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.


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.



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.



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?



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.



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
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.



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.


[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.


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.


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

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.


[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.


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).



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.


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.