The tectonic belt stretches approximately 400km from Lushan County to Wenchuan County in an east-west direction. The Longmenshan fault zone can be geometrically divided into several sections, including the Houshan Fault, the Central Fault, the Qianshan Fault, and the Foreland Basin(Chengdu Plain)Deformation Zone. The Central Fault is the main segment of the active tectonic belt in the Longmenshan region, and the Yingxiu-Beichuan Fault is one of the most active segments within this central section. The Yingxiu-Beichuan Fault has experienced numerous moderate and strong earthquakes throughout its history, including the Wenchuan earthquake 2008. The 2008 Wenchuan earthquake was ahigh destructive natural disaster that profoundly impacted the Chinese mainland, leading to significant economic losses and casualties. This earthquake caused extensive building collapses, leading to the loss of tens of thousands of lives, and triggered severe secondary geological disasters such as landslides, rockfalls, and mudflows, severely affecting the normal operation of transportation and communication infrastructure. The Yingxiu-Beichuan Fault was one of the key surface rupture zones during this earthquake. However, there is still some uncertainty about the slip rate of this fault.

The Baisha River segment examined in this paper is located in the southern part of the Yingxiu-Beichuan Fault, measuring approximately 14km long. This area contains 14 fractures of varying lengths and complex geometric structures, forming a fracture zone that reaches a maximum width of nearly 300m. The overall orientation of the rupture zone is about 50 degrees; however, the orientation of each small secondary rupture varies, with differences ranging from 0 to 90 degrees. The coseismic displacement along the Baisha River section displays complexity and diversity. The thrust movement primarily occurs on the northern and western walls, with some local thrust faults. Additionally, the strike-slip motion is predominantly right-lateral, exhibiting a maximum horizontal displacement of approximately 4.8m, although some local areas show left-lateral displacement.

Previous studies have employed various techniques, such as geology and geodesy, resulting in a wide range of slip rate estimates from 0.07mm/a to 1.1mm/a. The slip rate of fault is a crucial factor for analyzing the characteristics of fault activity and for studying regional kinematics and dynamic mechanisms. According to river terrace longitudinal profiles estimates, the fault has a vertical slip rate of about 0.3mm/a to 0.6mm/a. Estimates based on displaced landforms indicate a vertical slip rate between 0.07mm/a and 1.1mm/a. According to GPS observations, the horizontal slip rate in the Longmenshan fault zone has a limit of 2mm/a, but the slip rate of individual faults is lower than 0.7mm/a.

In recent years, remote sensing techniques have been extensively utilized to study surface rupture zones, particularly during significant seismic events. This paper primarily employs aerial and QuickBird satellite images captured before and after the earthquake. The resolution of the aerial images is nearly 1m, while the QuickBird satellite images have a resolution of 0.6m, both of which allow for precise interpretation of tectonic landforms. River terraces consist of terraced units, including terraced surfaces, steep terraces, terrace fronts, and terrace backs. As geomorphic markers that are relatively easy to identify and measure, river terraces are among the most essential geomorphic units in the quantitative study of active tectonics. They also serve as crucial geological relics documenting Quaternary tectonic movements and climate changes. By examining river terraces and their deformations, researchers can discuss the timing and scale of tectonic activity, making this a long-term area of research.

This paper focuses on the Baisha River section, situated in the southern part of the Yingxiu-Beichuan Fault. We employed geological and geomorphological methods along with optically stimulated luminescence dating, remote sensing interpretation, field investigations, and data analysis to assess the slip rate of the Baisha River section of the Yingxiu-Beichuan Fault within the Longmenshan fault zone. Additionally, we analyze the spatio-temporal variation characteristics of this slip rate. This study constrains the slip rate of the Baishahe segment of the Yingxiu-Beichuan Fault in the Longmenshan fault zone using 10 terrace cross-sections and terrace ages. The results indicate that the Yingxiu-Beichuan Fault Baisha River segment has a vertical slip rate since the Late Pleistocene ranges from(0.10±0.02)mm/a to(0.30±0.05)mm/a. Considering that only one event, the 2008 Wenchuan earthquake, is associated with the T1 terrace, we believe the calculated rate based on the dislocation and age of the T1 terrace may significantly deviate from reality. If we exclude the sliding rate of the T1 terrace, the vertical slip rate since the late Quaternary ranges between(0.10±0.03)mm/a and(0.30±0.05)mm/a. The linear fitting results indicate that the average vertical sliding rate since the late Quaternary is approximately 0.19mm/a.

These findings provide fundamental data for understanding the seismogenic structure of the Wenchuan earthquake and the overall characteristics of the Longmenshan fault zone, as well as for assessing its long-term seismic hazard.

Bedrock normal fault scarps, as classical topographic features and geomorphological markers along mountain range fronts, form in consolidated bedrock due to faulting in extensional settings. They generally preserve more complete records of paleo-earthquakes than fault scarps in unconsolidated sediments. With the development of technologies such as fault surface morphology measurement and terrestrial cosmogenic nuclide dating, bedrock fault planes have become a nice object for paleo-earthquake study in bedrock areas. The reconstruction of paleo-seismic history from a bedrock fault scarp in terms of the times, co-seismic slips and ages by a combination of quantitative morphological analysis, TCNs dating and other physical/chemical index has been proven feasible by several previous studies.

However, this success heavily relies on a suitable site selection along the bedrock fault scarp because erosional processes can exhume the bedrock fault surface, and the sedimentary processes can bury the bedrock fault surface. Namely, non-tectonic factors such as gully erosion, sediment burial, and anthropogenic activity make bedrock fault planes difficult to record and preserve paleo-seismic information.

Therefore, to successfully extract paleo-seismic information from the bedrock area, it is necessary to select suitable study points along the bedrock fault scarp in advance. Traditional survey and mapping methods are time-consuming and labor-intensive, and it is difficult to understand bedrock fault scarps. The resolution of satellite images cannot obtain the fine structure of bedrock fault scarps. Small unmanned aerial vehicle(sUAV), combined with Structure-from-Motion(SfM)photogrammetry has emerged over the last decade. It is used as an established workflow in acquiring topographic data by filling the spatial gap between traditional ground-based surveys and satellite remote sensing images. As a low-altitude photogrammetry technology, it can quickly obtain high-precision three-dimensional surface structures of bedrock fault scarps.

In this paper, taking the Majiayao bedrock fault scarp at the northern foot of Liulengshan in Shanxi Rift as an example, the high-precision and three-dimensional topographic data of the bedrock fault was obtained by using sUAV combined with SfM photogrammetry technology. The high-resolution and high-precision images of tectonic landforms can be obtained conveniently and efficiently by sUAV survey. The sUAV-obtained photos can be further processed by the SfM photogrammetry for generating a digital 3D structure of the bedrock fault scarp with true or shaded color.

The non-tectonic factors such as rock collapse, sediment burial, and gully erosion along the bedrock fault scarp are identified by interpreting the 3D model of the bedrock fault scarp. The profile shape characteristics of the erosion, burial and tectonic fault scarps are summarized through fine geomorphological interpretation and fault profile analysis. For the erosion profile, the hanging wall slope is down-concave, showing that the fault surface below the ground surface has been partially exposed. For the bury profile, the hanging wall slope shows an obvious concave-up shape, indicating that the lower part of the bedrock fault surface has been partially buried by the colluvium. For the tectonic profile, the hanging wall slope shows a smooth and stable slope, showing the exhumation of bedrock fault scarp is controlled purely by tectonics. Finally, the study sites suitable for paleo-earthquake study on bedrock fault surfaces were selected, showing the important role of sUAV aerial survey technology in the selection of paleo-earthquake study sites in bedrock areas.

