Resolving co- and early post-seismic slip variations of the 2021 MW 7.4 Madoi earthquake in east Bayan Har block with a block-wide distributed deformation mode from satellite synthetic aperture radar data

On 21 May 2021(UTC),an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau.The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake,and especially in proximity to the seismic gaps on the east Kunlun fault.Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake.Range offset displacements depict clear surface ruptures with a total length of~170 km involving two possible activated fault segments in the earthquake.Coseismic modeling results indicate that the earthquake was dominated by left-lateral strike-slip motions of up to 7 m within the top 12 km of the crust.The well-resolved slip variations are characterized by five major slip patches along strike and 64%of shallow slip deficit,suggesting a young seismogenic structure.Spatial-temporal changes of the postseismic deformation are mapped from early 6-day and 24-day InSAR observations,and are well explained by time-dependent afterslip models.Analysis of Global Navigation Satellite System(GNSS)velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block,but exhibits significant lateral heterogeneities,as evidenced by magnetotelluric observations.The block-wide distributed deformation of the east Bayan Har block along with the significant co-and post-seismic stress loadings from the Madoi earthquake imply high seismic risks along regional faults,especially the Tuosuo Lake and Maqên-Maqu segments of the Kunlun fault that are known as seismic gaps.

Multi-scale Decomposition of Co-seismic Deformation from High Resolution DEMs:a Case Study of the 2004 Mid-Niigata Earthquake

Decomposing co-seismic deformation is an immediate need for researchers who are interested in earthquake inversion analysis and geo-hazard mapping. However, conventional InSAR or digital elevation models （DEMs） imagery analyses only provide the displacement in the Line-of-Sight （LOS） direction or elevation changes. The 2004 Mid-Niigata earthquake in Japan provides lessons on how to decompose co-seismic deformation from two sets of DEMs. If three adjacent points undergo a rigid-body-translation movement, their co-seismic deformation can be decomposed by solving simultaneous equations. Although this method has been successfully used to discuss tectonic deformations, the algorithm needed improvement and a more rigorous algorithm, including a new definition of nominal plane, DEMs comparability improvement and matrix condition check is provided. Even with these procedures, the obtained decomposed displacement often showed remarkable scatter prompting the use of the moving average method, which was used to determine both tectonic and localized displacement characteristics. A cut-off window and a pair of band-pass windows were selected according to the regional geology and construction activities to ease the tectonic and localized displacement calculations, respectively. The displacement field of the tectonic scale shows two major clusters of large lateral components, and coincidently major visible landslides were found mostly within them. The localized displacement helps to reveal hidden landslides in the target area. As far as the Kizawa hamlet is concerned, the obtained vectors show down-slope movements, which are consistent with the observed traces of dislocations that were found in the Kizawa tunnel and irrigation wells. The method proposed has great potential to be applied to understanding post-earthquake rehabilitation in other areas.

Numerical simulation of influences of the earth medium's lateral heterogeneity on co- and post-seismic deformation

Many studies revealed that the Earth medium＇s lateral heterogeneity can cause considerable effects on the co- and post-seismic deformation field. In this study, the threedimensional finite element numerical method are adopted to quantify the effects of lateral heterogeneity caused by material parameters and fault dip angle on the co- and postseismic deformation in the near- and far-field. Our results show that： 1） the medium＇s lateral heterogeneity does affect the co-seismic deformation, with the effects increasing with the medium＇s lateral heterogeneity caused by material parameters; 2） the Lame parameters play a more dominant role than density in the effects caused by lateral heterogeneity; 3） when a fault＇s dip angle is smaller than 90, the effects of the medium＇s lateral heterogeneity on the hanging wall are greater than on the footwall; 4） the impact of lateral heterogeneity caused by the viscosity coefficient on the post-seismic deformation can affect a large area, including the near- and far-field.

Co-seismic deformation for the 2015 M_(W)7.8 Gorkha earthquake(Nepal)using near-field GPS data

Seasonal variations and common mode errors affect the precision of the Global Positioning System(GPS)time series.In this paper,we explore to improve the precision of coordinate time series,thereby providing a better detection of weak or transient deformation signals,particularly co-seismic signals.Based on 97 GPS stations,including the campaign and continuous GPS stations in Nepal and southern Tibet,we first consider seasonal variations and common errors,then obtain co-seismic deformation of the 2015 Gorkha earthquake in Nepal and southern Tibet.Our co-seismic rupture model is characterized by a shallow ramp and a deeper detachment fault,in agreement with the relocated aftershock sequence.Our results indicate that the earthquake rupture is mainly distributed in the upper-crustal fault,and the maximum slip is up to 8.0 m at~15.0 km depth located in the approximate-80 km east of the epicenter.The average slip is more than 5 m,and the total modelled magnitude is M_(W)7.84,consistent with the observed seismic moment.Our rupture model for the 2015 Gorkha earthquake suggests that the rupture zone is not only in the upper crustal Main Himalayan Thrust(MHT),but also spreads to the northern segment of the MHT.

