Over the past 25 years, satellite observations have revolutionised our understanding of Earth’s magnetic field. The pioneering Ørsted and CHAMP satellite missions marked the beginning of continuous magnetic field monitoring from space, offering invaluable insights into Earth’s interior and its geospace environment. Building on these missions, the Swarm satellite trio, launched in 2013, introduced simultaneous measurements from nearby spacecraft, enabling improved separation of the various magnetic sources.

The field continues to advance with the launch of the first "Macau Science Satellite" (MSS-1) in May 2023, operating in a low-inclination orbit, and the forthcoming NanoMagSat constellation that is currently in preparation. These missions present exciting opportunities to address longstanding scientific questions and explore new frontiers in geomagnetic research.

This talk will highlight the scientific challenges of utilising satellite magnetic data to investigate Earth’s magnetic field, from disentangling overlapping sources to advancing data interpretation techniques. It will also explore the opportunities offered by current and upcoming missions, emphasizing their potential to enhance our understanding of Earth’s interior dynamics, magnetospheric processes, and geospace interactions.

How to cite: Olsen, N.: Exploring Earth's Magnetic Field from Space: Challenges and Opportunities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2598, https://doi.org/10.5194/egusphere-egu25-2598, 2025.

Fault mechanics predicts that fault reactivation and slip occur when the shear stress exceeds the fault strength, potentially nucleating earthquakes. Following Anderson’s legacy, the evolution of tectonic stress over the seismic cycle results in different couplings between normal and shear stress. This coupling depends on (1) the fault’s orientation relative to the maximum principal stress and (2) the tectonic faulting style. Reverse faults, loaded by an increase in maximum principal stress, experience increases in both normal stress and shear stress during the interseismic phase. In contrast, normal faults, loaded by a decrease in minimum principal stress, undergo a reduction in normal stress as shear stress builds up. For instance, low-angle normal faults experience larger increases in normal stress for the same shear stress increment compared to Andersonian 60°-dipping normal faults.

Despite this rich variety of stress field evolution observed in nature, laboratory deformation experiments have predominantly focused on a single stress-field scenario: a reverse fault optimally oriented for reactivation. The choice of reversed faults is dictated by the geometry of the apparatus, and the optimal orientation is the simplest system to generate recurrent lab-quakes. This simple laboratory approach describes faults as planes embedded in elastic media.

Here, I summarize results we have collected in the past years by systematically investigating in the laboratory the role of fault orientation and tectonic faulting style under triaxial saw-cut configuration—broadening the range of scenarios beyond the single one described above. The results reveal the impact of stress field on both fault zone and surrounding host rock deformation.

For fault zones, our results on gouge-bearing faults show clear discrepancies when compared with theoretical reactivation based on Coulomb-Mohr criterion. Faults at higher angles to the maximum principal stress appear weaker, suggesting potential stress field rotation within the fault zone. Additionally, when the normal stress for reactivation is comparable, reverse faulting tends to promote stable creep, while normal faulting—due to greater compaction and stiffness of the fault zone—favors slip acceleration and instabilities.

Fault orientation also affects the stress state of the surrounding host rock over the seismic cycle. Optimally oriented faults behave like ideal spring-slider system: elastic energy accumulates in the host rock during the interseismic phase and is released via on-fault slip during the co-seismic phase, accompanied by precursor acoustic activity. In contrast, unfavorably oriented faults produce a more complex picture. The host rock becomes critically stressed, acoustic activity spreads throughout the host rock, and precursors to lab-quakes become undetectable.

These results highlight the potential of investigating in the laboratory the role of stress field on fault zone deformation and its interplay with the surrounding host rock during earthquake nucleation. By expanding laboratory observations to include a wider range of stress-field scenarios, we take one small step toward bridging the gap between simplified experiments and the complex fault systems observed in nature.

How to cite: Giorgetti, C.: The Role of Stress Field on Fault Reactivation: What We Can Learn from Experimental Rock Deformation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17929, https://doi.org/10.5194/egusphere-egu25-17929, 2025.

This study examines field-aligned currents (FACs) and polar electrojet (PEJ) characteristics during the extreme May 2024 geomagnetic storms across dawn, dusk, daytime, and nighttime in both hemispheres. FAC and PEJ intensities were up to 9 times greater than usual, with equatorward FACs reaching -44º Magnetic Latitude. Maximum FACs and PEJ are larger at dawn than dusk in the Northern Hemisphere but larger at dusk than at dawn in the Southern Hemisphere. Dawn and duskside FACs correlate best with Dst or solar wind dynamic pressure (Pd) in both hemispheres. On the dayside (nightside), most FACs in both hemispheres are primarily correlated with Pd (merging electric field, Em or Pd). The PEJs correlate largely with Dst and partly with Em and Pd. Duskside (nighttime) currents are located at lower latitudes than dawnside (daytime), and northern currents are positioned more poleward than southern currents. The latitudes of peak FACs are most strongly correlated with Dst or Pd in both hemispheres. However, in the northern daytime sector, they are primarily influenced by Em. The latitudes of peak PEJ show the strongest correlation with Dst or Pd in both hemispheres, except on the northern dawnside, where they are primarily influenced by Em. The qualitative relationships between peak current density, corresponding latitude, solar wind parameters, and the Dst index are derived.

How to cite: Wang, H., Lühr, H., and Cheng, Q.: Local Time and Hemispheric Asymmetries of Field-aligned Currents and Polar Electrojet During May 2024 Superstorm Periods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-396, https://doi.org/10.5194/egusphere-egu25-396, 2025.

The collision of the Indian and Eurasian plates ~ 55 Ma formed the Himalaya, one of the youngest mountain belts. This convergence led to two significant metamorphic stages: M1, which occurs under high pressure and low temperature in a thick crust, and M2, resulting from crustal thinning in a high-temperature, low-pressure environment, evolved the gneissic domes. This study provides the first apatite fission track (AFT) and zircon fission track (ZFT) thermochronological record from one of such gneissic domes in the NW Himalaya viz., the Gianbul Dome (GD). The dome is bounded by two extensional shear zones, namely the South Tibetan Detachment System (STDS) dipping towards NE and the Khanjar Shear Zone (KSZ) dipping towards SW.  The AFT cooling ages range from 14.2 ± 1.2 to 5.7 ± 1.1 Ma, and ZFT ages range from 22.8 ± 2.2 to 14.6 ± 0.9 Ma. The ZFT ages remain almost constant across the dome, suggesting thermal relaxation during this period, while the AFT ages are young towards the extensional shear zones of KSZ and STDS. The fission-track data, in combination with the published Ar-Ar and (U-Th)/He cooling ages, has been modeled using a thermo-kinematic inverse and forward model to analyze the processes that led to the exhumation of the dome. Various scenarios like river incision, lithology, deformation along faults like Main Himalayan Thrust, Main Central Thrust, STDS, glacier control, and erosion control over exhumation have been tested. Our results suggest that the extension of normal fault is the primary mechanism for the exhumation of the GD. The extension happened in two phases: (a) during the initial normal sense movement along the STDS when the reverse sense of shear was switched to the usual sense of shear during the early Miocene, and (b) during the Late Miocene. The initial phase of extension is a well-recognized phenomenon in the Himalayan orogen that has been explained through models like channel flow or ductile wedge extrusion. However, the first report of extensional activity along the STDS during the Late Miocene allows us to test whether it is a local phenomenon or a regional event that happened in the brittle stage. Thus, we compiled all the published geochronological and thermochronological data of all the prevailing gneissic domes in the Himalayas from west to east and ran the 3D thermokinematic model to assess the exhumation path of the rocks and brittle stage deformation history. Our results suggest that two phases of extension happened in the entire arc of the Himalayan orogen. The first phase facilitated the southwest migration of ductile materials of rocks from mid-crustal depths accompanying the extension because of gravitation, favoring the channel flow concept. The second phase of extensional collapse happened during ~7-3 Ma ago in the brittle stage. We hypothesize that a drop in gravitational potential energy led to the reactivation of extensional faults along the Himalayan arc. Thus, we propose that extensional collapse in the collisional mountain belts is a cyclic phenomenon that happens to attain a stable, steady state of the orogens.

How to cite: Patel, R. K., Adlakha, V., Mukherjee, K., Pundir, S., Pradhan, P., and Patel, R. C.: Extensional collapse of the Himalayan orogen in the Late Miocene., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1368, https://doi.org/10.5194/egusphere-egu25-1368, 2025.

The Kaliguman Shear Zone (KSZ) in northwestern India marks the boundary between the South Delhi Fold Belt to the west and the Aravalli Fold Belt to the east. Structural analysis reveals a narrow, high-strain zone characterized by the development of mica schist along this boundary. The principal structural orientation trends in the NE-SW direction. Strain analysis indicates that the rocks in this zone formed under transpressional deformation conditions.

The metamorphic history of the KSZ is well-preserved in the mica schists, which predominantly contain garnet and staurolite. Petrological and textural studies have helped establish the relative crystallization sequence of mineral phases during the metamorphic events. Examination of garnet porphyroblasts reveals a complex deformation pattern, reflecting pre-, syn-, and post-tectonic events associated with fabric formation. Geothermobarometric analysis indicates that the mica schists underwent amphibolite facies metamorphism. Phase equilibria analysis, supported by PT pseudosections, shows peak metamorphic conditions at approximately 590±10 °C and 4.7 kbar. Garnet isopleth plots suggest increasing pressure and temperature during metamorphism, which is consistent with the inferred PT path. Variations in the modal abundance of index minerals further corroborate this evolutionary trajectory. These findings support a model of crustal thickening for the KSZ. The textural control monazite age data from the mica schists confirms that the shear zone was formed during the early Neoproterozoic. The study provides valuable insights into the tectonic evolution of the contact between the Delhi and Aravalli Fold Belts, highlighting the role of shear zones in accommodating deformation and facilitating metamorphic processes during Neoproterozoic orogenic events.

Keywords: Kaliguman Shear Zone, Aravalli, Delhi Fold Belt, Neoproterozoic, NW India

How to cite: Mondal, S., Roy, A., and Chatterjee, S.: Neoproterozoic Tectonics of the Kaliguman Shear Zone: Implications for the Delhi-Aravalli Fold Belt Contact, NW India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1504, https://doi.org/10.5194/egusphere-egu25-1504, 2025.

       Bathymetry of marginal sea basins is commonly deeper than the half-space cooling prediction for large oceans, but what controls this pattern is poorly understood. Here, based on abundant seismic sections with increasingly available databases, we perform an enhanced approach that specifically corrects for post-spreading cooling to reassess thermal subsidence across the Southwest Subbasin (SWSB) and the broader South China Sea (SCS) basin. We attribute the current excessive subsidence of the SCS basin primarily as a response to the post-spreading cooling process, which has global applicability to other marginal sea basins and accounts for at least 86% of the observed depth anomaly. Additionally, the mode of magma supply during seafloor spreading plays a crucial role in shaping reconstructed shallower bathymetry of the SCS basin relative to predictions from the half-space cooling model. A stronger magma supply deriving from the regional subduction system can explain the relatively shallow depth developed during the opening of the SCS compared to large oceans. In contrast, a westward decayed magma supply, driven by localized rift propagation induced by the inherited pre-Cenozoic heterogeneous lithospheric structure of South China, attributes to subsidence discrepancies among sub-basins and within the SWSB.

        The sediment-corrected depth of most marginal seas is, on average, more than 500 m deeper than that of large oceans, with maximum anomalies ranging from -0.95 to -2.70 km (in 0.5° bins). The sediment-corrected depths exhibit statistically poor correlations with the spreading rate, indicating that the thermal evolution of marginal seas is not primarily controlled by the spreading rate, unlike large oceans. Neither can this anomaly be fully explained by dynamic topography driven by large-scale mantle convection or by localized variations in the degrees and patterns of subduction systems, although the latter may be an important factor influencing the bathymetry of still-active marginal seas. We interpret at least 44.5% of these anomalies as a result of long-term post-spreading thermal subsidence in inactive marginal seas, with magmatic processes influencing bathymetry during oceanic plate formation. We propose that the post-spreading secular cooling, together with the variable mode of magma supply and potential dynamic subsidence processes driven by subducting slabs, play pivotal roles in the formation of the topographic anomalies within the oceanic basins of marginal seas.

How to cite: Fang, P. and Ding, W.: Reconciling bathymetric anomalies of marginal sea basins through magmatic and cooling processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2072, https://doi.org/10.5194/egusphere-egu25-2072, 2025.

Slip characteristics of tectonic faults are highly correlated with earthquake risks. However, the stress conditions in-situ are not static, because tides and seismic waves produce dynamic stress disturbances. The effect of fluids also needs to be considered. The fault slip evolution considering both, stress perturbation and fluid pressure is poorly investigated in the laboratory.

We performed direct shear tests on saw-cut granite joints using a shear box device with external syringe pump. The lower part of the specimen was driven by constant load point velocity, and static/dynamic normal loads were applied to the upper part. LVDTs recorded horizontal and vertical movements: fault slip and vertical dilatancy, respectively. The impact of two factors are studied in the experiment: pore fluid pressure and applied normal stress oscillation amplitude.

In conclusion, static pore fluid pressure reduces effective normal stress and shear stiffness of the sheared fault. Under constant normal stress, the reduction in fault shear stiffness caused by fluids synchronously competes with the reduction in critical stiffness (K_c) as the effective normal stress decreases. The stick-slip events are most intensive under low fluid pressure and high normal stress. Under oscillating normal stress, as the normal stress oscillation amplitude increases, the overall fault shear strength weakens continuously. Frictional strengthening and aseismic slips always occur in the normal stress loading stage. Normal stress unloading leads to multi-step stick-slip behavior of the sheared fault. The fault normal deformation is controlled by both normal loading/unloading and asperity overriding. Increasing pore pressure and superimposed normal stress magnitudes lead to more dramatic shear stress changes, but the degree of seismic slip is reduced.

How to cite: Tao, K., Konietzky, H., and Dang, W.: Seismic fault slip affected by pore pressure and cyclic normal stress – deduced by lab investigations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2323, https://doi.org/10.5194/egusphere-egu25-2323, 2025.

Surface rupture caused by a strong earthquake is extremely hazardous to the safety of people’s lives. Understanding the rupture evolution mechanism of co-seismic faults and assessing the influence of fault area propagation is essential for disaster prevention and resilience. Since 2000, Hualien and nearby areas in eastern Taiwan have experienced 33  earthquakes, which is a good area to study the evolution of fault rupture. In this study, we propose a dynamic discrete element model to explain fault rupture evolution and use it to analyze the rupture behavior of the 2024 Mw7.4 earthquake of Hualian. This earthquake occurred near the northern Longitudinal Valley Fault (LVF), where crustal movement can be seen from the Milun Fault (MF) to the north part of the LVF. We use ALOS-2 data to identify major faults and the Interferometric Synthetic Aperture Radar (InSAR) method to access the spatial displacement on the surface of the study area. In order to simulate the complex geometry and corresponding deformation of the co-seismic rupture surface under the compound influence of multiple faults, we set a rock biaxial simulation test to obtain effective model parameters. We then established a series of dynamic models with different bond types and strengths based on the discrete element method. The model demonstrates the deformation along the fault rupture surface, corresponding to the observation results. The simulation results cover the rupture behavior of the fault and the displacement of the shallow fault under long time series, which can provide a reference for the subsequent seismic hazard assessment and fault displacement analysis.

How to cite: Guo, X., Aoki, Y., and Li, J.: Discrete element modeling of earthquake-induced fault rupture evolution: The 2024 Mw7.4 Hualien Taiwan earthquake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2827, https://doi.org/10.5194/egusphere-egu25-2827, 2025.

Meteorites that have impacted the Earth's surface in the past have created impact craters. Most of these craters have not been preserved in a form that allows for their contemporary identification, but some, especially in Central and Northern Europe, have been described and classified as geological structures formed by meteorite impacts. When a celestial body strikes the Earth's surface, it causes a temporary increase in temperature to several hundred degrees Celsius, sometimes exceeding the Curie temperature for ferromagnetic rocks and minerals that make up the near-surface layer. Magnetization is relatively stable from a geological time perspective. The magnetic record in magnetite is usually stable and is quite difficult to remagnetize (Fassbinder, 2015).

The impact leads to a change in the direction of magnetization in the minerals, which sometimes persists after the impact. This phenomenon is known as Thermoremanent Magnetization (TRM). It is characteristic of meteorite impact sites. This property is attributed to minerals cooled from high temperatures resulting from plutonic/volcanic processes or meteorite impacts. It is one of several types of remanent magnetization, but only this type will be present in impact structures (Fassbinder, 2015).

The project aims to conduct research in the field of applied geophysics and the magnetic properties of rock and mineral samples in the area of craters formed by meteorite impacts in the context of thermomagnetic anomalies.

As part of this project, proton magnetometer measurements have been conducted in the areas of the Morasko craters in Poland, the Dobele crater in Latvia, the Vepriai crater in Lithuania, and several craters in Estonia. Samples from the Estonian craters have been collected for paleomagnetic studies, which will soon be analyzed using a rotational magnetometer and a magnetic susceptibility instrument. The results of the magnetometric measurements are very promising and exhibit characteristic patterns of magnetic field anomalies typical of impact craters.

The project is funded under the 'Pearls of Science' program by the Ministry of Science and Higher Education of the Republic of Poland.

How to cite: Zawadzki, M., Godlewska, N., and Oryński, S.: Measurements of Earth's magnetic field anomalies caused by meteorite impacts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2898, https://doi.org/10.5194/egusphere-egu25-2898, 2025.

The Chatree Region, located in central Thailand, holds significant potential for gold exploration, hosting substantial mineral resources. The complex geological setting of this region, with its diverse lithologies and intricate structural controls, poses both significant opportunities and challenges for successful mineral exploration. Given these challenges, this study utilizes a geophysical approach focusing on magnetic data interpretation to enhance the precision and efficiency of identifying potential gold prospects.

Enhancements to the magnetic data were achieved through the application of Downward Continuation (DWC) and Automatic Gain Correction (AGC), which amplified near-surface features and improved signal clarity. Subsequently, by employing the Centre for Exploration Targeting (CET) Grid Analysis, zones of structural complexity, indicative of epithermal gold deposits were detected, which generated two heat maps, including Contact Occurrence Density (COD) and Orientation Entropy (OE). These maps revealed six major and seven minor potential gold prospect zones, providing a critical dataset for subsequent geological analysis. Geological correlations and lineament interpretation were then conducted to validate and refine the magnetic interpretations by integrating several filtered magnetic images with existing geological knowledge of the region. The results of this integrated approach show that many of the identified magnetic anomalies and lineaments correlate with known geology, highlighting the critical role of synthesizing advanced magnetic data analysis with geological expertise. This integration provides a valuable foundation for future exploration in the region and establishes an applicable methodological approach to other mineral exploration efforts.

How to cite: Pinkaew, K.: Identifying Prospective Areas for the Chatree Epithermal Gold Region from Airborne Magnetic Data Using Advanced Analyzing Techniques, with Interpretative Correlation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3794, https://doi.org/10.5194/egusphere-egu25-3794, 2025.

The differences in the tectonic interpretation of ophiolite suites have become a major issue of the debate in the tectonic reconstruction of an ancient orogenic belt, especially when it comes to subduction polarity. In this regard, the Sanjiang Paleo-Tethyan Orogenic Belt in the southeastern Tibetan Plateau provides an excellent case study. The Sanjiang Paleo-Tethyan Orogenic Belt in the northern, eastern, and southeastern Tibet is bounded by the western Jinshajiang‒Garzê‒Litang suture to the north and the Shuanghu‒Changning‒Menglian suture to the south and west. The southern Jinshajiang Suture separates the Zhongzha Block to the east and the eastern Qiangtang Block to the west. The tectonic nature of the NNW-trending southern Jinshajiang ophiolitic mélange remaining controversial. A detailed linear traverse mapping was c across the southern Jinshajiang ophiolitic mélange, with a focus on pillow lavas and the structural relationship between the lavas and their country rock (Paleozoic sedimentary rocks). The results of a field study, in conjunction with new geochronological data and geochemical data, have enabled the identification of the Zhongdian continental back-arc basin. This basin was filled with a flysch succession and at least two horizons of pillow basalt from 267 to 254 Ma. The fining- and thinning-upward nature of the sedimentary succession, widespread syndepositional folds and syndepositional breccias, and submarine channel sediments, as well as intensive basaltic volcanism suggest that this back-arc basin generated in a typical extensional environment. The inversion of the back-arc basin was completed within a relatively short period of one million years (254~253 Ma), resulting in the development of overturned folds of the flysch succession and a latest Permian to Early Triassic back-arc foreland basin in front of the folded belt. Whole-rock geochemical data for the basalts and coeval gabbros suggest that the petrogenetic process of the basalts in the back-arc basin is likely comparable to that of basalt in a rift system as well, which is a lithospheric extension induced uplift of lithospheric mantle and asthenosphere and allowing decompression partial melting of the mantle peridotite. The late stage pillow basalts exhibit a stronger arc signature than the earlier massive basalt and diabase. The Zhongdian back-arc basin is considered to be an extinct continental and arc-type back-arc basins, which are characterized by thick crust, shallow bathymetry, and may not evolve into “normal” oceans. The formation and inversion of the Zhongdian back-arc basin are believed to have been caused by rollback and subsequent break-off of the subducted oceanic slab. During the inversion, the crust shortening occurred predominantly in the back-arc basin, while the southwestern shoulder of the back-arc basin, which was weakly deformed, was shifted north-eastward for ~30 km. The formation process of the Zhongdian back-arc basin is comparable to that of a typical continental rift system, the asymmetric architecture of which has mostly been inherited by the structures formed during the basin inversion. The southern Jinshajiang ophiolitic mélange is representative of the inverted Zhongdian back-arc basin, which is a short-lived, partially mature oceanic basin.

How to cite: Xin, D., Yang, T., Xue, C., Jiang, L., and Xiang, K.: Formation and inversion of a short-lived continental back-arc basin in Southeastern Tibet, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3894, https://doi.org/10.5194/egusphere-egu25-3894, 2025.

The development of continental rift basins is often accompanied by multiple episodes of volcanic activity. The impact of these volcanic eruptions on the sedimentary filling process of the basin is a geological problem worth considering. This relationship is not only the premise for reasonably explaining the binary filling characteristics and development of sequences of volcanic rocks and sedimentary rocks in rift basins but also the key geological basis for the prediction of volcanic and sedimentary rock reservoirs in rift basins. On the basis of a large amount of three-dimensional seismic data, logging data and lithology data, we estimated the volcanic eruption period, volcanic rock mass and spatial shape of the Changling faulted depression in the Songliao Basin. We then studied the spatial distribution characteristics of lithofacies and sedimentary facies in the basin. Finally, we assessed the influence of volcanic eruptions on the type of sedimentary filling, the distribution of sedimentary facies and the spatial stacking of sedimentary strata. This study revealed that during the rapid rifting stage (Yingcheng Formation depositional period), the Changling faulted depression developed mainly fan delta, braided river delta and lacustrine sedimentary systems and experienced four phases of volcanic eruptions. The lithology, scale and spatial distribution of volcanoes were directly related to the activity and location of the basement faults in this area, reflecting the control that basement fault activity had on the volcanic eruptions. Moreover, the stacking form and eruption scale of volcanic rocks played a substantial role in the paleogeomorphology of the basin, which in turn affected the form of the source channel of the basin, causing changes in the sedimentary facies type and spatial distribution and changes in the spatial overlapping pattern of the sedimentary sequence. Moreover, volcanic eruptions provided different sources of debris to the continental lake basin. The differences in location and delivery methods of these materials complicate the rock structure and reservoir properties of the basin sandstone.

How to cite: Wang, H., Zhang, H., and Liu, A.: Influence of volcanic eruptions on the sedimentary filling of a continental rift basin — A case study of the Yingcheng Formation in the Changling faulted depression in the Songliao Basin, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4049, https://doi.org/10.5194/egusphere-egu25-4049, 2025.

Electrical image logs can intuitively reflect the development status and characteristics of dissolution pores, which is of significant importance for the development of oil and gas resources. However, traditional methods for identifying pores in electrical image logs are not only cumbersome and labor-intensive but also incapable of distinguishing between different types of pores. Moreover, the strong heterogeneity and dissolution effects in carbonate reservoirs result in significant variations in pore size and complex, diverse pore morphologies, making it difficult to extract pore parameters. To address these issues and challenges, this paper proposes a semantic segmentation model, FILnet, designed using computer vision technology and deep learning frameworks. This model aims to achieve intelligent recognition and segmentation annotation of pores of different scales in the wellbore region of electrical image logs. The data selection process involved using a sliding window to choose electrical log images containing dissolution pores and caves. Image processing techniques were then applied to complete and augment the images, thereby enhancing data diversity. Furthermore, a dual-attribute dataset was created using dynamic and static images from electrical image logs to assist the model in learning the semantic features of pores. Finally, the proposed model was compared with traditional pore identification methods, such as threshold segmentation. The results showed that FILnet demonstrated significant performance advantages on the dual dataset, with a mean intersection over union (MIoU) of 85.42% and a pixel accuracy (PA) of 90.54%. Compared to traditional pore identification methods, the deep learning semantic segmentation approach not only achieves recognition of different types of pores but also improves identification accuracy. This indicates that the network model and data processing methods proposed in this paper are effective and can achieve intelligent recognition and accurate segmentation of pores in electrical image logs.

How to cite: Zhuolin, L., Guoyin, Z., and Yifan, G.: Intelligent Pore Recognition Method for Carbonate Rock Electrical Image Logs Based on Deep Learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4896, https://doi.org/10.5194/egusphere-egu25-4896, 2025.

In northwest India, the South Delhi Fold Belt (SDFB) is a NE-SW trending region of the Neoproterozoic age, consisting of poly-deformed and poly-metamorphosed rocks. To the west lies the Marwar Craton, and the boundary between them is defined by a crustal-scale shear zone, dated to 810 Ma, known as the Phulad Shear Zone (PSZ). The syn-tectonic Phulad Granite, which runs along the PSZ, played a key role in stitching together the Marwar Craton and the SDFB during the 810 Ma tectonic event. Approximately 30 km to the east of the PSZ, a quartz monzonite pluton, emplaced within the calc-silicates of the SDFB, is observed. This study focuses on the meso- and micro-structures, as well as the geochemistry of the quartz monzonite, to better understand its emplacement conditions and the tectonic processes at that time.

In the field, the quartz monzonite exhibits a saccharoidal texture with a crude foliation, defined by the alignment of feldspar grains. The foliation in the monzonite has a mean orientation of 14°/67° E. The quartz monzonite is primarily composed of k-feldspar and plagioclase feldspar, with minor amounts of quartz, amphibole, and titanite. Microstructural analysis reveals features indicative of sub-magmatic, high-temperature deformation, suggesting that the rock underwent solid-state deformation. These microstructural characteristics of the quartz monzonite suggest a syn-magmatic deformation event. The foliation in the monzonite is broadly parallel to the mylonitic foliation in PSZ, further supporting the idea of a syn-tectonic emplacement. The geochemical study of the quartz monzonite displays a syn-collisional granite-type geochemical signature with a distinctly negative REE pattern. The REE pattern features suggest that garnet played a significant role in the petrogenesis. By integrating micro and meso-structural analyses with geochemical data, we infer that the emplacement of the quartz monzonite coincided with the development of the PSZ and the intrusion of the Phulad Granite. Despite the temporal overlap, the quartz monzonite and the Phulad Granite display significant geochemical differences, denoting distinct petrogenetic processes. Based on the integration of all available data, we propose that the quartz monzonite was emplaced during the 810 Ma collisional event, resulting from the partial melting of garnet-bearing mafic crust. While both quartz monzonite and Phulad Granite likely share a common source, the depth of melting was different. The greater depth of melting in the eastern portion suggests an eastward subduction of the Marwar Craton during this tectonic event.

How to cite: Ghosh, D. D. and Chatterjee, S. M.: Neoproterozoic magmatism in NW India and its implication for crustal evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5552, https://doi.org/10.5194/egusphere-egu25-5552, 2025.

In highly populated urban areas such as Tehran, with over 17 million inhabitants, identifying active faults is essential to hazard and risk management. Tehran is located in central Alborz within the Arabia-Eurasia collision zone. The region is the manifestation of interplay between structural systems of the western and eastern Alborz. The study area focuses on the Lavizan and Babaei fault-related fold structures as the main Quaternary features of the Tehran piedmont. Tehran's rapid urbanization in the past few decades has made it impossible to access fault traces and the associated geomorphic features in the field. This research is the first study which uses photogrammetric methods to extract detailed 3D data and digital terrain model (DTM) from archival imaging. Historical aerial photographs were acquired from 1955-1965, before the city's development. A DTM with a spatial resolution of about 86 centimeters, an orthophoto-mosaic, and a three-dimensional model were created employing photogrammetric methods. The geomorphic analysis of the model reveals lateral unidirectional eastwards growth of the Lavizan and Babaei structures during Pleistocene and Holocene. The presence of wind gaps developed from water gaps, and sharp fault scarps in the upper Pleistocene and Holocene geomorphic surfaces testify this lateral propagation. This study presents a typical example for a long-lasting tectonic activity and its Holocene continuation on the E-W fault-related fold structures, which directly affect urban areas in the Iranian metropolitan.

How to cite: Alizadeh, P., Shabanian, E., and Masoumi, Z.: Investigation of the Growth of Active Faults in the Tehran Metropolitan Employing Historical Aerial Photos and Photogrammetric Techniques, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6123, https://doi.org/10.5194/egusphere-egu25-6123, 2025.

In November 2023, the ESA Swarm constellation mission celebrated 10 years in orbit, offering one of the best-ever surveys of the topside ionosphere. Among its achievements, it has been recently demonstrated that Swarm data can be used to derive space-based geomagnetic activity indices, like the standard ground-based geomagnetic indices, monitoring magnetic storm and magnetospheric substorm activity. Given the fact that the official ground-based index for the substorm activity (i.e., the Auroral Electrojet – AE index) is constructed by data from 12 ground stations, solely in the northern hemisphere, it can be said that this index is predominantly northern, while the Swarm-derived AE index may be more representative of a global state, since it is based on measurements from both hemispheres. Recently, many novel concepts originated in time series analysis based on information theory have been developed, partly motivated by specific research questions linked to various domains of geosciences, including space physics. Here, we apply information theory approaches (i.e., Hurst exponent and a variety of entropy measures) to analyze the Swarm-derived magnetic indices around intense magnetic storms. We show the applicability of information theory to study the dynamical complexity of the upper atmosphere, through highlighting the temporal transition from the quiet-time to the storm-time magnetosphere around the May 2024 superstorm, which may prove significant for space weather studies. Our results suggest that the spaceborne indices have the capacity to capture the same dynamics and behaviors, with regards to their informational content, as the traditionally used ground-based ones. A few studies have addressed the question of whether the auroras are symmetric between the northern and southern hemispheres. Therefore, the possibility to have different Swarm-derived AE indices for the northern and southern hemispheres respectively, may provide, under appropriate time series analysis techniques based on information theoretic approaches, an opportunity to further confirm the recent findings on interhemispheric asymmetry. Here, we also provide evidence for interhemispheric energy asymmetry based on the analyses of Swarm-derived auroral indices AE North and AE South.

How to cite: Papadimitriou, C., Balasis, G., Boutsi, Z., and Giannakis, O.: Dynamical Complexity in Swarm-derived Storm and Substorm Indices Using Information Theory: Implications for Interhemispheric Asymmetry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6137, https://doi.org/10.5194/egusphere-egu25-6137, 2025.

We present high-resolution ocean bottom node (OBN) seismic data of the Dongfang 1-1 structure in the Yinggehai Basin of the South China Sea, which hosts China's largest offshore gas reservoir. The OBN seismic data reveals more continuous and detailed reflections compared to conventional seismic data, highlighting the internal structure and formation mechanism of a diapir-like structure. The seismic images show a tapered conical structure characterized by a concentric distribution of fractures, with a significant increase in fracture intensity and connectivity towards the center. These fractures, particularly the sub-vertical ones, are interpreted as natural hydraulic fractures formed due to intense overpressurization in the Lower Miocene strata, with formation pressure coefficients up to 2.2. The fractures are believed to have originated from thermogenic hydrocarbon gas generation and inorganic CO₂ production. The throughgoing fractures that traverse the entire Neogene succession, including the thick Upper Miocene sealing mudrocks, provide crucial pathways for deep gas-bearing fluids to charge the Pliocene sandstone reservoir. The study underscores the importance of natural hydraulic fractures in bypassing thick sealing sequences and conduiting fluids in deep overpressured environments. Moreover, our results may provide guidance for accurate geological interpretations of mud diapir-like structures in conventional seismic images in many other sedimentary basins.

How to cite: Meng, Q., Yang, B., Guo, Z., and Hao, F.: Architecture of a mud diapir-like structure: insights from ocean-bottom-node seismic data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6417, https://doi.org/10.5194/egusphere-egu25-6417, 2025.

This study explores the application of Fracture-Induced Electromagnetic Radiation (FEMR) for stress analysis in the Ramon Crater, a tectonically “stable” region in southern Israel. FEMR, an innovative geophysical method, detects electromagnetic pulses emitted during micro-fracturing events to infer stress orientations. Unlike traditional seismic techniques, FEMR is sensitive to subtle stress changes, making it suitable for regions with limited seismicity. Field measurements were conducted at nine locations using the ANGEL-M device, capturing high-sensitivity electromagnetic signals to determine the stress azimuth. The results revealed a dominant mean stress azimuth of 308°, aligning closely with the acute bisector of two principal joint sets in the region, WNW-ESE and NNW-SSE. These orientations correspond to historical compressional stress from the Syrian Arc Stress (SAS) regime and more recent extensional stress from the Dead Sea Stress (DSS) field. The superimposition of these regimes has created a complex tectonic environment, evidenced by features such as joint sets, fault planes, and basaltic dikes. FEMR measurements correlate with these geological indicators, confirming the technique’s ability to detect regional stress directions and their evolution over time. In the past decade, the method of FEMR has progressively gained impetus as a viable, non-invasive, cost-effective, real-time geophysical tool for stress analysis in various parts of the world. Its range lies in delineating tectonically active zones, landslide-prone weak slip planes, highlighting stress accumulation in mines and tunnels, etc. This study highlights FEMR’s viability for stress field analysis, especially in stable tectonic zones. Its ability to capture micro-crack activity and subtle stress shifts offers a detailed understanding of how tectonic forces shape regional geodynamics. While FEMR enhances stress detection capabilities, careful calibration with geological models is essential to differentiate transient stress changes from long-term tectonic trends. This research advances FEMR’s application in geophysical studies, particularly for monitoring stress fields in regions influenced by ancient and ongoing tectonic forces.

How to cite: Das, S. and Frid, V.: The Fracture Induced Electromagnetic Radiation (FEMR) technique as a tool for stress mapping: A case study of the Ramon Crater, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9651, https://doi.org/10.5194/egusphere-egu25-9651, 2025.

The slip behavior of the Altyn Tagh Fault (ATF) plays a key role in improving our understanding of the tectonic deformation processes shaping the Tibetan Plateau. In this investigation, a three-dimensional (3D) model representing the central segment of the ATF was constructed using discrete element numerical simulations to examine the main damage zones and stress distribution in the Akato Tagh Bend, AKsay Bend, and Xorkoli segments. The simulation results were then cross-referenced with fault orientation measurements from the northern Qaidam Basin and focal mechanism solutions (FMS) to assess their precision and reliability. The results indicate that the stress environment is stable in the linear strike-slip Xorkoli segment, whereas the stress distribution in the Akato Tagh Bend and AKsay Bend segments exhibits significant heterogeneity, with alternating regions of high and low stress. On the concave side of these bends, compressive stress accumulates, fostering the formation of local thrust faults or folds along the fault plane. Conversely, on the convex side, tensile stress dominates, promoting the development of normal faults or extensional fractures. In the restraining bend region, tensile stress remains horizontal, though its orientation shifts considerably as fault displacement increases. The bend segments also show significant variations in shear stress, which can lead to the creation of secondary fault features like Riedel shears. The intensity and distribution of shear stress are influenced by the curvature and bending angle of the fault, with larger bending angles in the Akato Tagh Bend producing more pronounced shear stress concentrations. Fractures are primarily concentrated at the fault tips, along fault intersections, and within the fault plane, with the fault damage zone being notably wider in the Akato Tagh Bend and AKsay Bend segments. As fault displacement increases, the width of the damage zone and fracture density initially increase rapidly before reaching a plateau. Moreover, the primary damage zone develops earlier in the restraining Akato Tagh Bend and AKsay Bend segments compared to the linear strike-slip Xorkoli segment, which absorbs more strain before the principal displacement zone forms. Therefore, the Akato Tagh Bend exhibits the highest fracture intensity, followed by the AKsay Bend and Xorkoli segment. These findings offer significant insights into the slip behavior and stress distribution along the ATF and enhance our understanding of the tectonic processes in the Tibetan Plateau.

How to cite: Chen, Z., Li, J., and Liu, G.: Stress Distribution and Fracture Development Along the Altyn Tagh Fault:Insights from 3D Discrete Element Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9784, https://doi.org/10.5194/egusphere-egu25-9784, 2025.

Monazite has the potential to place temporal constraints on the crustal melting in high-grade metamorphic rocks like granulites and migmatites. Melt loss in granulite-grade metamorphic rocks plays a key role in progressively depleting LREE in the residue and enhancing the dissolution of monazite during heating to the metamorphic peak. Newly formed monazite are therefore more abundant in leucosomes than the residue. Higher degree of partial melting and subsequent melt loss, therefore, poses a major hindrance to constraining the mobility of these elements in the micro-domain scale, particularly during the early stage of melting at amphibolite to granulite facies transition. To overcome such an issue and to understand the behavior of this mineral during the onset of granulite facies metamorphism, metamorphic rocks that have reached the P-T conditions culminating at the aforesaid transition should be targeted. Considering this, the present study has been carried out on charnockite from the northern Eastern Ghats Belt, India which underwent such transition (M₂) following crystallization during an earlier granulite facies metamorphic event (M₁). The rock is composed of plagioclase (Pl), K-feldspar (Kfs), quartz, orthopyroxene, biotite, and garnet with apatite, allanite, and monazite as accessory phases. The rock has well-developed gneissic foliation, demarcated by alternate biotite +garnet-rich and quartzofeldspathic layers. While both the feldspars show grain boundary migration recrystallization, quartz grains are deformed by sub-grain rotation recrystallization. Garnet is porphyroblastic and post-kinematic as it overgrows the matrix biotite. The former phase is closely associated with cuspate Kfs and quartz grains which developed as a result of incipient dehydration melting of moderately fluorine rich biotite during the aforesaid transition. Monazite grains are coarse (up to 200 µm across), mostly elliptical and either partially or completely replaced by the reaction rim of apatite+ thorite with an external corona of allanite in the biotite+garnet-rich layers. In case of partial replacement, the oscillatory-zoned relict monazite core is preserved. Th-rich patches are present in such cores. Interestingly, the coronitic assemblage overgrows the matrix biotite is always associated with porphyroblastic garnet. On the contrary, corona-free monazite grains are abundant in quartzofeldspathic layers. Spot dates from the oscillatory-zoned relict monazite core yield a weighted mean age of 960±6 Ma. Th-rich patches, showing prominent huttonite substitution, yield a weighted mean age of 938±7 Ma. Integrating monazite textural and age data, we interpret that the ca. 960 Ma represents the crystallization age of the charnockite magma which coincides with the M₁ metamorphic event of the Eastern Ghats Province (EGP). The ca. 938 Ma, additionally, corresponds to the age of the M₂ event when biotite dehydration melting occurred and porphyroblastic garnet was formed. Based on the textural evidence and mineral phase chemical data, we propose that the replacement of primary monazite occurred via coupled dissolution precipitation process in the presence of incipient melt originated during biotite dehydration melting. Such melt was fluorine rich and helped to mobilize REEs by forming REE-fluoride complexes and was incorporated in allanite corona. Monazite grains in quartzofeldspathic layers must have escaped the melting reaction and the melt-induced element mobility.   

How to cite: Ganguly, P., Banerjee, A., and Das, K.: Behavior of monazite during incipient dehydration melting of charnockite at the northern Eastern Ghats Belt, India: Insights on the mobility of REE at amphibolite-granulite facies transition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11645, https://doi.org/10.5194/egusphere-egu25-11645, 2025.

Predicting earthquakes remains one of the most profound challenges in seismology and a long-standing aspiration for humanity. Among the array of potential precursors, changes in the Earth’s magnetic field have emerged as a promising yet contentious avenue of research (e.g., De Santis et al., 2015). With advancements in satellite technology, especially with the advent of the European Space Agency’s Swarm mission, we now have the unprecedented ability to measure the magnetic field with extraordinary precision, unlocking exciting opportunities for earthquake forecasting.

In this study, we leverage data from Swarm satellites to investigate whether magnetic anomalies can serve as reliable precursors to earthquakes. Our approach integrates two complementary methodologies: a) global statistical analysis: We applied superposed epoch and spatial techniques to several years of global earthquake data, correlating it with Swarm's magnetic field measurements (De Santis et al., 2019; Marchetti et al., 2022); b) tectonic case study: We focused on major earthquakes occurring from 2014 to 2023 within the tectonically active Alpine-Himalayan belt (Alimoradi et al., 2024).

To analyze these events, we employed an advanced automated algorithm (De Santis et al., 2017) to detect magnetic anomalies in satellite data recorded up to 90 days prior to global earthquakes and up to 10 days before events in the Alpine-Himalayan region. The findings revealed compelling evidence of clear magnetic anomalies preceding earthquakes. Notably, in the Alpine-Himalayan case study, we observed a striking correlation between earthquake magnitude and the duration and intensity of these anomalies: larger earthquakes were associated with stronger and more prolonged signals.

Our predictive framework demonstrated remarkable performance, achieving an accuracy of 79%, a precision of 88%, and a hit rate of 84%. These results underscore the transformative potential of satellite-based magnetic field analysis, paving the way for an operational earthquake prediction system. Such a system could serve as a powerful tool for mitigating the devastating impacts of earthquakes and safeguarding communities worldwide.

The work has been developed in the framework of the following projects: UNITARY- Pianeta Dinamico (funds from MUR), SPACE IT UP (PNRR), Limadou Scienza + (ASI) and FURTHER (INGV).

References

Alimoradi, H., Rahimi, H., De Santis, A. Successful Tests on Detecting Pre-Earthquake Magnetic Field Signals from Space, Remote Sensing, 16(16), 2985, 2024.

De Santis et al., Geospace perturbations induced by the Earth: the state of the art and future trends, Phys. & Chem. Earth, 85-86, 17-33, 2015.

De Santis A. et al., Potential earthquake precursory pattern from space: the 2015 Nepal event as seen by magnetic Swarm satellites, Earth and Planetary Science Letters, 461, 119-126, 2017.

De Santis A. et al. Precursory worldwide signatures of earthquake occurrences on Swarm satellite data, Scientific Reports, 9:20287, 2019.

Marchetti D., De Santis A., Campuzano S.A., et al. Worldwide Statistical Correlation of eight years of Swarm satellite data with M5.5+ earthquakes, Remote Sensing, 14 (11), 2649, 2022.

How to cite: De Santis, A., Campuzano, S. A., Cianchini, G., Alimoradi, H., Perrone, L., and Rahimi, H.: Harnessing Swarm Satellite Magnetic Data to Revolutionize Earthquake Prediction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11991, https://doi.org/10.5194/egusphere-egu25-11991, 2025.

The Precambrian history of the Indian continent centers around several Archean cratonic nuclei, e.g. the Singhbhum Craton, the Bundelkhand Craton and the Aravalli Craton in the north; the Bastar Craton in the central-east, and the Dharwad Craton in the south. Apart from a group of less disturbed and unmetamorphosed Meso- to Neoproterozoic platformal sedimentary packages resting over deformed and metamorphosed Archean to Paleoproterozoic basement, several Neoproterozoic orogenic belts occur at the margins of these Archean cratonic blocks. These craton-margin orogenic belts are the areas of intense deformation and multiple phases of deep- to intermediate depth, and hence constitute the sites of major records of crustal-scale material recycling through plate movements. They occur on the east, south and west of the Archean cratonic clusters (conjugate north and south Indian cratonic blocks). Though major deep-crustal deformation and metamorphism in these craton-margin orogenic belts can be tracked mostly up to the earliest Neoproterozoic, exhumation-related reactivation seems to be more common in these belt around ca. 800–750 Ma. 

In this study, we shall highlight the east and west Indian marginal belts. We shall present the new data showing conditions of metamorphic pulses and their age from the rocks of the Mercara Shear Zone, marking the south-western boundary of the Archean (>3000 Ma) Dharwar craton. The results indicate at least four events; (1) ~2900 Ma; basin formation with supply from craton, (2) 2900–2700 Ma; age of prograde metamorphism, (3) 2700–2500 Ma, age of charnockite magmatism during Dharwar Orogeny with metamorphic peak, and (4) final reactivation at 830–730 Ma marking exhumation of deep crust during retrograde metamorphism along the crustal scale shear zone (stretching lineation and S-C fabric formation as last deformation event. We shall also review our group’s recent published data on the pressure-temperature-deformation-fluid-age histories during the orogenic reactivation of the western boundary, and the Chilka Domain of the northern Eastern Ghats Belt. Together we shall try to collate data showing the idea of a near-synchronous orogenic reactivation surrounding Indian cratonic cluster during middle to late Tonian Period with various preceding age gaps.

How to cite: Das, K., Bose, S., Ganguly, P., and Chatterjee, A.: Circum-Indian craton-margin orogenic reactivation during ca. 800-700 Ma: Tectonometamorphic characterization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14725, https://doi.org/10.5194/egusphere-egu25-14725, 2025.

Efficient handling of climate change issues in order to mitigate its negative impact of the flora and fauna of the earth, or on the pace of industrialization, is a big challenge in every disposition around the world.  Amongst the many options available, geological storage of CO₂ in the basalt formations is proving to be a promising one due to its large and pervasive occurrence, to facilitate stable carbonation of the sequestered CO₂, and with ready access to the basalt deposits for operational requirements. Laboratory testing and a few field   implementations showed that carbon dioxide injected in basalts would form stable carbonate minerals, keeping the substance in place for thousands of years.

This work applies the machine learning applications aimed at the classification of different facies in basalts, particularly flow tops and flow interiors, towards the selection of a sequestration site based on their relevant petrophysical characteristics.

After the facies were identified, several rock physics models were run with an outlook of predicting the elastic properties of basalt. Based on our results, we found the Differential Effective Medium (DEM) model enables the most accurate prediction with the least error as compared to Self-Consistent Approximation and Kuster-Toksӧz model. This finding provides a foundation for using the DEM model to create an initial reservoir matrix, which can be applied to simulate geomechanical changes upon CO₂ injection in Basalt. Additionally, facies classification aids in delineating zone boundaries within basalt flows, allowing for the selection of optimal injection sites based on their petrophysical properties.

How to cite: Nagarkoti, N., Kumar, T., Panwar, N., and Sharma, R.: Determination of Lithofacies and Elastic Behavior Modeling in Columbian River Basalt Group (CRBG) Formations , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17658, https://doi.org/10.5194/egusphere-egu25-17658, 2025.

The South Delhi Fold Belt (SDFB) within the northwestern Indian Shield is a Proterozoic NE-SW trending fold belt. The western boundary of the SDFB is defined by the Phulad Shear Zone, formed during a transpression regime around 820-810Ma. Granite rocks of ~1Ga have been documented from the western part of the fold belt and are linked with the formation of the Rodinia Supercontinent. These granites are closely associated with gabbroic rocks. The present study focuses on the geochemistry of these granites and the mafic rocks, as well as their field structure and petrography. 
The granites and the mafic rocks are confined to a narrow linear belt along the western part of the fold belt. Detailed field studiesreveal that the foliations in the granites, mafic and mylonites within PSZ share a common stress regime and are broadly synchronous. Geochemically these granites are ferroan, calc-alkalic, metaluminous to weakly peraluminous and their classification in granite discrimination diagrams confirms A-type and within plate granite. The mafic rocks exhibit a compositional range fromtholeiitic to calc-alkaline, with atrace element ratio resembling enriched mid-oceanic ridge basalt (E-MORB) type magma. The tectonic discrimination diagram suggestsrift-relatedmagmatism. Geochemical analysis of these bimodal magmatic compositions in the SDFB, encompassing both mafic rocks and A-type granites are typically associated with areas experiencing extensional tectonics, particularly rift-related magmatism. Integrating field structures, petrography and geochemistry of these granite and the mafic rocks suggests that the ~1Ga granite and the associated mafic rocks formed in an extensional regime and are not directly linked to the collisional assembly of the Rodinia Supercontinent.

How to cite: Manna, A., Chatterjee, S. M., Roy, A., and Sarkar, A. K.: Geochemistry of ~1Ga granite and associated mafic rocks from the South Delhi Fold Belt, NW India, and its tectonic significance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19572, https://doi.org/10.5194/egusphere-egu25-19572, 2025.

The Central High Atlas in Morocco is characterized by complex geological structures shaped by tectonic and magmatic processes. Gravimetry, a geophysical technique sensitive to subsurface density variations, plays a crucial role in exploring and understanding these features. This study provides a bibliometric analysis of global research on the application of gravimetry, with a specific focus on its use in the Central High Atlas.

The main objectives of this study are to identify global research trends and applications of gravimetry in the study of geological structures, analyze key contributors, scientific collaborations, and dominant themes in gravimetric research, and compare findings from studies conducted in the Central High Atlas with those from other regions worldwide.

A bibliometric analysis was conducted using data from Scopus and Web of Science databases. Keywords such as "gravimetry," "Central High Atlas," and "geological structure" were employed to extract relevant studies. The analysis utilized the R-bibliometrix package and VOSviewer software to map collaboration networks, visualize thematic clusters, and analyze global research trends over time.

The results reveal a significant increase in gravimetric studies over the last two decades, reflecting growing interest in its applications in mountainous regions like the Central High Atlas. The findings highlight deep-seated geological structures, active fault systems, and the relationship between gravimetric anomalies and tectonic processes. Moreover, a comparative analysis shows that studies in Morocco focus heavily on tectonic and magmatic processes, while research in other countries often emphasizes technological advancements and methodological innovations.

This bibliometric study underscores the importance of gravimetry as a tool for exploring complex geological structures in the Central High Atlas. It also highlights the need for stronger international collaborations and interdisciplinary research to advance gravimetric methodologies and foster knowledge exchange across regions.

How to cite: Assoussi, S., Hahou, Y., Khalifa, M., Saadaoui, F., and Oujane, B.: Gravimetric Investigation and Analysis of Tectonic Features and Mineralization Zones in the Central High Atlas (Morocco)., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20105, https://doi.org/10.5194/egusphere-egu25-20105, 2025.

This study evaluates the contributions of geophysics and remote sensing to structural mapping in the Central High Atlas region of Morocco. A bibliometric analysis was conducted using data collected from databases such as Scopus and Web of Science. Keywords related to geophysics, aeromagnetic, remote sensing, structural mapping, and the Central High Atlas were used to systematically identify relevant research articles. Analytical techniques, including citation analysis, co-authorship analysis, keyword analysis, and network analysis (using VOSviewer), were applied to explore research trends, collaborations, and key focus areas.

The findings highlight notable research trends in the application of geophysics and remote sensing, identifying key contributors, influential institutions, and pivotal publications in this domain. Research gaps and opportunities for further investigation were also uncovered. Visualization of research networks provided insights into collaboration patterns and thematic focus areas.

This study underscores the importance of geophysics and remote sensing in enhancing the understanding of the Central High Atlas's structural geology. It offers a foundation for future research, emphasizing the need for interdisciplinary collaboration and advanced methodologies to address existing research gaps and further explore the region's geological complexities.

How to cite: Saadaoui, F., Hahou, Y., Ousaid, L., Assoussi, S., and Oujane, B.: Geophysical and Remote Sensing Contributions to Understanding Geological Structures in the Central High Atlas (Morocco): A Review and Analytical Study., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20168, https://doi.org/10.5194/egusphere-egu25-20168, 2025.

The Congo craton is an early Archaean through Paleoproterozoic basement block in Central Africa. It consists of a vast heterogenous granulitic complex extending over 1200 km between the Lomami River (24°E) and the Atlantic coast in Angola. The well-exposed domains of the Congo craton are the Kasaï block, Tanzania block, West-Nile complex, and Ntem-Chailu complex. The latter represents the northwestern edge of the craton in southern Cameroon. The Memve'ele area belongs to the Ntem Complex, where recent investigations have highlighted various lithologies, including TTG gneiss and intensely sheared and folded charnockitic and granitic gneiss, pervasively intruded by younger monzogranite. This region provides a critical window into the complex tectonic evolution of one of Earth's oldest continental blocks. Both TTG and granitic gneiss are riddled with folded or sheared leucogranitic veins, suggesting a local origin through melting and dynamic recrystallization. This study presents a comprehensive investigation of the highly sheared Memve’ele mylonitic corridor. Through detailed field mapping, systematic kinematic analysis, and meticulous petrographic and microstructural studies, we aim to unravel the multiple deformation events that have shaped this region. U-Pb zircon geochronology was employed to precisely constrain the timing of these processes and to correlate them with regional tectonic events. The ultimate goal of this research is to better understand the broader geodynamic implications of these findings for the evolution of the Congo Craton. Initial results reveal that the Memve’ele area has undergone a complex polyphase deformation history, involving at least four distinct events. The early ductile deformation (D1) resulted in the development of a pervasive foliation and associated structures. Subsequent ductile-brittle deformation (D2) overprinted the earlier structures, while later brittle deformation events (D3 and D4) further modified the rock fabric. The studied mylonites yield Mesoarchean ages of 2927 ± 52 Ma. The presence of a sinistral shear zone within the area suggests that the region was subjected to significant shear stresses, likely related to regional tectonic processes such as continental collision or crustal extension. These findings have important implications for understanding the tectonic evolution of the Congo Craton and may provide insights into the potential for mineral exploration in the region.

How to cite: Takodjou Wambo, J. D., Ganno, S., Nzenti, J. P., and Asimow, P. D.: Archean shear tectonics in the Congo craton: insights from Petro-structural characterization and U-Pb geochronology of the Memve’ele mylonite, Southern Cameroon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20667, https://doi.org/10.5194/egusphere-egu25-20667, 2025.

The 660 km discontinuity serves as an important boundary for elucidating the dynamics of subducting slabs at this depth. Subducting slabs, characterized by their lower temperatures compared to the surrounding mantle, undergo distinct phase transitions. Harzburgitic compositions are the most gravitationally stable within the lower mantle transition zone, potentially incorporating up to 15 vol% akimotoite in their mineral assemblage. Recent experimental studies indicate that the transition from akimotoite to bridgmanite may be a critical factor in deciphering the complexities inherent to this region.  Additionally, discoveries of iron-rich natural analogs of akimotoite and bridgmanite in Suizhou L6 chondrite have attracted considerable scientific attention regarding the stability of these iron-rich phases. These analogs, identified as Hemleyite (Fe²⁺_0.48Mg_0.37Ca_0.04Na_0.04Mn²⁺_0.03Al_0.03Cr³⁺_0.01) SiO₃ and Hiroseite (Fe²⁺_0.44Mg_0.37Fe³⁺_0.1Al_0.04 Ca_0.03Na_0.02) (Si_0.89Al_0.11) O₃​, provide critical insights into the geochemical behavior and phase stability of iron-bearing silicates under extreme conditions. In this study, first-principles computational methods based on density functional theory (DFT) were employed to investigate the stability fields of these iron-rich phases under high-pressure and high-temperature conditions, aiming to elucidate the effects of Fe²⁺ incorporation on slab stagnation behavior. The analysis demonstrates a positive correlation between acoustic velocity contrasts and increasing Fe²⁺ concentration at the phase transition boundary, while the transition pressure decreases significantly. Additionally, the findings suggest that the overall steepness of the Clapeyron slope remains largely invariant with increasing iron content.

How to cite: Pandit, P., Chandrashekar, P., and Shukla, G.: Impact of Fe²⁺ incorporation on the structural and thermodynamic characteristics of the akimotoite-to-bridgmanite phase transition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-603, https://doi.org/10.5194/egusphere-egu25-603, 2025.

In rocks, brittle deformation depends on loading rating. With increasing rates, usually greater than ~10² s^-1 rock strength increases significantly that results intense fragmentation. Dynamic conditions necessary for rate dependent brittle failure can occur during impact events, seismic ruptures and landslides. Among the geoscientist and rock engineers, Split Hopkinson Pressure Bar (SHPB) is often used for the study of dynamic behavior of rocks under high strain rate condition. Present study focuses on strength behavior of sandstone over the range of strain rate (3.6×10^-5 - 2.4×10² s^-1) using compression testing machine and Split Hopkinson Pressure Bar (SHPB). The failure mode is also captured by high speed camera. The result demonstrates that dynamic compressive strength increases with increasing strain rate and follows Kimberley’s universal theoretical scaling relationship. Dynamic increase factor (DIF) also shows strong dependency on strain rate. The degree of fragmentation is also compared with existing theoretical fragmentation models. The average fragments size shows strong strain rate dependency over the entire testing range. With the increasing strain rate more pulverized state were observed after the failed specimens. Moreover, the mean fragment sizes are well described by power law function of strain rate.