This study illustrates that based on the high-precision three-dimensional surface structure of the bedrock fault plane from sUAV aerial survey, the existence of non-tectonic factors such as gully erosion, sedimentary burial and bedrock collapse can be clearly identified. These non-tectonic sites can be excluded when selecting suitable sites for paleo-earthquake study indoors. The shape analysis of bedrock fault scarp is also helpful to determine whether the bedrock fault surface is modified by surface process and suitable for paleo-seismic study. The sUAV aerial survey can play an important role in paleoseismic research in the bedrock area, which can accurately select the study points suitable for further paleo-seismic work in the bedrock area.

The spatial distribution and deformation characteristics of the coseismic surface rupture zone are the direct geomorphological expressions of deep fault activities on the surface, which not only record the information of seismic rupture and fault movement but also reflect regional stress and crustal movement. Therefore, prompt investigation on the surface rupture zone after the earthquake is helpful to understand tectonic activities of the seismogenic fault. However, fieldwork is limited by hazardous environments and secondary disasters in the earthquake zone. High-precision geomorphological observation technology can obtain unprecedented high temporal and spatial resolution of the earth's surface features without being restricted by natural conditions, and provide high-quality data for identifying historical earthquake surface ruptures, extracting surface coseismic displacement, and geological mapping of active structures, thus help to understand the rupture processes deeply. The photogrammetric method based on SfM(Structure from Motion)technology provides an effective technical way for fast acquisition of high-resolution post-earthquake topographic data and obtaining 3D geomorphic characteristics in a short time without the limitation of topography. Fuyun Fault is located on the southwest edge of the Altai Mountains. Fuyun M8.0 earthquake occurred in 1931 and produced a coseismic surface rupture zone with obvious linear characteristics. There also developed a large number of right-lateral gully offset, extrusion uplifts, pull-apart basins and a series of tectonic landforms related to strike-slip activities, which are still well preserved after several decades. In this study, the surface rupture zone of the 1931 Fuyun earthquake is selected as the study area. Based on aerial photogrammetry SfM method, a digital elevation model (DEM) with a resolution of 1m is generated, which can reflect micro-structural geomorphology and is suitable for fine geomorphology research in a small area. Combined with the shadow and color change of DEM data, the surface deformation characteristics such as seismic cracks and seismic mole tracks are identified, the surface rupture tracks are drawn in detail, and the surface rupture zone of Fuyun earthquake is segmented through the distribution of its geometric and tectonic geomorphological features. Using gullies as geomorphological markers, the smallest regional offset is regarded as the coseismic offset in the 1931 earthquake. We finally identified the right-lateral horizontal offset of gully along the rupture zone and measured it with software. The results show that the Fuyun earthquake surface rupture zone can be divided into 4 sections from north to south, each of which has different length, connected by compression uplift or pull-apart basin. The main type of surface rupture is shear crack, and there are also transpressional cracks, tension cracks, and tectonic geomorphological expressions such as mole track, ridge, and pull-apart basin. Based on the measurement of the horizontal offset of 194 groups of gullies, it is found that the average coseismic offset in the 1931 earthquake is(5.06±0.13)m, which is equivalent to the coseismic offset produced by similar magnitude earthquake. The area where the local absence or sudden change of coseismic offset occurs also has a good corresponding relationship with the geometry of stepover, which reflects the geometric location of the stepover to a certain extent. The results fill up the gap of the fine morphology of the Fuyun earthquake surface rupture zone and further demonstrate the good application value of high-resolution topographic data in the study of active structures.

Landform is the shape of the earth's surface, which is the combined influence of tectonic movement and surface erosion. Geomorphic indexes are the quantitative methods applied in geomorphology, aiming to extract the tectonic and erosion information from the surface morphology. Since the 1950s, the HI(Hypsometric Integral)had been used to quantitatively characterize the three-dimensional volume residual rate of drainage basins after erosion and to estimate the geomorphic evolution stage, and the relief had been used to evaluate the erosion response of regional tectonic uplift. Since the 1970s, with the construction of the stream power incision model, the k_sn(Steepness)based on the model has been widely used to estimate the distribution of uplift rate, and it has become an important branch of geomorphology to obtain the information contained in the landform by using geomorphic indexes. The quality of terrain data affects the research level of geomorphology. In the early stage of geomorphic research, field survey is the main method to carry out quantitative statistics of geomorphic units within a certain range. With the development of satellite remote sensing technology, DEM data are widely used in large-scale structural geomorphic research, such as the study of geomorphic parameters of orogenic belts. In recent years, with the further development of space exploration technology, a large number of high-quality DEM data have been produced. Based on these data, whether the geomorphic indexes methods which have been widely used in large-scale geomorphology research could be applied to small-scale geomorphology to extract more precise structural and geomorphic information has become an important issue of quantitative geomorphology research. In this paper, Dushanzi anticline in northern Chinese Tianshan foreland is taken as the research object to explore the application of geomorphic indexes methods to the study of small-scale geomorphology. Dushanzi anticline is a propagation fold formed in the foreland of Tian Shan Mountains as a result of the India-Eurasia collision and is still active since the Holocene. The geological outcrop of the Dushanzi anticline is about 90km². There are river channels which are well preserved on the anticline, providing an ideal area for the calculation of geomorphic indexes. Consequently, the area is an ideal place for the study of the application of geomorphic indexes methods in the small-scale geomorphology. Based on the 12.5m spatial resolution DEM from ALOS(Advanced Land Observing Satellite), we calculated the HI, k_sn and relief of the study area to explore their applicability to the study of small-scale geomorphology and then the geomorphic parameters are comprehensively analysed to discuss the structural and geomorphic information of anticline. The results indicate that: 1)In the quantitative study of small-scale geomorphology, the lower level drainage basins should be used to generate the HI on the premise of the accuracy of the data to improve the resolution of the HI results. Invalid data of small drainage basins should be eliminated in the process of calculating k_sn to ensure its accuracy although the density of the data will decrease. The smaller window should be used to calculate the relief on the premise of ensuring statistical error and research demand to improve the resolution of results. The higher resolution of DEM is helpful to improve the resolution and accuracy of the above indexes. 2)The results of geomorphic indexes indicate that the core of the anticline has higher uplift rate, larger erosion amount, smaller volume residual rate, and later stage of geomorphic evolution compared with the inclined end of the anticline and a continuous change of landform from intense down-cutting to topographic relaxation could be observed from the core to the inclined end of the anticline. The calculation results of geomorphic indexes are consistent with the geological facts of Dushanzi anticline, which shows that the geomorphic indexes methods are effective in the study of small-scale geomorphology.

