Maximum Slip Research Articles

Inversion of Fault Geometric Parameters Based on Mixture Density Networks: A Case Study of the 2013 Ms7.0 Lushan Earthquake in China

Mixture density networks (MDNs) are a class of neural network algorithms in the Bayesian framework that can invert for parameters and estimate the parameter uncertainties at the same time. We test MDNs by inverting the fault geometric parameters in a synthetic test with Okada’s model and demonstrate the efficiency and robustness of the model. To further describe the MDNs algorithm, we invert regional static GPS displacement data for the 2013 Ms7.0 Lushan Earthquake in China to obtain the fault geometric parameters. The inverted geometric parameters, which are in the form of distributions, agree well with the published solutions for this event once the 99.7% confidence interval are taken into account. The 99.7% confidence intervals of the strike and dip angles are [ $$187.5^\circ$$ , $$220.4^\circ$$ ] and [ $$20.76^\circ$$ , $$49.76^\circ$$ ], respectively. To demonstrate the applicability of the inverted geometric parameters, we invert the slip distribution of the Lushan earthquake with the inverted parameters and GPS displacements. From the slip distributions considering the distributions of the parameters, we obtain the 99.7% confidence intervals of the magnitude Mw, maximum slip and depth of maximum slip, which are [6.51, 6.65], [0.30, 0.74] m and [9.43, 13.61] km, respectively.

Similarities and Differences in the Rupture Processes of the 1952 and 2003 Tokachi‐Oki Earthquakes

AbstractWe investigated the similarities and differences between the rupture processes of the 1952 and 2003 Tokachi‐oki earthquakes (Mw ∼ 8) that occurred 51 years apart in the southernmost region of the Kuril subduction zone. This event pair is rare because seismic waveforms of both events were instrumentally recorded. We performed joint source inversion analyses of both earthquakes to better understand the rupture processes of this earthquake sequence. The dataset for the 1952 earthquake consists of teleseismic and strong motion data which were obtained by digitizing copies of analog seismograms. Two datasets were made for the 2003 earthquake to examine the effect of data limitation and to facilitate a comparison of the inversion results of the two earthquakes. One dataset consists of a large amount of teleseismic, strong motion, and geodetic data. The other dataset is similar to that of the 1952 earthquake. Our results show that the rupture propagation, slip areas, and maximum slip amounts were similar for the 1952 and 2003 earthquakes in the Tokachi‐oki region. However, there are two important differences: the 1952 earthquake was initiated by an Mw 6.1 subevent in the Tokachi‐oki region, and its rupture extended to the adjacent Akkeshi‐oki region. The similarity in the rupture pattern of the M8‐class earthquake pair suggests the persistence of asperities on the plate interface, while the differences imply a degree of variability in the initiation and termination of the cascading rupture process.

Frictional effect on circular armour wire lateral buckling in umbilicals

The present paper addresses the frictional effect on the circular armour wire lateral buckling in an umbilical for wet annulus condition. A nonlinear static finite element model is developed where only one single circular armour wire is simulated and the contact interface with the neighboring layer is represented by a deformable rigid toroid surface. The isotropic Coulomb friction model regularized with an elastic domain is implemented to simulate the shear interaction. Case studies are carried out by applying different axial compression and cyclic bending curvatures between zero and a maximum value in one bending direction. The minimal axial compression that may cause the armour wire lateral buckling after numerous bending cycles is approximately estimated by fitting the numbers of bending cycles to initiate the buckling under different axial compression through an empirical model. The friction coefficient and the maximum elastic slip employed in the Coulomb friction model are varied for the parametric studies, and their effects on the armour wire sticking-slipping status, the end shortenings and deflections in cyclic bending, the critical lateral buckling limit, as well as the stress state at the onset of lateral buckling are extensively discussed.

