In response to the ongoing India-Eurasia collision in the late Cenozoic, the Tianshan orogenic belt was reactivated and experienced rapid uplift. Strong uplifted topography results in that the mountains propagate from the range front toward the foreland basin to form several fan-shaped foreland thrust belts both on its north and south sides. These foreland thrust belts accommodate the most north-south convergence strain and control the regional deformation pattern. However, in contrast to the well-studied foreland thrust belts, the kinematics and deformation rate of the transition area between different foreland thrust belts have not been well-documented. Therefore, it is still unclear how the crustal shortening in the foreland basins changes along the east-west direction. Further, the deformation characteristics and seismic hazard in this region are poorly understood because quantitative information on active deformation is lacking.

The Wensu foreland thrust belt is located in the Kalpin and Kuqa foreland thrust systems' transition areas. In contrast to the Kuqa and Kalpin foreland thrust belts at its east and west sides, the Wensu foreland thrust belt propagated approximately 20km toward the basin and only developed one row of active thrust fault-anticline belts, namely the North Wensu thrust fault-anticline belt. The North Wensu structural belt shows clear evidence of tectonic solid activity because the late Quaternary sediments and river terraces have been faulted. However, this structural belt's kinematics and late Quaternary deformation rate remain poorly constrained. This study quantifies its deformation mode based on field geological mapping across the anticline. Our results indicate that the North Wensu structural belt is a fault-bending fold. Based on interpretations of detailed high-resolution remote sensing images and field investigations, five levels of river terraces can be identified along the Kekeya River valley. By surveying of the displaced terraces with an unmanned drone, the crustal shortening values of ~20.7m、 ~35.3m and ~46.9m are determined for the T3, T4 and T5 terraces, respectively. Our optically stimulated luminescence(OSL)dating yields a depositional age of(9.02±0.55)ka for the T3 terrace, (24.23±1.58)ka for the T4 terrace, and(40.43±3.07)ka for the T5 terrace. Thus, we estimate a crustal shortening of ~1.31mm/a in the late Quaternary(since approximately 40ka), and approximately 2.29mm/a in the Holocene for the North Wensu structural belt. Our results indicate that the deformation rate of the North Wensu structural belt exhibits an obvious increase in the Holocene. This phenomenon indicates that the strong earthquake activity on the North Wensu thrust belt has increased significantly in the Holocene, implying an irregular activity habit of the strong earthquake recurrence cycle on this tectonic belt. The propagation deformation toward the basin of the Wensu foreland thrust belt is very limited. Therefore, we suggest that the foreland thrust belt is a thick-skinned nappe structure and is dominated by high-angle thrust faulting. The tectonic deformation in the Wensu region seems to be characterized by considered vertical growth. Although the deformation rate is small, the uplift amplitude is significant in this region.

On Jan. 19, 2020, a magnitude 6.4 thrust earthquake occurred in Jiashi County, Xinjiang Uygur Autonomous Region, and the seismogenic structure is the Keping Fault. The epicenter of the earthquake is located inside the gravity monitoring network, which covers more than 90 gravity monitoring points from Aksu and Kuche to Kashgar and Wucha in the west, Taxkorgan in the south and Hetian area in the southeast. In this paper, the high-precision gravity measurement data in the western margin of the Tarim Basin from 2013 to 2020 before and after the earthquake are used and three absolute gravity measurement points at Kuche, Taxkorgan and Wushi are taken to provide space-time gravity reference constraint. Then, the test board method is used to carry out the field source resolution test, and combined with the theoretical gravity anomaly value of actual measurement points obtained by the gravity forward modeling method, the field source model parameters are obtained by the inversion method. Then, in light of “seeking the source by field and combining the field and source”, using the surface repeated gravity observation data, the point value sequence obtained based on the Bayesian gravity adjustment method, and the field source inversion method for the time-varying gravity signal, the paper evaluates the basic principle of equivalent source inversion method and the field source monitoring capability of the research area. The actual repeated gravity observation data are tested and inversed to obtain spatial and temporal variation characteristics of gravity field sources, as well as the dynamic variation of regional gravity field sources and the structure characteristics of apparent density of multi-period field sources before and after the earthquake in the study area in the last 10 years. Finally, the variation process of gravity field in the seismogenic tectonic area of the 2020 Jiashi magnitude 6.4 earthquake is analyzed and discussed in combination. The study concluded that the gravity survey network on the western margin of the Tarim Basin has a good ability to distinguish field source parameters around the epicenter of the Jiashi M_S6.4 earthquake, but its ability to monitor the interior Tarim Basin between the tectonic system on the west side of Hetian and Aksu is relatively weak. The significant gravity change before the Jiashi M_S6.4 earthquake started in 2017. The apparent density change showed a regional increasing trend as a whole, and the morphology first showed the EW orientation and gradually turned to the NEE orientation, which is consistent with the structural direction of the Keping fault system. The apparent density change trend weakened in 2019. After the earthquake, the apparent density demonstrated a NEE-directed decrease. Before and after the earthquake, the apparent density of the field source increased from positive to negative, and after the earthquake, this apparent density change was more consistent with the tectonic trend and extended to the entire Keping fault system, indicating that the field source change signal obtained from gravity monitoring is closely related to the seismic event and the structure-controlled field source environment change. After the Jiashi M_S6.4 earthquake, the apparent density of the field source decreased, which was consistent with Keping tectonic system. The lower apparent density appeared in the area from the epicenter of the earthquake to Atushi, which may be related to the redistribution of fluid material in the earth’s crust caused by the rapid isostatic adjustment of crustal material near the fault after the earthquake. However, the gravity data observed in April 2020 may still contain the coseismic effect information of the earthquake. The research methods and results of this paper can provide valuable reference for the study of source characteristics of time-varying gravity field and the analysis and interpretation of seismic gravity precursor signals, and also have important indicative significance for understanding the crustal tectonic activity patterns around the seismogenic zone and fault zone.

