With the acceleration of urbanization process, solving the earthquake and its associated disasters caused by buried active fault in urban areas has been a difficult issue in the construction of urban public security system. It is difficult to deal with the anti-seismic issues of cross-fault buildings using the existing techniques, therefore, reasonable setback distance for buried active fault in urban area is the only method for the planning and construction at the beginning. At present, theoretical research about setback for active fault is becoming more and more mature, and the mandatory national standard “Setback distance for active fault” will be enacted soon. As a result, how to work on the basis of these theories and national standards is in urgent. In recent years, the exploration of urban active faults was successively completed. However, there are no typical cases of how to make full use of the achievements of urban active fault projects in the follow-up work, and how to guide urban construction based on the project conclusions, so as to ensure urban safety and rational development of urban economy.

In this paper, taking a site along the Anqiu-Juxian Fault in the Tanlu fault zone in Xinyi city as an example, based on the results of 1︰10 000 active fault distribution map, and referring to the stipulation of national standard “Setback distance for active fault”, 12 shallow seismic survey lines with a spacing of less than 50m were laid out firstly, and the results of shallow seismic exploration show the existence of two high-dip faults in the site. Secondly, considering the shallow seismic survey results and the geologic site conditions, five rows of borehole joint profiles were selected along five of the shallow seismic survey lines. Based on the location of the faults and stratigraphy in the site revealed by the borehole joint profiles, and considering the latest research results of Quaternary stratigraphy and the conclusion of urban active faults detection, the west branch fault is constrained to be a Holocene active fault and the east branch fault is an early Quaternary fault. As a result, we precisely mapped the trace, dip and upper breakpoint of the fault in the site based on the shallow seismic exploration and joint borehole profile. The accurate positioning of the plane position of the active fault differs by about 200m from the 1:1000 strip distribution map.

According to the relevant national standards and scientific research results, active faults in the site shall be avoided. Based on the surface traces of active faults revealed by the accurate detection in the site, the active fault deformation zone was delineated, and the range of setback distance for active fault was defined outside the deformation zone. The detection results accurately determined the plane distribution of the active fault in the site, which meets the accuracy of the development and utilization of the site. Based on the accurately located active fault trace, and complying with the forthcoming national standard “Setback distance from active fault”, this study not only scientifically determines the setback distance for active fault in the site, but also releases the scarce land resources in the city. This result achieves the goal of scientifically avoiding potential dangerous urban hidden active fault and making full use of land.

The case detection process confirms that the results of urban active fault detection are still difficult to meet the fault positioning accuracy required for specific site development, and the range of active fault deformation zone within the site must be determined based on the precise positioning method for hidden active faults as stipulated in the national standard “Setback distance for active fault”. The national standard “Code for seismic design of buildings” only specifies the setback distance for active faults under different seismic intensity, but does not provide any clear definition of the accuracy of active fault positioning, so it is difficult to define the required active fault positioning degree and boundary range of the deformation zone of active fault in practice. The national standard “Setback distance for active fault” clearly defines various types of active fault detection and positioning methods, determines the scope of active fault deformation zone and the accurate setback distance for active fault in different cases. The specific case proves that before developing and utilizing specific sites along urban concealed active faults, relevant work shall be carried out according to the national standard “Setback distance for active fault” to effectively resolve the issue about the relations between urban development and urban safety, so the promulgation and implementation of national standard should speed up.

Beijing locates in the North China active tectonic block, where the NW- and NE-trending active faults are widely distributed, such as the Nankou-Sunhe Fault, the Shunyi-Liangxiang Fault, and the Xiadian Fault. Historically, large earthquakes frequently occurred along these faults, especially in the intersection of these two sets of faults, e.g. the 1679 Sanhe-Pinggu earthquake(M~8). Thus, it is of great significance to quantitatively study the faults’ basic parameters, including the fault trace, slip distribution, and rupture behavior, for accurate assessment of seismic hazard of Beijing area.
The Xiadian active fault locates at the eastern boundary of Beijing, near the Beijing Municipal Administrative Center. The 1679 Sanhe-Pinggu earthquake(M~8)occurred on this fault. Previous studies on this area have revealed clearly the bedrock geology, fault geometry, seismicity distribution as well as co-seismic deformation of this earthquake, which greatly improves the understanding of the activity behavior of the Jiadian active fault.
However, the previous studies have focused on the surface rupture of the 1679 earthquake, the complete rupture geometry and slip distribution have not yet been constructed, due to the restriction of high-resolution topographic data. Furthermore, the triangular slip distribution has widely occurred along active faults, especially along the typical normal faults. Whether the fine slip distribution of Xiadian Fault conforms to the case or not is still unclear.
In order to explore all those issues above, using low-costing high-resolution(0.5m)satellite images, we derived 1.0m grid size DEM to quantitatively explore the surface rupture along the Xiadian Fault. Detailed mapping and offset measurements revealed 5 left-stepping branches(~3km), with a total length of 12.3km for the coseismic rupture of the 1679 Sanhe-Pinggu earthquake. Slip distributions along the fault exhibit the arc-shaped geometry, and the maximum and average vertical offsets are ~3.2m and ~1.8m, respectively.
Such triangular shaped slip distribution has also been found along other typical normal faults, for instance, the Wairarapa Fault in New Zealand, the Afar Fault in East Africa, and Owens Valley Fault in California. Modeling of these measurements revealed 2 earthquakes with co-seismic vertical offset of ~1.8m and 1.7m, respectively. Reasonably, the maximum ~3.2m vertical offset possibly represents the cumulative vertical offset of 2 earthquakes, including the 1679 Sanhe-Pinggu earthquake.
Based on the relationships among the surface rupture length, average offsets, as well as moment magnitudes, the calculated size is comparatively small. Based on the cutting shape of the 2 sets of faults and the upper crust imaging by shallow seismic reflection profile, we propose that the current right-lateral shear deformation of the fault is decoupled with the existing extensional structures, and this hypothesis has been verified by the current focal mechanism solution.

