Among others, the session may 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: Wed, 30 Apr | Room K2
In recent years, the deployment of extensive passive seismic arrays across Western Australia has significantly advanced our understanding of lithospheric structures. At the forefront of these efforts is the WA Array program, a transformative 10-year initiative featuring 1,600 broadband stations spanning the entire state of Western Australia. Launched in late 2022, the program has started generating a highly valuable dataset. The data and model outputs from Phase One (from December 2022 to December 2023) mark a long-term effort to compile a state-wide, high-resolution model that will evolve over the course of the program. By integrating this new data with insights from past and ongoing geophysical, geochemical and geological studies, the project aims to unravel the intricate lithospheric structure of the region, ultimately creating detailed models that illuminate Western Australia’s geological history and evolution.
Initial findings reveal significant shallow and crustal features. Measurements of the very shallow subsurface show strong correlation with tectonic setting and also mapped palaeovalleys which have uses in estimation of seismic hazard for engineering projects and potential targets for mineral exploration. Crustal models show significant lateral and vertical variations across geological domains, with the Perth Basin standing out as a prominent low-velocity zone, indicative of basin infill and history of the rifting along the margin of the adjoining craton. The Moho displays flat, distinct transitions in cratonic regions but varies west of the Darling Fault, reflecting the region’s complex tectonic setting. A pervasive NE-SW trend in Moho depth, seismic velocities, and isotopic data suggests compositional segmentation of the Yilgarn Craton into discrete blocks, challenging lateral accretion models and highlighting the influence of deep structures on crustal evolution and resource distribution. Lithospheric imaging further reveals compositional and thermal variations, including deep tectonic features beneath the Yilgarn Craton. An estimate of the lithosphere-asthenosphere boundary exhibits strong spatial correlations between the maximum gradient of the boundary with surface mineralization zones. These observations support the idea that tectonic architecture exerts a fundamental control on resource deposits, consistent with established theories linking deep lithospheric processes to mineral systems. These findings provide valuable insights into the tectonic evolution and resource potential of Western Australia.
How to cite: Ebrahimi, R., Murdie, R., Yuan, H., O'Donnell, J. P., Johnson, S. P., and Gessner, K.: Shaping Western Australia's Geological Framework: Insights from the WA Array Phase One, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1672, https://doi.org/10.5194/egusphere-egu25-1672, 2025.
The structure and dynamics of the upper mantle control tectonics, seismicity, magmatism, and the development of mineral deposits. Seismic tomography maps spatial variations in seismic velocity and offers essential information on the variations of temperature in the mantle, the thickness and mechanical strength of the lithosphere, and the convection patterns below it. Thanks to the growth in the station coverage, tomographic models of Asia reveal increasingly detailed structures.
Here, we present a new waveform tomography model, ASIA2024, constrained by massive global and regional datasets. The data coverage used to construct ASIA2024 is maximised across the hemisphere centred at Asia. In China, in particular, dense national network data enhances the sampling. Our waveform tomography extracts structural information from surface waves and from S and multiple S body waves. The effects of errors are suppressed by statistical and targeted outlier analyses and the removal of the least mutually consistent data.
Extensive comparisons of contemporary tomographic models reveal both consensus features and differences between models and demonstrate relative advantages of different approaches and data types. ASIA2024 advances the resolution of the imaging compared to the state of the art at the scale of the continent. A prominent high-velocity anomaly at lithospheric depths shows the Indian cratonic lithosphere underthrusting and subducting beneath Tibet. In the transition zone below the plateau, a fragmented high-velocity anomaly indicates lithospheric remnants, probably from different phases of subduction. The lithosphere beneath most diamondiferous kimberlites—originally emplaced on thick cratonic lithosphere—is observed to be still thick at present. Relatively low velocities at kimberlite locations are indicative of craton-lithosphere thinning and are detected beneath northwestern Siberian Craton (Siberian Traps) and most of the Indian Shield (Deccan Traps and surroundings), with the exception of the intact cratonic lithosphere beneath northeastern Dharwar Craton. This suggests that the mantle plumes responsible for the traps have eroded the deep cratonic lithosphere.
Thin lithosphere and recent basaltic volcanism are observed in eastern Sino-Korean and Yangtze Cratons, with subduction, stretching, and rifting likely to have weakened and modified their cratonic roots. Cenozoic basalts are found exclusively where the lithosphere is observed to be thin. Beneath the Hainan volcanic region, a low-velocity anomaly is observed throughout the upper mantle, consistent with the previously proposed Hainan Plume feeding the magmatism. The shape of the anomaly indicates a complex morphology of the upwelling. Low-velocity anomalies in the mantle transition zone beneath the Hangai Dome and southern Siberian Craton are consistent with hot upwelling(s) and horizontal asthenospheric flow feeding the dispersed basaltic volcanism.
Sediment-hosted metal deposits tend to be located near contrasts in the thickness of the lithosphere, including craton boundaries and other substantial heterogeneities.
Intraplate seismicity is controlled by plate-boundary stresses and lateral variations of the lithospheric thickness and strength. Areas with relatively thin lithosphere across Asia tend to localise deformation and seismicity. The Gujarat seismic zone in India is collocated with an area of warm, thin lithosphere. This suggests a relationship between the occurrence of devastating earthquakes there and deformation in the mechanically weak part of the plate.
How to cite: Xu, Y., Dou, H., Lebedev, S., Chagas de Melo, B., van der Hilst, R., Wang, B., and Wang, W.: The upper mantle beneath Asia from seismic tomography, with inferences for the mechanisms of tectonics, seismicity, and magmatism, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1878, https://doi.org/10.5194/egusphere-egu25-1878, 2025.
The asthenosphere is commonly defined as an upper mantle zone with low velocities and high attenuation of seismic waves, and high electrical conductivity. These observations are usually explained by the presence of partial melt, or by a sharp contrast in the water content of the upper mantle. Low viscosity asthenosphere is an essential ingredient of functioning plate tectonics. We argue that a substantial component of asthenospheric weakening is dynamic, caused by dislocation creep at the base of tectonic plates. Numerical simulations of subduction show that dynamic weakening scales with the surface velocity both below the subducting and the overriding plate, and that the viscosity decrease reaches up to two orders of magnitude. The resulting scaling law is employed in an apriori estimate of the lateral viscosity variations (LVV) below Earth's oceans. The obtained LVV help in explaining some of the long-standing as well as recent problems in mantle viscosity inversions. This work has been supported by the Czech Science Foundation through project No. 23-06345S
Figure 1. Dynamic weakening below Earth’s oceanic plates. Vectors show the absolute plate velocities derived by Müller et al. (2019), obtained with a freely available software package GPlates. Sublithospheric dynamic weakening, w, showed in color, is computed from these velocities using our empirical law, w = 1.5 [1 − exp(−0.3 vP )]. The quantity w represents a first-order estimate of the LVV in the asthenosphere. Grey areas depict Earth’s continents, black and white lines show the major trenches and ridges, respectively (Coffin, 1998).
References:
Patočka, V., Čížková, H., & Pokorný, J. (2024). Dynamic component of the asthenosphere: Lateral viscosity variations due to dislocation creep at the base of oceanic plates. Geophysical Research Letters, 51, e2024GL109116. https://doi.org/10.1029/2024GL109116
Müller, R. D., Zahirovic, S., Williams, S. E., Cannon, J., Seton, M., Bower, D. J., Gurnis, M. (2019). A global plate model including lithospheric deformation
along major rifts and orogens since the triassic. Tectonics, 38 (6), 1884-1907, doi: 10.1029/2018TC005462
Coffin, M. (1998). Present-day plate boundary digital data compilation. University of Texas Institute for geophysics technical report, 174 , 5.
How to cite: Patočka, V., Čížková, H., and Pokorný, J.: Dynamic Component of the Asthenosphere: Lateral Viscosity Variations Due To Dislocation Creep at the Base of Oceanic Plates , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6882, https://doi.org/10.5194/egusphere-egu25-6882, 2025.
High seismic velocity keels extending to depths greater than 200 km underlie the oldest parts of continents, the Precambrian cratons. Although mantle xenoliths suggests that these keels formed early in Earth’s history, the preservation of deep, cold, and highly viscous roots for hundreds of millions of years in a convective mantle remains enigmatic. A classical view is that the excess density due to colder temperatures is compensated for by a light composition that stabilizes high viscosity roots. Here, we map the magnesium number (Mg#, a proxi for mantle depletion) and the Modal content of olivine within cratonic keels, based on the thermochemical interpretation of a global shear velocity model. This thermochemical interpretation requires mineralogical depletion and a decrease of compositional density beneath Precambrian cratons. We observe that depletion is strong above 150 km (Mg#>92), and decreases with depth down to the lithosphere-asthenosphere boundary (LAB). These conditions ensure cratons’s preservation for hundred to billions of years in a convective mantle, in agreement with mantle xenoliths suggesting that high viscous keels formed early in the history of cratons
How to cite: Debayle, E. and Ricard, Y.: Mapping depletion of continental roots with seismic waves., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11678, https://doi.org/10.5194/egusphere-egu25-11678, 2025.
We present a summary of all our seismological models based on surface wave observations. First, wen have updated our global SV model that is based on the waveform modelling of more than 3 millions Rayleigh waves recorded since 1976. The tomographic model is built using the same automated scheme as was presented in Debayle et al., GRL 2016, while the number of data has increased by a factor larger than 2. Second, we present new SV wave velocity and radial anisotropy, ξ, global model obtained from the joint inversion of multi-mode Rayleigh and Love wave data. The Rayleigh dataset has been also used in previous studies to constrain the azimuthal anisotropy, the quality factor Q and the melt content. All these models are based on self-consistent datasets and have been obtained with similar regularization and smoothing. All together they confirm that (1) there is no age dependence of the radial anisotropy ξ in the oceanic lithosphere while age is the main parameter controlling Vsv, (2) Positive (ξ > 1) radial anisotropy extends deeper (down to 300 km depth) beneath oceans than beneath continents (3) melt content and azimuthal anisotropy have a significant dependence with age under oceans, particularly under fast plates, (4) cratons appear fast, melt-free and anisotropic, down to 250-300 km depth for the azimuthal anisotropy and down to 150-200 km for the radial anisotropy, a depth coinciding with the detection of a positive velocity gradient, (5) ξ ≤ 1 anomalies are present in the deeper part of the cratonic roots (200-250 km) that could reflect past delamination or compression of the deep lithospheric roots. Out of these observations, we propose a conceptual model that enables reconciling a number of seismic observations. Finally, will present our new online tool (https://fascil.univ-lyon1.fr/) available to explore these tomographic models and to compare with existing ones.
How to cite: durand, S., ricard, Y., dubuffet, F., and debayle, E.: Global SV wave upper mantle model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12952, https://doi.org/10.5194/egusphere-egu25-12952, 2025.
Seismic observations are usually inverted for seismic velocity structure (Vp and Vs). By using Markov-chain Monte Carlo (McMC) inversion (i.e. solving the forward model and comparing it to the data many times and exploring the virtual space of possible solutions), it is possible to directly invert for rock type as a categorical variable (rather than its constituent minerals and parameters). McMC also manages any non-linear relationships that rock constituents and parameters may have with velocity that could result in non-convergence of a linear inversion.
We have developed a theoretical and software framework to perform an inversion of surface wave dispersion and P-wave tomography directly to crustal rock type and, by fixing surface and lithosphere-asthenosphere boundary temperature, temperature gradient.
This approach constrains the inversion to petrologically valid models rather than the larger space of seismologically valid models. Additionally, knowledge of rock type helps to facilitate interpretation by inferring, from the seismic observations, the various lithologies in an unbiased manner. In the crust, the forward model for inferring Vp, Vs, and density from rock type is slow. To overcome this, we calculate a look-up table of seismic properties for crustal rocks as a function of pressure and temperature.
We demonstrate the method with a synthetic test that shows that velocity and the silica content (mafic-felsic) of crustal layers can be reliably recovered as well as some indication of the main constituent minerals. Temperature and exact mineral assemblage are poorly constrained. A test transect of seven stations in the Eastern Alps indicate a mainly felsic upper crust with a more intermediate lower crust. Temperature, although not well constrained, shows an increase where historic magmatic activity between two major tectonic faults has been previously inferred.
How to cite: Mroczek, S., Tilmann, F., Zertani, S., John, T., Kästle, E., and Ke, K.-Y.: Joint inversion of surface dispersion and P-wave tomography for temperature and lithology: Methodology and case study in the Eastern Alps , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17757, https://doi.org/10.5194/egusphere-egu25-17757, 2025.
