Among others, the session will cover the following topics:
- Active- and passive-source imaging
- Full waveform inversion developments and applications
- Advancements and case studies in 2D and 3D imaging
- DAS imaging
- Interferometry and Marchenko imaging
- Seismic attenuation and anisotropy
- Developments and applications of multi-scale and multi-parameter inversion
- Joint inversion of seismic and complementary geophysical data
Orals: Tue, 5 May, 08:30–15:40 | Room D1
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 (Vs) 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 Vs 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-Vs 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, INDOVSV24, 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.
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.
Posters on site: Wed, 6 May, 10:45–12:30 | Hall X2
In this study, we develop 1D shallow subsurface velocity profiles from one year of ambient-noise measurements collected at the Mpala Research Centre, a nature and wildlife preservation area in Laikipia County, Kenya. The Mpala Research Centre is located in a rangeland shared by wildlife, livestock, and people, and experienced extreme drought in 2023. Water access in such times depends largely on shallow wells that are influenced by subsurface hydrogeology. In addition, there is growing interest in seismic wildlife monitoring based on interpreting ground-coupled animal vibrations whose amplitudes and dominant frequencies are shaped by local site effects. Both issues point to the need for information on the shallow subsurface structure. Mapping site specific shear-wave velocities (Vs) provides a common foundation to (i) relate stratigraphy to shallow groundwater availability and (ii) correct for spatial variability in amplification that biases wildlife signal detectability.
Motivated by these needs, we develop the first locally constrained Vs models in the Mpala area based on continuous seismic data (Jan 2023–Jan 2024) across a 15 broadband station array using ambient noise HVSR and passive seismic interferometry. The HVSR and Rayleigh wave dispersion measurements from the two methods are jointly inverted. The dispersion curves’ frequency band (≈ 2–9 Hz) provides depth sensitivity of ∼70–430 m, while HVSR constrains near-surface impedance contrasts. Across the station network, we estimate three consistent velocity contrasts in the upper 100 m, first at ∼ 1–4 m (Vs ∼ 280–500 m/s), then at ∼5–20 m (Vs ∼ 345–900 m/s), and finally at ∼ 15–50 m (Vs ∼ 1160–2600 m/s). The resulting Vs models support well siting and inform how to account for local site-amplifications effects for monitoring and modeling ground-coupled wildlife sensing at Mpala. For future work we recommend multi-scale seismic array configurations with both locally denser and targeted wider spacing to more reliably estimate both shallow depths and the overall geological structure. Improved dispersion-curve measurements help reduce uncertainty arising from the limited dispersion band, uneven station pair coverage, and capture possible lateral heterogeneity.
How to cite: Awuor, E., Li, C., Shiddiqi, H., Parisi, L., and Mai, P. M.: Shear-Wave Velocity Models of the Subsurface Critical Zone at Mpala, Kenya, from Ambient Noise, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12638, https://doi.org/10.5194/egusphere-egu26-12638, 2026.
The Anatolian Plateau is one of the most heterogeneous and seismically active segments of the Alpine–Himalayan orogenic belt. It was formed through the amalgamation of several microplates with the Eurasian Plate following the multi-episodic opening and closure of the Tethyan oceans. These complex tectonic processes have produced a highly heterogeneous lithospheric structure across Anatolia. Despite numerous local and regional scale tectonic and geophysical studies, a comprehensive and high-resolution image of the Anatolian lithosphere remains incomplete. To address this, we conducted ambient noise tomography to image the crust and upper mantle beneath the Anatolian Plateau using 2.5 years of continuous vertical-component seismic recordings from 135 broadband stations. By applying the double-beamforming method to cross-correlations, we extracted Rayleigh-wave phase velocities over periods of 8–120 s and group velocities over periods of 6–100s. Two-dimensional phase and group velocity maps are constructed using the Fast-Marching Surface Tomography (FMST) . To obtain a high-resolution three-dimensional shear-wave velocity model, a nonlinear Bayesian Markov Chain Monte Carlo (MCMC) approach was applied. The resulting Vs model reveals several key features. A low-velocity layer at depths of 10–30 km likely reflects partial melting or thermally weakened crust. A high-velocity layer at depths of 50–80 km, interpreted as evidence for a thin and laterally variable mantle lithosphere, with lithospheric thickness in eastern and central Anatolia ranging from 60 to 70 km, while the thickest lithosphere (~120 km) is observed beneath western Anatolia and the eastern Taurus Mountains. . A pronounced upper-mantle low-velocity anomaly beneath eastern to central Anatolia is interpreted as asthenospheric upwelling or lateral flow. Finally, two deep high-velocity anomalies beneath the southern margin of Anatolia are attributed to the subducting African lithosphere along the Hellenic and Cyprus trenches.
How to cite: Zarunizadeh, Z., Wang, K., Movaghari, R., Teknik, V., and Yang, Y.: Imaging Anatolian Lithospheric Structures using High-Resolution Double-Beamforming Ambient Noise Surface-Wave Tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8884, https://doi.org/10.5194/egusphere-egu26-8884, 2026.
Iceland is one the most active tectonic regions in the world. While previous seismic tomographic models have provided insights into subsurface structure, rifting and the presence of a mantle plume and melt, these models have lacked the multi-scale resolution to connect the near surface and crustal structure to the mantle. In order to advance our understanding on the lithospheric structure and how it relates to geothermal activity we require a high resolution full lithosphere model of Iceland.
Using recently acquired passive seismic data, we are constructing a new surface wave velocity model of Iceland by combining ambient noise and teleseismic earthquake data derived from phase velocity dispersion. We use a database of 205 seismic stations from a variety of permanent and temporary networks recorded between 1993 and 2024. We obtain Rayleigh and Love phase velocity dispersion curves from the cross correlograms using SeisLib (Magrini et al., 2022). For teleseismic earthquakes, we measure phase variation between nearby stations using a waveform cross-correlation method. We perform strict quality control to ensure that the dispersion measurements are robust since the instruments used are of different sensitivities, affecting the dispersion measurements at longer periods. The dispersion curves and phase variations are inverted for phase velocity maps between 4 – 100 seconds period.
