress orientation and/or magnitude. This study reports the result of a paleopiezometric analysis of calcite twins and stylolite roughness documented in Mesozoic carbonates cropping out in the Cingoli anticline, an arcuate fold in the Umbria-Marche Apennine Ridge (UMAR), where a complex fracturing sequence was highlighted in a previously published study. The stylolite roughness inversion technique (SRIT) was applied to tectonic stylolites related to early folding layer-parallel shortening (LPS), and the calcite twin inversion technique (CSIT) was applied to cements from veins related to either foreland flexure or LPS. Both inversion processes require somehow the knowledge of the depth at which deformation occurred, as the vertical stress is an input for SRIT in the case of its application to tectonic stylolites, and as the differential stress magnitudes obtained by CSIT combined to vertical stress magnitude provides access to the absolute principal stress magnitudes. Building on a previously published time-burial path valid for the studied strata at the Cingoli anticline that also predicted the timing of each deformation stage, we quantify differential and principal stress magnitudes at the scale of the anticline. Beyond regional implications, our approach helps improve our knowledge of the past stress magnitudes in folded carbonate reservoirs.

How to cite: Labeur, A., Beaudoin, N. E., Lacombe, O., Petraccini, L., and Callot, J.-P.: Reconstructing stress magnitude evolution in deformed carbonates: a paleopaleopiezometric study of the Cingoli anticline (North-Central Apennines, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8886, https://doi.org/10.5194/egusphere-egu22-8886, 2022.

Shear zones associated with major thrust faults generally record overprinting of deeper crustal deformation signatures by shallower crustal signatures due to faults climbing up-section along the transport direction. In this study, we investigate the deformation signatures related to the shallow crustal conditions on one such major thrust, the Ramgarh thrust (RT) from Sikkim Himalayan Fold Thrust Belt (FTB). RT is an intermediate crustal thrust that has recorded a translation of ~58-65 km and overprinting of deformation structures. RT acts as the roof thrust of Lesser Himalayan duplex, hence got reactivated several times, and records a long deformation history.

In Sikkim Himalaya, the frontal most exposure of the RT is near Setikhola (N26° 56.178’, E88° 26.607’) as ~57m thick shear zone that exposes the lower Lesser Himalayan Daling quartzite and phyllite in the hanging wall over Gondwana sandstone in the footwall. The mean bedding is oriented ~72°, 298°, and the mean dominant cleavage is ~ 70°, 305°. The outcrop forms the overturned forelimb of a fault-bend antiform. The outcrop is strongly fractured. Based on the angular relationship with respect to the bedding, three sets of fractures were identified. Low angle fractures (< 30° to bedding) constitute ~20.23 %, moderate (30° – 60° to bedding) and high angle fractures (60°- 90° to bedding) constitute ~39.88% of the total fracture population. The fractures are uniformly distributed throughout the stretch of the shear zone. Daling quartzites accommodate more number of fractures than the phyllites. Preliminary investigation indicates that the thicker beds have higher fracture intensity than thinner beds. Few of the fractures were identified as opening mode fractures based on their association with the plumose structures. ~ 17.3% of the total measured fractures records slickenline lineations. These shear fractures reveal two clusters on the stereonet (Set 1: ~90°, 098°; Set 2: ~77°, 331°). They have a dihedral angle of ~54⁰ and set 1 and set 2 are oriented ~ 27⁰ and ~ 32⁰ to the bedding respectively. Based on preliminary analysis, the local maximum principal stress (σ1) is oriented sub-horizontally with a SSW trend. Interestingly, this estimate is in agreement with the current global stress orientations from the Eastern Himalaya, where σ1 is near horizontal and trends NNE – SSW (Larson et al., 1999).

How to cite: Jk, A. and Bhattacharyya, K.: Preliminary fracture analysis from the frontal most exposure of a major roof thrust in the Eastern Himalaya: Insights from the Ramgarh thrust, Sikkim Himalaya., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9168, https://doi.org/10.5194/egusphere-egu22-9168, 2022.

We estimate paleostress orientations (σ1, σ2 and σ3), stress ratios (φ) and driving pressure ratios (R′) from the extension veins exposed within the Buxa dolomite of the frontal Main Boundary thrust (MBT) sheet in the Siang valley, Arunanchal Lesser Himalaya. Based on the angular relationship with the bedding, the fractures and veins were divided into low-angle (<30°), moderate-angle (~30°-60°) and high-angle (>60°) sets. Observations in the field as well as at a microscopic level indicate that the high- and moderate-angle veins overprint the low-angle veins implying that the latter are the oldest. The high-angle veins are the most dominant set (~49%; mean orientation: ~23°, ~141°) followed by the moderate- (~31%; mean orientation: ~70°, ~176°) and the low-angle (~20%; mean orientation: ~58°, ~224°) set. The poles to the low- and high-angle veins define a clustered distribution in the stereoplot indicating that the pore fluid pressure (Pf) was less than the intermediate principal stress (σ2) during the formation of these vein sets. In contrast, the poles to the moderate-angle veins mark a girdled pattern in the stereoplot indicating that the pore fluid pressure (Pf) exceeded the intermediate principal stress (σ2) during their formation. On applying the stress inversion method (Yamaji et al., 2010) to the veins, 5 different generations of veins are revealed. Preliminary microstructural study indicates that the low-angle veins are dominantly quartz-rich, whereas the high-angle veins are dominantly calcite-rich indicating the presence of multiple generations of veins. The study also indicates the presence of blocky texture in the veins with the growth direction of the mineral grains at a high angle to the vein wall. Based on the stress ratio (φ), driving pressure ratio (R′) and the orientation of stress axes associated with each generation, the different generations of veins most likely formed under different stress conditions.

How to cite: Behera, S. S. and Bhattacharyya, K.: Characterization of vein-sets and estimation of stress orientations and stress ratios from the Buxa dolomite, Main Boundary thrust (MBT) sheet, Siang Valley, Arunanchal Lesser Himalaya, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9169, https://doi.org/10.5194/egusphere-egu22-9169, 2022.

 

Estimating deformation conditions from shear zone rocks is critical in understanding its complex deformation history. However, often the deformation conditions from mylonite provide information on the finite deformed state conditions. On the contrary, if there are veins preserved, they may record incremental strain stages during progressive deformation. Thus, we used veins as incremental strain markers to evaluate the spatial and temporal variation in deformation conditions along the transport direction of a major shear zone. We estimated vein attributes at the microscopic scale, deformation temperature, flow stress, and strain rate from the Pelling-Munsiari thrust in the Sikkim Himalaya. It is a regionally folded thrust that acts as the roof thrust of a complex Lesser Himalayan duplex. The PT zone is exposed as ~938 m and ~188 m thick quartz-mica mylonite zone at the hinterland-most (Mangan) and the frontal exposures (Suntaley) in eastern Sikkim, respectively. The PT zone is subdivided into three domains where the protomylonite domain is surrounded by mylonite domains on both sides.

We recognize three different vein-sets based on the angular relationship to the mylonitic foliation. At both the locations of the PT zone, the low-angle (0-30°) is the dominant vein-set followed by moderate-angle (30-60°) and high-angle (60-90°). Based on the cross-cutting relationship, we find high-angle vein set is the youngest. The low-angle vein-sets are dominant in both these locations. We observed multiple crack-and-sealed events in Mangan, indicating repeated failure and mineral precipitation. In contrast, we do not observe any such texture in the veins that are preserved in the frontal exposure of the PT zone. At both the PT zones, there are higher distribution of veins near the footwall. In the hinterland, veins record coarser grain sizes in the protomylonite domain than in the mylonite domain. However, we observed a different trend in the frontal exposure, where veins from the mylonite domain record coarser grain sizes. In both locations, quartz grains dominantly exhibit the subgrain rotation recrystallization mechanism. We semi-quantitatively estimate a first-order deformation temperature using the recalibrated quartz recrystallization thermometer (Law, 2014). In the hinterland, the low-angle vein-set records the highest deformation temperature. In contrast, high-angle veins record higher deformation temperature in the foreland. Following Stipp et al. (2003) and Twiss (1977), we estimate flow stress from recrystallized quartz grain-size piezometer. The high-angle (~24.71MPa) vein-set records the highest flow stress in the hinterland. In comparison, moderate-angle (~29.55MPa) veins record the highest flow stress in the foreland exposure. Following Hirth et al. (2001), we estimated similar strain rates (~10-15 sec-1) from both locations. The three sets of veins record different deformation conditions in both locations suggesting different incremental strain stages. Interestingly, the high-angle veins record the fastest strain rate (~6*10-15 sec-1) in the hinterland most exposure, whereas, in the frontal part the moderate-angle veins record the fastest strain rate (~9*10-15 sec-1).

How to cite: Ranjan, R. and Bhattacharyya, K.: Estimation of deformation temperature, flow stress, and strain rate from the veins of an internal shear zone: Insights from Pelling-Munsiari thrust, Sikkim Himalaya, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9170, https://doi.org/10.5194/egusphere-egu22-9170, 2022.

The North Anatolian Fault experienced large earthquakes with 250–400 years recurrence time. In the Marmara Sea region,
the 1999 (Mw=7.4) and the 1912 (Mw =7.4) earthquake ruptures bound the Central Marmara Sea fault segment. Using
historical-instrumental seismicity catalogue and paleoseismic results (≃ 2000-year database), the mapped fault segments, fault
kinematic and GPS data, we compute the paleoseismic-seismic moment rate and geodetic moment rate. A clear discrepancy
appears between the moment rates and implies a signifcant delay in the seismic slip along the fault in the Marmara Sea. The
rich database allows us to identify and model the size of the seismic gap and related fault segment and estimate the moment
rate defcit. Our modelling suggest that the locked Central Marmara Sea fault segment (even including a creeping section)
bears a moment rate defcit 6.4 × 1017 N.m./year that corresponds to Mw ≃ 7.4 for a future earthquake with an average
≃ 3.25 m coseismic slip. Taking into account the uncertainty in the strain accumulation along the 130-km-long Central fault
segment, our estimate of the seismic slip defcit being ≃ 10 mm/year implies that the size of the future earthquake ranges
between Mw=7.4 and 7.5.

Reference:

[1] Meghraoui, M., Toussaint, R. & Aksoy, M.E. The slip deficit on the North Anatolian Fault (Turkey) in the Marmara Sea: insights from paleoseismicity, seismicity and geodetic data. Med. Geosc. Rev. 3, 45–56 (2021). https://doi.org/10.1007/s42990-021-00053-w

How to cite: Meghraoui, M., Toussaint, R., and Aksoy, M. E.: Stress evolution and slip deficit on the North Anatolian Fault (Turkey) in the Marmara Sea: insights from paleoseismicity, seismicity and geodetic data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11676, https://doi.org/10.5194/egusphere-egu22-11676, 2022.

EGU22-13201 | Presentations | TS2.2

Joint inversion of tectonic stress and magma pressures using dyke trajectories 

Frantz Maerten, Laurent Maerten, Romain Plateaux, and Pauline Cornard
    In volcano-tectonic regions, dyke propagation from shallow magmatic chambers are often controlled by ambient perturbed stress field. The variations of the stress field result from combining factors including, but not exclusively, the regional tectonic stress and the pressurized 3D magma chambers. In this contribution, we describe and apply a new multiparametric inversion technique based on geomechanics that can invert for both the far field stress attributes and the pressure of magma intrusions, such as stocks and magma chambers, constrained by observed dyke orientations. This technique is based on a 3D boundary element method (BEM) for homogeneous elastic half-space where magma chambers are modelled as pressurized cavities. To verify this approach, the BEM solution has been validated against the known 3D analytical solution of a pressurized cylindrical cavity. Then, the effectiveness of this technique and its practical use, in terms of mechanical simulation, is demonstrated through natural examples of dyke network development affected by magma intrusions of two different volcanic systems, the Spanish Peaks (USA) and the Galapagos Islands (Ecuador). Results demonstrate that regional stress characteristics as well as pressure of magma chambers can be recovered from observed radial and circumferential dyke patterns.

 

How to cite: Maerten, F., Maerten, L., Plateaux, R., and Cornard, P.: Joint inversion of tectonic stress and magma pressures using dyke trajectories, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13201, https://doi.org/10.5194/egusphere-egu22-13201, 2022.

EGU22-13203 | Presentations | TS2.2

Late Cenozoic faulting deformation of the Fanshi Basin (Northern Shanxi rift, China), inferred from paleostress analysis of mesoscale fault-slip data 

Markos D. Tranos, Konan Roger Assie, Yu Wang, Huimin Ma, Kouamelan Serge Kouamelan, Eric Thompson Brantson, Liyun Zhou, and Yanick Blaise Ketchaya

The Fanshi Basin is one of the NE-SW-striking depocenters formed along the northern segment of the fault-bounded Shanxi rift. In order to understand the crustal driving stresses that led to the basin formation and development, a paleostress analysis of a large number of fault-slip data collected mainly at the boundaries of the basin was accomplished. The stress inversion of these data revealed three stress regimes. The oldest SR1 was a Neogene stress regime giving rise to a strike-slip deformation with NE-SW contraction and NW-SE extension. SR1 activated the large faults trending NNE-NE, i.e., (sub) parallel to the main strike of the Shanxi rift, as right-lateral strike-slip faults. It was subjected to the Shanxi rift before the activation of the Fansi Basin boundary fault, i.e., the Fanshi (or Wutai) fault, as a normal fault. The next is a short-lived NE-SW extensional stress regime SR2 in the Early Pleistocene, which shows the inception of the basin's extension. A strong NW-SE to NNW-SSE extensional stress regime SR3 governed the northern segment of the Shanxi rift since the Late Pleistocene and is the present-day extension. It gives rise to the current half-graben geometry of the Fanshi Basin by activating the Fanshi (or Wutai) fault as a normal fault in the southern part of the graben. Because of the dominance of the NW-SE to NNW-SSE extension, which is perpendicular to the NE-SW extension, mutual permutations between σ3 and σ2 due to inherited fault patterns might occur while the stress regime changed from SR1 to SR3.

How to cite: Tranos, M. D., Assie, K. R., Wang, Y., Ma, H., Kouamelan, K. S., Thompson Brantson, E., Zhou, L., and Blaise Ketchaya, Y.: Late Cenozoic faulting deformation of the Fanshi Basin (Northern Shanxi rift, China), inferred from paleostress analysis of mesoscale fault-slip data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13203, https://doi.org/10.5194/egusphere-egu22-13203, 2022.

EGU22-13406 | Presentations | TS2.2

Paleoburial and paleostress history of a carbonate syn-rift reservoir : constraints from inversion of calcite twins and stylolite roughness in the Toca formation (Lower Congo Basin, South Atlantic) 

Boubacar Bah, Olivier Lacombe, Nicolas Beaudoin, Jean-Pierre Girard, Claude Gout, and Nicolas Godeau

To construct accurate geological models of reservoirs and better predict their properties, it is critical to have a good understanding of the burial and stress history of the host sedimentary basin over time. Stress and strain are important factors influencing the preservation or reduction of reservoir porosity and permeability. One way to access the orientations and magnitudes of paleostresses is to use paleopiezometers. This study aims at reconstructing the stress and burial history of the syn-rift Barremian (130-125 Ma) Toca Fm in the Lower Congo basin (West African passive margin) using stress inversion of calcite mechanical twins and sedimentary and tectonic, bedding-parallel stylolite. This combined approach was applied to two oriented borehole cores drilled in a poorly deformed oil field, offshore Congo, and provided constraints on both paleostress orientations and magnitudes. The timing of the different paleostress regimes documented was derived from a burial-time model reconstructed by use of TemisFlowTM.

The inversion of calcite twins was performed on a widespread early diagenetic cement (dated 127.4 ± 4.9 to 123.1 ± 7.7 Ma by U-Pb LA-ICPMS) and revealed two types of stress regimes. (1) An extensional stress regime with σ1 vertical and σ3 oriented either N50°±20° or N120°±20°, and mean differential stresses of 45 MPa for (σ1-σ3) and 20 MPa for (σ2-σ3). The NE-SW (N50°±20) extensional direction, which restores to N100° after moving back Africa to its position at Barremian times, marks the syn-rift extension that led to the opening of the South Atlantic. The 120° direction (~N-S after restoration) possibly reflects local perturbation and/or σ2-σ3 permutations during rifting in response to tectonic inheritance. (2) A compressional or strike-slip stress regime with horizontal σ1oriented ~E-W (and associated N-S extension) and mean differential stresses of 40 MPa for (σ1-σ3) and 15 MPa for (σ2-σ3). This suggests that the basin underwent a post-rift compressional history during the continuous burial of the Toca formation possibly related to the Atlantic ridge push effects. For the first time, we also reconstructed paleostress orientations from “tectonic” bedding-parallel stylolites, that developed during a tectonic extensional phase. The results point to a NE-SW extension consistent with the direction of the syn-rift extension revealed by calcite twinning. In order to constrain the sequence of stress evolution, we used the results of sedimentary stylolite roughness inversion paleopiezometry, which documents that the burial-related pressure solution in the Toca Fm occurred in the 400-1700m depth range (dissolution along 90% of stylolites halting between 700 and 1000m). Projection of this depth range onto the TemisFlowTM reconstructed burial-time curve of the Toca Fm indicates that vertical pressure solution was active between 122 and 95 Ma, and therefore that σ1 switched from vertical to horizontal around 95 Ma. Our study reveals that the Toca Fm has undergone a complex polyphase stress history during burial, with stress regimes evolving from extensional to compressional/strike-slip. It also illustrates the great usefulness of combining stress inversion of calcite twins and stylolite roughness with a burial-time model to constrain the stress history of a deeply buried reservoir.

How to cite: Bah, B., Lacombe, O., Beaudoin, N., Girard, J.-P., Gout, C., and Godeau, N.: Paleoburial and paleostress history of a carbonate syn-rift reservoir : constraints from inversion of calcite twins and stylolite roughness in the Toca formation (Lower Congo Basin, South Atlantic), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13406, https://doi.org/10.5194/egusphere-egu22-13406, 2022.

The NNW-SSE trending Koziakas-Itamos Mts of Western Thessaly, Central Greece, constitute the innermost part of the External Hellenides, i.e., the Hellenic fold-and-thrust belt, formed from the Tertiary orogenic (alpine) processes due to collision between the Apulia and Eurasia plates. Along these mountains, large ophiolite masses have thrust towards WSW over Mesozoic carbonate and clastic rocks, which in turn thrust over the Tertiary flysch rocks of the Pindos Unit. The mountains bound the NW-SE trending late-alpine Mesohellenic Trough to the east, filled with Late Eocene to Miocene molasse-type sediments, and the younger Thessaly basin filled up with Neogene and Quaternary sediments.

 

A detailed paleostress reconstruction based on the fault-slip analysis and the stress inversion through the TR method (TRM) unravels a multi-stage deformation history for the innermost parts of the Hellenic fold-and-thrust belt. More precisely, the late orogenic faulting deformation temporally constrained in Late Oligocene to Middle Miocene was originally driven by stress regimes that define an ENE-WSW ‘real’ compression normal to the orogenic fabric associated with mainly NE-directed back thrusts. The compression shifted to ‘hybrid’ with the activation of oblique- and strike-slip faults. After that stage, the hybrid compression predominates with counterclockwise changes in the trend of the greatest principal stress axis (σ1) from ENE-WSW to NNE-SSW. The last stage of the late-orogenic faulting deformation is an NW-SE orogen parallel extension segmenting and differentiating the NNW-SSE orogenic fabric along its strike.

 

Post-orogenic faulting deformation is driven by extensional stress regimes that caused the basin-and-range topography and the formation of well-established basins filled up with Late Miocene and younger sediments like the Thessaly basin. In particular, an ENE-WSW pure extension normal to the orogenic fabric has been defined. A general counterclockwise rotation of the least principal stress axis (σ3) occurred, initially giving rise to NE-SW  extension-transtension during Late Miocene-Pliocene and NNE-SSW extension-transtension since the Quaternary.

How to cite: Neofotistos, P. and Tranos, M.: Multi-stage late- and post-orogenic deformation history of the innermost Hellenic fold-and-thrust belt from a detailed paleostress reconstruction (Koziakas-Itamos Mts., Western Thessaly, Central Greece), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13463, https://doi.org/10.5194/egusphere-egu22-13463, 2022.

EGU22-658 | Presentations | PS6.1

Towards interior-atmosphere coupling on Venus: CO2 and H2O 

Iris van Zelst, Ana-Catalina Plesa, Caroline Brachmann, and Doris Breuer

Here, we show the first results of coupling a grey atmosphere model (i.e., we assume that the absorption coefficients are constant and hence independent of frequency) considering only CO2 and H2O as greenhouse gases to the geodynamic code Gaia (Hüttig et al., 2013). The evolution of the atmospheric composition of a planet is largely determined by the partial melting and volcanic outgassing of the interior. In turn, the composition of the atmosphere dictates the surface temperature of the planet (due to processes like the greenhouse effect), which is an important boundary condition for crustal and mantle processes in the interior of a planet. Venus in particular has a thick atmosphere at present with an abundance of the greenhouse gas CO2 and a small amount of water vapour. However, the surface conditions may have been much milder up to recent times (e.g., Way et al., 2016). Volcanic outgassing during the thermal history of Venus is thought to have significantly affected the planet's surface temperature and hence its global mantle evolution. Here, we calculate the outgassing of CO2 and H2O from the melt and then use the resulting partial pressures to calculate the surface temperature, which we then use as our boundary condition for the mantle convection. We compare our results to previous studies who employed similar coupled models to address the interaction between the interior and atmosphere of Venus (e.g., Noack et al., 2012; Gillmann & Tackley, 2014; Höning et al., 2021). Ultimately, we aim to consider more chemical species than CO2 and H2O to shed light on the Venus’ interior and atmosphere evolution. Therefore, we also show preliminary results of outgassing models that consider chemical speciation of the entire C-O-H system, i.e., CO2, H2O, H2, O2, CO, and CH4. 

How to cite: van Zelst, I., Plesa, A.-C., Brachmann, C., and Breuer, D.: Towards interior-atmosphere coupling on Venus: CO2 and H2O, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-658, https://doi.org/10.5194/egusphere-egu22-658, 2022.

The cold forearc mantle is a universal feature in global subduction zones and attributed to mechanically decoupling by the weak hydrous layer at the sub-forearc slab interface. Understanding the mechanical decoupling by the weak hydrous layer thus provides critical insight into the transition from subduction infancy to mature subduction since subduction initiation. Nevertheless, the formation and evolution of the weak hydrous layer by slab-derived fluids and its role during the transition have not been quantitatively evaluated by previous numerical models as it has been technically challenging to implement the mechanical decoupling at the slab interface without imposing ad hoc weakening mechanism. We here for the first time numerically demonstrate the formation and evolution down-dip growth of the weak hydrous layer without any ad hoc condition using the case of Southwest Japan subduction zone, the only natural laboratory on Earth where both the geological and geophysical features pertained to the transition since subduction initiation at ~17 Ma have been reported. Our model calculations show that mechanical decoupling by the spontaneous down-dip growth of the weak hydrous layer converts hot forearc mantle to cold mantle, explaining the pulsating forearc high-magnesium andesite (HMA) volcanism, scattered monogenetic forearc and arc volcanism, and Quaternary adakite volcanism. Furthermore, the weak hydrous layer providing a pathway for free-water transport toward the tip of the mantle wedge elucidates seismological observations such as large S-wave delay time and nonvolcanic seismic tremors as well as slab/mantle-originating geochemistry in the Southwest Japan forearc mantle.

 

How to cite: Lee, C. and Kim, Y.: Spontaneous formation and evolution of a weak hydrous layer at a slab interface: a numerical perspective, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2121, https://doi.org/10.5194/egusphere-egu22-2121, 2022.

EGU22-3062 | Presentations | PS6.1

Heat flow in the cores of Earth, Mercury and Venus from resistivity experiments on Fe-Ni-Si 

meryem berrada, Richard Secco, and Wenjun Yong

Recent theoretical studies have tried to constrain internal structure and composition of Earth, Mercury and Venus using thermal evolution models. In this work, the adiabatic heat flow at the top of the core was estimated using the electronic component of thermal conductivity (kel), a lower bound for thermal conductivity. Direct measurements of electrical resistivity (ρ) of Fe-10wt%Ni-wt%Si at core conditions can be related to kel using the Wiedemann-Franz law. Measurements were carried out in a 3000 ton multi-anvil press using a 4-wire method. The integrity of the samples at high pressures and temperatures was confirmed with electron-microprobe analysis of quenched samples at various conditions. Measurements of ρ at melting seem to remain constant at 135 µΩcm and 141 µΩcm on the solid and liquid sides of the melting boundary. The heat flow at the top of Earth’s CMB is greatly influenced by the light element content in the core. Interpolation of the measured thermal conductivity from this study with high pressure data from the literature suggest the addition of 10-16 wt%Ni and 3-10wt%Si in Earth core results in a heat flow of 6.8 TW at the top of the core. In Mercury, the presence of a thermally stratified layer of Fe-S at the top of an Fe-rich core has been suggested, which implies a sub-adiabatic heat flow on the core side of the CMB. The calculated adiabatic heat flux at the top of Mercury’s core suggests a sub-adiabatic from 0.09-0.21 Gyr after formation, which suggest a chemically driven magnetic field after this transition. Also, the heat flow in Mercury’s interior is estimated to increase by 67% from the inner core to outer core. It has been proposed that an Earth-like core structure for Venus is only compatible with the current lack of dynamo if Venus’ core thermal conductivity is 100 Wm−1K−1 or more. The thermal conductivity at Venus’ core conditions is estimated to range from 44-51 Wm−1K−1, in agreement with scenarios of a completely solidified core.

How to cite: berrada, M., Secco, R., and Yong, W.: Heat flow in the cores of Earth, Mercury and Venus from resistivity experiments on Fe-Ni-Si, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3062, https://doi.org/10.5194/egusphere-egu22-3062, 2022.

EGU22-3367 | Presentations | PS6.1

Melting relations of carbonates and trace element partitioning between carbonates and carbonate liquid in the Earth's upper mantle 

Melanie J. Sieber, Max Wilke, Marcus Oelze, Oona Appelt, Franziska D.H. Wilke, and Monika Koch-Müller

We examined the supra-solidus phase relations of the CaCO3-MgCO3 system and established trace element partition coefficient between carbonates and carbonate melt by conducting high pressure (6 and 9 GPa) and temperature (1300-1800 oC) experiments with a rocking multi-anvil press. It is well known that the major element composition of initial melts derived from low-degree partial melting of the carbonated mantle strongly depends on the melting relations of carbonates (e.g. 1, 2 and reference therein). Understanding the melting relations in the CaCO3-MgCO3 system is thus fundamental in assessing low-degree partial melting of the carbonated mantle. We show here to which extent the trace element signature of a pure carbonate melt can be used as a proxy for the trace element signature of mantle-derived CO2-rich melts such as kimberlites.

Our results support that, in the absence of water, Ca-Mg-carbonates are thermally stable along geothermal gradients typical at subduction zones. Except for compositions close to the endmembers (~Mg0-0.1Ca1-0.9CO3; Ca0-0.1Mg1-0.9CO3), Ca-Mg-carbonates will partially (to completely) melt beneath mid‑ocean ridges and in plume settings. Ca-Mg-carbonates melt incongruently to dolomitic melt and periclase above 1450 oC and 9 GPa making the CaCO3-MgCO3 a (pseudo-) ternary system as the number of components increases. Further, our results show that the rare earth element signature of a dolomitic melt in equilibrium with magnesite is similar to those of Group I kimberlites, namely that HREE are depleted relative to primitive mantle signatures. This implies that dolomite-magnesite solid solutions might be useful to approximate melting relations and melt compositions of low-degree partial melting of the carbonated mantle.

References

1  Yaxley, Ghosh, Kiseeva, Mallik, Spandler, Thomson, and Walter, CO2-Rich Melts in Earth, in Deep Carbon: Past to Present, Orcutt, Daniel, and Dasgupta, Editors. 2019, Cambridge University Press: Cambridge. p. 129-162.

2  Dasgupta and Hirschmann, The deep carbon cycle and melting in Earth's interior. Earth and Planetary Science Letters, 2010. 298 (1-2): p. 1-13.

How to cite: Sieber, M. J., Wilke, M., Oelze, M., Appelt, O., Wilke, F. D. H., and Koch-Müller, M.: Melting relations of carbonates and trace element partitioning between carbonates and carbonate liquid in the Earth's upper mantle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3367, https://doi.org/10.5194/egusphere-egu22-3367, 2022.

EGU22-4048 | Presentations | PS6.1

Convection and segregation in partially molten orogenic crust: application to the formation of Naxos migmatite domes (Greece) 

Olivier Vanderhaeghe, Aurélie Louis-Napoléon, Muriel Gerbault, Thomas Bonometti, Roland Martin, and Nathan Maury

The deep roots of the Archaean to Phanerozoic continental crust reveal domed structures of kilometer to deca-kilometer sizes. These domes are typically cored by migmatites, which attest of the dynamics of the partially molten crust and associated heterogeneous mass redistribution. We model here numerically the development of gravity instabilities in a continental crust heated from below with no lateral motion, simulating the conditions prevailing at the transition between orogenic climax and collapse. The chemical and physical heterogeneity of the crust is represented by deformable inclusions of distinct viscosity and density with power-law temperature and strain-rate dependent viscosities. We use the VOF Method (Volume Of Fluid, OpenFoam code) that reproduces well the coalescence and separation of inclusions, of sizes of a few hundred meters.

In previous work (Louis-Napoleon et al., GJI, 2021) we identified three distinct flow regimes depending on two Rayleigh numbers RaUM and RaPM, which characterize the solid and molten domains, respectively. A"suspension" regime (high RaUM and RaPM) describes the entrainment of the inclusons in the convective cells. A “stratification” regime (low RaUM and high RaPM) characterizes how the light inclusions amalgamate as floating clusters under the rigid upper crust, which can then form kilometer scale dome structures. A “diapirism” regime corresponds to the segregation of the heavy and light inclusions to to form layers at the bottom and top of the molten layer, respectively.

The present study incorporates 3D models that evidence the key role of the size and concentration of the inclusions for the “stratification” regime, and pinpoint the fundamental characteristics of Earth’s rocks heterogeneity at the crustal scale.

Application of our results to the kilometer-scale subdomes within the crustal-scale migmatite dome exposed on Naxos Island (Greece) probe basal heating for 5-10 Ma, below a 45 km thick crust. There, several cycles of zircon precipitation dated from 24 to 16 Ma have been interpreted in terms of convective motion (Vanderhaeghe et al., 2018). Three distinct configurations validate this scenario in which the viscosity and density distributions, and the basal heating time were varied. All configurations also lead to the final formation and preservation of domes cored by the low-viscosity-density material of a diameter of 2 to 5 km, at a depth of ca. 15 km. These results show that the efficiency of material redistribution within a partially molten crust depends on the flow regime associated to the development of gravitational instabilites and is very sensitive to the physical heterogeneity of the crust.

How to cite: Vanderhaeghe, O., Louis-Napoléon, A., Gerbault, M., Bonometti, T., Martin, R., and Maury, N.: Convection and segregation in partially molten orogenic crust: application to the formation of Naxos migmatite domes (Greece), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4048, https://doi.org/10.5194/egusphere-egu22-4048, 2022.

EGU22-5975 | Presentations | PS6.1

Water planet thresholds: The topographic scope for land atop a stagnant lid 

Claire Marie Guimond, John Rudge, and Oliver Shorttle

Small water budgets produce desert worlds and large water budgets produce water worlds, but there is a narrow range of water budgets that would grant a marbled surface to a rocky planet. A planet’s highest point can constrain this range in that it defines the minimum ocean volume to flood all land. Thus we take a first step in quantifying water world limits by estimating how minimum surface elevation differences scale with planetary bulk properties. Our model does not require the presence of plate tectonics, an assumption which has constricted the scope of previous studies on exoplanet land fractions. We focus on the amplitudes of dynamic topography created by rising and sinking mantle plumes—obtained directly from models of mantle convection—but also explore rough limits to topography by other means. Rocky planets several times more massive than Earth can support much less topographic variation due to their stronger surface gravity and hotter interiors; these planets’ increased surface area is not enough to make up for low topography, so ocean basin capacities decrease with planet mass. In cooler interior thermal states, dynamically-supported topography alone could maintain subaerial land on Earth-size stagnant lid planets with surface water inventories of up to approximately 100 ppm of their mass (or half Earth’s ocean mass fraction). Considering the overall cap to topography on such planets would raise this threshold ocean mass fraction by an order of magnitude. Current estimates of the surface water contents on TRAPPIST-1e to g place these planets near or above the ultimate topographic waterworld threshold, depending on their core masses.

How to cite: Guimond, C. M., Rudge, J., and Shorttle, O.: Water planet thresholds: The topographic scope for land atop a stagnant lid, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5975, https://doi.org/10.5194/egusphere-egu22-5975, 2022.

EGU22-8661 * | Presentations | PS6.1 | Highlight

Compositional constraints on the lifetime of habitable climates on rocky exoplanets 

Bradford Foley and Cayman Unterborn

An essential factor for the habitability of rocky exoplanets over geologic timescales is climate regulation via the carbonate-silicate cycle. Without such regulation, uninhabitably hot or cold climates could form, even for planets lying within their host star’s habitable zone. While often associated with plate tectonics, recent work has shown that the carbonate-silicate cycle can operate on planets in a stagnant-lid regime of tectonics, as long as volcanism is active. Volcanism drives release of CO2 to the atmosphere, without which climate could cool into a globally frozen state, and the creation of fresh rock for weathering, without which a CO2-rich hothouse climate could form. A key factor dictating how long volcanism can last on a rocky planet is the budget of heat producing elements (U, Th, and K) it acquires during formation. While not directly measurable for exoplanets, estimates on the range of heat producing elements (HPEs) can be made from stellar composition observations. We estimate a probability distribution of HPE abundances in rocky exoplanets based on the Hypatia catalog database of stellar U, Th, and K abundances, where Eu is used as a proxy for the difficult to measure U.

We then constrain how long volcanism, and hence habitable climates, can last on rocky exoplanets in a stagnant-lid regime using a simple thermal evolution model where initial HPE abundances in the mantle are randomly drawn from the distributions constructed from the Hypatia catalog. We further explore the influence of planet size and factors such as the initial mantle temperature and mantle reference viscosity in our models. Our models are conservative, meant to estimate the earliest time that volcanism could cease on rocky exoplanets. We find volcanism lasts for ~2 Gyrs, with 95% confidence intervals of 0.6-3.8 Gyrs for an Earth-sized planet, increasing modestly to ~3.5 Gyrs (95% confidence intervals of 1.4-5.8 Gyrs) for a six Earth mass planet. The variation in volcanism lifetime is largely determined by the K abundance of the planet, as K is a potent HPE and highly variable in stars. The likelihood of acquiring high enough abundances of the long half-life HPEs, Th or 238U, to power long-lived volcanism through these heat sources is low. In most cases even Th and 238U abundances at the high end of our observationally constrained probability distributions are not sufficient to power volcanism on their own, such that planets will see volcanism cease once K concentrations have decayed. Only with a high reference viscosity can Th or 238U potentially drive long-lived volcanism, as in this case volcanism can be sustained for a lower total radiogenic heat production rate.  

How to cite: Foley, B. and Unterborn, C.: Compositional constraints on the lifetime of habitable climates on rocky exoplanets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8661, https://doi.org/10.5194/egusphere-egu22-8661, 2022.

EGU22-10678 | Presentations | PS6.1

New insights into the formation of the pallasites from the Sericho meteorite from EBSD.  

Reina Hiramatsu and Martin Lee

The pallasite meteorites are composed of olivine crystals, Fe-Ni metal alloy and Fe-sulphide. Their formation environment was initially proposed to be at core-mantle boundaries of planetesimals (Scott et al., 1977., Geochemica et Cosmochemica Acta., p.349). However, recent studies using paleomagnetic techniques, and examining the metal concentrations across multiple pallasites, argues against the core-mantle boundary hypothesis (Nichols et al., 2021., Journal of Geophysical Research Planets., p.16). Ferrovolcanism models, which invoke Fe-FeS magma injection into mantle lithologies support paleomagnetism results, compositional trends, and olivine growth conditions (Johnson et al., 2020., Nature Astronomy., p.43). Here we present results from the recently found pallasite Sericho to further explore magmatic aspects of the ferrovolcanism hypothesis using optical microscopy together with SEM energy dispersive X-ray spectrometry (EDS) and electron backscatter diffraction (EBSD).

Sericho has a jigsaw-like texture of forsterite crystals in a troilite matrix. Crystallographic preferred orientations (CPO) of the olivine as determined by EBSD indicate a flow alignment, possibly due to the introduction of the Fe-Ni alloy resulting from upwelling within the planetesimal. Identification of a tabular inclusion within one of the olivine crystals suggests that Sericho experienced mild shock events in contrast to previously studied pallasites including Eagle Station. Our CPO results support the ferrovolcanism hypothesis and more work is underway to investigate olivine slip systems to find out type of internal misorientation is recorded within Sericho’s olivines.

How to cite: Hiramatsu, R. and Lee, M.: New insights into the formation of the pallasites from the Sericho meteorite from EBSD. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10678, https://doi.org/10.5194/egusphere-egu22-10678, 2022.

EGU22-11313 | Presentations | PS6.1

Solubility of water in peridotite liquids and the formation of steam atmospheres on rocky planets 

Paolo Sossi, Peter Tollan, James Badro, and Dan Bower

Atmospheres are products of time-integrated mass exchange between the surface of a planet and its interior. On Earth, the most significant of these events occurred when it existed in a magma ocean state, producing its earliest atmosphere. During this stage, both steam- and carbon-rich atmospheres may have been generated in equilibrium with a magma ocean [1, 2]. However, the nature of Earth’s early atmosphere, and those around other rocky planets, remains unclear for lack of constraints on the solubility of major atmophile elements in liquids of appropriate composition.

Here we determine the solubility of water in 14 peridotite liquids synthesised in a laser-heated aerodynamic levitation furnace [2]. We explore oxygen fugacities (fO2) between -1.5 and +6.4 log units relative to the iron-wüstite buffer at constant temperature (1900±50 °C) and total pressure (1 bar). The resulting fH2O ranged from nominally 0 to ~0.028 bar and fH2 from 0 to ~0.065 bar. The total H2O contents were determined by FTIR spectroscopy of polished thick sections by examining the intensity of the absorption band at 3550 cm-1 and applying the Beer-Lambert law.

We find that the mole fraction of dissolved water in the liquid is proportional to (fH2O)0.5, attesting to its dissolution as OH-. The solubility coefficient fit to the data yields a value of ~500 ppm/bar0.5, roughly 30 % lower than that determined for basaltic liquids at 1350 °C and 1 bar [3]. Therefore, more Mg-rich compositions and/or higher temperatures result in a significant decrease of water solubility in silicate melts. While the solubility of water remains high relative to that of CO2, we hypothesise that steam atmospheres may form under oxidising conditions, provided sufficiently high temperatures and H/C ratios in terrestrial planets prevail.

[1] Gaillard, F. et al. (2022), Earth Planet. Sci. Lett., 577, 117255. [2] Sossi, P.A. et al. (2020), Science Adv., 6, eabd1387. [3] Newcombe, M.E. et al., (2017), Geochim. Cosmochim. Acta, 200, 330-352.

How to cite: Sossi, P., Tollan, P., Badro, J., and Bower, D.: Solubility of water in peridotite liquids and the formation of steam atmospheres on rocky planets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11313, https://doi.org/10.5194/egusphere-egu22-11313, 2022.

EGU22-11544 | Presentations | PS6.1

Delineating driving mechanisms of Phanerozoic climate: building a habitable Earth 

Andrew Merdith, Benjamin Mills, Pierre Maffre, Yves Goddéris, Yannick Donnadieu, and Thomas Gernon

The fundamental drivers of Phanerozoic climate change over geological timescales (10–100s of Ma) are well recognised: degassing from the deep-earth puts carbon into the atmosphere, silicate weathering takes carbon from the atmosphere and traps it in carbonate minerals. A number of variables are purported to control or exert influence on these two mechanisms, such as the motion of tectonic plates varying the amount of degassing, the palaeogeogrpahic distribution of continents and oceans, the colonisation of land by plants and preservation of more weatherable material, such as ophiolites. We present a framework, pySCION, that integrates these drivers into a single analysis, connecting solid earth with climate and biogeochemistry. Further, our framework allows us to isolate individual drivers to determine their importance, and how it changes through time. Our model, with all drivers active, successfully reproduces the key aspects and trends of Phanerozoic temperature, to a much greater extent than previous models. We find that no single driver can explain Phanerozoic temperature with any degree of confidence, and that the most important driver varies for each geological period.

How to cite: Merdith, A., Mills, B., Maffre, P., Goddéris, Y., Donnadieu, Y., and Gernon, T.: Delineating driving mechanisms of Phanerozoic climate: building a habitable Earth, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11544, https://doi.org/10.5194/egusphere-egu22-11544, 2022.

EGU22-12614 | Presentations | PS6.1

A python package for fast interior modelling of terrestrial (exo-)planets using a Gibbs free energy minimization 

Fabian Seidler, Haiyang Wang, and Sascha Quanz

With increasing capabilities of characterizing small rocky exoplanets beyond our solar system, the question of their chemistry, geology and interior structure arises. Accompanied by observational facilities capabale of giving a deeper look into this topic than ever before, modelling of the interior structure of exoplanets has become a standard procedure in the emerging field of exogeology. Most often, these research uses a simplified mineralogy – consisting of the major phases formed by  MgxFe1-xSiO3 and Mg2xFe2(1-x)SiO4 -  to construct the density profile of the planets mantle. Others have used the more sophisticated, but computationally expensive procedure of Gibbs free energy minimization to find the mantle equilibrium mineralogy (and hence its thermodynamical properties) from the first order chemistry of the planet. Here, we present a new Python/Cython software package capable of quickly inferring exoplanet interior structure by using a linearized Gibbs free energy minimization procedure - written in Cython - along an adiabatic mantle gradient. This simplifies and speeds up the interior structure modelling, reaching a runtime of ~7 seconds on a standard desktop PC for an Earth-sized planet, compared to ≥ 2 minutes with another interior structure and mineralogy solver, ExoPlex. We will demonstrate the use of the codes and its first application results at the assembly.

How to cite: Seidler, F., Wang, H., and Quanz, S.: A python package for fast interior modelling of terrestrial (exo-)planets using a Gibbs free energy minimization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12614, https://doi.org/10.5194/egusphere-egu22-12614, 2022.

EGU22-12795 | Presentations | PS6.1

Experimental Phase Relations in the CaS-FeS and MgS-FeS Systems and their Bearing on the Evolution of Mercury 

Stefan Pitsch, Paolo A. Sossi, Max W. Schmidt, and Christian Liebske

Sulfide liquids in terrestrial environments are near mono-sulfidic and are FeS-rich with varying amounts of other chalcophile elements. At highly reducing conditions, as on Mercury, elements like Ca, Na and Mg can also form major components of sulfides and coexist with FeS [1,2,3].
Here, we re-examine the FeS-CaS and FeS-MgS binaries at 950 to 1600°C and 1100°C to 1500°C respectively, owing to the limited amount of data on these systems and the uncertainty in the eutectic point of the FeS-CaS binary [4, 5]. We use the determined phase compositions and inferred densities in the systems CaS-Fes and MgS-FeS (± additions of NaS) to assess mechanisms of sulfur accumulation on the surface of Mercury by gravitational separation of sulfides in a portential magma ocean [6].              Experiments were performed with stoichiometric mixes of pure components in graphite capsules sealed in evacuated silica tubes at ~10-5 bar. Quenched samples were prepared under anhydrous conditions, and phase compositions determined by energy-dispersive spectroscopy. Because quenched Ca-rich sulfide liquid is labile, its composition was estimated by mass balance and image analysis. The eutectic point of the CaS-FeS system was determined by experimentally bracketing various bulk compositions.           
The solubility of FeS in oldhamite is higher than previously reported, reaching 2.5 mol% at 1065 °C. The eutectic is located at 8.5 ± 1 mol % CaS, significantly poorer in CaS than previously suggested [4], at 1070 ± 5 °C. Our data suggest that solid solution phase compositions in the MgS-FeS binary are in accord with those reported in the only other study on this system [7]. However, we find that the liquid phase in equilibrium with MgS (ss) between 1150°C and 1350°C is more FeS-rich than suggested containing <10 mol% MgS up to 1350°C. 
Our data show that Ca dissolves extensively in sulfides under graphite-saturated conditions at low pressures, which may have prevailed during crust formation on Mercury [8]. The produced solid phases of the CaS-FeS binary are sufficiently light to be able to float in a Hermean magma ocean.

[1]          Skinner + Luce (1971) AmMin

[2]          Nittler + Starr et al., (2011) Science

[3]          Barraud + Coressoundiram + Besse (2021) EPSC2021

[4]          Dilner + Kjellqvist + Selleby (2016) J Phase Equilibria Diffus

[5]          Heumann (1942) Arch Eisenhuttenwes

[6]          Malavergne et al. (2014) Earth Planet. Sci. Lett.

[7]          Andreev et al. (2006) Russ. J. Inorg. Chem.

[8]          Vander Kaaden + McCubbin (2015) J. Geophys. Res. Planets

 

 

 

 

 

 

 

 

 

How to cite: Pitsch, S., Sossi, P. A., Schmidt, M. W., and Liebske, C.: Experimental Phase Relations in the CaS-FeS and MgS-FeS Systems and their Bearing on the Evolution of Mercury, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12795, https://doi.org/10.5194/egusphere-egu22-12795, 2022.

The interest of this research work is focused on the detection of possible pre-seismic perturbations related to medium-sized earthquakes (5≤Mw≤5.9) occurring in the upper ionized atmosphere (about 350 km above the Earth, ionospheric F2-region). For this specific purpose, we have exploited several geodetic data, derived through signal processing of dual-frequency permanent ground-based Global Positioning System (GPS)/Global Navigation Satellite Systems (GNSS) receivers, located at the Euro-Mediterranean basin.

To find out whether the ionospheric F2-layer is responsive to the energy released during the preparation periods of medium magnitude earthquakes, the Lorca seismic event (May 11th, 2011, Mw 5.1, Murcia region) was taken as an initial sample. For this shallow-focus earthquake (4 km depth), the longitude-latitude coordinates of the epicenter are 1.7114° W, 37.7175° N. As result, modeling regional ionosphere using GPS/GNSS-total electron content (TEC) measurements over the epicentral area through spherical harmonic analysis, allowing us to identify pre-earthquake ionospheric irregularities in response to the M5.1 Lorca event. After discerning the seismo-ionospheric precursors from those caused by space weather effects, via wavelet-based spectral analysis, these irregularities were identified about a week before the onset of the mainshock.

The seismo-geodetic technique adopted in this study validates our hypothesis that stimulates the existence of a strong correlation between deep lithospheric deformations and pre-seismic ionospheric anomalies due to moderate magnitudes.

Keywords: Murcia earthquake, Seismo-ionospheric precursors, Spherical harmonic analysis, Wavelet transform, GPS/GNSS-TEC, Lithospheric deformations, Regional F2-ionosphere maps.

How to cite: Tachema, A.: Could the moderate-sized earthquakes trigger pre-seismic ionospheric irregularities? Study of the 2011 Murcia earthquake in the Mediterranean region (SE-Spain)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1438, https://doi.org/10.5194/egusphere-egu22-1438, 2022.

EGU22-1505 | Presentations | NH4.1 | Highlight

Testing spatial aftershock forecasts accounting for large secondary events during on going earthquake sequences: A case study of the 2017-2019 Kermanshah sequence 

Behnam Maleki Asayesh, Hamid Zafarani, Sebastian Hainzl, and Shubham Sharma

Large earthquakes are always followed by aftershocks sequence that last for months to years. Sometimes, these aftershocks are as destructive as the mainshocks. Hence, accurate and immediate prediction of aftershocks’ spatial and temporal distribution is of great importance for planning search and rescue activities. Despite large uncertainties associated with the calculation of Coulomb failure stress changes (ΔCFS), it is the most commonly used method for predicting spatial distributions of aftershocks. Recent studies showed that classical Coulomb failure stress maps are outperformed by alternative scalar stress quantities, as well as a distance-slip probabilistic model (R) and deep neural networks (DNN). However, these test results were based on the receiver operating characteristic (ROC) metric, which is not well suited for imbalanced data sets such as aftershock distributions. Furthermore, the previous analyses also ignored the potential impact of large secondary earthquakes.

In order to examine the effects of large events in spatial forecasting of aftershocks during a sequence, we use the 2017-2019 seismic sequence in western Iran. This sequence started by Azgeleh M7.3 mainshock (12 November 2017) and followed by Tazehabad M5.9 (August 2018) and Sarpol-e Zahab M6.3 (November 2018) events. Furthermore, 15 aftershocks with magnitude > 5.0 and more than 8000 aftershocks with magnitude > 1 were recorded by Iranian seismological center (IRSC) during this sequence (12.11.2017-04.07.2019). For this complex sequence, we applied the classical Coulomb failure stress, alternative stress scalars, and R forecast models and used the more appropriate MCC-F1 metric to test the prediction accuracy. We observe that the receiver independent stress scalars (maximum shear and von-Mises stress) perform better than the classical CFS values relying on the specification of receiver mechanisms (ΔCFS resolved on master fault, optimally oriented planes, and variable mechanism). However, detailed analysis based on the MCC-F1 metric revealed that the performance depends on the grid size, magnitude cutoff, and test period. Increasing the magnitude cutoff and decreasing the grid size and test period reduces the performance of all methods. Finally, we found that the performance of all methods except ΔCFS resolved on master fault and optimally oriented planes improve when the source information of large aftershocks is additionally considered, with stress-based models outperforming the R model. Our results highlight the importance of accounting for secondary stress changes in improving earthquake forecasts.

How to cite: Maleki Asayesh, B., Zafarani, H., Hainzl, S., and Sharma, S.: Testing spatial aftershock forecasts accounting for large secondary events during on going earthquake sequences: A case study of the 2017-2019 Kermanshah sequence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1505, https://doi.org/10.5194/egusphere-egu22-1505, 2022.

EGU22-2152 | Presentations | NH4.1

Extension of the radon monitoring network in seismic areas in Romania 

Victorin - Emilian Toader, Constantin Ionescu, Iren-Adelina Moldovan, Alexandru Marmureanu, Iosif Lingvay, and Ovidiu Ciogescu

The Romanian National Institute of Earth Physics (NIEP) developed a radon monitoring network mainly for Vrancea seismic are characterized by deep earthquakes (a rectangle zone in longitude/ latitude 25.050/ 46.210 - 27.950/ 44.690, 60 Km – 250 Km). Few stations were relocated after a year of operation following inconclusive results regarding the relationship between radon and seismic activity. To the 5 stations that are in the Vrancea area (Bisoca, Nehoiu, Plostina, Sahastru and Lopatari) we added others positioned in areas with surface seismicity (Panciu, Râmnicu Vâlcea, Surlari and Mangalia). The last two are on the Intramoesica fault, which will be monitored in the future along with the Fagaras - Câmpulung fault. Radon together with CO2 - CO is monitored at Râmnicu Vâlcea within the SPEIGN project near a 40 m deep borehole in which the acceleration in three directions, temperature and humidity are recorded. The same project funded the monitoring of radon, CO2 and CO in Mangalia, which is close to the Shabla seismic zone. The last significant earthquake in the Panciu area with ML = 5.7 R occurred on 22.11.2014. The area is seismically active, which justified the installation of a radon detector next to a radio receiver in the ULF band within the AFROS project. Within the same project, radon monitoring is performed at Surlari, following the activity of the Intramoesica fault. In this location we also measure CO2, CO, air temperature and humidity. The first results show a normal radon activity in Panciu. The measurements in Surlari have higher values than those in Panciu, possibly due to the forest where the sensors are located. A special case is Mangalia where the data indicate more local pollution than the effects of tectonic activity. Radon CO2 and CO values vary widely beyond normal limits. The source of these anomalies may be the local drinking water treatment plant or the nearby shipyard. We also recorded abnormal infrasound values that are monitored in the same location. Determining the source of these anomalies requires at least one more monitoring point.

The purpose of expanding radon monitoring is to analyze the possibility of implementing a seismic event forecast. This can be done in a multidisciplinary approach. For this reason, in addition to radon, determinations of CO2, CO, air ionization, magnetic field, inclinations, telluric currents, solar radiation, VLF - ULF radio waves, temperature in borehole, infrasound and acoustics are made.

This research helps organizations specializing in emergencies not only with short-term earthquake forecasts but also with information on pollution and the effects of climate change that are becoming increasingly evident lately. The methods and solutions are general and can be applied anywhere by customizing them according to the specifics of the monitored area.

The main conclusion is that only a multidisciplinary approach allows the correlation of events and ensures a reliable forecast.

How to cite: Toader, V.-E., Ionescu, C., Moldovan, I.-A., Marmureanu, A., Lingvay, I., and Ciogescu, O.: Extension of the radon monitoring network in seismic areas in Romania, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2152, https://doi.org/10.5194/egusphere-egu22-2152, 2022.

EGU22-2979 | Presentations | NH4.1

TEC variation over Europe during the intense tectonic activity in the area of  Arkalochori of Crete on December of 2021 

Michael E. Contadakis, Demeter N. Arabelos, Christos Pikridas, Styllianos Bitharis, and Emmanuel M. Scordilis

This paper is one of a series of papers dealing with the investigation of  the Lower ionospheric variation on the occasion of an intense tectonic activity.In the present paper, we investigate the TEC variations during the intense seismic activity in Arkalochori of Crete on December 2021 over Europe. The Total Electron Content (TEC) data are been provided by the  Hermes GNSS Network managed by GNSS_QC, AUTH Greece, the HxGN/SmartNet-Greece of Metrica S.A, and the EUREF Network. These data were analysed using Discrete Fourier Analysis in order to investigate the TEC turbulence band content. The results of this investigation indicate that the High-Frequency limit fo of the ionospheric turbulence content, increases as aproaching the occurrence time of the earthquake, pointing to the earthquake epicenter, in accordane to our previous investigations. We conclude that the Lithosphere Atmosphere Ionosphere Coupling, LAIC, mechanism through acoustic or gravity waves could explain this phenomenology.

 

Keywords: Seismicity, Lower Ionosphere, Ionospheric Turbulence, Brownian Walk, Aegean area.

How to cite: Contadakis, M. E., Arabelos, D. N., Pikridas, C., Bitharis, S., and Scordilis, E. M.: TEC variation over Europe during the intense tectonic activity in the area of  Arkalochori of Crete on December of 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2979, https://doi.org/10.5194/egusphere-egu22-2979, 2022.

EGU22-3138 | Presentations | NH4.1

The Jun 15, 2019, M7.2 Kermadec Islands (New Zealand) earthquake as analyzed from ground to space 

Angelo De Santis, Loredana Perrone, Saioa A. Campuzano, Gianfranco Cianchini, Serena D'Arcangelo, Domenico Di Mauro, Dedalo Marchetti, Adriano Nardi, Martina Orlando, Alessandro Piscini, Dario Sabbagh, and Maurizio Soldani

The M7.2 Kermadec Islands (New Zealand) large earthquake occurred on June 15, 2019 as the result of shallow reverse faulting within the Tonga-Kermadec subduction zone. This work deals with the study of the earthquake-related processes that occurred during the preparation phase of this earthquake. We focused our analyses on seismic (earthquake catalogues), atmospheric (climatological archives) and ionospheric data (from ground to space, mainly satellite) in order to disclose the possible Lithosphere-Atmosphere-Ionosphere Coupling (LAIC). For what concern the ionospheric investigations, we analysed and compared the observations from the Global Navigation Satellite System (GNSS) receiver network and those from satellites in space. Specifically, the data from the European Space Agency (ESA) Swarm satellite constellation and from the China National Space Administration (CNSA, in partnership with Italian Space Agency, ASI) China Seismo-Electromagnetic Satellite (CSES-01) are used in this study. An interesting comparison is made with another subsequent earthquake with comparable magnitude (M7.1) that occurred in Ridgecrest, California (USA) on July 6 of the same year. Both earthquakes showed several multiparametric anomalies that occurred at almost the same times from each earthquake occurrence, evidencing a chain of processes that point to the moment of the corresponding mainshock. In both cases, it is demonstrated that a multiparametric and multilayer analysis is fundamental to better understand the LAIC in complex phenomena such as the earthquakes.

How to cite: De Santis, A., Perrone, L., Campuzano, S. A., Cianchini, G., D'Arcangelo, S., Di Mauro, D., Marchetti, D., Nardi, A., Orlando, M., Piscini, A., Sabbagh, D., and Soldani, M.: The Jun 15, 2019, M7.2 Kermadec Islands (New Zealand) earthquake as analyzed from ground to space, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3138, https://doi.org/10.5194/egusphere-egu22-3138, 2022.

EGU22-3194 | Presentations | NH4.1

Using Operational Earthquake Forecasting Tool for Decision Making: A Synthetic Case Study 

Chen Huang, Håkan Bolin, Vetle Refsum, and Abdelghani Meslem

Operational earthquake forecasting (OEF) provides timely information about the time-dependent earthquake probabilities, which facilitates resilience-oriented decision-making. This study utilized the tools developed within the TURNkey (Towards more Earthquake-Resilient Urban Societies through a Multi-Sensor-Based Information System enabling Earthquake Forecasting, Early Warning and Rapid Response Actions) project funded by the European Union’s Horizon 2020 research and innovation programme to demonstrate the benefits of OEF to the decision support system.  The considered tools are developed based on the state-of-the-art knowledge about seismology and earthquake engineering, involving the Bayesian spatiotemporal epidemic-type aftershock sequence (ETAS) forecasting model, the time-dependent probabilistic seismic hazard assessment, the SELENA (SEimic Loss EstimatioN using a logic tree Approach) risk analysis, cost-benefit analysis and the multi-criteria decision-making methodology. Moreover, the tools are connected to the dense seismograph network developed also within the TURNkey project and, thus, it is capable of real-time updating the forecasting based on the latest earthquake information and observations (e.g., earthquake catalogue). Through a case study in a synthetic city, this study first shows that the changes in the earthquake probabilities can be used as an indicator to inform the authorities or property owners about the heightened seismicity, based on which the decision-maker can, for example, issue a warning of the potential seismic hazard. Moreover, this study illustrates that OEF together with the risk and loss analysis provides the decision-maker with a better picture of the potential seismic impact on the physical vulnerabilities (e.g., damage, economic loss, functionality) and social vulnerabilities (e.g., casualty and required shelters). Finally, given the decision-maker’s preference, this study shows how the hazard and risk results are used to help the decision-maker to identify the optimal action based on cost-beneficial class and the optimality value computed based on the multi-criteria decision-making methodology.

How to cite: Huang, C., Bolin, H., Refsum, V., and Meslem, A.: Using Operational Earthquake Forecasting Tool for Decision Making: A Synthetic Case Study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3194, https://doi.org/10.5194/egusphere-egu22-3194, 2022.

EGU22-3337 | Presentations | NH4.1

Multiparametric and multilayer investigation of global earthquakes in the World by a statistical approach 

Dedalo Marchetti, Kaiguang Zhu, Angelo De Santis, Saioa A. Campuzano, Donghua Zhang, Maurizio Soldani, Ting Wang, Gianfranco Cianchini, Serena D’Arcangelo, Domenico Di Mauro, Alessandro Ippolito, Adriano Nardi, Martina Orlando, Loredana Perrone, Alessandro Piscini, Dario Sabbagh, Xuhui Shen, Zeren Zhima, and Yiqun Zhang and the Zhu Kaiguang's earthquake research group in Jilin University

Earthquake prediction has always been a challenging task, and some researchers have proposed that it is an even impossible goal, concluding earthquakes are unpredictable events. Such a conclusion seems too extreme and in contrast with several pieces of evidence of alterations recorded by several instrumentations from the ground, atmosphere, and more recently by Earth Observation satellite. On the other side, it is clear that searching the “perfect precursor parameter” doesn’t seem to be a good way, since the earthquake process is a complex phenomenon. In fact, a precursor that works for one earthquake does not necessarily work for the next one, even on the same fault. In some cases, another problem for precursors identification is the recurrency time between the earthquakes, which could be very long and, in such cases, we don’t have comparable observations of earthquakes generated by the same fault system.

In past years, we concentrated mainly on two aspects: statistical and single case study; the first one consists of some statistical evidence on ionospheric disturbances possibly related to M5.5+ earthquakes (e.g., presented at EGU2018-9468, and published by De Santis et al., Scientific Report, 2019), furthermore, some clear signals in the atmosphere statistically preceded the occurrence of M8+ events (e.g., presented at EGU2020-19809). On the other side, we also investigated about 20 earthquakes that occurred in the last ten years, some of them by a very detailed and multiparametric investigation, like the M7.5 Indonesia earthquake (presented at EGU2019-8077 and published by Marchetti et al., JAES, 2020), or the Jamaica earthquake investigation presented at the last EGU2021-15456. We found that both approaches are very important. Actually, the statistical studies can provide proofs that at least some of the detected anomalies seem to be related to the earthquakes, while the single case studies permit us to explore deeply the details and the possible connections between the geolayers (lithosphere, atmosphere and ionosphere).

In this presentation, we want to show an update of the statistical study of the atmosphere and ionosphere, together with a new statistical investigation of the seismic acceleration before M7.5+ global earthquakes.

Finally, we demonstrate that it is essential to consider the earthquake not as a point source (that is the basic approximation), but in all its complexity, including its focal mechanism, fault rupture length and even other seismological constraints, in order to try to better understand the preparation phase of the earthquakes, and the reasons for their different behaviour. These studies give hope and fundamental (but not yet sufficient) tools for the possible achievement, one day, of earthquakes prediction capabilities.

How to cite: Marchetti, D., Zhu, K., De Santis, A., Campuzano, S. A., Zhang, D., Soldani, M., Wang, T., Cianchini, G., D’Arcangelo, S., Di Mauro, D., Ippolito, A., Nardi, A., Orlando, M., Perrone, L., Piscini, A., Sabbagh, D., Shen, X., Zhima, Z., and Zhang, Y. and the Zhu Kaiguang's earthquake research group in Jilin University: Multiparametric and multilayer investigation of global earthquakes in the World by a statistical approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3337, https://doi.org/10.5194/egusphere-egu22-3337, 2022.

EGU22-3610 | Presentations | NH4.1

Mechanism of frictional discharge plasma at fault asperities 

Kiriha Tanaka, Jun Muto, and Hiroyuki Nagahama

The mechanism of seismic-electromagnetic phenomena (SEP) encouraged as precursors of earthquake forecast remains unrevealed. The previous studies reported that the surface charges of the frictional and fractured quartz are enough to cause electric discharge due to the dielectric breakdown of air. To verify the discharge occurrence, friction experiments between a diamond pin and quartz disk were performed under nitrogen gas with a CCD camera and UV-VIS photon spectrometer (e.g., Muto et al., 2006). The photon emission was observed at the pin-to-disk gap only during the friction. The photon spectra obtained from a friction experiment (normal stresses of 13-20 MPa, a sliding speed of 1.0×10-2 m/s, and a gas pressure of 2.4×104 Pa) showed that the photon was emitted through the second positive band (SPB) system of neutral nitrogen and the first negative band (FNB) system of ionized nitrogen. The estimated potential difference at the gap gave the breakdown electric field and surface charge density on the frictional surface at a gap, where photon was the most intense. These values were enough to cause dielectric breakdown of air. Therefore, the above results demonstrated that frictional discharge could occur on a fault asperity due to dielectric breakdown of ambient gases by frictional electrification. However, the details of electronic transition during the discharge and its type are unknown.
This study discussed the details of the gas pressure dependency for the photon emission intensity and distribution, and the discharge type using the electronic transition theory. Moreover, we compared the surface charge density estimated from the potential difference with that estimated from electron and hole trapping centre concentrations in the frictional quartz subsurfaces measured by electron spin resonance. From this comparison, we also discussed the possibility for the trapping centres to be the sources of the discharge. We could explain the nitrogen gas pressure dependency for the photon emission intensity and vibration temperature observed during our friction experiments using the electron transition theory. For example, Miura et al. (2004) reported that the gas pressure decreases with increasing vibration temperature of the SPB system and the relative intensity in the SPB system to the FNB system. This result showed that the vibration temperature and the relative intensity were about 2800 K and 0.1 during the friction experiment under a pressure of 2.4×104 Pa. The FNB system is related to negative glow charge and the discharge observed during the friction experiments was spark and/or glow discharges. The gas pressure decreases with increasing vibration temperature and molecule density as shown in several previous studies and decrease with increasing electron temperature and density as explained the electron transition theory. This implies that the increase in the free path of excited molecules as gas pressure decreases can result in the photo emission pattern change. The surface charge density of a frictional quartz surface estimated from the potential difference to be 5.5×10-5 C/m2 included in the range of 6.51×10-6–6.4×10-3 C/m² estimated from the trapping centre concentrations. Hence, the trapping centres can be the sources of the frictional discharge.

How to cite: Tanaka, K., Muto, J., and Nagahama, H.: Mechanism of frictional discharge plasma at fault asperities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3610, https://doi.org/10.5194/egusphere-egu22-3610, 2022.

EGU22-4417 | Presentations | NH4.1

The study of the geomagnetic diurnal variation behavior associated with Mw>4.9 Vrancea (Romania) Earthquakes 

Iren Adelina Moldovan, Victorin Emilian Toader, Marco Carnini, Laura Petrescu, Anica Otilia Placinta, and Bogdan Dumitru Enescu

Diurnal geomagnetic variations are generated in the magnetosphere and last for about 24 hours. These can be seen on the recordings of all magnetic observatories, with amplitudes of several tens of nT, on all magnetic components. The shape and amplitude of diurnal variations strongly depend on the geographical latitude of the observatory. In addition to the dominant external source from the interaction with the magnetosphere, the diurnal geomagnetic variation is also influenced by local phenomena, mainly due to internal electric fields. External influence remains unchanged over distances of hundreds of kilometers, while internal influence may differ over very short distances due to the underground conductivity. The ration of the diurnal geomagnetic variation at two stations should be stable in calm periods and could be destroyed by the phenomena that can occur during the preparation of an earthquake, when at the station inside the seismogenic zone, the underground conductivity would change or additional currents would appear. The cracking process inside the lithosphere before and during earthquakes occurrence, possibly modifies the under- ground electrical structure and emits electro-magnetic waves.

In this paper, we study how the diurnal geomagnetic field variations are related to Mw>4.9 earthquakes occurred in Vrancea, Romania. For this purpose, we use two magnetometers situated at 150 km away from each other, one, the Muntele Rosu (MLR) observatory of NIEP, inside the Vrancea seismic zone and the other, the Surlari (SUA) observatory of IGR and INERMAGNET, outside the preparation area of moderate earthquakes. We have studied the daily ranges of the magnetic diurnal variation, R=DBMLR/DBSUA, during the last 10 years, to identify behavior patterns associated with external or internal conditions, where DB= Bmax-Bmin, during a 24 hours period.

As a first conclusion, we can mention the fact that the only visible disturbances appear before some earthquakes in Vrancea with Mw> 5.5, when we see a differentiation of the two recordings due to possible local internal phenomena at MLR. The differentiation consists in the decrease of the value of the vertical component Bzmax-Bzmin at MLR compared to the USA a few days before the earthquake and the return to the initial value after the earthquake. These studies need to be continued in order to determine if it is a repetitive behavior, or if it is just an isolated phenomenon.

Acknowledgments:

The research was supported by: the NUCLEU program (MULTIRISC) of the Romanian Ministry of Research and Innovation through the projects PN19080102 and by the Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI) through the projects PN-III-P2-2.1-PED-2019-1693, 480 PED/2020 (PHENOMENAL) and PN-III-P4-ID-PCE- 2020-1361, 119 PCE/2021 (AFROS).

How to cite: Moldovan, I. A., Toader, V. E., Carnini, M., Petrescu, L., Placinta, A. O., and Enescu, B. D.: The study of the geomagnetic diurnal variation behavior associated with Mw>4.9 Vrancea (Romania) Earthquakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4417, https://doi.org/10.5194/egusphere-egu22-4417, 2022.

EGU22-5375 | Presentations | NH4.1 | Highlight

Non-tectonic-induced stress variations on active faults 

Yiting Cai and Maxime Mouyen

Non-tectonic processes, namely solid earth tides and surface loads such as ocean, atmosphere, and continental water, constantly modify the stress field of the Earth's crust. Such stress perturbations may trigger earthquakes. Several previous studies reported that tides or hydrological loading could modulate seismicity in some areas. We elaborate on this idea and compute the total Coulomb stress change created by solid earth tides and surface loads together on active faults. We expect that computing a total stress budget over all non-tectonic processes would be more relevant than focusing on one of these processes in particular. The Coulomb stress change is a convenient approach to infer if a fault is brought closer to or further from its critical rupture when experiencing a given stress status. It requires to know 1) the fault's rake and geometry and 2) the value of the stress applied on it, which we retrieve from a subduction zone geometry model (Slab2) and a loading-induced Earth's stress database, respectively. In this study, we focus on the Coulomb stress variations on the Kuril-Japan fault over the few last years. By applying this method to the entire Slab2 catalogue and other known active faults, we aim at producing a database of non-tectonic-induced Coulomb failure function variations. Using earthquakes catalogues, this database can then be used to statistically infer the role of the non-tectonic process in earthquakes nucleation.

How to cite: Cai, Y. and Mouyen, M.: Non-tectonic-induced stress variations on active faults, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5375, https://doi.org/10.5194/egusphere-egu22-5375, 2022.

EGU22-6296 | Presentations | NH4.1

Analysis of Swarm Satellite Magnetic Field Data before and after the 2015 Mw7.8 Nepal Earthquake Based on Non-negative Tensor Decomposition 

Mengxuan Fan, Kaiguang Zhu, Angelo De Santis, Dedalo Marchetti, Gianfranco Cianchini, Alessandro Piscini, Loredana Perrone, Xiaodan He, Jiami Wen, Ting Wang, Yiqun Zhang, Wenqi Chen, Hanshuo Zhang, Donghua Zhang, and Yuqi Cheng

In this paper, based on the Non-negative Tensor Decomposition (NTD), we analyzed the Y-component ionospheric magnetic field data as observed by Swarm Alpha and Charlie satellites before, during and after the 2015 (Mw=7.8) Nepal earthquake (April 25, 28.231°N 84.731°E). All the observation data were analyzed, including the data collected under quiet and strong geomagnetic activities. For each investigated satellite track, we can obtain a tensor, which is decomposed in three components. We found that the cumulative number of the inside anomalous tracks for one component of decomposition components (i.e., hs1, whose energy and entropy are more concentrated inside the earthquake-sensitive area, shows an accelerated increase which conforms to a sigmoid trend from 60 to 40 days before the mainshock. After that till the day before the mainshock, the cumulative result displays a weak acceleration trend which obeys a power law trend and resumed linear growth after the earthquake. According to the basis vectors, the frequency of the ionospheric magnetic anomalies is around 0.02 to 0.1 Hz, and by the skin depth formula the estimated depth of the mainshock is similar to the real one.

In addition, we did some confutation analysis to exclude the influence of the geomagnetic activity and solar activity on the abnormal phenomenon of the cumulative result for the hs1 component, according to the ap, Dst and F 10.7 indices. We also analyzed another area at the same magnetic latitude with no seismicity and find that its cumulative result shows a linear increase, which means that the accelerated anomalous phenomenon is not affected by the local time or due by chance.

At lithosphere, the cumulative Benioff Strain S also shows two accelerating increases before the mainshock, which is consistent with the cumulative result of the ionospheric anomalies. At the first acceleration, the seismicity occurred around the boundary of the research area not near the epicenter, and most of the ionospheric anomalies offset from the epicenter. During the second acceleration, some seismicity occurred closer to or on the mainshock fault, and the ionospheric anomalies appeared nearby the two faults around the epicenter, as well.

Furthermore, we considered combining with other studies on Nepal earthquake. Therefore, we noticed that the ionospheric magnetic field anomalies began to accelerate two days after the subsurface microwave radiation anomaly detected by Feng Jing et al. (2019). The spatial distribution of some ionospheric anomalies is consistent with the atmospheric Outgoing Longwave Radiation (OLR) anomalies found by Ouzounov et al. (2021). The latter occurred around two faults near the epicenter and the atmospheric anomalies occurred earlier than the ionospheric anomalies.

Considering the occurrence time of the anomalies in different layers, the abnormal phenomenon appeared in lithosphere, then transferred to the atmosphere, and at last occurred in the ionosphere. These results can be described by the Lithosphere Atmosphere Ionosphere Coupling model.

All these analyses indicate that by means of the NTD method, we can use all observed multi-channel data to analyze the Nepal earthquake and obtain a component whose anomalies are likely to be related to the earthquake. 

How to cite: Fan, M., Zhu, K., De Santis, A., Marchetti, D., Cianchini, G., Piscini, A., Perrone, L., He, X., Wen, J., Wang, T., Zhang, Y., Chen, W., Zhang, H., Zhang, D., and Cheng, Y.: Analysis of Swarm Satellite Magnetic Field Data before and after the 2015 Mw7.8 Nepal Earthquake Based on Non-negative Tensor Decomposition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6296, https://doi.org/10.5194/egusphere-egu22-6296, 2022.

A very strong earthquake of magnitude Mw8.2 struck the coastal zone of Alaska (USA), on July 29, 2021. This earthquake was felt around the Gulf of Alaska, on a wide offshore area belonging to USA and Canada. In order to identify an anomalous geomagnetic signal before the onset of this earthquake, we retrospectively analyzed the data collected on the interval June 17 - July 31, 2021, via internet (www.intermagnet.org), at the two geomagnetic observatories, College (CMO) - Alaska and Newport (NEW)-USA, by using the polarization parameter (BPOL) and the strain effect–related to geomagnetic signal identification. Thus, for the both observation sites (CMO and NEW), the daily mean distribution of the BPOL and its standard deviation (STDEV) are carried out using an FFT band-pass filtering in the ULF range (0.001-0.0083Hz). Further on, a statistical analysis based on a standardized random variable equation was applied to emphasize the following: a) the anomalous signature related to Mw8.2 earthquake on the both time series BPOL*(CMO) and BPOL*(NEW); b) the differentiation of the transient local anomalies associated with Mw8.2 earthquake from the internal and external parts of the geomagnetic field, taking the NEW observatory as reference. Consequently, on the BPOL*(NEW-CMO) time series, carried out on the interval 07-31 July, 2021, a very clear anomaly of maximum, greater than 1.2 STDEV, was detected on July 22, with 7 days before the onset of Mw8.2 earthquake.

How to cite: Stanica, D. A.: ANOMALOUS GEOMAGNETIC SIGNAL EMPHASISED BEFORE THE Mw8.2 ALASKA EARTHQUAKE OCCURRED ON JULY 29, 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7107, https://doi.org/10.5194/egusphere-egu22-7107, 2022.

Among the different parameters, the fluctuations of Earth's thermally emitted radiation, as measured by sensors on board of satellite systems operating in the Thermal Infra-Red (TIR) spectral range and Earth's surface deformation as recorded by satellite radar interferometry, have been proposed since long time as potential earthquake precursors. Nevertheless, the spatiotemporal relationship between the two different phenomena has been ignored till now.

On September 27, 2021, a strong earthquake of magnitude M5.8 occurred in Crete, near the village of Arkalochori at 06:17:21 UTC, as the result of shallow normal faulting. The epicenter of the seismic event was located at latitude 35.15 N and longitude 25.27 E, while the focal depth was 10 km. Since the beginning of June, almost 4 months earlier, more than 400 foreshocks ranging in magnitude from M0.5 to M4.8 were recorded in the broader area while the strongest aftershock (M 5.3) occurred on September 28th at 04:48:09 UTC.

10 years of MODIS Land Surface Temperature and Emissivity Daily L3 Global 1km satellite records were incorporated to the RETIRA index computation in order to detect and map probable pre-seismic and co-seismic thermal anomalies in the area of tectonic activation. At the same time, SAR images of the Sentinel-1 Copernicus satellite in both geometries of acquisition were used to create the differential interferograms and the displacement maps according to the Interferometric Synthetic Aperture Radar (InSAR) technique. Then, the two kinds of datasets (i.e thermal anomaly maps and crustal deformation maps) were introduced into a Geographic Information System environment along with geological formations, active faults, and earthquakes’ epicenters. By overlapping all the aforementioned data, their spatiotemporal relation is explored.

How to cite: Peleli, S., Kouli, M., and Vallianatos, F.: Investigating the spatiotemporal relationship between thermal anomalies and surface deformation; The Arkalochori Earthquake sequence of September 2021, Crete, Greece., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7148, https://doi.org/10.5194/egusphere-egu22-7148, 2022.

EGU22-7309 | Presentations | NH4.1

Wave-like structures prior to very recent southeastern Mediterranean earthquakes as recorded by a VLF/LF radio receiver in Athens (Greece) 

Dimitrios Z. Politis, Stelios M. Potirakis, Sagardweep Biswas, Sudipta Sasmal, and Masashi Hayakawa

A VLF (10 – 47.5 kHz) radio receiver with call sign UWA has recently been installed at the University of West Attica in Athens (Greece) and is continuously monitoring the lower ionosphere by means of the receptions from many transmitters, in order to identify any possible pre-seismic signatures or other precursors associated with extreme geophysical and space phenomena. In this study, we examine the case of three very recent strong mainshocks with magnitude Mw ≥ 5.5 that happened in September and October of 2021 in the southeastern Mediterranean. The VLF data used in this work correspond to the recordings of one specific transmitter with the call sign “ISR” which is located in Negev (Israel). The borders of the 5th Fresnel zone of the corresponding sub-ionospheric propagation path (ISR-UWA) are close in distance with the epicenters of the two earthquakes (EQ), while the third one is located within the 5th Fresnel zone of the specific path. In this work, we computed the morlet wavelet scalogram of the nighttime amplitude signal in order to check for any embedded wave-like structures, which would indicate the existence of Atmospheric Gravity Waves (AGW) before each one of the examined EQs. In our investigation, we also checked for any other global extreme phenomena, such as geomagnetic storms and solar flares, which may have occurred close in time with the examined EQs and could have a contaminating impact on the obtained results. Our results revealed wave-like structures in the amplitude of the signal a few days before the occurrence of these three EQs.

How to cite: Politis, D. Z., Potirakis, S. M., Biswas, S., Sasmal, S., and Hayakawa, M.: Wave-like structures prior to very recent southeastern Mediterranean earthquakes as recorded by a VLF/LF radio receiver in Athens (Greece), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7309, https://doi.org/10.5194/egusphere-egu22-7309, 2022.

EGU22-8280 | Presentations | NH4.1

Primary-level Site Effect Zoning in Developing Urban Areas Through the Geomorphic Interpretation of Landforms 

Zahra Pak Tarmani, Zohre Masoumi, and Esmaeil Shabanian

The site effect has a great impact on seismic hazard assessment in urban and industrial regions.
For instance, a layer of soft soil with a thickness of several meters amplifies seismic waves from
1.5 to 6 times relative to the underlying bedrock. Therefore, investigating the main characteristics
of Quaternary deposits such as the granulometry and mechanical layering is crucial in site effect
studies. These parameters are directly related to the local geologic/geomorphic setting and genesis
processes of the Quaternary deposits. Nevertheless, large cities in development countries have 
rapidly been enlarged covering Quaternary terrains before being evaluated for the site effect. This
rather rapid growth in urbanization interested us to take advantage of ancient aerial photographs
reprocessed with new image processing techniques in order to provide 3D terrain models from
such kind of areas before the recent urbanization. It helped us in the geomorphic terrain
classification and the detection of regions with different site effects originally caused by the
geomorphic setting and genesis of the Quaternary terrains. For example, site effect in a river flood
plain will be different from surrounding areas underlined by alluvial conglomerates or bedrock.
The main target of this study is investigating the primary-level site effect in Urmia city using 3D
geomorphic models derived from ancient aerial photos taken in 1955. Urmia in NW Iran is one of
the populated high-risk areas according to the standard regulations of earthquake in Iran, and
covers a wide region from mountainous areas to the ancient coast of Lake Urmia, with the Shahr
Chai River as the axial drainage. We created the 3D terrain model through the Structure from
Motion (SfM) algorithm. We have provided a detailed geomorphic map of Plio-Quaternary terrains
using the 3D Anaglyph view, Digital Elevation Model (DEM), and orthophoto-mosaic of the
region. It was complemented by granulometry and mechanical layering information from the
available geotechnical boreholes to reconstruct a shallow soil structure model for the area. It
allowed us establishing a primary-level site effect zoning for Urmia. Our results reveal the
presence of five distinct geomorphic zones, with different genesis processes and soil characteristics
from piedmont to coastal zones, which represent different soil structures and probable site effects.
This zoning paves the way for performing complementary site effect investigations with lower
time consummation and cost. The developed method, proposes a sophisticated tool to evaluate
primary site effect in areas covered by urbanization subjected to future natural hazards like
earthquake, landslide and flood before designing geophysical networks for the measurement of
quantitative site effect parameters such as Nakamura microtremor H/V and Multichannel Analysis
of Surface Waves.
Key words: Earthquake hazard, Site effect, Image Processing, Aerial photos, Quaternary geology, Structure from
Motion 

How to cite: Pak Tarmani, Z., Masoumi, Z., and Shabanian, E.: Primary-level Site Effect Zoning in Developing Urban Areas Through the Geomorphic Interpretation of Landforms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8280, https://doi.org/10.5194/egusphere-egu22-8280, 2022.

EGU22-8420 | Presentations | NH4.1

Ionospheric perturbations related to seismicity and volcanic eruptions inferred from VLF/LF electric field measurements 

Hans U. Eichelberger, Konrad Schwingenschuh, Mohammed Y. Boudjada, Bruno P. Besser, Daniel Wolbang, Maria Solovieva, Pier F. Biagi, Manfred Stachel, Özer Aydogar, Christoph Schirninger, Cosima Muck, Claudia Grill, and Irmgard Jernej

In this study we investigate electric field perturbations from sub-ionospheric VLF/LF paths which cross seismic and volcanic active areas. We use waveguide cavity radio links from the transmitters TBB (26.70 kHz, Bafa, Turkey) and ITS (45.90 kHz, Niscemi, Sicily, Italy) to the seismo-electromagnetic receiver facility GRZ (Graz, Austria). The continuous real-time amplitude and phase measurements have a temporal resolution of 1 sec, events are analyzed for the period 2020-2021. Of high interest in this time span are paroxysms of the stratovolcano Mt. Etna, Sicily, Italy. We show electric field amplitude variations which could be related to atmospheric waves, occurred at the active crater and propagated up to the lower ionosphere. This corresponds to vertical coupling processes from the ground to the E-region, the upper waveguide boundary during night-time. Ionospheric variations possibly related to earthquakes are discussed for events along the TBB-GRZ path, assumed is an area given by the so-called effective precursor manifestation zone [1,2]. The findings indicate statistical relations between electric field amplitude variations of the ITS-GRZ path in the VLF/LF sub-ionospheric waveguide and high volcanic activity of Etna. For earthquakes multi-parametric observations shall be taken into account to diagnose physical processes related to the events. In summary, VLF/LF investigations in a network together with automated data processing can be an essential component of natural hazards characterization.

References:

[1] Dobrovolsky, I.P., Zubkov, S.I., and Miachkin, V.I., Estimation of the size of earthquake preparation zones, PAGEOPH 117, 1025–1044, 1979. https://doi.org/10.1007/BF00876083

[2] Bowman, D.D., Ouillon, G., Sammis, C.G., Sornette, A., and Sornette, D., An observational test of the critical earthquake concept, JGR Solid Earth, 103, B10, 24359-24372, 1998. https://doi.org/10.1029/98JB00792

How to cite: Eichelberger, H. U., Schwingenschuh, K., Boudjada, M. Y., Besser, B. P., Wolbang, D., Solovieva, M., Biagi, P. F., Stachel, M., Aydogar, Ö., Schirninger, C., Muck, C., Grill, C., and Jernej, I.: Ionospheric perturbations related to seismicity and volcanic eruptions inferred from VLF/LF electric field measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8420, https://doi.org/10.5194/egusphere-egu22-8420, 2022.

EGU22-8426 | Presentations | NH4.1 | Highlight

Earthquake nowcasting: Retrospective testing in Greece 2019 - 2021 

Gerasimos Chouliaras, Efthimios S. Skordas, and Nikolaos Sarlis

Earthquake nowcasting [1] (EN) is a modern method to estimate seismic risk by evaluating the progress of the earthquake cycle in fault systems [2]. EN employs natural time [3], which uniquely estimates seismic risk by means of the earthquake potential score (EPS) [1,4] and has found many useful applications both regionally and globally [1, 2, 4-10]. Among these applications, here we focus on those in Greece since 2019 [2], by using the earthquake catalogue of the Institute of Geodynamics of the National Observatory of Athens[11–13] (NOA) for the estimation of the EPS in various locations: For example, the ML(NOA)=6.0 off-shore Southern Crete earthquake on 2 May 2020, the ML(NOA)=6.7 Samos earthquake on 30 October 2020, the ML(NOA)=6.0 Tyrnavos earthquake on 3 March 2021, the ML(NOA)=5.8 Arkalohorion Crete earthquake on 27 September 2021, the ML(NOA)=6.3 Sitia Crete earthquake on 12 October 2021. The results are promising and reveal that earthquake nowcast scores provide useful information on impending seismicity.

[1] J.B. Rundle, D.L. Turcotte, A. Donnellan, L. Grant Ludwig, M. Luginbuhl, G. Gong, Earth and Space Science 3 (2016) 480–486. dx.doi.org/10.1002/2016EA000185

[2] J.B. Rundle, A. Donnellan, G. Fox, J.P. Crutchfield, Surveys in Geophysics (2021). dx.doi.org/10.1007/s10712-021-09655-3

[3] P.A. Varotsos, N.V. Sarlis, E.S. Skordas, Phys. Rev. E 66 (2002) 011902. dx.doi.org/10.1103/physreve.66.011902

[4] S. Pasari, Pure Appl. Geophys. 176 (2019) 1417–1432. dx.doi.org/10.1007/s00024-018-2037-0

[5] M. Luginbuhl, J.B. Rundle, D.L. Turcotte, Pure and Applied Geophysics 175 (2018) 661–670. dx.doi.org/10.1007/s00024-018-1778-0

[6] M. Luginbuhl, J.B. Rundle, D.L. Turcotte, Geophys. J. Int. 215 (2018) 753–759. dx.doi.org/10.1093/gji/ggy315

[7] N.V. Sarlis, E.S. Skordas, Entropy 20 (2018) 882. dx.doi.org/10.3390/e20110882

[8] S. Pasari, Y. Sharma, Seismological Research Letters 91 (6) (2020) 3358–3369. dx.doi.org/10.1785/0220200104

[9] J. Perez-Oregon, F. Angulo-Brown, N.V. Sarlis, Entropy 22 (11) (2020) 1228. dx.doi.org/10.3390/e22111228

[10] P.K. Varotsos, J. Perez-Oregon, E.S. Skordas, N.V. Sarlis, Applied Sciences 11 (21) (2021) 10093. dx.doi.org/10.3390/app112110093

[11] G. Chouliaras, Natural Hazards and Earth System Sciences 9 (3) (2009) 905–912. dx.doi.org/10.5194/ nhess-9-905-2009

[12] G. Chouliaras, N.S. Melis, G. Drakatos, K. Makropoulos, Advances in Geosciences 36 (2013) 7–9. dx.doi.org/10.5194/adgeo-36-7-2013

[13] A. Mignan, G. Chouliaras, Seismological Research Letters 85 (3) (2014) 657–667. dx.doi.org/10.1785/0220130209

How to cite: Chouliaras, G., Skordas, E. S., and Sarlis, N.: Earthquake nowcasting: Retrospective testing in Greece 2019 - 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8426, https://doi.org/10.5194/egusphere-egu22-8426, 2022.

The visibility graph method has allowed to identify statistical properties of earthquake magnitude time series. So that, such statistical features in the time series have helped to classify the earthquakes sequences in different categories according with their tectonical sources related with their dynamical seismicity. The Tehuantepec Isthmus subduction zone, México, has showed different dynamical behavior before and after the M8.2 occurred on September 07, 2017. This behavior is associated with the temporal correlations observed in the magnitude sequences. With the aim to characterize these correlations we use the visibility graph method which has showed great potential to get the dynamical properties of studied system from the statistical properties in the network graph. In this study we investigate four periods: the first, between 2005 and 2012, the second (before the M8.2 EQ) from 2012 to 2017, the third from September 2017 to March 2018 corresponding to aftershocks period, and the fourth from April to December 2021, in order to find type of connectivity corresponding to each one, we have computed the distribution function P(k) of the connectivity degree k. Our results show the connectivity increases till the earthquake and decrease in the aftershocks period.

How to cite: Ramírez-Rojas, A. and Flores-Márquez, E. L.: Visibility graph analysis to identify correlations in the magnitude earthquake time series monitored in the Tehuantepec Isthmus subduction zone, México., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8718, https://doi.org/10.5194/egusphere-egu22-8718, 2022.

EGU22-8924 | Presentations | NH4.1 | Highlight

The Cascading Foreshock Sequence of the Ms 6.4 Yangbi Earthquake in Yunnan, China 

Gaohua Zhu, Hongfeng Yang, Yen Joe Tan, Mingpei Jin, Xiaobin Li, and Wei Yang

Foreshocks may provide valuable information on the nucleation process of large earthquakes. The 2021 Ms 6.4 Yangbi, Yunnan, China, earthquake was preceded by abundant foreshocks in the ~75 hours leading up to the mainshock. To understand the space-time evolution of the foreshock sequence and its relationship to the mainshock nucleation, we built a high‐precision earthquake catalog using a machine-learning phase picker—EQtransformer and the template matching method. The source parameters of 17 large foreshocks and the mainshock were derived to analyze their interaction. Observed “back-and-forth” spatial patterns of seismicity and intermittent episodes of foreshocks without an accelerating pattern do not favor hypotheses that the foreshocks were a manifestation of a slow slip or fluid front propagating along the mainshock’s rupture plane. The ruptured patches of most large foreshocks were adjacent to one another with little overlap, and the mainshock eventually initiated near the edge of the foreshocks’ ruptured area where there had been a local increase in shear stress. These observations are consistent with a triggered cascade of stress transfer, where previous foreshocks load adjacent fault patches to rupture as additional foreshocks, and eventually the mainshock.

How to cite: Zhu, G., Yang, H., Tan, Y. J., Jin, M., Li, X., and Yang, W.: The Cascading Foreshock Sequence of the Ms 6.4 Yangbi Earthquake in Yunnan, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8924, https://doi.org/10.5194/egusphere-egu22-8924, 2022.

EGU22-9690 | Presentations | NH4.1 | Highlight

Lesson learnt after long-term (>10 years) correlation analyses between satellite TIR anomalies and earthquakes occurrence performed over Greece, Italy, Japan and Turkey 

Valeria Satriano, Roberto Colonna, Angelo Corrado, Alexander Eleftheriou, Carolina Filizzola, Nicola Genzano, Hattori Katsumi, Mariano Lisi, Nicola Pergola, Vallianatos Filippos, and Valerio Tramutoli

In the recent years, in order to evaluate the possible spatial-temporal correlation among anomalies in Earth’s thermally emitted InfraRed radiation and earthquakes occurrence, several long-term studies have been performed. Different seismically active areas around the world have been this way investigated by using TIR sensors on board geostationary (e.g. Eleftheriou et al. 2016, Genzano et al., 2020, Genzano et al., 2021, Filizzola et al., 2022) and polar (e.g. Zhang and Meng, 2019) satellites.  Since the study of Filizzola et al. (2004) the better S/N ratio achievable by the geostationary sensors (compared with the polar ones) made this kind of sensors the first choice for this kind of long-term analyses.

In this paper the lesson learnt after 20 years of satellite TIR analyses are critically analyzed in the perspective of the possible inclusion of such anomalies among the parameters usefully contributing to the construction of a multi-parametric system for a time-Dependent Assessment of Seismic Hazard.

The more recent results achieved by applying the RST (Tramutoli et al., 2005, Tramutoli 2007) approach to long-term (>10 years) TIR satellite data collected by the geostationary sensors SEVIRI (on board MSG) - over Greece (Elefteriou et al., 2016), Italy (Genzano et al, 2020) and Turkey (Filizzola et al., 2022) – and  by JAMI and IMAGER (on board MTSAT satellites) over Japan (Genzano et al., 2021) will be also presented and discussed.

References

Eleftheriou, A., C. Filizzola, N. Genzano, T. Lacava, M. Lisi, R. Paciello, N. Pergola, F. Vallianatos, and V. Tramutoli (2016), Long-Term RST Analysis of Anomalous TIR Sequences in Relation with Earthquakes Occurred in Greece in the Period 2004–2013, PAGEOPGH, 173(1), 285–303, doi:10.1007/s00024-015-1116-8.

Filizzola, C., N. Pergola, C. Pietrapertosa, V. Tramutoli (2004), Robust satellite techniques for seismically active areas moni-toring: a sensitivity analysis on September 7, 1999 Athens’s earthquake. Phys. Chem. Earth, 29, 517–527. 10.1016/j.pce.2003.11.019

Filizzola C., A. Corrado, N. Genzano, M. Lisi, N. Pergola, R. Colonna and V. Tramutoli (2022), RST Analysis of Anomalous TIR Sequences in relation with earthquakes occurred in Turkey in the period 2004–2015, Remote Sensing, (accepted).

Genzano, N., C. Filizzola, M. Lisi, N. Pergola, and V. Tramutoli (2020), Toward the development of a multi parametric system for a short-term assessment of the seismic hazard in Italy, Ann. Geophys, 63(5) doi:10.4401/ag-8227.

Genzano, N., C. Filizzola, K. Hattori, N. Pergola, and V. Tramutoli (2021), Statistical correlation analysis between thermal infrared anomalies observed from MTSATs and large earthquakes occurred in Japan (2005–2015). JGR: Solid Earth, 126, e2020JB020108, https://doi.org/10.1029/2020JB020108

Tramutoli, V. (2007), Robust Satellite Techniques (RST) for Natural and Environmental Hazards Monitoring and Mitigation: Theory and Applications, in 2007 International Workshop on the Analysis of Multi-temporal Remote Sensing Images, pp. 1–6, IEEE. doi: 10.1109/MULTITEMP.2007.4293057

Tramutoli, V., V. Cuomo, C. Filizzola, N. Pergola, C. Pietrapertosa (2005), Assessing the potential of thermal infrared satellite surveys for monitoring seismically active areas: The case of Kocaeli (İzmit) earthquake, August 17, 1999. RSE, 96, 409–426. https://doi.org/10.1016/j.rse.2005.04.006

Zhang, Y. and Meng, Q. (2019), A statistical analysis of TIR anomalies extracted by RSTs in relation to an earthquake in the Sichuan area using MODIS LST data, NHESS, 19, 535–549, https://doi.org/10.5194/nhess-19-535-2019, 2019

How to cite: Satriano, V., Colonna, R., Corrado, A., Eleftheriou, A., Filizzola, C., Genzano, N., Katsumi, H., Lisi, M., Pergola, N., Filippos, V., and Tramutoli, V.: Lesson learnt after long-term (>10 years) correlation analyses between satellite TIR anomalies and earthquakes occurrence performed over Greece, Italy, Japan and Turkey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9690, https://doi.org/10.5194/egusphere-egu22-9690, 2022.

EGU22-10161 | Presentations | NH4.1 | Highlight

Analysis of VLF and LF signal fluctuations recorded by Graz facility prior to earthquakes occurrences 

Mohammed Y. Boudjada, Pier Francesco Biagi, Hans Ulrich Eichelberger, Patrick H.M. Galopeau, Konrad Schwingenschuh, Maria Solovieva, Helmut Lammer, Wolfgang Voller, and Masashi Hayakawa

We report in our study on earthquakes that occurred in Croatia and Slovenia in the period from 1 Jan. 2020 to 31 Dec. 2021. Those seismic events happened in a localized region confined between 13.46°E and 17.46°E in longitude and 45.03°N and 49.03°N in latitude. Maximum magnitudes Mw6.4 and Mw5.4 occurred, respectively, on 29 Dec. 2020, at 11:19 UT, and 22 March 2020, at 05:24 UT. We use two-radio system, INFREP (Biagi et al., 2019) and UltraMSK (Schwingenschuh et al., 2011) to investigate the reception conditions of LF-VLF transmitter signals. The selected earthquakes occurred at distances less than 300km from the Graz station (47.03°N, 15.46°E) in Austria. First, we emphasize on the time evolutions of earthquakes that occurred along a same meridian, i.e. at a geographical longitude of 16°E. Second, we study the daily VLF-LF transmitter signals that exhibit a minimum around local sunrises and sunsets. This daily variations are specifically considered two/three weeks before the occurrence of the two intense events with magnitudes Mw6.4 and Mw5.4. We discuss the unusual terminator time motions of VLF-LF signals linked to earthquakes occurrences, and their appearances at sunrise- or sunset-times. Such observational features are interpreted as disturbances of the transmitter signal propagations in the ionospheric D- and E-layers above the earthquakes preparation zone (Hayakawa, 2015).

 

References:

Biagi et al., The INFREP Network: Present Situation and Recent Results, Open J. Earth. Research, 8, 2019.

Hayakawa, Earthquake Prediction with Radio Techniques, John Wiley and Sons, Singapore, 2015.

Schwingenschuh et al., The Graz seismo-electromagnetic VLF facility, Nat. Hazards Earth Syst. Sci., 11, 2011

How to cite: Boudjada, M. Y., Biagi, P. F., Eichelberger, H. U., Galopeau, P. H. M., Schwingenschuh, K., Solovieva, M., Lammer, H., Voller, W., and Hayakawa, M.: Analysis of VLF and LF signal fluctuations recorded by Graz facility prior to earthquakes occurrences, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10161, https://doi.org/10.5194/egusphere-egu22-10161, 2022.

EGU22-10209 | Presentations | NH4.1

Enhancing Data Sets From Rudna Deep Copper Mine, SW Poland: Implications on Detailed Structural Resolution and Short-Term Hazard Assessment 

Monika Sobiesiak, Konstantinos Leptokaropoulos, Monika Staszek, Natalia Poiata, Pascal Bernard, and Lukasz Rudzinski

Applying the software BackTrackBB (Poiata et al., 2016) for automated detection and location of seismic events to data sets from Rudna Deep Copper Mine, SW Poland, lead to an enhancement of existing routine catalogs by about a factor of 10.000 in number of events. Following our hypothesis that all types of seismic events contribute to seismic hazard in a mine, we included all events from major mine collapses (M>3), recorded blasting works and detonations, to machinery noise. These enhanced data sets enabled a detailed spatio-temporal distribution of seismicity in the mine and a short-term hazard assessment on a daily basis.

In this study, we focus on the data from two days with major mine collapses: the 2016-11-29 Mw=3.4, and the 2018-09-15 Mw=3.7 events. The spatio-temporal distribution of seismicity of both days deciphered detailed horizontal and vertical structures and revealed the increase of seismic activity after the daily blasting work. The daily histograms exhibit similar patterns, suggesting the dominant influence of explosions on the overall seismicity in the mine. Using the enhanced data sets for short-term hazard assessment, we observed gaps in the activity rates before the main shocks. They were followed by sudden increase of seismicity, a simultaneous drop in seismic b-value, and an increase in exceedance probability for the assumed largest magnitude events. This demonstrates the usefulness of enhanced data sets from surface networks for revealing precursory phenomena before destructive mine collapses and suggests a testing strategy for early warning procedures.

How to cite: Sobiesiak, M., Leptokaropoulos, K., Staszek, M., Poiata, N., Bernard, P., and Rudzinski, L.: Enhancing Data Sets From Rudna Deep Copper Mine, SW Poland: Implications on Detailed Structural Resolution and Short-Term Hazard Assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10209, https://doi.org/10.5194/egusphere-egu22-10209, 2022.

EGU22-10222 | Presentations | NH4.1

Optimized setup and long-term validation of anomaly detection methods for earthquake-related ionospheric-TEC (Total Electron Content) parameter over Italy and Mediterranean area 

Roberto Colonna, Carolina Filizzola, Nicola Genzano, Mariano Lisi, Nicola Pergola, and Valerio Tramutoli

Near the end of the last century and the beginning of the new, different types of geophysical parameters (components of the electromagnetic field in several frequency bands, thermal anomalies, radon exhalation from the ground, ionospheric parameters and more) have been proposed as indicators of variability potentially related to the earthquakes occurrence. During the last decade, thanks to the availability of historical satellite observations which has begun to be significantly large and thanks to the exponential growth of artificial intelligence techniques, many advances have been made on the study of the seismic-related anomalies detection observed from space.

In this work, the variations in Total Electron Content (TEC) parameter are investigated as indicator of the ionospheric status potentially affected by earthquake related phenomena. In-depth and systematic analysis of multi-year historical data series plays a key role in distinguishing between anomalous TEC variations and TEC changes associated with normal ionospheric behavior or non-terrestrial forcing phenomena (mainly dominated by solar cycles and activity).

In order to detect the differences between the two types of variation, we performed an optimal setting of the methodological inputs for the detection of seismically related anomalies in ionospheric-TEC using machine learning techniques and validating the findings on multiple long-term historical series (mostly nearly 20-year). The setting was optimized using techniques capable of combining multi-year time series of TEC satellite data and multi-year time series of seismic catalogues, simulating their behaviors in tens of thousands of possible combinations and classifying them according to criteria established a priori. Input setup and validation were done by investigating possible links between TEC anomalies and earthquake occurring over Italy and Mediterranean area. We will show and comment the results of both, optimal input setting and statistical correlation analyses consequently performed, and we will discuss the potential impact of these on future developments in this field.

How to cite: Colonna, R., Filizzola, C., Genzano, N., Lisi, M., Pergola, N., and Tramutoli, V.: Optimized setup and long-term validation of anomaly detection methods for earthquake-related ionospheric-TEC (Total Electron Content) parameter over Italy and Mediterranean area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10222, https://doi.org/10.5194/egusphere-egu22-10222, 2022.

EGU22-10371 | Presentations | NH4.1

Utilizing machine learning techniques along with GPS ionospheric TEC maps for potentially predicting earthquake events 

Yuval Reuveni, Sead Asaly, Nimrod Inbar, and Leead Gottlieb

The scientific use of ground and space-based remote sensing technology is inherently vital for studying different lithospheric-tropospheric-ionospheric coupling mechanisms, which are imperative for understanding geodynamic processes. Current remote sensing technologies operating at a wide range of frequencies, using either sound or electromagnetic emitted waves, have become a valuable tool for detecting and measuring signatures presumably associated with earthquake events. Over the past two decades, numerous studies have been presenting promising results related to natural hazards mitigation, especially for earthquake precursors, while other studies have been refuting them. While highly impacting for geodynamic processes the controversy around precursors that may precede earthquakes yet remains significant. Thus, predicting where and when natural hazard event such as earthquake is likely to occur in a specific region of interest still remains a key challenging task in geo-sciences related research. Recently, it has been discovered that natural hazard signatures associated with strong earthquakes appear not only in the lithosphere, but also in the troposphere and ionosphere. Both ground and space-based remote sensing techniques can be used to detect early warning signals from places where stresses build up deep in the Earth’s crust and may lead to a catastrophic earthquake. Here, we propose to implement a machine learning Support Vector Machine (SVM) technique, applied with GPS ionospheric Total Electron Content (TEC) pre-processed time series estimations, extracted from global ionospheric TEC maps, to evaluate any potential precursory caused by the earthquake and is manifested as ionospheric TEC anomaly. Each TEC time series data was geographically extracted around the earthquake epicenter and calculated by weighted average of the four closest points to evaluate any potential influence caused by the earthquake. After filtering and screening our data from any solar or geomagnetic influence at different time scales, our results indicate that with large earthquakes (> 6 [Mw]), there is a potentially high probability of gaining true negative prediction with accuracy of 85.7% as well as true positive prediction accuracy of 80%. Our suggested method has been also tested with different skill scores such as Accuracy (0.8285), precision (0.85), recall (0.8), Heidke Skill Score (0.657) and Tue Skill Statistics (0.657).

How to cite: Reuveni, Y., Asaly, S., Inbar, N., and Gottlieb, L.: Utilizing machine learning techniques along with GPS ionospheric TEC maps for potentially predicting earthquake events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10371, https://doi.org/10.5194/egusphere-egu22-10371, 2022.

EGU22-10488 | Presentations | NH4.1

Results of the analysis of VLF and ULF perturbations and modeling atmosphere-ionosphere coupling 

Yuriy Rapoport, Volodymyr Reshetnyk, Asen Grytsai, Alex Liashchuk, Alla Fedorenko, Masashi Hayakawa, Volodymyr Grimalsky, and Sergei Petrishchevskii

The work continues one presented by us in 2021, which included the identification of three groups of periods in the VLF amplitude variations in the waveguide Earth-Ionosphere (WGEI) according to data of Japan receivers, obtained in 2014–2017. Periods of 5–10 minutes correspond to the fundamental mode of acoustic-gravity waves (AGW) near the Brunt–Väisälä period and were firstly revealed in VLF signals. Apart from these values, periods of 2–3 hours and possibly 1 week were also detected; the weekly periodicity is caused by anthropogenic influence on the VLF data. The problem with penetration of the ULF electric field to the ionosphere is investigated both within the dynamic simulation of the Maxwell equations and within the quasi-electrostatic approach. It is demonstrated that in the case of open field lines the results of dynamic simulations differ essentially from the quasi-electrostatic approach, which is not valid there. In the case of closed field lines, the simulation results are practically the same for both approaches and correspond to the data of measurements of plasma perturbations in the ionosphere. It is shown that the diurnal cycle is most clearly visible in the variations of the VLF amplitudes. Disturbances from various phenomena also appear in the VLF data series. One of the strongest geomagnetic storms during the analyzed time range was the event of St. Patrick's Day (March 17, 2015), which is not reflected in Japanese data because this event occurred at night for East Asia. The use of information entropy in the VLF signal processing was tested with the determination of the main features of information entropy. Variations in information entropy at different stations are discussed in detail. It has been found that information entropy shows maxima near sunrise and sunset. The location of these peaks relative to the moments of sunrise and sunset changes with the seasons that is probably connected with the solar terminator passage at the heights of the VLF signal propagation. A study of 109 earthquakes during 2014-2017 did not show a clear dependence of information entropy when using the superposed epoch analysis, although a slight decrease in information entropy was observed before a part of the earthquakes. The effect of solar flares on information entropy has been established, but this issue needs further study. We have developed a model describing the penetration into the ionosphere of a nonlinear AGW packet excited by a ground source. Complex modulation of the initial AGW includes acoustic waves with closed frequencies and random phases. The model is important for the interpretation of atmosphere–ionosphere coupling along with seismoionospheric one. We are working on the application of this model to the spectrum of the VLF waves in the WGEI and unified models of the atmosphere–ionosphere coupling due to AGW and electromagnetic field excited by the same source in the lower atmosphere. This model would be important for the understanding seismogenic and tropical cyclone influence on the ionosphere.

How to cite: Rapoport, Y., Reshetnyk, V., Grytsai, A., Liashchuk, A., Fedorenko, A., Hayakawa, M., Grimalsky, V., and Petrishchevskii, S.: Results of the analysis of VLF and ULF perturbations and modeling atmosphere-ionosphere coupling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10488, https://doi.org/10.5194/egusphere-egu22-10488, 2022.

EGU22-10961 | Presentations | NH4.1

Regional applicability of earthquake forecasts using geoelectric statistical moments: Application to Kakioka, Japan 

Hong-Jia Chen, Katsumi Hattori, and Chien-Chih Chen

Electromagnetic anomalies have become promising for short-term earthquake forecasting. One forecasting algorithm based on statistical moments of geoelectric data was developed and applied in Taiwan. The objective of our research was to investigate such a reliable, rigorously testable algorithm to issue earthquake forecasts. We tested the applicability of the forecasting algorithm and applied it to geoelectric data and an earthquake catalog in Kakioka, Japan with a long-term period of 26 years. We calculated the variance, skewness, and kurtosis of the geoelectric data each day, determined their anomalies, and then compared them with earthquake occurrences through the forecasting algorithm. We observed that the anomalies of variance, skewness, and kurtosis significantly precede earthquakes, suggesting that the geoelectric data distributions deviate from normal distributions before earthquakes. Furthermore, the forecasting algorithm can select robust optimal models and produce explicit forecasting probability for two-thirds of all experimental cases. Therefore, we concluded that the forecasting algorithm based on statistical moments of geoelectric data is universal and may contribute to short-term earthquake forecasting.

How to cite: Chen, H.-J., Hattori, K., and Chen, C.-C.: Regional applicability of earthquake forecasts using geoelectric statistical moments: Application to Kakioka, Japan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10961, https://doi.org/10.5194/egusphere-egu22-10961, 2022.

EGU22-11299 | Presentations | NH4.1

b-value and kinematic parameters from 3D focal mechanisms distributions in Southern California 

Andrea Carducci, Antonio Petruccelli, Angelo De Santis, Rita de Nardis, and Giusy Lavecchia

The frequency-magnitude relation of earthquakes, with particular attention to the b-value of Gutenberg-Richter law, is computed in Southern California. A three-dimensional grid is employed to sample relocated focal mechanisms and determine both the magnitude of completeness and the b-value for each node. Sampling radius and grid size are appropriately chosen accordingly to seismogenic source dimensions. The SCEC Community Fault Model is used for comparison of the main fault systems along with the calculated 3D distributions.

The b-values are compared to Aλ, a streamlined kinematic fault quantification, which does not use inversion processes since directly depends on individual rakes of focal mechanisms. Potential relationships between the two quantities are then computed through multiple regressions at increasing depth ranges: they may help to evaluate seismic hazard assessment in relating the frequency and size of earthquakes to kinematic features. The rheological transition from elastic to plastic conditions is computed, assuming different physical constraints, and its influence on b-value and Aλ is also analyzed. Among proposed linear, polynomial, and harmonic equations, the linear model is statistically valued as the most probable one to relate the two parameters at different depth ranges. b-values against Aλ results are implemented into a 3D figure, where point data are interpolated by “Lowess Smoothing” surfaces to visually check the constancy depending on depth.

How to cite: Carducci, A., Petruccelli, A., De Santis, A., de Nardis, R., and Lavecchia, G.: b-value and kinematic parameters from 3D focal mechanisms distributions in Southern California, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11299, https://doi.org/10.5194/egusphere-egu22-11299, 2022.

EGU22-11511 | Presentations | NH4.1 | Highlight

Earthquake forecasting probability by statistical correlations between low to moderate seismic events and variations in geochemical parameters 

Lisa Pierotti, Cristiano Fidani, Gianluca Facca, and Fabrizio Gherardi

Since late 2002, a network of six automatic monitoring stations is operating in Tuscany, Central Italy, to investigate possible geochemical precursors of earthquakes. The network is operated by the Institute of Geosciences and Earth Resources (IGG), of the National Research Council of Italy (CNR), in collaboration and with the financial support of the Government of the Tuscany Region. The areas of highest seismic risk of the region, Garfagnana, Lunigiana, Mugello, Upper Tiber Valley and Mt. Amiata, are currently investigated. The monitoring stations are equipped with multi-parametric sensors to measure temperature, pH, electric conductivity, redox potential, dissolved CO2 and CH4 concentrations in spring waters. The elaboration of long-term time series allowed for an accurate definition of the geochemical background, and for the recognition of a number of geochemical anomalies in concomitance with the most energetic seismic events occurred during the monitoring period (Pierotti et al., 2017).

In an attempt to further exploit data from the geochemical network of Tuscany in a seismic risk reduction perspective, here we present a new statistical analysis that focuses on the possible correlation between low to moderate seismic events and variations in the chemical-physical parameters detected by the monitoring network. This approach relies on the estimate of a conditional probability for the forecast of earthquakes from the correlation coefficient between seismic events and signals variations (Fidani, 2021).

Seismic events (EQ) are classified according to a magnitude threshold, Mo. We set EQ = 0, if no seismic events were observed with M < Mo, and EQ = 1, if at least a seismic event was observed with M > Mo. Chemical-physical (CP) events were defined based on their appropriate amplitudes threshold Ao, being CP = 0 if the amplitude A < Ao, and CP = 1 if A > Ao. Digital time series were elaborated from data collected over the last 10 years, where EQs were declustered and CPs detrended for external influences. The couples of events with the same time differences TEQ – TCP, between EQs and CPs, were summed in a histogram. Then, a Pearson statistical correlation coefficient corr(EQ,CP) was obtained starting from the covariance definition.

A conditional probability for EQ forecasting is estimated starting from the correlation coefficient in an attempt to use data from CP network of Tuscany in a seismic risk reduction framework. The approach consists in an evaluation of EQ probability in a defined area, given a CP detection by the station in the same area. The conditional probability P(EQCP), when a correlation between EQs and CPs exists and time difference is that evidenced by the correlation, is increased by a term proportional to the correlation coefficient as

 

with respect to the unconditioned probability P(EQ) when a CP event is detected, where P(CP) is the unconditioned probability of CP.

 

 

Fidani, C. (2021). Front. Earth Sci. 9:673105.

Pierotti, L. et al. (2017). Physics and Chemistry of the Earth, Parts A/B/C, 98, 161-172.

 

How to cite: Pierotti, L., Fidani, C., Facca, G., and Gherardi, F.: Earthquake forecasting probability by statistical correlations between low to moderate seismic events and variations in geochemical parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11511, https://doi.org/10.5194/egusphere-egu22-11511, 2022.

Some samples are given illustrating possible influences of the natural hazards those will occur in the future times for the seismic activities those occur at the present time in [1]. Those samples force to ask whether there exist operational connections originating from future time’s naturel events, NEs on the present time’s NEs or do not. The analytical basics orienting such cooperation are derived in here [2]-[3].

Both the past time’s NEs and the future time’s NEs are not exist at the present time’s NEs topology when we want to observe and measure all them at the same location in the present time as a matter of the event for the present time’s temporal and spatial metric or in a space-time differential displacement with other words [4]. This situation brings the fact on the absence and/or presence of NEs in a temporal topology as a principle about the occurrence of NEs in their specific manifolds [4]. The very simple example in below may be helpful to understand the fact:

Example 1: If you want to be a medical doctor in your future then you have to study and learn medical facts in an official way. Without doing this in your past times and present times you cannot earn the medical doctor degree in your future times.

Result 1: The future time’s NEs present cooperation in both the past and future time’s NEs.

Example 1 and connected result 1 illustrate the future time’s event of being medical doctor operates the past and present time’s event of learning medicine so the principle 1 in below brings the processes designing the cooperation among past, present, and future NEs:

Principle 1: There is either definitive and/or fuzzy cooperation among the NEs in the future time, pas time, and present time for NEs’ topology.

The retarded potential in gauge form is split into two parts: The first part is a part of Fourier transform given the future time’s NEs and the second part is a Fourier sinus transform. The first part involves the ingredients of future time’s NEs. The second part involves the ingredients of both NEs of past time and present time. The first part has the property as a forwarded potential. The second part fits to the properties as the events at the past and/or the present.

The principle 1 is checked during several earthquakes received in 1999-2004 [5]- [6] and some important results are shared in [1]. The present writer calls virtual earthquake (VEQ) future time’s earthquake activities cooperating with the past and/or present time’s seismic activities and presents the topological processes with their analytical extractions from the above-mentioned observations.

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1Sengor T, http://meetingorganizer.copernicus.org/ EGU2020/EGU2020-22589.pdf.

2Sengor T, Helsinki University of Tech., Electromagnetics Lab. Report 344, Nov. 2000, ISBN 951-22-5258-9, ISSN 1456-632X.

3Sengor T, Helsinki University of Tech., Electromagnetics Lab. Report 347, Dec. 2000, ISBN 951-22-5274-0, ISSN 1456-632X.

4Sengor T, Invited paper. doi:10.23919/URSI- ETS.2019.8931455

5Sengor T, http://meetingorganizer.copernicus.org/EGU2019/EGU2019-17127.pdf.

6Sengor T, Helsinki University of Tech., Electromagnetics Lab. Report 368, May. 2001, ISBN 951-22-5275-1, ISSN 1456-632X.

How to cite: Sengor, T.: Virtual Earthquakes Cooperating with Natural Hazards and Simultaneously Scheduled Seismic Activities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12275, https://doi.org/10.5194/egusphere-egu22-12275, 2022.

EGU22-12349 | Presentations | NH4.1 | Highlight

Multi-channel singular spectrum analysis of soil radon concentration, Japan: Relationship between soil radon flux and precipitation and the local seismic activity 

Katsumi Hattori, Kazuhide Nemoto, Haruna Kojina, Akitsugu Kitade, Shu kaneko, Chie Yoshino, Toru Mogi, Toshiharu Konishi, and Dimitar Ouzounov

Recently, there are many papers on electromagnetic pre-earthquake phenomena such as geomagnetic, ionospheric, and atmospheric anomalous changes. Ionospheric anomaly preceding large earthquakes is one of the most promising phenomena. Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model has been proposed to explain these phenomena. In this study, to evaluate the possibility of chemical channel of LAIC by observation, we have installed sensors for atmospheric electric field, atmospheric ion concentration, atmospheric Rn concentration, soil radon Rn concentration (SRC), and weather elements at Asahi station, Boso, Japan. Since the atmospheric electricity parameters are very much influenced by weather factors, it is necessary to remove these effects as much as possible. In this aim, we apply the MSSA (Multi-channel Singular Spectral Analysis) to remove these influences from the variation of GRC and estimate the soil Rn flux (SRF). We investigated the correlations (1) between SRF and precipitation and (2) between SRF and the local seismic activity around Asahi station. The preliminary results show that SRF was significantly increased by heavy precipitations of 20 mm or more in total for 2 hours. We proposed two types of models, a rainwater load model and a rainwater infiltration model, and it is appropriate for both models to work and (2) between SRF and local seismicity within an epicenter distance of 50 km from the station.

 

How to cite: Hattori, K., Nemoto, K., Kojina, H., Kitade, A., kaneko, S., Yoshino, C., Mogi, T., Konishi, T., and Ouzounov, D.: Multi-channel singular spectrum analysis of soil radon concentration, Japan: Relationship between soil radon flux and precipitation and the local seismic activity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12349, https://doi.org/10.5194/egusphere-egu22-12349, 2022.

EGU22-748 | Presentations | NH3.5

Insights on factors controlling rockslope failure from pre-event cracking 

Sophie Lagarde, Michael  Dietze, Conny Hammer, Martin Zeckra, Anne Voigtländer, Luc Illien, Anne Schöpa, Jacob Hirschberg, Niels Hovius, and Jens M. Turowski

In order to reduce the societal impact of mass-wasting events, we need observations to investigate the factors that control slope failure, such as the state of crack propagation along a failure plane. However, usually the failure plane is not accessible in-situ. Hence, cracks have to be monitored indirectly, for example using seismic methods.

We analysed the data from a seismometer array in the Illgraben catchment, Switzerland, that had registered a series of crack propagation and mass-wasting events, leading to a main event that happened on 2 January 2013. We used a state-of-the-art machine learning technique based on hidden Markov models to detect and classify the seismic signals of crack events. We obtained the temporal evolution of three signal types: (1) single crack signal, (2) rock avalanche and (3) rockfall activity due to debris remobilization. The temporal evolution of the number of cracks showed a linear trend in the weeks prior to the main mass-wasting event and, in the hours preceding the main event, a sigmoidal exponential growth. Using these observations, we propose a mechanistic model to describe the rupture of the failure plane. The model considers the internal parameter of the total crack boundary length as the primary control on failure plane evolution, in addition to the previously suggested crack propagation velocity control parameter. According to this model, internal parameters appear to be the dominant control for the failure plane growth at a slope scale.

 

How to cite: Lagarde, S.,  Dietze, M., Hammer, C., Zeckra, M., Voigtländer, A., Illien, L., Schöpa, A., Hirschberg, J., Hovius, N., and Turowski, J. M.: Insights on factors controlling rockslope failure from pre-event cracking, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-748, https://doi.org/10.5194/egusphere-egu22-748, 2022.

EGU22-1718 | Presentations | NH3.5

What causes transient deformations in the Åknes landslide, Norway? 

Andreas Aspaas, Pascal Lacroix, Lene Kristensen, Bernd Etzelmüller, and François Renard

Slow creeping landslides move at rates of millimeters to several meters per year. They can cause extensive damage to infrastructure and pose a major threat to human lives if failing catastrophically. Landslides can progressively weaken over time by rock mass damage processes that may occur by constant slow creep or sudden transient slips. Eventually, damage can lead to strain localization along the basal shear plane and catastrophic failure of the landslide. When observed, transient slip events, also called creep bursts, may induce short-term loading and hence can control landslide stability. These creep bursts correspond to short periods that can last several days where the displacement of a landslide accelerates and then decelerates. Here, we compiled and analyzed extensive multiphysics data series of the Åknes landslide, Norway. This landslide is moving at a slow rate of 6 cm per year and could generate a large tsunami wave in a fjord if it would rupture catastrophically. Based on the time series of an array of eight seismometers, five extensometers, seven borehole inclinometers and piezometer strings, and ten continuous GPS stations sampled with time resolutions down to 5 minutes over several years, we detected creep bursts in this landslide. These events interact with a distinct creep trend related to seasonal variations of rainfall and snowmelt. We analyze the creep bursts in regards to micro-earthquake activity and water pressure levels, to study their origin.

How to cite: Aspaas, A., Lacroix, P., Kristensen, L., Etzelmüller, B., and Renard, F.: What causes transient deformations in the Åknes landslide, Norway?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1718, https://doi.org/10.5194/egusphere-egu22-1718, 2022.

EGU22-1866 | Presentations | NH3.5

Spatial rockfall susceptibility prediction from rockwall surface classification 

Alexander R. Beer, Nikolaus Krumrein, Sebastian G. Mutz, Gregor M. Rink, and Todd A. Ehlers

Rockfall both is a major process in shaping steep topography and a hazard in mountainous regions. Besides increasing thread due to thawing permafrost-stabilization in high-elevation areas, there are abundant permafrost-free over-steepened rockwalls releasing rockfall due to other triggers. General rockfall event susceptibility is addressed to frost cracking, earthquake shacking and hydrologic pressure in the walls, and to geotechnical rock properties. Spatial rockwall surface surveys or scans (delivering 3D point clouds) have been used to both deduce rock fracture patterns and to measure individual rockfall events from comparing subsequent scans. Though, the actually measured rockwall topography data has rarely been used as a general predictor of rockfall susceptibility against the background of observed events.

In this study, we use a series of dm-resolved annual (2014 to 2020) terrestrial laser scan surveys along 5km2 of limestone cliffs in the Lauterbrunnen Valley, Switzerland. The annual scan data were hand-cut to remove vegetation and fringes, and then referenced to detect subsequent topographic change in the direction of the wall. From the change-detection point clouds individual rockfall event volumes were detected from cluster and filtering analyses. One surveyed rockwall section of 2014 was used as training data for our Bayesian classification model of rockfall susceptibility, while the adjacent remaining section served for model validation. We rasterized their 3D data points and calculated several surface parameters per cell, including roughness, topography, mean distances for the three main fracture systems, fracture density, local dip, percent of overhang area, normal vector change rate (called edge) and percentage of overhang area. For various parameter sets and different cell sizes (32m2, 52m2, 102m2, 152m2, 252m2, and 402m2), we trained Naïve-Bayes-Classifier models. These were then used to predict rockfall susceptibility per cell, based on our observations of surface parameters, and assessed using Kullback-Leibler Divergence analysis and the misclassification cost score.

Results indicate the overall best model (accounting for the parameters roughness, edge, topography and overhang area) and for the lowest cell size (32m2) could predict rockfall cells with a probability of 0.73 (against a mean of 0.3 for all cells). Predictions on another rockwall section with observed rockfall, located on the opposite side of the valley, verified the model’s applicability by both comparable probabilities (0.6 vs 0.25) and visual surveys on overhangs. We find our approach could reliably extend this spatial rockfall susceptibility classification to all Lauterbrunnen rockwalls. The classification model generally identified overhang areas and fractured zones as high rockfall risks, matching the general insight of these zones to be of major susceptibility. Interestingly, our method is based only on orientation-independent variables that are directly calculated from the 3D point cloud. Thus, it should be principally transferable to other sites of fractured limestone walls. Specifically, there is no need to determine fracture sets from the point cloud as is generally done for susceptibility studies, since we account for topography that would anyway be used to calculate fracture planes (facets). Hence, this method provides a simple means to predict spatial rockfall susceptibility, applicable for both hazard mapping and landscape evolution studies.

How to cite: Beer, A. R., Krumrein, N., Mutz, S. G., Rink, G. M., and Ehlers, T. A.: Spatial rockfall susceptibility prediction from rockwall surface classification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1866, https://doi.org/10.5194/egusphere-egu22-1866, 2022.

EGU22-2623 | Presentations | NH3.5

Detection of rockfall activity due to rock freezing and thawing by electronic geotechnical sensors in Slovenia 

Mateja Jemec Auflič, Ela Šegina, Tina Peternel, Matija Zupan, and Andrej Vihtelič

Rockfalls are caused by preparatory processes (weathering and crack propagation) that gradually degrade bedrock and by triggering g processes (freeze-thaw activity, precipitation events, earthquakes, snow avalanches, animals, or anthropogenic activities) that eventually release a rock block. Both processes are controlled by several factors representing the internal (geology), external (meteorology), and surface and near-surface conditions (topography, vegetation, snow cover, thermal conditions, chemical weathering, and hydrology) of the bedrock. In this paper, electronic geotechnical monitoring is developed to detect the rockfall activity due to rock freezing and thawing on two separate steep cliffs composed of igneous and carbonate rocks in the eastern part of Slovenia. The monitoring programme includes automatic recordings of rock temperatures and meteorological influencing factors (air temperature, humidity, and precipitation), tiltmeters, kit for measuring rock stress and deformability, laser distance meters, and crackmeters. During the 2020 field investigation, cracks and discontinuities were mapped and Rock Mass Rating (RMR) was estimated. The Hoek-Brown Geological Strength Index was determined to qualitatively assess surface conditions in inaccessible areas using visual assessments of tectonic ruptured walls. We will present the first preliminary results of the parameters monitored for 10 months, which will help interpret rockfall activity and identify freeze-thaw cycles.

 

Acknowledgement:  The research was funded by the Slovenian Research Agency (Research project J1-3024). The electronic geotechnical sensors were founded by Project »Development of research infrastructure for the international competitiveness of the Slovenian RRI Space – RI-SI-EPOS« The operation is co-financed by the Republic of Slovenia, Ministry of Education, Science and Sport and the European Union from the European Regional Development Fund.

How to cite: Jemec Auflič, M., Šegina, E., Peternel, T., Zupan, M., and Vihtelič, A.: Detection of rockfall activity due to rock freezing and thawing by electronic geotechnical sensors in Slovenia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2623, https://doi.org/10.5194/egusphere-egu22-2623, 2022.

EGU22-2810 | Presentations | NH3.5

Large rock avalanches into a glacial lake(s): a new chapter of the Patagonian Ice Sheet story 

Tomáš Pánek, Michal Břežný, Elisabeth Schönfeldt, Veronika Kapustová, Diego Winocur, and Rachel Smedley

Although ice retreat is widely considered to be an important factor in landslide origin, many links between deglaciation and slope instabilities are yet to be discovered. Here we focus on the origin and chronology of an exceptionally large landslides situated along the eastern margin of the former Patagonian Ice Sheet (PIS). Accumulations of the largest rock avalanches in the former PIS territory are concentrated in the Lago Pueyrredón valley at the eastern foothills of the Patagonian Andes in Argentina. Long-runout landslides have formed along the rims of sedimentary and volcanic mesetas, but also on the slopes of moraines from the Last Glacial Maximum. At least two rock avalanches have volumes greater than 1 km3 and many other landslide accumulations have volumes in the order of tens to hundreds of million m3. Using cross-cutting relationships with glacial and lacustrine sediments and using OSL and 14C dating, we found that the largest volume of landslides occurred between ~17 and ~11 ka BP. This period coincides with a phase of rapid PIS retreat, the greatest intensity of glacial isostatic uplift, and a fast dropping of the glacial lakes along the foothills of the Patagonian Andes. The position of paleoshorelines in the landslide bodies and, in many places, the presence of folded and thrusted lacustrine sediments at the contact with rock avalanche deposits indicate that the landslides collapsed directly into the glacial lake. Although landslides along the former glacial lobe of Lago Pueyrredón continue today, they are at least an order of magnitude smaller than the rock and debris avalanches that occurred before the drainage of the glacial lake around 10-11 ka BP. Numerical modeling results indicate that large postglacial landslides may have been triggered by a combination of rapid sequential glacial lake drawdowns and seismicity due to glacial isostatic adjustment. We conclude that in addition to direct links such as glacial oversteepening, debuttressing and permafrost degradation, the retreat of ice sheets and the subsequent formation of transient large glacial lakes can fundamentally alter slope stability, especially if the slopes are built by weak sedimentary and volcanic rocks.

How to cite: Pánek, T., Břežný, M., Schönfeldt, E., Kapustová, V., Winocur, D., and Smedley, R.: Large rock avalanches into a glacial lake(s): a new chapter of the Patagonian Ice Sheet story, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2810, https://doi.org/10.5194/egusphere-egu22-2810, 2022.

EGU22-2954 | Presentations | NH3.5

How does anisotropy control rock slope deformation? A discrete element modelling investigation 

Marius L. Huber, Luc Scholtès, and Jérôme Lavé

Deep-seated failures of rock slopes are partly controlled by structural, lithological and topographical factors. Among structural factors, layering, schistosity and foliation in rock material, which could be described as inherent anisotropy of the material, affect initiation and evolution of deep-seated rock slope deformation, especially in slow moving landslides.

In order to document such an influence of material anisotropy on slope stability, we carry out a parametric study using discrete element modelling (DEM). After a validation exercise for fully isotropic material, where we compare our numerical approach to an analytical slope stability solution, we introduce anisotropy (transverse isotropy) in our DEM model by inserting preferentially oriented and weakened bonds between discrete elements (weakness plane) to simulate two typical transverse isotropic lithologies, claystone and gneiss respectively. Considering these two lithologies, we then explore the influence of the weakness plane’s orientation with respect to the slope angle for both ridge and valley geometries.

We show that certain orientations of the weakness plane relative to the topographic slope favour deep-seated deformation. We also observe significant disparities in failure initiation, failure surface localisation, and mobilized volume depending on the weakness plane orientation. For instance, most unstable slopes occur when the weakness plane rises 10° to 30° less than the hillslope angle. These instabilities are associated with well-localized deformation at depth that when intersecting the surface mimic some of the morphological features (such as counter-slope scarps) that are commonly described along mountain ridges in association with slow-moving and deep-seated rock slope failures.

Our results help explain the appearance or absence of deep-seated failure in mountainous areas and allow to better assess slope failure hazard induced by anisotropic rock strength.

How to cite: Huber, M. L., Scholtès, L., and Lavé, J.: How does anisotropy control rock slope deformation? A discrete element modelling investigation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2954, https://doi.org/10.5194/egusphere-egu22-2954, 2022.

EGU22-3023 | Presentations | NH3.5

Rock slope dynamics in flysch formation under cold climate (part 1) : rock cracking and failure mechanism 

Francis Gauthier, Tom Birien, and Francis Meloche

Rockfalls are major natural hazards for road users and infrastructures in northern Gaspésie (Eastern Canada). In the last 30 years, more than 17 500 rockfalls have reached the two major road servicing the area. Rockfalls come from 10 to 100 m high flysch rockwall conducive to differential weathering. The retreat and settlement of weak rock strata (shale, siltstone) causes the gradual cantilevering of stronger rock strata (sandstone, greywacke), contributing to the development of tension cracks. The block, separated from the cliff, will eventually slide or topple on the eroding rock strata. These dynamics have been observed, but rarely studied with the objective of 1) determining the mechanical stresses and weathering conditions that promote rock cracking and 2) identifying the geometric conditions that control the final failure mode. We use the cantilever beam theory to model critical cantilever length (block size) and rock tensile strength. A frost cracking model (Rempel et al., 2016) was then used to explain the overestimation of the critical cantilever length and to verify whether the development of microfractures caused by frost damage can explain the decrease of the rock tensile strength over time. The results show that the areas of frost damage concentration correspond to those of maximum stress in the overhanging blocks. In order to identify the type of failure of these blocks, tests using a tilting table were carried out in laboratory. 405 tests were performed on 10 blocks characterized by different roughness coefficients and geometric ratios (height / length ratio, overhang length / total length of the block). The results, validated on natural blocks in the field, were used to identify the geometric conditions for stability, sliding, and toppling failure of overhanging block on an inclined plane. Such stability criteria could support the development of rock instability detection algorithm using high resolution 3D model.

How to cite: Gauthier, F., Birien, T., and Meloche, F.: Rock slope dynamics in flysch formation under cold climate (part 1) : rock cracking and failure mechanism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3023, https://doi.org/10.5194/egusphere-egu22-3023, 2022.

EGU22-3079 | Presentations | NH3.5

Rock slope dynamics in flysch formation under cold climate (part 3) : rockfall forecasting 

Jacob Laliberté, Francis Gauthier, and Birien Tom

Rockfalls are major natural hazards for road users and infrastructures in northern Gaspésie (Eastern Canada) where nearly 15 kilometers of road runs along 10 to 100 m high flysch rockwall. The Ministère des Transports du Québec (MTQ) has recorded more than 17 500 rockfalls that have reached the roadway since 1987, which represents a nearly permanent danger for users. In the late 90s, protective berms were erected to reduce the number of rocks reaching the roadway. Despite the efficiency of these infrastructures, more than a hundred events are still recorded each year. Based on previous studies showing that rock instabilities in this type of geology is strongly correlated with meteorological events, we used different machine learning methods (logistic regression, classification tree, random forest, neural network) to design the best operational rockfall prediction model. Three event variables based on different rock fall frequency and magnitude thresholds were created. Nearly one hundred weather variables were used to explain and predict events. Preliminary results show that thawing degree-days is one of the most effective variables explaining the occurrence of winter and spring rockfall events. In summer, rainfall intensity is the most potential explanatory variable. Finally, fall events appear to be more responsive to rain events and freeze-thaw cycles. In order to optimize the percentage of predicted events and reduce the false alarm ratio, it remains important to evaluate the impact of each parameter on the performance of the models. These models can be used operationally as decision support tools to predict days with high event probability.

