The Yingjing-Mabian-Yanjin tectonic zone(YMYTZ)is an important boundary structure between the southeastern margin of the Tibet Plateau and the Sichuan Basin. It consists of several small-scale secondary faults with different strikes and is generally characterized by the intersections of north-northwest oriented longitudinal faults and nearly east-west oriented transverse faults. The YMYTZ is seismically very active in the late Quaternary and hosted several moderate-strong earthquakes, including two M≥7 earthquakes since 1216AD, namely the 1216 Mahu earthquake and the 1974 Daguanbei earthquake. After the Daguanbei earthquake, several M≥6 earthquakes and hundreds of M≥5 earthquakes occurred along the YMYTZ to date, implying it is a newly generated seismotectonic belt. Even so, the activity of each fault is still unclear, bringing out great uncertainty in understanding the current crustal deformation pattern and in evaluating the regional seismic potential. Specifically, although several M≥6 earthquakes have occurred along the Leibo fault zone in the southern segment of the YMYTZ, the late Quaternary activity of the fault zone has not been well determined due to insufficient work as well as subsequent lack of solid evidence. The Leibo fault zone strikes NE-SW and spreads on the southeast flank of the Chenqiangyan-Shanzhagang anticline. It starts at the Huanglang township near the Mahu Lake, cuts through the Jingkou Mountain, Lianhuashi, and Leibo, and extends southwestwards to the vicinity of Lianlajue. The latest investigation shows that the Leibo fault zone consists of four subparallel right-lateral strike-slip faults named F₁—F₄ from the north to the south, respectively. These fault branches together constitute a 43km-long and 10km-wide structural belt. Previous paleoseismic work along the Leibo fault zone found that the faults ruptured the late Pleistocene sedimentary layers with their upward terminations covered by the undeformed Holocene deposits, implying it was active in the late Pleistocene and has not been active since the Holocene. However, the ground surface traces of the Leibo fault zone are the most obvious among the faults in the YMYTZ, and recent seismologic studies show strong seismic activity for the Leibo fault zone, bringing out a controversy about whether it is active in the Holocene or not.

To address the late Quaternary activity of the Leibo fault zone, we conducted detailed indoor deformed geomorphic feature interpretation on remote sensing imageries like 2m-resolution GF-2 imagery and high-resolution imageries on Google Earth, and further mapped the fault traces in the field using an unmanned aerial vehicle(UAV)derived digital orthographs and digital surface models(DSM). Based on the geological and geomorphological surveys, two trenches were excavated at Pengjiashan and Luohangou along the northern(F₂)and southern(F₄)branches of the Leibo fault zone respectively. On the trench walls, surface-rupturing paleoearthquakes were identified for each fault according to criteria for faulting events like cut-and-cover structures, scarps, and colluvial wedges. Subsequently, we collected and dated several radiocarbon samples from the sedimentary layers immediately before and after the rupturing events, and finally carried out stratigraphic sequence calibration using the acquired ages with the OxCal 4.4 program to constrain the timings of the revealed paleoearthquakes.

According to the identification criteria of paleoseismic events, it was revealed 3 paleoearthquakes in the Pengjiashan trench on the northern fault branch(F₂)and another 7 rupturing events in the Luohangou trench along the southern fault branch(F₄). Radiocarbon sample dating constrain the ages of the paleoearthquakes along F₂ to be 21190—20590BC(EP1), 20550—12120BC(EP2), and after 12090BC(EP3), while the latest two paleoseismic events on F₄ occurred 9270—5040BC(EL6)and after 5000BC(EL7). Our paleoseismic studies show that the LFZ has experienced several surface-rupturing earthquakes in the Holocene, verifying it is a Holocene active fault zone. Moreover, the ages of the paleoseismic events revealed on two fault branches do not overlap with each other, suggesting they are different paleoearthquakes so that the fault branches in the Leibo fault zone are independent seismogenic structures. By collecting and analyzing the magnitudes of strike-slipping earthquakes that have generated surface ruptures in western China since 1920, it is believed that the minimum magnitudes of the paleoearthquakes determined on the Leibo fault zone are 6.5. Through the empirical relationships between magnitude and surface rupture length, it is estimated that the LFZ has the capability to produce an earthquake with M≥7.

At 02:04 a.m. on May 22, 2021, a M_S7.4 earthquake occurred in the Maduo County, Qinghai Province, China. Its epicenter is located within the Bayan Har block in the north-central Tibetan plateau, approximately 70km south of the eastern Kunlun fault system that defines the northern boundary of the block. In order to constrain the seismogenic fault and characterize the co-seismic surface ruptures of this earthquake, field investigations were conducted immediately after the earthquake, combined with analyses of the focal parameters, aftershock distribution, and InSAR inversion of this earthquake.
This preliminary study finds that the seismogenic fault of the Maduo M_S7.4 earthquake is the Jiangcuo segment of the Kunlunshankou-Jiangcuo Fault, which is an active NW-striking and left-lateral strike-slip fault. The total length of the co-seismic surface ruptures is approximately 160km. Multiple rupture patterns exist, mainly including linear shear fractures, obliquely distributed tensional and tensional-shear fractures, pressure ridges, and pull-apart basins. The earthquake also induced a large number of liquefaction structures and landslides in valleys and marshlands.
Based on strike variation and along-strike discontinuity due to the development of step-overs, the coseismic surface rupture zone can be subdivided into four segments, namely the Elinghu South, Huanghexiang, Dongcaoarlong, and Changmahexiang segments. The surface ruptures are quite continuous and prominent along the Elinghu south segment, western portion of the Huanghexiang segment, central portion of the Dongcaoarlong segment, and the Huanghexiang segment. Comparatively, coseismic surface ruptures of other portions are discontinuous. The coseismic strike-slip displacement is roughly determined to be 1~2m based on the displaced gullies, trails, and the width of cracks at releasing step-overs.

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.

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.

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.

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.

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.

Kumukol Basin, located at the north margin of the Tibetan plateau, is separated from the Qaidam Basin by the Qimantag Range geographically. It is the transitional region between the Tibetan plateau and Qaidam Basin, and also the leading edge of the growing main body of the plateau. Nowadays, East Kunlun Fault and Altyn Tagh Fault, two significant strike-slip faults of Tibetan plateau, as well as the compressional Qimantag folding thrust system, delimit the southern, western and northern borders of the basin, respectively. Therefore, the study on the tectonic deformation and tectonic evolution of the basin will play an important role in understanding the style and mechanism of the eastward expanding of Tibetan plateau.
Although Kumukol Basin is delimited by strongly active strike-slip faults, a very large anticline is growing in the basin, with a similar strike of NWW-SEE to the Qimantag folding thrust system and the folds in Qaidam Basin, such as Youshashan fold, suggesting that the basin is compressional. In this study, the lateral growth of this anticline is revealed by the analysis on the topographic profiles and distribution of terraces. A conclusion, as well, is made that the large proluvial fan at the east segment of the anticline is a result of the glacier melt water based on the field survey and dating of terrace samples. According to the OSL and ¹⁰Be exposure ages, the age of the fan is 87.09±2.31ka～102.4±3.7ka, and accordingly, we can get a maximum uplift rate of(2.78±0.28)mm/a～(3.28±0.28)mm/a for the anticline since late Pleistocene. Tectonically, Kumukol Basin is highly similar to Qaidam Basin on its north, both are strongly active and controlled by the regional NEE compression stress field of the Altyn Tagh Fault at its south.

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.