Surface wave dispersion data, encompassing both fundamental modes and higher overtones, provide powerful constraints on the thermochemical structure of the upper mantle and mantle transition zone. Fundamental modes are predominantly sensitive to shallow structures within the lithosphere and upper asthenosphere, whereas higher overtones sample progressively greater depths, offering enhanced sensitivity to the mantle transition zone and the uppermost lower mantle. The joint utilization of fundamental and overtone dispersion therefore enables improved resolution of key mantle features, including the 410 km and 660 km discontinuities, and variations in thermal and compositional structure across depth.

We carried out an extensive sensitivity analysis. The results demonstrate that both fundamental and overtone dispersion curves exhibit strong sensitivity to upper mantle structure, with particularly pronounced responses at the 660 km discontinuity, where our thermodynamic models predict sharp contrasts in seismic velocity and density. In the uppermost lower mantle, extending to depths of approximately 1500 km, fundamental modes are significantly affected only at long periods (>200 s), whereas higher overtones show substantial sensitivity across a broad period range (20–150 s) with different behaviour for Rayleigh and Love waves.

A new machine learning strategy embedded within a thermodynamically self-consistent geophysical–petrological framework allows us to efficiently link thermochemical crustal and mantle structure and surface wave dispersion data (fundamental mode and overtones) preserving physically consistent relationships among temperature, composition, seismic velocities, and density. The machine learning algorithm is incorporated into an inversion strategy to image lithospheric, asthenospheric, transition zone and uppermost lower mantle thermochemical structure accounting for the topography associated with the 410 km and 660 km mineral phase transitions in a consistent manner.

These results highlight the critical role of overtone data in complementing fundamental mode observations and demonstrate that machine learning–based imaging substantially enhances the resolution of mantle transition zone models, particularly when the uppermost lower mantle is incorporated consistently within thermochemical frameworks. The machine learning framework also facilitates the incorporation of complex, non-linear relationships between seismic data and thermochemical properties.

How to cite: Mousavi, N., Fullea, J., Lebedev, S., and Bonadio, R.: Machine Learning–Based Imaging of the Upper Mantle and Transition Zone Using Fundamental and Overtone Surface Wave Dispersion within an Integrated Geophysical–Petrological Framework, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9566, https://doi.org/10.5194/egusphere-egu26-9566, 2026.

We have successfully developed a continental-scale multiparameter full-waveform tomographic model for China and adjacent areas, employing over 500,000 unique source-receiver pairs. Our model makes possible comprehensive characterization of structural heterogeneities within the lithosphere, asthenosphere, and mantle transition zone beneath this large region.  Here, we provide detailed tectonic interpretations of observed shear-wave velocity anomalies in the lithosphere and upper mantle beneath the Tibetan Plateau that are related to the India–Asia collision, and the western Pacific subduction zone.

The tectonic evolution of the Tibetan Plateau has been influenced by continental collision and postcollisional convergence of Indian and Eurasian plates, both of which have undoubtedly imposed their imprints on the lithosphere and upper-mantle structures beneath the collision zone. However, the mode by which the Indian Plate has subducted beneath Tibet, and its driving forces, have been highly uncertain. Here, our seismic evidence reveals flat subduction of the Indian Plate beneath nearly the entire plateau at ~300 km depth, implying that the slab may have transitioned to positive/neutral buoyancy and is no longer capable of supporting steep-angle deep subduction. The horizontal distance over which the flat slab slides northward increases from west (where it collides with the Tarim lithospheric keel) to east (where it has resided approximately north of the Songpan-Ganzi Fold Belt beyond the Qiangtang Block). The Asian lithosphere is subducting beneath northeastern Tibet without colliding with the Indian slab. The low-velocity zone, with a thickness of 50 to 110 km, sandwiched between the Tibetan crust and Indian slab, is positively correlated with the high-elevation, low-relief topography of Tibet, suggesting partial melting of the uppermost mantle that has facilitated the growth and flatness of the plateau by adding buoyant material to its base. We propose that deep mantle convective currents, traced to the Réunion plume and imaged as large-scale low-velocity anomalies from the upper mantle under the Indian Plate downward toward the uppermost lower mantle under the Baikal-Mongolia Plateau, are the primary force driving the ongoing India–Asia postcollisional convergence.

The mechanism behind intracontinental rifting far from plate boundaries remains a central question in geodynamics. The Baikal Rift Zone (BRZ), situated within the Eurasian continental interior, provides a critical case to investigate whether such rifting is a passive response to far-field tectonic stresses or an active process driven by mantle upwelling. Full-waveform tomographic results reveal that westward subduction and stagnation of the Pacific slab within the mantle transition zone have generated a big mantle wedge beneath East Asia, facilitating the development of large-aspect-ratio convection cells. This system produces focused asthenospheric upwelling, seismically characterized by significant negative radial anisotropy from the vertical mantle flow directly located beneath the BRZ beyond the western edge of the flat slab. The process provides primary buoyant forces that drive domal uplift, crustal extension, and ultimately localizes strain to initiate and sustain the continental rupture. The BRZ is a modern archetype of mantle-driven lithosphere-scale continental fracturing.

How to cite: Ma, J., Song, X., Bunge, H.-P., and Fichtner, A.: Mantle Structure beneath East Asia from Seismic Full-Waveform Inversion: Implications for Tibetan Plateau Growth and Western Pacific Subduction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19234, https://doi.org/10.5194/egusphere-egu26-19234, 2026.

The subduction zone in South America spans approximately 7500 km from around 10°N to about 60°S, making it the world’s longest continuous subduction zone. In this study, we focus on the northernmost part of the central Chile flat slab subduction zone, which stands out as one of the most prominent flat slabs in South America. Within this region, the Nazca plate subducts beneath the central Chile with a direction of N78°E at a convergence rate of 6.7 ± 0.2 cm a-1 and with a direction of N 78°E. To better understand factors controlling the distribution of volcanoes, plate coupling along the subducting plate interface, and the transition from normal to flat slab subduction, we have determined high-resolution Vp, Vs and Vp/Vs models in the central Chile subduction zone where normal slab subduction transits to flat slab subduction. In the study region spanning latitudes of 22° to 31°S, volcanoes to the north of latitude 25.5°S are underlaid by intensive intermediate-depth earthquakes, but those to the south are correlated with very few. Based on velocity features, we proposed that volcanoes to the north are likely caused by partial melting of mantle wedge by incorporation of fluids released during the dehydration reactions of various hydrous minerals in the slab that are responsible for inducing intermediate-depth earthquakes, while volcanoes to the south are likely caused by sub-slab hot materials migrating upwards through the tear or gap due to the transition from normal subduction to flat subduction. Along the plate surface constructed based on our inverted velocity models and relocated earthquakes, higher plate coupling is spatially correlated with lower Vp/Vs values and fewer earthquakes, whereas lower plate coupling is correlated with relatively higher Vp/Vs values and intensive small earthquakes. These features suggest that the plate coupling state is controlled by the existence of fluids along the plate interface, with high degree of fluids reducing plate coupling and causing the creep deformation. In the region where the flat slab subduction is evident, there exist apparent high velocity anomalies above the intraslab seismicity. This indicates that some buoyant materials such as oceanic plateaus, aseismic ridges and seamount chains that featured high velocity anomalies were subducted with the slab and caused the nominal flat subduction.

