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• Using remote sensing data, the statistical studies related to earthquake precursors increased significantly. • Most of them emphasized the existence of abnormal behaviors in precursors. • An attempt has been made to address the advances and challenges in the way of earthquake prediction. Due to the considerable loss of life and damages caused by powerful Earthquakes, along with the strengthening of structures and disaster management systems, many researches are being conducted associated with the possibility of creating Earthquake warning systems. However, no reliable scientific report on successful Earthquake prediction has been published so far. Although there are a couple of published scientific papers indicating the detection of unusual changes in physical and chemical parameters obtained from ground stations, but due to the limitations of in-situ measurement in terms of number, location, time and cost, there was no noticeable progress in Earthquake warning. After the advent of remote sensing satellites, the number of statistical studies related to Earthquake precursors increased significantly, and most of them emphasized the existence of abnormal behaviors in physical and chemical precursors around the time (about 1–30 days before) and locations of powerful Earthquakes. In this study, an attempt has been made to address the advances and challenges in the way of Earthquake prediction using satellite data and provide a perspective of the future of these researches. It should be noted that the increase in the number of satellites designed and launched specially for Earthquake studies, the variety of available Earthquake precursors (multi-precursor analysis), the development of classic and intelligent anomaly detection and predictor algorithms (multi-method analysis), the provision of intelligent systems for the integration of various precursors (fusion and decision systems), the creation of cloud storing and processing data services (Google Earth Engine, Giovanni, etc.) and the development of intelligent user interfaces for public, have made researchers more hopeful for the appearance of low-uncertainty Earthquake warning systems in the near future. [ABSTRACT FROM AUTHOR]

The ability to estimate earthquake source locations, along with the appraisal of relevant uncertainties, is paramount in monitoring both natural and human-induced micro-seismicity. For this purpose, a monitoring network must be designed to minimize the location errors introduced by geometrically unbalanced networks. In this study, we first review different sources of errors relevant to the localization of seismic events, how they propagate through localization algorithms, and their impact on outcomes. We then propose a quantitative method, based on a Monte Carlo approach, to estimate the uncertainty in earthquake locations that is suited to the design, optimization, and assessment of the performance of a local seismic monitoring network. To illustrate the performance of the proposed approach, we analyzed the distribution of the localization uncertainties and their related dispersion for a highly dense grid of theoretical hypocenters in both the horizontal and vertical directions using an actual monitoring network layout. The results expand, quantitatively, the qualitative indications derived from purely geometrical parameters (azimuthal gap (AG)) and classical detectability maps. The proposed method enables the systematic design, optimization, and evaluation of local seismic monitoring networks, enhancing monitoring accuracy in areas proximal to hydrocarbon production, geothermal fields, underground natural gas storage, and other subsurface activities. This approach aids in the accurate estimation of earthquake source locations and their associated uncertainties, which are crucial for assessing and mitigating seismic risks, thereby enabling the implementation of proactive measures to minimize potential hazards. From an operational perspective, reliably estimating location accuracy is crucial for evaluating the position of seismogenic sources and assessing possible links between well activities and the onset of seismicity. [ABSTRACT FROM AUTHOR]

In the southwestern area of the Kurile Islands subduction zone, three large earthquakes including the Mw8.2 1969 and the Mw8.3 1994 Hokkaido Toho-oki earthquakes and the Mw7.8 1975 tsunami earthquake occurred in almost the same location. The three main shocks and their aftershocks were re-determined simultaneously using a double-difference earthquake location method, HypoDD. As a result, the 1969 and the 1975 main shocks and their aftershocks were concentrated near the upper surface of the subducting Pacific plate, indicating that both events were plate boundary megathrust earthquakes as shown by previous studies. On the other hand, the 1994 main shock and its aftershocks were distributed within the Pacific plate indicating that the 1994 event was an intraslab event as reported by previous studies. The result that interplate earthquakes and intraslab earthquakes could be appropriately distinguished is strong evidence that the accuracy of hypocenter determination is sufficiently high. The centroid moment tensor solution of the 1994 main shock has two nodal planes which are parallel or normal to the Kurile Trench. According to the high-resolution hypocenter distribution obtained in the present study, the aftershocks appear to locate on the nodal plane normal to the trench, suggesting that the source fault ruptured by the 1994 main shock was not parallel but normal to the Kurile Trench. Moreover, we found that the Coulomb failure stress change (ΔCFS) produced by the trench-normal fault plane is more likely to trigger the largest aftershock than ΔCFS produced by the trench-parallel fault plane. [ABSTRACT FROM AUTHOR]

After impounding the Baihetan Water Reservoir in a historically seismically active area, numerous earthquakes occurred, but it is uncertain if they are connected to the impoundment. Based on the dense seismic network, this study used local earthquake tomography to construct high‐resolution VP (P‐wave velocity) and VP/VS models (P‐ to S‐wave velocity ratio) and update earthquake locations after the impoundment of Baihetan reservoir. Our study revealed that the reservoir water spreads from the dam site to the Qiaojia Basin and the Heishuihe branch, and pore pressure diffusion along faults induces many earthquakes. Reservoir water migrates through hidden faults and fractures beneath Hulukou, spreading to both sides and saturating some rocks below 7 km beneath the dam site‐Lianhuatang section, causing multiple magnitude 3.5+ earthquakes. This study reveals that reservoir water migration drives earthquakes in the reservoir area, offering new insights into seismogenesis following the Baihetan reservoir's impoundment, potentially applicable to understanding reservoir‐induced earthquakes in other reservoirs. Plain Language Summary: Numerous earthquakes occurred after the Baihetan reservoir impoundment. It is worth considering whether the significant seismicity was caused by fluid injection. We used the local earthquake tomography to construct high‐precision earthquake locations and high‐resolution 3D VP and VP/VS models of Baihetan reservoir after the impoundment. The 3D VP and VP/VS models reveal the penetration and diffusion range of reservoir water. The relationship between seismic locations and velocity models reveals that microearthquakes are induced by pore pressure diffusion caused by fluid migration, and some of the water‐saturated areas induced bigger earthquakes. Key Points: The highest resolution 3D VP and VP/VS models of the Baihetan reservoir are obtained by using a dense seismic arrayThe relationship between the change of medium structure and seismicity caused by the impoundment of Baihetan reservoir is revealedA new understanding of the seismogenesis of a large number of earthquakes occurred after the Baihetan reservoir impoundment are obtained [ABSTRACT FROM AUTHOR]

While deterministically predicting the time and location of earthquakes remains impossible, earthquake forecasting models can provide estimates of the probabilities of earthquakes occurring within some region over time. To enable informed decision‐making of civil protection, governmental agencies, or the public, Operational Earthquake Forecasting (OEF) systems aim to provide authoritative earthquake forecasts based on current earthquake activity in near‐real time. Establishing OEF systems involves several nontrivial choices. This review captures the current state of OEF worldwide and analyzes expert recommendations on the development, testing, and communication of earthquake forecasts. An introductory summary of OEF‐related research is followed by a description of OEF systems in Italy, New Zealand, and the United States. Combined, these two parts provide an informative and transparent snapshot of today's OEF landscape. In Section 4, we analyze the results of an expert elicitation that was conducted to seek guidance for the establishment of OEF systems. The elicitation identifies consensus and dissent on OEF issues among a non‐representative group of 20 international earthquake forecasting experts. While the experts agree that communication products should be developed in collaboration with the forecast user groups, they disagree on whether forecasting models and testing methods should be user‐dependent. No recommendations of strict model requirements could be elicited, but benchmark comparisons, prospective testing, reproducibility, and transparency are encouraged. Section 5 gives an outlook on the future of OEF. Besides covering recent research on earthquake forecasting model development and testing, upcoming OEF initiatives are described in the context of the expert elicitation findings. Plain Language Summary: The exact location, time, and magnitude of future earthquakes cannot be predicted. However, based on past earthquake sequences, it is possible to assess probabilities for future earthquakes. This is called earthquake forecasting. Operational Earthquake Forecasting (OEF) systems are designed to provide near‐real‐time authoritative earthquake forecasts, based on current earthquake activity, to aid the decision‐making of various societal stakeholders. Setting up these systems is complex, involving decisions about which model to use, how to best test the model, and how to turn earthquake probability estimates into practical information. This review captures the current state of OEF worldwide and analyzes expert recommendations on the development, testing, and communication of earthquake forecasts. Section 2 provides an overview of OEF‐related research and the background knowledge required to understand the other parts. Section 3 describes existing OEF systems of Italy, New Zealand, and the United States in detail. Section 4 discusses an elicitation of expert views on modeling, testing, and communicating earthquake forecasts (Mizrahi, Dallo, & Kuratle, 2023, https://doi.org/10.3929/ethz‐b‐000637239). Data from the elicitation allow to identify consensus and dissent on OEF issues and provide guidance for future earthquake forecasting efforts. Finally, Section 5 gives an outlook on future OEF‐related research and planned OEF efforts at various institutions. Key Points: We capture the state of earthquake forecasting systems in Italy, New Zealand, and the United States, and future plans in these and other countriesExperts encourage benchmark comparison, prospective testing, reproducibility and transparency, but avoid endorsing specific models or testsExperts stress the need to co‐design forecast communication products with end‐users to ensure their societal relevance and usefulness [ABSTRACT FROM AUTHOR]