How to cite: Gupta, N., Sharma, M. L., Iqbal, M. A., and Tripathi, A.: Dynamic Strength of rock under High strain rates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1033, https://doi.org/10.5194/egusphere-egu25-1033, 2025.

Adsorption-induced deformation is common in porous rocks, but its role in stressed porous rocks remains unclear. These changes in elasticity have critical implications for geological stability, particularly in regions experiencing alternating droughts and wet conditions. This study investigates elastic deformation in fine-grained sandstone under cyclic loading over 34 days, with humidity increased to near dew point. Adsorption-induced weakening decreases from over 40% to less than 10% as overburden pressure rises from 1 MPa to levels below crack initiation. Similar trends are observed in fine-grained granite. A multi-scale model combining contact mechanics and nanopore adsorption explains these results, highlighting stress competition between adsorption effects and overburden pressure. Adsorption weakening becomes negligible beyond burial depths of 200 meters in sandstone and 700 meters in granite. These findings improve understanding of near-surface geological hazards, such as exfoliation, landslides, and cliff failure, under extreme climatic events.

How to cite: Wu, R., Kang, H., Gao, F., Li, B. Q., Leith, K., Lei, Q., Gor, G., Selvadurai, P. A., Peng, X., Dong, S., and Li, Y.: Elasticity control through overburden and adsorption competition in porous media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1946, https://doi.org/10.5194/egusphere-egu25-1946, 2025.

Most models for dimensioning shallow geothermal heat exchangers consider that heat is only transferred by conduction. The ground water content is assumed to be constant with time. However, in the Vadose Zone (VZ) presenting important geothermal potential, the thermal properties of materials depend on the variable water content.

The literature review highlights that the relationships between thermal conductivity and water content are multiple and often very specific to certain nature of ground systems. The target of this work is therefore to characterize the thermal conductivity of a specific strongly heterogeneous site in order to discuss the limit of adaptability of these approaches and the robustness of the associated models.

Excavation of the Observatory of transfers in the Vadose Zone (O-ZNS) near Orléans (France) allowed us to extract VZ limestones from 7,20 to 20 m-depth, described as massive and weathered with heterogeneous fracture density. Two experimental approaches are used to determine thermal conductivity at different water content. The first is an empirical model that estimates thermal conductivity from acoustic velocity. P-wave acoustic velocities are obtained in dry and saturated conditions and then converted into thermal conductivity. These results are compared to direct thermal conductivity measurements obtained using the hot-wire method.

The indirect method seems to be well adapted for dry materials characterization. However, it presents inconsistencies for saturated or partially saturated materials. Indeed, we saw a conductivity decreases with water content, while theory predicts the opposite. The empirical model clearly shows its limitations when it comes to considering water in the pores of complex rocks. Nevertheless, on dry samples, the deduced thermal conductivity values are validated by direct measurements. The direct method makes it possible to observe the theoretical correlation between thermal conductivity and water content in order to adapt future models. Measurements show an increase in thermal conductivity with water content. But, in some samples, of rather massive appearance, poorly altered and fractured, water content has a relatively low impact on thermal conductivity. These variations raise questions about the effects of a specific microstructure on the correlation between water content and thermal conductivity. Indeed, on samples taken at 16.6 m-depth, the same mean value of thermal conductivity was observed regardless of water content, a behavior not observed on other samples.

The thermal conductivity data will be integrated in a new thermo-hydro model of the O-ZNS site, currently under development : i) to test the stability and consistency of the models and compare results with experimental data, and ii) to later calibrate the chosen model and apply it to different contexts.

How to cite: Dupuis, M., Abbar, B., Mallet, C., Voirand, A., Philippe, M., and Azaroual, M.: Caracterising Thermo Hydro Mechanical properties in complexe limestone formation (OZNS, Beauce aquifer, France), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2713, https://doi.org/10.5194/egusphere-egu25-2713, 2025.

Pore fluid pressure is known to significantly influence the mechanical strength of rocks. On one hand, an increase in pore fluid pressure may favor crack growth and thus trigger failure, while on the contrary, a decrease in pore fluid pressure will inhibit crack propagation and stabilize failure. On the other hand, whether pore fluid decrease or increases depends on the combination of: 1) pore-fluid pressure boundary conditions; 2) pore fluid pressure diffusion timescale relative to deformation timescales; 3) the latter governing the evolution of permeability and storage capacity within the system. Hence, whether pore fluid pressure will stabilize failure or not, via dilatant strengthening, will depend on a number of parameters, amongst which boundary conditions (drained or undrained), initial permeability, and strain rate must be included.

Here, we perform a comprehensive investigation into the mechanical strength of thermally cracked Westerly granite, in order to provide insights on pore fluid pressure evolution during rock failure. We conducted triaxial loading experiments on heat-treated Westerly granite samples (heated to 700 °C). In order to investigate the mechanical and hydraulic responses throughout the entire failure process, experiments were performed under both drained and undrained boundary conditions, at different strain rates (10^-4, 10^-5, 10^-6, and 10^-7 s^-1) and initial effective confining pressures (5, 20, and 40 MPa). All experiments were conducted at an initial pore pressure of 50 MPa. During each experiment, stress, strain, as well as pore pressure (using 8 in-situ pore pressure transducers) were monitored. Acoustic emission and the evolution of elastic P-wave velocities were also recorded. So far, our experimental results demonstrate that: 

• Water-saturated granites under undrained conditions show higher strength than drained ones, due to dilatant strengthening from reduced pore pressure at failure.
• Under drained conditions, the onset of pore pressure drop is governed by the competition between fluid diffusivity and volumetric strain rate.
• Dilatant strengthening under drained conditions is strain-dependent, with larger pore pressure drops at high (10^-4 /s) vs. low (10^-7 /s) loading rates.  

Our results highlight the importance of dilatant strengthening during the failure of crystalline rock. For instance, it is possible that a number of former studies realized under nominally drained water saturated conditions may have underestimated the effect of water weakening, due to important – yet unobserved at the time- dilatant strengthening happening, resulting in strength of dry and saturated specimen being almost equivalent.

Dilatant strengthening being most efficient at high strain rate, we can safely extrapolate that it is most efficient just before or just after failure. In particular, by stabilizing failure, it may explain long foreshock and aftershock sequences, as seem to be the case in at least some of the recorded AE sequences during our experiments. Finally, whether thermal pressurization is or not able to balance out (because of high velocity frictional heating) dilatant strengthening during dynamic rupture remains to be investigated.

How to cite: Lin, G., Fan, C., Chapman, S., Fortin, J., and Schubnel, A.: The competition between fluid diffusion and volume dilatancy during the failure process of thermally cracked Westerly granite, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3048, https://doi.org/10.5194/egusphere-egu25-3048, 2025.

The release of CO2 into the atmosphere is thought to be a major factor contributing to global warming, and technology for separating and recovering CO2 from the gases emitted from large-scale sources and storing it in deep underground aquifers (hereafter referred to as CCS: Carbon dioxide Capture and Storage) is already being used commercially in other countries as a measure to combat global warming. When starting a CO2 geological storage project, as part of risk management, it is necessary to consider whether there is a potential threat of causing seismic activity or ground deformation that could have a negative impact, and to plan and implement countermeasures. The Japan islands located in the convergent zone of four tectonic plates and are known as one of the most earthquake-prone countries in the world. Evaluating and predicting the impact of great earthquakes on reservoirs and cap rocks and disseminating this information to society is considered to be one of the important issues in terms of gaining social acceptance at the project planning stage. The authors are currently developing an earthquake response analysis method for evaluating the stability of CO2 geological storage sites in advance in the event of a great earthquake, but one of the issues is the physical properties of the ground to be input into the analysis model. It is well known that brittle rocks under atmospheric pressure show plasticity under confining pressures of tens to hundreds of MPa, and it is easy to imagine that soft sedimentary rocks also show similar mechanical behaviour. However, there are only a few cases of published high-pressure triaxial compression tests using drilling core samples collected from deep underground, for example. In this study, triaxial compression tests were conducted using sandstone and mudstone block samples (comprising the middle Pleistocene to the upper Pliocene) collected from outcrops and shaped into specimens (height 100 mm, diameter 50 mm) in the laboratory under confining pressures equivalent to CO2 storage sites. Regardless of the age of the sediment, the principal stress difference in mudstone increased to 1-2% axial strain, after which it remained almost constant. There was no clear yield point in the ‘stress-strain curve’, and the mudstone showed strain-hardening behaviour. The pore water pressure increased as the axial strain increased. In the sandstone, no clear shear surface was formed even at an axial strain of around 5%. The specimens did not become barrel-shaped after testing, but instead showed a shape of overall shrinkage. The volume change continued to decrease as the axial strain increased. This is thought to be because the difference in the principal stress did not reach its maximum strength. In the future, we plan to conduct experiments that take into account the pressure history (depositional depth and overburden) that the specimens have been subjected to in the past, before loading tests.

How to cite: horikawa, S., takemura, T., and kusunose, K.: High pressure triaxial compression test in soft sedimentary rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3958, https://doi.org/10.5194/egusphere-egu25-3958, 2025.

This study has the main purpose of investigating the micro-mechanisms involved in the expansion of anhydrite, a phenomenon that often occurs during excavations and may cause serious technical problems to civil tunnelling and other infrastructures (e.g., buildings, bridges, underground caverns). For this purpose, we developed an experimental investigation aimed at observing microscale changes occurring in anhydrite samples during water immersion by means of X-ray Computed Tomography (CT).  

We prepared six cylindrical specimens (diameter 10 mm and height 20 mm) of Triassic anhydrite from the Western Alps. Each of them was wrapped with an impervious cellophane sheet and partially submerged in calcium-sulphate saturated water. The upper surfaces were left in direct contact with air to force the water to cross the specimens. The specimens were put in water on the 15th of December 2023. Then, they were periodically scanned – over a total period of 1 year – through X-ray tomography using the CoreTOM scanner (TESCAN XRE) at Ghent University Centre for X-ray Tomography (UGCT), with a voxel size of 10 µm, as an EXCITE TNA project.

The elaboration of CT scans allowed to evaluate the volume and phase changes occurred during the test. All the specimens consistently showed a total expansion between 2% and 3% in volume. In addition, the multitemporal scans were examined using an algorithm of Digital Volume Correlation to deepen the mechanisms driving the expansion by visualizing the position where the expansion prevalently occurred.

The improved knowledge of the mechanism driving the process of expansion in anhydrite provides elements for a more accurate forecasting of the entity and the times of the phenomenon in real contexts (e.g., civil tunnelling, mining, slope stability, underground energy storage), driving to the possible refinement of existing constitutive models.

How to cite: Caselle, C., Ramon, A., Schröer, L., Cnudde, V., Bonetto, S. M. R., Mosca, P., Costa, E., Giordano, E., and Paschetto, A.: Volume and phase changes of swelling sulphates revealed through multitemporal micro-CT imaging , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4306, https://doi.org/10.5194/egusphere-egu25-4306, 2025.

    Electrical signal changes in process of loading rock to fracturing is an important rock petrophysical phenomenon, which is of great significance for understanding the abnormal electric field, magnetic field and electromagnetic radiation related to rock fracturing, geohazards and tectonic earthquake. Positive holes (P-holes) activation due to the broken of peroxy defects is one of the important mechanisms causing rock current, and peroxy defects are common in most of the crust rocks. During the loading of rock specimen, the activation, transmission and accumulation of P-holes in different place inside the rock are bound to be variable, and present as the spatial difference in the changes of electrical signals. However, the spatial differences in the changes of electrical signals during loading rock to fracturing and the correlation between the electrical signal and the internal physical-and-mechanical states of rock have not been well studied so far.

    Therefore, we carried out potential monitoring experiments in different areas of the rock under local stress and synchronous acoustic emission monitoring. The rock specimen was specially designed in 3D shape of cube-frustum. The lower cube acting as the loaded part was wrapped with copper foil and connect to the negative electrode of the potentiometers; while the upper square frustum acting as the free part were pasted with copper foil at three places and connect to the positive electrode of potentiometers, respectively, as in Fig. 1a.

    The experimental results, as in Fig. 1b, showed that during the early rock loading, the characteristics of potential changes in each area were basically the same, with slight differences in amplitude, which were directly related to the size of micro-crack development area in the corresponding part. When the loaded rock reached to macroscopic fracturing and got failure, the characteristics of potential change in different areas were significantly different (Fig. 1c), which were directly related to the formation of macroscopic fracture inside. When no macroscopic fracture surface was formed at the intersection zone of the free part and the loaded part below the potential monitoring area, P-holes would transmit upward to the upper surface of frustum along the stress gradient, resulting in the rise in potential. Conversely, if a macroscopic fracture surface was formed at the intersection zone (Fig. 1d), the upward transmission of P-holes would be blocked, and more P-holes reached the surface of the loaded cube, resulting in the decrease in potential. Furthermore, we kept loading the rock fragments after macroscopic failure, and found that during the friction or the relative slip process between fragments, the combined influence of furrow effect, adhesive friction and slip shear also led to P-holes activation and dislocation sliding, resulting in potential rising again. The potential risings in different areas were related to the degree of friction and the distribution of macroscopic fracture surfaces in the corresponding parts.

Figure 1 Experimental schema diagram and results. (a) Diagram of the experimental schema; (b) The variations of potentials; (c) Potential changes when the rock got failure; (d) Failure pattern. 

How to cite: Sun, L., Wu, L., Xu, Y., Zheng, T., Dong, G., Xie, B., and Mao, W.: Spatial Differences in Potential Changes of Rock Loaded to Fracturing: Characteristics and Mechanism, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5665, https://doi.org/10.5194/egusphere-egu25-5665, 2025.

This study focuses on the investigation of the chemical reactions involved in the phenomenon of anhydrite swelling, that is a well-known issue that may affect the functionality of underground infrastructures.

The study was performed on Triassic gypsum and anhydrite samples collected from an Alpine location (Signols, Oulx in the Susa Valley, Piedmont, Italy) and involved the investigation of the behavior of this material immersed in different aqueous solutions at various temperatures.

The influence of different aqueous solutions (distilled water, water with CaSO₄, water with MgCl₂, and water with NaCl)  on the solubility and precipitation of new crystals was evaluated at different temperatures (15°C, 40°C, and 60°C).

Both macro- and micro-scale observations were conducted before water immersion and after different time intervals. Macro-scale observations included the measure of the volume and the mass and the capture of photographical images with a camera. Micro-scale analyses involved the use of SEM-EDS to determine the mineralogical composition and examine the changes in micro-scale morphological features (e.g., growth of new crystals).

The experiment seeks to identify potential mineralogical transformation, particularly the hydration of anhydrite into gypsum, under the specified conditions. The findings will contribute to understanding the mechanisms influencing anhydrite swelling and its implications for geological and engineering applications.

How to cite: Giordano, E., Caselle, C., Costa, E., Bonetto, S. M. R., Paschetto, A., and Mosca, P.: Experimental analysis of crystal growth in anhydrite and its impact on swelling quantification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6576, https://doi.org/10.5194/egusphere-egu25-6576, 2025.

Istanbul is a unique city spanning two continents and one of the world's most populous cities. There is a significantly increasing demand for the construction of deep engineering structures, particularly transportation and infrastructure tunnels because of a population exceeding 16 million. Numerous projects, including intercontinental strait crossings, will be implemented over the coming decades to meet the city's needs. Istanbul’s complex geological structure, rugged topography, and earthquake risk make construction efforts more challenging. Generally, deep engineering structures in Istanbul are primarily constructed within the classic and carbonate rocks, which are part of the Istanbul Paleozoic Sequence. These sedimentary rocks are intersected by dikes composed of andesite, diabase, and dacite, which exhibit varying geometries. Due to the different engineering properties of these rock units, which have different geological origins, their behavior in deep underground excavation openings also varies. Engineering problems such as rock bursts, water inflows, and TBM (Tunnel Boring Machine) jamming arise during tunnel construction, leading to both cost overruns and time delay. In this study, the effect of dyke geometries on tunnel stability was analyzed using ITASCA’s Particle Flow Code (PFC), which employs the discrete element method (DEM). Models were calibrated based on field experiences and laboratory data of the host rocks and dykes obtained during tunnel construction on the Anatolian side of Istanbul. The uniaxial compressive strength and elasticity modulus values of the host rocks and dykes are 28 MPa and 46 MPa, 12 GPa, and 16 GPa, respectively. Initially, a base two-dimensional model with dimensions of 4 by 4 meters was calibrated using the flat-joint model, and upscaled to 80 by 60 meters to represent the tunnel environment. Additionally, models featuring singular and dual dyke geometries with different orientations were utilized in an environment containing a tunnel opening with a radius of 4 meters. Analyses were carried out on a total of 18 models, which included seven single dyke geometries with a dip angle varying between 0 and 90 degrees in 15-degree increments, six geometries featuring a secondary dyke with a horizontal dip angle of 0 degrees intersected by another dyke at 15-degree increments, and five models with two dykes positioned at dip angles of 15, 30, 45, 60, and 75 degrees relative to each other. Each model was run for up to 100,000 cycles under gravitational loading conditions, and data on force chains, fragmentations, stress, and strain values were collected using measurement spheres positioned at 0, 90, 180, and 270 degrees around the tunnel opening. According to the results obtained from the models, the highest deformation in the tunnel section was observed at 60 degrees in single dyke geometries, while in double dyke geometries, it was observed at 0-30, 0-45, and 0-60 degrees.

How to cite: Zengin, E. and Ündül, Ö.: Exploring Dyke Geometry Effects on Tunnel Stability Using Particle Flow Code, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7280, https://doi.org/10.5194/egusphere-egu25-7280, 2025.

In many geotechnical and tectonic settings, a fundamental understanding of the inelastic behavior of porous rocks under polyaxial compression is necessary. In this study, we present new true triaxial compression data obtained in the ductile regime on Bleurswiller sandstone with the size of 100mm X 50mm X 50mm. The deformed samples show a range of failure modes qualitatively similar to what was reported by earlier experimental studies performed in conventional conditions (axisymmetric compression). In particular, visual inspection and X-ray Computed Tomography imaging reveal compaction localization in all our deformed samples. The pore collapse model of Zhu et al. (2010) is extended to include the role of the intermediate principal stress and our new data for the onset of shear-enhanced compaction are in basic agreement with this extended model that includes three stress invariants. At constant minimum principal stress, the onset of shear-enhanced compaction tends to decrease slightly with increasing intermediate principal stress.

Published true triaxial data obtained in the brittle regime highlights the impact of the intermediate principal stress on the onset of dilatancy. The predictions of the conventional sliding wing crack model extended to true triaxial conditions are in poor agreement with these data. Our analysis suggests that the observed discrepancies are related to the influence of the intermediate principal stress on the effective shear stress on the wing cracks. Another energetic approach pioneered by Wiebols & Cook (1968) shows a better agreement with the experimental results, and predicts that at constant minimum principal stress, the onset of dilatancy would not be a monotonic function of the intermediate principal stress. Our new data and analysis will help the interpretation of inelastic deformation under polyaxial compression in various geotechnical and tectonic settings.

How to cite: Meng, F., Shi, L., Hall, S., Baud, P., and Wong, T.: Onset of Pore Collapse and Dilatancy in Porous Sandstone Under True Triaxial Compression: Experimental Observation and Micromechanical Modeling , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8113, https://doi.org/10.5194/egusphere-egu25-8113, 2025.

The swelling behavior of clay-sulfate rocks poses significant challenges in geotechnical engineering due to complex hydro-mechanical and chemical interactions. This study introduces a hybrid framework combining finite element modeling (FEM) with machine learning (ML) to efficiently analyze and predict the nonlinear behavior of swelling processes. We generated synthetic datasets representing swelling phenomena at the Staufen site, Germany, using a coupled hydro-mechanical FEM simulation in OpenGeoSys. A parametric analysis was conducted to systematically vary critical parameters, including Young's modulus, permeability, maximum swelling pressure, and air entry pressure, to capture the inherent uncertainty and variability of swelling processes. A constrained CatBoost ML model was trained on the FEM outputs to predict porosity, saturation, and displacement under varying hydro-mechanical conditions. Results demonstrate strong alignment between the ML surrogate and FEM simulations, achieving high accuracy while significantly reducing computational demands. Sensitivity analysis indicated the dominance of swelling pressure and Young's modulus in influencing swelling-induced deformation, while Monte Carlo simulations quantified prediction uncertainties. This contribution discusses the potential of integrating FEM with ML for site-specific risk assessment and mitigation planning in geotechnical engineering.

How to cite: Taherdangkoo, R., Mollaali, M., Ehrhardt, M., Nagel, T., and Butscher, C.: Integrating Finite Element Modeling and Machine Learning for Hydro-Mechanical Analysis of Swelling in Clay-Sulfate Rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8168, https://doi.org/10.5194/egusphere-egu25-8168, 2025.

Currently, there is insufficient confidence in the application of soft rock in major projects, leading to overly conservative design of foundation bearing capacity. Clarifying the stress distribution and failure process of soft rock foundation with depth offer guiding significant for determining the bearing capacity of soft rock foundation in practical geotechnical engineering. Based on the arch foundation project of the Fifth Bridge of the Lantian Yangtze River, this paper investigated the bearing capacity of soft rock foundations and its depth correction rule by analyzing field test results and numerical simulations.  A formula inversion model was established referencing current standards and relevant literature, and the depth correction coefficient k2 for soft rock foundation bearing capacity was calculated based on field test measurements.  Using finite element software PLAXIS 3D, a numerical model of soft rock foundations with variables including load plate burial depth and lateral limiting conditions was created under field conditions and calculate the simulated bearing capacity of soft rock foundations.  By combining results from both methods, the variation rule of soft rock foundation bearing capacity influenced by depth factors is analyzed, and the applicability of different research methods is discussed.  It is found that within a certain range, the bearing capacity of soft rock foundations has a linear positive correlation with burial depth, and after reaching 15d, it shows a gradual trend.  Finally, recommended values for the depth correction coefficient are 2.5 (for undetailed or poor foundation conditions) and 8.0 (for good foundation conditions with low weathering degree), with different values adopted according to site conditions.  Furthermore, the bearing capacity of soft rock foundations with free surfaces was discussed, offering a valuable reference for similar future engineering scenarios.  After the bearing capacity measurement and foundation deformation performance analysis, it was concluded that there is still a significant bearing capacity reserve, which provides essential data support for dimensional optimization.  This paper further substantiates that the bearing capacity of soft rock foundation can be significantly enhanced through in-depth modification, thereby offering meaningful reference and guidance for practical engineering applications.

How to cite: Yang, X., Gong, W., and Yang, H.: In-situ test and numerical verification of bearing capacity of soft rock foundation with depth, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10931, https://doi.org/10.5194/egusphere-egu25-10931, 2025.

The mechanical and technical characterization of bimunits (i.e., chaotic units consisting of hard blocks within a softer matrix), represents an untrivial challenge for researchers and practitioners. The main existing methods for their characterization require the estimation of the Volumetric Block Proportion (VBP). In real contexts, the VBP is typically estimated from point, linear, or areal measurements, making it strongly dependent on the availability of accessible outcrops and/or borehole data. To address this limitation, we evaluated the potential of geophysical (geoelectrical) methodologies for quantifying the Areal Block Proportion (APB) in bimunits. Specifically, we propose an approach for the analysis of electrical resistivity tomographies (ERTs) on bimunits, as outlined by Caselle et al. (2024). This approach is based on the fundamental research assumption that the electrical contrast between blocks and the matrix enables the discrimination of rock blocks in ERTs, provided their sizes exceed the resolution of the ERT. When block sizes are smaller, the ERT homogenizes the blocks-matrix mixture, producing an overall resistivity signature. This signature shows a positive proportionality with the percentage of blocks and can be used to estimate the ABP while still providing valuable information for bimunits characterization. This hypothesis was tested through numerical simulations and real ERTs, offering a preliminary validation of the proposed approach.  

Caselle, C., Comina, C., Festa, A., Bonetto, S. 2024. Electrical resistivity tomography for the evaluation of Areal Block Proportion (ABP) in bimunits: Modelling and preliminary field validation, Engineering Geology, 333, 107488, https://doi.org/10.1016/j.enggeo.2024.107488.

How to cite: Bonetto, S., Comina, C., Festa, A., and Caselle, C.: Evaluation of Aereal Block Proportion (ABP) for the mechanical characterization of bimunits using Electrical Resistivity Tomography , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11515, https://doi.org/10.5194/egusphere-egu25-11515, 2025.

Understanding the microstructural details of concrete is crucial for improving their material properties in structural applications within civil engineering. Digital Rock Physics (DRP) refers to a modern technique that enhances the understanding of the physical behavior of rocks or respectively concrete through microscale imaging of their internal structures. Based on the non-destructive method of high-resolution X-ray computed tomography (XRCT), which is still widely underestimated, it is possible to obtain information e.g., on phase distributions, volume characteristics like pore spaces and furthermore microstructures such as microcracks can be visualized. Here we used the XRCT to investigate the influence of external mechanical loading on concrete. XRCT images with different resolutions were performed under confining pressures of 0.1 MPa to 46 MPa. The generated and analyzed CT images of unloaded and loaded (i.e., due to external stress) concrete are compared with respect to any potential microstructural changes. We specifically examined the segmentation process and its impact on the determined effective material properties. Despite the many possibilities enabled by XRCT technology, there are still challenges in identifying microstructures or phases correctly, due to its relatively low resolution, which also complicates the assignment of their physical properties based on numerical simulations. For the interpretation of the concrete’s CT images, additional methods are needed. This applies in particular to grain and phase boundaries of individual aggregates, transition zones or very fine-pored phases. For this reason, the high-resolution image-based data from XRCT is combined with standard polarization and scanning electron microscopy (SEM). Together with these additional fundamental laboratory techniques, it is possible to receive more detailed information of the structure, detect internal changes at all scales and to get an optimal spatially segmented image of the concrete samples. It is possible to determine realistic synthetic scenarios for different loading situations, which enables the application of advanced numerical approaches. This study demonstrates the importance of understanding the internal microstructure of concrete-based structures to analyze the XRCT images and to identify the effects of external stresses in concrete and thus the factors that influence the accuracy of physical measurements at elevated pressure conditions.

How to cite: Beiers, L. M., Balcewicz, M., Lebedev, M., and Saenger, E. H.: Digital concrete physics - High-resolution X-ray computed tomography (XRCT) and microstructural investigations of concrete under confining pressures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11880, https://doi.org/10.5194/egusphere-egu25-11880, 2025.

Despite daily progress over half a century, rock deformation leaves significant challenges in understanding their underlying mechanics and providing accurate models. Experimental geologists developed various approaches to deform rock samples, but coupling them with X-ray tomography marked a turn in monitoring failure precursors and interpreting stress-strain curves. X-ray transparent triaxial presses become more advanced and equipped yearly, allowing the complete rheological study of earth material. 

The European Synchrotron Radiation Facility is the unique 4th generation synchrotron worldwide. Its Extremely Brilliant Source (EBS) allows the scan of samples encapsulated in thick autoclaves at high speed. It proposes a state-of-the-art fleet of triaxial presses capable of accurately measuring and observing the deformation of a rock sample while passively recording its acoustic emissions. It enables researchers to analyse fault movements, stress transfer, and energy release mechanisms at different sample sizes while precisely controlling stress, temperature, and deformation rates.

With comprehensive data analysis, such as crack segmentation and digital volume correlation coupled with acoustic events' time and spatial resolution, it is now possible to identify failure precursors at high spatial (X-rays) and soon temporal (acoustic) resolutions. One may also investigate phenomena with low amplitude or high frequency, which produce deformation but appear aseismic.

Here, we present the successful results of several teams that have used these devices and their latest technical developments.

How to cite: Cordonnier, B.: Cracking the Rock Mechanisms with the European Synchrotron Experimental Fleet., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18080, https://doi.org/10.5194/egusphere-egu25-18080, 2025.

The application of laser technology for drilling rocks has drawn the attention of scientists and engineers for decades (Xu et al., 2003; Buckstegge et al., 2016; Jamali et al., 2019; El Neiri et al., 2023), promising a revolution in well-drilling operations of the oil and gas industry and geothermal energy sector. High-power lasers can penetrate hard rock formations with greater rate and precision, without physical contact with the rock which eliminates wear on drill bits and subsequently reduces significantly drilling time and well completion costs. This work is a part of the DeepU Project that addresses problems of conventional drilling in search of cheaper and environmentally friendly drilling technique for the exploitation of geothermal energy. A series of laboratory-scale experiments were performed with the Ytterbium fiber laser with a wavelength of 1070±10nm, operating in continuous mode within a power range of 170-30000W. The temperature of the lasing process and IR imaging were recorded by thermo-camera FLIR GF77a with HSM mode allowing for gas visualization. The craters in laser-affected rocks were further investigated by photogrammetry and electron microscopy while ejected particles were collected and characterized. This comprehensive study has revealed the nature of petro-thermo-mechanical phenomena occurring during laser irradiation of rocks. The three observable processes are: thermal spallation, melting and vaporization. They are controlled mainly by power density (delivered to the rock surface), irradiation time and lithology (texture, mineral and chemical composition). The photogrammetric analysis of laser-affected rocks has shown the efficiency of the laser drilling process, expressed by the rate of penetration and specific energy i.e., the amount of energy necessary to remove a unit of volume. The microscopic study of lased surfaces has revealed the impact of the laser on the rock samples. Depending on the drilling regime the result was: 1) smoothly cut craters with shallow fractures generated by thermal spallation at lower power or 2) a rugged glass layer of vitrified molten rock formed by melting and vaporization at higher power. The power-dependent transition between the processes, thus drilling regime was defined for granite, sandstone and limestone. These results allowed to design and apply a DeepU thermal spallation laser system to successfully drill larger diameter boreholes (<10cm), and bring closer to the successful application of laser technologies in the geothermal field.

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

Buckstegge F., Michel T., Zimmermann M., Roth S., Schmidt M., 2016, PP, v. 83, p. 336–343, doi:10.1016/j.phpro.2016.08.035.

El Neiri M.H., Dahab A.S.A.H., Abdulaziz A.M., Abdelghany K.M., 2023, JEAS, v. 70, p. 98, doi:10.1186/s44147-023-00260-2.

Jamali S., Wittig V., Börner J., Bracke R., Ostendorf A., 2019, GEE, v. 20, p. 100112, doi:10.1016/j.gete.2019.01.001.

Xu Z., Reed C.B., Leong K.H., Parker R.A., Graves R.M., 2003, ICALEO, Laser Institute of America, p. P531, doi:10.2351/1.5060167.

How to cite: Slupski, P., Cerwenka, G., Chorowski, M., Di Sipio, E., Galgaro, A., Mallin, K., Manzella, A., Pasquali, R., Romanowski, A., Sassi, R., Steinmeier, O., and Pockele, L.: Laser-rock interactions, is drilling rocks possible with a laser?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19025, https://doi.org/10.5194/egusphere-egu25-19025, 2025.

The aim of the present study is to understand the strength behaviour of thermally treated sandstone under compression and tensile loading conditions, both in quasi-static and dynamic states. The sandstone specimens were thermally treated in a furnace for 24 hours at a heating rate of 5°C/min and then allowed to cool within the furnace. The specimens were divided into five temperature groups: 25°C, 200°C, 400°C, 600°C, and 800°C. Using a Universal Testing Machine (UTM) and a Split Hopkinson Pressure Bar (SHPB), the quasi-static and dynamic compressive and tensile strengths were determined. The study validates the applicability of Kimberley's universal scaling relationship for thermally treated sandstone under both loading condition. Additionally, the characteristic strain rate remains unchanged up to 400°C and significantly decreases thereafter. High-speed photography provided crucial insights into the failure characteristics under both compression and tensile loading conditions as the temperature increased. The findings are applicable to various geotechnical projects involving high temperatures and dynamic loading conditions.

How to cite: Tripathi, A., Khan, M. M., Pain, A., and Rai, N.: Strength Behavior of Thermally Treated Sandstone Under Quasi-Static and Dynamic Loading Conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19456, https://doi.org/10.5194/egusphere-egu25-19456, 2025.

The chemical characteristics of water present in the pores and fractures of the rock mass and the mineralogical rock composition determine the chemical processes that may take place in a geological formation. The chemical reactions occurring in a geotechnical problem play an important role because their development can influence on the mechanical and hydraulic behaviour of rock masses. For example, a change in the concentration of dissolved salts in groundwater can lead to a modification of the swelling potential or trigger and expansive or shrinkage response of clayey formations (Yustres et al., 2017). Therefore, a good knowledge of the chemistry involved in the rock mass is relevant both to understand and to predict the response of the geological media. This is of great importance in the case of the construction of critical civil infrastructures like energy and nuclear waste storage facilities.

Chemical effects are expected to occur in soils and rocks, and several variables may affect the intensity at which they take place. The literature describes several case histories in rocks where the effects of chemistry are more intense than in soils. Tunnels and foundations may respond hydraulically and mechanically under the influence of the chemical processes of the dissolution/precipitation of soluble minerals present in the rock. These phenomena are capable of leading to severe and rapid expansions that can result in infrastructure and building damage. The extreme expansions observed in anhydritic rocks are one example in which dissolution and precipitation processes affect the geotechnical behaviour (Alonso et al., 2013, Ramon & Alonso, 2018).

A coupled numerical model has been developed to address the chemical processes coupled to thermo-hydro-mechanical (THM) problems in geological media. The numerical model is capable to simulate general chemical processes and the associated hydraulic and mechanical effects. The formulation of the chemical interactions is implemented in a coupled manner within a Finite Element code for THM analysis in geological media (CODE_BRIGHT). The presentation will describe the details of the equations and hypothesis considered in the model. The simulation of a real case will be also analysed.

Alonso, E.E., Berdugo, I.R. and Ramon, A. (2013). Extreme expansive phenomena in anhydritic-gypsiferous claystone: the case of Lilla tunnel. Géotechnique 63 No. 7, 584 – 612

Ramon, A. and Alonso, E. E. (2018) Heave of a Building Induced by Swelling of an Anhydritic Triassic Claystone. Rock Mech. Rock Engng.: 51, Issue 9, pp 2881–2894.

Yustres, A., Jenni, A., Asensio, L., Pintado, X., Koskinen, K., Navarro, V., Wersin, P. (2017). Comparison of the hydrogeochemical and mechanical behaviours of compacted bentonite using different conceptual approaches. Applied Clay Science, 141: 280-291.

How to cite: Ramon, A. and Olivella, S.: Numerical analysis of the effects of chemistry on the THM behaviour of rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21626, https://doi.org/10.5194/egusphere-egu25-21626, 2025.

The Grande Oolithe is an oolitic limestone from the Middle Jurassic, present at various depths within the Upper Rhine Graben (Alsace, France). It has been identified as a prospective target for geothermal energy extraction. A comprehensive evaluation of the geothermal potential of this formation hinges on a detailed understanding of its mechanical and physical properties, in particular permeability. Previous studies on porous carbonates highlighted the diversity and the microstructural complexity of this rock type. Permeability could be strongly influenced in particular by the degree of cementation and the proportion of macro and micropores in limestones, which often have a dual porosity structure. To identify the parameters controlling fluid flow in the Grande Oolithe, we initiated a systematic study to map its permeability over the entire Upper Rhine Graben and quantify its possible variations with pressure.

Cylindrical samples were prepared from 18 blocks collected from several outcrops in Alsace. Porosity measured on 90 samples span from 4 to 26% for the different blocks, while permeability was found to range from 10⁻¹⁵ to 10⁻¹⁸ m². Our preliminary microstructural analysis and X-ray Computed Tomography data revealed a high degree of cementation in most of our samples and that the pore space is dominated by micropores, mostly of submicron sizes. For high-pressure experiments, we targeted so far the high-porosity/high permeability end-members, from Bouxwiller (GO) and Gueberschwihr (GU), with respective porosity of 25 and 20%. Both limestones are made of 99% calcite. Conventional triaxial experiments were performed at room temperature on water-saturated samples, in drained conditions with a constant pore pressure of 10 MPa and at effective pressures up to 100 MPa. The experiments were performed at a constant strain rate of 10^-5 s^-1 and permeability was measured using steady-state flow technique at different stages of deformation.

Under hydrostatic compression, permeability was found to decrease moderately in both GO and GU during the poroelastic stage and then more significantly beyond the onset of pore-collapse. The total permeability decrease was more pronounced in GO than in GU. At an effective pressure of 100 MPa, inelastic compaction resulted in a permeability reduction of a factor 15 in GO and a factor 4 in GU, while respective porosity reduction was 7.8% and 2.5%. Under triaxial compression, the permeability measured in samples deformed at various effective pressures showed somehow similar variations, in qualitative agreement with previous studies on permeability in porous carbonates under triaxial compression.

How to cite: Mammadov, S., Baud, P., Heap, M., Schuster, M., and Reuschle, T.: Permeability of oolitic limestones from the Upper Rhine Graben, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-484, https://doi.org/10.5194/egusphere-egu25-484, 2025.

Porous reservoir rocks like sandstones have gained utmost importance in the last decade as a potential sink for CO₂. Most of the targeted reservoirs are depleted oil and gas fields, which have caprocks to ensure the containment of the injected CO₂. Injecting CO₂ into porous reservoirs increases the pore pressure, reducing the effective horizontal and vertical stresses. Depending on the pre-injection stress condition and permeability of the reservoir, careful monitoring should be in place to define the upper limit of CO₂ injection pressure to prevent any permanent damage to the reservoir, which can lead to leakage or induced seismicity. Lab-scale experiments provide key insights into the deformation behaviour 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 (core plugs) collected from different depths of offshore North Sea under realistic reservoir stress and saturation conditions, with liquid CO₂ flow-through leading to failure. The P and S wave velocities along the core plugs were recorded every 15 s to assess the change in wave properties during deformation, fluid displacement and pore pressure build-up. 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 and amplitudes decrease sharply after the onset of plastic deformation, which can be attributed to the formation of microcracks in the coreplug due to increasing load. During displacement of brine with CO₂, velocities and amplitudes drop sharply. These indicators are used to develop a traffic light scenario for CCS operations to maintain safe stress conditions in the reservoir. The consistent correlation between the wave properties and mechanical response of the reservoir rocks reveals that constant monitoring of wave velocities during CO₂ injection can act as a cheaper and more efficient tool for monitoring stress state and plume movement in the reservoir, facilitating safer CO₂ storage operations.

How to cite: Chandra, D. and Barnhoorn, A.: Applicability of sonic velocities as a monitoring tool for subsurface CO2 plume migration and associated stress change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1802, https://doi.org/10.5194/egusphere-egu25-1802, 2025.

Pressure and stress perturbations associated with volcanic activity and geothermal production can modify the porosity and permeability of volcanic rock, influencing hydrothermal convection, the distribution of pore fluids and pressures, and the ease of magma outgassing. However, porosity and permeability data for volcanic rock as a function of pressure and stress are rare. We focus here on three porous tuffs from the Krafla geothermal system (Iceland). Triaxial deformation experiments showed that, despite their very similar porosities, the mechanical behavior of the three tuffs differs. Tuffs with a greater abundance of phyllosilicates and zeolites require lower stresses for inelastic behavior. Under hydrostatic conditions, porosity and permeability decrease as a function of increasing effective pressure, with larger decreases measured at pressures above that required for cataclastic pore collapse. During differential loading in the ductile regime, permeability evolution depends on initial microstructure, particularly the initial void space tortuosity. Cataclastic pore collapse can disrupt the low-tortuosity porosity structure of high-permeability tuffs, reducing permeability, but does not particularly influence the already tortuous porosity structure of low-permeability tuffs, for which permeability can even increase. Increases in permeability during compaction, not observed for other porous rocks, are interpreted as a result of a decrease in void space tortuosity as microcracks surrounding collapsed pores connect adjacent pores. Our data underscore the importance of initial microstructure on permeability evolution in volcanic rock. Our data can be used to better understand and model fluid flow at geothermal reservoirs and volcanoes, important to optimize geothermal exploitation and understand and mitigate volcanic hazards.

How to cite: Heap, M., Bayramov, K., Meyer, G., Violay, M., Reuschlé, T., Baud, P., Gilg, A., Harnett, C., Kushnir, A., Lazari, F., and Mortensen, A.: Compaction and permeability evolution of tuffs from the Krafla geothermal system (Iceland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2171, https://doi.org/10.5194/egusphere-egu25-2171, 2025.

Shale oil reservoirs are extremely tight, making it fundamental to evaluate their physical properties to exploration and development efforts. These properties are closely linked to the rock components (RC) and pore structure (PS). The significant complexity and heterogeneity inherent in the RC and PS pose considerable challenges for assessing the physical properties of these reservoirs. In specific depositional environments, a matching relationship between RC and PS exists. Identifying this relationship and associating microscale PS attributes with macroscale physical properties can expose substantial variations within shale oil reservoirs, aiding in the selection of optimal layers for exploitation and improving development efficiency.

This study focuses on the shale oil reservoirs of the Lucaogou Formation (P₂l) in the Jimusar Sag, marked by mixed-source sedimentation. Using a combination of thin section observations, XRD, TOC analysis, and EDS analyses, it characterizes the RC within the designated area. Moreover, the investigation employs LTNA experiments, MICP tests, and SEM to detail the PS attributes. Based on these experiments, the research analyzes the matching relationship between RC and PS in the shale oil reservoirs and the connection between microscale PS and macroscale physical properties, highlighting the control of physical properties by RC and PS. The findings reveal that pore types in these shale oil reservoirs predominantly consist of small pores and mesopores. Small pores, developed within K-feldspar, quartz, and clay minerals, are chiefly dissolution pores; mesopores occur between dolomite or plagioclase grains, characterized by a regular pore morphology. Porosity is governed by the presence of micropores, mesopores, and macropores, while permeability is principally influenced by mesopores and macropores. This established relationship between RC and PS in this study offers a reference for the efficient development of the P₂l shale oil reservoirs and can serve as a foundation for research into fluid-solid interaction and flow characteristics in porous media.

How to cite: Song, Z., Li, J., and Xiao, D.: Control of Physical Properties by the Matching between Rock Components and Pore Structure in Shale Oil Reservoirs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2429, https://doi.org/10.5194/egusphere-egu25-2429, 2025.

We constructed a thermo-viscoelasticity equation based on Lord-Shulman (LS) thermoelasticity with the Kelvin-Voigt (KV) model for viscoelasticity. The plane-wave analysis predicts two compressional waves and a shear wave. These two compressional waves are the fast-P and slow-P diffusion/wave (the T-wave), which have similar characteristics to the fast- and slow-P waves of poroelasticity, respectively. To overcome the nonphysical phenomenon of high-frequency P-waves in the thermo-viscoelastic (KV model), we established the thermo-viscoelasticity equation by combining LS thermoelasticity and the Zener and Cole-Cole model of viscoelasticity. Plane-wave analysis predicts two inflection points on the dispersion and attenuation curves; these are mainly affected by thermal diffusion and viscoelasticity. The dispersion curves of both types of P waves have two-level limit velocities of high frequency, and their attenuation curves also feature two attenuation peaks. Selecting appropriate parameters can cause the two-level limit velocities of high frequency and attenuation peaks to move or overlap. Finally, we consider the experiment data of P-wave velocity varying with frequency of two kinds of sandstone. Indeed, a Cole-Cole fractional model is needed to obtain a good match. These results are helpful for studying the physics of thermo-viscoelasticity and for testing experimental data and numerical algorithms for wave propagation.

How to cite: wang, Z., Fu, L., and jose, C.: The behaviour of wave propagation in linear thermo-viscoelastic media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2734, https://doi.org/10.5194/egusphere-egu25-2734, 2025.

The quality of the sandstone reservoir is critically influenced by the presence of clay coatings on the surfaces of quartz grains. These coatings play an essential role in determining porosity and permeability, key parameters that govern the storage and flow potential of sandstone reservoirs used for geothermal energy, groundwater, and hydrocarbons. This study employs a multiphase-field model, a versatile tool widely used in materials science, to simulate the complex interplay of interface motion and phase transitions within geological systems. By generating a detailed three-dimensional digital representation of sandstone, the model provides precise control over quartz grain coatings and composition, enabling a thorough investigation of their impact on reservoir properties. Two central aspects are explored: (1) the effect of varying clay coating coverage on quartz grains, and (2) the influence of coating distribution on the evolution of porosity and permeability during quartz precipitation. Computational fluid dynamics (CFD) simulations further quantify the changes in permeability at different stages of grain growth, revealing intricate relationships between the distribution of the coating, the properties of the rock, and the dynamics of fluid transport. The findings show that sandstones with a higher proportion of coated grains exhibit enhanced permeability due to the cement growth limiting effects of clay coatings on quartz grains. These insights provide a deeper understanding of the mechanisms that govern sandstone reservoir quality and offer practical implications for optimizing applications in geothermal energy, water resource management, and carbon and hydrogen storage.

How to cite: Kumar, A., Prajapati, N., Schneider, D., Busch, B., Hilgers, C., and Nestler, B.: Revealing the Hidden Dynamics of Clay-Coated Quartz Grains in Sandstone with Multiphase-Field Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3471, https://doi.org/10.5194/egusphere-egu25-3471, 2025.

Abstract

The rapid escalation of global warming, driven by anthropogenic carbon dioxide (CO₂) emissions, underscores the necessity of carbon capture and storage (CCS) technologies as a critical strategy for mitigating atmospheric CO₂ levels. Shale reservoirs, characterized by their extensive nanopore networks and heterogeneous pore structures, hold significant promise for CO₂ sequestration. This study investigates the storage and sequestration potential of shales from two distinct formations: the Lower Silurian Longmaxi Formation (TY1 group) and the Lower Cambrian Niutitang Formation (N206 group). A comprehensive suite of experiments, including XRD analysis, mercury intrusion porosimetry (MIP), low-pressure gas adsorption (N₂ and CO₂), field-emission scanning electron microscopy (FE-SEM), and mineralogical analysis, was employed to characterize pore structure, adsorption behaviour, and mineralogical controls on CO₂ storage. Moreover, a novel fractal parameter, succolarity along with conventional mass and surface fractal dimensions were used to depict the pore systems of the two groups.

Results reveal that the TY1 samples exhibit higher total organic carbon (TOC; up to 7.58%), greater microporosity, and stronger CO₂ adsorption energies (up to 34 kJ/mol) compared to the N206 samples, which display a more mesopore-dominated system and lower adsorption energies (28–30 kJ/mol). The Longmaxi Formation demonstrates superior pore connectivity and pore size distribution (PSD) homogeneity, enhancing both CO₂ retention and transport. Its higher carbonate content also suggests potential for mineral trapping through carbonation reactions. In contrast, the Niutitang Formation is characterized by higher total porosity (up to 2.4%) and mesoporous contributions, favouring rapid injection but limiting long-term retention. Meanwhile, the FE-SEM observations revealed that many authogenic minerals such as quartz, pyrite and rutile occupy the pore space in organic matters. It is much more prevalent in the N206 samples, which may be responsible for its lower microporosity.

Key findings include a strong correlation between TOC and micropore volume, as well as between clay minerals and mesopore-macropore attributes. These correlations highlight the dual role of organic matter and mineral content in determining gas adsorption capacity and flow dynamics. The TY1 group’s balanced micropore and mesopore contributions make it ideal for long-term CO₂ sequestration, while the N206 group’s larger pore sizes enhance its suitability for rapid injection and enhanced gas recovery (EGR) applications.

This study provides critical insights into the interplay of organic matter, mineral composition, and pore structure in controlling CO₂ storage potential in shale reservoirs. The findings emphasize the Longmaxi Formation's superior suitability for CO₂ storage and EGR, with implications for optimizing CCS strategies in similar shale systems globally.

How to cite: Bo, L., Bingsong, Y., Glover, P., Lorinczi, P., Kejian, W., and Panaitescu, C.: Comparative Analysis of CO₂ Sequestration Potential in Shale Reservoirs: Insights from the Longmaxi and Niutitang Formations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5004, https://doi.org/10.5194/egusphere-egu25-5004, 2025.

Domestic production of lithium is central to the UK’s industrial strategy. This will facilitate the energy transition and will be essential to safeguard lithium supply against geopolitical developments. To this end, two different styles of lithium extraction are being developed in Cornwall: (1) open-pit ‘hard-rock’ lithium mining at two locations in the St Austell Granite and (2) Li-enriched geothermal fluids produced through fracture-controlled fluid-rock interaction and flow. The latter resource is being evaluated for Direct Lithium Extraction (DLE) at multiple locations.

The work undertaken here will largely concern the geothermal lithium resource. In an early phase of research, the petrophysical properties of significant lithologies will be investigated, focusing on variation due to alteration around fractures. This will involve measuring the permeability, porosity, and electrokinetic properties (streaming potential and zeta potential) of core plugs; impedance spectrometry will also be carried out. Additionally, petrographic imaging, focused ion beam SEM imaging, and a combination of micro- and nano-CT scanning will be performed. Information gained in this phase of work will enhance interpretation of geophysical data and feed into prospectivity modelling. A subsequent phase of this research will, therefore, concern the analysis of pre-existing geophysical data, plus the acquisition and processing of new, pertinent geophysical measurements. Furthermore, petrophysical characterisation will permit modelling of the expected geophysical signatures of prospects of varying size, geometry, and potentially effective grade.

The formation and behaviour of the Cornish geothermal lithium resource will also be explored. Geochemical study will elucidate the chemical development of lithium-bearing groundwaters and may suggest the physicochemical consequences of water extraction at different rates. Self-potential signals will be used to recognise patterns of groundwater flow, feeding into a broader model of Cornish geothermal circulation.

Considering Cornwall as a case study, this work is expected to inform regional prospectivity for lithium-bearing geothermal brines; it could also enhance estimates of the geothermal energy potential of the region.

How to cite: Brabin, J. T., Glover, P. W. J., Torvela, T. M., Green, C. M., Shail, R. K., and Yeomans, C.: Developing methods for the location and characterisation of Li-bearing geothermal waters in Cornwall, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6979, https://doi.org/10.5194/egusphere-egu25-6979, 2025.

Effective stress is known to be a key factor affecting permeability measurements under geological conditions. As effective stress increases, the permeability of rock containing micro-fractures will decrease significantly. Based on laboratory measurement data, several scholars have come up with empirical equations to describe permeability changes with effective stress and found that there generally exists an exponential or power-law relationships. In this study, the experimental sample is a tight sandstone formation containing microfractures from Kuche Depression in Tarim Basin, China, where gas is produced from deep reservoirs of over 6000 m. Permeability was measured using the conventional pulse-decay method using an in-house true triaxial stress cell with maximum confining pressure of 120 MPa, pore pressure of 100 MPa and axial pressure of 250 MPa. The tight sandstone contains micro-fracture and an ambient porosity of 5%. Under the condition of high pore pressure (up to 80 MPa), the Knudsen number K_n＜0.01, and the gas slippage effect appears to have little impact on the permeability, characteristic in the Darcy flow state. As the confining pressure increases, the gas permeability decreases significantly, whereas as the pore pressure increases, the gas permeability increases. It has been shown that as the effective stress increases, the gas permeability decreases, and ln(K/K₀) shows an exponential relationship with (δ - δ₀) (subscript 0 represents the initial state). As the effective stress decreases, ln(K/K₀) shows a logarithmic relationship with (δ - δ₀). Under the condition of equal effective stress, ln(K/K₀) shows a linear relationship with pore pressure. In addition, we have also noticed a strong anisotropy in the permeability when differential axial stress was applied during the permeability measurement, reflecting a preferential distribution of microfractures in the tight sandstone measured.

How to cite: Yu, B., Liu, K., and Yu, L.: Experimental investigation of the relationship between permeability and effective stress for low-permeability sandstone with micro-fractures under high pressure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7924, https://doi.org/10.5194/egusphere-egu25-7924, 2025.

Lithium is a critical mineral in the fight against climate change:  it is used in electrical batteries for computing, in electric vehicles, and as local electrical storage for smoothing flow from intermittent sustainable power sources. According to the IEA, in 2023 lithium supply was mainly limited to China, Chile and Australia (85% for mining and 96% for refining), associating lithium supply with high geopolitical risk; a risk to which the UK and EU are exposed.

The UK has a world-class lithium resource in Cornwall, as mineable granite, but lithium is also dissolved in geothermal brines occupying fractures. These fluids have lithium concentrations at approximately 100 ppm (at 2000 m), but they also have order of magnitude lower levels of Na⁺, Mg²⁺ and Ca²⁺ compared with other brine deposits, which makes lithium extraction simpler. Furthermore, the geothermal nature of the brines may allow production plants to be powered by sustainable energy. The question remains, how much lithium-rich brine can be extracted? Here petrophysical fracture modelling can help.

This research reports on some of the modelling technology that can be used to understand lithium-rich brine flow during extraction. It is important to consider aspects of fracture connected volume and connectivity, and to find pragmatic quantitative methods for assessing and reporting such data. Fracture connectivity depends on the number of nodes where fractures interact, and the distance between nodes. Studies of these have been found to be fractal. If that is the case in Cornwall, it implies that aspects of the fracture network at different scales can be fractally extrapolated from measurements made at smaller or larger scales. Connected fracture volume is controlled by fracture length and aperture. These are also fractally distributed. Consequently, a reasonably reliable multiscale 3D model can be constructed in Fracman or FracpaQ.

The aperture, and to some extent the fracture length, changes as the stress regime changes. For example, significant brine drawdown could reduce the flow rate because  external stress acts to close fractures when the fracture fluid pressure is reduced, and hence also reduce connectivity. By contrast, a significant injection of brine from which lithium and heat has been extracted would have the opposite effect. Quantification of this can be carried out using electrical methods as well as non-invasive 3D imaging (CT or micro-CT). Consequently, it is important for the fracture model to be responsive to the changing stresses in the model that might result from different stress tensors and production scenarios.

Finally, geothermal brine flow is also controlled by the roughness of fracture surfaces, especially as fractures close during drawdown. The interacting asperities on the surfaces increase the tortuosity of fluid flow significantly, but they also prop fractures open when they would otherwise close. The fracture surfaces are also fractal, and this work shows both models of fractal fracture surfaces and the fluid flow through them. Examples are given which show that uncompressed fractal fracture surfaces with a fractal dimension of 2.349 can reduce fluid flow, in our scenario by 28%.

How to cite: Glover, P., Brabin, J., Torvela, T., and Yeomans, C.: Fracture Modelling and Geothermal Lithium, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9935, https://doi.org/10.5194/egusphere-egu25-9935, 2025.

Hydrate-based CO₂ sequestration in marine gas hydrate reservoirs is a promising dual-purpose strategy for carbon storage and energy recovery. However, geomechanical stability remains a critical challenge for ensuring safe geo-engineering operations, as it directly influences risks such as wellbore destabilization, subsea subsidence, and submarine landslides. Despite significant advancements, a systematic understanding of the geomechanical responses of marine hydrate reservoirs under CO₂ injection is still lacking. This study provides a comprehensive review of the formation stability associated with hydrate-based CO₂ sequestration, adopting a cross-scale and multi-method perspective. Three distinct storage strategies are discussed: (1) CO₂ sequestration above the hydrate zone, forming an artificial hydrate cap; (2) sequestration within the hydrate zone through immediate CH₄-CO₂ exchange; and (3) sequestration within the hydrate zone via later-stage replacement, producing mix-hydrates. We further evaluate experimental, numerical, and molecular-scale studies that investigate the geomechanical behavior of hydrate reservoirs across these scenarios. Key findings reveal several unresolved issues, including the debated mechanical superiority of CO₂ hydrates compared to methane hydrates and the absence of quantitative relationships linking hydrate saturation to reservoir mechanical performance. Additionally, commercial viability remains a significant hurdle, with integrated approaches such as the co-production of gas hydrates, shallow gas, and deep gas proposed as potential solutions. This review highlights critical knowledge gaps and identifies future research directions to advance hydrate-based CO₂ sequestration. By addressing these challenges, this work aims to support the safe and sustainable implementation of this emerging carbon storage technology.

How to cite: Zhang, Q., Song, Z., Chen, D., and Zi, M.: Is CO2 Sequestration in Marine Hydrate Reservoirs Geomechanically Stable? , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10606, https://doi.org/10.5194/egusphere-egu25-10606, 2025.

Digital rock models are becoming increasingly important in addressing the challenges of transitioning to sustainable energy. While traditionally employed to model fundamental petrophysical and geomechanical processes, their utility is expanding into critical applications such as carbon capture and storage (CCS), geothermal energy development, and subsurface energy storage. By using advanced imaging, simulation, and multi-scale analysis techniques, digital rock models provide a detailed understanding of pore-scale properties and their implications for fluid flow, geomechanics, and geochemistry. These insights are essential for optimizing low-carbon energy systems and ensuring reservoir integrity during energy storage and CO₂ sequestration. This work highlights some of the recent advancements in digital rock technologies and their contributions to innovative solutions in sustainable energy development.

Estimating the physical properties of rocks, a crucial and time-consuming process in the characterization of geothermal reservoirs, CCUS, and other renewable energy resources, has seen a shift from traditional laboratory experiments to the increasing use of digital rock physics. A key requirement of many forms of pore structure image analysis is that they require binary images to distinguish pore-space from non-pore-space (mineral phases). These are often obtained by thresholding grayscale SEM or X-ray tomographic images. In this study, we present the collection and processing of exceptionally high-quality two-dimensional images of carbonate rocks, with a resolution of 16-bit density and dimensions of 29056 × 22952 pixels. This dataset, subdivided into 155 smaller images of 2048 × 2048 pixels each, was further enhanced using data augmentation techniques such as rotation and reflection, creating a diverse and non-redundant set of training images.