The Daxing Fault is an important buried fault in the Beijing sub-plain, which is also the boundary fault of the structural unit between Langgu sub-sag and Daxing sub-uplift. So far, there is a lack of data on the shallow tectonic features of the Daxing Fault, especially for the key structural part of its northern section where it joins with the Xiadian Fault. In this paper, the fine stratigraphic classifications and shallow tectonic features of the northern section in the main Daxing Fault are explored by using three NW-trending shallow seismic reflection profiles. These profiles pass through the Daxing earthquake(M6¾)area in 1057AD and the northern section of the main Daxing Fault. The results show that seven strong reflection layers(T₀₁—T₀₃, T_Q and T₁₁—T₁₃)are recognized in the strata of Neogene and Quaternary beneath the investigated area. The largest depth of strong reflection layer(T₁₃)is about 550~850ms, which is interpreted as an important surface of unconformity between Neogene and Paleogene or basement rock. The remaining reflection layers, such as T₀₁ and T_Q, are interpreted as internal interfaces in Neogene to Quaternary strata. There are different rupture surfaces and slip as well as obviously different structural features of the Daxing Fault revealed in three shallow seismic reflection profiles. The two profiles(2-7 and 2-8)show obvious rupture surfaces, which are the expression of Daxing Fault in shallow strata. Along the profile(2-6), which is located at the end of the Daxing fault structure, a triangle deformation zone or bending fracture can be identified, implying that the Daxing Fault is manifested as bending deformation instead of rupture surfaces at its end section. This unique structural feature can be explained by a shearing motion at the end of extensional normal fault. Therefore, the Daxing Fault exhibits obviously different tectonic features of deformation or displacement at different structural locations. The attitude and displacement of the fault at the shallow part are also different to some extent. From the southwest section to the northeast section of the fault, the dip angle gradually becomes gentler(80°~60°), the upper breakpoint becomes deeper(160~600m), and the fault displacement in Neogene to Quaternary strata decreases(80~0m). Three shallow seismic reflection profiles also reveal that the Daxing Fault is a normal fault during Neogene to early Quaternary, and the deformation or displacement caused by the activity of the fault reaches the reflection layer T₀₂. This depth is equivalent to the sedimentary strata of late Early-Pleistocene. Therefore, the geometry and morphology of the Daxing Fault also reveal that the early normal fault activity has continued into the Early Pleistocene, but the evidence of activity is not obvious since the late Pleistocene. The earthquakes occurring along the Daxing Fault, such as Daxing earthquake(M6¾)in 1057AD, may not have much relation with this extensional normal fault, but with another new strike-slip fault. A series of focal mechanism solutions of modern earthquakes reveal that the seismic activity is closely related to the strike-slip fault. The Daxing Fault extends also downwards into the lower crust, and may be cut by the steeply dipping new Xiadian Fault on deep seismic reflection profile. The northern section of the Daxing Fault strikes NNE, with a length of about 23km, arranged in a right step pattern with the Xiadian Fault. Transrotational basins have been developed in the junction between the northern Daxing Fault and the southern Xiadian Fault. Such combined tectonic features of the Daxing Fault and Xiadian Fault evolute independently under the extensional structure background and control the development of the Langgu sub-sag and Dachang sub-sag, respectively.

The interaction between the continental-continental collision of the Indian-Eurasian plate and the westward underthrusting of Pacific plate is generally considered to be the cause of the destruction of North China Craton. At present, there are still doubts in the researches worldwide about the dynamic mechanism of the formation and evolution of the Ordos peripheral fault-depression system and the contemporary tectonic stress field.
The Hetao Basin is a Cenozoic fault basin located between the Ordos block and the Yinshan Mountains. Due to the effect of uplift of the Tibet Plateau and the continuous subduction of the Pacific plate, graben faulting of different intensities occurred in different periods of Cenozoic around the Ordos block. Late Quaternary lacustrine facies sedimentary strata are widely developed in Hetao Basin. The Haolaigou profile, Bianqianhao profile and the Langshan profile in this study are all located in Hetao Basin. According to the lithology and structural analysis of the upper Pleistocene series in the three profiles, angular unconformities of phase 1-2 are recorded in the lacustrine facies sediments with a thickness of about 10m. The dating results of the Haolaigou profile, Bianqianhao profile and Langshan profile show that the formation time of both unconformities is 80ka BP.
Using the tectonic geology, Quaternary geology, stratigraphy, sedimentology and a variety of dating methods, we also carry out a comprehensive study and obtain the following results:
(1)The analysis of lithological and structural features of Haolaigou profile, Bianqianghao profile and Langshan profile in the Hetao Basin shows that multi-phase angular unconformities events are recorded in the lacustrine strata of a thickness of nearly 10m. These unconformities represent the tectonic movement in the late Pleistocene period since the 80ka BP and they may be widely distributed in the North China region. They are probably the direct products of the latest tectonic movement in the Quaternary period.
(2)The present tectonic movement initiates at about 80ka BP. It not only causes multiple angular unconformity events, but also leads to the disappearance of the Hetao ancient lake. The rapid regional epeirogenetic uplifting of the Ordos block since 76.4ka BP should also be the specific manifestation of this tectonic movement. Because of the influence of the accelerated uplifting and eastward spreading of the Qinghai-Tibet plateau in the late Quaternary, the NEE thrusting effect of the Ordos block is enhanced and affected.

Geomorphic offsets displaced by coseismic surface rupture can be analyzed to identify earthquake recurrence behavior. Therefore, obtaining a sufficient and precise along-fault offset dataset is vital to identify long-term earthquake recurrence behavior. Furthermore, knowledge of along-fault slip distribution during a single-earthquake or multi-earthquakes is important for other reasons, including a better understanding of the relationship between earthquake size and coseismic displacements, fault kinematics and fault mechanics. A recent flourish of offsets-measuring software and high-resolution topographic data together offer an unprecedented opportunity to measure high-density fault offsets. Here, we introduce and compare two kinds of most popular software, LaDiCaoz and 3D_Fault_Offsets. We describe the workflow and principle of the two codes by taking a fault-offset example on the eastern Altyn Tagh Fault. LaDiCaoz iterates over the channel morphology and position parameters and determines the summed absolute elevation difference Σ[Δ(elevation)] between both transverse profiles. The optimal horizontal offset is defined by the parameter combination that results in the least mismatch between two profiles. Compared with LaDiCaoz, the principle of 3D_Fault_Offsets is more complicated by measuring the offset in three dimensions. It mathematically identifies and represents nine of the most prominent geometric characteristics of common sublinear markers along faults in three dimensions, such as the streambed(minimum elevation), top, free face and base of channel banks or scarps(minimum Laplacian, maximum gradient, and maximum Laplacian), and ridges(maximum elevation). By calculating best fit lines through the nine point clouds on either side of the fault, the code computes the lateral and vertical offsets between the piercing points of these lines onto the fault plane, providing nine lateral and nine vertical offset measures per marker. Through a Monte Carlo approach, the code calculates the total uncertainty on each offset. Although both 3D_Fault_Offsets and LaDiCaoz are developed based on the Matlab platform, there are significant differences in principles, linear marker, software interface, repeatability, input-file types, degree of automation, adaptability, output file types, etc. In this part, we compare and summarize their features, advantages, and disadvantages. Finally, we calculate the correlation of two groups of fault-offset data derived from the two methods along the eastern ATF. By doing this, we try to explore if the two methods can be crosschecked and to study how sinuosity of the linear geomorphic markers affect the measuring results. By discussing and comparing the accuracy of the two measuring methods, we consider that LaDiCaoz is better than 3D_Fault_Offsets in accuracy aspect. In our opinion, there exist some disadvantages in the both software, and higher automation and introduction of artificial intelligence will be the future development direction.

