On February 6, 2023, two destructive earthquakes struck southern and central Turkey and northern and western Syria. The epicenter of the first event(M_W7.8)was 37km west-northwest of Gaziantep. The earthquake had a maximum Mercalli intensity of Ⅻ around the epicenter and in Antakya. It was followed by a M_W7.7 earthquake nine hours later. This earthquake was centered 95km north-northeast from the first one. There was widespread damage and tens of thousands of fatalities. In response to these catastrophic events, in March 2023, a seismic scientific expedition led by China Earthquake Administration(CEA)was promptly organized to investigate the surface ruptures caused by these earthquakes. Here, we focus on the surface ruptures of the second earthquake, known as the Elbistan earthquake. The post-earthquake field survey revealed that the Elbistan earthquake occurred on the East Anatolian fault zone's northern branch(the Cardak Fault). This event resulted in forming a main surface rupture zone approximately 140km long and a secondary fault rupture zone approximately 20km long, which is nearly perpendicular to the main rupture.

We combined the interpretation of high-resolution satellite imagery and geomorphic investigations along the fault to determine the fault geometry and kinematics of the second earthquake event. The Elbistan earthquake formed a main surface rupture zone approximately 140km long, which strikes in an east-west direction along the Cardak Fault. The main rupture zone starts from Göksun in the west and extends predominantly eastward until the western end of the Sürgü Fault. It then propagates northeast along the southern segment of the Malatya fault zone. The entire Cardak Fault and the Malatya fault zone's southern segment are considered seismic structures for this earthquake. The overall surface rupture zone exhibits a linear and continuous distribution. Secondary ruptures show a combination of left-lateral strike-slip or left-lateral oblique-thrust deformation. Along the rupture zone, a series of en echelon fractures, moletracks, horizontal fault striations, and numerous displaced piercing markers, such as mountain ridges, wheat fields, terraces, fences, roads, and wheel ruts, indicate the predominance of pure left-lateral strike-slip motion for most sections. The maximum measured horizontal displacement is(7.6±0.3)m. According to the empirical relationship between the seismic moment magnitude of strike-slip faulting earthquakes and the length of surface rupture(SRL), a main rupture zone of 140km in length corresponds to a moment magnitude of approximately 7.6. Based on the relationship between the seismic moment magnitude and the maximum coseismic displacement, a maximum coseismic displacement of(7.6±0.3)m corresponds to a moment magnitude of about 7.5. The magnitudes derived from the two empirical relationships are essentially consistent, and they also agree with the moment magnitude provided by the USGS. Besides the main surface rupture zone, a secondary fault rupture zone extends nearly north-south direction for approximately 20km long. Unfortunately, due to the limited time and traffic problem, we did not visit this north-south-trending secondary fault rupture zone.

According to the summary of the history of earthquakes, it is evident that the main surface rupture zone has only recorded one earthquake in history, the 1544 M_S6.8 earthquake, which indicates significantly less seismic activity compared to the main East Anatolian Fault. Moreover, the “earthquake doublet” will inevitably significantly impact the stress state and seismic hazard of other faults in the region. Seismic activity in this area remain at a relatively high level for years or even decades to come. The east-west striking fault, which has not been identified on the published active fault maps at the western end of the surface rupture zone, and the north-east striking Savrun Fault, which did not rupture this time, will experience destructive earthquakes in the future. It remains unknown why the east-west striking rupture did not propagate to the Sürgü Fault this time. More detailed paleoearthquake studies are needed to identify whether it is due to insufficient energy accumulation or because this section acts as a barrier. If the Sürgü Fault, about 40km long, was to rupture entirely in the future, the magnitude could reach 7 based on the empirical relationship.

Considering the distribution of historical earthquakes along the East Anatolian fault zone, as well as the geometric distribution of the surface ruptures from the recent “earthquake doublet” and the surrounding active faults, it is believed that the future earthquake hazards in the northeastern segment of the East Anatolian fault zone, the northern segment of the Dead Sea Fault, and the Malatya Fault deserve special attention.

