This session shall promote the exchange of experiences using cutting-edge active and passive seismic techniques, or their combinations, to image and characterize both deep and shallow physical properties and structures of the lithosphere. We welcome contributions that utilize novel methods to enhance imaging resolution across various scales, as well as studies that integrate diverse datasets—such as gravimetric, magnetic, geochemical, petrological, and drill logging data—to provide a more comprehensive understanding of the lithosphere. We particularly encourage submissions from underrepresented scientific regions, Early-Career researchers, and those involved in Equality, Diversity, and Inclusion (EDI) initiatives.
Orals: Mon, 28 Apr | Room 0.51
Following the 2021 Tajogaite eruption, in la Palma Island, Canary Archipelago, the IMAGMASEIS project was launched to deploy a dense seismic network across the island. The network comprises 37 broadband seismometers, provided by the GFZ and the University of Granada, in addition to 20 permanent stations operated by the Spanish National Geographic Institute (IGN) and the Volcanological Institute of the Canary Islands (INVOLCAN). This network ensures dense coverage of the entire island, with inter-station distances of approximately 5 km and a maximum distance between stations of 40 km. This temporal network operated from September 2023 to October 2024.
One of the main objectives of this project is to enhance our understanding of the island's crustal structure. To achieve this, we derive P-wave receiver functions from teleseismic records and use them to construct 2D seismic profiles employing the Common Conversion Point (CCP) methodology. This approach allows us to image the Moho discontinuity across the island.
Our preliminary analysis indicates a shallow oceanic Moho in the southern part of the island, at depths of approximately 10 km, consistent with previous studies. In contrast, the northern part of the island reveals a more complex and thicker crustal structure. In this region, the accumulation of magma beneath pre-existing Moho discontinuity (magmatic underplating) may explain Moho depths reaching up to 30 km.
How to cite: Tortosa, J., Parera-Portell, J. A., Mancilla, F. D. L., and Almendros, J.: Preliminary Imaging of La Palma Island's Crustal Structure, Canary Archipelago, Using Receiver Functions from a Dense Broadband Network, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-435, https://doi.org/10.5194/egusphere-egu25-435, 2025.
The southeastern margin of the Tibetan Plateau is a tectonic transition zone between the Tibetan Plateau and Yangtze Craton of the South China Block. The lithosphere beneath the western corner of Yangtze Craton was not only modified by magma underplating and intraplating associated with the Emeishan plume during the Permian but has also been affected by Tibetan Plateau orogenesis since the early Cenozoic. Seismic-wave velocity structures of lithosphere can provide information about the mechanisms of plateau deformation and expansion, including analysis of P-wave receiver functions, surface-wave dispersion, and body-wave travel-time data. During the last decade, several models of lithospheric seismic velocity based on such data have been obtained for the southeastern Tibet. However, these models carry uncertainty because of the inherent lack of uniqueness in the data inversion process. In this study, we review published lithospheric seismic-velocity models of the southeastern margin of the Tibetan Plateau and discuss possible interpretations of the formation mechanism of large-scale low- or highvelocity zones. Most of the reviewed models reveal a large-scale NNE–SSW-trending high-velocity zone in the crust beneath the core of the Emeishan large igneous province that separates two large-scale lowvelocity zones and may act as a barrier to lower-crustal flow from central Tibet. We argue that this largescale high-velocity zone is located primarily in the middle–lower crust rather than in the upper or entire crust and that it represents the track of the Emeishan plume hotspot. The lateral extrusion of rigid blocks is inferred to be the dominant crustal-deformation mode in the southeastern margin of the Tibetan Plateau, whereas deformation induced by hypothesised lower-crustal flow may be limited to localized regions. However, both the lateral extrusion of rigid blocks and lower-crustal flow may be coexistent processes causing the observed crustal deformation pattern beneath the northern Sichuan–Yunnan diamond-shaped block.
Keywords: Seismic-velocity models; Emeishan mantle plume; Lower-crustal flow; Rigid-block lateral extrusion; Plume-strengthened lithosphere
How to cite: Yang, H., Hu, J., and Peng, H.: Seismic-velocity structure of the lithosphere beneath the southeastern margin of the Tibetan Plateau: Insights into geodynamic processes and deformation mechanisms, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1875, https://doi.org/10.5194/egusphere-egu25-1875, 2025.
Accurate determination of the Moho depth and seismic velocities is essential for understanding the Earth's crustal structure and geodynamic processes. A widely used approach for estimating Moho depth is the H-k stacking method. H-k stacking makes use of receiver functions and a grid search to identify which values of Moho depth and crustal VP/VS ratio are able to best reproduce arrival times of P-to-S converted phases, recorded in the Receiver Functions. Due to the crustal attenuation and local scattering, multiple converted P-to-S phases, namely PpPs and PsPs+PpSs, generally display lower amplitude with respect to P-to-S phase. To fully take into account this observation, the different P-to-S converted phases are given different importance (i.e. different weights) during the H-k stacking. However, such assumption can introduce bias due to the user-defined weights assigned to the different phase arrival times.
