Strong earthquakes(magnitude>6.5)typically cause coseismic surface ruptures of several kilometers or even hundreds of kilometers long on the surface. Coseismic surface rupture is the most intuitive geomorphic representation of an earthquake on the surface, and its geometry and distribution characteristics provide important information about the fault activity. Field investigation is the most basic means for research on coseismic surface fractures, but for areas that are hard to access or have harsh climatic environments, field investigation is often greatly limited. In recent years, the increasing abundance of high-resolution remote sensing images and the rapid development of photogrammetry methods can help us quickly obtain high-resolution topographic and geomorphic data of the study area, to better identify the fine geometry of the earthquake surface rupture zone and measure the offsets of geomorphic markers along the fault. The Litang Fault is a sinistral strike-slip fault located within the Sichuan-Yunnan rhombic block on the eastern edge of the Qinghai-Tibetan plateau. Several historical earthquake events have occurred on this fault, such as the 1890 and 1948 earthquakes, and clear seismic surface ruptures still exist along the fault so far. Previous studies have conducted a series of works on the coseismic surface rupture of this fault, but most of these works were based on field investigations or relatively low-resolution remote sensing images, and there is still a lack of fine research on the coseismic surface rupture of the fault. In this paper, the coseismic surface rupture of the 1890 earthquake which occurred on the Litang Fault was selected as the study object. To obtain high-resolution topographic data of this fault, the WorldView satellite stereo images were used to generate a 0.5-m-resolution orthophoto and a 1-m-resolution Digital Elevation Model(DEM)of the Litang fault based on the photogrammetry method. With the high-resolution topographic data, the fine geometry of the 1890 earthquake surface rupture zone was mapped in detail. The mapping results show that the total length of the surface rupture is about 27km, with an overall strike of N40°W. The rupture is mainly characterized by sinistral strike-slip motion, with a certain degree of dip-slip component in local areas. Except for the interval of approximately 6km with no surface rupture at the Wuliang River floodplain in the Litang Basin, the surface ruptures are relatively continuous at other locations. In addition, various rupture styles have been identified along the fault, including en echelon tension cracks, mole tracks, sag ponds, fault scarps, and displaced gullies. Furthermore, the sinistral offsets of 90 groups of linear geomorphic markers such as gullies and ridges were measured along the fault, which range from 1m to 82.4m. We further estimated the Cumulative Offset Probability Distribution(COPD)of the offsets located on the terrace I of the Wuliang River, which are all in the range of 0-9m. The COPD plot displays four distinct peaks at 1.3m, 2.4m, 4.3m, and6.1m, respectively. Previous studies have reported that the terrace I of Wuliang River formed at about(4 620±40)a BP. Thus, it can be indicated that the Litang fault may have experienced at least four strong earthquake events since(4 620±40)a BP, and the smallest peak of 1.3m may represent the coseismic displacement of the most recent 1890 earthquake. The rupture length of the latest 1890 earthquake was about 27km, and the coseismic sinistral offset was about 1.3m, yielding an estimated moment magnitude of M_W6.8-7.1. The coseismic offset of the other three earthquakes was about 1.8m, 1.9m, and 1.1m from old to new, respectively, yielding a magnitude estimate of M_W7.3, M_W7.3, and M_W7.0, with a size comparable to the 1890 earthquake. The research results fully demonstrate the potential of high-resolution remote sensing images in the study of fine characteristics of earthquake surface rupture.

As an important part of the land geomorphic unit, river is one of the main geological forces to shape the surface morphology. The fluvial geomorphic development characteristics are extremely sensitive to tectonic activities and record rich tectonic deformation information in geological history. Therefore, through the information extraction and quantitative analysis of bedrock river, we can reverse the relevant information about the tectonic evolution history. By extracting topographic information, comprehensively analyzing the spatial differences of fluvial geomorphological parameters, sieving the influencing factors such as tectonic, climatic and lithological characteristics, and quantifying the intensity of tectonic activity have become an important research tool for the segmental differences of active faults.

The Northern Zhongtiao Mountains Fault is an active fault that controls the uplift of the Zhongtiao Mountains and subsidence of the Yuncheng Basin, and can be divided into the Hanyang, Yongji, Yanhu and Xiaxian sections from south to north. The activity of each section of the fault is closely related to the shaping of the present-day topography of the Zhongtiao Mountains, and it is a typical area for applying quantitative analysis of fluvial landform to the study of the segmentation differences along the fault. So we can effectively study the distribution characteristics of tectonic activity in the fault zone through the river geomorphological features of Zhongtiao Mountains. In this paper, by extracting information on the river topography of the bedrock mountain watershed system on the northern slopes of the Zhongtiao Mountains, parameters such as the normalized steepness index k_sn, slope S, geometric features of the stream longitudinal profile of the drainage system, the location of the knickpoints and the amount of variant incision between upstream and downstream of the knickpoints are obtained. The results show that the bedrock channels on the northern slopes of the Zhongtiao Mountains has experienced accelerated incision in the longitudinal direction, and that the spatial variation of geomorphological parameters such as the normalized steepness index k_sn, slope S and fluvial incision in the lateral direction is dominated by tectonic uplift, with high values in the Hangyang-Yongji section and decreasing in a segmental manner towards the west, which is consistent with the topographic relief of the Zhongtiao Mountains, but contradicts the high slip rate area and the Cenozoic subsidence centre(the Salt Lake).

The geomorphic response to the slip rate is inconsistent with the topographic relief of the Zhongtiao Mountains, which is high in the west and low in the east. The high value area of geomorphic parameters reveals that the present active tectonic area of the Northern Zhongtiao Mountains Fault is located in the Hanyang-Yongji segment in the south, rather than the salt lake segment with high activity rate. The reason may be related to the migration of part of the activity of Huashan piedmont fault along the NE-trending hidden fault of Huayin Shouyang to the Hanyang Yongji segment of Zhongtiao Mountains. It suggests that the tectonic activity center of the Northern Zhongtiao Mountains Fault moves westward. Compared with the structural deformation caused by the change of sedimentary center, the time scale of river geomorphology response to structural deformation is shorter, and the landform is transformed most rapidly, which leads to the inconsistency between the geomorphological parameters and structural activities of the fault at the Northern Zhongtiao Mountains Fault.

