Search

The Ganzi‐Yushu fault (GYF) is one of the most seismically active fault systems in eastern Tibet, having experienced five M > 7.0 earthquakes over the past 300 years. Here, we use Sentinel‐1 InSAR data spanning from 2014 to 2023 to derive the interseismic velocity fields along the GYF. We calculate the strain rate fields for the entire fault system, which reveal localized strain accumulation along the GYF as well as along two secondary faults within the Bayan Har block. The inversion results obtained from the elastic block model indicate left‐lateral strike slip rates of 4.0–6.5 mm/yr along the GYF and five locked segments distributed along strike. Furthermore, we identify two shallow creeping segments on the InSAR velocity maps. Based on the locations of the creeping sections and their temporal decay characteristics, we infer that the shallow creep along the GYF is afterslip of the 2010 Yushu earthquake. Plain Language Summary: The 500 km‐long Ganzi‐Yushu fault is a main fault system in eastern Tibet. Investigating its slip behavior is crucial for assessing earthquake potential and understanding the deformation patterns in the region. Using space geodetic observations, we investigate the slip rate distribution along the Ganzi‐Yushu fault. The energy accumulation along the fault can be divided into five segments, which correspond remarkably well with the historical events. Besides the Ganzi‐Yushu fault, we find that two secondary faults within the Bayan Har block, which had not received much attention before, also exhibit significant seismic hazard. We identify two shallow creeping sections along the fault. By analyzing the spatio‐temporal characteristics of the shallow creeping sections, we confirm that they are associated with postseismic activity of the 2010 Yushu earthquake. Our results give insights into the regional deformation mode and seismic hazard. Key Points: Our large‐scale high‐resolution InSAR velocity fields reveal strain accumulation within the Bayan Har blockThere are five locked segments distributed along the Ganzi‐Yushu fault, which corresponds well with historical eventsWe identify two transient shallow creeping segments associated with afterslip of the 2010 Yushu earthquake [ABSTRACT FROM AUTHOR]

The 2021 MW 7.4 Maduo event occurred within the Bayan Har block in eastern Tibet, which provides an opportunity to investigate the stress conditions and rheology of faults within the block. Here, we perform dynamic rupture simulations based on the finite element method to explore the physical conditions underlying this earthquake and the factors that controlled the rupture process. We construct the model with a nonplanar fault inferred from the Interferometric Synthetic Aperture Radar (InSAR) data and aftershocks sequence relocation. Our dynamic model is controlled by slip‐weakening friction law with initial stress on fault resolved from a uniform regional stress field. The preferred model produces an average slip of ∼2.2 m with a maximum slip of ∼4.0 m. There are three asperities distributed along the strike, which have captured the main features of the Maduo event. The simulation results are consistent with the static GPS coseismic surface displacements, InSAR data, and displacement waveforms recorded by high‐rate GNSS stations. By comparing the results with the planar fault model and rotated stress fields, we find that the fault geometry and regional stress field are the primary factors that control the rupture process of the event. Moreover, we infer that the unfavorable orientation and fault bend lead to minor slips on the branch fault. Furthermore, we investigate the potential mechanisms of supershear rupture on the eastern fault segment. Plain Language Summary: The 2021 Maduo event ruptured on an intra‐block fault of the Bayan Har block in the Tibetan Plateau, which has aroused widespread interest among the scientific community. In this study, we perform physics‐based numerical simulations based on a nonplanar fault to reproduce the source process of the event. The surface displacements obtained from our dynamic model are in good agreement with the observations. As the other parameters are relatively simple in our model, the source process of the event is mainly controlled by the geometric fault complexities. Our results also help to constrain the orientation of the regional stress field. We find that the branch fault of the earthquake is unfavorably oriented in the regional stress field as well as the fault bend also impedes the rupture to propagate on it, which leads to a minor slip on the branch fault. Furthermore, we infer that the supershear rupture may be induced by the free surface in the earthquake. Key Points: Our dynamic model reproduced the first‐order rupture characteristics of the Maduo earthquakeThe main factor that controls the multipeak slip pattern of the Maduo event is fault geometryThe orientation of the regional stress field was determined through numerical experiments [ABSTRACT FROM AUTHOR]