How to cite: Gao, L., Chen, Z., Liu, Y., and Zhang, H.: High-resolution seismic tomography of the transition zone from normal to flat slab subduction in central Chile: implications for volcanoes, plate coupling and flat subduction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8666, https://doi.org/10.5194/egusphere-egu26-8666, 2026.

Compared to separate Vp and Vs models, Vp/Vs model is more sensitive to fuilds, melts and rock compositions. For south China, many studies have created Vp and Vs models of different resolutions, but no high-resolution Vp/Vs models are available. In this study, to better constrain tectonics and presence of fluids and melts in the south China lithosphere, especially the control of lithospheric structure on the formation of metal minerals, we adopt a modified double-difference seismic tomography method for directly inverting for Vp/Vs using body wave P and S arrival times.  We assembled earthquake arrival times recorded by the China Seismic Network (CSN) between 2008 and 2018. A total of 25,023 earthquakes were analyzed within the study region (107°–123°E, 18°–35°N), recorded by 1,998 seismic stations. After strict quality control and phase picking by the deep-learning based USTCPicker that is retrained from PhaseNet, 617,143 P-wave and 583,628 S-wave arrival times were obtained. In addition, more than 14 million P- and S-wave differential travel times were constructed from event pairs recorded at common stations, providing strong constraints for earthquake locations and velocity structures around the source region.

The inversion started from the USTClitho2.0 lithospheric model, and the inversion is parameterized on a three-dimensional grid extending from the surface to 180 km depth with grid intervals of 1° in latitude and longitude. After 14 iterations, the root-mean-square travel-time residual is reduced from 1.59 s to 0.17 s, indicating a substantial improvement in data fit. Checkerboard resolution tests demonstrate that the Vp/Vs structure is well resolved throughout most of the crust and the uppermost mantle down to ~80 km depth. At the depth of 20 km, wide-spread high Vp/Vs values are imaged in the Jiangnan orogen. Which is consistent with the reworked crust regime delineated by medium zircon Hf isotope values. At the depth of 40 km, high Vp/Vs values are mostly distributed in the southeastern Cathaysia block and along the southeast coast, corresponding to juvenile crustal domain with high zircon Hf isotope values. These correlations indicate that the reworked crust mainly occurs in the middle curst while juvenile crust happens in the lower crust. These different processes actually have some control on the formation of different metal ores. Overall, the resulting Vp/Vs model offers new insights into the distribution of fluids, lithological variations, and tectonic processes in south China.

How to cite: Zhang, G. and Zhang, H.: High-resolution Vp/Vs Tomography of the Crust and Uppermost Mantle beneath South China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10603, https://doi.org/10.5194/egusphere-egu26-10603, 2026.

This study utilizes high-resolution multi-parameter full-waveform inversion (FWI) models to investigate the structure, evolution, and destabilization mechanisms of the continental lithosphere beneath North America and Europe. The results reveal the widespread presence of vertically oriented high-velocity anomalies extending from the base of the lithosphere into the mantle transition zone beneath stable cratons. Combined with geodynamic modeling, these features are interpreted as signatures of lithospheric dripping or delamination processes driven by large-scale mantle flow associated with subducted slabs. This suggests that even long-lived, stable cratonic roots can undergo passive erosion and removal under specific mantle flow conditions.

Detailed analysis of shear-wave velocity profiles and seismic anisotropy further reveals a depth-dependent strength stratification within the lithosphere. In oceanic regions, a low-velocity, weak asthenospheric layer appears between ~70–200 km depth, whereas in cratonic regions, velocities remain significantly higher than reference models (e.g., STW105) down to ~250 km, indicating a cold and rigid lithospheric root. Anisotropy profiles show contrasting deformation behaviors: oceanic lithosphere exhibits weak anisotropy at shallow levels but stronger anisotropy at depth, reflecting active mantle flow beneath a brittle lid; in contrast, cratonic regions show relatively weak anisotropy overall but enhanced signals in the lower crust, possibly due to fossil deformation fabrics.These findings support a “sandwich-like” strength model of the lithosphere, characterized by alternating brittle and ductile layers. The presence of lower-crustal anisotropy suggests significant viscous flow, while upper mantle anisotropy indicates alignment with mantle flow patterns. Similar features are observed in North America, including strong azimuthal anisotropy in both the lower crust and around 100 km depth beneath the craton, further supporting the existence of vertically distributed, rheologically distinct domains.

Overall, this work provides important seismic constraints on the internal structure and dynamics of continental lithosphere. It demonstrates that cratonic lithosphere is not universally stable and can undergo modification through deep mantle processes. It also clarifies the nature of strength layering, deformation mechanisms, and interactions between tectonically active zones and stable lithospheric domains—key insights for understanding continental evolution and intraplate seismicity.

How to cite: Zhu, H.:  Investigating continental lithospheric dripping and deformation-constraints from multi-parameter seismic models , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2126, https://doi.org/10.5194/egusphere-egu26-2126, 2026.

Understanding how deep lithospheric processes govern the formation and distribution of critical raw materials is essential for supporting the energy transition. Carbonated mantle-derived magmas, particularly carbonatites, are the primary hosts of rare earth elements (REE) and critical metals such as Nb and Ta. Yet, the subsurface conditions that control their generation and emplacement remain unclear and are debated. Here, we present a continent-scale study linking lithospheric thermal structure, carbonated rocks, and primary mineral deposits across Africa.

We integrate state-of-the-art seismic tomography models with thermodynamic inversion (Lebedev et al. 2024; Xu et al. 2025) to construct a high-resolution (1° × 1°) temperature model of the African lithosphere and upper mantle down to 400 km depth. The map of the lithosphere–asthenosphere boundary (LAB), defined by the 1290 °C isotherm, reveals the regional-scale structure of thick cratonic roots and lithospheric thinning beneath areas of rifting and basaltic volcanism.

