The effect of heterogeneity (dissimilar materials) and geometry constituting an interface is an important problem in earthquake source mechanics. These two parameters in the fault interface are responsible for complex rupture propagation and instabilities compared to the homogeneous planar interface. Here, a boundary integral spectral method (BISM) is proposed to capture the in-plane rupture propagation in the non-planar bi-material interface. The conventional traction BISM suffers from the disadvantages of hyper singularity and regularisation is needed (Sato et al., 2020; Romanet et al., 2020; Tada and Yamashita, 1997). So, we are utilising the representation equation arising from the displacement formulation devised by Kostrov (1966). It uses the elastodynamic space-time convolution of Green’s function and traction component at the interface. These displacement boundary integral equations (BIEs) are the inverse equivalent of traction BIEs. When applied to an interface between heterogeneous planar elastic half-spaces, these displacement BIEs have yielded simple and closed-form convolution kernels (Ranjith 2015; Ranjith 2022). Displacement BIEs of this kind have not been utilised to analyse fracture simulation for non-planar bi-material interfaces until now. We assume the small slope assumption (Romanet et al., 2024) in our formulation to get the required displacement BIEs. Also, we expand the displacement BIEs of a non-planar bi-material interface to the leading order to obtain the non-planarity effects. Finally, we present a general spectral boundary integral formulation for a non-planar bi-material interface independent of specific geometry and traction distribution in a small fault slope regime.

How to cite: Kumar, S. and Kunnath, R.: Boundary integral spectral formulation for in-plane rupture propagation at non-planar bi-material interfaces, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8250, https://doi.org/10.5194/egusphere-egu25-8250, 2025.

Local heterogeneities on a steadily propagating crack front create persistent disturbance along the crack front. These propagating modes are termed as crack front waves. There have been numerous investigations in the literature of the crack front wave associated with a Mode I crack (for e.g., Ramanathan and Fisher, 1997, Morrissey and Rice, 1998, Norris and Abrahams, 2007, Kolvin and Adda-Bedia, 2024). It has been shown that the Mode I crack front wave travels with a speed slightly less than the Rayleigh wave. However, similar investigation of the Mode II rupture has got minimal attention. Although, Willis (2004) demonstrated that for a Poisson solid, Mode II crack front waves do not exist for crack speeds less than 0.715, explicit results on the speed of the crack front waves, when they exist, have not been reported in the literature. The focus of the present work is on a numerical investigation using a recently developed spectral boundary integral equation method (Gupta and Ranjith, 2024) to obtain the speed of the Mode II crack front waves. Further, the perturbation formulae for Mode II crack, developed by Movchan and Willis (1995) are exploited to validate the numerical results on the crack front wave speeds.

How to cite: Mouli, Y. S. C. and Kunnath, R.: Crack front waves under Mode II rupture dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14737, https://doi.org/10.5194/egusphere-egu25-14737, 2025.

Southeastern Tibet, a segment of the eastern Himalayan Syntaxis, is a significantly deformed area resulting from multistage subduction and the ongoing collision of the Indian and Asian tectonic plates. The region has a clockwise material movement around the indenting corner of the Indian plate, evident on the surface as strike-slip faults aligned with the Himalayan Arc. Numerous scientific studies have focused on the east-west extension and tectonic history of southeastern Tibet; however, the scientific enquiries regarding the depth constraints of the crustal flow process—specifically, whether it is confined to the middle crust or extends to the lower crust beneath southeastern Tibet—remain unresolved. This study employs ambient noise tomography to  examine a 3-D high-resolution crustal velocity model for the region, which is crucial for unravelling the mechanisms that regulate crustal deformation and evolution in active orogenic systems. To do this, we examined ambient noise data from 48 seismic stations of the XE network, operational from 2003 to 2004. We obtained Rayleigh wave phase velocities ranging from 4 to 60 seconds and subsequently inverted them to develop a 3-D shear wave velocity model of the region extending to depths of 50 km. Our results reveal persistent low shear wave velocity zones at depths of 15–25 km (within the mid-crust), notably observed between the Indus Tsangpo suture and the Bangong-Nujiang Suture. We contend that the detected low-velocity zones are only linked to mid-crustal channel flow, a mechanism presumably essential for comprehending crustal deformation. Our findings provide significant constraints on the depth localisation of crustal channel flow and the interaction of tectonic forces in southern Tibet, enhancing the overall comprehension of Eastern Syntaxial tectonics.