Earthquakes commonly occur in the sliding surface of the fault zone. The morphology of the sliding surface is the result of fault activities, and also it evolves with the activities. The irregular geometry of the fault plane affects the sliding resistance, the concentration and anisotropy of the stress distribution within the fault plane and the fault shear strength. So, the acquisition of high-precision morphological features is of great significance for studying the correlation between fault surface morphology and seismic nucleation, fracture propagation and termination. Due to the lack of reliable micron-scale morphological measurement apparatus, the study of the coherence of the fault surface morphology from large scale(unit: m-cm)to small scale(unit: μm)is subject to restrictions, as well as the study of the relationship between the micro-morphology of the experimental frictional surface and the rupture process. In order to improve the measurement accuracy of the fault plane and overcome the shortcomings of existing measurement methods, we have invented a morphology measurement system with independent intellectual property rights.
The measuring principle of this morphology measurement system is based on the laser rangefinder theory. The frame of this system consists of four parts: Braced Frame, Moving Scanner Unit, System-Controlling Unit and Data Collection Unit. Braced Frame is made up of high-adjustable frame, loading stage, dust-proof box and isolation platform, which is used to provide a vibration isolation, light proof and dust-proof measuring environment. Moving Scanner Unit contains a laser head and a two-dimensional translation stag, the laser head is used to measure vertical distance and a two-dimensional translation stage carrying a laser head moving in X-axis and Y-axis orientation to provide X, Y coordinate values. System-Controlling Unit includes two-dimensional translation stage controller, laser head controller and signal convertor. The function of this part is mainly to control operation of other parts. The Data Collection Unit is composed of computer system and software module. This part connects other parts for receiving and storing data. In order to improve the scan efficiency, we developed new software by which we can precisely control the measuring process and efficiently process the acquired data. The software is comprised of five modules: 1)Move Module, this module is used to control the original moving of the laser head relative to the two-dimension translation stage and display the 3-dimensional coordinate information in real time; 2)Set Parameters of Scan Area, the function of this module is to obtain the XY coordinate values of four corner points of the target area to scan; 3)Scan Method Module, though this part, we can control the point spacing in the X-axis orientation by inputting velocity of laser header, as well as the point spacing in X-axis orientation by inputting the Y-step parameter; 4)Pre-Scan Module, there are three functions in this module to inspect whether the z-value of the target area is beyond the range of the laser head or not, estimate consuming time for scanning the object area under the predefined parameters and to estimate the size of the result file; and 5)Scan Module, the function of this module is to store the scanning data.
We scanned the camera lens and the standard plate whose standard deviations are lower than 5μm to acquire the precision of the measurement system, and the results show that the precision of the plane positioning (X-axis and Y-axis direction)is better than 3.5μm; the vertical measurement precision is better than 4.5μm. The highest resolution of the measurement system is constrained by the performance of the laser head and two-dimension translation stage, and the horizontal resolution can reach 0.62μm, vertical resolution 0.25μm. When the needed resolution is lower than the highest, we can achieve it through adjusting the parameter of the velocity in the X-axis orientation and steps in the Y-axis orientation. To test the practical effect of the measurement system, we scanned an area of frictional surface of experimental rock using this system and obtained a high-resolution topography data. From the DEM interpolated from the cloud data, we can observe the striation on the fault plane and the variation of the roughness distribution. The roughness and slope distribution results show that the topography measurement system can meet our requirements for analyzing the microscopic morphology on the micrometer scale.
Compared with traditional measurement devices, the morphology measurement system has the following advantages: 1)The measurement system can obtain the data even in a valley region with a large dip angle on the surface because the vertically emitted beam by the laser head is practically perpendicular to the surface. So compared with other means, it can avoid producing a blank area of measurements and get a complete area; 2)the measurement system has a larger measurement range of 30cm×30cm. When the high-resolution measurement is performed on a large scale, the error caused by the registration of multiple measurement results can also be avoided.

The existence of asperity has been confirmed by heterogeneously distributed seismic activities along the slipping surface associated with recent huge earthquakes, such as the M8.0 2008 Wenchuan earthquake and M9.0 2011 Tohoku-Oki earthquake. The location of asperity embedded in the seismogenic depth always corresponds to the area of high value of the co-seismic displacement and stress drop where the elastic energy is accumulated during the inter-seismic periods. Fault segmentation is an essential step for seismic hazard assessment. So far, the fault trace is dominantly segmented by considering its geometric features, such as bends and steps. But the connection between the asperity and geometric feature of the slipping surface is under dispute. Research on correlation between geometric feature of surface rupture and co-seismic displacement is of great significance to understand the relationship of seismicity distribution to geometric morphology of sliding surface. To scrutinize the correlation between the geometric feature and co-seismic displacement, we compiled 28 earthquake cases among which there are 19 strike-slip events and 9 dip-slip events. These cases are mainly collected from the published investigation reports and research papers after the earthquake occurred. All the earthquakes’ magnitude is between M_W5.4~8.1 except for the M_W5.4 Ernablla earthquake. The range of the rupture length lies between 4.5~426km. Each case contains surface rupture trace mapped in detail with corresponding distribution of co-seismic displacement, but the rupture maps vary in projected coordinate system. So, in order to obtain uniform vector graphics for the following data processing, firstly, vectorization of the surface rupture traces associated with each case should be conducted, and secondly, the vector graphics are transformed into identical geographic coordinate system, i.e. WGS1984-UTM projected coordinate system, and detrended to adjust its fitted trend line into horizontal orientation. The geometric features of surface rupture trace are characterized from three aspects, i.e. strike change, step and roughness. Previous studies about the rupture geometry always describe the characteristics from the whole trace length, consequently, the interior change of the geometric characteristics of the rupture is overlooked. In order to solve this problem, a technique of moving window with a specified window size and moving step is performed to quantify the change of feature values along the fault strike. The selected window size would directly affect the quantified result of the geometric feature. There are two contrary effects, large window size would neglect the detail characteristics of the trace, and small window size would split the continuity of the target object and increase the noise component. So we tested a set of sizes on the Gobi-Altay case to select a proper value and choose 1/25 of the whole rupture length as a proper scaling. Here, we utilize the included angle value of the fitted line in the adjoining windows, Coefficient of variation and the intercept value of the PSD(Power Spectra Density)for characterizing the change of strike, step size and roughness. The rupture trace is extracted within every moving window to calculate the aforementioned feature values. Then we can obtain three sets of data from every rupture trace. The co-seismic displacement is averaged in piecewise with uniform interval and moving step along the fault strike. Then, the correlations between three kinds of feature value and the co-seismic displacement are calculated respectively, as well as the P-value of correlation coefficient significant test.
We divided cases into two groups according to the slip mode, i.e. strike-slip group and dip-slip group, and contrast their results. In the correlation result list, there is an apparent discrepancy in correlation values between the two groups. The values of the strike-slip group mostly show negative, which indicates that geometric feature of the rupture trace is in inverse proportion to the displacement. In dip-slip group, the values distribute around zero, which suggests the geometric features is irrelevant to the displacement. Through the analysis of the correlation between the surface rupture and co-seismic displacement, the following conclusions can be reached: 1)In comparison with the dip-slip earthquake type, the characteristics of surface rupture of strike-slip earthquakes have a higher-level of correlation with the distribution of the co-seismic displacement, which suggests that the geometric features of strike-slip active faults may have a higher reference value in the fault-segmentation research than the dip-slip type; 2)In most strike-slip events, there is a negative correlation between the geometric features and the co-seismic displacement, which implicates that the higher the feature values of the steps, strike change and roughness, the lower the corresponding co-seismic displacement is; 3)Among the three quantified features of the surface rupture trace, the ranking of relevancy between them and the co-seismic displacement is: step size>strike change>roughness.