Influenced by the far-field effect of India-Eurasia collision, Tianshan Mountains is one of the most intensely deformed and seismically active intracontinental orogenic belts in Cenozoic. The deformation of Tianshan is not only concentrated on its south and north margins, but also on the interior of the orogen. The deformation of the interior of Tianshan is dominated by NW-trending right-lateral strike-slip faults and ENE-trending left-lateral strike-slip faults. Compared with numerous studies on the south and north margins of Tianshan, little work has been done to quantify the slip rates of faults within the Tianshan Mountains. Therefore, it is a significant approach for geologists to understand the current tectonic deformation style of Tianshan Mountains by studying the late Quaternary deformation characteristics of large fault and fold zones extending through the interior of Tianshan. In this paper, we focus on a large near EW trending fault, the Baoertu Fault (BETF) in the interior of Tianshan, which is a large fault in the eastern Tianshan area with apparent features of deformation, and a boundary fault between the central and southern Tianshan. An M_S5.0 earthquake event occurred on BETF, which indicates that this fault is still active. In order to understand the kinematics and obtain the late Quaternary slip rate of BETF, we made a detailed research on its late Quaternary kinematic features based on remote sensing interpretation, drone photography, and field geological and geomorphologic survey, the results show that the BETF is of left-lateral strike-slip with thrust component in late Quaternary. In the northwestern Kumishi basin, BETF sinistrally offsets the late Pleistocene piedmont alluvial fans, forming fault scarps and generating sinistral displacement of gullies and geomorphic surfaces. In the bedrock region west of Benbutu village, BETF cuts through the bedrock and forms the trough valley. Besides, a series of drainages or rivers which cross the fault zone and date from late Pleistocene have been left-laterally offset systematically, resulting in a sinistral displacement ranging 0.93~4.53km. By constructing the digital elevation model (DEM) for the three sites of typical deformed morphologic units, we measured the heights of fault scarps and left-lateral displacements of different gullies forming in different times, and the result shows that BEFT is dominated by left-lateral strike-slip with thrust component. We realign the bended channels across the fault at BET01 site and obtain the largest displacement of 67m. And we propose that the abandon age of the deformed fan is about 120ka according to the features of the fan. Based on the offsets of channels at BET01 and the abandon age of deformed fan, we estimate the slip rate of 0.56mm/a since late Quaternary. The Tianshan Mountains is divided into several sub-blocks by large faults within the orogen. The deformation in the interior of Tianshan can be accommodated or absorbed by relative movement or rotation. The relative movement of the two sub-blocks surrounded by Boa Fault, Kaiduhe Fault and BETF is the dominant cause for the left-lateral movement of BETF. The left-lateral strike-slip with reverse component of BETF in late Quaternary not only accommodates the horizontal stain within eastern Tianshan but also absorbs some SN shortening of the crust.

