Minshan active block is located in Bayan Har block of Qinghai-Tibet Plateau. It is bounded by the Huya Fault and Minjiang Fault on the east and west sides of the block. In less than 100 years, there have been four earthquakes with M_S≥7.0 occurring along the eastern and western boundary faults, namely, the Diexi earthquake with M7.5 in 1933, two Songpan earthquakes with M_S7.2 in 1976, the Jiuzhaigou earthquake with M_S7.0 in 2017, and several earthquakes with M6.0~6.9. Such intensity and frequency of seismicity on either side of a relatively small intraplate active block is rare. Because the landforms along the active fault are mostly relatively gentle valleys with dense population and there is large terrain difference between the two sides of the valleys, each of the major earthquakes and the large-scale landslides it triggered were liable to cause serious casualties and property losses.
Therefore, how does the destructive seismic activity around the active block migrate in space, and is it closely related to the segmentation and coalescence of active faults?And what are the temporal development characteristics of major earthquake activities and earthquake sequences?The discussion of these questions will not only deepen our understanding of the location and time of future destructive earthquakes, but also promote the development of the hypothesis of active block theory. Compared with the Bayan Har block, the Minshan active block located in the eastern margin of the Qinghai-Tibet Plateau provides a unique experimental field for studying the temporal and spatial regularity of earthquake occurrence in the active block.
In this paper, 39 076 small earthquakes in Minshan active block and its adjacent areas from 2000 to 2019 were relocated using the double-difference location method, and 48, 110 seismic events in the study area were obtained by combining the earthquake catalogues recorded by instruments in the same area from 1972 to 1999. For the major earthquakes since the 1933 Diexi M7.5 earthquake, a thorough analysis was made on the spatial distribution characteristics of earthquake sequences in different periods, especially on the basis of formation of small earthquake bands, and the results show that: Since the Diexi M7.5 earthquake in 1933, the four M≥7.0 earthquake sequences are all distributed along the boundary zone of Minshan active block in space, indicating that the active block plays a controlling role in the process of large earthquake preparation. In terms of the determination of seismogenic structure, the strike of the seismogenic fault of the 1976 Songpan M_S7.2 earthquake is basically the same with that of the 2017 Jiuzhaigou M_S7.0 earthquake, but differs by 60°~70° with that of the 1976 Pingwu M_S7.2 earthquake. So, it is more reasonable that the seismogenic faults of these three major earthquakes belong to two earthquake rupture segments, among them, the seismogenic fault of Jiuzhaigou M_S7.0 earthquake in 2017 and Songpan M_S7.2 earthquake in 1976 is the NW-trending Shuzheng Fault, and that of the 1976 Pingwu M_S7.2 earthquake is the north segment of the Huya Fault. From the perspective of seismicity, the seismogenic fault of the 1933 Diexi earthquake should be the southern segment of Minjiang Fault. The 2017 Jiuzhaigou M_S7.0 earthquake occurred in the gap between the 1976 Songpan M_S7.2 earthquake and the Minjiang Fault. There are probably two seismic hazard areas around Minshan active block, which are located in the southern segment of Huya Fault and the middle segment of Minjiang Fault. The large earthquakes around Minshan block probably belong to foreshock-main shock-aftershock type. Therefore, from the perspective of earthquake prediction, it is suggested to strengthen monitoring of these two seismic gaps.

Historical records with time information are useful for determining the time of earthquake events, while the investigation of historical damage phenomena such as earthquake-triggered landslides can help determine the magnitude of historical earthquakes by analyzing the correlation among historical earthquake-caused landslides, historical earthquakes and related active faults. A series of small basins were developed along the southern segment of the Xiaojiang Fault(XJF), with relatively flat and open topography and concentrated human activities. In most of the southern segment of the XJF, the terrain is relative flat, but some landslide accumulations are still clear, which are obviously different from the surrounding settings and are easy to be identified. Based on remote sensing interpretation and field investigations, landslides with different scales have developed in more than 10 locations along the southern segment of the XJF. Some of them are large with a volume of more than 1 million m³, and some are small with a volume of less than 100 000m³. They are the ancient landslides with a stable state. These landslides are mainly distributed in basins and their border areas with gentle terrain slopes. They are likely to be earthquake landslides rather than rainfall induced. The main scarp angles of these landslides are relatively concentrated, most of which are between 29~31 degrees, indicating that these landslides are caused by one geological event. We use light detection and ranging(LiDAR) measurement technology to obtain the digital elevation model(DEM)data of the landslide development section. The generated three-dimensional topographic shadow map presented in this paper suggests that there is a close relationship between these landslides and the latest surface ruptures of the southern segment of the XJF, indicating that these landslides should be triggered by the latest seismic event along the southern segment of XJF. The fault section was faulted in the latest earthquake events on the surface, triggering clusters of landslides. Based on the age test results of samples from the trench on the landslide body and historical literature data, the co-seismic landslides were triggered in 1606AD. According to the latest research results of the earthquake surface rupture zone in the southern segment of the XJF and empirical formula, combined with the comparative analysis on the intensity of geological disasters and the number of casualties of different earthquake cases, the authors re-assess the magnitude of the 1606 Jianshui earthquake and find that the magnitude of this historical earthquake could not be less than 7½(≥7.5). It means that the southern segment of the XJF, as a part of Xianshuihe-Xiaojiang fault(XSH-XJF) system, shows strong activity and has the ability to generate large earthquakes. GPS observations have verified that the crustal material on the southeastern margin of the Tibetan plateau rotates clockwise around the Eastern Himalaya Syntaxis(EHS), which requires a continuous left-lateral strike-slip fault system as the eastern boundary. The results presented in this paper are useful for deeper study of such an eastern boundary.