With the development and breakthrough of a series of techniques such as the fault surface morphology measurement, the geochemical element determination and Quaternary dating methods, it becomes possible to study paleo-earthquake using information recorded by the bedrock fault surface. At present, more and more scholars domestic and overseas have carried out a large number of paleo-earthquake studies on bedrock fault surfaces in different professional perspectives and have achieved a series of innovative results. This paper systematically introduces the development history, the current situation and the basic principles and applications of paleo-earthquake study on bedrock fault surface. Moreover, after the thorough discussion of the existing problems in paleo-earthquake research of bedrock fault surface, some suggestions for optimizing the current work are proposed. Finally, on the basis of comparison of the characteristics, advantages and disadvantages of various research methods, the prospects and development trends of the bedrock fault paleo-earthquake study are predicted. Lots of weaknesses and limitations in the current study are pointed out in this paper:Firstly, for the method of faullt surface morphology measurement, different morphological expression parameters exist nowadays, however, their advantages and disadvantages are unknown. Secondly, the TCNs method still has a large uncertainty in the age determination of the paleo-earthquake, and the mature cosmogenic nuclides dating methods is too few to meet the dating requirements of different lithologic fault surfaces. Besides, a reliable relationship between relative dating parameters such as morphologicl and physicochemical characteristics and the absolute dating method such as TCNs are not closely established to build a reliable chronology framework. The last but not the least, the lack of mechanical research on the physical and chemical biological processes that the bedrock fault surface experienced before and after the faulting and exposure, and insufficient multi-method comprehensive comparison are also the obstacles for the paleo-earthquake study on bedrock fault surface. It is suggested that in the future study of paleo-earthquakes on bedrock fault surfaces, more attention should be paid to the following aspects:Firstly, strengthen the evaluation of the reliability, applicability and accuracy of the parameters of each morphological model in time and improve the mathematical model of current dating techniques, optimize the mechanism of cosmogenic nuclide production, and introduce new high-precision dating technology timely; Secondly, strive to establish a reliable age framework between relative dating index(X)and absolute dating age(T)regionally; In addition, the morphological structure and mineral compositions of bedrock fault surface are analyzed proactively on the microscopic scale, and the mechanical study is conducted on a series of physical, chemical and biological processes that the fault surface experienced before and after the exposure. At last, comprehensive and comparative research need to be conducted by the multi-disciplinary and multi-method approaches. In conclusion, the paleo-earthquake study on the bedrock fault surface is going through the processes from the qualitative description to the quantitative expression, from the single-disciplinary method to the multi-disciplinary integration, from the exploration of a certain technical index to the comprehensive application of multi-source data technology. The combination of relative dating indicators(X)and absolute dating(T), and putting more emphasis on the mechanical study on the microscopic scale are the development trends of paleo-earthquake study on the bedrock fault surface. The close combination of the paleo-earthquake study of the bedrock fault surface with the traditional method of trenching conducted in the Quaternary sediment region is considered to help more effectively reconstruct a more complete paleo-earthquake sequence and the faulting history on the active fault zone, thus a more reasonable evaluation of the regional seismic hazard can be obtained.

Fault-related tectonic geomorphologic features are integrated expressions of multiple strong seismological events and long-term surface processes, including crucial information about strong earthquake behavior of a fault. It's of great significance to identify the strong seismic activity information from faulted landscapes, which include the date and sequence of the seismic activities, displacements, active fault features, for studying the seismic rupture process, predicting the future seismic recurrence behavior and evaluating the seismic hazard of the fault.
However, due to the restriction of measuring techniques and the subsequent poor quality of the acquired data, it has been difficult to accurately extract such information from complex tectonic landforms to study active faults for a long time. Recently, "small Unmanned Aerial Vehicle(sUAV)" photogrammetric technique based on "Structure from Motion(SfM)" provides a cost-efficient and convenient access to high-resolution and high-accuracy "digital elevation models(DEMs)" of tectonic landforms.
This paper selects the Tangjiapo area at the Haiyuan Fault to conduct data collection, in which the structural and geomorphic features are well preserved. Using a small quadrotor unmanned aerial vehicle(Inpire 2), we collect 1598 aerial photographs with a coverage area of 0.72km². For calibrating the accuracy of the aerial data, we set 10 ground control points and use differential-GPS to obtain the spatial coordinates of these control points. We use model software Agisoft PhotoScan to process these digital pictures, obtaining high-resolution and high-accuracy DEM data with the geographic information, in which data resolution is 2.6cm/pix and the average density of point cloud is 89.3 point/m². The data with these accuracy and resolution can fully show the real geomorphic features of the landform and meet the requirements for extracting specific structural geomorphic information on the surface.
Through the detailed interpretation of the tectonic landforms, we identify a series of structures associated with the strike-slip fault and divide the alluvial fan into four stages, named s₁, s₂, s₃, and s₄, respectively.Wherein, the s₁ is the latest phase of the alluvial fan, which is in the extension direction of the Haiyuan Fault and there isn't any surface fracture, indicating that the s₁ was formed after the M8.5 Haiyuan earthquake in 1920. The rupture zone on the s₂ fan is composed of varied kinds of faulting geomorphologic landforms, such as a series of en echelon tension-shear fractures trending 270°~285°, fault scarps and seismic ridges caused by the left-lateral motion of the seismic fault. In addition, a number of field ridges on the s₂ fan were faulted by the 1920 Haiyuan M8.5 earthquake, recording the co-seismic displacements of the latest earthquake event. Relatively speaking, the surface rupture structure of the s₃ fan is simple, mainly manifested as linear fault scarp with a trend of 270°~285°, which may indicate that multiple earthquakes have connected the different secondary fractures. And a small part of s₄ fan is distributed in the southwest of the study area without fault crossing.
Furthermore, we measured the horizontal displacements of river channels and vertical offsets of fault scarps. The faulted ridge on the s₂ fan and faulted gully on the s₃ fan provide good linear markers for obtaining the fault left-lateral dislocation. We used the graphical dislocation measurement software LaDiCaoz developed based on Matlab to restore the gully position before the earthquake by comparing the gully morphology on both sides of the fault, and then determined the horizontal offset of s₂, which is(4.3±0.4)m and that of s₃ is(8.6±0.6)m. In addition, based on the DEM data, we extracted the fault scarp densely along the fault strike, and obtained the vertical offset of s₂, which is(4.3±0.4)m and that of s₃ is(1.79±0.16)m.
Moreover, we detect slope breaks in the fault scarp morphology. For compound fault scarps generated by multiple surface rupture earthquakes, there are multiple inflection points on the slope of the topographic section, and each inflection point represents a surface rupture event. Therefore, the slope break point on the scarp becomes an important symbol of multiple rupture of the fault. The statistical result shows that the slope breaks number of s₂ is 1 and that of s₃ is 2. Based on the analysis of horizontal displacements of river channels and vertical offsets of fault scarps as well as its slope breaks, two surface rupturing events can be confirmed along the Tangjiapo area of the Haiyuan Fault. Among them, the horizontal and vertical displacements of the older event are(4.3±0.95)m and(0.85±0.22)m, respectively, while that of the latest event are(4.3±0.4)m and(0.95±0.14)m, which are the coseismic horizontal and vertical offsets of the 1920 Haiyuan earthquake.
These recognitions have improved our cognitive level of the fine structure of seismic surface rupture and ability to recognize paleoearthquake events. Therefore, the high-resolution topographic data obtained from the SfM photogrammetry method can be used for interpretation of fine structure and quantitative analysis of microgeomorphology. With the development of research on tectonic geomorphology and active tectonics toward refinement and quantification, this method will be of higher use value and practical significance.

