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.

Pull-apart basin and push-up structure are the two most common and important structures formed within a strike-slip fault system. The term of pull-apart basin was firstly introduced when researchers discussing the formation of Central Death Valley, California. A pull-apart basin typically forms and develops between en echelon surficial strands or along a releasing bend of the transform fault. The diagonal cross-basin fault, formed diagonally within a pull-apart basin, connects the two en echelon strands bounding the basin. This type of fault not only plays an important role in the extinction of pull-part basin, but also controls the occurrence of large earthquakes. Therefore, it is of great significance to study the formation and evolution of cross-basin faults. However, compared with extensively studied pull-apart basins, fewer studies have been conducted on cross-basin fault, which greatly hampers our understanding of the structural evolution process of pull-apart basin and strike-slip fault. In this study, we take the Ganyanchi(Salt Lake)basin, the largest pull-apart basin located in the central part of the Haiyuan Fault, northeastern corner of the Tibetan plateau, as an example to investigate the character and general mechanism of the cross-basin fault. Geomorphological investigation, shallow artificial seismic exploration, and composite drilling geological survey are carried out along the cross-basin fault in Ganyanchi Basin. The main conclusions are listed as below: 1)The cross-basin fault in Ganyanchi Basin is a reverse strike-slip fault dipping to SW, rather than the previously claimed a strike-slip fault with significant normal component; 2)Although with a classic rhombic shape, the Ganyanchi Basin is actually an asymmetric pull-apart basin, which is mainly controlled by the northern boundary fault, i.e., the Nan-Xi Hua Shan Fault. Under the control of the Nan-Xi Hua Shan Fault, more than 680m thick growth strata were accumulated in the basin, and a rollover anticline was formed by the growth strata; 3)The example of the Ganyanchi asymmetric pull-apart basin suggests that a possible mechanism for the reverse cross-basin fault is probably the “straightening of strike-slip fault”, that is, the earlier formed antithetical normal fault adopts reverse component of straightened basin boundary fault, and then undergoes rotation and finally becomes a synthetical reverse fault with great strike-slip component. The rollover anticline, mainly controlled by the master boundary fault of an asymmetric pull-apart basin, may also partly contribute to the rotation of the cross-basin fault. As more natural pull-part basins needed to be investigated, caution should be taken when this suggested model is applied elsewhere.

Complex geometrical structures on strike-slip faults would likely affect fault behavior such as strain accumulation and distribution, seismic rupture process, etc. The Xianshuihe Fault has been considered to be a Holocene active strike-slip fault with a high horizontal slip rate along the eastern margin of the Tibetan plateau. During the past 300 years, the Xianshuihe Fault produced 8 earthquakes with magnitude≥7 along the whole fault and showed strong activities of large earthquakes. Taking the Huiyuansi Basin as a structure boundary, the northwestern and southeastern segments of the Xianshuihe Fault show different characteristics. The northwestern segment, consisting of the Luhuo, Daofu and Qianning sections, shows a left-stepping en echelon pattern by simple fault strands. However, the southeastern segment(Huiyuansi-Kangding segment)has a complex structure and is divided into three sub-faults: the Yalahe, Selaha and Zheduotang Faults. To the south of Kangding County, the Moxi segment of the Xianshuihe Fault shows a simple structure. The previous studies suggest that the three sub-faults(the Yalahe, Selaha and Zheduotang Faults of the Huiyuansi-Kangding segment)unevenly distribute the strain of the northwestern segment of the Xianshuihe Fault. However, the disagreement of the new activity of the Yalahe Fault limits the understanding of the strain distribution model of the Huiyuansi-Kangding segment. Most scholars believed that the Yalahe Fault is a Holocene active fault. However, Zhang et al.(2017)used low-temperature thermochronology to study the cooling history of the Gongga rock mass, and suggested that the Yalahe Fault is now inactive and the latest activity of the Xianshuihe Fault has moved westward over the Selaha Fault. The Yalahe Fault is the only segment of the Xianshuihe Fault that lacks records of the strong historical earthquakes. Moreover, the Yalahe Fault is located in the alpine valley area, and the previous traffic conditions were very bad. Thus, the previous research on fault activity of the fault relied mainly on the interpretation of remote sensing, and the uncertainty was relatively large. Through remote sensing and field investigation, we found the geological and geomorphological evidence for Holocene activity of the Yalahe Fault. Moreover, we found a well-preserved seismic surface rupture zone with a length of about 10km near the Yariacuo and the co-seismic offsets of the earthquake are about 2.5~3.5m. In addition, we also advance the new active fault track of the Yalahe Fault to Yala Town near Kangding County. In Wangmu and Yala Town, we found the geological evidence for the latest fault activity that the Holocene alluvial fans were dislocated by the fault. These evidences suggest that the Yalahe Fault is a Holocene active fault, and has the seismogenic tectonic condition to produce a large earthquake, just like the Selaha and Zheduotang Faults. These also provide seismic geological evidence for the strain distribution model of the Kangding-Huiyuansi segment of the Xianshuihe Fault.

