Orals: Mon, 4 May, 10:45–15:45 | Room -2.21
We present the analysis of the first known video of co-seismic slip on a natural fault. It was captured during the 2025 Mw 7.7 Mandalay earthquake (Myanmar) by a CCTV camera located a few meters away from the fault. By direct image analysis of the footage, we measure the slip and slip-rate functions from the natural coseismic rupture. The results show that the rupture propagated as a slip-pulse, with a local slip duration of 1.4 s and a maximum slip rate of 3.5 m/s ± 20%. We then fit two steady-state slip-pulse models to the measured slip-rate function, allowing us to estimate the mechanical properties of the fault: the slip-stress curve, the slip-weakening distance, the breakdown work and the energy release rate. This study shows the value of direct on-fault slip measurements for constraining those mechanical parameters, that are key inputs in dynamic rupture models.
How to cite: Latour, S., Lebihain, M., Bhat, H. S., Twardzik, C., Bletery, Q., Hudnut, K. W., and Passelègue, F.: Direct estimation of earthquake source properties from a single CCTVcamera (2025 Mw 7.7 Mandalay earthquake, Myanmar), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21737, https://doi.org/10.5194/egusphere-egu26-21737, 2026.
High-resolution imaging of crustal structure is critical for understanding deformation processes, lithospheric rheology, and seismic hazard in continental collision zones. Afghanistan and its surrounding regions lie at the junction of the Indian, Eurasian, and Arabian plates, hosting diverse tectonic environments that include major strike-slip fault systems, thick foreland and intracontinental basins, hot orogenic cores, and ongoing continental subduction beneath the Hindu Kush. Despite frequent damaging earthquakes, existing seismic velocity models are limited by sparse station coverage and the sensitivity of conventional methods to long wavelengths or near-vertical ray paths, resulting in poor resolution at seismogenic depths. Here, we address these limitations using earthquake inter-event interferometry, which exploits dense inter-source ray coverage to enhance lateral resolution in regions with uneven seismic networks and provides new constraints on crustal structure across Afghanistan and adjacent areas.
We analyzed a high-quality regional dataset of earthquakes recorded between 2006 and 2019 across Afghanistan, eastern Iran, Pakistan, Tajikistan, Turkmenistan, and Uzbekistan. Vertical-component seismograms were processed to retrieve empirical Green’s functions from both earthquake–station surface waves and inter-event correlations of Rayleigh-wave coda. Inter-event interferometry was applied under stationary-phase and minimum-separation conditions, and all paths were stacked using phase-weighted stacking to enhance signal coherence. Rayleigh-wave group velocities were measured with a multiple-filter technique and inverted for period-dependent two-dimensional group-velocity maps using fast-marching surface-wave tomography, with regularization optimized through L-curve analysis and resolution assessed by checkerboard tests. Local dispersion curves were then inverted for one-dimensional shear-wave velocity profiles and assembled into a quasi-three-dimensional Vs model extending to ~60 km depth.
The resulting shear-wave velocity model reveals pronounced lateral and vertical heterogeneity that closely tracks major tectonic provinces. Foreland and intracontinental basins appear as shallow low-velocity domains reflecting thick, weakly consolidated sediments, with contrasting depth evolution between rapidly strengthening foreland crust and basins that retain mid-crustal weakening near major fault systems. The Pamir and western Himalayan collision zone is characterized by a strong upper crust overlying laterally extensive middle- to lower-crustal low velocities, interpreted as thermally and fluid-weakened thickened crust associated with shortening, partial melting, and ductile flow. Farther east, the Hindu Kush exhibits narrow, localized low-velocity anomalies vertically linked to intense intermediate-depth seismicity, consistent with fluid-controlled weakening above the north-dipping Indian lithosphere. To the south, the Makran subduction zone forms the most vertically continuous low-velocity system, extending from the shallow accretionary prism to Moho-proximal depths and reflecting thick sediment accumulation, underplating, hydration, and high pore-fluid pressures above the subducting Arabian plate, bounded by a cold, mechanically strong backstop at the Sistan–Makran transition.
This study presents the first regional application of earthquake inter-event interferometry in Afghanistan, providing new constraints on crustal rheology, fault and suture architecture, and an improved seismic velocity framework for geodynamic analysis, earthquake location, and hazard assessment in a complex continental collision zone.
How to cite: Kazemnia Kakhki, M., Bokelmann, G., Shirzad, T., Sadidkhouy, A., and Esteve, C.: High-Resolution Crustal Imaging of Afghanistan from Earthquake Inter-Event Interferometry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13717, https://doi.org/10.5194/egusphere-egu26-13717, 2026.
California, located along the transform boundary between the Pacific and North American plates, hosts a complex fault system, a long history of damaging earthquakes, and frequent small earthquakes. While earthquakes arise from the buildup and release of elastic stress, detailed knowledge of principal stress orientations, absolute stress magnitudes, and fault instability remains limited. Understanding stress distribution and its interaction with faults is key to assessing tectonic evolution and seismic hazards. Here we obtain 810,562 high-quality focal mechanisms in California combining machine-learning-based phase pickers and REFOC algorithm, representing 51.5% of all relocated earthquakes from 1981 to 2021. These mechanisms enable us to invert for 2D and 3D stress models of California’s crust, including principal stress orientations, faulting style, R-ratio, and fault instability (how close each fault’s orientation is to optimal failure) for 350 major faults. The results reveal a heterogeneous stress field: transpressional regimes dominate the northern and central San Andreas Fault (SAF) system, strike-slip regimes dominate the southern SAF system, and transtensional regimes prevail in the Walker Lane and Eastern California Shear Zone. Stress rotations over ~50 km are closely related to fault geometry, interactions, and strain partitioning. Most faults with low instability are either less optimally oriented to fail under the background stress field or located in areas with recent major ruptures. These findings underscore the tight coupling between stress and fault systems in California and the value of continuous stress monitoring and improved modeling for time-dependent seismic hazard assessments and understanding ongoing tectonic processes.
How to cite: Cheng, Y., Bürgmann, R., Taira, T., Liao, Z., and Allen, R.: Stress model of California: Fault–stress interactions across a complex plate boundary system from focal mechanisms of small earthquakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11610, https://doi.org/10.5194/egusphere-egu26-11610, 2026.
Constraining seismic velocity discontinuities at depths of ~410 km (D410) and ~660 km (D660) is critical for understanding mantle dynamics. Receiver function (RF) studies have revealed the widespread presence of a low-velocity layer (LVL) immediately above D410, supporting the global water‐filter model. Numerical experiments further predict the occurrence of double LVLs above D410 under specific conditions. However, the relationship between LVL occurrence and underlying mantle processes remains poorly understood. Conventional RF analyses rely on careful selection of high-quality traces from multiple teleseismic events at individual stations, followed by slant stacking within a time window around the P-to-S converted phase (P410S) from D410. This approach reduces data coverage and reproducibility and depends on reference Earth velocity models to align RFs. Because true mantle velocity structure and discontinuity depths deviate from these models, slant stacking is often ineffective, particularly for weak and complex converted phases associated with LVLs above D410. In this study, we apply an automated, data-driven machine learning approach to delineate LVLs above D410 using RFs from global seismic stations. Our method aligns the P410S phase without invoking theoretical travel times, instead relying on patterns inherent in the data. We demonstrate that the resulting alignment is physically meaningful and directly reflects velocitystructure near D410. This automated framework significantly improves efficiency, objectivity, and reproducibility in RF analysis. Our results reveal three global patterns of seismic velocity structure near D410: (1) a thick LVL associated with cold mantle regions and subducting slabs; (2) a double LVL, with variable inter-layer spacing, linked to hot mantle and fast upwelling; and (3) a thin LVL correlated with slower upwelling. These observations indicate that LVLs above D410 are a global feature consistent with the water‐filter model, while their detailed characteristics reflect variations in mantle upwelling style beneath seismic stations.
How to cite: Koireng, T. R. and Bharadwaj, P.: Spatial variations of the low-velocity layer above the 410-km discontinuity and their relationship to mantle dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7533, https://doi.org/10.5194/egusphere-egu26-7533, 2026.