We observe low velocity in the upper and mid crust around the Western Volcanic Zone (WVZ), Eastern Volcanic Zone (EVZ) and Northern Volcanic Zone (NVZ) following closely with the rifts in Einarsson et al. (2006), and significantly lower velocity around the western edge of the Vatnajökull icecap. We also observe low velocity in central Iceland in the lower crust and upper mantle. We invert the phase velocity maps for shear velocity models of the lithosphere. This new model will contribute to providing high resolution imaging of the Icelandic lithosphere from the crust to mantle. We will in future jointly invert the velocity model with petrological data to model the geothermal structure of Iceland with a local focus at the Krafla volcanic complex.
How to cite: Owusu, B. A., Chambers, E. L., Bean, C. J., and Jónsdóttir, K.: Multi-scale Imaging of Iceland using Ambient Noise and Teleseismic Earthquakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7706, https://doi.org/10.5194/egusphere-egu26-7706, 2026.
The Haiyuan-Liupan Shan (HY-LPS) arcuate tectonic belt, located at the junction of the growth front of the Tibetan Plateau and the North China Craton, serves as a natural laboratory for investigating continental collision. Investigating the fine structure and dynamic processes in this area not only deepens our understanding of the debated growth and deformation patterns of the plateau, but also clarifies the interactions between the plateau and the adjacent craton. In this study, we establish a high-resolution three-dimensional crustal shear-wave velocity structure surrounding the HY-LPS arcuate tectonic belt using the surface wave imaging technique, utilizing ambient noise data from 219 broadband stations. The shear-wave velocity structure in this region exhibits a strong correlation with geological tectonics, consistent with the transformation of boundary faults from strike-slip to thrust. Low-velocity bodies are extensively distributed in the middle crust of the Longxi block, which is located at the northeastern margin of the Tibetan Plateau. The formation of these low-velocity anomalies may result from multifactorial interactions. Our results indicate that the upper and lower crusts in the Longxi block are decoupled, and the mid-crustal low-velocity bodies act as a detachment layer. This decoupling mechanism facilitates the growth of the plateau margin by enabling the upper crust to overthrust onto the craton, thereby contributing to the formation of the Liupan Shan. Furthermore, the lower crust of the Longxi block is found thickened due to the obstruction imposed by the North China Craton and intruded into the cratonic lower crust. The cratonic crust has been compromised due to the combined effects of tectonic compression and thermal erosion associated with the northeastward expansion of the Tibetan Plateau, which has facilitated the development of wedge tectonics.
How to cite: Zhao, P., Chen, J., Liu, Q., Gao, Y., Sun, A., Chen, Y., Chen, Y., Li, S., and Deng, W.: Wedge-Shaped Structure and Its Implications for the Haiyuan-Liupan Shan Arcuate Tectonic Belt Revealed by High-Resolution Ambient Noise Tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5044, https://doi.org/10.5194/egusphere-egu26-5044, 2026.
We construct a 3-D crustal shear wave velocity model of the Main Himalayan Thrust (MHT) beneath central Nepal using ambient noise adjoint tomography. The MHT is the major plate boundary fault accommodating India–Eurasia convergence and was the source of the 2015 Mw 7.8 Gorkha earthquake. This full-waveform inversion method uses the spectral-element method (SEM) and updates shear wave velocity directly from multicomponent empirical Green’s functions (EGFs). Previous studies suggest that the MHT exhibits substantial lateral variation and consists of north-dipping, imbricate thrust faults forming a duplex structure. These faults influence strain accumulation and rupture dynamics but their geometries remain poorly constrained by ray-based seismological imaging methods.
We analyze 11 months of continuous data from 42 stations of the NAMASTE (Nepal Array Measuring Aftershock Seismicity Trailing Earthquake) network, deployed about 50 days after the Gorkha earthquake and spanning the rupture zone with an average spacing of 20 km. From multicomponent ambient noise cross-correlations, we extract EGFs in the 5–40 s period band. Frequency-dependent traveltime misfits between EGFs and synthetic Green’s functions from SEM simulations are iteratively minimized using finite-frequency sensitivity kernels. The resulting model will provide improved constraints on MHT geometry and contribute to a better understanding of Himalayan tectonics and seismic hazard.
How to cite: Chalakkatta, V., Datta, A., and Ghosh, A.: Multicomponent Ambient Noise Adjoint Tomography of the Main Himalayan Thrust, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1192, https://doi.org/10.5194/egusphere-egu26-1192, 2026.
An accurate velocity model of the subsurface is required for many different applications and settings. Active and passive seismic data can both be used to derive meaningful seismic tomograms, but combining the two data sets remains challenging. In contrast to active seismic data, the hypocentral parameters of passive seismic data are not known and need to be considered during tomographic inversions.
Both, active and passive data sets have individual advantages and disadvantages. Therefore, combining them can be beneficial for obtaining a reliable velocity model. The spatial resolution and coverage of active seismic measurements can be tailored to specific applications and research questions, allowing targeted illumination of selected parts of the volume of interest with often relatively homogeneous ray density. However, the positioning of active sources and receivers is restricted to boreholes or the surface. In contrast, passive seismic data typically covers a larger volume and can illuminate regions that may not be accessible with active seismics, but the ray coverage of passive seismic data is often more heterogeneous, since seismic events commonly occur along fracture zones, leading to clustered source locations.
In our study, we show that a combined inversion of both data sets is feasible and allows their advantages to be exploited. The constraint provided by the active seismic data enables an iterative inversion of passive seismic source locations and seismic velocities using both data sets simultaneously. To combine the two data sets in a balanced and complementary way, we select only a subset of the passive seismic data for the inversion. This is achieved through a QR decomposition of the Jacobian, which ranks the information content of the passive seismic data relative to the information already provided by the active data set, thereby ensuring optimal complementarity. The method also enables an assessment of the appropriate amount of additional data to include in the inversion, helping to avoid overweighting densely sampled grid cells.
We apply this method to data from the BedrettoLab, an underground rock laboratory that serves as a testbed for geothermal injection experiments. From this test site, high-quality active and passive seismic data are available on a hectometer scale. With our approach, we increase the covered volume of the reservoir by a factor of 3 compared to the coverage purely based on active seismic data. We relocate the seismic events after each iteration, taking varying source locations due to the updated velocity model into account in the inversion. We further compare our results with a random data selection of passive seismic data, highlighting the importance of the optimized data selection, to maximize the illuminated volume.