Post-seismic relaxation process and vertical deformation following the 2008 Ms8.0 Wenchuan earthquake, China

The post-seismic horizontal and vertical deformations following the 2008 Ms8.0 Wenchuan earth- quake are inferred from GPS and precise leveling data. The post-seismic relaxation process is measured using GPS data from campaign stations located around the Longmenshan fault, and the derived decay time constant is 12 days. The evolution of the post-seismic vertical deformation is obtained from precise leveling data measured near the surface rupture. The results demonstrate that the hanging wall is uplifting and the foot wall is subsi- ding. The amplitude of the post-seismic deformation is lower than that of the co-seismic deformation. The re- gion with the largest post-seismic displacement is located on the leveling route between Maoxian and Beichuan on the hanging wall.

Time-space characteristics of viscoelastic post-seismic deformations corresponding to different rheology models

On a long time(>1 a)scale,the viscoelastic properties of mantle media significantly affect post-seismic deformation.The stress field disturbance in viscoelastic medium caused by fault slip gradually relax,and the relaxation process and its temporal-spatial characteristics are determined by the viscoelastic model.In this paper,we assume that the mantle media are types of common linear rheological models,i.e.,the Burgers body,the standard linear solid,and the Maxell body,and we calculate the dislocation Love number and Green function for a spherically symmetric,non-rotating,viscoelastic,and isotropic(SNRVEI)Earth model.The characteristics of the post-seismic relaxation deformations corresponding to the different models are compared.Our results show that for a short time period,the Burgers body and standard linear solid are similar;while for the long time period,the Burgers body and Maxwell body are similar.This suggests that the observations of post-seismic deformation on the surface have a great potential for the inversion of underground viscoelastic structures.However,the potential of using surface displacement to distinguish different rheological models is limited when the observation period is not long enough.

Co-seismic changes of Wenchuan Ms8.0 earthquake and six aftershocks recorded by four deformation instruments at Xuzhou seismostation

Co-seismic changes of Wenchuan Ms8.0 earthquake and six strong aftershocks were recorded by 4 digital deformation instruments at Xuzhou seismostation at an cpicentral distance of 1392 km. The result shows that the straln-step changes and wave motions are caused by the arrival of the corresponding surface waves. The shape and size of the step changes and the response time were different for different instruments, even they were located in the same rock body only 7.65 m to 10.57 m apart. This difference is probably a reflection of different instrument properties, such as sensitivity and frequency response. The earthquake-caused stress changes, which were mainly compression in Xuzhou, had an important triggering effect on far-field strain changes

Co-seismic displacements of 2011 Japan Mw9.0 earthquake recorded by far-field GPS stations

Co-seismic displacements of the 2011 Mw9.0 Japan earthquake recorded by GPS stations in China and surrounding areas showed a movement toward the epicenter. The horizontal displacements were up to 1 - 3 cm in northeastern China, 3 -8 mm in the North China, and 2 cm in the Korean peninsula. The vertical movements in China were small uplifts.

Co- and post-seismic slip analysis of the 2017 M_(W)7.3 Sarpol Zahab earthquake using Sentinel-1 data

The M_(w)7.3 Sarpol Zahab earthquake that occurred in the Zagros Fold-Thrust Belt(ZFTB) of Iran on November 12,2017 is the largest earthquake instrumentally recorded in the region.This earthquake provides an opportunity to investigate the slip behaviour and frictional properties of the fault,which is significant for assessing future seismic potential.In this study,we use Sentinel-1 images to map the coand post-seismic deformation to invert for the fault slip.The result indicates that most of the coseismic slip is buried in the depth range of 11-17 km,and the maximum slip is about 3.8 m at a depth of 15 km.The coseismic slip induces an increase of Coulomb stress in the unruptured area of the seismogenic fault plane,driving the afterslip.Based on the stress-driven afterslip,we obtain a frictional parameter of(ab)=(0.001-0.002) for the updip afterslip zone and(a-b)=0.0002 for the downdip afterslip zone in the framework of rate-and-state friction.The constitutive parameter(a-b) of the fault is very small,suggesting that the fault segments are close to velocity-neutral and may experience coseismic rupture.

Study on crustal deformation of the Ms6.6 Damxungearthquake in 2008 by InSAR measurements

Three Envisat images from ESA were used to derive the pre - and co-seismic deformation interfereograms caused by the Damxung Ms6. 6 earthquake of Oct. 6,2008 ,by using InSAR. The result shows no significant crustal motion more than 4 months before the earthquake, but a maximum co-seismic displacement of about 0.3 m in an epicentral area of 20 km × 20 km. The deformation field was symmetrically distributed about a NS axis, where the west side subsided and the east side uplifted. We used a linear elastic dislocation model in half space and a nonlinear constraint optimized algorithm to estimate the slip distribution along the fault. The results indicates that the epicenter is located at 90. 374°E ,29. 745°N with a moment magnitude of Mw6. 35. The earthquake is dominated by normal faulting with a maximum slip of 3 m on a 12 km × 11 km fault plane striking S189°W,dipping 60° to NW at a depth of 9.5 km,and is located at a sub-fault of the southeastern Piedmont of the Nyainqentanglha mountains. The relatively shallow depth of earthquake is related to relatively high heat flow in the area.

