Search

A devastating earthquake with moment magnitude 7.5 occurred in the Noto Peninsula in central Japan on 1 January 2024. We estimate the rupture evolution of this earthquake from teleseismic P‐wave data using the potency‐density tensor inversion method, which provides information on the spatiotemporal slip distribution including fault orientations. The results show a long and quiet initial rupture phase that overlaps with regions of preceding earthquake swarms and associated aseismic deformation. The following three major rupture episodes evolve on segmented, differently oriented faults bounded by the initial rupture region. The irregular initial rupture process followed by the multi‐scale rupture growth is considered to be controlled by the preceding seismic and aseismic processes and the geometric complexity of the fault system. Such a discrete rupture scenario, including the triggering of an isolated fault rupture, adds critical inputs on the assessment of strong ground motion and associated damages for future earthquakes. Plain Language Summary: On 1 January 2024, a moment magnitude 7.5 earthquake occurred in the northern Noto Peninsula, Japan. The strong ground motion and tsunami associated with the earthquake caused severe damage to buildings and infrastructure, resulting in at least 245 causalities in the affected areas. The Noto Peninsula is affected by northwest‐southeast compression, and active reverse faults are known along the northern coast of the peninsula and its offshore region. Before the 2024 earthquake, the source region experienced long‐lasting earthquake swarm activity, which is a set of seismic events without an obvious mainshock‐aftershock pattern. Our seismological analysis found that there was a 10‐s‐long initial rupture episode around the hypocenter that overlapped with the earthquake swarm region. The initial rupture was followed by a series of three different rupture episodes on differently oriented fault segments. This earthquake highlights a multi‐scale rupture growth across a segmented fault network after a very quiet initial rupture process that was controlled by the preceding earthquake swarms and associated aseismic deformation related to fluid injection from depth. The rupture process advances our understanding of earthquake source physics and can lead to a better assessment of future earthquake hazards. Key Points: The 2024 Mw 7.5 Noto Peninsula earthquake involves a multi‐segmented rupture sequence on differently oriented faultsThe long and quiet initial rupture domain coincides with the preceding earthquake swarm regionFluid‐induced earthquake swarms and a segmented fault network control the complex earthquake rupture growth [ABSTRACT FROM AUTHOR]

Very low‐frequency earthquakes (VLFs) are characterized by longer source duration and smaller stress drop than regular earthquakes of similar magnitude. Recent studies have shown their frequent correlation with low‐frequency earthquakes (LFEs) on shared faults. The underlying source processes governing the occurrence of VLFs and their interaction with LFEs remain elusive. Here, we employ a slip‐weakening model for slow earthquakes. By comparing the source parameters of simulations and observations, it is suggested that VLFs are slow self‐arresting earthquakes that self‐terminate within the nucleation patch. Additionally, we adopt a composite model to reproduce the records of the simultaneous occurrences of a VLF and an LFE in the Nankai area. Our results present the possibility that VLFs, LFEs, and regular earthquakes can be distinguished using a unified dynamic framework. Plain Language Summary: Earthquakes can be divided into two groups: regular earthquakes and slow earthquakes. Regular earthquakes are the results of quick shear slip on faults, while slow earthquakes are generated from slow transient movements along the faults and radiate anomalous small energy. The mechanism that drives their different source characteristics remains elusive. Here, we employ an independent and composite dynamic source model to elucidate the unique attributes of very low‐frequency earthquakes (LFEs), a type of slow earthquakes. By comparing the source parameters and waveforms of observations with simulations. The outcomes indicate that very LFEs potentially represent a seismic type that self‐terminate within the region where the rupture is initially triggered. Key Points: Very low‐frequency earthquakes (LFEs) are characterized by slow self‐arresting processesOur model can simultaneously reproduce both very low‐frequency and LFEThe slip‐weakening frictional model generates both fast and slow earthquakes [ABSTRACT FROM AUTHOR]

Large‐scale disturbance events provide ideal opportunities to directly study recolonisation processes in natural environments, via the removal of competitors and the formation of newly vacant habitat. A high magnitude earthquake in central New Zealand in 2016 created major ecological disturbance, with coastal tectonic uplift of up to ~ 6 m extirpating vast swathes of intertidal organisms. One of the affected species was Durvillaea antarctica (rimurapa or southern bull kelp), which is an important habitat‐forming intertidal macroalga capable of long‐distance dispersal. Across the complex fault system with varying amounts of uplift, the species was either locally extirpated or heavily reduced in abundance. We hypothesised that neutral priority effects and chance dispersal from other populations would influence which lineages would establish. We sampled individuals of D. antarctica across the uplift zone immediately after the earthquake in 2016 and then repeatedly sampled new recruits in the same areas between 2017 and 2020, using genotyping‐by‐sequencing to provide 'before' and 'after' genomic comparisons. Our results revealed strong geographic clustering but little evidence of new lineages establishing at disturbed sites, although populations at uplifted sites remain at remarkably low densities. We infer that recolonisation has thus far primarily originated from refugial, remnant patches within the uplift zone. To complement the phylogeographic analysis, we estimated oceanographic connectivity among the uplift zone sample locations. The connectivity modelling estimated that northbound dispersal of D. antarctica was more likely, but we have not yet detected southern genotypes in the recolonised populations. As the ongoing recolonisation process transitions from an ecological to an evolutionary timescale, change remains possible. This study provides the first genomic 'snapshots' of a natural recolonisation process following a large‐scale ecological disturbance event, and ongoing research has the potential to reveal important insight into both micro‐ and macroevolutionary processes. [ABSTRACT FROM AUTHOR]

How to effectively mitigate atmospheric delay signals in InSAR observations has long been a pressing problem in the InSAR community. Here we propose a new method, DetrendInSAR, that addresses this issue by incorporating the spatiotemporal characteristics of displacements and atmospheric delays as a‐priori information. This enables simultaneously modeling and estimating surface displacements, atmospheric delays, and other unmodeled long‐wavelength errors (e.g., orbit errors) in InSAR time series. We use both simulated‐ and real‐data experiments to validate the performance of the proposed method, and results show a 20%–70% reduction of RMSE values for the DetrendInSAR‐obtained displacements compared with four commonly‐used atmospheric delay reduction methods. We also show that the DetrendInSAR method is capable of capturing the spatial and temporal details of sudden deformation jumps as small as 1 cm, due to a magnitude 5.4 earthquake, in InSAR time series. Based on the DetrendInSAR‐corrected ascending and descending Sentinel‐1 InSAR time series, we calculate the 2‐year postseismic east and vertical displacements of the 2021 Mw 7.4 Maduo earthquake, which better illuminate the postseismic deformation. Plain Language Summary: Satellite Interferometric Synthetic Aperture Radar (InSAR) is a powerful tool for providing detailed information about ground surface movements caused by geohazards (e.g., earthquakes, volcanoes, and landslides). However, InSAR observations also contain noise contributions (e.g., atmospheric delays) in addition to the information of interest, making it difficult to accurately depict the ground movements and characterize the underlying mechanisms of geohazards. To separate the noise components from the deformation component in InSAR observations, we propose the DetrendInSAR method that utilizes the spatiotemporal characteristics of each component in InSAR observations as additional constraints. Results from simulated‐ and real‐data experiments demonstrate that the proposed DetrendInSAR method effectively reduces the noise components and achieves 20%–70% better results than commonly‐used strategies. For the real‐data case study, we calculated the two‐year postseismic displacement time series of the 2021 magnitude 7.4 Maduo earthquake, revealing more clearer and longer‐term postseismic surface displacements of this earthquake than in previous studies. Key Points: DetrendInSAR is a new pixel‐based method that simultaneously estimates deformation and atmospheric delays in InSAR time seriesThe method is validated using both simulated data and two‐year postseismic deformation data of the 2021 magnitude 7.4 Maduo earthquakeResults corrected by DetrendInSAR show 20%–70% reduction of RMSE values compared with four commonly‐used atmospheric signal reduction methods [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]

Ahi Tupua, the central section of the Taupō Volcanic Zone in the central North Island of New Zealand, encompasses Taupō and Ōkataina calderas and has been the most frequently active and productive silicic magma system worldwide during the Quaternary. The entire Taupō Volcanic Zone is underlain by the Hikurangi Subduction Zone where a Large Igneous Province, the Hikurangi Plateau, is being subducted, but Ahi Tupua exhibits much higher rates of magma output than either the northern or the southern sections. Trace element signatures of Ahi Tupua eruptive products suggest that both decompression melting and flux melting play a role in this rifted arc setting, with fluid flux signatures being more prevalent in regions of active caldera volcanism. Intermediate‐depth (50–300 km) earthquakes provide a means of studying faulting and fluid flow processes within and around the subducting slab beneath Ahi Tupua. Using data from the national seismic network and a 13‐station temporary network ("ECLIPSE"), we repick and relocate 397 intermediate‐depth earthquakes of magnitudes M2.5+ that occurred in a 29‐month interval, and compute focal mechanisms for a subset of 47 earthquakes. We observe some seismicity that may be within the mantle wedge but most of the relocated earthquakes occur within the crust and uppermost mantle of the subducted slab and exhibit a weak transition from predominantly normal‐faulting in the slab crust to predominantly reverse‐faulting in the slab mantle. No double seismic zone is observed beneath Ahi Tupua. These observations are consistent with dehydration of the slab and flow of slab‐derived fluids along existing faults into the mantle wedge, that drives flux melting and accounts for the distinctive geochemical signatures and voluminous output of Ahi Tupua calderas. Plain Language Summary: Ahi Tupua is a volcanic region in the North Island of New Zealand that is the most active silicic volcanic system on Earth. It includes the active caldera volcanoes Taupō and Ōkataina. This volcanic region lies above the Hikurangi Subduction Zone, and studies of past eruptions suggest that Ahi Tupua's high rate of activity is driven by fluids released deep in the subduction zone. In this study, we use seismic data from across the entire North Island to investigate earthquakes occurring at depths of 50–300 km within the Hikurangi Subduction Zone. We show that these earthquakes suggest that the subducting oceanic crust is releasing a substantial amount of water into the overlying mantle, causing a large amount of melting and, ultimately, the distinctive volcanism of Ahi Tupua. Key Points: We relocate 397 intermediate‐depth earthquakes beneath Ahi Tupua, central Taupō Volcanic Zone, and compute 47 focal mechanismsMost seismicity occurs within the slab crust and mantle, with subordinate mantle wedge and plate interface faultingHypocenters and focal mechanisms are consistent with slab‐derived fluid fluxing melting of the mantle wedge beneath Ahi Tupua [ABSTRACT FROM AUTHOR]

In multiple observed caldera‐forming eruptions, the rock overlying a draining magma reservoir dropped downward along ring faults in sequences of discrete collapse earthquakes. These sequences are analogous to tectonic earthquake cycles and provide opportunities to examine fault mechanics and collapse eruption dynamics over multiple events. Collapse earthquake cycles have been studied with zero‐dimensional slider‐block models, but these do not account for the complicated interplay between fluid and elastic dynamics or for factors such as the heterogeneous fault properties and non‐vertical ring fault geometries often inferred at volcanoes. We present two‐dimensional axisymmetric mafic piston‐like collapse earthquake cycle models that include rate‐and‐state friction, fully‐dynamic elasticity, and compressible viscous fluid magma flow. We demonstrate that collapse earthquake intervals and magnitudes are highly sensitive to inertial effects, evolving stress fields, fault geometry, and depth‐varying fault friction. Given the consistent earthquake cycles observed in most eruptions, this suggests that ring faults can quickly stabilize and often become nearly vertical at depth. We use the well‐monitored 2018 collapse sequence at Kı̄lauea as a case study. Our model can produce many features of Kı̄lauea seismic and geodetic observations, except for a significant amount of interseismic slip, which cannot be readily explained with simple rate‐and‐state friction parameterizations. Plain Language Summary: Many large volcanic eruptions involve caldera collapse, where the rock above a magma reservoir abruptly subsides as the reservoir drains. Collapse can cause large earthquakes and repressurize the magma reservoir, creating a repeating cycle that helps sustain eruptions over days‐months. We develop computational models to understand the rock and magma interactions involved in collapse earthquake cycles, using data from the 2018 eruption of Kı̄lauea. The models can explain many geophysical measurements and show that collapse eruptions are very sensitive to fault geometry and spatially variable rock properties. However, standard friction models do not readily explain large amounts of fault slip measured between collapse earthquakes, suggesting that other complexities should be considered. Key Points: We develop 2D axisymmetric fully‐dynamic caldera collapse earthquake cycle models with rate‐and‐state friction and compressible fluid flowCollapse earthquake sequences are highly sensitive to fault geometry as well as heterogeneous stresses and frictionOur models fit geophysical data except large interseismic slip distances suggesting processes beyond simple rate‐and‐state friction parameterizations [ABSTRACT FROM AUTHOR]

We present a new geodetic strain rate and rotation rate model for Greece that has been derived using a highly dense GPS velocity field. The spatial distribution and the resolved rates of the various velocity gradient tensor quantities provided updated constraints on the present‐day upper crustal deformation in the region and revealed new details not reported previously. The spatial distribution of the second invariant demonstrated that the overall magnitude of strain rates is highest across two well‐defined provinces. The first follows the North Anatolian Fault and its two branches within the north Aegean, crosses central Greece and through the Gulf of Corinth it terminates in western Greece, while the second encompasses the extensional province of western Turkey and the eastern Aegean Sea islands. Our estimates revealed that shearing affects some of the fault‐bounded grabens of central Greece that lie to the SW of the North Aegean Basin implying considerable oblique extension. We identified a narrow region of counterclockwise rotation whose location and kinematics have been induced by the net effect across the intersection of the clockwise rotating domains of western and central Greece. The Aegean microplate and the Anatolian plate are separated by a wide transition zone which accommodates the curved stretching of the entire plate system. In both edges of the Hellenic forearc the dominant mode of crustal strain is E‐W extension. We found that earthquakes of M ≥ 5.6 are spatially well‐correlated with high‐strain areas, indicating that strain rate mapping could be used to inform future probabilistic seismic hazard analyses. Plain Language Summary: Greece and its surroundings comprise a region of elevated seismic hazard because of the intense active deformation that is accumulated in earth's crust over time and which is expected to be released as earthquakes of various magnitudes. Given the importance of this relationship, we used a dense data set of GPS velocities to gain insight into the spatial distribution and patterns of the present‐day strain and rotation rates. We found that deformation is mostly concentrated across two zones. The first crosses the North Anatolian Fault, enters the north Aegean Sea, continues in central Greece and terminates in western Greece, while the second encompasses the eastern Aegean Sea islands and western continental Turkey. Across the first zone, the crust experiences various deformation modes due to the interaction of large lithospheric‐scale tectonic structures with smaller regions of localized faulting. Within the second zone, the crust is stretching in response to differences in direction and rate of movement between the Aegean microplate and the Anatolian plate. Comparison of strain rates with seismicity revealed that earthquakes with M ≥ 5.6 predominantly occur within high‐strain areas, giving implications that knowledge of the spatial distribution of tectonic deformation can augment seismic hazard analyses. Key Points: We present an improved geodetic strain and rotation rate model for Greece which reveals new details about active deformationThe strain rate field of Greece is a superposition of short‐ and long‐wavelength signals driven by local forces and large‐scale tectonicsEarthquakes over M 5.6 correlate well with high strain rates and consistently occur at areas where the second invariant exceeds 40 nstrain/yr [ABSTRACT FROM AUTHOR]