Comparisons with extensive compilations of mantle-derived igneous rocks reveal a systematic relationship between the lithospheric thickness and magma composition: basalt (66.1 ± 21.27 km), nephelinite and melilitite (97.1 ± 33.00 km), carbonatite (126.2 ± 43.36 km) and kimberlite (184.4 ± 44.90 km; both diamondiferous and barren). The new thermal model and the lithospheric thickness-magmatism relationship also provide insights into the distribution of primary mineral deposits. The known REE and critical metal (i.e. Nb, Ta) deposits in Africa are found to have similar LAB depths (120.9 ± 42.42, 123.6 ± 30.75 km, respectively) to that of locations with carbonatites. LAB depth of known diamond mines (192.0 ± 42.67 km) is similar to that of kimberlites in general.

The consistency between the average mantle geotherms for each rock type and the lab-measured pressure-temperature (P-T) conditions of carbonated peridotite melt generation confirms and cross-validates the models of mantle temperature and those of the origin of the magmatism (e.g., Gibson et al. 2024). Our results highlight the role of the lithospheric thermal architecture in controlling deep carbonated fluid–melt systems and associated critical raw materials, providing a geophysically grounded framework for targeting future exploration.

References

Gibson, S., McKenzie, D. and Lebedev, S., 2024. The distribution and generation of carbonatites. Geology, 52(9), 667-671.

Lebedev, S., Fullea, J., Xu, Y. and Bonadio, R., 2024. Seismic thermography. Bulletin of the Seismological Society of America, 114(3), 1227-1242.

Xu, Y., Lebedev, S. and Fullea, J., 2025. Average physical structure of cratonic lithosphere, from thermodynamic inversion of global surface-wave data. Mineralogy and Petrology, 119,  811–822.

How to cite: Sui, S., Xu, Y., Lebedev, S., Bowman, E., Fullea, J., and Gibson, S.: Thermal structure of the lithosphere across Africa and its controls on the generation of carbonated igneous rocks and primary mineral deposits, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18888, https://doi.org/10.5194/egusphere-egu26-18888, 2026.

Knowledge of planetary interior structure is essential for understanding the origin and evolution of the Solar System. Seismic full-waveform inversion (FWI) is currently the state-of-the-art method for imaging Earth's interior and has revealed mantle heterogeneities at increasingly finer scales. However, FWI solely images variations in seismic properties and, as a result, the thermal or/and chemical origin of such anomalies is poorly constrained. Mineral physics provides complementary constraints by linking seismic properties to temperature, pressure and composition through laboratory measurements. Over the past two decades, significant work has been done to integrate seismic observations with mineral physics predictions. Nevertheless, direct integration of FWI and thermodynamic calculations has not yet been achieved, limiting our ability to fully exploit the information contained in seismic waveforms to image changes in temperature and composition.

In this contribution, we present a novel framework that integrates state-of-the-art FWI techniques with mineral physics to directly invert seismic waveforms for mantle temperature and chemical composition. The forward model is based on pre-calculated tables of mantle properties, which provide the seismic properties to carry out wave propagation. The inverse problem is formulated as an optimisation problem where gradients of the objective function with respect to temperature and composition are required. For the seismic component, we employ the adjoint method. For the thermodynamic component, we developed a formalism accounting for the pressure–density coupling which is combined with the seismic part by exploiting the chain rule. This approach is tested on 2-D synthetic models containing thermal and compositional anomalies where P–SV elastic wave propagation is simulated. The optimisation problem is solved using the L-BFGS algorithm. The proposed framework successfully recovers anomalies in temperature and composition, while revealing a strong trade-off. Such non-uniqueness reflects the importance of taking into account both thermal and compositional variations and a priori information about them. The proposed framework enables the integration of diverse geophysical datasets as well as the incorporation of additional information on the potential origin of certain mantle anomalies based on petrological constraints, which are crucial to tackle the non-uniqueness of the inverse problem.

How to cite: Zunino, A., Munch, F. D., Ghirotto, A., Aloisi, G., and Fichtner, A.: Towards thermo-chemical full-waveform inversion: integrating mineral physics and seismology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7323, https://doi.org/10.5194/egusphere-egu26-7323, 2026.

We derive a regional 1-D attenuation (Q–1) model for the Dead Sea fault using moderate earthquakes (3.5 ≤ MW ≤ 4.5). QP and QS are estimated through spectral modeling of stations within 300 km, with corner frequencies independently constrained by the empirical Green’s function method to reduce parameter trade-offs. Q values are averaged across channels to examine distance dependence. We find a linear increase in Q with distance for both P and S waves, flattening beyond ~150 km, consistent with a crust–mantle phase transition. Deviations from this trend highlight low-Q zones along the plate boundary, associated with sedimentary basins. These results emphasize the crustal heterogeneity of the region and provide a foundation for future 3-D attenuation models.

How to cite: Wetzler, N. and J. Chaves, E.: Determination of regional attenuation using moderate earthquakes at the Dead Sea fault system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12393, https://doi.org/10.5194/egusphere-egu26-12393, 2026.

How to cite: Pedreira, D., Olivar-Castaño, A., Pulgar, J. A., Cabezas, S., Díaz-González, A., Manuel González-Cortina, J., and Gallastegui, J.: New data on the crustal structure of the Cantabrian Mountains in the western continuation of the Pyrenees: receiver function results from the CANALAB project, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22407, https://doi.org/10.5194/egusphere-egu26-22407, 2026.

NE Iberia marks the transition between compressive tectonics in the Pyrenees and the extensional regime along the Gulf of Lion and the Valencia Trough, and includes the Catalan Volcanic Zone, an alkaline volcanic zone field, which represents the southern branch of the European Cenozoic Rift System (ECRIS). While the large-scale geometry of the crust and the general trend of the anisotropy pattern are known from previous studies, new data acquired in the framework of the EPYSIM project allow for a more detailed characterization of these features.

The transition from the central Pyrenees to the Valencia Trough and the Gulf of Lion is defined by an abrupt crustal thinning. New data from two 60 km long profiles, one oriented NE-SW, parallel to the coastline, and the other oriented orthogonally, has been used to construct detailed pseudo-migrated receiver function sections. The coast-orthogonal profile, broadly oriented NW-SE, shows a decrease in crustal thickness from 35 km northwest of the Garrotxa Volcanic Field to 28 km beneath the La Selva Basin, reaching approximately 25 km near the coastline. The coast-parallel profile shows crustal thickness around 30 km in the west, thinning to approximately 25 km to the east, near the Gulf of Roses. Additionally, data acquired by a network of 60 stations covering NE Iberia with interstation distances of about 8 km has been analyzed used using the H-K method, providing independent constrains on crustal geometry.