Studying the viscosity of lower crust of Qinghai-Tibet Plateau according to post-seismic deformation

The viscosity of lower crust of Qinghai-Tibet Plateau on earth should be determined. It has become a predominant problem in quantitative research on geodynamics. Its order of magnitude will have a great influence on the results of quantitative modeling. To obtain the viscosity of lower crust of Qinghai-Tibet Plateau, this parameter was calculated by three methods. The first is based on the estimation on the temperature state of Qinghai-Tibet Plateau in the deep part, and the viscosity of lower crust of northern Plateau was recomputed with strain rate derived from rheology law and GPS observation. Effective viscosity of middle crust in Kunlun region is between 1020 and 1022 Pa·s, and that of lower crust is be- tween 1019 and 1021 Pa·s; the second is based on three kinds of rheological models used to fit the post-seismic deformation recorded by cross-over fault GPS sites set after Ms8.1 Kunlun earthquake in 2001. The viscosity of lower crust obtained by this method is of 1017 Pa·s order of magnitude. However, higher viscosity is required to fit the data of south fault better, and the lower one is required to fit the data of north fault better. The viscosity of lower crust, which was obtained by fitting the cross-over fault post-seismic deformation after Ms7.6 Luhuo earthquake in 1973, is of 1019 Pa·s order of magnitude. Non-linear relationship between effective viscosity and strain rate is ignored in the former research of effective viscosity. This research shows the difference of effective viscosity obtained from laboratory experiment, and shorter and longer time post-seismic deformation after large earthquakes can be explained in phase.

Mapping three-dimensional co-seismic surface deformations associated with the 2015 MW7.2 Murghab earthquake based on InSAR and characteristics of crustal strain

Three-dimensional(3 D) co-seismic surface deformations are of great importance to interpret the characteristics of coseismic deformations and to understand the geometries and dynamics of seismogenic faults. In this paper, we propose a method for mapping 3 D co-seismic deformations based on InSAR observations and crustal strain characteristics. In addition, the search strategy of correlation points is optimized by adaptive correlation distance, which greatly improves the applicability of the proposed method in restoring deformations in decorrelation areas. Results of the simulation experiment reveal that the proposed method is superior to conventional methods in both the accuracy and completeness. The proposed method is then applied to map the 3 D co-seismic surface deformations associated with the 2015 MW7.2 Murghab earthquake using ascending and descending ALOS-2 PALSAR-2 images. The results show that the seismogenic fault is the Sarez-Karakul fault(SKF), which is dominated by NE-SW strike slips with an almost vertical dip angle. The north section and the south segment near the epicentre have obvious subsidence along with a southwestward motion in the northwest wall, and the southeast wall has northeast movement and surface uplift trend along the fault zone. The strain field of the earthquake is also obtained by the proposed method. It is found that the crustal block of the seismic area is obviously affected by dilatation and shear forces, which is in good agreement with the movement character of the sinistral slip.

Influence of the 2011 Mw9. 0 Japan earthquake on groundwater levels in Chinese mainland

This paper gives a description of the co-seismic and post-seismic groundwater level changes induced in Chinese mainland by the 2011 Mw9.0 Japan earthquake, and the corresponding stress changes calculated on the assumption of linear elasticity. The result shows that the main types of changes were oscillations and step increases. The North-South Seismic Belt and the Shanxi Seismic Belt were the main areas affected by the earthquake.

Response of tilt and strain meters in Hubei province to the 2011 Mw9. 0 Japan earthquake

Tih and strain meters of the deformation-observation network in Hubei Province all responded to the Mw9.0 Japan earthquake on March 11,2011. By analyzing the co-seismic responses,we found that firstly there was essentially a linear correlation between response time and epicentral distance. Secondly, there was some correlation between maximum response amplitude and earthquake magnitude as well as between the duration and earthquake magnitude. Thirdly, the response amplitudes and decay rates were different for different types of instruments. Due to less data-sampling frequency, the deformation instruments, could not display the first motion of P and S waves, but responded mainly to far-field surface waves. Before the earthquake, the NS earthtide component recorded by the cave stainmeter at Yichang was distorted for nearly eight hours. While digital deformation observation did not show complete information about the earthquake source, it still reflected some key features of seismic-wave propagation.

Focal mechanism of the 2011 Mw7.1 earthquake in eastern Turkey from InSAR observation

We used two Envisat images from ESA to reveal the co-seismic deformation field caused by the Mw7.1 earthquake in eastern Turkey on Oct. 23,2011, and a linear elastic dislocation model in half space to estimate the corresponding fault geometry, location, and displacement. The result indicates that the earth- quake is caused mainly by a buried thrust and left-lateral strike faulting with an average slip of 1. 456 m on a fault plane of 30 km× 25 km at a depth of 18.4 kin.