Surface rupture zone of historical earthquake is the most intuitive geomorphological response to fault activity. The rupture pattern, coseismic displacement and its geometric spatial distribution are important for determining segmentation and long-term movement behaviors of active fault. In the Barkol Basin of Xinjiang, according to the comprehensive result from remote sensing image interpretation, field surgery, high-resolution small unmanned aerial vehicles photography, terrain deformation measurements and trench excavation on geomorphological points, not only the new surface ruptures of the two M71/2 historical earthquakes in Barkol in 1842 and 1914 were found and defined between Xiongkuer and the southwest of Barkol County in southwestern part of the basin, but also the latest deformation evidence of the EW fold-up faults in the eastern part of the Basin was identified.
Combined with the ancient document analysis of the two historical earthquakes, we finally conclude that the surface rupture zone in the western segment on the southern margin of the Barkol Basin is the seismogenic structure of the M71/2 earthquake in 1842. The surface rupture zone is mainly characterized by left-lateral strike-slip, roughly with en echelon arrangement spreading from Xiongkuer to the south of Barkol County. The length of the surface rupture zone determined by field investigation is at least about 65km, and the maximum horizontal displacement appears around the Xiongkuer Village. At the same time, the surface rupture zone gradually shows more significant thrust extrusion from west to east, and has a tendency of extension towards the central of the Barkol Basin. The average observed displacement of the entire surface rupture obtained by counting the coseismic offsets of multiple faulted gullies is(4.1±1.0)m, with the coseismic characteristic displacement of ~4m. The epicenter position should appear at the place with the largest horizontal dislocation amount near Xiongkuer Village.
In addition, the length of the fold-blind fault zone in the vicinity of the Kuisu Town and the eastward extension to the Yanchi Township of the Yiwu Basin, which was discovered in the center of the Barkol Basin, is about 90km. The folded blind fault causes significant fold deformation in the latest sedimentary strata such as floodplain, and in addition, as shown on many outcrop sections, the bending-moment faults associated with the coseismic fold deformation have ruptured the surface. Therefore, the location of the epicenter should be located at the maximum fold deformation, which is near the Kuisu Town. The new research results not only further improve the understanding of the epicenter location and seismogenic faults of the two historical earthquakes in the Barkol Basin, but also provide an important reference for analyzing regional seismic hazards.

The Xiaojiang fault zone is located in the southeastern margin of the Tibetan plateau, the boundary faults of Sichuan-Yunnan block and South China block. The largest historical earthquake in Yunnan Province, with magnitude 8 occurred on the western branch of the Xiaojiang Fault in Songming County, 1833. Research on the Late Quaternary surface deformation and strong earthquake rupture behavior on the Xiaojiang Fault is crucial to understand the future seismic risk of the fault zone and the Sichuan-Yunnan region, even crucial for the study of tectonic evolution of the southeastern margin of Tibetan plateau. We have some new understanding through several large trenches excavated on the western branch of the Xiaojiang fault zone. We excavated a large trench at Caohaizi and identified six paleoseismic events, named U through Z from the oldest to the youngest. Ages of these six events are constrained at 40000-36300BC, 35400-24800BC, 9500BC-500AD, 390-720AD, 1120-1620AD and 1750AD-present. The Ganhaizi trench revealed three paleoearthquakes, named GHZ-E1 to GHZ-E3 from the oldest to the youngest. Ages of the three events are constrained at 3300BC-400AD, 770-1120AD, 1460AD-present. The Dafendi trench revealed three paleoearthquakes, named E1 to E3 from the oldest to the youngest, and their ages are constrained at 22300-19600BC, 18820-18400BC, and 18250-present. Caohaizi and Ganhaizi trenches are excavated on the western branch of the Xiaojiang Fault, the distance between them is 400m. We constrained four late Holocene paleoearthquakes with progressive constraining method, which are respectively at 500-720AD, 770-1120AD, AD 1460-1620 and 1833AD, with an average recurrence interval of 370~440a. Large earthquake recurrence in the late Holocene is less than the recurrence interval of~900a as proposed in the previous studies. Thus, the seismic hazard on the Xiaojiang Fault should be reevaluated. We excavated a large trench at Dafendi, about 30km away south of Caohaizi trench. Combining with previous paleoseismological research, it is found that the western branch of Xiaojiang Fault was likely to be dominated by segmented rupturing in the period from late of Late Pleistocene to early and middle Holocene, while it was characterized by large earthquakes clustering and whole segment rupturing since late Holocene.

Ganyanchi (Salt Lake)basin, located in the central part of the Haiyuan Fault, northeastern corner of the Tibetan plateau, is the largest pull-apart basin along this fault. Due to its location in northeastern Tibet, the Ganyanchi Basin preserves an important sedimentary record of tectonism and climate change associated with progressive growth of the Tibetan plateau. The sediments of this basin also contain abundant information regarding the deformational history of the bounding strike-slip fault, i.e., the Haiyuan Fault. Therefore, a detailed study on the depository history of the Ganyanchi Basin is of great importance. Earlier studies only focused on regional geological mapping and paleoseismic research, however, no sedimentologic or chronological work has been done in the Ganyanchi pull-apart basin. To address this problem, we drilled a 328m-deep borehole, named HY-C8, at the south of the cross-basin fault and near the active depocenter, and employ magnetostratigraphic analyses and seismic reflection data to constrain the age and to deduce the evolving history of the basin. The deep borehole profile shows that the stratigraphy of the basin can be divided into three main units (Unit Ⅰ, Ⅱ and Ⅲ), which began to deposit at about 2.76, 2.33 and 1.78Ma, respectively. The grain size of the deposits manifests an upward thinning trend, which probably implies the profile is a characteristic retrogradational sequence. The magnetic susceptibility results indicate that the playa lake probably was formed at about 1.78Ma ago, the corresponding playa-lake deposits recorded more than eight high susceptibility sections, which are most likely due to the iron sulfides (such as melnikovite, pyrrhotine etc.)that were usually produced in high-lake-level and reduction conditions. A combination of boreholes and shallow seismic reflection data indicates that the Ganyanchi Basin is mainly controlled by the cross-basin fault and its northern boundary fault, and the depocenter, probably deeper than 550m, lies in between these two faults. Finally, the sedimentary facies of the Ganyanchi Basin experienced a four-stage evolving history:eluvial facies (before~2.76Ma)to alluvial fan facies (about 2.76~2.33Ma)to distal alluvial fan facies (2.33~1.78Ma)to playa lake facies (1.78Ma~present). Based on accumulation rates, the stage of playa lake can be divided into two subchrons, and the depositional rates of subchrons 2 (about 0.78Ma~present)is as high as 232.5m/Ma, which probably was caused by the activity along the cross-basin fault in the Ganyanchi Basin.