The mantle wedge seismicity of the Atacama segment of the Northern Chilean subduction, a region with complex slab geometry, has recently been mapped in a high-density seismicity catalog. In order to better constrain the underlying mechanisms responsible for its occurrence, we investigate the spatio-temporal evolution of the seismicity along the plate interface and within the overriding (upper) plate. We find that the b-value of the mantle wedge seismicity is consistently greater than 1, averaging around 1.5, and that for earthquakes of similar magnitude, there are few, if any, aftershocks in the mantle wedge compared to the interface seismicity. We also estimate the seismic wave velocities Vp and Vs according to the amount of serpentinization and compare to the results of recent high quality tomography images. We estimate that the region of active seismicity, located mainly between 450-550°C isotherms, corresponds to a partially serpentinized part of the mantle wedge while the corner of the cold nose, which corresponds to a fully serpentinized zone, is deprived from earthquakes.
How to cite: Gardonio, B., Münchmeyer, J., Brunet, F., Hernández-Soto, N., Auzende, A.-L., and Socquet, A.: The Chilean Mantle Wedge seismicity as a marker for serpentinization., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17464, https://doi.org/10.5194/egusphere-egu26-17464, 2026.
The Western Churchill Province (WCP) of northern Canada is a complex assemblage of Archean to Proterozoic crust, yet its lithospheric architecture remains incompletely constrained. We present a comprehensive receiver function study of crustal structure across the WCP using approximately 5,000 high-quality P-wave receiver functions recorded at 39 broadband seismic stations between 2000 and 2025. Data quality was ensured using DeepRFQC, a machine-learning–based automated quality control framework.
Crustal thickness and bulk composition were estimated through H–κ stacking, while harmonic decomposition and differential evolution inversion of receiver functions using RAYSUM were applied to investigate crustal anisotropy, dipping interfaces, and seismic velocity structure. The mean Moho depth across the WCP is 40 ± 5 km, with pronounced lateral variability. The deepest Moho is observed in the northernmost and southernmost regions, whereas the central WCP exhibits comparatively thinner crust.
Bulk VP/VS ratios are relatively uniform (1.76–1.79), consistent with predominantly felsic crust, although elevated values near northern Hudson Bay suggest localized mafic intrusions. Harmonic decomposition reveals coherent azimuthal patterns indicative of crustal anisotropy and dipping structures, with mid-crustal discontinuities identified at approximately 9 and 30 km depth.
The orientations of harmonic components correlate with regional magnetic anomalies and independent SKS shear-wave splitting measurements, implying strong coupling between crustal structure and lithospheric mantle fabric. Comparisons with Bouguer gravity anomalies indicate that gravity variations are primarily controlled by subsurface density variations, as reflected in VP/VS ratios, rather than by Moho topography. These results provide new constraints on the crustal architecture and lithospheric coherence of the Western Churchill Province.
How to cite: Sabermahani, S., Frederiksen, A., and Drayson, D.: Receiver Function Constraints in the Western ChurchillProvince, Northern Canada, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8116, https://doi.org/10.5194/egusphere-egu26-8116, 2026.
Two earthquakes with Mw 6.1 occurred in Sındırgı–Balıkesir, western Türkiye, within a few months (10 August 2025 and 27 October 2025). This short time separation provides a valuable opportunity to compare spatiotemporal changes in post-event seismicity and faulting parameters under broadly similar regional conditions, while also allowing potential differences in detection capability and catalogue completeness between the two periods to be handled explicitly.
In this study, a homogenised regional earthquake catalogue is analyzed within an explicit magnitude-of-completeness (Mc) framework to minimize bias arising from temporal variations in detectability when comparing the two post-event periods. Completeness is assessed in a time-dependent manner, and all subsequent analyses are conditioned on the estimated Mc to ensure a like-for-like comparison between the August and October sequences. The aftershock sequences are examined in both space and time, spatiotemporal clustering and migration patterns are evaluated from the mapped aftershock distributions, while temporal decay is characterized using the Omori–Utsu law by estimating and comparing sequence-specific decay parameters. In parallel, b-values are estimated from the Gutenberg–Richter frequency–magnitude distribution and their spatial variations are evaluated to identify potential heterogeneity in the post-event stress state and rupture environment across the source region.
To link seismicity patterns with faulting behaviour, focal-mechanism solutions are used to determine the dominant faulting styles, the principal P- and T-axis orientations, and the regional stress regime associated with each sequence. The joint interpretation of aftershock decay, b-value variability, and mechanism-derived faulting characteristics provides an integrated, catalogue-consistent comparison of post-event behaviour for the August and October 2025 earthquakes, and yields a consolidated description of how seismicity and faulting evolve in the Sındırgı region of western Türkiye following closely spaced moderate–large events.
How to cite: Tamtaş, B. D.: Seismicity characteristics of Sındırgı-Balıkesir in western Türkiye in the context of the 10 August 2025 (Mw=6.1) and 27 October 2025 (Mw=6.1) earthquakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13613, https://doi.org/10.5194/egusphere-egu26-13613, 2026.
Reliable, stable, and internally consistent moment magnitude (Mw) estimates are essential for seismic hazard assessment and earthquake source characterization. Full waveform inversion provides physically robust seismic moment estimates; however, its applicability is often constrained by data quality, network geometry, and modeling assumptions. Conversely, coda-based approaches are a more efficient alternative that are less sensitive to radiation pattern and path effects. This study presents a systematic comparison between coda-derived moment magnitudes (Mw-coda) estimated using the Qopen framework and those (Mw-ISOLA) obtained from moment tensor inversion conducted through the ISOLA software.
Analysis is based on the same dataset examined by Özkan et al. (2024), comprising 303 local earthquakes (2.5 ≤ ML ≤ 5.7) recorded by 49 broadband stations in the Sea of Marmara region, NW Türkiye. Qopen is utilized to jointly invert S-wave and coda-wave envelopes by employing Radiative Transfer Theory. This process yields frequency-dependent attenuation parameters and coda-derived source spectra, from which the Mw-coda is estimated. For a subset of these events with sufficient waveform quality and azimuthal coverage, independent seismic moment estimates are obtained through time-domain waveform inversion using ISOLA.
Overall, we aim to evaluate the agreement and consistency between Mw-coda and Mw-ISOLA in terms of magnitude scaling, scatter, and potential systematic bias, with particular emphasis on magnitude range, source depth, and signal-to-noise conditions in a tectonically complex region characterized by strong lateral heterogeneity and frequency-dependent attenuation.
How to cite: Özkan, B., Eken, T., Gaebler, P., Yolsal-Çevikbilen, S., and Taymaz, T.: Comparisons of Source Parameter Estimates Based on Moment Tensor and Coda Analysis Methods in the Sea of Marmara, NW Türkiye, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19204, https://doi.org/10.5194/egusphere-egu26-19204, 2026.
According to the China Earthquake Networks Center (CENC), an MS6.8 earthquake occurred in Dingri County, Tibet Autonomous Region, China, on January 7, 2025, with a focal depth of 10 km. The epicenter was located in the southern part of the Tibetan Plateau. Due to the northward push of the Indian Plate, a series of north-south trending rifts have formed within the block containing the epicenter. The seismogenic fault is identified as the Dengmocuo Fault in the southern segment of the Shenzha-Dinggye Rift. Within one week after the mainshock, 55 earthquakes of MS≥3.0 were recorded, including one aftershock of MS≥5.0—an MS 5.0 event on January 13th. Focal mechanism solutions from different institutions consistently indicate that the mainshock was an extensional rupture event with a nearly north-south striking plane, essentially consistent with the trend of the Shenzha-Dinggye Rift. Based on the CENC catalog, earthquakes of ML≥3.0 within the aftershock zone are overall distributed along a north-south orientation. The epicentral distribution map shows that, bounded by latitudes 28.8°N and 28.6°N, the aftershock zone can be divided into three main areas: northern, central, and southern. The mainshock is located in the southern area. ML≥3.0 aftershocks are primarily distributed in the northern and southern areas, with fewer and more scattered events in the central area.