How to cite: Laliberté, J., Gauthier, F., and Tom, B.: Rock slope dynamics in flysch formation under cold climate (part 3) : rockfall forecasting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3079, https://doi.org/10.5194/egusphere-egu22-3079, 2022.

EGU22-3128 | Presentations | NH3.5

Weathering, rock type, bedrock incision and landslides in a tropical environment: the Ruzizi gorge in the Kivu Rift, Africa 

Toussaint Mugaruka Bibentyo, Olivier Dewitte, Josué Mugisho Bachinyaga, Toussaint Mushamalirwa, Florias Mees, Charles Nzolang, and Stijn Dewaele

Tropical environments favour chemical weathering and regolith development. Weathering induces textural, mineralogical and chemical changes in rocks, modifying their strength and thus affecting slope stability. Degree of weathering is, however, not only a function of climatic conditions, but is also influenced by e.g. bedrock composition and structure, exposure length and intensity, and slope angle. To investigate the role of weathering and rock type on landslide occurrence, we focus on the Ruzizi Gorge in the Kivu Rift segment of the western branch of the East African Rift System. Stretching along the border between the DR Congo and Rwanda, development of this 40-km long bedrock river began about 10,000 years ago, rejuvenating the landscape at a very high rate, with rather invariant slope angles outside of the landslides. The gorge stretches across a region where two main types of rocks constitute the geological substrate, i.e. late Miocene to Pleistocene volcanic rocks and Mesoproterozoic metasedimentary rocks. The gorge is a hotspot of deep-seated landsides in the region, with slope failures of up to 2 km². For the present study, we sampled weathering profiles developed on both mentioned rock types, in each case with sampling points within and outside the landslides as well as within and outside the rejuvenated landscape. The chemical composition of rock and regolith samples was determined by Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP–OES) analysis, and their mineralogical composition by X-Ray Diffraction (XRD) analysis and thin section observations. Geotechnical tests were used to determine mechanical properties. Overall, we observe that lithological aspects alone control regolith characteristics, and that slope angle and exposure to landscape rejuvenation hence play no significant role. In areas with volcanic rock substrate, where the largest, mostly slide-type, landslides develop, stratified weathering profiles are observed. These profiles show a greater weathering depth than those over metasedimentary rocks, where flow- and avalanche-type landslides are more common. The regolith derived from volcanic rocks has higher clay content, greater plasticity and stronger cohesion than the sandy to silty weathering material that overlies the metasedimentary rocks. These preliminary results show that weathering and rock type are more important than landscape rejuvenation in controlling the type of deep-seated landslides.

How to cite: Mugaruka Bibentyo, T., Dewitte, O., Mugisho Bachinyaga, J., Mushamalirwa, T., Mees, F., Nzolang, C., and Dewaele, S.: Weathering, rock type, bedrock incision and landslides in a tropical environment: the Ruzizi gorge in the Kivu Rift, Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3128, https://doi.org/10.5194/egusphere-egu22-3128, 2022.

Since 1987, more than 17 500 rockfalls reaching a 70 km stretch of road have been reported by the Québec Ministry of Transport (MTQ) in northern Gaspésie. This natural hazard represents a nearly permanent danger for users. Earthquake, rainfall and freeze-thaw cycles are considered to be the main rockfall triggering factors. Although these events are well correlated with rockfall occurrences, it is not clear how they affect the failure mechanism. The first step in managing the risk rockfalls pose is to better understand the pre-failure processes that contribute to their development. The second step is to improve our ability to predict and anticipate rockfalls. This study aims to better understand the influence of climate-dependent variables on (1) the mechanical deformations of stratified sedimentary rock and (2) the climatic conditions conducive to rockfalls. Meteorological instruments including a 550 cm thermistor strings have been installed directly on a vertical rockwall located in northern Gaspésie. Mechanical deformations of the flysch sequence composed of sandstone, siltstone and shale was monitored using crack-meters. In addition, rockwalls were scanned with a terrestrial laser scanner (TLS) during specific pre-targeted meteorological conditions. Over a period of 18 months, 17 LiDAR surveys have allowed to identify 1287 rockfalls with a magnitude above 0.005 m³ on a scanned surface of 12 056 m². Irreversible deformations are mainly induced by rainfall and snowmelt (shrink-swell process in porous and clayey rock and/or hydrostatic pressure variations in discontinuities), by freeze-thaw cycles and to a lesser extent, by large thermal variations. Gradual settling measured in the siltstone strata causes destabilization of sandstone strata and the eventual fall of sandstone blocks. In winter, rockfall frequency is 12 times higher during a superficial thaw than during a cold period in which temperature remains below 0°C. In summer, rockfall frequency is 22 times higher during a heavy rainfall event than during a period mainly dry. Superficial freeze-thaw cycle (< 50 cm) causes mostly a high frequency of small magnitude events while deeper spring thaw (> 100 cm) results in a high frequency of large magnitude events. Influence of meteorological conditions on mechanical deformations and on rockfall frequency and magnitude is crucial in order to improve risk management since large magnitude events represent higher potential hazards. This study provides a classification of meteorological conditions based on their ability to trigger rockfalls of different magnitudes which could be used to implement an adequate preventive risk management.

How to cite: Birien, T. and Gauthier, F.: Rock slope dynamics in flysch formation under cold climate (part 2): rock deformations and rockfall triggering factors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3207, https://doi.org/10.5194/egusphere-egu22-3207, 2022.

The rock mass is strongly influenced by the presence of discontinuities and their role is also strongly regarded in rock mass characterization. Different traditional methods were developed for accessing the rock mass condition for safely designing engineering projects such as slopes, tunnels, foundations, etc. The progress in computational techniques has led to a significant understanding of rock mass related problems. Among them, the discrete fracture network (DFN) technique based on statistical distribution gains significant importance in examining the rock mass. The applicability of remote sensing techniques such as photogrammetry has made it easy to collect the essential data, which otherwise was difficult to acquire using scanline survey or window mapping. The study aims application of DFN in estimating block volume distribution and Rock Quality Designation (RQD) for finding the Geological strength index (GSI) of the rock mass. The results also compare the aggregate and disaggregate DFN with GSI estimated using traditional methods in the field. Along with the estimation of GSI using the existing chart method, the work also proposed the applicability of machine learning (ML) in predicting the GSI value. It is easy and handy to use a chart but becomes time-consuming when dealing with a larger dataset. We have developed a ML inbuilt python-based GUI tool to estimate the GSI value from block volume and joint condition parameters quickly.

How to cite: Singh, J., Pradhan, S. P., and Singh, M.: Characterization of a fractured rock mass using Geological Strength Index (GSI): A Discrete Fracture Network (DFN) and Machine learning (ML) approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3456, https://doi.org/10.5194/egusphere-egu22-3456, 2022.

EGU22-4199 | Presentations | NH3.5

Large landslides cluster along Patagonian Ice Sheet margin 

Michal Břežný, Tomáš Pánek, Stephan Harrison, Elisabeth Schönfeldt, and Diego Winocur

Deglaciation of mountain ranges promotes landslides of various scales and types, and many of them may present a major hazard. Traditionally, it is assumed that landslides are concentrated in the steepest, wettest, and most tectonically active parts of the orogens, where glaciers reached their greatest thickness. Based on our mapping of large landslides (>1km2) over an extensively large area of Southern Patagonia (~305,000 km²), we show that the distribution of landslides can have the opposite trend. The largest landslides within the limits of the former Patagonian Ice Sheet (PIS) cluster along its eastern margins occupying lower, tectonically less active, and arid part of the Patagonian Andes. In contrast to the heavily glaciated, highest elevations of the mountain range, the peripheral regions have been glaciated only episodically. However, a combination of glaciation, weak volcanic and sedimentary rocks, sufficient relief, and presence of large glacial lakes in the past, created favourable conditions for huge number of large landslides along eastern margin of PIS. We explain the scarcity of large landslides in the highest parts of the PIS by presence of strong granitic rocks and long-term glacial modification, that adjusted topography for efficient ice discharge. Our model is applicable only for large bedrock landslides, not for shallow slides and rock falls, which are abundant in the highest and western part of the Andes.

How to cite: Břežný, M., Pánek, T., Harrison, S., Schönfeldt, E., and Winocur, D.: Large landslides cluster along Patagonian Ice Sheet margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4199, https://doi.org/10.5194/egusphere-egu22-4199, 2022.

EGU22-4554 | Presentations | NH3.5

Evidence of volcanic debris avalanche propagation dynamics from sedimentological analysis of the Tenteniguada and Abona deposits, Canary Islands 

Symeon Makris, Matteo Roverato, Alejandro Lomoschitz, Paul Cole, and Irene Manzella

Debris avalanches (DA) are large landslide events characterised by long runouts and high mobility that poses a great hazard to communities close to volcanoes. Although many theories have been proposed to explain the excessive runout phenomenon, the mechanisms enabling the mobility remain unresolved and poorly constrained. As a result, it is still challenging for models and theoretical concepts to encompass DA deposit field observations.

DA deposits are complex; however, detailed study of their sedimentary architecture can provide information regarding their propagation processes. In this study, the deposits of two DAs in the Canary Islands: Tenteniguada DA, located on the east of Gran Canaria; and Abona DA on the southeast of Tenerife have been examined. Although they are located in nearby volcanic islands they occurred in different environments with different triggering processes, scale, material and their deposits suggest different propagation rheology. A detailed field study of the deposits was carried out in September 2021, mapping their facies and feature distribution and sedimentology. Structure from motion photogrammetry methodology has been used to generate high accuracy 3D models of outcrops and sample windows to quantify facies distribution. The data collected allow for evaluation of the effects of material properties, substrate and its geometry, and to assess aspects of the dynamics of the DAs. Therefore, it was possible to generate conceptual models for the transport and emplacement mechanisms of the two events corresponding to the observations and to relate them to the two debris avalanche distinctive characteristics by comparison.

In the Tenteniguada DA deposit, the degree of disaggregation is low, with large portions of the original edifice preserved along with their original stratigraphy, although displaced relative to each other by brittle deformation. In contrast, Abona DA is much more disaggregated. Monolithological blocks are microfractured and cataclased, and original stratigraphy is not preserved. There is no evidence of brittle deformation. The highly comminuted material has been elongated in a fluidised spreading flow, achieving a long runout on an erodible pumice substrate. Conversely, the Tenteniguada DA did not fully transition from a slide to a flow and has not generated a long runout while propagating in an active fluvial ravine. These findings suggest that the behaviour and the distribution of stresses was very different during propagation, owing to the properties and volume of the material in the flow and potentially the substrate properties and triggering mechanisms.

The present study highlights how the field examination of sedimentological, morphological, and structural features is vital in fully understanding DA propagation and emplacement mechanisms.

How to cite: Makris, S., Roverato, M., Lomoschitz, A., Cole, P., and Manzella, I.: Evidence of volcanic debris avalanche propagation dynamics from sedimentological analysis of the Tenteniguada and Abona deposits, Canary Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4554, https://doi.org/10.5194/egusphere-egu22-4554, 2022.

Excavations in soft rocks usually have to be performed by blasting with explosives or with heavy pneumatic hammers. However, in a certain period after excavation, their physical and mechanical properties begin to change to a level where even manual excavation can be used. These changes can be significant during the building design life, where the initial design solution of the slope cut may prove inappropriate, sometimes resulting in collapse. In this context, it is necessary to define the causes of changes in the soft rock physical and mechanical properties, and determine all the necessary parameters (primarily strength parameters, but also all others relevant to describe the change in rock properties over time) in all phases of expected change during construction or other applications (such as use of slope area, in case of abandoning the site in certain time period, etc.).

Furthermore, when preparing project documentation for construction, in the part where the calculations of the global stability of the building on the slope are performed, the possibility of significant changes in the shape of the slope during the structure/building design life are usually neglected. Therefore, this paper also presents the Fisher Lehmann model of the change of slope geometry during the period of construction use, and explains the influences of weathering factors on parameters of the soft rock over time by using laboratory simulation of weathering.

Combined changing the geometry of the slope and the properties of the rock can have a negative impact on the safety of the structure, which is explained and shown through an example of an abandoned construction pit at Bračka Street in Split, where the stability of neighboring residential houses is endangered. By using appropriate mathematical models of the slope morphology change, results of long term slope monitoring by TLS and appropriate software for slope stability analysis (Slide 2, RocScience), the time span in which the instability can occur for Bračka Street case study is determined for multiple possible future intervention scenarios.  

How to cite: Vlastelica, G., Duhović, A., and Relota, M.: Long term stability of an abandoned construction pit in Eocene flysch rock mass: case study of Bracka street construction site (Split, Croatia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4641, https://doi.org/10.5194/egusphere-egu22-4641, 2022.

EGU22-5318 | Presentations | NH3.5

Spatial/temporal distribution of rock slope failures along the trans-Himalaya highway between Gangtok and Yumthang (Sikkim, India) 

Reginald Hermanns, Ivanna Penna, Vikram Gupta, Henriette Linge, Rajinder Bhasin, John Dehls, Odd Andre Morken, and Aniruddha Sengupta

The ca. 80 km long trans-Himalayan highway between Gangtok and Yumthang has experienced at least three large rock slope failures (RSF) within the past 40 years and tens of smaller RSF related to the 2011 Sikkim earthquake. More than 30 conspicuous boulder deposits suggest that similar failures happened in the past. Since the largest of these deposits are located within the shallowest sections of otherwise 60 – 75° steep slopes, they are often the location of settlements. We have used Terrestrial Cosmogenic Nuclide (TCN) dating to understand better where and how often these events are likely to occur.

The trans-Himalayan highway connects the Lesser Himalaya, with a tropical to subtropical climate, with the cold-temperate climate in the Higher Himalaya north of the Main Central Thrust (MCT). This highway also crosses the orographic barrier, with rainfalls exceeding 3000 mm/yr in the south and less than 500 mm/yr in the north. On September 10th, 1983, a large RSF was triggered by “exceptional” rainfall and impacted the settlement of Manul, with an estimated life loss of 200 persons. Today, the deposit is covered by a dense tropical forest 30-m high that restricts detailed analysis. However, boulder size and boulder density on the surface suggest that it was a rock avalanche.

The second reported RSF is a rock avalanche with a volume of 12 million m3 that occurred close to the village of Yumthang on March 11th, 2015. This deposit overlies two generations of prehistoric rock-avalanche deposits. No trigger was reported.

The last reported RSF involved a volume of 8.7 million m3, occurred on August 13th, 2016 at Dzongu, NW of Mangan. While no trigger for the collapse was reported, satellite footage indicates at least ten years of pre-failure rock-slope deformation. The deposit has the typical carapace of a rock avalanche, but videos posted on social media instead suggest that it was a collapse that took place over several hours.

RSF deposits are found in similar numbers in both the Higher and Lesser Himalaya, with the highest concentration in the vicinity of the MCT and a second cluster close to the village of Yumthang. We sampled ten of the deposits for TCN dating, including two of the historic events. Both historic events returned zero ages. The two older deposits overlain by the 2015 Yumthang rock avalanche returned equally young ages, suggesting multiple recent events at that site within a short time. The zero ages of both historical events suggest that inheritance of nuclides prior to failure in the samples can be ruled out. The ages of the remaining deposits range from 0.2 to ~12 kyr. Several deposits have bimodal age distributions. Others have three different ages in different sectors of the deposit. These results show that multiple RSF similar to the Yumthang site often can affect the same slope sector, leaving deposits on the same slope sections. Thus, the 30 identified deposits by far are the lower limit of RSF failures in the study area and that the threat of RSF is high.

How to cite: Hermanns, R., Penna, I., Gupta, V., Linge, H., Bhasin, R., Dehls, J., Morken, O. A., and Sengupta, A.: Spatial/temporal distribution of rock slope failures along the trans-Himalaya highway between Gangtok and Yumthang (Sikkim, India), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5318, https://doi.org/10.5194/egusphere-egu22-5318, 2022.

EGU22-7249 | Presentations | NH3.5

Modelling Rockfall Source areas and hazard zoning along the Rhine-, Ahr- and Moselle-valleys in the Rhenish Massif, Rhineland-Palatinate, Germany 

Philip Süßer, Teemu Hagge-Kubat, Ansgar Wehinger, Michael Rogall, and Frieder Enzmann

Rockfall events, due to toppling or sliding rock slope failure are a common phenomenon within the Rhine-, Ahr- and Moselle-valley of the Rhenish Massif. Due to the dense traffic infrastructure, significant cases of damage with far-reaching economic and infrastructural consequences regularly occur in these areas. Therefore, there is a specific need for precautionary risk analysis in order to prevent further damage and to implement preventive measures. The research approach presented here aims to identify rockfall endangered zones for adjacent infrastructure in the valleys. It is assumed, that the main reason for these frequent occurrences are the high number of exposed rock faces and a complex fabric of intersecting foliation-, fracture- and cleavage- networks and faults. By using an index, calculated from the slope and real-surface area of high-definition LIDAR based DEM it is possible to extract areas with exposed rock faces as possible sources for rockfall modelling. To single out which parts of the outcrop are more likely to fail, we compute the aspect of natural occurring outcrops, characteristic of fabric orientations along which failure preferably takes place and pinpoint locations with highly varying directions. These intersection points, representing weakened areas within the outcrops serve as sources for our rock fall models using the Gravitational-Process-Path-Model by Wichmann (2017). Through the precise identification of the rockfall source areas and further input data like vegetation and relief energy numerous cases in the valley were modelled. By intersecting with real infrastructure data, it is possible to carry out risk assessments of specific sections of roads and railway lines. Validation using the mass movement database of the Rhineland-Palatinate Geological Survey and numerous ground checks show, that concrete rockfall events were plausibly simulated.

How to cite: Süßer, P., Hagge-Kubat, T., Wehinger, A., Rogall, M., and Enzmann, F.: Modelling Rockfall Source areas and hazard zoning along the Rhine-, Ahr- and Moselle-valleys in the Rhenish Massif, Rhineland-Palatinate, Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7249, https://doi.org/10.5194/egusphere-egu22-7249, 2022.

EGU22-7454 | Presentations | NH3.5

The Innonet project: understanding the capacity of flexible protection systems against rockfall in natural terrain 

Helene Hofmann, Manuel Eicher, Andreas Lanter, and Andrin Caviezel

In the last 30 years, rockfall barriers made of steel wire nets have become established worldwide as a protective solution, are meanwhile CE certified and the question inevitably arises as to the effect of natural impacts, i.e. impacts from boulders that strike the net at any point, possibly also rotating as they do so. In 2019 an Innosuisse-sponsored research project was granted to the WSL Institute for Snow and Avalanche Research SLF together with the industry partner Geobrugg, for testing fully instrumented rockfall barriers, in natural terrain in the Swiss Alps, aiming at finding improvements to the capacity of a rockfall barrier outside of the certification standards. The awareness that the capacity of a rockfall barrier is different depending on the impact location, and how to deal with the so-called remaining capacity of rockfall barriers, in load cases outside the approval tests, differ worldwide. In some countries, specialized designers are aware of this fact and solve the problem by over-dimensioning the rockfall barriers to ensure the availability of residual capacity outside of the middle field. In other countries however, authorities and/or designers assume that a 1000kJ rockfall system absorbs this energy even in marginal areas or in case of an eccentric hit. Protective solutions are consequently not necessarily designed properly. This research project tries to assess the performance and the residual capacity of rockfall barriers, after being impacted by various load cases, to improve the current knowledge. Several field campaigns were conducted, in which rocks of different shapes and sizes are projected into the netting of the rockfall barrier and its structure (cables and posts). The barrier is equipped with sensors to measure the loading on different elements of the protection system. In addition, the test blocks (up to 3’200 kg) are also equipped with sensors that measure the rotation and the acceleration during the fall and on impact with the barrier. In combination with high-resolution drone recordings and video recordings from different viewing angles, the trajectories and velocities of the individual blocks can be reconstructed in detail, enabling further insights into the interaction of all parameters. The barrier was left in place since construction and is enduring its third winter without maintenance. A field survey (snow depth and density, loads on cables, posts, etc) was undertaken in the winters 19/20 and 20/21, and further surveys will take place this current winter. This contribution will present the evaluation of the rockfall test data. It allows an understanding of the remaining capacity of a barrier, the influence of rockfall rotation onto the protection system itself as well as the importance of the impact location. Forces measured in the system show a variation of up to 40% when compared to the standard testing results. The goal is then to assess if additional tests can be carried out to the standardized tests, to better prepare a rockfall barrier for the field.

How to cite: Hofmann, H., Eicher, M., Lanter, A., and Caviezel, A.: The Innonet project: understanding the capacity of flexible protection systems against rockfall in natural terrain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7454, https://doi.org/10.5194/egusphere-egu22-7454, 2022.

EGU22-8504 | Presentations | NH3.5

Rockfall triggering mechanism analyzed from video using optical flow technique 

Chunwei Sun, Valérie Baumann Traine, Marc-Henri Derron, and Michel Jaboyedoff

This work presents an approach to identify the rockfall triggering mechanism from video employing Optical Flow Technique. The video was captured by phone camera on 3rd, October 2017 when the massive rockfall happened at a quarry in Le Locle Jura mountains, Switzerland. Time-series frames were extracted from the video and registered using SIFT (Scale-Invariant Feature Transform), kNN (k-nearest neighbor classification) and affine transformation algorithm, which efficiently eliminate the video jitters. After that, the transformation of pixels in the time-series image sequence and the correlation between adjacent frames are used to find the correspondence, so as to calculate the motion data of the object between adjacent frames by Optical Flow Technique. The instantaneous velocity of pixel movement of failure rock mass or debris on the video frames during rockfall dynamic behavior can be obtained. The basal failure surfaces and two main phases of the failure have been anlayzed for the rockfall triggering mechanism. The workflow proposed here can be applied in a slope disaster monitoring and early warning system to identify and track rockfall events effectively.

How to cite: Sun, C., Baumann Traine, V., Derron, M.-H., and Jaboyedoff, M.: Rockfall triggering mechanism analyzed from video using optical flow technique, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8504, https://doi.org/10.5194/egusphere-egu22-8504, 2022.

EGU22-9134 | Presentations | NH3.5

Observations of slope movements in mountain landforms using permanent in-situ GNSS instruments 

Jan Beutel and the PermaSense GNSS Team

Slope movements in mountain areas are abundant and diverse phenomena, with an extreme range in size and velocity, and constituted from different materials such as bedrock, debris, and ice. In the past two decades, many studies have observed accelerating trends in the surface velocities of these landforms, often attributed to global warming and its amplified impact on high mountains. Detailed data needed for quantitative analysis and modelling, however, remain scarce due to logistic and technical difficulties. In particular, state-of-the-art monitoring strategies of surface displacement in high-mountains rely either on geodetic terrestrial surveys or on remote sensing techniques. While these methods are beneficial for the establishment of long-term time series and distributed datasets of surface displacements, they lack high temporal resolution and are sensitive to data gaps. These characteristics limit their potential for underpinning detailed process understanding and natural hazard management procedures. By contrast, in-situ permanent instruments allow high temporal resolution without observation gaps, providing unprecedented information w.r.t. the processes at hand. Furthermore, continuous observations with short transmission delays are suitable for applications in real-time, essential for many aspects of natural hazard monitoring and early warning systems.

Here, we present a decadal dataset consisting of continuously acquired kinematic data obtained through in-situ global navigation satellite system (GNSS) instruments that have been designed and implemented in a large-scale multi field-site monitoring campaign across the Swiss Alps. The monitored landforms include rock glaciers, high-alpine steep bedrock as well as landslide sites, most of which are situated in permafrost areas. The dataset was acquired at 54 different stations between2304 and 4003 m a.s.l and comprises ~240’000 daily positions derived through double-difference GNSS post-processing. Apart from these, the dataset contains down-sampled and cleaned time series of weather station and inclinometer data as well as the full set of GNSS observables in RINEX format. Furthermore, the dataset is accompanied by tools for processing and data management in order to facilitate reuse, open alternative usage opportunities and support the life-long living data process with updates. To date, this dataset has seen numerous use cases in research as well as natural-hazard mitigation and adaptation measures. Some of those are presented in order to showcase the fidelity and versatility of the monitoring network.

How to cite: Beutel, J. and the PermaSense GNSS Team: Observations of slope movements in mountain landforms using permanent in-situ GNSS instruments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9134, https://doi.org/10.5194/egusphere-egu22-9134, 2022.

EGU22-9344 | Presentations | NH3.5

Assessment of Rockfall Hazard and 3D Trajectography based on Slope and Structural Settings: Case Study in Les Fréaux, France 

Tiggi Choanji, François Noël, Li Fei, Chunwei Sun, Charlotte Wolff, Marc-Henri Derron, Franck Bourrier, Michel Jaboyedoff, and Romain Gaucher

The case study is located in the municipality of Les Fréaux, France. The site consists of Cambrian-Ordovician of amphibolite and gneiss rock with complex structural geology that formed in mountainous and large valley with steep slopes and even overhanging rock walls. In this site, rockfall is a major hazard for access roads and houses.

To assess rockfall hazard in the vicinity of the elements at risk, LiDAR data have been analysed and field work done on site from 2020 to 2021.  Rockfall source areas were identified directly on 3D point clouds (PC) based on two criteria, which are large slope angles and kinematic analysis from structural identification of fault, folds and joints. Based on these source areas, several 3D point cloud trajectory models were processed using the freeware stnParabel, for various block diameters (d1, d2, d3) in order to determine the propagation and the probability of reaching the settlements or roads.

Preliminary simulation of trajectories based on several method of simulations results showed some potential directions are reaching the road and also leading to settlements.

How to cite: Choanji, T., Noël, F., Fei, L., Sun, C., Wolff, C., Derron, M.-H., Bourrier, F., Jaboyedoff, M., and Gaucher, R.: Assessment of Rockfall Hazard and 3D Trajectography based on Slope and Structural Settings: Case Study in Les Fréaux, France, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9344, https://doi.org/10.5194/egusphere-egu22-9344, 2022.

EGU22-9929 | Presentations | NH3.5

Preliminary analysis of potential daily cyclic movements on the surface of Brenva rockslide scar based on the GB-InSAR monitoring (Mont-Blanc massif, Aosta Valley, Italy) 

Li Fei, Charlotte Wolff, Davide Bertolo, Carlo Rivolta, Tiggi Choanji, Marc-Henri Derron, Michel Jaboyedoff, Fabrizio Troilo, Patrick Thuegaz, and Joëlle Hélène Vicari

With global warming, geological hazards such as rockfalls, rockslides and rock avalanches have increased in alpine areas recently. In many studies, this increase has been attributed to the redistribution of the slope stress field, fluctuations in the temperature field (surface layer thaws during summer), and changes in the seepage field (infiltration of snow and ice melting water), which are led by permafrost degradation and glacier retreat. On the other hand, it is necessary to assess the long-term effects of these changes on rock mass fatigue, which could lead to rock instability. The GB-InSAR technique can detect deformation in the mm range. It is ideal for monitoring small deformations caused by daily physical weathering or other factors in high mountains.

A GB-InSAR campaign was performed from 12 August 2020 to 19 October 2020 in the Brenva glacier basin to assess the displacement of the Brenva rockslide scar. We found a daily cycle of expansion and shrinkage on the scar surface during the summer after examining the movement of different control points along the line-of-sight (LOS). Consequently, we explored possible causes behind such displacement. In this case, we realized that the crest and trough of the displacement curve occurred at a certain period of each day. For instance, in the cases of control points 2, 7, and 8, most crests in the displacement curve occurred in the early morning of each day and the troughs in the late afternoon or evening of each day during 06 September and 13 September, with amplitudes of displacement around 0.15mm, 0.25mm, and 0.4mm, respectively. The preliminary correlation between air temperature and daily deformation shows that point 7 moves towards SAR as the air temperature increases, and away from SAR as the temperature decreases. This phenomenon means that such displacement could be caused by the daily changes in temperature (leading to thermal expansion and contraction of materials, and movement of ice in micro-macro cracks) in the rock mass and air.

However, a comprehensive analysis of the LOS displacement that consists of checking the raw data of GB-InSAR (i.e., radar signal comparison), setting more specific control points at locations with various dip directions, and clear correlation between meteorological data and displacement is undergoing to verify and explain such kind of displacement.

In conclusion, continuous daily physical weathering (behaving as cyclic movement) that led to rock mass fatigue probably exists on the surface of alpine slopes, and GB-InSAR could be an effective technique to detect such movement. Despite only slight daily displacement fluctuation on the surface, it could play a crucial role in the initiation of geo-disasters.

How to cite: Fei, L., Wolff, C., Bertolo, D., Rivolta, C., Choanji, T., Derron, M.-H., Jaboyedoff, M., Troilo, F., Thuegaz, P., and Vicari, J. H.: Preliminary analysis of potential daily cyclic movements on the surface of Brenva rockslide scar based on the GB-InSAR monitoring (Mont-Blanc massif, Aosta Valley, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9929, https://doi.org/10.5194/egusphere-egu22-9929, 2022.

Granite is distributed all over the world and one of the rock types that are very susceptible to various kinds of mass movements including rockfall, rock slide, debris slide and debris avalanche. For example in Japan, Hiroshima rainstorm disasters in 1999, 2014, and 2018, and southern Miyagi rainstorm disaster induced by typhoon 19 in 2019. This is because its special characteristics of formative processes and weathering behavior. The primary structures of granite have long been believed as orthogonal cooling joints since the pioneer work of Cloos (1921, 1922), but we found that a granite body has columnar joints near its roof using UAV and SfM. Whether granite has columnar joints or not leads to different mass movement types. Rock columns separated by columnar joints form high unstable rock towers or tors, which are susceptible to rockfalls. When rock columns are weathered under the ground, they form boulders surrounded by saprolite; when they are eroded to form hills they frequently fail during rainstorms and transform to debris avalanche or debris flow with high destructive potential because of large mass of boulders. Granite without columnar joints is not suitable for spheroidal weathering but is sheeted by unloading; sheeting forms dip slopes, on which rock slides occur. Some granite is micro-sheeted by unloading and micro-sheeted granite is weathered to form a loose soil layer beneath slope surfaces. Such soil layers are very prone to heavy rainfalls and frequently slide, transforming debris avalanches and debris flows.

Primary structures of granite and following weathering schemes thus define landslide behavior in granite areas.

How to cite: Chigira, M.: Primary structures of granite and following weathering schemes define landslide behavior in granite areas., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10843, https://doi.org/10.5194/egusphere-egu22-10843, 2022.

EGU22-11107 | Presentations | NH3.5

Estimating rockfall release scenarios based on a straightforward rockfall frequency model 

Christine Moos, Luuk Dorren, Michel Jaboyedoff, and Didier Hantz

A realistic quantification of rockfall risk is crucial for an effective and efficient prevention of damages. The estimation of realistic block and event volumes as well as their release frequencies remain a major challenge and are often based on mere expert estimation. Based on the analysis of the rockfall frequency and volume of a wide range of rock cliffs, Hantz et al. (2020) proposed a power law based model for the determination of rockfall magnitude-frequency aiming at a more objective approach for practitioners. It assumes that both, the released masses of rockfall events as well as the individual blocks of a rockfall event follow a power law distribution. The parameters of these distributions are determined using a simple classification of rock structure in combination with field measurements of blocks. In this study, we applied and tested the proposed rockfall frequency model (RFM) at 8 different sites at 7 locations in the Swiss Alps. The calculated frequencies of rockfall events and the derived block volumes were compared to release scenarios of official hazard assessments as well as inventory data. Block volume distributions of all sites could be well fitted by power law distributions (fitted b values between 0.69 to 1.69). The rockfall event and block volumes are in a comparable range as the scenarios of the official hazard assessments, but generally slightly larger. The differences increase with the return period. For all sites, the parameter sensitivity of the RFM is relatively large, in particular for return periods of 100-300 years. Nevertheless, the method proposed in this study allows for a more objective and consistent estimation of rockfall scenarios and thus has the potential to substantially improve the mostly opaque determination of rockfall scenarios. The results further show that the block volume scenarios for pre-defined return periods strongly depend on the considered cliff size, which does not appear to be consistently taken into account in current hazard assessments. However, the study should be extended to additional sites and the parameter estimation has to be optimised to come up with a consistent and transparent method to estimate rockfall frequencies in practice.

How to cite: Moos, C., Dorren, L., Jaboyedoff, M., and Hantz, D.: Estimating rockfall release scenarios based on a straightforward rockfall frequency model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11107, https://doi.org/10.5194/egusphere-egu22-11107, 2022.

EGU22-11320 | Presentations | NH3.5

Sentinel-1 InSAR Time-series Monitoring of the Unstable Rock Slopes in North Sikkim, India 

Gökhan Aslan, John Dehls, Reginald Hermanns, Ivanna Penna, Aniruddha Sengupta, and Vikram Gupta

The trans-Himalayan highway, between Gangtok and Yumthang, winds along steep valley sides, including a long section above the Teesta River. Many villages are precariously perched above the V-shaped valley bottoms. The highway is subject to frequent rainfall-triggered landslide events during monsoon season, disrupting transport and destroying infrastructure. The area has also experienced at least three large rock slope failures (RSF) within the past 40 years and many smaller RSF after the 2011 Sikkim earthquake (Martha et al, 2015). Earlier RSF, many prehistoric, have left at least 30 large boulder deposits along the valley. Several of those such as the Lanta Khola landslide get reactivated each monsoon season (Sengupta et al., 2011). A number of villages are located on these deposits, as they are frequently found in shallower sections of the valley slopes.

In the present study, Persistent Scatterer InSAR (PSI) has been employed, using Sentinel-1A and -1B Synthetic Aperture Radar (SAR) images acquired between 2015 and 2021 for selected historical landslides and landslide-prone areas along the Dzongu and Yumthang Valleys. Among them are the massive translational Dzongu landslide that occurred in 2016 near Mantam village forming a landslide dam (Morken et al., 2020), a large rock avalanche that occurred in 2015 in Yumthang valley (Penna et al., 2021), and several slope instabilities in the cities of Mangan and Mangshila.

Despite the challenges of dense vegetation and winter snow, we detected sufficient targets within the landslides, mainly over the scar areas, rock outcrops, building roofs, and landslide deposits. In this study, we compare the movement/settlement of these historic deposits with ongoing movement in prehistoric deposits. We look at linear vs seasonal components of ongoing deformation within the settlements built upon RSF deposits and discuss the implications with respect to possible catastrophic reactivation.

 

Martha, T. R., Govindharaj, K. B., & Kumar, K. V. (2015). Damage and geological assessment of the 18 September 2011 Mw 6.9 earthquake in Sikkim, India using very high-resolution satellite data. Geoscience Frontiers, 6(6), 793-805.

Morken, O. A., Hermanns, R. L., Penna, I., Dehls, J. F., & Bhasin, R. (2020, June). The Dzongu landslide dam: high sedimentation rate contributing to dam stability. In ISRM International Symposium-EUROCK 2020. OnePetro.

Penna, I. M., Hermanns, R. L., Nicolet, P., Morken, O. A., Dehls, J., Gupta, V., & Jaboyedoff, M. (2021). Airblasts caused by large slope collapses. Bulletin, 133(5-6), 939-948.

Sengupta, A., Gupta, S., and Anbarasu, K., 2010, Rainfall thresholds for the initiation of landslide at Lanta Khola in north Sikkim, India: Natural Hazards, v. 52, no. 1, p. 31-42.

How to cite: Aslan, G., Dehls, J., Hermanns, R., Penna, I., Sengupta, A., and Gupta, V.: Sentinel-1 InSAR Time-series Monitoring of the Unstable Rock Slopes in North Sikkim, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11320, https://doi.org/10.5194/egusphere-egu22-11320, 2022.

EGU22-11330 | Presentations | NH3.5

Climate change and slope stability in Iceland 

Thorsteinn Saemundsson and Jon Kristinn Helgason

Over the last decades climate has warmed up worldwide and changes have occurred in the general weather patterns. Where the increase in temperature has rapidly been gathering pace in the last decade. These changes have also been observed in Iceland. From 1980 to 2015 the average temperature increase has been 0,47°C per decade and the average precipitation has increased from 1500 mm/year to around 1600-1700 mm/year. The increased temperature changes have also resulted in more frequent thawing periods and rainfall events during winter months, especially in the lowlands.

Mass movements, including rock falls, rock avalanches, debris flows and debris slides, are common geomorphological processes in Iceland and thus present a significant and direct threat to many towns, villages, and farmhouses. Weather conditions, e.g. precipitation and temperature variations, and earthquake activity are the most common triggering factors for such activity in Iceland. During the last decades several, somewhat unusual, mass movements events have occurred in the island. These events have been unusual both regarding their size, increased frequency, their triggering factors and not at least the timing within the year they have occurred.

One of the most visible consequence of temperature rise in Iceland is the fast retreat and thinning of outlet glaciers and formation of proglacial lakes. The frequency of mass movements on outlet glaciers have increased considerably from the turn of the century compared to the last 4 decades of the 20th century. New discoveries of unstable slopes above outlet glaciers have also increased considerably from 2000.

In recent years, there has been an increasing interest worldwide in the influence of climate warming and possible decline of mountain permafrost on the occurrence of mass wasting phenomena. The rising frequency of rapid mass movements, such as debris flows, debris slides, rock falls and rock avalanches, in mountainous areas have been linked with mountain permafrost degradation. Several mass movements, which can be connected to thawing of mountain permafrost, have occurred in central N and NW parts of the island during the last decade.

Majority of landslides in Iceland in the past century have either occurred in relations with low-pressures systems that pass-through Iceland from August to November, bringing in high winds with heavy rainfall, or during spring snowmelt in May and June. But in the past two decades snowmelt and thawing periods are becoming more frequent and longer during wintertime resulting in higher frequency of slope failures during that time of year. Over the past 20 years’ large landslides events (> 300.000 m3) have become more frequent compared to the second half of the 20th century. 

Climate change certainly seems to be affecting slope stability in Iceland and is an increasing risk. Especially slopes close to retreating glaciers and those affected by thawing of mountain permafrost. Changes in temperature and precipitation patterns in late fall and during winter months are causing slope failures that were not as common in the past. 

How to cite: Saemundsson, T. and Helgason, J. K.: Climate change and slope stability in Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11330, https://doi.org/10.5194/egusphere-egu22-11330, 2022.

EGU22-11604 | Presentations | NH3.5

Airblast caused by large slope collapses 

Ivanna Penna, Reginald Hermanns, Pierrick Nicolet, Odd Andre Morken, John Dehls, Vikram Gupta, and Michel Jaboyedoff

The sudden impact of a large slope collapse on the ground can cause a high degree of comminution of rocks and trigger an extreme rush of air loaded with particles, called an airblast. The airblast can expand the destructive capacity of a large slope collapse far beyond the run-out of the rock mass. The first airblast event documented in detail occurred in 1881 as consequence of a large collapse at Elm in the Unthertal valley (Switzerland). People being blown over by the air pressure wave were reported. In 2015, two rock avalanche related airblasts occurred in the Himalayas. In March 2015, an airblast in Yumthang valley (Sikkim, India) knocked down and snapped trees 1.4 km away from the impact zone of a rock avalanche. In April 2015, an avalanche triggered by the Gorkha earthquake induced a violent airblast that caused several casualties in Langtang valley. The destruction of stone and wooden houses can be observed in video footage. The damage on trees can be traced over a distance of 3.5 km and 400 m above the impact zone of the avalanche on the opposite slope. The most recent documented event occurred in February 2021 in Chamoli (India), where the flattened forest extends over 20 hectares.

This work presents a back analysis of the April 2015 airblast in the Sikkim Himalayas (India) and compares it with several other airblasts documented around the world. We review the conditions a large slope collapse should meet to cause a significant airblast. We also formulate an equation that links the potential energy of collapses having airborne trajectory to the extent of the related airblast.

How to cite: Penna, I., Hermanns, R., Nicolet, P., Morken, O. A., Dehls, J., Gupta, V., and Jaboyedoff, M.: Airblast caused by large slope collapses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11604, https://doi.org/10.5194/egusphere-egu22-11604, 2022.

EGU22-11756 | Presentations | NH3.5

Integrated 3D geological and Finite Element modeling of slow rock-slope deformations affecting hydropower facilities 

Federico Agliardi, Antonio Carnevale, Matteo Andreozzi, Andrea Bistacchi, Margherita C. Spreafico, Federico Franzosi, Chiara Crippa, Massimo Ceriani, Carlo Rivolta, Giovanni B. Crosta, and Riccardo Castellanza

Slow rock-slope deformations are widespread in orogenic belts and pose significant threats to critical infrastructures, due to continuing slow movements and potential evolution to collapse. The analysis of related risks requires realistic models, accounting for the 3D complexity of both large landslides and infrastructures, often hampered by over-simplification of geological aspects.

We propose an integrated workflow for the 3D modeling of a complex system of deep-seated landslides affecting the N slope of Mt. Palino (Valmalenco, Italian Central Alps). The slope was carved by glacial and fluvial erosion in a complex metamorphic sequence including layers of metapelite, serpentinite, gabbro and gneiss with a regional foliation deformed in two folding stages. The slope hosts a hydroelectric power plant and related structures, affected by deformations observed since 1972. Site investigations (field surveys, full-core borehole drilling, seismic surveys) and deformation monitoring (EDM, GNSS, structural monitoring, GB-InSAR) show that the slope is affected by a deep-seated gravitational slope deformation, probably active before the LGM and partially collapsed, and by a system of nested large landslides, including a toe failure up to 200 m deep and two suspended rockslides affecting some of the structures.

We performed an accurate 3D geomodelling to provide sound constraints on the geometry, lithology, and mechanisms of the active landslides. By integrating all available geological data we reconstructed longitudinal and transversal cross-sections in MOVETM and performed implicit-surface interpolation in SKUA-GOCADTM, eventually obtaining solid objects corresponding to tectono-stratigraphic units that are dissected by the nested landslides. These volumes are populated with their rock mass properties, interpolated from boreholes and surface surveys. The geomodel shows a complex dome-and-basin folded structure, strongly constraining the spatial distribution and anisotropy of weaker rocks (e.g. serpentinites), and thus the geometry, kinematics, rock strength and shear zone properties of active landslides.

Based on the geomodel, we set up a continuum-based 3DFEM elasto-plastic model in MIDAS GTS-NXTM. Individual solids in the analysis domain were discretized into a 3D mesh of 150000 hybrid finite elements with variable size in the range 20-200 m. Rock masses were considered as Mohr-Coulomb materials with tensile cut-off and post-peak dilatancy, while shear zones were included explicitly. After stress initialization, the model was ran with a Shear Strength Reduction (SSR) technique. Model parameters were calibrated using a quantitative back-analysis approach, optimizing the fit between normalized GB-InSAR measured displacements and computed displacements, projected in the radar LOS. The calibrated model was validated against field evidence and effects on man-made structures, and provided a starting point for forward modeling of the slope response to groundwater perturbations. We considered the effects of groundwater changes for 5 scenarios of perched aquifers, and assessed critical conditions corresponding to different instability scenarios with different impacts on the hydropower facilities.

Our results show that an explicit account for 3D geometrical and geological complexities is key to a realistic modeling of large slope failure mechanisms, their impacts on critical infrastructures and the evaluation of related risks.

How to cite: Agliardi, F., Carnevale, A., Andreozzi, M., Bistacchi, A., Spreafico, M. C., Franzosi, F., Crippa, C., Ceriani, M., Rivolta, C., Crosta, G. B., and Castellanza, R.: Integrated 3D geological and Finite Element modeling of slow rock-slope deformations affecting hydropower facilities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11756, https://doi.org/10.5194/egusphere-egu22-11756, 2022.

EGU22-11877 | Presentations | NH3.5

Experimental study towards the investigation of scale effects in 3D granular slides 

Sazeda Begam and Valentin Heller

Granular slides can be defined as gravity-driven rapid movements of granular particle assemblies mixed with air and often also water. This ubiquitous phenomenon is not only observed in industrial applications such as hoppers, blenders and rotating drums, but also in natural contexts in the form of landslides, rockslides and avalanches. These granular slides in nature may cause devastation and human losses in their run-out path and indirect effects such as landslide-tsunamis, landslide dams and glacial lake outburst floods. The investigation of granular slides in nature is challenging due to the dangers in accessing the landslide locations in a timely manner and the challenges in predicting when and where they occur. Here, we use well defined and controlled three-dimensional (3D) laboratory experiments, building up on own (Kesseler et al., 2020*) and other studies, which were commonly limited to two dimensions (2D). The primary aim of the current study is to extend the scale effects investigation of Kesseler et al. (2020) to 3D and to provide new physical insight into 3D granular slides.

 

The experimental setup from Kesseler et al. (2020) has been upgraded from 2D to 3D by extending the side of the ramp and runout zone. The upgraded versatile 3 m long and 1.5 m wide ramp transitions via a curved section into a 3 m long and 2 m wide runout area. The measurement system, consisting of cameras recording the slide evolution and for general observations and a photogrammetry system to investigate the slide deposit shape including the runout, has been complemented with two laser distance sensors measuring the slide thickness along its centreline at two distinct positions during slide propagation.

 

In this initial study, we explore two different slide volume limits and, surprisingly, found a negative correlation between the slide volume and runout distance. Moreover, we identified a positive correlation between the slide thickness and slide volume. A positive correlation has also been identified between the maximum deposit height and the initial slide volume. Further, the good test repeatability is demonstrated with a detailed quantification and presentation of the characteristic variation plot at different time instances, involving the slide centroid and front velocities, the maximum slide thickness, the slide side expansion ratio and the locations of the slide deposit front- and backlines.

 

These findings may ultimately contribute to landslide and avalanche hazard assessments by providing an efficient and improved prediction of the slide kinematics, the slide evolution and the slide deposition features such as the runout distance. Moreover, once all experiments are conducted at different scales, we hope to be able to quantify and understand scale effects of granular slides and to improve the upscaling procedure from laboratory scale to nature.

 

 

*Kesseler, M., Heller, V., Turnbull, B. (2020) Grain Reynolds number scale effects in dry granular slides. Journal of Geophysical Research-Earth Surface 125(1):1-19.

 

How to cite: Begam, S. and Heller, V.: Experimental study towards the investigation of scale effects in 3D granular slides, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11877, https://doi.org/10.5194/egusphere-egu22-11877, 2022.

EGU22-11939 | Presentations | NH3.5

Investigation of rock slope failure processes in the Southern Swiss Alps 

Alessandro De Pedrini, Christian Ambrosi, Cristian Scapozza, Andrea Manconi, and Federico Agliardi

The evolution of rockslide processes towards failure events depends on the combination of geological and geomorphological properties, structural setting, and the glacial history of each site. The identification and analysis of the dominant factors affecting the spatial distribution and the temporal evolution of such massive phenomena are relevant not only for scientific purposes but also have large impacts on hazard assessments. Several large rockslide phenomena are located between five valleys north of Bellinzona, southern Swiss Alps, including the Riviera, Leventina and Blenio valleys in Canton Ticino, and the Calanca and Mesolcina valleys in Canton Grisons. The distribution of such phenomena is highly variable and appears to be higher along the eastern side of the Leventina Valley and the western side of the Blenio valley rather than in the rest of the region. Furthermore, the observed failure events range from 13.50 ka cal BP to 2002 CE, and many rockslides have not yet collapsed despite visible signs of surface deformation. The reasons for these differences in spatial and temporal distribution are yet unknown.  
Our research aims to define the influence and relationship of regional and local factors on the spatial and temporal rockslides distribution in this study area. We rely on an exceptional dataset including (i) detailed geological and geomorphological mapping of the area of study, (ii) a collection of historical data and scientific research on the activity of the large rock slope failures in Ticino and Grisons Cantons, (iii) detailed knowledge of the timing of deglaciation for several valleys of the Canton Ticino, (iv) a catalog of instabilities of the Canton of Ticino finalized in 2016, and (v) several results of current surface deformation activity constrained with satellite radar interferometry. Here we present the preliminary results of the activities performed to extend the rockslides catalog in the Calanca and Mesolcina valleys (Canto Grisons) obtained through the evaluation of stereo-photogrammetry datasets and evaluating the state of activity with satellite radar interferometry. Moreover, we will detail the approach used to set upslope stability modeling attempts at selected locations, combining techniques such as slope exposure dating, analysis of morphological parameters from digital elevation models, and analysis of structural data providing the dominant orientations of rock mass discontinuities.

How to cite: De Pedrini, A., Ambrosi, C., Scapozza, C., Manconi, A., and Agliardi, F.: Investigation of rock slope failure processes in the Southern Swiss Alps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11939, https://doi.org/10.5194/egusphere-egu22-11939, 2022.

EGU22-12009 | Presentations | NH3.5

Inventory and characterization of recent (<100 years) gravitational activity of the Queyras DSGSDs - South French Alps 

Clément Boivin, Jean Philippe Malet, Catherine Bertrand, and Yannick Thiery

Deep Seated Gravitational Slope Deformation (DSGSD) are gravitational processes damaging slopes over long periods of time. These processes may be reactived with the occurrence of smaller, shallow gravitational events. Thus, a better understanding of DSGSDs, from their formation to more catastrophic phases of activity, is an important goal  for natural hazard prevention in mountainous areas. .A first inventory of DSGSD in the Western Alps has been proposed by Crosta et al. (2013) with 1057 DSGSDs identified. A similar work has been conducted more recently at the scale of the French Alps by Blondeau (2018) who identified nearly 460 DSGSDs. Despite the importance of these works, there are still many Alpine sub-massifs where high concentrations of DSGSDs (Blondeau., 2018) have been recognized but where no detailed studies have been conducted. This is the case of the Queyras Massif (South French Alps). It is in this context that this study is carried out, with both the objectives of locating and characterizing the DSGSDs observed in this area and identifying their recent activity.

The proposed approach is based on quantitative geomorphological studies combining photo-interpretation of multi-date aerial imagery, analysis of DSMs and field observations. Quantitative description criteria are proposed to identify DSGSDs and discriminate them from large deep-seated landslides. Thirty DSGSDs are inventoried and their lithological and structural setting is analyzed. Analysis of multi-date aerial photographs and InSAR derived landslide velocities (NSBAS processing of Sentinel-1 observations; e.g. André et al., XX?) allow characterizing their gravitational activity.

How to cite: Boivin, C., Malet, J. P., Bertrand, C., and Thiery, Y.: Inventory and characterization of recent (<100 years) gravitational activity of the Queyras DSGSDs - South French Alps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12009, https://doi.org/10.5194/egusphere-egu22-12009, 2022.

EGU22-12124 | Presentations | NH3.5

Towards a national susceptibility map for rock avalanches 

Martina Böhme, Odd Andre Morken, Thierry Oppikofer, Reginald L. Hermanns, Ivanna Penna, Pierrick Nicolet, Marie Bredal, José Pullarello, and Francois Noël

Several rock avalanches with significant consequences have taken place in Norway during the last centuries. This has caused a high awareness with respect to this natural hazard. As a result, mapping of unstable slopes was initiated in 2006 and several high-risk unstable rock slopes have been identified and investigated in detail and today are monitored. Furthermore, the mapping program of unstable rock slopes has become systematic. Under this initiative, so far five out of eleven Norwegian counties have been analysed systematically for unstable rock slopes and the mapping has been completed for one of these counties. Registered slopes are mapped and classified based on a systematic hazard and risk classification system, established in 2012. This process is time intensive, and currently attention might not be given to the highest risk objects.

In order to get a rapid, complete national overview of potential large rock slope failures, as well as their total hazard and consequence potential, a national overview mapping project has been started. This will make it possible to better prioritize high risk objects in the systematic mapping program. The project will be divided into several steps: (1) systematic analysis of remote sensing data (e.g. detailed DEM, orthophoto and InSAR data) to locate potential unstable rock slopes; (2) a simplified hazard ranking; (3) semi-automated volume estimation; (4) automated run-out assessment; (5) and empirical displacement wave run-up height assessment.

In order to minimize the area that needs to be analysed in Step 1, presently known unstable rock slopes have been analysed. Results indicate that the study area can be restricted based on available relief, presence of inhabitants and distance to the shorelines (fjords and lakes). This makes it possible to reduce the study area significantly, from the total land area of Norway down to roughly one third of this. Furthermore, for this quick overview assessment we use a simplified hazard ranking that is based on signs of activity, visible grade of development and its volume.

The resulting susceptibility map will serve as a source to prioritize mapping and mitigation efforts, with respect to other natural hazards in Norway as well.

How to cite: Böhme, M., Morken, O. A., Oppikofer, T., Hermanns, R. L., Penna, I., Nicolet, P., Bredal, M., Pullarello, J., and Noël, F.: Towards a national susceptibility map for rock avalanches, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12124, https://doi.org/10.5194/egusphere-egu22-12124, 2022.

As a key part of landscape evolution and hazard to people in Alpine terrain, rock weathering leads to the breakdown and weakening of rock, causing rock fall and ultimately slope failure. Rock moisture availability is a major factor in these processes. It is understudied, partly due to a lack of reliable measurement techniques. Most frost weathering tests in the laboratory to date have been conducted with fully saturated specimens, which is often not the case under natural conditions.

As part of the DFG-funded CLIMROCK project, we performed laboratory based experiments in a climate cabinet looking at rock moisture movement during frost cracking cycles and its relation to rock weathering. A selection of Wettersteinkalk (limestone) blocks of 40 x 40 x 20 cm size were used, some of which were compact and some of which were highly fractured. The blocks saturated with water to different degrees (0%, 50%, 100%) and were insulated on the side faces. In different test runs, the base of the individual blocks were either left uncovered to allow water seeping through, also isolated at the base to create Different sensor types including Time Domain Reflectometry (TDR), Electrical Resistivity (ER) and Microwave sensor (MW) were used to quantify rock moisture levels and movement during freeze-thaw cycles of different duration. As a measure of relative rock weathering contact Acoustic Emissions (AE) loggers were used to detect subcritical cracking. Calibration of these instruments will be individual to each block.

Initial findings show marked movement of rock moisture at the beginning of the cycles with possible evidence of cryosuction down to 36cm depth from rock surface. Particularly strong moisture migration is seen in 50% and 100% samples at 25cm depth, though not when the sample is initially dry. There is also evidence of migrations to the freezing front and probable subsequent refreezing events.

Further test runs with different saturation levels (75%, 90%) are planned. Observations of moisture movements and weathering effects from the laboratory experiments will be applied to the interpretation of field rock moisture data from ongoing CLIMROCK studies in the Bavarian and Austrian Alps.

How to cite: Mitchell, A. and Sass, O.: Movement of moisture during frost cracking cycles: First laboratory results from the CLIMROCK project., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12182, https://doi.org/10.5194/egusphere-egu22-12182, 2022.

EGU22-12230 | Presentations | NH3.5

Toward national-covering dynamic rockfall simulations: adapting stnParabel with efficiency in mind 

François Noël, Thierry Oppikofer, Michel Jaboyedoff, Reginald Hermanns, Martina Böhme, and Synnøve Flugekvam Nordang

Working with 3D point clouds offers many benefits for reducing the subjectivity of rockfall simulations at a local scale. Indeed, many “dynamic” rockfall rebound models are strongly affected by the topography and the perceived surface roughness, which can be objectively represented with detailed terrain models. This reduces the need for complex time intensive back analyses and associated sensitive adjustments of parameters used for subjectively adjusting the simulations to the desired runout distances.

Predictable and reproductible simulations from a constrained set of parameters while still managing to reproduce observed runouts on a wide range of sites could be time saving for practitioners and their clients, ultimately improving quality at lower costs to the society. This could speed up the process for practitioners to deliver concise reports easier to interpret and quality-check by a wider range of employees on the client side.

However, working with 3D point clouds can have a steep learning curve and quickly becomes impractical at a larger scale for regional analysis, partially obscuring some of the previously mention advantages. To explore potential ways to circumvent these issues, a prototype of an algorithm that runs the stnParabel rockfall simulation freeware in batch was quickly implemented in 2020. It was developed to expand such dynamic simulation capabilities to larger regions and up to potentially national-covering capabilities.

Slight modifications were done on the impact detection algorithm to also work with high resolution gridded terrain models (DTMs) with a focus at not sacrificing the benefits of working on 3D point clouds. The sources biases due to the stretched grided cells underrepresenting the steep cliffs are worked around by randomly distributing the sources based on the 3D stretched surface occupied by the cells.

Preliminary results were produced regionally over 6000 km2, involving 115 000 000 simulated rockfalls with 10 m3 blocks of dimensions 3.8x3.2x1.8 m. The simulations were performed on the Norwegian national 1 m DTM from airborne LiDAR, up sampled to 50 cm cells for future proofing the approach. They were produced at a rate of about 15 000 000 simulated 3D trajectories per hour when ran on a small Ultrabook laptop with fast SSD.

The preliminary results from the dynamic rockfall model were then combined with databases of observed deposited blocks from previous rockfall events to act as a calibration guide for FlowR model. This simpler model based on gridded topographic-hydrologic spreading and sliding block approaches can be adjusted to produce a wide range of desired runouts envelopes from numerous processes, like rockfalls. The simpler simulations on 10 m DTM were used as a candidate for the revision of the national rockfall susceptibility mapping methodology.

The prototype approach to run detailed dynamic rockfall simulations regionally would require validations. Such potentially useful approach with objective dynamic simulations for hazard mapping as well as for the design of mitigation measures could then be shared through publications and be implemented in the distributed rockfall simulation freeware stnParabel. 

How to cite: Noël, F., Oppikofer, T., Jaboyedoff, M., Hermanns, R., Böhme, M., and Flugekvam Nordang, S.: Toward national-covering dynamic rockfall simulations: adapting stnParabel with efficiency in mind, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12230, https://doi.org/10.5194/egusphere-egu22-12230, 2022.

EGU22-12412 | Presentations | NH3.5

Automated delimitation of rockfall runout zones using high resolution trajectory modelling at regional scale 

Luuk Dorren, Christine Moos, and Christoph Schaller

More than ten years ago, Swiss-wide rockfall modelling was carried out to indicate potential hazard areas and rockfall protection forests within the framework of the SilvaProtect-CH project. The forest effect itself was not included in these models and only one block size (1 m3) was calculated. The aim of our study was to model rockfall runout zones using Rockyfor3D for block size scenarios ranging from 0.05 – 30 m3 with explicit inclusion of the protective effect of the forest for an area of approx. 7200 km2 in Switzerland and Liechtenstein with a 2m-resolution. For the determination of the start cells as well as the slope surface characteristics, we used the terrain morphometry derived from a 1m-resolution digital terrain model as well as the Swiss TLM geodata and information from geological maps. The forest structure was defined by individual trees with their coordinates, diameters and tree type (coniferous or deciduous). These were generated on the one hand from detected individual trees and on the other hand from statistical relationships between the detected trees, remote sensing-based forest structure type definitions and stem numbers from field inventory data. Based on the latter, we generated forest strata in addition to the detected individual trees. The delimited rockfall runout zones automatically derived from the simulated reach probability maps were validated with 1554 mapped historical rockfall events. The results of the more than 78 billion simulated trajectories showed that 94% of the mapped silent witnesses could be reproduced by the simulations and 78% were within the delimited runout zones. The median of the volume of the non-reproduced silent witnesses was 0.1 m3, which led us to a hypothesis, that these mapped blocks could partly be deposited fragments from larger blocks. We conclude that a rockfall simulation with explicit consideration of the forest effect at 2m-resolution with plausible results is possible for very large areas.

How to cite: Dorren, L., Moos, C., and Schaller, C.: Automated delimitation of rockfall runout zones using high resolution trajectory modelling at regional scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12412, https://doi.org/10.5194/egusphere-egu22-12412, 2022.

Technology advances and rising population has led to the establishment of geoengineering projects such as dams, tunnels, bridges, road network, etc. in the mountainous terrain which causes slope destabilization. National Highway-5 connects Shimla, Kinnaur, Kullu, and China border to the rest of the country. The route is of paramount importance for defense and security purposes. The area encompasses complex geomorphological and geological terrain and often encounters road cut slopes susceptible to failure. In the present study, a detailed geotechnical investigation is carried out around Dhalli Landslide (September, 2017) and Malyana Landslide (August, 2018) along NH-5, Shimla, Himachal Pradesh. RMR, SMR, kinematic analysis and numerical modeling using the finite element modelling (FEM) technique is applied for the aforementioned two slopes and its nearby area. Kinematic analysis of joint data shows that rocks are prone to mainly wedge and planar failures. The RMR results show that the slopes belong to fair (Class III) and weak (Class IV) category. The SMR results for the slopes show that slopes lie in the completely unstable (Class V) category, unstable (Class IV) category and in the partially stable (Class III) category. The Strength Reduction Factor (SRF) was calculated using RS2 module of Rocscience. The SRF for both the slopes was less than 1 which shows that the slopes are completely unstable. Dominating factors responsible for the slope instability are identified and accordingly, some suggestions are proposed to strengthen the stability of road cut slope.

 

How to cite: Singh, J., Thakur, M., and Kishore, N.: Slope Stability Assessment of Rock Slopes Using Finite Element Modelling Along National Highway-5, Shimla, Northwestern Himalaya, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12612, https://doi.org/10.5194/egusphere-egu22-12612, 2022.

EGU22-12639 | Presentations | NH3.5

A complete rockfall inventory across twelve orders of magnitude. 

Benjamin Jacobs, Florian Huber, and Michael Krautblatter

Understanding the magnitude-frequency relationship of rock falls is one of the most important issues for both geomorphologists assessing sediment budgets as well as public stakeholders evaluating rock fall hazards. Multi-temporal Terrestrial Laser Scanning (TLS) surveys, or more general LiDAR, is often applied to produce rock fall inventories of event magnitudes and their frequency. However, LiDAR-based rock fall inventories systematically miss or underestimate both ends of the magnitude bandwidth.

Here we present the first attempt of a complete rock fall inventory including the full spectrum of magnitudes, ranging from fragmental rock falls (cm³) to Bergsturz-sized events (106 m³). We combine rock fall inventories derived from multi-temporal TLS campaigns over six years, rock fall collectors and the historic record in a previously intensely investigated study area (Reintal, German Alps). We investigate which factors – such as structural geology, systematic sampling limitations or different rock fall processes – can lead to possible misinterpretation of rock fall inventories regarding geomorphic systems.

The study shows that (i) LiDAR-based rock fall inventories do not cover the full spectrum of rock fall magnitudes due to their limitations in temporal and spatial resolution, (ii) structural geological features control the magnitude/frequency relation beyond the roll-over of these inventories and (iii) taking fragmentation as well as a clear distinction between rock fall processes into account when analysing rock fall inventories is crucial.

How to cite: Jacobs, B., Huber, F., and Krautblatter, M.: A complete rockfall inventory across twelve orders of magnitude., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12639, https://doi.org/10.5194/egusphere-egu22-12639, 2022.

EGU22-12804 | Presentations | NH3.5

Collapse, fragmentation, high-speed boulders, and dust cloud: analysis of the 2017 Pousset (Cogne, Val D’Aosta) rockslide in Northern Italy 

Giovanni Crosta, Giuseppe Dattola, Fabio De Blasio, Camilla Lanfranconi, and Davide Bertolo

The dynamics of rock fragmentation during the collapse of a rock avalanche, a rockfall, or an extremely energetic rockfall, is insufficiently known (De Blasio et al., 2018). Fragmentation especially at the base of a rock avalanche may affect on the one hand the dynamics of the rock avalanche and the geometry of the final deposit. On the other hand, fragmentation in the upper layers produces a dust of rock particles which: i) impacts energetically with the surrounding areas, and in a later stage, ii) propagates as a dust cloud. Although such dynamics are commonly observed, they are still inadequately addressed.

Recently, a rock avalanche in the Italian Alps occurred in November 2017, giving us the possibility to investigate these phenomena in better detail. In particular, we analysed a  8,000 m3 collapse of serpentinites and metabasics (Grivola-Urtier metaophiolitic Unit) from the Pousset peak (Aosta Valley Region in Western Italian Alps). The peak collapsed from an average height of 2800 m a.s.l. to the foot of the slope 800 m below, where it completely disintegrated. The impact on the ground produced a rock dust cloud which subsequently flowed downstream over the successive few minutes.  The site was visited immediately after the event, and it was possible to investigate the fresh deposit of rock dust before alteration by climate or weathering. This collapse thus represents an interesting case study for trying to determine the energy threshold required for fragmentation and dust cloud formation, the redistribution of the kinetic energy after impact and the amount related to cloud generation within the energy balance.

After identifying in situ the main characteristics of the collapse, we then concentrated our efforts on a more quantitative understanding of the event via numerical calculations. We reproduced the blocks trajectories and computed the impact points where a strong energy dissipation occurred by using the 3D rockfall simulator code HY-STONE (Crosta & Agliardi 2004; Frattini et al. 2012). In these points, the block fragmentation has been taken place and the formation of dust occurred. Through laboratory analysis of dust samples collected from the few centimetres thick deposits on trees and paths, we determined the particle size frequency curves for each location. The fragmentation energy was then estimated by integrating the spectrum of the grains assuming that the fragmentation energy is proportional to the area just created.

Once obtained the fragmentation energy, we estimated the maximum speed and runout of the dust cloud and the settling time using a simple model for suspension flows. From the analysis of the results obtained in the three described procedures, the fragmentation energy was found to be a relatively small fraction of the initial energy of the landslide, and the calculated flow rate of the suspended powder was found to be compatible with the one observed, even though flowage parameters for the cloud still need to be understood from first principles. In conclusion this case study, even if volumetrically small (or perhaps because of it), may add interesting information on the ongoing debate about rock fragmentation in catastrophic events.

 

 

How to cite: Crosta, G., Dattola, G., De Blasio, F., Lanfranconi, C., and Bertolo, D.: Collapse, fragmentation, high-speed boulders, and dust cloud: analysis of the 2017 Pousset (Cogne, Val D’Aosta) rockslide in Northern Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12804, https://doi.org/10.5194/egusphere-egu22-12804, 2022.

Giant rock avalanche is extremely rare worldwide, while giant rock avalanche developed in suture zone has presented unique development characteristics. The suture zone is a product of plate moving and strong tectonic activity, where the appearance of a giant avalanche not only plays a barometer role for the regional disaster development environment but an indicator role for the complicated geological environment. In 2019-2021, the author has found a giant paleo-rock avalanche (name Basu avalanche) in the Bangonghu-Nujiang suture zone of the Tibetan Plateau. Some infrequent characteristics such as huge volume, development in nappe structure, and hyper-mobility (debris impact height > 600m) appeared for this giant rock avalanche. In this paper, based on the detailed investigation, 36Cl dating, and reconstructing the pre-avalanche terrain methods, the development, failure, and hyper-mobility of this giant rock avalanche have been analyzed. The result shows that: (1) The volume of the Basu avalanche is about 3.5×109m3, the residue is about 1.4×109m3 now. The avalanche occurred at 205.70±7.71ka B.P.(ka: millennium), subsequent the accumulation body occurred two times secondary landslides (name Duolasi landslide) at 17.57±0.72ka B.P. and 7.01±0.32ka B.P., respectively; (2) The nappe structure, formed from the uplift and orogeny process of the suture zone, controls the development and volume size of the Basu avalanche, while the strong earthquake is the biggest likely to trigger the avalanche finally failure because of the dense active faults distribution; (3) Because of the rich Ultrabasic clasts derived from the F2 fault and fine particles produced by cataclastic rock mass, the Basu avalanche formed the slide belt that thickness from centimeters to meters during the motion. The lubrication effect of the slide belt has dominated the avalanche debris's high-speed motion and hyper-mobility, the mechanism is that: due to the huge avalanche volume and induced the high pressure and closed slide belt environment, the slide belt fine-grain formed the lubrication layer with certain water involved, and the friction force sharply decreased; (4) Because of the Basu rock avalanche and the debris flow successive blocked the Leng River, the Leng River valley has experienced diversions process and the river valley from the ’S’ shape to approximate straight-line shape.

How to cite: Gao, Y. and Zhao, S.: A new perception in the development, failure, and hyper-mobility of a giant rock avalanche in the suture zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13034, https://doi.org/10.5194/egusphere-egu22-13034, 2022.

EGU22-16 | Presentations | ERE5.1

Statistical bounds on how induced seismicity stops 

Ryan Schultz, William Ellsworth, and Gregory Beroza

Earthquakes caused by human activities receive scrutiny due to the risks and hazards they pose.  Seismicity that occurs after the causative anthropogenic operation stops has been particularly problematic – both because of high-profile cases of damage caused by this trailing seismicity and due to the loss of control for risk management.  With this motivation, we undertake a statistical examination of how induced seismicity stops.  We borrow the concept of Båth’s law from tectonic aftershock sequences.  Båth’s law anticipates the difference between magnitudes in two subsets of seismicity as dependent on their population count ratio.  We test this concept for its applicability to induced seismicity, including ~80 cases of earthquakes caused by hydraulic fracturing, enhanced geothermal systems, and other fluid-injections with clear operational end points.  We find that induced seismicity obeys Båth’s law: both in terms of the magnitude-count-ratio relationship and the power law distribution of residuals.  Furthermore, the distribution of count ratios is skewed and heavy-tailed, with most earthquakes occur during stimulation/injection.  We discuss potential models to improve the characterization of these count ratios and propose a Seismogenic Fault Injection Test to measure their parameters in situ.  We conclude that Båth’s law quantifies the occurrence of earthquake magnitudes trailing anthropogenic operations.

How to cite: Schultz, R., Ellsworth, W., and Beroza, G.: Statistical bounds on how induced seismicity stops, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-16, https://doi.org/10.5194/egusphere-egu22-16, 2022.

EGU22-2160 | Presentations | ERE5.1

Identification of The Processes Triggering Induced Seismicity at the Enhanced Geothermal System of Basel (Switzerland) 

Auregan Boyet, Silvia De Simone, and Vìctor Vilarrasa

Felt induced seismicity compromises the public perception on the deployment of geothermal power-plants in urban areas. Large induced earthquakes have led to the shutdown of Enhanced Geothermal Systems (EGS), such as Basel (Switzerland) and Pohang (Republic of Korea). In the majority of induced seismicity cases in EGS, the largest events occur after shut-in. Different mechanisms can trigger induced seismicity. Pore pressure diffusion is established as the most common triggering mechanism. It reduces the effective normal stress acting across pre-existing fault surfaces, weakening the shear resistance and allowing slip of faults. However, this is not the only triggering mechanisms and it cannot explain the large magnitude of post-injection induces seismicity. Additional influencing processes are poromechanical elastic stressing, shear stress transfer and local tectonic settings. Considering theses mechanisms simultaneously can provide a better understanding of the causes of post-injection seismicity and could allow to develop strategies to mitigate the occurrence of earthquakes with high magnitude. To explain these processes, we investigate the induced seismicity that led to the closure of the Basel EGS project. We set-up a hydro-mechanical finite element numerical model which contains faults corresponding with the clusters of induced events at Basel. We study the reactivation of these pre-existing fractures using a viscoplastic model. We are able to identify the process combinations bringing faults to failure. During injection, faults fail due to pore pressure diffusion in the vicinity of the well, and due to poroelastic stressing further in the reservoir. After the injection shut in, poroelastic stressing and shear stress transfer trigger seismicity, being the most relevant triggering mechanisms of post-injection induced seismicity.

How to cite: Boyet, A., De Simone, S., and Vilarrasa, V.: Identification of The Processes Triggering Induced Seismicity at the Enhanced Geothermal System of Basel (Switzerland), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2160, https://doi.org/10.5194/egusphere-egu22-2160, 2022.

Occurred in the Delaware Basin, western Texas, near the town of Mentone, the Mw 5.0 Mentone earthquake is one of the largest induced earthquakes in the central US. Within 25 km of the epicenter, there are a few deep injection wells to the northwest injecting in the high permeable limestone layer at about 22 km averagely, as well as a lot of shallow wells injecting in the upper high permeable sandstone layer at around 18 km averagely. Between the shallow sandstone and deep limestone layers is a thick shale layer with low permeability, which excludes the possibility of downward percolation of the injected fluid in the shallow injection layer. However, the cumulative injection volume of shallow injection wells is about five times as much as that of deep injection wells. Motivated by this, we investigate whether the shallow injection wells may play a role in triggering the Mw 5.0 Mentone earthquake through the injection-induced coupled poroelastic stress perturbations. We first perform focal mechanism inversion and earthquake relocation with the Cut and Paste (CAP) and hypoDD methods, respectively, to constrain the fault plane on which the Mw 5.0 event occurred. A south-facing fault plane with strike/dip of 81o/52o is successfully fitted. We then calculate the change of the Coulomb failure stress (ΔCFS) caused by the shallow injection wells at the mainshock location based on the linear fully coupled poroelastic stress model. The calculated ΔCFS of shallow injection wells is approximately 20 kPa and it is mostly contributed by the change in coupled poroelastic stress. Based on findings from other studies, this value of ΔCFS is sufficient in reactivating faults that are well aligned with the local stress field. Since we only account for about half of the total injection volume from the shallow wells in the calculation, we also hypothesize that the actual perturbations caused by shallow injection wells via the coupled poroelastic stress change would be more prominent. Our result reveals the vital role of injection-induced coupled poroelastic stress in triggering seismicity, especially in low permeable geologic settings.

How to cite: Tan, X. and Lui, S. K. Y.: The non-negligible contribution of shallow injection wells on the triggering of the Mw 5.0 Mentone earthquake via coupled poroelastic stress perturbations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3271, https://doi.org/10.5194/egusphere-egu22-3271, 2022.

EGU22-4117 | Presentations | ERE5.1

Acoustic Precursors to Laboratory Induced Fault Slip and Failure 

Aukje Veltmeijer, Milad Naderloo, and Auke Barnhoorn

With human activities in the subsurface increasing, so does the risk of induced seismicity. For mitigation of the seismic hazard and limiting the risk, monitoring and forecasting are essential. A laboratory study was performed to find precursors to fault failure. In this study, Red Pfaelzer sandstones samples were used, which are analog to the Groningen gas reservoir sandstones. A saw-cut fault was cut at 35 degrees, and the samples were saturated. Fault slip was induced by loading the sample at a constant strain rate, and simultaneously active acoustic transmission measurements were performed. Every 3 seconds 512 S-waves were sent, recorded, stacked to reduce the signal-to-noise ratio, and analyzed. The direct seismic wave velocity, coda wave velocity, and transmissivity were monitored before and during the reactivation of the faulted samples. Different loading patterns and confining pressures were investigated in combination with active acoustic monitoring. Velocity and amplitude variations were observed before the induced fault slip and can be used as precursory signals. Two methods to determine changing velocities were used. Direct S-wave velocities are compared to velocity change obtained by coda wave interferometry. Both analyses gave similar precursory signals, showing a clear change in slope, from increase to decreasing velocities and amplitudes prior to fault reactivation. Fault reactivation is preceded by fault creep and the destroying of some of the asperities on the fault plane, causing the seismic wave amplitude and velocity to decrease. Combining all precursors, the onset of fault slip can be determined and therefore upcoming slip can be forecasted in a laboratory setting. Our results show precursory changes in seismic properties under different loading situations and show a clear variation to the onset of fault reactivation. These results show the potential of continuous acoustic monitoring for detection and forecasting seismicity and help the mitigation of earthquakes.

How to cite: Veltmeijer, A., Naderloo, M., and Barnhoorn, A.: Acoustic Precursors to Laboratory Induced Fault Slip and Failure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4117, https://doi.org/10.5194/egusphere-egu22-4117, 2022.

EGU22-4177 | Presentations | ERE5.1

Fault reactivation process in the laboratory: The role of stress cycling and pressurization rate 

Milad Naderloo, Aukje Veltmeijer, and Auke Barnhoorn

Over the last few decades, it has become apparent that different human activities in the subsurface, such as water waste injection, hydraulic fracturing, and geothermal energy production can lead to induced seismicity. Understanding the effects of fluid injection-related parameters on seismic response or evolution of it is essential for finding a method to manage and minimize the induced seismicity risk. Experimental and numerical studies indicate that varying injection patterns and rates can be used to effect and/or mitigate seismicity. However, most of the studies are for intact rock medium, and the mechanism of injection-induced seismicity of faulted rock medium is not clear yet. In this study, we performed fault reactivation experiments on faulted (saw-cut) Red Pfaelzer sandstones to provide new insight into the effect of stress/pressure cycling and rate on fault slip behavior and seismicity evolution. The saw-cut samples were subjected to two different reactivation mechanisms: 1) stress-driven and 2) injection-driven fault reactivation. Three different reactivation scenarios were performed during the stress-driven fault reactivation experiments: continuous sliding, cyclic sliding, and under-threshold cycling sliding. Ten AE transducers were used to detect microseismicity during the fault reactivation experiments, and consequently, different microseismic parameters, such as frequency-magnitude distribution (b-value), AE energy, and AE rate were estimated. Stress-driven fault reactivation experiments showed that (i) a below-threshold cycling scenario prevents seismicity and pure shear slip; however if the shear stress exceeds the previous maximum shear stress, seismicity risk increases drastically in terms of b-value, maximum AE energy, and magnitude. (ii) Compared to continuous sliding, cyclic sliding triggers less seismicity in terms of total b-value and large AE events due to the uniform reduction in roughness and asperity on the fault plane. (iii) By increasing the number of cycles, in general, the number of generated events and AE energy per cycle is reduced. Nevertheless, there is a risk of generating large AE events during the first cycles. In addition, results from the injection-driven fault reactivation experiments demonstrated that high injection rate results in higher peak slip velocity. Compared to the stepwise injection pattern, the cyclic recursive injection scenario showed higher peak slip velocity, due to the high hydraulic energy budget and fault compaction. A proper injection strategy needs to consider various factors, such as fault drainage, critical shear stress, injection rate, and injection pattern (frequency and amplitude). Our results demonstrate that selecting proper stress/pressure amplitude, and pressurization rate for the injection design strategy can help to reduce seismicity risk.  

How to cite: Naderloo, M., Veltmeijer, A., and Barnhoorn, A.: Fault reactivation process in the laboratory: The role of stress cycling and pressurization rate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4177, https://doi.org/10.5194/egusphere-egu22-4177, 2022.

EGU22-4204 | Presentations | ERE5.1

Injection-rate control on deformation and stress of an experimental fault in granite 

Yinlin Ji, Lei Wang, Hannes Hofmann, Grzegorz Kwiatek, and Georg Dresen

In this study, we conducted injection-driven shear tests on a sawcut fault in granite samples using a triaxial deformation apparatus. The granite samples were drilled from Odenwald basement rocks in Germany. The sawcut fault, inclined 30° to the sample axis, was ground using sandpaper with a particle size of 201 µm. Two boreholes (nominal diameter 1.8 mm) were drilled near the short edge of each sample half to allow direct fluid access to the fault surface. Eight strain gauges, and eight pairs of acoustic emission (AE) sensors attached on the sample surface were used to monitor the deformation, local strain and AE events. 

During the experiments, we first measured the peak shear strength of the faulted sample by advancing the axial piston at a constant rate of 1 µm/s under 36 MPa confining pressure and 1 MPa pore pressure. We then adjusted the shear stress to be 90% of the peak shear strength. Subsequently, the piston was fixed, and the first injection-driven shear test was initiated by injecting distilled water from the bottom borehole at a rate of 0.2 mL/min. We observed three full cycles of fast slip events until the injection pressure was increased up to approximately 18 MPa. We then reduced the pore pressure to the initial 1 MPa and the axial force was removed, followed by the second injection-driven shear test conducted at a higher injection rate of 0.8 mL/min using the same procedure as in the first test. We also observed three episodes of fast slip events until the injection pressure was increased to about 20 MPa. Fluid pressures were monitored continuously at the top and bottom boreholes. We employed a COMSOL model to obtain the time-dependent fluid pressure distribution along the sawcut fault during fluid injection.

For slow fluid injection, we find that the fault surface near the center experiences slight normal dilation and gradual shear stress release prior to the fast slip event. In contrast, for high-rate fluid injection, the same fault patch exhibits normal compaction and shear stress increase preceding fast slip. In both cases, significant normal dilation and abrupt shear stress drops were observed near the fault center during fast slip events. The distinct evolution of local fault deformation and stress are likely attributed to the distribution of slow slipping patches, as signified by the fluid pressure distribution and Mohr-Coulomb failure envelope. At slow injection rate, slow precursory slip may have occurred on the entire fault, initiating a fast slip event. In contrast, at higher rates, slow slip may have been localized around the injection port, resulting in local stress concentration beyond the slow slipping patch. Our results demonstrate that the evolution of local fault deformation and stress can be diverse in different fault patches, depending on the relative location to the fluid pressurized zone and the resulting slow slipping patch. This suggests that the strongly heterogeneous fault deformation should be considered when analyzing the precursors to injection-induced fault reactivation.

How to cite: Ji, Y., Wang, L., Hofmann, H., Kwiatek, G., and Dresen, G.: Injection-rate control on deformation and stress of an experimental fault in granite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4204, https://doi.org/10.5194/egusphere-egu22-4204, 2022.

EGU22-4703 | Presentations | ERE5.1

The DEEP Project: Innovation for De-Risking Enhanced Geothermal Energy Projects 

Federica Lanza and Stefan Wiemer and the DEEP team

The Swiss Energy Strategy 2050 anticipates that by 2050 up to ~7% of the future energy production will come from deep geothermal energy. Likewise, many other countries worldwide are investigating the potential of harnessing deep geothermal energy as a renewable solution. However, seismic risk reduction and reservoir efficiency is the current major coupled problem faced by Enhanced Geothermal System (EGS) reservoirs. Balancing risk and economic output is a key requirement in all EGS projects. The DEEP (Innovation for De-risking Enhanced geothermal Energy Projects) project is an international collaboration whose research-goal is to establish a full-scale protocol for real-time monitoring and risk analysis of potential seismicity triggered by EGS operations. To this end, the project will employ innovative seismic sensors, improved event-cataloguing techniques, fully probabilistic data-driven seismicity forecasts, and loss assessment strategies. In DEEP we plan to apply the so-called Adaptive Traffic Light System (ATLS) where forecasts are continuously updated with real-time data-feeds, providing an integrated and dynamic assessment of the seismic risk to the operators. Field test sites include the Frontier Observatory for Research in Geothermal Energy (FORGE) in Utah (USA), as well as at EGS sites in Germany and France. Parallel to the technology development, the project aims also at defining the next-generation good-practice guidelines and risk assessment procedures in order to reduce commercial costs and enhance the safety of future projects. Here, we will present an overview of the DEEP project to provide a framework for other DEEP presentations. We will also showcase a selection of results from new event detection and location algorithms based on machine learning and using Distributed Acoustic Sensing (DAS), as well as the results from a pilot test of the ATLS workflow for seismicity forecast models for the upcoming FORGE stimulation strategy.

How to cite: Lanza, F. and Wiemer, S. and the DEEP team: The DEEP Project: Innovation for De-Risking Enhanced Geothermal Energy Projects, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4703, https://doi.org/10.5194/egusphere-egu22-4703, 2022.

EGU22-5332 | Presentations | ERE5.1

Thermal stressing is likely to reactivate distant faults in hot sedimentary aquifers 

Iman Rahimzadeh Kivi, Estanislao Pujades, Jonny Rutqvist, and Victor Vilarrasa

The widespread development of geothermal energy is deemed to accelerate the transition to a low-carbon future. Hot Sedimentary Aquifers (HSA) provide cost-effective and non-intermittent geothermal resources. However, HSA development has reportedly been associated with seismic events, harming the public perception of exploiting these resources. This work digs deeper into thermo-hydro-mechanical (THM) mechanisms raised by water circulation in a HSA and their control on fault reactivation. We numerically simulate the problem by a 2D plane-strain model. The model consists of a porous and permeable hot aquifer sandwiched between the tight seal and base rocks and laterally bounded by two normal faults, representative of extensional tectonic environments. The horizontal injection-production well pairs are spaced 500 m apart at the middle of the aquifer, and the faults are located on each side of the doublet at a distance of 1 km. We consider two scenarios: low-permeability faults, mimicking a compartmentalized reservoir, and high-permeability faults, across which fluid flow takes place with further ease. We show that the fault permeability governs the hydraulic response of the reservoir. While the pore pressure slightly increases around the injector and decreases around the producer for the case of high-permeability faults, the compartmentalized reservoir experiences a global pore pressure decline. The latter is supported by the fact that the injected cold water is denser than the extracted hot water and occupies less space in the pore system. As soon as the thermal breakthrough occurs, which is after 12 years in the current setting, a more uniform temperature distribution across the doublet is established and the pressure begins to increase in the vicinity of the injector. Provided the high permeability of the reservoir rock, pore pressure and poroelastic stress perturbations impose rapid but minor effects on the fault stability. On the contrary, the cooling front formed around the injector lags much behind the pore pressure front toward the fault. The reservoir cooling contracts the rock and triggers stress reductions. Thermal stresses are transmitted much ahead of the cooled region and destabilize the fault located on the injection side. The fault begins to slip after 18 and 21 years of circulation for the high- and low-permeability scenarios, respectively. The reservoir pressure decrease in the latter case, attenuating the fault slip tendency, feeds into the observed difference in reactivation timings. Although thermal stresses initiate the slip, the static stress transfer jointly contributes to rupture nucleation along the fault. Interestingly, the slip-induced shear stress release, tied to a slip weakening frictional behavior, slows down elastic energy build-up on the other fault closer to the production well and impedes its reactivation. Our findings on the prolonged but dominant role of thermal stresses on the reactivation of distant faults have direct implications for safe and long-term production from geothermal systems.

How to cite: Rahimzadeh Kivi, I., Pujades, E., Rutqvist, J., and Vilarrasa, V.: Thermal stressing is likely to reactivate distant faults in hot sedimentary aquifers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5332, https://doi.org/10.5194/egusphere-egu22-5332, 2022.

EGU22-5398 | Presentations | ERE5.1

Characterizing induced seismic events in the Groningen gas field using an efficient Hamiltonian Monte Carlo sampler: a case study 

La Ode Marzujriban Masfara, Cornelis Weemstra, and Thomas Cullison

In May 2019, an earthquake with a magnitude of 3.4 (local magnitude) hit the area of the Westerwijtwerd village in the province of Groningen, the Netherlands. The event is the result of the gas extraction in the Groningen gas field and is one of the largest events to date. To better understand the source characteristics of the event, we apply a probabilistic full-waveform inversion technique that we recently developed to the event's recordings. Specifically, we use a variant of the Hamiltonian Monte Carlo (HMC) algorithm. When sampling high-dimensional model spaces, HMC is proven to be more efficient than the generic Metropolis-Hasting algorithm. Compared to probabilistic inversions of tectonic events, two main challenges arise while applying the algorithm. First, the prior information of the event is usually incomplete and inaccurate. That is, the only available information is (an estimate of) the hypocenter and origin time. Second, the frequency content of the induced event's seismograms is higher than that of typical tectonic events. This implies a higher non-linearity, which in turn complicates the ability of a probabilistic inversion algorithm to sample the model spaces, particularly when considering the first challenge. Consequently, to address both challenges, first, we develop a procedure to estimate the necessary prior information and use it as input to the HMC variant. Second, we run our HMC algorithm iteratively to mitigate the non-linearity. Using the relatively detailed velocity model of the Groningen gas field, we eventually estimate ten posteriors of the source parameters. The latter being the hypocenter (three parameters), the moment tensor (six independent parameters), and the origin time.  

How to cite: Masfara, L. O. M., Weemstra, C., and Cullison, T.: Characterizing induced seismic events in the Groningen gas field using an efficient Hamiltonian Monte Carlo sampler: a case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5398, https://doi.org/10.5194/egusphere-egu22-5398, 2022.

EGU22-5536 | Presentations | ERE5.1

Modeling of injection-induced seismicity in fractured rock masses with TOUGH3-seed hybrid solver 

Federico Ciardo and Antonio Pio Rinaldi

Injection of fluid in fractured reservoirs triggers seismicity that migrates away from injection point. The enlarging cloud of (micro-)seismicity can be driven by pore-fluid diffusion within fractured rock mass, thus propagating in space proportional to square root of time for an effective isotropic and homogenous medium, or by elastic-stress interactions between over-stressed pre-existing fractures.

In this contribution we adopt an hybrid approach to model seismicity evolution driven by pore-fluid propagation into a Discrete Fracture Network and apply it to a large-scale injection experiment at FORGE Test Site in Utah (USA). We couple a statistical seed model for seismicity with a physic-based solver for non-linear pore-fluid diffusion into a three-dimensional DFN (using TOUGH3). Local inelastic permeability changes mimick irreversible deformations and affect pore-fluid evolution and hence seismicity cloud.

Several synthetic catalogs are generated and compared with one generated with a pure physic-based numerical solver.

 

How to cite: Ciardo, F. and Rinaldi, A. P.: Modeling of injection-induced seismicity in fractured rock masses with TOUGH3-seed hybrid solver, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5536, https://doi.org/10.5194/egusphere-egu22-5536, 2022.

EGU22-5576 | Presentations | ERE5.1

Deciphering fluid extraction-induced earthquake nucleation in Groningen under rate-strengthening friction 

Meng Li, Andre R Niemeijer, Femke C Vossepoel, and Ylona van Dinther

Induced seismicity triggered by fluid injection or extraction has been studied extensively in recent years. However, models relying on a Mohr-Coulomb yield criterion for interseismic loading or using a linear slip-weakening friction law for dynamic earthquake rupture cannot quantify well how much aseismic slip accumulates prior to nucleation or how to explain nucleation. Instead, a rate-and-state friction law is extensively utilized in earthquake cycle models to resolve and understand earthquake nucleation. Moreover, laboratory experiments indicate that the relevant lithologies in the Groningen subsurface are velocity-strengthening under in-situ temperature, pressure and fluid chemistry conditions [1]. This property should in theory lead to a lower chance of earthquake nucleation, which makes it difficult to explain the occurrence of earthquakes in Groningen. We study how to explain earthquake nucleation under velocity-strengthening friction and how much aseismic slip can be expected. In this study, we model the normal-fault setup of the Groningen field under reservoir depletion with rate-and-state friction. Initial conditions are chosen to mimic healing over millions of years prior to gas production. We implement fault loading due to fluid pressure reduction and validate our loading stresses with analytical predictions in Jansen et al. [2]. We provide constraints on how much aseismic slip to expect during nucleation and evaluate its relevance to induced seismicity in Groningen. We systematically investigate scenarios with various fluid extraction rates and different rate-and-state friction properties (including rate-strengthening, rate-weakening and a mixture of both) of surrounding lithologies using constraints from laboratory observations. In this way we explore the rate of stress change needed for nucleation under rate-strengthening friction. Currently, we produced an event with slip rate below seismic rate. If seismic rates cannot be reached, we will add a second state variable describing cohesion weakening with time to assess how it affects earthquake nucleation. The impact of frictional property and stress rate to aseismic slip build-up and earthquake nucleation is compared to what is caused by varied reservoir off-set distance and fault dipping angle. Sequences of earthquakes and aseismic slips are studied to understand the long-term effect of fluid extraction, with the influence of the planned gas production termination taken into account. We find that during continuous fluid depletion earthquakes reoccur at increasing recurrence interval. Large dipping angle and relatively low Poisson ratio are necessary to achieve this if reservoir offset is zero. Slip or strain nucleation and distribution patterns produced by our models provide hints that can guide seismologists to identify aseismic slip from natural observations, which can in turn, support this study and constrain simulated fault properties. Ultimately, this will help to better understand the nucleation of induced seismicity with similar lithologies that are present across northwestern Europe and lead to a better understanding of the relevance of aseismic slip.

 

References

[1] Hunfeld, L. B., Niemeijer, A. R., & Spiers, C. J. (2017).  Journal of Geophysical Research: Solid Earth, 122(11), 8969-8989.

[2] Jansen, J. D., Singhal, P., & Vossepoel, F. C. (2019).  Journal of Geophysical Research: Solid Earth, 124, 7193– 7212.

 

How to cite: Li, M., Niemeijer, A. R., Vossepoel, F. C., and van Dinther, Y.: Deciphering fluid extraction-induced earthquake nucleation in Groningen under rate-strengthening friction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5576, https://doi.org/10.5194/egusphere-egu22-5576, 2022.

EGU22-5699 | Presentations | ERE5.1

Seismic to aseismic slip scaling during fluid injection experiments 

Luigi Passarelli, Louis De Barros, Antonio Pio Rinaldi, and Stefan Wiemer

A growing number of direct and indirect measurements and observation indicates that aseismic slip transients are often induced during fluid injection operation alongside with swarm-like seismicity. The detection of fluid-induced aseismic slip has made a paradigm shift on our understanding of the spatio-temporal evolution of earthquake activity during injection operation, classically interpreted as triggered by a diffusive front of high pore pressure. Instead, unclamping of the fault by pressurization induced by fluid injection creates the condition to nucleate synchronous aseismic and seismic slip transients.  In this scenario, the spatio-temporal evolution of the induced seismicity is driven by the stressing rate imparted at the leading edges of the aseismic rupture front. However, the relationship between the magnitude of aseismic slip and the hydraulic energy input in the system remains still elusive. A similar mechanism has been proposed for natural earthquake swarms triggered by shallow (5-10 km depth) slow slip events (SSEs), for which a robust power-law scaling has been demonstrated between seismic and aseismic slip. Notably, the power-law moment scaling of shallow SEEs and associated earthquake swarms has been interpreted with a mechanism of fault pressurization enhanced by intense fracturing in a seismogenic volume with abundance of crustal fluids. Similar fault conditions are at play for fluid-induced seismicity. Here, we collected several case studies of recorded induced aseismic deformation during injection experiments together with the accompanying seismic activity. We investigated the spatial distribution and temporal evolution of the seismicity with respect to the ongoing transient aseismic slip. We focused in particular on the seismic and aseismic slip budget of induced seismicity and compared it with previous scaling of SSEs. The aseismic and seismic moments of induced events are compatible with the power-law scaling of shallow natural earthquakes swarms triggered by SSEs, although a data gap exits for SSEs in 0-4 magnitude range, where no SSEs have never been recorded due to the low resolution of surface geodetic instrumentation. We performed also numerical simulation using a 3D hydro-mechanical model using realistic fault and hydraulic parameters in order to fill in the data gap. Our results serve as a basis to build up empirical models that incorporate aseismic slip together with injected volume and pressure to forecast seismicity during fluid-injection experiments.

How to cite: Passarelli, L., De Barros, L., Rinaldi, A. P., and Wiemer, S.: Seismic to aseismic slip scaling during fluid injection experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5699, https://doi.org/10.5194/egusphere-egu22-5699, 2022.

EGU22-6361 | Presentations | ERE5.1

A 3D ETAS model for forecasting spatio-temporal distribution of induced seismic events 

Hossein Ebrahimian, Fatemeh Jalayer, and Vincenzo Convertito

Methodology:

Induced earthquakes have peculiar characteristics such as, relatively shallow depths, small magnitude, correlation with field operations, non-GR recurrence law, and eventually non-homogenous Poisson recurrence time. Indeed, induced seismicity tends to cluster in limited volumes near the wells where field operations (e.g., fluids injection, extraction, fracking, etc.) are performed. A novel and fully-probabilistic simulation-based procedure is presented for providing temporal and volumetric predictions of induced events’ occurrence in a prescribed forecasting time interval (in the order of hours or days). The procedure aims at exploiting the information provided by the ongoing sequence in quasi-real time (even in the presence of very limited registered data) to adaptively update the seismicity forecasts based on the incoming information as it becomes available. The clustering of seismic events in volume (3D seismicity) and time is modelled based on an Epidemic Type Aftershock Sequence (ETAS) model. The proposed 3D ETAS model encompasses a decoupled depth-area volumetric probabilistic kernel that incorporates kernel density functions for areal extent as well as the focal depth. The ETAS parameters are going to be re-calibrated in order to take into account non-GR long-term temporal boundary conditions in case of induced seismicity. Moreover, exact spatial integrals will be used to consider the 3D boundary conditions. The proposed procedure considers the uncertainties in the earthquake occurrence model parameters in a Bayesian updating framework. Pairing up the Bayesian inference and the suitable efficient simulation schemes (using Markov Chain Monte Carlo Simulation) provides the possibility of performing the forecasting procedure with minimum (or no) need of human interference.

Application:

The procedure is demonstrated through retrospective forecasting of induced seismicity recorded at the Geysers geothermal field in northern California in the time period of 2011-2015. Injection of cold water and heavier liquids in the hot reservoir caused induced earthquakes with moment magnitudes in the range of [0.0, 4.0] and depth ranging up to 5 km. The proposed procedure is examined for both Bayesian updating of the proposed 3D ETAS model parameters and forecasting of the number of events of interest expected to occur in various time intervals before and after a number of main events within the seismic sequence. The seismicity is predicted within a confidence interval from the mean estimate. Adding a kernel density for the focal depth and moving towards the 3D seismicity forecasting leads to the forecasted number of events that better match the events that actually took place in the forecasting interval, as compared to the 2D ETAS model. Therefore, it is concluded that the proposed 3D ETAS model is quite effective in case of induced seismicity.

How to cite: Ebrahimian, H., Jalayer, F., and Convertito, V.: A 3D ETAS model for forecasting spatio-temporal distribution of induced seismic events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6361, https://doi.org/10.5194/egusphere-egu22-6361, 2022.

EGU22-7486 | Presentations | ERE5.1

Magnitude estimates of earthquakes induced by the geothermal stimulations in Espoo/Helsinki, southern Finland: a comparison of different approaches 

Amir Sadeghi-Bagherabadi, Tom Eulenfeld, Tommi A.T. Vuorinen, Annukka E. Rintamäki, and Gregor Hillers

In 2018 and 2020, two weeks-long geothermal reservoir stimulations were performed some 6 km below the Helsinki capital area, Finland. The seismic activity was recorded by a set of surface broadband sensors and 100 geophones installed by the Institute of Seismology, University of Helsinki, as well as Finnish National Seismic Network stations. The local magnitudes (ML) of the recorded earthquakes are estimated using a Finnish local magnitude scale and the local magnitude of the largest induced event was 1.8. We apply three different approaches for estimation of moment magnitudes (MW) to a data base of ~400 induced seismic events from the 2018 stimulation to explore the variability and sensitivity of the magnitude estimates. This is important for real-time monitoring and decision making when the induced event magnitudes approach the pre-defined magnitude limit, and to assess which trends can be robustly associated to earthquake source physics. (1) We employ a time-domain calculation of source parameters based on the application of Parseval's theorem to the integrals of the squared spectral displacement and velocity for the horizontal S-wave trains. The time window between the S-wave arrival time and twice the length of the S-wave travel time is considered for the S-wave train isolation. (2) We obtain moment magnitude estimates from an inversion of 50 s long three-component envelopes based on radiative transfer. (3) We apply a moment tensor inversion to 0.71 s long P and 0.81 s long S-wave signals. We fit a linear ML-MW conversion model to the values obtained from the different approaches. Considering the available local magnitude range between –0.5 and 1.8, a comparison of the linear conversion models shows that the moment magnitudes form the envelope inversion are systematically larger by ~0.2 units compared to those obtained from the moment tensor inversion. While the moment magnitudes determined by the time-domain calculation consistently exceed those of the envelope inversion for small local magnitudes (by ~0.2 units), they tend to yield similar estimates towards the larger local magnitudes. Other source parameter systematics include that the smallest seismic moment is obtained with the moment tensor inversion, and the largest with the time-domain equivalent of the spectral integrals. An initial extension of the analysis to 2020 data yields ML-MW as well as corner frequency-MW scaling relations that are, interestingly, different compared to the 2018 results; we will present updated results that inform about the reliability of these trends.

How to cite: Sadeghi-Bagherabadi, A., Eulenfeld, T., Vuorinen, T. A. T., Rintamäki, A. E., and Hillers, G.: Magnitude estimates of earthquakes induced by the geothermal stimulations in Espoo/Helsinki, southern Finland: a comparison of different approaches, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7486, https://doi.org/10.5194/egusphere-egu22-7486, 2022.

EGU22-7900 | Presentations | ERE5.1

Seasonal stress inversion trends and Coulomb stress changes of RTS in Song Tranh2 reservoir, Vietnam 

Izabela Nowaczyńska and Grzegorz Lizurek

The Song Tranh 2 hydropower construction is located in the Quang Nam province (central Vietnam), it has a reservoir volume of 740 million cubic meters of water and a dam height of 96 m. The reservoir was filled to capacity for the first time in February 2011. The seismicity in the vicinity of reservoir is example of reservoir triggered seismicity (RTS).  The natural seismic activity of the Song Tranh 2 reservoir is very low. After the reservoir was filled, the seismic activity increased, and the number and frequency of the tremors also changed as the water level changed. Water level changes are accelerating the tectonic process leading the critically stressed faults to slip. Data suggest that reservoir exploitation stress field changes as triggering origin of this seismicity. The stress inversion method was used to check if there were any seasonal trends. The inverted stress tensor and, in particular, the stress ratio, which is very sensitive to data quality and scope and difficult to accurately retrieve, can be influenced by porous pressure changes. Has been checked, how the average annual seismic activity is related to the change of the water level and if it implies the orientation of the principal stress during high and low water levels in the reservoir.  The pore pressure changes and the stress ratio changes were also estimated in relation to the high and low water level periods. Coulomb stress transfer is a seismic-related geological process of stress changes to surrounding material caused by local discrete deformation events.Importantly, Coulomb stress changes have been applied to earthquake-forecasting models that have been used to assess potential hazards related to earthquake activity. It is also often assumed that changes in pore fluid pressure induced by changes in stress are proportional to the normal stress change across the fault plane. Coulomb stress changes was also calculated for low and high water period.

How to cite: Nowaczyńska, I. and Lizurek, G.: Seasonal stress inversion trends and Coulomb stress changes of RTS in Song Tranh2 reservoir, Vietnam, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7900, https://doi.org/10.5194/egusphere-egu22-7900, 2022.

EGU22-7969 | Presentations | ERE5.1

Source mechanisms of earthquakes induced by the 2018 and 2020 geothermal stimulations in Espoo/Helsinki, southern Finland 

Annukka Rintamäki, Sebastian Heimann, Torsten Dahm, and Gregor Hillers

An experimental ~6 km deep enhanced geothermal system in Otaniemi, in the Helsinki capital region, southern Finland, was stimulated in 2018 and 2020. During the two stimulations that lasted seven and three weeks, respectively, signals of the induced earthquakes with a maximum local magnitude of 1.8 were recorded with dense and diverse seismic networks. The intraplate southern Finland setting of the experiment yields an intriguing opportunity to study earthquake and rock failure processes in the precambrian Fennoscandian Shield where the level of natural seismicity is comparatively low. The high confining pressure of 180 MPa at 6 km depth defines the key characteristics of the stress field, together with the previously estimated North-110-degrees-East direction of the maximum horizontal stress. The competent crystalline bedrock has very low attenuation, and yields high signal-to-noise ratio seismograms even at relatively high frequencies. We study the source mechanisms of ~250 induced earthquakes with Mw > 0.5. We perform probabilistic full moment tensor analysis with the Grond package of the software suite Pyrocko. We use data sets from the 2018 and 2020 stimulation experiments. Both experiments were monitored with more than 100 three-component surface stations operated by the Institute of Seismology, University of Helsinki, and 12 three-component borehole stations maintained by the St1 developer company installed at around 300 m depth. The diverse network elements help to evaluate the consistency of the results. We first present results of a detailed analysis of a small event subset characterized by the best data quality and solutions to assess the robustness of the different tensor components to different processing choices. This includes a comparison of surface and borehole sensor data. This allows us to conclude that the majority of the analysed earthquakes have a dominant reverse faulting mechanism and a small subset of events has strike slip mechanisms, which is compatible with solutions reported by the developer group. The predominant fault plane orientations are in agreement with the ambient stress conditions that also seem to control the thrust mechanism. Based on the best quality solutions we discuss the significance of the obtained non-double couple moment tensor components to assess if significant opening or closing elements in the induced earthquake source reflect genuine physical processes or spurious effects associated with imperfect resolution.

How to cite: Rintamäki, A., Heimann, S., Dahm, T., and Hillers, G.: Source mechanisms of earthquakes induced by the 2018 and 2020 geothermal stimulations in Espoo/Helsinki, southern Finland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7969, https://doi.org/10.5194/egusphere-egu22-7969, 2022.

EGU22-8224 | Presentations | ERE5.1

Broadband seismic instrumentation for monitoring CCS sites 

Will Reis, Marcella Cilia, Neil Watkiss, Sally Mohr, Rui Barbara, and Phil Hill

Carbon Capture and Storage (CCS) sites require microseismic monitoring before, during and after operations to ensure safety of operational personnel and the wider public.

The high dynamic range and low self-noise of broadband seismometers allows for the detection of low magnitude microseismic events which fall below the threshold of less sensitive geophones. Higher long-period sensitivity also allows the full source spectra of earthquakes to be accurately measured, resulting in more accurate magnitude estimations which improve the integrity of any microseismic monitoring system.

Borehole instruments such as the Güralp Radian are a natural fit for detecting low magnitude microseismic events. Optional high gain at the higher frequencies makes the Radian extremely suitable for monitoring low-magnitude induced events while retaining long-period sensitivity for larger ruptures. The slim form factor and omni-angle operation allows the instrument to easily be lowered into decommissioned wells with little information about the orientation at depth.

The Radian is currently being utilised by the British Geological Survey as part of the UK GeoEnergy Test Bed (GTB) to monitor and improve understanding of fluid flow through natural subsurface pathways. A string of 6 interconnected Radians provides vertical profiling around the injection site with a maximum of 8 units able to join in a single string. The Radian will detect and monitor small changes in the subsurface at the GTB as part of the suite of monitoring technologies deployed onsite. 

In addition to onshore networks, offshore depleted gas fields are becoming increasingly scrutinised for potential to store CO2. The advent of Güralp omnidirectional sensor technology combined with acoustic near-real-time data transmission means the Aquarius OBS provides a cost-effective solution for monitoring offshore CCS sites, with infrequent and rapid battery recharging and acoustic data extraction while the unit is still on the seafloor.

How to cite: Reis, W., Cilia, M., Watkiss, N., Mohr, S., Barbara, R., and Hill, P.: Broadband seismic instrumentation for monitoring CCS sites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8224, https://doi.org/10.5194/egusphere-egu22-8224, 2022.

EGU22-8688 | Presentations | ERE5.1

Analysis of the spatio-temporal evolution of the seismicity induced by hydraulic fracturing operations in Preston New Road, UK 

Riccardo Minetto, Agnès Helmstetter, and Ben Edwards

In August 2019 an hydraulic fracturing operation was carried out at the PNR-2 well in Preston New Road, UK. Hydraulic fracturing caused abundant seismic activity that culminated with a ML 2.9 event. This event prompted the operator (Cuadrilla Resources Ltd.) to halt any further stimulation of the well. The seismic activity was recorded by a downhole array of 12 sensors located in a monitoring well (PNR-1z). The operator released a seismic catalog created in real time during the fracturing operation. The catalog consists of 55555 events detected and located with a coalescence microseismic mapping method. The catalog also reports moment magnitudes, but no precise information on the method and on the parameters used to estimate them is available. In our study, we attempt to improve the number of detections and the location accuracy of the events by applying template matching and a double-difference relocation method, respectively. We also recalculate moment magnitudes using spectral fitting to look for any inconsistencies in the real-time catalog. Finally, we use the new information to better understand the spatio-temporal evolution of the seismicity and the dynamics that led to the ML 2.9 event.

How to cite: Minetto, R., Helmstetter, A., and Edwards, B.: Analysis of the spatio-temporal evolution of the seismicity induced by hydraulic fracturing operations in Preston New Road, UK, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8688, https://doi.org/10.5194/egusphere-egu22-8688, 2022.

EGU22-8716 | Presentations | ERE5.1

Numerical investigation of hydraulic stimulation strategies to mitigate post-injection seismicity in Enhanced Geothermal Systems 

Sri Kalyan Tangirala, Francesco Parisio, and Victor Vilarrasa

Enabling a widespread exploitation of Enhanced Geothermal Systems (EGS) around the world by tapping into the heat trapped by the radioactive granites demands a better understanding of the fluid-induced seismicity associated with their stimulation. Induced seismicity occurs not only during hydraulic stimulation, but also after shut-in. The induced earthquakes of Mw > 3 at Basel and Mw = 5.5 at Pohang are two well-known examples that have caused a negative public perception on EGS. Here, we numerically compare the effect of bleed-off on the mitigation of post-injection seismicity for three stimulation schemes: constant rate, step rate and cyclic injection. We find that applying bleed-off in the post-injection phase significantly reduces the post-injection induced seismicity when compared to not applying bleed-off in all the injection schemes.

How to cite: Tangirala, S. K., Parisio, F., and Vilarrasa, V.: Numerical investigation of hydraulic stimulation strategies to mitigate post-injection seismicity in Enhanced Geothermal Systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8716, https://doi.org/10.5194/egusphere-egu22-8716, 2022.

EGU22-9233 | Presentations | ERE5.1

Analysis of the pico-seismic response of a fractured rock volume to fluid injections in the Bedretto Underground Laboratory, Switzerland 

Virginie Durand, Martina Rosskopf, Katrin Plenkers, Anne Obermann, Miriam Schwarz, Linus Villiger, Men-Andrin Meier, Hansruedi Maurer, Domenico Giardini, and Stefan Wiemer and the Bedretto Team

The Bedretto Underground Laboratory for Geoenergies and Geosciences (BULGG) is a multidisciplinary laboratory on the hundred meter scale run by ETH Zurich. It is located in the Swiss Alps, in the middle of a 5.2km long horizontal tunnel, 1.0km below the surface. 
Seven 250-300m long boreholes have been equipped with different instruments: Acoustic Emission Sensors, Accelerometers, Fiber Optics (allowing simultaneous DTS, DSS and DAS measurements), Strainmeters and Pore Pressure Sensors. The variety of the instrumentation allows a multidisciplinary analysis of the response of the rock volume to fluid injections. The fluid injections are realized through a 400m injection borehole located in the center of the instrument network. It is divided into 14 intervals, allowing us to make injections at different depths.
We will first present the methods used to generate a pico-seismic catalog with precise locations and a magnitude of completeness as low as -5, and the associated challenges. Then, we show a preliminary analysis of the spatio-temporal evolution of the pico-seismicity generated by different injection protocols. We interpret the evolution of the seismicity in comparison with the injection parameters (i.e., injection pressure and rate) and the stimulated intervals.

How to cite: Durand, V., Rosskopf, M., Plenkers, K., Obermann, A., Schwarz, M., Villiger, L., Meier, M.-A., Maurer, H., Giardini, D., and Wiemer, S. and the Bedretto Team: Analysis of the pico-seismic response of a fractured rock volume to fluid injections in the Bedretto Underground Laboratory, Switzerland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9233, https://doi.org/10.5194/egusphere-egu22-9233, 2022.

EGU22-9373 | Presentations | ERE5.1

Variation in induced seismicity productivity by alteration of injection parameters: a comparative case study at three hydraulic fracturing wells in the Kiskatinaw area, British Columbia, Canada 

Marco Pascal Roth, Kilian B Kemna, Alessandro Verdecchia, Ricarda M Wache, Andres F Pena Castro, Rebecca M Harrington, and Yajing Liu

The Western Canada Sedimentary Basin (WCSB) has experienced an increase in hydraulic fracturing (HF) operations in the last decade, accompanied by an increase in the number of felt earthquakes, including a Mw 4.6 on 17 August 2015 near Fort St. John and a ML 4.5 (Mw 4.2) on 30 November 2018 near Dawson Creek. While only a small percentage of HF operations induce seismicity, the majority of moderate-sized earthquakes occur in close spatial proximity to HF wells and temporal proximity to individual HF injection stages within the tight shale play of the Montney Formation. Whereas statistical analysis of an enhanced seismicity catalog suggests that the majority of seismicity occurs following HF operations in the relatively older and deeper compartments of the Montney Formation (Lower Montney; LM) and a low number of events are associated with the relatively younger and shallower layers (Upper Montney; UM), the detailed association and triggering mechanism(s) remains unclear.

In this study, we investigate induced earthquake source parameter variations resulting from spatial and/or temporal alteration of injection parameters, including injection time, depth, and volume, at three well pads operating between 2018 and 2020 in the Kiskatinaw area. We use dense local station coverage to create an enhanced seismicity catalog with double-difference relative hypocenter relocations to highlight potential fault orientations, confirmed by focal mechanism solutions. We estimate static stress drop values at the individual well pads and their variation over time as well as variation with the choice of empirical Greens function. We also investigate the temporal changes of the VP/VS-ratio in localized areas following HF operations as a proxy for increased fracture density and/or compliance.

The case study at three specific sites targeting both the UM and LM layers investigates the relative influence of a number of factors on the spatial and temporal distribution of source properties. Factors include the scale of HF injection parameters, the target formation layer, and site-specific factors, such as localized fluid accumulation. Preliminary results show that injection in the UM generally leads to significantly fewer earthquakes than injection in the LM, and that lateral variations in compartment properties may significantly influence the seismic response. Moreover, we investigate if repetitive injection at the same wellhead may repeatedly (re)activate sets of faults/fractures and lead to increased hydraulic connectivity between the target sedimentary layers and deeper, pre-existing basement faults. An increase in connectivity would imply an increased potential for triggering large mainshocks.

How to cite: Roth, M. P., Kemna, K. B., Verdecchia, A., Wache, R. M., Pena Castro, A. F., Harrington, R. M., and Liu, Y.: Variation in induced seismicity productivity by alteration of injection parameters: a comparative case study at three hydraulic fracturing wells in the Kiskatinaw area, British Columbia, Canada, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9373, https://doi.org/10.5194/egusphere-egu22-9373, 2022.

EGU22-9575 | Presentations | ERE5.1

Reservoir triggered seismicity in tectonically stable and seismically active areas of Vietnam 

Grzegorz Lizurek, Konstantinos Leptokaropoulos, Monika Staszek, Izabela Nowaczyńska, and Anna Tymińska

Water reservoirs play important role in energy production in Vietnam. Numerous dams were designed and built for hydropower plants and water storage during the wet season and its release during dry season. They were built in a different tectonic settings. We present our experience of several years of monitoring and research on two sites: first, tectonic active area of Lai Chau (North Vietnam) and relatively stable area of Song Tranh in Central Vietnam. We observed different seismicity patterns in this areas. Area of active tectonics in Lai Chau was less active in terms of reservoir triggering, while almost aseismic area of Song Tranh was highly active after reservoir impoundment. We proved, that this activity was related with seasonal water level changes in reservoir. Moreover, low water period during service works was proved to be more active and with significantly higher seismic hazard than during initial production regime and after the refilling. It suggests that decrease of water level and following pore-pressure change destabilize minor faults being closer to failure, than main faults in the area. We also found multiplet events triggered on minor normal faults in shallow depth despite the strike-slip regime of regional tectonic stress field. On the other hand in the active area of Lai Chau we observed triggering both on existing active strike-slip faults and minor normal fault discontinuities. However, the difference between seismic activity parameters before and after impoundment except spatial distribution directly after first filling didn’t differ substantially. We can conclude, that in stable tectonic setting triggering effect is clear and related with pore-pressure changes caused by reservoir water level fluctuations, which is main seismogenic factor. On the other hand in active seismic area reservoir water level fluctuation seems to be too small to significantly influence seismic activity in the long term.

This work was partially supported by the research project no. 2017/27/B/ST10/01267, funded by the National Science Centre, Poland under the agreement no. UMO-2017/27/B/ST10/01267 (GL and IN) and partially supported by the research project no. 2021/41/B/ST10/02618, funded by the National Science Centre, Poland under the agreement no. UMO-2021/41/B/ST10/02618 (GL and AT) and partially by National Statutory Activity of the Ministry of Education and Science of Poland No 3841/E-41/S/2022 (MS)

How to cite: Lizurek, G., Leptokaropoulos, K., Staszek, M., Nowaczyńska, I., and Tymińska, A.: Reservoir triggered seismicity in tectonically stable and seismically active areas of Vietnam, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9575, https://doi.org/10.5194/egusphere-egu22-9575, 2022.

EGU22-9826 | Presentations | ERE5.1

Structurally controlled regional groundwater circulation: Origin of geothermal springs in Sri Lanka 

Dilshan Bandara, Thomas Heinze, Jeroen Smit, and Stefan Wohnlich

In the context of switching power generation towards renewable energy sources, the geothermal exploration of low enthalpy systems has gained interest also in regions with little to no recent tectonic or magmatic activity such as Sri Lanka. Sri Lanka has 9 low enthalpy systems with yet unknown heat generating mechanisms besides several existing hypotheses. Recent studies of such kind of low enthalpy geothermal systems hypothesize that fault network and recharge elevations are the main factors controlling the origin of the hot springs.

We studied the fault network, shear zones, and regional fracture networks to understand the heat flow causing the Sri Lankan hot springs. Remote sensing and geophysical methods were used to identify and analyze lineaments. We find that (1) The peak circulating temperatures of deeply circulating meteoric water depend on the elevation of the recharge zone for the corresponding hot spring. (2) Hot springs are formed in a terrain with a long fault / shear zone (starting from the highlands) when cross cuts with a regional fracture network occur in or near to the hot spring fields. (3) Highest number of hot springs in the country relates with the fault network that crosses the Mahaweli shear zone at the boundary of the two geological complexes Highland and Vijayan.

We conclude that the fault network that crosses both the central highlands and the Vijayan Complex plays a major role in the heating of deep percolating water, as it transports the water over more than hundred kilometers distance from the recharge zones to the hot springs. 

How to cite: Bandara, D., Heinze, T., Smit, J., and Wohnlich, S.: Structurally controlled regional groundwater circulation: Origin of geothermal springs in Sri Lanka, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9826, https://doi.org/10.5194/egusphere-egu22-9826, 2022.

EGU22-9880 | Presentations | ERE5.1

Numerical modelling of fluid-induced fault slip reactivation,application to Geo-Energy systems 

Jinlin Jiang, Pierre Dublanchet, Franҫois Passelègue, Dominique Bruel, and Frederic Pellet

Geothermal energy is one of the most promising techniques to exploit renewable energy resources from the Earth and to limit emissions of greenhouse gas. Deep geothermal exploitations are associated with long term fluid circulation and pressure perturbations at great depth, in fractured and faulted zones and are likely associated with a risk of triggering earthquakes. Such earthquakes are usually interpreted as the reactivation of rapid (m/s) shear slip on critically stressed faults caused by fluid flow and poroelastic stress changes. In some cases however, slow aseismic slip (m/d) can take place on faults in response to fluid flow. How fluid pressure perturbations reactivate aseimic or rapid slip still remains poorly understood. A better understanding of the hydromechanical processes controlling fault slip is therefore crucial to mitigate seismic hazards associated with geothermal exploitation.

In this framework, our study aims at constraining the influence of stress state, fluid injection rate, diffusivity and frictional failure criterion on the reactivation of slip on pre-existing faults through mechanical modelling of a set of laboratory experiments. The experiments consist of a fluid injection into a saw-cut rock sample loaded in a triaxial cell. Fault reactivation is triggered by injecting fluids through a borehole directly connected to the fault. This experimental setup is modelled by a 3D Finite Element Method (FEM) coupled with a solver of the fluid diffusion. The sample fault is modelled as a contact surface obeying slip-weakening Mohr-Coulomb friction law. This approach allows to compute slip and stress evolutions, as observed during the laboratory experiment. The FEM model is calibrated and is able to reproduce the experimental results. We show that fluid injection triggers a shear crack that propagates varying from 1 to 300 m/d along the fault. This approach can be used to investigate the relationship between fluid front and slip front during reactivation, which is an important issue to control the effects of fluid injections at depth.

How to cite: Jiang, J., Dublanchet, P., Passelègue, F., Bruel, D., and Pellet, F.: Numerical modelling of fluid-induced fault slip reactivation,application to Geo-Energy systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9880, https://doi.org/10.5194/egusphere-egu22-9880, 2022.

EGU22-10043 | Presentations | ERE5.1

The dynamic Coulomb stress changes caused by remoteearthquakes based on the borehole strainmeter data 

Fuzhen Li, TianXiang Ren, ShunLiang Chi, Huai Zhang, and YaoLin Shi

Sufficient shreds of evidence have proved the existence of the remote triggering effect of large earthquakes. To understand its mechanism, it is necessary to conduct detailed investigations on the influence of the far-field dynamic stress changes on the stress state of faults. As an important tool of ultra-broadband crustal stress monitoring, a four-component borehole strainmeter can directly record the dynamic changes of horizontal strain and stress caused by seismic waves. These data are of great importance to study the dynamic Coulomb stress changes and related triggering effects, but have not been paid sufficient attention to so far. This paper analyzes the data of the four-component borehole strainmeter at Gaotai and Tonghua stations, which recorded the far-field strain changes of four major earthquake events in the Pacific region in 2018. We successfully identify the seismic phases of P, S, and surface waves, and analyze the characteristics of different phases through the stress petal method. The dynamic stress changes are calculated, demonstrating the feasibility of using borehole strainmeter data to quantitatively study the triggering effect of teleseismic waves of earthquakes with different magnitudes at different epicentral distances. We find that the direction of the principal stress axis of the dynamic stress changes is generally consistent with the azimuth of the earthquake epicenter. We further discuss the Coulomb stress changes on the major faults near the stations. According to the results, the peak values of the dynamic Coulomb stress changes produced by four earthquakes on the fault planes near Gaotai and Tonghua stations are at the magnitude of hundreds of Pa, which are lower than the threshold value of dynamic triggering. This is also consistent with the observation that no dynamically triggered earthquakes are found on the faults. However, the idea and method of this paper provide useful insight into the detection of possible dynamic triggering of large earthquakes.

How to cite: Li, F., Ren, T., Chi, S., Zhang, H., and Shi, Y.: The dynamic Coulomb stress changes caused by remoteearthquakes based on the borehole strainmeter data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10043, https://doi.org/10.5194/egusphere-egu22-10043, 2022.

EGU22-10183 | Presentations | ERE5.1

The variability of seismo-acoustic nuisance patterns: a case study from the Helsinki geothermal stimulation 

Lukas Krenz, Sebastian Wolf, Alice-Agnes Gabriel, Gregor Hillers, and Michael Bader

With this contribution, we expand the discussion of effects that earthquakes induced by geo-energy projects can have on local communities, and that should probably be considered in future legislation or permitting processes. Inspired by consistent reports of felt and heard disturbances associated with the weeks-long stimulation of a 6-km-deep geothermal system in 2018 below the Otaniemi district of Espoo, Helsinki, we conduct numerical simulations of wave propagation in the solid earth and the atmosphere to assess the sensitivity of the ground shaking and audible noise patterns to various parameters. We explore the effects of three different local velocity models, realistic topography, variations of the source mechanism, and earthquake size on the loudness of the synthetic waves at frequencies up to 20 Hz, therefore reaching the lower limit of human sound sensitivity. We discuss the results of 18 elastic-acoustic coupled scenario simulations conducted on the Mahti high-performance computing infrastructure of the Finnish IT Center for Science CSC using the SeisSol wavefield solver. The computationally challenging simulations target the Otaniemi case study, i.e., we discretize a 12 km x 12 km x 15 km domain with a 2 km thick air layer over the solid earth domain. The earthquake point source is located at the 6.5 km deep location of the largest M1.8 event induced by the stimulation. In the target central area, we use a mesh with element lengths of about 14 m in the air and 97 m in the solid earth. Inside each element, we approximate the solution by a fifth-degree polynomial, by which we achieve a resolution of roughly 2.3 m in the air and 16 m in the earth. We develop an interactive visualization to facilitate instant access to the results governed by the different parameter combinations, where the synthetics are shown on top of a map of the Helsinki metropolitan region. This tool facilitates “what-if” analyses by quickly comparing the effects of fault orientation, source mechanism, and the velocity model. This supports effective communication of physics-based nuisance analysis to decision-makers and stakeholders, not only in environments such as the case study where there is little experience with natural earthquake phenomena. Together, these results resolve for the first time synthetic nuisance sound patterns at the 50 – 100 m scale in a densely populated capital region. The study highlights the mostly disregarded spatially variable audible effects that can negatively impact the public attitude towards geothermal stimulations, even if the ground shaking limits are safe, and it provides first estimates of the resources needed for comprehensive scenarios for future stimulation projects.

How to cite: Krenz, L., Wolf, S., Gabriel, A.-A., Hillers, G., and Bader, M.: The variability of seismo-acoustic nuisance patterns: a case study from the Helsinki geothermal stimulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10183, https://doi.org/10.5194/egusphere-egu22-10183, 2022.

EGU22-10392 | Presentations | ERE5.1

Modelling injection induced seismicity in the Hengill geothermal field 

Antonio Pio Rinaldi, Vanille Ritz, Shyam Nandan, Raymi Castilla, Dimitrios Karvounis, and Stefan Wiemer

The Hellisheiði Geothermal Field is situated in Southwest Iceland and composes the Southern part of the Hengill Volcanic System. This area is characterized by a complex triple junction between three tectonic features: the Reykanes Peninsula rifting, South Iceland Volcanic Zone and West Volcanic  Zone. Reinjection of spent geothermal fluids is distributed mostly in two areas (Gráuhnúkar and Húsmúli), comprising respectively 6 and 5 active injection wells. The Húsmúli reinjection area, commissioned in September 2011 and has seen significant seismicity associated with drilling and injection operations.
In the framework of the Geothermica project COSEISMIQ (http://www.coseismiq.ethz.ch/en/home/), a dense temporary network was installed to monitor the seismicity in the Hengill region between December 2018 and August 2021. With this enhanced network, novel analysis and relocation techniques, a high resolution relocated catalogue was curated and comprises over 3600 events in the Húsmúli area.
We use numerical models, some purely statistical (ETAS and Seismogenic index) and a hybrid model (TOUGH2-Seed) to reproduce observed seismicity in the Húsmúli reinjection area during the COSEISMIQ project. We employ a pseudo-forecasting approach and compare models performances
and fit to the recorded data.

How to cite: Rinaldi, A. P., Ritz, V., Nandan, S., Castilla, R., Karvounis, D., and Wiemer, S.: Modelling injection induced seismicity in the Hengill geothermal field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10392, https://doi.org/10.5194/egusphere-egu22-10392, 2022.

Heightened seismic activity due to human activities, such as wastewater injection, carbon storage and geothermal energy production, has been a rising problem in recent years. Various injection parameters and geological conditions have been shown to affect fault behaviour differently when fluid is injected on the faults, although existing observational studies about their effects often show contradictory results. Aseismic slip is also known to affect seismicity, but its exact contribution remains elusive.

To address these, we perform numerical modelling to study the effects of various injection parameters on fault slip behaviour. Our fully dynamic fault model is governed by the rate-and-state friction laws and spontaneously resolves all stages of an earthquake cycle and long-term fault slip. Our results show several interesting observations on the role of injection volume and rate: First, the injected volume can advance or delay the next earthquake if no earthquakes are directly triggered during perturbation. Second, if earthquakes are triggered, the number of triggered earthquakes is controlled by the rate at which fluid is injected, while the timings of the triggered earthquakes are controlled by the injected volume. Large triggered earthquakes are usually preceded by smaller precursors. Third, the pore-pressure threshold at which earthquakes are triggered changes depending on the injection parameters. In most cases, it increases with the volume of injected fluid, but in some cases when the injection is slow, it can also depend on the rate of injection. The change with respect to injection rate is not a smooth positive trend, however, as increasing the rate causes aseismic transients to grow stronger and transition into seismic events, thus advancing the triggering time and causing decrease in the threshold pore pressure in the process. Overall, the effects of perturbation do not end as soon as injection stops. Instead, heightened aseismic activities, as well as oscillating earthquake timings and magnitudes occur for multiple seismic cycles after the end of pore-pressure perturbation. We also see large variations in aseismic moment release under different perturbation scenarios and its intricate relationship with the resulted seismicity pattern, which confirms the vital role of aseismic slip in earthquake triggering. Similar to previous studies, we find that energy on the fault is primarily released aseismically.

Our results thus far are based on spatially uniform pore-pressure evolution, and we are currently developing models that resemble environments with temporally and spatially heterogeneous pore pressure by coupling the temporal evolution of pore pressure with spatial diffusion. We are also incorporating geologic information of the crustal medium, which will be more fitting for modelling realistic scenarios such as the injection-induced earthquakes in Oklahoma.  

How to cite: Mandal, R. and Lui, S.: Quantifying the effects of injection parameters on fault response under spatially homogenous and heterogenous pore-fluid conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10601, https://doi.org/10.5194/egusphere-egu22-10601, 2022.

Seismicity in western Romania is the result of tectonic processes that continuously shaped the landscape generating a fractured crust, which showed significant movements as a result of overall tectonic stress in the area as well as secondary effects such as erosion or lateral density fluctuations. At the same time, this region has an important natural resource, being identified here various deposits that have been intensively explored lately. The exploitation of these resources, as well as the development of the infrastructure in the region, led to the generation of anthropogenic seismic events. Due to the recent improvement of the Romanian Seismic Network, the coverage with seismic stations increased and these events were detected and located as natural tectonic events, contaminating the Romanian earthquakes (ROMPLUS) catalog.

To eliminate anthropogenic event contamination in the ROMPLUS catalog, we ran a complex statistical approach on the catalog data. In addition, to build a robust discriminant, we further applied cross-correlation and spectral analysis algorithms on the seismic waveforms recorded between 2014 and 2021 by the Surduc (SURR) and Gura Zlata (GZR) stations, which are located in the proximity of the major clusters of seismic events.

Our results showed a good distinction between tectonic and anthropogenic events and revealed that most of the clustered events are located near the explorations sites. We also noted that most of the events occurred during working hours. At the same time, the high similarity among these events indicates the existence of repetitive seismic sources.

How to cite: Varzaru, L.-C. and Borleanu, F.: Identifying anthropogenic seismic events generated in western Romania using statistical approaches and novel waveform processing techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10911, https://doi.org/10.5194/egusphere-egu22-10911, 2022.

EGU22-11183 | Presentations | ERE5.1

Detailing the relationship between hydraulic fracturing parameters and induced seismicity using small-magnitude earthquakes 

Rebecca M. Harrington, Kilian B. Kemna, Marco P. Roth, Ricarda M. Wache, and Yajing Liu

The extensive development over the last decade of low-permeability tight shale formations in the Western Canada Sedimentary Basin (WCSB) using hydraulic fracturing (HF) techniques for oil and gas exploration has been associated with  an increasing number of M3+ earthquakes (e.g., ML 4.5 on 30 November 2018 near Dawson Creek, and a Mw 4.6 on 17 August 2016 near Fort St. John). Avoiding economic losses due to operational shutdowns and mitigating damage caused by ground shaking requires developing quantitative relationships between operational parameters and the rate of fault activation in areas of low historical seismicity rates such as the WCSB.

Here we present the first results of a detailed study of the relationship between earthquake occurrence and operational parameters using dense seismic array and the British Columbia Oil and Gas Commission operational database to quantitatively assess the relative influence of operational parameters and geological conditions on earthquake generation. We first enhance a local, automatically generated seismic catalog of > 8000 events in the Kiskatinaw (Montney Formation) in the time period between July 2017 -  December 2020 area using a multi-station matched-filter approach.  We then use a machine learning picker as an independent detection algorithm for the same time period and retain events with the best initial locations detected by both the matched-filter and machine-learning approaches. The combined approach leads to  > 30,000 additional earthquakes, which we relocate using a double-difference technique, lowering the magnitude of completeness Mc from ~1.3 to ~0.2.

As shown by several previous studies, while most earthquakes show a clear spatio-temporal correlation with HF operations, the majority of HF operations are not associated with felt earthquakes (e.g., M3+). To investigate the correlation between individual HF stage stimulation and earthquake occurrence, we correlate operational and geological characteristics with > 13000 HF stages. Geological data consists of the target formation for injection, which consists of either the Lower or Upper Montney Formations for the majority of stages. We then use a gradient-boosted decision tree machine learning algorithm combined with an approach to explain the model predictions to assess whether a specific stage is seismogenic. The decision-tree-algorithm allows us to estimate the importance of each injection parameter for the generation of seismicity. First results show that the target formation is the most influential parameter, where the Lower Montney Formation is more prone to higher rates of seismicity. In addition, the total pumped fluid volume and the maximum treating pressure are the important injection parameters that are positively correlated with seismicity. In contrast, the average injection rate and breakdown pressure may be relatively less influencial. We will present the results for specific stages and discuss the importance of their injection parameters in relation to seismicity. Our results could help to determine why only some HF wells are seismogenic.

How to cite: Harrington, R. M., Kemna, K. B., Roth, M. P., Wache, R. M., and Liu, Y.: Detailing the relationship between hydraulic fracturing parameters and induced seismicity using small-magnitude earthquakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11183, https://doi.org/10.5194/egusphere-egu22-11183, 2022.

EGU22-11535 | Presentations | ERE5.1

Development of slow slip front during the nucleation of laboratory fluid-induced earthquakes 

Francois Passelegue and Pierre Dublanchet

Fluid injections are known to induce earthquakes in the upper crust. Recent studies have highlighted that fluid injections can contribute to the nucleation of instabilities close to or far from the injection site due to stress transfer induced by poroelastic processes. In addition, recent studies have suggested the maximum magnitude earthquake is expected to be a function of the volume injected. However, the development of the slip front related to the fluid pressure front, as well as its implications on the induced seismic sequence in time and space, remain poorly constrained in the laboratory and in natural fault systems.

Here, we investigated the influence of the initial normal stress (i.e., the permeability of the fault plane) and of the injection rate on the development of both the fluid pressure front and associated slip front during the nucleation stage of laboratory fluid-induced earthquakes. Experiments were conducted on saw cut samples of andesite, presenting a negligible bulk permeability compared to the fault plane one. Strain gauges were glued all around the fault surface to track, (i) the strain transfer associated with slip front propagation during injection and the rupture velocity during dynamic rupture propagation. The dynamics of the fluid pressure front was inverted from pore pressure measurements located at both edges of the fault. The evolution of the slip distribution due to the change in fluid pressure around the injection site was inverted from strain gauge measurements, assuming a 3D modelling of the sample specimen using the Finite Element Method. Our preliminary results show that the initial stress acting on the fault controls the development of the slip front during the nucleation of the instability. In addition, the larger the injection rate, and the faster the propagation of the slip front compared to the fluid pressure front. Finally, the scaling between the volume of fluid injected and the associated nucleation moment differs from the one relating the volume injected to the seismic moment.

 

How to cite: Passelegue, F. and Dublanchet, P.: Development of slow slip front during the nucleation of laboratory fluid-induced earthquakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11535, https://doi.org/10.5194/egusphere-egu22-11535, 2022.