To resolve the occurrence mechanism of the Luxian earthquake occurred near an active hydraulic fracturing well pad on 15 September 2021, we first use seismic waveforms to invert the focal mechanism solution and centroid depth, and then utilize Sentinel‐1 Synthetic Aperture Radar images and Global Navigation Satellite System observations to determine the seismogenic fault and slip distribution. Our results show that the Luxian event ruptured a previously‐unmapped southwest‐dipping reverse fault intersecting with one horizontal well of the well pad. Major slip occurred below the shale gas bed (∼4 km deep) but above the crystalline basement (∼7 km deep). Further analyses on preseismic surface deformation initiated in the northeast of the event reveal that pore pressure near the hypocenter was increased by ∼4.5 MPa. Consequently, fracking fluid injected through the horizontal well and other wells of nearby pads likely flowed directly into the fault zones and prompted the occurrence of the Luxian earthquake. Plain Language Summary: Due to huge casualties and property losses, the Ms 6.0 Luxian earthquake aroused wide public concern. Beyond that, at 0.85 km south of the epicenter, there is a hydraulic fracturing (HF) well pad (H79) that was operating before the earthquake occurrence. Therefore, people suspect that there was some relationship between the event and HF operations. We here jointly use seismic waveforms of regional permanent stations, Sentinel‐1 Synthetic Aperture Radar images, and Global Navigation Satellite System observations to determine the location and 3D geometry of the source fault. We find the fault intersecting with one horizontal well of the nearby pad, indicating that fracking fluid can flow directly into the fault zones and cause pressure perturbation with magnitudes comparable to the minimum principal stress. In addition, we also find preseismic deformation around the epicenter initiated after 29 May 2021. The deformation is likely linked to accumulation of fracking fluid injected during the drilling and HF operations of other pads. Further modeling reveals that the fluid accumulation increased pore pressure by ∼4.5 MPa near the hypocenter. The source fault likely suffered pressure diffusion before the operation of well pad H79 and was eventually reactivated by pressurization directly linked to HF stimulation. Key Points: The Luxian earthquake ruptured an unmapped south‐dipping reverse fault with major slip occurred in deep sedimentary formationsPreseismic surface deformation analyses indicate that fracking fluid accumulation likely caused pressure increase near the hypocenterThe source fault, intersecting with one horizontal hydraulic fracturing well, was likely reactivated by direct fault‐zone pressurization [ABSTRACT FROM AUTHOR]

When estimating a coseismic slip distribution with multiple observation types, the relative weight ratios (the contribution ratios of all kinds of actual observations in the joint inversion, which should be positive by default) and regularization parameter critically impact the inversion accuracy. In this paper, we propose a new method for determining the relative weights of multiple observations of jointing inversion slip distributions. This method regards the observations and the relative weight ratios as the training data sets and training parameters, respectively; in addition, the constructed Loss $Loss$ function was optimized by the gradient descent method and the exponential decay learning rate method under the TensorFlow platform (GDED). We compared the GDED method with the Helmert variance component estimation method (HVCE) and Akaike's Bayesian information criterion method (ABIC) by designing eight simulation experiments. These simulations included changing the errors and resolutions of the observations, the grid size, the strike angle and the dip angle of the fault, the moment magnitudes of earthquakes, the number of observation types, and the complexity of subduction‐zone earthquakes. We analyzed and discussed the characteristics of the above three methods in determining the relative weight ratios during the joint inversion process. The results of these simulation experiments showed that the GDED method and the ABIC method perform much better than the HVCE method when negative variance occurs in the HVCE method, while the accuracies of the slip distributions produced by the three methods were similar when no negative