Traditional method to generate Digital Elevation Model (DEM)through topographic map and topographic measurement has weak points such as low efficiency, long operating time and small range. The emergence of DEM-generation technology from high resolution satellite image provides a new method for rapid acquisition of large terrain and geomorphic data, which greatly improves the efficiency of data acquisition. This method costs lower compared with LiDAR (Light Detection and Ranging), has large coverage compared with SfM (Structure from Motion). However, there is still lack of report on whether the accuracy of DEM generated from stereo-imagery satisfies the quantitative research of active tectonics. This research is based on LPS (Leica Photogrammetry Suit)software platform, using Worldview-2 panchromatic stereo-imagery as data source, selecting Kumishi Basin in eastern Tianshan Mountains with little vegetation as study area. We generated 0.5m resolution DEM of 5-km swath along the newly discovered rupture zone at the south of Kumishi Basin, measured the height of fault scarps on different levels of alluvial fans based on the DEM, then compared with the scarp height measured by differential GPS survey in the field to analyze the accuracy of the extracted DEM. The results show that the elevation difference between the topographic profiles derived from the extracted DEM and surveyed by differential GPS ranges from -2.82 to 4.87m. The shape of the fault scarp can be finely depicted and the deviation is 0.30m after elevation correction. The accuracy of measuring the height of fault scarps can reach 0.22m, which meets the need of high-precision quantitative research of active tectonics. It provides great convenience for rapidly obtaining fine geometry, profiles morphology, vertical dislocations of fault and important reference for sites selection for trench excavation, slip rate, and samples. This method has broad prospects in the study of active tectonics.

Based on the digital waveforms of Xinjiang Seismic Network, the Hutubi M_S6.2 earthquake sequence (M_L ≥ 1.0) was relocated precisely by HypoDD.The best double-couple focal mechanisms of the main shock and aftershocks of M_L ≥ 4.0 were determined by the CAP method. We analyzed the characteristics of spatial distribution, focal mechanisms and the seismogenic structure of earthquake sequence. The results show that the main shock is located at 43.775 9°N, 86.363 4°E; the depth of the initial rupture and centriod is about 15.388km and 17km. The earthquake sequence extends unilaterally along NWW direction with an extension length of about 15km and a depth ranging 5~15km. The characteristics of the depth profiles show that the seismogenic fault plane dips northward and the faulting is dominated by thrusting. The nodal planes parameters of the best double-couple focal mechanisms are:strike 292°, dip 62° and rake 80° for nodal plane I, and strike 132°, dip 30° and rake 108° for nodal plane Ⅱ, indicating that the main shock is of thrust faulting. The dip of nodal planeⅠis consistent with the dip of the depth profile, which is inferred to be the fault plane of seismogenic fault of this earthquake. According to the comprehensive analysis of the relocation results, the focal mechanism and geological structure in the source region, it is preliminarily inferred that the seismogenic structure of the Hutubi M_S6.2 earthquake may be a backthrust on the deeper concealed thrust slope at the south of Qigu anticline. The earthquake is a "folding" earthquake taking place under the stress field of Tianshan expanding towards the Junggar Basin.

The Pishan M_S6.5 earthquake occurred in the west Kunlun piedmont area. According to the surface deformation data obtained by the Pishan M_S6.5 earthquake emergency field investigation team, combined with the positioning accuracy of spatial distribution of aftershocks information, the focal mechanism solutions and deep oil profile data, we think the Pishan M_S6.5 earthquake is a typical thrust faulting event, and the seismogenic structure is the Pishan reverse fault-anticline, which did not produced obvious surface fault zone on the surface. In the vicinity of the core of the Pishan anticline, we found some tensional ground fissures whose strikes are all basically consistent with the anticline. We propose that the surface deformation is caused by the folding and uplift of the anticline. The Pishan earthquake is a typical folding earthquake. The tectonic deformation of the west Kunlun piedmont is dominated by the thickening and shortening of the upper crust which is the typical thin-skinned nappe tectonic. The Pishan earthquake occurred in the frontal tectonic belt, the root fault of the nappe structure has not been broken, and we should pay attention to the seismic risk of the Tekilik Fault.

In the study of active faults, obtaining the exact age of the strata is an extremely important step. The optically stimulated luminescence (OSL) dating method, a technique closely related to thermoluminescence (TL), is developing extensively on dating for Quaternary sediments in recent years. Fukang Faults, located in the eastern Tianshan arc nappe tectonic zone, are typical arc thrusting faults. The dating samples collected from Dahuangshan trench of Fukang Fault zone are used to determine the activity of the fault. 23 OSL samples were obtained from the trench. We selected 4～11μm fine-grained quartz through pre-treatment process and analysed them by using sensitivity-corrected multiple aliquot regenerative-dose (SMAR) protocol. Equivalent dose (De) preheat plateau test is an often used approach to determine the appropriate preheat temperature in OSL dating. The preheat plateau test of sample LED12-297 shows that 220～260℃ are the appropriate preheat plateau temperature regions to get fundamental De. The dating results show that the OSL stratigraphic ages of the samples are consistent with stratigraphic sequence and that Fukang Fault is a Holocene active fault. It is found that the last event of Fukang Fault occurred (1.90±0.14) ka to (3.47±0.17) ka ago. The OSL ages and their related stratigraphic vertical displacement are used to calculate the vertical slip rate of the fault, which is 0.17mm/a.