The 2022 eruption at Mauna Loa, Hawai'i, marked the first extrusive activity from the volcano after 38 years of quiescence. The eruption was preceded by several years of seismic unrest in the vicinity of the volcano's summit. Characterizing the structure and dynamics of seismogenic features within Mauna Loa during this pre‐eruptive interval may provide insights into how pre‐ and co‐eruptive processes manifest seismically at the volcano. In particular, the extent to which seismicity may be used to forecast the location and timing of future eruptions is unclear. To address these questions, we construct a catalog of relocated seismicity on Mauna Loa spanning 2011–2023. Our earthquake locations image complex, sub‐kilometer‐scale seismogenic structures in the caldera and southwest rift zone. We additionally identify a set of streaks of seismicity in the volcano's northwest flank that are radially oriented about the summit. Using a rate‐and‐state friction model for earthquake occurrences, we demonstrate that the seismicity rate in this region can be modeled as a function of the stressing history caused by magma accumulation beneath the summit. Finally, we observe a mid‐2019 step change in the seismicity rate in the Ka'oiki region that may have altered the stress state of the northeast rift zone in the three years before the eruption. Our observations provide a framework for interpreting future seismic unrest at Mauna Loa. Plain Language Summary: In 2022, Mauna Loa erupted for the first time in 38 years. In the years before this eruption, the volcano had been generating a large number of earthquakes. We looked back at seismic data between 2011 and 2023 to detect and locate many more small earthquakes than were previously identified. Mapping out the locations of these earthquakes allows us to identify structures inside the volcano with high resolution. We also find evidence that the large number of earthquakes before the eruption was caused by accumulation of magma beneath the volcano's summit. Key Points: We construct a new catalog of 91,770 relocated earthquakes at Mauna Loa volcano spanning 2011–2023The new catalog details a decade of nonstationary inflation‐related seismicity and detailed structure in the caldera and rift zonesOur observations can provide a framework for understanding future episodes of pre‐eruptive seismic unrest at Mauna Loa [ABSTRACT FROM AUTHOR]

Tectonic landforms and surficial lithologic age are essential data for producing quality late Quaternary fault maps and predicting coseismic fault rupture location before an earthquake. However, we lack a clear understanding of the relationship between tectonic landforms and shallow earthquake processes and how lithologic age relates to landform preservation. We assess how fault location error (rupture‐to‐fault separation distance) and coseismic displacement residual (difference between observed and predicted coseismic displacement) vary with tectonic landform and lithologic age for four historical earthquakes. Certain tectonic landforms identified before these earthquakes correlate with lower fault location errors and median displacements below model predictions. Faults cutting Holocene units exhibit the largest location errors, reflecting surface processes that erode or bury fault evidence. This study shows that tectonic landforms and lithologic age have a significant impact on fault location uncertainty and coseismic displacement, which should be considered in fault mapping and fault displacement assessment. Plain Language Summary: Accurate maps of tectonic faults are essential for a variety of purposes including assessing seismic hazard, studying faults, and planning land‐use. These fault maps typically rely on identifying features in the landscape formed by past earthquakes. Remote sensing data sets like imagery and elevation support this process. However, a major challenge in fault mapping is figuring out how to best interpret what the landforms indicate about faulting. In this study, we analyzed how confident we are about the location of faults mapped before four historical earthquakes. We found that faults indicated by prominent landforms better indicate where subsequent earthquake ruptures will occur relative to faults indicated by less noticeable landforms. We also show that fault mapping in Holocene units (representing the most recent geologic time‐period) with meter‐scale remote sensing data is particularly challenging. Our findings support making better informed fault maps based on a deeper understating of how clues in the landscape connect to faulting processes. Key Points: Fault trace mapping is informed by tectonic landforms and surficial geologyUncertainty in fault location and predicted coseismic displacements correlate with tectonic landform type and lithologic ageFaults indicated by prominent tectonic landforms have relatively low fault location error and accommodate high displacement [ABSTRACT FROM AUTHOR]

This investigation concentrates on refining the accuracy of earthquake parameters as reported by various Saudi seismic networks, addressing the significant challenges arising from data discrepancies in earthquake location, depth, and magnitude estimations. The application of sophisticated machine learning techniques, particularly the Isolation Forest algorithm, has markedly enhanced the precision in the estimation of seismicity parameters by effectively identifying and eliminating outliers and discrepancies. A newly developed and refined seismicity catalog was employed to accurately determine key seismic parameters such as the magnitude of completeness ( M c ), a-value, and b-value, thereby underlining their indispensable role in regional seismic hazard assessment. The research underscores the substantial impact of data inconsistencies on the evaluation of seismic hazards, thereby advocating for the advancement of research methodologies within the field of seismotectonics. The insights derived from this study significantly contribute to a more profound understanding of the seismotectonic processes in the region. These insights are crucial for the development of comprehensive seismic hazard assessments and the formulation of targeted earthquake preparedness strategies, thereby enhancing resilience against seismic risks in the region. [ABSTRACT FROM AUTHOR]

The precise relocation of seismic events is critical for many engineering projects. Swarms of minor or micro earthquakes typically reveal stress concentration and spots of greater seismic hazards. Particularly in the context of deep underground mining, advanced techniques that can accurately relocate microseismicities are urgently in demand. Here, we developed a neural network-based modeling training method that can precisely relocate seismicities and invert for velocities at the same time, with preconfigured receiver network locations. Our model can be iteratively improved with field recorded data. We showed that, with roughly eight iterations, we can reasonably resolve for the earthquake locations for both clusters of events, namely spatially distributed with linear pattern or randomly scattered. Our initially trained model, which only focused on events that had a linear distribution pattern, was used as the base for the training of the subsequent models which could better resolve for randomly scattered event locations. Although we stopped at the eighth iteration, the process reported here can be continued, as the model will have a better performance with more iterations. [ABSTRACT FROM AUTHOR]

The use of seismic catalogs enhanced through advanced detection techniques improves the understanding of earthquake processes by illuminating the geometry and mechanics of fault systems. In this study, we performed accurate hypocentral locations, source parameters estimation and stress release modeling from catalogs of microseismic sequences nucleating in the complex normal fault system of the Southern Apennines (Italy). The application of advanced location techniques resulted in the relocation of ∼30% of the earthquakes in the enhanced catalogs, with hypocenters clearly identifying local patches on kilometer‐scale structures that feature consistent orientation with the main faults of the area. When mapping the stress change on the fault plane, the inter‐event distance compared to the size of the events suggests that the dominant triggering mechanism within the sequences is static stress transfer. The distribution of events is not isotropic but dominantly aligned along the dip direction. These slip‐dominated lineations could be associated with striations related to fault roughness and could map the boundary between locked and creeping domains in Apulian platform and basement. Plain Language Summary: The development of earthquake detection techniques, based on machine learning or similarity, has allowed an increase in the content of seismic catalogs of more than one order of magnitude. However, how much information can be extracted from these small fractures is still to be understood, especially in complex normal fault systems, such as the Apennine environment in Italy. For seismic sequences in Southern Apennines, we show that only a small portion (about 30%) of events in enhanced catalogs can be further characterized in terms of location and source properties. Nevertheless, the use of comprehensive catalogs allows the illumination of kilometric scale structures at depths between 8 and 15 km, to define mechanisms for seismicity evolution, mainly driven by static stress triggering, and to identify seismicity alignments along the slip direction, that can be associated with fault roughness or delimiting boundaries between locked and creeping regions. Key Points: Accurate earthquake location for enhanced catalogs unveils kilometric scale structures where seismic sequences occur in Southern ApenninesStatic stress transfer drives the evolution of these seismic sequences, with earthquakes dominantly distributed along the dip directionSlip‐dominated alignments of the seismicity could map the fault roughness or the boundary between locked and creeping domains [ABSTRACT FROM AUTHOR]

The paper presents the results of retrospective and tectonophysical analysis of the Tokachi-Oki earthquake source area on the September 25, 2003 (Mw = 8.3). Particular attention is paid to the Hidaka tectonic belt, the structures of which were affected by the Tokachi-Oki earthquake. The load–unload response ratio (LURR) method was applied at sufficient spatial (a square with a side of about 400 km) and temporal (continuous 20-year period) intervals to consider the results reliable. The forerunners of the Tokachi-Oki earthquake on the September 25, 2003, were revealed (on average, two years before the seismic event), which strictly determined the earthquake location. The data obtained with The method of cataclastic analysis (MCA), together with LURR data, made it possible to establish the stages of instability development in the Hidaka collision zone. The Hidaka tectonic belt became outlined by destruction zones (mainly horizontal compression) from 1997 to 2003 (up to the Tokachi-Oki earthquake). LURR anomalies were detected along the belt a couple of years before the earthquake. The prediction of the Tokachi-Oki earthquake by the LURR method is one of the most reliable in our practice. [ABSTRACT FROM AUTHOR]