The Pengxian blind fault is a typical active fault in the central Longmen Shan front belt. It has important reference value for understanding the growth mode and process of the eastern Tibetan plateau. Because the fault is covered by the thick Upper Cenozoic strata in the western Sichuan Basin, its three-dimensional spatial distribution, structural style and formation mechanism remain unclear. In this paper, based on several high-resolution 3-D seismic reflection profiles, together with near-surface geological data and borehole data, we investigate the structural geometry of the Pengxian blind fault and build a 3-D model based on the results. We analyze the shape and scale of underground spatial distribution of the fault through a three-dimensional fault model. According to the theory of fault-related fold and fold-accommodation fault, this paper discusses the forming mechanism of the Pengxian buried structures. The shallow tectonic deformation in front of Longmen Shan is closely related to the detachment layer of the Middle and Lower Triassic, and this detachment layer f1 horizontally propagates into the Longquanshan anticline in the western Sichuan Basin. The Pengxian buried fault is a typical fault-bend fold and the f1 horizontally propagates into the western Sichuan Basin with a fault slip of 3.5km. The Pengxian blind fault is a high angle(50°~60°)thrust fault developed in the front wing of the kink-band zone, striking NE-SW, with a total length of~50km; But the fault is not connected with the Dayi buried fault in the south section of Longmen Shan. They are two different faults, and this defines the scale of the Pengxian blind fault. This limitation makes sense for analyzing and evaluating the magnitudes of potential earthquake. All above study provides research basis for further analysis of the potential seismic risk in this area. The Pengxian blind fault is parallel to the anticlinal axis with small amount of offset as a fold-accommodation fault. We believe that the fault formation is related to the fold deformation of the fold front limb. The study reveals the geometry, kinematics and formation mechanism of the Pengxian active fault, and provides a basis for further analysis of fault activity and hazard. Therefore, there is little possibility of strong earthquakes at the Pengxian blind fault due to its formation mechanism of the fault which is generally characterized by fold deformation and shortening deformation. In this paper, we discuss the location of Pengxian blind fault in the middle of Longmen Shan and Sichuan Basin. Because the Pengxian buried structures are in the transition area, the shortening amount in Pengxian indicates that the absorption in the basin is quite limited. It reflects the blocking effect of Sichuan Basin. In the study, we find that the relationship between folds, faults and sediments is an important part of tectonic interpretation; the theory of fault-related fold and fold-accommodation fault is well used for analysis. This would have great significance for the study of structural deformation, which can help to build a three-dimensional model of fault.

The M_S7.0 Jiuzhaigou earthquake in Sichuan Province of 8 August 2017 triggered a large number of landslides. A comprehensive and objective panorama of these landslides is of great significance for understanding the mechanism, intensity, spatial pattern and law of these coseismic landslides, recovery and reconstruction of earthquake affected area, as well as prevention and mitigation of landslide hazard. The main aim of this paper is to present the use of remote sensing images, GIS technology and Logistic Regression(LR)model for earthquake triggered landslide hazard mapping related to the 2017 Jiuzhaigou earthquake. On the basis of a scene post-earthquake Geoeye-1 satellite image(0.5m resolution), we delineated 4834 co-seismic landslides with an area of 9.63km². The ten factors were selected as the influencing factors for earthquake triggered landslide hazard mapping of Jiuzhaigou earthquake, including elevation, slope angle, aspect, horizontal distance to fault, vertical distance to fault, distance to epicenter, distance to roads, distance to rivers, TPI index, and lithology. Both landsliding and non-landsliding samples were needed for LR model. Centroids of the 4834 initial landslide polygons were extracted for landslide samples and the 4832 non-landslide points were randomly selected from the landslide-free area. All samples(4834 landslide sites and 4832 non-landslide sites)were randomly divided into the training set(6767 samples)and validation set(2899 samples). The logistic regression model was used to carry out the landslide hazard assessment of the Jiuzhaigou earthquake and the results show that the landslide hazard assessment map based on LR model is very consistent with the actual landslide distribution. The areas of Wuhuahai-Xiamo, Huohuahai and Inter Continental Hotel of Jiuzhai-Ruyiba are high hazard areas. In order to quantitatively evaluate the prediction results, the trained model calculated with the training set was evaluated by training set and validation set as the input of the model to get the output results of the two sets. The ROC curve was used to evaluate the accuracy of the model. The ROC curve for LR model was drawn and the AUC values were calculated. The evaluation result shows good prediction accuracy. The AUC values for the training and validation data set are 0.91 and 0.89, respectively. On the whole, more than 78.5% of the landslides in the study area are concentrated in the high and extremely high hazard zones. Landslide point density and landslide area density increase very rapidly as the level of hazard increases. This paper provides a scientific reference for earthquake landslides, disaster prevention and mitigation in the earthquake area.

The two mainstream deformation models of the Tibet plateau are continental escape model and crustal thickening model, the former suggests that the NW-trending Karakoram Fault, Gyaring Co Fault, Beng Co Fault and the Jiali Fault as the Karakoram-Jiali fault zone is the southern border belt and that the dextral strike-slip rate is estimated as up to 10~20mm/yr. However, research results in recent years show that the slip rates along those faults are significantly less than earlier estimates. Taylor et al. (2003)suggest that the conjugate strike-slip faults control the active deformation in the central Tibet.
The lack of research on the slip behavior of the NE-trending faults in the central Tibet Plateau constrains our understanding of the central Tibet deformation model. Thus, we choose the NE-direction Qixiang Co Fault located at the north of the Gyaring Co Fault as research object. Based on the interpretation of satellite images, we found several faulted geomorphic sites. Using RTK-GPS ground control point and unmanned aerial vehicle (UAV)topographic surveying, we obtained less than 10cm/pix-resolution digital elevation model (DEM)in the Yaqu town site. We used the LaDiCaoz_v2.1 software to automatically extract the left-lateral offset of the largest gully on the terrace T₂ surface, which is (21.3±7.1)m, and the vertical dislocation of the scarp on the terrace T₂ surface, which is (0.9±0.1)m. The age of both U-series dating samples on the terrace T₂ is (4.98±0.17)ka and (5.98±0.07)ka, respectively. The Holocene left-lateral slip rate along Qixiang Co Fault is (3.56±1.19)mm/a and the vertical slip rate is (0.15±0.02)mm/a. The kinematic characteristics of the sinistral strike-slip with normal slip coincide with the eastward motion of the central Tibet plateau, and its magnitude is in agreement with its conjugate Gyaring Co Fault, suggesting that the deformation pattern of the central Tibetan plateau complies with the conjugate strike-slip faults mode.