In this paper, the seismic phase bulletin of 14381 earthquakes from January 1, 2009 to June 30, 2018 in the Weihe-Yuncheng Basin and its adjacent region were selected and analyzed. After removing the records with incomplete event information and insufficient station information, 11856 seismic events remained. A basic requirement for the double difference location method is that the distance between the pairs of seismic events is much smaller than the distance between the events and the stations and the linear scale of the velocity inhomogeneous body on the wave propagation path, so that the travel time difference between two earthquakes and the same station is only determined by the relative position between the two seismic events and the velocity of the seismic wave. In this case, the error caused by insufficient understanding of crustal structure can be effectively reduced and the result of relocation can be more accurate. Due to the large area, the whole study region was divided into three smaller parts for relocation of the events in order to reduce the influences of local structures. 8106 seismic events recorded by 52 stations were relocated using the double-difference location algorithm. It is found that the results constrained by the grid searching method are basically consistent with those obtained by other methods. The reliability of focal mechanism is affected by the number of initial motion and the azimuth distribution of the station. Therefore, when inversion of focal mechanism solution is carried out, earthquakes with more than 10 clear initial motion phases are selected, and the maximum azimuth gap between two stations with clear initial motion is required to be less than 90°. The azimuth coverage of the initial motion on the source sphere was measured according to azimuth and take-off angle distributions, and the focal mechanism solutions with poor coverage were eliminated. The contradiction ratio of focal mechanism solutions is less than 0.2. The average difference of b-axis of the best fitting solutions is less than 20°. Finally, the focal mechanism solutions of 346 seismic events with M_L≥2 were determined with initial motion of P and S waves. Normal type and strike-slip type earthquakes are widely distributed, accounting for more than 60% of all seismic events, and most of them are concentrated near fault zones. Before the formal inversion, the study area was divided into 1°×1° grids, and a series of damping coefficients were set to obtain the trade-off curve between the residual error of data fitting and the length of the stress field inversion model. The crustal stress field of 1°×1° grid in Weihe-Yuncheng Basin was obtained based on focal mechanism solution and stress tensor damping inversion method, and a certain number of depth profiles vertical to the faults were constructed for the analysis. The results show that compared with the original locations of seismic phase bulletin, the distribution of seismic events after relocation is more concentrated along the fault strike in plane. Vertically, they are densely distributed along the fault plane. There are more earthquakes in and around Shanxi graben, but the magnitude is generally small. The seismic activity in Weihe rift is relatively weak. Before the relocation, the focal depth distribution was concentrated in 5~10km, but after the relocation, the focal depth distribution changed significantly. The earthquakes were concentrated in the range of 10~25km, the overall focal depth was concentrated in the range of 20km, and a small number of earthquakes occurred in the range of 25~35km. The focal depth in the basin is relatively shallow with depth range of 5~15km. The focal depth at both ends of the basin tends to deepen, and the deepest depth can reach about 30km, which is consistent with the results of previous studies. The results of the depth profiles show that most of the fault planes in the study area have a large dip angle, similar to the occurrence of the surface, and some fault planes are even nearly vertical. The motion properties of fault structure and focal mechanism indicate that the faults in the study area are mainly normal and strike-slip ones. The results of stress field inversion indicate that the R values, which indicate the stress state, of the other regions are all less than 0.5 except for some areas in the southeastern margin of the research area. The stress state of Weihe-Yuncheng Basin tends to be tensile, and the maximum horizontal principal stress direction is nearly EW in Weihe rift and NNE and NEE in southern Shanxi rift, which is basically consistent with previous studies.

In the process of intense compression and shortening of the orogenic belt, a series of thrust faults and folds related to reverse faults developed in the piedmont. Determining the kinematic characteristics of these reverse faults and folds is of great significance for understanding the deformation mode of the orogenic belt. The Qilian Shan is located on the northeastern margin of the Tibetan plateau and is the front edge of the plateau expansion. The area has undergone strong tectonic activity since the Late Quaternary, with developed active structures and frequent earthquakes. There are a series of piedmont thrust faults and thrust related folds in the northern and southern margins of Qilian Shan. Compared with a large number of research results of active folds in Tian Shan area, the study of active folds in Qilian Shan is relatively weak. In the northern margin of the Qilian Shan, in addition to the study of individual active folds, most previous studies focused on the thrust faults in the northern margin of the Qilian Shan and the Hexi Corridor, and obtained the active characteristics of these faults. In the southern margin of Qilian Shan, that is, the northern margin of the Qaidam Basin, some studies have been carried out on paleoearthquakes and slip rate of the fault in the southern margin of Zongwulong Shan. However, the study on the late Quaternary folds in this area is relatively weak and there are only some sporadic works.
Shidiquan anticline is located in the intermountain basin surrounded by Zongwulong Shan and Hongshan in the northern margin of Qaidam Basin. It forms the first row fold structure in front of Zongwulong Shan with Huaitoutala and Delingha anticline. Constraining the tectonic geomorphic features of the Shidiquan anticline is of great significance for studying the crustal shortening in the northern margin of the Qaidam Basin and the expansion of the Qilian Shan to the Qaidam Basin. In this paper, the tectonic and geomorphic characteristics of Shidiquan anticline are obtained by means of geological mapping, high-precision differential GPS topographic profile survey, geological profile survey and cosmogenic nuclide dating. Field investigation shows that Shidiquan anticline is an asymmetric fold with steep south limb and gentle north limb, and is controlled by a blind reverse fault dipping northward. The age of the alluvial fan3 obtained from cosmogenic nuclide dating is(158.32±15.54)ka. This age coincides with the Gonghe Movement, indicating that the formation of Shidiquan anticline responds to the Gonghe Movement in the northeast margin of Tibetan plateau. The uplift rate of Shidiquan anticline since 158ka is(0.06±0.01)mm/a, and the shortening rate is(0.05±0.01)mm/a. The folding effect of Shidiquan anticline indicates that the folding of the intermountain basin in the northern margin of the Qaidam Basin, similar to the thrust shortening of the piedmont fault, plays an important role in regulating the shortening of the foreland crust.

Longshou Shan, located at the southern edge of the Alxa block, is one of the outermost peripheral mountains and the northeasternmost area of the northeastern Tibetan plateau. In recent years, through geochronology, thermochronology, magnetic stratigraphy and other methods, a large number of studies have been carried out on the initiation time of major faults, the exhumation history of mountains and the formation and evolution of basins in the northeastern Tibet Plateau, the question of whether and when the northeastward expansion of the northeastern Tibet Plateau has affected the southern part of the Alxa block has been raised. Therefore, the exhumation history of Longshou Shan provides significant insight on the uplift and expansion of the Tibetan plateau and their dynamic mechanism. The Longshou Shan, trending NWW, is the largest mountain range in the Hexi Corridor Basin, and its highest peak is more than 3 600m(with average elevation of 2800m), where the average elevation of Hexi Corridor is 1 600m, the relative height difference between them is nearly 2200m. This mountain is bounded by two parallel thrust faults: The North Longshou Shan Fault(NLSF)and the South Longshou Shan Fault(SLSF), both of them trends NWW and has high angle of inclination(45°~70°)but dips opposite to each other. The South Longshou Shan Fault, located in the northern margin of the Hexi Corridor Basin, is the most active fault on the northeastern plateau, and controls the uplift of Longshou Shan.Due to its lower closure temperature, the lower-temperature thermochronology method can more accurately constrain the cooling process of a geological body in the upper crust. In recent years, the low-temperature thermochronology method has been used more and more in the study of the erosion of orogenic belts, the evolution of sedimentary basins and tectonic geomorphology. In this study, the apatite (U-Th)/He(AHe) method is used to analyze the erosion and uplift of rocks on the south and north sides of Longshou Shan. 11 AHe samples collected from the south slope exhibit variable AHe ages between~8Ma and~200Ma, the age-elevation plot shows that before 13~17Ma, the erosion rate of the Longshou Shan is very low, and then rapid erosion occurs in the mountain range, which indicates that the strong uplift of Longshou Shan occurred at 13~17Ma BP, resulting in rapid cooling of the southern rocks. In contrast, 3 AHe ages obtained from the north slope are older and more concentrated ranging from 220Ma BP to 240Ma BP, indicating that the north slope can be seen as a paleo-isothermal surface and the activity of the north side is weak. The results of thermal history inverse modeling show that the South Longshou Shan Fault was in a tectonic quiet period until the cooling rate suddenly increased to 3.33℃/Ma at 14Ma BP, indicating that Longshou Shan had not experienced large tectonic events before~14Ma BP.
    We believe that under the control of South Longshou Shan Fault, the mountain is characterized by a northward tilting uplift at Mid-Miocene. Our results on the initial deformation of the Longshou Shan, in combination with many published studies across the northeastern margin of the Tibetan plateau, suggest that the compression strain of the northeastern margin of the Tibetan plateau may expand from south to north, and the Tibetan plateau has expanded northeastward to the southern margin of the Alxa block as early as Mid-Miocene, making Longshou Shan the current structural and geomorphic boundary of the northeastern plateau.