SUMMARY: The determination of seismic event locations with sparse networks or single-borehole systems remains a significant challenge in observational seismology. Leveraging the advantages of the location approach HADES (eartHquake locAtion via Distance gEometry Solvers), which was initially developed for locating clustered seismicity recorded at two stations, through the solution of a Distance Geometry Problem, we present here an improved version of the methodology: HADES-R (HADES-Relative). Where HADES previously needed a minimum of four absolutely located master events, HADES-R solves a least-squares problem to find the relative inter-event distances in the cluster, and uses only a single master event to find the locations of all events and subsequently applies rotational optimizer to find the cluster orientation. It can leverage iterative station combinations if multiple receivers are available, to describe the cluster shape and orientation uncertainty with a bootstrap approach. The improved method requires P- and S-phase arrival picks, a homogeneous velocity model, a single master event with a known location, and an estimate of the cluster width. The approach is benchmarked on the 2019 Ridgecrest sequence recorded at two stations, and applied to two seismic clusters at the FORGE geothermal test site in Utah, USA, with a microseismic monitoring scenario with a Distributed Acoustic Sensing in a vertical borehole. Traditional procedures struggle in these settings due to the ill-posed network configuration. The azimuthal ambiguity in such a scenario is partially overcome by the assumption that all events belong to the same cluster around the master event and a cluster width estimate. We are able to find the cluster shape in both cases, although the orientation remains uncertain. HADES-R contributes to an efficient way to locate multiple events simultaneously with minimal prior information. The method's ability to constrain the cluster shape and location with only one well-located event offers promising implications, especially for environments where limited or specialized instrumentation is in use. [ABSTRACT FROM AUTHOR]

When traversing through an active strike-slip fault, buried pipelines may be subjected to permanent ground deformation (PGD), causing large strains in the pipeline during an earthquake. The presence of bends near the fault-crossing zones may further increase the strain in the pipe. Moreover, it is well acknowledged that bends are the most vulnerable location to earthquake damage, mainly when compressive strain develops due to PGD. Hence, most design guidelines recommend constructing pipelines without field bends, elbows, and flanges crossing the fault zone. However, it is not always possible to provide only a straight segment of the pipeline, especially for blind faults where the location of the faults is unknown. Hence, the present study aims to investigate the response of buried continuous steel pipelines with field bends subjected to strike-slip faulting by conducting an extensive parametric study. A three-dimensional pipe-soil interaction model is developed in a finite element framework for this study. The pipeline response in terms of its maximum von-Mises stress and maximum longitudinal stress and strain due to fault crossing is studied for various influencing parameters such as pipe bend angle, soil strength, pipe burial depth, and distance of the fault trace from the bend. Based on the results obtained, suitable relationships in terms of modification factors over the response of a straight pipeline as a function of a few critical parameters are determined using regression analyses. It is concluded that providing bends to the pipeline can significantly affect its structural response when subjected to fault displacement when the fault trace is close to the pipe bend. The primary outcome of this investigation would be to suggest a simplified methodology to estimate the response of pipelines having field bends while crossing fault lines from the response of straight pipelines in a similar scenario. [ABSTRACT FROM AUTHOR]

This study compared earthquake location estimation using grid search and manta ray foraging optimization algorithm for synthetic and real earthquakes data from Van, Turkey. Both locating methods worked well, and they achieved similar results. The horizontal coordinates (latitude and longitude) of the earthquake were obtained successfully with both methods, from the inversion of the arrival times calculated from the noisy and noise-free synthetic earthquake data. However, there was some deviation in depth parameter for the noisy data. The location parameters obtained from the inversion of the real earthquake data using grid search and manta ray foraging optimization methods were in accordance with the solutions presented in previous studies. The depth parameters for the Van earthquakes did not fully match those in the previous studies, possibly due to differences in crustal velocity models. The depth parameters obtained for both Van earthquakes using both methods performed in this study are self-consistent at around 24 km. In addition, Disaster and Emergency Management Presidency and German Research Centre seismology centres also reached depth solutions near those in this study. The grid search method has some disadvantages compared with the manta ray foraging method, as it must be applied gradually, and delays reaching a solution. The manta ray foraging method is an easy, fast way to determine the kinematic location of earthquake hypocentres. [ABSTRACT FROM AUTHOR]

Different risk management activities, such as land-use planning, preparedness, and emergency response, utilize scenarios of earthquake events. A systematic selection of such scenarios should aim at finding those that are representative of a certain severity, which can be measured by consequences to the exposed assets. For this reason, defining a representative scenario as the most likely one leading to a loss with a specific return period, e.g., the 100-year loss, has been proposed. We adopt this definition and develop enhanced algorithms for determining such scenarios for multiple return periods. With this approach, we identify representative earthquake scenarios for the return periods of 50, 100, 500, and 1000 years in the Chilean communes of Valparaíso and Viña del Mar, based on a synthetic earthquake catalog of 20 000 scenarios on the subduction zone with a magnitude of Mw≥5.0. We separately consider the residential-building stock and the electrical-power network and identify and compare earthquake scenarios that are representative of these systems. Because the representative earthquake scenarios are defined in terms of the annual loss exceedance rates, they vary in function of the exposed system. The identified representative scenarios for the building stock have epicenters located not further than 30 km from the two communes, with magnitudes ranging between 6.0 and 7.0. The epicenter locations of the earthquake scenarios representative of the electrical-power network are more spread out but not further than 100 km away from the two communes, with magnitudes ranging between 7.0 and 9.0. For risk management activities, we recommend considering the identified scenarios together with historical events. [ABSTRACT FROM AUTHOR]

Türkiye is in a geography where many large and small-scale earthquakes occur due to its location in the earthquake zone. The Kahramanmaraş earthquake on February 6, 2023, and the Hatay earthquake on February 20, 2023, affected individuals with special needs and their families as well as individuals with typical development. This research aims to determine the experiences of experts who meet/support individuals with special needs and their families in the earthquake zone or any province and their recommendations regarding future disasters. Therefore, focus group interviews were conducted with five special education teachers and a psychological counsellor. According to the results of the research, four themes were reached: the needs, the difficulties, the positive aspects of interventions for individuals with special needs after the earthquake and recommendations for a future earthquake. The results obtained from the findings of this study were discussed together with previous studies in the literature and suggestions were made regarding before, during and after disasters. [ABSTRACT FROM AUTHOR]

The Sichuan basin (SCB) is situated at the southeastern edge of the Tibetan Plateau where widespread seismicity has occurred. In the past decades, seismic events occurred in and around SCB have been responsible for more than 100 thousand casualties. To quantify the present-day seismic hazard of this region, especially the densely populated Chengdu-Chongqing economic zone (CCEZ), we develop a probabilistic earthquake forecast model using strain rates derived from 187 Global Navigation Satellite System (GNSS) horizontal velocities, of which 102 velocity vectors are first released. The second invariant of the strain rate tensor suggests that the Shimian County and its surroundings are exposed to the highest seismic hazard in and around SCB. The second most dangerous area is located between 103-105°E. The Chongqing area is the least dangerous. The principal strain rate axes interior of the Sichuan basin suggest that this region is experiencing broad-scale extension, which according to our knowledge, is first revealed by our dense GNSS network. The comparison between the cumulative histograms of the second invariant of geodetic strain rate and earthquake count indicates that the geodetic strain rates in this region can serve as a reliable predictor of M≥6 earthquake locations. Thus, we proceed to calculate the total seismic moment anticipated for the entire area within the next 30 years. [ABSTRACT FROM AUTHOR]

The Lacq area in southwest France has been associated with continuous moderate induced seismic activity since 1969. However, the mechanisms driving this induced seismicity are not fully understood: reservoir depletion has been proposed as the main factor, and more recently wastewater injection has been suggested to play a more important role. The interpretation of these mechanisms relies heavily on the quality of earthquake locations, which we prove to be weak due to a lack of local instrumentation for several years. In order to provide the most complete and reliable induced event catalogue for the studies of the Lacq induced seismicity mechanisms and seismic hazard, we made an exhaustive compilation, analysis and improvement of all available catalogues. We also provided new earthquake detections and relocations in a 3-D velocity model from past and present temporary deployments never used for studying the Lacq area. Important remaining location uncertainties lead us to also carefully sort the events according to their location confidence, defining 3 classes of events (unconstrained location, location constrained within 2–3 km and 1–2 km, respectively). This new harmonized catalogue and the identification of well-constrained events, covering 50 yr of induced seismicity, allow us to propose that wastewater injection is almost certainly the main mechanism driving the seismicity, with (i) most of the constrained events located within the reservoir boundaries and (ii) the released seismic energy variations following variations in injection operations at different scales. In particular, we have also highlighted a change in the injection–seismicity relationship around 2010–2013. From 2013, despite lower injection volumes, seismicity remained persistent and some clusters of earthquakes were detected predominantly in spring, summer and early autumn, except in winter periods. From 2016, we observed a strong temporal relationship between days with higher rate/volume injections (approximately above 400 m3 d−1) and both clustered events and higher magnitude earthquakes (greater than 2.4). [ABSTRACT FROM AUTHOR]

Conclusion: This study constructed a high-resolution seismic catalog of 1,623 earthquakes that had occurred within 32 days in the Wulong Yinpan Reservoir area by using the deep-learning picking algorithm PhaseNet and the earthquake-location procedure Loc-Flow. A hidden fault extending up to approximately 20 km within the reservoir area was identified through analysis of precise earthquake locations and geological strata. We proposed that the increase in pore pressure caused by the intrusion of reservoir water in the sealed limestone layer results in induced seismicity along the hidden fault. Our finding sheds new insight on the importance of fluid pathways and fluid pressure in reservoir-induced seismicity and can facilitate seismic risk assessment in reservoir regions. [ABSTRACT FROM AUTHOR]