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.

Trench exposure is probably the most intuitive technological means of geology surveying work, and it is the key material to the right cognition of the delicate geological information. At the same time, trench is usually difficult to reserve, it needs to record the geological information of trench timely and accurately. The conventional methods of recording the delicate geological information of trenches are geology sketch and image mosaics technology, which mainly acquires the two-dimensional geological information. New data acquisition methods need to be explored for acquiring three-dimensional geological information. With the development of three-dimensional image technology, it is a new idea and method that terrestrial laser scanner and digital photogrammetry are applied to recording geological information of trenches.
This paper discusses the above problem by Miaodian 4^# landslide at the southern tableland in Jingyang County. The method of close-range photogrammetry to record the geological information is described as follows: 1)The photo-control-points on cleaned trench walls are established; 2)The photos from the surface of trench are collected by a Digital SLR Camera in the field. At the same time, measuring instrument can be used to measure the coordinates of the photo-control points; 3)The 3D model of the trench is reconstructed using the photogrammetric software(based on the processed photographs after the screening process and the coordinates of the photo-control points). In order to promote the application of this method, the paper also introduces the key technical problems of determining and setting up photo-control-points and scheme of photo acquisition. The 3D spatial data were acquired by methods described previously, which mainly include point cloud data, mesh, texture, orthomosaic, etc. The spatial resolution of the orthomosaic was 1.48mm/pix, and this high accuracy is enough to record millimeter-sized geological information. In order to verify the reliability of the results, the accuracy of close-range photogrammetry results is also verified and analyzed. The results show that the accuracy of close-range photogrammetry reached the centimeter level, and the level is close to the measurement equipment used in measuring the coordinates of photo-control-points. Therefore, the spatial resolution and accuracy of outcome data fully meet the requirements of recording the geological information.
Based on those 3D spatial data, the 2D and 3D geological applications of the data results were discussed in detail. First, the 2D geological application was discussed by taking the interpretation of trench profiles as an example. The technological processes mainly include creating orthomosaic, vectorization and interpretation. In the example, the interpretations of trench profiles were successfully completed using this method(Typically, the process of interpretation demands a combination of outdoor data recording and indoor experimental data). Specifically, the interpretations of small scale folds and thrust faults in the landslide deposit are obtained. Then, the 3D geological application was discussed by taking the data extraction of occurrence as an example. Extracting the feature points of 3D spatial data and computational method were described in detail. The occurrences of 3D model were contrasted to measurements of geological compass, and the two results are in good agreement. Based on the data of occurrence, they can be properly analyzed and further research can be developed from them. In this example, one can speculate about the forces and the motion state of the landslide after the data extraction of occurrence was synthesized and analyzed. And the results were normalized to the actual situation of the landslide.
Therefore, the 3D spatial data can be acquired quickly and accurately by extracting geological information from trench using close-range photogrammetry. Those outcome data include point cloud data, mesh, texture, orthomosaic, etc. The applications of those data could solve many complex engineering geological issues. Compared with the traditional methods, efficiency and security of field work are improved using photogrammetry technology, and it retains richer texture details than terrestrial laser scanning. Data results have traditional two-dimensional application functions. Moreover this data can achieve corresponding three-dimensional applications, which is deserved to be applied.