variance occurred; the GDED method can be used to prevent the occurrence of negative variance compared to the HVCE method and is more time efficient than the ABIC method. Furthermore, we applied these methods to invert the source parameters of the 2015 Mw 8.3 Illapel earthquake (in Chile), and the inversion results showed that the slip of the Illapel earthquake was mainly distributed at depths of approximately 10–50 km. The maximum slip of the Illapel earthquake was approximately 7.9 m, distributed 50–70 km northwest of the epicenter at depths of approximately 10–20 km. Plain Language Summary: Different geodetic observations have distinct characteristics due to their unique observation technologies; for example, global positioning system data have a high temporal resolution but a low spatial resolution, while InSAR data have a high spatial resolution but a low temporal resolution. The spatial and temporal resolutions of the inversion results can be guaranteed by combining these two observations to invert the coseismic slip distribution. The joint estimation of the coseismic slip distribution is a research hotspot in the field of seismic source parameter inversions. However, different combinations of relative weight ratios between these two observations may lead to great differences when jointing estimation of the slip distribution. Determining the relative weight ratios of all kinds of observations (actual observations and virtual observations) during the joint inversion process is a key issue. The previous methods used to solve this problem have shortcomings such as subjectivity, low computational efficiency, and unstable effects. Herein, we developed the GDED method and compared it with the HVCE method and ABIC method through system simulation experiments and actual earthquake experiments. Key Points: We proposed the GDED method to determine the relative weight ratios of multiple types observations for coseismic slip distribution inversionThe GDED method was more applicable than Helmert variance component estimation method (HVCE) method and Akaike's Bayesian information criterion method (ABIC) method through the eight simulation experimentsWe applied the GDED method, the HVCE method and the ABIC method to invert the source parameters of the 2015 Mw 8.3 Illapel earthquake [ABSTRACT FROM AUTHOR]

Three Mw > 5.5 earthquakes (Tyrnavos, Elassona and Verdikoussa earthquakes) struck the northern Thessaly, Greece, from 3 March to 12 March 2021, filling a significant seismic gap. We exploit Interferometric synthetic aperture radar data to investigate coseismic deformation of these events and the first half‐year postseismic deformation related to the Tyrnavos event. Our coseismic modeling reveals that the seismic sequence activated at least four unmapped low‐angle normal faults. However, postseismic analysis shows that afterslip propagates updip to a high‐angle shallow structure, indicating that the coseismic slip and afterslip jointly activated a ramp‐flat structure. By a comprehensive analysis of the inversions, fault distribution, relocated aftershocks and regional stress changes, we highlight that intersections between the main and secondary faults control the slip extent and rupture termination in each earthquake and that static stress transfers induced by earlier event encourage the rupture reinitiation of the later event. Plain Language Summary: As the largest events to hit the Tyrnavos basin since 1941 Mw 6.3 Larissa earthquake, the Thessaly seismic sequence consisting of three Mw > 5.5 earthquakes provides a rare chance to gain insight into the regional seismogenic structure as well as the rupture behavior of faults. Here, we combine coseismic Interferometric synthetic aperture radar observations and relocated aftershocks to explore the optimal seismogenic structure of the seismic sequence which ruptured at least four buried normal faults: one NE‐dipping main fault and one NNE‐dipping secondary fault for the Tyrnavos event, one NE‐dipping fault for the Elassona event and one antithetic SW‐dipping fault for Verdikoussa event. Further combined with an analysis of field investigation and postseismic observations following the Tyrnavos event, we find compared with coseismic slip at depths of 1.9–8.4 km on a gentle main fault, most afterslip is confined at depths of 0–1.7 km on a steep fault, which reveals a ramp‐flat structure. We further investigate the causes for cascading (stop‐start) rupture of the seismic sequence and find that fault intersections play a significant role in halting the rupture propagation, leading to a multi‐fault delayed rupture, and that static stress changes promote the restart of slip. Key Points: Coseismic deformation of the 2021 Thessaly seismic sequence and postseismic deformation following the mainshock are measured with Interferometric synthetic aperture radarAt least one ramp‐flat normal fault and three planar normal faults are activated during the 2021 earthquake sequenceIntersections between the main and secondary faults control the rupture propagation in each earthquake [ABSTRACT FROM AUTHOR]

