Coseismic Deformation Research Articles

Structural controls on coseismic rupture revealed by the 2020Mw 6.0 Jiashi earthquake (Kepingtag belt, SW Tian Shan, China)

SUMMARYThe Kepingtag (Kalpin) fold-and-thrust belt of the southern Chinese Tian Shan is characterized by active shortening and intense seismic activity. Geological cross-sections and seismic reflection profiles suggest thin-skinned, northward-dipping thrust sheets detached in an Upper Cambrian décollement. The 2020 January 19 Mw 6.0 Jiashi earthquake provides an opportunity to investigate how coseismic deformation is accommodated in this structural setting. Coseismic surface deformation resolved with Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) is centred on the back limb of the frontal Kepingtag anticline. Elastic dislocation modelling suggests that the causative fault is located at ∼7 km depth and dips ∼7° northward, consistent with the inferred position of the décollement. Our calibrated relocation of the main shock hypocentre is consistent with eastward, unilateral rupture of this fault. The narrow slip pattern (length ∼37 km but width only ∼9 km) implies that there is a strong structural or lithological control on the rupture extent, with updip slip propagation possibly halted by an abrupt change in dip angle where the Kepingtag thrust is inferred to branch off the décollement. A depth discrepancy between main shock slip constrained by InSAR and teleseismic waveform modelling (∼7 km) and well-relocated aftershocks (∼10–20 km) may suggest that faults within sediments above the décollement exhibit velocity-strengthening friction.

The Surface Process and Seismogenic Structure of the 2021 Ms 6.1 Biru, Central Tibet Earthquake

Abstract On 19 March 2021, the Ms 6.1 Biru earthquake occurred in central Tibet. Because of the limited number of stations, researchers have different understandings of the epicenter and the focal mechanism. In addition, when the earthquake occurred in a key location at the intersection of the strike-slip structure and the extensional structure in the Tibetan plateau, no seismogenic fault is associated with this earthquake, according to the known active faults. In this article, the focal mechanism solution, the meizoseismal area, the orientation of the long axis of the isoseismal lines, and the spatial distribution and geometric characteristics of earthquake fissures were obtained based on the Interferometric Synthetic Aperture Radar coseismic deformation field, inversion of the focal mechanism solution, and field investigation. The macroscopic epicenter was located approximately 13.17 km southeast from the instrumental epicenter, and the earthquake occurred in the seismotectonic background of south–north extrusion, east–west extension, and a mixture of strike-slip and normal faulting. The focal mechanism solution is the normal fault rupture of the northeast-trending main nodal plane. The earthquake caused regularly arranged coseismic ground fissures and damaged a myriad of buildings. The maximum intensity was VIII. The long axis of the isoseismal lines was in the northeast–southwest direction, thus showing a distinct hanging-wall effect. The seismogenic structure was a newly discovered northeast-trending normal fault with a partial sinistral component. The newly discovered seismogenic normal fault, together with the normal faults that have been identified in adjacent areas, is vital to the crustal deformation of the central Tibetan plateau.

Interseismic coupling along the Mexican subduction zone seen by InSAR and GNSS

In the Mexican subduction zone, the heterogeneous spatial density of the GNSS network is limiting the capability to measure and study the variability of the surface deformation field all along the subduction zone. To improve the spatial coverage of interseismic deformation estimates, we combine InSAR and GNSS data. We use four Sentinel-1 descending tracks covering a large part of the Mexican Pacific coast from Jalisco to Oaxaca, over the period from 2016 to 2019.5. The InSAR and GNSS time series, over the same 3.5-year period, are corrected for the coseismic deformations of two Mw>7 earthquakes but not for slow slip events (SSE) and postseismic surface displacements. We present estimates of mean surface velocities over the study period, which combine the linear inter-SSE trend and transient aseismic slip. By inverting these velocities, we estimate the short term coupling at the plate interface, which shows large lateral variations. InSAR data significantly improves the resolution of the inversion, compared to a model based only on GNSS data. Although not representative of long-term coupling in areas with large transient events, the short-term coupling estimates highlight the role of transient signals, such as slow slip events, on the coupling variability measured by geodesy. In agreement with GNSS times series over longer time period, the data also suggest that the Jalisco area (longitude from -106∘E to -104∘E), where no large transient events are observed, is highly coupled with a coupling ratio higher than 0.8.