The objective of this work is to train a machine-learning model capable of predicting porosity directly from the images. A convolutional neural network (CNN) was developed and modified for this purpose, using 60% of the dataset for training. The training process involves pre-labeled images, which are used to optimize the weights of the neural network. So far, the CNN has achieved an accuracy of 89.55% in predicting porosity during the training phase. Validation and testing datasets were employed to evaluate and refine the model’s performance, with ongoing efforts aimed at surpassing 95% accuracy in testing. Furthermore, we are working on analyzing the relational characteristics of porosity to expand the applicability of this approach. Initial work in 2D and 3D that has the power to discriminate between mineral phase, between connected and unconnected porosity, and to quantify the pore fluid-mineral surface area, are also in progress. This latter property is extremely relevant to CCS targets where the area for CO2 adsorption is an important parameter which is difficult to assess.

This research not only enhances our ability to quantify key petrophysical properties but also contributes to the development of sustainable energy technologies. The work has significant potential to enhance geothermal resource evaluation and advancing carbon capture and storage (CCS) initiatives, playing a critical role in the transition to low-carbon energy solutions.

How to cite: Alwan, W., Glover, P., and Collier, R.: Quantification of the microstructural properties of CCS and radioactive waste target rocks using Convolutional Neural Networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11103, https://doi.org/10.5194/egusphere-egu25-11103, 2025.

Feldspars are a common framework grain in sandstone reservoirs targeted for carbon capture and storage (CCS). They are mechanically weak under reservoir conditions and are very likely to react with CO₂ injected into saline aquifers or depleted hydrocarbon reservoirs.  Reactions could dissolve feldspar and precipitate new minerals to an extent that fundamentally changes reservoir properties and potentially mineralises injected CO₂. The current general consensus is that these features are unlikely to impact fluid migration during the injection lifespan of any CCS project. However, the response of feldspars to saturation with aggressive CO₂-enriched fluids under stressed reservoir conditions is poorly understood.

In this contribution, the magnitude of any “feldspar effect” is re-evaluated using sandstone samples obtained from the Lower Cretaceous Captain Sandstone in the Central North Sea, which is the target reservoir for CO₂ injection in the Acorn Project (UK). 

Firstly, using petrography, SEM analysis and Pb isotopic compositions of detrital feldspars, sediment provenance and subsequent diagenesis are shown to be significant drivers on feldspar composition and texture prior to injection. This is important because it is already understood that different feldspars react with CO₂-rich fluids at different rates: thus any feldspar effect could significantly vary within a reservoir with mixed provenance and burial history on a sub-basin scale. Secondly, we conducted a suite of novel reaction experiments conducted using a triaxial ‘Nimonic’ deformation rig to investigate chemical dissolution in sandstone core plugs saturated with both CO₂-enriched fluids and water under subsurface conditions. Experiments were run at CCS reservoir pressures (70MPa confining pressure, 50MPa pore fluid pressure) and a range of temperatures (80°C – 550°C) to accelerate reaction rates and promote geological reactions in a short timescale. Microstructural and elemental analysis of post-mortem experimental samples showed enhanced fracturing and dissolution of certain feldspars along with precipitation of secondary minerals, whereas other feldspars were apparently unaffected. Experiments performed above 400°C showed replacement and dissolution of K-feldspar grains with Ca-rich plagioclase and K-bearing clays.

The outcome of our re-evaluation is that the impact of feldspars in CCS reservoirs has likely been overlooked, but until further experimental work is carried out to constrain how quickly feldspar interactions will impact fluid flow within the reservoir, uncertainties will remain with regard to their impact on CO₂ injectivity and storage capacity.

How to cite: Farrell, N., Yang, L., Flowerdew, M., Badenszki, E., Mark, C., Ardo, B., Taylor, K., Waters, J., Hughes, L., and Paul, L.: Experimental and microstructural analysis of feldspar solubility in CCS reservoirs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11208, https://doi.org/10.5194/egusphere-egu25-11208, 2025.

Though the energy transition aims to phase out fossil fuels while continuing to exploit the subsurface for other storage solutions (e.g. geological CO₂ storage, temporary hydrogen storage), natural gas, as a low-carbon energy carrier, will continue to play a role in our energy mix for the foreseeable future. In general, human activities in the subsurface change the physical and chemical environment, which in turn can lead to surface subsidence and induced seismicity. These phenomena may continue even after activities have stopped, as observed for natural gas extraction from the giant Groningen Gas Field in the Netherlands. They are largely caused by deformation in the reservoir rock, driven by fluid pressure changes. However, in-situ strain measurements from the Groningen Gas Field demonstrate that the clay-rich over- and underburden formations of the reservoir are also affected by these fluid pressure changes, displaying slow compaction. To make accurate predictions of reservoir deformation and to allow reliable assessment of the associated surface subsidence and induced seismicity, a detailed understanding of the deformation processes controlling deformation in these clay-rich formations is needed. Understanding which processes caused deformation in past (hydrocarbon) operations will help in understanding what may happen now that we plan to store other fluids in the subsurface.

We performed rock mechanical experiments at in-situ conditions on the Opalinus Claystone (Switzerland), an analogue to the Groningen over- and underburden claystones, to assess the grain-scale mechanisms responsible for deformation. We designed an innovative and comprehensive multi-step experimental procedure that provides new, coherent data on the time-dependent deformation of clay-rich rocks. The experiments were performed in a triaxial compression apparatus, applying systematic steps of constant stress while controlling the pore fluid pressure in the sample. These steps were either stepped up or down in differential stress during an experiment. At each differential stress we systematically analyzed the instantaneous and time-dependent deformation.

We observed general compaction of the samples upon increasing stress, and time-dependent expansion of the sample when stepping down in stress. Our results demonstrate that deformation in clay-rich rocks is strongly affected by the fluid-transport properties of the rock. We infer that sorption of fluids to the clay-rich matrix plays an important role in the deformation of clay-rich rocks, along with frictional slip controlling grain rearrangement. However, matters are complicated by slow diffusion of pore fluid pressure, which leads to an additional time-dependent component. Overall, our results demonstrate that over half of the observed deformation is permanent, even at low differential stresses. A detailed understanding of the time-dependent deformation of clay-rich rocks is crucial for accurate predictions of the impact of human activities in the subsurface, as sorption of fluid to the clay material may also be important during CO₂ and hydrogen storage.

How to cite: Sep, M., Hangx, S., and de Bresser, H.: Time-dependent deformation of clay-rich rocks enveloping reservoirs exploited for geo-energy purposes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11807, https://doi.org/10.5194/egusphere-egu25-11807, 2025.

Seismoelectric (SE) methods are potentially interesting for subsurface characterization by exploiting the coupling between seismic waves and electromagnetic fields in fluid-saturated porous media. While traditional SE techniques have primarily focused on body-wave-induced signals, recent research has highlighted the significant advantages of surface wave-induced SE signals, including enhanced amplitudes and increased sensitivity to near-surface heterogeneities. These characteristics make surface wave-induced SE signals particularly valuable for detailed subsurface investigations.

We conducted controlled laboratory experiments using a water-saturated sandstone sample (19.7% porosity, 310 mD permeability) and a planar acoustic source to generate surface waves at a water-sandstone interface. SE signal variations were systematically measured as a function of receiver distance from the interface, and array-based measurements were performed to analyze the velocity and characteristics of the induced SE surface waves. High signal-to-noise ratio SE surface waves were successfully measured across multiple excitation frequencies (100 kHz, 200 kHz, 300 kHz, 400 kHz, and 500 kHz), demonstrating the robustness of the phenomenon across a broad frequency range.

Our results show that SE signals were only observed in the presence of the porous medium, confirming that they originate from the fluid-porous interface. The SE signal amplitude decayed rapidly with increasing distance from the surface, which is consistent with surface wave behavior. Notably, the SE waveforms exhibited propagation velocities matching those of acoustic surface waves. They showed significantly shorter durations and different frequency content than the corresponding acoustic signals, indicating potential for enhanced spatial resolution in subsurface imaging. Ongoing work focuses on extracting the dispersion and attenuation characteristics of the measured SE surface waves across different frequencies. These findings will provide a foundation for more effective geophysical workflows, particularly in scenarios requiring detailed near-surface characterization.

How to cite: Liu, Y. and Smeulders, D.: Acoustically Induced Seismoelectric Surface Waves at a Fluid-Saturated Sandstone Interface: Multi-Frequency Experimental Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13204, https://doi.org/10.5194/egusphere-egu25-13204, 2025.

This study integrates 3-D seismic reflection and petrophysical data to investigate the Lopingian bedded salt formations of the Delaware Basin, part of the Greater Permian Basin in the United States. Focusing on the Castile and Salado Formations, the analysis identifies a zone of thickened and deformed strata associated with an intra-salt fold-thrust belt in the southwestern portion of the seismic volume. Adjacent to this fold-thrust belt lies a geophysically distinct region termed the buffer zone.

Petrophysical analysis of the Castile Formation within the buffer zone reveals a unique composition, deviating from the expected cyclical anhydrite-halite members. Instead, this zone consists exclusively of anhydrite. This compositional anomaly challenges previous interpretations that halite absence results from dissolution, suggesting instead that gypsum deposition followed by conversion to anhydrite may have occurred.

The overlying Salado Formation displays significant heterogeneity and karst features, highlighting potential geohazards and complexities for underground energy storage. These findings emphasize the necessity of combining geophysical and petrophysical approaches to accurately characterize subsurface conditions, assess risks, and optimize the placement of salt caverns for energy storage applications.

How to cite: Schuba, N., Moscardelli, L., Dooley, T., Martinez-Doñate, A., and Melani, L.: Geophysical and Petrophysical Insights into Bedded Salt Formations: Implications for Underground Energy Storage in the Delaware Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14303, https://doi.org/10.5194/egusphere-egu25-14303, 2025.

Pore structure is a critical factor in evaluating the quality of a reservoir or cap layer, influencing storage capacity, fluid flow efficiency, and reaction rates. Standard approaches, including Mercury Intrusion Porosimetry (MIP), Gas Pycnometry, and Brunauer-Emmett-Teller (BET) analysis, provide essential information; they are limited in their ability to capture pore connectivity and pathway complexity. X-ray Computed Tomography (CT) provides a distinct perspective, enabling three dimensional visualization of pore structures and insights into pore connectivity within 3D images. Accurate porosity analysis using CT, however, depends on careful evaluation of the segmentation process, especially the selection of thresholding methods, which can introduce biases and impact the reliability of the results. To address these challenges, this study introduces a new workflow leveraging grey-level terrain parameters from CT images as a reference index. Interbedded samples of muddy sandstone and siltstone are analyzed, with CT-derived porosity compared to experimental results obtained from an AccuPyc Helium Pycnometer. This comparison assesses the reliability and accuracy of the data-driven approach. By reducing uncertainties associated with porosity thresholding, the proposed workflow aims to establish a robust framework for CT-based pore structure analysis. It highlights the ability of CT imaging to deliver detailed 3D pore analysis, thereby supporting improved predictions of reservoir properties and resource management.

How to cite: Liu, Y.-M., Kioka, A., and Huang, J.-J. S.: Data Driven Porosity Measurement for Non-homogeneous Sandstone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15144, https://doi.org/10.5194/egusphere-egu25-15144, 2025.

Carbon Capture and Underground Storage (CCUS) is not simply the reverse of the hydrocarbon extraction process. The injection of supercritical CO₂ involves different flow regimes (viscous, slip, Knudsen, and molecular diffusion) and the adsorption of CO₂ to mineral surfaces. Small pressure differences control the distribution of the gas and gravity controls the overall gas distribution. Under these circumstances reservoir heterogeneity strongly controls where the CO₂ goes. Consequently, it is important to have a quantitative description of this heterogeneity. Leeds University Petrophysics Group has been working on using fractals to describe heterogeneity and anisotropy of reservoirs at all scales for the past decade and to develop fractal reservoir models that account for flow at scales smaller than the seismic resolution. In this presentation we show how the fractal dimension of a bounded dataset can be measured, and the main influences on the accuracy of the measurement, taking account of the systematic uncertainties imposed by the finite boundary conditions, scale-dependent effects, and multifractal behaviour.

The approach has been used to carry out digital ‘logging’ of several reservoirs including the Chandon field (Offshore NW Australia) and is currently being implemented for the CCUS testbed Sleipner reservoir (UK North Sea). This logging differs from wireline logging in that it is carried out over an predefined area or seismic data as a function of depth. For the Chandon field, depth-averaged measurements have produced a fractal dimension of 2.15±0.18 (arithmetic mean±standard deviation) over the entire scale range. It is recognised that the fractal dimension of this reservoir is multifractal, with a fractal dimension of 2.06±0.19 in the 70-150 m scale range and 2.62±0.07 in the 200-400 m scale range. Hence, the reservoir is more heterogeneous at the larger scale. This work also has the advantage of providing a fractal dimension value as a function of depth. Our results show in each case that the fractal dimension varies significantly with depth and is dependent on lithofacies. The fractal dimension at both scales picks out apparent lithofacies, with the coarsening-up sequence in the top part of the reservoir (1950-2020 m, all depths TVDSS) associated with a decrease in fractal dimension, shalier units (2020-2035 m and 2080-2125 m) exhibiting high fractal dimensions, and cleaner units (2035-2080 m) showing much lower fractal dimensions. This is good evidence that this new Seismic Fractal Heterogeneity Log (SFHL) represents a measure of rock heterogeneity to horizontal flow at each depth. Work is ongoing concerning the discrimination of different fractal dimensions as a function of azimuth as well as vertically, which is especially important in reservoirs used in CCUS applications.

It is hoped that the new SFHL can provide the sought after quantitative measure of heterogeneity for use in quantifying and modelling CO₂ injection into CCUS reservoirs. The real advantage of this approach is that it can be applied to existing 3D and 4D seismic datasets in order to extract from them extra information and extra value. Future work will be aimed at developing the approach further.

How to cite: Yaghoobpour, M., Glover, P., and Lorinczi, P.:  Measuring the Fractal Dimensions of Reservoirs: A New Seismic Fractal Heterogeneity Log for Application to CCUS Prospects, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20882, https://doi.org/10.5194/egusphere-egu25-20882, 2025.

Tight sandstone reservoirs are a primary focus of research on the geological exploration of petroleum. However, many reservoir classification criteria are of limited applicability due to the inherent strong heterogeneity and complex micropore structure of tight sandstone reservoirs. This investigation focused on the Chang 8 tight reservoir situated in the Jiyuan region of the Ordos Basin. High-pressure mercury intrusion experiments, casting thin sections, and scanning electron microscopy experiments were conducted. Image recognition technology was used to extract the pore shape parameters of each sample. Based on the above, through grey relational analysis (GRA), analytic hierarchy process (AHP), entropy weight method (EWM) and comprehensive weight method, the relationship index Q1 between initial productivity and high pressure mercury injection parameters and the relationship index Q2 between initial productivity and pore shape parameters are obtained by fitting.Then a dual-coupled comprehensive quantitative classification prediction model for tight sandstone reservoirs was developed based on pore structure and shape parameters. A quantitative classification study was conducted on the target reservoir, analyzing the correlation between reservoir quality and pore structure and shape parameters, leading to the proposal of favourable exploration areas.The research results showed that when Q1 ≥ 0.5 and Q2 ≥ 0.5, the reservoir was classified as type I. When Q1 > 0.7 and Q2 > 0.57, it was classified as type I₁, indicating a high-yield reservoir. When 0.32 < Q1 < 0.47 and 0.44 < Q2 < 0.56, was classified as type II. When 0.1 < Q1 < 0.32 and 0.3 < Q2 < 0.44, it was classified as type III. Type I reservoirs exhibit a zigzag pattern in the northwest part of the study area. Thus, the northwest should be prioritized in actual exploration and development. Additionally, the initial productivity of tight sandstone reservoirs showed a positive correlation with the porosity, permeability, sorting coefficient, coefficient of variation, and median radius. Conversely, it demonstrated a negative correlation with the median pressure and displacement pressure. The perimeters of pores, their circularity, and the length of the major axis showed a positive correlation with the porosity, permeability, sorting coefficient, coefficient of variation, and median radius. On the other hand, they exhibited a negative correlation with the median pressure and displacement pressure. This study quantitatively constructed a new classification and evaluation system for tight sandstone reservoirs from the perspective of microscopic pore structure, achieving an overall model accuracy of 93.3%. This model effectively predicts and evaluates tight sandstone reservoirs. It provides new guidance for identifying favorable areas in the study region and other tight sandstone reservoirs.

How to cite: Song, X., Feng, C., Li, T., Zhang, Q., Pan, X., Sun, M., and Ge, Y.: Quantitative classification evaluation model for tight sandstone reservoirs based on machine learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-122, https://doi.org/10.5194/egusphere-egu25-122, 2025.

The time dependent Vp/Vs ratio (Scholz et al., 1973), preslip (Dieterich, 1978), and cascade models (Ellsworth and Beroza, 1995) are popular geophysical models used as earthquake precursors. Such geophysical models have generally focused on the physics of earthquake source regions (Yamashita et al., 2021). However, the physical properties of the off-fault region are also related to earthquake mechanics (Gudmundsson, 2004), which are strongly affected by the presence of fractures (Jayawickrama et al., 2024). While the presence of fractures affects the physical properties of rocks, inarguably, they alter the transport properties as well. In this investigation, it is speculated that such changes in the transport properties coupled with the seismic velocity in the off-fault regions could be used to develop an earthquake precursor model. To this end, cyclic deformation experiments were conducted on thermally cracked (at 800^oC) Aji granite, in analogy to damage, while simultaneously measuring the water permeability and the seismic velocity. However, unlike the conventional cyclic experiments, a stationary time was employed between each cycle (loaded to 0.6C, 0.7C, 0.8C, and 0.9C) around 0.1C (C: peak stress), in analogy to a stress relaxation period before the stress accumulation for the next event. With the initial stress build up, the seismic velocity increases while the permeability drops until the onset of dilation, where the trend is reversed from there onwards. Once the axial stress is released gradually, followed by an initial increase, the permeability becomes relatively stable, while the seismic velocity continues to drop. During the stationary period, a noticeable compaction was observed along with a seismic velocity increase and a permeability drop. Hence, indicated an overall healing in the damaged sample, under relaxed stress conditions. The dynamic crack density evolution also provides critical evidence for this. Moreover, with each cycle, the magnitude of velocity increment and the permeability drop becomes lower. Subsequent to the healing process as the stress builds up, the seismic velocity and the permeability follow a similar trend to the previous cycle. Hence the repeated compaction and dilation that the sample suffers with stress cycles is reflected by the seismic velocity and the permeability evolution. As such, the current investigation has proven the possibility of utilizing the evolution of permeability coupled with seismic velocity in the off-fault regions as a possible precursor to earthquakes.

How to cite: Jayawickrama, E. and Katayama, I.: Permeability and seismic velocity evolution of thermally cracked Aji granite during cyclic loading, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-804, https://doi.org/10.5194/egusphere-egu25-804, 2025.

Heterogeneities control rock properties, especially hydraulic, reactivity, and geophysical properties. Complex systems typically include multiple porosities at embedded scales, from the micro/meso cracks and pores to geological macro-fractures and karsts. This complex network plays interdependent roles and introduces difficulties in the characterization of the whole formation, especially with difficulties extrapolating laboratory interpretation to field investigation. A general and comprehensive workflow of the upscaling processes needs to be developed.

Our study focuses on the platform “Observatoire des transferts dans la Zone Non-Saturée” (O-ZNS, Orléans, France), an artificial excavation in the karstified and fractured limestone formation of Beauce aquifer. The observatory is composed of an exceptional well (20 m-depth, 4 m-diameter) surrounded by 8 cored boreholes. During the development of this platform, we excavated metric heterogeneous blocks to investigate different properties at an intermediate scale between laboratory and field. Our aim is to characterize these samples thanks to direct (micro)structure observation and quantification compared to petrophysical property measurements (transport and acoustic properties) to define their representative elementary volume (REV). The though protocol is a repetitive process including series of 3D scans and petrophysical measurements followed by cutting blocks in smaller and smaller parts. In complement, 3D scans made from photogrammetric reconstruction of the blocks provides digital models at various scales that help us in locating the geophysical heterogeneities with respect to the observed geological features at various scales.

For the biggest blocks, the carrying out of this protocol is challenging and tremendous. The key methodologies still need to be confronted to discussion.

We started the investigation on some intermediate blocks (around 30 to 50 cm-size). We highlight the possibility of measuring acoustic at different frequencies even on the rough surface of the block. Permeability can be obtained with air-measurements using a tiny-perm apparatus. Porosity is more challenging. As a first approximation, we estimate it assuming a certain grain density, and by measuring its dry weight and volume. Finally, 3D scans allow us to describe the embedded structure of the block, and to count and measure pores and cracks sizes. The first series of results are coherent, and we will be able to go a step-down and tentatively obtain the REV for all these properties. The final objective would be to define the link between the REV of the different explored properties, considering the heterogeneities.

How to cite: Mallet, C., Laurent, G., and Azaroual, M.: Petrophysical characterization of multi-scale heterogeneities of a vadose zone within continental limestone formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1285, https://doi.org/10.5194/egusphere-egu25-1285, 2025.

Traditionally, resistivity well logs have been used to determine water saturation (Sw) in oil and gas reservoirs based on Archie's Law. However, the intricate pore structure of tight carbonates poses challenges, as their electric conductivity does not adhere to this law, thereby complicating the assessment of water/gas saturation in gas reservoirs. To address this, the study analyzed SEM images of carbonate samples to understand the pore structures. Utilizing the Slice-Gans model, 3D digital cores were constructed and resistivity was simulated.

The findings reveal that as porosity increases, the cementation exponent m in Archie's formula also increases. Theoretical derivations indicate that this is primarily due to changes in the PTRR as porosity varies. Dolomite and calcite are the primary minerals in the carbonates studied, and the PTRR differs between dolomite and calcite pores. Consequently, the m value varies depending on the mineral composition. By applying a parallel conductive model, the m value for cores with different dolomite and calcite volume fractions can be calculated.

Additionally, the study analyzed rock resistivity experiment results and found that the saturation exponent n's value also varies with porosity, with a fitted relationship established. This enabled the creation of a final variable m and n model. When applied to practical logging data, the calculated Sw values were found to be consistent with the bounded water saturation obtained from nuclear magnetic resonance (NMR) experiments in gas layers, validating the accuracy of the new model.

How to cite: Nie, X., Sun, C., Yang, S., Zhou, Y., Liu, S., and Mei, Q.: A novel water saturation well logging evaluation model for tight carbonate gas reservoir based on pore-throat radius ratio from SEM images, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1565, https://doi.org/10.5194/egusphere-egu25-1565, 2025.

The mechanical properties and elastic anisotropy of shale oil reservoirs are influenced by factors such as lithology, pore structures, and fluids. Studying the dynamic and static elastic properties is crucial for predicting geological and engineering “sweet spots” in these reservoirs. While there has been extensive research on the static properties of shale, dynamic multi-frequency elastic anisotropy remains under-explored. This study investigates the anisotropic dispersion mechanism of favorable lithofacies (lamellar dolomitic shale with vertical and horizontal bedding) in the inter-salt shale oil reservoir of the Qianjiang Formation, by using multi-frequency measurement techniques including low-frequency stress-strain and high-frequency ultrasonic tests. Key findings include: 1) Terrestrial shale exhibited stronger elastic property dispersion than marine shale, attributed to high viscosity medium oil. Lamellar structures and interbedded fractures significantly contributed to this anisotropy; 2) Elastic property dispersion in partially oil-saturated states decreased from strong to weak with increasing frequency, likely driven by wave-induced fluid flow or intrinsic dissipation; 3) Elastic parameters measured perpendicular to bedding showed greater dispersion and pressure sensitivity than those measured parallel, with higher anisotropy and sensitivity at seismic frequencies; 4) Fluid saturation reduced pressure sensitivity of elastic parameters in the vertical direction while increasing it in the parallel direction; 5) Anisotropic Gassmann theory effectively explained P-wave velocity at low frequencies, though predictions for S- and P-wave velocities at higher frequencies were less accurate. This study provides a solid reference for understanding frequency-dependent properties of azimuthal anisotropy and offers valuable insights for seismic prediction of “sweet spots” in shale oil reservoirs.

How to cite: Zhao, J.: Experimental Studies on Anisotropic Dispersion of inter-salt Shale Oil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3795, https://doi.org/10.5194/egusphere-egu25-3795, 2025.

The EU-funded project GeoHEAT aims to develop new time- and cost-efficient methods for geothermal exploration. One part will be a georadar probe that can be used to characterize geological structures at elevated ambient temperatures. As the permittivity of the surrounding rock mass is of great importance for the optimal use of this probe, we are investigating the possibility of estimating this dielectric property using digital rock physics (DRP) and drill cuttings. With the latter being a by-product of exploration drilling, they represent a further potential approach at saving both time and costs, without the added expense of core sampling. Here we want to present the current state of our research and give an overview of preliminary insights and future challenges.

In order to determine the effective permittivity using DRP, a pore scale model is required. For this purpose, nano-computed tomography images are created and then segmented, whereby different phases are assigned to the gray value intensities of the scanned sample. The model is finalized by attributing physical properties to individual material particles in the location-dependent volume and is subsequently used to compute the effective permittivity with a solver utilizing the finite volume method. To optimize this process, standardized granite core samples from the Bedretto Lab in Switzerland are used, and the results are validated by comparing them to laboratory measurements of the same rock type for accuracy.

Since the extraction of these kinds of samples is expensive, requires interruption of drilling and can only be carried out for limited boreholes and depth sections, the next step is to investigate the use of cuttings, which are generally produced during drilling and transported to the surface with the drilling mud. We analyze to what extent the precision of the obtained results is affected by this more economic approach.

The analysis of core samples has yielded promising results, demonstrating a high level of accuracy in estimating effective permittivity values using DRP. In addition, ongoing investigations into the use of rock cuttings as a substitute have shown great potential for significantly reducing cost and time, while maintaining reliability of the determined rock property. These advances could improve the practical application of georadar probes, offer a more efficient approach to geothermal exploration and provide deeper insights into the geology of the subsurface.

How to cite: Kerkmann, N., Siegert, M., Kouamo Keutchafo, N.-A., and Saenger, E. H.: Estimating Effective Permittivity using Digital Rock Physics and Drill Cuttings – Preliminary Insights and Future Challenges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6497, https://doi.org/10.5194/egusphere-egu25-6497, 2025.

The complex pore structure and diverse mineralogy of shale impart specific elastic properties to the saturated rock, characterized by notable heterogeneity and pronounced frequency dependence. These intricate elastic behaviors of shale present challenges to conventional rock physics-based quantitative interpretation of reservoirs. This study employed an integrated approach combining cross-band rock physics measurement, digital rock imaging, and numerical simulations. The research focused on the inter-salt shale oil reservoir of the Qianjiang Formation (Jianghan Basin, China), to investigate anisotropy and dispersion phenomena. Initially, various scanning imaging techniques were applied to analyze the microstructural features of natural rocks, leading to the creation of a set of virtual cores by numerical reconstruction. Subsequently, static and dynamic elastic simulations were performed to monitor wave-induced fluid flow, revealing the influence of microstructure, mineral composition, and physical properties on dispersion and attenuation. Finally, based on the simulations, the applicability of various rock physical theories was evaluated, and we proposed a set of anisotropic dispersion theory models consistent with the geological characteristics and elastic response rules of shale oil reservoirs. The results compare satisfactorily with ultrasonic velocity, well-logging data, and stress-strain measurements. This approach underscores the value of integrative research, combining experimental data, theoretical models, and digital rock physics techniques, offering new insights into the refinement of quantitative reservoir characterization in complex geological environments.

How to cite: Yan, B., Zhao, J., Li, J., Ma, M., Sun, Y., Xiao, Z., Lu, C., Luo, X., Ma, J., and Sun, L.: Application of digital rock characterization and elastic simulation to rock physics modelling in shale reservoirs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7669, https://doi.org/10.5194/egusphere-egu25-7669, 2025.

Velocity dispersion and attenuation frequently occur in fluid-saturated reservoir rocks. However, most current reservoir prediction and fluid identification methods overlook the effects of seismic wave dispersion and attenuation. Instead, researchers primarily rely on frequency-independent elastic data and theoretical models. Frequency-dependent elastic parameters, in contrast, reveal more detailed information about reservoir fluids and significantly enhance the accuracy of fluid identification and reservoir prediction.Rock physics experiments and theoretical analyses have shown that rocks saturated with different fluids exhibit distinct velocity dispersion gradients. This finding underscores the potential of the velocity dispersion gradient as a reliable indicator for identifying target reservoirs. To extract the velocity dispersion gradient attribute, this study incorporates a frequency term into the Zoeppritz approximation and develops a frequency-dependent AVO  inversion equation. The study applies time-frequency analysis to seismic data, deriving the time-frequency spectrum. By integrating the time-frequency spectrum with the frequency-dependent AVO inversion equation, the method extracts the velocity dispersion gradient attribute.The study further analyzes how various factors influence the accuracy of dispersion gradient attribute inversion, using theoretical models and seismic physical analyses. It validates the reliability of the dispersion gradient inversion method and demonstrates its effectiveness in delineating reservoirs and identifying fluids.This research provides a robust approach for improving the precision of reservoir prediction and advancing fluid identification techniques.

How to cite: Zhang, Y., Ouyang, F., Qing, Y., Zhao, J., Li, Z., Ma, M., Yan, B., and Sun, Y.: Fluid identification and reservoir prediction based on frequency-dependent AVO inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7721, https://doi.org/10.5194/egusphere-egu25-7721, 2025.

The dolomite reservoir in the fourth member (Ma4) of the Ordovician Majiagou Formation is a significant gas reservoir in the Ordos Basin, China. It consists of thin layers within limestone, characterized by a mottled dolomitic limestone texture, with pores formed by complex diagenetic processes that result in low porosity values. These layers show minimal petrophysical contrast with the surrounding rock, complicating identification and property prediction using conventional elastic attributes like P- and S-impedances. To overcome this challenge, the study utilizes Lamé impedances (λρ and μρ), which expand the P- and S-impedance cross-plot space, enhancing the identification of reservoir zones. First, Lambda-rho and Mu-rho impedances were derived from logging data and cross-plotted to create a locally constrained rock physics template based on porosity and dolomite content along the vertical direction. This template was then applied to the Lambda-rho and Mu-rho attributes generated from seismic pre-stack inversion. The rock physics template (λμρ cross-plot) accurately predicted dolomite content and porosity from seismic data, achieving high precision compared to the conventional porosity and dolomite content logs. This study highlights the effectiveness of Lamé parameters (λμρ) in predicting and estimating reservoir property distributions, providing valuable insights into the geological origins of dolomite and advancing hydrocarbon exploration and development.

How to cite: Said, A., Zhao, J., Li, J., and Sun, Y.: Utilization of magic Lamé impedances on carbonate reservoirs' lithological and porosity characterization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7725, https://doi.org/10.5194/egusphere-egu25-7725, 2025.

Water is ubiquitous in crustal rocks and has been independently shown to increase and decrease rock elasticity via adsorption-induced weakening and saturation-related stiffening. Yet, the interplay of how weakening and stiffening effects concurrently control the rock elasticity remains unclear. Here, we examine the acousto-mechanical behavior of a free-standing sandstone subjected to gradual water infiltration with a downward-moving wetting front over 7 days. Using time-lapse ultrasonic and digital imaging techniques, we observe elastic weakening ahead of the wetting front, which is explained by an analytical model linking P-wave velocity decrease, adsorption-induced expansion and surface energy decrease established at the grain scale. As the wetting front moves through the probed region, the weakening effect diminishes, and P-wave velocity begins to increase, consistent with findings in granite. This shift is attributed to saturation-related stiffening, supported by an analytical model of partial water saturation. A numerical model simulating the profile of water saturation and vapor further validates these observations. Our research sheds light on a key question in rock deformation: how weakening and stiffening effects jointly control rock deformation during progressive wetting.

How to cite: Gao, F., Kang, H., Wu, R., Peng, X., Dong, S., Zhao, C., Leith, K., Gurevich, B., Li, B. Q., Lei, Q., Gor, G., and Selvadurai, P. A.: Moisture dynamics controls rock elasticity from weakening to stiffening, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9190, https://doi.org/10.5194/egusphere-egu25-9190, 2025.

GebPy is an open-source, Python-based tool developed to simulate synthetic geophysical and geochemical properties of minerals, rocks and entire rock sequences. It is based on the concept that the properties of a rock are fundamentally determined by its mineralogical composition and its interaction with fluids like water. By adopting a bottom-up approach, GebPy systematically builds from the mineral scale to the rock and sequence level, providing a robust framework for understanding and modeling geophysical and geochemical systems.

The modeling process begins at the mineral level, where properties such as density, volume, seismic velocity or gamma radiation are calculated based on chemical composition and fundamental physical and crystallographic principles. These properties are then combined to simulate the bulk properties of a rock, accounting for the proportional contributions of individual minerals. GebPy also integrates the effects of pore fluids, such as water, to provide a realistic representation of subsurface conditions.

One of the key strengths of GebPy is its scalability. Beyond individual minerals and rocks, the tool enables the simulation of entire rock sequences, generating idealized datasets that are highly valuable for geophysical applications. These include seismic modeling, well-log analysis and the evaluation of geophysical inversion techniques. This ability to model idealized systems provides insights into the fundamental principles governing geophysical and geochemical behavior, making GebPy a powerful resource for both theoretical and applied research.

The development of GebPy was inspired once by the study of well-log diagrams, which play a critical role in resource exploration. By generating synthetic well-log data under idealized conditions - free from natural imperfections such as fractures or measuring artifacts - GebPy provides a new perspective on how these diagrams might look in a perfect geological scenario. This approach not only enhances our understanding of the fundamental properties of rocks but also supports the development of advanced modeling techniques and the evaluation of uncertainty sources.

Looking ahead, GebPy’s development roadmap includes the integration of advanced techniques such as machine learning and the use of experimental data for calibrating input parameters like elastic properties of minerals. These enhancements will further expand its capabilities, enabling even more precise and comprehensive simulations. GebPy’s open-source nature ensures that it can be continuously improved and adapted by the geoscientific community, fostering collaboration and innovation.

GebPy represents an important step forward in the generation of synthetic geophysical and geochemical data. By providing a scalable and reliable framework for modeling minerals, rocks and sequences, it empowers researchers and practitioners to explore geological systems with precision and flexibility.

How to cite: Beeskow, M. and von Hagke, C.: GebPy - a Python-based, open source tool for the generation of synthetic geophysical and geochemical data of minerals, rocks and whole sequences, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10743, https://doi.org/10.5194/egusphere-egu25-10743, 2025.

Accurate analysis of rock pore structures is pivotal for predicting their performance in geological applications, such as CO₂ storage, geothermal energy extraction, and radioactive waste disposal. Advanced imaging techniques, such as Digital Rock Physics (DRP), have transformed the characterization of porous media by providing detailed insights into microstructural properties.

DRP employs high-resolution X-ray computed tomography (CT) to scan rock samples, generating 3D images that reveal pore structures, mineral phases, and fracture networks. This enables the computation of key rock properties, including porosity, permeability, thermal conductivity, and elastic moduli. These properties are critical for applications in sustainable energy production and seismic hazard monitoring.

The classical five-step workflow of DRP begins with the preparation of a high-resolution X-ray computed tomography (CT) image. This is followed by tomographic reconstruction of the image using simple back-propagation techniques. Next, preprocessing operations are conducted to assess and manage artifacts before proceeding to the segmentation of individual phases. Based on the segmentation results, key rock properties such as thermal conductivity, permeability, and elastic properties are computed by solving the corresponding physical equations.

The accurate segmentation of digital rock models into different phases and features holds a significant importance and remains a formidable challenge, as it directly impacts the precise characterization of subsequent physical properties. However, most studies using classical segmentation techniques, such as grayscale histogram processing or watershed algorithms usually relied on a binary segmentation process. This means that rock samples are divided into just two phases: pore and solid. This oversimplifies the complexity of multiphase rocks, neglecting the heterogeneity of, i.e., granitic rocks and compromising the accuracy of reservoir characterizations.

This study presents a multiphase geological segmentation approach for the Rotondo Granite, integrating geological ground truth for potential machine learning applications. By accounting for every distinct mineral phase within a granitic reservoir rock, this method moves beyond traditional binary segmentation, enabling a more detailed and accurate representation of rock microstructures. The improved segmentation accuracy enhances the precision of DRP analyses, contributing to more reliable underground reservoir assessments and supporting the transition toward sustainable energy technologies.

How to cite: Keutchafo Kouamo, N.-A., Balcewicz, M., Siegert, M., and Saenger, E. H.: A Multiphase Geological Segmentation of the Rotondo Granite, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11954, https://doi.org/10.5194/egusphere-egu25-11954, 2025.

Seismo-electromagnetic (SE) signals are created in fluid-saturated porous media by electrokinetic conversions at the pore scale. Two of these signals are frequently investigated: the first is a co-seismic wavefield, bounded to the propagating seismic waves, and the second is an electromagnetic (EM) wave created when a seismic wave passes through the interface between two porous media. Led by the effectiveness of SE phenomena in detecting thin layers (i.e., layers with thicknesses smaller than the seismic wavelength), many authors studied how a thin layer, or a combination of thin layers, can alter SE signals. In this context, the present work brings new experimental and numerical data as a means to further investigate the relation between the layer thickness and the EM interface-generated response. Particularly, we have noticed that the effect of layer thinning on the EM interface-generated waves is similar to what is observed for seismic waves, but with a maximum signal enhancing, due only to thickness, occurring when a layer has a thickness that is equal to half the wavelength of the P-wave impinging on the layer. We have also explored the effect of the pore-fluid electric conductivity on SE signals, since this parameter plays an important role on the SE fields. The fact that the EM interface-generated wave is very sensitive to contrasts of fluid conductivity, whereas seismic waves (and therefore the co-seismic) are, in effect, insensitive, is an appealing characteristic of SE exploration. By comparing experiments with simulations we have accessed the effect of fluid conductivity on SE wavefields, complementing previous studies with a quantitative analysis of the dependency of SE signals on this physical property. Moreover, we have evaluated the ability of the electrokinetic theory adopted in this study to predict our experimental data, and showed that it performs well in terms of waveform and amplitude behavior for all fluid conductivities considered.

How to cite: Martins-Gomes, V., Brito, D., Garambois, S., Barucq, H., Dietrich, M., and Bordes, C.: Experimental and numerical study of the seismo-electromagnetic signals created at thin porous-porous interfaces, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12039, https://doi.org/10.5194/egusphere-egu25-12039, 2025.

Reliable modelling of pore-scale network is critical to the understanding of fluid flow behaviour in a reservoir. This study presents the application of numerical techniques to high-resolution pore-network model derived from 3D micro-CT data obtained from scanning of core plugs of carbonate reservoirs from the Western Offshore basin. The methodology incorporates Direct Pore-Scale modelling, using computational fluid dynamics (CFD) techniques to solve flow field equations numerically, such as the Navier-Stokes equations. Adaptive mesh refinement within Finite Element Methods (FEM) and Finite Volume Methods (FVM) ensures accurate resolution of flow dynamics while maintaining numerical stability. Furthermore, the Lattice Boltzmann Method (LBM) is implemented to handle complex pore geometries and boundary conditions efficiently, with an advantage of large-scale parallelization to avoid interface tracking explicitly.

In parallel, Pore Network Models (PNMs) are integrated to represent pore spaces into simplified networks of pores and throats, preserving topological features for reconstructing the fabric of carbonate rock. These models are particularly effective to study collective behaviour across pores and complement direct methods by linking pore scale to sub-pore scale domain. Our approach addresses the computational intensity of sub-pore scale simulations and the limitations of network simplifications, that have implications on macroscopic properties such as Darcy-scale permeability for single-phase incompressible flows.

By integrating these approaches, we provide insights into accurate computation of mass fluxes and fluid-structure dynamics with high fidelity. Our results systematically analyse and compare numerical differences across methods to provide an understanding of the variability of computed properties, in our case single-phase incompressible absolute permeability. This facilitates in the resolution of complex fluid-structure dynamics and the development of optimized, stable, and consistent computational fluid dynamics (CFD) workflows for applications in enhanced hydrocarbon recovery and subsurface energy applications.

How to cite: Sulekh, K., Pandit, S., Shahi, A. K., and Singh, K. H.: Numerical analysis of pore scale processes in carbonate reservoirs from the Western Offshore basin in India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12316, https://doi.org/10.5194/egusphere-egu25-12316, 2025.

Seismoelectric phenomena, caused by electrokinetic coupling between seismic and electromagnetic fields, have attracted significant interest in geological reservoir characterization for their sensitivity to pore-fluid contrasts. Consequently, most studies have focused on seismic-to-electromagnetic conversions at fluid/poroelastic and poroelastic/poroelastic interfaces. However, when investigating permeable zones in unfractured media, often associated with geothermal reservoirs, poroelastic/elastic interfaces must be considered. To address this, we conducted laboratory and numerical experiments using a container filled with quartz sand saturated with a NaCl solution, with one of five thin layers made of different materials (four elastic and one poroelastic) embedded within the sand. Our numerical simulations assume an elastic medium as poroelastic using limiting values for certain physical parameters. The results confirm that seismoelectric conversion occurs at poroelastic/elastic transitions, showing a strong agreement between experiments and simulations. Furthermore, we inferred that the amplitudes of electromagnetic waves generated at poroelastic/elastic interfaces are mainly controlled by contrasts of dielectric permittivity.

How to cite: Brito, D., Bernardo, N., Martins-Gomes, V., and Bordes, C.: Seismoelectric conversion at poroelastic/elastic interfaces and the role of dielectric permittivity: experimental and numerical analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12758, https://doi.org/10.5194/egusphere-egu25-12758, 2025.

The transport of heat from the Earth’s interior to its surface is the main
driving force for many geological processes, like e.g. lithosphere dynamics and
mantle convection. To understand these processes, it is essential to capture
the spatially and temporally dependent temperature field of the Earth’s crust.
The structure of this temperature field is largely determined by the thermal
properties of the rocks. One of the key thermophysical properties is thermal
conductivity, which plays a critical role in various scientific and economic fields,
such as the study of sedimentary basins and geothermal potentials.
To characterize the thermal properties of various lithologies, measurements
on core samples are of ultimate interest. However, as coring is highly expen-
sive, drill cores are not often taken during drilling campaigns. Nonetheless, drill
cuttings would be available from nearly all drill holes. The drill cuttings can
be ground and compressed to form measuring tablets for thermal conductivity
tests, which changes the rock structure and thus also the thermal properties. An
alternative could be to embed drill cuttings in materials of known thermal prop-
erties like resin to prepare samples ready to be used with the widely available
Thermal Conductivity Scanner (TCS).
In this study, we present an innovative method for determining the thermal
conductivity of drill cuttings using TCS by preparing various samples drill cut-
tings embedded in epoxy resin. We investigate how grain size of the encased
cuttings affects the estimation of thermal conductivity with the TCS. To test
this novel approach, we use artificially produced drill cuttings, mini-cores em-
bedded in epoxy resin, and undisturbed reference samples. Our investigations
suggest that grain size and thermal edge effects resulting from embedding the
samples in resin can be corrected with sufficient precision to enable accurate
conclusions about the thermal conductivity of the undisturbed rock.

How to cite: Schulz, A., Kasburg, V., Goepel, A., and Kukowski, N.: Thermal Conductivity Measurements of in Resin-Embedded Cuttings Using the Optical Scanning Method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12870, https://doi.org/10.5194/egusphere-egu25-12870, 2025.

Understanding multi-phase pore-scale dynamics and their impact on bulk electrical properties is essential when monitoring reactive flow and transport processes  in many applications. This study introduces a novel experimental setup combining simultaneously Spectral Induced Polarization (SIP) acquisition with X-ray micro-computed tomography (µCT) for real-time monitoring. This innovative approach enables spectroscopic measurements, from mHz to kHz, to be directly correlated with dynamic imaging of pore-scale fluid and grain distributions. The setup features a custom-designed flow cell capable of operating under controlled pressure (up to 120 bars) and temperature (up to 100°C) allowing for real-time monitoring of dynamic petrophysical processes such as multi-phase flow, reactive transport, and mineral precipitation and/or dissolution.

In this contribution, we validate the experimental set-up under variable saturation conditions. Using a medium-grained sand sample,  we conducted a series of eight experiments transitioning from dry to fully saturated states, followed by three progressive partial desaturations steps via nitrogen gas injection and subsequent three progressive re-saturations. µCT scans were performed with 2001 projections and 17.21 µm voxel size resolution for each image. SIP data, spanning the 10 mHz – 45 kHz frequency range, were integrated with µCT-derived pore network models to analyze resistivity variations as functions of pore size, connectivity, and tortuosity.

Our results reveal that simultaneous Spectral Induced Polarization and X-ray micro-computed tomography measurements capture transient fluid redistribution processes, providing enhanced interpretability of bulk electrical responses. We observed significant hysteresis in Spectral Induced Polarization data during drainage and re-saturation cycles, linked to pore-scale fluid trapping and structural changes. Furthermore, resistivity predictions from the pore network model aligned closely with experimental data, validating the integration's robustness.

This novel experimental set-up lay the groundwork to the study of coupled structural and electrical dynamics in porous media, offering valuable insights into pressure and temperature dependant multi-phase subsurface processes including ones with mineral reactivity. By bridging the observation gap between pore-scale processes and bulk geophysical responses in 3D, this approach sets a new standard for experimental petrophysics.

How to cite: Omar, H., Bultreys, T., Rembert, F., Manoorkar, S., Caterina, D., Nguyen, F., and Hermans, T.: A Novel Experimental Set-up for Simultaneous Acquisitions of Spectral Induced Polarization and X-ray µCT Data in 3D Porous Media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13878, https://doi.org/10.5194/egusphere-egu25-13878, 2025.

Drilled-core samples (21ESDP-205, 21ESDP-206) collected from off eastern Geoje Island (Korea Strait) were used to characterize physical properties of the area with respect to sedimentary depth. Laboratory analyses of the acoustic and physical properties of the samples were conducted and shear-wave velocity, velocity ratio, poisson’s ratio, and velocity anisotropy were calculated. In particular, lithological characteristics of two drilled-core samples were interpreted using both visual description and geoacoustic and physical property data. In addition to visual description, a relationship between mean grain size and dry bulk density was used to interpret lithological characteristics. In other word, the values greater than approximately 1 g/cm³ in dry bulk density may be corresponded toward coarse grained sediments, except for the relationship caused by compaction effect. As a result, geoacoustic and physical property data at the two sites were in correlation with lithological characteristics alternating (mainly between sandy mud and muddy sand) at sedimentary depth. The relationships between velocity and porosity showed better correlation than those of between velocity and wet bulk density. Geoacoustic units (GAUs) identified from sites 21ESDP-205 and 21ESDP-206 were divided into 12 and 14 units with sedimentary depth, respectively, and geoacoustic models were developed for the sedimentary layers around these sites. The upper sediments in the study area were largely originated and redistributed from the Nakdong River, caused by sea-level changes during the Quaternary. These results suggest that sedimentary physical properties in the region were primarily controlled by depositional processes linked to the river, and that sea-level changes played a significant role as a dominant sedimentary process during the Quaternary.

How to cite: Kim, G. Y., Park, K., Hong, S.-H., Lee, G. S., Yoo, D.-G., and Kim, S.-P.: Geoacoustic model based on physical property characterization of Quaternary sediments off eastern Geoje Island, Korea Strait, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14022, https://doi.org/10.5194/egusphere-egu25-14022, 2025.

Compared to shallow coal seams, deep coal bed methane (CBM) is characterized by a higher content of free gas, which typically exhibits the traits of “immediate gas production upon well startup and high output upon gas production.” It has become an important natural gas resource for China to optimize its energy structure and achieve carbon peaking and carbon neutrality goals. Cleats serve as the primary pathways for gas desorption and migration in deep coal seams and act as weak structural planes of coal rocks, playing a crucial role in controlling both wellbore wall stability during drilling and fracture propagation during hydraulic fracturing. Therefore, the degree of Cleat development is regarded as a critical indicator for the efficient development of deep CBM. At present, most Cleat evaluation methods in coal rocks are derived from shallow coal seam studies, which primarily rely on compressional wave velocity and shear wave velocity characteristics. However, in deep coal seams subjected to high stress and strong compaction, Cleats often exhibit low aperture, resulting in weak logging responses. This makes the methods developed for shallow coal seams inapplicable, highlighting the lack of effective approaches for evaluating Cleats in deep coal seams. This study begins by conducting experiments on 70 coal rock samples with varying degrees of Cleat development. Combined with numerical simulations of coal rocks with different Cleat apertures, the experimental and simulation analyses Cleatly confirm the effectiveness of acoustic attenuation in evaluating Cleat development in deep coal seams. Compared to velocity and anisotropy, attenuation is more sensitive to Cleats with low aperture or partial closure. Based on dual-porosity medium theory and squirt flow theory, a rock physics characterization model of Cleat-related acoustic attenuation in deep coal seams is established. Subsequently, an inversion method for Cleat development degree based on acoustic attenuation is developed using an iterative method and applied to actual well evaluations. The results demonstrate that the proposed logging evaluation method for Cleat development based on acoustic attenuation more accurately reflects the degree of Cleat development. Compared to the velocity-based methods for shallow coal seams, the relative error is reduced from 27% to 18%, indicating that attenuation is more effective than velocity in assessing Cleat development in deep coal seams.

fig1. Comparison of Logging Evaluation Results for Cleat Development in Deep Coal Rocks

fig2. Comparison of Relative Errors in Logging Evaluation of Cleat Development in Deep Coal Rocks

How to cite: Ni, Z., Li, W., Liu, X., and Liang, L.: A Logging Evaluation Method for Cleat Development in Deep Coal Rocks Based on Acoustic Attenuation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15257, https://doi.org/10.5194/egusphere-egu25-15257, 2025.

Over the past few years, several scientific projects at Bochum University of Applied Sciences have developed new methods and procedures for determining the petrophysical properties of small rock samples. These workflows, which are part of Digital Rock Physics (DRP) and have been published in peer-reviewed journals, are based on the non-destructive testing of samples using X-ray computed tomography.

After the subsequent semi-automated segmentation - i.e. the identification of the pore space and different minerals in the 3D scan - the thermophysical, hydraulic and mechanical properties of the rock sample relevant for geothermal projects are calculated using numerical methods. The method can be applied to cuttings (drill cuttings produced during the drilling process). The method thus offers the possibility of determining the relevant rock parameters over the entire drilling section and without the use of expensive core drilling methods, which can save costs on one hand and significantly improve the database for the subsequent numerical simulation of the geothermal plant on the other

We present the first results of the ongoing SimBoL-project. A selection of Carbonate cuttings were scanned with a high-resolution CT device. Those digital images were transformed into digital rock samples which are the basis of numerical simulations to determine the permeability, the heat conductivity and the mechanical rock properties. A first qualitative comparison with borehole data is presented.

How to cite: Serje Gutierrez, A., Balcewicz, M., and Saenger, E. H.: Physical Properties of Carbonate Rock Cuttings vs. Borehole Data: Insights from Ongoing Research, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16147, https://doi.org/10.5194/egusphere-egu25-16147, 2025.

Advancing rock physics modeling is critical for understanding the physical properties of gas hydrate-bearing sediments and assessing hydrate reservoirs. This study presents a combined elastic and electrical rock physics framework to quantitatively characterize the morphology and distribution of pore-invasive gas hydrates, a dominant reservoir type in marine and permafrost environments. Elastic modeling, grounded in granular medium contact theory and Gassmann’s equation, reveals the influence of hydrate saturation and initial porosity on P- and S-wave velocities. However, these velocities alone are insufficient to uniquely constrain hydrate morphology. To overcome this limitation, we refined Archie's law by introducing an empirical ion concentration exponent, improving the sensitivity of electrical conductivity models to hydrate distributions within pores. By coupling these models, we simulate hydrate formation processes and evaluate their impact on seismic and resistivity properties. Our results highlight several key conclusions. First, experimental observations suggest that a uniform distribution of hydrates within the pore framework is most consistent with measured geophysical responses, despite the potential for ring-shaped saturation patterns during laboratory experiments. Second, we identify a distinct morphological evolution during hydrate growth: hydrate structures transition from grain-supporting to contact-cementing and finally to pore-filling morphologies as saturation increases. This progression is reflected in both velocity and resistivity trends, offering complementary insights into the hydrate formation process. This work not only advances the understanding of hydrate formation but also provides a robust framework for evaluating hydrate reservoirs, contributing to efforts in energy resource development and environmental management.

How to cite: He, T., Zhang, Q., Lu, H., Zi, M., and Chen, D.: Quantitative Characterization of Pore-invasive Gas Hydrate Morphology via Rock Physics Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18980, https://doi.org/10.5194/egusphere-egu25-18980, 2025.

On major plate-boundary fault zones, there is an expectation that large-magnitude earthquakes do not nucleate at shallow depths, but rather starting at depths of several km in the crust.  This depth dependence is generally understood  to be controlled by the frictional behavior of the sediments making up fault gouges, where velocity-strengthening friction and low effective stresses at shallow depths tends to produce stable fault slip.  The transition to velocity-weakening rocks at seismogenic depth has been suggested to be caused by a variety of diagenetic and low-grade metamorphic processes that lithify the sediments into more competent fault rocks.  Recent laboratory results on both natural fault rocks and desiccated clay-salt mixtures show that this is a viable mechanism, where velocity-weakening friction is seen in the lithified rocks having high cohesion and low porosity.  A remaining open question is whether the key ingredient for velocity-weakening friction is the porosity reduction, or the mechanical cementation.

Here, we test whether porosity reduction alone can induce velocity-weakening friction in powdered Rochester shale, an otherwise velocity-strengthening sediment.  We control the porosity by consolidating deionized water-saturated shale powders to a vertical stress of 86 MPa and shearing the samples under lower effective normal stresses of 0.1-10 MPa, for overconsolidation ratios (OCRs) of up to ~860.  We then measure the frictional properties of our overconsolidated samples with velocity-step tests from 10^-6–10^-5 m/s, repeated over long displacements to account for fading of the initial consolidation state with slip. 

We observe that overconsolidation induces an additional porosity reduction of 35-63%, relative to the porosity under normal consolidation. The velocity steps show predominantly velocity-strengthening friction; however, some scattered instances of velocity-weakening are observed for the highest tested OCR.  Analysis of the rate- and state-dependent friction parameters shows that the velocity steps in samples with the highest OCR have both larger values of “a” and large positive values of “b”, whereas the rest of the samples show predominantly negative values of “b”.  The observed pattern in “b” suggests that asperity contacts under shear, and therefore surface roughness is important.  This is supported qualitatively by photos of the shear surfaces, showing that for larger OCRs, a smaller proportion of the nominal surface area is in real contact during shear.  The results show that velocity-weakening friction begins to appear when the additional porosity reduction is ~55%, consistent with previous work.  However, the appearance of velocity-weakening friction due solely to porosity loss may require unrealistically large OCRs, and truly unstable sliding at depth likely requires cementation by mineralization.

How to cite: Ikari, M. and Hüpers, A.: Frictional slip behavior of highly overconsolidated fault gouge, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1722, https://doi.org/10.5194/egusphere-egu25-1722, 2025.

Fault geometric heterogeneities such as roughness, stepovers, or other irregularities are known to affect the spectra of radiated seismic waves that result from dynamic slip on a fault. To investigate the effect of normal stress heterogeneity on radiated spectra, we created a laboratory fault with a single, localized bump by utilizing the compliance and machinability of poly methyl methacrylate (PMMA). By varying the normal stress on the bump and the fault-average normal stress, we produced earthquake-like ruptures that ranged from smooth, continuous ruptures to complex ruptures with variable rupture propagation velocities, slip distributions, and mechanical stress drops. We used an array of eight piezoelectric sensors to measure vertical ground motions calibrated to determine source spectra and PGA for individual events. High prominence bumps produced complex events that radiated more high frequency energy, relative to low frequency energy, than continuous events without a bump. In complex ruptures, the radiated high frequency energy was spatially variable and correlated with local variations in peak slip rate and maximum mechanical stress drop caused by the bump. Continuous ruptures emitted spatially uniform bursts of high frequency energy as the rupture propagated along the fault. Near-field peak ground acceleration (PGA) measurements of complex ruptures show nearly an order-of-magnitude higher PGA near the bump than elsewhere. We propose that for natural faults, geometric heterogeneities may be a plausible explanation for commonly observed order-of-magnitude variations in near-fault PGA.

How to cite: Cebry, S. B. L. and McLaskey, G.: Heterogeneous high frequency seismic radiation from complex ruptures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3342, https://doi.org/10.5194/egusphere-egu25-3342, 2025.