The China Seismic Experimental Site (CSES) is located at the intersection of the Tibetan Plateau, South China Block, and Indian Plate and has complex geological settings and intense crustal deformation, making it one of the most seismically active areas in Chinese mainland. A high-resolution, three-dimensional (3D) crust-mantle velocity structure is crucial for understanding seismotectonic environments, lithospheric deformation mechanisms, and deep dynamic processes. We first constructed a high-vertical-resolution 3D initial velocity model using the joint inversion of receiver functions and surface waves and then obtained a 3D P- and S-wave velocity model (CSES-VM1.0) with the highest lateral resolution of 0.25° for the CSES using double-difference tomography. Owing to the limitations of the Sn observation data, the resolution of the S-wave velocity model in the lower crust and upper mantle was reduced, making it closer to the initial model provided by joint inversion. A comparison with explosive-source seismic data showed that the synthetic P-wave first-arrival travel times of the new model were closer to the observations than those of the previous velocity models. The velocity cross-sections across the source areas of the 2022 Lushan MS6.1 and Ludian MS6.8 earthquakes reveal that the former earthquake occurred near a weak contact zone between the Tibetan Plateau and Sichuan Basin, and the rupture of the latter earthquake occurred in a granitic area, with the northern end blocked by rigid high-velocity bodies. A clear high-velocity anomaly zone is distributed along the western margin of the Yangtze Block, revealing the spatial distribution of Neoproterozoic intermediate-basic intrusions. This high-velocity zone significantly controls the morphology of fault zones and influences the rupture processes of major earthquakes. Two northeast-southwest and north-south trending high-velocity anomalies were found near Panzhihua, potentially related to Neoproterozoic and Middle-Late Permian intermediate-basic intrusions. The imaging results revealed the spatial distribution of the Lincang granitoid batholith, the uplifted zone of the central axis fault in the Simao Basin, and the Ailaoshan complex belt in the southwestern CSES, demonstrating a higher spatial resolution compared to previous results. Our velocity model provides an essential foundation for deep structural studies, high-precision earthquake locations, and strong ground motion simulations in the CSES. [ABSTRACT FROM AUTHOR]

In the past two decades, the central portion of Campi Flegrei caldera has experienced ground uplift up to 15 mm/month, with an increase of rate, magnitude and extent of the seismicity. In this work, we perform multi‐scale precise earthquake relocation of the 2014–2024 seismicity, mapping in detail activated fault zones. We relate the geometry, extent, and depth of these zones with up‐to‐date structural reconstructions of the caldera. The current seismicity is mainly driven by ground‐uplift‐induced stress concentration on pre‐existing, weaker fault zones, some of which identified for the first time. These structures are not only related to the inner caldera and dome resurgence but also to volcano‐tectonic events of the last 10 ka. The extent of imaged fault segments suggests they can accommodate ruptures up to a moment magnitude 5.1, significantly increasing seismic hazard in the area. Plain Language Summary: During the past 2 yrs, there has been a marked increase in ground uplift, number and size of earthquakes at Campi Flegrei caldera. This increase in activity has raised concerns among the population and public authorities about the impact of seismic activity on buildings and infrastructure in the area and about the best actions to undertake during the seismic emergency to reduce the risk. Additionally, the possibility of a future volcanic eruption is being considered, although currently geochemical and geophysical monitoring shows no unequivocal signs of precursory phenomena. In this work, we map the last decade of seismicity with a new technique providing high‐precision earthquake locations that allow us to unveil the currently activated fault zones of the inner caldera. The results show a near‐elliptical distribution of seismicity at the global scale of the caldera, which at a smaller scale delineates complex seismogenic structures. The size of imaged faults suggests that earthquakes up to a moment magnitude 5.1 can occur, significantly increasing seismic hazard in the area. Key Points: High‐precision location of 2014–2024 seismicity in Campi Flegrei depicts active fault zones with unprecedented detailSeismicity occurs along different volcano‐tectonic structures including the caldera inner ring fault zone and faults bounding the Solfatara craterA new structure has been recognized in the eastern sector of the caldera, hosting the largest magnitude event in the analyzed period [ABSTRACT FROM AUTHOR]

Accurate earthquake source parameters are crucial for understanding plate tectonics, yet, it is difficult to determine these parameters precisely for offshore events, especially for outer‐rise earthquakes, as the limited availability of direct P or S wave data sets from land‐based seismic networks and the unsuitability of simplified 1D methods for the complex 3D structures of subducting systems. To overcome these challenges, we employ an efficient hybrid numerical simulation method to model these 3D structural effects on teleseismic P/SH and P‐coda waves and determine the reliable centroid locations and focal mechanisms of outer‐rise normal‐faulting earthquakes in northeastern Japan. Two M6+ events with reliable locations from ocean bottom seismic observations are utilized to calibrate the 3D velocity structure. Our findings indicate that 3D synthetic waveforms are sensitive to both event location, thanks to bathymetry and water reverberation effects, and the shallow portion of the lithospheric structure. With our preferred velocity model, which has Versus ∼16% lower than the global average, event locations are determined with uncertainties of <5 km for horizontal position and <1 km for depth. The refined event locations in a good match between one of the nodal strikes and the high‐resolution bathymetry, enabling the determination of the causative fault plane. Our results reveal that trench‐ward dipping normal faults are more active, with three parallel to the trench as expected, while five are associated with the abyssal hills. The significant velocity reduction in the uppermost lithosphere suggests abundant water migrating through active normal faults, enhancing both mineral alteration and pore density. Plain Language Summary: The subduction of oceanic plates plays a crucial role in recycling earth materials and generating the largest earthquakes and tsunamis. This process causes significant bending of the oceanic plate near the trench, where forces from frictional coupling on the plate interface and far‐field subduction loading act in opposite directions, forming a gentle bulge on the seafloor termed the outer‐rise region. This region is rich in shallow bending‐related earthquakes at shallow depths and is characterized by rough bathymetry bounded by faults. Identifying the relationship between these earthquakes and their hosting faults is critical for understanding the seismic and tsunami hazards and fault development in the outer rise. However, building up this link is impeded by large uncertainties of earthquake source parameters. Here, we employ an advanced numerical wavefield simulation approach to precisely handle the structural complexity near 8 ∼ M6 outer‐rise earthquakes, which allows use of far‐field seismic waveform data to constrain source parameters. Reliable earthquake locations and focal mechanisms, along with high‐resolution bathymetry, enable us to identify the causative faults. Dramatically low velocity structure of the subducting oceanic plate is also revealed through this process, which suggests a fluid‐rich outer rise region that efficiently recycles water into the deeper earth. Key Points: Centroid location and focal mechanism of outer‐rise earthquakes were reliably determined through 3D modeling of teleseismic body wavesAlong with high‐resolution bathymetry, reliable source parameters allow us to identify the ruptured faults hosting these normal events3D waveform modeling required a Versus ∼16% lower than the global average, suggesting a fluid‐rich oceanic lithosphere at the outer rise [ABSTRACT FROM AUTHOR]

Abstract—On February 6, 2023, two devastating earthquakes struck southern central Turkey, nine hours apart. The ground shaking from these earthquakes even swept over a significant part of northwestern Syria. In this paper, we consider the locations of the epicenters of these earthquakes against the prediction of the М ≥ 6.5 earthquake epicenters in Anatolia and adjacent regions, which was made in 1973 by I.M. Gelfand, V.I. Keilis-Borok and their colleagues using the Kora-3 pattern recognition algorithm based on morphostructural zoning data. We also present the results of early detection of the periods with an increased probability of the strongest earthquakes as determined by the medium-term prediction algorithm for the M8 earthquakes. It is found that the epicenters of the February 6, 2023 earthquakes occurred in a node identified in 1973 as potentially earthquake-prone for М ≥ 6.5, and both events occurred within the spatial and temporal coverage of the warning area diagnosed by the M8 algorithm in July 2021. [ABSTRACT FROM AUTHOR]

Seismic traveltime anomalies of waves that traverse the uppermost 100–200 km of the outer core have been interpreted as evidence of reduced seismic velocities (relative to radial reference models) just below the core–mantle boundary (CMB). These studies typically investigate differential traveltimes of SmKS waves, which propagate as P waves through the shallowest outer core and reflect from the underside of the CMB m times. The use of SmKS and S(m-1)KS differential traveltimes for core imaging are often assumed to suppress contributions from earthquake location errors and unknown and unmodelled seismic velocity heterogeneity in the mantle. The goal of this study is to understand the extent to which differential SmKS traveltimes are, in fact, affected by anomalous mantle structure, potentially including both velocity heterogeneity and anisotropy. Velocity variations affect not only a wave's traveltime, but also the path of a wave, which can be observed in deviations of the wave's incoming direction. Since radial velocity variations in the outer core will only minimally affect the wave path, in contrast to other potential effects, measuring the incoming direction of SmKS waves provides an additional diagnostic as to the origin of traveltime anomalies. Here we use arrays of seismometers to measure traveltime and direction anomalies of SmKS waves that sample the uppermost outer core. We form subarrays of EarthScope's regional Transportable Array stations, thus measuring local variations in traveltime and direction. We observe systematic lateral variations in both traveltime and incoming wave direction, which cannot be explained by changes to the radial seismic velocity profile of the outer core. Moreover, we find a correlation between incoming wave direction and traveltime anomaly, suggesting that observed traveltime anomalies may be caused, at least in part, by changes to the wave path and not solely by perturbations in outer core velocity. Modelling of 1-D ray and 3-D wave propagation in global 3-D tomographic models of mantle velocity anomalies match the trend of the observed traveltime anomalies. Overall, we demonstrate that observed SmKS traveltime anomalies may have a significant contribution from 3-D mantle structure, and not solely from outer core structure. [ABSTRACT FROM AUTHOR]