Complex Coseismic and Postseismic Faulting During the 2021 Northern Thessaly (Greece) Earthquake Sequence Illuminated by InSAR Observations

AbstractThree 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.

Quantitative Evaluation of Coseismic Deformations Induced by Seismogenic Faulting in Mining Exploration Area During the 2018 Xingwen and 2019 Changning Earthquakes, Sichuan, China

In the period between December 2018 and July 2019, a series of earthquakes (EQs), including the 16 December 2018 Ms 5.7 Xingwen mainshock and the 17 June 2019 Ms 6.0 Changning mainshock, struck the Changning shale gas exploration field in the southern margin of the Sichuan Basin. The Xingwen and Changning EQs both occurred on concealed faults, which led to hundreds of casualties, and affected a total of over 160 thousand people in southern Sichuan. The aftershock sequences following the Xingwen and Changning EQs were clustered in the vicinity of the Jianwu syncline and Changning anticline, respectively, and occurred mostly at depths of 3–7 km. In this study, coseismic surface deformation measurements obtained through differential interferometric synthetic aperture radar (D-InSAR) data were used to identify the faulting geometries and distributions. The coseismic deformation maps have maximum line-of-sight (LOS) displacements of ∼4.53 cm on the northwest side of the Xingwen EQ source fault and ∼7.84 cm on the southwest side of the Changning EQ source fault. The calculated static Coulomb stress changes indicated that most aftershocks occurred in increasing stress zones following the mainshock ruptures. From the InSAR deformation field, a complicated concealed seismogenic doublet fault was inferred, which predominately exhibited left-lateral strike-slip motion during the Xingwen and Changning EQs. The footwall ramp of the basement fault reactivated first, and resulted in the Xingwen EQ and concentrating stresses beneath the Changning anticline, which induced the Changning EQ half a year later. Compared with previous studies, we proposed that the fault network was lubricated by water that was injected during shale gas exploration, facilitating the occurrence of the Xingwen and Changning EQs. Such work evaluated the coseismic deformations of the Xingwen and Changning EQs, and derived the regional faulting distribution from aftershock sequences. It could provide useful information for monitoring and analyzing seismic activity around the hinge zones of folds in mining exploration areas, which contributes to effective risk assessment of disasters associated with seismic geo-environments.

Coseismic Displacement and Slip Distribution of the 21 May 2021 Mw 6.1 Earthquake in Yangbi, China Derived From InSAR Observations

On 21 May 2021, a Mw 6.1 earthquake struck Yangbi County, Yunnan Province, China. In this study, InSAR data from Sentinel-1 SAR images were processed to image the coseismic deformation fields of the Yangbi earthquake. Then, the optimal slip model was obtained by applying the particle swarm optimization method. The interferometry results revealed that the earthquake triggered obvious surface deformation near the epicenter, while the earthquake did not produce an obvious surface rupture zone from field investigation. The optimal slip model suggests that the strike of the seismogenic fault responsible for this event is 139°, the dip angle is 81°, and the average rake angle is -170°. Additionally, the slip was concentrated mainly at depths of 2–8 km, the maximum dip-slip amount was 0.5 m, and the cumulative seismic moment reached 1.43 × 1018 N⋅m, equivalent to a Mw 6.1 earthquake. The geodetic and geophysical inversion results demonstrate that the Yangbi earthquake was dominated by a steeply dipping dextral strike-slip rupture. The rupture fault generally strikes NNW-SSE, which is consistent with that of the Weixi-Qiaohou fault, and may be a relatively new fault formed by an E-W-oriented extension of the western boundary of the Sichuan-Yunnan block. Finally, based on the InSAR results in combination with the spatial distribution characteristics of ground fissures and the strong historical earthquakes, we analyzed the tectonic background preceding the Yangbi earthquake and analyzed the relationship between the Yangbi earthquake and strong historical earthquakes in the region, thereby providing empirical evidence for analyzing seismic risk and fault rupture parameters, interpreting seismic deformation characteristics, and better understanding the seismogenic background of the western boundary of the Sichuan-Yunnan block.