We collected waveform data for earthquakes of M≥3.0 within the aftershock zone from January 7 to 14. After quality screening, we determined the focal mechanism solutions for moderate and small earthquakes based on P-wave first motions, obtaining solutions for a total of 30 events. The results show that the focal mechanisms in the northern and central areas are predominantly strike-slip, although the number of solutions from the central area is limited. The focal mechanisms in the southern area are relatively complex, mainly characterized by extension with a subordinate strike-slip component. Subsequently, we inverted the regional stress field. Given that the aftershocks are basically aligned north-south with a narrow east-west distribution, we calculated the stress field from south to north at intervals of 0.2 degrees using a radius of 20 km. The calculation results show that the orientation of the maximum principal compressive stress (σ1) within the aftershock zone is essentially north-south, indicating that the overall rupture is dominated by east-west extension. Furthermore, the R-values from north to south are 0.8, 0.5, 0.1, and 0.2, respectively. This reveals a gradational stress pattern across the entire aftershock zone: "strong compression in the north → weak planar stress in the central area → weak compression in the south," with no abrupt changes. This suggests that the post-mainshock stress adjustment is continuous and controlled by the regional tectonic setting, with no significant stress discontinuity. A transition in the stress state from compression in the north to extension in the south is observed.
How to cite: Ma, Y. and Wang, Y.: Study on the Stress Characteristics of the Aftershock Sequence of the 2025 Dingri, Tibet MS6.8 Earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11123, https://doi.org/10.5194/egusphere-egu26-11123, 2026.
Earthquake locations derived from seismic phase arrival times are highly dependent on the velocity model used to predict theoretical travel times. In operational monitoring, simplified 1D velocity models are commonly used to ensure rapid processing, but such approximations may introduce systematic biases in hypocentral estimations, particularly in regions characterized by strong lateral heterogeneities. This issue is especially relevant in mainland France, where complex crustal structure challenges standard localization strategies.
In this study, we focus on quantifying the impact of different velocity models on earthquake locations, with particular emphasis on the contribution of a national 3D velocity model derived from passive seismic imagery. To minimize the influence of network geometry and isolate the effect of velocity structure, we rely on a high-quality reference catalog extracted from more than 88 000 seismic events reported in the CEA catalog since 1963 (Mazet-Roux, 2025). Event selection is based on Ground Truth (GT) criteria, which assess epicentral location accuracy solely from network geometry (Bondár et al., 2001; Bondár et McLaughlin, 2009). The 22 000 events satisfying the GT5 95% criteria, associated with an epicentral accuracy better than 5 km with a 95% confidence level, define our reference event set.
We relocate this reference catalog using two advanced location algorithms capable of incorporating complex velocity structures. NonLinLoc performs a fully probabilistic search of the solution space and estimates full hypocentral uncertainty distributions (Lomax, 2008; Lomax et al., 2009), while iLoc applies a hybrid, iterative approach optimized for high-precision earthquake location (Bondár and McLaughlin, 2009; Bondár and Storchak, 2011). These methods are first compared using a common 1D velocity model (. The impact of a regional 3D velocity model, obtained through the homogenization of multiple regional models constrained by passive seismic tomography (Arroucau, 2020; Arroucau et al., 2021), is then assessed using the probabilistic NonLinLoc approach.
Regardless of the location algorithm or velocity model considered, more than 95% of the reference events exhibit epicentral differences smaller than 5 km, reflecting the robustness of the GT-based event selection. The differences mainly concern depth estimates and the associated uncertainties.
Indeed, using a common 1D velocity model, significant differences arise in depth determination and associated uncertainties. NonLinLoc systematically converges toward free-depth solutions with quantified uncertainties, whereas iLoc fixes the depth for more than 55% of the events when depth is poorly constrained.
The introduction of the 3D velocity model leads to systematic changes in hypocentral depths, with inversions yielding statistically deeper events on average and uncertainty ellipses becoming better constrained compared to 1D velocity model, despite a slight statistical increase in depth uncertainty for reference events. Differences in depth uncertainties seem to reveal regional variability and possible dependence on event depth. Comparisons with well-documented seismic sequences and previous studies are discussed to better interpret the observed differences between velocity models.
How to cite: Pantobe, L., Mazet-Roux, G., Bollinger, L., Vallage, A., Bertin, M., and Vergne, J.: Relocation of a reference seismic events catalog: influence of 1D and 3D velocity models and location methods, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11852, https://doi.org/10.5194/egusphere-egu26-11852, 2026.
We succeeded to run Obspy—the popular seismic Python toolkit—entirely in the browser using WebAssembly and a novel, package distribution called
emscripten-forge. This breakthrough eliminates the need for local installations or complex backends for small to medium sized data.
Now, anyone can perform core seismic data analysis—including reading, processing, and visualizing seismological data—directly in their web browser,
on many devices, from desktops to mobile phones. For developers, Obspy's capacities can be embedded in ordinary static web sites that are highly
scalable, without any complex backend to maintain. Additionally, Large Language Models (LLMs) can command Obspy directly in the browser, allowing to build seismic applications driven by natural language.
The implications are profound. The lack of complex installations, backend maintenance, or specialized deployments, drastically simplifies using and
building seismic data analysis tools. Educators can incorporate hands-on seismology into curricula without technical overhead. Researchers can share
apps or notebooks, and explore data without fighting non-reproducible compute environments. Engineers in remote settings gain access to powerful
analytical tools on mobile devices. Users can interact with seismic data in the browser in natural language, lowering the barrier for non-experts and
professionals alike.
We will demonstrate this with JupyterLite, showcasing a fully functional, Jupyter environment with Obspy and scientific Python tools running completely in the browser, without any server and with LLM assistance. We will also highlight the limitations of in-browser execution, particularly regarding multi-threading, memory constraints and compute overhead. All of the demonstrated technology is open source, published under permissive licenses, and therefore available for anyone to use, modify, and build upon.
How to cite: Meschede, M., Corlay, S., and Beier, T.: Obspy + WebAssembly: Running AI-Assisted Seismic Analysis in the Browser, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18563, https://doi.org/10.5194/egusphere-egu26-18563, 2026.
Earthquake rupture forecasting is a critical component of seismic hazard analysis and requires identifying physically plausible rupture paths across complex fault networks. At its core, this task could be formulated as a large-scale combinatorial optimization problem, which involves selecting an optimal subset of fault segments from a set of candidates. Such problems pose significant challenges for traditional algorithms, as the number of admissible multi-fault ruptures grows combinatorially. Current operational workflows rely on locally applied plausibility filters. While computationally efficient, such greedy local heuristics risk excluding globally competitive rupture scenarios, particularly in regions with dense fault connectivity and competing rupture pathways.
This work investigates whether quantum annealing hardware can serve as a sampling accelerator for exploring the ensemble of physically plausible ruptures beyond what is currently accessible to classical approaches. Designing a problem formulation that remains scientifically meaningful while respecting the constraints of current quantum hardware (size, noise, etc.) is nontrivial, and naïve encodings often collapse under these limitations. We encode rupture plausibility modeling as low energy solutions to a quadratic unconstrained binary optimization (QUBO) problem defined on a fault-network middle graph. Binary variables represent activated fault segments, while local interaction terms encode Coulomb stress transfer (as a proxy for pairwise rupture compatibility), continuity preferences, and branching behavior. Here, we adopt a classical-quantum hybrid workflow: the quantum annealer is used to sample globally competitive rupture candidates, while classical post-processing implements physical constraints to filter out non-physical ruptures.
The workflow is demonstrated on a subset of the fault network used in the 2023 USGS National Seismic Hazard Model including over 200 fault segments, using both simulated thermal and quantum annealing on D-Wave hardware. Results show that our hardware-aware formulation and conditioning enable robust sampling on comparatively large fault-network instances. Views on quantum computing are polarized: some overstate its power, while others dismiss it as impractical. Our results help bridge this by establishing a concrete, testable pathway for integrating quantum annealing into rupture-modeling workflows on existing purpose-built quantum devices.
—---
This work is supported by the ICSC National Research Centre for High Performance Computing, Big Data and Quantum Computing (CN00000013, CUP D53C22001300005) within the European Union-NextGenerationEU program (National Recovery and Resilience Plan (PNRR) - Mission 4 Component 2 Investment 1.4.)
How to cite: Stallone, A., Dukalski, M., Diaferia, G., and Milner, K.: Using Quantum Annealing for Identifying Plausible Earthquake Rupture Paths in Fault Networks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18185, https://doi.org/10.5194/egusphere-egu26-18185, 2026.