The Anninghe Fault has been suggested as an important segment of the fault system along the eastern boundary of the Sichuan-Yunnan faulted block in the southeastern region of the Tibetan plateau. Reliable determination of the Late Quaternary slip rate on the Anninghe Fault is very helpful and significant for revealing deformation mechanism and kinematic characteristics of the Sichuan-Yunnan faulted block, which further helps us understand fault activity and seismic potential of the region. However, previous studies were focused mainly on the northern segment of the Anninghe Fault, while slip rate on its southern segment has been less studied. Therefore, in this paper, we chose two sites at Dashuigou and Maoheshan on the southern segment of the Anninghe Fault, and used high-resolution images of unmanned aerial vehicle (UAV)photogrammetry technology, detailed field survey, multiple paleoseismic trenching and radiocarbon dating methods to constrain slip rate on the southern fault segment of the Anninghe Fault. Specifically, we suggest that the slip rate at the Dashuigouo site is narrowly constrained to be~4.4mm/a since about 3^￣￣300a^￣￣BP based on a linear regression calculation method, and speculate that a slip rate of 2.6~5.2mm/a at the Maoheshan site would be highly possible, although we poorly constrained the whole deformation amount of the two branch faults at the Maoheshan site from multiple paleoseismic trenching. The data at the two sites on the southern segment show a consistent slip rate compared with that of the northern segment of the Anninghe Fault. Moreover, considering a similar paleoseismic recurrence interval on the two segments of the Anninghe Fault from previous studies, we further suggest that the fault activity and deformation pattern on the two segments of the Annignhe Fault appears to be well consistent, which is also in agreement with the regional tectonic deformation.

Alluvial fans that are in the process of development always show complex geomorphic features due to natural modification. Accordingly, analyzing these fans whether to be influenced by tectonic deformation is one of the technique difficulties in active tectonic studies. Complex alluvial fans are the focus of the study of active tectonics such as fracture mapping and activity behavior analysis, for they have often retained important structural information. Traditional measurement methods, such as satellite remote sensing, RTK GPS and Lidar, are difficult to meet the demand for the study of micro tectonic deformation because of the reason of accuracy or cost performance. The recent UAV photogrammetry technology, due to its many advantages such as low cost, high resolution, and efficiency of exporting DEM and DOM data, has been widely used in three-dimensional modeling, ground mapping and other fields. In the quantitative study of active tectonics, this technology fills up the deficiency in the research of the micro structure of the traditional measurement. Through detailed field investigations and paleoseismic trenching, we further used this technology to obtain the topographic data of a complex alluvial fan located at the southern marginal fault of Barkol Basin, Xinjiang. Pointing at the alluvial fans that are in the process of development, and on the basis of topographic analysis and image processing for DEM, we take the research method of secondary partitions of the geomorphic surface and cut the alluvial fans longitudinally according to the difference of its age. Through the establishment of profile cluster within each partition, separate analysis and data contrast with the adjacent partitions, we acquired the tectonic activity information during the development of alluvial fan. The tectonic vertical deformation of this alluvial fan is about 2.5m.

The Tan-Lu Fault Zone(TLFZ), a well-known lithosphere fault zone in eastern China, is a boundary tectonic belt of the secondary block within the North China plate, and its seismic risk has always been a focus problem. Previous studies were primarily conducted on the eastern graben faults of the Yishu segment where there are historical earthquake records, but the faults in western graben have seldom been involved. So, there has been no agreement about the activity of the western graben fault from the previous studies. This paper focuses on the activity of the two buried faults in the western graben along the southern segment of Yishu through combination of shallow seismic reflection profile and composite drilling section exploration.
Shallow seismic reflection profile reveals that the Tangwu-Gegou Fault(F₄)only affects the top surface of Suqian Formation, therefore, the fault may be an early Quaternary fault. The Yishui-Tangtou Fault(F₃)has displaced the upper Pleistocene series in the shallow seismic reflection profile, suggesting that the fault may be a late Pleistocene active fault. Drilling was implemented in Caiji Town and Lingcheng Town along the Yishui-Tangtou Fault(F₃)respectively, and the result shows that the latest activity time of Yishui-Tangtou Fault(F₃)is between(91.2±4.4)ka and(97.0±4.8)ka, therefore, the fault belongs to late Pleistocene active fault.
Combined with the latest research on the activity of other faults along TLFZ, both faults in eastern and western graben were active during the late Pleistocene in the southern segment of the Yishu fault zone, however, only the fault in eastern graben was active in the Holocene. This phenomenon is the tectonic response to the subduction of the Pacific and Philippine Sea Plate and collision between India and Asian Plate. The two late Quaternary active faults in the Yishu segment of TLFZ are deep faults and present different forms on the surface and in near surface according to studies of deep seismic reflection profile, seismic wave function and seismic relocation. Considering the tectonic structure of the southern segment of Yishu fault zone, the relationship between deep and shallow structures, and the impact of 1668 Tancheng earthquake(M=8(1/2)), the seismogenic ability of moderate-strong earthquake along the Yishui-Tangtou Fault(F₃)can't be ignored.

Cascade rupture events often occur along large strike-slip fault zone.The 1920 AD M 8¹/₂ earthquake ruptured all 3 segments of the Haiyuan Fault,and the Salt Lake pull-apart basin is the boundary between the west and middle segment of the fault.The data of trenching and drilling reveal 7 events occurring since last stage of late Pleistocene,and the two youngest events are associated with the historical records of 1092 AD (possibly) and 1920 AD respectively.These events are all large earthquakes with magnitude M>8,and the recurrence of them is characterized by earthquake clusters alternating with a single event.Now it is in the latest cluster which may last about 1000 years.Comparison of the paleoseismic sequence of this study and previous results reveals that the cross-basin fault in the Salt Lake pull-apart basin does not always rupture when cascade rupture events occur along the Haiyuan Fault,and likely ruptures only when the magnitude of the events is large (maybe M>8).Though there are many advantages in paleoseismic study in pull-apart basin,we should avoid getting the paleoseismic history of major strike-slip fault zones only depending on the rupture records of inner faults in pull-apart basins with large scale (maybe a width more than 3km).