Experimental investigation on composite beams under combined negative bending and torsional moments

In this study, straight composite steel-concrete beams were tested to investigate their mechanical performance under combined negative bending and torsional moments. Two specimens were used in this study, and different ratios between the applied negative bending and torsional moments were induced. Load and deflection relationships, strain development on the steel main girder and shear connectors (stud), and the slip development on the steel-concrete interface were recorded in the test and reported in this paper. The results indicate that increase of torsional moment will result in the significant decrease of the load-carrying capacities (e.g. yield load and ultimate load) of the specimens. It was also found that the normal strains of stud shear connectors in such beams are very large and non-negligible compared to their shear strains. In addition, the maximum interface slip was found occurring at around the 1/4 span, and the support conditions and serious crack of the concrete were considered to be the main causes. The research results obtained in this study can provide references for the design and analysis of steel-concrete composite beams subjected to the combined negative bending and torsional moments.

A Dynamic-Rupture Model of the 2019 Mw 7.1 Ridgecrest Earthquake Being Compatible with the Observations

AbstractWe explore the 2019 Mw 7.1 Ridgecrest earthquake dynamic rupture on the nonplanar fault with homogeneous dynamic parameters using a layered media model. Our model shows that this event produced an average of 1.9 m of right-lateral slip with a maximum slip of ∼4.2 m at the place near the epicenter, and the variation of fault-plane strike angles from the middle to the southeastern segment appears to have behaved as a “stress barrier,” which postponed the rupture. We also compare the synthetics based on our dynamic rupture with the field records and find good agreement with the static Global Positioning System (GPS) coseismic offsets and strong ground motion waveforms. Our work provides a dynamic-rupture interpretation of the Mw 7.1 Ridgecrest earthquake.

A study on structural performance of deconstructable bolted shear connectors in composite beams

An experimental study according to EC4 on deconstructable steel-concrete composite bolted shear connectors is carried out to investigate the effect of various bolt size, concrete strength, bolt strength and clearance size between the precast concrete slab and bolt on the static behaviour of this type of composite connection. Shear load capacity for the first bearing, average major slip at the first bearing, maximum shear load capacity per bolt, slip corresponding to the maximum shear load capacity, maximum average slip between the precast concrete slab and steel beam and failure modes are assessed. A total of 12 composite specimens were tested according to EC4 with different parameters using deconstrcutable bolted shear connectors. In addition, two steel-concrete composite connection specimens using welded headed stud shear connectors were tested as control specimens to determine the influence of prefabricated concrete panels and deconstructable friction-grip bolted shear connectors on the performance of the steel-concrete composite connection. The experimental results show that deconstrcutable steel-concrete composite bolted shear connectors have completely different behaviour compared to welded headed stud shear connectors. Furthermore, a 3D finite element model of the steel-concrete composite connection having precast concrete slabs and deconstructable bolted shear connectors was performed. Numerical model was verified against experimental results, and was shown to accurately simulate their observed structural behaviour.

Comparative Characteristics of Seismic and Deformation Effects for Three Great Subduction Megaearthquakes

The comparative characteristics of seismic and deformational effects of three great subduction megaearthquakes in Sumatra in 2004 (Mw = 9.2); in Maule, Chile, in 2010 (Mw = 8.8); and in Tohoku, Japan, in 2011 (Mw = 9.0) are considered. In all cases the main rupture at the time of the earthquake was located in the subduction zone on the surface of the oceanic lithospheric plate plunging gently beneath a continent or an island arc. The process of destruction in each focus is characterized by a megathrust, with a gentle inclination angle of ~8–18o, according to the definitions of its focal mechanism, in almost full compliance with a gentle dipping of the oceanic lithospheric plate. The displacement occurred in a locked area of the subducting plate extended for several kilometers below the ocean bottom to a depth of 30–40 km. In all three cases, the maximum coseismic slip, obtained according to the data of geodetic measurements, occurred in the upper 25 km of the locked area, while its lower part radiated coherent short-period seisms. The trace of the rupture on the surface, marked by the aftershock area, ranged from 400–600 km in the case of Tohoku and Maule earthquakes up to ~1500 km during the Sumatra earthquake. The rupture in the Maule and Tohoku earthquakes was bilateral, with its approximately symmetric propagation from the epicenter, while in the Sumatra earthquake the rupture spread unilaterally relative to the epicenter from southeast to northwest. The propagation time of the rupture also varied. If in the first two cases it was 140–160 s, for the Sumatra earthquake it lasted 500–600 s. The largest tsunami wave, up to 40–60 m in height, was recorded during the Tohoku earthquake, extending for more than 200 km along the coast of Sanriku province. The rupture during the megaearthquakes under discussion is not confined in depth to the locked seismogenic area, marked by the area of the aftershock nearest in time and the zone of maximum coseismic slips determined by the geodetic GPS measurements. The rupture continues aseismically (postseismic slip) in the transition zone from brittle to brittle-plastic slip to depths of ~60–80 km. In addition, there is evidence that the displacements on the megathrust can continue slightly deeper to the region of the brittle–plastic slip. Such episodic events of slow slip (“silent” or “slow” earthquakes) and “seismic tremor” were recorded in southwestern Japan and southern Chile. These differences in seismic and deformation effects can serve as evidence of the change in frictional properties with depth along the surface of the megathrust. It should also be recognized that the strength barriers and asperities on the megathrust surface expressed in certain geological structures or yet unclear nature of segments of high frequency radiation can manifest themselves in the character of distribution of the accompanying seismicity during the great subduction earthquakes.