Natural faults are typically surrounded by a damage zone consisting of fractures of varying scales and geometries, which can significantly influence the dynamics of earthquake ruptures. Numerical studies have shown that damage can affect rupture parameters such as velocity, style, and extent. However, only a limited number of experimental studies have examined the effect of damage on the rupture process, focusing primarily on the rupture speed. Here, we present direct experimental observations on how damage geometry can affect earthquake rupture dynamics on a planar fault. We use polymethyl methacrylate (PMMA) specimens with a pre-cut planar fault and create damage near the fault with varying crack geometry and spacings using laser cutting technology. We generate spontaneously propagating shear ruptures along the main faults and image the rupture using an ultra-high-speed camera operating at one million frames per second. By employing Digital Image Correlation (DIC) techniques, we obtain detailed evolution maps of velocities, displacements, and strains associated with the propagation of the ruptures. Initial results demonstrate that damage zone characteristics can significantly influence the slip velocity, rupture style, and speed, including the transition from sub-Rayleigh to supershear velocities. Such results can offer valuable experimental observations on how damage zones influence earthquake rupture dynamics and deepen the understanding of the complex interplay between fault structures and rupture processes.

How to cite: Ghosh, S. and Tal, Y.: The Effect of Fault Damage Zone on the Dynamics of Earthquake Ruptures: Experimental Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3648, https://doi.org/10.5194/egusphere-egu25-3648, 2025.

Cyclic fluid injection for industrial purposes within fault zones are commonly imposed, since they are observed to stabilize induced seismicity, often inducing aseismic slip along fault surfaces, without immediate seismic energy release (Zang et al., 2018; Noël et al., 2019; Ji et al., 2021a, 2021b, 2022). Even though dynamic variations of effective normal stress on fault zones due to both natural and anthropogenic causes are common (Chen et al., 2024), the impact of the perturbations and their frequencies on fault strength is less explored (Savage and Marone, 2007; Ferdowsi et al., 2015; Noël et al., 2019). The frequency of pore-pressure changes are  expected to impose a characteristic timescale, controlling the crossover from a drained to an undrained response, which in turn will promote markedly different deformation modes and rates (Passelègue et al., 2018).

In this work we present results from a coupled hydromechanical-discrete element model that simulates the response of a pre-stressed, fully saturated fault, filled with a granular fault gouge, subject to cyclic pore-pressure variations across frequencies of three orders of magnitude. For lower frequencies we see nucleation-arrest-nucleation dynamics within the granular rupture and for higher frequency we observe cyclic creep, both driven by pore-pressure perturbations. Within the frequency parameter space we see a crossover of the slip modes as we increase frequency, lower frequencies show unstable failure, while higher frequencies show creep. Our results might account for a) fluid induced slip stability in cyclic injection scenarios (higher frequencies) and b) low-frequency dynamic triggering of earthquakes.

How to cite: Parez, S., Sarma, P., and Aharonov, E.: Response of a fluid-saturated fault gouge to frequency varied cyclic pore-pressure variations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4426, https://doi.org/10.5194/egusphere-egu25-4426, 2025.

Laboratory studies have demonstrated that faults undergo dynamic weakening during large displacements (>1 m) at seismic slip velocities (>0.1 m/s). However, the role of this weakening in small-displacement induced earthquakes (M 3–4), such as those in the Groningen Gas Field (the Netherlands), remains unclear. To address this, we conducted seismic slip-pulse experiments on Slochteren sandstone gouges (SSG), derived from the gas reservoir, using a rotary-shear apparatus to provide decimeter-scale constraints on the dynamic fault slip of quartz-rich gouges. Pre-sheared gouge layers, confined between ~1.5 mm thick sandstone host blocks, were subjected to slip pulses under initial effective normal stresses of 4.9–16.6 MPa and pore fluid pressures of 0.1 and 1 MPa under undrained conditions. The experiments achieved peak velocities of 1.8 m/s, accelerations up to 42 m/s², and displacements of 7.5–15 cm, using either dry Argon or water as pore fluid at ambient temperatures. Our results reveal that water-saturated gouges weaken rapidly from a peak friction of ~0.7 to ~0.3, accompanied by early fast dilatancy followed by slower ongoing dilation, with minimal dependence on normal stress, slip acceleration, or displacement. In contrast, Argon-filled samples exhibited only minor weakening. Microstructural analysis shows no systematic relationship between the width of the principal slip zone (PSZ) and frictional work or power input densities, indicating that wear or heat production alone does not control PSZ growth. Instead, our thermo-hydro-mechanical (THM) numerical modeling suggests that thermal pore fluid pressurization, potentially involving water phase transitions at asperity scales, drives weakening in short-displacement, induced seismic events. To extend these small-scale laboratory findings to reservoir-scale processes, ongoing research focuses on discrete element modeling (DEM) at particle and gouge scales coupled with THM solutions. This includes calibrating the THM-DEM models at both grain and gouge scales using laboratory data from Groningen sandstone-derived samples. The calibrated models will be validated with recent data generated under fast slip conditions with varying pore fluids.

How to cite: Hung, C.-C., André, N., Aretusini, S., Spagnuolo, E., Chen, J., and Hamers, M.: Thermo-hydro-mechanical mechanisms in sandstone-derived fault gouges during simulated small-magnitude earthquakes from experiments and models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4873, https://doi.org/10.5194/egusphere-egu25-4873, 2025.

Compared to other kinds of fluid-related seismicity, reservoir-induced seismicity (RIS) is usually characterized by higher magnitudes. Seismic and water level monitoring and statistical modelling, however, do not provide comprehensive understanding of the RIS mechanism and controls. This study presents a novel finite element method-based 2D poro-visco-elasto-plastic fully dynamic earthquake model, specifically applicable to RIS simulations. In the first stage of the simulations, Drucker-Prager plasticity is used to generate a normal fault in the Earth’s upper crust with enhanced porosity, over a long time-scale of millions of years. In the second stage of the simulations, RIS is modelled under typical reservoir impoundment dynamics, producing four seismic sequences, triggered by pore pressure increase at the fault at shallow depth below the reservoir. This pressurization is released by aftershocks in every seismic cluster, accompanied by permeability hikes at the fault and associated with fault “valving” behaviour. A dynamic coseismic rupture phase driven by wave-mediated stress transfers coupled with rate-and-state dependent friction coefficient weakening is modelled, along with interseismic deformations. Coseismic crack opening in a dilatant regime, inducing porosity and permeability hikes especially emphasized at the fault, is implemented. The model component verifications demonstrate convincing agreement with theoretical predictions. The model allows investigation of spatio-temporal RIS characteristics and their controls. It may contribute to earthquake prediction in situ and facilitate earthquake mitigation policies.

How to cite: Katsman, R. and Ben-Avraham, Z.: A Dynamic Poro-Visco-Elasto-Plastic Earthquake Simulator with Spontaneous Dilatant Coseismic Rupture: Modelling Fault Deformations at Reservoir-Induced Seismicity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5024, https://doi.org/10.5194/egusphere-egu25-5024, 2025.

Understanding earthquakes mechanisms still represents a challenge, motivated by the large consequences of the numerous earthquakes occurring each year. The complexity of fault zones and fault behaviour requests to make some simplifications and to down-scale the studied system. In our work we borrow from the tribological approach the pin-on-disk experiment so that the two rough surfaces in contact through a series of asperities fault concept is downscaled to a single asperity sliding on a rough surface. The single asperity response to shearing induced by sliding and the evolution of friction are studied closely to understand the behaviour of the down-scaled fault, especially when the velocity is changing. Moreover, mono-asperity experimental tests are an effective way to construct new friction laws for numerical simulations.

The original experimental apparatus consists in a centimetric pin with a hemispherical extremity representing the fault asperity while a large flat rotating disk stands for the opposite surface of the experimental fault. Both pieces are made in the same carbonate rock (Carrara white marble) with controlled roughness. Under co-seismic conditions (contact size, contact normal stress) and with a rough track with presence of granular gouge, the lab-fault is submitted to different velocities (from 0.001 m/s up to 1m/s). A number of high-sampling-rate sensors are used to constrain the observation of the asperity-rough track contact during the simulated seismic events. Moreover, complete post-mortem analyses of the contact surfaces with optical microscopy, SEM and roughness images allow to quantify the mechanisms and to reconstruct friction scenarios in accordance with the time-series acquired during tests. A quasi 2D numerical twin is also created with the elementary discrete method software MELODY, in order to compare the different features observed on the pin or on the track.

In this present work, we focus on the change of wear mechanisms in the lab-fault due to changes in sliding velocity. Independently of the normal load applied, the Carrara white marble asperity-track system experiences weakening velocity due to frictional heating. The friction coefficient evolution during the co-seismic events and the post-mortem analyses put in contrast two regimes. At low velocity, the carbonate rock lab fault wears off at a constant rate producing a large amount of granular gouge. At high velocity, the contact surfaces are covered by viscous sintered material, which can be called mirror surfaces.

How to cite: Clerc, A., Mollon, G., Ferrieux, A., Lafarge, L., and Saulot, A.: Velocity influence on the friction and wear of a single-asperity lab-fault, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6563, https://doi.org/10.5194/egusphere-egu25-6563, 2025.

Faults can slip in diverse modes, ranging from slow, aseismic creep to dynamic, earthquake-generating rupture. Geological observations reveal that many fault zones consist of localized slip zones surrounded by a broader damage zone, where microcracks and fractures interact in complex ways. Friction laws propose that whether a fault will host a slow slip event or a fast dynamic rupture depends on the relative stiffness of these slip zones and the surrounding material. Conversely, the local stress field imposes such structures' evolution. Although the evidence for these complex interactions indicates the opportunity to incorporate this knowledge in the theoretical framework, collecting data on the spatiotemporal evolution of elastic properties at seismogenic depth is inherently challenging, leaving this possibility mostly unexplored.

Laboratory experiments provide a controlled environment for studying the evolution of fault mechanics and elastic properties. Elastic waves are governed by the same equations that relate wave speeds to dynamic moduli. Therefore, they offer a pathway to link laboratory observations to natural fault processes.

This study investigates how microstructural reorganization during fault deformation and fault zone structure formation affects fault zone stiffness and slip behavior using synthetic quartz gouge layers sheared in double-direct shear (DDS) configuration.
Our DDS setup is instrumented with piezoelectric transducers designed to generate and record predominantly compressional (P) or shear (S) waves. By carefully characterizing the source time function, we ensure that early arrivals in each recorded signal represent a single wave mode with minimal mode conversion or side reflections.

We then apply Full Waveform Inversion (FWI) to these early arrivals to reconstruct velocity models for both P- and S-waves as deformation progresses. The inverted models reveal spatiotemporal variations in the bulk and shear moduli, which we interpret as signatures of contact-area changes, grain size reduction, and other micromechanical processes relevant to frictional stability. In particular, the evolving elastic properties allow us to gauge how the local stiffness of the gouge zone evolves relative to applied stress, linking the observed velocity changes to the constitutive laws underpinning rate-and-state friction (RSF). While RSF implicitly links frictional strength to contacts dynamic through a state variable, our results illustrate how ultrasonic waveform acquisition and modeling can provide hints toward the explicit rewriting of such laws in terms of the evolution of elastic properties, an intermediate level of description easier related to micromechanical processes.

This approach highlights the potential for ultrasonic measurements in earthquake laboratory experiments to probe fault zone mechanics and outline a framework for integrating seismic imaging with frictional mechanics to better understand fault behavior across scales.

How to cite: De Solda, M., Mauro, M., Guglielmi, G., Pignalberi, F., and Scuderi, M.: Probing Fault Zone Evolution with Ultrasonic Measurements: Seismic Imaging in Laboratory Experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7148, https://doi.org/10.5194/egusphere-egu25-7148, 2025.

The geometrical roughness of faults results in significant stress heterogeneity across various length scales, thus affecting rupture and sliding behavior during earthquakes. The dilatancy behavior on rough joints also becomes much more complicated than on planar faults. Whether dilation or compaction will occur on rough faults, especially those with large asperity heights, during interseismic and seismic slips is still an open question. 

Here, we perform laboratory shear tests on rough faults with millimeter-scale asperity heights and analyze the four types of dilation or compaction behavior observed during stick-slip cycles. In the stick phases, dilatancy behavior inferred from the asperity contacts agrees well with the variation of normal displacement. The locations of acoustic emission (AE) events are also consistent with the potential surface damage regions estimated from the evolution of asperity contacts at various shearing displacements. Stick-slip events with compaction-dominant interseismic slip usually occur at large shear displacements on interlocking faults when overriding high asperities. In those stick-slip events, the proportion of large-magnitude AEs is lower, resulting in higher Gutenberg–Richter b values. A generalized schematic model is also proposed for the complex dilatancy behavior during stick-slip cycles.

The experimental results provide new insights into the effects of fault roughness on shear-induced dilatancy behavior and serve as valuable benchmarks for our numerical simulations considering visible contact evolutions during shear sliding on rough faults.

How to cite: Chai, S., Su, B., Zou, Y., and Zhao, Q.: Dilation or compaction? Laboratory insights into the role of fault roughness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7873, https://doi.org/10.5194/egusphere-egu25-7873, 2025.

Fluid pressure plays a crucial role in controlling fault reactivation in both natural and induced seismicity. The effective normal stress is linearly reduced by an increase in fluid pressure (P_f) with σ_eff = σ_n  - S · P_f, which lowers the frictional strength of the fault, τ=µ·σ_eff, increasing the potential for fault reactivation and seismic slip. Upon reactivation, slip can occur quasi-statically or dynamically depending on the interplay between σ_n and P_f and mediated by the S parameter, (the hydromechanical coupling) and by the rate-and-state properties of the fault materials. In this context, the fault zone structure dictates the frictional properties as well as the fault hydro-mechanical coupling, particularly when S ≠ 1 and reactivation might occur at effective stresses different than predicted.

In Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG, Switzerland), a target fault zone chosen for fluid-induced fault stimulation is characterized by a fractured host rock surrounding a sub-centimetric fault core with fault gouge and bare-rock asperities.  Therefore, to define slip mode of the target fault it is important to characterized the frictional properties of both fault gouge and bare-rock asperities taking advantage of a laboratory controlled experimental environment.

Fault stimulation by fluid injection was simulated in laboratory by increasing the P_f following an injection protocol suitable for the BULGG fluid stimulation. Experiments were performed on both the fault gouge sampled from the target fault and on bare rock surfaces sampled in the surrounding host rock. We employed a rotary shear apparatus (SHIVA) to perform fluid injection experiments. First, we imposed the stress conditions measured at depth in the underground laboratory, halved due to apparatus limitations: 7.5 MPa σ_eff, 7.5 MPa confining pressure and 2.5 MPa P_f. Second, we imposed a slip rate of 10^-5 m/s for 0.01 m to develop a stable fault core structure. Third, we applied a constant shear stress of 2.7 MPa, considering the slip tendency measured on the target fault (0.35). We then increased stepwise the P_f by 0.1 MPa every 150 s. After fault slip initiation, the maximum allowed slip velocity was 0.1-1 m/s. Between each of the experimental stages, permeability and transmissivity were measured with the gradient (Darcy) or P_f oscillations methods.

We show that fault reactivation and slip behavior are different between gouge and bare rocks: in gouge creep and dilatancy precede reactivation, whereas in bare rock surfaces reactivation is sudden and not preceded by neither tertiary creep nor dilatancy indicating that dynamic reactivation is promoted in smooth bare-rock surfaces. Moreover, gouge displays a higher friction (0.58 vs 0.49) and a lower hydraulic transmissivity (i.e., 10^-19 vs 10^-17 m³) than bare rocks.

Here we proceed to test a suite of constitutive models against our data: rate and state friction, (Rudnicki, 2023; Cappa et al., 2022), and a fully coupled poromechanical model (Dal Zilio et al., in prep.), to understand what are the physical processes controlling the onset and style of fault activation in the two fault core structures.

How to cite: Aretusini, S., Cornelio, C., Spagnuolo, E., Volpe, G., Pozzi, G., Dal Zilio, L., Selvadurai, P., and Cocco, M.: Fault core structure and the fault slip behavior during fluid injection: insights from laboratory friction experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7883, https://doi.org/10.5194/egusphere-egu25-7883, 2025.

Ophicalcites (carbonated ultramafic rocks) are commonly found when serpentinized mantle rocks are exposed to fluid-rock interaction in settings such as slip and damage zone of mid ocean ridges, transform faults and subduction zones. In this study, we analyze the frictional strength and healing properties of ophicalcites under hydrothermal conditions because of their possible role in the nucleation of “fast” (i.e., earthquakes) and slow slip events.

The ophicarbonates used in this study belong to the exhumed ophiolitic unit of Eastern Elba Island (Italy). The hand samples are black, red, and purple ophicarbonates and include veined breccias and cataclasites. The mineral assemblages, determined through optical microscopy and quantitative (Rietveld) X-ray powder diffraction, consist of serpentine (lizardite and chrysotile with rare relicts of pyroxene and olivine), talc and calcite veins. Hematite is only found in the red ophicalcite.

We conducted slide-hold-slide experiments with a rotary-shear apparatus coupled with a hydrothermal vessel (ROSA-HYDROS, Padua University, Italy) on a synthetic fault gouge derived from a red natural ophicalcite cataclasite with a composition of 26.9% lizardite and chrysotile, 12.3% talc, 57.6% calcite, 2.9% hematite and traces of smectite. The experiments were performed at an effective normal stress (σ_n^eff = σ_n - P_p) of 20 MPa, a fluid pressure (P_p) of 6 MPa, constant slip velocity of 10 µm/s between the holds (which lasted from 10 to 10.000 s) and temperatures ranging from 20 to 400°C. Our results show that, the “serpentinite” component dominates the bulk friction and the healing behaviour. For T≤ 200°C and in the presence of water in liquid state, the friction coefficient (µ = shear stress/σ_n^eff) is relatively low (µ = 0.35-0.45), poorly sensitive to fluid temperature and we observe creep.  Instead, for T ≥ 300°C and in the presence of water in vapor state, the µ is higher (= 0.80-0.90) and we observe stick-slip behaviour.

The experimental approach of this study aims to understand the nucleation of earthquakes or of slow slip events along mid ocean ridges and transform faults and to contribute to the assessment of seismic hazard associated with CO₂ storage by carbonation of serpentinite in deep reservoirs.

How to cite: Salvadori, L., Di Toro, G., and Tesei, T.: Frictional strength and healing behaviour of natural carbonated serpentinites at hydrothermal conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8673, https://doi.org/10.5194/egusphere-egu25-8673, 2025.

The ability of faults to regain strength between seismic events (frictional healing) is crucial to understand the seismic cycle. In lithologically heterogeneous faults, differences in healing rates among various rock types can lead to the locking of specific fault patches. These locked segments may store significant amounts of elastic strain energy, which can be dynamically released during earthquakes. Anhydrite is a key component of the Triassic Evaporites, the seismogenic layer responsible for destructive earthquakes in Central Italy, e.g. 2016 Mw 6.5 Norcia mainshock. Its complex mechanical behavior, strongly influenced by boundary conditions, remains underexplored. Minor variations in effective pressure, humidity, loading rate, and temperature alter healing properties, rheology, and fault slip behavior of anhydrite. These mechanical characteristics are inherently tied to its elastic properties. Hence, the broad spectrum of mechanical behaviors observed should correspond to an equally wide variation in its elastic moduli.

We performed dry and wet friction experiments on anhydrite gouge using the BRAVA2 biaxial apparatus. These experiments include Slide-Hold-Slide (SHS) sequences to investigate the healing properties of anhydrite by varying temperature between 20 and 100 °C. To inform mechanical data with the microphysical evolution of the fault, we equipped the sample assembly with PZT sensors in transmission mode. These sensors record ultrasonic wave (UW) propagation through the sample during SHS tests. Finally, mechanical and ultrasonic measurements were accompanied by comprehensive microstructural analysis.

At room temperature, distinct mechanical features emerge between dry and wet samples. Wet experiments are characterized by lower friction (μ = 0.49) and higher healing rate (β = 0.015) with respect to dry ones (μ = 0.6 and β = 0.004). In both wet and dry tests fault healing follows a log-linear dependence with hold duration, however, in wet samples this relationship occurs only after a characteristic cut-off time, tc (s). We report a log-linear increase of UW amplitude with hold time. Microstructural analysis of wet samples reveals shear localization and grain size reduction within multiple Y, B, and R shear bands. Conversely, dry samples predominantly feature distributed deformation within R shear bands and local S-C structures.

The observed differences between dry and wet experiments suggest that water-activated processes play a major role in controlling shear strength and healing properties of anhydrite. This hypothesis is corroborated by the presence of a cut-off time for wet healing measurements. We interpret tc as a necessary time for water-activated deformation mechanisms to effectively operate by increasing the healing rate.
The evidence of a log-linear relationship between UW amplitude and hold duration testifies that fault restrengthening is intimately related to gouge porosity reduction and fault zone evolution.

Our approach aims to correlate reductions in shear modulus with shearing along specific slip planes, which are known to be active through microstructural analyses. To achieve this goal, the relationship between complex frictional healing and the elastic properties of anhydrite will be investigated via the extraction of elastic moduli from UW velocities.

How to cite: Mauro, M., Guglielmi, G., De Solda, M., Trippetta, F., Collettini, C., and Scuderi, M.: Dynamics of frictional healing of anhydrite bearing faults imaged by ultrasonic waves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8830, https://doi.org/10.5194/egusphere-egu25-8830, 2025.

Recent observations of many large earthquakes suggest a pronounced interaction of seismic sequences and aseismic slip (Kato & Ben-Zion, 2020). Among them, the spatio-temporally clustered seismic sequences may be related to internal stress transfer through event-event triggering processes (Davidsen et al., 2021). These evolving stress correlations at different length scales may be a key component to earthquake nucleation. However, the coupling between aseismic deformation and seismic triggering remains poorly understood due to observational limitations. In this study, we performed a triaxial experiment at 50 MPa confining pressure on a Rotondo granite sample. The sample was pre-notched to induce localized stress concentrations. The deployment of distributed strain sensing (DSS), based on fiber-optic technology, captures the transient behavior of aseismic deformation leading to system-size failure. We show that, at peak stress (σ_p = 420 MPa), the strain first builds up and accelerates near the edges of notches. During a subsequent small stress drop (Δσ_d = 1.5 MPa), a sharp contrast between positive and negative strain rates appears. This asymmetric deformation reflects the local stress redistribution associated with the development of shear cracks emanating from the notches. Following this, a transient recovery is observed, as the concentrated strain rate transfers to the surrounding regions. This indicates that the shear crack is growing away from the notches towards the middle of sample. Acoustic emissions (AEs) recorded throughout the failure sequence were analyzed in conjunction with local strain rates, strain gradients, and the speed at which the strain concentrations propagate. This study provides novel insights into the spatio-temporal evolution of shear cracks, revealing the complex interplay between strain localization, aseismic transients, foreshock activity and stress redistribution during the preparatory phase preceding dynamic failure.

References:

Davidsen, J., Goebel, T., Kwiatek, G., Stanchits, S., Baró, J., & Dresen, G. (2021). What Controls the Presence and Characteristics of Aftershocks in Rock Fracture in the Lab? Journal of Geophysical Research: Solid Earth, 126(10), e2021JB022539. https://doi.org/10.1029/2021JB022539

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

How to cite: Chen, H., Selvadurai, P. A., Michail, S., Salazar Vásquez, A. F., Madonna, C., and Wiemer, S.: Spatio-Temporal Organization of Earthquakes: Insights from Aseismic Transients and Seismic Triggering in Rock Fracture, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8940, https://doi.org/10.5194/egusphere-egu25-8940, 2025.

The mechanisms that lead a fault in the brittle crust to catastrophically fail during fluid injection remain poorly understood. In traditional rock mechanics, significant effort has been devoted to developing fluid injection experiments that reactivate small specimen surfaces over their whole area. However, in natural settings, only a portion of the fault may initially experience an increase in fluid pressure and reactivation by enlarging the area of slip.

Therefore, it is important to explore further the processes that lead to nucleation on a localized patch subjected to fluid injection to involve a larger portion of the fault that are not initially subjected to the elevated fluid pressure. To do so, we developed a new bi-axial apparatus specifically designed to investigate the nucleation phase of fluid injection-induced earthquakes on large enough sample.

This apparatus accommodates slabs of rock with a sliding surface of 15 x 17 cm and 1 cm thick. It is equipped with two servocontrolled hydraulic rams capable of delivering horizontal and vertical forces up to 450kN. The fluid pressure (both upstream and downstream) and both rams are controlled by adapted Nova-Swiss hand pumps that are independently managed by EUROTHERM process controllers, which operate MAXXON brushless electric motors via ESCON digital servo-controllers. This setup enables precise servo-control of each piston and upstream and downstream pressure in either displacement or pressure mode, using feedback from LVDTs and pressure transducers, respectively.

We designed a new double L-shaped assembly that ensures a uniform shear stress distribution on the sliding surface prior to reactivation, as shown by finite element analysis. The assembly is equipped with eight piezoelectric transducers to record acoustic emissions (AE) and to conduct active velocity surveys, as well as strain and displacement gauges placed across the sliding surface to monitor local strains and finite displacements. The slip surface can be machined to form an area with an initial stress concentration around its tip so that slip can be initiated entirely by raising the fluid pressure in the ‘crack’. The sample material chosen is Pennant sandstone, a tight sandstone with high cohesive strength and very low porosity and permeability.

Here, we present a suite of preliminary experiments ranging from conventional stable/unstable frictional sliding to fluid injection-induced fault reactivation. Acoustic emissions were utilized to monitor the evolution of the seismic b-value and to locate AE events throughout the experiments.

How to cite: Bigaroni, N., Mecklenburgh, J., Chandler, M., Paul, L., and Rutter, E.: BeeAx: A New Biaxial Apparatus to Investigate Shallow Brittle Rock Deformation and Frictional Sliding, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10995, https://doi.org/10.5194/egusphere-egu25-10995, 2025.

Fault geometry is increasingly regarded as a key parameter that affects all aspects of the earthquake cycle, yet the in-situ geometry of active faults remains poorly resolved, and they are often modeled as largely planar. On the other hand, recent advances in sensing and computational abilities enable measuring the co-seismic slip of large earthquakes in high resolution, both on the surface and at seismogenic depths. Previous analytical and numerical studies showed that the slip distribution of an earthquake is mechanically linked to the fault geometry through its curvature, though this link has not yet been verified. Here we show experimental verification of this link, by measuring at high precision the shear slip profiles along non-planar interfaces in laboratory earthquakes. We trigger dynamic shear ruptures that propagate along the interface between two loaded and matching PMMA plates and, using image correlation of ultrahigh-speed photography, resolve the propagating ruptures and the resulting displacements. The plates are pre-cut along a desired geometry, and we compare the slip calculated from the geometry and the experimental shear slip at each pixel along the interface. We show that, as predicted analytically, fault curvature is correlated to slip gradient when the plates are in contact and anti-correlated when there is opening. These relationships are clearly visible in our results at all measured scales regardless of the rupture complexity. Our results suggest that variations of the co-seismic slip along a fault can be highly indicative of the in-situ fault geometry and, alternatively, that slip distribution may be predicted along a fault with known geometry.

How to cite: Gabrieli, T., Romanet, P., Tal, Y., and Schuderi, M. M.: Validating the link between fault geometry and slip distribution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12897, https://doi.org/10.5194/egusphere-egu25-12897, 2025.

Safe exploitation of high-enthalpy geothermal fields for energy production requires knowledge of the mechanical behavior of faults and the seismic cycle in the presence of hot, pressurized fluids. In geothermal reservoirs, fluids can exist in the liquid, liquid-vapor mixture, vapor, or supercritical fluid state. Here we investigate the frictional properties of simulated fault gouges derived from the main stratigraphic units present in Krafla Geothermal Field (Iceland) under realistic water temperature (T_f=100-400˚C) and pressure (P_f=10-30 MPa) conditions. These conditions correspond to water in the liquid, vapor, and supercritical state. 

Laboratory rotary shear, slide-hold-slide (SHS) experiments at a constant effective normal stress of 10 MPa are performed on gouges prepared from non-altered basalt (Krafla Fires eruptions, 1975-1984), chlorite-altered basalt (borehole KH-6, 708.5 m borehole depth), amphibole-altered basalt (borehole IDDP-01, 1686 m borehole depth), fine-grained basaltic dyke with scarce alteration (borehole IDDP-01, 1970 m borehole depth), and rhyolite (borehole KJ-39, 1637-1646 m borehole depth). All experiments are initiated with a 5 mm run-in slip at a loading point slip rate V of 10 μm/s followed by the SHS sequence with a hold time t_hold increased from 3 s to 10,000 s, separated by a slip interval of 1 mm.

The frictional strength μ_ss (friction coefficient during run-in) slightly increases with T_f in non-altered and amphibole-altered basalt and slightly decreases with T_f in chlorite-altered basalt, basaltic dyke, and rhyolite. However, for all rock types, μ_ss is higher (μ_ss__vap> μ_ss__sup and μ_ss__liq) when vapor is present (only exception, non-altered basalt with μ_ss__sup>μ_ss__vap> μ_ss__liq).

The frictional healing Δμ (frictional strength recovery during holds), is highest at T_f=400˚C in vapor and supercritical water. Still, the effect of T_f and the physical states of water on frictional healing rate (β=Δμ/log(1+t_hold/t_cutoff)) depends on rock type. In non-altered basalt, β increases with T_f but decreases in vapor water; in chlorite-altered basalt and basaltic dyke, β increases with T_f and is independent of the physical state of water; in amphibole-altered basalt and rhyolite, β is independent of both T_f and the physical state of water. However, systematic microanalysis of the deformed gouges is required to understand the underlying mechanisms. 

Lastly, for measured constant machine stiffness in this T_f-P_f range, all tested gouges show stable sliding (creep) at T_f=100˚C but become unstable (stick-slip) at T_f=200˚C (basaltic dyke) and T_f=300˚C (other rock types) regardless of the physical states of water. The highest stress drops during stick-slip are measured in supercritical water (non-altered basalt) or vapor (all the other gouges). Consistent with the seismological observations, our laboratory data show that the fault/fracture network in Krafla reservoir is less prone to nucleate earthquakes in the shallow hydrothermal system (T_f~170˚C, < 1 km depth), with most earthquakes located in the deep hydrothermal system (T_f≥300˚C, 1-2 km depth).

In conclusion, both temperature and the physical states of water should be considered when interpreting the seismicity in geothermal fields. 

How to cite: Wu, W.-H., Feng, W., Gomila, R., Tesei, T., Violay, M., Mortensen, A. K., and Di Toro, G.: The Effect of Temperature and Physical State of Water on the Frictional Properties of Gouges from Krafla Geothermal Field (Iceland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13704, https://doi.org/10.5194/egusphere-egu25-13704, 2025.

Laboratory investigations into the behavior of fault zones have been a significant focus in experimental rock mechanics over the past decades. Various approaches have been developed, ranging from analog models to testing natural samples in triaxial cells. The primary goal of the latter is to infer the physical mechanisms responsible for failure under realistic conditions encountered in natural settings, albeit on small sample sizes (e.g., centimeter scale). In contrast, analog modeling aims to replicate similar mechanical behavior by applying scaling laws to geometry and material properties.

To address the spatial scale limitations of classical rock mechanics, we developed new experiments that bridge the gap between traditional rock mechanics and analog experiments. These experiments utilize the unique capabilities of the DIMITRI setup, a giant true-triaxial apparatus (1.5m × 1.5m × 1m). Due to the size of this experimental device, the maximum stress it can apply is limited to 2 MPa per principal stress. Consequently, we chose polystyrene as an analog for rocks. The low elastic properties of polystyrene slow down physical processes, enabling comprehensive observation of rupture phenomena, from initiation to failure arrest. Our objective is to investigate the interplay between different types of slip occurring along the interface.

In this study, we conducted stick-slip experiments on large-scale polystyrene blocks with a pre-cut surface area of 1.5 m². We applied shortening rates ranging from 1 to 10 mm/min. Our experiments successfully reproduced stick-slip behavior, allowing us to observe variations in frictional behavior along the interface and identify different types of slip, from slow slip to dynamic slip.

How to cite: Bonnelye, A., Gouedar, A., and Faure-Catteloin, D.: PolystyQuakes : what can we learn from the use of polystyrene as analogue to earthquakes?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16260, https://doi.org/10.5194/egusphere-egu25-16260, 2025.

Faults are heterogeneous at all scales. Crustal faults extend for tens or hundreds of kilometers across which they intersect many different lithologies. In the fault core, meter-scale blocks are embedded within a shear zone mélange and, at the grain-scale, fault segments comprise patches of weak and strong minerals. This structural heterogeneity may be  associated with an heterogeneous stress distribution on-fault and has therefore been invoked to explain observations of different slip behaviours occuring simultaneously and at the same location on individual faults.

Conceptually, the structural and mechanical heterogeneity along fault is often described in terms of rheological asperities that can either be competent, have a velocity-weakening frictional behavior and tend to slip unstably or be less competent, have a velocity-strengthening frictional behaviour and slip stably. To understand the spectrum of slow, intermediate, and fast slips behaviors observed in nature, the laboratory studies have investigated the effect of rheological asperities on fault stability and slip behaviour. Laboratory experiments have been performed using mixtures of gouge materials with different frictional properties mixed homogeneously in various proportions or using spatially heterogeneous gouges with predefined layering perpendicular or parallel to the shear direction. In gouge samples prepared using talc-calcite mixtures, a 20% fraction of talc – the weak phase – was shown to drastically change the frictional properties of calcite gouge. However, recent results for vertically segmented gouges prepared from claystone and sandstone showed that fault friction and its rate-dependence are not simply controlled by the weakest lithology nor by a homogeneous mixture of the juxtaposing lithologies.

We performed friction experiments at room temperature in a servo-controlled biaxial apparatus using homogeneous and heterogeneous gouge samples prepared from calcite and talc minerals in various proportions by weight. Calcite and talc were chosen for their well-known antagonist frictional behaviour, as the strong velocity-weakening lithology and weak velocity-strengthening lithology, respectively. Heterogeneous gouge samples consist of a cylindrical inclusion of talc/calcite embedded within calcite/talc. For each experiment, two identical layers of gouge were placed in between three grooved sliding blocks, in a double-direct shear configuration, and a constant normal stress of 40 MPa was applied. Samples were sheared at a sliding velocity of 10 µm.s-1 until a steady state was reached. Velocity-stepping and slide-hold-slide sequences were then performed, under fully dry conditions. 

Overall, we observe that the coefficient of friction decreases with increasing talc content. However, depending on the geometry of the slip interface – a weak inclusion in a stronger and continuous lithology or the opposite – the decrease in strength associated with the presence of phyllosilicate minerals varies non linearly. Velocity weakening during shearing is reduced in the case of a strong calcite inclusion embedded in a weaker talc continuum. Our results show that the rheological heterogeneity associated with the presence of weak or strong inclusions exerts a second order control on the frictional behaviour of our simulated gouges.

How to cite: Carbillet, L., Guérin-Marthe, S., Hofer Apostolidis, K., and Violay, M.: Effect of strong and weak inclusions on the frictional behaviour of fault gouges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16382, https://doi.org/10.5194/egusphere-egu25-16382, 2025.

Subduction zone thrust fault systems accommodate deformation and guide the dynamics of converging tectonic plates. Investigating the frictional, healing, and deformation mechanisms at shallow depths within these zones is important for enhancing models of fault zone mechanics, slip behavior, and material transfer processes, as well as for understanding the nucleation and propagation of megathrust earthquakes. The Gova Fault Zone (GFZ), located within the basal portion of the Sestola-Vidiciatico Unit (SVU) in the Northern Apennines (Italy), offers a unique opportunity to examine the frictional properties, healing dynamics, and deformation processes within an exhumed erosive subduction channel.

The GFZ consists of multiple thrust surfaces that juxtapose highly folded and strained phyllosilicate-rich sediments derived from the upper plate (Marmoreto Marls, Fiumalbo Shales, FIU, and Civago Marls Fms., CIV) onto foredeep turbidites (Gova Sandstone Fm, GOV) of the lower plate.

We sampled the rocks in across the GFZ transect from the footwall GOV sandstones into the SVU shear zone, a sheared Civago marls and Fiumalbo shales.

Fault rocks were reduced to gouge and sheared in a rotary shear apparatus equipped with a hydrothermal vessel (RoSA+HYDROS, University of Padova) under an effective normal stress of 20 MPa and fluid pressure of 6 MPa, at both 25°C, and 200°C. We measured the friction and the time-dependent recovery of frictional strength during simulated interseismic periods (i.e., the healing).

The footwall GOV sandstone gouges are dominated by cataclastic processes, are frictionally strong and their friction increase from μ = 0.49 at 25°C to µ = 0.57 at 200° C. They are also characterized by positive healing and a transition from stable slip to stick-slip at 200° C.

The hangingwall rocks are frictionally weaker: the CIV marls show μ = 0.27 (25°C)-0.31 (200° C) and the FIU shales µ = 0.2 (25°C)-0.25 (200° C), display null/negative frictional healing rates. Both rocks maintained stable sliding, facilitated by phyllosilicate lamellae reorientation and buckling. The CAT, show intermediate friction µ = 0.37 (25°C)-0.42 (200° C) but negative healing rate slip behavior dominated by stable sliding.

The measured in the experiments of the footwall sandstones would, in nature, force strain to migrate into the weaker lithologies of the hangingwall. This “migration” of strain favors (1) the development of thrust surfaces within the hangingwall, such as the FIU on CIV contact, and contributes (2) to erosion, enabling the transfer of material from the upper plate to the lower plate. The positive frictional healing and stick-slip behavior at 200° C in the siliciclastic fault rocks (GOV) suggest a role of the footwall in favoring seismic slip nucleation. Conversely, the weakness and lack of frictional healing suggest a predominantly aseismic or slow slip behavior in the phyllosilicate-rich lithologies. Collectively, we found that frictional and microstructural heterogeneities between subducting sediments and the tectonic mélange at shallow depths may control the erosional vs. accretional character of subduction zones and be responsible for complex slip behavior within the frontal thrusts of subduction zones.

How to cite: Diamanti, R., Salvadori, L., Remitti, F., Mittempergher, S., Molli, G., Di Toro, G., and Tesei, T.: Frictional properties and healing in sedimentary subduction fault zones: insights from the Sestola-Vidiciatico unit, Northern Apennines., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17462, https://doi.org/10.5194/egusphere-egu25-17462, 2025.

We aim to determine the feedback between fault dynamics and fault gouge structures by examining gouge structures that formed during rupture and slip of initially intact granite under upper crustal conditions. Experiments were conducted under quasi-static (3·10^-5 mm/s), weakly dynamic (0.27 mm/s) and fully dynamic (≫1.5 mm/s) conditions, with or without fluids, and limited slip displacement (max. 4 mm). The extent in gouge amorphisation positively correlates with deformation rate, and we detected evidence of melting, e.g., magnetite nanograins, associated with the highest deformation rates. Gouge nanostructure is directly correlated to power dissipation rather than total energy input. The presence of amorphous material is shown to have no detectable impact on the strength evolution during rupture. We highlight that gouge textures, generally associated with large displacements and/or elevated pressure and temperature conditions, can form during small slip events (Mw <2) in the upper crust from initially intact materials.

How to cite: Incel, S., Ohl, M., Aben, F., Plümper, O., and Brantut, N.: Nanostructures as indicator for deformation dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17710, https://doi.org/10.5194/egusphere-egu25-17710, 2025.

Accurately modeling faulting in the so-called brittle crust remains a challenge due to limitations in numerical algorithms and problems in choosing realistic constitutive models. These challenges are reflected in difficulties linking observations across scales: from laboratory to outcrop and up to regional geology.

Here we present the Geotechnical Particle Finite Element Method (P-FEM), a large-deformation numerical tool developed to capture detailed progressive failure and fracturing using a non-local formulation.

A key advantage of P-FEM is its ability to simulate localized shear bands (fault zones with finite thickness) that naturally emerge independent of mesh discretization, both in thickness and orientation. Continuous remeshing further enables the modeling of large deformations within a Lagrangian framework, and techniques used to minimize numerical diffusion help producing realistic localized shear/fault zone patterns. Additionally, P-FEM benefits from its foundation in standard finite elements, allowing to use efficient and accurate solvers (tested through years by a large community of users) and a wide library of constitutive models to simulate various geo-materials, including non-cohesive soils and fault gouges, weak porous rocks (that could develop deformation/compaction bands), and “standard” brittle-frictional-plastic materials. Multiphysics implementations including fluid and heat flow are also available but will not be specifically discussed here.

These capabilities make P-FEM particularly suited for investigating fundamental tectonic processes such as (i) fault nucleation and growth in mechanically layered materials, (ii) the interplay between faulting and folding in thrust belts, and (iii) the development of fault damage and/or process zones in materials with heterogeneous mechanical properties. Our contribution will outline the P-FEM method and discuss its application to these tectonic problems.

How to cite: Bistacchi, A., Ciantia, M., Castellanza, R., Mittempergher, S., and Agliardi, F.: Applications of the Particle Finite Element Method (P-FEM) to faulting in the brittle crust, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17832, https://doi.org/10.5194/egusphere-egu25-17832, 2025.

Experimental observations on fault gouges suggest that shear localization is a prerequisite for the nucleation of instabilities. Synthetic gouges typically produce lab-quakes when the shear deformation is localized along sharp, knife-edge shear planes – a condition that satisfies the steady-state existence requirement of the rate-and-state friction framework. Similarly, exhumed fault cores exhibit shear planes so localized that they appear as mirror surfaces.

Yet, the scenario in nature is far more complex. Many faults contain multiple fault cores, multiple localized shear planes, cemented fault rocks, and evidence for fault core recycling. This suggests that deformation localized along a principal slip plane during an earthquake – unlike in controlled shear experiments – does not necessarily persist over the lifespan of a mature fault. While in laboratory gouge experiments the steady state corresponds to a microstructural fabric that does not evolve significantly over seismic cycles, fault rock fabrics in nature evolve significantly during the seismic cycle—remaining far from a simple localized steady-state fabric.

Here, we present a preliminary study aiming at reconciling these two perspectives: the laboratory-derived nucleation, which involves deviations from a pre-existing steady-state, and the field-derived nucleation, often occurring far away from any steady-state condition. To address this, we conducted double-direct shear experiments on quartz gouges at 30 MPa normal stress, reactivating faults via shear stress steps that allowed spontaneous fault acceleration or deceleration.

The novelty of our approach lies in (1) the different textural states imposed on the gouge before reactivation and (2) the integration of acoustic emissions monitored during fault acceleration with post-mortem microstructures. Specifically, we designed three textures: a pre-localized texture – with localized shear planes developed by prior shearing at constant velocity and normal stress of 30 MPa for a few millimeters; a homogeneous texture – compacted under a normal stress of 30 MPa without prior shearing before reactivation; and an overconsolidated homogeneous texture – compacted under normal stress of 60 MPa before reactivation at 30 MPa.

Preliminary results reveal clear correlations between acoustic emission rate, slip evolution, and the degree of localization in post-mortem microstructures. Pre-localized textures remain locked until a critical stress is reached, after which they abruptly accelerate. Homogeneous textures display slow, progressive acceleration, with increasing slip velocity at higher shear stresses. The overconsolidated texture exhibits intermediate behavior. The acoustic emission signature during low constant-velocity slip reflects the grain interactions typical of granular flow, while rapid acceleration produces impulsive lab-quake-like signals typical of localized rupture nucleation.

These preliminary observations suggest a feedback loop between the localization of deformation and instability growth. While this type of relationship between shear strain localization and slip rate is well-established for the co-seismic propagation phase, our observations indicate that it may play a role during the nucleation phase, challenging the steady-state assumption commonly derived from laboratory studies.

How to cite: Giorgetti, C., Pignalberi, F., Mastella, G., Scuderi, M. M., and Collettini, C.: Slip Localization versus Instability Nucleation Feedback Loop: A Laboratory Perspective from Gouge Deformation Experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18843, https://doi.org/10.5194/egusphere-egu25-18843, 2025.

Flash heating is a critical phenomenon in fault gouges, occurring during rapid slip events that generate temperature surges at the grains or asperity contacts. These abrupt temperature increases trigger mechanisms that weaken the gouge material, reducing its shear strength. This process plays a key role in modulating fault dynamics and can significantly impact the propagation of earthquakes [1, 2]. Although many studies have considered microscale friction of uniform or narrowly graded grain sizes, natural fault zones commonly consist of a wide range of particle sizes [3].

In this work, we used a three-dimensional discrete element framework to simulate shear in a granular fault gouge to replicate the rotary-shear experiment. A local temperature-dependent friction law was implemented in which the friction angle of a grain decreases sharply once its temperature exceeds a specified cut-off threshold [4], quantifying how grain size ranges influence the onset of thermally-activated weakening by varying the PSD of our simulated fault gouge—from monodisperse (all grains have the same size) to highly polydisperse (very broad size ranges)—and determining how this range modulates the onset of flash heat weakening. Our numerical results demonstrate that monodisperse samples distribute contact forces more evenly among grains, and that heating and subsequent weakening occur more synchronously across the sample. This uniform distribution of contact forces and thermal effects results in a drop in the macroscopic friction coefficient in a relatively abrupt way. In contrast, samples with polydisperse particles have a wide range of grain sizes, which can give rise to a heterogeneous stress state and thereby strengthen local frictional heating in some areas of the sample, thus allowing a gradual and disordered decline in the macroscopic friction coefficient. Thus, larger grains in polydisperse assemblies can be considered as stress bridges, sustaining higher values of contact forces; on the other side, small grains have lower thermal capacities (via small masses), and they heat up and soften quicker than larger ones with the same frictional work rate. Such a mixture of these aspects explains a larger percentage of weakened particles in polydisperse assemblies and its lower residual friction compared to samples with narrower PSDs. These results emphasize the importance of considering the natural heterogeneity of grain sizes in models of, and observations of temperature-dependent weakening in fault gouges. The polydispersity degree can have a dramatic impact on the rate and extent to which flash heating can induce a transition from a strong (frictional) resisting to a weakened state. Knowledge of these PSD-dependent processes leads to a more realistic representation of dynamic fault weakening and enhances our understanding of earthquake rupture dynamics at naturally heterogeneous fault zones.

References

[1] J.R. Rice. Journal of Geophysical Research: Solid Earth, 111(5), 2006.

[2] B.P. Proctor, T.M. Mitchell, G. Hirth, D. Goldsby, F. Zorzi, J.D. Platt, and G. Di Toro. Journal of Geophysical Research, Solid Earth, 119(iv):3076–3095, 2014.

[3] C. Marone and C.H. Scholz. Journal of Structural Geology, 11(7):799–814, 1989.

[4] A. Taboada and M. Renouf. Geophysical Journal International, 233(2):1492–1514, 2023.

How to cite: Shahabi, H. and Rattez, H.: The Influence of Particle Size Distributions on Flash Heating and Thermally Induced Weakening in Fault Gouges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21574, https://doi.org/10.5194/egusphere-egu25-21574, 2025.

After fifty years of mantle plume theory, the cause and effect remain subjects of intense debate. The scientific community is divided between those who believe that mantle plumes are fueled by a deep mantle source and those who argue for a shallow process related to plate tectonics. Although both the plume and plate hypotheses relate to the effect of thermal anomaly, few studies have attempted to explain the formation of initial thermal instability or the maintenance of magma sources for volcanism and large igneous provinces (LIPs). In this study, by considering the putative link between mantle dynamics, lithospheric breakup and flood basalts, we employ a three-dimensional spherical shell model to simulate the Earth's rifting process under thermal expansion. Based on the physical principles for the phase change of materials, we invoke a qualitative model of decompression-melting generation in rifting-induced abnormally-hot asthenosphere to explain that extra volume growth during the material phase change from solid to liquid can promote the coupling effect between pressure and temperature. Our fracture modeling shows that the shallow-based lithospheric process favors a no-root mantle plume as the source for volcanism. Continental rifting and breakup may be caused by the heat accumulation within the asthenosphere underneath the lithosphere, without the need for the existence of deep mantle plumes. Inversely, the fractures, particularly around triangle conjunctions, may release the stresses around their tips and accelerate the decompression melting, which in turn results in the thermal anomaly underneath the lithosphere inside which fractures develop. Our results reveal that pressure drops caused by uplift-induced rifting can accelerate decompression melting and provide the magma source for potential eruptions. Additionally, the significant increase in magma pressure, resulting from the abrupt volume expansion during the solid-to-liquid phase change, may act as the driving force of magma production. This process can become unstable if the coupling between melting pressure and temperature operates as a positive feedback loop. Such instability may lead to mantle dynamics emerging in a top-down pattern, offering insights into the rapid and voluminous magma eruptions characteristic of LIPs. Namely, the accumulated heat may result in expansion in the mantle which may promote uplifting, weakening and eventual breakup of the lithosphere, with huge outpouring of flood basalts, leading to the great events of LIPs. Furthermore, the associated cooling of the lithosphere occurs due to heat absorption during melting and heat loss during eruptions. This process provides a clear understanding of the short-lived yet massive nature of LIPs.

How to cite: Tang, C., Gong, B., and Chen, T.: Investigation into the formation of large igneous provinces from the perspective of Earth's breakup and induced decompression melting, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-146, https://doi.org/10.5194/egusphere-egu25-146, 2025.

Frictional strength of a fault surface is controlled by the yield strength of microscopic asperities. During any quasi-stationary contact, these asperities transiently creep to a characteristic nm-to-μm length scale to achieve a steady-state strain-rate, which governs the “state” evolution of the fault interface. In the Low-Temperature Plasticity regime, asperities predominantly deform through dislocation creep which is controlled by the dislocation density at the junction. While the density of the statistically stored dislocations (ρ_SSD) controls the steady-state deformation of the asperities, density of the geometrically necessary dislocations (ρ_GND) governs the transient creep.

We have designed a novel nanoindentation based cyclic deformation experiment to assess the evolution of dislocation densities at asperity contact with progressive hardening. Experiments with normal load ranging from 1 to 8 mN and 10 continuous deformation cycles conducted on single crystals of San Carlos Olivine reveal that with increasing iteration of deformation cycle, and thus strain-hardening, Yield Stress and the percentage of anelastic recovery increases nonlinearly. We show that progressive hardening increases the ρ_GND at asperity contact that alters the root-mean-square curvature of the asperity, while a similar increment in the ρ_SSD reduces the characteristic length scale of deformation and increases the macroscopic strength of the material. These observations further validates that the “contact quality” controls the “contact quantity” of nanoscale asperities. Integrating the experimental observations with the existing theories on scale-dependent strength of asperities and nanoscale surface roughness, we have developed a semi-analytical model that relates coefficient of friction with the characteristic length scale of asperity deformation, dislocation densities and roughness parameters. Our model predicts that increasing strain-hardening can reduce the frictional aging for a given amount of fault-normal strain, which provides a microphysical basis for understanding the rate-and-state based friction laws of natural fault surfaces. This study provides a novel mechanistic interpretation of the frictional evolution of nanoscopic self-affine rough surfaces and has potential applications in understanding the transient deformation of the lithospheric mantle.

How to cite: Mukherjee, R. and Misra, S.: Role of Strain Hardening in Frictional Aging of Nanoscale Asperity Contacts , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-912, https://doi.org/10.5194/egusphere-egu25-912, 2025.

Accurate initial geostress state is a prerequisite for the dynamic optimization design and construction of deep-buried tunnels, as well as for preventing disasters such as rockburst and large deformation. Inversion methods of the stress field for underground engineering, which utilize limited measurement data and numerical simulation techniques, have emerged as the primary approach. However, traditional inversion optimization models often treat stress components as independent scalars. This simplification overlooks issues of physical consistency and optimization complexity. Additionally, existing intelligent inversion methods, such as machine learning and heuristic optimization, require a large number of simulations, posing a challenge in balancing accuracy and efficiency. This issue becomes particularly problematic for large-scale tunnels in complex geological conditions where the computational time cost is exorbitantly high, thereby hindering the practical need for quick and precise stress field reconstruction.

To address these challenges, we propose a novel inversion method that integrates a tensor-based objective function with Bayesian optimization (TOF-BO). Concretely, this method regards the stress tensor as a whole, uses the Euclidean distance to measure the deviation between calculated and measured values during optimization, and formulates the objective function as the sum of deviations across all measurement points. Unlike traditional scalar objective functions, this tensor-based objective function preserves the physical correlations between stress components, reduces the dimensionality of the objective function, and effectively avoids the adverse effects of magnitude differences between components on optimization efficiency and accuracy. Given the objective function's dependency on costly simulation, we adopt Bayesian optimization, utilizing active learning to achieve global and efficient optimization.

This method was applied at the engineering site of a deep-buried tunnel under construction in southwestern China. The results showed that the TOF-BO method yielded satisfactory results (average accuracy=90.8%) with only 18 time-consuming numerical simulations, proving that the method can significantly reduce the demand for expensive simulations, effectively decrease computational costs, and possesses the ability to rapidly and reliably reconstruct the stress field within the study area. Compared to commonly neural network methods, the TOF-BO method improves accuracy by approximately 4.6% within the same time cost. In conclusion, the TOF-BO method provides an efficient and reliable solution for the inversion of geostress fields, demonstrating substantial potential for practical applications.

How to cite: Li, T. and Wei, D.: An Efficient Geostress Inversion Method and Its Application under Complex Geological Conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1749, https://doi.org/10.5194/egusphere-egu25-1749, 2025.

Thermal weathering has a long-term (decadal to millenia) effect on the physical and mechanical properties of rocks and can directly influence rockfall hazard. However, despite substantial research, the processes of rock degredation from thermal influences are not completely understood. This study analyzed data from two, 3-meter-deep boreholes spaced approximately 1.8 km apart in western Yosemite Valley, California (USA) subject to different thermal regimes. The boreholes were drilled horizontally into lithologically and macroscopically identical rock (El Capitan Granite) with no visible fractures. However, we located the two boreholes with different aspects, one on a sun-facing cliff with southern aspect, and one on a sun-shaded cliff with northern aspect. Sensors in the boreholes monitor temperature changes at 10-minute intervals and were installed from the surface to 3-m-depth at increasing increment intervals (i.e., at the surface, 5, 10, 20, 30, 50, 75, 100, 150, 200 and 300 cm). A comparison of the temperature data showed significant differences in rock surface temperatures and temperature gradients between the south- and north-facing cliffs. Between April and November 2024, the south-facing site showed a greater surface temperature range (51.2°C) and average (28.3°C) than the north-facing site (28.3°C range and 17.3°C average). At 3-m-depth, the south-facing site had a temperature range of 10.6°C (21.0°C average) compared to a 8.1°C range (13.1°C average) for the north-facing site. We also analyzed the borehole cores using applied ultrasonic P- and S-waves to calculate their dynamic elastic properties. Despite similar lithology and structure, significant differences were found between the sites. Samples from the south-facing slope, which receives more thermal energy given its location in the Northern Hemisphere, proved to be more weathered, coincident with rock of higher porosity and lower dynamic moduli. In contrast, rock samples from the north-facing and consequently wetter slope showed lower porosity, higher elastic moduli, and a more pronounced gradient of weathering towards the surface. We hypothesize that diurnal and annual thermal stress changes play a larger role in rock weathering than previously assumed, possibly exceeding the long-term influence of other factors, such as groundwater. However, further measurements of rock properties at multiple locations are required to confirm this hypothesis.

How to cite: Blahůt, J., Stock, G. M., Collins, B. D., Rastjoo, G., and Racek, O.: Investigating the effects of thermal weathering on bedrock cliffs using in-situ borehole monitoring in Yosemite Valley, California, USA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2916, https://doi.org/10.5194/egusphere-egu25-2916, 2025.

Fluids within low-porosity rocks are transported through networks of interconnected microcracks and fractures. Under crustal conditions, rocks are subjected to true triaxial stress states characterized by three unequal principal stresses, where σ₁>σ₂>σ₃. These triaxial stress states can influence the magnitude and direction of fluid flow in two ways. First, cracks may open, close, and/or slip depending on their orientation with respect to the anisotropic stress field, and thereby potentially reducing fluid flow in certain directions while enhancing flow in others. Second, once the magnitude of differential stresses surpasses the onset of dilatancy in the rock, new cracks form, providing additional pathways for fluid transport. The geometry of these new fractures, and therefore the direction of fluid flow enhancement, is also controlled by the anisotropic stress field.

Despite the fundamental role of triaxial stresses in controlling the magnitude and direction of fluid flow through the crust, very little is known regarding the anisotropy of permeability under true triaxial stress states. This knowledge gap exists primarily because experimental permeability measurements are typically conducted under axisymmetric stress states (σ₁>σ₂=σ₃​) with fluid flow and permeability usually measured only parallel to the σ₁​-direction. To address this, we have developed a new True Triaxial Apparatus (TTA) at UCL equipped with a pore fluid system to deform cubic, saturated rock samples under true triaxial loading while contemporaneously measuring permeability along all three loading axes and recording the output of acoustic emissions (AEs).

Results from tests conducted on 50 mm cubes of initially isotropic Etna basalt under true triaxial loading indicate that, under relatively low differential stresses (σ₁-σ₃<180 MPa), fluid flow is reduced by over one order of magnitude in the direction parallel to σ₁. Increasing the magnitude of stress along the σ₂ axis also results in a decrease in permeability along the same axis. The increase of differential stress eventually leads to an increase in AE hits, which further coincides with a sudden increase in permeability along the σ₂​-axis. Our results revealed two completely different anisotropic permeability behaviours during the progressive deformation of the rock. At lower differential stresses, permeability is stress-controlled and is characterised by the reduction of permeability parallel to σ_1. Increasing differential stresses beyond the onset of dilatancy in the rock results in the creation of new cracks that creates pathways for fluids parallel to the σ₂ axis. Further experiments and analysis are in progress to fully quantify and characterise these behaviours.

