The Haiyuan-Liupanshan tectonic belt is one of the most significant tectonic deformation areas in the northeastern Qinghai-Tibetan plateau with frequent strong earthquakes. It is an important opportunity to study the northeast extension of the Qinghai-Tibetan plateau and an ideal place to study the earthquake breeding process.

The published GPS observations show that the southwest side of the Haiyuan fault may still be undergoing deformation caused by the crustal viscoelastic relaxation effect of the 1920 Haiyuan M8.5 earthquake. And the publicly published leveling data results show local vertical deformation of the crust in the area west of the Liupanshan fault is significant. According to the seismic geological data, there exist historical earthquake rupture gaps in the middle and south sections of the Liupanshan fault and the southeast section of the Xiangshan-Tianjingshan fault in the Haiyuan-Liupanshan structural area, which have the background of strong earthquakes above M7.0. In view of the low spatial resolution of GPS and leveling observations, we need to use high-resolution crustal deformation fields to further study the crustal deformation characteristics of the above regions. Therefore, we further discuss the above issues in combination with InSAR observations.

The Sentinel-1A/B SAR data of two orbits covering the Haiyuan-Liupanshan fault from 2014 to 2020 were processed to obtain the current crustal deformation field in the line-of-sight direction. Furthermore, the high-density regional crustal deformation field was obtained by integrating InSAR and published GPS observations of the horizontal crustal movement velocity field on a time scale of 20 years. By comparing the observations of GPS, leveling and InSAR and high-resolution three-dimensional deformation integrated GPS-InSAR field, the characteristics of crustal deformation and strain field in the region are analyzed and discussed. The main conclusions are as follows:

(1)GPS and InSAR observations show that the post-seismic viscoelastic relaxation effect of the 1920 Haiyuan M8.5 earthquake may still be pronounced on the south side of the Haiyuan fault, but this conclusion is still speculative and needs to be confirmed by further observations;

(2)The high-resolution horizontal deformation field from GPS-InSAR shows that the decrease of the sinistral slip rate of the Haiyuan fault along the fault strike mainly occurs in the Middle East section. In contrast, the decrease of the middle and west sections is not significant, which may be related to the transformation of the left-lateral strike-slip to thrust nappe structure between the Haiyuan fault and the Liupanshan fault.

(3)GPS vertical and leveling observations both show that the vertical crustal deformation characteristics in the middle and south sections of the Liupanshan fault are similar to the vertical deformation of the Longmenshan fault before the Wenchuan earthquake. Considering the similar structural characteristics of the Liupanshan fault and the Longmenshan fault, and combining with the seismic and geological data, we believe that the Liupanshan fault may be in the relatively late stage of the earthquake breeding process. It can also be recognized by the high-resolution horizontal deformation and strain field derived from GPS-InSAR data. According to the fault motion parameters obtained in our study and the existing seismic and geological data, it is estimated that the maximum moment magnitude of an earthquake in the middle-south section of Liupanshan Mountain is approximately 7.5.

(4)The areas with rapid maximum strain accumulation in the study region are mainly concentrated in the vicinity of the Haiyuan fault and the left lateral shear zone between the Haiyuan fault and the Xiangshan-Tianjingshan fault. The dilatation strain rate west of the Liupanshan fault shows prominent compressive deformation characteristics corresponding to the nappe deformation in the Liupanshan tectonic area. The strain rate field in the southeast section of the Xiangshan-Tianjingshan fault is smaller than that of the surrounding area. There is a strain mismatch phenomenon, which may be related to the preparation for strong earthquakes. From the perspective of rotational deformation, the study area presents multiple deformation units, among which counterclockwise rotation corresponds to left-lateral strike-slip deformation(the left-lateral shear belt from the Haiyuan fault to the Xiangshan-Tianjingshan fault). In contrast, clockwise rotation corresponds to right-lateral strike-slip deformation(the right-lateral shear belt in the western margin of Ordos and Longxi block).