The quantitative analysis of morphologic characteristics of bedrock fault surface is a useful approach to study faulting history and identify paleo-earthquake. It is an effective complement to trenching technique, specially to identifying paleo-earthquakes in a bedrock area where the trenching technique cannot be applied. This paper focuses on the Luoyunshan piedmont fault, which is an active normal fault extending along the eastern boundary of the Shanxi Graben, China. There are a lot of fault scarps along the fault zone, which supply plentiful samples to be selected to our research, that is, to study faulting history and identify paleo-earthquakes in bedrock area by the quantitative analysis of morphologic characteristics of fault surfaces. In this paper, we calculate the 2D fractal dimension of two bedrock fault surfaces on the Luoyunshan piedmont fault in the Shanxi Graben, China using the isotropic empirical variance function, which is a popular method in fractal geometry. Results indicate that the fractal dimension varies systematically with height above the base of the fault surface exposures, indicating segmentation of the fault surface morphology. The 2D fractal dimension on a fault surface shows a ‘stair-like’ vertical segmentation, which is consistent with the weathering band and suggests that those fault surfaces are outcropped due to periodic faulting earthquakes. However, compared to the results of gneiss obtained by the former researchers, the characteristic fractal value of limestone shows an opposite evolution trend. 1)The paleo-earthquake study of the bedrock fault surface can be used as a supplementary method to study the activity history of faults in specific geomorphological regions. It can be used to fill the gaps in the exploration of the paleo-earthquake method in the bedrock area, and then broaden the study of active faults in space and scope. The quantitative analysis of bedrock fault surface morphology is an effective method to study faulting history and identify paleo-earthquake. The quantitative feature analysis method of the bedrock fault surface is a cost-effective method for the study of paleo-earthquakes in the bedrock fault surface. The number of weathered bands and band height can be identified by the segment number and segment height of the characteristic fractal dimension, and then the paleoearthquake events and the co-seismic displacement can be determined; 2)The exposure of the fault surface of the Luoyunshan bedrock is affected and controlled by both fault activity and erosion. A strong fault activity(ruptured earthquake)forms a segment of fault surface which is equivalent to the vertical co-seismic displacement of the earthquake. After the segment is cropped out, it suffers from the same effect of weathering and erosion, and thus this segment has approximately the same fractal dimension. Multiple severe fault activities(ruptured earthquake)form multiple fault surface topography. The long-term erosion under weak hydrodynamic conditions at the base of the fault cliff between two adjacent fault activities(intermittent period)will form a gradual slow-connect region where the fractal dimension gradually changes with the height of the fault surface. Based on the segmentation of quantitative morphology of the two fault surfaces on the Luoyunshan piedmont fault, we identified four earthquake events. Two sets of co-seismic displacement of about 3m and 1m on the fault are obtained; 3)The relationship between the fault surface morphology parameters and the time is described as follows:The fractal dimension of the limestone area decreases with the increase of the exposure time, which reflects the gradual smoothing characteristics after exposed. The phenomenon is opposite to the evolution of the geological features of gneiss faults acquired by the predecessors on the Huoshan piedmont fault; 4)Lithology plays an important role in morphology evolution of fault surface and the two opposite evolution trends of the characteristic fractal value on limestone and gneiss show that the weathering mechanism of limestone is different from that of the gneiss.

Since the 1970s, active tectonics has advanced from qualitative research to quantitative research. Many researchers focus on which qualitative parameters to obtain and how to obtain them. It is usually accepted that the following parameters are necessary for quantitative descriptions of active faults:length of a fault or segment, displacements, slip rates, and paleo-earthquake events. Because of the complex nature of problems concerned and limited capability of human recognition, there are still some errors and uncertainties in these parameters. Tectonic geomorphology provides a useful tool to help solve the problems above. Tectonic geomorphology could record long-term accumulation of tectonics, and quantize them by relevant parameters. Tectonic movements have been exerting significant influence upon formation of topography and landforms, and such processes are usually extremely slow over very long time which cannot be documented by human history and any instruments. Observations, especially direct measurements of various features of geomorphology can reveal details of tectonic movement, including slip on active faults. In the early time, such studies were usually limited in one or two parameters of geomorphology to characterize active tectonics. With rapid development of computer and DEM technologies, it is possible to use multiple parameters of landforms to describe regional tectonic activity. Previous work in this aspect focused on large scales, while a little on small scale faults or individual faults. And existing studies are mostly concerned with normal or thrust faults dominated by vertical motion. In this paper, we focus on the Nantinghe Fault, which is strike-slip fault. Based on high resolution DEM extracted from ALOS data, we extract 180 drainages along the Nantinghe Fault. Based on the relationship between deflection angles and faulting, we analyze the segmentation and activity. Using the distribution patterns of the factors, this study examines the geometry and activity of the Nantinghe Fault, which were obtained from comprehensive remote sensing interpretation and field investigations. The results provide an example for research on the relationship between faulting and landforms.

Tsunami is one of the most devastating natural coastal disasters. Most of large tsunamis are generated by submarine earthquakes occurring in subduction zones. Tsunamis can also be triggered by volcano eruptions and large landslides. There are many records about "sea-overflow" in Chinese ancient books, which are not proved to be tsunamis. Tectonics and historical records analysis are import to forecast and prevention of tsunami. Consider the tectonic environment of the China sea, the possibility of huge damage caused by the offshore tsunami is very small. And the impact of the ocean tsunami on the Bohai sea, the Yellow sea, and the East China sea is also small. But in the South China Sea, the Manila subduction zone has been identified as a high hazardous tsunamigenic earthquake source region. No earthquake larger than M_W7.6 has been recorded in the past 100a in this region, suggesting a high probability for larger earthquakes in the future. If a tsunamigenic earthquake were to occur in this region in the near future, a tragedy with the magnitude similar to the 2004 Indian Ocean tsunami could repeat itself. In this paper, based on tectonics and historical records analysis, we have demonstrated that potential for a strong future earthquake along the Manila subduction zone is real. Using a numerical model, we have also shown that most countries in the South China Sea will be affected by the tsunamis generated by the future earthquake. For China, it implies that the maximum wave height over 4.0 meter on China mainland, especially the Pearl River Estuary. But the island, local relief maybe influence the maximum wave. But it takes nearly 3 hours to attack China mainland, if there is the operational tsunami warning system in place in this region, should be greatly reduced losses. And the simulated results are conformable to historical records. It indicates that the tsunami hazards from Manila trench to China mainland worthy of our attention and prevention.

