Presentation type:
EMRP – Earth Magnetism & Rock Physics

EGU24-6574 | Orals | MAL16-EMRP | Louis Néel Medal Lecture

Inelastic compaction in porous carbonates 

Patrick Baud

The analysis of deformation and failure in many sedimentary settings hinges upon a fundamental understanding of inelastic behaviour, failure mode of porous carbonate rocks and their implications on fluid flow at various scales. The mechanical compaction behaviour of carbonate rock of a broad range of porosity has been investigated in the laboratory over a wide range of stress conditions in the last decades. The phenomenology of brittle failure and inelastic compaction in this rock type with often bimodal pore size distribution was found similar to that of sandstone. Inelastic compaction in limestone involved primarily cataclastic pore collapse and micromechanical analysis showed the strong influence of the micropore size on the yield stress. Compaction experiments on porous limestones also revealed a broad spectrum of complex failure modes. In situ X-ray Computed Tomography imaging combined with Digital Volume Correlation provided the first observations of discrete compaction bands in a high porosity limestone. Permeability variations in carbonates associated with shear-enhanced compaction and these failure modes were found significantly smaller than variations previously reported in porous sandstones of comparable porosities.

In geophysical applications such 4D reservoir monitoring and the production of geothermal reservoirs, an understanding of the mechanical and chemical effects of pore fluid is fundamental. The mechanical influence of pore fluid on different properties is characterized by effective pressure coefficients. For limestone with dual porosity, both effective stress coefficients for permeability and pore volume change were observed to be consistently greater than unity. This implies that microscopic homogeneity is not a valid approximation for a limestone with dual porosity, and a realistic model must explicitly differentiate between the macropores and micropores, as well as account for their interplay in controlling the hydromechanical behaviour. Recent data showed that a significant weakening effect of water could also be expected in most carbonates. 

How to cite: Baud, P.: Inelastic compaction in porous carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6574, https://doi.org/10.5194/egusphere-egu24-6574, 2024.

EGU24-10806 | ECS | Orals | MAL16-EMRP | EMRP Division Outstanding Early Career Scientist Award Lecture

Deformation and reaction of plagioclase-rich rocks at conditions of the lower continental crust 

Sarah Incel, Jörg Renner, Alexandre Schubnel, Loic Labrousse, Marie Baisset, and Lisa Katharina Mohrbach

Due to contrasting results between laboratory tests, geophysical data, and field observations, the strength of the plagioclase-rich lower continental crust remains a topic of debate. It has been shown that its strength highly depends on the presence of fluids as they trigger metamorphic reactions that can result in permanent weakening. An important metamorphic reaction in the lower continental crust is the breakdown or hydration of plagioclase and the associated growth of epidote-group minerals, kyanite, quartz, and jadeite/albite. To investigate the impact of this particular reaction on the strength of the lower continental crust, we combined experimental work, i.e., Griggs-deformation tests, with extensive microstructural observations of the recovered experimental samples. Experimental conditions were 1 to 1.5 GPa confining pressure, 550 to 950 °C, and for the deformation tests, we used strain rates ranging from 10-6 to 10-5 s-1. Our results reveal two main findings. First, deformed plagioclase aggregates as well as deformed granulite drill cores show that deformation-induced features in plagioclase grains, e.g., cleavage cracks and twin boundaries, act as nucleation sites for metamorphic reactions and melting. Consequently, reaction can progress faster in deformed samples as the effective reactive surface area is increased relative to undeformed counterparts. Second, when deformed under identical experimental conditions, pure epidote aggregates are consistently stronger or show equal strengths than pure plagioclase aggregates. Hence, a partial plagioclase breakdown, i.e., the exclusive growth of epidote-group minerals at low reaction progress, is not expected to result in permanent weakening. This result further strengthens the idea that a process akin to Zener pinning is a viable mechanism to cause long-term weakening in rocks.

How to cite: Incel, S., Renner, J., Schubnel, A., Labrousse, L., Baisset, M., and Mohrbach, L. K.: Deformation and reaction of plagioclase-rich rocks at conditions of the lower continental crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10806, https://doi.org/10.5194/egusphere-egu24-10806, 2024.

EMRP1 – Rock and Mineral Physics

EGU24-589 | ECS | Orals | EMRP1.2

Verification of susceptibility and density relationship from 3D joint inversion of airborne magnetic and gravity data in northern Victoria Land, East Antarctica, with petrophysical measurements 

Maximilian Lowe, Tom Jordan, Max Moorkamp, Jörg Ebbing, Nikola Koglin, Antonia Ruppel, Chris Green, Jonas Liebsch, Mikhail Ginga, and Robert Larter

Subglacial geology remains largely unknowns in Antarctica. Direct geological samples are limited to ice free regions along the coast, high mountain ranges or isolated nunataks, while the origin of geological material transported by glaciers themselves is often ambiguous. 3D singular and joint inversions of airborne gravity and magnetic data recovers subsurface density and susceptibility distribution. The relationship between both inverted petrophysical quantities provide crucial insight for subglacial geology and rock provinces interpretations. Validation of indirect derived subglacial geology models are critical but very challenging in Antarctica due to the sparsity of rock samples.

We present 324 new density and susceptibility measurements on rock samples from Northern Victory Land, East Antarctica. 251 samples have been measured at the National Polar Sample Archive (NAPA) from the Federal Institute for Geosciences and Natural Resources (BGR) in Berlin-Spandau, Germany and additional 73 samples were measured at the BGR in Hannover, Germany. We use the petrophysical measurements to validate our recent regional scale 3D joint inversion model of the Wilkes Subglacial Basin and the Transantarctic Mountains. Furthermore, we validate inversion results on a local scale of singular magnetic inversion based on high resolution airborne magnetic data with a flight line spacing of 500m in the Mesa Range.

We demonstrate that we can provide reliable discrimination between Ferrar Dolerites, Kirkpatrick Basalt and Granite Harbour intrusion rocks based on our local inversion model and that the recovered susceptibilities agree with those measured at rock samples from the study area. Furthermore, we show that regional scale inversion model of gravity and susceptibility distribution agrees for samples of the dominant crustal rock types. However, densities of small-scale dense intrusion bodies like Ferrar Dolerites are underestimated by the regional scale inversion, while the susceptibility range is correctly recovered.

Constraining subglacial geology with joint inversion of airborne potential field data is heavily depended on the resolution of the airborne survey, flight line coverage, the inversion scale, and the scale of the target feature. Regional scale inversion is adequate for large scale geological heterogeneities, which underestimate petrophysical quantities for small scale structures, while local scale inversions are able to resolve such structures but are more computational demanding and in the case of Antarctica lack ultra-high resolution airborne gravity data with a line spacing below 1000 – 500m.

How to cite: Lowe, M., Jordan, T., Moorkamp, M., Ebbing, J., Koglin, N., Ruppel, A., Green, C., Liebsch, J., Ginga, M., and Larter, R.: Verification of susceptibility and density relationship from 3D joint inversion of airborne magnetic and gravity data in northern Victoria Land, East Antarctica, with petrophysical measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-589, https://doi.org/10.5194/egusphere-egu24-589, 2024.

EGU24-974 | ECS | Posters on site | EMRP1.2

Dynamic Compressive Strength of Thermally Treated Barakar Sandstone 

Adarsh Tripathi, Mohammad Mohsin Khan, Nachiketa Rai, and Anindya Pain

Assessing the thermal influence on the dynamic mechanical properties of Barakar sandstone is crucial, notably in the examination of subsidence phenomena induced by underground coalmine fires in tandem with blast-induced loading. The Jharia region had been affected by underground coalmine fires, resulting in surface fracturing on both small and large scales. So, the objective of the study is to examine the impact of high temperature on the dynamic compressive strength of colliery sandstone subsurface samples, and its correlation with the mineralogical properties. To accomplish this objective, samples were subjected to a 24-hour heat treatment in a furnace at a controlled heating rate of 5°C/min, followed by natural cooling within the furnace. The samples were divided into five groups, each undergoing different thermal treatments at temperatures of 25°C, 200°C, 400°C, 600°C, and 800°C. The dynamic compressive strength was obtained by performing the dynamic compression tests on Split Hopkinson Pressure Bar setup. The results clearly indicate that up to a critical temperature i.e. 400°C, both quasi-static and dynamic compressive strength showing the minor strengthening effect. However, beyond this critical temperature, there is a significant decrease in strength, particularly up to 800°C. Additionally, for each temperature, the dynamic strength also exhibits an increasing trend with increase in strain rate. The study investigated the applicability of the Kimberley Theoretical Universal Scaling Law in predicting the dynamic compressive strength of thermally treated sandstone across different strain rates. Furthermore, it pinpointed the characteristic strain rate at which the dynamic compressive strength of thermally treated sandstone doubled in comparison to its quasi-static compressive strength.

How to cite: Tripathi, A., Khan, M. M., Rai, N., and Pain, A.: Dynamic Compressive Strength of Thermally Treated Barakar Sandstone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-974, https://doi.org/10.5194/egusphere-egu24-974, 2024.

EGU24-1531 | ECS | Orals | EMRP1.2

Outcrop analogue study of carbonate caprock stringers for CCS and geothermal reservoir: the petrophysical and petrothermal properties of the upper Muschelkalk in the Estopanyà salt wall (South-Central Pyrenees) 

Pedro Ramirez-Perez, Gabriel Cofrade, David Cruset, Irene Cantarero, Juan Diego Martín-Martín, Oriol Ferrer, Jean-Pierre Sizun, and Anna Travé

Salt is playing a principal role in the current energy transition. From diapirs to salt walls, salt structures are being proposed for a growing number of non-fossil energy purposes and carbon-neutral projects (i.e., geothermics, hydrogen storage in salt caverns or CCS). However, diapiric structures are not uniform and exhibit significant compositional and structural heterogeneities that prevent an easy characterization and exploration, thus increasing the risk of exploitation. Compositional heterogeneities within salt structures arise by the occurrence of different rocks inherited from the original Layered Evaporite Sequence (LES) and transported during salt flow or created through various diagenetic processes during diapirism (e.g., caprock formation).

One of the most common heterogeneities found in salt bodies is the presence of heterometric rock masses known as stringers. The limestones of the upper Muschelkalk (M3) facies (Middle Triassic) are the primary non-evaporitic lithological unit within the Triassic LES of the South-Central Pyrenees. These limestones are exposed throughout the South-Pyrenean fold-and-thrust belt embedded in mudrocks and gypsums of the Upper Triassic Keuper facies, forming the actual caprock exposures in the region. The Estopanyà salt wall is located in the westernmost part of the South-Central Pyrenean Zone, within the Serres Marginals thrust sheet. This area shows a well-preserved 58 km2 caprock exposure formed by Middle and Upper Triassic rocks that surround two adjacent salt-embedded basins known as the Estopanyà and Boix synclines. According to the stratigraphic record of these synclines, from the Upper Cretaceous to the Oligocene, the evolution of the area resulted in salt withdrawal leading to salt inflation and the occurrence of several E-W-oriented salt walls that were exposed during the deformation onset in the Lower Eocene (early Ypresian times).

The M3 stringers in the Estopanyà salt wall are embedded in a caprock matrix formed by the dissolution of halite on the surface, albeit its presence has been proposed at deeper levels based on gravimetric models. The stringers have been identified and mapped, forming decameter-thick and kilometre-long structures showing significant folding and fracturing as well as a well-preserved stratigraphic sequence. The basal part of these stringers is formed by a layered to tabular millimetre-to-centimetre-thick limestones whilst the upper part consists of tabular to massive centimetre to meter-thick limestones. The current contribution presents the petrophysical (i.e., mineral density, connected porosity, permeability and P-wave velocity) and petrothermal (thermal conductivity and specific heat capacity) properties of 40 samples collected throughout the eastern Estopanyà salt wall, covering the basal and upper succession of various stringers. The sample analysis enables us to discuss the factors controlling the studied rock properties and the viability of carbonate stringers as geothermal reservoirs and CCS, which is a novel study that can be replied in similar salt structures worldwide.

How to cite: Ramirez-Perez, P., Cofrade, G., Cruset, D., Cantarero, I., Martín-Martín, J. D., Ferrer, O., Sizun, J.-P., and Travé, A.: Outcrop analogue study of carbonate caprock stringers for CCS and geothermal reservoir: the petrophysical and petrothermal properties of the upper Muschelkalk in the Estopanyà salt wall (South-Central Pyrenees), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1531, https://doi.org/10.5194/egusphere-egu24-1531, 2024.

Tracking CO2 transport in subsurface rock during geological carbon sequestration has received significant attention. Although X-ray computed tomography (XCT) imaging techniques, visualization and quantification of CO2 behavior has been undertaken by previous researchers, little attention has been given to the nature of CO2 transport in a reservoir-caprock interface with well-developed pores in the reservoir and micro-fractures in the caprock. As the transition of two different pore systems, this complex system is crucial in controlling the sequestration safety case. We have used advanced time-lapse synchrotron imaging at in-situ pressure and temperature conditions to image the CO2 transport process in such an experimental system, for both gaseous and supercritical phases.

Dynamic XCT images of fluids and the pore- and fracture-system in the mudstone and sandstone couplet were acquired at high resolution (effective voxel size 1.625 µm). Strain maps following high-speed gaseous and supercritical CO2 (ScCO2) flooding were modelled using a digital volume correlation (DVC) method to reveal the hydro-mechanical effects. The results suggest that under the influence of brine, high-speed gaseous CO2 will not increase the total pore-throat volume and can even cause a reduction in permeability in sandstone due to fines migration induced by CO2 flooding. Clay behavior, notably dispersion in brine, migration of fines and swelling induced by CO2, plays a notable role in the opening and closing of pores/fracture. Fluid breakthrough occurred at 10.6 MPa during high-speed ScCO2 injection. The significant fracturing effect of high-speed ScCO2 resulted in the connection of natural fractures in the mudstone with newly developed secondary branches and also created larger pore space in the sandstone, leading to an increase in porosity by approximately 2.8 times in the mudstone and 1.6 times in the sandstone. Additionally, there was an approximate increase of 2.6 times and 8.6 times in the permeability of mudstone and sandstone, respectively, after CO2 phase transition. The concentrated strains around the main fracture in the mudstone and web-like strains around the boundary of granular minerals in sandstone show the different modes of action of ScCO2 when passing through a reservoir rock and caprock system. This work is of practical significance in improving understanding of CO2-fluid-rock interaction in a complex reservoir-caprock system.

How to cite: Taylor, K., Wang, K., and Ma, L.: 4D synchrotron imaging of CO2 transport in reservoir rocks and caprocks: Informing safe CO2 sequestration    , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1866, https://doi.org/10.5194/egusphere-egu24-1866, 2024.

EGU24-3448 | ECS | Posters on site | EMRP1.2

Quantifying the influence of the type and arrangement of conductive phases on the electrical properties of rocks using impedance spectroscopy  

Hadiseh Mansouri, Virginia Toy, Kevin Klimm, Sören Tholen, and Friedrich Hawemann

We have employed impedance spectroscopy to investigate the impact of chemical composition and microstructure on the electrical properties of geological samples. Our study focused on a metapelite sample containing graphite, extracted from a depth of 530 meters in borehole DT-1B as part of the DIVE (Drilling the Ivrea-Verbano zonE) project in Ornavasso, Italy. Additionally, we examined the electrical properties of synthetic mineral assemblages. These were created by combining quartz powders with variable amounts of graphite (1% and 5% by weight), muscovite (5% by weight), and biotite (5% by weight). The goal was to identify which conductive or semiconductive phases predominantly influenced the electrical behavior of the metapelite. Measurements were conducted using a Solartron-1260 Impedance/Gain-Phase Analyzer within a piston cylinder apparatus. The experiments were carried out at a pressure of 500 MPa, temperatures ranging from 22 to 1000 °C, nominally dry conditions, and across a frequency range from 0.1 Hz to 200 kHz.

All samples exhibited high electrical resistance (R > 106 Ω.m), low electrical conductivity (< 10-6 S/m) and behaved as capacitors, with a phase angle magnitude exceeding 70° for most frequency ranges at temperatures below 200 °C. A representative impedance spectrum (Nyquist plot) illustrates this behavior through a partial semicircular arc originating from the origin. An inverse relationship between electrical conductivity and temperature was observed in almost all samples when temperatures increased from 300 to 500 °C. This phenomenon is attributed to the presence of open grain boundaries in the samples, leading to electrical charge scattering. Notable variations in electrical behavior were observed at temperatures exceeding 600 °C, including a linear increase in electrical conductivity, changes in Nyquist plots such as a reduction in prominence of the ‘grain interior arc’ and an increase in significance of the ‘grain boundary arc’, a decrease in sample capacitance, and a significant decline in the phase angle's frequency dependency. Microstructural analysis reveals that these changes were associated with dehydration melting of mica in mica-bearing samples and the growth and interconnection of graphite grains in graphite-bearing samples. Variations in activation enthalpy with temperature suggested that impurity conduction and small polaron hopping played a crucial role at lower temperatures, while the diffusion of H and alkali ions (in mica-bearing samples) or carbon (in graphite-bearing samples) along grain boundaries became significant at higher temperatures.

The natural metapelite sample exhibited electrical conductivities similar to the quartz + 5% graphite sample at high temperatures, reaching 10-1.5 S/m at 1000°C. This is comparable to the conductivity levels typically measured by magneto-telluric (MT) surveys in Earth's crust.

How to cite: Mansouri, H., Toy, V., Klimm, K., Tholen, S., and Hawemann, F.: Quantifying the influence of the type and arrangement of conductive phases on the electrical properties of rocks using impedance spectroscopy , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3448, https://doi.org/10.5194/egusphere-egu24-3448, 2024.

EGU24-3734 | ECS | Posters on site | EMRP1.2

Spatio-Temporal Imaging of Instability and Transport of Pickering Nanodroplets in Porous Media 

Boxin Ding, Seyedeh Hannaneh Ahmadi, Steven Bryant, and Apostolos Kantzas

Featuring a large specific surface area with associated high reactivity, nanomaterials in various morphologies are ideal candidates for improved oil recovery (IOR), enhanced geothermal systems (EGS) and carbon capture utilization and storage (CCUS).  Encapsulation of solid nanomaterials within an oil-in-water (O/W) emulsion (i.e., Pickering emulsion) has been employed to prevent the aggregation and deposition of the nanomaterials in subsurface reservoirs in recent decades. Here, the dispersed phase droplets were decreased to nanoscale through a utilizable procedure. These nanodroplets were stabilized solely by polymer-coated magnetic iron oxide nanoparticles. Low-field NMR and X-ray CT were employed to constantly monitor the stability of Pickering nanoemulsions until phase separation. The polydisperse nanoemulsions are more easily separated due to the severely inhomogeneous chemical potentials of the emulsion droplets. Experimental and theoretical modeling results reveal that the Ostwald ripening is the main instability mechanism for nanoemulsions due to the very small droplets associated with a high surface area. The insolubility of long-chain hydrocarbons in water acts as a kinetic barrier to Ostwald ripening, making those nanoemulsions, both the Pickering and Classical (which is formed only by polymer) ones, inherently stable to Ostwald ripening.

The transport and retention of the Pickering nanodroplets in porous media is examined by X-ray CT imaging. Accordingly, in-situ transport of the nanoemulsions in a water-saturated sandpack was quantified spatiotemporally through X-ray CT. Effluents were collected and analyzed to further comprehend the nanoemulsion displacement and retention in porous media. Experimental results demonstrate that accumulation and retention of the nanodroplets in porous media are stimulated by ionic strength, nanodroplet size distribution, and nanoparticle wettability. Three transport modes in porous media (flow through with minimal retention, migration of accumulated nanodroplets, and retention of accumulated nanodroplets) can be achieved through carefully designing the nanoemulsion system.

These findings shed light on the fundamental understanding of the (nano-)colloidal dispersions transport in porous media and provide implications for IOR, EGS, and CCUS.

How to cite: Ding, B., Ahmadi, S. H., Bryant, S., and Kantzas, A.: Spatio-Temporal Imaging of Instability and Transport of Pickering Nanodroplets in Porous Media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3734, https://doi.org/10.5194/egusphere-egu24-3734, 2024.

The study of caprock assumes paramount significance, particularly in elucidating alterations in the sealing conditions of petroleum reservoirs. However, it is imperative that corresponding simulation experiments transcend a singular focus on CO2 and caprock, extending to a comprehensive study of the reservoir-caprock system. Experimental protocols were implemented, entailing the sequential flow of CO2-rich fluid first through the reservoir and subsequently through the caprock. The chosen samples and conditions were drawn from potential CO2 utilization and storage blocks in the Subei Basin, China, featuring sandstone reservoirs and mudstone caprocks. The experimental paradigm simulated the interaction when CO2 migrating along the sandstone and then reaching the mudstone caprock, spanning a duration of 37 days.

Results underscore that the introduction of CO2-rich fluid predominantly instigates the dissolution of sandstone reservoirs, with notable dissolutions observed in feldspar and clay minerals, while secondary mineral precipitation remains negligible. Upon the fluids traversal through the mudstone caprock, initial dissolution occurs in carbonate minerals, accompanied by continuous precipitation of secondary clay minerals. These secondary minerals not only occupy calcite dissolution pores but also precipitate on the surfaces of rock particles, asserting dominance in the water-rock reaction within the mudstone.

Supported by geological observations and numerical simulations, these experiments illuminate the material adjustment processes ensuing from the introduction of CO2-rich fluid into the reservoir-caprock system. The infusion of CO2-rich fluid induces mineral dissolution, augmenting pore space within the reservoir, with ion products subsequently transported to the mudstone caprock. Under conditions characterized by a slower flow rate and a more extensive water-rock reaction surface area in the mudstone caprock, the water-rock interaction accelerates the dissolution and reprecipitation of calcite and other minerals. The reprecipitated minerals effectively occupy caprock pores and fractures, thereby enhancing the caprock's sealing capacity.

How to cite: Zhou, B., Lun, Z., and Wang, B.: An Experimental Study of CO2 Flooding the Reservoir-caprock System: Implication for the Stability of Caprock during CO2 Intrusion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4095, https://doi.org/10.5194/egusphere-egu24-4095, 2024.

Linking the pore structure distributions and velocity-pressure relationship is important for understanding geological processes and in situ stress conditions. During the pressure loading, the pressure-velocity relationship is controlled by variation of pore-aspect-ratio spectrum distribution (pore-aspect-ratio vs. porosity) with pressure: on the one hand, the “flat crack” (aspect ratio) will be squeezed and closed, causing the large velocity variation in the low-pressure regimes; on the other hand, the shape and volume of the “round pore” (aspect ratio) are less sensitive to pressure, controlling the smaller velocity change at high pressures. The above pore-structure variation process and its effect on the velocity-pressure relationship allow us to invert and analyze the distribution characteristics from the laboratory velocity-pressure data.  

The power-law distribution has been universally applied to characterize the length and aperture distribution in natural fractures; however, it is still not well understood whether the pore-aspect-ratio spectrum distribution also follows the power law and how this power-law distribution relates to other power-law distributions of fractures. In this study, we examine the universality of the power-law relationship for the pore aspect ratio spectrum distribution and show that this distribution is the natural outcome of the power-law behavior of the length and aperture distribution in the rock fracture network.

We first collected laboratory ultrasonic velocity-pressure data for 52 rock samples with various porosities and lithologies. We then used a power law assumption to link the pore aspect ratio and porosity. The power-law exponents (hereafter referred to as the E factor) of the power-law distributions were successfully obtained by inverting the compiled velocity-pressure datasets. The inversion results showed a universal relationship between the E factor and porosity. We also demonstrated that the power-law distribution of the pore-aspect-ratio spectrum and the universal E factor-porosity trend can be explained using the length and aperture distribution characteristics of the microcrack system of rocks. This universal E factor-porosity trend provides a link between porosity and sensitivity of seismic velocities to pressure. Hence, our work not only emphasizes the relevance of natural fracture fractal distributions for a broad range of lithologies but also provides the parameterized method for relating the velocity-pressure relationship of any rock to porosity variation.

How to cite: Wang, H.-M., Tang, X.-M., and Doan, M.-L.: The power-law distribution of the rock pore structure: inversion and analysis of laboratory velocity-pressure data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4456, https://doi.org/10.5194/egusphere-egu24-4456, 2024.

EGU24-5512 | ECS | Posters on site | EMRP1.2

Prediction of Subsurface Physical Properties Through Machine Learning: The case of the Riotinto Mine. 

Abraham Balaguera, Pilar Sánchez-Pastor, Sen Du, Montserrat Torné, Martin Schimmel, José Fernández, Jordi Díaz, Jaume Vergés, Ramon Carbonell, Susana Rodríguez, and Diego Davoise

Recently, under the umbrella of a public-private collaboration project (CPP2021-009072), Atalaya Riotinto Minera S-L. and the CSIC through its institutes IGEO-Madrid and Geo3BCN-Barcelona, have undertaken an ambitious and innovative initiative to validate the applicability of state-of-the-art monitoring and prospecting systems for better tracking of deformations that may occur in the mine’s environment and to study the petrophysical properties and 3D structure of the mine subsurface. In this work, we present the results of machine learning (ML) models developed to predict various physical properties of rock (PPR) for classifying main lithologies. This analysis is based on over a thousand surface rock samples and nine wells with lithology descriptions and density logs. These data sets have allowed us to characterize the main geological units and formations comprising the subsurface of the Riotinto (RT) mine. A quality control process was applied to the PPR database through lithology and intervals to identify and correct outlier values. Multi-Layer Perceptron neural networks were employed to predict these outliers. Various mathematical and supervised machine learning models were developed to understand and predict PPR associated with different geological units. The models were compared to identify the most efficient and stable one. Additionally, new machine learning models were implemented to predict lithofacies based on PPR. These models were then used to predict PPR and classify lithofacies in wells within a mining site.

The results suggest that machine learning-based PPR prediction reduces uncertainty, providing a clearer understanding of the anisotropic characteristics of geological units. Apparent density, total porosity, and P-wave velocity properties were found to predict lithofacies with an accuracy of approximately 80%. In conclusion, this advancement not only redefines the precision with which lithofacies can be identified in the Riotinto mine but also establishes a new methodology for the lithological characterization of the subsurface, leveraging both well logs and direct measurements on surface samples. This study demonstrates the potential of using new ML techniques in mining and geology, as well as opening the door to the use of these models for 3D characterization of lithological units by integrating geophysical data at the exploratory level.

This work, financed with reference CPP2021 009072, has been funded by MCIN/AEI/10.13039/501100011033 (Ministry of Science, Innovation and Universities/State Innovation Agency) with funds from the European Union Next Generation/PRTR (Recovery, Transformation, and Resilience Plan).

Keywords: Machine Learning, Mining, Petrophysical Properties and Geological Characterization.

How to cite: Balaguera, A., Sánchez-Pastor, P., Du, S., Torné, M., Schimmel, M., Fernández, J., Díaz, J., Vergés, J., Carbonell, R., Rodríguez, S., and Davoise, D.: Prediction of Subsurface Physical Properties Through Machine Learning: The case of the Riotinto Mine., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5512, https://doi.org/10.5194/egusphere-egu24-5512, 2024.

EGU24-5612 | ECS | Posters on site | EMRP1.2

Pressure dependence of permeability in cracked rocks: experimental evidence of non-linear pore-pressure gradients from local measurements 

gang lin, Samuel Chapman, Dmitry Garagash, Jérôme Fortin, and Alexandre Schubnel

Understanding the coupling between rock permeability, pore-pressure and fluid-flow is crucial, as fluids play an important role in the Earth’s crustal dynamics. Here, we measured the distribution of fluid pressure during fluid-flow experiments on two typical crustal lithologies, a granite and a basalt. Our results demonstrate that the pore-pressure distribution transitions from a linear to a non-linear profile as the imposed pore-pressure gradient is increased (from 2.5 MPa to 60 MPa) across the specimen. This non-linearity results from the effective pressure dependence of permeability, for which two analytical formulations were considered: an empirical exponential or a modified power-law. In both cases, the non-linearity of pore pressure distribution is well predicted. However, using a compilation of permeability vs. effective pressure data for granitic and basaltic rocks, we show that our power-law model, based on crack micromechanics (combining Hertzian contact and cubic law theories), outperforms the exponential formulation at low effective pressures. 

How to cite: lin, G., Chapman, S., Garagash, D., Fortin, J., and Schubnel, A.: Pressure dependence of permeability in cracked rocks: experimental evidence of non-linear pore-pressure gradients from local measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5612, https://doi.org/10.5194/egusphere-egu24-5612, 2024.

EGU24-6120 | ECS | Posters on site | EMRP1.2

Access for free: How to get free-of-charge access to Dutch Earth scientific research labs through EPOS-NL  

Richard Wessels and Ronald Pijnenburg

Access to top research equipment facilitates top research. However, the research equipment needed may not always be available within individual institutes, while access to external facilities may not in all cases be affordable, or even possible. This restricts the research that any individual can do and hampers scientific breakthroughs, particularly across disciplines. To overcome this limitation, a collaborative infrastructure network was initiated: EPOS-NL (European Plate Observing System- Netherlands). EPOS-NL provides free-of-charge access to geophysical labs at Utrecht University, Delft University of Technology, and the Dutch geological survey of TNO, all in the Netherlands, for research within rock physics, analogue modelling of tectonic processes, X-ray tomography and microscopy. These labs include capabilities for among others: A) Mechanical and transport testing at crustal stress, temperature and chemistry conditions; B) Large-scale experiments, e.g. up to 30 m-scale fluid transport testing and particle tracking, or hydrostatic compression (< 100 MPa) of 6m long samples; C) Analogue tectonic modelling, including dynamic model imaging in 2D and 3D; D) X-ray tomography at sub-µm resolution; E) A correlative workflow for electron microscopy and microchemical mapping, down to nm resolution; and F) Microfluidics: Direct visualization of dynamic, physical and chemical fluid transport processes in the pore networks. As such, these labs can provide you with the means and expertise for your research into the fundamental processes governing the behavior of the Earth’s crust and upper mantle.

Access to EPOS-NL can be requested by applying to a bi-annual call, posted on www.EPOS-NL.nl. This involves submitting a short (1-2 page) research proposal. Research proposals are reviewed on the basis of feasibility and excellence, but generally have a high chance of success (~80% in previous rounds). Interested? Have a look on the EPOS-NL website – and apply!

How to cite: Wessels, R. and Pijnenburg, R.: Access for free: How to get free-of-charge access to Dutch Earth scientific research labs through EPOS-NL , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6120, https://doi.org/10.5194/egusphere-egu24-6120, 2024.

EGU24-7192 | Orals | EMRP1.2

Time-lapse Acousto-Mechanical Response to Moisture-Induced Reduction of Fracture Stiffness in Granite 

Rui Wu, Paul Selvadurai, Ying Li, Kerry Leith, Qinghua Lei, and Simon Loew

Water infiltration into crustal rocks, particularly through fractures, significantly impacts seismic wave propagation and the characterization of fracture systems. Our study (Wu et al, 2023a) investigates the acousto-mechanical behavior of fractured granite experiencing gradual water infiltration over 12 days. We reveal an order of magnitude difference in wave amplitudes when compared to intact granite, with a correlation between wave amplitudes and the movement of the wetting front. The laboratory experiments show that fracture stiffness decreases exponentially as the wetting front advances, indicating moisture-induced matrix expansion (Wu et al, 2023b) around the fracture leads to increased asperity mismatch and reduced stiffness. By back-calculating the fracture stiffness and capturing the effects of water infiltration on seismic attenuation through a numerical model, this research illuminates how elastic waves propagate across fractures undergoing moisture-induced expansion, a crucial aspect of fracture characterization and understanding of the near-surface environment's response to hydrological changes. Our research sheds light on an important question in fracture characterization: how elastic waves propagate across a fracture undergoing moisture-induced expansion.

Publications related to this research:

Wu, R., Selvadurai, P. A., Li, Y., Leith, K., Lei, Q., & Loew, S. (2023a). Laboratory acousto-mechanical study into moisture-induced reduction of fracture stiffness in granite. Geophysical Research Letters, 50, e2023GL105725. https://doi.org/10.1029/2023GL105725

Wu, R., Selvadurai, P. A., Li, Y., Sun, Y., Leith, K., & Loew, S. (2023b). Laboratory acousto-mechanical study into moisture-induced changes of elastic properties in intact granite. International Journal of Rock Mechanics and Mining Sciences, 170, 105511. https://doi.org/10.1016/j.ijrmms.2023.105511

How to cite: Wu, R., Selvadurai, P., Li, Y., Leith, K., Lei, Q., and Loew, S.: Time-lapse Acousto-Mechanical Response to Moisture-Induced Reduction of Fracture Stiffness in Granite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7192, https://doi.org/10.5194/egusphere-egu24-7192, 2024.

EGU24-7768 | Posters on site | EMRP1.2

Fast quantitative estimation method of fracture cavity porosity based on convolution deep neural network 

Zhean Zhang, Longcheng Liu, Qingyin Xia, Tingting Xie, and Yuqing Niu

       Traditional interpretation of imaging logging data often involves manually importing various data types to calculate the porosity of fractures in the target area. This process becomes challenging due to the lack of gas and oil information in the raw data, especially when dealing with less-than-ideal raw data. The proposed method addresses this challenge by offering a rapid estimation approach for fracture porosity that reduces manual work and enhances process efficiency within an acceptable error limit.  

       The estimation method relies on path morphology [1] and convolutional neural networks for the extraction of fracture and cavity parameters. Initially, a path morphology method is applied to identify inclined fractures, followed by the use of a rotation jamming algorithm [2] to obtain rectangles with the minimum area in each cavity. These rectangles incorporate the angle of the rectangle and the lengths of its short and long sides. Parameters related to horizontal fractures, vertical fractures, and cavities are then utilized for the estimation of porosity.

      The original imaging logging conductivity is processed to distinguish inclined fractures from other fractures during the extraction process. Traditional binarization and denoising methods are not directly applied since cavities on basic binary images are also white. Thus, specific curves need to be extracted from the original conductivity images using a path morphology algorithm. On the other hand, convolutional neural networks (CNNs) are required for the identification of the shape of restored cracks due to the influence of cavities on traditional mathematical fitting processes. LeNet and AlexNet, among various CNN algorithms, are employed for this purpose. Specifically, the modified AlexNet algorithm adopts the maximum pooling method, Softmax function in the output layer, and the Adam optimizer in the learning process to improve efficiency and reduce memory occupation. The related parameters of cavities, horizontal fractures, and vertical fractures are calculated by the rotation jamming algorithm after the extraction of inclined fractures. Traditional Hough transform is considered time-consuming for evaluating a large number of cavities, leading to the adoption of an alternative approach—obtaining circumscribed rectangles with minimum area in a connected domain. This approach improves computation speed by focusing on directions coinciding with the long side of polygons, treating the long and short sides of rectangles as the major and minor axes of ellipses. In a conductivity image, cavities contain both convex and concave closures simultaneously, requiring the filling of concave ones to convex before applying the rotation jamming algorithm. The effective porosity parameters can be obtained using the developed programs.

      The method offers high efficiency and automation, extracting various types of fractures along with cavities within an acceptable error limit, providing valuable information for geologists in evaluating high-potential targets.

[1]Li et al. Estimating Porosity Spectrum of Fracture and Karst Cave from Conductivity Image by Morphological Filtering. JJU, 2017, 47(04): 1295-1307.

[2] Toussaint, G.T. A simple linear algorithm for intersecting convex polygons. The Visual Computer 1, 1985: 118–123. 

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How to cite: Zhang, Z., Liu, L., Xia, Q., Xie, T., and Niu, Y.: Fast quantitative estimation method of fracture cavity porosity based on convolution deep neural network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7768, https://doi.org/10.5194/egusphere-egu24-7768, 2024.

EGU24-8600 | Orals | EMRP1.2

Response of the caprock's fluorescence parameters to the leakage of palaeo-oil zones 

Keshun Liu, Jiangxiu Qu, Ming Zha, and Xiujian Ding

Abstract: The northern part of the the Junggar Basin is the Siberian plate, and the western part is the Kazakhstan plate, which is an important part of the Central Asian orogenic belt. This study discusses how fluorescence parameters inside the mudstone caprocks of the Mobei Bugle and Mosuowan Bugle respond to the leakage of palaeo-oil zones. It is based on X-ray diffraction analysis, TOC testing, physical property testing, rock pyrolysis experiments, and image observation. First, using quantitative fluorescence technology, it was established that the appropriate particle size range for the study area mudstone is between 100 and 140 mesh by examining the QGF E intensity and sample loss rate of the control group. Then, the influence of retained primary hydrocarbons inside the mudstone on the test results of quantitative fluorescence technology is speculated to be relatively weak based on an analysis of the correlation between TOC value and total hydrocarbon value, TOC value and fluorescence parameters. The QGF index of the 5265-5302m reservoir in PD1 well ranges from 3.9 to 87.2, with an average of 16.18; the QGF index of the 7034-7195m reservoir in MS1 well ranges from 2.2 to 57.5, with an average of 11.6. The reservoirs of the PD1 and MS1 wells contain palaeo-oil zones, based on the QGF index classification criteria. Both image observation and micro resistivity imaging logging analysis demonstrate that the caprock's physical properties in the PD1 well are inferior to those in the MS1 well. The pore types of the PD1 well caprock are filled dissolution pores and residual intergranular pores, whereas the pore types of the MS1 well caprock are dissolution pores and microcracks. There is a discrepancy of approximately 9 times between the development density of fractures in the MS1 well caprock (0.989 pieces/m) and the PD1 well caprock (0.114 pieces/m). The palaeo-oil zone can be effectively sealed due to the poor physical properties of the PD1 well caprock. The oil testing conclusion of the reservoir is oil-water layer, with a daily oil production of 8.52t. Therefore, as the depth decreases, the QGF E intensity value decreases, and the QGF λmax and TSF R1 values reflect higher hydrocarbon maturity. The MS1 well caprock has good physical properties and cannot effectively seal the palaeo-oil zone. The oil testing conclusion of the reservoir is water layer, with a daily oil production of 4.4t. As the depth decreases, the QGF E intensity value increases, and the QGF λmax and TSF R1 values reflect lower hydrocarbon maturity. Comprehensive analysis suggests that the fluorescence parameters inside the caprock exhibit characteristics related to the degree and form of palaeo-oil zone leakage.

Keywords: Quantitative fluorescence technology, Fluorescence parameters, Mudstone caprock, Palaeo-oil zones

How to cite: Liu, K., Qu, J., Zha, M., and Ding, X.: Response of the caprock's fluorescence parameters to the leakage of palaeo-oil zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8600, https://doi.org/10.5194/egusphere-egu24-8600, 2024.

EGU24-8632 | Posters on site | EMRP1.2

Seismic properties of serpentinites under increasing pressure and temperature conditions 

Mai-Linh Doan, Heming Wang, Anne-Line Auzende, Stéphane Schwartz, Samuel Chapman, and Jérôme Fortin

Serpentinites result from the hydration of ultramafic rocks (e.g., peridotite and pyroxenite) that transform primary mineralogical assemblages (olivine-pyroxene) into different serpentine species (lizardite-chrysotile-antigorite) depending on the pressure-temperature (P-T) conditions (Schwartz et al, 2013) related to geodynamic context. Serpentinization mainly occurs from oceanic ridges at LP conditions to subduction zones at HP conditions and its extent needs to be quantified.

The Vp/Vs ratio is a tool of choice to distinguish serpentinite from other mafic to ultramafic rocks and thus to investigate the serpentinization extent. The seismic velocity of serpentinites depends on the type and the volume of serpentine species (lizardite/antigorite) present in the rock, as well as the microstructural evolution of the serpentinite, however, these topics remain poorly understood.

We selected blueschist and eclogitic serpentinite samples collected in the internal zone of the western Alps. One eclogitic serpentinite sample was also experimentally dehydrated at 700°C in standard pressure conditions. The petrology and (micro)structures of the samples were characterized using both 2D petrological thin sections and 3D X-ray tomography. We performed velocity measurements on the samples at low frequencies (quasi-static stress-strain method: 0.02-1000 Hz) and ultrasonic frequency (wave travel time method: MHz) at different effective pressures (low-frequency experiments: 2-25 MPa; ultrasonic experiments: 0-70 MPa). The description of experimental equipment and methodology can be found in Borgomano et al. (2020). The studied frequency range covers the field geophysical data frequency band and therefore provides better constraints for interpreting the serpentinization extent. As expected, the Vp/Vs ratio changes depending on the mineralogy: lizardite is characterized by higher Vp/Vs (2-2.1) and lower Vp (5200-5700 m/s) than antigorite with lower Vp/Vs (1.75-2) and higher Vp (6000-7000 m/s). Anisotropic structure due to mineral preferred orientation manifest by velocity variation with sample orientation: overall, the Vp and Vs anisotropy degree (Ap, As) of antigorite (Ap:3%-18%; As:1%-16%) are larger than those of lizardite (Ap:3%-9%; As:3%-8%). Furthermore, the seismic velocity of the serpentinite is almost unchanged with pressure and frequency, but pressure- and frequency-dependence of the velocity arise in the dehydrated antigorite sample: 1) in dry condition, with lower Vp/Vs ratio (1.46-1.6) and lower Vp (3500-4600 m/s) in the effective pressure range of 2-25 MPa and almost no frequency dispersion; 2) in water-saturated condition, with higher Vp/Vs ratio (1.87-1.89) and higher Vp (5060-5190 m/s) at ultrasonic frequency, as well as a significant velocity dispersion band linking the results from seismic frequencies to ultrasonic frequency. This study contributes to the calibration of seismic velocity profiles to track the mineralogical transition between lizardite and antigorite, which is related to increasing degrees of metamorphism.

 

References:

Schwartz et al. (2013). Pressure–temperature estimates of the lizardite/antigorite transition in high pressure serpentinites. Lithos, 178, 197-210.

Borgomano et al. (2020) An apparatus to measure elastic dispersion and attenuation using hydrostatic-and axial-stress oscillations under undrained conditions. Rev. Sci. Instrument, 91(3).

How to cite: Doan, M.-L., Wang, H., Auzende, A.-L., Schwartz, S., Chapman, S., and Fortin, J.: Seismic properties of serpentinites under increasing pressure and temperature conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8632, https://doi.org/10.5194/egusphere-egu24-8632, 2024.

EGU24-9014 | Orals | EMRP1.2

Influence of microplastic occurrence on complex conductivity of river sediments 

Shuai Li, Mingsa Xu, Yumeng Peng, and Xiangyun Hu

This study utilized an improved sand column experimental setup to investigate the effects of microplastic on Yangtze River bank sediments. The experiments conducted included Darcy experiments, electrokinetic experiments, and wettability experiments, together for the same sample. By varying the particle size of the microplastics in the samples, we were able to observe different response of the electrical properties as well as hydrogeophysical parameters in the samples.

Results show that increasing the mass fraction of mixed microplastics generally resulted in a significant decrease in sample electrical conductivity associated with an increase in permeability. These were expected to be due to the weak conductivity and strong hydrophobic properties of plastic particles, as well as the small adhesive forces between particles, which increased the pore space of the sediments and ultimately increased permeability. However, an anomalous increase trend was observed when decreasing the particle size of the mixed microplastics. Under this condition, increasing the concentration of same size plastic particles enhanced the electrical conductivity of the sediment sample. This anomaly phenomenon was reflected in both permeability and wettability, resulting in a decrease in sample permeability and a significant increase in sample hydrophobicity. Our observations using optical microscopy revealed two types of microplastic distribution in the sediments: one case was that microplastic particles were distributed within sediment pores and they did not touch each other, the other was that they were adsorbed onto sediment particle surfaces. We hypothesized that changes in the existence form of microplastics altered the double-layer structure of sediments, ultimately changing their hydrogeophysical parameters. This work has significance and relevance for electromagnetic-based characterization of microplastic-filled porous materials; for example, estimation of microplastic abundance in sediments.

How to cite: Li, S., Xu, M., Peng, Y., and Hu, X.: Influence of microplastic occurrence on complex conductivity of river sediments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9014, https://doi.org/10.5194/egusphere-egu24-9014, 2024.

EGU24-9568 | ECS | Orals | EMRP1.2

Reducing boundary effects during True Triaxial loading of rocks 

Ashley Stanton-Yonge, Thomas Mitchell, Philip Meredith, John Browning, and David Healy

Even though stresses in the crust are triaxial (𝜎1>𝜎2>𝜎3) the overwhelming majority of rock deformation experiments are conducted under axisymmetric (or conventional triaxial) loading (𝜎1>𝜎2=𝜎3). This configuration disregards the effect of 𝜎2 on the physical and deformation properties of rocks, thus complicating and degrading the extrapolation of results to natural crustal conditions. A True Triaxial loading configuration is necessary to overcome this simplification, however, these improvements in addressing real crustal conditions come at a cost, which is the challenging boundary conditions that arise from having six loading rams rather than just two. Two main loading boundary effects can severely impact the stress distribution and failure mechanism of samples deformed in a True Triaxial Apparatus (TTA): 1) the end friction effect caused by the stiffness contrast between the rock sample and the metal loading platens, and 2) the unstressed sample edges resulting from the requirement that loading platens must necessarily be slightly smaller than the rock specimen. Managing and reducing these boundary effects is fundamental for obtaining accurate and representative data from true triaxial experiments, and for the further development of these apparatuses.

A novel TTA developed in the UCL Rock & Ice Physics Laboratory was designed to subject cubic or cuboid rock samples to truly triaxial stresses through the independent control of six loading rams. The apparatus is equipped with a confining and pore pressure system that allows for the deformation of saturated samples whilst simultaneously measuring permeability along the three axes. A suite of Finite Element Method (FEM) models was implemented to evaluate the parameters that minimize loading boundary effects in UCL’s TTA for a 50 mm edge-length cubic sample of sandstone. Our results indicate that using aluminum loading platens (𝐸𝑠𝑎𝑚𝑝𝑙𝑒/𝐸𝑝𝑙𝑎𝑡𝑒𝑛=0.47) reduces the end friction effect by a factor of two compared to using steel platens (𝐸𝑠𝑎𝑚𝑝𝑙𝑒/𝐸𝑝𝑙𝑎𝑡𝑒𝑛=0.17). In addition, we find that elevated confining pressure significantly reduces the stress concentration produced by unstressed edges. Specifically, a confining pressure of 10 MPa eliminates tensile stresses at the sample corners. These results are currently being implemented into the experimental protocol and execution in UCL’s TTA in order to ensure that we obtain reliable true triaxial data. However, these observations are generic and could therefore contribute to improved development and operation of true triaxial loading systems generally.

How to cite: Stanton-Yonge, A., Mitchell, T., Meredith, P., Browning, J., and Healy, D.: Reducing boundary effects during True Triaxial loading of rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9568, https://doi.org/10.5194/egusphere-egu24-9568, 2024.

EGU24-9712 | ECS | Orals | EMRP1.2

Modeling of spectral induced-polarization measurements on cm-sized metallic spheres in sand-water-mixtures 

Dennis Kreith, Katrin Breede, Zeyu Zhang, Andreas Weller, and Matthias Bücker

The detection of metallic particles in the subsurface has been an important field in applied geophysics for several decades, e.g. in the exploration of ore deposits or in monitoring measurements at bioremediation sites. Due to the comparably high conductivity and high polarizability of metallic particles, geophysical methods using the electrical conductivity and especially induced polarization are highly suitable methods for applications of this kind.

To correctly interpret data measured in the field, a deep understanding of the underlying conduction and polarization mechanisms is necessary. Both, laboratory measurements with controlled experimental conditions and theoretical models describing the basic physical processes can help to achieve this kind of understanding. However, theoretical models usually are not suitable to be directly compared to laboratory measurements, because they usually consider idealized situations and exhibit a large number of free parameters that can not be controlled in measurements.

To overcome this gap, we compare experimental data of a cm-sized metallic sphere embedded in water-saturated sand with a corresponding theoretical model. To explain the remaining differences between measured and modeled data, we discuss how different processes, e.g. the geometry of the measurement setup or dissolved metal ions in the fluid, might affect the measurement and adapt our model accordingly. By doing so, we are able to reproduce the experimental results with the predictions by our theoretical model.

How to cite: Kreith, D., Breede, K., Zhang, Z., Weller, A., and Bücker, M.: Modeling of spectral induced-polarization measurements on cm-sized metallic spheres in sand-water-mixtures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9712, https://doi.org/10.5194/egusphere-egu24-9712, 2024.

EGU24-11028 | ECS | Posters on site | EMRP1.2

Experimental Analysis and Creep-Fatigue Damage Modeling of Sandstone Deformation related to Energy Storage Systems 

Deyan Tian, Zhengyang Song, Kavan Khaledi, Zhen Yang, and Florian Amann

The porous sandstone formations offer large capacities for the geological storage of clean energy sources like hydrogen and compressed air. This paper aims to investigate the deformation mechanisms in sandstone under the varying loading conditions. Employing a combined experimental and numerical approach, we investigate the mechanical behavior of sandstone under cyclic loading conditions. The results obtained in this study indicate three distinct deformation regimes in sandstone specimens developed under multi-level, multi-frequency cyclic loads, i.e.,1) instantaneous elastic deformation, 2) transient and steady-state strain due to creep, and 3) rapid deformation leading to fatigue failure, mainly driven by micro-crack development. In response to these deformation mechanisms, a viscoelastic-damage model is proposed. This model is based on the standard Burger's viscoelasticity combined with an energy-driven damage model to represent the creep-fatigue behavior in sandstone. The modeling results were verified by comparing the predictions with the experimental data. The experimental and numerical results presented an essential insight for designing and managing geological storage systems in sandstone formations.

How to cite: Tian, D., Song, Z., Khaledi, K., Yang, Z., and Amann, F.: Experimental Analysis and Creep-Fatigue Damage Modeling of Sandstone Deformation related to Energy Storage Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11028, https://doi.org/10.5194/egusphere-egu24-11028, 2024.

EGU24-11658 | ECS | Orals | EMRP1.2

Characterizing Rock Physical Properties in the Nevados de Chillán Geothermal System 

Valentina Mura, Gloria Arancibia, John Browning, David Healy, Julian Mecklenburgh, and Diego Morata

In geothermal systems the thermo-physical properties of the rocks change as they interact with fluids passing through the volcanic system and during discrete events such as earthquakes and magma intrusion. To characterize a geothermal system and the flow of fluid through a sub-volcanic complex, targeted rock physical tests are needed for the rocks of the area conducted at natural P-T conditions. Here, we present rock property characterization of the main geological units of the active Nevados de Chillan Geothermal System, located in the Southern Volcanic Zone (SVZ), an area with some of the largest geothermal potential in the Andes. 

Six representative blocks of the geothermal host reservoir and overlying strata were collected from the volcanic basement. The main geomechanical units of this system are (from oldest to youngest): 1) andesites, tuffs and breccia of the Cura-Mallin Formation (Miocene country rocks); 2) granodiorites and diorites of the Santa Gertrudis Bullileo Batholith (15.7 Ma and 5.9 Ma, respectively); and 3) hornfels from the contact between the granitoids and country rocks. Cylindrical core samples (26 mm diameter x 65 mm length) from each block were used to quantify density, porosity, and ultrasonic wave velocities at different confining pressures. All tests were carried out at the Rock Deformation Laboratory, University of Manchester. Polished thin sections were prepared from blocks of the same orientation as the cored directions and analyzed using petrographic.

Granodiorite has the lowest porosity at between <1 to 2% and the fastest P- and S-wave velocities (5.5 to 5.9 km/s and 3.1 to 3.5 km/s, respectively). The diorite has a higher porosity of between 4 to 6% which coincides with lower ultrasonic velocities (3.5 to 5.0 km/s and 3.5 to 5.0 km/s, respectively). This can be explained by the higher presence of macro, micro-fractures, and alteration minerals in the diorite. Hornfels has possess similar porosities (>2%) to the granodiorite and 4.8 to 5.7 km/s P-wave velocities and 2.7 to 3.3 km/s S-wave velocities. The andesitic lavas have porosities ranging 3-7%, while the tuffs and breccias have porosities of 12-30%. Elastic waves velocities in the andesitic lavas are around 2 km/s faster than the pyroclastic rocks.

Tests with cycles of increasing and decreasing hydrostatic pressure (up to approximately 150 MPa) show that granodiorite and diorite exhibit sharp increases in P-wave velocity (Vp). This is attributable to the stiffening of the rock from the progressive closure of pre-existing cracks. Above 40 MPa, the rate of increase in Vp with pressure reduces markedly, implying that the remaining porosity is less compliant. This is consistent with the maximum burial depth of the rocks suggesting that those cracks formed because of bringing the rocks to the surface.

Finally, in terms of microstructural observations, the granodiorites, diorites and hornfels have large intragranular and intergranular fractures with very high aspect ratio, which are commonly oriented and therefore impart anisotropy. In contrast, the andesitic, tuffs and breccias porosity is higher than the crystalline rocks and is mainly composed of intergranular pores with low aspect ratios and relatively isotropic.

How to cite: Mura, V., Arancibia, G., Browning, J., Healy, D., Mecklenburgh, J., and Morata, D.: Characterizing Rock Physical Properties in the Nevados de Chillán Geothermal System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11658, https://doi.org/10.5194/egusphere-egu24-11658, 2024.

In petrophysics, characteristic lengths are used to relate fundamental transport properties of porous media. However, these characteristic lengths have mostly been defined and tested in fully saturated conditions, with few exceptions. This contribution revisits the seminal work of Johnson-Koplik-Schwartz (JKS) length, which represents an effective pore size controlling various transport-related properties of porous media, such as permeability and electrical conductivity. A novel closed-form equation is presented to predict the behavior of this characteristic length in partially saturated media for different saturation states. Using previous models in the literature that predict the intrinsic and relative electrical conductivities under partially saturated conditions, we infer the JKS length as functions of water saturation and properties associated with the pore-size distribution of the considered porous medium. The proposed method allows for the direct estimation of effective and relative permeability through electrical conductivity measurements. This creates new opportunities for remotely characterizing partially saturated media. We believe that this new model has potential for various applications in reservoir (CO2 or hydrogen storage) and vadose zone studies.

How to cite: Jougnot, D., Thanh, L. D., Solazzi, S., and Luo, H.: Revisiting the Johnson-Koplik-Schwartz characteristic length to relate transport properties in partially saturated porous media, insights from a fractal-based petrophysical approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12012, https://doi.org/10.5194/egusphere-egu24-12012, 2024.

EGU24-12229 | ECS | Posters on site | EMRP1.2

Nanostructures as an indicator for deformation dynamics  

Sarah Incel, Markus Ohl, Frans Aben, Oliver Plümper, and Nicolas Brantut

Grain-size reduction – with amorphization or melting as its extreme forms – plays a crucial role in fault-zones dynamics, e.g., the nucleation or arrest of earthquakes. Previous experiments have been mostly conducted on powdered samples and structural investigations of experimentally generated fault-gouge material provide contrasting results when it comes to the initiation of melting during fault slip. In the present study, we deformed four intact Westerly granite samples, to decipher whether there is a correlation between failure mode, i.e., controlled, self-stabilised, or dynamic, and grain-size reduction within the developing fault gouge. Controlled failure took place over several hours, self-stabilised failure occurred within a few seconds and dynamic failure lasted less than a second. To test the influence of aqueous fluids on the grain-size evolution within fault gouges, two runs were performed on samples, dynamically failing either in the presence or absence of pore fluids. All samples were deformed at the same effective pressure of 40 MPa and displacements along the newly created faults were with 1.2 to 2.0 mm in a similar range. We investigated the microstructures of each sample using a scanning electron microscope (SEM) and cut two focused-ion beam (FIB) sections per sample from selected areas, located within the fault gouges, to analyse their nanostructures using a transmission electron microscope (TEM). At low magnification at the SEM, no striking differences between the different fault gouges are visible. Features resembling “cooling cracks” become apparent at the highest magnification at the SEM and are only found in the samples that failed dynamically. Major differences between the samples are only obvious when comparing their nanostructures using TEM imaging. In the high-resolution TEM images as well as with the aid of selected area electron diffraction (SAED), we observe a clear correlation between failure mode or rupture speed and grain-size reduction, with an increase in amorphous material as rupture speed increases. Regardless of the availability of fluids, the samples that underwent dynamic failure reveal similar nanostructures. Both exhibit flow structures created by amorphous material. We believe that latter is the result of melting as we find numerous structural and chemical evidence for melting, e.g., euhedral magnetite crystals of a few tens of nanometer with adjacent depletion halos. Such indicators for melting are absent in samples that failed in a controlled or self-stabilised manner, highlighting the importance of rupture speed on fault gouge melting.

How to cite: Incel, S., Ohl, M., Aben, F., Plümper, O., and Brantut, N.: Nanostructures as an indicator for deformation dynamics , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12229, https://doi.org/10.5194/egusphere-egu24-12229, 2024.

EGU24-12400 | ECS | Orals | EMRP1.2

Behavior of elastic properties in carbonates: scale does matter 

Cédric Bailly, Emmanuel Léger, Simon Andrieu, Jean-Baptiste Regnet, Mathis Bergogne, Gaël Monvoisin, Bertrand Saint-Bezar, Perrine Mas, Hermann Zeyen, and Benjamin Brigaud

Understanding the evolution of rock physical properties with changing scale is a critical challenge when characterising spatial subsurface heterogeneities. One of the possible approaches can be using elastic wave velocities at various scales, from laboratory to field, by solely tuning the sensing wavelength to the studied media. Theoretically, in the case of a dry, isotropic, and homogeneous porous medium, at all scales of investigation, the elastic properties are not dependent on the scales of analysis (non-dispersive medium). However, as already pointed out in the literature, carbonate rocks have very heterogeneous pore networks at different scales, which may lead to different Representative Elementary Volumes (REV) with changing scales. In our work, we assume that the elastic wavelength is equal to the upper bound of the REV.

In this study, we investigated marine carbonate rocks of Middle Jurassic age outcropping in the western part of France (Charentes, near Angouleme city) in four different quarries. A total of three REVs were investigated, always in dry conditions: i) the centimeter scale, acquiring P and S wave velocities (Vp, Vs) on 60 cylindrical samples of one inch-diameter using a central frequency of 500 kHz (wavelength ~ 1 cm); ii) the decimeter scale, acquiring more than 1500 measurements of Vp and Vs on outcropping carbonates with a frequency of 40 kHz (wavelength ~ 10 cm); and iii) the decameter scale acquiring seismic wave velocity measurements along a vertical profile (geophones connected to a vertical outcrop wall), where the 6 kg sledgehammer source was situated on the plateau, delivering a frequency of 100 Hz (wavelength ~ 10 m). In parallel, a thorough geological description was done at all the investigated scales, combining i) microscope-driven microstructure analysis of samples under the microscope, ii) sedimentary facies description of outcrops and iii) fracture orientation analysis on photogrammetric models of quarries.

The elastic wave velocity results were interpreted considering facies and diagenetic processes of sedimentary rock fabric. At the centimeter scale (i), for a given sedimentary facies, we show a clear control of diagenesis (cementation and dissolution) on the elastic properties, in agreement with the well-documented literature. At the decimeter scale (ii), horizontal and vertical Vp-Vs data were used to construct 2D acoustic property maps (1 square meter). Two extreme behaviors can be pointed out. On the one hand, velocity data are homogeneous and anisotropic in zones showing evidence of primary stratification and lithostatic compaction. On the other hand, data are heterogeneous and isotropic in zones exhibiting significant early diagenesis heterogeneities (“hardgrounds”). These results are thus linked to facies and diagenesis heterogeneities. Finally, at the decameter scale, seismic velocities clearly show an azimuthal anisotropy, mainly controlled by the occurrence of outcropping open joints from tectonic origin. Our study tends to highlight the crucial need to always characterise sedimentary facies, diagenesis evolution and structural overprint in carbonate reservoir rocks if one wants to interpret and correctly understand the multi-scale elastic properties of carbonates.

How to cite: Bailly, C., Léger, E., Andrieu, S., Regnet, J.-B., Bergogne, M., Monvoisin, G., Saint-Bezar, B., Mas, P., Zeyen, H., and Brigaud, B.: Behavior of elastic properties in carbonates: scale does matter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12400, https://doi.org/10.5194/egusphere-egu24-12400, 2024.

EGU24-12452 | Orals | EMRP1.2

Reservoir compaction during and after fluid production: A case study of the Groningen Gas Field 

Suzanne Hangx, Ronald Pijnenburg, Takahiro Shinohara, Mark Jefferd, Mohammad Hadi Mehranpour, and Christopher Spiers

Prolonged hydrocarbon production often leads to subsidence and seismicity in offshore and onshore hydrocarbon fields. In the Netherlands, tens of centimetres of subsidence has occurred above the Groningen Gas Field, with widespread induced seismicity during the 60+ years of its lifetime. These phenomena are driven by reservoir compaction at depth, resulting from gas extraction. Modelling the reversible, elastic component of compaction is straightforward. However, permanent deformation can also occur, the rate and effects of which are very poorly constrained. Furthermore, from smaller fields in the vicinity, it has already become clear that compaction may continue even now that production has stopped in 2023. To be able to confidently forecast the long-term surface impact of fluid production, for fields such as Groningen, and many other fields around the world, models are required that include the physical mechanisms responsible for reservoir compaction. These mechanisms are still poorly known and quantified at true reservoir conditions. Combining microstructural observations, obtained from field material and experimental work, and novel experimental mechanical data, obtained at simulated stress changes relevant to the reservoir, enabled us to identify the main grain-scale deformation mechanisms operating in the reservoir sandstone of the Groningen Gas Field. A key role is played by the thin intragranular clay layers present between the quartz grains making up the load-bearing framework. Compaction of and slip along these thin clay films has accommodated the permanent deformation accumulated during the production stage. After production is halted, experiments suggest that slow, time-dependent grain breakage will start to play a role as well. Microphysical models describing rate-insensitive compaction were implemented in Discrete Element models to assess sandstone compaction behaviour at the cm-dm scale. These numerical models can be used to evaluate reservoir compaction in different locations on the field due to pressure equilibration or repressurisation, with rate-sensitive mechanisms, such as stress corrosion cracking, to be added at a later stage, as their descriptions are still be developed. Eventually such small-scale numerical models should form the basis to upscale the sandstone behaviour to the reservoir scale.

How to cite: Hangx, S., Pijnenburg, R., Shinohara, T., Jefferd, M., Mehranpour, M. H., and Spiers, C.: Reservoir compaction during and after fluid production: A case study of the Groningen Gas Field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12452, https://doi.org/10.5194/egusphere-egu24-12452, 2024.

Carbon capture and storage (CCS) stands as a key technology for mitigating CO2 emissions, with depleted oil and gas fields being excellent candidates for geological storage. However, injection of relatively cold, high-pressure CO2 into higher temperature, low-pressure hydrocarbon reservoirs can induce cooling and potential freezing due to the temperature difference between the injected fluid and the reservoir, as well as Joule-Thomson cooling caused by the rapid expansion of the fluid upon entering the reservoir. This may impact wellbore integrity, and near-wellbore stability and injectivity, posing challenges for safe and cost-effective storage. To be able to accurately predict the impact of cooling on storage operations, it is important to quantify the impact of temperature cycling on the mechanical and transport properties of the rock formations in the near-wellbore area.

To address this, we performed thermal cycling experiments under realistic in-situ pressure-temperature conditions on sandstone analogous to typical hydrocarbon reservoir material. We used a novel apparatus comprising a hydrostatic pressure vessel placed inside a climate chamber providing a temperature range of -70°C to +180°C. Bleurswiller sandstone (Vosges, France; 24% porosity) was subjected to temperature changes from 100 °C to +40, +5, or -20°C at constant pore fluid pressure (5 MPa; 0.85 M NaCl brine) and confining pressure (10 or 25 MPa, i.e. similar to reservoirs of up to ~3 km depth). The effect of the rate of temperature change, brine saturation and the number of cycles on the volumetric behaviour of the sandstone were systematically investigated. Thermally treated samples were subsequently subjected to permeability measurements and conventional triaxial compression to evaluate the impact of confined temperature cycling on the transport and mechanical properties.

In all our thermal cycling experiments, we observed permanent volume change (compaction) with each cycle, though the amount of compaction decreased with subsequent cycles. Furthermore, our results showed that confined temperature cycling did not significantly alter the mechanical properties (strength, elastic properties) of Bleurswiller sandstone. This is in contrast to the strength reduction observed in other porous sandstones after unconfined thermal cycling. However, our thermally treated samples did exhibit a significant reduction in permeability by several orders of magnitude (κ = 10-15 to 10-16 m2 post-treatment) compared to untreated reference samples (initial κ = ~10-14 m2). Overall, permeability roughly decreased with increasing brine content (i.e. from dry to fully brine saturated), increasing number of thermal cycles, and increased temperature amplitude (i.e. more cooling). Temperature change rate did not affect the permanent volumetric strain or permeability reduction in samples that were only cooled. In experiments achieving sub-zero temperatures, including pore fluid freezing, slower temperature changes resulted in less permeability reduction.

How to cite: Amiri, S., Pijnenburg, R., and Hangx, S.: Effects of Temperature Cycling on the Mechanical and Transport Properties of Porous Sandstone: Implications for CO2 Storage in Depleted Hydrocarbon Reservoirs , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12566, https://doi.org/10.5194/egusphere-egu24-12566, 2024.

EGU24-13701 | Orals | EMRP1.2

Influence of Geochemical Features on Elastic and Fracture Behavior of Organic Matter 

Junliang Zhao, Pengyu Zhang, Wei Zhang, and Dongxiao Zhang

As the source material of hydrocarbon and a significant matrix constituent in organic-rich shale, organic matter influences not only the oil/gas generation and accumulation but also the mechanical behavior of shale formations. Previous researches have found that organic matter exhibits different mechanical properties from inorganic minerals, and proved that geochemical features could significantly affect the elastic behavior of organic matter in shale. Here, this work systematically investigates the influence of organic type and/or thermal maturation on mechanical behavior of organic matter. For elastic behavior, in conjunction with vitrinite reflection test, scanning electron microscope (SEM) observation, and micro-Raman analysis, nanoindentation is performed to measure the modulus of different macerals. The results indicate that with the same thermal maturity, inertinite has the highest Young’s modulus, while the modulus of bitumen is the lowest. In addition, with the increase of thermal maturity, the Young’s moduli of all kinds of maceral tend to increase, while the intensity ratio of D peak to G peak measured by micro-Raman analysis shows a decreasing trend, which indicates a higher degree of graphitization. For fracture behavior, maceral identification, focused xenon ion beam fabrication, and in situ fracture test are combined to analyze the deforming and fracturing process of different organic types. Micro cantilever beams are manufactured by using a xenon plasma focused ion beam-SEM (Xe PFIB-SEM), and then loaded in an environmental SEM (ESEM). Organic matter particle is set at the fixed end of cantilever beam, and the load is applied at the free end. Thus, the interaction between micro crack and organic matter can be observed and the corresponding mechanical data can be recorded. Test results indicate that the micro cantilever beams dominated by inertinite and vitrinite show the features of brittle failure, while those dominated by bitumen show the features of ductile failure. These microscale findings can support the upscaling model for precise prediction of mechanical properties at the macro scale, and assist with the understanding and interpretation of macroscopic elastic and fracture behavior in shale reservoirs.

How to cite: Zhao, J., Zhang, P., Zhang, W., and Zhang, D.: Influence of Geochemical Features on Elastic and Fracture Behavior of Organic Matter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13701, https://doi.org/10.5194/egusphere-egu24-13701, 2024.

EGU24-14953 | ECS | Orals | EMRP1.2

Exploring Seismoelectric Interface Responses at Poroelastic/Elastic Boundaries: numerical and experimental approaches 

Natael Bernardo, Victor Martins-Gomes, Clarisse Bordes, and Daniel Brito

Seismoelectric effects, arising from the interaction between seismic waves and electromagnetic fields, have attracted considerable scientific interest for their potential applications in subsurface characterization, geothermal exploration, and hydrocarbon prospecting. While most of previous research has predominantly focused on fluid/poroelastic and poroelastic/poroelastic interfaces, there has been a notable knowledge gap regarding the behavior of seismoelectric signals at poroelastic/elastic interfaces, a crucial aspect in many geological scenarios. This study addresses this gap by providing concrete evidence of interface responses within poroelastic/elastic transitions through experimental measurements of seismoelectric coseismic and interface responses. The experiments were conducted using a plastic container filled with Landes sand as the poroelastic medium, saturated  with NaCl. The container featured distinct interfaces with four different elastic media: glass, plastic, aluminium, and granite, as well as a poroelastic medium (Vosges sandstone) for comprehensive analysis.

The experiments were conducted separately for each interface, with specific focus on two different pore fluid conductivities (36 μS/cm and 100 μS/cm). Furthermore, numerical simulations enable a direct comparison between experimental data and theoretical predictions, leading to an excellent agreement between measured and simulated  data in particular regarding the amplitude and polarity of the seismoelectromagnetic signal generated at poroelastic/elastic interfaces. The present demonstration of the electromagnetic signature at poroelastic/elastic boundaries contribute to the overall understanding of seismoelectric phenomena, enhancing the toolkit available to geophysicists and improving the accuracy of subsurface assessments. 

How to cite: Bernardo, N., Martins-Gomes, V., Bordes, C., and Brito, D.: Exploring Seismoelectric Interface Responses at Poroelastic/Elastic Boundaries: numerical and experimental approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14953, https://doi.org/10.5194/egusphere-egu24-14953, 2024.

EGU24-15168 | ECS | Orals | EMRP1.2

Mechanical characterization of Freiberger Gneiss (Reiche Zeche, Germany) from laboratory to field scale 

Evangelos Korkolis, Elisabeth Kozlov, Bernard Adero, and Joerg Renner

Reservoir rock properties play an important role in the overall efficiency of petrothermal systems. Potentially interesting target formations for such systems include igneous and metamorphic rocks. For such lithologies with typically low porosity values, pre-existing fractures and foliation emerge as possible controlling factors of their hydraulic and mechanical behavior, respectively. Understanding the hydromechanical behavior of the reservoir rock is vital for the planning, execution and monitoring of hydraulic stimulation and exploitation, and continued safe operation. We inferred the elastic behavior of Freiberger gneiss from millimetre to tens of meters scale from laboratory and field measurements. Laboratory measurements were performed on samples prepared from blocks collected in the Reiche Zeche mine in Freiberg, Germany, and on cores retrieved from boreholes, drilled to perform hydraulic stimulation experiments as part of the STIMTEC (STIMulation TEChnologies) project. Controlled-source, P- and S-wave ultrasonic measurements were performed on samples and cores at room pressure and temperature conditions, covering a wide range of angles between wave-propagation direction and foliation, to characterize the degree of mechanical anisotropy of the gneiss. Magnitude and anisotropy of P-wave velocities determined from the laboratory measurements on the cores are in broad agreement with velocities calculated from in-situ sonic log measurements and active ultrasonic transmission experiments  (Boese et al., 2022) representing travel path lengths from meter to decameters in the rock mass, with a mean fracture distance of decimeters. At elevated pressures, ultrasonic measurements on cylindrical samples suggest the dominance of foliation over microcracks in determining the elastic behavior. The lack of a substantial reduction in velocities, deduced from in-situ active and passive microseismic analyses (Boese et al., 2022), except in highly deformed volumes, constrains the stiffness of the in-situ fractures.

Reference
Boese, C. M., Kwiatek, G., Fischer, T., Plenkers, K., Starke, J., Blümle, F., Janssen, C., and Dresen, G.: Seismic monitoring of the STIMTEC hydraulic stimulation experiment in anisotropic metamorphic gneiss, Solid Earth, 13, 323–346, https://doi.org/10.5194/se-13-323-2022, 2022.

How to cite: Korkolis, E., Kozlov, E., Adero, B., and Renner, J.: Mechanical characterization of Freiberger Gneiss (Reiche Zeche, Germany) from laboratory to field scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15168, https://doi.org/10.5194/egusphere-egu24-15168, 2024.

EGU24-15600 | ECS | Posters on site | EMRP1.2

Petrophysical rock typing integrated workflow in a Chilean greensand. 

Daniela Navarro-Perez, Quentin Fisher, Piroska Lorinczi, Jose Valderrama Puerto, Anibal Velasquez Arauna, and Martin Verdugo Dobronic

Petrophysical rock typing (PRT) is a key integrated workflow in reservoir characterization that utilizes petrophysical properties like permeability and porosity in conjunction with pore size distribution, typically derived from mercury capillary pressure measurements to classify from rich to poor reservoir quality rock units. However, the PRT workflow must encompass additional properties such as mineralogy, surface area, and clay distribution in tight rocks with a high clay mineral content to capture the microstructure and heterogeneity in such formations.

This case study focuses on the Zona Glauconitica (ZG) reservoir in the Magallanes basin, Chile, greensand with permeability ranging from 0.001 to 1 mD and total porosity between 10 and 25%v/v. Its high iron content is due to substantial amounts of chlorite and/or glauconite. The PRT workflow analyses ten petrophysical and mineralogical parameters using principal component analysis and K-means clustering, aiming to identify crucial patterns and correlations between rock properties and their storage potential. Multilinear regression (MLR) analysis was employed to determine the best-fit correlation for predicting pore throat radius at different mercury saturations from capillary pressure curves, using total porosity and gas permeability as input variables.

Four distinct petrofacies were identified as closely associated with clay minerals content, iron levels, permeability, porosity, and pore throat distribution. MLR best correlated the pore throat radius at 25%v/v mercury saturation with Pittman’s (1992) correlation. These findings offer significant promise as they contribute to enhancing and refining the existing petrophysical model. Future work extends this methodological approach to logging data across ten uncored wells, preceded by a validation process involving two cored wells. This iterative process will contribute to developing and validating an effective petrophysical model for the ZG reservoir, facilitating more precise and efficient evaluations of its production potential.

Pittman, E. D. 1992. Relationship of porosity and permeability to various parameters derived from mercury injection-capillary pressure curves for sandstone. AAPG Bulletin, 76, pp.  191-198.

How to cite: Navarro-Perez, D., Fisher, Q., Lorinczi, P., Valderrama Puerto, J., Velasquez Arauna, A., and Verdugo Dobronic, M.: Petrophysical rock typing integrated workflow in a Chilean greensand., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15600, https://doi.org/10.5194/egusphere-egu24-15600, 2024.

EGU24-16309 | ECS | Posters on site | EMRP1.2

Fault reactivation in clay-rich rocks – effects of water-clay interactions 

Markus Rast, Claudio Madonna, Paul A. Selvadurai, Antonio Salazar Vásquez, Quinn Wenning, and Jonas B. Ruh

Clay-rich rocks play an important role in critical practical applications, particularly as natural barriers in nuclear waste repositories and subsurface caprocks for CO2 storage. The interaction between electrostatically charged clay minerals and polar fluids (e.g., water) can lead to swelling or, under confined conditions, build-up of swelling stress. Fault closure by swelling in clay-rich rocks has been the focus of many studies. However, it remains unclear how water-clay interactions affect the stability of pre-existing faults, considering that in addition to changes in frictional properties, the stress state may also change due to the build-up of swelling stress.

This study addressed this gap by conducting triaxial friction experiments on oblique saw-cut cylindrical samples. The upper half of the sample consisted of a clay-rich rock (Opalinus claystone) and the lower half of a permeable sandstone (Berea sandstone). The first set of experiments determined the friction slip envelope of the sandstone-claystone interface without fluid injection, at confining pressures ranging from 4 to 25 MPa, and a constant axial loading rate of 0.1 mm/min. These experiments showed a frictional strength well below Byerlee’s law, indicating that the Opalinus claystone dictates the strength of the two-material interface.

Friction experiments with fluid injection were then performed at confining pressures of 10 and 25 MPa with a constant piston position (no axial loading) and an initial differential stress of about 70% of the expected yield stress. The aim was to compare the fluid pressures required to initiate slip in scenarios with and without fluid-clay interactions. For this, the experiments involved stepwise increases in fluid pressure through the injection of either deionized water (a polar fluid) or decan (a non-polar fluid). In one of the decane and one of the water injection experiments, fibre-optic strain sensors were attached to the sample surface. This allowed us to differentiate between poroelastic deformation within the matrix, deformation due to water-clay interaction, and elastic relaxation due to slip along the saw cut.

The friction slip envelope based on decane injection experiments is within the uncertainty of the friction slip envelope based on the experiments with no fluid injection. In contrast, the water injection experiments indicate a weakening of the frictional interface. We interpret this weakening to be due to the transition of the claystone from a solid rock to a mud close to the saw-cut surface. This weakening was evident even at ambient fluid pressure, although the apparent stress state was below the yielding stress, indicating the need to consider swelling stress in initial water injection scenarios. In summary, our data suggest that water-clay interactions may reactivate pre-existing faults due to (1) the change of the frictional properties and (2) the build-up of swelling stress.

How to cite: Rast, M., Madonna, C., Selvadurai, P. A., Salazar Vásquez, A., Wenning, Q., and Ruh, J. B.: Fault reactivation in clay-rich rocks – effects of water-clay interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16309, https://doi.org/10.5194/egusphere-egu24-16309, 2024.

EGU24-18323 | Posters on site | EMRP1.2

Combining Spectral Induced Polarization and X-ray micro-Computed Tomography imaging to reveal pore-scale dynamic processes occurring in volcanic hydrothermal systems 

Hamdi Omar, Tom Bultreys, David Caterina, Frédéric Nguyen, Lore Vanhooren, Sojwal Manoorkar, and Thomas Hermans

Many volcanoes host a hydrothermal system,  responsible for a large fraction of volcanic eruption. These eruptions do not expel magma but involve the forceful ejection of pre-existing rocks, volcanic gases, and steam, posing a significant threat to human safety. Recent catastrophic incidents underscore the difficulty in foreseeing sudden hydrothermal explosions, exposing our limitations in prediction. The challenge lies in the absence of distinct precursory signals, making it difficult to anticipate these events. These eruptions may be triggered by the introduction of mass and energy originating from magma, or alternatively, by the development of mineralogical seals above vents, devoid of any direct magmatic influence. Understanding and predicting these hydrothermal phenomena remain critical for mitigating their potential human and environmental impacts.

In the ERUPT research project, we study the geoelectrical response of volcano hydrothermal systems (VHS).  Here, we focus on the laboratory scale, where we amalgamate electrical properties, namely SIP (Spectral Induced Polarization) measurements, with X-ray pore-scale (4D µCT) imaging to unravel the intricate electrical signatures of volcanic systems on rock samples collected from Gunnuhver region (Iceland). SIP  is a geophysical method that measures the complex electrical impedance of a material as a function of a wide range of frequencies (Zimmermann et al., 2008). It is particularly useful for characterizing the electrical properties of porous media, and have been widely used to study rock samples from VHS (e.g., Lévy et al., 2019). SIP responses are sensitive to factors like surface area, pore size distribution, fluid content, as well as movement of fluids within the rock. On the other hand, X-ray µCT is an imaging technique that uses X-rays to create detailed, 3D images of the internal structure of a sample, such as internal morphology, porosity, other structural features of rocks at a micrometer scale, and quantify fluid pathways and flow dynamics within the rock. The synergy of combining these two methods can provide a more comprehensive understanding of the geoelectrical properties and internal structure of a rock sample as follow: by analyzing SIP responses at different frequencies and correlating them with the µCT images, we gain insights into how variations in geoelectrical properties relate to the movement of fluids within the rock matrix, as well as the influence of alteration or precipitation of minerals. As a first step, we developed a unique experimental set-up that enables to combine both methods (SIP and µCT) simultaneously. The noval prototype was thoroughly designed following specific technical features (e.g., dimensioning, materials) to ensure an optimal SIP signal acquisition under well controlled conditions of temperature and pressure, together with a high resolution 4D µCT imaging. This integrated approach is valuable for studies in geophysics, hydrogeology, and reservoir characterization, among other various relevant domains.

 

References

Lévy, L. et al. (2019) ‘Electrical resistivity tomography and time-domain induced polarization field investigations of geothermal areas at Krafla, Iceland: Comparison to borehole and laboratory frequency-domain electrical observations’, Geophysical Journal International, 218(3), pp. 1469–1489. https://doi.org/10.1093/gji/ggz240.

Zimmermann, E. et al. (2008) ‘A high-accuracy impedance spectrometer for measuring sediments with low polarizability’, Measurement Science and Technology, 19(10). https://doi.org/10.1088/0957-0233/19/10/105603.

How to cite: Omar, H., Bultreys, T., Caterina, D., Nguyen, F., Vanhooren, L., Manoorkar, S., and Hermans, T.: Combining Spectral Induced Polarization and X-ray micro-Computed Tomography imaging to reveal pore-scale dynamic processes occurring in volcanic hydrothermal systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18323, https://doi.org/10.5194/egusphere-egu24-18323, 2024.

We investigate the evolution of poro-mechanical, transport properties and strength characteristics of different sandstones during the cyclic underground hydrogen storage (UHS). Therefore, we selected three different types of sandstones: fine-grained St Bees (∅ =19~22%), coarse-grained Castlegate (∅=18~20%), and coarse-grained Zigong (∅=7~11%). These sandstones exhibit significant porosity, grain size, and mineralogical differences. The samples were imaged using micro-CT to characterise their initial microstructure and then subjected to cyclic loading experiments under hydrostatic as well as various deviatoric stress paths. The aim is to simulate the in-situ stress during cyclic UHS at depths of ~1.5-3km. The permeability of the samples was measured at different stress points. After completing the cyclic loading tests, we performed repeat micro-CT characterization as well as scanning electron microscopy (SEM) analysis to record the permanent changes in the microstructure caused by the stress cycles. The experimental results show that at shallower depths (low-stress state), the high porosity Castlegate sandstone (∅=18~20%) and the St Bees sandstone (∅=19~22%) exhibit an increase in elastic modulus during the tests, experiencing strain hardening due to compaction. The permeability of both sandstones decreases with an increase in mean stress, independent of the stress path. The fine-grained St Bees sandstone shows more significant accumulative inelastic strain and higher permeability loss than the coarse-grained Castlegate sandstone at the same stress state. In contrast, the low-porosity Zigong sandstone (∅=7~11%) shows no significant changes in mechanical properties, and its permeability loss is related to the closure of the initial microcracks. At greater depths (high-stress conditions), the mechanical and transport properties of the fine-grained St Bees sandstone exhibit an evident dependence on the stress path. During stress cycling under deviatoric stress conditions, the rock experienced a noticeable weakening indicated by a reduction in elastic modulus. The porosity of the sandstone decreased by 0.8~1.4% due to the combined effects of compaction and dilatancy, with a permeability loss exceeding 50%. The application of deviatoric stress led to lower permeability than hydrostatic tests conducted under the same mean stress. In contrast, the coarser-grained Castlegate and Zigong sandstones show an insignificant stress path dependence in their mechanical and transport properties. Due to compaction, these sandstones experience increased intergranular contact, leading to reduced porosity, increased elastic modulus, and strain hardening. The lower-porosity Zigong sandstone shows a higher sensitivity of permeability to stress than the higher-porosity Castlegate sandstone, which is related to its more complex pore structure. Microstructural analysis reveals that factors such as porosity, particle size, microfractures, and the presence and distribution of compliant components like clay minerals are the primary causes for the variations in the poro-mechanical and transport properties of the three sandstones under cyclic stress. Therefore, in addition to the depth of the reservoir, grain size (and their distribution) and mineralogical characteristics play a significant role in the selection of hydrogen storage candidates.

How to cite: Wen, M., Wang, Q., and Busch, A.: Evolution of poro-mechanical and transport properties of sandstones under different cyclic stress paths: Implications for underground hydrogen storage., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19226, https://doi.org/10.5194/egusphere-egu24-19226, 2024.

EGU24-20486 | ECS | Orals | EMRP1.2

Coupling Preferential Flow and Flow-induced Strain in Heterogeneous Rock-like Medium  

Arnold Bachrach and Yaniv Edery

Pressurized fluid injection into underground rocks occurs in applications like carbon sequestration, hydraulic fracturing, and wastewater disposal and may lead to human-induced earthquakes and to surface uplift. Yet, the full mechanical response of the underground to those injections is largely unknown. As the underground cannot be observed directly, experimental studies are crucial for understanding its mechanical reaction to fluid injection. Yet the need to maintain high pressure flow while tracking deformation complexes the execution of such experiments in comparison to standard mechanical tests. In this study we use a unique-transparent porous medium, made from chemically sintered Polymethyl Methacrylate (PMMA) beads, to simulate the underground rocks. We inject into the medium fluid at increasing pressure while measuring its internal plane-strain field as it deforms. We find that although the medium is constrained in its periphery, internal strains still occur perpendicular to the flow, compensated by the medium itself. While the medium’s overall strain shows clear reversibility, the internal perpendicular strain variations show very little to no recovery at all. Flow simulations over permeability fields, derived from the measured strain, reveal that internal strain variations have a significant impact on preferential flow within the medium. Together with the measured strain, the simulations results constitute a strong base for modeling the local heterogenous coupling between preferential flow and deformation in the underground due to fluid injections.

How to cite: Bachrach, A. and Edery, Y.: Coupling Preferential Flow and Flow-induced Strain in Heterogeneous Rock-like Medium , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20486, https://doi.org/10.5194/egusphere-egu24-20486, 2024.

EGU24-20513 | Posters on site | EMRP1.2

An innovative method to qualitatively measure the wettability of sandstone reservoirs based on the sequential extraction and fluorescence analysis 

Haijun Yan, Zhongnan Wang, Keyu Liu, Jing Yu, Guoqiang Zheng, Lidan Ji, Yilong Li, and Yuxiang Zhang

Wettability is a key factor controlling the flow and distribution of multiphase fluids in reservoirs. The study of reservoir wettability is of great significance to understand the mechanism of oil and gas migration and improving oil and gas recovery. The oil reservoirs have various wetting characteristics, including water wet, neutrally wet and oil wet states. The conventional methods for reservoir wettability analysis, including the contact angle, Amott index and the USBM index, have been currently established in the petroleum industry. The contact angle method is relatively simple, but it is not suitable for the reservoir samples with complex mineral composition and strong heterogeneity. Amott and USBM method based on oil-water displacement are encountering problems such as long test time and large errors, when applied to low-permeability and tight reservoirs. This study takes the low-permeability and tight sandstone reservoirs in the Ordos Basin as an example. Based on the measurement of oil and water content in the rock using the nuclear magnetic resonance, the Amott-Harvey index was tested. Then the twin powder sample was sequentially extracted for 72 hours with the fluorescence spectrum of the extracted organic matter was tested every 12 hours. The fluorescence spectrum of the crude oil in the same production layer was also tested, and then the relationship between the fluorescence characteristics of the extracted organic matter and the Amott-Harvey index was analyzed. Finally, a new method for rapid and qualitative evaluation of reservoir wettability was established. The conclusions were as follows: (1) Crude oil represents the characteristics of free hydrocarbons in the reservoir, and its fluorescence spectrum has a fluorescence intensity peak around 375 nm. (2) The firstly extracted organic matter contains both free hydrocarbons and adsorbed hydrocarbons, and its fluorescence spectrum has a double peak with a wavelength of 375nm as the main peak and 460nm as a secondary peak. The last extracted organic matter has a lower proportion of free hydrocarbons and a higher proportion of adsorbed hydrocarbons compared with firstly extracted one. The fluorescence spectrum mostly shows double peaks with the same fluorescence intensities at the wavelength of 375nm and 460nm. (3) The ratio of fluorescence intensity of the extracted organic matter at a wavelength of 460nm to 375nm (I460nm/I375nm) may reflect the coverage proportion of the rock surface by adsorbed hydrocarbons, and thus can be used as a parameter indicating the wettability of the rock. The I460nm/I375nm value of the last extracted organic matter has a strong correlation with the Amott-Harvey index, therefore it can be used to qualitatively evaluate the reservoir wettability.

How to cite: Yan, H., Wang, Z., Liu, K., Yu, J., Zheng, G., Ji, L., Li, Y., and Zhang, Y.: An innovative method to qualitatively measure the wettability of sandstone reservoirs based on the sequential extraction and fluorescence analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20513, https://doi.org/10.5194/egusphere-egu24-20513, 2024.

EGU24-1197 | ECS | Orals | EMRP1.3

A comparison of exfoliation joint formation mechanisms: what is the role of surface processes? 

Aislin Reynolds, Karl Lang, and Chloé Arson

The formation of granitic domes via exfoliation jointing produces some of the most celebrated and hazardous landforms on Earth. In 1904, G.K. Gilbert outlined three mechanisms to explain exfoliation jointing as: (1) related to the original cooling of the rock body, (2) related to decompression of the rock body as it is exhumed to the surface of the Earth, or (3) related to processes at Earth’s surface - a hypothesis recently supported by observations of thermal cycling in crack initiation and propagation. Despite more than a century of study, our understanding of the mechanisms driving exfoliation jointing remains incomplete. This research seeks to address the question: is the formation of exfoliation joints more sensitive to surface processes (e.g., biotite weathering, thermal cycling), topographic, or regional (i.e. tectonic) stresses? To test this hypothesis, we predicted the orientation of fractures subject to variable geologic conditions with a multi-scale weathering model of damage and fracture propagation implemented in the finite element method. We present predictions resulting from thermal contraction during cooling of the rock body, depressurization during rock exhumation, and regional tectonic compression. We then compare fractures generated under variable topographic stresses, surface weathering processes, and rock geochemistry (i.e., biotite fraction and orientation). By improving our understanding of how significantly pre-existing geologic conditions and rock fabrics influence fracturing, we can work towards disentangling this effect on observed fracture orientations and better interpret paleo-stresses for major tectonic events or potentially paleo-topography. Additionally, enhancing models for weathering mechanics and fracturing in granitic bodies may reveal sensitivities to changes in climate and critical zone evolution, with implications for the forecasting of rockfall hazards in relation to projected temperature and climatic changes.

How to cite: Reynolds, A., Lang, K., and Arson, C.: A comparison of exfoliation joint formation mechanisms: what is the role of surface processes?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1197, https://doi.org/10.5194/egusphere-egu24-1197, 2024.

EGU24-1670 | ECS | Posters on site | EMRP1.3

High-alpine rock slides controlled by pre-existing geological structures and brittle rock mass fracturing 

Reinhard Gerstner, Melina Frießenbichler, Michael Avian, Alexander Maschler, Christine Fey, Gerald Valentin, Markus Keuschnig, Volkmar Mair, Franz Goldschmidt, and Christian Zangerl

Deep-seated, high-alpine rock slides frequently occur in highly schistose, fractured, anisotropic rock masses. Many studies have shown that pre-existing geological structures are decisive for a rock slide’s initiation and kinematics, as they provide weakness zones that may be reactivated in the rock slide process. Besides this structural pre-disposition, internal deformation processes by brittle rock mass fracturing play an important role in the evolution of a rock slide. Nonetheless, the effect of multiscale rock mass fracturing due to the rock slide process is yet to be fully understood. Especially, as it is challenging to measure, characterize, and to numerically model these processes. In our contribution, we present three deep-seated rock slides located in the European Alps in heavily foliated, fractured rock masses with failure volumes above 500.000 m3 each. Focusing on these case studies, we investigate the internal deformation processes with a combined approach, comprising field mapping, laboratory testing, remote sensing, and numerical modelling.

During extensive geological field surveys, we mapped the geomorphological rock slide features and characterized the structural framework of each study site, yielding geometrical models of the rock slides. This provided the basis for our 2D distinct element modelling studies using UDEC, backed by lithological and rock mechanical laboratory investigations.

Whilst UDEC allows for modelling large displacement of blocks bounded by pre-existing discontinuities, it lacks the capability to simulate fracture initiation and propagation of new failure paths within intact blocks, thus neglecting brittle rock mass fracturing. We circumvent this constraint by tessellating the intact rock mass into random polygons – referred to as Voronoi elements. Here, we adapted the original Voronoi technique by assigning an asymmetry to the Voronoi elements, characterized by an elongated axis to consider rock mass anisotropy related to schistosity. By applying this approach, we modelled the fractured, anisotropic, metamorphic rock masses as a combination of pre-existing, field-related structures within a matrix of small, asymmetric Voronoi elements.

In order to confirm the model outputs, we used terrain and deformation data derived from various remote sensing techniques – e.g. satellite based synthetic aperture radar, terrestrial laser-scanning (Riegl VZ 4000) and several campaigns of unmanned aerial vehicle photogrammetry.

In our study, we were able to reproduce the failure mechanism and kinematics of all three rock slides in accordance with our remote sensing deformation data. Thereby, the asymmetric Voronoi tessellation proved to be feasible in reproducing the brittle rock mass fracturing processes in remarkable agreement with our observations in the field. Thus, our results show, how the formation and kinematics of deep-seated rock slides are controlled by the reactivation of pre-existing geological structures and brittle rock mass fracturing. In doing so, our integrated field, laboratory, and numerical modelling approach further contributes to a better understanding of rock slide initiation and kinematics in complex geological media.

How to cite: Gerstner, R., Frießenbichler, M., Avian, M., Maschler, A., Fey, C., Valentin, G., Keuschnig, M., Mair, V., Goldschmidt, F., and Zangerl, C.: High-alpine rock slides controlled by pre-existing geological structures and brittle rock mass fracturing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1670, https://doi.org/10.5194/egusphere-egu24-1670, 2024.

EGU24-3021 | ECS | Posters on site | EMRP1.3

Contribution of programming language to novel mine risk assessment project 

Pieride Mabe Fogang and Bingjie Huo

When excavating a tunnel, the stresses are distributed asymmetrically along the tunnel cross-section. Other factors, particularly slope friction force and excavation speed, can also contribute to the deformation and displacement of a tunnel. Despite this, several authors have used the complex potential method to predict the ground deformation surrounding the tunnel. However, their applicability to the ground response caused by the asymmetric stress distribution around the mine wall is analyzed in this context. This project, therefore, proposes an approximate solution on the slope to predict the mine cross-section deformation. The solution is based on the complex potential method to predict analytically and numerically the ground deformation around the tunnel. However, two variables called the “complex potential functions” for the Laurent series expansion are used for the stress redistribution to the tunnel boundary conditions. Data from the Datong mine case are used to justify the proposed analytical solutions. The solution is an essential guide for analyzing deformations in complex geological conditions and structures, such as steeper slopes.

How to cite: Mabe Fogang, P. and Huo, B.: Contribution of programming language to novel mine risk assessment project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3021, https://doi.org/10.5194/egusphere-egu24-3021, 2024.

Quantifying the changes in elastic properties of rocks during deformation is an important task. Effective Medium Theory (EMT), as formulated by Sayers & Kachanov (1995) relates the crack fabric (or damage) to the elastic properties. EMT has been successfully applied in the forward sense to predict the evolution of elasticity and related acoustic velocities in response to prescribed changes in crack density; and in the inverse sense to recover crack densities from laboratory measurements of acoustic velocities.  However, EMT fails to predict an important observation from laboratory studies of rock deformation: cyclic loading under uniaxial and conventional triaxial loads of rock samples can produce significant increases in Poisson’s ratio. These increases correlate with increasing number of cycles and with increasing crack density. This phenomenon has been known since the work of Walsh (1965), Brace et al. (1966) and Zoback & Byerlee (1975). More recent work by Heap & Faulkner (2008) and Heap et al. (2009; 2010) has extended the findings across a range of different lithologies.

Published EMT equations predict Poisson’s ratios that stay constant or decrease with increasing crack density. Resolving this discrepancy is important because Poisson’s ratio may play a key role in producing stress rotations in the damage zones of faults, thereby making them ‘weak’ and prone to slip even when the normal stress is high e.g. the San Andreas Fault (Faulkner et al., 2006; Healy, 2008). Building on the work of David et al. (2012 & 2020) incorporating the effects of crack closure, sliding on cracks (Kachanov, 1992) and grain boundaries (Sayers, 2018) during loading, and delayed back-sliding during unloading, closed form micromechanical equations have been derived to describe increases of Poisson’s ratio with increasing number of cycles. Critically, increases in Poisson’s ratio are predicted even without including the effects of new cracks. Examples are shown comparing the predicted changes in Poisson’s ratio using the newly derived equations to data from uniaxial and triaxial laboratory tests on cracked rocks.

How to cite: Healy, D.: Increases in Poisson’s ratio due to cyclic deformation in cracked rock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3893, https://doi.org/10.5194/egusphere-egu24-3893, 2024.

EGU24-5440 | Posters on site | EMRP1.3

Using AE based Machine Learning Approaches to Forecast Rupture during Rock Deformation Laboratory Experiments 

Sergio Vinciguerra, Thomas King, and Philip Benson

Parametric analysis of laboratory Acoustic Emission (AE) during rock deformation laboratory experiments has revealed periodic trends and precursory behaviour of the rupture source, as crack damage nucleates, it grows and coalesces into a fault zone. Due to the heterogeneity of rocks and the different effective pressures, finding a full prediction of rupture mechanisms is still an open goal.

4x10cm cylindrical samples of Alzo granite were triaxially deformed at confining pressures of 5-40 MPa, while AE are recorded by an array of twelve 1MHz Piezo-Electric Transducers. We trained a Time Delay Neural Networks (TDNN) on key seismic attributes derived from AE, such: Event rate, i.e. the negative log time difference between successive events; Amplitude, i.e. the average max amplitude of all waveforms for each single event AE; Source mechanism estimated from first-motion polarity spheres (King et al., JGR, 2021); Seismic scattering, i.e the ratio between high and low frequency peak delays (King et al., GJI, 2022); Vp/Vs ratios from vertical P-wave velocities and horizontal S-wave velocities for individual AE (King et al., GJI, 2023).

These timeseries are then classified by the TDNN as variations in stress and strain (target parameters). TDNN require continuous, regularly sampled data but AE are discrete and irregular. To transform the training data for the TDNN, parameters are smoothed in a weighted moving window of 100 AE events, where weighting is given towards high amplitude events that occur close in space together. Data processing is applied to waveform data from all experimental condition. Despite the inherent complexity in the raw data, clear increasing or decreasing trends are repeated at different experimental conditions.

Hyperparameters for the neural network are optimised using a Genetic Algorithm (GA) by evaluating the misfit between training target (mechanical data) and model output. Each model is trained on the 10 MPa dataset and validated on the 40 MPa dataset. Roles are reversed and the results summed. This approach ensures consistent trends in the training data (waveform parameters) whilst reducing bias towards a particular dataset. We then investigate 120 configurations for the training data following a ‘leave-one-out’ strategy. E.g., a model is trained on 5, 10 and 20 MPa datasets whilst omitting the Event rate parameter. The model is then validated on the 40 MPa dataset.

Model output on validation datasets demonstrate that the TDNN can classify AE-derived parameters as increasing variations in stress and strain. 10 and 40 MPa demonstrate the best fit and are likely linked to the GA optimisation, highlighting biases driven by the training data. Forecasting results for strain and stress reveal notable over- and under-estimations of values. However, both 10 and 40 MPa are generally accurate to within 20% further highlighting the feasibility of using a TDNN for forecasting the development of new fracture under conventional triaxial conditions.

How to cite: Vinciguerra, S., King, T., and Benson, P.: Using AE based Machine Learning Approaches to Forecast Rupture during Rock Deformation Laboratory Experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5440, https://doi.org/10.5194/egusphere-egu24-5440, 2024.

EGU24-5553 | Orals | EMRP1.3

Progressive rock failure under different loading conditions – sound and vision 

Ian Main, Maria-Daphne Mangriotis, Alexis Cartwright-Taylor, Andrew Curtis, Ian Butler, Andrew Bell, and Florian Fusseis

Catastrophic failure is the end result of a progression of damage towards brittle failure on a variety of system scales in the Earth. However, the factors controlling this evolution, and the relationship between deformation and the resulting earthquake hazard, are not well constrained.  In particular, induced seismicity is a growing cause of concern in the engineering required for the net-zero carbon transition, including subsurface storage of carbon and geothermal energy production, and mining for critical metals. Here we address the question of how to optimize operational controls to minimize induced micro-seismicity in a ‘scale-model’ laboratory experiment where we can simultaneously image the underlying damage using acoustic emissions (sound) and x-rays (vision). We confirm that using continuous servo-control to maintain a constant acoustic emission event rate slows down deformation compared to standard constant strain rate loading, and demonstrate that it also suppresses micro-seismic events of all sizes, including extreme events, and reduces the proportion of seismic to total strain. We develop a new model to explain these observations, based on the observed evolution of microstructural damage and the fracture mechanics of subcritical crack growth.  The model is validated with high precision (r~99%) by comparison with the independently-observed stress history and acoustic emission statistics.

Qualitative inspection of comparable grey-scale x-ray volumes between the two experiments (peak stress and post-failure after unloading) showed that at peak stress microcrack damage accumulated initially, in both samples and in the same area of each sample, as localised pore collapse, pore-emanating and Hertzian tensile intra- and trans-granular cracks and pore-emanating shear and tensile inter-granular cracks. These features were mostly similar in length and aperture, although the sample loaded only under constant strain rate showed a few longer and more open cracks. Strain localisation was apparent at the same stage in both samples, but there was some evidence of earlier en-echelon microcrack localisation in the sample loaded under a constant strain rate. Post-failure, microcracks were longer and more open in the sample loaded under a constant strain rate than in the sample loaded under a constant AE event rate. The visible proportion of damaged rock was greater, with a broader shear zone around two to three grains wide (compared with <1-2 grains) and a greater degree of cataclasis throughout. Off-fault microcracking was limited, but there were some trans- and inter-granular microcracks that extended up to four to five grains long in both samples. These were more common in the sample loaded under constant strain rate and tended to be more open. Finally, branching of the fault zone appeared to be more pronounced in the sample loaded under a constant strain rate.

Our results explain the effectiveness of seismic event rate control on seismic hazard mitigation in mining settings, and imply that it may be more effective in managing the risk from induced seismicity in a pre-emptive way than the commonly-applied ‘traffic light’ system, which is based on reacting after the fact to extreme events.

How to cite: Main, I., Mangriotis, M.-D., Cartwright-Taylor, A., Curtis, A., Butler, I., Bell, A., and Fusseis, F.: Progressive rock failure under different loading conditions – sound and vision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5553, https://doi.org/10.5194/egusphere-egu24-5553, 2024.

Macroscopic equilibrium statistical mechanics is first used to interpret and predict thermally driven microfracture in rock. Application of the theoretical framework to three heating and cooling experiments, performed on granite and reported between 1989 and 2017, provides strong evidence that the temperature-, pressure- and volume-dependent average microfracture population within a given rock volume can be treated as an equilibrium thermodynamic variable.  This observation, in turn, suggests that thermoelastic microfracture, in rock and similar granular solids, can be predicted and interpreted using standard, process- and history-independent equilibrium thermodynamics.  In order to place equilibrium rock fracture and healing in context, we then consider nonreversible, permanent, i.e., nonequilibrium fracture. Here, pictorial, physical, and quantitative analyses of several common, thermally driven rock fracture processes are presented, including: a) terrestrial thermal exfoliation of single grains from diurnally heated rock surfaces, b) non-terrestrial thermal exfoliation of thin, near surface rock layers, as recently observed, e.g., on Bennu, c) terrestrial and non-terrestrial thermally-driven through cracking, and d) initiation of c).  We show how the form of the continuum momentum and energy conservation equations for thermoelastic materials – here, rock- provides a powerful, intuitive framework for quickly visualizing and roughly predicting the fracture/weathering processes in a) through d).

How to cite: Keanini, R. and the US, Israel, UK, Japan, France Rock Fracture Collaboration: Equilibrium (reversible) and nonequilibrium (permanent) fracture in rock: equilibrium statistical mechanics theory and experiments, and physical/intuitive analysis of common nonequilibrium fracture modes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7023, https://doi.org/10.5194/egusphere-egu24-7023, 2024.

EGU24-8848 | ECS | Orals | EMRP1.3

Revealing the transition from brittle to ductile failure mode in Carrara marble through in-situ 4D X-ray imaging and acoustic emissions experiments 

Erina Prastyani, Benoît Cordonnier, Jessica McBeck, Lei Wang, Erik Rybacki, Georg Dresen, and François Renard

Rocks exhibit a brittle failure mode, leading to system-size failure through cataclastic faulting processes involving microfracture coalescence and frictional sliding, resulting in localized deformation. In contrast, the ductile failure mode can be described as a distributed deformation at the macroscopic scale, although there may be significant grain-scale heterogeneities. The transition between these two modes is an important research area because it is assumed to occur at the base of the seismogenic zone where large earthquakes may nucleate. Understanding strain evolution and partitioning between brittle and ductile failure modes may shed light on the preparation process for large earthquakes. To investigate the transition from brittle to ductile deformation, we performed two series of experiments on Carrara marble core samples: conventional triaxial experiments with acoustic emission recording at GFZ Potsdam, and dynamic in situ 4D X-ray imaging experiments on beamline BM18 at the European Synchrotron Radiation Facility.  Carrara marble is used as a rock model because this transition can be achieved at room temperature. We performed the experiments at room temperature and confining pressures between 5 and 100 MPa. For the synchrotron experiments, we segmented the images and implemented digital volume correlation (DVC) analyses between tomogram acquisitions to quantify the evolution of volumetric and shear strain components during the transition from the brittle to ductile regime. The results show that the transition is controlled by the dynamics of microfractures, even in the ductile regime. Below 40 MPa of confining pressure, deformation localizes along faults, particularly at 5 and 10 MPa. At 40 MPa, tomograms reveal the formation of a localized shear zone and macroscopically distributed deformation, resembling a semi-brittle regime. The DVC reveals the spatial extent of the strain directed into faults. A limited number of acoustic emissions recorded at this confining pressure revealed the prevalence of aseismic activity during deformation. Above 40 MPa, deformation shifts to a non-localized pattern at the core sample scale, involving the opening of microfractures, possibly due to the cataclastic flow mechanism accommodating this regime.

How to cite: Prastyani, E., Cordonnier, B., McBeck, J., Wang, L., Rybacki, E., Dresen, G., and Renard, F.: Revealing the transition from brittle to ductile failure mode in Carrara marble through in-situ 4D X-ray imaging and acoustic emissions experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8848, https://doi.org/10.5194/egusphere-egu24-8848, 2024.

EGU24-9339 | ECS | Orals | EMRP1.3

The role of grain fragmentation in understanding shear localization via DEM simulation 

Nathalie Casas, Guilhem Mollon, and Marco Maria Scuderi

Mature fault zones are formed by abrasive wear products, such as gouge, which results from the frictional sliding occurring in successive slip events. Shear localization in fault gouge is strongly dependent on, among others, fault mineralogical composition and grain size distribution, originating a wide variety of microstructural textures that may be related to different types of fault motion from aseismic creep, slow earthquakes to fast slip events. Within a quartz fault zone, one can encounter different stages of maturity, ranging from an incipient and poorly developed fault zone (i.e. discontinuous and thin gouge layer) to a mature fault zone that has experienced a lot of wear from previous sliding events (i.e. well-developed gouge layer). The localization of deformation within a mature gouge layer has been identified as possibly responsible for mechanical weakening and as an indicator of a change in stability within the fault.

However, to upscale the physics of shear deformation, we need to unveil the physical parameters and micro-mechanisms that govern shear localization. To gain insights on the role of dynamic changes in grain size (i.e. fragmentation), in slip behavior and fault rheology, we performed 2D numerical simulations of quartz fault gouges in a direct shear configuration using the Discrete Element Method (code MELODY). We can reproduce angular particles that can fragment during the simulation as the fault gouge accumulates strain. These experiments were performed to understand the micro-mechanical processes happening during fragmentation and shearing at a constant normal stress. Three mixtures of quartz were sheared to reproduce different initial grain size distributions within the fault (average grain sizes 100 μm, 10.5 μm, and a 50% mixture of both). The minimum grain size was set to 10 μm, meaning that all the coarser particles are subdivided into smaller ones (size 10 μm) that can fragment during the experiment.

Thanks to visual and data outputs, we can observe how particles behave during the compaction and shearing of the gouge. We use four main parameters to describe fault gouge evolution: the damage of coarse particles, the force chains, the change of porosity, and the kinetic energy linked to each particle breakage. Moreover, these numerical experiments were designed to reproduce and be directly compared with shear experiments realized on a double direct shear apparatus in the Laboratory (Casas et al., in prep). The fragmentation algorithm in the code can reproduce the shear localization observed within the real quartz microstructures and the progressive formation of Riedel bands. The connection between numerical and laboratory experiments gives important information on the connection between grain size distribution, shear localization, Acoustic Emissions, and the resulting fault slip behavior. In this context, the proportion between small/coarse particles within the fault plays an important role in controlling fault rheology.

How to cite: Casas, N., Mollon, G., and Scuderi, M. M.: The role of grain fragmentation in understanding shear localization via DEM simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9339, https://doi.org/10.5194/egusphere-egu24-9339, 2024.

EGU24-9811 | ECS | Posters on site | EMRP1.3

Multi-scale experimental deformation and damage initiation of clay-rich rocks  : Coupling ultrasonic wave propagation and  full field deformation measurements by digital image correlation (DIC) 

Matthieu Lusseyran, Alexandre Dimanov, Audrey Bonnelye, Jérôme Fortin, and Alexandre Tanguy

Understanding the damage processes in clay-bearing rocks is a decisive factor in geological engineering, and for instance considering nuclear waste deep geological repositories. But, more generally they may also contribute to localized deformation, and thus the rupture of fault gauges in seismic zones. However, owing to their complex mineralogy, multiscale microstructures and anisotropy, the mechanisms of clay-rich rock damage and their chronology are not yet well understood..

Here we focus on the impact of micro-damage on ultrasonic wave propagation velocity, which is confronted with the corresponding full deformation fields calculated by digital image correlation (DIC). 

The aim is to associate the acoustic signature with the active deformation mechanisms identified by DIC. To this end, an integrated experimental approach is proposed to  characterize localization and to identify the related deformation micro-mechanisms  during uniaxial compression of natural clayey rock samples (Tournemire shales) with two simultaneous measurements: 1) the evolution of P-wave velocity within the sample by active acoustics, 2) the development of the 2D mechanical full field by digital image correlation.

Both experimental techniques are well known, but the innovation of our approach is to combine simultaneously both measurements. Deformation localization is a multiscale problem, which obviously occurs at the sample scale, but also at the fines scales of the microstructure. Therefore, we developed two different experimental setups. On the one hand, during uniaxial compression with a standard MTS loading frame the macro-scale localization patterns are characterized by optical observations, which image resolution is well suited to the cm sample scale (sample diameter: 3.6 cm and double in length). On the other hand, in order to characterize the initiation of micro-damage at the microstructure scale of the composite type of rock, the same loading protocol is reproduced (while keeping the acoustic diagnosis) on smaller scale mm-sized specimens (sample diameter : 8 mm, double in length), using a home-designed miniature loading frame fit for an environmental scanning electron microscope (ESEM). The latter analysis is carried out under  controlled relative humidity  of RH = 80%, hence preventing the samples to dry out due to the high vacuum

A similar acoustic signature is identified at both scales of observation, in spite of the variations of experimental conditions imposed by the environmental SEM. We are therefore confident to be able to understand the fracturing process from micro-cracking initiation (microscale) to sample failure (macroscale), and to assess its impact on ultrasonic wave propagation.

How to cite: Lusseyran, M., Dimanov, A., Bonnelye, A., Fortin, J., and Tanguy, A.: Multi-scale experimental deformation and damage initiation of clay-rich rocks  : Coupling ultrasonic wave propagation and  full field deformation measurements by digital image correlation (DIC), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9811, https://doi.org/10.5194/egusphere-egu24-9811, 2024.

EGU24-9825 | Orals | EMRP1.3

Temperature “Memory” and Natural Rock Fracture at Earth’s Surface 

Martha-Cary Eppes, Christian David, Mike Heap, Patrick Baud, Thomas Bonami, Maxwell Dahlquist, Russell Keanini, Cyril Lacroix, Monica Rasmussen, Alex Rinehart, Youness El Alaoui, and Adrien Windenberger

Rock physics theory and experimental data suggest that fracture growth in rock proceeds not only as a function of synchronous stress and environmental conditions but also as a function of past fracture growth in response to those conditions. ‘Stress memory’ or ‘fatigue-limit’ fracture mechanics phenomena such as the Kaiser effect epitomize this idea. Many questions exist, however, as to if and how these phenomena impact the growth of fractures under natural environmental conditions. For example, to what extent does the orientation of past experienced stresses manifest in a rock’s response to stresses of the same magnitude?

Here we test for a memory of intergranular thermal stresses in two natural granite boulders of the same lithology for which we have 1 and 3 years of known temperature history, respectively. We hypothesize that cores extracted from the exterior portions of the boulders – that have necessarily experienced more and larger temperature fluctuations – will have more ‘memory’ of peak temperatures than those cores extracted from the boulder centers. In turn, we hypothesize that outer cores will crack less in response to temperature cycling than inner cores. For the first boulder, we measured P-wave velocities and connected porosities before and after 4 different oven heat treatments – heating up to 40, 45, 50 and 65 °C at a rate of at 20 °C/hr and cooling at an ambient rate over several cycles each. For two transects of cores extracted from the natural upward facing surface down, and the natural west-facing surface inward, we found that porosities increased after each subsequent heat treatment, but by larger amounts with distance away from the outer rock surface, as hypothesized. P-wave velocities, however, both increased and decreased with different heating cycles and positions. Therefore, for the second boulder, we extracted a top-down transect of 5 cores and, using a special-made rig, found that the samples exhibit significant P-wave velocity directional anisotropy. We subjected these cores to the same heat treatments as those of the first boulder, but this time orienting the samples identically in the oven with respect to their original positions in the boulder. Preliminary data show similar results as the first boulder, with the outermost core cracking the least (as interpreted from porosity changes) relative to the inner cores. Ongoing work will examine changes in P-wave velocity in different directions relative to measured anisotropy as a function of heat treatment cycles. This work has important implications for understanding if and how, with ongoing global warming, Earth’s rocks will respond to ‘new’ temperatures. 

How to cite: Eppes, M.-C., David, C., Heap, M., Baud, P., Bonami, T., Dahlquist, M., Keanini, R., Lacroix, C., Rasmussen, M., Rinehart, A., El Alaoui, Y., and Windenberger, A.: Temperature “Memory” and Natural Rock Fracture at Earth’s Surface, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9825, https://doi.org/10.5194/egusphere-egu24-9825, 2024.

EGU24-10099 | Posters on site | EMRP1.3

Multiscale experimental investigation of crystal plasticity and grain boundary sliding in rock salt using digital image correlation 

Xinjie Li, Alexandre Dimanov, Michel Bornert, Simon Hallais, and Hakim Gharbi

In the context of the global environmental crisis and the urgent need for energy transition and efficient energy storage solutions, salt caverns have gained attention as promising reservoirs for hydrogen. However, current literature predominantly focuses on deriving macroscopic constitutive relations, lacking crucial insights into the underlying physical mechanisms of deformation and damage active at various microscopic scales. This study addresses this gap by undertaking qualitative and quantitative investigations into the micro-mechanisms of rock salt, employing advanced micro-scale observation techniques. Natural rock salt from diverse mines and re-synthetic salts, produced through the cold compaction of grinded natural halite powder, are used to encompass a wide range of microstructural morphologies. Initial microstructure characterization involves SEM, EBSD, and CT, followed by classic uniaxial compressive tests coupled to optical microscopy monitoring. High-resolution images of the sample surface are continuously captured during testing, allowing for 2D full field measurements by subsequent application of digital image correlation techniques : the analysis of relative displacements of markers randomly distributed on the sample surface enables the retrieval of surface displacement fields and the calculation of the corresponding local strain fields over statistically representative domains. Segmentation of digital images and quantitative identification, specifically focusing on crystal slip plasticity and grain boundary sliding using an in-house computation program, reveal the complex local interactions of different micro-mechanisms. The estimation of the relative contributions of these mechanisms to global deformation all along the loading path, along with an analysis of the impact of salt grain size, provides insights into physically grounded micromechanical constitutive relations. These findings are essential for the safety assessment of industrial applications involving rock salt caverns with respect to short-term mechanical loading conditions relevant to daily hydrogen filling and withdrawal.

How to cite: Li, X., Dimanov, A., Bornert, M., Hallais, S., and Gharbi, H.: Multiscale experimental investigation of crystal plasticity and grain boundary sliding in rock salt using digital image correlation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10099, https://doi.org/10.5194/egusphere-egu24-10099, 2024.

EGU24-10753 | ECS | Orals | EMRP1.3

Non-linear softening and relaxation in rocks and geomaterials: a laboratory perspective 

Manuel Asnar, Christoph Sens-Schönfelder, Audrey Bonnelye, Georg Dresen, and Marco Bohnhoff

In rocks and other consolidated geomaterials, static or dynamic excitation leads to a fast softening of the material, followed by a slower healing process in which the material recovers all or part of its initial stiffness as a logarithmic function of time. This requires us to exit the framework of time-independent elastic properties, linear or not, and investigate non-classical, non-linear elastic behavior and its time dependency. Softening and healing phenomena can be observed during seismic events in affected infrastructure as well as in the subsurface. Since the transient material changes are not restricted to elastic parameters but also affect hydraulic and electric parameters as well as material strength – documented for instance by long lasting changes in landslide rates – it is of major interest to characterize the softening and recovery phases.

To characterize this behavior in a controlled environment, we perform experiments on Bentheim sandstone in a Materials Testing System triaxial cell with pore pressure and confining pressure control. Our sample is subjected to various static loading cycles in both dry and water-saturated conditions, while an active acoustic measurement setup allows us to monitor minute P-wave velocity changes, which can then be directly tied to dynamic elastic modulus changes.

Our transducer array allows us to observe the dynamic softening as well as the recovery processes in the sample during repeated loading phases of various time lengths. Observations indicate high spatial, frequency and lapse-time sensitivity of the observed velocity changes, indicating a rich landscape of concurrent effects and physical phenomena affecting our sample during these simple experiments.

To investigate the spatial and directional dependency of the velocity changes, we restrict the analysis to direct and reflected ballistic waves. Our observations indicate that, while stress-induced classical effects are clearly anisotropic as expected, the non-classical effects do not exhibit significant anisotropy. This allows us to rule out a number of physical phenomena as the cause for the non-classical effects. Most importantly, we conclude that the microscopic structures responsible for the reversible softening and healing processes are different from the cracks that induce the anisotropic acousto-elastic effect.

How to cite: Asnar, M., Sens-Schönfelder, C., Bonnelye, A., Dresen, G., and Bohnhoff, M.: Non-linear softening and relaxation in rocks and geomaterials: a laboratory perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10753, https://doi.org/10.5194/egusphere-egu24-10753, 2024.

EGU24-11304 | ECS | Orals | EMRP1.3

Frost damage in unsaturated porous media 

Romane Le Dizes Castell, Rosa Sinaasappel, Clémence Fontaine, Scott Smith, Paul Kolpakov, Daniel Bonn, and Noushine Shahidzadeh

Frost damage in porous materials is a weathering mechanism that can cause dangerous rockfalls or damage to built cultural heritage. The volume expansion of 9% when water freezes can be one of the cause of frost damage. This does not, however, explain why partially saturated porous stones also show damage despite the fact that ice should have room to grow. By performing experiments both at the scale of a single pore and in a real stone, we investigate the mechanism of frost damage at low water saturations at the pore scale and how it relates to macroscopic damage. We observe that the meniscus at an air-water interface confines the water in the pores. Because of this confinement, ice that forms will exert a pressure on the pore walls rather than growing into the pore. The amplitude of stress is found to be larger in small pores and when the meniscus has a larger contact angle with the walls. The contact angle is also observed to increase in the case of multiple freeze-thaw cycles, which increases the likelihood of damage. We find that cracks start first in the ice (being weaker than the confining material), followed by damage in the material itself. Remarkably, when multiple air-water interfaces are induced within limestone samples through a hydrophobic surface treatment, the stones are much more susceptible to frost damage than are uncoated stones, with cracks appearing preferentially at the hydrophilic-hydrophobic interface. This shows that indeed the meniscus confining the water during freezing and consequently the wetting properties are the relevant factors for frost damage in partially saturated porous stones

Reference: R. Le Dizès Castell, R. Sinaasappel, C. Fontaine, S. H. Smith, P. Kolpakov, D. Bonn, and N. Shahidzadeh, “Frost Damage in Unsaturated
Porous Media,” Physical Review Applied, vol. 20, p. 034025, Sept. 2023.

How to cite: Le Dizes Castell, R., Sinaasappel, R., Fontaine, C., Smith, S., Kolpakov, P., Bonn, D., and Shahidzadeh, N.: Frost damage in unsaturated porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11304, https://doi.org/10.5194/egusphere-egu24-11304, 2024.

EGU24-13010 | ECS | Posters on site | EMRP1.3

The influence of fluid pressure on the phase transition of brittle faulting 

Hao Chen, Paul Selvadurai, Antonio Salazar, Patrick Bianchi, Sofia Michail, Markus Rast, Claudio Madonna, and Stefan Wiemer

Recent observations of large earthquakes document the progressive localization of rock damage around future rupture zones that is also coupled with the spatial migration of foreshock sequences (Kato & Ben-Zion, 2020). This implies that the precursory deformation may act as a potential tracer for preparatory process that result in large earthquakes. It has also been observed that self-organization of the localized damage regions can govern the eventual macroscopic brittle failure in geomaterials (Renard et al., 2019). How the presence of fluid controls the self-organized precursory deformation along localized damage zone remains an open question. In this study, we have performed two triaxial compression experiments on dry and water saturated Berea sandstone, using distributed strain sensing (DSS) technology to visualize the strain field on the sample surface (Salazar Vásquez et al., 2022) with high spatial resolution. By tracking components of the strain field, specifically the region on the sample that sustained the largest incremental change in strain, we tested the effect of fluid on the predictability of phase transition between intact and failed state, under the context of critical hypothesis. Strain was progressively localized around the eventual faulting region for both samples, while a slow faulting was observed in the wet sample accompanied by a diffuse deformation pattern and unstable crack nucleation at failure. The results showed that, the failure in the dry sample was preceded by a critical power law acceleration of the largest increment, thus the dynamic faulting occurred in a well-defined singularity. The strain distribution also provided evidence for a predictable evolution of precursors. In contrast, the wet test showed evidence for a first-order transition with an exponential increase in largest increment, leading to an abrupt failure with a transient increase of strain. We interpreted this abrupt transition to be due to the increasing dominance of fluid-driven subcritical crack growth in the faulting. In this process, the local stress at crack tips decreases with crack lengthening, hence impeding the crack interaction and leading to an abrupt development of fault network. Our observation unravels the mechanisms of precursory deformation with fluid-assisted subcritical cracking, which has important implication in forecasting large earthquakes in nature.

 

References:

Kato, A., & Ben-Zion, Y. (2020). The generation of large earthquakes. Nature Reviews Earth & Environment, 2(1), 26–39. https://doi.org/10.1038/s43017-020-00108-w

Renard, F., McBeck, J., Kandula, N., Cordonnier, B., Meakin, P., & Ben-Zion, Y. (2019). Volumetric and shear processes in crystalline rock approaching faulting. Proceedings of the National Academy of Sciences, 116(33), 16234–16239. https://doi.org/10.1073/pnas.1902994116

Salazar Vásquez, A., Rabaiotti, C., Germanovich, L. N., & Puzrin, A. M. (2022). Distributed Fiber Optics Measurements of Rock Deformation and Failure in Triaxial Tests. Journal of Geophysical Research: Solid Earth, 127(8). https://doi.org/10.1029/2022JB023997

How to cite: Chen, H., Selvadurai, P., Salazar, A., Bianchi, P., Michail, S., Rast, M., Madonna, C., and Wiemer, S.: The influence of fluid pressure on the phase transition of brittle faulting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13010, https://doi.org/10.5194/egusphere-egu24-13010, 2024.

