The most significant feature of active faults on remote sensing images is fault lineament. How to identify and extract fault lineament is an important content of active fault research. The rapid development of remote sensing technology has provided people with extremely rich remote sensing data, and has also created the problem of how to choose suitable data for fault interpretation. In the traditional fault interpretation, people pay more attention to high-resolution optical images and high-resolution DEM, but optical remote sensing images are greatly affected by factors such as weather condition, vegetation and human impacts, and the time and economic costs for obtaining high-resolution DEM are relatively high. Due to the low resolution, the medium-resolution DEM(such as Aster GDEM, SRTM1, SRTM3, etc.)is generally used to automatically extract structural lineament, and then analyze the overall regional structural features, but it is rarely used to visually interpret active faults. ALOS-PALSAR DEM is generated from SAR images acquired by the phased array L-band synthetic aperture radar mission sensor of the Japanese ALOS satellite. It is currently a free DEM with the highest resolution(resolution of 12.5m)and the widest coverage. Based on ALOS-PALSAR DEM and ArcGIS 10.4 software, this paper generates a hillshade map and visually interprets the fault lineaments in the West Qinling Mountains. When generating a hillshade map, we set the light azimuths to be oblique or orthogonal to the overall trend of the linear structures, the light azimuths to be consistent with the slope direction of the hillslope, and the light dips to be a medium incident angle. Based on the hillshade map generated from ALOS-PALSAR DEM, this paper summarizes the typical performance and interpretation markers of fault lineaments on the hillshade map(generated by DEM), and visually interprets the V-shaped fault system in West Qinling Mountains where the research on fault geometry is limited based on the interpretation markers. The results of the research are as follows: First, this study discovers a number of fault lineament zones, including the fault lineament located between the Lintan-Dangchang Fault and the Guanggaishan-Dieshan Fault, the NE-directed fault lineament zone between the Lixian-Luojiapu Fault and the Liangdang-Jiangluo Fault, and the arc-shaped dense fault lineament zones distributed south of the Hanan-Daoqizi Fault and the Wudu-Kangxian Fault; Second, this study completes the geometric distribution images of the known active faults, such as the western and eastern sections of the Lintan-Dangchang Fault, the western and eastern sections of the Liangdang-Jiangluo Fault; Third, fault lineaments in the West Qinling Mountains exhibit a “V” shape, with two groups of fault lineaments trending NW and NE, whose tectonic transformation mainly consists of two kinds: mutual cutting and arc transition. The Lintan-Dangchang Fault cuts the Lixian-Luojiapu Fault, the Lintan-Dangchang Fault and the Guanggaishan-Dieshan Fault are connected with the Liangdang-Jiangluo Fault in arc shape, and the Tazang Fault is connected with the Hanan-Daoqizi Fault in arc shape. The research results show that ALOS-PALSAR DEM has an outstanding capability to display fault lineaments due to its topographic attributes and strong surface penetration. In circumstances when the surface is artificially modified strongly, the spectrum of ground objects is complex and the vegetation is dense, the ALOS-PALSAR DEM can display fault lineament that cannot be displayed on optical remote sensing images, indicating that the medium-resolution DEM is an effective supplement to high-resolution optical remote sensing images in the fault lineament interpretation. The research results are of great significance for improving the geometric image of the V-shaped fault system in the West Qinling Mountains. It is also the basis for further research on fault geometry, kinematics, regional geodynamics and seismic hazard.