We perform a comprehensive analysis of P-to-S and S-to-P receiver functions to investigate the lithospheric discontinuities across the Eastern Alps, Pannonian Basin, Carpathians, and Dinarides. The Pannonian Basin, situated in Central Europe, is characterized by thick sedimentary deposits of up to 7 km, resting on a crystalline basement. This basin is enclosed by young orogens, which exhibit thick crust due to prior tectonic activities, such as subduction and collision.
In this study, we provide several new geophysical maps derived from receiver function analysis, including the first detailed maps of sedimentary thickness, Conrad discontinuity, Moho depth, upper and lower crustal thickness, and lithospheric thickness. Our results reveal significant Moho depth variations: from 20-26 km beneath the sedimentary basins to 40-45 km beneath the Eastern Alps and Southern Carpathians. Additionally, we report that the lithosphere is relatively shallow (<90 km) in the Pannonian Basin, while in surrounding orogens, it deepens to 90-140 km, with corresponding variations in surface heat flow values.
Further, we analyse topographic signatures, such as actual, residual, and dynamic topography, to assess the contributions of mantle and crustal processes, as well as surface dynamics. Our findings provide crucial insights into the tectonic evolution and structure of the region, enhancing our understanding of the complex interplay between crustal thinning, lithospheric dynamics, and surface topography.
How to cite: Kalmár, D., Balázs, A., Petrescu, L., Hetényi, G., Stipčević, J., Kovács, I. J., and Bondár, I.: Mapping Lithospheric Discontinuities and Residual Topography in the Pannonian Basin and Surrounding Orogens, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-28, https://doi.org/10.5194/egusphere-egu25-28, 2025.
While extensively studied and well understood in certain regions, the Canadian Shield still presents significant challenges and uncertainties in its northern areas, particularly within the Churchill Province. Two major unresolved aspects in this region are the precise determination of Moho depth and the characterization of anisotropy.
To address these gaps, this study employs DeepRFQC, a state-of-the-art technique for rigorous quality control of receiver function signals. By analyzing all available signals across the area, DeepRFQC ensures that only high-quality data are selected, providing a robust foundation for subsequent analyses.
We used H-k stacking and Harmonic Decomposition to investigate the lithospheric structure. Calculated kappa (κ) values showed strong agreement with gravity data, underscoring the reliability of the results. Harmonic Decomposition revealed anisotropy patterns consistent with the regional stress field, offering new insights into the tectonic processes.
These findings suggest that the observed seismic anisotropy is closely aligned with the region’s predominantly NE-SW geological structures, providing a clearer understanding of the Churchill Province's lithospheric dynamics.
How to cite: Sabermahani, S. and Frederiksen, A.: Understanding the Northern Canadian Shield: Moho Depth, Anisotropy, and Tectonics from Receiver Functions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-495, https://doi.org/10.5194/egusphere-egu25-495, 2025.
The Eastern Mediterranean region is characterized by a complex tectonic setting, where the African and Arabian plates converge. This makes Lebanon a seismically active zone that has experienced major destructive earthquakes and could experience similar catastrophic events in the future. Accurate earthquake localization strongly depends on the velocity model used for event location (Gesret et al., 2015). Thus, it is of primary importance to characterize the subsurface structure in order to better locate and understand this seismicity. Characterizing the subsurface crustal structure beneath Lebanon remains challenging due to limited geophysical acquisitions. In this work, we use the P-wave receiver function method to image the subsurface structure beneath two permanent broadband stations, “BHL” and “HWQ”, operational since 2006, which offer a good azimuthal coverage required to characterize dipping interfaces or crustal anisotropy. This study is extended to include several temporary broadband stations distributed across the country to investigate variations in crustal thickness between different regions. Beneath the “BHL” station in western Lebanon, Bayesian inversion of arrival times for PS and PpS phases identifies a Moho boundary at a depth of 33 km, dipping 12° to the southeast. The uncertainties associated to this solution are also estimated thanks to the probabilistic framework. The dip direction aligns with the geological structures of the region. Beneath the “HWQ” station in northern Lebanon, inversion of arrival times and polarities of PS phases from two interfaces suggests an anisotropic lower crustal layer, with a slow axis plunging southwest. This study enabled us to image the crust beneath several broadband permanent and temporary stations and will contribute to the development of a 3D velocity model for Lebanon. In this work, earthquakes are localized using the probabilistic localization method, which will be compared to the deterministic approach commonly used by the National Center of Geophysics in Lebanon. This probabilistic method also provides uncertainty estimates, and allows to compare several velocity models in order to select the best velocity model to be used for event locations in Lebanon.
References
Gesret, A., Desassis, N., Noble, M., Romary, T. & Maisons, C. (2015). Propagation of the velocity model uncertainties to the seismic event location. Geophys. J. Int. (2015) 200, 52–66.
How to cite: Janbein, A., Gesret, A., Brax, M., and Makhoul, N.: Seismic imaging of the crustal structure beneath Lebanon and localization of earthquakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-586, https://doi.org/10.5194/egusphere-egu25-586, 2025.
How the Tibetan Plateau deformed in the Indian-Eurasian continental collision has been long debated, more specifically, over the relationship between the deep processes and surface structural complexity. Here, we use ambient noise tomography to obtain a high-resolution crustal S-wave velocity model beneath the Tibetan Plateau and adjacent areas involving a comprehensive dataset from over 500 stations. Our images reveal that the crustal flow should be in a limited scale according to the intermittent low-velocity zones (LVZs) observed in the middle crust at 20–40-km depth of the Tibetan Plateau. The distributions and strengths of LVZs further imply that different deep processes promote the surface deformation in various regions of the Tibetan Plateau. The LVZs in the northern plateau, collocated potassic magmatism and low velocity anomalies in the upper mantle, should be originated from the lithospheric delamination. However, in the southern plateau, the S-wave velocity showed an apparent lateral segmentation feature correlated with the north-south trending rifts. The feature indicates that the LVZs were likely controlled by the lateral tearing of the subducted Indian mantle lithosphere, which promotes the rifting deformation. Moreover, the LVZ in the central Tibet should have contributed to the formation of the conjugate strike-slip fault system. In the Tarim Basin, our model showed a high-velocity anomaly in the lower crust that may be related to ancient mantle plume activity.
How to cite: Tan, P., Chen, Y., Liang, X., Li, W., and Wu, C.: Crustal structure of the Tibetan Plateau and adjacent areas revealed from ambient noise tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9801, https://doi.org/10.5194/egusphere-egu25-9801, 2025.
Heterogeneities in subglacial geology and crustal properties can play a major role in determining the boundary conditions at the crucial interface between the solid earth and the cryosphere in Antarctica. Geothermal heat flow, a parameter closely tied to regional geology, can particularly influence the behaviour of the overriding icesheet. However, direct geological samples which could inform understanding of heat flow and other geological parameters are limited to ice free regions along the coast, high mountain ranges or isolated nunataks, while the origin of geological material transported by glaciers themselves is often ambiguous. Geophysical joint inversion of gravity and magnetic data can therefore play a key role in constraining the geological and crustal properties of the rocks hidden beneath the ice.
We present a 3D crustal model of Wilkes Subglacial Basin and Transantarctic Mountains based on joint inversion of airborne gravity and magnetic data using the “Variation of Information” inversion algorithm incorporated in the software JIF3D. The applied “Variation of Information” technique enforces a coupling in the objective function between inverted susceptibility and density distribution during the inversion. The objective function is minimized iteratively until a reasonable mismatch between observed and inverted data is reached. The coupling ensures that identical geometries in the inverted density and susceptibility distribution are found relating to shared gravity and magnetic sources. This technique provides an enhanced inversion result for interpreting subglacial geology since inverted geometries relate to both petrophysical quantities compared to separately inverting for density and susceptibility distributions.
Our model reveals a large body located in the interior of Wilkes Subglacial Basin interpreted as a batholithic intrusive structure, as well as a linear dense body at the margin of the Terre Adélie Craton. Density and susceptibility relationships of the anomalous bodies, together with their shapes in 3-dimensions are used to inform the composition and the origin of these crustal bodies. Comparing the density and susceptibility values recovered by our inversion with measurements on Antarctic rock samples indicates that the postulated batholitic intrusion is granitic in composition, but distinct from the Granite Harbour Igneous Complex described previously in the Transantarctic Mountains area. Emplacement of such a large volume of intrusive granite can potentially elevate local geothermal heat flow significantly, due to relative concentration of radiogenic heat producing elements such as U, K and Th. Finally, we present a new conceptual tectonic model for the region based on the inversion results, which includes passive margin development ~670 Ma, with the emplacement of the batholith intrusion before the Granite Harbour Suite.
How to cite: Lowe, M., Jordan, T., Ebbing, J., Moorkamp, M., Green, C., Lösing, M., Riley, T., and Larter, R.: The 3D Crustal Structure of Wilkes Subglacial Basin and Transantarctic Mountains in East Antarctica - inferred from Joint Inversion of airborne gravity and magnetic data., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5692, https://doi.org/10.5194/egusphere-egu25-5692, 2025.
In February 2023, Türkiye suffered two strong earthquakes with a scale of more than 7 Mw, causing serious human and property losses. Previous studies have been conducted close to this area, indicating that lithospheric deformation is mainly controlled by the strong interaction of the surrounding converging plates and is significantly influenced by the distribution of deep fluids. However, due to the sparse observations and resolution of seismic and electromagnetic imaging of subsurface structures, no high-resolution image reveals the relationship between deep structures and strong earthquakes in this region. An international cooperation project is funded to use seismology and electromagnetic data to understand deep structures and processes better. This study aims to apply the newly developed seismic technique to describe the geometry of the key interface in the lithosphere, and newly deployed MT data to reveal the distribution of fluid/partial melt. Constricting the content and spatial distribution of deep fluid, the deformation mechanism, and the fluid behavior of lithosphere under plate interaction will be discussed. The detailed results will be presented in this meeting.
How to cite: Deng, Y., Zhang, Z., Özyıldırım, Ö., Varilsuha, D., Li, X., Avsar, U., Yildiz, A., Bagci, M., and Kocaoglu, G.: Lithospheric structure beneath east Türkiye and implications for the 2023 doublet earthquakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1951, https://doi.org/10.5194/egusphere-egu25-1951, 2025.
The South China Sea (SCS) and its adjacent regions lie at the junction of the Eurasian, Pacific, and Indian plates, characterized by complex tectonic evolution and diverse lithospheric features. This study integrates magnetic anomaly, gravity, and heat flow data to investigate the lithospheric thermal structure, effective elastic thickness (Te) distribution, and dynamic processes in the region. Curie depth was constrained using EMAG2 magnetic anomaly data with traditional and improved centroid methods, and the lithospheric thermal structure was calculated using the steady-state heat conduction equation. Te was derived from the fan wavelet coherence method based on WGM2012 gravity data, topographic data, and Moho depth models, providing a comprehensive understanding of the thermal and mechanical properties of different tectonic units.
The results reveal that the lithosphere in the SCS basin is thin (40–50 km) with high geothermal gradients and heat flow, resulting in low thermal and mechanical strength and Te values of 10–15 km, indicative of young oceanic lithosphere. In contrast, the northern continental margins exhibit thicker lithosphere (>80 km) with lower heat flow and higher rigidity, reflected in Te values of 25–35 km, which align with craton stability and compressional forces from the Eurasian plate. Transitional crustal regions, such as the Xisha and Nansha Islands, exhibit intermediate lithospheric thickness (50–70 km), geothermal gradients, and Te values (10–20 km), representing a transition between oceanic and continental lithosphere. The subduction zones, such as the Manila Trench, display combined characteristics of lithospheric bending and mantle wedge thermal anomalies, with outer trench regions showing Te values of 15–25 km, while forearc regions exhibit significant weakening with reduced Te.
Dynamic analysis suggests that the diverse lithospheric thermal structure and Te distribution in the SCS reflect the combined effects of seafloor spreading, subduction, and extensional deformation. High temperatures and thin lithosphere in the basin support its extensional setting; low-temperature, high-Te features of continental margins indicate compressional deformation; transitional crust reflects dual controls from continental extension and oceanic spreading; and subduction zones demonstrate complex mechanical interactions, including lithospheric bending, compressional stresses, and mantle upwelling, which significantly impact lithospheric dynamics.
This study provides new insights into the thermomechanical and dynamic evolution of the lithosphere in the SCS and adjacent regions, offering a robust framework for regional tectonic and geophysical research.