High-precision and high-resolution topography are the basis of quantitative study of active tectonics. Traditional methods are mainly interpreted from the remote sensing image and can only obtain two-dimensional, medium-resolution DEM(5~10m grid unit)or local three-dimensional surface deformation characteristics. A combination of offset and micro-relief information is essential for understanding the long-term rupture pattern of faults, such as in seismic hazard evaluation. The recently developed high-resolution light detection and ranging(LiDAR)technology can directly carry out high-precision and omni-directional three-dimensional measurement of the landform, and provide fine geomorphologic data for the study of active tectonics, which is helpful to deepen the understanding of surface rupture process and fault activity characteristics. In this study, we take part of the Xiaohongshan Fault, the western segment of Xiangshan-Tianjingshan Fault located in Gansu Province(NE Tibet), as an example of how LiDAR data may be used to improve the study of active faults. Using the airborne LiDAR technology, we obtain the three-dimensional surface deformation characteristics with high accuracy and establish the three-dimensional topographic model of the fault geomorphic. A high-resolution digital elevation model(DEM)of the Jingtai-Xiaohongshan Fault was extracted based on high-precision LiDAR data. Then the faulted geomorphic markers(gullies, ridges and terraces)were measured in detail along the fault, and different offset clusters and long-term sliding vector of different segments of the fault were finally acquired. We obtained the 82 horizontal displacements and 62 vertical displacements of geomorphic markers. According to the offset amounts, we observed peaks in the histogram by using the method of cumulative offset probability density and interpreted that each peak may represent an earthquake that ruptured the Xiaohongshan Fault. The results show that the horizontal and vertical displacements fall into five clusters, and the smallest cluster may indicate the coseismic slip of the most recent earthquake, while the other clusters may represent the slip accumulation of multiple preceding earthquakes. The sliding vectors constrained by the horizontal and vertical displacement of several typical geomorphic markers show obvious differences on different segments of the fault. The results show that the fault segment is divided into three segments from west to east, which indicates that the fault activity is not uniform along the fault.

Due to the interaction between the Tibetan plateau, the Alxa block and the Ordos block, the western margin of Ordos(33.5°~39°N, 104°~108°E)has complex tectonic features and deformation patterns with strong tectonic activities and active faults. Active faults with different strikes and characteristics have been developed, including the Haiyuan Fault, the Xiangshan-Tianjingshan Fault, the Liupanshan Fault, the Yunwushan Fault, the Yantongshan Fault, the eastern Luoshan Fault, the Sanguankou-Niushoushan Fault, the Yellow River Fault, the west Qinling Fault, and the Xiaoguanshan Fault.
    In this study, 7 845 earthquakes(M≥1.0)from January 1st, 1990 to June 30th, 2018 were relocated using the double-difference location algorithm, and finally, we got valid locations for 4 417 earthquakes. Meanwhile, we determined focal mechanism solutions for 54 earthquakes(M≥3.5)from February 28th, 2009 to September 2nd, 2017 by the Cut and Paste(CAP)method and collected 15 focal mechanism solutions from previous studies. The spatial distribution law of the earthquake, the main active fault geometry and the regional tectonic stress field characteristics are studied comprehensively.
    We found that the earthquakes are more spatially concentrated after the relocation, and the epicenters of larger earthquakes(M≥3.5) are located at the edge of main active faults. The average hypocenter depth is about 8km and the seismogenic layer ranges from 0 to 20km. The spatial distributions and geometry structures of the faults and the regional deformation feature are clearly mapped with the relocated earthquakes and vertical profiles. The complex focal mechanism solutions indicate that the arc-shaped tectonic belt consisting of Haiyuan Fault, Xiangshan-Tianjingshan Fault and Yantongshan Fault is dominated by compression and torsion; the Yellow River Fault is mainly by stretching; the west Qinling Fault is characterized by shear and compression. The structural properties of the fault structure are dominated by strike-slip and thrust, with a larger strike-slip component. The near-north-south Yellow River Fault is characterized by high angle NW dipping and normal fault motion.
    Based on small earthquake relocation and focal mechanism solution results, and in combination with published active structures and geophysical data in the study area, it is confirmed that the western margin of Ordos is affected by the three blocks of the Tibetan plateau, the Alax and the Ordos, presenting different tectonic deformation modes, and there are also obvious differences in motion among the secondary blocks between the active faults. The area south of the Xiangshan-Tianjingshan Fault has moved southeastward since the early Quaternary; the Yinchuan Basin and the block in the eastern margin of the Yellow River Fault move toward the SE direction.