The September 5, 2022, M6.8 Luding earthquake occurred along the southeastern segment of the Xianshuihe fault zone. Tectonics around the epicenter area is complicated and several faults had been recognized. Focal mechanisms of the main shock and inversions from earthquake data suggest that the earthquake occurred on a northwest-trending, steeply dipping strike-slip fault, which is consistent with the strike and slip of the Xianshuihe fault zone. We conducted a field investigation along the fault sections on both sides of the epicenter immediately after the earthquake. NW-trending fractures that were recognized as surface ruptures during the earthquake, and heavy landslides along the fault section between Ertaizi-Aiguocun village were observed during the field investigations. There are no surface ruptures developed along the fault sections north of the epicenter and south of Aiguocun village. Thus it can be concluded that there is a 15.5km-long surface rupture zone developed along the Moxi Fault(the section between Ertaizi and Aiguo village). The surface rupture zone trends northwest and shows a left-lateral strike slip, which is consistent with the strike and motion constrained by the focal mechanism. The coseismic displacements were measured to 20~30cm. Field observations, focal fault plane, distribution of the aftershocks, GNSS, and InSAR observation data suggest that the seismogenic structure associated with the M6.8 Luding earthquake is the Moxi Fault that belongs to the southeastern segment of the Xianshuihe fault zone. Slip along the segment south of the epicenter generated this earthquake, and also triggered slip along a northeast-trending fault and the northwestern section of the Moxi Fault in the epicenter. So, the M6.8 Luding earthquake is an event that is nucleated on the section south of the epicenter and then triggered an activity of the whole fault segment.

Karlik Tagh and other lesser ranges of the easternmost Tian Shan are natural laboratory for studying the fault architecture of an active termination zone of an intraplate mountain belt. The Karlik Tagh is located at the easternmost Tian Shan which is active due to the collision of India plate and Eurasian plate in Cenozoic and this range represents the geomorphological and structural end of Tian Shan. Therefore, studying the geometry and kinematics of active faults distributed at this area has important implications for understanding the dynamics features of the end porting of the Cenozoic orogenic belt. This paper is focused on the North Karlik Tagh Fault(KTNF), which is an important active structure at the easternmost Tian Shan. This fault extends about 180km and is gently distributed between the Yiwu Basin and the north of Karlik Tagh. Based on remote sensing and detailed field research, we propose to subdivide the NKTF into 2 segments based on its variation in strike and motion characteristics.
At the west of the NKTF, the west segment is mainly distributed at south of Yanchi County and extends intermittently about 61km. The fault trace along Yanchi segment is obvious and expressed by several linear fault scarps on the foreland alluvial fan surfaces north of Karlik Tagh. Outcrop on a channel wall shows that the fault dips SW and thrusts directly to the NE. Topographic profiles across the scarps have shown that the minimum vertical offset is(1.3±0.5)m, which can be caused by a single earthquake rupture. The maximum vertical offset is(7.3±0.3)m. An OSL dating sample was obtained at 70cm below the T1 terrace surface. And we get the deposition age of(7.0±1.4)ka. Based on the OSL dating of deformed T1 terrace and the vertical displacement of(1.3±0.5)m of T1 and vertical displacement of(2.5±0.2)m of T2, a vertical slip rate of 0.19~0.35mm/a can be calculated. This vertical rate is slightly larger than that of the North Hami Basin Fault, which is consistent with the S-directed tilt of the Karlik Tagh.
At south of Xiamaya town, the east segment of NKTF changes its strike and bends to NE, extending nearly 95km. Toward the east, this fault is connected with the west end of Gobi-Tianshan fault system(GTSFS)at the border of China and Mongolia. There are clear evidences of recent activity of this fault, including well-preserved scarps and offset streams on the alluvial sediments. And this fault segment is very obvious because of linear features on the Google Earth image. About 23km southeast of Xiamaya town, the fault trace runs across a north-flowing river, causing remarkable sinistral offset of the T3/T2 terrace ridge with the maximum displacement of(172±20)m. At about 10km northeast of this river, the NKTF passes through a massif with steep slope on the south and gentle slope on the north. Field observation of a hand-dug outcrop has shown that this fault dips N156°E. In addition, the fault also displays reverse faulting component and dislocates the gravel-bearing silt sedment by about 2.0m.
At north of Karlik Tagh, several NW-trending faults can be interpreted on the satellite image. These faults extend short and form a clear boundary between bedrock and Quaternary sediments. Although there are no obvious deformations in the sediment such as diluvial fans or river terraces in the valley, the good linear characteristics on both sides of the valley indicate that these faults have been active since Quaternary. Because these faults are nearly parallel to the western segment of the northern margin of the Karlik Mountains, and there is no geomorphological evidence of horizontal movement of the faults, it can be inferred that the faults on both sides of the Adak Valley are mainly dominated by vertical movement.
The Karlik Tagh North Fault, together with, the north margin faults of Hami Basin and other NW-trending secondary faults in the north side of Karlik Mountain constitute the horse-tail end structure of Gobi-Tianshan sinistral strike-slip fault system, which regulates and absorbs the sinistral deformation of Gobi-Tianshan fault system and these faults present a positive flower structure in the cross-section. The uplift of Karlik Tagh is controlled by NW thrust fault and NEE left-lateral strike-slip fault, and this range is a typical transpressional mountain in the easternmost Tian Shan.