Investigation of the Thiva 2020–2021 Earthquake Sequence Using Seismological Data and Space Techniques

We investigate an earthquake sequence involving an Mw = 4.6 mainshock on 2 December 2020, followed by a seismic swarm in July–October 2021 near Thiva, Central Greece, to identify the activated structures and understand its triggering mechanisms. For this purpose, we employ double-difference relocation to construct a high-resolution earthquake catalogue and examine in detail the distribution of hypocenters and the spatiotemporal evolution of the sequence. Furthermore, we apply instrumental and imaging geodesy to map the local deformation and identify long-term trends or anomalies that could have contributed to stress loading. The 2021 seismic swarm was hosted on a system of conjugate normal faults, including the eastward extension of the Yliki fault, with the main activated structures trending WNW–ESE and dipping south. No pre- or coseismic deformation could be associated with the 2021 swarm, while Coulomb stress transfer due to the Mw = 4.6 mainshock of December 2020 was found to be insufficient to trigger its nucleation. However, the evolution of the swarm is related to stress triggering by its major events and facilitated by pore-fluid pressure diffusion. The re-evaluated seismic history of the area reveals its potential to generate destructive Mw = 6.0 earthquakes; therefore, the continued monitoring of its microseismicity is considered important.

Coseismic and Postseismic Fault Kinematics of the July 22, 2020, Nima (Tibet) Ms6.6 Earthquake: Implications of the Forming Mechanism of the Active N‐S‐Trending Grabens in Qiangtang, Tibet

AbstractThe N‐S‐trending grabens, the most prominent active structures in the Tibetan plateau, contain important information about the evolution and deformation mechanism of the plateau. The Ms6.6 earthquake that occurred in Nima, Qiangtang on July 22, 2020, provides an opportunity to investigate the kinematics of the grabens. Here, we use field survey and interferometric synthetic aperture radar to study the structural style, coseismic and postseismic deformation, fault slip, and stress changes of the Nima earthquake. The N‐S‐trending Qomo Ri graben (QRG) and the normal faults on the east and west sides are kinematically correlated with the NE‐trending sinistral Jiangaizangbu River and West Yibug Caka faults. The QRG is characterized by an extensional strike‐slip duplex and negative flower structure. The maximum coseismic deformation of the Nima earthquake is 29.4 cm in the line‐of‐sight direction observed by Sentinel‐1 ascending images. The coseismic slip model demonstrates that the NE20–30°‐striking fault caused the Nima earthquake has a maximum slip of 1.39 m and a main slip area at 4–12 km depth. The seismological fault may transit from a moderately dipping normal fault near the surface to a steeper strike‐slip fault at depth. Obvious postseismic deformation was observed in the stress‐enhancement area. The afterslip model shows that the mainshock fault is correlated with parallel normal faults to its west. We infer that the QRG was formed by local E‐W‐trending extension at the joints of the left‐stepping sinistral fault system, and the active normal faulting in the Qiangtang block favors stress localization.

Research on deformation characteristics of the 2021 Qinghai Maduo MS7.4 earthquake through coseismic dislocation inversion

Over the past 70 years, the Qinghai Maduo Ms7.4 earthquake (May 22, 2021) has been the only earthquake with a magnitude of ≥7 that has occurred within the Bayan Har Block. To investigate the deformation process of this earthquake, we acquired the Interferometric Synthetic Aperture Radar (InSAR) coseismic deformation field based on Sentinel-1 SAR images, which showed that the maximum line of sight (LOS) displacement was ~1 m. By combining this information with the results of our field investigation, the fault slip distributions were obtained by inversion using the single- and double-fault models, wherein the latter model showed better inversion results than that of the former. According to the inversion results, the overall rupture pattern was predominantly left-lateral strike-slip, with a released seismic moment of ~Mw7.5. Specifically, the principal seismogenic fault had a strike of 283°, dip of 91°, and maximum slip of 4.87 m; the branch fault along the eastern segment of the rupture had a strike of 110°, dip of 94°, and maximum slip of 2 m. Conversely, the results derived from the Global Navigation Satellite System (GNSS) strain rate field before the earthquake indicated that the Maduo earthquake occurred in East Kunlun,which is characterized by the largest maximum shear strain rate. The strain accumulation rate (~2.5 × 10−8/yr) was significantly lower than that of the Xianshuihe fault zone on the southern boundary of the Bayan Har block and the East Kunlun fault zone on its northern boundary. Furthermore, pre-seismic deformation near the seismogenic fault was relatively gentle, showing partial late seismogenic characteristics.

