An M_S6.4 earthquake occurred in Yangbi county, Dali Prefecture, Yunnan on May 21, 2021. It is the biggest earthquake in the region during past 40 years, and its epicenter is located in the southwest boundary of the Sichuan-Yunnan rhomboid block. The type of this earthquake is of a typical “fore-main-residual” type, and cause no surface rupture, its aftershock sequence was not distributed along any known fault in the vicinity. There have been several research results which are on the seismogenic structure of this earthquake that occurred in Yangbi county, but it is also necessary to use a different type and source of data, methods and perspectives thinking angles to verify these results and supply new understandings. In this paper, based on the Yangbi sequence(M_L≥2.0)digital waveform recording and its earthquake phase data recorded by Yunnan Seismic Network between May 18, 2021 and June 13, 2021, the Yangbi sequence is relocated by HypoDD double-difference method and the spatiotemporal Yangbi sequence is also analyzed. The focal mechanism solution and centroid depth of the larger earthquakes in the sequence is obtained by the Cut & Paste(CAP)method. The results indicate that the Yangbi earthquake is distributed along the NW-SE direction as a whole, and its extension length is about 34km. The foreshock sequence has an obvious spatiotemporal migration and has round-trip activity characteristics, while the aftershock sequence has irregular spatiotemporal migration characteristics. The depth range of the aftershocks is mainly between 4km and 13km, and there were a few aftershocks whose depth are below 4km, which is reflecting that this series of earthquakes occurred in the shallow layer of the upper crust, and the rupture of the main earthquake may not extend to the surface. The trend of the belt of the aftershock is generally from the direction NW to SE, which has the obvious spatial segmentation: the aftershocks, which are located in the northwest of the main earthquake epicenter, are rare and relatively concentrated, while the aftershocks, which are located in the southeast, are dense and the width of the aftershock zone becomes larger; The foreshock sequence occurred in the southeast side of the epicenter of the main earthquake, which basically overlapped with the location of the dense segment of aftershocks, indicating that the sparse aftershocks in the northwest side of the main earthquake should belong to the triggering type, while the main earthquake rupture may belong to the unilateral rupture type extending from the epicenter to the SE direction. Besides, its fracture length is about 37km and its downdip width is about 16km. The depth cross-section of the foreshock sequence indicates that the focal depth of the sequence earthquake is generally deep in the southwest and shallow in the northeast, and the fault rupture surface is inclined to SW, with a large dip angle. While the depth cross-section of the aftershock zone shows that the main earthquake rupture is obviously segmented: the NW segment of the sequence has a simple structure, which is there existed one earthquake cluster, while the SE segment is relatively complex, which is there probably composed of two high-dip faults with SW inclination. The centroid depth of the 29 M_S≥3.0 events in the Yangbi sequence, mainly range from 3km to 13km, and their focal mechanism solutions are mostly of right-handed strike-slip type with a nodal plane of high dip Angle in NW-SE direction, and possess a certain normal fault component. In the NW segment of the sequence, the focal properties are mainly dextral strike-slip, and a few earthquakes which have positive fault components shows that there is a NW trending earthquake cluster with a SW inclination. Although the SE segment is still dominated by strike-slip faults, there are more positive faults, of which are two NW trending faults with the SW inclination. This difference reflects that the SE segment is likely to bifurcate and develop into two faults. The main shock is a right-handed strike-slip rupture, the source parameters of fault plane Ⅰ are strike 139°, dip 78° and slip angle -¹64°, and the source parameters of fault plane Ⅱ are strike 45°, dip 74°, and slip angle -12°. The centroid depth of this main shock is 5.2km, which is close to the predominant focal depth of 8.9km obtained by repositioning, indicating that the earthquake occurred in the upper crust, and the depth of seismic activity in the earthquake area is shallow. According to the spatial and temporal distribution characteristics of relocated sequence, combined with the focal mechanism solutions of theYangbi series in Yunnan in May 2021, it is indicated that both the Yangbi earthquake sequence and the source fault plane Ⅰ of main shock are NW-SE trending, which is in good agreement with the middle section of the Weixi-Qiaohou-Weishan fault(the closest to the epicentre). In addition, the focal mechanism solution of the sequence earthquakes is consistent with the properties of the Weixi-Qiaohou-Weishan fault, both of which are right-lateral strike-slip type. We conclude that the seismogenic structure of the Yangbi earthquake may be correlated with the Weixi-Qiaohou-Weishan fault, but the epicentre distribution of the sequence earthquakes is different from that of the Weixi-Qiaohou-Weishan fault. It is confirmed that in this fault, the seismogenic structure of this earthquake is a right-lateral strike-slip secondary fault with a steep dip toward SW on the west side of the southern section. Besides, in this fault, there is another NW trending branch fault in the SE section. In addition, combined with the results of the existing regional tectonic stress field in the focal area, it is believed that the earthquake should be caused by a right-handed strike-slip activity in the focal area which is under the force of NNW-SSE direction.