The global coda-correlation wavefield is a mathematical representation of the seismic wavefield generated by large earthquakes, computed by cross-correlating the long-lasting coda waves recorded by a worldwide network of seismometers. Unlike the common assumptions that the cross-correlation functions are Green’s functions between station pairs, earthquake coda-correlation features arise from cross-terms of in reverberating body waves of common slowness that share common slowness characteristics a subset of propagation legs (e.g., Hrvoje & Phạm, 2018; Phạm et al., 2018). This wavefield has offered new constrains on the deep Earth's interior (e.g., Hrvoje & Phạm, 2018; Ma & Tkalčić, 2024). However, quantitative interpretation of these features for tomographic imaging has been hindered by the lack of distributed sensitivity kernels relating observed correlation signals to Earth structure heterogeneities.
In this study, we develop a forward modeling framework for the earthquake coda-correlation wavefield bypassing conventional cross-correlation of late-coda waveforms. The forward-modeled correlograms reproduce features obtained through conventional stacking with a significantly improved signal-to-noise ratio. Building on this framework, we derive finite-frequency traveltime banana-doughnut sensitivity kernels using adjoint methods (e.g., Tromp et al., 2010; Fichtner, 2014), which quantify how traveltime measurements of correlation features depend on perturbations in P-wave velocity, S-wave velocity, and density.
We compute sensitivity kernels for prominent correlation features (P*, ScS*, and others) at station separations ranging from 30° to 180°. The kernels reveal extensive sampling of Earth's mantle, outer core, and inner core, with spatial-sensitivity patterns fundamentally different from those of body waves in direct seismic wavefield. For antipodal station pairs, correlation features exhibit strong sensitivity throughout the deep interior, including regions poorly sampled by traditional seismic phases. Our results confirm that correlation features form through constructive interference of body-wave pairs with similar slowness, rather than representing Green's functions between station pairs.
This work establishes the theoretical foundation for coda-correlation tomography, enabling future three-dimensional imaging of Earth’s internal structure with unprecedented sampling of the deep interior. The sensitivity kernels provide a pathway to exploit the wealth of information contained in earthquake coda for high-resolution mantle and core tomography.
Reference
Ma, X. & Tkalčić, H. (2024) Low seismic velocity torus in the Earth's outer core: Evidence from the coda correlation wavefield, Sci. Adv., 10, 35, https://doi.org/10.1126/sciadv.adn55.
Fichtner, A. (2014). Source and processing effects on noise correlations. Geophys. J. Int., 197(3), 1527-1531. https://doi.org/10.1093/gji/ggu093
Phạm, T-S., Tkalčić, H., Sambridge, M. & Kennett, B.L.N. (2018) The Earth's correlation wavefield: late coda correlation, Geophys. Res. Lett., 45, https://doi.org/10.1002/2018GL077244.
Tkalčić, H., & Phạm, T.-S. (2018). Shear properties of Earth's inner core constrained by a detection of J waves in global correlation wavefield. Science, 362, 329. https://doi.org/10.1126/science.aau7649
Tromp, J., Luo, Y., Hanasoge, S., & Peter, D. (2010). Noise cross-correlation sensitivity kernels. Geophys. J. Int.,183(2), 791-819. https://doi.org/10.1111/j.1365-246X.2010.04721.x
How to cite: Wei, Z., Wang, S., Phạm, T.-S., and Tkalčić, H.: Sensitivity Kernels for Earthquake Coda-Correlation Wavefield Features and Applications to Global Seismology , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13130, https://doi.org/10.5194/egusphere-egu26-13130, 2026.
Repetitive rupture of the same asperity has been documented in various tectonic settings through the observation of highly correlated waveforms from co-located earthquakes. These events, known as repeaters, are of particular interest because they provide key constraints on small-scale fault processes and can be used to investigate slip rates on faults, aseismic deformation, earthquake nucleation... In fewer cases, highly similar earthquakes exhibiting polarity inversions at all recording stations have been identified. These so-called anti-repeaters are thought to rupture the same asperity with an inverted focal mechanism and are associated with specific driving processes. To our knowledge, no intermediate case involving rupture of the same asperity with a change in slip direction (rake) has been reported, despite the fact that such a scenario is theoretically plausible.
In this study, we search for such events within the aftershock sequence of the M7.1 Miyagi-Oki earthquake (26 May 2003), in the northeastern Japan subduction zone. This intermediate-depth intraslab sequence (70 km depth) exhibits a high seismicity rate and is well recorded by a dense seismic network. Using data from the 17 closest three-component broadband stations, we compute waveform coherence, cross-correlation and anti-correlation (flipped traces) for both P and S waves of close event pairs. We identify 40 pairs of highly similar earthquakes displaying polarity inversions at several (but not all) stations. After performing relative hypocenter relocation using correlation-derived time delays, we retain ten co-located pairs with high-quality waveform similarity and polarity inversion. By comparing measured amplitude ratios with synthetic radiation pattern ratios, we invert the rake change for each event pair.
At this stage, the physical mechanism responsible for this newly identified class of similar earthquakes, that we name ‘rake-changing repeaters’, is uncertain. A change in rake between successive ruptures of the same asperity likely reflects a highly localised modification of the stress field. It could be driven by transient pore-fluid pressure variations or stress perturbations induced with nearby moderate slip. The identification of rake-changing repeaters opens new perspectives for investigating the complexity of local faulting processes at depth, and complements existing insights from repeaters and anti-repeaters.
How to cite: Costes, L., Marsan, D., and Gardonio, B.: Rake-changing repeaters : a new class of co-localised similar earthquakes with both correlated and anti-correlated waveforms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12485, https://doi.org/10.5194/egusphere-egu26-12485, 2026.
Seismological signatures of aseismic slip include tectonic tremors, repeating earthquakes, and earthquake swarms. They are most commonly documented in subduction margins, where their depth distribution and temporal behavior reflect slab geometry, fluid release, and plate interface rheology. Their occurrence in continental collision belts, however, remains unclear. Taiwan provides a unique natural laboratory to address this gap. Here we investigate how earthquake swarms interact with repeating earthquakes (REs) and tectonic tremors, and how their coupling varies with depth along the west-dipping Central Range Fault.
Using a 24-year seismic catalog, we show that tremors (mostly >25 km), REs (15–25 km), and swarms (<20 km) align spatially along the same fault system but exhibit distinct recurrence behaviors and interaction thresholds. We find that temporal interaction among these phenomena is strongly depth-dependent and controlled by spatial overlap. Swarms and REs display the strongest coupling within shared fault segments, consistent with asperities being repeatedly loaded by surrounding aseismic creep and transient slip-rate accelerations, supported by the rapid diffusivity of catalogued swarms (several m²/s). In contrast, tremors occur in the lower crust under near-critical frictional conditions and generally interact with seismogenic activity only during periods of elevated aseismic slip, most notably following M6-class earthquakes. Tremors alone exhibit strong tidal modulation (~90% during increasing tidal levels), indicating markedly higher stress sensitivity at depth. Elevated Vp, Vs, and Vp/Vs ratios further delineate a high-stiffness, high–pore-fluid-pressure lower-crustal environment that enables tremor generation beneath the mountain root. Overall, these observations indicate that swarms, REs, and tremors represent depth-stratified manifestations of aseismic slip, with interaction style and stress sensitivity systematically varying with depth.
How to cite: Peng, W. and Chen, K. H.: Depth-dependent interaction of tectonic tremors, repeating earthquakes, and earthquake swarms in a collision zone of Taiwan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15736, https://doi.org/10.5194/egusphere-egu26-15736, 2026.
The Miryang Fault is an inferred fault located in the southeastern Korean Peninsula and is a part of the Yangsan Fault System, which trends NNE-SSW. Although the Miryang Fault appears as a distinct topographic lineament, its activity and characteristics remain poorly constrained due to a scarcity of direct geological and seismological evidence. We investigated seismic activity along the Miryang Fault to delineate subsurface fault structures using earthquake detection, high-precision hypocenter relocation, and focal mechanism analysis. We employed energy-ratio-based automatic detection and determined relative hypocenter locations using the double-difference method. Focal mechanism solutions were derived using P-wave first-motion polarities. Epicenters are concentrated to the west of the surface trace of the Miryang Fault and generally align with its strike. The hypocenters exhibit a strongly linear spatial distribution, distinctively separated into northern and southern clusters. The seismicity tends to become more spatially scattered northward, particularly beyond the northern termination of the surface trace of the Miryang Fault. The southern cluster is characterized by a higher frequency of larger earthquakes and a lower Gutenberg–Richter b-value compared to the northern cluster. Focal depths range from 5 to 20 km, with the southern region showing a narrower range and a concentration at greater depths. Principal Component Analysis of the hypocentral distribution reveals that the fault geometries for both clusters trend NNE-SSW and dip nearly vertically. Both clusters extend approximately 30 km along the strike. Focal mechanisms indicate predominantly dextral strike-slip motion, with strike and dip consistent with the geometry inferred from the spatial distribution. These findings provide new insights into the seismotectonic characteristics of the Miryang Fault and underscore its potential role in the active tectonics of the southeastern Korean Peninsula.