The May 21, 2021 Yangbi M_S6.4 earthquake occurred at the western boundary of the Chuandian tectonic block in southeast Tibetan plateau. The structural background is complex, with multiple active faults distributed around the epicenter area. Focal mechanism and seismic waveform inversion reveal that this earthquake is right-lateral strike-slip type with a NW-trending rupture plane. This accords with the strike and motion directions of the Weixi-Qiaohou and Red River faults along the western boundary of the Chuandian block.
We made a careful field investigation along the Weixi-Qiaohou Fault and around the epicenter area, and did not find any obvious earthquake surface rupture. But we observed a NW-trending ground fissure zone near the epicenter area to the west of the Yangbi County. This zone is divided into two sections, the Yangkechang-Paoshuitian section in the northwest and the Xiquewo-Shahe section in the southwest. These sections have a length of 2.5~3km and 3~3.5km, respectively, and are separated by a ~6km gap. They are characterized by NW-trending ground fissures with a width of several meters to tens meters. The formation of these fissures is inferred to be related to the tectonic movement under the ground, and the fissures have the following features: 1)they are not affected by the topography and cut the slope and range upward; 2)they are continuous and concentrated in a zone with a strike of NW 310°~320°, which is consistent with the belt of aftershocks and differs from the gravity fissures that usually have no regular strikes; 3)they usually have a plane dipping towards upslope(southwest), opposite to the valley; 4)they present shear property, not tensional. This zone thus is interpreted to be the surficial expression of the seismogenic fault of the Yangbi M_S6.4 earthquake.
Moreover, satellite image and field observation suggest that a~30km long linear structure with a NW strike traverses the epicenter area, which may suggest an undiscovered fault. Relocation of small earthquakes shows that the aftershocks are concentrated in a NW-trending belt that is consistent with the linear structure. Furthermore, the fissure zone lies in the northeast side of the aftershock belt, which suggests that the earthquake fault dips SW. Such a dip direction coincides with that of the observed fissure plane, and also agrees with the results from the focal mechanism and InSAR inversion. Both the focal mechanism and the waveform inversion result suggest that the Yangbi earthquake is a right-lateral strike-slip type, which is consistent with the type of the observed ground fissures. No displacement is observed on the fissures, with is also consistent with the InSAR inversion results that suggest the rupture did not break the surface. In addition, there is no coseismic deformation observed along the Weixi-Qiaohou Fault, which may indicate this fault did not move during this earthquake.
Based on our field investigation, in combination with the focal mechanism, aftershock distribution, and InSAR and GNSS inversion results, the seismogenic fault for this Yangbi M_S6.4 earthquake is believed to be a NW-trending(310°~320°)fault with a length of~30km, named as the Yangkechang-Shahe Fault. According to the location, size, and motion of the fault, it is suggested that the Yangkechang-Shahe Fault is a secondary fault of the Weixi-Qiaohou fault system. This fault has a slightly SW-dipping plane, and is dominated by right-lateral strike-slip motion, which may be a younger fault developed during the westward expansion of the western boundary of the Chuandian block.

