Focal Mechanisms Research Articles

The Unusual Seismic Activity from 2021 to 2024 in Eastern Austria: Insights from Seismic Sequences Relocation and Moment Tensor Inversion

ABSTRACT From 2021 to 2024, unusually strong seismic activity, including multiple sequences with five 3.8≤ML≤4.6 shocks, struck the Vienna basin and Mur-Mürz fault systems in Eastern Austria. Three earthquakes (ML 4.6, 4.5, and 3.8) occurred between March and May 2021. These earthquakes were followed by an increase in seismic activity in March 2023, with an ML 4.3 earthquake to the southwest of the 2021 events. In February 2024, an ML 4.5 earthquake occurred 10 km southwest of the ML 4.3 in 2023. We investigate activated faults relying on nonlinear relocations of the seismic sequences and probabilistic moment tensor inversion. The seismic sequences’ temporal evolution indicates a migration of seismic activity and a decrease of focal depths from northeast to southwest, suggesting a potential reactivation of the major fault systems in the region. The joint interpretation of the results shows distinct clusters along fault segments and focal mechanisms that match the region’s complex tectonic activity.

Database of Earthquake Focal Mechanisms for the East Arctic Region

In this paper, we present a description of a database of earthquake focal mechanisms, which is compiled from the data of international seismological agencies and literature sources for the East Arctic region. It consists of 595 focal mechanism solutions for 273 seismic events with M = 2.1–7.6, which occurred in 1927–2022. Information about the source depth, the scalar seismic moment, and the moment magnitude are also presented there for many events. In addition to the focal parameters, their quality assessments are available, which facilitates a comparison of different solutions in many cases. For user convenience, the database has a graphical interface that permits searching by various attributes (coordinates, time, magnitude, and depth). In terms of volume of the collected information, our database significantly exceeds all the analogues available at the present time. It can be used to perform a seismotectonic analysis, to estimate the stress–strain state of the lithosphere, and to assess seismic hazard for the entire East Arctic region or its separate areas. Implementation of the compiled database for comparison of different solutions of earthquake focal mechanisms and their seismotectonic analysis is illustrated in the paper on the example of seismic events occurred in the Olenek Bay of the Laptev Sea and adjacent territories. We suggest adding new information to the database every five years in future.

In Vivo Mapping of Human Ventricular Fibrillation in Brugada Syndrome: The Role of Repolarization Heterogeneity.

Brugada syndrome (BrS) is associated with ventricular fibrillation (VF). Different VF mechanisms have been described, and repolarization gradients were associated with VF in a BrS model. The aim of this study is to map VF in BrS with ECG imaging. Furthermore, spatial correlation between sinus rhythm maps and VF maps was evaluated. Inclusion criteria were (1) BrS diagnosis and (2) VF mapped with ECG imaging during right ventricle outflow tract ablation. VF mechanism was classified into (1) rotational, (2) focal, and (3) irregular. For comparison, 6 controls were enrolled. The following sinus rhythm maps were performed: activation, recovery time, and activation-recovery interval time. Spatial overlap between steep repolarization gradients (cliffs) at recovery time and activation-recovery interval time maps and initiating VF rotational activity was evaluated with photogrammetry. A total of 28 VF maps in 21 patients with BrS were analyzed. In the first ≈7 seconds of VF, rotational, focal, and irregular mechanisms were found. In 19 patients with BrS (90.5%) and none of the controls, a right ventricle outflow tract repolarization cliff only was found. In all these patients, the singularity point of the first initiating rotational VF activity spatially overlapped with the right ventricle outflow tract cliff. Abolition of right ventricle outflow tract repolarization cliffs was confirmed in all but 2 patients (94.3%). In one patient with recurrence, VF was mapped on the anterior right ventricle over a cliff that was not targeted at the first ablation procedure. In patients with BrS, repolarization heterogeneity has a critical role in VF. Repolarization cliffs might be a therapeutic target in VF ablation.

