The Bolokenu-Aqikekuduke Fault(Bo-A Fault)is a large-scale right-lateral strike-slip fault zone, which starts in Kazakhstan in the west, enters China along the NW direction, passes eastward through Alashankou, Lake Aibi and the southwestern margin of Turpan Basin, and terminates in the Jueluotage Mountain, with a total length of about 1 000km. At present, researches on the fault mainly focus on the area from Lake Alakol to Jinghe.
Through satellite images, it can be found that the Bo-A Fault enters the southwestern margin of the Turpan Basin in the SE direction, and offset various landforms such as river terraces and alluvial fans, forming clear linear features on the surface, which indicates that there have been obvious activities since late Quaternary in this fault section. However, no detailed research has been carried out on the tectonic deformation characteristics of the Bo-A Fault in this area. The active characteristics of the faults in the southwestern margin of the Turpan Basin are studied, and the results are helpful to understand the role of the Bo-A Fault in the Cenozoic tectonic deformation of the Tianshan Mountains.
The study area is located in the southwestern margin of the Turpan Basin, where three stages of alluvial-proluvial fans are developed. The first-stage alluvial-proluvial fan is called Fan3, which was formed earlier and its distribution is relatively limited, formed roughly in the early late Pleistocene; The second-stage alluvial-proluvial fan is called Fan2, which is the most widely distributed geomorphological surface in the study area. The geomorphic surface in this period was roughly formed from the late Pleistocene to the early Holocene. The third-stage alluvial-proluvial fan is called Fan1, which belongs to the Holocene accumulation, most of which are located at the outlet of gullies near the mountain passes, forming irregular fan-shaped inclined surfaces.
To the west of Zulumutaigou, the fault offset the Fan3 alluvial-proluvial fan, forming dextral dislocation and fault scarp of the gully on the surface. The measurement shows that the amount of the dextral dislocation produced by the fault is between 22m and 40m. The height of the scarp is 3.9~4.2m. The section exposed by the fault shows that the Paleozoic bedrock thrust northward onto the Quaternary gravel layer, and the fault fracture width is about 1m, which reflects that the Bo-A Fault also has a certain thrust component. On the east bank of Zulu Mutaigou, the fault offset the Fan3 alluvial-proluvial fan, and the measurement results show that the offset of the gully is between 46.3m and 70.2m. To sum up, the movement mode of the Bo-A Fault in the study area is dominated by dextral strike-slip.
On the Fan2 alluvial-proluvial fan at the northwest of Zulu Mutaigou, there are two secondary faults arranged in a right-step en-echelon pattern, forming high scarps with a height of 1.6~3.9m on the surface. Trench profiles reveal that both faults are SW-dipping thrust faults, thrusting from south to north, and they are preliminarily judged to be formed by the expansion of the Bo-A Fault into the basin.
There are mainly three stages of alluvial-proluvial fans developed in the study area. Although no specific dating results have been obtained in this work, we believe that the age of the Quaternary landforms in the study area is the same as that in the Chaiwopu Basin, which is only separated by a mountain. Quaternary geomorphological ages are basically the same. Through geomorphological comparison, we believe that the age of Fan2 alluvial-proluvial fan is 12~15ka, and the age of Fan3 alluvial-proluvial fan is 74ka. It is estimated that the dextral slip rate of the Bo-A Fault is about 1mm/a since the formation of Fan3, and the vertical movement rate of the fault is about 0.13~0.32mm/a since the formation of Fan2.
According to GPS observations and geological data, the NS-direction shortening rate in the East Tianshan area can reach 2~5mm/a. Through this study, it can be found that the Bo-A Fault also plays a role in regulating the near-NS-trending compressive stress in the East Tianshan area by accommodating the compression strain inside the Tianshan Mountains mainly through the NWW-directed right-lateral strike-slip motion. In addition, in the study area, the youngest fault scarp is located on the Fan2 alluvial-proluvial fan at the north of the main fault. It is preliminarily judged that the latest activity of the Bo-A Fault has a tendency to migrate from the mountain front to the basin.