Current earthquake forecasting approaches are mainly based on probabilistic assumptions, as earthquakes seem to occur randomly. Such apparent randomness can however be caused by deterministic chaos, rendering deterministic short‐term forecasts possible. Due to the short historical and instrumental record of earthquakes, chaos detection has proven challenging, but more frequently occurring slow slip events (SSE) are promising candidates to probe for determinism. Here, we characterize the SSE signatures obtained from GNSS position time series in the Hikurangi Subduction Zone (New Zealand) to investigate whether the seemingly random SSE occurrence is governed by chaotic determinism. We find evidence for deterministic chaos for stations recording shallow SSEs, suggesting that short‐term deterministic forecasting of SSEs, similar to weather forecasts, might indeed be possible over timescales of a few weeks. We anticipate that our findings could open the door for next‐generation SSE forecasting, adding new tools to existing probabilistic approaches. Plain Language Summary: Since earthquakes appear to occur randomly, the currently available probabilistic predictions are based on past earthquake records. These predictions estimate the likelihood of an earthquake of a given magnitude occurring within a defined time period. In contrast to such probabilistic approaches, deterministic systems are fully predictable, albeit often confined to short time scales due to their potential chaotic behavior. Probing for deterministic predictability in the earthquake cycle is intractable due to the limited historical instrumental record. However, frequently occurring slow slip events ‐ captured by transient GNSS displacements that can last several weeks ‐ provide a unique opportunity to explore deterministic predictability in these types of slow earthquakes. By studying GNSS time series from various stations on New Zealand's North Island, we have discovered evidence suggesting that these irregularly occurring slow slip events might be governed by chaotic determinism. This implies the potential to forecast both timing and magnitude of slow slip events a few weeks in advance using deterministic methods, much like we predict weather patterns. Consequently, our theoretical findings could therefore pave the way for innovative approaches to short‐term slow slip forecasting. Key Points: Nonlinear analysis of GNSS displacement time series unveils evidence for deterministic chaos in slow slip events in New ZealandOur theoretical findings imply that irregularly occurring slow slip events could potentially be forecasted a few weeks in advance [ABSTRACT FROM AUTHOR]

Large earthquakes can trigger smaller seismic events, even at significant distances. The process of earthquake triggering offers valuable insights into the evolution of local stress states, deepening our understanding of the mechanisms of earthquake nucleation. However, our ability to detect these triggered events is limited by the quality and spatial density of local seismometers, posing significant challenges if the triggered event is hidden in the signal of a nearby larger earthquake. Distributed acoustic sensing (DAS) has the potential to enhance the monitoring capability of triggered earthquakes through its high spatial sampling and large spatial coverage. Here, we report on an uncatalogued magnitude (M) 5.1 event in northeast Turkey, which was likely dynamically and instantaneously triggered by the 2023 M7.8 earthquake in southeast Turkey, located 400 km away. This event was initially discovered on ∼1,100 km of active DAS recordings that are part of an 1,850‐km linear array. Subsequent validation using local seismometers confirmed the event's precise time, location, and magnitude. Interestingly, this dynamically triggered event exhibited precursory signals preceding its P arrivals on the nearby seismometers. It can be interpreted as the signal from other nearby, uncatalogued, smaller triggered events. Our results highlight the potential of high‐spatial‐density DAS in enhancing the local‐scale detection and the detailed analysis of earthquake triggering. Plain Language Summary: Large earthquakes can trigger smaller ones even far away. This helps us understand more about how earthquakes start and develop. However, finding these smaller earthquakes can be difficult as sometimes they are hidden in the chaos of a bigger, nearby earthquake. There is a novel technology called Distributed Acoustic Sensing (DAS) that might help. DAS can listen for earthquakes over large areas and gives a more detailed picture of what's happening underground. In this study, we discovered a moderate‐size earthquake with a magnitude of 5.1 in Northeast Turkey that was triggered by a large earthquake with a magnitude of 7.8 in Southeast Turkey, using a DAS system that stretched over a thousand kilometers. We then checked this finding with conventional seismometers to be sure. Interestingly, this triggered earthquake showed precursory signals before its main shaking started, which could be signs of other smaller earthquakes happening nearby. Our findings deepen our understanding of how earthquakes interact with each other and offer insights into how earthquakes start. Our results also suggest that DAS could help us find and understand these triggered earthquakes, providing us with invaluable information for future seismology studies. Key Points: We find an uncatalogued M5.1 earthquake in NE Turkey dynamically and instantaneously triggered by the 2023 Mw 7.8 SE Turkey earthquakeWe uncover this event on a thousand‐kilometer linear distributed acoustic sensing array, then confirm its precise time, location, and magnitude with seismometersPrecursory signals of the M5.1 event are observed and are most likely resulting from other nearby events rather than its nucleation phase [ABSTRACT FROM AUTHOR]

Earthquake swarms are most commonly composed of small‐magnitude earthquakes. However, a recent study by Yoshida, Uchida, et al. (2023, https://doi.org/10.1029/2023GL106023) analyzed a swarm beneath the Noto Peninsula in Japan that, after more than two years of moderate‐magnitude seismicity, triggered the moment magnitude (Mw) 6.2 Suzu mainshock in May 2023. Based on high‐precision earthquake locations and a slip inversion of the mainshock, these authors found that the Mw 6.2 Suzu earthquake occurred on the updip extension of a fault that was active during the swarm, likely driven by increased fluid pressure. After publication of that paper, a much larger and more destructive Mw 7.5 event occurred nearby on 1 January 2024. These events underscore the potential for swarms to be precursors to large, damaging earthquakes. Forecasting the eventual evolution of swarms is currently very challenging but could be aided in the future by new observations and models. Plain Language Summary: Although earthquake swarms often only contain small earthquakes, occasionally they can trigger large, damaging earthquakes. Yoshida, Uchida, et al. (2023, https://doi.org/10.1029/2023GL106023) examined the triggering of a magnitude 6.2 earthquake in Japan, which caused extensive damage, following two years of smaller earthquakes. This sequence, like many swarms, may have been driven by elevated fluid pressure migrating upwards within the crust. After publication of that paper, a much larger and more destructive Mw 7.5 event occurred nearby. Forecasting the eventual evolution of ongoing swarms is currently very challenging but could be aided in the future by new observations and models. Key Points: Earthquake swarms can be precursors to damaging earthquakes, including the 1 January 2024, Mw 7.5 Noto Peninsula, Japan eventFluid pressure changes often drive swarm activity, and their degree of confinement may influence swarm evolutionDirect observations of fluids in fault zones combined with numerical modeling may aid swarm forecasting in the future [ABSTRACT FROM AUTHOR]

Understanding the scaling laws of source parameters is a fundamental subject in seismology. This study conducts spectral ratio analysis to estimate the source parameters for 409 shallow crustal earthquakes with Mw 3.2–6.0 in Japan. Subsequently, the source parameter scaling relations are investigated for a wide magnitude range by combining the results of this and previous studies. The spectral ratio method applied in this study provides the finite source properties of the localized area with large slip. The single asperity model, a simple heterogeneous source model with a single localized area with large slip, is used to estimate the stress drop since it can be more suitable to characterize earthquake sources than the standard homogeneous circular source. This investigation calibrates the constant to link the corner frequency and the source radius by comparing the corner frequency and source area estimated by the spectral ratio analyses. This calibrated constant is used to re‐calculate the stress drop of small earthquakes from the corner frequency estimated in previous studies. The stress drop and apparent stress increase with increasing magnitude up to Mw ∼ 5 and become magnitude‐independent for larger earthquakes. The radiation efficiency ranges typically from 0.1 to 1.0 and is independent of magnitude. The slip dependences of the stress drop, apparent stress, radiation efficiency, and fracture energy observed in this study are explained by the ones predicted from the slip‐weakening model incorporating the thermal pressurization effect. Thermal pressurization is one of the possible mechanisms explaining the observed source parameter scaling relations. Plain Language Summary: This study investigates the relationship between earthquake sizes and parameters characterizing the earthquake sources (source parameter scaling relations) to understand the difference between small and large earthquakes. The source parameters are estimated for shallow crustal earthquakes in Japan. Then, the source parameter scaling relations are obtained over a broad magnitude range by combining the results of this and previous studies. This investigation is based on a simple heterogeneous source model rather than the homogeneous circular source model, which has been widely used. A familiar hypothesis is that the sources of small and large earthquakes are physically similar (earthquake similarity). The results suggest that the earthquake similarity holds for earthquakes with a magnitude larger than about 5.0 but does not for small earthquakes. This study demonstrates that the observed source parameter scaling relations can be explained by the source parameter scaling relations predicted from the stress relaxation model incorporating the effect of the pore pressure rise within the fault core by frictional heating during seismic faulting (thermal pressurization of pore fluids). Thermal pressurization of pore fluids can be one of the significant mechanisms explaining the differences in the source parameter scaling relations for small and large earthquakes. Key Points: The single asperity model, a simple heterogeneous source model, is used rather than the standard homogeneous circular source modelThe apparent stress and stress drop increase with magnitude up to Mw ∼ 5 and become magnitude‐independent for larger earthquakesThermal pressurization is one of the possible mechanisms explaining the observed source parameter scaling relations [ABSTRACT FROM AUTHOR]

The b‐value in earthquake magnitude‐frequency distribution quantifies the relative frequency of large versus small earthquakes. Monitoring its evolution could provide fundamental insights into temporal variations of stress on different fault patches. However, genuine b‐value changes are often difficult to distinguish from artificial ones induced by temporal variations of the detection threshold. A highly innovative and effective solution to this issue has recently been proposed by van der Elst (2021, https://doi.org/10.1029/2020jb021027) by means of the b‐positive estimator, which is based on analyzing only the positive differences in magnitude between successive earthquakes. Here, we demonstrate the robustness of the estimator, which remains largely unaffected by detection issues due to the properties of conditional probability. We illustrate that this robustness can be further improved by considering positive differences in magnitude, not only between successive earthquakes but also between different pairs of earthquakes. This generalized approach, defined as the "b‐more‐positive estimator," enhances efficiency by providing a precise estimate of the b‐value while including a larger number of earthquakes from an incomplete catalog. However, our analysis reveals that the accuracy of the b estimators diminishes when earthquakes below the completeness threshold are included in the catalog. This leads to the paradoxical observation that greater efficiency is achieved when the catalog is more incomplete. To address this, we introduce the "b‐more‐incomplete estimator," where the b‐more‐positive estimator is applied only after artificially filtering the instrumental catalog to make it more incomplete. Our findings show the superior efficiency of the b‐more‐incomplete method. Plain Language Summary: Earthquake magnitudes can vary widely, and the b‐value is a common metric used to measure the frequency of earthquakes with large versus small magnitudes. In addition, the b‐value could serve as an indicator of the stress state of different fault patches, making it a valuable tool in earthquake research. However, since small earthquakes are often obscured by previous larger ones, determining whether changes in the b‐value are genuine or simply caused by detection problems can be challenging. To address this issue, a new approach called the b‐positive estimator has been recently developed. The method only considers positive changes in magnitude between successive earthquakes. In this study, we confirm that the b‐positive estimator is a powerful and effective technique to estimate the b‐value and is largely unaffected by issues related to detecting earthquakes. We extend the method by considering positive differences in magnitude, encompassing not only successive earthquakes but also different pairs of earthquakes. In particular we show that the b‐positive estimator is more efficient when the catalog is more incomplete. This allows us to develop modifications to the b‐positive method providing a more efficient tool to monitor the b‐value in ongoing seismic sequences. Key Points: Conditional probability detecting consecutive earthquakes makes positive magnitude difference distribution weakly affected by incompletenessThe b‐positive estimator can be enhanced by including more earthquake pairs, not only consecutive onesThe b‐positive estimator can be enhanced by making the catalog more incomplete [ABSTRACT FROM AUTHOR]

Teleseismic back‐projection imaging has emerged as a powerful tool for understanding the rupture propagation of large earthquakes. However, its application often suffers from artifacts related to the receiver array geometry. We developed a teleseismic back‐projection technique that can accommodate data from multiple arrays. Combined processing of P and pP waveforms may further improve the resolution. The method is suitable for defining arrays ad‐hoc to achieve a good azimuthal distribution for most earthquakes. We present a catalog of short‐period rupture histories (0.5–2.0 Hz) for all earthquakes from 2010 to 2022 with MW ≥ 7.5 and depth less than 200 km (56 events). The method provides automatic estimates of rupture length, directivity, speed, and aspect ratio, a proxy for rupture complexity. We obtained short‐period rupture length scaling relations that are in good agreement with previously published relations based on estimates of total slip. Rupture speeds were consistently in the sub‐Rayleigh regime for thrust and normal earthquakes, whereas a tenth of strike‐slip events propagated at supershear speeds. Many rupture histories exhibited complex behaviors, for example, rupture on conjugate faults, bilateral propagation, and dynamic triggering by a P wave. For megathrust earthquakes, ruptures encircling asperities were frequently observed, with downdip, updip, and balanced patterns. Although there is a preference for short‐period emissions to emanate from central and downdip parts of the megathrust, emissions updip of the main asperity are more frequent than suggested by earlier results. Plain Language Summary: Back‐projection is an earthquake imaging method based on seismic waveforms recorded remotely at a group of seismometers (seismic array). Here, we develop a new approach to combine backprojections from multiple arrays and seismic waveforms and use it to derive a catalog of large earthquake rupture histories from 2010 to 2022, providing a map view of the high‐frequency radiation emitted along the fault. The method automatically estimates the earthquake rupture length, speed, directivity, and aspect ratio. Based on these estimates, we obtained scaling relations between the earthquake magnitude and rupture length that agree with classical relationships. We identified strike‐slip earthquakes propagating at supershear, that is, faster than the shear wave speed, the usual limit for self‐sustaining rupture propagation. We observed complex rupture behaviors, for example, multiple faults activated, bilateral ruptures, and triggering of the main phase of a rupture by a primary (P) wave from the earliest part of the rupture. For subduction earthquakes, high‐frequency emissions were often observed, forming a ring around the fault interface patches (asperities) where the main slip occurs. There was a preference for high‐frequency radiation to emanate from central and deeper parts of the subducting plate interface, but shallower emissions were more frequent than expected from previous literature. Key Points: We provide a complete catalog of high‐frequency rupture histories for M ≥ 7.5 events 2010–2022We develop a semi‐automatic method for estimating rupture length, speed, directivity, and aspect ratioBoth encircling ruptures and emissions updip of slip asperities common in megathrust earthquakes [ABSTRACT FROM AUTHOR]