The precise determination of earthquake location is the fundamental basis in seismological community, and is crucial for analyzing seismic activity and performing seismic tomography. First arrivals are generally used to practically determine earthquake locations. However, first-arrival traveltimes are not sensitive to focal depths. Moreover, they cannot accurately constrain focal depths. To improve the accuracy, researchers have analyzed the depth phases of earthquake locations. The traveltimes of depth phases are sensitive to focal depths, and the joint inversion of depth phases and direct phases can be implemented to potentially obtain accurate earthquake locations. Generally, researchers can determine earthquake locations in layered models. Because layered models can only represent the first-order feature of subsurface structures, the advantages of joint inversion are not fully explored if layered models are used. To resolve the issue of current joint inversions, we use the traveltimes of three seismic phases to determine earthquake locations in heterogeneous models. The three seismic phases used in this study are the first P-, sPg- and PmP-waves. We calculate the traveltimes of the three seismic phases by solving an eikonal equation with an upwind difference scheme and use the traveltimes to determine earthquake locations. To verify the accuracy of the earthquake location method by the inversion of three seismic phases, we take the 2021 MS6.4 Yangbi, Yunnan earthquake as an example and locate this earthquake using synthetic and real seismic data. Numerical tests demonstrate that the eikonal equation-based earthquake location method, which involves the inversion of multiple phase arrivals, can effectively improve earthquake location accuracy. [ABSTRACT FROM AUTHOR]

The earthquake swarm in Palghar, western India, is a natural laboratory to understand long-duration seismogenesis. However, it requires an accurate estimation of the key parameters, such as earthquake locations and the velocity model of the region. Two separate studies performed by two organisations in India, the CSIR-National Geophysical Research Institute (NGRI) and the National Center for Seismology (NCS) reported significantly differing results from the first 8–12 months of earthquake monitoring in Palghar. CSIR-NGRI reported the depth of earthquakes in the range of 4–15 km, whereas NCS reported a much shallower depth down to 7 km only. We investigate the reason for this depth discrepancy by analysing datasets from the networks of both these organisations. We find that no available velocity models are able to reconcile the depth difference between the two datasets. Selection criteria generally adopted to determine a good velocity model, such as travel-time residuals and location errors, also failed to identify a suitable velocity model. Several synthetic tests helped us to identify that the network geometry and source-station separation are contributing factors to the observed depth difference. However, the main reason for the discrepancy was found to be inconsistent velocity models used for location at both networks. The main objective of our work is to estimate a velocity model which minimises the depth discrepancy between both datasets. In this regard, we synthetically generated hundreds of models with different VP and VP/VS ratios, followed by a grid search of VP and VP/VS ratios, which harmonises the location from the two datasets. The best model consists of a VP lying between 5.55–5.85 km/s and a VP/VS ratio between 1.77–1.81. For this velocity model, there is a greater overlap of the hypocentral clouds from both networks, and about 80% of the earthquakes of the CSIR-NGRI network were located within depths ≤ 7 km. We find that location errors vary seasonally, which is also related to the VP/VS of the crust. Since earlier studies have also found a strong correspondence between rainfall and seismicity in this region, we infer that the high VP/VS ratio might have been caused by the rainfall saturation of cracks in the Palghar seismicity zone. [ABSTRACT FROM AUTHOR]

This work investigates the characteristics of local seismicity within the State of Kuwait and discusses its potential tectonic and anthropogenic drivers. As Kuwait is an oil-producing country, the occurrence of earthquakes simultaneously with oil extraction may suggest a case of triggered or induced seismicity. Seismic activity inside Kuwait is monitored with high accuracy and continuously after the establishment of the Kuwait National Seismic Network (KNSN) in 1997 through an ambitious plan to study the micro-earthquake activity in Kuwait. This network recorded more than 1378 micro/minor local earthquakes. Two seismogenic areas are identified, both characterized by weak magnitudes and shallow focal depths. In the current work, several modern geophysical techniques are performed including earthquake location, waveform-based moment tensor inversion, moment tensor decomposition, stress drop analysis, and stress pattern assessment. The results suggest that local earthquakes in Kuwait involve tectonic and anthropogenic components. Further densification of the network may allow a robust discrimination in the future. [ABSTRACT FROM AUTHOR]

Induced earthquakes tend to be shallow, while tectonic events often occur in deeper parts of the Earth. A well-estimated hypocenter with uncertainties may help to evaluate whether an event is of an induced or tectonic origin. In this study, we focus on the development of a hypocenter method that helps to better define the source location of an earthquake and reduce the spatial error of the measurement. The hypocenter and the uncertainty is obtained by using the P- and S-wave phase time difference for a station and the P-wave traveltime differences between pairs of stations simultaneously in the hypocenter analysis. The uncertainty inherent to an imperfect reference velocity model, modelling, instrumental inaccuracy and phase time picking is propagated into the spacial hypocenter solution. A refined hypocenter methodology is successfully tested in a synthetic experiment with shallow (∼ 5 km), intermediate (∼ 10 km) and deep source points (∼ 15 km). The synthetic experiment indeed shows that it is possible to separate earthquakes by their depth solution, hence offering an indication that the event is either induced or tectonic. Case studies are presented of estimations of hypocenters and error ellipses for (1) induced seismicity at sites for gas storage in salt domes, geothermal production and gas extraction as well as (2) tectonic events. [ABSTRACT FROM AUTHOR]

In the Changning region of the Sichuan Basin, China, which has experienced decades-long injection of freshwater for commercial salt mining, a Ms 6.0 earthquake occurred in June 2019, along with four Ms >5 aftershocks. Using data from local and regional seismic stations, we determine accurate locations for this earthquake sequence, velocity structures, and excess pore fluid pressures of the source region. Our results show that the Ms 6.0 earthquake is extremely shallow (~1.6 km below mean sea level) and is associated with low Vs and high Vp/Vs values and excess fluid pressures, indicating a fluid-induced earthquake. The mainshock was likely the shallowest M >6.0 induced earthquake, and it was triggered by the combined effect of pore pressure increase from the diffusion of injected fluids, differential formation subsidence from salt caverns, and highly fractured slip-prone rocks enriched in quartz and silica content. Following Coulomb stress transfer from the mainshock, the sequence ruptured in a cascading manner involving preexisting oblique faults of varying dips. [ABSTRACT FROM AUTHOR]

In this study, the double-difference tomography (tomoDD) method is applied to jointly invert the three-dimensional (3-D) crustal velocity structure and earthquake locations in the Maduo area based on automatically and manually picked seismic phase data. The results show that: (1) We speculated that the seismogenic fault is the Kunlun Pass–Jiangcuo Fault based on the spatial distributions of the aftershocks and surface rupture and the strike slip nature of the fault and the mainshock. In addition, a continuous northwest-trending branch fault may exist on the north side of the western section of the Maduo aftershocks. (2) We speculated that the Maduo earthquake was a bilateral rupture based on the media strength of the upper crust and near the surface and the seismic distribution. The findings also provide evidence for the large-scale rupture of the Maduo earthquake. In addition, the high-velocity body to the upper right of the mainshock satisfactorily explains the unobvious rupture above the mainshock. The late weak seismicity indicates that the energy released during the earthquake rupture was sufficient, and it is concluded that the short-term seismic hazard is insignificant. (3) The low S-wave velocity and high wave ratio reflect the existence of crustal fluids in the Maduo area based on the results of previous studies. The Maduo earthquake occurred on the side of the biased high-velocity body in the high-low velocity transition zone, where the stress easily accumulates and is easily released. Therefore, we conclude that the Maduo earthquake accumulated significant stress in the source area. The crustal fluids encountered a hard slope-type high-velocity body and flowed upward into the seismogenic fault, weakening the seismogenic fault. The combined effect of both processes finally triggered the Maduo MS7.4 earthquake. [ABSTRACT FROM AUTHOR]

This study explores the potential of machine learning algorithms for earthquake prediction, utilizing fluid chemical anomaly data from hot springs. Six hot springs, located within an active fault zone along the southeastern coast of China, were carefully chosen as hydrochemical monitoring sites for an extended period of two and a half years. Using this data, a prediction model integrating six algorithms was developed to forecast M ≥ 5 earthquakes in Taiwan. The model's performance was validated against recorded earthquake events, and the factors influencing its predictive capability were analyzed. Our comprehensive analysis conclusively demonstrates the superiority of machine learning algorithms over traditional statistical methods for earthquake prediction. Additionally, including sampling time in the data sets significantly improves the model's predictive performance. However, it is important to note that the model's predictive performance varies across different hot spring and indicators type, highlighting the importance of identifying optimal indicators for specific scenarios. The model parameters, including the anomaly detection rate (P) and earthquake response time threshold (M), significantly impact the model's predictive capabilities. Therefore, adjustments are needed to optimize the model's performance for practical use. Despite limitations such as the inability to differentiate pre‐earthquake anomalies from post‐earthquake anomalies and pinpoint the precise location of earthquakes, this study successfully showcases the potential of machine learning algorithms in earthquake prediction, paving the way for further research and improved prediction methods. Plain Language Summary: This study explores the potential of utilizing machine learning algorithms for earthquake prediction based on hydrothermal fluid chemical anomaly data. An earthquake prediction model integrating six machine learning algorithms was developed using continuous hot spring hydrochemical monitoring data. The model's prediction performance was validated using actual earthquake event data, and various factors influencing its predictive capability were analyzed. The results demonstrate that the machine learning algorithm's prediction performance exceeds that of traditional methods, and the selection of hot springs, indicator types, and model parameters significantly impacts the model's prediction performance. This study successfully showcased the potential of machine learning algorithms in earthquake prediction, while also indicating new avenues for further research and improvement of prediction methods. Key Points: An earthquake prediction model based on machine learning using hydrochemical data from hot springs is proposed with sufficient accuracyThe earthquake prediction accuracy of the local outlier factor algorithm outperformed the traditional statistical methodThe predictive performance of the model varies across different hot springs, indicators type, and model parameters [ABSTRACT FROM AUTHOR]