As we all know, Eastern Tienshan and Altaid in central Asia accommodate~10mm/a crustal shortening, accounting for 1/4 shortening between India and Eurasia(~40mm/a). A substantial portion of these deformations was absorbed in Altaid in the north through a combination of right-lateral strike-slip and counterclockwise vertical axis rotation of crustal blocks, but how the crustal deformation was accommodated in Eastern Tienshan is still in debate. Based on the field investigation in Jianquanzi, Barkol Tagh and Karlik Tagh in Eastern Tienshan in recent years, we identified a sinistral strike-slip fault system mapped in Eastern Tienshan. From west to east, the Jianquanzi-Tuolaiquan Fault(JTF), South Barkol Basin Fault (SBF) and Central Karliktagh Fault(CKF)constitute the tectonic frame of this large-scale fault system, which plays an important role in adjusting the strain distribution during the process of orogening in Eastern Tienshan in Quaternary even since Ceonozoic era. The fault system displays different late-Quaternary characteristics when its orientation changes with regional tectonic principal stress(NE). Specifically, the EW-trending JTF exhibits sinistral slip with little vertical component which can extend to Xiongkuer segment on EW-NW-trending SBF. The EW-NW SBF displays sinistral slip from east of Luobaoquanto, Barkol County and reverse slip with little horizontal component at east of Barkol County. In easternmost, the WNW-EW trending CKF shows sinistral slip with no obvious vertical motion. This fault system's activity coupled in the orogenic process of easternmost Tienshan, adjusting and accommodating a portion of deformation included in the orogenic process, and in turn we suggest that the deformation associated with range front fault in the orogen root may not be the only decisive way of deformation releasing.

Nine earthquakes with M≥6 have stricken the northern segment of the Red River fault zone since the historical records, including the 1652 Midu M7 earthquake and the 1925 Dali M7 earthquake. However, there have been no earthquake records of M≥6 on the middle and southern segments of the Red River Fault, since 886 AD. Is the Red River fault zone, as a boundary fault, a fault zone where there will be not big earthquake in the future or a seismogenic structure for large earthquake with long recurrence intervals?This problem puzzles the geologists for a long time. Through indoor careful interpretation of high resolution remote sensing images, and in combination with detailed field geological and geomorphic survey, we found a series of fault troughs along the section of Gasha-Yaojie on the southern segment of the Red River fault zone, the length of the Gasha-Yaojie section is over ten kilometers. At the same time, paleoseismic information and radiocarbon dating result analysis on the multiple trenches show that there exists geological evidence of seismic activity during the Holocene in the southern segment of the Red River fault zone.

The 2008 Wenchuan earthquake occurred along the Longmen Shan fault zone, only five years later, another M7 Lushan earthquake struck the southern segment where its seismic risk has been highly focused by multiple geoscientists since this event. Through geological investigations and paleoseismic trenching, we suggest that the segment along the Shuangshi-Dachuan Fault at south of the seismogenic structure of the Lushan earthquake is active during Holocene. Along the fault, some discontinuous fault trough valleys developed and the fault dislocated the late Quaternary strata as the trench exposed. Based on analysis of historical records of earthquakes, we suggest that the epicenter of the 1327 Tianquan earthquake should be located near Tianquan and associated with the Shuangshi-Dachuan Fault. Furthermore, we compared the ranges of felt earthquakes(the 2013 M7 Lushan earthquake and the 1970 M_S6.2 Dayi earthquake)and suggest that the magnitude of the 1327 Tianquan earthquake is more possible between 6½ and 7. The southern segment of the Longmen Shan fault zone behaves as a thrust fault system consisting of several sub-paralleled faults and its deep structure shows multiple layers of decollement, which might disperse strain accumulation effectively and make the thrust system propagate forward into the foreland basin, creating a new decollement on a gypsum-salt bed. The soft bed is thick and does not facilitate to constrain fault deformation and accumulate strain, which produces a weak surface tectonic expression and seismic activity along the southern segment, this is quite different from that of the middle and northern segments of the Longmen Shan fault zone.

The distribution of earthquake rupture zone plays a very important role in determining location of epicenter and magnitude of historical earthquake. There is still argument about the seismogenic structure of the 1842 M7 Balikun earthquake and the 1914 M7 1/2 Balikun earthquake in the historical records in eastern Tienshan. Through field geological survey, we confirm that there exist 3 rupture zones in Eastern Tienshan. These rupture zones, Tazibulake rupture zone on the Jian Quanzi-Luo Baoquan Fault, north of Shanshan, Xiong Kuer rupture zone on the south Balikun Basin Fault and Yanchi rupture zone on the south Yiwu Basin Fault, are closely related to 2 historical earthquakes. Based on historical literature and current geological evidence analysis, we infer that Xiong Kuer rupture zone was produced by 1842 M7 earthquake and Yanchi rupture zone by 1914 M7 1/2 earthquake, while Tazibukale rupture zone may represent another unrecorded historical event. South Balikun Basin Fault disturbs Quaternary stratigraphy which has a ¹⁴C age of 3110±30 B.P in the south of Balikun County, ~100km to the east of Xiong Kuer rupture zone, therefore we can't preclude the possibility that Xiong Kuer rupture zone extends to the south of Balikun County. This region overlaps with the meizoseismal area based on the literature document, together with the fact that the impact of 1842 earthquake is no less than 1914 earthquake, we believe that the magnitude of 1842 earthquake is no less than that of the 1914 earthquake.