From 2017 to 2019, three destructive earthquakes (27 January 2017 Mw 4.7, 16 December 2018 Mw 5.2, and 3 January 2019 Mw 4.8) occurred in the Changning shale gas field in the southwest Sichuan Basin, China. Previous seismological studies attributed these events to hydraulic fracturing (HF), but were unable to identify the causative seismogenic faults and their slip behaviors. Here, we use Sentinel‐1 synthetic aperture radar data to measure surface deformation triggered by the three events and conduct geodetic inversions to characterize their rupture models. The resulting coseismic interferograms show prominent surface deformation with the maximum line‐of‐sight displacements of up to 4 cm. The inversion results show that all three earthquakes mainly ruptured sedimentary formations above the shale gas bed, in the upper 3 km of the crust, with slip magnitudes ranging from 8.5 to 15 cm, and stress drops ranging from ∼1.8 to ∼3.3 MPa. Their source faults intersect with horizontal HF wells, but do not root in the crystalline basement. Combined with the reported difficulty of increasing HF operation pressures prior to the three events, we argue that they were most likely induced by direct injection of pressurized fluids into the fault zones. Crustal deformation patterns inferred from regional topography and GPS velocities highlight that the Changning field is located within a triple junction region near the southeastern margin of the Tibetan Plateau with large deformation gradients; such conditions are not only favorable to the development of critically stressed faults, but also facilitate the occurrence of at least moderate magnitude earthquakes. Plain Language Summary: The number of earthquakes induced by the process of shale gas extraction through hydraulic fracturing (HF) has been increasing across the globe, with dozens of M > 4 events reported by the end of August 2021. Although most case studies on HF‐induced seismicity are from the United States and Canada, the southwestern Sichuan Basin (China), located to the southeast of the Tibetan Plateau, is another region with notable seismicity linked to HF operations, including dozens of moderate‐to‐large earthquakes. We here focus on the three largest Mw ≥ 4.7 earthquakes that occurred within the Changning shale gas field up to now. We use geodetic techniques to measure ground deformation caused by the three earthquakes and to further infer their ruptures at depth. Our results reveal that the three earthquakes occurred on shallow faults intersecting with horizontal HF wells, with little‐to‐no slip in the crystalline basement below the depth of 3 km. These questions the common theme of HF‐induced earthquakes having hypocenters proximal to basement rock, presumably associated with basement‐rooted faults, and suggests that the potential for ground shaking of HF‐induced earthquakes is more significant than previously understood. Key Points: The three events ruptured shallow faults within sedimentary formations above the shale gas bed rather than basement‐rooted faultsThe faults of the three events intersect with horizontal hydraulic fracturing wells and were likely reactivated by direct fault‐zone pressurizationHigh HF‐induced seismicity rate in the Changning area links to the proximity to a triple junction region with relatively high tectonic strain accumulation rates [ABSTRACT FROM AUTHOR]

We use mainly geodetic observations to constrain the fault geometry and coseismic distribution of the 2018 Kaktovik earthquake sequence, Alaska. We find that at least three faults were activated. The earthquake sequence ruptured mainly an ESE‐striking, SSW‐dipping strike‐slip fault and a secondary rupture on an SE‐striking, SW‐dipping normal fault. Slip also occurred on a small SSW‐striking fault plane, which is found first in geodetic data and further verified with geological data and focal mechanism solutions. We also map 6 months of postseismic deformation and find obvious displacements in the center of the Sadlerochit Mountains. A geological model is proposed to interpret the relationship between this earthquake sequence and the regional structure. We suggest that the 2018 Kaktovik earthquake sequence may first have occurred on a fault unknown prior to the mainshock and triggered slip on both the pre‐existing ramp structure below the Sadlerochit Mountains and a