A M_S6.4 earthquake occurred on May 21^th, 2021 at Yangbi, Yunnan. In this paper, high resolution InSAR coseismic deformation fields were obtained based on the ascending and descending track of Sentinel-1 SAR images. Based on the InSAR-derived deformation fields, the geometric model of the seismogenic fault was determined according to the aftershock relocation results. Then the fine coseismic slip distribution of the fault plane of Yangbi earthquake was inversed using a distributed sliding inversion method. Finally, the regional strain distribution and the Coulomb stress variation on the surrounding faults caused by coseismic dislocations and viscoelastic relaxation effect after earthquake were calculated, and the seismic risk of the seismogenic structure and the surrounding faults was discussed. The results show that the descending track co-seismic deformation field shows that the NE wall of the seismogenic fault moves close to the satellite, while the SW wall moves far away from the satellite, and the coseismic deformation is symmetrically distributed. The maximum LOS vectors were 8.6cm and 7.9cm, respectively, and the descending track profile showed a coseismic displacement up to 15cm. The fringes on the southwest side of the ascending track interferograms are relatively clear, showing movement close to the satellite, and the maximum LOS deformation magnitude is 5.7cm, while the interference fringes on the northeast side are not clear and the noise is obvious. The fault co-seismic dislocation is mainly of dextral strike-slip with a small amount of normal fault component. The coseismic slip mainly distributes at depths 2~10km, and the coseismic sliding rupture length is about 16km with the maximum slip of approximately 0.46m at a depth 6.5km. The average slip angle is 180° and the inverted magnitude is approximately M_W6.1. The causative fault did not rupture the surface. From the analysis of regional strain distribution and tectonic dynamic background, the Yangbi earthquake occurred in the region where the Sichuan-Yunnan rhomboid block is blocked in its process of SE movement by the South China block and deforms strongly. Combined with the analysis of the geometric occurrence and movement properties of faults, our study suggests that the causative fault of the Yangbi earthquake maybe is a branch of the Weixi-Qiaohou Fault or an unknown fault that is nearly parallel to it on the west side. This earthquake has a significant impact on the Coulomb stress of the Longpan-Qiaohou Fault, Chenghai Fault and Red River Fault in the southwestern Sichuan-Yunnan rhombic block. The Coulomb stress in the northern section of Red River Fault is the most significant. The cumulative Coulomb stress variations of the coseismic and 10 years after the earthquake show that the Coulomb stress variation has increased in the northwestern Yunnan tectonic area. This earthquake is another typical seismic event occurring in the southwest of the Sichuan-Yunnan block after the Lijiang M_S7.0 earthquake in 1996 and the Mojiang M_S5.9 earthquake in 2018. The risk of strong earthquakes in the regional extensional tectonic system in northwest Yunnan and in the north section of the Red River fault zone cannot be ignored.

A M_S6.4 earthquake occurred on January 19^th, 2020 at Jiashi, Xinjiang, this earthquake is another strong earthquake since the Jiashi M_S6~7 earthquake swarm events from 1997 to 2003, and the epicenter was located near the Kalpin nappe in the western part of southern Tianshan. The Kaplin nappe is located in front of southern Tianshan Mountains, which is a thin skinned thrust belt composed of a series of nearly NE-SW thrust nappes under the strong and sustained regenerative orogeny in the Tianshan area. There are some differences in focal positions and fault parameters given by different institutions, therefore in this paper, high resolution InSAR coseismic deformation fields were obtained based on the ascending and descending tracks of Sentinel-1 SAR images to obtain the focal mechanism. The 30m resolution SRTM DEM data is chosen as the external DEM to eliminate the phases caused by topography, the robust Goldstein filtering is applied for phase smoothing, and the Delaunay minimum cost flow method is used for phase unwrapping. The variation range of interference fringes shows that the east-west span of the earthquake deformation field is about 40km, and that of the north-south direction is about 20km, the displacement results show that the maximum uplift displacement is 5.9cm and the maximum subsidence is 3.7cm along the LOS direction of the ascending data, the maximum uplift displacement is 6.4cm and the maximum subsidence is 2cm along the LOS direction of the descending data. And then the InSAR-derived deformation fields are used to obtain the seismogenic mechanism of this earthquake, and to improve the computational efficiency, the quadtree segmentation method is used to desample the original high-resolution InSAR observations before inversion. The coseismic slip distribution of the causative fault was inversed using a uniform sliding inversion method based on a Bayesian approach, and then the fine slip distribution of the fault plane of Jiashi earthquake was inversed using the distributed slip inversion method based on the constrained least squares. It should be noted that the fault plane is set as the shovel shape according to the geometric relationship between the seismogenic fault parameters inverted by uniform sliding and the exposed position of the Kapling Fault on the surface during the distributed slip inversion. According to the difference between the observed and simulated values, it can be seen that the residual error of the inversion model is small, indicating the reliability of the inversion result. The final result shows that the epicenter is located at 39.9°N, 77.28°E and the strike and dip angle of the seismogenic fault is 276° and 10.7°, respectively, the maximum dip slip and strike slip of fault plane is about 0.29m and 0.03m, respectively, which are located at the depth of about 5km underground. The cumulative coseismic moment is 1.73×10¹⁸N·m from InSAR inversion, which is equal to the moment magnitude of M_W6.1 and the Kalpin Fault is supposed to be the causative fault. Then, regional GPS-derived surface strain rate, tectonic dynamic background, and regional deep and shallow structures were comprehensively analyzed. The results show that the Jiashi M_S6.4 earthquake is a typical thrust event that occurred in the thrust nappe of the southern Tianshan. The 2020 Jiashi event and the 1997—2003 Jiashi M6~7 earthquakes swarm are the results of rupture of many faults with different scales and properties. And these events are all controlled by the thrust nappe of southern Tianshan.