How to cite: Stanton-Yonge, A., Mitchell, T., Meredith, P., Healy, D., Browning, J., and Adamus, F.: Stress versus damage-induced permeability anisotropy under true triaxial stress states in Etna Basalt , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3325, https://doi.org/10.5194/egusphere-egu25-3325, 2025.

Fractures in rocks are ubiquitous, from grain-scale microcracks to crustal scale faults. Importantly, fracture networks allow crystalline rocks to store and transport fluids, which can then interact with rock-forming minerals and enhance rock deformation processes, leading to slow, progressive fracture growth that is time-, stress- and environment-dependent.

We previously reported progressive changes in physical and mechanical properties of granitoid boulders exposed at the surface from zero to around 100 ka in Eastern California, USA. We noted systematic decreases in tensile strength, uniaxial compressive strength, elastic modulus and seismic wave velocities, and systematic increases in porosity and permeability, with increasing surface exposure age. We postulated that the observed changes were likely functions of an increase in the level of crack damage over time. Hence, we interpreted the changes as reflecting progressive subcritical crack growth arising from ubiquitous, but relatively low magnitude environmental stresses acting continuously on the boulders over the extensive periods of exposure.

Here, to avoid ambiguity in interpretation, we report direct measurements of key fracture mechanical properties made on samples from the same boulders. The critical stress intensity factor for dynamic fracture propagation (fracture toughness, K_IC) was measured using the Double Torsion testing methodology. We also measured the pre-exponential offset (A) and the subcritical crack growth index (n) in the Charles’ Law relation: V = A (K_I/K_IC)ⁿ, using the same technique (where V is the crack growth rate). We find that K_IC decreases from around 2.0 MPa.m^-1/2 in fresh material to around 0.5 MPa.m^-1/2 in boulders exposed for around 90 ka, and that the A offset increases from -5 to +20. By contrast, we find no significant change in the n index, which has a value of around 60 ± 10, apparently regardless of exposure age.

These results suggest that the ease of nucleation and rate of growth of new cracks increases with exposure age, consistent with rocks weakening over time through decreasing strength. However, this is in direct contradiction with extensive field measurements that appear to show that the rate of crack growth (measured by crack intensity on thousands of rocks) decreases over time.

So, how do we reconcile these apparently contradictory observations? Here we observe that over exposure time, individual cracks can nucleate and then continue to grow under low imposed stress. However, this assumes that the stress reaching the crack tip does not change over time. But, in nature, the stress intensity (K_I) felt at the crack tip is a function of the stress propagating throughout the rock mass. As the bulk rock becomes more compliant (lower Young’s modulus) over exposure time, due to diffuse microcracking, the rock accommodates more elastic strain and translates a lower net stress intensity to each individual crack tip. Thus, we expect the overall rate of cracking in any rock mass to depend on the instantaneous ratio between the decreasing stress intensity factor and the decreasing fracture toughness (i.e., K_I/K_IC).

How to cite: Meredith, P., Nara, Y., Eppes, M.-C., Rasmussen, M., Keanini, R., Mushkin, A., and Mitchell, T.: Progressive changes in rock fracture mechanical properties with exposure age at the Earth's surface., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3556, https://doi.org/10.5194/egusphere-egu25-3556, 2025.

A model for progressive damage and permeability evolution in brittle rocks, accounting for inherent heterogeneity of rocks, has been developed. This model has been incorporated into a comprehensive three-dimensional coupled numerical framework for investigating stress-permeability dynamics throughout the rock fracturing process. Comparative analysis between simulations and experimental results validated the efficacy of the model. Subsequently, the study delved into the damage and failure mechanisms of rock specimens under uniaxial and triaxial compression, exploring the influence of confining pressure on failure plane orientation and the progressive alterations in permeability during damage and fracturing of rock. The findings show that the permeability evolution during fracturing hinges on the initiation, propagation, and coalescence of micro-fractures within rock. Initially, under loading, permeability reduction ensued due to micro-fracture compaction. Subsequent micro-fracture propagation led to a gradual permeability rise until unstable failure, prompting a sharp increase in permeability, denoting macroscopic fracture surface emergence. Furthermore, the mechanical attributes of rock specimens, fracture surface inclination, and permeability shifts were intricately inked to confining pressure: heightened confining pressure correlated with elevated compressive strength, reduced fracture angle, initial permeability levels, and alterations in permeability during macroscopic failure stages in rock samples.

How to cite: Xu, T., Liu, B., Zhu, W., and Li, Z.: A progressive damage and permeability evolution model for brittle rocks , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3905, https://doi.org/10.5194/egusphere-egu25-3905, 2025.

Mineralogical composition and porosity significantly influence the mechanical behavior of hydrocarbon reservoir rocks in crustal conditions. To understand the mechanical failure behavior and dynamic porosity changes with axial loading, triaxial compression experiments were conducted, in three distinct reservoir rock types: KG Basin Sandstone, Bombay High limestone, and Boise Sandstone. Initial porosities of collected samples varied; with KG sandstone at 30%-32%, Bombay limestone at 9.5%-12.7%, and Boise sandstone at 20.6%-25%, determined under dry testing conditions. A range of effective pressures (P_eff) was applied to investigate brittle faulting and cataclastic flow under dynamic axial loading. Both Boise and KG sandstones transitioned from a brittle dilatant regime to a compactive cataclastic flow regime, with Boise sandstone displaying brittle behavior up to 5 MPa P_eff and KG sandstone up to 50 MPa P_eff. Conversely, the Bombay limestone consistently exhibited compactive cataclastic flow at all tested experimental conditions. KG sandstone demonstrated highest peak strength relative to the other rock types due to its lower porosity. Additionally, Boise sandstone showed higher peak strength than Bombay limestone, primarily due to the presence of quartz within the sandstone matrix, which is more resistant relative to the carbonate minerals of limestone formations. In KG sandstone, there was a significant increase in porosity prior to sample failure, particularly up to 70 MPa P_eff, and the final porosity observed post-failure surpassed the initial porosity levels recorded, upto 50 MPa P_eff. In contrast, both Boise sandstone and Bombay limestone showed a continuous decrease in porosity with increasing differential loading throughout the experiment at all tested conditions. Deflection patterns of triaxial curves indicated a shift from shear-induced dilation to shear-enhanced compaction in both Boise sandstone (dilation up to 5 MPa P_eff) and KG sandstone (dilation up to 50 MPa P_eff), while the Bombay limestone predominantly displayed shear-enhanced compaction across all tested P_eff beyond a critical stress threshold. KG sandstone exhibited a transition from pre-failure dilatant to post-failure compactive inelastic strain with increasing P_eff, which contrasts with the post-failure compactive inelastic strain that was consistently observed in the case of the Bombay limestone.

    By integrating these petrophysical and mechanical parameters into reservoir management, hydrocarbon extraction can be made more effective and safer. These insights are essential for creating accurate geomechanical models, which are vital for strategic field operation planning, optimizing production rates, and maintaining reservoir stability.

How to cite: Dasgupta, A., Saha, P., Bal, A., and Misra, S.: Influence of triaxial compaction on the mechanical behaviour and porosity evolution of reservoir rocks., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6063, https://doi.org/10.5194/egusphere-egu25-6063, 2025.

Wildfires are an increasing global concern due to their profound impact on the environment and human life. These events affect a wide range of environments, from arid regions and forests to other highly flammable areas, such as the Bohemian Switzerland National Park in the Czech Republic. In 2022, a large-scale wildfire in this region—characterized by its sandstone rock formations near the Czech-German border—highlighted the importance of understanding the effects of extreme temperatures on rock properties. While wildfires occur almost annually in this region, the unprecedented scale of this event may have been exacerbated by factors such as wind and prolonged hot climate conditions influenced by ongoing climate change.

To investigate the impact of high temperatures on rock properties, we collected rock samples representing all major lithologies across Czechia, including sandstone and crystalline rocks. After preparing the samples, we exposed them to a controlled heating process, mimicking wildfire conditions. Samples were first dried at 105°C and then incrementally heated to 200°C, 400°C, 600°C, and 800°C, with ultrasonic P- and S-wave testing performed after each temperature stage to assess their dynamic elastic properties. The heating process was carefully designed to replicate natural wildfire conditions, including gradual temperature increases, targeted temperature suspension, and subsequent cooling.

Our findings reveal distinct thermal responses in rock properties. Sandstone and crystalline samples initially strengthened after heating to 200°C, likely due to changes in cementation. Beyond this point, progressive weakening occurred, with rocks reaching their weakest state at 800°C. These results align with previous studies, offering valuable insights into the thermal behavior of rock materials under wildfire conditions and contributing to a broader understanding of the environmental impacts of high-temperature events.

How to cite: Rastjoo, G., Blahut, J., Racek, O., Nguyen, X. X., and loche, M.: Assessing the Impact of Wildfires and High Temperature on Rock Properties on Diverse Lithologies in the Czech Republic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6366, https://doi.org/10.5194/egusphere-egu25-6366, 2025.

With the increasing exploration of the Bohai Bay area, deeply buried metamorphic rock paleoreef reservoirs have become a key focus of exploration. These reservoirs typically consist of fractures and dissolution cavities, exhibiting strong heterogeneity and characteristics of low porosity and permeability. Their pore structures are extremely complex, which brings considerable uncertainty to the classification of reservoir effectiveness. At the same time, the contribution of the rock skeleton to the resistivity logging values in metamorphic rock paleoreef reservoirs is much higher than that of formation fluids. Consequently, conventional fluid identification methods based on resistivity logging are significantly limited in these types of reservoirs. Thus, the effectiveness classification and fluid identification of metamorphic rock paleoreef reservoirs pose a considerable challenge to logging personnel.

This paper conducts an in-depth analysis of the logging response characteristics of pulse neutron logging in metamorphic rock paleoreef reservoirs, specifically the counting rates of inelastic gamma rays, the decay rates of gamma rays over time, and the counting rates of thermal neutron capture gamma rays. It proposes a novel method for fluid property identification in metamorphic rock paleoreef reservoirs using pulse neutron logging.

The analysis reveals that the gamma counting rate of the far-detector of pulse neutron logging is significantly influenced by high-density minerals such as biotite and pyroxene. A method for correcting the gamma counting rate based on lithology calibration for high-density rocks is thus introduced. When the reservoir contains gas or is a gas layer, the gamma long-short source distance counting rate for inelastic collisions shows a distinct “intersection” characteristic. This feature can effectively identify gas layers. When the reservoir is a liquid-bearing layer, a novel fluid identification method based on the reconstruction of the rock skeleton's relative atomic weight curve is proposed. This method first optimizes the multi-mineral model based on X-ray diffraction analysis to calibrate mineral content, then calculates the relative atomic weight of minerals based on the mineral element content, and finally derives the theoretical relative atomic weight curve for the rock skeleton along the entire well section. The effective reservoir is identified using the intersection feature between this theoretical curve and the macroscopic thermal neutron capture cross-section curve obtained from pulse neutron logging. Additionally, oil-water layers are discriminated based on oil and gas shows recorded in the field.

This innovative method for correcting the gamma counting rate based on lithology and reconstructing the relative atomic weight curve for fluid identification has been successfully applied to the effectiveness classification and fluid identification of the Paleoproterozoic paleoreef reservoirs in the BZ26 and BZ27 oilfields in the Bohai Bay. The logging interpretation accuracy exceeds 85%, which partially addresses the limitations of conventional resistivity logging in evaluating Paleoproterozoic paleoreef reservoirs.

How to cite: Meng, L., Li, J., and Xu, M.: Research on the Effectiveness Classification and Fluid Identification Methods of Complex Paleoreef Reservoirs Based on Pulse Neutron Logging, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8171, https://doi.org/10.5194/egusphere-egu25-8171, 2025.

The chalk cliffs of northern France are exposed to considerable erosion, resulting in a significant coastal retreat of up to 1 m per year on average. A key concern is how the mechanical properties of the chalk evolve under different weathering conditions. Previous research, based on a limited number of samples, has provided a preliminary understanding of potential changes in the mechanical properties of chalk in altered and unaltered states. As part of the DEPHY3GEO project, we conducted experiments on Saint Marguerite Chalk, which is part of the Newhaven Chalk Formation. Due to the inherent low strength of the chalk, some conventional displacement measurement techniques are inappropriate. Therefore, we used digital image correlation (DIC) coupled with basic acoustic measurements. Experiments were performed on chalk samples exposed to various weathering conditions, including salt solutions, fresh water, and thermal cycling. These experiments consisted of uniaxial and confined compression tests, which allowed us to evaluate the influence of weathering on the mechanical behavior of the chalk. Results show that water saturation of chalk rock significantly reduces by half or more its maximum compressive strength. Ongoing work will further investigate the weathering of chalk by studying its effect on micro- and macro-scale structures through structural analysis of cliff samples and scanning electron microscopy (SEM).

How to cite: Chalé, A., Bu, F., Jaboyedoff, M., Costa, S., Maquaire, O., and Kouah, M.: The Influence of Weathering on the Mechanical Properties of Chalk: Study of the Saint Marguerite Chalk , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11784, https://doi.org/10.5194/egusphere-egu25-11784, 2025.

Inherent complex internal architecture within fault zones, governed by diverse geological factors, results in heterogeneous mechanical variability, causing uncertainties in subsurface ground conditions. Therefore, understanding the spatial variations in mechanical stability in a fault zone is crucial to appropriate engineering mitigation plans and cost reduction for surface or subsurface infrastructure projects. The Great Glen Fault (GGF) is one of the major NE–SW trending strike-slip faults in Scotland, exhibiting complex internal architecture resulted from the multiple reactivation events and exhumation. The Torcastle block, a fault-bounded sliver within the fault core of the GGF, contains heterogeneous micaceous shear zones, faults, and local dykes cutting foliated psammitic–pelitic gneiss and quartzite. At the Torcastle block, this study synthesizes the parallel structural geological and engineering approaches to decipher the relationship between structural features and mechanical stability by mapping structural domains, topological nodes, fracture densities, and engineering Q-values. Four fracture types are classified based on the spatial distribution pattern and geometrical relationships with local faults and foliations. The heterogeneous spatial patterns of faults, fractures, and foliations at the Torcastle block define several fault-bounded structural domains. The geometrical properties of fractures are highly variable, but they clearly relate to the dyke distribution and local foliation trend in each domain. Mechanically weak zones, represented by low Q-values, are highly heterogeneous but concordant with the areas of high fracture and topological X and Y node density. These mechanically unstable zones are typically related to the following structural features in a fault zone, including major shear or fault strands and embedded blocks, intruded igneous dykes, abutting areas of faults with different orientations, and highly rotated blocks showing re-oriented local foliations. Correlation analysis between Q-values and other parameters, including fracture density, RQD, Jn, Jr, and X and Y node density, reveals different contributing patterns of each parameter to mechanical stability in each structural domain. Especially, the zone of highly rotated local foliations exhibits lower mechanical stability, despite relatively low fracture densities compared to other mechanically weak zones, due to increased fracture orientation variability and connectivity. The results of this study highlight the heterogeneous internal architecture of fault zones and their relationships with mechanical stability distribution, which shed insight into forecasting mechanically weak zones in rock masses and reducing geotechnical risks for subsurface engineering projects.

How to cite: Kim, N., Zoe K., S., Yannick, K., and Christopher D., J.: Deciphering Heterogeneous Mechanical Stability in an Exhumed Fault Zone through a Structural-Geotechnical Approach: A Case Study from the Great Glen Fault, Scotland., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11919, https://doi.org/10.5194/egusphere-egu25-11919, 2025.

Acoustic Emissions (AE), the laboratory analogs for seismic activity, offer a controlled environment to study deformation and failure mechanisms. By leveraging high-precision three-dimensional localizaton techniques, researchers can analyze ongoing these mechanisms during rock deformation experiments. The spatial resolution is thus crucial for increasing our capability to understand and predict failure modes in natural and engineered systems.

Despite recent advances in localization techniques, automated AE localization faces significant challenges. Conventional AE processing systems generally extract a limited set of parameters, such as arrival time defined as the first overcoming a given amplitude threshold. While these parameters provide the bulk information, they often overlook critical signal aspects, underestimating AE phenomena complexities and compromising the localization accuracy. In fact, amplitude thresholds may not capture accurately the signal onset, particularly in noisy or complex waveforms.

This study proposes a new methodology to improve source location accuracy and AE event classification by developing an automatic picking system tailored to seismic signal characteristics and set on Signal-to-Noise Ratio (SNR). The novel algorithm introduced here overcomes conventional amplitude-based thresholding by including broader waveform characteristics, source-receiver distance and wave propagation path. The analysis operates on multiple signal windows and provides uncertainty estimates, enabling more accurate AE location.

The AE source localization process was carried out using the Time Difference Of Arrival (TDOA) method, widely applied in rock deformation laboratory experiments. This approach considers signal arrival time differences at multiple transducers and, with a velocity model, estimates the three-dimensional coordinates of AE sources. The localization quality was assessed via four key parameters: 1) RMS (Root Mean Square) between observed and calculated arrival times, 2) localization errors along the three principal coordinates, 3) MAPE (Mean Absolute Percentage Error quantifying arrival time differences), and 4) the average azimuthal gap across three principal planes. These parameters quantify discrepancies in location accuracy and are employed to assess the final localization.

We applied our methodology to waveform data of AE recorded by an array of twelve 1 MHz piezo-electric transducers during conventional triaxial deformation of a 40 × 100 mm Darley Dale sandstone cylindrical sample (King et al., 2021) at 20 MPa confining pressure. We show that our approach reduces the localization errors and improves the AE detection and localization accuracy. By addressing conventional AE location limitations, this work advances AE-based monitoring toward more accurate and reliable results, providing higher resolution and improved information to describe the damage micro-mechanisms driving failure in stressed rocks. 

How to cite: Adinolfi, G. M., Chen, Y., and Vinciguerra, S. C.: Acoustic Emission Source Localization Techniques: A Methodology for Improved Localization Accuracy in Laboratory Deformation Experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12108, https://doi.org/10.5194/egusphere-egu25-12108, 2025.

Volcanic eruptions are often preceded by intense deformation and volcano-tectonic microearthquakes, which evidence the progressive failure of the volcanic edifice. Studying this process may be of interest for the more general understanding of the progressive failure of rocks.

Active volcanoes are pressurized by fluids and undergo considerable deformation prior to eruption. Surface deformation and seismicity are recorded continuously by volcanological observatory networks; both are due to the action of fluid pressure and rock weakening with deformation, and can be used to quantify fluid pressure variations and rock damage. In this talk we will show how coupling a simple fluid pressurization model with a seismicity-based damage model can be used to explain the surface deformations recorded on basaltic volcanoes. In particular, we will describe the foundations of the damage model. We'll show how damage, crack interaction and stress diffusion can explain the inverse Omori law often evidenced before eruptions, and the relationship between this law and entropy production during progressive rock failure. Finally, using a dataset from 24 pre-eruptive periods at Piton de la Fournaise, we’ll show how these concepts can be used to track the temporal evolution of the state variables that can help describe pre-eruptive processes.

How to cite: Got, J.-L., Peltier, A., and Marsan, D.: What can we learn from progressive rock failure in volcanoes?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12123, https://doi.org/10.5194/egusphere-egu25-12123, 2025.

The Universal Distinct Element Code (UDEC) based on Discrete Element Method (DEM) has gained widespread prevalence in simulating multiscale rock failure in varied branches of geotechnics. Simulation performance demonstrates a heavy reliance on modelling parameters. The trial-and-error approach and parametric sensitivity analysis have long been the primary method employed in the parametric calibration in UDEC. However, they share the drawbacks of excessive computational resources, high dependence on human subjectivity, and the challenge of handling high-dimensional and nonlinear complex parameter spaces. To address this issue, we employed artificial intelligence (AI) to handle multidimensional data and higher-order nonlinear relationships between modelling parameters and macroscopic responses of numerical models. A wide range of preset gradient-based modelling database was established to pre-train the machine learning model to map the parametric relationships. Then, this pre-trained model was combined with an experimental database with various lithologies to conduct an inverse search of the input parameters in UDEC. To further improve the estimates, a gradient-based hyperparameter optimisation, implemented via GridSearch, was applied to identify the optimal parameter set by minimising the loss function. The calculated modelling parameters were subsequently input into UDEC for simulation and validation. Hundreds of comparisons reveal that the simulated results by UDEC align closely with those from the experimental database, demonstrating the feasibility of our model. This research provides a substantive solution to the parametric calibration in UDEC, significantly improving both the reliability and convenience of UDEC simulations.

How to cite: Bu, F., Lin, R., Jaboyedoff, M., Derron, M.-H., Liu, W., and Xue, L.: AI calibration of modelling parameters in UDEC, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12136, https://doi.org/10.5194/egusphere-egu25-12136, 2025.

The formation of surface-parallel exfoliation fractures, or “sheeting joints,” in rock domes produces some of the most intriguing and celebrated landforms on Earth. In 1904, G.K. Gilbert outlined three mechanisms for exfoliation fracture formation: (1) contraction during original cooling, (2) decompression during exhumation, and (3) post-exhumation surface processes. Recent research, including direct measurements during spontaneous exfoliation, has emphasized the influence of solar heating on progressive (subcritical) fracture propagation. This study investigates the mechanisms driving exfoliation fracturing at Arabia Mountain, a biotite orthogneiss dome near Atlanta, Georgia (USA), which experienced a spontaneous exfoliation event in July 2023. Digital elevation model differencing and field observations revealed the event uplifted a ~250 m² area by ~30 cm, buckling sheets up to 12 cm thick, and leaving traces of rock fragments and dust thrown meters away from fractures. Following this event, we installed instrumentation during the summer of 2024 to monitor surface-parallel stresses, local seismic activity, and subsurface rock temperatures at the site. Multiple subsequent exfoliation events in June 2024 were captured in real-time, including direct observations of progressive fracture propagation and dynamic rupture during a period of high temperatures. Relative surface-parallel stresses measured at variable depths in two boreholes revealed clear daily cycles that appear correlated with diurnal patterns of solar heating. A decrease in stress magnitudes and rock temperatures and increased lag time with depth further supports links between rock stresses and solar heating at the surface.

These observations support the hypothesis that subcritical cracking can be initiated or propagated due to thermal stresses and highlight the critical role of solar heating in progressive rock fracturing. The implications of these findings extend beyond Arabia Mountain. The sensitivity of rock domes to thermally induced stresses elevate concerns for an increased hazard of spontaneous exfoliation and rockfall events with future climate warming. Understanding the interplay between thermal stresses, mechanical fracturing processes, and pre-existing damage is critical for predicting such hazards and improving mitigation strategies. Furthermore, our observations and monitoring results provide valuable insights into the fundamental mechanics of subcritical fracturing, which can aid in determining the influence of surface weathering and erosion—key processes impacting the evolution of rock domes. We highlight the importance of multidisciplinary research in advancing our understanding of exfoliation joint formation, and more broadly towards disentangling the impacts of climate change on rock dome stability and landscape evolution.

How to cite: Reynolds, A. N., Eppes, M. C., Collins, B. D., Peng, Z., and Lang, K. A.: Influence of solar heating on spontaneous rock exfoliation at Arabia Mountain, Georgia, USA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12839, https://doi.org/10.5194/egusphere-egu25-12839, 2025.

The Kırık Tunnel in Erzurum is an important route in the highway network designed to connect the northern and southern regions of Turkey. The tunnel, planned to be 7 km long, 10 m high and 7 m wide, passes through a geologically complex region. Preliminary investigations have revealed that the tunnel route is predominantly composed of clayey limestone and marl succession with variable slopes and orientations. During the tunnel construction works, a cave-in occurred during excavation after the water flow and a fault zone containing sandy-gravelly and organic matter was encountered at the 1+825+70 km section of the tunnel. The discovery of the crushed zone due to faulting necessitated a change in the tunnel design and it was decided to apply the back analysis method to understand the collapse mechanism. The deformation data affecting the tunnel were obtained with the help of load cells and back analysis was performed to determine the parameters of the collapse material from this deformation value at the time of collapse. Rock mass classifications were made using the parameters obtained from field and laboratory observations. As a result, with the help of Rocscience RS2, the collapse in the Kırık Tunnel was analyzed by finite element method and back analysis was performed. During the back analysis, the lateral vertical stress pressure acting on the faulted weak zone had to be re-evaluated. The k value changes in the numerical calculation model were examined from the existing approach methods and the comparison of these methods depending on the deformations in tunnel construction was given within the scope of the study. As a result of these data, new design parameters were found and grouting and support recommendations were given to overcome the stability problems in the tunnel. Accordingly, the lateral vertical stress ratio was taken as 1.6, which is normally 0.3, and the lateral pressure in the tunnel was determined as higher than the vertical pressure. With the new parameters, the unstable zone in the tunnel was theoretically crossed without any problems.

How to cite: Eslik, O., Undul, O., and Dogu, M. M.: The Effects of Unstable Fault Zones on Design Parameters of Tunnels (The Case of Erzurum Kırık Tunnel), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12997, https://doi.org/10.5194/egusphere-egu25-12997, 2025.

Understanding the damage processes in clay-bearing rocks is a decisive factor in geological engineering. But, more generally, they may also contribute to localized deformation and thus the rupture of fault gauges in seismic zones. Due to their physical and mechanical properties, such as low permeability, fracture healing potential, and effective radioactive elements adsorption capacity, several European countries plan to use these impermeable rocks to confine their nuclear waste in deep geological repositories. However, structural damage could lead to uncontrolled radionuclide dispersion by advective transport, thus the early detection of the damaging nucleation and evolution is decisive in geological engineering.

This study aims to explore the interplay between P-wave ultrasonic velocity and the micro-deformation mechanism identified by digital image correlation (DIC) in order to predict the failure of the sample.

To this end, uniaxial compression tests are performed on small-scale Tournemire shale samples (8 mm in width and twice as long) using a home-designed miniature loading frame under controlled relative humidity of RH = 75% and RH = 20%. These tests involve two simultaneous measurements: 1) the axial and lateral P-wave travel times, recorded by an active emission system, and 2) the full displacement field on the sample surface, based on Digital Image Correlation (DIC) applied to high-resolution optical or Environmental Scanning Electron Microscopy (ESEM) images. The latter allows for the calculation of 2D full strain fields in order to characterize the deformation at different scales while performing simultaneous acoustic measurements. The processed images are representative of two distinct scales: one at the microscale using the ESEM with a resolution of 24 nm/pixel and the other at the mesoscale using an optical camera with a resolution of 0.55 μm/pixel.

The results allow us to discuss the global evolution of the acoustic wave velocities during the uniaxial loading process with respect to the identified active micro-damage mechanisms.

How to cite: Lusseyran, M., Bonnelye, A., Dimanov, A., Fortin, J., Tanguy, A., Gharbi, H., and Dick, P.: Prediction of clay-rich rock failure coupling local and global non-destructive measurement techniques., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13049, https://doi.org/10.5194/egusphere-egu25-13049, 2025.

Rocks exhibit astonishing time dependent mechanical properties, like memory of experienced stress or slow dynamics, which refers to a transient recovery of stiffness after a softening induced by almost any type of loading. This softening and transient recovery is observed in the subsurface and in buildings after earthquake shaking, or in laboratory samples.

Our investigation of anisotropy of the slow dynamics effect under uniaxial loading in dry sandstone samples shows that it is observed independent of propagation direction, while the loading effect shows the expected anisotropy originating from the opening and closing of cracks. These observations put a number of novel constraints on the enigmatic physics of slow dynamics.

We conclude that transient changes in bulk stiffness are caused by sliding of oblique grain-to-grain contacts and resulting changes in frictional properties as empirically described by rate-and-state friction and observed in laboratory experiments across block contacts.

Connecting the nonclassical nonlinearity of heterogeneous materials to the powerful framework of rate-and-state friction provides an elegant explanation for the long searched-for origin of slow dynamics and potentially adds a new perspective for the monitoring of very early stages of material failure when deformation is still distributed in the bulk and just starts to coalesce towards a fracture.

Similar experiments conducted are conducted with fluid saturation under varying confining and effective pressures illuminate the complex impact of pore fluids on the slow dynamics response of the material.

How to cite: Asnar, M., Sens-Schönfelder, C., Bonnelye, A., Curtis, A., Dresen, G., and Bohnhoff, M.: Anisotropy reveals contact sliding and aging as a cause of post-seismic velocity changes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13545, https://doi.org/10.5194/egusphere-egu25-13545, 2025.

Through the application of Multi-temporal Interferometric Synthetic Aperture Radar (MTInSAR) for long-term monitoring of surface deformation, the Agency of Rural Development and Soil and Water Conservation (ARGSWC), Ministry of Agriculture, has identified 315 deep-seated landslide sites with protecting targets across Taiwan as of 2024. For this study, imagery from January 2022 to October 2023 from the ALOS-2 satellite, released by the Japan Aerospace Exploration Agency (JAXA), is used for the MTInSAR monitoring. Based on the MTInSAR surface displacement data, activity indices for the deep-seated landslide sites have been developed, including both the arithmetic mean and inverse area-weighted deformations. The k-mean clustering and risk matrix method are then employed to classify and rank the landslide activity. The analysis reveals that approximately 5.8%, 10.7% and 83.6% of the deep-seated landslide sites are classified as high, medium and low activity, respectively. In addition, statistical clustering techniques are applied to group the surface deformation data, which are then compared to slope units derived from the aerial LiDAR Digital Elevation Model (DEM) for the landslide sites. This approach helps to identify active landslide blocks or subzones within the landslide sites.

How to cite: Kuo, C.-Y., Au, S.-Y., Chan, Y.-H., Chen, R.-F., Chan, K.-C., Lin, E.-J., and Tsai, P.-W.: Monitoring Surface Deformation and Classifying Activity of Deep-Seated Landslide Sites Using Multi-Temporal InSAR, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14383, https://doi.org/10.5194/egusphere-egu25-14383, 2025.

The tensile strength of brittle rocks is commonly determined experimentally using the Brazilian test (splitting tensile strength test). For spatial and temporal upscaling of these experimental results, numerical methods are necessary to predict rock behaviour under complex geomechanical conditions such as foundation, slope stability, underground space and reservoirs studies, and to analyse the influence of individual parameters on the outcomes.

Previous studies on phase-field modeling of rocks often employed a single open flaw to simulate fracture initiation, and two to four open flaws to represent fracture propagation and failure. These flaws were generally arranged in a geometrically ordered pattern. However, in natural rock formations, microfractures are predominantly closed and exhibit a more or less random distribution depending on texture.

This study used a phase-field model to simulate brittle fractures in granite containing multiple randomly distributed, closed pre-existing microcracks, employing the principal stress criterion as the driving force in the phase-field evolution equation.

This study focuses on analyzing the sensitivity of the model to crack density, spatial distribution, and phase-field parameters. The effect of displacement rate was investigated, and phase-field parameters were calibrated accordingly. To demonstrate the presented approach's accuracy, numerical simulations are compared to experimentally obtained results showing that the approach is in principle capable of temporal and spatial upscaling when microstructural features are considered.

How to cite: Asghari Chehreh, H., Witte, L., Duda, M., and Backers, T.: Simulation of displacement rate effect on tensile rock failure using a phase-field fracture approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15632, https://doi.org/10.5194/egusphere-egu25-15632, 2025.

Rock fracturing plays a key role in both the formation of mountain landscapes and natural hazards. Weathering agents, such as daily thermal variations and precipitation, are some of the main triggers of the weathering and fracturing process. However, the mechanisms involved are not well understood, and questions remain about the thermo-mechanical stress field in the near surface of cliffs. 

To better understand the effect of thermal variation on mechanical stress variation at centimeter to meter scales, long-term recordings were made using repeatable ultrasonic acoustic sensors to measure both esound velocity and waveform changes. The acoustic sensors were placed on a few square meters of a 50 m limestone cliff above Chauvet Cave in the Ardeche region of southeastern France.

The results show that daily cycles of velocity changes are evident and appear to correlate with thermal fluctuations and variations in solar radiation. We propose that the velocity variations are due to thermal stress variations in the rock. During the hottest part of the day, the velocity variation causes an increase in compressive hydrostatic stress. At the same time, the spectral analysis of the impulse response shows daily variations with the appearance of high frequency content during the hottest part of the day. Thus, we propose that the hottest times of the day have the effect of expanding the rock surface and thus closing the fractures, which increases the high frequencies content. Conversely, during cooling periods, we can detect tensile stresses that are likely to open fractures and contribute to progressive subcritical cracking within the rock mass.

This work was funded by the European Research Council (ERC) under grant No. 101142154 - Crack The Rock project

How to cite: Rousseau, R., Starke, J., Guillemot, A., Baillet, L., Moreau, L., and Larose, E.: Time-lapse ultrasonic testing for monitoring stress and structural changes in rock cliffs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15953, https://doi.org/10.5194/egusphere-egu25-15953, 2025.

Due to the increasing impacts of global climate change in recent years, nations around the world have been grappling with frequent natural disasters. Taiwan, situated on the Pacific Rim seismic belt, is shaped by active orogeny, resulting in its rugged terrain. The island has experienced numerous typhoons, extreme rainfall, and complex hydrological conditions, making its mountainous areas particularly vulnerable to natural disasters. The accumulation of soil and sediment further alters the landscape of its watersheds, putting both infrastructure and residents at significant risk. This study therefore focuses on the monitoring and maintenance of slopes in Taiwan’s watershed areas.

Since the inspection of mountain roads is limited by terrain and vegetation, this study utilizes the high-resolution Digital Elevation Model (DEM) for geomorphometric analysis to precisely target landslide hot spots, and Unmanned Aerial Vehicles (UAVs) to observe more detailed topographical features. Meanwhile, the Normalized Difference Vegetation Index (NDVI) is used to interpret landslide and vegetation restoration status, while Multi-Temporal InSAR (MTInSAR) is employed to detect topographical changes and observe post-disaster alterations.

Taking the section between Chinhe and Fuxing (92K to 99K) of Taiwan Provincial Highway 20 as a case study, this highway serves as a critical horizontal transportation hub. Following the impact of Typhoon Morakot in 2009, the region has experienced highly unstable and complex hydrological conditions, resulting in persistent damage to its roads and bridges. This study primarily employs high-resolution LiDAR DEM to analyze pre- and post-disaster changes in terrain and river channels. Then the NDVI interpretation, derived from SPOT satellite imagery, reveals that the crown of the original landslide area has been actively developing, leading to the movement of rocks and debris. The MTInSAR results further corroborate this interpretation, confirming that the crown area of Yushui River remains prone to landslides, with new slide events and significant sediment accumulation in downstream areas.

In summary of the analysis and on-site data, the primary disaster-prone factors are the meandering of the Lanong River and the accumulation of soil and sand, leading to extreme instability in the alluvial fans on both banks. After multiple landslides, the damage mechanism is analyzed, revealing that the region is highly susceptible to tectonic activity. The initial results facilitate the overall slope stability evaluation and provide relevant agencies with governance and maintenance recommendations to enhance road safety.

Keyword：High-resolution Digital Elevation Model, DEM、Normalized Difference Vegetation Index,NDVI、Multi Temporal InSAR, MT-InSAR.

How to cite: Huang, Y.-T., Chen, R.-F., Chang, K.-J., Chen, T.-H., Chang, C.-S., Wang, C.-H., Syu, S.-J., Chuang, H.-K., and Chi, C.-Y.: Using high-resolution geomorphometry and normalized difference vegetation index (NDVI) to assess slope stability in the watersheds of Taiwan: A case study of the section between Chinhe and Fuxing, from 92K to 99K of Taiwan Provincial Highway 20., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16144, https://doi.org/10.5194/egusphere-egu25-16144, 2025.

Sea-wave impacts and near-surface thermal fluctuations are periodic stressors capable of exerting long-term mechanical effects that drive progressive rock mass failure and are regarded as a preparatory process for landslides. These processes pose significant hazards in coastal areas, which are expected to increase due to climate change. Despite scientific consensus identifying sea waves as a causative factor for slope instability, the mechanisms that govern subcritical crack growth and the transition to critical failures remain poorly understood. Failures often occur without any precursory signs and may happen even in the absence of major destabilizing forces.

To investigate the fatigue processes experienced by rock masses under periodic loading and to understand the mechanisms driving coastal cliff failure with a goal in hazard assessment, a coastal sector was instrumented, monitoring both subaerial and underwater environments. This monitoring focuses on the effects of stressors and corresponding rock mass deformations. As part of the TRIQUETRA Horizon EU project, the Ventotene Field Laboratory (VFL) was established and inaugurated in May 2024. The VFL was located in a portion of the tuffaceous sea cliff of the Punta Eolo promontory, where a thick succession of ignimbrite deposits (ascribable to the Parata Grande geological unit) experienced large instabilities in the past tens of years.  The cliff is still evolving with rockfall and rock toppling mechanisms, that are threatening the archaeological excavation of the Roman Villa of Giulia (of the 1^st century A.D.) and the Cemetery where Altiero Spinelli, the father of European thought, lies.

The monitoring system includes a fully equipped weather station, conventional geotechnical sensors, and specialized devices for measuring sea-wave characteristics. These devices include a sea-wave and currents Doppler profiler, dynamic titanium water-tight pressure gauges to assess wave impacts at the cliff base, and instruments to measure elastic and plastic deformation of the fractured rock mass, such as crack meters, a biaxial tiltmeter, thermocouples, and load cells.

Additionally, laboratory mechanical investigations were carried out to evaluate the strength and stiffness of the intact rock while examining the roles of water saturation and salt crystallization in rock weathering.

Findings from the first year of monitoring revealed notable responses of the fractured rock mass to intense rainfall events, which caused sharp and partially reversible fracture openings. Cyclical deformation, including dilation and block tilting, was observed in response to daily and seasonal temperature fluctuations. Data collected from the monitoring system have been used to inform a stress-strain finite difference numerical model to analyse the static influence of basal notches on slope predisposition, as well as the preparatory effects on slope stability of combined thermal and marine actions. Ongoing numerical and laboratory geomechanical analyses aim to provide a more comprehensive understanding of the progressive rock failure processes driving the evolution of these complex systems.

How to cite: Marmoni, G. M., Feliziani, F., Grechi, G., Montagnese, M., Bozzano, F., and Martino, S.: Progressive rock failure in coastal cliffs: analysis of preparatory and triggering actions in a field laboratory at the Island of Ventotene (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16797, https://doi.org/10.5194/egusphere-egu25-16797, 2025.

Heterogeneous porous structures, spanning multiple length scales from nano- to macro-levels, are found in both natural and engineered materials. To fully understand their mechanical and fracture behaviors, it is essential to explore the relationship between porosity and mechanical integrity at different scales. In this presentation, we focus on the mechanical responses of these complex structures, with a particular emphasis on the role of nano-porosity. Our approach combines multi-scale analysis, integrating molecular dynamics simulations at the atomistic level with phase-field fracture methods at the continuum level. This allows us to capture critical material properties from the nanoscale, examining how variations in porosity, pore shapes, and their interactions influence the macroscopic mechanical and fracture behaviors. We will present several case studies to highlight the significant impact of nano-pore morphology on the overall fracture response of porous materials.

How to cite: Newell, P.: Phase-Field Fracture Modeling of Porous Materials Informed by Molecular Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20480, https://doi.org/10.5194/egusphere-egu25-20480, 2025.

The world's energy supply depends critically on hydraulic fracturing (HF): HF operations utilize microseismicity to enhance subsurface permeability, so that hydrocarbons or geothermal heat can be extracted economically.  Unfortunately, HF also has the potential to induce larger earthquakes – with some projects being prematurely terminated because of perceived earthquake risks.  To de-risk HF, we use a suite of novel statistical tests called CAP-tests to discern if some physical process has restricted the growth of earthquake magnitudes.  We show that all stage stimulations at UK PNR-1z indicate bound fracture growth, implying a more controllable operation.  Contrastingly, stimulations at Utah FORGE and UK PNR-2 sequentially transitioned into unbound fault reactivation.  The problematic stages (that ultimately led to the termination of PNR-2) are clearly distinguishable using CAP-tests.  We postulate that our research can discriminate fracture stimulation from fault reactivation, contributing to the de-risking of HF operations worldwide.

How to cite: Schultz, R., Lanza, F., Dyer, B., Karvounis, D., Fiori, R., Shi, P., Ritz, V., Villiger, L., Meier, P., and Wiemer, S.: The bound growth of induced earthquakes could de-risk hydraulic fracturing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-110, https://doi.org/10.5194/egusphere-egu25-110, 2025.

Large fluid volume injections into the subsurface are increasingly common across a range of industrial and remediation activities. However, deep fluid injections are often associated with increased seismicity within a few hundred kilometers of the injection sites. The role of aseismic slip as an important precursory signal in induced-seismicity has gained importance in the community due to two reasons: (a) the time and length scales of injection-induced earthquakes are inconsistent with realistic diffusivities, and  fluid-transport models do not match observations, and (b) modern theories of fault weakening suggest that at very high fluid pressures, faults can experience aseismic slip for prolonged periods before ultimately transitioning to unstable, seismic failure driven by static stress transfer.

Our work investigates far-field microseism triggering in NE Texas and NW Louisiana within the Haynesville shale-gas field that has developed since 2008. It includes  the 2012 Mw 4.8 Timpson, TX earthquake, which has been attributed to wastewater injection. Seismicity from a temporary array and national monitoring show an increase in the number and magnitude of earthquakes in the area, with regular ML3 events near the Texas-Louisiana border. InSAR data indicate uplift around some injection wells. We consider multiple injection wells and compute the spatial distribution of geodetic strain rates derived from GNSS velocities and compare them with seismic strain rates from new earthquake data. In the decade following the 2012 event, several microseisms across the Texas-Louisiana border have been recorded, suggesting that critically stressed faults in the vicinity are being triggered in part by static stress transfer, as well as newer injection wells.  We compare fault orientations to current stress, consider Coulomb stress change from the Timpson event, and use fluid transport models to explain the seismicity and vertical land motion observed in the Haynesville Shale play area.

How to cite: Arzabala, E., Sarma, P., Hurtado-Pullido, C., Musila, M., and Ebinger, C.: Fluid-Induced Aseismic Slip: Far-Field Triggering and Static Stress Transfer in the Haynesville Shale Gas Field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3844, https://doi.org/10.5194/egusphere-egu25-3844, 2025.

Seismicity induced by water reservoir and fluid injection are widely known phenomena and have been studied for several decades. However, seismicity induced by crustal unloading in large open-pit mines are seldomly reported in the literature. Here we describe a case of seismicity associated with the large open-pit Cajati mine in SE Brazil, which has been operating for more than 40 years. The mine exploits carbonate rocks of a Mesozoic alkaline intrusion complex. The pit is 1.4 km long and 0.75 km wide reaching 300 m depth. The estimated amount of extracted rock is about 350 Mton. Nine earthquakes with magnitudes in the range 2.0-3.2 Mw have been recorded since 2009 by stations of the Brazilian Seismic Network (RSBR), some of them felt with intensities IV MM in nearby towns. The 2015 mainshock (3.2 Mw) caused expressive cracks in the mine benches, with up to 10 cm displacement. Epicenter relocation of the six largest events, using correlated P- and S-waves at regional distances, show that all events occurred in a single NNW-SSE oriented, 0.5 km long rupture aligned with the major axis of the pit, in agreement with the main trend of the micro-seismicity recorded by the local mine network. Focal mechanism was determined with two techniques: ISOLA envelope and FMNEAR using three stations at 100 to 160 km distance. Both methods show a reverse faulting mechanism with nodal planes oriented NW-SE to NNW-SSE.  This is consistent with the expected mechanism for crustal unloading in open-pit mines. The Cajati mine is located in the Ponta Grossa Arch, in the coastal ranges of SE Brazil, a region with low-velocities at lithospheric depths. This suggests lithospheric thinning that concentrates stresses in the upper crust. In addition, the NE-SW P axis orientation is parallel to the coast line, a pattern that favors concentration of the regional stresses due to continental/oceanic structural transition. Aeromagnetic data shows a clear NNW-SSE regional fault crossing the mine area. The Cajati mine-induced seismicity is a classic case where several positive factors contribute to the inducing mechanism: a) high stresses in the upper crustal, b) favorable orientation of a previously existing weak zone (related to the NNW-SSE fault during emplacement of the alkaline body), and large Coulomb stress changes of about 4 MPa from unloading of the vertical stresses.

How to cite: Assumpcao, M., Schirbel, L., Nogueira, J. A., Carvalho, J., Dias, L., and Bianchi, M.: Seismicity Induced by a Large Open Pit Mine in SE Brazil: Combination of Stress Concentration and Crustal Weakness., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4842, https://doi.org/10.5194/egusphere-egu25-4842, 2025.

we performed microseismicity detection and location using the deep learning method and obtained a high-precision earthquake catalog in the Changning gas field in China. It is found that the spatial and temporal characteristics of seismicity in the region are indicative of its correlation with industrial operations. The distribution of earthquakes at depth reflected variations in reservoir depth and provided valuable constraints on it. The horizontal layered distribution of earthquakes at depth is due to the formation of fracture surfaces from interconnected fractures near the reservoir during hydraulic fracturing (HF) operations, which clearly demonstrates how HF operations impact seismicity. We suggested that the horizontally layered distribution was driven by two fundamental mechanisms: reactivation of pre-existing faults during HF and injection of high-pressure fluids into the reservoir, leading to fracture creation. Several ML ≥4 earthquakes, which did not occur on well-defined seismogenic faults, may have been triggered by pore elastic coupling resulting from regional stress accumulation and fluid injection. Significantly, the ML 4.9 seismic sequence occurring at the basement indicates that fracking has reactivated and promoted pre-existing faults, highlighting the need for further investigation into potential seismic hazards in the region.

How to cite: Wen, Z. and Zhang, N.: The temporal and spatial evolution characteristics of induced  seismicity in the Changning shale gas field based on dense array , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5018, https://doi.org/10.5194/egusphere-egu25-5018, 2025.

Fluid injection-induced earthquakes present a significant challenge for geo-energy applications, such as geothermal systems and CO2 storage. Understanding the earthquake magnitude and frequency in response to fluid injection is of vital importance. Both the pressure and pressure rate are considered dominant parameters for the occurrence of induced earthquakes. Theoretical analyses of a spring-block model [1] have demonstrated that the reservoir response depends on the nondimensional pressure rate, defined as the ratio of the characteristic time of frictional slip to that of pressurisation. The pressure rate effect is most pronounced when this ratio falls within a narrow range of 10-4 to 10-3. These results have contributed to the interpreting laboratory experimental observations, however, the correlation between the injection rate and induced earthquakes at the field scale remains poorly understood.
This work develops a coupled hydro-mechanical model to simulate constant-rate fluid injection into a reservoir adjacent to a sealing, steeply-dipping, rate-and-state frictional fault, aiming to evaluate fault activation behaviour and the associated induced earthquake magnitude and frequency. The fault is modelled as a rate-and-state frictional contact with Mohr-Coulomb fault strength, and deemed to be reactivated when the shear traction on the fault exceeds the fault strength (frictional resistance), which depends on the fault sliding velocity. Rate-and-state fault slip dynamics are resolved using frictional contact modelling through a fully implicit, monolithically coupled finite element formulation. The fault is characterised by velocity-weakening frictional properties, allowing it to slip multiple times during fluid injection. A seismicity rate model is used to simulate the induced seismicity rate along the fault during fluid injection. Given that the nondimensional pressure rate depends on both the critical slip distance (related to the characteristic time of frictional slip) and the injection rate (related to the characteristic time of pressurisation), different combinations of the two parameters within the typical range of field values are examined to investigate the pressure rate effect on induced earthquake magnitude and frequency and seismicity rate.
Results have shown that the critical slip distance affects both the magnitude and frequency of induced earthquakes, whilst the injection rate primarily controls the frequency of induced earthquakes in typical field conditions. Notably, the induced earthquake frequency, along with the induced seismicity rate, shows a positive correlation with the pressure rate. However, the maximum induced earthquake magnitude does not appear to be significantly affected by the pressure rate within the typical range of field conditions. Based on the model results, the range of nondimensional pressure rate, within which the pressure rate effect is significant in field reservoir conditions, is identified. Outcomes of this work may provide valuable guidance for regulating injection rates to mitigate fluid injection-induced earthquakes in geo-energy applications.

Reference
[1] Rudnicki, J.W. and Zhan, Y., 2020. Effect of pressure rate on rate and state frictional slip. Geophysical Research Letters, 47(21), p.e2020GL089426.

How to cite: Cao, W. and Ma, T.: Pressure rate effect on the fluid injection-induced earthquake magnitude and frequency, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5080, https://doi.org/10.5194/egusphere-egu25-5080, 2025.

The connection between fluid pressure, reservoir permeability evolution, slow-slip events, and the triggering of larger earthquakes remains a crucial but unresolved issue in the study of fluid-induced seismicity. Understanding these interactions is essential for seismic hazard mitigation and optimizing subsurface fluid injection productivity.

Discrete Fracture Networks (DFNs) are commonly used to study hydraulic diffusion and seismic activity within fault systems. However, traditional DFN models often rely on quasi-static assumptions and a simple Mohr-Coulomb criteria for earthquake triggering. These limitations hinder their ability to capture dynamic phenomena, such as self-propagating slow-slip events, and they provide little insights into the earthquake dynamics.

This study  addresses these gaps by developing a 2D DFN model capable of simulating both fluid-induced slow-slip events and the potential for earthquake triggering. The model integrates hydraulic diffusion and slip processes governed by rate-and-state friction across several interacting faults within an impermeable, elastic rock matrix. A key innovation of this model is the dynamic evolution of fault permeability, which depends on normal traction changes and accumulated slip, consistent with laboratory and in-situ experiments.

The model was applied to two scenarios, both with and without permeability evolution: (1) fluid injection along a primary rough, rate-strengthening fault, where slow slip events occur and subsequently triggers microseismicity on secondary, smaller faults; and (2) fluid injection within a network of rate strengthening intersecting faults, where fluid diffusion reactivates slip throughout the network. In both cases, the simulated slow-slip events propagate faster than the fluid pressure diffusion front.

Interestingly, the migration patterns of microseismicity in the first case and slow slip in the second resemble diffusion processes, yet exhibit diffusivity values distinct from the imposed fault’s hydraulic diffusivity. This finding suggests that estimates of hydraulic diffusivity based solely on microseismicity front migration may not be accurate, in line with previous experimental and modeling studies.

These results highlight the influence of variable permeability and stress transfer caused by slow slip transients, offering valuable insights into induced seismicity within crustal reservoirs.

How to cite: Romanet, P., Scuderi, M. S., Ampuero, J.-P., and Cappa, F.: Impact of variable permeability in fault networks on fluid-induced seismicity dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5744, https://doi.org/10.5194/egusphere-egu25-5744, 2025.

A three-dimensional quasi-dynamic finite element method is developed to simulate fluid-induced seismicity on faults governed by rate-and-state friction. The coupled nonlinear hydro-mechanical equations governing both the fault and the surrounding rock matrix are solved simultaneously using the Imperial College Geo-mechanics Tool (ICGT), providing fluid pressure and displacement fields. This work highlights enhancements made to the friction module of ICGT, specifically the implementation of the augmented Lagrangian method to enforce fault surface contact constraints. This approach leverages the strengths of both the penalty method and Lagrange multipliers within the finite element framework. A stick-predictor slip-corrector algorithm is developed for the rate-and-state friction law to improve the convergence of the solution. The proposed numerical model captures the dynamic response of a fault to fluid injection, with the fault represented explicitly as a zero-thickness interface element in the mesh. To account for radiation damping effects and prevent unbounded slip rates within the quasi-dynamic framework, a velocity-dependent cohesion term is introduced into the shear stress formulation. The results emphasize the importance of selecting appropriate spatial mesh sizes and temporal time steps to ensure the convergence of the iterative Newton-Raphson solver. The simulation results show that pore pressure changes initiate an aseismic slip front that propagates along the fault, leading to failure in seismogenic zones. This method successfully captures all stages of the seismic cycle, including the transition from stick to slip behavior. 

How to cite: Hosseini, N., Paluszny, A., and Zimmerman, R. W.: Fluid-Driven Slip on a Three-Dimensional Fault with Rate-and-State Friction: A Finite Element Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6205, https://doi.org/10.5194/egusphere-egu25-6205, 2025.

Induced seismicity following fluid injection in geothermal reservoirs presents significant challenges for risk mitigation and hazard assessment. While numerous studies have focused on seismicity during active injection phases, less attention has been given to the critical post-injection period when seismic activity gradually subsides. In this study, we systematically analyze post-injection seismic decay at three prominent geothermal sites—Soultz-sous-Forêts (France), Cooper Basin (Australia), and Basel (Switzerland)—leveraging high-resolution industrial datasets. We thank the EPOS TCS-AH platform and CDGP for providing the data used in this study. This work was supported by the European Union’s Horizon 2020 research and innovation program (DT-Geo, grant agreement No. 101058129).

Using the Modified Omori Model, we characterize seismic event density decay rates and evaluate their dependence on operational and hydraulic parameters, such as wellhead pressure dynamics, injection duration, hydraulic energy, and reservoir diffusivity. Our results highlight the pivotal influence of sustained wellhead pressure and its dissipation rate (γ) on seismic decay, where faster pressure dissipation promotes fault stabilization and leads to reduced seismic activity. Secondary influences include cumulative injection volume and hydraulic energy, which moderate fault reactivation processes. The corner time parameter (c), marking the onset of seismic decay, shows limited correlation with operational metrics, suggesting the importance of site-specific geological properties.

By comparing the Modified Omori Model with alternative decay models (e.g., Cut-off Power Law, Gamma, and Stretched Exponential), we demonstrate its robustness in capturing the temporal evolution of seismicity across diverse geological settings. These findings highlight the critical role of wellhead pressure management in reducing trailing seismic risks and offer actionable insights for optimizing geothermal operations. This work contributes to a deeper understanding of post-injection seismicity, advancing risk management strategies for sustainable geothermal energy development.

How to cite: Wang, Z., Lengliné, O., and Schmittbuhl, J.: Post-Injection Seismic Decay Dynamics at Geothermal Sites: Insights from Wellhead Pressure and Hydraulic Energy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6627, https://doi.org/10.5194/egusphere-egu25-6627, 2025.

Monitoring induced seismicity is an indispensable part of risk management during the creation and operation of enhanced geothermal systems. Due to the relative scarcity of manually labeled, informative datasets of induced seismicity, it can be challenging to evaluate the performance of monitoring tools ahead of time. We have created continuous synthetic seismic waveform data for an induced seismicity sequence at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE). The data are based on a synthetic catalog that mimicks an injection-induced sequence at Utah FORGE and contains approximately 20 000 events occurring during 24 hours with the majority of events during the simulated hydraulic stimulation. Taking into account site-specific geology, induced event waveforms are computed using a spectral-element visco-elastic wave propagation solver and source-receiver reciprocity. Two types of seismic noise are added to create two subsets of test data: low-amplitude Gaussian noise and site-specific correlated noise. We test the retrieval of the known events from the continuous synthetic data using one real-time and one post-processing monitoring workflow based on SeisComP and MALMI  (MAchine Learning aided earthquake MIgration location). The results illustrate reliability and shortcomings of the two monitoring tools. For example, depending on the monitoring tool, the noise conditions and the behaviour of the sequence (injection vs. post-injection), the rate of detected events ranges from approximately 20% to 100%. In addition to this benchmark, the dataset generation also serves as a rough feasibility study for a digital “twin” of wave propagation in an enhanced geothermal system. While uncertainties concerning the elastic medium and receiver coupling, as well as the time to availability of observed induced event data and interpretations are likely to pose challenges, the performance of the reciprocal wave propagation modeling strategy is satisfactory for incorporation into a “twin” if updates to the geologic structure are infrequent.

How to cite: Ermert, L., Shi, P., Lanza, F., Tuinstra, K., Ritz, V., Finger, C., Obermann, A., Rinaldi, A., and Wiemer, S.: A synthetic benchmark dataset for induced seismicity monitoring, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7125, https://doi.org/10.5194/egusphere-egu25-7125, 2025.

The spatial distribution of hydraulic fracturing-induced seismicity is controlled by regional tectonics and local geological structures. In this study, we integrated a high-resolution shear velocity model from ambient noise imaging with 3D seismic reflection data to investigate structural influences on induced seismicity near an active hydraulic fracturing (HF) platform in the Sichuan Basin, China. We conducted continuous seismic monitoring throughout the fracturing period and located over 1,000 earthquakes within the 7 weeks of active stimulation. Tomographic model reveals a distinct first-order, EW-striking velocity boundary near the HF well. This lateral velocity discontinuity aligns closely with the 3D curvature attribute identified in seismic reflection data, with high-curvature areas corresponding to disrupted geological features like small-scale faults or stratigraphic discontinuities. Further quantitative analysis reveals that in addition to the spatial clustering near high-curvature areas, 70% of earthquakes are distributed on the high-velocity side and concentrated within a range of 500 meters from the HF well. Based on these observations, we infer that 1) the high-velocity anomalies are mechanically stronger and more susceptible to the release of cumulative elastic energy, and 2) pronounced attribute variations delineate the principal seismogenic structures responsible for hosting induced earthquakes. Consequently, regions with brittle rock properties and significant structural variations are more seismically sensitive under external fluid injection. Future work will involve applying the ETAS model to better understand the triggering mechanisms of induced seismicity, aiming to provide insights into the interaction between external fluid injection and localized stress perturbations.