secondary structure. Plain Language Summary: The 2018 Kaktovik event is the largest earthquake ever to be reported and recorded within the eastern Brooks Range and presents an unprecedented opportunity to study the regional tectonic structure and crustal deformation. Here, we present a detailed investigation into the seismogenic structure of this earthquake sequence, which ruptured mainly an ESE‐striking, SSW‐dipping strike‐slip fault and a secondary SE‐striking, SW‐dipping normal fault. Slip also occurred on a small SSW‐striking fault plane, which is found first in the geodetic data and further verified with seismic and geological data. Perhaps the most striking discovery from the InSAR observations of the Kaktovik earthquake sequence is that most of the displacement occurred on a fault whose existence was unknown prior to the earthquake sequence: a blind fault with no surface expression; additionally, a conjugate fault structure could have been triggered in this earthquake sequence. To explain the different orientations and kinematics of the two main ruptures (Faults 1 and 2), we use a ramp structure with variable geometry for the main fault zone: The first rupture has a higher dip and more strike‐slip, while the second rupture has a lower dip and a dominant normal component. Key Points: The coseismic deformation of the 2018 Kaktovik earthquake sequence is derived from Sentinel‐1 imagesLarge along‐strike variations in the coseismic deformation highlight the complexity of the ruptureWe propose a geological model to connect this earthquake sequence with the regional structure [ABSTRACT FROM AUTHOR]

Although the Papuan fold and thrust belt (PFTB) is thought to accommodate convergence between the Pacific and Australian plates, the possible strain partitioning and its kinematic controls in the region are poorly understood. On 25 February 2018, a devastating Mw 7.5 earthquake jolted the southern area of the PFTB, central Papua New Guinea. The detailed imaging of the source parameters of this large earthquake is an urgent demand for a better understanding of the tectonism in the region. Here we used spaceborne interferometric synthetic aperture radar data to carefully determine the possible ruptured faults and associated fault geometries and further estimated the detailed slip of the 2018 Mw 7.5 earthquake. We find that the earthquake involved multiple faults failure, and a four‐segment fault model can reasonably produce the complex coseismic deformation, especially the observed bimodal displacements. The earthquake was dominated by reverse fault motion, and significant slip of up to ~0.7 m was documented on faults extending at depths great than 25 km. An integrated analysis of the fracture complexities suggests that possible strain partitioning in the PFTB could be tightly coupled with regional fault geometries and lithospheric properties. Our findings on the deep brittle failures suggest that crustal shortening across the PFTB could primarily control the growth of fold and thrust belt in the central Papua New Guinea. Key Points: Complete coseismic surface deformation generated from InSAR helps determine ruptured faults and constrain the complex source parametersThe 2018 Mw 7.5 Papua New Guinea earthquake was characterized by deep‐seated reverse faulting with ruptures extending into depths of 25 kmThis event revealed the possible strain partitioning in the Papuan fold and thrust belt and can help explain its growth [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite System (GNSS) has proved to be a powerful tool for applications in meteorology. In this study, we propose a novel slant tropospheric delay (STD) model to obtain the vertical distribution of atmospheric refractivity based on a single ground‐based GNSS receiver. The new model is used to convert the STD into a function of the vertical gradient of temperature, and it is divided into two layers (above and below the tropopause) for integration. The optical vertical gradient of temperature can be estimated according to the STD obtained from the GNSS observations from a higher satellite elevation angle. The distribution of atmospheric refractivity can then be derived from the vertical gradient of temperature and the surface atmospheric refractivity. Moreover, to further improve the accuracy of the STD model‐derived atmospheric refractivity, we correct it using a "theoretical retrieval" method based on the STDs obtained at a lower elevation angle. The optical ranges of theoretical retrieval are obtained above and below 5 km. Finally, a search is performed for the value of atmospheric refractivity that best fits the model equations, and this value is taken as the final inversion result. Data collected from eight