On the basis of summarizing the circulation characteristics and mechanism of earthquakes with magnitude 7 or above in continental China, the spatial-temporal migration characteristics, mechanism and future development trend of earthquakes with magnitude above 7 in Tibetan block area are analyzed comprehensively. The results show that there are temporal clustering and spatial zoning of regional strong earthquakes and large earthquakes in continental China, and they show the characteristics of migration and circulation in time and space. In the past 100a, there are four major earthquake cluster areas that have migrated from west to east and from south to north, i.e. 1)Himalayan seismic belt and Tianshan-Baikal seismic belt; 2)Mid-north to north-south seismic belt in Tibetan block area; 3)North-south seismic belt-periphery of Assam cape; and 4)North China and Sichuan-Yunnan area. The cluster time of each area is about 20a, and a complete cycle time is about 80a. The temporal and spatial images of the migration and circulation of strong earthquakes are consistent with the motion velocity field images obtained through GPS observations in continental China. The mechanism is related to the latest tectonic activity in continental China, which is mainly affected by the continuous compression of the Indian plate to the north on the Eurasian plate, the rotation of the Tibetan plateau around the eastern Himalayan syntaxis, and the additional stress field caused by the change of the earth's rotation speed.
    Since 1900AD, the Tibetan block area has experienced three periods of high tides of earthquake activity clusters(also known as earthquake series), among which the Haiyuan-Gulang earthquake series from 1920 to 1937 mainly occurred around the active block boundary structural belt on the periphery of the Tibetan block region, with the largest earthquake occurring on the large active fault zone in the northeastern boundary belt. The Chayu-Dangxiong earthquake series from 1947 to 1976 mainly occurred around the large-scale boundary active faults of Qiangtang block, Bayankala block and eastern Himalayan syntaxis within the Tibetan block area. In the 1995-present Kunlun-Wenchuan earthquake series, 8 earthquakes with M_S7.0 or above have occurred on the boundary fault zones of the Bayankala block. Therefore, the Bayankala block has become the main area of large earthquake activity on the Tibetan plateau in the past 20a. The clustering characteristic of this kind of seismic activity shows that in a certain period of time, strong earthquake activity can occur on the boundary fault zone of the same block or closely related blocks driven by a unified dynamic mechanism, reflecting the overall movement characteristics of the block. The migration images of the main active areas of the three earthquake series reflect the current tectonic deformation process of the Tibetan block region, where the tectonic activity is gradually converging inward from the boundary tectonic belt around the block, and the compression uplift and extrusion to the south and east occurs in the plateau. This mechanism of gradual migration and repeated activities from the periphery to the middle can be explained by coupled block movement and continuous deformation model, which conforms to the dynamic model of the active tectonic block hypothesis.
    A comprehensive analysis shows that the Kunlun-Wenchuan earthquake series, which has lasted for more than 20a, is likely to come to an end. In the next 20a, the main active area of the major earthquakes with magnitude 7 on the continental China may migrate to the peripheral boundary zone of the Tibetan block. The focus is on the eastern boundary structural zone, i.e. the generalized north-south seismic belt. At the same time, attention should be paid to the earthquake-prone favorable regions such as the seismic empty sections of the major active faults in the northern Qaidam block boundary zone and other regions. For the northern region of the Tibetan block, the areas where the earthquakes of magnitude 7 or above are most likely to occur in the future will be the boundary structural zones of Qaidam active tectonic block, including Qilian-Haiyuan fault zone, the northern margin fault zone of western Qinling, the eastern Kunlun fault zone and the Altyn Tagh fault zone, etc., as well as the empty zones or empty fault segments with long elapse time of paleo-earthquake or no large historical earthquake rupture in their structural transformation zones. In future work, in-depth research on the seismogenic tectonic environment in the above areas should be strengthened, including fracture geometry, physical properties of media, fracture activity behavior, earthquake recurrence rule, strain accumulation degree, etc., and then targeted strengthening tracking monitoring and earthquake disaster prevention should be carried out.

The hypothesis that strong earthquakes in China mainland are controlled by the movement and interaction of active-tectonic blocks was advanced by Chinese scientists, with the remarkable ability to encompass geological and geophysical observations. Application of the active-tectonic block concept can illustrate 6 active-tectonic block regions and 22 active-tectonic blocks in mainland China and its neighboring regions. Systems of active-tectonic block boundaries are characterized by a zone of decades or hundreds of strong earthquakes. One of the greatest strengths of the modern active-tectonic block hypothesis is its ability to explain the origin of virtually all the M8 and 80% M7 earthquakes on the main continent in eastern Asia. In other words, active-tectonic block boundary stands in strong causal interrelation with recurrence behaviors of strong earthquakes and thus, it is possible to predict an earthquake occurrence in principle. After nearly two decades of development and improvement, the active-tectonic block hypothesis has established its theoretical foundation for the active tectonics and earthquake prediction, and is promoting the transition from probabilistic prediction to physical prediction of strong earthquakes. The active-tectonic block concept was tested by application to a well-documented, high-frequent earthquake area, and was found to be an effective way of describing and interpreting the focal mechanism and seismogenic environment, but there are still many problems existing in the active-tectonic block hypothesis, which confronts with rigorous challenges. Future progress will continue to be heavily dependent on the high-precision synthetic seismogram, especially of critical poorly documented settings. It is well known that strong earthquakes occur anywhere in the interactions among the active-tectonic block boundaries where there is sufficient stored elastic strain energy driving fault propagation, and then releasing the stored energy. Therefore, future studies will focus on the mechanism and forecast of the strong earthquake activity in the active-tectonic block boundary zone, with fault activity within the active-tectonic block boundary zone, quantifying current crustal strain status, upper crust and deep lithosphere coupling relation, strong earthquake-generating process and its precursory variation mechanism in seismic geophysical model as the main research contents, which are the key issues regarding deepening the theory of active-tectonic block and developing continental tectonics and dynamics in the modern earth science.

Slip rate is one of the most important parameters in quantitative research of active faults. It is an average rate of fault dislocation during a particular period, which can reflect the strain energy accumulation rate of a fault. Thus it is often directly used in the evaluation of seismic hazard. Tectonic activities significantly influence regional geomorphic characteristics. Therefore, river evolution characteristics can be used to study tectonic activities characteristics, which is a relatively reliable method to determine slip rate of fault. Based on the study of the river geomorphology evolution process model and considering the influence of topographic and geomorphic factors, this paper established the river terrace dislocation model and put forward that the accurate measurement of the displacement caused by the fault should focus on the erosion of the terrace caused by river migration under the influence of topography. Through the analysis of the different cases in detail, it was found that the evolution of rivers is often affected by the topography, and rivers tend to migrate to the lower side of the terrain and erode the terraces on this side. However, terraces on the higher side of the terrain can usually be preserved, and the displacement caused by faulting can be accumulated relatively completely. Though it is reliable to calculate the slip rate of faults through the terrace dislocation on this side, a detailed analysis should be carried out in the field in order to select the appropriate terraces to measure the displacement under the comprehensive effects of topography, landform and other factors, if the terraces on both sides of the river are preserved. In order to obtain the results more objectively, we used Monte Carlo method to estimate the fault displacement and displacement error range. We used the linear equation to fit the position of terrace scarps and faults, and then calculate the terrace displacement. After 100, 000 times of simulation, the fault displacement and its error range could be obtained with 95%confidence interval. We selected the Gaoyan River in the eastern Altyn Tagh Fault as the research object, and used the unmanned air vehicle aerial photography technology to obtain the high-resolution DEM of this area. Based on the terrace evolution model proposed in this paper, we analyzed the terrace evolution with the detailed interpretation of the topography and landform of the DEM, and inferred that the right bank of the river was higher than the left bank, which led to the continuous erosion of the river to the left bank, while the terraces on the right bank were preserved. In addition, four stages of fault displacements and their error ranges were obtained by Monte Carlo method. By integrating the dating results of previous researches in this area, we got the fault slip rate of(1.80±0.51)mm/a. After comparing this result with the slip rates of each section of Altyn Tagh Fault studied by predecessors, it was found that the slip rate obtained in this paper is in line with the variation trend of the slip rate summarized by predecessors, namely, the slip rate gradually decreases from west to east, from 10~12mm/a in the middle section to about 2mm/a at the end.