EGU24-13669 | Orals | EMRP1.3

Laboratory measurement of subcritical crack growth and healing in calcite using Double-Torsion tests 

Seiji Nakagawa, Yida Zhang, Hooman Dadras, Zhao Hao, Anne Voigtländer, and Benjamin Gilbert

Subcritical crack growth accelerates weathering of rocks and minerals, reduces the strength of rock slope, and affects the stability of subsurface faults. Under special circumstances, the produced cracks can also heal spontaneously (Self healing) regaining a part of the original tensile strength.  These crack behaviors are a manifestation of molecular-scale surface forces acting between the surfaces near the crack tip. As a part of the effort to understand how these forces control the subcritical crack growth and healing of geological materials, we examine the tensile crack behavior of calcite single crystals. A miniature Double-Torsion (DT) test system was developed for testing small plate samples (40 mm x 20 mm x 1.5 mm) cut out of optical-quality calcite single crystals (Iceland Spar crystals). These samples are oriented in such a way that the induced crack is along the (1014) plane (the primary cleavage plane). The main output of the experiment is the crack velocity (vc) vs the magnitude of applied driving force (stress intensity factor K or strain energy release rate G), which is a typical way to summarize the rate-dependent crack behavior. From the experiment, we have learned that (1) calcite exhibits strong healing behavior compared to materials such as glass or (amorphous) quartz in humid air and water, (2) healing is time dependent (the strength of a healed crack increases over time), (3) liquid water (rather than vapor) introduces strong hysteresis in the recracking vs healing behavior.   The obtained laboratory data are used to develop a mechanistic model for predicting macroscale crack behavior in rock, particularly in a water and electrolyte-rich environment.

How to cite: Nakagawa, S., Zhang, Y., Dadras, H., Hao, Z., Voigtländer, A., and Gilbert, B.: Laboratory measurement of subcritical crack growth and healing in calcite using Double-Torsion tests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13669, https://doi.org/10.5194/egusphere-egu24-13669, 2024.

EGU24-13927 | Orals | EMRP1.3

Strain history of the Pioneer fault, Idaho, USA – progressive deformation and associated crystallographic alteration. 

Elizabeth Petrie, Bradford Burton, Kelly Bradbury, and Genna Baldassarre

In south-central Idaho, a segment of the Pioneer fault, exposed at Little Fall Creek, has accommodated large magnitude Mesozoic shortening overprinted by Paleogene extension. The resulting 30 m thick fault damage zone records a history of fault reactivation and associated deformation in quartz veins, graphite concentration on slip surfaces, polyphase contractional and extensional microstructures, and micro- to outcrop-scale corrugated, mineralized and polished slip surfaces. The gently west dipping (207°/14°) fault zone separates Ordovician argillite in the hanging wall from Mississippian argillite and quartzite in the footwall and accommodated east-northeast directed shortening. However, polished slip surfaces within the fault zone document top-to-the-west translation with a mean slip vector 15°/272°, consistent with extensional unroofing of the Pioneer Mountains core complex.

Argillite in the fault damage zone varies from proto- to ultra-cataclasite and provides evidence for overprinting of contractional fabrics by extensional fabrics. The fault damage zone is characterized by multiple anastomosing slip-surfaces which indicate a history of slip surface interactions, fault growth, and reactivation. Early deformation features include graphitic foliations and stylolites, SC foliations, and ptygmatic folds consistent with shortening. Quartz veins, mica fish, and slip surfaces coated with graphite, amorphous carbonaceous material, and amorphous quartz phases, overprint the early deformation features and are associated with west-directed extension. Hydrothermal quartz veins that show at least five phases of deformation indicate multiple strain episodes and high strain rates. Raman spectroscopy and scanning electron microscope textural analysis of the graphite in the fault damage zone show a loss of crystallinity toward the primary slip surface. We infer the late-stage meso- to micro-scale features record seismic slip and fluid-rock interactions in a gently dipping fault zone.

How to cite: Petrie, E., Burton, B., Bradbury, K., and Baldassarre, G.: Strain history of the Pioneer fault, Idaho, USA – progressive deformation and associated crystallographic alteration., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13927, https://doi.org/10.5194/egusphere-egu24-13927, 2024.

EGU24-14362 | Posters on site | EMRP1.3

Salt-driven Progressive Fracturing of Alluvial Boulders Along the Hyper-arid Shoreline of the Dead Sea  

Amit Mushkin, Ronen Boroda, Uri Malik, Nadav Lensky, Eyal Haggai, Boris Muravin, and Rivka Amit

Rock weathering is ubiquitously observed at or near Earth’s surface as a fundamental component in many landscape evolution process. In arid landscapes, where limited moisture availability restricts the rate and effectiveness of chemical and biological weathering – salt weathering (regarded herein as the physical disintegration of rocks in the presence of salts) is commonly acknowledged as an especially effective mechanism for progressive weathering of rocks. While volumetric expansion and contraction of salts in response to changes in ambient moisture conditions are broadly recognized as the primary drivers of salt weathering, our understanding of the environmental conditions that produce such moisture dynamics in otherwise extremely dry settings, such as hyper-arid deserts, remains largely unknown.

Here, we present preliminary results from field-based acoustic emission (AE) measurements for boulders with salt-laden cracks perched on abandoned shorelines of the hypersaline Dead Sea. Continuous measurements since April 2023 revealed daily fracturing activity displaying a bi-modal distribution with AE activity peaks during the early predawn and afternoon hours when T changes are minimal and RH fluctuations reach maximum or minimum values, respectively. Time-lapse photography revealed a recurring pattern of salts that crystalize along the rock cracks during the afternoon AE peak hours and subsequently disappear towards the predawn AE peak hours. The appearance of salt crystals during lowest RH conditions (warmest afternoon hours) and their disappearance during highest RH conditions (coldest predawn hours) suggests that stresses induced by repeated cycles of salt deliquescence/efflorescence in response to daily fluctuations in atmospheric RH are most likely responsible for the bi-modal distribution of daily fracturing activity. This suite of new field-based measurements of salt-weathering activity in natural hyper-arid settings suggests that atmospheric RH fluctuations and the volumetric changes they induce in hygroscopic salts can be key drivers of progressive rock fracturing in extremely dry and salt-rich environments on Earth and possibly Mars where other moisture sources are limited to effectively non-existent.

How to cite: Mushkin, A., Boroda, R., Malik, U., Lensky, N., Haggai, E., Muravin, B., and Amit, R.: Salt-driven Progressive Fracturing of Alluvial Boulders Along the Hyper-arid Shoreline of the Dead Sea , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14362, https://doi.org/10.5194/egusphere-egu24-14362, 2024.

EGU24-16652 | ECS | Posters on site | EMRP1.3

Time- and stress-dependent elastic properties in a concrete structure; spotting internal damage footprints 

Marco Dominguez-Bureos, Celine Hadziioannou, Ernst Niederleithinger, and Christoph Sens-Schönfelder

Time- and stress-dependency of elastic properties are features particularly observed in a variety of complex solids, ranging from steel, polymers, and cracked structures, to rocks and concrete. Recently, considerable effort has been made to understand the underlying physics of these phenomena commonly regarded as Nonlinear Mesoscopic Elasticity (NME) in laboratory setups.

As a result, various models have been suggested to explain a range of NME phenomena like hysteresis, dynamic softening, and slow dynamics, among others. Due to the high sensitivity of NME to the presence of imperfections or internal damage on solids, there is a growing interest in taking the current models and applying them to construction materials for damage assessment.

Intending to observe and incorporate these models into real-condition structures, we carried out a 1-day multifrequency vibration experiment in a 24-meter-long reinforced concrete test bridge equipped with a pretension system, to investigate the possible presence of internal damage with vibration-based methodologies.

We used the pretension system to subject the specimen to eight compression states in its longitudinal direction (forces of 400kN at the highest, and 280kN at the lowest). At every compression state, we struck the structure in the vertical direction three times on the north and south sides of the bridge with an impulse drop weight. Throughout the whole experiment, we recorded ambient seismic noise at different frequency bands with a 14-six-component sensor array to measure the acceleration in the conventional translational components and the angular velocity (rotation rate), a 14-geophone array of 4.5 Hz of natural frequency, and four pairs of embedded ultrasound transducers were used to estimate relative velocity changes (dv/v) by applying the Coda Wave Interferometry (CWI) stretching technique. internal temperature of the concrete was also recorded to correct our measurements by first-order thermal effects.

At the material scale (ultrasound regime) we observe stress-dependent dv/v at four different locations in the specimen and describe them by using the acoustoelastic effect concept regarded as a classical nonlinear phenomenon. We also analyze the relative velocity drop and the subsequent healing process in the concrete triggered by the action of the drop weight. We used the model of Snieder and Sens-Schönfelder (2017) to numerically describe the relaxation process happening at different time scales in the specimen through a deterministic inversion procedure. The north side of the structure showed to have a higher acoustoelastic effect and higher velocity drops, as well as longer relaxation times, it is important to mention that there is evidence of external cracking in this span of the bridge.

We present preliminary results in the seismic frequency band (structural scale), where we expect to observe the influence of the vertical beams that support the bridge on the spatial distribution of changes in dv/v. Changes in the fundamental frequency of the structure as a function of the stress level are also expected.

With this work, we point towards the development of new nondestructive testing methodologies highly sensitive to small cracks and imperfections using conventional and non-conventional seismic instruments, and linear and nonlinear wave propagation models.

How to cite: Dominguez-Bureos, M., Hadziioannou, C., Niederleithinger, E., and Sens-Schönfelder, C.: Time- and stress-dependent elastic properties in a concrete structure; spotting internal damage footprints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16652, https://doi.org/10.5194/egusphere-egu24-16652, 2024.

EGU24-16840 | Posters on site | EMRP1.3

Are all lineaments the surface expression of faults and fractures? – A novel analysis using tunnel face mapping data from Norwegian road tunnels 

Espen Torgersen, Karoline Arctander, Thomas F. Redfield, Anne Kathrine Svendby, Anna Maria Dichiarante, and Mari Lie Arntsen

Lineaments are elongated elements in spatial data such as valleys and ridges on topographic maps, or linear lows and highs in aeromagnetic data. Topographic linear depressions (topolineaments) are generally considered as the morphological expressions of easily erodable, elongated rock bodies situated within a mechanically stronger rock mass. In most circumstances topolineaments are even directly interpreted as faults and fractures, which forms the basis for lineament analysis study to understand brittle deformation patterns. However, topolineaments may also be formed by other tectonic and non-tectonic causes, such as alternating layers, foliation traces, dikes etc., or river- and glacial erosion not controlled by any bedrock features. This mix of potential causes begs the question: “How robust is actually lineament analysis for characterizing and quantifying faults and fractures?”. Testing the topolineament vs. fracture-relationship is not straight forward since topolineaments are usually occupied by rivers or creeks and covered with colluvium, which prevents direct observation of rock types and bedrock structures.

Underground excavations allow for continuous logging of bedrock types, rock mass quality and fracture density and orientations, which is done routinely at tunnel face during tunnel construction. Here we make use of such underground data from a large dataset of Norwegian road tunnels to compare the position of topolineaments spatially and statistically with rock fracture density and orientations in the subsurface. The tunnel dataset comprises data from across Norway in areas with widely varying bedrock geology, tectonic evolution, and geomorphology (e.g. etched surface, alpine, lowlands), which allow for an evaluation of the robustness of lineament analysis in various settings. Topolineaments are acquired using a newly developed algorithm (OttoDetect) run on both 10x10m and 50x50m resolution digital elevation models. The algorithm ensures that tunnel data is compared to a homogeneous and reproducible lineament dataset without operator or hillshade illumination biases.

Preliminary results from tunnels in areas with etched geomorphology show that c. 75% of all topolineaments correspond to weakness zones in the bedrock (i.e. very high fracture densities/very low rock mass quality compared to the surroundings). Hit rate increases for longer lineaments, which generally correspond to thicker fault zones. At the same time, only up to c. 60% of all weakness zones mapped at tunnel face can be spatially associated to a topolineaments, which demonstrate that significant brittle deformation is not expressed as topolineaments. Further analysis will be carried out to build a statistically robust dataset on the validity of lineament analysis.

How to cite: Torgersen, E., Arctander, K., Redfield, T. F., Svendby, A. K., Dichiarante, A. M., and Arntsen, M. L.: Are all lineaments the surface expression of faults and fractures? – A novel analysis using tunnel face mapping data from Norwegian road tunnels, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16840, https://doi.org/10.5194/egusphere-egu24-16840, 2024.

EGU24-2384 | ECS | Orals | EMRP1.6

Frictional slip sequences in homogeneous and bimaterial interfaces 

Songlin Shi, Meng Wang, Yonatan Poles, and Jay Fineberg

Earthquake-like ruptures disrupt the frictional interface between contacting bodies and initiate frictional motion (stick-slip). The interfacial slip (motion) immediately resulting from a rupture during each stick-slip event is usually much smaller than the total slip recorded during the duration of the event. Slip after the onset of friction is generally attributed to the continuous motion of global ‘dynamic friction’. Here, we demonstrate that numerous hitherto invisible secondary ruptures are initiated immediately after each initial rupture by directly measuring the contact area and slip at the frictional interface. Each secondary rupture generates incremental slip that, when not resolved, may appear as steady sliding of the interface. Each slip increment is linked, via fracture mechanics, to corresponding variations of contact area and local strain. Cumulative interfacial slip can only be described if the effects of these secondary ruptures are taken into account. These weaker slip sequences can also be observed in bimaterial interfaces and exhibit strong directional effects. In addition, the seismic moments we estimate based on slip sequences are consistent with the Gutenberg-Richter (G-R) law. These results have important implications for our fundamental understanding of frictional motion and the important role of aftershocks within natural faults in generating earthquake-mediated slip/afterslip.

How to cite: Shi, S., Wang, M., Poles, Y., and Fineberg, J.: Frictional slip sequences in homogeneous and bimaterial interfaces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2384, https://doi.org/10.5194/egusphere-egu24-2384, 2024.

EGU24-3912 | ECS | Orals | EMRP1.6

Back-Propagating Rupture: Nature, Excitation, and Applications 

Xiaotian Ding, Shiqing Xu, Eiichi Fukuyama, and Futoshi Yamashita

In recent years, an intriguing feature of back-propagating rupture (BPR) has been reported during some earthquakes (Ide et al., 2011; Houston et al., 2011; Hicks et al., 2020; Okuwaki et al., 2021; Vallée et al., 2023). The occurrence of BPR challenges the classical interpretation of rupture propagation as a “forward” problem, while remaining less understood by the earthquake science community. Here, using fracture mechanics, we first argue that BPR is nothing but an intrinsic component of rupture propagation; however, its observability is usually masked by the superposition effect of interfering waves behind the primary, forward-propagating rupture front. We then suggest that perturbation to an otherwise smooth rupture process can break the superposition effect and hence can make BPR observable. To test our idea, we report results of mode-II rupture propagation from both numerical simulations and laboratory observations. By introducing a variety of perturbations (lateral variation in bulk or interfacial properties along the fault, singular stress drop, coalescence of two rupture fronts, etc.) during rupture propagation, we show that prominent phases of BPR indeed can be successfully excited. We further classify BPR into two modes: higher-order rupture or interface wave, depending on whether the already-ruptured fault is quickly healed and whether additional stress drop can be produced. Lastly, we propose several application potentials for BPR, such as constraining the velocity structure of fault zones, probing the mechanical state of faults, and studying the stability of perturbed slip along a homogeneous or bimaterial interface. Our study refines the understanding of the nature and complexity of rupture process, and can help improve the assessment of earthquake hazards.

How to cite: Ding, X., Xu, S., Fukuyama, E., and Yamashita, F.: Back-Propagating Rupture: Nature, Excitation, and Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3912, https://doi.org/10.5194/egusphere-egu24-3912, 2024.

EGU24-5187 | Orals | EMRP1.6

The similarity between ruptures in scaled laboratory seismotectonic models and slow earthquakes  

Fabio Corbi, Giacomo Mastella, Elisa Tinti, Adriano Gualandi, Laura Sandri, Matthias Rosenau, Silvio Pardo, and Francesca Funiciello

Modeling the seismic cycle requires multiple assumptions and parameters. Providing a quantitative assessment of the model behavior is pivotal for determining the degree of similarity between different scales and modeling strategies and for exploring dependencies with respect to selected parameters. Here we compare stick-slip ruptures nucleating spontaneously in scaled seismotectonic models (i.e., laboratory experiments capturing the first-order physics of the seismic cycle of subduction megathrusts) with slow earthquakes in nature. We rely on two non-dimensional parameters, namely the Ruina number (Ru) and system dimension (D) to quantify model behavior. Ru is proportional to the ratio of the asperity size to the critical nucleation size. Within the rate- and state friction framework, for velocity weakening asperities Ru controls the behavior of the system, which can be either periodic or not, and it can exhibit both slow and fast ruptures. D measures how complicated the system evolution is. D reveals how many variables are required to describe the seismic cycle because it tells us the minimum dimension needed to embed the observed dynamics. 

By coupling the Simulated Annealing algorithm and quasi-dynamic numerical simulations, we retrieve rate and state friction parameters characterizing single asperity models with different lateral extent of the velocity weakening patch. Similarly to slow earthquakes, we found optimal rate and state parameters indicative of low (< 4) Ru. We also found a direct proportionality between Ru and the lateral extent of the asperity. 

Next, we implement tools from non-linear time-series analysis and Extreme Value Theory to compute D from models of different sizes, materials, deformation rates and frictional configurations (single or twin asperities along strike). Our analysis supports the existence of a low dimensional attractor (D<5) describing the dynamics of scaled seismotectonic models. In particular, our models display D=3.0-4.2, which is remarkably similar to D=3.2 of slow earthquakes identified along the Cascadia subduction zone. Under the explored conditions, D appears more affected by the material behavior of the analog upper plate (i.e., gelatin vs. foam rubber) than by the lateral frictional segmentation of the megathrust.

Despite the different spatio-temporal scales, our results support a scenario where scaled seismotectonic models and slow earthquakes share similar dynamics.



How to cite: Corbi, F., Mastella, G., Tinti, E., Gualandi, A., Sandri, L., Rosenau, M., Pardo, S., and Funiciello, F.: The similarity between ruptures in scaled laboratory seismotectonic models and slow earthquakes , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5187, https://doi.org/10.5194/egusphere-egu24-5187, 2024.

EGU24-5767 | ECS | Posters on site | EMRP1.6

Towards a 2D model of Discrete Fracture Network with permeability and friction evolution for modeling fluid-induced seismicity  

Pierre Romanet, Marco Scuderi, Stéphanie Chaillat, Jean-Paul Ampuero, and Frédéric Cappa

Numerical modeling of Discrete Fracture Networks (DFNs) is commonly used to assess the behavior and properties of hydraulic diffusion and seismicity in the Earth’s crust within a network of fractures and faults, and to study the hydromechanical evolution of fractured reservoirs stimulated by hydraulic injection and production. The modelling of such fractures is typically carried out under a quasi-static approximation, and occasionally accounting for elasto-dynamics in single-rupture studies that assume a slip-weakening friction law. 

In this work, we develop a 2D DFN model to simulate fluid-induced seismicity that couples hydraulic diffusion and slip governed by rate-and-state friction on multiple interacting faults. The main goal of this numerical model is to establish a connection between laboratory derived friction parameters and field observations, enabling the inference of the long-term evolution of fractured reservoirs and crustal fault systems undergoing multiple earthquakes and (slow) slip events induced by fluid pressure perturbations.

In the model, the elastic interactions are computed with a boundary element method, accelerated by the hierarchical matrix method. We assessed the convergence of the method at fracture junctions and verified it does not create unphysical singularities. The use of rate-and-state friction makes it possible to model several seismic events over the injection duration.

The simulations will be later used to fit measurements of permeability and friction collected in laboratory experiments, in-situ observations of fault slip and opening from fluid injection experiments at decametric scale, and finally, induced seismicity at reservoir scale.

 

How to cite: Romanet, P., Scuderi, M., Chaillat, S., Ampuero, J.-P., and Cappa, F.: Towards a 2D model of Discrete Fracture Network with permeability and friction evolution for modeling fluid-induced seismicity , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5767, https://doi.org/10.5194/egusphere-egu24-5767, 2024.

EGU24-6284 | ECS | Posters on site | EMRP1.6

Fault drainage state and frictional stability in response to shearing rate steps in natural gouge 

Raphael Affinito, Derek Elsworth, and Chris Marone

Elevated pore fluid pressures are frequently implicated in governing fault zone seismicity. While substantial evidence from geodetic and geological studies supports this notion, there is a notable scarcity of experimental observations of how fluid pressure influences fault stability during shear. Understanding the precise interplay between porosity, fault slip rate, and frictional stability is pivotal for assessing the significance of processes like dilational strengthening or thermal pressurization in the context of seismic hazards. Here, we prepare fault gouges from the Utah FORGE enhanced geothermal field injection well 16A at depths corresponding to seismic events (between 2050 – 2070m). Experiments were conducted inside a pressure vessel and loaded under a true-triaxial stress state, replicating in-situ stress conditions observed at the Utah FORGE site. The applied fault normal stress and during the experiments were held constant at 44MPa. Pore fluid pressure was varied between successive experiments (13, 20, and 27 MPa) to span a range of effective stresses to examine impacts on fault dilation/compaction and the successive frictional stability. Different fluid pressure boundary conditions: constant volume or pressure were applied to explore how changes in shearing rate influence gouge stability thought the fault drainage state. Our data indicate that the Utah FORGE samples are velocity-neutral and transition to velocity-weakening behavior at elevated pore pressure and shear strains >7. We find dilatancy coefficients e = ∆f/∆ln(v), where f is porosity and v is fault slip velocity, consistent with quartz-feldspathic-rich rocks ranging from 5–12^10-4, indicating a conditionally unstable regime. Furthermore, our results demonstrate that the boundary conditions for pore fluids influence frictional stability viachanges in effective normal stress. For example, when pore volume has zero flux, an expansion in the void volume during slip results in a decrease in pore pressure, transitioning the system towards frictional stability. Our results indicate that the connectivity of pore conduits may be more important than the imposed pore pressure conditions when considering the impact on fault stability. We suggest that the interplay between fault slip and fluid mobility within a fault is a delicate balance for predicting and managing seismic hazards.

How to cite: Affinito, R., Elsworth, D., and Marone, C.: Fault drainage state and frictional stability in response to shearing rate steps in natural gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6284, https://doi.org/10.5194/egusphere-egu24-6284, 2024.

EGU24-7508 | Orals | EMRP1.6

A granular numerical model for the friction and wear of a lab-scale fault asperity 

Guilhem Mollon, Adriane Clerc, Amandine Ferrieux, Lionel Lafarge, and Aurelien Saulot

Seismic faults are often represented using two different and self-excluding conceptual models. In the first representation, seismic faults are seen as the interface between two surfaces of bare rock, with a roughness extending at all scales. These surfaces interact mechanically through a certain number of “asperities” which constitute the “real contact area”. When adopting this view, attention is paid on the statistics of the asperities population in the fault plane. Faults are thus considered as 2D objects, since their thickness is disregarded.

In the second representation, seismic faults are seen as mathematical planes separated by a certain thickness of granular gouge created by abrasive wear of the surfaces during previous slips. This view is analogous to the tribological “third body” theory, and is supported by field observations and experimental evidences of gouge creation in rotary shear and triaxial experiments. It is convenient to adopt this perspective when weakening phenomena within the gouge are to be spatially resolved in the direction orthogonal to the fault plane. Variations along this plane are then ignored, as well as fault roughness, and faults are mostly seen as 1D objects.

Unification of these two representations requires a better understanding of the interactions between geometrical asperities and a layer of gouge, and in particular of the phenomena that lead to the creation of the latter through the wear of the former. In this communication, we present a numerical model which aims at reproducing lab tests of millimetric single-asperity friction and wear. The model is essentially granular in order to represent the progressive degradation of the asperity along sliding, the separation of powdery matter, its successive ejection and reinjection by the contact (thanks to a periodicity in boundary conditions), and the build-up of a gouge layer. It also includes a coupling with continuum mechanics in order to maintain a meaningful stress field in the asperity beyond the region of degradable rock.

Numerical results show that: (i) the rate of wear of the asperity and the counterface are directly linked to the normal load applied to the contact; (ii) an established layer of gouge develops in the interface and controls the friction coefficient; (iii) a constant level of surface roughness is established after a sufficient sliding distance, both for the asperity and the counterface; (iv) an accurate control of the asperity boundary conditions is necessary in order to obtain repeatable friction and wear. These results are a first step towards a better understanding of the wear kinetics as a function of asperity geometry, load, and roughness, before the introduction of thermal aspects (including melting) in a future version of the model.

How to cite: Mollon, G., Clerc, A., Ferrieux, A., Lafarge, L., and Saulot, A.: A granular numerical model for the friction and wear of a lab-scale fault asperity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7508, https://doi.org/10.5194/egusphere-egu24-7508, 2024.

EGU24-7803 | ECS | Posters on site | EMRP1.6

Fluid driven seismic cycle modelling in subduction zones 

Betti Hegyi, Taras Gerya, Luca Dal Zilio, and Whitney Behr

The role of fluid flow in triggering earthquakes in subduction zones is a critical yet complex aspect in seismology. Despite extensive study through geological, geophysical observations, and laboratory experiments, fully understanding and modelling these processes within a coupled solid-fluid interaction framework remain challenging. This study employs a coupled seismo-hydro-mechanical code (i2elvisp) to simulate fluid-driven earthquake sequences in a simplified subduction megathrust environment. We incorporate non-uniform grid resolution, enhancing the resolution of seismic events within the subduction channel. The code integrates solid rock deformation with fluid dynamics, solving mass and momentum conservation equations for both phases, alongside gravity and temperature-dependent viscosity effects. Brittle/plastic deformation is modelled through a rate-dependent strength formulation, with slip instabilities governed by compaction-induced pore fluid pressurisation. Our approach demonstrates the significant impact of fluid pressurisation on deformation localization, achieving slip rates up to metres per second in a fully compressible poro-visco-elasto-plastic medium. By refining the vertical model resolution in the subduction channel to less than or equal to 200 metres, we ensure convergence in terms of event recurrence interval and slip velocity. The models successfully replicate various slip modes observed in nature, ranging from regular earthquakes (including partial and full ruptures) to transient slow slip phenomena and aseismic creep. This research focuses on the parameters influencing the dominant slip mode, their distributions, and interactions along a modelled subduction interface. Our findings indicate that the dominant slip mode and the earthquake sequences are significantly influenced by porosity, permeability, and temperature-dependent viscosity. We explore two distinct viscosity gradients in the subduction channel to represent subduction zones with differing thermal profiles. In 'hot' subduction models, the brittle-ductile transition commences at shallower depths than in 'cold' subduction cases, influencing the nucleation depth of seismic events. These viscosity variations markedly impact model evolution; regular earthquakes exhibit higher velocities and slip rates in 'hot' scenarios, which are also more conducive to hosting aseismic creep or slow slip events. In conclusion, our study elucidates the pivotal role of fluid pressure evolution in seismicity within subduction zones and provides deeper insights into earthquake source processes. Through comprehensive modelling and analysis, we enhance understanding of the complex dynamics governing fluid-induced seismic activity and contribute to the broader field of earthquake source processes. 

How to cite: Hegyi, B., Gerya, T., Dal Zilio, L., and Behr, W.: Fluid driven seismic cycle modelling in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7803, https://doi.org/10.5194/egusphere-egu24-7803, 2024.

EGU24-8381 | Posters on site | EMRP1.6

Transition from Unstable Slip to Rate-Dependent Creep Controlled by High Fluid Pressure 

Lei Zhang, Changrong He, and Sylvain Barbot

To investigate the frictional behavior of basalt under hydrothermal conditions, we apply sliding experiments using basalt gouge under the temperature of 100-600ºC, effective normal stress of 150MPa, and fluid pressure of 30MPa and 100MPa, respectively. Experiment results under 30MPa pore pressure show that basalt exhibits velocity-strengthening behavior at 100-200ºC and changes to velocity-weakening behavior at 400-600ºC; meanwhile, at 400ºC, velocity dependence of basalt evolves with slip from initial velocity weakening to velocity-strengthening. Results under 100MPa fluid pressure show a similar transition of velocity dependence at 300ºC; however, at higher temperatures of 400-600ºC, velocity strengthening behavior occurs, accompanied by strong slip weakening behavior at the slowest loading rate (0.04μm/s). During the velocity step, the experiment exhibits a rate-dependent creep without transient evolution with slip. Microstructure observation reveals significant differences between samples sheared under 30MPa and 100MPa fluid pressure. At higher fluid pressure and temperatures of 400-600ºC, the porosity of the basalt gouge layer is significantly reduced, and deformation is characterized by pervasive shear with no apparent localization. Such results suggest that the healing process/plastic deformation is activated at higher fluid pressure, leading to slip stability transition and slip-weakening of frictional strength.

How to cite: Zhang, L., He, C., and Barbot, S.: Transition from Unstable Slip to Rate-Dependent Creep Controlled by High Fluid Pressure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8381, https://doi.org/10.5194/egusphere-egu24-8381, 2024.

EGU24-8887 | ECS | Posters on site | EMRP1.6

High-velocity frictional behavior and microstructure evolution of quartz-bearing dolomite fault gouge 

Jianhua Huang, Bo Zhang, Junjie Zou, Honglin He, Jiaxiang Dang, and Jinjiang Zhang

        Abundant cherts (nodules and bands) were discontinuously hosted by dolostones of the Mesoproterozoic group Strata (∼1.5 Ga) in the Shanxi graben system, North China, where earthquakes are common. Measurements of the shear strength and stability of granular quartz reveal that quartz is a typical tectosilicate which exhibits high frictional strength and velocity-weakening properties. Conversely, dolomite is usually frictionally weak but velocity strengthening. The two minerals also behave differently during coseismic slip. Due to the high temperature generated by frictional heating, the thermal decomposition of dolomite usually results in calcite, periclase nanoparticles and carbon dioxide. However, quartz melts by friction at high temperatures. In order to investigate the role of quartz in dolomite fault rock during the process of coseismic slip, high velocity shear experiments were conducted on the quartz-bearing dolomite fault gouge taken from Yuguang Basin South Margin Fault (YBSMF), northeast of the Shanxi graben system. Also, we carried out high velocity experiments with the synthetic quartz-dolomite gouge with different mass ratio. For a slip velocity ≥ 0.1 m/s and normal stresses from 1.0 to 1.5 MPa, the friction values of the gouge decrease exponentially from a peak value of more than 0.5 to a steady-state value from 0.1 to 0.4. This high-velocity weakening feature was observed in the synthetic quartz-dolomite gouge as well as in the YBSMF gouge. With the increase of quartz content, the slip weakening distance (Dw) increases from 4.27 to 13.24 m, and the steady-state friction coefficient increases from 0.2 to 0.4 at 1.0 MPa normal stress and 1.0 m/s slip velocity. The textures of the gouge are characterized by grain comminution, R shear planes and localized deformation zone in the friction weakening stage. The slip surfaces are characterized by mirror-like smooth surface and nanoparticle aggregates. The theoretical calculation results show that the temperature inside the gauge layer did not exceed 300 °C during the experiments. However, the microstructures present that the dolomite experienced thermal decomposition, indicating that the temperature at the asperity exceeds 550 ℃. We suggest that thermal decomposition together with flash heating may lead to the slip-weakening behavior of quartz-bearing dolomite gauge, and the addition of quartz will increase of the strength of the dolomite gouge.

How to cite: Huang, J., Zhang, B., Zou, J., He, H., Dang, J., and Zhang, J.: High-velocity frictional behavior and microstructure evolution of quartz-bearing dolomite fault gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8887, https://doi.org/10.5194/egusphere-egu24-8887, 2024.

EGU24-9165 | ECS | Posters on site | EMRP1.6

Temperature and Physical State of Water Controls Frictional Healing of Basaltic Gouges from Krafla (Iceland) 

Wei-Hsin Wu, Wei Feng, Rodrigo Gomila, Telemaco Tesei, Marie Violay, Anette K. Mortensen, and Giulio Di Toro

Fault’s frictional strength and particularly its ability to heal during the interseismic period (fault frictional healing Δμ) is critical to understand the seismic cycle, yet the understanding of temperature and phase-dependent healing characteristics of natural geothermal conditions remains limited. Here we examined the frictional healing of both simulated fresh and chlorite-altered basaltic gouge from Krafla geothermal field (Iceland) under realistic geothermal conditions of water temperature Tf = 100-400 ˚C and pressure Pf = 10-30 MPa (water in liquid, vapor and supercritical state) by performing Slide-Hold-Slide (SHS) experiments. All experiments were performed under a constant effective normal stress of 10 MPa and initiated with a 5-mm run-in slip at a loading point slip rate V of 10 mm/s before the SHS sequence. For each SHS sequence, shearing was held from 3 s to 10,000 s, separated by a slip interval of 1mm. Our mechanical results indicate that frictional healing, the difference between peak friction reached upon re-shear and the steady-state friction before the hold, increases with increasing logarithm of hold time in all experiments, as suggested by previous studies. Meanwhile, frictional healing rate (β = Δμ/log(1+ thold/tcutoff)), commonly regarded as the quantification of the rate of healing, increases with increasing temperature for both fresh and altered basalt. For fresh basalt, β increases from 0.007 at Tf = 100 ˚C to 0.060 at Tf = 300 ˚C (liquid) before dropping to 0.036 at Tf = 400 ˚C (vapor) and eventually increases to 0.096 at Tf = 400 ˚C (supercritical). For altered basalt, β  increases continuously from 0.003-0.007 at Tf = 100 ˚C to 0.013-0.022 at Tf = 300 ˚C and reaches its maximum value of β = 0.024-0.035 at Tf = 400 ˚C (vapor) and β = 0.030 at Tf = 400 ˚C (supercritical). Besides this temperature-dependent relationship, the dramatic decrease of β in fresh basalt to values similar to those of altered basalt when water changed from liquid to vapor state also suggests that the physical state of water can control the healing rate. Subsequent microanalytical analyses (XRPD, XRF, SEM-EDS) performed on the deformed gouges from altered basalts suggest an increase in hydrothermal alteration with increasing temperature, as shown by a depletion in K2O at Tf ≥ 300 ˚C. SEM-BSE images of fine platy matrices in shear bands formed at Tf = 400 ˚C point towards a dissolution of quartz, pyroxene and plagioclase. Therefore, we suggest that the healing rate of both fresh and altered basalt not only scales with the ambient temperature but is also affected by the physical state of water, particularly in the case of fresh basalt, potentially related to more intense fluid-rock interactions with increasing temperature.

Keywords: frictional healing, frictional healing rate, hydrothermal fluids, basaltic gouge, Krafla geothermal field

How to cite: Wu, W.-H., Feng, W., Gomila, R., Tesei, T., Violay, M., Mortensen, A. K., and Di Toro, G.: Temperature and Physical State of Water Controls Frictional Healing of Basaltic Gouges from Krafla (Iceland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9165, https://doi.org/10.5194/egusphere-egu24-9165, 2024.

EGU24-9541 | Posters on site | EMRP1.6

Unraveling the micro-mechanics of shear deformation through acoustic attributes of quartz-muscovite mixtures 

Marco Scuderi, Nathalie casas, Giuseppe Volpe, and Cristiano Collettini

Mineralogy, fabric, and frictional properties are fundamental aspects of natural and experimental faults that concur in controlling the fault strength and the fault slip behavior. Mineralogy controls the fabric evolution influencing the micro-mechanisms at play during fault deformation and needs an in-depth investigation to better understand and foresee the frictional response of experimental faults. Classically, this investigation has been conducted by relating the fault frictional behavior to the post-experimental microstructures. However, this “classical” approach provides a direct but static view of the fault deformation where the evolution of fabric with deformation can be only speculated.

To investigate in “real-time” the deformation micro-mechanisms at play during the experiments, the recording and analyses of Acoustic Emissions (AEs) produced by the deforming fault gouge can provide new insights.

In this study, we present a systematic study of microstructural, mineralogical, frictional, and AEs analysis coming from a suite of frictional experiments in a double direct shear configuration (biaxial apparatus, BRAVA2). We conducted experiments on gouges made of bi-disperse and layered mixtures of quartz and phyllosilicate. These experiments were performed at a constant normal stress of 52MPa and under 100% humidity. The friction evolves with the phyllosilicate content from µ ~ 0.6 for 100% quartz to µ ~ 0.4 for 100% phyllosilicates. At the end of the experiments samples were carefully collected and prepared for microstructural analysis. The fabric of the experimental samples show an evolution from localized to distributed and foliated fabric with increasing amount of phyllosilicate content.

We then integrate specific features of AEs, such as amplitude and AE rate, to unveil the micro-mechanisms at play during the experimental fault deformation. Our results show that the overall AE behavior is controlled by mineralogy. Deformation of quartz gouge produces the largest number of AEs whereas phyllosilicates are almost not producing AEs. Furthermore, the AE behavior of bi-disperse mixtures of quartz and phyllosilicates is strongly controlled by the amount of phyllosilicates. In fact, increasing the amount of phyllosilicate, the number, the rate, and the amplitude of AEs decrease. This behavior could be explained by the lubricant role of phyllosilicates which hinder the interaction between quartz grains favoring foliation sliding as main deformation mechanism and thus reducing the frictional strength. These results suggest that for bi-disperse mixtures the AEs reflect the frictional behavior of the mixture. Layered quartz-phyllosilicates mixtures show instead a non-trivial acoustic emission behavior which cannot be directly related to the measured frictional strength of the layered mixture: friction is controlled by the frictionally weaker mineral phase, whereas the AEs are probably dependent by the interplay between the stronger and weaker phase of the layered mixture.

Our results show that fault fabric together with mineralogy strongly control the micro-mechanisms at play during deformation and therefore the frictional response. Our findings support the use of the AE analysis as a new tool for the investigation of the micro-mechanisms at play during deformation, improving our interpretation of the mechanical behavior of fault gouges.

How to cite: Scuderi, M., casas, N., Volpe, G., and Collettini, C.: Unraveling the micro-mechanics of shear deformation through acoustic attributes of quartz-muscovite mixtures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9541, https://doi.org/10.5194/egusphere-egu24-9541, 2024.

EGU24-9941 | ECS | Posters on site | EMRP1.6

Strengthen and limitations of ultrasonic wave testing: examples from Double Direct Shear experiments on gouge 

Michele De Solda, Michele Mauro, Federico Pignalberi, and Marco Scuderi

In the last decades, rock mechanics laboratory experiments have allowed framing earthquake physics as a frictional problem. When the accumulated stress on a fault exceeds the frictional forces holding it in place, a rapid acceleration occurs. This movement can be stable or unstable, involving phases of adhesion (stick) and rapid sliding (slip). In these terms, an earthquake results from the release of mechanical energy during one of these slip phases.

 

Modern friction theories propose that the frictional forces holding the fault in place are controlled by small asperities defining the real contact area (RCA). Therefore, understanding the mechanics of contacts on the fault and their evolution under stress and velocity changes can shed light on the microphysical processes underlying earthquakes.

 

In the laboratory, it is now possible to investigate the dynamics of experimental faults, predicting their instability behavior based on Rate and State Friction theory and its experimentally obtainable parameters (a-b, Dc). However, these parameters lack an explicit relationship with contact mechanics, necessitating additional measurements complementing the system's state information. One of the most widely used techniques for studying RCA during laboratory experiments involves investigating changes in acoustic transmissivity (velocity, amplitude) of generated and recorded ultrasonic waveforms (UW) passing through the sample during the deformation. At a given wavelength, analytical expressions for these quantities depend on the elastic properties and densities of the fault portion crossed by the wave. Simultaneous knowledge of stress conditions and elastic properties allows the formulation of constitutive laws for the evolution of contacts between fault asperities.

 

In double direct shear experiments (DDS) within biaxial apparatuses, the sample dimensions (gouge) impose stringent limits on the spatial and temporal resolution of the signal. These limits highlight the current sensor technology's deviation from the ideal behavior.

 

Here, we present a methodology and a waveform recording and synchronization protocol

implemented on the biaxial apparatus BRAVA2 in the Rock Mechanics and Earthquake Physics laboratory at Sapienza University of Rome. We focus on the types of sensors used and their specifications to provide accurate measurements of the deformation processes occurring within the gouge layers.

 

Several studies have conducted DDS experiments using UW, but they rarely take into account the characterization of the impulse signal, various reflections in the sample assembly, and conversion modes of the generated waveforms. These are all essential components to identify the interaction of the experimental system with the propagation of the ultrasonic waves, to exploit the received signal in its entirety.

We believe that a careful signal characterization is necessary to fully understand the physical processes during deformation within the sample and, consequently, to attempt upscaling to natural earthquakes.

How to cite: De Solda, M., Mauro, M., Pignalberi, F., and Scuderi, M.: Strengthen and limitations of ultrasonic wave testing: examples from Double Direct Shear experiments on gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9941, https://doi.org/10.5194/egusphere-egu24-9941, 2024.

EGU24-10564 | Posters on site | EMRP1.6

An efficient hybrid SBI-FD method for modeling fluid migration and fault-fluid interactions 

Yu-Han Wang and Elías Rafn Heimisson

The interactions between fluids and fault structures play a pivotal role in understanding fault slip behavior. Over the years, various numerical methods have been developed to simulate these interactions. Volume-based methods, like the finite difference method (FDM), excel in their capacity to handle the intricacies of real-world fault structures, including material heterogeneity. On the other hand, the spectral boundary integral method (SBIM) is renowned for its computational efficiency. Recently, a hybrid approach has garnered significant attention, offering the benefits of both volume-based and SBI methods. This hybrid method allows for the consideration of fault structures' heterogeneity while maintaining computational efficiency. In this study, we introduce a novel hybrid method that bridges the SBIM and the FDM to model fluid migration in fault structures. Through rigorous model verification, we establish that our hybrid method can achieve a remarkable speedup of up to one thousand times compared to the FDM. Furthermore, we conducted two parametric studies to address open questions in fluid migration modeling within fault structures. First, we investigate the mobility contrast ratio between the host rock and the damage zone to determine the limits under which we can assume a zero-leak-off interface. Second, we explore the role of fault zone width in maintaining the validity of this zero-leak-off assumption. Building upon these foundational investigations, we demonstrate the possibility of extending the numerical framework to describe fault-fluid interactions considering poroelastic coupling.

How to cite: Wang, Y.-H. and Rafn Heimisson, E.: An efficient hybrid SBI-FD method for modeling fluid migration and fault-fluid interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10564, https://doi.org/10.5194/egusphere-egu24-10564, 2024.

The slip behavior of crustal faults is known to be controlled by the mineralogic composition of the fault gouge. The exact properties determining the frictional behavior of geologic materials, including diverse remains an important question. Here, we use a geochemical approach considering the role of water-rock interactions. As a mechanism, we suspect that the mineral surface charge allows attractive and repulsive forces (Van Der Waals type), and that those forces may influence the static mechanical behavior of clays (cohesion, static friction).  On the other hand, we suspect that the water bound to the mineral surfaces may play a role during shearing.  To address these ideas, we measured the cation exchange capacity (CEC) of 10 different rock and mineral types, including non-clays and a range of phyllosilicate minerals, using CEC as a proxy for the mineral surface charge and the ability to bind water to the mineral surfaces.  For these materials, we conducted laboratory shearing experiments measuring the pre-shear cohesion, peak friction coefficient, residual friction coefficient, post-shear cohesion, and velocity-dependent friction parameters under 10 MPa effective normal stress.  
Our results show that low CEC materials (< 3 mEq/100g) tend to exhibit high friction, low cohesion, and show velocity-weakening frictional behavior. The phyllosilicate minerals exhibit larger CEC values up to 78 mEq/100g and correspondingly lower friction coefficients, higher cohesion, and velocity-strengthening frictional behavior. Zeolite exhibits a relatively high CEC value typical of phyllosilicates, but its strength and frictional characteristics are that of a non-clay with low CEC. This suggests that grain shape and contact asperity size may be more important for non-phyllosilicates. For phyllosilicates, we suggest that the systematic patterns in strength and frictional behavior as a function of CEC could be explained by water bound to the mineral surfaces, creating bridges of hydrogen or van der Waals bonds when the particles are in contact. Such bonding explains the large cohesion values for high-CEC materials under zero effective stress, whereas surface-bound water trapped between the particles under load explains low friction.  Beyond the results of this study, CEC appears to be a controlling factor for other properties such as permeability and even the amount of bound DNA in sediments.

 

How to cite: Ikari, M. and Conin, M.: Cation Exchange Capacity Quantifies the Link Between Mineral Surface Chemistry and Frictional-Mechanical Behavior of Simulated Fault Gouges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10969, https://doi.org/10.5194/egusphere-egu24-10969, 2024.

During natural and induced seismic activities, pore fluid pressure within fault zones and their surrounding rock may respond differently to stress variations, introducing additional complexities to seismic hazard assessment. While theoretical investigations have recognized the influence of such poroelastic heterogeneity on fault instability, incorporating phenomena like slip-induced dilation or compaction, the chosen poroelastic properties in these studies lack robust constraints from experimental measurements. Addressing this gap, our study focuses on quantifying the heterogeneity of poroelastic properties in the presence of a fresh fault, aiming to elucidate the coupling between poroelasticy and fault dilatancy during fault slip.

In our experimental investigation, we examined the evolving dynamics of pore pressure both on- and off-fault in initially intact Westerly granite samples. Applying confining stress of 100 MPa and a pore pressure of 60 MPa at two sample ends to replicate crustal settings, we induced a sliding fault plane through loading to failure under a constant strain rate. In the faulted samples, we measured the pore pressure response under sudden step loading in the direction of the maximum compression σ1. Each loading step of around 5 MPa was imposed incrementally increasing the differential stress from 5 MPa to approximately 80 MPa (frictional resistance) after achieving pore pressure equilibrium. Detailed measurements, including displacement, bulk deformation, differential stress, local pore pressure and acoustic emissions were recorded throughout these tests. A spring-slider model coupled with 1-D fluid diffusion was used to try to simulate experimental observations.

Our results indicate that both the shear zone and the bulk exhibit a diminishing Δp/Δσ1 with increasing differential stress. Measurements within the fault zone consistently yield positive values, surpassing those off the fault, with the discrepancy more pronounced at lower stress levels. In regions farther away from the shear zone, the off-fault response Δp/Δσ1 presents a smaller value compared to locations proximal to the fault zone and may even exhibit slight negativity. During fault slip, on-fault measurements exhibit an instantaneous increase upon step loading followed by a gradual decrease, as a result of the interplay between poroelasticity and fault dilatancy. These observations were effectively reproduced by the numerical model integrating the poroelastic measurements and rate-and-state fault friction with slip-dependent dilatancy. The implications of this investigation extend to an enriched understanding of the heterogeneity in poroelastic responses between fault zones and host rocks, serving as valuable benchmarks for informing future numerical simulations, particularly in the context of naturally formed fresh faults. 

How to cite: Liu, D. and Brantut, N.: Poroelastic heterogeneity in the presence of a fresh fault: experimental insights and numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10998, https://doi.org/10.5194/egusphere-egu24-10998, 2024.

EGU24-11200 | Orals | EMRP1.6

Influence of Injection rate and slip-induced dilatancy on the propagation of fluid-driven slip front 

Francois Passelegue, Pierre Dublanchet, Nicolas Brantut, and Hervé Chauris

A growing amount of evidence indicate that aseismic transients driven by overpressure play an important role in the triggering of induced seismicity. Understanding the physical control on aseismic slip development is thus important for seismic hazard assessment. We conducted an investigation into the propagation dynamics of a fluid-driven slip front along a laboratory frictional interface composed of granite. The experiments were carried out under a confining pressure of 90 MPa, with an initial uniform fluid pressure of 10 MPa. Fault reactivation was initiated by injecting fluids through a borehole directly connected to the fault.

Our findings reveal that the peak fluid pressure at the borehole leading to reactivation exhibits an increase proportionate to the injection rate. Employing three fluid pressure sensors and eight strain gauges strategically positioned around the experimental faults, we performed an inversion analysis to image the spatial and temporal evolution of (i) hydraulic diffusivity and (ii) kinematic fault slip during each injection experiment. Our inversion methods integrated both deterministic and Bayesian procedures, facilitating the tracking of the fluid pressure front along the fault interface and the subsequent propagation of the slip front over time.

The migration pattern shares many similarities with natural slow slip events suspected to play a role in the development of natural and induced earthquake swarms or aftershock sequences.  We demonstrate that increasing the fluid injection rate induces a transition from a quasistatic propagation of the slip front correlated with the increase in fluid pressure to a dynamic scenario where the slip front outgrows the fluid pressure front, accelerating during its propagation. Furthermore, we establish that temporarily shutting off fluid pressure during injection induces the propagation of a pore-pressure back-front, which halts the propagation of the slip front, aligning with theoretical expectations.

How to cite: Passelegue, F., Dublanchet, P., Brantut, N., and Chauris, H.: Influence of Injection rate and slip-induced dilatancy on the propagation of fluid-driven slip front, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11200, https://doi.org/10.5194/egusphere-egu24-11200, 2024.

EGU24-11407 | ECS | Posters on site | EMRP1.6

Laboratory Insight into the Evolution of the Seismic Potential of an Asperity due to Wear 

Sofia Michail, Paul Antony Selvadurai, Markus Rast, Antonio Felipe Salazar Vásquez, Patrick Bianchi, Claudio Madonna, and Stefan Wiemer

Faults in nature exhibit complex surface characteristics with patches of the fault (asperities) that may slip dynamically while other sections are more prone to creep (Beeler et al., 2011). Asperities forming in nature may be due to the geometric interactions between surfaces within a fault that contribute to complex stress states that are not well understood. Fault roughness is believed to play an important role in the control of the contact conditions established by asperities, directly affecting its potential to slip unstably. How the asperities are formed and how their seismogenic properties evolve due to wear is an important question with implications to slip budget and earthquake potential.

In this study, we performed a triaxial experiment at sequentially increasing confining pressures (Pc = 60, 80, 100 MPa) on a saw-cut sample of Carrara marble. We analysed the quasi-static frictional response that benefited from novel arrays of distributed strain sensors (DSS) obtained using fiber optics. This sensor offered unique insight into the axial strain with a spatial resolution of 2 mm. The frictional behaviour during the first confining pressure step exhibited a dynamic instability in the form of a stick-slip event (SS) that produced a measurable stress drop. In the subsequent confining pressure stages, where an increase in confining pressure translated to increased normal stress, the fault behaved in a stable manner and no dynamic instabilities were produced. This observation is inconsistent with frictional stability theory (e.g. Rubin and Ampuero, 2005) and required pre- and post-mortem campaigns into the surface characteristics and their evolution to explain this abnormal behaviour. Therefore, we employed experimental techniques (pressure sensitive film (PSF), optical and stylus profilometry) along with finite element (FE) model in ABAQUS to characterize the pressure and roughness.

The DSS array showed extensional axial strain closer to the edges of the fault, while only compression was expected in this triaxial loading test. The pre-experimental profilometry revealed an asperity located at the centre of the fault with a curvature ratio of h/L=0.1% inherited from the hand-lapping preparation, which dominated the initial contact conditions prior to the SS and explained the DSS observations. The DSS results were confirmed using a FE model which justified the effect of the fault geometry (h/L) on the strain response. After the SS, wear and smoothening of the central asperity was seen in roughness measurements. The profilometric measurements showed that gouge was deposed adjacent to the high normal stress asperity center (PSF) and were characterized by increased RMS roughness. These small amounts of gouge on the fault surface were sufficient to suppress the seismic response of the asperity. These findings show that the seismic potential of a carbonate (softer) asperity, may be highly influenced by the debris produced during wear. Its impact on earthquake nucleation could provide insight into large-scale earthquake preparation processes on carbonate faults in nature.

 

References:

  • Beeler, M., Lockner, D. L. and Hickman, S. H. (2001), Bull. Seis. Soc. Am., 91 (6): 1797–1804
  • Ampuero, J.-P. and Rubin, A. M. (2008), J. Geophys. Res., 113, B01302

How to cite: Michail, S., Selvadurai, P. A., Rast, M., Salazar Vásquez, A. F., Bianchi, P., Madonna, C., and Wiemer, S.: Laboratory Insight into the Evolution of the Seismic Potential of an Asperity due to Wear, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11407, https://doi.org/10.5194/egusphere-egu24-11407, 2024.

EGU24-11536 | Orals | EMRP1.6 | Highlight

Fault activation from up close 

Men-Andrin Meier, Domenico Giardini, Stefan Wiemer, Massimo Cocco, Florian Amann, Elena Spagnuolo, Paul Selvadurai, Elisa Tinti, Luca Dal Zilio, Alba Zappone, Giacomo Pozzi, Mohammadreza Jalali, and Valentin Gischig and the FEAR science team

Our understanding of earthquake rupture processes is generally limited by the resolution of available observations. In all but exceptional cases, earthquake observations are made at comparatively large distances from the rupture itself, which puts a limit on what spatial scales can be resolved. At the same time, it is clear that small scale processes may play a crucial, if not dominant, role for various seismogenic processes, including rupture nucleation, co-seismic weakening and stress re-distribution.

The Fault Activation and Earthquake Rupture ('FEAR') project aims at collecting and interpreting a multitude of earthquake-relevant observations from directly on and around the process zone of an induced earthquake. To this end, we attempt to activate a natural granitic fault zone in the BedrettoLab, at a depth of ~1km, after instrumenting the fault zone with a multi-domain and multi-scale monitoring system. The goal is to observe and study earthquake rupture phenomena in a natural setting, from unusually close distance.

In this talk, we outline the project status, the science goals, and the plans for the main experiments, which are scheduled for the years 2024 - 2026. Notable milestones we report on include

  • the identification and detailed characterisation of the target fault zone
  • the beginning of niche and tunnel excavations
  • laboratory experiments that characterise the frictional and mechanical behaviour of both gauge material and host rock of the target fault zone
  • development of numerical models for 2D and 3D dynamic rupture propagation
  • development of tailored monitoring methods for seismicity, strain, temperature, pressure, bio-geo-chemistry and other relevant observables
  • development of remote experiment control methods
  • test stimulations in a nearby rock volume of similar geology, with an already existing monitoring system, where we tested the influence of pre-conditioning injection protocols
  • similar test stimulations in the same volume where we aim at triggering a larger event (target Mw~0)
  • active seismic experiments in an underground salt mine, to calibrate the very- to ultra-high frequency (1k Hz - 500k Hz) acoustic emission sensors

Together, these and other efforts constitute the necessary ingredients we need for interpreting the near-source observations that we will collect during the fault activation experiments.

How to cite: Meier, M.-A., Giardini, D., Wiemer, S., Cocco, M., Amann, F., Spagnuolo, E., Selvadurai, P., Tinti, E., Dal Zilio, L., Zappone, A., Pozzi, G., Jalali, M., and Gischig, V. and the FEAR science team: Fault activation from up close, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11536, https://doi.org/10.5194/egusphere-egu24-11536, 2024.

EGU24-12986 | ECS | Posters on site | EMRP1.6

Exploring earthquake recurrence and nucleation processes with Foamquake and a variety of asperity configurations 

Elvira Latypova, Fabio Corbi, Giacomo Mastella, Jonathan Bedford, and Francesca Funiciello

The short seismic record with respect to the return time of large subduction earthquakes and the spatial fragmentation of available geophysical data represent unfavourable conditions for robust hazard assessment. Over the last decade, data from scaled seismotectonic models have become useful in filling the observational gaps of seismic and geodetic networks. Such models allow reproducing hundreds of analogue seismic cycles in a few minutes of experimental time and with the advantage of known and controllable boundary conditions. 

Here we present experimental results from Foamquake – an established 3D seismotectonic model, which simulates megathrust subduction. Recent technical advances in experimental monitoring have allowed us to include into our research a high-frequency camera to record model surface deformation at 50 Hz and a network of 5 accelerometers (located on the model surface) that measure the three components of acceleration at 1 kHz. To analyse the camera data, we used particle image velocimetry (PIV) to derive surface displacements, such as in a dense, homogeneously distributed geodetic network spanning updip to scaled depths that are often offshore and, therefore, typically under-monitored in natural subduction zones.

We performed 33 experiments exploring 10 different geometrical configurations of asperities along the analog megathrust. In particular, we varied the number of asperities, their size, location, and extra normal load. We observed that the rupture pattern of analogue earthquakes predictably changes as the extra normal load varies and the distribution of asperity configurations becomes more complex. Depending on the number and size of the asperities and the size of the barrier between them, we noticed different ratios between full and partial ruptures with different recurrence time (Rt) intervals. In some experiments we detected cascades of ruptures. We used the coefficient of variation (CoV) of recurrence time to quantify analog earthquakes periodicity. Most of our models display quasi-periodic analog earthquakes recurrence with CoV<0.5, but multi-asperity experiments with variable-size and extra normal load lean toward random behaviour as testified by CoV~0.8.

Future investigations include the following steps – exploring this great volume of data using machine learning, looking for spatial and temporal relationships between accelerometer and PIV displacements, and tracking in detail the aseismic processes that may precede and follow earthquake rupture.

How to cite: Latypova, E., Corbi, F., Mastella, G., Bedford, J., and Funiciello, F.: Exploring earthquake recurrence and nucleation processes with Foamquake and a variety of asperity configurations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12986, https://doi.org/10.5194/egusphere-egu24-12986, 2024.

EGU24-13117 | ECS | Posters on site | EMRP1.6

A model for the formation and propagation of faults from the coalescence of smaller-scale systems of cracks: Finite Element Method-based numerical approach 

Ludovico Manna, Giovanni Toscani, Matteo Maino, Leonardo Casini, and Marcin Dabrowski

The 2D, plane strain, Finite Element Method-based linear elastic model that I present aims to assess the differential stress response to variations in the geometric configuration of a system of multiple collinear elliptic cracks intercepting a body of rock undergoing elastic deformation. The assumption underlying this simulation is that a collection of thin voids in a continuum medium can replicate the features observed in a system consisting of rough fault profiles in partial contact subjected to shear. The linear elastic model is designed to reproduce the stress and displacement fields around a rough fault, with a specific focus on stress concentration around its contact asperities. The model also allows to record the principal stress field on the domain for a wide range of scales and geometric properties of the system of collinear cracks embedded in the deforming rock. Analyzing the dependence of differential stress on parameters describing the geometry of rough fractures allows for considerations on the primary factors influencing brittle failure. Additionally, the examination of principal stresses around the tips of the cracks helps evaluate the potential orientation of new fracture patterns that may emerge when the yield strength of the deforming material is locally exceeded. The magnitude and orientation of the principal stresses are also crucial for the understanding of fracture coalescence and frictional reactivation of shear cracks in an elastic rock, which in turn is one of the main factors that govern the seismic cycle of natural faults. Furthermore, a comparison of the results of the present model with recent wing crack models of brittle creep suggest that our code may also be useful to obtain estimates of the critical distance between cracks for their interaction to coalesce into larger fractures. The process is assumed to indefinitely continue at greater scales, which offers the chance to propose a model for fault formation and propagation.

How to cite: Manna, L., Toscani, G., Maino, M., Casini, L., and Dabrowski, M.: A model for the formation and propagation of faults from the coalescence of smaller-scale systems of cracks: Finite Element Method-based numerical approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13117, https://doi.org/10.5194/egusphere-egu24-13117, 2024.

EGU24-13433 | Orals | EMRP1.6

The effect of pressure drop and fluid expansion during rock fracturing by dynamic unloading 

Michele Fondriest, Fabio Arzilli, Benoit Cordonnier, Michael Carroll, and Mai-Linh Doan

The propagation of earthquake fault ruptures in the crust involve the generation of unloading stress pulses sufficiently large to induce dynamic failure of water-saturated rocks under tensional stresses and hydrofracturing. Similar processes are also activated during underground rock mass excavation activities in mines and tunnels. The current knowledge about rock fracturing via dynamic unloading is mainly limited to empirical records and numerical simulations, while there is a general paucity of experimental studies, due to difficulties in reproducing large instantaneous decompressions on rock samples using standard triaxial rigs. Until now rapid decompression and fracturing of large rock samples in dry conditions was reported only by using an unconventional gas-confined vessel.

Here, we report rock-fracture results for newly conceived rock decompression experiments, completed through the innovative use of a “cold-seal pressure vessel” (CSPV) apparatus which is routinely employed in experimental petrology. We applied instantaneous large decompressions on water-saturated rock samples equilibrated at high confinement (up to 200 MPa) and temperatures (up to 540°C). The tested rock samples were fine-grained Westerly granite, coarse-grained tonalite and micritic limestone. During the decompressions the rock samples hydrofractured due to the confinement dropping faster than the pore pressure within the rock. Porosity measurements, SEM imaging and X-ray µCT acquired before and after the tests suggest that the magnitude of dynamic fracturing not only positively correlates with the pressure drops but it mostly increases when the decompression is associated to a phase change of the pore water (e.g. supercritical fluid to subcritical gas) . Water vaporization or degassing imply an instantaneous volume expansion (up to 70 times) which critically enhances dynamic fracture propagation along rock grain boundaries. The induced fractures span from mm-long transgranular cracks to microcracks with submicrometric aperture. Therefore, synchrotron light high-resolution microtomography (final pixel resolution of 0.3 µm) was employed to fully resolve and quantify the 3D fracture networks of these deformed rock samples. Such unique dataset allowed us to determine at different scales the fracture intensity, aperture and connectivity of the dynamically induced fracture networks and to assess the key contribution of pore-water physical state changes on the initial stages of dynamic fracturing in rocks at crustal conditions. Such results will contribute to close a current knowledge gap in rock mechanics.

How to cite: Fondriest, M., Arzilli, F., Cordonnier, B., Carroll, M., and Doan, M.-L.: The effect of pressure drop and fluid expansion during rock fracturing by dynamic unloading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13433, https://doi.org/10.5194/egusphere-egu24-13433, 2024.

Establishing a constitutive law for fault friction is a crucial objective of earthquake science. However, the complex frictional behavior of natural and synthetic gouges in laboratory experiments eludes explanations. Here, we present a constitutive framework that elucidates the slip-rate, state, temperature, and normal stress dependence of fault friction under the relevant sliding velocities and temperatures of the brittle lithosphere during seismic cycles. The competition between healing mechanisms explains the low-temperature stability transition from steady-state velocity-strengthening to velocity-weakening as a function of slip-rate and temperature. In addition, capturing the transition from cataclastic flow to semi-brittle creep accounts for the stabilization of fault slip at elevated temperatures. The brittle behavior is controlled by the real area of contact, which is a nonlinear function of normal stress, leading to an instantaneous decrease of the effective friction coefficient upon positive normal stress steps. The rate of healing also depends on normal stress, associated with an evolutionary response. If these two effects do not compensate exactly, steady-state friction follows a nonlinear dependence on normal stress. We calibrate the model using extensive laboratory data covering various relevant tectonic settings. The constitutive model consistently explains the evolving frictional response of fault gouge from room temperature to 600º for sliding velocities ranging from nanometers to millimeters per second, and normal stress from atmospheric pressure to gigapascals. The frictional response of faults can be uniquely determined by the in situ lithology and the prevailing hydrothermal conditions.

How to cite: Barbot, S.: Constitutive behavior of rocks during the seismic cycle in non-isothermal, non-isobaric conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14003, https://doi.org/10.5194/egusphere-egu24-14003, 2024.

EGU24-14504 | Posters on site | EMRP1.6

The role of poroelasticity in rupture dynamics across fault stepovers 

Luyuan Huang, Luca Dal Zilio, and Elías Rafn Heimisson

Understanding earthquake rupture propagation across fault stepovers is pivotal for assessing the seismic hazard, offering vital insights into dynamic rupture processes within intricate fault geometries. However, the role of poroelastic effects within strike-slip fault systems featuring stepovers remains unexplored in dynamic models simulating Sequences of Earthquakes and Aseismic Slip (SEAS). Many existing models neglect poroelastic effects, and among those that consider them, a typical standard value of 0.8 is adopted for Skempton's coefficient B. Furthermore, a single dynamic rupture simulation is unable to address the frequency at which ruptures propagate through the stepover. Instead, these simulations only provide a binary status, indicating whether the ruptures jump or arrest. Thus, the investigation into how poroelasticity influences the likelihood of an earthquake jumping through a stepover emerges as a significant area of study. In response, we introduce a quasi-dynamic boundary element model that simulates 2D plane-strain earthquake sequences. This model incorporates undrained pore pressure responses affecting the fault's clamping and unclamping mechanisms and is governed by rate-and-state friction, with state evolution defined by the aging law. We first illustrate that dynamic rupture occurring in either left-lateral or right-lateral fault stepovers leads to a dynamic decrease (unclamping) or increase (clamping) in the effective normal stress. Dynamic variations of the effective normal stress depend on Skempton's coefficient. Consequently, higher Skempton's coefficients can promote rupture jumping across fault segments even for larger stepover distances. We then conduct a thorough parameter space study, evaluating the effects of Skempton's coefficient variations and stepover width on fault interactions within a fluid-filled porous environment. The likelihood of rupture jumping involves a trade-off between Skempton's coefficient and stepover width. We validate the numerical model by comparing it to an analytical solution that involves a plane strain shear dislocation on a leaky plane within a linear poroelastic, fluid-saturated solid. This validation demonstrates that a simple analytical solution, primarily dependent on fault dislocation and Skempton's coefficient, has the potential to effectively predict the pore pressure change. The critical jumping width for 50% chance of rupture jumping predicted by our model explains the threshold dimension of the fault step, above which ruptures do not propagate. This study highlights the significance of incorporating poroelastic effects on- and off-fault in understanding the dynamic variations of the effective normal stress, which could significantly alter the overall length of fault rupture.

How to cite: Huang, L., Dal Zilio, L., and Rafn Heimisson, E.: The role of poroelasticity in rupture dynamics across fault stepovers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14504, https://doi.org/10.5194/egusphere-egu24-14504, 2024.

EGU24-14566 | Posters on site | EMRP1.6

Frictional behavior of chlorite in large-displacement experiments under hydrothermal conditions 

Weifeng Qin, Lu Yao, Tongbin Shao, Wei Feng, Jianye Chen, and Shengli Ma

The frictional properties of faults are primarily controlled by their mineral composition, as well as ambient and deformation conditions, such as temperature, pore fluid, normal stress, and slip displacement. While many studies have been conducted to decipher how temperature and pore fluid may affect the frictional behavior of faults, less attention has been paid to the slip displacement effects, especially under hydrothermal conditions. By employing a rotary shear apparatus equipped with an externally-heated hydrothermal pressure vessel, we conducted large-displacement (up to 521 mm) friction experiments on chlorite under temperature (T) of 25 to 400℃ and pore water pressure (Pp) of 30MPa. The imposed effective normal stresses were 200 MPa and the slip rates ranged from 0.4 to 10 μm/s. The experiments unveiled significant slip strengthening in chlorite within the temperature range of 25 to 400 °C. Moreover, with increasing temperatures, there was an overall increasing trend in both the rate of slip strengthening and the ultimate frictional strength. For example, under T = 25 °C, the friction coefficients at displacements of 5, 90, and 521 mm were 0.33, 0.49, and 0.59, respectively, in contrast to 0.46, 0.79, and 0.88, respectively, at the same three displacements under T =400 °C. Under all the temperature and displacement conditions, chlorite exhibited velocity strengthening behavior without discernible temperature dependence, although the velocity-dependence parameter (a-b) increased with slip displacement. Microstructural analysis revealed that, the entire layer of the chlorite gouge experienced pervasive and intense shear deformation after slip of 521 mm, with extremely remarkable grain-size reduction. The thermogravimetrical and FTIR data of the deformed chlorite samples, together with the microstructural data, suggest that the dehydroxylation and the distortion of crystal structure of chlorite might occur during the friction experiments conducted at T ≥ 200 °C. Such changes may explain the more pronounced slip strengthening of chlorite with increasing temperatures towards 400 °C. This explanation can be further demonstrated by a comparative experiment conducted under varying temperatures (400°C for the first 100 mm of slip, followed by 25°C for the rest of 100 mm slip), wherein the friction coefficient at T = 25°C during the latter stage of slip remains as high as that at T = 400°C. These findings highlight the importance of slip displacement in controlling the frictional strength and its variations of chlorite-bearing faults at depths, and have profound implications for understanding the fault slip behaviors and earthquake mechanisms in subduction zones.

How to cite: Qin, W., Yao, L., Shao, T., Feng, W., Chen, J., and Ma, S.: Frictional behavior of chlorite in large-displacement experiments under hydrothermal conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14566, https://doi.org/10.5194/egusphere-egu24-14566, 2024.

EGU24-15205 | ECS | Posters on site | EMRP1.6

Initial stress distribution dictates nucleation location and complexity of the seismic cycle of long laboratory faults 

Federica Paglialunga, Francois Passelegue, and Marie Violay

Many aspects of earthquake physics are still not completely understood given its intrinsically complex nature. Among the others, the nucleation process; when and where an earthquake will occur, as well as its magnitude. Seismology is a commonly used method for studying earthquakes, but it faces challenges in accessing precise information about the physical processes taking place on the fault plane.

Here, we show how laboratory seismology can directly shed light on fault plane dynamics. Our approach involves reproducing in the laboratory on a large biaxial apparatus with a fault length of 2.5 m generated by two analog (PMMA) samples brought into contact. The experimental setup allows to impose both a heterogeneous loading distribution through the use of independent pistons loading the fault in the normal direction and specific boundary conditions (i.e. by modifying stopper and puncher dimensions). The stress state is measured through strain gauges at high frequency (40 KHz) along 15 locations along the fault. The experiments provide insights into two crucial aspects of laboratory earthquakes: (i) the nucleation location of ruptures and (ii) the complexity of the seismic cycle.

Our findings reveal that the initial on-fault stress distribution plays a significant role in both aspects. We observe that ruptures consistently nucleate in locations where the stress ratio τ/σn is the highest. Notably, such values change among experiments, challenging the widespread notion that a friction coefficient solely governs the onset of instability. Furthermore, we demonstrate how the heterogeneity of the initial prestress distribution along the fault controls the complexity of the seismic cycle. In certain cases, the seismic cycle manifests as system-size events with complete ruptures occurring regularly in time, devoid of precursors. Conversely, other initial stress distributions generate more complex cycles, characterized by multiple precursors before a main rupture, predominantly occurring in zones of elevated τ/σn (referred to as 'friction asperity'). The complexity of the seismic cycle can be described in terms of the number of precursory events, inter-event time, and the size of finite ruptures.

This study, carried out in a long laboratory fault, highlights the complexities that emerge when heterogeneous, hence more realistic, stress conditions are applied, providing valuable insights into the physics of natural earthquakes.

How to cite: Paglialunga, F., Passelegue, F., and Violay, M.: Initial stress distribution dictates nucleation location and complexity of the seismic cycle of long laboratory faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15205, https://doi.org/10.5194/egusphere-egu24-15205, 2024.

EGU24-15273 | ECS | Orals | EMRP1.6

Impact of multiscale heterogeneities on the nucleation of earthquakes 

Mathias Lebihain, Thibault Roch, Marie Violay, and Jean-François Molinari

Earthquake nucleation is traditionally described using cascading or slow pre-slip models. In the latter, nucleation occurs as the sudden transition from quasi-static slip growth to dynamic rupture propagation. This typically occurs when a region of the fault of critical size Lc, often called nucleation length, is sliding. This transition is relatively well-understood in the context of homogeneous faults. Yet, faults exhibit multiple scales of heterogeneities that may emerge from local changes in lithologies or from its self-affine roughness. How these multiscale heterogeneities impact the overall fault stability is still an open question.

Combining the nucleation theory of [Uenishi and Rice, JGR, 2003] and concepts borrowed from statistical physics, we propose a theoretical framework to predict the influence of brittle/ductile asperities on the nucleation length Lc for simple linear slip-dependent friction laws. Model predictions are benchmarked on two-dimensional dynamic simulations of rupture nucleation along planar heterogeneous faults. Our results show that the interplay between frictional properties and the asperity size gives birth to three (in)stability regimes: (i) a local regime, where fault stability is controlled by the local frictional properties, (ii) an extremal regime, where it is governed by the most brittle asperities, and (iii) a homogenized regime, in which the fault behaves at the macroscale as if it was homogeneous and the influence of small-scale asperities can be averaged.  

Using this model, we explore the overall stability of rough faults, featuring multiscale distributions of frictional properties. We also investigate the stability of velocity-neutral faults that features brittle asperities. Overall, our model provides a theoretical basis to discriminate which heterogeneity scales should be explicitly described in a comprehensive modelling of earthquake nucleation, and which scales can be averaged.

How to cite: Lebihain, M., Roch, T., Violay, M., and Molinari, J.-F.: Impact of multiscale heterogeneities on the nucleation of earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15273, https://doi.org/10.5194/egusphere-egu24-15273, 2024.

EGU24-18100 | ECS | Posters on site | EMRP1.6

Frictional Response of Clay-rich Sandstone to Pore-Pressure Oscillation Throughout Interseismic Periods 

Nico Bigaroni, Julian Mecklenburgh, and Ernest Rutter

During interseismic periods a fault at depth can experience non-constant effective normal stress due to fluctuations in the pore-fluid pressure. Pore-pressure oscillations may influence the healing capability of the fault and ultimately affect its reactivation. Thus, studying the behaviour of faults during interseismic periods is a critical factor in understanding the seismicity. Triaxial tests were conducted using saw-cut (45o) samples of Pennant Sandstone to investigate the influence of pore-pressure oscillations during slide-hold-slide (SHS) tests (th = 900 – 7300s) on its frictional behaviour and fault reactivation. The cylindrical samples were hydrostatically compacted at 30 MPa and pore-pressurized with argon gas at 5, 10 and 18 MPa resulting in effective normal stress (σ’n) 25, 20 and 12 MPa, respectively. Then the saples were deformed at a constant shear displacement rate ≈ 4.5 μm/s. To overcome the displacement hardening tendency of the sample geometry, we servo-controlled the confining pressure so that the resolved normal stress on the sliding surface is kept constant. Experimental observations revealed a significant influence of pore-pressure oscillation on the frictional behaviour resulting in an increase in both frictional healing and creep relaxation. Moreover, this effect was enhanced as the effective normal stress was increased further. To understand better the underling mechanism(s) that influences these time-dependent processes we coupled the frictional results with permeability measured using the oscillating pore pressure method during the SHS tests. Finally, we tested how the pore-pressure oscillation affected the fault reactivation by conducting creep experiments at constant shear stress while the fault was brought to reactivation via progressive increase in fluid pressure. Our results demonstrated how non-constant effective normal stress history during interseismic periods deeply affects the fault behaviour, with important implications for natural and human-induced seismicity.

How to cite: Bigaroni, N., Mecklenburgh, J., and Rutter, E.: Frictional Response of Clay-rich Sandstone to Pore-Pressure Oscillation Throughout Interseismic Periods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18100, https://doi.org/10.5194/egusphere-egu24-18100, 2024.

EGU24-19397 | Orals | EMRP1.6

The pulse-like dynamics of large earthquakes illuminated by a minimal elastodynamic model 

Fabian Barras, Einat Aharonov, and François Renard

Observations suggest that large earthquakes often propagate as self-healing slip pulses but the mechanical reason of this ubiquity remains debated. Pulse-like ruptures differ from the classical crack-like dynamics by the fact that the slipping portion of the fault is limited to the immediate vicinity of the propagating tip. In this work, we first propose a minimal model describing the dynamics of large earthquakes. In its simplest form, the model contains only two free parameters: a dimensionless stress parameter characterizing the initial state of stress along the fault and a ratio of elastic moduli. The model illuminates how self-healing slip pulses can be produced by the paucity of elastic strain energy that arises once the rupture dynamics interplays with the finite geometry of fault zones—even in the absence of additional mechanisms such as rate-dependent friction.

Next, we discuss the example of faults surrounded by a damage zone whose reduction in elastic wave velocity restricts the flow of strain energy to the rupture tip and promotes pulse-like rupture. Using the proposed model, we demonstrate how the contrast in wave velocities and the initial stress level in the fault zone mediate the propagation mode of the earthquake.

How to cite: Barras, F., Aharonov, E., and Renard, F.: The pulse-like dynamics of large earthquakes illuminated by a minimal elastodynamic model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19397, https://doi.org/10.5194/egusphere-egu24-19397, 2024.

Carbon capture and storage technology is a necessary means to achieve the temperature control goal of 1.5 degrees Celsius under the background of peak carbon dioxide emissions and carbon neutrality. The storage of carbon dioxide in oil and gas reservoirs has the advantages of high safety, large storage capacity, and less additional cost. The reservoir-caprock configuration can provide favorable space for the storage of carbon dioxide geological bodies. To make clear the distribution range of geological bodies suitable for carbon dioxide sequestration, taking the middle-south section of the eastern sag of Liaohe as an example, based on the model of the ratio of mud to ground and caprock effectiveness division, the control factors of caprock sealing were analyzed by entropy weight method combined with TOPSIS method, and the effective thickness of reservoir was determined by clarifying the relationship between reservoir lithology, physical properties, oil content and electricity. The results show that the lower limit of the effective caprock mud-to-ground ratio in the sand-mud interbedding sequence is 70.6%, and the sealing ability of caprock is mainly affected by the thickness of the fault and the thickness of the caprock single layer; The two sets of caprocks in the Shahejie Formation and Dongying Formation are relatively stable, with good fault-caprock configuration sealing, and the fault juxtaposition thickness in the Shahejie Formation is characterized by "thick in the north and thin in the south"; The effective reservoirs of the Dongying Formation are distributed in the whole region, the effective reservoirs of Es1 are distributed in the north of Rongxingtun, and the distribution range is smaller than that of the Dongying Formation, while the effective reservoirs of Es3 are mainly distributed in Huangyure area at the northern end of the study area, and the distribution range is further reduced. According to the reservoir-caprock configuration, carbon dioxide storage types can be divided into three types: shallow storage type, deep storage type, and multi-layer storage type. The lower caprock is well sealed and the lower effective thick reservoir controls the deep enrichment of carbon dioxide; The lower caprock is poorly sealed, and the effective thick reservoir in the middle or upper part controls the multi-layer enrichment of carbon dioxide; The lower caprock is poorly sealed, the upper caprock is well sealed, and the upper effective thick reservoir controls the shallow enrichment of carbon dioxide. The relationship between the effective thickness of the reservoir and the sealing ability of the caprock determines the vertical distribution series of carbon dioxide.

How to cite: li, H. and jiang, Y.: Study on Reservoir-caprock Configuration for Carbon Dioxide Sequestration in oil and gas reservoirs , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-86, https://doi.org/10.5194/egusphere-egu24-86, 2024.

EGU24-362 | ECS | Posters on site | ERE1.8

Towards net-zero: assessing the carbon storage potential of onshore saline aquifers in Brazil 

Francyne B. Amarante, Juliano Kuchle, and Mauricio B. Haag

Global warming poses a major challenge that humanity will face during the 21st century, requiring a significant reduction in anthropogenic CO2 emissions to mitigate the escalating global temperature. Several governments worldwide, including Brazil, have committed to achieving net-zero CO2 emissions by 2050, which will be impossible without Carbon Capture, Utilisation and Storage (CCUS) deployment. Ranked 12th globally in CO2 emissions (and 1st in South America), Brazil is in the early stages of studying CCUS. At present, CCUS efforts in the country primarily revolve around enhanced oil recovery, with limited exploration of CO2 injection in alternative geological settings. A total of 31 sedimentary basins span Brazilian territory, encompassing an area of approximately 6.4 million km2, 75% of which is situated onshore. The potential for CO2 storage in saline aquifers is gaining attention globally, proving a successful and effective approach in various sites. In this work we combine the available surface (geological maps, roads, and gas pipelines) and subsurface data (seismic lines and borehole data) to assess the logistics and feasibility of utilizing saline formations in onshore intracratonic basins as CO2 sinks, aiming to enable Brazil to reach net-zero CO2 emissions by 2050. Previous studies indicate that the Parnaíba, São Francisco, Amazonas, and Paraná basins present saline formations with favorable characteristics for CO2 injection, such as adequate depths, porosity, and permeability. Building upon prior research, we introduce the onshore portion of Espírito Santo Basin to the list of potential sinks, where the target saline aquifer is the pre-salt Mucuri Formation. Results show that greenhouse gases emissions from industrial processes are notably higher in the southeast region of Brazil. Within this region, two formations exhibit considerable potential for carbon sequestration in saline aquifers: (i) the Mucuri Formation, located in the onshore Espírito Santo Basin, reaching 350 m of thickness and shallowest depths of about 950 m, and (ii) the Rio Bonito Formation, in the proximities of the São Paulo state, with over 100 m of thickness and shallowest depths of about 650 m. For large-scale projects, CO2 transport in the region can be accomplished using the available infrastructure and the available gas pipelines, while smaller-scale research projects can utilize trucks, rail, and ships. Brazil's untapped potential for CCUS presents a unique funding opportunity from the private sector, marking a crucial step toward sustainable and impactful climate action.

How to cite: B. Amarante, F., Kuchle, J., and B. Haag, M.: Towards net-zero: assessing the carbon storage potential of onshore saline aquifers in Brazil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-362, https://doi.org/10.5194/egusphere-egu24-362, 2024.

EGU24-800 | ECS | Posters on site | ERE1.8

Ultrasonic Evaluation of Shales vis-à-vis Temperature: A Case Study from Permian Damodar Valley Basin 

Varun Dev Jamwal and Ravi Sharma

Despite constituting two-thirds of the sedimentary rock volume, shales are a few of the least understood rocks. The varied depositional processes and environments give rise to complexity and anisotropy in them. Understanding unconventional resources like shales becomes crucial given their abundance in the petroleum systems and reservoirs and their potential suitability for sub-surface carbon and radioactive waste storage. Therefore, paramount significance lies in understanding the petrophysical and rock physical characteristics of shales to develop feasibility models for the sustainable use of these rock types.
 
This investigation focuses on the Barren Measures and Raniganj Formation shales in the Damodar Valley of Eastern India, which are primarily rich in clays, carbon, and iron and are of fluvio-lacustrine origin. These relatively shallow formations can be good sites for storage and sequestration as they are overlain by shaley and clayey formations acting as traps. The anisotropy in shales is even more challenging as its imponderables range from a micro to a macro scale. This changes even further with factors like organic-hosted porosity and maturity. The inherent anisotropy in shales necessitates a multiscale examination. These multiscale discontinuities, coupled with parameters like organic matter and maturity, impact the elastic properties of the rocks, as evidenced by the ultrasonic evaluations.
 
In this study, acoustic characterization of samples was conducted using a benchtop ultrasonic wave propagation setup. The samples were clustered based on their colour and observed megascopic properties. Some sandstones were also included in the study to contrast sandstones with respect to shales. The wave velocities were determined for samples subjected to progressive heating up to 200°C (gas window), and the consecutive changes in the elastic parameters and resultant wave velocities of the rock were studied. Inputs from other methods utilizing different physics, such as FE-SEM, XRD were integrated to refine our interpretation. Notable changes were seen in wave velocities, especially in clusters with elevated organic content, while the density and Vp cross plots gave a good correlation with an R2 value of around 0.7.
This study advances our understanding of the impact of temperature on the elastic properties of shales, an aspect less explored than factors like stress and pressure. Thoroughly characterizing these parameters through acoustic methods provides critical insights into shale's storage capacity, carbon sequestration potential, and additional hydrocarbon recovery, specifically with respect to the Damodar Valley shales, aiding India to offset the projected peak of 4 GT CO2 emissions to achieve the carbon neutral goal promised at COP 26 and fulfilling UN Sustainable Development Goals.

How to cite: Jamwal, V. D. and Sharma, R.: Ultrasonic Evaluation of Shales vis-à-vis Temperature: A Case Study from Permian Damodar Valley Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-800, https://doi.org/10.5194/egusphere-egu24-800, 2024.

EGU24-1674 | ECS | Posters on site | ERE1.8

Using FracpaQ and seismic attributes to assess seismic scale fractures in carbonate reservoirs 

Hager Elattar, Richard Collier, and Paul W.J. Glover

Abstract: Fractured carbonate reservoirs are of great importance in the oil industry due to their significant role in global oil reserves and complex nature, where the majority of these reservoirs are naturally fractured, making them complex and challenging for oil recovery. The detection and characterization of fractures are essential for understanding the reservoir's petrophysical properties and hydrocarbon recovery potential as they play a critical role in reservoir performance. In this paper we have used 3D seismic from the Razzak field in the Western Desert, Egypt, with a specific focus on the Alamein dolomite reservoir. The reservoir holds significance due to its prolific oil-bearing nature, and featuring widespread lateral distribution in the northern Western Desert. Additionally, its contribution to an active Mesozoic petroleum system emphasizes its importance. Using Petrel software, the Alamein top and visible faults were identified, leading to the creation of a structural map illustrating the WSW-ENE axes of the Alamein's structural culminations in the southern part of the horst block. Owing to an extensional force during the Jurassic period with a NE-SW orientation, resulting from rifting, was evident, marked by the formation of normal faults associated with the opening of the Neotethys in the NE-SW direction. In the interpretation of 3D seismic data for Alamein dolomite reservoir, only one major listric normal fault was identified. However, the presence of minor faults or fractures, not easily discernible with conventional seismic techniques, is plausible. To address this, volume attributes were applied to detect subtle changes in seismic properties: (i) the curvature operation calculated the dip and azimuth angles, aiding in identifying structural complexities like faults and fractures, (ii) the maximum curvature value highlighted areas of steeply dipping or folded structures, (iii) Edge detection emphasized sharp boundaries, yet no hidden fractures or minor faults were revealed. The variance attribute yielded limited information, but Ant tracking on the variance cube effectively identified hidden minor faults and fractures. Incorporating the Ant track attribute into FRACPAQ software provided an objective methodology for quantifying fracture patterns, revealing NW-SE-oriented fracture segments in contrast to the WSW-ENE orientation of the major fault. Consequently, seismic attributes will unveil concealed fractures, and the application of FRACPAQ will prove effective in furnishing data on fracture orientation and length statistics.

Key words: FracpaQ; seismic attributes; fractured carbonate; Razzak field

How to cite: Elattar, H.A., Collier, R., and Glover, P. W. J.: Using FracPaQ and seismic attributes to assess seismic scale fractures in carbonate reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1674, https://doi.org/10.5194/egusphere-egu24-1674, 2024.

How to cite: Elattar, H., Collier, R., and Glover, P. W. J.: Using FracpaQ and seismic attributes to assess seismic scale fractures in carbonate reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1674, https://doi.org/10.5194/egusphere-egu24-1674, 2024.

Revealing the thermal structure of subsurface is crucial for various projects including geothermal energy exploitation, CCS and hydrocarbon exploration. For instance, temperature is one of the key physical underground parameters governing the type of Geothermal systems, whether injected CO2 remains in supercritical fluid stage and the depth of Golden Zone at where the hydrocarbon accumulations occur. Thus, understanding the temperature and geothermal gradient change in 1D-2D-3D sense indicates sweet spots and helps geoscientists to build more robust models to reduce the risks.

Based on this concept, this study aims to demonstrate the outcomes of a game-changer method which is the conversion of interval velocities into temperatures, thermal conductivities and heat flows by the help of recently proposed empirical relationships. As a case study, Northern Arabian Plate, SE Turkey is selected due to the neglection of thermal conditions in the area. Therefore, oil & gas industry-wide accepted methodologies have been applied to better understand thermal behaviour of the subsurface and how it has been controlled by regional tectonic edifices including large-scale thrust and strike slip faults.

In terms of methodology, as the first step, dynamic bottom hole temperatures of the wells have been converted into static ones by the help of “Temperature Analyser” web application. The converted temperature measurements have been used to generate regional temperature and geothermal gradient maps for every 500 meters. On the other hand, for 3D temperature models, seismic velocities have been converted into temperature cubes after calibration with the converted BHT measurements. Generated temperature cubes have been reflected on seismic sections to display lateral and vertical variations in temperature behaviour. It also allows the detection of meaningful temperature anomalies corresponding to possible fluid content.

The results reveal that abrupt temperature increase on maps directly coincides with the locations of oil producing fields. The same behaviour was noted globally both for hydrocarbon and geothermal fields. The change in temperature trend is also dominated by regional tectonics of the focus area. Large thrust fault systems act as boundaries for thermal anomaly regions while sinistral Mosul Fault Zone displaces and separates high temperature zones in a NW-SE sense. This movement can be easily associated with the Northern slip of the Arabian Plate since the continental collision occurred in the Miocene.

 

Based on these observations, the workflows and results of this study can be used for detailed investigation of subsurface geology, thermal conditions, and their effect on potential reservoirs for geothermal and CO2 storage. Workflows used to generate thermal models might allow the development of more efficient sustainable energy projects not only for the Northern sector of the Arabian plate but also for the other regions of the World.

How to cite: Uyanik, A.: Conversion of Interval Velocities into Thermal Models: A Game Changer Method for Subsurface Energy Exploitation Projects , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1739, https://doi.org/10.5194/egusphere-egu24-1739, 2024.

EGU24-2177 | Orals | ERE1.8

Short and long-term multiphase reactive transport processes during a pilot test of air injection into a sandstone gas storage facility 

Laurent De Windt, Irina Sin, Camille Banc, Anélia Petit, and David Dequidt

This study is based on unique field data on a 3-year pilot test during which air containing 8 mol% O2(g) was injected as a cushion gas into a natural gas reservoir, a carbonate-cemented sandstone aquifer located in the Paris Basin (France) [1]. The oxygen was fully depleted several months after injection completion, meanwhile CO2(g) was detected around 2–6 mol%; the pH decreased from 8 to 6, while reducing conditions shifted to mildly oxidizing ones with increasing concentration of sulfates in equilibrium with gypsum. After the test completion, the long-term evolution of the aquifer was assessed by a 15-year survey. The pH gradually returned to its near initial state and sulfates were reduced by 2 to 3 times. Data on the release of trace metals (Ba, Cu, Pb, Zn) during and after the test were also available.

Multiphase reactive transport models were developed on these field data using the HYTEC reactive transport code in 2D-reservoir configurations [1]. At the short-term scale, modeling focused on the gas-water-rock reactive sequence during the air injection: 1/ depletion of the injected O2(g) due to pyrite oxidation, 2/ leading to acidity production and dissolved sulfates, 3/ acidity buffering by calcite dissolution, 4/ followed by gypsum precipitation and CO2(g) exsolution. At the long-term scale, the modeling tackled with the progressive return to the baseline chemistry of the deep aquifer that was 1/ mostly driven by transport processes and 2/ to a lesser extent, slow water/rock chemical interactions.

These field-based models developed at short and long-term could be used as a workflow for other gas storage facilities, e.g. biomethane, compressed air, and CO2.

[1] Sin, I., De Windt, L., Banc, C., Goblet, P., Dequidt, D. (2023). Assessment of the oxygen reactivity in a gas storage facility by multiphase reactive transport modeling of field data for air injection into a sandstone reservoir in the Paris Basin, France. Science of The Total Environment 869, 161657.

How to cite: De Windt, L., Sin, I., Banc, C., Petit, A., and Dequidt, D.: Short and long-term multiphase reactive transport processes during a pilot test of air injection into a sandstone gas storage facility, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2177, https://doi.org/10.5194/egusphere-egu24-2177, 2024.

Kerogen is typically categorized in three types: type I is associated with lacustrine, type II associated with marine, and type III associated with terrestrial sources, respectively. The Kerogen type is a crucial factor affecting oil-generative properties as it significantly influences the initiation and potential for hydrocarbon generation in source rocks. Geoscientists traditionally use Rock-Eval pyrolysis to determine kerogen types, maturity, and pyrolysis reaction temperature (Tmax), and calculate hydrocarbon potential, essential factors in assessing oil reserves and understanding the oil window. Such method, however, has insufficient resolution and is time-consuming. In this study, we employ a temperature-dependent infrared (IR) spectroscopy method to precisely determine kerogen type, maturity, and Tmax. Specifically, our IR spectroscopy is combined with a numerical analysis model developed for the analysis of various organic matter samples. Through measurements of the IR spectra of samples at different temperatures (Heating-FTIR), we determine the maximum sedimentary burial temperature and the pyrolysis Tmax of kerogen. By applying the conversion formula by Shibaoka & Bennett (1977), (R0)a=Ra+btI*exp(cTm), we derive a virtual vitrinite reflectance, which is strongly correlated with our IR spectroscopy results, with insights into the maturation. This Heating-FTIR technique is a valuable tool for petroleum geology, facilitating the assessment of oil potential and maturity. Future refinement of the numerical model and improvement of the instrumentation are required to apply this technique to broader fields, such as sedimentary temperature for ancient geothermal gradient with better understanding of the sedimentary history.

How to cite: Chen, Y.-Y. and Chang, Y.-J.: Evaluation of Oil Source Rocks Using Temperature-dependent Infrared Spectroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2449, https://doi.org/10.5194/egusphere-egu24-2449, 2024.

EGU24-3199 | ECS | Posters virtual | ERE1.8

 Using Quantitative Diagenesis to characterise and understand carbonate CCUS prospects 

Omar Mohammed-Sajed, Fraidoon Rashid, Paul Glover, Richard Collier, and Piroska Lorinczi

Recent years have seen the growth of new techniques that combine conventional stratigraphic and observational approaches to characterizing the type, scope, extent, timing and effects of diagenetic processes with petrophysical measurements of their rock microstructure. These Quantitative Diagenetic (QD) techniques can be used to predict post- and pre-dolomitisation porosities and permeabilities as well as trace the pathway of the diagenetically evolving rock through different stages of diagenesis that may turn a low-quality carbonate reservoir into a high-quality reservoir, or vice versa. While these new QD techniques are becoming useful for the characterization of hydrocarbon reservoirs, they are also extremely useful in the characterization of carbonate reservoirs for prospective CCUS use. This paper will briefly explain some of the main approaches to QD including dolomitisation prediction, petrodiagenetic pathways, reservoir quality fields, and Fracture Effect Index (FEI), before examining how they can be used to ensure that the prospective CCUS target reservoir is sufficiently well characterized that effective reservoir modelling can take place, and that the volume, flow and trapping of CO2 in the reservoir can be effectively monitored. Dolomitisation is known to be affected by the presence of CO2, with CO2 dissolving in aqueous pore fluids to form carbonic acid that directly affects porosity through dissolution and indirectly by affecting the dynamics of the dolomitisation process itself. There are two current QD methods for predicting the change in porosity upon dolomitisation. One is affected by both the direct and indirect effects, while the other is only sensitive to the indirect effects. Both the direct and the indirect effects can be plotted on a petrodiagenetic pathway. The presence of fractures is also a key aspect of how injected CO2 will flow in a CCUS reservoir. The QD parameter FEI describes the change in permeability of a rock concomitant upon a unit change in fracture porosity (i.e., what increase in flow results from a given increase on fracture porosity). This varies depending upon the degree to which fractures are connected and can be extremely useful in predicting the flow of CO2 within a fractured legacy carbonate CCUS prospect. In summary, QD approaches have the potential to provide those who need to characterise and model carbonate CCUS prospects with new and useful tools.

 

How to cite: Mohammed-Sajed, O., Rashid, F., Glover, P., Collier, R., and Lorinczi, P.:  Using Quantitative Diagenesis to characterise and understand carbonate CCUS prospects, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3199, https://doi.org/10.5194/egusphere-egu24-3199, 2024.

EGU24-3696 | ECS | Posters virtual | ERE1.8

Simulation experiment evaluation and chemical kinetics prediction of the composition of n-alkanes components 

Song Bo, Haitao Xue, and Shuangfang Lu

          It is pivotal to predict the overall composition of subsurface oil and gas reservoirs to assess their fluidity, phase behavior, and recovery potential. Recognizing the significance of n-alkanes as key constituents of mature oil and gas, this study conducted a thermal simulation experiment of gold tube hydrocarbon generation on the source rock of Gulong Sag. The experiment included comprehensive analysis and measurement of the n-alkanes components in a representative sample. Subsequently, an empirical regression evaluation formula was established to evaluate the n-alkanes composition at various maturity stages. Furthermore, a chemical dynamics model for the formation of individual n-alkanes single molecule components was developed and calibrated based on the principles of chemical kinetics. Combined with the stratigraphic burial history and thermal evolution history of the target area, the distribution and evolution characteristics of n-alkanes components in different evolutionary stages of geological conditions can be quantitatively evaluated and predicted. Moreover, the phase behavior of n-alkanes components can be determined based on the evolution characteristics of these components. Experimental results indicate that the methane yield continues to increase with temperature under both heating rates. Additionally, the yield of n-C to n-C initially reaches its maximum with the temperature increase, and subsequently decreases. Furthermore, the hydrocarbon generation characteristics of n-alkanes follow a Gaussian distribution trend. The kinetic results demonstrate that the activation energy of n-alkanes falls within the range of 190-280 kJ/mol, while the distribution of pre-exponential factors is uneven. By considering the geological conditions, it has been determined that the light component in the Gulong Sag is currently experiencing a favorable generation period, whereas the heavy component has reached its peak formation stage, with some undergoing cracking. The oil and gas produced under these geological conditions exist as single-phase unsaturated fluids within volatile reservoirs. The evaluation value of the experimental regression formula, along with the predicted value from the dynamic model, aligns well with the experimental data, providing a solid foundation for the geological application of the model. Therefore, this research serves as a stepping stone towards furthering our understanding of hydrocarbon composition prediction, as well as evaluating phase behavior, mobility, and recovery of underground oil and gas in conjunction with geological conditions. 

How to cite: Bo, S., Xue, H., and Lu, S.: Simulation experiment evaluation and chemical kinetics prediction of the composition of n-alkanes components, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3696, https://doi.org/10.5194/egusphere-egu24-3696, 2024.

EGU24-3700 | ECS | Posters virtual | ERE1.8

Characteristics and factors controlling Permian shale gas reservoirs in the Hongxing area, Sichuan Basin, China 

BaiZHi Li, Nengwu Zhou, and Shuangfang Lu

Successful exploration of Permian shale gas in the Hongxing area has broadened shale gas exploration in the Sichuan Basin; however, the target layer is newly discovered, and reservoir research, which is key to shale gas exploration and development, is limited, thus restricting the screening and evaluation of the section containing the shale gas target layer. In this study, using organic carbon, whole-rock mineral analysis, scanning electron microscopy, low-temperature nitrogen adsorption, and other experimental methods, and by systematically identifying different lithofacies, we clarified the organic‒inorganic composition and microscopic pore structure characteristics of Permian shales in different phases of the Hongxing area and revealed the main factors controlling high-quality reservoirs and favorable lithofacies types for exploration. The results show that the shale in the study area mainly features six types of lithofacies: high-carbon siliceous shale (RS), high-carbon mixed shale (RM), high-carbon calcareous shale (RC), high-carbon muddy shale (RCM), low-carbon muddy shale (LCM), and low-carbon calcareous shale (LC). Organic pores are mainly present in RS, RM, RC, and RCM, while inorganic pores are dominant in LC and LCM. The pores are dominantly micropores, some mesopores are present, and very few macropores are present. Among them, the degree of micropore development is mainly affected by organic matter (abundance, maturity, and type), that of mesopores is mainly affected by clay minerals, and that of macropores is mainly affected by siliceous and clay minerals. There are obvious differences in the pore structure of different lithologies. The RS has the highest pore volume and specific surface area, with average values of 13.8×10-3 cm3/g and 21.57 m2/g, respectively, and its pore morphology is ink-bottle type, with pore diameters mainly <10 nm. The storage space of RM, RC, RCM, and LCM is moderate, with low-carbon argillaceous shale (LM) having the lowest.

How to cite: Li, B., Zhou, N., and Lu, S.: Characteristics and factors controlling Permian shale gas reservoirs in the Hongxing area, Sichuan Basin, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3700, https://doi.org/10.5194/egusphere-egu24-3700, 2024.

EGU24-3864 * | ECS | Orals | ERE1.8 | Highlight

From hydrocarbons to geothermal energy: a case study from the Dutch subsurface 

Annelotte Weert, Francesco Vinci, David Iacopini, Paul van der Vegt, Stefano Tavani, and Kei Ogata

The West Netherlands Basin, which has a long history in exploration as a former prosperous hydrocarbon province, is currently a geothermal hotspot. Being exploited since the 1950’s, most of its oil and gas fields are now in their final phase of production. In the past decade, interest shifted to sustainable energy sources. The geothermal industry in the area is developing quickly, helped by the legacy of the hydrocarbon industry: a wealth of publicly available seismic and well data. Currently, the area has 14 realized, and at least 3 projects in the development phase, with the Late Jurassic Nieuwerkerk Formation being the main target.

Conversely to petroleum systems, in which anticlines are the preferential target for hydrocarbon exploration, synclines are the most suitable sites for geothermal exploration. They offer higher temperatures with respect to the limbs and anticlines, and possible remaining hydrocarbons are not expected to be located inside the central portions of the synclines.

The West Netherlands Basin is a former rift basin that developed during the Mesozoic in the framework of the North Sea rift, and subsequently inverted during the Late Cretaceous. The Nieuwerkerk Formation was deposited during the last major rifting phase. Thus, the thickest packages of its fluvial-deltaic deposits are fault-controlled and commonly located in the synclines. The heterogeneity of fluvial reservoirs causes lateral and vertical quality variations in porosity, permeability and net-to-gross ratios. With the hydrocarbon industry focussing on the stratigraphic highs, there is only limited well data available for the central portions of the synclines.

With reprocessed 3D seismic data, our study uses an image processing approach, coupling traditional amplitude mapping with seismic attributes. This will help to reconstruct the evolution of the fluvial architecture of the Nieuwerkerk Formation over time. By tying the seismic with well data, a better prediction of the quality of the sandy bodies per location can be made. These results can be implemented in de-risking geothermal well planning across fluvial reservoirs in inverted rift basins.

How to cite: Weert, A., Vinci, F., Iacopini, D., van der Vegt, P., Tavani, S., and Ogata, K.: From hydrocarbons to geothermal energy: a case study from the Dutch subsurface, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3864, https://doi.org/10.5194/egusphere-egu24-3864, 2024.

EGU24-4657 | ECS | Orals | ERE1.8

Wave velocities as a proxy to forecast deformation during cyclic loading-unloading in porous reservoir rocks 

Debanjan Chandra, Barbara Perez Salgado, and Auke Barnhoorn

Porous reservoir rocks like sandstones have gained utmost important in the last decade as a potential sink for CO2. Most of the targeted reservoirs are depleted oil and gas fields, which has caprocks to ensure the containment of the injected CO2. Injecting CO2 into porous reservoirs increase the pore pressure, which therefore reduces the effective horizontal and vertical stresses. Depending on the pre-injection stress-condition and permeability of the reservoir, utmost care should be taken to define the upper limit of CO2 injection pressure, in order to prevent any permanent damage to the reservoir which can lead to leakage or induced seismicity. Lab-scale experiments provide key insights to the deformation behavior of reservoir rocks under different stress-conditions, which can be upscaled to understand reservoir scale processes. To simulate the stress perturbation caused by CO2 injection operations, we have subjected porous reservoir rocks (coreplugs) collected from different depths of offshore North Sea under cyclic axial loading and unloading with a confining pressure increment from 10-50 MPa between each cycle. The P and S wave velocities along the axial direction of the coreplugs were recorded in every 10 s to assess the change in wave properties during deformation. It was observed that during each loading cycle, wave velocities are highest at the elastic-plastic transition zone, which can be attributed to the compression of pores and closure of microcracks perpendicular to the loading direction. The wave velocities decrease sharply after the onset of plastic deformation, which can be attributed to the formation of microcracks in the coreplug due to increasing load. The static and dynamic Young’s modulus (E) of the coreplugs during each cycle of increasing confinement show linear increase. Plugs with lower porosity shows higher E with steeper increment at higher confining pressure. The correlation between the wave properties and mechanical response of the reservoir rocks under cyclic loading reveal that constant monitoring of wave velocities during CO2 injection can act as an efficient tool for monitoring stress-state of the reservoir, facilitating safer CO2 storage operations.

How to cite: Chandra, D., Salgado, B. P., and Barnhoorn, A.: Wave velocities as a proxy to forecast deformation during cyclic loading-unloading in porous reservoir rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4657, https://doi.org/10.5194/egusphere-egu24-4657, 2024.

EGU24-5508 | ECS | Orals | ERE1.8

Cushion gas requirements for hydrogen storage in global underground gas storage facilities 

Mayukh Talukdar, Chinmaya Behera, Niklas Heinemann, Johannes Miocic, and Philipp Blum
To ensure system security and flexibility, storing excess renewable energy as hydrogen is considered an integral component of future energy systems. Cyclic underground hydrogen storage (UHS) with injection production cycles is planned to meet energy demand until new subsurface sites are prepared for storage. To avoid geomechanical risks caused by dynamic pressure fluctuations during cyclic storage, cushion gas is stored in such reservoirs. Cushion gas requirements for sites are still unknown. Therefore, in this study, we calculate the cushion gas requirement of various hydrogen storage sites using reservoir properties.
 
Hydrogen requires less cushion gas by volume than methane. Cushion gas volume in UHS sites varies with the initial reservoir pressure, gas flow rate, well tubing size, and erosional velocity. Cushion gas requirement decreases with increasing reservoir pressure, increasing gas flow, increasing well tubing size, and decreasing erosional velocity. In the studied sites, cushion gas volume ranged from a few % (0-5%) to 99% of the total gas volume. Shallow sites cannot store much hydrogen because of the high cushion gas %. On the other hand, sites deeper than 1100 m are unsuitable owing to insufficient structural trapping and enhanced biogeochemical reactions. Considering these factors, we report the optimum cushion gas volumes for various underground storage sites worldwide.

How to cite: Talukdar, M., Behera, C., Heinemann, N., Miocic, J., and Blum, P.: Cushion gas requirements for hydrogen storage in global underground gas storage facilities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5508, https://doi.org/10.5194/egusphere-egu24-5508, 2024.

EGU24-7216 | ECS | Posters virtual | ERE1.8

Land Use Change Characteristics in the Pan-Pearl River Basin in China from 1985 to 2020 

Wei Fan and Xiankun Yang

The changes in land use/cover are essential aspects of studying the impact of human activities on the Earth's surface and global transformations. In this study, utilizing the ESRI Global Land Cover data (ESRI land cover 2020) and the China Land Cover Data (CLCD), along with historical imagery from Google Earth, a comparative analysis scheme for land use classification results was designed. The CLCD dataset was updated, leading to the creation of a land use dataset for the Pan-Pearl River Basin spanning from 1985 to 2020. This dataset was then employed for the analysis of land use changes in the Pan-Pearl River Basin over the past 35 years.The results indicate:(1) Among the seven land use types, the most significant changes in area occurred in the following order: build -up land, cropland, forest land, grassland, shrubland, waterbody, and barren. Notably, there was a substantial increase in the areas of build-up land and forest land, while cropland, grassland, and shrubland experienced significant decreases. The waterbody’area showed a slight overall increase trend.(2) The major land use types undergoing changes varied among sub-basins, with the intensity of land use change ranked as follows: Pearl River Delta region(1.9%) > Coastal rivers in southern Guangdong and western Guangxi(0.20%) > Dongjiang River Basin(0.13%) > Hanjiang River Basin(0.12%) > Xijiang River Basin(0.10%) > Beijiang River Basin(0.08%) > Hainan Island region(0.02%).(3) Within the sub-basins of the Pan-Pearl River Basin, the most significant increase was observed in the area of built-up land, exhibiting a continuous expansion trend with a total increase of 12184 km2. This increase was primarily due to the conversion of cropland, forest land, and waterbody. The most significant decrease occurred in cropland, with a total reduction of 10435 km2, mainly transitioning to built-up land and forest land. The phenomenon of built-up land encroaching on cropland was particularly prominent, especially in the Pearl River Delta region. Forest land also showed a decreasing trend, mainly attributed to cultivation and the encroachment of built-up land. The reduction in grassland area was more pronounced in the Xijiang River Basin, primarily transforming into forest land, cropland, and built-up land. The study reveals that the rapid development of socio-economics and industry, coupled with an increase in residents' consumption levels, serves as the primary driving force behind land use changes in the Pan-Pearl River Basin. Additionally, land use and management policies play a crucial role as driving factors in the region's land use changes. This research aims to provide a scientific basis for formulating policies related to the region's land resources and land management, holding significant importance for preserving ecological balance and fostering sustainable development in the basin.

How to cite: Fan, W. and Yang, X.: Land Use Change Characteristics in the Pan-Pearl River Basin in China from 1985 to 2020, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7216, https://doi.org/10.5194/egusphere-egu24-7216, 2024.

EGU24-7761 | Posters on site | ERE1.8 | Highlight

Reutilising hydrocarbon wells as deep heat exchangers to decarbonise heating in the Northern Netherlands  

Johannes Miocic, Jan Drenth, and Pieter van Benthem

To meet the climate targets outlined in the Paris Agreement, European Green Deal, and the goal of reducing dependence on fossil fuel imports per the REPower EU Action, decarbonizing and reducing energy consumption in the heating and cooling sector is imperative. This sector, a major contributor to household energy use, plays a pivotal role in achieving sustainable energy goals.

Geothermal energy, particularly through geothermal doublets, stands out as an ideal solution for supplying energy for space heating and cooling. However, the inherent risks associated with fluid exchange with the subsurface make it scientifically or politically challenging in certain areas. Addressing this concern, deep borehole heat exchangers function as closed-loop systems, eliminating fluid exchange with the subsurface.

In this study, we explore the feasibility of repurposing existing oil and gas wells in the Northern Netherlands as deep coaxial borehole heat exchangers to provide heat to local communities. Utilizing analytical solutions, we calculate the thermal power output of 365 gas wells suitable for retrofitting. These wells exhibit bottom hole temperatures exceeding 80°C, capable of delivering temperatures above 60°C or thermal powers exceeding 800 kW, depending on flow rate and inflow temperature.

Our analysis includes assessing the proximity of well locations to high-density heat demand neighborhoods within a 6 km radius, facilitating the provision of supply temperatures for future local heat district networks. Notably, heat loss from well to neighborhood generally remains below 2°C, ensuring sufficient heating power supply to nearby residential areas. Several well clusters demonstrate significant heat over-supply, suggesting the potential for transporting excess heat to more distant locations. In cases where heat supply from wells is too low, in particularly in neighbourhoods with very low building efficiency rating (<E), heat pumps can be utilised to supply the needed energy.

Our findings indicate that repurposing existing hydrocarbon wells as coaxial heat exchangers offers a viable option for providing low-carbon heating to numerous residential areas in the Northern Netherlands. However, the geographical distribution reveals that not all high heat demand neighbourhoods have well sites in proximity, underscoring the importance of implementing a diverse heat supply strategy.

How to cite: Miocic, J., Drenth, J., and van Benthem, P.: Reutilising hydrocarbon wells as deep heat exchangers to decarbonise heating in the Northern Netherlands , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7761, https://doi.org/10.5194/egusphere-egu24-7761, 2024.

EGU24-8307 | ECS | Posters virtual | ERE1.8

Using machine learning to discriminate between mineral phases and pore morphologies in carbonate systems 

Wurood Alwan, Paul Glover, and Richard Collier

Digital rock models are becoming an essential tool not only for the modelling of fundamental petrophysical processes, but in specific key applications, such as Carbon Capture and Underground Storage (CCUS), geothermal energy exploration, and radioactive waste storage. By utilizing advanced imaging and simulation techniques, digital rocks provide indispensable insights into the porous structures of geological formations, crucial for optimizing CO2 storage, enhancing geothermal reservoir characterization, and ensuring the secure containment of radioactive waste. This abstract aims to present new advances using digital rocks to study these pressing environmental and energy challenges.

Estimating the physical properties of rocks, a crucial and time-consuming process in both the characterisation of hydrocarbon, geothermal and CCUS resources, has seen a shift from traditional laboratory experiments to the increasingly prevalent use of digital rock physics. A key requirement of many forms of pore structure image analysis is that they require binary images showing pore-space vs. non-pore space (mineral phases). These are typically obtained by thresholding grey scale SEM or X-ray tomographic images to separate the two phases. In this paper, we have adapted a 2D process-driven MATLAB model to generate synthetic porous media images, laying the foundation for simulating authentic SEM images. The objective of the computational framework outlined in this study is to train a machine-learning model capable of predicting various types of porosity. Drawing inspiration from recent advances in machine learning applied to porous media research, our approach involves the development of deep learning models utilizing Convolutional Neural Networks (CNN). Specifically, we aim to quantitatively characterize the inner structure of the 2D porous media based on their binary images through the implementation of these CNN models. This framework consists of: (i) Generating synthetic porous media images through a process-driven model, (ii) training a neural network that takes a labelled synthetic image as input and gives two types of porosity as output, (iii) whereupon the trained model can be applied to provide types of porosities for new images that are not in the training database. The generated data are divided into training, validation, and testing datasets. The training dataset optimizes CNN parameters for accuracy, the validation dataset aids in hyperparameter selection and prevents overfitting, and the testing dataset evaluates the predictive performance of the trained CNN model.

This research not only advances the understanding of fundamental geological processes but also plays a crucial role in optimizing the utilization of renewable energy sources such as geothermal and contributing to the effective management of carbon capture and storage initiatives.

How to cite: Alwan, W.S., Glover, P. W. J., and Collier, R.: Using machine learning to discriminate between mineral phases and pore morphologies in carbonate systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8307, https://doi.org/10.5194/egusphere-egu24-8307, 2024.

How to cite: Alwan, W., Glover, P., and Collier, R.: Using machine learning to discriminate between mineral phases and pore morphologies in carbonate systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8307, https://doi.org/10.5194/egusphere-egu24-8307, 2024.

EGU24-8973 | ECS | Orals | ERE1.8

Assessing earthquake focal mechanisms in the North Sea for risk mitigation of large-scale CO2 injections 

Evgeniia Martuganova, David F. Naranjo Hernandez, Daniela Kühn, and Auke Barnhoorn

Decarbonisation of the European economy represents one of the current challenges to both society and the energy sector. The advancement and further application of carbon capture and sequestration (CCS) technologies are crucial components of the EU’s effort to become climate-neutral by 2050. The success of CCS depends heavily on understanding the present-day stress field to anticipate reservoir and cap rock response to fluid injection. Despite its importance, many proposed carbon storage sites in the North Sea are located in areas with little to no borehole stress data available, presenting a significant challenge.

Within the ACT project SHARP Storage framework, we have addressed this gap by generating a comprehensive earthquake bulletin for the North Sea, revealing spatial clusters of seismic events with the majority of earthquakes with ML < 4. Focal mechanisms of earthquakes are excellent indicators of crustal dynamics, which are essential for assessing the present-day stress field. Therefore, to improve the understanding of the in-situ stress conditions, we created a comprehensive workflow to evaluate focal mechanisms based on data from the North Sea (Kettlety et al., 2023). First, we developed a routine for the seismological bulletin to aggregate the recorded earthquakes from international seismological centres. The following step included retrieval of the waveforms from data centres and quality control routines, which included dead channels check, exclusion of files with significant recording gaps and low signal-to-noise ratio, and corrections of errors in the station XML files. Then, a subset of data traces with sufficient quality was selected for moment tensor computations using a Bayesian bootstrap-based probabilistic inversion scheme (see Heimann et al., 2018). Using existing focal mechanism solutions for the North Sea region, we calibrated our processing routine and then applied it to selected earthquakes (after 1990, M > 3.5) to expand the existing focal mechanisms database.

The newly computed focal mechanism solutions provide valuable insight into the present-day stress field in areas outside the main hydrocarbon provinces and improve the risk assessment of ongoing and future CCS projects. Furthermore, we will release our processing workflow as an open-source package and a new focal mechanisms database of the North Sea to establish a standard processing routine that can be readily utilised for similar seismological studies.

How to cite: Martuganova, E., Naranjo Hernandez, D. F., Kühn, D., and Barnhoorn, A.: Assessing earthquake focal mechanisms in the North Sea for risk mitigation of large-scale CO2 injections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8973, https://doi.org/10.5194/egusphere-egu24-8973, 2024.

EGU24-9206 | ECS | Orals | ERE1.8

Storage potential of CO2 by repurposing oil and gas-related injection wells in the Montney Play, northeast British Columbia, Canada 

Hongyu Yu, Bei Wang, Honn Kao, Ryan Visser, and Malakai Jobin

From 2005 to 2020, Canada achieved a 9.3% reduction in green house gas emission (69 Mt CO2 eq), meanwhile British Columbia witnessed a 5% increase (3.0 Mt CO2 eq) from 2007 to 2019. Exploiting unconventional oil and gas resources in northeast British Columbia (NEBC) has become the province’s second-largest source of greenhouse gas emissions. In pursuit of a cost-effective and seismic risk-aware approach for carbon emission reduction, this study evaluates the CO2 geological storage capacity in NEBC with a focus on repurposing existing injection wells for carbon storage.

We particularly emphasize the Montney and Debolt formations. These formations are the main targets of a diverse array of injection wells, including those for hydraulic fracturing, enhanced hydrocarbon recovery, and wastewater disposal. Three trapping mechanisms in the NEBC area are examined: physical and solubility trapping for wastewater disposal wells in the Debolt Formation, and physical and mineral trapping for hydraulic fracturing and enhanced recovery wells in the Montney Formation. Furthermore, we incorporate an assessment of seismic hazards, informed by the latest insights into injection-induced seismicity in NEBC, as a potential indicator of CO2 leakage risk.

Our findings underscore the favorable conditions of the Debolt Formation with lower seismicity hazard and a substantial CO2 storage capacity (19.3 Gt; ~284.4 years of CO2 emissions in BC). Depleted oil and gas reservoirs within the Montney Formation are also deemed suitable for CO2 storage, estimated at 1671.8 Mt (approximately 24.5 years), particularly in the Upper Montney due to its higher storage capacity and lower seismic risk.

Overall, this research offers an assessment of CO2 geological storage potential at the formation-scale in NEBC. The emphasis on well suitability and seismic risks effectively bridges the gap between the regional-scale geological assessments and site-scale engineering evaluations. It paves the path for future studies on addressing more practical topics related to the choices of project sites and injection strategies.

How to cite: Yu, H., Wang, B., Kao, H., Visser, R., and Jobin, M.: Storage potential of CO2 by repurposing oil and gas-related injection wells in the Montney Play, northeast British Columbia, Canada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9206, https://doi.org/10.5194/egusphere-egu24-9206, 2024.

EGU24-9509 | ECS | Orals | ERE1.8

Quantifying flow reduction during injection of CO2 into legacy hydrocarbon reservoirs for CCUS 

Qian Wang, Glover Paul, and Lorinczi Piroska

In the development of hydrocarbon fields, it is becoming known that CO2 injection (which is sometimes done to improve hydrocarbon production) can cause pore blockage and wettability alteration by the promotion of asphaltene deposition. In hydrocarbon reservoirs, the result is poor oil recovery performance during carbon dioxide (CO2) injection. If CO2 is being injected into a legacy hydrocarbon reservoir (i.e., one that still contains residual oil) the same process will occur. Once again, the ability of fluid (this time supercritical CO2) to flow will be impeded, but it is also possible that asphaltene deposition will also reduce the overall pore volumes in which CO2 could otherwise be stored. In this work, the residual oil distribution and the permeability decline caused by organic and inorganic precipitation after miscible CO2 flooding and water-alternating-CO2 (CO2-WAG) flooding have been studied by carrying out core-flooding experiments at high pressures and temperatures in an artificial three layer system. For simple CO2 injection during CCUS operations, flooding experimental results indicate that the low-permeability layers retain a large oil production potential even in the late stages of production, which could impede CO2 emplacement and provide significant heterogeneity, while the permeability decline due to asphaltene precipitation is more significant in high-permeability rocks. In contrast, we found that CO2-WAG can reduce the influence of heterogeneity on the oil production, but it results in more serious reservoir damage, with permeability decline caused by CO2–brine–rock interactions becoming significant. In addition, miscible CO2 flooding has been carried out for rocks with similar permeabilities but different wettabilities and different pore-throat microstructures in order to study the effects of wettability and pore-throat microstructure on formation damage. Reservoir rocks with smaller pore-throat sizes and more heterogeneous pore-throat microstructures were found to be more sensitive to asphaltene precipitation, making these less attractive for CCUS reservoirs. However, rocks with larger, more connected pore-throat microstructures became less water wet due to asphaltene precipitation to pore surfaces, ultimately leading to a lower pore volume in which CO2 can be stored. Taken together, there may be a case for not simply injecting CO2 in CCUS operations, but alternating the CO2 injection with injection of water in order to stabilise CO2 flow and reduce formation damage by asphaltene precipitation.

How to cite: Wang, Q., Paul, G., and Piroska, L.: Quantifying flow reduction during injection of CO2 into legacy hydrocarbon reservoirs for CCUS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9509, https://doi.org/10.5194/egusphere-egu24-9509, 2024.

Though global energy needs continue to grow, fossil fuels, and their associated CO2 emissions, are increasingly being opposed as our main source of energy. Instead, to achieve net zero greenhouse gas emissions goals, we are currently transitioning to more sustainable sources of energy, such as solar and wind power and geothermal energy, coupled with storage of waste, such as CO2. However, these new technologies come with their own challenges, as they continue to rely on (re-)use of the subsurface landscape. The intermittency of solar and wind power will require storage of renewably generated electricity. Hydrogen fuel has been marked as a potential energy carrier, enabling us to store large quantities of energy for prolonged periods of time, such as required to supply large industries or communities during winter months. To store this hydrogen fuel, the subsurface offers the largest storage space available, such as in (offshore) depleted hydrocarbon fields, but reproduction of the stored fluid is crucial. Geothermal energy production will require the extraction of hot fluids from depth and will often be performed in populated areas, close to the consumers, meaning that phenomena such as surface subsidence and induced seismicity are highly undesirable. The safe storage of CO2 for thousands of years also entails fluid injection, but containment is of vital importance to keep the CO2 out of our atmosphere. So though we have a vast history of exploitation of the subsurface through the oil and gas industry, which we can and should build upon, these new sustainable energy developments also pose their own, new challenges. While fluid production changes the physical equilibrium of the system, these new uses will also impact the chemical equilibrium through the injection of new fluids. Furthermore, containment and safety play an even bigger role than before to ensure the longevity of these new subsurface operations. In this contribution, I will outline what the challenges are that we are facing and how geoscientists can contribute to solving these challenges, across all areas from rock physics, geochemistry and hydrology, to sedimentology, structural geology and policy.

How to cite: Hangx, S.: Same same but different: the scientific challenges when re-using the subsurface for sustainable energy developments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12486, https://doi.org/10.5194/egusphere-egu24-12486, 2024.

EGU24-12846 | Posters on site | ERE1.8

Exploring the Relationship between CT Scanning Resolutions and Sandstone Porosity for CCS Applications 

Jyh-Jaan Steven Huang, Yao-Ming Liou, Arata Kioka, and Tzu-Ruei Yang

In the context of Carbon Capture and Storage (CCS), the porosity of potential storage formations is a critical factor. Our study explores this aspect using computed tomography (CT) to assess how different scanning resolutions impact the accuracy of porosity measurements. We employed three CT systems - Geotek RXCT (resolution ~20-150 μm), Bruker 1272 (resolution ~5 μm), and DELab μCT-100 (resolution ~9 μm) - to scan sandstone cores of varying porosities. The aim was to identify an optimal scanning resolution that balances detail with practicality for CCS evaluations.

This research addresses the challenges in high-resolution CT scanning, such as denoising effects that can alter accuracy, and the complexities of thresholding segmentation across various systems. Additionally, we examined the partial volume effect, crucial for interpreting pore sizes and distributions accurately.

Our preliminary results suggest that scanning resolution significantly affects the perceived porosity. Different resolutions uncover diverse aspects of pore structure, highlighting the importance of choosing an appropriate resolution. Advanced image processing techniques, including effective denoising and accurate thresholding, are vital for reducing errors in porosity measurement.

The study provides valuable insights into the use of CT scanning for CCS applications, emphasizing the need for a balanced approach in resolution selection and sophisticated image processing. These findings are instrumental in enhancing the reliability of geological evaluations for potential CCS sites, contributing to the broader efforts in carbon storage and climate change mitigation.

How to cite: Huang, J.-J. S., Liou, Y.-M., Kioka, A., and Yang, T.-R.: Exploring the Relationship between CT Scanning Resolutions and Sandstone Porosity for CCS Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12846, https://doi.org/10.5194/egusphere-egu24-12846, 2024.