The Bolokenu-Aqikekuduk fault zone(B-A Fault)is a 1 000km long right-lateral strike-slip active fault in the Tianshan Mountains. Its late Quaternary activity characteristics are helpful to understand the role of active strike-slip faults in regional compressional strain distribution and orogenic processes in the continental compression environment, as well as seismic hazard assessment. In this paper, research on the paleoearthquakes is carried out by remote sensing image interpretation, field investigation, trench excavation and Quaternary dating in the Jinghe section of B-A Fault. In this paper, two trenches were excavated on in the pluvial fans of Fan2b in the bulge and Fan3a in the fault scarp. The markers such as different strata, cracks and colluvial wedges in the trenches are identified and the age of sedimentation is determined by means of OSL dating for different strata. Four most recent paleoearthquakes on the B-A Fault are revealed in trench TC1 and three most recent paleoearthquakes are revealed in trench TC2. Only the latest event was constrained by the OSL age among the three events revealed in the trench TC2. Therefore, when establishing the recurrence of the paleoearthquakes, we mainly rely on the paleoearthquake events in trench TC1, which are labeled E1-E4 from oldest to youngest, and their dates are constrained to the following time ranges: E1(19.4±2.5)~(19.0±2.5)ka BP, E2(18.6±1.4)~(17.3±1.4)ka BP, E3(12.2±1.2)~(6.6±0.8)ka BP, and E4 6.9~6.2ka BP, respectively. The earthquake recurrence intervals are(1.2±0.5)ka, (8.7±3.0)ka and(2.8±3)ka, respectively. According to the sedimentation rate of the stratum, it can be judged that there is a sedimentary discontinuity between the paleoearthquakes E2 and E3, and the paleoearthquake events between E2 and E3 may not be recorded by the stratum. Ignoring the sedimentary discontinuous strata and the earthquakes occurring during the sedimentary discontinuity, the earthquake recurrence interval of the Jinghe section of B-A Fault is ~1~3ka. This is consistent with the earthquake recurrence interval(~2ka)calculated from the slip rate and the minimum displacement. The elapsed time of the latest paleoearthquake recorded in the trench is ~6.9~6.2ka BP. The magnitude of the latest event defined by the single event displacement on the fault is ~M_W7.4, and a longer earthquake elapsed time indicates the higher seismic risk of the B-A Fault.

The Bolokonu-Aqikekuduke fault zone(Bo-A Fault)is the plate convergence boundary between the middle and the northern Tianshan. Bo-A Fault is an inherited right-lateral strike-slip active fault and obliquely cuts the Tianshan Mountains to the northwest. Accurately constrained fault activity and slip rate is crucial for understanding the tectonic deformation mechanism, strain rate distribution and regional seismic hazard. Based on the interpretation of satellite remote sensing images and topographic surveys, this paper divides the alluvial fans in the southeast of Jinghe River into four phases, Fan1, Fan2, Fan3 and Fan4 by geomorphological elevation, water density, depth of cut, etc. This paper interprets gullies and terrace scarps by high-resolution LiDAR topographic data. Right-laterally offset gullies, fault scarps and terrace scarps are distributed in Fan1, Fan2b and Fan3. We have identified a total of 30 right-laterally offset gullies and terrace scarps. Minimum right-lateral displacement is about 6m and the maximum right-lateral displacements are(414±10)m, (91±5)m and(39±1)m on Fan2b, Fan3a and Fan3b. The landform scarp dividing Fan2b and Fan3a is offset right-laterally by (212±11)m. Combining the work done by the predecessors in the northern foothills of the Tianshan Mountains with Guliya ice core climate curve, this paper concludes that the undercut age of alluvial fan are 56~64ka, 35~41ka, 10~14ka in the Tianshan Mountains. The slip rate of Bo-A Fault since the formation of the Fan2b, Fan3a and Fan3b of the alluvial-proluvial fan is 3.3~3.7mm/a, 2.2~2.6mm/a and 2.7~3.9mm/a. The right-lateral strike-slip rate since the late Pleistocene is obtained to be 3.1±0.3mm/a based on high-resolution LiDAR topographic data and Monte Carlo analysis.

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.

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.

High-resolution satellite image interpretation and field investigation indicate that the surface rupture zone produced by the Yutian M_S7.3 earthquake is～25km long along a NS-trending fault at the western piedmont of a snow-covered range at the upper reach of the Yurungongkash River,about 20km south of the Ashikule Volcanoes.The surface rupture zone consists of different striking ruptures with both normal and left-lateral faulting components.The maximum left-lateral and vertical co-seismic slips measured in the field are～1.8m and～2.0m,respectively.Its seismogenic NS-trending fault belongs to the secondary structure at the NE-trending tensile area of the southwestern end of the Altyn Tagh Fault,which conforms to the eastward escape of the Kunlun-Qaidamu-Qilian block,relative to the Western Kunlun block.