The M_S7.1 earthquake in Wushi, Xinjiang on January 23, 2024, represents the largest earthquake in the Tianshan seismic belt since the 1992 Suusamyr M_S7.3 earthquake in Kyrgyzstan. Preliminary precise aftershock localization and initial field investigations indicate an NE-trending aftershock zone with a length of 62km that is concentrated at the mountain-basin transition area. This event produced geological hazards, including slope instability, rockfalls, rolling stones, and ground fissures, primarily within a 30-kilometer radius around the epicenter. The epicenter, located approximately 7 kilometers north of the precise positioning in this study, witnessed a rapid decrease in geological hazards such as collapses, with no discernible fresh activity observed on the steep fault scarp along the mountainfront. Consequently, it is inferred that the causative fault for this main shock may be an NW-dipping reverse fault, with potential rupture not reaching the surface.

Moreover, a surface rupture zone with a general trend of N60°E, extending approximately 2 kilometers, and displaying a maximum vertical offset of 1m, was identified on the western side of the micro-epicenter at the Qialemati River. This rupture zone predominantly follows the pre-existing fault scarp on higher geomorphic surfaces, indicating that it is not new. Its characteristics are mainly controlled by a southeast-dipping reverse fault, opposite in dip to the causative fault of the main shock. The scale of this 2-kilometer-long surface rupture zone is notably smaller than the aftershock zone of the Wushi M_S7.1 earthquake. Further investigation is warranted to elucidate whether or not the M_S5.7 aftershock and the relationship between the SE-dipping reverse fault responsible for the surface rupture and the NW-dipping causative fault of the main shock produced it.

In the global scale, ten destructive earthquakes with magnitude larger than 7 happen on average each year. Yet the number of small earthquakes with limited or even no damage but recordable by seismographs(magnitude between 2.5 and 4.5)is over one million per year. In between, there are hundreds to thousands of earthquakes with moderate to strong magnitude(magnitude between 5.5 and 6.5)with notable destructiveness. The massive moderate to strong earthquakes are often less noticed or even overlooked, with only very few exceptions which caused human casualties and/or structure damages due to the very shallow focal depths. For medium earthquakes, the traditional seismology means can obtain the source mechanism solution of earthquake, but because of the inherent fuzziness of the source mechanism, it cannot distinguish the fault plane from the auxiliary nodal planes, because earthquakes of this magnitude usually do not produce surface rupture, and the result error is large, so it is not suitable for the study of medium and small earthquakes. It is of fundamental significance to further study the source fault of the moderate earthquakes, and more independent methods other than traditional seismology, such as satellite geodesy are needed. As one of the most applied satellite geodesy technique, interferometry of SAR(InSAR)satellite images are commonly used to obtain coseismic deformation related to earthquakes. InSAR has very high spatial sampling, though the temporal sampling is very low, which is several days to over a month depending on the satellite revisit span. The precision of coseismic deformation by InSAR can reach 2~3cm, which is good enough to obtain the surface deformation caused by a moderate earthquake. It is noted that InSAR coseismic measurements can detect 1-dimensional(1D)deformation along Line-of-Sight(LOS)direction. With multiple observing modes including descending and ascending, the InSAR deformation data is very useful for identifying surface ruptures, and for source fault plane discrimination. As a new geodetic observation technology, InSAR uses the elastic dislocation model to obtain source parameters, and the inversion results of fault parameters and slip distribution are more reliable. On September 24th, 2019, an M_W6.0 earthquake hit New Mirpur, Pakistan. The nearest known fault to the epicenter is the Main Frontal Thrust on its south side. We used the Sentinel-1A SAR imagery(TOPS-model)to reconstruct the InSAR coseismic deformation fields generated by the 2019 M_W6.0 Pakistan earthquake along the ascending and descending tracks. The ascending and descending deformation fields indicate that coseismic deformation is asymmetric by a trend of NW-SE in the south secondary fault of the Himalayan frontal thrust fault, with a maximum LOS displacement of~0.1m. The structures of ascending and descending deformation are highly consistent with each other, but the LOS displacement of southern side is obviously larger than the northern side. The continuous change of interference fringes between uplift and subsidence areas shows that there is no coherent phenomenon caused by excessively large deformation gradient or surface rupture, which indicates that the seismic fault rupture did not reach to the ground surface. Two initial fault models constrained by InSAR deformation, with a southwest-dipping and northeast-dipping fault, were utilized in the inversion. We finally determined the northeast-dipping fault as the seismogenic fault by joint inversion of ascending and descending observations, combined with tectonic setting. Our fault model suggests that an obvious slip concentrated area is located in the depth of 2~4km, with a peak slip of~0.64m and a mean rake angle of~125°. The north-dipping thrust motion with a small amount of strike-slip component dominated the faulting. The earthquake occurred in the low-dipping subduction zone between the Indian and Eurasian plates. The dip angle of the fault plane is relatively low. When the fault is ruptured, the upper wall thrust southwards and the north wall subducted northwards. Due to the compressional nappe structure, the front end of the upper wall was uplifted and the back end was stretched to become the subsidence area. Seismogenic fault is the south secondary fault of the Himalayan frontal thrust fault inferred from our coseismic fault model and rupture kinematic features. Active faults on the land have caused many large destructive earthquakes, resulting in surface faults and promoting the development of tectonic landforms. The detailed observation of coseismic surface rupture not only provides basic information for understanding the earthquake itself and estimating the earthquake recurrence period, but also helps to interpret the tectonic and geomorphic features in other areas. Since the M_W6.0 earthquake in Pakistan in 2019, no studies have been reported yet on this earthquake using InSAR technology, so the study of this earthquake provides a rare opportunity to assess the seismic risk of active thrust faults and to study the seismicity of northern Pakistan.

