Digital topographic analysis, an important means in the research of active tectonics and tectonic geomorphology, has increasingly become one of the principal tools in the identification of active tectonic features and understanding of the development of the earth’s surface process. Indoor interpretation of surface fault trace plays a key role in the digital topographic analysis as it can provide the foundation for setting priorities and defining strategies in the subsequent field investigation. At present, the extraction of fault traces is often realized by assisting the traditional visual interpretation through the image enhancement method. The relevant subjective assessments lead to the amount of work and usually cause different results due to the differences in the interpretation experience of actual operators. At the same time, the field of quantitative research on geomorphic parameters is evolving very rapidly with the advances in the popularity of high-resolution digital topographic data. Therefore, intelligent and automatic extraction of surface fault traces has gradually become a promising research direction. The methods based on machine learning often rely heavily on the good programming foundation of the operator, which is a visible technical barrier. We present a semi-automated method using an ArcGIS toolbox with a set of tools to extract surface fault traces based on geomorphic constraints. The Hutubi and Dushanzi faults are two typical thrust faults located on the northern piedmont of the Tianshan Mountains and are chosen as examples. Excellent exposure of the surface fault traces in these two regions permits detailed mapping of fault traces and deriving shape factors of faults with high-resolution DEMs(digital elevation models). Additionally, they are two of the most-studied thrust faults in this area. Large-scale geological and geomorphological mappings of them and numerous achievements have been published. This creates possibilities for us to conduct comparison analysis on different major methods. Based on typical morphology characteristics of fault scarps, appropriate geomorphic parameters are selected. In practice, reverse fault scarps are distinctly defined into forward and backward ones according to whether their dip is the same as that of the neighboring geomorphic surfaces. Based on two sets of geomorphic constraints,two approaches are then illustrated, including slope calculation, gully extraction, data density analysis and process modeling. Through a detailed comparison of the final extraction results and previous visual interpretations of remote sensing data and field geomorphic investigations, the validity of the method proposed in this study is proven. This method provides a set of tools with user-friendly interfaces to realize step-by-step interpretation and emphasizes the importance of field-based geomorphic constraints at the same time. Moreover, many subtle fault traces which have not been recognized before are simultaneously revealed in the Dushanzi research area. The high-resolution DEMs guarantee the realization of picking out finer bits of fault information. Compared to traditional ways of working, the method has the advantage of automatically delineating reverse fault traces on the earth’s surface. This advantage can significantly reduce the efforts to manually digitize geomorphic features and improve efficiency. But many basic manual adjustment options for recognizing target characteristics also need to be set in extraction, because the distinguishing criterion of fault scarp and surrounding geomorphic landforms vary among different areas. In different specific circumstances, users can manually adjust relevant parameters for the extraction during the modeling process. Generally speaking, the more detailed constraints, the more confidence in the final delineation of fault traces. Subjective judgments are therefore particularly critical for conducting extraction under complex backgrounds. But improving the degree of automation of the whole process is still an important study direction. Future work is thus recommended to employ machine learning and explore appropriate evaluation methods to search for the optimal solution of intermediate parameters.

The southern Alashan block is located at the crustal front of the northern Tibetan plateau. It was initially considered as a relatively stable area with weak tectonic activity. In recent years, an increasing number of studies have shown that the Alashan block has undergone significant tectonic deformation since the Cenozoic. Multiple active faults with a horse-tail distribution are developed in the southern margin of the Alashan block. However, there is still controversy over the tectonic deformation patterns of these active faults. One view is that the fault system in the southern margin of Alashan is the result of the eastward extension of the Altyn Tagh Fault and belongs to the tail structure of the strike-slip fault. Another view is that the fault system in the southern Alashan block is the result of the revival of the pre-existing fault caused by the northward compression and thrust of the Tibetan plateau. Therefore, deciphering fault’s kinematics and slip rates since the late Quaternary in the southern Alashan block is crucial to understand the tectonic deformation pattern of the block and its response to Tibet’s northward growth. In this paper, combined with interpretations of remote sensing images and field investigations, we documented the Quaternary activity of the Beida Shan Fault, one of the major faults in the southern Alashan block, along the segment developed in Quaternary alluvium.

The Beida Shan Fault is a sinistral strike-slip fault with paralleled north and south branches that displaced the late Quaternary alluvial fans and terraces, forming offset gullies and fault scarps. According to the geometric distribution characteristics, activity and the landforms along the fault, we divided the fault into three segments: the Langwa Shan segment, the northern branch of the Jiapiquan Shan segment, and the southern branch of the Jiapiquan Shan segment. The fault is east-west trending, and the offset geomorphic features along the fault reveal that there are differences in the activity of different segments. The Langwa Shan segment is 10km long and developed at the junction of bedrock and alluvial fan. The fault trace is straight, and a series of gullies and ridges offset by the fault indicate that it is a sinistral strike-slip fault. The Jiapiquan Shan segment is 35km long and divided into two parallel north and south branches with a spacing of about 1.5km. The north branch fault strikes NE on the east side of Langwa Shan and has an angle of about 30° with the south branch fault. After extending about 2km to the northeast direction and entering the north side of Dahong Shan, the fault turns to the EW direction and is parallel to the south branch fault. It is distributed along the boundary between the bedrock and the alluvial fan with the south or north fault scarps and the secondary branch faults. To the east, the north branch fault is developed in bedrock, which is mainly characterized by offset gullies and ridges. The southern branch fault offset multi-stage alluvial fan, forming fault scarps of different heights and left-lateral offset gullies of different scales, and the exposed fault profiles show high angle reverse faults, which dip south or north, indicating that this segment is sinistral strike-slip.

Based on the 1.5m resolution DEM data obtained from UAV-SfM, we measured the horizontal displacement of fault landforms using the LaDiCaoZ software developed by Zielke et al.(2012) on the MATLAB platform. Combined with field survey data, we obtained the left-lateral horizontal displacements of 70 sites along the Beida Shan Fault. The sinistral offset of~1m is not included in slip distribution statistics due to limitations of the quantity and data accuracy. Statistical analysis of the displacements reveals that the left-lateral displacements along the fault are concentrated between 3m to 20m, with the majority in two pronounced peaks at 5.3m and 10.1m. The 5.3m peak contains the most data points, with 17 displacements data, accounting for 24% of the total, while the 10.1m peak contains 6 data points, accounting for 9% of the total. This indicates that the Beida Shan Fault has experienced multiple seismic events involving the displacement and rupture of stratigraphic layers on the surface.

An~8km-long surface rupture is discovered on the south fault branch, and it is represented by of fault scarps and of tens of centimeters 1~2m left-lateral displacement of small gullies. Fresh surface rupture and left-lateral offset gullies indicate the latest fault activity. Using the previously dated alluvial fan ages in Taohuala Shan, ~30km south of the Beida Shan, we calculated the late Pleistocene sinistral slip rate of 0.3~0.6mm/a along the Beida Shan Fault, which is consistent with the slip rate of the Taohuala Shan Fault estimated by Yu et al.(2017). Compared with the fault slip rate accommodated in the Hexi Corridor area and regional GPS rates, the southern Alashan block plays a significant role in absorbing deformation in response to the northern Tibetan growth.