The May 21, 2021, Maduo M_S7.4 earthquake in Qinghai Province caused serious disasters in Maduo County and its surrounding areas. The GNSS co-seismic displacement field data can play a key role in quickly determining the influence range of the earthquake and serving for the rapid investigation. After the earthquake, we immediately collected the data of 18 GNSS stations surrounding the epicenter, including 7 stations that recorded 1Hz high-frequency observation data. Various data were used to rapidly obtain the GNSS co-seismic displacements, such as, the 15-minute high-frequency data, 5 hours after earthquake and multi-day displacement data. In this paper, we used three methods to obtain the co-seismic displacement, including the dynamic difference method for 1Hz frequency data by GAMIT/GLOBK Track module, and the static difference method for the post-seismic 5-hour data and for the pre- and post-seismic multi-day data by GAMIT/GLOBK. The results are shown as follows:
(1)The dynamic difference method for 1Hz frequency data by GAMIT/GLOBK Track module has ability to quickly process the data and acquire the co-seismic displacement. When using the high-frequency data to obtain co-seismic displacement by Track module, it is suitable for the near field stations which have a large value of co-seismic deformation. However, in the far field, the accuracy of the solution is at cm level restricted by the distance of stations. In addition, the result of the Track is influenced by the stability of reference station. Although the results obtained by Track are not accurate, it can be used as a method to quickly judge the characteristics and amount of coseismic surface motion.
(2)Comparing the results obtained from the post-seismic 5-hour data and the pre- and post-seismic multi-day data, the GNSS stations’ displacements have good consistency in the magnitude, direction and influence range, especially in the near field. The difference of the results by the two methods is from 1mm to 4mm. Considering the processing accuracy of the GAMIT/GLOBK, the value of the difference is not unreasonably high. When the displacement value is small, it is difficult to obtain accurate results. In addition, the direction of the pre- and post-seismic multi-day result is consistent with that from the post-seismic 5-hour data, and the value increased. If we regard the result of the pre- and post-seismic multi-day data as the result of one day data after the earthquake which is included in the post-seismic displacement, this phenomenon coincides with the afterslip deformation, and the difference may be caused by the afterslip, especially in the near field. Although the difference exists, taking into account the timeliness and the overall consistency, we believe that using the postseismic 5-hour data to quickly obtain the co-seismic displacement is credible in an emergency.
(3)Based on the analysis of various results, it is preliminarily judged that the Maduo earthquake is dominated by left-handed strike-slip. The maximum displacement at the station QHMD, which is about 40km from the epicenter, is about 24cm to the west and 8cm to the north. The earthquake affected the area around epicenter including Maduo, Xining, Dulan, Delingha in the north, and Zebra and Ganzi areas in the south. From the comparison of the results of the static difference method for the 5 hours and multi-day data, it is believed that the post-seismic deformation taking place in the near field is significant, and continuous attention is required in the later stages.