How to cite: Behnen, K., Maurer, H., Hertrich, M., and Giardini, D.: Combined inversion of active and passive seismic data based on optimized data point selection, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19041, https://doi.org/10.5194/egusphere-egu26-19041, 2026.
High-resolution imaging of volcanic structures relies on accurate forward modeling of teleseismic
wavefields. In general, full waveform inversion requires global wavefield simulations, which are compu-
tationally expensive. To reduce this cost, localized waveform inversion or “box” waveform tomography
approaches have been developed. These methods compute the global wavefield once and inject the re-
sulting displacement and stress fields at the boundaries of a local region of interest. However, even
this initial global simulation can remain computationally demanding and depends on the choice of a
background model, such as one-dimensional or three-dimensional long-wavelength tomographic models.
Monteiller et al. (2021) have shown that this step can be significantly sped up by substituting the full
wavefield with a single plane wave, which is a valid approximation for teleseismic earthquakes. Moti-
vated by these results and in the context of Mount Fuji, we further simplify the forward modeling by
considering small regions, typically 100 × 100 × 50 km, a scale at which incoming teleseismic P waves
are expected to be close to planar at the boundaries. We present a series of synthetic experiments in
a two-dimensional Cartesian framework, placing seismic sources at various locations outside the study
region. We simulate wave propagation in background media defined by one-dimensional Earth models,
onto which two-dimensional slab-like perturbations are added. From the resulting wavefields, we esti-
mate slowness vectors and apparent velocities at the boundaries of the box and quantify deviations from
an ideal planar arrival, which allows us to assess the validity of the plane wave approximation. Thus,
we provide an efficient forward modeling strategy for high-resolution imaging of Mount Fuji and similar
volcanic systems. More generally, our results enable us to define practical criteria under which plane
wave injection can be justified.
How to cite: Mohammadi, H., Fuji, N., and Durand, S.: 2D Synthetic Wave Propagation Forward Modeling Toward High-Resolution Tomography of Mount Fuji, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9628, https://doi.org/10.5194/egusphere-egu26-9628, 2026.
Tomography and full waveform inversion studies are dependent on synthetic datasets. However, simulating teleseismic wave propagation in 3D remains computationally challenging, particularly when small-scale local structure is incorporated into the model. To overcome this issue, a range of strategies - including hybrid methods and coupling techniques - have been explored in recent years.
In this work, we evaluate RegHyM, an open-source package that couples AxiSEM with SPECFEM3D. Previous work using the package has demonstrated the feasibility of simulating P waves from explosive sources, but this has not been systematically validated. To expand the range of applications of the package for seismological studies, we model body and surface waves for earthquake sources and compare the synthetic waveforms with observed seismological data. In the present work, high-resolution 3D regional models are developed numerically accounting for surface topography and 3D velocity model. Simulations are carried out for the Alpine region as the region is not only seismically active but also hosts a widespread network of seismic stations with openly available data. Moreover, the region has been explicitly explored in the past to determine subsurface velocity models. The synthetic data simulated for different earthquakes is then validated through systematic comparison with real data up to frequency of 0.1 Hz.
In addition, we further extended the package to record spatial gradients of the wavefield, including strains and rotations, and present successful cases of these new capabilities within RegHyM. The complete package, now accompanied by a user manual, enables regional and teleseismic wave propagation at reduced computational cost, while preserving the detailed structure of the 3D local model.
Future work will focus on extending the validation of the package to telesismic wave propagation at higher frequencies and assessing the reliability of the synthetic surface waves through comparisons with seismological data.
How to cite: Hejazi Nooghabi, A., Dhabu, A., Monteiller, V., Matthießen, N., and Hadziioannou, C.: Coupled Numerical Simulation of Teleseismic Wave Propagation Incorporating Local Structural Features, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17818, https://doi.org/10.5194/egusphere-egu26-17818, 2026.
Full-waveform inversion (FWI) has emerged as a powerful tool for high-resolution seismic imaging. However, its application to crustal-scale and long-offset problems remains severely challenged by strong nonlinearity arising from long propagation paths, pronounced velocity contrasts, and the lack of sufficiently low-frequency data. These factors exacerbate cycle skipping and often cause gradient-based optimization methods to stagnate. In practice, crustal-scale FWI is predominantly performed within the standard reduced-space time-domain formulation, largely due to its favorable memory requirements and the efficiency of time-stepping schemes for solving large-scale wave equations. Nevertheless, this memory efficiency comes at the cost of increased ill-conditioning of the inverse problem, which is difficult to address adequately within the reduced-space framework.
Extended-space formulations based on Lagrange multiplier methods have proven effective in alleviating ill-conditioning and mitigating cycle skipping in FWI. However, time-domain implementations of these multiplier-based approaches for large-scale crustal imaging can be computationally demanding, primarily due to the cost associated with constructing and inverting the data-space Hessian. Recent developments employing Fourier-domain block-diagonal approximations and direct inversion strategies have improved the tractability of time-domain extended FWI. Despite these advances, the approach remains computationally intensive for realistic crustal-scale applications, as the Hessian must typically be recomputed at each iteration.
In this work, we introduce a dual-space formulation that recasts the inversion in the data space to estimation data-side Lagrange multipliers, or dual variables. These variables encode the multiple-scattering components of the data that are neglected in the conventional first-order Born approximation. Unlike standard FWI approaches, which iteratively update the velocity model to reduce data misfit, the proposed method focuses on estimating the dual variables responsible for the mismatch while keeping the background model fixed. Once these dual variables are estimated, the data are matched and the inverse problem is effectively solved. A key advantage of this formulation is that the wave-equation operators and the associated Hessian remain fixed throughout the inversion and therefore need to be constructed only once prior to the iterations. As a result, each iteration requires only two wave-equation solves. Moreover, the use of the exact Hessian eliminates the need for step-length tuning and leads to more stable and accurate updates.
Numerical experiments on large-scale acoustic models demonstrate that the proposed method achieves rapid convergence, enhanced robustness against cycle skipping, and computational efficiency suitable for crustal-scale time-domain seismic imaging.
How to cite: Sonbolestan, M., Zand, T., and Gholami, A.: An Efficient Dual-Space Formulation for Robust Crustal-Scale Full-Waveform Inversion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19051, https://doi.org/10.5194/egusphere-egu26-19051, 2026.