In the Cenozoic, under the influence of the collision of the India-Eurasia plate and the northward pushing after that, deformation occurred in the interior of the continent, and the crustal deformation is mainly absorbed by the thickening of the crust and the strike-slip movement of the fault. The GPS velocity field shows that the area north of Tianshan absorbs the shortening with a rate of~2mm/a. How the shortening with these rates is absorbed is a topic worthy of study. The West Junggar, located to the north of the Tianshan Mountains and developed with the inclined parallel strike-slip fault system is an important area of crustal shortening. The inclined parallel strike-slip fault system includes the east Tacheng Fault, Tuoli Fault and Daerbute Fault. Hence, the structural deformation of the Tuoli Fault in the late Quaternary is significant for understanding the structural deformation and crustal shortening absorption mode in the north of Tianshan Mountains.

In this study, two branches were found extending along the Tuoli Fault in the direction of NE based on remote sensing image interpretation. Field investigation to the two branch faults shows that many marker landforms were dislocated in the study area, including gullies and terrace riser. The two faults cross through the terraces developed in the Kapusheke River and the Tiesibahan River in this area, forming offset terrace riser. Because the terrace riser is in the retained bank of the river, the upper-layer terrace model is used to calculate the fault’s slip rate. The gullies are mainly distributed on the T3 terrace of the Kapushek River on the west branch fault. The horizontal dislocation of these gullies ranges from 10m to 37.5m, and the largest horizontal dislocation is located in the No. 8 gully, which is (37.5-4.1/+2.7)m. Since the actual value of the fault movement rate must be greater than the rate obtained by the sub-gully offset, we choose the maximum offset of the gully on the landform surface in calculating the slip rate. We used OSL(Optical Stimulated Luminescence)to date the age of the landform and used UAV(Unmanned Aerial Vehicle)photogrammetry technology to extract high-precision DEM of the study area. Then, we calculate the movement rate of the Tuoli Fault since the late Quaternary from the dislocations and the age of landmark landforms such as gullies and terraces. The results show that the Tuoli Fault comprises two branch faults in the east and the west, both of which are left-lateral horizontal strike-slip. The east branch fault produced a (89±31)m and (39±13)m horizontal dislocation on the T3 and T2 terrace of the Kapusheke River, respectively. Combined with the (52.9±5.1)ka of the T3 terrace age and (23.4±1.5)ka of the T2 terrace age, the horizontal slip-rate of (1.7±0.8)mm/a is calculated for the eastern branch fault. The western branch fault produced a horizontal dislocation of (34.0±6.8)m on the T2 terrace of the Tiesibahan River and 37.5⁽-4.1/+4.1)m of the gully on the T3 terrace of the Kapusheke River. Combined with (18.8±1.3)ka of the T2 terrace age, we obtained a sinistral slip rate of 1.8(+0.5/-1.3)mm/a for the western branch fault. The sinistral slip rate of two branch faults of the Tuoli Fault is similar to the sinistral slip rate of the east Tacheng Fault in the previous research results. This study result indicates that these parallel left-lateral strike-slip faults in the West Junggar area conform to the characteristics of the bookshelf faults structural model, and most of the compression shortening in the West Junggar area is absorbed by the parallel strike-slip movement of the fault system. So this fault system has played an important role in controlling the NS shortening of the crust in this region.

The top of the piedmont alluvial fan has the characteristic of fan-shaped terrain and gradually descending terrain in the downstream direction. Faulting of various natures will result in different geomorphic features of alluvial fan surface. The variation of slope aspect and height of the pure sinistral fault scarp at the top of the alluvial fan is analyzed firstly under the three conditions, namely, the fault plane is vertical, the fault plane inclines toward the upper stream of the river, and the fault plane inclines toward the downstream of the river. We have also analyzed the variation of slope aspect and height of the fault scarps at the top of the alluvial fan under different fault inclination conditions of inverse sinistral strike-slip fault and the sinistral strike-slip normal fault. The seven geomorphic types we analyzed above cover the geomorphic features caused by the activity of strike-slip faults at the top of alluvial fans, which can help us to analyze the formation of the landforms. Based on drone-measured terrain data, Google satellite images and field investigations, we found that the Dongbielieke Fault, which strikes northeast-southwest and is located in the eastern margin of the Tacheng Basin, Xinjiang, almost vertically passes through the Ahebeidou River which develops from southeast to northwest. The direction of central axis of the alluvial fan at Ahebedou River is northwest, with a north-facing slope. The fault activity has caused the development of an uphill-facing scarp that has a height of~5.2m and a slope aspect facing southeast on the top of the alluvial fan at the Ahebiedou River section of the Dongbielieke Fault. And on the piedmont alluvial fan 1km away on both sides of the river bed, the sinistral fault scarps have a northwest-facing slope aspect and a height of 1~5m. The river terraces are divided into five levels, the T2 on the left bank, T4 on the right bank and T5 terraces on the left and right banks of Ahebeidou River were affected by fault activity. Sinistral offsets and southeast-facing fault scarps were developed on the geomorphic surface. By using DispCalc_Bathy_v2, a script based on Matlab, we get the offsets of the river terraces from the high-resolution DEM data obtained by using UAV photogrammetry technology. The sinistral horizontal offsets of T2 on the left bank, T4 on the right bank and T5 terraces on the left and right banks of Ahebeidou River are(10.1±0.2)m, (10.6±0.7)m, (29.1±0.2)m and(20.0±0.7)m, respectively. The vertical displacements are(1.5±0.1)m, (3.6±0.3)m, (4.7±0.2)m and(5.2±0.1)m, respectively. The asymmetrical development of terrains on both sides of the river is affected by topography and fault activity. The terraces on the lower elevation right bank of the river are misplaced into the channel by sinistral strike-slip faulting to receive more erosion, so the offsets we measured on the left bank of the river are more reliable than that on the right bank. Through field surveys, we found two fault outcrops, indicating that the fault plane is inclined to the southeast. The young river terrace T2 was effected by faulting and a uphill-facing scarp was developed, which indicates that the latest faulting was of sinistral strike-slip with a normal component, but the fault scarp's aspect changed twice within a short area of two kilometers, which is not consistent with the geomorphological type caused by the strike-slip faulting on the top of the alluvial fan as we previously analyzed. According to the landform features and the strike-slip fault geomorphic model, a model for the geomorphic surface development of the Ahebiedou River section is established. In this model, we think the Dongbielieke Fault was an inverse sinistral strike-slip fault after the formation of an older phase geomorphic surface S1 in the area. The early fault activity formed a northwest-facing fault scarp at S1, the height of the scarp is about 10m. Then the alluvial fan(Fan1)began to develop, and the material brought by the flowing water deposited and buried the fault scarp at the exit of piedmont, resulting in the disappearance of the existing fault scarp in the piedmont. Then the characteristic of fault changed into left-lateral strike-slip with a normal component. The activity of normal fault with the fault plane dipping to SE would form a fault scarp facing SE on the geomorphic surface. With the gradually cutting of the river, river terraces began to form on both sides of the river, and the corresponding geomorphic features were formed under the influence of fault activities. A fault scarp with a slope facing southeast formed at both banks of the river's mountain outlet with a height of about 5.2m through several fault activities, and sinistral horizontal offsets of river terraces increased at the same time. And the height of the pre-existing northwest-facing scarp 1~2km away from both banks of the river's mountain outlet decreased to about 5m, which can be observed in the field. The eventual geomorphic surface is characterized by the features of downhill-facing scarp-no scarp-uphill-facing scarp-no scarp-downhill-facing scarp from southeast to northeast.