These observations highlight the interplay between velocity heterogeneity, structural attributes, and localized stress perturbations in driving induced seismicity. Similar correlations between local velocity structure and earthquake nucleation are observed at a nearby platform, where the majority of over 6000 detected earthquakes are preferentially located near a NE-SW oriented high-velocity structure east of the injection well. Interestingly, both platforms are characterized by sharp topographic relief, with their maximum gradient well aligning with the velocity boundaries. These integrated structural features may prove crucial in identifying local geological structures that are prone to instability and assist strategy development toward risk mitigation of HF-induced seismicity.

How to cite: Zhang, F., Chen, Y., Wang, R., Yu, H., Rinaldi, A. P., and Ritz, V.: Structural Controls on Earthquake Clustering in Hydraulic Fracturing: Insights from Velocity Model and Seismic Reflection Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7395, https://doi.org/10.5194/egusphere-egu25-7395, 2025.

Monitoring induced seismic harzards during the fluid injections has been a significant challenge for geo-energy development. Conventional approaches, such as the (adaptive) traffic light protocol and prediction methods based on statistical and machine learning regressions, often yield limited accuracy due to diverse geological conditions across regions. A promising direction lies in developing precursors to monitor fault reactivation more effectively.

Recent seismological studies have shown that aseismic slip loading is more prevalent than previously thought during fault activation induced by fluid injections (Yu et al., 2021a, b; Eyre et al., 2019, 2022). Slow earthquake signals, like Earthquakes characterized by Hybrid-frequency Waveforms (EHW), occur during the transition from fault creep to brittle rupture induced by fluid injection (Guglielmi et al., 2015). These signals are potential indicators for aseismic slip loading and fault reactivation. However, their longer rupture durations distinguish them from typical induced earthquakes, rendering classic source analysis methods ineffective for real-time monitoring.

To address this limitation, we propose ASTF-Net, a machine learning (ML) model designed to predict Apperant Source Time Function (ASTF) by deconvoluting Empirical Green's Function (EGF) waveform from target waveform in time domain. This approach provides reliable real-time estimates of source durations, to identify slow earthquake signals, specifically EHW, and offers a valuable tool for fault activation monitoring. A robust and well-sampled dataset is therefore crucial for the model's performance.

In this study, we present a dataset designed for developing a single-channel version of ASTF-Net and evaluate its effectiveness using basic ML-models. The dataset consists of three parts: ASTFs, EGFs, and target seismic waveforms. Synthetic ASTFs are generated using kinematic forward modeling with an elliptical rupture model to simulate earthquake events with magnitudes ranging from Mw 3.0 to 4.5 and stress drops between 5 and 20 MPa. These random ASTFs are calculated under various ray paths. We collect EGFs from hydraulic fracturing-induced earthquakes (M1.5-2.5) in the Southern Montney Play, western Canada, recorded by a network of 40 nodal/broadband seismic stations between 2017 and 2020. Synthetic target waveforms are then created by convolving ASTFs with corresponding EGFs. The dataset’s inputs consist of single-channel synthetic seismic waveforms and their corresponding EGFs, with ASTFs as outputs. To assess the generalization and robustness of the model, records from different stations are divided into training, validation, and four test sets with varying difficulty levels based on geographical locations and event counts. Notably, Test level 4 is human analysis results reported by Roth et al. (2022).

We evaluate model performance using basic ML architectures, including MLP, CNN, VGG and U-Net. Performance metrics include the Correlation Coefficient (CC) between predictions and labeled ASTFs, and the relative error in apparent source duration. CNN emerges as the most promising candidate for the further optimization, achieving the following CC > 0.9 across test levels: 87.9% (Level 1), 85.9% (Level 2), and 80.3% (Level 3). The percentages of relative error below 10% are 59.3%, 59.3%, and 51.2%, respectively, for the three levels.

How to cite: Pang, R., Yu, H., Li, G., Meng, H., Liu, Z., Su, C., Zha, D., and Tian, W.: Dataset preparation for Resolving Apparent Source Time Functions (ASTF) and Evalutions Using Basic ML-models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7718, https://doi.org/10.5194/egusphere-egu25-7718, 2025.

Risk modelling is a key tool for mitigating the seismic risk associated with geo-energy applications and CO₂ storage. Prior estimation of potential damages and mapping of affected communities enable, among other things, the feasibility assessment of geothermal projects in their planning phase and the allocation of appropriate resources for damage compensation. This promotes societal preparedness and acceptance towards such applications.  

With rising interest in geothermal energy in Switzerland, the Federal Office of Energy tasked the Swiss Seismological Service (SED) to extend the national Earthquake Risk Model ERM-CH23 (Papadopoulos et al., 2024) to include induced seismicity associated with geo-energy applications and CO₂ injection projects. Since these activities typically trigger shallow earthquakes with low-to-moderate magnitudes, the need arose to extend the range of modelled intensity measures towards intermediate periods, which are more sensitive to potential damage from the expected scenario ruptures. As ERM-CH23 already covers PGV and PSA at 1, 0.6 and 0.3 s, it was decided to additionally integrate PSA(0.4s) and PSA(0.2s). From the perspective of soil amplification modelling, we first verified that the existing ERM-CH23 local response layers (Bergamo et al., 2023) are suitable for induced seismicity scenarios. We then applied the procedure of Bergamo et al. (2023), i.e., combining empirical amplification factors with site proxies via geostatistical interpolation, to generate the additional soil response layers for PSA(0.4, 0.2s). Leveraging an extended ground motion database and proven site condition indicators, the maps cover the whole of Switzerland while achieving a fine spatial resolution (250 m); the high quality of the input datasets contributes to keeping the associated (and mapped) epistemic uncertainty (ϕ_S2S) within reasonable limits.

In addition to seismic risk modelling, the complete set of national soil amplification maps for PSA(0.2 - 1.0s) has also been incorporated into the GRID approach of the current revision of SED's Good-Practice Guide for managing induced seismicity in deep geothermal projects (Kraft et al., 2025). GRID (Geothermal Risk of Induced seismicity Diagnosis, Trutnevyte & Wiemer 2017) is a diagnostic tool developed to classify a project's induced seismicity risk. The PSA(0.2 - 1.0s) amplification maps have been collated to consistently chart soft soil areas (soil types D, E and F of the Swiss building code SIA 261) at the national scale, contributing to GRID’s “local amplification” indicator.

References

Bergamo, P., et al. (2023). A site amplification model for Switzerland based on site-condition indicators and incorporating local response as measured at seismic stations. Bull Earthquake Eng 21, 5831–5865. https://doi.org/10.1007/s10518-023-01766-z

Papadopoulos, A. N., et al. (2024). The Earthquake Risk Model of Switzerland, ERM-CH23, Nat. Hazards Earth Syst. Sci., 24, 3561–3578, https://doi.org/10.5194/nhess-24-3561-2024

Kraft, T., et al. (2025). Good-Practice Guide for Managing Induced Seismicity in Deep Geothermal Energy Projects in Switzerland, Version 3, Report of the Swiss Seismological Service (SED) at ETH Zurich, pp. 80, https://10.3929/ethz-b-000714220

Trutnevyte, E., & S. Wiemer (2017). Tailor-made risk governance for induced seismicity of geothermal energy projects: An application to Switzerland, Geothermics, 65, 295-312, https://doi.org/10.1016/j.geothermics.2016.10.006.

How to cite: Bergamo, P., Sunny, J., Grigoratos, I., Roth, P., Kraft, T., Panzera, F., and Wiemer, S.: Modelling soil response at the national scale for Switzerland in the framework of risk assessment of induced seismicity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8121, https://doi.org/10.5194/egusphere-egu25-8121, 2025.

Underground gas storage (UGS) systems are commonly used to balance seasonal fluctuations in demand and to secure strategic reserves by storing gas in geological trap formations. All underground industrial activities, including UGS, can affect the pore pressure and pre-existing stress state in seismogenic layers, potentially triggering earthquakes. Monitoring microseismicity in such a context is crucial, especially in urban areas. The study area of this work focuses on the Cornegliano Laudense UGS site, near Milan, one of 15 such sites in Italy, where the National Institute of Oceanography and Applied Geophysics (OGS) conducts seismic monitoring. In 2017, nine seismic stations were installed in accordance with national guidelines to establish a baseline of natural seismicity before the start of gas storage activities in December 2018.

Previous studies have shown that the central sector of the Po Plain has weak and deep seismicity due to crustal shortening between the Alpine and Apennine fronts. However, shallow seismicity has occasionally been recorded since monitoring began. Shallow seismicity was recorded both before and after the onset of storage activities, suggesting that it may be related to shallow tectonic structures. At the end of September 2024, the local seismic network detected its first seismic sequence, consisting of nine shallow microearthquakes with magnitudes between 0.9 and 1.3 ML and a depth of ~ 2.5 km. These seismic events occurred near a known thrust fault just outside the storage area.

We present preliminary results of a seismicity analysis performed to understand the origin of these shallow microearthquakes. Detection and location of such small earthquakes is challenging due to their low magnitude and low signal-to-noise ratio in this area. To improve detection, we applied a template matching technique based on the cross-correlation of continuous seismic data with well-located events, known as templates. This process revealed more than 150 seismic events throughout the entire monitoring period, with magnitudes ranging from -1 to 1.6 ML. Initially assigned to the locations of their templates, the hypocenter locations were refined by identifying P and S wave arrival times, where possible, applying both absolute (NonLinLoc) and relative (HypoDD) location methods. Our analysis also identified small clusters of past seismic events like those in the September 2024 sequence using a template matching method. For each sequence, we calculated composite focal mechanisms using the SKHASH code, combining polarities and S/P amplitude ratios for more reliable results. Finally, we examined seismicity diffusion patterns to assess potential fluid movement influences, as seismic events triggered by fluid intrusion often show characteristic spatial and temporal migration patterns.

How to cite: Fusco, M., Guidarelli, M., Romano, M. A., Sugan, M., Romanelli, M., Sandron, D., and Picozzi, M.: Application of methodologies for the analysis of microseismicity in industrial areas: a case study from underground gas storage in Cornegliano Laudense, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9387, https://doi.org/10.5194/egusphere-egu25-9387, 2025.

The Federal Seismic Survey at BGR routinely evaluates seismic events in Germany and neighbouring
countries on a daily basis. The results are supplemented by the outcomes of the seismological agencies of
the federal states of Germany and German universities and stored in an event database and in the German
earthquake catalogue, which is complete for earthquakes with magnitudes M_L ≥ 2.
Furthermore, the events are classified as natural earthquakes, induced earthquakes, or explosions (mostly
quarry blasts). A considerable number of the events are induced earthquakes. They originate from stress
changes due to human activity in the subsurface. The main causes of the induced events are coal mining,
potash salt mining, natural gas extraction and geothermal energy.
We describe the characteristics of the associated seismicity for the different mining regions in Germany. In
contrast to natural seismicity characterized by long-term tectonic processes, the number and strength of
induced seismicity can be strongly dependent on rather short-term temporal and spatial changes following
the mining process.
The seismicity in coal mining regions, e.g., decreased coinciding with the shutdown of coal mining, whereas
seismic activity in geothermal or natural gas fields show different behavior, increasing or decreasing
depending on the location. Additionally, the latter both types of induced seismicity show remarkable
peculiarities in their temporal behavior. Seismic events still occur with a delay after a geothermal power plant
was shut down. Seismic activity can start even several years after the start of extraction in a new natural gas
field.
We show the temporal course of induced seismicity over the last 10 years in dependence on the distinct
extraction types, compare it with the previous decades and discuss the main features. In addition, we also
investigate the magnitude-frequency relationship and the energy release of the induced earthquakes. We
determine these parameters regarding their originators as well as in relation to those of natural earthquakes.

How to cite: Plenefisch, T., Bischoff, M., Gaebler, P., Hartmann, G., and Wegler, U.: Induced seismicity in Germany during the last decade - an overview and update, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9673, https://doi.org/10.5194/egusphere-egu25-9673, 2025.

Construction and cyclic operation of multi-cavern systems within salt pillars present notable geomechanical challenges, including subsidence due to cavern convergence, pressure interactions between caverns, leakage and induced seismicity. Monitoring stations in the northeast of the Netherlands have consistently reported small seismic events (local magnitudes ≥ -2), the underlying physics of which are poorly understood. As the operational activity in the salt domes is expected to scale up due to the prospects of underground hydrogen storage (UHS) in salt caverns, it is crucial to investigate the mechanisms underlying the observed seismic events. More importantly, it is essential to quantify the probability of induced seismic events due to the increase in UHS projects.

This study aims to assess the probability of induced seismicity associated with the prospect of large-scale hydrogen storage (UHS) plans. To this end, it is crucial to understand, analyse, and quantify the mechanisms behind induced seismicity observed due to the salt cavern leaching and cyclic storage operations within the Dutch salt domes. As a necessary bench-mark step for our study, it is essential to explain the occurrence of small-scale events for the existing caverns. We commence by constructing simplified yet meaningful simulation models, which include the basic characteristics of the salt formation, salt cavern, operational conditions, and the presence of structural features in the salt formation as well as in the over- and side-burden. Subsequently, the deformation evolution of the system is quantified and the impact of uncertainties on stress and deformation is assessed. The simulation model will be coupled to a seismogenic source model to compute the spatio-temporal development of the seismic activity in the model due to the deformation evolution.

How to cite: van den Ameele, N., Hajibeygi, P. dr. H., van Gent, Dr. H., and Muntendam-Bos, Dr. A.: Quantification of the probability of induced seismicity associated with large-scale underground hydrogen storage in Dutch salt formations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10194, https://doi.org/10.5194/egusphere-egu25-10194, 2025.

Induced seismicity related to industrial operations including carbon storage, geothermal energy, hydraulic fracturing or wastewater disposal has become increasingly common over the last 15 years. To continue these operations with minimal impact on sites, populations and economic conditions of the operation, it is crucial to better understand the mechanisms that control induced earthquakes and the occurrence of these in both space and time.

This research focuses on enhancing statistical forecasts (using the seismogenic index model and ETAS), specifically for CO2 storage applications. This forecasting is essential for estimating the hazards associated with the operational life cycle of these sites. Additionally, based on these forecasts, we explore operational management strategies, aimed at providing real-time feedback and suggestions to operators. All model calibrations were performed using data from the Illinois Basin Decatur Project – a pilot CO2 storage initiative with injection performed from 2011 to 2014. The resulting forecasts are included within an ensemble forecast within the open-source Operational Forecasting of Induced Seismicity (ORION) toolkit.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

How to cite: Geffers, G.-M., Wang, C., Sherman, C. S., and Kroll, K. A.: Statistical Models to Forecast Induced Seismicity in CO2 Storage , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11791, https://doi.org/10.5194/egusphere-egu25-11791, 2025.

There is still uncertainty in the mechanisms controlling the increase in earthquake productivity and shale gas development in the southern Sichuan basin of China. In this study we take advantage of a more complete seismic catalog from local seismic stations, as well as injection data for two adjacent hydraulic fracturing wells, during March 2017 to January 2018, to investigate these mechanisms. To ensure the completeness and reliability, two seismic catalogs were effectively merged and uniformly scaled using the moment magnitude M_w scale. A spatiotemporal constraint framework was designed to extract induced earthquakes during the injection stages, and a series of seismic statistical methods were used to study the correlation between 885 earthquakes (M_w 0 to 4.6) and fluid injection. These include the ETAS model, and the nearest-neighbor-distance method. The results suggest most seismicity close to the wells are likely linked to the hydraulic fracturing process. For events associated with the N5 well pad, the cumulative number of earthquakes has a positive correlation with the cumulative injection volume. Through the use of the Seismogenic-Index, the difference of seismogenicity of different wells is obtained. We show that injected volume not only correlates with the number of induced earthquakes, but also correlate with the maximum seismic magnitude in the region. We demonstrate that this can then be used to retroactively forecast the induced seismicity. Although the injection at the  two well pads is similar, the N5 pad is associated with many more indued events compared to the N7 pad. Reflection seismic imaging indicates that faults and fractures are well developed beneath the target reservoir of N5, but not for N7. This indicates proximity to preexisting faults/fractures control the occurrence of inducing seismicity in the region. The possible cause of the M_w 4.6 earthquake is briefly analyzed by calculating the range of pore pressure diffusion, and the Coulomb stress change from poroelastic effects. This shows that induced seismicity in the southern Sichuan basin is controlled by both preexisting faults/fractures and injection fluid volume.

How to cite: Hu, J.: The productivity of induced seismicity in the southern Sichuan basin, China is controlled by injected volume and preexisting faults , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13985, https://doi.org/10.5194/egusphere-egu25-13985, 2025.

Earthquakes that occur during geothermal exploitation or any other fluid-injection activity (hydraulic fracturing, CO2 waste disposals…) are attributed to the reactivation of rapid slip along critical faults. This highlights the urgent need of comprehensive monitoring and mitigation strategies to ensure both energy production and environmental safety.

Our main objective is to develop numerical methods to infer the permeability enhancement during fault reactivation induced by fluid injection in the laboratory. To this end, we model an experimental protocol conducted on a rock sample with a saw-cut fault, led by F.X. Passelègue and collaborators from the EPFL and GéoAzur rock mechanics laboratories. At the beginning of the injection experiments, pore pressure was uniformly set to 10 MPa along the fault plane. The injection experiment was preceded by a loading phase, during which shear stress was increased to approximately 90% of the peak shear stress to bring the fault to a critically pre-slip state. Fluid was then injected along the fault at a constant rate of 1 Mpa/minute, with simultaneous measurements of pore pressure, slip, and shear stress recorded continuously.

To simulate the experimental process, we established a system of coupled partial and ordinary differential equations that describe the evolution of key variables, including permeability, porosity, fault slip, and pore pressure. These equations are solved numerically. The general behavior of our key variables generated by the model reproduces the trend observed in the data recorded in the laboratory. For an advanced data match we develop a deterministic inversion approach, specifically the adjoint state method, to infer the permeability model. We are currently focused on enhancing this inverse model.

How to cite: Ben Khaled, I., Dublanchet, P., Chauris, H., Passelegue, F., and Blanco Martin, L.: Inferring Permeability Enhancement During Fluid-Induced Fault Slip Reactivation In The Laboratory, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16675, https://doi.org/10.5194/egusphere-egu25-16675, 2025.

The heterogenous nature of geological formations is further complicated by natural and induced discontinuities such as fractures and faults. These geological features introduce a complex network of pathways and barriers that alter the local in-situ stresses as well as fluid flow dynamics. A comprehensive understanding of hydro-mechanical (HM) interactions during fluid injection experiments may provide insights into the effective manipulation of underground for energy extraction (e.g., hydraulic stimulation) as well as prediction and mitigation of induced seismicity in response to various stimulation techniques. Significant effort has been devoted to understand the rock-fluid interactions in energy contexts (e.g., shale gas, enhanced geothermal system) and earthquake seismology through various methodologies including laboratory studies, in-situ experiments and numerical simulations over the last decades. However, systematic studies of such interactions under in-situ conditions with natural heterogeneity require systematic manipulation of injection parameters in a well-characterized reservoir or underground research laboratory.

The BedrettoLab (Bedretto Underground Laboratory for Geosciences and Geoenergies) with a local overburden of over 1000 m, located in the Swiss Alps, is a suitable site for conducting such studies, as the rock volume has been well instrumented and characterized [Plenkers et al., 2023]. In a close collaboration between two running projects in BedrettoLab, i.e., VALTER (Validating of Technologies for Reservoir Engineering) and FEAR (Fault Activation and Earthquake Rupture), a series of controlled hydraulic stimulations were conducted where various HM pre-conditioning steps were included (or left out) in the injection protocol. The main objective of the HM pre-conditioning was to understand and control microseismicity by pre-determining the pressurized patch on the fault/fracture volume via the injection protocol prior to the main injection. The installed monitoring system captured ongoing HM processes during each hydraulic stimulation, enabling systematic testing of these pre-conditioning hypothesis across various fractures. In the next step, similar protocols were applied to the first stimulation experiment as part of the project which provided a comprehensive insight of the HM and seismogenic characteristics of the stimulated fault, in response to pre-conditioning.

How to cite: Jalali, M., Gischig, V., Selvadurai, P., Spagnuolo, E., Meier, M.-A., Dal Zilio, L., Rosskopf, M., Obermann, A., Rinaldi, A. P., Gholizadeh Doonechaly, N., Bröker, K., Osten, J., Hertrich, M., Maurer, H., Giardini, D., Wiemer, S., Cocco, M., and Amann, F. and the FEAR Team: Hydraulic Stimulations with Hydro-Mechanical Pre-Conditioning at the BedrettoLab, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17247, https://doi.org/10.5194/egusphere-egu25-17247, 2025.

The global development of Enhanced Geothermal Systems (EGS) and the increasing related occurrence of induced seismicity are topics of growing interest for the scientific community. One of the most recent EGS developments is in the Gonghe Basin, located in the northeastern Quinghai-Tibetan Plateau in China. The project is considered one of the most promising Hot Dry Rock (HDR) resources in the country due to the high temperature detected while drilling the first well in 2017 (236°C at a depth of 3705 m).

A surface seismic network of 20 three-component seismometers monitored the area around the wells GH01, GH02, and GH03 during the June – October 2021 injection and circulation phases. We used a beamforming method to detect and locate earthquakes. The beamforming process significantly improved the number of events detected, with over 10,000 detections (whereas previous research had identified roughly 2,600 events using an automated phase-picker for detections). The largest event had a magnitude of M_L 3.2, with the smallest events having magnitudes smaller than M_L -1. The increased event detection produced by the beamforming is fundamental for enhanced imaging of the faults and fractures activated by the geothermal stimulations. We compare the beamforming locations with those produced by manual phase picking for the largest events with M_L > 0.7.

Further seismological analysis has included analysis of shear wave splitting (SWS) phenomena, to understand the development of anisotropy in the reservoir during and after the injection procedures. Our results show that the fast S-wave polarization have a NE-SW orientation, congruent with the orientation of the maximum horizontal principal stress, characterized by a direction of NE55°. However, variations into the orientation are present at some stations, which could indicate additional geological complexity within the area.

How to cite: Bressan, S., Verdon, J., and Zhang, H.: Characterization of induced micro seismicity at the Gonghe geothermal project during the 2021 injection phase, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17271, https://doi.org/10.5194/egusphere-egu25-17271, 2025.

The Baihetan Hydropower Station, located on the eastern margin of the Tibetan Plateau, is the world's second-largest hydropower station in terms of installed capacity. The 289-meter-high dam will create a massive reservoir with a storage capacity of 20.6 billion cubic meters upstream of the Jinsha River. On April 6, 2021, the Baihetan Reservoir began its initial impoundment, leading to significant seismic activity at the intersection of the Xiaojiang, Zemuhe, and Daliangshan fault zones. These earthquakes were characterized by shallow focal depths and a general distribution along the reservoir area, indicating reservoir-induced seismicity. During the initial impoundment of the Baihetan Reservoir, two notable earthquakes occurred within the Tibetan Plateau, the Yangbi MS 6.4 earthquake and the Maduo MS 7.4 earthquake, with an interval of less than five hours between them.

This study utilizes data from a dense seismic array deployed in the Baihetan Reservoir area to analyze the remote dynamic triggering effects of these two earthquakes. Preliminary works indicate that the surface waves from the Yangbi MS 6.4 earthquake, which was approximately 330 km away, did not trigger any small earthquakes in the Baihetan Reservoir area, and there was no significant increase in microseismic activity within four hours after the earthquake. In contrast, the surface waves from the Maduo MS 7.4 earthquake, which was about 920 km away, triggered multiple small earthquakes when they reached the Baihetan Reservoir area. Additionally, precise earthquake relocations reveal the heterogeneous distribution of critical stress states in the Baihetan Reservoir area due to the impoundment process. These results provide insights into the mechanisms of reservoir-induced seismicity and the potential for remote dynamic triggering in the region.

How to cite: Liu, Z., Wu, T., and He, X.: Remote dynamic triggering of reservoir-induced seismicity during the initial impoundment of the Baihetan Reservoir, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17304, https://doi.org/10.5194/egusphere-egu25-17304, 2025.

To determine the source characteristics of mining-induced earthquakes, the corner frequency f_c, rupture radius r, seismic moment M₀, radiated seismic energy E_s, and stress drop Δσ of 80 micro-earthquakes with 1.0≤M_L≤3.3 in the Datong coal mine were calculated based on waveform records from the regional digital seismic network. The Scaling relationships between these parameters and M₀ were studied, and the reasons for the lower levels of corner frequency and stress drop in mining-induced seismicity were analyzed. The results show that the displacement spectrum of the source of mining-induced earthquakes in the Datong coal mining is consistent with the Brune model ω^-2 attenuation pattern. Using this ω^-2 model, the source parameters of micro-earthquakes in the Datong coal mine were estimated. The f_c ranges mainly from 0.82 to 4.64 Hz, the r ranges from 67.89 to 382.65 m, and the Δσ from 0.03 to 0.85 MPa. The M₀ estimated from the zero frequency limit ranges from 5.85e+10 to 7.66e+13 Nm, and the E_s ranges from 7.34e+4 to 7.07e+8 J. With the increase of M₀, the source parameters of r, Δσ, and E_s show an increasing trend, while the fc decreases gradually, exhibiting characteristics similar to tectonic earthquakes. Mining-induced earthquakes in the Datong coal mining area have lower corner frequencies and stress drop levels than tectonic earthquakes. This is mainly due to the artificial alteration of the initially stable geological structure and stress state during mining. This leads to deformation and micro-fracturing of the coal and rock mass in the roof and floor, approaching or reaching a critical, unstable state. With the continuous mining operation, mining-induced earthquakes occur in a lower-stress environment under the multiple coupling effects of the self-weight stress of the coal and rock mass and mining-induced stress disturbance.

How to cite: Li, L. and Liu, J.: Source Parameters and Scaling Relationships for Mining-induced Seismicity in the Datong Coal, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17776, https://doi.org/10.5194/egusphere-egu25-17776, 2025.

Identification of seismogenic zones in geothermal fields undergoing active fluid injection is an important issue for seismic hazard assessment in such destinations. It is well known that subsurface discontinuities can be successfully imaged using multiplets, i.e. seismic events with very similar waveforms. Very promising results of this method were obtained using the dataset from Prati-9 and Prati-29 injection wells at The Geysers geothermal field. With the use of multiplet analysis followed by double-difference relocation we imaged three fractures and one fault within the reservoir and described their different seismic response to injection.

In this work we present the current results of multiplet identification followed by double-difference relocation in two other geothermal sites: (1) Helsinki geothermal site (Finland), and (2) Coso geothermal field (California). The mentioned geothermal sites exhibit very different geological conditions. Helsinki site is a typical example of geothermal stimulation of crystalline Precambrian basement rocks in the area of very low background seismicity. On the contrary, Coso geothermal field is located in tectonically active volcanic area cut with a complex system of faults. Moreover, we extend the multiplet analysis performed in the area of Prati-9 and Prati-29 injection wells at The Geysers geothermal field by searching for multiplets in various frequency ranges. In this way seismic events from broader magnitude range can be included in the following relocation procedure. The multiplets identified within each frequency range are relocated separately. At the end, obtained images are stacked together using common reference events.

Our results confirm that relative relocation of similar seismic events with double-difference method can be successfully applied for the identification of seismogenic structures in geothermal areas exhibiting very different geological and tectonic complexity.

This research was supported by research project no. 2022/45/N/ST10/02172, funded by the National Science Centre, Poland, under agreement no. UMO-2022/45/N/ST10/02172. This work was also partially supported by a subsidy from the Polish Ministry of Education and Science for the Institute of Geophysics, Polish Academy of Sciences. This research was supported in part by PLGrid Infrastructure.

How to cite: Staszek, M., Rudziński, Ł., and Wiszniowski, J.: Multiplets as a tool for identification of seismogenic structures at various geothermal fields, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18119, https://doi.org/10.5194/egusphere-egu25-18119, 2025.

This study investigates an innovative approach to the earthquake location problem by simulating the use of Distributed Acoustic Sensing (DAS) technology deployed in a single vertical borehole. Traditional methods typically rely on extensive networks of seismometers distributed horizontally on the surface to accurately determine earthquake hypocenters. In contrast, this work examines the feasibility of deriving earthquake locations from DAS seismogram images recorded by 700 virtual receivers along a 3.5 km vertical cable in a well.

We evaluated multiple methodologies, including cross-correlation-based matching with a database of synthetic waveforms and advanced machine learning (ML) techniques such as convolutional neural networks (CNNs) and autoencoders. While the cross-correlation approach produced promising results for simple velocity models, it faced limitations when applied to more complex, realistic subsurface structures. To overcome these challenges, CNNs were employed to classify earthquake locations within a grid framework, and autoencoders were utilized to enhance the resolution of derived location images. The methodology was tested against two benchmark velocity models: the Marmousi model and a region-specific model derived from seismic exploration at a geothermal energy site.

Our findings highlight the potential of integrating DAS technology with ML for earthquake location imaging, particularly in environments with sparse seismic instrumentation. Our approach demonstrates promise in improving the efficiency and accuracy of seismic monitoring, especially in regions characterized by lateral velocity heterogeneities.

How to cite: Komeazi, A. and Rümpker, G.: Earthquake Location Imaging (ELI) for single-well Distributed Acoustic Sensing using Wavefield Classification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18529, https://doi.org/10.5194/egusphere-egu25-18529, 2025.

Developing geothermal energy projects require a clear understanding of seismic hazard potential in the subsurface, specifically, fault reactivation and induced seismic events of societal significance. The Californië geothermal field in South Eastern Netherlands is one such project where concern for disruptive seismicity has stalled development. Evaluating seismic hazards of structurally-controlled geothermal systems must include a clear understanding of subsurface geometries, specifics of the current stress field, and rock properties at depth. At Californië, although considerable subsurface data is available, the extent and specific geometries of local faults and fault topologies, including paleo-fault structures, stratigraphic formations, as well as the stress field at reservoir depths are not all well understood. This study addresses these uncertainties with a probabilistic approach to three-dimensional structural and geomechanical modeling, qualifying primary observations of structural features and evidence of the in situ stress state with a cumulative measure of their uncertainties. A number of structural geometric realizations are derived from these probabilistic uncertainties and analysed using the finite element method to evaluate slip tendency, dilation tendency, and fracture susceptibility. The results of these calculations provide meaningful distributions for fault stability considering uncertainties of in situ stress, structural geometries, and frictional properties to inform development and operational parameters and enable a finer evaluation of seismic hazards and further geothermal development.

How to cite: Jones, A., Kruszewski, M., and Amann, F.: Investigating fault reactivation potential for the Californië geothermal field (the Netherlands) by addressing uncertainties with probabilistic modeling of structures and in situ stress., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19108, https://doi.org/10.5194/egusphere-egu25-19108, 2025.

Triggering of earthquakes due to the filling of dam reservoir is attributed to mechanical disequilibria, build-up by pore pressure diffusion driven differences in deformation and stresses in the subsurface rocks, ultimately compensated by the reactivation of faults. This kind of earthquake, also known as Reservoir induced seismicity (RIS) has the characteristics of small magnitude, high intensity, shallow source and long period. In some cases, seismic activities have lasted for several decades after the initial impoundment (e.g. in Koyna-Warna, India). Various approaches have been made by researchers to comprehend the role of water reservoirs in triggering such unique events.  Modeling fluid-induced earthquakes requires coupling geomechanics, flow through porous media, and fault friction. A 2D poroelastic finite element model has been employed, incorporating coupled pore fluid diffusion and stress analysis along with contact interaction coupled to rate-and-state friction law, to simulate the stress change, deformation in rocks and fault slip due to reservoir impounding. Rate-and-state friction has been used with an aim to develop a modelling framework that can capture multiple earthquake sequences in order to understand the protracted RIS phenomenon. A fault is embedded in a 2D subsurface domain as contacting surfaces, the frictional behaviour along the fault surfaces is prescribed using a user subroutine FRIC in ABAQUS/Standard. The rate-and-state law has been defined in the subroutine. The ability of the subroutine to simulate multiple events of stick-slip motion has been checked using a simple spring-block slider analogy. The fault model is first initialised by simulating the in-situ field conditions, geostatic stresses are defined in the domain, frictional contact at the fault is established and zero pore pressure conditions are defined. After which, reservoir loading is applied on the top surface of the domain over a transient consolidation step and the pore pressure evolution down at the fault is studied. The decrease in fault strength is a result of increase in pore pressure that reduces the effective normal compressive stresses. The stress path, accumulated slip and friction coefficient at the midpoint of the fault is observed. The fault remains locked at the beginning, while the effective normal stress continues to decrease, at a point the fault strength drops and it starts to slip. Friction coefficient increases at the onset of slip, which is known as the direct effect, then decreases as the slip accelerates. Later, the fault rupture is arrested and the friction coefficient goes back to a higher value gradually. While simulating rupture in the fault, the contact interaction undergoes chattering when the fault slips abruptly, causing simulation to fail. In a non-dynamic analysis, instabilities will occur as the strain energy released due to fault slip cannot be dissipated. Contact damping has to be specified to dissipate the released energy. In the present study, only one event of fault slip has occurred. Increase in the pore pressure near the fault due to reservoir loading is not high enough for a second slip event.

Keywords: Reservoir Induced Seismicity, Poroelasticity, Rate and State Friction, Fault Slip

How to cite: Chakraborty, A., Gautam, S. S., and Dey, A.: Modeling Reservoir-Induced Seismicity using Rate-and-State Friction law , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19220, https://doi.org/10.5194/egusphere-egu25-19220, 2025.

Seismic tremor signals were recorded in 2021 by a temporary broadband seismic network deployed in the surroundings of the Domo de San Pedro geothermal field (DSPgf) in Mexico. A network-based covariance matrix approach was used to analyze those tremor-like signals, employing vertical-component data only. Seismic tremors were detected by identifying periods associated with low values of spectral width, defined as the width of the eigenvalue distribution of the network covariance matrix. These tremors occur in frequency bands ranging from 1 to more than 22 Hz, with durations varying from hours to months, and show higher amplitudes at closest stations to the active wells. The spectral characteristics of the DSPgf tremor-like signals reveal similarities to those found in volcanic and glacial environments, such as the presence of harmonic frequencies and spectral gliding. The sources of these tremor signals are located by back-projecting on a 3-D grid the dominant component of the wavefield obtained from the covariance matrix first eigenvector. Tremor locations indicate that the events originate within the zones of influence of the wells where geothermal operations occurred. We categorized four distinct tremor families based on spectral width signatures and compared them with detailed operational records. Our findings reveal that tremors at the DSPgf are associated with geothermal operations such as fluid extraction, wellbore maintenance, fluid re-injection, and changes in injection pressure. We propose a conceptual model of the first order tremor-generating mechanism for each tremor family.

How to cite: Muñoz-Burbano, F., Soubestre, J., Savard, G., Calò, M., Reyes-Orozco, V., and Ávalos, D.: Monitoring induced seismic tremor associated with fluid injection/extraction and mechanical operations at the Domo San Pedro geothermal field (Mexico), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19407, https://doi.org/10.5194/egusphere-egu25-19407, 2025.

Injection-induced earthquakes (IIEs) are commonly attributed to pore-pressure elevation and associated Coulomb stress changes, leading to widespread adoption of Traffic Light Systems (TLS) that primarily focus on injection rate modulation for hazard mitigation. However, recent field observations have identified aseismic slip as an alternative mechanism for fault reactivation during direct fault-zone fluid injection, with evidence showing that slip propagation can outpace fluid migration fronts. Despite these insights, the critical conditions that determine when aseismic slip becomes the dominant mechanism—particularly the role of injection parameters—remain poorly understood. Here, we present direct fault-injection experiments equipped with high-resolution monitoring of fault slips and fluid difussions. Our findings reveal two fundamental insights into IIE mechanisms: (1) When faults are subjected to specific combinations of injection rates and pre-stress conditions, aseismic slip can initiate and propagate beyond the fluid-pressurized zone, becoming the primary mechanism for IIEs. (2) In near-critically stressed faults, the maximum seismic moment release may remain elevated even after injection rate reduction, undermining a core assumption of TLS protocols. Overall, these observations highlight that fault stress conditions, rather than injection parameters alone, dictate the upper bound of seismic hazard. 

How to cite: Wang, C., Wang, P., and Xia, K.: How Does Injection Rate Control Injection-Induced Earthquakes?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19763, https://doi.org/10.5194/egusphere-egu25-19763, 2025.

For the transition to a low-carbon future, carbon capture and storage (CCS) is a field of intense research worldwide. However, the process needs to be monitored closely for induced seismicity, and this in turn requires a clear picture of the background seismicity of the immediate area around the storage site. This study focuses on assessing the background seismicity of the Gulf of Kavala in Greece, where an offshore CCS pilot is deployed within EU project COREu. However, a major challenge associated with this area is the scarcity of catalogued events due to its low seismicity, as well as the sparse seismic station distribution, owing also to geography. To overcome this challenge, in this study, state-of-the-art AI-based seismic detectors (EQTransformer and PhaseNet) are used to re-evaluate existing recordings and enrich the area’s catalogue with low-magnitude events. A two-stage approach is considered to take into account and resolve the particularities of this involved task. In the first stage, we evaluate the baseline performance of the adopted pre-trained AI-based detectors, using data from the Corinth Gulf area, selected because the seismic network there is significantly denser and the seismicity higher. Specifically, for our purposes, we used data from a microseismic sequence of more than 400 events recorded in the first half of 2021, with magnitudes ranging from 0.1 to 1. In the experiment we utilize recordings of the selected events from a total of 50 stations located around the seismic sequence, with distances out to several tens of kilometers, to build a dataset with a wide and representative range of recording SNRs. To assess the detectability of the events, for each event/station pair, we measure the output of the detectors in a time-window of 5 seconds around the event arrival, forming a (detector) response magnitude vs SNR curve. This is used as a guideline for determining a detection threshold that strikes a good balance between true and false positives. Through this successful application of the method in the Corinth Gulf area, we gained significant knowledge about the limitations and the necessary configuration of the methods. In the second stage of the study, we conduct a preliminary detection experiment on continuous recordings from Prinos, utilizing data from stations surrounding the target area. The outcome of this experiment is evaluated by expert seismologists, using a specially created visualization tool for assisting the evaluation process. The adopted two-stage approach leads to the detection of a considerable number of low-magnitude, previously undetected events, constituting a significant first step towards assessing the implementation of CCS  in the Prinos area.   

How to cite: Pikoulis, E.-V., Mavrokefalidis, C., Ktenidou, O.-J., and Sokos, E.: AI-assisted assessment of low-magnitude seismicity in the area of Kavala-Prinos (Greece) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20161, https://doi.org/10.5194/egusphere-egu25-20161, 2025.

The Western Canada Sedimentary Basin (WCSB) covers a vast area, extending from a zero edge along the Canadian Shield to the Canadian Cordillera in the west, where the basin is up to 7 km thick. Seismicity is largely concentrated within a ≈300km wide corridor, immediately east of the deformation front of the Canadian Cordillera. The northern half of the WCSB experiences natural earthquakes in the Mackenzie and Richardson Mountains, which are strongly influenced by plate-boundary interactions along the west coast of North America. To the south, seismicity in northeastern BC and western Alberta is characterized by localized induced (human-caused) seismic activity related to unconventional resource development during the last 15 years. This north-south partitioning of seismicity is reflected in Canada’s national seismic hazard maps, which consider only natural seismic hazards and highlight areas of relatively elevated seismic hazard in the Mackenzie and Richardson Mountains. However, since 2021 the seismic moment-release rates have become broadly similar in both southern and northern regions of the WCSB, despite relative seismic quiescence in the south from 2000 – 2014. Short-term seismic hazard maps for Alberta show localized areas of elevated seismic hazard that track temporarily and spatially varying levels of industry activity. The advent of large-scale carbon capture and storage (CCS) and geothermal projects could increase the potential for anthropogenic triggering of seismic activity.

How to cite: Eaton, D., Kao, H., Canales, M., and Shipman, T.: The big picture in western Canada: Induced seismicity from geo-energy applications is approaching the natural moment release rate of tectonically active northern regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20644, https://doi.org/10.5194/egusphere-egu25-20644, 2025.

The injection of water during hydraulic fracturing leads to effective normal stress reduction on faults and may trigger earthquakes. Different injection loading schemes may lead to various slip behaviors in fault zones. In addition to direct pressurization (i.e., direct reduction of effective normal stress), cyclic pressurization has also been introduced. In this study, to reveal the underlying seismic triggering mechanisms during hydraulic fracturing, we employ double direct-shear tests to investigate the frictional behaviors of fault gouges under sine-shaped normal stress oscillation (NSO) and direct reduction of normal stress, conducted at a reference background normal stress of 40 MPa and constant shear stress (CSS) conditions. In all experiments, during the slip process, the fault slip velocity initially increases (slip-acceleration stage) and then decreases (slip-deceleration stage). NSO can significantly reduce the peak slip velocity of a fault compared to the direct reduction of normal stress. Faults sliding at a higher acceleration rate during the slip-acceleration stage also show a higher deceleration rate during the slip-deceleration stage. Repeating the NSO on the same fault under identical conditions causes a gradual decrease in its peak slip velocity, indicating permanent changes in the fault during slips. Various factors, including the compaction effect on healing and the rate of normal stress reduction, control the different slip behaviors triggered by NSO. Quantifying controlling factors in the field and optimizing NSO parameters can effectively reduce the potential of seismic activity, which is critical for safe hydraulic fracturing operations.

How to cite: Gao, K. and Zhang, L.: Effects of Normal Stress Reduction on Seismic Triggering, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20902, https://doi.org/10.5194/egusphere-egu25-20902, 2025.

Compaction band formation and permeability evolution in volcanic rocks are key to understanding fluid transport and the potential for pore fluid pressurisation, impacting volcano eruption dynamics and volcanic hazards, geothermal energy extraction, and CO₂ sequestration. Compaction banding and permeability evolution are influenced by the geometry and alignment of pores. Laboratory studies on volcanic rocks have provided valuable insights, yet the heterogeneity of volcanic rock microstructures—particularly in pore geometry and distribution—presents challenges in predicting deformation and permeability changes across varied geological settings. This study systematically investigates the role of pore geometry on compaction band formation and permeability evolution in a porous lava.

A porous lava, a trachyandesite from a quarry near Volvic, France, known as "Volvic Bulleuse" (VB), was studied to explore the factors influencing compaction band and permeability evolution. The pores in VB with an average aspect ratio of 0.44, exhibit elongation along a preferred orientation within a groundmass dominated by plagioclase microlites. To investigate the effects of pore geometry, cylindrical samples were drilled along two orientations—parallel (VBY) and perpendicular (VBZ) to the pore major axis—such that in VBY samples, the pore major axis aligns with the cylinder’s long axis, while in VBZ samples, the axes are perpendicular. Both VBY and VBZ exhibited porosities ranging from 23–27%, as determined by gas pycnometry. In terms of permeability, measured along the cylinder’s long axis, VBY samples showed a value of approximately 10⁻¹⁴ m², while VBZ samples exhibited a lower permeability of around 10⁻¹⁵ m².

Triaxial deformation experiments demonstrated that VBZ samples—featuring pores perpendicular to the cylinder axis—are approximately twice weaker than VBY samples deformed at the same pressure. Microstructural analysis of deformed samples revealed that pore geometry has minimal influence on compaction band orientation at lower effective pressures, where compaction bands typically formed sub-perpendicular to the major principal stress, as is commonly observed. However, at higher pressures, compaction bands preferentially formed at angles of 45–50° to the loading direction in VBY samples, a development that is closely linked to the preferred orientation of the pores.

Additionally, we measure permeability during triaxial deformation under an effective pressure in the ductile regime (75 MPa), revealing significant changes in permeability due to deformation and pore orientation. Our analysis emphasizes pore structure's role in deformation and permeability evolution, with applications ranging from geothermal energy extraction to various subsurface fluid transport processes.

How to cite: Bayramov, K., Heap, M., Baud, P., and Lazari, F.: The Impact of Pore Geometry and Orientation on Permeability Evolution and Compaction Band Formation in Volcanic Rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-483, https://doi.org/10.5194/egusphere-egu25-483, 2025.

Understanding the impact of local stress states on computed permeability for fractured carbonates or any other lithotype is crucial to better assess the modalities of fluid flow in the subsurface. Considering Mesozoic fractured carbonates exposed along the flanks of the Viggiano Mt. of southern Italy, we investigate the control exerted by the local fracture networks on the output of DFN modelling of geocellular volumes whose dimensions are like those of the studied outcrops. Specifically, the following four sedimentary units are considered:

• Scarrone La Macchia II, (SLM II), well-layered, Sinemurian–Pleinsbachian carbonate succession of wackestone-packstones to grainstones arranged in discrete bed packages originally deposited in a low-energy, open lagoon environment.
• Scarrone la Macchia I, (SLM I), Toarcian oolithic carbonates characterized by bed amalgamation originally formed in a ramp setting rimmed by oolithic sand shoals.
• Piana del Buon Cuore (PBC), Lower Cretaceous - Upper Jurassic limestones whose clasts consist of oolites, oncolites and intraclasts deposited in a high-energy platform margin environment.

• The Il Monte (ILM), massive, amalgamated, Cretaceous carbonate rudstones and grainstones originally deposited along the paleo-slope of the carbonate platform.

By employing existing field data (Abdallah et al., 2023, 2024), we carried out Discrete Fracture Networks (DFN) modelling of 5 m-sided geocellular volumes including internal sub-volumes representative of single carbonate beds. This work was conducted by means of  high-resolution computational meshes provided by the dfnWork ® code, which is capable of non-reactive solute transport simulation, and constrain of imposed depth-equivalent stresses to assessing effective horizontal permeability (effk_xx, effk_yy).

Focusing on the results achieved for the Viggiano Mt. aquifer, we simulated depth conditions of 500m coupled with principal stress axes of ~13MPa (sv), 10 MPa (shmax, NW-SE), and 7.58 MPa (shmin, NE-SW). The theoretical aperture data were hence modulated by the local stress state conditions. SLM I, exhibits an increase in permeability anisotropy ratio as a function of the stresses, hence, leading to flow channelling within the network. Lagrangian solute transport simulation supports the afore-mentioned results by marked changes in primary flow path, increase in path tortuosity, as a function of stress, and delay in breakthrough time. Similar results were achieved for PBC and ILM units. Differently, SLM II undergoes the opposite effect, where the permeability ratio seems to reduce drastically at a depth of 500m and stabilizes after that. We infer this behaviour as due to non-linear-fluid-flow behaviour as a function of aperture closure or dilation, as seen in highly connected systems of fractures including both stratabound and non-stratabound elements. Accordingly, SLM II is characterized by efficient mechanical units made up of bed interfaces, which were able to compartmentalize the vertical growth of high-angle fractures.

This research highlights the complex behaviour of permeability anisotropy in fractured carbonate rocks, in response to depth-equivalent stresses, and the importance of building realistic geomechanically coupled-DFN models to estimate fluid-flow and storage properties of fractured rocks at depth.

How to cite: Abdallah, I. B., Hollis, C., Healy, D., Hyman, J. D., Prosser, G., and Agosta, F.: Stress-induced permeability anisotropy and fluid flow dynamics in a Mesozoic fractured carbonate aquifer of southern Italy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1131, https://doi.org/10.5194/egusphere-egu25-1131, 2025.

Assessing leakage mechanisms that compromise reservoir integrity is essential for effective geo-resource management and mitigating environmental risks. Reservoir leakages can occur via both anthropogenic pathways, such as active and inactive wells and pipelines, and natural pathways, including fractures and fault zones. Additionally, fault-valve action can temporarily disrupt sealing layers, allowing trapped fluids to migrate upward. Distinguishing between natural and human-induced causes of reservoir leakage is valuable but often challenging. To address this, we present an innovative approach that compares fluid circulation systems before and after the onset of reservoir exploitation. Present-day fluids are studied using standard groundwater sampling, modelling, and near-surface soil gas surveys. In contrast, paleo-fluids are analyzed using carbonate clumped isotope of fault-related calcite veins, along with fluid inclusion spectroscopy and microthermometry to determine parental fluid temperatures and compositions. We applied this approach to the giant Val d’Agri hydrocarbon reservoir in Southern Italy, a region characterized by: (i) high seismic hazard, with historical earthquakes up to magnitude 7; (ii) recent low-magnitude seismicity induced by oil extraction; and (iii) ongoing debate about industrial activities potentially triggering anthropogenic leakages. From our extensive dataset of fault-related calcite veins, we selected samples from Pleistocene-Holocene extensional-transtensional faults of the northeastern side of the valley, where productive oil wells are located. Carbonate clumped isotope analysis revealed precipitation temperatures of 160-180°C, while micro-Raman spectroscopy of fluid inclusions detected hydrocarbon phases matching those currently extracted from the reservoir. These findings suggest that past faulting, likely associated with strong earthquakes, temporarily breached the thick sealing layer, releasing trapped hydrocarbons. Considering present-day fluids, isotope analyses (carbon, boron, sulfate, and helium) from hydrogeochemical monitoring of nearby springs indicated long-term mixing between these hydrocarbons and shallow fluids. In summary, our multidisciplinary study demonstrates that natural leakage via fault-valve action occurred in the pre-exploitation period. Given the high seismic hazard in this region, we recommend incorporating these natural processes into future assessments to enhance environmental hazard mitigation and support sustainable hydrocarbon production management.

How to cite: Schirripa Spagnolo, G., Gori, F., Barberio, M. D., Boschetti, T., Marchesini, B., Ruggieri, G., Bernasconi, S., Caracausi, A., Sciarra, A., Paternoster, M., Novella, D., Barbieri, M., Petitta, M., Billi, A., and Carminati, E.: Fault leakages from the Val d’Agri hydrocarbon reservoir: a comparison between paleo- and present-day fluids, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1785, https://doi.org/10.5194/egusphere-egu25-1785, 2025.

Salt domes are considered as host rocks for long-term nuclear waste disposal. Groundwater flow in the near salt domes may lead to the transport of radionuclides into the biosphere. The following key factors that influence groundwater dynamics are the presence of brine as a result of salt dissolution, heat generation from radioactive waste and the "salt chimney effect"-a phenomenon in which the geothermal heat flux and high thermal conductivity of salt rock induce elevated temperatures around salt domes. The resulting temperature and salinity variations affect groundwater density (and viscosity), driving thermohaline convection in adjacent rock layers of the salt dome. Variable density and viscosity lead to coupled processes due to the highly nonlinear nature of the problem, which is challenging to model numerically. This study defines the fractured salt chimney problem and investigates for the first time the effect of fractures in the surrounding rock layers of a salt dome on thermohaline convection in these layers. Results show that the presence of fractures can have a strong impact on salt transport rates and the thermohaline convection patterns near salt domes.

How to cite: Suilmann, J. and Graf, T.: Numerical investigation of thermohaline convection in fractured-porous media near salt domes: the fractured salt chimney problem, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2742, https://doi.org/10.5194/egusphere-egu25-2742, 2025.

Fracture network develops in response to deformation in competent rocks and are often related to fault related folding (Allmendinger, 1982; Watkins et al., 2018). The Baghewala structure in the Bikaner-Nagaur sub-basin is a fault related anti-form that encompasses the Marwar Supergroup. The structure has a spatial extent of ~12 km² and is bounded by a major ENE-WSW trending reverse fault. The Upper carbonate (UC) Formation of Marwar supergroup here carries dominantly the dolomites and is traversed by extensive fractures that are visible in cores and image logs. This is a zone of severe mud loss and drilling complications.  

We study the image logs from 6 wells to decipher the fracture orientation, understand the deformation mechanism and the implications for drilling and hydrocarbon production. The interpreted fractures from image logs are observed to be dominantly high-angle (60°-90°) extensional fractures oriented along ENE-WNW direction with respect to the sub-horizontal bedding. Additionally, it is seen that the fractures are confined to dolomitic part of UC Formation. Spatially the wells nearer to the fold crest and fault show higher fracture intensity compared to the peripheral wells. The transpressional tectonics after the deposition of the Marwar Super group induced ~NW-SE compression that led to the formation of fault related Baghewala fold. Consequently, the outer arc extension resulted in formation of the syn-post folding fracture network (Price 1966). The fractures thus can be inferred as late-stage high angle fractures due to its orientation (Basa et al., 2019; Ahmed and Bhattacharyya, 2021) and relative prominence (Ismat and Mitra, 2001). Dolomites accommodate deformation by forming fracture networks and fracture intensity is higher, proximal to the fault zone and fold structure (Ahmed and Bhattacharyya, 2021). Thus, lithology and structural position played a role in the partitioning of fractures vertically and spatially.

We see the horizontal wells that are oriented sub-parallel to the fracture network have significant history of mud loss within UC compared to the wells whose profile trends at high-angle to fracture orientation. The deviated wells oriented along the major fracture network will encounter weak planes leading to drilling complications compared to profiles that are oriented across. Therefore, understanding orientation of fracture networks has implications in designing deviation profile of the wells. In low permeability rocks like dolomite, fractures can affect fluid flow due to increase or decrease in permeability (Hanks et al., 2004). The extensional fractures developed in the Baghewala structure can lead to increase in permeability in the reservoir zone also i.e. the competent Jodhpur sandstone. We see enhanced production in one well that is closer to the fault zone which may be due to the increased permeability effected by the fractures, but the data is limited to conclusively prove this. This study will help to design the well position and trajectory not only to avoid mud loss and drilling complications but also to increase production by optimally placing the wells in proximity to the higher fracture intensity after arriving at a Discrete Fracture Network (DFN) model.

How to cite: Ahmed, F. and Rai, T.: Fracture network mapping using image logs from Baghewala structure, Bikaner Nagaur sub-basin: Implications for well profile and hydrocarbon production, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3144, https://doi.org/10.5194/egusphere-egu25-3144, 2025.

Hydraulic fracturing is widely recognized as the most effective method for creating Enhanced Geothermal Systems (EGS). However, its application has been associated with induced seismicity, leading to the shutdown of several projects. As an alternative, low-viscosity fluids, such as CO2, may be used because they tend to generate complex fracture networks by inducing numerous small, isolated (remote) fractures without requiring high-pressure injection. Despite this potential, however, the mechanisms and conditions that govern the formation of such patterns remain poorly understood. This study identifies two critical factors through poroelastic analysis: (1) prolonged pressure diffusion facilitated by the low viscosity of the fluid, and (2) heterogeneity in Biot’s coefficient. To validate these findings, hydraulic fracturing experiments were performed on two types of marble: fine-grained marble, representing a homogeneous sample, and coarse-grained marble, representing a heterogeneous sample. Both water and CO2 were used as injection fluids. The results demonstrate that remote fractures only form in heterogeneous rocks when CO2 is used as injection fluid. These findings suggest the potential to develop a safe and innovative reservoir stimulation technique that effectively stimulates large surface areas by strategically alternating the viscosity of the injection fluid while maintaining low injection pressures.

How to cite: Yoshioka, K., You, T., Kanemaru, Y., Obata, N., Watanabe, N., and Sakaguchi, K.: Nucleation of remote hydraulic fractures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3991, https://doi.org/10.5194/egusphere-egu25-3991, 2025.

Faults are an important factor for geoenergy applications due to either their sealing or conducting properties or their mechanical behaviour. Consequently, (thermo-hydro-) mechanical numerical investigation of geoenergy applications often include faults in their modelled rock volume. It is often assumed, that faults can significantly alter the far-field stresses, impacting both magnitudes and the orientation. In contrast to the far-field, stress rotations in the vicinity of faults are clearly observed in numerous borehole stress analyses across the world.

(1) The impact of faults on the stress state at distances of several hundred meters to a few kilometres (far-field) is tested. Therefore, faults are modelled with different numerical representations, material properties, fault orientations w.r.t. the stress field, fault width, extent, and boundary conditions. The results show that the impact of faults on the far-field is negligible in terms of the principal stress magnitudes and orientations. Only in extreme cases, stress changes in the far-field (>1km) can be observed, but these are not significant considering the general uncertainties in stress field observations.

(2) Stress changes within the fault zone are investigated, too. Particularly, the material contrast between the intact rock and the damage zone and fault core is regarded. This contrast can be responsible for a dramatic change in the stress tensor, observed as a rotation of the principal stress axes. In general, the change in the stress field increases with increasing stiffness contrast. The orientation of the fault w.r.t. the background stress field and the relative stress magnitudes, particularly the differential stress, lead to further stress changes. A small angle between the fault and the maximum principal stress axis and a small differential stress promote stress changes.

The study indicates that the impact of faults on the stress field is mostly limited to the fault’s near-field. These models provide an upper limit of stress changes, as several factor which alter stress changes (joints, viscosity etc.) are not included. However, the stress changes depend on the acting processes and material properties. Furthermore, for models used for site investigation, the implementation method and the mesh resolution can play an important role. All these factors need to be considered when planning the setup of a model with faults and their implementation.