To address this limitation, we propose a novel algorithm that extends the traditional H-k stacking approach by introducing two additional dimensions: variable weights for the phase arrival times. This innovation enables us to compute H-k grids using a range of weight configurations and evaluate their probability. The optimal grid is selected based on its probability, thus we reduce the influence of subjective weight assignments.
By incorporating variable weights into H-k stacking, our approach aims to reduce bias and improve the robustness of Moho depth estimates. With this enhanced method we hope to contribute to a more precise picture of the Earth's crust and a better understanding of geodynamic processes.
How to cite: Ziegler, J. and Piana Agostinetti, N.: Refining Moho Depth Estimates from Receiver Functions, introducing variable Weights for P-to-S converted Phases, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8081, https://doi.org/10.5194/egusphere-egu25-8081, 2025.
The North China Craton (NCC) lost its stable craton characteristics in the Mesozoic. How the NCC continues to evolve after the Mesozoic is worth further investigation. Here, we determined high-resolution lithospheric structure of the NCC by joint inversion of body wave arrival times, surface wave dispersion data and receiver functions. The velocity image shows that the NCC has been greatly destructed with very thin lithosphere in the eastern part (~60-70 km). In comparison, beneath the western part, or mainly the Ordos basin, the lithosphere is thicker and is around ~120 km. Beneath the north-south gravity lineament (NSGL), there is a tunnel-shaped low velocity zone with its apex close to the Moho, suggesting the original lithosphere mantle in this part was completely destructed and metasomatized. Several high-velocity bodies are imaged below ~80-90 km in the eastern NCC, which are interpreted as delaminated lithosphere. Based on the depths of these delaminated bodies and geochemical data, we propose they most likely occurred in the Cenozoic. The lithosphere delamination in the Cenozoic is spatially consistent with the heat flow distribution, as it can trigger the upwelling of hot mantle materials. In addition, the velocity image also indicates that the eastern edge of the lithosphere mantle beneath the Ordos basin is under destruction, likely by the sustaining westward mantle flow. Based on the positive and negative εNd values of Cenozoic magma samples in the NCC, it can be further derived that the Cenozoic eastern NCC destruction is jointly controlled by convective mantle flow and lithosphere delamination.
How to cite: Zhang, H., Hao, A., Liu, L., Dai, L., Han, S., Fang, W., and Wan, B.: Cenozoic destruction of eastern North China craton evidenced by seismically imaged lithosphere delamination and Nd isotopes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5068, https://doi.org/10.5194/egusphere-egu25-5068, 2025.
The origin of the Aeolian Islands (southern Tyrrhenian Sea), is associated with the subduction process occurring between the African and European plates and resulting in a back-arc basin that hosts the ongoing volcanism. The crustal tectonic setting in this region is quite complex, with strike-slip, compressive, and extensional regimes coexisting within a few dozen kilometers, giving rise to significant active volcanic systems such as Mount Etna to the south, Vulcano Panaera and Stromboli to the north.
In this study, we focus on the moderate and low- magnitude seismicity recorded over the last 40 years in the region to image the crustal structure of the southern Tyrrhenian using the Enhanced Seismic Tomography workflow.
To enhance the reliability and resolution of the tomographic models, a thorough manual revision of most recent seismicity was performed, and data from DSS and wide-angle seismic experiments conducted in the early 1980s were incorporated. Results demonstrate that we can now finely resolve P-wave and S-wave seismic velocities, enabling us to describe subsurface geometries with unprecedented detail. This breakthrough provides new insights into the tectonic processes, offering new clues to solving this complex geological puzzle.
This study is funded by the INGV Pianeta Dinamico project 2023-2025 CAVEAT (grant no. CUP D53J19000170001) supported by the Italian Ministry of University and Research “Fondo finalizzato al rilancio degli investimenti delle amministrazioni centrali dello Stato e allo sviluppo del Paese”, legge 145/2018 and supported by the collaboration UNAM-INGV on the study of volcanic and geothermal systems.
How to cite: Calò, M., Di Luccio, F., Ursino, A., Scaltrito, A., Grandados Chavarría, I., Santana Cedillo, B. L., and Palano, M.: Crustal structure of the Aeolian islands (southern Italy) using 40 years of seismicity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7384, https://doi.org/10.5194/egusphere-egu25-7384, 2025.
The Tibetan Plateau plays a crucial role in Asian and global geomorphology and climate change, yet how it grew and how its deep geodynamic processes control surface systems remains unclear. We present a novel model to explain this by multistage bilateral subduction, lithospheric breakoff, and subsequent foundering. Modelling based on a global tomography method reveals four distinct stepwise high-velocity anomalies in the mantle. The high-resolution seismic velocity model was inverted using >16 million arrival times of P, Pn, pP, PP, PKP, and PKiKP phases from the International Seismological Center and EHB bulletins and ~3 million arrival times of P, PP, and PcP phases from the 1,034 China Seismic stations in Tibet. We also collected hundreds of volcanic rocks to analyze their spatio-temporal distribution in the Tibetan Plateau since 60 Ma. The locations and morphology of the remanent slabs associated with the subducted/subducting Neo-Tethyan Ocean, Greater Indian plate, and Asian lithosphere have been constrained using plate reconstruction and the surface igneous rock data. We find that discrete episodic surface volcanism and plate uplift at 56-44 Ma, 44-28 Ma, 28-18 Ma, and 18-0 Ma in the Tibetan Plateau coincide with the four-stage stepwise lithosphere processes. We observe paired slab-like anomalies during the second and third steps, indicating the simultaneous detachment of subducting lithosphere from opposing directions. Building upon this observation, we propose a two-sided breakoff model, where bilateral subduction and lithospheric gravitational subsidence triggered extensive volcanism and episodic uplift of the plateau. This model indicates that subsidence from both past and present lithospheric break-offs of the Indian and Asian plates spawned extensive volcanism that had a significant impact on climate patterns. By shedding new light on the deep-seated geodynamic mechanisms at play, our study establishes a systematic framework linking lithospheric processes and surface phenomena in Tibet.