How the Tibetan Plateau grew farther north from the India-Asia collision boundary has profound implications for understanding the mechanics of continental deformation and accretion. Lithospheric delamination and associated mantle upwelling have been inferred beneath the northern Tibetan Plateau, supported by widespread active magmatism coeval with the rapid uplift of the Hoh-Xil Basin since the Miocene. However, in-situ seismic constraints have been limited due to the region’s inaccessibility. In this study, we combine ambient noise tomography and shear wave splitting analysis to investigate the structures of the crust and upper mantle, using recently available data from linear seismic arrays across the Hoh-Xil Basin. Our three-dimensional S-wave velocity model reveals a partially molten crust in the Hoh-Xil Basin, manifested as widespread low-VS anomalies, which is spatially correlated with strong uppermost mantle low-velocity anomalies and young exposed magmatic rocks. Our new shear wave splitting measurements across the Hoh-Xil Basin reveal significant E-W-oriented splittings reflecting variability in mantle dynamics, as indicated by the estimated anisotropy depth of 150−200 km and the alignment closely with the absolute plate motion of the Tibetan Plateau. The delay times of these splittings peak at ~1.8 s in the northern Qiangtang Terrane and gradually decrease as SKS travel-time residuals increase toward the northern margin of the plateau, coinciding with the northward migration of young magmatism. These findings provide compelling evidence for the mantle upwelling beneath the Hoh-Xil Basin driven by extreme lithospheric thinning, suggesting that the plateau grew northward through lithospheric mantle removal and subsequent magmatic accretion.
How to cite: Li, W., Yuan, X., He, R., and Chen, Y.: Seismic evidence for lithospheric delamination-driven mantle upwelling beneath the northern Tibetan Plateau, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4463, https://doi.org/10.5194/egusphere-egu26-4463, 2026.
The deep-seated mantle dynamics beneath the Tarim Craton remain highly elusive. The active mantle plume model and passive mantle upwelling model caused by subduction and delamination have been suggested. In this research, we imaged the mantle transition zone (MTZ) structure beneath Tarim Craton using more than 50000 P-wave receiver functions obtained from the newly deployed seismic array in the basin and previously collected seismic data. To obtain the accurate true depths of the 410-km discontinuity (d410) and 660-km discontinuity (d660), we conduct crustal and mantle correction using several high-resolution 3-D crustal and mantle velocity models during time-to-depth migration. The depressed d410 (~10-15 km) and d660 are suggested by our previous research, which is interpreted to be caused by the mantle upwelling originating from the delaminated lithosphere stagnant near the d660 (Wu and Bao, 2024). However, the new preliminary results show a thinned MTZ beneath majority of the Tarim Craton, caused by the depressed d410 and uplifted d660. In the meanwhile, a thickened MTZ beneath the eastern Tarim Craton is imaged, resulting from the slightly depressed d410 and significantly depressed d660. Accordingly, the new results may indicate deep mantle upwelling beneath the Tarim Craton, consistent with the global-scale tomographic models. The lithospheric delamination near d660 beneath the eastern Tarim Craton is supported. But the origins and dynamics of the mantle upwelling and delamination should be further investigated using various methods such as thermo-mechanical numerical modeling.
Reference
Wu, Y., & Bao, X. (2024). The Mantle transition zone structure beneath the Pamir Plateau and western Tian Shan and adjacent regions. Journal of Geophysical Research: Solid Earth, 129, e2023JB028129. https://doi.org/10.1029/2023JB028129.
How to cite: Wu, Y. and Bao, X.: The mantle transition zone structure beneath the Tarim Craton and deep-seated dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5125, https://doi.org/10.5194/egusphere-egu26-5125, 2026.
The demand for raw materials has scaled exponentially in recent times due to their applications in various areas, including finished goods, energy, electronics, and lithium-ion batteries. The Koillismaa Layered Igneous Complex (KLIC) in northern Finland holds great potential to host several critical raw materials such as cobalt, nickel, PGEs, etc. It is a mafic-ultramafic complex spanning over a distance of ~50-60 km and is linked by a high gravity and magnetic anomaly. Drilling in the area confirmed the presence of ultramafic rocks at a depth of ~1.4 km from the surface. Extensive petrophysical and lab studies were conducted, and a preliminary Common Earth Model (CEM) was made mainly based on the potential field data inversion with constraints from the borehole. Two regional 2D seismic profiles were acquired under the ERA-MIN 3 sponsored SEEMS DEEP Project (2022-2025) with the aim to map the regional seismic reflectivity in the area and to constrain the geometrical architecture of the KLIC. The processing of the 2D seismic data followed the standard workflow, e.g., dip-moveout followed by the post-stack time migration with constant velocity. This procedure is effective for simple geological settings, i.e., with gentle dips. In the case of KLIC, the subsurface geology is structurally complex; therefore a transition from the standard time-domain imaging to the depth-domain imaging is required. One of the main challenge in doing this is the unavailability of a robust velocity model. We used first-arrival traveltime tomography (FATT) and acoustic Full Waveform Inversion (FWI) to build the high-resolution velocity model. We used the steepest-descent optimization algorithm, optimal-transport objective function, and inverted for the P-waves only using the vertical-component data. The depth details for the FATT-derived velocity model were limited to a few tens of meters from the surface as compared to ~1 km for the FWI-derived velocity model. For migration, we performed prestack Kirchhoff depth migration (KPreSDM) with both FATT- and FWI-derived velocity models. In the latter case, we did not observe much uplift in terms of the overall imaging, partially may be due to the lesser sensitivity of the ray-based KPreSDM towards the input velocity model and limited velocity details with depth. Therefore, we also tested least-square KPreSDM to obtain the depth image with better amplitude fidelity. We then tested wave-equation based Reverse Time Migration (RTM) due to its ability to better handle the complex media using both the derived velocity models. RTM with FWI-derived velocity model provided us with the best imaging overall until a depth of ~5-6 km, establishing the merit of these advanced methods for high-resolution seismic imaging of the geologically complex settings such as the KLIC. The obtained results showed good correlation with the available petrophysical data, observed gravity & magnetic highs, available CEM, and the controlled source electromagnetics-derived resistivity model, which was also acquired during the SEESM DEEP project. Overthrusting with regional-scale faults was imaged, and a funnel-shaped geometry of the KLIC was established. Seismic imaging also suggested a more structural or compositional heterogeneity within the mafic-ultramafic KLIC body.