The eastern Himalaya syntaxis is located at the southeastern end of the Qinghai-Tibet Plateau and is the area where the Eurasian plate collides and converges with the Indian plate. The Namjabawa is the highest peak in the eastern section of the Himalayas, and the Yarlung Zangbo River gorge is around the Namjabawa Peak. The NE-striking Aniqiao Fault with right-lateral strike-slip is the eastern boundary fault of the Namjabawa syntaxis. Motuo Fault is in the east of and parallel to the Aniqiao Fault, distributing along the valley of the Yarlung Zangbo River. The section of Yarlung Zangbo River valley at the eastern side of the Namjabawa area is located in the southern foothills of the Himalayas and belongs to the subtropical humid climate zone with dense tropical rainforest vegetation. Dense vegetation, large terrain elevation difference, strong endogenetic and exogenic forces, and abundant valley deposition bring enormous difficulty to the research on active faults in this area.
Since 1990s, surface morphology can be quantitatively expressed by digital elevation models as the rapid development of remote sensing technology. Geomorphic types and their characteristics can be quantified by geomorphological parameters which are extracted from DEM data, describing geomorphologic evolution and tectonic activity. But to date, researches based on quantitative geomorphic parameters are mainly focus on the differential uplift of regional blocks. In the study and mapping of active faults, surface traces of active faults are acquired by visual interpretation of remote sensing images. It has not been reported to identify the location of active faults via the change of quantitative geomorphic parameters. The distribution map of topographic elevation variation coefficient is suitable to reflect the regional erosion cutting and topographic relief, and the places with higher topographic elevation variation coefficient are more strongly eroded. In this paper, we attempt to identify the active faults and explore their distribution in the Yarlung Zangbo Gorge in the east of the Namjabawa Peak based on the application of two quantitative geomorphic parameters, namely, the topographic slope and the elevation variation coefficient.
Using the DEM data of 30m resolution, two quantitative geomorphic parameters of topographic slope and elevation variation coefficient in Namjabawa and its surrounding areas were obtained on the ArcGIS software platform. On the topographic slope distribution map, the slope of the eastern and western banks of the Yarlung Zangbo River near Motuo is steep with a slope angle of more than 30°. Under the background of steep terrain, there are gentle slope belts of 5°~25° distributing intermittently and NE-striking. On the distribution map of topographic elevation variation coefficient, the elevation variation coefficient of the Yarlung Zangbo River near Motuo is greater than 0.9. On the background of the high topographic fluctuation area, it develops gently topographic undulating belts with elevation variation coefficient of 0.2~0.9. The belts are intermittently distributed and northeastern trending. Through the field geological and geomorphological investigation and trench excavation, it is found that the abnormal strips of the above-mentioned geomorphological parameters are the locations where the active faults pass. The above results show that the quantitative analysis of the topographic slope and the coefficient of variation of elevation can help us find active faults in areas with large terrain slope, serious vegetation coverage and high denudation intensity.