EGU22-11538 | Presentations | ERE5.1

Triggering mechanisms of the induced seismicity at the Underground Gas Storage of Castor, Spain 

Victor Vilarrasa, Silvia De Simone, Jesus Carrera, and Antonio Villaseñor

Cushion gas injection at the Underground Gas Storage (UGS) project of Castor, Spain, induced hundreds of events, including thirteen with magnitude higher than 3.5 that were felt by the local population and led to project cancellation. The sequence of felt events comprises the three largest earthquakes (M4.08, M4.01 and M3.97) ever induced by any of the more than 640 UGS facilities around the world. The largest earthquakes occurred 20 days after shut-in, when pore pressure buildup had already dissipated. The induced earthquakes nucleated at depths ranging from 4 to 10 km, significantly deeper than the storage formation, which is located at 1.7 km depth. These features of the induced seismicity disregard pore pressure buildup as the triggering mechanism. Our analyses show that seismicity was induced by gas injection, which reactivated the critically stressed Amposta fault. The Amposta fault, which bounds the storage formation, is a mature fault with very low permeability as a result of clay accumulation into its core resulting from its 1,000-m offset. Pore pressure buildup, but specially buoyancy of the gas, which continued to act after shut-in, destabilized the Amposta fault aseismically. The accumulation of aseismic slip caused stress transfer, destabilizing a deep critically stressed fault. Subsequently, shear slip stress transfer combined with slip-driven pore pressure changes, induced the sequence of felt earthquakes. We conclude that the induced earthquakes at Castor could have been avoided because fault stability analysis reveals the high risk of inducing seismicity.

 

Reference

Vilarrasa, V., De Simone, S., Carrera, J. and Villaseñor, A., 2021. Unravelling the causes of the seismicity induced by underground gas storage at Castor, Spain. Geophysical Research Letters, 48, e2020GL092038

How to cite: Vilarrasa, V., De Simone, S., Carrera, J., and Villaseñor, A.: Triggering mechanisms of the induced seismicity at the Underground Gas Storage of Castor, Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11538, https://doi.org/10.5194/egusphere-egu22-11538, 2022.

EGU22-12474 | Presentations | ERE5.1

Impact of fracture length distribution on the injection-induced seismicity in fractured rocks 

Mohammad Javad Afshari Moein and Qinghua lei

Induced seismicity is a major challenge for fluid injection operations performed by geo-energy industry to exploit the underground resources. Despite recent developments in the understanding of induced earthquakes, many high-pressure fluid injection operations can still trigger unexpectedly large-magnitude events. A physical understanding of geological parameters controlling the induced seismicity is of central importance for improving our ability to forecast and mitigate the risk of inducing large earthquakes. Current physics-based numerical models are typically based on some simplifications that disregard the multiphysical interactions among fractures and faults. Therefore, the physical linkage between geometrical attributes of the fracture system and the statistics of induced seismicity is poorly understood. The final objective of this research is to determine the impact of fracture network properties on the spatiotemporal evolution of injection-induced seismicity and the emergence of large earthquake events.  

Here, we numerically capture the occurrence of seismic and aseismic slips in fracture systems, represented as discrete fracture networks (DFNs), spanning over two orders of magnitude over the length scale (1-100 m). Then, a 2D finite element model is used to simulate the coupled hydraulic and mechanical processes during fluid injection and analyze the occurrence of earthquakes. We present some preliminary results of our numerical simulations based on synthetic fracture network realizations. We particularly focus on power-law exponent of fracture length distribution and analyze the potential controls on the magnitude frequency of induced seismic events. The results of the analysis could have significant implications injection-related activities such as enhanced geothermal systems.

How to cite: Afshari Moein, M. J. and lei, Q.: Impact of fracture length distribution on the injection-induced seismicity in fractured rocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12474, https://doi.org/10.5194/egusphere-egu22-12474, 2022.

EGU22-12568 | Presentations | ERE5.1

Performance comparison of induced seismicity forecasting models with existing datasets 

Victor Clasen Repolles, Antonio Pio Rinaldi, Federico Ciardo, and Luigi Passarelli

Within the workflow of Adaptive Traffic Light System, it is important to evaluate the performance of different induced seismicity forecasting models in order to properly weight the forecasts during seismic hazard calculation. In this respect, we propose a standardize test bench approach capable of comparing outputs’ models (in terms of seismicity rate) and their uncertainties in real time. We test this approach using different models that are trained using existing datasets from geothermal exploration campaigns. Notably, we use two statistical models that link injection volumetric rate to seismicity rate with the difference that a Bayesian approach (EM1_BH) additionally adds epistemic uncertainty to the aleatoric uncertainty introduced in a purely frequentist approach (EM1_MLE), one pressure-based seismicity model (HM0_CAPS) based on 1D analytical solution for linear pore-fluid diffusion and finally one hybrid 1D model that includes a physic-based module for linear and non-linear pore-fluid diffusion linked to a stochastic model for seismicity generation using a seed approach (HM0_SEED and HM1_SEED). By using these different models and their uncertainties in our numerical investigations, we show the robustness of the proposed testbench approach.

How to cite: Clasen Repolles, V., Rinaldi, A. P., Ciardo, F., and Passarelli, L.: Performance comparison of induced seismicity forecasting models with existing datasets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12568, https://doi.org/10.5194/egusphere-egu22-12568, 2022.

The fluid's pore pressure represents the main geomechanics parameter to consider while planning for drilling operations and during production. Actually, a good understanding of overpressure origins leads to better characterize of the pore pressure, which materialized by the suggestion of several models to predict pore pressure. Therefore, the successful technical achievement of a drilling program is judged by the sustainable integrity of the well i.e. sealing effectiveness between different reservoirs. As a result, this should guarantee long-term water resources protection, rational production, and sustainable development.

                The studied cases (CI-11 and OKN-32 wells) reflect the direct effect of the integrity failure of the cased hole, leading to the groundwater and ecological safety of the major transboundary aquifers system in North Africa. This aquifer is known as the North-Western Sahara Aquifer System (NWSAS), which is shared between Tunisia, Algeria, and Libya. It's hosting huge reserves of non-renewable water, in an arid climate region. The assessment of the wells Jemna CI-11 in Tunisia and the Berkaoui OKN-32 in Algeria have concluded the integrity loss of the wellbore. These issues led to CI mass-water flowing behind the casing from the CI to the CT aquifers which characterize an internal blowout where water flows from the over-pressurized CI groundwater to the shallower CT groundwater. First, the case of the Haoud Berkaoui in 1984, (OKN-32 well) has induced a CI waters flow behind the casing causing the CT water resource contamination, which is ended with a surface crater collapse over a diameter of 320 m. Second, a quite similar accident happened in Jemna in 2015, (CI-11 well) where evidence of water flowing from CI to CT through a leaked-off casing has been discovered. Jemna CI-11, Berkaoui OKN-32, and probably many other ongoing similar accidents, could be classified as regional ecological disasters by massive water resources losses and contamination. The actual situation is far from being under control and the water contamination risk remains at a very high level.

                Finally, due to unsuitable drilling programs, drilling operation problems, and/or production casing corrosion, we suspect that dozens of oil and water wells may be involved in well integrity failure affecting the NWSAS groundwater resource. And since, we cannot diagnose easily internal blowout unless widespread contamination happened, we strongly recommend (1) a regional investigation and risk assessment plan which might offer better tools to predict and detect earlier well-bore isolation issues and (2) special attention to the cement bond settlement, evaluation, and preventive logging for existing wells to ensure effective sealing between the vulnerable water tables. Besides, in the CI-11 well accident, the recovery program was not efficient and there was no clear action plan. This increases the risk of action failure or time waste to regain control of the well. Consequently, we suggest preparing a clear and efficient action plan for such accidents in order to reduce their ecological consequences. This needs a further technical detailed study of drilling operations and establishment of the suitable equipment/action plan to handle blowout and annular production accidents.

How to cite: Khalfi, C., Ouhaibi, C., Ahmadi, R., and Dassi, L.: Role of the pore pressure profile on the protection of wellbore integrity and the groundwater: Case studies of well integrity issues of CI-11, in southern Tunisia, and OKN-32 in Algeria., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-278, https://doi.org/10.5194/egusphere-egu22-278, 2022.

EGU22-2425 | Presentations | ERE5.5

Effect of loading rate on mechanical behavior and deformation mechanisms in clay-bearing sandstones 

Takahiro Shinohara, Christopher Spiers, and Suzanne Hangx

Fluid extraction from subsurface reservoir sandstones frequently results in surface subsidence and induced seismicity, as observed in the Groningen Gas field (Netherlands). The cause lies in reservoir compaction driven by pressure depletion and the associated increase in effective overburden stress. Compaction in sandstones often includes elastic and significant inelastic components. The inelastic part is at least partly due to rate- or time-dependent processes, such as intergranular sliding or stress corrosion cracking. However, few mechanism-based rate/time-dependent compaction laws exist, despite the need to evaluate the impact of reservoir exploitation on field time scales (1-100 years). To help bridge this gap, we systematically investigated the effect of loading strain rate in the range from 10-3 to 10-9 s-1 in a series of triaxial compression experiments performed on water-saturated Bleurswiller sandstone samples with porosities of 21.07±0.15 % and composed of 66 % quartz, 28 % feldspar and 4 % clay. This material was chosen because of similarity to the Groningen sandstone but greater uniformity. We explored conditions of confining pressure (39 MPa), pore pressure (10 MPa) and temperature (100 °C) corresponding to in-situ values for Groningen. Axial strains up to 3 % were imposed. Our results showed combined elastic plus strain hardening (inelastic) loading behavior, up to a peak stress reached at 0.8-1.0 % strain, followed by strain softening towards a steady residual stress attained at 1.5-2.0 % strain. A systematic lowering of stress-strain curve levels was observed with decreasing strain rate, such that peak and residual stresses decreased respectively from 88 and 74 MPa at 10-3 s-1 to 70 and 61 at 10-9 s-1. No effect of loading rate is observed at differential stresses below ~ 50% of peak stress. At higher differential stresses up to peak, net sample stiffness (stress-strain curve slope) decreases with decreasing strain rate. Using the curve obtained at 10-3 s-1 as a reference, we determined the excess strains measured at rates of 10-4 to 10-9 s-1 at fixed differential stresses up to the peak. By extrapolating this empirical relation to field strain rates associated with gas production in Groningen (i.e. 10-12 s-1), it is estimated that ~30 % more compaction strain is developed under field conditions, at current differential stresses in the field (i.e. ~ 60 % peak stress), than in laboratory experiments at rates of 10-3 to 10-5 s-1. Additional experiments at varying temperature and confining pressure show sensitivities that suggest that the observed effect of strain rate is likely associated with a combination of time-dependent grain failure by stress corrosion and intergranular sliding. Work is in progress to assess the effect of varying mineralogy by conducting similar experiments on clay-free, quartz-rich Bentheimer sandstone. Our results show that time-dependent inelastic deformation plays an important role in estimating reservoir deformation and associated change in stress associated with fluid production from sandstone reservoirs, like the Groningen reservoir. Such effects could lead to underestimation of surface subsidence and induced seismicity, if not adequately accounted for. The present experiments thus provide important data for testing current models for rate-dependent reservoir compaction.   

How to cite: Shinohara, T., Spiers, C., and Hangx, S.: Effect of loading rate on mechanical behavior and deformation mechanisms in clay-bearing sandstones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2425, https://doi.org/10.5194/egusphere-egu22-2425, 2022.

Predicting the growth of fluid-driven fractures in geological systems is essential for the sustainable and efficient engineering of oil and gas reservoirs. The linear elastic hydraulic fracture mechanics (LHFM), which combines the linear elastic fracture mechanics and lubrication theory, has described well the fracture growth in brittle materials. However, the quasi-brittle nature of reservoir rocks may result in deviations of the fracture propagation from LHFM predictions. We have experimentally investigated the propagation of hydraulic fractures in quasi-brittle rocks under true triaxial stress conditions. We have performed HF injections in 250x250x250 millimeters Zimbabwe gabbro samples in the toughness-dominated growth regime. We use active acoustic monitoring to measure the evolution of fracture radius from diffracted waves and estimate fracture width from transmitted waves (Liu et al., 2020). Assuming a radial and uniformly pressurized crack, we find that LHFM predictions overestimate fracture radius inverted from diffracted acoustic waves but underestimate the measured injection fluid pressure. Using the same radial uniformly pressurized linear elastic fracture model, we also estimate an apparent toughness from the measured fracture radius and pressure. This estimated apparent toughness is not constant and tends to increase with fracture extent in some cases up to a constant value. We also obtain another estimate of fracture toughness from fracture width back-calculated from transmitted waves for a few snapshots of the fracture evolution. These two estimates of the fracture apparent toughness are mostly consistent, although higher values are obtained when the estimation is based on pressure measurement. We also observe an attenuation of transmitted waves across the fracture plane prior to the arrival of the fracture front obtained from diffracted waves. This allows us to estimate a process zone size in the range of two to six centimeters (depending on experiments). In addition, post-test micro-CT images reveal the presence of a microscale fracture path with some 3D crack branches and bridges. The thickness of such a crack band is a few millimeters on par with both grain size and the roughness of the fracture surface measured after the test. These experiments document an increase of the process zone size at the early stage, which stabilizes afterward in some of the experiments. It is important to note that complete separation of scales between fracture radius, process zone, and sample size is hardly achieved in these experiments. A non-negligible influence of the process zone may thus explain the reported deviation from LHFM predictions in gabbro. No effect of the minimum confining stress was visible in the range investigated here (0 to 10 MPa). The applied minimum stresses were always smaller than the reported peak tensile strength for this rock, a domain where the effect of the quasi-brittle nature of rocks is not anticipated to be significant based on recent theoretical results (Garagash, 2019; Liu & Lecampion 2021).

How to cite: Liu, D. and Lecampion, B.: Does the linear hydraulic fracture mechanics predict well the fracture growth in quasi-brittle rocks under laboratory conditions?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3445, https://doi.org/10.5194/egusphere-egu22-3445, 2022.

The increasing emission of greenhouse gases and increasing demand for energy supply are reasons to investigate geothermal energy systems where scCO2 is the working fluid. However, the complex dissolution and reaction of minerals during the heat production processes affect the performance of geothermal reservoirs. Thus, a comprehensive numerical model that includes the Thermal-Hydraulic-Chemical (THC) coupled physical-chemical processes was implemented in the open-source simulator DuMuX, to model the phase displacement, chemical dissolution, heat transport, and mineral reactions. The aim is to investigate the influence of these parameters on the overall geothermal reservoir performance. More precisely, this study investigates the effects of salt precipitation, mineral reactions, injection rate, injection temperature, and geothermal reservoir size on heat production rate and scCO2 sequestration. The simulation results show that the scCO2- calcite reaction decreases the reservoir heat production rate but increase the sequestration of scCO2. Moreover, its effects are proportional to the scCO2 injection rate but inversely proportional to the geothermal reservoir size. On the other hand, the dissolution of scCO2 in brine has the same influence as the reaction between scCO2 and calcite, benefiting the CO2 sequestration but minimizing the heat production rate of the geothermal reservoirs. Furthermore, the sensitivity analysis presents that the influence of chemical dissolution and mineral reactions are only significant when the injection rate is large and the reservoir size is small.

How to cite: Zhou, D., Tatomir, A., and Sauter, M.: Numerical investigation of the effects of chemical dissolution and mineral reaction on reservoir performances in CO2-plume geothermal systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6622, https://doi.org/10.5194/egusphere-egu22-6622, 2022.

EGU22-7156 | Presentations | ERE5.5

Hydro-mechano-chemical coupling in rock failure 

Anne Pluymakers, Aukje Veltmeijer, Milad Naderloo, Jon-Danilo Kortram, and Auke Barnhoorn

Understanding rock failure is key for the safe and efficient development of the subsurface. Gas storage (CO2, H2 or CH4), production of geothermal energy and the traditional extraction of hydrocarbons means fluid injection or extraction. These processes change the local stress state, but also local temperature or chemistry. Such use of the subsurface is about either keeping fluid where it is (storage) or making sure fluids come out with a sufficient but still safe rate. Since fault rocks are in many cases important fluid transport pathways, this needs a careful and complete understanding of how rocks fail. Therefore, a thorough understanding of the stages of deformation leading to failure is key, as well as any potential differences for different rock types and failure modes. We performed uniaxial compressive and triaxial experiments on limestone and sandstone to investigate the hydro-mechano-chemical coupling in rock failure, using active and passive acoustics to monitor the failure behaviour. All experiments are done at room temperature.

Using active acoustics for first arrival times is an established technique. We use here the more novel coda-wave interferometry technique to track deformation in triaxial tests at different confining pressures in sandstones and limestone, which deform respectively in a fully brittle or a semi-ductile manner. This shows that the first signs of failure can be picked up before the yield point, i.e. before the time it is picked up by any of the traditional bulk stress-strain signals used in experimental rock deformation. In uniaxial compressive experiments on the same brittle sandstone samples we show that the loading pattern can affect the final strength but also the maximum acoustic emission amplitude. Cyclic loading tends to systematically reduce the magnitude of the largest induced seismic event, whilst simultaneously also promoting more complex fracture patterns and disintegration. This implies that the risk of induced seismicity can be mitigated by changing the loading pattern in subsurface operations. Finally, we show that for reactive rocks under the right pressure and temperature conditions, changing the chemistry can have an effect on rock strength, where the effects depend on the internal rock structure. This research increases the understanding of rock failure and show the potential of monitoring for a safe and efficient development of the subsurface.

How to cite: Pluymakers, A., Veltmeijer, A., Naderloo, M., Kortram, J.-D., and Barnhoorn, A.: Hydro-mechano-chemical coupling in rock failure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7156, https://doi.org/10.5194/egusphere-egu22-7156, 2022.

Wormholes are an effective fluid conduit that dominate the flow path in karst aquifers and are artificially induced in geo-energy applications through acid injection. As acidic fluids infiltrate geologic formations, they react with the minerals in the formation. The reaction localizes and forms a dendritic dissolution pattern under certain conditions, known as the reaction infiltration instability. This instability is instigated by material heterogeneities in most computational models. However, studies have demonstrated that injection of water into a homogeneous plaster can initiate and grow wormholes. In this study, we show that material heterogeneities suppress the wormhole growth in carbonate rocks compared with a homogeneous counterpart. Wormholes were numerically simulated through injection of a strong acid (hydrochloric acid) under both homogeneous and heterogeneous permeability fields using a phase-field approach. The phase-field variable represents calcite dissolution in a diffused manner and is coupled with a reactive flow model assuming convective and diffusive acid transport in the liquid phase and significantly high surface reaction rate, which emulate typical high-rate matrix acidizing treatments in carbonate reservoirs. Heterogeneous permeability fields localize the flow in high-permeability domains and enhance the splitting and branching of wormholes. The length of the dominant wormholes can be suppressed as an increasing amount of acid infiltrates into the branched wormholes. Our findings indicate that material heterogeneities should not be treated as a trigger for wormholes in the numerical simulation but as one of the parameters to control their nucleation and growth. 

How to cite: Furui, K. and Yoshioka, K.: A Numerical Study of Wormhole Formation and Growth in Homogeneous and Heterogeneous Carbonate Rocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8971, https://doi.org/10.5194/egusphere-egu22-8971, 2022.

EGU22-11543 | Presentations | ERE5.5

2D & 3D numerical modeling of fluid-driven frictional crack growth for geothermal hydraulic stimulation  

Brice Lecampion, Alexis Sáez, and Regina Fakhretdinova

Hydraulic stimulation of deep geothermal reservoirs is necessary in order to establish economical flow rates between the injector and producer wells. Previous field experience in deep crystalline reservoirs have highlighted the importance to stimulate the well by zones in order to create several fractures along the well instead of carrying out a single large stimulation which typically results in the reactivation of only a few fractures along the open-hole section – thus resulting in poor reservoir coverage and low flow transmissivity. Localized hydraulic stimulation can be performed via packer-systems, and although different in their details, share similarities with stimulation operations performed in unconventional oil and gas reservoirs. The main differences are that i) propping agents are not typically used in crystalline geothermal reservoirs, ii) the injection pressure often remains lower than the minimum in-situ stress and iii) the long-term increase of permeability relies on the self-propping effect associated with the shear dilatant behaviour of pre-existing fractures. The type of fractures propagated during hydraulic stimulation thus exhibit both shear and tensile modes of deformation (different than the purely tensile hydraulic fractures).

Physics-based models are necessary in order to design the injection sequence and are typically used in conjunction with uncertainty analysis. We report our developments of  two and three-dimensional numerical models for the hydraulic stimulation of pre-existing fractures accounting for both shear and opening modes of deformation. The fracture behavior is modelled via a non-associated Mohr-Coulomb frictional elasto-plastic law with possible weakening/hardening of friction and dilatancy with slip, while the host rock is assumed linearly elastic. The fluid flow behaviour of the fracture accounts for opening and the associated permeability / storativity changes (with the possibility to use different type of permeability law). We solve in a fully coupled manner the resulting non-linear moving boundary hydromechanical problem.

We present several verification tests for the growth of a frictional shear crack growth in the plane of a pre-existing frature under the injection of fluid at constant rate in both 2D and 3D. Especially, we compare our numerical results with recent analytical solutions for the case of constant friction and constant hydraulic properties of the pre-existing fracture. We then discuss several examples combining shear dilatancy and its effect on flow properties as well as the possible tensile opening of the pre-existing stimulated fracture. Accuracy, robustness and numerical performance – critical for the use of the solver for engineering design - will be discussed as well as future improvements.

This work is sponsored by Geo-Energie Suisse A.G. and the Swiss Federal Office of Energy.

How to cite: Lecampion, B., Sáez, A., and Fakhretdinova, R.: 2D & 3D numerical modeling of fluid-driven frictional crack growth for geothermal hydraulic stimulation , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11543, https://doi.org/10.5194/egusphere-egu22-11543, 2022.

EGU22-11737 | Presentations | ERE5.5

Influence of chemo-mechanical processes and microstructural geometry on the mechanical behavior of geomaterials 

Hadrien Rattez, Alexandre Guével, Martin Lesueur, and Manolis Veveakis

The mechanical behavior of geomaterials depends primarily on their microstructure and in particular the geometry of their pores. This microstructure and its evolution in time due to deformation or chemical transformations also strongly affects the thermo-hydro-mechanical-chemical (THMC) processes in these porous materials. In the last decades, the development of micro-computed tomography has allowed to obtain accurate images of the rock-microstructures and how they evolve subjected to various factors. Many studies have used these 3D geometries of the porous space to characterize primary properties that depend on the microstructure, such as porosity, permeability or elastic moduli, by numerically solving field equations on µCT scan images of rock. For most projects of energy production or waste storage in geological media though, rocks eventually reach their limit of elasticity and the complementary plastic properties are needed to describe the full mechanical behaviour. In this contribution, we will show how we can assess the mechanical behavior of geomaterials in the long-term by solving nonlinear equations directly on realistic microstructures. First, we will discuss the necessary morphometric invariants that can be used in an upscaled constitutive law and show how we can predict the yield surface and its evolution with the chemical alteration of the rock from µCT scan images. Then, a phase field model that allows to simulate interface evolution is applied to investigate pressure solution creep at the grain scale and how it is influenced by microstructural geometry and catalyzing/inhibiting effects like temperature or clay content.

How to cite: Rattez, H., Guével, A., Lesueur, M., and Veveakis, M.: Influence of chemo-mechanical processes and microstructural geometry on the mechanical behavior of geomaterials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11737, https://doi.org/10.5194/egusphere-egu22-11737, 2022.

EGU22-1434 | Presentations | EMRP1.14

Multiscale analysis of physical rock properties at Stromboli Volcano: what controls the frictional properties?    

Thomas Alcock, Sergio Vinciguerra, and Phillip Benson

Stromboli volcano, located in the north-easternmost island of the Aeolian archipelago (Southern Italy) and well known for its persistent volcanic activity, has experienced at least four sector collapses over the past 13 thousand years. The most recent activity resulted in the formation of the Sciara del Fuoco (SDF) horseshoe-shaped depression and a tectonic strain field believed to have promoted flank collapses and formed a NE / SW trending weakness zone across the SDF and the western sector of the island. The tectonic strain field interplayed with dyking and fracturing appears to control the episodes of instability and the onset of slip surfaces. This study presents new data identifying areas of damage that could promote fracturing via remote sensing and rock friction measurements taken on rocks around the SDF and the coupled “weak” zone. We have carried out a multiscale approach by integrating satellite observations with block and sample scale physical and mechanical properties and frictional tests carried out in triaxial configuration on cm scale slabs. Over 5000 individual fractures have been at first processed through the MatLab toolbox FracPaQ to determine fracture density, slip and dilatancy tendency around the collapse scarp with results showing that dilation and slip 0.6< is more common the northern side of the SDF as well as around areas of eruptive activity.

Key units have been sampled on the field (Paleostromboli, Vancori and Neostromboli) with reference to SDF and the weak zone. Physical and mechanical properties defined using elastic wave velocities, electrical resistivity, uniaxial compressive strength and elastic moduli have been assessed and inverted for comparison to field scale geophysical investigations. Finally, direct-shear tests in triaxial configuration were carried out to explore the frictional properties using rectangular basalt slabs at 5 – 15 MPa confining pressure in dry and saturated conditions. Preliminary results show a variation in the friction coefficient (µ) between 0.55 and 0.7 with a general µ decrease with increasing confining pressure and saturation. The most porous Neostromboli units show the lowest friction.  This suggests that the textural and pre-existing crack damage variability due to the complex and different magmatic history and cooling rates do control the evolution of the frictional properties and evolving fracturing processes. Further work will structurally quantify the slip evolution throughout post-mortem microstructural observation in order to interpret the relations to the field scale weakness zone and the SDF.

How to cite: Alcock, T., Vinciguerra, S., and Benson, P.: Multiscale analysis of physical rock properties at Stromboli Volcano: what controls the frictional properties?   , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1434, https://doi.org/10.5194/egusphere-egu22-1434, 2022.

EGU22-4697 | Presentations | EMRP1.14

Laboratory assessment of rock fracturing state using infrared thermography 

Federico Franzosi, Stefano Casiraghi, Roberto Colombo, Chiara Crippa, and Federico Agliardi

 

The fracturing state of rocks is a fundamental control on their hydro-mechanical properties at all scales and provides a descriptor of the evolution of brittle deformation around faults, underground excavations, and slopes. Its quantitative assessment is thus key to several geological, engineering and geohazard applications.

Descriptors of rock fracturing are diverse depending on considered scale, fracture topology (traces, surfaces) and sampling dimension (linear, areal, volumetric). A complete representation of fracture distribution and abundance in a 3D space can be obtained in the laboratory by non-destructive imaging techniques (e.g. X-ray CT), in terms of volumetric fracture intensity (P32) and porosity (P33). Nevertheless, geophysical imaging is usually unable to resolve small objects in fractured media at field scale. Window and scanline sampling strategies are easily applied in the field to measure fracture intensity descriptors (e.g. P10, P21) or empirical rock mass quality indices (e.g. GSI), but are affected by scale and fracture orientation biases. Some authors suggested that rock mass fracturing states can be characterized by measuring their heating and cooling response through infrared thermography (IRT), but a physically-based, generalized approach to prediction is lacking.

In this perspective, we carried out an experimental study on the thermal response of rock samples with known fracturing state. We studied cylindrical samples of gneiss (7) and schist (8), pre-fractured in uniaxial compression that produced complex fracture patterns constrained by rock composition and fabrics.

Using MicroCT (voxel: 0.625 mm) we reconstructed the 3D fracture network and computed the P32 and P33 of each sample. Then, we set up cooling experiments in both laboratory and outdoor conditions. In laboratory experiments, samples were oven-heated at 80°C and let cool in a controlled environment. Sample surface temperature during cooling was imaged in time lapse using a FLIRTM T1020 IRT camera. In outdoor experiments, samples underwent natural solar forcing in a daily heating-cooling cycle.

The acquired multi-temporal thermal images were processed to extract: a) spatial temperature patterns corresponding to the response of individual features and fracture networks at different cooling steps; b) time-dependent cooling curves, described in terms of Cooling Rate Indices and a Curve Factor. These descriptors show statistically significant correlations with fracture abundance measures, stronger with P33 than with P32 and more robust for gneiss samples, characterized by more distributed fractures than schist. More fractured rocks cool at faster rates and the corresponding cooling curve shapes can be normalized to remove the effects of lithology and boundary conditions to obtain a predictive tool. Experimental results have been reproduced by 3D finite-element modeling of the cooling process in numerical samples including explicit fracture objects. Model results closely reproduce experimental data when fracture surfaces are included as convection surfaces, suggesting that overall sample cooling rates depend on the size of individual blocks forming the sample. Results of outdoor experiments show that differences in thermal response can be significantly detected even in natural conditions. Our results provide a starting point to develop an upscaled, quantitative methodology for the contactless in situ assessment of fracturing state of rock masses using thermal data.

How to cite: Franzosi, F., Casiraghi, S., Colombo, R., Crippa, C., and Agliardi, F.: Laboratory assessment of rock fracturing state using infrared thermography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4697, https://doi.org/10.5194/egusphere-egu22-4697, 2022.

Failure and fault slip in crystalline rocks is associated with dilation. When pore fluids are present and drainage is insufficient, dilation leads to pore pressure drops, which in turn lead to strengthening of the material. We conducted laboratory rock fracture experiments with direct in-situ fluid pressure measurements which demonstrate that dynamic rupture propagation and fault slip can be stabilised (i.e., become quasi-static) by such a dilatancy strengthening effect. We also observe that, for the same effective pressures but lower pore fluid pressures, the stabilisation process may be arrested when the pore fluid pressure approaches zero and vaporises, resulting in dynamic shear failure.

We use acoustic emission locations and our fluid pressure sensors to further detail dilatancy-induced stable failure by tracking the progression of the rupture front (i.e., creation of the fault) and the active slip patches of the newly formed fault. In doing so, we are able to link local pore pressure records to the position of the rupture front where dilation is strongest. We see minimal slip in the wake of the rupture front. Once the fault is completed, we observe that the entire fault slips for up to a few minutes, driven by pore pressure recharge of the fault zone. Hence, we directly observe decoupling of rupture and “after”-slip that would otherwise – in a dynamic failure – occur simultaneously.

All our observations are quantitatively explained by a spring-slider model combining slip-weakening behaviour, slip-induced dilation, and pore fluid diffusion. Using our data in an inverse problem, we estimate the key parameters controlling rupture stabilization: fault dilation rate and fault zone storage. These estimates are used to make predictions for the pore pressure drop associated with faulting, and where in the crust we may expect dilatancy stabilisation or vaporisation during earthquakes. For intact rock and well consolidated faults, we expect strong dilatancy strengthening between 4 and 6 km depth regardless of ambient pore pressure, and at greater depths when the ambient pore pressure approaches lithostatic pressure. In the uppermost part of the crust (<4 km), we predict vaporisation of pore fluids that limits dilatancy strengthening.

How to cite: Aben, F. and Brantut, N.: How dilatancy-induced pore pressure changes control rupture and slip during failure experiments in crystalline rock., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5711, https://doi.org/10.5194/egusphere-egu22-5711, 2022.

EGU22-7387 | Presentations | EMRP1.14

Permeability evoluation at the brittle to ductile transition in newberry volcano basalt 

Marie Violay and Gabriel Meyer

Superhot Rock (SHR) geothermal projects (e.g., Japan Beyond-Brittle Project, Iceland Deep Drilling Project, and Newberry Volcano) seek to extract heat from geothermal reservoirs where water reaches a supercritical state (≥ 400 °C). Exploiting such a resource could multiply the electrical power delivered by geothermal wells by almost an order of magnitude. However, SHR reservoirs are hosted in semi-brittle to ductile rocks where fluid flow, porosity, permeability, and rock mechanics are still poorly understood. We conduct experiments in a newly designed, internally heated, gas-confining triaxial apparatus (located at EPFL, CH) where we deform reservoir-type samples under realistic SHR temperature, pressure, and strain rate conditions. Deep well core samples (40 x 20 mm) of andesitic basalts (porosities of 8–10%) from Newberry Volcano (US), were subjected to increasing confinement pressure (25–100 MPa) and temperature (20–500 °C) while continuously recording gas permeability via harmonic permeability. Additionally, triaxial deformation experiments were done at strain rates of 10-6 s-1, confinement up to 100 MPa, temperature up to 500 °C, and up to 8% strain while recording permeability. Results were compared with granite samples from Lanhelin (Fr.). Samples were ductile (e.g., no localization of strain) at relatively low pressure–low temperature conditions (100 MPa, 200 °C). Moreover, permeability in samples subjected to hydrostatic conditions rapidly decreased several orders of magnitude from an initial value of 5.10-20 m2 to less than 10-22 m2  at 50 MPa and 200 °C, effectively impermeable. Thus, permeability decreases rapidly in the ductile regime with strain to reach below measurable values at around 3% strain, and it remains so during subsequent semi-brittle flow up to 8% strain. We interpret this rapid decay of permeability as a result of the conjoined effect of ductile pore collapse and plastic deformation of the poorly crystalline matrix present in the sample. These insights further underline the need for advanced, sustainable reservoir engineering techniques in order to extract heat from high enthalpy geothermal reservoirs.

How to cite: Violay, M. and Meyer, G.: Permeability evoluation at the brittle to ductile transition in newberry volcano basalt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7387, https://doi.org/10.5194/egusphere-egu22-7387, 2022.

EGU22-7429 | Presentations | EMRP1.14

Hydromechanical Coupling and Damage at a Retreating Glacier Margin 

Marc Hugentobler, Simon Loew, and Jordan Aaron

In deglaciating environments, rock slopes are affected by stress perturbations driven by mechanical unloading due to ice downwasting and concurrent changes in thermal and hydraulic boundary conditions. Since in-situ data is rare, the different processes and their relative contribution to slope damage remain poorly understood. Here we present detailed analyses of subsurface pore pressures and micrometer scale strain time-histories recorded in three boreholes drilled in a rock slope aside the retreating Great Aletsch Glacier (Switzerland). Additionally, we use monitored englacial water levels, climatic data, and annually acquired ice surface measurements for our process analysis.

At the timescale of days, diurnal meltwater cycles and rainfall infiltration into the glacier during summertime cause strong pressure fluctuations in the subglacial drainage channel that diffuse into the adjacent rock aquifer. We show that the pressure diffusion from the subglacial meltwater channel, through the fractured bedrock below the glacier ice, to the ice-free bedrock slope occurs under predominantly confined conditions. In the adjacent ice-free bedrock, rainfall infiltration can cause strong variations in the phreatic groundwater table of the slope. On the seasonal timescale, glacial hydraulic boundary conditions vary with high, relatively constant englacial water levels during wintertime and lower mean englacial water levels during summertime. Above ice elevations, snowmelt infiltration during springtime causes yearly maximum phreatic groundwater tables and a general recession over the rest of the year, that is interrupted by summertime rainfall infiltrations. The seasonality in hydraulic head levels of both the glacier and the rock slope controls the interaction of the two systems. On timescales of decades, phreatic groundwater levels in the rock slope are often assumed to be linked to the ice elevation of temperate glaciers. According to our data, this head boundary effect of the glacier is mainly effective during wintertime when it controls the minimum groundwater level in the slope.

Our results show that the variations in mechanical boundary conditions (or loads) caused by a temperate valley glacier on the adjacent rock slope are more complex than had been previously described. Our observed rapid bedrock strain signals coincide with some of the extreme englacial water level states, and are likely caused by rapid changes in the mechanical load of the glacier with an empty or water filled englacial drainage system. Similarly, but at seasonal timescales, the spring and fall transition time of the englacial hydrological system coincides with characteristic strain reactions in our bedrock slope. Our in-situ data show that these effects also promote progressive rock mass damage, probably similar to hydromechanical effects. Additionally, we show how a single extreme rainstorm event triggers hydromechanical damage exceeding the levels of two years exposition to all the other drivers for progressive rock mass damage in this environment.

The magnitude and impact of coupled cyclic processes in a paraglacial rock slope vary with location on the slope and the process considered. The strongest damage is observed directly at the actively reteating glacer margin and moves through the slope at relatively high speed.

How to cite: Hugentobler, M., Loew, S., and Aaron, J.: Hydromechanical Coupling and Damage at a Retreating Glacier Margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7429, https://doi.org/10.5194/egusphere-egu22-7429, 2022.

EGU22-7622 | Presentations | EMRP1.14

Impact of structural geology on the failure mechanisms of a rock fall site in a metamorphic rock mass (Hüttschlag, Austria) 

Reinhard Gerstner, Erik Kuschel, Gerald Valentin, Klaus Voit, Wolfgang Straka, and Christian Zangerl

The case study presented herein is located in the alpine environment of Austria (Hüttschlag), in the geologic unit of the Rauris Nappe, belonging to the Glockner Nappe System. The study site is composed of intensively foliated and fractured calc-mica schists and greenschists. Together with several generations of pre-existing discontinuity-sets, they form a rock mass, which has hosted multiple rock fall events since 2019. The rock fall events show a cumulative volume of 41 000 m3, with individual blocks of up to 200 m3 reaching the valley bottom.

In order to gain insights into the interplay between structural geology and the rock fall failure mechanism, we present a combined approach of methods. They act on multiple observation scales: At the micro-scale, intact rock samples are studied by petrographic microscopy of orientated thin sections. This provides insights into the mineralogy of the intact rocks and their inherent brittle and ductile microstructures (e.g. micro-cracks, folding).

In the field, advanced remote sensing techniques were applied, to perform medium- to large-scale investigations. For this purpose, a ground-based radar interferometer (GB-InSAR) was installed for several months. By this, the actual deformation of the unstable rock face and of the rock fall deposit at the slope´s foot was measured at mm resolution. Additionally, several campaigns of terrestrial laser scanning (TLS) enable us to derive high-resolution recordings of the inaccessible rock face, backed by 3D point cloud processing (LIS Pro 3D) tools. For additional displacement measurements and graphic representation of the results, unmanned aerial system photogrammetry (UAS-P) delivers a 3D model of the rock face.

Geological field investigations complete this combined approach, comprising the recording of lithological, hydrogeological and structural geological features. They embed the rock fall site in its geological setting and allow the creation of a 3D discontinuity network, validating the measurements derived from the advanced remote sensing techniques listed above.

The preliminary results promise interesting insights into the interplay between distinctive structural features and the failure mechanisms of the rock fall site in Hüttschlag, working on variable scales: From micro-structures to well-defined discontinuities, that may be reactivated in course of the rock fall process. This broad database serves as the basis for numerical modelling, intensifying the investigation of failure mechanisms. Furthermore, the high-resolution recordings of the instable rock face derived from UAS-P and TLS allow us to assess the potential failure volume of future rock fall events, contributing to the rock fall site´s hazard assessment subsequently.

How to cite: Gerstner, R., Kuschel, E., Valentin, G., Voit, K., Straka, W., and Zangerl, C.: Impact of structural geology on the failure mechanisms of a rock fall site in a metamorphic rock mass (Hüttschlag, Austria), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7622, https://doi.org/10.5194/egusphere-egu22-7622, 2022.

EGU22-9278 | Presentations | EMRP1.14

Multiscale characterization of chaotic rock body for mining backfill remediation 

Chiara Caselle, Sabrina Maria Rita Bonetto, Pietro Mosca, Arianna Paschetto, Davide Vianello, Andrea Garello, and Fabio Paletto

The sustainability of geomineral resourses’ exploitation may be assured only in presence of adequate plans for the re-use and reclamation of old or abandoned sites. Among the most commonly used techniques, mining backfill is largely employed for the stabilization of underground sites. This technique recreates the original stress state of the underground, assuring the definitive stabilization of the hypogea volumes, and reduces the risks due to the interference between underground tunnels and ground surface (e.g. possible collapses and surface subsidences). Despite these obvious advantages, careful evaluations are needed to assure the environmental sustainability, with particular attention to the interaction between the hydro-geological and permeability features of the rock body and the chemical properties of the backfill material.

The present research proposes an analysis of the advantages and the risks connected with this technique, examining a case study of mining backfill in an underground gypsum quarry at the end of the active exploitation. The considered quarry is located in Monferrato (NW Italy) and is exploited within chaotic Messinian deposits made of gypsum blocks (from centimeter-size to kilometer-size) included in a marly matrix. The study includes a campaign of field and laboratory tests (i.e. geological and geo-structural mapping and modeling, geophysical surveys, mechanical and permeability tests) that aim at characterize the permeability and mechanical behaviour of the rock mass.

How to cite: Caselle, C., Bonetto, S. M. R., Mosca, P., Paschetto, A., Vianello, D., Garello, A., and Paletto, F.: Multiscale characterization of chaotic rock body for mining backfill remediation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9278, https://doi.org/10.5194/egusphere-egu22-9278, 2022.

EGU22-228 | Presentations | EMRP1.15

Sensitivity study of C/O logging measurements by the Monte Carlo method 

Jozsef Gabor Szucs and Laszlo Balazs

Carbon oxygen ratio (C/O) logging is an important method for the accurate determination of hydrocarbon saturation in the reservoir region. One of the advantages of the measurement, that it is independent of Cl content. Furthermore, the insensitivity of high energy neutrons to the casing, makes it possible to use it in cased boreholes too. In addition to the application in the oil industry, monitoring of CO2 reservoirs is also possible. In our study, the modeling of the time-dependent coupled neutron-gamma field produced by the tool was carried out, using MCNP, a general-purpose Monte Carlo radiation transport code. The energy spectrum of gammas reaching the scintillation detector crystal were simulated in different detector positions, and different tool environments: reservoir rock, reservoir porosity, hydrocarbon saturation, and well status (cased or open). The effect of the parameters above are illustrated by vertical cross sections of the particle fluxes around the tool, and shown by the changes of the interpretation charts. By the introduction of a “goodness” factor, derived from the interpretation chart, the potential, and the limitations of C/O logging are investigated.

How to cite: Szucs, J. G. and Balazs, L.: Sensitivity study of C/O logging measurements by the Monte Carlo method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-228, https://doi.org/10.5194/egusphere-egu22-228, 2022.

EGU22-660 | Presentations | EMRP1.15

The role of pore space topology on ultrasonic wave propagation in volcanic rocks. 

Maria Del Pilar Di Martino, Luca De Siena, and Nicola Tisato

At the field scale, petro-elastic models linking seismic velocities with porosity have been widely used to estimate properties of reservoirs and subsurface domains in general. At the laboratory scale, frame elastic properties and porosity are not enough to predict the full ultrasonic wave propagation, and other factors like texture, pore space topology and fluid interactions play a significant role. In dry volcanic rocks characterized by larges vesicles, the heterogeneities triggering the perturbations of the ultrasonic wavefield mainly correspond to the pore space topology. However, the sensitivity of S-waveforms to the pore space has not been examined in volcanic rocks.

To assess the role of the pore space on ultrasonic wave propagation, we performed computational simulations on 2D synthetic samples analogous to volcanic rocks, resembling the acquisition of S-waveforms in laboratory experiments. The computational framework applied is the spectral-element method. The porosity and aspect ratio on the study samples was kept constant along the simulations to focus on the effect that the pore space parameters have on the wave arrival, amplitude, and shape of the waveforms.

This study shows that the pore space topology controls the waveform of ultrasonic waves in dry volcanic rocks, and parameters like amount, size, and even the location of the pores impact the elastic wave propagation independently of the porosity value. This finding has important implications for forward modelling seismic signals of heterogeneous volcanic media at the field scale.

How to cite: Di Martino, M. D. P., De Siena, L., and Tisato, N.: The role of pore space topology on ultrasonic wave propagation in volcanic rocks., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-660, https://doi.org/10.5194/egusphere-egu22-660, 2022.

EGU22-668 | Presentations | EMRP1.15

Homogenization of Poroelastic Media without a Representative Elementary Volume for Seismic Applications 

Edith Sotelo Gamboa, Nicolas D. Barbosa, Santiago G. Solazzi, Marco Favino, J. German Rubino, and Klaus Holliger

The substitution of a heterogeneous poroelastic medium by its homogenized viscoelastic representation is an effective technique to study its seismic response. This homogenization procedure reproduces the dispersive behaviour of the original fast P- and S-waves. This dispersive nature results from energy dissipation that occurs when a wave induces pressure gradients between the heterogenous parts of a poroelastic medium that are equilibrated by fluid exchange. The underlying homogenization approach is to apply oscillatory tests on a representative elementary volume (REV) of the poroelastic medium to find the equivalent moduli. The REV is a sample that is typical of the entire medium under consideration and that ensures results independent of boundary conditions. This is, the REV should be larger than the heterogeneities but much smaller than the medium size. Additionally, in poroelastodynamics, the size of the heterogeneities in the REV is dictated by the scale at which the wave-induced fluid exchange takes place. We focus on the mesoscale. At this scale, fluid exchange occurs between heterogeneities that are larger than the grain size but smaller than the wavelength. However, there are poroelastic media of interest that present heterogeneities of comparable size to that of the domain. Here, the REV concept does no longer apply since the poroelastic sample under examination is affected by the boundaries of the domain. For such scenarios, we propose a novel homogenization method that incorporates the boundary effects produced by the surrounding medium. In this method, we take a sample that consist of the affected poroelastic heterogeneity together with part of the embedding medium. Then, we perform the classical oscillatory tests over this ensemble. Finally, to obtain the homogenized moduli of the poroelastic medium, we perform the averaging of strain and stress only over this domain of interest. As examples, we present a poroelastic system of a single sand layer saturated with gas at the top and water at the bottom that is embedded in impermeable background. We also study a water-saturated poroelastic set consisting of a permeable fracture surrounded by a less permeable damage zone that is also embedded in impermeable background. We idealize these cases as 2D media, assuming that the poroelastic system is infinite along the layering plane but bounded perpendicular to it by impermeable half-spaces. The samples subjected to oscillatory tests consist of a piece of the semi-infinite poroelastic domain together with the corresponding bounding half-spaces. To test the viability and accuracy of the method, we compare reflectivities at the top interface of the half-space and homogenized medium against those obtained at the top interface of the half-space and the original poroelastic system. Results show that errors are of the order of 1 %. The proposed method can be readily extended to 3D and more complex models.

How to cite: Sotelo Gamboa, E., Barbosa, N. D., Solazzi, S. G., Favino, M., Rubino, J. G., and Holliger, K.: Homogenization of Poroelastic Media without a Representative Elementary Volume for Seismic Applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-668, https://doi.org/10.5194/egusphere-egu22-668, 2022.

EGU22-945 | Presentations | EMRP1.15

Controls on Sonic Velocity in Dolostones 

Moaz Salih, Ammar El-Husseiny, John J.G. Reijmer, Hassan Eltom, Abdallah Abdelkarim, and Mike A. Kaminski

Dolostones represent one of the major hydrocarbon reservoirs in the world. Understanding the elastic behavior of these units is crucial for hydrocarbon exploration and/or development. In this study, 100 samples from five formations within the Arabian Platform, were used to examine the main controlling factors on the sonic velocity of dolostones. A combination of field and laboratory analyses were conducted on the collected samples including; thin-section petrography, SEM, XRD, digital image analysis, porosity and permeability measurements, velocity measurements, and rock physics modeling. The studied samples have a wide range of porosity (1- 45%, averaging 18.5 %), and permeability (0.01 2000 mD, averaging 196 mD). Compressional VP and shear wave VS velocity ranges from 3.0 - 6.7 km/s, and 1.6 3.7 km/s, respectively. In general, porosity-velocity trajectory is showing a negative relationship with a coefficient of determination R2 of 0.82. However, some samples are deviated from this trendline due to their inherited and diagenetic parameters. These parameters include texture, mineralogy, pore type, and crystal size. Fabric-preserving dolostones have, relatively, higher velocities than non-fabric preserving dolostones. Although 95% of the studied samples are dominated by dolomite, samples with higher content of calcite and quartz, have lower velocities. Moldic and vuggy pore-dominated samples have, relatively, higher velocities than samples dominated by intercrystalline pores and microporosity. For non-fabric preserving dolostones, samples with larger crystals show higher velocities than samples with smaller crystals. Using equivalent pore aspect ratio (EPAR), a clear distinction between permeable (>10 mD) and tight (< 10 mD) samples can observed, where most of the permeable samples have high EPAR values, while the tight samples have low EPAR values. The result of this study might significantly help in the interpretation and understanding of the sonic logs and seismic data from dolostone strata.

How to cite: Salih, M., El-Husseiny, A., Reijmer, J. J. G., Eltom, H., Abdelkarim, A., and Kaminski, M. A.: Controls on Sonic Velocity in Dolostones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-945, https://doi.org/10.5194/egusphere-egu22-945, 2022.

EGU22-3523 | Presentations | EMRP1.15

How to discover ancient stress-levels preserved within fractures using the stress-memory effect of specific stiffness 

Christian Kluge, Lena Muhl, Daniel Schramm, and Guido Blöcher

Stress changes have a large impact on the hydraulic and mechanical properties of fractures and can be caused by varying the fluid pressure in a subsurface reservoir or by tectonic movements. Innovative tools to assess the stress conditions are still of major importance for most subsurface applications. We derived an experimental procedure to reveal stress signals preserved in fractures in the laboratory.

In a set of complex experiments various fractured low-permeability rocks, two sandstones and two crystalline rocks, were cyclically loaded in a MTS tri-axial compression cell. The preconditioned cylindrical samples were split into two halves to generate an artificial tensile fracture and a rigid shear displacement was applied before installing the sample into the apparatus. Two different loading scenarios were applied: “continuous cyclic loading” (CCL) and “progressive cyclic loading” (PCL). During continuous cyclic loading samples were loaded from 2 to 60 MPa in several repeated cycles. In the progressive cyclic loading experiments the hydrostatic confining pressure was increased using a step-wise function (15, 30, 45 and 60 MPa) and was unloaded after every sub-cycle, while the pore pressure was kept constant at a low level. The mechanical fracture closure was monitored continuously during the experiments using axial and circumferential extensometers and the specific fracture stiffness could be calculated at a very high resolution. The fracture permeability was measured continuously using four high-pressure fluid pumps. A 3D surface scanner was used to analyze the fracture surface geometry before and after the experiments to reveal possible changes to the surface topography as well as to quantify changes in aperture and contact-area ratio.

The specific fracture stiffness was shown to be irreversible when a fracture was hydrostatically loaded once. Further, a “stress-memory” effect of fracture stiffness could be shown during progressive loading. It is characterized by a change from non-linear to linear stiffness evolution when a previous stress-level is exceeded. This phenomena can be used to identify previous stress states preserved within fractures. Additionally, this data is important for elasto-plastic contact theories of rough fractures. The impact of progressive loading on fracture permeability evolution showed varying results based on the heterogeneity and mineral composition of each rock type and the resulting fracture geometry.

How to cite: Kluge, C., Muhl, L., Schramm, D., and Blöcher, G.: How to discover ancient stress-levels preserved within fractures using the stress-memory effect of specific stiffness, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3523, https://doi.org/10.5194/egusphere-egu22-3523, 2022.

EGU22-5185 | Presentations | EMRP1.15

NMR investigation of boundary condition effects on spontaneous imbibitionin Longmaxi shale 

Yong Liu, Yanbin Yao, Dameng Liu, and Chi Zhang

Spontaneous imbibition is an important process that wetting fluid displaces the non-wetting fluid in the rock by capillary force and is responsible for low flowback efficiency (<30%) of fracturing fluid and severe water blocking effects in shale gas reservoirs. It is crucial to understand the boundary condition effects on imbibition dynamics in shale and the shale-fluid interactions as they provide insights into fracturing fluid loss which can influence gas production. In this study, we designed imbibition experiments and used nuclear magnetic resonance (NMR) to investigate spontaneous imbibition behaviors and water-shale interactions in shale samples with varied boundary conditions including all-side-open (ASO), two-side-open (TSO), one-side-open (OSO), half-side-open (HSO) and two-side-closed (TEC) to. These five boundary effects in imbibition were analyzed by dividing the imbibition stages and comparing the imbibition dynamics. Key imbibition parameters including water saturation, gas recovery factor, residual gas saturation, imbibition capacity, diffusion ability, imbibition rate, and imbibition potential under the respective boundary conditions were selected to compare the imbibition features of five boundary effects. Our results elucidate the existence of three types of water imbibition patterns including the radial counter-current imbibition as shown in TEC boundary condition, the axial co-current imbibition as shown in OSO and TSO conditions, and the compound imbibition which exhibits both radial counter-current imbibition and axial co-current patterns as in ASO and HSO. T2 relaxation times in OSO and TSO shifted to larger relaxation times as imbibition occurred, demonstrating the induced microfractures were generated in water imbibition due to shale-water interactions. Furthermore, imbibition parallel to the bedding plane and imbibition vertical to the beddings have different water migration patterns due to bedding structures of shale. Our experiments contribute to the understanding of the mechanisms of how different boundary conditions affect imbibition dynamics and shale-water interactions in shale gas reservoirs, which is valuable to the interpretation of fracturing liquid retention processes.

How to cite: Liu, Y., Yao, Y., Liu, D., and Zhang, C.: NMR investigation of boundary condition effects on spontaneous imbibitionin Longmaxi shale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5185, https://doi.org/10.5194/egusphere-egu22-5185, 2022.

EGU22-5194 | Presentations | EMRP1.15

The poroelastic response of cracked Westerly granite to cyclical changes in load 

Bobby Elsigood, Nicolas Brantut, Philip Meredith, Tom Mitchell, and David Healy

The poroelastic behaviour of cracked rocks is expected to depend on the geometry and properties of the crack network. Any preferred orientation of microcracks produces anisotropy in physical rock properties, including poroelastic parameters. Under conventional triaxial loading there is an alignment of cracks parallel to the vertical direction of compression, leading to vertical transverse isotropy in the cracked rock.

Here, we repeatedly measured transversely isotropic poroelastic parameters during increasing amplitude cyclic loading in a sample of Westerly granite saturated with water. Independent step changes in confining pressure and differential stress were repeated at selected levels of differential stress to measure the change and reversibility in the transversely isotropic parameters throughout the loading and unloading cycles.

We used miniature differential pressure transducers which were located directly around the sample surface, allowing for direct measurement of the pore pressure in the sample. The direct measurements of pore pressure allow us to estimate undrained properties, including Skempton’s coefficients. Axial and radial strain gauges allow for the calculation of elastic moduli from the step changes in axial and radial stress. We determine the undrained moduli from the initial short-term response, and the drained moduli following pore pressure equilibration for each step change in stress.

Results show that the radial Skempton’s coefficient increases with increased differential stress, and the axial coefficient decreases and even becomes negative (where increases in axial stress cause a decrease in pore pressure) at high stress (i.e., about 80% of failure stress). During unloading, the measured Skempton coefficients are observed to be recovered, without hysteresis.

How to cite: Elsigood, B., Brantut, N., Meredith, P., Mitchell, T., and Healy, D.: The poroelastic response of cracked Westerly granite to cyclical changes in load, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5194, https://doi.org/10.5194/egusphere-egu22-5194, 2022.

EGU22-8360 | Presentations | EMRP1.15

Numerical modelling of pressure-dependent permeability in Bentheim sandstone 

Mirko Siegert, Marcel Gurris, and Erik H. Saenger

A method for the numerical determination of pressure-dependent permeability in sandstones is developed. The proposed method is restricted to a hydrostatic pressure load that is below the pore collapse pressure.

Our modelling approach is generally based on the idea of digital rock physics. Starting from a µCt-scan, the pore space of a given rock sample is detected and transferred into a numerical model. Subsequently, the stationary Stokes equations are solved, and the permeability is determined from the simulated pressure and velocity fields.

To model the pressure dependence, it is assumed that the deformation of the rock's micro-structure due to pore throat closing has a significant influence on the change in permeability. In our workflow, the respective pore throats between the individual grains of the original CT image are reconstructed using the watershed algorithm and combined in a separate phase of the numerical model. During several simulations, a steadily increasing artificial flow resistance is assigned to the pore throat phase and the respective permeability of the whole sample is determined. Finally, the pressure-dependent permeability curve can be reconstructed via a correlation between flow resistance and pressure load.

The proposed workflow is validated with externally published data of a Bentheim sandstone sample. It is observed that the model is generally able to reproduce the characteristics of a experimentally determined pressure-dependent permeability curve.

How to cite: Siegert, M., Gurris, M., and Saenger, E. H.: Numerical modelling of pressure-dependent permeability in Bentheim sandstone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8360, https://doi.org/10.5194/egusphere-egu22-8360, 2022.

EGU22-8775 | Presentations | EMRP1.15

Numerical investigation of hydro-mechanical responses of a single fracture embedded in a porous matrix 

Guido Blöcher, Christian Kluge, Mauro Cacace, Qinglin Deng, and Jean Schmittbuhl

We have conducted a flow-through experiment using a Flechtingen sandstone sample containing a single macroscopic fracture. Based on this experiment, we obtained range of various intrinsic rock parameters, such as permeability and specific stiffness of the combined matrix-fracture system under hydrostatic loading. In order to quantify the processes behind the laboratory observations, we carried out coupled hydro-mechanical simulations of the matrix-fracture system. Navier-Stokes flow was solved in the 3-dimensional open rough fracture domain, and back-coupled to Darcy flow and mechanical deformation of the rock matrix.

To capture the volumetric shape of the fracture, the two fracture surfaces were scanned using a 3D-profilometer (Keyence VR-3200) before and after the experiment. The resulting fracture surfaces were aligned using a grid-search algorithm and subsequently offset to mimic the shear displacement as applied during the laboratory experiment. Based on the obtained 3D representation of the fracture volume embedded in a porous media, the stress path of the laboratory experiment was simulated numerically. By means of the simulation results, values of fracture closure, increase of contact area, fracture permeability and fracture stiffness due to normal load on the fracture surface were obtained.

The results demonstrate that the numerical simulation could capture the elastic and inelastic behaviour as well as the related permeability alteration of the fracture domain. Both, the laboratory experiments as well as the numerical simulation indicate an inelastic deformation of the single fracture even at low normal stress. The inelastic deformation is expressed by an increase of the fracture contact area and therefore fracture stiffness with increasing stress. The increase in the contact area is due to a reduction in mean aperture and is therefore accompanied by a reduction in the fracture permeability. The development of the contact area is irreversible and thus indicates the maximum stress that the sample previously experienced. We call this behaviour "stress-memory effect".

We present the workflow to obtain the numerical results and a comparison with the laboratory experiment to show that the dominant processes were captured by the simulation.

How to cite: Blöcher, G., Kluge, C., Cacace, M., Deng, Q., and Schmittbuhl, J.: Numerical investigation of hydro-mechanical responses of a single fracture embedded in a porous matrix, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8775, https://doi.org/10.5194/egusphere-egu22-8775, 2022.

EGU22-9616 | Presentations | EMRP1.15

Electrical properties and anisotropy of schists and fault rocks from New Zealand’s Southern Alps under confining pressure 

Virginia Toy, Emma-Katherine Kluge, and David Lockner

Magnetotelluric inversions spanning the Pacific-Australian Plate boundary in New Zealand’s South Island indicate there is a localized zone of low electrical resistivity that is spatially co-incident with the mid-crustal part of the Alpine Fault Zone (AFZ), that currently accommodates shear strain by temperature-sensitive creep. We explored the source of this anomaly by measuring the electrical properties of samples collected from surface outcrops approaching the AFZ that have accommodated a gradient of systematic strain and deformation conditions. We investigated the effects of tectonite fabric, fluid saturated pore/fracture networks and grain surface conduction on the bulk electrical response and the anisotropy of resistivity of these samples measured under increasing confining pressures up to 200 MPa. We find that for fault rock protoliths, Haast and Alpine Schist, resistivity and change in anisotropy of resistivity with confining pressure (δ(ρ)/ δ(peff)) increases while porosity decreases approaching the AFZ. This indicates the electrical response is controlled by pore-fluid conductivity and modified during progressive metamorphism. AFZ mylonites exhibit low electrical resistivities at low porosities, and lower δ(ρ)/ δ(peff) than the schists. These reflect changes in both the porosity distribution and electrical charge transport processes in rocks that have experienced progressive grain size reduction and mixing of phases during development of mylonitic fabrics due to creep shear strain within the AFZ.

How to cite: Toy, V., Kluge, E.-K., and Lockner, D.: Electrical properties and anisotropy of schists and fault rocks from New Zealand’s Southern Alps under confining pressure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9616, https://doi.org/10.5194/egusphere-egu22-9616, 2022.

EGU22-9703 | Presentations | EMRP1.15

Inspecting internal magnetic field gradients in volcanic rocks 

Nadjib Chibati and Yves Geraud

Nuclear magnetic resonance (NMR) is being used since 1990 in the petroleum industry. NMR is a powerful tool for petrophysical properties estimation (porosity, permeability, pore size distribution, and irreducible saturation). Despite its large success in the conventional carbonate and sandstone reservoirs, some tight sandstones, volcanic and metamorphic rocks, contain a high amount of paramagnetic and clay minerals, which can complicate the interpretation of NMR results. These complications are due to the inhomogeneities of the internal magnetic field generated by the magnetic susceptibility contrast between the pore-fluid and the matrix. The magnitude of the internal gradients depends on the strength of the background magnetic field, magnetic susceptibility contrast, and pore size.

Many studies are focused on the investigation of the effect of clay and paramagnetic minerals on the internal gradient and their implications on the NMR-derived petrophysical properties mainly of the high magnetic susceptibility sandstones. The primary goal of this analysis is to investigate the magnitude of the internal magnetic gradient of volcanic rocks with different alteration grad and its relationship with the rock properties (magnetic susceptibility, iron, and manganese content, pore type, and pore size).

The data were collected using the Minispec q10®, with Larmor frequency of 10 MHz, on the water-saturated samples with magnetic susceptibility between 26.8 10-3 and -0.4 10-3 SI. The average effective internal gradient was calculated from the slope of the mean log relaxation rate (T2gm-1) versus the squared echo time (TE2). The preliminary results show that samples presented a multi-distribution of T2 peaks corresponding to the different pore types observed for these samples (micro, meso, and macropores). The average effective internal magnetic field gradient calculated from the slope of T2gm-1 vs TE2 ranges from 0 to 43.16 T.m-1. The average effective internal gradient increases with the increase of magnetic susceptibility and decreases as the T2gm increase, suggesting that the pore size also impact internal gradient magnitudes. However, No clear relation exists between iron content and average effective internal gradient.

How to cite: Chibati, N. and Geraud, Y.: Inspecting internal magnetic field gradients in volcanic rocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9703, https://doi.org/10.5194/egusphere-egu22-9703, 2022.

EGU22-10087 | Presentations | EMRP1.15

Seismic velocity variations generated by controlled hydrological changes : field and laboratory studies based on seismic noise crosscorrelation 

Thomas Gaubert-Bastide, Stéphane Garambois, Clarisse Bordes, Christophe Voisin, Daniel Brito, Philippe Roux, and Laurent Oxarango

Continuous seismic noise recordings has demonstrated a remarkable ablitiy to monitor changes of the investigated media at various scales. In this study, we focused on the link between seismic velocity variations (dv/v) derived from seismic noise cross-correlations between pairs of stations and hydrological variations observed both at the field and lab scales. The field-scale experiment was performed at the water supply pumping site of Crépieux-Charmy (Lyon, France). 99 3-C velocimeters were deployed during 20 days around an infiltration basin operated for managed aquifer recharge and designed to generate an hydraulic barrier to prevent a potential contamination from the nearby river. This dense seismic network set-up allowed to dynamically image the seismic velocity variations during two filling/drainage cycles of the basin. Punctual values extracted from computed high resolution tomographies of the velocity variations were compared to local measurements of the water table level using piezometers. A remarkable agreement was found between the 2 observables in particular during the establishment of a 3D dome in the water table. During drainage phases, systematic response delays were observed which are most probably due to variations of water content in the unsaturated zone between the basin and the water table.
To better understand these effects occurring in the critical zone, we tried to reproduce a similar monitoring experiment at the laboratory scale. A tank filled with sand was designed in order to characterize controled hydrological variations (water table depth, water saturation). We used continuous seismic sources deployed on the edges of the tank. The seismic noise was recorded using 10 3-C accelerometers . The combination of these two approaches at different scales provides a better understanding of the links between seismic velocity and hydrological (water table level and water content in the vadose zone) variations.

How to cite: Gaubert-Bastide, T., Garambois, S., Bordes, C., Voisin, C., Brito, D., Roux, P., and Oxarango, L.: Seismic velocity variations generated by controlled hydrological changes : field and laboratory studies based on seismic noise crosscorrelation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10087, https://doi.org/10.5194/egusphere-egu22-10087, 2022.

EGU22-10389 | Presentations | EMRP1.15

Correlation of magnetic pore fabrics with traditional pore fabric characterization and permeability anisotropy in typical sedimentary rocks and hot isostatically pressed samples 

Yi Zhou, Michele Pugnetti, Anneleen Foubert, Pierre Lanari, Christoph Neururer, and Andrea Biedermann

Pore-scale experiments are crucial to obtain pore geometry and distribution, i.e., pore fabrics, controlling preferred fluid flow directions in rocks. Pore fabrics are characterized to derive models, which are important for hydrocarbon exploration and geothermal applications. X-ray computed tomography (XRCT) is one typical method to obtain three-dimensional pore fabrics, but limited by its micron-scale resolution in 1-inch cores. Magnetic pore fabrics (MPFs) were proposed as a fast and efficient way to indirectly measure the pore fabrics, and target micropores down to 10 nm. Empirical relationships exist between MPFs and pore space properties, and between MPFs and permeability anisotropy. Previous studies investigated a limited number of rock types or plastic synthetic samples with simplified pores to compare MPFs, pore fabrics and permeability anisotropy. Permeability is commonly estimated from measurements parallel and perpendicular to the macroscopic fabric, and thus the measurement needs a priori information on the fabric orientation. This study integrates complementary measurements to characterize pore fabrics on various scales: pycnometer porosity, MPF, XRCT, and permeability anisotropy measurements. The specimens include various kinds of sandstones and carbonates to cover the main sedimentary lithologies, and hot isostatically pressed (HIP) samples of simple and controlled compositions to bridge the gap between the synthetic samples of previous studies and complex natural rocks. HIP samples were made by mixing calcite and muscovite powders in different proportions and grain sizes, and were cold pressed at 20 MPa and then hot pressed at 160 MPa and 670 °C. Full permeability tensors including confidence angles were determined, and each tensor was calculated from 7 directional permeability measurements for natural rocks. Considering the uniaxial symmetry of the HIP samples, 3 directional measurements are sufficient to calculate a tensor with confidence angles. One additional core from each block was scanned by XRCT with ~5.5 µm pixel size for 3D pore fabric analysis, prior to being impregnated with ferrofluid to measure MPFs. A total shape ellipsoid, representing the average XRCT-derived pore fabric, is compared with other second-order tensors, permeability anisotropy and MPFs. Initial data suggest that the maximum principal directions of permeability anisotropy, total shape ellipsoids and MPFs are coaxial in homogeneous samples with consistent pore space anisotropy. These confirmed quantitative correlations help to apply MPFs as an efficient method to determine pore fabrics and predict preferred flow direction.

How to cite: Zhou, Y., Pugnetti, M., Foubert, A., Lanari, P., Neururer, C., and Biedermann, A.: Correlation of magnetic pore fabrics with traditional pore fabric characterization and permeability anisotropy in typical sedimentary rocks and hot isostatically pressed samples, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10389, https://doi.org/10.5194/egusphere-egu22-10389, 2022.

Zeta potential is an important petrophysical property that controls electrostatic interactions between mineral, water, and non-aqueous phase fluids. These interactions play an important role in defining the wetting state of reservoir rocks. The zeta potential can be interpreted from the streaming potential measurements, which are shown to be an efficient means for a broad range of applications including monitoring of single- and multi-phase flows in subsurface settings, characterization of fracture networks, efficiency of CO2 sequestration, hydrogen underground storage and enhanced oil recovery. It is widely agreed that the zeta potential in carbonate rocks is controlled by the concentration of potential determining ions (PDI), but the understanding of this is still poor and there are very limited experimental data on quantitative characterization of the dependence of the zeta potential on concentration of negative potential determining ions (PDI) such as SO42-, CO32-, HCO3-, especially when their concentration is high and exceeds that of the positive PDIs.

In this study, the streaming potential method is used to investigate the zeta potential of natural carbonate rock samples in contact with natural aqueous solutions of low-to-high ionic strength and with varying concentration of sulphate (SO42-) and carbon (C4) related (HCO3-, CO32-) ions. In each set of experiments the total ionic strength was kept constant to eliminate the impact of concentration on the zeta potential. The study probed the concentration of negative PDIs that has never been reported before, with their respective lowest concentration consistent with previously reported values, and the highest concentration equal to the maximum achievable by stripping the tested solutions of Cl-.

Our results demonstrate that zeta potentials strongly depend on concentration of the negative PDIs, thus providing explicit empiric relationship between the zeta potential and a broad range of PDI concentration. Our findings improve the current understanding of the complex physicochemical processes that take place at calcite-water interface and provide important experimental data for surface complexation modelling of carbonate-brine systems.

How to cite: Atiwurcha, N., Derksen, J., Vega-Maza, D., and Vinogradov, J.: Zeta Potential of Intact Carbonate Core Samples Saturated with Natural Aqueous Solutions with Varying Concentration of Negative Potential Determining Ions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13060, https://doi.org/10.5194/egusphere-egu22-13060, 2022.

EGU22-13560 | Presentations | EMRP1.15

Do anomalously high Vp/Vs exist in porous reservoir rocks? 

Lucas Pimienta

Anomalously high seismic P- to S-wave velocity ratios (Vp/Vs) have been observed in subduction zones, in locations where varieties of earthquakes and slips are expected to occur, interpreted as highly pressurized heavily fractured zones. Assuming the rocks isotropic, Vp/Vs can be directly linked to rocks Poisson’s ratio in the elastic regimes relevant to both the field and laboratory measurements. From dedicated measurements across the frequency range it was shown that such insights hold, in agreement with a micromechanical model for isotropic micro-cracked rocks: Anomalously high Vp/Vs exist for any low porosity isotropic rocks of any mineral content, if heavily micro-fractured and at near-lithostatic fluid pressures, i.e. at very low Terzaghi effective pressure.

Extending that understanding, one could question if such anomalous Vp/Vs could also be observed and similarly explained in isotropic porous reservoir rocks. From the typical micromechanical inclusion models for predictions at the sample’s scale, such is unlikely as Poisson’s ratio should largely decrease with an increasing content of spherical pores. Yet, that is not what is measured in the relevant undrained elastic regime in well-cemented porous sandstones. For these, most rocks Poisson’s ratio remain anomalously high and comparable to that retrieved in low porosity rocks. Moreover, while models would then predict a dependence of Poison’s ratio to the liquid’s bulk modulus that is again not consistent with the measurements.

From comparing literature datasets reporting drained and undrained Poisson’s ratio and bulk modulus for sandstones of varying porosity, the aim of this work is to investigate and discuss (i) how the measured properties compare, (ii) if one property or the two deviate from existing models and why.

How to cite: Pimienta, L.: Do anomalously high Vp/Vs exist in porous reservoir rocks?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13560, https://doi.org/10.5194/egusphere-egu22-13560, 2022.

EGU22-209 | Presentations | EMRP1.16

Adjoint-state Method Based Strategy for Non-linear Seismic AVO Inversion 

Nisar Ahmed, Wiktor Waldemar Weibull, and Dario Grana

Seismic amplitude versus offset inversion has gained increased attention over the years and is a pragmatic tool applied to retrieve the seismic and petrophysical properties of the geological layers. The prediction of these petro-elastic properties plays an important role in litho-fluids identification and quantitative seismic reservoir characterization. However, imaging of these subsurface variables from the pre-stack seismic data requires minimizing the objective function and is generally solved by using a gradient-descent based optimization method. This method requires computing the gradients of the cost function with reference to the rock’s variables. We have introduced a model-based non-linear AVO inversion strategy that is based on the computation of the adjoint-state gradients. The forward seismic modelling is carried out by convolving the seismic wavelet with the reflectivity series modelled by using the linearized AVO approximation. The optimization method known as L-BFGS is implemented to attain the best optimal model. The novelty of this work is the adjoint-state solution of the linearized AVO equation. This inversion method has been successfully applied on single and multi-traced seismic data simulated with different seismic noise levels. The modelled examples show that the presented non-linear inversion method accurately extract the seismic properties including seismic (P and S) wave velocities and bulk density. Even at some realistic seismic noise levels, the true and extracted model show good agreement which demonstrates the wide application to solve the AVO inverse modelling problems.

How to cite: Ahmed, N., Weibull, W. W., and Grana, D.: Adjoint-state Method Based Strategy for Non-linear Seismic AVO Inversion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-209, https://doi.org/10.5194/egusphere-egu22-209, 2022.

EGU22-1147 | Presentations | EMRP1.16

Open access to Dutch Earth scientific research labs and data through EPOS-NL 

Ronald Pijnenburg and Richard Wessels and the EPOS-NL team

Top research into the geo-societal challenges of our densely populated planet requires optimized use of available research data, facilities, and funds. Such optimization is the main aim of the European Plate Observing System – Netherlands (EPOS-NL): the Dutch research infrastructure for solid Earth sciences. EPOS-NL provides free of charge, (inter)national access to a unique cluster of large-scale, geophysical labs and data centers at Utrecht University (UU), Delft University of Technology (TU Delft) and the Royal Netherlands Meteorological Institute (KNMI). Lab access can be requested by applying to one of our biannual calls. EPOS-NL labs that can be accessed include A) The Earth Simulation Laboratory at UU and the Petrophysics laboratory at TU Delft, where experimental rock physics and analogue modelling studies can be performed on the fundamental processes that govern the deformation and transport behavior of the Earth’s crust and upper mantle; and B) The Multi-scale Imaging and Tomography (MINT) facilities, distributed over UU and TU Delft. MINT provides unprecedented capabilities in 2D and 3D imaging and microchemical and crystallographic mapping, down to a resolution of several nanometers. EPOS-NL further works with data centers, researchers and industry to improve open access to essential Earth scientific data and models. These include key data relating to the seismogenic Groningen gas field in the Netherlands, notably Distributed Strain Sensing data of the gas reservoir, a Petrel geological reservoir model, developed by the field operator NAM (Nederlandse Aardolie Maatschappij), and a vast amount of seismological data maintained by the ORFEUS Data Centre. Access is provided in the framework of the European infrastructure EPOS, cf. FAIR (Findable, Accessible, Interoperable and Reusable) data principles. In that way, EPOS-NL contributes to shared and cost-effective research into the geo-societal challenges faced by our densely populated planet. See www.EPOS-NL.nl for more information.

How to cite: Pijnenburg, R. and Wessels, R. and the EPOS-NL team: Open access to Dutch Earth scientific research labs and data through EPOS-NL, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1147, https://doi.org/10.5194/egusphere-egu22-1147, 2022.

Determination of strength and deformation parameters of rocks are crucially important for many engineering structures. In recent decades, numerical modelling and analysis have become a critical part of engineering projects due to significant advances in software technologies and computational infrastructure. As with the dilemmas brought by every new development, differences between 2D and 3D modelling approaches need to be considered. In nature, rocks are exposed to stresses from multi-dimensions. In order to create representative and reliable models to assess the behaviour of rock, this natural phenomenon must have been taken into account. On the other hand, in many studies on rock mechanics and modelling, 2D models are used. The reasons behind this choice can be listed as computational load, time, effort, and the results being in the preferred and reliable range. In addition, it is an inevitable fact that the importance of 3D modelling will increase since developing technologies and engineering structures begin to push the limits of the known engineering experience of engineers. In this study, 2D and 3D models were created by using Particle Flow Code (PFC) for a Castlegate sandstone sample to evaluate the response of 2D and 3D models under similar stress conditions. For this purpose, uniaxial compressive strength, triaxial compressive strength, and tensile strength tests were performed on both intact rock and gapped (circular in 2D and spherical in 3D) models to obtain data from different scenarios. Although both models provide similar test results, 3D models offer much more detail, especially in parameters such as crack initiation, propagation, and stress localization. Here, it can be said that the differences in the behaviours arise from the number of the balls in 3D models, which is more than 3 times in 2D, and the number of contacts which is more than 6 times, respectively. However, because of this resolution, the model response to stress conditions is closer to nature. The computational load for the 3D model is much higher than the 2D model because of the resolution. Even though 3D models have some drawbacks compared to 2D models in terms of computational load, time, and effort, it can be said that the data they provide is much more representative and reliable, especially in terms of model behaviour.

How to cite: Zengin, E.: Representative and Reliable Modeling for Rock Materials: 2D vs 3D, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3008, https://doi.org/10.5194/egusphere-egu22-3008, 2022.

EGU22-3183 | Presentations | EMRP1.16

Using AE based Machine Learning Approaches to Forecast Rupture during Rock Deformation Laboratory Experiments 

Sergio Vinciguerra, Thomas King, and Philip Benson

Parametric analysis of laboratory Acoustic Emission (AE) during rock deformation laboratory experiments has revealed periodic trends and precursory behaviour of the rupture source, as crack damage nucleates, grows and coalesces into a fault zone. Due to the heterogeneity of rocks and the different effective pressures, finding a full prediction of rupture mechanisms is still an open goal. We consider the AE rates and the derived source mechanisms to constrain the stress-strain regime, while scattering and seismic velocity structure define the evolving medium state as the most important attributes for the neural network model to learn. 4x10cm samples of Alzo granite were deformed at confining pressures of 5-40 MPa, whilst AE are recorded. Source mechanisms, as well as AE rates with relation to incremental strain, highlight distinct pre-failure phases. Scattering and seismic velocity measurements indicate the evolving mechanical conditions. A 10MPa simulation test on a model trained with data from 5, 20 and 40 MPa highlights good accuracy when predicting sample failure.

It remains a challenge to generate a ‘generic’ model that can be applied over all experimental conditions. Nonetheless, estimation of parameter importance has highlighted that some physical parameters are better for predicting strain, whilst others are better at stress. This importance can vary in time, suggesting a strong sensitivity of AE properties to the dynamic conditions of the fault zone. Small input changes can strongly affect output, therefore multiple models need to be trained in order to confirm the stability of the forecast. We aim to improve the understanding of the analysis through the search of repeating trends and the identification of consistent variations in key time-varying trends. Seismic scattering shows an early relevance, interpreted as due to the breakup of low frequency surface waves as microcracks begin to coalesce. However the reduction of importance at the later phases of deformation is less obvious. Further investigations are needed to identify at which deformation stage individual parameters are more important and segment time series accordingly.

How to cite: Vinciguerra, S., King, T., and Benson, P.: Using AE based Machine Learning Approaches to Forecast Rupture during Rock Deformation Laboratory Experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3183, https://doi.org/10.5194/egusphere-egu22-3183, 2022.

EGU22-3748 | Presentations | EMRP1.16

Stress triggering and the spectrum of fault slip behaviors 

Federico Pignalberi, Marco Maria Scuderi, Corentin Noël, Chris Marone, and Cristiano Collettini

Tectonic fault zones are subject to normal stress variations with a wide range of spatiotemporal scales, resulting in stress field alteration. These perturbations can spread over a wide range of frequencies and amplitudes from the high frequency passage of seismic waves generated by earthquakes, to the low frequency of solid earth tides and underground fluid injection cycles. As a result of these normal stress perturbations, critically stressed faults can be reactivated. The resulting slip mode is then controlled by fault friction and elastic properties of the surrounding rock. Existing works show that complex behaviors may arise from the interplay between friction changes with slip and slip rate and stress perturbations.

To shed light on the mechanics of fault dynamic triggering we performed experiments in a Biaxial Apparatus in a Double Direct Shear configuration under critically stable stiffness conditions (K/Kc~1). We used powdered quartz gouge (Min-U-Sil 40) as starting material, and conducted experiments at reference normal stress of σn = 10-13.5 MPa. After shearing the material and reaching a steady state sliding, normal stress oscillations were applied with various amplitudes, varying from A = 0.5-2 MPa, and periods, T = 0.5-50 s. In addition, we used the laboratory derived friction parameters as input for forward modeling using Rate-and-State friction laws in order to assess if these laws can explain our data. Our results show that creeping faults, under critical stiffness conditions, are sensitive to normal stress perturbations showing a variety of slip behaviors depending on amplitude and frequency of the oscillations:

  • Oscillation frequency has a major effect on fault stability. Low and high frequencies cause a Coulomb-like response of the shear stress, that is accompanied by a complex frictional response with slow events and period doubling. At the critical frequency predicted by the Rate-and-State friction, we observe dynamic weakening resulting in regular stick-slip events.
  • Oscillation amplitude also plays a role with the main effect depending on the magnitude of the perturbation.
  • Using a modified Rate-and-State equation (Linker and Dieterich, 1992), we are able to accurately model the laboratory data.

Our results show that normal stress perturbation on a laboratory creeping fault, at critical stiffness condition, can reproduce the entire spectrum of fault slip behavior depending on the oscillation properties.

How to cite: Pignalberi, F., Scuderi, M. M., Noël, C., Marone, C., and Collettini, C.: Stress triggering and the spectrum of fault slip behaviors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3748, https://doi.org/10.5194/egusphere-egu22-3748, 2022.

EGU22-3813 | Presentations | EMRP1.16

Coda-Based Estimation of Source Parameters of Laboratory Acoustic-Emission Events 

Tatiana Kartseva, Nikolai Shapiro, Andrey Patonin, Vladimir Smirnov, and Alexander Ponomarev

We propose a coda-based estimation of source parameters of acoustic events recorded in laboratory experiments on rock deformation. Coda-waves are considered as the reverberation of the acoustic field in the tested sample. After multiple reverberations, the resulting wavefield can be approximated as nearly homogeneously distributed over the sample and with signal amplitudes decaying exponentially in time (linearly in a logarithmic scale). Within the framework of this model, the frequency-dependent coda amplitude at any moment of time is described as combination of a source spectra, of a decay rate combining internal attenuation with reverberation losses, and of a sensor response. One of the main difficulties with the laboratory experiments is that acoustic sensors are very difficult to calibrate and their absolute response function in most of cases remains unknown. With the simple reverberation model, the logarithms of coda amplitudes at different times and sensors and for multiple events are described by a system of linear equations that we solve in a least-square sense to find frequency-dependent decay rates and relative source spectra and sensor responses. In a next step, we compute spectral ratios between different events to eliminate the sensor responses and to estimate main source parameters such as corner frequencies and relative seismic moments. Additionally, we propose a new method for computing relative magnitudes (energy classes) of acoustic emission events from the coda envelopes and argue that it might be more robust comparing with estimations based on first arrivals.

We provide details of our data analyses tehnique and present first results of our new coda-based method applied to 30-600 kHz signals recorded during experiments carried out in the Research Equipment Sharing Center of IPE RAS “Petrophysics, Geomechanics and Paleomagnetism” on a controlled hydraulic press INOVA-1000 of the Geophysical Observatory ”Borok”, IPE RAS with granites of the Voronezh massif and Berea sandstones.

How to cite: Kartseva, T., Shapiro, N., Patonin, A., Smirnov, V., and Ponomarev, A.: Coda-Based Estimation of Source Parameters of Laboratory Acoustic-Emission Events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3813, https://doi.org/10.5194/egusphere-egu22-3813, 2022.

EGU22-5890 | Presentations | EMRP1.16

The effect of pore fluid chemistry on limestone deformation. 

Jon-Danilo Kortram, Auke Barnhoorn, and Anne Pluymakers

Active use of the subsurface alters the in-situ pore-fluid composition. For limestone, chemical interaction between the pore fluid and the rock has been shown to alter some of the mechanical parameters, though the exact nature of this mechano-chemical interaction is not yet fully understood. To address this, we performed tri-axial compressive experiments on two highly pure (>97% CaCO3) and well documented limestones: Indiana Limestone and Edwards White, which were saturated with different fluid compositions. We selected our samples to have a porosity within a narrow range: 23.2 ± 0.3% for Edwards White and 12.9 ± 0.5% for Indiana Limestone. Prior to testing, the rock samples were saturated under vacuum with a fluid solution, and left to equilibrate under vacuum at room temperature for 18 hours. The fluids used in our experiments are 1) CaCO3-saturated water, 2) a brine which has a composition representative for the Dutch subsurface, and 3) a solution of industrial corrosion inhibitor. Samples were tested at room temperature and confining pressures of 2.5, 5 and 10 MPa. In addition to the stress and strain data observed from these experiments, thin sections were made from the deformed samples to perform micro-structural analysis on the damage zone.

Our results show no mechano-chemical effects for Edwards White. However, the rock strength of the Indiana limestone samples changes due to the different pore fluids: At a confining pressure of 2.5 MPa the sample saturated with to CaCO3 solution failed at 49 MPa, compared to 47 MPa and 54 MPa for the samples that were saturated with the brine and the inhibitor solution respectively. At a confining pressure of 5 MPa both the sample tested with the CaCO3 solution and the brine solution failed at 57 MPa and the sample exposed to the inhibitor solution failed at 56 MPa. The samples tested at a confining pressure of 10 MPa respectively failed at: 76, 79 and 73 MPa.  These differences of 5 to 10% lead to a shift in the resulting failure envelopes depending on the pore fluid used in the experiments when describing the failure behaviour of these samples using the Mohr-Coulomb failure criterion: The group tested with CaCO3 solution had a cohesion of 11 MPa and the coefficient of friction of 0.67. For the samples tested with brine solution these values are 10 MPa and 0.71 respectively. For the group tested with inhibitor solution these values equal 15 MPa and 0.47 respectively. The experiments presented here serve as a baseline from which we can further determine which ions or compounds interact with the rock, and the nature of this interaction. For our follow-up work, we will continue by performing a detailed microstructural analysis to better understand the overall controls on the mechano-chemical interactions or the lack thereof. In follow-up experiments, we will narrow down the complexity of the fluid solutions so we can identify the effect of specific ionic species.

How to cite: Kortram, J.-D., Barnhoorn, A., and Pluymakers, A.: The effect of pore fluid chemistry on limestone deformation., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5890, https://doi.org/10.5194/egusphere-egu22-5890, 2022.

EGU22-6004 | Presentations | EMRP1.16

Disclosing the redox conditions in Central Portugal magmatism: the Manteigas granodiorite case study 

Cláudia Cruz, Joana Dias, Eric Font, Fernando Noronha, and Helena Sant'Ovaia

The presence of magnetite in granitoids is usually rare in the Iberia Peninsula, but can occur depending on the crystal fractionation processes and redox conditions. Here we studied the Manteigas granodiorite in order to characterize and quantify the nature and abundance of ferromagnetic minerals by using petrographic, Isothermal Remanent Magnetization (IRM) curves, and Frequency-dependent Susceptibility (KfD%) experiments. Igneous rocks of the Variscan age are particularly abundant in Central Portugal, including the Manteigas granodiorite that crops out in the Serra da Estrela region (Central Iberian Zone), Portugal. The Manteigas granodiorite is classified as a medium- to coarse-grained slightly porphyritic biotite rock and was dated by U-Th-Pb methods on zircon at 481.1 ± 5.9 Ma. Petrographic studies show that Manteigas is mainly composed of quartz, Ca-plagioclase, K-feldspar, and biotite. As accessory minerals, apatite, chlorite, magnetite ± hematite, and zircon are identified. Muscovite is rare and most of secondary origin. Monazite, sphene-leucoxene, and brookite-anatase are also present but in minor amounts. Microstructures indicate a slight deformation that is reflected in the undulatory extinction in quartz, microfractures in K- feldspar, and curved biotites. Sometimes microfractures in feldspar are filled by later Fe-oxide/hydroxide. Values of magnetic susceptibility (Km) indicate that the Manteigas granodiorite belongs to the magnetite-type rocks, with Km values higher than 1.9 x 10-3 SI (1.9 x 10-3 SI < Km < 188.37 x 10-3 SI). This is consistent with oxidizing conditions in the magma genesis [1]. Furthermore, the oxygen isotope composition (δ18O) measured on whole-rock samples ranges between 8.8 ‰ and 8.9 ‰ [1,2], which suggests a mantle contribution. The analysis of IRM data through the Cumulative Log-Gaussian (CLG) function with the software developed by Kruiver et al. [3] indicates the presence of a single ferromagnetic s.l. component, with values of mean coercivity (Log B1/2) of 1.61 mT and dispersion parameter (DP) of 0.36, typical of magnetite [4]. The value of the IRM at saturation (SIRM) of 18 A/m indicates a significant contribution of magnetite. We also fitted the IRM curve by using a Skewed Generalized Gaussian function with the MaxUnmix software [5] and obtained similar results. Kfd% analyses were conducted in four samples. Values of the Kfd% are inferior to 6%, suggesting a very weak contribution of superparamagnetic particles. Acknowledgments: The first author is financially supported by UIDP/04683/2020 project (FCT-Portugal). This work is also supported by national funding awarded by FCT under UIDB/04683/2020 project. References: [1] Sant’Ovaia, H., Olivier, P., Ferreira, N., Noronha, F., Leblanc, D. 2010. J. Struct. Geol. 32, 1450-1465. [2] Neiva, A., Williams, I.S., Ramos, J.M.F., Gomes, M.E.P. Silva, M.M.V.G., Antunes, I.M.H.R. 2019. Lithos 111, 186-202. [3] Kruiver, P.P., Dekkers, M.J., Heslop, D. 2001. Earth Planet. Sci. Lett. 189, 269–276. [4] Egli, R., 2003. J. Geophys. Res. 108, 2081. [5] Maxbauer, D.P., Feinberg, J. M., Fox, D.L. 2016.  Comput. Geosci. 95, 140–145.

How to cite: Cruz, C., Dias, J., Font, E., Noronha, F., and Sant'Ovaia, H.: Disclosing the redox conditions in Central Portugal magmatism: the Manteigas granodiorite case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6004, https://doi.org/10.5194/egusphere-egu22-6004, 2022.

EGU22-6331 | Presentations | EMRP1.16

Unveiling the magnetic mineralogy and magma flow dynamics within subvolcanic dykes from northern Portugal, Central Iberian Zone 

António Oliveira, Helena Sant'Ovaia, and Helena Brites

Several hypabyssal dykes and masses, generated during the Permo-Carboniferous, outcrop throughout southwest Europe. In Portugal, this magmatic event is related to the transition from a post-collisional to extensional setting that followed the Variscan orogeny and represented by porphyries, lamprophyres, and dolerites which intruded into older metasediments and granites. The magnetic mineralogy, susceptibility, and fabrics of selected dykes from northern Portugal were studied using methodologies such as IRM curve acquisition and treatment, frequency-dependence of the magnetic susceptibility (Kfd), and low-field AMS.

Based on the bulk magnetic susceptibility, the felsic lithotypes are paramagnetic (Km = 0.9-148.2 µSI) but mostly composed of diamagnetic minerals (i.e., quartz and feldspars). AMS in these rocks is mainly carried by iron-bearing silicates, such as biotite and cordierite, as well as ilmenite. However, other iron oxides, namely hematite, goethite, or fine-grained magnetite, also play an important role in the magnetic anisotropy. By contrast, in most of the mafic lithologies (Km = 238.2-15,640.7 µSI), magnetite is an essential component. Other iron-rich minerals such as biotite, amphibole, and pyroxene also influence the anisotropy of these rocks.

Following the IRM data treatment (Kruiver et al., 2001; Maxbauer et al., 2016), all samples reveal at least one magnetite grain population whose mean coercivities (B1/2) and dispersion parameter (DP) range from 18.2 to 70.8 mT and 0.26 to 0.40, respectively. Petrographic observations suggest that most magnetite composing the mafic rocks is multidomain-type. However, Kfd measurements (4.66-18.18%) indicate that superparamagnetic particles are likely to exist in some lithologies, inducing low bulk susceptibilities and anomalous AMS fabrics. On the other hand, inverse fabrics are probably associated with hydrothermal and/or post-magmatic alterations.

Many felsic specimens display a normal fabric, where the magnetic minerals were oriented along the magma flow direction within the dyke and undisturbed by tectonic strains. Such observation is compatible with the average low anisotropy degree (Ppara% = 0.92-4.28%), implying passive emplacement of the melts, and possibly reflects a weak contribution from single-domain-magnetite. Rare cases where the magnetic fabric is intermediate presumably point to more intense deformations.

Magnetite on the mafic rocks is mainly primary. By contrast, since the felsic dykes derived from anatexis of pelitic sources, their generation occurred under reducing conditions, being similar to Ilmenite-type granites. As such, most magnetite in the felsic samples is probably secondary, having resulted from exsolution from Fe-bearing minerals. However, the presence of primary magnetite cannot be ruled out due to possible magma mixing, as suggested by the coexistence of mantled and non-mantled feldspars. The less evolved member involved in the mixing process is likely to carry a more oxidized composition, bearing the potential to crystallize primary magnetite.

This work was supported by the Portuguese Foundation for Science and Technology (FCT), through the project reference UIDB/UIDP/04683/2020 and ICT (Institute of Earth Sciences). The main author is also financially supported by FCT through an individual Ph.D. grant (reference SFRH/BD/138818/2018). References: Kruiver, P.P., Dekkers, M.J., Heslop, D., 2001. Earth Planet. Sci. Lett. 189, 269–276. Maxbauer, D.P., Feinberg, J. M., Fox, D.L., 2016. Computers & Geosciences 95, 140–145.

How to cite: Oliveira, A., Sant'Ovaia, H., and Brites, H.: Unveiling the magnetic mineralogy and magma flow dynamics within subvolcanic dykes from northern Portugal, Central Iberian Zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6331, https://doi.org/10.5194/egusphere-egu22-6331, 2022.

EGU22-9866 | Presentations | EMRP1.16

Determination of parameters characteristic of dynamic weakening mechanisms during coseismic slip 

Chiara Cornelio, Elena Spagnuolo, Stefan Nielsen, Stefano Aretusini, Francois Passelègue, Marie Violay, Massimo Cocco, and Giulio Di Toro

While sliding at seismic slip-rates of ca. 1 m/s, a natural fault undergoes an abrupt decrease of its strength called enhanced dynamic weakening. Asperity-scale (<< mm) processes related to flash heating & weakening and meso-scale (mm-cm) processes involving shear across the bulk slipping zone related to frictional melting or viscous flow of minerals, have been invoked to explain pronounced velocity-dependent weakening. Here we present a compilation of ca. 100 experiments performed with two rotary shear apparatuses, i.e. SHIVA installed in INGV (Rome, Italy) and HVR installed, at the time of experiments, in Kyoto University (Japan). Cohesive rock cylinders of basalt, gabbro, tonalite, granite and calcitic marble were sheared under a range of effective normal stresses (sn=5-40 MPa), target slip-rates (Vt=0.1-6.5 m/s) and fluid pressures (from room humidity conditions RH or Pf=0, to Pf =15 MPa). We fit the measured shear stress evolution with slip with two dynamic weakening mechanisms models, which include, depending on rock type: (1) flash heating and bulk melting (granitoid, gabbro and basalt), (2) flash heating and diffusion creep (calcitic marble), (3) flash heating and dislocation creep (calcitic marble). We provide a set of optimized parameters, specific for each mechanism, that control the dynamic weakening.

Lastly, the modelling procedure allow us to estimate the slip-switch distance d0, i.e. the slip necessary for the complete transition from the asperity-scale to bulk slipping zone dynamic weakening mechanism. Our analysis shows that (1) the d0 decreases with increasing effective normal stress acting on the fault and, (2) for the same type of transition between dynamic weakening mechanisms (e.g., from flash heating to bulk melt lubrication) the d0 is a function of rock composition. The decrease of d0 with normal stress indicates that during earthquakes, bulk mechanisms dominate over asperity scale weakening mechanisms with increasing crustal depths. This study provides constitutive law parameters to be included in physically- and geologically-based dynamic earthquake rupture simulations.

How to cite: Cornelio, C., Spagnuolo, E., Nielsen, S., Aretusini, S., Passelègue, F., Violay, M., Cocco, M., and Di Toro, G.: Determination of parameters characteristic of dynamic weakening mechanisms during coseismic slip, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9866, https://doi.org/10.5194/egusphere-egu22-9866, 2022.

EGU22-162 | Presentations | EMRP1.17

Viscoplastic Rheological Modelling- A Realistic Approach to Natural Ductile Shear Zones 

Arnab Roy, Puspendu Saha, and Nibir Mandal

Crustal deformations generally undergo a brittle-ductile transition with depth, producing fault-dominated structures at shallow depths, replaced by ductile shear zones at middle and lower crustal levels. One of the keys to shear zone modelling concerns the choice of rheological approximations that can successfully reproduce the characteristic features of natural ductile shear zones in the models.  With the help of 2D FE (finite element) simulations, this study shows viscoplastic rheology as a suitable rheological approximation to predict the competing growth and orientations of multiple sets of secondary shear bands in a ductile shear zone. The viscoplastic rheology is modelled by combining bulk viscous weakening of the shear zone material and plastic yielding (Drucker-Prager criterion) to replicate strain-softening behaviour, where the instantaneous viscosity decreases nonlinearly with increasing strain. The cohesive strength of the material is also assumed to reduce with progressive plastic strain. This rheological combination allows us to replicate the various shear band networks found in crustal-level ductile shear zones. It also addresses the conditions for fluid flow into ductile shear zones, which leads to metamorphic reactions, mineralisation, etc. We validate our model results with field observations of similar shear band structures from the Eastern Indian Precambrian craton. The present study finally leads us to conclude that a pressure-dependent viscoplastic rheology is an ideal rheological approximation to model ductile shear zones extensively found in this craton.

How to cite: Roy, A., Saha, P., and Mandal, N.: Viscoplastic Rheological Modelling- A Realistic Approach to Natural Ductile Shear Zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-162, https://doi.org/10.5194/egusphere-egu22-162, 2022.

EGU22-3971 | Presentations | EMRP1.17

On the stability of carbonate-bearing faults at the brittle-to-ductile transition 

Francesco Figura, Carolina Giorgetti, Gabriel Meyer, and Marie Violay

The majority of the seismic events in the Mediterranean region are hosted in carbonate-bearing rocks at depths representative of the semi-brittle regime. Within this regime, both brittle behavior (i.e. deformation is localized on the fractures and on the faults) and ductile one (i.e. deformation is distributed and accommodated in the rock core) coexist. The influence of this interplay on the nucleation and propagation of seismic events is poorly studied. Up to now, most experimental work has been conducted far from in-situ conditions, mostly at room temperature and low confining pressure.

Here we constrain the frictional behavior of faults in carbonate rocks under conditions relevant for their brittle-to-ductile transition. Velocity-step experiments are performed through the HighSTEPS (Strain, TEmperature, Pressure, Speed) biaxial apparatus installed at EPFL, investigating sliding velocities from 10-6 m/s to 10-2 m/s. Experiments are conducted under different values of confining pressure (Pc 15 MPa and Pc 50 MPa) and normal stress (σn 29 MPa and σn 95 MPa) on the experimental faults, keeping the ratio between them constant (around 2). The local strain field along the fault was measured with strain gauges. The collected data were modeled with rate-and-state friction laws (RSFLs) to define the rate and state parameters relate to the critical condition for fault stability. Moreover, microstructural observations of the post mortem sample were conducted at the SEM, to investigate the deformation mechanisms active during the experiments.

These results shed light on the evolution of rate-and-state frictional parameters with depth, as well as their dependence on the strain partitioning between on-fault slip and bulk-accommodated deformation with increasing depth.

How to cite: Figura, F., Giorgetti, C., Meyer, G., and Violay, M.: On the stability of carbonate-bearing faults at the brittle-to-ductile transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3971, https://doi.org/10.5194/egusphere-egu22-3971, 2022.

EGU22-5029 | Presentations | EMRP1.17

The localized to ductile transition in porous rocks : experimental investigation on Volvic basalt. 

Gabriel Meyer, Marie Violay, and Michael Heap

With increasing depth, the rheology of rocks gradually transitions from brittle (localized, fractures) to ductile (homogeneous flow). Recently, it was demonstrated that, in the crust, the transitional zone might extend to shallower depth than previously thought (2km) with a zone where the deformation regime can be both localized and ductile (the LDT). In this regime, both extremely localized (fault slip) and distributed (cataclastic flow and/or plasticity) deformation may occur concurrently. This observation had great importance since the ductile regime is commonly thought to be aseismic and to mark the maximum depth of earthquake nucleation.

However, this observation was made experimentally in non-porous rocks; porous rocks on the other hand display an additional characteristic in that their ductile behaviour may consist in the formation of compactions bands which greatly impact the behaviour of porous reservoirs and systems (e.g., volcanoes). Moreover, ductile rocks are commonly believed to be aseismic, the potential coexistence of both ductile and localized regimes in reservoir rocks might therefore have great implications for induced seismicity mitigation.

Here, we present three conventional triaxial experiments on Volvic basalt (homogeneous, istropic, fine grain). We deformed cylindrical cores equipped with strain gages at 5MPa and room temperature until a sample-scale fracture nucleated and propagated. Subsequently, we increased confining pressure step wise, loading the sample every step until 0.2% irrecoverable strain was accumulated in the sample. In between confinement steps, the differential stress was unloaded. A pair of Linear Variable Differential Transformers (LVDTs) was used along with the strain gauges to accurately monitor the deformation behaviour of the samples.

We show that Volvic basalt transitions from being purely localized to being purely ductile over a rather narrow pressure range from 40 to 80 MPa. The transition initiates when the frictional strength of the fault equates the yield strength of the bulk and terminates when it becomes greater than the maximum strength of the bulk. In this pressure range, deformation is initially accommodated in the bulk (most likely by compaction bands) until strain hardening eventually leads to fault reactivation. Once both fault sliding and bulk flow are active, the partitioning of strain between the two can be described by the same empirical ratio as that already established for non-porous rocks, i.e. (σf - σy)/ (σflow - σy).

We conducted a second experiment at a faster strain rate (10-4 s-1) and show that faster deformation promotes brittle behaviour which pushes the LDT to greater confinement (i.e., greater depth).

Additionally, we conducted a similar experiment in the presence of water. In this case, the LDT occurs at lower confinement, showing that, fluids, by promoting ductile processes such as stress-corrosion, bring the LDT to shallower depth.

Our results are crucial for the understanding of reservoirs where ductile deformation (compaction bands) and induced earthquake mitigation have to be finely tuned.

How to cite: Meyer, G., Violay, M., and Heap, M.: The localized to ductile transition in porous rocks : experimental investigation on Volvic basalt., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5029, https://doi.org/10.5194/egusphere-egu22-5029, 2022.

EGU22-5863 | Presentations | EMRP1.17

Velocity-dependent friction of granitoid gouge under hydrothermal conditions: A contribution to understanding of fault zone seismicity 

Weijia Zhan, André Niemeijer, Natalia Nevskaya, Alfons Berger, Chris Spiers, and Marco Herwegh

Fault gouges of granitoid composition represent the principal non-cohesive tectonites within fault zones in the continental crust. Their velocity-dependent friction is crucial for understanding earthquake nucleation and the depth distribution of fault-related seismicity in granitoid shear zones (Wehrens et al. 2016; Blanpied et al. 1998). In the framework of rate-and-state friction laws (RSF), the friction parameter (a-b) is measured in sliding experiments to describe the velocity dependence of friction in fault gouges (Scholz, 1998). A velocity-strengthening system is frictionally stable, (a-b) >0, whereas a velocity-weakening system can be frictionally unstable, (a-b) <0. In earthquake mechanics, velocity weakening is prerequisite for stick-slip deformation, i.e. the nucleation of earthquakes. Although (a-b) values of granitoid gouge are sensitive to varying temperature conditions and sliding velocities, only a few studies have examined this velocity-dependence under hydrothermal conditions.

To address this issue, we conducted velocity stepping sliding experiments under hydrothermal conditions by using a ring shear apparatus. The powdered starting gouge was derived from a granitoid mylonite collected at the NAGRA Grimsel Test Site (Central Swiss Alps). The applied velocity steps were 1-3-10-30-100 μm/s. Pore fluid pressure and the effective normal stress were 100 MPa. Temperatures explored ranged from 20-650 °C. Values of (a-b) were obtained from RSF model inversions of the evolution of friction coefficients at mechanical steady state conditions. Our experiments showed pronounced changes in (a-b) values with across the full range of temperatures up to 650 °C and velocities investigated. At temperatures below ~100 °C and above ~400 °C, we observed mostly velocity strengthening with positive (a-b). In contrast, velocity weakening with negative (a-b) was observed between ~100 °C and ~400 °C. Samples deformed at a sliding velocity of 100 μm/s deviated slightly from this trend, as (a-b) values were negative between ~200 °C and ~400 °C.

The presented experimental study demonstrates a significant influence of temperature and sliding velocity on velocity-dependence during deformation of granitoid gouge. We suggest that the observed transitions in velocity dependence reflect an interplay of interactions. In terms of crustal faulting, our data suggest the existence of a seismogenic window that limits the depth distribution of earthquakes on faults in granitoid shear.

 

REFERENCES

Wehrens, P. C., Berger, A., Peters, M., Spillmann, T., Herwegh, M. 2016: Deformation at the frictional-viscous transition: Evidence for cycles of fluid-assisted embrittlement and ductile deformation in the granitoid crust, Tectonophysics, 693, 66-84.

Blanpied M. L., Tullis T. E., Weeks J. D. 1998: Effects of slip, slip rate, and shear heating on the friction of granite.

Scholz, C. H. 1998: Earthquakes and friction laws, Nature, 391, 37-42.

How to cite: Zhan, W., Niemeijer, A., Nevskaya, N., Berger, A., Spiers, C., and Herwegh, M.: Velocity-dependent friction of granitoid gouge under hydrothermal conditions: A contribution to understanding of fault zone seismicity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5863, https://doi.org/10.5194/egusphere-egu22-5863, 2022.

Amphibole is an important mineral in rocks of the lower crust and in subduction zones, forming as the product of metamorphic reactions and hydration of mafic rocks. As such, the textural and rheological properties of amphibole are of relevance for assessing the physical properties of these tectonic provinces. Aggregates containing amphibole grains often exhibit a strong texture, i.e., a crystallographic preferred orientation (CPO). Since amphibole possesses inherent anisotropic properties, the CPO will affect the bulk strength and elastic properties. However, amphibole’s rheological behavior is not well understood as its capability to deform purely via plastic deformation remains unresolved, previous studies suggesting numerous deformation mechanisms such as semi-brittle and cataclastic flow, dissolution precipitation, dislocation creep, recrystallization, micro-twinning, and diffusion assisted creep. Here, we use pre-textured natural samples cored at 60° to the foliation and lineation to investigate the deformation mechanism/s activated in a polycrystalline aggregate/rock of well-oriented amphibolite-rich hornblende. Samples from the Mamonia complex (Cyprus) with hornblende as the dominant mineral (> 70 % modal fraction) and strong initial alignment of the [001] axis were deformed using a Griggs-type solid-medium apparatus. Experiments were run at 1 GPa confining pressure, temperatures of 400 to 800 °C, and a strain rate of ~10-5 1/s. Samples show temperature-dependent differential stress that falls below the Goetze criteria (i.e., below the confining pressure, 1 GPa) - ~700, 500, and 200 MPa for samples deformed at 400, 600, and 800 °C, respectively. Microstructural analysis using Electron backscatter diffraction (EBSD) reveals folding and kink bands, accommodated by both plastic mechanisms, via dislocation glide on the hornblende easy slip system, and brittle mechanisms, via micro-fracturing along the crystal cleavage (110). We discuss the implications of the interplay and contribution of different deformation mechanisms for our ability to translate laboratory experiments to flow laws for the lower mantle and subduction zone interfaces.

How to cite: Boneh, Y., Sarah, I., and Renner, J.: Mechanism/s of deformation and strength of experimentally deformed hornblende-rich amphibolite with a strong pre-existing texture, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6966, https://doi.org/10.5194/egusphere-egu22-6966, 2022.

EGU22-7954 | Presentations | EMRP1.17

Experimental study of the impact of hydration extent on the strength of the lower continental crust 

Lisa Katharina Mohrbach, Joerg Renner, and Sarah Incel

Previous experimental data and field observations demonstrate that fluids have a significant influence on rock strength. The relation between strength and hydration extent of the lower continental crust is still poorly constrained and thus a matter of an ongoing debate. We tested the impact of hydration extent on the strength of rocks representing the lower continental crust by performing deformation experiments on various plagioclase-epidote mixtures as well as on natural granulite samples in a Grigg's type deformation apparatus. In these samples, the plagioclase component represents rocks of the lower continental crust and epidote reflects hydration extent, because, alongside with quartz, kyanite and jadeite or albite, it forms as a decomposition product of plagioclase at high-pressure/ high-temperature conditions in the presence of even small amounts of fluids. To quantify the relation between strength and epidote content, we conducted the tests on plagioclase-epidote powders with a grain size of 90-135 mm and plagioclase-epidote ratios of 100:0, 99:1, 98:2, 95:5, 90:10, 85:15, and 0:100. The pre-dried powders were first hot-pressed at 550 °C and a confining pressure of 1 GPa for 3 h in the Griggs apparatus. Mixtures were subsequently deformed at 1 GPa and 550 to 650 °C at strain rates of 5·10-6 to 5·10-5 s-1. All stress-strain curves show pronounced maxima followed by strain softening towards a final strength. The deformation data yield an exponential decrease of the ultimate strength with increasing epidote content. Investigations of the microstructures of samples deformed at 550 °C and 5·10-5 s-1 using the SEM and polarized light microscopy reveal cataclastic flow by grain-scale fracturing of both epidote and plagioclase and the rotation and alignment of epidote grains at angles between 60° and 70° to the maximum principal stress  σ1. In addition, plagioclase grains show pronounced undulatory extinction but we found no evidence for deformation twinning. Some samples exhibit networks of conjugate bands of fine-grained plagioclase surrounding larger plagioclase grains oriented at an angle of around 50° towards σ1. These bands are mostly visible in samples without epidote.

How to cite: Mohrbach, L. K., Renner, J., and Incel, S.: Experimental study of the impact of hydration extent on the strength of the lower continental crust, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7954, https://doi.org/10.5194/egusphere-egu22-7954, 2022.

EGU22-8320 | Presentations | EMRP1.17

The effects of grain size on semi-brittle flow in calcite rich rocks 

Christopher Harbord and Nicolas Brantut

Grain size is in an important microstructural parameter affecting both brittle and plastic deformation processes. In the low temperature brittle regime, larger grain size materials typically have lower strength, whereas in the plastic flow regime smaller grain size materials tend to be weaker. It is not clear how grain size impacts at intermediate conditions where deformation of rock is accommodated by coupled brittle and plastic deformation processes.

To investigate the role of grain size in the semi brittle regime we deformed three calcite-rich rocks, spanning 3 orders of magnitude in grainsize (0.006-2 mm). A gas medium triaxial apparatus was used at a range of confining pressures (200-800 MPa) and temperatures (20-400°C), and samples were loaded at a constant axial strain rate (1×10-5 s-1). Axial measurements of P-wave speed were performed during tests in order to infer the in-situ microstructural state of the sample.

Nearly all tests show strain hardening behaviour after yield, typical of semi-brittle deformation, which is quantified using the hardening modulus (h = ∂σ/∂ε). Grain size has a first order control on rock strength, with yield stress and h following a Hall-Petch type relationship at all P-T conditions. For a given temperature, h is low at low pressure (200 MPa) and accompanied by large decreases in wavespeed, and h increases at high pressure (>400 MPa) whereas velocity decreases by a smaller magnitude. This suggests that, at low temperature, strain hardening is relieved by microcracking. At constant pressure, wavespeed decreases significantly at 20°C with progressive deformation, but remains nearly constant at 400°C indicating a transition from dominatly brittle to fully plastic deformation with increasing temperature, in some cases with little change in the macroscopic strength.

Given that both strength and strain hardening behaviour depend on grain size, our data suggests that grain size dynamically impacts the long term rheology of the crust. Larger grain sizes will broaden the depth distribution of the brittle ductile transition and result in a weaker peak crustal strength.

How to cite: Harbord, C. and Brantut, N.: The effects of grain size on semi-brittle flow in calcite rich rocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8320, https://doi.org/10.5194/egusphere-egu22-8320, 2022.

EGU22-8365 | Presentations | EMRP1.17

Weakening mechanisms in dry, lower-crustal pseudotachylytes 

Kristina G. Dunkel, Luca Menegon, and Bjørn Jamtveit

Earthquakes are often regarded as agents of rheological weakening of the dry and mechanically strong lower crust. The weakening is typically attributed to fluid infiltration and resulting fluid-mediated metamorphism along the seismic fault.

On Moskenesøya in SW Lofoten (Northern Norway), we observe lower-crustal pseudotachylytes (frozen frictional melts that record fossil earthquakes) that are unusually dry. This presents us with an exceptional opportunity to study the processes affecting the rocks during and after an earthquake:

  • We can observe the pristine microstructures of the pseudotachylytes, not overprinted by later metamorphism, to elucidate the earthquake-generating mechanism.
  • We can study the further development of these dry pseudotachylytes after the seismic event.

We have previously described the composition and microstructures of the pristine pseudotachylytes, and concluded that transient stress pulses caused by shallower earthquakes are the most likely explanation for the occurrence of fossil earthquakes in the analysed rocks from Lofoten, with no evidence of other mechanisms such as thermal runaway or dehydration embrittlement.

In this contribution, we focus on the evolution of the pseudotachylytes after their formation. We study their development from the initial, pristine pseudotachylytes, via pseudotachylytes with slightly mylonitized margins, to ultramylonites. We use compositional and microstructural analyses, including electron backscatter diffraction (EBSD), to understand the weakening mechanisms in this dry system.

In the mylonitized margins of the pseudotachylytes, a slight shape-preferred orientation is developed and the quenching microstructures, such as microlites, are lost. The mineralogical composition (dominantly feldspars and pyroxenes) stays the same as in the pristine pseudotachylytes. In the ultramylonite, quartz and amphibole appear as accessory minerals, which means that we cannot completely exclude the presence of minor amounts of hydrous fluids; however, feldspars and pyroxenes persist as the main components of the rock. The foliation of the ultramylonite is not defined by phyllosilicates, but by a compositional banding, which suggest a phase separation and aggregation during shearing. EBSD data indicate that the main constituent phases deformed dominantly by grain size sensitive creep.

Our preliminary results suggest that even in the absence of fluids, pseudotachylyte-bearing seismic faults represent weak zones in the lower crust that are localizing viscous shear during post- and interseismic deformation, presumably due to the intense grain size reduction that facilitates grain-size sensitive mechanisms. 

How to cite: Dunkel, K. G., Menegon, L., and Jamtveit, B.: Weakening mechanisms in dry, lower-crustal pseudotachylytes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8365, https://doi.org/10.5194/egusphere-egu22-8365, 2022.

EGU22-10023 | Presentations | EMRP1.17

Seismic attenuation across the brittle-ductile transition 

Maria Aurora Natale Castillo, Magdala Tesauro, Mauro Cacace, Francois X. Thibault Passelegue, Lucas Pimienta, and Marie Violay

Rocks mechanical behaviour, and in particular, their transition from a brittle to a ductile deformation has been prevalently investigated through rheological experiments and numerical models. In conjunction with rocks mechanical studies, the analyses of seismic wave propagation can improve our knowledge of physical rocks behaviour and provide an alternative assessment of the brittle ductile transition (BDT).

In this study, we investigate the quantitative relationships between seismic attenuation and viscous rocks' rheology, especially across the BDT domain. For this purpose, we rely on the Burgers and Gassmann mechanical model to derive shear wave attenuation (1/Qs ), for several dry and wet crustal rheology, thermal conditions, and different strain rates values. This allows us to establish geothermal and mechanical conditions at which the BDT occurs and to cross-correlate this transition to computed shear seismic wave attenuation values. We observe that the variation with depth is related much more to the input strain rate than to the rock‘s rheology and thermal conditions, so that a fixed amount of Qs reduction can identify the average BDT depths for each strain rate used. Below the BDT depth, we observe a significant increase of the Qs reduction (up to 10-4 % of the surface value), depending also on rocks temperature and rheology. Since the greatest Qs reduction is estimated for the greatest input strain rate (10-13 s-1) and hot thermal conditions, the proposed method can find more applicability in tectonically active/geothermal areas.

We tested the obtained results by performing triaxial lab experiments, while monitoring ultrasonic P-waves, on a sample of Carrara marble, at ambient temperature and 180 MPa confining pressure. The transition from brittle to semi-brittle conditions is characterized by the increase of crack-density with a progressive rate reduction. At the same time, both the seismic velocity and energy significantly decrease during the first phase of deformation (brittle regime) and tend towards an asymptotic value, when the sample approaches the ductile deformation. We interpret the absence of an increase of energy loss at the BDT, as due to the persistent effect of the microfracturation. The last one usually accompanies the deformation mechanisms that occur at the BDT (e.g., pressure solution, twinning), masking the expected increase of attenuation at the beginning of the ductile conditions. This is a matter that still needs to be investigated.

How to cite: Natale Castillo, M. A., Tesauro, M., Cacace, M., Passelegue, F. X. T., Pimienta, L., and Violay, M.: Seismic attenuation across the brittle-ductile transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10023, https://doi.org/10.5194/egusphere-egu22-10023, 2022.

We provide here in situ evidence from a network of well-preserved extensional shear zones cutting a rift related lower crustal Reinfjord Ultramafic Complex, Seiland Igneous Province, that formed in the late Ediacaran. Our results can explain seismic events well below the seimic zone of continental rifts and associated CO2 emissions. Processses leading to catastrophic failure of the weakened rocks led to extremely high strain rates and the formation of pseudotachylites can be traced from a netwok og mm-m scale steeply dipping transtensional shearzones associated with gabbronoritc dykes to a 2km long low angle extensional shearzone. Deformation, initiated through a priming of the dyke-host rock interface by magmatic fluids, exploits subgrains and microfractures in olivine, with reactive CO2-bearing fluids leading to volume expanding reactions such as olivine + diopside + CO2 = Dolomite + enstatite, enhancing olivine grain fracturing. Fragmentation of the olivine grains and addition of weaker phases facilitated strain localization and local increases in strain rate by two orders of magnitude. Catastrophic failure of the weakened rocks led to extremely high strain rates and the formation of pseudotachylites in several cyclic events. The frictional heat raised the temperature above the dolomite forming reaction, causing release of CO2 and H2O along the fault, but also in the surrounding mafic-ultramafic rocks, forming veins around the shearzone. Fluid-rock interaction surrounding shear zones is highly variable and depends on bulk rock compositions. Thermodynamic modelling demonstrates that mineral reactions involving hydration and carbonation differ between dunitic rocks and the pyroxenitic dykes which intersect them. Alteration of dunitic rocks results in the formation of dominantly magnesite-anthophyllite-talc and talc-magnesite assemblages causing approximately 12% volume expansion, resultinig in a sharp reaction front contacts with the host rock. When the alteration zones cross the dunite-pyroxenite boundary the associated alteration has a more gradual boundary towards the unaltered rock and the alteration zone widens by approximately 40%. In contrast to the simpler dunite alteration assemblage, the pyroxenenitic dykes are altered to a complex mixture of cummingtonite-anthophyllite, magnetite and chlorite. Additionally, orthopyroxene is completely pseudomorphed by a mixture of cummingtonite and magnetite, whereas olivine xenocrysts are partly preserved and surrounded by a magnesite-anthophyllite assemblage. Other, open cavity-like areas are filled by chlorite, amphibole, and Mg-MgCa carbonates, indicating volume reduction during alteration of the pyroxene.Accordingly, dunite alteration effectuates a significant volume expansion, and are therefore only altered locally during seismic creep events. The pyroxenites are near volume neutral throughout interaction with the same fluids, and are thus more homogeneously altered. The formation of chlorite in hybrid compositions, such as the dykes in the lower crust, may create weak permeable zones that are consequently exploited as pathways for fertile mantle fluids and will hence also be the locus of ore bearing fluids moving to the upper crust.  We conclude that catastrophic failure along shear zones in lower crustal continental rifts is possible without remote stress events in the presence of pre-existing heterogeneities and volatiles. These zones also acted and transport conduits for volatiles from the lower crust to atmosphere.

How to cite: Sørensen, B. E., Ryan, E. J., Larsen, R., and Grant, T.: Infiltration of volatile-rich mafic melt in lower crustal peridotites provokes deep earthquakes, initiates km scale shearzones and volatile transfer from the lower crust to the atmosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10545, https://doi.org/10.5194/egusphere-egu22-10545, 2022.

EGU22-12465 | Presentations | EMRP1.17

Diopside microfabric development in lower-crust oceanic detachment fault zones 

Rhander Taufner, Claudia Trepmann, and Gustavo Viegas

Exhumation of oceanic core complexes occurs through large-scale extensional shear zones that expose parts of the deformed gabbroic lower crust. However, it is not well understood how these high-temperature shear zones nucleate and develop. Since diopside is traditionally described as a load bearing phase in deforming systems, its microstructures may record the deformation mechanisms involved in the progressive stages of shear zone development. In this study, we focus on the fabrics of diopside in both the host coarse-grained gabbro and the adjacent high-temperature shear zone from the Atlantis Bank (IODP Exp 360), in order to better constrain the role of diopside during strain localization in deep crustal detachment fault zones.

In the host rock directly in contact to the shear zone, diopside porphyroclasts display microfractures filled with fine-grained diopside (~ 65 µm) and minor amounts (~10%) of plagioclase, amphibole and Fe-Ti oxides with grain size ~ 30 µm that occur as interstitial phases. Diopside grains in the microfractures have little internal deformation and are interpreted as “new” grains. On the other hand, fragments of the host diopside within the fracture are distinguished by their larger diameters of ~200 µm and dominant cleavage planes that is systematically missing in the new grains. These microstructures indicate cataclastic deformation with later precipitation of plagioclase, amphibole and Fe-Ti oxides. Other diopside porphyroclasts in the host rock show undulatory extinction, low-angle grain boundaries and new grains with crystallographic orientations controlled by the host, indicating dislocation creep.

Diopside porphyroclasts within the shear zone show undulatory extinction as well as bent cleavage planes and exsolution lamellae. New grains of diopside (~35 µm) that occur rimming the porphyroclasts - concentrated at sites of strong undulatory extinction - have long axes correlating the orientation of the bent cleavages within the host. These new grains have a crystallographic orientation with poles of (100) planes close to the X-axis and [001] axes close to the Z-axis, and high angle boundaries (>140º) with misorientation axes clustered between [001] and [100]. We propose that these new grains are a result of dislocation glide and growth due to bending of the host diopside during the early stages of shear zone nucleation.

In the strain shadow of the porphyroclasts within the shear zone, new grains of diopside (~20µm) occur together with amphibole, plagioclase and Fe-Ti oxides. They are rounded, strain free, have random orientations and the amount of diopside decreases with distance from the host. These grains are interpreted to have precipitated from the pore fluid during ongoing deformation of the shear zone.

We suggest that diopside in the host rock was deformed by cataclasis associated with dislocation glide during nucleation of the shear zone at probably high stress, as indicated by the similar microfabric of diopside porphyroclasts in the shear zone compared to those in the host rock. Unlike, ongoing deformation localized within the shear zone is due to dissolution and precipitation, as indicated by the polyphase aggregates in the strain shadows and in the matrix. 

How to cite: Taufner, R., Trepmann, C., and Viegas, G.: Diopside microfabric development in lower-crust oceanic detachment fault zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12465, https://doi.org/10.5194/egusphere-egu22-12465, 2022.

EGU22-13212 | Presentations | EMRP1.17

Experimental deformation of talc at near-seismic deformation rates 

Charis Horn and Philip Skemer

Talc is a hydrous magnesium silicate with an extremely low coefficient of friction.  In recent years, the recognition that talc is present in many fault systems has led to the suggestion that talc strongly influences the strength of faults.  To understand the role of talc in the seismic cycle, we conducted high pressure and temperature torsional deformation experiments on specimens of natural talc at shear strain rates relevant to slow-slip earthquakes (~10-4 s-1).  Scanning transmission electron microscopy revealed decreasing talc grain sizes (from ~3-5 mm to <100 nm), alongside delamination and kinking of individual talc grains.  This microstructural evolution with progressive strain greatly increases the density of planar defects (including grain-boundaries), and is consistent both with observations of natural, talc-rich faults, and prior experimental work.  Nanoindentation tests at room temperature were performed on deformed specimens to assess precisely whether the observed microstructural changes also affect rheology. At these conditions, nanoindentation is assumed to produce deformation predominantly by intercrystalline frictional slip.  However, bulk hardness data determined from nanoindentation show that there is no change in indentation hardness with increasing strain or defect density, both for indents made parallel to and perpendicular to the shear plane.  Although the talc grains become increasingly damaged with strain, the overall strength of deformed talc does not change.  This suggests that accumulated slip on talc-bearing faults does not change their mechanical response or hazard potential.

How to cite: Horn, C. and Skemer, P.: Experimental deformation of talc at near-seismic deformation rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13212, https://doi.org/10.5194/egusphere-egu22-13212, 2022.

EGU22-418 | Presentations | EMRP1.18

Comparison Between Gravimetry and Radiometry Results: Alto do Sobrido-Ribeiro da Serra Case Study 

Ana Carvalho, Ricardo Ribeiro, Rui Moura, and Alexandre Lima

The Alto do Sobrido (AS) and Ribeiro da Serra (RS) Mines are old Sb-Au explorations. These are located in Gondomar, Portugal, on the inverse limb of the well-known structure called Valongo Anticline. In the AS Mine, the mineralization occurs near the contact between the Schist-Greywacke Complex (CXG) (Precambrian and/or Cambrian(?)) and the breccia of the base of the Carboniferous. In the RS Mine, the mineralization occurs only on the CXG. In both mines, the Sb-Au mineralization occurs in quartz veins and some stockworks.

A spatial correlation between the Sb-Au mineralization and the post-orogenic granites occurs in the Dúrico-Beirã Region according to Gumiel & Arribas (1987). Couto et al. (2007) also acquired data that suggests a genetic connection between this mineralization and non-outcropping granites. These granites may have been the source of fluids and a heat source that improved hydrothermal circulation and they have been observed in one of the RS Mine’s galleries.

With this hypothesis in mind, we intend to compare the data from a radiometric survey, which is a method that is radiometrically sensitive to K, Th and U at the near-surface, to the data from a gravimetric survey, which is a method that is sensitive to density anomalies at greater depths, in order to show if these granites could have chemically influenced its embedding rocks.

To make this comparison, we used the residual anomaly map from our gravimetric survey and the four maps obtained in the radiometric survey (total concentrations, K, eTh and eU). Firstly, we normalized all the grid maps to obtain grids with values between -1 and 1. Once this was complete, we multiplied each of the four radiometry maps to the residual anomaly map, obtaining the comparison maps.

On the resulting maps, we can observe high values in 3 different areas. The first corresponds to a lower value of gravimetric anomaly and a lower value of concentrations of all the elements. This area is located where the hypothesized non-outcropping granites are situated. The second area corresponds to high values on both methods. This matches the location of the lithologies from the Middle Ordovician to the Carboniferous, which are rocks of higher densities and higher concentration values of K, eTh and eU. The third area consists of lower gravimetric anomalies and lower concentrations of K and eU, and coincides with the location of the Ordovician quartzites. This area isn’t as visible on the eTh map, which is consistent with what was observed on the field.

We consider this approach to be a practical method to correlate the results of these two methods and an attempt to understand how the granite located at depth could have influenced these lithologies that today outcrop.

References

Gumiel, P., Arribas, A., 1987. Antimony Deposits in the Iberian Peninsula. Economic Geology, Volume 82, pp 1453-1463.

Couto, H., Borges, F. S., Roger, G., 2007. Late Palaeozoic orogenic gold-antimony deposits from the Dúrico-Beirã area (North Portugal) and their relation with hidden granitic apexes. Ninth Biennial SGA Meeting, Dublin. pp 609-612.

How to cite: Carvalho, A., Ribeiro, R., Moura, R., and Lima, A.: Comparison Between Gravimetry and Radiometry Results: Alto do Sobrido-Ribeiro da Serra Case Study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-418, https://doi.org/10.5194/egusphere-egu22-418, 2022.

EGU22-2416 | Presentations | EMRP1.18

Implications of reservoir heterogeneity for CO2 storage monitoring: A combined experimental and theoretical rock physics study 

Ismael Himar Falcon-Suarez, Michael Dale, and Nazmul Haque Mondol

Carbon Capture Utilization and Storage (CCUS) is an essential technology to meet net-zero carbon emission targets. Due to CO2 injection, original reservoir properties are altered. Early warning of potential CO2 injection-induced reservoir instability depends on our correct interpretation of the geophysical remote sensing data, particularly seismic and electromagnetic datasets. Using joint elastic-electrical datasets is a proven effective approach to simultaneously characterize mineral skeleton properties and pore fluid distribution, and therefore a powerful reservoir monitoring tool for CCUS.

To interpret large-scale elastic-electrical datasets, original rock properties and fundamental CO2-fluid-rock interactions are  preliminarily investigated by combining available well-logging data, lab-controlled experiments using rock samples, and rock physics theories; the latter two are inevitably dependent on one another. Despite we can mimic changing reservoir conditions in the lab and generate datasets that provide essential information to understand specific processes at the micro- and meso-scales (and serve as inputs for large-scale reservoir simulations), every experiment carries limitations inherent to the particular lab capabilities, together with the obvious time- and space-scale related uncertainties (i.e., core-scale experiments only partially describe the events occurring in the field). Then, we need theoretical rock physics to make experimental assumptions, and reciprocally we use the experimental data to validate models.

Physical and petrographic properties of reservoir rocks condition the degree of heterogeneity and anisotropy of the CO2 storage unit that, in turn, influence the total storage capacity and fluid migration. Original clay content, grain size distribution, mineralogy, porosity and permeability are among the most influencing parameters, particularly for low reactive siliciclastic formations (i.e., desired CO2 storage reservoirs). But these properties randomly change to some extent within any reservoir formation.

Here, we investigate how reservoir heterogeneity influences our geophysical interpretation of the potential CO2 storage site Aurora, offshore Norway. Recent studies suggest high clay content and porosity variability within the Johansen Formation sandstone, Aurora’s primary reservoir. Due to lack of Johansen Fm. samples, we selected three sandstone samples from the Central Graben, Offsore UK (Forties Formation), formed in a similar depositional environment, with similar mineralogical composition, and porosity (20 to 28%), clay content (10 to 26%) and permeability (1 to 8 mD) ranges. The elastic (from P- and S-wave velocities) and transport (from permeability and resistivity) properties of the tested samples were used to assess the influence of their intrinsic properties on the pore fluid distribution during CO2 injection and the permanent CO2-induced changes in the Aurora reservoir complex. We apply well-known rock physics theories, including effective stress law, Archie’s relationship, and the Biot-Stoll and White and Dutta-Ode models, for both to impose the most similar reservoir conditions according to our lab limitations and to assess the experimental results. We observe (i) elastic and transport properties variations (up to 15% and 30%, respectively) between samples, mainly related to porosity differences, and (ii) more significant permanent alterations post-CO2 injection in those with higher porosity and clay content. Our results show the importance of accounting for heterogeneity-related changes in sandstone reservoirs during/after subsurface CO2 storage activities for enhanced geophysical interpretation.  

How to cite: Falcon-Suarez, I. H., Dale, M., and Mondol, N. H.: Implications of reservoir heterogeneity for CO2 storage monitoring: A combined experimental and theoretical rock physics study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2416, https://doi.org/10.5194/egusphere-egu22-2416, 2022.

EGU22-4190 | Presentations | EMRP1.18

Joint inversion of DC resistivity and potential field data under different model weighting functions 

Maurizio Milano, Ramin Varfinezhad, and Maurizio Fedi

In this study we analyze the role of model weighting functions for resistivity and potential field data in both separate and joint inversion. We show that the model weighting function built with depth weighting and compacting factor, formerly formulated for the gravity and magnetics inversion, can be useful also for DC resistivity data modelling. The comparison was made using the depth weighting with different exponents and the roughness matrix under L1- and L2-norm Constrained Optimization. We then analyze the 2-D joint inversion of DC resistivity and potential field data, based on the above model weighting function and the cross-gradients constraint. We provide a number of synthetic cases to discuss the pro and cons of each model-weighting function and to examine the feasibility of the joint inversion algorithm. We then provide results from two real case datasets for mining and archeological exploration. The results show that the value of the β exponent is decisive for potential field problems, but it also leads to a faster convergence for the resistivity data inversion. Similarly, the role of compactness is important for modelling compact source from gravity and magnetic, and to warrant an even faster and compact solution for DC resistivity. On the other hand, the results of the joint inversion reveal that the cross gradient constraints allow a successful joint inversion even when resistivity and magnetic data are often not easily comparable.

How to cite: Milano, M., Varfinezhad, R., and Fedi, M.: Joint inversion of DC resistivity and potential field data under different model weighting functions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4190, https://doi.org/10.5194/egusphere-egu22-4190, 2022.

EGU22-4536 | Presentations | EMRP1.18

Transient rheology of the continental crust 

Sagar Masuti, Jun Muto, and Erik Rybacki

Postseismic relaxation after large earthquakes induces transient deformation of the solid Earth, particularly in the deeper part of the crust. The deformation of the upper and lower crust are mainly controlled by the rheological behavior of quartz and feldspar, respectively. The mechanical properties of quartz and feldspar at steady-state creep conditions are well constrained and flow law parameters are known from experimental calibrations. However, the physical mechanism underlying transient creep is poorly understood and the corresponding flow law parameters are unknown so far. Here, we constrain a constitutive framework that captures transient creep and steady state creep consistently using the mechanical data from laboratory experiments. The constitutive framework represents a Burgers assembly with a thermally activated nonlinear stress versus strain-rate relationship for the dashpots. Using the Markov chain Monte Carlo (MCMC) method, we uniquely determine the flow law parameters for both quartz and feldspar. We find an activation energy of 70±20 kJ/mol and a stress exponent of 2.0±0.1 for transient creep of quartz. For feldspar, the best-fit activation energies are 280±30 and 220±20 kJ/mol with stress exponents of 1.0±0.2 and 0.9±0.1 under mid- and high-temperature conditions, respectively. The stress exponents and activation energies of transient creep are consistently smaller than those of steady-state creep for both quartz and feldspar. The flow law parameters determined in this study could be used to quantify the contribution of transient creep in the postseismic deformation following a large continental earthquake. 

How to cite: Masuti, S., Muto, J., and Rybacki, E.: Transient rheology of the continental crust, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4536, https://doi.org/10.5194/egusphere-egu22-4536, 2022.