Moment tensors for small earthquakes and the stress regime in the mid-Atlantic United States

Focal mechanisms for small magnitude earthquakes (M ~ 1.3–4.1) in the mid-Atlantic region of the United States have been determined using a double-couple moment tensor inversion procedure. The 26 new focal mechanisms obtained, when combined with previously published mechanisms, show a pattern of reverse faulting in the easternmost portion of the study area and strike-slip faulting in the west, consistent with previous studies. The change in focal mechanisms from east to west helps to constrain the geographic location of the east-west transition in the stress regime to a NE-SW area within central Pennsylvania within proximity of the Allegheny Front. Stress inversions performed to constrain variations in the stress state across the region show that the maximum compressive stress varies only slightly, but that the near-vertical stress is the minimum compressive stress in the east and transitions to the intermediate compressive stress in the west, as expected for an east-west transition in reverse to strike-slip faulting. Analysis of driving forces causing the stress change suggests that tectonic terrane structure, glacial isostatic adjustment, and changes in gravitational potential energy have little effect on the stress field in this region, leaving the interaction of sublithospheric mantle flow with the eastern edge of the Laurentian cratonic lithosphere beneath central Pennsylvania as a primary explanation. The cratonic lithospheric keel may cause a deflection in mantle flow, thereby changing the stress field enough so that the magnitude of the vertical stress in relation to the minimum horizontal stress results in strike-slip as opposed to reverse faulting.

Seismogenic model of the 2023 MW5.5 Pingyuan earthquake in North China Plain and its tectonic implications

The 6 August 2023 MW5.5 Pingyuan earthquake is the largest earthquake in the central North China Plain (NCP) over the past two decades. Due to the thick sedimentary cover, no corresponding active faults have been reported yet in the epicenter area. Thus, this earthquake presents a unique opportunity to delve into the buried active faults beneath the NCP. By integrating strong ground motion records, high-precision aftershock sequence relocation, and focal mechanism solutions, we gain insights into the seismotectonics of the Pingyuan earthquake. The aftershocks are clustered at depths ranging from 15 to 20 km and delineate a NE-SW trend, consistent with the distribution of ground motion records. A NE-SW nodal plane (226°) of the focal mechanism solutions is also derived from regional waveform inversion, suggesting that the mainshock was dominated by strike-slip motion with minor normal faulting component. Integrating regional geological data, we propose that an unrecognized fault between the NE-SW trending Gaotang and Lingxian-Yangxin faults is the seismogenic fault of this event. Based on the S-wave velocity structure beneath the NCP, this fault probably extends into the lower crust with a high angle. Considering the tectonic regime and stress state, we speculate that the interplay of shear strain between the Amurian and South China blocks and the hot upwelling magma from the subducted paleo Pacific flat slab significantly contributed to the generation of the Pingyuan earthquake.

An Innovative Deep Learning Framework for Skin Cancer Detection Employing ConvNeXtV2 and Focal Self-Attention Mechanisms

An Innovative Deep Learning Framework for Skin Cancer Detection Employing ConvNeXtV2 and Focal Self-Attention Mechanisms

Acoustic emission evolution and fracture mechanism of rock for direct tensile failure

The failure mechanisms of engineering rock masses primarily involve tensile and shear failure. Differentiating between the acoustic emission (AE) signals generated during the tensile and shear damage processes in rock can provide a scientific basis for the classification of acoustic signals in field rock fracture monitoring. This paper presents a study on acoustic emission monitoring during the direct tensile testing of granite, proposing a method for classifying AE signals based on the damage and failure processes of the samples. Additionally, the classification of tensile and shear AE signals is explored. The main conclusions are as follows. The proportion of low-frequency signals (frequency <200 kHz) and high-frequency signals (frequency >200 kHz) in all AE signals was found to be 81.6 % and 19.4 %, respectively. Based on an integrated classification and statistical method for AE signals in rock tensile failure, which involves steps such as “denoising the raw waveform, time-frequency domain data transformation, fuzzification processing, extraction of dominant frequency and corresponding amplitude, and identification of secondary dominant frequencies,” the AE signals were categorized into two types, A and B. Type A signals accounted for an average of 7.6 %, while Type B signals made up 92.4 %. Based on the polarity determination method, the focal mechanisms of AE (Acoustic Emission) events were identified. In tensile events, the average proportion of Type A signals was 8.34 %, while the average proportion of Type B signals was 91.66 %. The Brazilian splitting test also yielded classification results similar to those obtained from direct tensile testing. Thus, it was preliminarily concluded that Type A signals, characterized by the presence of both a primary and secondary frequency, correspond to shear signals, whereas Type B signals, which only exhibit a primary frequency without a secondary frequency, correspond to tensile signals.