In response to the ongoing far-field effects of the India-Eurasia collision, the Tianshan Mountains experience rapid NS convergence, and most of the present N-S shortening is absorbed along the southern and northern edges. The resultant frequent large earthquakes have inspired many scientists to explore the neotectonic activity of the Tianshan Mountains. The eastern Qiulitage anticlinal belt located in the Kuqa depression, on the southern piedmont of the Tianshan Mountains, is a typical blind fault-related fold. The Kuqa M7$\frac{1}{4}$ earthquake in 1949 as typical folding earthquake once occurred on the northern limb of the eastern segment of the Qiulitage anticline, and the epicenter was near the Village of Kang which is sparsely populated. This earthquake is a typical folding earthquake whose dominant fault did not thrust onto the earth surface. Although many tectonic-induced scarps and deformed Quaternary strata have been reported, there are still no direct evidences for the surface ruptures and corresponding causative faults of this earthquake at present. And systematic understanding of paleoseismic events in Qiulitage area is also limited by the lack of relevant chronological researches.
We conducted 1︰50 000 scale geological mapping in the Qiulitage anticline area. The local surface geological characteristics are investigated based on interpretation of Google Earth image and confirmation in the field. Together with interpreted subsurface structure by petroleum seismic reflection profiles, the relationship between the active faults thrust on the surface, low-dip-angle decollement faults in deep, and fold deformation are subsequently qualitatively analyzed. In this study, the active faults which have thrust to the surface and generated fault scarps are focused on.
Totally five trenches were chosen and cleared up, two of which are located on the southern limb of the eastern Qiulitage anticline and the others are on its northern limb. And all excavation sites are situated on fresh fault scarps. We carefully interpreted different characteristics of tectonic deformation and sedimentary process which are correlated with paleo-seismic events from trenches. According to the OSL(Optically Stimulated Luminescence)and ¹⁴C dating results, a reliable chronological framework for the deformed stratigraphic sequences was established. Based on the classic successive limiting method, six paleoseismic events were finally constrained.
Some of these interpreted paleo-seismic events produced surface ruptures on the breakthrough faults simultaneously on the southern and northern limbs of the Qiulitage anticline, and others only caused local surface ruptures on its northern limb. In a broad sense, the surface ruptures caused by these paleoseismic events have similar characteristics to those which are popular among the low-dip-angle thrust faults on the southern piedmont of the Tianshan Mountains. And the two common phenomena are that multiple ruptures may occur a single fault and multiple faults may rupture simultaneously. We speculate that only when the displacement of master faults at depth is big enough, multiple shallow secondary faults can be triggered at the same time. Conversely, only one fault is active at one time. In other words, constrained by the length and displacement of dominant faults, not all paloseismic events can cause surface ruptures on the northern and southern limbs of the Qiulitage anticline at the same time.
The revealed paleoearthquakes may have a clustering feature since ~7.4ka. They behaved as follows: 1)Three events occurred during 5.7~7.4ka. 2)one event occurred during 3.3~4.7ka. 3)the latest cluster of events may be marked by the 1949 M_W7$\frac{1}{4}$ Kuqa earthquake. Thus, the earthquake sequences have a recurrence period of about 2.5~4ka.
Significantly, the incompleteness of the paloseismic events recorded in trenches and the quality and intrinsic error of the OSL dating samples can mislead judgments. It is inevitable that the time of paloseismic event cannot be constrained strictly. In our research area, because of the lack of seismic events between event E5 and event E6(7.25~19.1ka), there is a gap in seismic event records for up to~11.85ka. However, our result offers a relatively systemic event sequence to fill the gap in studies on paleoseismicity in this area. Whether there will be a strong shock after the 1949 M_W7$\frac{1}{4}$ Kuqa earthquake remains to be further studied in detail.

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.

Tanlu fault zone is the largest strike-slip fault system in eastern China. Since it was discovered by aeromagnetics in 1960s, it has been widely concerned by scholars at home and abroad, and a lot of research has been done on its formation and evolution. At the same time, the Tanlu fault zone is also the main seismic structural zone in China, with an obvious characteristic of segmentation of seismicity. Major earthquakes are mostly concentrated in the Bohai section and Weifang-Jiashan section. For example, the largest earthquake occurring in the Bohai section is M7.4 earthquake, and the largest earthquake occurring in the Weifang-Jiashan section is M8.5 earthquake. Therefore, the research on the active structure of the Tanlu fault zone is mainly concentrated in these two sections. With the deepening of research, some scholars carried out a lot of research on the middle section of Tanlu fault zone, which is distributed in Shandong and northern Jiangsu Province, including five nearly parallel fault systems, i.e. Changyi-Dadian Fault(F₁), Baifenzi-Fulaishan Fault(F₂), Yishui-Tangtou Fault(F₃), Tangwu-Gegou Fault(F₄)and Anqiu-Juxian Fault(F₅). They find that the faults F₃ and F₅ are still active since the late Quaternary. In recent years, we have got a further understanding of the geometric distribution, active age and active nature of Fault F₅, and found that it is still active in Holocene. At the same time, the latest research on the extension of F₅ into Anhui suggests that there is a late Pleistocene-Holocene fault existing near the Huaihe River in Anhui Province.
The Tanlu fault zone extends into Anhui Province and the extension section is completely buried, especially in the Hefei Basin south of Dingyuan. At present, there is little research on the activity of this fault segment, and it is very difficult to study its geometric structure and active nature, and even whether the fault exists has not been clear. Precisely determining the distribution, active properties and the latest active time of the hidden faults under urban areas is of great significance not only for studying the rupture behavior and segmentation characteristics of the southern section of the Tanlu fault zone, but also for providing important basis for urban seismic fortification. By using the method of shallow seismic prospecting and the combined drilling geological section, this paper carries out a detailed exploration and research on the Wuyunshan-Hefei Fault, the west branch fault of Tanlu fault zone buried in Hefei Basin. Four shallow seismic prospecting lines and two rows of joint borehole profiles are laid across the fault in Hefei urban area from north to south. Using ¹⁴C, OSL and ESR dating methods, ages of 34 samples of borehole stratigraphic profiles are obtained. The results show that the youngest stratum dislocated by the Wuyunshan-Hefei Fault is the Mesopleistocene blue-gray clay layer, and its activity is characterized by reverse faulting, with a maximum vertical offset of 2.4m. The latest active age is late Mesopleistocene, and the depth of the shallowest upper breaking point is 17m. This study confirms that the west branch of Tanlu fault zone cuts through Hefei Basin and is still active since Quaternary. Its latest activity age in Hefei Basin is late of Middle Pleistocene, and the latest activity is characterized by thrusting. The research results enrich the understanding of the overall activity of Tanlu fault zone in the buried section of Hefei Basin and provide reliable basic data for earthquake monitoring, prediction and earthquake damage prevention in Anhui Province.