On 8 August 8 2017, an M_S7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province. Field geological investigations did not find any co-seismic surface rupture in the epicenter area, implying that the seismogenic structure is likely a hidden active fault. Based on the results of the relocated aftershocks, the seismogenic fault was simulated and characterized using the SKUA-GOCAD software. The three-dimensional model of the seismogenic fault was preliminarily constructed, which shows that the main shock of the Jiuzhaigou M_S7.0 earthquake occurred at the sharp bending area of the fault surface, similar to the geometry of the active fault that generated several major earthquakes in the Songpan area during 1973-1976. Our study suggests that high seismicity of this area may be closely related to the inhomogeneous geometry of the fault surface. In this work, we collected the historical earthquakes of M ≥ 6.5, and analyzed the geometric and kinematic features of the active faults in the study area. A three-dimensional fault model for the 10 main active faults was constructed, and its limitation in fault modeling was discussed. It could provide evidence for analyzing the seismotectonics of historical earthquakes, exploring the relationships between earthquakes and active faults, and predicting major earthquakes in the future.

Fault traces contain abundant information associated with the fracture process and mechanism, so an accurate and quantitative description of their geometric characteristics is of great significance to perceiving the generation and development of faults. We collected 52 co-seismic surface ruptures and 300 active fault traces from across the world to analyse their geometric characteristics by the method of power spectrum density. Our results show that (1)the average power spectrum density has a distinct three-segment charateristic in the frequency domain. In the low frequency domain it represents the geometric characteristics of the boundary of tectonic block. In the medium frequency domain, the power spectrum density reflects the processes of lateral growth and connection of secondary faults, and the turn point on the 100 meters scale represents the effective resampling length, below which the power spectrum density characteristics are meaningless. (2)In the middle and high frequency domains, the power spectrum density curves of co-seismic surface ruptures show that there are obvious differences in roughness among three fault types, i.e. reverse > normal > strike-slip, which indicates that the geometric characteristics of co-seismic surface ruptures are controlled by the fault types. (3)Compared with co-seismic surface ruptures, active fault traces have much lower power spectrum density, indicating the roughness of active fault traces becomes lower with increasing numbers of rupturing events and the lengths of active history, i.e., the fault roughness is inversly proportional to its maturity.

The Huoshan piedmont fault is a small watershed region in Shanxi Province. We utilized the high-resolution DEM data and the stream-power incision model which describes the relationship between the tectonic uplift and fluvial incision to analyze the S-A double-log graph, concavity index (θ)and steepness index (logk_s) of the 64 channels across this fault and discuss their responses to the tectonic movement of the fault. The results show that (1)the S-A double-log graphs all exhibit an obvious convex form, which is the direct expression of the response to the situation that the bedrock uplift rate is higher than the fluvial incision rate. (2)All of the concavity index (θ)values of 64 channels are lower than 0.35 with an average value of 0.223, much lower than the empirical value (0.49)of the rivers in steady state. These low values are the quantitative reflections of the channels' slightly concave profiles. Meanwhile they imply that these channels across the fault are very young. There is no enough time for them to adjust the profiles through the fluvial incision to the steady state because of the fault's frequent and strong tectonic movements. (3)The steepness index values of the channels located in the Laoyeding Mt. are highest, while they are lower in the northern and southern mountains. Moreover, the steepness index values of the channels in the northern mountains, on average, are higher than those of the channels in the southern mountains. To a certain extent, this distribution of the steepness index corresponds to the difference in the uplift rates of the Huoshan piedmont fault. It means that the uplift rate of the middle fault segment in the Laoyeding Mt. is highest, and the uplift rate of the northern segment is higher than that of the southern segment.

Geomorphology could record long-term accumulation of tectonic movement and quantify it by relevant parameters.But because the influences of other factors such as climate and lithology,how to use the relevant parameters to reveal the relationship between geomorphology and tectonics is a research hot spot.In this paper,we utilize the variogram method and the cellular fractal model to estimate parameters such as the fractal dimension (D) and ordinate intercept (γ) from the SRTM3 DEM using a moving window operation.We compare the distribution characteristics of the parameters in different climate and lithology.The results indicate that the correlation between the parameters and lithology or climate is very poor.The fractal dimension (D) reveals a very good correlation with tectonics,which is low in tectonically inactive areas and high in active areas.It implies that fractal dimension (D) may be a new method for research of regional tectonic movement.

Daliangshan fault zone (DFZ) constitutes an indispensable part of Xianshuihe-Xiaojiang fault system which is one of the main large continental strong earthquake faults in China.Puxiong Fault,the east branch of middle segment of DFZ,is the longest secondary fault.Its paleoseismic activity plays an important role in evaluating regional seismic activity level and building countermeasures of preventing and reducing the earthquake damage.The active fault mapping as well as the study of paleoseismological trench in recent years illustrates that Puxiong Fault is a slightly west-dipping high-angle left-lateral strike-slip fault with strong activity since late Pleistocene.Two trenches excavated across this fault reveal 2 and 3 paleoearthquakes that ruptured the fault at 8206 BC-1172 AD,1084-1549 AD,and 17434-7557 BC,1577-959 BC and 927-1360 AD,respectively.The OxCal model combining the results from both trenches and the another one in previous study across the fault with the historical earthquake record yields the elapsed time of~0.7ka of the latest paleoearthquake event,and the interval time is~2.3ka between the last two events.In the model,the penultimate event is considered to be recorded in all trenches.As all the three trenches are located at north part of the Puxiong Fault whose strike is apparently different from the south part,the~57km long north secondary segment is supposed to be the seismogenic structure of the paleoearthquake.According to the empirical scaling laws between magnitude and rupture length,the magnitude of the surface ruptured paleoearthquake is estimated to be more than M7 with the coseismic displacement~3.5m.However,the difference between the time of the paleoearthquake events on the middle and south segments of DFZ illustrates their independence as earthquake fracture units,and furthermore,the lower connectivity and the new generation of DFZ.

As an important technology to paleoseismologic research, trenching has been used to identify paleo-earthquakes recorded in strata, combined with dating technology. However, there have been some bigger uncertainties and limitations. For instance, subtle strata in loess sediment cannot be interpreted only by naked-eye, which seriously affects identifying paleo-earthquake horizon and time. Therefore, how to improve the accuracy and reduce the uncertainty of paleo-earthquake identification is the important problem we are currently facing. Dongyugou loess section, located in the northeastern corner of Linfen Basin, Shanxi Province, cuts across the Huoshan piedmont fault. The section exposes not only the well-developed loess sequence, but also several obvious faulting events. Thus, this loess section is a better site to make a high resolution study to improve the accuracy and reduce the uncertainty of paleo-earthquake identification. Based on the high-resolution grain size and magnetic susceptibility analysis, and associated with visual interpretation by naked-eye, we made a high-resolution stratification of Dongyugou loess section, including high-resolution thickness of each stratum and its upper and bottom boundaries. Based on the high-resolution stratification and their comparison between two fault walls, we identified three earthquake events, which occurred after formation of u5-7, u4 and u2, corresponding to their stratification depth of 7.1m, 4.7m and 2.9m in hanging wall. Based on results of OSL dating and average sedimentation rate of hanging wall, we estimated that the three events occurred around 45.8ka(between (48.1±1.5)～(43.2±2.5)ka), 32.8ka(between (35.0±2.4)～(30.6±1.3)ka) and 23.3ka(between (26.4±0.8)～(20.9±0.7)ka). According to the thickness difference of three loess-paleosol sedimentary cycles between two fault walls, we calculated the coseismic vertical displacements of the three events as 0.5m, 0.4 and 1.3m, respectively. Compared with other segments of the Huoshan piedmont fault zone, we found the southernmost segment is the weakest, with longer recurrence interval of about 11ka and lower vertical slip rate of 0.048mm/a. The high-accuracy grain size and magnetic susceptibility analysis offers an effective method for reducing the uncertainties of the paleo-earthquake research in loess area.