SKS splitting along these profiles confirms the general E-W orientation of the fast polarization direction (FPD). Projection of results to the piercing point at 200 km depth suggests subtle difference between the Catalan Volcanic Zone, where FPDs are close to the E-W direction, and the south-western area, where they exhibit slightly higher azimuths. This difference may reflect the extension beneath the Valencia Though. Recent estimates of azimuthal anisotropy at the crust and uppermost mantle from surface wave tomography and previous Pn tomography results derived indicate strong variations in FPD orientation at different depths beneath NE Iberia, suggesting that each dataset is sensitive to anisotropy of different origins (e.g., cracks, frozen-in fabrics, asthenospheric flow)

The updated crustal geometry derived from receiver functions analysis and the regional seismic anisotropy pattern will be compared with recent geological models that integrate petrological and geochemical results of volcanic rocks, along with geophysical, structural and geochronological data. These models suggest that volcanism in the Catalan Volcanic Zone is controlled by crustal thinning and development of the NW-SE oriented Transverse Fault System.

This work has been supported by the EPYSIM Project, funded by the Spanish Ministry of Science and Innovation (Ref.: PID2022-136981NB-I00).

How to cite: Diaz, J., Parera-Portell, J.-A., Cruset, D., Jorde, S., and Vergés, J.: Crustal geometry and anisotropic signature beneath NE Iberia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6461, https://doi.org/10.5194/egusphere-egu26-6461, 2026.

Crustal anisotropy beneath a dense broadband seismic array across the Longmenshan fault belt is measured based on P-to-S converted phases from the Moho and an intra-crustal interface. The crustal thickness and the average Vp/Vs values are also estimated by a new H-k-c method. The crustal anisotropy in Aba sub-block mainly comes from the middle-lower crust and the NW-SE fast polarization directions (FPDs) may reflect the direction of the crustal flow. A sharp variation of FPDs is observed in the vicinity of the Longriba faults, combined with the Vp/Vs values and other geological and geophysical observations, we suggest the Longriba faults may block the eastward flow of crustal materials. East of the Longriba faults, the consistence between the FPDs and the direction of the maximum horizontal compression, and low Vp/Vs values indicated that the crustal thickening may be the dominant deformation mechanism in the Longmenshan sub-block. The crustal anisotropy in the Longmenshan fault belt is mainly manifested as fault-parallel FPDs, probably related to fluid-filled fractures in this area. The Sichuan basin is weakly anisotropic and the NE-SW FPDs may reflect the tectonic strike. Combined with previous observations, our results suggest that the crustal flow and crustal thickening are co-exist in the crustal deformation in eastern Tibet.

How to cite: Tan, P., Chen, Y., and Nie, S.: Crustal deformation in eastern margin of Tibetan Plateau from a dense linear seismic array, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2350, https://doi.org/10.5194/egusphere-egu26-2350, 2026.

The Youjiang Basin at the junction of Yunnan–Guizhou–Guangxi in South China hosts a major Carlin-type gold province, yet the deep crustal architecture and magmatic system that control fluid pathways remain debated. We analyze continuous ambient seismic noise recorded by 114 broadband stations of a dense temporary array from May 2011 to January 2012 (~260 effective days). Interstation Green’s functions are retrieved, Rayleigh-wave dispersion is measured, and a three-dimensional shear-wave velocity model from 0 to ~50 km depth is obtained via direct inversion of surface-wave dispersion. The model shows strong lateral heterogeneity: a high-velocity domain in the northwest aligns with carbonate-platform facies, whereas a broad low-velocity domain in the southeast matches clastic basin facies. Between 104° and 105°E, a gently dipping low-velocity band corresponds to slope-facies strata and likely represents a mechanically weak, fluid-favorable unit. Several SW–NE and NW–SE trending, steeply dipping low-velocity corridors delineate major boundary and intra-basin fault systems, consistent with deep-reaching conduits for magma and hydrothermal fluids. At depth, a Moho-adjacent high-velocity anomaly at ~35–40 km suggests mafic underplating, while lens-shaped high-velocity bodies at ~15–20 km beneath the main ore field indicate solidified felsic intrusions and magma chambers. Together these features define a two-tier magmatic system linked by faults, providing a physically consistent deep-to-shallow metallogenic framework in which deep heat and magmatic inputs drive fluid generation, faults focus upward transport, and favorable stratigraphic units promote fluid–rock interaction and gold precipitation. This crustal image links basin segmentation, fault-controlled connectivity, and multi-level magmatism, offering new geophysical constraints on tectono-magmatic processes and associated mineralization in the Youjiang Basin.

How to cite: Jialiang, J.: Ambient-noise tomography links crustal faults and magma chambers beneath the Youjiang Basin: a metallogenic framework for Carlin-type gold, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2347, https://doi.org/10.5194/egusphere-egu26-2347, 2026.

Ambient noise cross-correlations enable the extraction of multimodal surface waves, yet resolving their complex dispersion characteristics is essential for robust subsurface imaging. Using dense array data from the North China Plain, we resolve multicomponent multimodal Rayleigh and Love wave dispersion with unprecedented detail. The results reveal several distinct dispersion characteristics, including stronger excitation of higher modes on horizontal components, opposite polarity of the first higher mode on the ZR-RZ component, and a switching of the dominant Rayleigh mode between vertical and horizontal components at low frequencies. We also identify and confirm mode kissing between fundamental and first higher Rayleigh modes and guided P modes arising from normal mode and leaky mode coupling. These dispersion characteristics are primarily controlled by the shallow low-velocity sediments, which govern frequency-dependent mode excitation, polarity, and energy partitioning. Integrating these multicomponent multimodal observations improves the physical interpretability and reliability of subsurface imaging. 

How to cite: Yu, C. and Zhang, G.: Ambient-noise multicomponent multimodal dispersion characteristics in thick sedimentary basins, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2983, https://doi.org/10.5194/egusphere-egu26-2983, 2026.