How to cite: Mandi, A., Kumar, G., Bishoyi, N., and Tiwari, A. K.: 3-D Crustal Shear Wave Velocity Tomography Using Seismic Ambient Noise Data in Southeast Tibet, Close to Namcha Barwa Mountain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1178, https://doi.org/10.5194/egusphere-egu25-1178, 2025.

The tectonic framework of Bhutan Himalaya documents significant along-strike variability in crustal structure and deformation. To visualize this spatial and depth variability, we compile an extensive dataset of surface-wave phase velocities derived from seismic ambient noise and teleseismic earthquakes recorded by the temporary GANSSER network (2013-2014) in Bhutan, aiming to produce Rayleigh phase-velocity maps over the period range of 4 to 50 seconds. We translate the phase-velocity maps into a 3-D shear-wave velocity model stretching from the surface to a depth of 42 kilometres. The employed methodologies enable imaging of the upper to mid-crustal and lower crustal velocity anomalies with a lateral resolution of approximately 25 km. The obtained tomographic model fills a void in the prior established shear-wave velocity structure of Bhutan, encompassing depths from upper-crustal to lowermost crust. Our findings indicate notable mid-crustal to lower-crustal high phase velocity anomalies in central Bhutan (around 90.5). The presence of this significant anomaly within the mid- to lower crustal layer may indicate localized stress accumulation along the Main Himalayan Thrust (MHT) resulting from the interaction of the dipping and sub-horizontal Moho. This area might act as a stress concentration zone, resulting in increased deformation and enhanced shear-wave velocity in the crust. Minor fluctuations in velocity across latitude may result from variations in the local geometry of MHT (dip or ramp-flat transition). Localised high shear velocity in western Bhutan may indicate a zone of crustal thickening. Northeastern Bhutan exhibits modest shear velocity, possibly because of a flat Moho and the partial creeping behaviour of the MHT.

How to cite: Kumar, G. and Tiwari, A. K.: Multiscale Surface Wave Tomography of the Bhutan Himalayas using Ambient Seismic Noise and Teleseismic Earthquake Data , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1021, https://doi.org/10.5194/egusphere-egu25-1021, 2025.

In this study, we used the P-wave receiver functions (PRFs) to investigate the crustal structure of northern Morocco, located at the westernmost edge of the Mediterranean, near to the boundary between the African and Eurasian tectonic plates. This region is an integral part of the complex crustal deformation and tectonic system associated with the Alpine orogeny, characterized by concurrent compressional and extensional processes. These dynamics have led to the development of various structural and tectonic models aimed at explaining the area‘s geological evolution. The significant tectonic activity, evident in frequent seismic events, and complex lithospheric deformation, makes it an ideal location for studying crustal variations, lithospheric interactions, and mineralogical contrasts.

To achieve these objectives, we utilized high-quality seismic broadband data from the TopoIberia and Picasso seismic experiments, provided by the Scientific Institute, as well as from the broadband seismic stations operated by the National Center for Scientific and Technical Research (CNRST). The PRFs were extracted by decomposing teleseismic P-waves to isolate the effects of the local crustal structure. The dataset covers a wide range of regional stations, and the RFs provide detailed insights into crustal thickness, density and velocity contrasts, as well as deep discontinuities. Our preliminary results reveal significant variations in Moho depth, ranging from approximately 22.7 km in the eastern part of the region to 51.7 km in the western part. These variations correlate with changes in Vp/Vs and Poisson’s ratios, indicating mineralogical heterogeneity, with compositions spanning from mafic to felsic. These findings provide new constraints for tectonic models and enhance our understanding of the geodynamic processes involved, particularly the interactions between the crust and the upper mantle. This study not only improves our understanding of active tectonics and crustal composition in northern Morocco but also offers valuable insights for refining evolutionary models of the Western Mediterranean within its complex geodynamic context.