The role of fluids in earthquake swarms in northeastern Noto Peninsula, central Japan: insights from source mechanisms

AbstractA prolonged earthquake swarm has persisted since June 2018 in northeastern Noto Peninsula (central Japan), with activity focused into distinct southern, western, northern, and eastern clusters. To explore the role of fluids in the occurrence of this swarm, we analyzed the focal mechanisms of the earthquakes occurring from 1 January 2018 to 30 November 2022 and performed stress tensor inversions. The western, northern, and eastern clusters were dominated by a reverse fault-type mechanism with a horizontal P-axis oriented NW–SE. One of the nodal planes of those mechanisms aligns closely with the precisely relocated hypocenter distribution. The stress fields in these three clusters, as determined by stress tensor inversion, have maximum principal stresses oriented horizontally in the NW–SE direction and minimum principal stresses oriented vertically, aligning with the regional stress field. From these focal mechanisms and this stress field, we derived small misfit angles and large slip tendencies. These findings suggest that, in these three clusters, fluids diffused into faults largely aligned with the regional stress field, resulting in earthquakes with compatible focal mechanisms. Conversely, normal and strike-slip fault-type focal mechanisms, which are unfavorable to the regional stress field, dominated in the southern cluster. The estimated stress fields, deviating from the regional stress field, have maximum principal stresses closer to vertical and minimum principal stress oriented horizontally in the ENE–WSW direction. For earthquakes deeper than 15 km, this local stress field results in relatively larger misfit angles and lower slip tendency than the other clusters. These results suggest that those earthquakes in the southern cluster occurred on misoriented fault planes due to elevated pore fluid pressures. These findings provide strong evidence of the ascent of high-pore-pressure fluids from depth in the southern cluster and their subsequent diffusion into a southeast-dipping fault zone. Graphical Abstract

Diffusion coefficients calculations of 110mAg in ZrC at very high temperature using machine-learning interatomic potential

The ternary machine-learning interatomic potential for a Zr–C–Ag system was developed using first-principles calculations, moment tensor potential, and molecular dynamics simulations to calculate the diffusion coefficient of Ag in ZrC. The developed potential was utilized to investigate the vacancy formation energy, Ag substitutional energy, binding energy between Ag and vacancy, Ag interstitial energy, migration energy of Ag to an adjacent C vacancy in ZrC, and thermal expansion of ZrC. The results conformed to previously reported experimental and computational results, thereby validating the accuracy of the developed potential. The diffusion coefficients of Ag in ZrC0.94 and ZrC0.97 in the temperature range of 2800–3200 K were calculated using molecular dynamics simulations with the developed machine-learning interatomic potential. These calculation results can aid the safety analysis of radioactive 110mAg release in nuclear thermal propulsion reactors.

