Background: Seismology has accumulated extensive observational data, yet modern statistical methodologies have rarely been applied comprehensively to seismic datasets. Consequently, several long-standing interpretations, including magnitude distributions and aftershock decay laws, may reflect analytical constraints rather than physical processes. Re-examining earthquake behaviour using contemporary statistical tools provides an opportunity to reassess empirical relationships and clarify persistent ambiguities in seismic patterns. Objectives: This study applies modern statistical methods to complete seismic datasets to reassess magnitude distributions, aftershock decay, and three-dimensional active-zone structure, testing whether systematic temporal variations, including precursory changes before major earthquakes, can be objectively identified. Methods: Earthquake data were obtained from the Japan Meteorological Agency and analysed without any filtering, using a 1° latitude–longitude grid. The grid with the highest count in each year was examined, except for 2011, which focused on the Tohoku earthquake hypocentre. All calculations were performed in R, with three-dimensional visualizations generated using the rgl package. Hypocentre distributions were projected onto plate boundaries using principal component analysis (PCA) in two stages: 3D-to-2D dimensionality reduction and boundary-specific projection. Maps were verified and appropriately transformed to align with square-based latitude–longitude diagrams for quantitative analysis. Results: Analysis of hypocentre distributions in Japan identifies two major subducting boundaries, the East and Southwest, connected by the shallow Seto structure. Three-dimensional visualisations and Principal Component Analysis reveal these boundaries as planar yet gently curved, with deeper earthquakes concentrated along the Sanriku plate. The Pacific Plate subducts beneath surrounding plates, influencing lateral displacement of the Philippine Sea Plate and creating complex stress patterns. Hypocentre counts increase prior to major events, while deeper earthquakes tend to exhibit higher magnitudes. Aftershock decay follows a half-life process, with energy release distributed heterogeneously across regions, indicating that seismic activity is controlled by interactions between plate geometry, depth, and elastic properties. These findings provide a more robust framework for interpreting seismicity, revising plate boundary models, and informing risk assessment in Japan. Conclusion: Modern statistical analyses clarified Japan's plate boundaries, revised Pacific and Philippine Sea Plate configurations, and updated aftershock decay models, revealing temporal magnitude decay. These findings enhance understanding of earthquake mechanisms, improve seismic hazard assessment, and highlight the need for continued monitoring to address potential false negatives.

Earthquake monitoring systems (EQS) play a critical role in seismic hazard assessment and tectonic studies. A complete and accurate earthquake catalog improves our understanding of fault mechanisms and supports the development of strategies to enhance public safety and the resilience of infrastructure. We propose a foundation model to improve EQS performance through a two-stage framework. Stage 1 involves training the foundation model in a self-supervised manner using a U-Trans architecture, which combines a U-Net encoder-decoder structure with a compact convolutional transformer in the bottleneck layer. At this stage, the model learns to reconstruct corrupted seismic waveforms in both the time and frequency domains, enabling it to extract well-structured and informative features in the latent space. Stage 2 focuses on downstream earthquake tasks. The latent features extracted by the encoder are flattened and concatenated as an additional input channel to the downstream models, effectively guiding them toward better performance. The U-Trans network is trained on more than 2 million three-component seismograms collected from three open-source datasets, ensuring diverse coverage and robust feature extraction. Extensive testing demonstrates that incorporating the encoder's latent features significantly improves the performance of several key downstream tasks, including seismic phase picking, earthquake location, magnitude estimation, and P-wave polarity classification. Analysis of the latent space reveals that the extracted features strongly correspond to P- and S-wave arrival times, which are crucial for many earthquake monitoring applications.