EGU22-6760 | Presentations | EMRP1.18

Probing the micromechanical features of a fracture interface using a multi-physics approach: A numerical investigation relating asperity deformation with fluid flow 

Clay Wood, Chun-Yu Ke, Andy Rathbun, Jacques Riviere, Derek Elsworth, Chris Marone, and Parisa Shokouhi

The focus of this study is to elucidate the relation between elastodynamic and hydraulic properties of fractured rock subjected to local stress perturbations in relation to fracture aperture distribution. The goal of our integrated numerical and experimental investigations is to understand the mechanisms responsible for changes in fault zone permeability and elasticity in response to dynamic stressing in the subsurface (anthropogenic or seismic in origin). High-resolution (micron-scale) optical profilometry measurements combined with pressure sensitive films have been used to characterize fracture properties such as ‘true’ contact area, aperture distribution and morphology, as well as asperity deformation under applied loads in our experiments. These measurements allow a direct correlation between fracture properties and our lab measurements of fracture elastic nonlinearity and permeability. Using micron-resolution profilometry of centimeter-scale samples, we calculate the elastic deformation of fracture asperities to varying applied  stresses (static and dynamic) using Hertzian contact mechanics. Then, permeability is calculated for each applied stress (deformed asperities) using the parallel plate approximation, in which the Reynolds equation is solved using the finite difference method. This study is uniquely constrained, wherein we investigate the effect of measured deformation of real asperities on creating flow pathways through a fracture. Future work will include implementing contact acoustic nonlinearity (CAN) to model the change in transmission of acoustic waves across the fracture interface during stress perturbation.

How to cite: Wood, C., Ke, C.-Y., Rathbun, A., Riviere, J., Elsworth, D., Marone, C., and Shokouhi, P.: Probing the micromechanical features of a fracture interface using a multi-physics approach: A numerical investigation relating asperity deformation with fluid flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6760, https://doi.org/10.5194/egusphere-egu22-6760, 2022.

EGU22-9251 | Presentations | EMRP1.18

Assessing the pressure (in)dependence of cross-property relations 

Phillip Cilli and Mark Chapman

It is known that geological reservoir characterisation can be improved by the joint modelling and inversion of both electrical and elastic data, however the relationship between a rock’s electrical and elastic properties, which is intrinsic to these methods, is relatively uncertain. On top of this, estimating reservoir pressure from geophysical measurements is an essential part of the 3D and 4D monitoring of CO2 injection and hydrocarbon production, and while electrical and elastic properties are affected by pressure, the effect of pressure on electrical-elastic relations is less obvious.

Here we use the Cross-Property Differential Effective Medium approximation to model public-domain electrical-elastic laboratory measurements made on brine-saturated clean and mixed sandstones cores at 6 effective pressures ranging from 8 MPa to 60 MPa. Although the approximation is able to realise a large proportion of the electrical-elastic space bounded by the Hashin-Shtrikman bounds using a range of permissible parameter values, we find the model parameter, equivalent pore aspect ratio, varies very little as a function of pressure when modelling the measured data. Interestingly, we see equivalent pore aspect ratio changes exponentially as a function of pressure with an R2 value of over 0.99 when modelling clean sandstones, a trend which has been observed previously in single-property inclusion modelling. This small variance in the model parameter as a function of pressure corresponds to an observably small change in the samples’ electrical-elastic measurements with pressure.

We conclude the electrical-elastic properties of the examined clean and mixed brine-saturated sandstones are only weakly dependent on pressure and we demonstrate how a single, pressure-independent model parameter is able to model the electrical-elastic measurements of both the clean and mixed sandstones with reasonable accuracy over the full range of experimental pressures.

How to cite: Cilli, P. and Chapman, M.: Assessing the pressure (in)dependence of cross-property relations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9251, https://doi.org/10.5194/egusphere-egu22-9251, 2022.

EGU22-407 | Presentations | TS2.1

Strain localization along a detachment system: Deformation of natural dolomitic and calcitic mylonites (Mt. Hymittos, Attica, Greece) 

Mark Coleman, Bernhard Grasemann, David Schneider, Konstantinos Soukis, and Riccardo Graziani

Carbonate rocks can be thick, mineralogically-homogeneous packages, which accomodate strain in orogenic belts. Despite its contribution to rock strength, the deformation of dolomite as a major rock forming mineral is understudied in comparison to calcite, quartz, and feldspar. We use field, petrographic, and electron back scatter diffraction (EBSD) analyses of dolomitic and calcitic marbles to investigate the response of these rocks to different degrees of strain under greenschist facies. Mt. Hymittos, Attica, Greece, preserves a pair of Miocene top-SSW ductile-then-brittle low-angle normal faults dividing a tripartite tectonostratigraphy. The bedrock of the massif comprises sub-greenschist facies phyllites and marbles in the uppermost hanging wall unit, and high-pressure greenschist facies schists and marbles of the Cycladic Blueschist Unit in the lower two packages. Ductile mylonites in the footwalls of both detachments grade into brittle-ductile mylonites and finally into cataclastic fault cores. The dolomitic and calcitic marbles of the lower units deformed under greenschist facies conditions and their fabrics reflect the relative differences in strengths between these two minerals. In the middle tectonostratigraphic unit, dolomitic rocks are brittlely deformed and calcitic marbles are mylonitic to ultramylonitic with recrystallized grain sizes ranging from 55 to 8 μm. Within the lower package, dolomitic and calcitic rocks are both mylonitic to ultramylonitic with previous P-T data suggesting metamorphism at ~470 °C and 0.8 GPa. EBSD analysis of six dolomitic marbles of the lower unit reveals a progressive fabric evolution from mylonites to ultramylonites reflecting the magnitude of strain and decreasing temperature of deformation. In mylonitic domains, average grain diameters range from 70 to 25 μm. The mylonitic dolomite exhibits low-angle grain boundaries, internal misorientation zones and textures suggestive of subgrain-rotation recrystallization. This mylonitic fabric is crosscut by ultramylonite bands of dolomite with grain diameters of 15 to 5 μm, which overlaps with the dominant grain size of the subgrains formed within the mylonitic domains. In samples closer to the fault core, the ultramylonite fabric is predominant though boudinaged veins, and relict mylonite zones with coarser grains may still be observed. Uniformly ultramylonitic dolomitic marbles exhibit grain diameters of 40 to 5 μm; the majority of grain diameters are less than 15 μm. The ultramylonite bands have low degrees of internal misorientation and an absence of low-angle grain boundaries that, along with correlated misorientation diagrams, suggest the ultramylonitic dolomite grains are randomly oriented and deforming via grain-boundary sliding. Interstitial calcite grains within these samples may reflect creep-cavitation processes interpreted to have occurred syn-kinematically with grain-boundary sliding. The change from subgrain-rotation recrystallization to grain-boundary sliding is interpreted to reflect the interplay of grain-size sensitive and insensitive processes. Following grain size reduction, subsequent deformation was dominantly accommodated by grain boundary sliding. The dolomitic marbles of the lower unit deformed on the retrograde path from the high-pressure, mid-temperature portion of the greenschist facies. The position of the dolomitic ultramylonites immediately below the cataclastic detachment fault suggest these ultramylonites were deforming very close to the brittle-ductile transition suggesting ductile deformation at lower temperatures than might be predicted by deformation experiments.

How to cite: Coleman, M., Grasemann, B., Schneider, D., Soukis, K., and Graziani, R.: Strain localization along a detachment system: Deformation of natural dolomitic and calcitic mylonites (Mt. Hymittos, Attica, Greece), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-407, https://doi.org/10.5194/egusphere-egu22-407, 2022.

EGU22-2627 | Presentations | TS2.1

Constraining transformation weakening in plagioclase-pyroxene mixtures 

Amicia Lee, Holger Stünitz, Mathieu Soret, and Jacques Précigout

Mafic rocks are a key constituent of the oceanic and lower continental crust. Strain localisation and fabric development in these rocks is controlled by the active deformation mechanisms. From studies of natural rocks it has been established that strain localisation and weakening in mafic rocks is directly related to fluid availability and resultant mineral reactions. Understanding the interplay between reactions, fluid availability, and deformation aids in quantifying the stresses and rates of deformation processes. We have conducted an experimental investigation to constrain the weakening mechanisms in gabbro. Shear experiments were performed in a Griggs-type apparatus at 800-900°C, and 1.2-1.5 GPa with a shear strain rate of 10⁻⁵s⁻¹. The starting material consists of mixed powders with <100 µm sized grains of plagioclase and clinopyroxene from an undeformed sample of the Kågen Gabbro in Northern Norway. Experiments have been conducted with ‘as is’ (dried at 110°C) starting material and with 0.1% added water. The experiments at 800°C are very strong with a peak shear stress ~0.8 GPa whilst the 900°C experiments are weaker, reaching peak stresses of ~0.35 GPa. The 800°C experiments show evidence of mineral reactions with newly formed phases making up 10-25% of the sample. In these reaction zones, plagioclase and clinopyroxene have reacted to produce amphibole and garnet. Additionally S-C’ mylonitic fabrics have developed in these samples. The 900°C samples show minimal evidence for mineral reactions (2-5% new material) or crystal-plastic deformation mechanisms. The lack of mineral reactions in the rheologically weak experiments (900°C) and abundance of reaction products in the mechanically strong experiments (800°C) is conflicting to our inferences of natural studies. However, if partial melting takes place in the higher temperature experiments, it may account for the pronounced strength decrease. We plan to conduct EBSD and TEM analysis to determine crystallographic properties and accurate grain size and shape parameters in the fine grained reaction zones. Future experiments will use fully dried natural starting material (dried at 700-800°C) and An60 and end-member diopside, these experiments will be compared with our current experiments and be used to determine the exact weakening properties from impurities in the natural starting material.

How to cite: Lee, A., Stünitz, H., Soret, M., and Précigout, J.: Constraining transformation weakening in plagioclase-pyroxene mixtures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2627, https://doi.org/10.5194/egusphere-egu22-2627, 2022.

EGU22-2816 | Presentations | TS2.1

Cracking induced by dislocation creep in pure quartz shear bands of granitoids 

Jacques Précigout, Estelle Ledoux, and Laurent Arbaret

The production of micro-pores during viscous creep is a driving mechanism for fluid circulation in deep environments. However, strain-induced cracking in nature is nowadays attributed to grain boundary sliding (GBS), restricting this process to fine-grained ductile shear zones where rocks deform by diffusion creep. Here we give natural evidence of micro-cracking induced by dislocation creep, which is by far the dominant deformation mechanism in lithospheric rocks. Focusing on pure quartz shear bands across the Naxos western granite (Aegean Sea, Greece), we first document sub-micron pores that arise at grain and sub-grain boundaries. Their shape and location emphasize sub-grain rotation as a source of cracking. We then confirm that quartz is dominated by dislocation creep with evidence of a moderate to strong lattice preferred orientation (LPO) and many sub-grain boundaries, including at the margin of the pluton where the brittle/ductile transition was reached. These features coincide with (1) quartz grains located as inclusion into quartz porphyroclasts and (2) a dependency of the LPO strength on grain size. Our findings suggest that creeping cavities act as pumping sites for fluid to penetrate the crystal lattice and nucleate randomly oriented grains along sub-grain boundaries, accounting for (1) shear localization by enhancing hydrolytic weakening and (2) rock embrittlement through growth and interlinkage of cavities where phase nucleation is limited.

How to cite: Précigout, J., Ledoux, E., and Arbaret, L.: Cracking induced by dislocation creep in pure quartz shear bands of granitoids, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2816, https://doi.org/10.5194/egusphere-egu22-2816, 2022.

EGU22-3268 | Presentations | TS2.1

Diffusion creep of a Na-Ca-amphibole-bearing blueschist 

Leif Tokle, Lonnie Hufford, Luiz Morales, Claudio Madonna, and Whitney Behr

Blueschists are a major constituent rock type along the subduction zone interface and therefore critical to our understanding of subduction zone dynamics. Previous experimental work on natural blueschists focus on either seismic anisotropy or on the process of eclogization of a blueschist aggregate; however, little is known about the mechanical properties of blueschist rocks. We have conducted a suite of general shear deformation experiments in the Griggs apparatus to constrain the rheology of a blueschist aggregate. The sample material derives from a natural blueschist that was crushed into a powder. The powder consists of ~55% sodic amphibole, ~30% epidote, ~8% quartz, ~5% titanite, ~2% ilmenite, and <1% mica. Deformation experiments were conducted at 1.0 GPa confining pressure, temperatures of 650, 675, 700, and 750°C, and no water added. All of the deformation experiments were strain rate stepping experiments with either 4 or 5 strain rate steps per experiment with strain rates ranging from ~2.7e-5 to 5.2e-7 s-1. Based on the mechanical data we determine a stress exponent of 1.9 +/- 0.3. Microstructural and EDS analysis shows the initial Na-amphibole grains transform into a fine-grained aggregate of new Na-Ca-amphibole with lower Na and Si and higher Fe and Ca plus albite and ilmenite. The fine-grained aggregates accommodate the majority of the strain while epidote deforms by rigid body rotation or brittle deformation. Based on both the mechanical and microstructural observations, we interpret the fine-grained aggregates to be deforming by diffusion creep. Additional analyses will be conducted to constrain the grain size to develop flow law parameters to estimate the rheology of the subduction zone interface.

How to cite: Tokle, L., Hufford, L., Morales, L., Madonna, C., and Behr, W.: Diffusion creep of a Na-Ca-amphibole-bearing blueschist, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3268, https://doi.org/10.5194/egusphere-egu22-3268, 2022.

The presence of large volumes of eclogite in collision and subduction zones makes their formation and deformation highly relevant for the dynamics of convergent zones. There is however no consensus on the deformation behavior of eclogite. On the one hand, mylonitic eclogite shear zones showing evidence of dominant deformation by dislocation creep have frequently been reported. On the other hand, fluid supported formation and deformation has been recently suggested as a potential mechanism in eclogite whereby the main accommodating mechanism is dissolution-precipitation creep. This raises the question of the factors controlling the deformation behavior of eclogite.

In this contribution, we present microstructural, petrographical and chemical data from a series of eclogite samples derived from low Mg – high Ti gabbro collected at the eclogite type locality (Saualpe-Koralpe Complex, Eastern Alps, Austria). The rocks are characterized by a pronounced foliation defined by the shape preferred orientation of the major minerals (omphacite, amphibole, epidote and garnet). Minor quartz is observed at dilation sites. Overall, grains show rather straight grain boundaries and a uniform extinction. These features are interpreted as evidence of diffusion and dissolution-precipitation dominated formation and strain accommodation. Thermodynamic forward modelling indicates that eclogitization occurred at around 2 GPa and 640–680°C and was supported by fluid. Locally, the eclogite fabric is crosscut by veins showing a similar paragenesis as the host eclogite. However, they are enriched in quartz and epidote, depleted in garnet and show overall a coarser grain size. Depending on their initial orientation, the veins were either reactivated as flanking structures or foliation sub-parallel shear zones. The reactivated veins are characterized by undulatory extinction, twinning and subgrain formation, all being indicative of dislocation creep. The identical paragenesis and similar mineral chemistry indicates that reactivation occurred at conditions close to those of eclogitization. The investigated samples therefore testify that eclogite can deform by two different mechanisms at similar pressure-temperature conditions. Our investigations document that dissolution-reprecipitation is bound to the process of eclogitization and low strain rate whereas post-eclogitization strain localization is accommodated by dislocation creep.

How to cite: Rogowitz, A., Huet, B., and Schorn, S.: How to creep and when? Deformation mechanisms at the eclogite type locality (Saualpe-Koralpe Complex, Eastern Alps, Austria)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3477, https://doi.org/10.5194/egusphere-egu22-3477, 2022.

EGU22-3889 | Presentations | TS2.1

Feasibility of the mobile-lid regime controlled by grain size evolution 

Antonio Manjón-Cabeza Córdoba, Tobias Rolf, and Maëlis Arnould

One of the most discussed issues of whole-mantle geodynamic models is the need of an 'ad hoc' yield stress which is lower than any strength measurement of natural samples in the brittle or plastic regimes. It is commonly believed that grain size evolution, in particular grains size reduction due to dynamic recrystallization, may decrease the strength of the lithosphere and therefore aid the onset and persistence of the mobile-lid regime. In this work, we carry out an investigation of 2D whole-mantle annulus models with varying yield stress. We compare cases with different grain growth and grain reduction parameters to cases with constant grain size to make inferences on the feasibility of a plate-like convective regime as a function of the yield strength of the lithosphere.

Our results show that viscosity profiles of models with dynamic grain-size evolution are inherently different to those with constant grain size, and that those profiles vary little when changing grain-size evolution parameters. In this context, the lower mantle shows greater variations in viscosity than the upper mantle: with viscosity contrasts between upper and lower mantle and plume widths comparable to those of the Earth, in particular in models with enhanced grain growth. Furthermore, our models show that, while enhancing grain size reduction reduces episodicity and increases mobility up to some point, increasing grain growth favors mobile-lid convection even more. This is at odds with previous conceptions of the grain-size-evolution-induced mobile-lid regime, where grain groth should promote healing of the lithosphere and therefore inhibit subduction. We hypothesize that increased stiffness of the bottom of the lithosphere, together with a more viscous lower mantle, are the main reasons for the grain-grouth-favored mobile-lid regime.

How to cite: Manjón-Cabeza Córdoba, A., Rolf, T., and Arnould, M.: Feasibility of the mobile-lid regime controlled by grain size evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3889, https://doi.org/10.5194/egusphere-egu22-3889, 2022.

EGU22-4606 | Presentations | TS2.1

Strain localization in quartz-rich fault gouge at subseismic slip rates 

Chien-Cheng Hung and André Niemeijer

Understanding strain localization and development of shear fabrics within brittle fault zones at subseismic slip rates is crucial as they have critical implications for the mechanical strength and stability of faults and for earthquake physics. We performed direct shear experiments on ~1 mm thick layers of simulated quartz-rich fault gouge at an effective normal stress of 40 MPa, pore fluid pressure of 15 MPa, and temperature of 100°C. Microstructures were analyzed from strain hardening state (~1.3 mm displacement) to strain softening (~3.3 mm displacement) to steady-state (~5.6 mm) at different imposed shearing velocities of 1 µm/s, 30 µm/s, and 1 mm/s. We performed X-ray Computed Tomography (XCT) on sheared samples with a strain marker to analyze slip partitioning. To analyze and quantify localization from few hundreds to thousands of cross-section images, we used machine learning and developed an automatic boundary detection method to identify the type of shear fabrics and quantify the amount of them. Our results reveal that R1 and Y (or boundary) shears are the two major localization features that developed in a repeatable manner. Slip on R1 shears shows little dependency on both shear displacement and slip velocity and amounts to ~5 to ~30% of slip through the entire frictional sliding. On the other hand, Y and boundary shears show a strong correlation with displacement and velocity where more than 40% of strain was accommodated at steady-state for all velocities. However, Y and boundary shears become less prominent with increasing velocity, suggesting that velocity-weakening and the associated nucleation of unstable sliding are less likely to occur at higher slip rates as the overall friction behavior would be controlled by a thicker gouge layer. In other words, this suggests that Y shear development by grain size reduction is less efficient at high slip velocities which has important implications for the amount of heat generated during accelerating slip.

How to cite: Hung, C.-C. and Niemeijer, A.: Strain localization in quartz-rich fault gouge at subseismic slip rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4606, https://doi.org/10.5194/egusphere-egu22-4606, 2022.

Seismic rupture in strong, anhydrous lithologies of the lower continental crust requires high failure stress, in the absence of high pore fluid pressure. Several mechanisms proposed to generate high stresses at depth imply transient loading driven by a spectrum of stress changes, ranging from highly localised stress amplifications to crustal-scale stress transfers. High transient stresses up to GPa magnitude are proposed by field and modelling studies, but the evidence for transient pre-seismic stress loading is often difficult to extract from the geological record due to overprinting by coseismic damage and slip. However, the local preservation of deformation microstructures indicative of crystal-plastic and brittle deformation associated with the seismic cycle in the lower crust offers the opportunity to constrain the progression of deformation before, during and after rupture, including stress and temperature evolution.


Here, detailed study of pyroxene microstructures characterises the short-term evolution of high stress deformation and temperature changes experienced prior to, and during, lower crustal earthquake rupture. Pyroxenes are sampled from pseudotachylyte-bearing faults and damage zones of lower crustal earthquakes recorded in the exhumed granulite facies terrane of Lofoten, northern Norway. The progressive sequence of microstructures indicates localised high-stress (at the GPa level) preseismic loading accommodated by low temperature plasticity, followed by coseismic pulverisation-style fragmentation and subsequent grain growth triggered by the short-term heat pulse associated with frictional sliding. Thus, up to GPa-level transient high stress leading to earthquake nucleation in the dry lower crust can occur in nature, and can be preserved in the fault rock microstructure.

How to cite: Menegon, L. and Campbell, L.: High stress deformation and short-term thermal pulse preserved in exhumed lower crustal seismogenic faults (Lofoten, Norway), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4692, https://doi.org/10.5194/egusphere-egu22-4692, 2022.

EGU22-5108 | Presentations | TS2.1

Different mechanical behavior at the same P-T conditions in biotite-quartz assemblage: interconnectivity and composition effect of experimentally deformed mica 

Khadija Alaoui, Laura Airaghi, Holger Stünitz, Hugues Raimbourg, and Jacques Précigout

The effect of composition on microstructural development and mechanical strength was tested using mica-quartz-aggregates during deformation experiments.

This study used two chemically different biotite minerals mixed with quartz: (1) high F-phlogopite and (2) intermediate biotite in order to investigate the role of biotite-bearing systems for the development of shear zones and strain accommodation. Shear experiments (Griggs-type apparatus) were performed using mica (30 vol. %) and quartz (70 vol. %) assemblages at 750 and 800°C, 1000 MPa and a shear strain rate of ~10-5 s-1.

Mechanical results for the F-phlogopite-bearing assemblage indicate strong samples, approximately equivalent to pure quartz samples (Richter et al., 2018), deforming at differential stresses of 764-1097 MPa). F-phlogopite flakes are preferentially oriented parallel to the main shear direction, but poorly interconnected. Most of the strain is accommodated by quartz behaving as an interconnected network. Cathodoluminescence imaging reveals that quartz recrystallizes mainly by local pressure-solution and its strength controls the overall strain accommodation.

In contrast, intermediate biotite assemblages are significantly weaker and deform for lower differential stresses of 290-327 MPa, as expected for natural rocks. Biotite flakes form an interconnected network accommodating most of strain.

The interconnectivity of biotite grains thus plays a major role in weakening quartz-biotite assemblages. However, at similar P-T-strain and grain size conditions, the capacity of biotite grains to interconnect may also depend on its chemical composition, particularly considering the effect of trace elements incorporation (as fluorine) on the strength of the biotite interlayer bounds (Dahl et al., 1996, Figowy et al., 2021). This led us to conclude that different types of mica, behaving differently, strongly affect strength, deformation mechanism, and microstructure of the rock due to their structure, composition and stability fields.

How to cite: Alaoui, K., Airaghi, L., Stünitz, H., Raimbourg, H., and Précigout, J.: Different mechanical behavior at the same P-T conditions in biotite-quartz assemblage: interconnectivity and composition effect of experimentally deformed mica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5108, https://doi.org/10.5194/egusphere-egu22-5108, 2022.

EGU22-5127 | Presentations | TS2.1

Experimental strain localization in granitoid ultramylonites: Pre-fracturing vs. viscous strain localization 

Natalia Nevskaya, Weijia Zhan, Holger Stünitz, Alfons Berger, and Marco Herwegh

Rheological models of Earth’s granitoid mid- to upper crust are commonly based on the physico-chemical properties of the most abundant rock forming minerals quartz and feldspar. However, there is increasing field evidence that deformation in these rocks localizes in ultrafine-grained polymineralic shear zones, which are weaker than any of the end member minerals. Especially at the brittle to viscous transition, the localization and deformation mechanisms, i.e. the role of incipient brittle deformation vs. continuous viscous strain localization, is not yet fully understood.

To fill this gap in knowledge, ultramylonite samples with granitic composition from the Central Aar Granite (Aar Massif, Central Switzerland) were deformed using a Griggs type apparatus. The foliation of the ultramylonitic starting material was oriented 45° to the compression direction, to investigate the influence of grain size and composition on strain localization in the different mylonite bands. Two types of coaxial experiments were conducted at 650°C, and 1.2 GPa confining pressure: A) Discrete fractures were created before the shear deformation starts; B) No fractures were induced during an early stage of the experiment.

All experiments have in common that strain is accommodated in 20-100 µm wide viscous shear zones with elongated grains and minor grain size reduction. In these shear zones, most strain is further localized in 10-20 µm wide zones, showing dramatic grain size reduction down to few tens of nanometres. In the experimentally generated shear zones, both, brittle and viscous processes are active. In terms of overall rock strength, all newly formed ultrafine-grained shear zones are up to three times weaker than comparable experiments on pure quartz or coarser grained granites – which agrees well with field observations. Furthermore, pre-fractured type A) is up to two times weaker than the non-fractured type B), and the orientation and number of shear zones is also fundamentally different between the two experiment types.

This study confirms two weakening factors promoting different types of strain localization at the brittle to viscous transition: 1) The existence of fractures and their interconnectivity – facilitating highly-localized grain size reduction; 2) Initial sample heterogeneity by polymineralic composition and ultrafine grain size – generating grain size reduction along strain gradients by activating viscous processes. Further quantitative microstructural analyses will reveal the role of chemistry and the deformation mechanisms on the localization behaviour.

How to cite: Nevskaya, N., Zhan, W., Stünitz, H., Berger, A., and Herwegh, M.: Experimental strain localization in granitoid ultramylonites: Pre-fracturing vs. viscous strain localization, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5127, https://doi.org/10.5194/egusphere-egu22-5127, 2022.

EGU22-5371 | Presentations | TS2.1

Implementing 3D anisotropic viscosity calculations into ASPECT 

Ágnes Király, Menno Fraters, and Rene Gassmoeller

Olivine, the main rock-forming mineral of Earth's mantle, responds to tectonic stress by deforming viscously over millions of years. This deformation creates an anisotropic (direction-dependent) texture that typically aligns with the mantle flow direction. According to laboratory experiments on olivine, we expect this texture to also exhibit anisotropic viscosity (AV), with deformation occurring more easily when it is parallel to, rather than across, the texture. However, the direction dependency of lithospheric and asthenospheric viscosity is rarely addressed in geodynamic models.

 The open-source modeling package ASPECT can address AV in a 2D setting using the director method, where AV is present due to shape preferred orientation created by dike intrusions (Perry-Houts and Karlstrom, 2019). We have adapted this implementation for current versions of ASPECT and benchmarked it against similar Rayleigh-Taylor instability models by Lev and Hager (2008).

Unfortunately, a 2D method is inappropriate to address AV related to olivine crystallographic preferred orientation (CPO or texture), as, by default, olivine has three independent slip systems on which deformation can occur. Integrating anisotropic viscosity into 3D models would also allow us to use the actual laboratory-based parametrizations of the olivine slip system activities and texture parameters when describing the evolution of CPO and AV. One of the biggest challenges in addressing AV in a 3D setting is to find the full, rank 4, viscosity tensor, which can be done with a method similar to the one for the fluidity tensor in Király et al., (2021).

Here, we present the initial results of simple geodynamic setups (shear box, corner flow), where 3D olivine CPO develops, based on the D-Rex method (Fraters and Billen, 2021), and this CPO creates AV based on the micromechanical model described in Hansen et al., (2016).

Our goal is to create a tool within ASPECT that allows for CPO to develop and affect the asthenospheric or lithospheric mantle’s viscosity to improve modeling a wide range of geodynamic problems.

 

References listed:

Fraters, M.R.T., and Billen, M.I., 2021, On the Implementation and Usability of Crystal Preferred Orientation Evolution in Geodynamic Modeling: Geochemistry, Geophysics, Geosystems, doi:10.1029/2021GC009846.

Hansen, L.N., Conrad, C.P., Boneh, Y., Skemer, P., Warren, J.M., and Kohlstedt, D.L., 2016, Viscous anisotropy of textured olivine aggregates: 2. Micromechanical model: Journal of Geophysical Research: Solid Earth, doi:10.1002/2016JB013304.

Király, Á., Conrad, C.P., and Hansen, L.N., 2020, Evolving Viscous Anisotropy in the Upper Mantle and Its Geodynamic Implications: Geochemistry, Geophysics, Geosystems, v. 21, p. e2020GC009159, doi:10.1029/2020GC009159.

Lev, E., and Hager, B.H., 2008, Rayleigh-Taylor instabilities with anisotropic lithospheric viscosity: Geophysical Journal International, doi:10.1111/j.1365-246X.2008.03731.x.

Perry-Houts, J., and Karlstrom, L., 2019, Anisotropic viscosity and time-evolving lithospheric instabilities due to aligned igneous intrusions: Geophysical Journal International, doi:10.1093/gji/ggy466.

How to cite: Király, Á., Fraters, M., and Gassmoeller, R.: Implementing 3D anisotropic viscosity calculations into ASPECT, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5371, https://doi.org/10.5194/egusphere-egu22-5371, 2022.

EGU22-5979 | Presentations | TS2.1

Quartz grain fabric in shales and sandstones: Some contrasting behaviors 

Charles Aubourg, Hugo Saur, Peter Moonen, and Rebecca Stokes

Many processes are at work when a sedimentary rock deforms. Quartz grains, for example, can rotate rigidly in the matrix, or on the contrary, undergo processes of dissolution and crystallization. Microtomography allows us to image the 3D geometry of minerals at the micron scale and quantify their fabric. Here, we use the quartz shape fabric extracted from microtomography data to evaluate the mechanisms active during burial and deformation of several sedimentary rocks systems.

Our first examples are of shales developing a slaty cleavage oblique to bedding. For shales that have undergone moderate burial (Tburial max ~200°C) (Sigues locality, Pyrenees), we show that the quartz grains rotate very little in the clay matrix. Even with the development of a slaty cleavage, a significant proportion of quartz grains remain parallel to the bedding plane. This surprising result implies that the rigid rotation of quartz grains, even in a ductile clay matrix, is not effective. 

In shales having undergone deeper burial and temperatures approaching the lower greenschist facies (Tburial max ~280°C) (Lehigh Gap locality, Appalachian mountains), we show that the average short-axis of the grains is orthogonal to the cleavage plane.  We suggest that this shape preferred orientation results from preferential dissolution of quartz faces oriented perpendicular to sigma 1, thus resulting in a shape preferred orientation without significant grain rotation.

Our last example concerns fine-grained sandstones, slightly deformed and buried at a shallow depth. If we refer to the example of shales with little burial, we would expect a very strong control of the bedding on the quartz fabric, since at these P-T conditions we expected dissolution-precipitation processes to be sluggish, and grain rotation to be ineffective.  However, surprisingly, the quartz in this rock is well oriented in the fabric which is oriented perpendicular to the bedding.

How the quartz grains were reoriented in the fine-grained sandstone suggests relations still not well understood with the deformation of a porous rock and the cementing processes of the rock. The microtomography approach in fine-grained rocks opens a door to this understanding of the behavior of quartz grains in sedimentary rocks.

How to cite: Aubourg, C., Saur, H., Moonen, P., and Stokes, R.: Quartz grain fabric in shales and sandstones: Some contrasting behaviors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5979, https://doi.org/10.5194/egusphere-egu22-5979, 2022.

EGU22-6124 | Presentations | TS2.1

Shape Preferred Orientation at scale. From grain-scale aggregates to global mantle convection 

Albert de Montserrat, Manuele Faccenda, and Giorgio Pennacchioni

Earth's mantle rocks are poly-aggregates where different mineral phases coexist. These rocks may often be approximated as two-phase composites with a dominant phase and less abundant one (e.g. bridgmanite-ferropericlase composites in the lower mantle). Severe shearing of these rocks leads to a non-homogeneous partitioning of the strain between the different phases, with the composite developing a laminar fabric of weak and thin material where strain localizes. The resulting bulk rock is a mechanically anisotropic media that is hardened against normal stress, while significantly weakened against fabric-parallel shear stress.

Due to the large scale difference between the laminar gran-scale fabrics and regional-to-global geological processes, Earth’s rocks are idealised as homogeneous materials instead of multi-phase bodies in numerical models. Thus, a characterization of the rheology evolution of the bulk composite is necessary to better understand large-scale geological processes in which anisotropy may play a fundamental role. Recent three-dimensional numerical (de Montserrat et al. 2021) studies have shown that the degree of lateral interconnectivity of the weak and thin layers is rather limited, thus estimating the rheology of a composite with laminar fabrics by the idealized Voigt and Reuss averages for fibres yield a strong underestimation of the strength of the composite. Instead, we use a combination of numerical results and micro-mechanics to develop an empirical framework to estimate the evolution of the (anisotropic) rheology of such composites.

We apply this rheology framework to study the effects of fabric-induced directional-weakening/hardening on global mantle convective patterns. First order effects of extrinsic anisotropy of lower mantle material observed in our two-dimensional models are a decrease of the wavelength of convective cells, and up to a ~50% increase in the average mantle flow velocity caused by the weakening of the flow-parallel component of the viscosity tensor. The latter is particularly evident in mantle plumes, where the ascent and transfer of hot lower mantle material to lower depths is enhanced by the near-alignment of the weak  fabrics with the plume channel.  

How to cite: de Montserrat, A., Faccenda, M., and Pennacchioni, G.: Shape Preferred Orientation at scale. From grain-scale aggregates to global mantle convection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6124, https://doi.org/10.5194/egusphere-egu22-6124, 2022.

Quaternary deformation in the northern Chile coastal forearc is mainly accommodated by ubiquitous upper-plate faults cataloged as weak fault zones, however, the deformation mechanisms and the internal structure of these reactivated faults remain poorly understood. To solve this problem, we selected seven study sites from reactivated upper-plate faults of the northern Chile forearc (23-25°S). These faults formed during the Early Cretaceous and reactivated during the Quaternary forming conspicuous fault-scarps. Here we present a new characterization of the internal structure at the outcrop and microscopic scale. Samples for thin-sections and XRD were collected in several cross-sections across faults. We define 4 units conforming the internal structure: (1) A decimetric well-defined principal slip zone, referred here as active fault core (AFC), consisting of a gouge layer subunit bounded by a fault breccia subunit, (2) a metric inactive fault core (IFC), surrounding the AFC, composed mostly of cataclasites and in some cases, mylonites, (3) a host-rock unit corresponds mainly to Jurassic-Cretaceous dioritic-granitic intrusives and Jurassic andesites, and (4) a decametric damage zone affecting both the IFC and the host rock. Near the topographic surface, the gouge layer subunit consists of a grey/green ultrafine matrix (40-80%) partially to completely replaced by massive iron oxides. In some sites, the gouge layers are partially foliated or/and exhibit millimetric bands of chaotic microbreccia. Porphyroclasts correspond mainly to (1) highly quartz and plagioclase intracracked individual crystals (<0.4mm), (2) larger fragments (<1mm) generally sigmoidal-like of the IFC (cataclasites) indicating different degrees of cataclastic-flow. Transgranular microfractures are densely propagated through the boundaries of larger porphyroclasts, breaking grains into ever-finer fragments (constrained communition) and generating chaotic microbreccia halos in the boundaries that grade into an ultrafine gouge matrix. (3) Another portion of large porphyroclasts (>1mm) grade from S-C cataclasite at its cores to S-C ultra-cataclasites at its boundaries. Frictional sliding is propagated through this S-C fabric formed by the ultracataclasite boundaries, generating well-defined and smoothened surfaces between large porphyroclasts and gouge layers. Microfractures -commonly filled with quartz>calcite>albite>chlorite-epidote veins- propagate mostly through the gouge layers, which are in turn displaced by microfaults affecting the entire subunit. The IFC composition changes markedly along-strike but multiple-fault cores are ubiquitous. In Jurassic andesites, the IFC is defined by protocataclasites with layers of red gouge, In Jurassic to Cretaceous diorite-metadiorite protoliths the IFC is defined by S-C cataclasites with microstructures showing undulating extinction, subgrains, and bulging recrystallization of quartz, and ultracataclasite bands and green gouge layers developed under low greenschist facies conditions. The IFC formed in mylonitic rocks derived from Jurassic to Cretaceous granitoid includes bands of hydrothermally-altered green and red mylonites. The complex overprinted microtextures indicate a progressive exhumation and shearing of the IFC. The microtexture analysis reflects the evolution of this unit from high temperature-low stain rates formed at deep structural levels to low temperature-high strain rates near-surface. We interpret the highly accumulated strain in S-C ultracataclastic bands and S-C gouge layers of the IFC (constrained communition) reduces the fault frictional strength and promote the frictional slip of the quaternary reactivations of the AFC.

How to cite: González, Y., Jensen, E., and González, G.: Internal Structure and Microtextures of a Quaternary Upper-plate Fault Zone: A Case Study from the Atacama Fault System, Northern Chile., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6742, https://doi.org/10.5194/egusphere-egu22-6742, 2022.

EGU22-6926 | Presentations | TS2.1

Pulverized rock and episodic hydrothermal brecciation along the Median Tectonic Line, Japan 

Geri Agroli, Masaoki Uno, Atsushi Okamoto, and Noriyoshi Tsuchiya

The Median Tectonic Line is a major east-west-trending arc-parallel fault that separates Sanbagawa metamorphic rock and Ryoke granite. We present the novel field observation of possibly pulverized rock and its evolution toward the fault cataclasite/breccia in the Ichinokawa antimony deposit in Central Shikoku. Ichinokawa was considered as largest stibnite mine in the world with a huge stibnite aggregate in which occurs in the brecciated-pelitic schist of the Sanbagawa belt. Based upon the texture in the outcrop and particle size distribution (PSD), this breccia is classified into two types. Breccia-1 (bx-1) is characterized by a centimeter-meter (up to 5m) angular breccia-clast with minimum to no shear displacement and rotational block. This bx-1 subsequently grows to be highly comminuted to produce breccia-2 (bx-2) which appear to have chaotic-polymict clast with matrix-supported texture within the fault zone with variable width and cut the bx-1 by recognizable breccia margin. Both of these breccia are cemented by reddish rock-flour matrix consist of dolomite, quartz, mica, ± pyrite. In addition, bx-2 has a more rounded shape with most of the clast size being less than 50mm and it shows orientation nearly parallel to the fault plane under a thin section. Based on this macro and micro-scale observation breccia in Ichinokawa is more likely to form under different mechanisms. Pulverization is plausible to rupture the pelitic schist and generate bx-1 without rotating the fragment. Hydrothermal activity in this area can’t be neglected which is responsible to create bx-2 as a result of fluid injection and transporting comminuted-fragment of bx-1 into the damage/fault zone. This breccia also underpins the formation of stibnite deposits that mark the latest fluid activity in this area where quartz-stibnite±pyrite±kaolinte vein truncate both pelitic schists of bx-1 as well as bx-2.

How to cite: Agroli, G., Uno, M., Okamoto, A., and Tsuchiya, N.: Pulverized rock and episodic hydrothermal brecciation along the Median Tectonic Line, Japan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6926, https://doi.org/10.5194/egusphere-egu22-6926, 2022.

EGU22-7175 | Presentations | TS2.1

Weakening effect of grain-size reduction in granitoid shear zones 

Jonas B. Ruh, Leif Tokle, and Behr Whitney

Localization of strain during deformation of crustal rocks to form narrow shear zones requires some form of strain weakening. Bulk weakening of a deforming shear zone may for example result from geometric reorganization and interconnection of weak phases, from concentration of fluids or fluid-rich mineral phases, or from local temperature increase due to shear heating. A further potential weakening effect is work-related grain size reduction driven by dislocation creep, and the consequent activation of grain-size-sensitive diffusion creep in recrystallized zones.

To test the importance of grain size reduction for mechanical weakening of granitoid crustal shear zones, a numerical model of initially undeformed granitoid texture was set up and sheared to a total shear strain of 10. The numerical finite difference code solves for the conservation of momentum (Stokes) and mass with a visco-elasto-plastic rheology. The model setup outlines a naturally constrained multi-phase granitoid texture including quartz, plagioclase, and biotite. The domain measures 5x5 cm with top and bottom velocities describing simple shear, while the left and right prescribe periodic boundaries. For both quartz and plagioclase (anorthite), flow laws for dislocation and diffusion creep are implemented and act in parallel. Grain size evolution is implemented in the form of the paleowattmeter with mineral-specific grain growth laws. The 2D numerical setup of a complex multi-phase initial texture allows us to investigate grain size evolution in a progressively evolving system with a spatially and temporally varying stress field and with simultaneous geometric weakening associated with interconnection of weak phases, neither of which can be analyzed using analytical calculations.

Results show a reduction of grain sizes of quartz and plagioclase during shearing with quartz deforming dominantly under dislocation creep. Plagioclase behaves brittlely at low temperatures, with dominant diffusion creep at intermediate temperatures, switching to dislocation creep at high temperatures. Purely textural weakening of >60% occur at 550 °C. At lower temperatures, anorthite strength reduces given the brittle yield envelope and at higher temperatures, dislocation creep strength of quartz and anorthite converge, resulting in bulk shear and less textural weakening. Additional weakening related to grain size reduction relies on the activation of diffusion creep as the dominant deformation mechanism for anorthite. At 350 °C, anorthite strength is limited by brittle yield and no grain-size-induced weakening is detectable. For higher temperatures, additional grain-size-induced weakening ranges between 12–30 %, and thus represents an important factor for the initiation of granitoid crustal shear zones. The presented numerical study underlines the importance of grain size-related weakening of crustal shear zones, particularly at intermediate temperatures above the brittle-ductile transition (400–450°C) and below the activation of dislocation creep in plagioclase (>650°C).

How to cite: Ruh, J. B., Tokle, L., and Whitney, B.: Weakening effect of grain-size reduction in granitoid shear zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7175, https://doi.org/10.5194/egusphere-egu22-7175, 2022.

EGU22-7406 | Presentations | TS2.1

Correlative, cross-platform microscopy application reveals deformation mechanisms during seismic slip along wet carbonate faults 

Markus Ohl, Helen King, Andre Niemeijer, Jianye Chen, and Oliver Plümper

Faults in the upper crust are considered major fluid pathways, raising the need for deformation experiments under wet conditions that focus on the nanoscale interaction between gouge material and pore fluid. Friction experiments on calcite at seismic slip velocities show strong dynamic weakening behaviour attributed to a combination of grain-size reduction and nanoscale diffusion. The resulting syn-deformational physico-chemical interactions between fluid and calcite are key in deciphering deformation mechanisms and rheological changes during and after (seismic) faulting in the presence of a fluid phase. We conducted rotary shear deformation experiments (1 m/s, σn = 2 and 4 MPa) on calcite gouge with water enriched in 18O (97 at%) as pore fluid to track and quantify potential fluid – mineral interaction processes. With our correlative, cross-platform workflow approach, we integrate Raman spectroscopy, nanoscale, and Helium-Ion secondary ion mass spectrometry (nanoSIMS, HIMSIMS), focused ion beam – scanning electron microscope (FIB-SEM) and transmission electron microscopy (TEM) to characterise the nanostructure and analyse isotope distribution. Raman analyses confirm the incorporation of 18O into the calcite crystal structure, as well as the presence of amorphous carbon. We identify three new band positions relating to the possible isotopologues of CO32- (reflecting 16O substitution by 18O). In addition, we detect portlandite (Ca(OH)2), pointing to a hydration reaction of lime (CaO) with water. Raman and NanoSIMS maps reveal that 18O is incorporated throughout the deformed volume, implying that calcite isotope exchange affected the entire fault gouge. Based on oxygen self-diffusion rates in calcite we conclude that solid-state 18O – isotope exchange cannot explain the observed incorporation of 18O into the calcite crystals during wet, seismic deformation. Hydration of portlandite and calcite containing 18O, implies breakdown and decarbonation of the starting calcite and the nucleation of new calcite grains. Our results question the state and nature of calcite gouges during seismic deformation and challenge our knowledge of the rheological properties of wet calcite fault gouges at high strain rates. The observations suggest that the physico-chemical changes are a crucial part of hydrous calcite deformation and have implications for the development of microphysical models that allow us to quantitatively predict crustal fault rheology.

How to cite: Ohl, M., King, H., Niemeijer, A., Chen, J., and Plümper, O.: Correlative, cross-platform microscopy application reveals deformation mechanisms during seismic slip along wet carbonate faults, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7406, https://doi.org/10.5194/egusphere-egu22-7406, 2022.

EGU22-8484 | Presentations | TS2.1

Constraining wet quartz rheology from constant-load experiments 

Subhajit Ghosh, Holger Stünitz, Hugues Raimbourg, and Jacques Précigout

Quartz rheology in the presence of H2O is crucial for modelling (numerical and geophysical) the deformation behavior of the continental crust and gives important insights into crustal strength. Experimental studies in the past have determined stress exponent (n) values for flow law between ≤ 2 to 4, while the values for activation energy (Q) vary from ~120 to 242 kJ/mol. Here, we investigated the quartz rheology under high-pressure and high-temperature conditions, using a new generation hydraulically-driven Griggs-type apparatus. In order to develop a robust flow law for quartzite, we performed constant-load coaxial deformation experiments of natural coarse-grained (~ 200 μm) high purity (> 99 % SiO2) quartzite from the Tana quarry (Norway). Our creep tests were carried out at 750 to 900 °C on the as-is (no added H2O) and 0.1 wt.% of H2O added samples under 1 GPa of confining pressure. In contrast to earlier strain rate stepping experiments, the constant-load procedure needs lower strain at each step (≤1−2%) to achieve steady-state conditions. As a consequence, there is a very low amount of recrystallization. Importantly, we can determine the Q-value independently of the stress exponent (n). Microstructures from the deformed samples were characterized using polarized light microscopy (LM), SEM-cathodoluminescence (CL), and Electron backscatter diffraction (EBSD).

Our creep results for both the as-is and 0.1 wt.% H2O-added samples yield Q = 110 kJ/mol and n = 2. Our microstructural analysis suggests that the bulk sample strain is accommodated by grain-scale crystal-plasticity, i.e., dislocation glide (dominantly in prism <a>) with minor recovery by sub-grain rotation, accompanied by grain boundary migration and micro-cracking. It is inferred that strain incompatibilities induced by dislocation glide are accommodated by grain boundary processes, including dissolution precipitation and grain boundary sliding. These intra-grain and grain-boundary processes together resulted in a lower n-value of 2 for the quartzite.

Our new flow law predicts strain rates that are in much better agreement with the inferred natural values than the earlier flow laws. It further suggests that the strength of the continental crust considering quartz rheology is significantly lower than previously predicted.  

How to cite: Ghosh, S., Stünitz, H., Raimbourg, H., and Précigout, J.: Constraining wet quartz rheology from constant-load experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8484, https://doi.org/10.5194/egusphere-egu22-8484, 2022.

EGU22-9089 | Presentations | TS2.1

Experimental Investigation of Glaucophane Rheology Through General Shear Deformation Experiments 

Lonnie Hufford, Leif Tokle, Claudio Madonna, and Whitney Behr

Glaucophane is a major constituent mineral associated with subducted mafic oceanic crust at blueschist facies conditions. Viscous deformation of glaucophane has been documented in natural blueschists; however, no experimental study has characterized the specific deformation mechanisms that occur in glaucophane nor the flow law parameters. We are conducting a suite of general shear deformation experiments in a Griggs apparatus to investigate crystal-plastic deformation mechanisms and microstructures of deformed glaucophane over a range of experimental conditions. Experimental samples consist of glaucophane powder separated from natural MORB blueschists  from Syros Island, Greece. Our experimental suite thus far includes temperatures and pressures ranging from 650° to 750°C and 1.0 to 1.5 GPa, strain rates ranging from ~3x10-6/s to ~8x10-5/s (both constant-rate and strain-rate stepping), and different grain size populations from 75-90 µm, 63-125 µm , and 63-355 µm. The lowest temperature and the strain-rate-stepping experiments exhibit evidence for combined frictional-viscous deformation and provide constraints on the brittle-ductile transition in glaucophane at laboratory conditions. The constant-rate experiments conducted at higher temperatures show greater evidence for viscous deformation by dislocation creep, including kinked grains, deformation lamellae, undulose extinction, and bulging via bulge recrystallisation. Mechanical data from the strain-rate stepping experiments allow us to interpret what parameters have the largest effect on peak stress. When comparing experiments conducted at 1 GPa and initial powder grain sizes of 63-355 µm, we find temperature having the largest effect on peak stresses. The 700°C experiment with an initial deformation speed 5 times faster (LH038) than another 700°C strain-rate stepping experiment (LH042) has a ~90 MPa higher peak shear stress, whereas the 750°C strain-rate stepping experiment with an initial deformation speed 4 times faster than LH042 has a ~115 MPa lower peak shear stress. At the time of abstract submission, further constant-rate experiments are planned at slower strain-rates to continue exploring the laboratory conditions necessary to activate glaucophane crystal-plastic deformation mechanisms. These data will be used with further strain-rate stepping experiments to develop flow law parameters from mechanical data.

How to cite: Hufford, L., Tokle, L., Madonna, C., and Behr, W.: Experimental Investigation of Glaucophane Rheology Through General Shear Deformation Experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9089, https://doi.org/10.5194/egusphere-egu22-9089, 2022.

   Plate boundary dynamics remain incompletely understood in the context of thermo-chemical convection. Strain-localization is affected by weakening in ductile shear zones, and a change from dislocation to diffusion creep caused by grain-size reduction is one of the mechanisms that has been discussed. However, the causes and consequences of strain localization remain debated, even though tectonic inheritance and strain localization appear to be critical features in plate tectonics.

   Frictional-plastic faults in nature and brittle shear zones in the lithosphere may be weakened by high transient, or static, fluid pressures, or mechanically by gouge, or mineral transformations. Weakening in ductile shear zones in the viscous domain may be governed by a change from dislocation to diffusion creep caused by grain-size reduction. In mechanical models, strain weakening and localization in the shallow parts of the lithosphere has mainly been modeled by an approximation of brittle behavior using a pseudo visco plastic rheology in combination with a linear decrease of the yield strength of the lithosphere with increasing deformation (plastic-strain (PSS) softening). Strain weakening in viscous shear zones, on the other hand, may be described by a linear dependence of the effective viscosity on the accumulated deformation (viscous-strain (VSS) softening). These different types of strain weakening are further explored and compared to the predictions from different laboratory-based models of grain-size evolution for a range of temperatures and a step-like variation of total strain rate with time. Such a parameterized, apparent-strain, or “damage”, dependent weakening (SDW) rheology (mainly PSS) can successfully mimic more complex weakening processes in global mantle convection computations. While we focus on GSS rheology to constrain the parameters of SDW, the analysis is not limited to grain-size evolution as the only possible microphysical mechanism.

   The SDW weakening rheology allows for memory of deformation, which weakens the fault zone as well as the lithosphere for a longer period and allows for a self-consistent formation and reactivation of inherited weak zones. In addition, the memory effect and weakening of the fault zone allows for a more frequent reactivation at smaller strain rates, depending on the strain-weakening parameter combination. Reactivation within the models occurs in two different ways: a), as a guide for laterally propagating convergent and divergent plate boundaries, and b), formation of a new subduction zone by reactivation of weak zones. A longer rheological memory results in a decrease in the dominant period of the reorganization of plates due to less frequently formed new plate boundaries. In addition, the low frequency content of velocity and heat transport spectra decreases with a decreasing dominant period. This indicates a more sluggish reorganization of plates due to the weaker and thus more persistent active plate boundaries. These results show the importance of a rheological memory for the reorganization of plates, potentially even for the Wilson cycle.

How to cite: Fuchs, L.: Plate-boundary maintenance – formation, preservation, and reactivation in global plate-like mantle convection models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9584, https://doi.org/10.5194/egusphere-egu22-9584, 2022.

EGU22-9765 | Presentations | TS2.1

In-situ mechanical testing and characterization of olivine grain boundaries 

Diana Avadanii, Lars Hansen, Ed Darnbrough, Katharina Marquardt, David Armstrong, and Angus Wilkinson

The mechanics of olivine deformation play a key role in long-term planetary processes, such as the response of the lithosphere to tectonic loading or the response of the solid Earth to tidal forces, and in short-term processes, such as the evolution of roughness on oceanic fault surfaces or postseismic creep within the upper mantle. Many previous studies have emphasized the importance of grain-size effects in the deformation of olivine. However, most of our understanding of the role of grain boundaries in the deformation of olivine is inferred from comparison of experiments on single crystals to experiments on polycrystalline samples.

To directly observe and quantify the mechanical properties of olivine grain boundaries, we use high-precision mechanical testing of synthetic forsterite bicrystals with well characterised interfaces. We conduct in-situ micropillar compression tests at high-temperature (700°C) on low-angle (13° tilt about [100] on (015)) and high-angle (60° tilt about [100] on (011)) grain boundaries. In these experiments, the boundary is contained within the micropillar and oriented at 45° to the loading direction to promote shear along the boundary. In these in-situ tests, we observe differences in deformation style between the pillars containing the grain boundary and the pillars in the crystal interior. In-situ observations and analysis of the mechanical data indicate that pillars containing the grain boundary consistently support elastic loading to higher stresses than pillars without a grain boundary. Moreover, only the pillars without a grain boundary display evidence of sustained plasticity and slip-band formation. Post-deformation advanced microstructural characterization (STEM) confirms that under the conditions of these deformation experiments, sliding did not occur along the grain boundary. These observations support the hypothesis that grain boundaries are stronger than the crystal interior. 

These experiments on small deformation volumes allow us to qualitatively explore the differences between the crystal interior and regions containing grain boundaries. Overall, the variation in strain and temperature in our small scale experiments allows fundamental investigation of the response of well characterised forsterite grain boundaries to deformation. 

How to cite: Avadanii, D., Hansen, L., Darnbrough, E., Marquardt, K., Armstrong, D., and Wilkinson, A.: In-situ mechanical testing and characterization of olivine grain boundaries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9765, https://doi.org/10.5194/egusphere-egu22-9765, 2022.

EGU22-9842 | Presentations | TS2.1

Revisiting stylolites as a gage of overburden pressure – insights from fractal analysis 

Christoph von Hagke, Simon Hirländer, Kevin Frings, and Herfried Madritsch

Stylolites are ubiquitous structures generated by pressure solution primarily found in limestones. They and have been used as indicator for maximum stress a rock has suffered. This is commonly done by characterizing the fractal dimensions of stylolites. The current canon is the expectation from the theory that stylolites form through two physical pressure-driven regimes: low-frequency and higher-energetic - dominated by elastic forces and high-frequency lower-energetic dominated by surface tension. The so-called characteristic length separates both regimes, analytically marked by a kink in the power spectrum, which relates the energy contributions to the frequency.

However, determining this kink is not straightforward, and requires additional assumptions. We present a data set of stylolites recovered from a drill hole in the Alpine foreland basin. We mapped stylolites from different depths at sub-mm resolution semi-automatically and analyzed them using new methods of fractal analysis.

Excitingly, our preliminary studies did not identify the expected kink’s position from several different images of probes of drill cores, despite satisfactory reliability of laboratory preparation. Standard methods such as power spectral density, averaging wavelet coefficients, RMS, min/max, and rescaled range-based approaches revealed variations in their results, generally without evidence for a kink in the corresponding graphs. Implementing more recently developed methods such as adaptive fractal analysis could not improve the results. This finding challenges the classic interpretation of fractal characteristics of stylolites. 

How to cite: von Hagke, C., Hirländer, S., Frings, K., and Madritsch, H.: Revisiting stylolites as a gage of overburden pressure – insights from fractal analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9842, https://doi.org/10.5194/egusphere-egu22-9842, 2022.

EGU22-10101 | Presentations | TS2.1

The role of grain boundaries for the deformation and grain growth of olivine at upper mantle conditions 

Filippe Ferreira, Marcel Thielmann, and Katharina Marquardt

Crystal defects such as vacancies, dislocations and grain boundaries are central in controlling the rheology of the Earth’s upper mantle. Their presence influences element diffusion, plastic deformation and grain growth, which are the main microphysical processes controlling mass transfer in the Earth’s lithosphere and asthenosphere. Although substantial information exists on these processes, there is a general lack of data on how these defects interact at conditions found in the Earth’s interior. A better understanding of processes occurring at the grain scale is necessary for increased confidence in extrapolating from laboratory length and time scales to those of the Earth. We examined the evolution of olivine grain boundaries during experimental deformation and their impact on deformation in the dislocation-accommodated grain- boundary sliding (disGBS) regime. This may be the main deformation mechanism for olivine in most of Earth’s upper mantle. Our results suggest that grain boundaries play a major role in moderating deformation in the disGBS regime. We present observational evidence that the rate of deformation is controlled by assimilation of dislocations into grain boundaries. We also demonstrate that the ability for dislocations to transmit across olivine grain boundaries evolves with increasing deformation. Lastly, we show that dynamic recrystallization of olivine creates specific grain boundaries, which are modified as deformation progresses. This might affect electrical conductivity and seismic attenuation in the upper mantle. The effective contribution of grain-boundary processes (such as disGBS) on the rheology of the upper mantle is correlated to the amount of grain boundaries in upper mantle rocks, that is, their grain-size distribution and evolution. The grain-size distribution in the Earth’s mantle is controlled by the balance between damage (recrystallization under a stress field) and healing (grain growth) processes. However, grain growth, one of the main processes controlling grain size, is still poorly constrained for olivine at conditions of the upper mantle. To evaluate the effects of pressure on grain growth of olivine, we performed grain growth experiments at pressures ranging from 1 to 12 GPa using piston-cylinder and multi-anvil apparatuses. We found that the olivine grain-growth rate is reduced as pressure increases. Our results suggest that grain-boundary diffusion is the main process of grain growth at high pressure. Based on extrapolation of our experimental results to geological time scales, we suggest that at deep upper-mantle conditions (depths of 200 to 410 km), the effect of pressure on inhibiting grain growth counteracts the effect of increasing temperature. We present estimations of viscosity as a function of depth considering the grain-size evolution predicted here. Our estimations suggest that viscosity is almost constant at the deep upper mantle, which corroborates postglacial-rebound observations.

How to cite: Ferreira, F., Thielmann, M., and Marquardt, K.: The role of grain boundaries for the deformation and grain growth of olivine at upper mantle conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10101, https://doi.org/10.5194/egusphere-egu22-10101, 2022.

EGU22-10153 | Presentations | TS2.1

Does porosity really matter? A first model for dissolution-enabled deformation bands in low porosity rocks based on microstructural analysis of calcarenite from Cotiella Basin, Spain. 

Maria Eleni Taxopoulou, Nicolas E. Beaudoin, Charles Aubourg, Elli-Maria Charalampidou, and Stephen Centrella

We report for the first time deformation features functionally described as deformation bands developed in low porosity rocks. This observation contradicts existing knowledge that deformation bands develop only in highly porous rocks. The studied formation is a bioclastic calcarenite of the Upper Cretaceous Maciños Unit in the Cotiella Massif. It is part of a megaflap adjacent to a salt diapir that has experienced extensional tectonics before the Pyrenean contraction. The bands present thickness variations, and in places they imitate the appearance of stylolites. This observation raises the question: how do deformation bands form in low porosity rocks?

To answer the question, we combine field observations with microstructural analysis to identify the occurring processes for the formation of deformation bands within low porosity rocks. After using optical microscopy and cathodoluminescence spectroscopy to conduct a petrographic study, we observe that the rock underwent multiple diagenetic cycles before the deformation stage, confirming that its porosity was significantly reduced before the deformation stage. Subsequently, we characterized the quartz grains inside the host rock and the dissolution-enabled deformation bands, using non-destructive imaging techniques. Three-dimensional image analysis from X-ray microtomography scans shows low grain size variations between the quartz grains in the host rock and in the bands, suggesting minor grain fracturing along the bands. However, grain reorientation has been reported for the quartz grains inside the bands, in relation to those in the host rock. Strain analysis was performed from Electron Backscattered Diffraction measurements, revealing higher strain along the quartz grain contacts inside the deformation band, compared to those in the host rock and stylolites. Our current data suggest that new porosity was created from local dissolution of the matrix, so the less soluble quartz grains were placed in contact. By wrapping-up the above observations, we propose a conceptual model that demonstrates the genesis and evolution of dissolution-enabled deformation bands in low porosity rocks, through local dissolution of the micritic matrix and transient porosity increase.

How to cite: Taxopoulou, M. E., Beaudoin, N. E., Aubourg, C., Charalampidou, E.-M., and Centrella, S.: Does porosity really matter? A first model for dissolution-enabled deformation bands in low porosity rocks based on microstructural analysis of calcarenite from Cotiella Basin, Spain., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10153, https://doi.org/10.5194/egusphere-egu22-10153, 2022.

EGU22-10404 | Presentations | TS2.1

Influence of a yield stress on lower mantle dynamics: filtering and changing morphology of plumes and slabs 

Anne Davaille, Thibaut Chasse, Neil Ribe, Philippe Carrez, and Patrick Cordier

When a fluid can experience a "jammed" state, it will flow only when the local deviatoric stress becomes greater than a critical stress, the so-called  "yield-stress". Jamming can be caused by entangled dislocations in a mineral, or by the existence of a hard skeleton in a two-phase fluid. According to recent numerical modeling, a Bridgmanite lower mantle would predominantly deform by pure dislocation climb; and due to dislocations interactions, it would flow only for local deviatoric stress greater than a critical yield stress which depends on dislocation density. In a first set of fluid mechanics experiments in such a visco-plastic fluid, we showed that hot plumes would develop with a much thicker morphology than in newtonian fluids. Scaling laws derived from the experiments tightly relate the buoyancy and diameter of the hot plumes to the value of the yield-stress, as well as to the mantle microstructure (such as dislocation density and vacancy concentration). Yield stress values between 1 and 10 MPa, implying dislocation densities between 108 and 1010 m−2, would be sufficient to explain the thick plumes morphology observed in seismic tomography images; while low vacancy concentrations could explain the 1000 km-depth horizon also seen in tomography. 

In a second set of experiments, we show that the existence of a yield stress in a Bridgmanite lower mantle will also act as a filter regarding slab penetration in the lower mantle. Given slab buoyancy, a typical slab, 100 km-thick, could not overcome the lower mantle yield stress. So most of single slabs would be expected  to stagnate in the transition zone. However a pile of folded slab with a typical thickness around 400 km would have sufficient buoyancy and would penetrate into the lower mantle. This could explain the seismic tomographic observations regarding slabs in the transition zone and in the lower mantle, without the need to invoke a compositional stratification there.

How to cite: Davaille, A., Chasse, T., Ribe, N., Carrez, P., and Cordier, P.: Influence of a yield stress on lower mantle dynamics: filtering and changing morphology of plumes and slabs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10404, https://doi.org/10.5194/egusphere-egu22-10404, 2022.

EGU22-11133 | Presentations | TS2.1

Exploring the effect of mantle composite rheology on surface tectonics and topography 

Maelis Arnould, Tobias Rolf, and Antonio Manjón-Cabeza Córdoba

Earth’s surface dynamics and topography are tied to the properties and dynamics of mantle flow. In particular, upper mantle rheology controls the coupling between the lithosphere and the asthenosphere, and therefore partly dictates Earth’s surface tectonic behaviour and topographic response to mantle convection (dynamic topography). The presence of seismic anisotropy in the uppermost mantle suggests the existence of mineral lattice-preferred orientation (LPO) caused by the asthenospheric flow. Together with laboratory experiments of mantle rock deformation, this indicates that Earth’s uppermost mantle can deform in a non-Newtonian way, through dislocation creep. Although several studies suggest the potentially significant effect of upper-mantle non-Newtonian rheology on mantle convection (e.g. Schulz et al., 2020) and topography (e.g. Asaadi et al., 2011, Bodur and Rey, 2019), it is usually not considered in whole-mantle models of mantle convection self-generating plate tectonics.

 

Here, we investigate the effects of using a composite rheology (with both diffusion and dislocation creep) on surface tectonics and dynamic topography in 2D-spherical annulus models of mantle convection with plate-like tectonics and continental drift. We systematically vary the amount of dislocation creep by changing the activation volume for dislocation creep and the reference transition stress between diffusion and dislocation creep. We show that for low yield stresses promoting plate-like behavior in diffusion-creep-only models, modeling a composite rheology in the mantle favors more surface mobility while for large yield stresses which still generate plate-like motions in diffusion-creep-only models, a progressive increase in the amount of dislocation creep leads to stagnant-lid convection. We then compare the amplitudes and spatio-temporal distribution of dynamic topography in models with and without dislocation creep, in light of observed Earth present-day residual topography characteristics.

 

References:

Schulz, F., Tosi, N., Plesa, A. C., & Breuer, D. (2020). Stagnant-lid convection with diffusion and dislocation creep rheology: Influence of a non-evolving grain size. Geophysical Journal International, 220(1), 18-36.

Asaadi, N., Ribe, N. M., & Sobouti, F. (2011). Inferring nonlinear mantle rheology from the shape of the Hawaiian swell. Nature, 473(7348), 501-504.

Bodur, Ö. F., & Rey, P. F. (2019). The impact of rheological uncertainty on dynamic topography predictions. Solid Earth, 10(6), 2167-2178.

How to cite: Arnould, M., Rolf, T., and Manjón-Cabeza Córdoba, A.: Exploring the effect of mantle composite rheology on surface tectonics and topography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11133, https://doi.org/10.5194/egusphere-egu22-11133, 2022.

EGU22-11488 | Presentations | TS2.1

Ilmenite transformations in suevites from the Ries meteorite impact structure, Germany 

Fabian Dellefant, Claudia A. Trepmann, Stuart A. Gilder, Iuliia V. Sleptsova, and Melanie Kaliwoda

Glass fragments (Flädle) in suevites from Zipplingen within the Ries (Germany) meteorite impact structure contain round aggregates of polycrystalline ilmenite with various amounts of rutile, ferropseudobrookite (FeTi2O5), armalcolite ((Fe,Mg)Ti2O5) and titanite (CaTi[OSiO4]). The 10-100s µm sized aggregates often have a thin rim of µm-sized magnetite grains. The ilmenite grains are 5-10 µm in diameter and form an equilibrium fabric with 4-6-sided grains with smoothly curved grain boundaries and 120° angles at triple junctions, i.e. a so-called foam structure. The ilmenite grains have random crystallographic orientations and do not show any internal misorientations. Rutile, typically a few µm in diameter, is associated with similarly fine-grained ilmenite and a high amount of pores. Coarser polygonal ilmenite grains can also show a marked grain boundary porosity. Only rarely in the center of the aggregates, a deformed single ilmenite crystal occurs, indicating that the aggregates originated from shocked coarse ilmenite crystals from the target gneisses. Ferropseudobrookite is intergrown with remnants of original ilmenite grains or secondary ilmenite grains without foam structure. A vermicular intergrowth of ilmenite, rutile, and magnetite can be present at the rim, where armalcolite can be enriched in Mg.

We interpret that ferropseudobrookite formed at high temperatures (>1010°C) and reducing conditions from coarse ilmenite crystals originating from the target gneisses according to the following reaction: 2FeTiO3 → FeO + FeTi2O5. Some FeO migrated towards the rim due to the low oxygen fugacity, resulting in the observed porosity. Upon cooling, FeO migration caused ferropseudobrookite to disintegrate resulting in the formation of rutile and ilmenite: FeTi2O5 → FeTiO3 + TiO2. Silicate melt at the contact of the FeTi-oxides provided magnesium to form armalcolite from ferropseudobrookite and calcium to form titanite within fractures. Rapid cooling resulted in a shift in redox-conditions with the formation of pure Fe magnetite from FeO at the rim of the aggregates. Quenching of the system can explain the local preservation of ferropseudobrookite and armalcolite, whereas the ilmenite foam structure formed during back reaction of ferropseudobrookite at relatively slower cooling rates. The different cooling rates in the aggregates can be explained by the locally varying amount of surrounding superheated melt forming the Flädle-structure.

How to cite: Dellefant, F., Trepmann, C. A., Gilder, S. A., Sleptsova, I. V., and Kaliwoda, M.: Ilmenite transformations in suevites from the Ries meteorite impact structure, Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11488, https://doi.org/10.5194/egusphere-egu22-11488, 2022.

EGU22-12327 | Presentations | TS2.1

Strain localization and weakening during eclogite-facies transformation in experimentally deformed plagioclase-pyroxene mixtures 

Mathieu Soret, Holger Stünitz, Jacques Précigout, Amicia Lee, and Hugues Raimbourg

The rheology of mafic rocks buried at high to ultra-high-pressure conditions remains enigmatic. Minerals stable at these conditions are mechanically very strong (garnet, omphacite, glaucophane, zoisite, kyanite). In the laboratory, they show plastic deformation only at very high temperature (e.g. > 1000°C for pyroxene and garnet). Yet, viscous shear zones in mafic rocks metamorphosed at amphibolite and eclogite-facies conditions are commonly reported in fossil collisional and subduction zones. These shear zones localize and accommodate large amounts of strain by weakening of the host rocks. This weakening is interpreted as being induced by a transition from grain size insensitive to grain size sensitive creep, in particular with the activation of the dissolution–precipitation creep. However, the exact interplay between deformation, mineral reaction and fluid/mass transfer remains poorly-known.

We have conducted a first series of deformation experiments at eclogite-facies conditions on a 2-phase aggregate representative of mafic rocks. Shear experiments were performed in a new generation of Griggs-type apparatus (Univ. Orléans) at 850°C, and 2.1 GPa with a shear strain rate of 10⁻6 s⁻¹. The starting material consists of mixed powders with < 100 µm sized grains of plagioclase and clinopyroxene from an undeformed sample of the Kågen Gabbro in Northern Norway. Experiments have been conducted with ‘as is’ (dried at 110°C) starting material and with 0.2% added water.

The mechanical data indicate that the samples are first very strong with a peak differential stress at 1.4 GPa. Then, a significant weakening is observed with a stress decrease by 0.5 GPa. The high-strain sample is characterized by a strain gradient increasing toward the center of the shear zone. Metamorphic reactions occur throughout the sample, but the high-strain areas contain considerably more reaction products than the low-strain areas. The nucleation of new phases leads to a drastic grain size reduction and phase mixing, whose intensities are positively correlated with the strain intensity. The nature, distribution and fabric of the mineral products vary also progressively with the strain intensity.

  • In the low-strain areas, dissolution-precipitation processes mainly occur along grain boundaries: plagioclase is rimmed by zoisite and a secondary plagioclase more albitic in composition while clinopyroxene is rimmed by amphibole.
  • In the mid-strain areas, dissolution-precipitation processes are more pervasive: amphibole and a secondary more sodic clinopyroxene occurs in pressure shadows of primary clinopyroxene, while primary plagioclase is completely replaced by a fine-grained mixture of zoisite and quartz. Reaction products show a strong shape-preferred orientation parallel to the shear direction.
  • In the high-strain areas, dissolution-precipitation leads to the nucleation of a fine-grained mixture of garnet and secondary clinopyroxene, quartz and kyanite. Most reaction products have subhedral shape with no clear preferred orientation. Hydrous minerals (amphibole and zoisite) are not observed.

Our preliminary results indicate that strain at eclogite-facies conditions is preferentially accommodated and localized by dissolution-precipitation processes. Further micro-structural and geochemical analyses are required to quantify the exact interplay between the physical and chemical processes controlling the dissolution-precipitation creep.

How to cite: Soret, M., Stünitz, H., Précigout, J., Lee, A., and Raimbourg, H.: Strain localization and weakening during eclogite-facies transformation in experimentally deformed plagioclase-pyroxene mixtures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12327, https://doi.org/10.5194/egusphere-egu22-12327, 2022.

EGU22-12964 | Presentations | TS2.1 | Highlight | TS Division Outstanding ECS Award Lecture

Crustal stress across spatial scales 

Mojtaba Rajabi and Oliver Heidbach

The study of crustal stress examines the causes and consequences of in-situ stress in the Earth’s crust. Stress at any given point has several geological sources, including ‘short-term and local-scale’ and ‘long-term, ongoing and wide-scale’ source. In order to better characterise the crustal stress state, the analyses of both local- and wide-scale sources, and the consequences of their superposition are required. The global compilation of stress data in the World Stress Map database has increased significantly since its first release in 1992 and its analysis revealed large rotations of the stress tensor in several intraplate settings.

Large-scale stress analysis, so called first-order, (> 500 km) provides information on the key drivers of the stress state that result from large density contrasts and plate boundary forces. The analyses of stress at smaller-scales (< 500 km) have numerous applications in reservoir geomechanics, geo-storage sites, civil engineering and mining industry. To date, numerous studies have investigated the stress analysis from different perspectives. However, the stress, in geosciences, is still enigmatic because it is a scale-dependant parameter. It means, stress variations can be studied at both the ‘spatial-scale’ and ‘temporal-scale’. This paper aims to investigate the crustal stress pattern with a particular emphasis on the orientation of maximum horizontal stresses at various spatial-scales, ranging from continental scales down to basin, field and wellbore scales, to better evaluate the role of various stress sources and their applications in the Earth’s crust. The stress analyses conducted in this work shows that stress pattern at large-scales do not necessarily represent the in-situ stress pattern at smaller-scales. Similarly, analysis of just a couple of borehole measurements in one area might not yield a good representation of the regional stress pattern.

How to cite: Rajabi, M. and Heidbach, O.: Crustal stress across spatial scales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12964, https://doi.org/10.5194/egusphere-egu22-12964, 2022.

The rheology and mechanisms of strain localisation in the middle and lower crust is yet to be fully constrained, but advances in analytical techniques mean we can revisit previously studied areas and build upon understanding already gained.

A strain profile across a Laxfordian-age (2300-1700 Ma) amphibolite-facies shear zone at Upper Badcall, NW Scotland, provides an excellent backdrop to investigate the hydration-strain-deformation mechanism relationship in the granulite-facies garnet-pyroxene quartzofeldspathic gneiss host rock and cross-cutting 25 m wide isotropic dolerite Scourie dyke. Both the granulite faces gneissic banding and mafic dyke are initially oriented at a high angle to the shear zone boundary. With increasing proximity to the shear zone centre the host rocks become progressively rotated, more deformed and hydrated. Increasing strain results in new foliation development, general grain size reduction and full or partial replacement of pre-existing pyroxene and hornblende by lower-temperature hornblende.

Tatham and Casey (2007) showed the 65 m wide shear zone has an estimated maximum shear strain of 15, which drops to ~7 towards the edge of the shear zone, and falls to < 1 at distances ≥ 40 m from the shear zone centre. We present data from four new transects, taken at 50-100 m intervals along the mafic dyke, which detail the change in deformation style and patterns of strain localisation and intensity. Localised anastomosing high strain zones envelop lenses of undeformed dolerite, with 65-70% of protolith undeformed in the dyke 350 and 230 m from shear zone centre. This decreases to 30 and 0% of undeformed protolith 100 m from and within the shear zone, respectively. Mylonite sensu stricto makes up 10% of dyke at distances ≥ 100 m from the shear zone, which increases to 70% within the shear zone, while the remaining dyke forms a weak fabric evidenced by the shape change of mafic grain aggregates.

Microstructural analyses show a switch in dominant deformation mechanisms from dynamic recrystallisation 350 m from the shear zone, to dissolution-precipitation creep inside the shear zone, identified by a change in crystallographic and shape preferred orientation, and distinct microstructural observations. An introduction of ~10 area % quartz and a loss of feldspar in the mafic dyke inside the shear zone accompanies this switch in dominant deformation mechanisms. We outline microstructural observations characteristic of dissolution-precipitation creep within the shear zone, and propose localised infiltration of quartz-rich fluid facilitates a switch from dislocation creep to pervasive dissolution-precipitation creep resulting in rheological weakening and local strain localisation. Our results suggest that strain localisation in the mid crust may be highly dependent on local fluid availability as fluid presence may trigger a switch in deformation mechanism and, with that, significant localised rheological weakening.

Tatham, D.J. and Casey, M., 2007. Inferences from shear zone geometry: an example from the Laxfordian shear zone at Upper Badcall, Lewisian Complex, NW Scotland. Geological Society, London, Special Publications, 272(1), pp.47-57.

How to cite: Carpenter, M., Piazolo, S., Craig, T., and Wright, T.: The link between water infiltration, deformation mechanisms and strain localisation in the mid crust – an example from the Badcall shear zone, NW Scotland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13366, https://doi.org/10.5194/egusphere-egu22-13366, 2022.

EGU22-13371 | Presentations | TS2.1

Glaucophane plasticity and scale-dependent yield strength from nanoindentation experiments 

Alissa Kotowski, James Kirkpatrick, Christopher A. Thom, Sima A. Alidokht, and Richard Chromik

Subduction interface shear zones localize deformation and sustain plate-boundary weakness on million-year timescales, as well as host a variety of enigmatic seismicity and slow slip transients. A physical understanding of the steady-state and transient mechanics of subduction shear zones requires quantitative constraints of the plastic yield strength and deformation mechanism(s) of metamorphic rocks and minerals that occupy the plate interface. However, very little is known about the rheology of many hydrous minerals that occupy the plate interface, such as glaucophane (end-member sodic amphibole). This is partly because conventional deformation experiments meet technical challenges when trying to measure plasticity in the laboratory due to the stability field of glaucophane, the confining pressure needed to suppress fracture, and the limited range of trade-off between temperature and strain rate in experiments.

 

Here, we present preliminary results from room-temperature nanoindentation experiments on thin sections of glaucophane-rich rocks that produced crystal plasticity by dislocation glide under high-stress conditions. Nanoindentation produces in-situ confining pressure that typically inhibits brittle fracture during loading in favor of plastic deformation. Since the volume of deformation beneath the tips is very small compared to the grain size, each indent is essentially a single-grain mechanical test (i.e., effects of grain boundaries can be ignored). We convert load-depth data from two spheroconical tips of different radii to stress-strain curves to quantify the elastic-plastic transition and characterize post-yield behavior. We measure yield stress as a function of grain orientation. Both post-yield weakening and post-yield hardening occur, which likely reflect brittle fracture along micro-faults/cleavage planes, and dislocation bursts and pile-ups, respectively. Glaucophane hardness decreases with increasing length scale of deformation (i.e., indentation radius), capturing a “size effect” that may reflect an effective decrease in dislocation density as the volume of plastic deformation increases beneath the indent tip. This effect is well-constrained for many metals and some geologic materials, including olivine.

 

The mechanical tests provide a basis for interpreting microstructures of naturally-deformed blueschists, which suggest that glaucophane exhibits recovery-limited dislocation glide and dynamic recrystallization. Low-temperature plasticity may provide a micro-physical framework for long-term strain localization and transient brittle shear when meta-mafic rocks are deformed to high strain.

How to cite: Kotowski, A., Kirkpatrick, J., Thom, C. A., Alidokht, S. A., and Chromik, R.: Glaucophane plasticity and scale-dependent yield strength from nanoindentation experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13371, https://doi.org/10.5194/egusphere-egu22-13371, 2022.

EMRP2 – Geomagnetism

The investigation of planetary cores is of great interest to those seeking to better understand magnetic fields and the life-processes of planets. Like many large-scale systems, planetary cores are unable to be modelled perfectly by numerical simulations or physical experiments. However, it is of constant importance to improve numerical and experimental methods and designs to better replicate full-scale processes. Many previous studies have over-looked the effects of the inhomogeneous insulation from the Earth's mantle on convection in the core. A few numerical studies have taken this effect into consideration for rotating Rayleigh-Benard convection (RBC) in spherical geometries. Experimental models are desirable to further understand the motion of fluid in the center of planets; however, due to physical limits, spherical systems are difficult to recreate experimentally. Therefore, cylindrical geometries are useful to study varied thermal flux on sidewalls both experimentally and numerically. While some studies have numerically and experimentally considered changes in temperature along the sidewall, there has been little consideration for variations in heat flux, which is the more physically appropriate boundary condition. 


The present study seeks to explore rotating RBC in a cylindrical domain with sidewalls inhomogeneously insulated in an experimentally-achievable system. It is experimentally plausible that the material of a cylindrical cell could varying in thickness, and therefore thermal conductivity, or have patches of heating and/or cooling attached to the sidewall to vary the thermal flux on the side boundaries. To imitate this numerically, a sinusoidal pattern of increasing and decreasing heat flux is applied to the sidewall in two cases: one whereby heat flux fluctuates between positive and negative, and another whereby the heat flux is strictly positive. Additionally the mode and amplitude of the wave is considered. The mode will either match the mode of the system with insulating sidewall conditions or have a larger wavelength to better simulate planetary cores. The amplitude is increased as necessary to achieve significant results. For simplicity, the top and bottom boundary conditions are fixed temperature.


Changes in heat transport and temporal behavior are measured with a global Nusselt number, Nu, time series. Additional variables such as mean zonal flow, number and location of convection rolls, and transitions to time-dependence are considered. Results indicate that large-wavelength heat flux on the sidewalls causes two modes to inhabit the system, existing on opposite sides of the cylinder: the mode natural to the homogeneously insulated system exists where heat flux is high and a large-wavelength mode dominates where heat flux is lower. However, the implementation of heat flux along the sidewalls with the same wavelength of the insulated system results in near-time independence as the amplitude increases. These results indicate that variation in heat flux boundary conditions can cause significant changes in rotating RBC behavior. Experimental studies could be used to validate or refute these conclusions. Overall, it is clear that numerical studies of molten planetary cores heterogeneously heated by mantles must take these irregularities into consideration to improve our understanding of core convection. 

How to cite: Peifer, J., Bokhove, O., and Tobias, S.: Changes in pattern formation and behavior in rotating Rayleigh-Benard convection due to inhomogeneous thermal insulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-134, https://doi.org/10.5194/egusphere-egu22-134, 2022.

It was often shown how the anisotropy (due to turbulence) in the Earth’s outer core strongly influences some convection processes very important in the Core Dynamics. For instance, it was described how some instabilities in rotating magnetoconvection, described as usually by the analysis in term of normal modes, depend strictly on the anisotropic diffusion. Thus, we developed many models concerning the marginal modes (stationary and oscillating modes) of rotating magnetoconvection with different cases of anisotropy in the viscosity, thermal and magnetic diffusivities. In all cases, an anisotropy greater in the vertical direction parallel to gravity (“atmospheric anisotropy”) facilitates the convection, while an anisotropy greater in horizontal directions (“oceanic anisotropy”) inhibits some types of convection. This is linked with the balance among Magnetic, Archimedean and Coriolis forces in the Earth’s outer core.  

After recalling these former results concerning marginal modes, we present new results concerning the most unstable modes, namely the ones with maximum growth rate, with isotropic and anisotropic diffusivities.

Firstly, the state of the art about this topic in isotropic conditions is reminded, then our new approach on it is presented. We show that assuming a time-dependence only in the temperature perturbation (we call it T-case), like it was done in some former works, does not describe properly these modes in the Earth’s outer core. Indeed, this implies that some types of convection would occur only with some values of the dimensionless numbers unrealistic for the Earth (e.g., with too huge values of the Ekman numbers). We study the most general isotropic case (and we christen it G-case), namely the most unstable modes of convection with temperature, velocity and magnetic perturbations time-dependent. In this case the convection is much more facilitated than in the T-case: it occurs with much smaller values of Ekman and Elsasser numbers. Another model (named by us Q-case) with very small magnetic Prandtl number, namely with magnetic diffusivity much greater than viscosity, is considered. The Q-case results are very similar to the G-case ones. We demonstrate (and indicate) that Q and G cases can hold for the Earth (and for other planets).

We show that the anisotropy strongly influences the most unstable modes. Indeed, like in the marginal ones, the atmospheric anisotropy facilitates the occurrence of the most unstable modes convection, while the oceanic one inhibits it. Furthermore, we prove that, in contrast with isotropic case, in case of strong oceanic anisotropy the differences between Q and G cases can be significant for the Geodynamo.

Our approach allows to easily deal with very huge wave numbers and Rayleigh numbers as well as with very small Ekman numbers, what is usually not possible in the standard geodynamo simulations. This aspect and the growth rates search are useful to look for possible connections with small length and time scale analysis of the Geomagnetic field. 

How to cite: Filippi, E. and Brestenský, J.: The most unstable modes in rotating magnetoconvection with anisotropic diffusion in the Earth’s outer core, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-189, https://doi.org/10.5194/egusphere-egu22-189, 2022.

EGU22-1088 | Presentations | GD3.1

Observations of Inner Core Shear Waves with AlpArray 

On Ki Angel Ling, Simon Stähler, Doyeon Kim, Domenico Giardini, and The AlpArray Working Group

Although the solidity of Earth’s inner core is evidenced by normal mode data, the direct observation of inner core shear waves (J-waves) has remained challenging for decades due to their small amplitudes. Previous studies have presented evidence of J-waves in different seismic datasets (e.g., Okal and Cansi Y, 1998; Deuss et al., 2000; Cao et al., 2005; Wookey and Helffrich, 2008), however, the observability seems to be highly dependent not only on distance, but also on the location of the source and receiver, suggesting that amplification from specific 3D structures in the deep Earth is necessary to elevate the phase above noise for certain ray paths. Waszek and Deuss (2015) and Tkalčić and Phạm (2018) also found J-waves in global stacks and global correlation wavefield respectively, but these average over all possible source-receiver geometries and inner core structure.

To improve phase identification and discrimination, we use an approach that combines the array method of slant stacking and polarization filtering to enhance linearly polarized signals with the expected slowness and incident angle. We apply this technique on the data of the AlpArray Seismic Network, a large-scale seismic network in Europe that consists of over 600 broadband stations with a mean station spacing of 30-40km. An arrival consistent with PKJKP (in reference travel time, slowness, and polarization) is found from events in the source region reported by Cao et al. (2005). We present an overview of PKJKP candidate paths over distance based on observations with AlpArray. We also examine whether these observations correspond to specific depths or azimuths and investigate the effects of anisotropy or other three-dimensional earth structures​​​​​​.

How to cite: Ling, O. K. A., Stähler, S., Kim, D., Giardini, D., and AlpArray Working Group, T.: Observations of Inner Core Shear Waves with AlpArray, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1088, https://doi.org/10.5194/egusphere-egu22-1088, 2022.

EGU22-2363 | Presentations | GD3.1

Waves in the Earth’s core. 2: Diffusive Magneto-Coriolis waves. 

Jiawen Luo, Andrew Jackson, and Philippe Marti

Various types of waves exist in the Earth’s core. Waves associated with the magnetic field can leave a signature in the observed geomagnetic field, which may allow one to infer properties of the core. Among those, a balance of magnetic, Coriolis and pressure forces forms a type of waves known as Magneto-Coriolis (MC) waves. Previous studies of MC wave have mostly been focused on the ideal limit (without magnetic diffusion and viscous dissipation) with a columnar ansatz for the flow field. In this study, we investigate this problem by retaining the magnetic diffusion and three-dimensional flows in a full sphere. With several choices of axisymmetric background magnetic field, we analyse various branches of normal modes. The dependence of the normal mode's structure on the background field is clearly seen. A westward propagating branch with perfect columnar flows is found for some background B. We have also found eastward propagating modes constituted by flows with weaker columnarity. With the choice of Elsasser number Λ=1 (Coriolis and magnetic forces of similar magnitude), for axisymmetric background fields we find most of the MC modes have decay rates comparable or larger than their frequencies.

How to cite: Luo, J., Jackson, A., and Marti, P.: Waves in the Earth’s core. 2: Diffusive Magneto-Coriolis waves., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2363, https://doi.org/10.5194/egusphere-egu22-2363, 2022.

EGU22-3229 | Presentations | GD3.1

Phase Relations in the Fe-Si-H Ternary up to 125 GPa and 3700K: Implications for the Structure and Chemistry of Planetary Cores 

Suyu Fu, Stella Chariton, Vitali Prakapenka, Andrew Chizmeshya, and Sang-Heon Shim

Light elements play a key role in the chemical and physical processes of planetary Fe-rich metallic cores [1].  H and Si are believed important candidates in planetary cores and previous estimates indicate as much as 0.6 wt% H and 13 wt% Si in the Earth’s core [2, 3]. However, existing studies are on Fe-H or Fe-Si binary systems and knowledge on Fe-Si-H ternary at high pressure and temperature is still limited [4, 5]. We conducted a series of experiments to understand the impact of hydrogen on Fe-Si alloy system. Fe-Si alloys with three compositions, Fe-9Si (9 wt% Si), Fe-16Si (16 wt% Si), and FeSi (33.3 wt% Si), reacted with H separately up to 125 GPa and 3700 K in diamond-anvil cells by combining pulsed laser heating with high-energy synchrotron X-ray diffraction. Results show little H solubility in B20 and B2 phases of FeSi (0.3 wt% and <0.1 wt% H, respectively) up to 62 GPa, which is significantly smaller than H solubility in Fe metal (1.8 wt% H) [6]. The low H solubility in these phases is likely because of their highly distorted interstitial sites which are not favorable for H incorporation. We found that the low-Si alloys (Fe-9Si and Fe-16Si) convert into FeHx (fcc or dhcp), FeSi (B20 or B2), and Fe-Si-H ternary phases up to 125 GPa and 3700 K. Particularly, a Fe5Si3Hx phase is stable below 43 GPa and the cubic FeH3 can appear after reactions above 100 GPa. These results indicate that H alters the behavior of the Fe-Si system severely. Considering the various sizes and masses of planets in the solar and exoplanetary systems, the planetary cores can have a wide range of Si contents. If Fe-droplets in early magma ocean contain much Si, Si could limit the amount of H incorporated in the core. On the other hand, for cores with low Si, crystallization at the solid-liquid core boundary may result in formation of separate H-rich and Si-rich crystals in the solid core, potentially inducing heterogeneities in the region [7]. 

References:

1. Shahar, A., et al., What makes a planet habitable? Science, 2019. 364(6439): p. 434-435.

2. Tagawa, S., et al., Experimental evidence for hydrogen incorporation into Earth’s core. Nature Communications, 2021. 12(1): p. 2588.

3. Hirose, K., B. Wood, and L. Vočadlo, Light elements in the Earth’s core. Nature Reviews Earth & Environment, 2021. 2(9): p. 645-658.

4. Terasaki, H., et al., Hydrogenation of FeSi under high pressure. American Mineralogist, 2011. 96(1): p. 93-99.

5. Tagawa, S., et al., Compression of Fe–Si–H alloys to core pressures. Geophysical Research Letters, 2016. 43(8): p. 3686-3692.

6. Pépin, C.M., et al., New iron hydrides under high pressure. Physical review letters, 2014. 113(26): p. 265504.

7. Deuss, A., Heterogeneity and anisotropy of Earth's inner core. Annual Review of Earth Planetary Sciences, 2014. 42: p. 103-126.

How to cite: Fu, S., Chariton, S., Prakapenka, V., Chizmeshya, A., and Shim, S.-H.: Phase Relations in the Fe-Si-H Ternary up to 125 GPa and 3700K: Implications for the Structure and Chemistry of Planetary Cores, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3229, https://doi.org/10.5194/egusphere-egu22-3229, 2022.

EGU22-3349 | Presentations | GD3.1

CCMOC: A New View of the Earth's Outer Core Through the Global Coda Correlation Wavefield 

Xiaolong Ma and Hrvoje Tkalčić

Increasing seismic evidence has accumulated, suggesting that the Earth’s outer core consists of distinct layers of low P-wave velocities relative to the Preliminary Reference Earth Model (PREM) in the top and bottom of the liquid core. Seismically detected low velocity in the outer core could be linked with the stratification, essential for understanding the geodynamo and thermochemical evolution of the liquid core. However, a consistent globally-averaged radial structure of the outer core has not been obtained due to the incomplete coverage of sampling body waves. To remedy this problem, we explore the seismic structure of Earth's outer core by employing a new theoretical and observational concept termed coda correlation wavefield. We construct the global correlogram in the 15-50 sec period range by stacking cross-correlations of the long-duration coda waves from the selected ten large earthquakes. We then assemble a dataset of prominent correlation features from the global correlogram that are sensitive to the outer core. The waveforms of these features are fit by computing synthetic correlograms through various outer core models. The obtained optimal model displays P-wave velocities in both the outer core's top and bottom, consistent with Coda Correlation Reference Earth Model (CCREM) and reduced relative to PREM. The low seismic speeds in the top of the outer core could likely imply the formation of a thermal and/or compositional stratification.

How to cite: Ma, X. and Tkalčić, H.: CCMOC: A New View of the Earth's Outer Core Through the Global Coda Correlation Wavefield, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3349, https://doi.org/10.5194/egusphere-egu22-3349, 2022.

EGU22-3362 | Presentations | GD3.1 | Highlight

Imaging of Deep Planetary Interiors from Inter-source Correlations via a Single Seismograph 

Sheng Wang and Hrvoje Tkalčić

Global seismic imaging of the Earth's interior has come a long way in exploring and understanding the Earth’s internal structure and dynamics with the worldwide proliferation of seismographs. However, investigating planetary interiors, including detections of their deep structures, remains challenging because of the limited number of seismographs that are and will be deployed in the foreseeable future. Besides, the existing imaging methods based on observations of a direct seismic wavefield from seismic sources require the emergence of the seismic waves with distinguishable amplitudes. That condition restricts the seismic station locations for practical wave reflections or refractions from internal planetary interfaces to a limited angular distance range from the source.

Here, we explore a new way to image deep planetary interiors, especially the planetary cores, using a single seismograph. We first develop a novel procedure for constructing global inter-source correlograms and show that they contain many prominent features sensitive to the internal planetary structures. We demonstrate that a single station is sufficient to produce a global correlogram for the Earth. We then utilize a single-station correlogram and show the steps for detecting and quantifying the Earth’s and Martian cores interfaces. This provides a new paradigm for imaging deep planetary interiors on global scales.

How to cite: Wang, S. and Tkalčić, H.: Imaging of Deep Planetary Interiors from Inter-source Correlations via a Single Seismograph, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3362, https://doi.org/10.5194/egusphere-egu22-3362, 2022.

EGU22-3740 | Presentations | GD3.1

A laboratory model for iron snow in planetary cores 

Ludovic Huguet and Michael Le Bars

Top-down solidification has been suggested in the liquid cores of small planets, moons, and large asteroids. An iron snow is then thought to exist, consisting of the crystallization of free iron crystals at the top of these cores and of their settling in a stably stratified ambient, until they remelt in a hotter, deeper region. This inward crystallization and associated buoyancy flux may sustain dynamo action by convection below the remelting depth. However, thermal evolution models are up-to-now oversimplified, assuming a constant-in-time and homogeneous-in-space buoyancy flux at the bottom of the snow zone. We have shown from analog experiments that the buoyancy flux is heterogeneous in time and space, with intense snow events, corresponding to an explosion of frazil-ice,  separated by quiescent periods where the snow zone supercools. We found that a wide range of crystal sizes exists, with large crystals overshooting the convection region and challenging the thermodynamic equilibrium hypothesis underlying the evolution models. The spatio-temporal variability of the energy source obviously impacts the shape and intensity of the generated magnetic field, which may provide alternative explanations for the observed and surprising features of Mercury's and Ganymede's magnetic fields.

How to cite: Huguet, L. and Le Bars, M.: A laboratory model for iron snow in planetary cores, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3740, https://doi.org/10.5194/egusphere-egu22-3740, 2022.

The Earth’s rotation is not perfectly steady: both its rotation rate (its spin rate) and its orientation in space change in time due to the gravitational pull of the Sun and Moon. The precession-nutation response of the Earth to this external tidal forcing depends strongly on the planet’s deep interior structure. 
In particular, the existence of the Earth’s liquid outer core is known to produce a resonance in the nutation signal at a near-diurnal frequency (as measured in the Earth-bound rotating frame). Physically, this resonance corresponds to the excitation of free mode whereby the liquid core experiences a global rotation of uniform vorticity, hence its name: Free Core Nutation (FCN). 

In parallel, experimental and theoretical studies of fluid dynamics have since long demonstrated that rotating fluids can support oscillatory motions known as inertial waves, which are due to the restoring effect of the Coriolis force. In planetary situations where the fluid domain is bounded by solid boundaries, these oscillations become global, so that they are sometimes referred to as inertial modes. The Spin-Over Mode (SOM), is the simplest of these inertial mode, with uniform vorticity. Because of this and the fact that the SOM, like the FCN, has a near-diurnal frequency, the two modes have often been identified as one and the same. In a former study, we showed that the FCN is in fact a generalization of the SOM to the case of a (non-steadily) freely rotating planet (Rekier et al 2020). 

In the present work, we analyse the relation between the SOM and the FCN in more details by showing how the two modes can, in fact, coexist together in a planet subjected to external gravitational forcing. We also show that the proximity between the frequencies of the SOM and the FCN can have a significant effect on the shape and the intensity of the FCN resonance – represented by the transfer function for nutations – when viscous and/or electromagnetic coupling is introduced at the planet’s Core-Mantle Boundary (CMB). In particular, we estimate that this can cause an increase of ∼1 day in the (retrograde) period of the resonance as measured in the inertial frame. 

We conclude with a discussion on some of the implications of our findings for the nutations of other planetary objects like Mars and the Moon.

Reference:

  • Rekier, J., Trinh, A., Triana, S. A., & Dehant, V. (2020). Inertial modes of a freely rotating ellipsoidal planet and their relation to nutations. The Planetary Science Journal, 1(1), 20

How to cite: Rekier, J.: The Spin-Over Mode of freely rotating planets and its relation to their Free Core Nutation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3972, https://doi.org/10.5194/egusphere-egu22-3972, 2022.

EGU22-4635 | Presentations | GD3.1

Non-monotonic growth and motion of the South Atlantic Anomaly 

Hagay Amit, Filipe Terra-Nova, Maxime Lézin, and Ricardo Trindade

The South Atlantic Anomaly (SAA) is a region at Earth’s surface where the intensity of the magnetic field is particularly low. Accurate characterization of the SAA is important for both fundamental understanding of core dynamics and the geodynamo as well as societal issues such as the erosion of instruments at surface observatories and onboard spacecrafts. Here, we propose new measures to better characterize the SAA area and center, accounting for surface intensity changes outside the SAA region and shape anisotropy. Applying our characterization to a geomagnetic field model covering the historical era, we find that the SAA area and center are more time dependent, including episodes of steady area, eastward drift and rapid southward drift. We interpret these special events in terms of the secular vari‑ation of relevant large‑scale geomagnetic flux patches on the core–mantle boundary. Our characterization may be used as a constraint on Earth‑like numerical dynamo models.

How to cite: Amit, H., Terra-Nova, F., Lézin, M., and Trindade, R.: Non-monotonic growth and motion of the South Atlantic Anomaly, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4635, https://doi.org/10.5194/egusphere-egu22-4635, 2022.

EGU22-4857 | Presentations | GD3.1

A python interface for global geomagnetic field models: pymagglobal 

Maximilian Arthus Schanner, Stefan Mauerberger, and Monika Korte

We present pymagglobal, a simple to use python interface for global geomagnetic field models. Pymagglobal was developed to provide easy access to global, spherical harmonics based magnetic main field models over historical and paleomagnetic times. The software readily handles cubic-spline based geomagnetic field models stored in the same file format as gufm1 or the CALSxk model series out of the box. Models in other file formats can be incorporated with minimal effort using the python backend. The python interface can, e.g., give model curves for any location, time series of dipole moment or spherical harmonic coefficients or grids and maps of magnetic field components. 

Pymagglobal can be installed by a single command and comes with a command line interface and a GUI, that allows easy extraction and visualization of information from the models. Additionally, the python backend can be used to access the models, for example to generate synthetic data or refer to them in your own analysis. Emphasis is put on documentation and accessibility. The package is available via a git repository  and a custom website at https://git.gfz-potsdam.de/sec23/korte/pymagglobal.

How to cite: Schanner, M. A., Mauerberger, S., and Korte, M.: A python interface for global geomagnetic field models: pymagglobal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4857, https://doi.org/10.5194/egusphere-egu22-4857, 2022.

Geomagnetic field models are essential in the study of the physical processes that contribute to the Earth’s magnetic field. There are several groups that build models of the Earth’s magnetic field. These models essentially differ in the magnetic data and mathematical methods used during the model estimation, and in the represented sources of the geomagnetic field. It is then the users who choose the models that are most suitable for the study of the geophysical signals of interest. However, there is currently no single platform where field models are collected in a standardised way, and that provides information which helps users to find the best models for their purposes.

Here, we present the geomagnetic field model called CHAOS that is developed and regularly updated by the Technical University of Denmark. CHAOS provides estimates of the recent time-dependent and static internal magnetic fields, and the external magnetospheric field during quiet geomagnetic conditions. It is derived from magnetic data collected by the Swarm, CHAMP, Ørsted, SAC-C, CryoSat-2 satellite missions supplemented by ground observatory data. It is updated approximately every 4 months with the latest ground and satellite data; the current version CHAOS-7.9 covers the time from 1997 to November 2021.

The model is distributed in various formats. For the time-dependent internal field, B-spline coefficients for each spherical harmonic are provided in a similar format as traditionally used for the gufm1 historical field model and the CALS7K millennial timescale models. It is also provided in the shc-file format, which was developed and adopted for distributing spherical harmonic models determined in connection with the Swarm magnetic satellite mission. This format allows reconstruction of spline-based models from a dense sampling of the time series of the spherical harmonic coefficients and is easier for non-experts to use. A piecewise polynomial Matlab version is also available. For reading and evaluating the CHAOS model, we provide Fortran, Matlab and Python software. In particular, we have recently developed the ChaosMagPy Python package, which allows the CHAOS model (and other spherical harmonic field models) to be easily evaluated and visualized.

Although the shc-file format and ChaosMagPy have been developed primarily in support of the Swarm mission and the CHAOS model, they can be used more broadly for time-dependent spherical harmonic field models or serve as a starting point for the development of new tools that enable cross-disciplinary sharing of data and models.

How to cite: Kloss, C., Finlay, C. C., and Olsen, N.: Tools for sharing and evaluating the CHAOS geomagnetic field model and the shc-file format for time-dependent spherical harmonic models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6265, https://doi.org/10.5194/egusphere-egu22-6265, 2022.

EGU22-6447 | Presentations | GD3.1

A comparison between the magnetohydrodynamical modes of plesio-geostrophy and fully 3D calculations 

Daria Holdenried-Chernoff, Andy Jackson, and Stefano Maffei

An ever-expanding catalogue of satellite data has laid the foundations for new studies of Earth’s secular variation and acceleration. Studies that encode a-priori the axial rigidity conferred to core flows by the Earth’s rapid rotation have revealed novel fast dynamics and improved estimates for the magnetic field strength inside the core. Within this context, a new formalism christened “plesio-geostrophy” (PG) was developed by Jackson and Maffei (Proc. Roy. Soc. A, 476(2243), 2020) with the purpose of describing core dynamics in a regime closer to Earth's conditions. This model makes use of axial integration of the equations of fluid motion and magnetic induction to collapse all three-dimensional quantities into two-dimensional scalars. We report on new results within the PG formalism.

We consider the dynamics of a conducting, inviscid fluid in a full sphere subject to various background magnetic fields. The eigenmodes sustained by the Coriolis and Lorentz forces split into two branches: a fast and a slow one. We characterise these eigenmodes and compare their structure and frequency to fully three-dimensional results. Previous studies are extended by incorporating the effects of horizontal magnetic diffusion.

How to cite: Holdenried-Chernoff, D., Jackson, A., and Maffei, S.: A comparison between the magnetohydrodynamical modes of plesio-geostrophy and fully 3D calculations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6447, https://doi.org/10.5194/egusphere-egu22-6447, 2022.

It has been proposed that thermoelectric (TE) currents may be important in the vicinity of planetary core boundaries (Stevenson 1987, EPSL; Giampieri & Balogh 2002, P&SS). However, TE-induced core dynamics remain largely unstudied. To address this, we have conducted a series of laboratory experiments of turbulent Rayleigh-Bénard convection with a vertical magnetic field in a cylindrical cell filled with liquid gallium. Thermal measurements are taken at a fixed buoyancy forcing with varying Lorentz force. When buoyant inertia dominates, a large-scale overturning circulation cell develops, which imposes strong lateral temperature gradients onto the tank's top and bottom boundaries. In experiments equipped with electrically conducting boundaries, the large-scale circulation slowly precesses in azimuth when thermoelectrically induced Lorentz forces become comparable to buoyant inertial forces. Moreover, TE introduces an asymmetry in the system: this novel magnetoprecessional mode reverses its traveling direction when the magnetic field polarity is reversed. Extrapolating our results to Earth's core, we estimate the required net Seebeck coefficient to generate TE dynamics at CMB conditions. Furthermore, because TE-driven flows reverse direction as the magnetic field reverses, we hypothesize that thermoelectricity can provide a natural symmetry breaker by driving CMB (or ICB) core flows in opposite directions between normal and reversed geomagnetic field polarities. To test our hypothesis, we need to better constrain the electrical, thermal conductivity, and Seebeck coefficient of the CMB (or ICB), and gather observational evidence of geomagnetic secular variation during field reversals. This study is reported in Xu et al. 2022, JFM

How to cite: Xu, Y., Horn, S., and Aurnou, J.: A laboratory study of turbulent magnetoconvection: Could thermoelectricity induce asymmetry in geomagnetic secular variation?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6590, https://doi.org/10.5194/egusphere-egu22-6590, 2022.

EGU22-7290 | Presentations | GD3.1

The Kalmag and ArchKalmag14K geomagnetic field models: their derivation principle, properties and availability 

Julien Baerenzung, Maximilian Arthus Schanner, Monika Korte, Jan Saynisch, and Matthias Holschneider

The recent Kalmag and archaeomagnetic ArchKalmag14K models together represent the global geomagnetic field model evolution over the past 14000 years and resolve temporal scales of the order of a month over the last 122 years. They are obtained through the sequential assimilation of archeomagnetic and volcanic data, and survey, observatory and satellite data, respectively. Both these models provide full posterior information about the core field, and in the case of Kalmag also about other magnetic sources such as the lithospheric or some tidal fields. These models are made accessible online through different physical and statistical quantities associated with them. In this presentation, we will detail our modeling strategy, the type of results we are getting with it, and how the community can access and use our models by an online interface at https://ionocovar.agnld.uni-potsdam.de/Kalmag/ and https://ionocovar.agnld.uni-potsdam.de/Kalmag/Archeo/.

How to cite: Baerenzung, J., Schanner, M. A., Korte, M., Saynisch, J., and Holschneider, M.: The Kalmag and ArchKalmag14K geomagnetic field models: their derivation principle, properties and availability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7290, https://doi.org/10.5194/egusphere-egu22-7290, 2022.

EGU22-8071 | Presentations | GD3.1

Inertial waves excited by topography 

Fabian Burmann and Jerome Noir

We bring together two important features of planetary cores: 1) wave propagation in the fluid and 2) topography of the fluid-solid interface. On one hand, inertial waves contribute to the maintenance of quasi geostrophic motions or to the formation of elongated structures in rotating turbulence. On the other hand, topography of the core-mantle boundary has been prososed in various seismological and geodynamical studies and can modify the fluid flow in the core, for example, by altering global fluid modes. Here, we focus on inertial waves excited by topography.

We present results from a combined numerical and experimental investigation of inertial wave motion which is forced by an oscillating topography. To allow comparison with the theory of linear inertial waves, we use a complex topography characterised by a single wavenumber in the spectral domain. Both, the wavenumber and the frequency of the oscillations are varied, allowing us to characterise the transport of kinetic energy at different length scales as well as the interactions of direct and reflected inertial waves. 

How to cite: Burmann, F. and Noir, J.: Inertial waves excited by topography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8071, https://doi.org/10.5194/egusphere-egu22-8071, 2022.

EGU22-8509 | Presentations | GD3.1 | Highlight

BepiColombo at Mercury: First close-in magnetic field measurements from the southern hemisphere 

Daniel Heyner, Chris Carr, Uli Auster, Ingo Richter, Patrick Kolhey, Willi Exner, Johannes Mieth, Ferdinand Plaschke, Kristin Pump, Johannes Wicht, Benoit Langlais, Gerhard Berghofer, Daniel Schmid, Wolfgang Baumjohann, David Fischer, Timothy Horbury, Werner Magnes, Adam Masters, Jim Slavin, and Karl-Heinz Glassmeier and the MPO-MAG Team

The internal magnetic field of Mercury is best described by a northward offset dipole with almost zero obliquity. Its offset, weakness, axisymmetry and lack of secular variation still poses a challenge to dynamo theory. After NASA’s Mariner 10 flybys in the 1970’s and MESSENGER’s orbital mission in 2011-2015, BepiColombo performed a flyby at Mercury in October 2021. For the first time, magnetic field measurements are obtained from the southern hemisphere by the fluxgate magnetometer MPO-MAG. We will present an overview of the flyby data and compare the new in-situ data to magnetospheric models obtained from the previous missions to the innermost terrestrial planet. Does the flyby data reveal any secular variation? Has the dipole offset changed? These are some of the questions we will discuss with this unprecedented magnetometer data. We will close with a discussion on what is to be expected from the orbital phase of BepiColombo. 

How to cite: Heyner, D., Carr, C., Auster, U., Richter, I., Kolhey, P., Exner, W., Mieth, J., Plaschke, F., Pump, K., Wicht, J., Langlais, B., Berghofer, G., Schmid, D., Baumjohann, W., Fischer, D., Horbury, T., Magnes, W., Masters, A., Slavin, J., and Glassmeier, K.-H. and the MPO-MAG Team: BepiColombo at Mercury: First close-in magnetic field measurements from the southern hemisphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8509, https://doi.org/10.5194/egusphere-egu22-8509, 2022.

EGU22-8532 | Presentations | GD3.1

Dynamo models reproducing the offset dipole of Mercury’s magnetic field 

Patrick Kolhey, Daniel Heyner, Johannes Wicht, Thomas Gastine, and Ferdinand Plaschke

Since the discovery of Mercury’s peculiar magnetic field it has raised questions about the underlying dynamo process in its fluid core. The global magnetic field at the surface is rather weak compared to other planetary magnetic fields, strongly aligned to the planet's rotation axis and its magnetic equator is shifted towards north. Especially the latter characteristic is difficult to explain using common dynamo model setups. One promising model suggests that a thermal stably stratified layer right underneath the core-mantle boundary is present. As a consequence the magnetic field deep inside the core is efficiently damped by passing through the stably stratified layer due to the skin effect. Additionally, the non-axisymmetric parts of the magnetic field are vanishing, too, such that a dipole dominated magnetic is left at the planet’s surface. In this study we present new direct numerical simulations of the magnetohydrodynamical dynamo problem which include a stably stratified layer on top of the outer core, which can also reproduce the shift of the magnetic equator towards north. We revisit a model configuration for Mercury’s dynamo action, which successfully reproduced the magnetic field features, in which core convection is driven by thermal buoyancy as well as compositional buoyancy (double-diffusive convection). While we find that this model configuration produces Mercury-like magnetic field only in a limited parameter range (Rayleigh and Ekman number), we show that also a simple codensity model is sufficient over a wide parameter range to produce Mercury-like magnetic fields.

How to cite: Kolhey, P., Heyner, D., Wicht, J., Gastine, T., and Plaschke, F.: Dynamo models reproducing the offset dipole of Mercury’s magnetic field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8532, https://doi.org/10.5194/egusphere-egu22-8532, 2022.

EGU22-8916 | Presentations | GD3.1

Melting and phase relations of Fe-Ni-Si determined by a multi-technique approach 

Vasilije Dobrosavljevic, Dongzhou Zhang, Wolfgang Sturhahn, Jiyong Zhao, Thomas Toellner, Stella Chariton, Vitali Prakapenka, Olivia Pardo, and Jennifer Jackson

Many studies have suggested silicon as a candidate light element for the cores of Earth and Mercury. However, the effect of silicon on the melting temperatures of core materials and thermal profiles of cores is poorly understood, due to disagreements among melt detection techniques, uncertainties in sample pressure evolution during heating, and sparsity of studies investigating the combined effects of nickel and silicon on the phase diagram of iron. In this work (Dobrosavljevic et al. 2022), we develop a multi-technique approach for measuring the high-pressure melting and solid phase relations of iron alloys and apply it to Fe0.8Ni0.1Si0.1 (Fe-11wt%Ni-5.3wt%Si), a composition compatible with recent estimates for the cores of Earth and Mercury.

This approach combines results (20-83 GPa) from two in-situ techniques: synchrotron Mössbauer spectroscopy (SMS) and synchrotron x-ray diffraction (XRD). Melting is independently detected by the loss of the Mössbauer signal, produced exclusively by solid-bound iron nuclei, and the onset of a liquid diffuse x-ray scattering signal. The use of a burst heating and background updating method for quantifying changes in the reference background during heating facilitates the determination of liquid diffuse signal onsets and leads to strong reproducibility and excellent agreement in melting temperatures determined separately by the two techniques. XRD measurements additionally constrain the hcp-fcc phase boundary and in-situ pressure evolution of the samples during heating.

We apply our updated thermal pressure model to published SMS melting data on fcc-Fe and fcc-Fe0.9Ni0.1 to precisely evaluate the effect of silicon on melting temperatures. We find that the addition of 10mol% Si to Fe0.9Ni0.1 reduces melting temperatures by ~250 K at low pressures (<60 GPa) and flattens the hcp-fcc phase boundary. Extrapolating our results, we constrain the location of the hcp-fcc-liquid quasi-triple point at 147±14 GPa and 3140±90 K, which implies a melting temperature reduction of 500 K compared with Fe0.9Ni0.1. The results demonstrate the advantages of combining complementary experimental techniques in investigations of melting under extreme conditions.

Reference:

Dobrosavljevic, V. V., Zhang, D., Sturhahn, W., Zhao, J., Toellner, T. S., Chariton, S., Prakapenka, V. B., Pardo, O. S., Jackson, J. M. (2022). Earth and Planetary Science Letters (in press).

How to cite: Dobrosavljevic, V., Zhang, D., Sturhahn, W., Zhao, J., Toellner, T., Chariton, S., Prakapenka, V., Pardo, O., and Jackson, J.: Melting and phase relations of Fe-Ni-Si determined by a multi-technique approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8916, https://doi.org/10.5194/egusphere-egu22-8916, 2022.

EGU22-9908 | Presentations | GD3.1

Chirality of the Geodynamo from the Core’s buoyancy and Sense of Spinning 

Gunther Kletetschka

The geodynamo inside the liquid core is part of the Earth’s rotation. We discovered that electric currents in the heat exchanging liquid core need to follow the handedness of the spiraling liquids given by Coriolis force. Coriolis force splits the buoyant heat exchanging liquid into the two, north and south hemispheres, each with its unique handedness of spiraling convection systems. Convection spiraling model of the core fluid revealed that any planetary dynamo with a liquid conducitng core must have a two-component bimodal structure magnetic contribution, where, for Earth, the southern hemisphere is always associated with a dominating normal polarity component and northern hemisphere with a dominating component of reverse magnetic polarity. We show that the geodynamo would have a non-random distribution of the probability of generation of dynamo’s magnetic polarity, depending on a difference in a degree of buoyancy vigorousness between the two hemispheres.  In this work, the individual treatment of normal and reversed polarity durations revealed that while before 80 Ma geodynamo was generating predominantly normal polarity durations, after the Tertiary transition at ~ 60 Ma, the geodynamo produced predominantly reverse polarity durations. This observation of predominance of magnetic polarity durations is constrained by the existing temperature models near the core/mantle boundary (CMB) and we show a novel connection how a lower mantle temperature distribution may reorganize its convection pattern in the core and change the stability of the dipolar field in favor of a specific polarity.

How to cite: Kletetschka, G.: Chirality of the Geodynamo from the Core’s buoyancy and Sense of Spinning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9908, https://doi.org/10.5194/egusphere-egu22-9908, 2022.

EGU22-10532 | Presentations | GD3.1

Early Cambrian renewal of the geodynamo and the origin of inner core structure 

Tinghong Zhou, John Tarduno, Rory Cottrell, and Francis Nimmo

Seismic anisotropy observations indicate the presence of an innermost and outermost inner core, but the origin of this structure is unknown. Records of the past geomagnetic field provide a means to probe inner core evolution by establishing when growth started. The Ediacaran (~565 million-year-old) geodynamo was near collapse, with a strength 10 times weaker than that of the present-day consistent with model predictions for the field before the onset of inner core nucleation. But the timing of the key transition to stronger intensities typical of the Phanerozoic Eon, needed for establishing an exact onset age, has been unclear. We present single crystal paleointensity results from anorthosites of the early Cambrian (~532 million-year-old) Glen Mountains Layered Mafic Complex (Oklahoma). Data from single plagioclase crystals bearing single domain magnetite and titanomagnetite inclusions yield a time-averaged dipole moment of 3.5 +/- 0.9 x 1022 A m2, 5 times greater than that recorded in the Ediacaran Period. This rapid field recovery is the expectation at the start of inner core growth, as new thermal and compositional sources of buoyancy to power the geodynamo become available. We will discuss thermal models, which together with our new paleointensity results, allow us to constrain growth of the inner core and when its structure may have changed.

How to cite: Zhou, T., Tarduno, J., Cottrell, R., and Nimmo, F.: Early Cambrian renewal of the geodynamo and the origin of inner core structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10532, https://doi.org/10.5194/egusphere-egu22-10532, 2022.

EGU22-11293 | Presentations | GD3.1

Regional geomagnetic field model over the area comprising the South Atlantic Anomaly 

Saioa A. Campuzano, Angelo De Santis, and F. Javier Pavón-Carrasco

Taking advantage of the Swarm three-satellite magnetic field mission by ESA, launched on 22 November 2013 and still orbiting, and ground observatory magnetic data, we determine a spatiotemporal regional model for the geomagnetic field using the R-SCHA technique over the area comprising the South Atlantic Anomaly (SAA). The SAA is the region above the South Atlantic and South America where the geomagnetic field intensity is much lower than expected by a simple dipolar field. Its origin is deep in the outer core and is likely due to a reverse magnetic flux area that has been increasing in the last four centuries. On the basis of this model, we observe 1) the recent evolution of the anomaly from 2014 up to date, with a focus on its “tails” towards South Africa and West Pacific, 2) some features that can be related to important properties of the main geomagnetic field, such as its secular variation and the occurrence of geomagnetic jerks.

How to cite: Campuzano, S. A., De Santis, A., and Pavón-Carrasco, F. J.: Regional geomagnetic field model over the area comprising the South Atlantic Anomaly, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11293, https://doi.org/10.5194/egusphere-egu22-11293, 2022.

EGU22-11668 | Presentations | GD3.1

Exploring the dynamics of inward core solidification using analogue tank experiments 

Kathryn Dodds, James Bryson, Jerome Neufeld, and Richard Harrison

Given their small sizes and low central pressures, the cores of most asteroids are expected to have started crystallising at the core mantle boundary (CMB) instead of at their centre, as is the case for the Earth. This so-called top-down crystallisation is thermally unstable but compositionally stable, making the conditions for dynamo generation more difficult to achieve. Nevertheless, modern observations of Ganymede show an active magnetic field, where it has been suggested that solidification occurs away from the CMB as an iron snow. This model proposes that iron crystals grow in a snow zone and subsequently sink into the interior and melt, releasing dense fluid that drives convection and a magnetic field. However, whether this process could have occurred in asteroid cores is uncertain due to the significantly smaller adiabatic temperature difference between the CMB and the centre of their cores. This weak temperature gradient may also prevent crystallisation away from the CMB. Therefore, the power for a compositional dynamo may result from an increase in convective velocities caused by the formation of dense crystals at the CMB or turbulence caused by the settling of the crystals themselves.

To investigate these possibilities, we employ analogue tank experiments to explore the possible mechanisms driving convection during inward asteroid core crystallisation. An ammonium chloride solution is cooled from above with a layer of buoyant propanol separating the solution from the cold plate to prevent the growth of crystals on this boundary. Instead, the crystals form below the buoyant layer in a ‘snow zone’. We vary the temperature difference across this buoyant layer to investigate the different regimes that may exist. At each driving temperature difference, we measure the velocity fields of any fluid flow within the ammonium chloride solution using particle imaging velocimetry. This enables us to compare the convective velocities with and without crystallisation as well as develop scaling laws to apply the results of these experiments to models of core thermal evolution.

We find that the mean convective speeds increase by over an order of magnitude when the fluid is crystallising. This increase in speed is driven by an increase in the bulk density of the fluid in the snow zone due to the presence of a small crystal fraction. While the motion of crystals themselves do not induce any turbulence in the fluid due to their small size, they act to locally increase the density of the fluid, causing dense, crystal-rich plumes to emanate from the snow zone, which drive faster convective speeds throughout the fluid. This result provides a new mechanism for dynamo generation in inwardly crystallising cores, especially if remelting of falling iron crystals is delayed until deep within the core’s interior, as has recently been proposed for Mars, or if there is a nucleation barrier that causes significant undercooling before the onset of crystallisation. We also measure the temperature and composition as a function of depth within the tank, from which we may assess whether thermal equilibrium can be assumed when modelling snow zones in cores.

How to cite: Dodds, K., Bryson, J., Neufeld, J., and Harrison, R.: Exploring the dynamics of inward core solidification using analogue tank experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11668, https://doi.org/10.5194/egusphere-egu22-11668, 2022.

EGU22-12178 | Presentations | GD3.1

The influence of a stratified core on Mercury's librations 

Fleur Seuren, Santiago Andres Triana, Jérémy Rekier, Tim Van Hoolst, and Véronique Dehant

Earth-based measurements of Mercury's libration amplitude have been used previously to establish the existence of Mercury's liquid core and to estimate its size. However these previous works have not yet taken into account the internal core flows that can be induced by rotational variations such as librations. In the present study, we use a numerical linear model to investigate the effect that these internal flows might have on Mercury's libration amplitude and other observables. In particular we find that the inclusion of a stably stratified layer at the top of the core – the existence of which has been suggested by thermal evolution and numerical dynamo models – in most cases prohibits the transmission of any motion from the top of the core to its deeper parts and vice versa.

How to cite: Seuren, F., Triana, S. A., Rekier, J., Van Hoolst, T., and Dehant, V.: The influence of a stratified core on Mercury's librations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12178, https://doi.org/10.5194/egusphere-egu22-12178, 2022.

EGU22-13478 | Presentations | GD3.1

Velocity field reconstruction by Machine Learning during kinematic dynamo process 

Waleed Mouhali, Jae-Yun Jun, and Thierry Lehner

Generation and reversal of the Earth’s magnetic field have remained one of the most controversial topics.  It is well known that the Earth’s magnetic field is generated by dynamo action in the liquid iron outer core. This mechanism explains how a rotating, convecting, and electrically conducting fluid sustains a magnetic field.

In this study, we investigate the kinematic dynamo action associated with the well-known ABC-flow (see Dombre et al. [1986]). We focus on the “A = B = C = 1. Its dynamo properties have been assessed in 1981 by Arnold et al. [1981]. It belongs to fast dynamo action: a flow which achieves exponential magnetic field amplification over a typical time related to the advective timescale and not the ohmic diffusive timescale (in which case it is referred to as a “slow dynamo”).

We use DNS method for solving the kinematic dynamo problem, for which a solenoidal magnetic field evolution is governed under a prescribed flow by the induction equation.

In this work, we propose a deep learning method to solve the inverse dynamo problem by estimating the velocity field from the magnetic field. We train our deep learning algorithm from the velocity field and the magnetic field values obtained from the above flow model. Once the algorithm parameters are trained, the optimized algorithm is tested for the velocity field estimation from magnetic field. 

How to cite: Mouhali, W., Jun, J.-Y., and Lehner, T.: Velocity field reconstruction by Machine Learning during kinematic dynamo process, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13478, https://doi.org/10.5194/egusphere-egu22-13478, 2022.

EGU22-1388 | Presentations | GD9.2

A high-resolution record of vertically-resolved seawater salinity in the Caribbean Sea mixed layer since 1700 AD. 

Amos Winter, Davide Zanchettin, Malcolm McCulloch, Manuel Rigo, Clark Sherman, and Angelo Rubino

The Caribbean Sea in the tropical Atlantic is one of the major heat engines of the Earth and a sensitive area for monitoring climate variability. Salinity changes in the Caribbean Sea record changes in ocean currents and can provide information about variations in ocean heat transport. Seawater salinity in the Caribbean Sea has been monitored in recent decades, nevertheless, of all oceanographic environmental parameters salinity information before the instrumental period remains limited, due to the difficulty of reconstructing salinity, arguably the most difficult natural archives to recreate. We were able to reconstruct salinity changes in the Caribbean Sea from 1700 to the present from southwest Puerto Rico using slowly growing and long-lived scelerosponges from southwest Puerto Rico. These well-dated sponges are known to precipitate their skeletons in isotopic equilibrium (i.e., their record is not affected much by vital effects) and were retrieved from various depths in the mixed layer, from the surface to 90 m depth. We were able to establish salinity changes by deconvoluting stable isotopes (d18O) and trace element (Sr/Ca) proxies taken from the sponges at regular intervals. In this contribution, we will present the salinity record and illustrate the process for salinity reconstruction. We will also discuss how we determine how salinity changes in our record relate to radiative forcing as well as connect them with dominant mechanisms operating in the region, including changes in the position of the InterTtropical Convergence Zone and intensity of the Atlantic meridional Overturning Circulation over time.

How to cite: Winter, A., Zanchettin, D., McCulloch, M., Rigo, M., Sherman, C., and Rubino, A.: A high-resolution record of vertically-resolved seawater salinity in the Caribbean Sea mixed layer since 1700 AD., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1388, https://doi.org/10.5194/egusphere-egu22-1388, 2022.

EGU22-3134 | Presentations | GD9.2

Reconstructing the climate of the Extremadura region (SW Spain) from documentary sources 

José M. Vaquero, María C. Gallego, Nieves Bravo-Paredes, Víctor M.S. Carrasco, and Irene Tovar

In recent years, our research group has tried to improve the knowledge of the historical climate of the Extremadura region, located in the interior of the southwest of the Iberian Peninsula. Some results can be highlighted:

  • Temperature and precipitation indices were constructed for the period 1750-1840 from the correspondence of the Duke of Feria (Fernández-Fernández et al., 2014, 2015, 2017).
  • We have recovered many “pro pluvia” rogation dates (Domínguez-Castro et al., 2021) and we have seen their relationship with the North Atlantic Oscillation (Bravo-Paredes et al., 2020).
  • We have studied the catastrophic floods of the Guadiana River since AD1500 (Bravo-Paredes et al., 2021).
  • We have recovered more than 700,000 meteorological data from the Extremadura region taken in the 19th and early 20th centuries (Vaquero et al., 2022), including some uncommon series (Bravo-Paredes et al., 2019).

In recent months, we have started a study of the meteorological information published by the regional press of Extremadura in the last 150 years and here we will present some preliminary results.

References

Bravo-Paredes, N. et al. (2019) Tellus B 71, 1663597.

Bravo-Paredes, N. et al. (2020) Atmosphere 11(3), 282.

Bravo-Paredes, N. et al. (2021) Science of the Total Environment 797, 149141.

Domínguez-Castro, F. et al. (2021) Scientific Data 8, 186.

Fernández-Fernández, M.I. et al. (2014) Climatic Change 126, 107.

Fernández-Fernández, M.I. et al. (2015) Climatic Change 129, 267.

Fernández-Fernández, M.I. et al. (2017) Climatic Change 141, 671.

Vaquero, J.M. et al. (2022) Geoscience Data Journal. https://doi.org/10.1002/gdj3.131

How to cite: Vaquero, J. M., Gallego, M. C., Bravo-Paredes, N., Carrasco, V. M. S., and Tovar, I.: Reconstructing the climate of the Extremadura region (SW Spain) from documentary sources, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3134, https://doi.org/10.5194/egusphere-egu22-3134, 2022.

EGU22-3906 | Presentations | GD9.2

Earthquake detection in time-series of laser strainmeter measurements as a first step towards automatic signal classification. 

Valentin Kasburg, Alexander Breuer, Martin Bücker, and Nina Kukowski

Geophysical observatories around the world collect data on various natural phenomena within the Earth and on its surface. Many of these measurements are made automatically, sometimes at high sampling rates, so that enormous amounts of data accumulate over the years. Continuous analysis is important to classify current phenomena and decide which data are important and which can be downsampled later.

At Moxa Geodynamic Observatory, located in central Germany, several laser strainmeters have been installed in subsurface galleries in order to measure strain of the Earth's crust. These instruments run in north-south, east-west, and northwest-southeast directions. Nano-strain rates are determined with a sampling rate of 0.1 Hz almost continuously over distances of 26 and 38 m, respectively, since summer 2011.

Signals of tectonically induced crustal deformation are superimposed by other signals of greater amplitude, e.g., tides, changes in atmospheric pressure, hydrologic events such as heavy rainfall, and earthquakes. Classification of these events is important to better associate jumps in the temporal vicinity and to distinguish anomalies from instrument failures. To avoid time-consuming pattern recognition by hand, algorithms are required to do most of the work automatically. Due to recent advances in the field of artificial intelligence, it is possible to implement time series algorithms that are capable of unifying and automating many steps of data analysis. Although artificial intelligence applications are increasingly used to support data analysis, their use for time series of geophysical origin so far is not widespread outside of seismology.

In this contribution, an approach to automatically detect earthquakes in the strain data using 1D Convolutional Neural Networks is presented, including the generation of artificial training data with time series data augmentation. Also the training process and generation of new training data, based on classification by hand and false predictions of the trained model is described. The 1D Convolutional Neural Networks are able to identify almost all earthquakes in the strain data and have F1 values > 0.99, showing that their application has the potential to significantly reduce the time required in signal classification of observatory time series data.

How to cite: Kasburg, V., Breuer, A., Bücker, M., and Kukowski, N.: Earthquake detection in time-series of laser strainmeter measurements as a first step towards automatic signal classification., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3906, https://doi.org/10.5194/egusphere-egu22-3906, 2022.

EGU22-6814 | Presentations | GD9.2

Long term deformation and seismic observations at the Mont Terri rock laboratory 

Dorothee Rebscher, Senecio Schefer, Finnegan Reichertz, Yves Guglielmi, William Foxall, Inma Gutiérrez, and Edi Meier

The Mont Terri rock laboratory, located in the Swiss Jura Mountains, is dedicated to research on argillaceous rocks. Since its founding in 1996, the objective is the hydrogeological, geochemical, and geotechnical characterisation of Opalinus Clay in the context of nuclear waste repositories. More recently, the work has broadened to additional fields, covering potential uses of the deep geological subsurface such as geological storage of carbon dioxide and geothermal energy. With the excellent infrastructure, a comprehensive database, and the broad scientific and technological expertise, knowledge is enhanced e.g. through the advancement and comparison of approaches as well as the development and testing of novel investigation methods. These, as well as studies on feasibility and risk assessment, are of benefit also for underground laboratories in general and in situ explorations in different rock types worldwide. Due to the long-term commitment and the available gallery space of the research facility, elaborate as well as decade-long experiments can be implemented.

In order to detect, quantify, and understand short- and long-term deformations in the Mont Terri rock laboratory, quasi continuous time series are established employing various monitoring techniques. The latter complement each other in regard to their spatial dimensions, operational frequency optima, and their point or integral information. The approach combines

  • a 50 m long uniaxial hydrostatic levelling system (HLS, Type “PSI”, positioned along a gallery wall, measuring principle: electrical plate capacitors),
  • four mini-arrays of very-broad-band triaxial seismometers, installed in the rock laboratory (one under the HLS) as well as outside the rock laboratory at the surface,
  • and an array of high resolution, biaxial platform tiltmeters, with instruments situated close to the HLS and in various parts of the rock laboratory, integrated in other in situ experiments.

The observed signals and their analysis differ in space and time. They range from the detection of local nanoseismic as well as large tele seismic events, to the determination of earth tides, and to the identification of seasonal trends versus other long term geodetic movements. Besides the mutual comparison of the three deformation measurements, the time series provide valuable input for numerous scientific questions such as the stability of the rock laboratory as a whole or in its parts, the influence of excavation, ventilation, or fluid injection on rock matrix and faults. Long data series of ambient parameters, essential for interpretation of the deformation records, such as temperature, pressure, and humidity, are recorded by sensors integrated in the above listed instruments and are also of interest in further experiments performed by the Mont Terri Consortium.

How to cite: Rebscher, D., Schefer, S., Reichertz, F., Guglielmi, Y., Foxall, W., Gutiérrez, I., and Meier, E.: Long term deformation and seismic observations at the Mont Terri rock laboratory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6814, https://doi.org/10.5194/egusphere-egu22-6814, 2022.

EGU22-8343 | Presentations | GD9.2 | Highlight

Variations of the Earth magnetic field: From geomagnetic storms to field reversal 

Roman Leonhardt

The geomagnetic field, the Earth’s primary barrier against charged particles from the sun, varies on time scales from million years to sub-second fluctuations. In the past decades significant advances in measurement techniques, both ground and space based, paleo- and rock magnetic methods, as well as numerical and analytical simulations, improved our understanding of underlying processes and their consequences on our planet and on our society. Geomagnetic storms, often related to coronal mass ejections on the sun and their interaction with the Earth‘s magnetic field, pose a threat to our modern society as they affect satellites, disturb radio communication, and, in particular, damage power grids and cause electrical blackouts on a massive scale. Ground based measurements, which are used together with satellite data to investigate these events, point towards the occurrence of global scale major storms once every 100 years. When further looking at such observatory data, which is existing for the last few hundred years, it is also striking that the global Earth‘s magnetic field is gradually weakening, by more the 10% in the past 200 years. Paleo- and archeomagnetic investigations are used to extend our observational range into the past in order to clarify the significance and reasons of this field reduction. When looking even further into the past, complete flips of the geomagnetic field are recorded in geological archives like volcanic rocks and sediments. These geomagnetic field reversals, the last one happening about 770kyrs ago, are accompanied by strong reductions of the geomagnetic field strength and complex field behavior on the Earths surface, effects which are sometimes brought into connection with our modern observation of field reduction. This presentation will provide a comprehensive overview about geomagnetic field variations, and the necessity of using long timeseries for interpretation of its current state and future evolution.

How to cite: Leonhardt, R.: Variations of the Earth magnetic field: From geomagnetic storms to field reversal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8343, https://doi.org/10.5194/egusphere-egu22-8343, 2022.