Seismic radial anisotropy in southeastern Tibetan Plateau and its implications for regional geodynamic evolution

The southeastern Tibetan Plateau exhibits intricate crustal tectonics, encompassing recent seismic megathrust events. Previous research suggested the presence of north-south-oriented channelized viscous flow within the crust. However, recent investigations have unveiled a notable northeast-southwest-oriented geological structure, potentially rigid, intersecting with the presumed crustal channelized flow. Several questions persist regarding the composition of the northeast-southwest-oriented structure, the continuity of crustal channelized flow, and the interplay between them. In this study, dispersion data from a dense seismic array are employed to significantly refine regional crustal models for shear wave velocity and radial anisotropy through ambient noise tomography. The resulting high-resolution model further reveals the style of the crustal deformation and supports the interpretation that the northeast-southwest structure, which shows higher velocity and significant negative radial anisotropy, results from mafic material at the base of crust, obstructing the crustal channelized flow. However, the northeast-southwest structure is not as rigid as the Sichuan Block and exhibits depth-dependent deformation. The interpretation proves useful in further understanding regional earthquake focal mechanisms and strain distribution. Additionally, this research identified a region of generalized negative radial anisotropy in the crust of the western Chuan-Dian fragment, suggesting a reduced horizontal channel crustal flow in this area. Drawing upon various geophysical and geological evidence, we present a geodynamic evolution model, proposing a sequence of events: Permian plume activity resulting in mafic material at the base of the crust near Anninghe-Zemuhe fault, northward advancement of the east Himalayan syntaxis inducing crustal compressional stress field, reduced lower crustal channel flow in the western Chuan-Dian fragment leading to the regional east-west extension, and initiation of the Xianshuihe fault causing shift of strain concentration and depth-dependent deformation near the Anninghe-Zemuhe fault. The geodynamic model provides valuable insights into the regional distribution of crustal strain and the underlying mechanisms of large seismic events.

Coseismic geodetic and geophysical variations detected for the January 19th, 2021 San Juan earthquake. Tectonic implications

The coseismic surface variations and crustal deformation in the Central Precordillera region of San Juan (Argentina) as a consequence of the Mw 6.5 earthquake of January 19th, 2021 (2:46 UTC) were characterized by a multidisciplinary team, integrating information from Gravity, Seismology, GNSS and DInSAR (Synthetic Aperture Radar Differential Interferometry) techniques.Prior to the occurrence of the event, several periodic measures were taken at fixed reference points throughout San Juan province. The results of the data analysis show significant changes in height corresponding to the uplifting of a few centimeters of the hanging wall block in accordance with the estimated deformation obtained by the focal mechanism. In addition, the transcurrent component is evident in the GNSS vectors calculated after the earthquake. These results are consistent with the Gravity variations measured at the control points. This indicates the uplifting of the basement of Central Precordillera while the elastic Andean compressional deformation migrates N-E related to the Tulum lineament. The joint analysis of 4D gravity with GNSS heights shows an accumulation of deformation involving the lower crust prior to the earthquake, and the release of stresses with permanent deformation, which partially complies with the laws of isostasy in the Precordillera, after the earthquake.

Evidence for Low Effective Stress Within the Crust of the Subducted Gorda Plate from the 2022 December Mw 6.4 Ferndale Earthquake Sequence

Abstract Stress levels on and adjacent to megathrust faults at seismogenic depths remain a key but difficult-to-constrain parameter for assessing seismic hazard in subduction zones. Although strong ground motions have been observed to be generated from distinct, high-stress regions on the down-dip end of the megathrust rupture areas in many great earthquakes, we lack direct constraints on the stress level in the lower seismogenic portion of the Cascadia megathrust. On 20 December 2022, an Mw 6.4 strike-slip earthquake occurred near Ferndale, California, in southern Cascadia and likely ruptured the Gorda slab crust in the lower seismogenic portion, providing an opportunity to assess the stress level in this region. Here, we relocate the Ferndale mainshock and the first two weeks of aftershocks using a high-resolution 3D velocity model and estimate rupture dimensions, directivity, and stress drop for several Mw 4–5 aftershocks and recent earthquakes. The aftershocks define a strike-slip fault in the slab crust striking east-northeast, consistent with the mainshock focal mechanism. The orientation of this fault is about 45° off the ideally oriented fault plane given the stress state in the slab. The aftershock zone is extensive and broad in the forward direction of the mainshock rupture but still constrained within the volume of high VP/VS in the slab crust. Our stress-drop estimates are generally lower for Mw 4–5 earthquakes located in the slab crust compared to those a few kilometers deeper in the slab mantle. Combined, our results support a relatively low effective stress level in the vicinity of the megathrust in the lower portion of the seismogenic zone in southern Cascadia, likely due to elevated fluid pressures. Consequently, the ground motion in the onshore region above this low-stress seismogenic portion in southern Cascadia may not be as intense as that observed during great earthquakes in other subduction zones.