How to survey fault activity and determine seismogenic structures in a relatively stable and bedrock-distributed region is a challenging research work. Ruichang-Tonggu Fault and Yifeng-Jingdezhen Fault, distributed mainly at the pre-Cenozoic bedrock region, show the geological evidences of activity in the Quaternary and they are two important tectonic belts for the occurrence of moderate earthquakes in the central-northern Jiangxi Province. Fault gouge stripes can be found on the outcrop sections of the two faults. The imageries of the microstructures of fault gouge show abundant phenomena about the structural deformation, and it is clear that the fault gouge was formed by structural activity. As to the deformation modes, there are not only the Y-shears and R1-shears, which represent the localized-brittle deformation, but also the P-foliations, which reflect the ductile deformation in the microstructures of fault gouge. These features demonstrate that the micro-scale rapid deformation can exist in the seismogenic structure at the near-surface in the occurrence process of moderate earthquakes very possibly. The microstructures of soft material from the fault outcrop section at the southern segment of Hukou-Xingan Fault, which is inactive in the Quaternary, reflects that the soft material from the fault zone can also be the products of rainwater leaching and filling, or weathering in the later periods. Based on the macroscopic observation in the field, it is sometimes difficult to distinguish the differences of structurally-formed or non-structurally formed soft gunk in the fault zones, however, their differences in the microstructure on the slices grinded indoor are obvious. The relatively stable bedrock areas in South China often are not only favorable for the siting of major projects, such as nuclear power plant in China, but also the economically-developed, densely populated, urban agglomeration areas. The study of microstructure of fault gouge provides a technical reference approach for the identification of fault activity and the determination of seismogenic structure of moderate-strong earthquakes in assessing the seismotectonic environment in these regions.

The Chaohu-Tongling area in Anhui Province is a typical moderate-to-strong earthquake active area in the mainland of China. Four earthquakes occurred in this area, displayed as a NNE-trending zonal distribution, including the 1585 M5(3/4) Chaoxian earthquake and the 1654 M5(1/4) Lujiang earthquake, which formed a striking moderate-to-strong seismic activity zone. Field survey, shallow geophysical prospecting, drilling data, collection and dating of chronology samples and comprehensive analysis of fault activity indicate that the Fanshan, Xiajialing and Langcun faults are not active since Quaternary. The NNE-trending Tongling Fault is a buried middle-Pleistocene fault, but it can produce moderate-to-strong earthquakes and control the evolution and development of three en echelon geologic structures. The intensity of the four earthquakes is characterized by southward progressive decrease, which is in accordance with the characteristics that the subsidence range of Wuwei Basin is obviously larger than that of Guichi Basin to its south since late Cenozoic. In terms of deep structure, the characteristics of spatial distribution of Tongling Fault indicate that it corresponds to a NNE-striking Bouguer gravity anomaly gradient belt. So there is a spatial correspondence between the middle-Pleistocene Tongling Fault, the en echelon structures, the differential movement of the neotectonics, the Bouguer gravity anomaly gradient belt and the moderate-to-strong seismic activity belt in the Chaohu-Tongling area, indicating that they should be the tectonic indications of occurrence for moderate-to-strong earthquakes.

The surface ruptures produced by the 2016 M_W7.8 Karkoura earthquake, New Zealand are distributed in a belt with~170km long and~35km wide, trending generally in the NE-SW direction. There are at least 12 faults on which meter-scale displacements are identified and they were formed across two distinct seismotectonic provinces with fundamental different characteristics(Hamling et al., 2017; Litchfield et al., 2017). Although the trending directions of the seismic surface ruptures vary greatly at different locations, the ruptured faults can be generally divided into two groups with the NE to NEE direction and the NNW to N direction, respectively. The faults in the NNW-near NS direction are nearly parallel with 40~50km apart and featured by reverse movement with the maximum displacement of 5~6m. The faults in the NE-NNE direction, with the maximum of 25~30km apart are not continuous and featured by the dextral strike slip with the largest displacement of 10~12m. Even if some faults along the NE-NEE direction are end to end connected, their strikes differ by about 30°. The combination styles of the strike-slip fault surface ruptures along the NE-NEE direction can be merged into 3 categories, including en-echelon, bifurcation and parallel patterns. The scales of the fault surface ruptures with the same structural style could be obviously different in different areas, which results in significant changes in the widths of deformation zone, from tens of meters to hundreds of meters. En-echelon distributed surface rupture(section)can appear as a combination belt of meter-scale to dozens of meter-scale shear fracture with bulge and compressional shear fractures, and also can be characterized by the combination of the left-step en-echelon tensile shear fractures with a length of more than one hundred meters. The step-overs between surface rupture sections are clearly different in sizes, which can be dozens of meters, hundreds of meters to several kilometers. The spacing between parallel surface ruptures can be several meters, dozens of meters to several kilometers. Besides, as one of the prominent characteristics, the seismic surface ruptures caused by the Karkoura earthquake broke through the known distribution pattern of active faults. The surface ruptures can occur either on the previously thought inactive or unmapped faults, or break through the distribution range of previously realized active faults in the striking or lateral direction. The basic features about the distribution and widths of the surface ruptures induced by the 2016 M_W7.8 Karkoura earthquake, New Zealand presented in this paper might be helpful for understanding some seismic problems such as complex corresponding relationship between the active faults and the deep seismogenic structure, and the necessary measurements for engineering crossing active faults.