The northeastern corner of the Ordos Block in North China represents a critical tectonic transition zone where the right-lateral transtensional Shanxi Graben System (SGS) intersects with the left-lateral strike-slip Zhangjiakou-Bohai fault zone (ZBFZ), yet kinematic interactions between these major structures remain poorly constrained. Through integrated analysis of high-resolution satellite imagery, uncrewed aerial vehicle (UAV)-derived topography, and field investigations, we characterize the late Quaternary activity of four ENE-striking faults at the northern termination of the SGS, including the Huai’an Basin fault (HBF), Huashan Basin fault (HSBF), Yanggao-Tianzhen fault (YTF), and South Xionger Shan fault (SXSF). Systematic geomorphic offsets reveal consistent left-lateral strike-slip components along these faults that were originally interpreted as normal faults. Chronological constraints from optically stimulated luminescence and 14C dating yield left-lateral slip rates of 0.47 +0.10/−0.07 mm/yr (HBF), 0.16 +0.03/− 0.04 mm/yr (YTF), and 0.86 +0.17/−0.12 mm/yr (SXSF). The most recent surface-rupturing faulting events (MRSEs) are constrained to post−3.5 ka for the HBF, post−4520 calibrated yr B.P. (cal BP) to post−4296 cal BP for the HSBF, and between 19.38 ka and 5.88 ka for the SXSF. We interpret these faults as synthetic horsetail fault splays that accommodate strain transfer at the northwestern tip of the ZBFZ. Furthermore, we propose that the coeval right-lateral shear along the SGS and left-lateral shear along the ZBFZ jointly control active deformation in this region. Middle-lower crustal flow beneath this region likely also contributes to the deformation of the upper crust in this region. According to elapsed time since the MRSEs, we suggest elevated earthquake potential in the Yangyuan and Yuguang basins in the south compared to the Huai’an, Huashan, and Yanggao-Tianzhen basins in the north. Our findings provide critical insights into deformation mechanisms at the SGS-ZBFZ intersection and contribute to improved regional seismic hazard assessment in this complex transfer zone.

Abstract Theoretical studies suggest that earthquake source spectra vary systematically with azimuth in terms of corner frequency and strength of the high-frequency radiation. However, extracting such features from observations and their modeling by physics-based models remain unresolved, particularly for weak earthquakes. Here we analyze station-dependent (apparent) source spectra of 49 weak (Mw 3-5) earthquakes in Central Italy, which exhibit such azimuthal variability up to 25 Hz. Moreover, we reveal various station-averaged spectral decays, directivity effects, and positive correlations between corner frequency and spectral fall-off rates for all events. To explain the observations, we employ physics-based dynamic rupture models incorporating stochastic spatial heterogeneity in fault stress and friction. Broadband numerical simulations considering various strengths of heterogeneity replicate the observed spectral features across the full frequency range. This approach provides a framework for understanding azimuthal ground motion patterns, bridging observational seismology with physics-based modeling and offering improved constraints for seismic hazard assessment.

ABSTRACT Traditional slope stability analyses rely on acceleration-based models that often miss failure initiation in deformable slopes under seismic loading. This study evaluates an energy-threshold approach (EQ*) to predict failure onset. Shaking-table tests were performed on dry sand slopes with inclinations of 13°–20° and sand layer thicknesses of 0–6.5 cm. Results showed a linear relationship between input vibration energy (EEQ) and horizontal displacement (Δr) of a rigid surface block, largely independent of excitation frequency. For a 15° slope with a 6.5-cm sand layer, the regression was Δr = 0.49EEQ + 0.04 (R² > 0.9). A critical energy threshold (EQ* ≈ 1.0 J) marked the onset of sustained failure motion. Validation using documented slope failures confirmed the approach’s predictive capability. Compared with acceleration-based methods, the energy criterion is frequency independent and sensitive to soil conditions, supporting its integration into seismic hazard assessment and design frameworks for more reliable landslide risk mitigation applications.

Integrated seismic hazard assessment around Qom City, North-Central Iran, based on earthquake focal mechanisms, fault-slip data, and deterministic analysis

This study investigates the influence of source parameter variability—specifically stress drop and anelastic attenuation—on site response analysis using the Random Vibration Theory (RVT) framework. Site amplifications were computed for a representative site in the Aegean region of Türkiye using four different source parameter sets based on regional literature. A single set of randomized Vs profiles was used to account for subsurface variability, while varying source models enabled the evaluation of epistemic uncertainty in site amplification. The epistemic uncertainty associated with source parameters, expressed as τ_"source" , peaks at approximately 0.04 s, reflecting the sensitivity of high-frequency site response to stress drop and attenuation. The study provides a regionally calibrated quantification of source-parameter-driven epistemic uncertainty for the Aegean region. The findings emphasize the need to account for source-related uncertainty in seismic hazard assessment. Unlike most previous RVT-based studies, this work explicitly isolates and quantifies the effect of stress drop and attenuation on site amplification, highlighting a novel contributor to epistemic uncertainty. Future work should incorporate Monte Carlo simulation of source parameters to support PSHA applications.