Late Cenozoic and modern tectonic deformation in mainland China is mainly characterized by active block movement, and the average slip rate of faults in the fault zone at the block boundary is an important indicator for quantitatively measuring the intensity of fault activity. The Tianshan Mountains, as the largest revival orogenic belt within Eurasia, with crustal movement basically manifesting as near north-south deformation and a large number of strong seismic surface ruptures, is one of the regions with strong tectonic movement and one of the key seismic hazard zones in China. Many experts have conducted relevant studies on the Tianshan region using GPS technology and have obtained some useful conclusions. These studies have not divided and analyzed the fault zone in detail, but only divided the Tianshan seismic zone into several major fault zones, such as the eastern and western sections of the northern Tianshan, and the eastern and western sections of the southern Tianshan. In order to analyze the activity characteristics of the major faults in the Tianshan region more clearly, this paper refines the major faults and selects 14 major active faults in combination with the distribution of active faults in China proposed by Xu Xi-wei et al. 18 blocks are divided into secondary blocks in Tianshan region, with the major active blocks in the Tianshan region taken as the boundary; The GNSS data of the surrounding areas of 1999—2015 in the Tianshan seismic zone are collected in this paper and used to calculate the velocity field results, and the block locking depth and the slip rate of major faults are calculated using the elastic block model to quantify the seismogenic capacity of major faults. Because the fault closure will produce obvious elastic deformation gradient around the fault, the greater the depth of fault closure is, the greater the influence will be. The fault locking depth can be constrained by the method of GPS data fitting of this model, and the influence of fault locking depth is verified by the method of GPS minimum residual RMS in this paper. According to the optimal locking depth obtained in this paper, the velocity field in Tianshan area is simulated and calculated. The residual mean value of the velocity field simulated by the elastic block model is small, and the average velocity error in the east-west direction is 1.57mm/a, the average velocity error in the north-south direction is 1.72mm/a. At the same time, the slip rate of major faults is obtained. The results show that: the horizontal shortening of the whole Tianshan region is significant, which is consistent with the tectonic background of the region, and the shortening value in the southern Tianshan region is higher than that in the northern Tianshan region; the shortening tensile rate is significantly larger than the slip rate, which shows that the fault zone at basin mountain junction in the Xinjiang Tianshan region is dominated by backwash activity; the extrusion rate in the western section of the southern Tianshan fault zone is in a high value state, reaching(-6.3±1.9)mm/a, which is higher than that in the eastern part of the southern Tianshan; the extrusion rate in the western part of the northern Tianshan is also higher than that in the eastern part. All the strong earthquakes of magnitude 8 and more than 80% of the strong earthquakes of magnitude 7 and above in China occurred in the boundary zones of active blocks according to the historical records, the motion characteristics of the boundary zone of active blocks play an important role in controlling the generation and occurrence of earthquakes, and the seismicity of faults may be quantitatively calculated by the loss of seismic moment. In this paper, we collected a list of strong earthquakes of magnitude 6 and above in the Tianshan area since 1900, estimated the seismic moment release of the main faults in the Tianshan seismic zone based on the above list, and compared it with the calculated seismic moment accumulation to obtain the seismic moment loss of the corresponding fault. Among them, the maximum release of seismic moment of the Beiluntai Fault reached 8.69×10¹⁹N·m; due to the release of several moderate and strong earthquakes, the seismic moment of middle of Bo-A Fault and Keping Fault have not reached the deficit state at present, the surplus is -1.85×10¹⁹N·m and -3.06×10¹⁹N·m, respectively; The smallest area of earthquake release is the northern Tianshan mountain front fault, which is only 0.11×10¹⁹N·m, because there was only one earthquake with a magnitude of 6 in 1907, and the earthquake accumulation reached 11.53×10¹⁹N·m, generating an earthquake deficit of 11.42×10¹⁹N·m, which could produce a magnitude of 7.3 earthquake. The results show that front margins of the northern Tianshan Fault, the Maidan Fault, the north section of Ertix Fault and the west of Kashihe Fault have a large seismic moment loss and have the potential to generate earthquakes of magnitude 7 and above, while Beiluntai Fault and the middle section of the Keping Fault show a surplus state, and there is no possibility of a strong earthquake in a certain period of time in the future.