The work was partly funded by BGE SpannEnD 2.0 project, the Bavarian State Ministry of Education and Culture (Science and Arts) within the framework of the “Geothermal-Alliance Bavaria” (GAB), and the DFG (grant PHYSALIS 523456847).

How to cite: Ziegler, M., Reiter, K., Heidbach, O., Seithel, R., Rajabi, M., Niederhuber, T., Röckel, L., Müller, B., and Kohl, T.: Faults in geomechanical models – Necessary, nice, or nonsense?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8308, https://doi.org/10.5194/egusphere-egu25-8308, 2025.

Safe and controlled exploration of deep geothermal resources in future decades is a key pillar for successfully transitioning to a carbon-neutral economy. A largely untouched source of deep hot source rocks can be found in crystalline basement formations in many European regions. Hydraulic stimulations are required to harness this thermal energy. Past geothermal projects were not always publicly accepted due to unintended induced seismicity that accompanied the projects. Faults and entire fault systems are jointly responsible for these seismic events and must therefore be thoroughly understood before they may be stimulated, to minimize tremors and unintentional shaking.

The Bedretto Underground Laboratory for Geosciences and Geoenergies in Ticino, Switzerland allows for decameter scale stimulation experiments and access to deeply (> 1km) buried crystalline faults. A complex fault zone is hydraulically and petrophysically described as part of the FEAR project, using various field and laboratory techniques. Two sub-parallel boreholes obliquely intersecting the target fault are analyzed using geophysical image and sonic logs. Hydraulic tests on predefined, packered intervals in the form of pulse-, constant rate- and step-rate injection tests are implemented on field scale, deducing parameters such as hydraulic conductivity and injectivity. In addition, laboratory petrophysical experiments on samples retrieved from varying parts along the fault zone are performed to determine permeability under certain effective stresses, porosity, and p-wave velocity, among other properties. This allows for a cross-scale hydraulic and petrophysical comparison. Prior, structural geologists described and analyzed the target fault using core logging, outcrop, and fracture data. Correlations between structural, hydraulic, and petrophysical observations can be drawn.

How to cite: Schaber, T., Jalali, M., Ceccato, A., Zappone, A. S., Pozzi, G., Selvadurai, P., Spagnuolo, E., Gischig, V., Meier, M.-A., Hertrich, M., and Amann, F. and the FEAR Team: Multidisciplinary characterization of a complex fault zone in crystalline basement rock, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8404, https://doi.org/10.5194/egusphere-egu25-8404, 2025.

Switzerland aims to reach net-zero CO₂ emissions by 2050 (BAFU, 2021). Implementation of geological storage of CO₂ and geothermal heat mining to help achieve this aim requires reservoir properties to be assessed. The structural and permeability architectures of the target reservoirs are essential input for numerical models used to assess storage and production potential, minimize fluid injection and extraction uncertainties, and reduce exploration risks. The so-called Muschelkalk aquifer (Triassic) including the Schinznach Formation is regarded as one of the key potential aquifers for gas storage and hydrothermal geothermal systems in Switzerland (Chevalier et al., 2010). While the matrix permeability of the Schinznach Formation is relatively well known (Diamond et al., 2019), magnitude and distribution of its fracture permeability and structural controls on these fractures are poorly understood.

This study aims to assess the style and intensity of natural fracture networks in the Muschelkalk aquifer at sub-seismic scale and explain their regional variability. Outcrop analogues in the Wutach Gorge of southern Germany are used to improve understanding of lateral and vertical variability of fracture networks, including how they are influenced by regional structures. The Wutach Gorge is within the Tabular Jura and provides cliff exposures along 5–12 km-long E–W and N–S transects, aligning with and crossing fault strands of the Freiburg–Bonndorf–Bodensee Fault zone.

Insights from field observations contribute to ongoing work that supports the proposed pilot CO₂ injection test into the Schinznach Formation via an existing exploration borehole at Trüllikon in northern canton Zurich. A feasibility study (Diamond et al., 2023) assessed the reservoir properties at Trüllikon by building discrete fracture network models and computing their permeabilities from a combination of rock-matrix properties, vertical drill hole fracture logs, a horizontal fracture log from another nearby drill hole, and results from hydraulic tests. This multidisciplinary approach should provide a more robust basis for exploration for CO₂ storage sites and geothermal energy.

REFERENCES 

Chevalier, G., Diamond, L. W., & Leu, W. (2010). Potential for deep geological sequestration of CO2 in Switzerland: a first appraisal. Swiss Journal of Geosciences, 103, 427-455.

Diamond, L. W., Alt-Epping, P., Brett, A.C., Aschwanden, L. and Wanner, C. (2023) Geochemical–hydrogeological study of a proposed CO2 injection pilot at Trüllikon, Switzerland. Report 2023-7 submitted to the Swiss Geological Survey (swisstopo). Rock Water Interaction, University of Bern, 87 pp. https://doi.org/10.5281/zenodo.10938102

Diamond L.W., Aschwanden, L., Adams, A., and Egli, D. (2019) Revised potential of the Upper Muschelkalk Formation (Central Swiss Plateau) for CO2 storage and geothermal electricity. Slides of an oral presentation at the SCCER-SoE Annual Conference at EPFL-Lausanne, 4th Sept. 2019. 13 pp. http://static.seismo.ethz.ch/sccer-soe/Annual_Conference_2019/AC19_S3a_08_Diamond.pdf

BAFU (2021) Switzerland Long-Term Climate Strategy. 4 pp. https://www.bafu.admin.ch/dam/bafu/en/dokumente/klima/fachinfo-daten/langfristige-klimastrategie-der-schweiz.pdf.download.pdf/Switzerland's%20Long-Term%20Climate%20Strategy.pdf

How to cite: Brett, A. C., Caldeira, J., Samsu, A., Diamond, L. W., and Madritsch, H.: Fracture networks in the Muschelkalk aquifer of the external northen foreland of the Central Alps (CH/DE); implications for permeability, CO2 storage and geothermal potential, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8885, https://doi.org/10.5194/egusphere-egu25-8885, 2025.

Modeling fluid behavior in fractured rock is essential for geo-resource exploration and geological storage. This study utilizes a Discrete Fracture Network (DFN) approach to evaluate the efficiency of fractured systems in storing supercritical CO₂ (scCO₂). Synthetic fracture networks, generated using the dfnWorks suite (LANL), based on outcrop data, represent a range of fracture densities. Key parameters such as fracture count, volume, porosity, and permeability are statistically analyzed, and their most frequent values are used to create representative DFN models for fluid flow simulations.

Results reveal a direct correlation between increased fracture density and storage capacity, with storage values consistently below 10% of the total injected mass. A Fracture Efficiency Factor (Efr) is introduced, quantifying CO₂ retained in fractures relative to the total injected CO₂. This efficiency reduces theoretical capacity estimates by approximately one order of magnitude, aligning with previous analytical and dynamic reservoir-scale studies (e.g., Nordbotten et al., 2005; Ringrose, 2020; Rutqvist et al., 1998).

This approach enhances CO₂ storage capacity estimates by explicitly accounting for fracture network contributions. While reservoir-scale scCO₂ flow simulations using DFN models remain challenging, this method provides critical insights into the storage potential of fractured media.

How to cite: Romano, V., Proietti, G., Pawar, R., and Bigi, S.: Advancing CO₂ Storage Analysis in Fractured Rocks with Discrete Fracture Network Models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8886, https://doi.org/10.5194/egusphere-egu25-8886, 2025.

Geothermal energy represents a renewable energy source exploited for multiple purposes, including electricity, direct use, district heating and heat pumps. One of the most relevant problems in geothermal energy industry is the permeability of the reservoir, both for production and reinjection. Therefore, it is important to assess the fluid circulation in the reservoir and where deep fluids rise. Faults, fractures and active tectonics influence fluid behaviour and fluid-rock interactions in a geothermal context. It is necessary to estimate the role of faults and map as well as their distribution, as tectonic structures could act as barriers to fluid circulation or as preferential conduits. The Acque Albule Basin (AAB) is a case study representing one of the most important hydrothermal manifestations in central Italy. The AAB is a tectonically controlled basin, characterized by a huge hydrothermal manifestation (discharges in the order of m³/s). The deep hydrothermal activity is testified by the presence of a large and thick travertine deposits and several mineralized springs (T_max at the surface up to 23°C) in which warm fluids rise from the geothermal reservoir. These hot fluids circulate through the Meso-Cenozoic carbonate reservoir, highly affected by dissolution and brittle deformation. In this framework, travertine deposition is mainly controlled by the faults activity. Several geophysical surveys were carried out to evaluate the cap-rock of the geothermal reservoir, beneath the travertine plateau. The exploration provided a clearer view of the stratigraphy of the AAB and revealed the carbonate roof at 300-400 m. The carbonate rocks are overlain by some alluvial sediments and a travertine plateau from 10 m to 90 m. Based on the geophysical investigations, the measurement of diffuse CO₂ emissions from the soil was planned to ascertain the faults role in the hydrothermal circulation. Preliminary results show that the fault zone is characterised by an extremely low degassing (5/10 g m^-2d^-1). The low degassing could be related to the low-permeability of the alluvial and travertine deposits and/or by self-sealing processes through the main shear zone, which obstacle the upwelling of fluids and gases. The model will be improved with further regional CO2 surveys and δC¹³ analysis of CO₂ of gaseous samples taken from the soil.

How to cite: Emili, S., Reitano, R., Ranaldi, M., Tarchini, L., Carapezza, M. L., Giordano, G., Picciallo, M., and Faccenna, C.: Investigation of geothermal fluid circulation through the study of CO2 soil flux: an application to the Tivoli quarry area (Rome, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9882, https://doi.org/10.5194/egusphere-egu25-9882, 2025.

Deep geothermal energy is emerging as a key component of Switzerland’s Energy Strategy 2050. In the Canton of Vaud, projects target natural hydrothermal systems at depths of 800 to 1,000 meters, with temperatures ranging from 35 to 100°C, in Upper Malm limestone reservoirs. These limestones, with low matrix porosity and permeability, rely on well-connected fracture networks and karstic features to enhance fluid flow. However, subsurface data from seismic surveys and well data do not fully cover scale intervals that are relevant for reservoir characterization and modeling. To address this limitation, we use a virtual outcrop model (VOM) to characterize fractures in 3D, explore its potential to bridge the length-scale gap, and compare fracture patterns and kinematics between scales of observation. 
At Creux-du-Van, a unique continuous, 3D exposure of fractured and gently folded Upper Malm limestones in the Central Internal Jura Fold and Thrust Belt provides an exceptional opportunity for fracture characterization at the decimeter to hundreds of meters scale, allowing comparisons with previous structural interpretations at the regional, 1:500,000 to 1:25,000 scale. Approximately 700 fractures were interpreted from high-resolution VOMs, i.e., point clouds (~110 points/m²), of Creux-du-Van, derived from terrestrial LiDAR scanning. These fractures were classified based on vertical persistence, which is a relative measure for the extent to which they propagate across mechano-stratigraphic boundaries. Geometric parameters such as orientation, dimensions (length, width, and aspect ratio), and spacing were also quantified. Field-based structural analysis complements the digital dataset by providing kinematic and chronological interpretations of brittle structures linked to the tectonic evolution of the fold and thrust belt.
The lengths of regional strike-slip fault traces span four orders of magnitude, ranging from tens of meters to tens of thousands of meters, with a median of 177 meters. Their orientation, kinematic, and length relationships align with the multi-scale Riedel shear model (Ruhland, 1973)   forming the regional structural framework. Fractures in the VOM span scales from 0.1 to hundreds of meters, with a median length of 5 meters. Regional faults and VOM-derived fractures show an overlap in length distributions and consistency in fracture orientations and kinematics. Both align with the NW-SE compression inferred from field-based kinematic data and regional restorations associated with the Jura shortening event, demonstrating seamless characterization of brittle features across scales. 
This study seeks to further investigate the role of mechanical boundaries (e.g., stratigraphic boundaries, regional structures) in controlling reservoir compartmentalization. It also showcases the potential of outcrop analogues such as Creux-du-Van to support 3D characterization and analyses of fracture properties such as length distributions, orientation, and vertical persistence, ultimately contributing to the advancement of structural modelling of subsurface reservoirs for sustainable energy solutions.

How to cite: Caldeira, J. and Samsu, A.: Seamless Fracture Characterization with Virtual Outcrop Models: Fracture Geometry and Vertical Persistence at Creux-du-Van, Swiss Jura Mountains  , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11216, https://doi.org/10.5194/egusphere-egu25-11216, 2025.

Understanding and predicting the hydro-mechanical (HM) behavior of subsurface porous and fractured formations is key to a number of engineering applications, including fluid injection/extraction, construction/excavation, geo-energy production and deep geological disposal. The interaction between fluid pressure, deformations and stresses is particularly affected by the subsurface heterogeneity, which may lead to non-intuitive responses, such as effective stress reduction and pressure increase during fluid extraction. While the impact of large-scale heterogeneities is acknowledged in most studies and modeling efforts, the presence of heterogeneities at smaller scales cannot be included in reservoir-scale models and it must be encompassed into equivalent properties assigned to uniform materials.

In this work, we focus on the Biot effective stress coefficient, a central property determining the HM behavior of fluid-saturated geological media. When not simply assumed as equal to 1, this coefficient is estimated experimentally at the laboratory sample-scale or analytically through expressions valid for isotropic homogeneous materials. However, these approaches are not able to estimate a representative equivalent coefficient for fractured rocks, which are strongly anisotropic and prone to sample-size effects, with fracture lengths spanning several orders of magnitudes from millimeters up to hundreds of meters. By employing a theoretical framework to quantify an equivalent Biot coefficient for a fractured rock mass from the properties of both the porous intact rock and the discrete fracture network (DFN), it is possible to analyze the variability of this coefficient with the DFN properties and highlight the implications for the rock upscaled HM behavior, in the context of natural processes and engineering applications.

How to cite: De Simone, S.: The equivalent Biot coefficient reveals the effects of heterogeneity on the Hydro-Mechanical behavior of fractured rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11332, https://doi.org/10.5194/egusphere-egu25-11332, 2025.

Seismological observations show that earthquakes produce significant changes in the elastic and transport properties of active faults, with co-seismic drops in seismic wave velocities consistently followed by a slow post-seismic recovery, over months to few years. Such variations occur in volumes up to several hundred metres thick that correlate well with the dimensions of fault damage zones. This suggests the existence of a damage-recovery cycle within active fault zones, with the recovery phase possibly driven by a range of fluid-assisted re-strengthening “healing” mechanisms in the fractured medium and/or stress relaxation. Understanding how and how rapidly fractured rocks seal, regain their stiffness, and drive fluid flow in fault zones is fundamental to comprehend the mechanics of the brittle crust and for geo-engineering applications such as geothermal energy, ore deposits, the deep disposal of radioactive waste and CO2 sequestration.

At the Department of Geosciences of the University of Padua, a “percolation cell” apparatus has recently been installed to study long-term fluid-rock interaction under hydrostatic conditions with a maximum confining and pore pressure of 100 MPa and a maximum temperature of 250°C. Such apparatus is equipped with two syringe pumps and a back-pressure regulator that allow to monitor permeability evolution through time and a set of high-temperature P- and S- ultrasonic transducers to track changes of rock elastic properties in-situ. In addition, the pore fluid inlet circuit can flow into a stirred autoclave to pump solutions with controlled chemistry up to 20 MPa pore pressure and 200°C temperature through an externally heated pipe. Such an experimental apparatus allows to study both diffusion- and advection-dominated regimes within conditions representative for the upper crust.

Together with the experimental setup, here we present some preliminary long-term percolation tests in which de-ionized water was flowed at 25°C through rock cylinders of micritic limestones with mated and non-mated single fractures under 20 MPa confining pressure and 5 MPa pore pressure. The temporal evolution of permeability and elastic properties were monitored together with the fluid-chemistry at the outlet. Mechano-chemical processes along the fractures were also investigated through X-ray microtomography and SEM analyses.

How to cite: Fondriest, M. and Akker, I. V.: An experimental apparatus to investigate fluid-assisted long-term recovery of fractured rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12950, https://doi.org/10.5194/egusphere-egu25-12950, 2025.

Permeability in crystalline rocks, considered for use as geothermal reservoirs or deep geological repositories, is controlled by networks of well-connected fractures. Fracture connectivity depends on fracture orientation and density, which are influenced by tectonic and non-tectonic stresses, pre-existing foliations, and fracture zones. This study investigates fracture variability in the Devonian Wilsons Promontory granitic batholith of southeast Australia, which intruded Devonian metasediments that are unconformably overlain by Cretaceous rift-related sedimentary rocks.

Outcrop analogues allow 2D and 3D observation of fracture networks at scales from centimeters to hundreds of meters, complementing sub-meter-scale borehole data and regional lineament mapping. Additionally, digital outcrop models from uncrewed aerial vehicle (UAV) surveys enable fracture characterization in outcrops that are difficult to physically access, such as the granites in the study area. In this study, over 2,500 fractures were mapped and characterized from a UAV-derived point cloud. Most fractures strike NNW-SSE to N-S; they are are interpreted as extensional and to have formed coevally with NNW-SSE striking joints in outcropping Cretaceous rocks during regional uplift under NNW-SSE horizontal compression. Domains characterized by distinct fracture patterns are separated by meter-scale fracture zones, suggesting structural segmentation within the granite.

Future work will investigate the geometry and origin of these domain-bounding fracture zones and their links to mechanical heterogeneities in the granite. These insights will inform discrete fracture network (DFN) and hydrological models of granite reservoirs and repositories for spent nuclear waste. They will also support comparisons of brittle deformation in granitic versus siliciclastic rocks under shared tectonic regimes, relevant to energy projects involving multi-level, multi-lithology reservoirs.

How to cite: Samsu, A., Gasche, G., and Cruden, A. R.: Fracture Network Variability in Granite: Insights from Wilsons Promontory, Southeast Australia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13175, https://doi.org/10.5194/egusphere-egu25-13175, 2025.

As a key parameter affecting shale gas accumulation, the physical characteristics of shale reservoir are greatly affected by tectonic stress transformation and deformation, which not only affects the occurrence state of shale gas, but also determines the evaluation and exploration prospect of shale gas resource potential by changing the migration and enrichment of shale gas. In this study, shale samples were collected from two different faults based on the distance from each fault. Comparative analysis of the micro/nanopore structural characteristics and physical properties of these samples was carried out by scanning electron microscopy (SEM), liquid nitrogen adsorption and carbon dioxide adsorption. The results show that as brittle deformation is enhanced (from far away from the fault to inside the fault), the number of organic pores decreases overall, and the connectivity of microfractures and different pore types increase. The total pore volume and total pore specific surface area of shale both increase, the pore volume of mesopores decreases by 31%, and the macropores increase rapidly by 29%. The storage capacity of shale-related folds is higher than that of shale in faults, which is more conducive to the adsorption of shale gas. The permeability of shale in faults is higher than that of shale-related folds, which is more conducive to the seepage and migration of shale gas. The organic layer structure, which is the unique and very rare microstructure at the shale fault site (under shear), was observed inside the fault. It is believed that the organic matter in the shale at the fault site has transformed from the amorphous state at the initial stage of formation to the orientation of the aromatic lamellae to stretching and extension to an increase in the pore size and the enhancement of connectivity. In addition, inorganic nanoparticles were also observed at the fault site. Both structures are important for the small pores in the fault and the increase in reservoir space. When the fault forms a closed environment or tectonic activity ceases in the later period, the early fault location likely becomes a potential high-quality hydrocarbon generation reservoir. These results help improve the understanding of the physical properties of shale reservoirs and shale gas reservoir migration within fault structures and are of great significance for shale gas exploration, development and prediction.

How to cite: Li, X., Wang, J., Li, Z., and Wang, Z.: Impact of faulting on organic-rich shale reservoir structure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14230, https://doi.org/10.5194/egusphere-egu25-14230, 2025.

Abstract: Fracture propagation dynamics in complex geological formations is crucial for understanding cracking mechanism of deep rock and facilitating subsurface reconstruction and resource extraction. However, predominant mechanism-driven numerical model exist several inherent limitations: 1) Over-reliance on empirical formulas and simplified hydraulic fracture propagation model with multi-assumptions restrict its capacity for effectively characterizing the multi-physics coupling in 3-D space, thereby reducing the accuracy of fracture morphology. 2) Computational schemes such as finite element method (FEM) or discrete element method (DEM) involving extensive repetitive calculations, are resource-intensive and exhibit poor temporal efficiency, posing a challenge to engineering requirements. Therefore, a data-model-interactive neural proxy model combining the prior-knowledge from mechanism models and fitting efficiency of deep neural networks, is put forward to depict the fracture propagation dynamics in complex geological formation. Initially, a numerical model for fracture propagation is developed by implementing the 3-D discrete lattice method alongside the elastic-plastic constitutive equation. The coupling of rock deformation and fluid flow is iteratively processed in a stepwise manner to generate a sequence of fracture morphology evolution over time. These mechanism data will provide training samples for the subsequent neural proxy model. Secondly, the efficacy of the neural proxy model is contingent upon the richness and diversity of features presented in the training dataset, necessitating a close approximation of all conceivable scenarios. In light of the irregular spatial distribution of data resulting from the complex geological formation with strong heterogeneity, the Latin Hypercube sampling method is employed to ensure a uniform selection of all conditions, mitigating the potential data imbalance. Furthermore, the integration of numerical results with empirical measurements is employed to train the developed deep-neural networks, fitting high-dimensional mapping relationships among formation physical parameters, engineering parameters, and fracture morphology. Finally, the efficiency and the accuracy of the proposed method are verified by multi-level comparison experiments between real data and simulation results. Our research provides reliable technical support for rapid evaluation of formation fracturing potential in field and guidance of development process.

Keywords: Fracture propagation, Neural proxy model, Deep learning, Numerical simulation, Deep-formation

How to cite: Zhang, F., Tang, J., Fan, Y., Yang, J., Li, J., Chen, W., Wang, H., and Jia, Y.: Fracture Propagation Dynamics Predicted by Data-model-interactive Neural Proxy Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14719, https://doi.org/10.5194/egusphere-egu25-14719, 2025.

Geothermal resources are renewable sources of energy and raw materials. A sustainable utilization for the long-term preservation of the resource requires a site-specific plan that needs to be based on geological and hydrogeological reconstructions. Northern Croatia is rich in geothermal resources that are generally hosted in carbonate rocks. The occurrence of thermal waters (temperatures of 38-50°C) in the town of Daruvar has been documented since the Roman age. In this research, the characterization of the Daruvar carbonate thermal aquifer was detailed using an integrated approach combining hydrogeological and structural investigations and discrete fracture network (DFN) modeling. Hydrogeological investigations consisted in the well logging and pumping tests of a 190 m deep well in Daruvar. Structural investigations were conducted NE of Daruvar where the carbonate rock complex of the aquifer is exposed at the surface. They included the measurement of the discontinuity sets and the photogrammetric reconstruction of the outcrop. The results were used to calibrate a DFN model at the scale of the aquifer explored by hydrogeological investigations (700x700x150 m).

The porosity distribution of the aquifer was obtained from the neutron log of the well ranging from 0.03 to 9.1% (average = 2.7%). The permeability was calculated using transmissivity values from the analysis of pumping tests and literature data resulting in a range from 7.4 to 122.8 D (average = 46 D). Structural analyses in the outcrop analog of the aquifer depicted two dominant systems of discontinuities (241/65 and 296/75). A highly fractured section of the outcrop was selected for the statistical analysis of the geometrical features of the discontinuity network to derive the input parameters for the DFN modeling. Discontinuity aperture was estimated based on the calibration of the DFN model. The results show a linear and power correlation of the aperture with porosity and permeability, respectively. Considering the average porosity of the aquifer, the calibrated aperture value was 3 mm obtaining a permeability of 1.5×10⁵ D. Such high value was interpreted as connected to the porosity value used for the calibration, which was measured through the neutron log depicting the total porosity. On the other hand, the fluid flow and the aquifer permeability are influenced by the effective porosity, which is at least an order of magnitude lower than the total porosity in carbonate aquifers. This difference was accounted for by testing a “dual aperture” approach. Considering the experimental dataset, a porosity of 0.2% (10th percentile of the distribution) was tested. It resulted in a calibrated fracture aperture of 0.22 mm obtaining a permeability of 60.5 D, comparable with the experimental dataset.

The obtained results highlight the importance of integrating structural and hydrogeological approaches to investigate fractured aquifers. Structural data can be used to determine the architecture of the fracture network in the rock mass, while hydrogeological investigations supported by numerical modeling and structural results can provide a solid hydrogeological parametrization of the aquifer.

Acknowledgment: This research was funded by the HyTheC project of the Croatian Science Foundation, grant number UIP-2019-04-1218.

How to cite: Pola, M., Kosović, I., Urumović, K., Borović, S., Frangen, T., Pavić, M., Matoš, B., Pavičić, I., Bistacchi, A., Mittempergher, S., Casiraghi, S., and Benedetti, G.: Hydrogeological parametrization of a carbonate thermal aquifer through integrated pumping test and virtual outcrop reconstruction (Daruvar, Croatia), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15295, https://doi.org/10.5194/egusphere-egu25-15295, 2025.

Discrete Fracture Network (DFN) models have a widespread use when predicting hydraulic properties of fractured rock masses with different numerical and (semi-)analytical methods. However, recent advances in the way fracture network parameters are characterized in the field or in geophysical datasets are not completely reflected in input options of DFN simulators. For instance, to our knowledge no 3D DFN stochastic simulator is able to generate fracture networks with realistic topological relationships, and fracture spatial distributions different from a completely random Poisson distribution cannot be generated (so clustered or regular distributions cannot be modelled). This means that stochastic fracture networks cannot show realistic connectivity, with a strong impact on our possibility to model hydraulic properties.

Here we report on a comparative experiment where we have (i) reconstructed a 3D deterministic fracture network, based on rich outcrop data (Cretaceous platform limestones from Cava Pontrelli, Puglia, Italy), and stochastic DFNs with the same statistical parameters, and then (ii) we have modelled hydraulic properties with different semi-analytical (e.g. Oda method) and numerical methods (e.g. finite volumes implemented in DFNWorks).

Our preliminary results suggest that more advanced numerical methods are more sensitive to the quality of input data than simple semi-analytical methods. This is explained by the fact that for instance the Oda method simply ignores topology, connectivity, fracture height/length ratio and other important parameters.

How to cite: Favaro, S., Facci, M., Casiraghi, S., Mittempergher, S., and Bistacchi, A.: Comparing the impact of deterministic and stochastic fracture networks on modelling hydraulic properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16743, https://doi.org/10.5194/egusphere-egu25-16743, 2025.

Applied geoscience relies on robust structural models that are appropriately scaled and detailed to address specific challenges. However, the process of developing these models is influenced by human biases shaped by personal and professional experiences, area of expertise, cognition, and values. This diversity of approaches to geoscience interpretation, such as fracture characterisation, impacts the reliability of structural models, which are critical for geoenergy, resource and infrastructure applications. Ensuring robust interpretations is vital for improving safety, enhancing decision-making, and securing project success.

This study investigates the variability in fracture interpretations made by geoscientists analysing an aerial drone image of a fractured outcrop. We compare outputs such as fracture frequency, orientation & density, and network topology across participants to assess the variability in their observations and the uncertainty this develops.

Previous studies on 3D seismic data have shown that geoscientists’ experience and approach significantly impact structural models. Our research systematically assesses similar variability using remotely sensed outcrop data and shows that while our cohorts of geoscientists agree of the “big stuff”, there is less consensus when we examine the detail.

By illustrating these uncertainties, we can begin to inform improved interpretation workflows, team arrangements, assurance processes, and geoscience education and communication. Understanding biases in fracture interpretation is a critical step towards enhancing interpretational accuracy. Coupled with a clear idea of how “good” the structural model needs to be for the problem being solved and appropriate mitigation measures, (if necessary) this ensures better project outcomes and supports the development of reliable geoscience outputs across applications.

How to cite: Evans, L., Shipton, Z., Bond, C., Roberts, J., and Kim, N.: How Good is Your Fracture Model? Evaluating Human Biases and Uncertainty in Geoscientific Interpretations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16786, https://doi.org/10.5194/egusphere-egu25-16786, 2025.

Fault-related karst systems and silicification processes are important factors in controlling permeability heterogeneities in shallow crusts. In recent years, the interest in these processes has become more important since they significantly modify the texture, mineralogy, and petrophysical properties of carbonate reservoirs.

The hypogenic Morro Vermelho Cave, in the Irecê Basin, Bahia (Brazil), is a key study area for understanding the development of fault-related silicification and subsequent karstification along fault networks in dolomitized carbonate rocks of the Neoproterozoic Salitre Formation.

This contribution focuses on a tridimensional digital cave model analysis and a detailed outcrop and cave investigation to constrain fracture attitude, type, geometry, and kinematics. Field data show the presence of regional-scale E-W thrust data.

The Morro Vermelho cave is developed in the proximity of one of these thrusts and is mostly developed along silicified carbonates with bedding dipping 40° toward SE.

The analysis of the lidar model reveals that the cave has an irregular morphology with several branching passages controlled by major N-S to NNE-SSW thoroughgoing fractures.

Both 3D model and high-resolution structural mapping in the cave highlight the presence of high-angle N-S-oriented normal faults and the following fracture sets: E-W-striking sheared veins and joints, bed-parallel NE-SW-striking veins, fault-parallel N-S-striking veins and joints, and bed-perpendicular NW-SE-striking veins and joints.

The obtained results indicate that the silicification process was mostly controlled by regional-scale E-W-striking thrust, associated with the N-S shortening of the Brasiliano orogeny, whereas the Morro Vermelho cave developed mostly along bedding layers and small-scale N-S-oriented normal faults, system and related fractures. The fractures also controlled the occurrence of late-stage silica crusts that post-date the cave development.

We propose a preliminary conceptual model that includes different stages of silicification events and karstification related to fault systems and fracture networks, in alignment with the structural regional-scale evolution of the study area.

The findings might be highly significant for understanding the permeability characteristics of deeply buried pre-salt fractured carbonate reservoirs in offshore Brazil and other similar settings.

How to cite: Porta, F., Morandi, C., La Bruna, V., Auler, A., Bezerra, F. H. R., and Balsamo, F.: Structural control on silicification and hypogenic karst: insights from Morro Vermelho cave, Irecê Basin, Brazil , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17127, https://doi.org/10.5194/egusphere-egu25-17127, 2025.

Mesoscale fractures, with lengths between meters and hundreds of meters, cannot be effectively characterized in the subsurface, due to limitations of borehole and geophysical datasets. However, large quantitative structural datasets can be collected by combining field and remote sensing techniques in digital outcrop models (DOMs). These data can be then used to constrain stochastic models of subsurface fracture networks with the outcrop analogue approach. However, to date a methodology optimized to characterize all parameters of a fracture network remains elusive. In this contribution we present a workflow that leverages digital outcrop models including both pavement and wall exposures, allowing for a three-dimensional analysis. Different parameters are calculated starting from different types of support, so we collect orientation data on point cloud DOMs (PC-DOMs) of vertical outcrops with semi-automatic methods. These data are classified based on field observations and segmented using a k-medoid approach. The goodness-of-fit to orientation distributions is tested with a proper statistical treatment. Topological parameters are measured on the fracture network digitalized from textured surface DOMs (TS-DOM). Standard topological analysis only provides averaged information on the whole fracture network. In this contribution a novel approach called directional topology is presented, in which every node retains information about the branches that generated it. This not only provides a more comprehensive understanding of the network's connectivity but also allows for the extraction of quantitative parameters about the degree of abutting of a specific fracture set on another (on horizontal outcrops) and on the extent to which a set is stratabound (on vertical outcrops). The trace length, height and spacing distributions are measured with a robust innovative approach, accounting for the censoring bias with survival/reliability analysis. P21 data are collected distributing several grids of scan area with increasing edge length, and the representative elementary area is qualitatively defined. A particular focus will be placed on the calculation of the H/L ratio, often overlooked but of fundamental importance, as it is responsible of the jump in dimensionality in 3D stochastic models.

How to cite: Casiraghi, S., Benedetti, G., Bertacchi, D., Agliardi, F., Mittempergher, S., and Bistacchi, A.: Integrated Workflow for Parametrization of Fracture Networks in Digital Outcrop Models: Focus on Directional Topology and H/L ratio calculation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18626, https://doi.org/10.5194/egusphere-egu25-18626, 2025.

We investigate seismic waveform changes in time-lapse along supercritical CO₂-bearing faults from field data by analysing 4D seismic data from the Illinois Basin – Decatur Project. 1 million tonnes of CO₂ was injected into the Lower Mt. Simon continuously over a three year period from 2011-2014. It has been established that the injected CO₂ migrated vertically along faults at this site to reach the Middle and Upper Mt. Simon formations (Bukar et al., 2024). Time-lapse 3D vertical seismic profiles were acquired each year of injection in addition to a pre-injection baseline and a final survey two months post-injection. We study the time-lapse seismic waveforms in zones around previously interpreted faults. In post-stack, we observe waveform distortions in the monitor traces that manifest as phase changes when compared to the baseline traces. Interestingly, these distortions magnify with increasing injected CO₂ volume, and decrease post-injection. To further investigate potential causes of these phase changes, we study the data in pre-stack. We also attempt to discriminate the contribution of CO₂ saturation effects and pressure effects. This is crucial as pressure increase also causes a slowdown effect on seismic waves in fractured media due to positive physical strain (expansion) and an accompanied decrease in the rock bulk modulus. However, while CO₂ injection is typically accompanied by pressure increases, the pressure would typically decline more quickly than CO₂ would dissolve in brine; multiple pressure gauges at this site show a rapid decline in pressure once injection ceased. Therefore, time-lapse seismic acquired soon after stopping injection could offer insights. We also observe these distortions where faults have not been mapped – these could be CO₂-filled fault zones with small throws that are below seismic resolution. This could potentially be used to illuminate unseen faults after CO₂ injection.

References

Bukar, I., Bell, R., Muggeridge, A. H., & Krevor, S. (2024). Carbon dioxide migration along faults at the Illinois Basin – Decatur Project revealed using time shift analysis of seismic monitoring data. Geophysical Research Letters, 51, e2024GL110049. https://doi.org/10.1029/2024GL110049

How to cite: Bukar, I., Bell, R., Muggeridge, A., and Krevor, S.: Time-lapse seismic properties of CO2-filled fault zones: Field observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19549, https://doi.org/10.5194/egusphere-egu25-19549, 2025.

Let us focus on a specific question that may has an ability to build an efficient method toward extracting significantly major ingredients of pre-active events going ahead of significant seismic activities. What is the common point at the state spaces of significant earthquakes of Türkiye in 1999 and 2023? The answer comes from some live but non-instrumented observations, those are devised privately. Those observations are related to both waveguide and cavity effects of natural and/or manmade significant structures replaced in both underground and/or atmosphere. The effects are studied on the electromagnetic wave propagation at significant pre-seismic activities of both circularly cylindrical wave guide and cavity structures meshed in underground and/or atmosphere by considering the extended wave equations in irregularly deviating environs¹. Those structures have excessive dimensions as in subway tunnels² and/or layered guiding pathways in atmosphere³.

The answer comes from two big tunnels excavated before abovesaid two earthquakes of Türkiye. First is Mount Bolu Tunnel, that is almost finished in 2007 and begun in 1993 and second is New Mount Zigana Tunnel, that is finished in 2023 and begun in 2016. Why? First of all, both tunnels are into mounts area of Northern Anatolia. The reason is related to the changing character of seismic activities after 5.9 R (included) magnitude that converts the seismic activities to electromagnetic activities majorantly⁴.

There is one more tunnel process that still continues for constructions: Between Bahce (37° 12′ 0″ N, 36° 35′ 0″ E) and Nurdagi (37° 10′ 44″ N, 36° 44′ 23″ E) districts of Gaziantep Province, Türkiye. This tunnel construction may have a potential on future seismic activities as two tunnel constructions said in previous paragraph.

The cavities and tunnels behave as layered guiding pathways for propagating waves either homogeneous and/or inhomogeneous fillings; therefore, the activities of waveforms may propagate along long distances under the Earth; i.e., between NAF and SAF by suitable transmissions, propagations, and guiding of waves. The majorant contributions come through Casimir and Casimir-like activities from the boundary interfaces between different materials with specific conditions under stochastic processes. The propagating waves create similar effects among transmitters and receivers through atmosphere layers. Author calls transmission effect by the cavity tunneling and layered guiding pathways these effects.

Those circumstances are studied in above paragraphs by considering the state space formulation of equivalent electrical circuits models through the possible mechanical circuits into the Earth.

The equivalent circuit model governs the significant Seismic Activities, sSAs, by the interactions among source and sink structures available in the distributed networks of equivalent circuits. New constructions have the ability to trigger and produce sSAs close to both specific domains of sSAs and their neighbor domains even if they never generated sSAs in past, of tunnel projects in paragraph 3 and similar ones. Temporal intervals may not coincide with the time spans of excavations of sSAs processes and their triggering effects may either decrease, mostly and/or increase, asymptotically as depending to coupling activities in environ.

¹https://doi.org/10.1109/APS.1996.549734

²https://doi.org/10.5194/egusphere-egu2020-22589.

³ https://doi.org/10.1109/RAST.2003.1303999.

⁴ https://doi.org/10.5194/egusphere-egu2020-21121.

How to cite: Sengor, T.: The Cavity Tunneling and Layered Guiding Pathways in Significant Seismic Activities: Pre-fingerprints in Significant Earthquakes of Türkiye in 1999 and 2023, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-988, https://doi.org/10.5194/egusphere-egu25-988, 2025.

There has long been research on the phenomenon of abnormal microwave radiation emitted from the Earth's surface before a major earthquake. However, the enhanced microwave radiation received by satellite sensors is affected by a combination of factors such as surface vegetation, soil moisture, land surface temperature, and atmospheric environment. So far, it has been difficult to remove non-seismic interference through quantitative physical modeling, leaving only the earthquake-related additional components for earthquake precursor analysis and short-term earthquake prediction. To tackle with this, we developed a knowledge-guided deep learning model that leverages a large amount of remote sensing observation data for training, incorporating prior knowledge of earthquake anomaly analysis. In the modelling process, a large amount of multi-source data, such as surface microwave brightness temperature (MBT), land surface temperature (LST), surface vegetation index, soil moisture index, atmospheric water vapor content, cloud cover, land cover type, digital elevation model (DEM), and geological type, were collected, and a regression model between multiple factors and surface MBT were firstly established through deep learning methods. In the same way, another regression model was developed between non-temperature parameters and LST by using historical records. During the seismic window of one month before and after the target earthquake, the LST was obtained by using non-temperature data through the second regression model, and then was substituted it into the first regression model to get the MBT value that does not include the additional effects of earthquakes. Eventually, we can obtain the additional MBT value due to seismic activity by calculating the difference with the actual observation, which represents the earthquake-related MBT anomaly. Since the deep learning-based modeling is based on long time series data and the output results of the model already include the contribution of multiple factors on the surface to the MBT, the differential results are mainly affected by the additional impacts of the earthquake, so they can be considered 'pollution-free'. In other words, there is no need to use additional auxiliary data to discriminate and separate the non-seismic disturbances. For a specific target area, such as the Tibetan Plateau, after establishing a model based on historical data using the aforementioned method, we can obtain real-time earthquake MBT variations as the input data is continuously updated. This can be used to analyze and identify potential earthquake precursors, and consequently, for short-term earthquake prediction.

How to cite: Qi, Y., Mao, W., Wu, L., and Huang, B.: A Knowledge-Guided Deep Learning Model for Extracting Pollution-free Seismic Microwave Brightness Temperature Anomalies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1408, https://doi.org/10.5194/egusphere-egu25-1408, 2025.

In the last decades, the scientific community has been focused on searching earthquake signatures in the Earth's atmosphere, ionosphere, and magnetosphere. This work investigates an offshore Mw 5.5 earthquake that struck off the Marche region's coast (Italy) on November 9, 2022, with a focus on the potential coupling between the Earth's lithosphere, atmosphere, and magnetosphere triggered by the seismic event. Analysis of atmospheric temperature data from ERA5 reveals a significant increase in potential energy (Ep) at the earthquake's epicenter, consistent with the generation of Atmospheric Gravity Waves (AGWs). This finding is further corroborated by the MILC analytical model, which accurately simulates the observed Ep trends (within 5%), supporting the theory of Lithosphere-Atmosphere-Ionosphere-Magnetosphere Coupling. The study also examines the vertical Total Electron Content (vTEC) and finds notable fluctuations at the epicenter, exhibiting periodicities (7-12 minutes) characteristic of AGWs and traveling ionospheric disturbances. The correlation between ERA5 observations and MILC model predictions, particularly in temperature deviations and Ep distributions, strengthens the hypothesis that earthquake-generated AGWs impacted atmospheric conditions at high altitudes, leading to observable ionospheric perturbations. This research contributes to a deeper understanding of Lithosphere-Atmosphere-Ionosphere-Magnetosphere Coupling mechanisms and the potential for developing reliable earthquake prediction tools.

How to cite: Piersanti, M., D'Angelo, G., Recchiuti, D., Lepreti, F., Cusano, P., De Lauro, E., Carbone, V., Ubertini, P., and Falanga, M.: On the Ionosphere-Atmosphere-Lithosphere coupling during theNovember 9, 2022 Italian Earthquake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2283, https://doi.org/10.5194/egusphere-egu25-2283, 2025.

We discuss the potential impact of the Geospace environment on the significant earthquake preparation processes. In this work, we investigate the response of major seismic activity to geomagnetic storms with a joint analysis of solar wind, geomagnetic field, and earthquake catalog. As a test case, we processed the seven strongest earthquakes in Italy for the period  1980 - 2016:  Amatrice M6.2 of Aug 24, 2016; Visso M6.1 of 26 Oct 2016; Norcia M6.6 of 30 Oct 2016; Emilia-Romagnia M6 of May 20, 2012;  L’Aquila M6.3 of Apr 6, 2009;  Foligno M6 of Sep 26,1997  and  Irpina of M6.9 of 23 Nov 1980. All of the seismic events were preceded by geomagnetic storms, which satisfied a given criterion: at the time of geomagnetic storm onset, the high-latitude part of the longitudinal region, where in the future an earthquake occur, was located under the polar cusp, where the solar wind plasma would directly access the Earth’s environment [Ouzounov and Khachikyan, 2024]. The number of preceded storms varied for different earthquakes from two to five. This results in different time delays between the day of the magnetic storm onset and the day of earthquake occurrence; it ranges between 9-80 days. Because of the existing delay between a shocked solar wind arrival and earthquake occurrence up to some months, this may suggest that solar wind energy does not trigger earthquakes immediately (as it is believed at present); instead, it may accelerate the processes of lithosphere dynamics, such as fluid and gas upwelling, which are active participants in tectonic earthquakes. For comparison, we present the results of the same analysis applied to other territories of the Mediterranean region: the Anatolian Plate (Turkey) and Crete Island (Greece), which look strikingly similar.

How to cite: Ouzounov, D. and Khachikyan, G.: The impact of the geospace environment on earthquake preparation processes. Case studies for M>6 in Italy for 1980-2016, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3686, https://doi.org/10.5194/egusphere-egu25-3686, 2025.

In this study, we compared the results of multiparametric and multilayers investigations of three doublet earthquakes that occurred around the Arabian plate (M6.2 + M6.0 on 18 August 2014 close to Dehloran, Iran; M6.0 + M6.0 occurred on 15 July 2018 offshore Kilmia, Yemen and M6.0 + M6.0 occurred on 1 July 2022 close to Bandar-e Lengeh). We applied identical methods to the same dataset for all three cases. In particular, we investigated lithospheric, atmospheric, and ionospheric data six months before the three events. The lithosphere was investigated by calculating the cumulative Benioff strain with the USGS earthquake catalogue. Several atmospheric parameters (aerosol, SO₂, CO, surface air temperature, surface latent heat flux humidity, and dimethyl sulphide) have been monitored using the homogeneous data from the MERRA-2 climatological archive. We used the three-satellite Swarm constellation for magnetic data, analysing the residuals after removing a geomagnetic model. All the cases present some patterns of anomalies, and when comparing them, we noticed some similarities but also differences. We pointed out that the released energy by the three events is very similar and occurred around the same plate. Still, they involved two different tectonic contexts (compressional on the Iranian side and extensional and transcurrent on the African Plate border). For the above reasons, their comparison is very interesting. Some similarities seem to be explainable in the tectonic context, and some are caused by the ocean's influence at the epicentre location. However, we also identified some differences that still require further investigation and comparison with other case studies.

Finally, this work can be considered a preliminary test of an extensive investigation and systematical search of LAIC patterns before the earthquake occurrences and the study of the possible influence of focal mechanism, location, geological factors, and other constraints.

References :

Ghamry Essam; Marchetti Dedalo; Metwaly Mohamed. Geophysical Coupling Before Three Earthquake Doublets Around the Arabian Plate. Atmosphere 2024, 15, 1318. https://doi.org/10.3390/atmos15111318

How to cite: Ghamry, E., Marchetti, D., and Metwaly, M.: Similarities and differences of the preparation of three (M≈6) earthquake doublets around the Arabian Plate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5269, https://doi.org/10.5194/egusphere-egu25-5269, 2025.

Seismicity is the result of the interaction between tectonic plates in relative motion where the underlying mechanism of earthquake generation in seismic subduction areas is stick-slip. In reality, seismicity is a complex phenomenon as it involves processes that take place from within the Earth. A thorough understanding of seismicity requires theoretical and experimental approaches. The dynamics in subduction zones occur when two tectonic plates, one on top of the other, are in relative motion where the plate below is in motion due to convective processes within the Earth. Due to the roughness of both surfaces, the underlying mechanism that gives rise to seismicity is stick-slip. In this work, an experimental stick-slip model is proposed, which simulates the relative motion of two rough surfaces by the interaction of two blocks covered by sandpaper with a certain degree of roughness. In this experimental model, the interaction between rough surfaces (sandpaper), with a relative motion in opposite directions to each other, produces stick-slip events (synthetic seismicity), which mimic real seismicity. Here we present the first analyses of synthetic seismicity by calculating the Gutenberg-Richter law, temporal correlations and characterization in terms of organization and order from the Fisher-Shannon method for each synthetic catalogue.

How to cite: Ramírez-Rojas, A., Telesca, L., and Flores-Márquez, E. L.: Novel experimental design for the study of seismic processes based on the stick-slip mechanism., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5321, https://doi.org/10.5194/egusphere-egu25-5321, 2025.

Earthquake forecasting, combined with precise ground-shaking estimations, plays a pivotal role in safeguarding public safety, fortifying infrastructure, and bolstering the preparedness of emergency services. This study introduces a comprehensive workflow that integrates the epidemic-type aftershock sequence (ETAS) model with a preselected ground-motion model (GMM), facilitating accurate short-term forecasting of ground-shaking intensity (GSI), which is crucial for adequate earthquake warning for earthquake-prone regions like Taiwan. First, an analysis was conducted on a Taiwanese earthquake catalog from 1994 to 2022 to optimize the ETAS parameters. The dataset used in this analysis allowed for the further calculation of total, background, and clustering seismicity rates, which are crucial for understanding spatiotemporal earthquake occurrence. Subsequently, short-term earthquake activity simulations were performed using these up-to-date seismicity rates to generate synthetic catalogs. The ground-shaking impact on the target sites from each synthetic catalog was assessed by determining the maximum intensity using a selected GMM. This simulation process was repeated to enhance the reliability of the forecasts. Through this process, a probability distribution was created, serving as a robust forecasting for GSI at sites. The performance of the forecasting model was validated through an example of the Taitung, Taiwan earthquake sequence in September 2022, showing its effectiveness in forecasting earthquake activity and site-specific GSI. The other example is the Hualien, Taiwan earthquake sequence from April 2024, which serves as an excellent demonstration of a workflow designed to provide real-time aftershock forecasting following an M7.2 event. The proposed forecasting model can quickly deliver short-term seismic hazard curves and warning messages, facilitating timely decision-making.

How to cite: Hsieh, M.-C., Chan, C.-H., Ma, K.-F., Yen, Y.-T., Chen, C.-T., Chen, D.-Y., and Liao, Y.-W.: Toward Real-Time Forecasting of Earthquake Occurrence and Ground-Shaking Intensity Using ETAS and GMM: Insights from Recent Large Earthquakes in Taiwan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5493, https://doi.org/10.5194/egusphere-egu25-5493, 2025.

This study conducted a systematic analysis of the 2022 Chihshang earthquake sequence in eastern Taiwan, integrating multidimensional observational parameters related to the lithosphere, atmosphere, and ionosphere. High-resolution data from the MAGIC (Multidimensional Active fault of Geo-Inclusive observatory - Chihshang) at the Chihshang fault area provided a comprehensive and diverse dataset. The analysis revealed significant pre-earthquake anomalies across various parameters. These include a marked increase in soil radon concentration one month prior to the earthquake, concurrent anomalies in hydrogeochemical parameters (e.g., elevated groundwater temperature, reduced pH, and decreased chloride ion concentration), and active foreshock activity detected by a dense microseismic network starting mid-August, suggesting the development of microfractures within the lithosphere. Additionally, persistent OLR (Outgoing Longwave Radiation) anomalies, indicating hotspots near the epicenter, were observed from September 5 to 7. Pre-earthquake signals in TEC (Total Electron Content) were identified between August 20 and September 13 in two independent datasets, GIM-TEC and CWA-TEC.

Post-earthquake observations revealed a significant increase in CO₂ flux in the region, likely attributable to the release of deep-seated gas sources or enhanced permeability of the fault system. These combined observations suggest that all anomalies can be classified as short-term precursors, which can be interpreted within the theoretical framework of lithosphere-atmosphere-ionosphere coupling (LAIC). The findings also contribute to a deeper understanding of the earthquake preparation process. This study underscores the critical importance of real-time integration of multi-parameter observations, offering new insights and improvements for seismic hazard assessment and advancing the predictive capability of earthquake precursors.

How to cite: Fu, C.-C., Kuo-Chen, H., Mu, C.-H., Jhuang, H.-K., Lee, L.-C., Walia, V., and Tsai, T.-C.: Multiparameter observations of Lithosphere–Atmosphere–Ionosphere pre-seismic anomalies: Insights from the 2022 M6.8 Chihshang earthquake in southeastern Taiwan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8052, https://doi.org/10.5194/egusphere-egu25-8052, 2025.

Robust Satellite Techniques applied to long-term satellite TIR (Thermal InfraRed) radiances have
been, since more than 25 years, employed to identify those anomalies (in the spatial/temporal
domain) possibly associated to the occurrence of major earthquakes.
The results until now 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.
After the most comprehensive test performed over Greece, Italy, Turkey and Japan, here, we will
critically discuss the preliminary results achieved over California by applying RST analyses to
long-term series of GOES-17 radiances.

How to cite: Colonna, R., Filizzola, C., Genzano, N., Lisi, M., Mancusi, I., Pietrapertosa, C., and Tramutoli, V.: Recent achievements on the application of Robust Satellite Techniques to the short-term seismic hazard forecast, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8652, https://doi.org/10.5194/egusphere-egu25-8652, 2025.

Various types of changes in the characteristics of very low frequency (VLF) signals before earthquakes have been presented during the past few decades. Most of these changes have been observed on data with time sampling of the order of a few tenths of a second or of the order of minutes. Improvements in this sampling in recent years have indicated three new types of changes whose onsets have been observed a few minutes or tens of minutes before the earthquake. These changes manifest themselves as reductions in the VLF signal amplitude and phase noises, and excitation and attenuation of waves with small wave periods in both of these signal characteristics [1-5].

In this work, we present these changes and list the parameters in the time and frequency domains that are significant for statistical analyses. A central issue is the relationship of the changes with the characteristics of earthquakes, the observed signals, and their spread in the surrounding area. The presented analyses were conducted on data recorded by a VLF receiver in Belgrade, Serbia.

References:

[1] A. Nina, S. Pulinets, P.F. Biagi, G. Nico, S.T. Mitrović, M. Radovanović, L.Č. Popović, “Variation in natural short-period ionospheric noise, and acoustic and gravity waves revealed by the amplitude analysis of a VLF radio signal on the occasion of the Kraljevo earthquake (Mw = 5.4)”, Science of The Total Environment, 710, 136406, 2020.

[2] A. Nina, P. F. Biagi, S. T. Mitrović, S. Pulinets, G. Nico, M. Radovanović,  L. Č. Popović, “Reduction of the VLF signal phase noise before earthquakes”, Atmosphere 12 (4), 444, 2021.

[3] A. Nina, P. F. Biagi, S. A. Pulinets, G. Nico, S. T. Mitrović, V. M. Čadež, M. Radovanović, M. Urošev,  L. Č. Popović, “Variation in the VLF signal noise amplitude during the period of intense seismic activity in Central Italy from 25 October to 3 November 2016”, Frontiers in Environmental Science, 10, 10:1005575, 2022.

[4] A. Nina, “Analysis of VLF Signal Noise Changes in the Time Domain and Excitations/Attenuations of Short-Period Waves in the Frequency Domain as Potential Earthquake Precursors”, Remote Sensing, 16(2), 397, (2024)

[5] A. Nina “VLF Signal Noise Reduction during Intense Seismic Activity: First Study of Wave Excitations and Attenuations in the VLF Signal Amplitude”, Remote Sensing, 16(8), 1330, 2024.

How to cite: Nico, G., Nina, A., Biagi, P., Eichelberger, H. U., Boudjada, M. Y., and Popović, L. Č.: Noise reductions of VLF signals and excitation/attenuation of waves with small wave periods before earthquakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8809, https://doi.org/10.5194/egusphere-egu25-8809, 2025.

A critical review of geoelectrical monitoring activities carried out in seismically active areas is presented and discussed. The electrical resistivity of rocks is one of the geophysical parameters of greatest interest in the study of possible seismic precursors, and it is strongly influenced by the presence of highly fractured zones with high permeability and fluid levels. The analysis in this study was based on results obtained over the last 50 years in seismic zones in China, Japan, the USA and Russia. These previous works made it possible to classify the different monitoring strategies, to analyze the theoretical models for interpreting possible correlations between anomalies in resistivity signals and local seismicity, and to identify the main scientific and technological gaps. In addition, much attention is given to some recent work on the study of correlations between focal mechanisms and the shapes of anomalous patterns in resistivity time series, and to the new possibilities offered by the AI-based methods for geophysical data processing. Finally, new strategies and activities for investigating the spatial and temporal dynamics of the electrical resistivity changes in seismically active areas were identified.

How to cite: Lapenna, V.: Detecting DC Electrical Resistivity Changes in Seismic Active Areas: State-of-the-Art and Future Directions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9250, https://doi.org/10.5194/egusphere-egu25-9250, 2025.

Multi-hazard disaster risk analyses in coastal areas requires the integration of data and models concerning hazard, exposure and vulnerability data and models, all developed with high spatial resolution. Indeed, accurate high-resolution models and data are essential for properly assessing the impact of specific hazards that threaten coastal areas, such as tsunamis, floods, landslides, and coastal erosion. Nevertheless, this level of detail remains unachieved for many coastal hazards in various locations. Consequently, critical fine-scale differences in localized risk assessment are overlooked, leading to potential underestimations or overestimations of the actual risk to coastal communities. It is vital to address this gap in order to enhance the accuracy and reliability of risk assessments.

A key step in tsunami hazard and risk assessment involves the development of inundation maps, specifically maps describing inundated areas and related depths. To date, such maps are not yet available at proper resolution for the coastal areas of the Friuli-Venezia-Giulia Region (FVG). Accordingly, this study aims to enhance the characterization of tsunami hazard in the Northern Adriatic by developing detailed inundation maps and possibly addressing the identified research gaps. Leveraging on accurate and high resolution bathymetry and topographic data is crucial for reliable tsunami modelling for the FVG coastal areas. To this purpose, bathymetry and topographic data are refined and are used, along with existing databases of tsunamigenic earthquake sources, for modelling tsunami waves propagation and inundation by means of the NAMI DANCE code (e.g. Yalciner et al. 2014, Mediterranean Sea Oceanography and references therein).

Existing datasets from open access and local data sources are collected and then refined, particularly addressing inaccuracies in lagoon bathymetry. This involves incorporating high-resolution data and considering small-scale coastal features that can significantly impact tsunami inundation. Multiple bathymetry and topography datasets are used to develop high resolution refined data at 25 meters, and 10 meters resolution. The database of co-seismic seafloor displacement for all individual scenarios, developed based upon the DISS-3.3.0 database, is adopted to carry out a reappraisal of tsunami wave amplitude maps (Peresan & Hassan, MEGR 2024 and references therein) and to estimate realistic tsunami inundation maps. Additionally, tsunami sources caused by local earthquakes relevant to the FVG region are investigated, providing local scale maps of wave amplitudes and inundation estimates; this involves using appropriate fault rupture realisations for local tsunami scenarios (ITCS100&101), as specified in the DISS-3.3.0 database.

The outcomes from this study provide the basis for multi-scenario tsunami hazard assessment, contributing to the development of high-resolution and comprehensive tsunami hazard maps for the Northern Adriatic coasts. Moreover, along with high-resolution exposure maps, they contribute improving precision and accuracy of related risk assessment, and hence are an important step in preparedness, response, and prevention efforts in the framework of disaster risk management.