Abstract In this study, Machine Learning (ML)-based models were developed for the estimation of Pseudo Spectral Acceleration (PSA), a key parameter for identifying strong ground motion in seismic hazard assessments. A large dataset was generated using 1975 earthquake records ( 3.0 ≤ M ≤ 6.8), sourced from 63 strong ground motion stations in different regions of Türkiye. This dataset includes a total of 150,552 samples, which we divided into three groups based on their period (T) values. These 3 datasets were modeled by using 19 different ML algorithms and validated by using tenfold cross-validation. The performances of the models were compared by using Mean Squared Error (MSE), Root Mean Squared Error (RMSE), and R-squared (R 2 ) criteria. The models trained with the Ensemble Bagged Trees and Fine Tree algorithms were determined to be the best models according to test criteria. The Ensemble Bagged Trees model performed best in the T = 0.05–1.0 s range (R 2 = 0.90), while the Fine Tree model performed best in T = 1.0–1.9 s (R 2 = 0.94) and T = 2.0–4.0 s (R 2 = 0.89). Residual analyses showed that the prediction errors were randomly distributed around the zero line. Moreover, the PSA results of trained ML Models yielded results closer to the observed PSA curve. These results indicate that, within the compiled dataset, the evaluated ML models can predict PSA with lower errors and may serve as a complementary approach to GMPEs in future applications.

Accurate estimation of earthquake source parameters—such as moment magnitudes, corner frequencies, and stress drops—is essential for improving seismic hazard assessments and understanding earthquake physics. In this study, moment magnitudes (MW) are calculated for 31,581 earthquakes associated with wastewater injection in the Raton Basin (located along the border between northern New Mexico and southern Colorado) between 2016 and 2024 using radiative transfer theory to fit coda decay envelopes. Our results show that it is feasible to estimate moment magnitudes down to MW ~1 with coda envelopes from a small local monitoring network. Significant differences were found between MW and local magnitudes (ML) for small earthquakes (M < 3.0). A linear relationship was optimized to convert ML to MW: MW = 0.7ML + 0.96 and MW = 0.73 ML + 0.99 (for the events reported by the U.S. Geological Survey), which can be applied in future studies of Raton Basin seismicity. We find that b-values calculated employing different methods and using ML are approximately 1.0, while those using MW range from 1.2 to 1.4. A larger estimate of the b-value could influence interpretations of the statistical behavior of earthquakes associated with injection and consequently seismic hazard assessments based on a magnitude–frequency distribution. The potential differences between local versus moment magnitude-based earthquake statistics should be considered in other seismically active regions.

Abstract. Estimating the recurrence intervals and magnitudes of earthquakes for a given fault is essential for seismic hazard assessment but often challenging due to the long recurrence times of large earthquakes. Fault network geometry (i.e. spatial arrangement between faults) plays a key role in modulating stress interactions and, consequently, earthquake recurrence and magnitude. Here, we investigate these effects of fault network geometry using earthquake cycle models to generate numerous earthquakes on two different networks of normal faults in Italy: the Central Apennines, characterised by a wide network of faults offset across strike, and the Southern Apennines, a narrow fault network where faults are predominantly arranged along strike. For each region, we ran an earthquake cycle simulation on systems of seven normal faults generating approximately 150 earthquakes. In the Central Apennines, co-seismic stress transfer between faults promotes more heterogeneous stress, more partial ruptures, greater Mw variability and less periodic behaviour of large earthquakes (coefficient of variation of recurrence time, CV 0.1–0.9). In contrast, faults in the Southern Apennines experience more homogeneous stress loading, leading to a higher proportion of full-fault ruptures with more regular recurrence intervals (CV 0–0.4). In both fault networks, high long-term slip rate amplifies the effects of fault interactions: faults with higher long-term slip rate are more sensitive to positive stress perturbations from nearby faults compared to slower-moving faults. These results highlight that incorporating stress interactions from fault network geometry into seismic hazard models is particularly important for networks of faults offset across strike, where rupture behaviour is more variable.