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 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.

As the most active intracontinental orogenic belt in the world, the Tianshan orogenic belt has complex and diverse internal structural deformation patterns, and among them, the particularly striking is the linear straight U-type valley landscapes which cut inside the mountains by multiple NW-SE and ENE-WSW strike-slip faults. Many of the modern strong earthquakes in Tianshan orogenic belt are closely related to these strike-slip faults. Therefore, it is important to elaborate the activity characteristics of these faults to understand the deformation process inside the Tianshan Mountains belt. This paper focuses on one of the NW-SE right-lateral strike-slip fault (the Kaiduhe Fault), which lies inside the southeastern Tianshan. Typical offset landforms and scarp lineaments on the western segment of the Kaiduhe Fault can be used to study the activity characteristics and strike-slip rate. In particular, the fault cuts through the late Quaternary alluvial fans and a series of river gullies were right-laterally faulted, producing dextral offsets ranging from 3 to 248m. A digital elevation model (DEM)with resolution of 0.25m was established by using multi-angle photogrammetry technique to stripe about 12km linear tectonic landforms along the Kaiduhe Fault. Geological and geomorphic mapping in DEM with 22 high-resolution dextral offset measurements reveals that the dextral offsets can be divide into four groups of 3.5m, 7.0m, 11.8m and 14.5m. It is presumed from the approximately uniformly-spaced offsets that the coseismic offset was 3~4m. In addition, the exposure age of an older alluvial fan surface was about 235.7ka by in situ ¹⁰Be terrestrial cosmogenic nuclide method. Combining the exposure ages and the maximum dextral offset of 248m, we found that the strike-slip rate of the Kaiduhe Fault is about 1mm/a. It is found by this study that the Kaiduhe Fault plays an important role in regulating SN compression deformation within Tianshan Mountains, and it should also be the main stress-strain accumulation area which has the risk of occurrence of strong earthquake.

The Fodongmiao-Hongyazi Fault (FHF)is one of the most active faults of the northern Qilian thrust fault zone. The 1609 Hongyazi M7 1/4 earthquake occurred on the east segment of the FHF, an area with a complex geometry at the Mayinghe River site. The seismogenic pattern of this earthquake revealed by complex surface ruptures remains unclear. In this paper, we focus on active tectonic deformation around the Hujiatai anticline (HA)in the Mayinghe River site. Combining with topographic survey via dGPS across deformed terraces and alluvial fans, a field survey of the geological section across the HA, the characteristics of the active fold and several sub-faults were constrained. Meanwhile, combined with the seismic reflection profiles passing through the anticline, the correspondence relationship between surface expressions of this tectonic and the deep structure was discussed. According to our research, the HA is a result of northward propagation of the range-front thrust fault F₁. At the same time, a thrust fault F₂ with dextral strike-slip motion and a thrust fault F₄ were formed on the east side and north side of the HA, respectively. These two active faults accommodated local deformation. Trench results and ¹⁴C dating reveal that the 1609 Hongyazi M7 1/4 earthquake ruptured the T₁ terrace in the Huangcaoba site. Combined with previous field investigations and literature about the 1609 Hongyazi earthquake, we suggest that this earthquake occurred on the range-front fault F₁, and the depth of the hypocenter may be about 8~22km.

The Fodongmiao-Hongyazi Fault is a Holocene active thrust fault, belonging to the middle segment of northern Qilianshan overthrust fault zone, located in the northeastern edge of the Tibet plateau. The Hongyapu M7(1/4) earthquake in 1609 AD occurred on it. A few paleo-seismology studies were carried out on this fault zone. It was considered that four paleoearthquakes occurred on the Fodongmiao-Hongyazi Fault between(6.3±0.6) ka BP and(7.4±0.4) ka BP, in(4.3±0.3) ka BP, in(2.1±0.1) ka BP and in 1609 AD. The occurrences of the earthquakes suggested the quasi-periodic characteristic with a quasi-periodic recurrence interval between 1 600~2 500a(Institute of Geology, State Seismological Bureau, Lanzhou Institute of Seismology, State Seismological Bureau. 1993; Liu et al., 2014). There was no direct evidence for the Hongyapu M7(1/4) earthquake in 1609 AD from trench research in the previous studies. Great uncertainty exists because of the small number of the chronology data, as a few TL and OSL measurement data and several¹⁴ C data, and it was insufficient to deduce the exact recurrence interval for the paleoearthquakes.
Five trenches were excavated and cleared up respectively in the eastern segment, middle segment and western segment along the Fodongmiao-Hongyazi Fault. After detail study on the trench profiles, the sedimentary characteristics, sequence relationship of the stratigraphical units, and fault-cuts in different stratigraphical units were revealed in these five trenches. Four paleoearthquakes in Holocene were distinguished from the five trenches, and geology evidences of the Hongyapu M7(1/4) earthquake in 1609 AD were also found.
More accurate constraint of the occurring time of the paleo-earthquakes since Holocene on the Fodongmiao-Hongyazi Fault is provided by the progressive constraining method(Mao and Zhang, 1995), according to amounts of ¹⁴ C measurement data and OLS measurement data of the chronology samples from different stratigraphical units in the trenches. The first paleoevent, E4 occurred 10.6ka BP. The next event, E3 occurred about 7.1ka BP. The E2 occurred about 3.4ka BP. The last event, E1 is the Hongyapu M7(1/4) earthquake in 1609 AD.
Abounds of proofs for the occurrences of the events of E1, E2 and E3 were found in the trench Tc1, trench Tc2, trench Tc4 and trench Tc3, located in the eastern, middle and western segments of the Fodongmiao-Hongyazi Fault accordingly. It's considered that the events E1, E2 and E3 may cause whole segment rupturing according to the proofs for these three events found together in individual trenches. The event E4 was only found in the trench Tc5 profile in the west of the Xiaoquan village in the eastern segment of the Fodongmiao-Hongyazi Fault. The earthquake rupture characteristics of this event can't be revealed before more detailed subsequent research.
The time intervals among the four paleoearthquakes are ca 3.5ka, ca 3.7ka, and ca 3.0ka. The four events are characterized by ca 3.4ka quasi-periodic recurrence interval.