EGU24-13835 | ECS | Posters on site | ERE1.8

Characterising functionalised nanoparticles for improving fluid flow for CCUS in legacy hydrocarbon reservoirs  

Louey Tliba, Afif Hetnawi, Farad Sagala, Robert Menzel, Paul Glover, and Ali Hassanpour

In recent years there has been rapid development of nanoparticles (NPs). Nanoparticles can be used both as a probe into restricted spaces, such as the pores within a reservoir rock, and as tools for altering wettability or deliberately blocking pore throats to enhance fluid movement in less connected pores. Silica nanoparticles can have functional surfaces allowing them to react specifically to oils or water. Nanoparticles can be used to enhance oil production by releasing oil on mineral surfaces and improving fluid flow. However, they also have the potential for improving CO2 flow in CCUS reservoirs while enhancing the pore volume available for CO2 storage. In this paper we evaluate the performance of different non-functionalised and functionalised nanoparticles for enhancement of oil production, CO2 emplacement and gas flow. Different forms of silica NPs have been made, either unfunctionalized, or functionalised with branched amino-based polymer (hydrophilic) or a silane-based agent (hydrophobic). Their stability has been characterised using a range of laboratory methods. The microscopic performance of the nanoparticles has been measured using contact angle measurements. Their ability to enhance oil production and CO2 emplacement has been tested using imbibition and drainage experiments. 

The contact angles, measured in the presence of brine, no modified silica NPs, branched amino-based polymer (hydrophilic) modified silica NPs and silane-based agent (hydrophobic) modified silica NPs showed contact angle values of approximately 110°, 116°, 124°, and 136°, respectively. These results show that introduction of nanofluids led to a change in substrate wettability from water-wet to strongly water-wet. Notably amongst the tested nanoparticles the Silane-based NPs demonstrated the highest hydrophilic surface. The spontaneous imbibition tests conducted on various sandstone cores revealed that silane-based NPs yielded the highest oil recovery rates among the tested NPs. Specifically, these nanoparticles showed an approximate 12% and 50% enhancement in oil recovery compared to non-modified silica nanoparticle, and branched amino-based polymer (hydrophilic) modified silica NPs. In summary, nanofluids have been shown to substantially improve the wettability alteration of the rock surface from oil-wet to water-wet, which can lead to improve the volume and flow characteristics of legacy CCUS prospects. Our future plan is to investigate the enhancement of carbon dioxide (CO2) solubility in brine through the utilization of the prepared nanoparticles, with the objective of advancing carbon capture technologies.

How to cite: Tliba, L., Hetnawi, A., Sagala, F., Menzel, R., Glover, P., and Hassanpour, A.: Characterising functionalised nanoparticles for improving fluid flow for CCUS in legacy hydrocarbon reservoirs , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13835, https://doi.org/10.5194/egusphere-egu24-13835, 2024.

EGU24-14959 | Orals | ERE1.8

TRANSGEO - Transforming abandoned wells for geothermal energy production 

Hannes Hofmann, Julie Friddell, Ingo Sass, Thomas Höding, Katrin Sieron, Max Svetina, Monika Hölzel, Robert Philipp, György Márton, Balázs Borkovits, Klára Bődi, Alen Višnjić, Tomislav Kurevija, and Bojan Vogrinčič

TRANSGEO is a regional development project that aims to explore the potential for producing sustainable geothermal energy from abandoned oil and gas wells in central Europe.  Composed of 11 partner organizations and 10 associated partners in 5 countries, TRANSGEO is developing a Transnational Strategy and Action Plan to address this technical and economic opportunity.  Our primary objective is to support rural communities and industries in the energy transition by providing tools and information that highlight sustainable redevelopment priorities and opportunities.

To reach this objective and promote the switch from fossil fuels to green energy, TRANSGEO is developing reuse procedures for five different geothermal technologies and validating them via numerical modelling, to assess their performance in repurposing existing hydrocarbon infrastructure and determine the optimal reuse conditions and configurations.  The five geothermal technologies are Aquifer Thermal Energy Storage, Borehole Thermal Energy Storage, Deep Borehole Heat Exchangers, Enhanced Geothermal Systems, and Hydrothermal Energy production.  The modelling studies focus on reference sites in our study areas, the North German Basin, the South German Molasse Basin, the Vienna Basin, and the Pannonian Basin.  Comparison of varying wellbore and reservoir parameters in the numerical modelling studies will provide input to a new online well assessment tool which will be available publicly to determine well suitability and guide planning for future reuse projects.  The online tool will be informed by a database of abandoned wells in Austria, Croatia, Germany, Hungary, and Slovenia and will include local reference data, such as geology, topography, heat demand, and utilities.  This will facilitate well reuse by matching candidate wells with local energy demand and heating networks.  Additional work on socio-economic and policy analyses will provide financial and liability information for the 5 different geothermal technologies, across the project countries.  Finally, the partnership will propose a legal policy and incentive framework to facilitate and expand reuse of abandoned wells for geothermal energy production and storage across central Europe.

TRANSGEO is co-funded by the European Commission’s Interreg CENTRAL EUROPE programme.

How to cite: Hofmann, H., Friddell, J., Sass, I., Höding, T., Sieron, K., Svetina, M., Hölzel, M., Philipp, R., Márton, G., Borkovits, B., Bődi, K., Višnjić, A., Kurevija, T., and Vogrinčič, B.: TRANSGEO - Transforming abandoned wells for geothermal energy production, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14959, https://doi.org/10.5194/egusphere-egu24-14959, 2024.

EGU24-16266 | ECS | Orals | ERE1.8

Geological characterization of the “Fonts-Bouillants” helium discovery - France 

Russier Emma, Géraud Yves, Hauville Benoît, Tarantola Alexandre, Beccaletto Laurent, and Diraison Marc

Geological characterization of the “Fonts-Bouillants” helium discovery - France

Russier E1,2, Géraud Y2, Hauville B1, Tarantola A2 ,Beccaletto Land Diraison M1

1 45-8 ENERGY, France

2 GeoRessources, University of Lorraine, France

3 BRGM, F-45060, Orléans, France

 

ABSTRACT

Helium is essential for the manufacturing of many of our daily commodities such as optical fibres, computers or cell phones (semiconductors and processors), medical use (MRI scanners) or in other more specific applications such as airlifts, leak detection, gas chromatography or diving. Nowadays, Europe imports 100% of its helium needs from overseas and is facing regular shortages, reason why 45-8 Energy embarked five years ago on helium exploration and production in Europe.

 

Helium is a noble gas mostly coming from the natural radioactive decay of Uranium and Thorium contained in the crust and the basement. Its migration and accumulation are strongly linked to a vector fluid that can be CO2, N2, CH4 or water. Helium and its vector fluids are then trapped and sealed in a rock reservoir.

 

The Fonts-Bouillants area is located at the southern edge of the Paris Basin at the vicinity of the French Massif Central and Limagne rift. The 45-8 Energy project aims to jointly produce He and CO2 from a gas which is naturally seeping through the major Saint-Parize fault (SPF).  Geological origin and migration pathway of He are therefore key questions to define the exploration guide, in particular to locate production wells to produce the seeping gas and process it. A multidisciplinary approach involving geology, geophysics, petrophysics and geochemistry has therefore been deployed.

 

Because geological context was hardly documented in this area, a wide range of geophysical data were acquired or reprocessed and coupled with field geology to build a regional geological model. The initial geological model was considerably updated and a hidden and thick Late Palaeozoic depocenter was especially highlighted below the Mesozoic series. Well data in nearby analogous basins as well as outcrops enabled rock collections to conduct petrophysical and geochemical characterization. The main reservoirs discovered currently are in Triassic and Jurassic sandstones, and fault like Saint-Parize fault acted as barrier and drain. 

Our outcrops petrophysical and geochemical study highlight the importance of Late Palaeozoic basin for the helium system:

  • As a potential rock source, with higher U-Th concentrations (3-13.5, 8-24 ppm) than typical crustal U-Th concentrations (1.8 and 7.2 ppm, [1]).
  • As a potential migration pathway and reservoir, with sandstones and conglomerates porosity higher than 20% and permeability higher than 100 mD.

 

Finally, gas sampling was performed in local natural springs, but also during well testing conducted in shallow boreholes which have encountered gas bearing reservoirs in the Mesozoic along the SPF. Helium generation system was modelled with geochemical data from the rocks and the fluids and from the volumetric capacity of the Palaeozoic basin.

 

Keywords: Helium exploration, Geophysics, Petrophysics, Geochemistry

Themes: Helium exploration

 

References:

[1] Krauskopf, K. B., & Bird, D. K. (1967). Introduction to geochemistry (Vol. 721). McGraw-Hill New York.

 

How to cite: Emma, R., Yves, G., Benoît, H., Alexandre, T., Laurent, B., and Marc, D.: Geological characterization of the “Fonts-Bouillants” helium discovery - France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16266, https://doi.org/10.5194/egusphere-egu24-16266, 2024.

Natural gas storage is currently considered as one key pillar of the EU strategy to ensure security of energy supply. In view of CH4 storage, Oldenburg [1] demonstrated in a theoretical study that using CO2 as cushion gas instead of CH4 has the advantage of increasing natural gas storage capacities of geologic reservoirs by up to 30 %. This is due to CO2 undergoing a significant density change when its’ critical pressure is exceeded during CH4 injection. Kühn et al. [2] investigated a comparable scenario with CH4 gas storage in a closed cycle with CO2 in one reservoir to temporarily store and reuse wind and solar energy. However, the potential qualitative degradation of the stored CH4 due to mixing with the CO2 cushion gas has not yet been sufficiently addressed in terms of the impact of the modeller’s choice of diffusion coefficients. Hence, the present study focuses on a quantitative assessment of the mixing behaviour of CH4 and CO2 under consideration of dynamic binary diffusion coefficients in a reference numerical simulation benchmark [1,3]. The TRANSPORTSE numerical simulator [4,5] is used with dedicated measures to mitigate the initially high numerical dispersion, introduced by the benchmark’s relatively coarse grid discretisation. The simulation results show that the mixing region is substantially reduced if dynamic binary diffusion coefficients are applied instead of a global constant for both gas components. Consequently, it is demonstrated that previous numerical assessments of natural gas storage with a carbon dioxide cushion gas overestimate the simulated CH4-CO2-mixing area, and thus the calculated mixing losses. Hence, combined gas storage of CH4 and CO2 is more efficient than expected so far.

[1] Oldenburg, C. M. (2003) Carbon Dioxide as Cushion Gas for Natural Gas Storage. Energy Fuels 17(1), 240−246. https://doi.org/10.1021/ef020162b

[2] Kühn, M., Nakaten, N. C., Streibel, M., Kempka, T. (2014): CO2 Geological Storage and Utilization for a Carbon Neutral “Power-to-gas-to-power” Cycle to Even Out Fluctuations of Renewable Energy Provision. Energy Procedia, 63, 8044-8049. https://doi.org/10.1016/j.egypro.2014.11.841

[3] Ma, J., Li, Q., Kempka, T., Kühn, M. (2019) Hydromechanical Response and Impact of Gas Mixing Behavior in Subsurface CH4 Storage with CO2-Based Cushion Gas Energy & Fuels 33 (7), 6527-6541. https://doi.org/10.1021/acs.energyfuels.9b00518

[4] Kempka, T. (2020) Verification of a Python-based TRANsport Simulation Environment for density-driven fluid flow and coupled transport of heat and chemical species. Advances in Geosciences, 54, 67-77. https://doi.org/10.5194/adgeo-54-67-2020

[5] Kempka, T., Steding, S., Kühn, M. (2022) Verification of TRANSPORT Simulation Environment coupling with PHREEQC for reactive transport modelling. Advances in Geosciences, 58, 19-29. https://doi.org/10.5194/adgeo-58-19-2022

How to cite: Kempka, T. and Kühn, M.: Geologic CH4 storage with CO2 cushion gas: using dynamic binary diffusion coefficients instead of a global constant in numerical simulations is more precise and results in lower mixing losses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17184, https://doi.org/10.5194/egusphere-egu24-17184, 2024.

Since the end of the XIX century, many wells have been drilled worldwide for both Oil & Gas exploration purposes. Most of them are now abandoned and subjected to mining closure because exhausted or sterile. In the new epoch of energy transition scenario, the possibility to adapt and reuse these existing boreholes to exploit geothermal energy seems very promising. In fact, considering that approximately 40% of the total costs for a new geothermal project are devoted to drilling activity, the possibility of repurposing abandoned oil and gas wells offers a wide range of applications and exploitation of underground heat uses. The drilled borehole available data (e.g., underground temperature, lithology) provide helpful information about the sub-surface reservoirs, reducing the mining risk level, and wells allow direct access to the sub-surface heat energy. However, to develop a commercially viable geothermal power/thermal generating system, one must consider several factors, i.e., available prospecting, drilling and reservoir technologies, energy costs in the area, and resource durability.

This research aims to analyze the potential and feasibility of deep closed-loop systems solutions for heat and power energy production in Italy, in areas characterized by both normal and anomalous geothermal gradients and the distribution of available abandoned oil and gas wells. A prominent result is the development of a workflow leading to the feasibility assessment of deep closed-loop systems development, based on the identification of suitable abandoned O&G wells through the geological and thermal underground characterization and wells construction characteristics (diameter, depth, borehole material). Furthermore, a sensitivity analysis of the main parameters affecting most of the retrofitting of abandoned wells for geothermal purposes is performed thanks to thermal FEM modelling.

Finally, identifying the possible end-users in a suitable case study area, this research work provides preliminary insights into the quantity of thermal energy and electric power that this technology could produce.

How to cite: Facci, M. and Galgaro, A.: Numerical sensitivity analysis of energy performance of geothermal deep closed loop heat exchangers derived from the reuse of abandoned oil and gas wells, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17674, https://doi.org/10.5194/egusphere-egu24-17674, 2024.

EGU24-18605 | Orals | ERE1.8

Modelling dynamics of sedimentary basins: using geological history to predict subsurface activities at large-scale 

Claude Gout, Marie-Christine Cacas-Stentz, Adriana Traby, and Nathalie Collard

The dynamics of sedimentary basins is a complex combination of synchronous generally non-linear processes. In these natural systems, fluids migration and associated transfers play a fundamental role, even more so as they represent resources that are or may become essential for human societies. One way of assessing the potential of sedimentary basins is to model their past behaviour numerically.

Basin models have been developed since the 1990s for the needs of the oil industry, with the initial aim of assessing the thermal history, i.e. the maturation and expulsion of hydrocarbons from source rocks with variable kinetics and initial composition. These models are used for hydrocarbon prospect assessment in a wide range of sedimentary basins. They have evolved with the integration of the simulation of compaction mechanisms and fluid migration by Darcean single-phase or multi-phase flows. Still with an operational objective in mind, one of these models has been extended to simulate the transport of thermal energy and chemical elements in fluids, thereby helping to assess the geothermal and large-scale storage potential of a basin. The explicit representation of faults and unconformities, as well as the calculation of seal or reservoir formation fracturing as a function of fluid pressures, enables the plumbing system to be represented on a basin scale. In this network of drains, single- or multiphase fluids carrying compounds can interact with the rocks, according to the principles of reactive transport. Some of these simulations are being experimented using AI techniques. In these digital experiments, elements tracking could be a true added value for basin’s dynamics understanding.

A coupled simulation of this kind, combining conductive and advective thermal physics, mechanics (particularly of porous media), the hydraulics of multiphase fluids in porous media, chemistry of reactive transport and even the impact of bioactivity on basin’s fluids, representing geological processes in the subsurface on a large scale, makes it possible to quantify mass and energy transfers in the past. The result is a physically balanced model of the current spatial distribution of pressure, stress, temperature, mass, solid or fluid elements.

These results can be useful both in economic applications for first-order assessment of the resources of any sedimentary basin and in the scientific field for defining the boundary conditions of more specialised models. Initial experiments demonstrating the use of multiphysics models on a basin scale for CCS applications and geothermal energy assessment will be shown.

How to cite: Gout, C., Cacas-Stentz, M.-C., Traby, A., and Collard, N.: Modelling dynamics of sedimentary basins: using geological history to predict subsurface activities at large-scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18605, https://doi.org/10.5194/egusphere-egu24-18605, 2024.

With the advancement of exploration theory and technology, deep and ultra-deep carbonate rocks have gradually become an important new field for the development of oil and gas resources. High-quality carbonate reservoirs have become the focus of attention for oil and gas exploration and research in deep and ultra-deep fields. The Tarim Basin is the largest intracontinental oil and gas basin in China. The thick carbonate strata developed in the Lower Paleozoic are the main layers for oil and gas exploration, and the Ordovician carbonate strata are the main oil and gas producing layers. The predecessors have studied the tectonic evolution, sedimentary background and rock types of the Ordovician in the Tarim Basin. Combined with the analysis of the sedimentary thickness, lithology distribution and seismic profile structure of the Early Ordovician, it is believed that the Lower Ordovician sedimentary period inherited the Cambrian sedimentary pattern and transformed it into a gentle slope sedimentary background with a 'uplift-sag 'pattern, with obvious differentiation. Under the sedimentary background of the gentle slope of the Penglaiba Formation, the three paleo-uplifts of southwestern, northern and central Tarim are inherited geomorphological highs, and the inner gentle slope tidal flat facies is developed. The thickness of the stratum is obviously thinner, and it is mainly developed to represent the tidal flat environment. The periclinal part around the paleo-uplift is the middle gentle slope, which is characterized by dolomite and limestone interbeds. The proportion of granular rocks is high, which is a favorable development area for granular beaches. In this study, the deep drilling cores of the Lower Ordovician Penglaiba Formation in the central Tarim Basin were taken as the key research object, and the lithofacies, reservoir characteristics and dominant reservoir control factors of dolomite reservoirs were systematically analyzed by using macro-micro, qualitative-quantitative reservoir petrology analysis methods. Through research, it is clear that the rock types of the Lower Ordovician Penglaiba Formation in the central Tarim Basin are mainly crystalline dolomite and ( residual ) granular dolomite, and also contain a small amount of limestone, siliceous rocks and transitional rocks. There are various types of reservoir space, mainly including non-fabric selective dissolution pores, intercrystalline pores and various fractures. Combined with previous studies on the genesis and diagenetic evolution of the Lower Ordovician dolomite in the Tarim Basin, it is considered that the development of high-quality dolomite reservoirs in the Lower Ordovician Penglaiba Formation in the central part of Tarim Basin is controlled by many factors. It is the result of a combination of favorable sedimentary facies belts, short-term sea-level changes, exposure and dissolution, early dolomitization, and late tectonic hydrothermal adjustment and transformation.

How to cite: Li, X. and Xu, Q.: Development characteristics and controlling factors of deep dolomite reservoirs of Lower Ordovician in Tazhong area, Tarim Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20142, https://doi.org/10.5194/egusphere-egu24-20142, 2024.

Seismic data integration plays a pivotal role in enhancing the capabilities of geological modelling

software. Our current research focuses on the improvement of seismic interpretation tools within the

PZero software in the framework of the Geosciences IR project lead by the Italian Geological

Survey GitHub - andrea-bistacchi/PZero. The objective is to seamlessly incorporate seismic data

into the geological modelling workflow, enabling more comprehensive and accurate models of

subsurface structures.

The initial phase of our work involved using various libraries to import and analyze seismic

datasets, either 2D or 3D within the PZero framework. We have successfully achieved the

importation of SEGY files into PZero, marking a significant milestone in our efforts. Integrating

seismic data is a crucial step that sets the foundation for constructing detailed geological models,

allowing us to enhance our understanding of subsurface geological features.

Soon, our research trajectory aims to develop advanced algorithms for stochastic simulation tailored

explicitly for modelling clastic sedimentary alluvial plains. The ongoing work includes developing

advanced stochastic simulation algorithms tailored for modelling clastic sedimentary environments,

relevant to both conventional energy resources and emerging sustainable energy storage solutions.

These advancements in seismic data integration and simulation within PZero will significantly

contribute to the field of reservoir modelling. They provide a robust framework for predicting the

behavior of subsurface energy storage systems, which is pivotal in the transition to a low-carbon

energy future.

How to cite: Hussain, W. and Bistacchi, A.: Advancements in Seismic Data Integration and Stochastic Simulation for Geological Modeling in PZero, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22365, https://doi.org/10.5194/egusphere-egu24-22365, 2024.

EGU24-1522 | ECS | Posters on site | ERE2.9

Hydrochemical Indicators for Sustainable and Optimized Geothermal Use of Deep Groundwater  

Annette Dietmaier and Thomas Baumann

Geothermal heat and power generation are two of several competing uses of deep groundwater reservoirs. The stress state of these slowly regenerating systems is increasing as drinking water production from shallow resources suffers from anthropogenic influences: overexploitation, total depletion, and deterioration through anthropogenic contaminants are exacerbated by a climate change-induced failure to recharge. In contrast to shallow groundwater, deep aquifers are shielded from short-term influences, like contamination, by protective overlying strata. The groundwater age is generally much higher, indicating slow regeneration processes because the system is nearly closed in its natural state. Recent data, however, suggests that this assumption is not valid for many geothermal systems with high flow rates. Therefore, a careful assessment of all competing operations using deep groundwater reservoirs is required. It should focus on the interactions between different aquifers and those within the reservoirs, all leaving their marks on the waters’ hydrochemical composition.
The lack of dedicated monitoring wells around geothermal production and injection sites makes it difficult to quantify the development of these reservoirs’ flow patterns. Furthermore, regular complete analysis data are usually only available at long intervals of 12 months. Still, short-term flow path development is a crucial factor in assessing heat extraction efficiency. Impaired extraction due to preferential flow paths forming between production and injection sites will degrade overall operation efficiency.

Here, we challenge state-of-the-art practices for monitoring deep aquifers. Based on decades worth of hydrochemical data on groundwater extraction at both single-well operations and geothermal doublets, we discuss how hydrochemical signatures can help determine the grade of sustainability at which deep geothermal wells are operated. Acknowledging that these assessments depend on an adequate database, and that deep groundwater research is plagued by notorious data scarcity, we tested the application of virtual sensors to these wells was tested. Lab experiments complete the analysis, quantifying the kinetics of the fluid-matrix interactions between the injector and producer.

The outcomes of this dissertation include a statistically reproducible algorithm assessing how sustainably a well is operated, focusing on the inherent dynamics at play in deep groundwater. A series of regression analyses conclude that the databases associated with deep groundwater wells are still insufficient to train virtual sensors; however, they allow conclusions on the required minimum amount of hydrochemical analyses needed to adequately represent inter-seasonal fluctuations in the aquifer. Fluid-matrix interactions result in threshold values for hydrochemical changes, which serve as a trigger to review well operation strategies and to update hydraulic and thermal models. They also indicate that changes are likely following an increasing dynamic because the surface area available for reactions increases geometrically and in roughness. Our calibrated model shows that decreasing the injection temperatures and adding CO2 as a scaling inhibitor significantly increases the reservoir's reactivity.

Hydrochemical data can provide valuable insight into the flow processes in deep reservoirs, which are inaccessible otherwise. With smart sampling procedures and a tailored set of parameters, acquiring relevant data becomes feasible with relatively small financial investments.

How to cite: Dietmaier, A. and Baumann, T.: Hydrochemical Indicators for Sustainable and Optimized Geothermal Use of Deep Groundwater , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1522, https://doi.org/10.5194/egusphere-egu24-1522, 2024.

We develop a computation framework from scratch that allows us to conduct 3D numerical simulations of groundwater flow and heat transport in hot fractured reservoirs to find optimal placements of injection and production wells that sustainably optimize geothermal energy production.

We model the reservoirs as geologically consistent randomly generated discrete fracture networks (DFN) in which the fractures are 2D manifolds with polygonal boundary embedded in a 3D porous medium. The wells are modeled as line sources and sinks.
The flow and heat transport in the DFN-matrix system are modeled by solving the balance equations for mass, momentum, and energy.
The fully developed computational framework combines the finite element method with semi-implicit time-stepping and algebraic flux correction.
To perform the optimization, we use various gradient-free algorithms.

We present our latest results for several geologically and physically realistic scenarios.

How to cite: Partl, O. and Rioseco, E. M.: Optimization of geothermal energy production from fracture-controlled reservoirs via 3D numerical modeling and simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4164, https://doi.org/10.5194/egusphere-egu24-4164, 2024.

EGU24-4549 | ECS | Orals | ERE2.9

Geothermal Reservoir Deformation Monitoring Based on Coda Wave Interferometry 

Yunliang Wang, Jérôme Azzola, Dimitri Zigone, Olivier Lengliné, Vincent Magnenet, Jérôme Vergne, and Jean Schmittbuhl

Monitoring of geothermal reservoir deformation is essential for the normal development of the Enhanced geothermal system (EGS). Coda wave interferometry (CWI) with ambient noise is regarded as an effective and low-cost monitoring technique and draws more and more attentions. But the connection between the obtained CWI measurements and the undergoing physical changes of deep reservoir is still not so clear. In this study, we take Rittershoffen geothermal system (France) as a case study and conduct a series of forward simulations regarding the propagation of scattered wavefield through the deformed model considering acoustic-elastic effect based on Code_ASTER (mechanical loading) and SPECFEM2D (wave propagation). The simulations are based on a two dimensional numerical model with a scale of 12km (width)×20km (height), in which the upper reservoir model contains 8 layers to mimic Rittershoffen geothermal reservoir, the lower sub model with multiple circular inclusions is set to scatter the waves emitted from point source at bottom and produce scattered wavefield; two seismic stations are located at the top of the model. The model is first verified by reproducing the seasonal variation of relative wave velocity changes obtained from ambient noise cross-correlation functions (ANCCF) induced by the underground water table elevation changes. Based on the validated model, we study the effect of in-situ reservoir deformation on CWI measurements by modelling the hydraulic pressure increases on an open hole and the aseismic slip of an embedded fault which is based on the case of hydraulic injection of GRT-1 well, Rittershoffen. The result indicates the induced small reservoir deformation in both situations can be detected by CWI measurements, which helps us to have a better understanding about the connection between the obtained CWI measurements and the undergoing deformation of deep geothermal reservoir.

How to cite: Wang, Y., Azzola, J., Zigone, D., Lengliné, O., Magnenet, V., Vergne, J., and Schmittbuhl, J.: Geothermal Reservoir Deformation Monitoring Based on Coda Wave Interferometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4549, https://doi.org/10.5194/egusphere-egu24-4549, 2024.

EGU24-6571 | ECS | Orals | ERE2.9

From seismic re-processing to mechanic modelling, a new interpretation of the TRANSALP seismic section as a base for future geothermal energy projects, lower Inn Valley, Tyrol, Austria 

Simon Hinterwirth, Hugo Ortner, Marcellus Schreilechner, Heinz Binder, Ewald Lüschen, Makus Jud, Stefan Hoyer, Magdalena Bottig, and Esther Hintersberger

In western Austria, especially in Tyrol, the potential for geothermal energy use is unexplored. The project GeoEN Inntal is aiming to determine this potential and the risks for the use of geothermal energy in a complex tectonic setting in the Inn valley. The valley is bordered by the Permo-Mesozoic sedimentary succession of the Northern Calcareous Alps in the north and the south-east, as well as Upper Austroalpine basement units in the south. Since the early Late Cretaceous, during Eoalpine orogeny, the Austroalpine basement and its Mesozoic cover were involved in nappe stacking and folding. The nappe stack was again refolded and faulted in the Palaeocene-Eocene collision of Adria and the European distal margin, as well as in Oligocene-Miocene, when post-collisional processes lead to an eastward extrusion of crustal blocks, out-of-sequence thrusting and the development of major faults. One of these faults is the Inntal shear zone, a sinistral ENE-trending shear zone, controlling the course of the Inn valley (“Inntal” in German). The shear zone has a multi-phase activity and is kinematically linked with the Brenner normal fault south of Innsbruck, the Alpine basal thrust at the Alpine front, and the Sub-Tauern ramp, rooting below the Tauern window. As the deep subsurface of the Inn valley was only explored geophysically, but no exploration boreholes were drilled, little is known about these structures at depth. Here we present the reprocessed Inntal part of the TRANSALP seismic section, which serves as a base for multidisciplinary modelling approaches. As part of the GeoEN Inntal project, we present first results from our 3D modelling of fault geometry, results from mechanical modelling of the Inntal shear zone, as well as first temperature gradient assessment from hydrological modelling.

How to cite: Hinterwirth, S., Ortner, H., Schreilechner, M., Binder, H., Lüschen, E., Jud, M., Hoyer, S., Bottig, M., and Hintersberger, E.: From seismic re-processing to mechanic modelling, a new interpretation of the TRANSALP seismic section as a base for future geothermal energy projects, lower Inn Valley, Tyrol, Austria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6571, https://doi.org/10.5194/egusphere-egu24-6571, 2024.

EGU24-7499 | Orals | ERE2.9

Best practices in surface and subsurface natural fracture characterisation to advance carbonate geothermal reservoirs insights: a spotlight on the Geneva Basin, Switzerland.  

Pierre-Olivier Bruna, Jasper Hupkes, Myrthe Doesburg, Giovanni Bertotti, Andrea Moscariello, and Jérôme Caudroit

Naturally fractured geothermal reservoirs (NFGR) represent a challenging frontier for sustainable energy exploration and production. These reservoirs are characterised by the presence of complex fracture networks controlling hot fluid movement at depth. Unfortunately, these networks cannot be directly observed, and their properties need to be modelled. Classically, these models are based on statistic data obtained from outcrops and borehole data. Outcrops allow characterisation of the geometry of networks at a scale up to 100’s of meters. However, the analogy between surface and subsurface is not trivial and surprisingly, the notion that different fracture sets are genetically related is rarely used. Borehole core data provide the only direct sampling of the subsurface. However, cores are challenging and expensive to obtain. As an alternative, geophysical borehole images are acquired to observe fractures in the subsurface. However, the quality of these images is variable, making their interpretation uncertain. In this study, we aim to minimize the uncertainties related to fracture picking in borehole images to accurately recognise specific part of the network interpreted from the surrounding outcrops. This approach will provide new perspective in the characterisation of NFGRs.

We test our approach on the Geneva Basin, located in westernmost part of Switzerland. There, the Lower Cretaceous carbonate units are expected to host geothermal resources. Recently, an exploration well, GEo-01 was drilled in the Canton of Geneva to evaluate the geothermal potential of the Lower Cretaceous reservoir. The basin is bounded to the north by the Jura and to the south by the Saleve mountain and the Borne massif where the Lower Cretaceous rocks are outcropping. This area extends for about 1500 km2.

In these outcrops, we introduce the concept of discontinuity associations where sets of fractures, veins and stylolites which formed under a similar stress regime are grouped together. The characterisation of discontinuity associations allows to map the orientation of the maximal principal paleostress (σ1) of genetically related discontinuities. This method is a more robust way of reconstructing fracture-forming deformation events than assigning one deformation event per discontinuity set. We consistently identify three distinct associations over the investigated mountain ranges. Those associations are formed before the onset of fold-and-thrust belt and therefore constitute a background fracture network expected to be found in the targeted geothermal reservoir.

To prove this hypothesis, we looked for the same discontinuity associations in borehole images of GEo-01. This well disposes of a unique dataset of five independent interpretations of the same 122 m interval of Lower Cretaceous series. To quantify and reduce interpretation uncertainties, our study involves a comparative statistical analysis of these interpretations. The outcomes of this  analysis facilitate the identification of intervals where interpreters reached consensus and those where discrepancies emerged. We delved into the factors influencing interpretation agreement or divergence, considering fracture attribute variability, image log quality variation, and geology. We define guidelines to interpret fractures in the borehole images of the Lower Cretaceous of the Geneva Basin and ultimately validate the presence of the three discontinuity associations as background fractures in the geothermal reservoir.

How to cite: Bruna, P.-O., Hupkes, J., Doesburg, M., Bertotti, G., Moscariello, A., and Caudroit, J.: Best practices in surface and subsurface natural fracture characterisation to advance carbonate geothermal reservoirs insights: a spotlight on the Geneva Basin, Switzerland. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7499, https://doi.org/10.5194/egusphere-egu24-7499, 2024.

EGU24-8838 | ECS | Orals | ERE2.9

Influence of basement morphology on hydrothermal convection in the Upper Rhine Graben  

Rose-Nelly Ogandaga Capito and Dominique Bruel

The Upper Rhine Graben (URG) is the central segment of the European Cenozoic Rift System which is known for hosting some of Europe’s major geothermal anomalies. Historically, the region has been explored for its hydrocarbon resources and more recently the area has been targeted for deep geothermal energy. Since then, several heat and/or power plants have been commissioned and are currently in operation. However, despite the gradual development of the sector, the technical potential of the URG remains under-exploited. While the first deep geothermal projects benefited from thermal anomalies known at surface, new projects require costly exploration techniques to ensure a right combination of elevated temperature and sufficient permeability.

Several numerical modelling studies have attempted to reproduce thermal anomalies by integrating a complex three-dimensional geometry of the URG and assuming a topography-induced forced convection largely dominating free convection. As a result, the authors observe a basin-wide graben-perpendicular flow from the graben shoulders towards its center, with an upflow axis approximately below the Rhine River. These conclusions are in contrast to previous geochemical studies which suggest that deep brines discharged from the granitic basement are rather homogeneous on a large scale and have a common origine in deep Triassic sedimentary formations with temperatures close to 225 ± 25 °C. The brines would then migrate through sedimentary layers and permeable fault zones in the basement, from the center of the graben to its western flank, where they would flow up into horst structures such as Soultz or Landau. Moreover, this deep brine circulation in the central part of the graben is thought to be almost completely decoupled both from the circulation of less saline fluids in its upper part, in the Tertiary layers, and from flows along bordering faults, which would be characterized by a rapid recycling of meteoric water via deep circulation loops.

Here, we suggest that thermal anomalies in the French western border of the graben result from deep convective cells developing in the basement along the inclined basement-sediments interface without any help from external pressure forces. Therefore, we used the GeORG public database to build a simplified three-dimensional numerical model of the central part of the URG. Results are obtained using the OpenGeoSys software. Conceptual numerical experiments of thermo-hydraulically coupled simulations were carried out, assuming density-driven convective heat transport with thermal dependence of density and viscosity parameters. The first series of models were constructed without any faults, and we show that an integration of basement morphology, a depth-decreasing basement permeability and a fixed heat flow condition at the base of the model is sufficient to trigger multiple upwellings in the basement within a few million years. Current on-going work is to further calibrate the model to reproduce known existing temperature records and to observe how the integration of permeability heterogeneity or one or more fault zones can reorganize the convective system, thus allowing to trace an effective permeable pattern at larger scale. 

How to cite: Ogandaga Capito, R.-N. and Bruel, D.: Influence of basement morphology on hydrothermal convection in the Upper Rhine Graben , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8838, https://doi.org/10.5194/egusphere-egu24-8838, 2024.

EGU24-9960 | ECS | Orals | ERE2.9

An experimental demonstration of fault preconditioning for reduced seismic hazard 

Barnaby Fryer, Corentin Noël, Feyza Arzu, Mathias Lebihain, and François Passelègue

The mechanical stimulation of a fault or fracture in the case of an Enhanced Geothermal Reservoir (EGS) is generally reliant on inducing shear dilation of a targeted discontinuity. However, this same process can lead to the nucleation of a potentially-damaging seismic event. Here, a reservoir stimulation technique known as preconditioning is demonstrated experimentally for the first time. This technique consists of initially increasing the effective normal stress along the fault, in practice corresponding to a period of fluid production. Following this the fault is locally unloaded, corresponding to fluid injection. As the unloading continues, a slipping patch may form, eventually leading to dynamic rupture. However, the previously-induced high effective normal stress further along the fault acts as a fracture energy and reduced-stress-drop barrier, potentially resulting in rupture arrest. Here, a highly-instrumented (strain gauges, accelerometers, acoustic sensors, displacement sensors, load cells) biaxial apparatus is used to demonstrate this procedure, making use of the translucence of polymethylmethacrylate (PMMA) and a high-speed camera to image the development of propagating ruptures. It is demonstrated, as previously predicted from theory, that preconditioning has the ability to halt dynamic ruptures and may therefore be a viable stimulation technique resulting in reduced hazard in EGS stimulation. Specifically, experiments are performed at nominal normal stresses of 60, 90, and 120 bar, with preconditioning (or normal stress increase) corresponding to approximately 8, 16, and 24%; in addition to control cases with no preconditioning. Generally, preconditioning slows rupture propagation at 8% normal stress increase and completely halts it for larger values of preconditioning. It further results in a reduced shear stress drop, increased fracture energy, and reduced slip velocity. These results may one day have further implications for the potential of controlled stress release along natural faults.

How to cite: Fryer, B., Noël, C., Arzu, F., Lebihain, M., and Passelègue, F.: An experimental demonstration of fault preconditioning for reduced seismic hazard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9960, https://doi.org/10.5194/egusphere-egu24-9960, 2024.

EGU24-10336 | ECS | Posters on site | ERE2.9

Bayesian Evidential Learning Approach to Uncertainty Quantification in THM Model of Geothermal Energy Extraction in Deep Mines 

Le Zhang, Alexandros Daniilidis, Anne-Catherine Dieudonné, and Thomas Hermans

Utilizing existing deep mining systems for geothermal extraction not only facilitates the development of geothermal systems but also helps meeting the cooling requirements for deep mining operations. In this study, a thermo-hydro-mechanical model of geothermal extraction in deep mines is developed to investigate the evolution of mine galleries stability and temperature, and the temperature changes in geothermal production wells. The uncertainty in system responses is predicted through the Bayesian Evidential Learning framework.

Due to our limited understanding of the material properties and the scarcity of measurement data, uncertainties emerge in the forward simulations. Ideally, a comprehensive uncertainty analysis would be conducted to predict all possible outcomes and assess any risks. However, In light of the intractability of performing comprehensive uncertainty analyses in scenarios with vast unknown data, particularly due to the computational overhead of multiple inverse problem-solving, we employ the Bayesian Evidential Learning framework, which provides a feasible and rapid alternative for approximating prediction post-distributions and choosing the most informative data sets. Before implementing BEL, we employed Latin Hypercube Sampling to create 500 sets of realizations for forward simulations, and subsequently utilized global sensitivity analysis to evaluate the data's informational value, aiming to diminish the uncertainty in predictions. In this paper, the BEL framework is utilized to achieve two: firstly, to stochastically predict the responses of the system (stability and temperature) within the BEL framework, using machine learning to discover direct correlations between predictors (sensitive parameters) and targets (system responses). Subsequently, newly collected data can be utilized to predict the approximate posterior distributions of the corresponding gallery stability, temperature, and production well temperature, thus circumventing traditional data inversion steps. This framework can be adjusted to accommodate any predictions related to subsurface conditions; hence, our second goal involves predicting the system's long-term responses within the BEL based on short-term data collection, forecasting posterior distributions from the acquired short-term data, and validating the efficacy of this approach.

Our study indicates that in practical engineering, by (1) obtaining data of material properties and (2) key responses of short-term simulation, it is possible to predict the critical responses of the system in long-term geothermal extraction, thereby maximizing the information content of any measurement data while minimizing budget constraints and computational costs.

How to cite: Zhang, L., Daniilidis, A., Dieudonné, A.-C., and Hermans, T.: Bayesian Evidential Learning Approach to Uncertainty Quantification in THM Model of Geothermal Energy Extraction in Deep Mines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10336, https://doi.org/10.5194/egusphere-egu24-10336, 2024.

EGU24-10490 | Orals | ERE2.9

Seismic hazard related to deep geothermal operations (Part II) : iterative methodology for hazard assessment  

Julie Maury, Francesca De Santis, Mariane Peter-Borie, Emmanuelle Klein, Pascal Dominique, and Isabelle Contrucci

Ineris and BRGM published a good practices guide and recommendations for the management of seismicity induced by deep geothermal energy operations. It includes a method to assess the seismic incident hazard, defined as an event whose intensity could cause nuisances for the population, affect the local buildings and infrastructures and which could adversely impact the operating conditions and even the continuation of the project. This method has been developed based on more than 50 case studies consisting of projects representative of different types of geothermal systems where induced seismicity occurred or not. Based on an iterative approach, the method recommends hazard assessment at each key step of a geothermal project to benefit from the additional knowledge it bring. The main key steps identified are the initial assessment before frilling occur, a reevaluation just after drilling and a reevaluation before any potential stimulations. Hazard assessment is based on a decision tree approach, involving specific criteria for each project phase. The seismic incident hazard is rated with a score between 0 and 3. At the lowest level (0), no specific measures to manage induced seismicity are required. For level 1 and 2, monitoring and management methods must be developed. At level 3, the project is considered to be beyond potential induced seismicity management (it’s deviating from the plan) and operations must be suspended pending the outcome of further investigations. This method has been tailored for helping and guiding operators and French administration to consider and manage induced seismicity hazard for every deep geothermal project. 

How to cite: Maury, J., De Santis, F., Peter-Borie, M., Klein, E., Dominique, P., and Contrucci, I.: Seismic hazard related to deep geothermal operations (Part II) : iterative methodology for hazard assessment , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10490, https://doi.org/10.5194/egusphere-egu24-10490, 2024.

Besides the amount of a thermal fluid produced and its chemical composition, temperature is one of the key parameters for the utilization of hydrothermal heat. This applies in particular to geothermal fields with low temperature/low enthalpy, as too low extraction temperatures can mean the failure of a project, while higher temperatures can enable electricity generation or generally better economic efficiency. This concerns the undisturbed (natural) temperature in the reservoir as well as that of the produced fluid at the surface, which depends on the well completion, the undisturbed reservoir temperature, and the depth and contributions of hydraulically active zones. Subsequently, improved forecasts of both the undisturbed temperature and the production temperature with a valid estimate of their uncertainty are required to provide a reliable basis for field development and risk assessment.

In the national projects Geothermal-Alliance Bavaria and KompakT, we studied the temperatures in the North Alpine Foreland Basin in Bavaria, Germany. The carbonate rocks form one of Europe’s most important reservoirs for the use of deep geothermal energy, and projects for district heating and electricity generation have been realized here for more than 30 years.

We developed a good practice workflow for the correction of low-quality bottom hole temperature (BHT) values based on a probabilistic Monte Carlo approach. Using this workflow, we corrected BHTs from over 300 hydrocarbon and geothermal wells and predicted the natural temperature field inside the study area. The resulting temperature model is based on risk scenarios and contains a range of uncertainty, the extent of which depends on the uncertainty of the correction input parameters at the individual locations.

To study the short-term and long-term thermal behavior in the reservoir and the wellbore during production conditions, in 2019, a fiber optic cable was installed below the pump into the reservoir of a geothermal production well. We used distributed temperature sensing (DTS) to observe the hydraulically active zones and to thermally derive their contribution to the available heat amount.

The knowledge gained underlines the importance of flow zone characterization and can be used to improve existing temperature models and estimate what temperatures can really be expected during extraction.

How to cite: Schölderle, F. and Zosseder, K.: The Uncertainty of Temperature Predictions and the Influence of Flow Zones on the Production Temperature in a Low Enthalpy Geothermal Field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10641, https://doi.org/10.5194/egusphere-egu24-10641, 2024.

Geothermal projects relying on superhot rocks (SHR), such as the Japan Beyond-Brittle Project, Iceland Deep Drilling Project, and Newberry Volcano, aim to harness heat from geothermal reservoirs where water reaches a supercritical state (temperature ≥ 400 °C and pressure ≥ 22 MPa). Such projects could multiply the power output of geothermal power plants by a factor of ten, positioning them at the forefront of the energy transition. However, a major challenge hindering the widespread application of SHR is the fact that supercritical water resources are often found in regions of the crust where rocks exhibit ductile behavior, a rheological regime where the formation of large-scale fractures and cracking is hindered. However, these fractures are crucial for enabling water flow, and currently, the evolution of rock permeability and other hydraulic properties in this context remains largely unknown.

This study presents experiments conducted in TARGET, a newly designed gas-based triaxial apparatus located at EPFL, CH. Cylindrical cores of Lanhélin granite (40 x 20 mm) were deformed under an effective confining pressure of 100 MPa, temperatures ranging from 200 to 800 °C, and a strain rate of 10-6 s-1. Continuous recording of sample permeability using the pore pressure oscillation method was carried out during deformation. Moreover, post-mortem samples were retrieved and scanned at the ESRF synchrotron facility (Grenoble, FR) and the tomographs were used to reconstruct the 3D crack network. Flow in the sample was then modelled using the Avizo XLab extension and permeability was computed in the x y and z direction.

We report that Lanhélin granite transitions from being in the localized regime with the formation of a sample scale fracture to becoming ductile between 600 and 800°C. In the brittle, localized regime, sample permeability remains relatively constant throughout deformation. In the ductile regime, sample strength is halved, and beyond the initial decrease upon loading, permeability increases monotonically by more than an order of magnitude. These results suggest that sample bulk controls the sample permeability in our experiments. In localizing samples, fractures do not connect the ends of the rock core but concentrate all strain after nucleation, limiting permeability improvement through micro-cracking in the bulk. In the ductile regime, where no localization occurs, the bulk permeability of the rock continuously improves with strain. Flow modeling in post-mortem samples yielded permeability values up to seven orders of magnitude greater than in-situ measurements. This substantial difference is attributed to the effect of confining pressure on the crack network aperture. Despite this absolute difference, our modeling results confirm that flow in nominally ductile samples is controlled by bulk cracking rather than macroscopic fractures. Our study demonstrates that low-porosity rocks in the ductile regime can be more permeable than often anticipated. These results hold significant implications for the engineering of SHR reservoirs, showcasing the potential for permeability enhancement in ductile rocks.

How to cite: Meyer, G., Shahin, G., Cordonnier, B., and Violay, M.: Permeability of experimentally deformed ductile granite derived from in-situ measurements and post-mortem X-ray tomography: perspectives for superhot rock reservoirs., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10980, https://doi.org/10.5194/egusphere-egu24-10980, 2024.

EGU24-11082 | ECS | Orals | ERE2.9 | Highlight

Seismic hazard related to deep geothermal operations (Part I): identification of key criteria for hazard assessment  

Francesca De Santis, Julie Maury, Emmanuelle Klein, Mariane Peter-Borie, Isabelle Contrucci, and Pascal Dominique

Deep geothermal projects can trigger seismic events depending on geological context and operations. This seismicity is generally of low magnitude but, in some cases, larger events may occur, which could lead to geothermal project abandonment and could present risk to neighboring populations. Thus, development of deep geothermal projects requires the management of induced seismicity to control it and to avoid any surface disturbance. It is from this perspective that, in 2023, Ineris and BRGM published a guide of good practices and recommendations for operators and French administration involved in deep geothermal energy.

The guide provides recommendations for assessing geothermal-induced seismic hazard, depending on the type of geothermal system and its intrinsic and operational characteristics, at each key step of a project (i.e. from the exploration phase until the end of the project). A worldwide review of deep geothermal projects, carried out with the aim of identifying key factors triggering induced seismicity, has enabled the definition of the most relevant criteria to take into account in the hazard assessment. In this review, geothermal projects were chosen to be representative of different types of geothermal systems (e.g. deep sedimentary aquifers, volcanic and plutonic regions, deep dry crystalline basements, etc.) and operating conditions (e.g. well configuration, type of operation, etc.). Moreover, the review includes projects associated with several episodes of induced seismicity, ranging in magnitude from microseismicity (M < 2) to large seismic events (M > 5), as well as projects marked by the absence of induced seismic activity.

From the 53 projects and 77 seismic episodes analyzed in this review, we can state that not all geothermal projects are equally prone to seismic events. The occurrence and the intensity of induced seismicity are the results of interactions between several natural (intrinsic) and anthropogenic (operational) factors, often concomitant and dependent on each other. Seismic response of analyzed projects appears to be largely different depending on the type of geothermal system. Indeed, the type of geothermal system characterizes reservoir porosity, as well as heat transfer and fluid circulation modes in the reservoir. Other key factors include the presence of faults that can be critically loaded and/or connected with the basement, the use of EGS technologies, and situations where injected and produced volumes are highly unbalanced. These results allowed defining key criteria for seismic hazard assessment methodology proposed within the good practice guide.

How to cite: De Santis, F., Maury, J., Klein, E., Peter-Borie, M., Contrucci, I., and Dominique, P.: Seismic hazard related to deep geothermal operations (Part I): identification of key criteria for hazard assessment , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11082, https://doi.org/10.5194/egusphere-egu24-11082, 2024.

EGU24-11792 | ECS | Posters on site | ERE2.9

Structural characterization of hydrothermal fluid pathways in orogenic belts: Insights from the GeoTex project, Rhône Valley, Switzerland 

Timothy C. Schmid, Marco Herwegh, Alfons Berger, Sandro Truttmann, Larryn W. Diamond, Christoph Wanner, Daniela B. Van den Heuvel, Herfried Madritsch, and Tobias Diehl

Meteoric water may or may not infiltrate deeply into high-relief mountain ranges. Along its subsurface circulation path, the water heats up according to the background geothermal gradient and eventually emerges at lower elevation as thermal springs. Whether such topographically-driven circulation establishes or not depends on the host rock’s permeability and/or the hydraulic head. In terms of permeability, fault zones play an important role as they can provide preferential flow paths for fluids. This is particularly the case of active fault zones along which recurring slip counteracts clogging caused by mineral precipitation often found along non-active structures. Thus, the investigation of 4D fault and fracture geometries and their kinematics is a means to understand the locations and dynamics of geothermal systems in orogenic belts. Here, we present preliminary results from the ongoing GeoTex research project, which aims at better defining the geothermal potential of the Rhône Valley, an area of rugged topography in SW Switzerland. The Rhône Valley represents a geothermally active zone within the Alpine orogen, which is characterised by numerous thermal springs, regional-scale faults and enhanced seismic activity. It is therefore a promising setting to explore further for exploitation.

Based on structural data from fieldwork and quantitative remote sensing, we characterise fault geometries (i.e., spatial orientation, relationship of intersecting fault families as well as kinematics) in the vicinity of known thermal springs. Observable paleo-fluid pathways marked by veins and rock alteration are being considered as analogues for recent thermal water circulation. These circulation paths are linked to major Alpine structures in the underlying basement units, such as large-scale strike-slip faults or the axial planes of uplifting basement domes. Our results suggest spatial correlations between the locations of hydrothermal springs and the 3D structure of the host massifs. Specifically, basement–cover contacts exert geometric and lithologic control at some sites, whereas locally dilatant domains along strike-slip faults as well as intersections of fault families focus outflow at other sites. Through the above approach in combination with seismological data, we have derived conceptual models for fluid flow, which may help to predict the locations of blind active geothermal systems elsewhere in the Rhône Valley.

How to cite: Schmid, T. C., Herwegh, M., Berger, A., Truttmann, S., Diamond, L. W., Wanner, C., Van den Heuvel, D. B., Madritsch, H., and Diehl, T.: Structural characterization of hydrothermal fluid pathways in orogenic belts: Insights from the GeoTex project, Rhône Valley, Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11792, https://doi.org/10.5194/egusphere-egu24-11792, 2024.

The carbonate Upper Jurassic aquifer (UJA) in the South German Molasse Basin (SGMB) is the most important exploration horizon for geothermal energy supply in Bavaria. The UJA shows a complex hydrogeology caused by a heterogeneous geology with karstic features and deep fault zones.

The great interest in the Upper Jurassic aquifer for geothermal energy supply led to an increasing construction of geothermal power plants in the greater Munich area. Today, there are 18 geothermal power plants in this area used for district heating and electricity generation.

To guarantee a long and sustainable use of the geothermal resource, understanding the dynamics within the reservoir is important. Tracer tests are a key tool for investigating groundwater flow paths, detecting potential thermal breakthroughs, and minimizing negative interactions between geothermal power plants.

In recent years, several tracer tests have been conducted, and the growing number of projects will lead to even more tracer testing in the coming years. Future tracer tests need to be carefully designed, as there is, up to now, only a limited number of traditional tracer substances available for use in a deep geothermal setting under high temperatures and pressures. Therefore, we developed tracer management for the UJA, including guidelines for different tracer tests, the suitability of different tracers for usage in a geothermal setting, and recommendations for individual locations.

How to cite: Winter, T. and Zosseder, K.: Developing tracer management for long and sustainable use of the Upper Jurassic geothermal reservoir in South Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17350, https://doi.org/10.5194/egusphere-egu24-17350, 2024.

EGU24-17666 | Posters on site | ERE2.9

Mechanical stiffness and permeability of a reservoir-scale rough fracture during closure 

Jean Schmittbuhl, Qinglin Deng, Mauro Cacace, and Guido Blöcher

Natural or artificial fluid flow in deep fractured reservoirs, such as Enhanced Geothermal Systems (EGS), is primarily controlled by open fractures and faults, and is considered a key element for hydraulic performance. Flow along these fractures is strongly affected by channeling between fracture asperities and by deposits sealing the open fracture space due to mineral precipitation. Fracture asperities and fracture sealing also impact the mechanical behavior of fractures, especially their mechanical stiffness. Here, we study both the permeability and the stiffness of a rough fracture at the field scale during its closure.We base our approach on a well established self-affine geometrical model for fracture roughness. We develop a finite element model based on the MOOSE/GOLEM framework and conduct numerical flow experiments in a 256 × 256 × 256 m^3 granite reservoir hosting a single, partially sealed fracture under variable normal loading conditions. Navier-Stokes flow is solved in the embedded 3-dimensional rough aperture, and Darcy flow is solved in the surrounding poroelastic matrix. We study the evolution of the mechanical stiffness and fluid permeability of the fracture-rock system during fracture closure by considering the asperity yield and the depositing of fracture-filling material in the open space of the rough fracture. The evolution of the fault volume, fracture normal stiffness and permeability are monitored until fluid percolation thresholds are exceeded in two orthogonal directions of the imposed pressure gradient. Finally, we propose a physically based law for the stiffness and permeability evolution as a function of the fault volume. It is demonstrated that during closure, stiffness increases exponentially as the fault volume decreases. A strong anisotropy of the fracture permeability is also evidenced when reaching percolation thresholds.

How to cite: Schmittbuhl, J., Deng, Q., Cacace, M., and Blöcher, G.: Mechanical stiffness and permeability of a reservoir-scale rough fracture during closure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17666, https://doi.org/10.5194/egusphere-egu24-17666, 2024.

EGU24-18451 | ECS | Posters on site | ERE2.9

Large-scale reservoir modeling of the Vendenheim geothermal site (France) 

Javier Abreu Torres, Gergo Hutka, Mauro Cacace, Guido Blöcher, Vincent Magnenet, and Jean Schmittbuhl

During the Vendenheim deep geothermal project (Strasbourg Eurometropole, France), large induced seismic events led to the arrest of the project. Two important features of the induced seismicity were unexpected : the large distance to the wells of a cluster of seismic events (4-5km) and the occurrence of the largest event Mlv3.9 at the bottom of the wells, six months after shut-in. To better understand the mechanisms of seismicity, we develop within the framework of the DT-GEO project (Horizon Europe) a large-scale model (8kmx8kmx8km) of the area. We aim at performing in-silico experimentation to reproduce the geophysical responses of the geothermal reservoir with different geological geometries, different geomechanical properties and constrained with a variety of crustal stress conditions and variety of the external forcing representing the anthropogenic control. The model is based on the MOOSE/GOLEM framework (finite element approach) and integrate the public regional geological model GEORG that includes major lithologies and large-scale faults of the area. We will present the preliminary of coarse-grained simulations of the natural fluid circulation and fluid injections.

How to cite: Abreu Torres, J., Hutka, G., Cacace, M., Blöcher, G., Magnenet, V., and Schmittbuhl, J.: Large-scale reservoir modeling of the Vendenheim geothermal site (France), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18451, https://doi.org/10.5194/egusphere-egu24-18451, 2024.

EGU24-18565 | ECS | Posters on site | ERE2.9

Flow focusing associated with doublet operation 

Fahim Mumand and Jörg Renner

Heat and cold storage in the subsurface as well as geothermal energy provision intrinsically involve cyclic pumping operations, often in fields of several boreholes. We investigated the pressure and flow-rate fields resulting from the simultaneous periodic operation of two boreholes. The interference in pressure experienced by further (monitoring) boreholes can be assessed by an analytical solution when assuming radial flow from and to the pumping wells. This solution is derived through superposition, relying on the known solution for periodic pumping in a single well. The pressure gradient field, indicative of flow direction, is distorted from radial form, implying dominant flow and consequently heat advection between the two boreholes. We compared the analytical results to observations from field tests conducted in four boreholes located close to the northwestern banks of an artificial freshwater reservoir, the Kemnader See, at the southern city-limits of Bochum, Germany. In the light of the derived solutions, the field observations allow us to assess the role of inhomogeneity and fracture flow for the flow focusing between the pumping wells. Solving and investigating the hydraulic problem constitutes the necessary first step towards devising schemes for the optimization of cold and heat storage or geothermal energy provision by varying the period and phase of pumping coeval operations in several boreholes.

How to cite: Mumand, F. and Renner, J.: Flow focusing associated with doublet operation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18565, https://doi.org/10.5194/egusphere-egu24-18565, 2024.

EGU24-18812 | ECS | Orals | ERE2.9

Deep U-tube heat exchanger breakthrough: combining laser and cryogenics gas for geothermal energy exploitation – a perspective of laser-rock interactions 

Pawel Slupski, Enrico Zampieri, Eloisa Di Sipio, Adele Manzella, Riccardo Pasquali, Luc Pockele, Arno Romanowski, Raffaele Sassi, Olaf Steinmeier, and Antonio Galgaro

The technology envisioned in the DeepU project (Deep U-tube heat exchanger) is expected to revolutionize the geothermal energy sector, increasing the accessibility of deep geothermal resources for low-carbon heating and power generation. The ultimate project goal is to create a deep (>4 km) closed-loop connection in the shape of a U-tube exchanger by developing a fast and effective laser drilling technology. The project comprises the development of a novel drilling technique and its application via geothermal modeling at selected sites. A prototype of a drill-head has been realized, combining the laser system with drill strings, sustaining the coupled action of laser and cryogenic gas. The fine particles of drilled rocks are ejected to the surface in the gas stream via the borehole annulus. This contribution focuses on the project’s activities related to the laser-rock interactions studied in the experimental laser drilling tests based on previous works (Seo et al., 2022; Li et al., 2022a, 2022b). Three types of lithologies were selected for initial laboratory tests: granite, sandstone, and limestone (50 x 35 x 15 cm). Constant rates of penetration (ROP) upwards of 20 m/h have been achieved in all lithologies with borehole diameter reaching 18 cm. The petro-thermo-mechanical phenomena occurring during laser drilling, such as spallation, melting, and evaporation, were recognized and described. The drilling process was investigated by thermocamera imaging providing information about the most effective process induced by heating the rocks, up to 700°C. The laser working parameters and experimental setup were optimized regarding observed phenomena. In the next step, sections of boreholes were cut out and examined. The microscopic observations on the thermal unaffected and affected rocks’ thin sections have been performed with the use of polarized optical microscopy and scanning electron microscopy revealing micro-fracturing patterns of the rock induced on rock samples by the heating processes. The change of physic-mechanical properties of rocks was investigated and acknowledged in geothermal models. This innovative and comprehensive study revealed macro- and micro-scale phenomena occurring during laser drilling, contributing to the successful development of this new drilling method and subsequently its application for exploitation of geothermal energy from depths below 4 km.

This research is funded by the European Union (G.A. 101046937). However, the views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union or EISMEA. Neither the European Union nor the granting authority can be held responsible for them.

References

Li, G., Shi, D., Hu, S., Ma, C., He, D., and Yao, K., 2022a, Research on the mechanism of laser drilling alumina ceramics in shallow water: The International Journal of Advanced Manufacturing Technology, v. 118, p. 3631–3639, doi:10.1007/s00170-021-08190-0.

Li, Q., Zhai, Y., Huang, Z., Chen, K., Zhang, W., and Liang, Y., 2022b, Research on crack cracking mechanism and damage evaluation method of granite under laser action: Optics Communications, v. 506, p. 127556, doi:10.1016/j.optcom.2021.127556.

Seo, Y., Lee, D., and Pyo, S., 2022, The interaction of high-power fiber laser irradiation with intrusive rocks: Scientific Reports, v. 12, p. 680, doi:10.1038/s41598-021-04575-z.

How to cite: Slupski, P., Zampieri, E., Di Sipio, E., Manzella, A., Pasquali, R., Pockele, L., Romanowski, A., Sassi, R., Steinmeier, O., and Galgaro, A.: Deep U-tube heat exchanger breakthrough: combining laser and cryogenics gas for geothermal energy exploitation – a perspective of laser-rock interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18812, https://doi.org/10.5194/egusphere-egu24-18812, 2024.

EGU24-20414 | Orals | ERE2.9 | Highlight

A newly installed research infrastructure for geothermal energy in a subsurface sedimentary reservoir for direct-use heating: the TU Delft campus geothermal project 

Hemmo Abels, Auke Barnhoorn, Alexandros Daniilidis, David Bruhn, Guy Drijkoningen, Kaylee Elliott, Beer van Esser, Susanne Laumann, Piet Van Paassen, Liliana Vargas Meleza, Andrea Vondrak, Denis Voskov, and Phil Vardon

A geothermal doublet has been installed in a sedimentary reservoir for direct-use heating on the TU Delft campus, targeted to supply around 25 MW of thermal energy at peak conditions. This contribution presents the implementation and initial data collection from the doublet, including an initial evaluation of the logging and coring campaign. Nearly half of Netherlands natural gas consumption is allocated to heating, and the on-campus CO2 emissions from heating exceed 50%. The doublet has been designed with two primary aims of research and commercial heat supply, with the wells being completed in December 2023. The project will be operated by a commercial entity, and built into a larger thermal energy system including a high temperature underground storage system, with the first energy production planned in 2025. The research questions relate to field-scale geothermal operations, e.g. how reliable is the long-term energy production?, how do materials perform in the long-term? and how can geothermal projects be best monitored? The research programme involves the installation of a wide range of instruments alongside an extensive logging and coring program and monitoring network. The doublet has been cored, with substantial continuous samples from the heterogenous reservoir, alongside a large suite of open hole well logs in the reservoir and through casing logs in overlying geological units. A fiber-optic cable will monitor distributed pressure throughout the producer reservoir section, at approximately 2300m depth, which will be installed during commissioning. A local seismic monitoring network has been installed in the surrounding area with the aim of monitoring very low-magnitude natural or induced seismicity. The project is a key national research infrastructure and is being incorporated into the European EPOS (European Plate Observing System, https://www.epos-eu.org/), such that accessibility and data availability will be as wide as possible. All observations will be included in a digital-twin framework that will allow to make better decisions in future geothermal projects.

How to cite: Abels, H., Barnhoorn, A., Daniilidis, A., Bruhn, D., Drijkoningen, G., Elliott, K., van Esser, B., Laumann, S., Van Paassen, P., Vargas Meleza, L., Vondrak, A., Voskov, D., and Vardon, P.: A newly installed research infrastructure for geothermal energy in a subsurface sedimentary reservoir for direct-use heating: the TU Delft campus geothermal project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20414, https://doi.org/10.5194/egusphere-egu24-20414, 2024.

EGU24-20667 | ECS | Orals | ERE2.9

Generation of High Resolution Seismic Catalog Associated With the Production Phase 2021 - 2022 at the Balmatt Geothermal Site 

Rachit Gautam, Jannes L. Kinscher, Jean Schmittbuhl, Matsen Broothaers, and Ben Laenen

The Balmatt geothermal doublet, developed and managed by VITO (Flemisch Institute of Technological Research), targets the fractured Lower Carboniferous Limestone reservoir in the Campine Basin at the depth of 3000 m to 4000 m. The development of the project started in 2015 and the operation began in 2018. The geothermal plant consists of two active wells, one injection well and one production well. The geothermal production had to be suspended after the occurrence of a stronger ML 2.2 event on the 23rd of June 2019 which triggered a red alert status on the local traffic light system (TLS). Production was then resumed in April 2021, following an extension of the seismic monitoring network and an update of the TLS. Activities were suspended again in November 2022 after another strong ML 2.1 event was induced. Thanks to the network extension, current investigations aim at understanding in detail the main structural features (active faults) and hydromechanical processes involved in the generation of such larger events which will contribute to improving seismic forecast possibilities for future monitoring operations. Here we present insights into ongoing data processing to create a high resolution unbiased (complete) seismic catalog providing the basis for future interpretation of the spatio-temporal and energetic behavior of seismicity towards different production settings. Our current work focuses in particular on the development of an automatic detection routine based on continuous data of the deep borehole sensor (installed at the depth of 2052 m) by combining a machine learning based automatic events detection algorithm and template matching method. The events detection in the continuous data is complicated by the periodic malfunctioning of the sensor and the presence of aseismic noise which leads to the large number of false events detection. To address this issue and to minimize the number of false detections, we employ frequency and amplitude analysis of the seismic data. Secondly we analyze source attributes of the detected events which involve source mechanism inversion and source parameter determination as well as clustering analysis and constraining source location for noisy small magnitude events. Further more the comparison between the production data (injection pressure, temperature, volume etc.) with the results from the seismic analysis will provide us with better constrain on the hydromechanical characteristics of the reservoir and the relation between the geothermal operations and seismicity at Balmatt geothermal site. 

How to cite: Gautam, R., Kinscher, J. L., Schmittbuhl, J., Broothaers, M., and Laenen, B.: Generation of High Resolution Seismic Catalog Associated With the Production Phase 2021 - 2022 at the Balmatt Geothermal Site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20667, https://doi.org/10.5194/egusphere-egu24-20667, 2024.

EGU24-20785 | Orals | ERE2.9

The power generation potential of enhanced geothermal systems in ductile crust at >15 km depth 

Samuel Scott, Alina Yapparova, Philipp Weis, and Matthew Houde

This study explores the power generation potential of enhanced geothermal systems (EGS) at depths of >15 km, where continental crust typically exhibits ductile behavior at temperatures above 400 °C. We employed a numerical model to evaluate the response of such deep crustal rock to fluid injection-induced pressurization and cooling. Our simulations indicate that circulating 80 kg/s of water through rock initially at 425 °C could yield ~100-120 MWth (approximately 20 MWe) for two decades. Even after a century of fluid circulation, fluid temperatures at the production wells exceed 250 °C and thermal energy output exceeds 40 MWth. However, achieving effective permeability in the stimulated volume is crucial to developing an exploitable resource; our model suggests that bulk permeability values between ~10-15 and 10-14 m2 in a rock volume of 0.1 km3 are optimal. This range balances the need to avoid excessive injection pressures and the risk of rapid thermal depletion. As the reservoir cools, the transition from ductile to brittle behavior in rock is assumed, reducing fluid pressures but increasing the risk of fluid pathway short-circuiting, a common challenge in EGS operations. Our theoretical investigation underscores the importance of geological (e.g., rock temperature and permeability) and operational (e.g., injection rate) factors in harnessing the energy potential of the ductile crust. However, practical implementation hinges on revolutionary advancements in deep drilling technology and a better understanding of rock behavior under high temperature and pressure conditions.

How to cite: Scott, S., Yapparova, A., Weis, P., and Houde, M.: The power generation potential of enhanced geothermal systems in ductile crust at >15 km depth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20785, https://doi.org/10.5194/egusphere-egu24-20785, 2024.

EGU24-21025 | Orals | ERE2.9

Quantifying the 4D Seismic Density Evolution Caused by Geothermal Injection 

Zhiwei Wang, Olivier Lengliné, and Jean Schmittbuhl

The injection of geothermal water into subsurface rock formations often induces a cascade of seismic events. However, a comprehensive understanding of the resulting temporal and spatial seismic density evolution remains elusive. In this study, we meticulously analyze both spatial and temporal earthquake probability density distributions. Leveraging data from multiple injection sequences obtained from the EPOS TCS-AH through the EPISODES Platform, our objective is to elucidate the spatiotemporal evolution of seismic activity across distinct phases of water injection. We extend our focus to quantify seismicity during the post-injection phase and assess whether the largest magnitude event in each sequence aligns with the derived distribution. This time, our primary emphasis is on conducting the above-mentioned analysis on the 09/1993 Soultz-sous-Fôret sequence. Our research is supported by Horizon Europe under grant agreement No. 101058129 as part of the DT-Geo Project.

Our findings reveal a distinctive characteristic of seismic spatial density, marked by a sudden decay at extended distances. Remarkably, there is no significant divergence in spatial density decay observed before and after the cessation of injection. Furthermore, we observe that the occurrence of the maximum magnitude event coincides with the peak of the probability spatial density. Shifting to temporal density, we identify a close correlation with the increase in injection volume, displaying a skewed normal distribution. Notably, the maximum magnitude event aligns with the peak of the probability temporal density.

In essence, our research substantively contributes to a quantitative comprehension of the dynamic features governing the temporal and spatial evolution of seismic density during intensified water injection scenarios.

How to cite: Wang, Z., Lengliné, O., and Schmittbuhl, J.: Quantifying the 4D Seismic Density Evolution Caused by Geothermal Injection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21025, https://doi.org/10.5194/egusphere-egu24-21025, 2024.

The storage of surplus power generated by wind turbines or solar panels under favourable weather conditions is of significant importance for the successful transition of current energy systems. Surplus power can be used for hydrogen production or for charging batteries. However, there is also an option to store surplus power as mechanical energy due to the injection of water into the deep underground.

Basic investigations for the storage of mechanical energy were performed at the geothermal research well “Horstberg” in Germany. Here a large and highly conductive artificial fracture was created in the Buntsandstone formation at approximately 3800 m depth. For the hydraulic stimulation 20.000 m3 of fresh water were injected at a pressure of about 300 bar. In succeeding production tests, the water was produced back at a pressure level of about 200 bar and a significant portion of the energy used for injection would have been retrievable. Further injection and production tests, originally designed for cyclic heat extraction, showed that approximately half of the electric energy necessary for injection could have been recovered while producing. Obviously, a large portion of the hydraulic pump energy is stored in the underground as mechanical energy due to ballooning of the fracture and due to elastic compression of water and rock surrounding the fracture.

The efficiency of energy storage can be improved significantly by implementing a horizontal well design with multiple fractures. This is shown based on model calculations. If water is injected in parallel artificial fractures the static pressure level between the fractures increases, water losses into the far field decrease and the back-production is improved. Furthermore, overpressure reservoirs and low permeable rock are favourable. Thereby the injected water remains in the closed surrounding of the fractures and the complete artesian back production at high pressure is ensured. Overpressure formations seem to be widespread in the deep underground of sedimentary basins as in the North German Basin.

Mechanical energy storage in the deep underground should be combined with geothermal heat extraction. At the test site Horstberg thermal water at a temperature of more than 100°C was produced in cyclic tests. Numeric modelling results suggest that a thermal power of appr. 1 MW can be extracted by cyclic production in the long term via the large fracture in Horstberg.

For the realisation of this storage concept several challenges have to be met. Besides the creation of good underground conditions, the handling of the produced saline water and its reinjection without scaling or corrosion are serious issues. On the other hand the storage of surplus power as mechanical energy in the underground and its retransformation to power can be more efficient than the conversion into hydrogen and less expensive than battery storage. The reuse of abundant deep wells for energy storage could be a cost-efficient starting point for this concept.

How to cite: Tischner, T. and Jung, R.: Storage of mechanical energy and heat extraction via artificial fractures in low permeable rock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21854, https://doi.org/10.5194/egusphere-egu24-21854, 2024.

EGU24-4423 | Orals | ERE5.2 | Highlight

A comprehensive petrophysical databank of crystalline reservoirs for assessing deep geothermal exploration targets in Finland and abroad 

Michael Heap, Alan Bischoff, Toni Luoto, Thierry Reuschlé, Satu Vuoriainen, Marion Spitz, and Marianne Leon-Stackow

Context

As part of the Deep-HEAT-Flows project (https://deep-heat-flows.voog.com), we have collected a comprehensive geological and petrophysical dataset of crystalline reservoirs formed within fault zones and at the contact of igneous intrusions across Finland, evaluating their potential as deep geothermal reservoirs. Our investigations involve a range of laboratory-based experiments encompassing measurements of rock density, elastic wave velocity, electric resistivity, porosity, and permeability under various confining pressures, and the thermal properties of 120+ samples collected from diverse crystalline rocks. Additionally, we apply mineral and pore space caracterization techniques including petrography, micro-XRF spectrometry, SEM-EDS, hyperspectral imaging, and CT scans to understand the processes that control crystalline reservoir formation.

Findings

Our findings highlight a common trend among various petrophysiscal parameters: rock density, resistivity, elastic wave velocity, thermal conductivity, and heat capacity typically reduce as the porosity increases, a characteristic observed across many sedimentary and volcanic rocks. Reservoir quality is primarily determined by the morphology of the pore network, encompassing fractures and interconnected moldic, sieve, and interparticle pores. The most promising reservoir properties were observed in rocks intersected by regional shear zones and therefore affected by intense brecciation, cataclasis, and hydrothermal alteration, leading to a notable porosity of ~20% and permeability in the order of 10−12 m2 (1 darcy). Moreover, the contact margin of rapakivi intrusions also include fractured and hydrothermally altered rocks that have significantly high porosity and permeability. In detail, rocks dominated by fractures typically have little porosity (<4%) and exhibit extremely high permeability (~10−12 m2) only at low confining pressures, which sharply decreases to ~10−19 m2 as the confining pressure surpasses 20–30 MPa (corresponding to depths around 700–1000 m). From our dataset, only fractures linked to mineral dissolution have the potential to sustain permeability above 10−16 m2 at 50 MPa confining pressure (simulating depths of ~2 km). Conversely, rocks that underwent cataclasis and hydrothermal alteration exhibit comparatively milder permeability reductions, maintaining high values even when subjected to high confining pressures of 50 MPa. Throughout the entire dataset, a consistent observation emerges: mafic minerals are commonly substituted by chlorite and epidote, suggesting hydrothermal alteration processes occurring at relatively high temperatures (200–300 °C).

Implications for geothermal exploration

Exploring deep geothermal resources in crystalline settings offers a promising solution for direct space heating, industrial applications, and electricity generation. However, the typically low porosity and low permeability of crystalline rocks remain a key obstacle in deep geothermal exploration. The identification of hydrothermally altered rocks as potential deep geothermal reservoirs could mark a substantial shift in geothermal exploration within crystalline regions, broadening target prospects beyond the conventional focus on volcanic and rifting areas. Brecciation, cataclasis, fracturing, and mineral dissolution collectively contribute to the creation of exceptional reservoir properties, which have been widely overlooked in deep and ancient (over a billion years) crystalline settings. Our results hold paramount importance for identifying highly productive permeable zones within crystalline settings and also to the advancement of Enhanced Geothermal Systems that could prioritize the creation of more intricate fracture networks through thermal and chemical stimulation.

How to cite: Heap, M., Bischoff, A., Luoto, T., Reuschlé, T., Vuoriainen, S., Spitz, M., and Leon-Stackow, M.: A comprehensive petrophysical databank of crystalline reservoirs for assessing deep geothermal exploration targets in Finland and abroad, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4423, https://doi.org/10.5194/egusphere-egu24-4423, 2024.

EGU24-6192 | ECS | Posters on site | ERE5.2

Structural, petrophysical, and geophysical characterization of a fault zone in southern Finland – application for subsurface fluid flow in granitic settings 

Jon Engström, Alan Bischoff, Evgenii Kortunov, Mira Markovaara-Koivisto, Nikolas Ovaskainen, Nicklas Nordbäck, and Markku Paananen

Southern Finland crystalline basement was formed and modified during the 1.9–1.8 Ga Svecofennian orogeny, which constitutes a portion of the Fennoscandian Shield. The bedrock comprises supracrustal and early to late-orogenic igneous rocks of mafic to felsic compositions and is characterized by an overall high metamorphic grade associated with high-T and low-P conditions. The bedrock was subjected to multiple tectonic events of distributed deformation, first during a compressional stage, then followed by an extensional stage and finally  a transpressional stage.

Hence, the Kopparnäs study site in southern Finland has been subjected to several stages of ductile and brittle deformation. The site has been studied by the Geological Survey of Finland for several years, with special research emphasize on a subvertical E–W orientated multi-core fault zone that intersects granites, amphibolites, and migmatites. A drillhole cuts through this fault zone at 100 m depth. This drillhole has beed studied using downhole instrumentation, such as optical and acoustic imaging and diverse geophysical surveys (fullwave sonic, magnetic susceptibility, gamma density, natural gamma radiation, drillhole caliper and various electrical loggings). In addition, a comprehensive study of the drill core enables detailed geological and petrophysical characterization of the fault architecture, including recognition of fractures, alteration zones, and mineralization across the fault and its host rocks. These studies together with fluid flow measurements with a packer system, enable us to define subsurface properties for this fault zone.

The initial results suggest that faulting strongly impacts the petrophysical characteristics of the rock, typically increasing porosity and reducing bulk density. This change is most likely related to the fracturing at the site being often associated with mineral alteration and dissolution. These events altered and deformed the multiple fault cores in distinctively manner, affecting the subsurface fluid flow which can be observed in fluid chemical composition differences.

These studies are part of the FLOP project (FLOw Pathways within faults and associated fracture systems in crystalline bedrock) and the Deep-HEAT geothermal energy project. 

How to cite: Engström, J., Bischoff, A., Kortunov, E., Markovaara-Koivisto, M., Ovaskainen, N., Nordbäck, N., and Paananen, M.: Structural, petrophysical, and geophysical characterization of a fault zone in southern Finland – application for subsurface fluid flow in granitic settings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6192, https://doi.org/10.5194/egusphere-egu24-6192, 2024.

EGU24-7157 | ECS | Orals | ERE5.2

Reconstructing the geothermal reservoir model and estimating the structural permeability variation in the metamorphic terrane in Ruisui, Taiwan 

Yung-Ching Huang, Jian-Cheng Lee, Gong-Ruei Ho, Chih-Wen Chiang, Yi-Chia Lu, Sheng-Rong Song, Chih-Hao Yang, Chi-Hsuan Chen, and Yue-Gau Chen Chen

    This study identifies the key geothermal features in the metamorphic terrane within the Yuli belt (a metamorphic mélange) in Ruisui, eastern Taiwan, including fault-related pathways for hot fluids, cap rocks, and naturally fractured reservoirs, and builds a structural permeability distribution model. A preliminary geothermal reservoir model is created for a depth of 3 km, by integrating geological field analysis, magnetotelluric (MT) surveys, hot spring geochemistry, and data from 3 exploration wells. The low resistivity zones shown in MT results are beneath a unit of amphibole-albite schist, containing numerous ultra-mafic blocks at different sizes. We tentatively interpret the four MT low-resistivity zones as four possible reservoirs, which are associated with high-density jointed and faulted quartz-mica schists, underneath cap rocks of amphibole-albite schists, which reveal poor development of joints. The geochemical analysis of hot spring water indicates a high concentration of sodium ions, potentially originating from the amphibole-albite schist. We also observe surface exposures where water up to 50-60oC flows up through NW-SE trending sub-vertical faults with the downhole temperature up to 200oC at a depth of 0.9km.

    To determine whether the NW-SE vertical fault zones are suitable for open structures, which appear to be the major geothermal up-flows, we measure the orientation of faults and 3 sets of joints, most of which are sub-vertical in the field. The principal stress orientations are adopted as σ1 vertical, σ2 N120oE, and σ3 N30oE, by combining GPS observation, focal mechanisms of shallow earthquakes, and fault slickenlines measured in exposures. We conduct fault-slip inversion and obtain the stress ratio phi=0.51. Utilizing the Mohr-Coulomb failure criterion coupled with selected parameters, such as in-situ principal stresses, fluid pressures, and rock mechanical properties, our model indicates that steeply-dipping NW-SE trending (N120o-130Eo) joints and faults are mechanically prone to open as fluid infiltrating or injecting during thermal events.

    We furthermore measured the fracture length and density at the aforementioned hot spring exposure where 50-60oC hot fluid flows out from an NW-SE trending sub-vertical fault. The measuring result shows that the density of the fractures (or joints) decreases away from the fault core, thus we anticipate the joints tend to form on the microfractures created by the fault, which explains an increase of the permeability toward the fault. As for estimating the structural permeability along the NW-SE fault and open joints, the fracture aperture is calculated using linear elastic fracture mechanics, and then the permeability is estimated by using the cubic law for fluid flow in rock fractures. By doing so we obtain the structural permeability in the NW-SE fault zone, which exponentially decreases away from the fault core, and the permeability value ranges from 10-10 to 10-13 m2 at a distance of 10 m.

How to cite: Huang, Y.-C., Lee, J.-C., Ho, G.-R., Chiang, C.-W., Lu, Y.-C., Song, S.-R., Yang, C.-H., Chen, C.-H., and Chen, Y.-G. C.: Reconstructing the geothermal reservoir model and estimating the structural permeability variation in the metamorphic terrane in Ruisui, Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7157, https://doi.org/10.5194/egusphere-egu24-7157, 2024.

EGU24-8226 | ECS | Orals | ERE5.2

Fault core structure affects fault slip during fluid injection: insights from laboratory friction experiments 

Stefano Aretusini, Chiara Cornelio, Giuseppe Volpe, Giacomo Pozzi, Elena Spagnuolo, and Massimo Cocco

Natural faults when subjected to stimulation by fluid injection may result in slip acceleration because pore pressure (Pf) increases in the rock volumes inside and surrounding the fault zone leading to reduction of effective normal stress (σn’). Slip mode ranges from aseismic creep to seismic ruptures defining a spectrum of fault-slip behavior. Fault stimulation experiments will be conducted in the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG, Switzerland) to understand fault reactivation processes on a target well-identified fault zone, fully instrumented to monitor deformation and seismicity during both fluid injection and fault reactivation. This is envisioned in the ERC-Synergy FEAR (Fault Activation and Earthquake Rupture) project. In BULGG, the target fault zone has both a sub-centimetric fault core containing fault gouge and granite asperities in contact and other fractures in the surrounding rock volume.  Therefore, it becomes important to define the frictional properties and slip mode of both gouges and bare rock surfaces taking advantage of a laboratory controlled experimental environment.

Fault stimulation by increasing Pf was simulated in laboratory following an injection protocol suitable for the BULGG fluid stimulation. Experiments were performed on the target fault gouge and on bare rock surfaces made of nearby Rotondo Granite. We employed a rotary shear apparatus (SHIVA) allowing the fluid injection under a controlled shear stress. First, we imposed the stresses measured at depth in the underground laboratory, halved due to apparatus limitations: 7.5 MPa σn’, 7.5 MPa confining pressure and 2.5 MPa Pf. Second, we imposed a slip rate of 10-5 m/s for 0.01 m to have a reference texture. Third, we applied a shear stress so that an equivalent slip tendency of 0.35 (equal to the one measured in the target fault) is achieved (ca. 2.7 MPa) keeping it constant. We then increased stepwise the pore fluid pressure by 0.1 MPa every 150 s. After fault slip initiation, the maximum allowed slip velocity was 0.1 m/s. Between each of the experimental stages, permeability and transmissivity were measured with the gradient or Pf oscillations methods.

We show that reactivation occurs at lower Pf in bare rock surfaces (4.7 MPa) with respect to MC fault gouge (6.5 MPa), suggesting that the effective coefficient of friction, the ratio of shear stress and σn’, is larger in gouge (0.58) than in bare rock surfaces (0.49). Moreover, upon the application of last Pf step, reactivation is slower in fault gouge (150 s delay) with respect to bare rock surfaces (10 s delay), consistently with the lower hydraulic transmissivity measured for target fault gouge with respect to bare rock surfaces (i.e., 10-19 vs 10-17 m3). Our experiments also show that creep and dilatancy precede reactivation in fault gouge, whereas reactivation is sudden and not preceded by dilatancy in bare rock surfaces.

We suggest that well-oriented and smooth bare rock surfaces might be easily reactivated similarly to what observed for fault gouge during fluid stimulation. Our data and observations will contribute to shed light on the mechanics of faults and induced earthquakes by fluid stimulation experiments.

How to cite: Aretusini, S., Cornelio, C., Volpe, G., Pozzi, G., Spagnuolo, E., and Cocco, M.: Fault core structure affects fault slip during fluid injection: insights from laboratory friction experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8226, https://doi.org/10.5194/egusphere-egu24-8226, 2024.

EGU24-8619 | ECS | Orals | ERE5.2

Hydraulic Stimulation Experiments in a Decimeter-scale True Triaxial Compressive Apparatus 

Julian Osten, Mohammadreza Jalali, Alexander Cadmus, Leonie Welsing, Tom Schaber, Paul Cook, Yves Guglielmi, Raul Fuentes, and Florian Amann

Geothermal energy is considered a sustainable energy source for the transition to a carbon-neutral economy. In Central Europe, sufficiently hot source rocks are buried deep underground and comprise tight crystalline basement formations. To extract their thermal energy, hydraulic stimulation is used to create efficient heat exchangers in the context of Enhanced Geothermal Systems (EGS). Successful geothermal reservoir initiation requires a broad understanding of the hydro-mechanical coupling in fractured rock masses. For this reason, a decimeter-scale true-triaxial setup has been developed to conduct injection-driven shear tests under various stress conditions.

To gain a deeper insight into the hydro-mechanical processes involved in hydraulic stimulation, a true triaxial compressive apparatus at the decimeter scale is employed. The experimental setup consists of 30 x 30 x 45 cm cuboidal granite specimens, each containing an oblique saw-cut laboratory fracture with different surface properties. The fracture is crossed by two boreholes equipped with packers to isolate a fracture interval. Fluid injection into the isolated intervals follows the typical HTPF (hydraulic testing of pre-existing fractures) scheme, including stepwise pressure increases and decreases. Stress boundary conditions are introduced by three sets of oil-filled flatjacks, contained within a steel frame which allows a more realistic and accurate replication of the stress conditions experienced by geological formations during hydraulic stimulation experiments. Stresses for individual tests are manipulated from hydrostatic to strike-slip conditions to test for different end member states of slip tendency. Fracture and rock deformations are recorded by 16 linear variable differential transformer (LVDT) sensors mounted externally along the edges of the specimen, volume changes in the flatjacks and a newly developed borehole deformation probe (mini-SIMFIP).

How to cite: Osten, J., Jalali, M., Cadmus, A., Welsing, L., Schaber, T., Cook, P., Guglielmi, Y., Fuentes, R., and Amann, F.: Hydraulic Stimulation Experiments in a Decimeter-scale True Triaxial Compressive Apparatus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8619, https://doi.org/10.5194/egusphere-egu24-8619, 2024.

EGU24-9336 | ECS | Orals | ERE5.2

Fractal diffusion analyses of periodic pumping tests 

Victoria Alegria Jimenez Martinez, Yan Cheng, and Jörg Renner

We investigated the usefulness of the fractal diffusion equation, also known as generalized radial flow (GRF) equation, to characterize hydraulic properties and flow dimensions of the subsurface. Unlike other methods for deriving hydraulic properties that require selecting the flow dimension, analyses based on the GRF equation in principle constrain both, flow dimension and hydraulic properties. We utilized the GFR equation to analyze periodic pumping tests carried out in boreholes penetrating gneiss rocks in the research mine Reiche Zeche, Freiberg, Germany. These tests involved one injection borehole, where flow rate and injection pressure were recorded, and four monitoring boreholes, where pressure responses were monitored. Phase-shifts and amplitude ratios were derived through interference analysis, involving a comparison of the periodic signals of injection and monitoring pressure, as well as injectivity analysis, consisting of a comparison of the periodic flow rate and injection pressure. The pumping tests were conducted at three distinct intervals within the injection borehole, isolated by a double-packer probe and selected based on the characteristics of the fractures intersecting the borehole.  One interval contained a natural fracture zone characterized by a high fracture density with a high mean aperture. The others were previously hydraulically stimulated. While one of them had a single pre-existing fracture, the other was entirely intact before the stimulation that led to an induced fracture with feather geometry, as typical for a borehole that does not follow a principal stress axis. Several observations suggest that the gneiss volume is hydraulically heterogeneous: a) the hydraulic properties and flow dimensions vary with pumping period; b) estimated diffusivity values and flow dimensions differ for interference and injectivity analyses; c) discernible differences in diffusivity values and flow dimensions along diverse hydraulic paths, as determined by interference analysis. Furthermore, pressure dependence in hydraulic properties and flow dimensions are observed for all intervals. The hydraulic response of the fault-zone interval exhibits a greater sensitivity to variations in mean pumping pressure than the two stimulated intervals.

How to cite: Jimenez Martinez, V. A., Cheng, Y., and Renner, J.: Fractal diffusion analyses of periodic pumping tests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9336, https://doi.org/10.5194/egusphere-egu24-9336, 2024.

EGU24-9736 | ECS | Posters on site | ERE5.2

Characterization and 3D geometrical modelling of a complex fault zone for earthquake rupture experiments 

Alberto Ceccato, Peter Achtziger-Zupančič, Giacomo Pozzi, Alexis Shakas, Alba Simona Zappone, Daniel Escallon, Marian Hetrich, Mohammadreza Jalali, Xiaodong Ma, Men-Andrin Meier, Julian Osten, Florian Amann, Massimo Cocco, Domenico Giardini, and Stefan Wiemer

Fault zone geological and geometrical complexities are prime parameters playing a fundamental role in controlling the characteristics of both natural and induced seismicity. In the Bedretto tunnel (Switzerland), the Fault Activation and Earthquake Rupture (FEAR) project aims at triggering a Mw = 1 seismic event through fluid injection and stimulation of a natural fault zone situated in a large-scale (> 106 m3) fractured granite reservoir. The limited exposure of the fault zone in the tunnel, however, restricts the possibility to constrain in detail the geometrical and geological characteristics of the experimental target. Therefore, in order to constrain the geological and geometrical characteristics of the target fault zone, we have integrated structural analyses, borehole and core logging, and borehole ground penetrating radar (GPR).

Preliminary field investigations in the tunnel allowed to identify the complex fault structure characteristics, fault rock properties, and slip tendency in the current stress field of the selected fault zone. These results were compared to the structural observations obtained from field surveys and remote sensing, constraining the slip history, and lateral extent of the set of natural fault zones occurring on the surface above the Bedretto tunnel. Indeed, the lateral extent of the selected fault has been confirmed through the logging (optical/acoustic televiewer, fracture intensity, fracture typology) of exploration boreholes and the analyses of the related cores. The comparison between the geological characteristics of fault zones in the cores and the characteristics of the selected fault zone exposed in the tunnel allowed to confirm the occurrence of the same typology of fault zone further away from the exposure in the tunnel. In addition, GPR logging of the exploratory boreholes provided fundamental insights on the lateral continuity of the identified fault zones on the tunnel wall, as well as those identified in the borehole/core logging.

All geological and geometrical information have been integrated into a preliminary 3D geometrical model (in Leapfrog Geo), representing the overall geometry of the selected fault zone. This preliminary geometrical model has been validated against synthetic GPR profiles, computed through GPR forward modelling along the exploration boreholes.

The integrated results define the selected fault zone as a 3-7 m wide zone of higher density (up to 5/m), of variably oriented secondary fractures, and bounded by two main slip surfaces. The slip surfaces are irregularly decorated by phyllosilicate-rich gouge patches, filling the roughness of the fault surface. The lateral extension of each discrete fracture does not exceed 30 m in length, but the overall lateral continuity of the fault zone exceeds several hundreds of meters.

The presented integrated characterization approach allowed us to constrain a geologically-sound, first-order 3D geometrical model of a complex natural fault zone, validated against geophysical forward modelling. These preliminary results have fundamental implications for the expected experimental planning and outcomes, modelling and injection strategies, project logistics, as well as the design and deployment of the monitoring network around the stimulated fault zone.

How to cite: Ceccato, A., Achtziger-Zupančič, P., Pozzi, G., Shakas, A., Zappone, A. S., Escallon, D., Hetrich, M., Jalali, M., Ma, X., Meier, M.-A., Osten, J., Amann, F., Cocco, M., Giardini, D., and Wiemer, S.: Characterization and 3D geometrical modelling of a complex fault zone for earthquake rupture experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9736, https://doi.org/10.5194/egusphere-egu24-9736, 2024.

EGU24-10618 | ECS | Posters on site | ERE5.2

Systematic multi-stage hydraulic stimulation experiments in a hectometer-scale fractured rock volume at the Bedretto Underground Laboratory, Switzerland 

Kai Bröker, Xiaodong Ma, Nima Gholizadeh Doonechaly, Antonio Pio Rinaldi, Anne Obermann, Martina Rosskopf, Marian Hertrich, and Domenico Giardini and the BedrettoLab Team

Interest in engineered geothermal systems (EGS) has grown in the last decade due to their recognition as a low-emission, renewable energy source. EGS reservoirs with sufficiently high temperatures are located at depths of several kilometers, where the permeability of the crystalline basement rocks is insufficient for geothermal energy extraction. Permeability enhancement is accomplished through hydraulic stimulation, either by hydraulic shearing of natural fractures or shear zones, or through hydraulic fracturing of intact rock. The Bedretto Underground Laboratory for Geosciences and Geoenergies (BedrettoLab) in Switzerland serves as an in situ test-bed where hectometer-scale hydraulic stimulation experiments are conducted to better understand the seismo-hydromechanical response of fractured crystalline rock masses (Ma et al. 2022).

The geothermal testbed of the BedrettoLab is located in a 100 m long enlarged section of the Bedretto tunnel in the Swiss Central Alps, with an overburden of more than 1000 m of granite. Several characterization, monitoring, and two stimulation boreholes were drilled. One of the stimulation boreholes (referred to as ST1) is 400 m long, 45°-dipping, and was equipped with a multi-packer system that partitions the borehole into 15 intervals.

In this work, we present the structural and seismo-hydromechanical characterization of eight stimulation intervals closely observed using a dense monitoring network (see Plenkers et al. 2023 for the detailed network layout). We injected relatively small fluid volumes (0.35–14 m3) following a standardized injection protocol to compare the response of the targeted geological structures in each interval. Depending on the transmissivity of the interval, the stimulation was conducted pressure- or flow rate-controlled with several steps at constant pressure/flow rate. Despite the similarly oriented structures in each interval, the observed seismo-hydromechanical behavior is complex and heterogeneous. The detected seismicity follows multiple steeply-dipping and NE-SW striking planes (Obermann et al. 2024), which coincides with the direction of known pre-existing fault structures obtained from the geological characterization. In most intervals, a clear bilinear behavior on the pressure vs. flow rate plot marks a strong increase in injectivity above a certain reactivation pressure. Analysis of these reactivation pressures in comparison with the stress field, fracture and seismic cloud orientations implies that the stimulation mechanism is hydraulic shearing of the fractures rather than elastic opening (also known as hydraulic jacking).

References:

Ma, X., Hertrich, M., Amann, F., Bröker, K., Gholizadeh Doonechaly, N., et al. (2022). Multi-disciplinary characterizations of the BedrettoLab -- a new underground geoscience research facility. Solid Earth, 13(2), 301–322. https://doi.org/10.5194/se-13-301-2022

Obermann, A., et al. (2024). Picoseismic response of hectometer-scale fracture systems to stimulation with cm-scale resolution under the Swiss Alps, in the Bedretto Underground laboratory. In preparation for JGR: Solid Earth.

Plenkers, K., Reinicke, A., Obermann, A., Gholizadeh Doonechaly, N., Krietsch, H., et al. (2023). Multi-Disciplinary Monitoring Networks for Mesoscale Underground Experiments: Advances in the Bedretto Reservoir Project. Sensors, 23(6), 3315. https://doi.org/10.3390/s23063315

How to cite: Bröker, K., Ma, X., Gholizadeh Doonechaly, N., Rinaldi, A. P., Obermann, A., Rosskopf, M., Hertrich, M., and Giardini, D. and the BedrettoLab Team: Systematic multi-stage hydraulic stimulation experiments in a hectometer-scale fractured rock volume at the Bedretto Underground Laboratory, Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10618, https://doi.org/10.5194/egusphere-egu24-10618, 2024.

EGU24-11634 | ECS | Posters on site | ERE5.2

Fault Nucleation and Reactivation in Displaced Fault Systems: An Experimental Study 

Milad Naderloo, Jan Dirk Jansen, and Auke Barnhoorn

Understanding fault slip nucleation within the reservoir interval and its propagation beyond the reservoir is essential. Analytical and numerical studies have shown that, depending on the type of operation (injection/depletion), fault slip can nucleate at external or inner corners along the displaced fault system, driven by positive peak shear stresses. In the case of depletion, slip patches gradually start at the inner corners and grow towards the inner part of the reservoir, merging with further depletion. Conversely, injection or increased pore pressure leads to slip patches at external corners, potentially propagating beyond the reservoir into the overburden and underburden. We conducted triaxial experiments on small-scale (mm scale) cylindrical samples containing an entirely displaced vertical fault to investigate fault reactivation and slip nucleation in such settings. Two types of stress paths, monotonic and cyclic, were applied to examine the effects of stress patterns on slip nucleation. For this purpose, we utilized strain gauges to measure differential compaction along the displaced fault directly on the small-scale samples. Direct measurements with a strain gauge network adjacent to the displaced fault system during the monotonic test revealed that differential compaction intensifies from the top of the sample towards the internal corner at the center of the fault where different layers are juxtaposed vertically, indicating a variation in the stress field surrounding the fault plane. Furthermore, results from the cyclic test showed that the differential compaction increases with an increasing number of cycles. Our direct measurements near the displaced fault plane confirm/match the anomalies and peaks in stress observed in previous numerical and analytical studies.

How to cite: Naderloo, M., Jansen, J. D., and Barnhoorn, A.: Fault Nucleation and Reactivation in Displaced Fault Systems: An Experimental Study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11634, https://doi.org/10.5194/egusphere-egu24-11634, 2024.

EGU24-11723 | Orals | ERE5.2

Spatio-temporal evolution of permeability during quasi-static fault growth in granite 

Nicolas Brantut, Frans Aben, and Ado Farsi

In tight crystalline basement rocks such as granite, faults are known to be substantially more hydraulically conductive than the rock matrix. However, most of our knowledge of rock permeability in the laboratory and in the field relies on indirect inference, static measurements, or before/after datasets, and the spatio-temporal evolution of the permeability field during faulting remains unknown. Specifically, we would like to determine at which stage of the faulting process does permeability change most, and the degree of permeability heterogeneity along shear faults.

We conducted a series of triaxial deformation experiments in initially intact Westerly granite, where faulting was stabilised by monitoring the acoustic emission rate. At many stages from pre- to post-failure states, we paused deformation and imposed macroscopic fluid flow to characterise the overall permeability of the material. In addition, we measured the pore pressure distribution in the sample, and estimated apparent permeability at different locations along the fault, from the intact ligaments to damaged regions. We monitored the propagation of the macroscopic shear fault by locating acoustic emissions.

We find that average permeability increases dramatically (by around 3 orders of magnitude) near the peak stress, where the fault (as seen by acoustic emission locations) is not yet through-going. Post-peak evolution shows a more gradual increase in overall permeability, with local heterogeneities remaining along the fault, primarily controlled by small-scale fault geometry and the existence of undamaged regions as imaged by acoustic emission locations.

We conclude that permeability change and fluid flow focussing occurs at very early stages of faulting, and do not require substantial slip. Our results highlight the key role of fault geometry in the fine-scale permeability structure of basement rocks.

 

How to cite: Brantut, N., Aben, F., and Farsi, A.: Spatio-temporal evolution of permeability during quasi-static fault growth in granite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11723, https://doi.org/10.5194/egusphere-egu24-11723, 2024.

EGU24-11990 | Posters on site | ERE5.2

Microstructural Characterization of Fault Rocks from the Groningen Gas Field 

Ernst Willingshofer, Job Arts, Dallyn Rodrigues, Fadi Nader, Martyn Drury, Liviu Matenco, and Andre Niemeijer

Human activities in the subsurface such as geothermal energy production, CO2- and hydrogen storage, and gas extraction can affect the regional stress field and lead to induced seismicity. Gas production from the Groningen gas field in the northeast of the Netherlands has led to more than 300 shallow earthquakes with local magnitudes ML > 1.5 and up to a maximum magnitude of ML 3.6, resulting in substantial damage to buildings. Recent earthquake localization studies show that seismicity dominantly occurs on complex normal fault systems, at the depth of the Permian (Rotliegend) reservoir. These faults were formed during multiple tectonic phases from the Late Paleozoic to Early Cenozoic and may comprise breccias, cataclasites, fault gouges and clay smears. The fault strength and slip behaviour are controlled by its composition and microstructural state (porosity, grain size and shape, and presence of foliation within the fault core). Fluid-rock interactions and diagenetic processes during and after fault activity may have altered these characteristics and, hence, the strength and slip behaviour of the fault. Knowledge on the state and composition is thus required to reliably predict the maximum stress drop and seismic energy release upon fault reactivation. However, such knowledge is still lacking at present day.

With this study, we aim at characterizing the microstructures of fault gouges in the Groningen faults. We assess the mineralogy, porosity, and grain size distribution of natural samples from faulted core samples derived from the Groningen gas field. Well-log data is presented to show the representativeness of these samples in the larger context of the gas field. The observations on natural microstructures are then used to define simplified geometrical representations or scenarios that can be used as input for microphysical models. Microstructural characterization involves optical microscopy for quantitative petrography of both bulk rock and selected regions of interest (ROI) within the fault zone. Scanning Electron Microscopy (SEM) with Backscattered Electron (BSE), Cathodoluminescence (CL), and Energy-Dispersive X-ray Spectroscopy (EDX) is employed to analyse porosity, grain size, shape, and mineralogy of faulted regions.

Preliminary results show that the compositions of fault rocks differ from the host rock and that along-fault variability in mineralogy, cementation, and grain size are important to consider. We distinguish between four main types of fault gouges in the Groningen Rotliegend, based on their microstructural characteristics: (1) gouges consisting of quartz and feldspar grains embedded in a very fine clay matrix, (2) very fine-grained quartz-rich gouges, (3) quartz-cemented gouges, and (4) anhydrite-cemented gouges. We expect that induced fault movement in the first two gouges occurs by reactivation of the earlier produced fault gouges. Since quartz and anhydrite cementation is concentrated in the faults, reactivation of the latter two presumably occurs by cataclastic processes and gouge formation from the adjacent bulk rock rather than the cemented gouge. This suggests that a well constrained fault diagenetic history is required to infer which components of the fault material governs its frictional behaviour and hence the related seismic hazards. 

How to cite: Willingshofer, E., Arts, J., Rodrigues, D., Nader, F., Drury, M., Matenco, L., and Niemeijer, A.: Microstructural Characterization of Fault Rocks from the Groningen Gas Field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11990, https://doi.org/10.5194/egusphere-egu24-11990, 2024.

EGU24-13098 | Orals | ERE5.2

Heat Sensitive Epoxy Foam for Permeability Alteration in Fractured Geothermal Fields  

Dani Or, Rishi Parashar, Ying Yang, Manish Bishwokarma, and Satish Karra

Geothermal energy plays a growing role in the transition to renewable and carbon free energy sources. A challenge for many geothermal fields is how to enhance water-rock heat exchange either by creation of new fractures, or by blocking short-circuiting large conduits. Here we report a novel approach for blocking large conduits (faults and large fractures) using heat sensitive epoxy resin foam designed to be transported as discrete resin droplets to specific regions that are then activated (foamed and cure) in-situ at targeted temperatures. In contrast with alternative methods for reducing geothermal rock permeability such as silicate gels or heat responsive polymer microbeads targeting small aperture fractures < 0.1 mm, the epoxy foam can reduce the permeability of fractures with apertures up to several millimeters. Results from laboratory 2-D glass fracture model provide insights by visualizing the transport phase and subsequent temperature-sensitive foaming and curing transformations with associated flow pathway blocking. Modeling results for transport and foaming in simple fracture networks considering rheological properties and foaming (volume expansion) behavior will be presented. On going activities of rheological resin characterization; tuning of the foaming-curing to different temperature ranges; and consideration of resin dispersion using small droplets for enhanced transport will be discussed.  

How to cite: Or, D., Parashar, R., Yang, Y., Bishwokarma, M., and Karra, S.: Heat Sensitive Epoxy Foam for Permeability Alteration in Fractured Geothermal Fields , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13098, https://doi.org/10.5194/egusphere-egu24-13098, 2024.

EGU24-15749 | ECS | Posters on site | ERE5.2

Exploring the Hydro-Mechanical Behavior of Fractures Utilizing the mini-SIMFIP Probe 

Tom Schaber, Julian Osten, Mohammadreza Jalali, Alexander Cadmus, Leonie Welsing, Paul Cook, Yves Guglielmi, Raul Fuentes, and Florian Amann

The SIMFIP (Step-rate Injection Method for Fracture In-situ Properties) probe is a downhole displacement tool designed to measure injection-driven fracture displacement in an isolated borehole interval in three dimensions. The resulting displacement and interval pressure data can be used to estimate fracture characteristics such as fracture stiffnesses, strength and hydraulic properties from borehole measurements. SIMFIP results have also been successfully implemented in a stress inversion routine that allows the calculation of the full stress tensor from a single measurement.

As part of the SPINE (Stress Profiling IN Enhanced geothermal systems) project, a laboratory-scale deformation tool, the mini-SIMFIP probe has been developed. The probe, with a diameter of 20 mm and a length of 65 mm, can be installed in laboratory to study the 3D deformation of intact rock and fractures in different type of rocks. Preliminary tests were conducted in a decimeter-scale true triaxial test apparatus containing a cuboid granite sample with an oblique saw-cut laboratory fracture. Two boreholes crossing the fracture can be isolated and equipped with the mini-SIMFIP probe. Fluid injection into the isolated interval opens the fracture or induces hydraulic shearing under anisotropic stress conditions. The resulting dataset can be used to quantify measurement uncertainties associated with the field SIMFIP protocol, to benchmark stress inversion protocols against known stress boundary conditions, and gain better insight into hydro-mechanically coupled processes.

How to cite: Schaber, T., Osten, J., Jalali, M., Cadmus, A., Welsing, L., Cook, P., Guglielmi, Y., Fuentes, R., and Amann, F.: Exploring the Hydro-Mechanical Behavior of Fractures Utilizing the mini-SIMFIP Probe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15749, https://doi.org/10.5194/egusphere-egu24-15749, 2024.

Bentheim sandstone is regarded as a conventional georeservoir rock even at great depth, due to its mineral composition, homogeneity, micro- and macrostructure. Therefore it has been extensively tested for a variety of applications to understand its physical and mechanical properties under changing environmental conditions.

A recent study has shown how the simultaneous change of pressure, temperature and pore pressure, therefore recreating environmental conditions at selected depths, affects the evolution of permeability at depths, both when the rock is buried and when the rock is exhumed. The interaction between those variables has a complex effect on the permeability of Bentheim Sandstone, which could not have been identified by assessing individually the role of a variable. These results show that the permeability of such rock could be overestimated with classical studies and highlight the importance of investigating rock mechanical and hydraulic properties at georeservoir conditions. These experiments have been performed on intact samples.

However, rocks at depth contain fractures and faults, which may alter the interconnectivity of the pore space, hence the permeability of the rock itself. The deformation and failure of Bentheim Sandstone at high strain resulted in permeability loss due to the formation of comminuted material and grain crushing which lowered the pore space interconnectivity. No fractured sample has been tested under simultaneously changing environmental conditions.

To fill this gap, we replicate the experimental procedure used to test intact samples of Bentheim sandstone, both under simultaneously changing conditions and under a sequential variation of different variables, after the sample has been brought to failure. Our goal is to understand the importance of fractures on the permeability evolution at different simulated depths.

How to cite: Fazio, M. and Sauter, M.:  Permeability evolution of a fractured, porous and permeable sandstone at simulated georeservoir conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18390, https://doi.org/10.5194/egusphere-egu24-18390, 2024.

EGU24-18458 | ECS | Posters on site | ERE5.2

Variations in fracture distribution across Northern Bavaria – Towards large-scale geothermal fracture models 

Ruaridh Smith, Rahul Prabhakaran, Fabian Jakob, and Daniel Koehn

Natural faults and fractures form a critical component of fluid flow in low permeable reservoirs such as tight carbonates for a wide variety of applications including geothermal energy extraction. Fractured systems often control permeability in these reservoirs at the first order where properties of these networks are defined by fracture orientation, intensity, aperture, and connectivity. Accurately quantifying these network properties is vital in generating representations of the fracture networks at reservoir depth.

In regions with limited subsurface data (borehole and seismic), field data and outcrop analogues become an important source for characterising the fracture networks for modelling reservoirs at depth. Outcrops can be used to define several properties of the networks and information on the variation in the fracture distribution across defined areas.

The Franconian Basin is a major tectonic structure in Northern Bavaria containing Mesozoic sediments up to 3500m thick. It is a relatively under-researched region where limited subsurface data is available in comparison to the south in the Molasse Basin where geothermal exploration and production is well established with extensive subsurface datasets widely distributed. Increased geothermal gradients have been identified in Northern Bavaria, including surrounding the major urban areas presenting an opportunity to improve the understanding of the geothermal potential of the region. Several of the identified reservoir units in this region are primarily composed of low permeable carbonates where faults and fractures control primary reservoir flow. These units are also present as outcrop analogues in the Franconian Alb which can be utilised for surface fracture characterisation.

We present results analysing the variations in the fault and fracture systems from across the region captured from 1D measurements and 2D and 3D imaging of quarry and cave outcrops. Using these results, stochastic fracture models of the parts of the region can be generated, providing realisations of the fracture networks which can contribute to assessing the permeability and geothermal potential of the reservoirs in Northern Bavaria.

How to cite: Smith, R., Prabhakaran, R., Jakob, F., and Koehn, D.: Variations in fracture distribution across Northern Bavaria – Towards large-scale geothermal fracture models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18458, https://doi.org/10.5194/egusphere-egu24-18458, 2024.

EGU24-19263 | ECS | Orals | ERE5.2

The evolution of crack transmissivity under normal and shear stress before and after slip 

Lining Yang, Julian Mecklenburgh, and Ernest Rutter

Understanding the flow of fluids in the subsurface is of vital importance to geo-energy exploitation and disposal of waste fluids. In most situations, individual cracks can be more effective for fluid transport than fluids flowing through the porous matrix of the rock. The enhancement of a single crack in a low permeable rock can be over 1000 times. However, for both porous matrix flow and crack flow, the bulk permeability and crack transmissivity are all affected by the stress state in the lithosphere.

This study aims to investigate the influence of the Terzaghi effective normal and shear stress on the transmissivity of cleavage cracks under upper crustal conditions. Penrhyn slate was selected as samples for the experimental study because of its low porosity (<1%), permeability and slaty cleavage. The matrix permeability of Penrhyn slate is very low, ranging from 10-20 to 10-22 m2 when the effective pressure is in the range of 10 to 53 MPa measured by the oscillating pore pressure method (OPPM). The crack transmissivity ranged from 10-18 to 10-23 m3 when the effective pressure changed from 10 to 280 MPa. The experimental results show that the evolution of crack transmissivity of a single fracture under several cycles of pressurization and depressurization is similar to the trend found in permeability. The first application of the normal stress on fracture surfaces always produces a nonrecoverable loss in crack transmissivity. In the subsequent pressurization and depressurization, partially recoverable variations in transmissivity were observed, suggesting a linear elastic behaviour of crack closure. The highest peak effective pressure attained in the stress history affects the extent of subsequent recoverable crack transmissivity. When the fracture surface is subjected to a new higher peak stress, the crack transmissivity will no longer recover to its former low level but to a lower level, indicating a permanent transmissivity loss. Thus, the transmissivity has a memory of the previous maximum stress the fractured rock was subjected to.

The influence of shear stress on crack transmissivity was studied in Solnhofen limestone and Carrara marble samples with saw-cut ground smooth fractures and compared with the rough cleaved fractures of Penrhyn slate. The influence of shear stress was studied in two situations: (a) the stable (no-slip) condition at shear stress less than needed to promote slip on fracture (b) at shear stresses high enough to yield slip on the fractures. In situation (a), the cyclic increase and decrease of shear stress led to a continuous decrease in crack transmissivity. The magnitudes of this decrease in crack transmissivity decrease with more cycling. The transmissivity tended to decrease to a lowest value eventually but this lowest value can be regenerated by slip on the fracture. In situation (b), a single slip can decrease crack transmissivity. The decrease in crack transmissivity can be attributed to the formation and smearing of frictional wear products or gouges. Under the progressive compaction, there exists a lowest level of crack transmissivity which is independent of the normal stress.

How to cite: Yang, L., Mecklenburgh, J., and Rutter, E.: The evolution of crack transmissivity under normal and shear stress before and after slip, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19263, https://doi.org/10.5194/egusphere-egu24-19263, 2024.

EGU24-19710 | Orals | ERE5.2

Evolution of Microcracks in Damaged Natural Salt: Insights from 4D imaging 

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

Rocksalt formations are critical candidates for storing natural gas, hydrogen, compressed air energy, and radioactive waste. While pure, undisturbed rock salt deposits exhibit low porosity and impermeability when buried deeply, excavation leads to near-field microcracking and dilatancy in the salt, increasing porosity and permeability. Over time, the connectivity of brine- or water-vapor-filled microcrack networks in deformation-damaged salt is expected to decrease, partly due to dissolution-precipitation healing. In this study, we employ 4D (time-resolved 3D) microtomography to investigate the long-term evolution of dilated grain boundary and microcrack networks developed in deformation-damaged natural salt through brine-assisted processes. Our findings reveal substantial microstructural modification and healing occurring over periods ranging from days to a few months. Cracks and dilated grain boundaries undergo crystallographic faceting, necking, and migration, effectively "recrystallizing" the material and resulting in increased tortuosity and decreased connectivity of the crack network. Understanding the complex interplay between microcracking, healing, and permeability changes in deformation-damaged rock salt is of utmost importance for optimizing storage and disposal applications in geomechanics and physical chemistry. Our research contributes valuable insights to this field and informs the sustainable development and management of rock salt formations for diverse energy storage and waste management needs.

How to cite: Ji, Y., Spiers, C., Hangx, S., de Bresser, H., and Drury, M.: Evolution of Microcracks in Damaged Natural Salt: Insights from 4D imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19710, https://doi.org/10.5194/egusphere-egu24-19710, 2024.

EGU24-20381 | ECS | Posters on site | ERE5.2

Physical and mechanical characterization of veined rocks: Implications to a porphyry model 

Franco Robbiano, Luis Felipe Orellana, and Marie Violay

The brittle-ductile transition is an important mechanical shift within the Earth's lithosphere and, as a crucial interface between ascending hot magma and colder host rock, plays a fundamental role in fluid migration within hydrothermal systems. Traditionally assumed to occur at temperatures between 350 °C and 400 °C, recent studies challenge this assumption, revealing a temperature transition range dependent on minerals. Experimental and numerical investigations highlight significant variability, ranging from 260 °C in wet quartz to 700 °C for dry orthopyroxene within homogeneous mineral compositions.

This study delves into the complexities of this rheological barrier in the El Teniente Mafic Complex in Chile (currently a copper mine and formerly a hydrothermal system at the BDT), unraveling its impact on the migration of magmatic fluids. Building on previous research suggesting a self-sustaining mechanism that facilitates fluid movement over the brittle-ductile transition through overpressure-permeability waves and the formation of a dense, multi-episode vein network, our focus is on understanding deformation mechanisms and the localization of deformation and permeability at the BDT. Heat transfer models propose a dual paradigm of conduction and convection, adding to the complexity.

To address these challenges, we conducted a comprehensive series of physical and mechanical measurements on 34 cylindrical samples from the El Teniente Mafic Complex. This included analyses of density, porosity, elastic wave characteristics, and electrical conductivity under variable water conductivities. Elastic wave measurements were performed using 2.25 MHz transducers on both dry and saturated samples. Permeabilities were determined by the pulse decay technique for compact rocks, complemented by triaxial tests and local strain measurement using strain gauges, along with acoustic emission measurements on dry samples subjected to confinements similar to those near the mine.

Our results highlight consistently low porosity (below 1%) in the samples, with electrical conductivity, permeability, and strength controlled by veins. Particularly, at lower salinities, the metallic particle content and the orientation of the vein with respect to the loading axis significantly influence electrical conductivity and phase. At higher water conductivities, behavior is governed by connected porosity. Furthermore, favorably oriented veins emerge as crucial controllers of both permeability and mechanical resistance.

These observations align with a convection heat flow model in a porphyry system, providing significant insights into the complex interaction between rock and vein properties. The study uniquely focuses on fossil high enthalpy systems, shedding light on their complex behavior. Additionally, the article discusses constraints on model variables, fostering a comprehensive understanding of the brittle-ductile transition in magmatic-hydrothermal systems.

How to cite: Robbiano, F., Orellana, L. F., and Violay, M.: Physical and mechanical characterization of veined rocks: Implications to a porphyry model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20381, https://doi.org/10.5194/egusphere-egu24-20381, 2024.

EGU24-20658 | ECS | Posters on site | ERE5.2

Impact of Capillary Number, Fluid Viscosity Ratio, and Fracture Closure on Two-Phase Flow Regimes in Geological Fractures: An Experimental Study 

Amin Rezaei, Francesco Gomez, Oshri Borgman, Insa Neuweiler, and Yves Meheust

Accurately predicting fluid-fluid interface displacement in fractured reservoirs is paramount for optimizing subsurface operations, particularly in the context of enhanced oil recovery and geological carbon sequestration (GCS). However, a comprehensive understanding of two-phase flow behavior in fractures, including the impact of fracture closure, fluid viscosity ratio, and capillary number, is yet to be achieved. To address this challenge, we have developed an analog experimental setup to investigate the intricate relationship between fracture surface roughness and fluid-fluid interface displacement. Our experimental setup features a transparent fracture flow cell with self-affine rough-walled surfaces that are matched to each other above a chosen length scale (denoted below as the correlation length) and a precisely controlled mean aperture. Realistic synthetic fracture geometries were generated numerically. They are characterized by their Hurst exponent, fracture closure, and correlation length. High-speed imaging captures the dynamic spatial distribution of fluid phases within the fracture plane during drainage processes in a given fracture geometry. The mean aperture can be varied between experiments for a given geometry of the fracture walls. We investigate a comprehensive range of capillary numbers, spanning both viscous and capillary-dominated regimes, vary viscosity ratios, and characterize the resulting displacement regimes. Our results reveal a profound impact of fracture closure and correlation length on trapping efficacy, particularly in the capillary-dominated regime. These findings can be interpreted in terms of residual trapping of CO2 during GCS in fractured reservoirs.

How to cite: Rezaei, A., Gomez, F., Borgman, O., Neuweiler, I., and Meheust, Y.: Impact of Capillary Number, Fluid Viscosity Ratio, and Fracture Closure on Two-Phase Flow Regimes in Geological Fractures: An Experimental Study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20658, https://doi.org/10.5194/egusphere-egu24-20658, 2024.

EGU24-22156 | ECS | Posters on site | ERE5.2

FracAbility: A python toolbox for survival analysis in fractured rock systems 

Gabriele Benedetti, Stefano Casiraghi, Andrea Bistacchi, and Daniela Bertacchi

When analysing fractured rock outcrops, the fracture network's topology and length statistics are of fundamental importance. Past literature focused on adopting a non-parametric approach for the unbiased estimation of fracture length data mean, and with some additional steps, the variance of a population. However, technology improved, and necessities shifted. Now it is possible to quickly obtain dense length datasets with thousands of measurements and the emergence of stochastic DFNs increased the demand for parametric solutions to correctly fit several types of distributions. These conditions highlighted an absence of works on these topics. Of particular interest is the right censoring bias effect of the interpretational boundary on the fracture length statistics. We tackle this problem by applying survival analysis techniques, a branch of statistics that includes methods for modelling time to event data and correctly estimating the model’s parameters with data affected by censoring. Synthetic testing has been carried out, showing a reliable estimate of the distribution parameters with up to 80% of the total measurements being censored. Moreover, it is shown that the correction is independent from the orientation of the fracture set or boundary geometry. We propose FracAbility, a new open-source Python package capable to both analyse the topology of fracture networks and, by using the latest SciPy version, correctly fit different parametrical distributions on length data with right censored measurements. The library and the proposed approach have been applied to real world data, successfully correcting length distributions affected by censoring.

How to cite: Benedetti, G., Casiraghi, S., Bistacchi, A., and Bertacchi, D.: FracAbility: A python toolbox for survival analysis in fractured rock systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22156, https://doi.org/10.5194/egusphere-egu24-22156, 2024.

EGU24-2591 | Orals | ERE5.4

SRIMA: A fast tool to assess seismicity and seal integrity related to fluid injection. 

Peter Fokker, Loes Buijze, Maarten Pluymaekers, Chris Maaijwee, Harmen Mijnlieff, Job Mos, Bouko Vogelaar, Sjoukje de Vries, and Mark Vrijlandt

The safe and effective deployment of geothermal energy and storage of carbon dioxide requires an assessment of potential induced seismicity and fracturing through the seal above the reservoir. To aid such assessment we have built the SRIMA tool (Seal and Reservoir Integrity through Mechanical Analysis) and we have made it available online. The tool can be used in the Standard extended Seismic Hazard Analysis, which is part of the seismic hazard and risk assessment for geothermal projects in the Netherlands. SRIMA is a fast semi-analytical tool that provides a scenario-based analysis of pressure and temperature changes around an injection well, the resulting stress changes on nearby faults, reactivated fault area, the maximum credible earthquake magnitude, the resulting PGV distribution and an estimate of damage. SRIMA also computes the potential for development of tensile fracture in the seal and base. SRIMA has been designed to give first-order estimates of these results. The speed of the calculations facilitate them to be performed in a stochastic framework, which allows the assessment of failure probabilities.

 

SRIMA is based on semi-analytical expressions for the fast calculation of temperatures, pressures, and induced poro-elastic and thermo-elastic stresses due to the injection of cold fluid. The expressions for flow and induced stresses have been developed for a homogeneous, isotropic layer cake model under radial symmetry. In the injection layer the flow is assumed to be fully developed and temperature transfer is in an advective way. In the bounding seal and base layers, the pressure and temperature dynamics are assumed diffusive. The derived expressions capture the first-order characteristics of the pressure, temperature and stress changes. Validation of the expressions has been achieved through comparison with finite-difference and finite-element codes for temperature, pressure, and stress changes around an injection well. A fault without offset cutting through the seal, reservoir, and base can be specified within the model space. Poro-elastic and thermo-elastic stress changes are transformed to fault stresses and fault criticality. The fault area over which stresses are critical (i.e. fault reactivation occurs) is used to estimate the magnitude of the largest credible earthquake for each model scenario, assuming that the entire reactivated fault area participates in a single event, slip cannot propagate beyond the reactivated area, and all assumed slip over the fault area is seismic slip. An ensemble of magnitudes is converted to exceedance curves of peak ground velocities (PGV), using nationwide developed Ground Motion Prediction Equations. The resulting PGV distribution as a function of epicentral distance serves as input for calculating the probability of exceeding Damage State 1 using empirical fragility functions for unreinforced masonry buildings. This contribution will summarize details and assumptions behind each step.

How to cite: Fokker, P., Buijze, L., Pluymaekers, M., Maaijwee, C., Mijnlieff, H., Mos, J., Vogelaar, B., de Vries, S., and Vrijlandt, M.: SRIMA: A fast tool to assess seismicity and seal integrity related to fluid injection., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2591, https://doi.org/10.5194/egusphere-egu24-2591, 2024.

EGU24-2963 | ECS | Posters on site | ERE5.4

Intense fluid overpressure in the eastern slope of the Yinggehai Basin, South China Sea 

Baibing Yang, Qingfeng Meng, and Fang Hao

The gas-bearing Yinggehai Basin in the northern South China Sea is characterized by high pressure and temperature conditions. The Miocene strata in the eastern slope exhibit intense overpressure with a pressure coefficient exceeding 2.2. Understanding the characteristics of overpressure and clarifying its causes are very important for natural gas exploration and development in reservoirs with intense overpressure. This study identifies and characterizes the pressure structure in the eastern slope of Yinggehai Basin by utilizing formation pressure data from formation tests (MDT) and drill pipe tests (DST) in combination with conventional logging data (acoustic wave, density, and resistivity). The pressure distribution exhibits a distinct three-stage ladder structure. Overpressure initiates in the Lower Pliocene Yinggehai Formation, with a pressure coefficient of 1.2. The formation pressure increases sharply in the underlying Upper Miocene strata (1st member of the Huangliu Formation), with a pressure coefficient ranging from 1.4 to 1.8. The pressure coefficient increases to between 2.1 and 2.3 in the 2nd member of the Huangliu Formation.