The fault F₅ is considered as the most active fault in the Tanlu fault zone(Yi-Shu fault zone), which is located from Weifang of Shandong Province to Jiashan of Anhui Province, with a length of 360km. It has always been a focus of concern to many geoscientists because of its complexity and importance. But, for a long period of time, there exists biggish indetermination in the accurate position and active ages of the fault F₅ in Suqian section of Tanlu fault zone. Seismic reflection exploration is the main technique in present urban active faults detecting. In order to investigate the spatial distribution, characteristics and activities of the fault F₅ in covered terrains, we carried out a systematic survey to the fault with shallow seismic prospecting method and obtained the accurate position and development characteristics of the fault. The results show that the fault F₅ continues to develop toward south rather than ending at the Huancheng South Road of Suqian City. F₅ is mainly composed of two main faults, which dip in opposite directions and almost vertically. Near the Sankeshu town, F₅ is composed of three faults with right-stepping, forming a small pull-apart basin with length of 6km, width of 2.5km, controlling the deposition of Neogene and Quaternary strata. By combining the results of composite drilling section and trenching, we make a conclusion that the western branch of fault F₅ is a Holocene active fault, and the eastern branch is a Pleistocene active fault. Our general view is that fault F₅ is a Holocene active fault.

Anqiu-Juxian Fault is an important fault in the Tanlu fault zone, with the highest seismic risk, the most recent activity date, and the most obvious surface traces. Due to lack of credible geological evidences, there is big controversy on the Holocene activity in the Jiangsu segment of this fault. Research on the characteristics of late Quaternary activity in the Jiangsu segment of Anqiu-Juxian Fault, particularly its latest activity time, is of great significance to assessment of its earthquake ability and seismic risk. Based on field investigations on the Jiangsu segment of Anqiu-Juxian Fault, and combining with the results of fault activities identification on this fault in Suqian City, we discussed the characteristics of its activities in late Quaternary. Multiple geological sections we found in this study and the results of fault activities identification in Suqian City all indicate that there was an ancient seismic event occurring in middle period of Holocene in the segment from southern Maling Mountain to Suqian City; but the trench at Houchen village did not show any evidence of Holocene activity on the Chonggangshan segment of this fault. Based on method of shallow seismic exploration, we carried out a systematic exploration of this fault to get its accurate position and activity characteristics. The results show that Anqiu-Juxian Fault in Suqian City is mainly characterized by dextral strike-slip, associated with both thrusting and extensional movement in different positions. A series of low hills were formed along the fault in the north of Suqian City, and a small graben basin was formed in the south of Suqian City, both are controlled by the dextral strike-slip movement of this fault. The Jiangsu segment of Anqiu-Juxian Fault in general is characterized by dextral strike-slip with thrusting movement. But some parts of it are characterized by dextral strike-slip with extensional movement. The Jiangsu segment of Anqiu-Juxian Fault experienced a number of activities since the late Quaternary, with an obvious activity in Holocene. The seismic activities of Jiangsu segment of Anqiu-Juxian Fault have the characteristic of high intensity and low frequency. Its activities decrease gradually from north to south as a whole.

Active fault is one of potential geohazards in cities. Locating and dating buried active faults in urban areas have been a difficult issue in active fault exploration. In this paper, we take the detection of the buried active fault performed at Hehuan Road in the north of Suqian city as an example. We preliminarily mapped the fault through field investigation and shallow seismic reflection survey technique. Furthermore, based on the principle of doubling section method, we conducted multiple drilling to constrain the upper faulted point which is located in a range of 5m in horizon and 4.4~6.1m in depth. Finally, we determined the exact location and latest activity of the fault by trenching. Obviously, good results have been acquired on the accurate location and activity of the Suqian segment of Anqiu-Juxian Fault using multi-level and multi-means detection method. Besides, we observed from the detection at the Hehuan Road site that at least four paleoseismic events occurred during the past 80000 yrs, and the result indicates that the latest faulting event on the fault is younger than(5.9±0.3)ka BP and the buried active fault at the Hehuan Road is a Holocene active fault. The result of buried active fault detection at the Hehuan Road site provides quantitative parameters for evaluation of seismic hazards and planning the width of safety distance in Suqian City.

Nonvisibility(dieout)of fault strands occurs primarily in stratigraphic units associated with young paleoseismic events, which may cause misidentification of the young events and bring more uncertainties for seismic risk assessment. Based on previous related studies, this paper integrates case studies in mainland China to discuss the nonvisibility of fault strands and identification of young paleoseismic events. Nonvisibility of fault strands is prevailing in sandy, soil, silty, loess, and clay-sandy units, and is more possibly associated with strike-slip faults comparing with normal and reverse faults. Case studies on several trenches across surface ruptures produced by the Wenchuan earthquake and others located at different regions suggest that trench siting, excavation, and comprehensive analysis are key technical points to identify young paleoseismic events in the stratigraphic units where nonvisibility of fault strands is prone to occur. Stratigraphic units with more sequences have been suggested to be good sites for trenching to avoid misidentification produced by nonvisibility of fault strands. Multiple trenching is facilitated to lower the influence of local nonvisibility. Assumed extending of upper and lower units, grain sizes, color, and soil horizon are the basic methods to identify nonvisibility. Analysis of microstructures, grain sizes and magnetic susceptibility is one of the future studies related to identification of nonvisibility of fault strands.