Present‐Day Deformation Mechanism of the Northeastern Mina Deflection Revealed by the 2020 Mw 6.5 Monte Cristo Range Earthquake

AbstractThe 15 May 2020 Monte Cristo Range Mw 6.5 earthquake occurred in the northeast of the Mina deflection, which accommodates approximately a quarter of the relatively dextral motion between the Pacific and North American plates. The Monte Cristo Range event provides an opportunity to study the present‐day regional deformation mechanism and active tectonics. In this study, we investigate the source rupture process of the event using joint inversion of interferometric synthetic aperture radar and broadband seismic data. We find that the rupture propagates almost simultaneously on two main segments. The fault motion changes from the predominantly sinistral slip near the epicenter on the eastern segment to the oblique slip on the western segment, with a maximum coseismic slip of 0.8 m. Our results suggest that the accommodation of slip transfer localized in the northeastern Mina deflection tends to transform from the wrench‐ to extension‐dominated transtension.

Multi-Segment Rupture Model of the 2016 Kumamoto Earthquake Revealed by InSAR and GPS Data

The 2016 Kumamoto earthquake, including two large (Mw ≥ 6.0) foreshocks and an Mw 7.0 mainshock, occurred in the Hinagu and Futagawa fault zones in the middle of Kyushu island, Japan. Here, we obtain the complex coseismic deformation field associated with this earthquake from Advanced Land Observation Satellite-2 (ALOS-2) and Sentinel-1A Interferometric Synthetic Aperture Radar (InSAR) data. These InSAR data, in combination with available Global Positioning System (GPS) data, are then used to determine an optimal four-segment fault geometry with the jRi method, which considers both data misfit and the perturbation error from data noise. Our preferred slip distribution model indicates that the rupture is dominated by right-lateral strike-slip, with a significant normal slip component. The largest asperity is located on the northern segment of the Futagawa fault, with a maximum slip of 5.6 m at a 5–6 km depth. The estimated shallow slips along the Futagawa fault and northern Hinagu fault are consistent with the displacements of surface ruptures from the field investigation, suggesting a shallow slip deficit. The total geodetic moment release is estimated to be 4.89 × 1019 Nm (Mw 7.09), which is slightly larger than seismological estimates. The calculated static Coulomb stress changes induced by the preferred slip distribution model cannot completely explain the spatial distribution of aftershocks. Sensitivity analysis of Coulomb stress change implies that aftershocks in the stress shadow area may be driven by aseismic creep or triggered by dynamic stress transfer, requiring further investigation.

Stochastic Analysis of Tsunami Hazard of the 1945 Makran Subduction Zone Mw 8.1–8.3 Earthquakes