In the process of intense compression and shortening of the orogenic belt, a series of thrust faults and folds related to reverse faults developed in the piedmont. Determining the kinematic characteristics of these reverse faults and folds is of great significance for understanding the deformation mode of the orogenic belt. The Qilian Shan is located on the northeastern margin of the Tibetan plateau and is the front edge of the plateau expansion. The area has undergone strong tectonic activity since the Late Quaternary, with developed active structures and frequent earthquakes. There are a series of piedmont thrust faults and thrust related folds in the northern and southern margins of Qilian Shan. Compared with a large number of research results of active folds in Tian Shan area, the study of active folds in Qilian Shan is relatively weak. In the northern margin of the Qilian Shan, in addition to the study of individual active folds, most previous studies focused on the thrust faults in the northern margin of the Qilian Shan and the Hexi Corridor, and obtained the active characteristics of these faults. In the southern margin of Qilian Shan, that is, the northern margin of the Qaidam Basin, some studies have been carried out on paleoearthquakes and slip rate of the fault in the southern margin of Zongwulong Shan. However, the study on the late Quaternary folds in this area is relatively weak and there are only some sporadic works.
Shidiquan anticline is located in the intermountain basin surrounded by Zongwulong Shan and Hongshan in the northern margin of Qaidam Basin. It forms the first row fold structure in front of Zongwulong Shan with Huaitoutala and Delingha anticline. Constraining the tectonic geomorphic features of the Shidiquan anticline is of great significance for studying the crustal shortening in the northern margin of the Qaidam Basin and the expansion of the Qilian Shan to the Qaidam Basin. In this paper, the tectonic and geomorphic characteristics of Shidiquan anticline are obtained by means of geological mapping, high-precision differential GPS topographic profile survey, geological profile survey and cosmogenic nuclide dating. Field investigation shows that Shidiquan anticline is an asymmetric fold with steep south limb and gentle north limb, and is controlled by a blind reverse fault dipping northward. The age of the alluvial fan3 obtained from cosmogenic nuclide dating is(158.32±15.54)ka. This age coincides with the Gonghe Movement, indicating that the formation of Shidiquan anticline responds to the Gonghe Movement in the northeast margin of Tibetan plateau. The uplift rate of Shidiquan anticline since 158ka is(0.06±0.01)mm/a, and the shortening rate is(0.05±0.01)mm/a. The folding effect of Shidiquan anticline indicates that the folding of the intermountain basin in the northern margin of the Qaidam Basin, similar to the thrust shortening of the piedmont fault, plays an important role in regulating the shortening of the foreland crust.