How to cite: Hou, J., Fang, J., and Braitenberg, C.: Lithospheric Thermal Structure and Dynamic Processes of the South China Sea and Adjacent Regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4865, https://doi.org/10.5194/egusphere-egu25-4865, 2025.
Although the ease and accuracy of seismic interpretation are continually increasing thanks to the increasing amount of available data, computing power and new automatic interpretation techniques, it is still challenging to resolve fine-scale geological features at depth (e.g. faults) because of physical limitations. Indeed, seismic imaging techniques are based on frequency band-limited seismic data, and therefore they can only recover a smooth version of the true Earth, which is not suited for a proper geological interpretation below the decametric scale. Uncertainties and pitfalls in the interpretation of these fine-scale features can affect natural hazard mitigation strategies, and lead to overly optimistic model-based forecasts. To make sure that such subtle features are appropriately considered in subsurface uncertainty studies, we propose the use of a downscaling (or inverse homogenization) approach.
In this work, the downscaling is used to properly detect faults and quantify the uncertainty associated to fault parameters geometry and displacement. In particular, from a smooth representation of the real complex structures, obtained through seismic techniques, such as the well-known Full Waveform Inversion (FWI), the downscaling inversion aims to recover all the finer scale fault models compatible with the FWI solution. Because this is an ill-posed inverse problem, the inversion is cast into a Bayesian framework, which combines the information at larger scale coming from the data (FWI model) with some a priori knowledge on the fault structures in order to retrieve a probability distribution over the possible fine-scale models. A Markov Chain Monte Carlo (MCMC) algorithm is adopted to sample the model space and numerically evaluate the posterior probability distribution. This involves the stochastic generation of velocity model realizations where fault displacement is computed using a kinematic modeling approach and the fine-layering velocity is obtained through geostatistical simulations.
A significant advantage of this technique is that it can be applied to downscale a localized area of interest within a larger FWI dataset, consequently reducing memory consumption and computational cost. This latter is also reduced thanks to the inexpensive forward modeling operator (i.e., the non-periodic homogenization), making the stochastic inversion feasible compared to standard MCMC-based seismic inversion methods. The proposed methodology, validated on a synthetic data-case example, proves to be a reliable approach to resolve and quantify fault-related uncertainty.
How to cite: Ruggiero, G., Cupillard, P., and Caumon, G.: Quantifying fault-related uncertainty with inverse homogenization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19393, https://doi.org/10.5194/egusphere-egu25-19393, 2025.
The geodynamics of the Alps result from the collision and interaction of the African and Eurasian plates, starting with the closure of the Neo-Tethys Ocean in the Middle Jurassic. This led to subduction, mountain formation, and tectonic shifts, including slab rollback and back-arc basin formation. These processes shaped the complex geological structure of the Alps. Simultaneously investigating the crustal and upper mantle structures is crucial for seismologists to gain a deeper understanding of the geodynamic processes shaping the study region. To reach this aim, we employ Full Waveform Inversion (FWI) on teleseismic earthquakes recorded by AlpArray, SWATH-D, and CIFALPS2 networks to develop the first 3D high-resolution elastic multiparameter FWI model, including Vp , Vs, and density, extending from the surface to 700 km depth. The analysis of FWI models at the crustal scale along the Alps captures small-scale anomalies and velocity variations along fault zones, and reveals the subducted European lithosphere beneath the Adriatic. Our results show that Moho depth increases from the southwestern to the northwestern Alps, with a deeper Moho in the Central Alps compared to the Western Alps. In the Eastern Alps, two distinct Moho structures are identified: the Adriatic Moho, which remains flat at 40 km depth, and the European Moho, which extends southward to 60–65 km and subducts along the Penninic Front. At the upper mantle scale, FWI results show continuous subduction of the European slab beneath the Po Basin to 250 km in the Western Alps, with steeper subduction in the southwest and shallower dips in the north. In the Central Alps, the slab reaches 250 km without detaching, though low-velocity anomalies suggest potential slab tearing. In the Eastern Alps, FWI models indicate vertical slab extension beneath the Tauern window, with a low-velocity anomaly hinting at asthenospheric upwelling due to slab retreat.
How to cite: Mohammadi, N., Beller, S., Monteiller, V., and Operto, S.: Crustal and Upper Mantle Structure Variation Along the Alpine Chain Using Teleseismic Full Waveform Inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1215, https://doi.org/10.5194/egusphere-egu25-1215, 2025.
The imaging of onshore salt-related features remains a persistent challenge in seismic interpretation due to the complex seismic velocity fields and wavefield interactions associated with salt structures. This study explores the feasibility of applying full-waveform inversion (FWI) to a high-resolution onshore seismic dataset acquired for the mapping of potential carbon storage targets within the Gassum region, Denmark, to improve velocity model accuracy and structural characterization of the associated salt dome. The 2D dataset, collected using a dual-element acquisition system combining large-spread nodal and densely-spaced streamer sensors, offers good spatial and azimuthal coverage, making it a suitable candidate for testing advanced inversion techniques.
In this study, we apply FWI using a multi-scale approach to address issues such as cycle skipping and convergence, with initial models derived from ray-based traveltime tomography. By leveraging both low- and high-frequency components of the seismic data and adopting a systematic approach, this feasibility study aims to assess the extent to which FWI can resolve features such as stratigraphic onlaps, fault geometries, and thinning of roof strata above the salt dome. Early results suggest that FWI can enhance the resolution of velocity contrasts and detect velocity inversions, which may lead to improved imaging of previously unmapped features, including shallow and radially divergent faults and sedimentary pinchouts. Furthermore, the integration of FWI with geological data supports the hypothesis of asymmetric dome growth due to uneven loading during its evolution. Challenges such as cultural noise, crooked acquisition geometry, topography variations, parameter sensitivity, and the need for robust initial models remain key considerations.
The study demonstrates the potential of FWI to advance the understanding of salt dome evolution and its implications for geological carbon storage (GCS) in the onshore halokinetic environment. Specifically, the ability to refine structural interpretations and resolve velocity anomalies is helpful for assessing the suitability of halokinetic domes as potential GCS sites. The methodologies tested here can be adapted for use in other salt tectonic settings, offering a pathway for more detailed subsurface characterization in resource exploration and energy transition applications.
How to cite: Westgate, M. and Malehmir, A.: Feasibility of Full-Waveform Inversion for High-Resolution Imaging of Onshore Salt Domes: Case Study from Central Jutland, Denmark, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4050, https://doi.org/10.5194/egusphere-egu25-4050, 2025.
The novel technology of Distributed Acoustic Sensing (DAS) has gained widespread adoption over the last decade and is increasingly applied across various seismic applications. However, its use in Full-Waveform Inversion (FWI) remains limited. A key challenge in utilizing surface DAS data for FWI lies in the heightened sensitivity of DAS-measured strain data to the often highly heterogeneous near-surface compared to traditional inertial measurements. This sensitivity complicates the recovery of the velocity model in deeper regions, which are typically of primary interest.
To address this issue, we propose a new misfit function defined in a time-frequency-location-wavenumber domain, extending the concepts of time-frequency misfits into the spatial domain. By interpreting DAS data as a discrete sampling of a two-dimensional time-space wavefield, rather than a collection of seismograms, we uncover a symmetry between time and space. This symmetry allows us to process the DAS data in both its original domain and the transformed domain in a consistent manner across both domains. The transformation into the time-frequency-location-wavenumber domain is achieved via a two-dimensional Gabor transform, where phase and envelope misfits are defined analogously to their counterparts in the time-frequency domain.
By comparing the sensitivity kernels derived from misfit functions in the time-frequency-location-wavenumber domain with those from the time-frequency domain, we observe a threefold improvement in sensitivity to deeper velocity anomalies relative to near-surface anomalies. This enhancement significantly accelerates, and in high-noise environments enables, the effective use of DAS data in the context of FWI.
How to cite: Shimony, E. and Lellouch, A.: A new spatio-temporal misfit function for waveform inversion of DAS data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8984, https://doi.org/10.5194/egusphere-egu25-8984, 2025.
Spatially 3-dimensional seismic full waveform inversion (3D FWI) is a highly nonlinear and computationally demanding inverse problem that constructs 3D subsurface seismic velocity structures using seismic waveform data. To characterise non-uniqueness in the solutions we demonstrate Bayesian 3D FWI using an efficient variational method called physically structured variational inference to 3D acoustic Bayesian FWI. The results contain the true velocity model, and provide reasonable posterior uncertainty estimates, at a computational cost that is only an order of magnitude greater than that of standard, deterministic FWI. Furthermore, we employ a variational prior replacement methodology to calculate Bayesian solutions corresponding to different classes of prior information, and develop an effective approach to analyse those prior hypotheses by constructing Bayesian L-curves. This provides insight into the sensitivity of the inversion process to different prior assumptions. This opens the possibility that fully probabilistic 3D FWI can be performed at a sufficiently low cost to be practical in small FWI problems, and to be used to test different prior hypotheses.
How to cite: Zhao, X. and Curtis, A.: 3D Bayesian Full Waveform Inversion and Efficient Analysis of Prior Hypotheses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8651, https://doi.org/10.5194/egusphere-egu25-8651, 2025.
The southeastern margin of the Tibetan Plateau has experienced complex tectonic deformation since the Cenozoic collision between the Indian and Eurasian plates. In this study, Empirical Greens’ Functions (EGF) are extracted from the dense ChinArray (phase I) with over 350 broadband stations covering Yunnan and southern part of Sichuan, China. High-quality surface waves are selected from the EGFs and used for the Multi-Scale Time-Frequency Full Waveform Inversion (FWI) to construct a high-resolution crustal and uppermost mantle S-wave velocity model. Our results reveal a high-velocity anomaly extending from the upper crust down to ~100 km depth beneath the inner zone of the Emeishan Large Igneous Province, interpreted as a fossilized magma plumbing system within the lower crust and lithosphere. Additionally, two long low-velocity zones are bounded by major strike-slip faults, with large earthquakes predominantly occurring along these boundaries. The Xiaojiang Fault is first identified as a well-constrained low-velocity zone, cutting through the whole crust, separating the Yangtze and Sichuan-Yunnan high-velocity blocks, while the Red River Fault delineates the boundary between the Yangtze and Indo-China blocks at the lithospheric scale. The eastern boundary of the clockwise crustal material movement beneath the Southeastern Tibetan plateau might be further confined by the Xiaojiang Fault. The strong rotation movement along the Xiaojiang Fault potentially causes the shear heating or partial melting in the crust along the fault, consistent with the distribution of active crust-origin hot springs and high strain rate from GPS observations. In summary, this model shows higher resolution than the previous studies and provides new insights into the crust-lithosphere geodynamic processes and deformation patterns.
How to cite: Yao, S., Gao, Y., Rietbrock, A., Xu, T., Yang, T., and Xiao, H.: Seismic Structure of the Crust and Upper Mantle Beneath SE Tibet Revealed by Ambient Noise Full-Waveform Inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11055, https://doi.org/10.5194/egusphere-egu25-11055, 2025.
Knowledge of the Earth's interior relies on indirect information collected at or near the surface. Typically, data do not uniquely constrain the subsurface properties and are contaminated by noise, and therefore the solution of ill-posed inverse problems is required. Geophysicists have traditionally addressed such problems through deterministic approaches, seeking a single 'best-fitting' model defined by optimality criteria that reflect our understanding of the problem at hand. In recent decades, Bayesian approaches have become increasingly common, as they characterise the posterior probability distribution of the model conditioned on the observations, thereby quantifying uncertainty.
In this context, Markov chain Monte Carlo (MCMC) methods have emerged as a crucial tool as they allow sampling from posterior distributions of arbitrary complexity. At the core of many MCMC algorithms lies the Metropolis-Hastings scheme. This combines a proposal distribution with a probabilistic acceptance criterion to construct a Markov chain that has the desired target distribution as its stationary distribution. The algorithm is versatile as it rests on mild technical conditions on the proposal, and is thus widely adopted across a broad range of geoscientific inference problems. Yet when the parameter space is large or the forward models are computationally expensive---both common scenarios in geophysical applications---it can become inefficient, resulting in poor chain mixing and slow convergence to the target (posterior) distribution. These challenges underscore the importance of effective proposal mechanisms.