The need to acquire high-quality digital topographic data is evident throughout geoscience research. The use of these data elevates the research level of geosciences. Airborne and terrestrial light detection and ranging(LiDAR)are currently the most prevalent techniques for generating such data, but the high costs and complex post processing of these laser-based techniques restrict their availability. In the past few years, a new stereoscopic photogrammetry mapping method called Structure from Motion(SfM)has been applied in geoscience, in which the 3D digital topography is reconstructed using feature matching algorithms from overlapping photographs of multiple viewpoints. SfM only needs a series of overlapping images with no special requirements about the camera positions, orientations and lens parameters, making it possible to use images collected from an affordable SfM platform to rapidly generate high-quality 3D digital topography. This paper summarizes the basic principles and the SfM workflow, and shows that SfM is a low-cost, effective tool for geoscience applications compared to LiDAR. We use a series of digital aerial photos with~70% overlap collected at one-thousand-meter height to produce a textured(color)SfM point cloud with point density of 25.5/m². Such a high density point cloud allows us to generate a DEM with grid size of 0.2m. Compared with LiDAR point cloud, statistical analysis shows that 58.3% of LiDAR points deviate vertically from the closed SfM point by <0.1m and 88.3% by <0.2m. There is different SfM accuracy in different landforms. The SfM accuracy is higher in low dips and subdued landforms than in steep landforms. In consideration of relative vertical error of 0.12m in LiDAR data, SfM has a higher measuring accuracy compared with LiDAR.

Daliangshan Fault Zone (DFZ) constitutes a significant part of the eastern boundary of Sichuan-Yunnan Active Block (SYAB). Studying the activity and slip rate of this fault zone is not only of great significance in understanding the movement of tectonic blocks and crustal deformation at the southeastern margin of Tibetan plateau, but also valuable in seismic hazard assessment and mid- and long-term forecasting of earthquake in west Sichuan. Zhuma Fault is the east branch of northern segment of DFZ which consists of six branch faults. Based on the detailed field investigations and through the accurate RTK (GPS) surveying and dating of the displaced landforms, we find that Zhuma Fault has been active since Holocene with a dominant left-lateral movement pattern and constrain its slip rate to be 1.5~3.1mm/a. Furthermore, a trench was excavated which reveals two paleoearthquakes occurring within(50.3±5.7)~30ka BP and 30~(17.4±1.2)ka BP, respectively from the stratigraphic evidence and OSL dating data. Although the slip rate on the Zhuma Fault is a little smaller than that on the southern segment of DFZ, we suggest uniform slip rates on the DFZ in consideration of the existence of another branch faults on the northern segment. The similar slip rate on DFZ to those on Anninghe Fault Zone (AFZ) and Zemuhe Fault Zone (ZFZ) implies that DFZ possesses a comparable partitioning component of displacement of Xianshuihe-Xiaojiang Fault System (XXFS) to AFZ and ZFZ. Further, the sum of slip rates on central segment of XXFS shows a good agreement with that on northern or southern segment. Thus, it is suggested that the DFZ not only patches the gap generated by the deviation of the strikes of AFZ and ZFZ from the average strike of XXFS, thus, making it a perfect small arc on earth, but also covers the deficiency in displacement and slip rate between central segment and northern or southern segment to maintain the XXFS to be harmonious. Moreover, according to the sedimentary characteristics and dating data, it is revealed that the alluvial-proluvial fans along the Zhuma Fault are formed by the glacial melt water in the last deglaciation after the Younger Dryas cooling event and such landforms could be widely developed in this region.

The quantitative analysis of morphologic characteristics of bedrock fault surface is a useful approach to study faulting history and identify paleo-earthquake. It is an effective complement to trenching technique, especially to identify paleo-earthquakes in a bedrock area where the trenching technique cannot be applied. In this paper, we calculate the 2D fractal dimension of three bedrock fault surfaces on Huoshan piedmont fault in Shanxi graben, China using the isotropic empirical variogram. Taking average fractal dimensions of every horizontal tape and plotting them along the vertical axis, we find the fractal dimension presents pronounced segmentation in vertical direction. This step change of the average fractal dimensions demonstrates obvious segmentation of the fault surface morphology. Then, the segmentation of fault surface morphology, showing different exposure duration of each segment, is caused by periodic faulting earthquake, but not continuous erosion. Therefore, taking best normal fitting of average fractal dimensions of each segment as a characteristic value to describe the surface morphology of the fault surface segment, the characteristic value can be used to estimate the exposure duration of the fault surface segment and then the occurrence time of the faulting earthquake that made the segment exposed. The width of each fault surface segment can also be regarded as an approximate vertical coseismic displacement. Based on the segmentation of quantitative morphology of the three fault surfaces on the Huoshan piedmont fault, we identify three faulting earthquake events. Combined with trenching results reported by previous researches, we attempt to fit an empirical relationship between the exposure time and the morphological characteristic value on the fault. The co-seismic vertical displacement of a characteristic earthquake on the Huoshan piedmont fault is estimated to be 3.5m(3~4m), the average width of all middle fault surface segments. Moreover, the small gap of average 0.5~1m width between two adjacent segments, where fractal value increases gradually with the increased fault surface height, is inferred to be caused by erosion between two faulting earthquakes.

Airborne LiDAR (Light Detection And Ranging) provides a more advanced technique and more accurate basic data to describe geomorphological features and the latest surface deformation associated with active tectonics. How to apply this new technique and dataset to mapping of active fault and seismic hazard assessment is an important trend in the field of active tectonics. Taking the Dushanzi anticline-reverse fault zone in Xinjiang as test area, we made an experimental study on geologic mapping of active tectonics based on the LiDAR data. Firstly, we collected raw data using the airborne LiDAR technique, and obtained a raw point-cloud with a point density of 6.6 points/m² and an average space of 0.39m between any two points. Secondly, using twelve ground control points(GCP)which is acquired by static GPS measurement with accuracy up to millimeter, we evaluated the vertical error of the ground point-cloud data with density of 6.4 points/m², and the result shows a vertical error of 0.12m, mean square value 0.078m. Finally, using the inverse distance weighting algorithm, we obtained the digital elevation model(DEM)of 0.5m-resolution. The resolution of the DEM is high enough to describe and analyze spatially the fine feature of tectonic landform of the Dushanzi anticline-reverse fault zone. In this paper, we identify the fine tectonic landforms using merely the DEM visualization tools based on different virtual perspectives, different shades or different treatment methods. The active tectonics and their distribution identified based on the high resolution DEM derived from LiDAR are not only consistent with previous results identified from air-interpretation and field investigation, but also finer and more precise than the latter. In addition, these methods of data acquisition, quality inspection and data processing introduced in this paper are also applied to other active fault researches in which LiDAR data have been acquired.

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.