The migrating and enriching of fault gas during dynamic load-unload process are important indexes to evaluate the stress state and tectonic activity of underground medium. The Hutubi underground gas storage provides a natural experiment site for the analysis of the relationship between the gas geochemistry and the stress-strain status. In this paper, the soil gas concentrations of Rn, CO₂, Hg and H₂ during the gas injection in the Hutubi underground gas storage were analyzed. The results show that the soil gas contents and changing trend are close to the background value in the non-reservoir area and fault zone, which may reveal the weak activity of the fault. Significantly higher concentrations of soil gas H₂ and Hg are observed in the gas storage area, where H₂ maximum reaches 5.551×10^-4 and Hg maximum reaches 53ng/m³. Moreover, the abnormal soil gas H₂ and Hg measurement locations are more consistent. The variation trends of soil gas Hg, H₂, Rn, and CO₂may be related to the different gas generation and response mechanisms. The concentrations of soil gas H₂ and Hg are sensitive to the variation of pressure and the development of cracks in the underground gas storage, and they can reveal gas injection's effect on fault activity. This study provides a new basis for analyzing the influence of gas injection and withdrawal in Hutubi underground gas storage on fault activity.

On 16^th September 2013, an M5.1 earthquake occurred in Badong County, Hubei Province, which is the biggest one since the first water impounding in 2003 in the head region of the Three Gorges Reservoir area. The crustal velocity information is needed to determine the earthquake location and focal mechanism. By comparison, the 1-D velocity structure model from Zhao was adopted in this study. Double difference location method was applied to determine the precise locations of the M5.1 earthquake sequence. Relocation results show that the dominant distribution of this sequence is along NEE direction. In order to understand its seismogenic structure, focal depth profiles were made. Profile AA' was along the sequence distribution, and the earthquake sequence extended about 12km. Focal depth of mainshock is deeper than that of aftershocks, and earthquake rupture propagated laterally southwestward. The seismic profile BB' and CC' were perpendicular to profile AA', which represent the dip direction. Both profiles show that the focal depth becomes deeper toward southeast, and dip angle is about 50°. It means that the possible seismogenic fault strikes NEE and dips southeast. Focal mechanism could provide more information for judging the seismogenic structures. Many methods could obtain the focal mechanism, such as P-wave first motion method, CAP method, and some other moment tensor methods. In this paper, moment tensor inversion program made by Yagi Y is adopted. 12 regional seismic stations ranging from 100~400km are picked up, and before the inversion, we removed the mean and trend. The seismic waveforms were band pass filtered between 0.05 and 0.2Hz, and then integrated into displacement. Green's functions were calculated using the discrete wavenumber method developed by Kohketsu. The focal mechanism of the M5.1 mainshock manifests that the NEE-striking fault plane probably is the possible seismogenic fault, which is consistent with the analysis of focal depth profiles. The focal mechanisms of the M_L≥2.0 aftershocks are retrieved by P-wave first motion method, and the nodal plane I is in accordance with the earthquake sequence distribution and the fault plane of the mainshock. FMSI program was adopted to inverse the stress field in the earthquake area, and the results show that the earthquake sequence is under the control of the regional stress field. The earthquake sequence occurred on the stage of slow water unloading, and ETAS model was introduced to testify the influences of water level fluctuations on earthquakes. The results denote that the reservoir played a triggering role in the earthquake, however, the NEE-striking seismogenic fault is the controlling factor.

On 27^th and 30^th March 2014, an M4.2 and M4.5 earthquake sequence occurred in Zigui County, Hubei Province, and the earthquake sequence type is double seismic type. The two earthquake sequences occurred at the water unloading stage of the 175m trial impounding, and G-R relations showed the similar characteristics with that of the tectonic earthquakes. In order to verify the influences of dam reservoir on earthquake triggering, ETAS model was introduced, the results showed that the slow water level changes had little impact on the occurrence of earthquake. Double difference precision relocation results indicated that the two earthquake sequences occurred at the intersection part of a NE-striking fault and the NNW-striking Xiannvshan Fault, and the preferred direction of aftershock distribution was separately NE and NNW. Moment tensor inversion method and P wave initial motion method were used to determine the focal mechanisms of the two earthquakes, and the results indicated that the two earthquakes were controlled by the regional tectonic stress field and were of reverse-slip type. Comprehensive analysis showed that the M4.2 earthquake was caused by a small-scale fault striking NE with a big dip angle. From the hypocenter profile, it can be seen that the M4.2 earthquake sequence was restrained by an east-dip fault, and the M4.5 earthquake sequence was the product under the conjugate action of the NE-striking fault and the NNW-striking Xiannvshan fault.