The late-Quaternary deformation characteristics of the boundary fault zones are critical to understanding the crustal deformation of the Tianshan Mountains. Based on remote sensing image interpretation, field surveys, trenching and optically stimulated luminescence dating methods, we obtain the reliable activity evidences of the Maidan Fault in late-Quaternary.
The Maidan Fault is the boundary fault of the Tianshan Mountains and Tarim Basin. The fault, with a total length of 400km and the maximum width about 15～17km, comprises a series of secondary faults. During the late Quaternary, the fault was still very active. The fault dislocated the late-Quaternary landform surfaces, forming obvious scarps on the surfaces. The height of the scarps range several to hundred meters. Trench excavation shows that paleoearthquakes occurred on the faults during late Holocene. The vertical displacement caused by the last paleoearthquake event is above 2m. The different late Quaternary landforms with different vertical displacement heights indicate that several strong earthquake events have occurred on the Maidan Fault since the late Quaternary.
The discovery of activity on the Maidan Fault shows that the deformation does not focus solely on the newly born reverse fault and fold belt. Faults at the root of Kalpin nappe system have also participated in absorbing and partitioning some of the tectonic deformation. This phenomenon may explain why the shortening rate got by geology method of the Kalpin nappe structure is much less than that obtained by GPS. This deformation mode of the Tianshan orogenic belt is obviously different from the piggyback propagation as considered previously. The activities of the Tianshan root faults migrated to the frontal faults of the piedmont nappe, and the root fault activity weakened gradually. But the activity in Kalpin nappe structure does not accord with this mode. The root faults and the frontal faults of the Kalpin nappe structure are all obviously active, which indicates the nappe structure in the southwestern Tianshan is an out-of-sequence, or a non-sequence thrust system. This kind of structure mode brings new challenges to us in constructing seismogenic tectonic models and assessing seismic risk.

The Wangjiagou Fault set,a set of Holocene active faults,is located at western suburbs of Urumqi City.The faults dislocated the gravel platform of the mid Pleistocene and the third level terrace of the Wangjiagou east bank,generating apparent fault scarps of opposite-slope direction on the surface with clear geomorphic traces.There are a series of deformation indications on landform,such as seismic fault,scarp and upheaval.In the field,thirty-nine groups of data were measured by using line tape along the fault.Among them,six were measured on the third level terrace of the Wangjiagou,and the others on the mid Pleistocene platform.Based on the data measured across the fault,we obtain that the height of the scarps is 0.4～1.6m and the width of the fault deformation is about 50m on the third level terrace.And on the mid Pleistocene platform,the height of scarps is 1.5～5.0m and the width of the deformation is about 90m.After comparing the profile of strong topographic deformation zone with the trench section,we primarily recognize that the ratio of hanging wall to foot wall deformation width is 2: 1approximately.The widths of strong surface deformation belt on the mid Pleistocene platform and the third level terrace on the two walls are 60m,30m and 33m,17m,respectively.

The Wanyaogou Fault dislocates the Jurassic sandstone.The tilted bedrock becomes a natural barrier to the groundwater,and a water-rich stratum formed in the footwall which caused obvious resistance difference between the two walls of the fault.The electrical imaging is an effective way to detect the fault on this condition.The experimental electrical resistivity tomography survey was conducted to detect the Wanyaogao Fault.The results of 2-D resistivity inversion indicate that the electrical structures on both sides of the fault present obvious difference,the resistivity of the hanging wall is high,while that of the foot wall is low.And the interface of the high and low resistance regions inclines to the low resistance region.The electrical resistivity tomography survey was also conducted to detect other faults in Urmuqi which have similar tectonic characteristics with Wanyaogou Fault.And the electrical structures appear the similar abnormality.So the abnormal characteristic is an important indicator and basis for identification of fault in the Urumqi region.The faults in Urmuqi are almost all high-obliquity reverse faults.After comparing the electrical imaging with the trench section,we find the fault is not coincident with the borderline between the high and low resistance,but lies in the high resistance region.The fault inclination is reverse to the gradient direction of isolines.The fault location is near to the inflexion of the upper isolines.