Hetao fault-depression zone, the largest one of 4 fault-depression zones around the Ordos block, is characterized by intense tectonic activities. According to historical records, 2 large earthquakes, occurring in 849AD and 7BC respectively, were recognized to be located at this zone. However, there is still some dispute about the seismogenic structure of the 849AD earthquake, and there is no tangible geological evidence to support the view that the 7BC event occurred in Hetao fault-depression. In this paper, based on the image interpretation(from Google Earth), field investigation, trench excavation, and ¹⁴C and single grain OSL dating, we analyzed the tectonic landform and paleoseismic events on the Daqingshan piedmont fault, Wulashan piedmont fault and Langshan piedmont fault in the Hetao fault-depression zone. Furthermore, a comparative study of the latest rupture events on the 3 active faults was carried out. In order to lower the uncertainty of paleoseismic event dating, several effective measures, such as sampling according to the stratigraphic sequence, collecting multi samples in important strata, were adopted. Combining the previous achievements, the seismogenic structures of the 849AD earthquake and the 7BC earthquake were discussed. The results support that the Daqingshan piedmont fault is the seismogenic structure of the 849AD earthquake, and the latest surface rupture event of the Langshan piedmont fault may be related to the 7BC earthquake.

Lowering uncertainties of paleoseismic data is very important, which facilitates medium and long-term earthquake prediction and seismic risk assessment in paleoseismic studies. Among these uncertainties, paleoseismic timing is highly focused and its constraint is one of the most key factors in lowering uncertainties. To get the age as true as possible, choosing right dating, sampling methods and techniques on event ages are essential. Among the several primary dating techniques, radiocarbon dating is prior to the other methods. We should choose material that is breached completely during transportation for OSL dating, and samples that are hardly affected by kinds of factors for ¹⁰Be dating. Sampling at appropriate sites based on analysis of tectonic background and using sequential ages to constrain paleoseismic events are the primary keys of techniques on accurate event dating. Interval value is suggested for age constraint when using stratigraphic chronology. When there are multiple ages for different samples within a layer, we should choose the youngest and reliable age. These rules are recommended when constraining paleoseismic ages at a single site. Temporal and spatial correlation such as successive limit method, Z statistics, overlapping distributions likelihood approach, event window and ad hoc weighted overlap methods are the primary analysis approaches for event dating at multiple sites along faults or fault segments.

The Anninghe and Zemuhe Fault systems show characteristics of a left-lateral strike-slip movement since late Quaternary and they are located along the eastern boundary of the Sichuan-Yunnan Fault block in the southeastern region of the Tibetan plateau. The N-S striking Anninghe Fault is divided into the northern and southern segment around Mianning. The northern segment has an average recurrence interval of large earthquakes of about 500～700 years and a left-lateral slip rate of 4mm/a since Holocene. However paleoseismic behavior along the southern segment has been less focused. We excavated several trenches at Yuehua along the southern segment and used multiple radiocarbon dating to constrain the average recurrence interval of large earthquakes of this segment, which is about 600～800 years. The Zemuhe Fault has an average recurrence interval of paleoearthquakes of about 2300 years with a left-lateral slip rate of 2.4～3.6mm/a since Holocene. Comparing with the fault behavior between the Anninghe Fault and Zemuhe Fault, we find that the recurrence interval of the Anninghe Fault is shorter than that of the Zemuhe Fault and has a relatively larger left-lateral slip rate, indicating an inconsistent paleoseismic behavior. We suggest this inconsistence may be related to different strikes of the two faults, the uplift of the Luoji Shan and the distribution of the N-S trending strike-slip fault system on the south of the Anninghe Fault.

Normal faults, developed within extensional environment, are widely found in North China. Given the varieties in surface ruptures of different earthquakes and their depositional environment, some issues are needed to be paid much attention to in exposing the actual and complete history of paleoseismic events occurring along normal faults. In this paper, based on the existing knowledge about surface rupture characteristics of large earthquakes and indicators of normal fault, combining the cases study in China and the factors of geological, geomorphologic and climatic environment, some key techniques and methods in paleoseismic study on normal faults in mainland China are recommended as follows: (1)Choosing appropriate trenching sites according to local conditions. In the area where the faulted surface deposits are mainly alluvial-fluvial materials of piedmont or river and lake sediments, the trenching sites should try to meet following conditions: the geomorphy can reveal multiple fault events with not too large single displacement, the erosion(or denudation)of external force and the accumulation processes maintain relative balance, the sediments are medium-fine grained, and the samples for dating are easy to be collected. The sites where the faulted sediments are mainly composed of loess or secondary loess or sandy loam should be avoided to excavate trenches for paleoseismic study, however, if it cannot be avoided, the areas with weaker erosion and accumulation near small gullies are the choices to be considered, because these areas may have different deposits from upstream of the gullies, and some supplemental information such as tectonic landform are needed to substantiate the paleoseismic analysis.(2)Recording and analyzing the trench profiles in detail in the field. For the deposits(e.g. loess)with no stratification, the key observation point is the slight change in the color, grain and orientation, which may indicate the stratigraphic boundary. Indicating the scarp-derived deposits units such as colluvial wedge is the key to analyzing paleoseismic events, and the indicated elements conclude the messy configuration and nodules in the collapse facies, and the soil developed in the upper of the erosion facies. When the scarp-derived deposits are difficult to distinguish from normal strata, we should, by "brushing", "jabbing" or "microscopic analysis", try to analyze the color, grain, non-loess materials(e.g. small gravel, plant roots, etc.)and the enrichment degree of calcareous materials(e.g. calcium-mod, calcium-nodule, calcium-dot, calcium-filament, etc.), to identify the stratigraphic boundary.(3)Synthetically analyzing and checking the paleoseismic results combining other information. The appearances of the scarp-derived deposits revealed by trench are often obscure, so supplemental information from geomorphology and multiple trenches are necessary. Some techniques and methods, such as progressive constraining method of paleoseismic events, fault displacement constraining method, correlating method between multiple trenches, inversion and reconstruction of fault events, etc., are helpful for judging whether the paleoseismic results are actual and complete.