How to cite: Heo, D., Han, J., Kang, T.-S., Kim, S., and Rhie, J.: Subsurface geometry of the Miryang Fault, southeastern Korean Peninsula, inferred from high-precision earthquake relocation and focal mechanism analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16016, https://doi.org/10.5194/egusphere-egu26-16016, 2026.
Currently, when an earthquake with a magnitude (ML) of 3.5 or greater occurs ob the Korean Peninsula, the Korea Meteorological Administration (KMA) performs a post-event precision analysis to address parameters not captured during the real-time detection phase. To ensure consistent and operationally application, we developed the Post-Earthquake Precision Analysis System, which standardizes the entire workflow from data input to staged outputs.The system enhances location accuracy through precise hypocenter relocation, including relative relocation, and characterizes rupture geometry and kinematics using P-wave first-motion polarity and waveform inversion for focal mechanism solutions. Additionally, spectrum-based source parameter analysis is integrated to quantify the physical characteristics of the seismic source. To improve the completeness of the aftershock catalog, the system employs template matching to detect micro-seismic events that often go unnoticed.The Post-Earthquake Precision Analysis System was applied to major seismic events in the Korean Peninsula, yielding high-precision relocated hypocenters, focal mechanisms, and source parameters. We also generated enhanced aftershock lists and systematically organized the spatio-temporal evolution of each sequence in a standardized format. This study presents an operationally-ready analytical workflow and a core output framework for the systematic post-earthquake precision analysis of domestic seismic activity.
How to cite: Byun, A.-H., Jo, E., Choi, M., Choi, Y., Min, K., and Park, S.-C.: Establishment of a precision post-earthquake analysis system and its application to major earthquake on the Korean Peninsula, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8789, https://doi.org/10.5194/egusphere-egu26-8789, 2026.
Dynamic processes operating at continental plate margins, including associated igneous activity, lead to progressive reactivation and modification of the lithosphere and are recorded in the evolving structure of the continental crust. Crustal evolution is strongly controlled by crust–mantle interaction at the Moho, where changes in temperature, composition, and density can be induced by underplating or lithospheric destruction. Consequently, the Moho represents a critical interface at which continental growth, mechanical weakening, and lithospheric removal may occur. Seismic imaging of the uppermost mantle therefore provides direct constraints on the processes governing lithospheric evolution. In this study, we present three-dimensional P- and S-wave tomography of the uppermost mantle beneath the southern Korean Peninsula, derived from Moho-refracted waves. The tomographic models are used to estimate thermal and compositional variations by comparing observed seismic velocities with petrological predictions. A basalt–harzburgite mechanical mixture (MM) was adopted as the baseline model, while an equilibrium assemblage (EA) and an orthopyroxene (Opx)-enriched mantle were additionally considered to evaluate the effects of compositional variability on seismic velocities.
The results showed pronounced regional contrasts in seismic velocity, temperature, and composition. The Gyeonggi Massif and Gyeongsang Basin are characterized by relatively low Vp (≈7.65 km/s) and low Vp/Vs (≈1.73), consistent with a hot, harzburgite-rich mantle and a thin lithosphere. In contrast, the Yeongnam Massif exhibits high Vp (≈7.89 km/s) and high Vp/Vs (≈1.76), indicating a relatively cold mantle with a higher basaltic fraction (40%) within a thick lithosphere. These characteristics are consistent with independent constraints on lithospheric thickness. The hot and thinned harzburgite-dominated mantle is interpreted as the result of lithospheric modification by delamination or thermal erosion. In contrast, basaltic components preserved within the cold and thick lithosphere are interpreted as basaltic underplating associated with Mesozoic subduction, maintained by a stabilized lithospheric root. However, the combination of low Vp (≈7.65 km/s) and exceptionally low Vp/Vs (≈1.70) observed in the western Gyeonggi Massif cannot be explained by either the MM or EA models, whose minimum Vp/Vs values are 1.74 and 1.73, respectively. This discrepancy requires anomalous mantle conditions, such as strong Opx enrichment or pronounced seismic anisotropy. Despite their close spatial proximity, these contrasting mantle properties indicate that distinct geological processes operated beneath different regions of the Korean Peninsula during the Mesozoic–Cenozoic, and that the resulting thermal and compositional signatures are preserved in the uppermost mantle.
How to cite: Kim, M., Song, J.-H., and Kim, S.: Crust–Mantle Evolution beneath the Korean Peninsula Constrained by Temperature and Composition Estimated from Uppermost Mantle Tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16313, https://doi.org/10.5194/egusphere-egu26-16313, 2026.
We present new three-dimensional P- and S-wave velocity models of the northern Iberian Peninsula and Pyrenees using arrival times of local earthquakes and seismic ambient noise.
The arrival time dataset has been built in two steps. First, we have merged the existing seismic bulletins of permanent seismic networks in the region (IGN, ICGC, OMP). Second, we have compiled continuous waveforms of all temporary experiments in the region from 2010 to present and have been automatically picked using the deep-learning picker PhaseNet, substantially increasing data coverage in regions with sparse permanent instrumentation. Using this augmented arrival time dataset, we have inverted it simultaneously for P and S wave velocity structure and earthquake relocation. Since the region is too large for the flat-earth approximation used in the tomography code we have obtained multiple overlapping smaller models and calculated the final model by averaging the individual models.
To further enhance structural resolution, particularly in areas with limited earthquake ray coverage, we incorporated results from ambient noise tomography based on inter-station surface-wave dispersion measurements. These data provide complementary constraints on the shallow crust and improve lateral continuity of the velocity model, especially in aseismic regions and across major sedimentary basins.
The obtained P and S wave velocity models provide detailed images of the subsurface structure of the region, including parts that were poorly imaged before. The addition of arrival times picked at temporary stations has been of fundamental importance to illuminate the central part of the region, because of its low seismic activity and lack of permanent stations. Particularly well imaged are the sedimentary basins, including the southern Aquitaine basin, and the northern Ebro and Duero basins and their connection along the Rioja Trough.
How to cite: Villaseñor, A. and Chevrot, S.: Local earthquake and ambient noise tomography of the northern Iberian Peninsula and Pyrenees , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11950, https://doi.org/10.5194/egusphere-egu26-11950, 2026.
The Lower Taylor Valley, owing to the McMurdo Dry Valleys, are one of the coldest and driest desert ecosystems on the planet and represent a key natural laboratory for investigating permafrost, glacier dynamics, and subsurface geochemical and geophysical processes. In recent years, a systematic and dense field measurements of soil gas concentrations and fluxes revealed an anomalous greenhouse gas concentration not randomly distributed, but forming an elongated E–W oriented zones that follow the main principal axes of the valley. To investigate the structure of the permafrost and shallower crustal layers, as well as the preferential path controlling the multigas emissions, the geochemical surveys have been complemented, for the first time in this area, by passive seismic observations. To do that, a passive seismic experiment was carried out between December 24, 2024, and January 23, 2025, using an array of 15 three-component nodal sensors deployed in the central portion of the Lower Taylor Valley. The array geometry was designed in a spiral configuration to enhance azimuthal coverage, reaching a maximum aperture of 1.5 km. Despite the severe Antarctic environmental conditions, we successfully recorded about 25 days of continuous seismic data, constructing thus a dataset of high-quality recordings. Preliminary analyses revealed coherent seismic arrivals consistently recorded across the array. The signals are characterized by regular, high-frequency repeating peaks in the seismograms and were interpreted as icequakes originating from the Commonwealth Glacier at the northern boundary of the valley. Additionally, we also identified a variation in signal amplitude and frequency content among stations, suggesting a possible difference in local environmental conditions or subsurface properties affecting the seismic signal.