Surface ruptures and off-fault deformation of the October 2016 central Italy earthquakes from DInSAR data

Large magnitude earthquakes produce complex surface deformations, which are typically mapped by field geologists within the months following the mainshock. We present detailed maps of the surface deformation pattern produced by the M. Vettore Fault System during the October 2016 earthquakes in central Italy, derived from ALOS-2 SAR data, via DInSAR technique. On these maps, we trace a set of cross-sections to analyse the coseismic vertical displacement, essential to identify both surface fault ruptures and off-fault deformations. At a local scale, we identify a large number of surface ruptures, in agreement with those observed in the field. At a larger scale, the inferred coseismic deformation shows a typical long-wavelength convex curvature of the subsiding block, not directly recognizable in the field. The detection of deformation patterns from DInSAR technique can furnish important constraints on the activated fault segments, their spatial distribution and interaction soon after the seismic events. Thanks to the large availability of satellite SAR acquisitions, the proposed methodological approach can be potentially applied to worldwide earthquakes (according to the environmental characteristics of the sensed scene) to provide a wider and faster picture of surface ruptures. Thus, the derived information can be crucial for emergency management by civil protection and helpful to drive and support the geological field surveys during an ongoing seismic crisis.

Coseismic Deformation Field Extraction and Fault Slip Inversion of the 2021 Yangbi MW 6.1 Earthquake, Yunnan Province, Based on Time-Series InSAR

An earthquake of moderate magnitude (MW 6.1) occurred in Yangbi County, Dali, Yunnan Province, China, on 21 May 2021. Compared to strong earthquakes, the measurement of the deformation fields of moderate earthquakes is more susceptible to errors associated with atmospheric, orbital, and topographic features. We adopted a new time-series InSAR method to process preseismic and postseismic Sentinel-1A SAR time-series images and separated the coseismic deformation signals from various error signals. This method uses preseismic time-series interferograms to estimate the spatially correlated look angle error induced by the digital elevation model and the atmospheric and orbital errors in the master image. The preseismic and postseismic time-series interferograms were then segmented for spatio-temporal filtering to provide a precise estimate of the atmospheric and orbital errors in slave images. Such time-series processing accurately separates various errors from the coseismic deformation signal and prevents the coseismic deformation signal from being included as noise in the error estimation during filtering. Based on this approach, we effectively eliminated the masking of the deformation signal by the errors and extracted coseismic deformation field of the Yangbi MW 6.1 earthquake with high precision. The maximum LOS displacement in the ascending and descending tracks were determined to be −74 and −62 mm, respectively. Subsequently, we used the Geodetic Bayesian Inversion Software to invert the fault geometric parameters of this earthquake, and based on this inverted the rupture slip distribution using the least-squares method. The results showed that the fault orientation is 133.43°, dip angle is 76.98°, source depth is 5.5 km, fault sliding mode is right-lateral strike-slip. The moment magnitude (MW) was calculated to be 6.07.

Co-seismic deformation of the 2017 Mw 6.6 Bodrum–Kos earthquake in speleothems of Korakia Cave (Pserimos, Dodecanese, Greece)