On 8 September 2023 an MW 6.8 earthquake struck the High Atlas Mountains of western Morocco, about 70 km southwest from Marrakesh, causing significant devastation and casualties. In this study, we investigate a comprehensive geodetic data set, employing interferometric synthetic aperture radar measurements to assess the fault segment responsible for the seismic event. Our findings suggest two potential fault scenarios: either a transpressive NNW‐dipping high‐angle (70°) fault related to the Tizi n'Test alignment or a transpressive SSW‐dipping low‐angle (22°) fault associated with the North Atlas Fault, with slip (up to 2.2 m) only occurring on deeper parts of the fault. While seismic catalogs couldn't definitively determine the dip direction of the fault, evidence from mainshock locations, gravity and heat flow data and modeling, and active shortening direction suggest the activation of a low‐angle south‐westerly dipping oblique thrust of the North Atlas fault during the 2023 Moroccan earthquake. Plain Language Summary: On 8 September 2023, a powerful earthquake with a magnitude of 6.8 hit the High Atlas Mountains in western Morocco, causing significant damage and loss of life. In this research, a thorough geodetic analysis was conducted using a technique called interferometric synthetic aperture radar to identify the causative fault. The results suggest two potential fault scenarios: one involves a steeply dipping fault related to the Tizi n'Test crustal structure, while the other suggests a gently dipping fault associated with the North Atlas Fault. As far as existing aftershock records do not allow determination of the angle of the fault, clues from the locations of the mainshock, gravity and heat flow data and modeling, and the direction of active compression suggest that a gently dipping fault was likely activated during the 2023 earthquake in Morocco. Key Points: Coseismic ground deformation of the 2023 Morocco earthquake measured with interferometric synthetic aperture radar (InSAR) dataInSAR data allow for two possibilities: the rupture of an intramontane high‐angle fault or of a border low‐angle thrustBased on aftershock distribution, crustal thickness, and regional tectonic stress orientation, the low‐angle solution is more likely [ABSTRACT FROM AUTHOR]

The reliable estimation of earthquake magnitude and stress drop are key in seismology. The novel technology of distributed acoustic sensing (DAS) holds great promise for source parameter inversion owing to the measurements' high spatial density. In this study, I demonstrate the robustness of DAS for magnitude and stress drop estimation using the empirical Green's function deconvolution method. This method is applied to nine co‐located earthquakes recorded in Israel following the 2023 Turkey earthquakes. Spectral ratios were stacked along the fiber, and fitted with a relative Boatwright source spectral model. Excellent fits were obtained even for similar sized earthquakes. Stable seismic moments and stress drops were calculated assuming that the moment of one earthquake is known. DAS derived estimates were found to be more stable and reliable than those obtained using a dense accelerometer network. The results demonstrate the great potential of DAS for source studies. Plain Language Summary: Estimating earthquake magnitude and stress drop, the two most fundamental source parameters, is key for various seismological investigations, including earthquake self‐similarity and hazard mitigation. The extraction of source parameters requires that path and site effects are reliably deconvolved from source contributions. One approach is to deconvolve a small earthquake from a co‐located larger one in the frequency domain such that common path and site functions cancel and relative source function, between both earthquakes, remain. In this study, I apply the deconvolution approach to nine earthquakes that followed the 2023 Turkey earthquakes, recorded using distributed acoustic sensing (DAS) in Israel. DAS converts standard optical fibers into dense arrays, with seismic measurements every few meters along tens‐of‐kilometers long fibers. The deconvolution was calculated for different earthquake pairs and excellent fits were obtained with a relative source spectral model. Stable seismic moments and stress drops were calculated. These parameters were found to be more reliable than those obtained using a dense standard‐accelerometer network. The results demonstrate the great potential of DAS for source studies. Key Points: The spectral ratios approach was applied to nine earthquakes in Israel recorded by distributed acoustic sensing (DAS) and accelerometersAccurate relative magnitudes and stress drops were calculatedDAS can provide reliable source parameter estimates that may outperform accelerometers [ABSTRACT FROM AUTHOR]

Repeating earthquakes repeatedly rupture the same fault asperities, which are likely loaded to failure by surrounding aseismic slip. However, repeaters occur less often than would be expected if these earthquakes accommodate all of the long‐term slip on the asperities. Here, we assess a possible explanation for this slip discrepancy: partial ruptures. On asperities that are much larger than the nucleation radius, a fraction of the slip could be accommodated by smaller ruptures on the same asperities. We search for partial ruptures of repeating earthquakes in Parkfield using the Northern California earthquakes catalog. We find 3991 individual repeaters which have 4468 partial ruptures. The presence of partial ruptures suggests that the asperities of repeating earthquakes are much larger than the nucleation radius. However, we find that partial ruptures could accommodate only around 25% of the slip on repeating earthquake patches. A 25% increase in the slip budget can explain only a small portion of the long recurrence intervals of repeating earthquakes. Plain Language Summary: Repeating earthquakes happen on the same fault patch over and over again. They are thought to happen on locked patches surrounded by a slowly moving section of the fault. This slow‐moving fault loads the patch to failure. However, the observed slip on the repeating earthquake patches does not match the long‐term slip on the surrounding fault. This slip deficit means the time between earthquakes is longer than expected. We explore the possibility that some of the slip deficit is explained by slip happening in smaller earthquakes ("partial ruptures") in between the time of the larger magnitude repeating earthquakes. We search for partial ruptures in Parkfield, California using the Northern California earthquakes catalog, which contains many well‐located repeating earthquake sequences. We find that partial ruptures could accommodate up to 25% of the slip on repeating earthquake patches, but this is still not enough slip to explain why small repeating earthquakes occur about five times less often than one would expect. Key Points: We search for partial ruptures of repeating earthquakes in Parkfield, CaliforniaWe find partial ruptures, which suggests repeating earthquake asperities are many times larger than the nucleation radiusIncluding partial ruptures in the slip budget does not account for the repeaters' surprisingly long recurrence intervals [ABSTRACT FROM AUTHOR]

The magnitude‐frequency distribution (MFD) describes the relative proportion of earthquake magnitudes and provides vital information for seismic hazard assessment. The b‐value, derived from the MFD, is commonly used to estimate the probability that a future earthquake will exceed a specified magnitude threshold. Improved MFD and b‐value estimates are of great importance in the central and eastern United States where high volumes of fluid injection have contributed to a significant rise in seismicity over the last decade. In this study, we recalculate the magnitudes of 8,775 events for the 2011 Prague, Oklahoma sequence using a relative magnitude approach that depends only on waveform data to calculate magnitudes. We also compare the distribution of successive magnitude differences to the MFD and show that a combination of the magnitude difference distribution (MDFD) and relative magnitudes yields a reliable estimate of b‐value. Using the MDFD and relative magnitudes, we examine the temporal and spatial variations in the b‐value and show that b‐value ranges between ∼0.6 and 0.85 during the aftershock sequence for at least 5 months after the M 5.7 mainshock, though areas surrounding the northeast part of the sequence experience higher b‐values (0.7–0.85) than the southwestern part of the Meeker‐Prague fault where b‐value is the lowest (0.6–0.7). We also identify a cluster of off‐fault events with the highest b‐values in the catalog (0.85). These new estimates of MFD and b‐value will contribute to understanding of the relations between induced and tectonic earthquake sequences and promote discussion regarding the use of b‐value in induced seismic hazard estimation. Plain Language Summary: The magnitude‐frequency distribution and the b‐value are statistical parameters that describe how earthquake magnitudes are distributed in a catalog. These parameters are vital for hazard estimation of induced seismicity in the central and eastern United States, but they are not well understood in this region due to reasons including, but not limited to, catalog incompleteness, magnitude uncertainty between different magnitude types, and variable injection history. In this study, we reevaluate the previously cataloged magnitude estimates using a relative magnitude method to estimate the temporal and spatial variation in b‐value for the 2011 Prague, Oklahoma sequence. With the relative magnitude method, we reestimate magnitude for 81% of the events in the Prague sequence which are then utilized for b‐value estimation. We demonstrate the presence of consistently low b‐values during the aftershock sequence for at least ∼5 months following the mainshock and identify a trend of decreasing b‐value along the Meeker‐Prague fault as distance from the mainshock increases. These observations allow us to compare spatial and temporal b‐value variations of induced sequences to those observed in tectonic sequences. Key Points: The relative magnitude method allows for recalculation of earthquake magnitude without requiring location or geological dataRelative magnitudes combined with the b+ estimator gives a reliable estimate of b‐valueWe identify patterns of spatial and temporal variations in b‐value that are consistent with tectonic sequences [ABSTRACT FROM AUTHOR]

Recent studies in the earthquake magnitude‐frequency relation (b‐value) found that the b‐value can decrease with time before large earthquakes in the source area. Such a decrease even coincided with a burst of foreshocks immediately before the earthquakes implying a preslip migrating toward the nucleation zone. We systematically survey the b‐value variations in space and time in the source area of 17 earthquakes with magnitudes greater than ML 6.0 in Taiwan. We relocated the earthquakes released by the Central Weather Administration of Taiwan since 2012 as timing can provide a sufficiently low completeness magnitude (MC) of 1.5. We carefully determine the spatiotemporal search criteria on seismicity in the source area of all targeted earthquakes. We surveyed the temporal b‐value systematically using moving time windows with a given number of earthquake events with the magnitudes greater than MC. We found the b‐value decreased clearly for 2 days before the 2018 ML 6.3 Hualien earthquake, coinciding with a burst of ML 5.8 earthquake and its aftershocks nearby as foreshocks. The foreshocks migrated updip toward the hypocenter of the 2018 ML 6.3 Hualien earthquake and revealed a second decrease in the b‐value 10 hours before it occurred. The b‐value precursor primarily comes from a rapid reduction of small earthquakes in the foreshocks and agrees with recent key findings of preslip. However, there is no strong correlation between the b‐value precursor and coseismic slip. Apart from this, the b‐values did not change significantly in most cases of earthquakes in Taiwan before and after they occurred. Plain Language Summary: Direct evidence for the precursor of a large earthquake is rare and difficult to be quantified accurately. Earthquake magnitude‐frequency relation (b‐value) is a classic observation implying stress accumulation on a seismogenic fault. Scientists found that the b‐value can decrease within a few days before an impending large earthquake in the source area. Taiwan is one of the regions undergoing frequent M ≥ 6.0 earthquakes and can map the b‐value in high resolution based on the relocated earthquakes. This study systematically surveyed the b‐value in the source area of seventeen ML ≥ 6.0 earthquakes in Taiwan, probing into b‐value precursor in the 8‐year time series. We found that the b‐value had a robust decrease 2 days before the 2018 ML 6.3 Hualien earthquake, coinciding with the initiation of foreshocks nearby and at a downdip of the hypocenter of the 2018 ML 6.3 Hualien earthquake. The foreshocks showed clear evidence of precursor as they migrated updip toward the hypocenter with a second decrease in the b‐value 10 hours before the earthquake occurred. We found no evidence of a b‐value precursor in most of the targeted earthquakes that agrees with the knowledge of precursor as happening episodically and unexpectedly. Key Points: We found a b‐value precursor that coincides with foreshocks for 2 days before the 2018 ML 6.3 Hualien earthquake in the source areaThe b‐value precursor correlates with foreshock distribution in the source area and is likely uncorrelated to the high coseismic slipThere is no significant change in the b‐value before M ≥ 6.0 earthquakes in Taiwan in a majority of the cases that we analyzed [ABSTRACT FROM AUTHOR]

Elevated seismic noise for moderate‐size earthquakes recorded at teleseismic distances has limited our ability to see their complexity. We develop a machine‐learning‐based algorithm to separate noise and earthquake signals that overlap in frequency. The multi‐task encoder‐decoder model is built around a kernel pre‐trained on local (e.g., short distances) earthquake data (Yin et al., 2022, https://doi.org/10.1093/gji/ggac290) and is modified by continued learning with high‐quality teleseismic data. We denoise teleseismic P waves of deep Mw5.0+ earthquakes and use the clean P waves to estimate source characteristics with reduced uncertainties of these understudied earthquakes. We find a scaling of moment and duration to be M0 ≃ τ4, and a resulting strong scaling of stress drop and radiated energy with magnitude (Δσ≃M00.21 ${\Delta }\sigma \simeq {M}_{0}^{0.21}$ and ER≃M01.24 ${E}_{R}\simeq {M}_{0}^{1.24}$). The median radiation efficiency is 5%, a low value compared to crustal earthquakes. Overall, we show that deep earthquakes have weak rupture directivity and few subevents, suggesting a simple model of a circular crack with radial rupture propagation is appropriate. When accounting for their respective scaling with earthquake size, we find no systematic depth variations of duration, stress drop, or radiated energy within the 100–700 km depth range. Our study supports the findings of Poli and Prieto (2016, https://doi.org/10.1002/2016jb013521) with a doubled amount of earthquakes investigated and with earthquakes of lower magnitudes. Plain Language Summary: The vibration of the Earth's ground recorded at seismometers carries the seismic signatures of distant earthquakes superimposed to the Earth's natural or anthropogenic noise surrounding the seismic station. We use artificial intelligence technology to separate the weak signals of distant earthquakes from other sources of ground vibrations unrelated to the earthquakes. The separated signal provides new insights into earthquakes, especially those within the Earth's deep interior, most of which have not been investigated due to noise levels. In contrast with shallow earthquakes, deep earthquakes are less efficient at radiating energy, though they exhibit a higher rate of increase in both stress drop and radiated energy as they grow. This may suggest that deep earthquakes tend to be more confined fault surfaces. A dual mechanism between nucleation in the subduction‐zone core and propagation of larger events in the dry mantle explains our observations. Key Points: A neural network is used to double the number of earthquakes for source analyses compared to previous studies by improving the data qualityDenoising teleseismic waves improves the source signature in Mw5.0–6.0 events and reduces uncertainties over all magnitudesLarge deep earthquake ruptures are dissipative and compact relative to crustal earthquakes [ABSTRACT FROM AUTHOR]