How to cite: Singh, B., Gόrszczyk, A., Malinowski, M., and Karinen, T.: High-resolution seismic imaging of the Koillismaa Layered Igneous Complex, Northern Finland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17111, https://doi.org/10.5194/egusphere-egu26-17111, 2026.
Several high quality reflection seismic profiles were acquired over the Siljan Ring impact structure in the mid- to late-1980s using an explosive source and 80 to 120 channels. Furthermore, two deep boreholes, Gravberg-1 and Stenberg-1, were drilled to more than 6 km depth in the area in search for abiogenic gas. Boreholes to these depths in Precambrian rock are rare and provide some ground truth for interpretation of the seismic data. Results from the seismic data have been presented in a number of publications where we have demonstrated that data have (1) helped to improve our understanding of the impact cratering process (Juhlin and Pedersen, 1987, 1993), (2) allowed us to identify the source of some of the seismic reflectivity in Precambrian basement (Juhlin, 1990; Papasikas and Juhlin, 1997) and (3) provided preliminary mapping of the Moho in the area with near vertical incidence seismic data (Juhojuntti and Juhlin, 1998). Even though these studies were initiated more than 40 years ago, the data can still provide new insight into crustal structure and the potential to image it in detail. Reprocessing of the data in a consistent manner with modern software and careful merging of the various profiles allows different perspectives of the data to emerge compared to earlier results. In particular, a strong band of reflectivity at about 5 s TWT (c. 15 km) is present throughout most of the area. Reflections from this band appear to be of a different nature from the shallower more distinct reflections that are known to originate from dolerites that have intruded into the surrounding granitic rock. Whether or not all the shallow reflections originate from dolerites is still an open question. I will present the latest results from the reprocessing, an expanded interpretation of the crustal structure and some suggestions for future research.
Juhlin C., 1990, Interpretation of reflections in the Siljan Ring area based on results from the Gravberg-1 borehole, Tectonophysics, 173, 345-360.
Juhlin C. and Pedersen L. B., 1987, Reflection seismic investigations of the Siljan impact structure, Sweden, J. Geophys. Res., 92, 14113-14122.
Juhlin C. and Pedersen L.B., 1993, Further constraints on the formation of the Siljan impact crater from seismic reflection studies, Geologiska Föreningens i Stockholm Förhandlingar 115, 151-158.
Juhojuntti N. and Juhlin C., 1998, Seismic lower crustal reflectivity and signal penetration in the Siljan Ring area, central Sweden, Tectonophysics, 288, 17-30.
Papasikas N. and Juhlin C., 1997, Interpretation of reflections from the central part of the Siljan Ring Impact structure based on results from the Stenberg-1 borehole, Tectonophysics, 269, 237-245.
How to cite: Juhlin, C.: Another look at reflection seismic data acquired over the Siljan Ring impact structure, central Sweden, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5596, https://doi.org/10.5194/egusphere-egu26-5596, 2026.
The Burmese arc, located at the eastern Himalayan syntaxis formed by the collision between the Indian and Eurasian plates, is characterized by intense crustal deformation, active magmatic–metamorphic processes, and frequent seismicity. Imaging the low-velocity layer (LVL) atop the subducting Indian plate is crucial for understanding post-collisional magmatism and lithospheric dynamics in this region, yet its detailed structure remains poorly constrained. Using continuous seismic data recorded by the CMGSMO network between June 2016 and February 2018, we identified 11 intermediate-depth earthquakes within the subducting Indian plate beneath the central Burmese arc that exhibit prominent guided-wave signatures. We conducted two-dimensional finite-difference simulations for a representative event near 22°N and obtained a best-fitting velocity model through systematic comparisons between synthetic and observed seismograms, including waveform characteristics and arrival-time behavior of guided phases. The preferred model reveals a LVL atop the subducting plate, characterized by P-wave velocities of 6.4–6.9 km s⁻¹ and a thickness of 8–14 km. The observed spatial distribution of guided wave events further suggests lateral variability of the LVL, consistent with a localized tear zone in the subducting slab. We interpret the LVL as a partially molten layer generated by the combined effects of Monywa magmatism, thermally driven upwelling associated with slab tearing, and fluid release due to slab dehydration. These results highlight the role of slab tearing in controlling melt generation and transport beneath the Burmese arc and provide new seismic constraints on post-collisional lithospheric processes in the eastern Himalayan region.
How to cite: Peng, C., Zhou, Y., and Feng, J.: Low-velocity layer atop the subducting Indian plate beneath the Burmese Arc constrained by guided waves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6468, https://doi.org/10.5194/egusphere-egu26-6468, 2026.
The Pamir, located northwest of Tibet, constitutes part of Earth's largest active continental collisional orogen and represents an ideal natural laboratory for studying continental subduction. Although numerous structural models have been proposed, the morphology of subducting Indian and Asian lithospheric slabs remains poorly constrained. Using a Multi-Scale Sparsity traveltime tomography method and a comprehensive P-wave traveltime database compiled from ISC bulletins and phase picks from temporary seismic arrays, we present new P-wave velocity models that image detailed mantle structure beneath the Pamir and illuminate the geometry of the subducted slabs.
Our tomographic results reveal: 1) At sub-Moho depths, a southward-dipping high-velocity slab beneath the eastern Pamir underlies intermediate-depth earthquakes; 2) At the top of the upper mantle, relatively low velocities are shown in the Fergana Basin and Tianshan orogenic belt, while high velocities are observed beneath the Pamir Plateau and Tarim Basin; 3) At depths of 200–300 km, low-velocity anomalies persist beneath the Pamir, whereas high-velocity features are displayed beneath the Tianshan and Fergana Basin; and 4) At 250–400 km depth, a high-velocity zone beneath the Eastern Pamir Plateau is interpreted as lithospheric delamination.
How to cite: Guo, B., Chen, J., and Li, S.: Crustal and Upper-mantle Structure Beneath Pamir by Multi-Scale P-wave Traveltime Tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7433, https://doi.org/10.5194/egusphere-egu26-7433, 2026.