With the continuous collision of the India and Eurasia plate in Cenozoic, the Qilian Shan began to uplift strongly from 12Ma to 10Ma. Nowadays, Qilian Shan is still uplifting and expanding. In the northern part of Qilian Shan, tectonic activity extends to Hexi Corridor Basin, and has affected Alashan area. In the southern part of Qilian Shan, tectonic activity extends to Qaidam Basin, forming a series of thrust faults in the northern margin of Qaidam Basin and a series of fold deformations in the basin. The southern Zongwulong Shan Fault is located in the northeastern margin of Qaidam Basin, it is the boundary thrust fault between the southern margin of Qilian Shan and Qaidam Basin. GPS studies show that the total crustal shortening rate across the Qilian Shan is 5~8mm/a, which absorbs 20% of the convergence rate of the Indian-Eurasian plate. Concerning how the strain is distributed on individual fault in the Qilian Shan, previous studies mainly focused on the northern margin of the Qilian Shan and the Hexi Corridor Basin, while the study on the southern margin of the Qilian Shan was relatively weak. Therefore, the study of late Quaternary activity of southern Zongwulong Shan Fault in southern margin of Qilian Shan is of great significance to understand the strain distribution pattern in Qilian Shan and the propagation of the fault to the interior of Qaidam Basin. At the same time, because of the strong tectonic activity, the northern margin of Qaidam Basin is also a seismic-prone area. Determining the fault slip rate is also helpful to better understand the movement behaviors of faults and seismic risk assessment.Through remote sensing image interpretation and field geological survey, combined with GPS topographic profiling, cosmogenic nuclides and optically stimulated luminescence dating, we carried out a detailed study at Baijingtu site and Xujixiang site on the southern Zongwulong Shan Fault. The results show that the southern Zongwulong Shan Fault is a Holocene reverse fault, which faulted a series of piedmont alluvial fans and formed a series of fault scarps.The 43ka, 20ka and 11ka ages of the alluvial fan surfaces in this area can be well compared with the ages of terraces and alluvial fan surfaces in the northeastern margin of Tibetan Plateau, and its formation is mainly controlled by climatic factors. Based on the vertical dislocations of the alluvial fans in different periods in Baijingtu and Xujixiang areas, the average vertical slip rate of the southern Zongwulong Shan Fault since late Quaternary is(0.41±0.05)mm/a, and the average horizontal shortening rate is 0.47~0.80mm/a, accounting for about 10% of the crustal shortening in Qilian Shan. These results are helpful to further understand the strain distribution model in Qilian Shan and the tectonic deformation mechanism in the northern margin of Qaidam Basin. The deformation mechanism of the northern Qaidam Basin fault zone, which is composed of the southern Zongwulong Shan Fault, is rather complicated, and it is not a simple piggy-back thrusting style. These faults jointly control the tectonic activity characteristics of the northern Qaidam Basin.

With the development of photogrammetry technology and the popularity of unmanned aerial vehicles (UAVs)technology in recent years, using UAV photogrammetry technology to rapidly acquire high precision and high resolution topographic and geomorphic data on the fault zone has gradually become an important technical means. This paper first summarizes the basic principle and workflow of a new digital photogrammetry technology, SfM (Structure from Motion), which is simple, efficient and low cost. Using this technology, we conducted aerial image acquisition and data processing for a typical fault landform on the northern of Caka Basin in Qinghai. The digital elevation model (DEM)with 6.1cm/pix resolution is generated and the density of point cloud is as high as 273 points/m². The coverage area is 0.463km². Further, the terrain and slope data parallel to the fault direction are extracted by topographic analysis method, and combined with the contour map and the slope diagram generated by the DEM, a fine interpretation and quantitative study of complex multilevel geomorphic surfaces is carried out. Finally, based on the results of sophisticated interpretation of geomorphology, we got the vertical displacements of the T₁ terrace to the T₃ terrace as (1.01±0.06)m, (1.37±0.13)m and (3.10±0.11)m, and the minimum vertical displacements of the T₄ terrace and the T₅ terrace as (3.77±0.14)m and (5.46±0.26)m, respectively, through the topographic profile data extracted by DEM. Such vertical displacement parameters are difficult to obtain directly by traditional remote sensing images, which shows the great application prospect of UAV photogrammetry technology in the quantitative study of active tectonics.

The Langshan range-front fault (LRF)is a Holocene active normal fault that bounds the Langshan Mountain and Hetao Basin at the northwest corner of the Ordos Plateau. Paleoseismic trenching research at three sites, Dongshen Village trench (TC1), Qingshan trench (TC2)and Wulanhashao trench (TC3)from north to south was performed in this study to reveal the seismic hazard risk in Hetao Basin. The paleoevents ED1, ED2, ED3 from TC1 can be constrained to have occurred (6±1.3)ka, (9.6±2)ka and (19.7±4.2)ka respectively, while the paleoevent EQ1 from TC2 occurred about (6.7±0.1)ka and the paleoevents EW1, EW2, EW3 at TC3 took place about (2.3±0.4)ka, (6±1)ka and before 7ka respectively. In combination with paleoseismic results of previous researchers, the Holocene earthquake sequence of the LRF could be established as 2.3~2.43ka BP (E1), 4.41~3.06ka BP (E2), 6.71~6.8ka BP (E3), 7.6~9.81ka BP (E4), and (19.7±4.2)ka BP (E5). Although the possibility of missing events cannot totally be ruled out, based on the analysis on faulted geomorphology at Wulanhashao site, we argue the paleoearthquake history of the LRF during Holocene may be complete with an average recurrent interval about 2500 yrs. The apparent displacements associated with events E1, E3 and E4 are significantly larger than that of event, E2, that suggests that they might be great events with magnitudes 7.5 to even over 8 that ruptured the entire LRF, while the event E2 may be a smaller event that only ruptured a segment of the fault. The magnitude of event E2 might be about M7. This poses a significant seismic hazard to the area of the Linhe depression in the western Hetao graben region. With the further limitation of previous radiocarbon dating result near our trench site at Wulanhashao, the slip rate at Wulanhashao should be not smaller than, but close to 0.66mm/a since 15ka BP. And the slip rate at Qingshan site is supposed to be about 1.4~1.6mm/a since 6.8ka BP. Both our combined most recent paleoseismic cognition and current tectonic geomorphologic research results supports to reveal that the Langshan range-front fault now is an unsegmented fault, preferring to rupture the whole fault in a surface-rupture event. Considering the most recent event E1 and fault slip rate obtained above, the accumulated strain on the LRF could be estimated as about 1.52~3.94m. Given the ~2500a recurrent interval, we argue that the elapsed time since last major quake, E1, is approaching or even over the recurrence, and the seismic risk for another major quake is imminent, at least cannot be ignored.