On 13, April, 2010, a great earthquake of M_W7.0 occurred in Yushu County, Qinghai Province, which is another big one in China since 2008 Wenchuan earthquake. And with seismic wave data, InSAR data and field investigations, many researchers studied the focal mechanism and source rupture process of this earthquake and many valuable results were obtained. However, there are some arguments on the rupture velocity. Some think that this earthquake is a super-shear rupture event, and some insist on opposite opinion. In order to explore whether it is a super-shear rupture event or not, this study chooses the teleseismic wave data recorded by 33 seismic stations with epicentral distances between 30～90 degrees, good azimuth coverage and high signal-noise ratio to reexamine the rupture process using Yagi's program. By comparison of different given rupture velocities in the range of 2.5～5.5km/s, it is found that rupture velocity of 4.7km/s yields the smallest normalized misfit between the observed and synthetic waveforms. And the inversion result is more in accordance with field observation. The relationship between subfault dimension, rise time and rupture velocity is discussed, which shows that the rupture velocity is not so dependent on the two parameters. And by teleseisemic analyses using an envelope deconvolution method with an empirical Green's function, the location and timing of the high-frequency event also show a rupture velocity of 4.7 to 5.8km/s, which is apparently greater than the shear wave velocity in this region. By comprehensive analyses, it can be concluded that the super-shear rupture exists in this earthquake. According to our inversion result, the strike, dip, and rake angle of this earthquake separately is 300, 88 and 4. Beach ball shows the seismogenic fault is of strike-slip type, which is consistent with the Ganzi-Yushu Fault. And the rupture extended to the surface on the northwest and southeast segments of the Yushu Fault with the length of 19km and 31km. Due to the existence of pull-apart Longbao Basin, the central part where the epicenter is did not rupture. By comprehensive analysis, super shear rupture is one of the main reasons that caused serious damage to Yushu County.

Based on field investigation in the reservoir head area of the Yangtze Three Gorges,combining with its seismogeological background and past research achievements,the reservoir head area is divided into 31 predictive units,and together with 8 impact factors,the possibility and magnitude of reservoir induced seismicity(RIS)are predicted using statistical forecasting model.The results show as follows:(1)it is quite possible that M_L=3.0～4.5 earthquakes will be triggered along the Jiuwanxi-Lukouzi Fault and Xiannvshan Fault in the reservoir area;(2)According to the analysis of earthquakes at home and abroad,the RIS takes place mainly in carbonatite and igneous rocks,and concentrates in karst developing segment,yet it is little possible that earthquake happens in clastic rock area.From the predictive results,it is possible to trigger M_L 4.5～6.0 earthquake in two places,the limestone area of southern Badong and the limestone area on the Gaoqiao Fault;(3)Around the Gaoqiao Fault,tectonic reservoir-induced earthquake is quite likely to occur.Geological investigation shows that the M_L 5.1 Longhuiguan earthquake in 1979 was possibly related to the Gaoqiao Fault which had a certain activity during the early period of reservoir impounding.The maximum magnitude of earthquake happening around the Gaoqiao Fault reaches to M3.3.The bigger earthquakes might be induced near the reservoir segment of Gaoqiao Fault along with the water storing to the design level.

The Nujiang fault zone can be divided into two sections of SN and NE strike and is arc in plane. Its deformation is mainly dextral shear of Himalayan age which could be divided into transpression deformation in early stage and transtension deformation in late stage and has different characteristics in two sections. The transpression structure in early stage has developed mylonite zone and its plunge angle of lineation was different in two sections. In the section of NE strike,both doxtral shear and thrusting are quite clear. The transtension structure in late stage developed mainly in southern end of two sections and shaved progressive trend from south to north since Miocene epoch according to distribution characteristic of the oldest stratum in basin. The complexity of Nujiang fault zone in Himalayan age was caused by the inhomogeneity of deformation in time and space. These deformation features are described and analysed in detail in the paper.