Historical records of major earthquakes in the northwestern Indian Ocean along the Makran Subduction Zone (MSZ) indicate high potential tsunami hazards for coastal regions of Pakistan, Iran, Oman, and western India. There are fast-growing and populous cities and ports that are economically important, such as Chabahar (Iran), Gwadar (Pakistan), Muscat (Oman), and Mumbai (India). In this study, we assess the tsunami hazard of the 1945 MSZ event (fatalities ≈300 people) using stochastic earthquake rupture models of Mw 8.1–8.3 by considering uncertainties related to rupture geometry and slip heterogeneity. To quantify the uncertainty of earthquake source characteristics in tsunami hazard analysis, 1000 stochastic tsunami scenarios are generated via a stochastic source modeling approach. There are main objectives of this study: (1) developing stochastic earthquake slip models for the MSZ, (2) comparing results of the simulation with the existing observations of the 1945 event, and (3) evaluating the effect of uncertain fault geometry and earthquake slip based on simulated near-shore wave profiles. The 1945 Makran earthquake is focused upon by comparing model predictions with existing observations, consisting of far-field tsunami waveforms recorded on tide gauges in Karachi and Mumbai and coseismic deformation along the Pakistani coast. The results identify the source model that matches the existing observations of the 1945 Makran event best among the stochastic sources. The length, width, mean slip, and maximum slip of the identified source model are 270 km, 130 km, 2.9 m, and 19.3 m, respectively. Moreover, the sensitivity of the maximum tsunami heights along the coastline to the location of a large-slip area is highlighted. The maximum heights of the tsunami and coseismic deformation results at Ormara are in the range of 0.3–7.0 m and −2.7 to 1.1 m, respectively, for the 1000 stochastic source models.

Source model for the Mw 6.0 earthquake in Jiashi, China on 19 January 2020 from Sentinel-1A InSAR data

On January 19, 2020, an Mw 6.0 earthquake occurred in Jiashi, Xinjiang Uygur Autonomous Region of China. The epicenter was located at the basin-mountain boundary between the southern Tian Shan and the Tarim Basin. Interferometric Synthetic Aperture Radar (InSAR) is used to obtain the coseismic deformation field from both ascending and descending Sentinel-1A satellite images of the European Space Agency. The results showed that the coseismic deformation is distributed between the Kalping fault and the Ozgertaou fault. The earthquake produced significant deformation over an area of approximately 40 km by 30 km. The maximum and minimal displacements along the line of sight (LOS) are 5.3 cm and − 4.2 cm for the ascending interferogram and are 7.2 cm and − 3.0 cm for the descending interferogram, respectively. The fault geometry from the Multi peak Particle Swarm Optimization computation indicates that the seismogenic fault is a shallow low-dipping planar fault that is 4.58 km depth underground. The finite slip model inverted by the Steepest Descent Method implies that the rupture is dominated by a thrust fault. The slips are concentrated in a depth of 5–7 km with a maximum slip of 0.29 m. The estimated total seismic moment is 1.688 × 1018 Nm, corresponding to a magnitude of Mw 6.1. The seismogenic fault is the Kalping fault which has a listric structure. The coseismic deformation only occurred on the décollement layer and did not involve the ramp segment. The coseismic Coulomb stress changes have enhanced the stress on the deep margin of the Jiashi earthquake rupture area, indicating that there is still the possibility of strong earthquakes in this region in the future.

Coseismic Underground Rupture, Geometry, Historical Surface Deformations, and Seismic Potentials of the 28 March 2019 Mw 5.04 Mangya Earthquake Fault

AbstractThe 28 March 2019 Mw 5.04 Mangya earthquake damaged eight ongoing drilling boreholes in the oil‐production Yingxiong Ling (YXL) area, southwestern Qaidam of northern Tibet. The borehole damages provide an opportunity to measure directly the coseismic slips, the rupture area, and the seismic moment. The damages reveal the underground rupture area of 45.30 ± 10.24 km2, the maximum slip of 400 ± 13 mm, and the seismogenic fault dip of ~38.6°. These parameters generate a seismic moment of (1.81 ± 0.47) × 1017 Nm and a moment magnitude of 5.47 ± 0.16. Seismic exploration reveals that the geometry of the SZG ramp, the uppermost part of the multibend Yingxiong Ling thrust system, agrees primarily with the rupture plane derived from the borehole damages and one plane of the focal mechanism solution. This suggests that this earthquake resulted from slipping on the ramp. The hanging wall of the YXL thrust system forms the complex fault‐bend fold YXL anticlinorium. Active thrusting and folding along both edges of YXL attest to the southwestern vergence of this thrust system. Growth strata demonstrate average slip rates of the thrust system ranging from ~0.2 to ~0.3 mm/yr. The thrusted and folded recent alluviums along the southwestern edge indicate two thrusting events with coseismic slips of 1.7 ± 0.15 and 3.5 ± 0.15 m at 6.16 ± 0.52 and ~35.91 ka, respectively. The entire rupturing of the thrust system can produce Mw 7.65 ± 0.03 earthquakes.