Magmas, especially mafic ones, usually intrude into the upper crust as dikes. The intruded dike is often arrested before reaching the surface to make an eruption. Many geophysical observations, including geodetic measurements, have documented dike intrusions and arrests. Also, many theoretical considerations and analog experiments explored the mechanics of dike propagation and arrest. However, insights gained from theoretical considerations, analog experiments, and geophysical observations have yet to be well reconciled. This study attempts to reconcile geodetic measurements with insights gained from theoretical considerations and analog experiments to investigate how to forecast whether an intruded dike results in an eruption or not. This study considers four causes of dike arrests: (1) solidification of the intruded magma, (2) insufficient volume of dike intrusion, (3) negative buoyancy acting on the intruded magma, and (4) stress perturbation near the dike tip by a large earthquake. Then, this study investigates the cause of dike arrests associated with the 1997 and 1998 seismic swarm off the Izu Peninsula, Japan, and the 2015 failed eruption of Sakurajima volcano, Japan, as an example. This study suggests that the dike intrusions associated with the 1997 and 1998 seismic swarm off the Izu Peninsula are caused by insufficient volume of the dike, the loss of buoyancy, or both. The failed eruption of the 2015 Sakurajima eruption is most likely by insufficient volume. To investigate the contribution of geodetic data in understanding the cause of dike arrests, it is essential to consider the characteristics of geodetic data. They are: (1) geodetic data constrain the intruded volume and the location relatively well, (2) geodetic data cannot constrain the geometry of the intruded dike very well, (3) an assumption of the host rock as homogeneous halfspace underestimates the volume of the intruded dike and estimates the depth of the dike shallower than the true value. These limitations indicate that we cannot fully understand the cause of dike arrests solely from geodetic data. Independent information gained from, for example, the location of dike-induced earthquakes, seismic structures, or density structure from gravity anomalies or muon radiography helps better understand the cause of dike arrests. [ABSTRACT FROM AUTHOR]

Plate motion obliquity along the dominantly transform Queen Charlotte plate boundary (QCPB) peaks offshore Haida Gwaii. To investigate the effects of obliquity on plate boundary deformation, we analyze continuous seismic waveforms from temporary and permanent stations from 1998 to 2020 to generate a catalog of ∼50,000 earthquakes across Haida Gwaii. We use an automated technique based on auto‐regressive phase detection and onset estimation to obtain the initial seismic catalog, integrate existing catalogs, invert for 3D velocity structure using data from the best constrained period, and relocate the entire catalog using the new 3D velocity model. We investigate the seismically active sections of the transcurrent Queen Charlotte fault (QCF), noting that little seismicity locates directly along its bathymetrically defined trace. Instead, seismicity illuminates a complex system of segmented structures with variable geometries along strike. Other clusters highlight active shallow faults within the highly deformed Queen Charlotte terrace. Few aftershocks appear on the thrust plane of the 2012 Mw 7.8 Haida Gwaii earthquake except near its inferred intersection with the QCF at 15–20 km depths, suggesting elevated residual stress at the juncture of slip‐partitioning. Deep crustal seismicity (up to ∼20 km depths) beneath central Haida Gwaii aligned parallel to the strike of the thrust plane may represent landward underthrusting of the Pacific plate. Our results suggest possible coseismic strike‐slip rupture on the QCF during the 2012 earthquake and add support to the thesis that highly oblique transform boundaries are viable settings for subduction initiation. Plain Language Summary: We investigated the complex tectonics offshore Haida Gwaii, western Canada, where the Pacific and North American plates slide past one another obliquely. By compiling and analyzing the most comprehensive earthquake catalog in the area, spanning 1998–2020, we present the most detailed report to date of the earthquake‐producing structures in the region, including previously unidentified and highly segmented faults. Clusters of seismicity illuminate (a) a highly deformed terrace of elevated seafloor west of Haida Gwaii, (b) a complex and segmented fault system adjacent to the previously‐mapped surface trace of the main Queen Charlotte strike‐slip fault, and (c) the inferred fault intersection at depth between the subvertical Queen Charlotte fault (which hosted the 1949 magnitude 8.1 earthquake) and the shallowly dipping Haida Gwaii thrust (which hosted the 2012 magnitude 7.8 earthquake). We also speculate that the 2012 earthquake may also have involved some motion on the Queen Charlotte fault. These results contribute to better constraints on regional tectonics and hazards, and provide insights into the mechanisms of subduction initiation. Key Points: Seismicity off Moresby Island is distributed along multiple segments slightly off of the Queen Charlotte fault traceAftershocks at intersection of Queen Charlotte Fault with the 2012 Mw 7.8 thrust plane reflect residual stress at slip partitioning juncturePreviously undocumented deep seismicity beneath Haida Gwaii is consistent with an underthrusting Pacific Plate [ABSTRACT FROM AUTHOR]

Seismic source locations are fundamental to many fields of Earth and planetary sciences, such as seismology, volcanology and tectonics. However, seismic source detection and location are challenging when events cluster closely in space and time with signals tangling together at observing stations, such as they often do in major aftershock sequences. Though emerging algorithms and artificial intelligence (AI) models have made processing high volumes of seismic data easier, their performance is still limited, especially for complex aftershock sequences. In this study, we propose a novel approach that utilizes three‐dimensional image segmentation—a computer vision technique—to detect and locate seismic sources, and develop this into a complete workflow, Source Untangler Guided by Artificial intelligence image Recognition (SUGAR). In our synthetic and real data tests, SUGAR can handle complex, energetic earthquake sequences in near real time better than skillful analysts and other AI and non‐AI based algorithms. We apply SUGAR to the 2016 Kaikōura, New Zealand sequence and obtain five times more events than the analyst‐based GeoNet catalog. The improved aftershock distribution illuminates a continuous fault system with extensive fracture zones beneath the segmented, discontinuous surface ruptures. Our method has broader applicability to non‐earthquake sources and other time series image data sets. Plain Language Summary: Detecting and locating earthquakes is fundamental to seismology, volcanology, and tectonics. A number of emerging algorithms, including some based upon artificial intelligence (AI), have made processing large volumes of seismic data much easier. However, their performance is still limited, especially in clustered aftershock sequences whose signals overlap at observing seismographs. We propose a new, AI computer vision‐based approach to this problem, and develop it into a complete earthquake detection and location workflow, named SUGAR. Tests on synthetic and real earthquake data sets show that SUGAR characterizes complex earthquake sequences better than other AI and non‐AI algorithms or professional analysts. We apply SUGAR to the complex aftershock sequence of the 2016 Mw 7.8 Kaikōura, New Zealand earthquake, detecting five times more events than the analyst‐based GeoNet catalog. Whereas surface breaks of the Kaikōura earthquake are highly discontinuous, our improved aftershock distribution supports a continuous fault system surrounded by extensive fracture zones at depth. Our method has broader potential for other types of seismic sources and image series. Key Points: We propose a new seismic source detection and location approach based on the source‐scanning algorithm and 3D image segmentationThis approach outperforms human analysts and popular artificial intelligence (AI) and non‐AI based methods in characterizing intense aftershock sequencesThe resulting catalog of the 2016 Kaikōura earthquake sequence suggests a continuous fault system surrounded by extensive fracturing [ABSTRACT FROM AUTHOR]

Earthquake hypocentres are routinely obtained by a common inversion problem of P - and S -phase arrivals observed on a seismological network. Improving our understanding of the uncertainties associated with the hypocentral parameters is crucial for reliable seismological analysis, understanding of tectonic processes and seismic hazard assessment. However, current methods often overlook uncertainties in velocity models and variable trade-offs during inversion. Here, we propose to unravel the effects of the main sources of uncertainty in the location process using techniques derived from the Global Sensitivity Analysis (GSA) framework. These techniques provide a quantification of the effects of selected variables on the variance of the earthquake location using an iterative model that challenges the inversion scheme. Specifically, we consider the main and combined effects of (1) variable network geometry, (2) the presence of errors in the analyst's observations and (3) errors in velocity parameters from a 1-D velocity model. These multiple sources of uncertainty are described by a dozen of random variables in our model. Using a Monte Carlo sampling approach, we explore the model configurations and analyse the differences between the initial reference location and 100 000 resulting hypocentral locations. The GSA approach using Sobol's variance decomposition allows us to quantify the relative importance of our choice of variables. It highlights the critical importance of the velocity model approximation and provides a new objective and quantitative insight into understanding the sources of uncertainty in the inversion process. [ABSTRACT FROM AUTHOR]