Relocation and Stress Analysis of the 2018 Mandali-Sumar Earthquake Sequence, Iraq-Iran Border

The 2018 Mandali-Sumar earthquake sequence started in January 2018 at the Iraq – Iran border within the Low Folded Zone of the Zagros Fold-Thrust Belt. To study the fault that is responsible for this earthquake sequence, the relocation of 32 earthquakes was conducted. In addition, moment tensor solutions of 9 large earthquakes were collected to know the fault motion and stress regime in the study area. The Computer Programs in Seismology (CPS) was used to analyze waveform data taken from 33 seismic stations located in Iraq and Iran to relocate earthquakes. The location of the earthquake sequence based on the IRSC bulletin shows a scattered spatial distribution, but the results of the relocations show that the earthquakes of the sequences are aligned in a longitudinal feature parallel to an anticline limb located in Ilam and Kermanshah provinces near the Iraqi border. The moment tensor solutions indicate that the sequence is related to a thrust fault with a 342º strike direction, 35º NE dip angle, and 76º rake angle. The TENSOR program was used to perform formal stress inversion of moment stress axes, which revealed that the azimuth of the maximum horizontal stress axis is 63º. The epicenters of the sequence are located between the Mountain Front Fault to the NE and the Zagros Foredeep Fault to the Southeast. We believe that the 2018 Mandali-Sumar earthquake sequence is related to displacement on the surface of the Zagros Foredeep Fault within the uppermost basement and the lowermost Phanerozoic cover.

Seismotectonic map of the Sinai Triple Junction

The geodynamic evolution of the Sinai Triple Junction, a highly deformed and seismically active area, is controlled by the Red Sea rift, Gulf of Suez and Aqaba-Dead Sea conjunctions. However, the driving forces for the focusing deformation at crustal depths beneath this area are still ambiguous. Here, we provide an updated seismotectonic map of the area relying on updated seismological and geodetic datasets. A homogenized earthquake catalog has been compiled from well-located earthquakes (> Mw 2.0) by the Egyptian Seismic Network and International Seismological Center in the period between 1990 and 2020. We calculated the average b-value along three seismogenic zones including Gulf of Aqaba, northern Red Sea and Gulf of Suez that amount to 1.1, 0.99 and 0.97, respectively. Additionally, we complied and updated a comprehensive P-wave-based database for the fault plane solutions in the area for events with Mw > 3.5 till 2023. Furthermore, a unified velocity field for the region as well as slip-rate and locking-depth at the active fault segments were estimated from a consistent geodetic dataset from peer-reviewed GPS velocities between 1999 and 2018. Results indicate a dominant NNE left-lateral strike-slip fault with normal component along the Gulf of Aqaba. Pure NW-SE to WNW-ESE dip-slip normal faulting, associated with a strike-slip component in some cases, is dominating the northern and central parts of the Gulf of Suez, whereas pure normal dip-slip movement with an NNE–SSW extension in a horizontal direction is observed in the southern part of the gulf. The estimated slip-rate and locking-depths at the Aqaba fault segments falls between 4.8 and 4.9 mm/yr and 8–12 km, respectively.