How to cite: Wang, Z., Wang, J., Fu, X., Wilde, S. A., and Fu, Y.: Control of stepwise subduction and slab breakoff on volcanism and uplift in the Tibetan Plateau, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5345, https://doi.org/10.5194/egusphere-egu25-5345, 2025.
The structure and evolution of the lithosphere and underlying mantle control tectonics, magmatism, and natural resource development and distribution. Seismic tomography offers essential information on mantle temperature, the thickness and strength of the lithosphere, and the convection below it. Here, we report on the completion of a series of continent- and plate-scale waveform tomography studies using the automated multimode inversion of surface and S-wave waveforms. Together, the models cover all of the Earth’s continents and their surroundings and reveal a fascinating diversity of structures, while also indicating common mechanisms of lithospheric dynamics and evolution. Each model used global data coverage that was maximised witin the hemisphere centred at the continent. Structural information was extracted from Rayleigh waves and S and multiple S waves on over a million vertical-component-seismogram waveform fits. The effects of errors were minimised by statistical and targeted outlier analyses and the removal of the least mutually consistent data. The models advance the resolution of the imaging compared to the state of the art at the scale of the continents.
Cratonic lithosphere on all continents shows complexities and fragmentation. The lithosphere beneath most diamondiferous kimberlites—originally emplaced on thick cratonic lithosphere—is still thick at present. Relatively low seismic velocities at kimberlite locations are indicative of craton-lithosphere thinning and are detected at multiple locations in all continents with known kimberlites. Cenozoic basalts are found exclusively where the lithosphere is observed to be thin. Beneath some of the volcanic regions, low-velocity anomalies extend deep into the mantle, consistent with deep-mantle upwellings feeding the magmatism. Sediment-hosted metal deposits tend to be located near contrasts in the thickness of the lithosphere, including both craton boundaries and other substantial heterogeneities. Intraplate seismicity is controlled by plate-boundary stresses and by the lateral variations of the lithospheric thickness and strength. Areas with relatively thin lithosphere localise deformation and seismicity, provided that sufficient tectonic stress is transmitted into the plate interior.
References
Chagas de Melo, B, Lebedev, S, Celli, NL, et al., 2025. The lithosphere of South America from seismic tomography: Structure, evolution, and control on tectonics and magmatism, Gondwana Research, GR Focus - Invited Review, 138, 139–167. doi:10.1016/j.gr.2024.10.012.
Chua, EL, Lebedev, S. Waveform tomography of the Antarctic Plate, Geophysical Journal International, submitted.
Celli, NL, Lebedev, S, Schaeffer, AJ, Gaina, C, 2021. The tilted Iceland Plume and its effect on the North Atlantic evolution and magmatism, Earth and Planetary Science Letters 569, doi:10.1016/j.epsl.2021.117048.
Celli, NL, Lebedev, S, Schaeffer, AJ, et al., 2020. The upper mantle beneath the South Atlantic Ocean, South America and Africa from waveform tomography with massive data sets, Geophysical Journal International 221, 178–204. doi:10.1093/gji/ggz574.
de Laat, JI, Lebedev, S, Celli, NL, et al., 2023. Structure and evolution of the Australian plate and underlying upper mantle from waveform tomography with massive data sets, Geophysical Journal International 234, 153–189. doi:10.1093/gji/ggad062
Dou, H, Xu, Y, Lebedev, S, et al., 2024. The upper mantle beneath Asia from seismic tomography, with inferences for the mechanisms of tectonics, seismicity, and magmatism, Earth-Science Reviews, 255, doi:10.1016/j.earscirev.2024.104841
How to cite: Lebedev, S., Chua, E. L., Dou, H., Xu, Y., Chagas de Melo, B., de Laat, J., and Celli, N.: Waveform tomography of the Earth’s continents: Lithospheric structure and evolution and their controls on seismicity, magmatism and natural resources, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7088, https://doi.org/10.5194/egusphere-egu25-7088, 2025.
The thermal structure of the continental lithosphere and its evolution over geological time are critical to understanding the processes that govern its formation, dynamics, and long-term stability. Global shear-wave models, combined with heat-flow data, provide valuable first-order constraints on the large-scale temperature distribution and thickness of continental lithosphere (Cammarano and Guerri, 2017). However, seismic data alone offer limited resolution for absolute temperature estimates.
In contrast, xenolith and xenocryst analyses yield localized pressure-temperature (P-T) geotherms, providing direct constraints on thermal conditions and temporal variations at specific depths and regions.