The Kuqa depression is located in the middle segment of the southern Tianshan Mountains. There are four E-W extending rows of reverse fault and anticline zones in the depression. From the south Tianshan Mountains towards the Tarim basin, they are the mountain piedmont, the Kasangtuokai, the Qiulitag and the Yaken reverse fault and fold zones. After a month field working, we find the crustal shortening of the Kuqa depression in late Quaternary is almost caused by the Kasangtuokai, the Qiulitag and the Yaken reverse fault and fold zones. The reverse fault and anticline zones in the Kuqa depression are very different in tectonic feature. We accurately surveyed these tectonics with total station and differential GPS in order to get a new cognition of the deformation characteristic and the slip rate. Based on the deformation characteristics of conceptual fault-propagation fold and field investigation, we think the deformation of the fault-propagation fold in the Kuqa depression is caused by faulting rather than folding. The crustal shortening rate caused by the fault is approximately near to the actual rate. So we only surveyed the deformation near the fault. The Kasangtuokai anticline is a fault-propagation fold. From late Quaternary, the deformation of Kasangtuokai anticline is mainly caused by total-uplift of the hanging wall. The deformation rate is about 1.0～2.0mm/a. The deformation feature of the Dongqiulitag anticline is similar to that of the Kasangtuokai, while the crustal shortening rate is little more than that of Kasangtuokai, about 2.5mm/a. The Qiulitag anticline is a very complicated tectonic. It is a fault-bend fold. There are two reverse faults on the core and the north limb of the Qiulitag anticline. Its tectonic deformation includes two parts: the fold rise and the uplift of the hanging wall of the fault. By surveying and dating, we get the crustal shortening rate of the Qiulitag anticline limb of about 1.06～2.0mm/a. Considering the shortening of the core fault and southern limb, the total rate is possibly more than 3.0mm/a. The Yaken anticline is a blind thrust fault-anticline fold. Its shortening rate is 1.5～2.0mm/a. So the total crustal shortening rate of the Kuqa depression is more than 5.0～7.0mm/a from late Quaternary.

The distribution, tectonic style and new displacement and other features of the main active tectonics in Kuqa depression in the front of southern Tianshan were introduced in this paper. This depression is an “eye-shaped” tectonics in plane. It is composed of two fold zones in the south and north respectively. The northern one close to the main southern Tianshan Range is a southward thrusting fault-folding system. The most recent active fold in this system is the Kasangtuokai fold belt. The southern one close to the Tarim Basin is a northward thrust fault-fold system. The recent active folds in this system are the Qiulitage fault-fold belt and other young folds in its south, such as the Yaken fold. These two folding systems embrace the Baicheng Basin which likes an eyeball in the eyelids. The Kasangtuokai Fault with a length of 60km in the north and the Qiulitag Fault with the length over 200km in the south are the most important active faults in Kuqa depression. The younger and smaller folds in the south of Qiulitag anticline belt indicate the southward propagation of the thrust fault in Kuqa depression. The petroleum seismic profiles show that the folding and faulting processes are controlled by the detachment fault between the sediment cover and the basement of the basin. The depth of the detachment fault is around 10km and possibly defines the main seismogenic zone in the depression area.

The M_S 6.8 Bachu-Jiashi earthquake of Feb.24, 2003 occurred in the western Tarim Basin and is possibly the continuation of the Jiashi strong earthquake swarms in 1997-1998. However, its focal mechanism and rupture process are different from that of the Jiashi strong earthquake swarms, according to our preliminary study on its seismic tectonics with geomorphologic information from satellite images, the deep structures from the petroleum seismic exploration, the macro damage and isoseismic features from field investigation, the relocation of the epicenters of the aftershocks, and the regional seismic tectonics from both deep and surface tectonics. The occurrence of the M_S 6.8 Bachu-Jiashi earthquake is closely related with the revealed reverse fault on the Maigaiti slope belt between the Bachu uplift and Kashi depression in western Tarim Basin. The sites of the ground fissures found in the field fit with the revealed reverse fault. Isoseismal features are also corresponding to the rupture direction of the fault. These evidences indicate that the M_S 6.8 Bachu-Jiashi earthquake is the result of the southward rupturing from deep to shallow along a north-dipping reverse fault in Tarim Basin. This reverse fault is possibly the result of the propagation of the thrust fault-fold system named Kalpintag thrust belt in the front of Tianshan.