Focal mechanism determination by location-constrained deep learning: application to microseismic monitoring

Accurate and rapid determination of focal mechanism solutions is of great significance for real-time seismic monitoring. Previous deep learning approaches for focal mechanism determination typically use the waveform data, which is sensitive to the velocity model and inherently includes information about both the source location and the focal mechanism. We introduce a location-constrained deep learning algorithm for determining the focal mechanism for surface microseismic events. By using aligned P-wave data along with azimuth and take-off angle as input, we narrow the solution space for the focal mechanism problem and reduce the dependence on the velocity model. The model is trained using 40,000 theoretical samples generated with the geometry and velocity model of the field data. Validation tests, comparisons with a waveform-based network, velocity perturbation tests, and location error tests are performed to demonstrate the robustness and efficiency of our method. After applying the trained model to field data, the results demonstrate that our method is fast and achieves comparable accuracy to HASH results for high-quality events, making it promising for real-time microseismic monitoring.

Constraint on the background stress in the source region of the 2016 Kumamoto earthquake sequence based on temporal changes in elastic strain energies and coseismic stress rotation

SUMMARY We investigated the deviatoric stress magnitude of the background stress fields before the 2016 Kumamoto earthquake sequence in Japan based on temporal changes in elastic strain energies caused by the mainshock and coseismic stress rotation. We modelled the six components of background stress fields from stress orientations together with the parameter of effective friction coefficients (μ’ = 0.3, 0.15, 0.1, 0.05 and 0.03) using the 3-D Mohr diagram. We computed the absolute stress fields immediately following the primary events (the largest foreshock and mainshock) of the earthquake sequence by combining coseismic stress change fields with background stress fields. The total amount of elastic strain energy released by the mainshock increased with the effective friction coefficient. Considering the energy balance in which some part of the released energy must be consumed as radiated energy, we understood that the model with μ’ = 0.03 was unrealistic. We also examined the dependence of coseismic stress rotation on the effective friction coefficient. Furthermore, we applied a stress inversion method to moment tensor data of earthquakes to directly estimate coseismic stress rotation. Comparing the theoretical and estimated coseismic stress rotations, we concluded that the models with μ’ = 0.3 and 0.15 were more consistent with the observations than those with μ’ &amp;lt; 0.1. In the reasonable models, the deviatoric stress magnitudes were 37–65 and 39−70 MPa at a depth of 10 km on the northern and southern source faults, respectively.

The Multi‐Segment Complexity of the 2024 MW ${M}_{W}$ 7.5 Noto Peninsula Earthquake Governs Tsunami Generation

AbstractThe 1 January 2024, moment magnitude 7.5 Noto Peninsula earthquake ruptured in complex ways, challenging analysis of its tsunami generation. We present tsunami models informed by a 6‐subevent centroid moment tensor (CMT) model obtained through Bayesian inversion of teleseismic and strong motion data. We identify two distinct bilateral rupture episodes. Initial, onshore rupture toward the southwest is followed by delayed re‐nucleation at the hypocenter, likely aided by fault weakening, causing significant seafloor uplift to the northeast. We construct a complex multi‐fault uplift model, validated against geodetic observations, that aligns with known fault system geometries and is critical in modeling the observed tsunami. The simulations can explain tsunami wave amplitude, timing, and polarity of the leading wave, which are crucial for tsunami early warning. Upon comparison with alternative source models and analysis of 2000 multi‐CMT ensemble solutions, we highlight the importance of incorporating complex source effects for realistic tsunami simulations.

Using Resistivity Structure to Study the Seismogenic Mechanism of the 2021 Luxian Ms6.0 Earthquakes