How to cite: Baccheschi, P., Hailemikael, S., Sciarra, A., Wilson, G. S., Florindo, F., Beagley, J., Mazzoli, C., Davidson, L., Berquist, C., and Ruggiero, L.: Seismological and Geochemical Monitoring of Greenhouse Gas Emissions in the Lower Taylor Valley (McMurdo Dry Valleys, Antarctica), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10323, https://doi.org/10.5194/egusphere-egu26-10323, 2026.
Jointly with the 33rd expedition of Bulgarian Antarctica institution, the National Center of Meteorology (United Arab Emirates) installed its first broadband seismic station in Livingstone Island in Antarctica. This deployment aims to detect earthquakes, ice sheet dynamics, and volcanic activities. In addition to the exciting seismic stations on the island, the seismic installation includes two advanced seismometers, Trillium 120 and Trillium 40 (Nanometric), to accurately detect local, regional and tele seismic events.
The seismic station will be added value to the existing networks on the island as well as covering the gap analysis for more accurate data collection. In addition, since the station located near to active volcanic eruption (Deception Island), It will provide crucial data to interpret the interactions between seismic, cryosphere changes, and volcanic activities.
The project highlights continuous and reliable seismic recording in harsh polar environments. During the Bulgarian Expedition 34 (2025–2026), the data were collected and analyzed, demonstrating that there were no gaps or interruptions throughout the entire year of 2025.
The station is expected to become a vital tool for future studies, potentially integrating high-resolution seismic monitoring with glaciological and meteorological data collection. This comprehensive approach will enhance our understanding of the dynamic relationships among tectonic, cryosphere, and volcanic processes.
How to cite: Alameri, B., Alebri, K., Hamidatou, M., Alkaabi, A., and Megahed, A.: Continuous Seismic Observation under Extreme Environmental Conditions , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14941, https://doi.org/10.5194/egusphere-egu26-14941, 2026.
Surface wave tomography yields high resolution models for the seismic velocities
in the earth’s upper mantle. To extend the imaging into the mantle transition
zone and into the lower mantle below, additional constraints from teleseismic
body waves, which probe these deeper regions, are needed. Here, we combine a
large new dataset of teleseismic P and SV travel times obtained via an automatic
picking algorithm (Stampa et al., 2024), with waveform fits from Automated
Multimode Inversion (AMI; e.g. Dou et al. (2024)) in a joint inversion. The
sensitivity volumes for the teleseismic body waves used in the inversion are
approximated using ray tracing in a spherically symmetric background model.
For the P and SV arrival-time data sets, travel-time corrections are calcu-
lated to account for the differences induced by the ellipticity of the earth. The
frequency-dependent effects of anelasticity on the propagation of the teleseismic
waves are estimated and accounted for, using the measured central frequencies
of the waves’ arrivals. Travel time anomalies resulting from crustal structure
are estimated and accounted for using the ECM1 crustal model.
The preliminary results show a marked improvement in the resolution of
structure at depths below 400 km, in particular in regions of dense station
coverage, including Europe, North America, and the subduction zone regions
around the Pacific Ocean.
References
Dou, H., Xu, Y., Lebedev, S., de Melo, B. C., van der Hilst, R. D., Wang, B., &
Wang, W., 2024. The upper mantle beneath Asia from seismic tomography,
with inferences for the mechanisms of tectonics, seismicity, and magmatism,
Earth-Science Reviews, 255, 104841.
Stampa, J., Eckel, F., Keers, H., Lebedev, S., Meier, T., & AlpArray and
SWATH-D Working Groups, 2024. Automated measurement of teleseismic
P-, SH-and SV-wave arrival times using autoregressive prediction and the
instantaneous phase of multicomponent waveforms, Geophysical Journal In-
ternational , 239(2), 936–949
How to cite: Stampa, J., Lebedev, S., Meier, T., Keers, H., and Henriksen Krogh, J.: Joint inversion of a new global data set of teleseismic P and SV arrival times and the waveforms of surface and regional body waves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18156, https://doi.org/10.5194/egusphere-egu26-18156, 2026.
The Core-Mantle Boundary (CMB) is a critical interface influencing
Earth’s thermal and chemical evolution. Among the various features
in the CMB region, the D” seismic reflector—located approximately
300 km above the CMB—is of particular interest. Mineral physics
links this reflector, which generates distinct P- and S-wave reflec-
tions and increases S-wave velocity by 2–3 % and P-wave velocity by
0.5–2 %, to a phase transition from bridgmanite to post-perovskite.
If these reflections stem from the phase transition, variations in re-
flector depth directly reflect lateral changes in temperature and rock
composition near the CMB. In this study, we modelled phase transi-
tions across a range of temperature–composition conditions to pro-
duce synthetic seismograms, demonstrating how these factors influ-
ence velocity jumps, reflector depth, and reflectivity. We also com-
piled data from over 65 previous studies measuring the D” reflector’s
depth, addressing the lack of a coherent global map since the identifi-
cation of post-perovskite in 2004. Our compilation shows that shal-
lower reflector depths are found in seismically fast (cold) regions,
while deeper reflectors are found in seismically slow (hot) regions,
consistent with theoretical predictions of post-perovskite occurrence.
This global map establishes a consistent framework for comparing
phase transition models with seismic observations.
How to cite: Pahlings, J., Houser, C., Hernlund, J., and Thomas, C.: Mapping the D” Seismic Reflector: Insights from Phase Transition Modelling and Global Seismic Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18989, https://doi.org/10.5194/egusphere-egu26-18989, 2026.
In its routine analysis the Federal Seismological Survey at BGR evaluates local seismic earthquakes in Germany as well as teleseismic events. For the analysis of teleseismic events we use the seismic stations in Germany and in some cases stations from surrounding countries. Because the stations are far from the events, we apply array methods (f-k analysis) to identify distinct seismic phases and locate events. We use waveforms of the densely spaced Gräfenberg array sites (GRF) with an interstation distance of 10 to 15 km or of the large aperture German Regional Seismic Network (GRSN) stations if coherent phase picking is possible.
The majority of detected and evaluated phases are first-arriving phases, such as P phases and, at more distant epicentre distances, Pdiff and PKP phases. However, in the case of stronger events, we can also detect later phases, such as PP, PS, SS, PcP, ScS, SKS and others. These secondary phases are identified well via slowness, azimuth and travel time.
Here, we show some striking examples with PKP phases as well as later phases.
Events with PKP phases are numerous and mostly located within the subduction zones at Fiji and Tonga. Due to the epicentral distances of around 145 degrees the German stations are close to the caustic of PKP branches. Therefore, PKPdf, PKPbc, and PKPab often show strong amplitudes. In some cases all three branches as well as their corresponding depth phases are visible and can be picked.
Some of the later phases, such as SKP, are rarely observed. We investigate to what extent the magnitude, the focal depth and also the focal mechanism are responsible for the amplitude of the phase and thus for their visibility at German stations. In order to determine the influence of the focal mechanism, we use the solutions of international agencies and calculate radiation coefficients for the respective phase in the direction of the stations under consideration. This approach may help to decide whether an observed depth phase is a pP or sP phase, for example, and thus enables a better depth determination.
Another special feature are very late phases, such as PKKP. They run on the long path around the Earth to the station and have an azimuth shifted by 180 degrees to the short path. These phases may be misinterpreted as independent events. Here, we show an example.
How to cite: Plenefisch, T., Donner, S., Gaebler, P., Hartmann, G., Roß, O., Stammler, K., and Steinberg, A.: Observation and analysis of core and secondary teleseismic phases at broadband stations in Germany using array methods, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10804, https://doi.org/10.5194/egusphere-egu26-10804, 2026.
The 22 January 2024 Mw 7.0 Wushi earthquake (WSEQ) struck the Wushi Basin along the southern margin of the Tian Shan, Xinjiang, China. As the largest earthquake in the region since the 1992 Mw 7.3 Suusamyr earthquake (Kyrgyzstan), the WSEQ is among the few large earthquakes captured by high-quality observational datasets—including the earthquake early warning network operated by China Earthquake Administration before and a dense temporary seismic array deployed immediately after the mainshock in the Tian Shan region. This provides a rare opportunity to investigate fault network activation and rupture behavior in the tectonically active southern Tian Shan.
We picked and associated Pg/Sg phases using a neural network and the REAL method, respectively, followed by relocating all events via NonLinLoc and the double-difference relocation method. Focal mechanisms were also determined for aftershocks with M ≥4.