In this study, a detailed database of landslides triggered by the 25 April 2015 Gorkha (Nepal)M_W7.8 earthquake is constructed based on visual interpretation of pre- and post-earthquake high-resolution satellite images and field reconnaissance. Results show the earthquake triggered at least 47 200 landslides, which have a NWW direction spatial distribution, similar with the location and strike of the seismogenic fault. The landslides are of a total area about 110km² and an oval distribution area about 35 700km². On the basis of a scale relationship between landslide area (A)and volume (V), V=1.314 7×A^{1.208 5}, the total volume of the coseismic landslides is estimated to be about 9.64×10⁸m³. In the oval landslide distribution area, the landslide number density, area density, and volume density were calculated and the results are 1.32km^-2, 0.31%, and 0.027m, respectively. This study provides a detailed and objective inventory of landslides triggered by the Gorkha earthquake, which provides very important and essential basic data for study of mechanics of coseismic landslides, spatial pattern, distribution law, and hazard assessment. In addition, the landslide database related to an individual earthquake also provides an important earthquake case in a subduction zone for studying landslides related to multiple earthquakes from a global perspective.

In this paper, a method for measuring the color of Quaternary sediments based on digital image analysis is proposed, which has the advantages of simple and quick operation, and improving the research efficiency of sediment color. In order to demonstrate the feasibility of this method, the measurement results are compared with the traditional colorimetric measurement methods. The results show that:1) Both the traditional sediment color measurement method and the digital image color measurement method are controlled by sediment grain size. Sediment color research can be carried out on fine sand or finer sediments, but for medium grained sand and coarse sand, the error will be larger. Compared with the traditional measurement methods, digital image method can reduce the inherited color interference of coarse clastic sediments; 2) The particle size and water content of clastic sediments affect the numerical value of digital image sediment color. Generally, the wet-color values obtained by the digital image method are lower than the dry-color values obtained by using a spectrophotometer, and the color value variation is large, and the undulation of chromaticity/brightness curve is greater; 3) Compared with the traditional sediment color measurement method, digital image method has good consistency of color measurement of redness and yellowness, but the brightness is affected by uneven illumination, resulting in some error. Sediment digital image extraction of sediment color information can replace the indoor measurement method to a certain extent, and can be used to establish a more complete sediment color sequence under more complex sedimentary environment, so as to provide information for the Quaternary stratigraphic division, paleoclimate research, paleosol recognition and paleoearthquake event identification, thus expanding the application of colorimetric results to the geological direction.

The M_S7.0 Jiuzhaigou earthquake in Sichuan Province of 8 August 2017 triggered a large number of landslides. A comprehensive and objective panorama of these landslides is of great significance for understanding the mechanism, intensity, spatial pattern and law of these coseismic landslides, recovery and reconstruction of earthquake affected area, as well as prevention and mitigation of landslide hazard. In this paper, we use the trinity method of space, sky and earth to create a panorama of the landslides triggered by this event. There are 4 roads in the distribution area of the coseismic landslides. The Jinglinghai-Xiamo and Jiudaoguai-Jiuzhaitiantang road sections register the most serious coseismic landslides. The landslides are mainly of moderate-and small-scales, and also with a few large landslides and avalanches. A detailed visual interpretation of the coseismic landslides is performed in two areas of Wuhuahai(11.84km²) and Zharusi-Shangsizhai village(47.07km²), respectively. The results show the overall intensity of landsliding(1088 landslides, a total area 1.514km²) in the Wuhuahai area is much higher than those in the Zharusi-Shangsizhai village area(528 landslides, a total area 0.415km²). On the basis of a scene of post-earthquake Geoeye -1 satellite images, we delineate more than 4 800 coseismic landslides with a total occupation area 9.6km². The spatial pattern of these landslides is well related with the locations of the inferred seismogenic fault and aftershocks. Widely distributed earthquake-affected weakened slopes, residual loose materials staying at high-position slopes and in valleys have greater possibilities to fail again and generate new landslides or debris flows under the conditions of strong aftershocks or heavy rainfalls in the future. Geological hazard from these events will become one of the most serious problems in the recovery and reconstruction of the earthquake-affected area which should receive much attention.

The theories, techniques and methods for the exploration of active faults in the terrestrial domain are relatively mature, while such efforts in the water domain remain very few. In this study, the AAE shallow profiler was used to detect the underwater three-dimensional topography and active faults in the Qionghai area, Xichang for the first time. Based on the SKUA-GOCAD software platform and its DSI interpolation method, three-dimensional modeling of the exploration data was carried out. The survey profiles clearly reveal three different reflection interfaces, including the underwater interface, the interface between the silt layer and shallow sedimentary layer, and the bottom of the shallow sedimentary layer. The three-dimensional topography of the Qionghai area was mapped initially. Moreover, evidence of active faults was first found in several survey profiles from the reflection interface cutoff. This study also analyzed and discussed the working principle and characteristics of the AAE shallow profiler, including their parameters and various factors of exploration. The mapped three-dimensional topography and active faults in the Qionghai area of Xichang can provide a reference for research on the active tectonics underwater in the future.