Structural mapping and dating of damaged speleothems have been used to investigate earthquake records in caves, especially of large infrequent events. However, there are few reports of damages in caves visited before and after a particular earthquake, where the damage can be directly related to a recorded event. We mapped the previously unexplored Korakia Cave on Pserimos island in the Dodecanese (Greece) prior to the 2017 Mw 6.6 Bodrum–Kos earthquake. The Dodecanese is at the transition between the Aegean and Anatolian region and is known for its strong seismicity. Although several hundred stalactites with large height-to-width ratios are preserved on the roof of Korakia Cave, the cave has an extensive record of damaged speleothems, which have been caused by movements along normal faults. Here we present new data and 230Th/U-ages of paleoseismic events that are partly older than the limit of the dating method. A cave visit after the 2017 Mw 6.6 Bodrum–Kos earthquake revealed that c. 10 cm small stalactites, which were actively growing along fractures in the cave ceiling, had been chipped off by movements along the fractures during that earthquake. We conclude that movements along fractures or faults during seismic events can easily damage stalagmites and stalactites. However, damage related to the resonance frequency of the dripstones matching with the seismic wave frequency, which has been suggested to break dripstones with large height-to-width ratios, was not observed in Korakia Cave.

An Appraisal of Ground Failure and Hydrogeological Changes Associated with the 28 April 2021 Mw 6 Sonitpur Earthquake, Assam, India, Using Field Evidences and InSAR Measurements

Abstract Widespread damage and coseismic ground disturbances are generally associated with large magnitude and/or shallow focus earthquakes. Surprisingly, a deep focus (34 km), moderate magnitude earthquake (Mw 6) occurred near the Kopili fault zone in Sonitpur district, Assam, India, on 28 April 2021 and created intense ground shaking and extensive damage along the Brahmaputra Valley. We undertook a field survey within a day after the earthquake and carried out Interferometric Synthetic Aperture Radar (InSAR) analysis to map any coseismic ground deformation features. Our field survey revealed extensive liquefaction features and several coseismic secondary ground cracks along the alluvial tracts of the Brahmaputra River system. InSAR analysis revealed a sinistral slip up to ∼60 mm along a north-northwest–south-southeast-oriented previously unmapped lineament or fault. Field investigations revealed coseismic hydrological changes including a sudden rise and fall in the water level by 0.3–0.5 m followed by the injection of sand materials up to a thickness of 1.25 m in dug wells and the appearance of water in seasonally dried river channels and ponds. Interferometric coherence analysis during pre-, co-, and postseismic periods further confirmed the coseismic surge in water at five major tributary rivers of the Brahmaputra River. We speculate that the pressure difference at the shallow unconfined aquifer system of the mountain-front alluvial fan induced by coseismic stresses must have caused channeling of groundwater to the rivers and the contemporaneous water level fluctuations in wells. Amplification of seismic waves at the thick, unconsolidated sedimentary strata of the Brahmaputra Valley could have enhanced the extensive damage due to the 2021 Sonitpur earthquake. The present study has implications in estimating damage potential along the Brahmaputra Valley for future earthquakes.

Surface Displacement and Source Model Separation of the Two Strongest Earthquakes During the 2019 Ridgecrest Sequence: Insights From InSAR, GPS, and Optical Data

AbstractSince the occurrence of the 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence in the Eastern California Shear Zone, coseismic deformation following the two earthquakes has been intensively studied, and source modeling with interferometric synthetic aperture radar (InSAR), Global Positioning System (GPS) and seismological datasets has been favored. However, we recently found that the coseismic modeling of the two earthquakes constrained by the dense near‐field Planet‐Lab optical measurements can be more detailed than the previously estimated, which requires an accurate Planet‐Lab displacement. In this study, we improve the long wavelength orbital ramps correction method for obtaining a more accurate Planet‐Lab horizontal displacement field. The corrected dense near‐field Planet‐Lab data are firstly used together with the intermediate‐field GPS data to invert and distinguish the fault slip distribution for the two earthquakes. The same scheme is used to simultaneously invert the InSAR, SAR, GPS, and optical datasets, to improve the constraints on seismic source parameters. Our inversion results show that the joint‐event slip model is rougher than the two single‐event slip models, but it has a more concentrated slip pattern and larger slip amplitude in some zones. We show that adding a near‐field constraint of the Planet‐Lab data in the combined‐data inversion can reduce the slip parameter uncertainty and enhance the model resolution. The Coulomb failure stress changes on the southeastern Blackwater, the southern Owens Valley, and the central Panamint Valley faults are enhanced by about 0.4–0.8 bar by the 2019 Ridgecrest earthquake sequence.