Located in the intervening zone between Tibetan plateau and surrounding blocks, the Lintan-Dangchang Fault(LDF)is characterized by north-protruding arc-shape, complex structures and intense fault activity. Quantitative studies on its new activity play a key role in searching the seismogenic mechanism, building regional tectonic model and understanding the tectonic interaction between Tibetan plateau and surrounding blocks. The LDF has strong neotectonic activities, and moderate-strong earthquakes occur frequently(three M6~7 earthquakes occurred in the past 500 years, including the July 22nd, 2013, Minxian-Zhangxian M_S6.6 earthquake), but the new activity of the fault is poorly known, the geological and geomorphological evidence of the Holocene activity has not been reported yet. Based on remote sensing interpretation and macro-landform analysis, this paper studies the long-term performance of LDF. Based on the study of fault activity, unmanned aircraft vehicle photogrammetry and differential GPS, radiocarbon dating, etc., the latest activity of LDF is quantitatively studied. Then the research results, historical strong earthquakes and small earthquake distribution are comprehensively analyzed for studying the seismogenic mechanism and constructing regional tectonic models. The results are as follows: Firstly, the fault geometry is complex and there are many branch faults. According to the convergence degree of the fault trace and the fault-controlled macroscopic topography, the LDF is divided into three segments: the west, the middle and the east. The west segment contains two fault branches(the south and the north)and the south Hezuo Fault. The south branch of the west segment mainly dominates the Jicang Neogene Basin, and the south Hezuo Fault controls the south boundary of Hezuo Basin. The middle segment has more convergent and stable trace, consisting of the main fault and south Hezuo Fault, and these faults separate the main planation surface of the Tibetan plateau and Lintan Basin surface geologically and geomorphologically. The fault traces in the east segment are sparsely distributed, and the terrain is characterized by hundreds of meters of uplifts. The branch faults include the main fault, Hetuo Fault, Muzhailing Fault and Bolinkou Fault, each controlling differential topography. Secondly, the motion property of the LDF is mainly left-lateral strike-slip, with a relative smaller portion of vertical slip. The left-lateral strike-slip offset the Taohe River and its tributaries, gullies and ridges synchronously, and the maximum left-lateral displacement of the tributary of Taohe River can reach 3km. Meanwhile, the pull-apart basins and push-up ridges associated with the left-lateral fault slip are also developed in the fault zone. The performance of vertical slip includes tilting of the main planation surface, vertical offsets of the boundary and interior of Neogene basin and hundred meter-scale differential topography. The vertical offset of the Neogene is 300~500m. Thirdly, one fault profile was newly discovered in Gongqia Village, revealing a complete sequence of pre-earthquake-coseismic-postseismic deposition, and this event was constrained by the radiocarbon ages of pre-earthquake and post-earthquake deposition. The event was constrained to be 2090~7745aBP(confidence 2σ), which for the first time confirmed the Holocene activity of the fault. Fourthly, a gully with two terraces at least on the west side of Zhuangzi Village in the east segment of the main fault retains a typical faulted landform. The T2/T1 terrace riser of the gully has a left-handed dislocation of 6.3~11.8m, and the scarp height on terrace T2 is 0.4~0.7m, the radiocarbon age of the terrace T2 is7170~7310aBP, so the derived left-lateral strike-slip rate since the early Holocene in the east segment of the main fault is 0.86~1.65mm/a, and the vertical slip rate is 0.05~0.10mm/a. The derived slip rates are in line with the regional tectonic model proposed by the predecessors, so the LDF plays an important role in the internal deformation of the West Qinling. The clockwise rotation of the middle to east segments of the LDF acts as an obstacle to the left-lateral strike-slip motion, which inevitably leads to the redistribution and rapid release of stress, so earthquakes in the middle-east segment of the LDF are unusually frequent.

The Ebomiao Fault is a newly discovered active fault near the block boundary between the Tibetan plateau and the Alashan Block. This fault locates in the southern margin of the Beishan Mountain, which is generally considered to be a tectonically inactive zone, and active fault and earthquake are never expected to emerge, so the discovery of this active fault challenges the traditional thoughts. As a result, studying the new activity of this fault would shed new light on the neotectonic evolution of the Beishan Mountain and tectonic interaction effects between the Tibetan plateau and the Alashan Block. Based on some mature and traditional research methods of active tectonics such as satellite image interpretation, trenches excavation, differential GPS measurement, Unmanned Aircraft Vehicle Photogrammetry(UAVP), and Optical Stimulated Luminescence(OSL)dating, we quantitatively study the new activity features of the Ebomiao Fault.
    Through this study, we complete the fault geometry of the Ebomiao Fault and extend the fault eastward by 25km on the basis of the 20km-fault trace identified previously, the total length of the fault is extened to 45km, which is capable of generating magnitude 7 earthquake calculated from the empirical relationships between earthquake magnitude and fault length. The Ebomiao Fault is manifested as several segments of linear scarps on the land surface, the scarps are characterized by poor continuity because of seasonal flood erosion. Linear scarps are either north- or south-facing scarps that emerge intermittently. Fourteen differential GPS profiles show that the height of the north-facing scarps ranges from (0.22±0.02)m to (1.32±0.1)m, and seven differential GPS profiles show the height of south-facing scarps ranging from (0.33±0.1)m to (0.64±0.1)m. To clarify the causes of the linear scarps with opposite-facing directions, we dug seven trenches across these scarps, the trench profiles show that the south-dipping reverse faults dominate the north-facing scarps, the dipping angles range from 23° to 86°. However, the south-facing scarps are controlled by south-dipping normal faults with dipping angles spanning from 60° to 81°.