Most earthquakes result from fault activity under heterogeneous loading and complex physical properties, also affected by fault structure and interaction between faults. Such a complicated mechanism makes often failures of the "seismic gap" theory in the effort of medium-and long-term earthquake prediction. This study attempts to address this issue using the finite element method(FEM).The friction behavior of faults can be used to simulate the non-uniformity of rupture processes of the seismogenic structure. So we use the FEM containing non-linear friction to simulate fault ruptures in the Daliangshan sub-block and adjacent areas, and compare the results with time-space evolution of historical M_S ≥ 7 earthquakes since 1840 in this region. In the simulation, the sequence of large-batch fault contact nodes change from "stick state" to "slip state" in short time, which mimics the sudden fault slip and the occurrence of major earthquakes. The results show that the fault breaking lengths from simulation are largely consistent with the magnitudes of historical earthquakes in the study area, such as the 1850 Puge-Xichang M_S7.5, and 1887 Shiping M_S7.0 earthquakes. The simulation also shows the development of seismic gaps and "gap breaks" by major earthquakes on the Xianshuihe fault, such as 1955 Kangding M_S7.5 earthquake. Especially, the results illustrated the very long time of the seismogenic process of the 2008 Wenchuan M_S8.0 earthquake, and the corresponding sudden big rupture along the Longmenshan Fault, which is very similar to the observed surface rupture and very long incubation time and sudden co-seismic process. Then, this simulation is further applied to long-term earthquake prediction for the study area by calculation on a much longer time. The simulation results suggest that the Xiaojiang fault and the Zemuhe fault have relatively higher seismic risk, while moderate-sized earthquakes might occur on the Daliangshan fault and the Aninghe fault, and major earthquakes might rupture the northern segment of the Xianshuihe fault in a much longer time.

Since 1997, several major earthquakes occurred around the Bayan Har block in the Tibetan plateau, providing an opportunity to further understanding the mechanism of intraplate earthquakes. What is the effect of interactions among these events on the earthquake occurrence pattern is an issue to be addressed. In this article, we use the visco-elastic Coulomb stress changes model to calculate the stress interactions among the historical events close to or large than M_S7.0 since 1893 in the Bayan Har block. We apply the relationships between the slip rate and stress accumulation rate to transform the Coulomb stress changes into the influenced time. Then we remove such influence time from the occurrence years, and analyze the effects of the earthquake interactions on the clustering patterns of the historical earthquakes in the Bayan Har block. The results show that the major earthquakes in the Bayan Har block are characterized by a quasi-period of about 16 years from 1893 to 1973 and a clustering occurrence time period from 1997 to present following a relatively long quiescence period. The Bayan Har block is still in the active period with high probabilities of major quakes. We calculate the conditional probabilities of the rupture segments that did not rupture since 1893 of the boundary faults of the Bayan Har block in the next 30 years. The following faults or fault sections seem to be of major risk:The Maqin segment and the Maqu fault of the East Kunlun fault zone, the Awanang fault, the Luocha segment of the Tazhong fault, the Moxi segment of the Xianshuihe fault, and the Dangjiang fault. Other Fault segments in the Bayan Har block without seismic events since 1893 probably also have hazard of M_S7 earthquakes in the future.

As a part of the north-south seismic zone in China, a lot of M6.0-7.2 earthquakes have occurred in the margin faults of the Minshan block in history. This work attempted to characterize the geometry and activity of the north section of the Minjiang fault in this region based on high-resolution satellite images, geologic and geomorphic investigations, micro-geomorphic surveys, and trench excavation. The results show left-lateral-slip and Holocene activity of this structure. Along it, the offset landform has a continuous linearity on Ⅱ terraces near the Chuanpan village. The vertical height of the fault scarp measures 3.1 meters, which is almost the same as the accumulative horizontal displacement of the gully. The accumulative horizontal shortening due to faulting is 3.0 meters. Calculation using the model of displacement-dependent characteristic earthquakes shows both the vertical and horizontal co-seismic displacements and the horizontal shortening amount are about 1.0 meter. While strata dating suggests that the vertical and horizontal slip rates are all about 0.7-0.9mm/a, and the horizontal shortening rate is approximately 1.0-1.1mm/a. The excavated trench, perpendicular to the fault trace, reveals low-angle thrust dipping in 260åt 29°. From the relationship of the fault, colluvial wedge and stratigraphy ages, three palaeoseismic events are identified from youngest to oldest at 0-295a BP, 1 405-1 565a BP, and 2 750-2 875a BP, respectively, with recurrence intervals 1 110-1 565 years and elapsed time about 0-295 years。According to the relationship between magnitude and active parameters, it is considered that the northern segment of the Minjiang fault is capable of generating M7 or greater earthquakes. Now it is in the process of stress accumulation, having a certain seismic risk.

To establish an experimental, practical and open scientific experimental platform for earthquake monitoring and prediction, with reference to that of the southern California earthquake center(SCEC), China Earthquake Administration initiated a project for an experimental field in Sichuan and Yunnan Province in 2014. The chosen area is a seismically active region in the southeastern margin of the Tibetan plateau. A series of work compiling basic maps have been launched to collect fundamental data of this area including geologic structure, earthquake geology, geophysics, geodesy, and geochemistry. The map of earthquake surface ruptures in this region is one of these basic maps. This paper presents the compilation of this map. It includes earthquake epicenters, earthquake surface ruptures, faults, strata, magmatic rocks, and geographical data. This work summarized 87 destructive earthquakes, and 22 earthquake surface rupture zones, and analyzed the distribution characterization of earthquake epicenters, strata and magmatic rocks. The content in the map is reliable and integrated. This work will provide reliable earthquake-geology data for establishing geodynamics models and other future research of the national experimental field of earthquake monitoring and prediction in Sichuan and Yunnan Province.

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.

High-magnitude earthquake refers to an earthquake that can produce obvious surface ruptures along its seismogenic fault and its magnitude M is at least equal to 7.0. Prediction and identification of locations, where the high-magnitude earthquakes will occur in potential, is one of the scientific goals of the studies on long-term faulting behavior of active faults and paleo-earthquakes, and is also the key problem of earthquake prediction and forecast. The study of the geological and seismological signatures for identifying M≥7.0 earthquake risk areas and their application is an important part of seismic prediction researches. It can not only promote the development of earthquake science, especially the progress of earthquake monitoring and forecasting, but also be positive for earthquake disaster prevention and effective mitigation of possible earthquake disaster losses. It is also one of the earthquake science problems which the governments, societies and the scientific communities are very concerned about and need to be addressed.
Large or great earthquakes, such as the 2008 Wenchuan earthquake(M8.0), the 2010 Yushu earthquake(M7.1), the 2013 Lushan earthquake(M7.0)and the 2015 Gorkha earthquake(M_W7.8), have unceasingly struck the Qinghai-Tibet Plateau and its surrounding areas, which have been attracting attention of a large number of geoscientists both at home and abroad. Owing to good coverage of the seismic networks and GPS sations, a lot of high-quality publications in seismicity, crustal velocity structure, faulting beihavior have been pressed, which gives us a good chance to summarize some common features of these earthquakes. In this paper, seismogenic structural model of these earthquakes, faulting behavior of seismogenic faults, crustal mechanical property, recent straining environment and pre-earthquake seismicity are first analyzed, and then, five kinds of common features for the sismogenic faults where those earthquakes occurred. Those five kinds of commom features are, in fact, the geological and seismological signatures for identifying M≥7.0 earthquake risk areas. The reliability of the obtained sigatures is also discussed in brief. At last, based on the results of 1:50000 active fault mapping, and published seismic tomography and fault-locking studies, an experimental identification of the risk areas for the future large/great earthquakes in the North China and the Qinghai-Tibet Plateau is conducted to test the scientificity and applicability of these obtained sigantures.