The Hongyapu M7 1/4 earthquake in 1609 occurred on the Fodongmiao-Hongyazi fault, which is a Holocene active thrust in the middle segment of the northern Qilianshan overthrust fault zone, located in the north-eastern edge of the Tibet plateau. This earthquake caused death of more than 840 people, ruined the Hongyapu Village and had an affected area ca. 200km². Previous work provided different opinions on the length of the earthquake surface rupture zone, such as 60km from the Bailanghe western riverbank to the Fenglehe eastern river bank, and only 11km from the Hongyazi village to eastern edge of the Hujiatai anticline. And the surface rupture zone appears in the western and middle segments of the Fodongmiao-Hongyazi fault zone.
Our detailed geomorphic analysis and topographic survey found that the surface rupture zone with a total length of ca 95km is present on the new geomorphic surfaces which are slightly higher than the modern allvial-dilvial fans and riverbeds, which begins from the Hongshuiba river, Jiuquan in the west extending to the Toudaodongwan, southern Gansu in the east along the Fodongmiao-Hongyazi Fault. The surface rupture zone occurred later than 0 A D, proved by the study of trenchs and chronology. Compared to the previous research on the epicenters of the historical major earthquakes in and around the study region, this surface rupture zone is considereded to be the surface rupture zone of the Hongyapu earthquake of 1609 in Gansu provice.
Average vertical co-seismic displacement of the 1609 Hongyapu earthquake is 1.1m with maximum 1.8m, dominated by thrusting. The NNW striking Xiaoqun segment shows thrust with a component of dextral strike slip and the NEE-trending East Hongshancun segment is also mainly thrust but with sinistral strike slipp. The lateral movement could be caused by the local change of the fault strike direction.
Based on the length of surface ruptures, the maximum coseismic displacement and fault dipping, this event is estimated to be of ca. M_W7.0~M_W7.4, close to the M7 1/4 suggested by previous studies.

The Tian Shan Mountains is an active orogen in the continent. Previous studies on its tectonic deformation focus on the expanding fronts to basins on either side, while little work has been done on its interiors. This work studied the north-edge fault of the Yanqi Basin on the southeastern flank of Tian Shan. Typical offset landforms, and lineaments of scarps on the eastern segment of this fault were used to constrain the vertical displacement and shortening rates. Geological and geomorphic mapping in conjunction with high-resolution GPS differential measurement reveals that the vertical offsets can be divided into three groups of 1.9m, 2.4m and 3.0m, and the coseismic vertical offset was estimated as 0.5~0.6m. In situ ¹⁰Be terrestrial cosmogenic nuclide dating of three big boulders capping the regional geomorphic surface that preserved 3.0m vertical offset suggests that the surfaces were exposed at~5ka. Meanwhile, the lacustrine sediments from Bosten Lake within the Yanqi Basin suggest climate change during cooling-warming transitions was also at~5ka. The climate, therefore, controlled creation and abandonment of geomorphic surfaces in southern piedmont of Tian Shan. Combining the exposure ages and vertical offsets, we inferred that the east section of the north-edge fault in the Yanqi Basin has a dip slip rate 0.6~0.7mm/a,~0.5mm/a of vertical slip and~0.4mm/a of shortening since 5ka. Based on calculation of earthquake moment, we estimated that this fault is capable of generating M7.5 earthquakes in the future. This study provides new data for further understanding tectonic deformation of Tian Shan and is useful in seismic hazard assessment of this area.

The Fodongmiao-Hongyazi Fault belongs to the forward thrust fault of the middle segment of northern Qilian Shan overthrust fault zone, and it is also the boundary between the Qilian Shan and Jiudong Basin. Accurately-constrained fault slip rate is crucial for understanding the present-day tectonic deformation mechanism and regional seismic hazard in Tibet plateau. In this paper, we focus on the Shiyangjuan site in the western section of the fault and the Fenglehe site in the middle part of the fault. Combining geomorphic mapping, topographic surveys of the deformed terrace surfaces, optically stimulated luminescence (OSL) dating, terrestrial cosmogenic nuclide dating and radiocarbon (¹⁴C) dating methods, we obtained the average vertical slip rate and shortening rate of the fault, which are ~1.1mm/a and 0.9~1.3mm/a, respectively. In addition, decadal GPS velocity profile across the Qilian Shan and Jiudong Basin shows a basin shortening rate of~1.4mm/a, which is consistent with geological shortening rates. Blind fault or other structural deformation in the Jiudong Basin may accommodate part of crustal shortening. Overall crustal shortening rate of the Jiudong Basin accounts for about 1/5 of shortening rate of the Qilian Shan. The seismic activity of the forward thrust zone of Tibetan plateau propagating northeastward is still high.

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.

With the development of the techniques acquiring high-resolution digital terrain data,the digital terrain data acquisition technology has been widespread applied to the geoscience research.A revolutionary,low-cost and simply operative SfM (Structure from Motion) technology will make obtain high-resolution DEM data more convenient for researches on active tectonics.This paper summarizes the basic principles and workflows of SfM technology and processes and selects the Hongshuiba River area along the northern margin of the Qilian Shan to conduct data collection.We use a series of digital pictures to produce a texture with geographic information,in which data resolution is 6.73cm/pix and average density of point cloud is 220.667 point/m².The coverage area is 0.286km².Further,in order to compare the accuracy between SfM data and differential GPS (DGPS) data in details,SfM data are vertically shifted and tilt-corrected.After optimizing corrections of SfM data,the absolute value of elevation difference between two data substantially concentrates around 20cm,roughly equivalent to 2-folds of data error only after the elevation error correction.Elevation difference between two data is 10~15cm in 90% confidence interval.The maximum error is about 30cm,but accounts for less than 10%.Along the direction of fault trace,the height of fault scarp extracted from SfM data shows that vertical displacement of the latest tectonic activity in the east bank of Hongshuiba River is about 1m,and some minimum scarps height may be 0.3m.The results show SfM technology with high vertical accuracy can be able to replace differential GPS in high-precision topographic survey.After correcting of SfM data,elevation difference still exists,which may be associated with methods of generating DEM and SfM data accuracy,which in turn is controlled by the number and distribution of Ground Control Points (GCPs),photos density and camera shooting height,but also related to surface features,Fodongmiao-Hongyazi Fault