In this study, we integrate seismic constraints with xenolith-derived P-T estimates based on clinopyroxene compositions to enhance our understanding of the current thermal state of the global continental lithosphere. Furthermore, we assess whether and where significant temperature variations have occurred over time.
Our comparative analysis of seismically inferred temperatures and xenolith-derived P-T paths, accounting for their associated uncertainties, reveals spatial and temporal trends in the thermal evolution of the continental lithosphere. These findings also refine estimates of lithosphere-asthenosphere boundary (LAB) depths, offering new insights into the dynamic processes shaping the continental lithosphere.
How to cite: Cammarano, F., Sudholz, Z., and Priestley, K.: Integrating Xenolith Data and Seismic Models to Constrain the Thermal State and Evolution of the Continental Lithosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15735, https://doi.org/10.5194/egusphere-egu25-15735, 2025.
Among several imaging techniques, the P-wave Receiver Functions (RF) have been demonstrated to be particularly resourceful for retrieving different physical properties of the Earth, and for resolving the depth structures at different scales. It has now become a largely used standard tool for studying the crust and upper mantle, while initially the RF were mostly employed for inferring the average Moho depth beneath single stations, due to the prominent signal given by the P-to-s converted Moho phase and its multiples on the Radial (R) component.
In this talk are shown several examples of increasing complexity to dig out the extensive information that can be extracted from RF data-sets. Examples include 1D shear-wave velocities profiles retrieved by the R-RF; 2D imaging by common-conversion-point sorting; the harmonic decomposition of the R+T (Transverse) signal as advanced analysis tool for the extraction of 3D features (as inclined discontinuities and anisotropic layers). The versatile nature of the technique is shown as well by the different degree of vertical resolution, as it can discriminate the shallow crust layering, as sedimentary basins structures, and to image structures within the mantle, as the lithosphere-asthenosphere boundary. Finally, increasing amount of available teleseismic data collected at closely spaced stations and advanced computing capabilities, allow 3D volume reconstructions that contribute to the foundation of evolutionary models of the elastic properties of the subsurface.
How to cite: Bianchi, I.: Comprehensive Analyses of Receiver Function Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15273, https://doi.org/10.5194/egusphere-egu25-15273, 2025.
Posters on site: Mon, 28 Apr, 14:00–15:45 | Hall X1
Here we present a new North America’s lithospheric thermal and compositional model
constrained by integrated geophysical – lithological inversion of Rayleigh and Love surface
wave dispersion curves, supplemented by other geophysical data and models: surface heat flow
and average temperature, topography, Moho depth, P-wave seismic crustal velocities, and
sedimentary thickness. The dispersion curves cover North America with a 0.5 x 0.5 degree
spacing, with periods logarithmically increasing from 8 to 400 s. The curves are constructed by
merging dispersion curves from five different datasets: USANT15 (Ekstrom, 2017), FCL
(Schmandt et al., 2015), NA2014 (Schaeffer & Lebedev, 2014), NAT2020 (Celli et al., 2021)
and LL2019 (Lavoué et al., 2021). The inversion includes a three-layered crust where seismic
velocities and densities are lithologically linked through correlations from global petrophysical
data sets, and a lithospheric mantle layer defined both thermally and chemically. Mantle seismic
velocities and densities are computed as a function of the in-situ temperature and compositional
conditions using a self-consistent thermodynamic formalism. Our lithospheric models constrain
the thermal lithospheric structure of North America including shallow crust temperature and
subsurface temperature gradient maps of interest for geothermal energy studies.
How to cite: Clemente-Gómez, C., Fullea, J., Lebedev, S., and Xu, Y.: Mapping the North American thermal lithospheric structure through integrated geophysical –petrological inversion of surface wave data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3317, https://doi.org/10.5194/egusphere-egu25-3317, 2025.
An optical hologram is a recording of the interference between two different wavefields. One wavefield interacts with the objects to be imaged (the “object wave”) and the other does not (the “reference wave”). If only the reference wave is then shone through the recorded hologram, the objects are reconstructed visually in 3D. This occurs because the interference pattern encodes the phase information of the object wave.
In seismic imaging, the phase information of the seismic wavefield is directly recorded by seismometers. Therefore, a reference wave is not needed and the object can be reconstructed without. Because there is no real-world equivalent to shining light through the hologram in seismology, computational methods are needed. The closest seismic equivalent to optical holography is full-waveform inversion.
We demonstrate that a similar connection between optical holography and seismic imaging arises naturally in surface-wave propagation. To image any structure with surface waves, phase or group velocities are measured at different frequencies. The resulting dispersion curves are commonly biased by wavefield interference. Closely connected bias patterns can also be observed in the apparent arrival angles of wavefronts and the peak amplitude of surface wavegroups. Similar to the optical holography, the surface-wave patterns can also be explained as interference of the “object” and “reference” wave. In seismology, however, these interference patterns can be produced by two distinct mechanisms: the “object” wave could be emitted either by heterogeneous structure in case of deterministic surface waves propagating from earthquakes, or, in seismic interferometry, by additional isolated noise sources. Our results suggest that this effect a) should be carefully considered as a potential source for bias in imaging applications, and b) may reveal new opportunities for seismic imaging.