Seismic activity in the Northern Canadian Cordillera is characterized by diffuse earthquakes that extend hundreds of km northwest from the Yakutat collision zone. We use 25 months of broadband seismic data from Mackenzie Mountain Earthscope Project (MMEP), USArray Transportable Array (TA), and permanent Canadian National Seismic Network stations to present a local earthquake catalog with high sensitivity to small regional events. Deep learning techniques are adopted for both seismic phase detection and association. Event relocations are performed to provide well constrained estimates of earthquake depth distributions. Clusters of seismicity spanning the upper crust are located in the central Richardson Mountains, along the Tintina fault, and in the northeast Selwyn Basin. These clusters suggest that the core of the Richardson Anticlinorium is tectonically active and that the Tintina fault is a locus for low levels of active deformation. We interpret seismicity in the northeast Selwyn Basin as primarily occurring in the hanging wall of the Plateau thrust fault and suggest that some combination of localized duplex structures and lithological strength contrasts both within the Selwyn Basin and between abutting Paleozoic shelf sequences may be responsible for seismicity in the Mackenzie Mountain foreland. Plain Language Summary: The Northern Canadian Cordillera is situated inboard of a transition from a right‐lateral tectonic regime in coastal southeast Alaska to a subduction setting beneath southern Alaska. It presents a unique case study to examine the length scales over which tectonic deformation is able to permeate into a continental interior. In this study we use data from a relatively dense regional network of seismometers in order to present the most spatially complete catalog of earthquakes in the Northern Canadian Cordillera to date. We use machine learning techniques for the detection and classification of small magnitude earthquakes and use our results to analyze regional tectonics. Active faults that host earthquakes are identified and we use the earthquake depth distributions to further distinguish between mechanisms for regional stress transfer. We find evidence that the Tintina fault is presently active along a confined area at a low rate. We also find that low magnitude earthquakes do not generally occur within the Mackenzie Mountain Fold‐Thrust belt but are prevalent within the foreland Selwyn Basin. We also detect a pattern of relatively deep (∼30 km) earthquakes in the northern Richardson Mountains. Key Points: Small magnitude earthquakes extending to 25 km depth are detected throughout the Selwyn Basin in the Mackenzie Mountain forelandThe Tintina fault hosts a range of low magnitude earthquakes in the uppermost 15 km of crust within a 400 km zone along strikeDeformation in the Richardson Mountains is localized onto a narrow band of faults centered on the Richardson Anticlinorium [ABSTRACT FROM AUTHOR]

Earthquake early warning (EEW) systems aim to forecast the shaking intensity rapidly after an earthquake occurs and send warnings to affected areas before the onset of strong shaking. The system relies on rapid and accurate estimation of earthquake source parameters. However, it is known that source estimation for large ruptures in real‐time is challenging, and it often leads to magnitude underestimation. In a previous study, we showed that machine learning, HR‐GNSS, and realistic rupture synthetics can be used to reliably predict earthquake magnitude. This model, called Machine‐Learning Assessed Rapid Geodetic Earthquake model (M‐LARGE), can rapidly forecast large earthquake magnitudes with an accuracy of 99%. Here, we expand M‐LARGE to predict centroid location and fault size, enabling the construction of the fault rupture extent for forecasting shaking intensity using existing ground motion models. We test our model in the Chilean Subduction Zone with thousands of simulated and five real large earthquakes. The result achieves an average warning time of 40.5 s for shaking intensity MMI4+, surpassing the 34 s obtained by a similar GNSS EEW model. Our approach addresses a critical gap in existing EEW systems for large earthquakes by demonstrating real‐time fault tracking feasibility without saturation issues. This capability leads to timely and accurate ground motion forecasts and can support other methods, enhancing the overall effectiveness of EEW systems. Additionally, the ability to predict source parameters for real Chilean earthquakes implies that synthetic data, governed by our understanding of earthquake scaling, is consistent with the actual rupture processes. Plain Language Summary: Earthquake Early Warning (EEW) systems can evaluate the shaking impact soon after an earthquake occurs and send alerts to areas where strong shaking has not yet arrived. However, predicting shaking intensity for large earthquakes face challenges such as magnitude underestimation and rupture complexity, leading to inaccurate prediction. In our previous study, we proposed a machine learning model, called M‐LARGE, which can predict the magnitude of large earthquakes accurately and rapidly by utilizing surface deformation patterns recorded by HR‐GNSS. Here, we expand the M‐LARGE model to also predict the source location and fault size. This capability allows us to construct a fault, enabling forecasts of strong shaking 35–40 s before the shaking onset, longer than other similar methods. Our approach has the potential to improve the accuracy of EEW and reduce the impact of seismic hazards. Because the model is fully trained with simulated data, the successful prediction of real Chilean earthquakes indicates that our assumptions in simulating large earthquakes are sufficiently consistent with the rupture dynamics of actual events. Key Points: We train a ML model that utilizes HR‐GNSS data to predict source parameters and shaking intensity for large (M7.0+) earthquakesThe model yields a long median warning time of 35–40 s for MMI 4+ when tested on synthetic and real HR‐GNSS recordsOur model fills a critical gap in current EEW systems for large events and can operate in parallel with other methods for better warnings [ABSTRACT FROM AUTHOR]

Tsunamis can have devastating consequences for coastal communities. Yet hazards from future tsunamis are difficult to quantify due to their rarity in the instrumental record. Statistical earthquake catalogs have previously been used to quantify tsunami hazards. For the first time, we use a physics‐based synthetic earthquake catalog to assess probabilistic tsunami hazard in a local region. We analyze a 30,000‐year catalog to capture a wide range of the source complexity evident in tsunamigenic earthquakes. We produce models of land‐surface displacements and subsequent tsunamis from 2,585 earthquakes with magnitude > MW 7.0. Modeled slip of the Hikurangi and Tonga‐Kermadec subduction thrusts generated maximum wave heights at the coast of up to 28 m and these earthquakes pose the greatest tsunami hazard along New Zealand's coastline. The results provide a "proof of concept" for using earthquake simulators for probabilistic tsunami hazard models. They further present a platform upon which next‐generation probabilistic tsunami inundation models may be constructed. Plain Language Summary: Tsunamis with devastating, wide‐reaching consequences are significant hazards to nearly all of the world's coastlines that needs to be analyzed and quantified. Previous tsunami hazard studies have relied on sparse data retrieved from geological and/or probabilistic earthquake models to examine this infrequent but potentially deadly hazard. Consequently, they lack crucial information about the broad range of tsunami hazards resulting from local tsunamis. Our study represents the first time that a physics‐based synthetic earthquake catalog has been used to assess probabilistic tsunami hazard. It overcomes many of the challenges of previous tsunami hazard assessments. We model the tsunamis generated from 2,585 earthquakes which have magnitudes greater than 7.0 from 30,000 years of a synthetic catalog of earthquakes nucleating on both the subduction zones and crustal faults through New Zealand. Tsunami wave heights at the coast of up to 28 m were recorded. Additional analysis indicates that modeled earthquakes on the Hikurangi and Tonga‐Kermadec subduction thrusts pose the greatest hazard along many parts of New Zealand's coastline. Key Points: First use of a physics‐based synthetic earthquake catalog in tsunami hazard assessmentOur assessment demonstrates that near‐field seismic tsunamis can generate maximum wave heights at the coast of up to 28 m around New ZealandOur results provide a pathway toward next‐generation probabilistic tsunami risk modeling [ABSTRACT FROM AUTHOR]

We introduce the Ensemble Earthquake Early Warning System (E3WS), a set of Machine Learning (ML) algorithms designed to detect, locate, and estimate the magnitude of an earthquake starting from 3 s of P‐waves recorded by a single station. The system is made of six Ensemble ML algorithms trained on attributes computed from ground acceleration time series in the temporal, spectral, and cepstral domains. The training set comprises data sets from Peru, Chile, Japan, and the STEAD global data set. E3WS consists of three sequential stages: detection, P‐phase picking, and source characterization. The latter involves magnitude, epicentral distance, depth, and back azimuth estimation. E3WS achieves an overall success rate in the discrimination between earthquakes and noise of 99.9%, with no false positive (noise mis‐classified as earthquakes) and very few false negatives (earthquakes mis‐classified as noise). All false negatives correspond to M ≤ 4.3 earthquakes, which are unlikely to cause any damage. For P‐phase picking, the Mean Absolute Error is 0.14 s, small enough for earthquake early warning purposes. For source characterization, the E3WS estimates are virtually unbiased, have better accuracy for magnitude estimation than existing single‐station algorithms, and slightly better accuracy for earthquake location. By updating estimates every second, the approach gives time‐dependent magnitude estimates that follow the earthquake source time function. E3WS gives faster estimates than present alert systems relying on multiple stations, providing additional valuable seconds for potential protective actions. Plain Language Summary: We designed E3WS, an Earthquake Early Warning System (EEWS) using the first 3 s of seismic waves recorded by a single station. E3WS is the first EEWS entirely made of Artificial Intelligence algorithms. Our results show an improvement in magnitude estimates compared to existing single‐station based EEWS, such as Urgent Earthquake Detection and Alarm System and ElarmS, and slightly better localization. In order to track the magnitude of M > 7.0 earthquakes, whose source duration is typically longer than 6 s, we test E3WS on large earthquakes in real‐time scenarios. E3WS provides time‐dependent magnitude estimates that follow the earthquake source time functions. E3WS is highly exportable. Thanks to its simplicity, it can be installed in 32‐bit Single Board Computers like a Raspberry Pi 4, and of course in more complex 64‐bit processors. E3WS is not only theoretical, it is already running in alpha test mode as the core of the EEWS of Peru in construction. We believe that E3WS will provide valuable seconds to populations living at constant risk, giving the user extra seconds that may give them enough time to "drop, cover, and hold on" or to perform mitigation actions like stopping traffic, stopping elevators or evacuating the ground floor of buildings. Key Points: Earthquake Early Warning System (EEWS) with faster and robust preliminary estimates of magnitude and location to generate a first alertFirst EEWS designed purely with Artificial IntelligenceEarthquake Early Warning with continuous updates that follow the earthquake source time function [ABSTRACT FROM AUTHOR]

Frictional healing is fundamental to the seismic cycle and plays a role in the energy balance, dynamics, and recurrence interval of earthquakes and slow slip events. Although the healing behavior of quartz has been studied extensively, the role of clay content is less understood. We tested synthetic mixtures of quartz and smectite (10%–100% smectite) in a double‐direct shear configuration to measure frictional healing. We show that the magnitude and rate of healing decreases systematically with higher clay content (from 0.008/decade at 10% smectite to 0.002/decade at 100% smectite). Healing scales with both the magnitude of stress relaxation during holds and layer‐normal compaction of the gouge. We suggest this reflects the alignment of clay minerals, leading to saturation of the real area of contact that limits restrengthening during holds. The low healing rates of clay‐rich faults—together with rate‐neutral to rate‐strengthening friction—should promote frequent, small failures or stable sliding. Plain Language Summary: Healing is a time‐dependent strengthening process that makes it possible for faults to regain strength after an earthquake and fail again in future events. Faults are commonly hosted in clay‐rich, fine‐grained gouges. While there is a wealth of data on the frictional behavior of these gouges, there is a relative lack of data regarding their healing behavior. Here, we measure the change in frictional healing with increasing clay content using experimental deformation of synthetic fault gouges. We find that the amount and rates of healing decrease with clay content. This decrease is likely caused by the tendency for clay grains, which are elongate and plate‐shaped, to align and limit the ability for the fault gouge to increase the area of contact between grains, thus limiting healing. This small healing, together with their low strength and tendency toward stable behavior, may promote small frequent earthquakes—or inhibit earthquakes—on faults hosted in clay‐rich gouges. Key Points: We conducted experiments on a suite of quartz‐smectite mixtures to investigate the role of clay in frictional healingIncreasing smectite content reduces both healing and frictional strength, interpreted to result from saturation of real area of contactLow healing rates in clay‐rich gouges may favor more frequent and smaller failures than in quartz‐dominated gouges [ABSTRACT FROM AUTHOR]

This archeoseismologic study focuses on the Leukos settlement that thrived on the west coast of the forearc island of Karpathos in the 4th−6th centuries CE. The onshore site occupies the eastern rim of the offshore Karpathos Basin, the deepest Aegean basin, in a sector of the Hellenic forearc typically regarded as seismically insignificant. Investigations of faulting, sedimentary processes, and secondary earthquake effects (hydraulic fracturing, liquefaction, tilting, landslides) are integrated with observations of previously surveyed and newly discovered archeological remains to appraise syn‐ to post‐Early Byzantine seismicity and establish a sequence of faulting. Calibrated radiocarbon dates, the first from Karpathos, indicate intermittent faulting and seismicity spanning the 4th−10th centuries CE, likely contributing to the early 7th‐century CE abandonment of Leukos. The coseismic rupture of competent cobbles whose fractures are filled with fluidized sediment is an established paleoseismologic tool for recognizing earthquakes of magnitude Mw ≥ 6; this study extends that criterion to archeoseismology. This study underscores the need to evaluate land movements, sea‐level fluctuations, and shoreline migration for coastal archeological sites. A plausible Late Roman paleogeography emerges in which Leukos occupied a contiguous peninsula rather than surrounding three modern harbors. This study encourages re‐evaluation of seismic and tsunami hazards in the sector of the Hellenic forearc surrounding ancient Leukos and the Karpathos Basin. [ABSTRACT FROM AUTHOR]