In this presentation, we introduce a novel approach to designing Metropolis-Hastings proposals based on adaptive transport maps. The framework is inspired by recent developments from the field of Applied Mathematics linking Bayesian inference with Optimal Transport theory. The idea is to find a monotone, nonlinear transformation to recast a (complex) target probability distribution into a (simpler) reference distribution that is more amenable to standard MCMC steps. Our key contribution is to parameterise these transformations using invertible neural networks, ensuring monotonicity while gaining the flexibility and expressiveness that neural architectures afford.
The proposed method progresses iteratively. We begin with a standard sampling strategy (e.g., a random-walk Metropolis) to obtain initial draws from the target distribution. These samples inform the training of an invertible neural network that learns to map from the target to a simpler reference distribution, specifically a standard (multivariate) Gaussian. Subsequent proposals are then generated in the reference space, either as global independence moves or local perturbations, and are accepted or rejected following a suitably modified Metropolis-Hastings criterion. As more samples accumulate, the network's parameters are updated, improving overall sampling efficiency. Ultimately, the approach yields not only an ensemble of samples representative of the desired target distribution---just as in standard MCMC---but also a compact, learned representation of it in the network's weights.
We illustrate the proposed paradigm both theoretically and through examples. Preliminary results indicate that transport-map-enhanced MCMC has the potential to significantly accelerate Bayesian sampling across a range of applications.
How to cite: Magrini, F. and Sambridge, M.: Transport-map proposals for efficient MCMC sampling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13993, https://doi.org/10.5194/egusphere-egu25-13993, 2025.
Posters on site: Thu, 1 May, 16:15–18:00 | Hall X2
Understanding the crustal structure of the Himalayas and the geometry of the underthrusting Indian plate beneath the Himalayan arc provides crucial insights into regional tectonics and enhances earthquake hazard assessment in the region. This study focuses on the Kumaun-Garhwal Himalaya, a region that is proposed as a potential site for a future great earthquake. We obtained the 3D compressional wave (Vp), shear wave (Vs), and P-to-S wave velocity ratio (Vp/Vs) of the region. To achieve this, we employed joint inversion of body wave and surface wave datasets. This integrated approach overcomes the limitations of individual methods, providing a comprehensive view of the crustal structures. The analysis involved inverting the arrival times of 515 local earthquakes recorded at 41 broadband stations spanning the region and also analyzed continuous waveforms recorded by these stations between November 2006 and June 2008. The resulting crustal velocity structure and relocated earthquake hypocenters reveal a flat-ramp-flat geometry of the Main Himalayan Thrust (MHT). Furthermore, the findings offer critical insights into the crustal composition and its role in earthquake generation. These results enhance our understanding of the region's tectonic framework and contribute to better assessment and mitigation of seismic hazards in the Himalayan arc.
Keywords: Seismic tomography; Continental tectonics; Main Himalayan Thrust; crustal imaging.
How to cite: Ali T S, S. and Gupta, S.: 3D crustal structure of Kumaun-Garhwal (central) Himalaya from joint inversion of surface wave and body wave dataset., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-524, https://doi.org/10.5194/egusphere-egu25-524, 2025.
The crust, despite being the Earth's outermost layer, remains extremely challenging to study given its heterogeneity and complexities. High-resolution integrated tomographic studies at various scales are essential to indirectly obtain robust information on the compositional and physical properties of the crust. The Greater Alpine Crust (GAC), shaped by the Hercynian, Alpine, and Apennine orogenies, provides a natural laboratory for studying geodynamic processes at plate boundaries. These orogenies have driven the continuous evolution of the European crust from the Paleozoic era to the present day.
This study aims to obtain robust seismic constraints withing the GAC to assess lateral physical and compositional variations. Our approach primarily relies on phase velocity measurements of Rayleigh and Love waves derived from Ambient Noise (AN) tomography, and compressional-to-shear wave velocity ratio (Vp/Vs) and crustal thickness measurements obtained from Receiver Functions (RF). We then use a thermodynamic model, together with independent constraints such as petrology and heat flow data to make interpretations in terms of compositional variation of the crust.
46,041 Rayleigh and 40,028 Love dispersion curves were calculated, and maps of phase velocities were obtained from 3 to 35 seconds. Shear-wave velocity (Vs) maps were derived from surface-wave phase velocity measurements, via a Neighborhood Algorithm. The Molasse, Pannonian, Po, Adriatic, and Tyrrhenian basins are characterized by low Vs (< 2.8 km/s) down to 3 km depth. The Po and Adriatic basins are recognized as low velocity zones down to 10 km depth, with velocities below 3.5 km/s. From 15 km depth the highest velocities of the GAC are in the Tyrrhenian basin (> 4.4 km/s), where the Moho is shallow, while the continental crust presents velocities around 3.5 km/s. From 30 km depth the roots of the Alps, Apennines, Dinarides and Carpathians are clearly visible as relative low velocity zones.
Earthquake data recorded from 2015 to 2023 with a minimum magnitude of 5.5 and a maximum of 8.5, with epicentral distances from 25 to 95 degrees of the center of the study area, were used to calculate P-wave RFs at more than 400 seismic stations using iterative deconvolution. H-κ analysis was performed, using a Moho calculated from AN as a prior. Vp/Vs ratio and crustal thickness were obtained beneath each station. Within our study area, the Moho is deepest under the Alps, Apennines and Dinarides (> 50 km), and shallowest under the Hercynian basement and the sedimentary basins. The lowest Vp/Vs are found in the Moldanubian and Saxo-Thuringian belts (average ~1.70), while the sedimentary basins, and the Alpine and Apennine belts present the largest and most variable Vp/Vs (average ~1.78).
Finally, a comprehensive interpretation of crustal composition and temperature was conducted, integrating constraints from petrological data, heat flux measurements, and thermodynamic modeling. This approach resulted in a new, robust physical and compositional characterization of the GAC.
How to cite: Berger Roisenberg, H., Boschi, L., and Cammarano, F.: Physical and Compositional Characterization of the Greater Alpine Crust Using Seismic Observables, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-713, https://doi.org/10.5194/egusphere-egu25-713, 2025.
The lithosphere-asthenosphere boundary, or LAB, is a key element in plate tectonics as it separates the rigid lithosphere from the underlying convecting mantle. Its origin, though, is still not fully understood mainly due to its various definitions (thermal, compositional, etc.), which lead to different LAB depth predictions or measurements. In this study we use more than 34500 S-wave receiver functions to map the depth of the seismic LAB in Iberia and neighbouring regions. We found that the LAB in Iberia is generally shallow, especially along the eastern coast (70 km from the Gulf of Lion to the Alboran Sea) and more locally in the northwest of the peninsula. The LAB only exceeds 90 km depth in the Western Pyrenees and Iberian Range, where there is significant crustal thickening, and also in the Gulf of Cadiz. However, LAB depth and crustal thickness are not always correlated. Most of the major mountain ranges in the region (the Atlas, the Rif, the Betic System and the Pyrenees) feature areas where there is no lithospheric root, with thickened crust (>40 km) underlain by a shallow LAB (<90 km or even <80 km). The LAB depth gradient revealed that this discontinuity changes sharply along the subduction-transform edge propagator (STEP) fault in the Eastern Betics and the area of continental subduction in the Western Pyrenees. Several sublithospheric negative-velocity gradients (NVGs) also occur near these major lithospheric structures, but their origin seems diverse. The most notable NVG is an eastwards-dipping discontinuity under the Strait of Gibraltar, which we identify as the subducted lithosphere of the Gibraltar-Alboran slab. We link additional NVGs below the Alboran Sea to processes related to the slab and the STEP fault, possibly dehydration melting and/or inflow of hotter mantle materials, but the origin of a fourth NVG below the Western Pyrenees and northern Iberian Range is still up in the air.
How to cite: Parera Portell, J. A., Mancilla, F. D. L., Morales, J., Yuan, X., Heit, B., and Díaz, J.: The topography of the seismic Lithosphere-Asthenosphere Boundary in Iberia and adjacent regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-993, https://doi.org/10.5194/egusphere-egu25-993, 2025.
We present a comprehensive model of lithospheric structure extending to 300 km beneath France, derived from a joint inversion of teleseismic, gravity, and gradiometry datasets. Our analysis incorporates 27,935 relative travel time residuals sourced from the 193 French permanent seismic stations (EPOS-France), alongside 30,351 terrestrial gravity measurements and the complete gravity gradient tensor from GOCE satellite mission. The integration of these three complementary datasets enhances our understanding of lithospheric structures. Our joint inversion method allows for inverting the velocity-density relationship with independent model parametrization.
Through the velocity model, our findings reveal significant lateral variations in P-wave velocity, including a prominent orogen-parallel high-velocity anomaly that extends from the surface to a depth of 135 km, centered beneath the Pyrenees and the Southern Alps. Additionally, we identify a high-velocity body extending from the surface down to 80 km beneath the Massif Central. Notably, our density model highlights several key features, including a narrow high-density body between 10 and 40 km depth, known as the Ivrea body in the Alps. Our results are to compare with previous regional temporary inversions, especially for the northern Pyrenees where velocity and density models are not always coherent. These results contribute to a more nuanced understanding of the lithospheric dynamics in this geologically complex region.
How to cite: Dashti, F., Tiberi, C., Gautier, S., and vergne, J.: Comprehensive Lithospheric Structure of France: Joint Inversion of Seismic, Gravity, and Gradiometry Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1251, https://doi.org/10.5194/egusphere-egu25-1251, 2025.
In 2020, a comprehensive 3D reflection seismic survey was conducted over the Asse salt structure in Lower Saxony, Germany, to support the retrieval of radioactive waste from the salt mine. While the data has already been processed using conventional seismic imaging techniques, we present the results from applying the Fresnel-Volume-Migration (FVM) approach that we extended for considering anisotropy and anelastic attenuation. These enhancements aim to provide a more detailed and accurate characterization of the Asse region’s complex geology, which is crucial for the safe planning and execution of the waste retrieval process.
A wavefront construction (WFC) technique was employed to calculate the required Green’s functions for 3D anisotropic (TTI) velocity models. The WFC method was further extended to also calculate compensation traveltime fields (t*) for spatially varying Q-models. These t*-fields were then incorporated into the migration process to account for amplitude decay, phase shifts and dispersion due to anelastic attenuation, ultimately leading to a more accurate representation of subsurface reflectivity.
The method was applied to both synthetic 2D data as well as 3D subsets of the Asse seismic data set. Migration with anelastic compensation effectively corrected amplitude losses and phase distortions in the synthetic data. Furthermore, applying the anisotropic FVM to the 3D Asse data set significantly improved image quality. Additionally, the migration was performed in Common Offset Gather (COG) domain to facilitate muting of the corresponding Common Image Gathers (CIGs) and thereby significantly enhancing the quality of the resulting images.
Our study highlights the critical importance of integrating both anisotropy and anelastic attenuation into 3D seismic imaging to obtain reliable, high-resolution subsurface images. Accurate positioning and characterization of reflectors are essential for performing further quantitative seismic processing, e.g. AVO (Amplitude Versus Offset) analysis, which, in turn, facilitates more precise geological interpretations. The seismic imaging advancements developed here also offer promising applications for other applications, e.g. for mineral exploration, geothermal reservoir characterization, as well as within the radioactive waste disposal site selection process.
How to cite: Kühne, N., Hlousek, F., Buske, S., Bräunig, L., Becker, V., and Scholze, M.: Anisotropic Anelastic Fresnel-Volume-Migration of the Asse 3D Seismic Data Set, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2738, https://doi.org/10.5194/egusphere-egu25-2738, 2025.
The high amplitude J magnetic anomaly is usually described as corresponding to the M3-M0 anomalies of the M-series and marks the boundary with the Cretaceous Normal Superchron in the Central Atlantic. A seafloor spreading nature of J is undisputed, but remains debated a potential extension into the southern North Atlantic west of Iberia, with its implications for the kinematic reconstructions of the rift-to-drift transition of Iberia-Newfoundland margins. To image the structure of the J anomaly, coincident wide angle seismic, multichannel seismic and magnetic data were collected across the Mesozoic oceanic crust at ~31°N during the ATLANTIS cruise in 2022. A seismic tomography model reveals a complex velocity structure with significant lateral crustal thickness variation that is at odds with the classical view of a uniformly thick J anomaly crust. Instead of the invoked excess magma production, the structure supports complex variation of the seafloor spreading processes.