How to cite: Kolínský, P., Schippkus, S., and Hadziioannou, C.: Connecting optical holography and seismic imaging, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7439, https://doi.org/10.5194/egusphere-egu25-7439, 2025.
The West Bohemia/Vogtland region, situated at the intersection of the Saxothuringian, Teplá-Barrandian, and Moldanubian Units, is characterized by mantle-derived CO2 emissions, earthquake swarms, and Quaternary volcanism. To investigate the crustal structure and fluid-CO2 migration, we applied a joint inversion of body-wave and magnetotelluric data, producing three-dimensional models of P-wave velocity (Vp), S-wave velocity (Vs), and electrical resistivity (ρ). The joint inversion algorithm constrained geophysical models using variation of information (VI) coupling and updated earthquake locations via the double-difference method.
The results reveal linearly aligned patches of low Vp, high Vp/Vs, and low ρ along the Počátky-Plesná Fault Zone in the upper crust, indicating hydraulically conductive zones under critical stress. At ~10 km depth beneath the Nový Kostel focal zone, a prominent anomaly characterized by low Vp, high Vp/Vs, and high ρ suggests a fluid-CO₂ system under high pressure, likely explaining the triggering mechanisms of earthquake swarms. Near the Hartoušov Mofette Field, anomalies with low Vp, low Vp/Vs, and high ρ suggest a gas-dominated fracture network in the upper crust. These findings provide new insights into the interaction of tectonics, magmatism, and crustal fluids in this geodynamically active region.
How to cite: Wei, Y., Platz, A., Weckmann, U., and Moorkamp, M.: Characterizing fault-controlled fluid-CO₂ migration in West Bohemia/Vogtland through seismic and magnetotelluric joint inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13236, https://doi.org/10.5194/egusphere-egu25-13236, 2025.
Travel-time tomography uses the travel times of seismic waves between pairs of sources and receivers to constrain the elastic properties of the subsurface. However, the low rate of natural seismicity in Ireland limits the application of standard local earthquake tomography. This study uses seismic wave arrival times from controlled explosions generated during quarry and mining activities to refine the constraints on the velocity structure of the Irish crust.
Previous seismic studies have utilised (i) surface wave dispersion from teleseismic earthquakes, providing broad insights into the lithospheric structure, and (ii) spatially sparse seismic reflection and refraction profiles. While these studies have delineated major tectonic features, such as the late-Caledonian Leinster Granite and a crustal boundary linked to the closure of the Iapetus Ocean, the precise boundaries of these features remain unresolved. Subašić (2021) employed the FMTOMO package to compute a preliminary 3D travel-time tomography model of the Irish crust based on quarry blast data. FMTOMO (Rawlinson et al., 2006) uses a gradient-based subspace inversion scheme to derive a seismic velocity model from observed travel times. In this study, we re-evaluate and expand the input dataset used by Subašić (2021) and focus on optimising the regularisation parameters of the tomographic inversion.
Event classification into natural earthquakes and quarry explosions is performed using the spectral ratio method applied to S-wave trains, a procedure developed and routinely applied by the Irish National Seismic Network (INSN). The updated dataset includes 1,411 quarry blast events with P- and S-wave travel-time measurements from 2013–2014, a period of increased station density due to temporary seismic deployments. Quarry blasts, being surface explosions, are assumed to have well-constrained surface locations. A catalogue of 234 quarry sites in Ireland was initially compiled from satellite imagery by the INSN.
Hypocentre locations for each event are first calculated from phase arrival times and subsequently relocated to the nearest quarry. Given that quarry mines in Ireland typically range from hundreds of metres to a maximum of ~1.5 km in length, most events fall within the error margin of the initial locations. For events located beyond a 3 km radius of known quarries, additional searches for unrecorded sites were conducted. Satellite imagery inspections of these unclassified events identified 25 additional quarries. The operational status of these quarries during the study period was confirmed using historical imagery from Google Earth by comparing quarry areas before and after the analysed time frame.
To further enhance the dataset, we plan to incorporate quarry blasts recorded in 2024, following the deployment of additional seismic stations in Northern Ireland, alongside selected inland and offshore natural earthquakes. The final outputs will consist of P- and S-wave velocity models. Currently, the limited lithological information on the Irish basement constrains efforts to model the deep geothermal structure. P/S ratio maps derived from the velocity models will provide valuable insights into crustal lithology, addressing this gap.
How to cite: Chagas de Melo, B., Bean, C. J., Grannell, J., and Subašić, S.: Seismic Velocity Structure of the Irish Crust from Quarry Blasts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13460, https://doi.org/10.5194/egusphere-egu25-13460, 2025.
Seismic tomography is vital for understanding complex tectonic processes and assessing geological hazards in seismically active regions like Southern Taiwan, where the Eurasian continental subduction transitions into the Luzon Arc collision. To enhance the lateral and depth resolution of tomographic images, we expanded station coverage and addressed data gaps in mountainous areas by deploying the dense amphibious SALUTE array across this transition zone since October 2021. A machine learning (ML) approach was employed for precise and efficient P- and S-phase picking from three-component velocity waveform data recorded by totally 236 seismic stations, integrating the SALUTE array with existing permanent networks in southern Taiwan.