The degradation of fault scarps in unconsolidated deposits can be accurately simulated. Under the appropriate correction,high-accuracy digital models can be built for the fault scarps evolution. These models provide the basis for estimating the age of faulting. In this paper we measured a series of artificial fault scarps with different slope angles in frequency of once a month,and found that the artificial fault scarps with slope angle above 30° are in an unstable stage and a group of parameters are acquired. There are obvious differences in erosion thicknesses,daily erosion rates and annual recession rates of artificial fault scarps. Besides the greatest erosion thickness of 6.13mm on the slope of 80°,there is a peak value of 5.24mm at the scarp of 50°,and the erosion thicknesses then gradually reduce for other slopes. There are the similar distribution characters in the daily erosion rates and the annual recession rate. Besides the recession rate of (6.74±0.26)mm/a on the slope of 80°,the greatest value of (7.41±0.84)mm/a is observed at the scarp with slope angle of 50°.But there is an abnormally high value of (8.19±1.16)mm/a in recession rate for scarps with a slope of 30°,which may result from the low angle. As the angle reduces,the deviation of the erosion thickness from the recession distance becomes bigger. The average recession rate of 5.8mm/a can be used as the correction value of the evolution of the normal fault scarps in Shanxi rift system,though it is based on the measurement of one year and has larger limitations. In addition,there is an obvious difference between field observations and ideal model. The accumulation amounts at the foot of scarps are not equal to the erosion amounts of scarp surface,due to that part of weathering material was washed away by the rainwater. The experimental observations show that there are not obvious accumulations during the rainy season(until October)due to rushing of rainwater,but the loess accumulations appear at the foot of scarp after the snow melts in winter. According to the measurements of one year,41.6% of total erosion amount is washed away by rainwater at the scarp with slope angle of 80°,and for others scarps the results are 52.4%,47.6%,50.6%,60.5% at slope angles of 70°,60°,40°,respectively.

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.

Daliangshan Fault zone constitutes an important part of the eastern boundary of Sichuan-yunnan active block. The studies of slip rate along the fault is not only significant to the crust movement and deformation pattern on the southeast edge of Tibetan Plateau,but also has great value in seismic hazard assessment and mid-and long-term forecasting of earthquake of the Daliangshan region. Through detailed field work along the south segment of Daliangshan Fault zone,namely the Butuo Fault and the Jiaojihe Fault,and based on accurate RTK(GPS)survey for the alluvial fans and activity dating,we suggest that left-lateral slip rate of the south segment of the fault zone is between 2.5～4.5mm/a,and the slip rate of Jiaojihe Fault is slightly higher than that of the Butuo Fault. Due to partitioning of part of the strike-slip component on the Daliangshan Fault zone,there is an obvious deficit in the displacement and slip rate on the Anninghe-Zemuhe Fault,compared to the Xianshuihe and Xiaojiang Faults. Comparing to the slip rates between Daliangshan Fault and Anninghe-Zemuhe Fault,it is found that they have similar horizontal slip rate,indicating the seismicity level of the Daliangshan Fault will not be lower than that of Anninghe-Zemuhe Fault. As the Daliangshan Fault gradually replaces the role of Anninghe-Zemuhe Fault in the Xianshuihe-Xiaojiang Fault system,the seismicity on the Daliangshan Fault zone will increase,and the Dalianghan region will have a higher risk of earthquake damage.

When a reach of a stream is steepened with respect to the adjoining reach,it defines a topographic knickpoint.A knickpoint is supposed to be a response to the base-level changes,and the base-level of a drainage basin is influenced by the fault movement.The formation of a knickpoint on a gully long-profile,whose base-level is the footslope of the fault scarp,is associated very closely with the vertical movement of a fault,therefore,the ages of paleo-earthquake events can be estimated by the knickpoint series along the longitudinal profile of a gully.We have made a case study of the Huoshan Mts.Piedmont Fault,and extracted tens of gullies across the fault based on the high-resolution DEM data and identified out knickpoints in 23 gullies.There are 5 gullies with only one knickpoint which are laid on the fault.And there are two gullies having two knickpoints with the latest one laid on the fault.The positions of these knickpoints and their higher height ranging from 4～9m imply that there are several knickpoints superposed together and the knickpoints have not migrated upstream.The other 16 gullies respectively have 2～3 knickpoints.The latest knickpoints have been migrated upstream to a distance of 40～70m from the fault.The knickpoints of intermediate ages are at a distance of 150～150m upstream from the fault and the oldest ones at a distance of 300～500m.Under the conditions that the latest knickpoints are associated with the 1303 M_W8.0 Hongdong earthquake(Event Ⅲ)and that the gullies keep the same rate of headward erosion during the Holocene,Event Ⅱ is estimated to take place during 3336～2269a B.P. and Event Ⅰ is estimated to take place during 3336～2269a B.P. , respectively.The recurrence of events is about 1500～2600a.These results are consistent with those obtained through the trench investigations.

Field investigations on the 2008 surface rupture north to Shikan village show that the surface rupture is still significant in this section.The surface rupture changes its strike at the north of the town of Shikan and does not follow the previously mapped thrust which was initially considered the location the rupture traversed.Nevertheless,clear morphological expressions suggest repeated coseismic displacements along the fault trace the 2008 earthquake rupture followed.Contrast to the previous work,another 12-km-long rupture was found.It runs between Shikan town and Woqian village,trends 15°～45°,and shows thrusting with dextral slipping.The relatively large vertical and dextral strike-slip displacements of 2.1m and 3.0m respectively at Kuangpingzi do not suggest that co-seismic slip diminished gradually from a high value to a low one.The increased component of strike slip may suggest that the rupture ended as a strike-slip mode.Field observations suggest that the rupture terminates at the southwest of the Donghekou village about 20km north to Woqian village.

In the scientific investigation on the M_S 8.0 Wenchuan earthquake,different high-precision measuring instruments,such as electronic total station,GPS RTK,3D laser scanner,etc.were used widely to survey the landscape of co-seismic surface ruptures,and a wealth of information with the earthquake deformation were recorded timely,which ensured the quantitative analysis of related data.In this paper,we explored the characteristics of different means used in the micro-geomorphology survey and analyzed the advantages of different portfolios of the above-mentioned methods.Then,focusing on the examples,we discussed the advantages and limitations of three-dimensional laser scanner in recording and analyzing the information of seismic surface ruptures.Also we gave the prospects of the methods' application.

Surface ruptures of the M_S 8.0 Wenchuan earthquake are distributed mainly on the Longmenshan central fault and front-range fault,extending 235km and 72km,respectively.The ruptures exhibit complicated characters in geometry and kinematics.On the riverbed of Baisha river,a backthrust scarp was formed in the southwest of the major fault that comprises four right-step sub-faults,and precise topographical measurement shows a kinematic character of fault block and surface tilting in the rupture process;In Shiyan village,the master fault and the secondary fault formed an imbricate structure,and show as flexures and earthquake swells on ground surface.We analyzed the ruptures at Tongmakan village and Shiyan village,both locating on the central fault,by geometry and kinematics,and the results indicate that the earthquake rupturing along the central fault is mainly characterized by thrusting associated with right-lateral strike-slipping.This result is consistent with the focal-mechanism solutions which are promulgated by U.S.Geological Survey,Harvard University and China Earthquake Networks Center.In addition,the profiles of Tongmakan and Shiyan display different tilting directions,and the reason is that the former locates at the trailing edge of the fault,while the latter in the leading edge of fault.