We apply ambient noise tomography to continuous vertical component broadband seismic data between January 1, 2010 and December 31, 2011from the regional networks of 190 stations deployed by China Earthquake Administration in Hebei, Shanxi and Inner Mengolia. Ambient noise cross-correlations were performed to produce the Green's functions of each station-pair. Firstly, we used the multiple-filter analysis method to extract surface wave group and phase velocity dispersion curves from inter-station paths at periods from 7 to 40s. Then the study area was discretized into a 0.2°×0.2° grid to obtain the group and phase velocity distributions using O'ccam inversion method. After that, three dimensional (3-D) S-wave velocity structures from the surface down to 50km are inverted from group and phase velocities dispersion results. the results of S wave velocity distribution maps generally demonstrate good correlations with surface geological and tectonic features, and they also clearly revealed the lateral velocity variation in the crust. In the mid-upper crust, the basins are clearly resolved with low S wave velocity due to its thick sedimentary layer, and the Taihang and Yanshan uplifts show relative higher S wave velocity distribution. With the increase of depth (>30km), the S wave velocity distribution presents a contrary characteristic compared to that of the shallow layer, and the S wave velocity beneath the Taihang and Yanshan uplifts are much lower than basin areas, which is possibly correlated with the thickness of the crust. 3-D S wave velocity shows a low-velocity zone at~10~20km depth observed beneath the Tanshan-Hejian-Xintai-Cixian belt and Bohai Bay. the low-velocity zone at~20~30km depth beneath the Datong area may be associated with the thermal material in the crust-mantle. Our S wave velocity distribution maps clearly show that Taihang Mountains is not only the boundary of topography and tectonic zone, but also the transition zone of high and low S wave velocity.

Based on 60 records from the 20 stations within 100km to the epicenter of Lushan earthquake, the predominant period, period of peak response spectrum, duration of ground motion, and source duration are investigated. By the study, we conclude that within 100km to the epicenter, the scope of predominant period is 0.013~0. 275s in EW, NS and UD direction; the scope of period of peak response spectrum for 5% damping ratio is 0.03~0.65s; the scope of 90% ground motion durations is 5. 1~35. 9s; the scope of averaging source duration is 6.41 (EW), 6.05 (NS) and 5.47s (UD). Furthermore, based on the ground motion duration calculated by 20 stations dada, the predictive curve and equation of ground motion duration is regressed and compared with the recent equation of ground motion duration by Bommer (2009). We find that the ground motion durations of most stations are larger than predictively mean value by Bommer (2009), which means that the source effect of Lushan earthquake is relatively larger. Lastly, by the contour figure of ground motion duration and source duration, we conclude that the directivity character of duration is relatively apparent in NE direction. The relatively larger source duration and ground motion duration in NE direction indicate more energy release in the main shock of Lushan earthquake, which perhaps causes the relatively less aftershocks in this direction. The duration has no hanging wall effect, which perhaps results from the blind-reverse fault structure of Lushan earthquake.

Most of the regions in southeastern China are covered by thick Cenozoic sediments, or are the mountainous areas, so it is difficult to find and locate the active faults using the conventional geologic methods. The precisely relocated background seismicity in the seismically active region can be used to identify the buried active structure. In this paper, we investigated the relationship between regional tectonics and background seismicity, and interpreted the possible buried active faults in southeastern China using the relocated background seismicity. We relocated the background seismicity occurring in the region from 106°E to 122°E and from 22°N to 35°N between 1990 and 2014 using the doubble difference earthquake location algorithm. More than 51000 small earthquakes were relocated. In general, the relocated background seismicity corresponds well to the tectonics, showing the zonation features with typical seismicity pattern in each tectonic regime. It is observed that in the weakly active tectonic regime, the seismicity distributes dispersely or even scarcely, while in the strongly active tectonic region, the seismicity is highly clustered and organized to lineation pattern showing the same direction as the strike of the dominating fault zone. We interpreted the buried active faults using the lineation of seismicity. The inferred active faults are observed in the southeast coast region, the northwest Guangxi Province, the southeast boundary region of the Sichian Basin, and around the Huoshan Fault, many of which were not found by previous studies. The relocated hypocentral depth varies greatly in southeastern China. The shallowest earthquakes between 0 and 15km mainly distribute in the central region, indicating that the brittle deformation process only occurred in the upper crust, while the middle and lower crust are to be half-ductile and ductile deformation. There are earthquakes occurred in lower crust in the southeast coast region. The maximum depths distribute in the southeast boundary region of the Sichuan Basin, some are greater than 40km, indicating that the crust depth is larger than other places and the lower crust still sustains brittle deformation, which corresponds to the lower geothermal value and high crustal strength.

As the boundary between the northern edge of the Tibetan plateau and the Tarim Basin, the active left-lateral strike-slip Altyn Tagh Fault (ATF) is a first-order structure accommodating the ongoing continental collision between India and Asia and extends from northwestern Tibet to eastern Gansu Province with a whole length of ~1 600km. It is regarded as one of the most active fault in Euro-Asia block and has been segmented eleven rupture segments. This study utilizes the high-resolution image data (Google Earth) in combination with detailed field investigation on the Aksay segment of the ATF to scan the gully offset by Trimble VX, which suggests that the latest earthquake offset is 6~7m. Through trenching and radiocarbon dating of charcoal samples, paleoseismic events of this segment are analyzed. The trench has revealed many different deformed and dislocated strata, which display four paleoseismic events. Combined with the previous research and using the progressive constraining method, we constrained the paleoseismic events in this segment, and the results suggest that the penultimate and the most recent event occurred~1180a BP and 507~230a BP, respectively.