Using SeisBench and the pre-trained EQTransformer model for automatic phase picking, followed by phase association and event’s origin time and hypocenter determination with the Gaussian Mixture Model Associator (GaMMA) and event relocation using the hypo3D program with a 3D velocity model, we detected four times more seismic events than the CWA catalog for one-month test data. Moreover, P amd S arrival picks increased by about 1.7 and 1.8 times, respectively, demonstrating the potential of ML methods to improve earthquake catalogs and the following tomographic inversion.
After thoroughly validating all phase picks and removing false detections, we applied the LOTOS-12 tomography package to iteratively invert for 3-D P- and S-wave velocity models while simultaneously relocating earthquake sources. Preliminary results reveal a prominent velocity contrast of up to ±20% in the upper 20 km of the crust across the Chaochou Fault (CCF), with low velocities beneath the western sedimentary coastal plain and high velocities beneath the eastern metamorphic Central Range (CR). These onshore features are generally consistent with previous models. Besides, low-velocity crustal anomalies deepen eastward, and are underlain by a high-velocity structure, likely representing the eastward-subducting Eurasian slab. Incorporating offshore stations in our dataset has enabled us to resolve two isolated, shallow low-velocity anomalies beneath the Southern Longitudinal Trough and the Luzon Arc. Expanding station coverage along the CCF and in the CR and eastern offshore regions through the SALUTE array, we anticipate significant improvements in the tomographic images, with enhanced lateral and depth resolution and greater structural detail.
How to cite: Chen, L.-J., Hung, S.-H., and Ko, J. Y.-T.: Improving Seismic Tomography of Southern Taiwan and Eastern Offshore Regions from the SALUTE Amphibious Array and Machine Learning-Based Arrival Time Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14645, https://doi.org/10.5194/egusphere-egu25-14645, 2025.
The northeastern part of South Korea, Gangwon Province, is closely connected to major tectonic activities of the Korean Peninsula, such as the formation of the Taebaek Mountain ranges and the opening of the East Sea (Sea of Japan). Therefore, analyzing the velocity structure of Gangwon Province can provide insights into the tectonic history of the Korean Peninsula. We calculated receiver functions for 96 broadband and accelerometer seismic stations using 369 teleseismic event data (Mw ≥ 5.8, with epicentral distances from 30° to 90°), recorded between March 18, 2019, and May 31, 2024. We estimated Moho depth and Vp/Vs ratio in Gangwon Province using H-k stacking method, and we obtained 1-D S-wave crustal velocity models for each stations using joint inversion of receiver functions and surface-wave dispersion. Moho depth and Vp/Vs ratios derived from H-k stacking method ranged from 23.0 to 35.6 km and 1.68 to 1.85, respectively. Most stations located along the eastern coast exhibited relatively shallow Moho depth and high Vp/Vs ratios. From the 1-D S-wave crustal velocity models obtained using the joint inversion, we identified velocity inversion layer and mid-crustal discontinuities beneath several stations. The Moho depth was determined as the layer with an S-wave velocity exceeding 4.0 km/s and the largest velocity gradient, resulting in depths ranging from 23.9 to 35.7 km, which are consistent with the Moho depths obtained from H-k stacking. The trend of Moho depth distribution in Gangwon Province is shallow along the coast and deepens through the Taebaek mountain ranges, but it does not align with Airy isostasy. Accordingly, We calculated residual topography, and the result suggests the possibility of additional isostatic uplift along the Taebaek Mountain ranges and the eastern coast.
How to cite: Hwang, J.-Y., Chang, S.-J., Sohn, Y. J., and Kim, K.-H.: Crustal Velocity Structure and Unresolved Isostatic Uplift in Gangwon Province, South Korea, from Joint inversion analysis of Receiver Functions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14125, https://doi.org/10.5194/egusphere-egu25-14125, 2025.
The rise in seismic activity since the Mw 5.8 Gyeongju earthquake in 2016 has prompted a detailed study of subsurface fault systems in South Korea. Given the potential for a moderate earthquake to cause significant damage and loss of lives in the densely populated Seoul metropolitan area, investigating subsurface fault systems in this region is an urgent task. We jointly invert S-wave travel times and Rayleigh-wave phase and group velocities to identify subsurface seismogenic faults in the Seoul metropolitan area, taking advantage of the complementary resolutions of the three different datasets. We obtained 3,837 of S-wave relative arrival times from 74 broadband stations and 229 teleseismic earthquakes. Additionally, we obtained Rayleigh-wave group-velocity and phase-velocity dispersion curves with periods of 1 to 10 s from 962 and 1,822 station pairs, respectively, using ambient noise cross-correlations. We also incorporated phase velocity maps with periods from 10 to 30 s, previously measured using Helmholtz tomography. Our S-velocity model reveals clustered seismicity in northern Seoul aligned with a low-velocity anomaly, suggesting the presence of an underlying subsurface seismogenic fault. Sharp velocity contrasts are observed linearly along the Pocheon and the Wangsukcheon faults, which extend underneath Seoul to depths of 20~30 km in a southwestern direction. An isostatic gravity study suggests that the Daebo granite intruded during the Jurassic period and is widely distributed underground. This geological setting and the strong low-velocity anomaly observed along the Pocheon Fault indicate the potential presence of subsurface faults caused by rock heterogeneity.