We present new magnetic modeling for the ATLANTIS profile that constrains the geometry of the magnetic layers with the seismic velocity model, the basement and Moho topography, and the crustal thickness. We first show the canonical approach of modeling the oceanic crust as a constant thickness layer with alternating polarity blocks, which is not able to match neither the amplitude nor the wavelength of anomalies, either considering constant depth or integrating top of basement topography for the magnetic layer. This may be related to the slow spreading processes that tend to cancel short wavelength anomalies and decrease the anomaly amplitude, which strongly suggests that the crustal structure should be integrated in magnetic modeling, especially of non-fast spreading crust.
We used the seismic velocity structure to constrain the thickness of the magnetic layer, either from 6.0 or 6.5km/s isovelocity contour, or varying proportionally to total crustal thickness. Our results show that the M-series domain (up to M3n) can be modeled by defining the magnetic layer thickness as ~20% of total crustal thickness and with a simplified alternating polarity sequence. For the J-anomaly domain, however, a simple relation doesn’t apply, and adjustments in the layer thickness and magnetization are required. A progressive increase in magnetization is needed from the time of M3n onwards, reaching maximum values between M1r and M0r anomalies and decreasing towards the CNS. The magnetic layer thickness follows the same tendency. However, the crustal thickness varies in a much distinct way: maximum magnetization values are modeled at the thinner crust, and intermediate magnetization is kept for the region where the crust is thicker, already located at the CNS and offset of the highest anomaly amplitude.
These results challenge the use of classical methods to model oceanic magnetic anomalies generated at slow spreading centers, and more particularly, the classical view of the J-anomaly structure. A temporal lag is suggested between the source mantle processes that originated the alteration of magma composition to higher magnetization (mantle fertility / chemical composition) and the increase in crustal thickness (likely more related to mantle temperature).
Work supported by the Portuguese FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025, UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).
How to cite: Neres, M., Ranero, C., Prada, M., Grevemeyer, I., and Gómez de la Peña, L.: Magnetic modeling of the J anomaly and M-series at 31°N, NW Central Atlantic, constrained by crustal structure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3499, https://doi.org/10.5194/egusphere-egu25-3499, 2025.
A wide range of academic and practical applications require that we interrogate the Earth’s subsurface for answers to scientific questions. A common approach is to image the subsurface properties using data recorded at or above the Earth’s surface, and to interpret those images to address questions of interest. Seismic tomograph is one such method which has been used widely to generate those images. In order to obtain robust and well-justified answers, it is important to assess uncertainties in property estimates.
To solve seismic tomographic problems efficiently, mixture density networks (MDNs) have been used to estimate Bayesian posterior probability density functions (pdfs) which describe the uncertainty of tomographic images. However, the method can only be applied in cases where the number of data is fixed, and consequently cannot be used in a large number of practical applications that have variable sizes of data. To resolve this issue, we introduce graph neural networks (GNNs) to solve seismic tomographic problems. Graphs are data structures that provide flexible representation of complex, variable systems. GNNs are neural networks that manipulate graphs. GNNs can be combined with MDNs (called graph MDNs) to provide estimates of posterior pdfs for graph data. In this study we use graph MDNs to solve seismic tomographic problems by representing seismic travel time data using a graph. We demonstrate the method using both synthetic and real data, and compare the results with those obtained using Monte Carlo sampling methods. The results show that graph MDNs can provide comparable solutions to those obtained using Monte Carlo methods for problems with variable number of data. After training, graph MDNs estimate posterior pdfs in seconds on a typical desktop computer. Hence the method can be used to provide rapid solutions for similar problems with variable sizes of data. We therefore conclude that graph MDNs can be an important tool to solve many practical tomographic problems.
How to cite: Zhang, X., Wang, Y., and Zhang, H.: Rapid Bayesian Seismic Tomography using Graph Mixture Density Networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4114, https://doi.org/10.5194/egusphere-egu25-4114, 2025.
The eastern part of the Nankai Trough is a region of intense tectonic activity where the Philippine Sea Plate subducts beneath the Eurasian Plate. Large interplate earthquakes, such as the Tonankai and Tokai earthquakes, have repeatedly occurred in this area. A notable feature of the region is the paleo-Zenisu Ridge – a ridge subparallel to the trough axis – believed to be subducting beneath the accretionary prism. Previous studies have suggested that the extent of the paleo-Zenisu Ridge is closely linked to the distribution of rupture zones for megathrust and slow earthquakes. However, the precise extent and topography of the paleo-Zenisu Ridge remain poorly constrained.
Within the long-term collaborative project we aim to reconstruct the detailed seismic velocity structure of the eastern Nankai Trough using several dense 2-D wide-angle OBS datasets to better constrain the condition of the paleo-Zenisu Ridge and evaluate its critical role in the region’s tectonic and seismic dynamics. In this study, we apply first-arrival traveltime tomography and time-domain full-waveform inversion to recover high-resolution velocity models along two parallel OBS profiles (spaced ~20 km apart) acquired by JAMSTEC in the eastern Nankai Trough. These profiles integrate OBS data from two legacy seismic dasets (KR07-10_B and KR12-12_Z04; ~4.8 km OBS spacing) with recently acquired coincident profiles (KM23-13), where OBS instruments were deployed between the receiver positions of the legacy surveys. This integration results in datasets consisting of 80 and 97 OBS per profile, with an improved spacing of ~1.6 km.
The dense OBS spacing of the combined datasets enables stable FWI application up to 8 Hz, allowing for detailed reconstruction of the underlying structure of the accretionary wedge and subducting oceanic crust. Our results, combined with other high-resolution velocity models from the Tokai area of the Nankai Trough, reveal variations in the topographic relief of the paleo-Zenisu Ridge along the subduction front axis. These findings suggest a non-uniform impact of the subducting ridge on the overlying wedge, as well as variations in stress distribution, fluid migration, and seismic coupling along the subduction interface. By leveraging additional OBS profiles and advanced inversion techniques, this study enhances our understanding of the paleo-Zenisu Ridge and its role in shaping the tectonic framework of the eastern Nankai Trough.
How to cite: Górszczyk, A., Arai, R., Fujie, G., Shiraishi, K., Nakamura, Y., Nakanishi, A., and Qin, Y.: Structural Characteristics of Subducting Oceanic Ridges in the Eastern Nankai Trough Region Derived from FWI of OBS Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4219, https://doi.org/10.5194/egusphere-egu25-4219, 2025.
Full waveform inversion (FWI) has become the standard for high resolution subsurface imaging, in both academia and the industry. FWI is formulated as a data fitting procedure, where the fit between the observed and the synthetic seismograms is improved iteratively. The synthetic seismograms are computed through the numerical solution of a wave equation, they are compared to the observed ones, and the subsurface parameters are updated to improve this fit. This optimization problem is conventionally solved using gradient based optimization strategies, which update a given initial subsurface model iteratively. These optimization approaches often fail to converge to a meaningful solution, when the initial model does not explain the kinematics of the seismic data. That is, the time shift between the observed and synthetic seismograms in the initial model is too large. This is particularly true in active seismic experiments at the crustal scale, where the data lack low frequency content.
Our strategy relies on modifying the FWI algorithm, in order to help mitigate the ill-posedness of the problem. To do so, we introduce additional parameters to the problem, which help make FWI well behaved. Our strategy makes the receiver position a free parameter, which is included in the optimization. This allows our algorithm to better explain the data kinematically, when the model estimate is poor. Our approach gives rise to a challenging optimization sub-problem, which we solve using stochastic optimization strategies: namely, Markov-Chain Monte Carlo (MCMC), Simulated annealing methods, and Particle Swarm Optimization (PSO). The latter proved to be a good candidate for our problem. We have also investigated a deterministic optimization strategy, using a dynamic programming approach. This deterministic method is less expensive than the stochastic alternatives. We test our methods using various realistic synthetic cases, obtaining promising results. This has prompted us to extend the method to 3D FWI, and perform synthetic tests, in preparation for a real 3D data application. The preliminary 3D results in synthetic settings are promising.
How to cite: Benziane, M., Brossier, R., and Métivier, L.: Designing a robust seismic full waveform inversion scheme: an extension approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5885, https://doi.org/10.5194/egusphere-egu25-5885, 2025.
In 1989, as part of a collaborative effort involving 12 research institutions and known as the BABEL Project (Baltic and Bothnian Echoes from the Lithosphere), 2,268 km of crustal-scale seismic lines were acquired in the Gulf of Bothnia and the Baltic Sea. The lines were acquired using near-vertical reflection, and wide-angle refraction methods, providing insights into the evolution of plate tectonic processes during the Paleoproterozoic era.
The offshore, near-vertical seismic data were collected using a 3 km-long cable comprising 60 groups of 64 hydrophones, positioned at a depth of 15 m. An airgun array, consisting of six identical subarrays, was used as the seismic source and towed at a depth of 7.5 m. The group spacing, shot interval, and record length varied between the lines. Specifically, in this study, the record lengths for lines 3 and 4 were 25 s, with a group spacing of 50 m and a shot interval of 75 m, while for line 2, the record length was 23 s with a group spacing of 25 m and a shot interval of 62.5 m, respectively. A sampling rate of 4 ms was used for all three lines.
Lines 2, 3, and 4 in the Bothnian Bay are located between the volcanic-hosted massive sulphide belt of Skellefte in Sweden and Vihanti-Pyhäsalmi in Finland. Given the historic value of the data and within the scope of a mineral systems workflow, we have recovered these data digitally to take advantage of modern processing and imaging solutions. Original processing showed divergent reflectivity reaching the lower crust of a Precambrian crystalline basement in the Baltic Shield. In addition, a prominent dipping reflector extending into the upper mantle was imaged, offsetting the Moho by 5-10 km. These findings led to the suggestion, for the first time, of active plate tectonic processes during the Paleoproterozoic time.
The reprocessing work reveals reflections as shallow as 1 s and shows a series of individual reflections and diffraction signals. The Moho boundary is significantly improved in terms of both its signature and trackability and, as in previous investigations, we show a set of sub-Moho reflections dipping down to 23-25 s. Not only have we brought the data to life, but we have also turned them into compelling narratives, providing an enhanced understanding of lithospheric structures in this mineral-endowed region of the world.
Acknowledgments: This work is supported by the Smart Exploration Research Center. The center has received funding from the Swedish Foundation for Strategic Research (SSF) under grant agreement no. CMM22-0003. This is publication SE25-003.
How to cite: Koufopoulou, A., Malehmir, A., and Markovic, M.: Uncovering fossil subduction in a mineral-endowed Paleoproterozoic terrain: Reprocessing legacy BABEL seismic lines from Bothnian Bay, Sweden, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7164, https://doi.org/10.5194/egusphere-egu25-7164, 2025.
Reflection seismics is indispensable for understanding the structural framework of the crust and providing important constraints on mineral system studies. The non-uniqueness inherent in interpreting data from2D crooked seismic profiles acquired over complex geological structures can be reduced by performing 3D reflector orientation analysis (Calvert, 2017), but this requires good azimuthal coverage, which can be enhanced with the deployment of cross-spreads. A new 70-km long reflection seismic profile was acquired across the Palaeoproterozoic Peräpohja belt in northern Finland to shed new light on its structural framework and contribute to development of the new national mineral exploration program. Single-receiver and single-source acquisition was implemented, resulting in excellent data quality. Survey layout was optimized to extract 3D reflector orientations, and included eight additional cross-spreads extending up to 5 km from the survey line spaced every 7-8 km.
3D reflector orientation analysis was performed for both the inline data (i.e. along the main profile) as well as with the cross-spreads included. The main challenge to processing these data is obtaining an optimal refraction statics solution: in the first pass, a combination of 2D inline statics with 2D statics for each cross-spreads was applied. In the second pass, a 3D tomostatics solution was obtained for the complete dataset. The initial results of the reflection orientation analysis suggests that while the additional effort in acquiring the cross-spreads may not be justified for obtaining the structural image (cross-spreads bring more noisy data), orientation attributes (dip and strike) are better resolved, especially at shallower levels, and where gaps in azimuthal coverage are present (i.e. the profile was too straight). With current acquisition capabilities, cross-spreads can be acquired in a cost-effective manner, yet they should be carefully planted to provide reasonable signal-to-noise ratio data, essential for 3D statics and for the orientation analysis itself.
The new seismic data were acquired as a part of the REPower-CEST “Clean Energy System Transition” project, which received funding by the European Union (number 151, P5C1I2, NextGenerationEU).
How to cite: Malinowski, M. and Calvert, A.: A field test of 3D reflection orientation analysis along a 2D crooked line in northern Finland supplemented with additional cross-spreads, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7991, https://doi.org/10.5194/egusphere-egu25-7991, 2025.