The eastern Himalayan syntaxis is located on the leading edge of Indian-Eurasian plate collision, and the uplift rate of Namche Barwa area is higher than that of the peripheral zones, which is considered as the core position of the eastern Himalayan syntaxis(Uplift Center).It is indicated according to the recent regional earthquake observation results that, the seismic activity is poor in the area of Namche Barwa, but with strong seismic activity in its southeast region. In order to study the current geodynamical characteristics of the eastern Himalayan syntaxis, the elevation frequency distribution and hypsometry curve of Namche Barwa area, its northwest and southeast as well as the northeast Assam area is analyzed using DEM data. It is shown according to the result that, the Namche Barwa area is in the mature stage of erosion and the regional tectonic uplift and denudation are in the highly balanced status. Influenced by plateau-climate weather effect, the denudation of this area is relatively poor, which indicates that the uplift of the Namche Barwa area is relatively slow at present. The geomorphology in the northwest and southeast as well as in northeast Assam is in young evolutionary phase, belonging to erosive infancy, and the geomorphology of northeast Assam is closer to the early stage of infancy. The geomorphic evolution stage on northwest side reflects that the regional erosion is poor and it still belongs to plateau-climate area; Influenced by south subtropical monsoons, there is rich rainfall in the area from southeast Namche Barwa to Assam area, and this area still belongs to erosive infancy, even the geomorphic development degree of northeast Assam is lower as it suffers from strong erosion effect, which means that the tectonic uplift in east Namche Barwa is very intensive, and the northeast Assam has the highest uplift rate. It is considered according to the research that, under the mode that India Plate moves towards the north at present, the core position of the eastern Himalayan syntaxis(Uplift Center)moves towards the southeast, and the new core position may be located in northeast Assam, where there is intensive regional tectonic uplift with high potential of great earthquake.

Motuo Fault locates at the east of Namjagbarwa Peak in eastern Himalayan syntaxis.Based on the remote sensing interpretation,the previous work,and with the field investigation,this paper obtains the spatial distribution and movement characteristics of Motuo Fault in China,and geological evidences of late Quaternary activity.Two trenches in Motuo village and Dongdi village located in Yalung Zangbo Grand Canyon reveal that the Motuo Fault dislocates the late Quternary stratum and behaves as a reverse fault in Motuo village and normal fault in Dongdi village.Motuo Fault is dominated by left-lateral strike-slip associated with the faulted landforms,with different characteristics of the tilting movement in different segments.The trench at Didong village reveals the latest stratum dislocated is~2780±30 a BP according to radiocarbon dating,implying that Motuo Fault has ruptured the ground surface since late Holocene.The movement of left-lateral strike-slip of Motuo Fault is related to the northward movement process of Indian pate.

The concentration of soil gas He, H₂, N₂, O₂, CH₄, C₂H₆, Rn, Hg and flux of soil gas He, H₂, CH₄, Rn, Hg were surveyed at four sites(Xiaokou,Bazhiyao,Caixiangpu and Xiaonanchuan)in the southeastern part of Haiyuan Fault.Soil-gas concentrations of more than 200 samples were obtained.The results show that the background values of N₂/O₂,Hg,Rn were 4.2,50.4ng/m³and 5.8k Bq/m³,respectively. The maximum concentrations of He and CH₄ were 65.3 and 537.7ppm,respectively,at the end of the southeastern part of Haiyuan Fault.Furthermore,soil gas He and CH₄ were intensively degassed.The maximum flux of He and CH₄ in soil gas was 6.9and 390mg m^-2d^-1,respectively.These may be caused by stress concentration at the end of the southeastern part of Haiyuan Fault.H₂ and Rn in soil gas were powerful components as indicators of location of the southeastern part of Haiyuan Fault.The maximum concentrations of H₂ and Rn in soil gas were 369.7ppm and 38.3k Bq/m³ near the middle of the southeastern part of Haiyuan Fault.The maximum fluxes of H₂ and Rn in soil gas were 5.5mg m^-2d^-1 and 828.6m Bqm^-2s^-1,respectively.These may be related with the intensive rupture of the middle of the southeastern part of Haiyuan Fault.The anomalies of Hg in soil gas at the fault were good reference indicators.The maximum flux of Hg in soil gas was 211.2ng m^-2h^-1.