How to cite: Kim, M., Chang, S.-J., Witek, M., Lee, J., Chung, D., Kim, B., Park, S., and Hong, T.-K.: Joint Inversion of S-Wave Relative Travel Times and Rayleigh-Wave Phase and Group Velocity Dispersion Curves for the Estimation of Subsurface Seismogenic Faults in the Seoul Metropolitan Area, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14081, https://doi.org/10.5194/egusphere-egu25-14081, 2025.
Estimating the crustal velocity structure is crucial for understanding the tectonic evolution of continents. In particular, the structure of the near-surface crust provides critical insights into site effects, ground motion, and disaster prevention. In this study, we applied P-wave polarization analysis to estimate the shear-wave velocity structure beneath 75 seismic stations installed in Gangwon Province, South Korea, a region characterized by complex geological features. A total of 302 teleseismic events were utilized for this analysis. The P-wave polarization method relies solely on the incident angles of direct P waves recorded at individual stations, ensuring that the results are independent of the network's spatial density. P waveforms were bandpass-filtered using six different central frequencies ranging from 0.1 to 3.2 Hz, enabling the derivation of velocity structures across a broad range of depths. Additionally, we calculated depth sensitivity kernels for P-wave polarization at the six central frequencies using a numerical approach. P-wave polarization at frequencies of 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 Hz exhibited the highest sensitivity to shear-wave velocities at depths of 7.3, 4.3, 2.1, 1.1, 0.5, and 0.3 km, respectively. Based on these sensitivity kernels, the results demonstrate significantly improved accuracy compared to previous models and effectively capture geological features such as faults and rock distributions. Notably, the resolution at depths of several hundred meters, which are challenging to estimate using conventional seismic surveys or tomography methods, was enhanced. This highlights the potential of P-wave polarization analysis as a valuable tool for seismic imaging.
How to cite: Kim, K. and Chang, S.-J.: Near-surface to upper crustal shear-wave velocity structure beneath Gangwon Province, South Korea, using P-wave polarization analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14102, https://doi.org/10.5194/egusphere-egu25-14102, 2025.
Gangwon Province, located in the central part of the Korean Peninsula, is distinguished by fault structures that primarily follow a northeast-southwest orientation. Understanding the subsurface structure of this region is essential for assessing seismic hazards and accurately measuring seismicity. A recently deployed dense seismic network, with an average lateral spacing of ~50 km, enables the construction of a high-resolution crustal velocity model. We employed Helmholtz tomography using 101 broadband seismometers and accelerometers and 261 teleseismic events with epicentral distances of 5-90°, to obtain phase-velocity maps for periods of 10 to 40 s. By inverting these phase-velocity maps, we derived an S-wave velocity model spanning depths from the shallow crust to the uppermost mantle (5 to 50 km). Our results revealed northeast-southwest trending low-velocity anomalies along major faults in northern Gangwon Province, extending to depths of ~25 km. These low-velocity anomalies correspond to the intrusion orientations of granitic bodies generated through partial melting during the Mesozoic era. In contrast, the southern Gangwon Province exhibits a distinctly different velocity structure, lacking features indicative of granitic intrusions and showing low-velocity anomalies confined to shallow depths.
How to cite: Park, S., Chang, S.-J., Kim, K.-H., and Sohn, Y. J.: Crustal Structure of Gangwon Province in the Korean Peninsula from Helmholtz Tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14069, https://doi.org/10.5194/egusphere-egu25-14069, 2025.
Posters virtual: Mon, 28 Apr, 14:00–15:45 | vPoster spot 1
EGU25-1178 | ECS | Posters virtual | VPS21
3-D Crustal Shear Wave Velocity Tomography Using Seismic Ambient Noise Data in Southeast Tibet, Close to Namcha Barwa MountainMon, 28 Apr, 14:00–15:45 (CEST) | vP1.7
Southeastern Tibet, a segment of the eastern Himalayan Syntaxis, is a significantly deformed area resulting from multistage subduction and the ongoing collision of the Indian and Asian tectonic plates. The region has a clockwise material movement around the indenting corner of the Indian plate, evident on the surface as strike-slip faults aligned with the Himalayan Arc. Numerous scientific studies have focused on the east-west extension and tectonic history of southeastern Tibet; however, the scientific enquiries regarding the depth constraints of the crustal flow process—specifically, whether it is confined to the middle crust or extends to the lower crust beneath southeastern Tibet—remain unresolved. This study employs ambient noise tomography to examine a 3-D high-resolution crustal velocity model for the region, which is crucial for unravelling the mechanisms that regulate crustal deformation and evolution in active orogenic systems. To do this, we examined ambient noise data from 48 seismic stations of the XE network, operational from 2003 to 2004. We obtained Rayleigh wave phase velocities ranging from 4 to 60 seconds and subsequently inverted them to develop a 3-D shear wave velocity model of the region extending to depths of 50 km. Our results reveal persistent low shear wave velocity zones at depths of 15–25 km (within the mid-crust), notably observed between the Indus Tsangpo suture and the Bangong-Nujiang Suture. We contend that the detected low-velocity zones are only linked to mid-crustal channel flow, a mechanism presumably essential for comprehending crustal deformation. Our findings provide significant constraints on the depth localisation of crustal channel flow and the interaction of tectonic forces in southern Tibet, enhancing the overall comprehension of Eastern Syntaxial tectonics.