The 2022-2023 OHANA OBS deployment in the northeast Pacific Ocean provides a rich dataset for comprehensive seismic studies to explore the crust, lithosphere and asthenosphere in a 600-km wide region west of the Moonless Mountains. The study area covers mainly 40-to-50 Myr old Pacific lithosphere. A fundamental question to be addressed is whether this particular area has the signature of a typical oceanic lithosphere that has a normal plate cooling history. Alternatively, we seek evidence for a previously proposed reheating process, e.g. resulting from small-scale shallow-mantle convection. Given its location, the OHANA experiment contributes crucial data to the Pacific Array initiative.
We present the analysis of path-averaged Rayleigh wave dispersion curves obtained from earthquake records. The average dispersion across the OHANA network indicates lower shear velocities than expected for a 50-Myr old crust and lithosphere. Velocities in the mid-to-lower lithosphere appear to be 2-3% lower than expected. Compared to other recent broadband OBS deployments in the Pacific Ocean, we image a profound reduction in shear velocity throughout the entire asthenosphere though imaging fidelity declines with depth.
We observe strong and internally consistent azimuthal anisotropy, where the ‘fast direction’ places between fossil and modern plate motion directions. This anisotropy dominates over isotropic lateral heterogeneity in the crust and lithosphere.
How to cite: Laske, G., Collins, J., and Blackman, D.: Rayleigh Waves from the OHANA Project Indicate Low Mantle Velocities as well as Anisotropy in the Northeast Pacific, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8516, https://doi.org/10.5194/egusphere-egu26-8516, 2026.
The mantle transition zone (MTZ), bounded by seismic discontinuities near 410 and 660 km depth, plays a key role in mantle convection by regulating heat and material exchange between the upper and lower mantle. In this study, we image the MTZ structure beneath the East Sea (Sea of Japan) using common conversion point (CCP) stacking of teleseismic receiver functions from a dense array of broadband stations located on the Korean Peninsula and the Japanese Islands. The resulting CCP-stacked images reveal a generally thickened MTZ, likely reflecting the presence of the stagnant Pacific slab at the base of the MTZ. In contrast, a near-normal MTZ thickness is observed beneath Ulleung Island, potentially indicating localized thermal or compositional heterogeneity. These findings allow us to assess the relationship between MTZ structure and major tectonic processes in East Asia, providing constraints on mantle temperature, composition, and volatile content.
How to cite: Hwang, J.-Y. and Chang, S.-J.: Mantle transition zone imaging beneath the East Sea (Sea of Japan) using teleseismic receiver functions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8926, https://doi.org/10.5194/egusphere-egu26-8926, 2026.
Despite extensive studies have documented the structural styles of shallow thrust-nappe belts in the upper crust, the role of deep-seated inherited structures in foreland thrust evolution remains poorly constrained. This knowledge gap hinders in-depth investigations into the deep-shallow structural relationships and contact patterns between tectonic units in basin-range junction belt. The southern Tian Shan margin features extensive nappe-thrust belts with diverse deformation styles over >1000 km, offering an ideal natural laboratory to investigate this issue. We conducted a high-resolution crustal structure study in the southern margin of the western Tianshan, revealing the deep-shallow deformation architecture of the foreland thrust-nappe system. Three distinct units are identified: (1) The northern Tarim Basin exhibits high seismic velocities with a crustal thickness of ~45-48 km, where its lower crust intrudes into the Kashi fold-and-thrust belt (FTB); (2) Kashi FTB exhibits a crustal thickness of 53-70 km and is characterized by pronounced mid-lower crustal low-velocity zones (LVZs), indicating crustal thickening. The lower crust beneath northern Kashi FTB underthrust northward beneath the Tian Shan. (3) The southern Tian Shan margin has a crustal thickness of ~60 km, with velocity and discontinuity structures distinct from those in the Kashi FTB. The LVZ beneath the Kashi FTB not only accommodates significant crustal shortening but also facilitates the development of piedmont thrust-nappe structures. By serving as a detachment zone, it drives southward propagation of the nappes toward the northern Tarim Basin, forming basement-cored anticlines. Our findings reveal the complex crustal architecture of the southwestern Tian Shan, demonstrating that inherited structures control the formation and evolution of piedmont thrust-nappe tectonics.
How to cite: Chen, Y.: Deep crustal structure controls the deformation style of the foreland fold-and-thrust belt in south Tian Shan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15526, https://doi.org/10.5194/egusphere-egu26-15526, 2026.
The Groningen region in the northern Netherlands has experienced significant induced seismicity over the past decade due to long-term gas extraction. In addition to hydrocarbon production, the area is considered promising for geothermal energy development and CO₂ storage, highlighting the need for a detailed understanding of the deep subsurface structure. Such knowledge is crucial for enhanced seismic hazard assessment and sustainable subsurface utilization.
We present a teleseismic P-wave tomographic study of the crust and upper mantle beneath the Groningen region, using data recorded by the regional seismic network over the past 6 years. Teleseismic P-wave arrivals are enhanced through stacking and alignment across the network to mitigate high noise levels and improve the accuracy of picking. The resulting first-arrival times form the input dataset for a tomographic inversion performed using FMTomo. Although the Groningen dataset is characterized by high noise levels, the large volume of available data combined with the stacking approach yields a robust set of arrivals suitable for inversion. Due to the dense dataset covering a relatively small region, the resulting model will offer a high-resolution P-wave velocity model of the crust and upper mantle beneath Groningen. This tomographic model provides a foundation for improved waveform simulations of induced seismicity, enhancing our understanding of seismic wave propagation and ground-motion patterns, and contributing to more accurate seismic risk evaluation for current and future subsurface activities.
How to cite: de Laat, J. and Fadel, I.: Revealing the seismic structure of the crust and upper mantle beneath Groningen (NL) through fine-scale teleseismic P-wave tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20388, https://doi.org/10.5194/egusphere-egu26-20388, 2026.