To achieve very low ambient noise and thus very good conditions for long-term geophysical observations at a high level of instrumental accuracy in order to decipher also faint signals from Earth and environmental processes, sensors often are installed in the subsurface in galleries or in boreholes. This however, makes it necessary to consider the potential influence of the geological setting and properties of the surrounding rock formations and overburden.
Moxa Geodynamic observatory, located in a remote part of the Thuringian slate mountains, approximately 30 km south of Jena, provides an ideal setting to address this topic as it comprises two galleries, which are running perpendicular to each other. As the observatory is built at the toe of a relatively steep slope, coverage of the galleries varies along them. Further, the tectonic structure and hydrological settings of the overburden is rather complex.
Instruments sensitive to deformation, which include three laser strain meters measuring nano-strain, borehole tiltmeters and a superconducting gravimeter CD-034, together with other instruments, e.g. a node for the Global Network of Optical Magnetometers for Exotic physics (GNOME), are installed in various positions in the building of the observatory, close to the building, and in the galleries. The laser strainmeters record along three galleries in north-south, east-west and NW-SE directions. Further, information on fluid flow is gained from downhole temperature measurements employing an optical fiber and several groundwater level indicators, some of them installed in shallow boreholes. Additionally, information on environmental parameters is coming from a climate station and on the subsurface tectonic structure from various near surface geophysical data sets. 
Here, we present first results of an ongoing project which combines actual deformation recordings, structural and drillhole information to decipher how the tectonic structure of the and groundwater movement within the overlying slope on top of the observatory’s galleries may impact on the various instrumental recordings.

How to cite: Kukowski, N., Kasburg, V., Goepel, A., Schwarze, C., Jahr, T., and Stolz, R.: Impact of the geological setting of the overburden on long-time series recorded at underground geophysical observatories: case study from the FSU Jena Geodynamic Observatory Moxa (Thuringia, central Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11079, https://doi.org/10.5194/egusphere-egu22-11079, 2022.

EGU22-11916 | Presentations | GD9.2

Downscaling to high-resolution and correcting air temperature from the ERA5-Land over Ethiopia 

Mosisa Tujuba Wakjira, Nadav Peleg, and Peter Molnar

Climate information from in-situ observation networks can be used to significantly improve the accuracy of gridded climate datasets, even in data-scarce regions. We applied a bias correction and spatial disaggregation method on daily maximum and minimum ERA5-Land (ERA5L) 2-m air temperature dataset covering Ethiopia. Due to large gaps in the observed temperature data, the bias correction is based on the statistics rather than the complete time series. First, long-term daily, monthly and annual temperature statistics (mean and variance) were summarized for the time series obtained from 155 stations covering the period 1981-2010. Second, the temperature statistics were interpolated onto a 0.05° x 0.05° grid using an inverse non-Euclidean distance weighting approach. This method accounts for the effects of elevation, thus enabling downscaling of the temperature to a higher spatial resolution. Next, the ERA5L maximum and minimum temperature were bias-corrected using quantile mapping assuming a Gaussian distribution transfer function. The quantile mapping was performed at daily, monthly and annual time steps to reproduce the climatology, seasonality, and interannual variability of the data. The performance of the bias correction was evaluated using the leave-out-one cross-validation method. The cross-validation shows that the bias-corrected maximum (minimum) daily temperature has an improved mean absolute error value of 68% (52%) in comparison to the original ERA5L reanalysis air temperature bias. The bias-corrected dataset is therefore suggested as an alternative for the ERA5L and can be used in a wide range of applications in Ethiopia.

How to cite: Wakjira, M. T., Peleg, N., and Molnar, P.: Downscaling to high-resolution and correcting air temperature from the ERA5-Land over Ethiopia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11916, https://doi.org/10.5194/egusphere-egu22-11916, 2022.

Geomagnetic activity is a measure aimed to quantify the effect of solar wind upon the Earth's magnetic environment. The main structures in solar wind driving geomagnetic activity are the coronal mass ejections (CME) and the high-speed solar wind streams together with related co-rotating interaction regions (HSS/CIR). While CMEs are closely related to sunspots and other active regions on solar surface, the HSSs are related to solar coronal holes, forming a proxy of solar polar magnetic fields. This gives an interesting possibility to obtain versatile information on solar activity and solar magnetic fields from geomagnetic activity.

Various indices have been developed to quantify and monitor global geomagnetic activity. The most often used indices of overall geomagnetic activity are the aa index, developed by P. Mayaud and running already since 1868, and the Kp/Ap index, developed by J. Bartels and running since 1932. Both aa and Kp/Ap depict the increase of geomagnetic activity during the first half of the 20th century, and a steep decline in the 2000s. However, although the two indices are constructed from midlatitude observations using roughly the same recipe, they depict notable differences during the 90-year overlapping interval. While the Kp/Ap index reaches a centennial maximum in the late 1950s, at the same time as sunspots, the aa index has its maximum only in 2003. Also, the Kp/Ap is systematically relatively more active in the first decades until 1960s, while aa is more active thereafter. The Dst index was developed to monitor geomagnetic storms and the ring current since 1957. We have corrected some early errors in the Dst index and extended its time interval to 1932. This extended storm index is called the Dxt index. Here we study these long-term geomagnetic indices and their differences. We also use their different dependences on the main solar wind drivers in order to obtain new information on the centennial evolution of solar activity and solar magnetic fields.

How to cite: Mursula, K.: Long-term geomagnetic activity: Comparison and analysis of geomagnetic activity indices during the last 90 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12745, https://doi.org/10.5194/egusphere-egu22-12745, 2022.

EGU22-74 | Presentations | GI2.2

Experimental assessment of corrosion influence in reinforced concrete by GPR 

Salih Artagan, Vladislav Borecky, Özgür Yurdakul, and Miroslav Luňák

Corrosion is one of the most critical issues leading to damage in reinforced concrete structures. In most cases, the detection of corrosion damage is performed by visual inspection. Other techniques (drilling cores with petrography or chemical examination, potential measurements, and resistivity measurements) require minimum destruction since they can be utilized by reaching the reinforcement bar [1]. Recently, there has been an increasing trend to use Ground Penetrating Radar (GPR) as one of the emerging non-destructive testing (NDT) techniques in the diagnosis of corrosion [2].

This paper focuses on a series of GPR tests on specimens constructed from poor-quality concrete and plain round bar. These specimens were subjected to accelerated corrosion tests under laboratory conditions. The corrosion intensity of those specimens is non-destructively assessed with GPR, by collecting data before and after corrosion tests. For GPR tests, the IDS Aladdin system was used with a double polarized 2 GHz antenna. Based on GPR measurement, Relative Dielectric Permittivity (RDP) values of concrete, are calculated based on the known dimension of specimens and two-way travel time (twt) values obtained from A-scans. The change in RDP values of specimens before and after exposure to corrosion is then computed. Moreover, amplitude change and variation in frequency spectrum before and after corrosion exposure are analyzed.

The results of this experimental study thus indicate that corrosion damage in reinforced concrete can be determined by using several GPR signal attributes. More laboratory tests are required for better quantification of the impact of the corrosion phenomenon in reinforced concrete.

All GPR tests were conducted in Educational and Research Centre in Transport; Faculty of Transport Engineering; University of Pardubice. This work is supported by the University of Pardubice (Project No: CZ.02.2.69/0.0/0.0/18_053/0016969).

[1]        V. Sossa, V. Pérez-Gracia, R. González-Drigo, M. A. Rasol, Lab Non Destructive Test to Analyze the Effect of Corrosion on Ground Penetrating Radar Scans, Remote Sensing. 11 (2019) 2814. https://doi.org/10.3390/rs11232814.

[2]        K. Tešić, A. Baričević, M. Serdar, Non-Destructive Corrosion Inspection of Reinforced Concrete Using Ground-Penetrating Radar: A Review, Materials. 14 (2021) 975. https://doi.org/10.3390/ma14040975.

How to cite: Artagan, S., Borecky, V., Yurdakul, Ö., and Luňák, M.: Experimental assessment of corrosion influence in reinforced concrete by GPR, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-74, https://doi.org/10.5194/egusphere-egu22-74, 2022.

EGU22-1544 | Presentations | GI2.2

Dielectric Constant Estimation through Alpha Angle with a Polarimetric GPR System 

Lilong Zou, Fabio Tosti, and Amir M. Alani

As a recognised non-destructive testing (NDT) tool, Ground Penetrating Radar (GPR) is becoming increasingly common in the field of environmental engineering [1]-[3]. GPR uses electromagnetic (EM) waves which travel at specific velocity determined by the permittivity of the material. With the development of new GPR signal processing methodologies, finding information on the physical properties of hidden targets has become a key target. Currently, only three types of approach could be applied for the quantitative estimation of permittivity from GPR data, i.e., hyperbola curve fitting, common middle point (CMP) velocity analysis and full-waveform inversion. However, the main challenges for the estimation of permittivity from GPR backscattered signals are to provide effective and accurate strategy for prediction.

In this research, we used a dual-polarimetric GPR system to estimate the dielectric constant of targets. The system is equipped with two 2GHz antennas polarised perpendicularly each to one another (HH and VV). The dual polarisation enables deeper surveying, providing images of both shallow and deeper subsurface features. Polarimetry is a property of EM waves that generally refers to the orientation of the electric field vector, which plays here an important role as it allows either direct or parameterisation permittivity effects within the scattering problem in the remote sensing [4].

The aim of this research is to provide a novel and more robust approach for dielectric constant prediction using a dual-polarimetric GPR system. To this extent, the relationship between the relative permittivity and the polarimetric alpha angle have been investigated based on data collected by a GPR system with dual-polarised antennas. The approach was then assessed by laboratory experiments where different moisture sand targets (simulating the effect of different relative permittivity targets) were measured. After signal processing, a clear relationship between the alpha angle and the relative permittivity was obtained, proving the viability of the proposed method.

 

Acknowledgements

The authors would like to express their sincere thanks and gratitude to the following trusts, charities, organisations and individuals for their generosity in supporting this project: Lord Faringdon Charitable Trust, The Schroder Foundation, Cazenove Charitable Trust, Ernest Cook Trust, Sir Henry Keswick, Ian Bond, P. F. Charitable Trust, Prospect Investment Management Limited, The Adrian Swire Charitable Trust, The John Swire 1989 Charitable Trust, The Sackler Trust, The Tanlaw Foundation, and The Wyfold Charitable Trust.

 

References

[1] Zou, L. et al., 2020. Mapping and Assessment of Tree Roots using Ground Penetrating Radar with Low-Cost GPS. Remote Sensing, vol.12, no.8, pp:1300.

[2] Zou, L. et al., 2020. On the Use of Lateral Wave for the Interlayer Debonding Detecting in an Asphalt Airport Pavement Using a Multistatic GPR System. IEEE Transactions on Geoscience and Remote Sensing, vol. 58, no. 6, pp. 4215-4224.

[3] Zou, L. et al., 2021. Study on Wavelet Entropy for Airport Pavement Debonded Layer Inspection by using a Multi-Static GPR System. Geophysics, vol. 86, no. 3, pp. WB69-WB78.

[4] J. Lee and E. Pottier, Polarimetric Imaging: From Basics to Applications, FL, Boca Raton: CRC Press, 2009.

How to cite: Zou, L., Tosti, F., and Alani, A. M.: Dielectric Constant Estimation through Alpha Angle with a Polarimetric GPR System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1544, https://doi.org/10.5194/egusphere-egu22-1544, 2022.

EGU22-1849 | Presentations | GI2.2

On the use of Artificial Intelligence for classification of road pavements based on mechanical properties using ground-penetrating radar and deflection-based non-destructive testing data 

Fateme Dinmohammadi, Luca Bianchini Ciampoli, Fabio Tosti, Andrea Benedetto, and Amir M. Alani

Road pavements play a crucial role in the development of any construction as they provide safe surface on which vehicles can travel comfortably [1]. Pavements are multi-layered structures of processed and compacted materials in different thicknesses and in both unbound and bound forms with the function of supporting vehicle loads as well as providing a smooth riding quality. The condition of road pavement structures is susceptible to the impact of uncertain environmental factors and traffic loads, resulting in pavement deterioration over time. Therefore, the mechanical properties of pavements (such as strength, stiffness, etc.) need to be monitored on a regular basis to make sure that the pavement condition meets its prescribed threshold. The ground-penetrating radar (GPR) and deflection-based methods (e.g., the falling weight deflectometer (FWD)) are the most popular non-destructive testing (NDT) methods in pavement engineering science that are often used in combination to evaluate the damage and strength of pavements [2-4]. The layer thickness data from GPR scans are used as an input for deflection-based measurements to back-calculate the elastic moduli of the layers [2]. During the recent years, problems concerning the automatic interpretation of data from NDTs have received good attention and have simulated peer to peer interests in many industries like transportation. The use of Artificial Intelligence (AI) and Machine Learning (ML) techniques for the interpretation of NDT data can offer many advantages such as the improved speed and accuracy of analysis, especially for large-volume datasets. This study aims to train a dataset collected from GPR (2 GHz horn antenna) and the Curviameter deflection-based equipment using AI and ML algorithms to classify road flexible pavements based on their mechanical properties. Curviameter data are used as ground-truth measurements of pavement stiffness, whereas the GPR data provide geometric and physical attributes of the pavement structure. Several methods such as support vector machine (SVM), artificial neural network (ANN), and k nearest neighbours (KNN) are proposed and their performance in terms of accuracy of estimation of the strength and deformation properties of pavement layers are compared with each other as well as with the classical statistical methods. The results of this study can help road maintenance officials to identify and prioritise pavements at risk and make cost-effective and informed decisions for maintenance.

References

[1] Tosti, F., Bianchini Ciampoli, L., D’Amico, F. and Alani, A.M. (2019). Advances in the prediction of the bearing capacity of road flexible pavements using GPR. In: 10th International Workshop on Advanced GPR, European Association of Geoscientists & Engineers, pages 1-5.

[2] Plati, C., Loizos, A. & Gkyrtis, K. Assessment of Modern Roadways Using Non-destructive Geophysical Surveying Techniques. Surv Geophys 41, 395–430 (2020). 

[3] A. Benedetto, F. Tosti, Inferring bearing ratio of unbound materials from dielectric properties using GPR, in: Proceedings of the 2013 Airfield and Highway Pavement Conference: Sustainable and Efficient Pavements, June 2013, pp. 1336–1347.

[4] Tosti, F., Bianchini Ciampoli, L., D’Amico, F., Alani, A.M., Benedetto, A. (2018). An experimental-based model for the assessment of the mechanical properties of road pavements using GPR. Construction and Building Materials, Volume 165, pp. 966-974.

How to cite: Dinmohammadi, F., Bianchini Ciampoli, L., Tosti, F., Benedetto, A., and Alani, A. M.: On the use of Artificial Intelligence for classification of road pavements based on mechanical properties using ground-penetrating radar and deflection-based non-destructive testing data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1849, https://doi.org/10.5194/egusphere-egu22-1849, 2022.

EGU22-2166 | Presentations | GI2.2

Attenuation-compensated reverse-time migration of waterborne GPR based on attenuation coefficient estimation 

Ruiqing Shen, Yonghui Zhao, Hui Cheng, and Shuangcheng Ge

To the waterborne ground-penetrating radar detection, reverse-time migration (RTM) method can image the structure of the bottom of the water and locate the buried bodies. However, the image quality is limited by the attenuation of electromagnetic waves. How to compensate the attenuation becomes a critical problem. Some RTM methods related to the attenuation-compensated have been developed in recent years. We use the attenuation-compensated RTM based on the minus conductivity. However, the method is limited by the estimation of the attenuation coefficient. Here, we propose an attenuation-coefficient estimation method based on the centroid frequency downshift method (CFDS). In EM attenuation tomography, the centroid frequency downshift method works for attenuation estimation. Compared with the CFDS method in tomography, our proposal is based on the centroid frequency of the bottom-interface of water instead of the source wavelet. Thus, we can avoid the problem of the unknown source wavelet. The method is based on two assumptions: 1) GPR data can be regarded as zero-offset records. 2) Reflections from underwater interfaces are independent of frequency. In addition, the formula about the attenuation coefficient shows when the ratio between the conductivity and the product of the dielectric constant and the angular frequency is greater than one, the attenuation coefficient tends to be a constant. This does not meet the assumption that the attenuation coefficient is linearly related to frequency. We will select a proper frequency range to meet the linear relation by the spectral ratio method. Because the ratio of the signal spectrum of the bottom interface to the spectrum of the underwater interface is consistent with the change of the attenuation coefficient with frequency. Then, the CFDS method will acquire a linear attenuation coefficient with the frequency. Finally, we choose half of the central frequency to acquire the estimated attenuation coefficient. We design a layered waterborne GPR detection model, the conductivity of the silt layer varies between 0.1 and 0.01. The error of the conductivity estimation is below 10%. After acquiring the attenuation coefficient, the attenuation-compensated RTM works correctly and effectively.

How to cite: Shen, R., Zhao, Y., Cheng, H., and Ge, S.: Attenuation-compensated reverse-time migration of waterborne GPR based on attenuation coefficient estimation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2166, https://doi.org/10.5194/egusphere-egu22-2166, 2022.

EGU22-2253 | Presentations | GI2.2

An approach to integrate GPR thickness variability and roughness level into pavement performance evaluation 

Christina Plati, Andreas Loizos, and Konstantina Georgouli

It is a truism that pavements deteriorate due to the combined effects of traffic loads and environmental conditions. The manner or ability of a road to meet the demands of traffic and the environment and to provide at least an acceptable level of performance to road users throughout its life is referred to as pavement performance. An important indicator of pavement performance is ride quality. This is a rather subjective measure of performance that depends on (i) the physical properties of the pavement surface, (ii) the mechanical properties of the vehicle, and (iii) the acceptance of the perceived ride quality by road users. Due to the subjectivity of ride quality assessment, many researchers have worked in the past to develop an objective indicator of pavement quality. The International Roughness Index (IRI) is considered a good indicator of pavement performance in terms of road roughness. It was developed to be linear, transferable, and stable over time and is based on the concept of a true longitudinal profile. Following the identification and quantification of ride quality by the IRI, pavement activities include the systematic collection of roughness data in the form of the IRI using advanced laser profilers, either to "accept" an as-built pavement or to monitor and evaluate the functional condition of an in-service pavement.

On the other hand, pavement performance can vary significantly due to variations in layer thickness, primarily due to the construction process and quality control methods used. Even if a uniform design thickness is specified for a road section, the actual thickness may vary. It is expected that the layer thickness will have some probability distribution, with the highest density being around the target thickness. Information on layer thickness is usually obtained from as-built records, from coring or from Ground Penetrating Radar (GPR) surveys. GPR is a powerful measurement system that provides pavement thickness estimates with excellent data coverage at travel speeds. It can significantly improve pavement structure estimates compared to data from as-built plans. In addition, GPR surveys are fast, cost effective, and non-destructive compared to coring.

The present research developed a sensing approach that extends the capability of GPR beyond its ability to estimate pavement thickness. Specifically, the approach links GPR thickness to IRI based on the principle that a GPR system and a laser profiler are independent sensors that can be combined to provide a more complete image of pavement performance. To this end, field data collected by a GPR system and a laser profiler along highway sections are analyzed to evaluate pavement performance and predict future condition. The results show that thickness variations are related to roughness levels and specify the deterioration of the pavement throughout its lifetime.

How to cite: Plati, C., Loizos, A., and Georgouli, K.: An approach to integrate GPR thickness variability and roughness level into pavement performance evaluation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2253, https://doi.org/10.5194/egusphere-egu22-2253, 2022.

EGU22-2341 | Presentations | GI2.2 | Highlight

Monitoring of Bridges by Satellite Remote Sensing Using Multi-Source and Multi-Resolution Data Integration Techniques: a Case Study of the Rochester Bridge 

Valerio Gagliardi, Luca Bianchini Ciampoli, Fabrizio D’Amico, Maria Libera Battagliere, Sue Threader, Amir M. Alani, Andrea Benedetto, and Fabio Tosti

Monitoring of bridges and viaducts has become a priority for asset owners due to progressive infrastructure ageing and its impact on safety and management costs. Advancement in data processing and interpretation methods and the accessibility of Synthetic Aperture Radar (SAR) datasets from different satellite missions have contributed to raise interest for use of near-real-time bridge assessment methods. In this context, the Multi-temporal Interferometric Synthetic Aperture Radar (MT-InSAR) space-borne monitoring technique has proven to be effective for detection of cumulative surface displacements with a millimetre accuracy [1-3].

This research aims to investigate the viability of using satellite remote sensing for structural assessment of the Rochester Bridge in Rochester, Kent, UK. To this purpose, high-resolution SAR datasets are used as the reference information and complemented by additional data from different sensing technologies (e.g., medium-resolution SAR datasets and ground-based (GB) non-destructive testing (NDT)). In detail, high-resolution SAR products of the COSMO-SkyMed (CSK) mission (2017-2019) provided by the Italian Space Agency (ASI) in the framework of the Project “Motib - ID 742”, approved by ASI, are processed using a MT-InSAR approach.

The method allowed to identify several Persistent Scatterers (PSs) – which have been associated to different structural elements (e.g., the bridges piers) over the four main bridge decks – and monitor bridge displacements during the observation time. The outcomes of this study demonstrate that information from the use of high-resolution InSAR data can be successfully integrated to datasets of different resolution, scale and source technology. Compared to stand-alone technologies, a main advantage of the proposed approach is in the provision of a fully-comprehensive (i.e., surface and subsurface) and dense array of information with a larger spatial coverage and a higher time acquisition frequency. This results in a more effective identification and monitoring of decays at reduced costs, paving the way for implementation into next generation Bridge Management Systems (BMSs).

Acknowledgements: This research is supported by the Italian Ministry of Education, University and Research under the National Project “EXTRA TN”, PRIN2017, Prot. 20179BP4SM. Funding from MIUR, in the frame of the“Departments of Excellence Initiative 2018–2022”,attributed to the Department of Engineering of Roma Tre University, is acknowledged.Authors would also like to acknowledge the Rochester Bridge Trust for supporting research discussed in this paper. The COSMO-SkyMed (CSK) products - ©ASI- are provided by the Italian Space Agency (ASI) under a license to use in the framework of the Project “ASI Open-Call - Motib (ID 742)” approved by ASI.

References

[1] Gagliardi V., Bianchini Ciampoli L., D'Amico F., Alani A. M., Tosti F., Battagliere M. L., Benedetto A., “Bridge monitoring and assessment by high-resolution satellite remote sensing technologies”, Proc. SPIE 11525, SPIE Future Sensing Technologies. 2020. doi: 1117/12.2579700

[2] Jung, J.; Kim, D.-j.; Palanisamy Vadivel, S.K.; Yun, S.-H. "Long-Term Deflection Monitoring for Bridges Using X and C-Band Time-Series SAR Interferometry". Remote Sens. 2019

[3] Gagliardi V., Bianchini Ciampoli L., D'Amico F., Tosti F., Alani A. and Benedetto A. “A Novel Geo-Statistical Approach for Transport Infrastructure Network Monitoring by Persistent Scatterer Interferometry (PSI)”. In: 2020 IEEE Radar Conference, Florence, Italy, 2020, pp. 1-6, doi: 10.1109/RadarConf2043947.2020.9266336

How to cite: Gagliardi, V., Bianchini Ciampoli, L., D’Amico, F., Battagliere, M. L., Threader, S., Alani, A. M., Benedetto, A., and Tosti, F.: Monitoring of Bridges by Satellite Remote Sensing Using Multi-Source and Multi-Resolution Data Integration Techniques: a Case Study of the Rochester Bridge, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2341, https://doi.org/10.5194/egusphere-egu22-2341, 2022.

EGU22-2533 | Presentations | GI2.2

Monitoring of Airport Runways by Satellite-based Remote Sensing Techniques: a Geostatistical Analysis on Sentinel 1 SAR Data 

Valerio Gagliardi, Sebastiano Trevisani, Luca Bianchini Ciampoli, Fabrizio D’Amico, Amir M. Alani, Andrea Benedetto, and Fabio Tosti

Maintenance of airport runways is crucial to comply with strict safety requirements for airport operations and air traffic management [1]. Therefore, monitoring pavement surface defects and irregularities with a high temporal frequency, accuracy and spatial density of information becomes strategic in airport asset management [2-3]. In this context, Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) techniques are gaining momentum in the assessment and health monitoring of infrastructure assets, proving their viability for the long-term evaluation of ground scatterers. However, the implementation of C-band SAR data as a routine tool in Airport Pavement Management Systems (APMSs) for the accurate measurement of differential displacements on runways is still an open challenge [4]. This research aims to demonstrate the viability of using medium-resolution (C-band) SAR products and their contribution to improve current maintenance strategies in case of localised foundation settlements in airport runways. To this purpose, Sentinel-1A SAR products, available through the European Space Agency (ESA) Copernicus Program, were acquired and processed to monitor displacements on “Runway n.3” of the “L. Da Vinci International Airport” in Fiumicino, Rome, Italy.A geostatistical study is performed for exploring the spatial data structure and for the interpolation of the Sentinel-1A SAR data in correspondence of ground control points.The analysis provided ample information on the spatial continuity of the Sentinel 1 data, also in comparison with the high-resolution COSMO-SkyMed and the ground-based topographic levelling data, taken as the benchmark.Furthermore, a comparison between the MT-InSAR outcomes from the Sentinel-1A SAR data, interpolated by means of Ordinary Kriging, and the ground-truth topographic levelling data demonstrated the accuracy of the Sentinel 1 data. Results support the effectiveness of using medium-resolution InSAR data as a continuous and long-term routine monitoring tool for millimetre-scale displacements in airport runways. Outcomes of this study can pave the way for the development of more efficient and sustainable maintenance strategies for inclusion in next-generation APMSs.  

Acknowledgments and fundings: The authors acknowledge the European Space Agency (ESA), for providing the Sentinel 1 SAR products for the development of this research. The COSMO-SkyMed Products—©ASI (Italian Space Agency)- are delivered by ASI under the license to use.This research falls within the National Project “EXTRA TN”, PRIN 2017, supported by MIUR. The authors acknowledge funding from the MIUR, in the frame of the “Departments of Excellence Initiative 2018–2022”, attributed to the Department of Engineering of Roma Tre University

 References

[1]Gagliardi V., Bianchini Ciampoli L., D'Amico F., Tosti F., Alani A. and Benedetto A. “A Novel Geo-Statistical Approach for Transport Infrastructure Network Monitoring by Persistent Scatterer Interferometry (PSI)”. In: 2020 IEEE Radar Conference, Florence, Italy, 2020, pp. 1-6

[2]Gagliardi V, Bianchini Ciampoli L, Trevisani S, D’Amico F, Alani AM, Benedetto A, Tosti F. "Testing Sentinel-1 SAR Interferometry Data for Airport Runway Monitoring: A Geostatistical Analysis". 2021; 21(17):5769. https://doi.org/10.3390/s21175769

[3]Gao, M.; Gong, H.; Chen, B.; Zhou, C.; Chen, W.; Liang, Y.; Shi, M.; Si, Y. "InSAR time-series investigation of long-term ground displacement at Beijing Capital International Airport, China". Tectonophysics 2016, 691, 271–281.

[4]Department of Transportation Federal Aviation Administration (FAA), Advisory Circular 150/5320-6F, Airport Pavement Design and Evaluation, 2016

How to cite: Gagliardi, V., Trevisani, S., Bianchini Ciampoli, L., D’Amico, F., Alani, A. M., Benedetto, A., and Tosti, F.: Monitoring of Airport Runways by Satellite-based Remote Sensing Techniques: a Geostatistical Analysis on Sentinel 1 SAR Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2533, https://doi.org/10.5194/egusphere-egu22-2533, 2022.

EGU22-2712 | Presentations | GI2.2

Quality assessment in railway ballast by integration of NDT methods and remote sensing techniques: a study case in Salerno, Southern Italy 

Luca Bianchini Ciampoli, Valerio Gagliardi, Fabrizio D'Amico, Chiara Clementini, Daniele Latini, and Andrea Benedetto

Maintenance and rehabilitation policies represent a task of paramount importance for managers and administrators of railway networks to maintain the highest standards of transport safety while limiting as much as possible the costs of maintenance operations.

To this effect, high-productivity survey methods become crucial as they allow for timely recognition of the quality of the asset elements, among which the ballast layers are the most likely to undergo rapid deterioration processes. Particularly, Ground Penetrating Radar (GPR) has received positive feedback from researchers and professionals due to the capability of detecting signs of deterioration within ballasted trackbeds that are not recognizable by a visual inspection at the surface, through high-productivity surveys. On the other hand, satellite-based surveys are nowadays being increasingly applied to the monitoring of transport assets. Techniques such as Multi-temporal Interferometric Synthetic Aperture Radar (MT-InSAR) allows evaluating potential deformations suffered by railway sections and their surroundings by analyzing phase changes between multiple images of the same area acquired at progressive times. 

For both of these techniques, despite the wide recognition by the field-related scientific literature, survey protocols and data processing standards for the detection and classification of the quality of ballast layers are still missing. In addition, procedures of integration and data fusion between GPR and InSAR datasets are still very rare.

The present study aims at demonstrating the viability of the integration between these two survey methodologies for a more comprehensive assessment of the condition of ballasted track-beds over a railway stretch. Particularly, a traditional railway section going from Cava de’ Tirreni to Salerno, Campania (Italy), was subject to both GPR and MT-InSAR inspections. An ad hoc experimental setup was realized to fix horn antennas with different central frequencies to an actual inspection convoy that surveyed the railway stretch in both the travel directions. Time-frequency methods were applied to the data to detect subsections of the railway affected by the poor quality of ballast (i.e. high rate of fouling). In parallel, a two-years MT-InSAR analysis was conducted to evaluate possible deformations that occurred to the railway line in the period before the GPR test. In addition, results from both the analyses were compared to the reports from visual inspections as provided by the railway manager.

The results of the surveys confirm the high potential of GPR in detecting the fouling condition of the ballast layers at various stages of severity. The integration of this information to the outcomes of InSAR analysis allows for identifying whether the deterioration of the track-beds is related to poorly bearing subgrades or rather to excessive stresses between the aggregates resulting in their fragmentation.

Acknowledgments

This research is supported by the Italian Ministry of Education, University, and Research under the National Project “EXTRA TN”, PRIN2017, Prot. 20179BP4SM. Funding from MIUR, in the frame of the“Departments of Excellence Initiative 2018–2022”, attributed to the Department of Engineering of Roma Tre University, is acknowledged. The authors would also like to express their gratitude to RFI S.p.a. in the person of Eng. Pasquale Ferraro for the valuable support to the tests.

How to cite: Bianchini Ciampoli, L., Gagliardi, V., D'Amico, F., Clementini, C., Latini, D., and Benedetto, A.: Quality assessment in railway ballast by integration of NDT methods and remote sensing techniques: a study case in Salerno, Southern Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2712, https://doi.org/10.5194/egusphere-egu22-2712, 2022.

Detecting decay in tree trunks is essential in considering tree health and safety. Continual monitoring of tree trunks is possible using a digital model, which can contain incremental assessment data on tree health. Researchers have previously employed non-destructive techniques, for instance, laser scanning, acoustics, and Ground Penetrating Radar (GPR) to study both the external and internal physical dimensions of objects and structures [1], including tree trunks [2]. Light Detection and Ranging (LiDAR) technology is also continually employed in infrastructure and asset management to generate models and to detect surface displacements with millimeter accuracy [3]. Nevertheless, the scanning of structures using these existing state-of-the-art technologies can be time consuming, technical, and expensive.

This work investigates the design and implementation of a smartphone app for scanning tree trunks to generate a 3D digital model for later visualization and assessment. The app uses LiDAR technology, which has recently become available in smart devices, for instance, the Apple iPhone 12+ and the iPad Pro. With the prevalence of internet-of-things (IoT) sensors, digital twins are being increasingly used in a variety of industries, for example, architecture and manufacturing. A digital twin is a digital representation of an existing physical object or structure. With our app, a digital twin of a tree can be developed and maintained by continually updating data on its dimensions and internal state of decay. Further, we can situate and visualize tree trunks as digital objects in the real world using augmented reality, which is also possible in modern smart devices. We previously investigated tree trunks using GPR [2] to generate tomographic maps, to denote level of decay. We aim to adopt a data integration and fusion approach, using such existing (and incremental GPR data) and an external LiDAR scan to gain a full 3D ‘picture’ of tree trunks.

We intend to validate our app against state-of-the-art techniques, i.e., laser scanning and photogrammetry. With the ability to scan tree trunks within reasonable parameters of accuracy, the app can provide a relatively low-cost environmental modelling and assessment solution for researchers and experts.

 

Acknowledgments: Sincere thanks to the following for their support: Lord Faringdon Charitable Trust, The Schroder Foundation, Cazenove Charitable Trust, Ernest Cook Trust, Sir Henry Keswick, Ian Bond, P. F. Charitable Trust, Prospect Investment Management Limited, The Adrian Swire Charitable Trust, The John Swire 1989 Charitable Trust, The Sackler Trust, The Tanlaw Foundation, and The Wyfold Charitable Trust.

 

References

[1] Alani A. et al., Non-destructive assessment of a historic masonry arch bridge using ground penetrating radar and 3D laser scanner. IMEKO International Conference on Metrology for Archaeology and Cultural Heritage Lecce, Italy, October 23-25, 2017.

[2] Tosti et al., "The Use of GPR and Microwave Tomography for the Assessment of the Internal Structure of Hollow Trees," in IEEE Transactions on Geoscience and Remote Sensing, Doi: 10.1109/TGRS.2021.3115408.

[3] Lee, J et al., Long-term displacement measurement of bridges using a LiDAR system. Struct Control Health Monit. 2019; 26:e2428.

How to cite: Uzor, S., Tosti, F., and Alani, A. M.: Low-cost scanning of tree trunks for analysis and visualization in augmented reality using smartphone LiDAR and digital twins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3247, https://doi.org/10.5194/egusphere-egu22-3247, 2022.

The need to monitor and evaluate the impact of natural phenomena on structures, infrastructures, as well as on the natural environment, in recent years, plays a role of considerable importance for society also due to the continuous occurrence of "catastrophic events" which recently faster change our Planet.

Innovation and research have allowed a profound change in the data acquisition and acquisitions methodology coming to develop increasingly complex and innovative technologies. From an application point of view, remote sensing gives the possibility to easily manage the layer information which is indispensable for the best characterization of the environment from a numerical and a chemical-physical point of view.

NeMeA Sistemi srl, observant to the environment and its protection for years, began to study it using RADAR / SAR (Synthetic Aperture RADAR) data thanks to the opportunity to use in the best way the COSMO-SkyMed data through the tender Open Call for SMEs (Small and Medium Enterprises) of the Italian Space Agency in 2015.

Since then, NeMeA Sistemi srl has started a highly focused and innovative training that led us to observe the Earth in a new way. The path undertaken in NeMeA Sistemi srl is constantly growing and allowed us to know the RADAR / SAR data and the enormous potential.

The COSMO-SkyMed data provided is treated, processed and transformed by providing various information, allows you to identify changes, classify objects and artifacts measuring them.

In this context, NeMeA Sistemi srl in 2016 proposed a first project for the monitoring of illegal buildings in the Municipality of Ventimiglia (Liguria), with positive results. In this context, the final product was obtained with classic standard classification techniques of the SAR data.

 Following this positive experience, NeMeA Sistemi srl applied also to the regional call issued by Sardegna Ricerche for the Sardinia Region where the source of funding is the European Regional Development Fund (ERDF) 2014-2020.

The SardOS project (Sardinia Observed from Space), proposed by NeMeA Sistemi srl, aims to monitor and safeguard environmental and anthropogenic health in the territory of 4 Sardinian municipalities (Alghero, Capoterra, Quartu and Arzachena), also identifying the coast profiles, the evolutionary trend of sediments in the riverbed and buildings not present in the land registry. For environmental monitoring purposes, COSMO-SkyMed data are exploited and combined with bathymetric measurements acquired using the Hydra aquatic drone owned by NeMeA Sistemi srl. SAR data were processed using innovative specific territorial analysis algorithms in urban environment.

After these successful cases studies, which allowed the development of new services for the territorial monitoring and control, NeMeA Sistemi srl is working on a new project, 3xA (Creation of Machine Learning and Deep Learning algorithms dedicated to pattern recognition in SAR data). By exploiting Artificial Intelligence, the implemented algorithms use innovative unsupervised techniques to identify any changes.

The objective of this document is to provide an overview of the experience gained in NeMeA Sistemi srl, the value-added products and innovative services developed in the company aimed at environmental monitoring, the prevention of dangers and natural risks.

How to cite: Pennino, I.: A strategy of territorial control: from the standard comparison techniques to the Advanced Unsupervised Deep Learning Change Detection in high resolution SAR images, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3799, https://doi.org/10.5194/egusphere-egu22-3799, 2022.

EGU22-4437 | Presentations | GI2.2

Rebar corrosion monitoring with a multisensor non-destructive geophysical techniques. 

Enzo Rizzo, Giacomo Fornasari, Luigi Capozzoli, Gregory De Martino, and Valeria Giampaolo

Rebar Corrosion is one of the main causes of deterioration of engineering reinforced structure. This degradation reduces the service life and durability of the structures. Such degradation can result in the collapse of engineering structures. When the first cracks are noticed on the concrete surface, corrosion has generally reached an advanced stage and maintenance action is required. The early detection of rebar corrosion of bridges, tunnel, buildings and other civil engineering structures is important to reduce the expensive cost to repair the deteriorated structure. Several techniques have been developed for understanding the mechanism and kinetics of the corrosion of rebar, but the paper defines the interest of combining several NDT for field inspection to overcome the limitation of measuring instantaneous corrosion rates and to improve the estimation of the service life of RC structures. Non-destructive testing and evaluation of the rebar corrosion is a major issue for predicting the service life of reinforced concrete structures.

This paper introduces a laboratory test, that was performed at Geophysical Laboratory of Ferrara University. The test consisted in a multisensor application concerning rebar corrosion monitoring using different geophysical methods on a concrete sample of about 50 x 30 cm with one steel rebar of 10 mm diameter. An accelerating reinforcement bar corrosion using direct current (DC) power supply with 5% sodium chloride (NaCl) solution was used to induce rebar corrosion. The 2GHz GPR antenna by IDS, the ERT with Abem Terrameter and Self-Potential with Keithley multivoltmeter at high impedance were used for rebar corrosion monitoring. A multisensor approach should reduce the errors resulting from measurements, and improve synergistically the estimation of service life of the RC.

Each technique provided specific information, but a data integration method used in the operating system will further improve the overall quality of diagnosis. The collected data were used for an integration approach to obtain an evolution of the phenomenon of corrosion of the reinforcement bar. All the three methods were able to detect the physical parameter variation during the corrosion phenomena, but more attention is necessary on natural corrosion, that is a slow process and the properties of the experimental steel–concrete interface may not be representative of natural corrosion. However, each of these geophysical methods possesses certain advantages and limitations, therefore a combination of these geophysical techniques, with an multisensor approach is recommended to use to obtain the corrosion condition of steel and the condition of concrete cover.  Moreover, extrapolating laboratory results performed with a single rebar to a large structure with interconnected rebars thus remains challenging. Therefore, during the next experiments, special care must be taken regarding the design and preparation of the samples to obtain meaningful information for field application.

How to cite: Rizzo, E., Fornasari, G., Capozzoli, L., De Martino, G., and Giampaolo, V.: Rebar corrosion monitoring with a multisensor non-destructive geophysical techniques., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4437, https://doi.org/10.5194/egusphere-egu22-4437, 2022.

EGU22-4826 | Presentations | GI2.2

A 24 GHz MIMO radar for the autonomous navigation of unmanned surface vehicles 

Giovanni Ludeno, Gianluca Gennarelli, Carlo Noviello, Giuseppe Esposito, Ilaria Catapano, and Francesco Soldovieri

In the last years, unmanned surface vehicles (USVs) in marine environment have attracted considerable interest since they are flexible observation platforms suitable to operate in remote areas on demand. Accordingly, their usage has been proposed in several contexts such as research activities, military operations, environmental monitoring and oil exploration [1]. However, most of current USV remote control techniques are based on human-assisted technology thus a fully autonomous USV system is still an open issue [2].

The safety of the vehicle and the ability to complete the mission depends crucially on the capability of detecting objects on the sea surface, which is necessary for collision avoidance. Anti-collision systems for USVs typically require measurements collected from multiple sensors (e.g. Lidar, cameras, etc.), where each sensor has its own advantages and disadvantages in terms of resolution, field of view (FoV), operative range and so on [3].

Among the available sensing technologies, radar is capable of operating regardless of weather and visibility conditions, has moderate costs and can be easily adapted to operate within the marine environment. Furthermore, radar is characterized by an excellent coverage and high resolution along the range coordinate and it is also able to guarantee a 360° FoV in the horizontal plane.

Nautical radars are the most popular solutions to detect floating targets on the sea surface; however, they are bulky and not always effective in detecting small objects located very close to the radar.

This contribution investigates the applicability of a compact and lightweight 24 GHz multiple-input multiple-output (MIMO) radar originally developed for automotive applications to localize floating targets at short ranges (from tens to few hundreds of meters). In this frame, we propose an ad-hoc signal processing strategy combining MIMO technology, detection, and tracking algorithms to achieve target localization and tracking in a real-time mode. A validation of the proposed signal processing chain is firstly performed thanks to numerical simulations. After, preliminary field tests carried out in the marine environment are presented to assess the performance of the radar prototype and of the related signal processing.

 

References

  • [1] Zhixiang et al. "Unmanned surface vehicles: An overview of developments and challenges", Annual Reviews in Control, vol. 41, pp. 71-93, 2016
  • [2] Caccia, M. Bibuli, R. Bono, G. Bruzzone, “Basic navigation, guidance and control of an unmanned surface vehicle”, Autonomous Robots, vol. 25, no. 4, pp. 349-365, 2008
  • [3] Robinette, M. Sacarny, M. DeFilippo, M. Novitzky, M. R. Benjamin, “Sensor evaluation for autonomous surface vehicles in inland waterways”, Proc. IEEE OCEANS 2019, pp. 1-8, 2019.

How to cite: Ludeno, G., Gennarelli, G., Noviello, C., Esposito, G., Catapano, I., and Soldovieri, F.: A 24 GHz MIMO radar for the autonomous navigation of unmanned surface vehicles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4826, https://doi.org/10.5194/egusphere-egu22-4826, 2022.

EGU22-4912 | Presentations | GI2.2

Multiples suppression scheme of waterborne GPR data 

Yonghui Zhao, Ruiqing Shen, and Hui Cheng

Ground penetrating radar (GPR) is a geophysical method that uses high frequency electromagnetic waves to detect underground or internal structures of objects. It has been widely used in the Geo-engineering and environment detection. In recent years, GPR has played an increasingly important role in shallow underwater structure survey due to its advantages of economy, high efficiency and high accuracy. However, due to the strong reflection coefficients of water surface and bottom for electromagnetic waves, there are multiples in the GPR profile acquired in waters, which will reduce the signal-to-noise ratio of the data and even lead to false imaging, finally seriously affect the reliability of the interpretation result. With the increasing requirement of high-precise GPR detection in waters, multiple suppression has become an essential issue in expanding the application fields of GPR. In order to suppress multiple waves in waterborne GPR profile, a novel multiple wave suppression method based on the combination scheme of the predictive deconvolution and free surface multiple wave suppression (SRME). Based on the validity test of one-dimensional data, the adaptive optimizations of these two methods are carried out according to the characteristics of GPR data in waters. First, the prediction step of predictive deconvolution can be determined by picking up the bottom reflection signal. Second, the water layer information provided by the bottom reflection is used in continuation from the surface to the bottom to suppress the internal multiples. The numerical model and real data test results show that each single method can suppress most of the multiples of the bottom interface and the combination strategy can further remove the additional residues. The research provides a basis for the precise interpretation of GPR data in hydro-detection.

How to cite: Zhao, Y., Shen, R., and Cheng, H.: Multiples suppression scheme of waterborne GPR data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4912, https://doi.org/10.5194/egusphere-egu22-4912, 2022.

EGU22-4914 | Presentations | GI2.2

Sensing roadway surfaces for a non-destructive assessment of pavement damage potential 

Konstantinos Gkyrtis, Andreas Loizos, and Christina Plati

Modern roadways provide road users with both a comfortable and safe ride to their destinations. Increases in traffic demands and maximum allowable loads imply that roadway authorities should also care for the structural soundness of pavements. In parallel, budgetary limitations and frequent road closures for rehabilitation activities, especially in heavy-duty motorways, might guide the related authorities to focus their strategies on the preservation of pavements functional performance. However, structural issues concerning pavement damage remain on the forefront, as pavement’s service life extends beyond its design life; thus structural condition assessment is required to ensure pavement sustainability in the long-term.

 

Non-Destructive Testing (NDT) has played a major role during condition monitoring and evaluation of rehabilitation needs. Together with input from visual inspections and/or sample destructive testing (e.g. coring), NDT data help to define indicators and threshold values that assist the related decision-making for pavement condition assessment. The most indicative tool for structural evaluation is the Falling Weight Deflectometer (FWD) that senses roadway surfaces through geophones recording load-induced deflections at various locations. Additional geophysical inspection data with the Ground Penetrating Radar (GRP) is used to estimate pavement’s stratigraphy. Integrating the above sensing data enables the estimation of pavement’s performance and its damage potential.

 

To this end, a major challenge that pavement engineers face, concerns the assumptions made about the mechanical characterization of pavement materials. Asphalt mixtures, located on the upper pavement layers, behave in a viscoelastic mode because of temperature- and loading frequency- dependency, whereas in the contrary, simplified assumptions for linear elastic materials are most commonly made during the conventional NDT analysis. In this research, an integration of mainly NDT data and sample data from cores extracted in-situ is followed to comparatively estimate the long-term pavement performance through internationally calibrated damage models considering different assumptions for asphalt materials. Two damage modes are considered including bottom-up and top-down fatigue cracks that are conceptually perceived as alligator cracks and longitudinal cracks respectively alongside a roadway’s surface. As part of an ongoing research for the long-term pavement condition monitoring, data from a new pavement was considered at this stage indicating a promising capability of NDT data towards damage assessment.

 

Overall, this study aims to demonstrate the power of pavement sensing data towards structural health monitoring of roadways pinpointing the significance of database development for a rational management throughout a roadway’s service life. Furthermore, data from limited destructive testing enriches the pavement evaluation processes with purely mechanistic perspectives thereby paving the way for developing integrated protocols with improved accuracy for site investigations, especially at project-level analysis, where rehabilitation design becomes critical.

How to cite: Gkyrtis, K., Loizos, A., and Plati, C.: Sensing roadway surfaces for a non-destructive assessment of pavement damage potential, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4914, https://doi.org/10.5194/egusphere-egu22-4914, 2022.

EGU22-5731 | Presentations | GI2.2

Ultrasonic Scattering and Absorption Imaging for the Reinforced Concrete using Adjoint Envelope Tomography 

Tuo Zhang, Christoph Sens-Schönfelder, Niklas Epple, and Ernst Niederleithinger

Seismic and ultrasound tomography can provide rich information about spatial variations of elastic properties inside a material rendering this method ideal for non-destructive testing. These tomographic methods primarily use direct and reflected waves, but are also strongly affected by waves scattering at small-scale structures below the resolution limit. As a consequence, conventional tomography has the ability to unveil the deterministic large-scale structure only, rendering scattered waves imaging noise. To image scattering and absorption properties, we presented the adjoint envelope tomography (AET) method that is based on a forward simulation of wave envelopes using Radiative Transfer Theory and an adjoint (backward) simulation of the envelope misfit, in full analogy to full-waveform inversion (FWI). In this algorithm, the forward problem is solved by modelling the 2-D multiple nonisotropic scattering in an acoustic medium with spatially variable heterogeneity and attenuation using the Monte-Carlo method. The fluctuation strength ε and intrinsic quality factor Q-1 in the random medium are used to describe the spatial variability of scattering and absorption, respectively. The misfit function is defined as the differences between the full squared observed and modelled envelopes. We derive the sensitivity kernels corresponding to this misfit function that is minimized during the iterative adjoint inversion with the L-BFGS method. This algorithm has been applied in some numerical tests (Zhang et al., 2021). In the present work, we show real data results from an ultrasonic experiment conducted in a reinforced concrete specimen. The later coda waves of the envelope processed from the 60 KHz ultrasonic signal are individually used for intrinsic attenuation inversion whose distribution has similarity to the temperature distribution of the concrete block. Based on the inversion result of intrinsic attenuation, scattering strength is inverted from early coda waves separately, which successfully provides the structure of the small-scale heterogeneity in the material. The resolution test shows that we recover the distribution of heterogeneity reasonably well.

How to cite: Zhang, T., Sens-Schönfelder, C., Epple, N., and Niederleithinger, E.: Ultrasonic Scattering and Absorption Imaging for the Reinforced Concrete using Adjoint Envelope Tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5731, https://doi.org/10.5194/egusphere-egu22-5731, 2022.

EGU22-6168 | Presentations | GI2.2

An investigation into road trees’ root systems through geostatistical analysis of GPR data 

Livia Lantini, Sebastiano Trevisani, Valerio Gagliardi, Fabio Tosti, and Amir M. Alani

Street trees are a critical asset for the urban environment due to the variety of environmental and social benefits provided [1]. However, the conflicting coexistence of tree root systems with the built environment, especially with road infrastructure, frequently results in extensive damage, such as the uplifting and cracking of sidewalks and curbs, endangering pedestrians, cyclists, and road drivers’ safety.

Within this context, ground penetrating radar (GPR) is gaining recognition as an accurate non-destructive testing (NDT) method for tree roots’ assessment and mapping [2]. Nevertheless, the investigation methods developed so far are often inadequate for application on street trees, as these are often difficult to access. Recent studies have focused on implementing new survey and processing techniques for rapid tree root assessment based on combined time-frequency analyses of GPR data [3].  

This research also explores the adoption of a geostatistical approach for the spatial data analysis and interpolation of GPR data. The radial development of roots and the complexity of root network constitute a challenging setting for the spatial data analysis and the recognition of specific spatial features.

Preliminary results are therefore presented based on a geostatistical analysis of GPR data. To this end, 2-D GPR outputs (i.e., B-scans and C-scans) were analysed to quantify the spatial correlation amongst radar amplitude reflection features and their anisotropy, leading to a more reliable detection and mapping of tree roots. The proposed processing system could be employed for investigating trees difficult to access, such as road trees, where more comprehensive analyses are difficult to implement. Results' interpretation has shown the viability of the proposed analysis and will pave the way to further investigations.

 

Acknowledgements

The authors would like to express their sincere thanks and gratitude to the following trusts, charities, organisations and individuals for their generosity in supporting this project: Lord Faringdon Charitable Trust, The Schroder Foundation, Cazenove Charitable Trust, Ernest Cook Trust, Sir Henry Keswick, Ian Bond, P. F. Charitable Trust, Prospect Investment Management Limited, The Adrian Swire Charitable Trust, The John Swire 1989 Charitable Trust, The Sackler Trust, The Tanlaw Foundation, and The Wyfold Charitable Trust.

 

References

[1]         Tyrväinen, L., Pauleit, S., Seeland, K., & de Vries, S., 2005. "Benefits and uses of urban forests and trees". In: Urban Forests and Trees. Springer, Berlin, Heidelberg.

[2]         Lantini, L., Tosti, F., Giannakis, I., Zou, L., Benedetto, A. and Alani, A. M., 2020. "An Enhanced Data Processing Framework for Mapping Tree Root Systems Using Ground Penetrating Radar," Remote Sensing 12(20), 3417.

[3]         Lantini, L., Tosti, F., Zou, L., Ciampoli, L. B., & Alani, A. M., 2021. "Advances in the use of the Short-Time Fourier Transform for assessing urban trees’ root systems." Earth Resources and Environmental Remote Sensing/GIS Applications XII. Vol. 11863. SPIE, 2021.

How to cite: Lantini, L., Trevisani, S., Gagliardi, V., Tosti, F., and Alani, A. M.: An investigation into road trees’ root systems through geostatistical analysis of GPR data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6168, https://doi.org/10.5194/egusphere-egu22-6168, 2022.

EGU22-6251 | Presentations | GI2.2

Algorithms fusion for near-surface geophysical survey 

Yih Jeng, Chih-Sung Chen, and Hung-Ming Yu

The near-surface geophysical methods have been widely applied to investigations of shallow targets for scientific and engineering research. Various data processing algorithms are available to help visualize targets, data interpretation, and finally, achieve research goals.

Most of the available algorithms are Fourier-based with linear stationary assumptions. However, the real data are rarely the case and should be treated as nonlinear and non-stationary. In recent decades, a few newer algorithms are proposed for processing non-stationary, or nonlinear and non-stationary data, for instance, wavelet transform, curvelet transform, full-waveform inversion, Hilbert-Huang transform, etc. This progress is encouraging, but conventional algorithms still have many advantages, like strong theoretical bases, fast, and easy to apply, which the newer algorithms are short of.

In this study, we try to fuse both conventional and contemporary algorithms in near-surface geophysical methods. A cost-effective ground-penetrating radar (GPR) data processing scheme is introduced in shallow depth structure mapping as an example. The method integrates a nonlinear filtering technique, natural logarithmic transformed ensemble empirical mode decomposition (NLT EEMD), with the conventional pseudo-3D GPR data processing methods including background removal and migration to map the subsurface targets in 2D profile. The finalized pseudo-3D data volume is constructed by conventional linear interpolation. This study shows that the proposed technique could be successfully employed to locate the buried targets with minimal survey effort and affordable computation cost. Furthermore, the application of the proposed method is not limited to GPR data processing, any geophysical/engineering data with the similar data structure are applicable.

How to cite: Jeng, Y., Chen, C.-S., and Yu, H.-M.: Algorithms fusion for near-surface geophysical survey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6251, https://doi.org/10.5194/egusphere-egu22-6251, 2022.

EGU22-7009 | Presentations | GI2.2

Geoelectric data modeling using Mimetic Finite Difference Method 

Deepak Suryavanshi and Rahul Dehiya

Nondestructive imaging and monitoring of the earth's subsurface using the geoelectric method require reliable and versatile numerical techniques for solving differential equation that govern the method's physic. The discrete operator should encompass fundamental properties of the original continuum model and differential operator for a robust numerical algorithm. In geoelectric modeling, critical model properties are anisotropy, irregular geometry, and discontinuous physical properties, whereas vital continuum operator properties are symmetry, the positivity of solutions, duality, and self-adjointness of differential operators and exact mathematical identities of the vector and tensor calculus. In this study, to simulate the response, we use the Mimetic Finite Difference Method (MFDM), where the discrete operator is constructed based on the support operator [1]. The MFDM operator mimics the properties mentioned above for structured and unstructured grids [2]. It is achieved by enforcing the integral identities of the continuum divergence and gradient operator to satisfy the integral identities by discrete analogs. 

The developed algorithm's accuracy is benchmarked using the analytical responses of dyke models of various conductivity contrasts for pole-pole configuration. After verifying the accuracy of the scheme, further tests are conducted to check the robustness of the algorithm involving the non-orthogonality of the grids, which is essential for simulating response for rugged topography. The surface potential is simulated using structured grids for a three-layer model. Subsequently, the orthogonal girds are distorted using pseudo-random numbers, which follow a uniform distribution. To quantify the distortion, we calculated the angles at all grid nodes. The node angles emulate a Gaussian distribution. We characterize those grids as highly distorted, for which the angle at the grid node is outside 20 to 160 degrees interval. The numerical tests are conducted by varying degrees of grid distortion, such that the highly distorted cells are from 1% to 10% of the total cells. The maximum error in surface potential stays below 1.5% in all cases. Hence, the algorithm is very stable with grid distortion and consequently can model the response of a very complex model. Thus, the developed algorithm can be used to analyze geoelectrical data of complex geological scenarios such as rugged topography and anisotropic subsurface. 

[1] Winters, Andrew R., and Mikhail J. Shashkov. Support Operators Method for the Diffusion Equation in Multiple Materials. No. LA-UR-12-24117. Los Alamos National Lab.(LANL), Los Alamos, NM (United States), 2012.

[2] Lipnikov, Konstantin, Gianmarco Manzini, and Mikhail Shashkov. "Mimetic finite difference method." Journal of Computational Physics 257 (2014): 1163-1227.

How to cite: Suryavanshi, D. and Dehiya, R.: Geoelectric data modeling using Mimetic Finite Difference Method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7009, https://doi.org/10.5194/egusphere-egu22-7009, 2022.

EGU22-7547 | Presentations | GI2.2

Assessing Deformation Monitoring Systems For Supporting Structural Rehabilitation under Harsh Conditions 

Hans Neuner, Victoria Kostjak, Finn Linzer, Walter Loderer, Christian Seywald, Alfred Strauss, Matthias Rigler, and Markus Polt

This paper deals with the evaluation of four measuring systems for the detection of potential deformations that can occur during structural rehabilitation measures. For this purpose, a test object resembling the shape of a tunnel structure was constructed. The structural properties of this test object are discussed in the related paper by Strauss et. al submitted for the same session.

In the paper, the installed measuring systems are presented first. These are a lamella system based on fibre optics, an array of accelerometers, a digital image correlation system and a profile laser scanner based system. The operating principles of the systems are briefly introduced.

A long-term measurement on the object in an unloaded state, which extended over several weeks, enables statements about the capturing of temperature-related deformations, the temperature dependence of the measured values and drift effects of the investigated systems. Selective loading of the test object was generated via four screw rods and applied both in the elastic as well as in the plastic deformation range. This enabled knowledge gain regarding the precision and the sensitivity of the analysed measuring systems.

Environmental conditions may have a strong influence on the measurement values. The former can be determined by permanent installations on the structure and its operating conditions as well as by the undertaken rehabilitation measures. Representative for the first category we investigated the influence of magnetic fields and light conditions on the measuring systems. For the second category, strong dust formation and increased humidity were generated during a test procedure.

An assessment regarding data handling, including storage, transfer and processing, completes the investigation of the four measuring systems. A summarising evaluation concludes the article.

How to cite: Neuner, H., Kostjak, V., Linzer, F., Loderer, W., Seywald, C., Strauss, A., Rigler, M., and Polt, M.: Assessing Deformation Monitoring Systems For Supporting Structural Rehabilitation under Harsh Conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7547, https://doi.org/10.5194/egusphere-egu22-7547, 2022.

EGU22-8512 | Presentations | GI2.2

Verification of the performance of reinforced concrete profiles of alpine infrastructure systems assisted by innovative monitoring 

Alfred Strauss, Hans Neuner, Matthias Rigler, Markus Polt, Christian Seywald, Victoria Kostjak, Finn Linzer, and Walter Loderer

The verification of the structural behaviour of existing structures and its materials characteristics requires the application of tests and monitoring to gather information about the actual response. The comparison of the actual performance and the designed performance enables the verification of the design assumptions in terms of implied loads and materials resistance. In case of non-compliance of the designed with the current performance, the design assumptions need to be updated. The objective of this contribution is to provide a guidance for the verification of the performance of reinforced concrete profiles of alpine infrastructure systems like tunnels assisted by monitoring, testing and material testing.

The application of defined loads to a structure to verify its load carrying capacity is a powerful tool for evaluating existing structures. In particular, in this research different types of load tests are employed depending on the limit state which is being investigated on tunnel profiles, on the other hand, the system responses to validate the structural performance are recorded with monitoring systems innovative in tunnel systems, such as accelerometer arrays, fibre optic sensors, laser distance sensors and digital image correlation system, see also the related paper by Neuner et. al. In these studies we also pay special attention to the capabilities of Digital Image Correlation and Nonlinear Finite Element Analysis. Digital Image Correlation (often referred to as "DIC") is an easy-to-use optical method for measuring deformations on the surface of an object. The method tracks changes in the grayscale pattern in small areas called subsets) during deformation. 

Finally, we will present the process for the implementation and validation of proof loading concepts based on the mentioned monitoring information in order to derive the existing safety level by using advanced digital twin models.  

How to cite: Strauss, A., Neuner, H., Rigler, M., Polt, M., Seywald, C., Kostjak, V., Linzer, F., and Loderer, W.: Verification of the performance of reinforced concrete profiles of alpine infrastructure systems assisted by innovative monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8512, https://doi.org/10.5194/egusphere-egu22-8512, 2022.

EGU22-8594 | Presentations | GI2.2

Analysis of low-frequency drone-borne GPR for soil surface electrical conductivity mapping 

Kaijun Wu and Sébastien Lambot

In the VHF frequencies, the sensitivity of the reflection coefficient at the air-soil interface with respect to the soil electromagnetic properties, i.e., the dielectric permittivity and electrical conductivity, varies with frequency. The lower the frequency is, the lower the sensitivity to permittivity is and the larger the sensitivity to conductivity is. In this study, we investigated low-frequency drone-borne ground-penetrating radar (GPR) and full-wave inversion for soil surface electrical conductivity characterization. In order to have a good sensitivity to electrical conductivity, we operated in the 15-45 MHz frequency range. We conducted both numerical and field experiments, under the assumptions that the soil magnetic permeability is equal to the magnetic permeability of free space, and that the soil permittivity and conductivity are frequency-independent. Through the numerical experiments, we analyzed the sensitivity of the soil permittivity and electrical conductivity by plotting the objective function in the inverse problem. In addition, we analyzed the effects of modelling errors on the retrieval of the permittivity and conductivity. The results show that the soil electrical conductivity is sensitive enough to be characterized by the low-frequency drone-borne GPR. The depth of sensitivity was found to be around 0.5-1 m in the 15-45 MHz frequency range. Yet, the effects of permittivity cannot be neglected totally, especially for relatively wet soils. For validating our approach, we conducted field measurements with the drone-borne GPR and we compared results with electromagnetic induction (EMI) measurements considering two different offsets, i.e., 0.5 and 1 m, respectively. The lightweight GPR system consists of a handheld vector network analyzer (VNA), a 5-meter half-wave dipole antenna, a micro-computer stick, a GPS receiver, and a power bank. The good agreement in terms of absolute values and field structures between the GPR and EMI maps demonstrated the feasibility of the proposed low-frequency drone-borne GPR method, which appears thereby to be promising for precision agriculture applications.

How to cite: Wu, K. and Lambot, S.: Analysis of low-frequency drone-borne GPR for soil surface electrical conductivity mapping, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8594, https://doi.org/10.5194/egusphere-egu22-8594, 2022.

EGU22-8712 | Presentations | GI2.2

Estimation of point spread function for unmixing geological spectral mixtures 

Maitreya Mohan Sahoo, Arun Pattathal Vijayakumar, Ittai Herrmann, Shibu K. Mathew, and Alok Porwal

Geological materials are mixtures of different endmember constituents with most of them having particles smaller in size than the path length of incident light. The obtained spectral response (reflectance) from such mixtures is nonlinear which can be attributed to multiple scattering of light and the receiver sensor’s height from the incident surface. Assuming a sensor’s fixed instantaneous field of view (IFOV), variation in its field of view (FOV) by shifting its height affects the spatial resolution of acquired spectra. We propose to estimate the point spread function (PSF) for which the spectral responses of fine-resolution pixels acquired by a sensor are mixed to produce a coarse-resolution pixel obtained by the same. Our approach is based on the sensor’s unchanged IFOV obtaining spectral information from a smaller ground resolution cell (GRC) at a lower FOV and a larger GRC with an increased sensor’s FOV. The larger GRC producing a coarse resolution pixel can be modeled as a gaussian PSF of its corresponding center and neighboring fine-resolution subpixels with the center exerting the maximum influence. Extensive experiments performed using a point-based sensor and a push broom scanner revealed such variational effects in PSF that are dependent on the sensor’s FOV, the spatial interval of acquisition, and optical properties. The coarse-resolution pixels’ spectra were regressed with their corresponding fine-resolution subpixels to provide estimates of the PSF values that assumed the shape of a two-dimensional Gaussian function. Constraining these values as sum-to-one introduced sparsity and explained variability in the spectral acquisition by different sensors.  The estimated PSFs were further validated through the linear spectral unmixing technique. It was observed that the fractional abundances obtained for the fine-resolution subpixels convolved with our estimated PSF to produce its corresponding coarse-resolution counterpart with minimal error. The obtained PSFs using different sensors also explained spectral mixing at different scales of observation and provided a basis for nonlinear unmixing integrating spatial as well as spectral effects and addressing endmember variability. We performed our experiments with various coarse-grained and fine-grained igneous and sedimentary rocks under laboratory conditions to validate our results which were compared with available literature. 

How to cite: Sahoo, M. M., Pattathal Vijayakumar, A., Herrmann, I., Mathew, S. K., and Porwal, A.: Estimation of point spread function for unmixing geological spectral mixtures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8712, https://doi.org/10.5194/egusphere-egu22-8712, 2022.

EGU22-9441 | Presentations | GI2.2

Water use efficiency (WUE) Modeling at Leaf level of Cotton (Gossypium hirsutum L.) in Telangana, India 

Shreedevi Moharana and Phanindra BVN Kambhammettu

Water use efficiency (WUE) plays a vital role in planning and management of irrigation strategies. Considering the spatial scale, WUE can be quantified at scales ranging from leaf to whole-plant to ecosystem to region. However, the inter-relation and their associate is poorly understood. This study is aimed at stimulating WUE of irrigated cotton at leaf () and further investigate the role of environmental and biophysical conditions on WUE dynamics. This study was conducted in an agricultural croplands located in Sangareddy district, about 70 km west of Hyderabad, the capital city of southern state Telangana, India. Ground based observation were made such as soil moisture, photosynthetic parameters and meteorological parameters. Modelling leaf water use efficiency has been established. The stomatal conductance  and  of cotton leaves exposed to ambient CO2 were simulated using Ball-Berry (mBB) model. Moreover, the stomatal conductance  and  of Cotton leaves exposed to ambient CO2 is simulated using modified Ball-Berry model, with instantaneous gas exchanges measured around noon used to parameterize and validate the model. We observed a large diurnal (4.3±1.9 mmolCO2 mol-1H2O) and seasonal (5.16±1.51 mmolCO2 mol-1H2O) variations in  during the crop period. Model simulated  and  are in agreement with the measurements (R2>0.5, RMSE<0.3). Our results conclude that WUE is ruled by climatic as well as vegetative factors respectively, and are largely controlled by changes in transpiration over photosynthesis. This needs further investigation with extensive analysis by building library of in-situ measurements.

 

Keywords: Cotton, WUE, Irrigation, Stomatal conductance, Ball Berry Model

How to cite: Moharana, S. and Kambhammettu, P. B.: Water use efficiency (WUE) Modeling at Leaf level of Cotton (Gossypium hirsutum L.) in Telangana, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9441, https://doi.org/10.5194/egusphere-egu22-9441, 2022.

EGU22-9845 | Presentations | GI2.2

Implementation of an interoperable platform integrating BIM and GIS information for network-level monitoring and assessment of bridges 

Luca Bertolini, Antonio Napolitano, Jhon Diezmos Manalo, Valerio Gagliardi, Luca Bianchini Ciampoli, and Fabrizio D'Amico

Monitoring of critical civil engineering infrastructures, and especially viaducts and bridges, has become a priority nowadays as the ageing of construction materials may cause damages and collapses with dramatic consequences. Following recent bridge collapses, specific guidelines on risk classification and management, safety assessment and monitoring of existing bridges have been issued in Italy, by the Minister of Infrastructure as a mandatory code [1]. Accordingly, several laws and regulations have been issued on the same topic, emphasizing the crucial role of BIM-based procedures for the design and management of civil infrastructures [2, 3]. Within this context, monitoring operations are generally conducted by on-site inspections and specialized operators, and rarely by high-frequency ground-based Non-Destructive Testing methods (NDTs). Furthermore, the implementation of satellite-based remote sensing techniques, have been increasingly and effectively used for the monitoring of bridges in the last few years [4]. Generally, these crucial pieces of information are analyzed separately, and the implementation of a multi-scale and multi-source interoperable BIM platform is still an open challenge [5].

This study aims at investigating the potential of an interoperable and upgradeable BIM platform supplemented by non-destructive survey data, such as Mobile Laser Scanner (MLS), Ground Penetrating Radar (GPR) and Satellite Remote Sensing Information (i.e. InSAR). The main goal of the research is to contribute to the state-of-the-art knowledge on BIM applications, by testing an infrastructure management platform aiming at reducing the limits typically associated to the separate observation of these assessments, to the advantage of an integrated analysis including both the design information and the routinely updated results of monitoring activities.

The activities were conducted in the framework of the Project “M.LAZIO”, approved by the Lazio Region, with the aim to develop an informative BIM platform of the investigated bridges interoperable within a Geographic Information System (GIS). As on-site surveys are carried out , a preliminary multi-source database of information  is created, to be operated as the starting point for the integration process and the development of  the infrastructure management platform. Preliminary results have shown promising viability of the data management model for supporting asset managers in the various management phases, thereby proving this methodology to be worthy for implementation in infrastructure integrated monitoring plans.

Acknowledgements

This research is supported by the Project “M.LAZIO”, accepted and funded by the Lazio Region, Italy. Funding from MIUR, in the frame of the “Departments of Excellence Initiative 2018–2022”, attributed to the Department of Engineering of Roma Tre University, is acknowledged.

References

[1] MIT, 2020. Ministero delle Infrastrutture e dei Trasporti, DM 578/2020

[2] EU, 2014. Directive 2014/24/EU of the European Parliament and of the Council of 26 February 2014 on public procurement and repealing Directive 2004/18/EC.

[3] MIMS, 2021. Ministero delle Infrastrutture e della Mobilità Sostenibile, DM 312/2021

[4] Gagliardi, V. et al., “Bridge monitoring and assessment by high-resolution satellite remote sensing technologies”. In SPIE Future Sensing Technologies; https://doi.org/10.1117/12.2579700

[5] D'Amico F. et al., "A novel BIM approach for supporting technical decision-making process in transport infrastructure management", Proc. SPIE 11863;  https://doi.org/10.1117/12.2600140

How to cite: Bertolini, L., Napolitano, A., Diezmos Manalo, J., Gagliardi, V., Bianchini Ciampoli, L., and D'Amico, F.: Implementation of an interoperable platform integrating BIM and GIS information for network-level monitoring and assessment of bridges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9845, https://doi.org/10.5194/egusphere-egu22-9845, 2022.

Knowledge of the monument for its conservation is the result of a multidisciplinary work based on the integration of different data sources obtainable from historical research, architectural survey, the use of different imaging technologies. The latter are increasingly within the reach of conservators, architects and restoration companies thanks to the reduction of costs and to the effort to produce increasingly user-friendly imaging technologies both in terms of data acquisition and processing. The critical element is the interpretation of the results on which depends the effectiveness of these technologies in answering various questions that the restoration poses. Scientific literature suggests different approaches aimed at making the interpretation of imaging diagnostics easier, particularly by means of : i) the comparison between direct data (carrots, visual inspection) and results from non-invasive tests; ii) the use of specimens or laboratory test beds; iii) Virtual and Augmented reality (VR/AR) to be used as a work environment to facilitate the interpretation of non invasive imaging investigations. In particular, the reading and visualization of multiparametric information using VR/AR contents increases the standard modes for the transmission of knowledge of physical characteristics and state of conservation of the architectural heritage. This approach represents an effective system for storing and analysing heterogeneous data derived from a number of diverse non invasive imaging techniques, including Ground Penetrating radar (GPR) at high frequency, Infrared Thermography (IRT), Seismic tomography and other diagnostics techniques. In the context of Heritage Within Project, a VR/AR platform to interrelate heterogeneous data derived from GPR, IRT, Ultrasonic and sonic measurements along with  results finite element computations has been developed and applied to the Convent of Our Lady of Mount Carmel  in Lisbon to understand cause-and-effect mechanisms between the constructive characteristics, degradation pathologies and stress/deformation maps.

References

Gabellone F., Leucci G., Masini N., Persico R., Quarta G., Grasso F. 2013. Non-destructive prospecting and virtual reconstruction of the chapel of the Holy Spirit in Lecce, Italy. Near Surface Geophysics, doi: 10.3997/1873-0604.2012030

Gabellone F., Chiffi M., “Linguaggi digitali per la valorizzazione”, in F. Gabellone, M. T. Giannotta, M. F. Stifani, L. Donateo (a cura di), Soleto Ritrovata. Ricerche archeologiche e linguaggi digitali per la fruizione. Editrice Salentina, 2015. ISBN 978-88-98289-50-9

Masini N., Nuzzo L., Rizzo E., GPR investigations for the study and the restoration of the Rose Window of Troia Cathedral (Southern Italy), Near Surface Geophysics, 5 (5)(2007), pp. 287-300, ISSN: 1569-4445; doi: 10.3997/1873-0604.2007010 

Masini N., Soldovieri F. (Eds) (2017). Sensing the Past. From artifact to historical site. Series: Geotechnologies and the Environment, Vol. 16. Springer International Publishing, ISBN: 978-3-319-50516-9, doi: 10.1007/978-3-319-50518-3, pp. 575

Javier Ortega, Margarita González Hernández, Miguel Ángel García Izquierdo, Nicola Masini, et al. (2021). Heritage Within. European Research Project, ISBN: 978-989-54496-6-8, Braga 2021.

How to cite: Masini, N., Gabellone, F., and Ortega, J.: VR/AR based approach for the diagnosis of the state of conservation of the architectural heritage. The case of the Convento do Carmo in Lisbon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10538, https://doi.org/10.5194/egusphere-egu22-10538, 2022.

EGU22-11201 | Presentations | GI2.2

DIARITSup: a framework to supervise live measurements, Digital Twins modelscomputations and predictions for structures monitoring. 

Jean Dumoulin, Thibaud Toullier, Mathieu Simon, and Guillermo Andrade-Barroso

DIARITSup is a chain of various softwares following the concept of ”system of systems”. It interconnects hardware and software layers dedicated to in-situ monitoring of structures or critical components. It embeds data assimilation capabilities combined with specific Physical or Statistical models like inverse thermal and/or mechanical ones up to the predictive ones. It aims at extracting and providing key parameters of interest for decision making tools. Its framework natively integrates data collection from local sources but also from external systems [1, 2]. DIARITSup is a milestone in our roadmap for SHM Digital Twins research framework. Furthermore, it intends providing some useful information for maintenance operations not only for surveyed targets but also for deployed sensors.

Thanks to its Model-view-controller (MVC) design pattern, DIARITSup can be extended, customized and connected to existing applications. Its core component is made of a supervisor task that handles the gathering of data from local sensors and external sources like the open source meteorological data (observations and forecasts) from Météo-France Geoservice [4] for instance. Meanwhile, a recorder manage the recording of all data and metadata in the Hierarchical Data Format (HDF5) [6]. HDF5 is used to its full potential with its Single-Writer-Multiple-Readers feature that enables a graphical user interface to represent the saved data in real-time, or the live computation of SHM Digital Twins models [3] for example. Furthermore, the flexibility of HDF5 data storage allows the recording of various type of sensors such as punctual sensors or full field ones. Finally, DIARITSup is able to handle massive deployment thanks to Ansible [5] automation tool and a Gitlab synchronization for automatic updates. An overview of the developed software with a real application case will be presented. Perspectives towards improvements on the software with more component integrations (Copernicus Climate Data Store, etc.) and a more generic way to configure the acquisition and model configuration will be finally discussed.


References
[1] Nicolas Le Touz, Thibaud Toullier, and Jean Dumoulin. “Infrared thermography applied to the study of heated and solar pavement: from numerical modeling to small scale laboratory experiments”. In: SPIE - Thermosense: Thermal Infrared Applications XXXIX. Anaheim, United States, Apr. 2017. url: https://hal.inria.fr/hal-01563851.
[2] Thibaud Toullier, Jean Dumoulin, and Laurent Mevel. “Study of measurements bias due to environmental and spatial discretization in long term thermal monitoring of structures by infrared thermography”. In: QIRT 2018 - 14th Quantitative InfraRed Thermography Conference. Berlin, Germany, June 2018. url: https://hal.inria.fr/hal-01890292.
[3] Nicolas Le Touz, Thibaud Toullier, and Jean Dumoulin. “Study of an optimal heating command law for structures with non-negligible thermal inertia in varying outdoor conditions”. In: Smart Structures and Systems 27.2 (2021), pp. 379–386. doi: 10.12989/sss.2021.27.2.379. url: https://hal.inria.fr/hal-03145348.
[4] Météo France. Données publiques Météo France. 2022. url: https://donneespubliques.meteofrance.fr.
[5] Red Hat & Ansible. Ansible is Simple IT Automation. 2022. url: https://www.ansible.com/.
[6] The HDF Group. Hierarchical Data Format, version 5. 1997-2022. url: https://www.hdfgroup.org/HDF5/.

How to cite: Dumoulin, J., Toullier, T., Simon, M., and Andrade-Barroso, G.: DIARITSup: a framework to supervise live measurements, Digital Twins modelscomputations and predictions for structures monitoring., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11201, https://doi.org/10.5194/egusphere-egu22-11201, 2022.

EGU22-12743 | Presentations | GI2.2

Integrating Remote Sensing data to assess the protective effect of forests on rockfall:The case study of Monte San Liberatore (Campania, Italy) 

Alessandro Di Benedetto, Antonella Ambrosino, and Margherita Fiani

In recent years, great interest has been paid to the risk that hydrogeological instability causes to the territory, especially in densely populated and geologically fragile areas. 
The forests, exerting a natural restraint, play an important protective function for the infrastructures and settlements underneath from the danger of falling rocks that fall from the rocky walls. This protective action is influenced not only by issues related to the vegetation itself but also by the morphology of the terrain, as a steeply sloping land surface can significantly increase the momentum of the rolling rock.
The aim of our work is to design a methodology based on the integration of remote sensing data, in detail optical satellite images and LiDAR data acquired by UAVs, to identify areas most prone to natural rockfall retention [1]. The results could then be used to identify areas that need to be reinforced artificially (rockfall nets) and naturally (protective forests).
The test area is located near Monte San Liberatore in the Campania region (Italy), which was affected in 1954 by a disastrous flood, in which heavy rains induced the triggering of a few complex landslides in a region that was almost geomorphologically susceptible.  Indeed, there are several areas subject to high risk of rockfalls, whose exposed value is represented by a complex infrastructural network of viaducts, tunnels, and galleries along the north-west slope of the mountain, which is partly covered by thick vegetation, which reduces the rolling velocity of rocks detaching from the ridge. 
According to the Carta della Natura, the vegetation most present in the area is the holm oak (Quercus Ilex), an evergreen, long-lived, medium-sized tree. Its taproot makes it resistant and stable, able to survive in extremely severe environments such as rocky soils or vertical walls, so it is ideal for slope protection.
The first processing step involved the multispectral analysis on Pleiades 1A four-band (RGB +NIR) high-resolution satellite images (HRSI). The computed vegetation indices (NDVI, RVI and NDWI) were used to assess the vegetation health status and its presumed age; thus, the most resilient areas of the natural compartment in terms of robustness and vigor were identified. The average plant height was determined using the normalized digital surface model (nDSM).
Next, starting from the Digital Terrain Model (DTM), we derived the morphometric features suitable for the description of the slope dynamics: slope gradient, exposure with respect to the North direction, plane, and convexity profile. The DTM and the DSM were created by interpolating on a grid the LiDAR point cloud acquired via UAV. Classification of areas having similar characteristics was made using SOM (Self-Organizing Maps), based on unsupervised learning.
The classified maps obtained delimit the similar areas from a morphological and vegetation point of view; in this way, all those areas that tend to have a higher propensity for rock roll reduction were identified.

[1] Fanos, Ali Mutar, and Biswajeet Pradhan. "Laser scanning systems and techniques in rockfall source identification and risk assessment: a critical review." Earth Systems and Environment 2.2 (2018): 163-182.

How to cite: Di Benedetto, A., Ambrosino, A., and Fiani, M.: Integrating Remote Sensing data to assess the protective effect of forests on rockfall:The case study of Monte San Liberatore (Campania, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12743, https://doi.org/10.5194/egusphere-egu22-12743, 2022.

EGU22-13153 | Presentations | GI2.2

Integration of multiple geoscientific investigation methods for a better understanding of a water system: the example of Chimborazo glaciers melting effects on the Chambo aquifer, Ecuador 

Andrea Scozzari, Paolo Catelan, Francesco Chidichimo, Michele de Biase, Benito G. Mendoza Trujillo, Pedro A. Carrettero Poblete, and Salvatore Straface

The identification of the processes underlining natural systems often requires the adoption of multiple investigation techniques for the assessment of the sites under study. In this work, the combination of information derived from non-invasive sensing techniques, such as geophysics, remote sensing and hydrogeochemistry, highlights the possible influence of global climate change on the future water availability related to an aquifer in a peculiar glacier context, located in central Ecuador. In particular, we show that the Chambo aquifer, which supplies potable water to the region, does not contain fossil water, and it’s instead recharged over time. Indeed, the whole Chambo river basin is affected by the Chimborazo volcano, which is a glacerised mountain located in the inner tropics, one of the most critical places  to be observed in the frame of climate impact on water resources. Thanks to the infomation gathered by the various surveying techniques, numerical modelling permitted an estimate of the recharge, which can be fully originated by the runoff from Chimborazo melting glaciers. Actually, the retreat of the glaciers on top of the Chimborazo is an ongoing process presumably related to global climate change.

How to cite: Scozzari, A., Catelan, P., Chidichimo, F., de Biase, M., Mendoza Trujillo, B. G., Carrettero Poblete, P. A., and Straface, S.: Integration of multiple geoscientific investigation methods for a better understanding of a water system: the example of Chimborazo glaciers melting effects on the Chambo aquifer, Ecuador, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13153, https://doi.org/10.5194/egusphere-egu22-13153, 2022.

EGU22-13401 | Presentations | GI2.2

Tunnel deformation rate analysis based on PS-InSAR technique and stress-area method  

Long Chai, Xiongyao Xie, Pan Li, Biao Zhou, and Li Zeng

The permanent scatterer synthetic aperture radar interferometry (PS-InSAR) technique can detect the permanent scatterers(PSs) on the ground. But the deformation of PSs can’t be used to analyze the deformation of underground buildings below the ground surface directly, such as tunnels. In this paper, the process of tunnel deformation analysis using PSs data and stress-area method is proposed. The deformation data of PSs are used to fit the surface deformation of tunnel by kriging interpolation method. The stress area method is used to calculate the deformation of the soil above the tunnel, then the deformation of tunnel can be acquired. This process was applied to calculate the deformation of a tunnel in Shanghai, China. The results show that the fitted surface deformation rate data are accurate, with the maximum absolute difference of 1.45mm/y and the minimum difference of 0.11mm/y compared with the level monitoring data. The tunnel deformation rate calculated by this process is close to the measured deformation rate of the tunnel with error level in millimeters. The surface and tunnel deformation rate curves are similar in the tunnel extension direction. PS-InSAR technique has the advantages of acquiring large area, historical data of surface deformation. Combined with the process proposed in this paper, Large-scale tunnel deformation analysis can be achieved.

How to cite: Chai, L., Xie, X., Li, P., Zhou, B., and Zeng, L.: Tunnel deformation rate analysis based on PS-InSAR technique and stress-area method , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13401, https://doi.org/10.5194/egusphere-egu22-13401, 2022.

EGU22-13441 | Presentations | GI2.2

Collaborative use of ground monitoring and GPR data for the control of ground settlement in shield tunnel in soft soil 

Kang Li, Xiongyao Xie, Xiaobin Zhang, Biao Zhou, Tenfei Qu, and Li Zeng

In recent years, China's construction demand for shield tunnel in soft soil continues to increase, and the control of ground settlement in tunnel boring process affects the safety of the tunnel itself and its superstructure directly. Paying close attention to controlling the strata loss and the ground settlement by multiple means is important to ensure construction safety. In this paper, the intelligent real-time monitoring system with dual-frequency ground penetrating radar (GPR) is used to detect the quality of back-fill grouting of shield tunnel, while monitoring points are arranged on the ground surface to acquire the settlement values in real time. The collaborative analysis of ground and underground monitoring results reveals the relationship between grouting and settlement values, and realizes the dynamic guidance on grouting operation, which helps to achieve the purpose of controlling ground settlement better. Last but not least, this paper proposes an outlook on a multiple-data fusion system based on cloud computing platform to adapt to more complex and multiple data in the future, so as to achieve the higher accuracy, efficiency and intelligence of monitoring data analysis.

How to cite: Li, K., Xie, X., Zhang, X., Zhou, B., Qu, T., and Zeng, L.: Collaborative use of ground monitoring and GPR data for the control of ground settlement in shield tunnel in soft soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13441, https://doi.org/10.5194/egusphere-egu22-13441, 2022.

EGU22-13515 | Presentations | GI2.2

Application of ground penetrating radar (GPR) in look-ahead detection of slurry balance shield machine 

Weiwei Duan, Xiongyao Xie, Yong Yang, Kun Zeng, Huiming Wu, Li Zeng, and Kang Li

The shield machine has become the mainstream of subway tunnels construction because of its safety and efficiency. But with the continuous development of urban construction, the environment of subway tunnel construction is becoming more and more complex. In the process of shield tunnels construction in southern cities of China, slurry balance shield machines often encounter various obstacles, such as large diameter boulders and concrete pile foundations, which result in accidents of shield machine sticking. Therefore, it is necessary to quickly and accurately detect the distribution of obstacles in front of shield excavation face in advance so that operators can in time take measures to reduce the occurrence of such accidents. Ground penetrating radar (GPR) is a method widely used in engineering geological exploration. It has advantages of small working space, high efficiency and no damage compared with other detecting methods. When the GPR antenna is mounted on the cutter head of the shield machine, the obstacles in the stratum ahead of the shield machine can be detected in real time. Under this condition the GPR antenna’s real work mode is that it will rotate with the cutter head to form a circumferential survey line. Based on Finite-Difference-Time-Domain-Method (FDTD), authors use the common numerical simulation software (GPRMAX) to make simulations of GPR circumferential detection under the antenna array rotating with the cutter head, which verifies the theoretical feasibility of this method. By simulating radar emission and reflection pattern of electromagnetic wave, we study the propagation pattern of the reflect wave after encountering the obstacles and conclude the image pattern to establish the foundation for image recognition of obstacles. Due to the radar wave being susceptible to electromagnetic interference, GPR is still lack of engineering practice in shield advanced detection. To reduce the interference of the surrounding metal cutter head, a new strip radar antenna with a shielding shutter is designed to improve the directivity of electromagnetic wave propagation. Several antennas are fixed at several slurry openings of the cutter head of slurry balance shield machine to form radar antenna array and improve detection efficiency and accuracy.

How to cite: Duan, W., Xie, X., Yang, Y., Zeng, K., Wu, H., Zeng, L., and Li, K.: Application of ground penetrating radar (GPR) in look-ahead detection of slurry balance shield machine, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13515, https://doi.org/10.5194/egusphere-egu22-13515, 2022.

EGU22-91 | Presentations | NP4.1

The role of teleconnections in complex climate network 

Ruby Saha

A complex network provides a robust framework to statistically investigate the topology of local and long-range connections, i.e., teleconnections in climate dynamics. The Climate network is constructed from meteorological data set using the linear Pearson correlation coefficient to measure similarity between two regions. Long-range teleconnections connect remote geographical sites and are crucial for climate networks. In this study, we discuss that during El Ni\~no Southern Oscillation onset, the teleconnections pattern changes according to the episode's strength. The long-range teleconnections are significant and responsible for the episodes' extremum ONI attained gradually after onset. We quantify the betweenness centrality measurement and note that the teleconnection distribution pattern and the betweenness measurements fit well.

How to cite: Saha, R.: The role of teleconnections in complex climate network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-91, https://doi.org/10.5194/egusphere-egu22-91, 2022.

EGU22-1831 | Presentations | NP4.1

Quantifying space-weather events using dynamical network analysis of Pc waves with global ground based magnetometers. 

Shahbaz Chaudhry, Sandra Chapman, Jesper Gjerloev, Ciaran Beggan, and Alan Thompson

Geomagnetic storms can impact technological systems, on the ground and in space, including damage to satellites and power blackouts. Their impact on ground systems such as power grids depends upon the spatio-temporal extent and time-evolution of the ground magnetic perturbation driven by the storm.

Pc waves are Alfven wave resonances of closed magnetospheric field lines and are ubiquitous in the inner magnetosphere. They have been extensively studied, in particular since  Pc wave power tracks the onset and evolution of geomagnetic storms.  We study the spatial and temporal evolution of Pc waves with a network analysis of the 100+ ground-based magnetometer stations collated by the SuperMAG collaboration with a single time-base and calibration. 

Network-based analysis of 1 min cadence SuperMAG magnetometer data has been applied to the dynamics of substorm current systems (Dods et al. JGR 2015, Orr et al. GRL 2019) and the magnetospheric response to IMF turnings (Dods et al. JGR 2017). It has the potential to capture the full spatio-temporal response with a few time-dependent network parameters. Now, with the availability of 1 sec data across the entire SuperMAG network we are able for the first time to apply network analysis globally to resolve both the spatial and temporal correlation patterns of the ground signature of Pc wave activity as a geomagnetic storm evolves. We focus on Pc2 (5-10s period) and Pc3 (10-45s period) wave bands. We obtain the time-varying global Pc wave dynamical network over individual space weather events.

To construct the networks we sample each magnetometer time series with a moving window in the time domain (20 times Pc period range) and then band-pass filter each magnetometer station time-series to obtain Pc2 and Pc3 waveforms. We then compute the cross correlation (TLXC) between all stations for each Pc band. Modelling is used to determine a threshold of significant TLXC above which a pair of stations are connected in the network. The TLXC as a function of lag is tested against a criterion for sinusoidal waveforms and then used to calculate the phase difference. The connections with a TLXC peak at non zero lag form a directed network which characterizes propagation or information flow. The connections at TLXC lag peak close to zero form am undirected network which characterizes a response which is globally instantaneously coherent.

We apply this network analysis to isolated geomagnetic storms. We find that the network connectivity does not simply track Pc wave power, it therefore contains additional information. Geographically short range connections are prevalent at all times, the storm onset marks a transition to a network which has both enhancement of geographically short-range connections, and the growth of geographically long range, global scale, connections extending spatially over a region exceeding 9h MLT. These global scale connections, indicating globally coherent Pc wave response are prevalent throughout the storm with considerable (within a few time windows) variation. The stations are not uniformly distributed spatially. Therefore, we distinguish between long range connections to avoid introducing spatial correlation. 

How to cite: Chaudhry, S., Chapman, S., Gjerloev, J., Beggan, C., and Thompson, A.: Quantifying space-weather events using dynamical network analysis of Pc waves with global ground based magnetometers., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1831, https://doi.org/10.5194/egusphere-egu22-1831, 2022.

EGU22-2014 | Presentations | NP4.1

OBS noise reduction using music information retrieval algorithms 

Zahra Zali, Theresa Rein, Frank Krüger, Matthias Ohrnberger, and Frank Scherbaum

Since the ocean covers 71% of the Earth’s surface, records from ocean bottom seismometers (OBS) are essential for investigating the whole Earth’s structure. However, data from ocean bottom recordings are commonly difficult to analyze due to the high noise level especially on the horizontal components. In addition, signals of seismological interest such as earthquake recordings at teleseismic distances, are masked by the oceanic noises. Therefore, noise reduction of OBS data is an important task required for the analysis of OBS records. Different approaches have been suggested in previous studies to remove noise from vertical components successfully, however, noise reduction on records of horizontal components remained problematic. Here we introduce a method, which is based on harmonic-percussive separation (HPS) algorithms used in Zali et al., (2021) that is able to separate long-lasting narrowband signals from broadband transients in the OBS records. In the context of OBS noise reduction using HPS algorithms, percussive components correspond to earthquake signals and harmonic components correspond to noise signals. OBS noises with narrowband horizontal structures in the short time Fourier transform (STFT) are readily distinguishable from transient, short-duration seismic events with vertical exhibitions in the STFT spectrogram. Through HPS algorithms we try to separate horizontal structures from vertical structures in the STFT spectrograms. Using this method we can reduce OBS noises from both vertical and horizontal components, retrieve clearer broadband earthquake waveforms and increase the earthquake signal to noise ratio. The applicability of the method is checked through tests on synthetic and real data.

How to cite: Zali, Z., Rein, T., Krüger, F., Ohrnberger, M., and Scherbaum, F.: OBS noise reduction using music information retrieval algorithms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2014, https://doi.org/10.5194/egusphere-egu22-2014, 2022.

EGU22-2097 | Presentations | NP4.1 | Highlight

Medium- to long-term forecast of sea surface temperature using EEMD-STEOF-LSTM hybrid model 

Rixu Hao, Yuxin Zhao, Xiong Deng, Di Zhou, Dequan Yang, and Xin Jiang

Sea surface temperature (SST) is a vitally important variable of the global ocean, which can profoundly affect the climate and marine ecosystems. The field of forecasting oceanic variables has traditionally relied on numerical models, which effectively consider the discretization of the dynamical and physical oceanic equations. However, numerical models suffer from many limitations such as short timeliness, complex physical processes, and excessive calculation. Furthermore, existing machine learning has been proved to be able to capture spatial and temporal information independently without these limitations, but the previous research on multi-scale feature extraction and evolutionary forecast under spatiotemporal integration is still inadequate. To fill this gap, a multi-scale spatiotemporal forecast model is developed combining ensemble empirical mode decomposition (EEMD) and spatiotemporal empirical orthogonal function (STEOF) with long short-term memory (LSTM), which is referred to as EEMD-STEOF-LSTM. Specifically, the EEMD is applied for adaptive multi-scale analysis; the STEOF is adopted to decompose the spatiotemporal processes of different scales into terms of a sum of products of spatiotemporal basis functions along with corresponding coefficients, which captures the evolution of spatial and temporal processes simultaneously; and the LSTM is employed to achieve medium- to long-term forecast of STEOF-derived spatiotemporal coefficients. A case study of the daily average of SST in the South China Sea shows that the proposed hybrid EEMD-STEOF-LSTM model consistently outperforms the optimal climatic normal (OCN), STEOF, and STEOF-LSTM, which can accurately forecast the characteristics of oceanic eddies. Statistical analysis of the case study demonstrates that this model has great potential for practical applications in medium- to long-term forecast of oceanic variables.

How to cite: Hao, R., Zhao, Y., Deng, X., Zhou, D., Yang, D., and Jiang, X.: Medium- to long-term forecast of sea surface temperature using EEMD-STEOF-LSTM hybrid model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2097, https://doi.org/10.5194/egusphere-egu22-2097, 2022.

In this presentation, we introduce the IMFogram method ( pronounced like "infogram" ), which is a new, fast, local, and reliable time-frequency representation (TFR) method for nonstationary signals. This technique is based on the Intrinsic Mode Functions (IMFs) decomposition produced by a decomposition method, like the Empirical Mode Decomposition-based techniques, Iterative Filtering-based algorithms, or any equivalent method developed so far. We present the mathematical properties of the IMFogram, and show the proof that this method is a generalization of the Spectrogram. We conclude the presentation with some applications, as well as a comparison of its performance with other existing TFR techniques.

How to cite: Cicone, A.: The IMFogram: a new time-frequency representation algorithm for nonstationary signals, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2560, https://doi.org/10.5194/egusphere-egu22-2560, 2022.

EGU22-2922 | Presentations | NP4.1

Constraining the uncertainty in CO2 seasonal cycle metrics by residual bootstrapping. 

Theertha Kariyathan, Wouter Peters, Julia Marshall, Ana Bastos, and Markus Reichstein

The analysis of long, high-quality time series of atmospheric greenhouse gas measurements helps to quantify their seasonal to interannual variations and impact on global climate. These discrete measurement records contain, however, gaps and at times noisy data, influenced by local fluxes or synoptic scale events, hence appropriate filtering and curve-fitting techniques are often used to smooth and gap-fill the atmospheric time series. Previous studies have shown that there is an inherent uncertainty associated with curve-fitting processes which introduces biases based on the choice of mathematical method used for data processing and can lead to scientific misinterpretation of the signal. Further the uncertainties in curve-fitting can be propagated onto the metrics estimated from the fitted curve that could significantly influence the quantification of the metrics and their interpretations. In this context we present a novel-methodology for constraining the uncertainty arising from fitting a smooth curve to the CO2 dry air mole fraction time-series, and propagate this uncertainty onto commonly used metrics to study the seasonal cycle of CO2. We generate an ensemble of fifitted curves from the data using residual bootstrap sampling with loess-fitted residuals, that is representative of the inherent uncertainty in applying the curve-fitting method to the discrete data. The spread of the selected CO2 seasonal cycle metrics across bootstrap time-series provides an estimate of the inherent uncertainty in curve fitting to the discrete data. Further we show that the approach can be extended to other curve-fitting methods by generating multiple bootstrap samples by resampling residuals obtained from processing the data using the widely used CCGCRV filtering method by the atmospheric greenhouse gas measurement community.

How to cite: Kariyathan, T., Peters, W., Marshall, J., Bastos, A., and Reichstein, M.: Constraining the uncertainty in CO2 seasonal cycle metrics by residual bootstrapping., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2922, https://doi.org/10.5194/egusphere-egu22-2922, 2022.

EGU22-4795 | Presentations | NP4.1

Robust Causal Inference for Irregularly Sampled Time Series: Applications in Climate and Paleoclimate Data Analysis 

Aditi Kathpalia, Pouya Manshour, and Milan Paluš

To predict and determine the major drivers of climate has become even more important now as climate change poses a big challenge to humankind and our planet earth. Different studies employ either correlation, causality methods or modelling approaches to study the interaction between climate and climate forcing variables (anthropogenic or natural). This includes the study of interaction between global surface temperatures and CO2; rainfall in different locations and El Niño–Southern Oscillation (ENSO) phenomena. The results produced by different studies have been found to be different and debatable, presenting an ambiguous situation. In this work, we develop and apply a novel robust causality estimation technique for time-series data (to estimate causal influence between given observables), that can help to resolve the ambiguity. The discrepancy in existing results arises due to challenges with the acquired data and limitations of the causal inference/ modelling approaches. Our novel approach combines the use of a recently proposed causality method, Compression-Complexity Causality (CCC) [1], and Ordinal/ Permutation pattern-based coding [2]. CCC estimates have been shown to be robust for bivariate systems with low temporal resolution, missing samples, long-term memory and finite length data [1]. The use of ordinal patterns helps to extend bivariate CCC to the multivariate case by capturing the multidimensional dynamics of the given variables’ systems in the symbolic temporal sequence of a single variable. This methodology is tested on dynamical systems data which are short in length and have been corrupted with missing samples or subsampled to different levels. The superior performance of ‘Permutation CCC’ on such data relative to other causality estimation methods, strengthens our trust in the method. We apply the method to study the interaction between CO2-temperature recordings on three different time scales, CH4-temperature on the paleoclimate scale, ENSO-South Asian monsoon on monthly and yearly time scales, North Atlantic Oscillation-surface temperature on daily and monthly time scales. These datasets are either short in length, have been sampled irregularly, have missing samples or have a combination of the above factors. Our results are interesting, which validate some existing studies while contradicting others. In addition, the development of the novel permutation-CCC approach opens the possibility of its application for making useful inferences on other challenging climate datasets.


This study is supported by the Czech Science Foundation, Project No.~GA19-16066S and by the Czech Academy of Sciences, Praemium Academiae awarded to M. Paluš.


References:
[1] Kathpalia, A., & Nagaraj, N. (2019). Data-based intervention approach for Complexity-Causality measure. PeerJ Computer Science, 5, e196.
[2] Bandt, C., & Pompe, B. (2002). Permutation entropy: a natural complexity measure for time series. Physical review letters, 88(17), 174102.

How to cite: Kathpalia, A., Manshour, P., and Paluš, M.: Robust Causal Inference for Irregularly Sampled Time Series: Applications in Climate and Paleoclimate Data Analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4795, https://doi.org/10.5194/egusphere-egu22-4795, 2022.

Rainfall time series prediction is crucial for geoscientific system monitoring, but it is challenging and complex due to the extreme variability of rainfall. In order to improve prediction accuracy, a hybrid deep learning model (VMD-RNN) was proposed. In this study, variational mode decomposition (VMD) is first applied to decompose the original rainfall time series into several sub-sequences according to the frequency domain. Following that, different recurrent neural network (RNN) models are utilized to predict individual sub-sequences and the final prediction is reconstructed by summing the prediction results of sub-sequences. These RNN models are long short-term memory (LSTM), gated recurrent unit (GRU), bidirectional LSTM (BiLSTM) and bidirectional GRU (BiGRU), which are optimal for sequence prediction. The root mean square error (RMSE) of the predicted performance is then used to select the ideal RNN model for each sub-sequences. In addition to RMSE, the framework of universal multifractal (UM) is also introduced to evaluate prediction performances, which enables to characterize the extreme variability of predicted rainfall time series. The study employed two rainfall datasets from 2001 to 2020 in Paris, with daily and hourly resolutions. The results show that, when compared to directly predicting the original time series, the proposed hybrid VMD-RNN model improves prediction of high or extreme values for the daily dataset, but does not significantly enhance the prediction of zero or low values. Additionally, the VMD-RNN model also outperforms existing deep learning models without decomposition on the hourly dataset when evaluated with the help of RMSE, while universal multifractal analyses point out limitations. 

How to cite: Zhou, H., Schertzer, D., and Tchiguirinskaia, I.: Combining variational mode decomposition and recurrent neural network to predict rainfall time series and evaluating prediction performance by universal multifractals, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6014, https://doi.org/10.5194/egusphere-egu22-6014, 2022.

EGU22-6281 | Presentations | NP4.1

Application of information theoretical measures for improved machine learning modelling of the outer radiation belt 

Constantinos Papadimitriou, Georgios Balasis, Ioannis A. Daglis, and Simon Wing

In the past ten years Artificial Neural Networks (ANN) and other machine learning methods have been used in a wide range of models and predictive systems, to capture and even predict the onset and evolution of various types of phenomena. These applications typically require large datasets, composed of many variables and parameters, the number of which can often make the analysis cumbersome and prohibitively time consuming, especially when the interplay of all these parameters is taken into consideration. Thankfully, Information-Theoretical measures can be used to not only reduce the dimensionality of the input space of such a system, but also improve its efficiency. In this work, we present such a case, where differential electron fluxes from the Magnetic Electron Ion Spectrometer (MagEIS) on board the Van Allen Probes satellites are modelled by a simple ANN, using solar wind parameters and geomagnetic activity indices as inputs, and illustrate how the proper use of Information Theory measures can improve the efficiency of the model by minimizing the number of input parameters and shifting them with respect to time, to their proper time-lagged versions.

How to cite: Papadimitriou, C., Balasis, G., Daglis, I. A., and Wing, S.: Application of information theoretical measures for improved machine learning modelling of the outer radiation belt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6281, https://doi.org/10.5194/egusphere-egu22-6281, 2022.

EGU22-7256 | Presentations | NP4.1

Identifying patterns of teleconnections, a curvature-based network analysis 

Jakob Schlör, Felix M. Strnad, Christian Fröhlich, and Bedartha Goswami

Representing spatio-temporal climate variables as complex networks allows uncovering nontrivial structure in the data. Although various tools for detecting communities in climate networks have been used to group nodes (spatial locations) with similar climatic conditions, we are often interested in identifying important links between communities. Of particular interest are methods to detect teleconnections, i.e. links over large spatial distances mitigated by atmospheric processes.

We propose to use a recently developed network measure based on Ricci-curvature to visualize teleconnections in climate networks. Ricci-curvature allows to distinguish between- and within-community links in networks. Applied to networks constructed from surface temperature anomalies we show that Ricci-curvature separates spatial scales. We use Ricci-curvature to study differences in global teleconnection patterns of different types of El Niño events, namely the Eastern Pacific (EP) and Central Pacific (CP) types. Our method reveals a global picture of teleconnection patterns, showing confinement of teleconnections to the tropics under EP conditions but showing teleconnections to the tropics, Northern and Southern Hemisphere under CP conditions. The obtained teleconnections corroborate previously reported impacts of EP and CP.
Our results suggest that Ricci-curvature is a promising visual-analytics-tool to study the topology of climate systems with potential applications across observational and model data.

How to cite: Schlör, J., Strnad, F. M., Fröhlich, C., and Goswami, B.: Identifying patterns of teleconnections, a curvature-based network analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7256, https://doi.org/10.5194/egusphere-egu22-7256, 2022.

EGU22-8399 | Presentations | NP4.1

Using neural networks to detect coastal hydrodynamic phenomena in high-resolution tide gauge data 

Felix Soltau, Sebastian Niehüser, and Jürgen Jensen

Tide gauges are exposed to various kinds of influences that are able to affect water level measurements significantly and lead to time series containing different phenomena and artefacts. These influences can be natural or anthropogenic, while both lead to actual changes of the water level. Opposed to that, technical malfunction of measuring devices as another kind of influence causes non-physical water level data. Both actual and non-physical data need to be detected and classified consistently, and possibly corrected to enable the supply of adequate water level information. However, there is no automatically working detection algorithm yet. Only obvious or frequent technical malfunctions like gaps can be detected automatically but have to be corrected manually by trained staff. Consequently, there is no consistently defined data pre-processing before, for example, statistical analyses are performed or water level information for navigation is passed on.

In the research project DePArT*, we focus on detecting natural phenomena like standing waves, meteotsunamis, or inland flood events as well as anthropogenic artefacts like operating storm surge barriers and sluices in water level time series containing data every minute. Therefore, we train artificial neural networks (ANNs) using water level sequences of phenomena and artefacts as well as redundant data to recognize them in other data sets. We use convolutional neural networks (CNNs) as they already have been successfully conducted in, for example, object detection or speech and language processing (Gu et al., 2018). However, CNNs need to be trained with high numbers of sample sequences. Hence, as a next step the idea is to synthesize rarely observed phenomena and artefacts to gain enough training data. The trained CNNs can then be used to detect unnoticed phenomena and artefacts in past and recent time series. Depending on sequence characteristics and the results of synthesizing, we will possibly be able to detect certain events as they occur and therefore provide pre-checked water level information in real time.

In a later stage of this study, we will implement the developed algorithms in an operational test mode while cooperating closely with the officials to benefit from the mutual feedback. In this way, the study contributes to a future consistent pre-processing and helps to increase the quality of water level data. Moreover, the results are able to reduce uncertainties from the measuring process and improve further calculations based on these data.

* DePArT (Detektion von küstenhydrologischen Phänomenen und Artefakten in minütlichen Tidepegeldaten; engl. Detection of coastal hydrological phenomena and artefacts in minute-by-minute tide gauge data) is a research project, funded by the German Federal Ministry of Education and Research (BMBF) through the project management of Projektträger Jülich PTJ under the grant number 03KIS133.

Gu, Wang, Kuen, Ma, Shahroudy, Shuai, Liu, Wang, Wang, Cai, Chen (2018): Recent advances in convolutional neural networks. In: Pattern Recognition, Vol. 77, Pages 354–377. https://doi.org/10.1016/j.patcog.2017.10.013

How to cite: Soltau, F., Niehüser, S., and Jensen, J.: Using neural networks to detect coastal hydrodynamic phenomena in high-resolution tide gauge data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8399, https://doi.org/10.5194/egusphere-egu22-8399, 2022.

EGU22-8899 | Presentations | NP4.1

Body wave extraction by using sparsity-promoting time-frequency filtering 

Bahare Imanibadrbani, Hamzeh Mohammadigheymasi, Ahmad Sadidkhouy, Rui Fernandes, Ali Gholami, and Martin Schimmel

Different phases of seismic waves generated by earthquakes carry considerable information about the subsurface structures as they propagate within the earth. Depending on the scope and objective of an investigation, various types of seismic phases are studied. Studying surface waves image shallow and large-scale subsurface features, while body waves provide high-resolution images at higher depths, which is otherwise impossible to be resolved by surface waves. The most challenging aspect of studying body waves is extracting low-amplitude P and S phases predominantly masked by high amplitude and low attenuation surface waves overlapping in time and frequency. Although body waves generally contain higher frequencies than surface waves, the overlapping frequency spectrum of body and surface waves limits the application of elementary signal processing methods such as conventional filtering. Advanced signal processing tools are required to work around this problem. Recently the Sparsity-Promoting Time-Frequency Filtering (SP-TFF) method was developed as a signal processing tool for discriminating between different phases of seismic waves based on their high-resolution polarization information in the Time-Frequency (TF)-domain (Mohammadigheymasi et al., 2022). The SP-TFF extracts different phases of seismic waves by incorporating this information and utilizing a combination of amplitude, directivity, and rectilinearity filters. This study implements SP-TFF by properly defining a filter combination set for specific extraction of body waves masked by high-amplitude surface waves. Synthetic and real data examinations for the source mechanism of the  Mw=7.5 earthquake that occurred in November 2021 in Northern Peru and recorded by 58 stations of the United States National Seismic Network (USNSN) is conducted. The results show the remarkable performance of SP-TFF extracting P and SV phases on the vertical and radial components and SH phase on the transverse component masked by high amplitude Rayleigh and Love waves, respectively. A range of S/N levels is tested, indicating the algorithm’s robustness at different noise levels. This research contributes to the FCT-funded SHAZAM (Ref. PTDC/CTA-GEO/31475/2017) and IDL (Ref. FCT/UIDB/50019/2020) projects. It also uses computational resources provided by C4G (Collaboratory for Geosciences) (Ref. PINFRA/22151/2016).

REFERENCE
Mohammadigheymasi, H., P. Crocker, M. Fathi, E. Almeida, G. Silveira, A. Gholami, and M. Schimmel, 2022, Sparsity-promoting approach to polarization analysis of seismic signals in the time-frequency domain: IEEE Transactions on Geoscience and Remote Sensing, 1–1.

How to cite: Imanibadrbani, B., Mohammadigheymasi, H., Sadidkhouy, A., Fernandes, R., Gholami, A., and Schimmel, M.: Body wave extraction by using sparsity-promoting time-frequency filtering, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8899, https://doi.org/10.5194/egusphere-egu22-8899, 2022.

EGU22-9626 | Presentations | NP4.1

A Recurrence Flow based Approach to Attractor Reconstruction 

Tobias Braun, K. Hauke Kraemer, and Norbert Marwan

In the study of nonlinear observational time series, reconstructing the system’s state space represents the basis for many widely-used analyses. From the perspective of dynamical system’s theory, Taken’s theorem states that under benign conditions, the reconstructed state space preserves the most fundamental properties of the real, unknown system’s attractor. Through many applications, time delay embedding (TDE) has established itself as the most popular approach for state space reconstruction1. However, standard TDE cannot account for multiscale properties of the system and many of the more sophisticated approaches either require heuristic choice for a high number of parameters, fail when the signals are corrupted by noise or obstruct analysis due to their very high complexity.

We present a novel semi-automated, recurrence based method for the problem of attractor reconstruction. The proposed method is based on recurrence plots (RPs), a computationally simple yet effective 2D-representation of a univariate time series. In a recent study, the quantification of RPs has been extended by transferring the well-known box-counting algorithm to recurrence analysis2. We build on this novel formalism by introducing another box-counting measure that was originally put forward by B. Mandelbrot, namely succolarity3. Succolarity quantifies how well a fluid can permeate a binary texture4. We employ this measure by flooding a RP with a (fictional) fluid along its diagonals and computing succolarity as a measure of diagonal flow through the RP. Since a non-optimal choice of embedding parameters impedes the formation of diagonal lines in the RP and generally results in spurious patterns that block the fluid, the attractor reconstruction problem can be formulated as a maximization of diagonal recurrence flow.

The proposed state space reconstruction algorithm allows for non-uniform embedding delays to account for multiscale dynamics. It is conceptually and computationally simple and (nearly) parameter-free. Even in presence of moderate to high noise intensity, reliable results are obtained. We compare the method’s performance to existing techniques and showcase its effectiveness in applications to paradigmatic examples and nonlinear geoscientific time series.

 

References:

1 Packard, N. H., Crutchfield, J. P., Farmer, J. D., & Shaw, R. S. (1980). Geometry from a time series. Physical review letters, 45(9), 712.

2 Braun, T., Unni, V. R., Sujith, R. I., Kurths, J., & Marwan, N. (2021). Detection of dynamical regime transitions with lacunarity as a multiscale recurrence quantification measure. Nonlinear Dynamics, 1-19.

3 Mandelbrot, B. B. (1982). The fractal geometry of nature (Vol. 1). New York: WH freeman.

4 de Melo, R. H., & Conci, A. (2013). How succolarity could be used as another fractal measure in image analysis. Telecommunication Systems, 52(3), 1643-1655.

How to cite: Braun, T., Kraemer, K. H., and Marwan, N.: A Recurrence Flow based Approach to Attractor Reconstruction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9626, https://doi.org/10.5194/egusphere-egu22-9626, 2022.

EGU22-11064 | Presentations | NP4.1

The Objective Deformation Component of a Velocity Field 

Bálint Kaszás, Tiemo Pedergnana, and George Haller

According to a fundamental axiom of continuum mechanics, material response should be objective, i.e., indifferent to the observer. In the context of geophysical fluid dynamics, fluid-transporting vortices must satisfy this axiom and hence different observers should come to the same conclusion about the location and size of these vortices. As a consequence, only objectively defined extraction methods can provide reliable results for material vortices.

As velocity fields are inherently non-objective, they render most Eulerian flow-feature detection non-objective. To resolve this issue,  we discuss a general decomposition of a velocity field into an objective deformation component and a rigid-body component. We obtain this decomposition as a solution of a physically motivated extremum problem for the closest rigid-body velocity of a general velocity field.

This extremum problem turns out to have a unique,  physically interpretable,  closed-form solution. Subtracting this solution from the velocity field then gives an objective deformation velocity field that is also physically observable. As a consequence, all common Eulerian feature detection schemes, as well as the momentum, energy, vorticity, enstrophy, and helicity of the flow, become objective when computed from the deformation velocity component. We illustrate the use of this deformation velocity field on several velocity data sets.

How to cite: Kaszás, B., Pedergnana, T., and Haller, G.: The Objective Deformation Component of a Velocity Field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11064, https://doi.org/10.5194/egusphere-egu22-11064, 2022.

EGU22-11118 | Presentations | NP4.1

Explainable community detection of extreme rainfall events using the tangles algorithmic framework 

Merle Kammer, Felix Strnad, and Bedartha Goswami

Climate networks have helped to uncover complex structures in climatic observables from large time series data sets. For instance, climate networks were used to reduce rainfall data to relevant patterns that can be linked to geophysical processes. However, the identification of regions that show similar behavior with respect to the timing and spatial distribution of extreme rainfall events (EREs) remains challenging. 
To address this, we apply a recently developed algorithmic framework based on tangles [1] to discover community structures in the spatial distribution of EREs and to obtain inherently interpretable communities as an output. First, we construct a climate network using time-delayed event synchronization and create a collection of cuts (bipartitions) from the EREs data. By using these cuts, the tangles algorithmic framework allows us to both exploit the climate network structure and incorporate prior knowledge from the data. Applying tangles enables us to create a hierarchical tree representation of communities including the likelihood that spatial locations belong to a community. Each tree layer can be associated to an underlying cut, thus making the division of different communities transparent. 
Applied to global precipitation data, we show that tangles is a promising tool to quantify community structures and to reveal underlying geophysical processes leading to these structures.

 

[1] S. Klepper, C. Elbracht, D. Fioravanti,  J. Kneip, L. Rendsburg, M. Teegen, and U. von Luxburg. Clustering with Tangles: Algorithmic Framework and Theoretical Guarantees. CoRR, abs/2006.14444v2, 2021. URL https://arxiv.org/abs/2006.14444v2.

How to cite: Kammer, M., Strnad, F., and Goswami, B.: Explainable community detection of extreme rainfall events using the tangles algorithmic framework, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11118, https://doi.org/10.5194/egusphere-egu22-11118, 2022.

EGU22-11667 | Presentations | NP4.1

Spurious Behaviour in Networks from Spatio-temporal Data 

Moritz Haas, Bedartha Goswami, and Ulrike von Luxburg

Network-based analyses of dynamical systems have become increasingly popular in climate science. Instead of focussing on the chaotic systems aspect, we come from a statistical perspective and highlight the often ignored fact that the calculated correlation values are only empirical estimates. We find that already the uncertainty stemming from the estimation procedure has major impact on network characteristics. Using isotropic random fields on the sphere, we observe spurious behaviour in commonly constructed networks from finite samples. When the data has locally coherent correlation structure, even spurious link-bundle teleconnections have to be expected. We reevaluate the outcome and robustness of existing studies based on their design choices and null hypotheses.

How to cite: Haas, M., Goswami, B., and von Luxburg, U.: Spurious Behaviour in Networks from Spatio-temporal Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11667, https://doi.org/10.5194/egusphere-egu22-11667, 2022.

EGU22-12351 | Presentations | NP4.1

VAE4OBS: Denoising ocean bottom seismograms using variational autoencoders 

Maria Tsekhmistrenko, Ana Ferreira, Kasra Hosseini, and Thomas Kitching

Data from ocean-bottom seismometers (OBS) are inherently more challenging than their land counterpart because of their noisy environment. Primary and secondary microseismic noises corrupt the recorded time series. Additionally, anthropogenic (e.g., ships) and animal noise (e.g., Whales) contribute to a complex noise that can make it challenging to use traditional filtering methods (e.g., broadband or Gabor filters) to clean and extract information from these seismograms. 

OBS deployments are laborious, expensive, and time-consuming. The data of these deployments are crucial in investigating and covering the "blind spots" where there is a lack of station coverage. It, therefore, becomes vital to remove the noise and retrieve earthquake signals recorded on these seismograms.

We propose analysing and processing such unique and challenging data with Machine Learning (ML), particularly Deep Learning (DL) techniques, where conventional methods fail. We present a variational autoencoder (VAE) architecture to denoise seismic waveforms with the aim to extract more information than previously possible. We argue that, compared to other fields, seismology is well-posed to use ML and DL techniques thanks to massive datasets recorded by seismograms. 

In the first step, we use synthetic seismograms (generated with Instaseis) and white noise to train a deep neural network. We vary the signal-to-noise ratio during training. Such synthetic datasets have two advantages. First, we know the signal and noise (as we have injected the noise ourselves). Second, we can generate large training and validation datasets, one of the prerequisites for high-quality DL models.

Next, we increased the complexity of input data by adding real noise sampled from land and OBS to the synthetic seismograms. Finally, we apply the trained model to real OBS data recorded during the RHUM-RUM experiment.

We present the workflow, the neural network architecture, our training strategy, and the usefulness of our trained models compared to traditional methods.

How to cite: Tsekhmistrenko, M., Ferreira, A., Hosseini, K., and Kitching, T.: VAE4OBS: Denoising ocean bottom seismograms using variational autoencoders, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12351, https://doi.org/10.5194/egusphere-egu22-12351, 2022.

EGU22-13053 | Presentations | NP4.1

Causal Diagnostics for Observations - Experiments with the L63 system 

Nachiketa Chakraborty and Javier Amezcua

Study of cause and effect relationships – causality - is central to identifying mechanisms that cause the phenomena we observe. And in non-linear, dynamical systems, we wish to understand these mechanisms unfolding over time. In areas within physical sciences like geosciences, astrophysics, etc. there are numerous competing causes that drive the system in complicated ways that are hard to disentangle. Hence, it is important to demonstrate how causal attribution works with relatively simpler systems where we have a physical intuition. Furthermore, in earth and atmospheric sciences or meteorology, we have a plethora of observations that are used in both understanding the underlying science beneath the phenomena as well as forecasting. However in order to do this, optimally combining the models (theoretical/numerical) with the observations through data assimilation is a challenging, computationally intensive task. Therefore, understanding the impact of observations and the required cadence is very useful. Here, we present experiments in causal inference and attribution with the Lorenz 63 system – a system studied for a long time. We first test the causal relations between the variables characterising the model. And then we simulate observations using perturbed versions of the model to test the impact of the cadence of observations of each combination of the 3 variables.

How to cite: Chakraborty, N. and Amezcua, J.: Causal Diagnostics for Observations - Experiments with the L63 system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13053, https://doi.org/10.5194/egusphere-egu22-13053, 2022.

An accurate understanding of dynamical similarities and dissimilarities in geomagnetic variability between quiet and disturbed periods has the potential to vastly improve Space Weather diagnosis. During the last years, several approaches rooted in dynamical system theory have demonstrated their great potentials for characterizing the instantaneous level of complexity in geomagnetic activity and solar wind variations, and for revealing indications of intermittent large-scale coupling and generalized synchronization phenomena in the Earth’s electromagnetic environment. In this work, we focus on two complementary approaches based on the concept of recurrences in phase space, both of which quantify subtle geometric properties of the phase space trajectory instead of taking an explicit temporal variability perspective. We first quantify the local (instantaneous) and global fractal dimensions and associated local stability properties of a suite of low (SYM-H, ASY-H) and high latitude (AE, AL, AU) geomagnetic indices and discuss similarities and dissimilarities of the obtained patterns for one year of observations during a solar activity maximum. Subsequently, we proceed with studying bivariate extensions of both approaches, and demonstrate their capability of tracing different levels of interdependency between low and high latitude geomagnetic variability during periods of magnetospheric quiescence and along with perturbations associated with geomagnetic storms and magnetospheric substorms, respectively. Ultimately, we investigate the effect of time scale on the level of dynamical organization of fluctuations by studying iterative reconstructions of the index values based on intrinsic mode functions obtained from univariate and multivariate versions of empirical mode decomposition. Our results open new perspectives on the nonlinear dynamics and (likely intermittent) mutual entanglement of different parts of the geospace electromagnetic environment, including the equatorial and westward auroral electrojets, in dependence of the overall state of the geospace system affected by temporary variations of the solar wind forcing. In addition, they contribute to a better understanding of the potentials and limitations of two contemporary approaches of nonlinear time series analysis in the field of space physics.

How to cite: Donner, R., Alberti, T., and Faranda, D.: Instantaneous fractal dimensions and stability properties of geomagnetic indices based on recurrence networks and extreme value theory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13342, https://doi.org/10.5194/egusphere-egu22-13342, 2022.

EGU22-650 | Presentations | G4.3

Investigation of different geoid computation techniques in the frame of the ModernGravNet project 

Vassilios Grigoriadis, Vassilios Andritsanos, Dimitrios Natsiopoulos, and Georgios Vergos

In the frame of the “Modernization of the Hellenic Gravity Network” project, we aim at computing a high resolution and accuracy geoid for Greece. For this reason, we selected initially two test areas in northern and southern Greece covering an area of about 100 km2 each, where gravity and GNSS/leveling measurements were carried out. Based on these recent, well documented and reliable measurements, we investigate the use of different techniques for the determination of the geoid, including Least-Squares Collocation, FFT and Input-Output Systems, following the Remove-Compute-Restore approach. For the remove/restore part, we examine different Residual Terrain Modeling schemes along with the use of older and recent Global Geopotential Models. Moreover, we compute the geoid-quasigeoid separation term using different approaches. We then validate the results obtained against the new GNSS/leveling measurements across the test areas and draw conclusions towards the determination of a regional geoid for Greece.

How to cite: Grigoriadis, V., Andritsanos, V., Natsiopoulos, D., and Vergos, G.: Investigation of different geoid computation techniques in the frame of the ModernGravNet project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-650, https://doi.org/10.5194/egusphere-egu22-650, 2022.

EGU22-711 | Presentations | G4.3

The deep structure of the Richat magmatic intrusion (northern Mauritania) from geophysical modelling. Insights into its kinematics of emplacement 

El Houssein Abdeina, Sara Bazin, Gilles Chazot, Hervé Bertrand, Bernard Le Gall, Nasrrddine Youbi, Mohamed Salem Sabar, Mohamed Khalil Bensalah, and Moulay Ahmed Boumehdi

The famous circular structure of Richat, sometimes referred to as “the eye of Africa”, is located in the northwestern part of the Taoudeni basin, in the central part of the Mauritanian Adrar plateaus. It is expressed at the surface as a slightly elliptical depression, about 40 kilometers in diameter, marked by concentric ridges of Proterozoic-Lower Paleozoic sediments. Its origin as resulting from either a meteorite impact or a deep magmatic intrusion, has been long debated. Modelling of high-resolution airborne magnetic data as well as satellite gravity data reinforces the intrusion hypothesis. Geophysical modelling has been calibrated by determinations of rock properties from various types of magmatic lithologies sampled in the field. The three complementary types of geophysical data allow us to image at various scales and depths the buried structures of the Richat magmatic complex, to determine the areas most affected by hydrothermal alteration and finally to elaborate a kinematic model for its emplacement. We emphasize that : (1) the Richat intrusion is characterized by the presence of two important circular magnetic signals that coincide with gabbroic ring dykes partly exposed at the surface, (2) its overall circular structure rests above a deep mafic (gabbroic) body, (3) the upwelling of magma at the surface has been facilitated by the presence of concentric faults and (4) the central zone of the complex recorded intense hydrothermal alteration. This case study aims to provide insights for similar types of magma-induced ring structures observed worldwide.

How to cite: Abdeina, E. H., Bazin, S., Chazot, G., Bertrand, H., Le Gall, B., Youbi, N., Sabar, M. S., Bensalah, M. K., and Boumehdi, M. A.: The deep structure of the Richat magmatic intrusion (northern Mauritania) from geophysical modelling. Insights into its kinematics of emplacement, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-711, https://doi.org/10.5194/egusphere-egu22-711, 2022.

EGU22-780 | Presentations | G4.3

Effect of Gravity Data Coverage on the Gravity Field Recovery: Case Study for Egypt (Africa) and Austria 

Hussein Abd-Elmotaal and Norbert Kühtreiber

The coverage of the gravity data plays an important role in the geoid determination. This paper tries to answer whether different geoid determination techniques would be affected similarly by such gravity data coverage. The paper presents the determination of the gravimetric geoid in two different countries where the gravity coverage is quite different. Egypt (representing the same situation in Africa) has sparse gravity data coverage over relatively large area, while Austria has quite dense gravity coverage in a significantly smaller area. Two different geoid determination techniques are tested. They are Stokes’ integral with modified Stokes kernel, for better combination of the gravity field wavelengths, and the least-squares collocation technique. The geoid determination has been performed within the framework of the non-ambiguous window remove-restore technique (Abd-Elmotaal and Kühtreiber, 2003). For Stokes’ geoid determination technique, the Meissl (1971) modified kernel has been used with numerical tests to obtain the best cap size for both geoids in Egypt and Austria. For the least-squares collocation technique, a modelled covariance function is needed. The Tscherning-Rapp (Tscherning and Rapp, 1974) covariance function model has been used after being fitted to the empirically determined covariance function. The paper gives a smart method for such covariance function fitting. All geoids are fitted to GNSS/levelling geoids for both countries. For each country, the computed two geoids are compared and the correlation between their differences versus the gravity coverage is comprehensively discussed.

How to cite: Abd-Elmotaal, H. and Kühtreiber, N.: Effect of Gravity Data Coverage on the Gravity Field Recovery: Case Study for Egypt (Africa) and Austria, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-780, https://doi.org/10.5194/egusphere-egu22-780, 2022.

EGU22-787 | Presentations | G4.3

GOCE SGG data downward continuation to the Earth’s Surface 

Georgios S. Vergos, Eleftherios A. Pitenis, Elisavet G. Mamagiannou, Dimitrios A. Natsiopoulos, and Ilias N. Tziavos

The combination of GOCE Satellite Gravity Gradiometer (SGG) data with local free-air gravity anomalies, towards the estimation of improved geoid and gravity field models, requires their downward continuation to the Earth’s surface (ES). Within the GeoGravGOCE project, which aims to explore the local improvements in geoid and gravity field modeling offered by GOCE, optimal combination of GOCE and surface data was sought in order to acquire insights of their contribution especially over poorly surveyed areas. GOCE SGG data are first pre-processed, to filter out noise and reduce long-wavelength correlated errors, and are consequently reduced to a mean orbit (MO) so that downward continuation to the Earth’s surface can be carried out. The reduction from the orbit level to a MO was performed by estimating GGM gradient grids per 1 km from the MO to the maximum orbital level, and then linearly interpolating for the reduction from the actual satellite height. Having determined the filtered GOCE filtered SGG data to a MO, the next step referred to their downward continuation to the ES. Gravity anomalies from XGM2016 generated on the ES have been used as ground truth and were upward continued to the MO in the spectral domain through the input output system theory method. The evaluation of GOCE SGG data to the MO with GGM-derived gradients is performed using a Monte-Carlo annihilation method finding the global minimum of a cost function that may possess several local minima. The GOCE data that satisfy the aforementioned criteria of this simulated annealing method are frozen and the steps mentioned above are repeated until all generated SGG data meet the criterion. The developed procedure can be successfully applied for downward continuation of GOCE SGG from a MO to the ES for regional gravity field applications. The present work summarizes the results achieved while the evaluation is performed against local free-air gravity anomalies and residuals to XGM2019.

How to cite: Vergos, G. S., Pitenis, E. A., Mamagiannou, E. G., Natsiopoulos, D. A., and Tziavos, I. N.: GOCE SGG data downward continuation to the Earth’s Surface, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-787, https://doi.org/10.5194/egusphere-egu22-787, 2022.

EGU22-927 | Presentations | G4.3

Practical implementation of the IHRF employing local gravity data and geoid models 

Riccardo Barzaghi and Georgios Vergos

With the definition of the International Height Reference System (IHRS) and the development of a roadmap for its implementation through the International Height Reference Frame (IHRF), an analytical evaluation of the various approaches for the practical determination of potential values at IHRF is necessary. In this work we focus on two main approaches to estimate geopotential values at IHRF stations. The first approach resides on the use of either local gravity anomalies and gravity disturbances around each site and the geopotential determination based on Stokes’ and Molodensky’s boundary value problems, respectively. In this scheme, the influence of the classical residual terrain model (RTM) reduction as well as that of RTM effects based on spherical harmonics expansion of the topographic potential are investigated. Furthermore, the introduction of possible biases within the various pre- and post-processing steps are thoroughly investigated, as e.g., during the estimation of station geometric heights, along with the influence of the quasi-geoid to geoid separation estimation. In the second approach, we investigate the determination of geopotential values based on either national and regional geoid models, i.e., resembling the case that access to local gravity data is not available, and the determination has to be based on some available geoid model. In the present work we analyze the theoretical and methodological steps that need to be followed in each approach, identifying the possible sources of biases. Finally, some early results are presented aiming at providing a roadmap and an error assessment for the practical realization of the IHRF.

How to cite: Barzaghi, R. and Vergos, G.: Practical implementation of the IHRF employing local gravity data and geoid models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-927, https://doi.org/10.5194/egusphere-egu22-927, 2022.

EGU22-1602 | Presentations | G4.3

Comparison between towed absolute and shipborne 3C fluxgate magnetic measurements in shallow water. Applications for marine geophysical surveys. 

Hugo Reiller, Jean-François Oehler, Sylvain Lucas, Guy Marquis, Didier Rouxel, and Marc Munschy

We compare marine magnetic measurements simultaneously acquired with absolute and three-component fluxgate sensors to evaluate their respective benefits for marine geophysical mapping and detection surveys.

Shom collected the data in shallow waters, in the Bay of Brest (France) and in the Iroise Sea, during two cruises in the Fall 2021. As per standard practice, an absolute Overhauser magnetometer was towed 180 m behind the 60 m-long Laplace and Lapérouse hydrographic vessels. In addition, two vector magnetometers were temporarily installed at the top of the ship’s mast and on the roof of a 10 m-long launch. Scalar data were processed following Shom’s standards: shift to sensor position, layback adjustments, removal of gyrations and spikes, filtering and calculation of magnetic anomalies by removing the IGRF model (Alken et al., 2021) and reducing external variations measured at a local reference station. Vector data were corrected for the strong magnetic fields generated by the hull and other steel components of the ship by the application of a “scalar compensation” using a least-squares regression analysis (Leliak, 1961) on data from figures of merit. The compensated vector data then need to be low-pass filtered to remove uncorrected variations of attitude and heading. Magnetic anomalies were finally computed by removing the median value for each profile and reducing external variations from the same local reference station.

Our first results show that maps of total-field anomalies derived from vector data acquired on the ship are very close to those of the absolute data upward-continued to the altitude of the mast. This similarity suggests that it is possible to perform good-quality magnetic surveys without the constraint of having to tow an instrument. The different processing steps however raise the detection threshold for anthropogenic objects lying on the seafloor or partially buried. Vector data acquired on smaller launchs are much more complicated to compensate as ranges of pitch, roll and heading variations are greater than for a large ship and potentially imperfectly sampled by the figures of merit.

How to cite: Reiller, H., Oehler, J.-F., Lucas, S., Marquis, G., Rouxel, D., and Munschy, M.: Comparison between towed absolute and shipborne 3C fluxgate magnetic measurements in shallow water. Applications for marine geophysical surveys., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1602, https://doi.org/10.5194/egusphere-egu22-1602, 2022.

EGU22-1673 | Presentations | G4.3

Crustal structures from receiver functions and gravity analysis in central Mongolia 

Alexandra Guy, Christel Tiberi, and Saandar Mijiddorj

3D forward gravity modelling combined with receiver function analysis characterize the structures of the southern part of the Mongolian collage. Recently, a multidisciplinary approach integrating potential field analysis with geology and magmatic geochemistry demonstrate that relamination of an allochtonous felsic to intermediate lower crust played a major role in southern Mongolia structure. Relamination of material induces a homogeneous layer in the lower crust, which contrasts with the highly heterogeneous upper crustal part composed of different lithotectonic domains. The seismic signals of the 48 stations of the MOBAL2003 and the IRIS-PASSCAL experiments were analyzed to get the receiver functions. The resulting crustal thickness variation is first compared with the topography of the Moho determined by the 3D forward modeling of the GOCE gravity gradients. In addition, seismic stations south of the Hangay dome display significant signal related to the occurrence of a low velocity zone (LVZ) at lower crustal level. The receiver function analysis also revealed a significant difference between the crustal structures of the Hangay dome and the tectonic zones in the south. Finally, these seismic analysis inputs such as crustal thickness, strike and dips of the seismic interfaces as well as the boundaries and the lithologies of the different tectonic zones constitute the starting points from the 3D forward gravity modelling. The combination of these two independent methods enhances the occurrence and the extent of a low velocity and a low density zone (LVLDZ) at lower crustal level beneath central Mongolia. These LVLDZ may demonstrate the existence of the relamination of a hydrous material in southern Mongolia.

How to cite: Guy, A., Tiberi, C., and Mijiddorj, S.: Crustal structures from receiver functions and gravity analysis in central Mongolia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1673, https://doi.org/10.5194/egusphere-egu22-1673, 2022.