Slip rates and paleoearthquakes along the east segment of the Guanggaishan–Dieshan fault zone, West Qinling Range, NW China

The WNW-trending Guanggaishan–Dieshan fault (GDF) is located in the West Qinling Range at a site of tectonic junction between the Tibetan plateau, the Sichuan basin and the Ordos block. Tectonically, this region is bounded by the East Kunlun fault to the southwest, the West Qinling fault to the north, and the Longmenshan fault to the southeast. The activity of the GDF is essentially related with the northeastward expansion of the Tibetan Plateau and associated strain partition between the East Kunlun fault and the West Qinling fault. This study reported the sense of fault movement, rate of fault slip, and the timing of three paleoseismic events on the east segment of the Guanggaishan–Dieshan fault (EGDF) with which no historical earthquake has been documented before. We focused our investigation on three branch faults in the central part of the EGDF using a range of study methods, e.g. structural mapping, paleoseismological trenching, unmanned aircraft vehicle photogrammetry, differential GPS survey, as well as radiocarbon and optically stimulated luminescence dating. Our new results highlighted: (1) the EGDF is dominated by the left-lateral sense of movement with a minor component of dip slip, (2) the range-bounding branch is characterized by a maximum left-lateral slip rate of 0.72 ± 0.34 mm/year and a maximum vertical-slip rate of 0.13 ± 0.03 mm/year, respectively. Kinematics of the EGDF is similar to many other active faults in the West Qinling Range, together they play a joint role in accommodating and transferring the residual left-lateral slip of the East Kunlun Fault. Three paleoseismic events were identified on the range-bounding fault based on two types of event markers: cut-cover relation and colluvial deposition. The ages of the most recent two events are estimated to be 2765–3320 cal. year BP and 12,775–13,005 cal. year BP and the age of the oldest event is as early as 18,495–32,950 cal. year BP. In contrast, there is no compelling evidence to show paleoseismic event along the rest two branches, and further work is needed to demonstrate this.

Late Pleistocene slip rate of the central Haiyuan fault constrained from optically stimulated luminescence, 14C, and cosmogenic isotope dating and high-resolution topography

Abstract To better constrain the long-term millennial slip rate of the Haiyuan fault in its central part, we revisited the site of Daqing, where there are multiple paired offset terraces. We used 0.1-m-resolution terrestrial light detection and ranging (LiDAR) and uncrewed aerial vehicle imagery to survey the offset terraces, quantify their geomorphology, and map the fault trace. From these observations, we refined the geomorphological interpretation of the site, measured terrace riser offsets, and determined their relation to terrace formation. The well-constrained age of the highest terrace, T3, at 13.7 ± 1.5 ka, determined from a combination of surface and subsurface optically stimulated luminescence, 14C, and terrestrial in situ 10Be cosmogenic radionuclide dating, associated with an offset of 88 m, yields a late Pleistocene minimum slip rate of 6.4 ± 1.0 mm/yr. The less-well-constrained offset (72 ± 3 m) of the T3/T2 riser base and the age (>9.3 ± 0.6 ka) of terrace T2 yield a maximum slip rate of 7.7 ± 0.6 mm/yr. The smallest offset of a gully incised into T1 of 6.0 ± 0.5 m is potentially associated with the most recent slip event that occurred in the last millennia. Overall, these offsets and ages constrain a geological rate of 5–8 mm/yr (preferred rate >6.4 mm/yr), similar to geodetic estimates. Our collocated high-resolution topography and precise chronology make it possible to reveal the geomorphic complexities of terrace riser offsets and their postformational evolution, and to show how previously determined geological rates along the fault were both under- and overestimated.

Effect of Different Bond Parameters on the Mechanical Properties of FRP and Concrete Interface.