The Shanxi Graben System is one of the intracontinental graben systems developed around the Ordos Block in North China since the Cenozoic, and it provides a unique natural laboratory for studying the long-term tectonic history of active intracontinental normal faults in an extensional environment. Comparing with the dense strong earthquakes in its central part, no strong earthquakes with magnitudes over 7 have been recorded historically in the Jin-Ji-Meng Basin-and-Range Province of the northern Shanxi Graben System. However, this area is located at the conjunction area of several active-tectonic blocks(e.g. the Ordos, Yan Shan and North China Plain blocks), thus it has the tectonic conditions for strong earthquakes. Studying the active tectonics in the northern Shanxi Graben System will thus be of great significance to the seismic hazard assessment. Based on high-resolution remote sensing image interpretations and field investigations, combined with the UAV photogrammetry and OSL dating, we studied the late Quaternary activity and slip rate of the relatively poorly-researched Yanggao-Tianzhen Fault(YTF)in the Jin-Ji-Meng Basin-and-Range Province and got the followings: 1)The YTF extends for more than 75km from Dashagou, Fengzhen, Inner Mongolia in the west to Yiqingpo, Tianzhen, Shanxi Province in the east. In most cases, the YTF lies in the contact zone between the bedrock mountain and the sediments in the basin, but the fault grows into the basin where the fault geometry is irregular. At the vicinity of the Erdun Village, Shijiudun Village, and Yulinkou Village, the faults are not only distributed at the basin-mountain boundary, we have also found evidence of late Quaternary fault activity in the alluvial fans that is far away from the basin-mountain boundary. The overall strike of the fault is N78°E, but the strike gradually changes from ENE to NE, then to NWW from the west to the east, with dips ranging from 30° to 80°. 2)Based on field surveys of tectonic landforms and analysis of fault kinematics in outcrops, we have found that the sense of motion of the YTF changes along its strikes: the NEE and NE-striking segments are mainly normal dip-slip faults, while the left-laterally displaced gullies on the NWW segment and the occurrence characteristics of striations in the fault outcrop indicate that the NWW-striking segment is normal fault with minor sinistral strike-slip component. The sense of motion of the YTF determined by geologic and geomorphic evidences is consistent with the relationship between the regional NNW-SSE extension regime and the fault geometry. 3)By measuring and dating the displaced geologic markers and geomorphic surfaces, such as terraces and alluvial fans at three sites along the western segment of the YTF, we estimated that the fault slip rates are 0.12~0.20mm/a over the late Pleistocene. In order to compare the slip rate determined by geological method with extension rate constrained by geodetic measurement, the vertical slip rates were converted into horizontal slip rate using the dip angles of the fault planes measured in the field. At Zhuanlou Village, the T₂ terrace was vertically displaced for(2.5±0.4)m, the abandonment age of the T₂ was constrained to be(12.5±1.6)ka, so we determined a vertical slip rate of(0.2±0.04)mm/a using the deformed T₂ terrace and its OSL age. For a 50°dipping fault, it corresponds to extension rate of(0.17±0.03)mm/a. At Pingshan Village, the vertical displacement of the late Pleistocene alluvial fan is measured to be(5.38±0.83)m, the abandonment age of the alluvial fan is(29.7±2.5)ka, thus we estimated the vertical slip rate of the YTF to(0.18±0.02)mm/a. For a 65° dipping fault, it corresponds to an extension rate of(0.09±0.01)mm/a. Ultimately, the corresponding extensional rates were determined to be between 0.09mm/a and 0.17mm/a. Geological and geodetic researches have shown that the northern Shanxi Graben System are extending in NNW-SSE direction with slip rates of 1~2mm/a. Our data suggests that the YTF accounts for about 10% of the crustal extension rate in the northern Shanxi Graben System.

