On January 8, 2022, an earthquake of M_W6.7 occurred in Menyuan County, Qinghai Province. The epicenter of the earthquake is located in the middle eastern section of the Qilian Mountains seismic belt on the northeast edge of the Qinghai-Tibet Plateau. Under the northward push by the Qinghai-Tibet Plateau plate, and the push and subduction in the northeast direction of the Qilian Mountains, and also blocked by the Alxa block and affected by the push in the southwest direction of the Longshou Mountains uplift area at its front edge, a ramp structural pattern of compressive depressions was formed in the Hexi Corridor basins area. As a result, most of the active faults in this area are mainly NW-trending, and the active features are mostly characterized by compressional thrusting and strike slip. This paper reconstructs the coseismic deformation field of Menyuan earthquake through the European Space Agency Sentinel-1A C-band radar satellite data and D-InSAR technology, determines the geometric characteristics of the seismogenic fault through the inversion method of optimum fault slip distribution, and determines the seismogenic fault of this earthquake. The results show that the deformation range of the radar line of sight is -0.42~0.7m for the ascending track deformation field and -0.63~0.72m for the descending track deformation field, and the maximum deformation locates in the Lenglongling section. The data of ascending and descending tracks show that there are two obvious deformation regions with a butterfly-like stripe pattern. The sign of LOS deformation variable observed in InSAR deformation field of ascending and descending orbits in the same area is opposite. Combined with the flight direction of ascending and descending satellites, it is determined that the motion of seismogenic fault is mainly left-lateral strike slip. Among them, the Lenglongling Fault and Tolaishan Fault pass through the fracture surface revealed by InSAR deformation field, which means that the above fault is highly likely to be the seismogenic fault of the Menyuan earthquake in 2022. At the same time, the SE-trending Lenglongling Fault on the east side passes through the fracture surface, with a surface fracture length of about 20km. The EW-trending Tolaishan Fault on the west side also passes through the fracture surface, with a fracture length of about 5km. And then, according to the field geological survey results of this earthquake, taking the InSAR coseismic deformation field data as constraints and based on Okada elastic dislocation model, the geometric structure of the seismogenic fault and the fine slip distribution characteristics of the fracture surface are determined. The inversion results reveal that there are two slip regions, of which the slip is mainly concentrated in the Lenglongling fault section, with a maximum left-lateral slip of 3.66m and a maximum slip depth of 5km. There is also a maximum sinistral slip of 1.95m occurring at a depth of 5km in the Tolaishan Fault. It is inferred that the seismogenic fault is the western section of Lenglongling Fault which also ruptured the Tolaishan Fault on its west.

On this basis, Coulomb33 software is used to calculate the static Coulomb stress changes generated by the Menyuan earthquake at different depths(5km, 10km, 15km and 20km). The Coulomb stress change image within 300km of the epicenter shows a typical four-quadrant distribution characteristic. There are four fan-shaped stress increase and decrease areas at 5km underground. The area with the largest increase in stress is near the Beiyuan Fault of Tuole Mountain in the west of the epicenter of Menyuan earthquake. The increase of stress is over 0.03MPa, greater than the trigger threshold of 0.01MPa. The stress increase coverage area in the south of the epicenter further expanded, with a stress increase of more than 0.03MPa, inducing many aftershocks distributed linearly in the NWW direction along the epicenter. According to the overall analysis, most of the subsequent earthquakes in Menyuan occur at a depth of 10~12km, which is in good agreement with the stress increase area at the corresponding depth. At the same time, for the NW-SE area and NE-SW end of the rupture in the epicenter, the area with ΔCFS≥0.01MPa is worthy of attention for the subsequent risk.

Finally, based on the GPS velocity field relative to the Ordos block, it is analyzed that the Lenglongling area moves in the NE direction relative to the Ordos block as a whole, the GPS velocity vector north of the Lenglongling Fault decreases, and the movement direction turns to NNW. Using GPS velocity field to calculate the principal strain rate, shear strain rate, surface strain rate and principal compressive stress in Lenglongling area, it is shown that there is a significant high value area of surface strain in Lenglongling area. The principal strain rate is NE compression, and the peak value of shear strain rate is located on the north side of Lenglongling Fault and the east section of Minle-Damaying Fault. Its strain accumulation indicates that the area is still in a high stress state, and the seismic activity may continue to be strong in the future. The regional surface strain rates show obvious compression characteristics, and the principal strain rates show NE-SW compression and NW-SE extension. Overall, the source area of the Menyuan earthquake is still under the push in the NNE direction of the eastern Himalaya syntaxis of the Indian plate. It can also be seen that the Menyuan earthquake occurred in the high value area of the maximum shear strain rate and the compression area of the surface strain. The occurrence of the Menyuan earthquake in the Lenglongling area of the North Qilian Mountains on the northeast edge of the Qinghai-Tibet Plateau and its current high stress accumulation indicate that the Lenglongling Fault may still be active today.

On this basis, the seismogenic structural characteristics and seismogenic relationships of the two Menyuan earthquakes in 2016 and 2022 are further discussed. The 2016 Menyuan earthquake is located on the extension line of the Minle-Damaying Fault. The seismogenic fault is a SW-trending thrust fault. The fault extends in NW-SE direction on the surface along the front of the mountain, and its deep part may converge to the detachment layer at the bottom of the Qilian Mountains together with the Lenglongling Fault. The fault has the potential to generate destructive earthquakes. The 2016 M_W5.9 Menyuan earthquake and the 2022 M_W6.7 Menyuan earthquake have different seismogenic mechanisms, but the seismogenic faults all belong to the North Qilian Mountains active fault zone, most of which control the boundary of the Neogene basins. Both earthquakes are the local adjustment of stress accumulation in the region as a whole, and the expression of the northeastward pushing of the Qinghai Tibet Plateau. Some scholars believe that Lenglongling fault zone, Jinqianghe Fault, Maomaoshan fault zone and Laohushan Fault jointly constitute the “Tianzhu earthquake gap”. The occurrence of three Menyuan earthquakes in 1986, 2016 and 2022 has drawn continuous attention to the fault activity and seismic risk of this area.