Traditional ambient noise tomography contains two steps: (1) inverting the 2D phase and/or group velocity maps at different periods based on the dispersion curves of each station pair and (2) point-wise inversion to obtain 1D shear wave velocity model at each grid node and then gather together to obtain a 3D velocity model. In the first step, most studies use the travel-time tomography method based on ray theory or 2D finite-frequency sensitivity kernel that assumes the surface wave travels along the great circle path. This could introduce travel-time biases when surface wave propagates away from the great circle in complex media and further affect the imaging results.
To consider the ray bending effect and the finite-frequency effect simultaneously and to balance the computational efficiency and accuracy, we consider modeling the propagation of surface wave by solving the 2-D membrane wave equation. Sensitivity kernels with respect to phase velocity are constructed using the adjoint method, which could capture significant deviation of the ray path from the great circle path when the velocity perturbation is larger than 20%. Checkerboard tests have been applied to demonstrate the effectiveness of the new tomography method, compared with the finite-frequency tomography method based on analytical solutions. We test our method with ambient noise data in Southern California.
How to cite: Li, Z. and Yang, Y.: Membrane Wave Equation-Based Ambient Noise Adjoint Tomography: Verification and Application, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9302, https://doi.org/10.5194/egusphere-egu25-9302, 2025.
Most published shear-wave (VS) velocity models of cratons include a VS increase with depth below the Moho, with a maximum at 100-150 km depth. This feature is seen in regional and global 3D tomography models and in regional 1D VS profiles. Taken at face value, it implies an oscillatory geotherm, with a ubiquitous temperature decrease below the Moho, which is implausible. The VS increase with depth has thus been attributed to strong compositional layering in the lithosphere. One recent model postulated widespread hydration and metasomatism in the uppermost cratonic mantle, decreasing VS just below the Moho. An alternative model suggested a strong enrichment of the lower cratonic lithosphere in eclogite and diamond, increasing VS but implying an unusual lithospheric composition. Here, we assemble a representative dataset of phase-velocity curves of Rayleigh and Love surface waves for cratons globally, including the all-craton averages, averages over regions in southern Africa, and interstation measurements elsewhere. We perform both thermodynamic and purely seismic inversions and show that the sub-Moho VS increase is not required by the data. Models with equilibrium, conductive lithospheric geotherms and ordinary, depleted-peridotite compositions fit the surface-wave data fully. A model-space mapping quantifies the strong trade-off between seismic velocities just below the Moho and at 100-150 km depth, which is the cause of the ambiguity. The reason why most seismic models contain a VS increase with depth below the Moho is regularization that penalizes deviations from global average reference models, which are much slower than cratonic VS profiles.
How to cite: Davison, F., Lebedev, S., Xu, Y., Gibson, S., Civiero, C., and Fullea, J.: Reconciling seismic and thermo-chemical models of cratonic lithosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9408, https://doi.org/10.5194/egusphere-egu25-9408, 2025.
Imaging of the Moho discontinuity in the trench-outer-rise region of the Japan Trench is a challenging task due to the structural changes that occur in the oceanic crust. This area is shaped by bending-related faults and petit-spot volcanism, which introduce fractures, hydration, and high porosity to the crust. These processes influence seismic velocities and disrupt sedimentary layers. Volcanic activity adds further complexity by creating uneven structures like cracks, dikes, and sills, which weaken seismic signals and make it harder to detect the Moho. These structural changes call for advanced seismic techniques and detailed data to accurately map the crust-mantle boundary.
In this study we examine the structure of the oceanic plate near the Japan Trench, focusing on identifying the Moho discontinuity and related crustal features. Our study relies on a 100-kilometer-long 2D seismic dataset collected by JAMSTEC in 2017. The data were gathered using 40 Ocean-Bottom Seismometers (OBS) placed 2 kilometres apart, capturing wide-angle seismic signals. Such acquisition setting provides a robust framework for analysing the subsurface with the imaging techniques employed in this study.
We employ two imaging techniques that complement each other in addressing the geological complexities of the region. First, we use Reverse Time Migration (RTM) - wavefield-based imaging approach - to produce highly detailed image of discontinuities in the crust and uppermost mantle. RTM was instrumental in identifying the high-resolution Moho and characterizing the variations in the crust-mantle interface. The method allows for handling areas with complex geological structures, such as those affected by bending-related faults and volcanic intrusions, making it an invaluable tool for this study. In addition, we address the challenges of conventional seismic imaging in regions with highly fractured crusts caused by subduction-related bending. To overcome these challenges, we employ the second technique, known as kinematic migration of slope data. The slope represent the horizontal component of the slowness vector at reciprocal receiver position (air-gun shot position) and is calculated as the difference of picked arrival times of the Moho reflection divided by the receiver distance. This approach significantly reduces uncertainties in identifying the Moho discontinuity.
The combination of RTM and kinematic migration proved highly effective in imaging the Moho discontinuity and revealed valuable details about the crust-mantle boundary. By leveraging these complementary techniques, the study successfully overcame the challenges posed by the region's geological complexity. These results demonstrate the importance of high-resolution imaging in advancing our understanding of Earth's interior. The ability to map the Moho with precision not only improves interpretations of subsurface structures but also contributes to broader tectonic and geophysical research. This study underscores the critical role of innovative methodologies in exploring complex geological environments, paving the way for future discoveries.
How to cite: Amirzadeh, Y. and Górszczyk, A.: Reverse Time Migration and Kinematic Migration Approaches for Imaging the Moho in the Outer-Rise Region of the Japan Trench, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9516, https://doi.org/10.5194/egusphere-egu25-9516, 2025.
Tibetan Plateau is resulted from the collision between India and Eurasia ca 55 Ma. The fate of the subducted Indian crust has long been debated. The Hi-CLIMB seismic experiment (Nábělek et al., 2009) presented images indicating that the southern Tibetan Plateau was under-thrusted by the Indian plate up to ~31°N, and the Indian crust was partially decoupled from the mantle below. However, the structure and the dynamics of the underlying mantle remain enigmatic. Various geodynamic models have been proposed to explain the behavior of the mantle lithosphere across this collision zone. These include hypotheses involving lithospheric delamination, rollback, tearing, etc. Further information about the lithospheric mantle beneath Tibetan Plateau is required to better understand the history and current state of this continental collision. In this study, we conduct full-waveform inversion of P-wave and its coda using 14 teleseismic events recorded by the Hi-CLIMB stations, which mainly consist of an 800-km long sub-linear array of 189 broadband seismometers spaced at 5-15 km. Our analyses yield high-resolution 3-D models for the P- and S-wave speeds along with density in the south-central Tibetan Plateau, which covers key geological features including the Genge basin, the Himalayas, and the Lhasa and Qiangtang terranes. Our model resolves P- and S-wave velocity structures from the surface down to ~400 km depth and the density structure in the uppermost 100 km. Our new 3-D multi-parameter model is integrated with results from geochemical and geothermal simulations to evaluate the existing tectonic models, which sheds new light on the state of the Indian lithosphere beneath Tibetan Plateau.
How to cite: Zhu, Q., Fuji, N., Prigent, C., Singh, S., and Zhao, L.: Full-waveform Box Tomography for the Lithospheric Structure in South-central Tibetan Plateau, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9580, https://doi.org/10.5194/egusphere-egu25-9580, 2025.
Variations of seismic wave speed, in particular shear-wave velocity (vs), are largely temperature controlled in the Earth’s mantle. Seismic tomography models thus provide us with insights into upper mantle temperature variations, the rheological configuration of the deep lithosphere and, thus, zones susceptible to strain localization within tectonic plates. With this contribution, we introduce V2RhoT_gibbs, an open-source Python tool for converting vs from upper mantle seismic tomography models to temperature and density in a self-consistent thermodynamic manner.
Our conversion approach utilizes an open-source Gibbs-free energy minimization algorithm (Perple_X), which computes the thermodynamically stable phase and mineral assemblages for a given mantle chemical composition (in terms of major oxides of the (Na2O-)CaO-FeO-MgO-Al2O3-SiO2 system) and a wide range of pressures and temperatures. Users of our tool can choose from different thermodynamic databases to constrain the Gibbs-free energy minimization and thus produce lookup tables for upper mantle pressure-temperature conditions and the associated variations in modal composition and simultaneously calculated bulk rock physical properties (e.g., seismic velocities and thermal conductivities). V2RhoT_gibbs is developed to analyze these lookup tables and hence consider the complex, non-linear relations between vs, temperature and mechanical properties. The tool corrects the pre-calculated anharmonic seismic velocities for anelastic attenuation effects and partial melts, and finally allocates thermodynamically consistent values for temperature and density to the vs‑depth-pairs in upper mantle tomographic models.
We will illustrate and discuss the differences between different chemical compositions, representing various degrees of upper mantle depletion, with respect to their effects on the vs-converted temperature and density fields. In addition, we will show V2RhoT_gibbs conversion results to discuss derived depth variations of the thermal lithosphere-asthenosphere boundary for different tectonic settings (convergent and divergent plate boundaries). Finally, we will discuss challenges and possible solution strategies regarding the interpretation of vs variations in the shallowest upper mantle.
How to cite: Bott, J., Kumar, A., Zarifikoliaee, S., May, T., Jiménez-Munt, I., Gomez Dacal, M. L., and Scheck-Wenderoth, M.: Upper mantle shear-wave velocity conversions to temperature and density: open-source V2RhoT_gibbs sheds light into challenges and possibilities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10504, https://doi.org/10.5194/egusphere-egu25-10504, 2025.
The 3D western alpine lithosphere presents a complex structure and remains subject of active geophysical investigation. In this context, we propose and apply new techniques to combine seismic and gravity data. In particular, we set up a Bayesian inversion of Bouguer gravity anomaly data for the 3D distribution of density at crustal and lithospheric scales. We use the Bouguer gravity anomaly map after Zahorec et al., (2021) across the western Alps.
In our setup, we introduce a priori information based on existing seismic tomography models (e.g. Nouibat et al., 2022), to guide the exploration of model geometries for target density distributions. We also use flexible constraints based on known ρ-vS conversion laws (e.g. Brocher, 2005), to define a pool of candidate density models consistent with rock-physics constraints and laboratory observations.
The 3D forward gravity modeling is achieved by discretizing the target volume area into unitary voxels of constant density, accounting for surface topography as well. By pre-computing the gravity effect of each voxel, we significantly decrease the computational cost of forward modeling, thus allowing an exploration of the parameter space with a Monte Carlo sampling approach. In particular, we implement a Markov chain Monte Carlo (McMC) algorithm in a Bayesian framework.
To address the lower resolution power of gravity data, we reduce the dimensionality of the model space by describing volumetric structures with a level-set approach, based on the available seismic tomographic models. This allows to 1) incorporate a priori knowledge of the crustal structure from seismic investigations into the inversion setup and 2) define complex laterally-heterogeneous density structures with a lower number of parameters. While we allow deviations from exact ρ-vS conversion laws, the bayesian framework allows to highlight existing trade-offs among density and geometry, and to tackle the non-uniqueness that often affects gravity data inversions. Finally, this setup allows to benchmark a seismic tomographic model against gravity data while providing a new density model.
We produce a new 3D density model of the western alpine lithosphere, including the Ivrea Geophysical Body at the boundary between the European and Adriatic tectonic plates. Our setup allows us to compare the resolved density values with seismic tomography models locally and with surface geology as well, providing new constraints on subsurface rock structure and composition.
How to cite: Scarponi, M., Bodin, T., and Tauzin, B.: Bayesian tomography-driven inversion of Bouguer gravity: application to the western Alps, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11926, https://doi.org/10.5194/egusphere-egu25-11926, 2025.
The Transantarctic Mountains, a major escarpment separating East and West Antarctica, are of enigmatic origin. The component of their topography which arises due to transient mantle processes (dynamic topography) can be constrained by quantifying and removing the isostatic contribution to topography to define residual elevation. In this way, insight into shaping of the Transantarctic Mountains by mantle processes can be gained. This method is dependent on accurately constraining the thickness and density of the crust and overlying ice in order to sufficiently account for isostatic loading. The TAMNNET seismic network offers an opportunity to study the crustal architecture of the northern Transantarctic Mountains using passive seismic techniques. Autocorrelations of spectrally whitened P-wave coda signals and high frequency (2 - 4 Hz) P-S receiver functions utilise ice sheet reverberations to forward model properties and thicknesses of the ice and subglacial layer. This new method allows for the presence and extent of subglacial sediment to be assessed, characterisation of the subglacial geology and hydrology based on seismic velocities and Vp/Vs ratio, and insight into the temperature of the ice sheet, all of which have important implications for ice sheet dynamics. Crustal architecture is modelled using lower frequency (0.5 - 2 Hz) receiver functions and empirical relationships between seismic velocity, density and pressure. Using these results to correct for isostatic topography and ice loading yields residual elevations of 1 - 2 km, consistent with the presence of Neogene volcanism in the region, mantle upwellings imaged in tomographic models, and thinned lithosphere identified through rare-earth element modelling of basalts from the Erebus and Hallett Volcanic Provinces. Collectively, these observations imply that dynamic mantle convective processes are integral to the origin and evolution of the northern Transantarctic Mountains, shedding light on the interplay between tectonic processes in the West Antarctic Rift System and the margin of the East Antarctic Craton.