Following laboratory experiments and friction theory, slow slip events and seismicity rate accelerations observed before mainshocks are sometimes interpreted as evidence of a nucleation phase. However, such precursory observations still remain scarce and are associated with different time and length scales, raising doubts about their actual preparatory nature. We study the 2017 Valparaiso Mw = 6.9 earthquake, which was preceded by aseismic slip accompanied by an intense seismicity, suspected to reflect its nucleation phase. We complement previous observations, which have focused only on precursory activity, with a continuous investigation of seismic and aseismic processes from the foreshock sequence to the post‐mainshock phase. By building a high‐resolution earthquake catalog and searching for anomalous seismicity rate increases compared to aftershock triggering models, we highlight an over‐productive seismicity starting within the foreshock sequence and persisting several days after the mainshock. Using repeating earthquakes and high‐rate GPS observations, we highlight a transient aseismic perturbation starting 1‐day before the first foreshock and continuing after the mainshock. The estimated slip rate over time is lightly impacted by large magnitude earthquakes and does not accelerate toward the mainshock. Therefore, the unusual seismic and aseismic activity observed during the 2017 Valparaiso sequence might be interpreted as the result of a slow slip event starting before the mainshock and continuing beyond it. Rather than pointing to a possible nucleation phase of the 2017 Valparaiso mainshock, the identified slow slip event acts as an aseismic loading of nearby faults, increasing the seismic activity, and thus the likelihood of a large rupture. Plain Language Summary: Both laboratory experiments and friction theory show that earthquakes do not begin abruptly but are preceded by an accelerating slip associated with a seismicity increase. On the field, however, such precursory observations still remain scarce and are associated with different characteristic time and length scales, raising doubts that they actually reflect the same nucleation phenomena. We study the 2017 Valparaiso M = 6.9 earthquake, which was preceded by both a slow slip and an intense seismicity suspected to reflect such nucleation phase. We complement previous studies, that have focused only on precursory activity, with a continuous investigation of seismic and slow slip before and after the mainshock. Using refined earthquake detection tools, we highlight a seismicity excess starting before and persisting several days after the mainshock. Using repeating earthquakes and high‐resolution GPS, we show that the slow slip does not accelerate toward the mainshock, but continues after it. Therefore, rather than pointing to a possible accelerating nucleation phase of the Valparaiso mainshock, we suggest that the slow slip drives an enhanced seismic activity that is not mainshock‐directed. Within such slow‐slip driven seismicity, the probability of triggering a large earthquake (subsequently considered as the mainshock) is increased. Key Points: We use a high resolution seismic catalog and GPS to investigate seismic and aseismic process before and after the Valparaiso mainshockAn unusually high seismicity and a slow slip event is continuously observed from the foreshock sequence up to days after the mainshockRather than a nucleation phase of the mainshock, the slow slip event acts as an aseismic loading of nearby faults during the entire sequence [ABSTRACT FROM AUTHOR]

Due to the lack of recognized creep on dip‐slip faults, the nature of fault creep and its role in the generation of large earthquakes is largely unexplored. The Chihshang fault in Taiwan serves as one of the best examples of a thrust creeping fault in the world, exhibiting a fast creep rate of 2–3 cm/year and the capability of producing magnitude six earthquakes. Land‐based geodetic measurements are less sensitive to fault slip with depth, especially for the deeper portion of the seaward dipping fault. Taking advantage of slip rates inferred from repeating earthquake sequences (RESs) at greater depths (up to 30 km), we present a method that embeds RES‐derived slip rates into the neighboring fault patch for geodetic data inversion. Using the geodetic and seismological data from 2007 to 2011, we achieve a higher resolution of inter‐seismic slip rate distribution below a depth of 10 km. The inferred low coupling ratio establishes an extensive creeping area that coincides with a location of abundant RES and earthquake swarms. The inferred high coupling ratio, on the other hand, delineates a locked area corresponding to the two co‐seismic slip zones of the 2003 Mw 6.8 Chengkung and 2022 Mw 6.7 Yuli earthquakes. The transition zone marking the gradual change from fully locked to shallow creeping areas appears to coincide with the post‐seismic slip area of the 2003 Chengkung event. Using the fault coupling model, the moment rate deficit measured in the two locked areas is capable of generating a Mw 6.8 event every 78 years to the south and a Mw 6.7 event every 28 years to the north. This moment rate deficit is decreased by 10% when the closely located Central Range fault is considered in a two‐fault model, leading to the slightly longer recurrence interval on the Chihshang fault. The two‐fault model potentially contributes to a better understanding of the regional inter‐seismic deformation, which is recommended to be adopted in the future studies of seismic hazard assessment. Plain Language Summary: Large earthquakes can occur on the creeping faults that slowly slip at the surface but accumulate energy at greater depth. How much different portions of the fault slip annually is the key question for seismic hazard assessment. However, for a seaward‐dipping thrust fault like the Chihshang fault in Taiwan, finding the answer is difficult because the loss of resolution at the greater depth (>10 km) due to a lack of offshore data. Taking advantage of the slip rates inferred from repeating earthquakes that mainly occurred at 10–30 km depth, we present a method that embeds repeating events data into the geodetic inversion for higher resolution of inter‐seismic slip model. We found that the areas slipped faster during the inter‐seismic period (higher inter‐seismic slip rate) coincides with the location of abundant repeating earthquakes and swarm events; The areas with lower inter‐seismic slip rate on the other hand, correspond to the zones that slipped during the 2003 Mw 6.8 Chengkung and 2022 Mw 6.7 Yuli earthquakes. By calculating how much and where the seismic energy was released through inter‐seismic slip rate, we are able to identify two separate zones on the Chihshang fault that is capable of generating a ∼Mw 6 event every 28 to the north and 78 years to the south of the fault, respectively. Key Points: We present a method that embeds repeaters‐derived slip rates into the neighboring fault patch for geodetic data inversionWe achieve a higher resolution of inter‐seismic slip rate distribution below a depth of 10 km, on a seaward‐dipping thrust faultThe inferred low coupling ratio establishes an extensive creeping area, coinciding with the location of active repeaters and swarm events [ABSTRACT FROM AUTHOR]

The recently identified Prompt Elasto‐Gravity Signals (PEGS), generated by large earthquakes, propagate at the speed of light and are sensitive to the earthquake magnitude and focal mechanism. These characteristics make PEGS potentially very advantageous for tsunami early warning, which relies on fast and accurate estimation of the magnitude of large offshore earthquakes. PEGS‐based early warning does not suffer from the problem of magnitude estimation saturation, that P‐wave based early warning algorithms have, and could be faster than Global Navigation Satellite Systems (GNSS)‐based systems while not requiring a priori assumptions on slip distribution. We use a deep learning model called PEGSNet to evaluate the possibility to estimate in real time the evolution of the magnitude of big earthquakes in the tsunamigenic zone of Chile. The model is a Convolutional Neural Network (CNN) trained on a database of synthetic PEGS—simulated for an exhaustive set of possible earthquakes distributed along the Chilean subduction zone—augmented with empirical noise. The approach is multi‐station and leverages the information recorded by the seismic network to estimate as fast as possible the magnitude and location of an ongoing earthquake. Our results indicate that PEGSNet could have estimated that the magnitude of the 2010 Mw 8.8 Maule earthquake was above 8.7, 90 s after origin time. Our offline simulations using real data and noise recordings further support the instantaneous tracking of the source time function of the earthquake and show that deploying seismic stations in optimal locations could improve the performance of the algorithm. Plain Language Summary: Tsunami early warning requires the fast and reliable estimation of an earthquake magnitude provided by Earthquake Early Warning (EEW) systems. EEW systems are currently limited by the propagation speed of P‐waves, which rely on as natural information carriers. Even more problematic, EEW systems based on the first seismic arrivals tend to saturate with earthquake magnitude, and can become unreliable for magnitudes above 8. The recent discovery of Prompt Elasto‐Gravity Signals (PEGS), which comprise gravitational changes generated by earthquakes, has raised hope to overcome these limitations because they travel at the speed of light, much faster than P‐waves. We use PEGS to re‐train the previously developed deep learning model PEGSNet to track the magnitude evolution of big earthquakes in the Chilean subduction zone, historically affected by tsunamis. Given the scarcity of big earthquakes, we simulate signals to train the model using synthetic sources and the seismic stations available in 2010 and 2021, augmented with empirical noise recorded by those stations. PEGSNet tracks the moment release 90 s after the origin time. The performance of PEGSNet is limited by the seismic network configuration, the number of stations and the level of noise in the data, but could be useful for tsunami warning. Key Points: A Prompt Elasto‐Gravity Signals‐based early warning algorithm for ChileOur algorithm could have estimated the magnitude of the Maule earthquake 90 s after origin timeDeployment of seismic stations at optimal locations could greatly enhance the algorithm performance [ABSTRACT FROM AUTHOR]

We considered various non‐uniformities such as branch faults, rotation of stress field directions, and changes in tectonic environments to simulate the dynamic rupture process of the 6 February 2023 Mw 7.8 Kahramanmaraş earthquake in SE Türkiye. We utilized near‐fault waveform data, GNSS static displacements, and surface rupture to constrain the dynamic model. The results indicate that the high initial stress accumulated in the Kahramanmaraş‐Çelikhan seismic gap leads to the successful triggering of the East Anatolian Fault (EAF) and the supershear rupture in the northeast segment. Due to the complexity of fault geometry, the rupture speed along the southeastern segment of the EAF varied repeatedly between supershear and subshear, which contributed to the unexpectedly strong ground motion. Furthermore, the triggering of the EAF reminds us to be aware of the risk of seismic gaps on major faults being triggered by secondary faults, which is crucial to prevent significant disasters. Plain Language Summary: On 6 February 2023, the south‐central Türkiye was hit by two major earthquakes with magnitudes of Mw 7.8 and Mw 7.6 respectively. Among them, the complex rupture process and unexpected ground motion of the Mw 7.8 event attracted the attention of seismologists. In this paper, the 3D dynamic rupture process of this mainshock is simulated based on complex multi‐fault system and heterogeneous initial stress. And the simulation results are in good agreement with the observations. Our results show that high initial stress is required for the EAF to be triggered. The supershear rupture occurred only in certain fault segments and is unable to sustain itself in a significant area on the fault due to the along‐strike variations in fault geometry and strength. More importantly, the dynamic model suggests that we must be alert to the risk of major fault being triggered by earthquakes on nearby small faults, especially when there are seismic gaps on the major fault. Key Points: The high initial stress accumulated in the seismic gap leads to the successful triggering of the East Anatolian FaultThe change of fault geometry in the southwest segment prevented the sustained supershear ruptureThe risk of earthquake nucleation on the secondary fault triggering the major fault rupture and the related disaster was highlighted [ABSTRACT FROM AUTHOR]

Stress accumulation and release reflected by acoustic emissions (AEs) during shearing of granular materials provide important information on failure mechanisms in seismic faults and landslides controlled by stick‐slip. Among many characteristics (amplitude, energy, counts, and frequency) of AE signals generated by stick‐slip, stress changes corresponding to various frequency AEs in different stages of the stick‐slip process are not clear, which limits our knowledge of the characteristics of precursory signals before stick‐slip failure. To better understand the physical mechanisms of granular stick‐slip, we monitored the mechanical and AE signals using high‐frequency (2 MHz) synchronous acquisition during constant‐speed shear of packs of uniform glass beads with different sizes at different normal stresses. The release rate of AE energy was found to accelerate with the dilatation of the sample volume, and the stress drop of stick‐slip was augmented with the increase of normal stress and particle size. Three characteristic events of single cycle stick‐slip were observed in this study: main slip, minor slip, and microslip. We analyzed the AE frequency spectra of these three event types. Both main slip and minor slip corresponded to stress drop and generated high‐frequency AEs (about several hundred kHz), while the AE frequencies generated by microslip were lower (about tens of kHz) and exhibited stress strengthening, which were not apparent in previous studies due to the low frequency of acquisition. We propose that the microslip is mainly due to sliding on grain contacts, while the main slip and minor slip resulted from breakage and reforming of force chains. Low‐frequency AEs from microslip may suggest a crucial precursor of seismic faults and landslides. Plain Language Summary: The occurrence of earthquakes of similar magnitude (quasi‐periodic earthquakes) in a fault zone every few decades is thought to be controlled by stick‐slip of fault gouges. The mechanical evolution of fault gouges prior to earthquake occurrence is extremely complex and difficult to predict. However, many studies have observed the presence of significant microslip prior to stick‐slip failure of seismic faults, which may provide precursor information for an impending earthquake. Laboratory study of stick‐slip nucleation and failure mechanisms in granular materials provides important understanding of the physical mechanisms of quasi‐periodic earthquakes. Our experimental results of high‐frequency acoustic emission (AE) and ring‐shear simultaneous acquisition showed that stick‐slip failure (corresponding to the occurrence of an earthquake) leads to a decrease in the shear resistance of a granular system, generating high‐frequency acoustic signals. Increments of microslip increased the shear resistance of the granular system, and were recorded as low‐frequency acoustic signals before failure occurred. We suggest that the stick‐slip nucleation and failure were controlled by grain friction and collision, respectively. The different AE frequencies of the two may shed light on the precursor monitoring of quasi‐periodic earthquakes. Key Points: Stick‐slip failure was associated with high‐frequency (∼105 Hz) acoustic emissions (AEs) and micro‐slip during stick‐slip nucleation was associated with low‐frequency (∼104 Hz) AEsHigh‐frequency AEs may be caused by particle collisions after force‐chain breakageLow‐frequency AEs may be caused by particle friction during force‐chain adjustment and may suggest important precursors of laboratory earthquakes [ABSTRACT FROM AUTHOR]