We utilized the logging curve combination method, Bowers effective stress method, and Bowers acoustic-density crossplot method to differentiate between two types of overpressure origins: loading and unloading type, and further evaluated their contribution rate to overpressure. Loading overpressure primarily accounts for the overpressure observed in the Yinggehai Formation, contributing to pore pressure with a range from 51% to 93%. In contrast, the overpressure in the Huangliu Formation is predominantly of the unloading type, contributing to pore pressure from 35% to 46%. Additionally, we analyzed the genetic mechanism of overpressure, utilizing lithology, subsidence rate, organic matter maturity, and seismic attribute data. We find that the loading overpressure in the Yinggehai Formation is attributed to unbalanced compaction of mudstone due to rapid sedimentation (sedimentation rate > 500m/ Ma). The unloading intense overpressure in the Miocene strata is most likely caused by the vertical transmission of overpressured fluid along faults and fractures. Our findings provide implications for complex pressure structure, overpressure evaluation, and genetic mechanisms in sedimentary basins.

How to cite: Yang, B., Meng, Q., and Hao, F.: Intense fluid overpressure in the eastern slope of the Yinggehai Basin, South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2963, https://doi.org/10.5194/egusphere-egu24-2963, 2024.

In the aggregate quarries in Çiftalan and Ağaçlı (Eyüpsultan, Turkey) regions, grovak-shale type rocks belonging to the Thracian Formation are used as concrete and asphalt aggregates. After crushing, these rocks are classified into 0-5 mm, 5-12 mm and 12-24 mm sizes and marketed as concrete and asphalt aggregates. Aggregates with sizes larger than 5 mm can be used directly in concrete and asphalt applications without any washing process, while aggregates with sizes smaller than 5 mm are called fine aggregates and are marketed after the washing process since the methylene blue value is too high for concrete and aggregate. After the washing process, grains smaller than approximately 100 microns in size (especially clay minerals) are stockpiled in waste sites. Within the scope of this study, it is aimed to produce sinter aggregates with strength that can be used in concrete from these waste materials. It was determined that the waste materials with a grain diameter of less than 100 micron consisted of 28.6% quartz, 21.9% albite, 17% muscovite, 24.9% chlorite and 3.6% calcite minerals. In addition to minerals, 3.4% organic matter was detected. In addition, the main oxide compositions of these wastes were determined, and it was found that 54.51% SiO2, 18.1% Al2O3, 19.66% sum of fluxes (CaO, Na2O, Fe2O3, K2O, MgO) and 5.8% loss on ignition. Within the scope of determining the thermal properties of the wastes, DTA analyzes were carried out and it was determined that two different endothermic reactions took place in the range of 500-600 °C and 700-800 °C, thus dehydroxylation reactions took place in these temperature ranges. In the range of 1000-1100 °C, it was determined that an exothermic reaction, that is, a new phase or several phases were realized. Considering these thermal properties of the wastes, 1100 °C was determined as the sintering temperature. For the sintering process, the samples were first dried at 105 °C and then milled and powdered again. The powdered samples were placed in a metal cell with a diameter of 5 cm and a height of 10 cm and then compressed with a load of 200 kg per cm2. The compressed samples were heated to 1100 °C in a high temperature furnace with a temperature increase of 10 °C per minute and kept at 1100 °C for 30 minutes and then allowed to cool in the furnace. Since the height of these sintered cylindrical specimens was less than 10 cm, the Brazilian test method was used to determine their strength. As a result of the experiment, it was determined that the Brazilian test strengths of 3 different specimens reached 8.8 MPa, 9.6 MPa and 15.7 MPa. Considering the strength values obtained, it was determined that ideal products for concrete and asphalt aggregate can be produced from the dust wastes released in these aggregate quarries. 

How to cite: Avci, E. and Tugrul, A.: Utilization of clay-containing aggregate sludge waste as structural concrete and asphalt aggregate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4757, https://doi.org/10.5194/egusphere-egu24-4757, 2024.

EGU24-5213 | Posters on site | ERE5.4

A  constraint-enhanced machine learning model for predicting hydraulic conductivity of unsaturated bentonite 

Reza Taherdangkoo, Thomas Nagel, and Christoph Butscher

The accurate determination of hydraulic conductivity in unsaturated bentonite is important for the modeling of subsurface thermo-hydro-mechanical and chemical processes. This study introduces a new hybrid approach, employing a constrained CatBoost algorithm coupled with a genetic algorithm for hyperparameter tuning. We benchmarked the effectiveness of the constrained CatBoost model against various data-driven regression models, including lasso, elastic net, polynomial regression, k-nearest neighbors, decision tree, bagging tree, random forest, and standard CatBoost. Our findings demonstrate that the constrained CatBoost model excels in providing accurate estimations of the hydraulic conductivity of compacted bentonite during the wetting phase. The model adequately captures the U-shaped correlation between hydraulic conductivity and suction and reflects the influence of temperature changes on hydraulic conductivity. Furthermore, the bootstrapping analysis, conducted across 800 iterations, confirms the stability and robustness of the constrained CatBoost model. This work provides a reliable tool for predicting hydraulic conductivity in diverse environmental and engineering contexts.

How to cite: Taherdangkoo, R., Nagel, T., and Butscher, C.: A  constraint-enhanced machine learning model for predicting hydraulic conductivity of unsaturated bentonite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5213, https://doi.org/10.5194/egusphere-egu24-5213, 2024.

EGU24-6340 | Posters on site | ERE5.4

Stress transfer and poroelastic mechanisms to elucidate seismicity triggered by reservoirs 

Sandro Andrés, David Santillán, Miguel Ángel Santoyo, and Luis Cueto-Felgueroso

Induced seismicity has attracted increasing research interest in recent times. This phenomenon is generally associated with fluid injection or extraction wells, in energy industry activities such as hydrocarbon extraction/injection, CO2 sequestration, geothermal energy or underground storage of green hydrogen. However, there are other human activities that can induce or trigger seismic events, such as oscillations in the surface water level due to the construction of hydraulic infrastructures.

Surface water level oscillations, whether natural or anthropogenic, can alter the pore pressure regime in the subsurface. Although these alterations usually have a moderate magnitude, they can destabilize faults that were already close to overcoming their slip resistance and eventually trigger an earthquake. On the other hand, the fault slip itself alters the pressure regime due to the undrained response of the porous medium, caused by the sudden deformation of the fault surrounding area. This undrained pressure, which can take up to weeks to dissipate, can alter the stress state of other nearby fractures and trigger new earthquakes or aftershocks.

In this work we present numerical simulations of the underground area around the Itoiz dam (Spain). We simulate the subsurface as a saturated poroelastic medium, with a fully coupled scheme between fluid flow and solid deformation in the porous medium. Through a seismological analysis we start from series of recent earthquakes to locate geological faults. With our numerical model we study how the undrained effect produced by this series of events can destabilize other nearby faults. We also add the effects of the oscillations in the reservoir level following the historical series of the last years.

Our numerical simulations indicate that in the case of the Itoiz dam, the most recent seismic swarm could have been triggered by the stress transfer from the previous events, which, together with the filling of the reservoir, may have destabilized faults that were critically stressed for failure. Our simulations can contribute to explore how the combined effect of the undrained pressure by the fault slip and the oscillations of the reservoir can trigger faults that, due to the natural state of stress, are already close to slip. Also to clarify if the most relevant mechanism is the oscillation of the reservoir level or the undrained pressure trigger, which according to bibliographic analysis can be of the same magnitude. This could apply to other cases of seismicity induced by hydraulic infrastructures or in general by oscillations in the surface water level.

Acknowledgements

This research Project has been funded by the Comunidad de Madrid through the call Research Grants for Young Investigators from Universidad Politécnica de Madrid under grant APOYO-JOVENES-21-6YB2DD-127-N6ZTY3, RSIEIH project, research program V PRICIT.

How to cite: Andrés, S., Santillán, D., Santoyo, M. Á., and Cueto-Felgueroso, L.: Stress transfer and poroelastic mechanisms to elucidate seismicity triggered by reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6340, https://doi.org/10.5194/egusphere-egu24-6340, 2024.

Cobalt is often released into the natural environment through industrial waste from alloying industries and acid mine drainage. Additionally, it exists as a radionuclide (60Co) contributing to high-level radioactive waste. Smectite is a mineral that can be useful for adsorption and isolation of this element. In this investigation, Cheto-type montmorillonite (Cheto-MM), a source clay mineral of The Clay Mineral Society's (CMS) with well-established characteristics, was used as the primary material. The study aimed to assess how cobalt adsorption is affected by the adsorption site in the presence of interlayer water and after subsequent dehydration through heating. Adsorption kinetics and adsorption isotherm models were employed to explore the cobalt adsorption mechanism on Cheto-MM.

Results demonstrated notable variations in adsorption characteristics post-dehydration and subsequent shrinkage. Approximately 38% of cobalt was found to adsorb at the edge of Cheto-MM, while about 62% was adsorbed at the interlayer site, indicating the significant influence of the interlayer on cobalt adsorption in Cheto-MM. Adsorption kinetic models showed that the cobalt adsorption kinetics on Cheto-MM can be explained by a pseudo-second-order model. Moreover, isotherm experimental result was best represented by the Langmuir isotherm adsorption model. This study provides fundamental insights into cobalt adsorption characteristics on montmorillonite, emphasizing distinct adsorption sites. Such findings are instrumental in predicting smectite's adsorption behavior in high-level radioactive waste disposal sites in the future.

How to cite: Kim, Y. and Jang, Y.: Cobalt adsorption on montmorillonite: investigating the influence of dehydration on adsorption properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8326, https://doi.org/10.5194/egusphere-egu24-8326, 2024.

Large scale subsurface gas storage in porous reservoirs can play an important role in the energy transition. Geological storage of carbon dioxide will mitigate CO2 emissions while underground energy storage, for example in the form of hydrogen gas, can be used to balance out the renewable energy production and demand. To investigate the feasibility of large scale subsurface gas storage in porous reservoirs, simulation models are needed that accurately capture the multi-phase flow behaviour in porous rock. Important input parameters for reservoir simulators are relative permeability and capillary pressure which highly depend on the wettability of the system. In this presentation, we will show results of different experimental techniques to characterize and visualize gas transport in porous rock including a novel experimental device to characterize wettability under the impact of different driving forces.

How to cite: Boon, M.: Experimental characterization of multi-phase flow in porous rock relevant for subsurface gas storage, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8330, https://doi.org/10.5194/egusphere-egu24-8330, 2024.

Scaling refers to the accumulation of solid precipitates on the surfaces of pipes, heat exchangers, and other equipment across various industrial processes, notably within geothermal systems. This process can lead to decreased efficiency and increased maintenance needs, highlighting the importance of accurate prediction and control methods.

Hydrogeochemical models tend to overestimate the extent of scalings, especially if the scalings are caused by a disruption of the lime-carbonic acid equilibrium due to degassing in the geothermal fluid. This is because the models are not capable to describe diffusion-limited crystal growth, partial volume effects, and local saturation states adequately. In this study we introduce a novel approach by coupling a multiphase CFD-model (OpenFOAM) for the description of the gas phases in the produced geothermal fluids with PhreeqC to simulate the hydrochemical effects of the stripping of CO2 by the gas phase. This results in a model with high spatial and temporal resolution which allows to quantitatively differentiate between processes in the fluid and the processes taking place at the solid interfaces (pipe walls or matrix).

The code is validated with published experiments in bubble columns. The coupling results in a highly flexible model which can account for different hydrochemical conditions, different matrix, and varying gas composition using a well established thermodynamic database. Transfer to other hydrochemical conditions is therefore facilitated.

How to cite: Omidi, M. and Baumann, T.: Coupling OpenFOAM and PhreeqC to quantify local disruptions of hydrochemical equilibria due to bubble formation and stripping of CO2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8331, https://doi.org/10.5194/egusphere-egu24-8331, 2024.

EGU24-10763 | ECS | Posters on site | ERE5.4

Pore pressure evolution in media with isotropic and anisotropic permeability - analytical and numerical solutions 

Tatia Sharia, Andreas Rietbrock, Birgit Müller, and Thomas Niederhuber

Understanding perturbations caused by underground fluid injection and extraction is essential for steady long-lasting operations of subsurface energy systems (e.g. geothermal systems). The systems are often too complex to obtain precise analytical solutions and computationally expensive to have fine numerical results. Simplified settings give the benefit of understanding the role of driving geological parameters as well as examining the limits of each approach. In this study, we focus on the influence of permeability on pore pressure and present analytical and numerical solutions of spatial and temporal evolutions of pore pressure in an elastic homogeneous porous media with isotropic and anisotropic permeabilities. We use COMSOL Multiphysics to build a 3D finite element model with injection/production wells and investigate where the numerical solutions of the spatially limited volume coincide and diverge from corresponding analytical solutions of pore pressure in infinite media.

How to cite: Sharia, T., Rietbrock, A., Müller, B., and Niederhuber, T.: Pore pressure evolution in media with isotropic and anisotropic permeability - analytical and numerical solutions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10763, https://doi.org/10.5194/egusphere-egu24-10763, 2024.

EGU24-11143 | ECS | Orals | ERE5.4

Estimation of seismic velocity changes in a HT-ATES system using THM modelling 

Clara Fraile, Thomas Kohl, and Emmanuel Gaucher

In Central Europe, a substantial emitter of CO2 in the energy sector corresponds to the thermal energy required for heating and cooling. Seasonal underground heat storage presents a viable option for storing excess heat generated during the summer months for usage in winter, reducing the need for conventional sources of energy. Today, high-temperature aquifer thermal energy storage (HT-ATES) systems are attracting large interest as they represent a sustainable means of meeting heat demand.

In HT-ATES systems, hot water is injected into a reservoir during summer, while exchanged cold water is injected over the winter season. These fluctuations in temperature and pressure have an impact on the geomechanical and thermo-hydraulic properties of both the reservoir and the surrounding layers. Monitoring the changes in the reservoir properties is a critical aspect of running a heat storage system safely and efficiently. We try to determine whether active seismic imaging could be a suitable method to characterize the temporal and spatial evolution of the reservoir.

With view on designing future geophysical assessment and monitoring systems, we first perform thermo-hydro-mechanical (THM) modelling to estimate the variations in the poroelastic properties due to the geothermal processes. Our modeling is based on the characteristics of the DeepStor demonstrator, currently under development in the north of Karlsruhe (Germany), at the Karlsruhe Institute of Technology (KIT). The three layers model includes different mechanical properties with one borehole. The simulation of cyclic hot water injection and production over time allows to quantify its effect on the underground material properties. In addition to assessing the expected operational parameters of the DeepStor demonstrator, we test additional injection schemes with varying underground properties to simulate the different ranges of porosity changes and look at their effects on the elastic properties.

Linking the THM model parameters to seismic sensitive variables such as velocities and impedances, through empirical equations, allow us to determine the conditions under which active seismic surveys could effectively detect these changes. This approach provides a valuable tool for evaluating the potential of active seismic imaging for monitoring HT-ATES systems.

How to cite: Fraile, C., Kohl, T., and Gaucher, E.: Estimation of seismic velocity changes in a HT-ATES system using THM modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11143, https://doi.org/10.5194/egusphere-egu24-11143, 2024.

EGU24-12464 | ECS | Posters on site | ERE5.4

From pore to well - identifying clay mineral distribution in sandstones using SWIR spectroscopy 

Dmitry Bublik, Sebastian Mulder, and Johannes Miocic

Fluid extraction from geological formations for purposes of subsurface utilization leads to a pore pressure drop in reservoirs and potentially to compaction and seismicity. The geomechanical behaviour, and thus production-related compaction, of siliciclastic reservoirs is governed by the composition of reservoir sandstones, which includes porosity, grain size distribution, and detrital and authigenic mineralogy.

One siliciclastic reservoir which is undergoing compaction related to fluid extraction is the Rotliegend of the Groningen gas field. In this research, we investigate potential approaches to upscale the sandstone composition from the micro-scale (thin sections, plugs) to the well and reservoir scale eventually.

Previous research has highlighted that among the petrographic properties, the presence of authigenic clays tends to affect the geomechanical behaviour the most. Intragranular clays can affect the overall stiffness of the individual grains while the presence of the pore-filling clays  and clay rims may result in grain slip or pressure solution in loaded rock samples. In particular, we are defining the fractions of the clay-coating minerals (illite, kaolinite, etc.) and their effect on the inelastic deformation of reservoir sandstone as well as paying close attention to the presence of chlorite as its distribution corresponds to the areas associated with increased subsidence and seismicity.

We employed Short-Wave Infrared (SWIR) spectroscopy, a non-destructive and time-efficient technique, to obtain the mineralogical composition of core slabs from the Groningen Gas field. The SWIR data, based on a resolution of 200 µm pixels, allows for a detailed analysis of compositional variation within the Upper Rotliegend Group. Verification of the SWIR results against a comprehensive petrographic dataset, including X-ray diffraction, thin section descriptions, and modal point count analysis highlights that SWIR data primarily captures qualitative variations in mineralogy rather than providing precise numerical values. Combination of sedimentary facies, SWIR spectroscopy data and conventional petrographic studies allows to generate descriptive mineralogical trends for each of the studied wells.

Ultimately, the results of our research will serve as a foundation for selecting the samples, designing geomechanical experiments to test the proposed hypotheses, and as the means to select the upscaling and modelling approaches to develop a detailed model of the Dutch subsurface that matches well the existing heterogeneous structures. The derived 3D reservoir composition model of the Groningen gas field will be combined with the results of the deformation experiments to link reservoir composition to geomechanical behaviour. This will enable an updated, more realistic, 3D geomechanical model of the Groningen gas field that can be utilised by other researchers to better predict future compaction and subsidence.

How to cite: Bublik, D., Mulder, S., and Miocic, J.: From pore to well - identifying clay mineral distribution in sandstones using SWIR spectroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12464, https://doi.org/10.5194/egusphere-egu24-12464, 2024.

EGU24-14166 | Posters on site | ERE5.4

Anion Transport Through Bentonite Under Various Geochemical Conditions 

Magdalena Krol, Farhana Chowdhury, Sifat Papry, Md Abdullah Asad, Pulin Mondal, Tarek Rashwan, and Ian Molnar

The use of bentonite clay in industrial applications is widespread: it is used as an engineered barrier for long-term management of radioactive wastes, CO2 storage, landfill liners, and contaminant containment. These applications have diverse environmental conditions ranging from various temperatures, pHs, saline contents, and ionic concentrations. Since bentonite is a low permeability clay, anion transport is diffusion dominated but geochemical reactions can also play a significant role and transport will be affected by environmental conditions. In this study, anion transport (bisulfide) under various conditions was examined using experimental and numerical techniques to understand the various geochemical and surface mediated reactions that are occurring in the bentonite. The case study presented is for the use of bentonite in long term storage of nuclear waste but can be extended to other applications.

First, diffusion experiments were performed to examine the transport and reactive nature of bisulfide (HS-) through bentonite compacted at dry density of 1090-1330 kg m-3. Experimental data of bisulfide transport were fitted using the inverse solution technique of Hydrus-1D model and different fitting parameters (e.g., diffusion, sorption, and reaction sink). Simulation results suggest that the HS- sorption/reaction affecting itsdiffusive transport through bentonite can be modeled using a simple nonlinear adsorption process.

Second, batch experiments were performed to understand the maximum allowable sorption that could take place under key geochemical conditions, including temperature, pH, and ionic strength. The results of batch sorption experiments performed suggest that HS- sorption increases with increasing temperature but decreases with increasing pH and ionic strength.

Lastly, since transport and reactive processes are interconnected, the results of these experiments were incorporated into a 1D transport COMSOL model to understand which geochemical process governs bisulfide transport through bentonite. Various processes were examined including linear and non-linear sorption, reactive transport, and anion exclusion. The model was validated using the experiments and showed that HS- was retained in the bentonite due to reactive processes and anion exclusion effects.

How to cite: Krol, M., Chowdhury, F., Papry, S., Asad, M. A., Mondal, P., Rashwan, T., and Molnar, I.: Anion Transport Through Bentonite Under Various Geochemical Conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14166, https://doi.org/10.5194/egusphere-egu24-14166, 2024.

EGU24-15531 | ECS | Orals | ERE5.4

Effects of pore fluid chemistry  on the localized to ductile transition of sandstone. 

Francesco Lazari, Gabriel Meyer, and Marie Violay

In geothermal reservoirs, pore fluid chemistry can affect mechanical and hydraulic properties of rocks inducing mineral dissolution, precipitation, weakening and alteration. Moreover, with increasing pressure and temperature deformation mode can change from localized to ductile (diffused), leading to a major decrease in permeability, thus affecting the exploitability of the reservoir. The effect of fluid chemistry on the transition between localized and ductile deformation of rocks is still marginally understood.

To investigate the effect of water presence and fluid chemistry on localized and ductile deformation, two sets of triaxial experiments (at 20 and 100 MPa effective confinement pressure, in the localized and ductile field respectively) were performed on a porous silicate sandstone (Adamswiller sandstone), dry, with deionized water and with a 6 M NaCl solution (Na+ rich solution), with a 0.1 M HCl solution (pH 1 solution) and a 0.1 M NaOH solution (pH 13 solution). To complement the mechanical properties, complex spectral electrical conductivity was measured during deformation to monitor pore fluid ion content; pore fluid was collected at the beginning and at the end of the experiments and analyzed with ICP-MS; post-mortem microstructural analyses were performed.

In the localized domain, both water presence and pore fluid chemistry had a marginal effect on the strength of the rock, leading to a 5/10% strength reduction over dry rock strength indipendently of the pore fluid composition. In the ductile domain, de-ionized water weakens the rock by 25%, a Na+-rich or pH 1 fluid leads to a 35% weakening and a pH 13 fluid weakens the rock by 40% over dry rock strength. Spectral electrical conductivity does not change during localized deformation, while it increases by 2 to 5 times during ductile deformation when the rock is saturated with deionized water; conductivity does not change with the Na+-rich fluid regardless of the deformation mode and conductivity decreases by half an order of magnitude with both pH 1 and pH 13 fluids both with localized and ductile deformation.

 
 

How to cite: Lazari, F., Meyer, G., and Violay, M.: Effects of pore fluid chemistry  on the localized to ductile transition of sandstone., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15531, https://doi.org/10.5194/egusphere-egu24-15531, 2024.

EGU24-16640 | ECS | Orals | ERE5.4

Decentralized CO2 storage in unfavorable conditions: An example from Switzerland 

Thanushika Gunatilake, Antonio Pio Rinaldi, Alba Zappone, Yingqi Zhang, Dominik Zbinden, Marco Mazzotti, and Stefan Wiemer

The escalating global temperature necessitates immediate action to mitigate greenhouse gas emissions. Geological Carbon Storage (GCS) technology has emerged as a promising solution, specifically by injecting carbon dioxide (CO2) into geological formations, particularly deep saline aquifers. However, finding ideal geological reservoir conditions, including caprock stability and storage capacity, is a rare occurrence.

This study comprehensively assesses the potential for CO2 storage in the Triemli saline aquifer in Zurich, Switzerland. The goal is not only to demonstrate the feasibility of CO2 storage in Switzerland but also to emphasize the viability of decentralized storage with multiple small injection point, for emitters like medium -sized citiesin regions with geologically challenging subsurface conditions. Through numerical simulations, we explore CO$_2$ injection, migration, and long-term reservoir stability to bridge the gap between theoretical estimates and practical feasibility.  Our findings underscore the potential of deep saline aquifers for CO2 storage in Switzerland, particularly in the Swiss Molasse Basin and the adjacent Folded Jura, identified as crucial regions for effective CO2 storage. Employing advanced methods and strategic injection techniques, such as multiple vertical or horizontal injection points along a single well, could optimize this storage capacity to approximately 3 million tons of CO2 over the same period.

How to cite: Gunatilake, T., Pio Rinaldi, A., Zappone, A., Zhang, Y., Zbinden, D., Mazzotti, M., and Wiemer, S.: Decentralized CO2 storage in unfavorable conditions: An example from Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16640, https://doi.org/10.5194/egusphere-egu24-16640, 2024.

Deep underground geological disposal is widely accepted as one of the most appropriate ways for the long-term safety and management of radioactive waste. The heat generated by the nuclear waste decay brings elevated temperature increase, which may affect the thermo-hydro-mechanical (THM) behaviour of the host rock. A correct evaluation of the thermal impacts on the host rock behaviour is important for the design of the underground geological disposal.

With the temperature increases, thermal pressurization is observed both in the small (laboratory) and large (in-situ) scale tests. Physically, the overpressure induced by the discrepancy of the thermal expansion coefficient between the solid and fluid phases may potentially induce fracture re-opening and propagation. The host rock located in the middle of two adjacent cells may suffer shear or tensile failure, which is dependent on the intensity of the thermal power and the distance between the neighbouring cells. Some research work also shows that soil characteristics like cohesion, elastic modulus and water viscosity are influenced by the rise in temperature [1]. To investigate the thermally induced change on the mechanical property of host rock, triaxial compression tests were conducted at the University of Lorraine at different temperatures (20, 40, 60, 80, 100 and 150 °C), confining pressures (0, 4 and 12 MPa) and samples orientations (parallel and perpendicular to the bedding plane). The results showed the transitory overpressure induced by the thermal dilation during the initial heating, and the degradation of the mechanical strength of the host rock with the increase in temperature [2].

Based on the experimental observations, the triaxial compression tests are represented in a two-dimensional axisymmetric coupled THM model. The modelling is composed of the two steps: isotropic loading (increase confining stress and temperature), and shear process (increase axial loading). The numerical FEM code is LAGAMINE from the University of Liège. The Callovo-Oxfordian (COx) claystone, relying on its low permeability and good plasticity, has been selected as the host rock for the underground geological disposal in Meuse/Haute-Marne in France. The objective of this study is to introduce thermal-mechanical modelling involved with thermal plasticity. The cohesion of the host rock is defined as a function of the temperature to describe the thermally induced change of mechanical behaviour of the host rock. This model will then be validated against experimental observations in the laboratory and further applied to the large-scale heating test.

ACKNOWLEDGEMENT

This study was performed in the framework of the European Joint Programme on Radioactive Waste Management (EURAD). EURAD has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 847593.

REFERENCES

[1] Laloui, L. and Cekerevac, C., 2003. Thermo-plasticity of clays: an isotropic yield mechanism. Computers and Geotechnics, 30(8), pp.649-660. Doi : https://doi.org/10.1016/j.compgeo.2003.09.001.

[2] Gbewade, C.A.F., Grgic, D., Giraud, A. and Schoumacker, L., 2023. Experimental study of the effect of temperature on the mechanical properties of the Callovo-Oxfordian claystone. Rock Mechanics and Rock Engineering, pp.1-22. Doi : https://doi.org/10.1007/s00603-023-03630-7.

How to cite: Song, H. and Collin, F.: A thermal-mechanical constitutive modelling for Callovo-Oxfordian Claystone in the context of nuclear waste disposal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16781, https://doi.org/10.5194/egusphere-egu24-16781, 2024.

EGU24-16823 | ECS | Orals | ERE5.4

A multi-scale model to study gas transport processes in clay materials 

Gilles Corman and Frédéric Collin

In the field of radioactive waste confinement, the question of gas transfers in clay formations is a crucial issue. A certain amount of gas, such as Hydrogen may be generated during the exploitation phase in the nearfield by the deterioration of the metal components of the system. As the host medium is characterised by a very low permeability, various gas transport processes could occur as a function of gas accumulation and pressurization [1], including the development of preferential gas pathways through the sound rock mass, which could lead to undesirable changes in the favourable containment properties of the host rock.

There is a growing body of experimental evidences [2, 3] that natural heterogeneities and pre-sxisting fractures in clay-rich materials represent preferred weaknesses for the process of opening discrete gas-filled pathways. Capturing the related transport mechanisms therefore requires to go from macroscopic to microscopic scale. Hence, a multi-scale modelling approach that models the micro-scale effects explicitely on their specific length scale and couples their homogenized effects to the macro-scale is proposed in the present work. Based on a periodicity assumption of the microstructure, a relevant Representative Element Volume (REV) is defined based on experimental data, which makes it possible to idealise the flow behaviour of the material microstructure with different families of discontinuities, and an assembly of tubes substituting the porous matrix blocks. This complete hydraulic constitutive model is solved at the scale of the microstructural constituents, and is directly affected by the mechanical effects tackled at the macroscopic scale, which makes the whole model hydro-mechanically coupled.

This model has been subsequently applied to simulate a gas injection test parallel and perpendicular to the bedding of initially saturated samples of Boom Clay [3]. This analysis provides a rather good agreement with the experimental results in terms of pressure response, outflow volume and average axial strain. In addition, it allows to simulated the creation of a preferential flow pathway along the sample axis (Figure 1b, top), which serves as basis to numerically reproduce the development of random pathways through the sample in plane strain state (Figure 1b, bottom), and aims to improve the mechanistic understanding of the gas transport processes at play in clayey barriers.

[1] P. Marschall, S. Horseman, and T. Gimmi. Characterisation of Gas Transport Properties of the Opalinus Clay, a Potential Host Rock Formation for Radioactive Waste Disposal. Oil & Gas Science and Technology Rev. IFP, 60(1):121-139, 2005. 

[2] Harrington, J.F., Milodowski, A.E., Graham, C.C., Rushton, J.C., & Cuss, R.J. (2012). Evidence for gas-induced pathways in clay using a nanoparticle injection technique. Mineralogical Magazine, 76(8):3327–3336.

[3] Gonzalez-Blanco, L., Romero, E., Jommi, C., Li, X. & Sillen, X. (2016). Gas migration in a Cenozoic clay: Experimental results and numerical modelling. Geomechanics for Energy and the Environment, 6:81–100.

How to cite: Corman, G. and Collin, F.: A multi-scale model to study gas transport processes in clay materials, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16823, https://doi.org/10.5194/egusphere-egu24-16823, 2024.

EGU24-17117 | ECS | Posters on site | ERE5.4

Insight into the micromechanisms of gas breakthrough in water-saturated clay-rich geomaterials – Implications for CO2 sequestration 

Craig Allsop, Matteo Pedrotti, and Alessandro Tarantino

The successful deployment of carbon dioxide (CO2) geological sequestration in porous media is reliant on the sealing efficiency of the overlying, clay-rich caprock to act as a physical barrier. Clay-rich caprock formations are considered favorable materials to act as a seal due to them characteristically consisting of small pores providing high capillary entry pressures, hence preventing the intrusion of a non-wetting fluid.

The juxtaposition and availability of deep seated (buried) caprock-reservoir systems to carbon capture and storage clusters may not be available. Therefore, the assessment of shallow seated, weakly consolidated caprock-reservoir systems (e.g., Sleipner) will be required. Our experimental campaign tests analogous caprock geomaterials which have relatively high compressibility, representative of shallow seated (buried or less indurated) clay-rich caprocks.

Past experimental campaigns demonstrate that CO2 breakthrough is dominated by the creation of very localized channels across the sealing barrier which occur at pressures far lower than the one predicted by the Laplace’s equation [1]. However, limited data characterizing these pathways exists. Furthermore, the physical indicators of susceptibility which underly the micro-mechanisms of failure (e.g., fracturing), are still only postulated for clay-rich geomaterials.

where Pc* is the capillary breakthrough pressure [kPa], ψ, reflects pore shape [-], Ts, interfacial tension between water and gas (e.g., CO2), and θ, represents wettability [°].

An innovative experimental set-up which allowed for the onset of surface crack formation to be captured during gas injection (representing the non-wetting fluid in CO2 geological sequestration) into intact clay-rich geomaterials is presented. This allowed for the investigation of physical indicators of susceptibility to gas breakthrough via localized pathways.

Results on different fracture patterns when non-wetting gas (i.e., air) is injected into consolidated clay show the formation of large fractures that nucleate from within the sample. Upon air pressurization, before fracture formation, the sample undergoes volumetric deformation (i.e., consolidation), as the resulting action of the vertical stress applied at the air-water interface (menisci). Once a fracture forms deformation stops and breakthrough occurred at lower pressures than traditionally recorded. The mechanisms of air intrusion are expected to be of a similar nature as CO2 intrusion. Post-mortem assessment of the internal nature of these localized pathways was then visualized using xCT imaging.

As a continuum mechanics framework will not predict fracture formation under our test conditions, it appears that the experimental evidence support the underlying hypothesis that disjoining pressure governs the mechanisms that ultimately control fracture formation and thus, eventually CO2 breakthrough. The disjoining pressure is governed by the electrostatic double-layer interactions, van der Waal’s dispersion forces, structural forces, and solvation forces.

If the pore size distribution is such that high gas pressures are required to overcome capillarity, the gas pressure will force single clay particles apart, displacing water form adjacent interparticle spaces. This represents a localized failure mechanism at the clay interface, resulting in fracture nucleation. It is expected that clay displaying large swelling pressures will subsequently display high gas entry pressure, termed “pathway dilation”. Therefore, pressurized gas will enter a dilated pathway at lower pressures than anticipated.

How to cite: Allsop, C., Pedrotti, M., and Tarantino, A.: Insight into the micromechanisms of gas breakthrough in water-saturated clay-rich geomaterials – Implications for CO2 sequestration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17117, https://doi.org/10.5194/egusphere-egu24-17117, 2024.

The utilisation of geothermal heat as a form of clean energy is experiencing global growth. Many sites designated for geothermal energy extraction are in regions with elevated heat gradients, such as Iceland and Japan. However, the repercussions of the migration of cold fluids in rock formations at high temperatures, and the subsequent fracturing of the host rock, which is relevant in the context of deep geothermal energy systems, remains insufficiently understood.  In this study, we explore the three-dimensional evolution of fractures in 50×9.8×1 mm3  homogeneous slabs of various brittle rocks, subjected to a thermal shock of ΔT=580°C, through numerical simulations over 10 seconds. Initially, we validate our numerical approach using a benchmark of Al2O3  slab, and subsequently, we examine fracture development in granite, basalt, and shales. Our numerical methodology employs a three-dimensional finite-element-based simulator to model thermo-mechanical deformation. The in-house code is a fully coupled THM code which considers damage to predict fracture initiation. Fracture growth is predicted per fracture tip using stress intensity factors. The code uses adaptive meshing and NURBS for fracture surfaces to facilitate mesh-independent fracture growth. In our simulations, we apply triangles and tetrahedra elements to discretise surface and volume elements, respectively. Our results show the development of dozens of fractures in bi- or tri-modality, which penetrate up to 85% of the depth of the slab, for the various simulations. These results demonstrate both qualitative and quantitative agreement between the simulated slab and the benchmark by reproducing the same intertwined short-long fracture patterns and modal distribution of fracture lengths. Furthermore, they illustrate how the fracturing rates (ranging between 1-100 mm/sec), fracture length distribution (unimodal, bimodal or trimodal), and penetration depth of fractures in front of the shock front vary among the different brittle rock types.

How to cite: Suchoy, L., Paluszny, A., and Zimmerman, R. W.: Fracture growth using fully coupled thermo-mechanical model in brittle rocks during thermal shock and resulting network patterns, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17626, https://doi.org/10.5194/egusphere-egu24-17626, 2024.

EGU24-18636 | ECS | Posters on site | ERE5.4

Physics-based numerical evaluation of High-Temperature Aquifer Thermal Energy Storage (HT-ATES) in the Upper Jurassic reservoir of the German Molasse Basin 

Kalliopi Tzoufka, Guido Blöcher, Mauro Cacace, Daniela Pfrang, and Kai Zosseder

Concepts of High-Temperature Aquifer Thermal Energy Storage (HT-ATES) (> 50 °C) are investigated for system application in the Upper Jurassic reservoir (Malm aquifer) of the German Molasse Basin (North Alpine Foreland Basin). The karstified and fractured carbonate rocks exhibit favorable conditions for conventional geothermal exploitation of the hydrothermal resource. Here, to further assess the sustainability of HT-ATES development in the Upper Jurassic reservoir, a physics-based numerical analysis is performed. With an estimated heating capacity of ca. 21 MW over half a year, our approach aims at determining numerically the efficiency of heat storage under the in-situ Upper Jurassic reservoir conditions and locally feasible operation parameters.

The numerical models build upon datasets from three operating geothermal sites at depths of ca. 2000-3000 m TVD located in a subset of the reservoir which is dominated by karst-controlled fluid fluxes. Commonly considered as a single homogeneous unit, the 500 m thick reservoir is subdivided into three discrete layers based on field tests and borehole logs from the three considered sites. This introduced vertical heterogeneity with associated layer-specific enhanced permeabilities allows to examine potentially arising favorable heat transfer, and in combination with the facilitated high operation flow rates to evaluate thermal recoveries in the multilayered reservoir.

Computation results reveal that the reservoir layering induces preferential fluid and heat migration primarily into the high-permeability zone, while thermal front propagation into the lower permeable rock matrix is restricted. The simulations further display the gradual temperature increase in the warm wellbore and its surrounding host rock, and the consequent progressive improvement in the heat recovery efficiencies. Despite the elevated permeability that may trigger advective heat losses, heat recovery factor values range from ca. 0.7 over the first year of operation to over 0.85 after 10 years of operation. An additional scenario is examined with fluid injection solely in the high permeable zone, in order to quantify potential improvement in the recovery efficiency by omitting fluid injection in the lower-permeability layers where heat propagation is diminished. This is due to the geometrical shape of the thermally perturbed rock volume as heat losses occur at the interface between thermal front and adjacent reservoir rock. Consequently, conclusions on the performance of the two different system designs under this layered reservoir setting are derived. All simulations account for density and viscosity variation through the IAPWS (International Association for the Properties of Water and Steam) thermodynamic property formulations. Results show that density-induced buoyant fluxes which would considerably decrease thermal efficiencies are inhibited, and thus the prevailing heat transport mechanism is forced convection.

How to cite: Tzoufka, K., Blöcher, G., Cacace, M., Pfrang, D., and Zosseder, K.: Physics-based numerical evaluation of High-Temperature Aquifer Thermal Energy Storage (HT-ATES) in the Upper Jurassic reservoir of the German Molasse Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18636, https://doi.org/10.5194/egusphere-egu24-18636, 2024.

EGU24-19122 | ECS | Posters on site | ERE5.4

Operational Monitoring of Thermal Dynamics in Deep Geothermal Production and Injection Wells with Fiber Optics from the Surface to the Reservoir 

Aurelio Andy, Felix Schölderle, Daniela Pfrang, and Kai Zosseder

In order to gain insights into the hydraulic and thermal long-term behavior of deep geothermal boreholes during operation, a fiber-optic monitoring (FOM) system was implemented at the Stadtwerke Munich's (SWM) geothermal plant 'Schäftlarnstrasse' in the national project Geothermal-Alliance Bavaria (GAB). The permanently installed fiber optic cables enable continuous measuring of the temperature in boreholes with high spatial and temporal resolution via Distributed Temperature Sensing (DTS) and of acoustics/vibration via Distributed Acoustic Sensing (DAS). In 2019, one production and one injection well were equipped with FOM in different setups and have been collecting data since then. In the injector, the cable was cemented behind the anchor pipe in the upper section of the borehole, whereas the producer was equipped with a fiber-optic cable until the total depth of the reservoir. Additionally, a fiber-optic gauge provides pressure and temperature at the top of the reservoir in this well.

Among other things, precise inflow profiling in the reservoir section of the producer could be carried out using the temperature data, which helps deepen the understanding of the hydraulic behavior of the reservoir. Changes over time in the temperature of the produced thermal water can be traced back to changes in the hydraulically active zones or inflow temperatures in the reservoir. Other factors that influence the wellhead temperature, such as borehole heat losses to the surrounding rock, can be quantified using the DTS data.

At the beginning of 2024, a third fiber-optic cable will be installed in an injection well at the Schäftlarnstrasse geothermal site. A similar setup as in the production well will allow for continuous measuring in the entire borehole until total depth (TD) and pressure and temperature from p/T gauges at the top of the reservoir and at TD. Therefore, both production and injection conditions in the reservoir and wellbore will be continuously monitored at all depths using DTS and DAS for the first time.

We present the first interpretations of the data collected from the newly installed FOM in the injection well as well as insights into the long-term monitoring of the hydraulic and thermal dynamics in the production well to underline the importance of permanent downhole monitoring to ensure efficient and sustainable use of the geothermal reservoir.

How to cite: Andy, A., Schölderle, F., Pfrang, D., and Zosseder, K.: Operational Monitoring of Thermal Dynamics in Deep Geothermal Production and Injection Wells with Fiber Optics from the Surface to the Reservoir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19122, https://doi.org/10.5194/egusphere-egu24-19122, 2024.

EGU24-19876 | ECS | Orals | ERE5.4

Weathering and creep in rocks modelled at the microscale 

Hadrien Rattez, Alexandre Sac-Morane, and Manolis Veveakis

Many natural processes and energy-related project in the subsurface involve the interactions between the porous rock and the fluids inside the pores. In particular, the fluid can interact with the solid matter by various dissolution-precipitation reactions that can modify the microstructure geometry and thus change the mechanical behavior of the rock and its failure potential or directly induce a creep of the rock. These chemo-mechanical couplings can have important implications for storage applications and induced seismicity. In this contribution, we will show discrete element simulations performed at the microstructural scale of porous matter. First, we will show that the dissolution of the cement in sedimentary rocks strongly influence the lateral earth pressure coefficient. The value of this coefficient tends to an attractor by increasing the degree of dissolution, which can lead to stress redistribution at the reservoir scale and promote faulting or induced seismicity. Secondly, we will show a numerical framework coupling discrete element with a phase field model allowing to capture grains shape changes due to local precipitation or dissolution. This model is applied to study the phenomenon of intergranular pressure-solution and allows to reproduce the creep behavior of the material in compaction. It enables also to study the competition between grain rearrangement and pressure solution in fault gouges to induce a rate dependency of the fault mechanical behavior.

How to cite: Rattez, H., Sac-Morane, A., and Veveakis, M.: Weathering and creep in rocks modelled at the microscale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19876, https://doi.org/10.5194/egusphere-egu24-19876, 2024.

EGU24-20645 | ECS | Posters on site | ERE5.4

Joule-Thomson cooling and phase transitions during CO2 injection in depleted reservoirs 

Lucy Tweed, Jerome Neufeld, and Mike Bickle

Depleted oil and gas reservoirs are attractive sites for CO2 sequestration. However, the injection of CO2 into depleted reservoirs carries the potential for significant Joule-Thomson cooling, when dense, supercritical COis injected into a low-pressure reservoir. The resulting low temperatures around the well-bore risk causing thermal fracturing and/or freezing of pore waters or precipitation of gas hydrates which would reduce injectivity and jeopardise near-well stability. Injection into reservoirs at subcritical pressure also leads to a phase transition from liquid to vapour CO2. This is accompanied by cooling, due to the latent heat of vaporisation, and dramatic changes in fluid properties including density, compressibility and viscosity.

We present models of non-isothermal flow of CO2 in the near well-bore region, which demonstrate the controls on cooling and constrain the different pressure-temperature regimes that can emerge. We show that during radial injection, with fixed injection rate, transient Joule-Thomson cooling can be described by similarity solutions at early times. The positions of the CO2 and thermal fronts are described by self-similar scaling relations. The scaling analysis here identifies the parametric dependence of Joule-Thomson cooling. We present a sensitivity analysis which demonstrates that the primary controls on the degree of cooling are the injection rate and Joule-Thomson coefficient. The analysis presented provides a computationally efficient approach to assessing the degree of Joule-Thomson cooling expected during injection start-up, providing a complement to full numerical simulations.

How to cite: Tweed, L., Neufeld, J., and Bickle, M.: Joule-Thomson cooling and phase transitions during CO2 injection in depleted reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20645, https://doi.org/10.5194/egusphere-egu24-20645, 2024.

EGU24-21553 | Posters on site | ERE5.4

Analysis of Wellbore Integrity using DTS Monitoring and Numerical Modelling in the Practice of ATES 

Guido Blöcher, Liang Pei, Stefan Kranz, Christian Cunow, Lioba Virchow, and Ali Saadat

Surplus heat as stored in an ATES (Aquifer Thermal Energy Storage) system in summer could partly meet the increasing demand of energy in winter. Better assessment on the wellbore integrity permits sustainable operation of such systems. Therefore, an artesian flow test was conducted in a research well located in Berlin, Germany. In this test, artesian flow of 16.8°C from Jurassic sand at depths from 220 m to 230 m was produced at 14°C and at a flow rate of 3.6m3/h from the annular space between the production casing and the anchor casing. The depth-resolved temperature at the production casing as monitored using the distributed temperature sensing (DTS) technique manifested the depths of the artesian aquifer. A hydro-thermal coupled numerical model for the artesian flow was calibrated by matching the simulated flow rate to the wellhead-measured values. The simulated and the DTS-monitored temperatures suggested that the heating-up in the near-wellbore materials by the artesian flow was hindered by the deployment-related inclusion of water behind the anchor casing, and the cooling in these materials in the shut-in test stage was enhanced by such inclusion. 

How to cite: Blöcher, G., Pei, L., Kranz, S., Cunow, C., Virchow, L., and Saadat, A.: Analysis of Wellbore Integrity using DTS Monitoring and Numerical Modelling in the Practice of ATES, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21553, https://doi.org/10.5194/egusphere-egu24-21553, 2024.

EGU24-2751 | ECS | Orals | ERE5.5 | Highlight

Thermo-mechanical properties and fracture behavior of granite at pore scale: implications for geological storage 

Chengkang Mo, Junliang Zhao, and Dongxiao Zhang

Geological storage of energy and carbon dioxide requires a deep knowledge of the complex thermo-hydro-chemo-mechanical processes that affect the stability and performance of reservoir rocks. In this study, we investigate the thermo-mechanical properties and mesoscale fracture behaviors of four key minerals in granites: quartz, plagioclase, amphibole, and biotite. We use a combination of experimental and analytical techniques to reveal the microscale mechanisms of rock failure under high temperature and tensile loading.

We perform nanoindentation tests under dynamic heating–cooling cycles to measure the reduced modulus and hardness of the minerals. We also conduct mode I fracture tests under tensile loading conditions to evaluate the fracture toughness and tortuosity of the granite. We observe the dynamic crack propagation and fracture morphology of minerals using scanning electron microscopy. We analyze the structural and physio-chemical changes at high temperatures using X-ray diffraction, thermogravimetric analysis, and Fourier’s transform infrared spectroscopy.

We find that the thermo-mechanical properties and fracture behaviors of the minerals are governed by three main factors: the alterations in mineral structure, the aperture of open cracks along cleavage planes, and the degree of heterogeneity due to mineral composition complexity. We identify two different damage modes in granite: catastrophic and non-catastrophic failure modes. We explain the underlying mechanisms of each mode and show that catastrophic failure has precursory signs, while non-catastrophic failure does not.

Our results provide new insights into the microscale mechanisms of rock failure under high temperature and tensile loading, which have implications for the macroscopic understanding of rock behavior in geological storage applications. By elucidating the microscale intricacies, this study enhances our understanding of the multifaceted interactions that influence the stability and performance of rocks, and supports the development of improved geological storage strategies, such as carbon sequestration and enhanced energy storage.

How to cite: Mo, C., Zhao, J., and Zhang, D.: Thermo-mechanical properties and fracture behavior of granite at pore scale: implications for geological storage, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2751, https://doi.org/10.5194/egusphere-egu24-2751, 2024.

EGU24-3433 | ECS | Orals | ERE5.5

Pore scale assessment of disrupted hydrochemical equilibria in geothermal systems 

Lilly Zacherl and Thomas Baumann

Many geothermal plants in the north alpine foreland basin (NAFB) are affected by the precipitation of calcium carbonate and struggle with efficiency losses and sometimes safety problems. The adaption and implementation of predictive maintenance strategies relies on the accuracy of the prediction and make sense if the costs of early maintenance are significantly less compared to the costs of a replacement of failed parts. Therefore, the accurate description of the kinetics of inorganic precipitations have to be extended to include the fluid dynamics and the interaction of the precipitates with different materials used in the geothermal cycle. The experimental concept also applies to fluid-rock interactions which can alter the properties of the reservoir.

The parametrization of transferable hydrogeochemical models performs best with data on a single interface, single crystal level. This data allows to elucidate the underlying process kinetics and improve existing strategies. The combination of Raman spectroscopy and Quartz crystal microbalance (QCM) opened a way to quantify the formation of carbonate precipitates. Here, the QCM can measure the total mass of attached particles while Raman microscopy identifies the crystal polymorph. Running these experiments in microfluidic channels allows to assess the effects of physical stress on the formation and to test inhibition and removal stratgies.

The QCM sensor was placed in a microfluidic channel and tap water (carbonate rich, Ca2+ concentration approx. 2.25 mM, pH approx. 7.50) and sodium hydroxide (0.10 M) were injected through the two inlet channels. As the lime carbonic acid equilibrium shifts due to the pH increase, precipitations are formed. The adhesive forces on different materials (SiO2, aluminium, steel) were studied by changing the flow velocities and chemical cleaning processes were mimicked by injecting an acid (HCl).

The precipitation of CaCO3 on the QCM sensor (sensitivity in the low mg-range) was less than 20% of the theoretical amount. This underlines the importance to include the fluid dynamics into the assessment models. The experimental data under dynamic conditions was modelled with a combination of CFD simulations with PhreeqC: The particle flow velocity and the precipitates formed depend on the depth as well as local equilibrium changes. The preferred location of scaling could be adequately simulated. This quantification of the effects of the shear stress and the material properties on the scaling efficiency is a further step towards predictive maintenance strategies and a solid comprehensive site assessment during the planning stage, which should improve the sustainability and the much-needed attractiveness of this energy sector.

How to cite: Zacherl, L. and Baumann, T.: Pore scale assessment of disrupted hydrochemical equilibria in geothermal systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3433, https://doi.org/10.5194/egusphere-egu24-3433, 2024.

CO2-oil-rock interactions and complex pore structure affect the sweep efficiency (ES) and wettability, thus having a significant impact on CO2 enhanced oil recovery in tight oil reservoirs. In this study, we selected 10 rock plugs from the Yanchang Formation, Ordos Basin in China. First, casting thin sections and mercury intrusion capillary pressure were performed to investigate the microscopic pore structure characteristics of the tight rock samples. The results show that pore structure can be divided into three types (RT-I, RT-II, and RT-III) from good to poor qualities. On this basis, CO2 floodings using the Nuclear Magnetic Resonance technique were performed to investigate the influence of pore structure on the ES in large (PL) and small (PS) pore throat intervals. With the increase of displacement pressure, the oil recovery of RT-I, RT-II and RT-III are about 70.9%, 67.8% and 10.16%, respectively. The ES of PL of all samples are similar, while the ES of PS decrease subsequently for the three types. Pressure, mineral composition and the complex pore structure are attribute to the differences. On one hand, higher displacement pressure leads to lower interfacial tension and viscosity, resulting in higher oil recovery. On the other hand, CO2 is more likely to vaporize the light oil components, resulting in the asphaltene precipitation. Quartz with a smooth surface is not easy to precipitate, while most clay minerals are easier to absorb asphaltene and are likely to alter the wettability of pore surfaces. Thus, in comparison to RT-III, the ES of RT-I with a higher quartz content is higher in PS. In addition, the worse the relationship between pore structure configurations, the greater the capillary pressure, causing the different ES between RT-I and RT-II. The findings in this study shed a light on the understanding of complex mechanisms for CO2 EOR in tight oil reservoirs.

 

How to cite: Cheng, Y., Qu, Y., and Cheng, X.: Effect of pore structure and CO2-oil-rock interactions on sweep efficiency of CO2 EOR in tight sandstone reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3479, https://doi.org/10.5194/egusphere-egu24-3479, 2024.

The characterization of reservoir rocks depends on the absolute permeability as a crucial parameter. To estimate this property numerically, one can employ a combination of digital rocks and Stokes flow simulation through the Lattice Boltzmann Method (LBM). In previous studies, the LBM has typically been implemented as an iterative process, wherein iterations are repeated until the parameter estimates between consecutive iterations reach a certain threshold level. However, we argue that this termination criterion is unsuitable and may compromise the accuracy of simulation results.

In this study, we investigate the convergence of the LBM through various tests, including the Poiseuille flow between parallel plates and different types of digital rocks (such as dune sand, sandstone, and carbonates). We find that the logarithm of the relative error, when compared to the estimate at infinite time (representing a stable state), demonstrates a linear relationship with the number of iterations. This linear relationship suggests an exponential rate of convergence. On the other hand, if we rely on the difference in errors between consecutive iterations as the termination condition, the simulation may not reach a stable state.

Instead, we propose a more accurate termination criterion for the LBM simulation by analyzing the decay trend of the error difference. This criterion provides a practical and appropriate approach for the characterization of reservoir rocks. Additionally, we offer a theoretical explanation for the convergence rate, which is linked to the spectral radius of the iterative matrix in linear algebra.

How to cite: Liao, Q.: Convergence Behavior of Lattice Boltzmann Method for Pore-scale Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4648, https://doi.org/10.5194/egusphere-egu24-4648, 2024.

Horizontal well multi-stage and multi-cluster fracturing technology has played an important role in unconventional reservoir development. However, traditional methods rarely investigated fracturing fluid flow characteristics in reservoirs with abundant natural fractures. Furthermore, affected by the stress interference from dense number of fracturing clusters, some perforations do not form fractures. For deep shale reservoirs, failure to consider these contents may result in unsatisfactory fracturing results for deep shale reservoirs.

An innovative approach is introduced in this paper. This innovation can be based on natural fracture development, fracture propagation law and reservoir composition characteristics. The flow regularity of fracturing fluid inside natural fractures was characterized through CT scanning experiments. Numerical simulation is used to analyze fracture propagation in fracturing horizontal well with multi-stage and multi-cluster. Core full component test experiment was conducted to analyze compressibility. In response to the above results, different fracturing process is adopted, the length of fracturing section is adjusted, the number of fracturing clusters is set. Then the fracturing design scheme of each segment is formulated and the fracturing effect and operation lessons of actual wells are analyzed. 

The results show that obvious pressure interference between developed section and undeveloped section of natural fracture, fracturing fluid first enters the extended natural fracture and then enters other fractures. Therefore, the temporary plugging of the extended natural fracture weakens its preferential tendency to enter the fluid and ensures the uniform migration of fracturing fluid to each fracture. Numerical simulation shows that some perforations do not form effective fractures, due to stress interference caused by excessive number of perforations. Hence, a fracturing scheme with fewer perforation times is adopted to reduce stress interference and improve the efficiency of perforating fracture formation. The results also observe that the reservoir contains plenty of brittle minerals such as calcite, which is easy to cause fractures. However, high silicon content easily form, extremely irregular fracture. Consequently, the fracturing scheme of shortening the length of fracturing section is adopted to strengthen the control of fracture expansion. The fracturing evaluation of the effect shows that the initial production of the well was 6.59 ×104 m3 with a flowback rate of 15.5%. Microseismic monitoring data shows that the reconstruction volume has increased from the original 9.70 ×104 m3 to 1.06 105 m3, the fracturing effect is remarkable.

The conclusion of this research supports for deep shale fracturing design and has a vital practical application significance. Compared with conventional fracturing methods, the fracturing performance is significantly improved results from weakening the advanced fluid tendency of natural fractures, decreasing the stress interference between clusters and strengthening the fracture control.

Key words: deep shale; natural fracture; stress interference; brittle mineral content; temporary plugging technology

How to cite: Di, S., Ma, S., Wei, Y., Cheng, S., Miao, L., and Liu, M.: Effective fracturing strategy considering natural fracture, stress interference and rock component—A practical application of Dingshan block in Sichuan Province of China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5027, https://doi.org/10.5194/egusphere-egu24-5027, 2024.

In low-permeability reservoirs, strong molecular interactions exist at the solid-liquid interface, necessitating the overcoming of the threshold pressure gradient in shale oil extraction. A profound comprehension of molecular interactions between oil and reservoir matrix is crucial to develop a productive strategy for enhanced oil recovery. Molecular dynamics simulation has become an important method for analyzing microscopic mechanisms of some static properties and dynamic processes. In this study, a molecular model of shale oil was built based on the reported experimental results and simulation. Subsequently, the molecular model was utilized to build a flow model within three matrix pores: kerogen, quartz, and portlandite. A comprehensive analysis of the interfacial effects and size effects on the threshold pressure gradient was undertaken. Emphasis was placed on elucidating the influence of the adsorption behaviors (stable adsorption, unstable adsorption, non-adsorption) of polar components at the interface on the flow of shale oil. The utilization of the critical shear stress facilitated the accurate prediction of the threshold pressure gradient of shale oil within large pores. Moreover, within the context of the flow model of shale oil in nanoscale pores, we conducted some explorations into oil displacement by CO2. This work suggests fresh ideas for studying the oil-matrix interactions on the nanoscale and provides theoretical guidance for shale oil exploitation.

How to cite: Cui, F. and Wang, F.: Micromechanical mechanism of oil-rock interaction and the availability analysis of shale oil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6006, https://doi.org/10.5194/egusphere-egu24-6006, 2024.

EGU24-6961 | ECS | Orals | ERE5.5

Nanoscale Wettability of Oil/Rock Interface and its Impact on Occurrence and Flooding 

JiaNing Fan and FengChao Wang

Mineral wettability plays a pivotal role in determining residual oil distribution and devising effective displacement strategies for enhanced oil recovery. Through molecular dynamics simulations, we investigated the surface wettability of various typical minerals, revealing the complete spreading of modeled crude oil over most mineral surfaces. Our research introduces an efficient method for calculating the spreading coefficient of modeled crude oil on mineral surfaces, allowing accurate predictions of its spreading state with a notable reduction in calculation time compared to traditional methods. Furthermore, the study explores the impact of various components within crude oil on mineral surface wettability, emphasizing microscopic interactions between these components and minerals. In nanopore channels, the diverse wettability of oil/rock interface results in varied occurrence forms, such as droplets, films, or columns, which are also different in the water flooding process. In addition, with the introduction of various components in crude oil, due to their different interactions with oil/water/rock, we found that these components can be evenly mixed with modeled crude oil or exist at the oil-water interface. Therefore, the introduction of this component changes the properties of oil-water interface, affects the form of oil occurrence and the process of flooding. These insights contribute to a comprehensive understanding of mineral surface wettability and its correlation with crude oil composition, providing valuable guidance for optimizing reservoir management and refining production strategies in the pursuit of enhanced oil recovery.

How to cite: Fan, J. and Wang, F.: Nanoscale Wettability of Oil/Rock Interface and its Impact on Occurrence and Flooding, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6961, https://doi.org/10.5194/egusphere-egu24-6961, 2024.

CO2 injection can effectively promote the development and utilization of shale oil. The interaction between CO2, shale oil and pore structure has attracted much attention as a key mechanism for oil resource exploitation. Therefore, we established a pore network model, injected shale oil and CO2 successively into the model, and studied the occurrence state of miscible fluid at the nanoscale. This study takes the shale of Lucaogou Formation in Jimsar Sag of Junggar Basin as the research object. Nano-CT and scanning electron microscopy are used to observe the pore structure of shale layer by layer, and the pore structure is transformed into a molecular model layer by layer, and finally superimposed into a pore network molecular model. Through the analysis of crude oil group components and chromatography-mass spectrometry, the characteristics of crude oil components are identified and the corresponding molecular models are established. The occurrence state of shale oil in the pore network model is simulated by molecular dynamics. CO2 is injected into the system to simulate the occurrence state of the miscible fluid. The fluid density in the system is analyzed, the interaction force between CO2, shale oil and pore structure is calculated, and the capacity models of adsorbed oil, free oil and CO2 storage are established. The reliability of the model is verified and applied by combining production data and experimental tests. This study plays a crucial role in advancing the understanding of CCUS (carbon capture, utilization, and storage) and the geological theory of shale oil and gas. It also has the potential to overcome the challenges and limitations in shale oil production technology, thus making significant contributions to this field.

How to cite: Lin, X. and Li, Z.: The mutual feedback mechanism between CO2 and multiphase fluids during CO2 injection into shale oil reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8286, https://doi.org/10.5194/egusphere-egu24-8286, 2024.

EGU24-9227 | ECS | Posters on site | ERE5.5 | Highlight

Rock Reconstruction with Deep Generative Network 

Qinglong Cao and Yuntian Chen

The reconstruction of Digital Rock is a crucial challenge in understanding the microstructure of rocks and its impact on pore-scale flow through numerical modeling. This is particularly significant due to the typically large samples required to address inherent uncertainties. Despite notable advancements in traditional process-based techniques, statistical methods, and recent popular deep learning models, there is a limited focus on deep learning approaches specifically tailored for reconstructing rocks with predefined properties, such as porosity. To address this gap, our research employs Artificial Intelligence Generative Component (AIGC) technologies to precisely generate rock structures with specified properties. Our experimental results demonstrate the successful application of our method in reconstructing rock images based on target properties. The generation of randomly reconstructed samples with distinct rock properties holds promise for advancing research in pore-scale multiphase flow and uncertainty quantification in subsequent studies.

How to cite: Cao, Q. and Chen, Y.: Rock Reconstruction with Deep Generative Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9227, https://doi.org/10.5194/egusphere-egu24-9227, 2024.

The tight sandstone reservoir features the development of micro- and nano-scale pores and micro-fractures, contributing to a complex pore-throat structure. This complexity results in an indistinct charging sequence of oil and gas in different types of storage spaces during the accumulation period, thereby escalating the challenges associated with the exploration and development of tight oil and gas. Focusing on the Fuyu oil reservoir in the northern Songliao Basin, this study integrates large-field-of-view stitched scanning electron microscopy with mineral surface scanning techniques. Innovatively, a micro-nano scale comprehensive reservoir evaluation method, incorporating both pores and micro-fractures, is proposed. Within the study area, three predominant pore-fracture combination types are identified: intergranular pore-clay mineral shrinkage fractures, intergranular pore-brittle mineral intergranular fractures, and intragranular pore-clay mineral shrinkage fractures. Building upon this, Wood's alloy, exhibiting high-temperature rheological properties, is injected into rock cores under various pressure conditions. It is observed that with increasing injection pressure, the alloy injection process demonstrates a structured order, with a clear preference for charging intergranular pore-fractures over clay mineral-related pores. Furthermore, the alloy injection efficiency curve exhibits a distinctive parabolic shape. Based on the characteristic properties of Wood's alloy and crude oil, the injection pressure is equivalently transformed, reconstructing the micro-scale charging process of tight oil under reservoir conditions. Consequently, a sequential charging model for tight reservoirs is established, encompassing micro-nano-scale intergranular pore-fractures, nano-scale clay mineral intragranular pores, and shrinkage fractures. This model considers parameters such as source-reservoir pressure difference, storage space type, fluid properties, etc. From both qualitative and quantitative perspectives, it clarifies the microscopic accumulation sequence of tight reservoirs. This research focuses on the development of a new multi-scale evaluation method for tight reservoir storage spaces, combining fluid injection with visualization technology. The findings are crucial for the microscopic sweet spot evaluation and efficient development of tight reservoirs.

How to cite: Liu, J. and Jiang, Z.:  Investigation of Pore-Fracture Charging Sequences in Tight Reservoirs Based on Multi-Stage Pressure Injection Experiments with Wood's Alloy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12139, https://doi.org/10.5194/egusphere-egu24-12139, 2024.

EGU24-13458 | ECS | Orals | ERE5.5 | Highlight

Machine Learning for mechanical classification of organic-rich shale based on high-speed nanoindentation 

Su Jiang, Junliang Zhao, and Dongxiao Zhang

In conjunction with scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS), quasi-static nanoindentation has been widely used to investigate the mechanical properties of minerals and organic matters in shale at micro scale. However, due to the limited test efficiency of conventional nanoindentation measurement and the demand of mineralogical identification which is achieved by SEM observation and EDS analysis, the research scheme in previous works can be time-consuming and complicated. This work attempts to develop a new micromechanical research scheme with high test efficiency and automatic mineralogical identification. A newly-developed high-speed nanoindentaion technique is used to characterize the mechanical properties distribution of a shale sample from the Yanchang Formation in the Ordos Basin, China. Then, the mineralogical distribution in the corresponding areas is obtained by using MAPS Mineralogy. Finally, logistic regression is applied to link the mechanical properties distribution and mineralogical distribution, and to realize the automatic mineralogical identification based on nanoindentation results. In addition, to further investigate the influence of characterization experiments on machine learning results, the characterization abilities, including lateral spatial resolution, detection depth, and signal spacing, of the two experimental methods are compared. The detection depth of MAPS Mineralogy is markedly higher than that of nanoindentation, which means that the material volume detected by the two methods is different. The lateral range responding to applied force and incident electrons determines that the signal of data points at the boundary can be a mixture of two or more minerals. The influence of such detection depth difference and boundary effect is also discussed.

 

 

How to cite: Jiang, S., Zhao, J., and Zhang, D.: Machine Learning for mechanical classification of organic-rich shale based on high-speed nanoindentation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13458, https://doi.org/10.5194/egusphere-egu24-13458, 2024.

    The characterization of the microscopic pore systems in organic-rich shales is crucial for comprehending the occurrence mechanisms and flow behaviors of shale oil. Although various image processing techniques have advanced the study of shale pore systems recently, challenges such as unclear boundaries of pore structures, interwoven connectivity, high similarity, and complex topological structures remain unresolved. In this study, a comprehensive investigation of the multiscale pore structure in organic-rich shale is presented, through the examination of 20 lacustrine shale samples from the Paleogene Kongdian Formation. These samples were analyzed using a variety of techniques, including N2 adsorption, mercury intrusion capillary pressure (MICP), nano X-ray CT, and Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM). Furthermore, We innovatively propose a machine learning-based multi-objective panoramic segmentation modeling method. This approach allows for precise segmentation and rapid panoramic modeling of various instances across different semantic categories and the gaps between these instances. It enables the creation of a more comprehensive multi-scale porous network model, which will be more conducive to future simulations of multi-physical processes such as fluid dynamics permeation models.
    We combine the dilated convolutions suitable for semantic segmentation with the feature pyramid structure favorable for instance segmentation to achieve precise panoramic segmentation. This approach accurately segments and represents various components in SEM images, including interparticle pores, intraparticle pores, organic pores, microfractures, feldspar, quartz, dolomite, calcite, clay minerals, and organic matter.In the three-dimensional reconstruction of FIB images, we innovatively employ registration based on contextual relationship sequences to accurately expand the reconstruction scope of pore pathways. Simultaneously, the use of an octree data structure index in constructing pore network structures enhances efficiency and speed. 
   The results show that the overall pore sizes range from 5 nm to more than 50 μm, consisting of abundant nanopores and a small quantity of micropores, and the dominant pores are in the range of 5 nm -200 nm. Through three-dimensional characterization of different types of pore networks, the transport behavior of shale oil within nanoslits was simulated, and it is proposed that fluid migration path is mainly controlled by the content of minerals, whether laminae are developed, and organic matter content. This study offers a promising solution for optimizing the automatic processing of microscopic images for pores, the combination of methods can provide pore structure characterization from sub-nanoscale to macroscale, spanning four orders of magnitude, which is crucial for improving the understanding of reservoir mechanisms and the hydrocarbon potential of lacustrine shale.

How to cite: Li, G., Xin, B., and Li, Z.: Applying Machine Learning Methods Based on Panoptic Segmentation, Context Registration, and Octree Indexing for Multiscale Pore Structure and Connectivity of the Organic-rich shales in Bohai Bay Basin, East China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19274, https://doi.org/10.5194/egusphere-egu24-19274, 2024.

EGU24-1896 | ECS | PICO | ERE5.8 | Highlight

An Integrated GNSS-SAR Approach to Improve Ground Deformation Analysis in the Field of Geo-energies: activities planned within the SMILE project 

Osmari Aponte, Andrea Gatti, Eugenio Realini, Riccardo Barzaghi, and Fernando Sansò

The SMILE network, part of the Marie Sklodowska-Curie doctoral network funded by the Horizon Europe (2021-2027) program, undertakes an innovative role in addressing geo-energy project challenges while promoting net-zero greenhouse gas emissions in line with global sustainability goals.

A segment of the SMILE network is dedicated to addressing the issue of ground deformation analysis. This research aims to develop a software tool that capitalizes on Global Navigation Satellite System (GNSS) data, coupled with Synthetic Aperture Radar (SAR) inputs and ground modeling information. This abstract outlines the methodological framework for the anticipated software development.

In the initial phase, we aim to integrate the high temporal resolution GNSS data with the high spatial resolution of SAR data. The goal of this process is to combine the advantages of both data types while minimizing their limitations. SAR provides extensive spatial detail but has limited temporal frequency and directional sensitivity. On the other hand, GNSS data provides comprehensive three-dimensional vectors with high temporal frequency, but spatially limited to the points where GNSS stations are located.

Merging the displacement measurements from GNSS and SAR requires temporal synchronization and the reconciliation of their different displacement vectors: GNSS captures vertical, east, and north components, and SAR measures in the line-of-sight direction. The optimal joint operation for this task is proposed through a Kalman filter. Due to the complexity of building a joint filter, the proposed method seeks to first analyze by considering the projected displacements only in the vertical direction. In this case, the measure in the line-of-sight of the SAR satellite will be projected in the vertical direction.

The next phase will focus on an innovative approach to enhance the covariance matrix within the Kalman filter algorithm. Instead of using a homogeneous and isotropic constant covariance in time, this enhancement strategy will harness observed data as input. Primarily, it will smooth the covariance evolution in time, exploiting past observations; this may improve the stability of the outcomes. The method under development proposes to improve the covariance modeling further by enabling the consideration of anisotropic and non-homogeneous scenarios. Finally, the proposed method aims to integrate the monitoring data into Thermo-Hydro-Mechanical (THM) modeling.

The proposed expansion is expected to bring significant advancements in ground deformation analysis, improving its resolution and precision. The tool will integrate GNSS and SAR datasets into a comprehensive ground deformation analysis suitable for geomatics applications within geo-energy projects.

How to cite: Aponte, O., Gatti, A., Realini, E., Barzaghi, R., and Sansò, F.: An Integrated GNSS-SAR Approach to Improve Ground Deformation Analysis in the Field of Geo-energies: activities planned within the SMILE project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1896, https://doi.org/10.5194/egusphere-egu24-1896, 2024.

EGU24-2815 | PICO | ERE5.8

Degradation pathways and mechanisms of oilwell cement exposed to H2S under high temperatures 

Liwei Zhang, Yue Yin, kaiyuan Mei, Xiaowei Cheng, Yan Wang, and Hanwen Wang

The extraction of geothermal energy faces the hazard of H2S, a highly toxic and strongly corrosive gas. H2S exposure can lead to the failure of oilwell cement, decreased extraction efficiency, and even pose serious risks to operational personnels near the wellsite. High temperature is a prominent environmental feature in geothermal resource extraction. However, current research works primarily focus on the corrosion effects of H2S on cement at moderate to low temperatures. This study utilizes Class G oilwell cement to conduct corrosion experiments of cement by H2S under high temperature in a H2S-rich reaction vessel. The impact of H2S on the structure, chemical composition, and mechanical strength of oilwell cement is analyzed via SEM-EDS, XRD, nanoindentation tests, and unconfined compressive strength tests. The results indicate a reduction in compressive strength for cement samples corroded by H2S. The surface nano-hardness and elastic modulus of cement samples decrease while the internal values of nano-hardness and elastic modulus significantly increase. Under the corrosion of H2S, the structure of cement is characterized by a yellow and black surface layer and stratified cracks. The external surface of the cement exhibits a yellow color due to the formation of pyrite (FeS2), while internally, pyrrhotite (FeS) and gypsum (CaSO4.2H2O) are generated.

How to cite: Zhang, L., Yin, Y., Mei, K., Cheng, X., Wang, Y., and Wang, H.: Degradation pathways and mechanisms of oilwell cement exposed to H2S under high temperatures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2815, https://doi.org/10.5194/egusphere-egu24-2815, 2024.

EGU24-3952 | PICO | ERE5.8 | Highlight

Hydrogeochemical Modeling of Opalinus Clay: Insights from CO2 Injection Experiments at Mont Terri Rock Laboratory 

Ümit Koç, Jérôme Corvisier, Dominique Bruel, and Laura Blanco Martin

Within the context of CO2 injection, understanding the properties of potential caprocks, particularly clay-rich ones such as Opalinus Clay and their potential evolution is crucial for safe and effective carbon capture and storage (CCS) initiatives. This study presents hydrogeochemical models developed to investigate interactions between groundwater, Opalinus Clay caprock and CO2, focusing on chemical evolution under varying pCO2 levels across different layers of the clay.

Utilizing a comprehensive dataset derived from CO2 injection experiments conducted at the Mont Terri Rock Laboratory and published pore water chemistry of Opalinus Clay, hydrogeochemical models of a potential reservoir and caprock system were constructed employing PHREEQC and CHESS geochemical modeling softwares. These models were designed to simulate and comprehend the intricate processes governing groundwater-CO2-rock interaction within the reservoir-caprock interface and through the stratified layers of Opalinus Clay.

The models aimed to elucidate the chemical evolution of the groundwater as it interacts with the Opalinus Clay under different pCO2 conditions. By considering variations in pCO2 levels representative of potential CCS scenarios, the simulations provided insights into the geochemical alterations occurring within the caprock and their implications for its integrity over time.

The findings of these hydrogeochemical models offer valuable insights into the potential consequences of CO2 injection into reservoirs whose caprocks are formed of Opalinus Clay, informing risk assessment and mitigation strategies for CCS applications. Moreover, these constructed hydrogeochemical models not only serve as a crucial foundation for comprehending the intricate thermal-hydro-mechanical-chemical (THMC) coupling mechanisms within caprocks like Opalinus Clay but also contribute to a deeper understanding of the complex interplay between pore water chemistry, rock properties, and varying pCO2 levels, essential for ensuring the long-term security and effectiveness of subsurface CO2 storage.

How to cite: Koç, Ü., Corvisier, J., Bruel, D., and Blanco Martin, L.: Hydrogeochemical Modeling of Opalinus Clay: Insights from CO2 Injection Experiments at Mont Terri Rock Laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3952, https://doi.org/10.5194/egusphere-egu24-3952, 2024.

In the realm of harnessing geothermal energy, groundwater heat pumps exhibit superior thermal efficiency when compared to closed-loop geothermal heat pumps. However, the outlook for progress remains less than promising. A primary obstacle stems from the improper extraction of groundwater, which can disrupt the stress field in subsurface structures and potentially trigger land subsidence. This concern is particularly pronounced in unconsolidated soils found in coastal sedimentary plains, where the additional threat of severe flooding disasters looms. Furthermore, artificial pumping processes may give rise to coupled hydraulic phenomena, exemplified by the reverse water level fluctuations. This transient anomalous changes in hydraulic head occurs in adjacent aquifers during the initial stages of pumping from a confined aquifer, induced by strain propagation. The magnitude of the hydraulic head elevation varies from a few centimeters to several tens of centimeters, posing a challenge to the accurate interpretation of groundwater monitoring data for land subsidence prevention. Geothermal heat pump systems can also induce changes in the temperature and thermal strain of geological layers. Consequently, understanding how this strain-induced hydraulic head responds to temperature fluctuations becomes a research question. In our investigation, the hydraulic and mechanical responses of a three-layer aquifer system to groundwater pumping were assessed through thermoporoelastic numerical simulations. The simulated reverse hydraulic head changes align with field observations documented in the literature. The findings of this numerical investigation indicate that when we recharged the water into the ground, the initial head decrease is likely to occur in proximity to a recharge well within an unpumped clay layer. These deformation-induced head changes eventually dissipate following the hydraulic propagation of unsteady state drawdown from the pumped aquifer into adjacent layers. In the event of reverse water level fluctuation, it is shown that temperature has no obvious influence on the hydraulic variation, both the head variation and happening time. It is also suggested that the propagation of thermally induced strain is slower than that of hydraulically induced strain and the effect appears much later.

How to cite: Yue, L. and Aichi, M.: Numerical Investigation of Reverse Water Level Fluctuations under Non-Isothermal Conditions with a Fully Coupled Thermal-Hydro-Mechanical Model for Geothermal Heat Pump Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5401, https://doi.org/10.5194/egusphere-egu24-5401, 2024.

EGU24-5492 | PICO | ERE5.8

A Neural Network to Reduce Subsurface Uncertainty Based on Ground Deformation Measurements 

Tian Guo, Haiqing Wu, and Víctor Vilarrasa

Subsurface uncertainty is large because we have limited access to it. Reducing uncertainty is important for geo-energies in order to increase the reliability of the simulation results used to define safe operation conditions. In particular, subsurface uncertainty can be reduced by analyzing ground deformation. A clear example of this is the CO2 storage project at In Salah, Algeria, where a double lobe ground deformation shape revealed the presence of a vertical fault zone at depth. Here, we propose a workflow to reduce subsurface uncertainty by inferring the subsurface characteristics from ground deformation measurements. As a foundation step of the workflow, we train a supervised neural network-based regression approach for predicting ground deformation caused by reservoir pressurization due to fluid injection. To train the neural network, we use a recently developed analytical solution to assess ground displacement in response to pressurization of a reservoir that is intersected by a permeable or an impermeable fault (https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4503451). The instantaneous solution provided by the analytical solution allows us to generate a large dataset to train the neural network. We have varied eleven variables, including fault and reservoir geometry and mechanical properties. Simultaneously, a simplified parametric space analysis is also performed. Results show that the reservoir thickness, Biot´s coefficient, and the pore pressure buildup impact the displacement the most. This study highlights that an appropriately trained neural network can effectively predict the ground deformation and give insights into the corresponding subsurface characteristics.

How to cite: Guo, T., Wu, H., and Vilarrasa, V.: A Neural Network to Reduce Subsurface Uncertainty Based on Ground Deformation Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5492, https://doi.org/10.5194/egusphere-egu24-5492, 2024.

EGU24-6245 | ECS | PICO | ERE5.8

Improving PSI Capabilities on Ground Deformation Monitoring for The Application of Geo-Energy Projects.  

Maria Carmelia Ramlie, Paula Olea-Encina, Michele Crosetto, and Oriol Monserrat

PSI Technique remains a powerful remote sensing method in terms of ground deformation monitoring, which makes it useful for monitoring geo-energy projects such as geothermal and CO2 sequestration where movement is always detected. The monitoring is a crucial supporting component to ensure the smooth progress of geo-energy development. However, PSI Technique still faces some problems that affects the accuracy of the detection. This can be caused by data and related to the terrain of the study areas, such as vegetation, buildings, and the direction of the ground deformation. The goal is to counteract this is by combining multiple sensor images, both low resolution and high resolution. These can be obtained from the wide range of satellites available today such as Sentinel-1, TerraSAR, COSMO-SKYMED, and NISAR. This technique is supposed to increase the temporal sampling for a more comprehensive time series, redundancy to improve accuracy and robustness of PSI analysis, wider coverage by exploiting at each site the data that offers best performances. Aside from the expected improvement, some challenges in developing this technique will be presented. Most of the challenges are due to the difference in satellites’ characteristics, such as resolution, pixel spacing, wavelength, and geometry. The technique is planned to be applied on several study areas. The purpose of this is to study the effects of different terrain characteristics on the re-sampling process, tuning processes, and the result of the processing. One of the study areas will serve as the benchmark of the research.

How to cite: Ramlie, M. C., Olea-Encina, P., Crosetto, M., and Monserrat, O.: Improving PSI Capabilities on Ground Deformation Monitoring for The Application of Geo-Energy Projects. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6245, https://doi.org/10.5194/egusphere-egu24-6245, 2024.

EGU24-6264 | ECS | PICO | ERE5.8

Relationship between Environmental Factors and Radar Amplitude: Illinois Basin – Decatur Project case study 

Paula Olea-Encina, Maria Carmelia Ramlie, Oriol Monserrat, and Michele Crosetto

2023 was claimed as the beginning of the “Global Boiling Era”. For this reason, geo-energies are key to provide a green and clean future. Geothermal energy, and geologic carbon injection/storage are the main types of geo-energies. Both have in common the underground fluid movement and the consequent ground motion dynamics.

One of the main techniques for analyzing ground motion is Persistent Scattered Interferometry (PSI), which allows us to estimate ground deformation over time from radar satellite data. PSI techniques calculate the temporal displacement in the so-called persistent scatterers by filtering the data based on amplitude value. Generally, the main cause for amplitude variability is the change in the surface properties over time, primarily due to changes in environmental factors (land cover/land use, vegetation dynamics, temporal water presence, or soil moisture). The main concern with these changes is that they may result in phase shifts, which could be misinterpreted as range displacements.

Improving the understanding of the environmental factors could improve the understanding of ground deformation over time. Therefore, environmental factors analysis and PSI can be integrated seamlessly into a workflow since the launch of the Copernicus Programme, combining Sentinel-1 and Sentinel-2 data. The goal of this research is to explore the relationship between environmental variables and amplitude values. This research is framed in the MultidiSciplinary and MultIscale approach for assessing coupLed processes induced by geo-Energies (SMILE) Project. The study site is the Illinois Basin – Decatur Project (IBDP), which is a carbon dioxide injection and storage located in the United States. IBDP is in the north part of Decatur city, the vegetation is mainly woodland and prairie; with a humid subtropical climate, with an annual precipitation over 1000 mm.

The analysis focuses on three areas near IBDP: wetland area, crop area, and woodland area. Performing a spatio-temporal analysis of the vegetation index (NDVI), soil moisture index (NDWI), and temporal water presence (NDWI) obtained from Sentinel-2 data between 2015 to 2023 and comparing these datasets with the amplitude time series from Sentinel-1 imagery for the same period. The results show that the woodland area has a high mean amplitude value with low dispersion; the wetland area has a low mean amplitude value with high dispersion; and the crop area has a medium mean amplitude value with medium dispersion.

The vegetation index for the woodland area has 7 month per year values over 0,4, showing a presence of high photosynthetic activity, which can be related to the low value of dispersion amplitude; while the wetland area only 3 months per year has a value over 0,4, that can be source of the high dispersion amplitude. While the crop area is 6 months over the threshold. The results of the analysis performed showed that the use of environmental indices can help in the interpretation of the dispersion amplitude in the PSI analysis. The next step is to consider more environmental variables such as snow cover, land cover/land use, or temperature in the analysis of amplitude, as well as consider different polarizations, among others.

How to cite: Olea-Encina, P., Ramlie, M. C., Monserrat, O., and Crosetto, M.: Relationship between Environmental Factors and Radar Amplitude: Illinois Basin – Decatur Project case study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6264, https://doi.org/10.5194/egusphere-egu24-6264, 2024.

EGU24-7497 | ECS | PICO | ERE5.8

Decay of seismic noise at shallow boreholes: Observations from Groningen. 

Oleh Kalinichenko, Leo Eisner, Frantisek Stanek, Umair Waheed, Sherif Hanafy, and Zuzana Jechumtalova

Long-term seismic monitoring arrays are often deployed to shallow boreholes to reduce the seismic noise. We investigate noise level decay in shallow boreholes. A large number of publicly available data with such deployment is available at the seismic monitoring array near the town of Groningen, which allows also characterization of the seismic noise decay in shallow boreholes in urban environments. We study noise distribution at 4 sites from this array. Each site includes 5 receivers deployed in shallow vertical boreholes with 50 meters intervals between the surface and 200 m depth. We show there is no difference between noise levels during the summer and winter at the borehole instruments. However, we observe diurnal variation at all depth levels. We also show there are higher noise levels throughout weekdays and lower during weekends and state holidays. These changes are not only observed at the surface but also at the deepest receivers. This implies that the dominant source of this noise is anthropogenic and it penetrates to depths of 200 meters even at frequencies exceeding 5 Hz. This observation is contradicting the common assumption that the seismic noise consists of the surface waves.

How to cite: Kalinichenko, O., Eisner, L., Stanek, F., Waheed, U., Hanafy, S., and Jechumtalova, Z.: Decay of seismic noise at shallow boreholes: Observations from Groningen., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7497, https://doi.org/10.5194/egusphere-egu24-7497, 2024.

EGU24-8100 | PICO | ERE5.8 | Highlight

CO2 storage in saline aquifers: multi-scale processes visualized using the Sleipner case 

Tae Kwon Yun, Mateja Macut, Katja Schulze, Philip Ringrose, and Carl Fredrik Berg

Injection of dense-phase CO2 in a saline sandstone aquifer involves several processes which ideally work together to ensure effective long-term storage. The main processes are flow of free-phase CO2 (controlled by viscous and gravity forces), residual trapping at the pore scale, structural trapping at the scale of geological heterogeneities and dissolution in the aqueous phase.  Assessment of possible lateral and vertical migration along high-permeability layers or faults and fractures will also require stress-sensitive flow models which consider the phase behaviour of CO2, and the associated coupled thermal-hydraulic-mechanical-chemical processes.
Many insights into these complex processes can be obtained by analysis of the time-lapse seismic data at Sleipner CO2 storage project in Norway, in conjunction with findings derived from the quantitative and qualitative uncertainty analysis of the medium-scale flow experiments at the Mont Terri Rock Laboratory (Switzerland), involving periodic injections over long-term (CO2LPIE). The insights at Sleipner include the effects of internal shale layers and shale breaks in controlling the actual multi-layer CO2 distributions, the likely contribution of different of trapping mechanisms and the effectiveness of the overlying caprock. Another set of insights gained from these data are estimates of the effective use of the pore space at different length scales. The seismic imaging datasets can be used to show that at the scale of whole storage unit the overall storage efficiency is in the range of 2-5%, with the result depending very much on how the storage volume is defined. When the effects of areal and vertical sweep efficiency are considered, the fraction of the pore space occupied by CO2 rises to around 40-50%.
We illustrate these multi-scale processes using seismic data, analytical analysis, example flow models and 3D/4D visualization. Use of Invasion Percolation (IP) flow models is contrasted with multiphase (finite difference) flow simulators. With this approach CO2 migration problems will be addressed, as well as various open-source research codes will be used to develop enhancements for handling fluid mixing between hydrocarbon and CO2 phases in brine-saturated media. Moreover, coupled thermal modelling is found to be important at this site due to significant temperature changes as the CO2 plume expands and rises within the formation. Next to classic PC screen display, we empower the visualization by using the extended reality (XR) platform for geoscience, BaselineZ. This allows for true 3D (holographic) display in virtual reality (VR) as well as remote and interactive collaboration around the Sleipner dataset and thus leads to new insights. 

How to cite: Yun, T. K., Macut, M., Schulze, K., Ringrose, P., and Berg, C. F.: CO2 storage in saline aquifers: multi-scale processes visualized using the Sleipner case, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8100, https://doi.org/10.5194/egusphere-egu24-8100, 2024.

EGU24-10213 | PICO | ERE5.8

How THM Changes in Layered Geological Systems Influence Stability of Fractured Networks 

Anas Sidahmed and Christopher Mcdermott

Various geo-energy applications such as geothermal energy, Carbon Capture and Storage (CCS) and underground heat storage are some of the technologies leveraged to realize Paris Agreement goals by cutting greenhouse gases emissions (GHG). However, these applications require in-depth understanding of the effect of coupled Thermal, Hydraulic, Mechanical and Chemical (THMC) processes that take place in the deep subsurface geological layers. This study focuses on the modeling of THM coupled processes in heterogeneous layered reservoirs.

When geological heterogeneities exist in the subsurface, each layer will have its own thermal, geomechanical and geological properties such as thermal conductivity, thermal expansion coefficient, porosity, permeability, Young’s modulus, Poisson’s ratio and so on. These variations in the properties add more complexity to the behavior of coupled THM processes of the system, which in turn requires sophisticated modeling approaches. To reduce complexity, the subsurface layers can be bundled into groups called “geomechanical facies” based on the mentioned material properties from THM characteristics perspective.

The work in this paper is based on key generic features of actual geo-energy applications where simulation modeling has been utilized to demonstrate how coupled THM processes are affected in heterogenous layers compared to homogenous layers. Hypothetical heterogenous layers have been divided into sets of distinct geomechanical facies. OpenGeoSys (OGS) open-source Finite Element based THMC code was utilized to build the run simulation models.

The results demonstrate that variations in the rock thermal, hydraulic and mechanical properties among different neighboring layers have a significant and individually different impact on stress mapping and distributions in addition to strain transfer to the surface. Geomechanical stability of the system parts that are more prone to failure such as fractures and faults were assessed using Factor of Safety (FOS) analysis which are based on stress distribution and rock mechanical properties. Results suggest that geological heterogeneity has more significant impact on hard rocks compared to soft rocks. The latter (i.e., soft rocks) have the ability to maintain sealing capability of caprocks because they are more ductile and have more room for further deformation prior to failure.

The simulation modeling results in this study contributes to the understanding of the key THM processes involved in heterogenous layered systems. Furthermore, this work provides valuable insights towards developing more generic design criteria and predictive models for various geo-energy applications which can be tailored and used in the design of the particular systems.

How to cite: Sidahmed, A. and Mcdermott, C.: How THM Changes in Layered Geological Systems Influence Stability of Fractured Networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10213, https://doi.org/10.5194/egusphere-egu24-10213, 2024.

EGU24-17949 | ECS | PICO | ERE5.8

Modelling coupled hydro-mechanical processes of gas flow in the Opalinus Clay 

Matthijs Nuus, Antonio Pio Rinaldi, Robert Cuss, Manuel Sentis, Jocelyn Gisiger, Bastian Graupner, Fabiano Magri, Frederic Bernier, and David Jaeggi

Deep geological repositories rely on a natural geological barrier with a low permeability to ensure radioactive waste containment and prevent radionuclide transport into the biosphere. For the Swiss repository concept, the Opalinus Clay formation is considered as the natural geological barrier. After high-level radioactive waste are disposed of in a repository within the host-rock, corrosion of metal containers in anaerobic conditions can result in the release of hydrogen. Due to the low-permeability of the host-rock, elevated gas pressures are expected. If the gas pressure exceeds the minimum principal stress, fracturing of the rock could occur. It is therefore important to assess the possible impacts of this process on the integrity of the repository such as a possible increase of the permeability of the host formation.

Production of hydrogen is anticipated to span more than 100,000 years, and understanding how gas transport occurs in a low-permeable host-rock is therefore an important aspect for the long-term safety of the repository. Gas transport can generally be subdivided in four different mechanisms: (1) advective-diffusive flow, (2) visco-capillary two-phase flow, (3) dilatancy-controlled gas flow and (4) gas transport along macroscopic tensile fractures. Gas flow rate and the microstructure of the host rock largely control the dominating gas transport mechanism, but the exact variables determining the process are poorly quantified.

The GT (Gas Transport) experiment at Mont Terri was designed to study the pressure and deformation effects after injecting gas into the Opalinus Clay. Helium was injected with increasing pressure increments until a gas breakthrough was observed. The borehole into which the helium was injected was surrounded by eight observation boreholes providing deformation and pore pressure observations.The results of the experiment have been used to create a coupled hydro-mechanical model using TOUGH-FLAC, which couples the multiphase flow and heat transport simulator TOUGH3 with the geomechanical simulator FLAC3D. The model uses the helium injection rates as input and computes the resulting pressure and deformation responses. By running models with different transport mechanisms (e.g. two-phase only, both two-phase and dilatancy, allowing fracture formation) and by comparing the pressure and deformation results with the observations, insight is gained into the dominant transport mechanisms in the Opalinus Clay. Preliminary results reveal a slow build-up of strain and a relatively small pressure drop after gas injection begins, suggesting that dilatancy-controlled gas flow occurred.

How to cite: Nuus, M., Rinaldi, A. P., Cuss, R., Sentis, M., Gisiger, J., Graupner, B., Magri, F., Bernier, F., and Jaeggi, D.: Modelling coupled hydro-mechanical processes of gas flow in the Opalinus Clay, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17949, https://doi.org/10.5194/egusphere-egu24-17949, 2024.

EGU24-18589 | ECS | PICO | ERE5.8

Investigating the Effect of Fracture Properties on Peclet Number of Enhanced Geothermal Systems 

Khashayar Khezri, Emad Jahangir, Dominique Bruel, and Murad Abuaisha

Understanding heat transfer mechanisms in subsurface environments is crucial for deep geothermal energy exploitation. Despite multiple studies on heat transfer in porous media, the combination of different heat transfer mechanisms with fracture networks leads to uncertainty in the temperature distribution in geothermal sites.

More specifically, heat convection and conduction are two major mechanisms responsible for heat transfer in porous media. Conduction occurs through rock matrix and is more dominant than convection in intact rocks due to their low porosity. However, fracture networks in rocks increase fluid transfer in certain directions, making convection more important in heat transfer. At a certain point, it becomes difficult to identify which mechanism is more prevalent. Besides this difficulty, achieving a balance between these two key mechanisms and determining the optimal Peclet number is very crucial for the geothermal energy industry to extract adequate volume of water at the desired temperature, which is essential for smooth operation of geothermal systems. In this study, a two dimensional coupled thermo-hydraulic model in COMSOL is developed to simulate heat transfer mechanisms in enhanced geothermal systems on field scale. Characteristic time variables based on hydraulic and thermal diffusivities are defined to monitor heat distribution through the domain caused by each mechanism. Finally, a sensitivity analysis is performed to identify how the temperature is affected by rock (thermal and hydraulic) parameters and fracture patterns. The simulation results indicate that the Peclet number is highly dependent on fracture network.

How to cite: Khezri, K., Jahangir, E., Bruel, D., and Abuaisha, M.: Investigating the Effect of Fracture Properties on Peclet Number of Enhanced Geothermal Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18589, https://doi.org/10.5194/egusphere-egu24-18589, 2024.

EGU24-18886 | ECS | PICO | ERE5.8 | Highlight

Multi-scale study on fluid-rock interaction in caprock and reservoir rocks for enhanced CO2 sequestration 

Prescelli Annan, Claudio Madonna, Antonio Pio Rinaldi, and Alba Zappone

In the context of geological CO2 sequestration, understanding the complex interaction between reactive fluids and the rock matrix is pivotal in efficient and safe carbon storage. This paper presents a recently initiated research plan, spanning laboratory and pilot scale, covering two main scenarios: A) reactive reservoir rocks (e.g. basalt and peridotite), and B) claystone saline aquifers with sandstone reservoir rocks and claystone caprock. To investigate the specific effects of CO2 exposure on rock properties, we propose a 1-2 year exposure experiment on intact rock core samples. The experiment will be conducted using a batch reactor system equipped with continuous pH monitoring and carefully controlled to replicate in situ salinity, pressure and temperature levels. Before, during and after exposure, samples will be analysed using CT scanning to detect changes in porosity, and mechanical and physical properties will be assessed before and after exposure. Preliminary characterisation of the cores prior to exposure to CO2 will also be presented.

In parallel decameter scale experiments spanning many months of CO2 injection are conducted at the Mont Terri underground rock laboratory in Switzerland. The experiments involve observing the injection of CO2-saturated brine into a fault zone within Opalinus Claystone—an analogue caprock. This contributes to a more comprehensive understanding of fluid injection on fault reactivation, particularly within the context of leakage processes at shallow depths crucial to CO2 storage security. Preliminary results on clay deformation in response to rapid increase of injection pressure will be presented.

This research plan aims to understand reactive processes in different geological contexts fundamental to carbon storage strategies. Operating at multiple scales - from laboratory to pilot scale analysis - our study aligns with the session's broader goal of advancing the understanding and predictive capabilities of coupled processes induced by geoenergy applications. By sharing preliminary results and fostering collaboration, we aspire to maximise the scientific results of our laboratory experiments and contribute to the scientific community's search for sustainable solutions in carbon storage strategies.

How to cite: Annan, P., Madonna, C., Rinaldi, A. P., and Zappone, A.: Multi-scale study on fluid-rock interaction in caprock and reservoir rocks for enhanced CO2 sequestration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18886, https://doi.org/10.5194/egusphere-egu24-18886, 2024.

EGU24-703 | ECS | Orals | NH3.5 | Highlight

Integrated Monitoring and Multi-Hazard Early Warning System for Himalayan Region: Insights from the Chamoli Disaster of 2021 

Anil Tiwari, Kalachand Sain, and Amit Kumar

The material/rock failure is not a sudden progression but is preceded by multiple progressive nucleation phases during which relaxation or rearrangement of material leads to creep and accelerates with time before any major rupture. The monitoring of Himalayan surficial dynamics is challenging and expensive to access for scientific research purposes. The unfelt destructions produced by the surficial mass movement activities can only be recognized by satellite images if other monitoring is not possible. We focused on the Chamoli region, which is the most vulnerable or hazard-prone region in the NW Himalaya. Recently, on 7th February 2021, a huge rock-ice mass detached from the Raunthi peak at a height of 5600 m in the Chamoli district of Uttarakhand Himalaya. We found several pre-collapse and unfelt activities,in a post-mortem study, which were recorded at nearby highly sensitive broad-band seismic stations and radon detector instruments. The integrated study of the recorded signatures allows us to reconstruct the complete dynamic time-dependent nucleation phases, which intensify as time gets closer to the main detachment. Continuous monitoring of vulnerable regions, coupled with the identification and characterization of precursory signals, holds the fundamental clue for hazard mitigation. After the Chamoli disaster, we are more focused on monitoring unfelt activities and anomalies linked to hazards in the proximity of potentially endangered zones and also planning to deploy multi-parametric instruments such as automatic weather stations (AWS), broad-band seismometers (BBS), automatic water level recorders (AWLR) and infrasound array for real-time monitoring and integrated analysis with a view to forewarn against the hazards in the Himalayan terrain. The dense network of sensors will allow us to collect high-quality data and crucial information as a way forward for disaster mitigation and societal benefit.

How to cite: Tiwari, A., Sain, K., and Kumar, A.: Integrated Monitoring and Multi-Hazard Early Warning System for Himalayan Region: Insights from the Chamoli Disaster of 2021, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-703, https://doi.org/10.5194/egusphere-egu24-703, 2024.

EGU24-3808 | ECS | Orals | NH3.5

The mountains are falling and I must go: paraglacial landslide response to glacier debuttressing in southern Alaska 

Jane Walden, Mylène Jacquemart, Bretwood Higman, Romain Hugonnet, Andrea Manconi, and Daniel Farinotti

Glacier mass loss due to anthropogenic climate change has far-reaching implications, one of which is the destabilization of paraglacial slopes. The buttressing force, or the support provided by the glacier to adjacent valley walls, changes and eventually decreases to zero as glaciers dwindle. However, the processes governing this (de-)buttressing, the amount of support glaciers can provide, and to what extent glacier retreat is responsible for landslide (re-)mobilization are still poorly understood. Paraglacial landslides can be hazardous, especially in the proximity of deep water, where a catastrophic failure has the potential to produce a tsunami.

We investigated eight large (roughly 20 to 500 million m3) paraglacial landslides in southern Alaska, a region which is experiencing some of the fastest glacier retreat worldwide. The selected landslides have varying degrees of ice contact: some are still experiencing active glacier retreat and thinning, others have already lost contact with the glacier. One of the selected landslides has undergone catastrophic failure, the others have not. We reconstructed the deformation history of the eight sites using Landsat images from the 1980s to present and automated and manual feature tracking. The slope evolution was then compared to ice thinning rates, ice velocity changes, the proximity of the landslide to the glacier terminus, environmental conditions, and seismic energy. 

We found that both thinning and retreat are sufficient conditions for landslide (re-)activation. In two cases we documented periods of acceleration for slopes where ice is still present at the landslide toe but thinning rapidly. In two further cases, substantial thinning did not correspond to any detectable motion. In four cases we observed a rapid retreat of the glacier terminus as the glacier retreated progressively up-fjord which led to the sudden onset of slope motion. This acceleration suggests decreased stability, which may be important in close proximity to water-filled basins, where rapid retreat due to calving is common and catastrophic landslides can cause tsunamis if they impact the water. The association of reduced glacier-slope contact, especially at rapidly retreating termini, with accelerated slope deformation suggests that buttressing is indeed an important stabilizer for paraglacial slopes. Furthermore, the off-and-on nature of deformation suggests there are critical thresholds for buttressing that, when crossed, leave slopes prone to rapid change.

How to cite: Walden, J., Jacquemart, M., Higman, B., Hugonnet, R., Manconi, A., and Farinotti, D.: The mountains are falling and I must go: paraglacial landslide response to glacier debuttressing in southern Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3808, https://doi.org/10.5194/egusphere-egu24-3808, 2024.

EGU24-3812 | Orals | NH3.5

Millions of years of landslides in the Patagonian tableland 

Tomáš Pánek, Jakub Kilnar, Michal Břežný, and Diego Winocur

Dating the lifespan of slow-moving landslides poses a major challenge, typically limited to the most recent slope evolution within maximally 103 to 104 years. The Patagonian tableland, characterized by plateau basalts overlying weak sedimentary and volcaniclastic rocks, ranks among Earth's largest landslide provinces. Certain contiguous landslide areas, shaped mainly by rotational slides and spreads, exceed 1000 km2, affecting hundreds of kilometers of mesa escarpments. Our new landslide mapping in eastern Patagonia has allowed us to establish an unprecedentedly long history of landslide evolution, utilizing cross-cutting relationships with dated chronological markers such as glacial moraines and trimlines, lacustrine and marine paleoshorelines, and lava flows. Our findings indicate that the escarpments of the Patagonian plateaus primarily evolved in a retrogressive mode. Both mesas within (or nearby) and outside Pleistocene ice limits involve landslides with topographic footprints that have persisted for over 1 Ma; the oldest documented landslide rim is overlain by a lava flow with a 40Ar/39Ar age exceeding 5 Ma. Even in the most arid parts of the Patagonian tableland, repeated landslide reactivations occurred in the Quaternary, including the Late Holocene. In the western glaciated area, this is likely due to glaciation/deglaciation pulses, while in the eastern extraglacial part, it is probably associated with wetter periods linked to the strengthening of the eastern Atlantic circulation. We conclude that the Patagonian tableland boasts the longest documented landslide topographic footprints on Earth. Future research should prioritize high-resolution (direct radiometric) dating of landslide (re)activations and their correlation with paleoenvironmental changes.

How to cite: Pánek, T., Kilnar, J., Břežný, M., and Winocur, D.: Millions of years of landslides in the Patagonian tableland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3812, https://doi.org/10.5194/egusphere-egu24-3812, 2024.

EGU24-3817 | Posters on site | NH3.5

Failed Patagonian tableland: landslides distribution and controls 

Jakub Kilnar, Tomáš Pánek, Michal Břežný, and Diego Winocur

Argentinian Patagonia is formed mostly by tableland relief created by Cenozoic basaltic efusions, general uplift and relief inversion. The tableland is vastly effected by landslides. Using TanDEM-X we manually maped 30 000 km2 of landslides in the Patagonian tableland and conducted spatial analysis of their distribution and controls. Based on relative dating to lava efusions, glaciation and paleoshorlines we propose, that the landslide activity in the region spans across several millions of years. In contrary to general knowledge of landslide distribution, most of the landslides in the Patagonian tableland are located in low-seismicity, tectonicaly stable, semiarid to arid conditions. We propose, that the leading landslide distribution control is the tableland stratigraphy: basaltic caprock overlaying weak sedimentary and volcanoclastic rocks. The caprock protects the underlying weak rocks and thus it becomes elevated above the surroundings over time, forming plateaus and mesas. As long as the topography of the formed tableland becomes high enough to laterally expose underlaying weak rocks, the tableland margins becomes unstable and collapse. It starts as lateral spreading a rotational landslides and later often evolve to flow-like mass movements. Many of the plateaus and mesas in the Patagonian tableland are fringed by almost continuous landslides. Some mesas are already completly consumed by landslides. This study helps to understand distribution and evolvement of landslides in volcanic tablelands.

How to cite: Kilnar, J., Pánek, T., Břežný, M., and Winocur, D.: Failed Patagonian tableland: landslides distribution and controls, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3817, https://doi.org/10.5194/egusphere-egu24-3817, 2024.

EGU24-4203 | Orals | NH3.5

Development of counterscarps by flexural toppling of schist in the Bedretto valley, Swiss Alps 

Masahiro Chigira, Satoru Kojima, Andrea Pedrazzini, Fei Li, and Michel Jaboyedoff

We investigated the geological structure and the development of DGSD in the south side of the Bedretto Valley, Swiss Alps by field survey, topographic analysis, trenching, and 14C dating.

The Bedretto valley has major slope breaks approximately 300 m above the current valley bottom, which separate the area into two domains. Above the slope breaks, and in the catchments of the tributaries of the Bedretto valley, large flexural toppling occurs with counterscarps and troughs on two ridges between tributaries. Their hinges expose on the side of each ridge to suggest that the flexural toppling reaches to the depth of 200 m. The two large flexural toppling accompanied settling down of a wedge-shaped ridge top, which is bounded by two face-to-face normal faults. Below the slope breaks and on the side slopes of Bedretto valley, smaller but sharper counterscarps and terraces, which are of the incipient stage of counterscarps, develop. These counterscarps and troughs appeared by the preferential shearing along tectonic faults, which are pervasive in the area with a ~30 m average spacing. They are nearly parallel to the steeply-dipping schistosity; the faults may originate as lateral faults but reactivated as normal gravitational faults.

Deformation of the trenched sediments suggests that the flexural toppling occurred intermittently along a fault during three events, in which the first event had the largest dip slip of 30 m, much larger than the displacements of the subsequent events.

The third event at least was probably induced by an earthquake shaking, which is strongly suggested by the injection of fault gouge into the overlying sediments in the trough. Such injection should have been caused by pore pressure build up during earthquake shaking.

How to cite: Chigira, M., Kojima, S., Pedrazzini, A., Li, F., and Jaboyedoff, M.: Development of counterscarps by flexural toppling of schist in the Bedretto valley, Swiss Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4203, https://doi.org/10.5194/egusphere-egu24-4203, 2024.

EGU24-5228 | ECS | Orals | NH3.5

Influence of structural geology on rock slope failure in a paraglacial environment: insights from the Southern Swiss Alps 

Alessandro De Pedrini, Andrea Manconi, Christian Ambrosi, Federico Agliardi, and Christian Zangerl

The onset and development of large rock slope failures in alpine environments are influenced by a combination of multiple factors, including lithology, inherited structural features on different scales, and the morpho-climatic history of the region. In the Southern Swiss Alps, seven large rock slope failure accumulations can be recognized along the five valleys north of Bellinzona, (Riviera, Leventina and Blenio in Canton Ticino, Calanca and Mesolcina in Canton Graubünden).  
The region exposes a predominance of crystalline rocks as orthogneiss and paragneiss with similar mechanical characteristics, an aspect that limits the lithological control on the rock slope failures. In addition, the availability of detailed geochronological documentation of both glacial retreat following the Last Glacial Maximum LGM and the major slope collapses motivated the search for a potential correlation, which, however, has not been found (De Pedrini et al. 2023). 
For this reason, slope failures in this region are potentially controlled by the peculiar structural setting. 
In this work, we aim at investigating the impact of structural geology on style of activity and timing of the rock avalanches and deep rockslides of the region. We rely on a catalog of the instabilities (Ambrosi and Czerski, 2016 and De Pedrini et al. 2023) and lineament mapping based on the visual interpretation on 0.5 to 2 m resolution hillshade (swissALTI3D multidirectional Hillshade, Federal Office of Topography swisstopo) and stereo-photogrammetry of aerial strips (Image strips swisstopo, Federal Office of Topography swisstopo). The manual tracing of lineaments is compared with an automatic lineaments tracing performed on surface models of Switzerland in the form of a classified point cloud (swissSURFACE3D, Federal Office of Topography swisstopo). Knowledge on structural lineaments and site-specific field surveys allow us to identify the proper structural setting for each large rock slope failure (already collapsed, active or dormant), and to study structural patterns that may promote slope response after deglaciation at regional scale.
The results of this analysis, aimed at the definition of the influence of glacial retreat plus the influence of structural geology, could provide an additional instrument to the comprehension of the paraglacial slope response in crystalline rocks and could thus represent an added value for long-term hazard assessment.

How to cite: De Pedrini, A., Manconi, A., Ambrosi, C., Agliardi, F., and Zangerl, C.: Influence of structural geology on rock slope failure in a paraglacial environment: insights from the Southern Swiss Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5228, https://doi.org/10.5194/egusphere-egu24-5228, 2024.

EGU24-5417 | ECS | Posters on site | NH3.5

Numerical modeling of collapsed deep-seated gravitational slope deformations: insights from Velka Fatra Mts., Slovakia 

Andrius Toločka and Veronika Kapustová

Large-scale deep-seated gravitational slope deformations (DSGSDs) are common but not highly investigated phenomena around the world. In the Carpathian Mountains, they played an important role during the Quaternary evolution of typical core mountain ridges formed by crystalline basement and surrounded by Mesozoic deposits. There is evidence that most of the biggest catastrophic rock slope failures (collapses) in the Carpathian Mountains appeared exactly in areas that are affected by DSGSDs. Two DSGSD-affected slopes (Brdo and Žlebiny) on the northeast side of the Velka Fatra Mountains (Western Carpathians, Slovakia) have been subjected to a detailed investigation involving geomorphic mapping, remote sensing analysis, structural data collection, and numerical modeling. To improve our understanding of these gravity-induced processes, we performed a back-analysis of collapsed DSGSDs through a 4-stage continuum-based finite-element model set up using the RS2 code (Rocscience). We used geomechanical rock data from fieldwork and previous laboratory tests, as well as interpretation in RSData software (Rocscience), to obtain the major rock mass parameters for the models. Results show that these DSGSDs are strongly predisposed by regional geological structures given by the intersection of bedding planes, joint sets, and thrust faults. The numerical modeling approach and performed back-analysis have enabled a better view of the development of these deep-seated slope failures in the Velka Fatra Mountains. It suggests a high diversity of mechanisms leading to the origin of these DSGSD cases. The main causal factors influencing their development have been bedrock structure, the lithological composition of dolomite and limestone layers, thrust faulting, and, finally, deep weathering of the rock mass. Both cases have deep basal shear zones and a few series of gravitational faults associated with complex joint sets. According to the numerical modeling results, Brdo DSGSD shows a typical scenario of a symmetrical sackung surrounded by shallow landslide areas, while Žlebiny DSGSD developed into a one-sided deep-seated slide with a few large-scale tilted rock blocks.

How to cite: Toločka, A. and Kapustová, V.: Numerical modeling of collapsed deep-seated gravitational slope deformations: insights from Velka Fatra Mts., Slovakia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5417, https://doi.org/10.5194/egusphere-egu24-5417, 2024.

A fixed point in geodesy is a stable survey point that fulfils the following two conditions: The point is known in coordinates from a previous survey (by position and/or height) and the point is permanently marketed (stabilised) in nature. Fixed points serve as reference points for surveys of all kinds. To determine the coordinates of the fixed points in the modern European reference system ETRS89, not only all previously measured GNSS vectors are used, but also all terrestrial observations measured since 1906, i.e. direction, elevation angle and distance measurements (Otter et al., 2017). More than 20.000 individual RTK measurements on these fixed points by using APOS (Austrian Positioning Service) complete the measurement dataset. Approximately 60.000 triangulation points (TPs) form a three-dimensional point network throughout Austria, whereas about 70 % of all TPs have multiple measurements. Fixed points should be stable, but this is not always the case, as fixed points are often influenced in their spatial position by gravitational mass movements, among other factors.

We have interpreted the entire elevation model/hill shade of Austria (1-metre resolution, based on ALS-data) and mapped all DSGSDs that manifest themselves geomorphologically in the terrain. This data set was intersected with the fixed points in order to identify those points that lie within a DSGSD. By analysing the results of the individual fixed point survey epochs, conclusions can be drawn about deformation rates of mass movements after excluding possible sources of error and statements can be made retrospectively up to the year in which the particular point was created (Otter et al., 2017).

Overall the fixed point measurements of the Federal Office of Metrology and Surveying Austria (BEV) represent a high quality and long term dataset that stands for its own and can support other slope monitoring methods. The interpretation of the dataset concerning slope deformations is not trivial but can deliver information of the range of movements over decades with uncertainties of 0 to 1.5 cm.

By combining different data sources (InSAR, ALS, in-situ measurements, fixed points, ...) we can present a preliminary, comprehensive data set on the activity status and often associated deformation rates of DSGSDs in Austria.

References:

Otter, J.; Imrek, E.; Melzner, S. (2017) Geodätische Grundlagenvermessung als Werkzeug in der Naturgefahrenanalyse in: Wimmer-Frey, I.; Römer, A.; Janda, C. [Hrsg.] Angewandte Geowissenschaften an der GBA. Wien, S. 147–152.

 

 

How to cite: Ostermann, M. and Blauensteiner, F.: Analysing geodetic fixed point survey time series to evaluate the long-term activity of DSGSDs in Austria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5578, https://doi.org/10.5194/egusphere-egu24-5578, 2024.

EGU24-6268 | Posters on site | NH3.5

Enhancing rockfall modelling through an integrated workflow, from source area definition to susceptibility zoning 

Roberto Sarro, Mauro Rossi, Paola Reichenbach, Pablo Vitali Miranda-Garcia, and Rosa María Mateos

The main complexity of rockfall modelling lies in the need for a series of dedicated methodological choices and assumptions. Despite specific aspects of modelling have been largely discussed in the literature, a comprehensive methodology to assess susceptibility posed by rockfalls is still missing. To fill this gap, we have proposed a novel workflow in this study, including methods for identifying source areas, deterministic runout modelling, classifying runout modelling output to establish an objective rockfall probabilistic susceptibility zonation, and comparing and validating the results. This methodology is applied to the island of El Hierro (Canary Islands, Spain), where rockfalls pose a significant threat to structures, infrastructure, and the population.

In the first stage, three different approaches were proposed to identify rockfall source areas, ranging from scenarios with limited data availability to those with extensive topographic, geological, and geomorphological information. The first approach employed a morphometric criterion, establishing a slope angle threshold to identify source areas. The second approach used a statistical method employing Empirical Cumulative Distribution Functions (ECDF) of slope angle values. The third method employed a probabilistic modelling framework that combined multiple multivariate statistical classification models, using mapped source areas as dependent variables and thematic information as independent variables.

Subsequently, a rockfall simulation was carried out using a physically based model using the maps of the three source areas as input. A key result of the rockfall modelling simulations was the rockfall trajectory count maps. These maps, highlighting areas prone to rockfall on El Hierro, indicated the probability that a given pixel would be affected by these processes.

Then, this study also explores the strategies to validate the rockfall susceptibility model outputs, using different types of inventories. Therefore, to get susceptibility maps with a probabilistic approach, two classification methods were applied: unsupervised and supervised statistical techniques using distribution functions. The unsupervised classification used only the raster map of rockfall trajectory counts, while the supervised classification considered additional data on areas already affected by rockfalls.

Diffused metrics comparing modelled and observed values (i.e., ROC plots and correspondent AUCROC) can be used to show the performances of susceptibility models, regardless the adopted classification approach. Finally, the six susceptibility maps were compared to emphasize the impact of source area definition on the distribution of rockfall trajectories.

In summary, the methodology proposed provides guidance for an objective and reliable rockfall modelling, supporting civil protection, emergency authorities, and decision-makers in evaluating and assessing potential rockfall impacts. This contributes to enhanced rockfall hazard assessments and improved mitigation strategies on the island of El Hierro and potentially in similar geological settings globally.

How to cite: Sarro, R., Rossi, M., Reichenbach, P., Miranda-Garcia, P. V., and Mateos, R. M.: Enhancing rockfall modelling through an integrated workflow, from source area definition to susceptibility zoning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6268, https://doi.org/10.5194/egusphere-egu24-6268, 2024.

EGU24-6335 | Orals | NH3.5 | Highlight

Infrasound analysis of break-off events  from Planpincieux glacier, Mount Blanc, Italy 

Emanuele Marchetti, Fabrizio Troilo, Paolo Perret, Giacomo Belli, Duccio Gheri, and Claudia Sanchez

Glacier break-off events constitute a severe hazard in Alpine regions and their effects are expected to increase soon because of climate changes. Within this rapidly changing scenario, the development and implementation of new monitoring solutions and warning systems, able to detect collapses and possibly estimate the volumes, is of critical importance.

In this paper we present the analysis of avalanching activity from Planpincieux glacier (Aosta valley) through infrasound data collected by a small aperture (~ 150 m) array deployed at short distance (~ 2000 m) from the hanging front. The analysis is performed over five time periods between August 2020 and December 2022 summing up into 360 days. From a data set of confirmed events, infrasound wave parameters (intensity, peak amplitude, frequency and duration) are compared with collapse volumes estimated from photogrammetry and experimental relations are defined.

Morerover, characteristics of infrasound signals of confirmed events are used to extract signals that are likely produced by collapses from the whole dataset of infrasound detections and a volumetric flux of collapses from the front of the Planpincieux glacier is derived through time.

 

How to cite: Marchetti, E., Troilo, F., Perret, P., Belli, G., Gheri, D., and Sanchez, C.: Infrasound analysis of break-off events  from Planpincieux glacier, Mount Blanc, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6335, https://doi.org/10.5194/egusphere-egu24-6335, 2024.

EGU24-6627 | ECS | Posters on site | NH3.5

Landslides on the growing folds of the Kura fold-and-thrust belt (Azerbaijan, Georgia) 

Michal Břežný, Tomáš Pánek, Hans-Balder Havenith, and Alessandro Tibaldi

Rising hillslopes in the active fold-and-thrust regions present new landslide-prone slopes. However, studies investigating landslides in newly formed fold-and-thrust belts are limited. In this research, we analyse landslide occurrences in the Kura fold-and-thrust belt, a geologically active region at the southern edge of the Greater Caucasus. This area has experienced significant tectonic shaping over the last 2-3 million years, affecting Miocene to Quaternary sediments. Using satellite imagery, we identified about 1600 landslides, a quarter of which are active. These landslides, although occupying less than 1% of the land, are predominantly found at higher elevations and areas with greater relief. They mainly occur in regions elevated by tectonic forces, especially on steep anticlines and valley slopes cut by active faults. Our findings lead to a conceptual model for the temporal evolution of landslide patterns in weak sediment-based fold-and-thrust belts: 1) Initially, slow deformations at thrust fronts lead to landslides in deep valleys intersecting the uplifting hanging walls. 2) As anticlines rise and steepen, they become more prone to planar sliding when dip slopes exceed friction angle, and valley development creates additional dip slopes resulting in widespread landslides. 3) Finally, erosion lowers relief, forming badlands and reducing landslide occurence.

How to cite: Břežný, M., Pánek, T., Havenith, H.-B., and Tibaldi, A.: Landslides on the growing folds of the Kura fold-and-thrust belt (Azerbaijan, Georgia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6627, https://doi.org/10.5194/egusphere-egu24-6627, 2024.

EGU24-6726 | Orals | NH3.5

A modified Voellmy rheology for modeling rock avalanches 

Stefan Hergarten

Voellmy's rheology was originally developed for snow avalanches in the 1950s. However, it has also been widely applied to rock avalanches and to debris flows. In its original form, Voellmy's rheology assumes that the effective friction is the sum of Coulomb friction and a velocity-dependent term. While the Coulomb friction term is necessary for letting avalanches stop after a finite time, it causes problems with regard to the long runout of huge rock avalanches. This long runout requires Coulomb friction coefficients much lower than typically assumed for granular media, which finally result in unrealistically smooth morphologies of the deposits. In this presentation, numerical simulations with a recently published modified version of Voellmy's rheology are shown and compared to the conventional version. The modified version assumes two distinct regimes of Coulomb friction and velocity-dependent friction with a transition at a critical velocity derived from the concept of random kinetic energy. The modified rheology explains the long runout of huge rock avalanches without assuming an artificially low Coulomb friction coefficient. Furthermore, it produces hummocky deposit morphologies even with isolated hills similar to toma hills.

How to cite: Hergarten, S.: A modified Voellmy rheology for modeling rock avalanches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6726, https://doi.org/10.5194/egusphere-egu24-6726, 2024.

Landslides, as a ubiquitous type of mass wasting phenomena, occur under various geological and environmental conditions and exhibit diverse failure patterns. Among various factors, weathering has been widely recognised as one of the primary drivers on landslide evolution over geological timescales. However, how weathering induces slope instabilities, including how pre-failure rock mass degradation contributes to the landslide failure development and post-failure deposition of mobilised geomaterials, has not been fully understood. In this study, we develop a novel, physics-based unified computational framework to capture weathering-induced landslide evolution over multiple time scales, from the long-term pre-failure rock mass deformation to the short-term slope rupture and post-failure runout dynamics. Weathering laws and failure criteria are coupled to capture the combined effects of time-dependent strength degradation and strain-driven damage processes, while a frictional velocity-weakening law is adopted to characterise the rapid movement of yielded masses. The non-linear governing equations of landslide dynamics are solved using an implicit particle finite element framework that can model all the landslide stages from the long-term material degradation to short-term failure and runout. We further investigate the effects of weathering conditions (type and rate), geological properties (fracture sets and rock matrix) and slope geometry (angle and shape) on the failure patterns. Our high-fidelity numerical simulations capture the emergence of diverse landslide failure patterns resulting from the complex interplay among rock lithology, fracture distribution, weathering process, and gravitational forcing. Our numerical results show that matrix-dominated weathering tends to produce shallow landslides, while fracture-dominated weathering promotes the occurrence of deep landslides. For fracture-dominated weathering, the orientation of pre-existing fractures and the slope ratio significantly control the failure mode (e.g. falling, toppling, sliding, etc.), which further affects post-failure runout behaviour. Our computational framework opens the door to investigating and understanding weathering-induced rock slope failure evolution across spatial and temporal scales.

How to cite: Wang, L., Loew, S., Gu, X., and Lei, Q.: Emergence of diverse failure patterns in weathering-induced landslides: Insights from high-fidelity particle finite element simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6969, https://doi.org/10.5194/egusphere-egu24-6969, 2024.

In the realm of natural Earth-surface processes, such as mass movements exemplified by rock avalanches, a substantial entrainment of bed material along their trajectory is a common occurrence, amplifying both volume and run-out distance. The heightened mobility of these rapid gravity flows has been frequently ascribed by numerous researchers to the complete or partial fluidization of path material induced by swift undrained loading. An intriguing question arises: are there additional entrainment mechanisms at play in this process? To address this query, we executed a series of flume experiments designed to replicate rock avalanches overriding a saturated bed material. Our experimental findings revealed that the overriding flow induced a state of fluidization in the bed material, rendering it viscous. Furthermore, we observed that the rapid loading by the overriding debris increased pore pressure at the base, although it did not reach the threshold of complete fluidization. Rheological analysis of the bed material unveiled significant shear-thinning behavior, with viscosity diminishing rapidly as shear strain rate increased. Consequently, we posit that the concurrent effects of excess pore pressure at the basal layer and shear-thinning rheology in the flowing mass contributed to the fluidization of bed material and the ensuing extended run-out distance. This discovery offers a plausible natural elucidation for the extraordinary mobility of rock avalanches and holds promise for refining the precision and reliability of numerical simulations through the integration of the viscous model derived from our experimental endeavors.

How to cite: Zheng, Y. and Hu, W.: Flume tests and rheological experiments provide insights into the fluidization of bed material induced by shear thinning during the entrainment of rock avalanches., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7405, https://doi.org/10.5194/egusphere-egu24-7405, 2024.

EGU24-7631 | ECS | Posters on site | NH3.5 | Highlight

Causes, consequences and implications of the 2023 Lake Rasac GLOF, Cordillera Huayhuash, Peru 

Adam Emmer, Oscar Vilca, Cesar Salazar Checa, Sihan Li, Simon Cook, Elena Pummer, Jan Hrebrina, and Wilfried Haeberli

Glacierized Peruvian mountain ranges are experiencing accelerated glacier ice loss, including the second highest mountain range – Cordillera Huayhuash – which has lost about 40% of its glacier area (deglaciated area of approximately 34 km2) since the 1970s. The exposure of a new land is associated with various processes including the formation and evolution of glacial lakes, changing stability conditions of mountain slopes, and rapid mass movements. In this study, we integrate the analysis of meteorological data, remotely sensed images and field observations in order to document the most recent large mass movement-induced glacial lake outburst flood (GLOF) from moraine-dammed Lake Rasac (February 2023). We found that the triggering mass movement (the failure of Rasac arête ridge with an estimated volume of 1.1 to 1.5 ∙ 106 m3) occurred from the frozen rock zone with cold, deep-reaching permafrost and was preceded by several small magnitude precursory events. The stability reduction of the frozen rocks in the detachment zone most likely relates to deep warming, but not to critical conditions of warm permafrost with unfrozen water. Further, we describe the surprisingly short-distanced process chain (attenuated by the Lake Gochacotan located 3.5 km downstream from the detachment zone) and analyze the transport of large boulders with the use of hydrodynamic modelling, revealing that flow velocities > 5 m/s must have been reached in case of translational motion and > 10 m/s in case of rotational motion of the largest transported boulders (diameter > 3.5 m). This study helps us to understand (i) mechanisms, amplification and attenuation elements in GLOF process chains; and (ii) altering frequency-magnitude relationships of extreme processes in rapidly changing high mountain environments on regional scale (both large magnitude rockfalls and GLOFs). Considering the recent Peru-wide GLOF inventory published in 2022, this event corroborates the assumption of increasing frequency of large mass movement-induced GLOFs originating from warming permafrost in recent decades. 