Sanwei Shan Fault is located in the north of Tibet, which is a branch of eastern segment of Altyn Tagn fault zone. This fault is distributed along the boundary of fault facet and the Quaternary, with the total length of almost 150km. The fault is a straight-line structure read from the satellite image. Based on the spatial distribution of the fault, three segments are divided, namely, Xishuigou-Dongshuigou segment, Dongshuigou-West Shigongkouzi segment and West Shigongkouzi-Suangta segment, these three segments are distributed by left or right step.Though field microgeomorphology investigation along Sanwei Shan Fault, it has been found that two periods of alluvial-pluvial fans are distributed in front of Sanwei Shan Mountain, most of which are overstepped. Comparing the distribution of alluvial-pluvial fans with their formation age in the surrounding regions, and meanwhile, taking the results of optical stimulated luminescence(OSL) dating, it's considered that the formation age of the older alluvial-pluvial fans, which are distributed in northern Qilian Shan, inside of Hexi Corridor and western Hexi Corridor(including the Sanwei Shan piedmont fans), is between later period of late Quaternary and earlier period of Holocene. The gullies on the older fan and ridges have been cut synchronously. The maximum and minimum sinistral displacement is 5.5m and 1.7m, but majority of the values is between 3.0~4.5m. Taking the results from the OSL dating, we conclude that the minimum sinistral strike-slip rate is(0.33±0.04) mm/a since 14 ka BP and(0.28±0.03) mm/a since 20 ka BP.

The NE-trending Xinyi-Lianjiang fault zone is a tectonic belt, located in the interior of the Yunkai uplift in the west of Guangdong Province, clamping the Lianjiang synclinorium and consisting of the eastern branch and the western branch. The southwestern segment of the eastern branch of Xinyi-Lianjiang fault zone, about 34km long, extends from the north of Guanqiao, through Lianjiang, to the north of Hengshan. However, it is still unclear about whether the segment extends to Jiuzhoujiang alluvial plain or not, which is in the southwest of Hengshan. If it does, what is about its fault activity? According to ‘Catalogue of the Modern Earthquakes of China’, two moderately strong earthquakes with magnitude 6.0 and 6.5 struck the Lianjiang region in 1605 AD. So it is necessary to acquire the knowledge about the activity of the segment fault, which is probably the corresponding seismogenic structure of the two destructive earthquakes. And the study on the fault activity of the segment can boost the research on seismotectonics of moderately strong earthquakes in Southeast China. In order to obtain the understanding of the existence of the buried fault of the southwestern segment, shallow seismic exploration profiles and composite borehole sections have been conducted. The results indicate its existence. Two shallow seismic exploration profiles show that buried depth of the upper breakpoints and vertical throw of the buried fault are 60m and 4~7m(L5-1 and L5-2 segment, the Hengshan section), 85m and 5~8m(L5-3 segment), 73m and 3~5m(Tiantouzai section), respectively and all of them suggest the buried fault has offset the base of the Quaternary strata. Two composite borehole sections reveal that the depth of the upper breakpoints and vertical throws of the buried segment are about 66m and 7.5m(Hengshan section) and 75m and 5m(Tiantouzai section), respectively. The drilling geological section in Hengshan reveals that the width of the fault could be up to 27m. Chronology data of Quaternary strata in the two drilling sections, obtained by means of electron spin resonance(ESR), suggest that the latest activity age of the buried fault of the southwestern segment is from late of early Pleistocene(Tiantouzai section) to early stage of middle Pleistocene(Hengshan section). Slip rates, obtained by Hengshan section and Tiantouzai section, are 0.1mm/a and 0.013mm/a, respectively. As shown by the fault profile located in a bedrock exposed region in Shajing, there are at least two stages of fault gouge and near-horizontal striation on the fault surface, indicating that the latest activity of the southwestern segment is characterized by strike-slip movement. Chronology data suggest that the age of the gouge formed in the later stage is(348±49) ka.

Based on geological and geomorphologic characteristics of the surface faults acquired by field investigations and subsurface structure from petroleum seismic profiles, this paper analyzes the distribution, activity and formation mechanism of the surface faults in the east segment of Qiulitage anticline belt which lies east of the Yanshuigou River and consists of two sub-anticlines:Kuchetawu anticline and east Qiulitage anticline. The fault lying in the core of Kuchetawu anticline is an extension branch of the detachment fault developed in Paleogene salt layer, and evidence shows it is a late Pleistocene fault. The faults developed in the fold hinge in front of the Kuchetawu anticline in a parallel group and having a discontinuous distribution are fold-accommodation faults controlled by local compressive stress. However, trenching confirms that these fold-accommodation faults have been active since the late Holocene and have recorded part of paleoearthquakes in the active folding zone. The fault developed in the south limb near the core of eastern Qiulitage anticline is a low-angle thrust fault, likely a branch of the upper ramp which controls the development of the eastern Qiulitage anticline. The faults lying in the south limb of eastern Qiulitage anticline are shear-thrust faults, which are developed in the steeply dipping frontal limb of the fault-propagation folds, and also characterized by group occurrence and discontinuous distribution. Several fault outcrops are discovered near Gekuluke, in which the Holocene diluvial fans are dislocated by these faults, and trench shows they have recorded several paleoearthquakes. The surface anticlines of rapid growth and associated accommodation faults are the manifestations of the deep faults that experienced complex folding deformation and propagated upward to the near surface, serving as an indicator of faulting at depth. The fold-accommodation faults are merely local deformation during the folding process, which are indirectly related with the deep faults that control the growth of folds. The displacement and slip rate of these surface faults cannot match the kinematics parameters of the deeper fault, which controls the development of the active folding. However, these active fold-accommodation faults can partly record paleoearthquakes taking place in the active folding zone.

Fold-accommodation faults, secondary faults subordinated to the principal fold, are of much significance to accommodate strain variation in different parts of the rock during the evolution of folding. They are generally found in groups. And each of them has limited displacement and does not connect with the main detachment. After the geological survey in the East Qiulitage anticline zone, we find that the secondary faults accompanying fold scarps in this area are out-of-syncline thrusts and also give an instance of secondary faults occurring later than the folding. The fact that the secondary faults in fold scarps force the hanging wall to move upward relative to the footwall not only makes the terrace tilting and increases the slope of fold scarps, but also affects the authenticity in calculating regional shortening increment. The theoretical results show that if we do not consider the increased fold scarps height influenced by the secondary faults, the shortening increment is 51.42m. Otherwise, the value will be 45.23m and the difference between them is 6.19m. Because the deviation is 13.7% of the total shortening increment, the contributions of fold-accommodation faults to the calculation should not be ignored. The fold scarps in the northern and southern flanks of the East Qiultiage anticline depend on same bedrock type and formation mechanism. But three levels of fold scarps were found in the cross section of less than 300 meters in horizontal distance. This fact indicates that the active kink band of northern part is more closed because of higher compressive stress and faster lifting, which produce a large number of secondary faults in the fold scarps only in the northern flank. Therefore, the study of secondary faults is of significance in understanding of regional tectonic evolution and interaction between folds and faults. But there still exist many problems: 1)Limited by the observing scope, discontinuous distribution of secondary faults and variations of displacement along fault, we may underestimate the influence of secondary faults and the theoretical result should be the minimum. 2)What is the quantitative relationship among the increased height of fold scarps, the transfer slip and the dip of secondary faults?3)If secondary faults only grow in active kink band, how will they affect fold scarp?More examples of fold-accommodation faults are needed for further research.