The question "what arrests an earthquake rupture?" sits at the heart of any potential prediction of earthquake magnitude. Here, we use a one‐dimensional, thin‐elastic‐strip, minimal model, to illuminate the basic physical parameters that may control the arrest of large ruptures. The generic formulation of the model allows for wrapping various earthquake arrest scenarios into the variations of two dimensionless variables τ¯k ${\bar{\tau }}_{k}$ (initial dimensionless stress parameter on the fault) and G¯c ${\bar{G}}_{c}$ (dimensionless fracture energy), valid for both in‐plane and antiplane shear loading. Our continuum model is equivalent to the standard Burridge‐Knopoff model, with an added characteristic length scale, H, that corresponds to either the thickness of the damage zone for strike‐slip faults or to the thickness of the downward moving plate for subduction settings. We simulate the propagation and arrest of frictional ruptures and derive closed‐form expressions to predict rupture arrest under different conditions. Our generic model illuminates the different energy budget that mediates crack‐ and pulse‐like rupture propagation and arrest. It provides additional predictions such as generic stable pulse‐like rupture solutions, stress drop independence of the rupture size, the existence of back‐propagating fronts, and predicts that asymmetric slip profiles arise under certain pre‐stress conditions. These diverse features occur also in natural earthquakes, and the fact that they can all be predicted by a single minimal framework is encouraging and pave the way for future developments of this model. Plain Language Summary: Untangling the dynamics that governs the propagation and arrest of earthquakes is still challenging, mainly because of the few constraints available on the fault zone geometry, the constitutive properties of fault materials, as well as fault rheology during the rupture event. The present study aims at formulating a model containing a minimal number of parameters to describe the dynamics of large earthquakes. Despite its simplicity, this minimal model is able to reproduce several salient features of natural earthquakes that are still debated (e.g., various arrest scenarios, stable pulse‐like rupture, back‐propagating front, asymmetric slip profiles). We demonstrate how the proposed model can be used to simulate the propagation and arrest of large earthquakes, which are controlled by local variations of shear stress and material properties on the fault. With this simple and generic description, the proposed model could be readily extended to account for additional processes controlling the dynamics of large earthquakes. Key Points: A minimal model of frictional rupture describes large earthquake rupturesTwo parameters, the dimensionless pre‐stress and fracture energy, account for previously proposed mechanisms of earthquake arrestThe model illuminates the different energy balance that drives crack‐like and pulse‐like ruptures and control the asymmetry of slip profiles [ABSTRACT FROM AUTHOR]

Nepal is an actively deforming region due to its tectonic setting that hosts destructive earthquakes including the recent 2015 Mw 7.8 Gorkha earthquake. To better understand the physics of earthquakes and better assess the seismic hazard in the region, a highly resolved 3‐D structure of the crust is essential. This study presents a new 3‐D S‐wave velocity structure of the crust using ambient noise tomography (ANT). In relation to the 2015 earthquake, we show that the lateral variation of S‐wave velocity likely controls the rupture propagation and arrest. This study further constrains crustal discontinuities beneath Nepal including the Main Himalayan Thrust (MHT) using teleseismic P‐wave coda autocorrelation. The MHT geometry correlates well with sizeable low S‐wave velocity zones obtained from the ANT and separated by two ramps. The southernmost first ramp is where the 2015 Gorkha earthquake nucleated that we map up to the source model of the 1934 historical earthquake in Eastern Nepal. The northernmost second ramp is adjacent to the mid‐crustal low velocity zone beneath south Tibet. In between the two ramps, we interpret the horizontal low velocity zone as the interseismic creeping patch of the MHT with down‐dip extent of 50–70 km length and 90–100 km in correspondence with the Mw 7.8 2015 and 8.4 1934 source models, respectively. A systematic mapping of the low‐velocity zones in relation to the MHT integrated with GPS geodesy along with the respective slip from individual past earthquake ruptures can help decipher the paradox of maximum Himalayan earthquake magnitudes. Plain Language Summary: Nepal is located near the plate boundaries between the Indian and Eurasian plates, resulting in damaging earthquakes in the region. However, we do not know exactly what controls the earthquake processes beneath Himalaya Nepal due to its complex geological settings and lack of detailed seismic properties beneath this region. Here we present the detailed shear (S)‐wave velocity image up to 60 km depth beneath Himalaya Nepal that shows how fast/slow the S‐wave propagates, relating to the material properties in crust beneath Himalaya. We used data extracted from recordings of noise coming from, for example, ocean and atmosphere. We also utilized the conversion and reverberation of compressional waves that are sensitive to the sharp transition of material properties. The estimated S‐wave velocity near surface is consistent with material found on the surface of the crust. Here, we show that MHT can be described as a system of low‐velocity zones connected by two ramps. The first ramp is located near the hypocenter of 2015 Gorkha earthquake and second beneath South Tibet. The low velocity between two ramps is considered as interseismic creeping patch. A systematic mapping of such low‐velocity zone beneath all the Himalaya may allow a better understanding of the earthquake hazard. Key Points: Main Himalayan Thrust (MHT) as a system of sizeable low‐velocity zones connected by rampsInferred MHT interseismic patches with different length scales in correspondence of the 2015 and 1934 earthquakesLateral variations of S‐wave velocity across MHT likely control the rupture of the 2015 Gorkha earthquakes [ABSTRACT FROM AUTHOR]

Earth's crust is continuously subjected to oscillatory stress perturbations due to the solid Earth and ocean tides. The seismic response to such stress modulations carries information on earthquake physics and crustal properties. Experimental and observational studies suggested but could not demonstrate that the strength of tidal modulation of seismicity increases before large earthquakes. We tested this hypothesis by (a) developing a new, comprehensive 10‐year long earthquake catalog preceding the 6 July 2019 magnitude 7.1 Ridgecrest, CA earthquake, and (b) applied our novel method for extracting a statistical signal of tidal modulation. Our results show enhanced tidal sensitivity of seismicity along the fault starting about 1.5 years before the mainshock, corroborating the hypothesis. This observation suggests that small magnitude earthquakes may be used to gain insight into subtle changes in fault conditions, bringing new promise for studying the earthquake preparation process. Plain Language Summary: The solid Earth experiences tides, like the ocean, it deforms under the gravitational attraction of the Sun and Moon. This deformation induces an oscillatory stress change in the crust with small peak‐to‐peak amplitudes of the order of 1 kPa (about 1% of the atmospheric pressure). Tidal stresses weakly influence the rate of earthquake occurrence and the characteristics of this modulation carry information on earthquake physics and crustal properties. On the basis of experimental and field observation studies, it has been proposed that the modulation of seismicity by the tides increases before a large earthquake. We tested this hypothesis by analyzing 10 years of seismicity before the M7.1 2019 Ridgecrest, CA earthquake. We first built a new, comprehensive earthquake catalog with our automated method and used our novel method to extract the signal of tidal modulation throughout the study period. We found that seismicity became strongly modulated by the tides about 2 years before the mainshock, thus corroborating the hypothesis. Key Points: Seismicity in the Ridgecrest area is modulated by the solid Earth tidesPeak seismicity occurs when tidal Coulomb stress or stress rate favors ruptureStrength of tidal triggering is gradually increasing in the rupture area about 2 years before the Mw 7.1 2019 mainshock [ABSTRACT FROM AUTHOR]

On 3 August 2014, a destructive earthquake with a magnitude of 6.5 occurred in the Ludian region in Yunan, China, causing heavy casualties. However, the seismogenic structure of the Ludian earthquake is still unclear. To address this issue, we have developed a three‐dimensional joint inversion algorithm for magnetotelluric data and seismic body wave arrival times based on the cross gradient structural similarity constraint, which utilizes the complementary advantages of the two different datasets. We use arrival times of P‐ and S‐waves from 6,369 local earthquakes recorded by 30 seismic stations and magnetotelluric impedances from 127 MT stations to perform the joint inversion to construct a combined 3‐D P‐wave velocity (Vp), S‐wave velocity (Vs), and resistivity models and the locations of relocated aftershocks in the source region of the Ludian earthquake. Our models show significant low Vp/Vs ratios and low resistivity in the upper crust of the main shock zone, and the relocated aftershocks form an L‐shaped zone. Based on petrophysical studies and analysis of the cross‐plots of different physical properties, we infer the existence of cracks/fractures and fluids as well as high quartz contents in the source region. These fluids may play a key role in promoting the Ludian earthquake by reducing the effective normal stress of the fault zone, and the existence of high quartz contents further makes the crustal rocks in the source region more brittle. Our study provides a new evidence how the properties of the crust in the focal area have some control on the genesis of moderate to large earthquakes. Plain Language Summary: On 3 August 2014, a magnitude Ms 6.5 earthquake struck the Ludian County in Yunnan Province, China. Although the earthquake magnitude is moderate, it caused unusually severe damages. To further investigate the genesis mechanism for this earthquake, we have developed a 3‐D joint inversion system for two types of geophysical data: Magnetotellurics (MT) and body wave arrival times. We present this new method of using MT and seismic arrival time data to construct 3D subsurface models of the Ludian earthquake region based on both datasets. Our study shows low Vp/Vs ratios and low resistivity in the source area, and the aftershocks form an L‐shaped zone. On the basis of petrophysical experiments and cross‐plot analysis of different physical properties, we infer that there are cracks/fractures and fluids in the source area. In addition, the source region is also rich in quartz, which make the crustal rocks in the source region more brittle. These fluids may play an important role in promoting the occurrence of the Ludian earthquake. Our study shows that the structure properties have important control on the genesis of moderate to large earthquakes. Key Points: 3D joint inversion of magnetotelluric data and seismic body wave arrival times has been developed based on cross gradient constraintMore structurally consistent velocity and resistivity models are obtained for the source region of the 2014 M6.5 Ludian earthquakeThe earthquake source region is associated with low Vp/Vs and resistivity values, indicating the presence of fluids and high quartz contents [ABSTRACT FROM AUTHOR]

A devastating doublet of earthquakes with moment magnitude MW 7.9 and MW 7.6 earthquakes contiguously occurred in SE Türkiye near the NW border of Syria. Here we perform a potency‐density tensor inversion to simultaneously estimate rupture evolution and fault geometry for the doublet. We find the initial MW 7.9 earthquake involved discrete episodes of supershear rupture and back‐rupture propagation, and was triggered by initial rupture along a bifurcated splay of the East Anatolian Fault. The second MW 7.6 event was triggered by the earlier MW 7.9 event, and it involved more extensive supershear rupture along a favorably curved fault, and was likely stopped by geometric barriers at the fault ends. Our results highlight the multi‐scale cascading rupture growth across the complex fault network that affects the diverse rupture geometries of the 2023 Türkiye earthquake doublet, contributing to the strong ground shaking and associated devastation. Plain Language Summary: On 6 February 2023, devastating dual earthquakes; moment magnitude 7.9 and 7.6 events struck southern Türkiye near the northern border of Syria. The two earthquakes were only separated ∼90 km and ∼9 hr apart. The strong shaking from the two earthquakes caused significant damage to the buildings and people, having caused over 50,000 fatalities in Türkiye and Syria. The source region is where the Anatolian, Arabian and African plates meet, developing the network of faults that hosted the large devastating earthquakes. Seismological analyses using observed seismic waveforms are effective for rapidly estimating how the rupture of the two earthquakes evolves over such distinctively oriented and possibly segmented faults. We use the globally observed seismic records to simultaneously estimate rupture evolution and fault geometry of the earthquake doublet. We find the sequence of both earthquakes involves curved and segmented fault ruptures, including the back‐propagating rupture for the initial earthquake, which is facilitated by the complex active fault network. The 2023 earthquake doublet displays the irregular rupture evolution and diverse triggering behaviors both in a single event and across the earthquake sequence, which provide critical inputs in both our understanding of earthquake‐rupture dynamics and better assessment of future damaging earthquakes. Key Points: An earthquake doublet of MW 7.9 and MW 7.6 ruptured multiple segments and curved faultsInitial splay fault rupture triggered a large MW 7.9 rupture involving pulses of back‐propagating supershear ruptureMulti‐scale rupture growth in a complex fault network may facilitate diverse rupture behaviors and triggering interactions in the doublet [ABSTRACT FROM AUTHOR]

The 2016 Mw 5.9 Menyuan earthquake occurred near the Haiyuan fault system in the northeastern Tibetan plateau. Although some kinematic properties of this event have been investigated, more dynamic properties still need to be clarified. First, we use the empirical Green's function method to obtain this event's apparent source time functions (ASTFs), which present a bell shape with a duration of 3s and corresponding smooth spectra. We then conduct dynamic rupture simulations, which are well constrained by the seismic and geodetic observations, to explore more in‐depth source properties. The results show that the characteristics of ASTFs can be explained by the self‐arresting rupture model, which implies that the rupture propagation of this event may spontaneously terminate before reaching the barriers. This result suggests that the initial conditions when this earthquake nucleated may have controlled the rupture process. Our work contributes to understanding the stopping mechanism of some moderate earthquake ruptures. Plain Language Summary: A quantitative understanding of what controls earthquake rupture propagation is important, helping to estimate the eventual magnitude of a future earthquake and thus has significant implications for earthquake hazard assessment. Previous studies indicate that the complex fault geometry and the heterogeneous material properties of the fault zone can influence earthquake rupture propagation. In this study, we first use the empirical Green's function approach to obtain the single‐peak apparent source time functions for the 2016 Mw 5.9 Menyuan earthquake, and the corresponding spectra have no spectral troughs. We then conduct the spontaneous dynamic rupture simulations, which are well constrained by the geodetic and seismic observations, to reveal more source properties. The features of apparent source time functions can be well explained by the self‐arresting rupture process, which implies that the rupture propagation might spontaneously stop without external interference. This result indicates that this earthquake's rupture propagation might have been deterministic by the initial conditions in which it prepared for rupture. Key Points: The apparent source time functions (ASTFs) of the 2016 Mw 5.9 Menyuan earthquake display a bell shape and corresponding smooth spectraThe features of ASTFs can be explained by the self‐arresting rupture model, implying that the rupture propagation might spontaneously stopThe dynamic rupture simulations are constrained by the interferometric synthetic aperture radar data and strong ground motion observations [ABSTRACT FROM AUTHOR]