The tectonics of Taiwan are characterized by the complex convergence of the Philippine Sea Plate (PSP) and the Eurasian Plate (EP). While the general orogenic structure is known, resolving the detailed morphology of the subducting slabs, the forearc basement, and shallow volcanic reservoir systems remains challenging with classical travel-time tomography. Here, we present high-resolution 3-D tomographic models of density, VP, VS, and the VP/VS ratio of Taiwan, obtained by inverting complete teleseismic waveforms from 36 P and 18 SH events. We utilized data from 240 broadband stations, including those from permanent networks and temporary experiments. In our final FWI model, the Eurasian slab is imaged as a continuous eastward-dipping high-velocity anomaly in southern Taiwan but exhibits a distinct slab gap north of 23.6°N at depths greater than 130 km. This discontinuity likely facilitates toroidal mantle flow around the slab edge, consistent with geodynamic models. A high-velocity body in the upper crust along the eastern Central Range is interpreted as the underthrusted forearc basement. Our model also identifies distinct low-velocity, high VP/VS bodies beneath the Tatun Volcano Group (TVG) and Turtle Island, indicative of crustal magma reservoirs. The reservoir beneath the TVG appears dome-shaped with an apex at ~6 km depth, while the reservoir beneath Turtle Island is volumetrically larger and connects to a hydrated mantle wedge, suggesting a fluid-rich magmatic source. These findings provide new constraints on the tectonic evolution, slab dynamics, and volcanic structures in Taiwan, and highlight the potential of teleseismic FWI for crust and upper-mantle imaging.
How to cite: Kan, L.-Y., Kuo-Chen, H., Chevrot, S., and Monteiller, V.: Seismic Imaging of the Crust and Upper Mantle beneath Taiwan Using Full-Waveform Inversion of Teleseismic Body Waves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16537, https://doi.org/10.5194/egusphere-egu26-16537, 2026.
To understand the implication of geodynamics in intercontinental subduction of Indian plate and Burmese plate, sediment deposits in the North-East India, Indo-Burma Ranges (IBR) and surrounding regions, a better resolved image is needed to interpret the findings. The structure and geodynamics in North-East India and surrounding region are studied using the fundamental mode rayleigh wave group velocity tomography. As there is a good coverage of stations in and around the region resulting in dense source-receiver pair ray cross paths, we get a better resolution than previously reported studies. The tomographic results show thicker sediments in Bengal Basin thins from west to east and crustal nature varies from north to south as continental to oceanic. The southern IBR shows consistent lower group wave velocity at all periods. Comparing both Bengal Basin and IBR, the velocity variation reveals about the oblique subduction of Indian plate below the Burmese plate. The Shillong Plateau and Mikir hills show low velocity at lower periods, but at higher periods it exhibits high velocity indicating presence of sediments in upper layers.
We present preliminary constraints on crustal structure beneath the Indo-Burma Ranges (IBR) using receiver functions from the IK (IISER Kolkata) and XR (BIMA) seismic network. Stacked radial receiver functions from these stations yield clear Ps and multiple phases, allowing stable H–κ estimates. Crustal thickness and Vp/Vs variation indicates notable heterogeneity in along East-West and North-South trend of IBR. Thicker crust in the central IBR and comparatively thinner crust towards the frontal zone likely reflect variations in deformation, composition and Indian plate – IBR convergence dynamics. These first order results provide essential inputs for upcoming high resolution imaging of the region.
How to cite: Sahu, S. and Borah, K.: Crustal Structure and Geodynamic Implications of the Indo-Burma Ranges and Surrounding Regions from Surface Wave Tomography and Receiver Function Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16910, https://doi.org/10.5194/egusphere-egu26-16910, 2026.
Northeast India is among the most seismically vulnerable regions of the world due to its complex tectonic framework, high population density, and the presence of thick sedimentary layers that can strongly amplify seismic waves. As a result, even moderate earthquakes may cause substantial damage. Previous surface wave investigations in this region have been largely restricted to Rayleigh wave tomography. In this study, we present the first high resolution Love wave tomography of Northeast India, providing new insights into the shear wave velocity structure of the crust and upper mantle. Love wave dispersion data are used to derive one–dimensional (1D) shear wave velocity models, which are subsequently combined to construct a three dimensional (3D) shear wave velocity model of the region. The reliability of the imaged structures is evaluated through resolution analysis to ensure that observed velocity variations represent realistic subsurface features. Because Rayleigh and Love waves are sensitive to different components of shear wave velocity, discrepancies between their velocity structures are used to investigate radial anisotropy within the lithosphere. The combined analysis of Rayleigh and Love wave results provides important constraints on the anisotropic properties of the crust and upper mantle and their tectonic significance.
In addition to structural imaging, we assess the seismic hazard of Northeast India through estimation of the Gutenberg–Richter b–value, which reflects the relative occurrence of small and large earthquakes. The calculated b–values indicate generally high tectonic stress and an elevated potential for large earthquakes across the region. Within the Indo–Burma Ranges (IBR), the southern, central, and northern segments all exhibit b–values below 1.0, suggesting significant seismic hazard. The Mikir Hills show notably low b–values, lower than those reported in earlier studies, whereas the Shillong Plateau records b–values consistent with previous estimates. A depth dependent analysis reveals pronounced changes in b–values at specific depths, which appear to correlate with the Moho discontinuity. In the IBR, a marked transition occurs at approximately 50 km depth, while similar changes are observed at ~30 km beneath the Mikir Hills and ~35 km beneath the Shillong Plateau. These observations suggest a strong relationship between seismicity patterns and the crust–mantle boundary, highlighting the role of lithospheric structure in controlling earthquake generation.
Overall, this study integrates high resolution Love wave tomography with seismicity analysis to advance our understanding of the subsurface structure, radial anisotropy, and seismic hazard of Northeast India, emphasizing the need for continuous monitoring and improved earthquake preparedness in this tectonically active region.
How to cite: Kumari, M., Sahu, S., and Borah, K.: Love Wave group Velocity tomography and Seismic b-Value Analysis of Northeast India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17055, https://doi.org/10.5194/egusphere-egu26-17055, 2026.
First-arrival traveltime and slope tomography has been routinely applied to velocity imaging of marine seismic data, particularly for ocean-bottom seismometer (OBS) surveys. However, strong seafloor undulations and the presence of a water layer introduce significant challenges for accurate traveltime modeling and reliable imaging of shallow subsurface structures. In particular, wave propagation through the water layer can substantially degrade seismic illumination and, consequently, reduce the resolution of sedimentary layers beneath the seafloor. In this study, we develop a topography-dependent first-arrival traveltime and slope tomography method based on a body-fitted curvilinear grid that explicitly accounts for complex seafloor topography. The subsurface velocity structure is inverted using first-arrival waves of OBS data, enabling robust imaging of the shallow crust beneath irregular bathymetry. To mitigate the adverse effects of the water layer, we further incorporate a redatuming strategy, in which observed data are downward continued to a virtual receiver surface located at the seafloor. This approach effectively suppresses water-layer interference and enhances subsurface illumination. Synthetic checkerboard tests demonstrate that redatuming significantly improves the recovery of velocity anomalies, particularly in shallow sedimentary layers where conventional slope tomography suffers from limited resolution. We further apply the proposed method to the GO_3D_OBS benchmark model. The results show a clear enhancement in the resolution and accuracy of shallow velocity structures after redatuming, confirming the effectiveness of the proposed workflow for OBS seismic imaging in the presence of complex bathymetry.