The horizontal movement of the Helan Shan west-piedmont fault is important to determination of the present-day boundary between the Alashan and North China blocks as well as to the exploration of the extent of the northeastward expansion of the Tibetan plateau. Field geological surveys found that this fault cuts the west wing of the Neogene anticline, which right-laterally offset the geological boundary between Ganhegou and Qingshuiying Formations with displacement over 800m. The secondary tensional joints (fissures)intersected with the main faults developed on the Quaternary flood high platform near the fault, of which the acute angles indicate its dextral strike slip. The normal faults developed at the southern end of the Helan Shan west-piedmont fault show that the west wall of this fault moves northward, and the tensional adjustment zone formed at the end of the strike slip fault, which reflects that the horizontal movement of the main fault is dextral strike slip. The dextral dislocation occurred in the gully across the fault during different periods. Therefore, the Helan Shan west-piedmont fault is a dextral strike slip fault rather than a sinistral strike slip fault as previous work suggested. The relationship between the faulting and deformation of Cenozoic strata demonstrates that there were two stages of tectonic deformation near the Helan Shan west-piedmont fault since the late Cenozoic, namely early folding and late faulting. These two tectonic deformations are the result of the northeastward thrust on the Alashan block by the Tibet Plateau. The influence range of Tibetan plateau expansion has arrived in the Helan Shan west-piedmont area in the late Pliocene leading to the dextral strike slip of this fault as well as formation of the current boundary between the Alashan and North China blocks, which is also the youngest front of the Tibetan plateau.

In tectonically active regions, geomorphic features such as fluvial terraces can be interpreted as the consequence of tectonic and climatic forcing. However, deciphering and distinguishing tectonic impacts and climate changes remain a challenge. In this study, we examine the terraces along the Hongshuiba river and Maying river, which flow across the Fudongmiao-Hongyazi fault in the northern margin of the Qilian Mountains. Our purpose is to analyze the relative roles of tectonics and climate in shaping orogenic topography in this area. 8~9 levels of river terraces were identified through field observations, interpretation of satellite images and using DEMs. According to relative heights and ages of T₅ of the Hongshuiba river and T₆ of the Maying river, the incision rates are calculated to be (10.2±2.0)mm/a and (12.2±2.8)mm/a, respectively. Furthermore, the thrust rate along the Fodongmiao-hongyazi fault was determined based on offset terraces and OSL dating, which are ten times less than river incision rates approximately. Comparing the uplift rate and incision rate in the northern margin of the Qilian Mountains and adjacent areas, we inferred that climate change is the most plausible controlling factor in the evolution of the river terraces, while tectonics plays a minor role in this process.

Qilian Shan and Hexi Corridor, located in the north of Tibetan plateau, are the margin of Tibetan plateau's tectonic deformation and pushing. Its internal deformations and activities can greatly conserve the extension process and characteristics of the Plateau. The research of Qilian Shan and Hexi Corridor consequentially plays a significant role in understanding tectonic deformation mechanism of Tibetan plateau. The northern Yumushan Fault, located in the middle of the northern Qilian Shan thrust belt, is a significant component of Qilian Shan thrust belt which divides Yumushan and intramontane basins in Hexi Corridor. Carrying out the research of Yumushan Fault will help explain the kinematics characteristics of the northern Yumushan active fault and its response to the northeastward growth of the Tibetan plateau.Because of limited technology conditions of the time, different research emphases and some other reasons, previous research results differ dramatically. This paper summarizes the last 20 years researches from the perspectives of fault slip rates, paleao-earthquake characteristics and tectonic deformation. Using aerial-photo morphological analysis, field investigation, optical simulated luminescence(OSL)dating of alluvial surfaces and topographic profiles, we calculate the vertical slip rate and strike-slip rate at the typical site in the northern Yumushan Fault, which is(0.55±0.15)mm/a and(0.95±0.11), respectively. On the controversial problems, namely "the Luotuo(Camel)city scarp" and the 180 A.D. Biaoshi earthquake, we use aerial-photo analysis, particular field investigation and typical profile dating. We concluded that "Luotuo city scarp" is the ruin of ancient diversion works rather than the fault scarp of the 180 A.D. Biaoshi earthquake. Combining the topographic profiles of the mountain range with fault characteristics, we believe Yumu Shan is a part of Qilian Shan. The uplift of Yumu Shan is the result of Qilian Shan and Yumu Shan itself pushing northwards. Topographic profile along the crest of the Yumu Shan illustrates the decrease from its center to the tips, which is similar to the vertical slip rates and the height of fault scarp. These show that Yumu Shan is controlled by fault extension and grows laterally and vertically. At present, fault activities are still concentrated near the north foot of Yumu Shan, and the mountain ranges continue to rise since late Cenozoic.

High-precision and high-resolution topographic data are the basis of quantitative study of active tectonics. The appearance and rapid development of photogrammetry method provide an economical and effective technical means for obtaining high precision terrain data. Compared with traditional measurement methods, the photogrammetry method can be carried out in a wide range without being limited by the ground visibility conditions, and the measurement cost is also relatively low. Especially in recent years, with the rapid development of computer vision theory and efficient automatic feature matching algorithm, a 3D reconstruction technique called "Structure from Motion"(SfM)was introduced into the photogrammetry method, greatly improving the automation of the photogrammetry method. This paper mainly introduces the basic principle and the development of photogrammetry method, and also summarizes the application of photogrammetry method in the study of active tectonics, and finally demonstrates the great application potential of photogrammetry method in the quantitative study of active tectonics by displaying a specific application example.

LiDAR, as a newly developed surveying technology in recent decades, has been widely used in engineering survey, protection of cultural relics and topographic measurement, and it has also been gradually introduced to studies of tectonic activities. Although the digital photography technology has been used in the study of palaeoearthquake, the information would be still acquired by traditional geological sketch from trenches. Due to the limitation of photography itself, it is difficult to overcome the distortion of information. With its high information content, accuracy, convenience, safety and easy operation, LiDAR, as a new technology, broadens the access to data and information for palaeoearthquake study.

Interactions of two global-scale geodynamic systems control Cenozoic tectonic evolution of continental eastern Asia: the collisional and convergent system between Indian and Eurasian plates, the subduction and back-arc extensional system along the western Pacific and Indonesian oceanic margins. The warm and broad Tethys Ocean separates the Indian plate in the south from the Eurasian plate in the north, while the former subducts beneath the latter. In the meanwhile, the Pacific plate continuously subducts westward beneath the Eurasian plate. As the rate of subduction decreases with the time, back-arc extensional basins began to form due to trench rollback along the subduction zone. Though it is still under debate on the timing of initiation of collision between India and Eurasia, the main stage or significant collision probably took place between 55 and 45Ma. The collision and subsequent penetration of India into Eurasia cause retreat of the Tethys Ocean, crustal thickening of the southern and central Tibet, uplifting of Proto-Tibetan plateau, and southeastward extrusion of crustal material of Tibetan plateau. The timing and direction of extrusion of Tibet's crustal material coincide with acceleration of trench rollback of back-arc extensional system along the western Pacific and Indonesian oceanic margins. The collision caused shortening and trench rollback induced extension appear to form a causal "source-sink relationship". In the period of 30 to 20Ma, the northeastward convergence of the Tibetan plateau increased as the southeastward extrusion slowed down that in turn caused northeastward and eastward growth of the plateau. The Main Boundary Thrust became southern collisional boundary between the Indian and Eurasian plates. The northern deformational boundary migrated to the Kunlun Fault zone, forming compressional foreland basins such as the Qaidam, Hexi Corridor, and Longxi Basins. The rapid trench rollback has decreased along the subduction and back-arc extensional system along the western Pacific and Indonesian oceanic margins. As a result, the Japan Sea has ceased extension and the North China Plain Basin has changed from rifting to thermal subsidence. The east-west direction extension initiates in the interior of Tibetan plateau since approximate 10Ma ago, forming a series of north-trending grabens and half-grabens in the high altitudes above 5 000m. In the same time, the Tibetan plateau grows outward so that the Qilian Shan uplifted to form a major mountain range along the northern boundary and the Longmen Shan uplifted again to form an about 4000 relief with respect to Sichuan Basin. Along the eastern coast of Eastern Asia, subduction of Pacific plate beneath the Eurasian plate has accelerated to terminate back-arc extension.