GNSS stations and nearby radiosonde stations in 2016 were used to verify the new method. Using the radiosonde‐derived values as a reference, the accuracy of the STD model‐derived atmospheric refractivity was improved by 13.4% compared with the traditional technique. In addition, again using the radiosonde‐derived values as a reference, the accuracy of the atmospheric refractivity derived with the optically corrected method was improved by 20.4% compared with the uncorrected STD model. Key Points: We propose a novel slant tropospheric delay (STD) model to obtain the vertical distribution of atmospheric refractivityWe also studied the discontinuity of the vertical distribution of refractivity [ABSTRACT FROM AUTHOR]

Determining the motion of the North American plate is difficult due to horizontal intraplate deformation, caused mainly by glacial isostatic adjustment (GIA) in the parts of the plate that are not deforming tectonically. Determination of plate motions also depends on whether the geocenter of the geodetic reference frame coincides with the center of plate rotation. Any difference/error in the International Terrestrial Reference Frame geocenter will introduce an apparent deformation of the plate. We address the plate rotation and what correction models can best account for this internal deformation. We use continuous GPS sites located far from active tectonic boundaries to derive the velocity field in the eastern United States with uncertainties based on a colored noise model. We hypothesize that the velocities will be described by a rigid plate model once the deformation due to GIA and any geocenter/plate rotation center errors have been removed. We find the smallest intraplate residuals with both a geocenter correction and the ICE‐6G model applied. We further compare the coastal GPS vertical velocities with mean relative sea level change rate and find a ~1.9 mm/year difference, which matches the long‐term average global sea level change rate from tide gauges. The entire North American plate is deforming when analyzed at the ~1 mm/year level, and there is no instantaneously stable part due to the long‐wavelength GIA deformation. An accurate estimate of plate rotation cannot be determined from a geographic subset of the plate but only by removing the strain component via a GIA model or a simultaneous estimation of the spatially varying strain rate. Key Points: We use GPS sites with long observation spans to derive the GPS velocity field for the eastern United States with uncertainties based on a colored noise modelWe find the smallest intraplate residuals when we remove a geocenter correction to the ITRF and the ICE‐6G glacial isostatic adjustment model before estimating the angular velocity of North AmericaWe compare the vertical motion rate from GPS with the mean sea level change rate from tide gauge data corrected for variations in sea surface height change and find a ~1.9 mm/year difference between these two, consistent with mean sea level rise over the tide gauge period [ABSTRACT FROM AUTHOR]

We use Sentinel‐1 radar imagery to explore the coseismic and postseismic surface displacements associated with the 2016 MW 6.2 Lampa earthquake in southern Peru. Based on coseismic interferograms, the preferred slip model links to a blind south southeast striking, south southwest dipping normal fault with a shallow dip (45.2°) and a peak slip of 0.71 m at depth ~5.3 km, which is consistent with seismic solutions. Postseismic interferograms, derived from two tracks of the Sentinel‐1A/B satellites using a small baseline subset method, show subsidence up to ~3 cm in the first year after the mainshock. The kinematic inversions of interferometric synthetic aperture radar (InSAR) observations imply that the postseismic surface displacements observed in 1 year after the earthquake are governed by afterslip occurring along the updip extension of the coseismic slip patches. To further improve the data fitting, we generate a fault with variable strike to refine the kinematic afterslip model. The stress‐driven afterslip forward modeling shows that the postseismic deformation is controlled by afterslip distributed at the edge of the compact coseismic slip area. The surface displacement predictions of the poroelastic rebound show subsidence of the hanging wall, but the magnitude of the displacements is small compared to the observed signal. We as well test a collection of viscoelastic relaxation models and find that the predicted surface displacements are not consistent with the observations. The InSAR results show that the strike of the seismogenic fault is quasi‐parallel to the Vilcanota normal fault system and both the fault associated with earthquake and Vilcanota normal fault dip in the same direction. Therefore, we suspect that the causative fault of this 2016 event may be a normal fault belonging to a "domino" faulting system. Key Points: Coseismic and postseismic deformation of the 2016 Lampa earthquake were derived from the InSAR observationsThe inversion results suggest that the seismogenic fault of the Lampa earthquake is a blind, southwest dipping normal faultInSAR time series analysis that shows postseismic deformation of the Lampa earthquake mainly locates just updip of the coseismic rupture [ABSTRACT FROM AUTHOR]