Consideration of near-field directivity effects in probabilistic seismic hazard assessment: a case study over North–East India

Retraction Note: On the Probabilistic Seismic Hazard Assessment in Kazakhstan

Türkiye is a country at high seismic risk due to its location on active tectonic zones. Therefore, regional-scale studies to reduce earthquake risk are of great importance. In this study, the soil-geotechnical properties, existing building stock, settlement patterns, and historical earthquake records of the Saraydüzü district of Sinop province, located close to the North Anatolian Fault Zone, were examined in detail. Seismic hazard assessment, Vs(30)-based soil classification, building inventory analysis, and earthquake scenario modeling were performed during the analysis. ELER v3.0 software was used in scenario development, and the Erdik and Eren (1983) model was applied as an empirical attenuation relation specific to Turkish conditions. In the scenario developed based on the February 6, 2023, Kahramanmaraş-centered earthquake, calculations based on 14588 residences projected to suffer severe or collapsed damage indicate that approximately 1508 people could lose their lives, with a loss of life rate of approximately 10335 for every 100 structures. Using an injury/death ratio of 2.019 for the same earthquake, it was estimated that approximately 3044 people could be injured. Multiplying the total of 17197 moderately and severely damaged residences by the 2024 average household size of 2.61 people in Turkey and subtracting the number of deaths, it was determined that approximately 43377 people would be in need of shelter. In the second scenario, using the parameters of the August 17, 1999 Izmit Gulf Earthquake, the number of residences with severe/collapsed damage was calculated as 322. Applying a 26% loss of life ratio, it was estimated that approximately 84 people could lose their lives. Similarly, using an injury/death ratio of 2.515, it was determined that 211 people could be injured, and based on household size, approximately 3155 people would need shelter. The results demonstrate that medium-sized settlements can be as high a seismic risk as large cities, clearly demonstrating the importance of disaster preparedness in such regions. It is evaluated that these analyses, specifically conducted in Saraydüzü, will be instructive for other settlement areas with similar characteristics and will contribute to Türkiye's earthquake response processes at a local scale.

Summary We present a forward waveform modeling study to investigate the regional crustal structure of the central-southern Apennines, along a NNE-SSW profile. The profile cross-cuts the Apenninic chain axis and extends from the eastern Adriatic domain, characterized by a thick crust and thick seismogenic layer, to the western Tyrrhenian domain, dominated by tectonic thinning, distributed CO2 gas emissions at the surface and volcanic structures. This region hosted the largest earthquakes in recent history, making precise knowledge of the crustal structure crucial for a comprehensive understanding of seismogenesis and seismic hazard assessment. We analyzed and modelled seismic data from two lower-crustal strike-slip earthquakes in the eastern segment of the profile (2018 Mw 5.1 and 2023 Mw 4.6), recorded by the Italian National Seismic Network (IV). The two events, located along the target NNE-SSW linear profile, provide a unique opportunity to study the westward propagation and evolution of seismic phases. Using a 2D numerical modeling approach, we modelled direct (Sg) and Moho-reflected (SmS) phases on transverse component seismograms, comparing the synthetic to the observed waveforms in terms of arrival times and waveform shapes. A faster Adriatic lower crust with an average shear-wave velocity of 3.85 km/s supports the hypothesis of distributed crustal mafic intrusions at the margin between the Apenninic chain and Adriatic foreland. We estimate a local Adriatic Moho depth of 38 km, in agreement with previous investigations. Furthermore, we identify a strong attenuation zone across the Apenninic chain axis, extending directly from the surface down to 10 km depth, significantly impacting both seismogenic processes and waveform propagation. This first, regional-scale waveform study highlights the significance of waveform analysis for constraining seismic velocities and interface velocity contrasts in the Southern Apennines mountain range.

The Abu Dabbab seismic zone is located along Egypt's Red Sea margin, stands out as one of the most active seismic regions in the Eastern Desert. Characterized by frequent micro earthquakes, swarm like activity, and notable historical events. To enhance understanding of its tectonic framework, 408 earthquakes (Ml 0.7-3.0) recorded in 2004 were analyzed using digital waveform data from a temporary local seismic network consisting of ten vertical short period seismometers. Focal mechanisms were determined from P-wave first-motion polarities and classified using ternary plots. The analysis revealed a diverse range of faulting styles normal, strike slip, reverse, and oblique with clear depth dependent patterns. Shallow events (0-5km) were dominated by normal and strike slip faulting, intermediate depths (5-10km) showed increased reverse and oblique components, while deeper events (> 10km) were primarily normal faulting. Stress tensor inversion across three depth intervals indicated a multiphase stress regime: shallow depths exhibited alternating faulting styles due to localized stress variations; intermediate depths revealed a heterogeneous stress field with mixed faulting regimes; and deeper levels showed a dominant normal faulting regime, consistent with the extensional tectonics of the Red Sea Rift. Overall, the stress field is shaped by NE-SW compression and SE-NW extension, with deformation concentrated along NW-SE and NE-SW trending faults. These findings underscore the combined influence of regional rift-related extension and local factors such as magmatic intrusions and crustal heterogeneity in driving seismicity at Abu Dabbab. This study yields important insights into depth dependent stress patterns and active faulting, enhancing seismic hazard assessments and highlighting the region's potential as a sustainable geothermal energy source within a tectonically dynamic environment.