How to cite: Emmer, A., Vilca, O., Salazar Checa, C., Li, S., Cook, S., Pummer, E., Hrebrina, J., and Haeberli, W.: Causes, consequences and implications of the 2023 Lake Rasac GLOF, Cordillera Huayhuash, Peru, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7631, https://doi.org/10.5194/egusphere-egu24-7631, 2024.

EGU24-8202 | ECS | Posters on site | NH3.5

Mapping release and propagation areas of permafrost-related rock slope failures in the French Alps: A new methodological approach at regional scale 

Maeva Cathala, Florence Magnin, Ludovic Ravanel, Luuk Dorren, Nicolas Zuanon, Frederic Berger, Franck Bourrier, and Philip Deline

Permafrost-affected rockwalls are increasingly impacted by the effects of climate change and rising air temperature leading to rock slope failures, threatening human lives and infrastructure. Populations and policy makers need new methods to anticipate these potential hazards and their consequences.  The aim of this study was to propose a mapping approach of susceptible release areas of rock slope failures and resulting runout distances at a regional scale to identify hotspots for hazard assessment.

To do so, we used an inventory of 1389 rock slope failures (volume > 102 m3)recorded in the Mont-Blanc massif from 2007 to 2019 and determined the topographical and permafrost conditions that are most prone to their triggering using a digital terrain model and a permafrost map. These conditions are used in a multi-criteria GIS approach to identify potential unstable slopes at the French Alps scale. Then, the potential release area map is used as input to map the runout of potential events, using a propagation model based on a normalised area dependant energy line principle. The resulting maps of release and propagation areas could be used to point out human assets and lakes which could be impacted by rock slope failure hazards. In this communication we will show how theses maps can be used to identify potential hotspots for a regional hazard assessment.

This work is a first step to identify hot spots for a regional hazard assessment where more detailed analyses will be required to evaluate potential risks at a local scale.

How to cite: Cathala, M., Magnin, F., Ravanel, L., Dorren, L., Zuanon, N., Berger, F., Bourrier, F., and Deline, P.: Mapping release and propagation areas of permafrost-related rock slope failures in the French Alps: A new methodological approach at regional scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8202, https://doi.org/10.5194/egusphere-egu24-8202, 2024.

EGU24-8891 | ECS | Orals | NH3.5

Climate change impact on rock avalanches in metamorphic rock masses in Tyrol, Austria 

Lukas Prandstätter, Christian Zangerl, Christine Fey, Tatiana Klisho, and Herbert Formayer

Rockfalls and rockslides are a common hazard in alpine terrain and are major factor of alpine landscape evolution. They are characterized by a complex combination of geological, hydrological, geomechanical and meteorolocical processes and occur in a wide variety of geological and structural settings and in response to various loading and triggering processes. In the Alps in particular, extremely rapid rock avalanches reaching a volume of several 10000 m3 or more have the potential to cause serious damage to both humans and infrastructure. As global warming progresses, the meteorological and climatological factors that influence rock avalanche formation will change. Especially, in the high mountain environment rock avalanches are strongly influenced by climate change due to thawing of permafrost and the retreat of glaciers. Less obvious is the influence of climate change on the formation of rock avalanches at lower altitudes, and thus there is a need for additional research.

In this study, we investigate the impact of global warming on selected rock avalanche case studies with volumes above several tens of thousands of cubic meters. The study area covers approx. 3400 km2 in the metamorphic rock mass of the Ötztal Stubai Crystalline, the Silvretta and the Glockner Nappes as well as the units of the Engadin Window of the Tyrolian Alps, Austria.

The aim of this work is to identify the processes that led to our case studies and if these processes are influenced by climate change factors, such as changes in temperature, precipitation, freeze-thaw cycles, snow coverage, etc. The climatic factors will be investigated in terms of both their short-term and long-term influence on the trigger mechanisms.

Advanced remote sensing techniques were used on site to carry out small to large-scale investigations. Terrestrial laser scanning (TLS) and Airborne laser scanning (ALS) enables us to create high-resolution recordings of inaccessible rock faces, supported by 3D point cloud analyzing tools. In addition, where TLS campaigns are not possible, we use an unmanned aerial vehicle (UAV) photogrammetry system that provides 3D point clouds and delivers a 3D model of the site. Geological field investigations were performed to record lithological, hydrogeological and structural features. This results in a comprehensive geological model of the failure area. A 3D discontinuity network was developed based on the combined analyses of remote sensing and discontinuity mapping data, providing the basis for structural geological analyses and distinct element modelling studies.

With regard to the above criteria, we have selected several case studies. Most of the case studies are located well above 2500 m above sea level in glaciated or recently glaciated areas. For all case studies, we were able to document at least one rock avalanche event with a volume exceeding several 10000 m3. A high-resolution climate model was created for the documented events. We then began to collect and evaluate the existing literature on the individual case studies.

How to cite: Prandstätter, L., Zangerl, C., Fey, C., Klisho, T., and Formayer, H.: Climate change impact on rock avalanches in metamorphic rock masses in Tyrol, Austria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8891, https://doi.org/10.5194/egusphere-egu24-8891, 2024.

EGU24-9085 | Orals | NH3.5 | Highlight

Probabilistic rockfall hazard and risk analysis along the El Portal Road in Yosemite National Park (California, USA) 

Federico Agliardi, Paolo Frattini, Greg M. Stock, Teseo Tosi, Camilla Lanfranconi, and Brian D. Collins

Yosemite National Park attracts millions of visitors each year with its stunning landscape, characterized by 1000 m high granite cliffs that are highly susceptible to rockfalls. Between 2010 and 2020, more than 300 rockfalls affected the 12 km long El Portal Road, used by 30% of visitors to enter the park, causing road closures and fatalities. Since National Park policies limit engineering mitigation on natural slopes, risks along roads are managed through traffic practices based on local hazard evaluation.

In this perspective we developed a probabilistic risk analysis workflow, aimed at estimating the annual probability of loss of life for people driving a vehicle along the road. The analysis was carried out for every 10-m-long segment of each travel lane, to and from Yosemite Valley. We based our analyses on 3D rockfall runout simulations performed with the Hy-STONE simulator, and on rockfall event (1857-2022) and vehicle traffic data collected by the U.S. National Park Service. Runout simulations were performed over 18 km2 with a spatial accuracy of 1 m. Simulation parameters were calibrated by back-analysis of past events and validated with field evidence. Fifteen million trajectories were simulated for five volume scenarios (0.01-100 m3), providing local information of transit frequency and kinetic energy.

A probabilistic hazard analysis was developed using the probabilistic rockfall hazard analysis (PRHA) method (Lari et al, 2014), which calculates the kinetic energy that can be exceeded in N years for each road segment. The method integrates different rockfall volume scenarios, with specific return times, in a probabilistic framework accounting for modelling uncertainties. For each considered scenario, the annual rockfall onset frequency was derived by a magnitude-frequency (MF) curve, based on the Yosemite event data from 2010-2020 and combined with a field-based talus MF curve, to redistribute frequency among blocks disaggregated during runout. The annual rockfall frequency at each slope segment was then calculated by combining the onset frequency with the transit frequency provided by runout simulations. The exposure analysis, dependent on block size, vehicle size and speed, considered the probability of a vehicle being in the path of a falling block when it reaches each road segment. Since blocks coming from different sources may converge to a common location based on the 3D topography, we reconstructed the distribution of kinetic energy at each target road segment.

The probability of exceeding specific energy values, combined with the annual frequency of rockfall occurrence, allowed deriving probabilistic hazard curves for each scenario and for the ensemble. Based on expected kinetic energy and considering the number of visitors passing along the road every day as well as assumptions on the vulnerability of vehicles, we calculated the possible annual number of casualties for each road segment and the entire road, to identify the road sectors with the highest risk. Computed risk varies in time with clear weekly and seasonal patterns depending on the number of daily visitors and the weather conditions. Our study will provide park managers with tools to make adaptive decisions for managing risk in dynamically changing conditions.

How to cite: Agliardi, F., Frattini, P., Stock, G. M., Tosi, T., Lanfranconi, C., and Collins, B. D.: Probabilistic rockfall hazard and risk analysis along the El Portal Road in Yosemite National Park (California, USA), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9085, https://doi.org/10.5194/egusphere-egu24-9085, 2024.

EGU24-10312 | Orals | NH3.5

Deep-seated gravitational slope deformations in Sierra Nevada, Spain: insights from InSAR, geomorphic and stability analyses 

Jorge Pedro Galve, Cristina Reyes-Carmona, Federico Agliardi, Mara Cannarozzi, José Vicente Pérez-Peña, Marcos Moreno-Sánchez, David Alfonso-Jorde, Daniel Ballesteros, Davide Torre, José Miguel Azañón, and Rosa María Mateos

Sierra Nevada (Spain) is a mountain range thoroughly studied from a geological-geomorphological perspective due to its anomalously high local relief and the ongoing debate about its origin and geological structure. From the standpoint of slope dynamics, several studies have carried out, but it was not until last year that deep-seated gravitational slope deformations (DSGSDs) were described in this mountain range. Their recognition was facilitated by synergizing geomorphological assessments with data from two well-established techniques: Differential Synthetic Aperture Radar Interferometry (DInSAR) and Landscape Analysis using the normalized channel steepness index (ksn), a geomorphic index commonly used to outline landscape perturbations in tectonically-active mountain ranges. Systematic evaluation of ksn anomalies along rivers illuminated key DSGSD sectors that were studied in detail. This approach resulted in a novel inventory of 17 DSGSDs in the southwestern sector of the range, providing an initial figure of the widespread occurrence of large DSGSDs in Sierra Nevada.

In a second phase, we conducted a detailed study of two slopes affected by DSGSDs in the Poqueira catchment, which provided new insights into Sierra Nevada’s DSGSDs. There, we characterized slope deformations by detailed morpho-structural mapping supported by fieldwork and interpretation of optical and LiDAR-derived imagery, resulting in morpho-structural maps and interpretative cross-sections. Collected data allowed setting up a series of 2DFEM multistage elasto-plastic models, parametrized by laboratory data and field rock mass assessment and validated with field evidence and DInSAR data. The studied cases are characterized by multiple nested landslides that become increasingly shallow, deformed, and active towards the valley. The geometry and kinematics of DSGSDs seem to be partially influenced by the orientation of foliation, indicating rock mass anisotropy, with dip slopes mainly exhibiting translational movements and anti-dip slopes demonstrating prevalence of rotational motions. We tested our initial hypothesis that these slope instabilities in the region were initiated because the development of fluvial incision, favored by the active tectonics and uplifting of the range. Preliminary findings of our analyses suggest that fluvial incision was a key trigger of DSGSDs in Sierra Nevada, but not the only one. Model simulations emphasize that, in addition to fluvial incision, rock mass anisotropy and long-term seismic activity played a crucial role in the onset and accumulation of large deformations of high slopes across the region, favoring the occurrence of significant mass movements. Considering this, rough estimates regarding the timing of incision and seismic activity suggest that initial DSGSD onset took place over a timescale of 104-105 years.

How to cite: Galve, J. P., Reyes-Carmona, C., Agliardi, F., Cannarozzi, M., Pérez-Peña, J. V., Moreno-Sánchez, M., Alfonso-Jorde, D., Ballesteros, D., Torre, D., Azañón, J. M., and Mateos, R. M.: Deep-seated gravitational slope deformations in Sierra Nevada, Spain: insights from InSAR, geomorphic and stability analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10312, https://doi.org/10.5194/egusphere-egu24-10312, 2024.

EGU24-10488 | Posters on site | NH3.5

Advanced Discontinuity Detection Algorithm for Geological Formations Using High-Density Point Cloud Data 

Antonin Chale, Michel Jaboyedoff, and Marc-Henri Derron

Advanced Discontinuity Detection Algorithm for Geological Formations Using High-Density Point Cloud Data

Antonin Chale, Michel Jaboyedoff, Marc-Henri Derron

Geological hazard analysis relies on precise identification and characterization of discontinuities in rock formations, crucial for evaluating rock stability. While techniques such as Structure-from-Motion (SFM) and Light Detection and Ranging (LiDAR) have significantly advanced high-density 3D point cloud (PC) data acquisition, detecting structural irregularities in complex geological formations remains a challenge. We have developed a new discontinuity detection algorithm that emulates human visual perception. The algorithm employs multi-angle scanning, point cloud optimization techniques, and efficient multiprocessing to comprehensively survey the point cloud. Density maps are generated to identify and determine the orientation of discontinuities, proving effective in both synthetic models and real LiDAR data. The algorithm comprises three primary steps: an initial point cloud scan, density map generation, and visualization of discontinuities with their initial orientation. A secondary scan focuses on the density map, projecting data into a 2D representation to detect a second vector orientation, crucial for identifying discontinuity sets. Thanks to the previous steps we can deduce the orientation of the discontinuity sets. While the algorithm’s capability to handle both synthetic and real-world data sets highlight its potential significance in structural analysis, ongoing work aims to enhance its applicability for larger and more complex datasets. But also, the possibility of extracting the points involved in the different discontinuity sets.

 

References:

Adrián J. Riquelme, A. Abellán, R. Tomás, M. Jaboyedoff, (2014)  " A new approach for semi-automatic rock mass joints recognition from 3D point clouds," Computers & Geosciences, Volume 68, 2014, Pages 38-52.

Matthew J. Lato, Malte Vöge, (2012) "Automated mapping of rock discontinuities in 3D lidar and photogrammetry models," International Journal of Rock Mechanics and Mining Sciences, Volume 54, 2012, Pages 150-158.

How to cite: Chale, A., Jaboyedoff, M., and Derron, M.-H.: Advanced Discontinuity Detection Algorithm for Geological Formations Using High-Density Point Cloud Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10488, https://doi.org/10.5194/egusphere-egu24-10488, 2024.

The steep terrain in mountainous areas poses a significant threat to people's safety due to frequent geological hazards(e.g., rockfall and slope collapse), making effective management, monitoring, and timely issuance of alerts and warnings are crucial for highway authorities. Previous studies focus on studying the rainfall thresholds for possible rockfall occurrence. Recently, machine learning using seismic signals has been applied to detect rockfall events and monitor rockfall activity. However, supervised machine learning algorithms have relied on predefined labels, and the limited accumulation of data makes predicting model reliability challenging. The time-consuming model training can limit the practical application of the above models. In response to both aforementioned challenges, we first selected the roadside slope with relatively high activity of rockfalls and earthquakes as the study site and installed a seismic station on the crest of the slope. Then, we use an unsupervised machine learning framework to reveal patterns from unlabeled data and cluster seismic signals in continuous seismic records in the single three-component seismic station. Using continuous seismic data over one year, our approach combines a deep scattering network, features extraction, and features cluster to detect structures of signal segments. To illustrate the framework, a deep scattering network performs convolution and pooling on the three-component seismic signal data to extract multiscale information and construct scattering coefficients. For feature extraction, four different algorithms were employed: principal components analysis (PCA), independent components analysis (ICA), singular value decomposition (SVD), and Uniform Manifold Approximation and Projection (UMAP). Subsequently, we cluster the primary features using unsupervised learning algorithms such as K-means and Gaussian Mixture Model(GMM). We demonstrate the group categories belonging to rockfall events with in-situ data time-lapse images and videos. An approach proposed in this study could achieve rapid model training for building on-site rockfall warning systems using only single-station seismic records. Our high capability recognition model of rockfall events is ready to be implemented globally with high rockfall activity.

 

Keywords: unsupervised machine learning, deep scattering network, rockfall, seismic records, on-site early warning 

How to cite: Li, Y.-R. and Chao, W.-A.: A fast unsupervised deep learning algorithm using seismic records of a single station for roadside rockfall recognition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14088, https://doi.org/10.5194/egusphere-egu24-14088, 2024.

EGU24-15526 | ECS | Posters on site | NH3.5

Investigation into rockslides by the adaptive rock discrete fracture analysis (RDFA) method 

Bin Gong and Tao Zhao

The rock discrete fracture analysis (RDFA) method was proposed as a combination of the rock failure process analysis method and the discrete element method. Leveraging the statistical strength theory and contact mechanics, it can effectively capture the intricate continuum-discontinuum behaviors inherent in rock mechanics, encompassing fracture and fragmentation phenomena. Enabled by a sophisticated nodal updating scheme, RDFA can dynamically adjust nodes at critical crack tips in accordance with strength criteria, facilitating accurate modeling of zero-thickness crack initiation and propagation. Noteworthy is its capacity to accommodate the inherent heterogeneity of rock masses, enabling holistic consideration of localized damage and fine crack development. Rigorously validated through the Brazilian disc and uniaxial compression tests, RDFA consistently aligns with the analytical solutions and experimental data. After that, it was applied to analyze the rockslide characteristics at the Anshan Road station in the Qingdao metro, China, and illuminated crucial insights. The results show that in the presence of 60° oriented joints with 5m spacing, the high stress concentration primarily emerged at the slope toe, leading to the localized tensile damage and the formation of a sliding surface. Subsequent rock sliding induced compression and collision among blocks, precipitating continuous failure within the sliding body. Additionally, the presence of intermittent joints notably contributed to progressive rockslide, particularly triggering the localized failures in the lower part of the slope.

How to cite: Gong, B. and Zhao, T.: Investigation into rockslides by the adaptive rock discrete fracture analysis (RDFA) method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15526, https://doi.org/10.5194/egusphere-egu24-15526, 2024.

EGU24-15711 | ECS | Orals | NH3.5

Rockfalls risk assessment along a E45 motorway section in South Tyrol (Italy) 

Francesco Lelli, Leonardo De Rosa, Lucia Simeoni, Francesco Ronchetti, Vincenzo Critelli, and Alessandro Corsini

The E45 motorway in South Tyrol (Italy) is exposed to rockfalls in many locations. For this reason, a significant number of rockfall risk reduction measures (nets, barriers, etc) has been progressively installed since its construction. Planning of further mitigation and monitoring measures can benefit from the assessment over a large-area and at adequate scale, of the exposure to rockfalls and of the associated risk, a piece of knowledge that this study has provided for a 13.5 km motorway section.

First, susceptibility mapping has been carried out using bivariate statistical methods with supporting evidences from an inventory of rockfalls occurrences covering the period 1993 to 2020. This has allowed to define potential rockfall detachment zones located upslope the E45. For each zone, rockfall runout modelling with RocPro3D software by considering 0.5 m and 2.0 m blocks diameter and high-resolution Lidar DTM has allowed to assess potential interactions between rockfall and different motorway structures (i.e. viaduct piers, tunnel entrances and road embankments). Spatial-temporal frequency of 2 m diameter rockfall (i.e. n° of rockfalls per year and unit area) has been assessed on the basis of the inventory of rockfalls occurrences and of the overall extent of slopes resulting highly susceptible to rockfalls. On such basis, the expected rockfall triggering frequency (n° events/year) in each source area has been assessed by considering its extension.  Hazard has been assessed by using an heuristic matrix-based approach that combines frequency and geomechanics (expressed by the GSI) of the rock masses. Rockfall spatial impact frequency, energy and bounce height determined by runout models have been used to establish exposure and vulnerability (i.e. expected damage level) of the motorway infrastructures. Finally, risk has been evaluated in function of hazard and vulnerability (by using combination matrices tailored to each type of interaction of rockfall – on infrastructures taken into consideration.

Results allowed us to determine and map that, out of the total 13.5 km motorway section considered, about 1.5 km for 0.5 m diameter blocks, and about 3.2 km considering 2.0 m diameter blocks, should be considered at high to very high rockfall risk. This result is also relevant with respect to the identification of priorities for more in-depth slope-scale surveys and monitoring of rockfalls in the perspective of further structural and non-structural mitigation measures implementation.

How to cite: Lelli, F., De Rosa, L., Simeoni, L., Ronchetti, F., Critelli, V., and Corsini, A.: Rockfalls risk assessment along a E45 motorway section in South Tyrol (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15711, https://doi.org/10.5194/egusphere-egu24-15711, 2024.

EGU24-16064 | ECS | Posters on site | NH3.5

Back analysis of the 2023 rockfall event of Martigny (Switzerland): trajectography prediction to future potential hazard along road 

Tiggi Choanji, Antonin Chale, Wei Liu, Li Fei, François Noël, Marc-Henri Derron, and Michel Jaboyedoff

In this study, we back analysed a rockfall that occurred on a road in Martigny, Switzerland, on 15 March 2023 to determine the trajectory involving block fragments of approximately 43 m3 in total with block maximum 15 m3 and to identify factors that could contribute to future rockfalls in the area. A combination of remote sensing techniques such as LiDAR, photomosaic, and SfM (Structure for Motion) from drone have been performed to reconstruct the rockfall event and to predict the future potential for rockfalls. Our results suggest that the rockfall was caused by a combination of factors, including the  sliding failure mechanism occurred along a surface deeping to the valley with an angle of 54.5o, the presence of jointed and cracks in the rock with high aperture. A series of 10,000 of block propagations using the scarring model algorithm from stnParabel to produce an area of deposition in agreement with observation made in the field, with corresponding energy line from simulation average has an angle of 35.5 o. The trajectories of blocks are attributed to the high damping effects of the ground conditions and the vineyard rock fences which reduced the distance travelled by the falling rock, and the vineyard terraces slope angle lower than the average slope. While rock protections fences have been installed for protection on the falling block area, however there is a need to consider additional measures, as the rock structure in this area is larger than the width of the cliff face, which makes it more susceptible to rockfalls. Such study points out that the calibration of rockfall simulation based on only few blocks is very challenging.

How to cite: Choanji, T., Chale, A., Liu, W., Fei, L., Noël, F., Derron, M.-H., and Jaboyedoff, M.: Back analysis of the 2023 rockfall event of Martigny (Switzerland): trajectography prediction to future potential hazard along road, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16064, https://doi.org/10.5194/egusphere-egu24-16064, 2024.

Rock avalanches are one of the most destructive geological phenomena in mountainous regions. Understanding the dynamics and characteristics of rock avalanche movement plays a crucial role in assessing the potential hazards. However, the prediction for rock avalanche propagation is still challenging. Our study used an inventory of rock avalanches from Central Asia containing 412 historical cases from 6 countries provided by A. Strom. Considering several input parameters, the machine learning-based approach of extreme gradient boosting with grid search optimization was proposed. Input parameters including confinement type, headscarp height, mean slope angle of headscrap, length and width of the headscarp base, source volume, and maximal height drop (Hmax) are analyzed and discussed. Our proposed model can multi-output the distance of propagation L and the total impacted area, which outperformed by comparison with other machine learning models. Eleven rock avalanche events in Uzbekistan were introduced to demonstrate that the proposed model can be applied to prediction for limited parameters. For future work, we intend to propose a Convolutional Neural Network (CNN) architecture that combines spatial inputs and metadata as input in machine learning. Spatial inputs including elevation, slope, aspect, curvature, and lithology were used for our proposed model. Additionally, the CNN-based deep learning approach might be possible to predict rock avalanches which are characterized by complex terrain with multiple source areas and diverging paths. 

How to cite: Lin, R.: Travel distance prediction for rock avalanche based on machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16109, https://doi.org/10.5194/egusphere-egu24-16109, 2024.

EGU24-16313 | ECS | Orals | NH3.5

Quantitative vulnerability assessment of buildings susceptible to slow-kinematic landslides 

Francesco Poggi, Francesco Caleca, Davide Festa, Olga Nardini, Francesco Barbadori, Matteo Del Soldato, Claudio De Luca, Francesco Casu, Riccardo Lanari, Nicola Casagli, and Federico Raspini

An approach for assessing the quantitative vulnerability, through empirical fragility and vulnerability curves, of masonry buildings exposed to slow-kinematic landslides is described. More in detail, the fragility curves express the probability of exceeding a given level of damage for a range of landslide intensity values. Starting from these ones, the vulnerability curve provides the mean level of damage severity to a given building (or aggregate of buildings) in relation to the landslide intensity value. The application of the vulnerability curve is exploited in the quantitative risk analysis (QRA), that quantifies the probability of a given level of loss.

The Department of Earth Sciences of the University of Florence has catalogued the severity damage landslide-induced to over four thousand masonry buildings gathered from in situ surveys in the northern Apennines. Moreover, to retrieve the fragility and, consequently, the vulnerability curves for buildings, the proposed method exploits the results of spaceborne Advanced Differential Interferometry SAR (A-DInSAR) analysis. In particular, such a method considers the landslide intensity value equal to the module of the vertical (up-down) and horizontal (east-west) deformation velocity obtained by properly combining ascending and descending Sentinel-1 DInSAR products, retrieved through the P-SBAS (Parallel-Small Baseline Subset) method developed at IREA-CNR.

This approach to assess the vulnerability has been integrated within the well-known QRA procedure, which is based on the application of the risk equation (R=H*V*E), where:

R is the landslide risk in terms of economic loss;

H is the hazard retrieved from the susceptibility map available for the entire Italian territory;

V is the vulnerability obtained directly from the equation of the vulnerability curve;

E is the exposure of buildings assessed from average real estate market parameters reported in the OMI (Osservatorio Mercato Immobliare).

The effectiveness of the proposed procedure has been tested over the municipality of Zeri (Massa-Carrara, Italy), where a large-scale landslide risk map has been produced. In particular, for each building of the study area, the hazard, the vulnerability, the exposure and the risk associated with it, are presented. The analysis estimates a total risk of 33.2 million euro for the Zeri municipality and the identification of specific buildings at highest risk. The provided result can be useful for the civil protection activities of the local administrator identifying areas with higher potentiality of damage on structures.

How to cite: Poggi, F., Caleca, F., Festa, D., Nardini, O., Barbadori, F., Del Soldato, M., De Luca, C., Casu, F., Lanari, R., Casagli, N., and Raspini, F.: Quantitative vulnerability assessment of buildings susceptible to slow-kinematic landslides, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16313, https://doi.org/10.5194/egusphere-egu24-16313, 2024.

EGU24-17618 | ECS | Posters on site | NH3.5

Monitoring techniques for rockfall hazard across Malta, Mediterranean Sea. 

Christopher Gauci, Emanuele Colica, Daniel Fenech, and George Buhagiar

The Maltese Islands are exposed to a variety of environmental impacts because of their geographic position, one such impact being coastal hazards arising from erosion, exacerbated by climate change. The prevailing mitigation approach has traditionally been based on visual assessment of risk in specific sites rather than scientifically gathered information as an evidence basis for action to mitigate such risks. Constant monitoring is required to identify the probability and patterns of these events, which would assist in prediction. This was done using in situ measurements which include tiltmeter readings and topographic nail distances.  Certain sites were chosen across the Maltese islands for both installations, selected through historical research and other datasets including dangerous signage installations. Several nails were designated between primary and secondary signifying more stable to unstable cliff edge respectively. Distances using a total station were then taken from primary nails to the secondary nails for consecutive datasets. Tilt plates were installed in three areas with the nails and data recorded by positioning the tiltmeter at different directional axis. 

How to cite: Gauci, C., Colica, E., Fenech, D., and Buhagiar, G.: Monitoring techniques for rockfall hazard across Malta, Mediterranean Sea., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17618, https://doi.org/10.5194/egusphere-egu24-17618, 2024.

EGU24-17946 | ECS | Orals | NH3.5

Rock avalanche runout prediction for suggested failure scenarios. Case study of Cima del Simano rockslide (Switzerland) 

Charlotte Wolff, Michel Jaboyedoff, Andrea Pedrazzini, and Marc-Henri Derron

Rock avalanches events pose significant concerns in mountainous regions characterised by deep and narrow valleys. This has not deterred the ongoing development in these areas, where population settlements and infrastructure continue to expand, becoming increasingly susceptible to these risks. Cima del Simano instability in the Swiss Alps, located in the narrow Blenio Valley, is a deep-seated rockslide which could trigger such events in the future. A previous work outlined several scenarios for the rockslide failure defined by a specific area, volume (ranging from 2.30x105 m3 to 4.30x106 m3), and susceptibility to happen.

Given the proximity of a major road and several villages on both sides of the Valley, there is a real need to evaluate the potential runout distance in the event of rupture and propagation of the different failure scenarios. 

Literature often presents two distinct approaches for estimating the runout distance and the impacted area, both based on the retrospective analysis of historical landslide occurrence. The first approach is through empirical equations linking volumes of failure V and Fahrböschung angles f (tanf=aV^(-b), with a and b two empirical parameters to determine). The second approach consists in numerically simulating the flow propagation by means of dedicated software and by applying specific rheological models. 

This present work suggests applying both those techniques to evaluate the area that would be affected in the case of a rock avalanche at Cima del Simano, triggered by one of the suggested scenarios. We evaluated the runout distance for different angles f estimated based on the empirical relationship, and Dan3D for simulating the propagation applying the Voellmy rheology. Four simulations were conducted by varying the friction coefficient μ [-] and the parameter of turbulence ξ [m.s-2] in order to assess the minimal and maximal possible propagation in terms of runout distance L and lateral spreading based on domain of validity of those parameters according to literature. 

The distances L obtained empirically are longer than the ones from the simulations. This can be explained by the frontal confinement of the flow slowing down the propagation. The study is completed by an evaluation for each scenario of the probability of exceeding a certain distance L using existing statistical models for f variations. 

Additionally, the numerical simulations highlight the areas in gullies where debris are deposited during the flow propagation. Those areas can be sources for subsequent debris flow events. In a second step, we conducted an analysis of areas susceptible to debris flow with Flow-R and compared them with former debris flow events for validation. 

This study aligns with risk management to assist in making informed decisions regarding the evacuation plan in the event of a rupture and propagation of an important volume at Cima del Simano. 

How to cite: Wolff, C., Jaboyedoff, M., Pedrazzini, A., and Derron, M.-H.: Rock avalanche runout prediction for suggested failure scenarios. Case study of Cima del Simano rockslide (Switzerland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17946, https://doi.org/10.5194/egusphere-egu24-17946, 2024.

EGU24-18131 | Orals | NH3.5 | Highlight

Introducing uncertainty in hazard analysis in a simple way: example of rockfalls 

Michel Jaboyedoff

One of the main problems of risk assessment is to evaluate the uncertainty of the results. One relevant solution is to provide exceedance curves based on simulations of the risk calculation (Macciotta et al., 2016; Jaboyedoff et al. 2021), as can be done with CAT models. Instead of performing a single calculation, up to 106 are performed with imputed viability based on different approaches such as observed distributions, standard probabilistic laws such as Poisson or uniform distribution, expert knowledge based on triangular distributions, etc. This can be done on the basis of a "deterministic calculation" of the risk, which allows a better assessment of the uncertainty of the risk.

Drawing upon a precedent risk calculation study within a road corridor, a novel risk calculation methodology is suggested, employing stochastic simulations to introduce variability across the parameters in the risk equation. The outcome manifests as an exceedance curve akin to those generated by catastrophe models. This approach systematically introduces uncertainty into the risk calculation, providing a simplistic means to address inadequately documented cases with limited data. This approach tends to minimise risk or call risk calculations into question.

 

References:

Jaboyedoff, M., Choanji, T., Derron, M.-H., Fei, L., Gutierrez, A., Loiotine, L., Noel, F., Sun, C., Wyser, E. & Wolff, C. 2021. Introducing Uncertainty in Risk Calculation along Roads Using a Simple Stochastic Approach. Geosciences, 11, doi: 10.3390/geosciences11030143.

Macciotta, R., Martin, C.D., Morgenstern, N.R. & Cruden, D.M. 2016. Quantitative risk assessment of slope hazards along a section of railway in the Canadian Cordillera—a methodology considering the uncertainty in the results. Landslides, 13, 115-127, doi: 10.1007/s10346-014-0551-4.

How to cite: Jaboyedoff, M.: Introducing uncertainty in hazard analysis in a simple way: example of rockfalls, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18131, https://doi.org/10.5194/egusphere-egu24-18131, 2024.

EGU24-20066 | ECS | Orals | NH3.5 | Highlight

Interdisciplinary insights into an exceptional giant tsunamigenic rockslide on September 16th 2023 in Northeast Greenland 

Kristian Svennevig, Stephen Hicks, Thomas Lecocq, Anne Mangeney, Clément Hibert, Niels Korsgaard, Antoine Lucas, Marie Keiding, Alexis Marboeuf, Sven Schippkus, Søren Rysgaard, Wieter Boone, Steven Gibbons, Kristen Cook, Sylfest Glimsdal, Finn Løvholt, Matteo Spagnolo, Jelle Assink, William Harcourt, and Jean-Philippe Malet and the VLPGreenland

On September 16th, 2023 at 12:35 UTC, a 25.5 M m3 rockslide occurred on the slope of Dickson Fjord in Northeast Greenland. The rockslide impacted a gully glacier, leading to a rock and ice avalanche that entered the fjord causing an up to 200 m high tsunami with observable runup up to 100 km away. The event produced an unprecedented very long period (VLP) seismic event observable on seismic stations worldwide for up to nine days. Here we focus on reconstructing the dynamics of the landslide, while detailed analysis of the VLP seismic signal is presented by Widmer-Schnidrig et al. in Session GM2.1.

Detailed analysis of the landslide reveals that a large body of metamorphic rock, with dimensions up to 150 m thick, 480 m wide, and 600 m long, dropped westwards along a foliation-parallel failure plane. The impact shattered a 200 m-wide outlet glacier, entraining 2.3 M m3 of glacier ice. The event was dynamically preconditioned by the progressive thinning of the glacier that supported the toe of the unstable slope. Subsequent investigations of satellite images and seismic records indicate that up to five minor landslides occurred in the years prior to the largest event in Sept. 2023, and one subsequent landslide has also been recorded.

Seismic signals generated by the landslide-tsunami were observed at nearby seismic stations, providing insights into its dynamics. The seismic signatures, including emergent high-frequency arrivals and low-frequency signals, match with characteristics of landslides involving glacial ice. Infrasound signals were also detected up to 3310 km away.

To reconstruct the landslide run-out, seismic waveforms from the closest stations were analyzed, resulting in a maximum force of 192×109 N, corresponding to a mass estimate of 78-103×109 kg, equating to a volume of ca. 29-38 M m3, consistent with results from photogrammetric reconstruction. The inverted run-out path indicates the initial rockslide impact with the gully wall, followed by entry into the water. The whole slide lasted c. 90 seconds. An independent numerical model to simulate the landslide force-history is in overall agreement with the seismic inversion results. Simulations of the landslide induced tsunami compare well with observations of the tsunami run-up, and also show evidence of longer lasting seiche action.

The landslide is the first glacial debuttressing landslide known from Greenland, and the first tsunamigenic landslide of this magnitude recorded in Northeast Greenland. 

How to cite: Svennevig, K., Hicks, S., Lecocq, T., Mangeney, A., Hibert, C., Korsgaard, N., Lucas, A., Keiding, M., Marboeuf, A., Schippkus, S., Rysgaard, S., Boone, W., Gibbons, S., Cook, K., Glimsdal, S., Løvholt, F., Spagnolo, M., Assink, J., Harcourt, W., and Malet, J.-P. and the VLPGreenland: Interdisciplinary insights into an exceptional giant tsunamigenic rockslide on September 16th 2023 in Northeast Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20066, https://doi.org/10.5194/egusphere-egu24-20066, 2024.

EGU24-20256 | ECS | Posters virtual | NH3.5

Deciphering the force history of 2021 Chamoli rockslide 

Athul Palliath, Himangshu Paul, N Purnachandra Rao, and Venkatesh Vempati

Landslides are a significant hazard, particularly for those living in mountainous regions where the terrain is steep and unstable. Unfortunately, continuous monitoring of landslides is challenging due to their unpredictable nature. However, recent advancements in high-quality, dense broadband seismic networks have made it possible to study the spatial and temporal evolution of mass wasting processes through the analysis of seismic signals. The 2021 Chamoli rockslide which originated from a glaciated ridge of the Ronti Mountain in the western Himalaya caused severe damage to a hydropower project in downslope region and a casualty of about 80 people. CSIR-National Geophysical Research Institute established a regional seismic network in the Uttarakhand Himalaya which provides a great scope to understand this event in greater detail. We have performed dynamic inversion of the long period seismic waves generated by the rockslide to derive its force history. We used multistation data from Uttarakhand regional seismic network. We used IRIS syngine to generate Green’s function based on ak135 velocity model. Long period seismic waveforms from 6 stations within a distance of 80 km were chosen to perform inversion based on the signal to noise ratio and azimuthal coverage. The inversion is done using python package called lsforce. We reconstruct the force time history of the landslide, from the initial detachment of the rock mass to its impact on the ground. The peak upward vertical force corresponds to the detachment and peak downward vertical force corresponds its  the imapct  onto the ground. The result agrees with the centroid single force inversion done for the phases of detachment and impact of the landslide. The result obtained from force time history can be used to constrain parameters for the numerical simulation of the landslide to understand its dynamics in detail.  

How to cite: Palliath, A., Paul, H., Rao, N. P., and Vempati, V.: Deciphering the force history of 2021 Chamoli rockslide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20256, https://doi.org/10.5194/egusphere-egu24-20256, 2024.

EGU24-22276 | Posters on site | NH3.5

Topographic changes in the high-altitude walls of the Mont Blanc massif: quantification at different spatial and temporal scales  

Daniel Uhlmann, Michel Jaboyedoff, Ludovic Ravanel, Joëlle Hélène Vicari, and Marc-Henri Derron

Long-term topographic changes at high altitude in the Alps, at different spatial and temporal scales, are challenging to quantify, often due to lack of direct evidence. Historic rockfalls are not always visually evident and their debris is frequently consumed by surrounding glaciers, and hanging glaciers leave no moraines to mark their evolution. Remote sensing techniques such as Light Detection and Ranging (LiDAR) have become powerful tools for precisely quantifying geomorphometric changes in the 21st century. However, rates of change based on the short time intervals of data produced since the advent of these modern techniques might not reflect longer-term trends. Especially considering the acceleration of Alpine zone erosion rates driven by cryospheric warming trends, extending the record towards the beginning of the 20th century can help resolve if the current rates are anomalous or consistent with the past. To extend the record of topographic changes of rock and glacier surfaces, Structure-from-Motion (SfM) photogrammetry techniques exploiting archival imagery can be used to create 3D models of past Alpine zone topography with which modern LiDAR can be combined to quantify longer-term rates of change. Combining archival SfM and recent LiDAR 3D models allows the estimation of historical erosion rates and glacier surface height change in the Mont-Blanc massif from the southeast face of Grand Pilier d’Angle (GPA; 4,243 m a.s.l.) from 1929-2021, the Brouillard Pillars (BP; 4150 m a.s.l.) from 1950-2021, the Aiguille du Midi (AdM; 3,842 m a.s.l.) from 1909-2022, and the Aiguille Verte (4,122 m a.s.l.) from 1932-2021. 1-year-interval LiDAR surveys of the GPA and AdM from 2020-2021 and 2021-2022, respectively, provide high-resolution erosion rates for a reference against the rates calculated with the SfM method. The GPA had erosion rates of 5.9±2.3mm year-1 and 8.5±0.1 mm year-1 for the 1929-2021 and 2020-2021 time-intervals, respectively. The BP had a rate of 1.0±0.39 mm year-1 for the period 1950-2022, and the AdM had a 16.4± 0.9 mm year-1 rate from 2021-2022. The 6 hanging glaciers of the AdM north face had an average surface height change of -9.39 m from 1909-2022. SfM models from archival photographs show an increase in the annual erosion rate of the GPA.

How to cite: Uhlmann, D., Jaboyedoff, M., Ravanel, L., Vicari, J. H., and Derron, M.-H.: Topographic changes in the high-altitude walls of the Mont Blanc massif: quantification at different spatial and temporal scales , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22276, https://doi.org/10.5194/egusphere-egu24-22276, 2024.

EGU24-22438 | Posters on site | NH3.5

The Steinsholtsjökull rockslide and GLOF in January 1967, South Iceland – a geophysical hazard likely to reoccur elsewhere in Iceland? 

Thorsteinn Saemundsson, Daniel Ben-Yehoshua, Greta Wells, Sinah Toscka, and Andrew J. Dugmore

This paper presents new estimates of the dimensions and impact of the 1967 Steinsholtshlaup in Iceland in order to understand better the event, the hazards it generated, its long-term legacy and the implications for both landscape interpretation and hazard planning in areas of contemporary valley glaciation. On 15th of January 1967 a major rockslide occurred on the northern face of the Innstihaus mountain in southern Iceland, which overlooked the valley glacier called Steinsholtsjökull. The slide occurred during intensive snowmelt, that followed heavy snow accumulation in December 1966. The landslide was a complex paraglacial response to decades of down wasting of Steinholtsjökull. Since the 19th century high stands of the Little Ice age in Iceland, Icelandic glaciers have probably lost about 16% of their mass. Warm conditions in the 1920s and 1930s drove rapid glacier retreat in southern Iceland and resulted in the formation of many pro-glacial lakes, one of which formed in front of Steinsholtsjökull as the terminus of the glacier retreated up valley and the surface down wasted.  The Innstihaus rockslide displaced the southern margin of the glacier and broke up a large amount of the glacier surface. The resulting down valley avalanche of rock incorporated glacier ice, swept into a proglacial lake and the confined pro-glacial valley of Steinsholtsdalur, creating a GLOF that left a trail of ice, rock debris and landscape transformation that entirely overprinted the pre-existing pro-glacial landscape. The Steinsholtsá river was displaced from the centre line of the valley to its southern margin. About 5km from the site of the cliff collapse, boulders up to 80m3 in size were scattered immediately beyond the confluence of the proglacial valley with a wider valley sandur. A paper published by Kjartansson in 1967 recorded the immediate aftermath of the GLOF, but left many questions unanswered, and there have been no subsequent publications. A better understanding of this event is important because, circumstances similar to those found in the Steinsholtsdalur valley prior to 1967 have developed in numerous glacial environments around Iceland’s ice caps.  As in many other montane areas, increased temperatures over the last thirty years have driven renewed and rapid retreat of valley glaciers. Across Iceland, existing proglacial lakes have expanded and many new ones have formed. These glacier fluctuations have affected the stability of neighbouring mountain slopes, which are resulting in slope deformation and mass movements. The potential for a major geomorphological incident in areas that both attract tourists year-round and have seen a recent related infrastructure development raises serious concerns and stresses an urgent need to study and monitor these environments.

How to cite: Saemundsson, T., Ben-Yehoshua, D., Wells, G., Toscka, S., and Dugmore, A. J.: The Steinsholtsjökull rockslide and GLOF in January 1967, South Iceland – a geophysical hazard likely to reoccur elsewhere in Iceland?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22438, https://doi.org/10.5194/egusphere-egu24-22438, 2024.

The Fracture-Induced Electromagnetic Radiation (FEMR) phenomenon has been substantially investigated as a prolific geophysical tool and provided a precursor to geohazards such as landslides, earthquakes, and rockburst hazards. Several lab-scale experiments on materials such as chalk, rocks, glass, ceramics, granite, etc., have been conducted to correlate between experimental observations and theoretical formulations of the physical parameters of FEMR generations such as crack dimensions, crack velocity, frequency of crack propagation, and finally draw an analogy with earthquake events. The FEMR working principle for Earth’s fracture detection is based on generating geogenic electromagnetic radiation from the brittle rock bodies subjected to differential stress in the near-surface of the Earth’s crust. When external stimuli, such as significant deviatoric stresses in thrust or shear zones due to active tectonic forces, induce stress on these rock bodies, microcracks form and propagate. The "Process zone" at the crack tip contains numerous microcracks and dipoles that emit FEMR waves in the kHz to MHz frequency range. As microcracks coalesce and lead to macro failure, the amplitude of FEMR pulses diminishes. FEMR pulses show less attenuation than seismic waves, making them a more efficient precursor to potential tectonic activities. They are an early warning sign for earthquakes a few hours or days before the event. The current study consisted of FEMR surveys along a segment of the active Dead Sea transform (DST) from Sodom to Jericho. This coincided with a 6.3 magnitude (Mw) aftershock earthquake (EQ) in the Turkey-Syrian region on February 20, 2023, where the last measurement was taken 2 hours before the EQ. Several FEMR parameters (e.g., Benioff strain release, frequency, rise time, hits or activity, and energy) along with their associated crack dimensions were analyzed after filtering the raw data and comprehending their trends leading up to the EQ. This study investigated the Benioff Strain plot and other parameters in three consecutive stages of earthquake nucleation leading to the EQ. In the first stage, there's an increase in FEMR hits and frequency, accompanied by a decrease in rise time (T') and crack dimensions. The second stage is characterized by a decline in FEMR hits and crack width while all continue to increase. Notably, the second stage accumulates the second highest energy, likely due to a high-stress drop. The third stage features a steady increase in FEMR hits and energy and an abnormal increase in crack dimensions, perhaps signifying an upcoming event of macro failure. The cyclic trend in FEMR hits suggests periods of high activity and silence, possibly related to stress changes during crack propagation. Because the measurements were taken a few hours before the earthquake, this survey provides valuable insights into the modulation of FEMR parameters before an earthquake. The results obtained from this analysis could bridge the gap between lab-scale and large-scale studies of stress-induced rock collapses and provide a befitting precursor to such disastrous natural calamities.

How to cite: Das, S. and Frid, V.: The Fracture Induced Electromagnetic Radiation (FEMR) induced along the Dead Sea Transform fault before the Syrian-Turkey earthquake (Mw-6.3) on 20.2.2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-360, https://doi.org/10.5194/egusphere-egu24-360, 2024.

This study investigates the early seismo-ionospheric signals preceding the 7.8 magnitude Turkey earthquake sequence on February 6, 2023. The main shock struck at 01:17:35 UTC in Şehitkamil, Gaziantep in southern Turkey near the northern border of Syria. About nine hours later, a strong 7.5 magnitude aftershock occurred to the northeast of the first main quake.

The present work is based on the analysis of the ionospheric behavior in response to these successive major earthquakes, using space-based GPS/GNSS (Global Positioning System/Global Navigation Satellite Systems) data. Employing geodetic data derived from both Turkish national (TUSAGA) and international (IGS) permanent receivers, we generated a local ionospheric map covering the seismogenic zone of southern Turkey. The aim is to reconstruct the time series of ionospheric Total Electron Content (TEC) and discern any potential anomalies in this signal. The diurnal variation of the ionospheric TEC shows homogeneity in the spatiotemporal pattern of the GNSS_TEC signal, except for January 12, 2023. At noon on this day, the ionospheric TEC reaches its maximum value (98.41 TECu), exceeding 250% of the mean value in the temporal series. This anomalous behavior prompted application of a robust statistical approach to exclude outliers, combined with wavelet transform analysis to capture the time-frequency characteristics of the ionospheric responses. These steps validated the results, indicating a potential seismic influence on the ionosphere approximately three weeks before the mainshock.

This research represents an important step to understanding seismo-ionospheric interactions, highlighting the complex relationship between crustal motions and ionospheric dynamics. Anomalies identified in the ionosphere prior to the major seismic event in Turkey suggest that the approach developed could be promising for predicting earthquakes. Further validation and collaboration are essential to refine these results and advance seismic risk assessment.

Keywords: 2023 Turkey earthquake, GPS/GNSS-TEC data, Pre-earthquake ionospheric anomaly, Crustal-Ionospheric Synergy.

How to cite: Tachema, A.: Exploring early seismo-ionospheric signs preceding the February 6, 2023, Turkey earthquake (Mw 7.8): Preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2942, https://doi.org/10.5194/egusphere-egu24-2942, 2024.

EGU24-3264 | Orals | NH4.1 | Highlight

6 years results of EQ precursors research by using CSES-01 onboard and the following step of  IMCP  

Xuhui Shen, xuemin zhang, zhima Zeren, Shufan Zhao, Qinqin Liu, Roberto Battiston, Angelo De Santis, Tiger Liu, Valerio Tramutoli, Livio Conti, and Rui Yan
As the first geophysical field observation satellite mission in China, CSES-01 has been operating in orbit for six years and, based on its optimal performance, it will prolong its life after CSES-02's launch in orbit in order to partly overlap the two missions. In retrospect, CSES-01 acquired an amount of data such as geomagnetic field, low-frequency electromagnetic waves, in-situ plasma content, and temperature, charged particles as well ionospheric plasma, while more than 70 M7+  and 700 M6+  earthquakes  have been recorded in the globe, together with a series of space weather and volcano phenomena. 
The large amount of data collected has provided new ground for in depth exploration on statistical analysis of earthquake precursors as well as providing clear evidence for the feasibility of space-based co-seismic observation, helping the development of quantitative modeling of the Lithosphere-Atmosphere-Ionosphere Coupling mechanism focusing on its atmospheric and electromagnetic wave channel.
The following prospect plan, CSES-02, is under development by China-Italy joint team and is due to launch in 2024, which means that we will have two CSES satellites simultaneously in orbit from 2024. Such an increase in observational capabilities will strongly support the implementation of multi-parametric observation systems, both from the ground and from satellites, capable of significantly improving precision and reliability of earthquake forecasts. In addition, the new International Meridian Circle Project  (IMCP)   will be implemented as a ground-based observation network with its primary objectives of monitoring the geomagnetical field, space weather, and interaction among Lithosphere-Atmosphere-Ionosphere. The main tasks of IMCP are global data sharing, joint research on space weather and natural hazards, global change, and many other science fields. 

How to cite: Shen, X., zhang, X., Zeren, Z., Zhao, S., Liu, Q., Battiston, R., De Santis, A., Liu, T., Tramutoli, V., Conti, L., and Yan, R.: 6 years results of EQ precursors research by using CSES-01 onboard and the following step of  IMCP , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3264, https://doi.org/10.5194/egusphere-egu24-3264, 2024.

EGU24-6001 | Orals | NH4.1

Investigation of VLF/LF electric field variations related to magnitude Mw≥5.5 earthquakes in the Mediterranean region for the year 2023 

Hans Eichelberger, Mohammed Y. Boudjada, Konrad Schwingenschuh, Bruno P. Besser, Daniel Wolbang, Maria Solovieva, Pier F. Biagi, Patrick H. M. Galopeau, Ghulam Jaffer, Christoph Schirninger, Aleksandra Nina, Gordana Jovanovic, Giovanni Nico, Manfred Stachel, Özer Aydogar, Cosima Muck, Josef Wilfinger, Irmgard Jernej, and Werner Magnes

Strong natural hazards together with their societal impact are usually accompanied by multiple physical phenomena which can be an important information source about the underlying processes.  
In this study we statistically analyze the lithosphere–atmosphere–ionosphere couplings of magnitude Mw5.5+ earthquakes (EQs) in the year 2023 with the aid of sub-ionospheric VLF/LF radio links. The electric field amplitude and phase measurements with a temporal resolution of one second are from the seismo-electromagnetic receiver facility in Graz (GRZ), Austria (Galopeau et al., 2023), which is part of the INFREP network. The spatial extend of the study area has the range [-10°E ≤ longitude ≤ 40°E] and [20°N ≤ latitude ≤ 50°N], in total are 17 EQs according to the United States Geological Survey (USGS) data base, among them the Turkey–Syria EQs (main shocks Mw7.8 and Mw7.5) and the Morocco Mw6.8 EQ. We apply the night-time amplitude method (Hayakawa et al., 2010) for all available paths, of particular importance are the transmitter links TBB (26.70 kHz, Bafa, Turkey), ITS (45.90 kHz, Niscemi, Sicily, Italy), and ICV (20.27 kHz, Tavolara, Italy). Relevant crossings are determined by the size of the Dobrovolsky-Bowman relationship (Dobrovolsky et al., 1979; Bowman et al., 1998).
A major finding is the statistically significant electric field variation of the TBB-GRZ link related to the Turkey–Syria EQ sequence. A physical interpretation is based on atmospheric gravity waves (AGWs) which could alter the E-layer in the lower ionosphere during nighttime and modulate the height of the waveguide cavity.

References:

Galopeau et al., A VLF/LF facility network for preseismic electromagnetic investigations, Geosci. Instrum. Method. Data Syst., 12, 231–237, 2023, https://doi.org/10.5194/gi-12-231-2023
Dobrovolsky et al., Estimation of the size of earthquake preparation zones, PAGEOPH 117, 1025–1044, 1979, https://doi.org/10.1007/BF00876083
Bowman et al., An observational test of the critical earthquake concept, JGR Solid Earth, 103, B10, 24359-24372, 1998, https://doi.org/10.1029/98JB00792
Hayakawa et al., A statistical study on the correlation between lower ionospheric perturbations as seen by subionospheric VLF/LF propagation and earthquakes, JGR Space Physics, 115(A9), 09305, 2010, https://doi.org/10.1029/2009JA015143

How to cite: Eichelberger, H., Boudjada, M. Y., Schwingenschuh, K., Besser, B. P., Wolbang, D., Solovieva, M., Biagi, P. F., Galopeau, P. H. M., Jaffer, G., Schirninger, C., Nina, A., Jovanovic, G., Nico, G., Stachel, M., Aydogar, Ö., Muck, C., Wilfinger, J., Jernej, I., and Magnes, W.: Investigation of VLF/LF electric field variations related to magnitude Mw≥5.5 earthquakes in the Mediterranean region for the year 2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6001, https://doi.org/10.5194/egusphere-egu24-6001, 2024.

EGU24-6275 | Posters virtual | NH4.1

TEC variation over Europe during the intense tectonic activity in the area of SE Turkey on February of 2023. 

Michael E. Contadakis, Christos Pikridas, Styllianos Bitharis, and Emmanuel 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 the transition between the Dead Sea fault and the East Anatolian fault (SE Turkey) on February 6th, 2023. The Total Electron Content (TEC) data are been provided by 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, East Anatolian Fault.

 

How to cite: Contadakis, M. E., Pikridas, C., Bitharis, S., and Scordilis, E.: TEC variation over Europe during the intense tectonic activity in the area of SE Turkey on February of 2023., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6275, https://doi.org/10.5194/egusphere-egu24-6275, 2024.

EGU24-6407 | Orals | NH4.1 | Highlight

 Multi-parameter study of the pre-earthquake phase associated with the Kahramanmaraş sequence in Türkiye on February 6th, 2023.  

Dimitar Ouzounov, Sedat Inan, Pavel Kalenda, Libor Neumann, Sergey Pulinets, Jann-Yenq Liu, Xuhui Shen, Rui Yan, Jana Rušajová, Menas C. Kafatos, and Patrick Taylor

We study critical lithosphere/atmosphere /ionosphere coupling processes that precede earthquake events. Soon after the M7.8 and M7.5 in Kahramanmaraş, Türkiye on Feb 6, 2023, Kahramanmaraş earthquakes, we started collecting and processing multi-parameter data from ground, atmosphere, and satellite observations, such as 1/ Vertical static pendulums data from the European network; 2/ Hydrogeochemical data for electrical conductivity and major ion contents from the spring water samples near Kahramanmaraş ; 3/ Outgoing long-wavelength radiation (OLR) obtained from satellites NPOESS; 4/ Ionospheric plasma observations from China/Italy Seismo-Electromagnetic Satellite (CSES1);5/Electron density variations in the ionosphere via GPS Total Electron Content (GPS/TEC) and 6/ Atmospheric chemical potential (ACP) obtained from NASA assimilation models. We have detected two temporal groups of pre-earthquake anomalies: A/few months in advance - hydrogeochemical anomalies lasting up to six months and vertical static pendulums lasting two months ahead of the seismic rupture and B/few days in advance -  OLR and ACP anomalies showed an abnormal increase on Jan 15-30, along with the plasma electron and oxygen ion density from the CSES1 satellite which is highly correlated with electron density variations in the ionosphere from GPS/TEC. Two groups of identified anomalies relate to different stages of Kahramanmaraş earthquake preparation processes. The first type was linked to the crustal deformation phase and was associated primarily with the coupling processes of the lithosphere-atmosphere. Based on the cross-event analysis of major seismicity in the regions, we found similarities in the pre-earthquake pattern occurrence between the M7.8/M7.5 2023 Kahramanmaraş sequence and the M7.2 Van Earthquake of 2011 and two other major events.

We show that we could extract new information about the different stages of earthquake preparation processes by combining ground and near-space data according to the physical concept of LAIC.

How to cite: Ouzounov, D., Inan, S., Kalenda, P., Neumann, L., Pulinets, S., Liu, J.-Y., Shen, X., Yan, R., Rušajová, J., Kafatos, M. C., and Taylor, P.:  Multi-parameter study of the pre-earthquake phase associated with the Kahramanmaraş sequence in Türkiye on February 6th, 2023. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6407, https://doi.org/10.5194/egusphere-egu24-6407, 2024.

EGU24-7299 | ECS | Orals | NH4.1

Groundwater geochemical anomalies in Mt. Conero area (central-eastern Italy) related to the pre- and post- 5.2 and 5.5 Mw Marche offshore seismic events (November 9, 2022) 

Lorenzo Chemeri, Marco Taussi, Davide Fronzi, Jacopo Cabassi, Alberto Tazioli, Alberto Renzulli, and Orlando Vaselli

It is well established in geosciences that Mw > 4 earthquakes are expected to produce changes in the geochemistry of the waters circulating close to epicentral area. Therefore, such modifications are commonly considered as precursory signals and strictly related to the earthquake preparation processes and seismic cycles. Since most of these changes are transitory and site-sensitive, the identification of possible and suitable seismic precursors represents one of the major challenges for geoscientists. Consequently, the development of multi-parametric water monitoring networks located in earthquake-prone areas is a fundamental step toward a better understanding of the relationship between the seismic cycle and the occurrence of possible tracers.

The northern offshore area of the Marche Region was hit by 5.2 and 5.5 Mw earthquakes (Lat. 43.9830, Long. 13.4240, 5 km depth) on November 9, 2022 during which no fatalities or serious damages were recorded. In this work we report the preliminary results obtained from a pre- and post-seismic monitoring focused on waters collected from three piezometers (with a depth ranging from 15 to 30 m) located in the Mt. Conero Area (central-eastern Italy): Monte Acuto (MAC), Vallemiano (VAL), and Betelico (BET), situated ca. 40-50 km from the epicenter. All waters were sampled within 48 hours from the mainshock and periodically (on a monthly or quarterly basis) collected for one year after the event. The water chemistry of BET sample was available from May to October 2022, i.e., up to six months before the event. While the water samples MAC and VAL did not show any relevant chemical and isotopic variations, those collected from BET displayed strikingly significant modifications. The geochemical facies, characterized by a calcium-bicarbonate and a TDS (Total Dissolved Solids) < 1000 mg/L, typical of shallow aquifers, indeed became sodium-chlorine with TDS > 3500 mg/L, since the end of June 2022, i.e., about four months before the mainshock. About a week after the main events, the water chemistry returned to be Ca-HCO3. Boron, Li, Sr and Rb concentrations also showed significant increments starting from June whereas those of Fe, Mn, Ni, Cu, Zn and Pb displayed overwhelming increases (up to 50 times their pre-seismic values) in those samples collected in the days following the mainshocks. Consequently, particular emphasis was placed on addressing the origin of these changes and evaluating their possible relation with the seismic event. We can hypothesize that a mixing process between shallow aquifer and Na-Cl connate (or thermal) waters occurred, the latter being widely reported in the Adriatic foredeep deposits. The observed chemical variations might likely be related to changes in the relative pressure between superimposed and separated aquifers triggered by modifications in the stress rates associated with the seismic cycle. Moreover, variations in the hydraulic heads resulting in a temporary connection between two distinct aquifers would also explain the transitory changes detected at BET. If confirmed, these variations would be among the most strikingly impressive geochemical evidences ever detected before a seismic event or, at least, ever reported in the literature.

 

 

How to cite: Chemeri, L., Taussi, M., Fronzi, D., Cabassi, J., Tazioli, A., Renzulli, A., and Vaselli, O.: Groundwater geochemical anomalies in Mt. Conero area (central-eastern Italy) related to the pre- and post- 5.2 and 5.5 Mw Marche offshore seismic events (November 9, 2022), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7299, https://doi.org/10.5194/egusphere-egu24-7299, 2024.

EGU24-8281 | Posters virtual | NH4.1

Potential earthquake precursory pattern of large Alpine- Himalayan earthquakes as seen by magnetic Swarm satellites 

Angelo De Santis, Homayon Alimorady, and Habib Rahimi

 Before the occurrence of an earthquake and when the lithosphere is in a state of critical stress accumulation, the lithosphere could react- with the so-called earthquake precursors. One of these precursors is the magnetic field, which, under proper conditions, may produce anomalies due to accumulated stress in the crust before an earthquake occurs. Since several years ago, it has been possible to observe the Earth's magnetic field through satellites. The Swarm satellite mission of the European Space Agency was launched at the end of 2013. It is composed of three identical specialized satellites for observing the Earth's magnetic field. Here, using the magnetic measurements provided by Swarm satellites, we investigate the possibility of identifying several anomalous magnetic signals before the occurrence of earthquakes, which are possibly related to lithosphere-atmosphere-ionosphere coupling. In this study, the earthquakes with a magnitude greater than 5.0 occurred from 2014 to 2023 in the Alpine-Himalayan belt under geomagnetically quiet conditions were examined. Using the algorithm applied to the data from 10 days before the earthquake, obvious anomalies in the components of the magnetic field are identified. Furthermore, a significant relationship between the length (duration) of the anomaly and the magnitude of the earthquake was observed and the empirical relationship between them was estimated. For instance, with the enhancement in the magnitude of the earthquake, the duration of the anomaly also increases.

In addition, significant relationships are also found between other parameters and the magnitude of the earthquake with an acceptable correlation.

We also performed a confutation analysis synthetizing a random catalogue of earthquakes and made again the correlation with the satellite anomalies: the results were far different from those obtained with real data, so confirming the validity of those results.

How to cite: De Santis, A., Alimorady, H., and Rahimi, H.: Potential earthquake precursory pattern of large Alpine- Himalayan earthquakes as seen by magnetic Swarm satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8281, https://doi.org/10.5194/egusphere-egu24-8281, 2024.

EGU24-8894 | Posters virtual | NH4.1

Attempts to include geomagnetic anomalies into the existing Romanian Operational Earthquake Forecast 

Iren Adelina Moldovan, Victorin Emilian Toader, Andrei Mihai, Alexandru Marmureanu, and Constantin Ionescu

Our study analyzes the possibility to include geophysical parameters in the existing OEF (Operational Earthquake Forecasting) application based on the geochemical detected anomalies correlated with short-term changes in seismicity rates and occurrence of medium sized intermediate depth earthquakes.

The study aims to decide which of the geomagnetic anomalous signals can be considered to be a reliable precursor of Vrancea, Romania moderate sized earthquakes that occurred in the last decade. The anomalies were observed using different processing methods: polarization, diurnal variation, differential analysis between two stations or simple visualization at only one station and the standard deviation from the mean value.

The existing OEF application for the Vrancea area based on geochemical parameters is using the standard deviation, time gradient, cross correlation, and linear regression customized for the geological specificity of the area under investigation. For anomaly detection is used the short-time-average through long-time-average trigger (STA/LTA) method on time-integral data. The daily–seasonal variation of parameters is correlated with atmospheric conditions and temperature in the borehole to avoid false decisions. The probability and epistemic uncertainty of the gas emissions act as input into a logical decision tree.

During the study period, in Vrancea seismogenic zone there have been recorded 25 earthquakes with moment magnitude Mw>4.5, at intermediate depth. The Geomagnetic data are obtained from Muntele Rosu (MLR) Seismological Observatory and Plostina (PLOR) of NIEP, situated inside Vrancea seismogenic zone as primary station, and from Surlari (SUA) National Geomagnetic Observatory, part of the International Real-time Magnetic Observatory (Intermagnet), as remote station, unaffected by medium size earthquake preparedness processes. We have assumed that the zone of effective manifestation of the precursor deformations is a circle with the radius taken from the equation of Dobrovolsky, 1979.  Geomagnetic indices taken from GFZ (https://www.gfz-potsdam.de/kp-index) were used to separate the global magnetic variation from possible local seismo-electromagnetic anomalies, that might appear in a seismic area like Vrancea zone and to ensure that observed geomagnetic fluctuations are not caused by solar-terrestrial effect.

Acknowledgments: This paper was carried out within AFROS Project PN-III-P4-ID-PCE-2020-1361, 119 PCE/2021, supported by UEFISCDI, Nucleu Program SOL4RISC, supported by MCI, project no PN23360201, and PNRR- DTEClimate Project nr. 760008/31.12.2023, Component Project Reactive, supported by Romania - National Recovery and Resilience Plan

How to cite: Moldovan, I. A., Toader, V. E., Mihai, A., Marmureanu, A., and Ionescu, C.: Attempts to include geomagnetic anomalies into the existing Romanian Operational Earthquake Forecast, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8894, https://doi.org/10.5194/egusphere-egu24-8894, 2024.

EGU24-10341 | Orals | NH4.1

Study of VLF phase and amplitude variations before the Turkey Syria Mw 7.8 EQs 

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

We investigate the recent earthquakes (EQs) that occurred on 06 February 2023 principally in the central southern part of Turkey and north western of Syria. The tectonic plate movements between Anatolian, Arabian and African plates are well known to be subject to EQs. The coordinate of the epicenter was 37.08°E and 37.17°N with depth in the order of 10 km and a magnitude Mw7.8. Beside aftershocks, a few hours later a strong Mw7.7 earthquake occurred in the same region . We consider in this analysis the Bafa VLF transmitter (TBB) signal emitting at frequency of 26.7 kHz and localized in the Anatolia region (Turkey) at longitude of 27.31°E and latitude of 37.40°N. TBB transmitter signal is daily monitored by the VLF Graz facility (Biagi et al., 2019; Galopeau et al., 2023) with a sufficient signal to noise ratio principally during night observations. We study the variations of the phase and amplitude of TBB signals, as detected by Graz facility (15.43°E, 47.06°N) few weeks before the earthquakes occurrence. It is essential to note that the geographical latitudes of the epicenter and the TBB transmitter are about 37°N, and the distance, in the order of 850 km, is found smaller than the radius of the earthquake preparation zone, as derived from Dobrovolsky et al. (1979), when considering the magnitude of the seismic event, i.e. Mw7.8. We have applied the terminator time (TT) method to make evident the presence of sunrise and sunset time shifts at terminators one week to ten days before EQs.  We discuss essentially the anomalies, in the phase and the amplitude of TBB transmitter, which are probably linked to the electron density variations at the formation and the destruction of the ionospheric D-E-layers.

 

References:

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

Dobrovolsky et al., Estimation of the size of earthquake preparation zones, Pageoph, 117, 1979.

Galopeau et al., A VLF/LF facility network for preseismic electromagnetic investigations, Geosci. Instrum. Method. Data Syst., 12, 2023.

How to cite: Boudjada, M. Y., Biagi, P. F., Eichelberger, H. U., Galopeau, P. H. M., Schwingenschuh, K., Solovieva, M., Nico, G., Lammer, H., Voller, W., and Stachel, M.: Study of VLF phase and amplitude variations before the Turkey Syria Mw 7.8 EQs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10341, https://doi.org/10.5194/egusphere-egu24-10341, 2024.

EGU24-11940 | Posters on site | NH4.1

Non-extensivity study of the seismicity along the Mexican Pacific coast based on the Tsallis q-statistical approach. 

Alejandro Ramírez-Rojas, Elsa Leticia Flores-Márquez, and Leonardo Di G. Sigalotti

The Mexican Pacific coast has presented significant seismic activity due to the tectonic processes that have generated it. This coast, from Baja California until Chiapas is matched with three tectonic settings, to the north, a dispersion zone is presented in Baja California and Cortes Sea, at the middle, conforming by Jalisco, Colima and Michoacan states, La Rivera Plate is the principal source of seismicity and, finally the seismic activity in Guerrero, Oaxaca and Chiapas is driven by the Cocos Plate subduction. According with the catalogues published by the SSN, the yearly number of earthquakes occurred is very different at each zone is very different being Cocos plate the subduction zone that has produced the major number of earthquakes. We analyzed the catalogues of six zones of the Mexican Pacific coast in the period between 2000 and 2023. Based on the Tsallis q-statistical approach it is possible to assess the temporal changes of the non-extensivity by fitting the cumulative number of earthquakes with the generalized Gutenberg-Richter. Our preliminary results show differences in the fitting of the q-values for the six studied regions. These results are consistent with a pervious analysis, where it was observed that the highest q-value was obtained in Jalisco zone, while Oaxaca region reported the lowest q-value.

How to cite: Ramírez-Rojas, A., Flores-Márquez, E. L., and Sigalotti, L. D. G.: Non-extensivity study of the seismicity along the Mexican Pacific coast based on the Tsallis q-statistical approach., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11940, https://doi.org/10.5194/egusphere-egu24-11940, 2024.

EGU24-12838 | Orals | NH4.1

Nicaragua seismicity study in terms of entropy fluctuations in natural time domain 

Elsa Leticia Flores-Marquez, Xochilt Esther Zambrana-Areas, and Alejandro Ramirez-Rojas

Nicaragua is located on the western margin of the Caribbean plate near its interaction with the Cocos plates. The Caribbean plate is surrounded by four major tectonic plates: Cocos at the southwest, Nazca at the south, the North American and South American to the north and southeast respectively. The Cocos plate subducts the Caribbean plate at rates of aproximately 70 to 90 mm/yr having a steeper dip around 75° and 80°. The Central American subduction zone is seismically active. The associated volcanic arc consists mainly of basaltic-andesitic quaternary volcanic rocks (predominantly pyroclastic and lava flows). The seismicity, although constant, has not exceeded earthquakes of Ms 7.3. We analyzed the period between 2000 and 2023 in terms of entropy in natural time domain. Our analysis in terms of Gutemberg-Richter law shows b-value fluctuation ranging between 0.53 and 1.03 by year. Regarding the analysis of entropy fluctuations, it indicates the correlations are short-range, so we consider that the seismic sequence behaves as a Markovian process.

How to cite: Flores-Marquez, E. L., Zambrana-Areas, X. E., and Ramirez-Rojas, A.: Nicaragua seismicity study in terms of entropy fluctuations in natural time domain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12838, https://doi.org/10.5194/egusphere-egu24-12838, 2024.

EGU24-13120 | Orals | NH4.1 | Highlight

Local Solid Earth Tides and Their potential use in assessing and forecasting the risk of seismic hazards 

Francesco Vespe, Jan Dousa, Carlo Doglioni, Eleonora Ficini, Olimpia Masci, Giovanni Nico, Jakub Nosek, Pavel Vaclavovic, Gianluca Sottili, Davide Zaccagnino, Luis Mendes, and Francisco Amarillo-Fernandez

This work presents some results achieved in the frame of TILDE project (Tidal Interplate Lithospheric Deformation of Earth). The main goal of TILDE project was the estimation of Local Solid Earth Tides (LSET); i.e. models which depends on the geographical position of the selected sites. The LSET models are built estimating Love and Shida numbers for each station and for each tidal constituents. The objectives were to investigate possible correlations between LSET and geological/geophysical events, such as tectonic plates movements, earthquakes and volcanic activities. GNSS data collected at 98 stations, split into global and regional networks have been used. The global network consists of 73 GNSS stations which have piled up a stack of data 20 years long. The regional networks consist of 25 stations, 7 located in New Zealand, 1 in Kamchatka, and 17 stations in Italy for which 3 year-long time series of data are available.

The LSET models have been achieved using GNSS coordinates expressed both in geocentric XYZ and local NEU references, estimated in Precise Post Processing mode, with a sampling rate in turn of 1 day and 3 hours.  Different GNSS solutions have been generated according the objectives of the project. The first one is the background solution in which the full IERS2010 tides model has been applied. The second solution is obtained by switching off the tides model. The third one is the solution in which only the Long-Periodic Tides (LPT) has been switched off. This last solution has been applied in order to lower the level of flickering of GNSS time series when Love and Shida numbers of LPT had to be estimated.

This analysis showed that there is a correlation between the latitude measured from the tectonic equator and Love numbers. This confirms the theory that moon tides contribute to trigger tectonic movements.

An interesting result, relevant for the assessment and potential precursiveness of the risk of seismic hazards, was the correlation found between the variation in time of Love numbers of diurnal (K1) and semi-diurnal (M2) tides and the occurrence of earthquakes nearby GNSS sites.  At this purpose we selected GNSS global stations which were at a distance <200 Km from the epicentre of EQ events. The investigation has outlined that almost the seismic events are got ahead by a downfall of Love numbers. It seems that each earthquake event cannot be characterized only by the type of slip occurred along faults: compressive (i.e., reverse fault), extensional (i.e., normal fault), strike slip or combination of them. This result could be explained with the rigidity of the crust/mantle which play a major role in triggering seismic events. For smaller values of Love number we have indeed a more rigid response of Earth to Tidal forcing.

How to cite: Vespe, F., Dousa, J., Doglioni, C., Ficini, E., Masci, O., Nico, G., Nosek, J., Vaclavovic, P., Sottili, G., Zaccagnino, D., Mendes, L., and Amarillo-Fernandez, F.: Local Solid Earth Tides and Their potential use in assessing and forecasting the risk of seismic hazards, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13120, https://doi.org/10.5194/egusphere-egu24-13120, 2024.

EGU24-13277 | Orals | NH4.1

Study of ionospheric variations from a global network of VLF antennas 

Patrick Galopeau, Mohammed Boudjada, Hans Eichelberger, Ashanthi Maxworth, Pier Biagi, and Konrad Schwingenschuh

We present a system which records electromagnetic signals, in the Very Low Frequency (VLF: 3 kHz – 30 kHz) and Low Frequency (LF: 30 kHz – 300 kHz) range, 24 x 7 x 365, with the goal of identifying ionospheric variations. An individual system consists of a monopole antenna, a pre-amplifier, a power supply, a central computer, a GPS unit, and a recording device. Several receivers will be implemented around the globe in a network. The first implementation of the system was done in Graz (Austria), the second one will be in Guyancourt (France), a third one in Réunion (France) and a fourth one in Moratuwa (Sri Lanka). Each reception device will allow a continuous daily monitoring of transmitter signals in the VLF and LF frequency bands. This network will be devoted to the study of ionospheric variations, in particular, those linked to the solar activity, but also those associated with seismic activity with the purpose to identify electromagnetic earthquake precursors.

How to cite: Galopeau, P., Boudjada, M., Eichelberger, H., Maxworth, A., Biagi, P., and Schwingenschuh, K.: Study of ionospheric variations from a global network of VLF antennas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13277, https://doi.org/10.5194/egusphere-egu24-13277, 2024.

Among many precursors related with geology, geophysics and geochemistry field, the geomagnetic field is one of the most sensitive factors of seismic activity. Current works basically analyzed scalar values of multiple components separately or the ratio of vertical component and horizontal component to extract electromagnetic radiation anomalies in different frequency range. However, the relationship of induced magnetic horizontal vector (IMHV) and earthquake light generated by pressure-simulated rock current (PSRC) was initially proved in M7.3 Fukushima earthquake of 16 March 2022. The geomagnetic anomalies obtained by current methods originate from alternating electromagnetic fields instead of rock current, which lack the investigation of the direction information of seismic geomagnetic disturbance vector. 
By combining observational evidence from existing rock current experiments with the volumetric scaling effect, the intensity of current generated by the compressed crustal rock mass in seismogenic areas was estimated to be over 1 MA when the magnitude reaches 7 or above. Based on Biot-Savart's law, the magnetic field disturbance intensity generated by the rock current in three-dimensional space was simulated in this study. The simulation results indicate that magnetic field disturbances ranging from several nanotesla to tens of nanotesla can be generated at approximately 600 km from the rock current, which can be easily captured by the existing dense distribution of ground-based observatory networks (e.g., INTERMAGNET, MAGDAS).
This paper aims to propose an analysis method based on seismic geomagnetic disturbance vectors and validate it using the 2007 M7.3 Peru earthquake as a case study. In this method, two arbitrary geomagnetic stations around the seismogenic area are selected to obtain the magnetic variation of multiple geomagnetic component (e.g., declination horizontal, and vertical component), which are then synthesized into the disturbance vectors. Subsequently, the intersection line of the two vector planes of the magnetic field disturbances is determined based on the concept of forward intersection, allowing for an approximate estimation of the orientation of the rock current. Finally, the spatial relationship between multiple disturbance vectors and the rock current is assessed to determine if Biot-Savart's law is satisfied.
Taking the 2007 Peru earthquake as a research case, magnetic anomalies in both horizontal and vertical components were detected prior to the earthquake at two geomagnetic stations (i.e., the HUA station from INTERMAGNET and the ANC station from MAGDAS) located within 300 km from the epicenter. The method proposed in this study was utilized to further analyze the data, revealing that the rock currents obtained from the disturbance vectors were distributed around the seismogenic area. Besides, the combination of geological data and the positive holes theory also provided confirmation of the presence of rock types capable of generating current carriers in the seismogenic area. The method proposed in this study, to a certain extent, can effectively verify the spatiotemporal correlation between geomagnetic anomalies and seismic activities, which enables the localization of stress-locked regions and can serve as an effective approach for detecting seismic magnetic anomalies and short-term earthquake forecasting.

How to cite: Xie, B., Wu, L., and Mao, W.: New analysis method of seismic geomagnetic disturbance vector using ground-based observation: a case study of the 2007 Peru earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13546, https://doi.org/10.5194/egusphere-egu24-13546, 2024.

EGU24-14043 | Posters virtual | NH4.1

Lithosphere-atmosphere-ionosphere coupling processes for 2022 Luding Ms6.8 earthquake in China 

Xuemin Zhang, Angelo De Santis, Jing Liu, Saioa Campuzano, Na Yang, Serena D’Arcangelo, Xinyan Ouyang, Mariagrazia De Caro, Gianfranco Cianchini, Muping Yang, Cristiano Fidani, Xinyan Li, Martina Orlando, Hong Liu, Loredana Perrone, Lei Nie, Alessandro Piscini, Dario Sabbagh, and Maurizio Soldani

Due to the significant earthquake-related perturbations observed in the ionosphere by ground-based stations and space-borne satellites, scientists have increasingly focused on the studying the possible coupling mechanism among lithosphere, atmosphere and ionosphere. In this work, we contribute to this research, analyzing the phase of preparation of the 2022 Ms6.8 Luding (China) earthquake with a multi-parameter and multi-level approach from ground and satellite data taken in lithosphere, atmosphere and ionosphere, including the b value, earth resistivity, ELF magnetic field emissions, atmospheric electric field, surface temperature, foF2 from Ionosonde, GNSS TEC, magnetic field and electron density from CSES and Swarm satellites, etc. The results are encouraging confirming a chain of processes starting from ground and proceeding to the above atmosphere and ionosphere.

How to cite: Zhang, X., De Santis, A., Liu, J., Campuzano, S., Yang, N., D’Arcangelo, S., Ouyang, X., De Caro, M., Cianchini, G., Yang, M., Fidani, C., Li, X., Orlando, M., Liu, H., Perrone, L., Nie, L., Piscini, A., Sabbagh, D., and Soldani, M.: Lithosphere-atmosphere-ionosphere coupling processes for 2022 Luding Ms6.8 earthquake in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14043, https://doi.org/10.5194/egusphere-egu24-14043, 2024.

EGU24-18372 | ECS | Posters on site | NH4.1

Robust Satellite Techniques for seismic prone area monitoring: recent achievements and future perspective toward a multi-parametric t‐DASH system 

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

After more than 25 years of studies it is possible to draw a balance of the efforts, based on the application of Robust Satellite Techniques to long-term satellite TIR (Thermal InfraRed) radiances, to identify (isolating them from all the others possible sources) those anomalies (in the spatial/temporal domain) possibly associated to the occurrence of major earthquakes.

The results achieved by processing multi-annual (more than 10 years) time series of TIR satellite images collected in different continents and seismic regimes, showed that more than 67% of all identified (space-time persistent) anomalies occur in the pre-fixed space-time window around the occurrence time and location of earthquakes (M≥4), with a false positive rate smaller than 33%. Moreover, Molchan error diagram analysis gave a clear indication of non-casualty of such a correlation, in comparison with the random guess function.

Here, we will critically discuss the results up to now achieved by applying long-term RST analyses in different part of the world. Moreover, we will also discuss the common and/or peculiar elements of success/failure respect to the possibility to build and implement a multi-parametric system for a time‐Dependent Assessment of Seismic Hazard (t‐DASH).

How to cite: Colonna, R., Filizzola, C., Genzano, N., Lisi, M., Pergola, N., and Tramutoli, V.: Robust Satellite Techniques for seismic prone area monitoring: recent achievements and future perspective toward a multi-parametric t‐DASH system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18372, https://doi.org/10.5194/egusphere-egu24-18372, 2024.

EGU24-20006 | Orals | NH4.1

Seismic LCAI Coupling Supported by Pressure Stimulated Rock Current: Multi-parameter Observations and Numerical Simulation 

Lixin Wu, Busheng Xie, Dingyi Wu, Xiao Wang, Ziqing Wang, Yifang Ding, Youyou Xu, and Wenfei Mao

Multiple parameters anomalies appeared before medium-strong earthquakes have long been observed and analyzed. The spatio-temporal relations of multiple anomalies were attributed to the coupling of lithosphere, coversphere, atmosphere and ionosphere (LCAI in brief) related with the seismogenious activity and final shocking. However, the mechanism of LCAI coupling is not yet clear and the process of LCAI coupling is much fuzzy, which hinders the scrutinizing of reported anomalies, and leads to great difficulty in discriminating the inconsistency for single parameter as well as the uncertainty among multiple parameters.

From laboratory experiments on rock specimens partly loaded to fracturing we discovered that there were pressure stimulated rock current (PSRC) developing with the applied pressure, and there was stepped increment of PSRC as well as sharp rise of PSRC appearing in the late phase of loading rock to failure. The measured PSRCs were measured in an amplitude of 2~8000na, which depending on rock-minerals and porewater of different rock specimen. The enhancement of surface infrared radiation and the reduction of surface rock dielectric, which lead subsequently to the enhancement of microwave brightness temperature (MBT), could be attributed the production of PSRC and its propagation to rock surface both in laboratory and seismogenious zone.

Ground observations in Luding, China, and Fukushima, Japan, showed that the arriving of PSRC from underground was able to disturb the near-surface electric field, and led further to the local atmospheric ionization and earthquake light near ground surface. Abnormal drop of atmospheric electric field and simultaneous rise of MBT were observed preceding the M6.8 Luding earthquake, 2022, and earthquake lighting and horizontal magnetic vector disturbance were observed accompanying with the M7.3 Fukushima earthquake, 2023.

The arrival of PSRC from seimogenious zone or hypocenter is to change the atmospheric electric field, which was believed being able to penetrate upward from ground surface to ionosphere. An atmospheric electric field penetration model was modified and used to simulated the ionospheric disturbance due to the seismic PSRC inhomogeneous appeared on ground surface. The ionospheric TEC disturbance related with the M8.0 Wenchuan earthquake in 2008, the M9.0 Tohoku earthquake in 2011, the M7.8 Nepal earthquake in 2015 and the M7.5 Turkey earthquake in 2022 were carefully simulated, respectively, according to the position of MBT anomalies or supposed PSRC occurrence. The simulation results were visualized in a 3D spheroid space and contrasted to the reported TEC anomalies retrieved from satellite or ground observations. Particularly for the great Nepal earthquake in 2015, we scrutinized the observed multiple anomalies, including TEC and VLF, possible related with the LCAI coupling, and rooted the seismic anomalies to the simulated underground high-stress accumulation regions on and above the subduction fault.

How to cite: Wu, L., Xie, B., Wu, D., Wang, X., Wang, Z., Ding, Y., Xu, Y., and Mao, W.: Seismic LCAI Coupling Supported by Pressure Stimulated Rock Current: Multi-parameter Observations and Numerical Simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20006, https://doi.org/10.5194/egusphere-egu24-20006, 2024.

EGU24-428 | ECS | Orals | TS1.6

AFTERSLIP of 6 FEBRUARY 2023 KAHRAMANMARAS EARTHQUAKE SEQUENCE : PRELIMINARY RESULTS 

Efe T. Ayruk, Muhammed Turğut, İlay Farımaz, Mehmet Köküm, Roger Bilham, and Uğur Doğan

The Mw 7.8 earthquake of 2023 ruptured the southern (main) branch of the East Anatolian Fault (EAF), followed by the Mw 7.6 earthquake on the northern (Çardak Fault) branch of the EAF nine hours later. In March, we installed ten carbon-rod extensometers across segments of the main and northern branches of the ruptured faults, where potential slip deficits were considered possible, to investigate if afterslip continues. It is important to measure afterslip to understand the behaviour of a fault, if any, resulting from stresses associated with local coseismic slip deficits.  Seven of these extensometers recorded less than a few millimetres of slip since March. In Göksun near the western end of the Çardak fault, we recorded more than a 25 mm of accelerating afterslip preceding local aftershocks of magnitude ≤Mw5.1.

The Mw 6.8 Elazığ-Sivrice earthquake of January 24, 2020, and the Mw 7.8 Kahramanmaraş earthquake of February 6, 2023, stopped in the Pütürge region, where it is named as Pütürge Gap. To understand why these two earthquakes terminated there, an array of five extensometers were ultimately deployed. One of the extensometers, which is 52 m long, shows that slip > 3.8 mm/yr continues at depth. Extensometers spaced 45 km apart recorded an eastward propagating subsurface creep event in September 2023. Four cGPS stations recording at 5 Hz were installed in an array to better investigate the subsurface evolution of aseismic slip on the Pütürge Fault in the village of Taşmış.

How to cite: Ayruk, E. T., Turğut, M., Farımaz, İ., Köküm, M., Bilham, R., and Doğan, U.: AFTERSLIP of 6 FEBRUARY 2023 KAHRAMANMARAS EARTHQUAKE SEQUENCE : PRELIMINARY RESULTS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-428, https://doi.org/10.5194/egusphere-egu24-428, 2024.

EGU24-2299 | ECS | Posters on site | TS1.6

Estimate of seismic fracture surface energy from pseudotachylyte-bearing faults 

Silvia Aldrighetti, Giulio Di Toro, and Giorgio Pennacchioni

Earthquakes are the result of propagation at ∽km s-1 of a rupture and associated slip at ∽m s-1 along a fault. The total energy involved in a seismic event is unknown, but qualitatively most of it is dissipated by rock fracturing and frictional heat. Seismic fracture energy G (J m-2) is the energy dissipated in the rupture propagation and can be estimated by the inversion of seismic waves. However, its physical significance remains elusive. G may include the contributions of both rock fracturing (energy to form new rock surfaces US, J m-2) and fault frictional heating (Q, J m-2) per unit fault area. Here we determine both US and Q in natural and experimental pseudotachylyte-bearing faults, following the approach used by Pittarello et al. (2008). In fact, in pseudotachylytes, or solidified frictional melts produced during seismic slip, (i) US is proportional to the surface of new fragments produced in both the slip zone and in the wall rocks, and (ii) Q is proportional to the volume of frictional melt.

The selected natural pseudotachylytes belong to the east-west-striking, dextral, strike-slip Gole Larghe Fault Zone (Adamello, Italian Alps). To estimate US we employed Electron Back-Scatter Electrons (EBSD), High Resolution Mid Angle Back-Scattered Electrons (HRMABSD) and Cathodoluminescence-Field Emission Scanning Electron Microscopy (CL-FESEM). In particular, CL-FESEM imaging reveals a microfracture network in the wall rocks that cannot be detected with the other techniques. In the pseudotachylyte-bearing fault, the microstructural analysis reveals (i) a high degree of fragmentation of the wall rock adjacent to the pseudotachylyte fault vein (formed along the slip surface), with clast size down to <90 nm in diameter, and (ii) a systematic difference in fracture density and orientation of the microfractures in the two opposite wall rock sides of the fault. In fact, in the northern wall rock the fracture density is low and the microfractures are oriented preferentially east-west, while in the southern wall rock the fracture density is high and oriented preferentially north-south. Instead, this asymmetric microfracture pattern is absent in the experimental pseudotachylytes produced by shearing pre-cut cylinders of tonalite (the rock that hosts natural pseudotachylytes) in the absence of a propagating seismic rupture. Thus, the formation of the asymmetric microfracture pattern is associated with the propagation of the seismic rupture and, therefore, can be used to estimate US.

In natural pseudotachylytes, fracture density decreases exponentially from the pseudotachylyte-wall rock contact towards the wall rock. The rock volumes with highest coseismic damage at the contact with the pseudotachylytes were assumed to represent the host-rock damage preceding frictional melting along the slip zone. Based on this assumption, US was estimated in the range 0.008-1.35 MJ m-2, while Q was estimated from the thickness of the pseudotachylyte vein to be ∽32 MJ m-2. In the case of the Gole Larghe Fault, numerical modelling of seismic rupture propagation yields fracture energies G in the range 8-67 MJ m-2 suggesting that US is a subordinate component of G and that most of the seismological fracture energy is heat.

How to cite: Aldrighetti, S., Di Toro, G., and Pennacchioni, G.: Estimate of seismic fracture surface energy from pseudotachylyte-bearing faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2299, https://doi.org/10.5194/egusphere-egu24-2299, 2024.

EGU24-3922 | ECS | Orals | TS1.6

Detection of Immediate Foreshocks Using Dense Seismic Array: A Case Study of the 2021 Ms 6.4 Yangbi aftershock sequence 

Fengjiang Ju, Haoran Meng, Xiaofei Chen, and Chunquan Yu

Advancing our understanding of earthquake nucleation process can shed lights on earthquake prediction, early warning, and hazard assessment. Foreshocks, which usually refer to smaller earthquakes that occur before an earthquake, exhibit good temporal and spatial correlations with the mainshock. Investigating the relationship between foreshocks and mainshocks can therefore provide valuable insights into earthquake nucleation mechanisms and contribute to the improvement of earthquake prediction and early warning capabilities.

A recent study on the 2019 Mw 7.1 Ridgecrest earthquake sequence suggests that immediate foreshocks often share similar waveforms to the P-waves of subsequent earthquakes, differing only in amplitude. This similarity is believed to arise from the fractal nature of fault fracture processes. Consequently, there might be many immediate foreshocks with similar waveforms hidden in ambient noise that have gone undetected. Two methods have been proved to be effective in detecting small events: the Matched Filter Technique (MFT) and the Source-Scanning Algorithm (SSA). The MFT relies on template events to detect small events by stacking cross-correlograms between the waveforms of the templates and potential events. The conventional MFT, however, requires that the small events be located in the vicinity of one of the template events and does not provide the accurate locations of detected events. On the other hand, SSA is a migration-based approach that involves stacking non-negative waveforms, envelopes, and their extended characteristic functions. However, due to their tendency to provide absolute locations, SSA are heavily influenced by the accuracy of the velocity model and struggle to accurately detect earthquakes that are obscured by noise.

In our study, we prioritize the accuracy of relative event locations when studying the relationship between foreshocks and mainshocks. To address this concern, we have developed an advanced method that combines the strengths of cross-correlation and beamforming analyses. This method allows us to detect and relatively locate small seismic events simultaneously using dense array data. For the 2021 Ms 6.4 Yangbi  aftershock sequence, we first compute the cross-correlograms of the contentious records with the P-waves/S-waves of the target earthquake, respectively. We then grid searches around the hypocenter using N-th root stacking to detect and locate the immediate foreshocks. Upon detecting numerous immediate foreshocks, we proceed to statistically quantify the earthquake nucleation process or investigate the nucleation mechanism.

How to cite: Ju, F., Meng, H., Chen, X., and Yu, C.: Detection of Immediate Foreshocks Using Dense Seismic Array: A Case Study of the 2021 Ms 6.4 Yangbi aftershock sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3922, https://doi.org/10.5194/egusphere-egu24-3922, 2024.

EGU24-4427 | Orals | TS1.6

Big Slip on Small Faults - How Does Extreme Fault Slip Occur on Short-to-Moderate Length Faults 

Kevin P. Furlong, Matthew W. Herman, and Kirsty A. McKenzie

A general correlation between maximum co-seismic fault slip and fault length has been well constrained by observations from numerous earthquakes occurring on many crustal faults. In spite of this global consistency, there are notable examples of co-seismic fault slip magnitudes that far exceed the expected maxima for the fault dimensions.  Two instances of extreme fault slip that occurred on short-to-moderate length upper-plate faults in subduction systems, where the megathrust lies at shallow depths are the 2016 Kaikoura (New Zealand) earthquake, and the 1855 Wairarapa (New Zealand) earthquake. In both cases, co-seismic fault slip was 5 to 10 times greater than expected from the rupture length - fault slip scaling relationships. The typical crustal fault model  is a fault with a brittle-to-ductile transition at depth; in this scenario, co-seismic slip is inhibited by viscous resistance from the deeper, ductile component of the fault.  In contrast, the tectonic characteristics of faults that experience extreme co-seismic slip, involve upper plate faults that truncate against the megathrust at seismogenic depths (i.e. are fully frictionally coupled over their entire depth extent). During a megathrust earthquake, the plate interface unlocks and upper-plate faults that extend to the ruptured plate interface transiently experience free-slip boundary conditions on both their upper (surface) and lower (megathrust) ends. As a result, such upper-plate faults can potentially experience full strain release (and therefore maximum slip), independent of their length. For appropriately oriented faults, this effect may be enhanced by co-seismic stress changes associated with the megathrust earthquake. 

Geologic evidence of large displacement (and/or displacement rate) upper-plate faults in other subduction systems indicates this process may commonly occur. One example is a set of upper-plate faults along the Cascadia margin (near Newport, Oregon), that have strike-slip geologic slip rates, averaged over 10s of thousands of years, exceeding tens of mm/yr and approaching local plate convergence rates. These upper-plate Cascadia faults are also located where the plate interface is sufficiently shallow and seismogenic, indicating that these high-slip, upper-plate faults are likely frictionally locked over their entire depth range. In spite of the high overall slip rates of these upper-plate faults, because they are locked along their entire depth extent between earthquakes,  they may be unrecognized by inter-seismic geodetic observations.

How to cite: Furlong, K. P., Herman, M. W., and McKenzie, K. A.: Big Slip on Small Faults - How Does Extreme Fault Slip Occur on Short-to-Moderate Length Faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4427, https://doi.org/10.5194/egusphere-egu24-4427, 2024.

EGU24-4550 | Posters on site | TS1.6

Characterizing shallow creep along the Dead Sea pull-apart basin using geodetic observations 

Yariv Hamiel and Roger Bilham

We use geodetic measurements to characterize aseismic deformation along the western boundary fault of the Dead Sea pull-apart basin, which is located at the southern part of the sinistral Dead Sea Fault. This research provides constraints on patterns and timescales of deformation and its dependence on regional tectonics and the rheology of the upper crust. We use creepmeter, GNSS, InSAR and airborne LiDAR observations and show transient aseismic slip on the western boundary fault of the Dead Sea basin. A biaxial creepmeter with a 30 s sampling interval was installed in early 2021 showing high extensional deformation (an average rate of ~8.6 mm/yr), which is consistent with the ~30 cm of subsidence recorded 2017-2019 differential LiDAR data. The data imply modulated slip on a 60° dipping normal fault with maximum slip rates of ~0.5 µm/hour starting in late August and varying close to zero in late April. We attribute these large movements to local tectonics, sediment compaction, thermo-elastic response and dissolution of subsurface salt responsible for the formation of sink-holes in the region. The creepmeter measurements also show some sinistral deformation with an average rate of ~2.1 mm/yr, comparable to the rate of 2.5±0.4 mm/yr that was observed for the Sedom Fault, the southernmost segment of the western boundary fault, using GNSS data. Several minor creep events were detected by the creepmeter. The 19 Feb 2022 creep event lasted more than an hour following heavy rain in this area with abrupt sinistral slip of ~2.5 mm preceding dilation and dip-slip by 20 minutes. Small Baseline Subset (SBAS) analysis of InSAR data reveals up to 7mm/yr of line-of-sight deformation across the western boundary fault, north of the creepmeter. It also reveals high subsidence rate (up to ~20 mm/yr) along the southern shores of the Dead Sea Lake that can be explained by high compaction rate of clay sediments and reduction of pore pressure along the lake shores. This high subsidence rate is also observed in our near shore GNSS stations. Our results indicate that deformation within the Dead Sea basin is not solely controlled by the active tectonics. The observed vertical deformation is apparently modulated by the response of sediments to seasonal variations of local conditions.

How to cite: Hamiel, Y. and Bilham, R.: Characterizing shallow creep along the Dead Sea pull-apart basin using geodetic observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4550, https://doi.org/10.5194/egusphere-egu24-4550, 2024.

EGU24-4561 | Orals | TS1.6

Boso seismicity swarm propagation driven by slow slip stress change 

Baptiste Rousset, Asaf Inbal, Roland Bürgmann, Naoki Uchida​​, Anne Socquet, Lou Marill, Takanori Matsuzawa, and Takeshi Kimura

The interactions between aseismic slip and seismicity is mostly studied during postseismic afterslip associated with the generation of aftershocks following large earthquakes. However because of the large stress perturbations produced by the coseismic rupture, it remains difficult to distinguish the contribution of the coseismic stress perturbation and the effects of stresses induced by the afterslip on the triggering of aftershocks. Studying seismicity triggered by slow slip events enables us to understand the direct effect of aseismic slip on the generation of the seismicity. While most subduction slow slip events are deep-seated, at the down-dip edge of seismogenic zones accompanied by tectonic tremors, some are also observed at shallower depths associated with seismic swarms. Among them are the well-studied Boso slow slip events located on the Sagami trough, between 10 and 20 km depth. Recorded every ~4 years since 1996, they are always accompanied by swarms of Mw 1 to 5 earthquakes on their northern and western flanks. Being located right beneath the Boso Peninsula coastline, the kinematics of these slow slip events is particularly well imaged by dense GNSS and tiltmeter networks. In this study, we model the time dependent aseismic slip of the 2018 Boso slow slip event, with the largest moment released of all Boso slow slip events, by inverting time step by time step the slip on the fault with joint GNSS and tiltmeter data. We do not impose arbitrary temporal smoothing in the inversion and find that the well constrained fault slip is first growing and then migrating southwestward with a migration speed of ~ 2 km/day. In order to model the interaction with the seismicity, we compute the Coulomb stress change due to the transient slip on receiver faults located in 9 cubes centered in the seismicity swarm and parallel to the subduction interface. From June 2nd to June 18th, the seismicity is migrating up-dip at a rate of 1 km/day. This migration period coincides with the peak slip rate and with Coulomb stress produced by the slow slip migrating updip together with the seismicity, indicating a causal relationship. Adopting a rate and state friction formalism to explain the nucleation of the seismicity, we finally investigate the ensemble of parameters, in particular the constitutive parameter that relates changes in stress to logarithmic changes of slip velocity, the effective normal stress and the tectonic stressing rates, that can explain the seismicity rate. 



How to cite: Rousset, B., Inbal, A., Bürgmann, R., Uchida​​, N., Socquet, A., Marill, L., Matsuzawa, T., and Kimura, T.: Boso seismicity swarm propagation driven by slow slip stress change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4561, https://doi.org/10.5194/egusphere-egu24-4561, 2024.

EGU24-5061 | ECS | Orals | TS1.6

Complex Frictional Behavior of Clay and Implications for Slow Slip  

Giuseppe Volpe, Cristiano Collettini, Jacopo Taddeucci, Chris Marone, and Giacomo Pozzi

The shallowest region of subduction megathrust accommodates deformation by a spectrum of seismic modes including continuous aseismic creep and peculiar seismic phenomena as slow slip events. However, the mechanisms behind these phenomena remain enigmatic because they are not explained by conventional frictional models. This because the shallowest regions of subduction zones are characterized by unconsolidated, clay-rich lithologies that, nominally, cannot nucleate seismic events due to their frictionally weak and rate-strengthening attributes. Here we present laboratory friction experiments showing that clay-rich experimental faults with bulk rate strengthening behavior and low healing rate can contemporaneously creep and nucleate slow slip events. These instabilities are self-healing, slow ruptures propagating within a thin shear zone and driven by structural and stress heterogeneities. We propose that the bulk rate-strengthening frictional behavior promotes the observed long-term aseismic creep whereas local frictional mechanism causes slow rupture nucleation and propagation. Our results illustrate the complex behavior of clay-rich lithologies, providing a new paradigm for the interpretation of the genesis of slow slip as well as significant implications for seismic hazard.

How to cite: Volpe, G., Collettini, C., Taddeucci, J., Marone, C., and Pozzi, G.: Complex Frictional Behavior of Clay and Implications for Slow Slip , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5061, https://doi.org/10.5194/egusphere-egu24-5061, 2024.

The acoustic emissions (AEs) produced during the shearing of granular materials reflect the accumulation and release of stress, offering valuable insights into the failure mechanisms of seismic faults and stick-slip-controlled landslides. While various characteristics such as amplitude, energy, counts, and frequency of AE signals generated by stick-slip have been studied, the stress changes corresponding to different frequency AEs at various stages of the stick-slip process remain unclear. This knowledge gap hinders our understanding of the precursory signals leading to stick-slip failure. In order to enhance our comprehension of the physical mechanisms underlying granular stick-slip, we conducted monitoring of both mechanical and AE signals using high-frequency (2 MHz) synchronous acquisition. This was done during the constant-speed shearing of packs containing uniform glass beads of different sizes under varying normal stresses. Our findings revealed an accelerated release rate of AE energy in tandem with sample volume dilatation. Additionally, the stress drop during stick-slip increased with higher normal stress and particle size. This study identified three distinct events during a single cycle of stick-slip: main slip, minor slip, and microslip. We analyzed the AE frequency spectra associated with each of these events. Main slip and minor slip correlated with stress drop, generating high-frequency AEs (approximately several hundred kHz). In contrast, microslip produced lower AE frequencies (around tens of kHz) and exhibited stress strengthening. These characteristics, overlooked in prior studies due to low-frequency acquisition, suggest that microslip is primarily a result of sliding on grain contacts, while main slip and minor slip arise from the breakage and reformation of force chains. The low-frequency AEs from microslip may serve as a crucial precursor to seismic faults and landslides, providing a deeper understanding of the granular stick-slip phenomenon.

How to cite: Gou, H. and Hu, W.: Detection of Stick-Slip Nucleation and Failure in Homogeneous Glass Beads Using Acoustic Emissions in Ring-Shear Experiments: Implications for Recognizing Acoustic Signals of Earthquake Foreshocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5252, https://doi.org/10.5194/egusphere-egu24-5252, 2024.

EGU24-5921 | ECS | Posters on site | TS1.6

Interaction of fault slip with fast fluid pressure transients in subduction zones 

Avinash Gupta, Nikolai M. Shapiro, Jean-Paul Ampuero, Gaspard Farge, and Claude Jaupart

This study investigates the dynamic interplay between fluids and fault slip transients in the portion of subduction zones subject to slow earthquakes. The permeable subduction interface in this region is believed to be saturated with fluids supplied by metamorphic dehydration reactions in the downgoing plate. Following Farge et al. (2021), we consider a model of a heterogeneous subduction channel filled with low-permeability plugs that behave as elementary fault-valves. Such a system is characterized by an intermittent fluid transport and rapid and localized pressure transients. Episodic rapid build-ups and releases of the fluid pressure affect the frictional strength on the fault and can result in transient slip accelerations. To study the possible effect of episodic fast fluid pressure variations on fault slip, we use numerical simulations in a 2D in-plane shear geometry. The fault is governed by rate-and-state friction, with velocity-strengthening steady-state properties, and is forced with time and spatially variable pore fluid pressure. In an initial set of tests, we show that periodic pore pressure oscillations can accelerate the fault slip akin to observed slow slip events. We then investigate how the fault slip responds to more complex and “realistic” pore pressure histories generated by the dynamic permeability model of Farge et al. (2021). Our results underscore the possible role of input fluid flux and permeability structure in determining the variations of fault slip and, in particular, in facilitating the slow slip events. 

How to cite: Gupta, A., Shapiro, N. M., Ampuero, J.-P., Farge, G., and Jaupart, C.: Interaction of fault slip with fast fluid pressure transients in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5921, https://doi.org/10.5194/egusphere-egu24-5921, 2024.

EGU24-7813 | Posters on site | TS1.6

The role of serpentinized mantle on thrust-fault earthquake dynamics offshore SW Iberia 

Manel Prada, Sara Martínez-Loriente, Jonas B. Ruh, and Valentí Sallarès

The present-day Eurasia-Africa plate convergence offshore SW Iberia gives rise to a diffuse plate boundary marked by deep lithospheric thrust and strike-slip faults. The Horseshoe Abyssal Plain Thrust (HAT) stands out as a key structure accommodating plate convergence, and it has been the site of deep (> 30 km depth) and large magnitude (Mw > 6) earthquakes. Additionally, the HAT has been proposed to be the source of the 1755 Lisbon earthquake (estimated Mw≥8.5), one of the most destructive earthquakes and tsunami in the history of Europe. The geometry of the fault and the physical properties of rocks surrounding it have been determined through tomographic models derived from controlled-source seismic data. Although large earthquakes along the HAT primarily occur at considerable depths within the peridotitic mantle (~40 km depth), the fault intersects a region of serpentinized mantle at shallower depths (10-20 km depth). In contrast to peridotite that undergoes seismic deformation, the frictional behaviour of serpentinized peridotite depends on factors such as pressure, water content, temperature, and slip velocity. Laboratory measurements indicate that serpentinite transitions from rate-strengthening behaviour at plate tectonic rates to rate-weakening at seismic slip rates. This dual nature suggests that large deep earthquakes, nucleated in pristine peridotite, could rupture seismically through the weaker serpentinized peridotite. While this mechanism has been proposed to explain the HAT's potential to generate large tsunamigenic earthquakes, it remains untested. In this study, we use dynamic rupture numerical simulations to investigate the role of serpentinized peridotite in the rupture process and the tsunamigenic potential of the HAT. In particular, we explore various frictional scenarios to determine the slip pattern necessary to account for the previously estimated tsunamigenic uplift associated with the 1755 Lisbon earthquake.

How to cite: Prada, M., Martínez-Loriente, S., B. Ruh, J., and Sallarès, V.: The role of serpentinized mantle on thrust-fault earthquake dynamics offshore SW Iberia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7813, https://doi.org/10.5194/egusphere-egu24-7813, 2024.

Topographic features such as seamounts can influence the buoyancy of the slab and the short- and long-timescale mechanical properties of the subduction interface. How seamounts in the trench interact with the upper plate accretionary wedge during subduction— their stress field, their potential for ‘decapitation’, and their ability to host large megathrust earthquakes— is not fully understood. We utilize exhumed rocks to investigate seamount–upper plate interactions at shallow subduction interface conditions. 

We focus on a 250-m-thick cross-section of deformed, weakly metamorphosed basalt, limestone, chert, argillite and greywacke exposed in the inboard part of the Chugach accretionary complex near Grewingk glacier, southern Alaska. Temperatures from Raman spectroscopy on graphite yield ~260°C, suggesting deformation and metamorphism down to ~15-20 km depth. Detrital zircon data from greywacke lenses within and outside the shear zone overlap within error suggesting emplacement over less than ~1 m.y. at ~167 Ma. 

Basalts in the shear zone are dismembered into ~3 slices up to 35 m thick, all of which contain limestone patches suggesting the basalt is derived from the seamount’s very top (limited decapitation). The basalt slices are bounded by high-strain melange-like shear zones up to 25 m thick, interpreted to represent décollements along which the seamount slices were underplated. These mélange belts exhibit a block-and-matrix texture with a macroscopically ductile argillite and chert matrix, and pervasively disaggregated and brittlely deformed greywacke and basalt lenses. Both the matrix and the blocks show several generations of dilational and shear veins, suggesting high fluid pressures and low differential stresses. Features suggesting deformation at fast (potentially seismic) strain rates include fluidized cataclasites, but these do not extend along strike for more than 0.25 m and do not occur within the larger (m-to-dm-scale) basalt lenses, suggesting that large-magnitude earthquakes were limited during seamount underplating. Instead, the observed mix of brittle and macroscopically ductile deformation at high fluid pressures is more consistent with a potential record of shallow tremor and slow slip.

Our findings support geophysical observations and numerical models that suggest relatively weak mechanical and seismic coupling between seamounts and the overriding plate, and are consistent with recent suggestions (e.g. for the Hikurangi margin) that sediment envelopes around subducting seamounts are conducive to slow slip and tremor.

How to cite: Behr, W., Akker, I. V., and Rast, M.: Deformation processes during seamount dismemberment and underplating along the shallow subduction interface: a case study from the Chugach Complex, Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8244, https://doi.org/10.5194/egusphere-egu24-8244, 2024.

EGU24-8731 | ECS | Posters on site | TS1.6

Implications of tourmaline frictional and rheological experiments on fault strength and sliding stability in southern Tibet 

Xinze Li, Yongsheng Zhou, Lining Cheng, and Jianfeng Li

A large number of tourmaline fault mirrors are exposed in the north-south normal fault system in the southern part of the Tibetan Plateau. Microstructure analysis shows that the tourmaline fault mirror has the characteristics of co-seismic high speed friction sliding and high temperature plastic rheology. In order to reveal the mechanical process of friction-rheological strength and co-seismic slip of tourmaline fault, the frictional and rheological experiments were carried out on the gas-medium triaxial high temperature and high pressure experimental system using undeformed tourmaline in southern Tibet to determine the formation conditions of tourmaline fault mirror. The effective normal stress of frictional experiments is 100Mpa.The pore water pressure is 30MPa. The temperature is 25-500℃, and the shear slip rate is switched between 1μm·s-1, 0.2μm·s-1, 0.04μm·s-1. The experimental results show that stick-slip occurs at 200-350℃, and the speed weakens at 400℃ and 500℃. The rheological experiment temperature is 850-950℃. The pressure is 300MPa, and the strain rate is switched between 2*10-5s-1, 1*10-5s-1, 5*10-6s-1, 7.5*10-6s-1. The experimental results show that the natural tourmaline sample is mainly fractured flow under the experimental conditions. The strength of hot-pressed dry tourmaline sample decreases with increasing temperature. The rheological strength of water samples synthesized by hot pressing was significantly reduced.

How to cite: Li, X., Zhou, Y., Cheng, L., and Li, J.: Implications of tourmaline frictional and rheological experiments on fault strength and sliding stability in southern Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8731, https://doi.org/10.5194/egusphere-egu24-8731, 2024.

EGU24-8767 | ECS | Posters on site | TS1.6

A semi-automatic detection for transient events in northern Apennines using strainmeters and GNSS data 

Roxane Tissandier, Adriano Gualandi, Lauro Chiaraluce, Enrico Serpelloni, Mike Gottlieb, Catherine Hanagan, and Chris Marone

Low-angle normal faults (i.e. with a dip < 30°) were assumed to have a very low seismic potential (Sibson et al., 1985). However, several observations have shown that earthquakes and aseismic slip can occur along such faults. For instance, the Alto Tiberina Fault (ATF), a 60-km long normal fault with a 15° low angle dip located in the active sector of the Northern Apennines (Italy), is seismically active as well as is actively accommodating part of the Apennines extensional strain. However, the relative contribution of seismic and aseismic slip on it is still unclear. The central and northern Apennines experienced several seismic sequences in the recent decades and a Mw ∼ 4.6 aseismic event accompanied by a seismic swarm of similar or smaller size was also recorded in 2013-2014 along two synthetic and antithetic fault in the hanging-wall of the ATF (Gualandi et al., 2017). The interactions between such minor conjugate faults and the ATF compose a system undergoing complex behavior making the area an ideal candidate to improve our understanding of interactions between different slipping modes. We benefit from data of the Alto Tiberina Near Fault Observatory (TABOO-NFO; Chiaraluce et al., 2014) looking for aseismic events on the ATF and its surrounding faults. The dense network of GNSS, seismometers and borehole strainmeters provides a rarely attained high spatial (inter-distance < 10km) and temporal (from 2009 to nowadays) resolution framework enabling the study of the ATF fault system slip history. We search for transients with a semi-automatic detection tool of slow slip events based on kinematic inversions of strainmeters time series. We also test if these events interact with larger seismic events of the region. We present the strain time series processed with the EarthScope Strain Tools (EarthScope Consortium) and the preliminary signals detected with our tool. The fine analysis of the ATF would help better constraining the behavior of faults and more generally large events. 

How to cite: Tissandier, R., Gualandi, A., Chiaraluce, L., Serpelloni, E., Gottlieb, M., Hanagan, C., and Marone, C.: A semi-automatic detection for transient events in northern Apennines using strainmeters and GNSS data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8767, https://doi.org/10.5194/egusphere-egu24-8767, 2024.

EGU24-9007 | Orals | TS1.6 | Highlight

A mechanical insight into the continuous chatter of a fault volume 

Harsha Bhat, Michelle Almakari, Navid Kheirdast, Carlos Villafuerte, and Marion Thomas

In recent decades, there has been a proliferation of observations related to spatiotemporally intricate slip events occurring in fault systems. These events encompass a spectrum of transient energy releases, ranging from slow slip events to low-frequency earthquakes (LFEs) and tremors, in addition to the more familiar creep and fast ruptures. The prevailing focus in recent research has been to interpret these events by considering variations in frictional behavior along the fault plane.

However, it is crucial to acknowledge the inherent geometric complexity of fault systems across multiple scales. Recent studies have illuminated the significance of incorporating a fault volume or damage zone surrounding the fault in the analysis of slip dynamics. In the context of this study, we endeavor to investigate the influence of "realistic" fault geometry on the dynamics of slip events. To achieve this, we approach the problem from three interrelated perspectives:

  • Forward Source Modeling: We employ forward source modeling techniques to simulate and understand the behavior of slip events.
  • Bridging Source Modeling and Observations: We establish a connection between our source modeling and observed data by generating synthetic surface records that can be compared to actual observations.
  • Energy Budget Analysis: We meticulously analyze the variations in the energy budget that occur throughout the earthquake cycles to gain insights into the mechanics of slip events.

Our primary objectives include deciphering how deformation within the volume is accommodated by both the off-fault damage zone and the primary fault. Specifically, we aim to determine the proportion of the supplied moment rate that is absorbed by off-fault fractures during an earthquake cycle. Additionally, we seek to unravel how the diverse sequences of complex behavior observed on the fault plane manifest in the signals recorded by seismic stations. This entails assessing the distinct contributions of the main fault and off-fault fractures to the radiated signals detected at the monitoring stations. Lastly, we delve into the evolution of the medium's energy budget throughout the earthquake cycles and evaluate the dissipative contribution of off-fault fractures to ascertain their energetic role in the context of earthquake cycles.

How to cite: Bhat, H., Almakari, M., Kheirdast, N., Villafuerte, C., and Thomas, M.: A mechanical insight into the continuous chatter of a fault volume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9007, https://doi.org/10.5194/egusphere-egu24-9007, 2024.

EGU24-9169 | ECS | Posters on site | TS1.6

A spectrum of fault slip behaviors induced by fluid injection on a rate-and-state fault depending on time of injection relative to its natural fault cycle 

Silvio Pardo, Elisa Tinti, Martijn Van den Ende, Jean-Paul Ampuero, and Cristiano Collettini

Fluid induced seismicity represents a significant issue for numerous activities related to geo-energy production. Enhanced geothermal systems, enhanced oil recovery, disposal of wastewater and carbon dioxide capture and storage are associated with subsurface fluid injection that can change the state of stress within the crust and can induce or trigger earthquakes. In several regions, M>3 earthquakes occurred following fluid injection, whereas in others seismicity has been accompanied by slow slip events. Although several mechanisms have been proposed to explain slow slip associated with fluid injection, the conditions leading to the observed spectrum of fault slip behavior still remain elusive. Here we used a quasi-dynamic boundary element method, the QDYN earthquake cycle simulator, to model the response of a fault governed by rate-and-state friction to fluid injection within a reservoir. We imposed low long-term loading rates to simulate a fault located in an area of slow active deformation, leading to natural earthquake cycles with very long recurrence times. We then imposed fluid pressure perturbations (one-way coupling) at different stages of the seismic cycle, to evaluate pore-pressure effects on the triggering of the next event. 

Our results show that for injection at high fluid pressure, earthquakes are in general immediately triggered (during injection or soon after) irrespective of the stage (early or late) of the seismic cycle, whereas at lower fluid pressure fast triggering is observed only when injecting in the late stages of the seismic cycle. Our models produce a spectrum of fault slip behavior, from regular to slow earthquakes. The latter are observed for specific fluid pressure, flow rate and injection time relative to the seismic cycle. The physics underlying this complex slip behavior remain to be explained, and further studies are required to define the injection conditions that favor the occurrence of slow slip instead of regular earthquakes.

How to cite: Pardo, S., Tinti, E., Van den Ende, M., Ampuero, J.-P., and Collettini, C.: A spectrum of fault slip behaviors induced by fluid injection on a rate-and-state fault depending on time of injection relative to its natural fault cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9169, https://doi.org/10.5194/egusphere-egu24-9169, 2024.

EGU24-9437 | Orals | TS1.6

Creeping sections on continental strike slip faults as the signature of deep fluid upwelling 

Romain Jolivet, Dmitry Garagash, Dublanchet Pierre, and Jorge Jara

Aseismic slip has been recognized over the last 50 years as one of the modes of elastic stress accommodation by large tectonic faults. Long strike slip faults have been imaged with InSAR and scrutinized with GNSS networks and creepmeters, revealing the strikingly ubiquitous occurrence of aseismic slip globally. From the 600-km-long creeping section of the Chaman to the 70 km-long Ismetpasa creeping section along the North Anatolian Fault, geodetic imaging illustrates the rich behavior of such aseismic slip, from mm-scale transient episodes of slip to seemingly continuously sliding fault segments.

Most models explaining the occurrence of aseismic slip along continental faults rely entirely on an ad hoc parameterization of the frictional rheology of the fault. While the friction law governing slip along faults has been determined from laboratory experiments, the inference of the constitutive parameters of such friction law entirely derives from reproducing geodetic data in most cases. In particular, most creeping sections are interpreted as the signature of rate-strengthening material, diffusing stress through stable sliding. However, most rocks at seismogenic depths exhibit a rate-weakening behavior and some even show transient episodes of slip incompatible with purely strengthening properties. In addition, other mechanisms, including complex geometric configuration of faults or fluid circulation may offer the conditions for slow slip. Therefore, the direct inference of constitutive properties of a fault zone from kinematic observations may not be simple.

We propose here a model in which upwelling of fluids sourced in the upper mantle through a vertical fault zone leads to the conditions for slow slip, irrespective of the fault constitutive properties. We map aseismic slip along three different fault zones, including the North Anatolian Fault (Turkiye), the San Andreas Fault (USA) and the Leyte fault (Philippines) and find a systematic relationship between the effective locking depth and the occurrence of aseismic slip. Our model explains this modulation of locking depth along strike and the subsequent modulation of surface shear stressing rate with the along strike variation in the mantle fluid source. This model applied to fault segments with relatively high mantle fluid source leads to low effective normal stress, large nucleation size of a frictional instability, and predicts occurrences of shallow aseismic slip. We perform numerical modeling to show that the critical parameter is the flux of upwelling fluid through the fault zone, which increase leads to the widening of the near-surface region of aseismic slip and transition to full-fault aseismic slip at large enough flux. We finally discuss the potential sources of fluids explaining such behavior.

How to cite: Jolivet, R., Garagash, D., Pierre, D., and Jara, J.: Creeping sections on continental strike slip faults as the signature of deep fluid upwelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9437, https://doi.org/10.5194/egusphere-egu24-9437, 2024.

EGU24-9595 | Orals | TS1.6

Exploring the impact of frictional heterogeneities on the seismic cycle: Insights from laboratory experiments 

Corentin Noël, Pierre Dublanchet, and François Passelègue

Deformation within the upper crust is mainly accommodated through slip on fault systems. These systems can accommodate slip via different modes, going from aseismic creep (i.e., stable motion) to dynamic earthquake (i.e., unstable motion). Notably, a single fault is not confined to a specific slip mode, as recent geodetic observations have indicated that a single fault can exhibit both stable and unstable motions. The distinct slip behaviours have been attributed to fault spatial heterogeneity of the frictional properties, rheological transitions, or geometrical fault complexities.

To comprehensively characterize the impact of frictional heterogeneities, we deformed heterogeneous fault samples in a triaxial apparatus, at confining pressure ranging from 30 to 90 MPa. The fault planes, sawcut at a 30° angle from the sample axis, consisted of two materials: granite and marble. Experiments were conducted for both marble asperities embedded in granite and vice versa, alongside homogeneous fault samples of single lithology. The selection of granite and marble was based on their different mechanical and frictional characteristics, with granite exhibiting seismic behaviour, while marble demonstrated aseismic behaviour across the pressure range tested.

Our findings reveal that the stress drops of seismic events are dependent on fault composition, with faults containing higher granite content exhibiting larger seismic events. In addition, by coupling the inversion of the kinematic slip from strain-gauge measurements and the records of acoustic activity during experiments, we demonstrate that the nucleation and propagation of seismic events are significantly influenced by lithological heterogeneity on the fault plane. In the case of homogeneous faults, the seismic event nucleation is relatively straightforward, initiating in the highest stressed region and propagating uniformly. Conversely, heterogeneous faults display more intricate nucleation patterns, often featuring multiple nucleation regions converging into a major dynamic event. The dynamic event propagation is expedited when traversing granite areas and more restrained within the marble. Remarkably, our experiments demonstrate that heterogeneities are required in order to induce earthquake afterslip. These results emphasize the crucial role of fault heterogeneity in earthquake nucleation and propagation, highlighting that even minor lithological heterogeneities are sufficient to complicate laboratory earthquake dynamics.

How to cite: Noël, C., Dublanchet, P., and Passelègue, F.: Exploring the impact of frictional heterogeneities on the seismic cycle: Insights from laboratory experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9595, https://doi.org/10.5194/egusphere-egu24-9595, 2024.

EGU24-9961 | Orals | TS1.6 | Highlight

Do earthquakes start with precursory slow aseismic slip? 

Quentin Bletery and Jean-Mathieu Nocquet

The existence of an observable precursory phase of aseismic slip on the faults before large earthquakes has been debated for decades. We conducted a global search for short-term precursory slip in GPS data. We summed the displacements measured by 3026 high-rate (5-minutes sample) GPS time series—projected onto the displacements expected from precursory slip at the hypocenter—during 48 hours before 90 (moment magnitude ≥7) earthquakes. Our approach revealed a ≈2-hour-long exponential acceleration of slip before the ruptures, suggesting that large earthquakes do start with a precursory phase of slip acceleration. The results have since been questioned as being due to an unfortunate combination of common mode noise in GPS time series. We investigate this possibility along with complementary tests to quantify the likelihood of the proposed pre-slip and the common mode hypotheses.

How to cite: Bletery, Q. and Nocquet, J.-M.: Do earthquakes start with precursory slow aseismic slip?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9961, https://doi.org/10.5194/egusphere-egu24-9961, 2024.

EGU24-10783 | Orals | TS1.6

Fluid-induced failure and sliding of a gouge-filled fault zone: Hysteresis, creep, delay and shear-strengthening. 