Influenced by the far-field effect of India-Eurasia collision, Tianshan Mountains is one of the most intensely deformed and seismically active intracontinental orogenic belts in Cenozoic. The deformation of Tianshan is not only concentrated on its south and north margins, but also on the interior of the orogen. The deformation of the interior of Tianshan is dominated by NW-trending right-lateral strike-slip faults and ENE-trending left-lateral strike-slip faults. Compared with numerous studies on the south and north margins of Tianshan, little work has been done to quantify the slip rates of faults within the Tianshan Mountains. Therefore, it is a significant approach for geologists to understand the current tectonic deformation style of Tianshan Mountains by studying the late Quaternary deformation characteristics of large fault and fold zones extending through the interior of Tianshan. In this paper, we focus on a large near EW trending fault, the Baoertu Fault (BETF) in the interior of Tianshan, which is a large fault in the eastern Tianshan area with apparent features of deformation, and a boundary fault between the central and southern Tianshan. An M_S5.0 earthquake event occurred on BETF, which indicates that this fault is still active. In order to understand the kinematics and obtain the late Quaternary slip rate of BETF, we made a detailed research on its late Quaternary kinematic features based on remote sensing interpretation, drone photography, and field geological and geomorphologic survey, the results show that the BETF is of left-lateral strike-slip with thrust component in late Quaternary. In the northwestern Kumishi basin, BETF sinistrally offsets the late Pleistocene piedmont alluvial fans, forming fault scarps and generating sinistral displacement of gullies and geomorphic surfaces. In the bedrock region west of Benbutu village, BETF cuts through the bedrock and forms the trough valley. Besides, a series of drainages or rivers which cross the fault zone and date from late Pleistocene have been left-laterally offset systematically, resulting in a sinistral displacement ranging 0.93~4.53km. By constructing the digital elevation model (DEM) for the three sites of typical deformed morphologic units, we measured the heights of fault scarps and left-lateral displacements of different gullies forming in different times, and the result shows that BEFT is dominated by left-lateral strike-slip with thrust component. We realign the bended channels across the fault at BET01 site and obtain the largest displacement of 67m. And we propose that the abandon age of the deformed fan is about 120ka according to the features of the fan. Based on the offsets of channels at BET01 and the abandon age of deformed fan, we estimate the slip rate of 0.56mm/a since late Quaternary. The Tianshan Mountains is divided into several sub-blocks by large faults within the orogen. The deformation in the interior of Tianshan can be accommodated or absorbed by relative movement or rotation. The relative movement of the two sub-blocks surrounded by Boa Fault, Kaiduhe Fault and BETF is the dominant cause for the left-lateral movement of BETF. The left-lateral strike-slip with reverse component of BETF in late Quaternary not only accommodates the horizontal stain within eastern Tianshan but also absorbs some SN shortening of the crust.

With the continuous collision of the India and Eurasia plate in Cenozoic, the Qilian Shan began to uplift strongly from 12Ma to 10Ma. Nowadays, Qilian Shan is still uplifting and expanding. In the northern part of Qilian Shan, tectonic activity extends to Hexi Corridor Basin, and has affected Alashan area. In the southern part of Qilian Shan, tectonic activity extends to Qaidam Basin, forming a series of thrust faults in the northern margin of Qaidam Basin and a series of fold deformations in the basin. The southern Zongwulong Shan Fault is located in the northeastern margin of Qaidam Basin, it is the boundary thrust fault between the southern margin of Qilian Shan and Qaidam Basin. GPS studies show that the total crustal shortening rate across the Qilian Shan is 5~8mm/a, which absorbs 20% of the convergence rate of the Indian-Eurasian plate. Concerning how the strain is distributed on individual fault in the Qilian Shan, previous studies mainly focused on the northern margin of the Qilian Shan and the Hexi Corridor Basin, while the study on the southern margin of the Qilian Shan was relatively weak. Therefore, the study of late Quaternary activity of southern Zongwulong Shan Fault in southern margin of Qilian Shan is of great significance to understand the strain distribution pattern in Qilian Shan and the propagation of the fault to the interior of Qaidam Basin. At the same time, because of the strong tectonic activity, the northern margin of Qaidam Basin is also a seismic-prone area. Determining the fault slip rate is also helpful to better understand the movement behaviors of faults and seismic risk assessment.Through remote sensing image interpretation and field geological survey, combined with GPS topographic profiling, cosmogenic nuclides and optically stimulated luminescence dating, we carried out a detailed study at Baijingtu site and Xujixiang site on the southern Zongwulong Shan Fault. The results show that the southern Zongwulong Shan Fault is a Holocene reverse fault, which faulted a series of piedmont alluvial fans and formed a series of fault scarps.The 43ka, 20ka and 11ka ages of the alluvial fan surfaces in this area can be well compared with the ages of terraces and alluvial fan surfaces in the northeastern margin of Tibetan Plateau, and its formation is mainly controlled by climatic factors. Based on the vertical dislocations of the alluvial fans in different periods in Baijingtu and Xujixiang areas, the average vertical slip rate of the southern Zongwulong Shan Fault since late Quaternary is(0.41±0.05)mm/a, and the average horizontal shortening rate is 0.47~0.80mm/a, accounting for about 10% of the crustal shortening in Qilian Shan. These results are helpful to further understand the strain distribution model in Qilian Shan and the tectonic deformation mechanism in the northern margin of Qaidam Basin. The deformation mechanism of the northern Qaidam Basin fault zone, which is composed of the southern Zongwulong Shan Fault, is rather complicated, and it is not a simple piggy-back thrusting style. These faults jointly control the tectonic activity characteristics of the northern Qaidam Basin.