EGU22-1899 | Presentations | G4.3

Bathymetric Effects on Geoid Modeling 

Xiaopeng Li, Miao Lin, Jordan Krcmaric, Yuanyuan Jia, Ck Shum, and Daniel Roman

Bathymetric data over lake areas are not included in previous NGS (National Geodetic Survey) geoid model computations. Mean lake surfaces are used as the bare rock surface during the modeling. This approximation treats the water body as rocks with the same size, and causes errors that can be avoided. This study uses the bathymetric model to rigorously compute the volume of water bodies instead of treating them as rocks, during geoid modeling. To make fair comparisons and show the effects clearly, three sets of geoid models are generated with the same theory currently used at NGS, and with the same parameters. Model-Base is computed without bathymetric information of the water body. In this model, the real water bodies are simply replaced by rocks. Model-Condensed and Model-Density are generated with bathymetric information. The treatments of water bodies are different between the two models, but both are based on the hypothesis of mass conservation. The water bodies are condensed into the equivalent rocks in the Model-Condensed, leading to the geometrical shape changes in the lake area. In the Model-Density, the density of each topographical column bounded by the lake surface and geoid is taken as the average of the density of water and rock bodies included in this column, resulting in the density changes in the lake area. The study area is focused on the Great Lakes area of North America. The geoid model differences between Model-Condensed and Model-Base range from -18 to 25 mm, forming a Gaussian distribution. The distribution of the geoid model differences between Model-Density and Model-Base are not in a Gaussian form, and their values are in the range between -1 and 18 mm. Both the nearby GNSS/Leveling bench marks from US and the multi-year averaged altimetry data are used to validate the results. Consistent geoid model precision improvements of about 2 mm are confirmed around the Lake Superior, which is the deepest and largest lake, over all selected frequency bands of the Stokes’s kernel. The numerical results prove the importance of considering water bodies in the determination of a high-accuracy geoid model over the Great Lakes area.

How to cite: Li, X., Lin, M., Krcmaric, J., Jia, Y., Shum, C., and Roman, D.: Bathymetric Effects on Geoid Modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1899, https://doi.org/10.5194/egusphere-egu22-1899, 2022.

EGU22-2625 | Presentations | G4.3

Magnetic and gravimetric modeling of the Monchique magmatic intrusion in south Portugal 

Gabriela Camargo, Marta Neres, Machiel Bos, Bento Martins, Susana Custódio, and Pedro Terrinha

The Monchique alkaline complex (MAC) crops out in southern Portugal with a roughly elliptical shape of about 80 km2 elongated along ENE-WSW direction. The MAC dates to Late Cretaceous (69-72 Ma) and intrudes the Carboniferous Flysh formation of the South Portuguese Zone. At the surface, it comprises two main types of syenites: a central homogeneous nepheline syenite surrounded by a heterogeneous syenite unit, and some less expressive outcrops of mafic rocks (gabbros, hornfels, breccia and basalts). This igneous complex belongs to the Upper Cretaceous West Iberia alkaline magmatic event, characterized by alkaline magmatism of sublithospheric origin and active from approximately 100 Ma to 69 Ma.

The Monchique region hosts the most active seismic cluster of mainland Portugal, with low magnitude earthquakes (M < 4) that occur along lineations with NNE–SSW and WNW–ESE preferred orientation.

In this work we study the Monchique region through gravimetric and magnetic methods in order to: 1) better understand how the MAC influences the geomagnetic and gravimetric field in the region; 2) to create a new and consistent 2D and 3D model for the intrusion; and 3) to help constraining the origin of the observed seismicity and its possible relation with the existence of subcropping magmatic bodies.

We process recently acquired data - ground gravity survey (49 points) and drone-borne aeromagnetic survey – and integrate it with existing data. The interpretation of gravimetric results is complemented by density analysis of magmatic and host rocks. We perform 3D magnetic and gravity inversion to model the geometry of gravity and magnetic sources, and 2D magnetic forward modeling along a representative profile.

The calculated Bouguer gravity anomaly shows a positive gradient towards the southwest with a negative peak in the center of the Monchique mountain. However, when applied the terrain correction (complete Bouguer anomaly), this peak vanishes. This is justified by the similar mean density values for the syenite and host rocks, respectively 2560 kg/m3 and 2529 kg/m3.

The new aeromagnetic data allows for mapping the Monchique magnetic anomaly with unprecedented detail and reveal a 10 km elongated anomaly with 30 m wavelength with maximum 1707 nT amplitude. 3D susceptibility inversion models show a 15km long body with maximum depth between 5-10km, and susceptibility >0.02 SI, in agreement with previous susceptibility analysis in the region. The highest magnetic signal is found at Picota hill (east), but the deepest parts of the intrusion seem to be bellow Foia hill (west). It is noteworthy that earthquake hypocenters concentrate at depths of 5-20 km, thus below most of the modeled magmatic intrusion.  

This work was developed for the MSc thesis of GCC, in the frame of ATLAS project (PTDC/CTA-GEF/31272/2017), POCI-01-0145-FEDER-031272, FEDER-COMPETE/POCI 2020) partly funded by FCT. FCT is further acknowledged for support through projects UIDB/50019/2020-IDL, PTDC/CTA-GEF/1666/2020 and PTDC/CTA-GEF/6674/2020.

How to cite: Camargo, G., Neres, M., Bos, M., Martins, B., Custódio, S., and Terrinha, P.: Magnetic and gravimetric modeling of the Monchique magmatic intrusion in south Portugal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2625, https://doi.org/10.5194/egusphere-egu22-2625, 2022.

The presence of subglacial sediments is important in enabling streaming ice flow and may be a critical controlling factor in determining the onset regions of ice streams. Improving our knowledge of the location of sedimentary basins underlying large ice sheets will improve our understanding of how the substrate influences the ice streams.  Advancing our understanding of the interaction between subglacial sediments and ice flow is critical for predictions of ice sheet behavior and the consequences on future climate change. To date, no comprehensive distribution of onshore and offshore sedimentary basins over Antarctica has been developed. The goal of this project is to use a combination of large-scale datasets to characterize known basins and identify new sedimentary basins to produce a continent-wide mapping of sedimentary basins and provide improved basal parametrizations conditions that have the potential to support more realistic ice sheet models. The proposed work is divided into three main steps. In the first step, the Random Forest (RF), a supervised machine learning algorithm, is used to identify sedimentary basins in Antarctica. In the second step, a regression analyses between aerogravity data and topography is done to evaluate the gravity signal related to superficial heterogeneities (i.e. sediments) and compare the results to the depth of magnetic sources using the Werner deconvolution method. Last, the correlation between sedimentary basins and ice streams is investigated. Here, we will present the preliminary results from Step 1. The Random Forest uses ensemble learning method for classification and regression. The classification rules for this present work are based on the geophysical parameters of major known sedimentary basins. First we classify the known basins with all available geophysical compilations including topography, gravity and magnetic anomalies, sedimentary thickness, crustal thickness, geothermal heat flux, information on the geology, rocky type and bedrock geochemistry, and then use the Random Forest machine learning algorithm to classify the geology underneath the ice into consolidated rock and sediments based on these parameters.

How to cite: Constantino, R. R., Tinto, K. J., and Bell, R. E.: Using random forest machine learning algorithm to help investigating the relationship between subglacial sediments and ice flow in Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2658, https://doi.org/10.5194/egusphere-egu22-2658, 2022.

EGU22-3409 | Presentations | G4.3

Short-wavelength Bouguer anomaly and folding with disclination in the northeastern Japan 

Mitsuhiro Hirano and Hiroyuki Nagahama

In the northeastern Japan arc with the active compressive stress field since ~3 Ma, it is reported that a characteristic relationship between crustal deformation including faulting and short-wavelength (< 160 km) Bouguer anomalies. According to previous studies, active faults tend to be located in negative regions, which are caused by cracks and volumetric strain due to accumulated fault dislocation. Especially, it is shown that in strain concentration zones with active faults and muti folding, the effect of accumulated fault dislocation forms the negative zones of gravity anomaly along the northeastern Japan arc, impacting the pattern of short-wavelength Bouguer anomalies throughout the entire arc. In this presentation, we extend this concept further and discuss the positive and negative zones of gravity zones along the entire northeastern Japan arc from the geometrical viewpoint of folding with one of the defect, disclination. Folding is described by Euler-Schouten curvature tensor, which defines the protrusion of included space (e.g., two-dimensional Riemannian space) from enveloping space (e.g., three-dimensional Euclid space). Based on previous studies, the density of earthquake occurrence is proportional to the curvature of the plastic folding deformation of the crust, which is related to Euler-Schouten curvature, and fault dislocation also accumulates at the regions with its high curvature. The row (accumulation) of fault dislocation can be replaced by the disclination, and Riemann-Christoffel curvature, derived from Euler-Schouten curvature tensor, also expresses disclination density. In particular, angular folding with local curvature accompanied by a pair of disclination is called Kink folding, forming the mass-loss or mass-excess regions around disclination. Since Kink folding can approximately be the same as the undulating region bounded by several faults (fault block) in strain concentration zones, it is expected that the northeastern Japan arc has not only negative zones of gravity anomaly but also positive zones along the arc due to the mass-loss or mass-excess regions around disclination. Therefore, we conclude that the positive and negative zones of gravity anomaly along the northeastern Japan arc reflect the geometric condition of the crust with disclination.

How to cite: Hirano, M. and Nagahama, H.: Short-wavelength Bouguer anomaly and folding with disclination in the northeastern Japan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3409, https://doi.org/10.5194/egusphere-egu22-3409, 2022.

EGU22-3615 | Presentations | G4.3

Moho depth evaluation using GOCE gradient data and Least Square Collocation over Iran 

Carlo Iapige De Gaetani, Hadi Heydarizadeh Shali, Sabah Ramouz, Abdolreza Safari, and Riccardo Barzaghi

Investigating the crustal architecture, specifically the discontinuity interface between the upper mantle and lower crust of the Earth, so-called Moho, can be done in three prevailing techniques, namely lithology, seismicity, and gravity. In contrast to using the information from analyzing the characteristics of rocks and seismic waves, which are sparsed and expensive, inverting gravity data of satellite missions such as GOCE and GRACE is a suitable alternative for such purposes.

The present paper attempts to map the Moho surface using the gravity data as we considered a simplified Earth model based on three shells including the core, mantle and crust with a potential T on a given sphere outside this body. In this notation, by subtracting the topographic effects, compensating for density anomalies in the crust, and other known constants from the observation that are given on and outside the mean Earth radius, one is left with the potential of a single layer on the mean Moho sphere by taking into consideration the Helmert condensation approach. In planar approximation, this is to say that the topography is formally referred to an xy plane and also the condensation surface which is a plane, situated at a depth D below the previous one. Therefore, relating the topographic load of a mass column with height h over the same elementary area element at depth d, the measure of how deep the crust is sinking into the mantle material as a consequence of the load, we can interpret the Moho variations with respect to some mean crustal thickness.

To do this inversion, we applied the Least Square Collocation (LSC) approach which uses the functional relationships between the quantities, the auto-covariance and cross-covariance matrices based on a covariance function between observations and the unknowns. Practically, after constructing the required residual data, an empirical covariance is estimated, then fitted to analytical one to define the required covariance models.

Finally, the Moho variations has been estimated in an active tectonic zone created by the continental collision of the Arabian plate from South-West and Turan shield from North-East with respect to a mean Moho depth equal to 45 km. Results of this study are comparable and much the same with other studies so that different rheological zones of Iranian plateau can be seen in this estimated map of Moho. For instance, a maximum depth is estimated for Sanandaj-Sirjan zones in South-East and minimum depth for Caspian Sea in North.

How to cite: De Gaetani, C. I., Heydarizadeh Shali, H., Ramouz, S., Safari, A., and Barzaghi, R.: Moho depth evaluation using GOCE gradient data and Least Square Collocation over Iran, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3615, https://doi.org/10.5194/egusphere-egu22-3615, 2022.

EGU22-4230 | Presentations | G4.3

Crowd modelling: Launching an open gravity-modelling call to challenge the Balmuccia peridotite body 

György Hetényi, Ludovic Baron, Matteo Scarponi, Shiba Subedi, Konstantinos Michailos, Fergus Dal, Anna Gerle, Benoît Petri, Antonio Langone, Andrew Greenwood, Luca Ziberna, Mattia Pistone, Alberto Zanetti, and Othmar Müntener

Modelling of geophysical data is often subject to choices made by the researcher undertaking the work. The level of structural complexity in the model, the bounds on parameters imposed by a priori knowledge, the thoroughness and efficiency in exploring the parameter space may all lead to bias in determining what the best fitting models can be.

To avoid bias from our own ideas in constraining the subsurface shape of a given density anomaly, we hereby invite anyone interested to create their own models. This is planned by sharing the same gravity data measured in the field, the same digital elevation model, the main features of the local geological maps, and bounds on the encountered rock density values. These data will be shared openly, in the form of a modelling challenge: each participating researcher or group is expected to submit their solution(s). All these will be compared during a dedicated workshop, ultimately resulting in a joint publication.

The target of this modelling challenge is the world-famous Balmuccia peridotite body (45.84°N, 8.16°E) in the Ivrea-Verbano Zone (IVZ). Here mantle rocks are naturally exposed at the surface, in the broader context of the IVZ, a middle- to lower crustal terrain along the Europe-Adria plate boundary’s eastern side. The surface exposure of the Balmuccia peridotite is ~ 4.4 km N-S by 0.6 km E-W, with outcrop elevation changes exceeding 1000 m. About 150 new gravity data points have been measured within a radius of 3 km from the centre of the peridotite body, along more or less accessible paths and slopes. The measurements have been carried out with a Scintrex CG-5 relative gravimeter, tied to a reference point, and all points located via differential GPS with typical vertical precision of a few cm. Farther away regional gravity data is available at few km spacing.

Beyond the modelling challenge, the interest in constraining the subsurface shape of the Balmuccia peridotite body is its future target role in the ICDP DIVE continental drilling project (www.dive2ivrea.org).

How to cite: Hetényi, G., Baron, L., Scarponi, M., Subedi, S., Michailos, K., Dal, F., Gerle, A., Petri, B., Langone, A., Greenwood, A., Ziberna, L., Pistone, M., Zanetti, A., and Müntener, O.: Crowd modelling: Launching an open gravity-modelling call to challenge the Balmuccia peridotite body, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4230, https://doi.org/10.5194/egusphere-egu22-4230, 2022.

EGU22-4803 | Presentations | G4.3

Separation of gravimetric and magnetic anomalies with different degrees of regionality in the Eastern Carpathians, Romania 

Natalia-Silvia Asimopolos and Laurentiu Asimopolos

The gravity and magnetic anomalies separation operation consists in determining the number of sources, the characteristics of each (depth, density, shape, and dimensions) so as to result in cumulative total anomaly, measured at the Earth’s surface. This separation has to be done in the context of the fundamental ambiguity of gravimetric and magnetic information, based on the cause-effect ratio. There are various methods for achieving this separation of anomalies. This paper presents some examples of the use of the moving average method and the polynomial trend surfaces. In particular, we presented the results of the mobile mediation with different windows compared to the tendency surfaces with different degrees, for a case study in Eastern Carpathians mountains area. For this study we used data available from several sources.

From the International Gravimetric Bureau we used gravimetric data for the WGM2012 geoglobal model: Bouguer anomaly for density 2.67 g / cm3, outdoor anomaly, isostatic anomaly, gravitational disturbance and altitude.

From the geophysics portal of the Geological Institute of Romania we used the magnetic data resulting both from the scanning of the national geomagnetic maps and from the catalogs of measurements from the archive. We also used the deep geological sections made on the basis of seismic data, corroborated with gravimetric and magnetic data that cross the Eastern Carpathians.

Other data used for depth correlations were the isobath map of the Moho surface, the Conrad surface, the geoid, and the quasigeoid.

For the study of deep tectonics based on all the data used we used the correlation coefficient between various parameters, calculated in movable windows of different sizes both in plan and in space. For this we have developed specific calculation programs.  The moving average is a direct method for separating regional effects and local (residual) effects. Polynomial trend surfaces analysis contributes to the recognition, isolation and measurement of trends that can be calculated and represented by analytical equations, thus achieving a separation in regional and local variations. The analytical expressions of the polynomial trends based on the least squares method were calculated, highlighting the regional trend caused by the deep structures. Then, by calculating the residual values resulting from the difference between the initial values and the trend values from the network nodes used, we highlighted the superficial local effects. We also obtained information about the regional trend caused by geological structures at medium and large depths, by calculating the difference between gravity parameters, obtained with different moving average windows or tendency surfaces with different degrees, interpolated in same network.

How to cite: Asimopolos, N.-S. and Asimopolos, L.: Separation of gravimetric and magnetic anomalies with different degrees of regionality in the Eastern Carpathians, Romania, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4803, https://doi.org/10.5194/egusphere-egu22-4803, 2022.

EGU22-6489 | Presentations | G4.3

Drone-magnetic survey along the Alentejo coast (SW Portugal): a quest for the intruded Messejana fault 

Diogo Rodrigues, Marta Neres, Pedro Terrinha, Machiel Bos, and Bento Martins
 
 

How to cite: Rodrigues, D., Neres, M., Terrinha, P., Bos, M., and Martins, B.: Drone-magnetic survey along the Alentejo coast (SW Portugal): a quest for the intruded Messejana fault, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6489, https://doi.org/10.5194/egusphere-egu22-6489, 2022.

EGU22-6615 | Presentations | G4.3

Examination of magnetic map variability and uncertainty: crustal magnetic anomalies in oceanic areas 

Richard Saltus, Arnaud Chulliat, Brian Meyer, and Martin Bates

To paraphrase a common model aphorism: “all magnetic maps are wrong, some are useful”. In other words, all maps of the Earth’s magnetic field are subject to uncertainty, both observationally and dynamically. Depending on the intended use of the map, this uncertainty will have varying implications. For those of us who build and use magnetic maps it is important to gain understanding of the uncertainty in these maps to ensure that they are clearly presented and suitable for a given use.

Uncertainty evaluation is a general challenge that affects all magnetic maps and models, but here we concentrate on maps of magnetic anomalies (i.e., perturbations of the Earth’s main field primarily due to variations in magnetic minerals in the crust and shallow mantle) in oceanic areas.

Magnetic anomaly maps for oceanic regions are typically representations of gridded data. The grids are built from available data which generally consists of marine trackline data with a range of ages, collection parameters and uncertainty in original observations. Data coverage and trackline geometries are highly variable around the world. For example, near-shore regions in the Northern Hemisphere tend to be well sampled, whereas open ocean portions of the Southern Hemisphere are poorly sampled.

Quantification of cell by cell uncertainty for magnetic anomaly grids can be subdivided into two regimes: cells containing data and cells without data. For cells containing data, factors such as point-wise observation uncertainty, number of observations, and spatial distribution of data, can be analysed to estimate grid value uncertainty. For interpolated cells, factors such as distance to nearest data cells, local field behavior, and uncertainty in surrounding cells are relevant.

Using NOAA/NCEI trackline marine data for portions of the Caribbean Sea and North Atlantic we are constructing and testing uncertainty models and methods for representing this uncertainty for a variety of magnetic map uses. For a marine magnetic anomaly grid of a portion of the North Atlantic at a 4 km grid interval (the same grid interval used by our global EMAG2 magnetic anomaly compilation), the calculated cell level uncertainty ranges from 20 nT to 150 nT with a mean value of 90 nT. This mean value is similar to the average grid uncertainty of 100 nT/cell that we estimated for marine areas of EMAG2v3. Different gridding approaches, including kriging or minimum curvature algorithms, yield variations in individual cell values, but these variations fall within our estimated uncertainty ranges. 

How to cite: Saltus, R., Chulliat, A., Meyer, B., and Bates, M.: Examination of magnetic map variability and uncertainty: crustal magnetic anomalies in oceanic areas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6615, https://doi.org/10.5194/egusphere-egu22-6615, 2022.

EGU22-6671 | Presentations | G4.3

Accuracy requirements of the gravity measurements for sub-centimetre geoid 

Ismael Foroughi, Spiros Pagiatakis, Mehdi Goli, and Stephen Ferguson

In this contribution, we estimate the uncertainty (error) of the input gravity measurements needed for the determination of the geoid with an internal sub-centimetre accuracy. The accuracy of the geoid height is a function of the resolution/accuracy of the input gravity and topographical data, and the methodology used to solve a geodetic boundary value problem. The purpose of this study is to estimate the maximum allowable error in the terrestrial gravity measurements based on a required standard deviation of the error in the geoid heights (e.g., ≤1cm). This is done with an assumption of a known Digital Elevation Model (DEM), and an Earth Gravitational Model (EGM) along with their error estimates.

 

We use the one-step integration method (one-step kernel) for the determination of the geoid. In this method, the anomalous gravity at any surface above the geoid is estimated by integrating over the geoid-level disturbing potentials in harmonic space. By applying the covariance law to the one-step integration method, the error of the gravity measurements at the Earth's surface can be estimated using the expected error of the geoid heights. Taking advantage of the remove-compute-restore technique, we estimate the error of the residual surface gravity measurements using the (known) error estimates of the topographical and EGM corrections.  

 

We select the Colorado test area (35°N - 40°N, 250°E - 258°E) to generate a 1¢×1¢ grid of geoid random errors with a standard deviation of 1cm. We use the topographical data from the Shuttle Radar Topography Mission (SRTM) Ver. 3.0. and the global model of DIR_R5 up to degree/order 140 to apply the remove-compute-restore technique. The uncertainty estimate of the SRTM heights and the covariance matrix of the spherical harmonic coefficients of the DIR_R5 are used to calculate the errors of the topographical gravitational attraction and low-degree EGM signals on the geoid heights and surface anomalous gravity data.

 

Our preliminary results show that to achieve a sub-centimetre accuracy in the Colorado area, we require grid surface gravity measurements with a standard deviation of less than 2.5mGal. This result is optimistic as in the geoid determination process, the anomalous gravity data are downward continued from the Earth’s surface to the geoid, whereas this step is not required in our experience. Besides, we assume a constant standard deviation of 1cm for all the errors of the geoid heights, whereas such high accuracy may not be needed in high mountains. We will provide further results for the elevation-dependent geoid error and also investigate the effect of downward continuation on our results.     

How to cite: Foroughi, I., Pagiatakis, S., Goli, M., and Ferguson, S.: Accuracy requirements of the gravity measurements for sub-centimetre geoid, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6671, https://doi.org/10.5194/egusphere-egu22-6671, 2022.

EGU22-7769 | Presentations | G4.3

Two-dimensional gravity and magnetic model along a new WARR profile in the transition zone from the Precambrian to Palaeozoic platform in the southern Baltic 

Małgorzata Ponikowska, Stanislaw Mazur, Tomasz Janik, Dariusz Wójcik, Michał Malinowski, Christian Hübscher, and Ingo Heyde

Defining a transition zone between the Precambrian East European Craton (EEC) and the Palaeozoic West European Platform (WEP) is still a matter of discussion despite a large body of geophysical and geological data. The main tectonic feature of the transition zone is the Teisseyre-Tornquist Zone (TTZ), which has been variously interpreted over the past decades mainly because of a thick (c. 10 km) Palaeozoic and Mesozoic sedimentary cover masking its crustal architecture.  We investigated the crustal structure of the TTZ using a 270-km long wide-angle reflection/refraction profile (WARR) measured along 15 ocean-bottom seismometers and 2 land stations during the course of the RV MARIA S. MERIAN expedition ‘MSM52’. This NE to SW profile is oriented nearly parallel to the Polish coast, located ~ 48 km south of the Danish island of Bornholm. We prepared a two-dimensional gravity and magnetic forward model along this profile, using the Geosoft GM-SYS software with layers of infinite length. The basis for the potential field modelling is a seismic velocity model that has been prepared through trial-and-error forward modelling.

The seismic velocity model shows a continuity of the lower and middle crust of the EEC towards the basement of the WEP. The synthetic magnetic profile is smooth and indicates that the seismic data accurately revealed the geometry and depth of the magnetic (crystalline) basement. However, the model was unable to replicate short-wavelength, high-amplitude magnetic anomalies in the ENE section of the profile, probably representing iron oxide mineralisation in the crystalline basement of the EEC. The gravity model shows 3 areas of misfit between the synthetic and observed gravity profile. The most prominent misfit coincides with the NE boundary of the TTZ. To remedy the misfit, we produced two alternative gravity models that deviate from the seismic velocity model in the problematic area. One model postulates a crustal keel underneath the NE section of the TTZ and the other suggests the presence of a middle crust magmatic intrusion. Both models equally and adequately reduce the misfit of the gravity model.

Our models suggest a SW-ward continuation of the Baltica middle and lower crust through the TTZ and seem to preclude the coincidence of the Caledonian Thor suture with the TTZ. An important perturbation of the upper crust and sedimentary cover within the latter is mostly associated with the superimposed effects of Devonian-Carboniferous and Permian-Mesozoic extension. The only conspicuous compressional event confirmed by our data is the Late Cretaceous-Paleogene inversion of the Permian-Mesozoic basin. Due to limited resolution, our models did not reveal the effects of Caledonian nor Variscan shortening, including the Caledonian Deformation Front.

This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316.

How to cite: Ponikowska, M., Mazur, S., Janik, T., Wójcik, D., Malinowski, M., Hübscher, C., and Heyde, I.: Two-dimensional gravity and magnetic model along a new WARR profile in the transition zone from the Precambrian to Palaeozoic platform in the southern Baltic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7769, https://doi.org/10.5194/egusphere-egu22-7769, 2022.

EGU22-8228 | Presentations | G4.3

New insights to characterize the La Cerdanya basin structure from 3D gravity modelling 

Pilar Clariana, Roberto Muñoz, Concepción Ayala, Fabián Bellmunt, Perla Piña-Varas, Ruth Soto, Anna Gabàs, Albert Macau, Félix Rubio, Carmen Rey-Moral, and Joan Martí

The acquisition and interpretation of gravity and magnetic data represents a cost-effective tool in geophysics since it allows to determine the geometry and distribution of the density and magnetic properties at depth of the subsurface rocks. The study area, where gravity and magnetic data have been interpreted, is the La Cerdanya basin (Eastern Pyrenees), a Neogene ENE-WSW oriented half graben located in the Axial Zone, the central part of the Pyrenees mainly formed by Paleozoic rocks. It is situated in the NW block of the La Tet fault and its Neogene sediments lie unconformably on top of the Paleozoic basement. Its dimensions are approximately 30 km long and 7 km wide. The tectonic evolution and geometry of the La Cerdanya basin is not well known and this work aims to add new constraints to help solving the Neogene tectonic evolution of the Eastern Pyrenees and to improve the knowledge of its 3D geometry. 

The magnetic anomaly map of the study area, based on airborne magnetic data, shows very little contrasts of the magnetic properties between the Neogene rocks of the La Cerdanya basin and the Paleozoic rocks surrounding it. Gravity data consist of previous and new acquired gravimetric stations and the residual Bouguer anomaly map shows density contrasts big enough to model the geometry of the basin and the neighbor intrusive bodies. They have been incorporated into a 3D geological model based on available geological and petrophysical data using the 3D GeoModeller software. The 3D potential fields model has been made taking into account the three most representative units outcropping in the study area: the Neogene rocks, the Late Carboniferous intrusive bodies and the Paleozoic basement. The resulting potential fields response of the model is consistent with the observed data. The 3D model shows a basin slightly deeper than shown in previous works and has helped to better define the 3D geometry of the basin and the along-strike geometry of the La Tet fault.

How to cite: Clariana, P., Muñoz, R., Ayala, C., Bellmunt, F., Piña-Varas, P., Soto, R., Gabàs, A., Macau, A., Rubio, F., Rey-Moral, C., and Martí, J.: New insights to characterize the La Cerdanya basin structure from 3D gravity modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8228, https://doi.org/10.5194/egusphere-egu22-8228, 2022.

Magnetic surveys employing Uncrewed Aerial Systems (UAS) allow a fast and affordable acquisition of high-resolution data. We developed a self-built carbon-fiber frame which can be used to attach magnetometers 0.5 m below an UAS. In order to remove undesired signals from the magnetic recordings that originate from the aircraft and that can cause strong heading errors, we apply calibration processes often referred to as magnetic compensation. These processes are usually applied for manned aerial surveys for both scalar and vector magnetometer data and require flying a calibration pattern prior to a survey. We recently published open-source software written in Python to process data and compute compensations for both scalar and vector magnetometers. We tested our method with two commercially available magnetometer systems (scalar and vector) by flying dense grid patterns over a test site using different suspension methods (magnetometer system attached to 2.8 m long tethers, fixed on the landing gear of the UAS, and fixed on our frame configuration). The accuracy of the magnetic recordings was assessed using both standard deviations of the calibration pattern and tie-line cross-over differences from the grid survey. Our frame configuration resulted after magnetic compensation in the highest accuracy of all configurations tested. The frame also allows for the acquisition of aeromagnetic data under a wide range of flight conditions. This is of great advantage compared to the often-used tethered solutions to avoid recording the aircraft’s signals. Since tethered payloads are prone to rotations and swing motions, they require skilled pilots and can be difficult to fly safely. In contrast to that, our system is easy to use and due to its high in-flight stability, even fully autonomous flights are possible. Since the calibration flights that are required for magnetic compensation need to be collected in areas with low magnetic gradients, it can be difficult to find suitable locations in areas with strong magnetic gradients – such as in volcanic and geothermally active regions. However, a survey collected at the location of the calibration site can be used to evaluate the geological magnetic signal. The compensation process involves then two successive evaluations of the compensation parameters. First, an approximate evaluation of the compensation parameters is done assuming a constant value of the magnetic field at the calibration site. The resulting compensation parameters are then used to compensate the survey data collected over the calibration site and evaluate the magnetic field along the calibration pattern trajectory. Second, the compensation parameters are reevaluated taking the magnetic field variations into account. We tested this double calibration scheme on recordings that were collected over the Krafla geothermal area in the Northern Volcanic Zone of Iceland. The double calibrated data resulted in higher accuracy than a single calibration showing that this method can improve magnetic compensation in magnetically high-gradient areas.

How to cite: Kaub, L., Bouligand, C., and Glen, J. M. G.: Collecting and calibrating magnetic data from surveys with Uncrewed Aerial Systems (UAS) and an approach for regions with strong magnetic gradients, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11258, https://doi.org/10.5194/egusphere-egu22-11258, 2022.

EGU22-11302 | Presentations | G4.3

Gravimetric quasi-geoid of the Baltic Sea and comparison to GNSS levelling, DTU21 and tide gauges 

Hergeir Teitsson and René Forsberg

A gravimetric quasi-geoid model, based on the latest FAMOS database release, has been computed for the Baltic Sea region, aiming for a best-possible model on the sea, while not focusing on the surrounding land.

 The geoid computation is based on the FFT remove-compute-restore method. XGM2019 is used as global reference field, with a Wong-Gore linear tapering from 180 to 200. No terrain corrections are included in the computation, since these are not expected to contribute to the accuracy of the model on the sea.

The gravimetric quasi-geoid model is compared to a GNSS-levelled ITRF2008 zero-tide dataset, the altimetry based DTU21 Mean Sea Surface dataset, and to a few tide gauge stations distributed throughout the region. Some preliminary comparisons to the GNSS-levelling dataset indicates that the gravimetric geoid has an accuracy of ±25 mm in the region surrounding the Baltic Sea.

How to cite: Teitsson, H. and Forsberg, R.: Gravimetric quasi-geoid of the Baltic Sea and comparison to GNSS levelling, DTU21 and tide gauges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11302, https://doi.org/10.5194/egusphere-egu22-11302, 2022.

EGU22-12321 | Presentations | G4.3

eXperimental jOint inveRsioN (XORN) project: first results of a 3D joint gravity and magnetic inversion 

Martina Capponi and Daniele Sampietro

The Earth crust represents less than 1% of the volume of our planet but is exceptionally important as it preserves the signs of the geological events that shaped our planet. This thin layer is the place where the natural resources we need can be accessed (e.g.  critical raw materials, geothermal energy, water, oil and gas, minerals, etc.). For these reasons, a thorough understanding of its structure is crucial for both scientific and industrial future activities. It is well known that potential fields methods, exploiting gravity and magnetic fields, are among the most important tools to recover fundamental information on the Earth crust. In recent years, thanks to the increasing availability of seismic/seismological data and to gravity and magnetic satellite missions, the crust has been thoroughly investigated and modelled at global and continental scales. However, despite this progress, it remains poorly understood in many regions as global models are often too coarse to provide detailed information about the regional and local dynamics.  

With this respect, the challenge to be faced nowadays is represented by the development of ad-hoc techniques to fully exploit these different geophysical global data and to merge them with regional datasets compiled at the Earth’s surface. Currently, the different sources of information when analysed individually suffer from non-uniqueness. Magnetic and gravity signals detect different crustal parameters and rarely coincide because various combinations of geological structures generate similar observations outside the sources. A promising solution is represented by the joint processing in a consistent way of both gravity and magnetic fields data, possibly incorporating the available geological knowledge and constraints coming from seismic acquisitions, in such a way to reduce the space of possible solutions. 

In the eXperimental jOint inveRsioN (XORN) project, funded by the European Space Agency through the EO4society program, Geomatics Research & Development srl (GReD) together with Laboratoire Magmas et Volcans (LMV) of Clermont Auvergne University will develop an innovative algorithm aiming at performing complete 3D joint inversion of gravity and magnetic fields properly constrained by geological a-priori qualitative information. The developed algorithm will be used within the project to recover a 3D regional model of the Earth crust in the Mediterranean Area in terms of density and magnetic susceptibility distribution within the volume, and in terms of depths of the main geological horizons. Within this regional case study particular attention will be given to the bathymetric layer thus defining and testing a strategy that could potentially be applied worldwide to improve our knowledge of this layer which is fundamental for every application that aims at studying (e.g. for tsunami hazards), conserving and sustainably using the oceans, seas and marine resources. 

The first results about technical developments will be here presented together with preliminary modelling aspects of the Mediterranean test case. 

How to cite: Capponi, M. and Sampietro, D.: eXperimental jOint inveRsioN (XORN) project: first results of a 3D joint gravity and magnetic inversion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12321, https://doi.org/10.5194/egusphere-egu22-12321, 2022.

EGU22-12459 | Presentations | G4.3

Geologic and Tectonic units in the Iranian Plateau from present and future satellite missions 

Carla Braitenberg, Tommaso Pivetta, Alberto Pastorutti, and Magdala Tesauro

The objective of this work is to investigate the geologic and tectonic units in the Iranian plateau in relation to the information that can be obtained from the gravity field observed from space. The objective requires to collect seismologic tomography, seismicity, geodetic observations of crustal movements, a database of active faults, active seismic investigations of sediment depths, heat flow measurements and to use this information as a constraint for gravity inversion with the present available satellite-derived gravity field. The gravity field correlated to the topography defines blocks of the plateau, which indicates varying crustal rigidity (Pivetta and Braitenberg, 2020). We find that mechanisms of vertical growth are tied to crustal thickening, coherently identified from the gravity field, seismic tomography and isostasy. Persistent high density crustal blocks are identified for instance SE of Isfahan, which require further investigation and validation, also in relation to magmatism. The study is embedded in a major project addressing the “Intraplate deformation, magmatism and topographic evolution of a diffuse collisional belt: Insights into the geodynamics of the Arabia-Eurasia collisional zones” financed by the Italian Ministry (PRIN 2017). When defining the density structure and its uncertainties, the question appears, what improvements on the knowledge of the structure, seismic faults, and on the block-structure can be expected from future gravity missions, with a payload of quantum gradiometers and atom-clocks in a multi satellite configuration. The geophysical sensitivity to quantum gravimetry in space is of interest to the MOCAST+ ASI project, a follower project of the MOCASS ASI project, in which the geophysical sensitivity of the quantum gradiometer payload has been studied (Pivetta et al., 2021).

Pivetta, T., & Braitenberg, C. (2020). Sensitivity of gravity and topography regressions to earth and planetary structures. Tectonophysics, 774, 228299. https://doi.org/10.1016/j.tecto.2019.228299

Pivetta, T., Braitenberg, C. & Barbolla, D.F. (2021) Geophysical Challenges for Future Satellite Gravity Missions: Assessing the Impact of MOCASS Mission. Pure Appl. Geophys. https://doi.org/10.1007/s00024-021-02774-3

How to cite: Braitenberg, C., Pivetta, T., Pastorutti, A., and Tesauro, M.: Geologic and Tectonic units in the Iranian Plateau from present and future satellite missions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12459, https://doi.org/10.5194/egusphere-egu22-12459, 2022.

EGU22-12634 | Presentations | G4.3

Lithospheric architecture across the Zagros Orogen as sensed by the integration of isostatic analysis, gravity inversion, and seismic tomography 

Alberto Pastorutti, Carla Braitenberg, Tommaso Pivetta, and Magdala Tesauro

Regional-scale geophysics is a central tool in improving the knowledge on geologic and tectonic units and on their structural relationships in a complex convergent setting. Harmonization, reduction, and integrated modelling of data such as gravity models and seismic tomographies allows to constrain the geometry and properties of geologic bodies at depth and to test hypotheses on their evolution. In the context of an interdisciplinary project involving multiple Italian institutions, “Intraplate deformation, magmatism and topographic evolution of a diffuse collisional belt: Insights into the geodynamics of the Arabia-Eurasia collisional zones”, we present the result of an integrated analysis across the Zagros Orogen. It represents the most active collisional zone in the Iranian plateau, consequent to the NE-ward subduction of the Neo-Tethyan Ocean.

 

We integrate models of surface topography and gravity through isostatic analysis, i.e. by enquiring the relationship connecting the two observables – the former expressing the load on the lithosphere, the latter a proxy of the crust-mantle boundary undulations. We developed and employed two independent methods, one relying on plate flexure and providing estimates on the spatial distribution of the integrated rigidity of the lithosphere, the other a non-parametric residualization method, based on topo-gravity regression analysis (Pivetta and Braitenberg, 2020). We refine their estimates by including the additional information provided by locally available models of sedimentary infills, in order to correct the loads, and by seismological Moho depth data (e.g. Gvirtzman et al., 2016), to mitigate ambiguities in the crustal thickness inferred from gravity inversion. This analysis allowed the isolation of different rigidity domains - which reflect the assemblage of tectonic provinces and the shallow expression of deep structures - and to obtain the anomalous quantities (e.g. residual gravity disturbance, residual topography) which the initial model does not explain. These include intra-crustal loads, which correlate with areas affected by magmatism and can provide further constrain on the geometry of buried structures.

 

We then improve these estimates with the data derived from seismic tomographies, including the recent shear-wave velocity model by Kaviani et al. (2020). By employing a velocity-to-density conversion strategy and gravity forward modelling, we show the impact of prior reduction of gravity data for upper-mantle signal sources. In addition to that, we use tomography-derived temperature modelling to estimate the variations of lithospheric strength profiles throughout the study area, comparing it with the independently estimated flexural rigidity.

 

Pivetta, T., & Braitenberg, C. (2020). Sensitivity of gravity and topography regressions to earth and planetary structures. Tectonophysics, 774, 228299. https://doi.org/10.1016/j.tecto.2019.228299

Gvirtzman, Z., Faccenna, C., & Becker, T. W. (2016). Isostasy, flexure, and dynamic topography. Tectonophysics, 683, 255–271. https://doi.org/10.1016/j.tecto.2016.05.041

Kaviani, A., Paul, A., Moradi, A., Mai, P. M., Pilia, S., Boschi, L., Rümpker, G., Lu, Y., Zheng, T., Sandvol, E. (2020). Crustal and uppermost mantle shear wave velocity structure beneath the Middle East from surface wave tomography. Geophysical Journal International, 221(2), 1349–1365. https://doi.org/10.1093/gji/ggaa075

How to cite: Pastorutti, A., Braitenberg, C., Pivetta, T., and Tesauro, M.: Lithospheric architecture across the Zagros Orogen as sensed by the integration of isostatic analysis, gravity inversion, and seismic tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12634, https://doi.org/10.5194/egusphere-egu22-12634, 2022.

EGU22-12704 | Presentations | G4.3

Joint inversion of gravity and electromagnetic data — New constraints on the 3-D structure of the lithosphere beneath Central Mongolia 

Matthew Joseph Comeau, Max Moorkamp, Michael Becken, and Alexey Kuvshinov

Joint inversion of complementary datasets is an important tool to gather new insights and aid interpretation, especially in regions which show structural complexity. Using the joint inversion framework jif3D [1] with a newly developed coupling for density and resistivity, based on a variation of information approach which is a machine-learning method that constructs a possible relationship between the properties [2], we combine satellite gravity measurements with electromagnetic data, from broadband and long-period magnetotellurics [3,4,5,6].

Central Mongolia is located in the continental interior, far from tectonic plate boundaries, yet has a high-elevation plateau and enigmatic widespread low-volume basaltic volcanism [7,8,9]. The processes responsible for developing this region remain unexplained and there are questions about its tectonic evolution. A recent project employed thermo-mechanical numerical modeling [10] to simulate the temporal evolution of various tectonic scenarios, offering an opportunity to test hypotheses and determine which are physically plausible mechanisms. Constraints on lithospheric properties, e.g., density distribution, are important for evaluating the geodynamic models. Furthermore, they can help shed light on questions regarding the nature of lower crustal electrical conductors [11], which may be related to tectonically-significant low-viscosity zones.

We will present preliminary results that provide new constraints on the 3-D structure of the lithosphere beneath Central Mongolia, as well as a roadmap for moving towards integrating geophysical results into geodynamic modeling to better understand the evolution of the lithosphere.

 

References:

[1]  Moorkamp, M. et al. 2011. A framework for 3-D joint inversion of MT, gravity and seismic refraction data. Geophysical Journal International, 184(1). https://doi.org/10.1111/j.1365-246X.2010.04856.x 

[2]  Moorkamp, M., 2021. Deciphering the state of the lower crust and upper mantle with multi-physics inversion. ESSOAr. https://doi.org/10.1002/essoar.10508095.1 

[3]  Comeau, M.J., et al., 2018. Evidence for fluid and melt generation in response to an asthenospheric upwelling beneath the Hangai Dome, Mongolia. Earth and Planetary Science Letters, 487. https://doi.org/10.1016/j.epsl.2018.02.007 

[4]  Käufl, J.S., et al., 2020. Magnetotelluric multiscale 3-D inversion reveals crustal and upper mantle structure beneath the Hangai and Gobi-Altai region in Mongolia. Geophysical Journal International, 221(2). https://doi.org/10.1093/gji/ggaa039 

[5]  Becken, M., et al., 2021a. Magnetotelluric Study of the Hangai Dome, Mongolia. GFZ Data Services. https://doi.org/10.5880/GIPP-MT.201613.1 

[6]  Becken, M., et al., 2021b. Magnetotelluric Study of the Hangai Dome, Mongolia: Phase II. GFZ Data Services. https://doi.org/10.5880/GIPP-MT.201706.1 

[7]  Comeau, M.J., et al., 2021a. Images of a continental intraplate volcanic system: from surface to mantle source. Earth and Planetary Science Letters, 587. https://doi.org/10.1016/j.epsl.2021.117307 

[8]  Papadopoulou, M., et al., 2020. Unravelling intraplate Cenozoic magmatism in Mongolia: Reflections from the present-day mantle or a legacy from the past? Proceedings of the EGU. https://doi.org/10.5194/egusphere-egu2020-12002 

[9]  Ancuta, L.D., et al., 2018. Whole-rock 40Ar/39Ar geochronology, geochemistry, and stratigraphy of intraplate Cenozoic volcanic rocks, central Mongolia. Geological Society of America Bulletin, 130. https://doi.org/10.1130/b31788.1 

[10]  Comeau, M.J., et al., 2021b. Geodynamic modeling of lithospheric removal and surface deformation: Application to intraplate uplift in Central Mongolia. Journal of Geophysical Research: Solid Earth, 126(5). https://doi.org/10.1029/2020JB021304

[11]  Comeau, M.J., et al., 2020. Compaction driven fluid localization as an explanation for lower crustal electrical conductors in an intracontinental setting. Geophysical Research Letters, 47(19). https://doi.org/10.1029/2020gl088455 

 

 

 

How to cite: Comeau, M. J., Moorkamp, M., Becken, M., and Kuvshinov, A.: Joint inversion of gravity and electromagnetic data — New constraints on the 3-D structure of the lithosphere beneath Central Mongolia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12704, https://doi.org/10.5194/egusphere-egu22-12704, 2022.

The U.S. National Geodetic Survey (NGS), an office of the National Oceanic and Atmospheric Administration (NOAA), is preparing for the release of a new vertical datum, the North American-Pacific Geopotential Datum of 2022 (NAPGD2022). This new datum will be based on a high degree spherical harmonic model of the Earth’s gravitational potential, and will yield a geoid undulation model (GEOID2022) to calculate orthometric heights from GNSS-derived ellipsoid heights.

As part of the preparation for the new vertical datum, NGS has computed annual experimental geoid models (xGEOID) since 2014. The xGEOID model released in 2020 (xGEOID20) uses an updated digital elevation model (DEM) composed of TanDEM-X, MERIT, and USGS 3DEP data. The DEMs are merged together to create a seamless elevation model across the extent of the xGEOID20 model. The accuracy of the merged DEM is tested using independent datasets such as GPS observations on leveled bench marks and ground elevations from ICESat-2. The effect of the updated DEM on the geoid model is also determined by comparing geoid models computed with previous DEMs to the new xGEOID20 model, and with comparisons to the NGS Geoid Slope Validation Survey lines.

How to cite: Krcmaric, J.: Development and evaluation of the xGEOID20 Digital Elevation Model at NGS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13101, https://doi.org/10.5194/egusphere-egu22-13101, 2022.

EGU22-13195 | Presentations | G4.3

4D Antarctica: recent aeromagnetic, aerogravity and satellite data compilations provide a new tool to estimate subglacial geothermal heat flux 

Fausto Ferraccioli, Ben Mather, Egidio Armadillo, Rene Forsberg, Jörg Ebbing, Jonathan Ford, Karsten Gohl, Graeme Eagles, Chris Green, Javier Fullea, Massimo Verdoya, and Juan Luis Carillo de la Cruz

Geothermal heat flux (GHF), coupled with subglacial topography and hydrology, influences the flow of the overlying Antarctic ice sheet. GHF is related to crustal and lithospheric structure and composition and tectonothermal evolution, and is also modulated by subglacial sedimentary basins and bedrock morphology. Despite its importance for both solid earth and cryosphere studies, our knowledge of Antarctic GHF heterogeneity remains limited compared to other continents- especially at regional scale. This is due to the paucity of direct measurements and the spatial gap wrt much larger scale geophysical proxies for GHF, based on continental-scale magnetic and seismological predictions that also differ considerably from each other in several regions. To reduce this major knowledge gap, the international community is increasingly active in analysing geophysical, geological and glaciological datasets to help constrain GHF (e.g. Burton-Johnson et al., SCAR-SERCE White Paper, 2020). Here we focus on 4D Antarctica- an ESA project that aims to help link bedrock, crust, lithosphere and GHF studies, by analysing recent airborne and satellite-derived potential field datasets. 

We present our recent aeromagnetic, aerogravity and satellite data compilations for 5 study regions, including the Amundsen Sea Embayment sector of the West Antarctic Ice Sheet (e.g. Dziadek et al., 2021- Communications Earth & Environment) and the Wilkes Subglacial Basin (WSB), the Recovery glacier catchment, the South Pole and Gamburtsev Subglacial Mountains and East Antarctic Rift region. We apply Curie Depth Point (CDP) estimation on existing aeromagnetic datasets and compilations in our study regions conformed with SWARM satellite magnetic data (Ebbing et al., 2021- Scientific Reports). We tested the application of different methods, including the centroid (e.g. Martos et al., 2017, GRL) and Bayesian inversion approaches of Curie depth and uncertainty (e.g. Mather and Fullea, 2019- Solid Earth) and defractal and geostatistical methods (e.g. Carrillo-de la Cruz et al., 2021- Geothermics). We then compare our CDP results with crust and lithosphere thickness and interpretations of crustal and lithospheric setting.

Using our new aeromagnetic interpretations we define Precambrian and early Paleozoic subglacial basement in East Antarctica that is mostly concealed beneath Phanerozoic sedimentary basins and ice sheet cover. This enables us to discuss whether different basement provinces differ in terms of CDP estimates (as expected), or if these are either not or only partially resolved. A particularly informative case is the WSB. Here our magnetic assessments of GHF heterogeneity for the Terre Adelie Craton, Wilkes Terrane and Ross Orogen can be indirectly tested by exploiting independent geological and geophysical information derived from their Australians correlatives, namely the Gawler and Curnamona cratons and the Delamerian Orogen. 

Our Curie depth estimates yield geologically reasonable thermal boundary conditions required to initialise new thermal modelling efforts in several study areas. However, developing 3D models of crust and lithosphere thickness and intracrustal composition (as a proxy for the ranges of radiogenic heat production and thermal conductivity) with reasonably detailed crustal architecture, derived from both potential field and seismological datasets is a key next step to constrain Antarctic geothermal heat flux heterogeneity at higher-resolution ice stream scale.  

How to cite: Ferraccioli, F., Mather, B., Armadillo, E., Forsberg, R., Ebbing, J., Ford, J., Gohl, K., Eagles, G., Green, C., Fullea, J., Verdoya, M., and Carillo de la Cruz, J. L.: 4D Antarctica: recent aeromagnetic, aerogravity and satellite data compilations provide a new tool to estimate subglacial geothermal heat flux, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13195, https://doi.org/10.5194/egusphere-egu22-13195, 2022.

EGU22-13231 | Presentations | G4.3

Geostatistical Gravity Inversion for Estimating Sub-Ice-Bathymetry 

Jonas Liebsch, Jörg Ebbing, Hannes Eisermann, and Graeme Eagles

Sub-ice-bathymetry is an important boundary condition when modelling the evolution of ice shelves and ice sheets. Radar sounding is a proven method to reveal the sub-ice-topography beneath grounded ice. However, it fails to image the bathymetry beneath the floating ice shelves due to the strong radar reflectivity of sea water. As an alternative, the inversion of gravity measurements has been used increasingly frequently in recent years. To overcome the ambiguity of inverse modelling, this method benefits from independent depth constraints derived from direct measurements distributed throughout the model area, such as by active seismic, hydroacoustic, and radar methods.

Here, we present a novel geostatistical approach to gravity inversion and compare it to the classical and more commonly used FFT approach. Instead of only fitting individual points, we also include the spatial continuity of the sub-ice morphology. To do so, we calculate a variogram that fits the available depth measurements and derive a covariance matrix from it. The covariance matrix and an initial bathymetry model obtained by kriging together describe an a-priori probability density. For the inversion, the model bathymetry is related to the measured gravity using a quasi-Newton method, for which the derived probability density serves as the inversion’s regularization term. We successfully apply the algorithm to airborne gravity data across the Ekström ice shelf (Antarctica) and compare our results with those of previous studies based on the classical approach. The simplified addition of constraints both for the geometry and the density structure in our approach proves to be advantageous.

How to cite: Liebsch, J., Ebbing, J., Eisermann, H., and Eagles, G.: Geostatistical Gravity Inversion for Estimating Sub-Ice-Bathymetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13231, https://doi.org/10.5194/egusphere-egu22-13231, 2022.

EGU22-1279 | Presentations | SM5.4

Imaging the upper crust with ambient seismic noise in natural and urban environments 

Jordi Diaz, Sergi Ventosa, Martin Schimmel, Mario Ruiz, and Ramon Carbonell

The SANIMS project is focused on the development and application of methods based on seismic ambient noise to image and monitor natural and human-altered environments focusing on two test sites; the Cerdanya Basin in the eastern Pyrenees, and the city of Barcelona. Broad-band and short-period seismometers and a high-density node network have been used to acquire new data.

Broad-band data has been processed using the frequency-dependent phase cross-correlation and time-scale phase-weighted stacking to extract Rayleigh and Love waves. We have obtained Rayleigh and Love group and phase velocities for periods in the 1.5 – 4 s range, that will be inverted to velocity-depth models. The preliminary results show higher velocities to the North, with a well-defined zone with lower than average velocities around the Cerdanya Basin. The geometry of the basin basement has also been investigated using the amplitudes of ambient noise, HVSR methods and RFs, obtaining consistent results. The recently acquired high-density data has already been processed in terms of amplitude variations and will be integrated with the tomographic images.

The data acquired in Barcelona has first been used to monitor human activity during the COVID19 pandemic. Amplitude variations of seismic noise allow to delineate the main geological units of the Barcelona area. HVSR measures using the new data expand the already available results, hence improving the existing seismic hazard maps, and will allow analyzing eventual temporal variations in the measurements. As in the Cerdanya Basin, the data will be used to extract Rayleigh waves and invert for velocities.

Both datasets will also be used to analyze the applicability of the methods based on Rayleigh wave ellipticity inversion of ambient noise and earthquake data to provide S-velocity depth profiles. We expect that the use of ambient noise methods will allow to map the basement and to obtain new higher resolution ambient noise tomographic images of the upper crust in the Cerdanya Basin and to better constrain the subsoil properties of Barcelona. The results in both areas will allow comparing the performance of these methodologies in quiet and noisy areas.

This is a contribution of the SANIMS project (RTI2018-095594-B-I00)

How to cite: Diaz, J., Ventosa, S., Schimmel, M., Ruiz, M., and Carbonell, R.: Imaging the upper crust with ambient seismic noise in natural and urban environments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1279, https://doi.org/10.5194/egusphere-egu22-1279, 2022.

EGU22-3056 | Presentations | SM5.4

Imaging potential geothermal resources in the Hengill volcanic area (Iceland) with active-source seismics recorded by a dense nodal array 

Lea Gyger, Pilar Sánchez-Pastor, Hansruedi Maurer, Anne Obermann, and Stefan Wiemer

The Hengill area, located a few km west of Reykjavik, is situated on the triple junction of three large geological features: the onshore section of the Mid-Atlantic Ridge, called the Reykjanes Peninsula Oblique Rift, the Western Volcanic Zone and the South Iceland Seismic Zone. This area hosts two large-scale geothermal power plants, Nesjavellir and Hellisheiði. Both are producing electricity and hot water. Hengill is also one of the targets of the Iceland Deep Drilling Project that aims at finding and exploiting supercritical fluids.

In summer 2021, a nodal network of 500 5 Hz geophones was deployed in the area over a period of 2 months. It complemented seismic data from a network of broadband stations that were already deployed earlier. In July 2021, a vibroseis experiment was conducted in the area in form of two surveys performed by a fully electrical seismic vibrator truck.  The seismic waveforms were recorded by parts of the nodal network. In this study, we focus on the survey conducted along the road leading to the Nesjavellir geothermal power plant, in Mosfellsheiði. The aim of the survey in Mosfellsheiði is to obtain new insights on a low-velocity anomaly as well as on a yet poorly understood seismic cluster that has been detected in the area by previous studies.

To study the velocity and attenuation structure of the area, we computed a first arrival travel time tomography and an attenuation profile. Finally, we compared our results with an existing 3D seismic ambient noise tomography Vs model of the area as well as with known local subsurface properties, such as resistivity and mineralogy.

The final results of this vibroseis study could be useful for finding new geothermal resources in the Nesjavellir area.

How to cite: Gyger, L., Sánchez-Pastor, P., Maurer, H., Obermann, A., and Wiemer, S.: Imaging potential geothermal resources in the Hengill volcanic area (Iceland) with active-source seismics recorded by a dense nodal array, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3056, https://doi.org/10.5194/egusphere-egu22-3056, 2022.

EGU22-4592 | Presentations | SM5.4

Discovery of scattered subvolcanic complexes that feeded the volcanism in the area of Etna 

Graziella Barberi, Domenico Patanè, Luciano Scarfì, and Mauro Coltelli

In this work we present a new tomographic inversion of the velocity structure and hypocenter parameters at Mt. Etna, carried out by the larger seismic dataset never used than to the previous tomographies. The result of tomographic inversion, including the 3D distributions of P and S velocities, Vp/Vs ratio, and accurate source locations, has been obtained based on the integration of active seismic data (151.403 P-phases from 4.112 shots) acquired during the 2014 TOMO-ETNA experiment (EC-FP7 MED-SUV and EUROFLEET2 MED-SUV.ISES projects) and 10.955 selected local earthquakes data (218.473 P-phases and 39.073 S-phases), recorded by a total number of 262 stations of the INGV permanent seismic network and from the onland and OBS temporary network. For the inversion we used the tomoDDPS algorithm [Zhang et al., 2009] and the input velocity model previously obtained with the PARTOS code (Moreno et al. 2016), considering a total number of 1.580.343 P and 228.663 S differential times.

Based on our data selection and inversion strategy, we obtain a strongly improved 3-D high-resolution Vp, Vs and Vp/Vs models both onland and offshore the volcano, discovering for the first time, in the peripherical part of the edifice: i) on-land, the presence of two subvolcanic complexes in the south-eastern and southern flanks, west to Acicastello-Acitrezza and Paternò and Motta, respectively, where the Etna’s ancient volcanisms (500 to 110 ka) manifested and ii) the presence of a ca. N-S oriented high velocity anomaly (5.0-6.5 km/s) located offshore southeast of Etna area, suggesting a clear interplay between submarine volcanic manifestations and tectonic setting. This body extending from about the sea level to ca. 8 km b.s.l. confirms the observation of a large and intense magnetic positive anomaly (>700 nT) related to deep sources (Cavallaro et al., 2016), evidenced by the magnetic survey carried out during TOMO-ETNA.

 

How to cite: Barberi, G., Patanè, D., Scarfì, L., and Coltelli, M.: Discovery of scattered subvolcanic complexes that feeded the volcanism in the area of Etna, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4592, https://doi.org/10.5194/egusphere-egu22-4592, 2022.

EGU22-5048 | Presentations | SM5.4 | Highlight

An integrated geophysical approach for imaging of the Semail ophiolite 

Simone Pilia, Mohammed Ali, Mike Searle, Anthony Watts, Brook Keats, and Tyler Ambrose

The Semail ophiolite, a thick thrust sheet of Late Cretaceous oceanic crust and upper mantle, was obducted onto the previously rifted Arabian continental margin in the Late Cretaceous, and now forms part of the United Arab Emirates (UAE)-Oman mountain belt. A deep foreland basin along the west and SW margin of the mountains developed during the obduction process, as a result of flexure due to loading of the ophiolite and underlying thrust sheets. Structural and compositional complexities (e.g., presence of thick sand dunes, relatively shallow high-velocity and dense ophiolite structure) have made geophysical imaging of the sub-ophiolite and mid-lower crustal structure particularly challenging.

A combination of active and passive-source seismic techniques, potential field modelling and surface geological mapping are used to constrain the stratigraphy, velocity structure and crustal thickness beneath the UAE-Oman mountains and its bounding basins. Depth-migrated multichannel seismic-reflection profile data are integrated in the modeling of traveltimes from long offset reflections and refractions, which are used to resolve the crustal thickness and velocity structure along two E-W onshore/offshore transects in the UAE. Additionally, we apply receiver function and virtual deep seismic sounding methods to distant earthquake data recorded along the two transects to image crustal thickness variations. Seismic and geological constraints from the transects have been finally used to model gravity and magnetic anomaly data along two coincident profiles.

Geophysical methods define the Semail ophiolite as a high-velocity, high density, > 15 km thick body dipping to the east. The western limit of the ophiolite is defined onshore by the Semail thrust while the eastern limit extends several km offshore, where it is defined seismically by a ~40–45° normal fault. Emplacement of the ophiolite has probably flexed down a previously rifted continental margin, thus contributing to subsidence of flanking sedimentary basins. The new crustal thickness model presented in this work provides evidence that a crustal root is present beneath the Semail ophiolite, suggesting that folding and thrusting during the obduction process may have thickened the pre-existing crust by 16 km.

How to cite: Pilia, S., Ali, M., Searle, M., Watts, A., Keats, B., and Ambrose, T.: An integrated geophysical approach for imaging of the Semail ophiolite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5048, https://doi.org/10.5194/egusphere-egu22-5048, 2022.

EGU22-6839 | Presentations | SM5.4 | Highlight

Controls on early-stage, magma-poor rifting from top-to-bottom seismic imaging of the Malawi (Nyasa) Rift 

Donna Shillington, James Gaherty, Christopher Scholz, Andrew Nyblade, Patrick Chindandali, Richard Wambura Ferdinand, Gabriel Mbogoni, Emily Hopper, Natalie Accardo, Gabrielle Tepp, Ashley Grivalja, David Borrego, and Gabriel Mulibo

Few constraints are available on variations in extension with depth and along-strike in early stage continental rift systems, leaving many questions on the mechanisms of extension and the controlling factors. The Malawi (Nyasa) Rift in the southern East Africa Rift System exemplifies an active, magma-poor, weakly extended continental rift. Between 2014-2016, we collected a multi-faceted, amphibious, active- and passive-source seismic dataset across the northern Malawi Rift as a part of the SEGMeNT (Studies of Extension and maGmatism in Malawi aNd Tanzania) interdisciplinary experiment. Together, analysis and integration of these seismic imaging datasets provide a comprehensive portrait of the style and amount of stretching throughout the lithosphere and along strike.  Broadband scattered-wave imaging and wide-angle seismic reflection/refraction data reveal substantial variations in extension with depth, with much more thinning of the lithospheric mantle than the crust (stretching factors of 3.8 and 1.7, respectively). The modest observed reduction in velocity below the rift from both broadband surface- and body-wave imaging can be explained with small thermal perturbations and without melt. Lower velocities and complex patterns of anisotropy underlie the Rungwe Volcanic Province to the north of the Malawi Rift, suggesting focused lithospheric modification, melting and complex mantle flow below this localized volcanic province.  Active-source seismic refraction and multi-channel seismic (MCS) reflection data quantify cumulative extension accommodated by the border faults and intrarift faults. Border faults have throws up to ~8 km and bound half graben basins. Intrarift faults are also relatively large (throws up to 2.5 km) and active, and they are estimated to account for ~20-25% of cumulative upper crustal extension. Along-strike variations are observed in faulting and in crustal and lithospheric stretching. In this presentation, we will synthesize these seismic imaging results and compare them with complementary constraints, including from other parts of the SEGMeNT project .

 

How to cite: Shillington, D., Gaherty, J., Scholz, C., Nyblade, A., Chindandali, P., Wambura Ferdinand, R., Mbogoni, G., Hopper, E., Accardo, N., Tepp, G., Grivalja, A., Borrego, D., and Mulibo, G.: Controls on early-stage, magma-poor rifting from top-to-bottom seismic imaging of the Malawi (Nyasa) Rift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6839, https://doi.org/10.5194/egusphere-egu22-6839, 2022.

EGU22-6878 | Presentations | SM5.4

Calibrating sediment thickness utilizing receiver functions and borehole data 

Shubham Agrawal, Caroline Eakin, and John O'Donnell

A blanket of sedimentary and regolith material covers approximately three-quarters of the Australian continent, obscuring the crustal geology below and potential mineral resources within. Sedimentary basins also trap seismic energy increasing seismic hazard and generating noisy seismograms that make determining deeper crustal and lithospheric structure more challenging. The most fundamental question that can first be asked in addressing these challenges is how thick are the sediments? Borehole drilling and active seismic experiments provide excellent constraints, but they are limited in geographical coverage due to their expense, especially when operating in remote areas. On the other hand, passive-seismic deployments are relatively low-cost and portable, providing a practical alternative for initial surveys. Here we utilize receiver functions obtained for both temporary and permanent seismic stations in South Australia, covering regions with a diverse sediment distribution. We present a straightforward method to determine the basement depth based on the arrival time of the P-converted-to-S phase generated at the boundary between the crustal basement and sedimentary strata above. Utilizing the available borehole data, we establish a simple predictive relationship between Ps arrival time and the basement depth, which could then be applied to other sedimentary basins with some consideration. The method is found to work best for Phanerozoic sediments and offers a way to determine the sediment-basement interface in unexplored areas requiring only temporary seismic stations deployed for < 6 months.

How to cite: Agrawal, S., Eakin, C., and O'Donnell, J.: Calibrating sediment thickness utilizing receiver functions and borehole data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6878, https://doi.org/10.5194/egusphere-egu22-6878, 2022.

EGU22-9491 | Presentations | SM5.4

Cluster Analysis of Velocity Profiles around Hudson Bay using Unsupervised Machine Learning 

Akash Kharita and Amy Gilligan

Understanding deep crustal structure can provide us with insights into tectonic processes and how they affect the geological record. Deep crustal structure can be studied using a variety of seismological techniques such as receiver function analysis, and surface and body wave tomography. Using models of crustal structure derived from these methods, it is possible to delineate tectonic boundaries and regions that have been affected by similar processes. However, often velocity models are grouped together in a somewhat subjective manner, potentially meaning that some geological insight may be missed. Cluster analysis, based on unsupervised machine learning, can be used to more objectively group together similar velocity profiles and, thus, put additional constraints on the deep crustal structure.

In this study, we apply hierarchical agglomerative clustering to the shear wave velocity profiles obtained by Gilligan et. al. (2016) from the joint inversion of receiver functions and surface wave dispersion data at 59 sites surrounding Hudson Bay. This location provides an ideal natural laboratory to study Precambrian tectonic processes, including the 1.8Ga Trans-Hudson Orogen. We use Ward linkage to define the distance between clusters, as this gives the most physically realistic results, and after testing the number of clusters from 2 to 10 find there are 5 main stable clusters of velocity models. We then compare our results with different inversion parameters, clustering schemes (K-means and GMM), results obtained for Vp (P-wave velocity) and ρ (Density), as well as results obtained for profiles from receiver functions in different azimuths and found that, overall, the clustering results are consistent.

The clusters that form correlate well with the surface geology, crustal thickness, regional tectonics and previous geophysical studies concentrated on specific regions. The profiles in the Archean domains (Rae, Hearne and Superior) were clearly distinguished from the profiles in the Proterozoic domains (Southern Baffin Island and Ungava Peninsula). Further, the crust of Melville Peninsula is found to be in the same cluster as the crust of western coast of Ungava Peninsula, suggesting similar crustal structure. Our study shows the promising use of unsupervised machine learning in interpreting deep crustal structure to gain new geological insights.

How to cite: Kharita, A. and Gilligan, A.: Cluster Analysis of Velocity Profiles around Hudson Bay using Unsupervised Machine Learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9491, https://doi.org/10.5194/egusphere-egu22-9491, 2022.

EGU22-10828 | Presentations | SM5.4

Seismic Tomography of Peninsular Malaysia Inferred from Teleseismic Earthquake 

Abdul Halim Abdul Latiff

While there are several geological characterizations of Peninsular Malaysia based on the surface geological study, subsurface evaluation based on the seismic data is still lacking. In this work, tomography of the studied region is being investigated through teleseismic earthquake recorded by several seismic stations located along the peninsula. Throughout the tomography analysis, the 1D ak135 global velocity model is used for computing the travel times from the earthquake source to the edge of the 3-D model. In addition, a similar 1-D ak135 model also being used as the starting model for iterative tomography inversion within the 10.5°N to 0.5°S and 96.5°E to 108.0°E boundary region. The seismological data used for this tomography analysis was acquired from 11 stations that shared with International Seismological Centre (ISC) database and Malaysia Meteorological Department (MMD) respiratory. In total, there were 1598 teleseismic earthquakes events recorded in between 2005 to 2016 which satisfy the criteria of 6.0  or larger. Prior to the iterative travel-time computation, the model’s sensitivity and reliability towards the external changes in the data noise and initial conditions were evaluated through the checkerboard resolution test. The synthetic reconstruction images show that the pattern of the checkerboard anomaly is properly recovered at depth of 30 km, 60 km and 90 km with corresponding high and low wave speed have been recovered as per input model. From the 3580 P-wave arrival time, tomography output is generated at 30 km depth interval, from within the crustal layer of 30 km depth, till the uppermost mantle structure of 300 km depth. In addition, the North-South and East-West sections of the peninsula are produced for a better interpretation of the crustal and uppermost mantle layers in the region. In general, the variation from fast to slow wave speed is noticeable in the Northwards trend, apart from KGM station in the Southern Peninsular Malaysia where a slower velocity recorded compared to its surrounding. The Earth’s structure beneath the SRIT, SKLT, SURA, IPM and KUM stations are experiencing a relative negative wave speed perturbation, while the positive wave speed perturbation is recorded beneath JRM, KOM and BTDF stations. The slower wave speed is recorded in Southern Thailand region and continue southward to the North-West part of Peninsular Malaysia, indicated the sedimentation of Semanggol formation that consists of Carboniferous marine shales. It also concluded that Western-Eastern belt separation of the Malay Peninsula is clearly evident from the velocity contrast. In summary, the latest tomography analysis retrieve from teleseismic earthquake provides a new dimension of the subsurface analysis within the Malay Peninsula region.

How to cite: Abdul Latiff, A. H.: Seismic Tomography of Peninsular Malaysia Inferred from Teleseismic Earthquake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10828, https://doi.org/10.5194/egusphere-egu22-10828, 2022.

EGU22-10944 | Presentations | SM5.4

Active time-reverse imaging: Defect detection by coda waves in digital concrete physics 

Martin Balcewicz, Claudia Finger, and Erik H. Saenger

The localization of defects (i.e., fractures or damages) is essential in evaluating and assessing concrete in, for example, bridges. For this reason, this study presents a non-destructive testing method used primarily in passive seismology applied to active ultrasonic waveforms. Changes in the coda wave can provide information about the defect location by comparing two measurements with and without a defect.

The signal comparison of active transducer signals recorded with several receivers for material before and after an applied load is the basis of Active Time-Reverse Imaging (A-TRI). This study applies the TRI technique to the signal-based analysis of reinforced concrete specimens' acoustic emission (AE). Classical time-reverse modeling uses recorded passive signals, recorded laboratory, or field experiments as input. The recorded wavefield is reversed in time and backpropagated numerically through an adequate medium representation. The wavefield will then ideally focus on the original source location. In contrast to the standard passive TRI method, an active ultrasound method using the generated wavefield from an active source is used in A-TRI. The general workflow is divided into two basic steps: (1) Ultrasonic waves are emitted from single or multiple transducers on the surface and propagate through the original medium. Several receivers record the signals. (2) The experiment is repeated with precisely the same setting after a specific loading scenario. However, the potential damage is to be detected in this case. The difference of both signals is reversed in time and used as the input signal for a time-reverse simulation to locate the defect.

We see the A-TRI method as a complementary method to typically used coda-wave interferometry (CWI) to detect velocity changes in the medium. On the other hand, A-TRI can precisely determine the location of the defect. In the following, a feasibility study is presented in which the A-TRI method is applied to a synthetic data set to localize the defect.

How to cite: Balcewicz, M., Finger, C., and Saenger, E. H.: Active time-reverse imaging: Defect detection by coda waves in digital concrete physics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10944, https://doi.org/10.5194/egusphere-egu22-10944, 2022.

EGU22-11712 | Presentations | SM5.4

Crustal structure beneath northern Myanmar: preliminary results from ambient noise tomography 

Yanling Liang, Xiaohui Yuan, Bernd Schurr, Frederik Tilmann, Wei Li, and Oo Than

Adjoining the Eastern Himalayan Syntaxis, linking to the Indian slab indentation northward and Andaman slab subduction eastward, Myanmar is one of the most complicated and active tectonic regions in the world, and exposed to a high seismic hazard. The Burmese arc consists of the Indo-Burman Ranges (IBR), an accretionary wedge in the west and the Central Myanmar Basin in the east. It is bounded in the east by the seismically active Sagaing Fault to the Shan Plateau which is part of the Asian plate. Intermediate-depth seismicity below Myanmar occurs at depths up to ~150 km, generally understood to be related to the subducting Burma slab.  An important open question concerns the transition from oceanic subduction to continental subduction/collision along the Burmense arc. The transition is also thought to affect the upper plate crust. In this study, we collected ambient noise data set based on a temporary seismic array in Myanmar in order to constrain the variation of crustal structure. The station array includes 30 broadband stations from a temporary network (code 6C 2019-2021) at GEOFON data center. They were deployed by the German Research Centre for Geosciences (GFZ) and the Department of Meteorology and Hydrology of Myanmar (DMH) across the eastern IBR and Central Myanmar Basin in early 2019  with an average interstation distance of ~60 km and data are available to 2020 for most stations. We calculated the cross-correlations daily for all available station pairs through the NoisePy code and stacked further into yearly time-series. We measured Rayleigh wave group and phase velocity dispersions from cross-correlations by using the frequency-time analysis (FTAN) and calculated maps of phase dispersion. As a next step, we will construct a detailed crustal and upper mantle structure beneath Myanmar.

How to cite: Liang, Y., Yuan, X., Schurr, B., Tilmann, F., Li, W., and Than, O.: Crustal structure beneath northern Myanmar: preliminary results from ambient noise tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11712, https://doi.org/10.5194/egusphere-egu22-11712, 2022.

The imaging of volcanic structures by means of seismic techniques is aimed at the structural characterization and monitoring purposes. The quiescent volcano of the Solfatara belong to the caldera of the Campi Flegrei Italy, a resurgent nested caldera that has been extensively investigated through active seismic investigation.

The fumaroles of Bocca Grande and Bocca Nuova at the Solfatara volcano, represent some of the main markers of deep magmatic shallow hydrothermal activity. In this article we identify the gas accumulation zone using the attributes and scaled Poisson ratio extracted from multi-2D seismic profiles. The 400 m long profiles,  have been acquired during the active experiment RICEN (Repeated Induced Earthquake and Noise) performed in the context of the EU project MEDSUV between May and November 2014. The seismic arrays were deployed along the NE-SW and NW-SE directions within the crater across the zones of the fumaroles and the “fangaia”.

The time- and depth-sections are reconstructed after applying residual statics, DMO corrections, CMP gathering, and the post-stack Kirchhoff migration technique. The energy, root mean square, envelope, and sweetness attributes have been computed and extracted for determining the maximum and minimum values of amplitude zones on the migrated, post-stack seismic sections. Furthermore, we have investigated the time-gain attribute, which is used to interpret deep reflectors, and the variance attribute, that is a geometrical attribute providing information on location of faults, discontinuities, and chaotic zones. To better detail the reflectivity of shallow events, enhanced by the post stack attributes, the Amplitude Versus Offset (AVO) technique has also been used to discriminate and identify shallow gas pockets. The seismic profile, seismic attributes, and near-surface structural interpretation of the Solfatara volcano have been combined into a final structural image of the Solfatara subsoil. This show a clear evidence of the fluids trapping zones at 10-50 m depth beneath the crater's surface, as well as their migration paths down to 150 meters depth.

How to cite: Gammaldi, S., Ismail, A., and Zollo, A.: The updated multi-2D image of the gas accumulation zone inferred by seismic attributes and AVO analysis at the Solfatara Volcano, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11885, https://doi.org/10.5194/egusphere-egu22-11885, 2022.

EGU22-11919 | Presentations | SM5.4

Monitoring the b-value unravels critical stress-changes along magma pathways: results from Etna volcano 

Marco Firetto Carlino, Luciano Scarfì, Flavio Cannavò, Graziella Barberi, Domenico Patanè, and Mauro Coltelli

The analysis of the b-value, i.e. the slope of the Gutenberg & Richter frequency-magnitude distribution of earthquakes, provides the chance to investigate the local stress conditions with great resolution, especially in active volcanic areas, where seismic productivity is generally high.

In this work we investigated the seismicity of Mt. Etna between 2005 and 2019, focusing on one of the largest known episodes of unrest in December 2018, when most of the intruding magma aborted its ascent inside the volcano. We found a possible stress concentration zone along magma pathways that may have inhibited the occurrence of a larger, more complete eruption. The b-values time series strongly increase about 19 days before the December 2018 unrest event, while a sharp drop of b started 2 days in advance. 

Our results suggest that the study of the b-value, in broader correlation with other monitoring measurements, may offer an opportunity to investigate the volcano state and improve the assessment of impending volcanic eruptions.

How to cite: Firetto Carlino, M., Scarfì, L., Cannavò, F., Barberi, G., Patanè, D., and Coltelli, M.: Monitoring the b-value unravels critical stress-changes along magma pathways: results from Etna volcano, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11919, https://doi.org/10.5194/egusphere-egu22-11919, 2022.

EGU22-12205 | Presentations | SM5.4

Variation of crustal thickness in Borneo and Sulawesi 

Harry Telajan Linang, Amy Gilligan, Jennifer Jenkins, Simone Pilia, Tim Greenfield, Nicholas Rawlinson, Pepen Supendi, Felix Tongkul, and Sri Widiyantoro

The Southeast Asia (SEA) region is tectonically very active as it accommodates the northward movement of the Indo-Australian plate in the south and the westward movement of the Philippine Sea plate in the east. Borneo and Sulawesi are located in the centre of SEA, which is our area of interest. Borneo has an intraplate setting, while Sulawesi is situated above several microplate boundaries. For that reason, Sulawesi is seismically and volcanically more active than Borneo. The tectonic link and evolution between the two islands are not well understood as we are missing some fundamental knowledge, such as the variations in their crustal thickness and structure. This includes the provenance of their respective lithosphere, which may have Eurasian and/or East Gondwana origin.

Here, we show the results obtained from the receiver function (RF) study on seismic stations in the region to have a better understanding of the crust and mantle lithosphere beneath the two islands. The RF study includes H-k stacking, time-depth migration of the RF and inversion to estimate crustal thickness and the shear speed variation with depth. The finding from this study shows that the crust in Sulawesi is much more complex than that of Borneo. The crustal thickness gradually changes throughout Borneo, with northern Borneo having an overall thicker crust than other parts of the island. In Sulawesi, the crustal thickness is much more varied across small distances, especially along the northern and southern arms of the island.

We also show some results from the Virtual Deep Seismic Sounding (VDSS) method, which we only applied to the seismic stations in northern Borneo. We used VDSS on Northern Borneo to learn more about its complex tectonic history, such as the two subduction episodes and a continent-continent collision in a recent geological time scale. Our finding reveals a band of alternating thick and thin crust striking NE-SW in this region, which we believed resulted from extensional tectonics related to the Sulu Sea basin opening in the Miocene.

How to cite: Linang, H. T., Gilligan, A., Jenkins, J., Pilia, S., Greenfield, T., Rawlinson, N., Supendi, P., Tongkul, F., and Widiyantoro, S.: Variation of crustal thickness in Borneo and Sulawesi, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12205, https://doi.org/10.5194/egusphere-egu22-12205, 2022.

EGU22-795 | Presentations | GI5.3

Mapping of Agricultural Subsurface Drainage Systems Using Time and Frequency Domain Ground Penetrating Radars 

Triven Koganti, Ellen Van De Vijver, Barry J. Allred, Mogens H. Greve, Jørgen Ringgaard, and Bo V. Iversen

Agricultural subsurface drainage systems are installed in naturally poorly drained soils and areas with a rising water table to drain the excess water, eradicate soil salinization issues and increase crop yields. Globally, some of the most productive regions are a result of these artificial drainage practices. The installation of drainage systems provides many agronomic, economic, and environmental benefits. However, inevitably, they act as shortened pathways for the transport of undesired substances (nutrients, pesticides, and pathogens) through the soil profile promoting their increased leaching and offsite release to the surface water bodies. This drainage water cause potential eutrophication risk to the aquatic ecosystem. For example, the hypoxic zone in the Gulf of Mexico and harmful algal blooms in Lake Erie can be linked to the nitrogen and phosphorus losses from the Midwest USA agricultural areas. Hence, the knowledge of the location of these installations is essential for hydrological modelling and to plan effective edge-of-field mitigation strategies such as constructed wetlands, saturated buffer zones, denitrifying bioreactors, and phosphate filters. Moreover, their location is also important either in order to initiate repairs or retrofit a new drainage system to the existing one. Nevertheless, subsurface drainage installations are often poorly documented and this information is inaccurate or unavailable, inducing the need for extensive mapping campaigns. The conventional methods for drainage mapping involve tile probing and trenching equipment. While the use of tile probes provide only localized and discrete measurements, employing trenching with heavy machinery can be exceedingly invasive and carry a risk of severing the drainage pipes necessitating costly repairs. Non-destructive soil and crop sensors might provide a rapid and effective alternative solution. Previous studies show ground penetrating radar (GPR) to be especially successful; owing to its superior resolution over other near-surface geophysical methods. In this study, we tested the use of a stepped-frequency continuous wave (SFCW) 3D-GPR (GeoScope Mk IV 3D-Radar with DXG1820 antenna array) at study sites in Denmark and a time-domain GPR (Noggin 250 MHz SmartCart) at study sites in the Midwest USA to map the buried drainage pipes. The 3D-GPR mounted in a motorized survey configuration and mobilized behind an all-terrain vehicle proved certainly advantageous to get full coverage of the farm field area and provided the flexibility of adjusting the frequency bandwidth depending on the desired resolution and penetration depth (PD). Two different approaches were tested to estimate the PD and comparisons were made with electrical conductivity data measured using an electromagnetic induction instrument. With the impulse GPR, data collected along limited parallel transects spaced a few meters apart, spiral and serpentine segments incorporated into random survey lines proved sufficient when used adjacently with unmanned aerial vehicle imagery. In general, a better success can be expected when the average soil electrical conductivity is less than 20 mS m-1 and it is a recommendation to perform the GPR surveys preferably in a direction perpendicular to the expected drain line orientation when the water table is at/below the drainage pipes’ depth.

How to cite: Koganti, T., Van De Vijver, E., J. Allred, B., H. Greve, M., Ringgaard, J., and V. Iversen, B.: Mapping of Agricultural Subsurface Drainage Systems Using Time and Frequency Domain Ground Penetrating Radars, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-795, https://doi.org/10.5194/egusphere-egu22-795, 2022.

EGU22-948 | Presentations | GI5.3

Quad-polarimetric radar measurements autonomously obtained with an ice-rover at Ekström Ice Shelf, East Antarctica 

M.Reza Ershadi, Reinhard Drews, Inka Koch, Jonathan Hawkins, Keith Nicholls, Joshua Elliott, Falk Oraschewski, Richard Hanten, Cornelia Schulz, Sepp Kipfstuhl, and Olaf Eisen

Acquisition of quad-polarimetric radar data on ice sheets gives insights about the ice-fabric variability with depth and consequently can deliver essential constraints on the spatially variable ice rheology. Polarimetric measurements are collected manually in most ground-based surveys, discretely sampling a limited profile range. Measurements are time-intensive and often do not cover critical areas such as shear zones where field safety is a concern. Autonomous rovers can provide an alternative that optimizes for time, sampling resolution and safety.  

Here, we present an autonomous acquisition technique of quad-polarimetric radar data using a rover. This technique is based on a previous layout that has proven its capacity to navigate in various snow conditions but did not yet actively trigger the geophysical instruments attached. We upgraded the rover with a novel Robotic Operating System (ROS2) that interfaces simultaneously with a real-time positioning GPS and an automatic phase-sensitive radio-echo sounder (ApRES) with multiple transmitters multiple receivers. Like this, the rover can autonomously steer to pre-destined waypoints and then take static measurements at those locations also in areas where field safety might be compromised. We demonstrate this proof-of-concept on the Ekström Ice Shelf Antarctica, where we acquired densely spaced polarimetric radar data measurements. The rover’s operating system offers many opportunities for other measurement principles, e.g., densely spaced co-polarized data suitable for synthetic aperture radar (SAR) processing.

How to cite: Ershadi, M. R., Drews, R., Koch, I., Hawkins, J., Nicholls, K., Elliott, J., Oraschewski, F., Hanten, R., Schulz, C., Kipfstuhl, S., and Eisen, O.: Quad-polarimetric radar measurements autonomously obtained with an ice-rover at Ekström Ice Shelf, East Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-948, https://doi.org/10.5194/egusphere-egu22-948, 2022.

EGU22-1144 | Presentations | GI5.3

Ground Penetrating Radar survey at the archaeological site of Qubbet El-Hawa, Aswan, Egypt 

José A. Peláez, Juan L. Soler, Rashad Sawires, Alejandro Jiménez, and José M. Alba

The necropolis of Qubbet el-Hawa is located in West-Aswan, Upper Egypt. It looks like a huge dune covering the massive Nubian Sandstone Group, hosting one of the most densely occupied cemeteries of Ancient Egypt, dating back to c. 2500 B.C. to the Roman Period. Here we present the used methodology and the conducted ground-penetrating radar (GPR) survey accomplished in the Qubbet El-Hawa site.

Three different geological formations have been differentiated in the studied area. From bottom to top, the Abu Agag, the Timsah and the Um Barmil formations, which mainly belong to the Nubian Sandstone Group. The conducted GPR survey was accomplished in the Timsah Formation, the most heterogeneous formation of all of them, in which along its outcrops can be observed several stratigraphic discontinuities, being usually the alternation of lutite (mainly claystone), sandstone, and iron oxides, arranged in alternating layers varied in thickness from 5 to 10 cm, and from 30 to 50 cm thick blocks.

The studied area, 20 m width × 45 m length, showing a near-constant slope of about 35°, was surveyed using 250 and 500 MHz shielded antennas in a dense array pattern. Although dry eolian sand and sandstone rocks do not display a clear difference in their electromagnetic characteristics, the conducted survey was able to discriminate/define the interface among the underlying sandstone and the sand cover. This good behavior could be attributed to the different overlapping layers including ferruginous sediments and claystone. This was possible even when the studied area exhibits a steep slope, as well as many loose rocks in some parts, coming from the outcrops, that made the measurement difficult to carry out in some cases.

The interface among the underlying sandstone formation and the sand cover is acceptably resolved, providing some very useful data to archaeologists about the near-surface shape of the bedrock and their possible willingness to host some graves.

How to cite: Peláez, J. A., Soler, J. L., Sawires, R., Jiménez, A., and Alba, J. M.: Ground Penetrating Radar survey at the archaeological site of Qubbet El-Hawa, Aswan, Egypt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1144, https://doi.org/10.5194/egusphere-egu22-1144, 2022.

EGU22-1785 | Presentations | GI5.3

Ground Penetrating Radar and passive seismic investigation at the villa of Madonna dell’Alto in Campi Salentina (Lecce, Italy) 

Emanuele Colica, Sebastiano D'Amico, Giorgio Rizzo, and Raffaele Persico

We will present the results of Ground Penetrating Radar ([1-3] and passive seismic [4] prospections performed in the villa of Madonna dell’Alto in Campi Salentina (in the outskirts of Lecce, southern Italy). The structure dates back to the nineteen’s century.  The villa presents a peculiar structure having a central room of a hexagonal shape surrounded by several other small rooms.  GPR prospecting has been performed in a central hexagonal room acquiring data on an orthogonal grid having a spacing of 25 cm. The GPR system used was a Ris Hi-Mode manufactured by IDSGeoradar s.r.l. and equipped with a dual antenna at central frequency 200 and 600 MHz.  A classical processing composed of zero timing, background removal, gain vs. depth. 1D filtering, Kirchhoff migration and depth slicing was applied on the data. The propagation velocity exploited for the migration algorithm was c=12 cm/ns. In this area, from the slices, we have noted an apparent target at the time depth of 390 cm. However, a comparison with the Bscans revealed that it is most probably due to the effects of the walls and the ceiling of the room where the measurements were taken. Single GPR lines were also taken in the other rooms of the villa where some potential anomalies have been identified. However, another campaign is planned in order to extend the data collection and interpretation.

Furthermore, within the Villa a set of seismic passive measurements have been taken by the means of a portable seismograph. The data where acquired both inside the structure in correspondence of the GPR investigation as well as on top of the structure. Data were processed by applying the H/V and the H/H [4] techniques.

Acknowledgements

This study was supported by a STSM Grant from COST Action SAGA: The Soil Science & Archaeo-Geophysics Alliance - CA17131 (www.saga-cost.eu), supported by COST (European Cooperation in Science and Technology www.cost.eu). We are also grateful to the Institute for the Electromagnetic Sensing of the Environment IREA-CNR, which put at our disposal the system with which the GPR measurements were taken.

References

[1] G. Gennarelli, I. Catapano, F. Soldovieri, R. Persico, On the Achievable Imaging Performance in Full 3-D Linear Inverse Scattering, IEEE Trans. on Antennas and Propagation,  vol. 63, n. 3, pp. 1150-1155, March 2015.

[2] F. Gabellone, G. Leucci, N. Masini, R. Persico, G. Quarta, F. Grasso, “Nondestructive Prospecting and virtual reconstruction of the chapel of the Holy Spirit in Lecce, Italy”, Near Surface Geophysics, vol. 11, n. 2, pp. 231-238, April 2013.

[3] E. Colica, A. Antonazzo, R. Auriemma, L. Coluccia, I. Catapano, G. Ludeno, S. d’Amico, R. Persico, GPR investigation at the archaeological site of Le Cesine, Lecce, Italy, Information Science Vol. 12 n. 10, 412, https://doi.org/10.3390/info12100412, 2021.

[4] Panzera F., D'Amico S., Lombardo G., Longo E., 2016. Evaluation of building fundamental periods and effects of local geology on ground motion parameters in the Siracusa area, Italy. Journal of Seismology, 20, 1001-1019, doi:10.1007/s10950-016-9577-5

How to cite: Colica, E., D'Amico, S., Rizzo, G., and Persico, R.: Ground Penetrating Radar and passive seismic investigation at the villa of Madonna dell’Alto in Campi Salentina (Lecce, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1785, https://doi.org/10.5194/egusphere-egu22-1785, 2022.

The Monte Abatone Project, jointly developed between the Campania University “Luigi Vanvitelli” (Caserta) Prof. F. Gilotta, the Tuscia University (Viterbo) Prof. M. Micozzi and A. Coen, the Bonn University, Prof. M. Bentz and ISPC (CNR) is based on the development of an integrated research employing different methodologies to reconstruct the limits of the necropolis and the location of all different tombs. This necropolis is one of the main important necropolis of Cerveteri, located 60 km north of Rome (Latium, Italy). In the period 1950-1960, several tombs have been discovered and excavated, though still many remain hidden underneath the subsurface. In the period between 2018 - 2021, geophysical surveys have been carried out to investigate the unexplored portions of the ancient Etruscan Necropolis, to provide a complete mapping of the position of the tombs. Ground Penetrating Radar and the Magnetometric methods have been systematically employed to investigate about twelve hectares of the necropolis. GPR system SIR 3000 (GSSI), equipped with a 400 MHz antenna with constant offset, SIR4000 (GSSI) equipped with a dual frequency antenna with 300/800 MHz and the 3D Radar Geoscope multichannel stepped frequency system were employed to survey the selected areas where the presence of tombs was hypothesized from previous archaeological studies.

All the GPR profiles were processed with GPR-SLICE v7.0 Ground Penetrating Radar Imaging Software (Goodman 2020). The basic radargram signal processing steps included: post processing pulse regaining; DC drift removal; data resampling; band pass filtering; background filter and migration. With the aim of obtaining a planimetric vision of all possible anomalous bodies, the time-slice representation was calculated using all processed profiles showing anomalous sources up to a depth of about 2.5 m. The obtained results clearly show the presence of a network of strong circular or rectangular features, linked with the buried structural elements of the searched chamber or pit tombs. Together with archaeologists, these anomalies have been interpreted to have a good matching with the expected searched tombs. The obtained results have enhanced the knowledge of the necropolis layout and mapping. After the geophysical surveys, direct excavations have been conducted, which brought to light few of the investigated structures. The obtained results, after the excavation, have been compared and integrated with the geophysical maps to define the keys for the interpretation.

References

Campana S., Piro S., 2009. Seeing the Unseen. Geophysics and Landscape Archaeology. Campana & Piro Editors. CRC Press, Taylor & Francis Group. Oxon UK, ISBN 978-0-415-44721-8.

Goodman, D., Piro, S., 2013. GPR Remote sensing in Archaeology, Springer: Berlin.

Piro S., Papale E., Zamuner D., Kuculdemirci M., 2018. Multimethodological approach to investigate urban and suburban archaeological sites. In “Innovation in Near Surface Geophysics. Instrumentation, application and data processing methods.”, Persico R., Piro S., Linford N., Ed.s. pp. 461 – 504, ISBN: 978-0-12-812429-1, pp.1-505, Elsevier.

How to cite: Piro, S. and Verrecchia, D.: New integrated GPR surveys, using different frequencies, with direct archaeological excavations to locate chamber tombs in Monte Abatone necropolis, Cerveteri (Italy)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2481, https://doi.org/10.5194/egusphere-egu22-2481, 2022.

EGU22-2509 | Presentations | GI5.3

An innovative processing applied to GPR data gathered in the archaeological site of Le Cesine, Lecce, Italy 

Ilaria Catapano, Giovanni Ludeno, Emanuele Colica, Sebastiano D’Amico, Antonella Antonazzo, Rita Auriemma, Luigi Coluccia, and Raffaele Persico

This contribution deals with a GPR prospecting performed in the archaeological site of Le Cesine, Lecce, Southern Italy [1]. The measurement campaign was performed in the framework of a short-term scientific mission (STSM) funded by the European Cost Action 17131 (acronym SAGA), and aimed to map the subsoil of three wide areas in order to address and rationalize future archaeological excavations. As an innovative aspect, beyond a traditional data processing [2], each one of the collected B-scans was processed by means of an innovative data processing, which is based on an inverse scattering algorithm [3-4] accompanied by a shifting zoom procedure [5]. This latter makes possible a computationally effective microwave imaging of electrically large spatial domains and imitates, in a suitable way, the truncation applied on the migration integral, theoretically extended on an infinite observation line but practically necessarily limited to a finite line. For each investigated area, the B-scans, as elaborated by means of the innovative data processing procedure, were combined in order to obtain a depth slice visualization of the investigated areas. As it will be shown at the conference, the obtained images revealed the presence of buried ruins, maybe ascribable to structures related to an ancient Roman harbour. These results motivated founding request for archaeological excavations, which hopefully will be possible to execute in the next few years, and will confirm or correct the hypotheses suggested by the GPR survey as enhanced by the innovative data processing.

 

Acknowledgements

This study was supported by a STSM Grant from COST Action SAGA: The Soil Science & Archaeo-Geophysics Alliance - CA17131 (www.saga-cost.eu), supported by COST (European Cooperation in Science and Technology www.cost.eu).

References

[1] E. Colica, A. Antonazzo, R. Auriemma, L. Coluccia, I. Catapano, G. Ludeno, S. d’Amico, R. Persico, GPR investigation at the archaeological site of Le Cesine, Lecce, Italy, Information Science Vol. 12 n. 10, 412, https://doi.org/10.3390/info12100412, 2021.

[2] F. Gabellone, G. Leucci, N. Masini, R. Persico, G. Quarta, F. Grasso, “Nondestructive Prospecting and virtual reconstruction of the chapel of the Holy Spirit in Lecce, Italy”, Near Surface Geophysics, vol. 11, n. 2, pp. 231-238, April 2013.

[3] I. Catapano, G. Gennarelli, G. Ludeno and F. Soldovieri, "Applying Ground-Penetrating Radar and Microwave Tomography Data Processing in Cultural Heritage: State of the Art and Future Trends," in IEEE Signal Processing Magazine, vol. 36, no. 4, pp. 53-61, July 2019,.

[4] G. Gennarelli, I. Catapano, F. Soldovieri, R. Persico, On the Achievable Imaging Performance in Full 3-D Linear Inverse Scattering, IEEE Trans. on Antennas and Propagation,  vol. 63, n. 3, pp. 1150-1155, March 2015.

[5] R. Persico, G. Ludeno, F. Soldovieri, A. De Coster, S. Lambot, 2D linear inversion of GPR data with a shifting zoom along the observation line, Remote Sensing, 9, 980; doi: 10.3390/rs9100980, open access, 2017.

How to cite: Catapano, I., Ludeno, G., Colica, E., D’Amico, S., Antonazzo, A., Auriemma, R., Coluccia, L., and Persico, R.: An innovative processing applied to GPR data gathered in the archaeological site of Le Cesine, Lecce, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2509, https://doi.org/10.5194/egusphere-egu22-2509, 2022.

EGU22-3152 | Presentations | GI5.3

GPR prospecting in the archaeological site of Cavallino, Lecce, Italy 

Raffaele Persico, Grazia Semeraro, Corrado Notario, and Ilaria Catapano

In this abstract we propose the results of GPR measurements [1-2] performed in a site of cultural interest. In particular, the measurements were performed in a rectangular area inside the Messapic archaeological ancient settlement of Cavallino, close to Lecce (southern Italy) with a RIS-Hi model GPR system manufactured by IDSGeoradar s.r.l. and belonging to the Institute for the Electromagnetic Sensing of the Environment IREA-CNR. The data processing was performed according to a classical sequence of steps provided by zero timing, background removal, gain vs. depth, 1D filtering and time domain migration [3]. Afterwards, slicing was performed too and the results were georeferenced in QGIS thanks to the coordinatives of the four vertex of the rectangular area. The results indicate that there are some possible Messapic remains in the investigated area and suggest somehow the most promising point for a future localized excavation.  Future development will regard further processing of the data with an inverse scattering [4] algorithm accompanied with a shifting zoom procedure, that will make it possible to apply the inverse scattering approach to an electrically large domain [5].

 

Acknowledgments

This work is supported by the project AMOR – Advanced Multimedia and Observation services for 
the Rome cultural heritage ecosystem, financed within the call ESA 5G for L’ART (Business Applications programme).

References

[1] F. Gabellone, G. Leucci, N. Masini, R. Persico, G. Quarta, F. Grasso, “Nondestructive Prospecting and virtual reconstruction of the chapel of the Holy Spirit in Lecce, Italy”, Near Surface Geophysics, vol. 11, n. 2, pp. 231-238, April 2013.

[2] R. Persico, S. D'Amico, L. Matera, E. Colica, C. De, Giorgio, A. Alescio, C. Sammut and P. Galea, GPR Investigations at St John's Co‐Cathedral in Valletta. Near Surface Geophysics, vol. 17 n. 3, pp. 213-229. doi:10.1002/nsg.12046, 2019.

[3] G. Gennarelli, I. Catapano, F. Soldovieri, R. Persico, On the Achievable Imaging Performance in Full 3-D Linear Inverse Scattering, IEEE Trans. on Antennas and Propagation,  vol. 63, n. 3, pp. 1150-1155, March 2015.

[4] I. Catapano, G. Gennarelli, G. Ludeno and F. Soldovieri, "Applying Ground-Penetrating Radar and Microwave Tomography Data Processing in Cultural Heritage: State of the Art and Future Trends," in IEEE Signal Processing Magazine, vol. 36, no. 4, pp. 53-61, July 2019,.

[5] R. Persico, G. Ludeno, F. Soldovieri, A. De Coster, S. Lambot, 2D linear inversion of GPR data with a shifting zoom along the observation line, Remote Sensing, 9, 980; doi: 10.3390/rs9100980, open access, 2017.


 

How to cite: Persico, R., Semeraro, G., Notario, C., and Catapano, I.: GPR prospecting in the archaeological site of Cavallino, Lecce, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3152, https://doi.org/10.5194/egusphere-egu22-3152, 2022.

EGU22-5163 | Presentations | GI5.3

Deep Learning Strategies for Target Classification via Tomographic Ground Penetrating Radar 

Michele Ambrosanio, Stefano Franceschini, Maria Maddalena Autorino, and Vito Pascazio

Subsurface and underground exploration and monitoring are of interest for several applications which span from geoscience and archaeology to security and safety areas [1, 2]. In the framework of non-destructive testing, ground penetrating radar (GPR) represents a valuable technology that has been extensively exploited for the detection and characterization of buried objects. Nevertheless, this remote sensing modality has some limitations related to the generated output, since these images of the underground require an expert user for their interpretation. Moreover, identifying and characterizing buried objects still represent a non-trivial task [3].

To this aim, several algorithms have been developed to face the aforementioned issues efficiently and automatically. In this context, approaches based on deep learning and convolutional neural networks (CNNs) have been proposed in the past years and recently gained a lot of attention by the scientific community [4]. Despite their efficiency, these approaches require many cases to perform the training step and improve their classification performance.

In this abstract, the case of a multistatic GPR system is considered via two-dimensional numerical simulations to classify the kind of underground utility automatically in areas in which both water and natural gas pipes can be located. More in detail, some discussions on the classification performance by adopting different topologies and network architectures will be dealt with.

 

[1] Persico, R., 2014. Introduction to ground penetrating radar: inverse scattering and data processing. John Wiley & Sons.

[2] Catapano, I., Gennarelli, G., Ludeno, G. and Soldovieri, F., 2019. Applying ground-penetrating radar and microwave tomography data processing in cultural heritage: State of the art and future trends. IEEE Signal Processing Magazine, 36(4), pp.53-61.

[3] Ambrosanio, M., Bevacqua, M.T., Isernia, T. and Pascazio, V., 2020. Performance Analysis of Tomographic Methods Against Experimental Contactless Multistatic Ground Penetrating Radar. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 14, pp.1171-1183.

[4] Kim, N., Kim, S., An, Y.K. and Lee, J.J., 2019. Triplanar imaging of 3-D GPR data for deep-learning-based underground object detection. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 12(11), pp.4446-4456.

How to cite: Ambrosanio, M., Franceschini, S., Autorino, M. M., and Pascazio, V.: Deep Learning Strategies for Target Classification via Tomographic Ground Penetrating Radar, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5163, https://doi.org/10.5194/egusphere-egu22-5163, 2022.

EGU22-5568 | Presentations | GI5.3

Multi-illumination and multi-view GPR measurements for Through-the-Wall radar imaging 

Cristina Ponti, Andrea Randazzo, Alessandro Fedeli, Matteo Pastorino, and Giuseppe Schettini

The use of Ground Penetrating Radar (GPR) as a non-destructive technique for the localization and imaging of buried targets is nowadays widely used in the fields of civil engineering, archeology, and geology. In traditional GPR applications, the transmitting antenna is placed in air, whereas targets are embedded in a background of different permittivity, which may be given by a soil or a construction material. However, the GPR architecture can be also applied to the case of targets located in air but hidden from the illumination field radiated by the transmitting antenna by a dielectric discontinuity, as in the case of the Through-the-Wall (TW) radar applications, where targets inside a building interior must be localized and imaged [1]. In this work, a commercial GPR equipment is employed to perform an experimental campaign on a TW scene, where two targets of different reflectivity, i.e., a metallic cylinder and a wooden bar, are located behind a masonry wall in a laboratory environment. To increase the information on the scattered fields, the scanning of the transmitting and receiving antennas is performed in a fully multi-bistatic manner, through a multi-view and multi-illumination mode, along a horizontal line parallel to the wall, and keeping the antennas in direct contact with it. The transmitting antenna is a transducer emitting a pulsed signal, with frequency centered at 1 GHz. The imaging of the buried targets has been performed through a novel two-step inverse-scattering technique, that is based on a regularization scheme developed in the framework of variable exponent Lebesgue spaces [2], [3]. In particular, the norm exponent function is directly built from the available data through an initial processing of the data, based on a beamforming approach or on a truncated singular value decomposition (TSVD) technique [4]. The whole frequency spectrum of the measured data is exploited, as the scattered field from the pulsed signals is extracted on a set of frequencies through a Fast Fourier Transform. The proposed approach, applied to the measured data, shows good reconstruction capabilities and a reduction of artifacts.

 

[1] M. G. Amin, Ed., Through-the-Wall Radar Imaging. Boca Raton, FL: CRC Press, 2011.

[2] C. Estatico, A. Fedeli, M. Pastorino, and A. Randazzo, ‘Quantitative microwave imaging method in Lebesgue spaces with nonconstant exponents’, IEEE Trans. Antennas Propag., vol. 66, no. 12, pp. 7282–7294, Dec. 2018.

[3] A. Randazzo, C. Ponti A. Fedeli, C. Estatico, P. D’Atanasio, M. Pastorino, G. Schettini, ‘A two-step inverse-scattering technique in variable-exponent Lebesgue spaces for through-the-wall microwave imaging: Experimental results’, IEEE Trans. Geosci. Remote Sens., vol. 59, no. 9, pp. 7189–7200, Sep. 2021.

[4] A. Randazzo, C. Ponti, A. Fedeli, C. Estatico, P. D’Atanasio, M. Pastorino, G. Schettini, ‘A Through-the-Wall Imaging Approach Based on a TSVD/Variable-Exponent Lebesgue-Space Method’, Remote Sens., vol. 13, 17 pp., 2021.

How to cite: Ponti, C., Randazzo, A., Fedeli, A., Pastorino, M., and Schettini, G.: Multi-illumination and multi-view GPR measurements for Through-the-Wall radar imaging, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5568, https://doi.org/10.5194/egusphere-egu22-5568, 2022.

EGU22-5813 | Presentations | GI5.3

From Multiresolution to the System-by-Design based GPR Imaging 

Francesco Zardi, Lorenzo Poli, and Andrea Massa

Ground Penetrating Radar (GPR) is a technology of high interest due to its many applications [1], requiring to process the collected data to retrieve the shape and/or electromagnetic (EM) characteristics of the imaged objects. Such a task can be formulated as an Inverse Scattering Problem (ISP), whose solution poses paramount challenges due to the ill-posedness and non-linearity [1]. Therefore, "smart" solution approaches must be developed capable of fully exploiting the available/acquired information to achieve satisfying reconstructions with limited computational resources. In this framework, the development of innovative GPR imaging methodologies is an active research area of the ELEDIA Research Center at the University of Trento, Italy. GPR microwave imaging strategies based on the Multiresolution (MR) paradigm demonstrated significant improvements in terms of reconstruction accuracy and inversion time [2]-[5]. The strength of the MR framework stems from balancing the number of unknowns with the amount of available data, reducing the non-linearity of the ISP. Moreover, it allows a straightforward exploitation of the "progressively-acquired" information on the imaged domain, resulting in a mitigation of the ill-posedness. Effective MR strategies have been recently proposed based on the exploitation of stochastic optimization algorithms [4] to mitigate the risk of false solutions. Recently, an MR-based solution strategy has been proposed that exploits an Inexact Newton method developed in Lp spaces to achieve better regularization of the subsurface ISP thanks to the joint processing of multiple spectral components of GPR data [5]. Another solution paradigm significantly improving the performance of GPR data inversion is the System-by-Design (SbD) [6][7]. The SbD, defined as "a framework to deal with complexity" in EM problems [6] leverages on the recent advancements in the area of Learning-by-Examples techniques and it allows a proper reformulation of the ISP enabling the "smart" reduction of its unknowns and the definition of a fast surrogate model to markedly reduce the computational burden of multi-agent evolutionary-inspired optimization tools [6][7]. 

References

[1] R. Persico, Introduction to Ground Penetrating Radar: Inverse Scattering and Data Processing. Hoboken, New Jersey: Wiley, 2014.
[2] M. Salucci et al. “GPR prospecting through an inverse-scattering frequency-hopping multifocusing approach,” IEEE Trans. Geosci. Remote Sens., vol. 53, no. 12, pp. 6573-6592, Dec. 2015.
[3] M. Salucci et al., “Advanced multi-frequency GPR data processing for non-linear deterministic imaging,” Signal Process., vol. 132, pp. 306–318, Mar. 2017.
[4] M. Salucci et al., “Multifrequency particle swarm optimization for enhanced multiresolution GPR microwave imaging,” IEEE Trans. Geosci. Remote Sens., vol. 55, no. 3, pp. 1305-1317, Mar. 2017.
[5] M. Salucci et al., “2-D TM GPR imaging through a multiscaling multifrequency approach in Lp spaces,” IEEE Trans. Geosci. Remote Sens., vol. 59, no. 12, pp. 10011-10021, Dec. 2021.
[6] A. Massa and M. Salucci, “On the design of complex EM devices and systems through the System-by-Design paradigm - A framework for dealing with the computational complexity,” IEEE Trans. Antennas Propag., in press (DOI: 10.1109/TAP.2021.3111417).
[7] M. Salucci et al., "Learned global optimization for inverse scattering problems - Matching global search with computational efficiency," IEEE Trans. Antennas Propag., in press (DOI: 10.1109/TAP.2021.3139627).

How to cite: Zardi, F., Poli, L., and Massa, A.: From Multiresolution to the System-by-Design based GPR Imaging, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5813, https://doi.org/10.5194/egusphere-egu22-5813, 2022.

EGU22-7170 | Presentations | GI5.3

Reconstruction of GPR data using multiple-point geostatistics 

James Irving, Chongmin Zhang, Mathieu Gravey, and Grégoire Mariéthoz

A common challenge in the processing and analysis of ground-penetrating radar (GPR) reflection data is the reconstruction of missing traces. Gap filling, for example, may be required where data could not be recorded in the field in order to reduce artifacts produced during migration. Similarly, proper visualization and imaging of a GPR profile requires an even trace spacing, meaning that trace regularization is typically needed when the data are acquired in continuous mode using a fixed trace acquisition rate. Lastly, we may wish to increase the spatial resolution of a GPR dataset through trace densification, whereby new traces are reconstructed between existing ones, in order to improve data interpretability. 

A number of methods have been proposed for the reconstruction of missing GPR data over the past few decades, which vary in their degree of complexity and underlying assumptions. Simple strategies such as linear, cubic, and sinc interpolation can be highly effective, but only in the absence of spatial aliasing. When aliasing is present, other methods that exploit the predictability and/or sparseness of the GPR data, commonly in a transformed domain, may be utilized. However, such methods often involve overly simplistic assumptions about the data structure (e.g., that windowed portions of data can be described by sum of plane waves), which can lead to unrealistic and linear results as gaps in the data become large. Finally, all current reconstruction approaches lead to a single "best" estimate of the missing traces based on the existing measurements and some explicit or implicit choice of prior information, with no consideration of the corresponding uncertainty.

Here, we attempt to address these shortcomings by considering a GPR data reconstruction strategy based on the QuickSampling (QS) multiple-point geostatistical method. With this approach, GPR traces are simulated via sequential conditional simulation based on patterns that are observed in nearby high-resolution data (training images). To demonstrate the potential of this approach, we show its successful application to a variety of examples involving gap filling, regularization, and trace densification.

How to cite: Irving, J., Zhang, C., Gravey, M., and Mariéthoz, G.: Reconstruction of GPR data using multiple-point geostatistics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7170, https://doi.org/10.5194/egusphere-egu22-7170, 2022.

EGU22-8022 | Presentations | GI5.3

Qualitative-enhanced full-waveform inversion of ground penetrating radar data 

Alessandro Fedeli, Valentina Schenone, Matteo Pastorino, and Andrea Randazzo

Ground penetrating radar (GPR) prospection of underground scenarios is proven useful in numerous fields, from geophysics to structural engineering. At present, most of the typically deployed approaches make use of qualitative processing of GPR data [1]. Nevertheless, despite their increased complexity, full-waveform inversion (FWI) methods are emerging as a key tool to provide a complete characterization of the buried region under test [2].

This contribution aims at presenting an innovative qualitative-enhanced FWI strategy that combines the benefits from these different classes of GPR processing methods. In more detail, on the one hand a synthetic aperture-based technique retrieves a first qualitative map of the buried structures. On the other hand, the dielectric properties of buried targets are found by an FWI approach formulated in the unconventional context of nonconstant-exponents Lebesgue spaces [3]. The FWI procedure exploits the qualitative map for guiding the unknown update, as well as for constructing the nonconstant-exponent function. Both numerical and experimental results are discussed to assess the proposed inversion procedure.

[1] R. Persico, Introduction to Ground Penetrating Radar: Inverse Scattering and Data Processing. Hoboken, New Jersey: Wiley, 2014.

[2] M. Pastorino and A. Randazzo, Microwave Imaging Methods and Applications. Boston, MA: Artech House, 2018.

[3] V. Schenone, A. Fedeli, C. Estatico, M. Pastorino, and A. Randazzo, “Experimental Assessment of a Novel Hybrid Scheme for Quantitative GPR Imaging,” IEEE Geoscience and Remote Sensing Letters, vol. 19, pp. 1–5, 2022.

How to cite: Fedeli, A., Schenone, V., Pastorino, M., and Randazzo, A.: Qualitative-enhanced full-waveform inversion of ground penetrating radar data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8022, https://doi.org/10.5194/egusphere-egu22-8022, 2022.

EGU22-13149 | Presentations | GI5.3

GPR Prospecting Close to a Roman Amphitheatre in an Urban Environment 

Raffaele Persico and Giuseppe Muci

In the present contribution we will present the results of a GPR [1-3] measurement campaign performed in St. Oronzo Square, Lecce, Italy, aimed to investigate and monitor the status of the Roman amphitheatre present in the square. The “ambulacra” of this amphitheatre in particular are currently buried under the square and only partially accessible. Also, further part of the amphitheatre are still buried, and cannot be excavated because of the presence of posterior structures, in some cases of historical relevance in their turn. The georeferencing of the results has been achieved in QGIS. Indeed, no GPS was available when the measurements were performed. However, the shape of the prospected areas, wedged in the ways around the amphitheatre has allowed a correct georeferencing. A home-made MATLAB code has helped to this pros.

 

References

[1] R. Persico, S. D'Amico, L. Matera, E. Colica, C. De, Giorgio, A. Alescio, C. Sammut and P. Galea, GPR Investigations at St John's Co-Cathedral in Valletta, Near Surface Geophysics 17, 3, 2019, pp. 213-229. doi: 10.1002/nsg.12046.

[2] E. Colica, A, Antonazzo, R. Auriemma, L. Coluccia, I. Catapano, G. Ludeno, S. D’Amico, R. Persico, GPR Investigation at the Archaeological Site of Le Cesine, Lecce, Italy, Information 2021, 12, 412, https://doi.org/10.3390/info12100412

[3] G. Gennarelli, I. Catapano, F. Soldovieri, R. Persico, On the Achievable Imaging Performance in Full 3-D Linear Inverse Scattering, IEEE Trans. on Antennas and Propagation,  63, 3, March 2015, pp. 1150-1155.

How to cite: Persico, R. and Muci, G.: GPR Prospecting Close to a Roman Amphitheatre in an Urban Environment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13149, https://doi.org/10.5194/egusphere-egu22-13149, 2022.

EGU22-5010 | Presentations | GI5.1

Science and technology in deep unerground laboratories 

Aldo Ianni

Deep Underground Laboratories (DULs) are large research infrastructures with a minimum rock overburden equivalent to one km water equivalent. In DULs the flux of muons from cosmic rays is reduced by several order of magnitude with respect to the surface. This allows to perform research on very rare events, such as exotic radioactive decays, double beta decays, low energy neutrino and dark matter interactions. The phenomenon of neutrino oscillations has been discovered in DULs back in 1998. Solar neutrinos were first observed in a DUL in 1968. As of today thanks to research carried out in DULs over four decades we have studied in detail the energy production mechanisms in the sun’s core. In 1987 neutrinos from a core collapse supernova in the Large Magellanic Cloud were observed confirming our basic understanding of this high energetic event. DULs, at present, are equipped with more sensitive and better performing experiments to improve significantly these early studies. The large SuperKamiokande detector in Japan can observe as many as ten thousand events for a core collapse supernova at the center of our galaxy. The Borexino experiment in Italy has observed CNO neutrinos which contribute to only 1% of the energy production in the sun but are very important for more massive stars. All these crucial measurements could have not been possible without operating experiments in a deep underground site.

In the last decade the research horizon in DULs has expanded to include gravitational waves, geophysics, astrobiology, and biology in underground environments.

DULs are equipped with facilities to measure low levels of radioactivity by means of different techniques. This offers a unique opportunity to study living organism in a low radioactivity environment, namely with a significant reduction of cosmic rays and neutrons with respect to surface. DULs are being used by a large community of scientists ranging from astrophysicists, particle physicists, geophysicists, and biologists. There are 14 DULs in operation worldwide which correspond to about one million cubic meters excavated.

In the talk a brief review of DUL’s main features and research activities will be discussed. 

How to cite: Ianni, A.: Science and technology in deep unerground laboratories, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5010, https://doi.org/10.5194/egusphere-egu22-5010, 2022.

EGU22-6987 | Presentations | GI5.1

Underground workings as a most suitable place for the development of mining technologies - a case study from Polish copper mines 

Krzysztof Fulawka, Piotr Mertuszka, Witold Pytel, Marcin Szumny, and Lech Stolecki

The current EU policy emphasizes the necessity of the development of more safe and efficient mineral raw exploitation methods. The higher extraction rate and lowest possible environmental footprint of mining activities are the main goals of many international projects. Still, as recent experiences have shown it is challenging to develop new technologies in standard laboratory conditions. This is due to the inability to reproduce the environments present in most of the underground sites. Therefore post-mining underground workings seem to be the most suitable places for the development, validation and testing of new, more efficient mining technologies.

Such activities are continuously performed in KGHM Polish Copper mines, which are the test sites for numerous national and international research projects aimed at improving machinery, monitoring systems, mining methods and safety of work in underground conditions.  

In the present research, the recent experiences of KGHM CUPRUM company in terms of the development of new mining technologies fitted to Polish underground copper mines have been presented.

How to cite: Fulawka, K., Mertuszka, P., Pytel, W., Szumny, M., and Stolecki, L.: Underground workings as a most suitable place for the development of mining technologies - a case study from Polish copper mines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6987, https://doi.org/10.5194/egusphere-egu22-6987, 2022.

EGU22-8784 | Presentations | GI5.1

Empowering Underground Laboratories Network Usage 

Eija-Riitta Niinikoski, Jari Joutsenvaara, Julia Puputti, Ossi Kotavaara, Marton Magyar, and Marko Holma

Underground laboratories provide unique environments for science, research and business, but many are not known or stay underutilised. Some of the underground laboratories are located or are planned to be built around the Baltic Sea region. In this work, the main outcomes of the EUL and the BSUIN projects will be presented.

The Baltic Sea Underground Innovation Network (BSUIN [1]) started in 2017 (ended in 12/2020), bringing together 13 (initially 14) partners with the common goal to help the underground laboratories to overcome the underutilisation and develop their practices, business models and marketing for attracting new users. The Empowering the Underground Laboratories Network Usage in the Baltic Sea Region (EUL, 1-12/2021 [2]) tested the developed tools and, with the feedback, helped the project partners to develop the tools further. The tools included the EUL Innovation platform (https://undergroundlabs.network/), the customer management relationship and marketing strategies, and social media coverages with various approaches to find the optimal practices for the platform and the actual laboratories.

The underground laboratories [3] participating in the BSUIN and EUL projects are:

  • Callio Lab, located at a 1.4-km deep base metal mine in Pyhäjärvi, Finland,
  • ÄSPÖ Hard Rock Laboratory, SKB´s final repository research site for spent nuclear fuel, Oskarshamn, Sweden,
  • Ruskeala Underground Laboratory, located at the Ruskeala Mining Park, Sortavala, Russia,
  • Educational and research mine Reiche Zeche, Freiberg, Germany,
  • Underground Low Background Laboratory of the Khlopin Radium Institute, located at the heart of St. Petersburg, Russia, and
  • The Conceptual Lab developed and coordinated by the KGHM Cuprum R&D centre, Poland.

The EUL and BSUIN projects are funded by the Interreg Baltic Sea Region Programme.

[1]         J. Joutsenvaara, “BSUIN - Baltic Sea Underground Innovation Network,” EGUGA, p. 11212, 2020, Accessed: Jan. 11, 2022. [Online]. Available: https://ui.adsabs.harvard.edu/abs/2020EGUGA..2211212J/abstract.

[2]         E.-R. Niinikoski, “Empowering Underground Laboratories Network Usage in the Baltic Sea Region,” in EGU General Assembly Conference Abstracts, 2021, pp. EGU21--14791.

[3]         M. Ohlsson et al., “Six Underground Laboratories (ULs) Participating in the Baltic Sea Underground Innovation Network,” EGUGA, p. 22403, 2020, Accessed: Jan. 11, 2022. [Online]. Available: https://ui.adsabs.harvard.edu/abs/2020EGUGA..2222403O/abstract.

How to cite: Niinikoski, E.-R., Joutsenvaara, J., Puputti, J., Kotavaara, O., Magyar, M., and Holma, M.: Empowering Underground Laboratories Network Usage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8784, https://doi.org/10.5194/egusphere-egu22-8784, 2022.

EGU22-11619 | Presentations | GI5.1

Sky-high opportunities deep underground – Callio Lab research centre 

Julia Puputti, Jari Joutsenvaara, Ossi Kotavaara, and Eija-Riitta Niinikoski

One of the northernmost deep underground laboratories (DULs) in Europe can be found at Callio Lab, operating at the Pyhäsalmi Mine in Finland. What began as purely an underground physics centre in the early 2000s has been expanded into an international, multi- and transdisciplinary research centre known as Callio Lab. Its activities are coordinated by the University of Oulu Kerttu Saalasti Institute (KSI). Callio Lab is a founding member of the European Underground Laboratories Association, a part of the DULIA network, and a part of the national FIN-EPOS research infrastructure network. [1].

With underground mining ending in spring 2022, Callio Lab is a key element of the repurposing activities conducted under the CALLIO - Mine for Business concept. CALLIO will continue activities at the mine-site until at least 2025 [2]. Owing to the unique environment and circumstances, Callio Lab research can be conducted underground at seven deep underground laboratories found at various depths, as well as above-ground [3].

Callio Lab has conducted and facilitated research in fields ranging from particle physics and geosciences to underground food production and remote sensing. The operating environment presents versatile opportunities also in the study of circular economy, muography, and space and planetary sciences. Notable projects at Callio Lab have included the international EIT RM funded MINETRAIN, Interreg Baltic Sea Region funded BSUIN, and H2020 funded GoldenEye projects [4-6].

The operating environment at Callio Lab is well-known due to characterisation activities conducted during previous projects, datasets acquired from decades of research, and an extensive microseismic monitoring network. Callio Lab has a logistically ideal location, and the DULs themselves can be accessed via the incline tunnel or elevator shaft. The existing infrastructure and facilities, in-depth understanding and application of underground risk management and conditions, and well-established operating methodology ensures Callio Lab the capacity to successfully operate and facilitate a wide range of activities. [1,3].

[1] Callio Lab, www.oulu.fi/en/callio-lab, 11 Jan 2022

[2] Mine for Business – Callio – Pyhäjärvi, Finland, www.callio.info, 1 Jan 2022

[3] Callio Lab – Underground Center for Science and R&D, www.calliolab.com, 11 Jan 2022

[4] MINETRAIN, www.minetrain.eu, 8 Jan 2021

[5] Baltic Sea Underground Innovation Network, www.bsuin.eu, 11 Jan 2022

[6] GoldenEye EU H2020 funded project, www.goldeneye-project.eu, 11 Jan 2022

How to cite: Puputti, J., Joutsenvaara, J., Kotavaara, O., and Niinikoski, E.-R.: Sky-high opportunities deep underground – Callio Lab research centre, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11619, https://doi.org/10.5194/egusphere-egu22-11619, 2022.

EGU22-400 | Presentations | G1.1

Investigation of earthquake precursors using magnetometric stations in Japan 

Hamideh Taherinia and Shahrokh Pourbeyranvand

Earthquakes are one of the most devastating natural disasters, and their impact on human society, in terms of casualties and economic damage, has been significant throughout history. Earthquake prediction can aid in preparing for this major event, and its purpose is to identify earthquake-prone areas and reduce their financial and human losses. Any parameter that changes before the earthquake in a way that one can predict the earthquake with a careful study of its variations is called a precursor. Recently, more attention has been paid to geophysical, geomagnetic, geoelectrical, and electromagnetic precursors. In the present study, the geomagnetic data of three stations, obtained through INTERMAGNET, with a distance of less than 500 km to the 5 Sep. Japan earthquake are investigated. Then the method of characteristic curves is used to remove the effect of diurnal variation of the geomagnetic field. After that, by examining the anomalies which are more distinct after implementation of the method, the cases are matched with the seismic activities of the region. By separating the noise from the desired signal, a pure anomaly can be observed. Among the various magnetic components, the horizontal components are more suitable than the others for the proposed process because of more variations in the geomagnetic field in the vertical direction due to the presence of the geomagnetic gradient. In the present study, one year of magnetic data, including three stations and for X, Y, and Z components, and seismic data for Japan are used to implement this method. The method is based on plotting different magnetic field components in specific time intervals in the same 24 hours frame. This will lead to a plot which shows the geomagnetic nature of each component of the geomagnetic field for each station After averaging the values for every point at the horizontal axis of the plot, which is a unit of time depending on the sampling (hourly mean, minute mean, etc.) a curve will be obtained which is called the characteristic curve. Then we reduce the characteristic curve values from geomagnetic data to reveal the anomalies, free of diurnal variation noise so that the possible anomalies related to earthquakes will be shown more distinctly. After drawing the components of the magnetic field and removing the daily changes from each of the components, we can observe the anomalies related to the earthquakes to justify the observed anomalies better and considering the standard deviation for each component, pre-seismic anomalies have a more significant distinction than the original data for being studied as a seismic precursor. After all, further investigation revealed the presence of a magnetic storm during the time period under investigation. This led to uncertainty in the feasibility of using the geomagnetic data in the present study as a precursor. However, several other pieces of evidence confirm the existence of precursory geomagnetic phenomena before earthquakes. Thus based on the current data and results, it is not possible to conclude the applicability of precursory geomagnetic studies and further data and studies are required.

How to cite: Taherinia, H. and Pourbeyranvand, S.: Investigation of earthquake precursors using magnetometric stations in Japan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-400, https://doi.org/10.5194/egusphere-egu22-400, 2022.

EGU22-1545 | Presentations | G1.1

A first attempt at a continental scale geothermal heat flow model for Africa 

Magued Al-Aghbary, Mohamed Sobh, and Christian Gerhards

Reliable and direct geothermal heat flow (GHF) measurements in Africa are sparse. It is a challenging task to create a map that reflects the GHF and covers the African continent in in its entirety.

We approached this task by training a random forest regression algorithm. After carefully tuning the algorithm's hyperparameters, the trained model relates the GHF to various geophysical and geological covariates that are considered to be statistically significant for the GHF. The covariates are mainly global datasets and models like Moho depth, Curie depth, gravity anomalies. To improve the predictions, we included some regional datasets. The quality and reliability of the datasets are assessed before the algorithm is trained.

The model's performance is validated against Australia, which has a large database of GHF measurements. The predicted GHF map of Africa shows acceptable performance indicators and is consistent with existing recognized GHF maps of Africa.

How to cite: Al-Aghbary, M., Sobh, M., and Gerhards, C.: A first attempt at a continental scale geothermal heat flow model for Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1545, https://doi.org/10.5194/egusphere-egu22-1545, 2022.

EGU22-1590 | Presentations | G1.1

The Effects of Seasonal Variation on GPS Height Component 

Nihal Tekin Ünlütürk and Uğur Doğan

In this study, the effects of seasonal variation on the vertical position accuracy of GPS calculated by time series analysis of continuous GPS stations were investigated. Weather changes, water vapor in the atmosphere affect the position accuracy of GPS and cause fluctuations in GPS height values. It is also known that the height component has more air passage changes. Since it is easier to interpret the effects of the height component due to its topographic features and seasonal changes are more effective than the rest of the country, four continuous GPS stations, covering the 2014-2019 date range, from the Turkish National Permanent GNSS Network (TUSAGA-Aktif) were used in the East of Turkey were chosen. The daily coordinates of the stations were obtained as a result of GAMIT/GLOBK software solution. By applying time series analysis to the daily coordinate values of the stations, statistically significant trend, periodic and stochastic components of the stations were determined. As a result of the analysis, the vertical annual velocities of the stations and the standard deviations of the velocities were determined.

For the stations determined according to the ellipsoid heights, the velocity and standard deviation values of the height component were calculated for each month, season and year. As the ellipsoid height increases, the velocity and its standard deviation values decrease. While the minimum velocity values are observed for the station with the lowest ellipsoidal height in winter, for the station with the highest ellipsoidal height in autumn, the minimum their standard deviation values are determined in winter for the station with the lowest ellipsoidal height, and in summer for the station with the highest ellipsoidal height. According to the results obtained, the coordinate displacements caused by seasonal variation may be important and their effects should be considered especially in high precision geodetic surveys.

In addition, the velocity values of the stations were calculated for different years, and a decrease was observed in the height component depending on the observation duration. As the observation duration for the height component increases, both the velocity values and their standard deviation values decrease. In order to avoid velocity estimation error completely, the data length should be more than 4.5 years.

Keywords: GPS height compenent, GPS time series, Seasonal effect, Velocity estimation

How to cite: Tekin Ünlütürk, N. and Doğan, U.: The Effects of Seasonal Variation on GPS Height Component, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1590, https://doi.org/10.5194/egusphere-egu22-1590, 2022.

EGU22-2447 | Presentations | G1.1

Regional modeling of water storage variations in a Kalman filter framework 

Viviana Wöhnke, Annette Eicker, Laura Jensen, and Matthias Weigelt

Water mass changes at and below the surface of the Earth cause changes in the Earth’s gravity field which can be observed by at least three geodetic observation techniques: ground-based point measurements using terrestrial gravimeters, space-borne gravimetric satellite missions (GRACE and GRACE-FO) and geometrical deformations of the Earth’s crust observed by GNSS. Combining these techniques promises the opportunity to compute the most accurate (regional) water mass change time series with the highest possible spatial and temporal resolution, which is the goal of a joint project with the interdisciplinary DFG Collaborative Research Centre (SFB 1464) "TerraQ – Relativistic and Quantum-based Geodesy".

A method well suited for data combination of time-variable quantities is the Kalman filter algorithm, which sequentially updates water storage changes by combining a prediction step with observations from the next time step. As opposed to the standard way of describing gravity field variations by global spherical harmonics, we will introduce space-localizing radial basis functions as a more suitable parameterization of high-resolution regional water storage change. A closed-loop simulation environment has been set up to allow the testing of the setup and the tuning of the algorithm. In a first step only simulated GRACE data together with realistic correlated observation errors will be used in the Kalman filter to sequentially update the parameters of a regional gravity field model. However, the implementation was designed to flexibly include further observation techniques (GNSS, terrestrial gravimetry) at a later stage. This presentation will outline the Kalman filter framework, introduce the regional parameterization approach, and address challenges related to, e.g., ill-conditioned matrices and the proper choice of the radial basis function parameterization.

How to cite: Wöhnke, V., Eicker, A., Jensen, L., and Weigelt, M.: Regional modeling of water storage variations in a Kalman filter framework, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2447, https://doi.org/10.5194/egusphere-egu22-2447, 2022.

EGU22-2963 | Presentations | G1.1

Experimenting with automatized numerical methods 

Naomi Schneider and Volker Michel

The approximation of the gravitational potential is still of interest in geodesy as it is utilized, e.g., for the mass transport of the Earth. The Inverse Problem Matching Pursuits (IPMPs) were proposed as alternative solvers for these kind of problems. They were successfully tested on diverse applications, including the downward continuation of the gravitational potential.

It is well-known that, for such linear inverse problems on the sphere, there exist a variety of global as well as local basis systems, e.g. spherical harmonics, Slepian functions as well as radial basis functions and wavelets. Each type has its specific pros and cons. Nonetheless, approximations are often represented in only one of them. On the contrary, the IPMPs enable an approximation as a mixture of diverse trial functions. They are chosen iteratively from an intentionally overcomplete dictionary such that the Tikhonov functional is reduced. However, an a-priori defined, finite dictionary has its own drawbacks, in particular with respect to efficiency.

Thus, we developed a learning add-on which uses an infinite dictionary instead while simultaneously reducing the computational cost. The add-on is implemented as constrained non-linear optimization problems with respect to the characteristic parameters of the different basis systems. In this talk, we give details on the matching pursuits and, in particular, the learning add-on and show recent numerical results with respect to the downward continuation of the gravitational potential.

How to cite: Schneider, N. and Michel, V.: Experimenting with automatized numerical methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2963, https://doi.org/10.5194/egusphere-egu22-2963, 2022.

EGU22-3240 | Presentations | G1.1

Oceanic load tides in the western United States 

Hilary Martens, Mark Simons, Luis Rivera, Martin van Driel, and Christian Boehm

The solid Earth’s deformation response to surface loading by ocean tides depends on the material properties of Earth’s interior. Comparisons of observed and predicted oceanic load tides can therefore shed new light on the structure of the crust and mantle. Recent advances in satellite geodesy, including altimetry and Global Navigation Satellite Systems (GNSS), have improved the accuracy and spatial resolution of ocean-tide models as well as the ability to measure precisely three-dimensional surface displacements caused by ocean tidal loading. Here, we investigate oceanic load tides in the western United States using measurements of surface displacement made by a dense array of GNSS stations in the Network of the Americas (NOTA). Dominant tidal harmonics from three frequency bands are considered (M2, O1, Mf). We compare the empirical load-tide estimates with predictions of surface displacements made by the LoadDef software package (Martens et al., 2019), with the goal of refining models for Earth’s (an)elastic and density structure through the crust and upper mantle of the western US.

How to cite: Martens, H., Simons, M., Rivera, L., van Driel, M., and Boehm, C.: Oceanic load tides in the western United States, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3240, https://doi.org/10.5194/egusphere-egu22-3240, 2022.

EGU22-3605 | Presentations | G1.1

Impact of Offsets on Assessing the Low-Frequency Stochastic Properties of Geodetic Time Series 

Kevin Gobron, Paul Rebischung, Olivier de Viron, Alain Demoulin, and Michel Van Camp

Understanding and modelling the properties of the stochastic variability -- often referred to as noise -- in geodetic time series is crucial to obtain realistic uncertainties for deterministic parameters, e.g., long-term velocities, and helpful in characterizing non-modelled processes. With the ever-increasing span of geodetic time series, it is expected that additional observations would help better understanding the low-frequency properties of the stochastic variability. In the meantime, recent studies evidenced that the choice of the functional model for the time series may bias the assessment of these low-frequency stochastic properties. In particular, the presence of frequent offsets, or step discontinuities, in position time series tends to systematically flatten the periodogram of position residuals at low frequencies and prevents the detection of possible random-walk-type variability.

 

In this study, we investigate the ability of frequently-used statistical tools, namely the Lomb-Scargle periodogram and Maximum Likelihood Estimation (MLE) method, to correctly retrieve low-frequency stochastic properties of geodetic time series in the presence of frequent offsets. By evaluating the biases of each method for several functional models, we demonstrate that neither of these tools is reliable for low-frequency investigation. By assessing alternative approaches, we show that using  Least-Squares Harmonic Estimation and Restricted Maximum Likelihood Estimation (RMLE) solves part of the problems reported by previous works. However, we evidence that, even when using those optimal methods, the presence of frequent offsets inevitably blurs the estimated low-frequency properties of geodetic time series by increasing low-frequency stochastic parameter uncertainties more than that of other stochastic parameters.

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How to cite: Gobron, K., Rebischung, P., de Viron, O., Demoulin, A., and Van Camp, M.: Impact of Offsets on Assessing the Low-Frequency Stochastic Properties of Geodetic Time Series, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3605, https://doi.org/10.5194/egusphere-egu22-3605, 2022.