This research is a contribution to the RETURN Extended Partnership (European Union Next-Generation EU—National Recovery and Resilience Plan—NRRP, Mission 4, Component 2, Investment 1.3—D.D. 1243 2/8/2022, PE0000005).

How to cite: Hassan, H. M. and Peresan, A.: High resolution tsunami inundation maps: towards multi-hazard risk analysis., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9938, https://doi.org/10.5194/egusphere-egu25-9938, 2025.

In recent decades, significant efforts have been devoted to understanding and interpreting the link between ionospheric perturbations and natural or anthropogenic phenomena, such as seismic activity, electrical or geomagnetic storms, and unidentified radio emissions. This is achieved through various methods among which is also the study of electromagnetic (EM) wave propagation in the very low frequency (VLF, 3–30 kHz) and low frequency (LF, 30–300 kHz) bands. These bands enable long-distance communication, navigation, and military applications, including submarine contact, AM broadcasting, lightning detection, and weather systems. Due to their long wavelengths, VLF and LF waves exhibit unique propagation characteristics. VLF waves propagate globally by using Earth-ionosphere waveguides, reflecting off the D and E layers as skywaves, and are influenced by solar and atmospheric conditions. LF waves primarily rely on ground waves for extensive coverage, although they can also utilize ionospheric reflection (skywaves) for longer-distance communication.

This paper introduces fundamental concepts related to VLF/LF electromagnetic wave emission, propagation, reception, and the perturbing factors that affect them. Additionally, it presents key findings from the European INFREP Receivers Network, which studies seismo-ionospheric anomalies linked to earthquake activity. Established in 2009, the INFREP network monitors VLF/LF signals from transmitters across Europe and neighboring regions. The network currently comprises 10 receivers, built by Elettronika (Italy), and operates at a sampling rate of one sample per minute. The Romanian segment of INFREP includes two receivers, operational since 2009 and 2017, with only brief interruptions, notably during the pandemic when travel restrictions hindered access to the observatories.

The paper discusses the current state of the INFREP network and outlines methods for providing near real-time data access. It highlights advancements in real-time electromagnetic data transmission, archiving, and the use of 2D and 3D online signal visualization and processing techniques. Data access is available through the INFREP headquarters in Graz, Austria (https://infrep.iwf.oeaw.ac.at/data-access/) and the National Institute for Earth Physics in Romania (https://mg.infp.ro/d/ch-aqZXIz/vlf-lf-radio-data?orgId=1&from=now-6M&to=now). The paper also shares findings from the detection of potential ionospheric anomalies in EM signals preceding large earthquakes that occurred between 2012 and 2024. All anomalies are analyzed in correlation with space weather events and extreme meteorological phenomena.

This paper was carried out within 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., Eichelberger, H. U., Biagi, P. F., Boudjada, M., Anghel, M., Manea, L. M., Mihai, A., and Antonescu, B.: Investigation of VLF/LF electromagnetic wave propagation as recorded by the receivers of the INFREP network, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10351, https://doi.org/10.5194/egusphere-egu25-10351, 2025.

Multi-hazard disaster risk reduction and mitigation require high-resolution exposure models that grasp the characteristics of assets at the local scale. High-resolution exposure models may allow improving precision/accuracy of risk and damage assessments, especially for hazards which are characterised by high spatial variability or may be influenced by the presence of the assets, such as tsunami or flooding. We propose a methodology for developing a high-resolution population and residential buildings exposure models, to be used for multi-hazard risk reduction purposes at the local scale.  This method has been tested and validated for a selected coastal area in the upper Adriatic, exposed to multiple hazards including earthquakes, tsunamis, meteorological events and coastal erosion. For the development of the population exposure model, a high-resolution population density data, collected at global scale, is combined with the national population census data, leveraging  both on the accuracy of the national census and on the resolution of the global data. Also, the building census data is complemented with exposure indicators extracted from digital building footprints from the Carta Tecnica Regionale Numerica (CTRN),  which is missing in census data, such as average built area, total built area, replacement cost, height and plan regularity. The final exposure layers are assembled at two resolutions: 100 meters and 30 meters, with information also provided at the census unit level. We discuss the development and use of these layers for multi-risk assessment and their potential combination with artificial intelligence. 

This research is a contribution to the projects: RETURN Extended Partnership (European Union Next-Generation EU—National Recovery and Resilience Plan—NRRP, Mission 4, Component 2, Investment 1.3—D.D. 1243 2/8/2022, PE0000005); PRIN-PNRR project SMILE: Statistical Machine Learning for Exposure development, funded by the European Union- Next Generation EU, Mission 4 Component 1 (CUP F53D23010780001). 

How to cite: Badreldin, H., Scaini, C., M Hassan, H., and Peresan, A.: High-resolution exposure models for coastal cities in Northern Adriatic for multi-risk analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10353, https://doi.org/10.5194/egusphere-egu25-10353, 2025.

Japan is frequently hit by major earthquakes, such as the 2011 off the Pacific coast of Tohoku Earthquake and the 2024 Noto Peninsula Earthquake, which cause enormous human and economic losses. Short-term forecast of earthquakes is effective for mitigating such damage, but this has not been achieved to date. On the other hand, there have been reports of electromagnetic phenomena preceding major earthquakes in various frequency bands, including precursor phenomena in the VLF/LF band (3-300 kHz). In this study, we investigated earthquake-related VLF/LF signals, which has strong electromagnetic emissions due to lightning activity, and it is important to discriminate the VLF/LF signals from those due to lightning activity. In this study, two approaches were attempted: (1) development of a source localization method using VLF/LF broadband interferometry and (2) removal of signals caused by lightning discharges using machine learning.
The first approach is expected to spatially discriminate between VLF/LF signals related to earthquakes (which are located near the epicenter and do not move) and signals related to lightning activity (which move with fronts and thunderclouds). The second is to utilize machine learning technology, which has been rapidly developed in recent years, for detection and removal of lightning discharge signals. For example, Wu et al. at Gifu University have succeeded in classifying lightning discharge waveforms in the thunderstorm activity process with an accuracy of approximately 99% using a machine learning technique called Random Forest. In this study, machine learning is expected to efficiently discriminate and eliminate known lightning discharge signals from a large amount of observation data with high accuracy, and analyze the remaining unknown signals to efficiently investigate the relationship between lightning and earthquakes. In this paper, we will describe the specific methods and results of the above two approaches.

How to cite: Hattori, K., Ota, Y., Yoshino, C., and Imazumi, N.: Construction of a VLF/LF band interferometer using a capacitive circular flat-plane antenna and discrimination and identification of observed VLF/LF band signals by machine learning: Preliminary results, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10447, https://doi.org/10.5194/egusphere-egu25-10447, 2025.

Electric field amplitude and phase measurements between narrowband VLF/LF transmitters and receivers in the sub-ionospheric waveguide are affected and altered by man-made and natural sources (Nina 2024; Boudjada et al., 2024a,b). In this study we investigate Mw≥5.0 earthquakes (EQs) which occurred in Europe during the year 2024 based on data from the INFREP receiver network (Biagi et al., 2019; Moldovan et al., 2015; Galopeau et al., 2023). In the selected Mediterranean area with geographical longitude [-10°E, 40°E] and latitude [30°N, 50°N] the United States Geological Survey EQ catalog (USGS, 2025) provides 20 events with Mw≥5.0. For these EQs we apply the night-time amplitude method and consider variations in the terminator times (Hayakawa et al., 2010). The main radio links that cross the EQ prone areas are from transmitters localized in the southern part of Europe, including TBB (26.70 kHz, Bafa, Turkey), ITS (45.90 kHz, Niscemi, Sicily, Italy), and ICV (20.27 kHz, Tavolara, Italy). 

We find statistically significant electric field anomalies for various VLF/LF paths, particularly for events with higher magnitudes. The continuous VLF/LF electric field amplitude and phase datasets can be important parameters for real-time observations and services to assess seismic hazards and disturbing physical phenomena within the waveguide.

References:

Biagi, P.F., et al., The INFREP network: Present situation and recent results, OJER, 8, 101-115, 2019. https://doi.org/10.4236/ojer.2019.82007

Boudjada, M.Y., et al., Unusual sunrise and sunset terminator variations in the behavior of sub-ionospheric VLF phase and amplitude signals prior to the Mw7.8 Turkey Syria earthquake of 6 February 2023, Remote Sens., 16, 4448, 2024. https://doi.org/10.3390/rs16234448

Boudjada, M.Y., et al., Analysis of pre-seismic ionospheric disturbances prior to 2020 Croatian earthquakes, Remote Sens., 16, 529, 2024. https://doi.org/10.3390/rs16030529

Galopeau, P.H.M., 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

Hayakawa, M., 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

Moldovan, I.A., et al., The development of the Romanian VLF/LF monitoring system as part of the International Network for Frontier Research on Earthquake Precursors (INFREP), Romanian Journal of Physics, 60 (7-8), 1203-1217, 2015. Bibcode: 2015RoJPh..60.1203M https://rjp.nipne.ro/2015_60_7-8/RomJPhys.60.p1203.pdf

Nina, A., VLF signal noise reduction during intense seismic activity: First study of wave excitations and attenuations in the VLF signal amplitude, Remote Sens., 16, 1330, 2024. https://doi.org/10.3390/rs16081330

USGS, United States Geological Survey earthquake catalog, https://www.usgs.gov/programs/earthquake-hazards, as of Jan 2025.

How to cite: Eichelberger, H. U., Boudjada, M. Y., Nina, A., Besser, B. P., Wolbang, D., Solovieva, M., Biagi, P. F., Galopeau, P. H. M., Schirninger, C., Moldovan, I.-A., Nico, G., Stachel, M., Aydogar, Ö., Muck, C., Wilfinger, J., and Jernej, I.: Sub-ionospheric VLF/LF waveguide electric field investigation from Mw≥5.0 earthquake events with multiple receivers in Europe, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13142, https://doi.org/10.5194/egusphere-egu25-13142, 2025.

Intense earthquakes have been natural phenomena that produce enormous disasters, mainly in large urban areas, due to the intense energy released in a very short period. Earthquakes are inevitable natural phenomena, and up to now, they cannot be predicted. On February 6, 2023, a M 7.8 earthquake occurred in southern Türkiye, near the northern border of Syria. This earthquake was followed by a M 7.5 earthquake to the north. The relative motions of three major tectonic plates (Arabian, Eurasian, and African) and one smaller tectonic block (Anatolian) are responsible for the seismicity in Türkiye. Recently, Onur investigated the aftershock distribution and its relation to energy release on the faults and Coulomb stress change areas, his study allowed the relocation of two-catastrophic earthquakes. In the present work we analyze the behavior of multifractality and its complexity parameters calculated from the catalog of seismic magnitudes during a period of 14 years monitored within two regions of Türkiye: the first one (west) between (35-42) Latitude, (25-34) Longitude and the second one (East) between (35-42) Latitude and (34-42) Longitude, being this area where the doublet occurred. Our results show differences in both multifractality and its complexity measures between the two regions. These findings may be indicators of expected seismicity in each region.

How to cite: Flores-Marquez, E. L., Ramirez Rojas, A., and Pérez-Oregon, J.: Comparative multifractal study of seismicity in two seismic zones of Türkiye in the period from 2010 to 2024., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13210, https://doi.org/10.5194/egusphere-egu25-13210, 2025.

Despite advances in satellite remote sensing, predicting large earthquakes, remains a significant challenge due to the unpredictable nature of these events. To address this challenge, our study, building upon the achievements of the French DEMETER satellite, focuses on atmospheric and space electrical variations as potential indicators of ionospheric D-region precursors to earthquakes. This approach is expected to contribute to the enhancement of short-term prediction capabilities. For this purpose, we would like to introduce our CubeSat PRELUDE (Precursory electric field observation CubeSat Demonstrator), a tiny satellite dedicated to the earthquake precursor detection and elucidated the physical mechanism. PRELUDE is scheduled for launch in JFY2025 as part of JAXA’s Innovative Satellite Technology Demonstration Program. This study presents the results of the system design, development, and mission planning of the PRELUDE, aimed at clarifying the physical mechanisms behind the statistically significant earthquake precursor ionospheric phenomena. PRELUDE is a 6U CubeSat specialized in VLF electromagnetic wave intensity observation, weighing 8 kg. To achieve miniaturization, it incorporates a drive recording function to downlink only the data surrounding the EQ epicenter to ground stations, reducing data storage and transmission requirements. Additionally, it hybridizes the Langmuir and electric field probes, typically found on satellites weighing over 100 kg like DEMETER, into a compact design suitable for CubeSats weighing just a few kilograms. The hybrid sensor unit extends booms bidirectionally by 1.5 m from the satellite using a folding extension mechanism, In this presentation, we show the satellite design requirements for elucidating the mechanism of earthquake precursor phenomena.

How to cite: Kamogawa, M., Yamazaki, M., and Sone, N.: Design of the PRELUDE CubeSat for investigating ionospheric D-region earthquake precursor, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14706, https://doi.org/10.5194/egusphere-egu25-14706, 2025.

Masonry structures are one of the most vulnerable to severe and extensive damage in terms of previous earthquakes. It is significant to quickly evaluate the seismic damage levels of masonry structures, to reduce casualties and economic losses caused by earthquakes. However, traditional methods based on manual judgment or finite element simulations tend to be relatively slower . In this paper, a machine learning-based rapid prediction method was proposed for assessing the seismic damage of masonry structures. By analysis of building data from several cities and combining ground motion with structural characteristics, 11 impact factors were identified as input variables. The LM-BP neural network model was developed by a backpropagation (BP) neural network with strong nonlinear modeling capabilities, and by the Levenberg-Marquardt (LM) algorithm. The accuracy and stability of the model were verified by comparing the predicted values with actual earthquake examples. The results show that the selected seismic damage impact factors can accurately reflect the structural damage level. By comparing methods using parameters on either the structure or ground motion, the predictive accuracy of the proposed method is significantly enhanced. It provides a basis for post-earthquake structural safety assessments and disaster prevention and mitigation work.

How to cite: Zhang, L., Liu, Y., Liu, L., and Zhu, B.: Rapid prediction method of earthquake damage to masonry structures based on machine learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14734, https://doi.org/10.5194/egusphere-egu25-14734, 2025.

Earthquakes are among the most frequent yet unpredictable natural hazards, posing substantial risk to human safety and infrastructure globally, particularly, when large-magnitude earthquakes occur. This highlights the urgent need to develop innovative and alternative methodologies for rapidly assessing the intensity of ground shaking following an earthquake.

This study explores the application of the Machine Learning Estimator for Ground Shaking Maps (MLESmap) methodology in New Zealand, a region characterized by  high seismic activity.

MLESmap utilizes extensive datasets of high-fidelity, physics-based seismic scenarios to rapidly estimate ground-shaking intensity in near real-time following an earthquake. This methodology has demonstrated evaluation times similar to those of empirical ground motion models, while offering superior predictive accuracy in the two previously tested regions: the Los Angeles basin and the South Iceland Seismic Zone (SISZ).

To adapt MLESmap for New Zealand’s seismicity, seismic simulations tailored to the unique geological and tectonic context of the region are implemented. Specifically, we use the dataset generated by CyberShake NZ, a probabilistic seismic hazard analysis (PSHA) software developed by the University of Canterbury. Using this software, a total of 11,362 finite-fault rupture simulations were performed across the region and seismic hazard results were calculated on a grid of 27,481 synthetic seismic stations. A ‘forward’ simulation approach was adopted due to the large number of output locations relative to rupture locations, the optimisation of the grid for each rupture and the intention to include plasticity.

The expected results aim to demonstrate the applicability of MLESmap to New Zealand, providing ML-based tools for rapid response actions. This study also takes the first steps in applying cascading effects to MLESmap, in order to improve the overall risk assessment and to advance prevention efforts through innovative and multidisciplinary methodologies.

©2023 ChEESE-2P Funded by the European Union. This work has received funding from the European High Performance Computing Joint Undertaking (JU) and Spain, Italy, Iceland, Germany, Norway, France, Finland and Croatia under grant agreement No 101093038.

How to cite: Blanco Prieto, R., Monterrubio Velasco, M., Bradley, B., Schill, C., and de la Puente, J.: Machine Learning based EStimator for ground shaking maps workflow applied to New Zealand, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16143, https://doi.org/10.5194/egusphere-egu25-16143, 2025.

The region near the India-Eurasia plate boundary has a long history of large earthquakes. Over the past century, more than 50 earthquakes with magnitudes of 7 or greater have occurred within 500 km of the Indo-Eurasian collision zone. These include the 2015 M7.8 Nepal earthquake, the 1934 M8.0 Bihar-Nepal earthquake, the 1950 M8.6 Assam earthquake, and the 1905 M7.9 Kangra earthquake. The January 7, 2025, M7.1 earthquake in the southern Tibetan Plateau further underscores the seismic significance of this region. This study examines the temporal variation in seismicity within the Indo-Eurasian collision zone and its adjacent areas by utilizing historical records and instrumentally recorded earthquake data from 1900 to 2024. Based on seismic behaviour, clustering of events, and tectonic structures, the collision zone is divided into 26 distinct seismic zones. The temporal variation in seismicity for each zone is analyzed, and a susceptibility index, ESI₆, is calculated. This index considers the return period of earthquakes with Mw ≥ 6 and the time elapsed since the last Mw ≥ 6 earthquake in each zone. The ESI₆ represents the number of pending Mw ≥ 6 earthquakes in each seismic zone. Ten zones with high ESI₆ values (>2.5) have been identified; these zones were seismically active in the past but have remained without major earthquakes for the last three decades. To mitigate potential losses and raise awareness, it is critical to implement GPS monitoring of plate movements, satellite-based deformation monitoring, and seismic health assessments of crucial infrastructure in these silent zones.

How to cite: Kumar, S.: Spatio Temporal Analysis of Earthquake Potential in the Indo-Eurasian Collision Zone: Identifying Future Seismic Hotspots Using the Earthquake Susceptibility Index, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16591, https://doi.org/10.5194/egusphere-egu25-16591, 2025.

Recent seismic hazard assessments in Mayotte have highlighted the island's significant exposure to site effects during earthquakes. These effects are closely linked to its complex geological setting, characterized by altered volcanic formations whose heterogeneous geometry leads to strong spatial variations in ground motion. In response to governmental requests, a site effects map is being developed to raise public awareness and support risk-informed urban planning.

A novel methodology for site effects mapping has recently been developed at BRGM, integrating airborne electromagnetic (AEM) data with borehole logs, geological maps, and seismic data (MASW and H/V measurements). This approach was tested on three test sites covering 12 km² of Mayotte surface, and it has demonstrated its potential in imaging the geological interfaces responsible for site effects. However, the current methodology relies on expert-driven data interpretation, making its large-scale application highly labour-intensive and costly. To overcome this limitation, partial automation of the data processing is required in order to handle larger datasets efficiently.

Machine learning techniques offer a promising solution to address this challenge. The test sites provided a unique training dataset, associating resistivity profiles derived from AEM data with the position of geological interfaces responsible for site effects within the soil column. These interface locations were determined through the integration and interpretation of all available geological and geophysical data, including MASW, H/V measurements, and borehole logs. Using this dataset, we trained various models, including Random Forest and Convolutional Neural Networks (CNN), to predict the localization of geological interfaces responsible for site effects based on AEM data.

Preliminary results indicate that the CNN model shows good performances on this task. Nevertheless, further improvements require the expansion of training datasets, underscoring the significant investment needed to generalize this approach to other regions. Future research will focus on refining predictive models and optimizing data acquisition to support large-scale implementation.

How to cite: Gracianne, C., Breuillard, H., Mato, C., Reninger, P.-A., Roullé, A., Raingeard, A., and Rusch, R.: Automated Site Effects Mapping in Mayotte Using Airborne Electromagnetic Data and Machine Learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17662, https://doi.org/10.5194/egusphere-egu25-17662, 2025.

Finding a sustainable solution to disaster risk mitigation needs to consider different aspects of the disaster’s impact along with social, economic, and physical characteristics of the region. In this regard, a desirable solution for disaster risk mitigation for a region is the one tailored to the local characteristics. These local characteristics not only help measure the different aspects of a disaster impact but also portray existing pressing issues as priorities. While the former can be modeled using risk and resilience assessment models, the latter can be measured from experts’ points of view. Ultimately, the combination of the expert’s perception on important issues and the output of risk and resilience assessment models can be used to evaluate the optimality of each disaster risk mitigation solution.

In this research, a Multi-Criteria Decision Analysis (MCDA) framework is developed to provide an evaluation of each disaster risk mitigation. The developed framework is designed to be able to run on the action-outcome results from risk and resilience assessment models and the cardinal ranking of the decision criteria, representing decision-makers’ expert opinion on the priorities in mitigating and managing disaster risk. The developed MCDA framework is very practical as it can run on action-outcome results, and these results are accessible from a large variety of risk and resilience assessment models. Furthermore, the developed MCDA framework takes into account the uncertainty in the risk and resilience assessment models. In compatibility with running on minimal available information, the MCDA’s decision model is simplified to one layer with a single layer of the decision criteria.

Additionally, as the number of competing mitigation solutions might increase rapidly in practice, the MCDA framework is developed to handle a huge number of alternatives more efficiently and with relatively limited computational resources. The MCDA framework is developed based on the CAR method of eliciting the preferences among mitigation alternatives. The final results evaluate the competing disaster risk mitigation solution based on available data (as processed by risk and resilience assessment models) and the expert’s opinion on important issues and their preferences on the important aspects of disaster impact. As such, the final results provide an estimation of the expert’s belief on the desirability of each of the disaster risk mitigation solutions.

This MCDA framework is developed as part of the Horizon Europe project MEDiate (Multi-hazard and risk-informed system for Enhanced local and regional Disaster risk management). This project is dedicated to creating a decision-support system (DSS) for disaster risk management that not only takes into account the complexities of multiple interacting natural hazards but also tailors the final solution to the characteristics, priorities, and concerns of the local communities and decision-makers. The MEDiate framework is implemented on four different testbeds (Oslo (Norway), Nice (France), Essex (UK), and Múlaþing (Iceland)), each of which has a different multi-hazard pair and different socio-economic characteristics. The deployment of the developed MCDA framework on different natural hazards and socio-economic characteristics shows its flexible practicality.

How to cite: Yeganegi, M. R., Komendantova, N., and Danielson, M.: Measuring the experts’ perception about the suitability of natural disaster risk mitigation solutions using minimal risk assessment information, a Multi-Criteria Decision Analysis approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17936, https://doi.org/10.5194/egusphere-egu25-17936, 2025.

The ultimate objective of our research is to explore the potential of Machine Learning in the dynamic creation of up-to-date exposure layers for buildings. This effort involves integrating remote sensing images, ancillary data such as national census information, and crowdsourced data collected by trained citizens. The crowdsourcing activity builds on a previous successful initiative developed within the CEDAS (building CEnsus for seismic Damage Assessment) project, which engaged high school students from North-East Italy in collecting data on buildings that were either unavailable from conventional exposure data sources or not easily retrievable via remote sensing techniques (Scaini et al., 2022).

To this end, we are developing a complex multimedia information system via web platform designed to collect, process, store, and distribute information to different knowledge users (policymakers, territorial planners, citizens) with targeted visualization strategies. The crowdsourcing initiatives are taking place in selected municipalities of Tuscany and Friuli regions (Italy), exposed to different natural hazards, such as earthquakes, tsunamis and landslides.  An online questionnaire has been created to assist the user in building data collection and minimize input errors. Simultaneously, building data, along with their photos, are stored in a structured database for research purposes.  For instance, building data and images are used as learning set to train a machine learning algorithm to identify specific features such as roof type, number of floors, and the presence of a basement. These algorithms can then be included in the online questionnaire to facilitate further data collection by automatically suggesting features associated to the buildings. A dedicated visualization tool is being developed on the web platform to showcase the effectiveness of this method in recognition of building features. We will demonstrate the data visualization tools developed on the web platform so far, highlighting the key features of the available exposure databases. The web platform is designed to provide an easy-to-use tool for communicating with various knowledge users, while also enhancing disaster awareness and preparedness, which is attained exploring and collecting data on the built environment.

This study is a contribution to the ongoing PRIN 2022 PNRR project SMILE “Statistical Machine Learning for Exposure development” (code P202247PK9, CUP B53D23029430001) within the European Union-NextGenerationEU program.

How to cite: Artese, M. T., Varini, E., Gagliardi, I., Ciocca, G., Piccoli, F., Rota, C., Del Soldato, M., Bianchini, S., Scaini, C., Peresan, A., and Brondi, P.: A web platform for crowdsourced collection, processing, and visualization of exposure data on buildings, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18225, https://doi.org/10.5194/egusphere-egu25-18225, 2025.

Seismogenic mechanism of strong earthquakes plays a fundamental role in disaster prevention. Electromagnetic methods, which are sensitive to fluid, have been widely adopted in the study on seismogenic structure and earthquake physics. Due to the increasing environmental disturbances and limited understanding on electromagnetic anomalies, electromagnetic data cannot fully show their potential values in disaster prevention. We propose an integrated work on seismogenic structure, identification of electromagnetic disturbances, and mechanism of seismo-electromagnetic anomalies. Based on the tests of synthetic and field data, we demonstrate that the multiple electromagnetic methods can reveal the feature of the multi-scaled seismogenic structure. With the developments of the new methodology based on deep learning and the seismo-electromagnetic coupling model, one can investigate the spatio-temporal characteristics of electromagnetic anomalies and their possible relationship with earthquakes. This study may contribute to the study on earthquake forecast and disaster prevention.

How to cite: Huang, Q.: Seismo-electromagnetism: observations and mechanisms, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21907, https://doi.org/10.5194/egusphere-egu25-21907, 2025.

The Alaskan mainland overlies the subducting Pacific plate and Yakutat microplate as they subduct beneath the southern margin of the North American plate. South-central Alaska features massive volcanoes of different types, including intraplate volcanoes, Aleutian arc volcanoes, and a group of densely clustered volcanoes called the Wrangell volcanic field (WVF). How the Denali volcanic gap (DVG) formed and why the Wrangell volcanoes are clustered remain vigorously debated. Investigating the crustal thermal structure can be crucial for understanding subsurface magmatic activity. Seismic attenuation, or the quality factor Q, usually provides good constraints on the viscoelastic structure and is sensitive to thermodynamic processes in the lithosphere, such as partial melting and high-temperature magmatism. Regional Lg-waves propagating in the continental crust waveguide are an ideal phase for investigating crustal attenuation. In this study, based on vertical-component waveform data recorded by 20 permanent and temporary seismic networks in Alaska, we established a high-resolution broadband crustal Lg-wave attenuation model for Alaska and nearby regions. Strong Lg attenuation is observed beneath the volcanoes in south-central Alaska, indicating thermal anomalies and possible melting in the crust. In contrast, the central Yakutat terrane and DVG are characterized by weak Lg attenuation, suggesting the existence of a cool crust that prevents hot mantle materials from invading the crust. This cool crust is likely the reason for the DVG. Quarter-toroidal crustal melting with strong attenuation is revealed around the Yakutat terrane. This curved zone of crustal melting, possibly driven by toroidal mantle flow, weakly connects the Wrangell and Buzzard Creek-Jumbo Dome magmatic chambers.

This research was supported by the National Natural Science Foundation of China (42430306 and 42404067), the China Postdoctoral Science Foundation (2024M751295) and the Postdoctoral Fellowship Program of CPSF (GZC20240638).

How to cite: Yang, G., Zhao, L.-F., Xie, X.-B., He, X., Zhang, L., and Yao, Z.-X.: Lg-wave attenuation tomography in the Alaskan mainland: Implications for the formation of volcanic gap and clustered volcanism, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-193, https://doi.org/10.5194/egusphere-egu25-193, 2025.

Understanding Lg wave attenuation provides valuable insights into crustal properties such as temperature, partial melting, and fractures, making it a crucial tool for studying crustal material flow in tectonically active regions. Central-southwestern China, encompassing the eastern Tibetan Plateau, Sichuan Basin, Qinling Orogenic Belt, and nearby areas, is a key region for such research due to its complex tectonic activity driven by the collision between the Indian and Eurasian plates. However, many questions remain about the pathways and barriers that influence the eastward migration of crustal material from the Tibetan Plateau. To tackle these challenges, we treat unresolved 3-D structural effects in Lg spectral amplitude as Gaussian-distributed modeling errors. This approach supports our SVD-based inversion method, enabling reliable estimation of crustal attenuation and thorough evaluation of model resolution and reliability. By incorporating site response corrections into the traditional two-station (TS) method and integrating it with reversed two-station (RTS) and reversed two-event (RTE) techniques, we effectively minimized the impact of source and site effects, enhancing the accuracy of attenuation tomography. Utilizing over 34,000 Lg waveforms from 257 crustal earthquakes, we constructed a high-resolution broadband Lg wave attenuation model across a frequency range of 0.05–10.0 Hz. The findings reveal complex attenuation patterns that correlate with regional tectonic and crustal features, offering fresh insights into the pathways and barriers affecting the eastward flow of material from the Tibetan Plateau.

How to cite: Hu, Y., Chen, Y., and Liu, R.: Two-station Lg wave attenuation tomography in  Central-Southwest China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-718, https://doi.org/10.5194/egusphere-egu25-718, 2025.

In recent years, 3D seismic velocity models of the southern Apennines–Calabrian Arc border region have improved the definition of crustal structures at the northern edge of the Ionian subduction zone (see, e.g., Totaro et al., JoG, 2014). In this sector, a seismic gap, supported by the absence of major earthquakes in historical catalogues (https://emidius.mi.ingv.it/CPTI15-DBMI15/), was previously hypothesized by paleoseismological evidence (Cinti et al., SRL, 2015). In the upper crust, a low-velocity anomaly of both P- and S-waves was detected between the Calabrian and southern Apennines domains, characterized by higher velocities (Totaro et al., JoG, 2014). The low velocity- anomaly may be related to fluid rising along several SW-NE-oriented faults crossing Italy from the Tyrrhenian to the Ionian coasts (Minissale et al., Earth-Sci Rev, 2019). Seismic-wave attenuation is highly sensitive to fluid storage within geological structures. When scattering attenuation and absorption, the two primary attenuation mechanisms, are separated and mapped in space and time, they can constrain fluid migrations through tectonic structures (Reiss et al., GRL, 2022; Gabrielli et al., GRL  2023). For this study, we collected 3690 waveforms from 112 earthquakes (M≥3.0, hypocentral depth≤20km) that occurred in the area between September 2004 and October 2024. We used the MuRAT3.0 suite (De Siena et al., JVGR, 2014; Napolitano et al., SR, 2024) to map proxies of scattering attenuation and absorption (peak-delay times and late-time coda attenuation) in space. The results mark the presence of high-attenuation anomalies, potentially associated with sources of geothermal energy comprised in the low-velocity anomaly described by Totaro et al. (JoG, 2014). Seismic attenuation models provide complementary information to velocity tomography on the area's complex 3D structure. The results are jointly interpreted with those coming from geophysical and geological investigations (e.g., Totaro et al., BSSA, 2015; Brozzetti et al., JStructGeol, 2017; De Ritis et al., Tectonics, 2019), fully characterizing the crustal structure of the study area.

How to cite: Adam Alddoum Adam, M., De Siena, L., Presti, D., Scolaro, S., and Totaro, C.: Seismic attenuation tomography: new insights into fluid dynamics in the Northern Calabrian region (Italy) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-871, https://doi.org/10.5194/egusphere-egu25-871, 2025.

Seismic attenuation has long been an important measurable property of rocks, valuable for eliminating path information from source models and understanding seismic hazards. Over the last 30 years, total attenuation and its two primary components—seismic scattering and absorption—have emerged as state-of-the-art tomographic attributes ranging from planets to the core, to the lithosphere, to rocks. Following the rise of seismic interferometry, stochastic seismic wavefields, once the exclusive domain of the “Heterogeneous Earth” community, have now become vital data for attenuation tomography in tectonic and volcanic settings.

Despite the importance of seismic tomography for Earth Sciences, few open-access codes combine the rigorous treatment of seismic data with novel tomographic tools in a collaborative environment. MuRAT has been a complete solution for seismic attenuation, scattering, and absorption imaging since 2014. It includes modules that provide coherent- and incoherent-wave forward models based on ray theory and radiative transfer equations that seismologists can define using simple SAC files. Fully coded in Matlab^©, it links to community-wide inversion packages and is thought of as a fully cooperative environment based on GitHub. The package has been applied to all crustal scales, from stable continental regions to hundreds-meter- active surveys in volcanic areas.

MuRAT3 (https://github.com/LucaDeSiena/MuRAT) is the first full 3D release of this code. It is specifically designed to integrate state-of-the-art forward-modelling tools from seismology to push current frequency and scale boundaries in seismic attenuation imaging. Here, I will present the last benchmark in attenuation imaging, illustrating how the code works, its success stories, its limitations, and the direction to follow to mitigate them.

How to cite: De Siena, L. and the MuRAT Team:  MuRAT3: A new generation of Multi-ResolutionAttenuation Tomography., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1937, https://doi.org/10.5194/egusphere-egu25-1937, 2025.

The eastern margin of the Tibetan Plateau is an area with the youngest uplift, strongest deformation, and frequent occurrence of large earthquakes. Seismic velocity can constrain the lithosphere's rheological strength and crustal flow distribution, allowing the deformation to be explored for the crust and upper mantle. However, seismic velocity is related to rock strength and composition and reflects the rock's elastic behavior. As a direct anelastic observation of deep temperature and rheological strength, seismic attenuation can decrease the multiplicity of geodynamic interpretation. We construct a broadband high-resolution attenuation model for the lithosphere in the eastern margin of the Tibetan Plateau by using regional seismic phases propagating in the crust and uppermost mantle. A rheological strength structure was obtained from a seismic attenuation model of the lithosphere. The dynamic origins of the distribution of soft, ductile materials can be investigated. Hence, the tectonic evolution and seismogenic environment under the lithospheric compression and collision can be detected in the eastern margin of the Tibetan Plateau. This research was supported by the National Natural Science Foundation of China (U2139206).

How to cite: Zhao, L.-F., Xie, X.-B., He, X., Li, R.-J., Chang, X., and Yao, Z.-X.: Seismic Q model and lithosphere rheology in the eastern margin of the Tibetan Plateau, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2326, https://doi.org/10.5194/egusphere-egu25-2326, 2025.

The Wave Gradiometry Method (WGM) measures spatial gradients of the wavefield within a subarray to extract phase velocity, wave propagation direction, amplitude perturbation, and radiation pattern within a subarray (Langston, 2007; Cao et al., 2020; Liang et al., 2023). The phase velocity can then be analyzed with respect to azimuths to determine azimuthal anisotropy. The Azimuth-Dependent Dispersion Curve Inversion (ADDCI, Liang et al., 2020) method is used in conjunction with the WGM to extract both 3D velocity and 3D azimuthal anisotropy. Amplitude perturbation accounts for geometrical spreading relative to propagation distance, intrinsic attenuation, and wave scattering within the medium. By eliminating the effects of scattering and geometrical spreading, the dispersion curve of attenuation is obtained, allowing for the determination of the medium's 3D attenuation.

The method is applied to the seismic waveforms collected by the ChinArray conducted in the southeastern Tibetan plateau. The arrays have an average station spacing of 35km. Our results show large variations in fast propagation directions (FPD) and magnitude of anisotropy (MOAs) with depths and blocks. The FPDs are positively correlated with plate moving directions measured by GPS. Low-velocity zones (LVZs) in the middle to lower crust are widely distributed in the Songpan Ganze Terrane and the north Chuan-Dian block. However, the LVZs are not well represented across the Lijiang-Xiaojinghe fault towards the southeastern Tibetan plateau. Low 1/Q values are found in the Sichuan basin and Emeishan Large Igneous Province at all depths. For the Tibetan plateau, low 1/Q values are found at depths shallower than 50km, while high 1/Q values are present at 50km and deeper depths. The low attenuation, combined with the FPDs being dominantly perpendicular to the movement directions of the materials, contradicts the lower crust flow model. However, the pure shearing crust shortening model, which involves the thrusting and folding of the upper crust and the lateral extrusion of blocks, may be the primary mechanism responsible for the growth of the southeastern Tibetan Plateau.

References：

Liang, C., Cao, F., Liu, Z., & Chang, Y. (2023). A review of the wave gradiometry method for seismic imaging. Earthquake Science, 36(3), 254-281. https://doi.org/10.1016/j.eqs.2023.04.002

Cao, F., C.Liang*, Yihai Yang, Lu Zhou, Zhiqiang Liu, Zhen Liu (2022). 3D velocity and anisotropy of the southeastern Tibetan plateau extracted by joint inversion of wave gradiometry, ambient noise, and receiver function, Tectonophysics, https://doi.org/10.1016/j.tecto.2022.229690

Liang, C., Liu, Z., Hua, Q., Wang, L., Jiang, N., & Wu, J. (2020). The 3D seismic azimuthal anisotropies and velocities in the eastern Tibetan Plateau extracted by an azimuth‐dependent dispersion curve inversion method. Tectonics, 39, e2019TC005747. https://doi.org/10.1029/2019TC005747

Langston C A. Wave gradiometry in two dimensions (2007). Bulletin of the Seismological Society of America, 97(2): 401-416, https://doi.org/10.1785/0120060138

How to cite: Liang, C. and Cao, F.: The 3D attenuation and anisotropy structure extracted by the Wavegradiometry method resolves the uplift mechanism of the southeastern Tibetan Plateau, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2351, https://doi.org/10.5194/egusphere-egu25-2351, 2025.

The fault damage zone is a region surrounding an earthquake fault interface where rocks are significantly fractured due to tectonic movements and historical large earthquakes on the fault. The rock fractures within the damage zone absorb and scatter seismic waves, causing amplitude decay in different frequency ranges. In this study, we use ambient noise attenuation tomography to image the fault damage zones in two tectonic settings: a transform fault in southern California and a thrust fault in western Sichuan. According to dynamic rupture models, a preferred rupture direction leads to asymmetric damage zones adjacent to the fault interface. In the Ramona array example for the San Jacinto Fault, the velocity contrast across the strike-slip fault interface leads to a preferred rupture direction towards northwest, resulting in more pronounced damage on the side with higher-velocity at depth. In the Hongkou array example for the Longmenshan Fault, significant rock damage is observed at ~ 1 km depth in the footwall side of the thrust fault interface due to upward rupture propagation from seismogenic depths. Combined with ambient noise differential adjoint tomography, a more detailed S-wave velocity model can be derived, facilitating the interpretation of tectonic structure across the fault interface and further constraining the asymmetric nature of the observed fault damage zones as predicted by dynamic rupture models.

How to cite: Liu, X., Beroza, G., Ben-Zion, Y., and Li, H.: Revealing fault damage zones using ambient noise tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3594, https://doi.org/10.5194/egusphere-egu25-3594, 2025.

      A typical triple junction in Colombia is critical for understanding the plate convergence and coupling among the South American plate and the subducting Nazca and Caribbean plates (González et al., 2023). However, locating this triple junction is challenging due to the complex geodynamic evolution and uncertainty in the plate boundaries. Magmatic arc activity has been diverse and discontinuous due to varying subduction angles, resulting in blocks with distinct rheological properties and thermal structures (Lagardère and Vargas, 2021). Seismic Lg waves are a prominent phase in high-frequency regional seismograms (e.g., Gutenberg). Compared with velocity data, seismic wave attenuation is more sensitive to deep materials' temperature and rheological strength (Boyd et al., 2004; Zhao et al., 2013). Therefore, we developed a high-resolution Lg-wave attenuation model for Colombia and surrounding areas to constrain crustal magmatic activity, linking deep dynamic processes with surface volcanism and determining potential plate boundaries at the crustal scale. The ancient and stable Guinan Shield is characterized by weak Lg attenuation. In contrast, the area encompassing Central America, western Colombia, and Ecuador features strong Lg attenuation and concentrated volcanoes, indicating thermal anomalies or partial melting in the crust. Low Q_Lg is shown near the Caldas tear along 5.5°N, speculating that a hydrothermal uplift channel caused by the Nazca plate tear may exist at depth. Based on our results and other geological and geophysical data, the thermal distribution due to the subduction of the Nazca and Caribbean plates suggests that the boundary between the subducting Nazca and Caribbean slabs beneath the South American plate may be located at 7.5°N, and that the potential location of the triple junction may be located at 7.5°N, 77°W. This research was supported by the National Natural Science Foundation of China (U2139206, 41974061, 41974054).

References

Boyd, O. S., Jones, C. H., & Sheehan, A. F. (2004). Foundering Lithosphere Imaged Beneath the Southern Sierra Nevada, California, USA. Science, 305(5684), 660–662.
Hey, R., 1977. Tectonic evolution of the Cocos-Nazca spreading center. Geol. Soc. Am. Bull. 88, 1404.
González, R., Oncken, O., Faccenna, C., Le Breton, E., Bezada, M., Mora, A., 2023. Kinematics and Convergent Tectonics of the Northwestern South American Plate During the Cenozoic. Geochem. Geophys. Geosystems 24, e2022GC010827.
Lagardère, C., Vargas, C.A., 2021. Earthquake distribution and lithospheric rheology beneath the Northwestern Andes, Colombia. Geod. Geodyn. 12, 1–10.
Kellogg, J.N., Vega, V., Stailings, T.C., Aiken, C.L.V., Kellogg, J.N., 1995. Tectonic development of Panama, Costa Rica, and the Colombian Andes: Constraints from Global Positioning System geodetic studies and gravity, in: Geological Society of America Special Papers. Geological Society of America, pp. 75–90.
Vargas, C.A., Ochoa, L.H., Caneva, A., 2019. Estimation of the thermal structure beneath the volcanic arc of the northern Andes by coda wave attenuation tomography. Front. Earth Sci. 7, 208. 
Zhao, L.-F., Xie, X.-B., He, J.-K., Tian, X., & Yao, Z.-X. (2013). Crustal flow pattern beneath the Tibetan Plateau constrained by regional Lg-wave Q tomography. Earth and Planetary Science Letters, 383, 113–122. 

How to cite: Tian, B., Liu, Z., Zhao, L.-F., Xie, X.-B., Vargas, C. A., and Yao, Z.-X.: High-resolution Lg attenuation structure of the Colombian crust and its implications for the volcanic mechanism and plate boundary, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3917, https://doi.org/10.5194/egusphere-egu25-3917, 2025.

Surface or shallow subsurface water and ice have been reported on Mars, but sustaining life requires more than just the presence of liquid water. A mechanism to preserve water over geological timescales is essential, and a deep-water reservoir could fulfill this role. However, the volatile content of Mars’ deeper mantle remains poorly constrained. Using seismic data from global tectonic marsquakes and meteorite impacts recorded by the InSight mission, we observed weak attenuation in Mars’ deep mantle (500–1500 km) relative to Earth’s. This weak attenuation likely results from lower water content, larger grain size, and/or reduced oxygen fugacity in the martian mantle. Assuming mantle mineral grain sizes on Mars are similar to those on Earth, Mars’ upper mantle appears relatively dry, with water content estimated at less than 13–24% of Earth’s. If deep water exists on Mars today, it is most likely confined to the basal mantle layer (~ 1550–1700 km) at the core-mantle boundary, potentially the only viable deep-water reservoir for the red planet.

How to cite: Li, J.: Evidence for Weak Attenuation in Mars’s Deep Mantle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4001, https://doi.org/10.5194/egusphere-egu25-4001, 2025.

This study investigates the three-dimensional seismic velocity and attenuation structures of the eastern Sino-Korean Craton through the analysis of an extensive dataset from China and South Korea. The dataset comprises 87,260 earthquakes recorded by 680 Chinese seismic stations since 2008 and 5,400 earthquakes recorded by 483 South Korean stations since 2017. The methodological framework includes 1D velocity model inversion, event relocation, and manual picking of Pg, Pn, Sg, and Sn arrivals, assisted by a machine-learning-based picking approach. A modified ray-tracing technique, optimized for tracking later Pg and Sg arrivals, is employed in double-difference velocity tomography to construct the velocity model. Attenuation factors (t*) for P-waves and S-waves are estimated via source spectral analysis. These factors, combined with the velocity model and arrival time data obtained in velocity tomography, are integrated into attenuation tomography. The dense coverage of seismic ray paths across the Yellow Sea and Bohai Sea enhances resolution, particularly in the boundary regions between mainland China and the Korean Peninsula.

The results identify a high-velocity zone extending from the Sulu Orogenic Belt northeastward through the northern and central Yellow Sea to the western Korean Peninsula, corresponding to the collision zone between the Yangtze and Sino-Korean blocks. Additionally, a low-velocity zone is observed from the crust of the South Yellow Sea to the mantle beneath Halla Volcano, suggesting post-collision extensional processes in the southern Yellow Sea Basin and a potential connection to volcanic activity. Preliminary seismic attenuation results exhibit features generally consistent with the velocity structure, providing insights into the region’s geodynamic evolution and comprehensive understanding of its tectonic and geological history.

How to cite: Liu, Y., Hong, T.-K., Lee, J., Park, S., Celis, S., Lee, J., and Kim, B.: 3D Seismic Velocity and Attenuation Structures of the eastern Sino-Korean Craton, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5292, https://doi.org/10.5194/egusphere-egu25-5292, 2025.

Anelasticity is an intrinsic property of the Earth that causes energy reduction of propagating seismic waves. Accurate 3D anelastic full waveform modeling and inversion are important for imaging high resolution velocity and attenuation structures of the Earth, which will provide crucial insights into the plate tectonics and geodynamic processes. In the presence of strong attenuation, wavefield simulation requires a strong stability preserving time discretization scheme. Otherwise, wavefield simulation could be inaccurate or unstable over time if not well treated. In this work, we choose the optimal strong stability preserving Runge Kutta (SSPRK) method for the temporal discretization and apply the fourth order MacCormack scheme for the spatial discretization. Theoretical and numerical analyses show that, compared with the traditional fourth order Runge-Kutta method, the SSPRK has a larger stability condition number and can better suppress numerical dispersion. As a result, our method can largely improve the computational efficiency during numerical modeling. Based on our forward anelastic modeling method and in the framework of the scattering integral method, we develop a new method for computing the 3D waveform sensitivity kernels that accounts for full physical-dispersion and dissipation attenuation. The Northwestern United States region is chosen as an example to verify the accuracy of the computed 3D velocity and attenuation sensitivity kernels. Finally, we construct a 3D high resolution model of velocity and attenuation structure of the crust and upper mantle in Eastern Tibet using real seismic waveform data, which provides important constraints on the processes of crustal and mantle extrusion in Eastern Tibet.

Acknowledgments

Nian Wang is supported by the National Natural Science Foundation of China (42204056) and China Postdoctoral Science Foundation (2021M690087).

How to cite: Wang, N., Shen, Y., and Yang, D.: 3D anelastic full waveform modeling and inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5308, https://doi.org/10.5194/egusphere-egu25-5308, 2025.

3D attenuation tomography of the upper mantle is important for understanding the temperature and rheological structures of the Earth’s interior as well as the related geodynamic features and mechanisms. However, robust surface-wave attenuation tomography is still challenging due to the strong trade-off between the intrinsic attenuation and the scattering due to the complex effects of 3D wave-speed and density heterogeneities in the surface-wave amplitude records. Based on tracking surface-wave travel times and amplitudes from seismic array data, here we upgraded the theory of Helmholtz tomography by accounting for the scattering effects and present a new method called Helmholtz Multi-Event Tomography to invert for the variation of surface-wave attenuation. The synthetic inversions based on 3D forward simulations in anelastic media validate the effectiveness of our new method. We then demonstrated the resulting surface-wave attenuation model can be applied to an iterative depth inversion that reveals the 3D variation of intrinsic attenuation of the upper mantle. Our study provides an innovate and promise way to generate accurate and precise attenuation models of the upper mantle from surface-wave data with low computational cost.

How to cite: Bao, X. and Wang, N.: Upper-Mantle Attenuation Tomography Using Surface Waves Recorded by Regional 2D Seismic Arrays, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5378, https://doi.org/10.5194/egusphere-egu25-5378, 2025.

In volcanic areas, seismic attenuation is greatly influenced by the presence of hot rocks and magma. This makes the spatial distribution of attenuation highly inhomogeneous and three-dimensional. The attenuation model can be expressed in terms of the attenuation coefficient α or the quality factor Q, both of which depend on the frequency of seismic waves. Hot rocks and magma affect especially S-wave propagation very strongly. In addition to attenuation, the S-wave velocity and the ratio of P-wave and S-wave velocities also change significantly.

To find the relationship between seismic S-wave attenuation and S-wave velocity, we studied the Reykjanes Peninsula region in SW Iceland, where intense volcanic activity has been ongoing since 2019. This area is monitored by the local seismic network REYKJANET, which consists of 17 stations. We have used 8602 seismic rays that link 680 earthquake foci to the Reykjanet stations. We determined the average value of the α and Q attenuation parameters as a function of frequency. We also determined the average seismic velocities vp and vs along these rays. We calculated the correlation between attenuation and seismic velocities. It turns out that there is a statistically significant dependence between these parameters.

The findings can be used to map the occurrence of magma in the upper crust in volcanic regions and thus contribute to the prediction of volcanic eruptions.

How to cite: Malek, J. and Fojtikova, L.: Correlation between seismic attenuation and S-wave velocity in the volcanic region of Reykjanes, Iceland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5672, https://doi.org/10.5194/egusphere-egu25-5672, 2025.

Sikkim Himalaya is an actively deforming part of the Himalayan orogen which formed as a result of an impactful continental-continental collision. Recent studies have characterized the region by bimodal seismicity resulting from a dynamic multi-fault system against the backdrop of spatially varying geological and geophysical features. In this study, we attempt to map the distribution of crustal inhomogeneity beneath Sikkim Himalaya using peak delay time (T_pd) analysis of the S-wave envelope. Quantitative estimations at 6 Hz central frequency shows predominant path dependence (B > 0.5) suggesting strong multiple forward scattering due to presence of inhomogeneities. Further, we produced 3-D peak delay perturbation (ΔLog(T_pd)) map to investigate the depth distribution of inhomogeneities. Spatial variation maps at six distinct depths reveal high ΔLog(T_pd) between 0-15 km in the south, southwestern Sikkim, and eastern Nepal region which elucidate the presence of a highly heterogeneous decollement surface along which the Indian plate is underthrusting beneath the Tibetan plateau. On the contrary, the shallow crust of northern Sikkim portrays negative ΔLog(T_pd) which evidences an undeformed medium, corroborated with the lack of seismicity at shallower depths. Investigation of the depth section along the southeast-northwest direction reveals a zone of highly deformed crust across MHT with prevalent micro-seismic activity. The said zone coincides with low S-wave velocity and low coda attenuation parameter which transpires to the presence of numerous inhomogeneities with the possible presence of fluid as well. We also observe deformation in the foothills of Himalaya possibly induced due to the upliftment of the Shillong plateau.  

How to cite: Singh, C., Dutta, A., and Singh, A.: Discerning crustal deformation patterns beneath Sikkim Himalaya, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6331, https://doi.org/10.5194/egusphere-egu25-6331, 2025.

Seismic attenuation tomography is a valuable geophysical method for imaging complex geological assessments at local and regional scales. It effectively detects melt, fractures, and strain conditions in rocks, and its reliability has been confirmed through laboratory experiments.

This study focuses on locating the Collalto underground gas storage (UGS) in the eastern Southern Alps of Northern Italy through seismic attenuation tomography. It represents the first multiscale attenuation imaging of the Montello thrust, which belongs to the segment of the Alpine boundary thrust covering about 100 km from Vicenza to Pordenone. The region faces medium to high seismic hazards, monitored by a local seismic network managed by the National Institute of Oceanography and Applied Geophysics in Trieste.

Using data from this network and the Murat code, we analyzed scattering, absorption, and total attenuation, interpreting results alongside geological-structural data. Our models confirm the principal attitude of the Montello thrust system, also highlighting minor faults that distribute deformation and seismic activity.

At a local scale, the absorption model highlights the methane-rich volume (Collalto UGS) as notably attenuative, indicating the method's effectiveness in detecting fluids. It also reveals deeper attenuative patches that anti-correlate with seismicity, suggesting a deeper layer of fluids likely influencing tectonic behavior.

These results open the path for further interdisciplinary research to develop comprehensive seismotectonic models integrating seismic activity with rock properties and deformation patterns.

How to cite: Talone, D., Maria Adelaide, R., Luca, D. S., Mariangela, G., Marco, S., Laura, P., Giusy, L., and Rita, D. N.: Multi-scale attenuative imaging of the Collalto UGS area and the Montello thrust system (eastern Southern Alps, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6650, https://doi.org/10.5194/egusphere-egu25-6650, 2025.

Layering or stratification, as well as volume (spatial) heterogeneity and rough boundaries between the layers (the interface roughness), are ubiquitously present in natural environments and caused by combination of many processes, for instance, by regular gravity-controlled vertical sedimentation, as well as continuous and discrete irregularity due to granular microstructure, presence of solid inclusions, gas bubbles, voids, and spatial fluctuations of their volume concentration. In this paper, we consider wave propagation, scattering, and attenuation in a stack of elastic layers with various types of irregularities (or scattering mechanisms), represented by volume heterogeneity within the layers and roughness of the interfaces in between, and given by spatial continuous and discrete variations of material parameters. A general idea of suggested here theoretical approach originates from one used in acoustics to consider underwater sound propagation for calculating the coefficient of reflection of compressional plane waves from a stack of fluid homogeneous layers with flat interfaces (modeling, for example, discretely stratified water-like sediments) using the reflection coefficients of each interface. We show that a similar, but a more general matrix approach, can be developed to include scattering mechanisms, such as interface roughness and volume heterogeneity, as well as different types of media and waves, for instance compressional and shear seismic waves (vertically and horizontally polarized) in elastic, viscoelastic, and poroelastic layers. A general full-wave solution for an arbitrary number of such layers is described in terms of transition matrix coefficients, or T-matrixes, taken from a set of simpler solutions for a plane wave transformation, reflection and scattering from, and transmission through, a single layer located between two homogeneous half-spaces and therefore isolated from interactions with other boundaries. Inside of this layer, for simplicity, scattering mechanisms are isolated as well - either a rough interface or volume heterogeneity is allowed. These simplified T-matrix solutions (found separately for each “isolated” layer and interface of the system) provide inputs to a set of integral equations which describe interactions between different layers and interfaces. Then a general solution, the scattering amplitude or T-matrix of the whole stack of layers can be obtained using an iterative procedure that starts from a simple case of two half-spaces at the basement. As an example, scattering from a heterogeneous elastic layer is considered resulting in explicit expressions for the coherent reflection loss and the incoherent scattering strength. Applications to remote sensing of underwater sediments and sea ice are discussed. [Work supported by ONR and BSF].

How to cite: Ivakin, A.: Modeling of wave propagation in multi-layered environments with rough interfaces and volume heterogeneities: A T-matrix approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7512, https://doi.org/10.5194/egusphere-egu25-7512, 2025.

In local earthquake seismology depth-dependent elastic models of P- and S-wave velocities are indispensable, e. g. to locate earthquakes. If not only travel times but also amplitudes of seismic waves are important, elastic Earth models are insufficient and visco-elastic models are required to include intrinsic absorption of seismic waves. This applies e. g. to the estimation of moment magnitudes and to physics-based ground motion modeling in seismic hazard analysis. The estimation of seismic attenuation parameters of the Earth is significantly more difficult than the estimation of velocities for two reasons: (1) Scattering attenuation as well as intrinsic absorption contribute to the attenuation of seismic waves and it is essential to separate these two effects. (2) Seismic attenuation parameters are inherently frequency dependent, whereas the frequency dependence of seismic P- and S-wave velocities can be neglected in almost all cases. Due to the lack of information, attenuation is often completely neglected in seismic wave simulation, standard values for seismic Q are used, or frequency dependence and depth dependence are ignored. To solve this issue, we develop a computer code, 'QEST - Q estimation'. The code is based on a forward modeling using radiative transfer theory in depth-dependent velocity and attenuation models and a global inversion scheme based on a genetic algorithm. Besides frequency and depth dependent intrinsic as well as scattering attenuation parameters, earthquake source spectra and frequency dependent site amplifications are also a result of the inversion with QEST. We applied the technique to seismograms of earthquakes in three regions: the Upper Rhine Graben (Germany), the Leipzig-Regensburg fault zone (Germany) and the Alaska Subduction Zone (Alaska). These regions were selected to represent exemplary areas with thick sedimentary layers, without thick sedimentary layers and the lithosphere and asthenosphere, respectively. Results show a clear depth and frequency dependence of both, scattering attenuation as well as intrinsic absorption, within the thick sediments of the graben. In contrast, the Leipzig-Regensburg fault zone exhibits a clear frequency dependence of the attenuation parameters, albeit only a smaller depth dependence, while the results of the Alaska Subduction Zone show a depth and frequency dependence that is particularly evident in the scattering attenuation.

How to cite: van Laaten, M. and Wegler, U.: Intrinsic and Scattering Attenuation of Shear Waves: Depth- and Frequency-Dependent Attenuation Insights using the QEST Code, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8259, https://doi.org/10.5194/egusphere-egu25-8259, 2025.