This paper presents double shear tests performed to investigate factors influencing the bond behavior between basalt fiber-reinforced polymer (BFRP), glass fiber-reinforced polymer (GFRP) laminate, and concrete blocks. In detail, thirty-six twin concrete blocks strengthened with the aforementioned FRP types were tested to evaluate the influence of FRP length, width, and thickness, and their bonding behavior. The 2D-DIC (digital image correlation) technique and several strain gauges bonded along the laminate were used to measure the strain distributions of the FRP-to-concrete interface. The failure mode, ultimate load, load–slip, strain distribution, and bond–slip relationships between the laminates and concrete were analyzed. Furthermore, bond–slip curves were compared with some other existing literature models. The results from the experiment showed that the ultimate load, peak bond stress, and slip increased with the increase in the BFRP and GFRP laminates length, width, and thickness. The values of peak shear stress and the corresponding maximum shear slip were significantly different because of the above-mentioned factors’ influence on them. The bond interface that contributes to the bearing of the shear load may grow to an extent and later shift from the loaded end when debonding progresses. Finally, the fractured surfaces of the failed FRP laminates were examined using scanning electron microscope (SEM), revealing that FRP rupture, debonding in concrete, and debonding in an adhesive–concrete interface were the main failure types.

Comparative Study of Dimensionality and Symmetry Breaking on Nanoscale Friction in the Prandtl–Tomlinson Model with Varying Effective Stiffness

Friction Force Microscopy (FFM) measurements on NaCl immersed in ethanol display an increase of the effective contact stiffness with the applied load. This stiffness is estimated from the measured local contact interaction of the tip with the NaCl surface and the Prandtl–Tomlinson (PT) parameter, which reflects the relation between the corrugation stiffness and the effective contact stiffness. Different from FFM measurements in ultrahigh vacuum, for measurements in ethanol surroundings the PT parameters showed a maximum with the applied load. We incorporated this measured load-dependent effective stiffness together with the load-dependent amplitude of the corrugation energy into simulations based on the PT model, and studied its effect on the lateral friction for symmetric 1D and 2D potentials, as well as for an asymmetric 1D potentials. The simulations reproduced the experimentally observed non-monotonous behavior of the PT parameter, and enabled a glimpse on the relation of the characteristic observables (mean maximal slip forces and stiffness) with respect to their governing parameters (corrugation energy, effective stiffness). In all, apart from large deviations from symmetry in the interaction potential, the PT parameter provides a reliable estimate for nanoscale friction over periodic surfaces.

Seismic structure and tectonics of the continental wedge overlying the source region of the Iquique Mw8.1 2014 earthquake

On April 1, 2014, a large earthquake (Mw = 8.1) ruptured the central part of a historic seismic gap in northern Chile. In order to study the relationship between the co-seismic rupture characteristics and the crustal structure of the subduction zone, we processed a trench-perpendicular seismic reflection profile acquired across the zone of maximum slip and generated a P-wave velocity model. The results show a frontal prism in the continental wedge characterized by low velocities that increase rapidly towards the shore and acted as a barrier for trench-ward propagation of aftershocks. Landward, a transition zone with increasing upper crust velocity (4–5 km/s) concentrates most of the aftershocks. In addition, a trench-ward dipping set of fault zones is observed along the continental wedge associated to the Iquique forearc basin formation (1.5 km thick at the depocenter on this profile). We identify three stratigraphic units within the basin. A landward tilt and thickness increase is detected in each stratigraphic unit, along with growth strata and domino structures, suggesting landward migration of syn-extensional deformation in response to basal subduction erosion. By extrapolating our results to the plate boundary and based on published focal mechanisms of intra-crustal seismicity, we find a strong spatial correlation between the Iquique basin and the highest slip area for the 2014 earthquake, suggesting long-term extensional deformation due to coseismic tensional stresses.