How to cite: Dunn, A., White, N., and Larter, R.: Passive seismic insights into the subglacial environment, crustal architecture, and dynamic topography of the northern Transantarctic Mountains, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12315, https://doi.org/10.5194/egusphere-egu25-12315, 2025.
The Mariana subduction zone, with its relatively simple oceanic subduction structure and water-rich environment, serves as a unique natural laboratory for studying mantle hydration processes and the lithosphere-asthenosphere boundary (LAB). In this study, we analyze passive-source Ocean Bottom Seismometer data from stations deployed across both the forearc and incoming plate regions to investigate the S-wave velocity structure beneath the central Mariana region. By extracting multi-frequency teleseismic receiver functions and surface wave dispersion data, and applying a transdimensional Bayesian joint inversion method that explicitly accounts for water-layer effects, we achieve a high-resolution characterization of the lithospheric subsurface structure. Our findings confirm significant mantle hydration, consistent with previous studies, and reveal a distinct low-velocity zone at the LAB. Unlike conventional passive-seismic studies, which typically describe the LAB as a single sharp velocity reduction, our results indicate a rapid velocity decrease followed by an equally sharp increase, delineating a ~10 km thick melt-rich zone. Our findings highlight the importance of treating the LAB as a complex system rather than a simple boundary, as the melt-rich zone acts as a lubricant, significantly reducing viscosity and facilitating decoupling of the lithosphere from the asthenosphere, thus enabling plate motion.
How to cite: Zhang, J. and Wang, X.: Ponded Melt-Rich Zone at the Base of Lithospheric Plate in Central Mariana Revealed Using Ocean Bottom Seismometer Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14179, https://doi.org/10.5194/egusphere-egu25-14179, 2025.
The European continent undergoes a series of complicated tectonic processes since the closure of the Tethyan Ocean, including oceanic plate subduction, continental plate subduction, continental collision and orogeny. High resolution 3-D mantle structure under the European plate is key to investigate its geodynamic evolution history. Full waveform seismic inversion for mantle structure has become feasible with the advent of accurate 3D wave propagation codes and the use of adjoint sources to compute the gradient of misfit functions between data and synthetics. The adjoint source, in this approach, depends on how a misfit is defined between data and synthetics. The time or phase shift between data and synthetic has been used in most full waveform inversions for mantle structure. Waves that sample the upper mantle, however, are almost always multi-pathed due to discontinuities, the low velocity zone as well as large amplitude lateral variations, leading to complex waveforms that cannot be fully captured by time/phase shifts. Here we use the normalized correlation coefficient between data and synthetics as a misfit function to simultaneously capture both the phase and relative amplitude information of the waveform, and perform full waveform inversion on a large data set of three component seismic data from Europe. The global 3-D tomography model S362WMANI combined with crustal model EPcrust comprises our starting model. The adopted numerical solver for the wave equation is SPECFEM3D_GLOBAL, a high-accuracy numerical simulation package based on the spectral-element method. We adopt multi-stage inversion method to iteratively enhance the frequency range of the inversion. Our preliminary results show significant improved resolution of the upper mantle structure and provide key constraints on the deep subduction processes of micro-plates in the Europe region.
How to cite: Shen, H., Tao, K., and Zhao, L.: Mapping mantle structure of the European plate based on seismic full-waveform inversion methods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14243, https://doi.org/10.5194/egusphere-egu25-14243, 2025.
Surface wave tomography based on dispersion is an important approach for resolving the velocity structure of the crust and upper mantle. Traditional surface wave tomography methods based on dispersion data typically require first construction of 2D phase/group velocity maps, followed by a point-wise inversion of dispersion data to derive 1D profiles of shear wave velocity as a function of depth at each grid point, and finally forming the 3D velocity model. However, the 2D tomography method based on ray theory has a strong dependence on the selection of the initial velocity model and regularization parameters. Furthermore, the eikonal tomography method requires dense observations. Therefore, we propose a surface wave tomography method based on a physics-informed neural network, which can construct the phase/group velocity maps of multiple frequencies simultaneously, eliminating the need for repeated separate inversion for each frequency. The network comprises two branches, one branch takes in the coordinates of the virtual source and station as well as period as input to fit the observed surface wave travel times, and the other branch takes in the station coordinates and period to predict the phase/group velocity. The two branches are constrained by the eikonal equation. After the training is completed, the velocity of each grid point in each period can be quarried using the neural network and form the group/phase velpcity maps for each period. We tested the new method using data from the Feidong dense array and the Weifang dense array, and compared the tomography results with those of the traditional method. The test results demonstrate that the new method is a meshless tomography method with data adaptive resolution. In addition, this method does not require an initial velocity model or explicit regularizations. It is highly automatic, simple, and easy to use, with potential to combined with existing dispersion curve automatic extraction methods for automatic tomography without human intervention.
How to cite: Yang, S. and Zhang, H.: Physics-Informed Neural Networks for multi-frequency surface wave tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14481, https://doi.org/10.5194/egusphere-egu25-14481, 2025.
Sedimentary basins in the southern Brazilian continental margin have gained special attention in recent years due to hydrocarbon research. Detailed geodynamic models help to understand the basins' evolution, and the choice of the right constraints helps to improve them. However, the oceanic lithosphere structure in this area is poorly investigated by seismological methods, because of the lack of stations. We study the variations in the lithospheric velocity structure along the southern Brazilian passive margin using two types of databases elaborated from the records of 23 stations of the Brazilian Seismographic Network, between 2011 and 2023. The first database is composed of 4781 group velocity dispersion curves generated by 547 teleseismic events of M>5.0 that occurred in the mid-Atlantic ridge and Sandwich Islands, these curves show periods between 15 and 400s, however for higher periods than 100s there are greater uncertainties which makes the dispersion velocities too unstable to be interpreted. The second database contains 226 dispersion curves derived from 30 local events, with magnitudes between 3.0 and 4.0M, that occurred in the offshore region of the Brazilian margin, these curves show periods between 4 and 12 seconds, which sample shallow depths providing important detailed information of the stretched platform region, that can not be sampled by teleseismic data because the absence of short periods.
The regionalization was performed in both databases to identify regional patterns and obtain velocities at different points of interest, between 20 and 40 km are observed velocities with more continental signatures to the south of 20°S, which may be associated with the extension of the continental shelf, while to the north of 20°S are observed higher velocities, indicating a more oceanic lithosphere. Deeper than 40 km, the areas closer to the margin present higher velocities that decrease up to ~100km depth, as far as we have an acceptable resolution. We also observe less strong velocity anomalies with depth, reflecting a more homogeneous lithosphere. Close to 20ºS latitude is observed a negative anomaly for depths greater than 40 km, suggesting a correlation with Trindade's plume. The regionalized curves extracted in points closest to the platform are consistent with PREM continental velocities up to 30 km, while depths between 30 and 70 km present higher velocities than PREM reference model. Previous studies also found similar velocity patterns in the continental margin; however, these do not present results at shallower depths, such as close to the bottom of the crust and the top of the mantle lithosphere.
The regionalization of the local database gives us essential information up to 10km depth, where important basins and the pre-salt region are located. Despite the low quantity of curves, it is possible to observe a clear positive velocity anomaly at 5km depth, that matches with the pre-salt limits as well as with the Brazilian offshore seismicity. The final 1D inverted velocity models will be interpreted and linked with existing geological and geophysical information to improve the knowledge of the basins in the Brazilian margin.
How to cite: Rivadeneyra-Vera, C., Bianchi, M., and Sacek, V.: Lithospheric structure velocity in the Southern Brazilian margin from surface wave analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14738, https://doi.org/10.5194/egusphere-egu25-14738, 2025.
It is significant to constrain the anisotropic crustal and lithospheric structures of the North China Craton (NCC) to understand the mechanisms of craton destruction. The NCC consists of the cratonic Ordos block, the Shanxi Rift, and the severely destructed eastern NCC. The Datong volcano zone (DVZ), which is located in the northern Shanxi Rift, suggests active magmatism and volcanism during the Cenozoic. In contrast, the magma-poor southern Shanxi Rift poses a significant challenge in demonstrating the rifting mechanism and processes. Using the database from ChinArray, we obtain anisotropic Rayleigh-wave phase velocity maps by Eikonal tomography and further invert for the 3-D S-wave structure and its azimuthal anisotropy. Strong azimuthal anisotropy with fast polarization directions parallel to the edge of the low-velocity zone is revealed at a depth of 50~60 km to the west of the DVZ, which is the uppermost mantle near Moho. Our results suggest that the magmatic underplating transfers horizontally in the northern NCC and causes ongoing craton destruction by thermal and chemical erosion. We propose that the subduction of the Paleo-Asian Ocean during the Mesozoic, which is a pre-existing structure, may have contributed to lithospheric activation and localized lithospheric thinning in the northern NCC and results in the north-south differential lithospheric deformation. Similar to the Shanxi Rift, other rift systems, such as the Baikal Rift and the Eastern African Rift, may also be the consequence of the lateral motion of an adjacent cratonic block on its margins. The presence of magmatism within the rift zone is mainly dependent on pre-existing structures, such as subduction.
How to cite: Ji, C., Huang, Z., and Bokelmann, G.: Ongoing craton destruction driven by pre-existing structures in the central North China Craton, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15334, https://doi.org/10.5194/egusphere-egu25-15334, 2025.
The eastern margin of the Adriatic plate stands out for its tectonic complexity and geohazard potential in Europe, which are dominated by the northeast-directed subduction and collision of the Adriatic plate with the Eurasian plate beneath the Balkan. Beneath the southern Dinarides (northern Albania), the Adriatic plate is believed to be shallower than 150 km whereas the plate penetrates down to 200 km depth beneath the northern Hellenides (central and southern Albania). Further south, the Kefalonia transform fault system (KTFS, northwestern Greece) is believed to represent the transition from continental subduction of Adriatic plate to the oceanic subduction of the Ionian plate. Recent studies proposed different conception models including horizontal and vertical slab tearing beneath these transitions. Despite the importance of this region, seismic imaging is still insufficient to resolve these fundamental geodynamic processes.
To answer these important geodynamic questions, we employ the advanced wavefield-injection teleseismic full waveform inversion (TELEFWI) to image the seismic velocity structure beneath Albania. The TELEFWI explores waveform recordings from 9 high-quality teleseismic earthquakes recorded by 50 broadband stations from the ANTICS array (Albanian Tectonics of Continental Subduction, FDSN code X3, 2022-2024). TELEFWI reveals detailed structures from the crust down to 220 km in depth, with spatial resolution of 20 km for the P wave velocity from crust down to the upper mantle and 15 km for the S wave in the crust and uppermost mantle.
The new velocity model displays a strong eastward-dipping high-velocity anomaly in the upper mantle down to at least 150 km for the whole study domain, which we suggest to be the expression of the subducting Adriatic plate. The Adriatic plate displays westward-retreating pattern in the upper mantle to the coast beneath southern Albania. Meanwhile, multiple high velocity anomalies in depth probably indicates multi-phase slab break-off events at depths of 100 to 150 km beneath southern Albania. In contrast, the Adriatic plate remains relatively flat for over 100 km from the coast to the inland and then dips into the upper mantle beneath northern Albania, but the anomaly is relatively weaker compared to the south. Strong low-velocity anomalies in the upper crust are observed beneath the basins, probably representing the thick sediment layer.
In summary, this study provides a high-resolution velocity model for the first time based on teleseismic full waveform inversion and sheds light on the Adriatic plate configuration beneath its eastern margin.
How to cite: Gao, Y., Rietbrock, A., Frietsch, M., Agurto-Detzel, H., Kufner, S., Dushi, E., Rama, B., Koxhaj, D., Tilmann, F., Schurr, B., Yuan, X., Heit, B., and He, B.: Unraveling the Adriatic Plate Configuration beneath Albania with Teleseismic Full Waveform Inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16082, https://doi.org/10.5194/egusphere-egu25-16082, 2025.