We present a high-resolution image of the crust and lithospheric mantle beneath the Kashmir basin and surrounding Panjal traps of northern India that form the largest contiguous outcropping of the Permian (289 Ma) Himalayan volcanic groups, to a depth of 160 km, utilizing data from 22 seismological stations deployed in 3 phases between 2014 and 2024. The velocity structure is computed through joint inversion of receiver functions and Rayleigh wave group velocity dispersion data (period of 5-100s), alongside structural imaging using common conversion point (CCP) migration. The velocity image reveals several important crustal features: (i) Compared to global continent crust, the Kashmir-Panjal crust is more felsic with velocity of ~3.5 km/s to a depth of 40 km (ii) An anomalous feature of this region is a 25-30 km thick underplated high velocity layer (Vs>4.0 km/s) at the base of the crust. (iii) Moho depth is ~75 km in the southwestern part of the Kashmir valley, whereas it is ~65 km in the northeastern part. (iv) The Main Himalayan Thrust (MHT) is identified as a flat and low shear wave velocity (Vs ~3.1 and 3.4 km/s) structure located above crystalline Indian crust (Vs of ~3.6 km/s). In the shallow mantle, we observe a 30-40 km thick west dipping low velocity (4.3-4.4 km/s) channel at a depth of 90-120 km. This is the first report of such a low velocity channel in the western Himalaya. It’s genesis requires further investigation, currently in progress.

How to cite: Saha, G., Parvez, I. A., Kumar, V., Rai, S. S., and Gaur, V. K.: Lithospheric structure of the Kashmir basin and Panjal traps, western Himalaya: Insights from Seismic Imaging, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4201, https://doi.org/10.5194/egusphere-egu26-4201, 2026.

Imaging the anisotropic shear-velocity structure of the lithosphere-asthenosphere system is key to understanding the Earth’s internal dynamics and the mechanics of plate tectonics, whose nature and working mechanism remain debated across the geosciences. Global tomography robustly resolves long-wavelength shear-velocity structure, but the uneven distribution of earthquake sources and receivers reduces the capacity of current methods to resolve short-wavelength and shallow structure. Ambient noise offers an independent dataset that provides complementary path coverage for investigating Earth’s structure and enhances our understanding of the physical nature of the lithosphere-asthenosphere system by improving resolution in regions that remain insufficiently resolved.

In this work, we use the Earth’s hum at 30-270 s periods to produce a global probabilistic model of the shear-wave velocity of the upper mantle and its uncertainties. We extract empirical Green’s functions from 1989-2004 continuous records at 389 broadband stations using the wavelet-phase cross-correlation and time-scale phase-weighted stacking. Then, frequency-time analysis and the spectral method yield 55615 R1 and 23467 R2 group-velocity, and 56539 R1 phase-velocity Rayleigh-wave dispersion curves, primarily on new paths. Finally, we solve the inversion problem using the two-step method, employing probabilistic continuous inverse theory to construct phase- and group-velocity maps in the regionalization step, and transdimensional inference for the depth inversion.

The phase and group velocity maps we obtain compare well with velocity maps derived from earthquakes. Similar velocity anomalies are observed at all periods, including the cratons, the African rift system and the Pacific belt, and the mid-ocean ridges. Given the strong complementarity between the ambient-noise and earthquake datasets, and the fact that the model derived from ambient noise alone is already accurate, a joint inversion has the potential to enhance the imaging of the lithosphere-asthenosphere system in global mantle models.

How to cite: Ventosa, S. and Bodin, T.: A global Bayesian seismic shear-wave velocity model of the upper-mantle using seismic hum, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9674, https://doi.org/10.5194/egusphere-egu26-9674, 2026.

Reliable geological characterization is critical for the safety assessment and planned waste retrieval at the Asse II nuclear repository in Germany. Conventional seismic imaging provides structural information but lacks the resolution needed to resolve detailed variations in velocity. In this study, we apply 3D acoustic full waveform inversion (FWI) to a high-fold, wide-azimuth land seismic dataset acquired over the Asse II site. To reduce nonlinearity and cycle skipping, we focus on an early-arrival FWI strategy targeting refracted and diving waves, combined with careful data conditioning and a multiscale frequency inversion workflow. The inversion uses a First-arrival time tomography (FATT) P-wave velocity model as the initial model and inverts frequencies from 8 to 20 Hz. Gradient preconditioning, source wavelet estimation, offset muting and windowing are applied to stabilize convergence. The resulting 3D velocity model provides improved resolution and is consistent with the initial the established geological horizons of the area. These results provide a promising velocity model for our future investigations such as elastic FWI and support mine stability analysis, and long-term safety assessment of the Asse II repository.

How to cite: Rezaei, A., Houpt, L., and Bohlen, T.: Early-Arrival 3D Acoustic Full Waveform Inversion at the Asse II Repository: A Case Study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13694, https://doi.org/10.5194/egusphere-egu26-13694, 2026.

The Offshore Godavari Basin, located along the Eastern Continental Margin of India (ECMI)), is a major pericratonic rift basin and an important location for hydrocarbon industries. In this study, we analyse a 50-km-long 2D seismic profile, acquired by Oil and Natural Gas Corporation Limited (ONGC), from the KG-DWN-98/2 block within Godavari Basin. The profile traverses the continental shelf-slope transition, where seafloor water depth increases from ~100 m on the shelf to ~1.3 km in the slope region. The dataset comprises 861 air-gun shots, with each shot gather containing 955 traces. The shot spacing is 50 m, while the hydrophone group interval is 6.25 m, resulting in a CDP spacing of 3.125 m. We have processed the seismic data using a conventional workflow that included geometry merging, band-pass filtering, WEMA, CDP sorting, velocity analysis, NMO correction, Radon filtering, stacking, and post-stack time migration. Preliminary interpretation of the processed seismic section reveals a seafloor characterized by southward dipping uneven topography. A thick pile of sedimentary deposits overlie the southward dipping continental basement in which landward verging growth faults in the shelf region between CDPs 7000-15000 and large scale seaward verging thrusts in the slope region are developed from southern end of the profile to CDP-5000. A folded deposit composed of clay observed at TWT 5-6s of the slope region. The migrated section further illustrates shale diapirism wherein over-pressured shale rises through denser sedimentary deposits and uplifts the overlying formations, creating unique styled fault-bounded highs and anticlines. The process might have involved reactivation of the extensional faults at the basement, causing uplift of previously subsiding area. The study will finally sheds light upon the sea-level fluctuation and its relation with the sediment dynamics of the Godavari river and associated neotectonism.

How to cite: Papney, S., Ghosal, D., and Nathaniel, D. M.: Investigating Offshore Godavari Basin Morphotectonics using high-resolution seismic data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20982, https://doi.org/10.5194/egusphere-egu26-20982, 2026.

Controlled Source Seismic (CSS) data are key to understanding the structure and composition of the lithosphere at different scales. They are highly valuable both in their own right and as input to multidisciplinary studies and Earth system modelling. The challenge for scientists is to find existing data, assess their relevance for a particular purpose, and eventually get access and permission to reuse selected data sets.