Living with disaster is an objective reality that human must face especially in China. A large number of earthquake case studies, such as the 2008 Wenchuan earthquake, 2010 Yushu earthquake, 2014 Ludian earthquake, have demonstrated that earthquake heavy damage and casualties stem from ground-faulting or rupturing along seismogenic active fault, near-fault high ground accelerations and building catastrophic structural failure. Accordingly, avoidance of active faults may be an important measure to effectively reduce earthquake hazard, which may encounter in the future, but how to avoid an active fault and how much a setback distance from the active fault is required to ensure that the ground faulting and rupturing has no any direct impact on buildings. This has been the focus of debate both for domestic and foreign scholars. This paper, first of all, introduces the definition of active fault. Then, quantitative analyses are done of the high localization of earthquake surface ruptures and relationship between the localized feature of the coseismic surface ruptures and building damages associated with the measured widths of the historical earthquake surface rupture zones, and an average sstatistic width is obtained to be 30m both for the earthquake surface rupture zones and heavy damage zones along the seismogenic fault. Besides, the widths of the surface rupture zones and spatial distribution of the building damages of the 1999 Chi-Chi earthquake and 2008 Wenchuan earthquake have also been analyzed to reveal a hanging-wall effect:Width of surface rupture zone or building damage zone on the hanging-wall is 2 or 3 times wider than that on its foot-wall for a dip-slip fault. Based on these latest knowledge learnt above, issues on avoidance object, minimum setback distance, location requirement of active fault for avoidance, and anti-faulting design for buildings in the surface rupture zone are further discussed. Finally, we call for national and local legislatures to accelerate the legislation for active fault survey and avoidance to normalize fault hazard zoning for general land-use planning and building construction. This preventive measure is significantly important to improve our capability of earthquake disaster reduction.

Active fault survey, which is one kind of fundamental researches for reducing disaster risk from earthquake, has been implemented by multiple governmental agencies since the early 1990s in China. Chinese government sponsored some active fault survey projects these years. These researches and projects use a series of thematic maps to describe their processes, results and achievement. Since geography information science was introduced in late 1990s and applied since 2000s to these active fault survey projects, seismologists and experts began to draw thematic maps by this new technology. A convenient and fast way for seismologists and experts to produce atlas of active fault survey products is an important accelerator to achieve these projects.This paper studies on the rapid methodology of producing active fault survey atlas, which is basically built on the processes and contents of active fault projects in recent years, and introduces the methodology on two aspects of standardization and software development. This study has been applied to the ongoing active fault survey projects, and resulted in more effective process, normative data and beautiful atlas. Thus these researches will be easier to be used in future application such as publication, internet sharing, and city development. This methodology has reference value to similar map-producing system in standardization and software development.

It is well known that the slip rate of Kunlun Fault descends at the east segment, but little known about the Awancang Fault and its role in strain partitioning with Kunlun Fault. Whether the sub-strand(Awancang Fault) can rupture simultaneously with Kunlun Fault remains unknown. Based on field investigations, aerial-photo morphological analysis, topographic surveys and ¹⁴C dating of alluvial surfaces, we used displaced terrace risers to estimate geological slip rates along the Awancang Fault, which lies on the western margin of the Ruoergai Basin and the eastern edge of the Tibetan plateau, the results indicate that the slip rate is 3mm/a in the middle Holocene, similar to the reduced value of the Kunlun Fault. The fault consists of two segments with strike N50° W, located at distance about 16km, and converged to single stand to the SE direction. Our results demonstrate that the Awancang fault zone is predominantly left-lateral with a small amount of northeast-verging thrust component. The slip rates decrease sharply about 4mm/a from west to east between the intersection zone of the Awancang Fault and Kunlun Fault. Together with our previous trenching results on the Kunlun Fault, the comparison with slip rates at the Kunlun fault zone suggests that the Awancang fault zone has an important role in strain partitioning for east extension of Kunlun Fault in eastern Tibet. At the same time, the 15km long surface rupture zone of the southeast segment was found at the Awancang Fault. By dating the latest faulted geomorphologic surface, the last event may be since the 1766±54 Cal a BP. Through analysis of the trench, there are four paleoearthquake events identified recurring in situ on the Awancang Fault and the latest event is since (850±30)a BP. The slip rate of the Awancang Fault is almost equivalent to the descending value of the eastern part of the east Kunlun Fault, which can well explain the slip rate decreasing of the eastern part of the east Kunlun Fault(the Maqin-Maqu segment)and the characteristics of the structure dynamics of the eastern edge of the Tibet Plateau. The falling slip rate gradient of the eastern Kunlun Fault corresponds to the geometric characteristic. It is the Awancang Fault, the strand of the East Kunlun Fault that accommodates the strain distribution of the eastward extension of the east Kunlun Fault. This study is helpful to seismic hazard assessment and understanding the deformation mechanism in eastern Tibet.

Over the past nearly 20 years, there is a huge development in active fault database related technologies in China, mass of active fault data has provided us important basis for researching on earthquake and disaster reduction, etc. However, with the appearance of huge amount of active fault data, lots of problems have emerged, such as data redundancy, inefficient management and information islands, etc. One of the major reasons is lack of efficient method to share the active fault data we owned.By study and comparison, we find that WebGIS is a good solution to solve the problem of active fault data publishing and sharing. WebGIS has well combined the advantages of traditional GIS and internet technologies, it could also share geographic data quickly, provide abundant browsing, searching and analysis functions. Based on the project of "China Earthquake Active Fault Detection—The North China Tectonic Region", and taking the foundational database information sharing platform of the active fault detection and survey as an example, the paper introduces the key technologies of active fault data sharing platform with latest WebGIS technology. The sharing system, which employs ArcGIS Server 10.0 as the GIS server, and utilizes MS-Silverlight technology at the client side, makes use of three-layer architecture which is popular in current B/S mode. To guarantee the security of the database on the internet, data source in the backend of the system is a simplified version of the active fault database of the North China tectonic region. Finally, the system has realized the publishing and sharing of 1 ︰ 50000 active fault mapping and main geophysical survey lines in North China tectonic region, and moreover, it provides some conventional map operations as well as fault searching and locating functions.The wide use of active fault data decides the significance of sharing system. It is very convenient to use this lightweight data sharing system to provide important basis for relevant industries, such as urban planning, land use and engineering site option, etc.