How to cite: Zhou, X., Gorszczyk, A., and Guo, G.: Topography-dependent first-arrival traveltime and slope tomography with redatuming for improved velocity imaging: applied to ocean-bottom seismometer data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18891, https://doi.org/10.5194/egusphere-egu26-18891, 2026.
Petit-spot volcanoes are small-volume alkaline volcanic features that form on the seafloor of the outer-rise region of subduction zone. Their tectonic significance became evident in the early 2000s, when it was recognized that they are not related to mantle plumes or hotspots, but instead are likely associated with fracturing induced by plate flexure. The prevailing hypothesis suggests that as an oceanic plate approaches a subduction zone, it bends and undergoes extensional stress - particularly at its base - leading to the formation of deep-seated fractures. These fractures provide pathways for small volumes of melt to migrate upward and reach the seafloor. Petit-spot volcanoes also play an important role in modifying the physical and chemical parameters of the incoming plate. However, several aspects of their genesis remain uncertain, particularly how large-scale fractures develop within the lithosphere and how these structures manifest within the oceanic crust and uppermost mantle.
To gain insight into the geological architecture underlying the petit-spot volcanic province at the Japan Trench, we employ high-resolution seismic imaging techniques integrated with magnetic observations. Our analysis is based on a full-waveform inversion (FWI) velocity model constrained by ocean-bottom seismometer (OBS) data, complemented by reverse time migration (RTM), kinematic migration (KM), bathymetry, and magnetic anomaly data.
The FWI velocity model forms the foundation of other imaging results and is rigorously validated through real-synthetic data fitting, which demonstrate a strong agreement between both waveforms. Compared to previous tomographic models for this region, the improved kinematic accuracy and resolution enable imaging at greater depths and allow the interpretation of fine-scale features, highlighting velocity contrasts and structural interfaces. Migration results further confirm the robustness of the velocity model by accurately positioning deep structures near the Moho discontinuity and providing improved images of fault-related structures that cut through the crust and locally disrupt the Moho.
The velocity model reveals a layered oceanic crust with pronounced lateral heterogeneity. We identify three prominent low-velocity zones (LVZs) within the crust. The westernmost LVZ extends laterally beneath a strongly reflective Moho and is interpreted as a hydrated and mechanically weakened lower crust associated with bending-related faulting. Two additional, more localized LVZs are bounded by steeply dipping discontinuities that extend from the seafloor into the upper mantle, indicating deep fault zones capable of channeling fluids. Beneath the Moho, reduced seismic velocities in the uppermost mantle near the trench suggest significant serpentinization, consistent with the presence of bending-related faults and proximity to the subduction zone. Farther seaward, mantle velocities increase, indicating reduced hydration. A distinct high-velocity mantle domain is identified farther east, separated by sharp discontinuities that correlate with variations in Moho reflectivity and magnetic anomaly patterns.
Comparison with bathymetric and magnetic data reveals that deep seismic structures align with intersections of bending-related normal faults and abyssal-hill faults, as well as with a fossil propagating spreading center. These observations demonstrate that inherited tectonic fabric exerts a strong control on fault penetration depth, mantle hydration, and the crust–mantle architecture of the petit-spot volcanic province at the Japan Trench.
How to cite: Górszczyk, A. and Amirzadeh, Y.: Crust–Mantle Architecture of the Pacific Plate Beneath the Japan Trench Petit-Spot Province Revealed by Seismic Imaging and Magnetic Anomalies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9390, https://doi.org/10.5194/egusphere-egu26-9390, 2026.
The geological structure of the Japan Trench outer-rise is complex due to the deformation of the subducting oceanic crust. This region underwent structural modification due to subduction-related plate flexure, which facilitated the development of bending-related faults and the formation of petit-spot volcanoes. These tectono-magmatic processes increased fracturing, hydration, and porosity and decreased the continuity of reflectors, all of which adversely affect seismic wave propagation. Additionally, the emplacement of these magmatic features, such as dikes and sills, introduces structural heterogeneities that scatter seismic energy, making the seismic imaging of this geological setting difficult.
In this study, we investigate the upper crustal structure of the oceanic plate at the Japan Trench outer-rise using two-dimensional multichannel seismic (MCS) reflection data acquired by JAMSTEC during cruise KR15-07 with a 6 km long, 444-channel streamer. The study area has a water depth of approximately 6 km, and this deep-water setting, combined with the limited streamer length, restricted offset coverage, and posed significant challenges for seismic reflector imaging in the upper oceanic crust.
The first goal of this study is to determine the depth of the sedimentary layers and to identify normal faults associated with the subduction of the oceanic plate. To achieve this, we first apply standard processing steps and prestack time migration, followed by the prestack depth migration to obtain the final reflectivity model.
As a second objective, we estimate an acoustic impedance model from the migrated reflectivity section using a regularized inversion framework. Acoustic impedance is known as an identifier of the subsurface properties that are related to lithology, porosity, pore filling, and other factors that characterize the subsurface. The problem of estimating acoustic impedance using reflection series data can be expressed as an inverse problem. In our case, the inversion incorporates a combined Tikhonov–Total Variation (TV) regularization scheme, optimized for reconstructing piecewise-smooth models. This formulation decomposes the impedance model into a smooth component, constrained by Tikhonov regularization, and a blocky component, constrained by the TV regularization. This hybrid approach mitigated the limitations of individual regularization methods.
According to the obtained results from reflectivity and the acoustic impedance models, bending-related normal faulting and petit-spot volcanism significantly modify the upper crust, producing strong lateral heterogeneities within the sedimentary section.
How to cite: Amirzadeh, Y., Górszczyk, A., and Singh, B.: Reflectivity Imaging and Impedance Inversion of Seismic Data from the Outer-Rise Area of the Japan Trench, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18960, https://doi.org/10.5194/egusphere-egu26-18960, 2026.