How strain is distributed and partitioned on individual faults and folds on the margins of intermontane basins remains poorly understood. The Haermodun(Ha) anticline, located along the northern margin of the Yanqi Basin on the southeastern flank of the Tian Shan, preserves flights of passively deformed alluvial terraces. These terraces cross the active anticline and can be used to constrain local crustal shortening and uplift rates. Geologic and geomorphic mapping, in conjunction with high-resolution dGPS topographic surveys, reveal that the terrace surfaces are perpendicular to the fold's strike, and display increased rotation with age, implying that the anticline has grown by progressive limb rotation. We combine ¹⁰Be terrestrial cosmogenic nuclide(TCN) depth profile dating and optically stimulated luminescence(OSL) dating to develop a new chronology for the terraces along the Huangshui He since 550ka. Our in situ ¹⁰Be dating of fluvial gravels capping strath terraces suggests a relationship between the formation and abandonment of the terraces and glacial climate cycles since the middle-late Pleistocene. These data indicate that the formation of the four terraces occurred at ~550, ~430, ~350, and~60ka. We suggest that episodes of aggradation were facilitated by high sediment supply during glacial periods, followed by subsequent incision that led to abandonment of these terraces during deglaciation. Combining uplift and shortening distance with ages, we found the vertical uplift gradually decreased from 0.43 to 0.11mm/a, whereas the shortening rate was constant at ~0.3mm/a since the anticline began to grow. The shortening rates of the Ha anticline from geomorphology agree with current GPS measurements, and highlight the importance of determining slip rates for individual faults in order to resolve patterns of strain distribution across intermontane belts.

Paleoearthquake study is a basic research that can be favorable for the understanding of deformation pattern, intensity and time scale of the fault structure. The Yanqi Basin is an intermountain basin located in the eastern part of southern Tianshan Mountains. The present-day tectonic stress field of the basin is dominated by compression with strike-slip component. Both the north and the south marginal faults are Holocene active faults. The Kaiduhe Fault on the southern margin is a strike-slip fault. The Hejing Fault on the northern margin is a neogenic thrust-fold belt dominated by thrust faulting and extending towards the basin. The Hejing thrust fault has the potential to generate M7 earthquake in the future. Therefore, it is important to study the rupture model and time series of paleoearthquakes of the Hejing thrust fault-fold belt. According to the surveys, the major thrust fault at the south limb of the Haermodun anticline thrusts inwards the basin, with a dip angle of 30°, producing three paleoseismic scarps in T₁ terrace and washland. We determine the time series of six paleoseismic events by the cut-cover relationship of marker stratums in five trenches, date the age of stratums and colluvial wedges by ¹⁴C and OSL dating method, and obtain the recurrence intervals of the paleoseismic events using progressive constraining method. The rupture models of the Hejing fault are summarized. The fault F₁ ruptured in every paleo seismic event, but fault F₂ only ruptured in event E, F₃ only ruptured in event D and E. In other words, Event D ruptured the three faults simultaneously, Event E ruptured two faults, and the other events only ruptured fault F₁. There exist both certainty and uncertainty in the rupturing of Hejing thrust fault in the paleo-earthquakes.

With rapid improvement in resolution of three dimensional topographic data, more and more high-resolution remote sensing data are applied in the study of geomorphology and seismo-geology. The contour map, hill shading map and hypsometric tint map are original visualization methods of plan view for three dimensional topographic data. They all have their own advantages and have been widely used in screen display and plane graphics, and they usually are mixed and merged to enhance the expression ability of information as a complement to each other. But the results still can not completely satisfy the demand of displaying and exploring the hiding information. As a result, how to utilize sufficiently the high-resolution remote sensing data and various visualization methods to make better expression of topography and detect small geomorphic features has been concerned by many scientists.
A new topographic parameter, termed openness, and a new visualization method, termed RRIM, have been developed to enhance the three-dimension effect and produce a fine image of topographic structure with no shade, which does not need any professional ability for its audiences and additional instruments. In the meanwhile, the RRIM has the incomparable predominance in identifying the subtle tectonic geomorphic features, which is very important in the research of geomorphology. If the three dimensional topographic data have the highest resolution and positioning accuracy relative to the hand-held measuring devices in field work, the geomorphologic interpretation work indoors will take place of the field work in a large extent. As a result, the new visualization not only can improve work efficiency, but also reduce the amount of field work. For forest area, tough natural conditions area and no access area which are of research value, RRIM provides a better method and has an important practical value.
Finally, we hope that the new visualization method can play a larger role in geomorphologic interpretation work, especially in active tectonics research and active fault mapping.

Since the Wenchuan earthquake,the seismic hazard of the northeastern segment of the Longmenshan Fault zone as well as the Hanzhong Basin has drawn more and more concerns. However,the essential data needed for further analysis on the seismic hazard in this region is scarce at present time,hence there is an urgent need for an in-depth study on the activities of faults around the basin. The faults around the Hanzhong Basin include five main faults,namely,the northern margin fault of Hanzhong Basin,the southern margin fault of Hanzhong Basin,the Qingchuan Fault,the Chaba-Lin'ansi Fault and the southern margin fault of Liangshan. Based on several detailed field investigations on the geometric distribution,movement nature and active ages of the five faults,and with consideration of previous work,our study shows that the late-Quaternary tectonic activity in the basin is relatively intense in west and weak in east. The west section of the north-margin fault of the Hanzhong Basin(east of Baohe)was active in early late Pleistocene,while its eastern section(west of Baohe)was active in middle Pleistocene. The south-margin fault of the basin was also active in middle Pleistocene. And the three faults in the southwest of the basin were all active in late Pleistocene. This activity pattern of high in the west and low in the east is also demonstrated by the difference in thickness of Quaternary system and the distribution of small earthquakes.

Taking tectonic geomorphology of southeastern Ganzi-Yushu Fault zone as the research object,and based on remote sensing interpretation,the paper investigates the late Quaternary activity of the southeastern segment of Ganzi-Yushu Fault zone through trenching and detailed field investigation on several typical sites. We analyze the landscapes and calculate the late Quaternary slip rates along the fault zone at the sites in Shengkang township,Renguo township,Cuoa township,and Ria township,respectively.The horizontal and vertical slip rates are (7.6?0.5)mm/a and (1.1?0.1)mm/a at Shengkang township,(8.0?0.3)mm/a and (1.1?0.1)mm/a at Renguo township. And horizontal slip rate of Cuoa township is (10.3?0.4)mm/a.The horizontal and vertical slip rates of Ria township are (10.8?0.8)mm/a and (1.1?0.1)mm/a,respectively. Both trenches at Renguo township and Cuoa township have revealed several paleoearthquake events. Though there are some differences in fault tectonic styles revealed between the two trenches,the fault motion on this segment is of strike-slip with a certain amount of thrust component on the whole. Associated with the analysis of paleoearthquake events and slip rate,it is found that the southeastern Ganzi-Yushu Fault zone is subject to intensive activity since late Quaternary,especially since Holocene.