The European research infrastructure for solid Earth sciences EPOS (European Plate Observing System) was designed to solve such problems. It is a multidisciplinary, distributed research infrastructure that facilitates the integrated use of data, data products, and facilities from the solid Earth science community. FAIR principles are put into practice, enabling access to data and products from hundreds of scientific data services across Europe. Data services provided by EPOS are defined in a bottom-up approach by the experts in the respective thematic communities. However, CSS data are not available through EPOS. Primarily, because EPOS was lacking the support of a dedicated CSS community.

At EGU24, a community building effort started with the aim of bringing CCS data to EPOS. Early on, the informal community defined two targets: Firstly, to develop a data model for data set discovery, as no existing standards or common practices for describing CSS data sets could be identified. Secondly, to develop and provide best practices for the publication of academic data sets. As of early 2026, a data service that works with an EPOS test-environment was implemented successfully, and the data model is being tested. Community and technical integration with EPOS will be discussed during SPM58 at EGU26.

This presentation focuses on the discovery data model (“scientific metadata”). Discovery data connect the user from a single entry point (the EPOS portal) with the data, which are distributed, i.e. stored at various locations. To make this practically feasible, the following requirements were established: i) sufficient detail to describe complex datasets, ii) a limited set of obligatory attributes, to avoid conflicts that could shut out potential data providers, and iii) the use of controlled vocabularies wherever possible. Core (obligatory) attributes state that a data set exists and includes information on survey and campaign names, year, geolocation, content, access via URI and license. These are supplemented by (optional) descriptive and technical attributes, which are meant to provide scientists with sufficient information for the selection of relevant data sets. The former include information on organisations, purpose, source and sensor types, scale, processing and description. The latter provide details like spacings, offsets, number of points and channels.

A successful data discovery is meant to conclude with accessing the selected data via the URI provided in the core attribute. These URIs resolve to a (human and machine-readable) landing page at the data repository that contains details on the mode of access, citation and other information that is regarded as relevant by the data provider.

The CSS community invites interested colleagues to participate and contribute (please contact the first author).

How to cite: Lorenz, H. and the EPOS CSS community: EPOS CSS - Facilitating the discovery and reuse of Controlled Source Seismic data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5358, https://doi.org/10.5194/egusphere-egu26-5358, 2026.

The Zagros–Himalaya collision zone is among the most active and structurally complex convergent boundaries on Earth, making it a critical region for investigating plate tectonics, mountain-building processes, and seismic hazards. Despite substantial research on segments of this belt, significant gaps persist, particularly in understudied areas such as the Makran subduction zone and Central Asian microcontinents. In this study, we developed a high-resolution 3D shear-wave velocity (V_s) model to investigate the lithospheric structure of the Makran subduction zone and Central Asia. We analyzed fundamental-mode Rayleigh wave group velocity dispersion curves from regional earthquakes within the period range of 6.5–80 s. Variations in velocity gradients across the V_s model enabled the estimation of spatial changes in key lithospheric discontinuities, including the sediment–basement interface and the Moho depth. The thickest sedimentary layer (15–20 km) occurs in the Makran Accretionary Wedge. Additional thick basins (>10 km) include the Jazmurian and Mashkel Depressions, the Amu Darya-Tajik Basin, and the southwestern Helmand Block. The thinnest continental crust (35–40 km) occurs beneath the Lut and Helmand Blocks that are surrounded by thicker, highly deformed crust (50–65 km) in the Zagros Collisional Belt and the Hindu Kush Mountains. The oceanic Moho depth beneath the Arabian Plate, within the Makran Accretionary Wedge, ranges from 20 to 30 km. The subduction angle of the Arabian slab steepens beneath the southern margins of the Jazmurian and Mashkel Depressions, reaching depths greater than 60 km beneath the Bazman–Sultan Volcanic Arc. Dominant low-V_s anomalies in the Hindu Kush and Central Asian regions indicate uppermost mantle deformation resulting from the ongoing convergence between the Arabian, Indian, and Eurasian Plates.

How to cite: Ahmadzadeh Irandoust, M., Yu, C., Sobouti, F., and Priestley, K.: Lithospheric Structure of the Makran Subduction Zone and Central Asian Microcontinents Based on Surface Wave Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10056, https://doi.org/10.5194/egusphere-egu26-10056, 2026.

How oceanic plates cool and thicken with age remains a subject to debate, with several thermal models supported by apparently contradictory data. Combining a novel imaging technique that balances resolution and uncertainty with finite-frequency surface-wave measurements (Latallerie et al., Seismica, 2025), we build tomographic model SS3DPacific to revisit the cooling style of the oceanic lithosphere beneath the Pacific ocean (Latallerie et al., GRL, 2026). Resolution analysis indicates a strong vertical smearing that biases estimates of the apparent lithospheric thickness, limiting the ability to discriminate between the half space and plate cooling models. Laterally, a pattern of anomalous bands in seismic velocity aligned with fracture zones points to additional lateral complexities in the lithosphere, complicating simple age-trend analyses.

How to cite: Koelemeijer, P., Latallerie, F., Walker, A., Maggi, A., Lambotte, S., and Zaroli, C.: New insights into the cooling of the oceanic lithosphere from surface-wave tomographic inferences, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7242, https://doi.org/10.5194/egusphere-egu26-7242, 2026.

Surface wave imaging based on ambient noise cross-correlation technology is one of the most significant advancements in geophysical imaging over the past two decades, widely applied to shear wave velocity structure imaging from near-surface to lithospheric scales. In recent years, with breakthroughs in array-based surface wave techniques, ambient noise surface wave imaging has entered a new phase of studying overtone surface waves. The inclusion of overtone surface waves effectively enhances the ability of surface wave dispersion curve inversion to constrain subsurface structures, particularly low-velocity layers in the crust and lithosphere.

However, in three-dimensional imaging, array methods typically treat the velocity structure inverted from an array as a spatially averaged result, assigning it to the centroid of the array for interpolation. This approach introduces spatial averaging effects, which, to some extent, affect the accuracy of phase velocity and horizontal spatial resolution, while the size and shape of sub-arrays may also influence the results.

To address these issues, we recently developed a framework involving multiple random Voronoi polygon partitioning and spatial phase velocity re-inversion (SPFI). By generating a large number of observations of varying sizes and shapes using random methods, and establishing mathematical relationships between horizontal spatial distributions of phase velocity and observed dispersion curves, we successfully resolved the issues of adaptive partitioning in array-based surface wave methods and improved estimation of horizontal resolution. This report primarily introduces the aforementioned new array-based multi-mode surface wave method and its recent progress in imaging continental lithospheric structures.