    The Ebomiao Fault is dominated by left-lateral strike-slip activity, with a small amount of vertical-slip component. From the submeter-resolution digital elevation models(DEM)constructed by UAVP, the measured left-lateral displacement of 19 gullies in the western segment of the Ebomiao Fault are(3.8±0.5)~(105±25)m, while the height of the north-facing scarps on this segment are(0.22±0.02)~(1.32±0.10)m(L₃-L₇), the left-lateral displacement is much larger than the scarp height. In this segment, there are three gullies preserving typical left-lateral offsets, one gully among them preserves two levels of alluvial terraces, the terrace riser between the upper terrace and the lower terrace is clear and shows horizontal offset. Based on high-resolution DEM interpretation and displacement restoration by LaDiCaoz software, the left-lateral displacement of the terrace riser is measured to be(16.7±0.5)m. The formation time of the terrace riser is approximated by the OSL age of the upper terrace, which is (11.2±1.5)ka BP at (0.68±0.03)m beneath the surface, and(11.4±0.6)ka at (0.89±0.03)m beneath the surface, the OSL age (11.2±1.5)ka BP at (0.68±0.03)m beneath the surface is more close to the formation time of the upper terrace because of a nearer distance to sediment contact between alluvial fan and eolian sand silt. Taking the (16.7±0.5)m left-lateral displacement of the terrace riser and the upper terrace age (11.2±1.5)ka, we calculate a left-lateral strike-slip rate of(1.52±0.25)mm/a for the Ebomiao Fault. The main source for the slip rate error is that the terrace risers on both walls of the fault are not definitely corresponded. The north wall of the fault is covered by eolian sand, we can only presume the location of terrace riser by geomorphic analysis. In addition, the samples used to calculate slip rate before were collected from the aeolian sand deposits on the north side of the fault, they are not sediments of the fan terraces, so they could not accurately define the formation age of the upper terrace. This study dates the upper terrace directly on the south wall of the fault.
    Since the late Cenozoic, the new activity of the Ebomiao Fault may have responded to the shear component of the relative movement between the Tibetan plateau and the Alashan Block under the macroscopic geological background of the northeastern-expanding of the Tibetan plateau. The north-facing fault scarps are dominated by south-dipping low-angle reverse faults, the emergence of this kind of faults(faults overthrusting from the Jinta Basin to the Beishan Mountain)suggests the far-field effect of block convergence between Tibetan plateau and Alashan Block, which results in the relative compression and crustal shortening. As for whether the Ebomiao Fault and Qilianshan thrust system are connected in the deep, more work is needed.

The NE margin of Tibetan plateau outspreads northeastward in late Cenozoic. The west Qinling locates at intervening zone among Tibetan plateau, Sichuan Basin and Ordos block, and is bounded by East Kunlun Fault in the southwest, the north margin of West Qinling Fault in the northeast, and the Longmen Shan Fault in the southeast. The west Qinling has been experiencing intense tectonic deformation since late Cenozoic, accompanying by uplift of mountains, downward incision of rivers, frequent moderate-strong earthquakes, vertical and horizontal motion of secondary faults, and so on. A series of "V-shape" faults are developed in the transfer zone between East Kunlun Fault and north margin of West Qinling Fault. The NWW-NW striking faults include Tazang Fault, Bailongjiang Fault, Guanggai Shan-Die Shan Fault, and Lintan-Dangchang Fault; EW-NEE-NE striking faults include Ha'nan-Qingshanwan-Daoqizi Fault, Wudu-Kangxian Fault, Liangdang-Jiangluo Fault, and Lixian-Luojiapu Fault. Among them, the Southern Guanggai Shan-Die Shan Fault (SGDF)is one of the principle branch which accommodates strain partitioning between the East Kunlun Fault and the north margin of west Qinling Fault. Although some works have been done and published, the geometry of SGDF is still obscure due to forest cover, bad traffic, natural and manmade reworks. In this paper, we collected remote sensing images with various resolutions, categories, imaging time. The selected images include composite map of Landsat image (resolution is 28.5m among 1984-1997, and 14.5m among 1999-2003), Landsat-8 OLI image (15/30m), Gaofen-1 (2m/8m), Pleiades (0.5m/2m), DEM (~25m)and Google Earth image (submeter resolution). After that, we reinforced tectonic information of those images by Envi5.2 software, then we interpreted SGDF from those images. As indoor interpretation fulfilled, we testified indoor interpretation results through geomorphological and geological investigation. Finally, we got fault distribution of SGDF. Conclusions are as follows:First, remote sensing image selection and management is crucial to indoor interpretation, and image resolution is the only factor we commonly consider before, however, things have changed in places where there is complex weather and dense vegetation. Image categories, imaging time and bands selected for compositing in pretreatment and etc. should all be taken into consideration for better interpretation. Second, SGDF distributes from Lazikou town in the