Studying postseismic deformation of the 2010–2011 Rigan earthquake sequence in SE Iran using geodetic data

In this paper, we study the spatial distribution and temporal evolution of the postseismic deformation of the 2010–2011 Rigan earthquake sequence which occurred at the southern termination of the East Lut fault system, southeast Iran. One-year GPS measurements after the Rigan earthquake sequence reveals right-lateral postseismic displacement along the East Chahqanbar fault and left-lateral postseismic displacement along the South Chahqanbar fault. To investigate the deformation variations in time and space, InSAR time-series of COSMO-SkyMed images is applied using the Small Baseline Subset algorithm. The results confirm a clear cumulative postseismic signal increasing to 8 mm during the first five months following the first mainshock in the direction of the coseismic displacement. The cumulative postseismic displacements are well correlated with the cumulative number of the aftershocks and their associated moment release. Considering this correlation and the observation of a sharp discontinuity along the coseismic fault in the displacement map, it is concluded that the after-slip mechanism is responsible for the observed postseismic deformation in the study region. This study is the first observation of a short-term postseismic motion in eastern Iran through geodetic data in contrast with long-lasting postseismic displacements following the earthquakes that occurred around Lut block. Modeling of the postseismic displacement results in a distributed slip pattern with a maximum slip of 0.8 m on the fault plane responsible for the 2010 Rigan coseismic deformation. This indicates that the postseismic deformation on barriers remained unbroken during the mainshock.

Shallow slip of blind fault associated with the 2019Ms 6.0 Changning earthquake in fold-and-thrust belt in salt mines of Southeast Sichuan, China

SUMMARYAn earthquake with a magnitude of Ms 6.0 and shallow focal depth of ∼4 km struck the Changning county, Sichuan province, China on 2019 June 17. The hypocentre is located in the fold-and-thrust belt with plentiful shale gas and salt mine resources. One hypothesis is that the shallow fault could be affected by the artificial pressure water injection including the disposal of wastewater, fracking shale gas extraction and salt mining in Changning area. In this study, SAR (Synthetic Aperture Radar) images, historical earthquakes, aftershocks and seismic reflection data were collected to jointly investigate the characteristics of the 2019 Changning earthquake. The source model inferred from the InSAR coseismic deformation observation reveals that the 2019 Changning earthquake is attributed to a blind fault dipping to southwest with dominant thrust and sinistral strike slip. Moreover, a small shallow fault developing within the Changning anticline was triggered by the main shock, which contributed to the surface displacements as observed in the north of the epicentre. The estimated maximum slip of 0.49 m is located at the depth of ∼1.9 km, ∼9 km northwest of the epicentre. The Coulomb failure stress change caused by the previous two large earthquakes, which occurred in the hydraulic fracturing area, suggesting that they have little effect on the initial rupture of the 2019 Changning earthquake. Despite this, they have a positive triggering effect on the fault rupture in the northwest of the seismogenic fault. In addition, the analysis on the relation between the positive Coulomb failure stress change and the aftershocks suggests that the aftershocks may have different motion patterns from the main shock. The analysis also shows the earthquakes occurrence in the seismogenic zone may be affected by the high pore pressure due to the long-term injection of salt mining for more than three decades.

Multifault complex rupture and afterslip associated with the 2018 Mw 6.4 Hualien earthquake in northeastern Taiwan

SUMMARYWe investigate the coseismic and post-seismic deformation due to the 6 February 2018 Mw 6.4 Hualien earthquake to gain improved insights into the fault geometries and complex regional tectonics in this structural transition zone. We generate coseismic deformation fields using ascending and descending Sentinel-1A/B InSAR data and GPS data. Analysis of the aftershocks and InSAR measurements reveal complex multifault rupture during this event. We compare two fault model joint inversions of SAR, GPS and teleseismic body waves data to illuminate the involved seismogenic faults, coseismic slip distributions and rupture processes. Our preferred fault model suggests that both well-known active faults, the dominantly left-lateral Milun and Lingding faults, and previously unrecognized oblique-reverse west-dipping and north-dipping detachment faults, ruptured during this event. The maximum slip of ∼1.6 m occurred on the Milun fault at a depth of ∼2–5 km. We compute post-seismic displacement time series using the persistent scatterer method. The post-seismic range-change fields reveal large surface displacements mainly in the near-field of the Milun fault. Kinematic inversions constrained by cumulative InSAR displacements along two tracks indicate that the afterslip occurred on the Milun and Lingding faults and the west-dipping fault just to the east. The maximum cumulative afterslip of 0.4–0.6 m occurred along the Milun fault within ∼7 months of the main shock. The main shock-induced static Coulomb stress changes may have played an important role in driving the afterslip adjacent to coseismic high-slip zones on the Milun, Lingding and west-dipping faults.