Traditional method to generate Digital Elevation Model (DEM)through topographic map and topographic measurement has weak points such as low efficiency, long operating time and small range. The emergence of DEM-generation technology from high resolution satellite image provides a new method for rapid acquisition of large terrain and geomorphic data, which greatly improves the efficiency of data acquisition. This method costs lower compared with LiDAR (Light Detection and Ranging), has large coverage compared with SfM (Structure from Motion). However, there is still lack of report on whether the accuracy of DEM generated from stereo-imagery satisfies the quantitative research of active tectonics. This research is based on LPS (Leica Photogrammetry Suit)software platform, using Worldview-2 panchromatic stereo-imagery as data source, selecting Kumishi Basin in eastern Tianshan Mountains with little vegetation as study area. We generated 0.5m resolution DEM of 5-km swath along the newly discovered rupture zone at the south of Kumishi Basin, measured the height of fault scarps on different levels of alluvial fans based on the DEM, then compared with the scarp height measured by differential GPS survey in the field to analyze the accuracy of the extracted DEM. The results show that the elevation difference between the topographic profiles derived from the extracted DEM and surveyed by differential GPS ranges from -2.82 to 4.87m. The shape of the fault scarp can be finely depicted and the deviation is 0.30m after elevation correction. The accuracy of measuring the height of fault scarps can reach 0.22m, which meets the need of high-precision quantitative research of active tectonics. It provides great convenience for rapidly obtaining fine geometry, profiles morphology, vertical dislocations of fault and important reference for sites selection for trench excavation, slip rate, and samples. This method has broad prospects in the study of active tectonics.

The Longmenshan fault zone is located in eastern margin of Tibetan plateau and bounded on the east by Sichuan Basin, and tectonically the location is very important. It has a deep impact on the topography, geomorphology, geological structure and seismicity of southwestern China. It is primarily composed of multiple parallel thrust faults, namely, from northwest to southeast, the back-range, the central, the front-range and the piedmont hidden faults, respectively. The M_S8.0 Wenchuan earthquake of 12^th May 2008 ruptured the central and the front-range faults. But the earthquake didn't rupture the back-range fault. This shows that these two faults are both active in Holocene. But until now, we don't know exactly the activity of the back-range fault. The back-range fault consists of the Pingwu-Qingchuan Fault, the Wenchuan-Maoxian Fault and the Gengda-Longdong Fault. Through satellite image(Google Earth)interpretation, combining with field investigation, we preliminarily found out that five steps of alluvial platforms or terraces have been developed in Minjiang region along the Wenchuan-Maoxian Fault. T₁ and T₂ terraces are more continuous than T₃, T₄ and T₅ terraces. Combining with the previous work, we discuss the formation ages of the terraces and conclude, analyze and summarize the existing researches about the terraces of Minjiang River. We constrain the ages of T₁, T₂, T₃, T₄ and T₅ surfaces to 3~10ka BP,~20ka BP, 40~50ka BP, 60ka BP and 80ka BP, respectively. Combining with geomorphologic structural interpretation, measurements of the cross sections of the terraces by differential GPS and detailed site visits including terraces, gullies and other geologic landforms along the fault, we have reason to consider that the Wenchuan-Maoxian Fault was active between the formation age of T₃ and T₂ terrace, but inactive since T₂ terrace formed. Its latest active period should be the middle and late time of late Pleistocene, and there is no activity since the Holocene. Combining with the knowledge that the central and the front-range faults are both Quaternary active faults, the activity of Longmenshan fault zone should have shifted to the central and the front-range faults which are closer to the basin, this indicates that the Longmenshan thrust belt fits the "Piggyback Type" to some extent.