Einat Aharonov, Pritom Sarma, Renaud Toussaint, and Stanislav Parez

Many previous studies have explored the role of granular media in controlling friction of faults. A gap exists though in understanding the failure process and sliding of a fluid-saturated fault gouge. Here we use a coupled 2D DEM-fluid code to simulate fault-gouge as a layer of grains, sheared by a constant stress boundary. We explore and compare two scenarios: 1) a dry granular layer, in which shear stress on the top wall is incrementally increased, or 2) a fluid-saturated granular layer, into which fluid is injected, so that fluid pressure is incrementally increased. Once the applied stress/pressure is high enough, the layer fails and starts accelerating, until it reaches a steady-state sliding rate (determined by the layers’ velocity-strengthening friction). We next incrementally step-down the shear stress or fluid pressure. Consequently, the slip-rate is observed to slow down linearly with decreasing stress/pore-pressure, until the layer finally stops, at a stress/pressure lower than that required to initiate the failure. Both the dry and fluid-saturated granular systems exhibit two main behaviors: 1) velocity-strengthening friction, following the mu(I) rheology, 2) a hysteresis effect between friction and velocity, porosity and grain coordination numbers. The hysteresis and strain-rate dependence agree with previous experimental, numerical and theoretical results in dry granular media, yet our work suggests these behaviors extend to fluid-filled granular media. We theoretically predict the transient and steady-state observations for dry and fluid-saturated layers, using the mu(I) friction rheology with an added component of hysteresis. Importantly, we show that fluid-filled faults exhibit a process which is absent in dry systems: fluid-injected layers may exhibit failure delay, with some time passing between pressure rise and failure. We link this delay to pre-failure creeping dilative strain, interspersed by small dilative slip events. Our numerical and analytical results may explain: (i) field measurements of fault creep triggered by fluid pressure rise (e.g. via injection), (ii) fault motion which is triggered by fluid-injection but continues even after fluid pressure returns to its pre-injection level. (iii) observed delay prior to failure in fluid-injection experiments.

How to cite: Aharonov, E., Sarma, P., Toussaint, R., and Parez, S.: Fluid-induced failure and sliding of a gouge-filled fault zone: Hysteresis, creep, delay and shear-strengthening., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10783, https://doi.org/10.5194/egusphere-egu24-10783, 2024.

EGU24-10887 | Orals | TS1.6

Localizing slow deformation holds crucial information related to seismicity patterns precluding brittle failure in crystalline rocks 

Paul Antony Selvadurai, Antonio Felipe Salazar Vasquez, Patrick Bianchi, Claudio Madonna, Leonid Germanovich, Alexander M. Puzrin, Carlo Rabaiotti, and Stefan Wiemer

A growing number of observations made using geodetic approaches have been able to detect large preparatory regions that experience accelerated deformation prior to and in close proximity to an earthquake’s hypocenter. An uptick in localized seismicity has also been observed in these regions and represents an opposite end-member of the spectra of deformation, in both space and time, from the opposite broad and slow process. If and how these preparatory observations are linked are not well understood. To study this, we conducted a triaxial experiment on a granitic rock sample instrumented with calibrated acoustic emission (AE) sensors and a distributed strain sensing (DSS) method using fibre optics. These two technologies were sensitive to seismic (100 kHz to 1 MHz) and aseismic (DC to 0.4 Hz) deformation at our sample scale and these were monitored as it was loaded and experienced brittle shear failure. DSS measurement allowed us to visualize the emergence of slow, heterogeneous strain fields that localized well before the failure of the sample. In the early stages of localized deformation, the regions exhibiting preferential damage were growing and doing so without producing seismicity. However, when approaching failure, these regions accommodating slow deformation began to accelerate and now produced clusters of seismicity. The cumulative seismic moment of the precursory seismicity was a fraction of the total anelastic deformation (< 0.1%) precluding the runaway dynamic failure. We also examined the clustering and frequency-magnitude distribution of the seismicity with respect to the localized strain field. In the later stages, moments prior to nucleation, the b-value begins to drop and becomes anti-correlated to the rapidly accelerating average volumetric strain rate measured using the DSS array. This observation better constrains the hypothesis that dilation of the relatively large preparation zone can host larger precursory earthquakes therein. These findings can help constrain models that better replicate the physics associated with the large spectrum of brittle deformation and will in turn help with our understanding of preparatory earthquake processes.

How to cite: Selvadurai, P. A., Salazar Vasquez, A. F., Bianchi, P., Madonna, C., Germanovich, L., Puzrin, A. M., Rabaiotti, C., and Wiemer, S.: Localizing slow deformation holds crucial information related to seismicity patterns precluding brittle failure in crystalline rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10887, https://doi.org/10.5194/egusphere-egu24-10887, 2024.

Natural fault zone are complex objects. They not only consist of a fine-grained narrow fault core where the extensive shearing is observed, but it is also surrounded by pervasively fractured rocks, within an intricate 3-D geometry. If fault slip behavior is intrinsically linked to the properties of the fault core, the complex structure of fault zone systems impacts the rheological properties of the bulk, which influence the modes of deformation, and slip, as underlined by recent observations. Fault zone structure is therefore of key importance to understand the mechanics of faulting. Within the framework of a micromechanics based constitutive model that accounts for off-fault damage at high-strain rates, this numerical study aims to assess the interplay between earthquake ruptures along non-planar fault and the dynamically evolving off‐fault medium. We consider 2D inplane models, with a 1D self-similar fault having a root mean square (rms) height fluctuations of order 10-3 to 10-2 times the profile length. We explore the dynamic effect of fault-roughness on off-fault damage structure and on earthquake rupture dynamics. We observe a high‐frequency content in the radiated ground motion, consistent with strong motion records. It results from the combined effect of roughness-related accelerations and decelerations of fault rupture and slip rate oscillations due to the dynamic evolution of elastic moduli. These scenarios underline the importance of incorporating the complex structure of fault zone systems in dynamic models of earthquakes, with a particular emphasis on seismic hazard assessment.

How to cite: Thomas, M. Y. and S. Bhat, H.: Combined Effect of Brittle Off-Fault Damage and Fault Roughness on Earthquake Rupture Dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12095, https://doi.org/10.5194/egusphere-egu24-12095, 2024.

EGU24-12752 | Posters on site | TS1.6

Healing of fault surfaces: a field vs. experimental perspective 

Telemaco Tesei, Giancarlo Molli, Silvia Mittempergher, Giacomo Pozzi, and Francesca Remitti

“Fault healing” is the ability of fault rocks to recover strength after rupture, due to a combination of several physical processes that include cementation, compaction, asperity growth etc. Healing is fundamental in the earthquake physics because it allows for the repeated accumulation of energy along faults over multiple seismic cycles. Fault healing is commonly studied in the laboratory, through Slide-Hold-Slide (SHS) tests and cementation experiments. However, laboratory measurements and the microstructures of experimental fault rocks are difficult to compare with natural rocks, due to the difference in kinetics of physical mechanisms and the small spatio-temporal scale of experiments.

Here, we review the field and microstructural evidence of various processes of fault healing along a carbonatic fault surface, taking advantage of an outstanding case study: the Pietrasanta Normal Fault (NW Tuscany, Italy). In the field, the most common evidence of fault healing is the occurrence of cohesive fault rocks (cataclasites) and veins, but other fault surface properties may influence the re-strengthening of fault surfaces: e.g. adhesion phenomena (sidewall ripouts and fault surface patches) and geometrical complexity.

We compare these observations with frictional healing experiments carried out on carbonatic fault rocks, in which both fault gouges and cohesive slip surfaces were used. We propose that a fault surface composed by “patches” of cohesive fault rocks bounded by anastomosing slip zones are the result of complex cycles of gouge formation and healing, which modulate the interplay of adhesion and localization along the fault surface.

How to cite: Tesei, T., Molli, G., Mittempergher, S., Pozzi, G., and Remitti, F.: Healing of fault surfaces: a field vs. experimental perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12752, https://doi.org/10.5194/egusphere-egu24-12752, 2024.

In earthquake research, the discovery and ongoing investigation of interseismic transient processes has revealed that faults are non-steady between large earthquakes. These transients are typically identified in continuously operating tectonic GNSS stations, whereby an acceleration away from the average interseismic rates of displacement can be identified with a variety of time series analysis methods. However, the features of these transients can vary depending on the processing strategy employed to derive displacement time series from the raw GNSS observables.

In the processing strategy, the definition of the geodetic datum is necessary to determine global terrestrial reference frames (TRFs), providing an accurate and stable absolute reference of Earth's locations. It is essential for comprehending the dynamic changes in Earth's geometry driven by factors like tidal and non-tidal loading, plate tectonic seismic activity, and ongoing climate change. Therefore, just as geodesy aims for accuracy and stability in the TRF, the datum definition—i.e., the realization of the TRF-defining parameters origin, orientation, and scale—may emerge as a critical factor in processing GNSS networks for geodynamic purposes.

The purpose of this study is to assess up to what extent the transient velocities obtained from GNSS-derived displacement time series change under different regional and global datum definitions for the Cascadia subduction zone and Hikurangi margin; regions with very well-known catalog of interseismic transient tectonic events. In our study, we process data from Cascadia to produce network solutions both NNR (No-Net-Rotation) and NNR+NNT (No-Net-Translation) constraint for regional and global datum definition, respectively. We employed dual-frequency ionosphere-free linear combination observations from 125 GNSS stations for the time between 2015 and 2020. The same GNSS processing strategy is then followed for the Hikurangi subduction zone using a set of 72 stations from the GeoNet project as well as the same control stations used for Cascadia spanning from 2002 to 2010.

For the Cascadia displacement time series, we find variations in transient velocities under different datum definitions emphasizing the need for a comprehensive understanding of its impact on dynamic geophysical processes. Processing and analyses of the New Zealand data is ongoing and results will be presented, along with recommendations for both regions on how to reduce the occurrence of likely non-tectonic transients in the displacement time series. Ultimately, our results may have implications for improving the estimate of the slip budget at plate boundaries that is released aseismically.

How to cite: Garcia, C., Bedford, J., Männel, B., and Glaser, S.: Impact of datum definition on transient velocities from GNSS displacement time series in Networks mode: A Case Study of Cascadia Subduction Zone and Hikurangi margin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12979, https://doi.org/10.5194/egusphere-egu24-12979, 2024.

EGU24-13514 | ECS | Posters on site | TS1.6

Discrepant stress distributions around instability regions: A new view for earthquake nucleation zones prediction 

Lin Zhang, Jianye Chen, Bowen Yu, and Miao Zhang

It is believed that seismic failure conditions are sensitive to strain-softening behavior of nominal rock or fault gouge, and that precursors prior to a big earthquake (i.e., tectonic trains, water level changes, and Vp/Vs anomalies, etc) are provided by the acceleration of local slip. Previous studies of earthquake nucleation on laboratory faults show that the initiation of unstable fault slip is spatiotemporal dependent and consists of an interval of fault preslip (or creep) that localizes and accelerates to a dynamically propagating rupture. We pose that perturbation-type experiments can provide a natural condition to help analyze the potential mechanisms between instability events and the stress loading. In this study, we conducted three sets of double-direct shear experiments on a 300 mm long fault filled with gypsum-rich gouges, under normal stress of 10 MPa superimposed with perturbations of various amplitudes (i.e., 0-0.5 MPa) and a fixed frequency (0.1 Hz). The result showed that during each cycle of the stick slip behavior, the applied normal stress perturbations were redistributed along the fault zone as revealed by the along-fault strain measurement in the normal direction. As such, the fault can be divided into different zones characterized by varied coupling with respect to the applied perturbations. We found, coincidently, nucleation of the final instability, as revealed by the strain measurement in the shear direction, tended to occur at the boundary between the so-called strong and weak coupling zones (‘Transition Zone). Moreover, local normal stress near the nucleation zone also showed some weakening prior to the instability, which was similar to that seen in the local shear stress, and hereafter referred to as ‘normal failure’. Based on these observations, we proposed an empirical equation to fit the normal strain or stress data, giving the distribution of the coupling coefficient (c-value) and the anomaly (a-value) along the simulated fault. Finally, we applied the proposed equation to fit the water level data from 6 monitoring stations along the fault that hosted a nature earthquake (~ML 4). The fitting results predicted a Transition Zone, which was close to the hypocenter. In the end, we propose that this approach can be tested widely to natural observations of various precursory signals, especially those considered to be sensitive to fault-normal deformation (“dilatation” or “compaction”), such as water level, soil gas, and Vp/Vs anomalies. Hopefully, the results can shed some lights on the location of the earthquake nucleation zone. 

How to cite: Zhang, L., Chen, J., Yu, B., and Zhang, M.: Discrepant stress distributions around instability regions: A new view for earthquake nucleation zones prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13514, https://doi.org/10.5194/egusphere-egu24-13514, 2024.

EGU24-13838 | ECS | Posters on site | TS1.6

Slip Behaviors Controlled by Rheological and Frictional Properties of A Two-Phase Mélange in Subduction Shear Zones 

Jun Xie, Xiaotian Ding, and Shiqing Xu

A rich spectrum of slip behaviors, spanning from aseismic creep (mm/yr) to seismic slip (m/s), has been observed in many subduction zones and some strike-slip faults. Slow earthquakes, intermediate between these two end-member modes, exhibit transitional slip behaviors in fault sections adjacent to the seismogenic zone. Focusing on subduction zones, it is shown that they experience deformation not only along discrete fault planes but also over distributed frictional-viscous shear zones, the latter of which are thought to be responsible for the observed diverse slip behaviors. Here we employ a frictional-viscous mélange model consisting of brittle blocks surrounded by a viscous matrix to investigate its influence on slip behaviors. By varying the mélange's rheological and frictional properties, we observe a diverse range of slip behaviors. We also reproduce the source scaling relations observed in natural faults, including the relation between seismic moment and duration and that between moment magnitude and stress drop. Additionally, we find a close link between the modeled shear zone deformation patterns and the various geological structures observed in natural fault zones. Our study demonstrates that the interaction between the frictional and viscous compositions of the mélange is responsible for the resulting slip behaviors and their transitions under different compositional ratios. These results provide useful clues for constraining the environmental and rheological conditions of different subduction zone sections from the observed slip behaviors.

How to cite: Xie, J., Ding, X., and Xu, S.: Slip Behaviors Controlled by Rheological and Frictional Properties of A Two-Phase Mélange in Subduction Shear Zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13838, https://doi.org/10.5194/egusphere-egu24-13838, 2024.

EGU24-15197 | ECS | Posters on site | TS1.6

Deformation microstructure of the fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea 

Sejin Jung, Ji-Hoon Kang, Youngwoo Kil, and Haemyeong Jung

The 5.5 magnitude (Mw) earthquake in Pohang, South Korea in 2017 was one of the largest triggered earthquakes at an enhanced geothermal system (EGS) site. Faults that ruptured in Pohang were not identified by preliminary geological investigations or geophysical surveys, and the subsequent study of the fault rocks at the Pohang EGS site was limited to depths of 3790–3816 m. In this study, we present new observations of fault rocks from drill cuttings retrieved from the Pohang EGS. The drill cuttings obtained from 3256 to 3911 m contained “mud balls,” which showed a clay matrix with foliation and a cataclastic texture, indicating a typical fault gouge or breccia. Furthermore, the mud ball samples retrieved from depths of 3256 m and 3260 m contained black fragments. Scanning and transmission electron microscopy revealed that the black fragments consisted of glass-like material, which is indicative of frictional melting during coseismic slip (Jung et al., 2023). The presence of these black fragments suggests that at least one seismic event had occurred at the Pohang EGS site prior to the hydraulic stimulation test.

Jung, S., J. -H. Kang, Y. Kil and H. Jung, 2023, Evidence of frictional melting in fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea. Tectonophysics, 862, 229964.

How to cite: Jung, S., Kang, J.-H., Kil, Y., and Jung, H.: Deformation microstructure of the fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15197, https://doi.org/10.5194/egusphere-egu24-15197, 2024.

EGU24-15878 | ECS | Orals | TS1.6

Fault orientation in earthquake seismic precursors: insights from the laboratory 

Carolina Giorgetti and Nicolas Brantut

Faults in the brittle crust lie at any orientation to the far-field stress. However, laboratory experiments designed to investigate earthquake physics commonly simulate favorably oriented faults, potentially overlooking the complexity of natural fault behavior. Here, we assess the role of stress field orientation in fault reactivation and earthquake precursors by conducting triaxial saw-cut experiments with laboratory faults oriented at different angles to the maximum principal stress, ranging from 30° to 70°. The samples were instrumented with strain gauges and piezo-electric sensors. Laboratory well-oriented faults describe a rather simple system in which the elastic energy is stored via the deformation of the surrounding host rock during the inter-seismic period and released via on-fault slip during the co-seismic phase with associated precursor acoustic activity. Consistent with previous laboratory data, an abrupt increase in the on-fault acoustic emission rate occurs shortly before the laboratory earthquake. A more complex picture emerges when deforming laboratory misoriented faults. Particularly, acoustic emissions and strain gauge data indicate that when the fault is misoriented, off-fault permanent deformation occurs well before fault reactivation. The stress state in the host rock surrounding the fault is indeed far beyond the one required for the onset of inelastic deformation. In this case, acoustic activity distributed in the rock volume during the pre-seismic phase is associated with permanent deformation in the critically stressed host rock and is not a direct precursor to the following laboratory earthquake. Unlike well-oriented faults, laboratory mis-oriented faults lack detectable seismic precursors. The laboratory-observed increase in acoustic activity prior to, but not precursor of, mis-oriented fault reactivation impacts our understanding of earthquake precursors in natural faults.

How to cite: Giorgetti, C. and Brantut, N.: Fault orientation in earthquake seismic precursors: insights from the laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15878, https://doi.org/10.5194/egusphere-egu24-15878, 2024.

EGU24-16581 | ECS | Posters on site | TS1.6

Interpretable Embedding of Laboratory Stick-Slip Acoustic Emission Time Series 

Rens Elbertsen, Ivan Vasconcelos, and André Niemeijer

Laboratory stick-slip experiments are a simple analogue for the earthquake cycle. The acoustic emissions (AE) of these experiments have been shown to contain hidden patterns. Machine Learning (ML) can extract these patterns and information on the fault state can be inferred (e.g. shear stress and time to failure). Two different ML approaches have been used in the past: 1) ensemble tree models, which are relatively easy to evaluate why they made a certain prediction, but only look at a snapshot in time and 2) deep neural networks using Long Short-Term Memory (LSTM), which have the ability to find patterns in the temporal changes in the signal, but act more as a black-box model, so the final predictions are hard to evaluate. Here we introduce an additional step in the workflow that can be used to allow the ensemble tree models information about the temporal changes of the input features. Furthermore, it is able to quantify and visualize whether a pattern is repetitive or not. Like earlier studies we start by calculating (statistical) features using a rolling window on the AE. The features are not directly used as the input of the model, but are placed in a larger Hankel matrix, where the consecutive time windows are the rows of the matrix. Using Principal Component Analysis (PCA) and Uniform Manifold Approximation and Projection (UMAP) we create an embedded version of this array that holds temporal information of features calculated in the previous step. Visual inspection of these embeddings shows that some features map to very distinct patterns that are repetitive over the majority of the stick-slip cycles. The advantage of this method is that an inverse mapping is easily available, allowing for an interpretable embedding of the data.

How to cite: Elbertsen, R., Vasconcelos, I., and Niemeijer, A.: Interpretable Embedding of Laboratory Stick-Slip Acoustic Emission Time Series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16581, https://doi.org/10.5194/egusphere-egu24-16581, 2024.

EGU24-18746 | ECS | Posters on site | TS1.6

Analyzing Earthquake Energy: Unveiling the Spectrum of Fault Behavior in Terms of Moment, Duration, and Rupture Speed 

Navid Kheirdast, Harsha Bhat, Michelle Almakari, Carlos Villafuerte, and Marion Thomas

Seismic observations confirm that natural fault systems radiate waves across a continuum of frequency and amplitude. Within this spectrum, faulted systems exhibit a continuous range of slip rates, allowing them to irreversibly dissipate energy stored in rocks over a broad range of seismic moment. Despite advancements in observations and numerical modeling models, the question on how a given fault system can host such a wide range of ruptures, including slow ruptures, VLFEs, LFEs, and fast earthquakes needs a careful attention. Addressing this question requires a framework rooted in fracture mechanics, which explores the rate at which energy provided to a crack drives the rupture front forward and how this process radiates energy throughout the medium.

This work delves into the question of how frictional instability and mechanical interactions between faults and fractures, particularly concerning the geometrical distribution of off-fault damage, can generate observed rupture patterns in seismic catalogs. A model of a representative fault system is proposed, featuring a main fault embedded within a fractured zone where all fractures can slip independently. The length distribution of the off-fault fractures follows a power-law. The study then explores the fracture processes within the system, examining rupture speed from an energetic standpoint and exploring the impact of the damaged zone on the supply or reduction of energy to the process zone, ultimately influencing whether ruptures propagate rapidly or slowly.

The influence of this process is further examined by analyzing the amount of energy radiated away from the fault system. Moment-radiated energy and moment-fracture energy scaling relationships will be presented as mechanical quantities that both slow and fast earthquakes adhere to on a common curve. We will discuss radiation efficiency as a function of rupture speed to illustrate how a fault adjusts its rupture speed according to the energy provided to it and the amount of its breakdown work. The effect of damage on the process zone of the rupture will be discussed to examine how interactions between multiple fractures supply or detract energy to an active process zone, affecting its rupture speed and, consequently, the fast or slow advancement of the front.

How to cite: Kheirdast, N., Bhat, H., Almakari, M., Villafuerte, C., and Thomas, M.: Analyzing Earthquake Energy: Unveiling the Spectrum of Fault Behavior in Terms of Moment, Duration, and Rupture Speed, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18746, https://doi.org/10.5194/egusphere-egu24-18746, 2024.

EGU24-20753 | Posters on site | TS1.6

Using small-magnitude earthquakes to investigate the interplay between seismic and aseismic deformation along the Hellenic Subduction System 

David Essing, Kaan Cökerim, Gian Maria Bocchini, and Rebecca M. Harrington

The Hellenic Subduction System (HSS) in the eastern Mediterranean is the oldest active subduction margin on earth. It is a segmented boundary that hosts the continuum of faulting styles over a ~200km range in depth and can generate large earthquakes with high tsunamigenic potential.  The complexity of deformation styles and rates leave key aspects of the system poorly understood. For example, historical records of Mw<8 earthquakes fail to explain the current observed convergence rate (~35mm/year), and recent geodetic measurements suggest that the degree of locking within the system is heterogeneous. The density of geodetic measurements is increasing rapidly, nevertheless, the inherent time lag required to accumulate data that will enable identifying regions that undergo slower (than seismic) deformation transients will necessitate inferences from seismic signals. In this work, we aim to further close the observational gap between heterogeneous deformation styles and rates using the features of seismicity distributions to infer where deformation rates, and by inference, locking, vary most.   

To that scope, we will present new results of an enhanced earthquake catalog that we will use to explore the spatio-temporal distribution of seismicity features (e.g., b-value, effective stress drop, seismic-moment-release skewness) to infer variability in deformation rates and loading. Catalog enhancement exploits data from the temporary (EGELADOS) broadband seismometer network that operated between 2005 until 2007 combined with permanent stations leading to a station spacing of ~40 km and covering the entire southern Aegean Sea. We first use the combined network to detect earthquakes using machine learning approaches (EQTransformer, PhaseLink) for detection, phase picking and association. After performing initial locations using NonLinLoc combined with a 1D velocity model and quality control procedure, we enhance the number of small-magnitude detections using a multi-station template-matching approach. Next, we scan the enhanced high-resolution catalog for distinct spatial and temporal patterns of seismicity using unsupervised clustering. We then quantify the clustered seismicity using b-value, effective stress drop, and seismic-moment-release skewness (among other parameters). We will present our clustering results in the context of the variability in slip phenomena related to earthquake-earthquake interactions (e.g., static and dynamic triggering) as well as in the context of external forcing (e.g., aseismic triggering or fluid migration).  

The preliminary results that we will present will provide a basis for our more broad-scale study of interplay between seismic and aseismic deformation. In particular, where the latter is gradually becoming increasingly resolvable using GNSS data within the HSS, this work will provide a basis for links with geodetically observed deformation in the future.  

How to cite: Essing, D., Cökerim, K., Bocchini, G. M., and Harrington, R. M.: Using small-magnitude earthquakes to investigate the interplay between seismic and aseismic deformation along the Hellenic Subduction System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20753, https://doi.org/10.5194/egusphere-egu24-20753, 2024.

EGU24-20908 | ECS | Posters on site | TS1.6

Double Direct Shear Experiments as an interacting two fault system:  insights from laboratory seismic cycles on fault interaction  

Giacomo Mastella, Federico Pignalberi, Carolina Giorgetti, and Marco Scuderi

Double direct shear experiments serve as established methods for delving into the physics of laboratory earthquakes. Using a biaxial shearing apparatus with dual fault configurations, these friction experiments simulate real Earth faults' behaviors during loading and failure. 

Despite the presence of distinct layers, double direct shear experiments are commonly perceived as a unified fault system, where the evolution of fault zone properties captured through passive or active seismic imaging can be correlated with the instantaneous stress state affecting both layers uniformly. To further explore the physics of seismic cycles generated in this setup, we perform friction experiments aiming to independently monitor the behavior of each fault layer. In our experiments, we use granular quartz (medium grain size 40 µm) to simulate fault gouge, amd we vary the normal load and shear velocity, allowing us to modify the apparatus's loading stiffness, which relies on the critical fault rheologic stiffness (kc). In the Rate-and-State framework, increasing the normal load results in an  increase of kc, pushing the system towards instability, occurring when k/kc <1, where k is the fault stiffness. Under 50 MPa of  normal loads and 10 µm/s of loading rate, these conditions result in highly non-cyclic seismic cycles marked by significantly variable stress drops and recurrence times. This situation offers an exceptional opportunity to investigate stress partitioning between the two layers and understand their interactions. Experiments are monitored using high-frequency calibrated piezoelectric sensors with a sampling rate of 6 MHz, placed on each of the two forcing blocks. Such a sampling rate allows us to clearly distinguish the time delay between the Acoustic Emissions (AEs) generated from microslip events in different layers. Phase arrivals are detected using retrained, Deep Learning-based algorithms. By associating these phase arrivals using the DBSCAN clustering algorithm, we classify events as occurring on a single gouge layer or on both layers. Subsequently, we analyze the catalog of AEs,, and single seismic waveforms, in terms of general characteristics and frequency content, to look for differences in the physical sources generating them. Unsupervised clustering may help identify classes of AEs linked to specific stages within seismic cycles. By potentially using established supervised Machine Learning technique, it would be possible to verify the relation between AEs variance for each layer and macroscopic apparatus features, like instantaneous friction or time to failure. All of these techniques reveal differences in acoustic energy released before failure for each layer, observations that can be associated to changes in fault physical properties, asperity scale processes and/or  grains sliding or fracturing. In conclusion, our findings demonstrate that double-direct shear experiments can emulate a system of interacting double faults. In such a context, the continuous monitoring of AEs can provide insights into the stress partitioning between the two layers, a process that may guide the nucleation of major slip events as well as the long term behavior of the system. Additionally, our analysis may be helpful to investigate processes like fault interactions, faults synchronization, static, and dynamic stress triggering.

How to cite: Mastella, G., Pignalberi, F., Giorgetti, C., and Scuderi, M.: Double Direct Shear Experiments as an interacting two fault system:  insights from laboratory seismic cycles on fault interaction , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20908, https://doi.org/10.5194/egusphere-egu24-20908, 2024.

The faceting behaviour of olivine controls many properties on the grain surface such as diffusion and storage.  This behaviour and its effects are poorly understood due to the difficulty of examining them and the many controls that are on this paper.  In this talk I shall present a thermodynamic model of olivine faceting and how it is controlled by temperature, pressure, iron, grain size and water content.  In turn I shall discuss how this faceting then controls other important properties such as storage of water on the grain boundaries and how these are perhaps an overlooked sink in the Earth’s mantle.

How to cite: Muir, J.: Olivine faceting and water storage: A complex dynamic anisotropic sink, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2395, https://doi.org/10.5194/egusphere-egu24-2395, 2024.

A connected set of singularity points is called the singularity line. Along this line, the slowness surfaces (or phase velocity surfaces) of different wave modes coincide. For anisotropic models, the singularity lines are mostly known in transversely isotropic media (Crampin and Yedlin, 1981). Recently, it was shown that they also can be defined in the special types of orthorhombic media: degenerate (Stovas et al, 2023b) and pathological (Stovas et al, 2023a). Singularity line can also exist in the low symmetry anisotropic models, monoclinic and triclinic (Khatkevich, 1963; Vavrycuk, 2005; Roganov et al, 2019).

In this paper, we focus on singularity lines in monoclinic media with a horizontal symmetry plane. We define the singularity lines in all coordinate planes, and in vertical planes of arbitrary azimuthal orientation. Since the monoclinic anisotropic model can be considered as the transversely isotropic medium with a vertical symmetry axis being perturbed with the multiple azimuthally non-invariant fracture sets, identification of singularity lines can give additional constraints in inversion of seismic data for fracture prediction. The singularity lines being converted into the group velocity domain results in continuous bands in the group velocity surface (traveltime surface) shaping the lacunas for S1 wave and internal refraction cones for S2 wave associated with strong anomalies in wave amplitudes.

The singularity directions satisfy the following polynomial equations (Alshits, 2004; Roganov et al., 2019), , where  are the third-order polynomials given by the elements of the Christoffel matrix. Resolving this system of equations, we define the conditions (in terms of stiffness coefficients) for existence of singularity lines in vertical planes. The Sylvester criterion is applied to control the physical realizable model. Mostly, the obtained models have singularity lines formed by S1 and S2 waves, while one model has singularity line composed of S1S2 and PS1 legs connected by the triple PS1S2 singularity point.

 

 

References

Alshits, V.I., 2004, On the role of anisotropy in crystalloacoustics, In: Goldstein R.V., Maugin G.A. (eds) Surface Waves in Anisotropic and Laminated Bodies and Defects Detection. NATO Science Series II: Mathematics, Physics and Chemistry, vol 163. Springer, Dordrecht.

Crampin, S., and M. Yedlin, 1981, Shear-wave singularities of wave propagation in anisotropic media, J. Geophys., 49, 43–46.

Khatkevich, A.G., 1963 Acoustic axes in crystals, Sov. Phys. Crystallogr. 7, 601–604.

Stovas, A., Roganov, Yu., and V. Roganov, 2023a, On pathological orthorhombic models, Geophysical Prospecting, 71(8), 1523- 1539.                                                                    

Stovas, A., Roganov, Yu., and V. Roganov, 2023b, Degenerate orthorhombic models, Geophysical Journal International, accepted for publication.                  Roganov, Yu., Stovas, A., and V. Roganov, 2019, Properties of acoustic axes in triclinic media, Geophysical Journal, 41(3), 3-17.                                                    Vavrycuk, V., 2005, Acoustic axes in triclinic anisotropy, The Journal of the Acoustical Society of America 118, 647-653.

How to cite: Stovas, A.: Singularity lines for monoclinic media with a horizontal symmetry plane, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2468, https://doi.org/10.5194/egusphere-egu24-2468, 2024.

How continental plate boundary faults develop with depth has been under debate. We inverted SKS shear wave splitting data along the San Andreas Fault (SAF) into two layers of anisotropy using a Bayesian inversion. While the two layers are statistically required, the fast polarization directions of the upper layer do not match the strike of the SAF as previously reported. To capture the lithospheric shear zone, we progressively decrease the upper limit of the delay time of the upper layer. In northern California where SAF strikes 140-150, the upper layer fast directions get close to these azimuths when the delay time is reduced to ~0.5 s. In southern California where the SAF strikes 120-130, the upper layer fast directions capture the SAF with delay times of a similar magnitude. For olivine LPO with vertical shear plane, these delay times translate to a anisotropy layer of 40 km thickness, or a depth of 70 km from the surface, assuming the seismogenic zone in the crust is too localized to influence the SKS splitting. This depth coincides with the depth of lithosphere-asthenosphere boundary independently estimated. The lower-layer fast directions are in between the absolute plate motion directions of the American and the Pacific plates, or at least agree with that predicted from surface wave study in northern California. We picture a vertical continental shear zone widening to at least 200 km at the bottom of the lithosphere, transitioning to a horizontal shear regime in the asthenosphere driven by plate motions. This architecture of continental shear zone is consistent with our understanding of the rheology of crust and mantle.

How to cite: Kuo, B.-Y., Peng, C.-C., and Wang, P.-C.: Structures of the continental shear zone beneath the San Andreas Fault inferred from two-layer modeling of SKS splitting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3339, https://doi.org/10.5194/egusphere-egu24-3339, 2024.

The seismic moment tensor, which represents the equivalent body-force system of the seismic source (Backus and Mulcahy, 1973), may exhibit non-double couple components (NDCs) when the earthquake occurs on a planer fault if the source medium is anisotropic (Aki and Richards, 1981; Kawasaki and Tanimoto, 1981). Kawakatsu (1991, GRL) reported that the NDCs of the moment tensors for shallow earthquakes from the Harvard CMT catalog (Dziewonski et al.,1981; predecessor of GCMT) exhibit a systematic characteristic dependent on faulting types. Specifically, the sign of NDC on average systematically switches between normal-faulting and reverse-faulting. The average NDC parameter ε (Giardini, 1983) is negative for thrust faulting and positive for normal faulting. This behavior can be explained if the source region is transversely isotropic with a vertical symmetry axis (radially anisotropic). In fact, the transverse isotropy model of PREM at a depth of 24.4 km predicts the observed systematic NDC pattern, although the magnitude is slightly underestimated, indicating the potential to enhance our understanding of the lithospheric transverse isotropy using the NDC of the moment tensors.

To investigate the lithospheric transverse isotropy structure utilizing the NDCs of the moment tensors, we propose a novel inversion scheme, building upon the approaches employed by Vavrycuk (2004) and Li, Zheng, et al. (2018) for deep and intermediate-depth earthquakes, but with necessary modifications to address shallow sources (Kawakatsu, 1996, GJI). Synthetic tests conducted under conditions of random faulting indicate the potential to constrain the S-wave anisotropy (ξ) and the fifth parameter (ηκ; Kawakatsu, 2016, GJI). However, in realistic scenarios where a predominant stress regime influences earthquake occurrence to limit the diversity of faulting types, a significant correlation between these two parameters is anticipated, especially in regional-scale cases. Preliminary application of this method to real data sourced from the GCMT catalog suggests that the lithospheric transverse isotropy of PREM serves as a suitable initial model. However, some adjustments may be necessary, particularly regarding the fifth parameter, to enhance the model's fidelity in representing observed NDCs of the moment tensors.

How to cite: Kawakatsu, H.: Characterizing Lithospheric Transverse Isotropy via Non-double Couple Components of Moment Tensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3697, https://doi.org/10.5194/egusphere-egu24-3697, 2024.

The continental lithosphere of the Iranian plateau is complicated by a multitude of tectonic processes resulting from the convergence between the Arabian and Eurasian plates. In order to investigate the deformation mechanisms of the uppermost mantle, this study presents a radial anisotropy model beneath the Iranian Plateau constructed by long period (10-100 s) Rayleigh and Love waves from ambient noise data. The broadband Rayleigh and Love signals are extracted from continuous data recorded by 88 seismic stations using a double-beamforming algorithm. Due to utilizing long period surface waves, we apply finite-frequency ambient noise tomography to generate two-dimensional dispersion maps. These phase velocity maps are consistent with those obtained from conventional methods. Finally, we invert Rayleigh and Love local phase velocity dispersion curves using a Bayesian Markov chain Monte Carlo inversion method. The obtained radial anisotropy model shows negative values in Central Iran suggesting a horizontal character of the minerals likely due to a channelized asthenospheric flow in the upper mantle.

How to cite: Movaghari, R. and Yang, Y.: Uppermost mantle radial anisotropy based on double-beamforming of ambient noise cross correlation beneath Iranian plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3769, https://doi.org/10.5194/egusphere-egu24-3769, 2024.

Complex tectonics and significant crustal anisotropy are observed at the intersection of the Red River Fault (RRF) and the Xiaojiang Fault (XJF) in the southern Sichuan-Yunnan block, in the SE Tibetan Plateau. The fast S polarization of upper crustal anisotropy varies from NW-SE in the west to NE-SW in the east near the Yimen region. However, small-scale anisotropic structures remain challenging due to limited measurements. Using two years of seismic data from the temporary linear HX Array and permanent stations, this study employed machine learning to construct a high-precision earthquake catalog for S-wave splitting, revealing the upper crustal anisotropy. The new catalog has nearly twice as many earthquakes as the China Earthquake Networks Center. The seismicity is concentrated in the Yimen region with various strike-slip faults, which has a strong correlation with high- and low-velocity boundaries, especially near the edge of the low-velocity zone. Spatial variations in upper crustal anisotropy along the HX Array correspond to geological structures and regional stress. Despite a dominant NE-SW PFS (i.e., fast S-wave polarization) in the Yimen region, stations show dual dominant directions with high values of DTS (i.e., delay times between split S-waves), indicating intricate tectonic and stress interactions. The middle segment of the RRF shows significantly lower DTS values than either side, along with a vertically distributed earthquake swarm, possibly indicating locked structures with high seismic hazard. A comparison between the upper and whole crustal anisotropy reveals consistent deformation within blocks and nearly orthogonal deformation near the RRF and the XJF. The boundary faults likely play a crucial role in influencing the crustal anisotropy both horizontally and vertically. The faults like the Shiping-Jianshui and the Puduhe, running parallel to the RRF and the XJF, are believed to affect the crustal structure. This study highlights that microseismic detection enhances earthquake catalog completeness, providing insights into detailed structures [supported by NSFC Projects 42074065 & 41730212].

How to cite: Li, Y., Gao, Y., and Tian, J.: Microseismic records based on machine-learning reveal the crustal anisotropy beneath the southern Sichuan-Yunnan block in the SE Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4528, https://doi.org/10.5194/egusphere-egu24-4528, 2024.

EGU24-7126 | ECS | Posters on site | GD7.1

Seismic anisotropy of the crust and upper mantle beneath eastern Pamir 

Changhui Ju, Junmeng Zhao, Qiang Xu, and Guohui Li

The East Pamir seismic experiment (8H) was conducted in the eastern Pamir and the adjacent Tarim Basin from August 2015 to May 2017. Utilizing seismograms from the 8H network and nine permanent seismic stations operated by the China Earthquake Administration, we computed shear wave splitting parameters through cluster analysis of the minimum energy method. A total of 452 high-quality individual SKS-splitting measurements were obtained at 39 seismic stations. Given the predominant availability of events with a back-azimuth (BAZ) around ~110° and the absence of a broad range of BAZ values, we opted for a single-layer anisotropic model to interpret the measurements.

The upper mantle seismic anisotropy structure in the Western Himalayan Syntaxis (WHS) exhibits distinctive regional characteristics in various regions. Group A comprises 15 stations situated near the Alai Valley and the Tien Shan with a northeast-oriented Fast Polarization Direction (FPD), aligned with the strike of the orogen and the Absolute Plate Motion (APM) azimuthal direction (~80°) of the Eurasian plate. This group exhibits relatively larger Delay Time (DT) and may be originated from the oriented arrangement of olivine crystals in the mantle lithosphere of the Eurasian continent during the northward subduction of the Indian continent. Group B consists of 21 stations located in the eastern Pamir and adjoining Tarim Basin, demonstrating a curved orientation. While this orientation contradicts the APM direction, it approximately parallels the trend of large-scale surface structures. Combining these observations with previous imaging results, we propose that during the northward advancement of the Indian continent, mantle material flow (escape) in the Pamir-Hindu Kush region formed seismic anisotropy structures similar to those in the Western Himalayan Syntaxis (WHS).

How to cite: Ju, C., Zhao, J., Xu, Q., and Li, G.: Seismic anisotropy of the crust and upper mantle beneath eastern Pamir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7126, https://doi.org/10.5194/egusphere-egu24-7126, 2024.

EGU24-8306 | ECS | Posters on site | GD7.1

Modulation of crustal and mantle flow systems by a heterogeneous cratonic root: Evidence from seismic azimuthal anisotropy analysis 

Lin Liu, Stephen Gao, Kelly Liu, Sanzhong Li, and Youqiang Yu

In contrast to many prior studies that relied on station-averaged shear-wave splitting (SWS) measurements and sparsely distributed stations, this study takes advantage of the recent deployment of broadband seismic stations at intervals of less than 50 km to explore the intricate seismic azimuthal anisotropy between the dynamic Tibetan Plateau and the stable North China Craton. Our analysis encompasses 6,409 high-quality individual SWS measurements from 465 closely spaced stations located along the boundary of the northeastern Tibetan Plateau and the western North China Craton. Notably, twenty of these stations show splitting parameters with a π/2 periodicity based on azimuthal variations, indicating a complex double-layer horizontal anisotropy structure. The anisotropy of the upper layer is linked to ductile flow in the middle-to-lower crust originating from the Tibetan Plateau. This flow encounters the rigid lithosphere of the Alxa Block, leading to a bifurcation into northeastward and southeastward directions. The anisotropy in the lower layer, exhibiting fast orientations in an NW-SE direction, is consistent with the observed one-layered anisotropy and aligns with the absolute plate motion (APM) of the Eurasian plate. The coherence in the spatial distribution of splitting parameters indicates that the predominant source of observed anisotropy is asthenospheric flow. This mantle flow exhibits a southeastward orientation beneath the Alxa block, transitioning to an almost eastward direction along the thinner lithospheric passage between the Ordos and Sichuan cratonic keels. This pattern unveils the influence of cratonic edges in modulating localized mantle flow systems.

How to cite: Liu, L., Gao, S., Liu, K., Li, S., and Yu, Y.: Modulation of crustal and mantle flow systems by a heterogeneous cratonic root: Evidence from seismic azimuthal anisotropy analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8306, https://doi.org/10.5194/egusphere-egu24-8306, 2024.

EGU24-8694 | Orals | GD7.1

A new method to measure seismic anisotropy of the upper mantle directly from the width and orientation of the particle motion of shear waves  

Luděk Vecsey, Jaroslava Plomerová, and AlpArray, AlpArray-EASI, PACASE Working Groups and AdriaArray Seismology Group

Splitting of shear waves proves their propagation within an anisotropic medium. Frequently used methods of evaluating of upper mantle anisotropy search for two parameters - the delay time of the slow split shear wave and the polarization direction of the fast split shear wave. The parameters retrieved by the standard methods such as energy minimization on the transverse component of the shear waveforms or eigenvalue of cross-correlation matrix suffer from e.g., ubiquitous noise, errors in sensor orientation and numerous so-called ‘null splits’ or unrealistically large values. However, well-resolved splitting parameters from core-mantle refracted shear SK(K)S phases are limited to relatively narrow fans of back azimuths. Such incomplete back-azimuth coverage prevents modelling anisotropic structures with symmetry axes oriented generally in 3D, i.e., with tilted axes, to be compatible with 3D anisotropic models from independent observables.  Generally used averages of time delays and polarization pairs lead to simplified models of the upper mantle, which concentrate on modelling the present-day flow in the sub-lithospheric mantle.

Therefore, we propose a new method directly exploiting variations in width and orientation of particle motion (PM) of split shear waves, which allows measuring anisotropic characteristics for a larger amount of waveforms and improves azimuthal coverage in a region. We characterize the PM by two parameters, the PM width and the PM orientation. At each station, we plot the normalized width of the PM as a ratio of lengths of the minor to major axes in dependence on back-azimuths. Variations of the PM width with back-azimuth exhibit oscillations with several extremes of different amplitudes. Such behaviour results from wave propagation through the anisotropic upper mantle. One of the advantages of the method is that the width of the PM is invariant of potential mis-orientation of sensors.

We test the PM method on a set of SKS waveforms recorded at a subset of stations included in several recent or running passive seismic experiments (EASI, AlpArray, PACASE, AdriaArray). The stations form a band of about 200km broad running from the western Bohemian Massif through the Eastern Alps to the Adriatic Sea. Stations characterized by similar variations of the PM parameters group into sub-regions, which are compatible with the main tectonic features of the whole region. The formation of such lithospheric blocks of similar anisotropic signals is in agreement with 3D self-compatible anisotropic models of the mantle lithosphere domains derived from independent observables. We present complementary studies of the anisotropic structure of the mantle lithosphere in contributions by Zlebcikova et al. (GD7.1, EGU 2024), which shows anisotropic model of the upper mantle derived from 3D coupled anisotropic-isotropic teleseismic tomography (code anitomo), and in contribution by Kvapil et al. (GD7.1, EGU 2024), in which anisotropic structure of the lower crust is modelled from ambient noise.

How to cite: Vecsey, L., Plomerová, J., and Working Groups and AdriaArray Seismology Group, A. A.-E. P.: A new method to measure seismic anisotropy of the upper mantle directly from the width and orientation of the particle motion of shear waves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8694, https://doi.org/10.5194/egusphere-egu24-8694, 2024.

EGU24-8851 | Orals | GD7.1

Constraining D" seismic anisotropy with reflections and splitting 

Christine Thomas and Angelo Pisconti

Detection of D" anisotropy is usually carried-out with shear wave splitting analysis. To constrain azimuthal anisotropy and infer mineralogy and deformation style, a number of crossing paths is necessary. Here we use an approach that utilises the polarity of P- and S- wave reflections from the D" discontinuity, compared with the main phases P and S, and combines these measurements with ScS splitting results. Using deformation scenarios for a number of lower(most) mantle candidate materials, we calculate the reflection coefficient for P and S-wave reflections and ScS splitting predictions. From our modelling, a clear distinction between different anisotropic media is possible by using both types of observations together. Furthermore, the approach allows to use only a single direction to distinguish between different scenarios. We apply the method to the Central/South Atlantic and South Africa, across the border of the large-low seismic velocity province (LLSVP). Shear wave splitting observations suggest that anisotropy is present in this region of the mantle, in agreement with previous studies that partially sampled this region. Modelling the observations with lattice preferred orientation and shape preferred orientation of materials expected in the D" region, we find two domains of mineralogy and deformation: sub-horizontally aligned post-perovskite outside the LLSVP, beneath the South and Central Atlantic, which is replaced by up-tilted aligned bridgmanite within the LLSVP beneath South Africa.

How to cite: Thomas, C. and Pisconti, A.: Constraining D" seismic anisotropy with reflections and splitting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8851, https://doi.org/10.5194/egusphere-egu24-8851, 2024.

EGU24-8905 | Posters on site | GD7.1

Anisotropic structure of the central European lower crust from ambient noise inversion 

Jiří Kvapil, Jaroslava Plomerová, and AlpArray, AlpArray-EASI, PACASE Working Groups and AdriaArray Seismology Group

Previous research of the Bohemian Massif (BM) crust with the use of ambient noise tomography (ANT) indicates a transversely isotropic structure of the lower crust (Kvapil et al. 2021). In this study, we have developed a new approach for evaluations of localised seismic anisotropy by travel time integration method.

The method calculates synthetic Rayleigh (vertical ZZ correlation) and Love (transverse TT correlation) velocities and derives the vSH/vSV from the initial 3D isotropic vSV model. The higher ratio of measured vSH/vSV to synthetic vSH/vSV indicates the existence of velocity anisotropy in the lower crust of the BM in the reference ANT model (Kvapil et al., 2021). The new method evaluates azimuthal variations of the synthetic parameters due to heterogeneities reflecting local geology effects and corrects the observed velocity ratios. Then the 1D stochastic joint (ZZ, TT) inversion is applied to retrieve the depth dependence of the velocity ratio. We use cross-correlation of ambient noise and earthquake data from seismic stations included in the AlpArray, PACASE, and Adria Array passive seismic experiments and data from the PASSEQ experiment, which complement the sparse coverage in the northern part of the BM.

Seismic anisotropy records the stress/strain conditions of each originally independent tectonic microplates during the formation of the BM crust. We demonstrate that synthetic modelling over the reference isotropic velocity model is an efficient tool for extracting radial and azimuthal shear velocity anisotropy in the lower crust directly from Rayleigh and Love wave dispersion curves. Regions with consistent parameters of seismic anisotropy correlate well with the major tectonic units of the BM. We show that variations in azimuthal and radial anisotropy of the lower crust on a regional scale can provide constraints for the reconstruction of geodynamic processes during the formation of the BM. We present complementary studies of the anisotropic structure of the mantle lithosphere in contributions by Zlebcikova et al. (GD7.1, EGU 2024), which shows an anisotropic model of the upper mantle derived from a 3D coupled anisotropic-isotropic teleseismic tomography (code anitomo), and in contributions by Vecsey et al. (GD7.1, EGU 2024), suggesting a new method for evaluation of anisotropy from shear waves.

How to cite: Kvapil, J., Plomerová, J., and Working Groups and AdriaArray Seismology Group, A. A.-E. P.: Anisotropic structure of the central European lower crust from ambient noise inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8905, https://doi.org/10.5194/egusphere-egu24-8905, 2024.

EGU24-8928 | Posters on site | GD7.1

Anisotropic tomography of the upper mantle beneath the Eastern Alps and the Bohemian Massif 

Helena Žlebčíková, Jaroslava Plomerová, Luděk Vecsey, and AlpArray Working Groups

Teleseismic body waves recorded during passive seismic experiments allow us to investigate isotropic velocities of the Earth’s upper mantle in a great detail, on scales of tens of kilometres. However, most of the tomography studies neglect the body-wave anisotropy completely or limit it either to azimuthal or radial anisotropy. We have developed a code called AniTomo for coupled anisotropic-isotropic travel-time tomography of the upper mantle (Munzarová et al., Geophys. J. Int. 2018) which allows for inversion of relative travel-time residuals of teleseismic P waves simultaneously for 3D distribution of P-wave isotropic-velocity perturbations and anisotropy of the upper mantle. We assume weak anisotropy of hexagonal symmetry with either ‘high-velocity’ axis a (lineation) and low velocity (b,c) plane or ‘low-velocity’ axis b and high velocity plane (a,c) (foliation) that is oriented generally in 3D. Such an approach of searching for orientation of the symmetry axes freely in any direction is unique and more general in comparison with the published methods that usually assume only horizontal or vertical orientation of the high-velocity symmetry axis. The code represents a step further from modelling homogeneously anisotropic blocks of the mantle lithosphere (e.g., Vecsey et al., Tectonophysics 2007; Plomerová et al., Solid Earth 2011) towards modelling anisotropy arbitrarily varying in 3D. We present complementary studies of anisotropic structure of the mantle lithosphere in contributions by Vecsey et al. (GD7.1, EGU 2024), suggesting a new method for evaluation of anisotropy from shear waves and in contribution by Kvapil et al. (GD7.1, EGU 2024), in which anisotropic structure of the lower crust is modelled from ambient noise. 

We have applied the AniTomo code on P-wave travel time deviations recorded during passive seismic experiments AlpArray-EASI (2014-2015) and AlpArray Seismic Network (2016-2019) to image the upper mantle large-scale anisotropy beneath the western part of the Bohemian Massif and the Eastern Alps. We interpret the P-wave tomography results along with results of splitting parameters from core-mantle refracted shear waves at 240 broad-band stations in about 200 km broad and 540 km long band along 13.3° E longitude. The code allows to control the depth variations and an extent of the fabric. The joint inversion/interpretation allows for distinguishing which type of the models (a-axes model or b-axis model) approximates better the anisotropic structure.

The derived anisotropic-velocity models of the mantle lithosphere cluster into domains with boundaries coinciding with boundaries of the main tectonic sub-regions. These domains are compatible with domains inferred from a joint interpretation of directional variations of P-wave travel-time residuals and SKS-wave splitting parameters. The coincidence of boundaries of the anisotropic models of the mantle lithosphere domains with main tectonic features, correlation of the anisotropy depth extent with the LAB models as well as a decrease of anisotropy strength in the sub-lithospheric mantle support fossil origin of the directionally varying component of the detected anisotropic fabrics of the continental mantle lithosphere.

How to cite: Žlebčíková, H., Plomerová, J., Vecsey, L., and Working Groups, A.: Anisotropic tomography of the upper mantle beneath the Eastern Alps and the Bohemian Massif, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8928, https://doi.org/10.5194/egusphere-egu24-8928, 2024.

EGU24-9012 | ECS | Posters on site | GD7.1

Seismic Anisotropy in Northwest Himalaya from core refracted shear (SKS) and direct S waves  

Rupak Banerjee, Frederik Tilmann, Supriyo Mitra, Tuna Eken, Keith Priestley, and Sunil Wanchoo

Recent enhancement in instrumentation in the northwest (NW) Himalaya provides an unprecedented dataset to study the deformation due to the Indo-Eurasia convergence. The NW Himalaya is unique in terms of hosting a seismic gap and a flat-ramp geometry at its decollement. We determine azimuthal  seismic anisotropy using core refracted shear waves (SKS) and interpret the results to develop insight about the prevailing geodynamics. Here, 459 raypaths with moment magnitude (Mw) >= 5.5, recorded at 15 seismographs of the J&K Seismological NETwork (JAKSNET), operational between 2013 and 2022, are used. To avoid contamination from direct S and SKiKS phases, we analyze the data within the epicentral distance range of 90°-125°, filtered at 0.04-0.2 Hz. We perform a 2-D grid search over the splitting parameters (delay time and fast axis azimuth) and compute their optimum values, for which the energy of the transverse component is minimum (MTE) after correcting for the inferred splitting. Simultaneously, the Rotation Correlation (RC) method is employed to calculate the delay time and fast axis azimuth corresponding to the maximum correlation coefficient between the splitting-corrected horizontal components. We use selection criteria based on the quality factor and the signal-to-noise ratio (SNR) to determine the measurements to be used for station averaging. The quality factor depends on the similarity of results obtained from the RC and MTE methods, hence helps in avoiding subjective interpretation about the quality of the measurement. The non-null splitting measurements passing these selection criteria are then used for station averaging applying the circular mean method and the energy map stacking method. We observe mostly N-S to NE-SW trending fast axes azimuths (13 of 15 stations); this direction corresponds to the absolute plate motion of India in a no-net rotation frame. The two remaining stations show average NW-SE fast directions, which are parallel to the mountain front, but also these stations show somewhat contradictory single splitting measurements, and one of those two anomalous stations is located very close to stations with NE-SW fast measurements, so we will not interpret these. The mean delay times range from 1.5-3.3 s, with the majority of the stations exhibiting > 2s split time being situated on the foreland basin deposits of the Sub-Himalaya. The high absolute Indian plate motion of 51 mm/yr appears to align the upper mantle olivine beneath the orogeny and NE oriented fast axes track the mantle flow manifested by the basal shear of the plate motion. To complement the SKS data, which are dominated by results with eastern backazimuths and corresponding initial polarisation, we further measured splitting for direct S-wave with the reference station method. Here, the correlation between the horizontal traces of the target and reference stations is maximised after correcting the target trace with trial splitting parameters and differences in gain; the reference station trace has previously been corrected for SKS splitting. We will present direct S splitting measurements from 370 events with Mw>=5.5 and distance within 40°-80° with an interstation spacing of <120 km.

How to cite: Banerjee, R., Tilmann, F., Mitra, S., Eken, T., Priestley, K., and Wanchoo, S.: Seismic Anisotropy in Northwest Himalaya from core refracted shear (SKS) and direct S waves , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9012, https://doi.org/10.5194/egusphere-egu24-9012, 2024.

EGU24-12689 | Orals | GD7.1

Full waveform anisotropic tomography of the transition zone beneath the south west Pacific 

Dorian Soergel, Utpal Kumar, Nicolas Valencia, and Barbara Romanowicz

The presence of ponding slabs at the base of the mantle transition zone (600-700 km) has been well known for a long time and can be explained by the changes in material properties related to phase changes around this depth. However, recent tomographic studies have shown the presence of slabs stagnating at larger depths of around 1000 km. While geodynamic simulations and experiments provide different insights, seismic tomography is crucial to constrain these geodynamic models. More specifically, seismic anisotropy is of particular interest to understand the dynamics of the mantle because of its sensitivity to the flow of mantle material.

The south-west pacific zone is an area with a very complex tectonic setting, with several subduction zones in a relatively small area, illuminated by a very high level of seismicity. It is thus of particular interest to understand the dynamics of the extended transition zone. As such, it has been the object of numerous tomographic studies, including high-resolution full-waveform tomography. In most cases, these studies only invert for radial anisotropy, as azimuthal anisotropy is generally more difficult to measure. However, azimuthal anisotropy is equally important as radial anisotropy and a proper interpretation in terms of mantle flow requires both. We present updated results of a full-waveform inversion of the region including azimuthal anisotropy recovered from body and surface waveforms and XKS-splitting data.

How to cite: Soergel, D., Kumar, U., Valencia, N., and Romanowicz, B.: Full waveform anisotropic tomography of the transition zone beneath the south west Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12689, https://doi.org/10.5194/egusphere-egu24-12689, 2024.

EGU24-12788 | ECS | Posters on site | GD7.1

P-wave anisotropic tomography unveils the crustal structure of Etna volcano (Italy) 

Rosalia Lo Bue, Francesco Rappisi, Marco Firetto Carlino, Elisabetta Giampiccolo, Ornella Cocina, Brandon Vanderbeek, and Manuele Faccenda

Mount Etna (Italy), renowned for its persistent eruptive activity, is a hazardous volcano shaped by the intricate interplay between magma uprising and a complex tectonic and geodynamic context. Despite extensive monitoring, seismic tomography encounters challenges in accurately depicting the shallow-intermediate P-wave velocity structures, primarily due to the common assumption of isotropy. This study discards such simplification, employing a novel methodology (Vanderbeek and Faccenda, 2021) to simultaneously invert for perturbations to P-wave isotropic velocity and three additional anisotropic parameters (i.e., magnitude of hexagonal anisotropy, azimuth, and dip of the symmetry axis).

By analysing the seismicity recorded in the Mt. Etna area from 2006 to 2016, we constructed 3D anisotropic P-wave tomography models to better constrain the crustal structure of Etna volcano within the framework of its local tectonic setting. The revealed anisotropy patterns are consistent with the structural trends of Etna, unveiling the depth extent of fault segments. We identify a high-velocity volume, deepening towards northwest, recognized as the collision-related subducting foreland units (i.e. Hyblean foreland carbonate slab; Firetto Carlino et al., 2022) that appear to confine a low velocity anomaly, hypothesized to be the expression of a deep magmatic reservoir. A likely tectonic-origin discontinuity affects the subducting units, facilitating the transfer of magma from depth to the surface. This geological setting may explain the presence of such a very active basaltic strato-volcano within an atypical collisional geodynamic context. 

This research improves our understanding of the dynamics governing magma and fluid ascent beneath the volcanic edifice and emphasises the importance of considering anisotropy in seismic investigations. It contributes to our framework for understanding volcanic processes and mitigating associated risks.

 

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.

Firetto Carlino, M., Scarfì, L., Cannavò, F., Barberi, G., Patanè, D., & Coltelli, M. (2022). Frequency-magnitude distribution of earthquakes at Etna volcano unravels critical stress changes along magma pathways. Communications Earth & Environment, 3(1), 68.

How to cite: Lo Bue, R., Rappisi, F., Firetto Carlino, M., Giampiccolo, E., Cocina, O., Vanderbeek, B., and Faccenda, M.: P-wave anisotropic tomography unveils the crustal structure of Etna volcano (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12788, https://doi.org/10.5194/egusphere-egu24-12788, 2024.

EGU24-13005 | Orals | GD7.1

Azimuthal and radial anisotropy in the upper mantle from global adjoint tomography 

Ebru Bozdag, Ridvan Orsvuran, Lijun Liu, and Daniel Peter

Earth’s upper mantle and lithosphere show significant evidence for anisotropy related to deformation and composition. First-generation GLAD (GLobal ADjoint) models (GLAD-M15 (Bozdag et al. 2016), GLAD-M25 (Lei et al. 2020), GLAD-M35 (Cui et al. submitted)) are radially anisotropic in the upper mantle. Starting from GLAD-M25, we performed 25 conjugate gradient iterations and constructed model GLAD-M50-AZI by including azimuthal anisotropy in the parameterization of the inverse problem. We inverted azimuthally anisotropic normalized parameters Gc’ and Gs’ simultaneously with vertically and horizontally polarized shear waves beta_v and beta_h, respectively. Due to our parameterization, our data set consists of only minor- and major-arc Rayleigh and Love waves from 300 globally distributed earthquakes. GLAD-M50-AZI captures plate motions globally well, which are also supported by the transverse isotropy, specifically at the subducted slabs and mid-ocean ridges. Furthermore, it approaches continental-scale resolution in regions with good data coverage depicting smaller-scale tectonic and flow patterns, giving us a chance to have a more detailed and unified view of the anisotropy globally. In the next step, we explore how anisotropy derived from seismic tomography compares to geodynamical modeling observations to have better insight into mantle dynamics. We perform numerical simulations to compute synthetic seismograms and full-waveform inversion on Texas Advanced Computing Center’s Frontera system. 

How to cite: Bozdag, E., Orsvuran, R., Liu, L., and Peter, D.: Azimuthal and radial anisotropy in the upper mantle from global adjoint tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13005, https://doi.org/10.5194/egusphere-egu24-13005, 2024.

EGU24-13585 | ECS | Orals | GD7.1

Exploring the Development of Shear Wave Radial Anisotropy in the Lower Mantle due to Slab-induced Plume Generation from LLSVPs 

Poulami Roy, Bernhard Steinberger, Manuele Faccenda, and Juliane Dannberg

Seismic anisotropy, which involves directionally dependent wave propagation, is likely to occur in the lowermost few hundreds km of the mantle, especially at the edges of Large Low Shear Velocity Provinces (LLSVPs). This anisotropy may be indicative of significant deformation, potentially due to mantle flow interacting with the sides of these provinces or the generation of mantle plumes. In this study, we investigate subducted slab induced plume generation from an LLSVP boundary and the flow behaviour of the lower mantle using compressible 2-D and 3-D mantle convection models in the geodynamic modeling software ASPECT combined with mantle fabric simulation in ECOMAN. In our geodynamic simulation, we assume that the LLSVPs are chemically distinct piles with intrinsically high viscosity. We use the Clapeyron slope of the phase transition from Bridgmanite to post-Perovskite from the previous mineralogical study by Oganov & Ono (2004) in the mantle fabric calculation. Modeling lattice preferred orientation of Bridgmanite and post-Perovskite in the lower mantle reveals that the lower mantle is overall isotropic except the regions of plume conduits and the surroundings of the subducted slab where vertically polarized shear wave (Vsv ) is faster. The generation of anisotropy are caused by the accumulation of high finite strain in these regions. The bottom 300 km of the lower mantle is characterized by fast horizontally polarized shear wave (Vsh ) beneath the subducted slab which deflects to fast Vsv at the margins of the LLSVPs due to the rheological contrast between the highly viscous LLSVP and less viscous ambient mantle. Our result shows that six possible slip systems [100](010), [100](001), [010](100), [001](100), [110](-110) and [-110](110) of Bridgmanite and the slip system [100](001) of post-Perovskite can produce a fast Vsv in the plume generation zones where post-Perovskite transforms to Bridgmanite and fast Vsh at the base of the subducted slab where post-Perovskite is preserved in the D”. However, our models do not show anisotropy inside of the LLSVPs and the subducted slab, possibly because of their high viscosity. Our findings are comparable with the previous seismic observations beneath the Iceland plume where Vsv > Vsh and the slab-driven flow at the base of the mantle beneath the northeastern Pacific Ocean where Vsh > Vsv .

How to cite: Roy, P., Steinberger, B., Faccenda, M., and Dannberg, J.: Exploring the Development of Shear Wave Radial Anisotropy in the Lower Mantle due to Slab-induced Plume Generation from LLSVPs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13585, https://doi.org/10.5194/egusphere-egu24-13585, 2024.

EGU24-14416 | Orals | GD7.1

Examining Depth Origin of Anisotropy in an Active Orogenic Belt of Taiwan Using Shear Wave Splitting Results from the Formosa Array. 

Ratna Mani Gupta, Hsin-Hua Huang, Po-Fei Chen, Cheng-Horng Lin, and Cheng-Chien Peng

The Taiwan orogenic belt originates from the collision between the Philippine Sea Plate (PSP) and the Eurasian Plate (EU) with a subduction polarity reversal. The reversal around northern Taiwan creates a complex geodynamic process from subduction waning to post-collision extension. We study the deformation fabric with the shear wave splitting (SWS) method to unravel this tectonic complexity using multiple core phases (PKS, SKS, and SKKS, hereafter XKS). Prevailing SWS research acknowledged the presence of orogen-parallel anisotropy. However, recent studies with numerical modeling and coherency analysis suggested that the anisotropy source is in the asthenosphere. A recent dense seismic array (Formosa Array) of 148 seismic stations in northern Taiwan enables us to revisit this debate with improved spatial and back azimuthal coverage of the SWS measurements. The results show distinct variations in fast direction (Φ) from different back-azimuths and a much larger average delay time (dt) of ~2 sec compared to that derived from local subduction events (at 100-250 km depth). Application of the Fresnel zone and spatial coherency analysis also support an asthenospheric source for the observed anisotropy. The findings emphasize the need for depth-source analysis of anisotropy to better elucidate the responsible mechanisms of complex tectonic settings.

How to cite: Gupta, R. M., Huang, H.-H., Chen, P.-F., Lin, C.-H., and Peng, C.-C.: Examining Depth Origin of Anisotropy in an Active Orogenic Belt of Taiwan Using Shear Wave Splitting Results from the Formosa Array., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14416, https://doi.org/10.5194/egusphere-egu24-14416, 2024.

EGU24-14883 | ECS | Posters on site | GD7.1

Modeling pressure-dependent seismic anisotropy in the lower mantle reveals anisotropic discontinuity at 1000 km 

John Keith Magali, Christine Thomas, Jeffrey Gay, Angelo Pisconti, and Sebastien Merkel

There is growing evidence, both from a modelling perspective and seismic observations, that seismic anisotropy in the lower mantle is localized around penetrating slabs where large straining is anticipated. It is believed that the high stresses experienced near the slab activate dislocation creep mechanisms that drive the crystallographic preferred orientation (CPO) of bridgmanite aggregates. Still, deformation mechanisms in bridgmanite remain enigmatic. In recent years, deformation experiments in bridgmanite subjected to mantle temperatures and pressures suggest that its microstructures evolve with pressure, providing another perspective on the debated structure and deformation in the lower mantle. Using this information, we develop a numerical technique that calculates pressure-dependent large-scale seismic anisotropy in a pyrolitic mantle with variable velocity gradients. As a first test, we use the method to predict seismic anisotropy by calculating anisotropic reflection coefficients of underside reflections off a depth corresponding to 50 GPa where pressure-induced slip transitions in bridgmanite are expected. For this, we consider two simple deformation styles: (1) uni-axial compression, akin to vertically penetrating slabs, and (2) simple shear associated with corner-type flows. Finally, we demonstrate a multiscale approach that calculates large-scale seismic anisotropy from a fully time-dependent thermo-chemical model of free subduction with latent heating and phase transitions. The result is a long-wavelength equivalent azimuthal and radial anisotropy maps that are actually comparable to a seismic tomography model. We demonstrate how such an approach can create discontinuities in anisotropy at ~1000 km and provide insights as to how it relates to the heterogeneous distribution of the 1000-km discontinuity.

How to cite: Magali, J. K., Thomas, C., Gay, J., Pisconti, A., and Merkel, S.: Modeling pressure-dependent seismic anisotropy in the lower mantle reveals anisotropic discontinuity at 1000 km, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14883, https://doi.org/10.5194/egusphere-egu24-14883, 2024.

EGU24-15225 | ECS | Orals | GD7.1

Exploring Mantle Dynamics of the Cascadia Subduction System through Anisotropic Tomography with Transdimensional Inference Methods 

Brandon VanderBeek, Gianmarco Del Piccolo, and Manuele Faccenda

The Cascadia subduction system is an ideal location to investigate the nature of mantle flow and associated driving forces at a convergent margin owing to the dense network of on- and off-shore seismic instrumentation. While numerous shear wave splitting and tomography studies have been performed with these data, they have produced conflicting views of mantle dynamics collectively referred to as the Cascadia Paradox. On the overriding plate, splitting observations are consistent with large-scale 3D toroidal flow while off-shore splitting patterns are more easily explained by 2D plate-driven flow. Either geometry is difficult to reconcile with seismic tomographic models that image a fragmented Juan de Fuca slab descending beneath the Western USA. However, these observations offer only an incomplete image of Cascadia mantle structure. Shear wave splitting provides a depth integrated view of anisotropic fabrics making inferences regarding the 3D nature of mantle deformation difficult. Prior high-resolution body wave tomography typically neglects anisotropic effects which can in turn yield significant isotropic imaging artefacts that complicate model interpretation. To overcome these limitations, we invert P-wave delay times for a 3D hexagonally anisotropic model with arbitrarily oriented symmetry axes using the reversible jump Markov chain Monte Carlo algorithm. This stochastic imaging approach is particularly well-suited to the highly non-linear and under-determined nature of the anisotropic seismic tomography problem. The resulting ensemble of solutions allows us to rigorously assess model parameter uncertainties and trade-off between isotropic and anisotropic heterogeneity. We investigate whether the fragmented nature of the subducted Juan de Fuca slab is a well-resolved feature and to what extent its geometry trades off with anisotropic parameters. In light of our new 3D anisotropic model, we re-evaluate the Cascadia Paradox and attempt to reconcile disparate views of Western USA mantle dynamics.

How to cite: VanderBeek, B., Del Piccolo, G., and Faccenda, M.: Exploring Mantle Dynamics of the Cascadia Subduction System through Anisotropic Tomography with Transdimensional Inference Methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15225, https://doi.org/10.5194/egusphere-egu24-15225, 2024.

EGU24-16887 | ECS | Posters on site | GD7.1

The effect of centimeter-scale folding and crenulation on anisotropy homogenization of schists and phyllites from the NW-Tauern Window (Eastern Alps, Austria) 

Dustin Lang, Rebecca Kühn, Rüdiger Kilian, Hannah Pomella, and Michael Stipp

The interpretation of seismic data in orogens is usually difficult to decipher as structural information is limited to surface and borehole data. Seismic interpretations very much depend on the elastic wave velocity model, which in the simplest case is a function of rock composition. Seismic velocities can also be anisotropic, i.e. depend on the wave propagation direction inside the rock. Seismic anisotropy can be subdivided into intrinsic (crystallographic preferred orientation (CPO)) and extrinsic (shape preferred orientation, compositional layering or fractures) anisotropy. Microstructures in thin section scale have an impact not only on millimeter-scale but also on larger anisotropies in the field such as meter- to kilometer-scale folds. Here we explore the effect of microstructure (mainly folding and crenulation) on the homogenization of seismic anisotropy from samples of millimeter to thin section scale.

The investigated samples are phyllosilicate- and graphite-rich samples (Innsbruck quartzphyllite and Bündner schist) from the N-S running Brenner Base Tunnel Project (NW-Tauern Window). Phyllosilicate-rich sections with layers of different composition and structure were selected from drill core samples of the exploration tunnel. The CPO of phyllosilicates and graphite from 1.5 – 3.5 mm thick cylinders was measured using high energy X-ray diffraction at DESY (Hamburg, Germany) and the ESRF (Grenoble, France). Pole figure data was directly extracted using single peak fitting. The CPO of quartz was determined by using EBSD. Seismic velocities for each sample were computed using µXRF-based modal composition and single crystal stiffness tensors. We measured the smallest representative volume element which we consider to be undisturbed by microstructural effects. Therefore, we estimate an upper bound of expected intrinsic velocity anisotropies. Thin section-scale anisotropies were modeled from the upper bound anisotropy and the observed microstructure, i.e., small-scale folding. Computed velocities were compared to Vp-anisotropy measurements on the drill cores.

The velocity anisotropy is primarily governed by the content and distribution of phyllosilicates and graphite. Given the crystal symmetry and the low single crystal elastic anisotropy, phases such as feldspar, quartz or calcite can be considered as irrelevant with respect to seismic anisotropies. The simulation of a crenulation cleavage has a stronger impact than centimeter-size folding: The crenulation cleavage reduces the anisotropy for example from 14 % to 12 %. Centimeter-size folding with observed interlimb angles of 140° in contrast is negligible.

The effect of microstructures like centimeter-scale folds and crenulation has only a limited impact on anisotropies of foliated rocks during homogenization from millimeter to thin section-scale. We assume that during homogenization to a larger scale, the effect of folding with small interlimb angles or different fold axes within the homogenized volume will have a stronger influence on seismic anisotropy.

How to cite: Lang, D., Kühn, R., Kilian, R., Pomella, H., and Stipp, M.: The effect of centimeter-scale folding and crenulation on anisotropy homogenization of schists and phyllites from the NW-Tauern Window (Eastern Alps, Austria), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16887, https://doi.org/10.5194/egusphere-egu24-16887, 2024.

EGU24-17055 | ECS | Orals | GD7.1

Deformation of the Indian Lithosphere from radial anisotropy: Signatures of laterally varying plate geometry beneath Tibet and hotspot volcanism beneath the Deccan Plateau.  

Arijit Chakraborty, Monumoy Ghosh, Siddharth Dey, Shubham Sharma, Sankar N. Bhattacharya, and Supriyo Mitra

The Indian Lithosphere has been shaped by multiple tectonic processes, which include break-up from the Gondwana Supercontinent, traversing over the Reunion and Kerguelen hotspots, collision with Eurasia, and underthrusting beneath the Himalaya and Tibetan Plateau. Seismic velocity structure and radial anisotropy of the lithosphere preserves imprints of these  tectonic processes and related deformation. We perform joint-modeling of fundamental-mode Rayleigh (LR) and Love (LQ) wave group-velocity dispersion, for periods between 10 and 120s, to obtain radially anisotropic shear-wave velocity structure across India, Himalaya and Tibet. 1D path-average dispersion curves, computed for ~14700 regional earthquake-receiver raypaths, has been passed through systematic quality control of signal-to-noise ratio (>3), elimination of multipathed energy using polarization analysis, and removal of overtone interference, by synthetic tests. These 1D dispersion data are combined through a tomographic formulation to obtain 2D maps. The tomographic parametrization is done using  4906 nodes as apex of triangular elements of side 1°. LR and LQ fundamental-mode group-velocity dispersion data at these nodes are the observation input to the joint inversion. The inversion is done in 2-steps, first by parameterizing the model as isotropic layers and using an isotropic inversion scheme to obtain the best fitting Vs model; second using this output Vs model into an anisotropic inversion scheme, implemented using Genetic Algorithms (GA). GA exhaustively searches the model-space composed of Vsh, Vph and Xi[Vsh^2/Vsv^2] as free parameters. The fit to both LR and LQ datasets significantly improve in the anisotropic inversion. 

 

Results are presented as 2D depth-slice maps and cross-sections constructed using bilinear interpolation. The main findings from our models are lateral variation in the voigt-average Vs beneath the Tibetan Plateau at depth between 80-140 km. Western Tibet has high Vs and positive Xi, while Central-Eastern TIbet has Low Vs and negative Xi. From cross-sections across both regions, we infer that the dip and underthrusting of the Indian Plate beneath Tibet has lateral variation. The high Vs and positive anisotropy in Western Tibet indicates a shallow underthrusting of the Indian lithosphere up to the Tarim Basin, with simple-shear deformation. Where as, the lower Vs and negative anisotropy in Central-Eastern Tibet is a result of partial-underthrusting of India at a steeper-angle up to the Bangong-Nujiang Suture, and pure-shear deformation of thickened Tibet Lithosphere beneath North-Central Tibet. A negative anisotropy signature along the Reunion volcanic track is observed between 100 and 160 km depth. We infer this to be the signature of  Reunion hotspot volcanism in the Indian lithosphere caused by the vertical ascent of a huge volume of melt arising from the plume-head. Similar observations are also made beneath the track of the Kergulean hotspot. 

How to cite: Chakraborty, A., Ghosh, M., Dey, S., Sharma, S., Bhattacharya, S. N., and Mitra, S.: Deformation of the Indian Lithosphere from radial anisotropy: Signatures of laterally varying plate geometry beneath Tibet and hotspot volcanism beneath the Deccan Plateau. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17055, https://doi.org/10.5194/egusphere-egu24-17055, 2024.

EGU24-17743 | Orals | GD7.1

Predicting seismic anisotropy in the upper mantle using supervised deep-learning 

Andrea Tommasi, Nestor Cerpa, Fernando Carazo, and Javier Signorell

Both elastic and viscoplastic behaviors of the Earth’s upper mantle are highly anisotropic, because olivine, which composes 60-80% of the mantle, has a strong intrinsic anisotropy and develops strong crystal preferred orientations (CPO). Predicting the evolution of anisotropy with strain is essential to: (1) probe indirectly the deformation in the mantle based on seismic measurements and (2) accounting for the deformation history when simulating the long-term dynamics of the Earth. However, traditional micro-mechanical approaches to model the evolution of CPO-induced elastic and viscous anisotropies are too memory-costly and time-consuming for coupling into geodynamical simulations. To speed up the prediction of seismic anisotropy in the mantle, we developed deep-learning (DL) surrogates trained on a synthetic database built with viscoplastic self-consistent simulations of texture evolution of olivine polycrystals in typical 2D geodynamical flows. A first challenge was the choice of memory-saving representations of the CPO. Training the DL models on the evolution of the elastic tensor components avoided the need of storing the CPOs. However, the major challenge has been to prevent error compounding in a recursive-prediction scheme – where a model prediction at a given time step becomes the input for the next one - to evaluate the anisotropy evolution along a flow line. We implemented multilayer feed-forward (FFNN), ensemble, and transformer neural networks, obtaining the best efficiency/accuracy ratio for the FFNN. The results highlight the importance of (1) the standardization of the outputs in the training stage to avoid overfitting in predictions, (2) the statistical characteristics of the strain histories in the training database, and (3) the influence of non-monotonic strain histories on error propagation. Predictions for complex unseen strain histories are accurate, much more time-efficient and memory-costly than the traditional micro-mechanical models. Our work opens thus new avenues for modeling the strain-controlled evolution of mechanical anisotropy in the Earth’s mantle. This work was supported by the European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation programme [grant agreement No 882450 – ERC RhEoVOLUTION.

How to cite: Tommasi, A., Cerpa, N., Carazo, F., and Signorell, J.: Predicting seismic anisotropy in the upper mantle using supervised deep-learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17743, https://doi.org/10.5194/egusphere-egu24-17743, 2024.

EGU24-18148 | ECS | Orals | GD7.1

Trans-dimensional Mt. Etna P-wave anisotropic seismic imaging 

Gianmarco Del Piccolo, Rosalia Lo Bue, Brandon Paul VanderBeek, Manuele Faccenda, Ornella Cocina, Marco Firetto Carlino, Elisabetta Giampiccolo, Andrea Morelli, and Joseph Byrnes

Trans-dimensional inference identifies a class of methods for inverse problems where the number of free parameters is not fixed. In seismic imaging these methods are applied to let the data, and any prior information, decide the complexity of the models and how the inferred fields partition the inversion domains. Monte Carlo trans-dimensional inference is performed implementing the reversible-jump Markov chain Monte Carlo (rjMcMC) algorithm; the nature of Monte Carlo exploration allows the algorithm to be completely non-linear, to explore multiple possibilities among models with different dimensions and meshes and to extensively investigate the under-determined nature of the tomographic problems, showing quantitative evidence for the limitations in the data-sets used. Implementations of this method overcome the main limitations of traditional linearized solvers: the arbitrariness in the selection of the regularization parameters, the linearized iterative approach and in general the collapse of the information behind the solution into a unique inferred model.

We present applications of the rjMcMC algorithm to anisotropic seismic imaging of Mt. Etna with P-waves. Mt. Etna is one of the most active and monitored volcanoes in the world, typically investigated under the assumption of isotropic seismic speeds. However, since body waves manifest strong sensitivity to seismic anisotropy, we parametrize a multi-fields inversion to account for the directional dependence in the seismic velocities. Anisotropy increases the ill-condition of the tomographic problem and the consequences of the under-determination become more relevant. When multiple seismic fields are investigated, such as seismic speeds and anisotropy, the data-sets used may not be able to independently resolve them, resulting in non-independent estimates and corresponding trade-offs. Monte Carlo exploration allows for the evaluation of the robustness of seismic anomalies and anisotropic patterns, as well as the trade-offs between isotropic and anisotropic perturbations, key features for the interpretation of tomographic models in volcanic environments. The approach is completely non-linear, free of any explicit regularization and it keeps the computational time feasible, even for large data-sets.

How to cite: Del Piccolo, G., Lo Bue, R., VanderBeek, B. P., Faccenda, M., Cocina, O., Firetto Carlino, M., Giampiccolo, E., Morelli, A., and Byrnes, J.: Trans-dimensional Mt. Etna P-wave anisotropic seismic imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18148, https://doi.org/10.5194/egusphere-egu24-18148, 2024.

EGU24-21240 | Posters on site | GD7.1

Anisotropy and XKS-splitting from geodynamic models of double subduction: Testing the limits of interpretation 

Jan Philipp Kruse, Georg Rümpker, Frederik Link, Thibault Duretz, and Harro Schmeling

We utilize three-dimensional geodynamic models to predict XKS-splitting in double subduction scenarios characterized by two outward-dipping slabs. These models are highly applicable in various realistic settings, such as the central Mediterranean. Our primary focus is on the analysis of XKS-splitting, a key geophysical observable used for inferring seismic anisotropy and mantle flow patterns.Our models simulate the concurrent subduction of two identical oceanic plates separated by a continental plate. The variation in the strength of the separating plate causes a transition from a retreating to a stationary trench. The models offer detailed insights into the temporal evolution of mantle flow patterns, particularly the amount of trench-parallel flow induced by this specific type of subduction.In the subsequent step, we employ the well-known D-Rex model to estimate Crystallographic Preferred Orientation (CPO) development in response to plastic deformation resulting from mantle flow. Based on the D-Rex model results, which incorporate the full elastic tensor of a deformed multiphase polycrystalline mantle aggregate, we derive synthetic apparent splitting parameters and splitting intensities at virtual receivers placed at the surface using multiple-layer anisotropic waveform modeling. To identify regions with pronounced depth-dependent variations of anisotropic properties, particularly the fast polarization directions, we define a complex anisotropy factor dependent on the apparent splitting parameters and splitting intensities.Finally, using the apparent splitting parameters, we conduct two-layer model inversions at selected locations characterized by a large complex anisotropy factor. The two-layer model provides apparent splitting parameters as a result of analytical waveform modeling for two anisotropic layers. We observe that while several models can effectively explain the apparent splitting parameters, only a subset can accurately reproduce the depth-dependent anisotropic properties. Our findings unequivocally demonstrate that a classical XKS-splitting analysis can effectively identify areas characterized by complex anisotropy and provide accurate approximations of the depth-dependent variations of anisotropic properties within these regions. However, caution is warranted when interpreting results obtained through inversion based on a two-layer analysis.

How to cite: Kruse, J. P., Rümpker, G., Link, F., Duretz, T., and Schmeling, H.: Anisotropy and XKS-splitting from geodynamic models of double subduction: Testing the limits of interpretation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21240, https://doi.org/10.5194/egusphere-egu24-21240, 2024.

EGU24-415 | ECS | Orals | TS8.1

The South Atlantic Magmatic Province: An Integration of Early Cretaceous LIPs in the West Gondwana 

Antomat Avelino de Macedo Filho, Alisson Oliveira, Valdecir Janasi, and Maria Helena Hollanda

Extensive igneous activity, currently identified from NE Brazil and western Africa to the Falkland Islands and South Africa, preceded the fragmentation of the Western Gondwana supercontinent in the Early Cretaceous. The Paraná-Etendeka Magmatic Province (PEMP) is characterized by continental basaltic flows and igneous plumbing systems in SE South America and its African counterpart. In NE Brazil, dyke swarms and sill complexes compose the Equatorial Atlantic Magmatic Province (EQUAMP). A prominent feature of EQUAMP is the Rio Ceará-Mirim dyke swarm, an arcuate igneous plumbing system approximately 1,100 km in length. Aeromagnetic data suggests that the Rio Ceará-Mirim dykes stretch from the corner of South America to the northwest border of the São Francisco Craton. At this point, the dykes shift orientation to the NNW, extending towards the south, where they appear to connect with the Transminas dyke swarm (northern PEMP). The apparent continuity of dykes as a single entity would constitute a massive transcontinental swarm of about 2,300 km. A similar relationship is observed for the Riacho do Cordeiro (southern EQUAMP) and Vitória-Colatina (northern PEMP) dykes, indicating continuity across the São Francisco Craton of about 1,600 km. This study, supported by new petrological, geochemical, isotopic, and geochronological data, combined with geophysical and geodynamical analyses, demonstrates that the Transminas and Vitória-Colatina dyke swarms share the same composition and age as the Rio Ceará-Mirim and Riacho do Cordeiro dyke swarms, respectively. The set of new evidence supports a genetic connection between the PEMP and EQUAMP. Therefore, they can be collectively referred to as a single large igneous province related to the early stage of the South Atlantic rifting process in the West Gondwana realm: The South Atlantic Magmatic Province.

How to cite: Avelino de Macedo Filho, A., Oliveira, A., Janasi, V., and Hollanda, M. H.: The South Atlantic Magmatic Province: An Integration of Early Cretaceous LIPs in the West Gondwana, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-415, https://doi.org/10.5194/egusphere-egu24-415, 2024.

EGU24-1934 | ECS | Posters on site | TS8.1

The hypothesis of a lost Cenozoic “Himalandia” between India and Asia 

Liang Liu, Lijun Liu, Jason Morgan, Yi-Gang Xu, and Ling Chen

            The type of lithosphere subducted between India and Tibet since the Paleocene remains controversial; it has been suggested to be either entirely continental, oceanic, or a mixture of the two. As the subduction history of this lost lithosphere strongly shaped Tibetan intraplate tectonism, we attempt to further constrain its nature and density structure with numerical models that aim to reproduce the observed history of magmatism and crustal thickening in addition to present-day plateau properties between 83˚E and 88˚E. By matching time-evolving geological patterns, here we show that Tibetan tectonism away from the Himalayan syntaxis is consistent with the initial indentation of a craton-like terrane at 55±5 Ma, followed by a buoyant tectonic plate with a thin crust, e.g., a broad continental margin (Himalandia). This new geodynamic scenario can explain the seemingly contradictory observations that had led to competing hypotheses like the subduction of Greater India versus largely oceanic subduction prior to Indian indentation.

How to cite: Liu, L., Liu, L., Morgan, J., Xu, Y.-G., and Chen, L.: The hypothesis of a lost Cenozoic “Himalandia” between India and Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1934, https://doi.org/10.5194/egusphere-egu24-1934, 2024.

EGU24-2317 | Posters on site | TS8.1

Rayleigh-wave Ambient Noise Investigation for the OHANA Experiment in the NE Pacific 

Gabi Laske, Grace Atkisson, Sujania Talavera Soza, John Collins, and Donna Blackman

The OHANA experiment comprises a 15-month deployment of 25 broadband ocean bottom seismometers (OBSs) in the northeast Pacific Ocean, about halfway between Hawaii and the North American west coast. The primary objective of this project is to explore the crust, lithosphere and asthenosphere in a 600~km wide region west of the Moonless Mountains, covering mainly 40-to-50 Myr old Pacific lithosphere. A fundamental question to be addressed is whether this particular area has the signature of a typical oceanic lithosphere that has a normal plate cooling history. Alternatively, we seek evidence for a previously proposed reheating process, e.g. resulting from small-scale shallow-mantle convection. 

The new data enhance seismic imaging in a regional as well as in a global context. Regionally, short-period ambient noise and long-period earthquake-derived Rayleigh wave dispersion provide the centerpiece for imaging the crust and upper mantle. In  a top-down approach,
we start with the assembly and analysis of ambient-noise cross-correlation functions between 5 and 25 s. We present an initial assessment of high signal-to-noise quality cross-correlation functions. We derive path-averaged dispersion curves for the fundamental mode and present tomographic images from initial inversions. 

Furthermore, our cross-correlation functions contain prominent waveforms from overtones that can help improve resolution as a function of depth.

How to cite: Laske, G., Atkisson, G., Talavera Soza, S., Collins, J., and Blackman, D.: Rayleigh-wave Ambient Noise Investigation for the OHANA Experiment in the NE Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2317, https://doi.org/10.5194/egusphere-egu24-2317, 2024.

EGU24-2624 | ECS | Posters on site | TS8.1

Ridge-dual hotspots interaction and potential hotspot-hotspot interaction in the Southeastern Indian Ocean  

Yiming Luo, Jian Lin, Zhiyuan Zhou, Fan Zhang, Xubo Zhang, and Jinchang Zhang

We investigated the impacts of the Kerguelen and Amsterdam-St. Paul (ASP) hotspots on mantle evolution and crustal accretion of nearby spreading ridges in the Southeastern Indian Ocean. Gravity analysis revealed enhanced magmatism and thickened crust along the ridge caused by the Kerguelen and ASP hotspots. By employing plate motions derived from the GPlates global plate reconstruction model, along with the ASPECT 3-D mantle convection code, we presented a comprehensive depiction of the ridge-dual hotspot system, which has been relatively underexplored in previous research. Model results indicated that the Kerguelen hotspot had a significantly greater influence on mantle temperature and ridge crustal thickness compared to the ASP hotspot. Furthermore, there is evidence suggesting a potential interaction between the dual hotspots, leading to the migration of ASP plume materials towards the Kerguelen plume.

How to cite: Luo, Y., Lin, J., Zhou, Z., Zhang, F., Zhang, X., and Zhang, J.: Ridge-dual hotspots interaction and potential hotspot-hotspot interaction in the Southeastern Indian Ocean , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2624, https://doi.org/10.5194/egusphere-egu24-2624, 2024.

EGU24-2711 | ECS | Orals | TS8.1

Links between large volcanic eruptions, basal mantle structures and mantle plumes 

Annalise Cucchiaro, Nicolas Flament, Maëlis Arnould, and Noel Cressie

As part of mantle convection, mantle plumes rise from the deep Earth, leading to volcanic eruptions during which large volumes of mafic magma are emplaced at Earth’s surface over a few million years. In 1971, Jason Morgan showed that seamount chains could be used to calculate the absolute motion of tectonic plates above fixed mantle plumes. This ground-breaking work notably led to the study of the relationship between Earth’s deep interior and its surface. Mantle plumes have been critical to constrain absolute plate motions in Earth’s recent geological past, with the development of both fixed-hotspot and moving-hotspot plate-motion models. Recent studies also revealed a statistical link between large volcanic eruptions and basal mantle structures in space and time, suggesting that large volcanic eruptions, mantle plumes, and hot basal structures are intrinsically connected. In these studies, mantle plumes were considered as the implicit process connecting volcanic eruptions at the surface to hot basal mantle structures. Geodynamic models suggest that mantle plumes are generated by two large antipodal hot basal mantle structures, up to ~1,200 km thick, and shaped by subducted oceanic crust through time. Here, we systematically compare three volcanic-eruption databases, four global tomographic models, and six reconstructions of past global mantle flow, to investigate the spatio-temporal links between volcanic eruptions, hot basal mantle structures, and modelled mantle plumes from 300 million years ago to the present day. We find that large volcanic eruptions are spatially closer to fixed and moving hot basal mantle structures than to modelled mantle plumes, because mantle plumes cover an area that is five orders of magnitude smaller than the area covered by hot basal mantle structures. The strength of the spatial-statistical relationships is largest between volcanic eruptions and modelled mantle plumes and, overall, it is larger between volcanic eruptions and moving basal mantle structures than between volcanic eruptions and fixed basal mantle structures.  This suggests that large volcanic eruptions are preferentially associated with mantle plumes generated from the interior of mobile basal mantle structures, which is in sharp contrast to previous studies that suggested mantle plumes are generated from the edges of fixed basal mantle structures.

How to cite: Cucchiaro, A., Flament, N., Arnould, M., and Cressie, N.: Links between large volcanic eruptions, basal mantle structures and mantle plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2711, https://doi.org/10.5194/egusphere-egu24-2711, 2024.

EGU24-4020 | ECS | Orals | TS8.1

Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction 

Björn Heyn, Grace Shephard, and Clint Conrad

Between about 130 and 75 Ma, the Arctic was impacted by widespread and long-lived volcanism known as the High Arctic Large Igneous Province (HALIP). HALIP is a very unusual large igneous province because it exhibits prolonged melting over more than 50 Myr with pulses of activity, an observation that is difficult to reconcile with the classic view of large igneous provinces and associated melting in plume heads. Hence, the suggested plume-related origin and classification of HALIP as a large igneous province has been questioned, and alternative mechanisms have been invoked to explain at least part of the volcanism. However, the Arctic also exhibits a very complex and time-dependent tectonic history that includes cratons, continental margins and rifting, all of which are expected to interact with the rising plume and affect its melting behaviour.

 

Here, we use 2-D numerical models that include melting and melt migration to investigate a rising plume interacting with a lithosphere of variable thickness, i.e. an extended-basin-to-craton setting. Models reveal significant spatial and temporal variations in melt volumes and pulses of melt production, including protracted melting for at least about 30-40 Myr, but only if feedback between melt and mantle convection is accounted for. In particular, we find that melt migration transports heat upwards and enhances local lithospheric thinning, resulting in a more heterogeneous distribution of melting zones within the plume head underneath the Sverdrup Basin. Once the thicker continental and cratonic lithosphere move over the plume, plume material is deflected from underneath the Greenland craton and can then re-activate melting zones below the previously plume-influenced Sverdrup Basin, even though the plume is already ∼500 km away. Hence, melting zones may not represent the location of the deeper plume stem at a given time. Plume flux pulses associated with mantle processes, rifting of tectonic plates or magmatic processes within the crust may alter the timing and volume of secondary pulses and their surface expression, but are not required to generate pulses in magmatic activity. Hence, we propose that the prolonged period of rejuvenated magmatism of HALIP is consistent with plume impingement on a cratonic edge and subsequent plume-lithosphere interaction. Based on melt fractions, our models suggest that HALIP magmatism should exhibit plume-related trace element signatures through time, but potentially shifting from mostly tholeiitic magmas in the first pulse towards more alkalic compositions for secondary pulses, with regional variations in timing of magma types.

How to cite: Heyn, B., Shephard, G., and Conrad, C.: Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4020, https://doi.org/10.5194/egusphere-egu24-4020, 2024.

The India-Asia convergence has persisted since the onset of collision at ~55 Ma, indicating the driving forces of Indian indentation do not disappear on continental collision in the convergence process. What drives ongoing India-Asia convergence? This puzzle cannot be well resolved by the traditional theory of plate tectonics and the concept of Wilson Cycle. Consequently, questions concerning the primary driving force of the ongoing India-Asia convergence and the magnitude of this force still await an answer. Previous works have proposed multiple candidates for the primary driver of India-Asia convergence, including the continental subduction of the Indian lithosphere under Tibet, oceanic subduction at the Sumatra-Java trench, as well as the basal drag exerted by the mantle flow on the base of Indo-Australia plate. Here we present global geodynamic models to investigate the driving forces behind the India-Asia convergence, which produce good fits to the observed motions, stresses and strains within the Indo-Australia plate. On this basis, we quantitatively calculate the magnitude of effective forces of boundary forces (slab pull and ridge push) and basal drag. We conclude that the Sumatra-Java subduction is the primary driver of the ongoing India-Asia convergence. Indo-Australia plate motion is driven at the Sumatra-Java trench, impeded along the Himalaya, which could increase the shear stress within the plate. Different from the recent emphasis on the basal drag as a dominant driving force for the India-Asia convergence, this study shows that basal drag acts as the resisting force for the northeastward motion of the giant Indo-Australia plate, though it serves as a driver in some local regions.

 

How to cite: Zheng, Q. and Hu, J.: Driving forces for the ongoing India-Asia convergence: insight from global high-resolution numerical modeling of mantle convection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4314, https://doi.org/10.5194/egusphere-egu24-4314, 2024.

EGU24-4754 | Orals | TS8.1

Mantle plumes imaged by seismic full waveform inversion: from the core-mantle-boundary to surface hotspots 

Barbara Romanowicz, Federico Munch, and Utpal Kumar

With recent progress in resolution in global seismic mantle imaging provided by numerical wavefield computations using the Spectral Element Method and full waveform inversion, Jason Morgan’s suggestion from over 50 years ago that mantle plumes may be rooted at the core-mantle boundary (CMB) has been confirmed. Yet the imaged plumes present intriguing features that contrast with the classical thermal plume model and should inform our understanding of mantle dynamics. Among other features, they are broader than purely thermal plumes, and do not extend straight from the CMB to the corresponding hotspot volcanoes, but they are frequently deflected horizontally in the extended transition zone (400-1000 km depth), so that their lower mantle location can be significantly offset (as much as a 1000 km) from their surface expression. They appear to be thinner in the upper mantle. This, together with similar horizontal flattening observed in subduction zones suggests a change in the radial viscosity structure of the mantle that may occur deeper than usually assumed to be related to the 660 km phase change. The fattest plumes have been shown to be anchored within the perimeter of the large low shear velocity provinces (LLSVPs) and an increasing number of them appear to house mega-ultra low velocity zones within their roots.  Moreover, in the upper mantle, they appear to be associated with regularly spaced low velocity channels aligned with absolute plate motion.

We discuss these features in the light of recent regional imaging updates in the south Atlantic and beneath Yellowstone, contrasting the corresponding mantle plumes, and in particular showing mounting evidence that the LLSVPs are not compact “piles” extending high above the CMB, but rather a bundle of thermo-chemical plumes feeding secondary scale convection in the top 1000 km of the mantle.

How to cite: Romanowicz, B., Munch, F., and Kumar, U.: Mantle plumes imaged by seismic full waveform inversion: from the core-mantle-boundary to surface hotspots, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4754, https://doi.org/10.5194/egusphere-egu24-4754, 2024.

EGU24-6247 | ECS | Posters on site | TS8.1

Slab dynamics in the mantle: a back-to-basics approach 

Abigail Plimmer, Huw Davies, and James Panton

Subduction is one of the most fundamental processes on Earth, linking the lithosphere and mantle and is a key driving force in mantle circulation. Despite this, and the advancement of geophysical methods which allow us to better understand mantle dynamics, our understanding of slab behaviour is still limited. The Earth is a very complex system, and so conclusions regarding slab dynamics are also sensitive to the interplay between countless processes acting within the mantle. 

There is much to learn about slab sinking in the mantle from considering a single 'perfect' plate, such that the dynamics can be isolated from any pre-established or distal processes. We present a range of 3D spherical mantle circulation models which evolve from the initial condition, driven by a 'perfect' plate at the surface. Each of these plates comprises a rectangular geometry, bound by a subduction zone on one side, a spreading ridge on the opposite side, and two tranform faults on the adjacent edges. We vary the geometry of the plate, both in terms of the length of the subducting trench, and the distance from the trench to the ridge, and vary the plate velocity.

We will report the slab behaviour in terms of plate geometry, mantle properties, and plate velocity, focussing on the evolution of downwellings, upwellings and other mantle structures in response to mantle circulation models driven solely by a single plate at the surface.

How to cite: Plimmer, A., Davies, H., and Panton, J.: Slab dynamics in the mantle: a back-to-basics approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6247, https://doi.org/10.5194/egusphere-egu24-6247, 2024.

EGU24-6549 | ECS | Posters on site | TS8.1

Utilizing Euler poles for the evaluation of plate rigidity in numerical mantle convection models 

Taiwo Ojo, Joshua Guerrero, Chad Fairservice, Pejvak Javaheri, and Julian Lowman

We implement an innovative method of plate identification for the purpose of evaluating plate motion in numerical mantle convection models. Our method utilizes an existing tool,  Automatic Detection Of Plate Tectonics (ADOPT), which applies a tolerance (threshold) algorithm to elevation maps, to detect candidate plate boundaries at the surface of 3-D spherical mantle convection models. The logarithm of the strain-rate field yields a well-defined elevation map where local maxima lineations indicate spreading centres, zones of convergence, transform faults or diffuse deformation zones. For the plates found by ADOPT’s analysis, we determined rotation (Euler) poles implied by the velocities  within  the plate interiors. Subsequently, we examined the velocity field of each model plate for its agreement with rigid motion about the Euler poles.  We apply our method to snapshots taken from three previously published mantle convection calculations that appear to generate plate-like surface behaviour. Self-consistently generated model plates were obtained by combining a highly temperature-dependent viscosity with a yield stress that adds a strain-rate dependence to the viscosity, thus allowing for both intra-plate low strain-rate and weakening along tightly focussed plate boundaries. We generally identify more (and smaller) rigid plates for low yield stress or low threshold. Strong agreement of the surface velocities with rigid-body rotation around Euler poles is found for many of the plates identified; however, some plates also exhibit internal deformation. Regions that show a departure from rigidity can be decomposed into subsets of rigidly moving plates. Thus, the identification of a mantle convection model's maximally rigid plate surface may require plate boundary detection at both low and high thresholds. We suggest that as global mantle convection models superficially converge on the generation of plate boundary network similar to those observed with plate tectonics (including transform fault generation), testing for plate rigidity through the determination of Euler poles can serve as a quantitative measure of plate-like surface motion.

How to cite: Ojo, T., Guerrero, J., Fairservice, C., Javaheri, P., and Lowman, J.: Utilizing Euler poles for the evaluation of plate rigidity in numerical mantle convection models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6549, https://doi.org/10.5194/egusphere-egu24-6549, 2024.

EGU24-6630 | Posters on site | TS8.1

Gondwanan Flood Basalts Linked Seismically to Plume-Induced Lithosphere Instability 

Ya-Nan Shi and Jason Morgan

Delamination of continental lithospheric mantle is now well-recorded beneath several continents. However, the fate of delaminated continental lithosphere has been rarely noted, unlike subducted slabs that are reasonably well imaged in the upper and mid mantle. Beneath former Gondwana, recent seismic tomographic models indicate the presence of at least 5  horizontal fast-wavespeed anomalies at ~600 km depths that do not appear to be related to slab subduction, including fast structures in locations consistent with delamination associated with the Paraná Flood Basalt event at ~134 Ma and the Deccan Traps event at ~66 Ma. These fast-wavespeed anomalies often lie above broad slow seismic wavespeed trunks at 500-700 km depths beneath former Gondwana, with the slow wavespeed anomalies branching around them. Numerical experiments indicate that delaminated lithosphere tends to stagnate in the transition zone above a mantle plume where it shapes subsequent plume upwelling. For hot plumes, the melt volume generated during plume-influenced delamination can easily reach ~2-4×106 km3, consistent with the basalt eruption volume at the Deccan Traps. This seismic and numerical evidence suggests that observed high wavespeed mid-mantle anomalies beneath the locations of former flood basalts are delaminated fragments of former continental lithosphere, and that lithospheric delamination events in the presence of subcontinental plumes induced several of the continental flood basalts associated with the multiple breakup stages of Gondwanaland. Continued upwelling in these plumes can also have entrained subcontinental lithosphere in the mid-mantle to bring its distinctive geochemical signal to the modern mid-ocean spreading centers that surround southern and western Africa.

How to cite: Shi, Y.-N. and Morgan, J.: Gondwanan Flood Basalts Linked Seismically to Plume-Induced Lithosphere Instability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6630, https://doi.org/10.5194/egusphere-egu24-6630, 2024.

EGU24-7075 | Orals | TS8.1

Absence of surface volcanism and the indeterminate evidence for continental mantle plumes 

Simone Pilia, Giampiero Iaffaldano, Rhodri Davies, Paolo Sossi, Scott Whattam, and Hao Hu

There are rare occurrences on Earth where mantle plumes intersect with continents, resulting in surface volcanism.Unlike their more common counterparts in oceanic lithosphere, where the ascent of melts is facilitated by a thinner lithosphere, identifying continental plumes is challenging. Surface volcanism, traditionally a key indicator of mantle plumes, may play a diminished role in regions characterized by complex tectonics and variations in lithospheric thickness.

Eastern Oman provides an excellent example where a continental mantle plume has remained undetected due to the absence of current surface volcanism. The region exhibits evidence of intraplate basanites, although with an age of ~35-40 Ma. Given their geochemical signature, these alkaline rocks likely originated from a mixture of melts from a plume-derived source and those from a lithosphere-derived component. Using P- and S-wave arrival-time residuals from distant earthquakes, we image a new mantle plume in eastern Oman, which we name the Salma plume. This continental plume is revealed in our 3-D P- and S-wave tomographic models as a 200 km low-velocity conduit extending to at least the base of the upper mantle, and located below the area of Tertiary intraplate volcanism. Despite experiencing minimal shortening since the Paleogene, the shallow-marine sediments of the Salma Plateau in eastern Oman reach elevations exceeding 2000 meters. Ongoing uplift, indicated by elevated Quaternary marine terraces, suggests that the plateau is still rising. The present uplift rate is modest but maps of residual topography show a positive trend in eastern Oman that can be associated to the presence of a plume.

Incorporating a geodynamic perspective, our analysis of noise-mitigated Indian plate motion relative to Somalia reveals that India underwent a constant-velocity reorientation of approximately 15˚  from 48 to 30 Ma, concurrent with the arrival of the plume head beneath eastern Oman. We quantitatively demonstrate that increased asthenospheric flow induced by the plume flux in eastern Oman, adjacent to the Indian plate in the Eocene, may be responsible for deflecting the Indian plate path, as indicated in kinematic reconstructions.

The consequence of ignoring a plume in Oman is that we were unable to understand many of the enigmatic observations from plume impingement at ~40 Ma. Our study underscores the potential of combining seismology, geology, geochemistry, and geodynamics to be a more effective approach for detecting continental plumes than relying solely on surface volcanism, and has transformed our understanding of the tectonic evolution of the area and beyond.

How to cite: Pilia, S., Iaffaldano, G., Davies, R., Sossi, P., Whattam, S., and Hu, H.: Absence of surface volcanism and the indeterminate evidence for continental mantle plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7075, https://doi.org/10.5194/egusphere-egu24-7075, 2024.

EGU24-7255 | Orals | TS8.1

Short-period (400 kyr) pulsation of the Réunion plume 

Vincent Famin, Xavier Quidelleur, and Laurent Michon

Many hotspots worldwide display evidence of fluctuating magmatic emplacement rates in their history, at periods of 1-20 Myr, indicative of changing melt production within underlying mantle plumes. Here we report unprecedentedly short fluctuations of magmatic activity in the Réunion hotspot, emblematic because it started with the Deccan traps suspected to have caused the Cretaceous-Paleogene mass extinction. Using K-Ar geochronology, field observations, and geomorphology, we reconstructed the volcanic history of La Réunion and Mauritius islands, the two latest manifestations of the Réunion hotspot. Our reconstruction reveals coeval magmatic activity pulses and rest intervals for the two islands over the past 4 Ma. The period of these pulses, of ~400 kyr, is an order of magnitude shorter than any fluctuation found on other hotspots. Given the distance between La Réunion and Mauritius (~230 km), this synchronous short-period pulsation of the Réunion hotspot cannot stem from the lithosphere (≤70 km thick), and must be attributed to deeper plume processes. Moreover, this ~400 kyr periodicity coincides with the recurrence time of magmatic phases in the Deccan traps, suggesting that the pulsation began with the initiation of the hotspot. We propose that the Réunion plume is regularly pulsing with a periodicity of ~400 kyr, possibly since the Cretaceous-Paleogene transition, thus delivering extremely short-period waves of magma to the surface, synchronous over hundreds of kilometers. Understanding the geodynamic causes of this superfast beat of the Réunion plume is the objective of the four-year project “Plum-BeatR”, funded by the Agence Nationale de la Recherche (ANR- 23-CE49-0009), starting in 2024.

How to cite: Famin, V., Quidelleur, X., and Michon, L.: Short-period (400 kyr) pulsation of the Réunion plume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7255, https://doi.org/10.5194/egusphere-egu24-7255, 2024.

Plate tectonics plays a pivotal role in shaping the Earth's surface and is intricately linked to internal processes, including the subduction of cold slabs and the ascent of hot mantle plumes. Statistical analyses have unveiled a strong correlation between the distribution of large igneous provinces (LIPs) over the past 320 Ma and two large low-velocity provinces (LLVPs) beneath Africa and the Pacific Ocean. Consequently, hypotheses have emerged suggesting the long-term stability of these LLVPs. However, numerical modeling challenges this notion, suggesting that these basal mantle structures are mobile. To resolve these debates, we attempt to study these basal mantle structures from the evolution of intermediate-scale thermochemical anomalies. We report such an intermediate-scale thermochemical anomaly beneath the NW Pacific Ocean based on existing tomographic models and use paleogeographically constrained numerical models to study its evolution. Considering different plate configurations in North Pacific, our models consistently show that this anomaly was separated from the Perm anomaly by the subduction of the Izanagi slab in the Cretaceous. After the separation, it generated a mantle plume, inducing an oceanic plateau that got subducted beneath Kamchatka in Eocene. This scenario is consistent with multiple lines of evidence, including the seismic anomaly in the lower mantle, a seismically detected megameter-scale reflector that coincides with the subducted oceanic plateau and changes in Pacific Plate motion that correlated with the Eocene trench-plateau collision. We propose that intermediate-scale low velocity structures constantly undergo segregation and coalescing, and are sources of plumes that lie outside the two major LLVPs. Merging of the reported anomaly with the Pacific LLVP suggests the latter is still under assembly.

How to cite: Zhang, J. and Hu, J.: Segregation of thermochemical anomaly and associated deep mantle plume outside the large low-velocity provinces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8432, https://doi.org/10.5194/egusphere-egu24-8432, 2024.

EGU24-8563 | ECS | Orals | TS8.1

UPFLOW body wave tomography of the whole mantle column beneath the Azores-Madeira-Canaries region 

Maria Tsekhmistrenko, Ana Ferreira, and Miguel Miranda

We present initial tomographic findings from the ERC-funded UPFLOW (Upward mantle flow from novel seismic observations) project, showcasing results from a large-scale passive seismology experiment conducted in the Azores-Madeira-Canaries region between July 2021 and September 2022. Recovering 49 out of 50 ocean bottom seismometers (OBSs) in a ~1,000×2,000 km2 area with an average station spacing of ~150-200 km, we analyze approximately ~8000 multi-frequency (T ~2.7-30 s) body-wave travel time cross-correlation measurements derived from UPFLOW OBS data and over 120 teleseismic events. A preliminary P-wave tomographic model is presented, offering insight into the region's mantle dynamics.

Furthermore, by integrating UPFLOW's OBS data with global seismic data from both temporary and permanent stations, we expand the dataset to around 600,000 multifrequency measurements. This comprehensive dataset is employed to construct a global P-wave model, providing enhanced resolution throughout the entire mantle column beneath the Azores-Madeira-Canaries region. A comparative analysis with existing global tomography models is performed, and we discuss the geodynamical implications of our new, high-resolution model.

How to cite: Tsekhmistrenko, M., Ferreira, A., and Miranda, M.: UPFLOW body wave tomography of the whole mantle column beneath the Azores-Madeira-Canaries region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8563, https://doi.org/10.5194/egusphere-egu24-8563, 2024.

EGU24-8567 | Orals | TS8.1

Iceland plume and its magmatic manifestations: LIP-Dornröschen in the North Atlantic 

Alexander Koptev and Sierd Cloetingh

The North Atlantic region is a prime example of the interaction between plate tectonic movements and thermal instabilities in the Earth’s mantle. The opening of the Labrador Sea/Baffin Bay and the North Atlantic, the widespread volcanism and the localized uplift of the topography in Greenland and the North Atlantic are traditionally attributed to the thermal effect of the Iceland mantle plume. However, several prominent features of the region – the temporal synchrony of magmatism and break-up events, the symmetrical configuration of the Greenland-Iceland-Faroe Ridge, and the diachronous domal uplift of the North Atlantic rifted margins – have inspired alternative, “non-plume” views. According to these, the North Atlantic Igneous Province (NAIP) and Iceland magmatism originate from plate tectonic processes sourced in the shallow upper mantle, at odds with the unequivocal presence of deep-seated low-velocity seismic anomalies beneath Iceland and the isotopic signatures of plume-derived melts in Cenozoic magmatic units.

We resolve apparent contradictions in the observations and reconstructions and reconcile end-member concepts of the Late Mesozoic-Cenozoic evolution of the North Atlantic realm. We show that simultaneous Paleocene (~62-58 Ma) magmatism in Western Greenland/Baffin Island and the British Isles, which together form the NAIP, is driven by two processes accidently coinciding in time: 1) the propagation of the Labrador Sea/Baffin Bay spreading axis has overlapped with the ~100-80 Ma dated segment of the Iceland hotspot track near the West Greenland margin, while 2) the actual tail of the Iceland plume has reached the eastern continental margin of Greenland, allowing a horizontal flow of hot plume material along corridors of relatively thinned lithosphere towards Southern Scandinavia and Scotland/Ireland. In this framework, the subsequent formation of the symmetrical Greenland-Iceland-Faroe Ridge can be coherently explained by the continuous supply of hot plume material through an established channel between Eastern Greenland and the British Isles. In contrast to the Scotland/Ireland region, the South Norway continental lithosphere remains too thick to enable localized uplift of the topography and melting immediately after plume lobe emplacement at ~60 Ma. Therefore, the development of topographic domes in Southern Scandinavia only started ~30 Myr later in the Oligocene as a consequence of increasing ridge-push compression that built up during the opening of the Norwegian-Greenland Sea.

The evolution of the North Atlantic region shows that a thermal anomaly that has been hidden below a thick lithosphere for tens of Myr without signs of excessive magmatism can be re-initialized (or “re-awakened”) by the lateral propagation of spreading ridges or by the tapping of its source beneath thinner segments of the overlying lithosphere due to horizontal plate movements. We dub this type of Large Igneous Province (LIP) as LIP-Dornröschen (LIP-Sleeping Beauty). We hypothesise that the term LIP-Dornröschen may be applicable to a broad family of LIPs, including Precambrian and oceanic LIPs. This means that the interpretation of the timing of LIP formation from the perspective of mantle dynamics should be treated with caution, as there may be delays between the timing of upwelling in the mantle and detectable magmatic manifestations at or near the Earth’s surface.

How to cite: Koptev, A. and Cloetingh, S.: Iceland plume and its magmatic manifestations: LIP-Dornröschen in the North Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8567, https://doi.org/10.5194/egusphere-egu24-8567, 2024.

EGU24-9504 | ECS | Orals | TS8.1

Depth dependence of mantle plume flow beneath mid-ocean ridges 

Sibiao Liu, Fan Zhang, Lei Zhao, Xubo Zhang, and Jian Lin

Hotspot-related anomalies observed in mid-ocean ridge systems are widely interpreted as the result of upwelling mantle plumes interacting with spreading ridges. A key indicator of this interaction is 'waist width', which measures the distance of plume flow along the ridge. Current scaling laws for waist width, premised on a gradual decrease in plume temperature along the ridge, often overlook sub-ridge longitudinal thermal variations, potentially biasing width measurements at various depths. In this study, we refined waist width measurements by tracking the material flow and its thermal diffusion from the plume source in plume-ridge interaction models. These non-Newtonian viscoplastic models integrate ridge spreading, lithospheric cooling with hydrothermal circulation, and mantle dehydration. Model results show that the hot plume initially boosts upwelling from the deep mantle to near the dehydration zone, followed by a slowdown and lateral spread across and along the ridge. In addition to strongly correlating with plume flux and spreading rate, the pattern and distance of plume flow vary with depth. At deeper depths, the plume expands radially in a pancake-like thermal pattern with shorter along-ridge distances, while shallower, it shows an axial pipe-like dispersion over longer distances, forming a concave structure. This is shaped by the cooling of the plume material during the phase of decelerated upwelling and along-ridge dispersion within the dehydration zone and cooling of the oceanic lithosphere associated with plate spreading. Estimates of plume buoyancy flux, derived from both material- and isotherm-tracking waist widths, show significant variations at different depths, suggesting that understanding depth-dependent plume dynamics beneath mid-ocean ridges is crucial for reconciling the observed discrepancies in buoyancy flux estimates.

How to cite: Liu, S., Zhang, F., Zhao, L., Zhang, X., and Lin, J.: Depth dependence of mantle plume flow beneath mid-ocean ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9504, https://doi.org/10.5194/egusphere-egu24-9504, 2024.

EGU24-9647 | Posters virtual | TS8.1

Influence of the Kerguelen hotspot on eastern Indian lithosphere by trans-dimensional Bayesian inversion of Rayleigh wave dispersion data 

Nirjhar Mullick, Vivek Kumar, Gokul Saha, Shyam S. Rai, and Thomas Bodin

Mantle plumes play major role in modifying the continental lithosphere producing rifts and massive amounts of basaltic volcanism as the anomalously hot mantle undergoes decompressive melting. If conditions are favourable the rift may widen and a new ocean is formed. During the break up of Eastern Gondwana at ~ 130 Ma, the Kerguelen mantle plume influenced the separation of India from Antarctic and Australian plates and generation of the Eastern Indian Ocean. Eastern India-Bangladesh region (83-94ºE, 21-26ºN) carries imprints of the plume activity in the form of the Rajmahal and Sylhet traps and their subsurface expression in Bengal basin and extensive lamproytes. Existing geophysical studies of the region are mainly crustal scale and do not explicitly refer to the Kerguelen plume activity providing geophysical evidence for the same. We present here lithospheric shear velocity structure of the region up to a depth of ~ 175 km by trans-dimensional Baysian inversion of Rayleigh group velocity dispersion data (7-100s at 1º X 1º resolution). Using the same, we investigate the influence of the Kerguelen plume on the lithosphere of the Eastern India-Bangladesh region that comprises the Eastern India craton, the Bengal basin, the Bhrahmaputra basin, Bangladesh and the Shillong- Mikir plateau.

How to cite: Mullick, N., Kumar, V., Saha, G., Rai, S. S., and Bodin, T.: Influence of the Kerguelen hotspot on eastern Indian lithosphere by trans-dimensional Bayesian inversion of Rayleigh wave dispersion data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9647, https://doi.org/10.5194/egusphere-egu24-9647, 2024.

EGU24-10288 | Posters on site | TS8.1

Heterogeneous mantle source of Mauna Loa volcano (Hawai’ian plume) revealed by Sr-isotope and trace elements signatures of olivine-hosted melt inclusions 

Adrien Vezinet, Blas Barbera, Alexander V. Sobolev, Valentina G. Batanova, Charbel Kazzy, and Aleksandr V. Chugunov

Melt inclusions hosted in highly magnesian olivine crystals have proven invaluable for probing the composition of the mantle through time since their geochemical signature is reflecting that of parental melt. Additionally, the geochemical study of melt inclusions has shown to be more suited to identify the heterogeneity in the magma from which they crystallized, particularly the chemically depleted domains [1, 2]. Here, we will present new major, minor & trace elements, H2O contents and Sr-isotope signature of more than 300 olivine-hosted naturally quenched melt inclusions from Pu’u Wahi (910 yr-old) and Puʻu Mahana (ca. 50 kyr-old), two ash cones associated with Mauna Loa, the largest shield volcano of the Hawai’ian seamount chain. In order to have a high degree of confidence in the geochemical proxies, Sr-isotope and trace elements analyses were conducted through laser ablation split stream (LASS) protocol on top of EPMA and Raman (for H2O contents) analytical spots. Preliminary results in our new set of inclusions show the presence of high (Sr/Ce)N inclusions, previously interpreted as indicating either gabbro influence in the source of the plume [3] or interactions between plagioclase-rich cumulates and percolating mantle-derived melts [4]. Further, “ultra-depleted melts”, UDM, indicated by K2O contents < 0.1 wt.% identified in [1], have also been re-identified in this new set of inclusions (not analyzed for Sr-isotope yet). 87Sr/86Sr of non-UDM inclusions ranges from 0.70361±0.00025 to 0.70427±0.00025, i.e. analogous to the most recent TIMS values [4, 5]. Additional LASS analyses will be conducted before the meeting. The full set of analyses will be confronted to published results on the same volcano [1, 3-6] and integrated in a larger framework of interactions between mantle plume and consequences for plate tectonic.

References:

  • Sobolev, A.V., et al., Nature, 2011. 476(7361).
  • Stracke, A., et al., Nature Geoscience, 2019. 12(10).
  • Sobolev, A.V., et al., Nature, 2000. 404(6781).
  • Anderson, O.E., et al., Geochemistry, Geophysics, Geosystems, 2021. 22(4).
  • Reinhard, A., et al., Chemical Geology, 2018. 495.
  • Sobolev, A.V., et al., Nature, 2005. 434(7033).

How to cite: Vezinet, A., Barbera, B., Sobolev, A. V., Batanova, V. G., Kazzy, C., and Chugunov, A. V.: Heterogeneous mantle source of Mauna Loa volcano (Hawai’ian plume) revealed by Sr-isotope and trace elements signatures of olivine-hosted melt inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10288, https://doi.org/10.5194/egusphere-egu24-10288, 2024.

EGU24-10507 | ECS | Posters on site | TS8.1

The density and viscosity of a bilithologic plume-fed asthenosphere 

Jia Shao and Jason Morgan

Pyroxenites are generated by the subduction of sediments and oceanic basalts into the deep mantle. These rocks, together with the larger volume fraction of their surrounding mantle peridotites make up a lithologically heterogeneous two-component mantle, sometimes called a ‘marble-cake’ or ‘plum-pudding’ mantle. Geochemical and petrological observations have shown that pyroxenites play a significant role in the genesis of oceanic island basalts (OIB). However, the consequences of preferential pyroxenite melting on bulk mantle properties have yet to be systematically explored. For example, how does the plume melting process modify a plum-pudding mantle’s bulk density and viscosity? This question could be very important, in particular if the asthenosphere is formed by material from upwelling, melting plumes.

To explore the above questions, we use the thermodynamic software Perple_X to determine densities for different degrees of depleted (i.e. partially melted) peridotites and pyroxenites. We then include these relations into a one-dimensional numerical simulation code for the upwelling and pressure-release melting of a potentially wet multi-component mantle. We investigate the density changes associated with the melting of this idealized mantle’s pyroxenites and peridodites, and also the viscosity change by assuming that the reference viscosity of pyroxenite is 10-100 times that of dry peridotite at similar P-T conditions, since the peridotite’s olivines are the weakest large volume-fraction minerals in the upper mantle. We have explored the effects of mantle temperature, initial water contents, initial fractions of pyroxenites and peridotite, peridotite solidi, and the thickness of the overlying lithosphere which will affect the depth-interval of upwelling and melting. Preliminary results show that significant density and viscosity changes should take place during plume upwelling and melting. ~30% partial melting of pyroxenite would lead to a net bulk density reduction of 0.3%, comparable to the thermal buoyancy associated with a ~100° temperature increase. As long as the surrounding peridotites do not melt, the mixture’s aggregate viscosity will remain that of wet peridotitic mantle; after the peridotites have melted a percent or so, the aggregate viscosity will increase 10-100-fold to that of dry peridotite. This could lead to the formation of a 10-100x asthenospheric viscosity restitic hotspot swell root. Eventual peridotitic melting will reduce the density of the more depleted peridotites relative to fertile peridotite as originally noted by Oxburgh and Parmentier (1977), but to a lesser degree than the density reduction associated with the preferential removal of pyroxenites by their partial melting. A dynamical consequence is that the asthenosphere is likely to be strongly stratified by density, with its most pyroxenite-depleted materials likely to rise to form a layer along the base of the overlying oceanic lithosphere. 

How to cite: Shao, J. and Morgan, J.: The density and viscosity of a bilithologic plume-fed asthenosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10507, https://doi.org/10.5194/egusphere-egu24-10507, 2024.

EGU24-10967 | ECS | Posters on site | TS8.1

From plumes to subduction network formation and supercontinent break-up 

Michaël Pons, Stephan V. Sobolev, Charitra Jain, and Elodie Kendall

The evolution of modern plate tectonics is described by the Wilson cycle, which portrays the dynamics of the supercontinental cycle through the interaction of the oceanic plate with the continental plate over periods of hundreds of millions of years. This cycle is characterized by a phase of supercontinent assembly and enhanced orogenic collision, followed by a phase of supercontinent fragmentation and dispersal, as shown by the geological record. The dynamics of the Wilson cycle is intrinsically linked to mantle convection and subduction dynamics. While the assembly phase appears to follow a degree-2 mantle convection style, the mechanism responsible for supercontinent fragmentation is still debated. We hypothesize that the dispersal phase is mostly governed by trench roll-back from subductions and mantle plumes. To test this hypothesis, we have built a series of 2D and 3D geodynamic models of the Earth on a global scale using the ASPECT code. We have tested different scenarios in which we prescribe the distribution of the supercontinent Rodinia at 1Ga or Pangea at 250 Ma and let the models evolve self-consistently.  In some model variants, the strength of the supercontinent and that of the surrounding oceanic area is changed. We will present our preliminary results and discuss the dynamics of continental dispersal and its link to subduction and mantle dynamics. In particular, 3D models will demonstrate how regional plume-induced retreating subduction zones evolve into a global network of subduction zones and tectonics plate boundaries which ultimately leads to the break-up of the supercontinent.