west, extending through Pingding town, Zhou County, Huama town, then terminating at Majie town of Wudu district in the east, the striking direction is mainly NWW, and it could be roughly divided into 3 segments:Lazikou-Heiyusi segment, Pingding-Huama segment, and Huama-Majie segment, with their length amounting to 47km, 32.5km, 47km, respectively. The arrangement pattern between Lazikou-Heiyusi segment and Pingding-Huama segment is right-stepping, and the arrangement pattern is left-stepping bending between Pingding-Huama segment and Huama-Majie segment. Third, SGDF controlled magnificent macro-topography, such as fault cliff, fault facet, which often constitute the boundary of intermontane basins or erosional surfaces to west of Minjiang River. Micro-geomorphic expressions were severely eroded and less preserved, including fault scarps, fault troughs, sinistral offset gullies and geomorphic surfaces. Finally, SGDF mainly expresses left-lateral dominated motion, only some short branch faults with diverting striking direction exhibit vertical dominated motion. The left-lateral dominated component with little vertical motion of SGDF is consistent with regional NWW-striking faults as Tazang Fault, Bailongjiang Fault and Lintan-Dangchang Fault, also in coincidence with regional boundary faults such as east Kunlun Fault and north margin of west Qinling Fault, illustrating regional deformation field is successive in west Qinling, and NWW striking faults show good inheritance and transitivity on differential slip rate between east Kunlun Fault and west Qinling Fault. The geometry of SGDF makes quantitative studies possible, and also provides scientific basis for keeping construction away from fault traces.

Three-dimensional scanning with LiDAR has been widely used in geological surveys. The LiDAR with high accuracy is promoting geoscience quantification. And it will be much more convenient, efficient and useful when combining it with the Unmanned Aerial Vehicle (UAV). This study focuses on UAV-based Laser Scanning (UAVLS)geological field mapping, taking two examples to present advantages of the UAVLS in contrast with other mapping methods. For its usage in active fault mapping, we scanned the Nanpo village site on the Zhangxian segment of the West Qinling north-edge fault. It effectively removed the effects of buildings and vegetation, and uncovered the fault trace. We measured vertical offset of 1.3m on the terrace T₁ at the Zhang river. Moreover, we also scanned landslide features at the geological hazard observatory of Lanzhou University in the loess area. The scanning data can help understand how micro-topography affects activation of loess landslides. The UAVLS is time saving in the field, only spending about half an hour to scan each site. The amount of average points per meter is about 600, which can offer topography data with resolution of centimeter. The results of this study show that the UAVLS is expected to become a common, efficient and economic mapping tool.

On July 22,2013,the Minxian-Zhanxian M_S 6.6 earthquake occurred at the central-northern part of the South-North Seismic Belt. In the area,complicated structural geometries are controlled by major strike-slip fault zones,i.e.the Eastern Kunlun Fault and the Northern Frontal Fault of West Qinling. The distribution of related seismic disasters,namely,the ellipse with its major axis trending NWW,is in good accord with the strike of the Lintan-Tanchang Fault. Severe damages in the meizoseismal area of the Minxian-Zhangxian M_S 6.6 earthquake are located within the fault zone. So it is considered that the earthquake related damages are closely related to the complicated geometry of the Lintan-Tanchang Fault,and it also indicates that the earthquake is the outcome of joint action of its secondary faults. Based on field investigations,and by integrating the results of previous studies on active tectonics,structural deformation and geophysical data,it can be inferred that the southward extension of the Northern Frontal Fault of West Qinling and the northeastward extrusion of the Eastern Kunlun Fault in the process of northeastward growth of Tibetan plateau are the main source of tectonic stress. Basic tectonic model is provided for strong earthquake generation on the Lintan-Tanchang Fault.

We divide the north margin of Western Qingling Fault zone into six segments on the basis of new geology data,namely,Baoji,Tianshui,Wushan,Zhangxian,Huangxianggou and Guomatan segment from east to west.Each segment not only can rupture independently,but also can rupture together with others.The probability of seismic potential on these six segments and two combination segments is computed with the time-dependent seismic potential probability estimate method.We find from the result that,both the Huangxianggou and Zhangxian segments have the biggest probability of rupture in the future; and Tianshui segment is the second.If there will be a combined rupture,it is most likely to happen in Huangxianggou and Zhangxian segments,both of which have higher earthquake risk.We also compute b value along the fault zone.The image of b value indicates a high accumulated stress on the Huangxianggou and Tianshui segments.So we suppose that the two areas are the main locations where strong earthquakes may occur in the future.