Yellow River Fault is the longest, deepest fault in the Yinchuan Basin, also is the eastern boundary of the basin. Because its north section is buried, its activity and slip rate remains unknown, which made a negative impact on understanding the evolution and seismic hazard of the Yinchuan Basin. In this study, a composite drilling section with a row of drillholes were laid out along the northern section of the Yellow River Fault based on the results of shallow seismic exploration near the Taole Town, where oil seismic exploration data are available. Fault activity and slip rate are obtained by measuring the age of samples of holes. The results show that the northern section of the Yellow River Fault is a late Pleistocene or Holocene Fault, its accumulative displacement is 0.96m since (28.16±0.12)ka BP, with an average slip rate of 0.04mm/a, which is significantly lower than the southern section. The activity intensity of the northern section of the Yellow River Fault is significantly lower than the southern section since Late Quaternary. In the Yinchuan Basin, the Helanshan eastern piedmont fault is the most active fault since late Quaternary, next is the Yellow River Fault, then, the Yinchuan buried fault and Luhuatai buried fault. Although the Yellow River Fault is the deepest and the longest fault, its maximum potential earthquake is magnitude 7, this seismogenic capability is weaker than the relatively shallower Helanshan eastern piedmont fault, on which occurred the Pingluo M8 earthquake in 1739 AD. Yinchuan Basin is the result of long-term activities of the four major faults, which shaped the special structure of the different parts of Yinchuan Basin. The Yellow River Fault controlled the evolution of the south part of Yinchuan Basin. The two-layer crustal stretching model can help us understand the structural deformation between the upper crust and the lower crust beneath Yinchuan Basin. Deformation of the upper crust is controlled by several brittle normal faults, while the deformation of the lower crust is controlled by two ductile shear zones. The shear sliding on Conrad discontinuity coordinates the extensional deformation of different mechanical properties between the upper and the lower crust. Yellow River Fault might have cut deeply into the Moho in Mesozoic, the tectonic activity in Yinchuan Basin began to migrate and was partitioned into several faults since the beginning of the Cenozoic, mainly in the Helanshan eastern piedmont fault. This may be the reason why the Yellow River Fault has lower seismogenic capability than the shallower Helanshan eastern piedmont fault.

The Yabrai range-front fault is a normal fault,which is about 120km long,trends N60°E and distributes along the southeast margin of the Alashan block. In this paper,we focus on the geomorphology and kinematics of the Yabrai range-front fault,and discuss the implications of the fault for the regional tectonics.
This fault consists of three segments and the most active one is located in the southwest,which has a length of about 35km. The about 1～2m-high scarp,stretching almost the full segment,might be the result of the latest earthquake event. Fresh free surface indicates that the elapsed time of the last event should not be long.
The middle segment is about 31km in length. The results suggest that just a single fault is developed along the piedmont of the Yabrai Shan,and there is no evidence of recent activity on this fault. In contrast to the simple geometric structure of the middle segment,the northeast segment consists of several faults. The scarps of the most recent earthquake event,which are clear but discontinuous,are about 0.5～1.5m high and some are up to 2m. Although the scarps along the southwest and northeast segments of the fault are similar,it is difficult to suggest they are caused by the same earthquake without precise dating.
The seismic reflection profile suggests that the Yabrai range-front fault came into being as a normal fault in Cretaceous,when the Tibetan plateau did not emerge at that time. Therefore,we conclude that the Yabrai range-front fault is not the consequence of the Indo-Asian collision. But this region plays a great role in constraining the tectonic evolution of the Alashan block and therefore,the Tibetan plateau.

The April 20,2013,M_S 7.0 Lushan earthquake occurred along the southwestern part of the Longmen Shan Fault zone. Tectonics around the epicenter area is complicated and several NE-trending faults are developed. Focal mechanisms of the main shock and inversions from finite fault model suggest that the earthquake occurred on a northeast-trending,moderately dipping reverse fault,which is consistent with the strike and slip of the Longmen Shan Fault zone. NE-trending ground fissures and soil liquefaction along the fissures,heavy landslides along the Dachuan-Shuangshi and Xinkaidian Faults were observed during the field investigations. No surface ruptures were found in the field work. GPS data indicate that the fault on which this earthquake occurred is a fault east of or near the Lushan county and the earthquake also triggered slip on the fault west of the Lushan county. Field observations,GPS data,focal fault plane,focal depth,and distribution of the aftershocks suggest, that the seismogenic structure associated with the M_S 7.0 Lushan earthquake is the décollement beneath the folds of the eastern Longmen Shan. Slip along this decollement generated the earthquake,and also triggered the slip along the Dachuan-Shuangshi and Xinkaidian Faults.

On April 20,2013,a strong earthquake of M_S 7.0 struck the Lushan County,Sichuan Province of China. In this paper,basic information of the April 20,2013 Lushan earthquake,historical earthquakes in the Lushan earthquake struck area and associated historical earthquake-triggered landslides were introduced firstly. We delineated the probable spatial distribution boundary of landslides triggered by the Lushan earthquake based on correlations between the 2008 Wenchuan earthquake-triggered landslides and associated peak ground acceleration(PGA).According to earthquake-triggered landslides classification principles,landslides triggered by the earthquake are divided into three main categories: disrupted landslides,coherent landslides,and flow landslides. The first main category includes five types: rock falls,disrupted rock slides,rock avalanches,soil falls,and disrupted soil slides. The second main category includes two types of soil slumps and slow earth flows. The type of flow landslides is mainly rapid flow slides. Three disrupted landslides,including rock falls,disrupted rock slides,and soil falls are the most common types of landslides triggered by the earthquake. We preliminary mapped 3883 landslides based on available high-resolution aerial photographs taken soon after the earthquake. In addition,the effect of aftershocks on the landslides,comparisons of landslides triggered by the Lushan earthquake with landslides triggered by other earthquake events,and guidance for subsequent landslides detailed interpretation based on high-resolution remote sensing images were discussed respectively. In conclusion,based on quick field investigations to the Lushan earthquake,the classifications,morphology of source area,motion and accumulation area of many earthquake-triggered landslides were recorded before the landslide might be reconstructed by human factors,aftershocks,and rainfall etc. It has important significance to earthquake-triggered landslide hazard mitigation in earthquake struck area and the scientific research of subsequent landslides related to the Lushan earthquake.