How to cite: Pons, M., V. Sobolev, S., Jain, C., and Kendall, E.: From plumes to subduction network formation and supercontinent break-up, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10967, https://doi.org/10.5194/egusphere-egu24-10967, 2024.

While the temperature drop across the thermal boundary layer (TBL) at the base of the mantle is likely > 1000 K, the temperature anomaly of plumes, which are believed to rise from that TBL is only up to a few hundred K. Reasons for that discrepancy are still poorly understood. It could be due to a combination of (1) the adiabat inside the plume being steeper than in the ambient mantle, (2) the plume cooling due to heat diffusing into the surrounding mantle as it rises, (3) the hottest plume temperature representing a mix of temperatures in the TBL, and not the temperature at the core-mantle boundary (CMB), (4) plumes not directly rising from the CMB due to chemically distinct material at the base of the mantle, (5) a plume-fed asthenosphere which is on average warmer than the mantle adiabat, reducing the temperature difference between plumes and asthenospheric average. Here we use the ASPECT software to model plumes from the lowermost mantle and study their excess temperatures. We use a mantle viscosity that depends on temperature and depth with a strong viscosity increase from below the lithosphere towards the lower mantle, reaching about 1023 Pas above the basal TBL, consistent with geoid modelling and slow motion of mantle plumes. With a mineral physics-derived pyrolite material model, the difference between a plume adiabat and an ambient mantle adiabat just below the lithosphere is about two thirds of that at the base of the mantle, e.g. 1280 K temperature difference at the CMB reduces to about 835 K at 200 km depth. In 2-D cartesian models, plume temperature drops more strongly and is rather time variable due to pulses rising along plume conduits. In contrast, 3-D models of isolated plumes are more steady and, after about 10-20 Myr after the plume head has reached the surface, their temperatures remain rather constant, with excess temperature drop compared to an adiabat for material directly from the CMB usually less than 100 K. This extra temperature drop is small because plume buoyancy flux is high. Hence the above points (2) and (3) do not contribute much to reduce temperature of isolated 3-D plumes. In our models, the asthenosphere is on average about 200-400 K hotter than the mantle beneath, due to plume material feeding into it. While this appears to reduce the plume temperature anomaly, a resulting cooler mantle adiabat also corresponds to an even stronger temperature drop in the basal TBL, offsetting that effect. In the Earth, plumes are likely triggered by slabs and probably rise preferrably above the margins of chemically distinct piles. This could lead to reduced excess temperatures, if plumes are more sheet-like, as the 2-D models, or temperature at their source depth is less than at the CMB.

How to cite: Steinberger, B. and Roy, P.: Why are plume excess temperatures much less than the temperature drop across the core-mantle boundary?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11566, https://doi.org/10.5194/egusphere-egu24-11566, 2024.

EGU24-11719 | Orals | TS8.1

Prospects of Neutrino Oscillation Tomography of the Earth  

Veronique Van Elewyck, Joao Coelho, Yael Armando Deniz Hernandez, Stephanie Durand, Nobuaki Fuji, Edouard Kaminski, Lukas Maderer, Eric Mittelstaedt, and Rebekah Pestes

Much has been learned about the deep Earth through a combination of geophysical constraints, theories of Earth’s formation, and seismic measurements. However, such methods alone cannot directly resolve the full structure of the inner Earth, e.g. in terms of matter density, composition and temperature distributions.

Complementary information about Earth’s interior can be provided by small, nearly massless elementary particles called neutrinos that propagate through the Earth. Neutrinos exist in different flavours and are known to experience a quantum phenomenon of flavour oscillation as they propagate. With an extremely small chance of interacting with matter, neutrinos can travel long distances through very dense materials (e.g., the Earth’s core). For atmospheric neutrinos of energy ~GeV crossing the Earth, the flavour oscillation patterns are distorted due to coherent forward scattering on electrons along their path. Measuring the flavour, energy and angular distributions of such neutrinos therefore provides sensitivity to a new observable of geophysical interest: the electron number density in the layers of matter traversed.

After a short introduction to the concepts of neutrino oscillation tomography, we will discuss the potential of this method to address open questions concerning inner Earth's structure and composition (such as the amount of light elements in the core and the nature of LLSVPs), the status of sensitivity studies, and the perspectives opened by the next generation of atmospheric neutrino detectors.

How to cite: Van Elewyck, V., Coelho, J., Deniz Hernandez, Y. A., Durand, S., Fuji, N., Kaminski, E., Maderer, L., Mittelstaedt, E., and Pestes, R.: Prospects of Neutrino Oscillation Tomography of the Earth , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11719, https://doi.org/10.5194/egusphere-egu24-11719, 2024.

The Rajmahal Traps is one of the two major Large Igneous Provinces (LIPs) that erupted in the Indian subcontinent in the Mesozoic. The trap was the product of activity at the Kerguelen hotspot, located in the Indian Ocean, that initiated around 117 Ma. Earlier studies on the eruption location of the Rajmahal trap show that its location does not coincide with the present-day location of the Kerguelen Hotspot. This difference in the paleo-locations could be the result of mantle dynamics beneath the Indian Ocean during the Cretaceous and has been explained with concepts such as the multiple diapir-single plume model, the migration pathway of the hotspot beneath the mantle, and the complex plume-ridge interaction.

In this study, we use paleogeographic reconstruction software GPlates to reconstruct the paleogeography of the Rajmahal Traps on the Indian subcontinent plate in an Antarctica fixed reference frame since 117 Ma to pin-point the paleo-location of the Kerguelen hotspot and eruption location of the Rajmahal trap along with the tectonic changes that the Indian Ocean was encountering. The mantle structure below the Indian Ocean was further studied using publicly available P-wave tomography data. The paleogeographic reconstruction linked to the mantle structure hints towards the presence of a tree-like hotspot-plume structure beneath the Kerguelen hotspot where a deep-seated single plume feeds into various fissures at the surface which are active at different points in time.

Our kinematic analysis for the Indian Plate reveals significant changes in the velocity of the plate since the Cretaceous at specific points in time in response to tectonic activities initiated by the plumes present in the Indian Ocean. These activities that link to changes in the velocity include interactions with the Morondova plume (velocity increase at 90 Ma) and Reunion hotspot (velocity increase between 78 – 62 Ma), and other processes like continental collision (velocity decrease at 56 Ma and between 50-43 Ma) and slab pull (velocity increase at 56 Ma). Using this new velocity profile, we have developed a revised velocity model for the drift of the Indian subcontinent since the Cretaceous.

How to cite: Guleriya, S., Beniest, A., and Tiwari, S. K.: Change in eruption location in Kerguelen hotspot and Kinematic Reconstruction of Rajmahal Trap:  Implications for Cretaceous to present day Geodynamics of Indian plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11883, https://doi.org/10.5194/egusphere-egu24-11883, 2024.

EGU24-12584 | Orals | TS8.1

Robust hotspot origin far from LLSVP margins 

John Tarduno

W. Jason Morgan’s seminal development of plate tectonic theory set the foundation for current investigations of mantle convection and the nature of deep mantle plumes. More recently, hotspots have been proposed to occur at the edges of stationary African and Pacific large low shear velocity provinces (LLSVPs) and that this has a special significance in terms of plume/hotspot generation. The basis for this proposed global correlation has in turn been challenged, and whether LLSVPs edges are the sites of initial mantle plume formation debated. A different approach is to consider hotspots with the greatest buoyancy flux because to be successful, any global model should be able to explain their origin. In all analyses of buoyancy flux, the Pacific’s Hawaiian hotspot, which figured prominently in Jason’s early papers, stands out above all others. However, paleomagnetic and age-distance relationships indicate that the Hawaiian hotspot originated >1500 km N of the Pacific LLSVP and subsequently drifted to its edge where it may have become anchored. The hotspot with the highest buoyancy flux in the Atlantic is Iceland, which is far from the African LLSVP. Iceland represents the youngest of three past episodes of extraordinary volcanism affecting the North Atlantic-Arctic region, namely the North Atlantic Tertiary Volcanic Province, the High Arctic Large Igneous Province, and the Siberian Traps. This recurrent volcanism spanning more than 250 million years requires either drift of a single pulsing plume, or separate plumes, generated far from the edge of the proposed stationary African LLSVP. Thus, the nature and histories of these robust hotspots in the Pacific and Atlantic imply an origin distinct from stationary LLSVPs.  

How to cite: Tarduno, J.: Robust hotspot origin far from LLSVP margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12584, https://doi.org/10.5194/egusphere-egu24-12584, 2024.

EGU24-13570 | Orals | TS8.1

Changes in the Rate of Ocean Crust Production Over the Past 19 Myr: Implications for Sea Level, Mantle Heat Loss, and Climate 

Colleen Dalton, Timothy Herbert, Douglas Wilson, and Weimin Si

The rate of ocean-crust production exerts control over mantle heat loss, sea level, seawater chemistry, and climate. Reconstructing ocean-crust production rates back in time relies heavily on the distribution of present-day seafloor age. Different strategies to account for the incomplete preservation of older seafloor have led to differing conclusions about how much production rates have changed since the Cretaceous, if at all. We have constructed a new global synthesis of ocean-crust production rates along 18 mid-ocean ridges for the past 19 Myr at high temporal resolution.  We find that the global ocean-crust production rate decreased by ~37% from its maximum during 19-15 Ma to its minimum during 6-4 Ma. Our ability to resolve these changes at a statistically significant level is due to the availability of many new plate reconstructions at high temporal resolution and our use of an astronomically calibrated magnetic time scale with small uncertainties in reversal ages. We show that the reduction in crust production occurred because spreading rates slowed down along almost all ridge systems. While the total ridge length has varied little since 19 Ma, some fast-spreading ridges have grown shorter and slow-spreading ridges grown longer, amplifying the spreading-rate changes. The change in crust production rate skews the seafloor area-age distribution toward older crust, and we estimate that sea level may have fallen by as much as 32-37 m and oceanic heat flow may have been reduced by 6%. We also show, using a simple model of the carbon cycle, that the inferred changes in tectonic degassing resulting from the crust-production changes can account for the majority of long-term surface-temperature evolution since 19 Ma.

How to cite: Dalton, C., Herbert, T., Wilson, D., and Si, W.: Changes in the Rate of Ocean Crust Production Over the Past 19 Myr: Implications for Sea Level, Mantle Heat Loss, and Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13570, https://doi.org/10.5194/egusphere-egu24-13570, 2024.

EGU24-13786 | ECS | Posters on site | TS8.1

Counterflow and entrainment within a buoyant plume-fed asthenosphere 

Xianyu Li, Jia Shao, Guanzhi Wang, Yanan Shi, and Jason Morgan

Laboratory and numerical experiments and boundary layer analysis of the entrainment of buoyant asthenosphere by subducting oceanic lithosphere (cf. Morgan et al., Terra Nova, 2007) implies that slab entrainment is likely to be relatively inefficient at removing a buoyant and lower viscosity asthenosphere layer. Such asthenosphere would instead be mostly removed by accretion into overlying oceanic lithosphere, both at mid-ocean ridges where a ~60-km compositional lithosphere forms due to the melt-induced dehydration of upwelling peridotitic mantle, and later with the thermal growth of  overlying oceanic lithosphere. When an oceanic plate subducts, the lower (hot) side of a subducting slab entrains a 10– 30 km-thick downdragged layer, whose thickness depends upon the subduction rate and the density contrast and viscosity of the asthenosphere, while the upper (cold) side of the slab may entrain as much by thermal ‘freezing’ onto the slab as by mechanical downdragging.  

Here we use 2-D numerical experiments to investigate the dynamics of entrainment and counterflow at subduction zones. We explore situations with both stable subduction geometries and slab rollback. Due to its low viscosity, a plume-fed asthenosphere is particularly likely to be stratified in its internal density, with variable amounts of plume melt-extraction leading to variable pyroxenite fractions and associated vertical density stratification within a bilithologic ~80-90% peridotite, ~10-20% pyroxenite asthenosphere. While this type of vertical density stratification appears to lead to similar predicted entrainment by subducting slabs, it will generate more complex patterns of asthenospheric counterflow that involve shallower and time-dependent counterflow behind the subducting slab.

How to cite: Li, X., Shao, J., Wang, G., Shi, Y., and Morgan, J.: Counterflow and entrainment within a buoyant plume-fed asthenosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13786, https://doi.org/10.5194/egusphere-egu24-13786, 2024.

EGU24-13826 | ECS | Posters on site | TS8.1

Understanding Ni-Cu Sulphide Deposits in a Plate Tectonic and Mantle Convection Context 

Isadora Page, Ben R. Mather, Nicole Januszczak, Michele Anthony, and R. Dietmar Muller

Nickel-Copper (Ni-Cu) sulphide deposits are a diverse class of deposits, formed during the cooling and crystallisation of metal-rich mafic to ultramafic magmas. Despite sharing several key ore-forming processes, many of these deposits form in contrasting geologic environments and periods. The objective of this research project is to investigate the spatial and temporal distribution of Ni-Cu sulphide deposits in a mantle convection and plate tectonic context, and to explore the influence of different mantle and tectonic parameters on their origins and occurrence. We first determine the location of these deposits in relation to relevant geologic and tectonic features through time, including subduction zones, large igneous provinces (LIPs), and mantle plumes. Using a 1 billion year plate model we extract key parameters relating to subduction, as well as the spatio-temporal distribution of LIPs through time. Employing an associated geodynamic model, we identify model mantle plumes and quantify their key properties. Preliminary findings indicate that certain mantle plumes associated with deposits exhibit increased plume flux in the upper mantle preceding deposit formation, and that many deposits are spatially associated with LIPs throughout their formation history. For several deposits located in convergent margin settings, we have identified a notable spike in subduction volume and convergence rate during a 50-100 million year period prior to the onset of mineralisation. While the angle of the subducting slab is highly variable throughout the evolution of these deposits, several deposits are associated with a distinct steepening of the subducting plate in the lead-up to deposit formation. The findings of this study aim to contribute new insights into the dynamic processes governing the genesis of magmatic Ni-Cu sulphide deposits. These insights aid in our understanding of the interplay between mantle dynamics, plate tectonics, and deposit formation, and hold implications for future critical mineral exploration.

How to cite: Page, I., Mather, B. R., Januszczak, N., Anthony, M., and Muller, R. D.: Understanding Ni-Cu Sulphide Deposits in a Plate Tectonic and Mantle Convection Context, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13826, https://doi.org/10.5194/egusphere-egu24-13826, 2024.

EGU24-13939 | ECS | Posters on site | TS8.1

Numerical exploration of the dynamics of the subduction plate boundary channel  

Guanzhi Wang, Jason P. Morgan, and Paola Vannucchi

The plate ‘interface’ at subduction zones has often been idealized as a single fault with ‘asperities’, however there is increasing evidence that plate boundary motions typically occur across a ~100-1000m channel or shear zone. Here we investigate the dynamics of slip in a mechanically heterogeneous plate boundary shear zone, and will typically use periodic boundary conditions to model the channel at a ~m-scale.  In contrast to most previous numerical studies, we imagine that this shear zone is embedded within finite strength wall-rock associated with the downgoing and overriding plates that themselves are capable of subduction-related deformation, for example during bend-faulting of the lower-plate or a forearc deformation event. We first look at how stress-concentrations can form by the clogging of strong blocks in a channel with a weaker matrix. We find that the strength of the surrounding wall-rock will play a key role in the channel’s response to a clogging event. In general, a clogging event can be mitigated by failure of surrounding relatively weak wallrock along the edges of a subduction channel in the conceptual process put forward by von Huene et al. (2004) to drive basal erosion of the forearc. We also consider cases where metamorphic transitions have led to the existence of weaker blocks within a stronger matrix. In this case, frequent tremor-like failure of the weak blocks can coexist with rarer earthquake failure of the stronger surrounding matrix.  Finally we explore the mechanical effects of channel widening and narrowing events that will invariably lead to a component of local pressure-driven flow within a subduction shear channel. Numerical snapshots and videos are used to visualize these potential modes of subduction shear zone deformation.

How to cite: Wang, G., P. Morgan, J., and Vannucchi, P.: Numerical exploration of the dynamics of the subduction plate boundary channel , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13939, https://doi.org/10.5194/egusphere-egu24-13939, 2024.

EGU24-14528 | Posters on site | TS8.1

Using Dynamic Topography and Seismic Tomography to explore the compensation of seafloor in oceanic and back-arc basins 

Jialei Qiu, Nadia Padavini, Paola Vannucchi, and Jason Morgan

Both dynamic topography and seismic tomography have played crucial roles in providing invaluable insights into the Earth's interior structure and geological processes. Here we explore to what degree dynamic topography within ocean and back-arc basins can be correlated with the upper mantle seismic structure that has been imaged in recent high-resolution global models.

To explore the global ocean dynamic topography associated with subsurface mantle convection, we need to remove the influences of known contributing factors to seafloor relief such as the cooling of the ocean floor and the thickness of the ocean crust and sediments. We developed a series of scripts in PyGMT and MATLAB to do this, based on seafloor ages in GPLATES and sediment/crust information in CRUST1.0. With these corrections for near-surface structure, we obtained global average residual-depth values that serve as a basis for analyzing global subsurface structures linked to the asthenosphere and upper mantle, which we then compare to the vertically averaged shear-wave seismic structure above the transition zone. Our preliminary study highlights that the significant ~km-difference in dynamic topography between the Philippine back-arc basin and the Lau-Tonga backarc appear to be linked to a major difference in asthenosphere thickness and density beneath these two regions.

How to cite: Qiu, J., Padavini, N., Vannucchi, P., and Morgan, J.: Using Dynamic Topography and Seismic Tomography to explore the compensation of seafloor in oceanic and back-arc basins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14528, https://doi.org/10.5194/egusphere-egu24-14528, 2024.

EGU24-16479 | Posters on site | TS8.1

H, He, and seismic evidence for a bilithologic plume-fed asthenosphere  

Jason P. Morgan and W. Jason Morgan

Chemical diffusion in the mantle has typically been viewed to play a negligible role in geodynamic processes.  However, diffusion rates for water (H) and helium (He) are large enough that they lead to observable differences between pyroxenite-rich melting associated with ocean island volcanism (OIB) and more peridotite-rich melting associated with mid-ocean ridge basalts (MORB). Laboratory measurements of diffusion rates of H and He at ambient mantle temperatures in olivine are of order ~10 km/1.7Gyr for He and ~250 km/1.7 Gyr for H. If the mantle is an interlayered mixture of recycled oceanic basalts and sediments surrounded by a much larger volume of residual peridotites, then chemical diffusion can shape the mantle in two important ways.  Hydrogen will tend to migrate from peridotites into adjacent pyroxenites, because clinopyroxene has a much stronger affinity for water than the olivine and orthopyroxene that form the bulk of mantle peridotites. Therefore pyroxenite lithologies will typically have twice or more the water content of their surrounding damp peridotites. This will strongly favor the enhanced melting of pyroxenites that is now mostly agreed to be a common feature of the OIB source. Radiogenic 4He will have the opposite behaviour — it will tend to migrate from where it is produced in recycled incompatible-element-rich (e.g. U and Th-rich) pyroxenites into nearby, larger volume fraction, but U+Th-poorer peridotites, while the radioisotopes of Ar and Ne that are also produced by the decay of the incompatible elements K, U, and Th will diffuse much less, and thus remain within their original pyroxenite source.  This effect leads to lower 4He/21Ne and 4He/40Ar ratios in OIB in comparison to the predicted values based on the mantle’s bulk geochemistry, and complementary higher 4He/21Ne and 4He/40Ar ratios in the MORB source that is formed by the plume-fed asthenospheric residues to OIB melt extraction at plumes.

 The recent observation of a 150-km-deep positive shear velocity gradient (PVG) beneath non-cratonic lithosphere (Hua et al., 2023) is further evidence for the initiation of pyroxenitic melting at this depth within the asthenosphere. It also implies that lateral temperature variations at this depth are quite small, of order +/- 75°C. This near uniformity of temperatures near both mantle plumes and mid-ocean ridges is, in turn, strong evidence in favor of the hypothesis that the asthenosphere is fed by mantle plumes. We propose that two filtering effects occur as plumes feed the asthenosphere, removing both the hottest and coldest parts of upwelling plume material. First, the peridotite fraction in the hottest part of upwelling plume material melts enough for it to dehydrate, thereby transforming this fraction into a more viscous and buoyant hotspot swell root that moves with the overlying plate, not as asthenosphere. Second, since plume material is warmer than average mantle, it is more buoyant, creating a natural density filter that prevents any cooler underlying mantle from upwelling through it. These rheological and density filters make the asthenosphere sampled by melting at mid-ocean ridges have a more uniform temperature than its typical underlying mantle.

How to cite: Morgan, J. P. and Morgan, W. J.: H, He, and seismic evidence for a bilithologic plume-fed asthenosphere , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16479, https://doi.org/10.5194/egusphere-egu24-16479, 2024.

EGU24-17078 | ECS | Orals | TS8.1

Insight into the formation of the Siberian Large Igneous Province: A study of olivine-hosted melt inclusion in meimechite 

Mateo Esteban, Alexander Sobolev, Valentina Batanova, Adrien Vezinet, Evgeny Asafov, and Stepan Krasheninnikov

Meimechite (i.e., rare high MgO and TiO2 ultramafic rocks) concluded the Permo-Triassic Trap magmatism ca. 250 Ma-ago, known as a Siberian Large Igneous Province (SLIP) in the Meimecha-Kotui region, northern Siberia (e.g. [1]). In addition to their elevated MgO contents, meimechite’s melts display almost no crustal contamination, making them ideally suited to investigate the mantle source of the SLIP. Formerly, two opposing models were evoked for the origination of the meimechite: i) the hottest phanerozoic mantle plume [1] or ii) water fluxing of the asthenospheric mantle in a long-lived subduction zone [2]. Based on an extended analytical workflow we will shed new light on the source of these unusual rocks.

Here we present new results for more than 300 olivine-hosted homogenized melt inclusions from Siberian meimechite including major, minor and trace elements, water and Sr-isotopes contents (EPMA, LA-ICP-MS and Raman spectrometry) along with the chemical composition of their host olivine (EPMA, LA-ICP-MS). When encountered, spinel inclusions were analysed by EPMA for major element abundances.

We show that the Siberian meimechite crystallised from a highly magnesian (MgO > 22 wt%) parental melt deficient in H2O compared to Ce and K concentrations, which was degassed of most of its CO2 and likely part of its H2O while rising to shallower depths. Three independent geothermometers (Mg-Fe and Sc-Y olivine melt and Al olivine-spinel) confirm the high crystallisation temperature of the Siberian meimechite, ca. 1400oC. Furthermore, the calculated potential temperatures (over 1500oC) imply a mantle plume origin of the Siberian meimechite and, consequently, of the SLIP.

Initial 87Sr/86Sr values of melt inclusions reveal heterogeneous populations ranging from 0.7022±0.0002 to 0.7039±0.0004 suggesting mixing between at least two depleted mantle components. The less depleted group has an average Bulk Silicate Earth (BSE) model age of 876±88 Ma, whereas the more depleted group is significantly older with an average model age of 1716±76 Ma. All source components display significantly fractionated proxies of continental crust extraction (Nb/U, Th/U and Ce/Pb [3]), indicating major events of continental crustal formation and deep recycling of residual lithosphere before the Proterozoic Eon.

References:

[1] – Sobolev, A.V., et al., Russ. Geol. Geophys., 2009 and references therein. [2] – Ivanov, A.V., et al., Chem. Geol., 2018. [3]- Hofmann, A.W. et al. EPSL, 1986.

How to cite: Esteban, M., Sobolev, A., Batanova, V., Vezinet, A., Asafov, E., and Krasheninnikov, S.: Insight into the formation of the Siberian Large Igneous Province: A study of olivine-hosted melt inclusion in meimechite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17078, https://doi.org/10.5194/egusphere-egu24-17078, 2024.

EGU24-17341 | ECS | Orals | TS8.1

The Influence of Mantle Plumes on Plate Tectonics 

Ingo L. Stotz, Berta Vilacís, Jorge N. Hayek, Sara Carena, Anke Friedrich, and Hans-Peter Bunge

Our understanding of plate tectonics and mantle convection has made significant progress in recent decades, yet the specific impact of mantle plumes on plate tectonics remains a topic of controversy. The motions of the Earth’s lithosphere serves as a powerful lens into the dynamic behavior of the asthenosphere and deeper mantle, helping to untangle such controversies. Surface observations, therefore, provide important constraints on mantle convection patterns through space/time. Among these observations, the record of plate motion changes stands out, as it enables the geographical identification of torque sources. Consequently, surface observations provide essential constraints for theoretical models and numerical simulations.

The analytical Poiseuille flow model applied to upper mantle flux in the asthenosphere offers a robust and testable prediction: Poiseuille flow induced plate motion changes should coincide with regional scale mantle convection induced elevation changes. Mantle plumes can generate such pressure driven flows, along with intraplate magmatism and induce buoyancy-driven uplift that leaves an imprint in the sedimentary record.

Here, I will present a synthesis of geological and geophysical observations, supported by analytical calculations, to illustrate that a significant number of plate motion changes can be attributed primarily to torques originating from mantle plumes.

How to cite: Stotz, I. L., Vilacís, B., Hayek, J. N., Carena, S., Friedrich, A., and Bunge, H.-P.: The Influence of Mantle Plumes on Plate Tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17341, https://doi.org/10.5194/egusphere-egu24-17341, 2024.

Models depicting the plate kinematic development of the Indian Ocean have a range of applications including in paleogeographic studies and in formulating and testing ideas about plume/plate interactions. Until now, these applications have been forced to tolerate egregious model/observation inconsistencies concerning the relative motion history of India and Madagascar. Whilst the Phanerozoic record of these motions begins with ∼90 Ma basalts that erupted along a narrow rift basin, all modern plate kinematic models for the Indian Ocean predict hundreds of kilometres of relative motions, in diverse and conflicting senses, over several tens of millions of years prior to the eruptions. The diversity of these predicted motions suggests they are artefacts that arise from differing approaches taken to modelling the development of the eastern and western parts of the ocean, rather than a reflection of insufficient or absent geological observations. In this contribution, I present a new model for the early plate kinematic development of the Indian Ocean that is constrained by observational evidence for relative plate motion azimuths in the Enderby and western Bay of Bengal basins and by explicitly maintaining a rigid mid- and early Cretaceous Indo-Malagasy body. This approach requires the model to feature two small tectonic plates between the continental margins of eastern India and East Antarctica. The older of the two, Mandara, is an intraoceanic plate in the Enderby Basin that may have formed in relation to delivery of excess melt from the Kerguelen plume to the basin's mid-ocean ridge. The younger plate, Vasuki, in the western Bay of Bengal Basin, also accommodated plume-related melt at its boundaries, in its case from the Marion and possibly also the Crozet plume. The model shows this plate transporting Sri Lanka ∼800 km southwards along the eastern Indian continental margin to its present location. The model also requires the presence of around half a million square kilometres of continental crust beneath the Kerguelen Plateau, which lies within the range of published observation-led estimates of its extent. Neither the absence of evidence for relative motions between India and Madagascar prior to ∼90 Ma, nor the modelled Euler rotation pole's location afterwards, are consistent with suggestions that traction forces related to the ascent of the Marion plume drove the mid-Cretaceous onset of subduction in the western Neotethys.

How to cite: Eagles, G.: A new model of plate kinematics describing the early development of the Indian Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17862, https://doi.org/10.5194/egusphere-egu24-17862, 2024.

EGU24-18017 | Orals | TS8.1

Flexural Pumping and the Origins of Petit-Spot Volcanism 

Paola Vannucchi, Yanan Shi, Ting Yang, Gou Fujie, and Jason P. Morgan

Most volcanic activity on Earth is linked to well-known processes like plate tectonics and mantle plumes, typically through mechanisms such as flux-melting in subduction zones and decompression-melting at ridges and mantle plumes. However, recent discoveries point to a different origin for some intraplate volcanism, a key example being 'Petit-Spots'—small volcanic mounds that erupt on incoming plates near subduction zones. Here we propose that flexural pumping, occurring as the subducting slab unbends, transports fluids released by intra-slab dehydration to the slab's base where these fluids induce flux-melting in the warm slab base and asthenosphere beneath the slab. Counterflow in the buoyant asthenosphere beneath the subducting plate further expands the region of petit-spot volcanism. This mechanism not only explains the origin of petit-spot volcanism but also suggests a broader conceptual model for generating low-degree melts in the oceanic asthenosphere.

How to cite: Vannucchi, P., Shi, Y., Yang, T., Fujie, G., and Morgan, J. P.: Flexural Pumping and the Origins of Petit-Spot Volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18017, https://doi.org/10.5194/egusphere-egu24-18017, 2024.

EGU24-18296 | ECS | Posters on site | TS8.1

How could a single Iceland Plume produce the widely scattered North Atlantic Igneous Province volcanism? New clues from Britain and Ireland. 

Raffaele Bonadio, Sergei Lebedev, David Chew, Yihe Xu, and Javier Fullea

The extensive Paleocene magmatism of the British and Irish Tertiary Igneous Province (BITIP)—a part of the North Atlantic Igneous Province (NAIP)—was accompanied by significant uplift and exhumation, as evidenced by geothermochronological and other data. The enigmatic origins of the volcanism and uplift are debated. The Iceland Hotspot reached the North Atlantic at that time and could probably supply anomalously hot asthenospheric material to the volcanic areas of NAIP, but they were scattered over a broad area thousands of kilometres across. This motivates alternative, non-plume explanations.

Here, we obtain a map of the lithosphere-asthenosphere boundary (LAB) depth in the region using thermodynamic inversion of seismic surface-wave data. Love and Rayleigh phase velocity maps in broad period ranges were computed using optimal resolution tomography with direct model error estimation and supplied the data for the inversion.

Our results reveal a consistently thinner-than-average lithosphere beneath the Irish Sea and surroundings, encompassing northern Ireland and western Scotland and Wales. The Paleocene uplift, BITIP volcanism and crustal underplating are all located in the same regions, which are underlain, consistently, by anomalously thin lithosphere.

The previously unknown lithospheric anomalies we discover yield a new insight into how the Iceland Plume could cause volcanism scattered over the vast NAIP. Plume material is likely to have flowed into pre-existing areas of thin continental lithosphere, whose thickness was then reduced further by the erosion by the hot asthenosphere. The thinning of the lithosphere and the presence of hot asthenosphere beneath it can account for the uplift, volcanism and crustal underplating. The localisation of the plume material in scattered thin-lithosphere areas, such as the circum-Irish-Sea region, can explain the wide scatter of the volcanic fields of NAIP.

How to cite: Bonadio, R., Lebedev, S., Chew, D., Xu, Y., and Fullea, J.: How could a single Iceland Plume produce the widely scattered North Atlantic Igneous Province volcanism? New clues from Britain and Ireland., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18296, https://doi.org/10.5194/egusphere-egu24-18296, 2024.

The X-discontinuity at 300 km beneath the Hawaiian hotspot has been hypothesized to require at least 40% basalt, a figure that would far exceed the plume's buoyancy and thus be irreconcilable with initial entrainments.
We had previously explored the potential for large basalt accumulations to form over time by simulating a section of the plume conduit, with known quantities of basaltic material flowing in as discrete heterogeneities. For entrainments of 10-20%, we had estimated average accumulations of 20-25% at ~300 km depth.
While this simplified setting recreated segregation of the denser material, it did not feature a realistic plume. On the other hand, employing mechanical mixture compositions hamper quantitative analyses of the recycled basalt.

I have overcome this issue by developing a novel implementation to the ASPECT code.
My advancement features a mechanical mixture composition (82% harzburgite — 18% basalt) for both the background mantle and the plume. The recycled material is then added to the self-consistent rising plume in the form of compositionally distinct basaltic heterogeneities. By combining these two approaches, I was able to successfully reproduce and quantify material segregation while keeping an accurate plume composition.

Preliminary results, conducted in a 2000 km * 1000 km 2D domain, with entrainments of 10-20%, and a maximum resolution of 0.98 km in the heterogeneities, show average basalt accumulations of 20-22% around 300 km depth. Occasional, transient peaks at 31% and 35% can be observed for plumes incorporating 15% basalt. Over the model time (20 Ma), the denser material tends to sink between 360-660 km depth, generating large average accumulations of 35-40%. 

This new strategy not only opens promising scenarios by overcoming long-standing model limitations, but also reinforces the potential for mantle plumes to accumulate more denser material than classically thought, shedding further light on the controversial link between the X-discontinuity and the Hawaiian plume activity.

How to cite: Monaco, M.: A Novel Implementation to Simulate Basalt Segregation in the Hawaiian Mantle Plume Overcomes Model Limitations and Elucidates the Origin of the X-discontinuity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18845, https://doi.org/10.5194/egusphere-egu24-18845, 2024.

EGU24-19459 | ECS | Posters on site | TS8.1

Influence of small-scale convection on the cooling of oceanic lithosphere at slow and fast spreading ridges 

Raghu Ram Gudipati, Marta Pérez-Gussinyé, and Javier García-Pintado

Classic models of continental rifting predict that after continental break-up, the extended lithosphere returns to its original thermal state (McKenzie, 1978). At this time, the heat-flow should decrease from the proximal margin sectors, where the radiogenic crust is still relatively thick, towards its distal sectors, where the crust has extensively thin and the thermal lithosphere thickness approximates that of the adjacent untinned continental lithosphere. This should occur after approximately ~50 Myr for 120 km thick continental lithosphere (McKenzie, 1978). Although, good quality heat flow data is very scarce along margins, some of them, such as the Voring basin, show instead increasing heat flow towards the distal margin sectors ~60 Myr after break-up (Cunha et al., 2021). Recent numerical models have suggested, instead, that the lithosphere under the hyper-extended continental margins, does actually not return towards its original thermal thickness, instead it acquires a thickness which is similar to that of the adjacent plate, resulting in higher heat-flow towards the distal margins at ~80-100 Myr after break-up (Perez-Gussinye et al., 2023). In those models, the delay in thermal relaxation under the hyper-extended margins is caused by small-scale convections cells, a process which also prevents the oceanic lithosphere to infinitely cool and is responsible for the flattening of the oceanic bathymetry at old ages. Interestingly, the models show that the delay in thermal relaxation under both the hyper-extended rifted margins and the old oceanic crust increases with decreasing rifting and spreading velocity, such that is most obvious in ultra-slow margins and adjacent oceanic basins (Perez-Gussinye et al., 2023). Here we use updated 2D numerical models which include the thermal consequences of serpentinisation, melting and melt emplacement to understand the thermal evolution of oceanic plates and compare the resulting plate structure, heat-flow and bathymetry with the observations from seismic LAB structure, and global heat-flow and bathymetry databases.

 

References

Cunha, T.A., Rasmussen, H., Villinger, H. and Akinwumiju, A.A., 2021. Burial and Heat Flux Modelling along a Southern Vøring Basin Transect: Implications for the Petroleum Systems and Thermal Regimes in the Deep Mid-Norwegian Sea. Geosciences, 11(5), p.190.

McKenzie, D., 1978. Some remarks on the development of sedimentary basins. Earth and Planetary science letters, 40(1), pp.25-32.

Pérez-Gussinyé, M., Xin, Y., Cunha, T., Ram, R., Andrés-Martínez, M., Dong, D. and García-Pintado, J., 2024. Synrift and postrift thermal evolution of rifted margins: a re-evaluation of classic models of extension. Geological Society, London, Special Publications, 547(1), pp.SP547-2023.

How to cite: Gudipati, R. R., Pérez-Gussinyé, M., and García-Pintado, J.: Influence of small-scale convection on the cooling of oceanic lithosphere at slow and fast spreading ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19459, https://doi.org/10.5194/egusphere-egu24-19459, 2024.

EGU24-19570 | ECS | Orals | TS8.1

The tectonic evolution of the western North American margin since the Devonian 

Andres Felipe Rodriguez Corcho, Sabin Zahirovic, Michele Anthony, Dene Tarkyth, Christopher Alfonso, Maria Seton, Dietmar Muller, Bruce Eglington, and Basil Tikoff

The western North American margin records multiple phases of rifting and convergence, resulting from the interaction between western Laurentia, rifted continental fragments, and intra-oceanic terranes originating in the Panthalassa and Pacific oceanic plates. Quantitative plate reconstructions of this margin have prioritised diverging interpretations regarding the subduction polarities of eastern Panthalassa terranes during Jurassic to Cretaceous times. These discrepancies arise from the reliance on either seismic tomography or surface geology as the first-order constraint for determining subduction polarity. We present an updated tectonic reconstruction for western North America from the Devonian to present day. In this new model, we reconcile geological histories based on surface geology, geochronology, paleomagnetism and isotopic data, with interpretations of seismic tomography. The new reconstructions account for the tectonic evolution of the Alaska orocline, western Canada and western United States (US) and south-western (SW) North America, which have not been implemented in detail in previous tectonic models. Our model suggests that most of the terranes of western North America were rifted off Laurentia and Baltica during Devonian to Triassic extension and trench-retreat. Following back-arc rifting and opening, many of the terranes (e.g. Insular, Intermontane, Angayucham) experienced an intra-oceanic phase before accreting to the continental margin of North America at different times, between Early Triassic to Late Cretaceous times. The model illustrates the collision of the Angayucham Terrane, counterclockwise rotation and orocline formation in Alaska during the middle Jurassic. In western US and SW North America, the model showcases Jurassic to Cretaceous extension and rifting. Extension starts first in western US (170-145 Ma) and is then propagated south, causing the opening of the Bisbee Basin (161-105 Ma). The model also captures the Late Cretaceous collision of the Insular Terrane, which triggered transpression, terrane translation for thousands of kilometers and clockwise rotation in western US during Late Cretaceous to Paleogene times. Our updated model highlights the importance of surface geology in constraining the polarity of ancient subduction zones interpreted from seismic tomography.

How to cite: Rodriguez Corcho, A. F., Zahirovic, S., Anthony, M., Tarkyth, D., Alfonso, C., Seton, M., Muller, D., Eglington, B., and Tikoff, B.: The tectonic evolution of the western North American margin since the Devonian, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19570, https://doi.org/10.5194/egusphere-egu24-19570, 2024.

Geodynamicists have long proposed that mantle convection creates dynamic topography — a long-wavelength, low-amplitude signal extending beyond plate tectonics. This predicts transient vertical Earth surface movement of 1–2 km across thousands of horizontal kilometers at any location, including continental interiors. Despite these claims, experts working on local observations, using the multitude of high-resolution geological, sedimentological, and geomorphological data, face challenges in finding clear evidence to unequivocally support dynamic models of whole mantle convection, including the plume mode. Moreover, regional-scale stratigraphic techniques, such as sequence stratigraphy, which enabled hydrocarbon exploration, invoke unconformities on multiple scales but, from their far-field perspective, render correlation to distinct geodynamic events difficult.

To circumvent this scaling and correlation problem, I propose to reverse the stratigraphic perspective to an outwards-directed view. This approach requires a theoretical geodynamic framework and the identification of tectonic events (center, near field), such as magmatic arcs, flood basalts, or uplifted domes, followed by outward-directed geological mapping of regional-scale stratigraphic unconformities —predicted by theory— to distal regions. This approach is analogous to the way in which paleoseismologists examine so-called event horizons, i.e., unconformities in the stratigraphic record adjacent to fault scarps that preserve a record of the Earth's surface at the time of earthquake rupture.

This event-based stratigraphic mapping method (EVENT-STRAT) enables analysis of geological events on geological maps compiled at regional to continental scales. The technique connects local work into a continent-scale framework, allowing identification of transient patterns related to dynamic mantle-derived events. The EVENT-STRAT mapping method is designed to visualize geological effects resulting from both the plate and the plume mode of mantle convection. The toolbox consists of the hiatus mapping method (Friedrich 2019, Geological Magazine) and the event-based stratigraphic framework mapping (e.g., Friedrich et al. 2018, Gondwana Research). The upcoming EVENT-STRAT mapping method involves multiple polygonal stacking to analyze various stratigraphic event horizons, such as hiatus surfaces and unconformities. The most significant current challenge is to add the high-precision stratigraphic data compiled on local chronostratigraphic charts to continent-scale geological maps. This effort requires the attention of geological surveys on international scales seeking to compile theory-based geodynamic-stratigraphic parameters on the next generation of global and continent-scale geological maps.

How to cite: Friedrich, A. M.: Geodynamic Stratigraphy — Defining the Need for Mapping Strategies to link Models of Mantle Dynamics to Surface Processes on Geological Scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19837, https://doi.org/10.5194/egusphere-egu24-19837, 2024.

EMRP2 – Geomagnetism

Delineation of Subsurface Tectonic Structures Using Gravity, Magnetic and Geological Data in the Sarir-Hameimat Arm of the Sirt Basin, NE Libya

By

Mohamed Saleem1 and Hana Ellafi2

1 &2 Petroleum Research Center

 

 

ABSTRACT

The study area is located in the eastern part of the Sirt Basin, in the Sarir-Hameimat arm of the basin, south of Amal High. The area covers the northern part of the Hamemat Trough and the Rakb High. All of these tectonic elements are part of the major and common tectonics that were created when the old Sirt Arch collapsed, and most of them are trending NW-SE. This study has been conducted to investigate the subsurface structures and the sedimentology characterization of the area and attempt to define its development tectonically and stratigraphically.

About 7600 land gravity measurements, 22500 gridded magnetic data, and petrographic core data from some wells were used to investigate the subsurface structural features both vertically and laterally. A third-order separation of the regional trends from the original Bouguer gravity data has been chosen. The residual gravity map reveals a significant number of high anomalies distributed in the area, separated by a group of thick sediment centers. The reduction to the pole magnetic map also shows nearly the same major trends and anomalies in the area. Applying the further interpretation filters reveals that these high anomalies are sourced from different depth levels; some are deep-rooted, and others are intruded igneous bodies within the sediment layers. The petrographic sedimentology study for some wells in the area confirmed the presence of these igneous bodies and defined their composition as most likely to be gabbro hosted by marine shale layers. Depth investigation of these anomalies by the average depth spectrum shows that the average basement depth is about 7.7 km, while the top of the intrusions is about 2.65 km, and some near-surface magnetic sources are about 1.86 km. The depth values of the magnetic anomalies and their location were estimated specifically using the 3D Euler deconvolution technique. The obtained results suggest that the maximum depth of the sources is about 4938m.

The total horizontal gradient of the magnetic data shows that the trends are mostly extending NW-SE, others are NE-SW, and a third group has an N-S extension. This variety in trend direction shows that the area experienced different tectonic regimes throughout its geological history.

How to cite: Saleem, M. and Ellafi, H. and the Mohamed Saleem: Delineation of Subsurface Tectonic Structures Using Gravity, Magnetic and Geological Data, in the Sarir-Hameimat Arm of the Sirt Basin, NE Libya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2060, https://doi.org/10.5194/egusphere-egu24-2060, 2024.

EGU24-2767 | Posters on site | EMRP2.2

Origins of the high-amplitude magnetic anomaly zone in the northern South China Sea continental margin 

Wen-Bin Doo, Yin-Sheng Huang, and Hsueh-Fen Wang

Similar to the feature in the U.S. East Coast, an obvious roughly NE-SW trending high-amplitude magnetic belt (NSCSMA) appears in the northern South China Sea (SCS) continental margin, which extends from southwest Taiwan to the area about 114.5°E and 20°N. The likely cause of this magnetic high is important and interesting but still controversial. This study uses wavelet spectrum analysis, 2-D magnetic modeling, and compact inversion to constrain its causative sources. Our analysis results show the evidence indicating that the geometry and depth of the causative magnetic sources were varied along the strike of the NSCSMA (~15 km in the east and ~25 km in the west). Based on our findings and previous studies, we proposed that the major causative source of the NSCSMA could be the serpentinized upper mantle material.

How to cite: Doo, W.-B., Huang, Y.-S., and Wang, H.-F.: Origins of the high-amplitude magnetic anomaly zone in the northern South China Sea continental margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2767, https://doi.org/10.5194/egusphere-egu24-2767, 2024.

EGU24-4792 | Orals | EMRP2.2

Comparison and understanding of sparse magnetization vector inversion 

Yang Ou, Jie Zhang, Dingyu Jia, Yang Li, and Yi Yang

Magnetization vector inversion (MVI) is an effective method for interpreting magnetic data without knowing the magnetization directions. Nevertheless, the serious nonuniqueness problem makes it difficult to obtain satisfactory results without proper constraints. Several constrained methods have been applied to the magnetization vector inversion to produce reliable results. To better understand these issues and provide some improvements, we compared and evaluated different forms of magnetization vector inversion: (1) magnetization vector inversion in Cartesian coordinates (MVI-C); (2) magnetization vector inversion in spherical coordinates (MVI-S); and (3) compact magnetization vector inversion with magnitude constraints. Magnetization vector inversion incorporates prior information or assumptions about subsurface geological structures into the model objective function and solves the optimal problem with respect to the data and the model objective function to recover the desired features. We first analyze different model objective functions and then test these methods against synthetic and real datasets. Theoretical analysis and tests reveal that the linear relationship in the rectangular coordinate system simplifies the calculation process, but it is difficult to apply reasonable constraints, which results in a lack of correlation in the direction of magnetization; moreover, the distribution is not concentrated. It is easy to constrain the magnetization magnitude and direction in the spherical coordinate system, and better results can be obtained. However, due to the nonlinear relationship, the calculation complexity increases, and the inversion results are heavily dependent on the initial model. The method based on the modulus constraint establishes the relation between components in the Cartesian coordinate system, but the direction cannot be constrained. Therefore, we believe that the magnitude and direction of magnetization should be constrained simultaneously in the rectangular coordinate system to obtain a fast, stable, and accurate inversion method.

How to cite: Ou, Y., Zhang, J., Jia, D., Li, Y., and Yang, Y.: Comparison and understanding of sparse magnetization vector inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4792, https://doi.org/10.5194/egusphere-egu24-4792, 2024.

EGU24-5563 | ECS | Posters on site | EMRP2.2

High-resolution magnetic and gravimetric map of the South of Salamanca (Spain): tectonic insights and implications on Sn-W mineralization 

Irene DeFelipe, Alberto Santamaría Barragán, Irene Pérez-Cáceres, Puy Ayarza, Imma Palomeras, Mariano Yenes, Juan Gómez Barreiro, Raúl Prieto, Mercedes Rivero-Montero, and Yolanda Sánchez-Sánchez

Within the Iberian Peninsula and specifically in the Iberian Massif (the westernmost outcrop of the Variscan orogen in Europe), several aeromagnetic anomalies stand out, and many of them are related to late-Variscan gneiss domes. However, some of them are not fully understood because: 1) they are not clearly linked to extensional structures and/or gneiss domes, 2) they are not related with the outcropping rocks, and/or 3) the aeromagnetic map does not provide enough resolution to relate them with the local geology. For example, the Salamanca Magnetic Anomaly (SAMA), in the central-western part of Spain, is a conspicuous reverse polarity magnetic anomaly that features a maximum amplitude of 56.1 nT. However, it does not show any relationship with the magnetic properties of outcropping rocks. In this regard, preliminary studies show that the outcropping Ordovician Slates present randomly reverse polarity Natural Remanent Magnetization which is compatible with that of the SAMA but with very low intensity. Therefore, we have undertaken a large magnetic survey of this anomaly and its continuation to the south. Gravity has also been measured in an effort to constrain the source of the SAMA. The study area, which extends to the south of the city of Salamanca is affected by the Alba-Villoria NE-SW oriented Alpine fault that puts into contact Neoproterozoic and Paleozoic rocks of the Iberian Massif with Cenozoic sedimentary rocks. In addition, the Variscan Salamanca Detachment Zone, a late-Variscan extensional structure allowed deep rocks and crustal melt products to reach shallow crustal levels, probably easing Sn-W mineralization in the area. Our new Bouguer and magnetic anomaly data depict the Alba-Villoria Fault and show a straightforward correlation between gravity and magnetic maxima. Although the magnetic maxima could be the potential field response of dense and magnetic slates common in the area, the ones measured do not present high magnetic susceptibility. Accordingly, this new data might indicate that late-Variscan extension triggered the intrusion of dense and magnetic basic rocks in a process that could have contributed to Sn-W mineralization.

Acknowledgements: We thank the funding provided by the Junta de Castilla y León and Fondo Europeo de Desarrollo Regional (SA084P20), the Fundación Memoria de D. Samuel Solórzano Barruso grant (FS3-2021), Grant PID2020-117332GB-C21 (MCIN/AEI/10.13039/501100011033) and TED2021-130440B-I00 (MCIN/AEI/10.13039/501100011033) and EU NextGenerationEU/PRTR. IDF received support from the Ayuda para la recualificación de sistema universitario español 2021-2023 and MRM from the Programa Margarita Sala, Ministerio de Universidades and UCM (CT18/22).

How to cite: DeFelipe, I., Santamaría Barragán, A., Pérez-Cáceres, I., Ayarza, P., Palomeras, I., Yenes, M., Gómez Barreiro, J., Prieto, R., Rivero-Montero, M., and Sánchez-Sánchez, Y.: High-resolution magnetic and gravimetric map of the South of Salamanca (Spain): tectonic insights and implications on Sn-W mineralization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5563, https://doi.org/10.5194/egusphere-egu24-5563, 2024.

EGU24-7682 | Orals | EMRP2.2

Potential field signature of a late-Variscan extended realm. Implications for western Iberia Sn-W mineralization 

Puy Ayarza, Mercedes Rivero Montero, Juan Gómez Barreiro, José Ramón Martínez Catalán, Pablo Calvín, Yolanda Sánchez Sánches, and Immaculada Palomeras

The internal part of the Central Iberian Arc (CIA) features a number of long-wavelength, high amplitude aeromagnetic anomalies that overlap gneiss domes developed during late Variscan extension. Some of the largest anomalies are located at the core of the CIA and coincide with the western Iberia Sn-W belt, e.g., the Porto-Veira-Guarda Magnetic Anomaly (PVGMA) and the Central System Magnetic Anomaly (CSMA). Despite both of them lying on top of the products of crustal extension and melting (granites and migmatites), outcropping rocks do not feature high magnetic susceptibilities, raising the question about the origin of the anomalies.

In the last two years, ground high-resolution magnetic and gravity surveying has been carried out in the northern part of the CSMA, in the boundary between igneous rocks and their metamorphic host rocks. The latter are part of thermal domes developed in the latest stages of Variscan extension. Results show that magnetic highs coincide with gravity highs, thus indicating that the source of the anomalies is probably basic rocks. Indeed, scarce outcropping gabbros have magnetite, and feature a moderate magnetic susceptibility, but a very high magnetic remanence (Qn<400) of reverse polarity and directions that match those of the Kiaman superchrone, compatible with the age of gabbros (305-294 Ma). Furthermore, the characteristics of the magnetic anomalies, featuring long wavelengths, indicate that magnetic rocks (gabbros) abound at depth.

The sole existence of gabbros, albeit scarce, in the study area indicates that the mantle was involved in late Variscan extension in this part of the CIA. Crustal thickening associated to the development of the CIA must have produced lithospheric instabilities that eased the entrance of mantle melts, including metals like Sn and W, nowadays highly demanded.

Acknowledgements: Projects SA084P20, TED2021-130440B-100 and PID 2020-117332GB, MS (UCM, CT18/22)

How to cite: Ayarza, P., Rivero Montero, M., Gómez Barreiro, J., Martínez Catalán, J. R., Calvín, P., Sánchez Sánches, Y., and Palomeras, I.: Potential field signature of a late-Variscan extended realm. Implications for western Iberia Sn-W mineralization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7682, https://doi.org/10.5194/egusphere-egu24-7682, 2024.

EGU24-8386 | Posters on site | EMRP2.2

Image of the crust and upper mantle tectonic structure and associated mineral systems of the central Norwegian Caledonides from 3D inverse geoelectrical models 

Svetlana Kovacikova, Graham Hill, Sofie Gradmann, Radek Klanica, Gokhan Karcioglu, Jan Vozár, Jochen Kamm, Pankaj Mishra, Maxim Smirnov, and Oskar Rydman

The current effort to move to more renewable energy sources and away from a petroleum based energy economy, ‘Net Zero’, places a renewed need for improving identification and characterization of mineral deposits in order to provide the materials required. Recent work, has demonstrated the benefit of larger aperture investigations of mineral systems for both determining the processes responsible for their emplacement as well as identifying indicative geophysical signatures associated with metal endowment. The central Norwegian Caledonides historically represent a zone of large mineral endowment, though; the large-scale structural history and process that formed the mineralization remain enigmatic. Formation and concentration of metals into economic mineral deposits requires a combination of processes operating at different scales. With the near surface mineral deposit being a small component of the larger mineral system which encompasses deep fluid sources and metals, an energy source for driving circulation pathways for the migration of enriched fluids, a depositional mechanism responsible for the formation of the deposit and a fluid outflow. The Norwegian mineral deposits lie within the allochthonous nappes, detached from the original Precambrian Svecokarelian and Sveconorwegian basement and having undergone tens to hundreds of km of lateral transport. Regional scale geophysical modelling of petrophysical properties has the ability to characterize and identify the structure and process occurring throughout the entire mineral system  and determine indicative structures at mid-lower crustal depths indicative of economically viable near surface regions of metal endowment (i.e. the near surface mineral deposit). To determine the processes associated with formation of the Norwegian Caledonides and its associated mineral deposits a dense network of ~300 broadband magnetotelluric soundings covering the period range 10-3-103s have been collected over two field campaigns in 2022 and 2023 in the Trondelag area of central Norway. Phase tensor analysis indicates that the data set is 3D at all scales – we have modelled the MT data using a 3D approach (GoFEM) capable of incorporating the rugged topography of the survey area. Preliminary modeling results reveal lithospheric-scale structural controls associated with known near surface mineral deposits and processes related to the lateral transport from the underlying lower crustal source regions. As such, regional geophysical surveys offer both an economic and environmentally friendly approach to large-scale exploration efforts through identification of regional scale structural controls that are indicative of metal endowment.

How to cite: Kovacikova, S., Hill, G., Gradmann, S., Klanica, R., Karcioglu, G., Vozár, J., Kamm, J., Mishra, P., Smirnov, M., and Rydman, O.: Image of the crust and upper mantle tectonic structure and associated mineral systems of the central Norwegian Caledonides from 3D inverse geoelectrical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8386, https://doi.org/10.5194/egusphere-egu24-8386, 2024.

EGU24-8633 | ECS | Posters on site | EMRP2.2

A Streamlined Neural Network Architecture for Magnetic Data Inversion 

Xiaoqing Shi, Hua Geng, and shuang Liu

Data-driven methods based on deep learning have been applied to magnetic inversion and achieved excellent results. However, the existing neural network structures used for inversion are relatively complex, resulting in increased computational costs. Different from the inversion structure of existing encoder-decoder structures, this study designed a streamlined neural network inversion architecture based on the characteristics of magnetic anomaly forward modeling. The network structure only contains a decoder that maps magnetic anomaly data to a three-dimensional magnetic susceptibility model, which can save computational costs. First, the single-channel input data is transformed into multi-channel data through a transformation, then it is transformed into the dimensions of the magnetic susceptibility model through a four-layer decoder, and then the multi-channel data is transformed into a single channel through transformation, and finally the output is 3D magnetic susceptibility model. The transformation coefficients are trained by neural network. The neural network structure designed by this method is interpretable. It can reduce the parameters that need to be trained, reduce training time, and achieve high accuracy. It was verified through simulated and measured magnetic anomaly data, and high-precision inversion results were obtained. This idea can also be generalized to the inversion of other data.

How to cite: Shi, X., Geng, H., and Liu, S.: A Streamlined Neural Network Architecture for Magnetic Data Inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8633, https://doi.org/10.5194/egusphere-egu24-8633, 2024.

Gravity surveys constitute an important method for investigating the Earth’s interior based on density contrasts related to Earth material differentials. Because lithology depends on the environment and the period of formation, there are generally clear boundaries between rocks with different lithologies. Inversions with convex functions for approximating the L0 norm are used to detect boundaries in reconstructed models. Optimizations can easily be found because of the convex transformations; however, the volume of the reconstructed model depends on the weighting parameter and the density constraint rather than the model sparsity. To determine and adapt the modelling size, a novel non-convex framework for gravity inversion is proposed. The proposed optimization aims to directly reduce the L0 norm of the density matrix. An improved iterative hard thresholding algorithm is developed to linearly reduce the L0 penalty during the inner iteration. Accordingly, it is possible to determine the modelling scale during the iteration and achieve an expected scale for the reconstructed model. Both simple and complex model experiments demonstrate that the proposed method efficiently reconstructs models. In addition, granites formed during the Yanshanian and Indosinian periods in the Nanling region, China, are reconstructed according to the modelling size evaluated in agreement with the magnetotelluric profile and density statistics of rock samples. The known ores occur at the contact zones between the sedimentary rocks and the reconstructed Yanshanian granites. The ore-forming bodies, periods, and processes are identified, providing guidance for further deep resource exploration in the study area.

How to cite: Zhu, D.: Gravity inversion using L0 norm for sparse constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9436, https://doi.org/10.5194/egusphere-egu24-9436, 2024.

EGU24-10535 | ECS | Orals | EMRP2.2

Can salt basins be modelled by magnetic data? A successful case study in the Eastern Mediterranean  

Luigi Bianco, Mahmoud Abbas, Luca Speranza, Bruno Garcea, and Maurizio Fedi

We discuss the analysis of magnetic data in salt basins and their potential role as a key tool in these scenarios. The study was performed on the magnetic data of a deep-water area in the offshore Egypt, Eastern Mediterranean. The reduced to pole (RTP) magnetic anomalies was computed and filtered with the discrete wavelet transform (DWT) for the regional-residual separation. The filtered anomalies were interpreted as due to the contrast between the sedimentary layers and the diamagnetic salt dome. The multiscale boundary analysis allowed the extraction of lineaments representative of the salt bodies. Moreover, the inversion of the data using a 3D non-linear non-iterative technique produced a map of the salt in the area, which was derived without constraints from seismic or other external information. from the magnetic data interpretation was performed. It needed only a local estimation of the depth to the salt in few points, as provided by Euler deconvolution of magnetic data. This result well agrees with the top of the salt interpreted from the seismic data. Our findings are not obvious and demonstrate the potential of magnetic surveys as a self-consistent and low-cost tool in the exploration of salt basins, especially when the higher resolution seismic interpretation  could suffer of possible pitfalls or seismic data are inaccessible.

How to cite: Bianco, L., Abbas, M., Speranza, L., Garcea, B., and Fedi, M.: Can salt basins be modelled by magnetic data? A successful case study in the Eastern Mediterranean , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10535, https://doi.org/10.5194/egusphere-egu24-10535, 2024.

EGU24-13204 | Posters on site | EMRP2.2

Subsurface 3D modeling of Pantelleria island (Italy) using gravity data. 

Luca Samperi, Giovanna Berrino, and Filippo Greco

Pantelleria is a 84 km2 extended volcanic island located in the Mediterranenan Sea between Sicily (Italy) and Tunisia. Previous studies described that in Pantelleria island both tectonic structures and the volcano-tectonic features had a common tectonic origin controlled by a NW-SE directed extension in accordance with the regional trend of the Sicily Channel arising interest for multiapproach investigations.

Indeed, in the last decades this area has been field of widespread analysis useful for the investigation of the volcano-tectonic and tectonic activity, as well as for geodetic study and resources exploration.

Our approach focused on the gravimetric analysis of Pantelleria island and in particular we provided a 3D inverted model of the area, starting from in-situ gravity measurements. The 250 m model resolution has been endorsed by the presence of a total of  290 measurement stations, distributed both onshore and offshore and acquired during some field surveys up to 2006; 236 of them were already published and inverted in past using 2.5D modelling. Input data consisted of a database containing Bouguer anomaly data reduced using a  density of 2500 kg/m3 and referred to the Geodetic Reference System 1980 (GRS80) Ellipsoid.

As a result, the 3D modelling allowed exploring density differences through the about 4 km depth, emphasizing interesting geological structures.

Such results would help any drilling program in the island (e.g. for geothermal purposes), lead to more successful drilling programs, and serve as well-constrained geologic input to improve the accuracy of future numerical (e.g. reservoir) models.

How to cite: Samperi, L., Berrino, G., and Greco, F.: Subsurface 3D modeling of Pantelleria island (Italy) using gravity data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13204, https://doi.org/10.5194/egusphere-egu24-13204, 2024.

We introduce a novel estimation technique to assess the overall mass variations of the Greenland and Antarctica ice sheets. Interpreting GRACE data encounters a significant challenge due to the leakage effect resulting from the presence of outlying melting ice bodies, causing gravitational effects to interfere with each other. Our estimation employs an innovative approach that leverages the non-uniqueness of the gravity field, using a hypercompact model of the sources through an iterative inversion. Furthermore, thanks to to the extreme compactness of the sources, our method enables a more unambiguous quantification of total mass loss in the study area. We apply our method to time-varying NASA GRACE (Gravity Recovery and Climate Experiment) Stoke's coefficient data spanning from 2002 to 2017. Over a 15-year period, the GRACE and subsequent GRACE-FO missions provided a distinctive to map the Earth's gravitational field time variations. In recent years, recognizing the ice sheet's total mass response to climate change has become pivotal in comprehending phenomena such as sea level rise associated with grounded ice melting and quantifying the retreat of ice sheet fronts in polar regions, offering the scientific community a fresh perspective on unknown ice sheet dynamics.

How to cite: Maiolino, M., Fedi, M., and Florio, G.: ECS (Extremely compact sources) potential field filtering. The case of Greenland and Antarctica ice mass balance (2002-2017)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13296, https://doi.org/10.5194/egusphere-egu24-13296, 2024.

EGU24-13361 | Posters virtual | EMRP2.2

Swarm observations of ULF wave activity and plasma instability activity around extreme geophysical events 

Georgios Balasis, Angelo De Santis, Gianfranco Cianchini, Constantinos Papadimitriou, Omiros Giannakis, and Stelios M. Potirakis

In November 2023, the ESA Swarm constellation mission celebrated 10 years in orbit, offering one of the best-ever surveys of the geomagnetic field and the topside ionosphere. Swarm provides an ideal platform for observing ultra-low frequency (ULF) waves and thus offers an excellent opportunity for space weather studies. For this purpose, a specialized time-frequency analysis (TFA) toolbox has been developed for deriving Pc1 (0.2-5 Hz) and Pc3 (20-100 MHz) wave indices, thus making it a useful tool for the study of magnetic storms. The TFA toolbox is also capable to identify in Swarm time series another category of natural-source electromagnetic signals, i.e., the post-sunset Equatorial Spread-F (ESF) events or plasma bubbles. There have been several studies suggesting that ULF pulsations may be associated with earthquakes. Previous studies refer mainly to the detection of these signals in ground-based magnetometer measurements. Besides, we note only a handful of studies that have been attempted to correlate ULF pulsations with seismic activity, using space-borne magnetometer measurements provided by Low Earth Orbit (LEO) satellites (e.g., CHAMP, DEMETER). Therefore, in this study we focus on the ULF pulsation and ESF activity observed by Swarm satellites during a time interval centered around the occurrence of the August 2016 Central Italy earthquake. Swarm has offered a variety of interesting observations around the time of this earthquake that could be associated with the occurrence of this extreme geophysical event.

How to cite: Balasis, G., De Santis, A., Cianchini, G., Papadimitriou, C., Giannakis, O., and Potirakis, S. M.: Swarm observations of ULF wave activity and plasma instability activity around extreme geophysical events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13361, https://doi.org/10.5194/egusphere-egu24-13361, 2024.

EGU24-18236 | ECS | Posters on site | EMRP2.2

Using potential field data to investigate high-pressure sources of energy in deeply serpentinized mantle rocks 

Zeudia Pastore, Alberto Vitale Brovarone, Jérôme Gattacceca, Nathan Church, Francesco Ressico, Veronica Peverelli, Yoann Quesnel, Minoru Uehara, and Dilyara Kuzina

Serpentinization of ultramafic rocks is a key process in forming natural hydrogen. In deep settings, such as subduction zones, this process can be kinetically favored by high P-T conditions making the study of mantle rocks from these settings a compelling target for high-pressure sources of energy. Serpentinization of peridotites can lead to the formation of magnetite and it is commonly associated with a decrease in density and an increase in magnetization of the protolith rock. Gravity and magnetic methods can therefore be used to map and quantify the extent and degree of serpentinization. Here, we used a comprehensive dataset consisting of ground and Unmanned Aerial Vehicle (UAV) magnetic data, gravity data, and an extensive petrophysical data collection to explore the natural hydrogen potential in exhumed mantle rocks from the Monte Maggiore (MM) massif, in Corsica. The MM massif consists of a ∼4 km2 peridotite body, intruded by mafic pods and gabbroic dykes and surrounded by blueschist-facies continental units. It represents sub-continental mantle that underwent tectonic and magmatic evolution during the rifting stage of the Jurassic Ligurian Tethys oceanic basin and successive Alpine subduction to blueschist-facies conditions. On-going geochronological and geochemical investigations suggest that serpentinization occurred primarily in subduction making this area a suitable case study to investigate the formation of high-pressure sources of energy in such settings. We analyzed densities and magnetic properties of rocks from more than 100 sites across the massif and we used these data to identify domains exhibiting different degree of serpentinization and to model the current 3D structure of the massif using both forward and inverse modeling approaches. We estimated a minimum volume of the MM massif of 1.2 km3 and a vertical extent to a depth of 428 m below sea level. We used the modeled volumes and the amount of magnetite within each domain as a proxy for a conservative estimation of natural H2 production.

How to cite: Pastore, Z., Vitale Brovarone, A., Gattacceca, J., Church, N., Ressico, F., Peverelli, V., Quesnel, Y., Uehara, M., and Kuzina, D.: Using potential field data to investigate high-pressure sources of energy in deeply serpentinized mantle rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18236, https://doi.org/10.5194/egusphere-egu24-18236, 2024.

EGU24-18708 | ECS | Posters on site | EMRP2.2

A new approach of monitoring CO2 storage in deep saline aquifers from time-lapse gravity data 

Maurizio Milano and Maurizio Fedi

Here we assessed surface gravity monitoring as tool for detecting the CO2 plume in deep saline aquifers during the injection and post-injection phases. We used the available benchmark model of the Johansen reservoir to conduct the simulation of CO2 storage at about 3 km of depth for 70 years and using different injection rates. We calculated the gravity response at surface from the estimated models of reservoir density and saturation at different time intervals. The forward calculation is achieved by assuming a tetrahedral mesh discretization, such as to ensure an accurate and detailed reconstruction of the complex reservoir.

We proposed a new approach for monitoring the mass stored into the reservoir based on the DEXP method, which allows an effective reduction of interference effects from nearby sources and provide accurate results even when the anomaly is incompletely defined, due to a not proper areal coverage of the survey.

This study clearly shows that the appropriate choice of the injection rate strongly impacts on the ability to recover useful gravity signal at the surface, beyond the measurement error threshold. We also provide an in-depth analysis of the effect of noise on the mass change estimates.

Our approach could be a valid tool for conducting real time monitoring of the CO2 as it could accurately determine the effective mass stored in the reservoir. This is particularly important as it does not require information about the source and could make surface gravity surveying as an independent monitoring strategy.

How to cite: Milano, M. and Fedi, M.: A new approach of monitoring CO2 storage in deep saline aquifers from time-lapse gravity data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18708, https://doi.org/10.5194/egusphere-egu24-18708, 2024.

EGU24-19287 | ECS | Orals | EMRP2.2

A new detailed Bouguer anomaly for the exploration of the deep geothermal reservoir in SW-Belgium 

Quentin Campeol, Nicolas Dupont, Ivan Pavel Nanfo Djoufack, Louis Christiaens, Franck Martin, and Olivier Kaufmann

Located next to the Variscan front, the center of the Hainaut (SW-Belgium) is known for its deep geothermal potential. Indeed, the geothermal reservoir of the Carboniferous limestones, located in the Brabant Parautochton, currently supplies water at a temperature of between 65°C and 72°C from three deep wells in the Mons area. Although the use of geothermal energy is one of the main solutions to decrease or abandoning fossil energies, it is still very limited in this area. This situation is partly due to major uncertainties in the structure and the geometry of the reservoir which are holding back public and private investments and delay geothermal projects.

 

For these reasons, we have conducted new geophysical surveys in the center of the Hainaut region for the last fifteen years. Among these, two gravimetric surveys in relation to the More-Geo project (ERDF funding) were carried out in 2019 and in 2022. As the production levels in the geothermal reservoir of the Carboniferous limestones are karstified, replacing massive anhydrites, the study of gravimetry disturbance is appropriate. The main goal is to provide information about deep geological structures and precisely on the geothermal reservoir by refining the localisation and the extent of karstified and anhydrite levels.

 

The result of the 2019 and 2022 surveys is a new dataset of 13,000 measurements spread over 3,400 stations located in an area of 820 km². The classical Bouguer anomaly has been obtained after a full processing of the instrumental gravimetric measurements, using exclusively open-source Python libraries.

 

Special attention is given to the terrain correction which in our case is based on the modelisation of the topographic surface by rectangular prisms and on the evaluation of the gravitational influence of these prisms. The method used combines a “large-scale” terrain correction modelling the topography up to 167 km in extent with prisms of 25 m resolution and a “local” terrain correction correcting the inaccuracies of the first grid with prisms of 1 m resolution over a more limited area.

 

Results are the mapping of the Bouguer anomaly, the upward continuation, upward derivative and horizontal derivative obtained with the interpolation method of equivalent sources. The two last maps are at the base of structural interpretations of the Paleozoic basement. These results and specifically the processing will be a key to refine the localisation and the extent of deep geothermal targets within the Paleozoic basement. This will require specific processing taking into account the thick and highly heterogeneous Meso-Cenozoic cover of the Mons Basin.

How to cite: Campeol, Q., Dupont, N., Nanfo Djoufack, I. P., Christiaens, L., Martin, F., and Kaufmann, O.: A new detailed Bouguer anomaly for the exploration of the deep geothermal reservoir in SW-Belgium, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19287, https://doi.org/10.5194/egusphere-egu24-19287, 2024.

EGU24-19549 | ECS | Orals | EMRP2.2

New aeromagnetic anomaly compilations help unveil regional-scale Antarctic subglacial geothermal heat flux heterogeneity 

Jonathan Ford, Fausto Ferraccioli, Ben Mather, Egidio Armadillo, Rene Forsberg, Joerg Ebbing, Karsten Gohl, Graeme Eagles, Chris Green, Javier Fullea, and Massimo Verdoya

A new continent-wide aeromagnetic anomaly compilation for Antarctica, conformed at longer wavelengths with SWARM satellite magnetic data includes recent international datasets collected after the ADMAP 2.0 compilation analysed within the 3D Earth project of ESA.

This ADMAP 2.0+ product includes: 1) ROSETTA data collected by a US-NZ team over the Ross Ice Shelf; 2) reprocessed US-German and UK data collected over the Amundsen Sea Embayment; 3) German, Danish, UK- Argentina-Norwegian data over the Recovery ice stream catchment; 4) ESA PolarGAP data over South Pole and 5) enhanced vintage datasets for the Gamburtsev Subglacial Mountains and Wilkes and Dome C regions in East Antarctica. A new digital database was assembled using updated line data holdings and all data were levelled. microlevelled and stitched together via grid stitching approaches and subsequently differentially continued to 4 km and re-gridded on a 4 km grid mesh.

Here we use this new aeromagnetic anomaly compilation to re-assess Antarctic geothermal heat flux (GHF) heterogeneity, a critical basal boundary condition that influences Antarctic ice sheet flow and subglacial melting patterns and hydrology, and is related to crustal and lithospheric structure, composition, and heat production.

Within the 4D Antarctica ESA project we applied Curie Depth Point (CDP) estimation using the centroid, modified centroid and fractal/defractal approaches. Our new CDP map reveals regions of enhanced GHF along the coast of the Amundsen Sea Embayment, in agreement with independent seismological estimates. Potential thermal anomalies within the West Antarctic Rift System (WARS) also underlie the Byrd Subglacial Basin. Linear rift related anomalies are now imaged more clearly beneath the Siple Coast ice streams and active subglacial lake districts.

In East Antarctica, the new CDP estimates over the enigmatic WSB are significantly deeper compared even to the coldest sectors of the WARS. This suggests that if Mesozoic to Cenozoic extension affected this region, it mostly occurred at upper crustal levels rather than the whole lithosphere, in general agreement with relatively sparse seismological evidence for a predominantly cratonic lithospheric environment. A particularly intriguing region of enhanced GHF is identified in Dronning Maud Land. We propose that this could arise from lithospheric thinning perhaps associated with delamination processes, which have been independently inferred from petrological signatures in post-orogenic granitoids, emplaced after the pan-African age assembly of Gondwana. Alternatively, this feature could reflect thermal anomalies related to much later passive margin formation during Gondwana rifting and break up.

Finally, we discuss intriguing GHF anomalies inferred in the Dome C and Dome A subglacial lake regions in interior East Antarctica. We suggest the hypothesis that these anomalies relate to anomalously high intracrustal heat production, such as observed in Australia in some Proterozoic terranes, or to ill-constrained reactivation of the inherited structural architecture, This includes major Proterozoic and younger Pan-African age orogenic belts that may have been reactivated in response to far field stresses during Mesozoic to Cenozoic Gondwana break up and subsequent sea floor spreading processes.

How to cite: Ford, J., Ferraccioli, F., Mather, B., Armadillo, E., Forsberg, R., Ebbing, J., Gohl, K., Eagles, G., Green, C., Fullea, J., and Verdoya, M.: New aeromagnetic anomaly compilations help unveil regional-scale Antarctic subglacial geothermal heat flux heterogeneity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19549, https://doi.org/10.5194/egusphere-egu24-19549, 2024.

EGU24-19904 | Orals | EMRP2.2

A compact MEMS gravimeter with sub ng performance 

William T. Pike, Constantinos Charalambous, Simon Calcutt, and Ian Standley

We present the performance of a MEMS accelerometer capable of sub-migroGal Allan variance out to a period of 1000 s. The gravimeter incorporates a monocrystalline silicon suspension and capacitive sensing with electromagnetic feedback. The gravimeter is capable of operation over 10 degree tilt range under Earth gravity, allowing unsupervised operation after remote deployment with a three-axis gapleran geometry. The suspension incorporates temperature compensation to minimse the need for thermal isolation.  The overall mass of the instrument is about 0.6 kg mass,  including the packaged sensor heads, the electronics board and associated connectors and cabling with a power requirement of less than 400 mW.  The performance and resource profile make this a promising instrument for both terrestrial deployment in extreme environments as well as planetary deployment.

How to cite: Pike, W. T., Charalambous, C., Calcutt, S., and Standley, I.: A compact MEMS gravimeter with sub ng performance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19904, https://doi.org/10.5194/egusphere-egu24-19904, 2024.

EGU24-21105 | Posters on site | EMRP2.2

Mapping a Gondwana suture zone integrating magnetic methods and geology at the SE Brazilian continental margin 

Raphaela Lopes de Andrade Silva, Renata da Silva Schmitt, Natasha Santos Gomes Stanton, and Guilherme Gonçalves Martins

According to previous reconstructions, the South Atlantic Ocean is the biggest gap of
Gondwana, with important crustal limits that controls convergent and divergent tectonic
events since the Paleoproterozoic. In the SE Brazilian continental margin, a Cambrian NE-SW
suture zone is marked by an expressive magnetic anomaly onshore that extends offshore to
the proximal Santos basin (Rio de Janeiro). This suture separates two contrasting geological
terranes: a Neoproterozoic magmatic domain (Oriental Terrane), to the west, and a
Paleoproterozoic gneissic terrane, to the east (Cabo Frio Tectonic Domain). The focus is to
determine how this suture extends offshore, hence determining the nature of the basement
that constitutes the continental margin, and how it continues in depth, determining the
orientation of the Ediacaran paleo subduction zone. We made a geological and geophysical
integration aiming to characterize the magnetic pattern of terranes and structures in order to
determinate the geometry and dip direction of the suture in depth. The methodology included
the generation and interpretation of aeromagnetic images combined with geological mapping.
Also, two magnetic sections were made on field along the suture zone and modeled on GMSYS
adopting magnetic susceptibility values obtained both on field and laboratory. The studied
area comprises mainly two geological units separated by a thrust fault (suture zone): dioritic to
granitic Paleoproterozoic rocks with metabasite layers (Região dos Lagos Complex - RLC) and
Ediacaran aluminous paragneisses with calcsilicate layers (Palmital Succession). Based on the
amplitude (intensity), geometry, magnetic signal’s texture and lineament pattern, in map view,
two domains were defined: A1 and A2. The A1 is correlated with the Paleoproterozoic
gneisses, with high amplitude, long wavelength (55 km) with numerous magnetic rectilinear
and curvilinear lineaments. Amplitude ranges between -100 and 452 nT, mostly higher than
150 nT. A2 coincides with the Palmital paragneisses, defined by a low frequency, long
wavelength (55 km) magnetic domain, with amplitudes <0 nT, resulting in a lateral contrast of
more than 500 nT with A1, where the magnetic gradient decreases to NW. Magnetic
lineaments display a preferential NE-SW direction, but in A1 a deep NW-SE fabric occurs, that
might be related with the Paleoproterozoic tectonic fabric. The suture is represented by a high
positive curvilinear lineament, extending offshore, crossing the coastline to SW before
inflecting to the east. Modeling and geological/magnetic maps correlation suggest that the
suture dips to NW. 

How to cite: de Andrade Silva, R. L., da Silva Schmitt, R., Santos Gomes Stanton, N., and Gonçalves Martins, G.: Mapping a Gondwana suture zone integrating magnetic methods and geology at the SE Brazilian continental margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21105, https://doi.org/10.5194/egusphere-egu24-21105, 2024.

EGU24-21317 | ECS | Posters on site | EMRP2.2

Potential fields characterization of inaccessible areas: multiscale analysis of the West Antarctic Rift System 

Giuseppe Ferrara, Fauso Ferraccioli, and Maurizio Fedi

We used potential field data to help unravel the geological characteristics of the West Antarctic rift system, one of the largest and least known rift systems on our planet. A comprehensive understanding of this region is lacking, as it is covered by the West Antarctic Ice Sheet (WAIS), which reaches thicknesses of over 3 km. Aeromagnetic and aerogravity datasets collected by the British Antarctic Survey (Ferraccioli et al., 2007) were analyzed via a multiscale analysis (Fedi et al., 2015) useful for identifying the main structural lineaments, i.e., contacts, dykes, sills, volcanic bodies and intrusions in the Pine Island Glacier catchment of WAIS. Our results reveal that several regions are characterized by contact-type sources associated to fault systems bordering major magma-rich rift basins, like the Pine Island Rift, Byrd Subglacial Basin, and Bentley Subglacial Trench, as well as those associated with Pine Island glacier tributaries, which lie at high angle wrt to the glacier trunk and rift basins. Furthermore, we identified magmatic sources near or off-rift zones, such as the edges of the Bentley Subglacial Basin, which allow a better understanding of the sub-ice depth of the magmatic sources. In addition, our results provide new information about the main magmatism trends and their average depths. We thus showcase that potential field anomalies allow a better comprehension of the West Antarctic Rift System regional geology, tectonic architecture and magmatic patterns. This research opens interesting scenarios about the extent and position of magmatic sources and on how they contribute towards shaping the sub-ice topography within this sector of the rift system, which in turn is a primary control on ice sheet flow in this highly dynamic and potentially unstable sector of WAIS. In conclusion, potential field analysis with a multiscale approach emerges as a pivotal tool and provides valuable insights into continental rifting processes, especially in inaccessible areas such as West Antarctica, where there are only very few geological outcrops.

How to cite: Ferrara, G., Ferraccioli, F., and Fedi, M.: Potential fields characterization of inaccessible areas: multiscale analysis of the West Antarctic Rift System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21317, https://doi.org/10.5194/egusphere-egu24-21317, 2024.

EGU24-22338 | ECS | Orals | EMRP2.2

Toward an optimal assessment of UAV vertical magnetic gradient arrangement 

Filippo Accomando, Giovanni Florio, Bastien Dupuy, and Madeline Lee

Among the geophysical methods, magnetic surveys are ones of the most used and reliable techniques to investigate archaeological sites. These targets are usually shallow sources generating weak amplitude anomalies. The vertical gradient measurements are preferred to the magnetic fields since it has a better sensitivity to the magnetic contributions due to shallow sources (the gradient fields decay faster than the magnetic field) and a better ability to distinguish and separate interfering anomaly due nearby sources. 
Thanks to the large deployment of UAV (Unmanned Aircraft System) of the recent years, in this work, we arranged a gradiometric system, trying one of the first attempts of vertical gradient measurements by drones for archaeological applications. These mobile platforms help to cover very large areas (this should help to follow better the long and regular shape of buried buildings) maintaining the same resolution of traditional ground surveys, with less times and risk and over sites of difficult access. However, the measurement of vertical gradients in drone-borne magnetometry is generally not taken into consideration, as it poses additional challenges to the survey and successive data processing 
In this work, we arranged the magnetic sensors as a gradiometric system, obtaining a direct estimate of the vertical magnetic gradient in a single flight. We conducted our surveys with the Geometrics Micro-Fabricated Atomic Magnetometer (MFAM).

How to cite: Accomando, F., Florio, G., Dupuy, B., and Lee, M.: Toward an optimal assessment of UAV vertical magnetic gradient arrangement, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22338, https://doi.org/10.5194/egusphere-egu24-22338, 2024.

EGU24-22342 | ECS | Orals | EMRP2.2

Iterative Ratio Method: a method to map the depth to the Moho from gravity anomalies 

Dingding Wang, Wanyin Wang, and Giovanni Florio

Interfaces characterized by a density contrast are widely distributed in the Earth's interior, and their depths can be recovered by inversion of gravity data. A key parameter of the interface inversion is the density contrast. We propose to estimate a constant density contrast by a new method: the iterative-ratio method. It is based on the approximate invariance of the product between depth and a constant density contrast and on the availability of several depth constraints. The estimated density contrast is used to update the interface depth. By processing the synthetic Moho models, the inversion results show that the method is slightly affected by data noise and by the number of constraints, but it is sensitive to the constraint uncertainty. The method is finally demonstrated by mapping the Moho of the Santos basin (Brazil) according to the depth constraints and the regional gravity anomalies.

How to cite: Wang, D., Wang, W., and Florio, G.: Iterative Ratio Method: a method to map the depth to the Moho from gravity anomalies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22342, https://doi.org/10.5194/egusphere-egu24-22342, 2024.

The Beishan Orogen, located in the southernmost part of the Central Asian Orogenic Belt, comprises ophiolitic complexes, passive-margin strata, arc assemblages, and Precambrian basement rocks, recording oceanic subduction, accretion of oceanic materials onto continental margins, and continental-arc collision. However, debates surrounding its origin and evolution persist, attributed in part to the absence of high-resolution geophysical data, leading to varying interpretations in tectonic evolution models regarding the involved terranes and paleo-subduction polarity (Li et al., 2023). In this study, we present an electrical resistivity model of the crust and uppermost mantle in the Beishan Orogen from magnetotelluric (MT) data. The resistivity model suggests an overall resistive upper crust, with conductive features indicating paleo-suture zones and tectonic boundaries. The high resistivity lithosphere beneath Niujuanzi indicates both north- and southward subduction of the Hongliuhe-Xichangjing Ocean, potentially unveiling remnants of a cold fossil oceanic lithosphere. Conductors in mantle wedges on both sides of the high resistivity body are inferred to result from recycled carbonates introduced deep into the Earth through oceanic subduction, which is substantiated by recent laboratory measurements (Jing et al., 2023). These measurements demonstrate that even unmelted carbonates can enhance electrical conductivity through cation exchange reactions with silicates in the lower crust and uppermost mantle.

*This research is funded by the National Natural Science Foundation of China (42074089, 41774087, 41404060).

Reference

Jing, C., Hu, H., Dai, L., Sun, W., Wang, M., Hu, Z., 2023. Recycled carbonates elevate the electrical conductivity of deeply subducting eclogite in the Earth’s interior. Commun Earth Environ 4, 276. https://doi.org/10.1038/s43247-023-00936-w

Li, J., Wu, C., Chen, X., Zuza, A.V., Haproff, P.J., Yin, A., Shao, Z., 2023. Tectonic evolution of the Beishan orogen in central Asia: Subduction, accretion, and continent-continent collision during the closure of the Paleo-Asian Ocean. GSA Bulletin 135, 819–851. https://doi.org/10.1130/B36451.1

How to cite: Zhou, L., Zhang, L., and Jin, S.: Magnetotelluric Evidence for the Paleo-Subduction Polarity and Recycled Carbonates within the Beishan Orogen, Southern Central Asian Orogenic Belt , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-715, https://doi.org/10.5194/egusphere-egu24-715, 2024.

EGU24-2343 | ECS | Posters on site | EMRP2.4

Electromagnetic Insights: 3D Subsurface Modeling of Al-Hassa, Saudi Arabia 

Abid Khogali, Panagiotis Kirmizakis, Konstantinos Chavanidis, Abdul Latif Ashadi, Tilman Hanstein, Alexandros Stampolidis, Emin Candansayar, and Pantelis Soupios

Al-Hassa area features Saudi Arabia's largest oasis and one of the world's largest naturally irrigated land. Moreover, Al-Hassa area is very close to Ghawar, known as the largest conventional oil-field in the world. Additionally, more than 280 natural springs used in the past to water the farmland where the water in some of the springs, is used to be warm. The quality of water also exhibits spatial variations, hinting at a complex subsurface that must be characterized. Finally, the available geological information from outcrops, are very limited, since the majority of the study area is covered by a sand-layer. Based on the above, it seems that this important for its natural resources (oil & gas, groundwater, low-enthalpy geothermy) area is partly unexplored or the data are not available. The purpose of this work is to reconstruct the 3D subsurface geophysical structure of the study area by combining different geophysical electromagnetic (EM) methods. Thus, three EM geophysical methods to construct a detailed 3D model of the subsurface were applied. Specifically, 46 magnetotelluric (MT) stations, 6 audio magnetotelluric (AMT) stations, and 35 transient electromagnetic (TEM) stations were acquired within Al-Hassa National Park. The data from all these EM soundings were processed and integrated to achieve the highest resolution from the surface to the maximum depth of investigation. 2D and 3D processing, and joint interpretation was applied to all EM data. The EM findings were confirmed by gravity measurement conducted in the same area. The integration of various geophysical data sets, including TEM, MT, AMT and gravity data, uncovers lateral discontinuities in resistivity, a complex structure, and fracture zones acting as pathways or barriers to groundwater flow. This comprehensive modelling approach offers invaluable insights into the subsurface dynamics, enhancing our understanding for the complexity of the study area.

How to cite: Khogali, A., Kirmizakis, P., Chavanidis, K., Ashadi, A. L., Hanstein, T., Stampolidis, A., Candansayar, E., and Soupios, P.: Electromagnetic Insights: 3D Subsurface Modeling of Al-Hassa, Saudi Arabia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2343, https://doi.org/10.5194/egusphere-egu24-2343, 2024.

EGU24-2628 | Orals | EMRP2.4 | Highlight

Seismo-tectonics and magma chambers revealed by the 3D resistivity model in western Yunnan 

Qinghua Huang, Tao Ye, Xiaobin Chen, and Huiqian Zhang

Based on broadband magnetotelluric (MT) array data, we have obtained the three-dimensional (3-D) electrical resistivity model in western Yunnan, the southeastern Tibetan Plateau where the Quaternary intraplate Tengchong volcanism and seismic activities occur. Our MT model clearly reveals three conductive bodies in the depth ranges of 10–30 km in the Tengchong volcano area, which we interpret as three middle-lower crustal magma chambers associated with the Tengchong volcanism. Seismogenic faults in the Gaoligong Shear Zone (GLGSZ) are characterized by subvertical conductive zones bounded by resistive upper crustal layer on both sides. Earthquakes of moderate magnitudes near the GLGSZ have all occurred within the conductive fault zones at the bottom of the upper resistive crust. Our model also suggests a bifurcation of the crustal flow in western Yunnan, with a southwestern branch running into the Tengchong Block north of the Dayingjiang Fault and a southeastern branch flowing into the Baoshan Block. The current study provides evidence from electrical resistivity structure for the middle-lower crustal magma chambers in the Tengchong volcano area and detailed 3-D electrical structure of crustal channel flow in this active tectonic region.

How to cite: Huang, Q., Ye, T., Chen, X., and Zhang, H.: Seismo-tectonics and magma chambers revealed by the 3D resistivity model in western Yunnan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2628, https://doi.org/10.5194/egusphere-egu24-2628, 2024.

EGU24-3588 | ECS | Orals | EMRP2.4 | Highlight

3D ground-penetrating radar to characterize near-surface environments: Advances in data analysis and integrated geophysical interpretation 

Philipp Koyan, Julien Guillemoteau, Tim Klose, and Jens Tronicke

Ground-penetrating radar (GPR) is a widely acknowledged tool for imaging near-surface environments in various geological, hydrological, and sedimentological applications. In complex and heterogeneous settings, applying 3D GPR is crucial to correctly image subsurface architecture and, thus, to prevent misinterpretations. Recent advancements in GPR system design and instrumentation enable the collection of densely sampled 3D GPR datasets with superior resolution, establishing 3D GPR as a standard for near-surface structure imaging.

This study showcases the latest developments in analyzing and interpreting 3D GPR datasets. We demonstrate how GPR datasets and derived structural models contribute to a detailed understanding of complex near-surface environments. Using selected case studies, we present integrated interpretation approaches combining 3D GPR data and models, respectively, with the results of 3D electromagnetic induction surveying, 2D electrical resistivity tomography as well as 1D geophysical and geological borehole logging. Such a strategy allows for a more comprehensive and reliable near-surface characterization by integrating detailed 3D structural information with electrical/petrophysical property distributions and geological information, surpassing the limitations of typical 2D single-method interpretation approaches.

How to cite: Koyan, P., Guillemoteau, J., Klose, T., and Tronicke, J.: 3D ground-penetrating radar to characterize near-surface environments: Advances in data analysis and integrated geophysical interpretation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3588, https://doi.org/10.5194/egusphere-egu24-3588, 2024.

EGU24-5602 | ECS | Posters on site | EMRP2.4

Regional Magnetotelluric Studies across Mongolia: Report on New Measurements, New Models, and Implications for Intracontinental Deformation, Deep Mineral Systems, and Intraplate Volcanism 

Rafael Rigaud, Matthew J. Comeau, Erdenechimeg Batmagnai, Mikhail Kruglyakov, Alexey Kuvshinov, Michael Becken, Shoovdor Tserendug, and Sodnomsambuu Demberel

We are investigating the lithospheric properties and lithospheric architecture beneath Mongolia with three-dimensional models of the electrical resistivity generated from magnetotelluric measurements. In addition, thermo-mechanical numerical modelling, with geophysically-guided constraints, is being used to provide valuable insights by testing the mechanical viability of different hypotheses for the temporal evolution and dynamic processes within this region.  

Mongolia is located between the relatively stable Siberian craton and the extensional regime near the Baikal rift zone to the north and to the south the North China and Tarim cratons that have a northward-directed compressional regime. Due to its location, it is an excellent region to study intracontinental deformation. Furthermore, enigmatic continental intraplate basaltic volcanism of the Cenozoic age exists across Mongolia. In addition, this region contains economically important mineral zones (copper and gold), with the origin and evolution of the mineral systems linked to the whole-lithosphere architecture, crust-mantle interactions, and mantle convection dynamics.   

Magnetotelluric data has been collected across Western, Central, and Eastern Mongolia. Three field campaigns in 2016, 2017, and 2018 collected more than 328 sites on an array (50 km spacing) and along three dense profiles (3-15 km spacing) that focused on the Hangai Dome (plateau) and Gobi-Altai (Arkhangai, Bayankhongor) over an area of approximately 800 km (north-south) by 400 km (east-west). Between 2020 and 2022, the array was extended to the east with 77 sites collected across central-east Mongolia (Bulgan, Selenge, Tuv, Uvurkhangai, Dundgovi; 400 by 200 km), including 34 sites along an 810 km long north-south profile crossing the Mongol-Okhotsk suture zone. In late 2022, 79 measurements were acquired in northern Mongolia across the Hovsgol region and Darhad (200 by 200 km) with an array and several profiles, which connect to data west of Lake Baikal. In early 2023, 38 sites were collected in central-east Mongolia (Umnugovi; 200 by 200 km), completing the eastern array. Later in 2023, a major field campaign was launched that successfully collected 150 measurements in western Mongolia (Zavkhan, Uvs, Govi-Altai, Khovd) over an area of approximately 500 by 400 km. This included an array (50 km spacing) and three dense profiles (5-10 km spacing). This gives approximately 700 magnetotelluric measurements collected over a total area of approximately 1000 km (north-south) by more than 1150 km (east-west).   

This is a large area that approaches the scope of several other regional and national magnetotelluric survey programs. What’s more, this dataset fills an important gap between the existing magnetotelluric data across China and the Tibetan Plateau with several profiles across the Siberian Craton, in principle completing a remarkable transect of 4000 km across a variety of tectonic domains.  

In this presentation, we will report on the new measurements. They will be integrated into the previously collected dataset, and new models will be generated that incorporate all data. We will also present new models of western, central and eastern Mongolia that provide insights on the properties, structure, and evolution of the Hangai Dome, the Mongol-Okhotsk suture and the Central Asian Orogenic Belt.  

How to cite: Rigaud, R., J. Comeau, M., Batmagnai, E., Kruglyakov, M., Kuvshinov, A., Becken, M., Tserendug, S., and Demberel, S.: Regional Magnetotelluric Studies across Mongolia: Report on New Measurements, New Models, and Implications for Intracontinental Deformation, Deep Mineral Systems, and Intraplate Volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5602, https://doi.org/10.5194/egusphere-egu24-5602, 2024.

EGU24-5910 | ECS | Orals | EMRP2.4 | Highlight

Deep learning techniques applied to 3-D probabilistic inversion of controlled-source electromagnetic data in a marine environment 

Matias Elias, Marina Rosas-Carbajal, and Fabio I. Zyserman

We designed an computer efficient, probabilistis 3-D inversion algorithm for CSEM data. It is commonly known that multiple physical descriptions of the subsurface fit the geophysical data equally well, due to incomplete measurement coverage, incomplete physical description of the problem, and model overparameterization. A probabilistic inversion approach allows us to explicitly account for data and model uncertainty. Probabilistic inversion is a demanding process in terms of the number of forward model computations required to sample the posterior probability density function of model parameters. Therefore, we use an efficient sampling algorithm (DREAM(ZS)combined with strategies to optimize the forward model by approximations and error estimation with deep learning techniques. Regarding the latter, we propose an alternative (approximate) approach to our forward model for simulating the electromagnetic (EM) response which reduces the computing time, and we quantify the modeling error committed directly in the inversion process. Thus, we create a statistical error-model related to the approximate EM response by training a Spatial Generative Adversarial Network (SGAN). In contrast to other neural networks, the SGAN training process has the particularity of being a competition between a Generator, which creates fake samples of the training set, and a Critic, which scores the quality of both true or fakesamples. After training the Generator results in a parametric model of the probability density function of the training set (modeling errors). This parametric error-model is incorporated into the inversion process as a complement to correct and quantify the error in our approximate forward model. To test our methodology we first proposed a synthetic experiment of a marine exploration environment. The implementation and subsequent training of the network allowed us to show that SGAN is useful to generate a statistical error-model. The comparison between a set of samples created with the Generator and the training set shows similarities in the statistical properties of both. Thus, we obtain a parameter-reduced error-model capable of representing the different components of the EM response at a considerable number of receivers and frequencies. In addition, the inversion process is significantly accelerated by introducing the forward model approximations, and the incorporation of the statistical error-model improved the determination of the true parameters in our synthetic test case. We then applied our methodology to the inversion of CSEM data acquired in a marine environment.

How to cite: Elias, M., Rosas-Carbajal, M., and Zyserman, F. I.: Deep learning techniques applied to 3-D probabilistic inversion of controlled-source electromagnetic data in a marine environment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5910, https://doi.org/10.5194/egusphere-egu24-5910, 2024.

Imposing structural constraints between grids of variable sizes is problematic because different geophysical techniques employ different grid divisions. We propose a new collaborative inversion approach and utilize it to invert the proposed 2-D ATEM and 2-D Magnetic Methods with Induced Polarization (IP) effects, which overcomes the problem of imposing cross-gradient constraints at different grid sizes. The grid mapping technique is included into the iterative collaborative inversion process by the inversion strategy. The combined data inversion results show that the technique may successfully leverage data complements to improve the accuracy of the medium boundary description results. The concept is suitable to collaborative inversion of geophysical methods with arbitrary grid divisions and successfully solves the problem of mismatched grid divisions in collaborative inversion.

How to cite: Lei, D. and Ren, H.: A cooperative inversion of airborne transient electromagnetic and magnetic methods based on grid mapping, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7184, https://doi.org/10.5194/egusphere-egu24-7184, 2024.

EGU24-8201 | ECS | Posters on site | EMRP2.4

Regional-scale magnetotelluric data processing and interpretation in Transdanubia, Hungary 

Renáta Szebenyi and János Kiss

Magnetotellurics is often used as a tool in general geologic research. At the Supervisory Authority for Regulatory Affairs (SARA), Hungary, one of our aims is to form large-scale magnetotelluric (MT) key sections in order to be able to gain new insights into the diverse geologic and tectonic settings of our area through mapping the distribution of rocks’ electrical properties. For this purpose, MT sections have been created which cross Hungary from one country border to the other. Mainly archived MT data is used but, in some cases, new field measurements are needed to fill data gaps in the created profiles.

One of the magnetotelluric key sections is the MTOA-02 which crosses the western part of Hungary in a NW-SE direction. It is composed of three archived sub-sections and new supplementary MT stations which were measured during the past year in order to fill a 20 km long part of the profile without data. All these data were integrated into the dataset, analyzed and processed together which resulted in an approximately 210 km long magnetotelluric section. The processing of the data in this way is considered a novelty in the institute’s activity since previously, archived sub-sections were not handled together, they were only processed separately at the period of their acquisition.

As a part of data processing filtering, smoothing, the correction of static shift, 1D, and 2D inversions were carried out. For the interpretation both inversion results and observations from raw magnetotelluric data were used accompanied with information from other geological-geophysical methods (gravity, magnetism, geologic maps and cross sections) to confirm our conclusions from the resistivity profiles. As a result, main tectonic elements and geologic units were identified. Main structural lines include the Rába line, Balaton line, Kapos line and Mecsekalja line. Identified geologic units are as follows: the Penninic Unit and the subducted European passive margin, the Austroalpine Unit, the Transdanubian Range Unit, the Mid-Hungarian Megaunit, the Tisza Megaunit and Miocene sedimentary rocks filling the Pannonian back-arc basin. During data analyzes, we have noticed that phase-depth sections may be used to identify the depth of the Pre-Cenozoic basement in certain areas where low resistivity sedimentary rocks filling the basins do not show significant resistivity contrast with the underlying strata and hence the basement cannot be distinguished accurately on resistivity sections. This may help interpretations in the area of the Little Hungarian Plain.

How to cite: Szebenyi, R. and Kiss, J.: Regional-scale magnetotelluric data processing and interpretation in Transdanubia, Hungary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8201, https://doi.org/10.5194/egusphere-egu24-8201, 2024.

EGU24-9665 | ECS | Posters on site | EMRP2.4

The potential of the electromagnetic induction method to monitor temperature changes in the near-surface 

Maria Carrizo, Dieter Werthmüller, and Evert Slob

Geothermal heat production might pose the risk of degrading groundwater quality due to temperature changes, which may lead to ecological and economic impacts. Monitoring and quantifying spatial and temporal changes in the groundwater temperature are challenging but necessary for reliable environmental evaluations. Electromagnetic Induction (EMI) measurements have been extensively used in environmental monitoring, since Electrical Conductivity (EC) is very sensitive to changes in the groundwater properties, such as the presence of contaminants or changes in fluid temperature. Subsurface EC estimates can be obtained through the inversion of EMI measurements in a non-invasive and cost-effective way. However, these estimates are inherently ambiguous because of the ill-posed nature of the inverse problem.

In this project, we investigate how to provide an accurate EC estimation of the subsurface using EMI measurements, with the aim of understanding the near-surface groundwater temperature evolution. We test two different inversion methodologies to estimate horizontally layered EC models. The first, using a search in a pre-computed and stored database containing a discrete version of the full solution space finds the model that fits the data best in the least squares sense. The second, using a gradient descent optimization. We tested the method using different numerical scenarios. We show that for a horizontally 3-layered model using a gradient descent optimization might be insufficient to obtain an accurate estimate. Moreover, we demonstrate that the in-phase part of the measurement contains information about the electrical conductivity that might be useful to include in the estimation. Finally, our results give insight into the challenges and limitations of the estimation of EC horizontally layered models using frequency domain EMI data in the context of geothermal operations in the Netherlands.

How to cite: Carrizo, M., Werthmüller, D., and Slob, E.: The potential of the electromagnetic induction method to monitor temperature changes in the near-surface, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9665, https://doi.org/10.5194/egusphere-egu24-9665, 2024.

EGU24-11238 | Orals | EMRP2.4

Application of transient electromagnetic to understand infiltration in farmlands in karst areas of Yucatan, Mexico 

Adrian Flores Orozco, Lukas Aigner, Isidro Montes-Avila, Clemens Moser, Fernanda Cerca-Ruiz, Germán Giácoman-Vallejos, and Antonio Cardona-Benavides

Rising temperatures as well as accompanying changes in precipitation rates and periods due to climate change demand an efficient use of water resources for farming. The Yucatan peninsula (Mexico) is not only affected by the climatic changes per se but also by their consequences, such as the deepening of the groundwater table and seawater intrusion, enhanced by population growth. These threats call for the development of efficient irrigation methods to maintain farming activities. Moreover, the management of water resources needs to consider irregular water infiltration as well as groundwater flow and storage due to the presence of fractures, caves and low permeable limestone associated to the karstic geology of the peninsula. We evaluate the application of the transient electromagnetic (TEM) method to gain information about subsurface architecture, in particular to identify the presence of unknown cavities that may act as preferential flow paths. The TEM is a geophysical method well suited for hydrogeological investigations in karst environments as it resolves the subsurface electrical conductivity without galvanic contact with the ground and with a higher spatial resolution compared to borehole data. The TEM survey was planned for a depth of investigation of ca. 60 m across a citrus farm on the Yucatan peninsula where treated wastewater is used for irrigation. While such practice minimizes the exploitation of groundwater, some concerns have been raised about the possible contamination of the aquifer due to with the use of treated wastewater. The difference in the electrical conductivity between the treated wastewater and the groundwater due to their different chemical composition renders the TEM as a suitable method to delineate pathways of the irrigation water within the subsurface as well as hydraulic connections with the aquifer. In a first step, the TEM soundings were inverted independently to enhance the spatial variability associated to the complexity of the karst system. Interpretation of the resulting electrical models in terms of the aquifer geometry and preferential flow paths took into account the existing information from boreholes and irrigation points. We also conducted a sensitivity analysis of the resolved model parameters after the inversion of the data, to better evaluate the interpretation of our results. In a second step, we conducted a stochastic analysis of the TEM data to quantify the uncertainty of our results, in particular, regarding the resolved geometry of the aquifer. Our results reveal changes in the electrical conductivity at different depths and across the farmland. High conductivity values, which were observed close to the surface, are related to the infiltration of the treated wastewater. Deeper variations in electrical conductivity reveal the presence of caves and other preferential flow paths for groundwater. Areas revealing high resistivity values are associated with less karstified rocks that may act as hydraulic barriers.

How to cite: Flores Orozco, A., Aigner, L., Montes-Avila, I., Moser, C., Cerca-Ruiz, F., Giácoman-Vallejos, G., and Cardona-Benavides, A.: Application of transient electromagnetic to understand infiltration in farmlands in karst areas of Yucatan, Mexico, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11238, https://doi.org/10.5194/egusphere-egu24-11238, 2024.

EGU24-12696 | ECS | Posters on site | EMRP2.4 | Highlight

Investigating the GIC index levels in the Mediterranean region during the strongest magnetic storms of solar cycle 25 

Adamantia Zoe Boutsi, Georgios Balasis, Stavros Dimitrakoudis, Ioannis A. Daglis, Kanaris Tsinganos, Constantinos Papadimitriou, and Omiros Giannakis

Geomagnetically Induced Currents (GICs) flowing along electrically conductive infrastructure, such as power transmission lines, are produced by a naturally induced geoelectric field during geomagnetic disturbances, such as magnetic storms. GICs can cause widespread blackouts across power grids, resulting in the loss of electric power. Although GIC intensity is greater in high latitudes, recent studies highlight the importance of considering GIC risks for countries located in the low and middle latitudes, including the Mediterranean region. GIC index is a proxy of the geoelectric field calculated entirely from geomagnetic field variations. Following a recent study where we investigated the GIC index levels for the Mediterranean (i.e., Greece, Italy, France, Spain, Algeria, and Turkey) for the most intense magnetic storms of solar cycle 24 (2008–2019), here we expand the analysis to encompass solar cycle 25. From the beginning of solar cycle 25 six major magnetic storms occurred with Dst index ≤ -100 nT. The three most intense magnetic storms (-163 nT < Dst < -212 nT) occurred in March, April and November 2023. We focus on those to compare with previous results showing that GIC index increases are well correlated with Storm Sudden Commencements (SSCs) and shed more light upon the expected GIC activity levels in the Mediterranean region during extreme events.

How to cite: Boutsi, A. Z., Balasis, G., Dimitrakoudis, S., Daglis, I. A., Tsinganos, K., Papadimitriou, C., and Giannakis, O.: Investigating the GIC index levels in the Mediterranean region during the strongest magnetic storms of solar cycle 25, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12696, https://doi.org/10.5194/egusphere-egu24-12696, 2024.

The forward modelling for curl-curl equations is the fundament for time-harmonic electromagnetic (EM) problems in geophysics. The simulations with the discretized partial differential equations (PDE) are computationally intensive and crucial to practical geophysical EM problems like Magnetotelluric/Controlled Source EM. However, most published algorithms for curl-curl PDEs are still CPU-based and cannot utilize the rapid development of modern large-scale multi-GPU parallel architectures. Based on previously proposed CPU-based divergence-free modelling algorithm, we develop a hybrid parallel paradigm to exploit the high-throughput of interconnected heterogenous parallel systems equipped with multiple GPUs. The large sparse linear system derived from the staggered-grid finite-difference approximation of curl-curl problem is decomposed into sub-domains and solved efficiently with a mixed-precision Krylov subspace GPU algorithm in parallel. To demonstrate how the practical inversion problems can be substantially accelerated, we test the new algorithm with both the synthetic and real-world 3D models, for forward/adjoint calculations. The test results show a promising ~3.5x improvement regarding the computation speed on a small NVIDIA® HGX based system, over a conventional CPU-base server cluster with 12 nodes. This may significantly reduce the computation time and carbon footage for large-scale frequency domain EM inversion problems and brings the possibility of near real-time EM imaging, as in engineering and environmental applications.

How to cite: Dong, H. and Sun, K.: Multi-GPU accelerated parallel modelling for geophysical electromagnetic inversions , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13759, https://doi.org/10.5194/egusphere-egu24-13759, 2024.

EGU24-14779 | ECS | Orals | EMRP2.4 | Highlight

Exploration of IOCG deposits in Queensland, Australia using geophysical models of Ernest Henry copper mine 

Faraz Sakhaeyan, Sayyed Mohammad Abtahi Forooshani, and Hamzeh Sadeghisorkhani

The  Ernest Henry copper mine is one of the main Australian copper resources and a typical Iron Oxide Copper Gold (IOCG) deposit case. These deposits have specific geophysical signatures, e.g., considerable magnetic susceptibility and low resistivity due to magnetite mineralization. This research studies the geophysical models estimated via the inversion of magnetic and magnetotelluric in the Ernest Henry mine area. We also conducted these inversions in two other areas close to the Ernest  Henry mine, named A and B, which show magnetic anomalies similar to the Ernest Henry mine. Then, we compared the estimated models in these areas with those in  Ernest Henry's area. Three-dimensional inversion of magnetic data using the Li and Oldenburg algorithm revealed masses with magnetic susceptibilities higher than 0.019, 0.048, and 0.011 in SI units in the Ernest Henry, A and B areas, respectively. All the masses were extending from the surface to depths of one to three kilometres. Next, impedance analyses of magnetotelluric data indicated a two-dimensional behaviour of the Earth up to a frequency of 1 Hz in all the areas. Also,  we conducted two-dimensional inversions of these data along a profile for each area. A comparison of the estimated resistivities demonstrated a relatively conductive mass with a resistivity of less than 30 ohmm at depths of 5 km and beyond in all three areas. These models also demonstrated a decrease in the resistivity along the fault lines within the ranges, corresponding to the location of masses with relatively significant magnetic susceptibility identified during the magnetic data inversions. Geochemical analysis of copper grade variations in exploratory boreholes drilled in areas A and B indicated an increase in copper concentration exceeding 400 ppm in both areas. The structure of the estimated geophysical models in areas A and B and those estimated in the Ernest Henry area is similar. Besides, geochemical analysis of copper grade in exploratory boreholes drilled in areas A and B indicated an increase in copper concentration exceeding 400 ppm in both areas. Therefore, we deduce the possibility of IOCG copper mineralization deposits similar to the Ernst Henry mine in areas A and B. Meanwhile, since the concentrations of probable mineralizations have occurred along a fault zone in all the models, we suspect that the mineralization likely originated from hydrothermal solutions. These solutions spread from fault lines adjacent to highly resistive intrusive masses to the surface, causing the mineralization of magnetite and copper ores.

How to cite: Sakhaeyan, F., Abtahi Forooshani, S. M., and Sadeghisorkhani, H.: Exploration of IOCG deposits in Queensland, Australia using geophysical models of Ernest Henry copper mine, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14779, https://doi.org/10.5194/egusphere-egu24-14779, 2024.

EGU24-15298 | ECS | Posters on site | EMRP2.4

Parallel inversion of drone-based electromagnetic data for near-surface geophysical prospecting 

Longying Xiao, Cedric Patzer, and Jochen Kamm

The rapid development of geophysical systems utilizing drones facilitates mineral exploration with more efficient and economical data collection. To align the progress of hardware advancement and meet the model complexity needs for exploration, we aim to develop an efficient and robust 3D inversion code to interpret the drone-based EM data. Here, we present the framework of the implementation and show some preliminary results of the development.

We use a total electric field formulation with curl-conforming Nédélec elements to solve Maxwell equations in the frequency domain. Octree grids are used to accommodate the meshing of even large models at adequate resolution, separately in forward and inverse domains. A direct solver (MUMPS) is applied to solve the linear system of equations of the forward problem. The code is implemented in C++ and allows for easy adaptation for various sources and data types.

Currently, to solve the inverse problem, we minimize the misfit using a Gauss-Newton scheme with explicit computation of the Jacobian. The implementation was built on the deal.II library, where the interface wrappers allow to use MUMPS and PETSc for numerically intensive computations, such as system equation solving (MUMPS) and inversion model update (PETSC Conjugate Gradient solver). Currently, the code is parallelized using MPI throughout for both forward and inverse modeling and additionally OpenMP for MUMPS only.

The code is planned to be a reliable and competent imaging tool, that can be applied for both commercial and educational use. Currently, the code is under the development and testing stage. The preliminary results will be shown on-site.

How to cite: Xiao, L., Patzer, C., and Kamm, J.: Parallel inversion of drone-based electromagnetic data for near-surface geophysical prospecting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15298, https://doi.org/10.5194/egusphere-egu24-15298, 2024.

EGU24-15344 | Posters on site | EMRP2.4 | Highlight

Imaging the Electrical Resistivity Structure of a Locked Fault Segment: The Ganos Fault example 

Bülent Tank, Ruken Yazıcı, Esra Doğukan, Tunç Demir, Gözde Taşseten, Pınar Duran, and Tannaz Assar

The Ganos Fault, in the westernmost part of the North Anatolian Fault Zone (NAFZ), stayed quiet for approximately 146 years before two catastrophic events shook the area in the summer of 1912. The historical records point out that two devastating activities shook both sides of the Marmara Sea in 1766, too. Following the 1766 events, on August 9th, 1912, two blocks of the dextral Ganos Fault shifted one more time to create an Mw = 7.4 event near Mürefte in Tekirdağ. Nearly a month later, further to the west, the fault zone moved on September 13th, forcing another disastrous Mw= 6.8 earthquake. Almost 112 years have passed since then (leaving approximately 34 more years to complete the recurrence), and the Ganos Fault is again acting as a seismic gap. In brief, the Ganos Fault tends to generate another series of earthquakes in the region, and the fault zone characteristics of this locked segment are poorly known. In this study, magnetotellurics (MT) method is utilized to image the crustal electrical resistivity structure for deciphering the fault zone geometry. With this object in mind, simultaneous electric and magnetic observations were made at nearly 40 sites in two campaigns. For each observation point, the collected data were transferred to the frequency domain where the electromagnetic impedance tensor elements were calculated with robust processing algorithms (Birrp) for wideband frequencies. Following the dimensionality analyses performed with various tools such as Groom and Bailey decomposition, phase tensor analysis, etc., which eventually pointed out a geo-electric strike angle of nearly ~N60oE, numerical models based on two- and three-dimensional algorithms (such as MT2D and ModEM) were developed to image the fault zone properties of the Ganos Fault. Several numerical models were calculated to realize the influence of the coast-effect caused by the Marmara Sea. Pre-modeling analysis results and the final models suggest that (i) the geo-electric strike angle of ~N60oE agrees well with the earlier results, the geology and the fault’s geometry, (ii) the Ganos Fault acts as a geological boundary between the Eocene-aged Keşan Formation in the north and Miocene-aged Çengelli Formation in the south, (iii) while the Keşan Formation defines a continuous tubular highly resistive zone (~500- 800 Ωm) that may be acting as the seismogenic zone along the Ganos Fault, the Çengelli Formation appears to be less resistive in coherent with the ages of the formations highlighted earlier, (iv) the aforementioned resistive block reaches to a depth of nearly 15 - 18 km and this feature may mark the bottom of the seismogenic zone.          

How to cite: Tank, B., Yazıcı, R., Doğukan, E., Demir, T., Taşseten, G., Duran, P., and Assar, T.: Imaging the Electrical Resistivity Structure of a Locked Fault Segment: The Ganos Fault example, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15344, https://doi.org/10.5194/egusphere-egu24-15344, 2024.

EGU24-16111 | ECS | Posters on site | EMRP2.4

An efficient workflow for airborne electromagnetic data processing for advanced applications. 

Wouter Deleersnyder, Thomas Hermans, and David Dudal

Airborne electromagnetics made its first successful entry into mineral exploration applications, mainly by interpreting anomalies in the data. Airborne EM methods will increasingly be used for more advanced large-scale applications, such as mapping the fresh saltwater interface. Every step in the data interpretation is crucial in this regard. We believe the state-of-the-art (such as in [1]) is a good starting point for an initial data interpretation, though not the endpoint. We propose a workflow for airborne EM processing, where the current state-of-the-art may be too limited for your advanced applications. It consists out of four steps:

1. First processing with Quasi(or pseudo)-2D/3D inversion (with your favourite or typical smooth inversion scheme, such as in [1])

2. If the sharpness of the obtained inversion model is inappropriate, perform a tunable regularization with the inversion model from step 1 as the initial model. This can be achieved with wavelet-based regularization schemes [2], where prior information can be incorporated by the choice of the wavelet or, in the absence of prior information, the non-uniqueness can be assessed with the ensemble approach.

3. Where is multidimensionality a possible issue? In steps 1 and 2, we have used a 1D forward approximation, potentially yielding multidimensionality issues. An appraisal method, such as [3], enables the assessment of an inversion model obtained with 1D forward approximation for areas that do not fit the true multidimensionality of the observed data because it deviates from the 1D assumption.

3. Re-interpret zones with significant multidimensionality with either full 3D simulations or a surrogate model [4], replacing the computationally demanding 3D full simulations.

 

[1] Siemon, B., Auken, E., & Christiansen, A. V. (2009). Laterally constrained inversion of helicopter-borne frequency-domain electromagnetic data. Journal of Applied Geophysics, https://doi.org/10.1016/j.jappgeo.2007.11.003.

[2] Deleersnyder, W., Maveau, B., Hermans, T., & Dudal, D. (2023). Flexible quasi-2D inversion of time-domain AEM data, using a wavelet-based complexity measure. Geophysical Journal International,  https://doi.org/10.1093/gji/ggad032.

[3] Deleersnyder, W., Dudal, D., & Hermans, T. (2022). Novel airborne em image appraisal tool for imperfect forward modeling. Remote Sensing, https://doi.org/10.3390/rs14225757.

[4] Deleersnyder, W., Dudal, D., & Hermans, T. (2023, February). Machine learning assisted fast forward 3D modelling for time-domain electromagnetic induction data–lessons from a simplified case. In EGU General Assembly 2023, Location: Vienna, Austria, https://doi.org/10.5194/egusphere-egu23-12015.

How to cite: Deleersnyder, W., Hermans, T., and Dudal, D.: An efficient workflow for airborne electromagnetic data processing for advanced applications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16111, https://doi.org/10.5194/egusphere-egu24-16111, 2024.

EGU24-20378 | ECS | Orals | EMRP2.4

Seismic constrained magnetotelluric inversion for iron orebody at Gällivare, Sweden 

Georg Andreas Donoso, Oskar Rydman, Maxim Yu Smirnov, Niklas Juhojuntti, and Harald Van Den Berg

The Norrbotten region (Northern Sweden) boasts a rich history of mineral exploration, particularly in the Kiruna and Gällivare areas. Both passive and active geophysical exploration methods, specifically magnetotelluric (MT) and seismic measurements, have played pivotal roles in guiding mineral exploration in this region. In this study, we propose an MT inversion method constrained by interpreted 3D seismic reflections in the Gällivare area of northern Sweden, with a focus on a known iron orebody, primarily composed of magnetite. Constraints were introduced using a covariance matrix created from interpreted 3D seismic reflection surfaces. 

Between 2016 and 2021-2023 (as part of the D-REX project), Luleå University of Technology and LKAB collaborated to collect broadband magnetotelluric data from 116 stations around Gällivare. The survey covered a total area of 15 x 15 km, with a site spacing of approximately 1 km where allowed by terrain conditions. Similarly, in the same area, 3D seismic data was acquired by a service company, made available as 3D stacked data. For this study, a subset of the acquired MT data was used to limit the modelling domain to the area covered by 3D reflection seismic, resulting in a square area of approximately 5 x 5 km, comprising 17 MT stations. Only higher frequencies (10^-3 to 1Hz) were considered to focus on the shallow area where seismic reflections are prominent (approximately 2000 m depth). 

The MT data were inverted using the ModEM code on a 120 x 120 x 50 meters grid with 10 growing boundary cells in horizontal directions and 30 in the vertical direction, facilitating valid electromagnetic boundary conditions during the inversion process. The dense discretization was chosen to better delineate the interpreted seismic surfaces. Subsequently, observed seismic reflection features, expected to be associated with an orebody of interest, were manually picked and interpreted. A Python code was developed to convert the interpreted surfaces into a binary 3D grid, matching the one used for the MT inversion in ModEM. This grid was exported and converted into a covariance matrix, utilized as a smoothing constrain to limit the interaction between cells inside and outside of the observed seismic surface in the inversion model. For comparison purposes, the same MT subset was also inverted using the same parameters but without a covariance matrix constraint.  

Upon comparing the results of both inversions, it was observed that the constrained model converges faster. This is advantageous not only for reduced computing time but also because the mathematical model stabilizes more quickly while achieving similar residual RMS values in both cases.  The resulting electrical resistivity model exhibits a more geological behaviour after including the smoothing constraint, aligning with the surface behaviour observed in the seismic data. 

The successful application of MT inversion methods constrained by seismic data is anticipated to reduce uncertainty in the electrical resistivity models of orebodies in the Gällivare mining area when compared to MT surface measurements alone, thereby enhancing confidence in the final inversion results and exploration efforts. 

How to cite: Donoso, G. A., Rydman, O., Yu Smirnov, M., Juhojuntti, N., and Van Den Berg, H.: Seismic constrained magnetotelluric inversion for iron orebody at Gällivare, Sweden, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20378, https://doi.org/10.5194/egusphere-egu24-20378, 2024.

EGU24-20520 | ECS | Posters on site | EMRP2.4

Investigating Quick Clays in Norway Using CSRMT Data 

Shunguo Wang, Martin Landrø, Mehrdad Bastani, Kenneth Duffaut, Ståle E. Johansen, and Robin A. Rørstadbotnen

Recent years have witnessed an alarming increase in quick-clay landslides in Nordic countries, such as in Alta (Norway), Gjerdrum (Norway), and Stenungsund (Sweden), resulting in substantial damages and loss of lives. This study focuses on the application of geophysical methods, particularly the Controlled-source Radio-magnetotelluric (CSRMT) technique, to understand the characteristics and model the geometry and possibly dynamics of quick clay in these regions. The CSRMT method, combines Radio-magnetotelluric (RMT) and Controlled-source Magnetotelluric (CSMT) techniques and offers an innovative approach for investigating the electrical resistivity of subterranean structures, crucial for identifying quick clay zones. The Rissa region in Norway provides a unique opportunity for this research due to its historical context and existing infrastructure for geophysical studies. The catastrophic Rissa landslide of 1978 led to an extensive national quick clay mapping initiative, forming the basis for this study. We have also collected Distributed Acoustic Sensing (DAS) data at Rissa, intending to integrate it with CSRMT data for comprehensive analysis.

Borehole analyses at the Rissa site reveal a relatively simple stratigraphy with a flat terrain and a marine clay stratum about 20 meters thick. Quick clay layers, identifiable due to their higher electrical resistivity compared to marine clays, are sandwiched in borehole samples. Our study utilizes (CS)RMT to model these layers and assess the impact of seasonal variations on their characteristics. Data collection involved a 250-meter long CSRMT profile with a 10-meter station spacing conducted in both summer and winter seasons. The EnviroMT instrument from Uppsala University was used for data acquisition. This time-lapse approach was critical to study the resistivity differences due to seasonal variation at the quick clay site.

Results from modelling the CSRMT data show a four-layer model including L1-L4. L2 appeared thicker in winter, possibly due to reduced freshwater. Conversely, in some locations, L2 appeared thicker. These findings show that CSRMT data can distinguish resistivity differences at a quick-clay site due to seasonal variations. This research offers significant insights into the modelling of seasonal variations of the resistivity related to changes in the water content which in turn might lead to development of areas with quick clays. The integration of CSRMT and DAS data presents a novel approach to studying these phenomena, potentially aiding in better understanding and predicting quick-clay landslide triggering. The findings are not only crucial for academic research but also have profound implications for infrastructure planning and disaster management in regions prone to quick-clay landslides.

How to cite: Wang, S., Landrø, M., Bastani, M., Duffaut, K., Johansen, S. E., and Rørstadbotnen, R. A.: Investigating Quick Clays in Norway Using CSRMT Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20520, https://doi.org/10.5194/egusphere-egu24-20520, 2024.

EGU24-1383 | ECS | PICO | CR5.1

Basal debris at an Antarctic ice rise revealed by seismic amplitude-vs-angle analysis.  