How to cite: Li, Z., Chen, J., Shi, C., and Chen, X.: Advances in Array-based Overtone Surface Wave Imaging and Its Application to Lithospheric Structure Imaging, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22737, https://doi.org/10.5194/egusphere-egu26-22737, 2026.

Multimode surface-wave dispersion provides critical constraints on crustal and lithospheric velocity structures, with higher modes offering complementary sensitivity to different depth ranges compared to the fundamental mode. However, extracting reliable multimode information from seismic event records remains challenging under realistic observation conditions. Unlike ambient noise wavefields, seismic-event wavefields are strongly influenced by source radiation patterns, wavefront curvature, and complex angular structures, particularly when events occur within or near dense seismic arrays. Consequently, most existing multimode surface-wave methods rely on far-field plane-wave assumptions or azimuthal selection strategies, which limit their applicability for complex source–receiver geometries.

In this study, we propose a unified framework for extracting multimode surface-wave dispersion from seismic records by explicitly accounting for source radiation effects in the wavefield representation. Starting from a polar-coordinate description of the surface-wave displacement field, the wavefield is decomposed into angular components associated with different azimuthal orders, allowing isotropic and anisotropic contributions introduced by double-couple sources to be separated. This angular decomposition enables different Bessel-function components (e.g., zeroth- and higher-order terms) to be treated independently, thereby mitigating modal interference that commonly affects conventional frequency–Bessel approaches.

Furthermore, by exploiting the theoretical equivalence between the polar-coordinate formulation and a two-dimensional spatial Fourier transform, the proposed framework reformulates the conventional Bessel-integral representation into a unified and computationally efficient 2D Fourier-domain implementation. This transformation substantially simplifies the dispersion-spectrum calculation while preserving physical consistency, enabling robust multimode dispersion extraction under arbitrary array geometries without imposing far-field assumptions or azimuthal filtering.

Synthetic experiments and applications to dense-array seismic data demonstrate that the proposed method reliably retrieves both fundamental and higher-mode dispersion over a broad frequency range. The resulting multimode constraints provide improved resolution for seismic imaging of crustal and lithospheric structures, highlighting the potential of the framework for high-resolution studies using modern dense-array deployments.

How to cite: Han, W. and Laiyu, L.: A unified framework for extracting multimode surface-wave dispersion from seismic records accounting for source radiation patterns, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2399, https://doi.org/10.5194/egusphere-egu26-2399, 2026.

Surface-wave azimuthal anisotropy provides important constraints on crustal deformation and stress fields. However, its imaging in direct surface-wave tomography remains challenging due to strong parameter trade-offs and the need for carefully tuned smoothing and damping in conventional grid-based inversions, particularly when isotropic velocity and anisotropic parameters are inverted simultaneously (e.g., Fang et al., 2015; Liu et al., 2019).

In this study, we extend the Poisson-Voronoi parameterization of Fang et al. (2020) to direct surface-wave azimuthal anisotropy tomography using a data-adaptive ensemble framework. Model parameters are represented on multiple Poisson-Voronoi realizations that are stochastically generated and subsequently refined according to raypath density, allowing the parameterization to adapt to spatial variations in data coverage. For each realization, the inversion is performed in a reduced parameter space, and individual solutions are combined through a misfit-based ensemble strategy in which poorly constrained realizations are down-weighted. This ensemble-based formulation requires only a limited number of control parameters, minimizes subjective regularization choices, and enables straightforward assessment of model uncertainty and stability across realizations, making the approach largely automated and accessible for users without extensive experience in inverse theory.

We apply the method to a dense seismic array deployed in southwestern China using Rayleigh-wave phase velocity dispersion measurements extracted from ambient noise interferometry. The resulting azimuthal anisotropy model reveals coherent and geologically interpretable patterns associated with major tectonic structures, demonstrating the effectiveness of data-adaptive Poisson-Voronoi ensemble inversion for imaging surface-wave azimuthal anisotropy in dense array settings.

References

Fang, H., Yao, H., Zhang, H., Huang, Y., & van der Hilst, R. (2015). Direct inversion of surface wave dispersion for three‐dimensional shallow crustal structure based on ray tracing: methodology and application. Geophysical Journal International, 201(3), 1251–1263. https://doi.org/10.1093/gji/ggv080

Fang, H. et al. (2020) Parsimonious Seismic Tomography with Poisson Voronoi Projections: Methodology and Validation, Seismological Research Letters, 91(1), pp. 343–355. Available at: https://doi.org/10.1785/0220190141.

Liu, C., Yao, H., Yang, H. Y., Shen, W., Fang, H., Hu, S., & Qiao, L. (2019). Direct Inversion for Three‐Dimensional Shear Wave Speed Azimuthal Anisotropy Based on Surface Wave Ray Tracing: Methodology and Application to Yunnan, Southwest China. Journal of Geophysical Research: Solid Earth, 124(11), 1139411413.

How to cite: Liu, X., Yao, H., Fang, H., and Liu, Y.: Direct Surface-Wave Tomography of Azimuthal Anisotropy Using a Data-Adaptive Ensemble Approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7800, https://doi.org/10.5194/egusphere-egu26-7800, 2026.

The structure of the lithosphere-asthenosphere system beneath the Indian Ocean remains one of the most enigmatic and relatively understudied among the world's ocean basins, mainly because of its complex geological settings and diverse seismotectonic features. Therefore, the present study aims to delineate the shear‐wave velocity structure of the Lithosphere–Asthenosphere System beneath the Indian Ocean using surface wave tomography. For this analysis, we considered waveforms from events sampling the study region with a magnitude ≥ 5.0, recorded at 856 selected seismic stations operated under 44 seismic networks, with epicentral distances between 20° and 100°. To ensure high data quality, only waveforms with a signal-to-noise ratio (SNR) ≥ 2.5 were retained. Dispersion analysis was then performed on the pre-processed data to manually pick the dispersion curves. This procedure resulted in ~32,000 Rayleigh-wave dispersion curves, with periods ranging from 18 to 180 s. These high-quality dispersion measurements were used to derive regionalized Rayleigh‐wave group velocities, which were subsequently inverted using a trans-dimensional approach to obtain the shear wave velocities. The resulting 3D shear velocity model, INDOV_SV24, provides an improved lateral resolution of 200 to 600 km down to depths of 300 km, significantly enhancing the resolution compared with previous studies. This model shows excellent correlation with surface tectonics and accurately delineates significant features such as mid-oceanic ridges and subduction zones. Intriguingly, our model and tectonic regionalization results identify a distinct low-velocity anomaly oriented in the SW-NE direction with a localized strong low-velocity anomaly/reservoir in the north-eastern side within the Indo-Australian Diffusion Plate Boundary (IADPB) zone. This observation aligns with seafloor age data, indicating a relatively younger age (~40 Ma) in this region compared to its surrounding areas. The strong low-velocity anomaly/reservoir (DPB_LVZ) within the IADPB zone on the western side of the Sunda subduction zone (SSZ) may result from the accumulation of asthenosphere material from the ridges near the sub-slab side of the subducting Sunda plate, along with upwellings facilitated from deeper sources. These seismological findings strongly suggest ongoing active dynamics in the Indo-Australian Diffusion Plate Boundary Zone.