Our results are as follows: 1) The seismogenic fault of the WSEQ strikes northwest, correponding to a moderately-dipping, oblique-reverse main-fault rupture; 2) The mainshock triggered reactivation of a series of small-scale faults, and aftershock distribution is closely linked to these active faults in the study area; 3) Aftershocks are concentrated on subfaults rather than the main fault; and a shallowly buried subfault produced distinct surface rupture whereas the main fault is completely blind. This fault network, misaligned with the prevailing background stress field, likely forms through a reactivation of inherited weak planes.
These results illustrate that structural inheritance strongly controls fault geometric architecture and underscores the complexity of seismic activity and rupture behavior within the active fault network.
How to cite: Yin, X., Li, T., Cui, H., Chen, J., Chen, J., and Guo, B.: Interlacing ruptures of the 2024 Wushi Mw 7.0 earthquake (Chinese Tian Shan) revealed by dense seismic array observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10685, https://doi.org/10.5194/egusphere-egu26-10685, 2026.
Türkiye is one of the most seismically active regions due to the complex tectonic collisions relative to the Eurasian, African, and Arabian plates in the Eastern Mediterranean region. These tectonic motions have formed two major strike-slip structures: the right-lateral North Anatolian Fault Zone (NAFZ) and the left-lateral East Anatolian Fault Zone (EAFZ). The province of Sındırgı-Balıkesir is located in the southern Marmara region at central-western Türkiye. It is positioned near the southern branches of the NAFZ and the Aegean graben system, where extensional forces in Western Anatolia are observed. In this region, the active faults generally exhibit NE-SW and NW-SE orientations. On October 27, 2025, a magnitude, Mw 6.0 earthquake occurred in Sındırgı-Aktaş near Balıkesir. Understanding the source characteristics of this event is crucial for defining the local fault mechanisms and tectonics, improving seismic hazard and risk assessments, and performing more accurate ground motion analyses in this region. This study aims to resolve the source parameters and rupture characteristics of this earthquake. The seismological waveform data retrieved from the national networks. operated by Disaster and Emergency Management Authority (AFAD) and Kandilli Observatory and Earthquake Research Institute (KOERI). The earthquake source parameters were estimated using the ISOLA software package. To achieve high precision in estimating the seismic moment and focal mechanism, both point-source and potentially multiple-source inversions are performed. This comparison aims to better characterize the fault behaviour within the Sındırgı segment with respect to previously published PDE reports in the region.
How to cite: Küçük, D. and Taymaz, T.: Source Characteristics of the 27 October 2025 Mw 6.0 Sındırgı-Balıkesir Earthquake Sequence in Western Türkiye, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10736, https://doi.org/10.5194/egusphere-egu26-10736, 2026.
The Anatolian Plate has a complex tectonic structure. This is mainly caused by the northward movement of the Arabian Plate and subduction along the Hellenic Arc. Many large earthquakes in Türkiye occur along the right-lateral North Anatolian Fault and the left-lateral East Anatolian Fault. Western Anatolia is dominated by north-south extension. This extension formed the Aegean Extensional Province, which includes E-W trending grabens and NW-SE oriented active faults. One of the key structures in this area is the Simav Fault Zone (SFZ). In this study, we focused on the 28 September 2025 Kütahya-Simav (Mw 5.5) earthquake located on the SFZ. Earthquake catalogs provide basic source information. However, they are often not enough to fully describe fault geometry and fault segmentation. For this reason, a detailed source analysis is needed. In this study, we present a moment tensor solution for the 2025 Kütahya-Simav earthquake. The analysis is carried out using the ISOLA and regional waveform inversion. Broadband seismic data from the AFAD and KOERI networks are used. Both point-source and possible multiple-source inversions are performed. These inversions are used to estimate the focal mechanism, seismic moment, and centroid depth. The quality of the solutions is evaluated using Variance Reduction (VR) and Condition Number (CN) values. The results are compared with previous studies and historical data from the Simav Fault Zone. This allows us to obtain a more reliable solution than standard catalog results. The findings explain the present stress pattern and fault behavior in the Kütahya-Simav region.
How to cite: Altuntaş, N. and Taymaz, T.: Source Characteristics of the 28 September 2025 Mw 5.5 Kutahya-Simav Earthquake Sequence in Western Turkiye, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7814, https://doi.org/10.5194/egusphere-egu26-7814, 2026.
The b-value of the Gutenberg-Richter law represents a fundamental parameter for characterizing earthquake size distributions and assessing crustal stress conditions.
Numerous studies have demonstrated a significant relationship between the b-value and the tectonic stress regime. While low b-values are often associated with stress accumulation and potential precursors to large earthquakes, their applicability as universal precursors remains debated.
This study investigates the spatial and temporal evolution of the b-value preceding large earthquakes (M≥5.5) in regions characterized by contrasting tectonic settings and fault kinematics. We examine geographically and tectonically different areas—such us Italy, China, New Zealand, and Myanmar—which encompass different stress regimes and plate boundary configurations. By systematically analyzing local seismic catalogs from these contrasting regions, we assess whether b-value variations constitute a universal feature of the seismic cycle, or are primarily modulated by region-specific crustal properties.
Each study area is selected according to the seismogenic structures responsible for the target earthquakes. The completeness magnitude (Mc), defined as the lowest magnitude threshold above which the catalog reliably records all or nearly all earthquakes in the region, is rigorously determined as a function of time according to well-established methodologies.
We estimate Mc using the most appropriate method for each region, including either the maximum curvature method or the 90% goodness-of-fit criteria, to ensure robust results.
The b-value is subsequently estimated using the maximum likelihood approach over appropriate spatiotemporal windows preceding each mainshock.
We present preliminary results showing that systematic b-value drops are observed in most cases. Our findings support the hypothesis that such variations represent a robust indicator of progressive stress accumulation. This comparative approach suggests that b-value monitoring can provide valuable precursory signals for seismic hazard assessment across different tectonic contexts.
How to cite: Orlando, M., De Caro, M., and Montuori, C.: Spatial and temporal evolution of the b-value: A comparative analysis across different tectonic settings, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19351, https://doi.org/10.5194/egusphere-egu26-19351, 2026.
The Local Magnitude (ML), was the earliest proposed magnitude scale, allows for rapid determination based on observed amplitudes and a zero magnitude reference amplitudes (A0) derived from local events. However, the amplitudes are susceptible to external factors, the physically robust Moment Magnitude (Mw) was proposed. The previous studies showed a 1:1 relationship between ML and Mw for ML < 6.5 in Southern California; however, ML in Taiwan tend to overestimate when compare to Mw due to different regional attenuation characteristics. Although the previous study has recalibrated the logA0 attenuation model for shallow earthquakes in Taiwan, deep events exhibit an even more significant overestimation, averaging overestimate 0.528. Therefore, this study aims to discuss deep earthquakes in the Taiwan and establish a new logA0 attenuation model for deep events. Since models relying solely on hypocentral distance (R) result in depth-dependent residuals, a depth term (D) was incorporated to account for the physical characteristic of deep seismic waves often propagating through high-Q plates. The derived regression model is:
logA0 = 0.097 - 1.587logR - 0.0014R + 0.417logD ± 0.273
The results demonstrate that logA0 attenuation varies distinctly with distance at different depths, aligning with Richter mentioned that different depth events require distinct calibration. Furthermore, the logA0 value at a hypocentral distance 100 km differs from that of shallow event models, indicating the difference in attenuation properties. The recalibrated ML demonstrates no depth dependency and a consistent 1:1 relationship with Mw, with a standard deviation ±0.160. This study proposed model provides a rapid and precise ML calculation. This new model enhances the reliability of real-time hazard assessment and reduces magnitude conversion errors in catalog combination.
How to cite: Lin, X.-Y. and Wu, Y.-M.: Discussion of Local Magnitude (ML) Scale for Deep Earthquakes in Taiwan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3299, https://doi.org/10.5194/egusphere-egu26-3299, 2026.
The Hälsingland region in central Sweden, within the Proterozoic Fennoscandian Shield, lies near a transition from relatively shallow Moho depths (<45 km) in the west to deeper Moho depths (>50 km) in the east. The region lies close to a broad east-west transition in lower-crustal seismic velocities reported in regional models. Furthermore, it is a seismically active region, host the southernmost surface scarp of a glacially triggered fault identified in Sweden, and therefore, represents a region of elevated seismic hazard. The reason for the elevated seismicity in the region is unknown, but it has been proposed that it is hosted by the postulated Hudiksvall fault crossing the region with an NNE-SSW orientation.