Using the complete core drilling method,we completed two boreholes on both sides of Xiadian active fault on which an M8.0 earthquake occurred in 1679.From rock cores of the two boreholes,we collected ¹⁴C,OSL and TL samples and determined their depositional ages. According to the geochronological data,and in combination with the sedimentary features of the formation in borehole cores,the late Pleistocene strata in XD1 hole can be divided into four stratigraphic sections. And the late Pleistocene revealed by borehole XD6 can also be divided into four stratigraphic sections. Late Pleistocene can be juxtaposed in the two boreholes; the deposition times of corresponding stratigraphic sections are also consistent. We collected some samples from XD1(on the upthrown plate)at a 0.5 meters interval roughly,and from XD6(downthrown plate)at a 1.0 meters interval. In State Key Laboratory of Earthquake Dynamics,we determined the FeO content with potassium permanganate titration method,and the Fe₂O₃ content using phenanthroline spectrophotometry. Comparing the Fe²⁺/Fe³⁺ ratio in same borehole core,we can find that the Fe²⁺/Fe³⁺ ratio of gray-black sediment is greater than gray-yellow sediment in the same drilling,and gray-black sediment is in a strongly reducing environment. When the same sedimentary strata are gray-black sediments,Fe²⁺/Fe³⁺ ratio in the strata on the fault's downthrown plate is larger than that on the upthrown plate. The reducing environment for the deposits on the fault's downthrown plate is stronger than the upthrown plate.

The Yanqi Basin is an important depression area of the Tianshan Mountains near the northeast margin of the Tarim Basin. The Hejing thrust-fold belt,a renascent thrust-fold belt with intense tectonic activity,is located on the north margin of the Yanqi Basin. We calculated the shortening and uplifting of the Hejing thrust-fold belt since Quaternary to analyze the tectonic activities of this region,then,made a preliminary estimation of the shortening and uplifting rate in the Yanqi Basin and compared the result with other areas to demonstrate the role of the Yanqi Basin in the tectonic deformation of Tianshan in late Cenozoic. With few seismic data but abundant attitude of stratum and fault,we restituted the geometry of the fold to calculate the shortening and uplifting of the fold and slip of the fault on the Hejing thrust-fold belt which has a simple and intact structural pattern,and obtained the shortening amount of 1.79km,0.88km and 26m,respectively since early Pleistocene(1.8Ma),middle Pleistocene(780ka) and late Pleistocene(80ka). The respective shortening rate is estimated as 0.99mm/yr,1.13mm/yr and 0.33mm/yr. The intensity of tectonic activity is not constant on the Hejing thrust-fold belt since the beginning of deformation. Compared with the result of crustal deformation,Yanqi Basin,as a major depression on southeastern Tianshan Mountains,absorbs most of crustal shortening of this area(86°～88°E)and exhibits strong deformation of the newborn thrust-fold belt on the northern margin of the basin.

Reverse fault-anticline is an important structure form in Tianshan area.The study on the syntagmatic relation and formation mechanism between active faults and anticline in reverse fault-anticline will help understand the structure system under extrusion stress.Haermodun anticline is a neogenic thrust-anticline in the north margin of the Yanqi Basin.It is the product of reverse fault extending to the inside of the basin.The main reverse fault of the anticline thrusts inwards the basin,with a dip angle of 30°.The present-day tectonic movement is intense along the fault.By interpreting aerial photos of the Haermodun anticline,measuring the scarp profiles and excavating trenches across the fault,we find that three different types of faults have been developed on the different levels of river terraces crossing the anticline,namely,the main reverse fault in front of the anticline forelimb(southern limb),the back thrust fault on the forelimb and the bending-moment normal fault on the top of the anticline,respectively.The main reverse fault has produced three scarps on T₁ terrace,with heights of 4m,0.8m and 1.8m,respectively,and a high scarp on T₂ terrace with a height of 16m.The back thrust fault has produced 2-4 reverse scarps,with the height up to 4m The bending-moment normal fault has produced about 10 scarps on all levels of terraces except T₁ on the top of anticline,and the height of a single scarp can reach 14.5m.The older the terrace,the higher the total height of scarp.Analysis on the geneses of the three faults reveals that the main reverse fault controls the growth of the Haermodun anticline.The back thrust faults help the main reverse fault release the compressive stress,and the part between the main reverse fault and the back thrust fault is extruded.The bending-moment normal fault is produced in the top of anticline.The top of the anticline is a tensional stress area.Back thrust fault and main reverse fault are synchronous.But the scale of back thrust fault is several times smaller than the main reverse fault.Bending-moment normal faults are synchronous with fold deformation.Accompanying the beginning of fold deformation,the bending-moment normal faults began to expand and grow gradually downwards from the top of anticline,synchronously.

The Hejing reverse fault-fold zone locates on the northern margin of the Yanqi Basin which lies in the south Tianshan Mts.The zone has been growing since early-Quaternary till now.The Xiaermudeng and Haermodun anticlines in the western of Hejing reverse fault-fold are discussed in this paper.Based on the analysis of satellite images and DEM(digital elevation model)data with the spatial resolution of 25m as well as field observation,our results suggest that the Xiaermudeng and Haermodun anticlines have uplifted and propagated laterally during the late Quaternary.Stream-flow direction,topographic sections,decrease of elevation of wind gap and hypsometric analysis indicate that Xiaermudeng anticline uplifted preceding the Haermodun anticline.We also believe that the Xiaermudeng anticline grows laterally from middle to side and Haermodun anticline grows laterlally from west to east.The flows crossing the anticline have diverted eastward under the tectonic movement during the Quaternary,producing a series of wind gaps with straths lowering from west to east.In the Xiaermudeng anticline area,from middle to the side,the drainage density(Dd)is decreased(5.37km^-1 to 2.65km^-1 and 3.07km^-1),and the slope of catchment is increased.The anticline of Haermodun shows a main deformation pattern of uplift and lateral propagation from west to east.The drainage density is decreased(3.87km^-1 to 2.37km^-1),the catchment has steep slope(4° to 6°),the hypsometric curve is from concave-convex to concave-down and the hypsometric integral (∫) is increased(0.45 to 0.76),Moreover,11 topographical cross-sections transecting the anticlines also reveal the lateral propagation from west to east of the Hejing reverse fault-fold zone.