The Cascadia subduction zone (CSZ) is known to host M9 megathrust ruptures; however, no such event has occurred in historical observation. The distribution and characteristics of small‐ to moderate‐sized earthquakes can be used to determine the behavior of the megathrust fault but are notably absent offshore the CSZ due to the distance from onshore seismometers. We use automated subspace detection coupled with an onshore‐offshore seismic deployment to find small‐magnitude earthquakes in the offshore seismogenic zone and analyze their locations in the context of interseismic locking and seismogenic zone extent. We detected and located 5,282 earthquakes, 4,096 of which had been previously undetected. We find that the downdip extent of the seismogenic zone as defined by interplate seismicity agrees with the 20% locking contour of the Schmalzle et al. (2014, https://doi.org/10.1002/2013GC005172) geodetic model and extends deeper than predicted by previous thermal models. We cannot determine the updip extent of the seismogenic zone; this may be due to a lack of templates for detection in the updip source area, stress shadows updip of asperity loading, and/or strong locking to the trench. We present a map of possible asperities determined by the small earthquakes in this study. Our asperity locations and extents show some, but not complete, agreement with the asperities modeled from the 1700 M9 rupture and geodetic locking models, and good agreement with the paleo‐rupture extents determined from offshore turbidites and forearc basin‐based asperity estimates. This highlights the need of continued offshore observations over time, and to elucidate fine‐scale variation in locking. Plain Language Summary: Subduction zones host the world's largest earthquakes, with many subduction zones capable of M9 megathrust ruptures. The size and ground motion of these great earthquakes depend on how much of the fault slips seismically and the portions of the fault that promote stronger plate locking between earthquake ruptures. Great earthquakes are known to have occurred in the Cascadia subduction zone, the most recent of which was a M9 in 1700. Despite the geologic evidence for these past great earthquakes, there are no historical observations of large‐ to great‐earthquakes to directly assess where the fault slips seismically or is strongly locked. Additionally, few interplate earthquakes have been observed along this plate boundary. We use a data set acquired with temporary ocean‐bottom seismometers and coastal land‐based seismometers to search for interplate earthquakes that were missed using land seismic stations alone, due to their location primarily offshore. We use the locations of these newly detected earthquakes to map seismogenic extent on the plate boundary and areas of strong plate locking, which will produce higher energy release during an earthquake rupture. Key Points: We develop an earthquake catalog using an amphibious data set and subspace detection targeting Cascadia subduction zone interplate eventsLocations of interplate seismicity detected in this study are used to delineate downdip extent of the seismogenic zone and asperity distributionAsperities agree somewhat with models of geodetic locking and 1700 M9 asperities, and closely match paleo‐rupture extents and forearc basins [ABSTRACT FROM AUTHOR]

The Húsavík‐Flatey Fault Zone (HFFZ) is the largest strike‐slip fault in Iceland and poses a high seismic risk to coastal communities. To investigate physics‐based constraints on earthquake hazards, we construct three fault system models of varying geometric complexity and model 79 3‐D multi‐fault dynamic rupture scenarios in the HFFZ. By assuming a simple regional prestress and varying hypocenter locations, we analyze the rupture dynamics, fault interactions, and the associated ground motions up to 2.5 Hz. All models account for regional seismotectonics, topo‐bathymetry, 3‐D subsurface velocity, viscoelastic attenuation, and off‐fault plasticity, and we explore the effect of fault roughness. The rupture scenarios obey earthquake scaling relations and predict magnitudes comparable to those of historical events. We show how fault system geometry and segmentation, hypocenter location, and prestress can affect the potential for rupture cascading, leading to varying slip distributions across different portions of the fault system. Our earthquake scenarios yield spatially heterogeneous near‐field ground motions modulated by geometric complexities, topography, and rupture directivity, particularly in the near‐field. The average ground motion attenuation characteristics of dynamic rupture scenarios of comparable magnitudes and mean stress drop are independent of variations in source complexity, magnitude‐consistent and in good agreement with the latest regional empirical ground motion models. However, physics‐based ground motion variability changes considerably with fault‐distance and increases for unilateral compared to bilateral ruptures. Systematic variations in physics‐based near‐fault ground motions provide important insights into the mechanics and potential earthquake hazard of large strike‐slip fault systems, such as the HFFZ. Plain Language Summary: The Húsavík‐Flatey Fault Zone (HFFZ) is the largest strike‐slip fault in Iceland, located in the Tjörnes Fracture Zone in Northern Iceland where the largest earthquakes in Iceland have occurred. At present the seismogenic potential of HFFZ suggests that an earthquake of magnitude ∼7 is possible, which poses a high earthquake hazard in the region. In this study, we generate a set of plausible earthquake rupture scenarios on the HFFZ that account for multi‐physics, regional geology and topo‐bathymetry. We simulate the corresponding seismic ground motions by exploring various assumptions, for example, in terms of slipping fault geometry and hypocenter locations. Our simulated scenarios have comparable magnitudes with historic events. The physics‐based ground motion scaling conforms to new empirical ground motion models, but shows varying ground motion variability with distance. Our study provides an overview of multiple rupture scenarios on the HFFZ and suggests that an ensemble of physics‐based dynamic rupture scenarios can complement classical seismic hazard assessment methods to better characterize the hazard in tectonically and seismically complex regions, especially in data‐scarce regions. Key Points: Observational constrained dynamic rupture scenarios of the Húsavík‐Flatey Fault Zone match expected regional earthquake scaling and magnitudesSegmented fault geometry, hypocenter location, fault prestress and roughness affect rupture dynamics and ground motionsOur physics‐based scenarios show magnitude‐consistent average attenuation relationships and match empirical ground motion models [ABSTRACT FROM AUTHOR]

Subducting seamounts are recognized as one of the key features influencing megathrust earthquakes. However, whether they trigger or arrest ruptures remains debated. Here, we use analog models to study the influence of a single seamount on megathrust earthquakes, separating the effect of topography from that of friction. Four different model configurations have been developed (i.e., flat interface, high and low friction seamount, low friction patch). In our models, the seamount reduces recurrence time, interseismic coupling, and fault strength, suggesting that it acts as a barrier: 80% of the ruptures concentrate in flat regions that surround the seamount and only smaller magnitude earthquakes nucleate above it. The low‐friction zone, which mimics the fluid accumulation or the establishment of fracture systems in natural cases, seems to be the most efficient in arresting rupture propagation in our experimental setting. Plain Language Summary: Seamounts ‐ extinct volcanoes ‐ are ubiquitous features of the seafloor of subducting plates. During their descent toward the mantle, seamounts are squeezed between the overriding‐ and subducting plates, creating a geometrical and mechanical discontinuity that is thought to control the largest earthquakes that occur on Earth. It is not known, however, whether they trigger or arrest earthquakes, as a variety of observations have been used to support one or the other hypothesis. Here, we tackle this subject using scaled laboratory models that allow reproduction of large earthquakes. Our models support a scenario where subducting seamounts primarily arrest rupture propagation, limiting therefore expected maximum magnitudes. Our models also suggest that subducting seamounts might influence the recurrence time of large earthquakes by decreasing their frequency. Key Points: We investigated the effect of seamount subduction on megathrust earthquakes by isolating the role of geometry from that of frictionSeamounts act primarily as barriers to earthquake propagation, promoting small ruptures and decreasing seismic couplingReduced friction displays maximum barrier efficiency, a configuration likely associated with fluids or fracture systems in nature [ABSTRACT FROM AUTHOR]

Based on the collation and collection of a large number of data, we construct an induced earthquake database, QuakeQuake, and report a total of 193 human‐induced earthquake cases in China. 155 human‐induced earthquakes in China recorded in the global‐induced earthquake database (HiQuake) are revisited and re‐arranged by compiling the Chinese literature. The human‐induced earthquakes in QuakeQuake database are classified into three levels of reliability, strong, moderate and weak levels, based on both human‐induced processes and seismic activity. Three main categories including reservoir‐induced earthquakes, mine‐induced earthquakes and other induced earthquakes in China are sorted based on data recording and types of the induced earthquakes. Most of the induced earthquakes with strong level in QuakeQuake database are mainly minor earthquakes (3 ≤ M < 4.5). The focal depth of reservoir‐induced and mining‐induced earthquakes is within 30 and 8 km deep, respectively. The active type of source faults of the large induced earthquakes is mainly thrust type with the highest proportion. The largest observed magnitude of the induced earthquakes (MMAX) correlates positively with the injection/extraction volume, reservoir dam heights, reservoir capacity and lithology of the reservoir area. Nine volume intervals corresponding to each induced earthquake type are figured out. Based on the analysis of the mechanisms of human‐induced earthquakes in China, the main mechanisms of surface mass loading are karst collapse or gas explosion, pore water pressure effect and gravity energy release. Underground material extraction is mainly induced by the compaction of different reservoirs. Two injection types of underground material are gas injection and water injection. Gas injection is related to continuous stress loading and unloading. Two induction mechanisms of water injection are the increase of fault pore pressure and the change of fault load condition. [ABSTRACT FROM AUTHOR]

Rupture dynamics along a heterogeneous fault is studied in the framework of the recently developed damage‐breakage rheological model. The model utilizes a fault structure accommodating shear and wear in a heterogeneous weak fault‐core a few centimeters thick, separating two blocks with damage level gradually decreasing toward the host rock. We first demonstrate the similarity of the static stress field around a fault, represented by a three‐body tribosystem, to the one developed around a rough frictional interface. We show that both models predict heterogeneous stress field pattern. We then apply simulations of rupture on heterogeneously damaged faults. We show that increasing initial heterogeneity amplitudes is associated with smaller events with lower slip rates. The simulations further allow us to quantify the amount of accumulated damage correlative with wearing. During the propagating rupture, the strength of the fault‐core evolves, leading to higher wear generation along relatively strong zones or barriers. The total wear production in a given event is strongly dominated by the initial damage heterogeneity. Processing of synthetic seismograms shows excess energy radiation of high‐frequency seismic waves comparing to the expected radiation from planar faults. This radiation is enhanced with the increase in the variability of fault strength heterogeneity. Further calculations of the scaled energy show good fit with previous seismological and laboratory observations and demonstrate the impact of fault heterogeneity on radiated energy during dynamic rupture. Therefore, initial fault heterogeneity, manifested by fault‐core strength or by geometrical irregularity controls many aspects of earthquake rupture, including slip displacement and velocity. Plain Language Summary: Earthquakes are triggered when the stress build‐up on rocks exceeds the resistance to fracture of fault material. When faulting occurs, energy is generated in the fault zone and radiated through the rock body to the surface. The ground motions and their durations strongly depend on the earthquake rupture characteristics such as the amount of displacement, velocity, and directivity. Many studies modeled natural faults as planar frictional interfaces that failed and were displaced during earthquakes. Yet, geological observations and seismological measurements demonstrated that this is probably a naive picture, and fault zones are very heterogeneous, including complicated geometry and variation of strength along and across them. Here we examine the effect of such initial heterogeneities on earthquake and show that the heterogeneity of the rock strength in the fault core itself strongly affects earthquake dynamics. In particular, larger magnitude earthquakes are predicted for the more homogenous fault. We also find that higher fault heterogeneity would result in excess high‐frequency radiation. Considering these effects on ground motion around the fault, we show that seismological records may capture these differences in fault characteristics during earthquakes. Key Points: Initial damage level and its heterogeneity along the fault core control dynamics and seismic moment of simulated rupture eventsWear production is affected by the initial damage distribution. During slip, higher wear accumulation is calculated for barriers along faultsHigh variability of fault damage heterogeneity significantly enhances high‐frequency radiation [ABSTRACT FROM AUTHOR]

By providing unrivaled resolution in both time and space, volcano seismicity helps to chronicle and interpret eruptions. Standard earthquake detection methods are often insufficient as the eruption itself produces continuous seismic waves that obscure earthquake signals. We address this problem by developing an earthquake processing workflow specific to a high‐noise volcanic environment and applying it to the explosive 2008 Okmok Volcano eruption. This process includes applying single‐channel template matching combined with machine‐learning and fingerprint‐based techniques to expand the existing earthquake catalog of the eruption. We detected an order of magnitude more earthquakes, then located, relocated, determined locally calibrated magnitudes, and classified the events in the enhanced catalog. This new high‐resolution earthquake catalog increases the number of observations by about a factor of 10 and enables the detailed spatiotemporal seismic analysis during a large eruption. Plain Language Summary: Volcanic eruptions are some of the most challenging events to study seismically. The eruption itself continually excites seismic waves that hide the signatures of the accompanying earthquakes. The jetting of the plume, explosions, and impact of material on the ground all combine to create a blind spot in the seismological record. In this work, we develop a workflow that can overcome these limitations and reveal events that would otherwise remain hidden in the high‐noise, continuous seismic record. We utilize a combination of machine‐learning and related methods to increase the number of observed events by almost one order of magnitude. We determine the locations of the events using modern, high‐precision methods and use these locations with a customized, calibrated local magnitude scale for the region, which is necessary for volcanoes where seismic waves decay much faster than in the regions where standard magnitude scales were developed. We also automatically separate ordinary earthquakes from the more unusual long‐period ones and see an increase in detectability of both populations. The combined workflow now allows us to illuminate potentially the most interesting, and certainly most obscure, parts of the volcanic seismic cycle. Key Points: We develop a complete workflow suitable for co‐eruptive seismicity, which is inaccessible by normal seismic methodsWe combine different detection algorithms to increase the number of events of an explosive volcanic eruption by almost an order of magnitudeAutomated classification detects both long‐period and ordinary volcanic earthquakes [ABSTRACT FROM AUTHOR]

Here we propose a methodology for Earthquake Early Warning (EEW) able to issue the alert based on the real‐time estimation of the epicentral area where a peak ground Intensity measure is expected to exceed a user‐set ground shaking level. The method provides in output a P‐wave‐based, time‐evolutive "early" shake map. It combines the peak ground velocity predictions available from the observed P‐wave amplitudes and from the region‐specific ground motion prediction equation, using progressively updated estimates of earthquake location and magnitude. The P‐wave displacement, velocity and acceleration amplitudes are jointly measured on a progressively expanded P‐wave time window while the earthquake location and magnitude are evaluated using the first P‐arrival time and displacement amplitudes at near source stations. A retrospective analysis of the 2016, Mw 6.5 Central Italy earthquake records shows that depending on the network density and spatial source coverage, the method naturally accounts for effects related to the earthquake rupture directivity and spatial variability of strong ground motion related to crustal wave propagation and site amplification. Within 1.5 s from the first alert (5.15 s after the origin time), the simulated performance of the system in predicting the event ground shaking is very high: in the 40 km‐radius area that suffered an Intensity MCS VIII–IX, 41 over 42 strong‐motion instrumented sites would have been successfully alerted, with only one false alarm. Even considering the calculated blind‐zone of 15 km radius, a 15–55 km wide annular area would have received the alert 2–14.5 s before the occurrence of the strong ground shaking. The proposed EEW method evolves with time in a way that it minimizes the missed alarms while increasing successful alarms and to a lesser extent false alarms, so it is necessary for the end‐user to accept these possibilities and account for them in a probabilistic decision scheme depending on the specific safety actuation measure to be undertaken in real‐time. Plain Language Summary: Only few seconds pass between an earthquake rupture starting and seismic waves causing disastrous effect on populations and buildings. Earthquake Early Warning (EEW) systems are advanced seismic monitoring infrastructures aimed to benefit of this delay by triggering alerts and pilot safety actions that may mitigate losses. Here we propose a new method that issues the alert based on the real‐time tracing of the area where the strong motion is predicted to exceed a user‐set threshold. The predictions are derived from the early signal amplitudes radiated from the earthquake source using data‐driven relations. A retrospective study of the 2016, Mw 6.5 Central Italy earthquake shows that the method is high performing in rapidly delineating the potential damage zone, naturally accounting for the spatial variability of strong ground motion related to source, path and site effects. Five seconds after the origin time the system predicts the 40 km‐radius area that suffered an MCS Intensity VIII‐IX with almost all strong‐motion sites that would have been successfully alerted. Our time‐evolutive EEW method mitigates losses for false‐alert‐tolerant users, setting the threshold and alert times based on their specific safety actions thus averaging between the system quickness in alerting and in the shaking predictions accuracy. Key Points: A shaking‐forecast‐based earthquake early warning system issuing the alert based on the real‐time tracing of the potential damage zone (PDZ)It naturally accounts for the complex source effects and spatial variability of strong motion related to path and site effectsThe method playback shows to be high performing in rapidly delineating the PDZ of the 2016 Mw 6.5 Central Italy earthquake [ABSTRACT FROM AUTHOR]