Northern Thailand, situated within the complex Sunda Tectonic Plate, shows significant seismic activity due to its proximity to major tectonic boundaries; however, it often has lower to medium magnitudes. One of the delineated active fault zones is the Phayao Fault Zone (PFZ), which generated an Mw 6.3 earthquake in 2014. Its further south located Pan Segment is also active, but with lower magnitudes. However, understanding and characterizing its seismicity is essential for ongoing seismic hazard assessment of the area. To overcome the challenges, waveform inversion techniques in combination with multiple velocity models were employed, with the aim to characterize the seismic source parameters of earthquakes in this area. Hypocentres were determined with exceptional precision and subsequently validated by applying a velocity model that demonstrated the highest double-couple percentage. This indicates the model's efficacy in precisely calculating hypocentral parameters in this specific geological context. Our findings unveil a complex interplay between right-lateral strike-slip and reverse faulting mechanisms, consistent with a transpressional tectonic regime in the Pan Segment. This regime reflects the accommodation of regional compressional stresses superimposed on the dominant strike-slip motion along the Phayao Fault Zone, thereby yielding a significant contribution to seismic hazard assessment in Northern Thailand. The study also underscores the need for further research to refine these models and methodologies, thereby enhancing our understanding of the seismic characteristics of earthquakes in such regions. Methodologies and insights gained here could serve as a model for characterizing seismic source parameters in other understudied low-seismicity regions globally.

Abstract Magnetic signatures preserved in rocks have long provided insight into Earth's evolution, revealing processes from plate tectonics to the habitability of Earth. While large impacts are known to impose extreme stresses (>1 GPa) and heat that fundamentally alters magnetic records, lower stresses typical of earthquakes have been considered magnetically undetectable. We show that magnetic responses to sub‐GPa stresses can be precisely calibrated, enabling three‐dimensional paleostress reconstructions in rocks—even stresses of just a few MPa can fully reset magnetic signals without heat or deformation. This newly revealed magnetic sensitivity to stress opens a powerful, non‐destructive pathway to detecting paleostress fields in the elastic crust, offering new opportunities for improving seismic hazard assessment, interpreting impact processes, and re‐evaluating magnetic records across Earth and Planetary sciences.

ABSTRACT Building on a previously developed bedrock dataset, this study extends the Azores Plateau ground motion simulations to include soil-amplified records and introduces a comprehensive validation framework. Soil amplification is modeled using one-dimensional soil profiles. A stochastic source-based approach is employed to generate the dataset, incorporating randomization of input-model parameters to account for the aleatory uncertainty in seismic activity. The accuracy of the dataset is verified through a comprehensive validation framework, showing that the randomization effectively captures variance and inter-period correlation observed in records. This work provides a robust dataset for advancing seismic hazard and risk assessment in the Azores Plateau.

Seismic Motion Simulation and Seismic Hazard Assessment of Active Faults in Yancheng, Jiangsu

Abstract The Fairbanks region of central Alaska is part of a broad zone of intraplate crustal deformation, situated north of the Denali fault and north of the ongoing collision and flat-slab subduction of the Yakutat oceanic plateau. Seismicity in the Fairbanks region occurs both in diffuse areas as well as in well-defined lineaments, such as the left-lateral Salcha fault, which hosted the 1937 Ms 7.3 earthquake. Starting with the regional seismicity catalog, we perform waveform cross-correlation, network-matched filtering, and relative relocation to obtain an enhanced seismicity catalog over the time period 2014–2024. Based on the relocated catalog, we interpret a set of 15 fault segments, including two conjugate faults and two new faults east of the previously documented fault system. Considering the combined seismicity in the Minto and Fairbanks regions, the median depth of seismicity decreases from east (6 km) to west (20 km). Our interpreted faults provide guidance for future tectonic modeling and assessment of seismic hazards in this region.