InSAR derived co-seismic deformation triggered by the Mihoub (Tell Atlas of Algeria) 28 May 2016 (Mw = 5.4) earthquake combined to geomorphic features analysis to identify the causative active fault

In this work,we applied Sentinel 1A Synthetic Aperture Radar (InSAR) data from the European Space Agency, acquired before and after the event, to study the surface deformation induced by the Mihoub 28 May 2016 earthquake (Mw = 5.4) occurred in the Tell Atlas of Algeria.The deformed area is 10 km-long trending NE-SW and located about 6 km southwest of the locality of Mihoub, the most affected urban locality (I0= VIII, EMS scale). The displacement signal in the InSAR data showed up to 4 cm uplift and up to 12 cm subsidence zones indicating where the earthquake took place. The fault corresponds to the boundary between the uplift (hanging wall) and subsidence (footwall) zones.The short time between the two used images minimises uncertainties, and the used SentiNel Application Platform software (SNAP V7.0) ensures the topographic and orbital phases corrections. The geomorphic features analysis, including the shape of the uplifted area and the drainage diversion, indicate that the deformed area corresponds to an asymmetrical fold, a typical active structure in the Tell Atlas region. The slip model indicates one single patch with a max slip of ̴ 20 cm at a depth of 5 km on 60° northwest dipping and N°60 striking reverse fault. The results show that the Mihoub fault is most likely NW-dipping.

Deformation Intensity Distribution and Zoning of Seismic Deformation Fields in Near-Fault Areas

To describe the distribution law of the degree of stratigraphic deformation in the cross-fault region under the influence of fault dislocation, the concept of deformation intensity is introduced, and a computational model of the coseismic deformation field in the cross-fault region is established based on the dislocation model theory and the rich fault inversion parameters in the Sichuan–Tibet region. According to the deformation law of a typical earthquake in Yushu, key sections and parameters are selected for analysis. The results show that the maximum dislocation of the deformation field in the cross-fault region decays from the fault rupture to the surface, and the deformation influence extends from the upper edge of the fault to the surface, with an overall funnel-shaped symmetric distribution. The deformation intensity is elliptically distributed in the vertical profile. The maximum deformation of the strata across the fault within the burial depth of the structure is fitted to fill the lack of the existing statistical equation of coseismic deformation without considering the burial depth factor. Finally, the strata are zoned by deformation intensity according to the degree of deformation to provide a reference for the seismic protection of structures in the near-fault area.

The Sensitivity of Tsunami Impact to Earthquake Source Parameters and Manning Friction in High-Resolution Inundation Simulations

In seismically active regions with variable dominant focal mechanisms, there is considerable tsunami inundation height uncertainty. Basic earthquake source parameters such as dip, strike, and rake affect significantly the tsunamigenic potential and the tsunami directivity. Tsunami inundation is also sensitive to other properties such as bottom friction. Despite their importance, sensitivity to these basic parameters is surprisingly sparsely studied in literature. We perform suites of systematic parameter searches to investigate the sensitivity of inundation at the towns of Catania and Siracusa on Sicily to changes both in the earthquake source parameters and the Manning friction. The inundation is modelled using the Tsunami-HySEA shallow water code on a system of nested topo-bathymetric grids with a finest spatial resolution of 10 m. This GPU-based model, with significant HPC resources, allows us to perform large numbers of high-resolution tsunami simulations. We analyze the variability of different hydrodynamic parameters due to large earthquakes with uniform slip at different locations, focal depth, and different source parameters. We consider sources both near the coastline, in which significant near-shore co-seismic deformation occurs, and offshore, where near-shore co-seismic deformation is negligible. For distant offshore earthquake sources, we see systematic and intuitive changes in the inundation with changes in strike, dip, rake, and depth. For near-shore sources, the dependency is far more complicated and co-determined by both the source mechanisms and the coastal morphology. The sensitivity studies provide directions on how to resolve the source discretization to optimize the number of sources in Probabilistic Tsunami Hazard Analysis, and they demonstrate a need for a far finer discretization of local sources than for more distant sources. For a small number of earthquake sources, we study systematically the inundation as a function of the Manning coefficient. The sensitivity of the inundation to this parameter varies greatly for different earthquake sources and topo-bathymetry at the coastline of interest. The friction greatly affects the velocities and momentum flux and to a lesser but still significant extent the inundation distance from the coastline. An understanding of all these dependencies is needed to better quantify the hazard when source complexity increases.