How to cite: Sundaran, S., Bommoju, P. R., and Maurya, S.: INDOVSV24: A 3D shear wave velocity model of the Lithosphere-Asthenosphere system beneath the Indian Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-293, https://doi.org/10.5194/egusphere-egu26-293, 2026.

How to cite: Nagesh, C., Abreu, R., and S. Arnaiz-Rodríguez, M.: The Virtual Receiver Approach: Probing the Internal Structure of Large Low-Seismic-Velocity Provinces, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13543, https://doi.org/10.5194/egusphere-egu26-13543, 2026.

The advanced imaging technique reverse time migration (RTM) requires solving the partial differential wave equation, for which an analytical solution is infeasible and numerical methods are necessary. A significant challenge in numerical methods arises from inaccuracies in derivatives approximation, making the wave's velocity frequency-dependent and causing numerical dispersion. It is an unphysical artifact that degrades modeling and imaging, particularly at higher frequencies and over time. Avoiding numerical dispersion at high frequencies requires finer spatial grids, which substantially increase computational costs to achieve high-resolution imaging results.
The modified nearly analytical discretization (MNAD) method reduces numerical dispersion by incorporating additional analytical relations through solving both the wavefield and its spatial gradient fields numerically, employing them in higher-order derivative approximations, and improving spatial derivative estimation via energy conservation optimization. 
MNAD is introduced for RTM in large-scale studies, where leveraging compact stencils and coarser spatial and temporal grids enables high-resolution imaging with substantially lower computational and memory costs compared to conventional finite difference (FD) methods. Furthermore, adjoint-state imaging is enhanced with a novel data boundary condition interpolation using MNAD gradient fields, mitigating aliasing effects in recovered images from data recorded at half the Nyquist rate. The proposed approach provides a powerful opportunity for imaging, reducing the required number of sources/receivers and alleviating acquisition costs.
Synthetic experiments validate the method's performance in modeling and imaging on coarser grids than FD methods and in maintaining stability over longer times. Further, the MNAD-based RTM application to ocean bottom seismometer (OBS) data in a large-scale study confirms its capability to achieve high-resolution images with reduced computational costs. Finally, imaging with data sampled at half the Nyquist rate highlights the potential of the proposed approach for minimizing acquisition costs without sacrificing resolution and suffering from aliasing.
These findings affirm MNAD as a robust and efficient alternative to FD methods for large-scale, high-resolution imaging, offering significant advantages in computation, storage, and acquisition efficiency.

Acknowledgement: This work was supported by the Polish National Science Center, grant UMO 2023/51/D/ST10/02603.

How to cite: Zand, T.: Reverse Time Migration Using Modified Nearly Analytical Discretization for Large-Scale High-Resolution Imaging, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7954, https://doi.org/10.5194/egusphere-egu26-7954, 2026.

Tectonic tremors in subduction zones are commonly attributed to shear slip along the plate interface, but their potential link to fluid processes in the overriding crust remains debated. Here, we apply a novel elastic reverse-time migration method to teleseismic waveforms recorded by a quasi-linear dense seismic array in central Mexico to image subsurface fluid pathways with unprecedented resolution. Our results reveal two vertically oriented discontinuities featured with negative amplitudes—interpreted as low-velocity fluid-filled fracture networks—that connect the subducting Cocos slab to tremor source regions in the overriding plate to facilitate fluid migration upwards from slab dehydration. These fracture zones are spatially correlated with both northern and southern tremor clusters of the well-known “sweet spot.” It is also observed that some tremors have harmonic spectra, further supporting they are related to fluid resonance in the fracture zones of overriding plate. The findings demonstrate that crustal fractures, not only interface slip, govern tremor generation in weakly coupled flat slab systems. These findings redefine fluid-mediated tremor mechanisms in this flat-slab subduction zone and make it necessary to reassess seismic hazards in regions where deep fluid fluxes interact with overriding plate faults.

How to cite: Zou, P., Cheng, J., Zhang, H., and Wang, T.: Teleseismic Imaging Reveals Fluid Pathways Governing Tectonic Tremor Genesis in the Central Mexico Flat-Slab Subduction Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15823, https://doi.org/10.5194/egusphere-egu26-15823, 2026.

Numerical methods for solving the wave equation have been widely adopted in seismology to simulate earthquakes and other seismic phenomena, with the goal of better understanding the underlying physical processes. Commonly used approaches, such as finite-difference methods and spectral element methods, have been extensively studied in terms of their numerical properties, computational cost, and accuracy in modelling the Earth’s response to seismic phenomena.

The recently introduced distributional finite-difference method (DFDM) is a novel approach to seismic wave modelling, aiming to combine advantages of established methods to achieve high accuracy at reduced computational cost. While recent studies have shown the accuracy of DFDM by comparing it to existing methods, a comprehensive investigation of the numerical properties governing its cost and accuracy in the context of solving the wave equation has not yet been carried out.

In this contribution, we focus on two key numerical properties: stability and numerical dispersion. We assess the trade-offs between time-step restrictions and accuracy, and introduce a cost metric to quantify the computational effort required to achieve a prescribed dispersion error threshold. Our results show that, although DFDM has more restrictive stability bounds, it provides superior dispersion performance at lower spatial resolutions compared to conventional methods. This makes DFDM particularly attractive for applications with stringent memory constraints, such as global-scale simulations or full-waveform inversion. These results provide practical guidance for selecting numerical methods in large-scale, physics-based wave simulations.

How to cite: Aloisi, G., Zunino, A., Keating, S., and Fichtner, A.: Stability and numerical dispersion properties of the distributional finite-difference method, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7964, https://doi.org/10.5194/egusphere-egu26-7964, 2026.