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.

In order to quantitatively analyze the reliability of the composite fault plane solution of small earthquakes, the Bootstrap sampling technique is introduced into the grid search method, and the ideas and methods for calculating the confidence interval from the grid search method are proposed initially. There are two sample sets that can represent the characteristics of the composite fault plane solution. One sample set is the optional solutions obtained by the grid search method and the other is obtained by the Bootstrap sampling technique. Then, we calculate the confidence intervals of the two sample sets (P, B and T axis). The research results of tectonic stress field in southern Jiangxi Province are relatively few. In view of such situation, we use the focal mechanism solutions of small earthquakes to calculate and analyze the composite fault plane solution and the confidence interval. This study shows that the confidence interval of the principal stress axis can be obtained well by both of the sample methods. The reliability of the results and the confidence range of the principal stress axis can be better represented by the confidence intervals. The middle principal stress in southern Jiangxi Province is nearly vertical, and the maximum and minimum principal stresses are nearly horizontal. The direction of maximum principal stress is NWW-SEE and that of the minimum principal stress is NNE-SSW. And, the area is in a strike-slip stress regime. The results are consistent with previous studies, and the stress directions obtained by previous researchers are within the confidence interval calculated by this paper.

The geological structure exposed by paleoearthquake trenches is the key material to the right cognition of fault activity and paleoearthquake. However, paleoearthquake trenching inevitably destroys active tectonic geomorphic evidence and trench exposures are usually difficult to reserve. The conventional process of recording the delicate geological information, manually constructing photomosaics by image-editing software, is time-consuming and produces undesirable artificial distortions. Herein, we explored the process of constructing trench orthophotomosaics and the 3D image model using the Image-based Modeling technology and applied it to the Liutiaohe trench across the Tianqiaogou-Huangyangchuan Fault, Gansu Province. Based on the 3D image modeling and orthophotomosaic, we firstly constructed the control points and scale bars on cleaned trench walls and collected photos of all sections of the trench with a digital camera in the field, and then reconstructed the 3D model of the trench through the Agisoft PhotoScan, an efficient image-based modeling software, and finally yielded the 3D image model of the trench and othophotomasaics of the trench exposures. The results show that the automated workflow can produce seamless, sub-millimeter-level high-resolution photomosaics more quickly, with precision in the centimeter range, and the 3D image model is of great help to identify strata and geological structures in trenches with much lower capital and labor costs and low expertise levels compared with LiDAR, meanwhile, the 3D archive benefits the share and communication and even allows future reinterpreting the site using new insights.

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.

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.

Based on field investigation and laboratory analysis,we discussed the slip mode of F₁ in thenorthern segment of the Yishu active fault in this paper. The macroscopic identification and analysis of the composition of clay minerals of fault gouge shows that it slowly sliped with the mode of creeping before late Pleistorene,while micro features indicate that it strongly stick-sliped before Pleistocene.Along with the study of chronology,it is preliminarily interpreted as variousstages from sticking-slipping slide to creep.This result is of practical significance to earthquakeprediction and engineering construction in the area nearby the Yishu fault zone.

Shanxi graben system is one of the most famous strong earthquake belts on China Continent. In this paper, the problems on recurrence and migration of the historic strong earthquakes (M≥6), the precusory anomalies of the intermediate and strong earthquakes (41/3≤M<7) before M≥7 earthquakes occurring, and linear segmentation of the strain accumulation curves are discussed. The temporary trends of the recent and future seismicities are analysed. Finally the possible seismic risk areas in which intermediate and strong earthquake may occur are also outlined in the graben system.

In the paper, the regional stress and the stress state on plane and along profile in Ma-17 well area are calculated using two-dimensional finite element technique of linear elastic theory for studing stress condition affecting sensitivity of water table in this well. The result indicates that there is a stress concentration during perparation of stronger earthquake in North China.

To illustrate quantitatively the formation mechanism of the rightstep faults, an ela-sto-visco-plastical three-dimensional model with a discontinuous pre-existing buried fault is presented and solved numerically by a general total initial strain procedure. Body force and localized upward force at the model base as well as a rightlateral couple acting beneath the upper crust are required to develop horizontal tensional stress above the buried fault with a direction perpendicular to the long axis of these basins.

The magnetotelluric response to the two dimension structures has been numerically modeled by use of the finite element method.Itcan be concluded that in the two dimension structure area in the North China Plain,rather than the lateral ones,one dimension inversion of longitudinal apparent resistivity plot can provide accurate information on real distribution of deep earth conductivity.The principle of two dimension forward magnetotelluric sounding has been presented,and then derived expression as well as the two profile models following two profiles obtained from magnetotelluric sounding along with other relevant data.The calculation has been carried out for two curves of apparent resistivity corresponding to polarized orientationas well.The two measuring profiles are across the Tangshan seismic zone (Malanyu-Bege-zuang) and NNE-trending tectonic zone partly passing the Beijing area,respectively.

From the analysis of the distribution of strong earthquakes, the deep-seated crustal structures and the medium conditions, the authors of this paper attempt to divide the faults within the earth's crust into six groups and to estimate the depth and characteristics of seismo-pregnant layers. The motion of upper mantle materials, the faulting and seismicity are a common source-contemporaneous. The occurrence of strong earthquakes is directly controlled by the activities of both deeply penetrating faults and faults of basaltic layers.

The Yihe-Suhe fault belt is a Mesozoic rift structure, consisting of many secondary faults. The left lateral strike-slip motion along these faults between the Jurassic and the Cretaceous periods appears to be the initial stage of development of the rift. Then a florishing stage of faulting depression and extension was in Cretaceous time. Since the Tertiary period it had become a compressonal tectonic belt characterized by the intensive folding and thrusting, and the rift is disappeared.

The deformation and failure of rock masses are in general governed by the preexisting discontinuities and the local fissures induced by the state of stress, because these weak planes increase the deformability and reduce the strength of the rock mass. The mechanical properties of a rock system are thus determined by its interior structure and texture, as well as by the boundary conditions, such as the loading path, the constrained displacement and the geometry of the system.This paper describes a three-dimensional finite element model of the rock mass, where a fault underlain closely with or without a solf layer is dipping an angle of 60°or 90°between the fault plane and the horizontal axis. The external forces different in magnitude and direction are imposed at the boundaries, the effect of the intermediate principal stress, σ₂, on the concentrated stress level at the fault tip is studied as well.Numerical results similar to that of both the field and the laboratory tests confirm that present model provides physically measurful simulation and thus can be used to study the stress distribution of a geological body under different boundary conditions and thus to evaluate the geological background causing a huge earthquake.