Over the past few years, there has been a noticeable change in the occurrence of seismic disasters in Sichuan, China. The focus has shifted from Western Sichuan to the previously more stable Southeastern Sichuan. The recent Ms6.0 earthquake in Luxian, Southeastern Sichuan, on 16 September 2021, has once again captured the interest of scholars, who are closely examining the seismogenic environment and potential seismic hazards in the region. We conducted a magnetotelluric (MT) array survey in the Luxian earthquake area to explore the deep seismogenic environment of the 2021 Luxian Ms6.0 earthquake zone and understand the potential effects of industrial extraction on seismic activities. Here are the insights we obtained: Underneath the anticline in the Luxian Ms6.0 earthquake area, there is a structure that mainly exhibits high resistance. On the other hand, beneath the syncline, a structure with medium to low resistance is observed. The epicenter of the mainshock was identified near the intersection of high- and low-resistance media within the Fuji syncline area. Smaller aftershocks that followed the mainshock were mainly concentrated in the low-resistance layers at depths of 3–5 km in the Fuji syncline area. MT survey results have confirmed the existence of a detachment zone in the shallow crust near the epicenter of the Luxian Ms6.0 earthquake. It is believed that this detachment layer played a significant role in the seismogenic process of the Luxian Ms6.0 earthquake. During different stress conditions, this layer became active and caused the compression and faulting of a hidden fault below, resulting in the Luxian Ms6.0 earthquake. After the main earthquake, a series of smaller aftershocks with varying focal mechanisms occurred as the stress fields continued to release. It is important to note that the Luxian Ms6.0 earthquake highlights the ongoing high stress levels in the southern region of the Sichuan Basin. This emphasizes the need for continued monitoring and consideration of potential seismic hazards in the southern Sichuan area.

Multiscale monitoring and analysis of complex rupture and source mechanisms of mining-related seismicity on fault networks

Mining-related seismicity poses significant challenges in underground coal mining due to its complex rupture mechanisms and associated hazards. To bridge gaps in understanding these intricate processes, this study employed a multi-local seismic monitoring network, integrating both in-mine and local instruments at overlapping length scales. We specifically focused on a damaging local magnitude (ML) 2.6 event and its aftershocks that occurred on 10 September 2022 in the vicinity of the 3308 working face of the Yangcheng coal mine in Shandong Province, China. Moment tensor (MT) inversion revealed a complex cascading rupture mechanism: an initial moment magnitude (Mw) 2.2 normal fault slip along the DF60 fault in an ESE–WNW direction, transitioning to a Mw 3.0 event as the FD24 and DF60 faults unclamped. The scale-independent self-similarity and stress heterogeneity of mining-related seismicity were investigated through source parameter calculations, providing valuable insights into the driving mechanism of these seismic sequences. The in-mine network, constrained by its low dynamic changes, captured only the nucleation phase of the DF60 fault. Furthermore, standard decomposition of the MT solution from the seismic network proved inadequate for accurately identifying the complex nature of the rupture. To enhance safety and risk management in mining environments, we examined the implications of source reactivation within the cluster area post-stress-adjustment. This comprehensive multiscale analysis offers crucial insights into the complex rupture mechanisms and hazards associated with mining-related seismicity. The results underscore the importance of continuous multi-local network monitoring and advanced analytical techniques for improved disaster assessment and risk mitigation in mining operations.

Implications of a Reverse Polarity Earthquake Pair on Fault Friction and Stress Heterogeneity Near Ridgecrest, California

AbstractWe apply the Matrix Profile algorithm to 100 days of continuous data starting 10 days before the 2019 M 6.4 and M 7.1 Ridgecrest earthquakes from borehole seismic station B921 near the Ridgecrest aftershock sequence. We identify many examples of reversely polarized waveforms, but focus on one particularly striking earthquake pair with strongly negatively correlated P and S waveforms at B921 and several other nearby stations. Waveform‐cross‐correlation‐based relocation of these events indicates they are at about 10 km depth and separated by only 115 m. Individual focal mechanisms are poorly resolved for these events because of the limited number of recording stations with unambiguous P polarities. However, relative P and S polarity and amplitude information can be used to constrain the likely difference in fault plane orientation between the two events to be 5–20°. We explore possible models to explain these observations, including low effective coefficients of fault friction and short‐wavelength stress heterogeneity caused by prior earthquakes. Although definitive conclusions are lacking, we favor local stress heterogeneity as being more consistent with other observations for the Ridgecrest region.