EGU22-3766 | Presentations | G1.1

Application of the Generalized Method of Wavelet Moments to the analysis of daily position GNSS time series. 

gael kermarrec, davide cucci, jean-philippe montillet, and stephane guerrier

The modelling of the stochastic noise properties of GNSS daily coordinate time series allows to associate realistic uncertainties with the estimated geophysical parameters (e.g. tectonic rate, seasonal signal). Up to now, geodetic software based on Maximum Likelihood Estimation (MLE) jointly inverse a functional (i.e. geophysical parameters) and stochastic noise models. This method suffers from a computational time exponentially increasing  with the length of the GNSS time series, which becomes an issue when considering that the first permanent stations were installed in the late 80’s – early 90’s having recorded more than 25 years of geodetic data. Combining this issue with the tremendous number of permanent stations blanketing the world (i.e. more than 20,000 stations), the processing time in the analysis of large GNSS network is a key parameter. 

Here, we propose an alternative to the MLE called the Generalized Method of Wavelet Moments (GMWM). This method is based on the wavelet variance, i.e. a decomposition of the time series using the Haar wavelet. We show the first results and compare them with the MLE in terms of computational efficiency and absolute error on the estimated parameters. The versatility of this new method is its flexibility of choosing various stochastic noise models (e.g., Matérn, power law, flicker, white noise, random walk), and its robustness against outliers. Additional developments to account for deterministic components such as seasonal signal, offsets or post-seismic relaxation is easy. We explain the principle beyond the method and apply it to both simulated and real GNSS coordinate time series. Our first results are compared with the estimation using  the Hector software.

How to cite: kermarrec, G., cucci, D., montillet, J., and guerrier, S.: Application of the Generalized Method of Wavelet Moments to the analysis of daily position GNSS time series., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3766, https://doi.org/10.5194/egusphere-egu22-3766, 2022.

Considering that the precise orbit and clock products provided by international GNSS service (IGS) were of a magnitude different from those required by the global geodetic observing system (GGOS) in accuracy of 1 mm, the Lomb-Scargle periodogram was used to analyze the systematic deviation and the periodical deviation between the precise products of GNSS analysis centers (ACs) and the IGS final precision products. On this basis, a deviation correction model was established based on the least square method for the correction of precision parameters. The deviation correction results show that the standard deviation of the precise clock decreases by 15.4% on average, the standard deviation of the radial orbit decreases by 33.3% on average, and the standard deviation of the ensemble effects of radial orbit and clock decreases by 24.0% on average. The signal-in-space user ranging error (SISURE) also significantly decreases from the level of centimeters to millimeters. The positioning verification results of the 15 stations show that the consistency between the positioning results of the precision products using single AC and the positioning results of IGS final precision products is also improved after deviation correction, and the average improvement ratio of three ACs is 14.3%. It is proved that the deviation correction model can effectively improve the consistency between the precision products of ACs and the final products of IGS.

How to cite: Hou, Y., Chen, J., and Zhang, Y.: Characteristics analysis and correction of GPS precise products in analysis centers based on Lomb-Scargle periodogram, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6864, https://doi.org/10.5194/egusphere-egu22-6864, 2022.

EGU22-8369 | Presentations | G1.1

Accuracy of velocities from annually repeated GPS campaigns 

D. Ugur Sanli, Ece Uysal, Deniz Oz Demir, and Huseyin Duman

The determination of GPS velocity accuracy and velocity uncertainty has been one of the topics of interest to researchers in recent years. Velocity and velocity uncertainty from continuous GPS data have been studied as deeply as possible, but velocity and velocity uncertainty from campaign measurements are still the subject of ongoing research. Recent studies have shown that the positioning accuracy of GPS PPP is latitude-dependent. At the same time, the velocity and velocity uncertainty produced by the PPP should also be treated in the same way. In this sense, it is necessary to make a global assessment. NASA JPL offers researchers a rich global database constituting GNSS time series analysis results across the globe. In this study, an experiment is conducted to determine the velocity quality of GPS campaign measurements from around 30 globally distributed stations of the IGS network. This time, our motivation is to determine the accuracy and uncertainty of GPS campaign rates from at least 4 years of data, which are performed annually on the same date. As in our previous study, we decimated coordinate components from the NASA JPL time series to generate GPS campaigns. In other words, we use 24-hour data for annual campaign measurements and repeat campaigns on three consecutive days each year. The deformation rates from NASA JPL were considered real and the accuracy of the deformation rates produced by our experiments was evaluated. Preliminary findings suggest that velocity deviations from the truth may be more severe, at 4 mm/year horizontally and 10 mm/year vertically. In the presentation, we discuss the ground truths that lead to this bias and the global distribution of velocity accuracy and velocity uncertainty.

How to cite: Sanli, D. U., Uysal, E., Oz Demir, D., and Duman, H.: Accuracy of velocities from annually repeated GPS campaigns, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8369, https://doi.org/10.5194/egusphere-egu22-8369, 2022.

EGU22-10879 | Presentations | G1.1

Efficient Parameter Estimation of Sampled Random Fields Using the Debiased Spatial Whittle Likelihood 

Frederik J Simons, Arthur P. Guillaumin, Adam M. Sykulski, and Sofia C. Olhede

We establish a theoretical framework, an algorithmic basis, and a computational workflow for the statistical analysis of multi-variate multi-dimensional random fields - sampled (possibly irregularly, with missing data) and finite (possibly bounded irregularly). Our research is practically motivated by geodetic and scientific problems of topography and gravity analysis in geophysics and planetary physics, but our solutions fulfill the more general need for sophisticated methods of inference that can be applied to massive remote-sensing data sets, and as such, our mathematical, statistical, and computational solutions transcend any particular application. The generic problem that we are addressing is: two (or more) spatial fields are observed, e.g., by passive or active sensing, and we desire a parsimonious statistical description of them, individually and in their relation to one another. We consider the fields to be realizations of a random process, parameterized as a Matern covariance structure, a very flexible description that includes, as special cases, many of the known models in popular use (e.g. exponential, autoregressive, von Karman, Gaussian, Whittle, ...) Our fundamental question is how to find estimates of the parameters of a Matern process, and the distribution of those estimates for uncertainty quantification. Our answer is, fundamentally: via maximum-likelihood estimation.  We now provide a computationally and statistically efficient method for estimating the parameters of a stochastic covariance model observed on a regular spatial grid in any number of dimensions. Our proposed method, which we call the Debiased Spatial Whittle likelihood, makes important corrections to the well-known Whittle likelihood to account for large sources of bias caused by boundary effects and aliasing. We generalise the approach to flexibly allow for significant volumes of missing data including those with lower-dimensional substructure, and for irregular sampling boundaries. We build a theoretical framework under relatively weak assumptions which ensures consistency and asymptotic normality in numerous practical settings including missing data and non-Gaussian processes. We also extend our consistency results to multivariate processes. We provide detailed implementation guidelines which ensure the estimation procedure can still be conducted in O(n log n) operations, where n is the number of points of the encapsulating rectangular grid, thus keeping the computational scalability of Fourier and Whittle-based methods for large data sets. We validate our procedure over a range of simulated and real world settings, and compare with state-of-the-art alternatives, demonstrating the enduring practical appeal of Fourier-based methods, provided they are corrected and augmented by the procedures that we developed.

How to cite: Simons, F. J., Guillaumin, A. P., Sykulski, A. M., and Olhede, S. C.: Efficient Parameter Estimation of Sampled Random Fields Using the Debiased Spatial Whittle Likelihood, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10879, https://doi.org/10.5194/egusphere-egu22-10879, 2022.

Geomagnetic data at Kiruna station (KIR) in Sweden has been expected to be affected by the iron ore mine because high conductance underground generally means depressed ΔZor dZ/dt compared to ΔH or dH/dt, where Z and H are downward and horizontal components, respectively, Δ indicates deviation, and we took 1-min average of 1-sec resolution data when defining d/dt values. We examined the 1-sec resolution magnetometer data using both frequency-domain (i.e., standard magnetotellurics) and time-domain analyses, and compared general behaviours with the other high-latitude stations on the same longitude (Hornsund: HRN, Abisko: ABK, Lycksele: LYC, Uppsala: UPS, Nurmijärvi: NUR) for the same period (September 2014-2020).

Surprisingly, we found KIR anomaly only in time-domain derivative dB/dt and not in the frequency domain spectrum. To quantify this anomaly, we examined the standard deviation of each parameter (1-min average of 1-sec resolution values) over 3 hours. With this quantification, the level of anomaly was about the same between old magnetometer until 2019 and new magnetometer from 2020. The anomaly is somewhat present in both dZ/dt and dH/dt but is the clearest in the ratio of dZ/dt to dH/dt.  On the other hand, neither ΔZ nor ΔH showed anomaly. Furthermore, no anomaly is recognized in the inclination I (=atan(Z/H)), i.e., ΔI nor dI/dt. From all of these, we believe that the observed anomaly is caused by underground iron ore deposit and not by the magnetometer filtering setting. The reason why the anomaly is found only in d/dt values is not clear, but we suspect that the iron ore deposit might cause time delay between dZ/dt and dH/dt when step-like variation dominates as the input variation, which is often the case with auroral activity. In such variation, neither the frequency domain analyses, nor simple time domain analyses (ΔB) show any anomaly.

We applied this method to the other meridians (three meridians in North America). We could not find any anomaly similar to what KIR data showed. However, we found another type of anomaly (on dI/dt) in Barrow, Alaska. It can be related to its location, surrounded by the arctic sea in both east and west, but we have not yet found an appropriate interpretation.

[Acknowledgements:  This work resulted from a 2021 summer internship study at the Swedish Institute of Space Physics, Kiruna.   The 1-sec resolution geomagnetic data are obtained from INTERMAGNET and are originally provided by SGU (Sweden: UPS, LYC, KIR, ABK), FMI (Finland: NUR), PAS (Poland: BEL, HLP, HRN), GSC (Canada: BLC, CBB, FCC, IQA, OTT, RES, STJ, YKC), USGS (USA: BRW, CMO, FRD, SHU, SIT), IPGP (France: CLF), ZAMF (Austria, WIC), and ASCR (Czech: BDV).]

How to cite: Longeon, B. and Yamauchi, M.: Iron deposit effect observed in Kiruna geomagnetic fluctuations: Indications for an improved approach of magnetotellurics searching methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-168, https://doi.org/10.5194/egusphere-egu22-168, 2022.

EGU22-3867 | Presentations | EMRP2.12

The evaluation of crustal field influence to geomagnetic cutt-off rigidities 

Patrik Jakab and Pavol Bobík

The cut-off rigidities of cosmic rays usually do not reflect the influence of the crustal geomagnetic field. Due to the weakness of the crustal field effect to the cosmic rays trajectories are very minor. However, two regions of the world have a crustal field with significantly higher values. The effect of the crustal field in those regions is evaluated. The consequences for the approach of cosmic rays to Earth's surface (top of the Earth atmosphere) in the last decades are analyzed and discussed. Presented are suggestions for possible modification of models for evaluation of Earth's magnetosphere transparency for cosmic rays.

How to cite: Jakab, P. and Bobík, P.: The evaluation of crustal field influence to geomagnetic cutt-off rigidities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3867, https://doi.org/10.5194/egusphere-egu22-3867, 2022.

EGU22-3976 | Presentations | EMRP2.12

The 2019-2020 geomagnetic jerk as observed by southern African magnetic observatories. 

Amoré Nel and Pieter Kotzé

Rapid secular variation pulses in the Earth’s geomagnetic field have been identified during the last decade. In particular the 2019-2020 event is the latest in a series of rapid secular variation events observed at the Earth’s surface which are thought to be the result of rapid oscillations at the core surface approximately at a depth of 3000 km. In Southern Africa the 2019-2020 pulse has been analysed using data from 4 observatories located at Hermanus, Hartebeesthoek, Keetmanshoop and Tsumeb, and found that the 2019-2020 event occurred with varying strengths in the different components at a particular observatory, while different observatories in the region showed strong individual characteristics. These rapid changes in the secular variation patterns at individual magnetic observatories in this study can also be influenced by the South Atlantic Anomaly (SAA) where the geomagnetic field has been diminishing at a very rapid rate over the past 400 years in comparison to regions at similar latitudes around the globe. Results will be compared to the global CHAOS field model derived from ground and SWARM satellite data.

How to cite: Nel, A. and Kotzé, P.: The 2019-2020 geomagnetic jerk as observed by southern African magnetic observatories., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3976, https://doi.org/10.5194/egusphere-egu22-3976, 2022.

The International Geomagnetic Reference Field (IGRF) is a multi-institute model of the Earth’s magnetic field, compactly described by sets of up to 195 spherical harmonic (Gauss) coefficients to degree and order 13, which allows the continuous evaluation of the field at any location and time on or above the surface. It is developed from satellite and ground-based magnetometer data and describes the large-scale variation of the magnetic field in space and time under quiet conditions. While much effort has been made on improving the forecast of the secular variation of the field over the five-year intervals between release and renewal, less emphasis has been placed on understanding the spatial errors from a user point of view. We estimate the large-scale time-invariant spatial uncertainty of the IGRF based on the globally averaged misfit of the model to semi-independent ground-based measurements at repeat stations and observatories between 1980 and 2021. As the ground measurements are reduced to quiet-time values, the external field is minimized. We find the 68.3% confidence interval is 87 nT in the North (X) component, 73 nT in the East (Y) component and 114 nT in Vertical (Z) component. Due to the Laplacian distribution of the residuals, the standard deviations are larger at 144, 136 and 293 nT, respectively.

How to cite: Beggan, C.: Evidence-based uncertainty estimates for the International Geomagnetic Reference Field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4172, https://doi.org/10.5194/egusphere-egu22-4172, 2022.

The paper considers the reason for the displacement of the magnetic axis relative to the axis of rotation of the Earth for the case of the quartz nature of the dipole magnetic field. A model based on a ring with a current with an uneven distribution of charges along the circumference of the ring is considered. It is shown that the magnetic axis shifts from the axis of rotation towards a greater concentration of charges and, conversely, with a decrease in the concentration of charges. The issue of reducing the number of gravity-oriented quartz crystals in areas of volcanic activity is discussed. The temporal correlation of the beginning of accelerated drift of the Earth's north magnetic pole with the development of volcanic and tectonic activity in the Yellowstone caldera is shown. Attention is drawn to the fact that the Earth's north magnetic pole is shifting towards the geographical pole relative to the geographical coordinates of the Yellowstone caldera.

How to cite: Zhumabayev, B. and Vassilyev, I.: The relationship of the displacement of the north magnetic pole with volcanic activity in the Yellowstone caldera, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4530, https://doi.org/10.5194/egusphere-egu22-4530, 2022.

EGU22-5000 | Presentations | EMRP2.12

Disturbance Storm Time (Dst) index estimation using deep learning applied to Swarm satellite data 

Gianfranco Cianchini, Alessandro Piscini, Angelo De Santis, and Saioa Arquero Campuzano

Computed from the intensity of the globally symmetrical equatorial electrojet (Ring Current) measured by a series of near-equatorial geomagnetic observatories, the Dst (Disturbance Storm Time) is an hourly index of magnetic activity. To give the estimation of the Dst index through the magnetic data measured by the Swarm three-satellite mission, we selected and trained an Artificial Neural Network (ANN). From November 2014 to December 2019, we collected a big Swarm magnetic dataset, confined in space to three very narrow belts of low-to-mid latitude, to better resemble the geographic distribution of the four geomagnetic observatories used to estimate at ground Dst. We also extended the analysis to mid latitude locations to increase the number of satellite samples. By using a Deep Learning architecture and based on its performance, we selected the best topology and trained the network testing its modelling capabilities. The outcomes show that the ANN is able to give a reliable fast estimation of the Dst index directly from Swarm satellite magnetic data, especially during magnetically disturbed periods.

How to cite: Cianchini, G., Piscini, A., De Santis, A., and Arquero Campuzano, S.: Disturbance Storm Time (Dst) index estimation using deep learning applied to Swarm satellite data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5000, https://doi.org/10.5194/egusphere-egu22-5000, 2022.

EGU22-8344 | Presentations | EMRP2.12

Analysis of the Last Reversal, Last Excursions and important HoloceneAnomalies of the Geomagnetic Field using the Eccentric Dipole and a 360-Dipole Ring Mode 

Alicia González-López, Maria Luisa Osete, Saioa A. Campuzano, Pablo Rivera-Pérez, Alberto Molina-Cardín, and F. Javier Pavón-Carrasco

Eccentric dipole can be considered the next approximation of the geomagnetic field after the
generally used geocentric dipole. Considering that during reversals, excursions and important
anomalies the non-dipole contributions are relevant, we study the evolution of the eccentric
dipole during the last reversal (Matuyama-Brunhes transition, ~780 ka), last excursions
(Laschamp, ~41 ka and Mono-Lake, ~34 ka), the Levantine Iron Age Anomaly (LIAA, ~1000 BC)
and the South Atlantic Anomaly (SAA, from 700 AD to present day) according to
paleoreconstructions (IMMAB4, LSMOD.2, SHAWQ-Iron Age and SHAWQ2k, respectively). In
order to get as much as information as possible from the eccentric dipole, we design a simple
model based on 360-point dipoles evenly distributed in a ring close to the Inner Core Boundary
that can be reversed and/or changed their magnitude. We calculate the evolution of the
modeled eccentric dipole according to the 360-dipole ring model reproducing the eccentric
dipole from the paleoreconstructions. If we consider that each point dipole could be associated
to convective columns in the outer core of the Earth, we can relate the evolution of the eccentric
dipole with potential variations in the outer core that cause its displacement. We observe that
the modeled eccentric dipole moves away from regions where dipoles start to reverse (which
are the cases for the reversal, excursions and the SAA) and towards regions where there are
anomalous high-moment dipoles (such as the LIAA). The results show that the eccentric dipole
paths during the events studied correlate well to Core Mantle Boundary low heat flux regions
that is consistent with the development of instabilities in the geomagnetic field.

How to cite: González-López, A., Osete, M. L., A. Campuzano, S., Rivera-Pérez, P., Molina-Cardín, A., and Pavón-Carrasco, F. J.: Analysis of the Last Reversal, Last Excursions and important HoloceneAnomalies of the Geomagnetic Field using the Eccentric Dipole and a 360-Dipole Ring Mode, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8344, https://doi.org/10.5194/egusphere-egu22-8344, 2022.

EGU22-9173 | Presentations | EMRP2.12

Geomagnetic Observatory at Lampedusa Island: Characterization of local magnetic activity and comparison with the other Italian observatories 

Domenico Di Mauro, Mauro Regi, Stefania Lepidi, Alfredo Del Corpo, Guido Dominici, Paolo Bagiacchi, Giovanni Benedetti, and Lili Cafarella

At present, the geomagnetic observatory at Lampedusa (south of Sicily — Italy, geographic coordinates 35°31′N; 12°32′E, altitude 33 m a.s.l. - provisional IAGA code: LMP) is the southernmost point of observation in European territory, and since 2007 it contributes at filling the spatial observational gap in the whole south Mediterranean and North African areas. A signature of very low electromagnetic noise is expected at LMP, since it is located in the inner part of a wild park with limited access, far away from the urbanized areas of the island. LMP lies in the middle of the Mediterranean Sea, while the other two Italian observatories (Castello Tesino – CTS and Duronia - DUR, in North and central Italy, respectively) are located in the continental territory.

Comparisons among the three observatories, in both time and frequency domains, allow to magnetically characterize the Italian territory. Both 1-minute and 1-second data for the years 2017-2020 are analyzed under a statistical approach and also single event analysis is performed. Superposed Epoch Analysis (SEA) of geomagnetic data from the three observatories returns individual responses to external triggers during geomagnetic storms as well as SSC and SI events, indicating that in correspondence to impulsive inputs a peculiar feature arises at LMP, probably as contribution of electric currents in the surrounding sea salt water. Magnetic responses in the Ultra-Low-Frequency (ULF, 1 mHz–5 Hz) range from spectral, local Signal-to-Noise Ratio (SNR) analyses under different local time are computed, showing that the signal emerges mainly during morning hours, as expected for upstream waves related ULF source waves: in particular, the distinct narrow band characteristic of SNR at LMP indicates that the ULF signals are here mainly uncontaminated by local Field Line Resonance (FLR) as at DUR and CTS, while lower noise levels estimated at LMP suggest a smaller anthropogenic contamination in this frequency range. Moreover, for the first time at such low latitudes in the Mediterranean region, we find evidence of FLR events on Duronia–Lampedusa intermediate field line with the application of the gradient method, a consolidated technique that provides estimates of the ULF standing wave frequencies.. Results from data retrieved by geomagnetic observatories, whose long time series of data are of primary importance, demonstrate a unique contribution in characterizing the magnetospheric response to external events.

How to cite: Di Mauro, D., Regi, M., Lepidi, S., Del Corpo, A., Dominici, G., Bagiacchi, P., Benedetti, G., and Cafarella, L.: Geomagnetic Observatory at Lampedusa Island: Characterization of local magnetic activity and comparison with the other Italian observatories, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9173, https://doi.org/10.5194/egusphere-egu22-9173, 2022.

EGU22-10727 | Presentations | EMRP2.12

Exploration of spectral energy from marine and modeled magnetic anomalies 

Andreina Garcia-Reyes and Jérôme Dyment

The spectral method has been widely used in various branches of science since it simplifies the analysis of periodic signals. In the case of geophysics, Fourier transform is used to decompose the signal into different wavelengths, and to associate the gradient of the spectral energy to the depth of the source (after Spector and Grant, 1970). This last association is mostly applied in gravity and magnetism, that is, from sources that produce a contrast of density or magnetic susceptibility with respect to the medium. Large part of the mathematical operators used in geophysics rely on the Fourier analysis.

In this work, we set out an analysis of the spectral energy of the magnetic signal in three and two dimensions. We apply this analysis to three cases: the first case, the classical approach, corresponds to the spectral energy calculated from synthetic magnetic anomalies, produced by bodies of simple geometry. In the second case, we use marine magnetic anomalies on a regional scale, specifically of the Caribbean plate, and finally, a third case, where we apply the method on a marine area covering a few square kilometers. Our objective was primarily to explore and characterize the spectral response from another perspective: that of the spectral cube and to estimate depths of magnetic sources from methods previously used to derive only the depth of the Curie isotherm. A first trial in the application of this method was carried out by Garcia-Reyes and Dyment (2020). However, the application of this in other areas allows evaluating its sensitivity to factors such as scale, resolution and quality of the data, the proximity of the source and geometry of the source. This exercise allows us to validate the approach in estimating depths of sources in the subsurface, and in turn, it is a step forward in understanding the spectral cube and the information it provides.

Our results allow us to offer a mapping of the depth of the magnetic sources (detectable in the spectra), and in turn, a three-dimensional view of their spectral energy. These sources are generally correlated with geological structures, as is the case with the results obtained for the Caribbean plate. Beyond the major developments of the spectral method in geophysics, we suggest that the information inscribed in the spectral signature of magnetic anomalies can still be further explored.

 

References:

GARCIA-REYES, Andreina and DYMENT, Jérôme (2020). Spatial Power Spectral Density Distribution of Magnetic Sources in the Gulf of Mexico and Caribbean Plate. In : AGU Fall Meeting Abstracts. p. GP012-0009.

Spector, A., & Grant, F. S. (1970). Statistical models for interpreting aeromagnetic data. Geophysics, 35(2), 293-302.

How to cite: Garcia-Reyes, A. and Dyment, J.: Exploration of spectral energy from marine and modeled magnetic anomalies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10727, https://doi.org/10.5194/egusphere-egu22-10727, 2022.

The capacity of oceanic crust to record geomagnetic polarity reversals makes sea-surface magnetic anomalies an essential tool to study plate tectonics. The anomalies are usually well-defined at magmatic spreading centers, but are distorted and eventually disappear on magma-poor mid-ocean ridges such as the ultraslow Southwest Indian Ridge (SWIR), making their interpretation difficult. We attribute the variability of the SWIR sea-surface magnetic anomalies to the alternance of magmatic spreading and detachment faulting. A three-layer magnetic model is used to simulate the influence of such an alternance on the sea-surface magnetic anomalies. Conversely, observed magnetic profiles at the SWIR are modelled to unravel their off-axis crustal structure and past mode of spreading. The intruding gabbro bodies on the footwall of detachment faults play a major role in explaining the variability of sea-surface magnetic anomalies at slow and ultraslow spreading ridges.

How to cite: Zhou, F. and Dyment, J.: Variability of Sea-surface Magnetic Anomalies at Ultraslow Spreading Centers: Consequence of Detachment Faulting and Contrasted Magmatism?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11119, https://doi.org/10.5194/egusphere-egu22-11119, 2022.

During geomagnetic storms rapid magnetic variations cause large, sharp enhancements of the magnetic and geoelectric field at mid-latitudes. These present a potential hazard to grounded technology such as high voltage transformers, pipelines and railway systems. Spatio-temporal quantification can provide insight into the magnitude and configuration of their potential hazard. We perform a wavelet decomposition on both European ground-based magnetometer measurements and modelled Geomagnetically Induced Currents (GICs) from the high voltage grid of Great Britain (GB).  A wavelet decomposition localizes the signal in the time-frequency domain, and we show that in both magnetometer observations, and modelled GIC response, the Haar wavelet extracts the signal power and waveform at the signal fastest rate-of-change.

We then use Haar wavelet cross-correlation of the GIC in the grounded nodes to build a time-varying network of GIC coherent response around the GB grid during intense geomagnetic storms [1]  including the 2003 Halloween storm. We find a highly intermittent (few 10s of minutes duration) long-range coherent response that can span the entire physical grid at most intense times. The spatial pattern of coherent response seen in the GIC flow network does not simply follow that of the amplitude of the rate of change of B field that is estimated via the Haar wavelet. Coherent response is excited across spatially extended clusters comprised of a subset of nodes that are highly connected to each other, with a tendency for east-west linkages following that of the physical grid, simultaneous with  the overhead presence of the auroral electrojet and the inducing component of the magnetic field. This can quantify the spatial and temporal location of increased hazard in specific regions during large storms by including effects of both the geophysical and engineering configuration of the high voltage grid.

[1] L. Orr, S. C. Chapman, C. Beggan, Wavelet and network analysis of magnetic field variation and geomagnetically induced currents during large storms, Space Weather (2021) doi: 10.1029/2021SW002772

 

How to cite: Chapman, S., Orr, L., and Beggan, C.: Wavelet cross-correlation dynamical network of the coherent GIC response to intense geomagnetic storms in the high voltage grid of Great Britain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1769, https://doi.org/10.5194/egusphere-egu22-1769, 2022.

EGU22-3006 | Presentations | EMRP2.13 | Highlight

Modelling space weather impacts on UK railway signalling systems 

Cameron Patterson and Jim Wild

Track circuits are widely used signalling systems that use electrical currents to detect the presence or absence of a train in predefined sections of a railway network, as such, they are susceptible to interference from geomagnetically induced currents.

This work aims to determine the impact space weather has on realistic track circuits across geologically different regions of the UK under various storm conditions by using the Spherical Elementary Current System method of geomagnetic field interpolation, a ground conductivity model of the UK, a 1D-layered model to provide estimations of the geoelectric field and track circuit modelling techniques developed by Boteler (2021).

Early results of a modelled section of the West Coast Main Line in North West England will be presented.

How to cite: Patterson, C. and Wild, J.: Modelling space weather impacts on UK railway signalling systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3006, https://doi.org/10.5194/egusphere-egu22-3006, 2022.

EGU22-3218 | Presentations | EMRP2.13

Assessing the impact of weak and moderate geomagnetic storms on UK power station transformers 

James Wild, Zoe Lewis, and Matthew Allcock

It is well documented that space weather can impact electricity infrastructure, and several incidents have been observed in recent decades and directly linked to large geomagnetic storms (e.g. the Hydro Quebec incident in 1989). However, less is understood aboutthe impact of lower-level geomagnetically induced currents (GICs) on the health of transformers in the long term. In this study, the long term impact of geomagnetic activity  on 13 power station transformers in the UK is investigated. Dissolved gas measurements from 2010–2015 were used to look for evidence of a link between degradation of the transformer and heightened levels of the global SYM-H index and dB as measured at Eskdalemuir magnetometer station in southern Scotland. First, case studies of the most significant storms in this time period were examined using dissolved gas analysis (DGA) methods, specifically the Low Energy Degradation Triangle (LEDT). These case studies were then augmented with a statistical survey, including Superposed Epoch Analysis (SEA) of multiple storm events. No evidence of a systematic space weather impact can be found during this time period, likely owing to the relatively quiet nature of the Sun during this epoch and the modernity of the transformers studied.

How to cite: Wild, J., Lewis, Z., and Allcock, M.: Assessing the impact of weak and moderate geomagnetic storms on UK power station transformers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3218, https://doi.org/10.5194/egusphere-egu22-3218, 2022.

In this research the analysis of shutdowns in long power line SS147AL169A in Almaty power grid for 2016-2021 was done. For the analyzed period, there were 16 emergency shutdowns. 6 of them occurred due to evident external causes. Other 10 cases analyzed for the possibility of a connection with the geomagnetic environment. Initial analysis showed a possible connection between the automatic operation of relay protection and the presence of geomagnetically induced currents. This is due to the geomagnetic situation, which was before the moment the relay was triggered. At the moment, more detailed calculations are being carried out.

This research has been/was/is funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP00000000).

How to cite: Nurgaliyeva, K.: Analysis of correlations between geomagnetic storms and emergency shutdowns in the part of Almaty power grid for 2016-2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3317, https://doi.org/10.5194/egusphere-egu22-3317, 2022.

EGU22-6243 | Presentations | EMRP2.13 | Highlight

Estimating the Geoelectric Field, Transmission Line Voltages, and GICs During a Geomagnetic Storm in Alberta, Canada 

Darcy Cordell, Martyn Unsworth, Benjamin Lee, Cedar Hanneson, David Milling, Hannah Parry, and Ian Mann

Estimating the effect of geomagnetic disturbances on infrastructure is an important problem since they can induce damaging currents in electric power transmission lines. In this study, an array of magnetotelluric (MT) impedance measurements in Alberta and southeastern British Columbia are used to estimate the geoelectric field resulting from a magnetic storm on September 8, 2017. The resulting geoelectric field is compared to the geoelectric field calculated using the more common method involving a piecewise-continuous 1-D conductivity model. The 1-D model assumes horizontal layers, which result in orthogonal induced electric fields while the empirical MT impedance data account for fully 3-D electromagnetic induction. The geoelectric field derived from empirical MT impedance data demonstrates a preferential polarization in southern Alberta, and the geoelectric field magnitude is largest in northeastern Alberta where resistive Canadian Shield outcrops. The induced voltage in the Alberta transmission network is estimated to be ~120 V larger in northeastern Alberta when using the empirical MT impedances compared to the piecewise-continuous 1-D model. Transmission lines oriented northwest-southeast in southern Alberta have voltages which are 10-20% larger when using the MT impedances due to the polarized geoelectric field. As shown with forward modelling tests, the polarization is due to the Southern Alberta British Columbia conductor in the lower crust (20-30 km depth) that is associated with a Proterozoic tectonic suture zone. This forms an important link between ancient tectonic processes and modern-day geoelectric hazards that cannot be modelled with a 1-D analysis. The geoelectric field model and resulting line voltage is compared to differential magnetometer GIC measurements on one transmission line near the Heartland transformer in northeastern Alberta.

How to cite: Cordell, D., Unsworth, M., Lee, B., Hanneson, C., Milling, D., Parry, H., and Mann, I.: Estimating the Geoelectric Field, Transmission Line Voltages, and GICs During a Geomagnetic Storm in Alberta, Canada, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6243, https://doi.org/10.5194/egusphere-egu22-6243, 2022.

EGU22-6442 | Presentations | EMRP2.13

Investigating the levels of Geomagnetically Induced Currents in the Mediterranean region during the most intense geomagnetic storms of solar cycle 24 

Adamantia Zoe Boutsi, Georgios Balasis, Ioannis A. Daglis, Kanaris Tsinganos, and Omiros Giannakis

Geomagnetically Induced Currents (GIC) constitute an integral part of space weather research and are a subject of ever-growing attention for countries located in the low and middle latitudes. A series of recent studies highlights the importance of considering GIC risks for the Mediterranean region. Here, we exploit data from the HellENIc GeoMagnetic Array (ENIGMA), which is deployed in Greece, complemented by magnetic observatories in the Mediterranean region (Italy, France, Spain, Algeria and Turkey), to calculate values of the GIC index, i.e., a proxy of the geoelectric field calculated entirely from geomagnetic field variations. We perform our analysis for the most intense magnetic storms (Dst < -150 nT) of solar cycle 24. Our results show that GIC indices do not exceed low activity levels despite the increase in their values, at all magnetic observatories / stations under study during the selected storm events.

How to cite: Boutsi, A. Z., Balasis, G., Daglis, I. A., Tsinganos, K., and Giannakis, O.: Investigating the levels of Geomagnetically Induced Currents in the Mediterranean region during the most intense geomagnetic storms of solar cycle 24, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6442, https://doi.org/10.5194/egusphere-egu22-6442, 2022.

EGU22-9495 | Presentations | EMRP2.13

Combining geoelectric field modelling and differential magnetometer data to validate GIC modelling in the UK High voltage power transmission grid 

Juliane Huebert, Ciaran Beggan, Gemma Richardson, Natalia Gomez Perez, and Alan Thomson

Geomagnetically induced currents (GICs) have been identified as a hazard to the UK power grid and the security of electricity supply during severe geomagnetic storms. In order to monitor, model and forecast GICs, sophisticated models of the ground electric field and the network topology are required. We present a detailed analysis of differential magnetometer (DMM) and magnetotelluric (MT) data in the UK that allow the verification and validation of our network model for the UK power transmission grid. Combining the observation of line GICs measured with DMM in the past three years and the MT impedance tensor estimated at several locations in the UK shows an excellent fit of prediction and observation of GICs when using realistic modelled ground electric fields. This validates our whole network model allowing us to use it with confidence for real time and forecasting as well as extreme event analysis.

How to cite: Huebert, J., Beggan, C., Richardson, G., Gomez Perez, N., and Thomson, A.: Combining geoelectric field modelling and differential magnetometer data to validate GIC modelling in the UK High voltage power transmission grid, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9495, https://doi.org/10.5194/egusphere-egu22-9495, 2022.

The space environment near Earth is constantly subjected to changes in the solar wind flow generated at the Sun. Examples of this variability are the occurrence of powerful solar disturbances, such as coronal mass ejections (CMEs). The impact of CMEs on the Earth's magnetosphere perturbs the geomagnetic field causing the occurrence of geomagnetic storms. Such extremely variable geomagnetic fields trigger geomagnetic effects measurable not only in the geospace but also in the ionosphere, upper atmosphere, and on the ground. For example, during extreme events, rapidly changing geomagnetic fields generate intense geomagnetically induced currents (GICs). In recent years, GIC impact on the power networks at middle and low latitudes has attracted attention due to the expansion of large-scale power networks into these regions. This work presents the analysis of the geoelectric field determined by the use of the MA.I.GIC. (Magnetosphere - Ionosphere - Ground Induced Current) model, on May 12, 2021 Geomagnetic Storm over the northern hemisphere. In addition, we discriminate between the ionospheric and magnetospheric origin contribution on the geoelectric field in Europe and on the Northern America in order to evaluate their relative contribution to the GIC amplitude.

How to cite: Piersanti, M., D'Angelo, G., and Recchiuti, D.: On the possible magnetospheric and ionospheric sources of the geoelectric field variations during the May 2021 Geomagnetic storm., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1249, https://doi.org/10.5194/egusphere-egu22-1249, 2022.

EGU22-1416 | Presentations | EMRP2.15

Extraction of ground magnetic signatures from solar quiet current systems in sub-auroral regions 

Veronika Haberle, Aurélie Marchaudon, Aude Chambodut, and Pierre-Louis Blelly

In order to monitor space weather events and their impacts, ground magnetic field data has proven to be a long-lasting and powerful source of information. For the determination of space weather effects, it is essential to extract and understand the evolution of the quiet-time magnetic field. However, the data shows a high degree of complexity since the Earth’s magnetic field is a superposition of sources that cover a broad amplitude and frequency spectrum. In sub-auroral regions, it is well understood that the solar quiet current system contributes to the quiet signal with smooth patterns that depend on season and local time, having distinct periods of 24 hours and beneath.

In this work, we apply signal filtering techniques on time-series magnetic data from ground observatories in sub-auroral regions. In order to extract the solar quiet current contributions, we use its specific periods of 24h and beneath and analyse the results with respect to season, local time, and day-to-day variability between 1991 and 2019. Careful investigations and interpretation of the contributing sources are given, confirming the main contribution to the filtered signal is the solar quiet current system. This implies that the filter approach is able to extract the quiet magnetic field variations and due to its simplicity may be used for real-time determination of the quiet magnetic field, including magnetic baselines. 

How to cite: Haberle, V., Marchaudon, A., Chambodut, A., and Blelly, P.-L.: Extraction of ground magnetic signatures from solar quiet current systems in sub-auroral regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1416, https://doi.org/10.5194/egusphere-egu22-1416, 2022.

EGU22-1797 | Presentations | EMRP2.15

A parameter for the solar cycle variation in geomagnetic activity as quantified by bursts in the AE and SMR indices 

Aisling Bergin, Sandra Chapman, Nicholas Moloney, and Nicholas Watkins

Geomagnetic storms have the potential for significant impact on a wide range of technologies, including aviation, communications and power transmission grids. The likelihood of occurrence of geomagnetic storms varies with the solar cycle of level of activity, and each solar cycle has a unique amplitude and duration. The space weather response at earth then varies within and between successive solar cycles and can be characterized by the statistics of bursts, that is, time-series excursions above a threshold, in geomagnetic indices derived from ground based magnetometer observations. We consider non-overlapping 1 year samples of the minute-resolution auroral electrojet index (AE) and the minute-resolution SuperMAG-based ring current index (SMR), across the last four solar cycles. These indices respectively characterize high latitude and equatorial geomagnetic disturbances. We propose that average burst duration T and burst return period R (that is, the time between successive upcrossings of the threshold) form an activity parameter, T/R [1] which characterizes the fraction of time the magnetosphere spends, on average, in an active state for a given burst threshold. If the burst threshold takes a fixed value, T/R for SMR tracks sunspot number, while T/R for AE peaks in the solar cycle declining phase. Level crossing theory directly relates T/R to the observed index value cumulative distribution function (cdf). For burst thresholds at fixed quantiles, we find that the probability density functions of T and R each collapse onto single empirical curves for AE at solar cycle minimum, maximum, and declining phase and for -SMR at solar maximum. Moreover, underlying empirical cdf tails of observed index values collapse onto common functional forms specific to each index and cycle phase when normalized to their first two moments. Together, these results offer operational support to quantifying space weather risk which requires understanding how return periods of events of a given size vary with solar cycle strength.

 

[1] A. Bergin, S. C. Chapman, N. Moloney, N. W. Watkins, Variation of geomagnetic index empirical distribution and burst statistics across successive solar cycles, J. Geophys. Res, in press (2022)

How to cite: Bergin, A., Chapman, S., Moloney, N., and Watkins, N.: A parameter for the solar cycle variation in geomagnetic activity as quantified by bursts in the AE and SMR indices, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1797, https://doi.org/10.5194/egusphere-egu22-1797, 2022.

EGU22-2259 | Presentations | EMRP2.15

Power density dissipated by field-aligned currents in the topside ionosphere 

Fabio Giannattasio, Giuseppe Consolini, Igino Coco, Michael Pezzopane, and Alessio Pignalberi

The response of the magnetosphere-ionosphere (MI) system to the forcing by plasma of solar origin gives rise to several phenomena relevant to Space Weather. In particular, part of the energy injected into the ionosphere by means of field-aligned currents (FACs) connecting the magnetosphere with the high-latitude ionosphere is converted into mechanical energy and dissipated via Joule heating. Under reasonable assumptions, in the direction parallel to the geomagnetic field the only relevant contribution to dissipation is from the Ohmic term. Dissipated power density may significantly affect the physical parameters characterizing the upper ionosphere, such as electron temperature and density, and alter its chemical composition. This can result, for example, in the increased atmospheric drag and affect the satellite orbits. For this reason, understanding the dissipation of FACs in the topside ionosphere is important to shed light on the physical processes involved in MI coupling. Power density dissipated by FACs in crossing the topside ionosphere can be estimated by using Swarm data. Here, for the first time, we show statistical maps of power density features dissipated by FACs by using six-year time series of electron density and temperature data acquired by the Langmuir Probes onboard the Swarm A satellite (flying at an altitude of about 460 km) at 1 s cadence, together with the field-aligned current density product provided by the ESA’s Swarm Team at the same cadence. Maps of the same quantity under different levels of geomagnetic activity are also shown and discussed in light of the previous literature.

This work is partially supported by the Italian National Program for Antarctic Research under contract N. PNRA18 00289-SPIRiT and by the Italian MIUR-PRIN grant 2017APKP7T on "Circumterrestrial Environment: Impact of Sun-Earth Interaction".

How to cite: Giannattasio, F., Consolini, G., Coco, I., Pezzopane, M., and Pignalberi, A.: Power density dissipated by field-aligned currents in the topside ionosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2259, https://doi.org/10.5194/egusphere-egu22-2259, 2022.

EGU22-3338 | Presentations | EMRP2.15

Geomagnetically Induced Currents over Kazakhstan during Large Geomagnetic Storms 

Saule Mukasheva, Alexey Andreyev, Vitaliy Kapytin, and Olga Sokolova

The paper shows that during very large magnetic storms (VLMS), the energy systems of Kazakhstan are exposed to geomagnetically induced currents for quite a long time (from tens of minutes to several hours). The minute values of the magnetic field vector B or its components Bx, By, Bz during four very large geomagnetic storms with a local geomagnetic activity K-index≥7 were used to calculate the values of geomagnetically induced currents:

- September 26-28, 2011, VLMS, Sc, duration 54 h 00 min, K-index =7;

- June 22-25, 2015, VLMS, Sc, duration 78 h 30 min, K-index =8;

- October 24-28, 2016, VLMS, duration 93 h 00 min, K-index =7;

- May 12-17, 2021, VLMS, Sc, duration 17 h 25 min, K-index =7.

Sc – a sudden commencement of strong storms.

The data of four magnetic observatories of the INTERMAGNET network, whose geomagnetic latitudes are close to the geomagnetic latitudes of the southern and northern borders of Kazakhstan were considered: Alma-Ata Observatory, Kazakhstan (code AAA, 43.25°N, 76.92°E); Novosibirsk Observatory, Russia (code NVS, 54.85N, 83.23E); Irkutsk Observatory, Russia (code IRT, 52.17°N, 104.45°E) and the Beijing Ming Tombs Observatory, Beijing, China (code BMT, 40.3°N, 116.2°E).

Variations of the Bx component of the geomagnetic field during the four considered very large magnetic storms according to the observatories AAA, NVS, IRT, BMT showed variability from 50 nT to 150 nT for several hours.

Also, based on measurements of geomagnetic observatories AAA, NVS, IRT, BMT, the analysis of variations of the horizontal component H of the magnetic field vector and its time derivative (dH/dt) was carried out. Histograms of the distribution dH/dt and histograms of the distribution of the directions H and dH/dt are constructed.

It is shown that the energy systems of Kazakhstan are exposed to geomagnetically induced currents when dH/dt/ varies from 17 nT/min and more. The geomagnetic-induced current is estimated based on the calculation that the electromotive force of self-induction is proportional to the rate of change in the magnetic field strength. According to preliminary calculations, the values of geomagnetic-induced currents are fractions of mA. For more accurate calculations, it is necessary to take into account the topology of the electrical system, the composition of the underlying surface and other factors that determine the degree of susceptibility of individual elements of the power system.

This research has been/was/is funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP09259554).

How to cite: Mukasheva, S., Andreyev, A., Kapytin, V., and Sokolova, O.: Geomagnetically Induced Currents over Kazakhstan during Large Geomagnetic Storms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3338, https://doi.org/10.5194/egusphere-egu22-3338, 2022.

EGU22-4513 | Presentations | EMRP2.15

Markovian features of the Super-MAG Auroral Electrojet Index 

Simone Benella, Giuseppe Consolini, Mirko Stumpo, and Tommaso Alberti

Earth's magnetospheric dynamics displays dynamical complexity during magnetic substorms and storms. This complex dynamics includes both  stochastic and deterministic features, which manifest at different timescales. In this work, we investigate the stochastic properties of the  magnetospheric substorm dynamics by analysing the Markovian character of the SuperMAG SME time series, which is used as a proxy of the energy  deposition rate in the auroral regions. In detail, performing the Chapman-Kolmogorov test, the SME dynamics appears to satisfy the Markov condition  below 100 minutes. Moreover, the Kramer-Moyal analysis allows to highlight that a purely diffusive process is not representative of the magnetospheric  dynamics, as the fourth order Kramers-Moyal coefficient does not vanish. As a consequence, we show that a model comprising both diffusion and  Poisson-jump processes is more suitable to reproduce the SME dynamical features at small scales. A discussion of the similarities and differences  between this model and the actual SME properties is provided with a special emphasis on the metastability of the Earth’s magnetospheric dynamics.  Finally, the relevance of our results in the framework of Space Weather is also addressed.

How to cite: Benella, S., Consolini, G., Stumpo, M., and Alberti, T.: Markovian features of the Super-MAG Auroral Electrojet Index, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4513, https://doi.org/10.5194/egusphere-egu22-4513, 2022.

EGU22-4570 | Presentations | EMRP2.15 | Highlight

Building a GIC forecasting tool based on geomagnetic and solar wind data: challenges and future avenues 

Rachel L. Bailey, Roman Leonhardt, Christian Möstl, Ciaran Beggan, Martin Reiss, Ankush Bhaskar, and Andreas Weiss
Measurements of geomagnetically induced currents (GICs) in the Austrian power transmission grid have been carried out since 2014 at multiple locations. Following an analysis of the scales of GICs across the grid, we now look into forecasting the GICs from incoming solar wind data. Using nearby geomagnetic field measurements stretching back 26 years, we can estimate the local geoelectric field and consequently the GICs over longer time periods. We apply a machine learning method based on recurrent neural networks to this dataset combined with solar wind data as input. In this talk, we present the final method to forecast both the local geoelectric field E and the GICs in substations in the Austrian power grid, with our model results being compared to GIC measurements from recent years. We will discuss the current status of the model, outline limitations, and consider future applications.

How to cite: Bailey, R. L., Leonhardt, R., Möstl, C., Beggan, C., Reiss, M., Bhaskar, A., and Weiss, A.: Building a GIC forecasting tool based on geomagnetic and solar wind data: challenges and future avenues, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4570, https://doi.org/10.5194/egusphere-egu22-4570, 2022.

EGU22-4733 | Presentations | EMRP2.15

Swarm Fast Track spherical harmonic model of the external magnetic field to degree and order 3 

Natalia Gomez Perez and Ciaran Beggan

The development of satellite measurements over the past four decades has allowed us to understand the magnetic field in the Earth environment at higher temporal and spatial resolution than before. This is most evident for satellite ensembles such as ESA’s Swarm constellation which allows simultaneous global coverage with three independent satellites.

Thanks to Swarm’s particular configuration, we can take advantage of the Local Time sampling difference between Swarm A/C and Swarm B in order to estimate the low degree variation of the external magnetic field in latitude and longitude. We separate the external and induced fields measured at satellite altitude, and obtain the spherical harmonic decomposition of each source to degree and order 3 twice per day. However, there is a trade-off between spatial and temporal resolution and clear disadvantages occur when the measured field varies rapidly during a geomagnetic storm, since the method used will result in coefficients of the averaged field over the chosen time interval rather than the peaks.

We compare our results with previous models of the external field during the St Patrick storm 2015, which used up to four different local time simultaneous coverage, as well as during quiet times and lesser storms using our own solutions. We find good agreement in each case.

In this talk we will describe the algorithm and methodology used and show results over the lifetime of the Swarm mission to date (2013-). A new daily product for the Swarm mission (MMA_SHA_2E) is being developed.

How to cite: Gomez Perez, N. and Beggan, C.: Swarm Fast Track spherical harmonic model of the external magnetic field to degree and order 3, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4733, https://doi.org/10.5194/egusphere-egu22-4733, 2022.

EGU22-5792 | Presentations | EMRP2.15

Utilisation of geomagnetic data and indices for GIC applications 

Larisa Trichtchenko

The development of mitigation capabilities to counteract the detrimental impacts of space weather on critical ground infrastructure, such as power lines, pipelines and cables, depends on the availability of the observations of their causes as well as monitoring of the subsequent results.
Although direct monitoring of critical infrastructure response to GeoMagnetic Disturbances (GMD) has become more advanced in recent years, observations of geomagnetic variations continue to play the most important role in all aspects of development of safe and robust operational procedures and technology, from the forecast of geomagnetically induced currents (GIC) to their climatological studies.
This presentation shows how different types of geomagnetic data are utilised, from 3-hour and 1-hour geomagnetic indices to 1 sec. geomagnetic data, and from real-time to multi-year climatology in order to provide forecasts of GIC, identify the effects of different geomagnetic patterns on infrastructure response or provide “climatology” for network design considerations.  

How to cite: Trichtchenko, L.: Utilisation of geomagnetic data and indices for GIC applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5792, https://doi.org/10.5194/egusphere-egu22-5792, 2022.

EGU22-6037 | Presentations | EMRP2.15

Statistical and spectral study of geomagnetic storm forecasting 

Laurentiu Asimopolos, Natalia-Silvia Asimopolos, Alexandru Stanciu, and Adrian-Aristide Asimopolos

The purpose of this study is to analyze the associated spectrum of geomagnetic field, frequencies intensity and the time of occurrence of geomagnetic storms. Also, we set out to analyze the possibility of predicting these geomagnetic storms.

A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by solar coronal mass ejections, coronal holes or solar flares. Solar wind shock wave typically strikes the Earth’s magnetic field 24 to 36 hours after the event.

This only happens if the shock wave travels in a direction toward Earth. The solar wind pressure on the magnetosphere will increase or decrease depending on the Sun's activity. These solar wind pressure changes modify the electric currents in the ionosphere. The data used in this paper are acquired within the Surlari Observatory, and additional information to characterize the geomagnetic storms analyzed, we obtained from the specialized sites such as www.intermagnet.org and www.noaa.gov. Information about geomagnetic data from other observatories, as well as planetary physical parameters allowed us to perform comparative studies between the data recorded in different observatories.

We calculated the variation of the correlation coefficients, with mobile windows of various sizes, for the recorded magnetic components at different latitudes and latitudes. Also, we have used for this purpose a series of filtering algorithms, spectral analysis and wavelet with different mather functions at different levels.

Wavelets allow local analysis of magnetic field components through variable frequency windows. Windows that contain longer time intervals allow us to extract low-frequency information, average ranges of different sizes lead to extraction of medium frequency information, and very narrow windows highlight the high frequencies or details of the analyzed signals. The wavelet functions describe the orthogonal bases with signal approximation properties, while the orthonormal bases in the Fourier analysis are made up of sinusoidal waves.

Estimation of geomagnetic field disturbances is similar to the standard problem of estimating a signal disturbed by signal theory.

The term noise refers to any modification that changes the periodic or quasi-periodic characteristics of the original signal.

The Dst index is used to assess the severity of geomagnetic storms and to determine the effects of the solar wind on space and terrestrial infrastructures and is very important to be able to predict the effects of the geomagnetic storm.

The numerical experiments presented in this paper are part of different methodological categories, with the same purpose, but with different approaches. The common goal is the prediction of geomagnetic disturbances and the methodologies used comparatively are Fourier spectral deconvolution, autoregressive models on time series and recurrent Long Short Term Memory (LSTM) neural networks that are capable of long-term dependence.

How to cite: Asimopolos, L., Asimopolos, N.-S., Stanciu, A., and Asimopolos, A.-A.: Statistical and spectral study of geomagnetic storm forecasting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6037, https://doi.org/10.5194/egusphere-egu22-6037, 2022.

EGU22-6096 | Presentations | EMRP2.15

Pressure-Gradient current at high latitude from Swarm measurements 

Giulia Lovati, Paola De Michelis, Giuseppe Consolini, and Francesco Berrilli

The pressure-gradient current is among the weaker ionospheric current systems arising from plasma pressure variations. It is also called diamagnetic current because it produces a magnetic field which is oriented oppositely to the ambient magnetic field, causing its reduction. The magnetic reduction can be revealed in measurements made by low-Earth orbiting satellites flying close to ionospheric plasma regions where rapid changes in density occur. This type of current can be revealed at both low and high latitudes and more generally in all those regions where the plasma pressure gradients are greatest. In the recent past, most studies have focused on low latitude, in the equatorial belt, while only a few papers have focused on high latitudes. Here these currents, although weak, may pose additional challenge since they seem to appear preferentially at the same geographic locations.

Using geomagnetic field, plasma density and electron temperature measurements recorded onboard ESA Swarm constellation from April 2014 to March 2018, we reconstruct the flow patterns of the pressure-gradient current at high-latitude ionosphere in both hemispheres, and investigate their dependence on magnetic local time, geomagnetic activity, season and solar forcing drivers. Although being small in amplitude, these currents appear to be a ubiquitous phenomenon at ionospheric high latitudes, characterized by well defined flow patterns, which can cause artifacts in main field models. Our findings can be used to correct magnetic field measurements for diamagnetic current effect, to improve modern magnetic field models, as well as understanding the impact of ionospheric irregularities on ionospheric dynamics at small-scale sizes of a few tens of kilometers. All these points are important in the framework of space weather effect modeling and confirm the key role of Swarm mission in providing information even on phenomena of very weak signature.

How to cite: Lovati, G., De Michelis, P., Consolini, G., and Berrilli, F.: Pressure-Gradient current at high latitude from Swarm measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6096, https://doi.org/10.5194/egusphere-egu22-6096, 2022.

EGU22-6269 | Presentations | EMRP2.15

Dawn-dusk asymmetry of solar flare-driven ionospheric current at high latitudes 

Pierre Cavarero, Masatoshi Yamauchi, Magnar G. Johnsen, Shin-Ichi. Ohtani, and Janet Machol

Solar flares are known to enhance the ionospheric electron density and thus influence the D- and E-region electric currents in the sunlit hemisphere.  The resultant geomagnetic disturbances (called "crochet") are found at both low latitudes and high latitudes with a minimum in between.  The subsolar response, with short-lived and symmetric changes around the subsolar region, is understood as a temporal re-distribution of the electron density.  However, no systematic study has been made of the high-latitude responses, covering the auroral oval, the cusp, and the dayside sub-auroral region.  Even global patterns are not well described or understood.  

Using data from GOES satellites and SuperMAG, we made a statistical study of the high-latitude geomagnetic responses to X-class solar flares in the northern polar region.  First, we needed to create a reliable X-flare database that we could use to get precise timings of when the flares start and when they stop. We merged XRS databases from different GOES satellites to create a X-class solar flare database between 1984 and 2017, gathering 331 X-flares over 34 years.  

For all these X-flares, we plotted the geomagnetic disturbance (∆B) on a polar map during the periods when the X-ray flux exceeds 1e-4 W/m2 (>X1 flare).  Plots were made also for merged data, i.e., different events on the same map organized by geographic coordinates and local time to obtain the average disturbance pattern caused by the flares.  Large events (∆B >300 nT) were excluded to minimize the contamination from substorm events.  

In these "merged" plots, we classify the data by season (summer - 4 months, equinox ±2 months, winter 4 months), flare intensity (X1-X2 flares and >X2 flares), and maximum ∆B among all stations > 65° GGlat (< 100 nT and 100-300 nT). 

 

Except for winter, we found a large poleward ∆B which peaks at 13-16 LT, particularly for > X2 flares, but no enhancements in the pre-noon sector.  This asymmetry, surprisingly, remains even after we consider IMF By polarity.  We do not have any plausible explanation for this result, and we will discuss it during the presentation.

 

[Acknowledgement: This work is resulted from a 2021 summer internship study at the Swedish Institute of Space Physics, Kiruna.   The GOES X-ray data is provided by NOAA (USA). The geomagnetic data at high latitudes are obtained from SuperMAG and are originally provided by DTU (Denmark), TGO (Norway), FMI (Finland), SGO (Finland), SGU (Sweden), GSC (Canada), USGS (USA), AARI (Russia), PGI (Russia), IZMIRAN (Russia), BAS (UK), BGS (UK), IPGP (France), PAS (Poland), ZAMF (Austria), and ASCR (Czech)]

How to cite: Cavarero, P., Yamauchi, M., Johnsen, M. G., Ohtani, S.-I., and Machol, J.: Dawn-dusk asymmetry of solar flare-driven ionospheric current at high latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6269, https://doi.org/10.5194/egusphere-egu22-6269, 2022.

EGU22-6336 | Presentations | EMRP2.15

Swarm-derived indices of geomagnetic activity 

Constantinos Papadimitriou, Georgios Balasis, Adamantia Zoe Boutsi, Alexandra Antonopoulou, Georgia Moutsiana, Ioannis A. Daglis, Omiros Giannakis, Giuseppe Consolini, Jesper Gjerloev, and Lorenzo Trenchi

Ground-based indices, such as the Dst, ap and AE, have been used for decades to describe the interplay of the terrestrial magnetosphere with the solar wind and provide quantifiable indications of the state of geomagnetic activity in general. These indices have been traditionally derived from ground-based observations from magnetometer stations all around the Earth. In the last 7 years though, the highly successful satellite mission Swarm has provided the scientific community with an abundance of high quality magnetic measurements at Low Earth Orbit (LEO), which can be used to produce the space-based counterparts of these indices, such the Swarm-Dst, Swarm-ap and Swarm-AE indices. In this work, we present the first results from this endeavour, with comparisons against traditionally used parameters. We postulate on the possible usefulness of these Swarm-based products for a more accurate monitoring of the dynamics of the magnetosphere and thus, for providing a better diagnosis of space weather conditions.

How to cite: Papadimitriou, C., Balasis, G., Boutsi, A. Z., Antonopoulou, A., Moutsiana, G., Daglis, I. A., Giannakis, O., Consolini, G., Gjerloev, J., and Trenchi, L.: Swarm-derived indices of geomagnetic activity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6336, https://doi.org/10.5194/egusphere-egu22-6336, 2022.

EGU22-8015 | Presentations | EMRP2.15

Towards an improved proxy for geomagnetically induced currents (GICs) 

Fernando Jorge Gutiérrez Pinheiro, Marta Neres, M. Alexandra Pais, Joana Alves Ribeiro, Rute Santos, and João Cardoso

The irregular variation of geomagnetic activity caused by the solar wind interaction with the magnetosphere/ionosphere (space weather) occurs in wide temporal and amplitude ranges. Major geomagnetic storms can induce geoelectric fields in the Earth conducting layers (through the lithosphere and down to the mantle), which may, in turn, be responsible for generating geomagnetically induced currents (GICs). The vulnerability of grounded conducting infrastructures, particularly electrical power transmission systems, to GICs, makes it important to understand the relation between the varying geomagnetic field components and the generated GICs, as well as the role of the local conductivity, i.e., geology, on the inducing process. Looking for proxies that better translate this relation is an open matter of debate.

In this work, we present a comprehensive study of several possible candidates for GIC proxies. We use geomagnetic time series from the Portuguese mid-latitude Coimbra observatory (COI) to calculate geomagnetic indices considering different periods (whole-storm duration, 3-h, 1-h and 1-min), with different focuses on the field components or their derivatives, and discuss their advantages and limitations. We compare the computed indices with both GIC simulations of the Portuguese mainland high voltage power network (150, 220 and 400 kV) (Alves Ribeiro et al., 2021), and observations from a Hall effect sensor based system installed at a power transformer located in the vicinity of Coimbra. 
We then propose a better GIC proxy, an index obtained from geomagnetic field components filtered by convolution with a uniform conductivity Earth model filter (EGIC index), based on previous work by Marshall et al (2010,2011). We search for empirical parameters that may contain information on local conductivity effects and power network geometry.

This study is funded by national funds through FCT (Portuguese Foundation for Science and Technology, I.P.), under the project MAG-GIC (PTDC/CTA-GEO/31744/2017). FCT is also acknowledged for support through projects UIDB/50019/2020-IDL, PTDC/CTA-GEF/1666/2020 (MN) and PTDC/CTA-GEO/031885/2017 (MN). CITEUC is funded by FCT (UIDB/00611/2020 and UIDP/00611/2020). We acknowledge the collaboration with REN (Redes Energéticas Nacionais).

References:
Alves Ribeiro J., F.J. Pinheiro, M.A. Pais, 2021. First Estimations of Geomagnetically Induced Currents in the South of Portugal. Space Weather, 19(1)
Marshall R. A., C. L. Waters, M. D. Sciffer (2010). Spectral analysis of pipe‐to soil potentials with variations of the Earth’s magnetic field in the Australian region. Space Weather 8.5
Marshall, R. A., et al (2011). "A preliminary risk assessment of the Australian region power network to space weather." Space Weather 9.10

How to cite: Gutiérrez Pinheiro, F. J., Neres, M., Pais, M. A., Alves Ribeiro, J., Santos, R., and Cardoso, J.: Towards an improved proxy for geomagnetically induced currents (GICs), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8015, https://doi.org/10.5194/egusphere-egu22-8015, 2022.

EGU22-8752 | Presentations | EMRP2.15

A quasi-real time geomagnetic activity index from ground based measurements at geomagnetic observatories run by italian INGV for space weather nowcasting 

Paolo Bagiacchi, Lili Cafarella, Alfredo Del Corpo, Domenico Di Mauro, Stefania Lepidi, and Mauro Regi

The geomagnetic observatories managed by INGV (Istituto Nazionale di Geofisica e Vulcanologia), both in Italy and Antarctica, send data to a server and the data are collected and stored in a MySQL database. The database has been operating for almost two decades and it is implemented on a local server which serves also as a web portal for the data display and distribution. By analyzing the data of all the INGV geomagnetic observatories at middle and polar latitudes, i.e. the values of the H, D and Z components, the F module and the K indices, the algorithm aims to distinguish the activity of the Earth's magnetic field in the following categories: “Quiet Period”, “Local disturbance” and “Magnetic Activity”, possibly distinguishing, within the latter, the level and the kind of event (sudden impulse, sudden ionospheric and magnetic disturbance driven by solar flare, magnetic storm or substorm). A preliminary automatic procedure allows to detect possible instrumental failure from a comparison between the vector components and the total field intensity in each observatory. A second level of check allows to discriminate local or regional against global features with the final goal to reject local noise, possibly of anthropic nature, eventually present in a single observatory through a majority logic based procedure. After these first filtering steps an automatic software procedure provides an empirical estimation of the current  Magnetic Activity (nowcasting) organized according to the above three possible categories. The embedded algorithm in the procedure operates on the geomagnetic field element (H, D, Z and F) and the local K indices of all observatories. The operations that the algorithm performs are aimed to identify the impulsive components in the signal, which are caused by external events. The quiet field component is removed from the signal, leaving the impulsive components present in the signal almost unaltered. If in the residual field is present a significant activity (with respect to an appropriate threshold) a procedure is performed that distinguishes between an isolated impulse or a cluster of impulses, by using time windows of different sizes. The whole procedure allows us to generate two different geomagnetic activity indices, one at low and the other at high latitude. In a final step we compute a cross correlated geomagnetic index comparing processed data at low and high latitude to retrieve a large spatial scale index.

How to cite: Bagiacchi, P., Cafarella, L., Del Corpo, A., Di Mauro, D., Lepidi, S., and Regi, M.: A quasi-real time geomagnetic activity index from ground based measurements at geomagnetic observatories run by italian INGV for space weather nowcasting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8752, https://doi.org/10.5194/egusphere-egu22-8752, 2022.

EGU22-9999 | Presentations | EMRP2.15

Long-term Trends and Occurrence Distributions of Geomagnetic Fluctuations as Revealed by 35 Years of CARISMA Observations at 5s Cadence 

Stavros Dimitrakoudis, Ian R. Mann, Andy Kale, and David K. Milling

The rate of change of the horizontal component of the geomagnetic field is a useful proxy for determining the severity of geomagnetically induced currents (GIC). While contemporary measurements for geomagnetic disturbances (GMD) are available from a number of arrays, short timescale datasets are not ideal for the characterisation of extreme events since their data sets are rarely indicative of the most extreme geomagnetic conditions. In the absence of long duration data sets, statistical methods have to be employed to assess the overall longer timescale historical power occurrence distributions, so as to extrapolate the behaviour of their high-end tail and which is required for the assessment of extreme events. Conversely, the CANOPUS array, subsequently expanded and operated as the CARISMA magnetometer array (www.carisma.ca), has been in continuous operation in Canada since 1986, first with a 5-second and then more recently with a 1-second cadence. Using that long timebase dataset we are able to evaluate the occurrence distributions of 5-second cadence measurements for over 10,000 operational days for each of several stations. Of particular significance for the expected magnitude of extreme events is an assessment of whether the disturbances follow a power law or log-normal distribution. Such indications can inform risk assessments on the potential for extremely hazardous GICs, for example in the estimation of a 1-in-100-year event. The CANOPUS/CARISMA GMD occurrence distributions, overall, appear to be well-approximated by log-normal rather than power law distributions. However, for extreme events, the local time at which the largest GMD typically occurs rotates away from the midnight sector, such that the largest events in the tail of the distribution most often occur instead at dawn. This has significant implications for assessing the size of expected extreme GMD events, and indeed the local time of the largest vulnerability, with clear applications for assessing extreme space weather impacts on the electric power grid. 

How to cite: Dimitrakoudis, S., Mann, I. R., Kale, A., and Milling, D. K.: Long-term Trends and Occurrence Distributions of Geomagnetic Fluctuations as Revealed by 35 Years of CARISMA Observations at 5s Cadence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9999, https://doi.org/10.5194/egusphere-egu22-9999, 2022.

EGU22-10681 | Presentations | EMRP2.15

Causality and information transfer in interactions of solar wind, radiation belts and geomagnetic field 

Pouya Manshour, Constantinos Papadimitriou, George Balasis, Milan Palus, Simon Wing, Ioannis A. Daglis, Reik Donner, Adamantia Zoe Boutsi, Giuseppe Consolini, Juergen Kurths, and Bruce T. Tsurutani

Understanding physical processes that drive dynamics of the radiation belts - the high-energy charged particle population trapped by the geomagnetic field in the inner magnetosphere, is of great importance for science and society. In fact, this population dynamically interacts with the solar wind and geomagnetic field over various temporal and spatial scales, and can have significant impacts on its surrounding environment, including hazards to satellites and astronaut health. Understanding the relevant acceleration mechanisms of these particles can help not only to uncover the underlying physics, but also to improve our ability to predict and to protect. Despite numerous attempts over several decades, unfolding the dynamics of interactions in such systems is still one of the challenging research areas and has not yet been achieved, due to the complex and nonlinear underlying physics of the radiation belts. However, information theory is not constrained by such limitations and has proven itself to be a powerful non-parametric approach to discover the causal interactions among different nonlinear complex systems, and can be considered complementary to physics-based approaches. In this work, we apply entropy-based causality measures such as conditional mutual information to determine the information transfer between various variables including different solar wind parameters and geomagnetic activity indices obtained from NASA’s OmniWeb service and omnidirectional electron fluxes from the MagEIS units onboard Van Allen Probe B in the outer radiation belt, ranging in energy from a few keV to several MeV. We find significant information flow from low energy electrons into high energy ones as well as from some solar wind/geomagnetic field parameters into electron fluxes of various energies. We are confident that our results provide great prospects for future targeted research on the dynamical mechanisms underlying radiation belts dynamics.

This work has benefitted from discussions within the International Space Science Institute (ISSI) Team # 455 “Complex Systems Perspectives Pertaining to the Research of the Near-Earth Electromagnetic Environment.”  P.M. and M.P. are supported by the Czech Science Foundation, Project No. GA19-16066S and by the Czech Academy of Sciences, Praemium Academiae awarded to M. Paluš.

How to cite: Manshour, P., Papadimitriou, C., Balasis, G., Palus, M., Wing, S., Daglis, I. A., Donner, R., Boutsi, A. Z., Consolini, G., Kurths, J., and Tsurutani, B. T.: Causality and information transfer in interactions of solar wind, radiation belts and geomagnetic field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10681, https://doi.org/10.5194/egusphere-egu22-10681, 2022.

EGU22-10887 | Presentations | EMRP2.15

Swarm as an EMIC Wave Monitor: Applications for Radiation Belt Modelling and Specification 

Ivan Pakhotin, Ian Mann, Louis Ozeke, Leon Olifer, and Stavros Dimitrakoudis

The outer belt electron radiation belt is highly dynamic, responding to a superposition of a variety of acceleration and loss processes imposed along the electron drift orbits to produce increases and decreases in flux on timescales from minutes, to hours, days and years. These trapped relativistic so-called ‘satellite killer’ electrons can penetrate spacecraft shielding and cause damage to internal electronics and single-event upsets. Understanding and predicting the radiation belt environment, therefore, is valuable for the understanding and mitigation of these potentially catastrophic impacts. Magnetic measurements from the constellation of Swarm satellites in low-Earth orbit (LEO) can be used to monitor the populations of electromagnetic ion cyclotron (EMIC) waves along their orbits. This is significant for radiation belt applications since these waves are believed to be potentially responsible for some fast losses of radiation from the Van Allen belts through fast scattering into the loss cone. Despite being far from the equatorial plane where most of the radiation belts are trapped, the propagation of EMIC waves along field lines allows an assessment of these wave populations from LEO, Swarm and similar satellites in LEO traversing the radiation belts four times in each approximately 90-minute orbit. Here we demonstrate how Swarm can be used to detect and characterize the EMIC wave populations, and compare the observed EMIC wave populations to simulations of two strong magnetic storms where radiation belt modeling based on radial diffusion demonstrated the likelihood of a missing fast loss process and which might be explained by EMIC wave-particle interactions. The current state-of-the-art for the incorporation of EMIC-related wave losses is based on empirical means, related for example to solar wind compressions. Here we investigate, despite the often spatio-temporally localized character of some EMIC wave populations, whether magnetic field data from the Swarm constellation could be used in an observational data-constrained approach for the inclusion of EMIC wave losses in radiation belt modelling. LEO satellites have the advantage over high-apogee near-equatorial satellites in that the latter only cross L-shells comparatively slowly; similarly, the interpretation of EMIC wave location from ground-based magnetometer networks is complicated by propagation in the ionospheric duct. Through the use of multi-spacecraft techniques, and/or those which utilise electric and magnetic data together, we demonstrate how it is possible to reliably disentangle EMIC waves from nearby field-aligned currents. Such techniques provide hitherto unprecedented observation capability for the specification of EMIC waves from LEO for use in radiation belt modelling. Future work could examine the utility of such data for both improving the accuracy of radiation belt models, and for the nowcasting and even forecasting of belt dynamics.

How to cite: Pakhotin, I., Mann, I., Ozeke, L., Olifer, L., and Dimitrakoudis, S.: Swarm as an EMIC Wave Monitor: Applications for Radiation Belt Modelling and Specification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10887, https://doi.org/10.5194/egusphere-egu22-10887, 2022.

EGU22-11323 | Presentations | EMRP2.15

Information flow within the magnetosphere-ionosphere system: insights from ensemble-based transfer entropy 

Mirko Stumpo, Giuseppe Consolini, Simone Benella, and Tommaso Alberti

When the interplanetary magnetic field is characterized by nearly-southward conditions, the near-Earth magnetospheric environment and, specifically, the plasma circulation and the magnetospheric-ionospheric current systems undergo to some dynamical changes to dissipate the excess of energy-momentum and mass transfer from interplanetary medium to the magnetosphere. Geomagnetic storms and magnetospheric substorms are the macroscopic manifestation of such a response and their relation is one of the critical issues of the magnetospheric dynamics. In this framework, a very old and widely debated topic is the storm-substorm relations, such as for instance the role of substorms in developing a storms. In recent years, some novel methods developed in the ambit of the information theory, such us the transfer entropy, have been applied to unveil the directionality of the information flow between storms and substorms (De Michelis et al., 2011, Stumpo et al, 2020). However, these results have been partially criticised suggesting that there is not a clear net transfer of information between substorms to storms. However, the use of information theory methods which relies on time averages could hide the dynamics of the information flow. Indeed, the absence of a net information exchange between storms and substorms may be due to the fact that it is enhanced only during activity periods, so that it may be canceled out if transfer entropy is computed by averaging together quiet and activity periods.Here, we attempt an instantaneous estimation of the magnetospheric internal transfer of information during the occurrence of geomagnetic storms using an ensemble-based transfer entropy analysis. In detail using some geomagnetic indices as proxies of magnetospheric-ionosphere dynamics during geomagnetic storms, we investigate the directionality of the information flow within the magnetosphere-ionosphere system during the occurrence of periods of magnetic storms and substorms.

This work received funding by Italian MIUR-PRIN grant 2017APKP7T on Circumterrestrial Environment: Impact of Sun-Earth Interaction.

How to cite: Stumpo, M., Consolini, G., Benella, S., and Alberti, T.: Information flow within the magnetosphere-ionosphere system: insights from ensemble-based transfer entropy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11323, https://doi.org/10.5194/egusphere-egu22-11323, 2022.

EGU22-11344 | Presentations | EMRP2.15

Comparing long short-term memory and convolutional neural networks in SYM-H index forecasting 

Federico Siciliano, Giuseppe Consolini, and Fabio Giannattasio

Geomagnetic indices can have a central role in the mitigation of ground effects due to space weather events, for instance when their reliable forecasting will be achieved. To this purpose, machine learning techniques represent a powerful tool. Here, we use two conceptually different neural networks to forecast the SYM-H index: the long short-term memory (LSTM) and the convolutional neural network (CNN). We build two models and train both of them using two different sets of input parameters including interplanetary magnetic field components and magnitude and differing for the presence or not of previous SYM-H values. Both models are trained, validated, and tested on a total of 42 geomagnetic storms among the most intense that occurred between 1998 and 2018. Results show that both models are able to well forecast SYM-H index 1 hour in advance. The main difference between the two stands in the better performance of the one based on LSTM when SYM-H index is included in the input parameters and, contrarily, in the better performance of the one based on CNN for predictions based only on interplanetary magnetic field data.

How to cite: Siciliano, F., Consolini, G., and Giannattasio, F.: Comparing long short-term memory and convolutional neural networks in SYM-H index forecasting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11344, https://doi.org/10.5194/egusphere-egu22-11344, 2022.

EGU22-13154 | Presentations | EMRP2.15

Time derivative of the geomagnetic field has a short reset time 

Mirjam Kellinsalmi, Ari Viljanen, Liisa Juusola, and Sebastian Käki

Space weather, like solar eruptions, can be hazardous to Earth’s electric grids via geomagnetically induced currents (GIC). In worst cases they can even cause city-wide power outages. GIC is a complicated phenomenon, closely related to the time derivative of the geomagnetic field. However, behavior the time derivative is chaotic and has proven to be challenging to predict. In this study we look at the geomagnetic field orientations at different magnetometer stations in the Fennoscandian region during active space weather conditions.  We aim to characterize the magnetic field behavior, to better understand the drivers behind strong GIC events. One of our main findings is that the direction of time derivative of the geomagnetic field has a very short “reset time“, only a few minutes. We conclude that this result gives insight on the time scale of the ionospheric current systems, which are the primary driver behind the time derivative’s behavior.

How to cite: Kellinsalmi, M., Viljanen, A., Juusola, L., and Käki, S.: Time derivative of the geomagnetic field has a short reset time, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13154, https://doi.org/10.5194/egusphere-egu22-13154, 2022.

EGU22-916 | Presentations | EMRP2.16

Joint Probabilistic Inversion of 3D Magnetotelluric and Seismic Data in Southeast Australia 

Maria Constanza Manassero, Juan Carlos Afonso, Alison Kirkby, Alan Jones, Ilya Fomin, and Karol Czarnota

In the context of whole-lithosphere structure, the joint inversion of magnetotelluric (MT) with seismic data is particularly interesting as they provide complementary information on the thermal structure, fluid pathways and water content. Both data sets can put tight constrains on the first-order thermal structure and mineralogical structure of the lithosphere, but only MT is strongly sensitive to anomalous features such as hydrogen content, minor conductive phases and/or small volumes of fluid or melt. This makes joint inversions of MT with other observables a powerful means to detect fluid pathways in the lithosphere including the locus of partial melting, ore deposits and hydrated (or metasomatized) lithologies. This unique potential of joint inversions of MT with other datasets has given impetus to the acquisition of collocated MT and seismic data over large regions. Concrete examples are the US Array, Sinoprobe in China, and the AusLAMP/AusArray in Australia. These multi-disciplinary programs are providing high-quality seismic and MT data with unprecedented resolution and coverage, allowing the pursuit of large-scale 3D joint inversions to image the structure, dynamics and evolution of the whole lithosphere and upper mantle.

 

Within probabilistic approaches the solution to the inverse problem is given by the so-called posterior probability density function which provides complete information about the unknown parameters and their uncertainties conditioned on the data and modelling assumptions. Joint probabilistic inversions of MT and seismic data have been successfully implemented in the context of 1D MT data only. For the cases of 2D and 3D MT data, however, the large computational cost of the MT forward problem has been the main impediment for pursuing probabilistic inversions, as the number of forward solutions required are typically on the order of 105 – 107. To overcome this limitation, we have recently presented a novel strategy [2,3], called RB+MCMC, that computes 3D MT surrogate models and uses complementary parameterizations to couple different data sets. This strategy reduces the computational cost of the 3D MT forward solver and allow us to perform full joint probabilistic inversions of MT and other datasets for the 3D imaging of deep thermochemical anomalies.

 

In this contribution, we first illustrate the benefits and general capabilities of our method for 3D joint probabilistic inversions of MT with other datasets using whole-lithosphere synthetic models. Last, as part of the Exploring for the Future program, we present results of the first joint probabilistic inversion of 3D MT in southeast Australia using the AusLAMP data and a seismic velocity model derived from teleseismic tomography [4]. These results demonstrate the capabilities of our conceptual and numerical framework for 3D joint probabilistic inversions of MT with other geophysical data sets and open up exciting opportunities for elucidating the Earth’s interior in other regions.

 

 

 

References

[1] Afonso, J.C. et al., (2016), Journal of Geophysical Reseach, 121, doi:10.1002/2016JB013049

[2] Manassero, M. C., et al., (2020), Geophysical Journal International, 223(3), doi: 10.1093/gji/ggaa415

[3] Manassero, M. C., et al., (2021), doi: 10.1029/2021JB021962

[4] Rawlinson, N., et al., (2016), Tectonophysics, doi: 10.1016/j.tecto.2015.11.034

How to cite: Manassero, M. C., Afonso, J. C., Kirkby, A., Jones, A., Fomin, I., and Czarnota, K.: Joint Probabilistic Inversion of 3D Magnetotelluric and Seismic Data in Southeast Australia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-916, https://doi.org/10.5194/egusphere-egu22-916, 2022.

EGU22-1034 | Presentations | EMRP2.16

Geothermal Exploration of the Baia Mare Region (Romania) with Magnetotellurics – Responses, Analysis and 1D Models 

Maik Neukirch, Alexander Minakov, Maxim Smirnov, Carmen Gaina, Ionelia Panea, Anca Isac, Marine Collignon, Alexandru Zlibut, Cosmin Coverca, Bogdan Sebastian Paralescu, and Ana-Maria Henriuc Morosan

Geothermal energy extracted from hydrothermal systems can play a key role in mitigating the effects of climate change, while meeting the world’s increasing energy demand. Moreover, not only does it represent a highly economic and adaptive source of renewable energy, but it is genetically related with the formation of ore deposits which are necessary to fuel our energy transition.

The presented study is part of a larger multidisciplinary and international project that aims at investigating the geothermal potential of the Baia Mare region, in northern Romania and for which geological, geochemical, hydrogeological and geophysical data have been. In this framework, the magnetotelluric (MT) method is used to study the hydrothermal system and more specifically to locate heat sources, highlight the presence of fluids and identify the system’s structure.

The largest cluster of measurements with anomalously high heat flow values in Romania (100-160 mW/m2) is situated in the greater Baia Mare region, revealing this area as a prime interest for geothermal exploration. The study area is located within the Neogene Inner Carpathians volcanic arc. Crustal hydraulic properties and associated hydrothermal systems are possibly controlled by the regional Dragos-Voda strike-slip fault zone, which could also provide a pathway for late Miocene magmatic intrusions and lava flows. The associated magmatic plumbing system crosscuts the Neogene sedimentary deposits of the Pannonian Basin. The region is known for surface hot springs, salt and metal mining, which all suggest the presence of a hydrothermal system that could be exploited for geothermal energy.

Broadband magnetotelluric transfer functions have been obtained at 24 sites in the Baia Mare region ranging from 300 Hz up to around 1000s using two MTU instruments from Luleå University of Technology. In addition, we collected continuous telluric broadband recordings at the Surlari National Geomagnetic Observatory to be used as remote reference data together with data from other INTERMAGNET observatories. We applied non-stationary, robust remote processing, which allowed to improve poorly constrained estimates of the impedance tensor in the MT dead band (1 to 10s). Phase tensor and impedance maps provide data overview and a first glimpse of subsurface structures. The preliminary 3D inversion results are presented.

How to cite: Neukirch, M., Minakov, A., Smirnov, M., Gaina, C., Panea, I., Isac, A., Collignon, M., Zlibut, A., Coverca, C., Paralescu, B. S., and Henriuc Morosan, A.-M.: Geothermal Exploration of the Baia Mare Region (Romania) with Magnetotellurics – Responses, Analysis and 1D Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1034, https://doi.org/10.5194/egusphere-egu22-1034, 2022.

EGU22-2196 | Presentations | EMRP2.16 | Highlight

Advances in electromagnetic imaging in the presence of well casings: algorithms and field experiments 

Rita Streich, Gurban Orujov, and Andrei Swidinsky

Controlled-Source Electromagnetic (CSEM) methods have the potential to be powerful geophysical tools for imaging and monitoring the distribution of electrically resistive fluids, such as freshwater aquifers, CO2 injected into the subsurface or hydrocarbons during oil and gas production.  However, the presence of metallic infrastructure (steel well casings, pipelines etc.) presents an enormous challenge, because the highly conductive metal masks the electromagnetic response of subsurface geology and distorts any associated time-lapse changes. Therefore, numerical techniques to predict and mitigate the contamination caused by pipelines and casings on CSEM surveys are critical for real world imaging and 4D applications near any such metal objects.

In a collaborative project between the Colorado School of Mines and Shell, we have developed CSEM modeling and inversion tools that can handle realistic scenarios with multiple vertical as well as deviated casings and complex pipeline networks, as will be encountered in mature oil field environments. First, we implemented a forward modeling code based on the Method of Moments technique, which effectively turns the casings into extra sources, such that we do not need to discretize them into excessive numbers of very small model cells. We used this modeling tool to demonstrate quantitatively how steel casings impact synthetic and real time-lapse EM data. The forward modeling code was then combined with a newly developed Gauss-Newton inversion engine, which by itself has been demonstrated to provide images of superior resolution, depth penetration and data fit with less dependency on initial conditions compared to previous quasi-Newton inversion engines.

In this contribution, we first demonstrate on synthetic data that the combination of these two algorithms provides high-quality electrical resistivity images in the immediate vicinity of well casings. Then, we show encouraging results of applying the new tools to field trial data acquired over known casings under semi-controlled conditions. The images obtained are nearly free of casing imprint and subsurface geology could be recovered. These results suggest that this technology may enable us to explain severely distorted field data that were previously uninterpretable.

How to cite: Streich, R., Orujov, G., and Swidinsky, A.: Advances in electromagnetic imaging in the presence of well casings: algorithms and field experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2196, https://doi.org/10.5194/egusphere-egu22-2196, 2022.

EGU22-2268 | Presentations | EMRP2.16

New insights of airwave in controlled-source electromagnetic offshore data 

Shunguo Wang, Steven Constable, Arnold Orange, and Ståle Emil Johansen

The marine controlled-source electromagnetic (CSEM) method has been used for offshore natural resource exploration for a few decades, and it has the potential to be used for offshore CO2 storage monitoring. Airwaves, previously treated as distortions, often dominate marine CSEM data when the offshore seawater is shallower than a couple of kilometers. Therefore, different methods have been proposed to distinguish and then correct the airwaves in marine CSEM data. In this study, we analyzed the airwave features by different model parameter perturbations with two-dimensional (2D) modeling. After a thorough study of differentiated EM fields and Poynting vectors for each single model component, we summarize the airwave propagation features and sensitivities regarding different modeling parameters. Particularly, the scenario with and without an oil reservoir or CO2 storage is carefully studied. It turns out that the airwave can provide useful information at certain transmitter and receiver offsets. Nevertheless, we propose to model the airwave as what it is in the marine CSEM data rather than correct it before feeding the offshore CSEM data to inversion. This idea is demonstrated with a field example from offshore of Svalbard, Norway.

How to cite: Wang, S., Constable, S., Orange, A., and Johansen, S. E.: New insights of airwave in controlled-source electromagnetic offshore data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2268, https://doi.org/10.5194/egusphere-egu22-2268, 2022.

EGU22-3498 | Presentations | EMRP2.16 | Highlight

Magnetotelluric investigations in the Ubaye seismic swarm region, Western Alps: a connection between electrical conductivity, fluids, and earthquakes? 

Svetlana Byrdina, Jean-Luc Got, Laurent Metral, Philip Hering, Marion Baques, Louis De Barros, Stephane Garambois, Philippe Gueguen, and Volker Rath

The Ubaye Region is a seismically active region in the Western Alps (France), regularly struck by seismic swarms characterized by a high number of small to moderate earthquakes, such as in 2003–2004 or 2012–2015. While some earthquakes could be associated with known faults, the character of the observations (high seismicity – low deformation rate) requires complex driving processes beyond local or regional tectonics. Most conceptual models involve fluids present down to depths of several km, and/or long-range transport.

Magnetotellurics (MT) is known to be an efficient imaging method sensitive to crustal fluids. During 2020/21, a data set of 30 MT sites was acquired, covering a signal period ranging between 10-4 to 104 s, with generally all 5 components measured. Data quality was generally satisfactory up to 3 s and sometimes up to 100 s. Major problems were related to topography (including logistics), and to the presence of electromagnetic noise, only to be mitigated by advanced processing methods (FFMT). For the 3-D inversion required by the data (phase tensors, WAL, topography), we have chosen a joint inversion of induction vectors, phase tensors and off-diagonal impedances (previously corrected for static shift with help of phase tensor inversion). This allowed us to obtain the best 3-D model using the ModEM inversion code, explaining all three data types reasonably well.

The main findings from this investigation include (a) a prominent conductor (down to 20 Ωm) located along the axis of the swarm zone, though generally above it; (b) a regional dominance of the Penninic Front in the East and the overridden Mesozoic (Dauphinoise) sediments in the West, both not fully covered by the current survey; (c) strike directions that agree well with most of the mapped faults and focal mechanisms of the strongest seismic events.

Uncertainties associated with the insufficient data coverage in some of the most interesting zones were studied by analysing the sensitivities provided by the inversion and direct forward modelling of significant model features. In general, this led to the conclusion that our sensitivity does reach the border of the seismic swarm activity, but does not cover its depth extent. Due to the gap in data in the central area of interest, the geometry and connectivity of the main conductor remains a hypothesis. Thus, a truly quantitative characterization of prominent identified structures is not currently possible and should be better assessed with additional measurement sites. The different conceptual models proposed for the origin of the seismic swarm activity will be discussed in the light of the MT imaging, and the associated uncertainties.

How to cite: Byrdina, S., Got, J.-L., Metral, L., Hering, P., Baques, M., De Barros, L., Garambois, S., Gueguen, P., and Rath, V.: Magnetotelluric investigations in the Ubaye seismic swarm region, Western Alps: a connection between electrical conductivity, fluids, and earthquakes?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3498, https://doi.org/10.5194/egusphere-egu22-3498, 2022.

The Bohemian Massif is part of the geodynamically active European Cenozoic Rift System and represents its easternmost termination. The study area is situated at the junction of three different Variscan tectonic units and hosts beside the Eger Rift a series of different fault systems. The entire region is characterized by ongoing magmatic processes in the intra-continental lithospheric mantle expressed by, e.g., the occurrence of repeated earthquake swarms, the presence of Quaternary volcanoes, and massive degassing of mantle-derived CO2 in mineral springs, mofettes as well as. Several geoscientific studies suggest that fluid circulation along the deep-reaching faults seems to play an important role in explaining the underlying geodynamic processes. As part of an ICDP drilling programme, we applied the Magnetotelluric (MT) method with the goal to contribute to the understanding of the physical and chemical processes and interaction that led to the magma and fluid transport by mapping potential fluid pathways from the crust-mantle boundary up to the surface. Here, we present 3D inversion models of two different overlapping regional and one local MT experiments located in the Cheb basin close to the Hartoušov mofette field. The most prominent large-scale conductivity features of the regional models are several channels from the lower crust to the surface, possibly representing pathways for fluids into the earthquake swarm region, mofette fields, and known spas. However, such a conductive channel is absent in the local model beneath the surface expression of the mofettes. We will test two different hypotheses, namely a vertical ascending channel versus lateral fluid migration. Results from synthetic modelling studies and available geoscientific constraints hint that such a channel might exist directly beneath the mofette field, but due to the given data quality, station distribution, and the subsurface conductivity structure within a conductive sediment basin, it might be challenging to resolve.

How to cite: Aleid, B., Weckmann, U., Platz, A., and Mair, J.: Magnetotellurics in the Eger Rift: Regional and local three-dimensional subsurface imaging and modelling of fluid pathways from the crust-mantle boundary to the surface, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4884, https://doi.org/10.5194/egusphere-egu22-4884, 2022.

EGU22-5056 | Presentations | EMRP2.16

Joint inversion of Magnetotelluric Data and Surface-Wave Dispersion Curves using Correspondence Maps 

Monica Aquino, Guy Marquis, and Jerome Vergne

We use a correspondence map approach to jointly invert surface-wave dispersion curves and magnetotelluric data for subsurface shear velocity and resistivity but also for a possible relationship between them. Our first experiments consist of inversions of synthetic data computed from models linked by linear and second-order polynomial relationships. Our methodology produces joint inversion model-pairs (resistivity-shear velocity) from where 80% fit the 'observed' parameter relationship within a 5% error vs only 1%  of the separate inversion model-pairs for the linear relationship experiment. For the non-linear relationship synthetic test, 85% of the joint inversion model-pairs fit the 'observed' relationship within a 5% error while just 40% of the separate inversion model-pairs. This reduces the number of acceptable models without compromising the data fit ('reduction of non uniqueness'). Using the non-linear synthetic data we show how to select an appropriate polynomial degree for joint inversion. Having validated the approach with synthetic cases, we applied our methodology to field data from the ECOGI and EstOF surveys in North Alsace, France. We compare separate and joint inversions and we find that the 1D subsurface models obtained from joint inversions are more similar to previous models documented in the area than the separate inversion models. We are currently extending this work to higher dimensions. At the spatial scale of our problem, sensitivity analysis suggests that shear velocity models can benefit from the lateral sensitivity of the magnetotelluric data.

How to cite: Aquino, M., Marquis, G., and Vergne, J.: Joint inversion of Magnetotelluric Data and Surface-Wave Dispersion Curves using Correspondence Maps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5056, https://doi.org/10.5194/egusphere-egu22-5056, 2022.

EGU22-6586 | Presentations | EMRP2.16

Deep images of electrical conductivity in Parnaiba basin - NE Brazil 

Sergio Luiz Fontes, Artur Benevides, Liliane Panetto, Ved Prakash Maurya, Emanuele Francesco La Terra, and Antonio Padilha

Long period magnetotelluric (LMT) stations were deployed on an array format covering much of the Parnaíba basin and western edge of the Borborema Province in NE Brazil. A grid with 56 LMT stations (from 10 s to over 104 s) with 70 km spacing were acquired during periods of acquisition varying from 2-3 weeks up to 6 months through two field campaigns between November 2018 and July 2019. This study is the first of this kind undertaken in Brazil, much in line with the American EarthScope, the Chinese SiinoProbe and AUSLAMP - Australia array initiatives suggesting the way forward for a comprehensive understanding of large 3D electrical structures of the continental crust and the lithospheric mantle in the entire country.  The results already published show that the resolution of the models obtained is comparable to the inversions of seismic tomography, the sensitivity of the MT method being superior in sensing the melting fraction, temperature and water content in the mantle. As an example, the 70 km spacing between EarthScope stations proved adequate to delineate the main structural features of the middle crust to the upper mantle of the United States. The Parnaíba Basin is a cratonic basin that has been formed by sedimentary mega sequences deposited along the Phanerozoic, after the formation of the Gondwana Supercontinent, with sedimentation expanding over the Borborema Province. The basin's evolution was conditioned by subsidence processes along unstable crustal areas at the end of the Brazilian cycle and demarcated by grabens, fault zones and magmatism. The shallow sediments of the basin (around 2.5 to 3.4 km maximum) however widely spread 60,000 km2 cover prominent crustal features including the location of the trans-Brazilian lineament, limits of the Borborema Province, Amazon craton and other important shear and suture zones that may be important to better understand the evolutionary geodynamics of the supercontinents. The time series of electric and magnetic fields recorded in the field have been passed through extensive quality control analysis and then were robustly processed in the frequency domain generating good quality impedance tensor and tipper transfer functions. Currently we are concentrating our efforts on testing several parameters (e.g. mesh design, starting resistivity, damping and covariance analysis) involved in the 3D inversion nonlinear conjugate gradient ModEM code. Following the best practical procedures suggested by previous MT studies to avoid bad impact on the inversion results, misfits have been achieved nRMS ~ 2.2 in joint inversion of impedance tensor and tipper and nRMS < 2 for separate inversion of these transfer functions. Notwithstanding, preliminary resistivity models present good agreement with previous geophysical studies in the area and portray remarkable large-scale middle crust and deep conductive structures inside the covered area. Since there are several geodynamic processes associated with this area and electrical signatures may still exist the MT data set can be an important key to understand the evolution of the pan-African cycle and unravel new findings related to the formation of the Parnaiba basin.

How to cite: Fontes, S. L., Benevides, A., Panetto, L., Maurya, V. P., La Terra, E. F., and Padilha, A.: Deep images of electrical conductivity in Parnaiba basin - NE Brazil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6586, https://doi.org/10.5194/egusphere-egu22-6586, 2022.

EGU22-7541 | Presentations | EMRP2.16

The detection of the magnetic fields induced by ocean circulation - An observing system simulation experiment 

Aaron Hornschild, Jan Saynisch-Wagner, Julien Baerenzung, Christopher Irrgang, and Maik Thomas

The movement of conductive seawater through Earth's magnetic field leads to electromagnetic induction processes in the oceans. The resulting radial magnetic fields have been successfully modeled and, in the case of tidal-induced magnetic fields, also identified in satellite magnetometer data. However, the magnetic signals caused by ocean circulation have still remained unobserved.
We introduce a new method to detect these signals using an observing system simulation experiment. Our approach relies on a Kalman filter-based assimilation of satellite magnetometer data. A key aspect of identifying ocean-induced signals is separating them from other magnetic contributions. For this separation, we used both estimations of the temporal behavior and spatial constraints as prior information. The observing system simulation experiment allows us to evaluate the proposed method.  
We present the results of this evaluation and report on the detectability of magnetic fields induced by ocean circulation.

How to cite: Hornschild, A., Saynisch-Wagner, J., Baerenzung, J., Irrgang, C., and Thomas, M.: The detection of the magnetic fields induced by ocean circulation - An observing system simulation experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7541, https://doi.org/10.5194/egusphere-egu22-7541, 2022.

The Boso Peninsula is one of the most tectonically active regions in Japan due to its location on a plate boundary. Focal zones of the past enormous earthquakes (1703 Genroku Kanto Earthquake (M8.2), the 1923 Taisho Kanto Earthquake (M7.9)) and slow slip events (SSE) region are located southwest and southeast of the peninsula, respectively. Therefore, it is important to survey the subsurface resistivity structure of these regions from a geophysical point of view. The magnetotelluric (MT) survey was conducted to clarify the resistivity structure from 2014 to 2016. However, observed MT data was contaminated by artificial noise sources (e.g., leak current from DC-driven trains and power lines). Conventional noise reduction methods using remote reference (Gamble et al., 1979) and robust statistics such as BIRRP (Chave and Thomson. 2004) are inadequate to deal with the noise. The reason is that the noise included in Boso MT data is originated from a near field source and is coherent between the magnetic field and the electric field.

Therefore, we propose a NEW method using MSSA(Multi-channel Singular Spectrum Analysis) to reduce the influence of the noise. MSSA can decompose multiple time series to several principal components (PCs). In our new method, choosing PCs based on the correlation between each component, they are discriminated into trend components, quasi-periodic components (=interested MT signal), and noise components. We applied MSSA to 7ch (5ch for observation site data (horizontal magnetic field, vertical magnetic field, and horizontal electric field) and 2ch for reference site data (horizontal magnetic field)) to extract 'clean' MT data from noisy Boso MT data. In this presentation, the results of time series and MT analysis applying this method will be presented.

How to cite: Kaneko, S., Mogi, T., Yoshino, C., and Hattori, K.: Development of noise reduction method based on MSSA (Multi-channel Singular Spectrum Analysis)     -Application to near field noise observed in Boso Peninsula, Japan-, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12240, https://doi.org/10.5194/egusphere-egu22-12240, 2022.

EGU22-13529 | Presentations | EMRP2.16 | Highlight

Marine controlled source electromagnetic inversion data from a field at Campos basin SE-Brazil, post-salt reservoirs constrained by seismic and well log 

Artur Benevides, Naser Meqbel, Sergio Fontes, Williams Lima, Gary Egbert, Paulo Werdt, and Emanuele La Terra

This work presents results from a controlled source electromagnetic (CSEM) set of inversion runs of real data in the Campos basin, Southeast Brazil. The Campos basin is in the Brazilian east margin, with origin in the Neocomian stage of the Cretaceous period 145–130 million years ago during the breakup of the supercontinent Gondwana (South America and Africa split). The clastic reservoirs in this basin have been the largest oil producer in Brazil for the past three decades. The present challenge in exploring clastic reservoirs has moved to deeper waters, enforced by the complex geology posed by the tectonics associated with giant salt domes. Electromagnetic (EM) methods are sensitive to subsurface resistive variations and have been frequently used in exploration programs for fresh water, mining and for hydrocarbon (HC), mainly in joint approaches with seismic to minimize ambiguity in the interpretations. Reservoirs filled with HC are generally more resistive than the host rocks which is an advantage for the EM method. Combining resistive models with seismic results considerably improves the resolution of the subsurface structures and the geometry of the HC reservoirs. A set of 40 Controlled Source EM (CSEM) receivers were deployed at the seafloor (water thickness is around 1.7 km) in a grid-shape array with varying spacing between 5 km to 10 km. The electric field components have been recorded from an active electromagnetic source towed 50 m above the seafloor. The processed data consist of inline components of the horizontal electric field (Ex and Ey) for four main frequencies (0.125 Hz, 0.25 Hz, 0.5 Hz and 1.25Hz). The CSEM 3D inversion models have been obtained using the modified version of Modular System for EM inversion (ModEM code) which is under development within a research project at Observatório Nacional – Brazil. Preliminary 3D CSEM inversion results yielded a good agreement with resistivity values observed in the well logs. In the second step of this work, information from seismic and well logs are being introduced as a priori information to improve resolution of the CSEM inversion in different scenarios involving hydrocarbon accumulations in thin post-salt reservoirs in Campos basin. 

How to cite: Benevides, A., Meqbel, N., Fontes, S., Lima, W., Egbert, G., Werdt, P., and La Terra, E.: Marine controlled source electromagnetic inversion data from a field at Campos basin SE-Brazil, post-salt reservoirs constrained by seismic and well log, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13529, https://doi.org/10.5194/egusphere-egu22-13529, 2022.

EMRP3 – Paleomagnetism and Environmental Magnetism

EGU22-640 | Presentations | SSP1.2

DeepStor-1 exploration well at KIT Campus North (Upper Rhine Graben, Germany) 

Schill Eva, Florian Bauer, Ulrich Steiner, Bernd Frieg, and Thomas Kohl

DeepStor-1 is the exploration well to the Helmholtz research infrastructure "DeepStor". DeepStor focuses on the investigation of high-temperature heat storage at the rim of the fromer oil-field „Leopoldshafen“. It is located about 10 km north of the city of Karlsruhe (Germany). The DeepStor-1 well is planned to reach the Pechelbronn group at 1‘460 m, i.e. it includes nearly the entire Oligocene sediments at the site. Seismic investigation reveal a structurally undisturbed section that below 200 m depth covers the Landau, Bruchsal, Niederrödern and Froidefontaine Formations. Cores will be taken from the entire section below 820 m. In addition to coring, the logging program is planned to include besides technical logging, a caliper-, self-potential-, temperature-, dual latero-, natural gamma spectrometry-, neutron-gamma porosity-, sonic-, elemental capture spectroscopy-, as well as image-logs in the sections 215-820 m as well as 820-1460 m. Drilling of DeepStor-1 is planned between 2022 and 2023.

How to cite: Eva, S., Bauer, F., Steiner, U., Frieg, B., and Kohl, T.: DeepStor-1 exploration well at KIT Campus North (Upper Rhine Graben, Germany), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-640, https://doi.org/10.5194/egusphere-egu22-640, 2022.

EGU22-1019 | Presentations | SSP1.2

Dating the serpentinite mud production of Fantangisña seamount using calcareous nannofossils and planktonic foraminifera biostratigraphy (IODP Expedition 366). 

Arianna Valentina Del Gaudio, Werner E. Piller, Gerald Auer, and Walter Kurz

The Izu-Bonin Mariana (IBM) convergent margin is located in the NW Pacific Ocean (12° N to 35° N) and represents, to the best of our knowledge, the only setting where recent episodes of serpentinite mud volcanism took place. The IBM arc-system started to form around 50-52 Ma when the Pacific Plate began to subside below the Philippine Plate and the eastern Eurasian Margin. On the Mariana forearc system, which constitutes the southward region of the IBM, a high number of large serpentinite mud volcanoes formed between the trench and the Mariana volcanic arc. Their origin is linked to episodic extrusion of serpentinite mud and fluids along with materials from the upper mantle, the Philippine plate, and the subducting Pacific plate to the sea floor, through a system of forearc faults. Among them, Fantangisña seamount was drilled during IODP Expedition 366. Cored material comprises serpentinite mud and ultramafic clasts that are underlain by nannofossil-rich forearc deposits and topped by pelagic sediments.

Integrated calcareous nannofossil and planktonic foraminifera biostratigraphy was performed on Sites U1497 and U1498, which are at the top of the serpentinite seamount and on its most stable southern flank, respectively. A total of nine bioevents were recorded in this study, permitting the establishment of a valid age-depth model for Site U1498A which allows for the definition of the latest phase of activity of Fantangisña serpentinite mud volcano. In particular, the emplacement of the mud production was detected between 6.10 (Late Miocene, Messinian) to 4.20 (Early Pliocene, Zanclean). This time interval is defined by nannofossil bioevents LO Reticulofenestra rotaria and FO of Discoaster asymmetricus. Furthermore, our analyses reveal that the latest stage of the serpentinite mud activity occurred 4 Ma later than the age proposed by a previous study (10.77 Ma) and is coeval with the initiation of the rifting in the Mariana Trough recorded at 7-6 Ma.

The age depth model also shows a rapid shift in sedimentation rates (11.80 to 94.71 m/Myr) during the Middle Pleistocene, which corresponds to a change in deposition of distinct serpentinite mud units, likely associated with the regional tectonic activity (different stages of seamount accretion and subduction and/or changes in the forearc extension related to the slab rollback).

How to cite: Del Gaudio, A. V., Piller, W. E., Auer, G., and Kurz, W.: Dating the serpentinite mud production of Fantangisña seamount using calcareous nannofossils and planktonic foraminifera biostratigraphy (IODP Expedition 366)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1019, https://doi.org/10.5194/egusphere-egu22-1019, 2022.

EGU22-1277 | Presentations | SSP1.2 | Highlight

The Cenozoic Arctic Climate and Sea Ice History - Scientific objectives, challenges and implementation update of IODP Expedition 377 (ArcOP) 

Ruediger Stein, Kristen St.John, and Jeremy Everest

The Arctic is both a contributor to climate change and a region that is most affected by global warming. Despite this global importance, the Arctic Ocean is the last major region on Earth where the long-term climate history remains poorly known. Major advances in understanding were achieved in 2004 with the successful completion of IODP Expedition 302: Arctic Coring Expedition – ACEX – implemented by ECORD, marking the start of a new era in Arctic climate exploration. Although the ACEX results were unprecedented, key questions related to the Cenozoic Arctic climate history remain unanswered, largely due to a major mid-Cenozoic hiatus (or condensed interval) and partly to the poor recovery of the ACEX record. Building on ACEX and its cutting-edge science, IODP Expedition 377: Arctic Ocean Paleoceanography (ArcOP) has been scheduled for mid-August to mid-October 2022. The overall goal of ArcOP is the recovery of a complete stratigraphic sedimentary record on the southern Lomonosov Ridge to meet the highest priority paleoceanographic objective: the continuous long-term Cenozoic Arctic Ocean climate history with its transition from the early Cenozoic Greenhouse world to the late Cenozoic Icehouse world. Furthermore, sedimentation rates two to four times higher than those of ACEX will permit higher-resolution studies of Arctic climate change in the Neogene and Pleistocene. Key objectives are related to the reconstruction of the history of circum-Arctic ice-sheets, sea-ice cover, Siberian river discharge, and deep-water circulation and ventilation and its significance within the global climate system. Obtaining a geologic record of a 50-60 million year time span will provide opportunities to examine trends, pat­terns, rates, causes, and consequences of climate change that are important and relevant to our future. This goal can be achieved through (i) careful site selection, (ii) the use of appropriate drilling technology and ice management, and (iii) applying multi-proxy approaches to paleoceanographic, paleoclimatic, and age-model reconstructions.

In August 2022, a fleet of three ships, the drilling vessel “Dina Polaris” and the powerful icebreakers “Oden” and “Viktor Chernomyrdin”, will set sail for a location on Lomonosov Ridge in international waters far from shore (81°N, 140°E; 800-900 m of water depth). There, the expedition will complete one primary deep drill site (LR-11B) to 900 meters below seafloor (mbsf) which is twice that of the ACEX drill depth – certainly a challenging approach. Based on detailed site survey data, about 230 m of Plio‐Pleistocene, 460 m of Miocene, and >200 m of Oligocene‐Eocene sedimentary sequences might be recovered at this site. In addition, a short drill site (LR-10B) to 50 mbsf will be supplemented to recover an undisturbed uppermost (Quaternary) sedimentary section to ensure complete recovery for construction of a composite section spanning the full age range through the Cenozoic.

In this talk, background information, scientific objectives and an update of the status of planning and implementation of the ArcOP Expedition will be presented. For further details we refer to the ArcOP Scientific Prospectus (https://doi.org/10.14379/iodp.sp.377.2021).

How to cite: Stein, R., St.John, K., and Everest, J.: The Cenozoic Arctic Climate and Sea Ice History - Scientific objectives, challenges and implementation update of IODP Expedition 377 (ArcOP), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1277, https://doi.org/10.5194/egusphere-egu22-1277, 2022.

EGU22-1509 | Presentations | SSP1.2 | Highlight

A Campaign of Scientific Drilling for Monsoon Exploration in the Asian Marginal Seas 

Peter Clift, Christian Betzler, Steven Clemens, Beth Christensen, Gregor Eberli, Christian France-Lanord, Stephen Gallagher, Ann Holbourn, Wolfgang Kuhnt, Richard Murray, Yair Rosenthal, Ryuji Tada, and Shiming Wan

International Ocean Discovery Program (IODP) conducted a series of expeditions between 2014 and 2016 that were designed to address the development of monsoon climate systems in Asia and Australia. Significant progress was made in recovering Neogene sections spanning the region from the Arabian Sea to the Japan Sea and south to western Australia. High recovery by advanced piston core (APC) technology has provided a host of semi-continuous sections that have been used to examine monsoonal evolution. Use of half APC was successful in sampling sand-rich sediment in Indian Ocean submarine fans. The records show that humidity and seasonality developed diachronously across the region, although most regions show drying since the middle Miocene and especially since ~4 Ma, likely linked to global cooling. The transition from C3 to C4 vegetation often accompanied the drying, but may be more linked to global cooling. Western Australia, and possibly southern China diverge from the general trend in becoming wetter during the late Miocene, with the Australian monsoon being more affected by the Indonesian Throughflow, while the Asian Monsoon is tied more to the rising Himalaya in South Asia and to the Tibetan Plateau in East Asia. The monsoon shows sensitivity to orbital forcing, with many regions having a weaker summer monsoon during times of Northern Hemispheric Glaciation. Stronger monsoons are associated with faster continental erosion, but not weathering intensity, which either shows no trend or decreasing strength since the middle Miocene in Asia. Marine productivity proxies and terrestrial environmental proxies are often seen to diverge. Future work on the almost unknown Paleogene is highlighted, as well as the potential of carbonate platforms as archives of paleoceanographic conditions.

How to cite: Clift, P., Betzler, C., Clemens, S., Christensen, B., Eberli, G., France-Lanord, C., Gallagher, S., Holbourn, A., Kuhnt, W., Murray, R., Rosenthal, Y., Tada, R., and Wan, S.: A Campaign of Scientific Drilling for Monsoon Exploration in the Asian Marginal Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1509, https://doi.org/10.5194/egusphere-egu22-1509, 2022.

EGU22-1679 | Presentations | SSP1.2

Direct evidence of high pore pressure at the toe of the Nankai accretionary prism 

Joshua Pwavodi and Mai-Linh Doan

The Nankai Trough is a locus of slow slip, low frequency earthquakes and Mw>8 classical earthquakes. It is assumed that high pore pressure contributes substantially to earthquake dynamics. Hence, a full understanding of the hydraulic regime of the Nankai accretionary prism is needed to understand this diversity of behaviors. We contribute to this understanding by innovatively integrating the drilling and logging data of the NanTroSEIZE project. We focus on the toe of the accretionary prism by studying data from Hole C0024A drilled and intersected the décollement at 813 mbsf about 3km away from the trench.

Down Hole Annular Pressure was monitored during drilling. We perform a careful quantitative reanalysis of its variation and show localized fluid exchange between the formation and the borehole (excess of 0.05m3/s), especially in the damage zones at the footwall of the décollement.

Pore pressure was estimated using Eaton’s method on both drilling and sonic velocity data. The formation fluids are getting significantly over-pressurized only a few hundred meters from the toe of the accretionary prism near the décollement with excess pore-pressure (P*≈0.04–4.79MPa) and lithostatic load (λ≈88-0.96 & λ*≈0.1-0.62 ) contributing to maximum 62% of the overburden stress.

The hydraulic profile suggests that the plate boundary acts as a barrier inhibiting upward fluid convection, as well as a lateral channel along the damage zone, favouring high pore pressure at the footwall. Such high pressure at the toe of the subsection zone makes high pressure probable further down in the locus of tremors and slow slip events.

How to cite: Pwavodi, J. and Doan, M.-L.: Direct evidence of high pore pressure at the toe of the Nankai accretionary prism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1679, https://doi.org/10.5194/egusphere-egu22-1679, 2022.

EGU22-1729 | Presentations | SSP1.2

IODP Expedition 386 “Japan Trench Paleoseismology”: Mission Specific Platform Giant Piston Coring to track past megathrust earthquakes and their consequences in a deep-sea subduction trench. 

Michael Strasser, Ken Ikehara, Jeremy Everest, and Lena Maeda and the IODP Expedition 386 Science Party

International Ocean Discovery Program (IODP) Expedition 386, Japan Trench Paleoseismology (offshore period: 13 April to 1 June 2021; Onshore Science Party: 14 February to 14 March 2022) was designed to test the concept of submarine paleoseismology in the Japan Trench, the area where the last, and globally only one out of four instrumentally-recorded, giant (i.e. magnitude 9 class) earthquake occurred back in 2011. “Submarine paleoseismology” is a promising approach to investigate deposits from the deep sea, where earthquakes leave traces preserved in the stratigraphic succession, to reconstruct the long-term history of earthquakes and to deliver observational data that help to reduce uncertainties in seismic hazard assessment for long return periods. This expedition marks the first time, giant piston coring (GPC) was used in IODP, and also the first time, partner IODP implementing organizations cooperated in jointly implementing a mission-specific platform expedition.

We successfully collected 29 GPCs at 15 sites (1 to 3 holes each; total core recovery 831 meters), recovering 20 to 40-meter-long, continuous, upper Pleistocene to Holocene stratigraphic successions of 11 individual trench-fill basins along an axis-parallel transect from 36°N – 40.4°N, at water depth between 7445-8023 m below sea level. These offshore expedition achievements reveal the first high-temporal and high spatial resolution investigation and sampling of a hadal oceanic trench, that form the deepest and least explored environments on our planet.

The cores are currently being examined by multimethod applications to characterize and date hadal trench sediments and extreme event deposits, for which the detailed sedimentological, physical and (bio-)geochemical features, stratigraphic expressions and spatiotemporal distribution will be analyzed for proxy evidence of giant earthquakes and (bio-)geochemical cycling in deep sea sediments. Initial preliminary results presented in this EGU presentation reveal event-stratigraphic successions comprising several 10s of potentially giant-earthquake related event beds, revealing a fascinating record that will unravel the earthquake history of the different along-strike segments that is 10–100 times longer than currently available information. Post-Expedition research projects further analyzing these initial IODP data sets will (i) enable statistically robust assessment of the recurrence patterns of giant earthquakes, there while advancing our understanding of earthquake-induced geohazards along subduction zones and (ii) provide new constraints on sediment and carbon flux of event-triggered sediment mobilization to a deep-sea trench and its influence on the hadal environment.

 

How to cite: Strasser, M., Ikehara, K., Everest, J., and Maeda, L. and the IODP Expedition 386 Science Party: IODP Expedition 386 “Japan Trench Paleoseismology”: Mission Specific Platform Giant Piston Coring to track past megathrust earthquakes and their consequences in a deep-sea subduction trench., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1729, https://doi.org/10.5194/egusphere-egu22-1729, 2022.

EGU22-1917 | Presentations | SSP1.2

Operations and Initial Results from IODP Expedition 396: Mid-Norwegian Continental Margin Magmatism and Paleoclimate 

Sverre Planke, Christian Berndt, Ritske Huismans, Stefan Buenz, Carlos A. Alvarez Zarikian, and Expedition Scientists

The NE Atlantic conjugate volcanic rifted margins are characterized by extensive breakup-related magmatism recorded by basalt flows, volcanogenic sediments, magmatic underplates, and intrusive complexes in sedimentary basins and the crust. Onset of this voluminous magmatism is concomitant with the global hot-house climate in the Paleogene, and the injection of magma into organic-rich sedimentary basins is a proposed mechanism for triggering short-term global warming during the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma).

The aims of IODP Exp. 396 (August-September 2021) were to drill three transects on the mid-Norwegian continental margin to sample 1) hydrothermal vent complexes formed by eruption of hot fluids and sediments above sill intrusions (Modgunn Transect), 2) Paleogene sediments, with particular focus on the Paleocene-Eocene transition (Mimir Transect), and 3) basalt and sub-basalt sequences across the volcanic rifted margin and the initial oceanic crust (Basement Transect). A total of 21 boreholes were drilled, successfully coring all nine primary and one alternate sites. A comprehensive suite of wireline logs was collected in eight boreholes. Most of the sites were located on industry-standard 3D seismic reflection data, whereas additional high-resolution 2D and 3D P-Cable site survey data were acquired across six sites which were highly useful during the Mimir and Modgunn transect drilling. In total, more than 2000 m of core were recovered during 48 days of operations, including more than 350 m of basalt, 15 m of granite, and 900 m of late Paleocene to early Eocene sediments. Drilling was done using a combination of RCB, XCB, and APC drill bits, commonly with half-advances (c. 5 m) to optimize core recovery. Particularly high recovery (almost 100%) was obtained by half-length APC coring of Eocene sediments in two holes on the outer Vøring Margin, whereas basaltic basement recovery was above 60% in seven holes.

Expedition 396 probed the key elements of a typical volcanic rifted margin and the associated sedimentary archive. Of particular importance is the Modgunn Transect, where we drilled five holes through the upper part of a hydrothermal vent complex with a very expanded Paleocene-Eocene Thermal Maximum (PETM) interval dominated by biogenic ooze and volcanic ash deposits. The expedition also recovered an unprecedented suite of basalt cores across a volcanic rifted margin, including both subaerial and deep marine sheet flows with inter-lava sediments and spectacular shallow marine pillow basalts and hyaloclastites, as well as high-resolution interstitial water samples to assess sediment diagenesis and fluid migration in the region. Lastly, we recovered the first cores of sub-basalt granitic igneous rocks and upper Paleocene sediments along the mid-Norwegian continental margin. Collectively, this unique sample archive offers unprecedented insight on tectonomagmatic processes in the NE Atlantic, and links to rapid climate evolution across the Cenozoic.

How to cite: Planke, S., Berndt, C., Huismans, R., Buenz, S., Alvarez Zarikian, C. A., and Scientists, E.: Operations and Initial Results from IODP Expedition 396: Mid-Norwegian Continental Margin Magmatism and Paleoclimate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1917, https://doi.org/10.5194/egusphere-egu22-1917, 2022.

EGU22-2525 | Presentations | SSP1.2

Biological sulfate reduction in deep subseafloor sediment of Guaymas Basin 

Toshiki Nagakura, Florian Schubert, and Jens Kallmeyer and the IODP Exp. 385 Scientists

Sulfate reduction is the quantitatively most important process to degrade organic matter in anoxic marine sediment and has been studied intensively in a variety of settings. Guaymas Basin, a young marginal ocean basin, offers the unique opportunity to study sulfate reduction in an environment characterized by organic-rich sediment, high sedimentation rates, and high geothermal gradients (100-958°C km-1). We measured sulfate reduction rates (SRR) in samples of the International Ocean Discovery Program (IODP) Expedition 385 using incubation experiments with radiolabeled 35SO42- carried out at in-situ pressure and temperature. Site U1548C, outside of a circular hydrothermal mound above a hot sill intrusion (Ringvent), has the highest geothermal gradient (958°C km-1) of all eight sampling sites. In near-surface sediment from this site, we measured the highest SRR (387 nmol cm-3 d-1) of all samples from this expedition. At Site U1548C SRR were generally over an order of magnitude higher than at similar depths at other sites. Site U1546D also had a sill intrusion, but it had already reached thermal equilibrium and SRR were in the same range as nearby Site U1545C, which is minimally affected by sills. The wide temperature range found in the stratigraphic section at each drill site leads to major shifts in microbial community composition with very different temperature optima. At the transition between the mesophilic and thermophilic range around 40 to 60°C, sulfate-reducing activity appears to be decreased, particularly in more oligotrophic settings but shows a slight recovery at higher temperatures.

How to cite: Nagakura, T., Schubert, F., and Kallmeyer, J. and the IODP Exp. 385 Scientists: Biological sulfate reduction in deep subseafloor sediment of Guaymas Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2525, https://doi.org/10.5194/egusphere-egu22-2525, 2022.

EGU22-2909 | Presentations | SSP1.2 | Highlight

Microbial survival through high metabolic rates in a deep and hot subseafloor environment 

Florian Schubert, Felix Beulig, Rishi Ram Adhikari, Clemens Glombitza, Verena Heuer, Kai-Uwe Hinrichs, Kira Homola, Fumio Inagaki, Bo Barker Jørgensen, Jens Kallmeyer, Sebastian Krause, Yuki Morono, Justine Sauvage, Arthur Spivack, and Tina Treude

A fourth of the global seabed sediment volume is buried at depths where temperatures exceed 80 °C, a previously proposed thermal barrier for life in the subsurface. Here, we demonstrate, utilizing an extensive suite of radiotracer experiments, the prevalence of active methanogenic and sulfate-reducing populations in deeply buried marine sediment from the Nankai Trough subduction zone, heated to extreme temperature (up to ~120 °C). Sediment cores were recovered during International Ocean Discovery Program (IODP) Expedition 370 to Nankai Trough, off the cost of Moroto, Japan. The steep geothermal gradient of ~100 °C km-1 allowed for the exploration of most of the known temperature range for life over just 1 km of drill core. Despite the high temperatures, microbial cells were detected almost throughout the entire sediment column, albeit at extremely low concentration of <500 cells per cm³ in sediment above ~50 °C. In millions of years old sediment a small microbial community subsisted with high potential cell-specific rates of energy metabolism, which approach the rates of active surface sediments and laboratory cultures. Even under the most conservative assumptions, potential biomass turnover times for the recovered sediment ranges from days to years and therefore many orders of magnitude faster than in colder deep sediment.

Our discovery is in stark contrast to the extremely low metabolic rates otherwise observed in the deep subseafloor. As cells appear to invest most of their energy to repair thermal cell damage in the hot sediment, they are forced to balance delicately between subsistence near the upper temperature limit for life and a rich supply of substrates and energy from thermally driven reactions of the sediment organic matter.

How to cite: Schubert, F., Beulig, F., Adhikari, R. R., Glombitza, C., Heuer, V., Hinrichs, K.-U., Homola, K., Inagaki, F., Jørgensen, B. B., Kallmeyer, J., Krause, S., Morono, Y., Sauvage, J., Spivack, A., and Treude, T.: Microbial survival through high metabolic rates in a deep and hot subseafloor environment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2909, https://doi.org/10.5194/egusphere-egu22-2909, 2022.

EGU22-3165 | Presentations | SSP1.2 | Highlight

Drilling Overdeepened Alpine Valleys (ICDP-DOVE): Age, extent and environmental impact of Alpine glaciations 

Flavio Anselmetti and Marius Buechi and the ICDP-DOVE Team

The sedimentary infill of glacially overdeepened valleys (i.e. eroded structures below the fluvial base level) are, together with glacial geomorphology, the best-preserved (yet underexplored) direct archives of extents and ages of past glaciations in and around mountain ranges. ICDP project DOVE (Drilling Overdeepened Alpine Valleys) Phase-1 investigates five drill cores from glacially overdeepened structures at several complementing locations along the northern front of the Alps and their foreland. Two of these drill sites, both in the former reaches of the Rhine Glacier, have been successfully drilled in 2021 with excellent core recovery of 95 %: i) The borehole in Basadingen in Northern Switzerland reached a depth of 253 m, and ii) The Tannwald site in Southern Germany consists of one cored borehole to 165 m and two nearby flush boreholes; all three sites will allow a series of crosshole geophysical experiments. Three previously drilled legacy cores from the Eastern Alps are included in the DOVE Phase-1: iii) a core from Schäftlarn, located in the Isar-Loisach glacier catchment, was drilled in 2017 down to a depth of 199 m; iv) the Neusillersdorf drill site, located in the southern German Salzach Foreland glacier area, recovered a sequence down to 136 m (incl. 116 m of Quaternary strata); and v) the drill site Bad Aussee in Austria is located in the area of the Traun Glacier at an inneralpine location. It recovered almost 900 m of Quaternary sediments.

All the sites will be investigated with regard to several aspects of environmental dynamics during the Quaternary, with focus on the glaciation, vegetation, and landscape history. For example, the geometry of overdeepened structures will be investigated using different geophysical approaches (e.g. seismic surveys) to better understand the process of overdeepening. Sedimentological analyses in combination with downhole logging, investigation of biological remains and state-of-the-art geochronological methods will allow to reconstruct the filling and erosion history of the troughs. We expect significant and novel data relating to the extent and timing of the past Alpine glaciations during the Middle-to-Late Quaternary glacial-interglacial cycles. Besides these basic scientific goals, this proposal also addresses a number of applied objectives such as groundwater resources, geothermal energy production, and seismic hazard assessment.

A successful DOVE Phase-1 will lay the ground for an upcoming Phase-2 that will complete the panalpine approach. This follow-up phase will investigate paleoglacier lobes from the western and southern Alpine margins through drilling sites in France, Italy and Slovenia.

How to cite: Anselmetti, F. and Buechi, M. and the ICDP-DOVE Team: Drilling Overdeepened Alpine Valleys (ICDP-DOVE): Age, extent and environmental impact of Alpine glaciations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3165, https://doi.org/10.5194/egusphere-egu22-3165, 2022.

EGU22-3372 | Presentations | SSP1.2

Re–Os geochemistry of altered dacitic rock at Site U1527, IODP Expedition 376: Implications for the Re cycle in intraoceanic arcs 

Mizuki Ishida, Tatsuo Nozaki, Yutaro Takaya, Junichiro Ohta, Qing Chang, Jun-Ichi Kimura, Kentaro Nakamura, and Yasuhiro Kato

The Re–Os isotopic system is a powerful tool for both geochronology and tracing various geochemical processes. Because the Os isotopic ratio (187Os/188Os) distinctly differs between modern seawater (∼1.06) and hydrothermal fluid (∼0.13), the Re–Os isotopic system is potentially a sensitive tracer of subseafloor fluid flow and the release or uptake of hydrogenous/magmatic Re and Os. The effect of alteration on the Re–Os budget in oceanic crust has been examined for mid-ocean ridge basalt (MORB) and lower oceanic crustal gabbro. In contrast, applications of the Re–Os system in intraoceanic arc settings are limited mainly to fresh igneous rocks; the role of hydrothermal alteration has not yet been examined.

Here, we provide a depth profile of Re–Os geochemistry at Site U1527, located on the NW caldera rim of the Brothers volcano hydrothermal field in the Kermadec arc, which was drilled during International Ocean Discovery Program (IODP) Expedition 376 in 2018. Volcaniclastic rocks from Hole U1527C that had experienced various degrees of high- and low-temperature hydrothermal alteration were analyzed for bulk chemical composition as well as Re–Os concentrations and isotopes. The concentration of Re varied from 0.172 to 18.7 ppb, and that of Os ranges from 9.7 to 147.1 ppt. Hydrothermal alteration usually resulted in the Re uptake by rocks, but a part of Re was released into the ocean by later oxidative weathering. Compared with Re, Os mobility resulting from hydrothermal alteration was limited. Before alteration, our samples likely had homogenous 187Os/188Os of between 0.13 and 0.14, whereas alteration added hydrogenous Os to some drill core sections in two different ways. Elevated 187Os/188Os with Ba enrichment and abundant pyrite occurrence suggests Os precipitation induced by subseafloor mixing of seawater and high-temperature hydrothermal fluid. The highest Re and Os concentrations at Hole U1527C, found in the same interval, were associated with high concentrations of Bi, Sb, and Tl. In contrast, elevated 187Os/188Os without Ba and Os enrichment can be explained by adsorption of seawater-derived radiogenic Os onto Fe hydroxide during seawater ingress into volcaniclastic rocks with a high matrix volume.

Intense Re enrichment at Hole U1527 relative to the high-temperature alteration zone in altered MORB may be related to abundant pyrite precipitation and high Re content in primary arc magmas. We propose that degassed Re from shallow intraoceanic arc magmas may be sequestered by subseafloor high-temperature alteration. Part of the stored Re might also be released into the ocean by later oxidative seawater circulation and seafloor weathering, raising a question about the role of alteration zones in the Re cycle in subduction zones. This study is one of the first attempts to apply the Re–Os system to altered rocks in arc settings, and future research should provide more information about the fate of Re in intraoceanic arcs and the detailed role of hydrothermal alteration in the Re cycle on the Earth.

How to cite: Ishida, M., Nozaki, T., Takaya, Y., Ohta, J., Chang, Q., Kimura, J.-I., Nakamura, K., and Kato, Y.: Re–Os geochemistry of altered dacitic rock at Site U1527, IODP Expedition 376: Implications for the Re cycle in intraoceanic arcs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3372, https://doi.org/10.5194/egusphere-egu22-3372, 2022.

EGU22-3428 | Presentations | SSP1.2

Hipercorig Hallstatt History (H3) reveals a high-resolution Late Pleistocene to Holocene sediment record at Lake Hallstatt (Salzkammergut, Austria) 

Marcel Ortler, Achim Brauer, Stefano C. Fabbri, Kerstin Kowarik, Jochem Kueck, and Michael Strasser

The innovative, new drilling technique of the Hipercorig platform (Harms et al., 2020, https://doi.org/10.5194/sd-28-29-2020) enables to recover undisturbed long cores of sediment archives, and hence allows us to study past environmental conditions and changes. Here we present initial results from the Hipercorig Hallstatt History (H3) lake drilling campaign 2021, which succeeded to recover two parallel cores (core A: 41m, core B: 51m) from 122 m water depth providing a high-resolution record, within the UNESCO World Heritage Cultural Landscape Hallstatt-Dachstein/Salzkammergut, Austria. The Hallstatt-Dachstein region has a history of over 7,000 years of human salt mining and is one of the oldest documented cultural landscapes worldwide.

We present physical- and litho-stratigraphy based on borehole logging (of hole B), non-destructive core logging data, visual core and lithofacies description, Core-Log-Seismic-Correlation and initial age modelling using 14C dating. The core logging covers (i) x-ray computed tomography, (ii) multi-sensor-core-logger data with Gamma-Ray attenuated bulk density, magnetic susceptibility and visible light photo spectroscopy. The upper ~15 m of the sediment profile can be unambiguously correlated with previous cores (Lauterbach et al., submitted) thus confirming that the sediments are truly representative for Lake Hallstatt. The entire stratigraphic succession comprises two major lithostratigraphic units: The Holocene unit (0-40 m below lake floor (mblf)) and the Late Pleistocene unit (> 40 m). The Holocene unit consists of variably laminated (sub-mm to 5 mm) dark gray clayey-silty carbonate mud interbedded with up to 5.5 m thick mass-movement deposits and thick turbidites. The Late Pleistocene sedimentary succession comprises very thin bedded (1-3 cm) medium gray silty clayey carbonate mud, with some laminated (<1 cm) intervals and multiple cm-thick light gray turbidites. Within the Late Holocene unit, there is a prominent yellowish gray clastic interval of ~4 m with faintly mm- to cm-scale laminated sediments. Another remarkable characteristic of the Holocene unit is the occurrence of at least four major mass-movement deposits containing pebbles (up to 3 cm in diameter) and six thick turbidite deposits >1 m with different sediment colors and compositions.

Detailed multi-proxy analyzes of the Lake Hallstatt cores will provide new insights into the early history of human settlement and salt mining in this Alpine region and their relation to environmental and climatic conditions and meteorological and geological extreme events.

How to cite: Ortler, M., Brauer, A., Fabbri, S. C., Kowarik, K., Kueck, J., and Strasser, M.: Hipercorig Hallstatt History (H3) reveals a high-resolution Late Pleistocene to Holocene sediment record at Lake Hallstatt (Salzkammergut, Austria), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3428, https://doi.org/10.5194/egusphere-egu22-3428, 2022.

EGU22-3534 | Presentations | SSP1.2

Reconstructing the moisture availability of Central Mexico over the past 500,000 years using borehole logging data 

Mehrdad Abadi, Christian Zeeden, Arne Ulfers, and Thomas Wonik

Assessing the moisture history of Central Mexico reveals the responses of tropical areas to variation in past climate. Central Mexico has several long-lived lakes, which are potentially important paleoclimate archives. Lake Chalco in Central Mexico contains a ~300 m lacustrine sequence, which were deposited over a period of ~500,000 years. We conducted Spectral Gamma Ray (SGR) measurements across the lacustrine deposits of Lake Chalco to reconstruct the moisture availability over the past. The SGR data reflect the presence of naturally occurring radioactive elements including potassium (40K) and the equilibrium decay series of uranium (U) and thorium (Th). Natural sources of gamma radiation in lacustrine deposits of Lake Chalco are from volcanic ash deposition and detrital input of eroded sediments containing radioactive elements. However, redox conditions in the lake water influence the mobility of soluble U through conversion to more stable reduced phases. To extract the primary non-volcanic signals, we detected and removed signals from embedded tephra layers in the lacustrine sediments of Lake Chalco. We developed a moisture proxy by calculating the probability of authigenic U distributed across the lake sediments. We expect that an increasing U content in proportion to the content of K and Th indicate redox conditions in lake bottom water as a result of rising lake level. To evaluate this moisture proxy, we examined differences in the percent of the diatom species that are indicative of a deeper lake from literature. Results suggest that Lake Chalco likely formed prior or within MIS13, and the lake level rose gradually over time until the interglacial period of MIS9. Moisture levels are higher during the interglacial than glacial periods and interglacial periods show higher moisture variability. While glacial periods have less moisture, two periods, MIS6 and MIS4, still have a higher likelihood of authigenic U and more moist conditions. In order to determine potential regulators of moisture, we compared models containing the drivers of Earth’s orbital cycles, carbon dioxide and sea surface temperature. Carbon dioxide, eccentricity, and precession are all key drivers of the moisture content of Lake Chalco over the past 500,000 years. High levels of atmospheric CO2 have a positive effect on the moisture in Mexico while eccentricity and precession consistently have negative effects on lake moisture. Obliquity and δ18O have weaker effects on moisture in Mexico, probably due to the equatorial high-altitude region far away from poles, oceans and ice sheets.

How to cite: Abadi, M., Zeeden, C., Ulfers, A., and Wonik, T.: Reconstructing the moisture availability of Central Mexico over the past 500,000 years using borehole logging data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3534, https://doi.org/10.5194/egusphere-egu22-3534, 2022.

EGU22-3538 | Presentations | SSP1.2 | Highlight

Deformation mechanisms along the Main Marmara Fault around the ICDP-site GONAF 

Magdalena Scheck-Wenderoth, Mauro Cacace, Oliver Heidbach, Marco Bohnhoff, Murat Nurlu, Naiara Fernandez Terrones, Judith Bott, and Ershad Gholamrezaie

The Main Marmara Fault (MMF) in NW Turkey south of Istanbul is a segment of the North Anatolian Fault Zone (NAFZ) that constitutes a right-lateral continental transform fault.  Several well-documented strong (M7+) earthquakes indicate that the MMF poses a great risk to the Istanbul metropolitan region. A 150 km long stretch of the MMF has not ruptured since 1766 and the recurrence time of 250 yrs for M7+ events derived from historical records indicate that the fault is overdue. We introduce a new project addressing how the rheological configuration of the lithosphere in concert with active fluid dynamics within the crust and mantle influence the present-day deformation along the MMF in the Marmara Sea region. We test the following hypotheses: (1) the seismic gap is related to the mechanical segmentation along the MMF which originates from the rheological configuration of the crust and lithosphere; (2) variations in deformation mechanisms with depth in response to variations in temperature and (fluid) pressure exert a first-order control on the mode of seismic activity along the MMF, and, (3) stress and strain concentrations due to strength and structural variability along the MMF can be used as an indicator for potential nucleation areas of expected earthquakes. To assess what mechanisms control the deformation along the MMF, we use data from the ICDP GONAF observatory (International Continental Drilling Programme – Geophysical Observatory at the North Anatolian Fault) and a combined work flow of data integration and process modelling to derive a quantitative description of the physical state of the MMF and its surrounding crust and upper mantle. Seismic and strain observations from the ICDP-GONAF site are integrated with regional observations on active seismicity, on the present-day deformation field at the surface, on the deep structure (crust and upper mantle) and on the present-day stress and thermal fields. This will be complemented by numerical forward simulations of coupled thermo-hydraulic-mechanical processes based on the observation-derived 3D models to evaluate the key controlling factors for the present-day mechanical configuration of the MMF and to contribute to a physics-based seismic hazard assessment.