The July, 22, 2013 M_S6.6 Minxian-Zhangxian earthquake occurred in the Lintan-Dangchang Fault belt which is located in the northeast Tibet Plateau. Recent tectonic activities show that the Lintan-Dangchang Fault is a thrust fault with strike-slip component. However, the spatial pattern and mechanism of the recent tectonic activity along this fault have not been analysed in detail before the occurrence of the Minxian-Zhangxian earthquake. For better understanding the differential recent tectonic uplift of this fault, drainage basins and river networks were extracted based on ASTER GDEM data in this study. Hypsometric integral and the stream length gradient were calculated. The geomorphic indices analysis results suggest the differential tectonic uplift along the Lintan-Dangchang Fault. The areas experiencing strong tectonic uplift were identified which locate at the west of the Lintan County and around Minxian County. Besides, high geomorphic indices values are associated with epicenters of the historical earthquakes, which demonstrates the importance of the quantitative geomorphic analysis. Our results suggest that the overall tectonic uplift along the Lintan-Dangchang Fault is not very strong. However, certain segments which are experiencing relative high tectonic uplift have the potential of generating moderate or even large earthquakes. Under the regional NE-SW compressional stress caused by the northeastward expansion of the Bayankala block, the tectonic uplift of the fault may relate to the local stress concentration.

In this paper, adopting nonlinear finite-element method for faults with frictional contact, single fault and conjugate faults are calculated and compared respectively. And conjugate faults system is analyzed about its structural significance, combined with preparation and occurrence of strong earthquakes in the capital circle region. Study shows that seismogenic process of typical conjugated fault system from lock to unlock is well explained by Coulomb friction criteria, and unstable events can take place alternately along conjugate faults. The slip behavior of seismogenic tectonic model of great earthquake composed of two conjugate faults is verified. The numerical simulation as well as the analysis and discussion on the results provide scientific basis for earthquake forecasting and monitoring in areas where conjugate faults have developed.

On August 3, 2014, an M_S6.5 earthquake happened in the Ludian County, Zhaotong City of Yunnan Province. This earthquake caused a large number of landslides. In order to study the spatial distribution of the coseismic and pre-earthquake landslides, a 44.13km² area at the junction of Ludian County, Qiaojia County and Huize County along the Niulanjiang River is selected in this study. By visual interpretation of the Google Earth pre-earthquake high resolution images and the coseismic aerial data of 0.2m resolution of this area, the landslide databases of pre-earthquake and coseismic are established. The result shows that there are 284 pre-earthquake landslides, and 1053 earthquake-induced landslides. Then with the help of 10m×10m resolution DEM data and the GIS, the extracted factors of elevation, slope angle, slope aspect, curvature, lithology, earthquake intensity and drainages are used to analyze the spatial distribution of the coseismic and pre-earthquake landslides by adopting LAP(Landslide Areas Percentage)and LND(Landslide Number Density). The results show that areas with elevation <1 200m and 1 200～1 300m are prone to landslides whatever pre-earthquake or coseismic. With the slope gradient increasing, it is much more prone to landslide, and the area of <10°, close to the rivers, is also much susceptible. The advantage slope aspect is almost near S direction. Concave slope(when the curvature is negative)is much susceptible to landslides, and with the curvature decreasing, the landslide susceptibility gets higher. The region of limestone with dolomitic limestone is sensitive to landslide; in the areas consisting of basalt and volcanic breccia, the slope stability is greatly reduced under the effect of seismic force. The larger the intensity is, the more landslides happened. For either pre-earthquake or coseismic landslides, there is a positive correlation between landslide spatial distribution and the distance to rivers. The large pre-earthquake landslides have effective influence on LAP.

The M_S6.5 Ludian earthquake occurred on 3 August 2014 in Yunnan, China. The epicenter of this earthquake is located in the Dalingshan sub-block, a boundary region among the Bayan Har block, the Sichuan-Yunnan block and the South China block, which is dominated by the left-lateral and thrust-slip faults. The studies on the characteristics of the crustal deformation, the mechanism of strong earthquakes and stress changes after the M_S6.5 Ludian earthquake in the Daliangshan sub-block will help us understand the tectonic implication of the earthquake and facilitate further in-depth studies in the region.
This article introduces the slip behavior around the Daliangshan sub-block and strong earthquake distribution on the faults. Using the GPS data in the southeastern Tibetan Plateau, this study analyzes the motions of sub-blocks bordering the Daliangshan sub-block and the slip behavior of the boundary faults in the block model, and estimates the crustal motion in the Daliangshan sub-block after removing the whole block motion of the sub-block. It can be shown clearly that the Daliangshan sub-block has absorbed the compression via the Xianshuihe Fault, the Anninghe Fault and the Longmenshan Fault. Due to the compression from the boundary faults, the crustal motion in the sub-block is mainly characterized by the north-northwest trending left-lateral strike-slip faults. The boundary faults of the Daliangshan sub-block are mainly characterized by strong earthquakes with magnitude larger than M7 in the history. But in the interior of the Daliangshan sub-block, there are mainly the moderate earthquakes. The M_S6.5 Ludian earthquake ruptured the Baogunao-Xiaohe Fault, a left-lateral strike-slip fault associated with the main thrust Ludian-Zhaotong Fault and the Lianfeng Fault, where the whole thrust slip rate of the two faults is about 2.4mm/a.
Around the epicenter of the Ludian earthquake, there are strong earthquakes larger than M7 recorded in the nearby region, which might have impact on the occurrence of the Ludian earthquake. Also, the Ludian earthquake may further affect the occurrence of subsequent earthquakes. In this paper, we have calculated the static Coulomb failure stress changes (ΔCFS) on the fault plane of the Ludian earthquake induced by the 3 nearby big earthquakes, including the M7 1/2 earthquake in 1850 on the Zemuhe Fault and the M7 3/4 earthquake in 1733 on the Xiaojiang Fault. The M_S6.5 Ludian earthquake ruptured the north-northwest trending Baogunao-Xiaohe Fault, which is associated with the main thrust fault system of the Zhaotong-Ludian Fault and Lianfeng Fault. In our results, the Ludian earthquake was promoted by the M7 3/4 in 1733 on the Xiaojiang Fault and the M7 1/2 in 1850 on the Zemuhe Fault earthquakes. From the Coulomb failure stress change calculation, the ΔCFS value is about 0.03MPa, which may advance the occurrence of the M_S6.5 Ludian earthquake obviously. The calculations also showed opposite results of ΔCFS from the Ludian earthquake on the Yongshan M_S5.0 earthquake of 17 August and on the Yuexi M_S5.0 earthquake of 1 October in 2014. The former one is not much related to Ludian earthquake, but to the normal seismicity in the reservoir area as to the minus value of ΔCFS, while the Yuexi M_S5.0 earthquake was promoted by the M_S6.5 Ludian earthquake. Moreover, the M_S6.5 Ludian earthquake has advanced, to a certain extent, the enhancement of Coulomb failure stress on the northern segment of the Daliangshan Fault, Ebian Fault, eastern segment of the Zhaotong-Ludian Fault and the southern segment of the Zemuhe Fault, and has enhanced the earthquake energy accumulation of these faults.