In order to explore the constraint degree of GNSS and InSAR data on the Maduo earthquake under the layered earth model structure, and to understand the cause of the Maduo earthquake and the danger of the surrounding area, this paper uses D-InSAR technology to obtain the InSAR co-seismic deformation field of the Maduo earthquake on May 22,2021. Based on GNSS and InSAR data, the co-seismic slip model and fault plane stress distribution of the Maduo earthquake are jointly inverted. This paper calculates the Coulomb stress changes caused by 14 M ≥ 7 strong earthquakes co-seismic, post-seismic viscoelastic relaxation and inter-seismic tectonic stress loading of 19 fault segments in the Bayan Har block research area (96°E-106°E, 29°N-36°N) since 1900. The results show that: (1) The maximum Line Of Sight (LOS) deformation obtained based on the ascending and descending InSAR data was about 0.9 m. The maximum slip amount of GNSS + InSAR joint inversion is 4.87 m, which is located in the Dongcao Along Lake section (∼98.6°E). Combined with the stress drop distribution of the fault surface, it is found that the Maduo earthquake is dominated by strike-slip. (2) The historical strong earthquakes delayed the Maduo earthquake by nearly 103 years. The 1937 Huashixia earthquake, the 1947 Dari earthquake, the 1963 Dulan earthquake, and the 1973 Luhuo earthquake had the greatest stress unloading effect, which was equivalent to delaying the Maduo earthquake by 53 years, 21 years, 11 years, and 17 years, respectively. The cumulative Coulomb stress at the source location of the Maduo earthquake reached 0.0112 MPa. Most area of the fault sections such as the East Kunlun Fault, the Maduo-Gande Fault, the western and eastern sections of the Dari Fault, the western and eastern sections of the Qingshuihe Fault, the Ganzi-Yushu Fault, and the eastern section of the Kunlunshankou-Jiangcuo Fault are in the Coulomb stress loading area, which should be paid attention to. [ABSTRACT FROM AUTHOR]

Regional-scale swarms of subparallel linear topographic features, known as lineament domains, are a common feature of planetary surfaces. Lineament domains are superficial manifestations of the crustal stress field trajectory. Notably, one of the effects of active tectonics is seismicity. Italy is one of the most seismically active regions in the Mediterranean, with many destructive earthquakes that have occurred in past centuries. Here, we assess the seismic meaning of the main lineament domain in the tectonically active region of Central Italy. We describe the use of an automated analysis of satellite imagery coupled with spatial grid analysis to identify three lineament domains of the Central Apennines. Spatial and azimuthal comparisons of the main lineament domain (i.e., the Apennine Domain), with the known locations of earthquakes (moment magnitude of Mw > 5.5) that occurred during the past century, revealed the most seismically active tectonic areas and their spatial distributions. Further, we present a conceptual seismo-geodynamic model for the Central Apennines, which is characterized by regional arching and explains the presence of an extensional tectonic regime in the upper crustal layer of the active Apennines fold-and-thrust belt. [ABSTRACT FROM AUTHOR]

In South Iceland, populated and agricultural areas are at risk of earthquakes due to their location within the South Iceland Seismic Zone (SISZ). In 2008, two moderate‐sized earthquakes (M5.8 and M5.9) occurred in Ölfus, the western end of this highly active transform zone. We analyze temporal seismic velocity variations (dv/v) related to the Ölfus earthquake doublet, using cross‐correlations of ambient noise in the frequency range of 0.1–3.0 Hz. The two mainshocks decrease the average velocity by 0.8% at the nearest stations. The co‐seismic changes are most noticeable from 0.7 to 1.7 Hz and affect a 40 km wide region. We present a first‐time comparison of dv/v to crustal deformation, seismicity, co‐seismic volumetric stress changes and reported PGA distribution for the Ölfus doublet. Ground accelerations caused by mainshocks at intermediate distances suggest that strong shaking‐related damage may contribute to the co‐seismic dv/v decrease. A rapid velocity increase (0.3%) in a month after the co‐seismic drop indicates crustal rock healing. We find 3‐months of post‐seismic decorrelation, followed by a nearly permanent velocity decrease (0.2%) confined to a shallow layer (1 km) until the end of the observation period. Afterslip and pore fluid effects in the near‐source region are likely to influence post‐seismic dv/v. We demonstrate that seismic interferometry can contribute to future fault‐zone monitoring operations in the SISZ by detecting small changes in velocity. Plain Language Summary: Strong earthquakes can occur in southwestern Iceland due to plate motions, posing a threat to human life and infrastructure. In 2008, two earthquakes struck the Ölfus region, causing widespread damage in the epicentral area. Sensitive instruments record naturally occurring ambient seismic signals which are originated from ocean waves, wind, and anthropogenic activity. A dramatic drop in seismic wave velocity is common during major quakes. The state‐of‐the‐art seismic methods based on these ambient waves allow us to detect minor changes in the velocity of seismic waves. We employ continuously recorded seismic data from three instruments to analyze for the first time such seismic velocity fluctuations related to moderate size earthquakes in Iceland. To interpret the complex mechanisms underlying these changes, we make use of multiple available data sets and compare them to our observations. Our findings suggest that seismic velocities decreased over a wide area, possibly due to earthquake‐induced ground shaking and rock damage. This study shows that velocity variations can be effectively measured with even sparsely placed seismometers and that they can be used in the future to monitor seismic zones in Iceland. Key Points: We apply ambient noise seismic interferometry to the 2008 Mw 6.1 south Iceland earthquake doubletTemporal seismic velocities decrease at the time of the earthquakes and recover post‐seismically up to 40 km in the upper crustThe co‐seismic and post‐seismic velocity changes correlate with GPS displacements [ABSTRACT FROM AUTHOR]

Until now, numerous efforts have been made to find earthquake precursors. One of the factors that can predict the occurrence of future earthquakes is a decrease in the b-value parameter. In this study, for the metropolis of Tehran, with a population of over 8 million, located on or near many active faults, it is estimated that if the maximum seismic potential of these faults happened again, the greatest disaster in human history would occur. In this case, the analyses indicate a minimum of several hundred thousand casualties and sometimes more than a million. In the current study, various faults around Tehran were investigated, and given that the faults on Tehran have not had serious seismic activity for over a thousand years, this article focused exclusively on adjacent faults, particularly the Eshtehard faults. Therefore, in the current study, the seismicity and tectonics of western Tehran were investigated by analyzing seismic parameters using earthquake data collected from 2003 to 2023. In general, the investigation of the temporal changes in the study area showed that the b-value decreased before the December 20, 2017, earthquake and an increasing trend afterward. Observing anomalies in the b-value before and after the main movement in the area shows that changes in this parameter can be considered a precursor for estimating the time and location of earthquakes. Therefore, a useful step can be taken toward knowing the local seismic hazards by using earthquake data recorded by seismic networks and continuously monitoring the changes in the b-value. [ABSTRACT FROM AUTHOR]

The tomography results reveal not only distinct velocity structures in different tectonic zones but can also provide valuable insights into the geological features of the area. This study presents the results of 2D Rayleigh wave tomographic maps obtained in NE Iran. For this purpose, we used the recorded waveforms of more than 500 earthquakes with M > 4 that occurred between January 2000 and October 2020 at 165 stations. The calculated tomographic maps cover a period range of 3 to 36 s, providing the 3D VS model to analyze crustal structure at depths ranging from 2 to 30 km. At shorter periods, the tomographic maps are primarily influenced by sediment thickness, with the presence of thick sediment layers (~ 10 km) responsible for the observed low VS anomalies (< 3.1 km/s) in the study area. At longer periods, the tomographic maps highlight the structural characteristics of the middle-lower crustal layers and, somewhere, the depth variations of the Moho discontinuity. The VS model also confirms the correlation between tectonic fractures and known faults in the study area as boundaries of seismotectonic provinces. Moreover, a distinct area was observed beneath the Binalud foreland, which we interpreted as a suture zone, as suggested by previous studies. The reliability of the resolved anomalies was supported through a series of tests, including checkerboard and earthquake location uncertainties. These tests demonstrated the robustness of the results and provided confidence in the accuracy of the findings. [ABSTRACT FROM AUTHOR]

This study presents an updated view of the effects of the 1940 Vrancea earthquake. Recently compiled studies in the literature from the time of the event, as well as other studies, present the opportunity to gain additional and relevant information regarding this large-magnitude event. The effects of this earthquake on various locations in Romania are compared to those observed after the subsequent large Vrancea earthquake of 1977. An assessment of the economic losses caused by the seismic event is also attempted. The seismic vulnerability of some building typologies commonly used before 1940 is assessed by employing the earthquake damage data and the well-known macroseismic method. The impact of this event on the design and construction practices in Romania is evaluated using the collected information as well. Finally, the policy of repair and strengthening of buildings applied after the event is also discussed, and case studies are presented. [ABSTRACT FROM AUTHOR]