Keywords: Teleseismic event, P-wave, Receiver functions, Seismic Network, Vp/Vs ratio, Poisson ratio, Crustal structure, Mineralogical composition, Seismotectonics, Northern Morocco.

How to cite: Zakarya, H., El Moudnib, L., Badrane, S., Zeckra, M., and Lharti, S.: Continental Crustal Structure Beneath Northern Morocco Deduced from Teleseismic Receiver Function: Constraints into structure variation and compositional properties., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9078, https://doi.org/10.5194/egusphere-egu25-9078, 2025.

Ambient noise surface wave imaging has become a powerful tool for mapping subsurface velocity structures. Recent advancements in seismology, including the widespread deployment of high-density arrays such as nodal seismometers and Distributed Acoustic Sensing (DAS) systems, have facilitated the use of subarray-based methods for surface wave dispersion data extraction, such as phase-shift, F-K, and F-J methods. Alternatively, dispersion data can also be derived from two-station approaches, such as the FTAN method. However, integrating dispersion data extracted from subarrays and two-station methods remains challenging. In this study, we propose a joint inversion framework that combines these two types of surface wave dispersion data to achieve improved constraints on subsurface structures. We demonstrate its accuracy and practical applicability by conducting numerical experiments and applying the method to field data. The proposed approach introduces intrinsic spatial smoothing constraints. It effectively integrates subarray and two-station dispersion measurements, resulting in better imaging of subsurface shear-wave velocity structures compared to using either dataset alone. The versatility and potential of this method highlight its promising applications in a wide range of geophysical scenarios.

How to cite: Luo, S.: Joint inversion of surface wave dispersion data derived from subarrays and two-station methods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20181, https://doi.org/10.5194/egusphere-egu25-20181, 2025.

Coal seam floor water hazards, caused by stress changes resulting from coal mining, are a common type of mine water disaster, and their monitoring and prevention are critical for mine safety. The mine resistivity method, a geophysical exploration technique, is widely used for monitoring and detecting such water hazards due to its high sensitivity to water-bearing structures. In practical monitoring, it is necessary to rapidly and accurately invert apparent resistivity data. However, traditional linear inversion methods are prone to local optima, leading to biased results. In contrast, deep learning-based inversion methods utilize data mining to train networks, avoiding reliance on initial models and enabling fast computation of global optimal solutions.

This study constructs a multi-layer convolutional and skip-connected U-Net model to capture resistivity features at different scales. The model is trained and validated using synthetic data to evaluate its inversion accuracy and efficiency in monitoring coal seam floor water hazards. The results show that the U-Net-based inversion method can accurately identify low-resistivity anomalies associated with water hazards in the coal seam floor and quickly achieve the global optimal solution.

The method is further applied to the inversion of resistivity models with complex boundaries to simulate the impact of stress changes caused by coal mining on the formation of floor water hazards. The results demonstrate that this method is several times faster than traditional linear inversion methods, while maintaining high consistency with the actual model. Therefore, this inversion method provides an efficient new tool for monitoring coal seam floor water hazards and holds great promise for advancing technologies in mine water disaster prevention and geological exploration.

How to cite: Wang, H. and Hu, Y.: Research on mine electrical resistivity inversion method based on Deep Learning Method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5528, https://doi.org/10.5194/egusphere-egu25-5528, 2025.