Ronan Agnew, Alex Brisbourne, Adam Booth, and Roger Clark

Reconstructing past ice sheets is important for understanding the response of modern ice sheets to changes in climate. The evolution of the Weddell Sea Sector’s grounding line since the last glacial maximum (LGM) to its present position remains ambiguous; previous authors have proposed hypotheses both of monotonic grounding line retreat and of rapid grounding line retreat followed by readvance. However, distinguishing these scenarios with current observations remains difficult. To explore these scenarios, we report seismic measurements of basal properties at KIR, an ice rise in the Weddell Sea Sector, West Antarctica. A three-component seismic survey enabled detection of the compressional (P) wave reflection and the converted (PS) wave reflection (an incident P wave converted to a shear wave at the base-ice reflector) from the base of KIR. Amplitude-vs-angle (AVA) analysis aims to constrain the physical properties (namely density, seismic velocity, by measuring the variation of reflectivity with incidence angle at the reflector. By jointly inverting the AVA responses of the PP wave reflection and the PS reflection, we increase the confidence in the interpretation of the base-ice properties. 

Analysis of PP and PS AVA responses at KIR indicates that the reflection arises from a material with a P wave velocity of 4.03 ± 0.05 km/s, an S wave velocity of 2.16 ± 0.06 km/s and a density of 1.44 ± 0.06 g/cm3; these properties are consistent with a reflection from a layer of entrained basal debris, with 20-30% debris by volume. The observed properties are not indicative of interference at a thin layer, as observed beneath glaciers elsewhere. The absence of deeper subglacial reflections indicates a poorly-defined boundary between this basal debris layer and the underlying subglacial material, which we therefore propose consists of frozen sediments . If this interpretation is correct, the presence of a debris layer overlying basal frozen sediment indicates a potential retreat/readvance scenario for KIR. A possible scenario is a previous episode of flow during which KIR may have been weakly grounded as an ice rumple, followed by grounding on the lee side of the bathymetric high and subsequent freezing of subglacial sediments. However, the origin of such a homogeneous and debris-rich layer remains unclear. The indication of a reflection from a basal debris layer raises questions about whether conventionally interpreted basal reflections can truly be considered as such, and whether these interpretations may mask the true nature of the underlying subglacial material. This ambiguity may be most effectively reconciled by borehole sampling.

How to cite: Agnew, R., Brisbourne, A., Booth, A., and Clark, R.: Basal debris at an Antarctic ice rise revealed by seismic amplitude-vs-angle analysis. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1383, https://doi.org/10.5194/egusphere-egu24-1383, 2024.

EGU24-4532 | ECS | PICO | CR5.1

Conductive textile electrodes for time-efficient ERT surveys performed in coarse-blocky mountain environments 

Mirko Pavoni, Jacopo Boaga, Alexander Bast, Matthias Lichtenegger, and Johannes Buckel

Electrical resistivity tomography (ERT) is one of the most accurate geophysical techniques to distinguish between frozen and unfrozen ground in permafrost areas. Performing the measurements, however, requires considerable logistics and time efforts. This is mainly due to the fact that optimal galvanic contact between the electrodes and the ground surface is necessary to collect reliable ERT datasets. Therefore, the traditional steel-spike electrodes must be steadily coupled between the boulders and wet with salt water on coarse blocky surfaces. To further decrease the contact resistances, sponges soaked in salt water can be inserted between the spike and the surface of rocks. Nevertheless, this traditional coupling system is particularly time-consuming, making it challenging to collect several ERT survey lines in a single workday in mountain environments. Recently developed conductive textile electrodes were applied to facilitate the deployment of ERT arrays in rock glacier environments. Instead of hammering the steel spikes, the conductive textile electrodes can be easily pushed between the boulders and wet with less water (compared to the sponges). Consequently, this new electrode approach decreases the time needed to prepare an ERT array. In this work, we evaluate the performance of the textile electrodes by comparing these with the traditional electrode approach, considering common investigation lines. This comparative test has been carried out in three test sites, which present different lithologies, surface characteristics and using different electrode spacing. The collected datasets were statistically analysed with robust regression analysis and Wilcoxon rank-sum test to examine the accuracy and significant differences between the two electrode systems regarding contact resistances, injected electrical current, measured apparent resistivities, reciprocal error, and inverted resistivity values. The obtained results demonstrate that conductive textile electrodes are suitable to collect reliable ERT datasets and, consequently, applying this approach in future ERT measurements performed in high mountain environments with coarse blocky surfaces (e.g. rockfall deposits, blocky slopes, or rock glaciers) would allow to acquire more survey lines (e.g. realisation of pseudo-3D geometries) extending the characterisation of the subsurface.

How to cite: Pavoni, M., Boaga, J., Bast, A., Lichtenegger, M., and Buckel, J.: Conductive textile electrodes for time-efficient ERT surveys performed in coarse-blocky mountain environments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4532, https://doi.org/10.5194/egusphere-egu24-4532, 2024.

EGU24-5435 | PICO | CR5.1

Demonstrating a large UAV for Antarctic environmental science 

Tom Jordan and Carl Robinson

Airborne survey is one of the most important observational techniques in environmental science. This is especially true in polar settings where access is challenging and observational requirements, such as ice sounding radar, in situ study of turbulent atmospheric processes, cloud cover, or requirements for high resolution potential field data, limit use of satellite data. Although critical, airborne survey using traditional platforms, such as the versatile twin otter aircraft operated by the British Antarctic Survey (BAS), come with a relatively high logistical, financial, and environmental (CO2) footprint. Larger UAV’s offer an alternative, but as yet un-realised, lower impact platform to deliver the same, if not more scientific data.

Through the Innovate UK SWARM project BAS is collaborating with Windracers to trial their large (10 m wing span) Ultra UAV as a platform for environmental science. Making use of the large (700 L/max 100 kg), easily accessible payload bay and a series of interchangeable payload floors this trial will be carried out in February/March 2023. The science payloads will include: Atmospheric (turbulence probe), environmental (hyperspectral and visual cameras), cryosphere (600-900 MHz accumulation radar), and potential field geophysics (gravity/magnetic sensors). The missions, between 10 and 330 km long, will be flown beyond visual line of sight (BVLOS) of the operator using the Distributed Avionics autopilot, including take-off and landing, which will be overseen by an in-field safety pilot.

Here we present the first results of this trial, including our experience integrating BVLOS UAV operations with traditional aircraft in an Antarctic context and initial results and lessons learned from the four trailed instrument suites. Our demonstration will be an important milestone in the transition to widespread use of larger UAVs for environmental science. We will discuss how the reduced environmental and logistical impact can open up new opportunities in Antarctic and beyond.

How to cite: Jordan, T. and Robinson, C.: Demonstrating a large UAV for Antarctic environmental science, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5435, https://doi.org/10.5194/egusphere-egu24-5435, 2024.

EGU24-5751 | ECS | PICO | CR5.1

Firn Density Distribution and Annual Snow Water Equivalent Estimates from Ground Penetrating Radar 

Akash Patil, Christoph Mayer, and Matthias Braun

Abstract: Accurate estimation of glacier volume-to-mass conversion relies on a thorough understanding of firn density, both in-depth and over time. Ground-penetrating radar (GPR) serves as a suitable geophysical tool to trace internal reflection horizons (IRHs) and estimate the physical properties of different layers. Our goal is to characterize the IRHs as annual layers and ascertain the spatial firn density-depth profile in the accumulation zone of the Aletsch glacier.

The process involves identifying IRHs from radargrams and iteratively selecting the annual layers by excluding unreasonable layer structures. For an accurate estimation of firn density distribution, it is necessary to derive the velocity-depth profile of electromagnetic waves within the firn zone. The common mid-point (CMP) method was applied to track the velocity distribution within the firn body. Additionally, a method was introduced to estimate the velocity-depth profile for longer GPR profiles by backtracking the calculated velocity from the CMP gather.

To validate IRHs as annual firn layers, we utilized annual accumulation measurements at a nearby stake for Snow Water Equivalent (SWE) estimation. The resulting firn density-depth profile was compared to different firn densification models, considering regional meteorological information. This approach enables us to determine a reliable density-depth function for bulk SWE computations. The study also addresses uncertainties associated with selecting IRHs as annual layers and enhances the application of local volume-to-mass estimates.

How to cite: Patil, A., Mayer, C., and Braun, M.: Firn Density Distribution and Annual Snow Water Equivalent Estimates from Ground Penetrating Radar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5751, https://doi.org/10.5194/egusphere-egu24-5751, 2024.

EGU24-7654 | ECS | PICO | CR5.1

Coupling Solid Earth and ice temperature models to estimate geothermal heat flow 

Judith Freienstein, Wolfgang Szwillus, Marion Leduc-Leballeur, Giovanni Macelloni, and Joerg Ebbing

Geothermal heat flow (GHF) is a key element of Solid Earth-cryosphere interactions. However, polar regions as Antarctica are only sparsely covered with heat flow determinations from boreholes, so one must rely on interpolation or regression models of GHF (e.g. machine learning) from other sources to derive a regional map. Interpolation/regression of GHF in this manner depends strongly on the available sparse boreholes, which can distort the resulting regional map.

Additional information can be gained from the SMOS (Soil Moisture and Ocean Salinity) satellite by inferring ice temperature profiles with a Bayesian inversion from remote sensing microwave radiometer data. This retrieval uses geothermal heat flow as a free parameter so that it provides a posterior distribution of the GHF needed to explain the ice temperature profiles.

We aim to reconcile geophysical geothermal heat flow models with the ice temperature profiles and improve the estimates of GHF with this coupling.

We use stationary thermal modelling where we force the ice temperature and lithospheric temperature model to converge at the base of the ice. Using stochastic inversion, we estimate the thermal parameters in the lithosphere. The posterior distribution of the retrieval as constraint for the GHF is included as prior distribution to the inversion to the stationary thermal modelling so that the GHF with the highest likelihood can be estimated.

With our approach, we can evaluate a GHF distribution that both explains the ice temperature and lithospheric temperature models and covers large parts of Antarctica.

How to cite: Freienstein, J., Szwillus, W., Leduc-Leballeur, M., Macelloni, G., and Ebbing, J.: Coupling Solid Earth and ice temperature models to estimate geothermal heat flow, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7654, https://doi.org/10.5194/egusphere-egu24-7654, 2024.

EGU24-8245 | ECS | PICO | CR5.1

Sensitivity Study for Seismic Waves Guided in an Ice Pack: Influence of the Frequency Content and Snow Layer Thickness Covering the Ice 

Hooshmand Zandi, Ludovic Moreau, Ludovic Métivier, and Romain Brossier

Studying Arctic sea ice is essential as it plays an important role in climate regulation, influencing weather
patterns, as well as impacting the local ecosystems and living conditions of people. Among different
methods for collecting data and studying sea ice, seismology has proved to be an efficient way to extract
the ice properties, from which the mechanical behavior of sea ice can be explored. Seismic data recorded on
sea ice, using 3-component geophones, are used as a starting point to derive useful information regarding
the ice. To devise an efficient inversion method for deriving ice properties, an effective tool would be
necessary to generate synthetic data in a way that encompasses the physics of sea ice. While there are
approximate solutions to wave propagation problem in a floating ice layer based on plate theory, which is
based on the assumptions of homogeneity of the ice layer and valid at low values of frequency×wavelength,
numerical counterparts such as wavenumber integration method and finite element method have been
also used to to create synthetic waveforms. The numerical methods have shown the limitations of these
approximate solutions in modeling wave propagation; nonetheless, the effects of these limitations on the
estimations of the location of icequakes and thickness of ice need to be investigated.

In this study, these limitations are explored. To do this, two possible scenarios that can happen in
practice are taken into account: (1) when there is high-frequency content in the source generating the
seismic data, and (2) when the physical model includes a snow layer overlying the ice layer. First, we
will show the limitations of the approximate solutions for these two cases by comparing the waveforms,
derived from these approximate solutions, with those of a numerical method at a given distance from
the source. The numerical used here is spectral element method. Then, the effects of these limitations
on the estimations of icequake location and ice thickness are explored in an inversion process, in which
synthetic data are created using the approximate solutions. Results indicate that when there are high-
frequency content in the data and a snow layer on top of the ice, the use of the approximate solutions
to generate synthetic data introduces bias in the estimation of ice thickness and source-receiver distance
in the inversion process. This bias is in the form of underestimations, smaller ice thicknesses and smaller
source-receiver distances. Furthermore, to tackle the biases associated with the inversion method based on
the approximate solutions, a novel strategy is adopted, where a database of simulations using the proposed
numerical method is built for various models of ice and snow. Here the inversion comprises of searching
in the database to find the best ice thickness and source-receiver distance for each icequake. In addition,
the database-based inversion reduces the computational cost. Thanks to this inversion strategy, and
using real data recorded on sea ice, the ice thicknesses along different source-receiver paths are estimated
efficiently, from which a 3D map of ice thickness is constructed.

How to cite: Zandi, H., Moreau, L., Métivier, L., and Brossier, R.: Sensitivity Study for Seismic Waves Guided in an Ice Pack: Influence of the Frequency Content and Snow Layer Thickness Covering the Ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8245, https://doi.org/10.5194/egusphere-egu24-8245, 2024.

EGU24-9857 | ECS | PICO | CR5.1

Broadband Spectral Induced Polarization in Permafrost Peatlands of Northern Sweden  

Madhuri Sugand and Andreas Hördt

Permafrost peatlands, located in the Arctic and high mountain regions, are typically known to be ice-rich. This is primarily linked to significant water content and often oversaturation, a characteristic property of peat soil. The current understanding of the effects of human-induced climate warming suggests that these regions are approaching a climatic tipping point with substantial permafrost thaw expected in the coming decades. Ice content is an important parameter for modelling permafrost evolution and at present limited studies exist that determine its in-situ spatial distribution in such areas.

The geophysical method known as high-frequency induced polarisation (HFIP) is advantageous for cryohydrological research in these environments. This method can capture the frequency-dependent polarisation of ice (also termed dielectric relaxation peak), which occurs within the range of 100 Hz to 100 kHz and is expressed by complex resistivity. Therefore, by analysing the spectral behaviour of this complex resistivity within the target frequency range the distribution and quantity of ice can be estimated.

The results from the latest field campaign conducted at Storflaket mire and Stordalen mire in Abisko, Sweden, are presented. Two-dimensional HFIP profiles were measured to resolve the near-surface unfrozen layer (no-ice) and the underlying frozen layer (ice-bearing). The measurements were performed in late summer when the depth of the unfrozen layer was at its maximum. Field data are inverted as independent frequencies to obtain the spectral variation of complex resistivity. No-ice and ice-bearing regions are classified by the presence of the relaxation peak. Subsequently, a two-component mixture model, with one component as ice and the second as the surrounding matrix, is applied to determine ice content distribution. Boundary constraints and starting parameters are chosen using the spectral analysis of the inverted complex resistivity. The model accuracy is evaluated using unfrozen layer probing and a permafrost core extracted along the HFIP profile. The HFIP-derived ice content distribution is consistent with unfrozen layer probing, i.e., the classification of no-ice and ice-bearing regions is successful. The model tends to underestimate ice content percentages compared to permafrost core laboratory measurements. This discrepancy can be explained since laboratory measurements are based on gravimetric water content and assumes all pore-water is frozen. However, it is known that residual pore-water is present in these soils even below 0°C. Additionally, it is observed that the model performs well when the ice content percentage is 10% or greater and its applicability might be limited in scenarios where the ice content is less than 10%.

The latest results are discussed in comparison with previous findings from Heliport, a permafrost mire also located in Abisko. In the Heliport study, HFIP successfully resolved the complex resistivity and ice content distribution on a larger scale. Building on the field knowledge gained at Heliport, this study incorporates improvements in electrode configuration setup, data acquisition speed, and minimising cable-earth coupling effects. The findings contribute to the understanding of the induced polarisation of permafrost peatlands, which is an underexplored area from a geophysical perspective.

How to cite: Sugand, M. and Hördt, A.: Broadband Spectral Induced Polarization in Permafrost Peatlands of Northern Sweden , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9857, https://doi.org/10.5194/egusphere-egu24-9857, 2024.

EGU24-10814 | ECS | PICO | CR5.1

Analysis of H/V spectral ratio curves from passive seismic data acquired on glaciers worldwide 

Julien Govoorts, Koen Van Noten, Corentin Caudron, Bergur Einarsson, Thomas Lecocq, Sylvain Nowé, Finnur Pálsson, Jonas Pätzel, and Harry Zekollari

Estimations of bedrock topography below glaciers and ice thickness are vital for quantifying freshwater availability for surrounding populations and understanding the contribution of melting glaciers to sea-level rise in the context of global warming. While active seismology is commonly used for ice thickness estimation, the utilization of passive methods remains relatively rare. Passive seismology solutions offer cost-effectiveness, non-invasiveness and continuous monitoring capabilities that present valuable benefits in glaciological research.

Over the past two decades, numerous seismic stations have been deployed on glaciers worldwide for various purposes. Through passive seismology approaches, these seismic stations could show their potential as new sources of ice thickness measurements and feed the related database. For this purpose, we analyzed data of 3-components seismic sensors from different deployments as well as data from open access databases, such as IRIS, employing the Horizontal-to-Vertical Spectral Ratio (HVSR) technique. HVSR has been predominantly used in microzonation studies to determine site effects and the thickness of sediments in sedimentary basins.  Even though the use of this technique in glacial seismology is quite new, HVSR has been already utilized to estimate in-situ ice thickness, to retrieve the basal properties or to detect cavities under the ice.

Our primary objective is to demonstrate the potential of the HVSR technique to retrieve in-situ ice thickness on different glaciers. Subsequently, we will compare the HVSR results with different data sources including models, ground-penetrating radar or active seismology. By performing this comparison we evaluate the limitations of the HVSR method in an icy environment. We investigate these limitations by studying the effect of other natural agents such as wind on the H/V amplitude and fundamental frequency retrieved from the HVSR curves. Having a global understanding of these influences will eventually help deciphering variations in continuous H/V monitoring.

How to cite: Govoorts, J., Van Noten, K., Caudron, C., Einarsson, B., Lecocq, T., Nowé, S., Pálsson, F., Pätzel, J., and Zekollari, H.: Analysis of H/V spectral ratio curves from passive seismic data acquired on glaciers worldwide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10814, https://doi.org/10.5194/egusphere-egu24-10814, 2024.

EGU24-11300 | PICO | CR5.1

Icequakes beneath Thwaites Glacier eastern shear margin  

Emma C. Smith, Ronan Agnew, Adam D. Booth, Poul Christoffersen, Eliza J. Dawson, Lucia Gonzalez, Marianne Karplus, Daniel F. May, Nori Nakata, Andrew Pretorius, Paul Summers, Slawek Tulaczyk, Stephen Vietch, Jake Walter, and Tun Jan Young

The stability of Thwaites Glacier, the second largest marine ice stream in West Antarctica, is a major source of uncertainty in future predictions of global sea level rise. Critical to understanding the stability of Thwaites Glacier, is understanding the dynamics of the shear margins, which provide important lateral resistance that counters basal weakening associated with ice flow acceleration and forcing at the grounding line. The eastern shear margin of Thwaites Glacier is of interest as it is poorly topographically constrained, meaning it could migrate rapidly, causing further ice flow acceleration and drawing a larger volume of ice into the fast-flowing ice stream.  

In this study, we present an analysis of ~4000 icequakes, recorded over a two-year-period on a broadband seismic array deployed across the eastern shear margin of Thwaites Glacier. The array consisted of seven three-component seismometers, deployed around a central station in a circle, roughly 10 km in diameter.  We use an automated approach to detect and locate “high-frequency” seismic events (10-90 Hz), the majority of which are concentrated in clusters around the ice-bed interface on the slow-moving side of the shear margin, as opposed to within the ice-stream itself. The event waveforms exhibit clear shear-wave splitting, indicative of the presence of an anisotropic ice fabric, likely formed within the shear margin, which is consistent with published radar studies from the field site. Initial analysis of the split shear-waves suggests that they can be used to better constrain the region's ice fabric, and likely used to infer past shear margin location and assess the future stability of this ice rheology.

How to cite: Smith, E. C., Agnew, R., Booth, A. D., Christoffersen, P., Dawson, E. J., Gonzalez, L., Karplus, M., May, D. F., Nakata, N., Pretorius, A., Summers, P., Tulaczyk, S., Vietch, S., Walter, J., and Young, T. J.: Icequakes beneath Thwaites Glacier eastern shear margin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11300, https://doi.org/10.5194/egusphere-egu24-11300, 2024.

EGU24-11386 | PICO | CR5.1

Towards a unified description of the count rate – snow water equivalent relationship in cosmic-ray neutron sensing 

Benjamin Fersch, Markéta Součková, Paul Schattan, Nora Krebs, Jannis Weimar, Carsten Jahn, Peter Martin Grosse, and Martin Schrön

The observation of near-ground cosmogenic neutrons enables the monitoring of various water storage variations at the land surface at the field scale including soil moisture and the water content of snow layers. The parabolic neutron-count versus soil moisture function is quite uniform among different locations, and soil types and requires typically a one-time-only in situ reference observation. For the detection of snowpack water equivalent (SWE) variations by cosmic-ray neutron sensing such a uniform approach has so far not been developed. Therefore, the establishment of new cosmic-ray snow monitoring sites requires substantial in situ measurements for obtaining the local relationship of SWE amounts and neutron count rates. Observations suggest that the relationship is quite uniform for grass-vegetated locations which is different to what is found for stony ground.

Within the framework of the research unit Cosmic Sense, we generated extensive in situ measurements of snow water equivalent and cosmogenic neutron count rates at various sites with differing elevations in the German and Austrian Alps. From these data, we investigate commonalities among the site conditions and if the varying patterns of the relationships can be reasonably explained by physical reasons and therefore be modeled with a unified approach.

How to cite: Fersch, B., Součková, M., Schattan, P., Krebs, N., Weimar, J., Jahn, C., Grosse, P. M., and Schrön, M.: Towards a unified description of the count rate – snow water equivalent relationship in cosmic-ray neutron sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11386, https://doi.org/10.5194/egusphere-egu24-11386, 2024.

EGU24-11729 | ECS | PICO | CR5.1

A physically-based fractal model for predicting the electrical conductivity in partially saturated frozen porous media 

Haoliang Luo, Damien Jougnot, Anne Jost, Aida Mendieta, and Luong Duy Thanh

Macro-scale transport properties (e.g., electrical conductivity, effective excess charge density and hydraulic conductivity) can be conceptualized as capillary bundle models, in which the pore structure of porous medium is viewed as a bundle of capillary tubes of varying sizes. This approach can be used to understand and address the relationship between the petrophysical properties and the geometry of soil phases. When the temperature of porous medium decreases below the freezing temperature, the soil physical properties (transport properties) change drastically. This is attributed to the complexity of the heterogeneous formation of ice in the porous medium. Therefore, understanding better pore ice formation from microscale insights is crucial to describe the evolution of electrical conductivity with temperature in frozen porous medium. In this study, we consider that capillary radius and tortuous length follow fractal distributions, and that total conductance at the microscale scale is determined by the Gibbs-Thomson and Young-Laplace effects as well as by the surface complexation model. A new capillary bundle model is then proposed using an upscaling procedure, which considers the effects of both bulk and surface conductions. Based primarily on an electrical resistance apparatus and the NMR method, a series of laboratory experiments are carried out to study the influence of initial water saturation and salinity on electrical conductivity under unfrozen and frozen conditions. Additionally, the rationality and validity of the proposed model were successfully verified with published data in the literature and experimental data of this study. Our new physically-based model for electrical conductivity opens up new possibilities to interpret electrical and electromagnetic monitoring to easily infer changes in key variables such as liquid water content and moisture gradients.

How to cite: Luo, H., Jougnot, D., Jost, A., Mendieta, A., and Thanh, L. D.: A physically-based fractal model for predicting the electrical conductivity in partially saturated frozen porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11729, https://doi.org/10.5194/egusphere-egu24-11729, 2024.

EGU24-12583 | PICO | CR5.1

Locating subglacial cavities and investigating basal conditions on glaciers with ambient seismic noise: toward acquisition optimization. 

Eric Larose, Noelie Bontemps, Antoine Guillemot, and Laurent Baillet

Subglacial cavities may trap a considerable quantity of liquid water, causing devastating outburst floods in densely populated mountain areas. Both active and passive geophysical methods are employed for the glacier-bedrock interface and intra-glacial characterization, including Ground Penetrating Radar (GPR), refraction seismic, borehole measurements, and surface nuclear magnetic resonance (SNMR). 

Ambient seismic noise can be collected by light and dense arrays at a relatively moderate cost, and allows to access some mechanical properties of the glacier, including the detection and localization of ice cavities and, possibly, basal detachment, taking advantage of spectral anomalies in the horizontal-to-vertical-spectral ratio (HVSR) and in the Vertical-to-Horizontal spectral ratio (VHSR). Specifically, a peak in the VHSR indicates a low impedance volume beneath the surface [1,2]. As a simple picture, we can refer to the “bridge” vibrating mode, where the vertical displacement in the middle of the bridge largely dominates other components of the movement.  Antunes et al. [2] furthermore noticed that the VHSR gives information about seismic energy anomalies generated by fluids in reservoirs since the wavefield is polarized mainly in the vertical direction.
In this work, we apply the HVSR and VHSR techniques to locate a subglacial water-filled cavity in the Tête Rousse glacier (Mont Blanc area, French Alps), using 15 days of data collected in may, 2022 [3]. The results also confirm the general basal conditions of the glacier suggested by other methods, locating temperate areas of the glacier where basal detachments are possible.

We evaluate the optimal seismic noise record duration to obtain a reliable and stable mapping of the VHSR over the glacier to properly locate the main cavity (or secondary cavities). In our case, results suggest that 6 days of record are enough to detect and locate a cavity

 

[1] Saenger, E-H. et al: A passive seismic survey over a gas field: Analysis of low-frequency anomalies, Geophysics, 74 (2), O29–O40 (2009).

[2] Antunes V. et al: Insights into the dynamics of the Nirano Mud Volcano through seismic characterization of drumbeat signals and V/H analysis. Journal of Volcanology and Geothermal Research, 431 (2022).

[3] A. Guillemot, N. Bontemps, E. Larose, D. Teodor, S. Faller, L. Baillet, S. Garambois, E. Thibert, O. Gagliardini, C. Vincent: Investigating Subglacial Water-filled Cavities by Spectral Analysis of Ambient Seismic Noise : Results on the Polythermal Tête-Rousse Glacier (Mont Blanc, France), Geophys. Res. Lett. accepted (2024). DOI:10.1029/2023GL105038

How to cite: Larose, E., Bontemps, N., Guillemot, A., and Baillet, L.: Locating subglacial cavities and investigating basal conditions on glaciers with ambient seismic noise: toward acquisition optimization., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12583, https://doi.org/10.5194/egusphere-egu24-12583, 2024.

The Totten Glacier is a fast moving glacier that serves as a major outlet of the East Antarctic Ice Sheet. During December 2018 and January 2019, we deployed a 12 station broadband seismic array near the grounding zone of the Totten Glacier. We observed a significant number ( > 10,000) of repeating basal stick-slip icequakes across the region. Much of this seismic activity was dominated by higher frequency events (20-75 Hz) similar in size and temporal character (“bursty”) to those found in previous studies, such as those on the Rutford Ice Stream and Greenland Ice Sheet. Additionally, we observe a large number of repeating events dominated by lower frequencies (< 10 Hz) that have larger magnitudes and longer inter-event time than the high-frequency seismic activity. We will provide an overview into both the temporal and spatial variability of this seismic activity and discuss implications for fast flow in the region.

How to cite: Winberry, P.: Repeating Glacier Seismicity Near the Totten Glacier Grounding Zone., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12865, https://doi.org/10.5194/egusphere-egu24-12865, 2024.

EGU24-13124 | ECS | PICO | CR5.1

Exploring englacial hydrology with surface nuclear magnetic resonance 

Laura Gabriel, Marian Hertrich, Raphael Moser, Christophe Ogier, Hansruedi Maurer, and Daniel Farinotti

The amount and distribution of liquid water inside a glacier are relevant for its dynamics, related natural hazards or for sediment transport. Experimentally investigating the glacier's hydrology is challenging because of restricted accessibility, investigation depth, material properties, and environmental factors. In addition, the subglacial drainage network is highly dynamic and undergoes diurnal and seasonal changes.

This contribution investigates the application of surface nuclear magnetic resonance (SNMR) to characterize the liquid water distribution within Swiss Alpine glaciers. Analogous to magnetic resonance imaging (MRI) in medicine, SNMR utilizes an oscillating magnetic field to excite nuclear spins of hydrogen atoms within water molecules. The subsequent spin relaxation is then analyzed, providing insights into the probed material. In simpler terms, this process allows us to directly detect liquid water in ice and gain information on its spatial distribution.

We conducted a first SNMR field survey on Rhonegletscher in the summer of 2023. During this survey, we tested various measurement configurations, including separate-loop measurements and the application of noise-compensation loops. The latter proved crucial for subsequent data processing. After carefully optimizing the processing scheme, we extracted SNMR signals in several recordings despite the poor signal-to-noise ratio. The results were compared to 1D forward-modelled data, suggesting that the average water content in the survey area lay between 0.7 and 1.2 %. In addition, we could show that a homogenous water distribution over the entire ice column cannot explain the observed data and that we need to consider more complex subsurface models including at least one additional water layer. Specifically, our ongoing research aims to identify which configurations of the subglacial water distribution (e.g., homogenous water distribution vs layered water-ice structure resulting from an englacial water channel) are distinguishable experimentally. Moreover, the study seeks to optimize measurement design and data processing methodologies to acquire information more efficiently, and effectively handle the expected low signal-to-noise ratios.

In future field campaigns, we intend to deploy SNMR for selected glaciological case studies within the Swiss Alps. A primary focus will be on efficiently detecting water pockets that may pose a potential risk of downstream flooding upon rupture. Similarly, we want to investigate the extent to which we can distinguish cold from temperate ice.

How to cite: Gabriel, L., Hertrich, M., Moser, R., Ogier, C., Maurer, H., and Farinotti, D.: Exploring englacial hydrology with surface nuclear magnetic resonance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13124, https://doi.org/10.5194/egusphere-egu24-13124, 2024.

EGU24-13663 | ECS | PICO | CR5.1

 Assessing the rate of ice fracture using co-located geophysical surveys on the Brunt Ice Shelf, Antarctica 

Emma Pearce, Oliver Marsh, Alex Brisbourne, and Thomas Hudson

The rate of fracture-induced ice instability is an important factor contributing to uncertainties in sea level projections used for global flood mitigation planning. While the occurrence of ice fracturing at critical stress thresholds is well-documented, the detailed mechanisms controlling fracture timing, rate, and orientation are not fully understood. This gap is particularly evident in differences in fracture behaviour across varying ice types, such as meteoric ice and ice mélange. Observations on the Brunt Ice Shelf reveal a unique behaviour, where rifts deviate from the pathway predicted by the principal stresses to avoid thick blocks of meteoric ice. Their growth rate is significantly reduced when required to cross through these blocks. This stands in contrast to observations on other ice shelves, such as Larsen C, where rift propagation is slower in marine ice bands.

Here we use co-located geophysical methods, seismic and ground-penetrating radar (GPR), to assess the fracture pattern and dynamics and the relationship to ice properties at the leading edge of two active rifts, Halloween Crack and Chasm 2, on the Brunt Ice Shelf.

By determining the depth of seismic events using P to Rayleigh wave amplitude ratios, we estimate a theoretical maximum dry crevasse depth—the depth at which fracturing can occur without the presence of englacial water. Additionally, GPR data are used to precisely locate rift terminations and identify refrozen layers associated with seawater intrusion into the firn layer. Combining these data, we provide new insight into the mechanisms controlling fracture propagation within the Brunt Ice shelf. The synthesis of observations from Chasm 2 and Halloween Crack contributes to a comprehensive understanding of fracture mechanics, enhancing our knowledge of regional-scale ice dynamics.

How to cite: Pearce, E., Marsh, O., Brisbourne, A., and Hudson, T.:  Assessing the rate of ice fracture using co-located geophysical surveys on the Brunt Ice Shelf, Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13663, https://doi.org/10.5194/egusphere-egu24-13663, 2024.

EGU24-13683 | ECS | PICO | CR5.1

Testing four Sentinel (1 and 2) and MODIS Fractional Snow Cover products for the evaluation of five Alpine Cosmic Ray Neutron Sensing sites 

Nora Krebs, Paul Schattan, Valentina Premier, Abraham Mejia-Aguilar, and Martin Rutzinger

Above-ground cosmic ray neutron sensing (CRNS) is an emerging technique for the investigation of dynamics in soil moisture, snow water equivalent (SWE), and vegetation at a spatial scale of several hectares. The measurement principle is based on the moderation of natural secondary cosmogenic neutrons by hydrogen atoms. On the earth surface hydrogen atoms are mainly bound in water molecules. However, at complex research sites the signal distinction between various water sources remains challenging. Especially in alpine terrain and at elevated topography, hydrological features are linked in an intricate patchwork, hampering signal discrimination. Satellite observations offer valuable complementary surface information and are commonly provided at a spatial resolution that meets the integrated footprint area of the CRNS detector. In this study we investigate if the interpretation of the CRNS signal can be enhanced by the use of remote sensing products. We compare three readily available fractional snow cover (FSC) products based on Sentinel (1 and 2) and MODIS and one reference FSC Sentinel-2 scene-based machine learning product at the approximate footprint resolution of CRNS, comprising a circular area of 250 m radius. The performance of all four products is assessed at five CRNS sites in the Austrian and Italian Alps that represent a variety of environmental properties, ranging from flat to steep topography, from low to high elevation and from sparse to abundant vegetation cover. At three sites, the presence and absence of snow can be validated by local snow height measurements. The analysis shows that remote sensing snow cover information can be extracted on around 80% of the analyzed days, demonstrating the use of FSC products for the estimation of snow cover duration and timing. Comparing the four products shows overall agreements and allows to deduce product-specific thresholds for the distinction of snow-covered and snow-free situations. Further, pairing remote FSC observations with neutron count measurements provides a first indication on the complexity of local hydrogen pool dynamics and consequent requirements on the calibration routine for ambient water monitoring with CRNS. We conclude that satellite-based FSC products can be used to fortify the choice of CRNS observation location and period prior to the detector installation and for a robust and viable first-order assessment of expected CRNS site conditions. Remote sensing FSC products and CRNS measurements hold complementary data that can mutually benefit snow observations and should be explored further in the future.

How to cite: Krebs, N., Schattan, P., Premier, V., Mejia-Aguilar, A., and Rutzinger, M.: Testing four Sentinel (1 and 2) and MODIS Fractional Snow Cover products for the evaluation of five Alpine Cosmic Ray Neutron Sensing sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13683, https://doi.org/10.5194/egusphere-egu24-13683, 2024.

EGU24-14420 | PICO | CR5.1

Using seismic and gravity data to constrain subglacial seafloor stratigraphy in the vicinity of the Kamb Ice Stream grounding line, Ross Ice Shelf, Antarctica 

Andrew Gorman, Gary Wilson, Huw Horgan, Gavin Dunbar, Caitlin Hall, Jenny Black, Bob Dagg, Matthew Tankersley, and Laurine van Haastrecht

The sedimentary units beneath the Ross Ice Shelf in the vicinity of the Kamb Ice Stream grounding line on the Siple Coast of the eastern Ross Ice Shelf play an important role in evaluating past advances and retreats of grounded ice in West Antarctica through the Quaternary. This region is an ongoing focus for drilling efforts that involve melting through the ice shelf and recovering sediments from beneath the seafloor. Seismic (and to a lesser extent gravity) methods have played a critical role in establishing a stratigraphic framework for these sediment sampling endeavours. Approximately 73 km of seismic data have been collected in this region during three seasons since early 2015, complemented by finely sampled gravity transects and a coarser regional gravity grid. Data acquisition provides localised coverage of the sub-ice-shelf ocean and sediments in a region where ROSETTA-Ice airborne-gravity data identified a gravity low. Seismic acquisition parameters have varied from survey to survey, but all involve explosive charges frozen into a hot-water-drilled holes that are recorded by conventional geophones buried in the firn. Such an acquisition configuration provides imaging of the ice shelf and underlying geological units. Processed seismic data show a mostly flat layered seafloor lying beneath the ocean cavity with at least 200 m of sub-horizontally layered sedimentary strata containing several mappable unconformities that are identified as distinct reflective horizons in the seismic data as well as reflection terminations and pinchouts in overlying and underlying units. These unconformities could correspond to past glacial erosion episodes as the position of the grounding line in this region has migrated landward and oceanward. Gravity modelling suggests that the thickness of the sedimentary basins in the region are variable beyond what we see in the shallow (few hundred metre) penetration of the seafloor.

How to cite: Gorman, A., Wilson, G., Horgan, H., Dunbar, G., Hall, C., Black, J., Dagg, B., Tankersley, M., and van Haastrecht, L.: Using seismic and gravity data to constrain subglacial seafloor stratigraphy in the vicinity of the Kamb Ice Stream grounding line, Ross Ice Shelf, Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14420, https://doi.org/10.5194/egusphere-egu24-14420, 2024.

EGU24-14548 | ECS | PICO | CR5.1

Applications of geophysical techniques for the analysis of the internal structure and understanding of the hydrological system of the Kinzl Covered Glacier, Cordillera Blanca, Peru  

Velnia Chacca Luna, Widmark Harrinson Jara Infantes, Manuel Antonio Cosi Fajardo, Milagros Lizbeth Aquino Morales, Leila Mamani Yampi, Sara Cachay, and Juan Carlos Torres Lázaro

The Cordillera Blanca is currently home to 384 covered glaciers, which constitutes 46.5 % of the total of 825 covered glaciers registered in the 20 glacier ranges of Peru, according to data provided by the Glacier Inventory 2023 (INAIGEM, 2023). Therefore, in the framework of climate fluctuations driven by global warming, covered glaciers stand out as crucial elements, as their level of thawing is much slower in response to climate variability and in contrast to their debris- free glacier counterparts. This characteristic consolidates them as increasingly essential and valuable water resources.

The objective of the study is to determine the physical characteristics of the Kinzl Covered Glacier, located in the Cordillera Blanca, by applying the geophysical methods of ground penetrating radar (GPR) and vertical electrical sounding (VES). The methodology employed includes georadar profiling and point soundings to understand the composition and distribution of materials and the physical properties of the glacier. From the detailed analysis of electrical soundings and georadar profiles, a correlation of both methods has been achieved through the resistivities obtained and established for similar environments, with phases of reflected signals coming from the contours of the interfaces identified in the radargrams analysed and interpreted. This correlation has provided us with a comprehensive understanding of the internal characteristics of the Kinzl Covered Glacier, where three horizons have been identified: The first horizon composed of variable surface debris, ranging from 2 to 9 metres thick, with resistivities that remain above 16k Ohm.m; the second horizon composed of massive ice with debris, fluctuating between 40k and 300k Ohm.m and with thicknesses ranging from 40-60 metres, parallel to this horizon we also have massive ice corroborated by values of 400k and 6000k Ohm.m with thicknesses exceeding 60 metres and below this we have a third horizon composed of bedrock with average resistivity between 1.2k and 9k Ohm.m. These data found in the Kinzl Covered Glacier fit with those frequently found in glacial-periglacial deposits in the Andes.

The results provide a comprehensive understanding of the internal characteristics of the Kinzl Covered Glacier, highlighting its relevance for understanding the complexity and implications for glacial dynamics. These findings are valuable for numerical modelling, glacier risk management and water resource management.

How to cite: Chacca Luna, V., Jara Infantes, W. H., Cosi Fajardo, M. A., Aquino Morales, M. L., Mamani Yampi, L., Cachay, S., and Torres Lázaro, J. C.: Applications of geophysical techniques for the analysis of the internal structure and understanding of the hydrological system of the Kinzl Covered Glacier, Cordillera Blanca, Peru , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14548, https://doi.org/10.5194/egusphere-egu24-14548, 2024.

EGU24-15907 | PICO | CR5.1

Long-term refraction seismic monitoring: a reliable method to detect ground ice loss at mountain permafrost sites 

Christin Hilbich, Bernd Etzelmüller, Ketil Isaksen, Coline Mollaret, Sarah Morard, Cécile Pellet, and Christian Hauck

Geophysical monitoring becomes more and more popular in permafrost environments due to its remarkable success to detect permafrost thawing and spatio-temporal changes in the ground ice content. Mostly geoelectric methods such as Electrical Resistivity Tomography (ERT) are applied due to the strong differences in the electrical properties between frozen and unfrozen state. However, seismic properties also change markedly upon freezing/thawing and time-lapse refraction seismic tomography (RST) has been shown to be applicable to permafrost over smaller time scales (e.g., Hilbich 2010). The reason why only few studies employ long-term seismic monitoring in permafrost is probably due to the higher logistical effort required.

At two Swiss permafrost monitoring sites (Schilthorn and Stockhorn) yearly RST surveys are conducted using the same setup for more than 15 years, in addition to standard borehole temperature, climatic and ERT measurements (www.permos.ch). The monitoring aim is to image the interannual changes of the thickness of the active layer as well as differences in ice content within the permafrost layer below.

Additional long-term observations are available from RST (and contemporary ERT) surveys from several mountain permafrost sites in Norway that were initially conducted to characterise permafrost conditions around boreholes drilled in 1999/2008 (Juvvasshoe/Jotunheimen), and 2007/2008 (Iskoras/Finnmark, Guolasjavri/Troms, and Tronfjell, cf. Isaksen et al. 2011, Farbrot et al. 2013). These surveys were repeated with the same geometry in 2019 after 11 years in northern Norway, and after 8 and 20 years in southern Norway. As for the Swiss sites, temperatures from all these boreholes show a clear warming trend over the last 1-2 decades (Etzelmüller et al, 2020, 2023).

We here present the observed long-term changes in electrical resistivity and seismic P-wave velocity based on a) annually repeated measurements in the Swiss Alps, and b) on long-term repetition in northern and southern Norway. The geophysical changes are related to the observed borehole temperature increase during the same period (Etzelmüller et al. 2023) and analysed with respect to climate-induced thawing. We evaluate the advantages and disadvantages of seismic monitoring compared to the more standard ERT monitoring. Finally, the results are also analysed with respect to their suitability for future ERT-seismic joint inversion approaches in a monitoring context.

 

References

Etzelmüller B, Guglielmin M, Hauck C, Hilbich C, Hoelzle M, Isaksen K, Noetzli J, Oliva M and Ramos M 2020. Twenty years of European mountain permafrost dynamics—the PACE legacy. Environ. Res. Lett. 15 104070 DOI 10.1088/1748-9326/abae9d

Etzelmüller B, Isaksen K, Czekirda J, Westermann S, Hilbich C, Hauck C 2023. Rapid warming and degradation of mountain permafrost in Norway and Iceland. The Cryosphere. 17.5477-5497.10.5194/tc-17-5477-2023.

Farbrot H, Isaksen K, Etzelmüller B, Gisnås K 2013. Ground Thermal Regime and Permafrost Distribution under a Changing Climate in Northern Norway. Permafrost Periglac.,24(1):20-38. https://doi.org/10.1002/ppp.1763

Isaksen K, Ødegård RS, Etzelmüller B, Hilbich C, Hauck C, Farbrot H, Eiken T, Hygen HO, Hipp T 2011. Degrading mountain permafrost in southern Norway - spatial and temporal variability of mean ground temperatures 1999-2009. Permafrost Periglac.,22(4):361-377, https://doi 10.1002/ppp.728.

Hilbich C 2010. Time-lapse refraction seismic tomography for the detection of ground ice degradation, The Cryosphere, 4, 243–259, https://doi.org/10.5194/tc-4-243-2010, 2010.

How to cite: Hilbich, C., Etzelmüller, B., Isaksen, K., Mollaret, C., Morard, S., Pellet, C., and Hauck, C.: Long-term refraction seismic monitoring: a reliable method to detect ground ice loss at mountain permafrost sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15907, https://doi.org/10.5194/egusphere-egu24-15907, 2024.

EGU24-16320 | PICO | CR5.1

Quieting of hydraulic tremor: sudden changes in frictional conditions in subglacial channels 

Małgorzata Chmiel, Nicoletta Caldera, Fabian Walter, Gerrit Olivier, Daniel Farinotti, Alberto Guadagnini, Dominik Gräff, Manuela Köpfli, and Florent Gimbert

The state and evolution of subglacial channels strongly impact glacier motion and as a result the mass balance of flowing ice bodies. Yet, the subglacial environment is difficult to access and thus often poorly constrained over significant temporal and spatial scales. This limits our understanding of complex subglacial hydraulic processes and consequently ice dynamics.

Seismology can help overcome these observational constraints, providing new insights into fundamental processes in the cryosphere, such as frictional sliding and subglacial water flow. However, different seismogenic processes of the cryosphere often overlap in both time and space. Differentiating between them and interpreting associated seismic signals require appropriate methodological and instrumental approaches.

Here, we investigate subglacial channel dynamics at the Rhone glacier (Switzerland) over one month in the summer of 2020, focusing on periods coinciding with glacier sliding episodes. To this end, we leverage the sensitivity of near-bed borehole geophones combined with seismic interferometry and beamforming techniques.

We show that the hydraulic tremor, generated by turbulent water flow and resulting pressure variations acting against the subglacial channel bed and walls, acts as a dominant, stable, and coherent noise source. Beamforming analysis reveals the directional stability of the hydraulic tremor and points toward the junction of two subglacial hydraulic channels from which stick-slip asperities originate. The analysis also reveals instances of sudden hydraulic tremor quieting, in agreement with previous observations before and after seismogenic sliding episodes. We explain this quieting as sudden changes in frictional conditions within the subglacial channel corresponding to a rapid transition between a fully and partially filled channel. We discuss channel properties (geometry and bed conditions) that are needed to satisfy the physical conditions for the frictional quieting mechanism. Our analysis offers new insights into the complex mechanical interactions between ice, water, and bed properties and the hydraulic control of glacier sliding.

How to cite: Chmiel, M., Caldera, N., Walter, F., Olivier, G., Farinotti, D., Guadagnini, A., Gräff, D., Köpfli, M., and Gimbert, F.: Quieting of hydraulic tremor: sudden changes in frictional conditions in subglacial channels, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16320, https://doi.org/10.5194/egusphere-egu24-16320, 2024.

EGU24-17134 | ECS | PICO | CR5.1

Lightweight In-Situ Analysis of snow density and accumulation 

Johanna von Drachenfels, Helle Astrid Kjær, and Josephine Lindsey-Clark

A critical factor in accurate Surface Mass Balance predictions of the Greenland Ice Sheet is the availability of spatially and temporally extensive snow accumulation data (Montgomery et al., 2018). Currently, this data remains deficient due to incomplete geographical coverage and poor temporal resolution (Sheperd et al., 2012).

An innovative approach to expanding the existing dataset is the utilization of the LISA box: a portable Lightweight In-Situ Analysis system designed for fast and straightforward snow and ice core measurements (Kjær et al., 2021), which speeds up the delivery of the results. With the LISA box, the sample cores are melted, and continuous flow analysis of chemical impurities and conductivity in the meltwater reveals annual peaks and climatic horizons. This information allows for dating of the single ice and snow layers. The registration of the melt speed furthermore permits the determination of the layer thickness, while the layer density can be inferred with an additional measurement of the meltwater flowrate. By combining these insights, past accumulation rates, as indicated by the volume of annually deposited snow, can be reconstructed.

Here we present updates to the existing LISA box enhancing its abilities to further analyse for density variations in snow and firn cores.

How to cite: von Drachenfels, J., Kjær, H. A., and Lindsey-Clark, J.: Lightweight In-Situ Analysis of snow density and accumulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17134, https://doi.org/10.5194/egusphere-egu24-17134, 2024.

EGU24-17421 | PICO | CR5.1

Lake ice seismicity: seismic and acoustic observations 

Cedric Schmelzbach, Christoph Wetter, Simon Stähler, John Clinton, Zinan Lyu, Maria Mesimeri, and Frédérick Massin

Seismic events (icequakes) associated with floating ice sheets on lakes are a frequently observed phenomenon. We find at our study site on the frozen Lake St. Moritz in the Swiss Alps typically a clear diurnal pattern with hundreds to thousands of icequake signals per hour during night time, while the rate of observed events during daytime is about two orders of magnitude smaller. The seismicity rate shows a significant correlation with temperature changes. It is therefore assumed that the generation of the ice quakes is related to melting and freezing processes as well as the extension and contraction of the ice. Potentially the seismicity rate is also moderated by loading and unloading due to human activities on the ice and/or lake level changes.

These ice quakes generate seismic waves that propagate through the thin ice sheet as plate waves modulated by the air and water half-spaces above and below the ice (quasi-guided waves). One member of this wave-type family, the quasi-Scholte waves, are characterised by distinct dispersion that can be observed with seismic sensors on the ice. Furthermore, the seismic waves traveling through the ice couple into the air leading to audible seismo-acoustic signals. One particularity of the ice-air coupling is a so-called coincidence phenomenon. The particular velocity-frequency combination where the seismic wavelength in the ice matches the apparent acoustic wavelength in the air leads to a resonance phenomenon. Observation of the related coincidence frequency allows us, for example, to infer on the ice thickness from the acoustic observations with a low cost microphone above the ice only. Recording the acoustic signals with small microphone arrays enables additionally, for example, locating the source of the seismo-acoustic signal.

Combined observations of the seismic and acoustic signals provide new insights into the seismicity of lake ice which has rarely been studied in the past. The seismo-acoustic signals have the potential to provide information about the ice properties such as thickness and ice quality as well as waxing and waning processes of ice sheets. These observations are relevant for safe operations on the ice but also to complement other remote-sensing observations with autonomous in situ seismo-acoustic measurements for climate studies.

How to cite: Schmelzbach, C., Wetter, C., Stähler, S., Clinton, J., Lyu, Z., Mesimeri, M., and Massin, F.: Lake ice seismicity: seismic and acoustic observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17421, https://doi.org/10.5194/egusphere-egu24-17421, 2024.

EGU24-17767 | PICO | CR5.1

Glaciological characterization of Little Dome C: Influence of ice flow on the future Beyond Epica – Oldest Ice Core drilling project 

Robert Mulvaney, Carlos Martín, Catherine Ritz, Luca Vittuari, Massimo Frezzotti, and Olaf Eisen

An ice core is being drilled near Little Dome C, a small promontory about 30km downstream from the summit of Dome C, to extract a continuous record of climate over the last 1.5 million years. Present and past ice flow conditions are important to interpret the ice core because the surface velocity at the drilling site is about 40 mm/yr and the oldest ice in the record was deposited in the surface about 10km upstream of the drilling site. Here we explore newly acquired and existing geophysical data to describe present ice flow and investigate signs of past changes. We present new GNSS data that describes the subtle but complex local surface velocity, and ApRES radar data that provides englacial strain-rates along the flow path from the summit of Dome C and bulk englacial crystal orientation fabric. Ice currently flows from Dome C summit along the ridge to Little Dome C, even though a subtle uphill slope, but basal conditions are variable along the path due to the strong basal topography. Of special interest is an ice unit in contact with the bedrock with variable thickness up to about 300m that is vertically stagnant and produce a strong radar reflection.  This basal unit is not present in an area of strong melting about 5km upstream from the drilling site. The crystal orientation fabric reflects the ice flow horizontal extension along the path and changes with depth on ice flow properties following climatic transitions and, more intriguing, indicate a possible change in ice flow extension at the beginning of the Holocene. We aim to facilitate detailed ice flow models to better interpret the ice core data.  

How to cite: Mulvaney, R., Martín, C., Ritz, C., Vittuari, L., Frezzotti, M., and Eisen, O.: Glaciological characterization of Little Dome C: Influence of ice flow on the future Beyond Epica – Oldest Ice Core drilling project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17767, https://doi.org/10.5194/egusphere-egu24-17767, 2024.

EGU24-17917 | PICO | CR5.1

Using received laser signal intensity to measure snow and ice surface properties automatically  

Alexander Prokop, Florian Tolle, Jean-Michelle Friedt, and Eric Bernard

In the context of climate warming it is a common scientific goal to study and monitor surface and volume changes of glaciers and melting dynamics of its snow and ice. Therefore several measurement techniques exist to track permanently ice melting e.g. DGPS stations on glaciers, Smart stake, and snow and ice depth measurements via e.g. ultrasonic depth sensors to create time series of snow and ice loss or gain. None of the existing methods measure if actually liquid water is present and melting occurs, this is later concluded by interpretation of the geometric data. The capability of the laser sensor to do so via the reflectance value, in fact the received signal intensity, we consider as a big advantage and worth investigating further as a direct measure of snow or ice melt that helps not only to analyze glacier dynamics but is also important e.g. for providing reliable ground truth data for satellite remote sensing. When melting of snow and ice occurs, water changes the reflectance properties as due to absorption of the laser in water, only a portion of the laser is reflected. This allows determining if liquid water is present at the surface measured. We present the data collected in the last 2 melting seasons of the Austre Lovénbreen glacier near Ny Alesund, Svalbard. We show how we classify wet snow and wet ice hours with confidence and are able to compute melting rates. The single point measurement is put into context to area wide LiDAR measurements and melting dynamics of the glacier are analyzed. The data was verified against visual inspections from automatic cameras, data from an automatic weather station both located in the glacier catchment and ice melt was measured in close proximity with a SmartStake station.

How to cite: Prokop, A., Tolle, F., Friedt, J.-M., and Bernard, E.: Using received laser signal intensity to measure snow and ice surface properties automatically , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17917, https://doi.org/10.5194/egusphere-egu24-17917, 2024.

EGU24-18177 | ECS | PICO | CR5.1

Applying Cosmic-Ray Neutron Sensing in Highly Heterogeneous Conditions: Monitoring Snow Water Equivalent in Periods with Partial Snow Coverage 

Paul Schattan, Jan Schmieder, Markus Köhli, Christine Fey, and Martin Schrön

Cosmic-Ray Neutron Sensing (CRNS) constitutes an emerging method for monitoring soil moisture and snow dynamics at intermediate spatial scales of several hectares. In complex environments such as mountain regions, however, the presence of areas with a high contrast of hydrogen content was found to cause a hysteresis in the relationship between neutron counts and water equivalent. A simulation study using the newly developed hierarchical scenario tool YULIA (Your URANOS Layer Integration Assistant) for the Monte-Carlo neutron simulation model URANOS was conducted to quantify the effect of snow-free areas on above-ground neutron sensing of the snow water equivalent (SWE). It was found that the size and distance of the snow free patches have the largest impact on the neutron flux. The simulations also showed a sensitivity of the signal towards soil moisture and SWE. Correction functions were developed and validated with observed CRNS measurements and LiDAR based distributed SWE maps. The main aim of the correction procedure is to estimate SWE under partly snow-covered conditions. Furthermore, also the soil moisture of the snow-free areas can be inferred if the SWE distribution is known. The latter can be used for other high-contrast CRNS applications like monitoring soil moisture in the presence of ponding water.

How to cite: Schattan, P., Schmieder, J., Köhli, M., Fey, C., and Schrön, M.: Applying Cosmic-Ray Neutron Sensing in Highly Heterogeneous Conditions: Monitoring Snow Water Equivalent in Periods with Partial Snow Coverage, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18177, https://doi.org/10.5194/egusphere-egu24-18177, 2024.

EGU24-18639 | PICO | CR5.1

Stick-slip imaging through the GPR phase: Turning  temperate ice 'noise' into signal 

Johannes Aichele, Christophe Ogier, and Barthélémy Anhorn


Ground Penetrating Radar (GPR) is a major tool to investigate, map and monitor polar ice sheets and alpine glaciers. Alpine glaciers are often composed of temperate ice, which has significantly different backscatter properties from cold ice. Radar attenuation is much stronger in temperate ice than in cold ice, because the radar signal encounters strong scattering in temperate ice. 
A major candidate for this scattering is the presence of liquid water inclusions, which are much smaller than the radar wavelength. The large contrast between water and ice dielectric permittivity would explain the diffuse radar scattering in temperate ice. Indeed, recent numerical modelling of the radar signal in temperate ice confirmed the contribution of liquid water inclusions on the scattering of the radar signal (Ogier, 2023). 
Here, we investigate if the strong scattering caused by liquid water inclusions, which is usually treated as noise, can be in fact exploited to unravel dynamic processes inside the glacier. This strong scattering results in large radar phase variations in space, which remain constant over short timescales (hours - days), during which the glacial water content remains constant. During that timescale, however, the mountain glacier might experience sudden internal deformation due to intermittent sliding at the glacier base, also called glacier stick-slip.  This deformation might be resolved using difference imaging and the spatio-temporal properties of the radar phase.
We numerically model radar wave propagation throughout temperate ice (i.e. with the presence of liquid water inclusions) before and after an idealized glacier deformation and show, that through phase difference imaging the internal movement of the sub-wavelength scatterers can be mapped. 
Finally, we discuss how this novel type of monitoring could be applied in the field, which is planned for spring 2024.

 

Ogier, Christophe, Dirk-Jan van Manen, Hansruedi Maurer, Ludovic Räss, Marian Hertrich, Andreas Bauder, and Daniel Farinotti. 2023. “Ground Penetrating Radar in Temperate Ice: Englacial Water Inclusions as Limiting Factor for Data Interpretation.” Journal of Glaciology, September, 1–12. https://doi.org/10.1017/jog.2023.68.

How to cite: Aichele, J., Ogier, C., and Anhorn, B.: Stick-slip imaging through the GPR phase: Turning  temperate ice 'noise' into signal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18639, https://doi.org/10.5194/egusphere-egu24-18639, 2024.

EGU24-19098 | PICO | CR5.1

Observing glacier bed topography: the H/V spectral method applied on a dense seismic array as a simple alternative to radar 

Florent Gimbert, Neil Ross, Tifenn Le Bris, Guilhem Barruol, Tun Jan Young, Samuel Doyle, Stephen Livingstone, Andrew Sole, Adrien Gilbert, Ryan Ing, Liz Bagshaw, Mike Prior-Jones, and Laura Edwards

Accurate knowledge of glacier bed topography is critical for quantifying ice volumes and modelling ice and subglacial hydrology dynamics. Bed topography observations are traditionally obtained from airborne and ice penetrating radar, which offers the crucial advantage of recovering the detailed glacier structure over a range of scales. A main difficulty with radar, however, is that waves can be strongly scattered and attenuated by englacial heterogeneities, in particular by water inclusions, which can potentially limit the applicability of the technique under certain conditions.

Here we present a case study on Isunguata Sermia, West Greenland, where we conducted an ice penetrating radar survey together with dense seismic array acquisitions from 87 nodes spread over a 1 km2 area. We show that, in the area of investigation, radar observations were only partially successful in identifying the ice-bed interface, likely due to the thick warm ice, presence of some surface water and near-surfacing crevassing and other englacial structures. The H/V analysis performed over the seismic array yielded surprisingly coherent estimates of ice thickness, along with its spatial variation along and across the glacier. These findings raise questions about the interpretation of traditional radar measurements under certain glacier conditions, and how dense seismic arrays could retrieve bed topography more systematically. 

How to cite: Gimbert, F., Ross, N., Le Bris, T., Barruol, G., Young, T. J., Doyle, S., Livingstone, S., Sole, A., Gilbert, A., Ing, R., Bagshaw, L., Prior-Jones, M., and Edwards, L.: Observing glacier bed topography: the H/V spectral method applied on a dense seismic array as a simple alternative to radar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19098, https://doi.org/10.5194/egusphere-egu24-19098, 2024.

EGU24-20308 | ECS | PICO | CR5.1

“Determination of Hydric Potencial through Geoelectric and Piezometric methods in the Ichickcollcococha Wetland, Pachacoto Hydrographic Unit, Cordillera Blanca, Perú.”  

Leila Maribel Mamani, W. Harrinson Jara, Velnia Chacca Luna, Juan C. Torres, Helder Mallqui, Manuel Cosi, Cristian Quispe, and Milagros Aquino

Abstracts

High-Andean bofedales are vegetated wetlands that play a crucial role in the context of climate change by facilitating the capture of carbon dioxide and regulating water. However, global warming has led to the glacial retreat of major snow-capped peaks, such as the Pastoruri Glacier, resulting in water scarcity that directly impacts these ecosystems. Hence, there is a pressing need to study them. This research aims to characterize the physical structure of the Ichickcollcococha bofedal, located in the Pachacoto Hydrographic Unit in the southern sector of the Cordillera Blanca, Peru. The objective is to determine its water storage potential during periods of high precipitation and drought. The study employs the Vertical Electrical Sounding (VES) geophysical prospecting method, corroborated by vibrating wire piezometers installed in the Ichickcollcococha bofedal. This method allows for a detailed analysis of the subsurface resistive properties, generating geo-electric profiles that detail the internal structure of the bofedal.

Three horizons have been identified: the upper layer is loosely composed of organic material (vegetation, cushioned bofedales) with high moisture content, reaching a depth of approximately 1.5 meters and average resistivity values around 431 Ohm.m. The second layer extends to a depth of 11 meters with resistivities of 67 Ohm.m, corresponding to organic materials such as peat and saturated sands. The third horizon, with estimated depths of 80 meters and resistivities around 1301 Ohm.m, corresponds to underlying limestone rock. The data obtained from the Ichickcollcococha bofedal align with characteristic values of glacial-origin peat bogs.

The findings of this study provide a comprehensive understanding of the internal characteristics of the Ichickcollcococha bofedal, highlighting its contribution to the knowledge of its internal dynamics and its implications for the water potential of high-Andean bofedales. Furthermore, the results offer valuable information for modeling and water resource management.

Keywords: Bofedal, Hydric potential, geoelectric method, VES.

How to cite: Mamani, L. M., Jara, W. H., Chacca Luna, V., Torres, J. C., Mallqui, H., Cosi, M., Quispe, C., and Aquino, M.: “Determination of Hydric Potencial through Geoelectric and Piezometric methods in the Ichickcollcococha Wetland, Pachacoto Hydrographic Unit, Cordillera Blanca, Perú.” , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20308, https://doi.org/10.5194/egusphere-egu24-20308, 2024.

EGU24-21232 | ECS | PICO | CR5.1

Quantifying Ground Ice in Tien Shan and Pamir Permafrost: A Comprehensive Petrophysical Joint Inversion Study Applying the electrical Geometric Mean Model  

Tamara Mathys, Christin Hilbich, Coline Mollaret, Christian Hauck, Tomas Saks, Ryksul Usubaliev, Bolot Moldobekov, Zhoodarbeshim Bektursunov, Muslim Azimshoev, Hofiz Navruzshoev, and Martin Hoelzle

Central Asian Mountain regions (Tien Shan and Pamir) are expected to be significantly impacted by climate change, affecting water availability and natural hazards. The cryosphere plays a crucial role in many watersheds of the region by providing water for hydropower station, irrigation, and domestic use downstream. At the same time, retreating glaciers and thawing permafrost increase the risk of natural hazards. Therefore, cryosphere monitoring systems are necessary to provide baseline data for estimating future water availability and detecting dangerous hazard zones. Despite the large areas underlain by permafrost in the Tien Shan and Pamir Mountain ranges, data on permafrost distribution, characteristics and evolution are scarce. However, quantitative estimations of permafrost subsurface components, especially water and ice contents, are needed to evaluate the consequences of current climate change on mountain permafrost environments.

Recent field-based investigations have emphasised the coupled use of geophysical techniques, e.g., by employing the Petrophysical Joint Inversion scheme (PJI, Wagner et al., 2019) that combines electrical resistivity and seismic refraction p-wave velocity data to estimate the four phases present in the subsurface (volumetric contents of air, water, ice, and rock). The traditional PJI implementation relies on Archie’s law (Archie, 1942) as one of the primary petrophysical equation to link resistivity to porosity and water content. Archie's law is generally considered valid when electrolytic conduction dominates, a condition that is not universally justified for dry and coarse blocky substrates and landforms in mountainous terrain. Recognizing this limitation, Mollaret et al. (2020) introduced the electrical Geometric Mean Model as an alternative implementation in the PJI. The Geometric Mean Model  assumes random distributions of the four phases and offers the advantage of including the fractions of ice and air in the petrophysical equation for resistivity, which are not present in Archie’s law. In this study, we assess the feasibility and effectiveness of using the Geometric Mean Model within the PJI framework across an extensive geophysical dataset comprising 22 profiles in Central Asia (Kyrgyzstan and Tajikistan). Our research encompasses diverse landforms, including moraines, rock glaciers, talus slopes, and fine-grained sediments. Our goals are to (i) evaluate the performance of the Geometric Mean Model in comparison to Archies law across different landforms and (ii) address the existing data gap concerning mountain permafrost and ground ice contents in the Central Asian region.

References

Archie, G. E. (1942). The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics. Transactions of the AIME, 146(01), 54–62. https://doi.org/10.2118/942054-G

Mollaret, C., Wagner, F. M., Hilbich, C., Scapozza, C., & Hauck, C. (2020). Petrophysical Joint Inversion Applied to Alpine Permafrost Field Sites to Image Subsurface Ice, Water, Air, and Rock Contents. Frontiers in Earth Science, 8, 85. https://doi.org/10.3389/feart.2020.00085

Wagner, F. M., Mollaret, C., Günther, T., Kemna, A., & Hauck, C. (2019). Quantitative imaging of water, ice and air in permafrost systems through petrophysical joint inversion of seismic refraction and electrical resistivity data. Geophysical Journal International, 219(3), 1866–1875. https://doi.org/10.1093/gji/ggz402

How to cite: Mathys, T., Hilbich, C., Mollaret, C., Hauck, C., Saks, T., Usubaliev, R., Moldobekov, B., Bektursunov, Z., Azimshoev, M., Navruzshoev, H., and Hoelzle, M.: Quantifying Ground Ice in Tien Shan and Pamir Permafrost: A Comprehensive Petrophysical Joint Inversion Study Applying the electrical Geometric Mean Model , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21232, https://doi.org/10.5194/egusphere-egu24-21232, 2024.

EGU24-2809 | Posters on site | ERE1.9

A small coil transient electromagnetic system for quick subsurface mapping  

Pradip Maurya, Esben Auken, and Thue Bording

Transient Electromagnetic (TEM) methods are widely used in near-surface geophysical exploration. Traditional ground-based TEM systems utilize large transmitter loops (25x25 to 50x50 m²) to investigate depths between 200 and 300 meters, yielding 15-20 soundings per day. To enhance efficiency in shallower investigations (0 - 100 m), we introduce a compact TEM system with a small coil setup for rapid deployment and mobility, increasing data collection rates along extensive transects.

 

The novel system comprises a 3x3 m transmitter loop with two turns and an equivalently sized offset receiver loop with four turns, separated by 10 m to minimize coil coupling and ensure unbiased signals. Operating as a single-moment setup, it achieves a peak current of 5 Amp or 10 Amp, turning off in approximately 7 µs. Unbiased measurement begins at 10 µs post turn-off, extending to a late gate of 3 ms. Both transmitter and receiver are integrated into a portable unit powered by lightweight lithium-ion batteries. A dedicated mobile application for Android and iOS devices controls the system, facilitating real-time monitoring of data curves and system parameters like current and temperature.

With this system, two people can collect a 400 m profile in under 60 minutes, significantly faster than Electrical Resistivity Tomography (ERT) methods. The presentation will cover the system's layout, operational methodology, depth capabilities, and validation against the Danish National TEM Test Site. Comparative analyses will underscore its efficiency and effectiveness in aquifer layer mapping, offering a compelling alternative to traditional ground-based systems.

How to cite: Maurya, P., Auken, E., and Bording, T.: A small coil transient electromagnetic system for quick subsurface mapping , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2809, https://doi.org/10.5194/egusphere-egu24-2809, 2024.

EGU24-5979 | Posters on site | ERE1.9

Time-domain denoising of CSAMT data base on long short-term memory 

Zhiguo An, Bingcheng Xu, Ying Han, and Gaofeng Ye

Controlled-source audio-frequency Magnetotellurics method (CSAMT) partially overcomes the drawbacks of weak natural field signals. However, substantial interference is an inevitable part of field surveys in practice, which negatively impacts signal quality. We require new denoising techniques since traditional techniques, such as Fourier transformation, which compute apparent resistivity directly from frequency-domain data, are insufficient in our situation. CSAMT denoising research is currently lacking, nevertheless. This research proposes the use of long short-term memory (LSTM) neural networks to denoise CSAMT signals in the time domain, given their good performance in processing Magnetotelluric (MT) data as shown by prior studies. We seek to directly extract the desired frequency signal for denoising from the time series data, in contrast to conventional denoising techniques. Since noise and target frequency signals are mixed together in MT data, the only way to suppress noise is to find the characteristics of the noise in the time series. CSAMT, on the other hand, differs from MT in that it uses an artificial transmitting source and fixes the valid signal frequency within a temporal window. This makes it possible to extract target frequency signals directly without taking into account the intricate properties of noise. In order to complete the noise suppression job, we created a neural network in this study that is based on bidirectional LSTM. This method was able to partially handle the difficulty of denoising when the data's SNR falls below 0 dB and, on average, enhance the signal-to-noise ratio (SNR) of CSAMT data by roughly 20 dB after executing both simulated and measured data testing.

How to cite: An, Z., Xu, B., Han, Y., and Ye, G.: Time-domain denoising of CSAMT data base on long short-term memory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5979, https://doi.org/10.5194/egusphere-egu24-5979, 2024.

EGU24-7179 | Posters on site | ERE1.9

Early Detection of Coal Fire inside the Coal Stock Pile by 4D ERT Monitoring 

Myeong Jong Yi, Soocheol Jeong, and Seungwook Shin

Coal-fired power plant requires huge storage of coal. During the storage of coal, heat is accumulated inside the stock piles and eventually results in the self-combustion or coal fire, which is a very serious problem in the fuel management and environmental aspect of the power plant facilities. To detect and forecast the coal fire, various methods had been suggested but there are no proven early warning technology until today. Since the resistivity of the coal is strongly affected by temperature, we suggested the ERT (Electrical Resistivity Tomography) monitoring technology to identify the heat accumulation inside the coal stock pile, which can eventually provide an early warning method of coal fire in the power plant facilities. To prove the technology, we prepared a small scale coal stock pile and electrodes were placed on the bottom of the stock pile. In the inside of the coal pile, temperature was continuously increased by using heating tools and ERT monitoring data were acquired for a few days until real coal fire take place on site. The whole ERT monitoring data were processed and we tried the 4D inversion to obtain changes of 3D resistivity distribution with temperature changes. In the 4D inversion results, we could identify the systematic change of resistivity values due to the heating process. Although resistivity is increased in the very early heating stage, increased resistivity is evident with the increase of coal temperature until self-combustion of coal. Therefore, we could prove that 4D ERT monitoring technology is a very promising method to detect and forecast the coal fire in the power plant facility.

How to cite: Yi, M. J., Jeong, S., and Shin, S.: Early Detection of Coal Fire inside the Coal Stock Pile by 4D ERT Monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7179, https://doi.org/10.5194/egusphere-egu24-7179, 2024.

EGU24-9430 | ECS | Posters virtual | ERE1.9

Characterization of contaminated site using electrical resistivity and induced polarization methods 

Jian Meng, Teng Xia, Xinmin Ma, Ruijue Zhao, and Deqiang Mao

Soil and groundwater contamination has been widely concerned because of its impact on industrial, agricultural production, and even human health. Accurate delineation of contaminant distribution is the basis for successful remediation strategies. Traditional drilling based methods are costly and less efficient. Geophysical methods, particularly electrical resistivity (ERT) and induced polarization (IP), are sensitive to soil and groundwater contamination and have been proven very effective. However, there were still some pressing issues to be resolved, such as IP mechanism of contaminant, data acquisition, inversion strategies and monitoring system. In this study, we proposed the conceptual model of IP response for LNAPLs in-situ remediation process based on laboratory columns and sandboxes IP measurements, and quantified the effect of contaminant removal on IP parameters. In addition, the IP data acquisition method were improved for contaminated site surveys, doubling the detection depth and significantly increasing the IP data quality. Moreover, we propose a refined structure-constrained method that updates the smooth weights of all eight elements surrounding a boundary element using three different magnitudes. Combined with the joint interpretation of multisource data, detection accuracy was improved and the number of boreholes was reduced. We have applied ERT and IP techniques to more than 30 contaminated sites and proved their effectiveness.

How to cite: Meng, J., Xia, T., Ma, X., Zhao, R., and Mao, D.: Characterization of contaminated site using electrical resistivity and induced polarization methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9430, https://doi.org/10.5194/egusphere-egu24-9430, 2024.

The Badain Jaran Desert, located in the western part of the Inner Mongolia Autonomous Region in China, distinguishes itself from typical deserts by its abundance of lakes and rich groundwater reserves. At the Badain Jaran Desert, 153 magnetotelluric sounding stations have been explored to perform one-dimensional and three-dimensional inversion analyses of the collected magnetotelluric dataset. The results of one-dimensional inversion at each sounding station, where the top interface of the first underground low-resistivity layer is less than 400 meters, were used to build a map of the potentiometric surface level of the study area. This map aligns closely with the findings from hydrological surveys. The three-dimensional resistivity model indicates the existence of a conductive layer at the deep of 2-3 km, interpreted as a sandstone-confined aquifer, located between the mountain areas surrounding the Badain Jaran Desert and its clusters of lakes. 
Moreover, there is an almost vertical conductive zone underneath the lake cluster, which is interpreted as the discharge area of the confined aquifer. This zone is related to the upward flow of deep groundwater through fractures, replenishing both the lakes and the shallow groundwater, while the surrounding mountainous regions of the desert act as the recharge areas for this confined aquifer. Finally, an estimation of the volumetric percentage of saline fluid in the confined aquifer was derived based on the electrical conductivity model of pore-fluid saturated sandstone, yielding the saline fluid content that meets the resistivity/conductivity range conditions of the confined aquifer.

How to cite: Yi, X., Ye*, G., Jin, S., Wei, W., and Zhang, Y.: Groundwater Recharge Mechanisms in the Lake Clusters of the Badain Jaran Desert and the Salinity of Confined Aquifers Based on the Electrical Conductivity Model of Pore-fluid Saturated Sandstone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15176, https://doi.org/10.5194/egusphere-egu24-15176, 2024.

EGU24-15575 | ECS | Posters on site | ERE1.9

Insights into geological and hydrogeological characteristics using airborne geophysical investigations of former opencast lignite mining areas 

Elisabeth Schönfeldt, Olaf Cortes Arroyo, Marcus Fahle, Bernhard Siemon, Silvio Janetz, and Erik Nixdorf

The region Lusatia in northeastern Germany, which is located about 100 km south of Berlin, is strongly affected by over a century of both former and on-going opencast lignite mining. Although, there is an abundance of borehole data from former excavation surveys both varying data quality and heterogeneous coverage is a challenge for deriving spatially continuous subsurface properties. To overcome these obstacles we combined airborne geophysical investigations with borehole data. Different machine learning-algorithms (Random Forest and K-means) are used to determine spatially and depth-related insights into the variability of geological and hydrogeological characteristics. An aeroelectromagnetic (AEM) survey was carried out in summer 2021 using BGR’s (German Federal Institute for Geosciences and Natural Resources) helicopter, which covered flight lines of 1680 km in an area of about 200 km². First results show that the machine learning approach can predict fine-grained sediments (clay and silt) in untrained areas and can distinguish between clusters of mining-affected regions and undisturbed ones. The results of the study will be further used to improve the parameterization of existing regional groundwater flow models to address challenges of water allocation in the region of Lusatia.

How to cite: Schönfeldt, E., Cortes Arroyo, O., Fahle, M., Siemon, B., Janetz, S., and Nixdorf, E.: Insights into geological and hydrogeological characteristics using airborne geophysical investigations of former opencast lignite mining areas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15575, https://doi.org/10.5194/egusphere-egu24-15575, 2024.

EGU24-15611 | ECS | Posters on site | ERE1.9

The first application of a new 3D octree finite element inversion framework to CS/MT data 

Cedric Patzer, Longying Xiao, and Jochen Kamm

At GTK we are currently developing the entire workflow of the controlled source EM (CSEM) method, ranging from data acquisition to time series processing to modelling and inversion. Part of this work is the development of a 3D modelling and inversion framework, which is mostly done within the DroneSOM project. The flexible implementation allows not only for modelling and inversion of semi-airborne drone EM data, but also land-based CSEM/MT data. The forward problem is solved using the finite element method on hexahedral meshes. We separate forward and inverse mesh using octree mesh refinement. This helps in solving the trade-off between the required accuracy in the forward modelling and computational cost. It is also a great tool to combine different multiresolution EM data (e.g., CSEM and MT) in a single comprehensive inversion framework. This work will focus on first applications of land-based CSEM and (CS)MT.

In 2022 we collected controlled source MT data using a grounded electric dipole transmitter along the Koillismaa ultra-mafic intrusion in North-Eastern Finland. Despite transmitter receiver offsets of 3-5 km far field condition does not apply for frequencies below 4kHz, which permits the use of standard MT inversion. Here we show first inversion results of these data using our new EM inversion routine taking the transmitter position into account. In addition to the active source MT data, we also collected conventional MT data on a larger scale crossing the Koillismaa intrusion. Our inversion routine also allows the inversion of MT data. We are thus showing first inversion results of joint inversion of both datasets. 

How to cite: Patzer, C., Xiao, L., and Kamm, J.: The first application of a new 3D octree finite element inversion framework to CS/MT data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15611, https://doi.org/10.5194/egusphere-egu24-15611, 2024.

EGU24-18165 | ECS | Posters on site | ERE1.9 | Highlight

Mapping Subsurface Conductivity: Challenges and Progress in Italy's MARGE Project 

Giulia Pignatiello, Igino Coco, Michele De Girolamo, Manuele Di Persio, Fabio Giannattasio, Valerio Materni, Luca Miconi, Massimo Miconi, Giovanna Lucia Piangiamore, Gerardo Romano, Valentina Romano, Lucia Santarelli, Vincenzo Sapia, Sabina Spadoni, Simona Tripaldi, Roberta Tozzi, Agata Siniscalchi, and Paola De Michelis

In Italy, the MARGE initiative, an abbreviation for Geoelectromagnetic Risk Map for Central Italy, strives to create an extensive map of subsurface electrical conductivity by analyzing natural electric and magnetic fields.

Led by the National Institute of Geophysics and Volcanology in collaboration with the University of Bari and the Institute of Environmental Analysis Methodologies at CNR, his project involves establishing measurement points distributed on a grid spaced approximately 50 km apart.

However, this endeavor faces significant challenges in the central region of the Italian peninsula due to extensive urbanization, numerous electromagnetic disturbances from railways and high-voltage power lines, and challenging topography, making finding suitable land parcels a complex task.

The MARGE project aims to gather broad-band and long-term magnetotelluric data, focusing on two primary objectives: utilizing magnetotelluric data to outline large-scale lithospheric structures in the Central Apennines and developing maps of the geoelectric field in Central Italy to support Space Weather modeling and critical infrastructure vulnerability analysis.

Presenting our initial findings, we discuss encountered challenges and potential solutions identified in this ongoing project.

How to cite: Pignatiello, G., Coco, I., De Girolamo, M., Di Persio, M., Giannattasio, F., Materni, V., Miconi, L., Miconi, M., Piangiamore, G. L., Romano, G., Romano, V., Santarelli, L., Sapia, V., Spadoni, S., Tripaldi, S., Tozzi, R., Siniscalchi, A., and De Michelis, P.: Mapping Subsurface Conductivity: Challenges and Progress in Italy's MARGE Project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18165, https://doi.org/10.5194/egusphere-egu24-18165, 2024.

EGU24-19540 | ECS | Posters on site | ERE1.9

Uncertainty estimation of conductive thin plates parameters through a Bayesian approach 

Alessandro Vinciguerra, Guy Marquis, Jean-François Girard, Grant Harrison, and Elodie Williard

The uranium deposits of the Athabasca basin (Canada) represent one of the world’s highest-grade uranium resources. They are unconformity-related type at the base of relatively flat-lying sequences, where faults acted as circulation paths for hydrothermal fluids. The fault zones often contain graphitic mineralization and hence represent a valuable exploration guide of small lateral extension but detectable by electromagnetic (EM) surveys. Time-domain EM (TEM) is the method of choice for uranium exploration in the Athabasca, and taking into account the frequencies involved we can approximate the graphitization along the fault as a conductive thin plate.

To better determine the geometry of the deposit, it might be crucial to recover the subsurface resistivity and the geometric parameters of the plate (position, dip, depth, azimuth etc.). Moreover, the assessment of the uncertainty associated to the parameters can help to evaluate the reliability of geological models and to guide the subsequent drilling activities.

A quantitative approach consists of employing Bayesian inversion algorithms, which allows to exploit the prior information available. Indeed, Bayesian inversion algorithms aim to solve the inverse problem statistically returning the posterior probability density function (ppdf). In particular, they are based on the Bayes theorem, which relates the prior information (e.g. from geological and petrophysical models) with the likelihood function to assess the posterior probability density function and thus the uncertainty. We implement the Differential Evolution Markov Chain algorithm (DEMC), a multi-chain approach that integrates the Metropolis selection rule with population evolution to sample the ppdf. The chains run in parallel and each current model is updated drawing two other chains and exploiting the models at the previous iteration. After an initial stage of burn-in, the algorithm reaches the stationary regime where the chains start sampling the ppdf resulting at the end in an ensemble of models. From these models the moments of first and second order (mean and variance) are computed obtaining the uncertainty of the inverse problem solution. As forward operator we employ the LEROI forward code developed by CSIRO (AMIRA), which computes the TEM response of one or more conductive 3D thin plates embedded in a horizontally layered earth.

In this work we propose the DEMC inversion of TEM data as a tool to assess thin plates parameters and uncertainty in the context of uranium exploration.

 

How to cite: Vinciguerra, A., Marquis, G., Girard, J.-F., Harrison, G., and Williard, E.: Uncertainty estimation of conductive thin plates parameters through a Bayesian approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19540, https://doi.org/10.5194/egusphere-egu24-19540, 2024.

EGU24-20965 | ECS | Posters on site | ERE1.9

Development of 9000 m level hadal OBEM 

Sixuan Song, Ming Deng, Zhen Sun, Xianhu Luo, and Kai Chen

Taking the sea area near the southern part of the Mariana Trench as a typical area is crucial for deep structural research in marine geology and geophysics. The magnetotelluric (MT) method has advantages such as large detection depth, sensitive to low resistance reactions, low cost, and high efficiency. The application of MT in deep water requires instruments with high reliability and stability, low noise, wideband, low power consumption, and miniaturization. The ocean bottom electromagnetic receiver (OBEM), as one of the important instruments for MT in deep water observation, its performance directly affects the quality of detected data.

In response to the shortcomings of the existing 6000 m level OBEM, there is an urgent need to develop a 9000 m level hadal OBEM. According to the requirements, we have focused on overcoming the challenges of weak E-field measurement technology, low-power and low-noise M-field measurement technology, low-power underwater acoustic release technology, and water surface large-scale recycling technology. We have achieved lower noise, longer underwater operation time, and efficient operations, providing reliable and stable instruments for hadal MT observation.

We have developed a chopper amplifier that matches deep water E-field sensors, analyzed the causes of injected charges, and adopted a scheme that combines peak filtering technology and dead zone technology to suppress residual misalignment generated during the chopper modulation, effectively reducing 1/f noise in the circuit, expanding the input range, and improving input impedance.

An orthogonal fundamental mode fluxgate based on digital demodulation is developed. Digital closed-loop real-time processes such as high-precision ADC, digital synchronous demodulation, digital integration, and high-precision large dynamic range DAC are used to reduce the switching charge noise introduced by analog circuits. Developing adaptive closed-loop feedback control algorithms to achieve fast feedback compensation with low noise and large dynamic range can help improve key parameters such as noise bandwidth, and input range of sensors.

We adopt a deep-water acoustic release system, pressure-resistant acoustic transducer, and control module prototype. Hydroacoustic communication controls the opening of the constant current source and the electrocorrosion decoupler. This solution reduces the size of the instrument and only relies on a single glass ball to achieve the floating of the instrument. The system integrates commands such as status query, electrocorrosion on and off. The status information includes distance, electrocorrosion status, battery voltage, etc. The propagation distance of acoustic signals is greatly increased, improving the success rate of underwater acoustic communication.

The glass ball is equipped with a beacon module, which is controlled by acoustic signals to activate the AIS, achieving real-time transmission of the OBEM position. Besides, high-power LED flashing is controlled to facilitate nighttime recycling and further reduce the cost of offshore operations.

In August 2023, 5000 m level test was conducted in the southern South China Sea. It is preliminarily verified the MT measurement, which has been improved in terms of low power consumption, low noise, and adaptability to deep sea. In the future, we will conduct test verification in deeper sea.

How to cite: Song, S., Deng, M., Sun, Z., Luo, X., and Chen, K.: Development of 9000 m level hadal OBEM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20965, https://doi.org/10.5194/egusphere-egu24-20965, 2024.

At present, we are using commercial ground penetrating radar (GPR) to inspect tunnel walls, conduct an underground geological structure assessment and anticipate geology behind the tunnel face. A variety of metal objects, include portal frame, forklift, and excavator, can cause back reflection in the GPR profile during the test in the tunnel. Typically end users of GPR are unable to appropriately interpret the GPR profile because they are unware of what is actually coming from back reflection in the air and projection into the ground penetrating radar profile or from subsurface. They really need some method to identify real reflection signals from underground sources.

The GPR antenna transmits electromagnetic (EM) waves that can travel all space, including the air, the interface between the ground and the air, and the subsurface. During EM travel in the air, there is some back reflection from the air object to be recorded in the GPR profile during data collection in the field. We need to measure and recognize and elimate this back reflection interference noise. We have made electromagnetic waves absorbent block configuration for the GPR antenna that can complete cover the GPR antenna. We have done the comparative experiments tests with and without electromagnetic waves absorbent block have been conducted in the field, the results show that, without this block, GPR profile recorded many back reflection from the air objects, while the GPR antenna with covering electromagnetic waves absorbent block can only record the refection from surbsurface during data collection in the field, and it is clear GPR profile. This allows the GPR end user direct interpret the GPR profile only with reflection from surbsurface as it may completely eliminate back reflection from the air object.

How to cite: Deng, X.: A method to collect clear profile with Ground Penetrating Radar in tunnel, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21417, https://doi.org/10.5194/egusphere-egu24-21417, 2024.

EGU24-21924 | Posters on site | ERE1.9

Measuring Induced Polarization signals from deep seated magma chamber – preliminary results from a pilot survey in Finland 

Bitnarae Kim, Jacques Deparis, Mathieu Darnet, Francois Bretaudeau, Simon Vedrine, Julien Gance, Jochen Kamm, Uula Autio, Cedric Patzer, and Suvi Heinonen

In this study, we conducted an extensive geophysical survey to explore the potential of electrical resistivity methods in delineating deep ore deposits within between Koillismaa Intrusion and Näränkävaara intrusion, northeastern Finland. Preliminary investigations in 2022, including magnetic, gravity and audio-magnetotelluric (AMT) methods, along with drilling, uncovered significant anomalous structures in the survey area. Subsequent drilling of an exploration well provided positive lithological indications of a ultramafic igneous rock at more than 1.5 km depth, which are very likely of the same age as the layered intrusions in the area. Borehole data indeed revealed that the Archaean basement gneiss extends down to approximately 510 m, underlain by a granite dyke with interspersed thin layers of pyroxenite and peridotite. Notably, peridotite layers around 1500 m depth exhibited distinct magnetic and IP responses in core data.
We employed electrical methods at the site, including electrical resistivity tomography (ERT) and induced polarization (IP). To cover a large-scale area, 25 transmitter dipoles, each 1 km long and using three different transmitter systems, were deployed and data were recorded at 119 receiver stations. This work presents the acquisition and preliminary results from the ERT-IP surveys. During the processing of ERT and IP data, we utilized full time-series data recorded across the four lowest main frequencies (from 0.0625 Hz to 8Hz) to capture voltage data in a steady state. Apparent resistivity data were derived from the stacked voltage data, while IP data were initially extracted from these decay curves of these stacked voltage data and subsequently processed in the frequency domain (outphasing). Analysis of the resistivity and IP responses revealed notable IP signals at depths exceeding 1.5 km. Meanwhile, the resistivity data indicated generally very high values, around 10,000 ohm-m, with complex variations observed near the surface. This study demonstrates the efficacy of ERT and IP methods in delineating deep-seated mineral deposits, with the deep-depths IP responses being particularly noteworthy.

How to cite: Kim, B., Deparis, J., Darnet, M., Bretaudeau, F., Vedrine, S., Gance, J., Kamm, J., Autio, U., Patzer, C., and Heinonen, S.: Measuring Induced Polarization signals from deep seated magma chamber – preliminary results from a pilot survey in Finland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21924, https://doi.org/10.5194/egusphere-egu24-21924, 2024.

This study employs gravity modelling to investigate the subsurface geometry of a pull-apart basin located in Elazığ, Turkey. The study area is situated along the East Anatolian Fault Zone—a major active system that recently produced two devastating M7.0+ earthquakes at Kahramanmaraş in February 6, 2023.

Recently collected gravity data, comprising approximately 600 data points from Sivrice and Gezin provinces, form the basis of our investigation. Preliminary examinations show that the gravity anomalies in Gezin are notably lower than those in Sivrice, suggesting a deeper basement for the former. We aimed to estimate the subsurface model using a proprietary computer program. Given the known different geological units with constant density contrasts, the program was employed to deduce their geometry up to a maximum depth of 350 meters in 2D. A total of 16 sections were modeled—8 each for Sivrice and Gezin provinces—yielding RMS values consistently below 0.1 mGals. Next, quasi-3D and 3D models were prepared for Talwani models at Sivrice and Gezin. We assumed the geometry beneath Lake Hazar to be similar to the bathymetry of the lake, assigning sediment thickness to estimate the basement in this part. The individual models were then integrated into a full 3D representation of the geometry of the basin.

Our findings suggest that the pull-apart basin situated here is in its extinction phase, with pull-apart tectonics no longer active, and only strike-slip movement along main East Anatolian Fault is observed. Notably, slips along the main fault have impacted the basement geometry. This study contributes valuable insights into the current state of the basin, emphasizing the importance of 3D modelling in unraveling the complexities of pull-apart basins.

How to cite: Aydın, N. G. and İşseven, T.: Gravity Modelling of a Pull-Apart Basin in Elazığ, Turkey: Unraveling the 3D Basement Geometry (Preliminary Results), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-397, https://doi.org/10.5194/egusphere-egu24-397, 2024.

EGU24-1294 | Posters on site | G4.3

Voxel-based Density Models for Accurate Gravitational Field Computation 

Benjamin Haser, Thomas Andert, and Roger Förstner

Asteroids and moons are promising targets for physical space exploration. The use of physically-based simulations within a virtual environment for (deep) space missions can significantly benefit the testing and validation of guidance, navigation, and control algorithms. This approach offers advantages in terms of cost and time efficiency. Especially for orbit propagation and landing maneuvers, information about the gravitational field is crucial. However, several factors contribute to the complexity of this task, such as limited information available about the inner structure of celestial bodies. The lack of detailed knowledge about their shapes further adds to the challenge.

This study presents a voxel-based mass concentration (MASCON) method to model detailed and realistic density distributions, enabling accurate gravity field determinations. We chose a cube with constant density as first case due to the perfect shape reconstruction and the availability of an analytical solution for its gravity field. To validate our results, we calculated the surface gravity and compared it with the analytical solution, ensuring the accuracy of our calculations. Furthermore, the surface gravity is derived for different resolutions and compared against other state-of-the-art methods like the polyhedral method that provides a closed-form analytical solution of the gravity field for homogeneous density. The other two methods for validation also use a MASCON approach, one utilizing polydisperse sphere packing and another with MASCON represented in spherical coordinates. The relative errors of the gravitational acceleration between the four methods will be evaluated for a cube and sphere, with homogeneous density.

The second aspect of this study was to create a tool that generates realistic density distributions. We are able to successfully reproduce natural environments by placing body-specific restrictions on three-dimensional Perlin noise with additional normalization. The simulator can add the following structural features to the density distribution: an arbitrary number of centralized or decentralized shells, with varying thickness and densities, anomalies of arbitrary size and shape, only restricted by its maximum permille of the body's volume. Furthermore, we implemented different normalization techniques to keep the mass of all generated bodies fixed. Our results show that the tool can generate realistic density distributions and calculate the corresponding gravitational field correctly. The data generated here is used to train Machine Learning and Deep Learning algorithms for gravity inversion.

 

How to cite: Haser, B., Andert, T., and Förstner, R.: Voxel-based Density Models for Accurate Gravitational Field Computation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1294, https://doi.org/10.5194/egusphere-egu24-1294, 2024.

Precise determination of Moho topography holds paramount importance in advancing our comprehension of Earth's structural characteristics, geodynamic phenomena, and the exploration of resources. This study introduces an innovative methodology employing conditional Generative Adversarial Networks (cGAN) to unveil Moho topographies from observed gravity anomalies. To address the scarcity of real Moho datasets for training the cGAN model, we meticulously generated a comprehensive set of quasi-realistic synthetic training data using the FFT filtering technique. The forward estimation of gravity anomalies, arising from synthetic Moho topographies, was assessed through spherical prism-based gravity modeling. These estimated anomalies served as input data for the training of the cGAN model. For evaluating the efficacy of our developed cGAN algorithm in deriving Moho architecture, we conducted a comparative analysis against a conventional inversion scheme. This assessment utilized various synthetic datasets and a real case study in Southern Peninsular India, renowned for its geological diversity and ancient continental tectonic blocks. The established Bott's inversion scheme was employed as a benchmark to validate the Moho surface estimation obtained through the Deep Learning approach. To mitigate the impact of diverse factors such as topography, bathymetry, sediments, crustal and mantle heterogeneities, observed gravity anomalies underwent meticulous corrections using spherical prism-based forward gravity modeling for real case studies. The gravity contribution exclusively associated with the pure Moho was subsequently inverted using both the cGAN and traditional Bott's inversion schemes. Crucial hyperparameters, including the mean Moho depth and density contrast between the crust and mantle, were determined by utilizing seismic constraints. Our results underscore the potential of the cGAN and spherical prism-based gravity modeling approach in accurately predicting Moho topography. This study provides valuable insights into high-resolution Earth's Moho architecture and contributes to advancing our understanding of geodynamic processes, facilitating resource exploration endeavours with reduced computational demands.

How to cite: Roy, A., Sharma, R. K., Jash, D., and Kallukalam, T. J.: Innovative Insights into Earth's Interior: Moho Topography Estimation using Conditional Generative Adversarial Networks from Observed Gravity Anomalies , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1405, https://doi.org/10.5194/egusphere-egu24-1405, 2024.

EGU24-2837 | ECS | Orals | G4.3

Joint inversion of airborne gravity and magnetic data for the crustal structure in central Dronning Maud Land 

Mikhail Ginga, Jörg Ebbing, Antonia Stefanie Ruppel, Andreas Läufer, and Graeme Eagles

Topography and physical conditions at the base of the Antarctic ice sheet are critical inputs for studies of its present and future ice discharge, and of subglacial geology and hydrology. Airborne gravity and magnetic data, especially when interpreted jointly can help us to link the geology from outcrops towards the coastal areas to unknown subglacial regions further inland. Here we use airborne geophysical data obtained during the joint AWI-BGR campaign WEGAS/GEA between 2015 and 2017 in central Dronning Maud Land (DML) as input for a novel joint inversion scheme. With regard to Gondwana reconstruction, this region is critical because it hosts the ice-covered Forster Magnetic Anomaly, a prominent lineament crossing central DML for some 100s of kilometers south of the main mountain chain. This lineament, originally interpreted as the main pan-African suture of East and West Gondwana, likely represents the eastern margin of Kalahari and its boundary to the Tonian Oceanic Arc Super Terrane (TOAST). In the inversion using the software jif3D, sources of the gravity and magnetic field are combined through a coupling method which decreases the variation of information (VI), so data misfit and model dissimilarity are minimized simultaneously. The model results can be classified in geologically meaningful provinces by applying cluster analysis based on machine learning. Our joint inversion approach improves previous interpretations and sheds light on the crustal architecture of the study area, contributing to further studies on the interaction between the ice sheet and the underlying solid earth.

How to cite: Ginga, M., Ebbing, J., Ruppel, A. S., Läufer, A., and Eagles, G.: Joint inversion of airborne gravity and magnetic data for the crustal structure in central Dronning Maud Land, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2837, https://doi.org/10.5194/egusphere-egu24-2837, 2024.

In Western Europe, the Variscan belt contacts Avalonia along the Rhenohercynian Suture, a result of Early Carboniferous continental collision. Moving east of the Harz Mts., the Rhenohercynian suture disappears beneath a thick sedimentary sequence of the Permian-Mesozoic basin. Its extension is either truncated by major NW-SE strike-slip faults like the Elbe, Odra, or Dolsk faults or bends under the cover of a thick sedimentary succession. The extension of Avalonia into Poland is challenging to determine, with the thinned margin of Baltica considered the substratum of the Permian-Mesozoic basin. Deep seismic soundings show that the thinned margin of Baltica reaches the NW-SE oriented Dolsk or Odra fault, potentially bringing the crust of Baltica into direct contact with the crust of the Variscan internides of the Bohemian Massif. Along the Dolsk fault, there is the two-layered, low-velocity Variscan crust in the SW that contacts the three-layered Baltica crust. The geometry of this contact remains unknown, but the lower, high-velocity crust of Baltica may extend southwest to the Odra fault. In the basement of the sedimentary sequence between the Dolsk and Odra faults, low-grade metamorphosed phyllites with a metamorphic age of approximately 360 Ma are found. They apparently represent a fragment of Variscan metamorphic nappes.

The Variscan front is oriented NE-SW in Western Europe, but in Poland, it bends by 90° to the NW-SE direction, continuing to the border of Ukraine. In southeastern Poland, the front enters the slope of the East European Platform, constituting an undisputed example of a direct contact between the Variscan belt and Baltica. If the geometry of the Variscan front reflects the structure of the orogen, the edge of Baltica must have initially played the role of a transform margin with a right-lateral displacement. NW-SE strike-slip faults, parallel to this margin, truncated the Rhenohercynian and other Variscan sutures from the NE. The following accretion event resulted in NE-SW shortening, either thin-skinned, leading to folding of the external fold-and-thrust belt, or thick-skinned, resulting in the emplacement of the Variscan nappe stack on the Baltica margin.

The last folding of external Variscides in Poland occurred around 305 Ma and was immediately followed by the emplacement of a large igneous province at the Carboniferous to Permian transition. The centre of magmatism was in NE Germany, the area of greatest crustal thinning. The origin of the igneous province was linked to plate boundary forces leading to extension and continental rifting. The latter produced the Mid-Polish trough, an elongated continental rift running NW-SE parallel to the Teisseyre-Tornquist zone. Permian rifting further attenuated the Baltica margin and, jointly with coeval magmatism, reshaped the margin of Baltica masking its contact with the Variscan belt. Toward the east, the continuity of the Variscan internides was disrupted by early Mesozoic rifting in the area of the present-day Carpathians.

How to cite: Mazur, S.: From Carboniferous convergence to Permian continental rifting – the interaction of Baltica with the Variscan belt of Europe at the time of the Pangaea assembly, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4560, https://doi.org/10.5194/egusphere-egu24-4560, 2024.

The South China Sea, situated at the convergence of the Tethys and Pacific tectonic domains, holds immense geological significance due to its interaction with multiple tectonic plates (Hall 2002; Hayes and Nissen 2005; Metcalfe 2011). With its abundant sedimentary basins, the region is of paramount importance for geological and structural studies, particularly in relation to its potential for oil and gas resources. In this study, we propose the utilization of satellite gravity data to analyze the tectonic structure of the South China Sea, focusing on three key areas:

1. High-resolution construction of gravity gradient anomalies and fault identification: By integrating Fast Fourier Transform algorithms with satellite gravity anomalies and high-resolution terrain elevation data, we obtaina comprehensive dataset of full tensor gravity gradient information. Through spatial analysis of this data, we successfully identify 17 significant and deep faults, as well as partition the study area into 9 distinct tectonic units characterized by well-defined geological structures.

2. Moho Depth Determination and Interpretation: Employing an improved regularization Bott's method, we determine the Moho depth using information obtained from sonar-buoy detection and submarine seismograph detection profiles. Regularization parameters are introduced to ensure the smoothness of the inversion results. By analyzing the distribution characteristics of the Moho and its relationship with tectonic units, we conduct a comprehensive analysis to comprehend the coupling between shallow and deep structures. The resultsreveal distinct regional characteristics in the depth distribution of the Moho surface in the South China Sea, shedding light on the distribution of continental crust, oceanic crust, and the ocean-continent transition zone.

3. Comprehensive Geophysical Analysis: We employ a combination of seismically constrained Moho undulation, gravity data, gravity gradient anomalies, and unconstrained 3D correlation imaging to investigate the crustal structure of the South China Sea. Integrating various geophysical datasets, we gain a deeper understanding of the distribution of continental crust, oceanic crust, and transitional crust within the region. Notably, the results shows that the trench-island arc-back arc basin systemplays a pivotal role in the active continental margin of the Western Pacific. This comprehensive analysis provides valuable insights into the tectonic dynamics and geological processes occurring in the South China Sea region.

*This study was supported by y the Basic Frontier Science Research Program of the Chinese Academy of Sciences (No. ZDBS-LY-DQC028).

Reference:

Hall, R. (2002). Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations, J. Asian Earth Sci. 20:353–431.

Hayes, D.E., Nissen, S.S. (2005). The South China Sea margins: implications for rifting contrasts, Earth Planet Sci. Lett., 237: 601–616.

Metcalfe, I. (2011). Tectonic framework and phanerozoic evolution of Sundaland, Gondwana Res., 19 (1): 3–21.

How to cite: Guo, D.: Constrained Gravity Inversion for the Moho Depth and Tectonic Patterns in South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4845, https://doi.org/10.5194/egusphere-egu24-4845, 2024.

EGU24-6228 | Posters on site | G4.3

Harnessing Modern 3D Gravity Analysis Techniques: A Study of the Ligurian Offshore Area 

Hans-Jürgen Götze, Ronja Strehlau, Denis Anikiev, Anke Dannowski, and Magdalena Scheck-Wenderoth

This interdisciplinary study describes the integration of gravity field analysis, curvature techniques and various spatial applications. The data are based on land-based Free Air and Bouguer gravity data from the AlpArray Gravity Research Group, complemented by recent satellite missions. New seismic and seismological data from the AlpArray initiative and the German MB-4D Priority Program were used as independent boundary conditions for the 3D modeling and inversion of the gravity data. Prior to this modeling, Euler deconvolution, terracing/clustering techniques, and advanced filtering methods were employed to reveal intricate details of the region's gravitational signatures. For example, a distinct zoning of gravity is observed in the central part of the Ligurian Sea, pointing to traces of past rifting processes. Analysis of various curvature parameters (e.g., dip-, min-, max- and shape-curvature) of the processed gravity fields, in particular gradients and residual fields support the identified zonation of the gravity fields, which reflect the geological structures in the crust. The final 3D modeling of the Ligurian Sea area is based on a previous density model of the entire Alpine region and includes density distribution of the upper mantle. These densities were derived from tomographic velocity models, accounting for petrology, temperature, and pressure. Additional information of the upper crust was obtained from the refraction seismic results of the LOBSTER project, offering a comprehensive understanding of spatial phenomena. Calculations of the gravitational potential energy (GPE) provide additional information on local stresses, facilitating a deeper understanding of the flexural rigidity in the area. By elucidating the relationship between processing techniques and 3D modeling, this work advances interdisciplinary interpretation crucial for geological studies in the Ligurian offshore area.

How to cite: Götze, H.-J., Strehlau, R., Anikiev, D., Dannowski, A., and Scheck-Wenderoth, M.: Harnessing Modern 3D Gravity Analysis Techniques: A Study of the Ligurian Offshore Area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6228, https://doi.org/10.5194/egusphere-egu24-6228, 2024.

EGU24-6402 | Posters on site | G4.3

Participative gravity-modelling challenge to constrain the Balmuccia peridotite body (Ivrea-Verbano Zone, Italy) 

György Hetényi, Ludovic Baron, Matteo Scarponi, Shiba Subedi, Konstantinos Michailos, Fergus Dal, Anna Gerle, Benoît Petri, Jodok Zwahlen, Antonio Langone, Andrew Greenwood, Luca Ziberna, Mattia Pistone, Alberto Zanetti, and Othmar Müntener

The Balmuccia peridotite exposes relatively fresh mantle rocks at the Earth’s surface, and as such it is of interest for geologists and geophysicists. The outcrop is a kilometre-scale feature, yet its extent at depth is insufficiently imaged. Our aim is to provide new constraints on the shape of the density anomaly this body represents, through 3D gravity modelling. In an effort to avoid personal or methodology bias, we hereby launch an invitation and call for participative modelling. We openly provide all the necessary input data: pre-processed gravity data, geological map, in situ rock densities, and digital elevation model. The expected inversion results will be compared and jointly analysed with all participants. This approach should allow us to conclude on the shape of the Balmuccia peridotite body and the associated uncertainty. This crowd effort will contribute to the site surveys preparing a scientific borehole in the area in frame of project DIVE. The full description, the dataset, as well as the tentative timeline can be found at https://zenodo.org/records/10390437

How to cite: Hetényi, G., Baron, L., Scarponi, M., Subedi, S., Michailos, K., Dal, F., Gerle, A., Petri, B., Zwahlen, J., Langone, A., Greenwood, A., Ziberna, L., Pistone, M., Zanetti, A., and Müntener, O.: Participative gravity-modelling challenge to constrain the Balmuccia peridotite body (Ivrea-Verbano Zone, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6402, https://doi.org/10.5194/egusphere-egu24-6402, 2024.

Coseismic gravity changes provide significant information for the study of the mechanisms of large earthquakes and for developing fault models (Sun, 2012). In this research,  coseismic gravity changes of the 2008 Ms8.0 Wenchuan earthquake in China were studied by using gravity observation data and simulation based on a fault model.

Firstly, a fine processing of relative and absolute gravity data from the Longmenshan Gravimetric Network was carried out and observed gravity change of 22 stations near this earthquake were obtained; Secondly ,simulation of coseismic gravity changes was conducted based on half-space dislocation theory using the fault model obtained by Wang et al(2008) through inversion with multiple types of geodetic survey data, including GPS, INSAR, and leveling, and the results were compared with the observations..

It was found that the observed and simulated results are basically consistent, showing that the significant changes are mainly concentrated in the near-rupture zone in the hanging wall of the Yingxiu–Beichuan fault and that the changes decrease rapidly away from the rupture zone. The changes exhibit a positive to negative trend from east to west in the footwall of the Yingxiu–Beichuan fault and have a distribution characterized by alternate positive and negative changes in the hanging wall of the fault. This demonstrates the reliability of the observed results and the reasonableness of the fault model used in this paper.

In the near-rupture zone on the west and east sides of the Yingxiu–Beichuan fault, there are still some differences between the observed and simulated results. The trends in the spatial distribution of these differences exhibit a deviation similar to “phase delay”; in other words, an observed result deviates from the corresponding simulated result in terms of spatial position, which is speculated to be caused by errors in the geometric parameters and in the slip distribution of the fault model. After the slip distribution of  the Pengguan fault model was modified based on the actual surface rupture distribution, the simulated result at the Hongjiawan station near the eastern boundary of the fault model showed greater consistency with the observed result. This indicates that the observed gravity change results in this paper can provide an important reference for further detailed study of the fault model.         

            Fig1.Schematic of the Chengdu Gravimetric Network                        Fig2.Spatial distribution of observed gravity changes and simulated results

 

 

How to cite: Hao, H. and Hu, M.: Coseismic gravity changes of the 2008 Wenchuan earthquake in China observed by surface gravimetric data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7561, https://doi.org/10.5194/egusphere-egu24-7561, 2024.

EGU24-8059 | Posters on site | G4.3

Enhancing sub-ice geology in East Antarctica with Self-Organizing maps based on gravity, magnetic and radar data 

Jörg Ebbing, Jonas Liebsch, and Kenichi Matsuoka

Sub-ice geology significantly influences the dynamics and future evolution of the Antarctic Ice Sheet, but largely inaccessible for direct sampling. Here, we present an approach, where we use a Self-Organizing Map (SOM) to describe sub-glacial properties. Based on attributes derived from gravity, magnetics and radar data from the NASA Operation Ice Bridge dataset in East Antarctica, we train a SOM, where attributes are selected to best represent sub-glacial conditions. Therefore, we study the trade-offs between these data sets helping to identify for which properties these are most sensitive.
The trained SOM identifies the outlines of the main geological structures beneath the ice and supplements models based on inverse and forward modelling. In contrast to such often regional interpretations, the SOM captures small-scale structures at the ice bed, as we illustrate with case examples, and highlights areas with inconsistencies in existing geological interpretations. The SOM can furthermore be used as input for inverse modelling of the physical properties of the sub-glacial geology in Antarctica.

How to cite: Ebbing, J., Liebsch, J., and Matsuoka, K.: Enhancing sub-ice geology in East Antarctica with Self-Organizing maps based on gravity, magnetic and radar data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8059, https://doi.org/10.5194/egusphere-egu24-8059, 2024.

EGU24-8934 | Posters on site | G4.3

What can we learn from magnetic surveys at different scales? Geological insight from mineral to airborne surveys in the Bjerkreim-Sokndal Layer Intrusion, Norway 

Suzanne McEnroe, Madeline Lee, Yuleika Madriz, Richard Gloaguen, Zeudia Pastore, Peter Lelièvre, and Nathan Church

Multiple magnetic surveys, including fixed-wing, helicopter-borne, uncrewed aerial vehicle (UAV), and ground magnetics have been acquired over parts of the Bjerkreim-Sokndal layered intrusion (BKS) in Rogaland, Norway. The Proterozoic 230 km2 Bjerkreim-Sokndal layered complex intrudes into anorthosites and hosts recurrent megacyclic units (MCU) with varying cumulus and critical minerals. Some MCUs are associated with strong magnetic remanence, resulting in Koenignsberger ratios (Q ratio) over 5 and anomalies of 12 000 nT below background.  A comparative analysis of these surveys over the Bjerkreim Lobe provide insights into what features can be mapped at different scales. Here we focus on new geological details provided by UAV, ground, and mineral scale surveys.  A UAV can typically operate at a maximum altitude of 150 m above terrain to a minimum of tens- of centimeters in ideal conditions. Thus, UAV magnetic surveys are optimal for understanding the change of a magnetic anomaly with varying source-separation through multiple flight altitudes. Survey altitudes by UAVs overlap with the source-sensor separation of ground and low-altitude crewed flights, therefore allowing a comparative analysis.

In 2023, the Norwegian University of Science and Technology and Helmholtz Institute Freiberg acquired coincident magnetic survey grids by UAV and ground magnetometer over key sites in the Bjerkreim lobe. Here we compare results of crewed-, uncrewed-, and ground-based data collected over the eastern margin of the Bjerkreim lobe and assess how these impact subsequent geologic interpretations. The petrophysical database for the survey area also contains > 1500 previously collected samples in combination with surface geometry information. This database in combination with the extensive lateral magnetic survey data at various sensor heights and other available complementary geophysics, including gravity, provide excellent parameters and constraints for forward modelling and inversions.

In the Bjerkreim lobe two MCU have significant magnetic remanence where anomalies are several thousand nT below background due to natural remanent magnetizations that are typically > 15 A/m. Therefore, an additional focus is on understanding the nature of the magnetic mineralogy using high-resolution scanning magnetic microscopy. These large amplitude magnetic anomalies may also cause logistical challenges for both airborne- and ground magnetic surveying. UAVs employ onboard magnetometer for navigation and attitude corrections which can be impacted by these large magnetic gradients. Similarly, significant noise or sensor drop-outs when the sensor’s dead zone is aligned with these large, often steep, magnetic gradients.

How to cite: McEnroe, S., Lee, M., Madriz, Y., Gloaguen, R., Pastore, Z., Lelièvre, P., and Church, N.: What can we learn from magnetic surveys at different scales? Geological insight from mineral to airborne surveys in the Bjerkreim-Sokndal Layer Intrusion, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8934, https://doi.org/10.5194/egusphere-egu24-8934, 2024.

EGU24-9258 | ECS | Orals | G4.3

Moho Depth Model and Structural Characteristics of China and Adjacent Regions 

Zhixin Xue, Dongmei Guo, Jian Fang, and Huiyou He

The Moho interface is an important parameter for describing the structure and morphology of the Earth's crust, and it is of significant importance in the study of the formation and evolution of the crust and mantle, as well as deep-seated dynamic processes (Stern et al., 2018). Existing Moho models derived from seismic data often suffer from inaccuracies due to irregular distribution and regional imbalances of seismic data. However, with the development of gravity satellite technology, high-precision satellite gravity data has injected new vitality into the study of lithospheric tectonic features and crustal evolution. In this study, constrained by seismic data (Li et al., 2013; Zhang et al., 2021), we utilized an improved regularized Bott method (Uieda et al., 2017) to invert high-precision satellite gravity data and obtained a high-precision unified Moho depth model for the East Asian region, encompassing both land and sea areas. The research results show that the Moho depth model exhibits a continuous increase in depth from east to west, and its overall distribution in the horizontal direction is non-uniform, displaying distinct regional block features. This paper provides a high-resolution and high-precision Moho model for studying the evolution of the East Asian continental tectonics and plate interactions, and further discusses the macrostructural framework and geological implications of East Asia.

References

Li Y Gao M, Wu Q. Crustal Thickness Map of the Chinese Mainland from Teleseismic Receiver Functions [J]. Tectonophysics, 2013, 611.

Stern, Robert, J, et al. Continental crust of China: A brief guide for the perplexed [J]. Earth Science Reviews the International Geological Journal Bridging the Gap Between Research Articles & Textbooks, 2018.

Uieda L, Barbosa V. Fast nonlinear gravity inversion in spherical coordinates with application to the South American Moho [J]. Geophysical Journal International, 2016.

Zhang J , Yang G , Tan H , et al. Mapping the Moho depth and ocean-continent transition in the South China Sea using gravity inversion [J]. Journal of Asian Earth Sciences, 2021, 218(3–4):104864.

How to cite: Xue, Z., Guo, D., Fang, J., and He, H.: Moho Depth Model and Structural Characteristics of China and Adjacent Regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9258, https://doi.org/10.5194/egusphere-egu24-9258, 2024.

EGU24-10299 | ECS | Orals | G4.3

Satellite gravity validation by new airborne gravimetry in coastal regions of Antarctica and Norway 

Bjørnar Dale, Sebastian Bjerregaard Simonsen, Ove Christian Dahl Omang, Tim Enzlberger Jensen, and René Forsberg

Airborne gravimetry provides gravity observations of higher spatial resolution than what can be obtained from satellite gravity field measurements, and together with terrestrial measurements they augment the satellite observations to determine high-resolution geoid models. Satellite altimetry in coastal and ice-covered regions is known to have significant errors. We use modern strapdown gravimetry for the surveys and compare the indirect method, using Kalman filtering, and the direct filtering method for the processing. We present the result of strapdown gravimetry for two airborne campaigns conducted in Antarctica 2022 and Norway 2023. During both campaigns the sensors used were an iMAR navigation-grade inertial measurement unit together with a geodetic GNSS receiver.

The 2022 campaign covered part of the sea-ice covered Weddell Sea and was surveyed as a piggyback activity as part of the ESA CRYO2ICE and NERC DEFIANT 2022 Antractica campaign. The 2023 airborne campaign was carried out in the coastal region of Norway near Trondheim. In both areas the data were compared to satellite altimetry and other gravity data from ship or airborne surveys. Both campaigns show improvements in spatial resolution and accuracy of the new mGal-level airborne gravimetry data when compared to satellite altimetry and older marine gravity observations.

How to cite: Dale, B., Bjerregaard Simonsen, S., Christian Dahl Omang, O., Enzlberger Jensen, T., and Forsberg, R.: Satellite gravity validation by new airborne gravimetry in coastal regions of Antarctica and Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10299, https://doi.org/10.5194/egusphere-egu24-10299, 2024.

EGU24-11380 | ECS | Orals | G4.3

Gravity inversion of sub-ice shelf bathymetry in West Antarctica using a geostatistical Markov Chain Monte Carlo approach 

Michael Field, Emma MacKie, Lijing Wang, and Atsuhiro Muto

Sub-ice-shelf bathymetry controls the delivery of warm water to the ice-shelf bottom in West Antarctica, making the bathymetry beneath ice shelves in the Amundsen Sea critical inputs to ice-sheet and ocean models. Previous estimates of the bathymetry have often used deterministic inversion frameworks or do not account for the non-uniqueness of the inverse problem, and ultimately lack robust uncertainty quantification. To provide more robust and reproducible bathymetry models, we implement a random walk Metropolis-Hastings Markov Chain Monte Carlo (MCMC) inversion approach, which iteratively generates model perturbations using random Gaussian fields and forward models the gravity disturbance of proposed bathymetry models. After convergence, our approach samples the posterior distribution allowing for estimation of the mean and variance of the bathymetry while providing realistic models of the sub-ice-shelf bathymetry. An ensemble of bathymetry models can then be used in ice-sheet and ocean simulations to propagate the uncertainty in bathymetry to dynamic ice processes, resulting in better uncertainty quantification of future sea-level rise. In addition to providing more robust bathymetry models, this work provides a step forward in the reproducibility of geophysical inversions by leveraging the growing open-access geoscientific computing ecosystem of Python.

How to cite: Field, M., MacKie, E., Wang, L., and Muto, A.: Gravity inversion of sub-ice shelf bathymetry in West Antarctica using a geostatistical Markov Chain Monte Carlo approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11380, https://doi.org/10.5194/egusphere-egu24-11380, 2024.

EGU24-12072 | Posters on site | G4.3

3D joint inversion of regional magnetotelluric, seismic, gravity and magnetic datasets to image lithospheric structure of Ireland 

Dmitry Molodtsov, Duygu Kiyan, and Christopher Bean

Regional gravity and magnetic surveys are essential sources of information about the structure and geodynamics of the lithosphere. However, geologically meaningful inversion of gravity and magnetic data usually requires integration with other geophysical methods. We have developed a 3-D joint inversion framework that has the flexibility of using independent inversion codes and model discretizations for each of the included methods, is easily expandable and supports a wide range of the coupling constraints. Here we show its application to the regional geophysical datasets available in Ireland. We present the results of joint inversion of long-period magnetotelluric data, seismic traveltimes, and land gravity – a multiparameter geophysical model of the crust and uppermost mantle of the whole Ireland. On a smaller scale, we present the results of joint inversion of gravity, airborne magnetic and magnetotelluric data for the Limerick Basin, focusing on imaging of a Carboniferous volcanic structure.  The main aim is to better understand the Pb-Zn mineral systems which are controlled by the tectonics of the basement and lower crust. Exploration-scale geophysical surveys and geothermal exploration will also benefit from the regional 3-D geophysical models.

How to cite: Molodtsov, D., Kiyan, D., and Bean, C.: 3D joint inversion of regional magnetotelluric, seismic, gravity and magnetic datasets to image lithospheric structure of Ireland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12072, https://doi.org/10.5194/egusphere-egu24-12072, 2024.

EGU24-12510 | ECS | Orals | G4.3 | Highlight

Are there thick sediments within South Pole Basin? Investigating the lithology of SPB using COLDEX airborne geophysics  

Megan Kerr, Duncan Young, Weisen Shen, Gregory Ng, Shivangini Singh, Dillon Buhl, Jamin Greenbaum, Shuai Yan, and Donald Blankenship

Because sedimentary basins may exert considerable control over ice sheet dynamics and basal heat flow, it is vital to constrain the extent, thickness, and level of consolidation of sediments throughout the continent and at local scales. Until recently, the South Pole Basin (SPB), situated between the Gamburtsev Subglacial Mountains, the Transantarctic Mountains, and Recovery Subglacial Highlands, has been one of Antarctica's least-explored regions. Previous studies based on seismic and machine learning models, including those by Baranov & Morelli (2023) and Li et al. (2022), have characterized SPB as a sedimentary basin with sediment thicknesses exceeding 1 km. Conversely, a seismic study conducted by Zhou et al. (2022) identifies SPB as a region with little to no sedimentary rock. A lack of dense geophysical data as well as the inherent difficulty of studying geology beneath the Antarctic Ice Sheet introduced a large amount of uncertainty into these assessments. Recent airborne radar, gravity, and magnetics data collected by the Center for Oldest Ice Exploration (COLDEX) has revealed two distinct geomorphological provinces within South Pole Basin: the southern portion of SPB which exhibits relatively smooth, reflective bedrock, while the northern SBP manifests as much rougher terrain. The abrupt boundary between Inner and Outer SPB is associated with the onset of subglacial melting, inferred from a rapid thinning of the basal layer, decreased ice sheet surface slope, and presence of subglacial lake-like features. In addition to surficial differences, these provinces are marked by distinct free-air, Bouguer, and isostatic gravity signatures. A large, arc-shaped magnetic high parallel to Recovery Subglacial Highlands cuts across SBP, facilitating a robust depth to basement analysis and providing constraints for gravity inversions. By integrating COLDEX data with previous airborne surveys and newly collected seismic data, we offer a revised geological interpretation of the South Pole Basin and discuss its tectonic history, potential for groundwater storage, and the preservation of ancient ice in this region.

How to cite: Kerr, M., Young, D., Shen, W., Ng, G., Singh, S., Buhl, D., Greenbaum, J., Yan, S., and Blankenship, D.: Are there thick sediments within South Pole Basin? Investigating the lithology of SPB using COLDEX airborne geophysics , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12510, https://doi.org/10.5194/egusphere-egu24-12510, 2024.

Joint inversion can utilize multiple geophysical datasets to supplement or enhance the information on subsurface structures, improve the resolution and certainty of recovered subsurface structures, and provide broad prospects for various geophysical application scenarios. Model coupling is crucial in joint inversion, and there are two main coupling methods based on structural similarity and petrophysical information. These two coupling methods have their own advantages and disadvantages. The structural similarity-based coupling method can obtain structurally similar models without prior information, but the assumption of structural similarity between models is not always valid. The petrophysics-based coupling method provides finer constraints on physical property values, and its difficulty lies in acquiring petrophysical information, which is usually imprecise and incomplete in the inversion region. Joint inversion using a single model coupling approach is insufficient to face complex joint inversion situations. Combining the two coupling methods can complement the structural similarity of the model in the inversion of incomplete petrophysical information.

We develop a novel joint inversion method based on the extended alternating direction method of multipliers (eADMM), which is compatible with multiple model coupling methods and reduces non-uniqueness and uncertainty more effectively. Multiple model coupling methods are contained in an indicator function, which requires the model to satisfy specific mathematical sets, allowing the various models to satisfy arbitrary relationships and ranges. The inequality constraints and linear and nonlinear relational equations extracted from the petrophysical information are expressed directly in mathematical sets, and the structural similarity coupling is implemented by a constraint set that requires a cross-gradient of zero between models. The solution of the indicator function in the eADMM framework is converted into a projection function, and we develop corresponding projection algorithms for multiple constraint sets of both model coupling strategies. The constraint sets are also spatially flexible. Regions with complete petrophysical information and regions requiring increased structural similarity can be constrained by the corresponding sets, respectively.

We apply the method to gravity and magnetic data to test its performance. We compare the performance of our method with that of the joint inversion using a single coupling method for incomplete petrophysical information, including petrophysical information for partial regions and partial geologic units. Synthetic examples show that regions and geologic units with known petrophysical information are recovered with accurate geometric boundaries and physical property values closer to the true values, and structural similarity coupling provides structural information for unknown regions or geologic units, recovers more accurate geometric structures and reduces model uncertainty. The new joint inversion method provides higher resolution models than the traditional joint inversion method, and the inversion results are closer to the true model.

How to cite: Wang, K. and Yang, D.: joint inversion of gravity and magnetic data with petrophysical and structural coupling constraints using indicator functions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14351, https://doi.org/10.5194/egusphere-egu24-14351, 2024.

EGU24-14771 | ECS | Orals | G4.3

Joint inversion of potential field data to unmask sub-ice geology, from a case study in Scandinavia to application in NE Greenland 

Agnes Dakota Wansing, Jörg Ebbing, Max Moorkamp, and Björn Heincke