The Lenglongling Fault(LLLF) is a major active left-lateral strike-slip fault along the northeastern margin of the Tibetan plateau. Fault slip rate is of great significance for researching the dynamics of tectonic deformation in NE Tibetan plateau and understanding the activity and seismic risk of the fault. However, slip rate of the LLLF, which remains controversial, is limited within~3~24mm/a, a relatively broad range. Taking Niutougou site(37.440 2°N, 102.094 0°E)and Chailong site(37.447 3°N, 102.063 0°E) in the upstream of Talihua gully in Menyuan County, Qinghai Province as the research objects, where faulted landform is typical, we analyzed the displacement evolution model and measured the slip amounts by back-slip of the faulted landform using high-resolution DEM from Terrestrial LiDAR and high-precision satellite images of Google Earth, and by collecting and testing samples from stratigraphic pit excavated in the faulted landform surface and stripping fresh stratigraphic section, we determined the abandonment age of the surface. Holocene slip rate obtained from Niutougou site and Chailong site is(6.4±0.7)mm/a and(6.6±0.3)mm/a, respectively, which have a good consistency. Taking into account the error range of the slip rate, the left-lateral slip rate of the LLLF is(6.6±0.8)mm/a since Holocene, which is between the previons results from geological method, also within the slip rate range of 4.2~8mm/a from InSAR, but slightly larger than that from GPS((4.0±1.0)mm/a). Late Quaternary slip rate of Qilian-Haiyuan fault zone, which displays an arc-shape distribution, turns to be the largest in LLLF region. The most intensive uplift in the LLLF region of the NE Tibetan plateau confirms the important role of the LLLF in accommodating the eastward component of movement of Tibetan plateau relative to the Gobi-Ala Shan block from one side.

The southern segment of the Xiaojiang Fault (SSXF) is located at the intersection of the Xianshuihe-Xiaojiang Fault and Red River-Ailao Shan fault systems in the southeast margin of the Tibetan plateau. Based on the interpretation of remote sensing image, the SSXF clearly shows the linear feature and continuous distribution as a single, penetrating fault. It has a total length of about 70km, trends generally about 20° to the northeast and protrudes slightly in the middle to the east. A typically geomorphologic phenomenon about the synchronous left-lateral dislocation of ridges and gullies can be found at Liangchahe, Longtan Village along the SSXF. The distribution of faults, the sedimentary features, attitude variance and the primary dating results of the offset strata in the trench section across fault sag ponds reveal three paleoseismic events rupturing obviously the surface, which demonstrates that the SSXF has the ability of recurrence of strong earthquakes. High-precision topographic map about two gullies and the platform between them with synchronous dislocation is acquired by using the Trimble 5800 GPS real-time difference measurement system. The dislocation is (18.3±0.5)m. As the top geomorphologic surface between the above two gullies and their adjacent area, the terrace surface T₂ stopped accepting deposits at ~2606a, based on the linear regression analysis of three dating data. According to the geological method, a sinistral strike-slip rate of (7.02±0.20)mm/a on the SSXF in the Holocene is obtained, which has a good consistency with the results provided by using GPS data. The preliminary results about the Holocene activity and slip rate of the SSXF demonstrate that the southward or south-southeast motion of the Sichuan-Yunnan block in the SE Yunnan region has not been absorbed by the possible shortening deformation and the sinistral strike-slip rate of the SSXF has not been drastically reduced. The SSXF is a Holocene fault with obvious activity. This preliminary understanding provides some basic geological data for the seismic risk evaluation of the SSXF in the future, and for the establishment and inspection of the seismotectonic model about the Sichuan-Yunnan block.

Magnetic Induced Polarization(MIP) is one kind of electrical conductivity methods,which measures magnetic field point by point rather than measuring the electric field difference between two electrodes in Electric Induced Polarization(EIP).Compared to EIP,MIP surveys have certain merits,such as:bigger detection depth,higher resolution,capable to provide useful information through highly conductive overburden and high-resistance or low-resistance cover,no need for grounding,and etc.It will be a deep exploration technology and applied to areas such as low-resistance overburden,Gobi desert,bedrocks which have been a major impediment to EIP surveys.In order to test the ability of obtaining IP anomaly in MIP surveys,we carried out a trial comparative study between MIP and EIP(Time-domain IP method and multi-frequency phase IP method included) in a mining area in China.Test results show that there is a good consistency in the IP anomaly about the two detection methods measured in the same survey lines and it will provide a basis for the further studies of MIP.In the paper the basic principles,techniques,and data processing of this method(MIP) are discussed,and the results between Magnetic Induced Polarization and Electric Induced Polarization are analyzed.