An M_S 7.0 earthquake attacked southern segment of the Longmenshan Fault zone on 20 April 2013, in Lushan County, Sichuan Province, southwest of China. The seismic intensity of the meizoseismal area of the Lushan event is Ⅰ Ⅹ(the Chinese Seismic Intensity Scale). The meizoseismal area strikes NE, and is approximately 24km long and 11km wide. In the post-earthquake emergency scientific survey, some members found a series of co-seismic surface rupture signs at Longmen Township, one of the most damaged areas by this quake, north of Lushan County. The reported typical surface rupture signs include intensive shear-fissures along the channel at Zhanghuo Group, rotation of bricks near a white tower at Wanghuo Group, and lots of extensive cracks. On the basis of analyzing such surface rupture signs, Han et al., (2013)deduced that there might be a blind fault along Lushan County and Longmen Township(named the Lushan-Longmen presumed blind fault), and this fault probably was the seismogenic fault. Therefore, to confirm whether there is a potential seismogenic fault along Lushan and Longmen is very important not only to research of seismogenic fault for this earthquake but also to the reconstruction in the disaster-hit areas. Through surface ruptures surveying and trench excavating, we conclude that: there are no co-seismic surface ruptures at Longmen. Meanwhile, artificial seismic prospecting outcome, which shows nonexistence of the Lushan-Longmen presumed blind fault at least 800m below the ground surface, also supports our idea. Consequently, the reported shear-fissures and extensive cracks are not produced by the seismogenic fault, but most likely by ground shaking during the earthquake.

In general,the displacement produced by a magnitude 6～7 earthquake is relatively small,even does not reach the surface,so it is difficult to be preserved in geological records. On the other hand,the seismogenic fault of such earthquakes is easy to be considered incorrectly as a non-active fault since Holocene,consequently overlooking the real seismic hazard in the future. To solve this problem,we propose a type of faults that are capable of generating M6～7 earthquakes,but with weak surface activity and cannot produce conspicuous surface displacement. To recognize such faults from geological records,which have no visible evidence of activity since middle-late Pleistocene,is the key to intermediate-and long-term earthquake prediction. The specific procedures of the technology are as follows: First,we determine the seismotectonic setting of the tectonic system in which the target fault lies. Second,we establish the relation between the target fault and other active faults in the same tectonic system,which have records of historical earthquakes or paleoearthquakes. Then we compare varied seismogenic units in the same-order structure,same tectonic system,and varied stages in the same tectonic process. The case studies demonstrate that this is an effective method for intermediate-and long-term earthquake prediction. The cases studied include the Puduhe-Xishan Fault in Kunming City,Hanzhong Basin in the north section of the Longmen Shan Fault zone,Dachuan-Shuangshi Fault in the south section of the Longmen Shan Fault zone,and the Guguan-Guoshun Fault of the Longxian-Baoji Fault zone. These faults all show weak activities on the surface and have potential for earthquakes with estimated magnitude 6.5～7.0.In addition,by estimation using this method,the Taoyuan-Guichuan Fault of the Longxian-Baoji Fault zone has a seismic risk of M6.0～6.5 earthquake,and the Longxian-Qima-Mazhao Fault is capable of producing an earthquake about M7.5.

Lingqiu Basin is located in the northeast of the Shanxi graben system,where a M_S 7.0 earthquake occurred in 1626.The achievement of active fault research in this basin could contribute not only to the study of the seismogenic structure of the earthquake in 1626,but also to the research of the types of large earthquakes in Shanxi graben system. Much work has been conducted here,laying the foundation for the active fault study in this area. However,the spatial distribution and activity of several major faults,and the seismogenic structure of the earthquake in 1626 are still in discussion. This paper analyzes the geomorphologic characteristics in the whole basin via interpreting SPOT5 images,SRTM3 and fieldwork,and acquires some new knowledge of the major faults in combination with trenching. The activity of the main segment of the piedmont fault of Taibaiwei Mountains is limited to the late Pleistocene; The NEE-striking Shuijian-Luoshuihe Fault has obvious geomorphic features to the west of Lingqiu County,and the geomorphic feature of the fault is not remarkable to the east of the county. Its latest event left a 1m-high fault scarp on the surface. The NW-striking Huashanhe Fault behaves as a hinge fault. In the northern basin,the fault dips west,producing a height difference of about 10m in terrace T1 of the Huashanhe River. In the southern basin,the fault dips east. Profiles and geomorphic features show the south segment of the fault is an active strike-slip fault with a high angle. Thus,we consider the earthquake in 1626 resulted from the conjugated action of the NEE-striking Shuijian-Luoshuihe Fault and the NW-striking Huashanhe Fault.

The M_S8.0 Wenchuan earthquake is a rare earthquake of fold-reverse fault type in mainland China. The rupture zone of Wenchuan earthquake is an indispensable case which can be used to study the surface co-seismic deformation of reverse fault and discuss the paleoseismic records. Based on the geologic and geomorphic features along the rupture zone of Wenchuan earthquake,we choose the Pingtong,Dengjia and Liulong three sites which were deformed only in the Wenchuan earthquake to analyze the characteristics of co-seismic deformation. And we combine with paleoseismic studies in the Yingxiu and the Guixi areas to discuss some key techniques in the paleoseismic study of the fold-reverse fault type. The conclusion shows surface deformation types include fault dislocation,bending dislocation and fold deformation. The cut-cover relationship of colluvial wedge,fault and strata is the feasible evidence of the fault dislocation type. But the indicator for bending dislocation and fold deformation types emphasizes the unconformity on the hanging wall,growth strata on the footwall and sudden change of maker strata position between the hanging wall and footwall. The multiple relationship of fault scarp height is related to paleoseismic times in some degree,but it is not wise to decide the paleoseismic times simply by a direct division of the height of fault scarp by the co-seismic displacements. In addition,there are two important paleoseismic indicators for identifying paleoseismic event on low-angle thrust,that is,the sudden change of displacements in maker strata and the cut-cover relationship of thin-long colluvial wedge,fault and strata. A good paleoseismic study needs to consider many factors and use more evidences with consideration of local conditions to support or supplement the analysis.