To enhance the understanding of the geometry and characteristics of seismogenic faults in the Beijing-Tianjin-Hebei region, we relocated 14 805 out of 16 063 earthquakes (113°E-120°E, 36°N-43°N) that occurred between January 2008 and December 2020 using the double-difference tomography method. Based on the spatial variation in seismicity after relocation, the Beijing-Tianjin-Hebei region can be divided into three seismic zones: Xingtai-Wen'an, Zhangbei-Ninghexi, and Tangshan. (1) The Xingtai-Wen'an Seismic Zone has a northeastsouthwest strike. The depth profile of earthquakes perpendicular to the strike reveals three northeast-striking, southeast-dipping, high-angle deep faults (>10 km depth), including one below the shallow (<10 km depth) listric, northwest-dipping Xinghe fault in the Xingtai region. Two additional deep faults in the Wen'an region are suggested to be associated with the 2006 M 5.1 Wen'an Earthquake and the 1967 M 6.3 Dacheng earthquake; (2) The Zhangbei-Ninghexi Seismic Zone is oriented north-northwest. Multiple northeast-striking faults (10-20 km depth), inferred from the earthquake-intensive zones, exist beneath the shallow (<10 km depth) Xiandian Fault, Xiaotangshan Fault, Huailai-Zhuolu Basin North Fault, Yangyuan Basin Fault and Yanggao Basin North Fault; (3) In the Tangshan Seismic Zone, earthquakes are mainly concentrated near the northeast-striking Tangshan-Guye Fault, Lulong Fault, and northwest-striking Luanxian-Laoting Fault. An inferred north-south-oriented blind fault is present to the north of the Tangshan-Guye Fault. The 1976 M 7.8 Tangshan earthquake occurred at the junction of a shallow northwest-dipping fault and a deep southeast-dipping fault. This study emphasizes that earthquakes in the region are primarily associated with deep blind faults. Some deep blind faults have different geometries compared to shallow faults, suggesting a complex fault system in the region. Overall, this research provides valuable insights into the seismogenic faults in the Beijing-Tianjin-Hebei region. Further studies and monitoring of these faults are essential for earthquake mitigation efforts in this region. [ABSTRACT FROM AUTHOR]

The development of machine learning technology enables more robust real-time earthquake monitoring through automated implementations. However, the application of machine learning to earthquake location problems faces challenges in regions with limited available training data. To address the issues of sparse event distribution and inaccurate ground truth in historical seismic datasets, we expand the training dataset by using a large number of synthetic envelopes that closely resemble real data and build an earthquake location model named ENVloc. We propose an envelope-based machine learning workflow for simultaneously determining earthquake location and origin time. The method eliminates the need for phase picking and avoids the accumulation of location errors resulting from inaccurate picking results. In practical application, ENVloc is applied to several data intercepted at different starting points. We take the starting point of the time window corresponding to the highest prediction probability value as the origin time and save the predicted result as the earthquake location. We apply ENVloc to observed data acquired in the southern Sichuan Basin, China, between September 2018 and March 2019. The results show that the average difference with the catalog in latitude, longitude, depth, and origin time is 0.02°, 0.02°, 2 km, and 1.25 s, respectively. These suggest that our envelope-based method provides an efficient and robust way to locate earthquakes without phase picking, and can be used in earthquake monitoring in near-real time. [ABSTRACT FROM AUTHOR]

The top of the subducting plate is a thick, complex zone where the heterogeneous structure likely controls earthquake rupture processes. Imaging this heterogeneous channel typically involves active‐source methods with limited depth penetration, or low‐resolution teleseismic methods. To access short wavelengths at greater depth, we use high‐frequency P‐to‐S (PS, 1–15 Hz) mode‐converted arrivals from nearby earthquakes >50 km deep to image the plate interface at vertical scales <1 km. We use 37 broadband stations in southcentral Alaska between 2007 and 2008 at 10–15 km spacing, spanning the great 1964 earthquake rupture zone and adjacent deeper slow slip and tremor regions. The central 21 stations record high‐amplitude PS arrivals converting from the megathrust region, at depths corresponding to the top of a prominent low‐velocity zone (LVZ) in receiver function images. The PS/P amplitude ratio (APS_P) varies along strike and with depth of the conversion point but is independent of earthquake location and varies slowly between adjacent stations. APS_P changes with slab depth, indicating changes in lithology or fluid content of the plate interface, consistent with transitions in slip behavior from locked to slow slip. High APS_P cannot be explained by a velocity step or a single low‐velocity, high Vp/Vs layer, but requires several alternating high and low‐velocity layers. These observations indicate that the LVZ is a highly heterogeneous channel at multiple scales, resembling a subduction channel or sheared zone of metasediment and altered crust as observed in many exhumed subduction zones. Plain Language Summary: The largest earthquakes in the world occur in subduction zones. The contact between the overriding and subduction plates, the megathrust, hosts great earthquakes and less hazardous slow slip and tremor events. The location of these depends on the fault's physical properties, but there is a discrepancy between the structures different seismic imaging techniques observe. To address this issue, our study uses a previously underutilized P‐to‐S (PS) signal from local in‐slab earthquakes, which start as a P wave and converts to an S wave at the plate interface. The conversion occurs in the megathrust fault zone, and the arrival amplitude depends on the properties across it. The high amplitudes of PS compared to P across the array favor a model that represents the interface as a broad shear zone, where the velocity and number of layers create variability in the amplitudes. Mapping the amplitudes shows high variability in the fault properties at a finer scale than typical passive seismic imaging techniques. Key Points: Southcentral Alaskan stations record high amplitude arrivals converting from P to S at the megathrust for local earthquakes >50 km deepThe timing of P‐to‐S conversions varies between stations requiring a conversion from top of the subducting plateArrival amplitudes change coherently across the megathrust, indicating lithology or fluid changes at tens of km spatial scale [ABSTRACT FROM AUTHOR]

The article provides a comprehensive earthquake catalogue for the eastern Alps from 1977 to 2022, focusing on seismic activity in NE Italy. The National Institute of Oceanography and Applied Geophysics manages the Monitoring System for NE Italy, which monitors and researches earthquakes in the region. The catalogue includes earthquake locations and magnitudes, and the article explains the data sources and methods used. It also discusses the reliability of earthquake solutions and the selection process for creating the final catalog. The document is a list of references and citations for scientific papers and reports on earthquake monitoring, location determination, magnitude calculation, and historical analysis in northeastern Italy. These sources are valuable for researchers studying earthquakes in the region. [Extracted from the article]

The incompleteness of earthquake catalogs is a well‐known issue caused by our technical limitation in detecting the small‐to very small‐magnitude seismicity falling near or below the background seismic noise. The detection of small‐magnitude events is fundamental for improving our knowledge of geometry and kinematics of seismogenic sources and the spatio‐temporal characteristics of seismicity, thus leading to better models for seismic hazard. Template‐matching (TM) is a powerful technique that, based on similarity measure (cross‐correlation) of seismic waveforms, allows to detect hidden earthquakes that are similar to known events (called templates). The high computational effort often limits such technique to small areas and for short time frames (less than 1 year). In this work, we present the first application of template‐matching at regional scale for the Italian Peninsula, focusing on the Southern Apennines. We use about 3,600 high‐quality events as templates, scanning 6‐year long continuous recordings (2009–2014), at more than 180 stations of the INGV network. About 20,000 new events are found, showing a comparable quality to the template catalog in terms of hypocentral solution, reaching a decrease of the magnitude of completeness of about one unit. To highlight the improved quality of the TM catalog, we report two main examples regarding the Sannio‐Matese area, where TM allowed us to unravel relevant details on the spatio‐temporal distribution of the local seismicity. Plain Language Summary: The natural and man‐made seismic noise is commonly higher than the signal of small‐size earthquakes, which represents the vast majority of the seismic activity. Identifying these hidden events is crucial for gaining a better understanding of fault structures, their location, and overall characteristics. A powerful technique for the retrieval of hidden seismicity is template‐matching, based on the comparison of known earthquakes with the continuous recording of a network of seismic stations. However, due to the high computational demand, the use of template‐matching is usually limited to small areas (e.g., volcanoes) and/or small time periods. In this study, we provide the first application of template‐matching at regional scale for the Italian Peninsula, specifically in the area of Southern Apennines. We analyze 6 years of continuous recording from more than 180 stations. Starting from about 3,600 templates, we detected over 20,000 previously hidden earthquakes with uncertainties on the earthquake location that are low and comparable to those of the initial templates. To demonstrate the potential of such an enriched earthquake catalog for future research, we focused on the Sannio‐Matese region. For the earthquake sequence in the Matese area that occurred between 2013 and 2014, template‐matching revealed a consistent level of background seismicity before the onset of the sequence, whereas no activity was reported in the official catalog. In the nearby Sannio area, we identified several earthquake clusters at unusual depths, indicating a sudden increase in the depth of seismic activity. These observations could significantly contribute to improving the seismic hazard model for the area. Key Points: First application of template‐matching at regional scale in the Southern Apennines (Italy) for the retrieval of hidden seismicityThe study results in 20,000 new detections, a five‐fold increase with respect to the starting catalogFocusing on the Sannio‐Matese area, we show how such a high‐resolution catalog enhances the spatio‐temporal characterization of seismicity [ABSTRACT FROM AUTHOR]

Given the abundance and importance of earth retention structures, the problem of seismic earth pressure has attracted not only the research community but also industry and government establishments. The dynamic response, even in the case of the simplest retaining wall, presents a complex problem of soil–structure interaction, encompassing a multitude of competing and complementary factors. This article presents a thorough and critical evaluation of notable analytical and field studies related to the dynamic earth pressures acting on retaining walls. Despite numerous studies spanning nearly a century regarding seismically induced lateral earth pressures, there remains a noticeable disparity between theoretical understanding and the actual field performance of retaining structures during seismic events. This review underscores the necessity for a more meticulous examination of dynamic analysis techniques and the existing design methodologies for retaining structures. [ABSTRACT FROM AUTHOR]