Glaciers, which store nearly 70% of the Earth's freshwater, are undergoing significant changes due to accelerating melting caused by climate change. A better understanding of their behavior and mechanisms is therefore crucial for the years to come. To study these processes, a dense seismic array was deployed on the Argentière Glacier in the Mont Blanc massif (French Alps). The sensor array consists in 98 3-component seismic stations which continuously recorded surface displacements over 35 days in early spring 2018. This period coincided with rising temperatures and rapid glacier evolution, so the sensors captured thousands of events, mostly icequakes.
The aim of this study is to reconstruct the glacier's structure and study icequake mechanisms using elastic Full Waveform Inversion (FWI) on the 3-component data. As the data come from a passive seismic experiment, we have no information about the sources. Before reconstructing the structure it is therefore necessary to work on source parameters estimation. These parameters include spatial localization and mechanism.
First, we detect and localize the icequakes inside the glacier using a beamforming method called Matched Field Processing (MFP). The detected icequakes are observed to be located mostly at the positions of crevasses on the glacier's surface. Then, we decompose the icequake mechanism into a moment tensor and a time signature wavelet. To estimate these two parameters, we develop a joint inversion method based on waveform analysis using an iterative alternating minimization algorithm. The type of mechanism and the source orientation are then interpreted through the eigenvalue and eigenvector decomposition of the estimated moment tensor. The Fundamental Lune representation is employed to statistically study the distribution of more than 14,000 icequake mechanisms within the glacier, revealing a significant proportion of opening and closing mechanisms associated with crevasses. In certain areas, Double-Couple (DC) mechanisms can also be observed, potentially corresponding to crevasse fault slip events.
Using the estimated source parameters, FWI can be applied to reconstruct the glacier structure. A 3D synthetic crevasse model was created to mimic reality, incorporating the three observed crevasse clusters on the glacier, to evaluate the effectiveness of FWI in reconstructing the model in a given frequency-band. The parameters used in the model include S-wave and P-wave velocities, as well as density. The inversion results reveal several key findings: first, multi-parameter inversion with both S-wave velocity and density yields better results. Second, crevasses can be accurately reconstructed within the considered frequency band, provided the source parameters are well-estimated. Finally, the accuracy of source mechanism estimation significantly impacts the quality of crevasse reconstruction. Importantly, iterating between mechanism estimation and structure reconstruction yields improved results, providing promising insights.
How to cite: Grange, A., Brossier, R., Métivier, L., and Roux, P.: Glacier structure and icequakes characterization at Argentière using elastic full waveform inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16712, https://doi.org/10.5194/egusphere-egu25-16712, 2025.
The Xinfengjiang Water Reservoir (XWR) in the northwest of Heyuan city, Guangdong province, China, has hosted a large number of earthquakes since its impoundment. It is one of the reservoirs that have experienced earthquakes of magnitudes greater than 6, making it one of the most active seismic zones in Guangdong. After the significant increase in seismic activity since the reservoir water storage, many researchers have conducted a series of geophysical studies in the area. However, because of the station coverage restrictions, the detailed seismic structures within XWR have not been resolved, and the understanding of its seismic mechanism and future earthquake disaster risk are still unclear. In this study, we construct a high-resolution shear-wave velocity model in the whole crust at depths from the surface to ∼30 km based on both permanent and temporary stations deployed surrounding the XWR using ambient noise tomography. The permanent stations belong to the Guangdong Earthquake Early Warning Network, including stations equipped with broadband velocity instruments and stations equipped with acceleration strong motion instruments. The temporary stations belong to a short-period seismic array deployed surrounding the XWR in 2023, with a continuous recording duration of 30 days. The imaging results above 5 km show that, with the Heyuan-Shaowu Fault as the boundary, the XWR shows a high-speed anomaly and the Heyuan Basin shows a low-speed anomaly. We also found significant low wave velocity anomalies below the XWR at depths of 5-15 km. Although we have only obtained preliminary velocity models at the crustal scale in the area and made some discoveries, it can still promote a deeper understanding of the crustal structural characteristics and seismic mechanisms of the XWR and its adjacent areas.
References
Ye, X. W., Deng, Z. H., Huang, Y. M., Liu, J.-P., Wang, X.-N., Liu, J., & Tan, Z.-G. (2017). The characteristics of 3D P-wave velocity structure of Middle-upper crust and reservoir water infiltration-diffusion in Xinfengjiang Reservoir of Guangdong. Chinese Journal of Geophysics, 60(9), 3432–3444.
He, L., Sun, X., Yang, H., Qin, J., Shen, Y., & Ye, X. (2018). Upper crustal structure and earthquake mechanism in the Xinfengjiang Water Reservoir, Guangdong, China. Journal of Geophysical Research: Solid Earth, 123, 3799–3813.
Dong, S., Li, L., Zhao, L., Shen, X., Wang, W., Huang, H., et al. (2022). Seismic evidence for fluid-driven pore pressure increase and its links with induced seismicity in the Xinfengjiang Reservoir, South China. Journal of Geophysical Research: Solid Earth, 127, e2021JB023548.
How to cite: Lyu, Z., Ye, X., and Wen, G.: Seismic ambient noise imaging of Xinfengjiang reservoir and adjacent areas, Guangdong, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16767, https://doi.org/10.5194/egusphere-egu25-16767, 2025.
Distributed Acoustic Sensing (DAS) is becoming a standard solution for ocean-bottom seismological acquisition by providing a dense and long-distance measurement of ground deformation along offshore submarine fiber-optic cables. In the context of an offshore deployment in Central Chile, fiber-optic cables provide real-time seismic data dominated by scattered and converted phases. In a previous work, we have developed a methodology to determine both the velocity and thickness of the shallow sedimentary layer under the fiber using surface waves and split P-waves. Our current objective is to enhance the crustal imaging by identifying fault zones characterized by strong wavefront scattering and sharp lateral velocity contrasts, and sedimentary basins geometry at sub-kilometer scales in the same area, using scattered surface waves.
We focus on seismic events recorded along a 150-km-long fiber in Central Chile. After partitioning the wavefield to separate direct waves from surface waves, we compute local backprojections of the scattered wavefield. By analyzing multiple seismic events across different frequencies, we investigate variations in wave propagation at multiple scales. The resulting energy profiles reveal spatially resolved fault zone structures and sharp lateral contrasts that align with topographic and structural features. Additionally, using standard seismic noise processing procedures, we compute time-domain cross-correlation functions, autocorrelations, and spectral densities. These analyses provide further insights into the behavior of surface waves near reflector features. For instance, we identify lateral discontinuities associated with basin edges by measuring their frequency-dependent resonance.
Finally, to assess the seismogenic potential of the imaged structures, we will compare the geographical distribution and extent of the detected structures with the shallow seismicity automatically detected in the area using DAS data.
How to cite: Vernet, C., Rivet, D., Trabattoni, A., and Baillet, M.: Seismic Imaging from scattered waves using Distributed Acoustic Sensing offshore Central Chile, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16907, https://doi.org/10.5194/egusphere-egu25-16907, 2025.
During the Quaternary, the Rhine Glacier formed several overdeepened valleys, including the Tannwald Basin (ICDP site 5068_1, Germany) about 45 km North of Lake Constance. These structures form sedimentary climate archives and thus help to understand climate dynamics in the Alps.
To obtain very high-resolution images of the sediment, seismic crosshole data was acquired using a high-frequency borehole source that predominantly generates SH-waves. The source was excited very meter at 78 to 143 m depth, and the wavefield was recorded at a depth of 105 to 134 m using an eight-station three-component geophone string in a second borehole 28 m away. Given the receivers are spaced 2 m apart along the receiver string, it was moved by 1 m after shooting at all positions. The orientation of both the source and the receivers was done manually, though a calibrated compass attached to the receiver string facilitated this procedure, in constrast to the source orientation.
The SH-data is characterized by a high level of complexity, despite the lithology from a core obtained from one of the boreholes suggesting a predominantly homogeneous material, i.e., fine glaciolacustrine sediments. Additionally, the high-frequency, large-amplitude, long-coda P-wave masks the SH-wave arrivals.
In preparation for full-waveform inversion (FWI), we mute the trigger peak at time zero, perform data reorientation to account for misaligned sources and receivers, apply a 3D-to-2D spreading correction, delay the wavefield by 0.1 s to ensure convergence of the source-time-function inversion, and normalize the data shot-wise. In a previous study, we derived a traveltime tomography model from an additionally acquired SV-wave dataset, which we use as a starting model.
We apply 2D elastic mono-parameter (vSH) time-domain FWI using the finite-difference method to invert the transverse component data. To mitigate the non-linearity of the problem, we use the multi-stage approach with frequencies starting at 100 Hz. To reduce the effects of source and receiver coupling, the global correlation norm is chosen as the misfit function. The misfit is minimized iteratively by means of an optimization through the quasi-Newton l-BFGS algorithm, which reduces the memory requirements and provides faster convergence. Furthermore, to reduce short-wavelength artifacts, the gradients are smoothed with a Gaussian filter. Source-time-function inversion is performed by a stabilized Wiener deconvolution in the frequency-domain using the Newton method with Marquardt-Levenberg regularization. Additionally, we apply frequency-adaptive time-windowing to precondition the data.
Despite the limited parameter space in the isotropic SH-case, the FWI does not yield convincing results. In this study, we explore the potential factors contributing to this outcome, including the data quality and properties, as well as our FWI approach.
How to cite: Beraus, S., Köhn, D., Burschil, T., Buness, H., Bohlen, T., and Gabriel, G.: High-resolution SH-wave crosshole seismic full-waveform inversion in the glacially overdeepened Tannwald Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17666, https://doi.org/10.5194/egusphere-egu25-17666, 2025.
The Nankai Trough, where the Philippine Sea Plate converges beneath the Eurasian Plate, is situated off SW Japan and is one of the most seismically active subduction zones in the world, producing earthquakes such as the 1944 Tonankai and 1946 Nankai events. Within the Nankai Trough, the region of Shikoku is a geologically distinct segment located within the Tonankai and Nankai rupture zones. Shikoku is distinct due to the presence of a geological backstop, where the rigid forearc crust of the Eurasian Plate resists deformation, causing the compression and thickening of the accretionary prism. This backstop effect creates a structural boundary that influences sediment accretion, tectonic stress distribution, and seismic rupture behavior. The subducting Shikoku Basin crust is thinner and has a shallower dip angle in comparison to the other parts of the trench. The shallow subduction angle beneath Shikoku leads to highly heterogeneous stress and deformation patterns in the accretionary prism compared to steeper-dipping segments. Previous studies employing wide-angle seismic reflection and refraction surveys and tomographic methods have provided valuable insights into the broad-scale structure of the region. These efforts have delineated the geometry of the subducting Philippine Sea Plate and regional velocity structures within the accretionary prism and forearc. However, conventional methods often fail to resolve heterogeneities and variations in the deep subduction interface that critically influence seismic coupling. Furthermore, the role of Shikoku’s unique backstop configuration and the characteristics of the subduction interface at depths exceeding 40 km remain poorly constrained due to the limited resolution of traditional imaging techniques.
To overcome this, we take advantage of wide-angle data from ocean-bottom seismometers (OBS) spaced at 5 km along seismic profiles SK01, SK02, and SK03, acquired between 2009–2010 by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We carry out Full Waveform Inversion (FWI) of the OBS data, a cutting-edge seismic imaging method leveraging the complete seismic waveform data to produce high-resolution velocity models of the subsurface. FWI iteratively refines the velocity model by minimizing discrepancies between observed and simulated seismic waveforms, enabling higher resolution at greater depths with unprecedented accuracy.
The obtained high-resolution velocity models provide a clear representation of previously under-resolved features in the off-Shikoku region, particularly the crustal structure and geometry of the Moho. These models overcome the limitations of traditional methods in imaging the subsurface at greater depths, addressing critical gaps in geological interpretation and advancing our understanding of tectonic processes in the region. By revealing fine-scale details of the subducting crust and Moho, this study further aids in developing effective planning for megaquakes and tsunami risk strategies and provides insights that could be applied to other regions with similar tectonic characteristics.
How to cite: Yadav, A., Górszczyk, A., and Almeida, R.: Enhanced Subsurface Imaging of Western Nankai Trough Using Full Waveform Inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21263, https://doi.org/10.5194/egusphere-egu25-21263, 2025.