The main purpose of paleoseismic study is to distinguish or reveal deformation evidence of large earthquakes recorded by geologic and geomorphic features,and obtain corresponding seismic parameters such as timing,recurrence behavior,and coseismic displacement of large earthquakes. To achieve the aforementioned scientific aim,whether a trenching site preserves evidence of a complete paleoseismic sequence since late Quaternary and contains multiple measurable samples or not,and whether it can accurately identify paleoseismic events and collect well-constrained samples on events or not,all of these problems are directly responsible for reliabilities on assessment of future large earthquake hazard. Due to special displacement styles on strike-slip faults,good trenching sites are not widespread. Through comprehensive analysis on characteristics of coseismic surface ruptures and influencing factors on several trenching cases,we suggest micro-landforms such as depressions,basins,troughs,sag ponds,successive-offset channels,continuous scarp-derived deposit and multiple geomorphic surfaces are likely to be good trenching sites for paleoseismic studies on strike-slip faults. Multiple trenching or three-dimensional trenching should be the primary layout on strike-slip faults. Offsets of micro-landform across a fault,young stratigraphic units overlying on faulted units,locally distributed scarp-derived colluvial deposits,filled fissures,abrupt increases or decreases in displacement of different stratigraphic units on a fault,warping in different degrees,and multiple periodic paleo-sag ponds accumulation,all of these deformation evidences are good indicators for identifying paleoseismic events. To narrow uncertainties of paleoseismic studies,we should base on an organized research process and make a technical proposal and sophisticatedly conduct trenching work. Conclusions need to be repeatedly checked and widespread discussed,and also we should pay much attention on details and use more evidence to support or supplement analysis.

In this paper,P5 stereo images and GeoEye-1 image are firstly processed and analysed in order to extract digital elevation model(DEM)and divide stratum.The perpendicular root mean square of extracted DEM is within 5meters in residual elevation report using methods of check point and visual inspection.According to the stratigraphic classification,measure points which are located at boundary or inner stratum are chosen at regions with better triangular facet of rock and stable attitude,and then the attitude of stratum is extracted using three-dimensional data of the measure points through programming in MATLAB environment based on three-point method or multiple-point fitting method.Based on field survey,the measurement residual of dip angles is within 6 degrees,and 85% are less than 4 degrees.And the root mean square of the angles is less than 3 degree.At the same time,seasons of residual generation are concluded,including geological structure,topography,accuracy of DEM,matching degree of DEM and images,the location of chosen point and so on.It is suggested that the method of stratigraphic attitude extraction using P5 stereo images and GeoEye-1 image is less restricted by worse natural conditions.Not only can the method restrict the profile of shallow tectonics,but also can cover the shortage of attitude of stratum and have great significance for reducing uncertainty of Kalpin thrust tectonic deformation research.It provides a new way for quantitative research of structural geology,and also provides references for similar regions.

Slip rate of active faults is deterministic to compare active earthquake behaviors among different faults or different segments along a fault,and also it is a key parameter for seismic hazard assessment.Geologically reliable estimation on slip rate is subject to two active tectonic parameters,the cumulative displacement produced by multiple surface-rupturing seismic events and the corresponding true ages, respectively.Generally, for strike-slip faults,we carefully measure geomorphic expressions,such as deformation or offset produced by multiple faulting on river terrace,alluvial-fluvial fans or gullies,and then integrate geochronological constraint from dating on these geomorphic expressions.Based on the above two crucial parameters,we further determine slip rates along faults.However,this paper is attempted to use another deformation of geomorphic expression,a growth model for a small triangular pull-apart basin(sag pond),to constrain fault slip rate at the Daqingliangzi section of Zemuhe Fault on the southeastern margin of the Tibetan Plateau.Based on several three-dimension trench excavations,reliable radiocarbon dating at the bottom of stratigraphic unit in the triangular pull-apart basin(sag pond),detailed field investigation along the Daqingliangzi section of Zemuhe Fault and accurate RTK(GPS)survey,we suggest that Holocene average left-lateral slip rate of the Zemuhe Fault is constrained between 2.4±0.2mm/a and 3.6mm/a,which is a little smaller than those estimated by other geoscientists,however this strike-slip rate is much more accordant with paleoseismic recurrence behaviors and present velocity field obtained from GPS measurement across the Zemuhe Fault.

There are five different levels of alluvial fans developed at Sanchakou in the south edge of the Kalpintag Mountains.Kalpintag Fault has faulted three younger alluvial fans on which fault scarps caused by the latest fault activities are perfectly retained.To estimate the vertical slip magnitude and rates of the Kalpintag Fault during the late Quaternary,we investigated the latest evidences from the topographic and geomorphic survey of the fault scarps on the fans using differential GPS and the exposure ¹⁰Be age of amalgamated samples on the surface of abandoned fans.We estimated the cosmogenic nuclide contents accumulated during the post-depositional processes in the amalgamated samples on the fans collected from nearby active gullies.The vertical displacements of fault scarps we measured on the T₁,T₂ and T₃ alluvial fans are 0.6±0.05,1.3±0.05 and 3.0±0.05m,respectively.Based on the ¹⁰Be exposure age of each alluvial fan,we calculated the vertical slip rate on T₁,T₂,T₃ alluvial fans to be 0.15±0.02,0.16±0.02 and 0.15±0.02mm/a since(20.22±1.91)ka BP,with a corresponding crustal shortening rate of the Kalpintag Fault to be 0.18～0.44mm / a.The uplift rate since the formation of the T₄ and T₅ alluvial fans is 0.51±0.05 and 0.58±0.05mm/a,respectively,which is slightly bigger than that of T₁,T₂ and T₃ alluvial fans.