The mechanisms of unusual shallow intraplate earthquakes that occasionally occur in stable cratons remain poorly understood. Here we analyze coseismic and postseismic displacement fields associated with the 2016 Petermann Ranges earthquake in central Australia using interferometric synthetic aperture radar data. The earthquake ruptured a previously unmapped fault and was dominated by thrust slip motion of up to 95 cm within the top 3 km of the crust. Postseismic deformation analysis suggests that a combination of poroelastic rebound and afterslip are responsible for the observed signals. The inferred afterslip overlapping spatially with the coseismic rupture highlights that the postseismic slip is coupled with the pore fluid flow around the fault zones. Analysis of historic groundwater‐level changes suggests that shallow seismicity around the Petermann Ranges may have been triggered by environmental stress perturbations due to the fluctuations of groundwater level; however, it is not easy to document statistical significance of this correlation. Plain Language Summary: Shallow surface‐rupturing earthquakes have been observed globally. However, how these events are triggered and why they sometimes occur within stable continents is largely unknown. We carefully study the coseismic and postseismic deformation of a 2016 Mw 6 earthquake in central Australia to determine the source parameters and slip distributions. We find the coseismic slip and early afterslip are concentrated at depths shallower than 3 km, and poroelastic rebound substantially contributes to the early period of postseismic deformation. We further investigate potential mechanisms to explain rock failure at such shallow depth and find a possible relationship between the fluctuations of groundwater level and the occurrence of shallow seismicity in the region. The results of this study help shed light on the processes and causes of shallow earthquakes. Key Points: Coseismic slip of the 2016 Mw 6 Petermann Ranges earthquake is concentrated at shallow depths between 0 and 3 kmPostseismic displacements are governed by a combination of poroelastic rebound and afterslipThe occurrence of shallow earthquakes might be caused by groundwater levels changes in central Australia [ABSTRACT FROM AUTHOR]

The Mw 7.1 Anchorage earthquake on 30 November 2018 beneath the south‐central Alaska is a rare intermediate‐depth event larger than Mw 7 that occurred in a complex subduction region, where the young Yakutat oceanic terrane wedges in the continental‐oceanic plate collisional region between the Pacific oceanic plate and the North American plate. We use both ascending and descending Sentinel‐1 satellite Interferometric Synthetic Aperture Radar (InSAR) images to construct the coseismic displacement associated with this earthquake, which shows a nearly circular deformation pattern with a subsidence of ~4 cm in line of sight direction. Combining coseismic GPS data, we determine the focal mechanism of this event dominated by normal faulting with N‐S striking of 186° and westward dipping of 64° by using a uniform slip model. Then we find a preferred slip model with both geodetic data and teleseismic data, suggesting the main slips are concentrated on a depth of 55–75 km. The total released moment of our preferred slip model is 5.32 × 1019 N·m, equivalent to Mw 7.1. The rupture process includes two peaks terminating at about 18 s and indicates a unilateral rupture with its front propagating northwestward direction at an average speed of 2.5 km/s. In comparison with the detailed seismic image in this region, this event just occurred in the Yakutat terrane beneath a low velocity zone, suggesting it was caused by slab tear but not slab boundary breaking and determining the lower boundary of shallow thrust‐slip in the Alaska subduction zone. Key Points: An intermediate‐depth earthquake with ~4 cm coseismic displacement is revealed by InSAR measurementsThe determined rupture slips are concentrated on depth 55–70 km beneath a low velocity zone in the Yakutat terraneThe normal faulting was driven by downdip extensional stresses due to slab bending [ABSTRACT FROM AUTHOR]