Coseismic Slip Model of the 2021 Maduo Earthquake, China from Sentinel-1 InSAR Observation

The 2021 Maduo earthquake occurred in the interior of the Bayan Har block of the Tibetan Plateau. We used space-born radar interferometry to study the coseismic deformation of this earthquake. Sentinel-1 InSAR observations along ascending and descending orbits provide the coseismic deformation. Pixel offset tracking method is used to complement InSAR observations near the rupture zone. The surface trace of the ruptured fault can be clearly mapped by InSAR observations. We constructed a three-dimensional coseismic slip model constrained by interferograms and pixel offset tracking in the form of a geodetic inverse problem. The coseismic slip model demonstrates that: (1) the Maduo earthquake was a left-lateral strike-slip event with moment magnitude of 7.4; (2) the peak slip is approximately 8 m and is located at a depth of 4 km; (3) a ‘shallow slip deficit’ of the Maduo earthquake is observed; (4) the ruptured faults are found to be dipping northward with a high dipping angle (80 degrees). This study has important implications on earthquake hazard evaluation of the Bayan Har block.

InSAR Constrained Downdip and Updip Afterslip Following the 2015 Nepal Earthquake: New Insights into Moment Budget of the Main Himalayan Thrust

We use ALOS-2 and Sentinel-1 data spanning 2015–2020 to obtain the post-seismic deformation of the 2015 Mw 7.8 Nepal earthquake. ALOS-2 observations reveal that the post-seismic deformation was mainly distributed in four areas. A large-scale uplift deformation occurred in the northern subsidence area of the co-seismic deformation field, with a maximum uplift of ~80 mm within 4.5 yr after the mainshock. While in the southern coseismic uplift area, the direction of the post-seismic deformation is generally opposite to the co-seismic deformation. Additionally, two notable deformation areas are located in the region around 29° N, and near the MFT, respectively. Sentinel-1 observations reveal post-seismic uplift deformation on the north side of the co-seismic deformation field with an average rate of ~20 mm/yr in line-of-stght. The kinematic afterslip constrained by InSAR data shows that the frictional slip is distributed in both updip and downdip areas. The maximum cumulative afterslip is 0.35 m in downdip areas, and 0.2 m in the updip areas, constrained by the ALOS measurements. The stress-driven afterslip model shows that the afterslip is distributed in the downdip area with a maximum slip of 0.3 m during the first year after the earthquake. Within the 4.5 yr after the mainshock, the estimated moment released by afterslip is ~1.5174 × 1020 Nm,about 21.2% of that released by the main earthquake.

Source model for buried thrust-dominated earthquakes using partial InSAR displacements: the 2018 Lombok, Indonesia, earthquake sequence

SUMMARY A remarkable earthquake sequence struck the island of Lombok in Indonesia during the period from 2018 July 28 to August 19. In this study, we use Sentinel-1 and ALOS-2 radar images to investigate the deformation related to these events. The co-seismic surface deformation was pre-dominated by uplift without surface rupture. It is worth noting that some of the rupture of the Lombok sequence is offshore. For the thrust-dominated island earthquakes, whether the incomplete onshore deformation obtained by InSAR observation can well constrain the geometry of the underground faults is a question worthy of attention. Considering the positional relationship between the deformation and the island, we assumed two types of deformation distribution mode. Through simulation experiments, we found that when the major deformation for the second mode is less than about half, the nonlinear inversion results will be unstable. According to source models of each event, the Lombok sequence may have ruptured the Flores thrust. The peak magnitudes of slip for three events are 1.59, 1.93 and 2.87 m. The large magmatic plumbing systems of Rinjani volcano play a critical role during the cascading fault rupture of the Lombok event. Stress changing map indicates that the earlier events promote the later events. There is an obvious seismic gap in the northern part of the Sumbawa region and this region has the potential to form some moderate earthquakes in the future.