In this study, we employ inversion of teleseismic receiver functions (RFs) and apparent S-wave velocity (Vs_app) for 45 available permanent and temporary seismological stations between approximately 60–63°N to map key crustal discontinuities in the region, including the boundary between upper and lower crust, the thickness of high-velocity lower crust (HVLC), and the Moho depth.
We compare the crustal model to Bouguer gravity, aeromagnetic data, and seismicity, allowing us to test candidate structures that may correlate with the occurrence of earthquakes, such as the reported NNE–SSW-trending geophysical anomaly that has been interpreted as a possible crustal boundary and the postulated NW-dipping, NNE-striking Hudiksvall fault previously inferred from 3D geophysical-geological modelling. On a regional scale, our model is consistent with previous crustal models, showing thickening of the crust to the east and south. However, the increased station density due to new data from temporary stations in the area reveals finer-scale details. Comparison with the Swedish National Seismic Network earthquake catalogue shows that clusters of seismicity in the study area tend to occur preferentially near depth changes in crustal discontinuities. Most prominently, the seismicity localizes along the greatest change in crustal thickness, as well as upper crustal thickness while the relationship with lower crustal thickness is more complex. Our preliminary analysis suggests that seismicity is focused along major changes in crustal architecture. Whether these changes in crustal structure are related to the postulated Hudiksvall Fault can currently not be determined.
How to cite: Ak, E., Schiffer, C., Lund, B., and Eggertsson, G.: The Crustal Structure in the Hälsingland Region, Central Sweden, and Implications for Seismotectonics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11035, https://doi.org/10.5194/egusphere-egu26-11035, 2026.
A network of fourteen broadband seismic stations has been established in the foreland basin of the Bhutan Himalaya to investigate the seismically active Dhubri-Chungthang Fault Zone (DCFZ). To assess station reliability and data integrity, a detailed analysis of ambient noise was carried out. Power spectral density (PSD) estimates were generated for each site, and the recorded noise from January 2024 to December 2024 was compared with globally recognised reference models. The findings indicate that the observed noise levels remain consistently within the global limits. The study also reveals that the instrumental tilt exerts a significant influence on the horizontal channels of broadband sensors. Mapping noise across multiple period bands shows the impact of different noise sources, including human activity, surface and body waves, and atmospheric pressure variations. Temporal fluctuations in noise amplitudes reveal seasonal changes in the short-period, microseism, and long-period bands. Overall, the results characterise the spatial and temporal variability of ambient noise in the area while confirming the stability and robustness of the seismic installations.
How to cite: Bala, S., Singh, C., and Singh, A.: Seismic noise environment in and around Dhubri-Chungthang Fault Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9652, https://doi.org/10.5194/egusphere-egu26-9652, 2026.
Full-waveform inversion (FWI) has matured over the last decade to produce high-resolution global wavespeed models down to minimum periods of 30 s. While current models agree on large scales, they exhibit structural differences at shorter wavelengths depending on the assimilated data and inversion strategy. REVEAL is a global-scale FWI model utilizing a multi-scale, whole-waveform inversion strategy. To mitigate cycle-skipping, data is incrementally bandpass-filtered and inverted from long to short periods. Currently, REVEAL inverts all phase windows in 1-hour seismograms; this conservatively preserves known body-wave structure while incorporating new surface wave structure.
However, the use of 1-hour seismograms limits the model's sensitivity to the Southern Hemisphere, where receiver density is significantly lower than in the Northern Hemisphere. To address this, we present preliminary work on a next-generation model that incorporates 3.5-hour seismograms. These longer time series capture both minor- and major-arc surface wave arrivals. Including major-arc waves (epicentral distances > 180°) significantly increases sensitivity to structure in the Southern Hemisphere. Starting from the current REVEAL model, we revise the long-period structure (60–200 s) using a multi-scale approach, beginning with 100–200 s and terminating at 60–200 s. We simulate full viscoelastic wavefields using the spectral-element solver Salvus on global fourth-order cubed-sphere meshes. Adjoint sources are calculated using a time-frequency phase misfit, and optimization is performed via mini-batch stochastic trust-region L-BFGS.
How to cite: Schiller, C. J., Keating, S., Afanasiev, M., Marty, P., and Fichtner, A.: Global full-waveform inversion using a surface wave orbital, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12709, https://doi.org/10.5194/egusphere-egu26-12709, 2026.
In the classic children's story “The House At Pooh Corner” by A. A. Milne (1928), Eeyore is relieved that there has not been an earthquake lately in the Hundred Acre Wood. This statement has a seismological story behind it that we present here, such that other seismologists may use it in their seismology science communication efforts. We also have a corresponding science communication project ourselves: The Science Storyteller (see EOS2.1).
Milne's Winnie-the-Pooh stories are largely autobiographical and inspired by the imaginary adventures of his son, Christopher Robin, and his stuffed animals. The book therefore takes place in Sussex (UK), where Milne lived. Large earthquakes are not common in the UK. Why then, is Eeyore talking about them?
Diving into the historical earthquake databases of the UK (British Geological Survey) reveals that several earthquakes occurred in the region a couple of years before the publication of this second Winnie-the-Pooh novel. Three events are of particular interest: a 1926 Ml4.8 event in Ludlow, West Midlands, and Ml5.5 and Ml5.4 events in 1926 and 1927, respectively, near the Channel Islands. Calculating the intensity attenuation in the UK on the European Macroseismic Scale (Grünthal, 1998) reveals that the 1926 Ludlow and 1926, 1927 Channel Islands earthquakes could have been felt in Sussex (intensity 2.8, 3.6, and 3.5, respectively). Historical data also reveals a recording of intensity 5 in West Sussex for the Ml5.5 Channel Islands earthquake (Amorèse et al., 2020). The repeated and higher intensity Channel Islands events are therefore the most likely earthquakes to be felt by Milne. Earthquakes in this intraplate setting are rare and likely due to reactivation of existing faults due to distant regional stresses. Eeyore's worry about the next earthquake is therefore fully justified - revealing a titbit of seismology history in this beloved story.
References
Amorèse, D., Benjumea, J., & Cara, M. (2020). Source parameters of the 1926 and 1927 Jersey earthquakes from historical, instrumental, and macroseismic data. Physics of the Earth and Planetary Interiors, 300, 106420.
Grünthal, G. (1998). European macroseismic scale 1998 (EMS-98).
How to cite: van Zelst, I., Lythgoe, K., Gilligan, A., and Jenkins, J.: Why is Eeyore talking about earthquakes? The fascinating seismology story behind Winnie-the-Pooh , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11569, https://doi.org/10.5194/egusphere-egu26-11569, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 1b
EGU26-21099 | ECS | Posters virtual | VPS24
Double-Couple and Full Moment Tensor Solutions of the 2015 Nepal AftershocksTue, 05 May, 14:00–14:03 (CEST) vPoster spot 1b
The 2015 Mw 7.8 Gorkha earthquake was followed by numerous aftershocks that provided important information on active faulting in central Nepal. Accurate moment tensor estimations are essential for determining the source parameters of these seismic events. In this study, we determine double-couple and full moment tensor solutions for selected aftershocks of the 2015 Nepal earthquake sequence using a regional 1D velocity model.
The waveform data recorded by the temporary broadband network (NAMASTE) are used to analyse 51 aftershocks with M > 3.5. A library of Green’s functions is computed using the frequency–wavenumber method based on a 1D velocity model of the Nepal region. Synthetic waveforms derived from the Green’s functions are used to invert the waveform data for moment tensor estimation. Both body waves and surface waves are used in the inversion, and they contribute separately to the moment tensor solutions. The analysis focuses on regional waveforms in relatively higher frequency ranges.
Both double-couple–constrained and full moment tensor inversions are performed, and the resulting source parameters are examined in terms of waveform fit, centroid depth, and fault-plane orientation. This work presents a set of moment tensor solutions for the 2015 Nepal aftershocks using a 1D regional velocity model and provides a reference for future studies using more complex velocity structures.
How to cite: Lahon, P., Silwal, V., and Mahanta, R.: Double-Couple and Full Moment Tensor Solutions of the 2015 Nepal Aftershocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21099, https://doi.org/10.5194/egusphere-egu26-21099, 2026.