Volcanic inflation and deflation often precede eruptions and can lead to seismic velocity changes (dv/v $dv/v$) in the subsurface. Recently, interferometry on the coda of ambient noise‐cross‐correlation functions yielded encouraging results in detecting these changes at active volcanoes. Here, we analyze seismic data recorded at the Klyuchevskoy Volcanic Group in Kamchatka, Russia, between summer of 2015 and summer of 2016 to study signals related to volcanic activity. However, ubiquitous volcanic tremors introduce distortions in the noise wavefield that cause artifacts in the dv/v $dv/v$ estimates masking the impact of physical mechanisms. To avoid such instabilities, we propose a new technique called time‐segmented passive image interferometry. In this technique, we employ a hierarchical clustering algorithm to find periods in which the wavefield can be considered stationary. For these periods, we perform separate noise interferometry studies. To further increase the temporal resolution of our results, we use an AI‐driven approach to find stations with similar dv/v $dv/v$ responses and apply a spatial stack. The impacts of snow load and precipitation dominate the resulting dv/v $dv/v$ time series, as we demonstrate with the help of a simple model. In February 2016, we observe an abrupt velocity drop due to the M7.2 Zhupanov earthquake. Shortly after, we register a gradual velocity increase of about 0.3% at Bezymianny Volcano coinciding with surface deformation observed using remote sensing techniques. We suggest that the inflation of a shallow reservoir related to the beginning of Bezymianny's 2016/2017 eruptive cycle could have caused this local velocity increase and a decorrelation of the correlation function coda. Plain Language Summary: Before eruptions, volcanoes inflate due to the rising magma from below. Previous studies have found that these deformations can lead to small changes in the properties of the surrounding rock. We use passive image interferometry, a method that relies on the omnipresent background vibration of the Earth—mostly induced by the oceans, to measure these changes at the Klyuchevskoy Volcanic Group in Kamchatka, Russia. However, in Kamchatka, this background noise is masked and distorted by small earthquakes and tremors originating from the volcanoes themselves. We combine machine learning techniques with established monitoring methods to find times when these tremors remain similar. Afterward, we use data from these time periods in the conventional way to observe changes in the soil and the rock. Our results show that rain‐ and snowfall and the thickness of the snow cover exert the strongest influence on the properties of the rocks. Additionally, we found that a large magnitude 7.2 earthquake, which struck Kamchatka during our study, caused a slight weakening of the rocks due to microstructural damage. We register changes shortly before an eruption and suggest a connection to the beginning of an eruptive cycle in 2016. Key Points: Fluctuating noise conditions lead to distortions in noise interferometry studies, which we avoid with the help of machine learningThe seismic velocity on Kamchatka is affected by numerous mechanisms, amongst them environmental, tectonic, and volcanic eventsWe observe a velocity increase at Bezymianny during February 2016 and link it to the beginning of the eruptive cycle [ABSTRACT FROM AUTHOR]

The September 2022 Ms 6.8 Luding earthquake broke more than 230 years of seismic calm on the Moxi fault, providing a unique opportunity to understand its seismogenic environment, rupture dynamics, and seismic hazard. Using teleseismic body waves, regional strong‐motion observations, GNSS, and InSAR data, we decipher the spatiotemporal rupture evolution of the mainshock. Combining the elastic dislocation model with surface creep, we find that the coseismic slip correlates closely with a locked patch with a loading rate of 9.7 mm/yr, but the creeping rate is insufficient to make up the shallow slip deficit. Notably, the Luding earthquake ruptured only ∼1/4 of the Moxi seismic gap, and it further increased the stress in the unruptured northern part. We thus argue that the Moxi fault has the potential for magnitude 7+ earthquakes in the near future, although geodetic prediction may overestimate the actual seismic moment released by the coseismic rupture. Plain Language Summary: The Xianshuihe fault is an area of intense tectonic activity on the Tibetan Plateau and plays an important role in accommodating the postcollisional convergence of the Eurasian and Indian plates. However, the Moxi fault, at the southeastern end of the Xianshuihe fault, has remained seismically quiescent since the last Ms 7.75 event in 1786. In September 2022, a Ms 6.8 Luding earthquake struck the Moxi seismic gap, resulting in destructive landslide damage, with 93 people dead and 25 missing. Using seismic and geodetic recordings, we recover its space‐time rupture process in detail. Our model reveals an asymmetric bilateral rupture with dominant propagation and maximum slip to the SSE. It is important to note that the 2022 Luding earthquake ruptured only the southern Moxi seismic gap, leaving the northern part unruptured. Based on the departure time of the last major earthquake and the slip rate obtained from the elastic dislocation model, we estimate the unreleased seismic energy of the Moxi fault, indicating that it still has the potential for strong earthquakes. Besides, the Luding earthquake further increased its seismic hazard through stress transfer. Therefore, we should pay great attention to the kinematic state of the Moxi fault at this time. Key Points: The kinematic evolution of the Luding earthquake is revealed by seismic and geodetic observationsThe coseismic slip asperity from 3 to 20 km depth correlates closely with the preseismic surface creep and locked patchThe unruptured Moxi seismic gap still has the potential for magnitude 7+ earthquakes and deserves further attention [ABSTRACT FROM AUTHOR]

Hjalli‐Ölfus is the westernmost segment of the east‐west transform South Iceland Seismic Zone (SISZ), which is the eastward extension of the ∼ENE‐trending transtensional Reykjanes Peninsula (RP). Historically, the area has shown an interactive behavior with the Hengill volcanic system to the north and the central SISZ to the east. We analyzed the state of stress and faulting mechanisms in Hjalli‐Ölfus between July 1991 and December 1999, in connection with the Hengill inflation episode (Feigl et al., 2000, https://doi.org/10.1029/2000JB900209) and the 13th November 1998 Mw 5.1 Hjalli‐Ölfus earthquake. We find that this region predominantly hosted oblique‐normal and left‐lateral strike‐slip events (4–10 km‐depth), with most nodal planes oriented along ∼ENE or ∼WSW directions (75° ± 15° or 255° ± 15°). We identify 5 stages of stress evolution from January 1991 to December 1999 over which Hjalli‐Ölfus experiences both spatial and temporal shifts in stress‐states. The Hengill inflation likely loaded both the fissure zone and western Ölfus, culminating in the Mw 5.4 (Hengill) and Mw 5.1 (Hjalli‐Ölfus) earthquakes. Following these events, the maximum compressive stress (SHmax) orientation near the location of the Mw 5.1 earthquake showed a ∼5°–7° counterclockwise swing, compared to SHmax before June 1998. The average SHmax (∼40° ± 1°) and minimum principal stress (σ3 ${\sigma }_{3}$ ∼ 130° ± 1°) are comparable to geological trends in the RP. We conclude that Hjalli‐Ölfus shows clockwise SHmax rotation upon loading, while a stress‐drop reverses the rotation. We also posit that the region, especially the western end, behaves like the RP during interseismic periods. Plain Language Summary: Iceland hosts a predominantly rifting plate boundary that is offset by two ∼east‐west trending, horizontally sliding (transform‐faulting) segments, one in the north and the other in the south. The southern segment, known as the South Iceland Seismic Zone (SISZ), is seismically productive and is flanked by diverging volcanic arms. The SISZ has hosted several moderate to large earthquakes on north‐south faults that cut across it. However, the westernmost end of the SISZ, also known as Hjalli‐Ölfus, differs from the rest of the SISZ as it seems to host earthquakes in an ∼east‐northeast direction, similar to its western, rifting neighbor, namely, the Reykjanes Peninsula. The activity in Hjalli‐Ölfus also seems to be responsive to volcanic/magmatic activity in the Hengill volcano to its north. This suggests the existence of multiple stress fields—volcanic, tectonic, or both—acting on the Hjalli‐Ölfus segment. Here, we study earthquakes in Hjalli‐Ölfus from January 1991 to December 1999, including a magnitude 5.1 earthquake in November 1998, to identify possible stress changes along the segment over time. Results indicate that magmatic deformation and seismic activity near the Hengill volcano directly influence the seismic productivity of Hjalli‐Ölfus, and that this seismicity is similar to that of the Reykjanes Peninsula. Key Points: Hjalli‐Ölfus predominantly hosts oblique‐normal and left‐lateral strike‐slip earthquakes on faults that orient in ∼ENE‐WSW directionsStress‐changes due to the Hengill inflation and seismicity are reflected as rotations in the maximum horizontal stress (SHmax) orientationsThe state of stress in Hjalli‐Ölfus mimics that of the Reykjanes Peninsula during interseismic periods [ABSTRACT FROM AUTHOR]

We use a dense seismic array of 1,108 vertical‐component geophones within a 600‐m footprint to detect thousands of small earthquakes near an active strand of the San Jacinto fault zone in southern California during a 26‐day period. We first correct site effects using multichannel cross‐correlations of the P‐waves of 256 cataloged earthquakes, and then perform beamforming analysis on the continuous waveforms in a slowness range from −0.4 to 0.4 s/km in both the east and north directions. At each time step, we identify the beam slowness with maximum amplitude and apply a picking algorithm to identify 13,408 events. These detections include over 55.6% of the events in the Quake Template Matching (QTM) catalog for all of southern California during the same time period and 70% of those within 100 km of the array. In addition, we detect over 10,000 new events, not in the QTM catalog. Many of these events can also be seen in records from nearby borehole seismic stations. Measured slownesses for the catalog and newly‐discovered events group into clusters that can be associated with QTM earthquake locations, but with slowness values considerably distorted from predictions based on a 1‐D velocity model, presumably owing to strong velocity heterogeneity near the San Jacinto Fault. Amplitudes of the detected events obey a Gutenberg‐Richter distribution with a b‐value close to one. Foreshocks are common among these detected events, increasing in rate before mainshocks following an inverse Omori's law. Plain Language Summary: We show that an array of over 1,000 seismometers located on a small patch of the San Jacinto Fault in southern California can detect many times more earthquakes than those in standard earthquake catalogs. Although accurate locations cannot be obtained for most of these newly identified events, their amplitudes indicate they obey similar scaling with size as larger magnitude earthquakes. Many of the larger events are preceded by foreshocks and the foreshock rate increases in the time leading up to the mainshocks. Our results suggest that future deployments of small‐aperture seismometer arrays could be used to complement existing seismic networks to probe earthquake activity in great detail. Key Points: We detect over 13,000 seismic events during 26 days in 2014 using a dense nodal array on the San Jacinto fault zone in southern CaliforniaMost of the detections are newly discovered earthquakes not in existing catalogsForeshocks are common among these earthquakes, increasing in the rate before their mainshocks following an inverse Omori's law [ABSTRACT FROM AUTHOR]

High‐velocity friction experiments on simulated fault gouges sheared at high normal stress and to low displacement are particularly relevant to induced seismicity, which is becoming an important topic in fault mechanics. Using a new, improved set‐up, which allows simulation of fault stress and fluid pressure (P $P$) conditions approaching in‐situ reservoir values, we performed ring‐shear experiments on simulated fault gouges prepared from the source‐, reservoir‐, and caprock‐formations of the Groningen gas field. Pre‐sheared gouges were subjected to a rotational slip pulse reaching ∼1.0 m/s peak velocity and 13–16 cm total displacement at effective normal stresses (σne ${\sigma }_{n}^{e}$) of 5–31 MPa and P $P$ up to 5 MPa, using water or dry nitrogen as pore fluid. All water‐saturated gouges show strong dynamic weakening within a few cm of slip, with the lowest dynamic friction (0.2–0.4) measured at the highest σne ${\sigma }_{n}^{e}$. By contrast, the weakening was subtle in experiments using nitrogen. Our analyses focus on the high‐P $P$ experiments, which are more realistic and show a distinct dependence of constitutive parameters (e.g., slip‐weakening rate) on σne ${\sigma }_{n}^{e}$, in the form of empirical linear, power‐law or exponential relations. The results provide much‐needed constraints for numerical modeling of induced rupture propagation in the Groningen field. Based on temperature‐ and P $P$‐measurements made in near‐direct contact with the active shear band, and using "post‐mortem" microstructures, we exclude previously‐proposed dynamic weakening mechanisms (e.g., flash heating or thermal pressurization) and suggest that water pressurization at heated asperity or grain contacts explains the weakening seen in our high‐P $P$ experiments. Plain Language Summary: In the Groningen gas field of the Netherlands, induced seismic events have occurred since the 1990s. The strongest event occurred in 2012 with a magnitude of MW 3.6. How faults slip during such small magnitude earthquakes (i.e., magnitude 3–4) is not clear, despite several recent studies. We conduct laboratory experiments to simulate the pulse‐like (i.e., short but rapid) fault slip behavior characteristic for small magnitude human‐induced seismicity, using a newly designed experimental set‐up enabling monitoring of the slip behavior under stress and displacement closer to conditions relevant to faults in Groningen. We find that the different rock types present in the Groningen field offer various levels of resistance to rupture of small earthquakes, which is crucial information for modeling earthquakes and understanding seismic hazard and risk. In addition, based on observations of fluid pressure, temperature and dilatation during the experiments, we propose a fault weakening mechanism occurring on the micrometer scale, that can explain our observations. Key Points: Wet faults in Groningen gas field lithologies weaken significantly in a short seismic slip pulse while dry ones do notWe observed fluid depressurization and dilation during seismic slip pulse, which is opposite to what is expected from thermal pressurizationSmall earthquake rupture experiences different resistance and slip weakening behaviors within different lithologies in the Groningen field [ABSTRACT FROM AUTHOR]