On July 22,2013,an earthquake of M_S 6.6 occurred at the boundary between Minxian County and Zhangxian County,Gansu Province of China. Many landslides were triggered by the earthquake and the landslides were of various types,mainly in falls,slides,and topples occurring on loess cliffs,and also including soil deep-seated coherent landslides,large-scale soil avalanches,and slopes with cracks. Most of the landslides were distributed in an elongated area of 250km²,parallels to the Lintan-Dangchang Fault, with about 40km in length and the largest width of 8km. Landslides occurrence shows obvious difference along the central line of the elongated area,corresponding to different characteristics of different segments of the seismogenic fault. The elongated landslides main distribution area and the location of the epicenter indicate that the direction of the fault rupture propagation is from southeast-east to northwest-west. Finally,two probable reasons causing the horizontal distance of about 10km between the central line of the elongated area and the Lintan-Dangchang Fault are presented.

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.

Field investigation and damage evaluation of the Lushan M7.0 earthquake have revealed that the seismogenic fault of this earthquake is a typical blind fault with thrust component and there is no distinct surface rupture or deformation zone. The earthquake caused severe damage and failure such as mountain landslide,bedrock collapse,sand liquefaction on near-fault region and tensional fractures. In order to estimate the influence of strong ground motion on damage distribution,based on the inversion of slip distribution and rupture process on the source fault of the Lushan 7.0 earthquake,strong ground motion simulation is carried out with finite-fault model and three-dimension crust model of Lushan area and its adjacent region. In the finite-fault model,the rupture source is characterized as a low-angle fault plane with inhomogeneous slip distribution. The maximum slip on fault plane is up to 150cm. For the three-dimension crust model,deep fault structure,steep terrain and basin have been taken into account and described by different physical parameters. In this paper,the numerical simulation results of strong ground motion about Lushan main earthquake reveal two following major characters. The first is that the distribution characteristics of peak acceleration values,peak velocities and peak displacements on the ground surface shows good consistency with the seismic damage investigation. On the hanging-wall of the causative fault,high intensity of strong ground motion mainly concentrates on Baosheng,Longmen and the northern area of Lushan,which are located within the IX meizoseismal area. Around the area of Longmen town,the maximum acceleration of UD component reaches up to 350gal and the maximum transient displacement is up to 110cm,which are consistent with recordings and investigations. The second conclusion from simulation results is that the strong ground distribution and propagation process are influenced by basin effect and steep terrain. Seismic wave propagated back and forth in intermountain basins,combining with the amplification of thin soil layers,which directly caused and increased the earthquake damage.

K-Feldspar MDD(Multiple Diffusion Domain)and fission track are two commonly-used methods in low closure temperature thermal chronometry.By modeling both the feldspar ³⁹ Ar/⁴⁰ Ar data and the fission track age and track-length data,the thermal history that sample underwent can be revealed and the effective temperature range of both feldspar ³⁹ Ar/⁴⁰ Ar method and fission track method is extended.Because of the multiple resolution of modeling,it is important to restrict the modeling process to gain a reasonable result,though it seems difficult.The possible problem in modeling thermal history is presented in this paper,and the helpful method that can be used to improve the result is illustrated by the sample collected along Saishitengshan in the northern margin of Qaidam Basin.Three rapid cooling events,occurring at 130～150Ma,30～40Ma and 5～10Ma respectively,in northern margin of Qaidam Basin are revealed by feldspar MDD method and fission track method.

According to the new investigation in the northern Hexi corridor,remains of two surface rupture zones are discovered on the southern margin fault of Helishan.One rupture has the length of about 7km and the other about 10km.The two surface rupture zones might be produced by the nearest earthquake event.On the surface rupture zones,there are continuous scarp and free face caused by rupture.The scarp is about 1～1.5m high and on some site is up to 2m nearly.According to the OSL result,the nearest T₁ terrace and higher flood plain forming 3000a BP are dislocated by the fault.All above reveal that the rupture age should be later than that of T₁ terrace.But in the historical data and earthquake catalogue,we didn't find related information about the fault and surface rupture in this area.The 180 AD M 8 Biaoshi earthquake and 756 AD M 7 Zhangye-Jiuquan earthquake are documented in historical data.It is inferred by textual research that the two earthquakes are related with the northern marginal fault of Yumushan in the south of basin.Due to lack of reliable evidence,there still exist many arguments on this inferred conclusion.So we hold that the two surface rupture zones were produced by one of the two large earthquakes or another unrecorded historical event.The research on the activity and surface rupture of this fault can offer valuable information for the tectonic study and strong earthquake risk estimate of this region in the future.

Based on the field work and seismic reflection profiling data,the paper investigates the deformation characteristics of the Longquanshan Fault zone.The main thrust fault of the Longquanshan Fault belt lies in the west of the Longquanshan anticline and has different properties from northeast to southwest.In the north segment and south segment of the Longquanshan Fault,the plane of fault dips to northwest and is uncontinuous,but in the middle segment,the plane of fault dips to southeast and is continuous.Therefore,the middle part of the fault is the main segment of the Longquanshan Fault.Structural geometries of the middle segment of the fault suggest classical fault-propagation folding and the fault ruptured along different axial directions.Historical earthquakes and geomorphological response to activity of the Longquanshan Fault indicate that the fault was active from the early Pleistocene to late Pleistocene,and its activity is weak since the late Pleistocene,and gradually decreases from south to north.

Xiongpo anticline locates in Chengdu Basin,to the southeast of Longmenshan tectonic zone.It is an important deformation area where the Longmenshan thrust-nappe structure intrudes into the Chengdu Basin.The Pujiang-Xinjin Fault is an associated fault to Xiongpo anticline.The deformation mode between the fault and anticline fold is in concordance obviously.The geologic section across the anticline indicates that the south segment of Xiongpo anticline is an asymmetric fold and the northeast segment is symmetric,wide and gentle relatively.The fold includes Mesozoic and pre-Mesozoic strata.The topographical investigation reveals that the faulting is always associated with folding.At the northeast part of fold,the fold axial direction is parallel to the fault strike.Near the fault,the strata dips are remarkably different and the height difference of topography is large.The investigation of the Pujiang-Xinjin Fault did not reveal any obvious fault profiles and new activity characteristics.The Pujiang-Xinjin Fault has no influence on the gullies and T1 terraces widely developed in this area,but it controls the pluvial terrace which corresponds to T4 terrace of Nanhe river(the first-order branch of Minjiang River).The OSL age of the pluvial terrace is older than 130ka.All above indicates that the activity age of the Pujiang-Xinjin Fault is at the early-Quaternary.By the late-Quaternary,the faulting weakened or was nearly inactive.So in the area,the major tectonic character is faulting associated with fold deformation,which is also the major deformation mode of Xiongpo anticline.