Here, we disentangle a complex disturbance deposit sequence attributed to the ~M 7 1873 CE Brookings earthquake from lower Acorn Woman Lake, Oregon, USA, using sedimentological techniques, computed tomography, and micro-X-ray fluorescence. The lower portion of the sequence is derived from schist bedrock and has characteristics similar to a local landslide deposit, but is present in all cores, suggesting that it is the result of high frequency (>5 Hz) ground motions from a crustal earthquake triggered the landslide. In contrast, the upper portion of the sequence is similar to a deposit attributed to the 1700 CE Cascadia subduction earthquake (two-sigma range of 1680-1780 CE): the base has a higher concentration of light-colored, watershed-sourced silt derived from the delta front followed by a long (2-5 cm) organic tail. The soft lake sediments are more likely to amplify the sustained lower frequency accelerations (<5 Hz) of subduction earthquakes, resulting in subaquatic slope failures of the delta front. The upper portion of the 1873 CE deposit, however, has an even higher concentration of watershed-sourced silt as compared to the 1700 CE deposit, which is suspected to be the result of shaking-induced liquefaction of the lake’s large subaerial delta. The tail of both the 1873 CE and 1700 CE deposits is explained as the result of flocculation that occurred during sustained shaking. A preliminary literature search suggests that flocculation may occur during low frequency (<4-5 Hz) water motion that is sustained for an extended period of time (~minutes). The subduction interpretation of the upper portion of the 1873 CE deposit is supported by the observation of a small local tsunami offshore and the presence of a possible seismogenic turbidite attributed to the 1873 CE Brookings earthquake in southern Oregon sediment cores.

These results are important to regional seismic hazards for several reasons. Southern Cascadia crustal earthquakes, not previously recognized as a threat in southern Oregon, have the potential to cause damage to infrastructure, including the Applegate dam and buildings and other structures at Oregon Caves National Monument. They also identify a previously unrecognized recent southern Cascadia subduction earthquake. Finally, the close temporal relationship between these two types of earthquakes, not observed elsewhere in the downcore record, may be early evidence of the transition of the Walker Lane belt into a transform fault as predicted.

How to cite: Morey, A. E., Shapley, M. D., Gavin, D. G., Goldfinger, C., and Nelson, A. R.: A complex deposit sequence from a small, southern Cascadia lake suggests a previously unrecognized subduction earthquake immediately followed a crustal earthquake in 1873 CE, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11849, https://doi.org/10.5194/egusphere-egu25-11849, 2025.

How to cite: Motti, A.: Active and capable faults (FAC) and buildings in Norcia, interventions carried out and possibile technicolor and regulatory actions., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5076, https://doi.org/10.5194/egusphere-egu25-5076, 2025.

The sedimentary architectures of paleo-river channels and their associated floodplains play a crucial role in shaping alluvial aquifers. Meandering point bars, known for their high permeability, enhance groundwater recharge, while floodplains serve as natural filters, regulating both the vertical and lateral movement of groundwater. Geophysical methods, particularly Ground Penetrating Radar (GPR), facilitate high-resolution imaging of subsurface features, allowing for detailed mapping of sedimentary structures and hydrogeological characteristics. This study focuses on a paleo-meandering point bar and its adjacent floodplain deposits within a heterogeneous alluvial aquifer in North 24 Parganas, West Bengal. Four GPR survey sites were analyzed, three along the meandering channel axis and one on the adjacent floodplain, using 200 MHz and 80 MHz antennas to capture subsurface features up to a depth of 20 meters. Six radar facies (RF) and three types of radar bounding surfaces (RS) including chute channels, lateral accretion surfaces, and erosional surfaces were identified, corresponding to various sedimentary lithofacies. Towards the meandering apex, the paleochannels displayed well-defined, continuous, and horizontal subparallel RF indicative of top silty clay deposits that increase in thickness. In contrast, wavy, inclined, sub-horizontal RF indicates channel sand deposits, which exhibit a decrease in thickness toward the meander apex. The GPR profiles of the floodplain revealed sub-horizontal laminated RF, typical of finer silt and clay deposits at greater depths. The comparison of RF and RS at different scales highlights distinct depositional patterns between meandering channel deposits and floodplain sediments. This study emphasizes the importance of integrating multi-frequency GPR data to interpret sedimentary processes in fluvial-sedimentary environments, providing valuable insights into the sedimentary architecture and hydrogeological properties of the paleo-meandering system.

How to cite: Dutta, A. D., Gogoi, H., Bose, O., Bhowmik, T., Sengupta, P., and Mukherjee, A.: Characterizing Sedimentary Facies of Meandering Paleochannel and Floodplain Deposits using Multi-Frequency Ground Penetrating Radar: A Case Study from the Western Part of Bengal Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18491, https://doi.org/10.5194/egusphere-egu25-18491, 2025.