How to cite: Mandi, A., Kumar, G., Bishoyi, N., and Tiwari, A. K.: 3-D Crustal Shear Wave Velocity Tomography Using Seismic Ambient Noise Data in Southeast Tibet, Close to Namcha Barwa Mountain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1178, https://doi.org/10.5194/egusphere-egu25-1178, 2025.
EGU25-9078 | ECS | Posters virtual | VPS21
Continental Crustal Structure Beneath Northern Morocco Deduced from Teleseismic Receiver Function: Constraints into structure variation and compositional properties.Mon, 28 Apr, 14:00–15:45 (CEST) | vP1.9
In this study, we used the P-wave receiver functions (PRFs) to investigate the crustal structure of northern Morocco, located at the westernmost edge of the Mediterranean, near to the boundary between the African and Eurasian tectonic plates. This region is an integral part of the complex crustal deformation and tectonic system associated with the Alpine orogeny, characterized by concurrent compressional and extensional processes. These dynamics have led to the development of various structural and tectonic models aimed at explaining the area‘s geological evolution. The significant tectonic activity, evident in frequent seismic events, and complex lithospheric deformation, makes it an ideal location for studying crustal variations, lithospheric interactions, and mineralogical contrasts.
To achieve these objectives, we utilized high-quality seismic broadband data from the TopoIberia and Picasso seismic experiments, provided by the Scientific Institute, as well as from the broadband seismic stations operated by the National Center for Scientific and Technical Research (CNRST). The PRFs were extracted by decomposing teleseismic P-waves to isolate the effects of the local crustal structure. The dataset covers a wide range of regional stations, and the RFs provide detailed insights into crustal thickness, density and velocity contrasts, as well as deep discontinuities. Our preliminary results reveal significant variations in Moho depth, ranging from approximately 22.7 km in the eastern part of the region to 51.7 km in the western part. These variations correlate with changes in Vp/Vs and Poisson’s ratios, indicating mineralogical heterogeneity, with compositions spanning from mafic to felsic. These findings provide new constraints for tectonic models and enhance our understanding of the geodynamic processes involved, particularly the interactions between the crust and the upper mantle. This study not only improves our understanding of active tectonics and crustal composition in northern Morocco but also offers valuable insights for refining evolutionary models of the Western Mediterranean within its complex geodynamic context.
Keywords: Teleseismic event, P-wave, Receiver functions, Seismic Network, Vp/Vs ratio, Poisson ratio, Crustal structure, Mineralogical composition, Seismotectonics, Northern Morocco.
How to cite: Zakarya, H., El Moudnib, L., Badrane, S., Zeckra, M., and Lharti, S.: Continental Crustal Structure Beneath Northern Morocco Deduced from Teleseismic Receiver Function: Constraints into structure variation and compositional properties., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9078, https://doi.org/10.5194/egusphere-egu25-9078, 2025.
EGU25-1021 | ECS | Posters virtual | VPS21
Multiscale Surface Wave Tomography of the Bhutan Himalayas using Ambient Seismic Noise and Teleseismic Earthquake DataMon, 28 Apr, 14:00–15:45 (CEST) | vP1.8
The tectonic framework of Bhutan Himalaya documents significant along-strike variability in crustal structure and deformation. To visualize this spatial and depth variability, we compile an extensive dataset of surface-wave phase velocities derived from seismic ambient noise and teleseismic earthquakes recorded by the temporary GANSSER network (2013-2014) in Bhutan, aiming to produce Rayleigh phase-velocity maps over the period range of 4 to 50 seconds. We translate the phase-velocity maps into a 3-D shear-wave velocity model stretching from the surface to a depth of 42 kilometres. The employed methodologies enable imaging of the upper to mid-crustal and lower crustal velocity anomalies with a lateral resolution of approximately 25 km. The obtained tomographic model fills a void in the prior established shear-wave velocity structure of Bhutan, encompassing depths from upper-crustal to lowermost crust. Our findings indicate notable mid-crustal to lower-crustal high phase velocity anomalies in central Bhutan (around 90.5). The presence of this significant anomaly within the mid- to lower crustal layer may indicate localized stress accumulation along the Main Himalayan Thrust (MHT) resulting from the interaction of the dipping and sub-horizontal Moho. This area might act as a stress concentration zone, resulting in increased deformation and enhanced shear-wave velocity in the crust. Minor fluctuations in velocity across latitude may result from variations in the local geometry of MHT (dip or ramp-flat transition). Localised high shear velocity in western Bhutan may indicate a zone of crustal thickening. Northeastern Bhutan exhibits modest shear velocity, possibly because of a flat Moho and the partial creeping behaviour of the MHT.
How to cite: Kumar, G. and Tiwari, A. K.: Multiscale Surface Wave Tomography of the Bhutan Himalayas using Ambient Seismic Noise and Teleseismic Earthquake Data , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1021, https://doi.org/10.5194/egusphere-egu25-1021, 2025.