Due to the ongoing collision between Indian and Eurasian plates, the internal blocks of the Tibet plateau are experiencing eastward extrusion. Resulting from the blocking of the Sichuan Basin along the eastern boundary of the Bayanhar block, the plateau begins to rotate clockwise around the eastern syntaxis, and continues to move toward the IndoChina Peninsula. Such process forms the Hengduan Mountains with thousands of gullies in the Sichuan-Yunnan region, and generates major earthquakes across the entire Red River Fault, where infrastructures and residents are seriously threatened by the frequent earthquakes. InSAR observations feature a high spatial resolution and short intervals, ranging from several days to over a month, depending on the satellite revisit period.
On May 21, 2021, an earthquake struck the Yangbi city. This event provides a rare opportunity to look at the local tectonic and seismic risk in the north of the Red River Fault. We processed the Sentinel-1 SAR data with D-InSAR technology and generated the surface deformation caused by the Yangbi M_S6.4 earthquake occurring on May 21, 2021. Due to the abundant vegetation and moisture in Yunnan, significant atmospheric noise needs to be corrected for the derived InSAR displacement field. The results show a maximum deformation of~0.07m in line-of-sight for ascending track and~0.08m for descending track. The quality of interferogram on the ascending track is low, and only one of the quadrans can be distinguished, the rest of the interferogram is regarded as phase noise. However, the descending interferogram contains two deformation regions, with its long axis roughly along the NW-SE direction. The northeast part of interferogram moves towards the satellite, while the southwest part moves away from the satellite. The InSAR interferograms pattern shows a right-lateral strike-slip movement. Then, we combined coseismic displacement data obtained from the Global Navigation Satellite System(GNSS)and InSAR(both the ascending and descending)to invert the coseismic slip model of the Yangbi earthquake. The inversion test shows that our data cannot give strong constraints for the dip orientations, and the two slip models with opposite dip orientation can explain the observations within the noise level. No matter what the dip orientation is, the slip models show that the coseismic slip concentrated at depth of 2~10km, with a maximum slip of~0.8m, which corresponds to a moment magnitude of M_S6.4, and is consistent with body-wave-based focal mechanism. But the relocated aftershocks in 3 hours immediately after the mainshock reveal a SW-dipping fault plane 10km away to the west of Weixi-Qiaohou-Weishan Fault, we therefore conclude that the Yangbi earthquake ruptured a SW-dipping dextral fault, which is previously unknown. To analyze the effects of the Yangbi earthquake on the seismic risk of the regional dextral faults, we estimated the Coulomb stress change caused by our preferred slip model. The Coulomb stress at 7.5km depth is negative, indicating stress unloading, while the Coulomb stress at 15km depth is positive, indicating slightly loading, but still less than the empirical triggering threshold. The results indicate that Yangbi earthquake partially relieved the strain accumulated on the nearby faults, thus restraining the seismic risk of these faults.

InSAR coseismic deformation fields caused by the Maduo M_W7.3 earthquake occurring on May 22, 2021 were generated using the C-band Sentinel-1A/B SAR images with D-InSAR technology. The spatial characteristics, magnitude of coseismic deformation and segmentation of the seismogenic fault were analyzed. The surface rupture trace was depicted clearly by InSAR observations. In addition, the coseismic slip distribution inversion was carried out constrained by both ascending and descending InSAR deformation fields and relocated aftershocks to understand the characteristics of deep fault slip and geometry of the seismogenic fault. The regional stress disturbance was analyzed based on coseismic Coulomb stress change. The results show that the Maduo M_W7.3 earthquake occurred on a secondary fault within the Bayan Har block which is almost parallel to the main fault trace of the Kunlun Fault. According to field investigation, geological data and InSAR surface rupture traces, the seismogenic fault is confirmed to be the Kunlunshankou-Jiangcuo Fault. The rupture length of seismogenic fault is estimated to be~210km. The NWW direction is followed by the overall displacement field, which indicates a left-lateral strike-slip movement of seismogenic fault. The maximum displacement is about 0.9m in LOS direction observed by both ascending and descending InSAR data. The inversion result denotes that the strike of the seismogenic fault is 276°and the dip angle is 80°. The maximum slip is about 6m and the average rake is 4°. The predicted moment magnitude is M_W7.45, which is overall consistent with the result of GCMT. An obvious slip-concentrated area is located at the depth of 0~10km. The coseismic Coulomb stress change with the East Kunlun Fault as the receiver fault shows that the Maduo earthquake produced obvious stress increase near the eastern segment of the East Kunlun Fault. Thus the seismic risk increases based on the high interseismic strain rate along this segment, which should receive more attention. In addition, the coseismic Coulomb stress change with the Maduo-Gande Fault as the receiving fault indicates that the Maduo earthquake produced an obvious stress drop near the western part of the Maduo-Gande Fault, which indicates that the Maduo earthquake released the Coulomb stress of the Maduo-Gande Fault, and its seismic risk may be greatly reduced. However, there is a stress loading effect in the intersection area of the Maduo-Gande Fault and the Kunlunshankou-Jiangcuo Fault. Considering that aftershocks of Maduo earthquake will release excess energy, the greater earthquake risk may be reduced.