How to cite: Scheck-Wenderoth, M., Cacace, M., Heidbach, O., Bohnhoff, M., Nurlu, M., Fernandez Terrones, N., Bott, J., and Gholamrezaie, E.: Deformation mechanisms along the Main Marmara Fault around the ICDP-site GONAF, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3538, https://doi.org/10.5194/egusphere-egu22-3538, 2022.

EGU22-3793 | Presentations | SSP1.2

Legacy DSDP and ODP data suggest a paradigm shift in methane hydrate stability in the Mediterranean Basin 

Cristina Corradin, Angelo Camerlenghi, Michela Giustiniani, Umberta Tinivella, and Claudia Bertoni

The global reservoir of submarine gas hydrates is favored by the cold temperature of oceanic bottom water and the generally low geothermal gradients along passive continental margins. The continental margins of the land-locked Mediterranean basin are a remarkable exception for the lack of evidence of extensive presence of gas hydrates. Using public data of the physics and chemistry of the subsurface available from 44 Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) wells as lithologic logs, downhole temperature measurements, and pore water salinity values, and observed physical characteristics of bottom waters, we model the theoretical methane hydrate stability zone (MHSZ) below the seafloor and in the water column.

We find important positive pore water salinity anomalies in the subsurface indicating the pervasive presence of concentrated brines up to saturation concentration of halite and gypsum (> 300 ‰). The resulting sub-bottom MHSZ is thinner by up to 90-95% with respect to its thickness calculated assuming constant salinity with depth equal to bottom waters salinity. In the Eastern Mediterranean deep basins the thickness of the subsurface MHSZ is largest (up to ~ 350 m) and the anomaly induced by subsurface brines is highest (~ -300 m), while in the Alboran, Western Mediterranean, Tyrrhenian, Sicily Channel, Adriatic and Aegean basins the MHSZ, where present, thins to less than 100 m with mostly negligible anomaly induced by the presence of subsurface brines.

Modelling results suggest that subsurface brines can produce dramatic reductions of the thickness of the MHSZ only where the geothermal gradient is low (Eastern Mediterranean). We have modelled the same brine-induced limiting effect on the thickness of the MHSZ in synthetic cases of high and low heat flow to simulate Western and Eastern Mediterranean subsurface thermo-haline conditions. The salinity effect is attenuated by the thermal effect in the Western Mediterranean that produces the most relevant thinning of the MHSZ.

The distribution of the MHSZ resulting from the modelling coincides well with the distribution of the Late Miocene salt deposits which limit further the possibility of formation of gas hydrates acting as low permeability seal to the up-ward migration of hydrocarbon gases.

This modelling exercise provides a robust explanation for the lack of evidence of widespread gas hydrates on Mediterranean continental margins, with the exception of areas of local methane upward advection such as mud volcanoes, and it outlines a number of local hydrate-limiting factors that make this basin unfavorable to gas hydrate occurrence.

How to cite: Corradin, C., Camerlenghi, A., Giustiniani, M., Tinivella, U., and Bertoni, C.: Legacy DSDP and ODP data suggest a paradigm shift in methane hydrate stability in the Mediterranean Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3793, https://doi.org/10.5194/egusphere-egu22-3793, 2022.

EGU22-4022 | Presentations | SSP1.2 | Highlight

Half-precession signals in marine an terrestrial records – connecting IODP/ICDP sites from the equatorial Atlantic to Greenland 

Arne Ulfers, Christian Zeeden, Silke Voigt, Mehrdad Sardar Abadi, and Thomas Wonik

The characteristics of half-precession (HP) cycles (~9,000 - 12,000 years) is still poorly understood, despite their appearance in numerous records. We analyse HP signals in a variety of different marine and terrestrial proxy records from Europe and the Atlantic Ocean, investigate the temporal evolution of the HP signal from the early/middle Pleistocene to the present, and evaluate the potential of the HP to reflect the connectivity of climate systems over time.

We apply filters on the datasets that remove the classical orbital cycles (eccentricity, obliquity, precession) and high frequency signals, and focus on the bandwidth of HP signals. Wavelet annalysis and correlation techniques are used to study the evolution of specific frequencies through the different records.

In addition to a connection of HP cycles with interglacials, we observe a more pronounced HP signal in the younger part of several proxy records. Besides, we observe a trend of more pronounced HP signals in low latitude records compared to high latitudes. This is in agreement with the assumption that HP is an equatorial signal and can be transmitted northward via various pathways. The appearance of HP signals in mid- and high-latitude records may thus be an indicator for the intensity of the transporting mechanisms. We suggest that the African Monsoon plays a major role in this context, as its magnitude directly influences the climate systems of the Mediterranean and Southern Europe. In order to better understand the African climate variability, both equatorial marine and terrestrial records will be examined with respect to HP.

How to cite: Ulfers, A., Zeeden, C., Voigt, S., Sardar Abadi, M., and Wonik, T.: Half-precession signals in marine an terrestrial records – connecting IODP/ICDP sites from the equatorial Atlantic to Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4022, https://doi.org/10.5194/egusphere-egu22-4022, 2022.

Together with amphibole and garnet, epidote-group minerals are one of the three most important heavy minerals found in orogenic sediments (Garzanti and Andò, 2007). Their chemical composition and optical properties vary markedly with temperature and pressure conditions, and thus provide useful information in provenance analysis on the metamorphic grade of source rocks.

The aim of this study is to devise an efficient and quick method, with micrometric resolution to distinguish among the different species of the epidote group during routine point-counting of heavy-mineral slides, which can be applied on a vast ranges of grain-sizes from fine silt to medium sand.

The geochemical variability of epidote-supergroup minerals from different source rock collected in different sectors of the Alpine orogenic belt was first investigated by coupling Raman Spectroscopy, Scanning Electron Microscopy, and Energy-dispersed X-ray Spectroscopy (SEM-EDS). The geochemical composition, optical properties, and Raman fingerprints of these standard epidote grains were described and in-house database of Raman spectra was created, combining geochemical data and Raman response in the low wavenumbers region and OH stretching bands. A program, written in Matlab® language, has been established which allows to obtain a quick estimate of the amount of iron from the Raman spectra in the clinozoisite-epidote series.

Raman spectra of detrital epidotes contained in turbiditic sediments of the Bengal Fan (IODP Expedition 354) were next compared with Raman spectra of epidote-group standards to determine their composition. The identification and relative amount of detrital epidote, clinozoisite and zoisite in silt- and sand-sized deep-sea sediments contribute to constrain the metamorphic grade of Himalayan source rocks, reconstruct the erosional evolution of the Himalayan orogen, and provide information on climate change and strengthening of the Indian Ocean monsoon throughout the Neogene and Quaternary.

Key words: epidote, provenance, Himalaya, Raman spectroscopy, Microprobe analyses, optical microscope.

Garzanti, E., Andò S., 2007. Plate tectonics and heavy-mineral suites of modern sands. In: Mange, M.A., Wright, D.T. (Eds.), Heavy Minerals in Use, Developments in Sedimentology Series, 58. Elsevier, Amsterdam, pp. 741-763.

How to cite: Limonta, M., Andò, S., Bersani, D., France-Lanord, C., and Garzanti, E.: Raman identification of epidote-group minerals in turbiditic sediments from the Bengal Fan (IODP Exp. 354): a complementary tool to better constrain metamorphic grade of source rocks., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6161, https://doi.org/10.5194/egusphere-egu22-6161, 2022.

A 6-meter drill core from Merensky Reef, Bushveld Complex, South Africa, was scanned in detail with a drill core scanner based on Laser Induced Breakdown Spectroscopy (LIBS). The purpose of the investigation was to visualize variations in the chemical composition along the core, and following a mineral classification of the LIBS data, of variations in the mineral chemical composition, e.g. of Fe/Mg, Cr/Al, and Ca/Na ratios, as well.

The LIBS technology is based on atomic emission spectroscopy, in which the excitation of the atomic species occurs in-situ on the sample surface. The excitation source was a pulsed 50 mJ 1064 nm Nd:YAG laser, and the emitted light was collected with a high-resolution wide-range echelle spectrograph with CCD detector. This approach for measuring mineral chemical ratios such as Mg/Fe, Cr/Al, and Ca/Na, is based on the strength of LIBS in detecting chemical variations using intensity ratios within a single matrix, which in this application is one single particular type of mineral phase. For validation purposes, selected samples were analysed with bulk chemical analysis and electron probe microanalysis as well.

Distinct trends could indeed be extracted from the 6 m core section through the Merensky Reef. From a saw-cut core surface without further preparation, a continuous record could be extracted consisting of Mg/Fe of orthopyroxene, Ca/Na of plagioclase, bulk chemical patterns, modal composition, and direct neighbourhood. The data can be used to highlight the presence of unusual patterns and to relate them to Ni, Cu, PGE or other mineralization. When applied to different core sections, it may become an important tool for comparing lateral variability of diagnostic horizons in vertical sequences in layered intrusions such as Merensky Reef and UG-2.

How to cite: Meima, J., Rammlmair, D., Junge, M., and Nikonow, W.: Continuous measurement of Mg/Fe and Ca/Na ratios with scanning Laser Induced Breakdown Spectroscopy in 6 meter of drill core through Merensky Reef, Bushveld Complex, South Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7513, https://doi.org/10.5194/egusphere-egu22-7513, 2022.

EGU22-8339 | Presentations | SSP1.2

How was the Bushveld Complex assembled? A search for cryptic layering in ICDP drillcores from the Main Zone 

Robert B. Trumbull, Ilya V. Veksler, Wilhelm Nikonov, and Dieter Rammlmair

The Main Zone of the Bushveld Complex in South Africa is the most voluminous but least studied part of the world’s largest igneous intrusion. Modal layering is poorly developed compared with the units above and below (Upper and Critical Zones, resp.), and most of the ca. 3000 meter-thick Main Zone consists of monotonous gabbronorite, occasionally grading into norite and anorthosite. An exception is the ultramafic “Pyroxenite Marker” near the top of the Main Zone, which is present regionally in the complex and represents a major event of magma recharge into the chamber. However, studies of drillcore through the Main Zone in the Bushveld Northern limb (Ashwal et al., 2005; Hayes et al., 2017) found evidence for layering by periodic variations in rock density at vertical length-scales of 40 to 170 m. This implies there were many more episodes of magma recharge than previously thought.

Our study in the Eastern Limb of the complex tests if cryptic layering in the Main Zone is a local phenomenon or is regionally developed like the Pyroxenite Marker. The first step, reported here, was a vertical profile of bulk density data (Archimedes method) for a 1450 m section of the upper Main Zone below the Pyroxenite Marker. Samples were taken at 1 to 5 m intervals and the results show several intervals of density variations at length-scales of 30 to 120 m, comparable to those previously described in the Northern Limb. Periodicity in density changes is not so well developed as in the earlier study, and we identified several 50 to 75 m intervals where density variations are below 0.05 g/cm3. The second step of the study will use multispectral and laser-induced breakdown spectroscopy (LIBS) scanning to provide modal mineralogy profiles of the same drillcore samples used for density measurement. After cryptic modal layering is documented in this way, follow-up petrologic-geochemical studies at the layer boundaries will aim to characterize the composition and temperature of the magmas involved.

For this project the Bushveld Complex Drilling Project (BVDP) provided access to the BH7771 borehole, donated by Impala Platinum’s Marula mine.

References:

Ashwal, L..D., Webb, S.J. and Knoper, M.W. (2005) S. Afr. Jour. Geol., 108, 199-232.

Hayes, B., Ashwal, L.D., Webb, S.J. and Bybee, G.M. (2017) Contrib. Mineral. Petrol., 172, 13.

How to cite: Trumbull, R. B., Veksler, I. V., Nikonov, W., and Rammlmair, D.: How was the Bushveld Complex assembled? A search for cryptic layering in ICDP drillcores from the Main Zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8339, https://doi.org/10.5194/egusphere-egu22-8339, 2022.

EGU22-8952 | Presentations | SSP1.2

‘SaltGiant’ drilling in the Sorbas Basin: Structural, Petrophysical and Geochemical characterization of the Messinian Salinity Crisis deposits 

Fadl Raad, Philippe Pezard, Cesar Viseras, Francisco J. Sierro, Luis M. Yeste, Javier J. Aguila, Paula Jerez, Andrea Schleifer, Fabio Meneghini, Cinzia Bellezza, Johanna Lofi, Angelo Camerlenghi, and Giovanni Aloisi

The Late Miocene deposits in the Sorbas Basin (Spain) have been of an extreme importance in the understanding of the Messinian Salinity Crisis (MSC) events (5.97-5.33 Ma). They consist of four formations. The pre-crisis Abad marls topped by the evaporitic Yesares gypsum member, followed by two non-evaporitic units known as the Sorbas and Zorreras members. Those deposits have been widely explored and studied thanks to the numerous outcropping sections in the basin.


The ‘SaltGiant’ European Training Network held a training school in October 2021 in the Sorbas Basin, where four boreholes (named SG0, 1, 2 and 3) covering most of the Messinian Salinity Crisis sequence, were drilled, cored and logged in this context along an overall thickness of about 175 m. The drillings took place inside and in the vicinity of the Torralba gypsum mine. It allowed for the first time in the scientific non-industrial domain, access to a continuous and non-outcropping succession of the Messinian deposits in the Sorbas basin. In addition to the recovered cores, borehole geophysical data were obtained from the four holes and digital images of the area were collected with a drone. Prior to the drilling, an OBO (Outcrop / Behind Outcrop) workflow was followed, which will allow integrating the outcrop and subsurface data by combining the 3D geometry of geobodies with geophysical information.


Optical borehole wall images provide mm-scale images of the borehole walls, highlighting the sedimentological and structural characteristics of the deposits. Downhole geophysical measurements included acoustic velocity, electrical resistivity and natural spectral gamma ray, which allowed determining the petrophysical characteristics of the penetrated lithologies. In addition to the petrophysical logs, a Vertical Seismic Profiling was performed in holes SG2 and SG3, including a multi-offset VSP survey in hole SG3.


The petrophysical characterization of the Messinian deposits will provide a reference case study for the lithologic characterization of MSC deposits in the subsurface elsewhere. VSP analysis provided an in-field preliminary seismic velocity evaluation in the encountered formations. Preliminary results confirm the astronomical precession-driven cyclicity observed elsewhere in the Messinian gypsum. Further processing and analyses of the large amount of acquired data will lead to identifying the astronomical and possibly higher-frequency cyclicity in the post-evaporitic deposits in the Sorbas member.

How to cite: Raad, F., Pezard, P., Viseras, C., Sierro, F. J., Yeste, L. M., Aguila, J. J., Jerez, P., Schleifer, A., Meneghini, F., Bellezza, C., Lofi, J., Camerlenghi, A., and Aloisi, G.: ‘SaltGiant’ drilling in the Sorbas Basin: Structural, Petrophysical and Geochemical characterization of the Messinian Salinity Crisis deposits, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8952, https://doi.org/10.5194/egusphere-egu22-8952, 2022.

EGU22-10040 | Presentations | SSP1.2

A profile through fast-spreading oceanic crust in the Oman ophiolite: reference frame for the crustal drillings within the ICDP Oman Drilling Project 

Jürgen Koepke, Dieter Garbe-Schönberg, Dominik Mock, and Samuel Müller

The Oman Ophiolite is the largest and best-investigated piece of ancient oceanic lithosphere on our planet. This ophiolite was target of the Oman Drilling Project (OmanDP) within the frame of ICDP (International Continental Scientific Drilling Program) which aimed to establish a comprehensive drilling program in order to understand essential processes related to the geodynamics of mid-ocean ridges, as magmatic formation, cooling/alteration by seawater-derived fluids, and the weathering with focus on the carbonatisation of peridotites.

Over two drilling seasons, the OmanDP has sampled the Samail Ophiolite sequence from crust to basal thrust. The total cumulative drilled length is 5458 m, with 3221 m of which was at 100% recovery. These cores were logged to IODP standards aboard the Japanese drilling vessel Chikyu during two description campaigns in summer 2017 and 2018. 

Here we present the main results of the working groups of the Universities Hannover and Kiel, focusing on the magmatic accretion of the Oman paleoridge. During 5 field campaigns these groups established a 5 km long profile through the whole crust of the Oman ophiolite by systematic outcrop sampling, providing the reference frame for the 400 m long OmanDP drill cores. The profile contains 463 samples from the mantle, through gabbros up to the dike/gabbro transition. Identical samples have been analyzed by several methods (bulk rock geochemistry, mineral analysis, Isotope geochemistry, EBSD analysis).

The results allow implication on the mechanism of accretion of fast-spreading lower oceanic crust. Depth profiles of mineral compositions combined with petrological modeling reveal insights into the mode of magmatic formation of fast-spreading lower oceanic crust, implying a hybrid accretion mechanism. The lower two thirds of the crust, mainly consisting of layered gabbros, formed via the injection of melt sills and in situ crystallization. Here, upward moving fractionated melts mixed with more primitive melts through melt replenishments, resulting in a slight but distinct upward differentiation trend. The upper third of the gabbroic crust is significantly more differentiated, in accord with a model of downward differentiation of a primitive parental melt originated from the axial melt lens located at the top of the gabbroic crust. Our hybrid model for crustal accretion requires a system to cool the deep crust, which was established by hydrothermal fault zones, initially formed on-axis at very high temperatures.

How to cite: Koepke, J., Garbe-Schönberg, D., Mock, D., and Müller, S.: A profile through fast-spreading oceanic crust in the Oman ophiolite: reference frame for the crustal drillings within the ICDP Oman Drilling Project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10040, https://doi.org/10.5194/egusphere-egu22-10040, 2022.

EGU22-10406 | Presentations | SSP1.2

Assessing the well logging data from the Lake Bosumtwi (Ghana) 

Christian Zeeden, Mathias Vinnepand, Stefanie Kaboth-Bahr, William Gosling, Jochem Kück, and Thomas Wonik

Insights into the climate variability of western Africa during the Pleistocene epoch have thus far been limited by the lack of well-dated, high-resolution terrestrial climate archives. The missing information on the climate evolution of western African hampers our understanding of the proposed pan-African evolution of our species. The ~294 m lacustrine sedimentary sequence raised from Lake Bosumtwi by the International Continental Drilling program in 2004, encompassing the last ~1.1 Ma, offers the best opportunity provide a climatic benchmark record in western Africa. However, the establishment of a chronology for this record has proven challenging. To try and improve our understanding of the climatic evolution during the last ~1.1 Ma in western Africa, we will use the high-resolution downhole logging data (natural gamma ray, GR) and magnetic susceptibility data from core logging from Site 5, which is situated in the centre of Lake Bosumtwi. To maximise the robustness of this record we will try to correlate data from downhole logs with core data. This approach has help improve interpretation of logging signals and environmental reconstructions for other long lake records, such as e.g. Lake Ohrid.

How to cite: Zeeden, C., Vinnepand, M., Kaboth-Bahr, S., Gosling, W., Kück, J., and Wonik, T.: Assessing the well logging data from the Lake Bosumtwi (Ghana), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10406, https://doi.org/10.5194/egusphere-egu22-10406, 2022.

EGU22-11265 | Presentations | SSP1.2

Heterogeneous deformation across the Papaku fault, Hikurangi accretionary prism 

Rebecca Kühn, Annika Greve, Rüdiger Kilian, Marcel Mizera, and Michael Stipp

At the Hikurangi convergent margin the Pacific plate is subducted westward beneath the Australian plate. This margin has been the location of major earthquakes as well as slow slip events related to the ongoing subduction. Drill site U1518 which was drilled during IODP Expedition 375, 73 km offshore Gisborne (New Zealand), targeted the Papaku fault, a splay fault of the major decollement in sediments of the frontal accretionary prism. We selected samples from the mostly hemipelagic, weakly consolidated mudstones in the fault zone, as well as from hangingwall and footwall. In order to investigate localized and distributed deformation in the fault zone, we analysed composition, microstructure and crystallographic preferred orientation (CPO). For that we applied µXRF measurements and optical microscopy, as well as synchrotron texture analysis at DESY in Hamburg.

The samples from hanging- and footwall sediments show a relatively homogeneous microstructure with local compositional layering. While CPO strength in the hangingwall is slightly increasing with depth for all analysed clay mineral phases, the CPO in the footwall samples is in general lower and does not show a clear trend with depth. This might be interpreted as different deformation histories in hangingwall and footwall which is in accordance with previous studies. Fault zone samples show a variety of microstructures, such as mingling of different sedimentary components, locally overprinted by microfaults. CPO strength in the faulted sediments is also variable, with zones showing strong alignment of phyllosilicates and zones showing weak alignment of phyllosilicates. Variations in CPO and variable distribution of sedimentary components indicate a heterogeneous deformation within the fault zone which might be due to local compositional variations.

How to cite: Kühn, R., Greve, A., Kilian, R., Mizera, M., and Stipp, M.: Heterogeneous deformation across the Papaku fault, Hikurangi accretionary prism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11265, https://doi.org/10.5194/egusphere-egu22-11265, 2022.

EGU22-931 | Presentations | EMRP3.2

Quantifying mathematical uncertainties in Micromagnetic Tomography results 

Frenk Out, David Cortés-Ortuño, Karl Fabian, Tristan van Leeuwen, and Lennart de Groot

The recently developed Micromagnetic Tomography (MMT) technique allows precise recovery of magnetic moments of individual magnetic grains in a sample. By combining high resolution scanning magnetometry and micro X-ray computed tomography (MicroCT) MMT has the potential to become an important asset in rock-magnetic and paleointensity studies. However, uncertainties in magnetic moment solutions obtained through MMT are yet enigmatic, making a geologic application of MMT results uncertain. Therefore, we have made a first attempt in addressing those mathematical uncertainties surrounding MMT, by studying the effect of five parameters that directly influence the uncertainty of magnetic moment solutions: grain concentration of the sample, thickness of the sample, size of the sample's surface, noise level in the magnetic scan, and sampling interval of the magnetic scan. The effect of MicroCT errors are not included in this study, since those errors are better solved by improving the experimental routine than by mathematical corrections. We assess how well the magnetic moments are resolved as function of the aforementioned five parameters by setting up series of numerical models in which we assign dipole magnetizations to randomly placed grains. We perturb per model the surface magnetic field with different instrumental noise levels and sample these fields with a varying interval. The MMT inversion provides the magnetic moment per grain, and additionally produces the covariance matrix and standard deviations, which are used to define a statistical uncertainty ratio and signal strength ratio for each solution. We show that the magnetic moments of a majority of grains under realistic conditions are solved with very small uncertainties. However, increasing the grain density and sample thickness carry major challenges for the MMT inversions. Fortunately, we can use the newly defined signal strength ratio to extract grains with the most accurate solutions, even from these challenging models. Thereby we have developed an quantitative routine to individually select the most reliable grains from MMT results. This will ultimately enable determining paleodirections and paleointensities from large subsets of grains in a sample using MMT.

How to cite: Out, F., Cortés-Ortuño, D., Fabian, K., van Leeuwen, T., and de Groot, L.: Quantifying mathematical uncertainties in Micromagnetic Tomography results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-931, https://doi.org/10.5194/egusphere-egu22-931, 2022.

In the region under study, two main types of geodynamical processes are developed: (1) final collisional and (2) initial spreading. The geodynamic-paleomagnetic mapping makes it possible to reveal not only the multilevel structural heterogeneity but also display complex elements of the geodynamics of different ages inherent in the junction (transition) zones. Just for these complex regions, paleomagnetic mapping is especially important, since makes it possible to obtain significant information unattainable by any other geological-geophysical methods. The methodology of paleomagnetic mapping of the complex junction zones is based on the integration of the mapping techniques for both continental and oceanic platforms: paleomagnetic reconstructions, results of radiometric dating of magnetized rocks, biogeographical studies, satellite data examination, plate tectonic reconstructions, and utilization of results of various geophysical surveys. All these data are used for the integrated identification of mapped geological bodies and structures. For paleomagnetic mapping, two different reference areas were selected: spreading area with younger traps (Sea of Galilee, northern Israel), and collisional area with older traps (Makhtesh Ramon, southern Israel). The supplemented edition of the paleomagnetic map of the Sea of Galilee region (northern Israel) was extended to the south where the Belvoir uplift exists with the detailed reference well, and a complex of radiometric dating of the Cenozoic traps is developed. The map has been significantly detailed due to analyzing new data from structural, radiometric, and paleomagnetic researches, which has expanded the understanding of both the tectonic-structural peculiarities and development of this complex area (Eppelbaum et al., 2022). The subterrane Makhtesh Ramon (southern Israel), is collisionally joined with the Arabian-Nubian part of Gondwana. The Ramon subterrane contains various tectonic units formed during the pre-collisional, collisional, and post-collision stages of its paleogeodynamic evolution. In this paleomagnetic scheme and diagram of geodynamic reconstructions, not all subterrane, but the edge of its submerged part corresponds to erosion-tectonic depression, and includes outcrops of Lower Cretaceous, Jurassic, Triassic, and Late Cenozoic (Eppelbaum and Katz, 2015). These rocks are penetrated by a variety of Mesozoic traps, whose radiometric age ranges from 165.7 to 93.8 Ma, and contain scattered ophiolite outcrops of the Sakharonim basalts. These ophiolites are associated with absorption of the Triassic-Jurassic crust of the Neotethys Ocean in Hauterivian and relate to the Levantine phase of tectogenesis. The pre-collision formations preceding this phase are represented by basalts dykes (Omolon and Gissar superzones) and laccolites of mainly alkalic olivine gabbro associated mostly with the Gissar superzone. Tectonic-paleomagnetic mapping as a new type of combined geological-geophysical survey contributed to an essential understanding of the junction zone of the Mesozoic Terrane Belt and the Dead Sea Transform.

 

Eppelbaum, L.V. and Katz, Yu.I., 2015. Eastern Mediterranean: Combined geological-geophysical zonation and paleogeodynamics of the Mesozoic and Cenozoic structural-sedimentation stages. Marine and Petroleum Geology, 65, 198-216.

Eppelbaum, L.V., Katz, Y.I. and Ben-Avraham, Z., 2022. Advanced combined geophysical-geological mapping of the Sea of Galilee and its vicinity, In: (A. di Mauro, A. Scozzari, S. Soldovieri, Eds.), "Instrumentation and Measurement Technologies for Water Cycle Management", Springer, 1-23.

How to cite: Eppelbaum, L. and Katz, Y.: Geodynamic-paleomagnetic mapping of the heterogeneous geological structure of the junction zone of the Mesozoic Terrane Belt and the Dead Sea Transform, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1919, https://doi.org/10.5194/egusphere-egu22-1919, 2022.

EGU22-2437 | Presentations | EMRP3.2

End-Member Modelling Analysis (EMMA) of pseudo-Thellier style experiments to derive absolute paleointensities from lavas 

Liz van Grinsven, Tristan van Leeuwen, and Lennart de Groot

Absolute paleointensities are notoriously hard to obtain, because conventional thermal Thellier paleointensity experiments often have low success rates for volcanic samples. The thermal treatments necessary for these experiments potentially induce (magnetic) alteration in the samples, preventing a reliable paleointensity estimate. These heating steps can be avoided by pseudo-Thellier measurements, where samples are demagnetized and remagnetized with alternating fields. However, pseudo-Thellier experiments intrinsically produce relative paleointensities. Over the past years attempts were made to calibrate pseudo-Thellier results into absolute paleointensities for lavas by mapping laboratory induced ARMs to the thermally acquired NRMs. Naturally occurring volcanic rocks, however, are assemblages of minerals differing in grain size, shape, and chemistry. These different minerals all have their own characteristic mapping between ARMs and thermal NRMs. Here we show that it is possible to find these characteristic mappings by unmixing the NRM demagnetization and the ARM acquisition curves into end-members, with an iterative method of non-negative matrix factorization.  In turn, this end-member modelling approach allows for the calculation of absolute paleointensities from pseudo-Thellier measurements.

 

We tested our end-member model approach using a noise-free mathematical data set, yielding a perfect reconstruction of the paleointensities. When adding noise up to levels past what is expected in natural samples, the end-member model still produces the known paleointensities well. In addition, we made a synthetic dataset with natural volcanic samples from different volcanic locations that were given a magnetization by a known magnetic field in the lab. The applied fields ranged between 10-70 . The average absolute difference between the calculated paleointensity and the known lab-field is around  for the 2 to 4 end-member model, where the paleointensity of almost all flows can be retrieved within a deviation of ± . The average difference between calculated paleointensities for the 3 end-member model is -1.7 . The deviations between the paleointensities and the known lab-fields are therefore almost Gaussian distributed around the expected values.

 

To assess whether the end-members produced by our analysis have a physical meaning, we measured the Curie temperatures of our samples. These Curie measurements show that there is a relationship between the abundances of the end members of the 3 end-member model in the samples and their dominant Curie temperatures. This indicates that even whilst the spectrum of Curie temperatures and hence composition of iron-oxides in the sample set is continuous, the calculated end-members of the 3 end-member model are related to magnetic minerals present in the samples. Although the two datasets in our study show that there is potential for using this end-member modeling technique for finding absolute paleointensities from pseudo-Thellier data, these synthetic datasets cannot be directly related to natural samples. Therefore, it is necessary to compile a dataset of known paleointensities from different volcanic sites to find the universal end-members.

How to cite: van Grinsven, L., van Leeuwen, T., and de Groot, L.: End-Member Modelling Analysis (EMMA) of pseudo-Thellier style experiments to derive absolute paleointensities from lavas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2437, https://doi.org/10.5194/egusphere-egu22-2437, 2022.

The Tibetan Plateau is composed of multiple accreted terranes, including (from south to north) the Tethyan Himalaya, the Lhasa, the Qiangtang, the Songpan-Ganzi and the Qaidam-Qilian terranes. The drift history of the Qiangtang Terrane and the timing of the Lhasa–Qiangtang collision are under debate. To contribute to this topic, we paleomagnetically investigate the Middle-Upper Jurassic limestones of the Yanshiping Group in the Zaduo area (32.5°N, 95.2°E), in the Eastern Qiangtang Terrane (Tibetan Plateau, China). A major challenge in paleomagnetism is the possibility of remagnetization that interferes with paleogeographic reconstructions. In this study, both thermal and alternating field demagnetizations were carried out to isolate the characteristic remanent magnetization (ChRM). Despite the positive reversals test, rock magnetic information points to a remagnetized ChRM that resides in stable single-domain (SSD) magnetite grains with cogenetic superparamagnetic (SP) particles. The co-occurreance of SSD and SP magnetites generates distinct rock-magnetic properties often refer to as the ‘remagnetized fingerprint’ in limestones. This remagnetization process is also manifested by the widespread occurrence of gypsum veinlets in the limestones. The site-mean direction of the 12 sites after tilt-correction is Ds = 30.6°, Is = 35.6°, κs = 182.9, α95 = 3.2°, corresponding to a palaeolatitude of ∼19.7°± 2.8°N for the study area. The corresponding palaeopole (59.8°N, 202.7°E with A95 = 2.8°) points to an NRM acquired after the India–Eurasia collision. The original sediments were likely anoxic because of the high organic carbon fluxes that prevailed during their deposition. After the India–Eurasia collision, it is envisaged that conditions became more oxic, giving rise to oxidation of iron sulphides to authigenic magnetite and the CRM acquisition. The Zaduo area in the Eastern Qiangtang Terrane has experienced ∼15.7° ± 3.2° (∼1740 ± 350 km) of latitudinal crustal shortening since the Eocene. In addition, the clockwise rotation responding to the India–Eurasia collision is also detected in the Zaduo area.

How to cite: Fu, Q., Yan, M., and J.Dekkers, M.: Remagnetization of the Jurassic limestones in the Eastern Qiangtang Terrane (Tibetan Plateau, China): Implications for the India-Eurasia collision, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2854, https://doi.org/10.5194/egusphere-egu22-2854, 2022.

Since the advent of the anisotropy of magnetic susceptibility (AMS) method, magnetic fabric has become a widely used tool to unravel the internal architecture of granite plutons, with an impressive boom of AMS studies in the 1990s and 2000s. This "boom period" generated a large body of data and led to significant advances in our understanding of how the structural inventory of plutons records magma flow, emplacement, and regional deformation. On top of that, the AMS is capable of revealing an incredible level of detail, especially in combination with mathematical modeling, as to the type, kinematics, and intensity of finite strain. One of the most intriguing discoveries is the key role of AMS in decrypting multiple fabrics that may reflect heterogeneous superposition of intrusive processes by tectonic deformation. Despite a recent decline of interest in the AMS studies, a number of exciting issues still remain to be explored, namely how to use the magnetic anisotropy to interpret the spatio-temporal melt evolution in "fossil" magma chambers and its potential in recording the past motion of lithospheric plates.

How to cite: Žák, J.: Magnetic fabric of granite plutons: from anisotropy to processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3174, https://doi.org/10.5194/egusphere-egu22-3174, 2022.

EGU22-4519 | Presentations | EMRP3.2

Micromagnetic modelling and single particle multipole expansions from Micromagnetic Tomography 

David Cortés‐Ortuño, Karl Fabian, and Lennart de Groot

Micromagnetic Tomography is a technique that combines X-ray micro tomography and scanning magnetometry data to obtain magnetic information of individual grains embedded in a sample. Recovering magnetic signals of individual grains in rock samples and synthetic samples provides a new pathway to study the rock-magnetic properties of remanent magnetizations that are crucial to paleomagnetic studies. This is possible by numerically inverting the surface magnetic signal for the magnetic potential of individual magnetic grains via their spherical harmonic expansion [1]. Resulting magnetic moment solutions are uniquely determined as dipole and higher order multipole moments, which has been proved in [2]. Furthermore, the higher order multipole signals in the magnetic particles are an indication that the grains carry complex magnetic orderings, such as multi-domain or vortex configurations [3]. In this work we show that the magnetic moment information can be used to constrain the internal magnetic configuration of individual grains using micromagnetic modelling. We first review the multipole expansion method used in Micromagnetic Tomography [3]. Further, we show three dimensional micromagnetic modelling results to predict the multipole signal of magnetic particles in different local energy minimum magnetization states. We show that for certain grains it is possible to uniquely infer the magnetic configuration from the inverted magnetic multipole moments. This result is crucial to discriminate single-domain particles from grains in more complex configurations. Our investigation proves the feasibility to select statistical ensembles of magnetic grains based on their magnetization states, which opens new possibilities to characterize stable paleomagnetic recorders in natural samples. 

[1] L. V. de Groot, K. Fabian, A. Béguin, M. E. Kosters, D. Cortés-Ortuño, R. R. Fu, C. M. L. Jansen, R. J. Harrison, T. van Leeuwen, A. Barnhoorn. Micromagnetic tomography for paleomagnetism and rock-magnetism. Journal of Geophysical Research: Solid Earth, 126:e2021JB022364, 2021.
[2] K. Fabian and L. V. de Groot. A uniqueness theorem for tomography-assisted potential-field inversion. Geophysical Journal International, 216(2):760–766, 2018.
[3] D. Cortés‐Ortuño, K. Fabian and L. V. De Groot. Single particle multipole expansions from Micromagnetic Tomography. Geochemistry, Geophysics, Geosystems, 22:e2021GC009663, 2021.

How to cite: Cortés‐Ortuño, D., Fabian, K., and de Groot, L.: Micromagnetic modelling and single particle multipole expansions from Micromagnetic Tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4519, https://doi.org/10.5194/egusphere-egu22-4519, 2022.

EGU22-4546 | Presentations | EMRP3.2

Magnetocrystalline anisotropy of out-of-phase magnetic susceptibility in hematite 

Frantisek Hrouda, Josef Ježek, and Martin Chadima

 Out-of-phase component of AC magnetic susceptibility (opMS) in four single crystals of hematite from Minas Gerais, Brazil was investigated. The phase angle ranges from 1° to 6° along the c-axis and slightly exceeds 25° along the basal plane (in the standard field 400 A/m at the operating frequency 1220 Hz). The opMS in the basal plane shows strong field dependence and virtually no frequency dependence. Along the c-axis, opMS is at least three orders lower and increases with field only slowly; it is similar at the frequencies 976 Hz and 3,904 Hz, while it is clearly higher at 15,616 Hz. The opMS vs. T curve measured along basal plane drops acutely between 680 °C and 710 °C, evidently indicating the Curie (Néel) temperature of hematite. The same curve along c-axis passes more or less parallel to the abscissa in the entire temperature interval investigated.

Directional opMS was measured in 320 independent directions from which the opAMS tensor was calculated using standard linear technique. The minimum opAMS directions are parallel to the c-axis, while the maximum and intermediate opAMS directions lie within basal plane. The differences between measured values and those calculated from the opAMS tensor are relatively small in the vicinity of the maximum opAMS direction and very high in the vicinity of the minimum opAMS direction. All this indicates that the second rank tensor is not the best representative of the spatial variation of the directional opMS of hematite single crystals. In multi-crystal assemblages, however, summation of many oriented grains filters out the non-tensorial parts of the grain opAMS and the resultant opAMS is well represented by a tensor. This result is similar to that of in-phase magnetic susceptibility in hematite investigated in Hrouda et al. (2020).

How to cite: Hrouda, F., Ježek, J., and Chadima, M.: Magnetocrystalline anisotropy of out-of-phase magnetic susceptibility in hematite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4546, https://doi.org/10.5194/egusphere-egu22-4546, 2022.

EGU22-5153 | Presentations | EMRP3.2

Petrofabric patterns of two contrasting plutons: example of Penedos and Borralha granites (Montalegre, Northern Portugal) 

Ana Gonçalves, Helena Sant'Ovaia, and Fernando Noronha

The Penedos-Borralha area is located inside the Galícia-Trás-os-Montes Zone where Silurian metasediments and Variscan granites outcrop. Three Variscan ductile deformation phases were recognized: D1 (360-337Ma); D2 (337-320Ma) and D3 (320-310Ma). D3implied a regional subvertical crenulation (N120ºE) and the deformation of syn-D3 granites (321–312Ma). This contribution results from a multidisciplinary approach (viz., fieldwork, petrography, and anisotropy of magnetic susceptibility (AMS)) for the understanding of the magnetic anisotropy patterns of Penedos (PG, post-D3) and Borralha (BG, syn-D3). PG occurs as circumscribed outcrop in a triple point marked by the contact between BG, Borralha tonalite and metasediments. PG is a leucocratic, medium- to coarse-grained granite with garnet. BG occurs as a WNW-ESE outcrop and is composed of biotite-rich, medium- to coarse-grained porphyritic granite. At the outcrop scale, oriented patterns were not observed in PG; however, the BG exhibits K-feldspar megacrysts and phyllosilicates N120ºE oriented. The main mineralogical features observed in BG are quartz displaying strong undulose extinction and subgranulation, K-feldspar with poikilitic texture, plagioclase presenting curved twins and well-developed kinked phyllosilicates. In turn, PG presents quartz displaying slightly undulose extinction, slightly stretched plagioclase, euhedral garnet crystals and phyllosilicates occurring as clustered flakes. The petrofabric studies were obtained using AMS providing scalar (magnetic susceptibility, Km and paramagnetic anisotropy, Ppara) and directional (magnetic foliation, ⊥K3 and lineation, K1) parameters. The Kmindicated paramagnetic behaviour for both BG and PG (53.9 and 30.39µSI, respectively) classifying them as ilmenite-type granites.BG exhibits the highest Ppara values (4.4%), result of the strong K-feldspars and biotite alignment. In contrast, PG exhibits the lowest Ppara values (1.89%) compatible with the no-oriented patterns. The ⊥K3 in the PG are very heterogeneous ranging from NW-SE to E-W; generally, the ⊥K3 are subvertical in the E side, where the PG is intrusive in the metasediments and subhorizontal in the W side, where the PG cuts the BG. Concerning the K1 the PG display NNE-SSW to W-E azimuths with subhorizontal to intermediate dips. In the BG, the ⊥K3, essentially subhorizontal, tends to be parallel to the contacts with the regional rocks and the K1are strongly subhorizontal with azimuths ranging from WNW-ESE to ENE-WSW. Considering this multidisciplinary approach is clear that the petrofabric obtained for both granites resulted from distinct phenomena. The PG petrofabric was inherited from magmatic stages, where the K1 trajectories suggest the location of a feeder zone in the SE border and continuous magmatic flow to NW. The evidence of subvertical ⊥K3 in the E side of PG suggests a tongue-shaped intrusion thicker on this side. In contrast, the BG petrofabric was acquired in the subsolidus and resulted from tectonic processes. The obtained petrofabric agrees with the proposed classification of BG and PG as a syn-D3 and post-D3 granites, respectively. These analyses applied to two contrasting intrusions allowed us to verify that the AMS depend on several parameters and must be interpreted with caution.

Acknowledgments: This work was supported by national funding awarded by FCT - Foundation for Science and Technology, I.P., projects UIDB/04683/2020 and UIDP/04683/2020.

How to cite: Gonçalves, A., Sant'Ovaia, H., and Noronha, F.: Petrofabric patterns of two contrasting plutons: example of Penedos and Borralha granites (Montalegre, Northern Portugal), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5153, https://doi.org/10.5194/egusphere-egu22-5153, 2022.

EGU22-5251 | Presentations | EMRP3.2

Characterizing ferrofluid properties for a more reliable and quantitative interpretation of magnetic pore fabric studies 

Andrea Regina Biedermann, Michele Pugnetti, Yi Zhou, and Josep M Parés

Magnetic anisotropy is a time-efficient and powerful tool to characterize the anisotropy of pore space in ferrofluid-impregnated rocks. Empirical correlations exist between magnetic pore fabrics and the shape preferred orientation of pores, as well as between magnetic pore fabrics and permeability anisotropy. Up to now, quantitative interpretation has been challenging, and one reason is the variability of ferrofluids and their properties that have been used in different studies. Namely, the susceptibility of the ferrofluid largely controls the degree of measured magnetic anisotropy. Being a colloidal solution of superparamagnetic particles, ferrofluid displays magnetic properties that are both frequency- and time-dependent. This in turn affects the quantitative interpretation of magnetic pore fabrics. This study sheds light on the magnetic properties of the ferrofluids used in pore fabric studies, with a particular focus on processes such as particle aggregation and sedimentation, and how these affect ferrofluid impregnation as well as the measured pore fabrics. Further, interactions between the ferrofluid and the rock that lead to changes in magnetic properties are studied. These results will form the basis for future quantitative interpretation of magnetic pore fabric studies in groundwater, CO2 or hydrocarbon applications.   

How to cite: Biedermann, A. R., Pugnetti, M., Zhou, Y., and Parés, J. M.: Characterizing ferrofluid properties for a more reliable and quantitative interpretation of magnetic pore fabric studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5251, https://doi.org/10.5194/egusphere-egu22-5251, 2022.

EGU22-5353 | Presentations | EMRP3.2

Anisotropy of magnetic susceptibility (AMS) study of magma transport in Mount Calanna Dyke swarms of Mount Etna, Italy 

Rasia Shajahan, Elena Zanella, Sara Mana, Andrew Harris, and Benjamin Van Wyk de Vries

Dykes and Sills are the primary subvolcanic bodies that transport magma from the deep-seated magma reservoir or from the shallow magma chamber. The mechanism of magma transport and emplacement in dyke swarms is significant, as their passage from magma chamber through the crust to the surface or near-surface settings can provide valuable information on source and how magma has interacted with crustal rocks.

Here, we are presenting the preliminary findings obtained from the Anisotropy of Magnetic Susceptibility (AMS) and Palaeomagnetic analysis to study the magma transport mechanism and emplacement history of  Mount Calanna dyke swarms of Mount Etna. In order to find their magnetic fabrics, we systematically sampled 45 oriented hand samples from 11 dykes where at least two samples were collected from both dyke boundary and centre. Using the obtained AMS fabrics, we attempt to find the emplacement mechanisms of dykes in Mount Calanna and its relationship to Mount Etna.

AMS technique provides valuable information regarding the dyke emplacement such as whether the Mount Calanna dykes are feeders, and whether they are the result of polycentric, vertical or lateral magma flow. Based on the intersection of the AMS axis with the dyke plane, we were able to identify two classes, one where the dyke plane intersects with the maximum principal susceptibility axes (Kmax) and the other where the dyke plane intersects with the minimum principal susceptibility axes (Kmin). Nevertheless, the variation in the shape parameter from centre to boundary shows the effect of shear, magma viscosity and the host rock strength on magma emplacement. The Paleomagnetic techniques enable us to unravel the relative timing of the injection of the dykes and the possible tectonic control on their emplacement.

How to cite: Shajahan, R., Zanella, E., Mana, S., Harris, A., and Van Wyk de Vries, B.: Anisotropy of magnetic susceptibility (AMS) study of magma transport in Mount Calanna Dyke swarms of Mount Etna, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5353, https://doi.org/10.5194/egusphere-egu22-5353, 2022.

EGU22-7202 | Presentations | EMRP3.2

Magnetic fabric study of the Dejvice loess/paleosol sequence (Prague, Czech Republic) 

Martin Chadima, Michaela Žatecká, Kristýna Kolaříková, Balazs Bradák, and Jaroslav Kadlec

In this contribution, we present a rock magnetic and magnetic fabric study of the Dejvice loess/paleosol sequence with an aim to demonstrate how rock magnetic methods can be very effective tools for detecting paleoenvironmental, pedogenic, and post-depositional processes. This study covers the 15-meter-long loess/paleosol section which was recently temporarily accessible during the underground construction works in the Vienna House Diplomat Hotel in Prague. The exposed part of the sequence contained at least four different paleosol horizons and covered the time interval from ca. 130 ky to recent. For the purpose of this study, 425 orientated samples (8 ccm) were collected evenly covering the studied section.

In general, loess sequences contain variable amount of detrital magnetic particles derided from the source material. In addition, in warmer interglacials periods, pedogenesis results in formation of paleosol horizons which are magnetic enhanced by the in-situ neo-formed nanoscale ferromagnetic particles.

The applied rock-magnetic techniques included measurements of (1) magnetic susceptibility (MS), (2) frequency-dependent susceptibility (kFD), (3) out-of-phase magnetic susceptibility (opMS), and (4) viscous magnetization (Mv). While MS very sensitively reflects the relative amount of all magnetic particles, the other methods (kFD, opMS, and Mv) mirror solely the contribution of the neo-form nanoscale particles. In addition to these rock magnetic parameters, (5) anisotropy of magnetic susceptibility (AMS) was measured in order to obtain magnetic fabric reflecting the preferred orientation of magnetic minerals. Magnetic fabric can be primarily interpreted in terms of paleotransport directions but it may also provide some evidences for post-depositional reworking and/or movements.

All paleosol horizons possess significantly higher values of MS, kFD, opMS and Mv. This indicates that the increased amount of magnetic particles in paleosols is exclusively due to the magnetic enhancement caused by the neo-formation of nanoscale particles during pedogenesis. In addition, the values of kFD, opMS, and Mv mutually intercorrelate very tightly. This indicates that all these independent methods are reliable proxies for the quantification of ultra-file particles in loess/paleosols horizons.

In addition of the paleotransport direction, the magnetic fabric reflects secondary sedimentary processes. This involves the displacement of clastic particles by flowing water and the redeposition of the material along the slope. The direction of movement of these sediments corresponds to the current geomorphology of the surroundings. We can conclude that the section was not deposited solely by the aeolian processes.

How to cite: Chadima, M., Žatecká, M., Kolaříková, K., Bradák, B., and Kadlec, J.: Magnetic fabric study of the Dejvice loess/paleosol sequence (Prague, Czech Republic), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7202, https://doi.org/10.5194/egusphere-egu22-7202, 2022.

EGU22-7592 | Presentations | EMRP3.2

Rock-magnetic characteristics of the Cryogenian–Ediacaran volcano-sedimentary section of the northwest Siberian Platform (Igarka Uplift) 

Anna Chernova, Dmitry Metelkin, Boris Kochnev, Vasiliy Marusin, and Sergey Zakharov

We present the rock-magnetic results obtained from the sedimentary and magmatic rocks of the Igarka Uplift (northwestern margin of the Siberian Platform). This part of the study is an integral stage of paleomagnetic research that is extremely important for a better understanding of the Siberian geological history in the Neoproterozoic. The studied objects are located in the Lower Yenisei River near the Sukharikha River mouth and comprise red-colored siliciclastic rocks (sandstones, gravelites) of Gubinskaya (Cryogenian) and Izluchina (Ediacaran) formations  (Kochnev et al., 2020, 2021) and three dolerite sills intruded in the Gubinskaya formation.

We have analyzed the primary rock-magnetic parameters – magnetic susceptibility (K), anisotropy of magnetic susceptibility (AMS), natural remanent magnetization (NRM), and Koenigsberger ratio (Q). K in dolerites is 20–45*10-3 SI unit and NRM is 100–500 mA/m that is two orders of magnitude higher than in the sedimentary rocks studied. Q is low in both types of rocks (0.1–1) but noticeably rises to 2–3.7 in the baked contact rocks indicating an impact of chemical magnetization. Among the magnetic minerals, magnetite and hematite are identified according to the temperature demagnetization curves.

The AMS data (degree of anisotropy P, the AMS-ellipsoid shape and distribution of the axes) estimate preservation of the primary magnetic texture, the amount of deformation and cleavage in rocks, and suggest hydrodynamic conditions and paleoflow directions during accumulation of the sediments.

Most of the studied rocks have a low degree of anisotropy – less than 5%, mostly at 1–2%. Sedimentary rocks of the Gubinskaya Formation have the oblate form of the AMS ellipsoid. In the planar-bedded fine-grained sandstones, minimal axis (K3) is normal to the bedding planes that is typical for the calm or slow-current conditions. In the cross-bedded coarse-grained sandstones and gravelites  the maximum axis K1 is steeply inclined to the  bedding surfaces (50-70 degrees) that supports intense hydrodynamics. It should be noted that the anisotropy values do not exceed 1% in the coarse-grained rocks. As for the Izluchina Formation rocks the degree of anisotropy is higher (6–8%) and the orientation of the axes is rather related to the cleavage and the direction of stress.

In the dolerite sills, the degree of anisotropy is 3–6% that suggests weak deformation of the magnetic texture. Distribution of the ellipsoid axes is not in accordance to the shape and strike of the magmatic bodies and probably mirrors a stress impact. In the baked contact zone, AMS ellipsoid is flattened along the contact plane with the K3 being perpendicular to it.

So far, we can conclude that in the most cases the primary magnetic texture is preserved or slightly disturbed but further paleomagnetic studies will be carried out taking into account the data obtained.

This work was financially supported by the Russian Science Foundation grant no. 21-17-00052.

How to cite: Chernova, A., Metelkin, D., Kochnev, B., Marusin, V., and Zakharov, S.: Rock-magnetic characteristics of the Cryogenian–Ediacaran volcano-sedimentary section of the northwest Siberian Platform (Igarka Uplift), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7592, https://doi.org/10.5194/egusphere-egu22-7592, 2022.

EGU22-8469 | Presentations | EMRP3.2

On the feasibility of Paleomagnetic Euler Pole Analysis 

Leandro C. Gallo, Mathew Domeier, and Facundo Sapienza

Owing to the inherent axial symmetry of the Earth’s magnetic field, paleomagnetic data only directly record the latitudinal and azimuthal positions of crustal blocks in the past, and paleolongitude cannot be constrained. An ability to overcome this obstacle is thus of fundamental importance to paleogeographic reconstruction. Paleomagnetic Euler pole (PEP) analysis presents a unique means to recover such information, but prior implementations of the PEP method have incorporated subjective decisions into its execution, undercutting its fidelity and rigor. Here we introduce an optimization approach to PEP analysis that addresses some of these deficiencies---namely the objective identification of change-points and small-circle arcs that together approximate an apparent polar wander path. Equipped with a new analytical approach to PEP analysis we turn to consider its feasibility in terms of its potential in the context of the theoretical and practical limitations of paleomagnetic data. In this presentation, we will share some key insights that emerged through experimentation with randomly-drawn plate kinematic models.

How to cite: Gallo, L. C., Domeier, M., and Sapienza, F.: On the feasibility of Paleomagnetic Euler Pole Analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8469, https://doi.org/10.5194/egusphere-egu22-8469, 2022.

Three-dimensional shapes of 68 magnetite grains in pyroxene and 234 magnetite grains in plagioclase, were obtained by “slice-and-view” focused-ion-beam nanotomography (FIB-nt) on mineral separates from the Bushveld Intrusive Complex, South Africa. Electron backscatter diffraction (EBSD) determined the orientation of the magnetite inclusions relative to the crystallographic directions of their silicate hosts. For each particle, hysteresis loops in 20 equidistributed field directions were calculated by the finite-element micromagnetic code MERRILL. For each direction, the averages over the particle ensemble were compared to corresponding hysteresis loops measured with a vibrating sample magnetometer (VSM) on silicate mineral separates from the same samples. FIB-nt combined with micromagnetic modelling allows to explore the mechanisms controlling the magnetic anisotropy for each individual particle and to analyze the combined effect for bulk magnetic properties. This combination is of interest for anyone who interprets magnetic anisotropy because it helps understanding how domain states and crystal alignment in natural samples influence the measured anisotropy. Our results demonstrate that natural particle shapes, their orientations and domain states control the anisotropy of magnetic remanence, coercivity and susceptibility in natural particles. We can show for our specific examples, how the connection between mineral texture and magnetic anisotropy depends on specific domain states. Our data explain why natural magnetite particles at the transition between single-domain and single or multiple vortex states do not always follow the relation between axis orientation and  magnetic anisotropy which is theoretically expected for simple particle shapes.

How to cite: Nikolaisen, E. S., Harrison, R. J., Fabian, K., and McEnroe, S. A.: Anisotropy of magnetic susceptibility and hysteresis parameters for natural magnetite particle assemblages: Micromagnetic analysis of focused-ion-beam nanotomography data with MERRILL, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8528, https://doi.org/10.5194/egusphere-egu22-8528, 2022.

EGU22-8926 | Presentations | EMRP3.2

Spasmodic deformation in the Southwest of the Gondwana boundary, Upper Paleozoic of Ventana ranges in Argentina 

Renata N. Tomezzoli, Guadalupe Arzadún, Natalia Fortunatti, Nora N. Cesaretti, María B. Febbo, Juan M. Calvagno, and Giselle Choque

At the east of the Ventana Ranges, Buenos Aires, Argentina, outcrops the Carboniferous-Permian Pillahuincó Group (Sauce Grande, Piedra Azul, Bonete and Tunas Formation). We carried out an Anisotropy of Magnetic Susceptibility (AMS) study on Sauce Grande, Piedra Azul and Bonete Formation that displays ellipsoids with constant Kmax axes trending NW-SE, parallel to the fold axes. The Kmin axes are orientated in the NE-SW quadrants, oscillating from horizontal (base of the sequence-western) to vertical (top of the sequence-eastern) positions, showing a change from tectonic to almost sedimentary fabric. This is in concordance with the type and direction of foliation measured in petrographic thin sections which is continuous and penetrative to the base and spaced and less developed to the top. We integrated this study with previous Tunas Formation results (Permian). Similar changes in the AMS pattern (tectonic to sedimentary fabric), as well as other characteristics such as the paleo-environmental and sharp curvature in the apparent polar wander path of Gondwana marks a new threshold in the evolution of the basin. Those changes along the Pillahuincó deposition indicate two different spasms in the tectonic deformation that according to the ages of the rocks are 300-290 Ma (Sauce Grande to Bonete Formation deposition) and 290-276 Ma (Tunas Formation deposition). This Carboniferous-Permian deformation is locally assigned to the San Rafael (Hercinian) orogenic phase, interpreted as the result of rearrangements of the microplates that collided previously with Gondwana, and latitudinal movements of Gondwana toward north and Laurentia toward south to reach the Triassic Pangea.  

How to cite: Tomezzoli, R. N., Arzadún, G., Fortunatti, N., Cesaretti, N. N., Febbo, M. B., Calvagno, J. M., and Choque, G.: Spasmodic deformation in the Southwest of the Gondwana boundary, Upper Paleozoic of Ventana ranges in Argentina, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8926, https://doi.org/10.5194/egusphere-egu22-8926, 2022.

The research objects are magmatic bodies from the southern, central and northern parts of the Bashkirian megazone (the Southern Urals tectonic domain which extends from the south-east to the north-west for 300 km). Most of the studied intrusions have the Riphean age. In the Riphean the Bashkirian megazone (BM) was a part of the East European craton (2). The emplacement of most studied bodies is associated with the Mashak magmatic event (the Lower Riphean-Middle Riphean boundary), which marks the breakup of the super-continent Nuna (2). During the Late Paleozoic the rocks of the Bashkirian megazone were involved in the collision. During this process most of BM rocks was remagnetized.

Paleomagnetic analysis showed that the Late Paleozoic secondary remanence component present in 28 intrusive bodies from different parts of BM. In general, calculated paleomagnetic directions form a tight group in the geographic coordinate system, but the mean directions for some districts are statistically different. These differences may be related to: 1) local tectonic movements of the individual blocks within the Bashkirian megazone; 2) slightly different time of remagnetization; 3) insufficient averaging of secular variations of the geomagnetic field. To resolve this issue, further studies and more paleomagnetic data are required.

Given that paleomagnetic directions are more tightly grouped in a geographic coordinate system than in a stratigraphic coordinate system, the Late Paleozoic component is post-folding.

Distribution of this component does not reveal any regular features (for example, continuous trend from south to north, etc.) Thus, the differences of the mean paleomagnetic directions for various localities can not be explained by the migration of the remagnetization front. Also, the mean pole for all studied regions is close to the mean for 18 poles of Stable Europe with an age of 279-299 Ma (1).

We suggest that the component has a thermoviscous nature. Different minerals-carriers of magnetization show the same directions, evenly distributed over the magmatic rocks of the entire BM. Probably, the studied component of remanence was formed at the moment of partial stress relief at the final stage of collision and collapse of orogen in the Southern Urals. Also, this component could have formed during the exhumation of the BM to the surface at the time of formation of the South Ural thrust faults system.

Based on the obtained data, we can conclude that remagnetization in the Bashkirian megazone occurred approximately in the same time (279-299 Ma) and after the end of the main Late Paleozoic fold deformations in this area. By this time, the Bashkirian megazone was stable relative to the East European craton.

References:

1."Global Paleomagnetic Database" (GPMDB, v. 4.6, 2005), Pisarevsky S.A.

2. Puchkov V.N., Bogdanova S.V, Ernst R.E., Kozlov V.I., Krasnobaev A.A., Söderlund U., Wingate M.T.D., Postnikov A.V., Sergeeva N.D. The ca. 1380 Ma Mashak igneous event of the Southern Urals // Lithos. - 2013. - V.174. – P. 109-124.

How to cite: Anosova, M. and Latyshev, A.: The origin of the Late Paleozoic remagnetization in the Bashkirian megazone(the Southern Urals)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9766, https://doi.org/10.5194/egusphere-egu22-9766, 2022.

EGU22-10591 | Presentations | EMRP3.2

Assessing the source of out-of-phase AMS in magnetite rich igneous rocks 

Lot Koopmans and William McCarthy

Anisotropy of magnetic susceptibility (AMS) studies have proven valuable in identifying subtle or cryptic petrofabrics, significantly broadening the scope of quantitative petrofabric analyses. An exciting development in magnetic anisotropy techniques is the ability to resolve an AMS response into an in-phase (ipAMS) and out-of-phase (opAMS) component using an AGICO KLY-5a Kappabridge. Because the opAMS response is produced by ferromagnetic minerals (whereas ipAMS is the result of the sum of all contributing components), it has the potential to record ferromagnetic sub-fabrics1. However, in natural rock specimens the origin of the opAMS response remains unclear  and previous research has published conflicting reports on exactly which magnetic populations contribute to the opAMS response1,2.

Our study attempts to understand the source of the opAMS signal in magnetite-rich mafic samples from the Younger Giant Dyke Complex in southern Greenland3.  We conduct magnetic characterisation experiments alongside AMS measurements on 22 samples, including temperature-susceptibility, magnetic saturation, hysteresis, and first-order reversal curve experiments. Our samples have absolute out-of-phase susceptibility values between 2x10-7 and 6.75x10-4 SI units, above the detection limit of the KLY-5a Kappabridge. Three distinct relationships are observed between ipAMS and opAMS responses; 1) a parallel ip/op response, suggesting the two AMS responses have an identical source, 2) perpendicular ip/op responses, suggesting a mineralogical control on the AMS response, and 3) ip/op responses at an oblique angle to each other, suggesting two distinct magnetic subfabrics. Surprisingly, 87% of our samples return a negative out-of-phase susceptibility, which is unexpected for ferromagnetic samples.

Magnetic characterisation experiments identify three magnetically distinct sample groups; A) relatively low coercivity, which we suggest represent a multi-domain (MD) dominated system, B) relatively high coercivity samples, which we interpret to have  a significant proportion of super-paramagnetic/single-domain (SPM/SD) magnetite as well as MD grains, and C) similar to B but with a smaller proportion of SPM/SD grains. Comparing ipAMS/opAMS Groups 1–3 to the magnetic characterisation Groups A–C, we find no consistent correlation between the rock’s magnetic mineralogy and the observed opAMS response. The difference in opAMS and ipAMS principal axes orientations therefore does not appear to be controlled by the varying proportion of MD or SPM/SD magnetite.

This result is surprising, as a correlation between ferromagnetic properties and opAMS is expected since opAMS is governed by ferromagnetic grains only. We propose three hypotheses which may explain our results; 1) there is an error in the way the data is processed using the standard software, causing negative susceptibility responses and apparent axes flipping, 2) SPM/SD magnetite may only carry an AMS signal in some of the samples, convoluting the interpretation of opAMS, or 3) viscous relaxation (caused by SPM/SD magnetite) may generate a much stronger opAMS response, resulting in a disproportionate influence on the opAMS signal whilst remaining masked in magnetic characterization experiments. Each hypothesis is assessed in our study and we recommend that further development is required before opAMS is routinely applied to petrofabric studies.

 

1Hrouda et al., 2017. GJI., 2Hrouda et al., 2020. PEPI., 3Koopmans et al., 2021. GEUS.

How to cite: Koopmans, L. and McCarthy, W.: Assessing the source of out-of-phase AMS in magnetite rich igneous rocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10591, https://doi.org/10.5194/egusphere-egu22-10591, 2022.

In this study, we have carried out a laboratory simulation of the low-temperature oxidation (below Tc) of titanomagnetite carrying a primary thermoremanent magnetization (TRM) created in Blab=25-50 µT. The initial material was natural basalt P72/4 from the Red Sea rift zone containing unoxidized (degree of oxidation Z =0) titanomagnetite with ulvöspinel content x=0.5 (Fe2.5Ti0.5O4).

Cubic basaltic samples containing titanomagnetite were annealed in air in weak field Ban=50-100μT at temperature Tan=260 Cfor maximum time t=1300 hours. One group of samples were annealed in the magnetic field perpendicular (Ban⊥TRM) and other parallel (Ban∥TRM) to the primary TRM. Thellier's-Coe double-heating method in argon atmosphere were conducted using all samples with different Z.

As for Ban∥TRM, the calculated field value (Bcalc) obtained from Thellier-Coe’s procedure coincided with the laboratory field (Blab) for all annealing times except t=1300 hours. This result indicates the applicability of the Thellier-Coe method of paleointensity determination on basalt containing titanomagnetite of low and medium degrees of oxidation (Z<0.5).

However, inadequate results were obtained from samples annealed in a magnetic field perpendicular to primary TRM(Ban⊥TRM). In this case, the calculated value of the Bcalc field for t=12 hours are overestimated by ~40%, and for t=400 and 1300 hours is underestimated by ~20% relative to the TRM creation field.

We conclude that reliability of paleointensity data of oxidized titanomagnetite depends on the direction between magnetic field and TRM during the oxidation process.

 
 
 

How to cite: Grachev, R.: The effect of magnetic field direction during the low-temperature oxidation of titanomagnetite bearing TRM on paleointensity determinations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12194, https://doi.org/10.5194/egusphere-egu22-12194, 2022.

EGU22-12396 | Presentations | EMRP3.2

Central and Southern Adriatic islands: tectonic implications of new paleomagnetic results 

Emö Márton, Vlasta Ćosović, Gábor Imre, and Máté Velki

The Central and Southern Adriatic islands, situated offshore of the Split-Dubrovnik segment of the mainland, belong to the External Dinarides. Their dominant tectonic trend is W-E, significantly different from the general Dinaric NW-SE orientation. For this reason, they are often regarded as belonging to a distinct tectonic unit, and sometimes a vertical axis counterclockwise (CCW) rotation is invoked to explain the deviation from the general tectonic trend.

In this paper, new paleomagnetic results are presented from Late Jurassic through Paleocene shallow water limestones from the Central and Southern Adriatic islands. For the localities sampled for paleomagnetic investigation, the sedimentological properties and the stratigraphic ages, based on the foraminifera population, were checked by microscopy investigation. The paleomagnetic analysis was carried out on field oriented drill cores, according to standard laboratory processing. The results were evaluated statistically on locality level. Overall-mean paleomagnetic directions were computed for several age groups and the age of the acquisition of the remanence was estimated from between-locality fold tests for a number of age groups. Comparison with earlier published results from the Northern Adriatic islands and from Stable Adria lead to the conclusion that the Central and Southern Adriatic islands had not rotate with respect to the Northern ones and even more importantly, stable Adria and the offshore External Dinarides must have moved as an integrated unit, at least from the Albian on.

This work was financially supported by the National Development and Innovation Office of Hungary project K 128625.

How to cite: Márton, E., Ćosović, V., Imre, G., and Velki, M.: Central and Southern Adriatic islands: tectonic implications of new paleomagnetic results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12396, https://doi.org/10.5194/egusphere-egu22-12396, 2022.

EGU22-12665 | Presentations | EMRP3.2

Analysis of S-C magmatic structures through magnetic fabric investigation at the Arroio do Silva Pluton, southernmost Brazil 

João Fontoura, Maria de Fátima Bitencourt, Jairo Savian, and Ricardo Trindade

The study of plutonic rocks is an important tool for unravelling the tectonic conditions of any area. The Arroio do Silva Pluton (ASP), in southernmost Brazil, comprises a syenite-monzonite-diorite association from Neoproterozoic post-collisional setting. Despite being well characterized with petrological and geochemical data, this association of rocks lacks a deeper understanding of its structural and geophysical aspects. ASP maps show four distinct neighbouring bodies, but concordant structural data suggest that they represent one single body in sub-surface. Regional structural analysis reveals a steeply-dipping, NW-striking magmatic foliation in three of the four ASP outcropping areas, with no indication of linear structure. Although foliation demonstrates a constant structural pattern for most areas on a regional scale, variations of the planar fabric are also observed, indicating a more complex internal geometry for the pluton. Anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM) are largely used in Earth Sciences to determine the magnetic fabric consistent with the macroscopic foliation and lineation. This work presents the results of AMS and AARM studies in a key outcrop of the ASP, aiming to compare structural and magnetic fabrics. The structures along the approximately 140m-long section were interpreted as a magmatic S-C pair. Heterogeneous progressive shearing along the NW-striking subvertical C-foliation leads to alternate zones where the S-foliation is intact and zones where it is progressively displaced. When not affected by C-planes, the S-foliation is sub-horizontal and marked by aligned 010 faces of K-feldspar. A total of 124 specimens (36 drills) were obtained from 7 sites distributed along the outcrop, located in one of the ASP central bodies. A magnetic mineralogy investigation was conducted by hysteresis loops, thermomagnetic and IRM acquisition curves. Magnetic susceptibility ranges from 0.4 to 13.3 x 10-3 SI. Shape parameter (T) ranges from -0.581 to 0.473, and anisotropy degree (P) ranges from 1.055 to 1.107. As positive values of T (triaxial/oblate) are associated with the sub-horizontal foliation, and negative values (triaxial/prolate) with foliation interpreted as C-planes, the structural interpretation of zones where shearing was not effective preserving foliation S is coherent when compared to the AMS scalar data. No solid-state deformation is observed in ASP, so P values are not expected to vary significantly. Hysteresis loops, thermomagnetic and IRM curves point to magnetite as the main magnetic carrier. Magnetic and magmatic foliations are predominantly concordant, with minor variations. Magnetic lineation plunges at shallow angles in both structures. In the portions where sub-horizontal foliation is dominant, lineation plunges NW, while in the regions where shear was effective, magnetic lineation plunges NNW-N. This leads to the interpretation of dextral kinematics. The field structural data, together with magnetic data, indicate that the ASP registers a local transcurrent dextral shearing in the magmatic stage. From the observation of similar magnetic mineralogy between the structures, together with the absence of solid-state deformation, it is proposed that the ASP records a late stage of the transpressive event, as described for older units of this area.

How to cite: Fontoura, J., Bitencourt, M. D. F., Savian, J., and Trindade, R.: Analysis of S-C magmatic structures through magnetic fabric investigation at the Arroio do Silva Pluton, southernmost Brazil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12665, https://doi.org/10.5194/egusphere-egu22-12665, 2022.

EGU22-13488 | Presentations | EMRP3.2

Ferromagnetism of magnetite-bearing plagioclase from oceanic gabbro 

Olga Ageeva, Stuart Gilder, Gerlinde Habler, and Rainer Abart

Oriented needle shaped magnetite inclusions in plagioclase may give rise to magnetic anisotropy of individual plagioclase grains and, in case of preferred orientation of the plagioclase grains, contribute to magnetic anisotropy of the bulk-rock. Understanding how oriented magnetite inclusions generate magnetic fabrics in single grains of plagioclase is important for interpreting rock magnetic fabrics and for correcting paleomagnetic data. Plagioclase grains from oceanic gabbro dredged at the Mid Atlantic Ridge (11-17°N) were analyzed using optical microscopy, electron backscatter diffraction (EBSD), as well as alternating field demagnetization and anisotropy of magnetic remanence (AMR) measurements to investigate the influence of the shape orientation distribution of acicular magnetite inclusions on the magnetic properties of magnetite bearing plagioclase grains.

In pristine magmatic plagioclase, the needle elongation directions form a 30° wide girdle distribution parallel to the pl(010) plane. This girdle distribution is insensitive to twinning after the Albite, Pericline, Carlsbad and Manebach laws. The statistical maximum in the inclusion orientation lays in the pl(010) plane, closely parallel to the pl[001] direction. The overall shape orientation distribution of the magnetite inclusions produces a triaxial magnetic anisotropy ellipsoid with the minimum axis direction sub-perpendicular to the pl(010) plane and the maximum axis sub-parallel to the pl[001] direction.

The vector of natural remanent magnetization parallels the maximum AMR axis direction indicating that the magnetic anisotropy caused by the magnetite inclusion fabric controls the paleomagnetic signature. In hydrothermally modified plagioclase, most or all magnetite needles are oriented parallel to the pl[001] direction and a prolate rotational ellipsoid of remanent magnetization with the maximum remanent magnetization parallel to pl[001] should occur.

Plagioclase-hosted magnetite inclusions are particularly stable recorders of the paleomagnetic filed. The magnetic anisotropy arising from the anisotropic shape orientation distribution of the magnetite inclusions may, however, bias the magnetic record, an effect that needs to be accounted for in paleomagnetic reconstructions or for absolute paleointensity experiments.

This work was supported by the Austrian Science Fund (FWF): I 3998-N29, and by the Russian Foundation for Basic Research, Grant no. 18-55-14003.

How to cite: Ageeva, O., Gilder, S., Habler, G., and Abart, R.: Ferromagnetism of magnetite-bearing plagioclase from oceanic gabbro, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13488, https://doi.org/10.5194/egusphere-egu22-13488, 2022.

EGU22-2670 | Presentations | EMRP3.3

Record of Geomagnetic Instabilities during the Brunhes: preliminary results from IODP Expeditions 384 and 395C from North Atlantic Ocean 

Anita Di Chiara, Sara Satolli, Sarah Friedman, and Science Party Expedition 395 Science Party

Throughout its history, the Earth’s magnetic field has undergone changes in its polarity. These changes vary in scale, from millennial (excursions) to hundreds of thousands or millions of years (reversal). Constraining the chronology of these geomagnetic instabilities is fundamental to understanding Earth’s dynamo processes and their surface expressions. Moreover, a detailed geomagnetic instability time scale (GITS) refines its applicability as an accurate correlation and dating tool (magnetostratigraphy) for sedimentary and volcanic sequences and it is fundamental to understanding several aspects of past climate. Indeed, periods of geomagnetic instability are usually associated with a weak field. This in turn weakens the efficiency of the Earth’s magnetic field shielding enhancing the production of cosmogenic isotopes which play a significant role on modulating climate by either directly or indirectly influencing factors such as the total or spectral solar irradiance. In this study, we present a preliminary record of geomagnetic instabilities during the Brunhes (0-0.778 Ma), based on intercorrelation of paleomagnetic data from five marine sedimentary cores collected during the IODP Expeditions 384 and 395C from the North Atlantic Ocean along the Reykjanes ridge. Two of the drilling sites are nearby the ODP Sites 983 and 984 (Channell et al., 2002) providing an opportunity to cross correlate our preliminary results.

How to cite: Di Chiara, A., Satolli, S., Friedman, S., and Expedition 395 Science Party, S. P.: Record of Geomagnetic Instabilities during the Brunhes: preliminary results from IODP Expeditions 384 and 395C from North Atlantic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2670, https://doi.org/10.5194/egusphere-egu22-2670, 2022.

EGU22-4682 | Presentations | EMRP3.3

A detailed Middle and Late Pleistocene cyclostratigraphic record using rock magnetism and palaeosol proxies in the Middle Dnieper basin loess domain 

Dmytro Hlavatskyi, Natalia Gerasimenko, Volodymyr Bakhmutov, William Wimbledon, Oleksandr Bonchkovskyi, Semyon Cherkes, Illia Kravchuk, Ievgen Poliachenko, and Viktor Shpyra

A combined pedostratigraphic and rock magnetic study of four loess-palaeosol sequences in the Middle Dnieper area, Ukraine (at Gunky, Zamozhne, Vyazivok and Stari Kaydaky) have been performed in order to determine the suitability of these sites for rock magnetic cyclostratigraphy and the establishment of magnetostratigraphic markers. Two geomagnetic events – the Matuyama/Brunhes boundary (at 780 ka) and Unnamed excursion (at 430 ka) – have been detected at the long Vyazivok loess-paleosol record (Hlavatskyi et al., 2016; Hlavatskyi and Bakhmutov, 2020). The till of the Dnipro glaciation (MIS 6) and the corresponding thick loess (U-L2), present in all sections, and faunal remains at the Gunky section, typical for MIS 11 (Markova, 2004), serve as reliable age benchmarks for developing a comprehensive cyclostratigraphic model. The studied sections are most similar by their rock magnetic and palaepedological characteristics to the Hungarian loess-palaeosol sequences (Udvari-U2 and Paks), which are also located in the temperate climatic zone. These sections can be related to the «Chinese» type of formation of magnetic properties, with very low magnetic susceptibility values in loesses and higher values in palaeosols. However, the magnetic susceptibility pattern in palaeosols of northern Ukraine is distorted by the later cryoturbation and gleying processes of the subsequent cold phases. In contrast to the Chinese, Danube and southern Ukrainian loess sequences, these sites are characterized by much lower concentration of ferrimagnetic material, especially in the Lubny (U-S5, correlative of MIS 13) and Potyagaylivka (U-S2/MIS 7) palaeosols. The highest magnetic enhancement is characteristic for the Lower Zavadivka (U-S4/MIS 11), Upper Zavadivka (U-S3/MIS 9) and, in part, the Pryluky­-Kaydaky (U-S1/MIS 5) pedocomplexes. Rock magnetic investigations show predominance of pseudo-single domain magnetite in palaeosols and higher proportion of hematite in loesses. It is suggested that wet conditions in northern Ukraine, which periodically appeared due to its closeness to the ancient ice fronts, facilitated the oxidation of ferrimagnetic grains and the formation of high coercive minerals.

Acknowledgements. The research was supported by the National Research Foundation of Ukraine grant 2020.02/0406 "Magnetic proxies of palaeoclimatic changes in the loess-palaeosol sequences of Ukraine".

References:

Hlavatskyi D.V., Kuzina D.M., Gerasimenko N.P., Bakhmutov V.G. 2016. Petromagnetism and palaeomagnetism of Quaternary loess-soil sediments of Vyazivok section (Dnieper Lowland). Geofizicheskii Zhurnal (Geophysical Journal), 38 (6). 186-193. http://dx.doi.org/10.24028/gzh.0203-3100.v38i6.2016.91903

Hlavatskyi D.V., Bakhmutov V.G. 2020. Magnetostratigraphy and magnetic susceptibility of the best developed Pleistocene loess-palaeosol sequences of Ukraine: implications for correlation and proposed chronostratigraphic models. Geological Quarterly, 64 (3). 723–753. http://dx.doi.org/10.7306/gq.1544

Markova, A.K. 2004. A reconstruction of the Lichvin interglacial paleolandscape based on material of small mammals from East Europe. Izvestia RAS, Ser. Geography, 2. 35–59. (in Rus.)

How to cite: Hlavatskyi, D., Gerasimenko, N., Bakhmutov, V., Wimbledon, W., Bonchkovskyi, O., Cherkes, S., Kravchuk, I., Poliachenko, I., and Shpyra, V.: A detailed Middle and Late Pleistocene cyclostratigraphic record using rock magnetism and palaeosol proxies in the Middle Dnieper basin loess domain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4682, https://doi.org/10.5194/egusphere-egu22-4682, 2022.

EGU22-6011 | Presentations | EMRP3.3

Late Cretaceous true polar oscillation artifact: further evidence for Earth’s long-term rotational stability 

Rory Cottrell, John Tarduno, and Richard Bono

Determining Earth’s stability with respect to the spin axis sets boundary conditions for understanding the planet’s deep mantle and interpreting records of past climate. Analyses of global paleomagnetic data sets have suggested very limited polar wander since the Mid-Cretaceous (Cottrell and Tarduno, 2000; Tarduno and Smirnov, 2001). However, this conclusion has been challenged by calls for a Late Cretaceous true polar oscillation whereby the entire solid Earth rotated by 12 degrees, and then rotated back, 86 to 78 million years ago (Mitchell et al., 2021). This posit is based on paleomagnetic data from a dense sampling (approximately 1000 limestone samples) and automated magnetic measurements yielding data from magnetic polarity chrons 34 to 32n in the Italian Apennines. Herein, we analyze these data and find that the oscillation signal across magnetic chrons polarity 33r to 33n exceeds the maximum speed constrained by mantle viscosity (2.4 degrees/myr; Tsai and Stevenson, 2007) and is thus physically implausible. When considered in the light of prior paleomagnetic and rock magnetic studies on these rocks, the data point to an unrecognized overprint magnetization carried by authigenic hematite. This overprint has a differential angular effect on the normal and reversed polarity primary remanences, creating biased magnetic directions and attendant false polar wander. This artifact serves as a cautionary tale with respect to paleomagnetic analyses, but also further highlights the remarkable stability of Earth relative to the axis since at least the mid-Cretaceous which sets the planet apart from smaller planetary bodies which may have experienced polar wander. Principal differences are that external forces since the lunar forming impact are too small to drive such motion, and Earth’s mantle viscosity structure which dampens any potential motion driven by changes in its mass heterogeneities.

How to cite: Cottrell, R., Tarduno, J., and Bono, R.: Late Cretaceous true polar oscillation artifact: further evidence for Earth’s long-term rotational stability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6011, https://doi.org/10.5194/egusphere-egu22-6011, 2022.

The Izu-Bonin-Mariana (IBM) subduction system is a key natural laboratory providing fundamental insights into subduction dynamics and the evolution of associated upper plate magmatism. To investigate the processes associated with subduction initiation and the subsequent evolution of the Philippine Sea plate, International Ocean Discovery Program (IODP) Expedition 351 recovered a complete sedimentary sequence and the top of the underlying volcanic basement at Site U1438 located in a rear-arc position. This offers a unique opportunity to study for the first time and in extreme detail the styles, products, and timing of the volcanic events that marked the emplacement, growth, and demise of the Kyushu-Palau volcanic arc within the IBM system. Here we report a magnetostratigraphy for Site U1438 based on ~60,000 remanence directions isolated from 1063 archive half-core sections and 429 discrete specimens. This identified 112 well-constrained magnetic reversals that may be correlated with the geomagnetic polarity timescale. When combined with additional biostratigraphic and geochronological constraints, this allows construction of a high-resolution age model for Site U1438 and the determination of changes in sedimentation rates during the evolution of the Kyushu-Palau arc. These age constraints show that following subduction initiation at ~52 Ma, diffuse volcanism in both the forearc and rear-arc preceded the initial emplacement of the Kyushu-Palau arc at 44.2 Ma, which then grew through four compositionally distinct eruptive phases until 29.2 Ma. Rollback of the Pacific slab then triggered rifting of the arc (29.2-24.3 Ma), leading to back-arc spreading in the Shikoku and Parece-Vela basins.

How to cite: Maffione, M. and Morris, A.: Timing of Tectonic and Magmatic Events in the Philippine Sea Plate since 50 Ma from High-Resolution Magnetostratigraphy of IODP Site U1438, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8684, https://doi.org/10.5194/egusphere-egu22-8684, 2022.

The question of the total duration of the Siberian Traps magmatic activity in the Siberian platform and its correlation with the Permian-Triassic boundary is still being contentious, remaining essential for a number of studies, especially for the possible links with the end-Permian global biotic crisis.

The aim of this work was to obtain for the first representative and reliable paleomagnetic data on the section of the Samoedsky Formation using the modern instrumental base of paleomagnetic studies to estimate the magmatic activity duration. The Samoedsky Formation lies at the top of the Permian-Triassic volcanic section of the Norilsk region. The major part of the Norilsk tuff-lava pile, except for the lowermost Ivakinsky Formation, corresponds to the normal magnetic polarity interval [1]. Although the paleomagnetic investigation of the Samoedsky Formation basalts was performed previously [1, 2], this interval still remains complicated and the issue of its relation to the normal or reverse polarity interval has not been resolved.

During the field work oriented samples were taken (233 samples from 11 sites) from the lava flows of the Samoedsky Formation in the Verkhnyaya Talovaya river valley (the Norilsk region). At the laboratory stage alternating field and thermal demagnetization were carried out using SQUID SRM, JR-6 (AGICO) magnetometers and MMTD80 thermal furnace.

Based on the results of calculations with the Enkin software package [3], it can be concluded that the three uppermost lava flows of the Samoedsky Formation are magnetized in reversed polarity, which confirms the latest data [1]. Other studied flows demonstrate the normal polarity. Thus, the emplacement of the Samoedsky Formation and consequently the entire lava sequence of the Norilsk region corresponds not only to the LT1n1n chron (the first normal polarity chron of the Lower Triassic), but also to the part of the reverse polarity chron LT1n1r [1], which also affects the correlation of the sections of the Siberian Traps LIP different regions.

References

1. Latyshev A.V., Fetisova A.M., Veselovskiy R.V. Linking Siberian Traps LIP Emplacement and End-Permian Mass Extinction: Evidence from Magnetic Stratigraphy of the Maymecha-Kotuy Volcanic Section // Geosciences. 2020. V. 10. № 8. P. 295.

2. Gurevitch, E.L., Heunemann, C., Rad’ko, V., Westphal, M., Bachtadse, V., Pozzi, J.P., Feinberg, H. Palaeomagnetism and magnetostratigraphy of the Permian-Triassic northwest central Siberian Trap Basalts // Tectonophysics. 2004. V.379. P. 211–226.

3. Enkin R.J. A computer program package for analysis and presentation of paleomagnetic data. Pacific Geoscience Centre, Geol. Surv. Can., 1994. P. 16.

 

How to cite: Latanova, E. and Latyshev, A.: Magnetic stratigraphy of the Samoedsky Formation, the upper part of the Siberian Traps LIP section in the Norilsk region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10447, https://doi.org/10.5194/egusphere-egu22-10447, 2022.

The Eastern Paratethys is a former epicontinental sea that in the Late Miocene was spread over the vast areas of Eastern Europe and Central Asia. Combining three major subbasins – The Dacian (Carpathian foreland), the Euxinian (Black Sea) and the Caspian basins, the Eastern Paratethys played a vital role in the regional climate, paleobiogeography and ecosystem sustainability. At around 11.6 Ma the Eastern Paratethys became hydrologically isolated from the global ocean due to the tectonic closure of its gateways. For the next 5.5 Ma (up until 6.1 Ma), the Eastern Paratethys turned into a megalake that was trapped in the Eurasian interior. Warming and drying of the climate during so-called Sarmatian Stage (12.65-7.65 Ma) disbalanced precipitation/evaporation ratio in the megalake and thus provoking extreme water-level fluctuation of several hundred meters. Subsequent changes in the water chemistry and temperatures drove the regional ecosystems to the edge of extinction.

The paleoenvironmental evolution of the Eastern Paratethys has been mainly inferred from geological record of the Black Sea and partly Dacian Basin. At the same time, reconstruction and dating of Sarmatian hydrological and faunal changes for the Caspian region remains uncomprehended.

Here, we present our new magnetostratigraphic data on Sarmatian record from the Caspian region (Karagiya Depression, Kazakhstan) and compare it with the data from the other Eastern Paratethys subbasins (the Dacian and Euxinian Basins). Sedimentological observations together with magnetostratigraphic constraints indicate incompleteness of the lower (Volynian) and upper Sarmatian (Khersonian) deposits in the studied section. The middle (Bessarabian) and upper Sarmatian (Khersonian) s.l. begin as transgression events within reversed zones preliminary correlated to C5r.2r (11.188 – 11.592 Ma) and to C4Ar.2r (9.426 - 9.647 Ma) respectively. Sarmatian deposits are transgressively overlain by Maeotian deposits with the boundary occurring within a small reversed chron preliminary correlated to C3Br.3r (7.499 – 7.537 Ma).

The newly acquired polarity patterns suggest that the major Sarmatian paleohydrological events in the Caspian segment were coherent with the other parts of the Eastern Paratethys. However, the complexity of polarity patterns and highly condensed character of the section require further refinement of magnetostratigraphic age constraints.

 

How to cite: Lazarev, S., Krijgsman, W., and Vasilyan, D.: On the age and expression of extreme Sarmatian hydrological changes of the Eastern Paratethys in the Caspian Basin (Late Miocene, Kazakhstan)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11020, https://doi.org/10.5194/egusphere-egu22-11020, 2022.

EGU22-12603 | Presentations | EMRP3.3

Magneto-biostratigraphic succession of the Jaca Basin (Southern Pyrenees, Spain): insights on the Middle Eocene Climatic Optimum. 

Oriol Oms, Hug Blanchar, Jaume Dinarès-Turell, Jordi Ibañez-Insa, Joaquim Verdaguer, Alba González-Lanchas, Alejandro Gil-Delgado, José-Abel Flores, and Eduard Remacha

Magnetostratigraphy is a basic method to provide age constrains when trying to identify paleonvirmental changes in sedimentary successions. This is particularly important in the case of the Middle Eocene Climatic Optimum (MECO), which is a climatic perturbation not exactly coincident with a biostratigraphic boundary and having a peak Ca 40.2 Ma. We introduce the Jaca basin record (Southern Pyrenees) where expanded sedimentary successions record several Eocene climatic episodes. Combined magneto-biostratigraphic dating of these successions is carried out in the Hecho Group (deep clastic systems) and in its vertical successions to the Sabiñánigo and Belsué-Atarés deltaic systems.

New magnetostratigraphic data permit the identification of paleopolarities on the basis of stable demagnetization results from the marls of the deltaic successions. Counting of 32 species of calcareous nanoplankton for biostratigraphic purposes has permitted to identify several biozones throughout the basin. With respect to the MECO, the CNE14/15 biozones boundary has been clearly identified, which is close to c18r/c18n reversal.

A multiproxy study is carried out including mineralogical, elemental and isotopic data from X-ray diffraction, X-ray fluorescence and bulk rock C/O stable isotopes, with the aim to achieve a paleoenvironmental proxy permitting the identification of the MECO.  Ultimately, the integrated chronostratigraphic and multiproxy characterization of the studied sections will permit to understand how deltaic systems reacted the MECO climatic event.

How to cite: Oms, O., Blanchar, H., Dinarès-Turell, J., Ibañez-Insa, J., Verdaguer, J., González-Lanchas, A., Gil-Delgado, A., Flores, J.-A., and Remacha, E.: Magneto-biostratigraphic succession of the Jaca Basin (Southern Pyrenees, Spain): insights on the Middle Eocene Climatic Optimum., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12603, https://doi.org/10.5194/egusphere-egu22-12603, 2022.

Volcanic rocks are believed to be reliable recorders of changes in the Earths magnetic field in the past. Paleomagnetic data from volcanic edifices is used to make reconstructions of the behavior of the Earth’s magnetic field through time. Recently, however, it became evident that volcanic rocks may not always record the ambient magnetic field accurately. Therefore, we set out to test the accuracy of paleomagnetic data recorded by Mt. Etna lavas by (1) directly measuring the magnetic field above the current topography, i.e. the field that would be recorded by a future flow in that location; and (2) by assessing the paleomagnetic information in historical (1850 – today) flows.

Mt. Etna is characterized by an irregular topography with ridges and gullies that may give rise to local magnetic anomalies that a new flow would record. We measured the ambient geomagnetic field on Mt. Etna with a three-component fluxgate magnetometer at five sites along the length of three paths with an irregular surface. Paths were walked perpendicular to ridges and gullies and measurements were made every meter at different heights above the ground. We found that the declination varies between -17.5 and 18°, and on average differs -3.3° from the expected geomagnetic field. The inclination has a range between 44.4 and 59.5° and is on average 52.3°, while 53.4° is expected. Lastly, the intensity varies between 37.2 and 50.4 µT and is on average 44 µT, with an expected value of 45.2 µT. The deviation with respect to the expected value decreases as function of height above the flow for the inclination and intensity, while the variation in declination does not improve. Most importantly, the variations in inclination and intensity correlate with topographic features: both inclination and intensity are higher above ridges and lower in gullies.

The second part of our study consisted of compiling an overview of literature data on historical Mt. Etna flows and combining this with newly measured paleomagnetic data from 12 sites from 9 different flows with ages between 1865 and 2002. We observed the same trends in this data compilation as in our field observations: the reported inclinations and intensities are often too low.

Our observations have consequences for paleomagnetic sampling strategies in rugged volcanic terrain. To avoid sampling a local magnetic anomaly, samples should be taken spread out over a larger area, preferably meters apart and from different parts of the flow. While this will lead to a higher degree in scatter in paleodirections and a lower precision parameter k, they will better represent the Earth’s magnetic field at the time of cooling. Paleodirections with a high k or paleointensities with a low uncertainty most likely sample a local magnetic anomaly arising from the underlying terrain.

How to cite: Meyer, R. and de Groot, L.: Local magnetic anomalies in rugged volcanic terrain explain bias in paleomagnetic data: consequences for sampling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1227, https://doi.org/10.5194/egusphere-egu22-1227, 2022.

EGU22-1499 | Presentations | EMRP3.4

Paleomagnetism of Middle Devonian pillow lavas from Germany 

Rosa A. de Boer, Annique van der Boon, Peter Königshof, and Lennart V. de Groot

For decades, scientists have tried to obtain paleomagnetic data from Devonian rocks, but acquiring accurate data from this time period remains problematic. The lack of data has traditionally been interpreted as caused by overprinting during the Kiaman reverse superchron, but recent studies have suggested that the field could have had a non-dipolar configuration. Either way, overprinting is a common problem, although an overprinting mechanism is sometimes lacking. In other cases, data is not interpretable due to large scatter, and a clear explanation has not been found to date.

The lack of paleomagnetic data from the Devonian significantly hampers the fundamental understanding of long-term (>100 Myr) magnetic field behaviour and the creation of geodynamo models. However, paleointensities can sometimes be successfully determined, and show that the field was weak to extremely weak during the Late Devonian, with values similar to the Ediacaran.

To further constrain the onset of the weak field period, we sampled a succession of Middle Devonian pillow lavas that outcrop in the Philippstein Quarry near Braunfels, Germany. These lavas are subject to some faulting, but are fresh looking and consist of unaltered, unmetamorphosed igneous rock. Pillow lavas cool quickly, which leads to stable magnetic behavior, making them well-suited for magnetic analyses.

Here we present our results of traditional paleomagnetic analyses to determine the direction and intensity of the Devonian paleomagnetic field.

How to cite: de Boer, R. A., van der Boon, A., Königshof, P., and de Groot, L. V.: Paleomagnetism of Middle Devonian pillow lavas from Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1499, https://doi.org/10.5194/egusphere-egu22-1499, 2022.

EGU22-1812 | Presentations | EMRP3.4

New spherical harmonic global geomagnetic field models for the Matuyama-Brunhes reversal 

Ahmed Nasser Mahgoub, Monika Korte, and Sanja Panovska

The geomagnetic field is created by the motion of molten iron inside the liquid outer core of the Earth. It has undergone a number of drastic changes over geological time, the most notable of which are field reversals, in which the magnetic north and south poles change locations. Because sediments can retain information about past magnetic field directional and intensity changes through depositional or post-depositional remanent magnetization acquisition mechanisms, oceanic sediment cores can be used to track reversals. Lavas also document reversals by spot readings of thermal remanent magnetization. The Matuyama-Brunhes reversal (MBR) was the last time the Earth’s poles reversed, and it is documented by the largest number of sediment records compared to earlier reversals. Investigating the MBR globally therefore can help to understand the physical processes that occur in the Earth’s core. A few global spherical harmonic (SH) models have previously been proposed for the MBR. However, the number, distribution, and timescale reliability of the input data are limitations of these models, the last one of which has been published more than 10 years ago. In this study, we take advantage of new sediments and lava data for the MBR that have been published since these models were developed, and often have better age control and higher temporal resolution than data used in previous SH models. Smoothing splines were used to examine the temporal resolution of all sediment records in our new global compilation, and the results show a median smoothing time of 350 years (±200 years). We present a new global SH geomagnetic field model for the MBR, constructed from 67 sediment cores and 93 lava sites that span the last 900-700 ka and have a reasonable geographical distribution. In addition, we investigate the robustness of model features by deriving models from sub-sets of data, e.g., using only well-dated, high-resolution sediment data that are consistent with surrounding records (if any exist). The model’s featured will be discussed, including (1) field morphology at the CMB and at the Earth’s surface; (2) axial dipole (AD) and non-axial dipole (NAD) power at the CMB; and (3) magnetic energy of AD and NAD fields at the Earth’s surface. Furthermore, we will compare the current models to the previous MBR models.

How to cite: Mahgoub, A. N., Korte, M., and Panovska, S.: New spherical harmonic global geomagnetic field models for the Matuyama-Brunhes reversal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1812, https://doi.org/10.5194/egusphere-egu22-1812, 2022.

EGU22-2185 | Presentations | EMRP3.4

Micromagnetic modeling of a magnetic unstable zone and its geological significances 

Yuqin Wang, Kunpeng Ge, and Wyn Williams

Abstract

Recent micromagnetic simulations have found that particles in the size region of the single domain (SD) to single vortex (SV) transition zone are prone to poor thermal and field stabilities that could adversely affect the accuracy of interpretations of paleomagnetic recordings. In this study, we attempt to evaluate the internal magnetization characteristics of these magnetically unstable (MU) particles and the influence on paleomagnetic observations by simulating the magnetic behaviour of 68-104 nm truncated octahedral magnetite particles via the MERRILL modelling software. We found that: (i) The size region of the "MU zone" for grains of cubic octahedral shape is different with cubic octahedrons and spheres, indicating the zone may be controlled by the geometry and shape of particles; (ii) The MU zone has a range of 79-91 nm region, which is dominated by a hard-axis aligned single vortex (HSV); (iii) MU particles are unstable as a function of temperature. Finally, the numerical fitting of hysteresis parameters for experimental data suggests that the influence of such MU particles in samples cannot be ignored, especially for samples with fine-grained magnetic minerals as the primary magnetic recording carriers. This research has extended our understanding of the behaviour of the "MU zone" and its significance on paleomagnetic records.

 

How to cite: Wang, Y., Ge, K., and Williams, W.: Micromagnetic modeling of a magnetic unstable zone and its geological significances, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2185, https://doi.org/10.5194/egusphere-egu22-2185, 2022.

EGU22-3175 | Presentations | EMRP3.4

Paleomagnetism of the Glen Mountains Layered Complex: Dipolar field behavior at ~530 Ma 

Kenneth Kodama, Frank Tetto, and John Tarduno

Results from the Sept-Îles intrusive suite suggest that the Earth’s magnetic field reached ultra-low intensities at 565 Ma (~3 μT, Bono et al., 2019) during the Ediacaran Period. Additional evidence from this study suggests abnormally high paleosecular variation (S= ~26˚). Other studies of Ediacaran rocks indicate very high reversal frequencies. Based on this abnormal geomagnetic field behavior, Bono et al. (2019) suggested inner core nucleation at about 565 Ma. Therefore, we conducted a detailed paleomagnetic study of the early Cambrian (206Pb/238U age of 532.49±0.12 Ma, Wall et al., 2020) Glen Mountains Layered Complex (GMLC) of southwestern Oklahoma to assess behavior of the geomagnetic field 30 myr later. One hundred ninety independently oriented cores were drilled from 17 sites collected from the anorthosites of the GMLC. Primary paleomagnetic directions were isolated by thermal and alternating field demagnetization. Magnetic susceptibility versus temperature and isothermal remanence acquisition experiments both indicate that low-Ti magnetite is the dominant remanence carrier, although minor pyrrhotite is seen in some samples. Nearly antipodal directions, collected from different sites, pass a simple reversals test, confirming that geomagnetic field polarity reversals are recorded (Roggenthen et al., 1981) and that the GMLC anorthosites carry a primary remanence. Paleosecular variation recorded by the GMLC (S=10.9˚) for a paleolatitude of 10.3˚ is in agreement with Smirnov et al.’s (2011) tabulation of paleosecular variation for 1.0-2.2 Ga intrusive and extrusive igneous rocks. A reversed polarity paleopole for the complex is located at 26.1°E, 25.3 °N (A95 = 7.4°). Our results suggest that the geomagnetic field returned to stable, dipole-dominated behavior by about 530 Ma.

Bono, et al. (2019). Nature Geoscience, 12(2), 143-147.

Smirnov, et al. (2011). PEPI, 187(3-4), 225-231.

Roggenthen et al., (1981) GRL, 8, 133-136.

Wall et al. 2020, Geology, 49, 268-272.

How to cite: Kodama, K., Tetto, F., and Tarduno, J.: Paleomagnetism of the Glen Mountains Layered Complex: Dipolar field behavior at ~530 Ma, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3175, https://doi.org/10.5194/egusphere-egu22-3175, 2022.

EGU22-4123 | Presentations | EMRP3.4

Characterising the Triassic Palaeomagnetic Field with an Aim to Investigate the Mesozoic Dipole Low. 

Ben Handford, Andy Biggin, Augusto Rapalini, Marcela Haldan, Cor Langereis, Mariana Monti, Mónica López de Luchi, Annique van der Boon, Pablo Franceschinis, and Banusha Kugabalan

Palaeomagnetic field behaviour within the Triassic is relatively poorly documented in comparison with other periods from across the last ca 250 Ma. Developing a more complete understanding of the Triassic field has important implications for discussion surrounding the Mesozoic Dipole Low (MDL) and the processes that govern field intensity and reversal regimes. We have conducted the first palaeosecular variation study that incorporates Triassic virtual geomagnetic pole (VGP) data, and analysed this data within the context of the average reversal frequency for the period. We observed remarkably similar VGP dispersion patterns from the late Permian, after the Permo-Carboniferous Reversed Superchron, until the onset of the Cretaceous Normal Superchron, despite fluctuating mean reversal rates. We have also completed palaeointensity experiments on samples with a range of lithologies collected from two localities in Argentina as well as pillow basalts from northern Italy. Previously published radiometric ages place our sampled lithologies across all three Triassic epochs, presenting an opportunity to populate the palaeointensity record at multiple ages across the ~50 Ma lacuna. Results were obtained utilizing a range of methods, the IZZI+ thermal Thellier, Shaw, and pseudo-Thellier. Estimates of virtual dipole moment from these experiments will be presented and discussed in the context of their reliability, and importance in better defining the MDL.

How to cite: Handford, B., Biggin, A., Rapalini, A., Haldan, M., Langereis, C., Monti, M., López de Luchi, M., van der Boon, A., Franceschinis, P., and Kugabalan, B.: Characterising the Triassic Palaeomagnetic Field with an Aim to Investigate the Mesozoic Dipole Low., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4123, https://doi.org/10.5194/egusphere-egu22-4123, 2022.

EGU22-4779 | Presentations | EMRP3.4

Palaeosecular variation in the Miocene and the first non-zonal time-averaged field model of that era. 

Yael Engbers, Richard Bono, Richard Holme, and Andy Biggin

Reconstructions of the geomagnetic field behaviour over long periods of time throughout history are important for understanding of geomagnetic field evolution and documenting the longevity of certain features. Statistical studies of palaeosecular variation inform us regarding the structure and behaviour of the geomagnetic field. Here we present a new data compilation, PSVM, of high-quality directional data from the Miocene era (5.3 – 23 Ma). Our compilation comprises 1454 sites from 44 different localities, each with at least 10 sites. We use this database to calculate new Model G parameters for PSVM with varying selection criteria. Our preferred database, , has the selection criteria of n ≥ 5, k ≥ 50, a Vandamme cutoff applied and at least 2 reversals shown within the 10 or more sites of a locality. This produced a Model G fit with a parameter of 15.7° (13.0° - 18.7°). This value is substantially higher than any of the Model G a parameters published for the past 10 Myrs or any other studied era, implying a less stable geomagnetic field in the Miocene. PSVM also enables the creation of the first non-zonal time-averaged field (TAF) models of the Miocene, called MTAM1. After separating our data into normal (PSVMN) and reversed (PSVMR) datasets, separate models for the two states were created. No substantial differences were found between the models (MTAM1N and MTAM1R, respectively), suggesting symmetry in the morphology of the magnetic field in the Miocene. There is no evidence for a previously hypothesised "memory" of the field after a reversal for this era. Instead, non-dipole structure appears to reverse simultaneously with the dipolar structures. After observing this symmetry, we compute a TAF model for the complete Miocene dataset (PSVM), enhancing the data distribution and thus the robustness of the model. In all versions of the models, a reverse flux patch (RFP) is seen under the South Atlantic. Our findings suggest a more variable magnetic field in the Miocene era compared to the past 10 Myrs, implying that the geodynamo was driven by a more strongly convecting liquid core producing a less dipole dominated field on average. In addition, we found a recurring RFP under the South Atlantic that was sufficiently frequent and stationary to appear in a TAF model, giving evidence for a recurring or consistent anomalous feature in the South Atlantic region in the Miocene, with longevity on a multi-million-year timescale.

How to cite: Engbers, Y., Bono, R., Holme, R., and Biggin, A.: Palaeosecular variation in the Miocene and the first non-zonal time-averaged field model of that era., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4779, https://doi.org/10.5194/egusphere-egu22-4779, 2022.

EGU22-4862 | Presentations | EMRP3.4

High-resolution inclination records from Sites U1418 and U1419 in the Gulf of Alaska (IODP Expedition 341) 

Julie Heggdal Velle, Maureen Walczak, Brendan Reilly, Guillaume St-Onge, Joseph Stoner, Stewart Fallon, Alan Mix, Christina Belanger, and Matthias Forwick

International Ocean Drilling Program (IODP) Expedition 341 in the Gulf of Alaska recovered a 112-meter-long sedimentary record from the continental slope at Site U1419. At this site, an exceptionally expanded late Pleistocene sequence (sedimentation rates >100 cm/kyr) combined with a high-resolution radiocarbon chronology (Walczak et al., 2020), provide an opportunity to study Paleomagnetic Secular Variations (PSV) on centennial to millennial timescales over the past ~43,000 years.
Natural and laboratory-induced magnetic remanence were measured on u-channels using the stepwise AF demagnetization procedure. In addition to continuous magnetic susceptibility measurements, hysteresis parameters were obtained on 95 discrete samples, and IRM acquisition curves on 9 discrete samples to obtain additional information on the magnetic mineralogy of the sediment. Due to the influence of lithology, magnetic mineralogy, depositional and post-depositional processes, Site U1419 is not suitable for paleointensity studies. However, with removal of intervals influenced by the environmental signal and/or coring deformation, the high sedimentation rates at this site have helped to preserve a reliable record of inclination. Because of signal to noise issues, inclination as measured after the 20 mT AF demagnetization step provides the most accurate estimate. This is demonstrated by comparing the U1419 inclination to a stack of the shipboard inclination at Site U1418 on a new age model developed from 19 radiocarbon dates on U1418 and 18 magnetic susceptibility-based tie-points to site survey core EW0408-87JC (Praetorius et al., 2015). This independently replicated inclination record verifies centennial to millennial scale variations in the Gulf of Alaska that can now be compared with other northeast Pacific and western North American records to begin deciphering geomagnetic variability and provide a new stratigraphic correlation tool for 15 and 30 cal kyr BP interval in this region.

How to cite: Velle, J. H., Walczak, M., Reilly, B., St-Onge, G., Stoner, J., Fallon, S., Mix, A., Belanger, C., and Forwick, M.: High-resolution inclination records from Sites U1418 and U1419 in the Gulf of Alaska (IODP Expedition 341), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4862, https://doi.org/10.5194/egusphere-egu22-4862, 2022.

EGU22-6552 | Presentations | EMRP3.4 | Highlight

Geomagnetic Excursion Record Preserved In The Speleothem From Western Caucasus: First Data 

Dmitriy Gavrushkin, Alexander Pasenko, Roman Veselovskiy, and Dmitriy Rudko

The study of the geomagnetic field evolution on minor timescales, in particular of such significant events as geomagnetic reversals and excursions, has acquired particular relevance nowadays due to the increased attention of mankind to the environment. The question of how exactly abrupt changes in the characteristics of the geomagnetic field affect the climate and biosphere remains largely debatable; the idea of ​​the speed and dynamics of these changes is also very vague. "Classical" geological objects and existing methods provide limited opportunities for highly detailed reconstructions of geomagnetic field variations; therefore, paleomagnetologists are looking for new objects and approaches to solve this problem. The research that we have begun involves the use of speleothems to study secular variations of the geomagnetic field.

This study presents paleomagnetic records of two drill-cores from the flowstone from Vorontsovskaya cave, located on the western flank of the Caucasus Mountains in the valley of the river Kudepsta. Preliminary results indicate the presence of a geomagnetic excursion record in both drill-cores. Further study of the samples from Vorontsovskaya cave will make it possible to compare the discovered event with known excursions, as well as to clarify its age, duration, and dynamics.

How to cite: Gavrushkin, D., Pasenko, A., Veselovskiy, R., and Rudko, D.: Geomagnetic Excursion Record Preserved In The Speleothem From Western Caucasus: First Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6552, https://doi.org/10.5194/egusphere-egu22-6552, 2022.

The Earth’s magnetic field displays a rich spectrum of variations spanning from a few months to millennia. Decadal to centennial variations, often called secular variation (SV), are generated by induction due to convective motions of the Earth’s liquid core. They are at the heart of the current displacements of the South Atlantic Anomaly (SAA), decrease of the axial dipole and the rapid acceleration of the North magnetic pole. Although modern satellite and observatory measurements only span the past century, historical records can improve our knowledge of the dynamics causing the SV for the past 500 years and paleomagnetic data for the past millennia. Focusing on the last millennium, we attempt at reconstructing the magnetic field using 3D dynamo simulations as background models and combining them with historical and paleomagnetic data through a Data Assimilation (DA) framework. We use an Ensemble Kalman Filter and explore covariance localization methods that can allow both for stability and small ensemble sizes. We also explore the impact of the underlying dynamo model characteristics in reconstructing core flows and magnetic structures both in synthetic and real DA scenarios. Finally, we aim at presenting a reanalysis of the dynamo state over the past millennium as well as predictions for the next one, with focus on the SAA, dipole evolution and magnetic pole trajectories. 

How to cite: Sanchez, S. and Fournier, A.: Assimilation of historical and paleomagnetic data into dynamo models - reanalysis and predictions of the geomagnetic field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7740, https://doi.org/10.5194/egusphere-egu22-7740, 2022.

EGU22-8535 * | Presentations | EMRP3.4 | Highlight

A first regional model of the past Earth’s magnetic field from Africa for the last 4,000 years 

F. Javier Pavón-Carrasco and Anita Di Chiara

Holocene geomagnetic data from large areas such as the oceans, the African and South American continents, constitute only the 4–6% of the global datasets, limiting our understanding of the geomagnetic field features and evolution. So far, 48 studies from Africa sensu latu are available, the 14.5% of studies from Southern Africa, the 23% from Central Africa and 62.5% from the Norther Africa. About half of them are from archaeomagnetic data, and the rest are from volcanic and sedimentary records. Here, after selecting the available volcanic and archaeomagnetic data following a set of 3 FAIR (findability, accessibility, interoperability and reproducibility) principle-based criteria, we build a first regional geomagnetic model for Africa covering the last 4000 years, based on the revised version of the spherical cap harmonic analysis in 2 dimensions. The new regional model helps understanding the most important feature of the modern geomagnetic field anomaly, the South Atlantic Anomaly. The model shows, at the Earth’s surface, the westward migration of the SAA from the Indian Ocean over Africa since 1100 AD. Finally, we test the new model as a paleomagnetic dating tool by re-dating previous archaeomagnetic data from Africa, confirming that, despite being based on a still sparse database, it can be used to date other African archeological sites and the many active and dormant volcanoes of the East African System.

How to cite: Pavón-Carrasco, F. J. and Di Chiara, A.: A first regional model of the past Earth’s magnetic field from Africa for the last 4,000 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8535, https://doi.org/10.5194/egusphere-egu22-8535, 2022.

EGU22-9209 | Presentations | EMRP3.4

Joint inversion of paleomagnetic and cosmogenic isotope data for modeling the global geomagnetic field 

Sanja Panovska, Monika Korte, Florian Adolphi, Norbert Nowaczyk, and Dirk Scherler

The Earth's magnetic field varies on a range of spatial and temporal scales. Recent models, spanning the past 100 ka, greatly improved our knowledge of the long-term changes of the geomagnetic field, and geomagnetic excursions - events associated with strong directional deviations and low field intensities. However, these models are limited by the spatial and temporal data distribution, and magnetic and age uncertainties of underlying data. Variations in the production of cosmogenic radionuclides, such as 10Be from ice cores and sediments, provide an independent proxy of paleointensity variations for a range of timescales. This study demonstrates the potential of a joint inversion of paleomagnetic data with cosmogenic nuclide production rates to reconstruct the geomagnetic field evolution over the past 70 ka. Here, we present a global compilation of 10Be records, converted to magnetic field intensity, and compare them to paleomagnetic sediment records. General trends of the virtual axial dipole moment (VADM) stacks derived from the two data sets agree well. Two models have been constructed: GGFSS70-10Be where the converted 10Be records are used similarly to the paleomagnetic records, and GGFSS70-10Be-DIP where the converted 10Be data have been considered to be a function of the dipole only (the first three Gauss coefficients). These models are compared to the previously published GGFSS70 model based on paleomagnetic data only. Geomagnetic excursions are reconstructed in the multi-proxy models: the most pronounced Laschamps event (41 ka) and a few other excursional signatures at the times of the Norwegian-Greenland Sea and Mono Lake/Auckland excursions. Model predictions and global field maps show that the cosmogenic isotope records have regional effects on the reconstructed variations (Greenland, South/Southern Ocean, east-equatorial Pacific), especially those with high resolution (Greenland ice cores). The 10Be records not only provide an independent source of information on the geomagnetic field, thus confirming the reliability of the paleomagnetic records, they also improve the global geomagnetic field reconstructions over long timescales.

How to cite: Panovska, S., Korte, M., Adolphi, F., Nowaczyk, N., and Scherler, D.: Joint inversion of paleomagnetic and cosmogenic isotope data for modeling the global geomagnetic field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9209, https://doi.org/10.5194/egusphere-egu22-9209, 2022.

The goal of our research is to obtain new data of geomagnetic field intensity in the Eastern Europe in the Bronze Age.  The arhaeomagnetic study of fired ceramic from the Grishinsky Istok III settlement was done. The settlement Grishinsky Istok III is situated in the Oka region of Ryazan district of Russia (54о41′, 40о57′). The studied collection of pottery fragments of that archaeological site pertains to the “textile” ceramics of Bronze Age.  The age of pottery fragments corresponds to the ~ 1500-1300 years B.C. The composition of the ferromagnetic fraction of the studied samples has been examined by the thermo-magnetic analysis.   The dependence of the saturation magnetic moment on temperature in the magnetic field and determination of the Curie points were carry out with an analyzer of ferromagnetic fraction. Thus based on the thermo-magnetic analysis one can conclude that the main carrier of the thermo remanent magnetization of the samples is relatively resistant to heat maghemite. The size of grains lies in a pseudo single domain area. The determination of the ancient magnetic field intensity was carried out by modified Thellier method. Fifteen geomagnetic field intensity determinations were obtained. The geomagnetic field intensity varies between 37 and 66 µT with an average value of about 50 µT.  Acquisition of new data about the Earth’s magnetic field during the Bronze Age makes it possible to advance the studies of geomagnetic variations. This work was supported by the Russian Foundation for Basic Research, project no. 19-55-18006 and the State task of the Schmidt Institute of Physics of the Earth RAS no. 0144-2019-0006.

How to cite: Pilipenko, O., Nachasova, I., and Azarov, E.: Archeomagnetic investigation of textile ceramics from Grishinsky Istok III  settlement  (Oka  Region, Ryazan district, Russia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9718, https://doi.org/10.5194/egusphere-egu22-9718, 2022.

EGU22-9790 | Presentations | EMRP3.4 | Highlight

Rapid Auroral Wandering During the Laschamps Event 

Agnit Mukhopadhyay, Sanja Panovska, Michael Liemohn, Natalia Ganjushkina, Ilya Usoskin, Michael Balikhin, Daniel Welling, and Katherine Garcia-Sage

41 thousand years ago, the Laschamps geomagnetic excursion caused Earth’s magnetic field to drastically diminish to ~4% of modern values and modified its dipole-dominated structure. While the impact of this geomagnetic event on environmental factors and human lifestyle has been contemplated to be linked with modifications in the geospace environment, no concerted investigation has been conducted to study this until recently.

We present an initial investigation of the global space environment and related plasma environments during the several phases of the Laschamps event using an advanced multi-model approach. We use recent paleomagnetic field models of this event to study the paleomagnetosphere with help of the global magnetohydrodynamic model BATS-R-US. Here we go beyond a simple dipole approximation but consider a realistic geomagnetic field configuration. The field is used within the global magnetohydrodynamic model BATS-R-US to generate the magnetosphere during discrete epochs spanning the peak of the event. Since solar conditions have remained fairly constant over the last ~100k years, modern estimates of the solar wind were used to drive the model. Finally, plasma pressure and currents generated by BATS-R-US at their inner boundary are used to compute auroral fluxes using a stand-alone version of the MAGNIT model, an adiabatic kinetic model of the aurora.

Our results show that changes in the geomagnetic field, both in strength and the dipole tilt angle, have profound effects on the space environment and the ensuing auroral pattern. Magnetopause distances during the deepest phase of the excursion match previous predictions, while high-resolution mapping of magnetic fields allow close examination of magnetospheric structure for non-dipolar configurations. Temporal progression of the event also exhibits rapid locomotion of the auroral region over ~250 years along with the movement of the geomagnetic poles. Our estimates suggest that the aurora extended further down, with the center of the oval located at near-equatorial latitudes during the peak of the event. While the study does not find evidence of any link between geomagnetic variability and habitability conditions, geographic locations of the auroral oval coincide with early human activity in the Iberian peninsula and South China Sea.

How to cite: Mukhopadhyay, A., Panovska, S., Liemohn, M., Ganjushkina, N., Usoskin, I., Balikhin, M., Welling, D., and Garcia-Sage, K.: Rapid Auroral Wandering During the Laschamps Event, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9790, https://doi.org/10.5194/egusphere-egu22-9790, 2022.

EGU22-9876 | Presentations | EMRP3.4

Paleomagnetic data from Siberian Ediacaran rocks (Yenisei Ridge and Olenek Uplift) 

Evgeny Vinogradov, Dmitriy Metelkin, Sergey Zakharov, Victor Abashev, Kristina Pakhomova, and Andrey Eliseev

Paleomagnetic results obtained from rocks of Ediacaran age in several localities in Siberia display co-existence of two magnetization components, one shallowly component and the other one is steeply inclined. Both components pass criteria for a primary magnetization. The conventional interpretation of paleomagnetic results in such cases have been rejected as dynamically implausible. In search of the reasons for the irregular behavior of the geomagnetic field in the Ediacaran, the study compares the key Ediacaran sections of the Yenisei Ridge and the Olenek Uplift, which are close in age.

The first paleomagnetic data for the Vorogovka Group were obtained in the northwest of the Yenisei Ridge. Age of deposits, according to different authors, from Cryogenian to Ediacaran. However, recent data indicate that the age of sedimentation within the Vorogovka basin is less than 585 million years. In the southwestern margin of the Siberian platform, the Taseeva Group is of considerable interest for paleomagnetic studies. New data on the age make it possible to significantly narrow the formation interval of the series to the Late Ediacaran, and also to refine the paleomagnetic pole calculated for the upper and lower formations of the Taseeva Group. In the Vorogovka and Taseeva groups, the shallowly inclined component of magnetization is more often present, while the steeply inclined component is less common.

Over the past several years, we have carried out paleomagnetic studies of the Precambrian rocks of the Olenek Uplift, including the Late Ediacaran Maastakh and Khatyspyt formations, as well as intrusions of the Tas-Yuryakh volcanic complex that break through them. In both sedimentary and igneous rocks of the Olenek Uplift, only a steeply inclined component of magnetization is present.

The results of the studies of paleointensity in basalts of the Tas-Yuryakh volcanic complex indicate an ultra-low intensity of the Earth's magnetic field at the end of the Ediacaran. These results confirm that the explanation for the disparate paleomagnetic data for the Ediacaran period must be sought in the behavior of the geomagnetic field, and not in tectonic reasons.

This work was financially supported by the Russian Science Foundation grant no. 21-17-00052.

How to cite: Vinogradov, E., Metelkin, D., Zakharov, S., Abashev, V., Pakhomova, K., and Eliseev, A.: Paleomagnetic data from Siberian Ediacaran rocks (Yenisei Ridge and Olenek Uplift), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9876, https://doi.org/10.5194/egusphere-egu22-9876, 2022.

EGU22-187 | Presentations | EMRP3.5

Rockmagnetic based environmental reconstruction of Galería and Gran Dolina caves in Sierra de Atapuerca (Burgos, Spain) 

Serena D'Arcangelo, Fátima Martín-Hernández, and Josep M. Parés

Magnetic properties of sediments can furnish an environmental reconstruction of the deposition time. In our study we intend to understand the climatic – paleoenvironmental conditions at the time the earliest hominins found in Europe, and especially the well-known archaeological sites at Sierra de Atapuerca, in Burgos, Spain. The sites assemblage is found in a multi-layered karstic system, and includes a number of caves filled with both interior (distal) and entrance sediments. We focused our attention on two caves, which belong to the so-called “Trinchera” (trench) sites, namely Galería and Gran Dolina. The latter has produced thousands of fossils and artefacts since 1995, when the first hominin remains were reported, and soon became a Pleistocene landmark in studies on early human settlement outside the African continent. Our already published study on Gran Dolina presents more variability of magnetic properties in cave-entrance sediments than in the cave-interior, as expected for the exterior influence on the grain size and iron oxides concentration.

Now, we start to investigate the Galería site to correlate it with the nearest cave and to better understand the paleoenvironmental context at the time early humans inhabited the area. In particular, we confined our attention to identify the magnetic minerals present into Covacha de los Zarpazos (the lower studied part of Galería) with backfield and IRM curves determined by a magnetic Variable Field Translation Balance (VFTB). This analysis allows us to individuate a more precised reconstruction of the environmental conditions of the deposition time, also with a comparison of a pollen study and X-Ray Fluorescence (XRF) in-situ study for a major precision.

How to cite: D'Arcangelo, S., Martín-Hernández, F., and M. Parés, J.: Rockmagnetic based environmental reconstruction of Galería and Gran Dolina caves in Sierra de Atapuerca (Burgos, Spain), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-187, https://doi.org/10.5194/egusphere-egu22-187, 2022.

EGU22-4141 | Presentations | EMRP3.5

Authigenic magnetite in soils: pollution fingerprints in a former wolfram mining 

Helena Sant'Ovaia, Claudia Cruz, and Eric Font

The North of Portugal is particularly rich in metallic mineral resources, whose exploitation dates back to the 19th century. The important amount of mining wastes resulting from the tungsten mining activities deposited in tailing represent a source of pollutants that are emitted, released, or leached to the surrounding environment.  It is well documented that improper mining waste disposal will result in air, soil, and water pollution. This environmental legacy, and the contamination caused by the mining waste disposal, is far from being properly assessed, namely the impact on the soils of the surrounding areas. We studied the mining area associated with Regoufe granite where several tungsten-rich deposits occur in and around the granite body, and whose exploitation stopped in the fifties of the 20th century.

In this study, magnetic methods are used to identify ferromagnetic minerals in soils sampled in the surrounding area of Regoufe mine, which serve as tracer for anthropogenic pollutants. We measured the mass specific (χ) and frequency-dependent (Kfd%) magnetic susceptibility and we acquired isothermal remanent magnetization (IRM) curves of eight granitic soil samples from the mining area. Our results show that χ is comprised between 2.82 and 477.20 × 10-8 m3/kg, which indicates that besides diamagnetic and paramagnetic particles, ferromagnetic minerals are present in variable concentrations. Kfd%, which reflects the concentration of superparamagnetic (SP) grains, and particularly those close to the threshold SP – single domain  is relatively low and comprised between 1.21 and 2.48%, indicating a very weak contribution of SP particles. IRM curves were treated by a  cumulative Log-Gaussian (CLG) and a Skewed Generalized Function (SGG) using the the software developed by Kruiver et al. (2001) and the MAXUnMix software (Maxbauer et al., 2016), respectively. All IRM curves were fitted by using a single component with mean coercivity (B1/2) of 53.7-61.7 mT and DP of 0.27-0.29, typical of fine-grained magnetite. SIRM values are comprised between 1.69 and 14.71 × 10-2 Am2/kg, suggesting that the large variability observed in the values of magnetic susceptibility results from a heterogenous distribution of magnetite among the studied samples. The S-ratio varies between 0.989 and 0.992, indicating that magnetite is the main magnetic carrier of the studied samples. The mean coercivity (B1/2~60mT) of this magnetite population is significantly higher than the typical mean coercivity of pedogenic or detrital magnetite (Egli, 2003). DP of 0.27-0.28 are also lower than the DP values for pedogenic or detrital magnetite (typically ~0.34-0.36) pointing to the presence of authigenic magnetite resulting from the pollution of the mining waste deposits. More investigation is required to evaluate the extent of the polluted areas and their impacts on the environment.

Acknowledgements: This work is financed by the project SHS - PROJETO NORTE-01-0145-FEDER-000056, and also by national funding awarded by FCT - Foundation for Science and Technology, I.P., projects UIDB/04683/2020 and UIDP/04683/2020. References: Egli, R., 2003. J. Geophys. Res. 108, 2081. Kruiver, P.P., Dekkers, M.J., Heslop, D. 2001. Earth Planet. Sci. Lett. 189, 269–276. Maxbauer, D.P., Feinberg, J. M., Fox, D.L. 2016.  Computers & Geosciences 95, 140–145.

 

How to cite: Sant'Ovaia, H., Cruz, C., and Font, E.: Authigenic magnetite in soils: pollution fingerprints in a former wolfram mining, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4141, https://doi.org/10.5194/egusphere-egu22-4141, 2022.

EGU22-6653 | Presentations | EMRP3.5

Frontiers in quantitative paleogeography and paleomagnetism 

Mat Domeier, Maëlis Arnould, Athena Eyster, Leandro C. Gallo, Derya Gürer, Ágnes Király, Boris Robert, Tobias Rolf, Facundo Sapienza, Grace E. Shephard, Nick Swanson-Hysell, Bram Vaes, Annique van der Boon, Lei Wu, and Yiming Zhang

The last few years have been marked by a number of motivating novel ideas and methodological advancements in paleomagnetic analysis (e.g. trans-hierarchical uncertainty propagation), observational and theoretical geodynamics, and paleogeographical modeling (e.g. optimisation and Bayesian approaches). Many of these developments offer new insights on, and/or approaches to estimating, the past motions of tectonic plates—but so far these developments have largely unfolded in isolation of one another. In November 2021 an international group of 15 young scientists with highly complementary backgrounds (spanning the aforementioned fields) gathered to explore and discuss these exciting new developments and to brainstorm strategies that may enable their integration. We anticipate that the integration of these diverse new ideas and methods will open new frontiers in plate tectonic research, and notably lead to much better-constrained paleogeographic models. In this presentation, we will share some of the insights and strategies that emerged from the workshop, including the advantages of conducting paleomagnetic analysis at the site-level, the application of emerging paleomagnetic Euler pole analysis frameworks, and the use of insights extracted from Earth-like geodynamic models (which self-generate plate tectonic behavior) to further constrain the results of these paleomagnetic methods. We also present some preliminary results of early experiments putting these strategies into practice on a paleomagnetic dataset from North America.  

How to cite: Domeier, M., Arnould, M., Eyster, A., Gallo, L. C., Gürer, D., Király, Á., Robert, B., Rolf, T., Sapienza, F., Shephard, G. E., Swanson-Hysell, N., Vaes, B., van der Boon, A., Wu, L., and Zhang, Y.: Frontiers in quantitative paleogeography and paleomagnetism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6653, https://doi.org/10.5194/egusphere-egu22-6653, 2022.

EGU22-7425 | Presentations | EMRP3.5

Magnetic properties of Baltic Sea ferromanganese concretions 

Joonas Wasiljeff, Johanna Salminen, and Joonas Virtasalo

Ferromanganese concretions are abundant in many parts of the coastal Baltic Sea and hence provide an important yet underused archive to investigate these shallow sea areas in detail. Coastal sea areas can be best described as filters, and they have a focal role in the biogeochemistry of riverine nutrients and suspended particles during their transport to open sea. Colloidal iron and manganese oxyhydroxides, originating from the surrounding catchment area and/or from adjacent anoxic sediments, accumulate and ultimately lead to the authigenic formation of ferromanganese concretions at an unusually fast growth rate, generally in low-carbon environments with limited sedimentation. The porous concretions come in various sizes and shapes, and host diverse microbial communities with reductive and oxidative metabolisms that can affect both the concretion growth and dissolution. Despite that, the specific formation mechanisms and (bio)mineralization processes of different concretion morphotypes are poorly constrained.

We have investigated the magnetic properties of Baltic Sea ferromanganese concretions of different morphotypes, depositional environments, water depths and geographical locations. While the magnetic mineral concentrations change according to salinity and water depth, the concentrations are also seemingly controlled by the concretion morphotype. Preliminary results of laboratory remanences also indicate the magnetic mineral assemblages are dominated by SD-sized ferrimagnetic particles with magnetic properties similar to those of magnetosomes. The possible presence of magnetotactic bacteria within the concretions provides novel insights into the biogeochemistry of low sediment accumulation and low-carbon coastal environments of the Baltic Sea.

This research is part of the Fermaid project, funded by the Academy of Finland grant 332249.

How to cite: Wasiljeff, J., Salminen, J., and Virtasalo, J.: Magnetic properties of Baltic Sea ferromanganese concretions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7425, https://doi.org/10.5194/egusphere-egu22-7425, 2022.

EGU22-8839 | Presentations | EMRP3.5

First order reversal curves (FORCs) as indicators of magnetic PM sources 

Hassan Aftab Sheikh and Richard John Harrison

Real-time monitoring of particulate matter (PM) is performed by traditional air quality monitors using size-fractionated light-scattering laser photometers or gravimetric analysis. However, these quick methods do not fully characterise the particulates, in particular, the more toxic metals such as Fe. Here, we propose the use of first order reversal curves (FORCs) as a method to discriminate different sources of anthropogenic magnetic particles. FORCs is a useful magnetic characterisation technique that is sensitive to particle size, mineralogy and domain state. By measuring known sources of particulates, we hope to come up with a ‘magnetic’ proxy in a heterogenous source of PM in the air using principal component analysis (PCA). FORC fingerprints for exhaust, non-exhaust vehicular sources, resuspended dust and train-related PM are distinct, providing a cost-effective way to monitor relative proportions in the ambient air. The first set of specimens involved measuring FORCs on known, size-fractionated brake abrasion dust on an accelerating gradient magnetometer. Processed FORCs for brake dust residue specimens show a distinct combination of narrow central ridge, extending from 0 to up to 200 mT, and a low-coercivity, vertically spread multi-domain signal. Similarly, known exhaust-pipe residue samples were measured, displaying a more conventional ‘magnetite-like’ signal comprising a lower coercivity central ridge (0-80 mT) and a tri-lobate signal attributed to vortex state and/or magnetostatic interactions. Tyre and road wear samples are generally low-coercivity and vertically spread, hinting at mostly coarser, resuspended dust that has settled down. Third set of data involved measuring gravimetric specimens from London Underground. The source of magnetic particulates in fundamentally the same but different ventilation rates on platforms meant the ‘fingerprints’ were different. Principally, FORC fingerprints are sensitive to grain size, mineralogy and total magnetic content, demonstrating a low-cost approach for identifying different proportions of magnetic particulates. These data will be complemented by measurements with high-resolution microscopy such as TEM and EELS to characterise the magnetic state of particulates and add value to conventional air quality monitoring systems.

How to cite: Sheikh, H. A. and Harrison, R. J.: First order reversal curves (FORCs) as indicators of magnetic PM sources, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8839, https://doi.org/10.5194/egusphere-egu22-8839, 2022.

EGU22-8871 | Presentations | EMRP3.5

Machine Learning models for Moment Magnetometry applied to High-Resolution Magnetic Maps 

Michael Volk, Raisa Trubko, Roger Fu, and Brendan Meade

Paleomagnetic measurements of natural remanent magnetization were – until recently -- performed on large, millimeter to centimeter-sized rock samples using classical rock magnetometers. Developments of magnetic imaging (i.e., quantum diamond microscope (QDM) and scanning SQUID microscope) allow for the measurement of individual, weakly magnetic (10-16 Am2) particle clusters within a sample. However, this increased spatial resolution adds to the complexity of the magnetic signal and requires novel approaches in analyzing the data.

Commonly, the magnetic moment of sources within a sample are analyzed by dipole inversion, meaning fitting a dipole signal to a cropped part of a magnetic map. While this gives accurate results for sources that are well separated and dipole-like in character, recovering net magnetic moments from complex maps proved difficult. 

Machine learning (ML) has been used to study a vast number of problems and has become a part of our daily lives. Here, we present the first ML model to predict net magnetic moments from magnetic maps. Our ML models consist of three simple convolutional neural networks for source declination, inclination, moment magnitude, each of which has been trained on a large (500k) synthetic map dataset. The models are tested against several datasets, varying in size, source distribution and resolution. Our models can quickly and accurately recover the magnetic moment, even for very complex (i.e., low dipolarity) maps. The accuracy of the models is < 8˚ for inclination and declination and < 10 % for moment. Surprisingly, we find little correlation in the prediction accuracy to the dipolarity of the map. These results show that ML is a promising alternative to dipole inversions, especially for maps with low dipolarity parameters, where traditional dipole inversions can fail.

How to cite: Volk, M., Trubko, R., Fu, R., and Meade, B.: Machine Learning models for Moment Magnetometry applied to High-Resolution Magnetic Maps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8871, https://doi.org/10.5194/egusphere-egu22-8871, 2022.

EGU22-12541 | Presentations | EMRP3.5

Determining Demagnetization Energy and Internal Stress in Natural Magnetite Bearing Samples 

Annemarieke Béguin, Karl Fabian, Nathan Church, and Suzanne McEnroe

The stability and acquisition of remanent magnetization in Earth and planetary rocks is controlled by the magnetization state of magnetic particles. Magnetic properties are often characterized by magnetic grain size. Besides grain size, also stress, magnetostatic interactions, and grain shape influence and modify magnetic stability. Moreover, internal stress in magnetite may substantially affect remanence acquisition and might be responsible for enhanced remanence for which the processes are often still enigmatic.

To better understand the impact of internal stress on the efficiency of remanence acquisition, their contribution needs to be separated from the magnetostatic and demagnetizing energy contributions. Direct observations of the influences of magnetocrystalline and stress anisotropy on the magnetic behavior of magnetite are obscured by the large demagnetizing energy. A new temperature-dependent hysteresis measurement and evaluation procedure was developed by Béguin & Fabian, (2021), which allows the determination and separation of demagnetizing energy and internal stress. The validity of the method was demonstrated for a suite of synthetic magnetite samples under different stress conditions.

Here we present the first results of applying the new scaled reversible work (SRW) method to a set of natural magnetite bearing samples. We used samples with homogeneous and heterogeneous microstructures and end-member stress-free magnetite samples. The magnetic behavior as function of temperature is less ideal for the natural samples than for the previously studied synthetic magnetite samples, for example, the Curie temperatures are less distinct. Here we present how these challenges can be overcome, and present additional evaluation steps to ease the interpretation of the temperature-dependent hysteresis data.

How to cite: Béguin, A., Fabian, K., Church, N., and McEnroe, S.: Determining Demagnetization Energy and Internal Stress in Natural Magnetite Bearing Samples, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12541, https://doi.org/10.5194/egusphere-egu22-12541, 2022.

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