The Xiangshan-Tianjingshan fault zone is an important part of the arc tectonic zone in northeastern Tibet, whose eastern segment is characterized by primarily left-lateral slip along with thrust component. In contrast, the fault movement property on the western segment of the Xiangshan-Tianjingshan fault zone is more complicated. According to the offset geomorphic features and cross sections revealed by the trenches and outcrops, the western segment is mainly a left-lateral strike-slip fault with normal component, and only accompanied with reverse component at specific positions. To determine the genetic mechanism of fault movement property on the western segment, we obtained three main factors based on the integrated analysis of fault geometry:(1)Step-overs:the left-stepping parallel faults in a sinistral shear zone create extensional step-overs and control the nearby and internal fault movement property; (2)terminal structures:they are conductive to stop rupture propagation and produce compressive deformation at the end of the fault trace; and(3)double bends:strike-slip faults have trace that bends such that slip between two adjacent blocks creates a compressive stress and thrust fault. Additionally, the Tianjingshan sub-block moves to SEE and creates an extensional stress at the end of the sub-block associated with normal faults. It shows that the Xiangshan-Tianjingshan fault zone has a complex evolution history, which is divided into two distinctive periods and characterized by laterally westward propagating.

The Xiangshan-Tianjingshan Fault zone is an integral part of the northeastern Tibet plateau fault system, and the 1709 earthquake of M7 1/2 happened on the eastern segment of this fault. But there remains a fresh surface rupture produced by the latest earthquake and a lot of gullies left-laterally dislocated synchronously along the western segment of the Xiangshan-Tianjingshan Fault zone, which has no historical records. To determine the western segment's seismicity since the Late Quaternary, we measured 240 horizontal offsets of the gullies or ridges and 62 vertical offsets, combining with the field geologic investigation and satellite remote sensing decipherment. Characteristics of distribution of the horizontal and vertical offsets are obtained by projecting the measured displacements along the stretch of the fault. Through probability density simulation and frequency statistical analysis for the horizontal offsets, the results show that there are obvious grouping character and multiple relationships. The six groups of horizontal offsets may represent 6 paleoearthquakes, with a similar event sequence in the trench excavated on the western segment. The coseismic offset of the latest earthquake is 3m, and the cumulative offsets produced by other older earthquakes is 6m, 9m, 12m, 16m and 20m, respectively, and each earthquake has a similar coseismic offset. Therefore, we suppose that the activity on the western segment of the Xiangshan-Tianjingshan Fault zone obeys a characteristic slip model since Late Quaternary.

The April 20,2013,M_S 7.0 Lushan earthquake occurred along the southwestern part of the Longmen Shan Fault zone. Tectonics around the epicenter area is complicated and several NE-trending faults are developed. Focal mechanisms of the main shock and inversions from finite fault model suggest that the earthquake occurred on a northeast-trending,moderately dipping reverse fault,which is consistent with the strike and slip of the Longmen Shan Fault zone. NE-trending ground fissures and soil liquefaction along the fissures,heavy landslides along the Dachuan-Shuangshi and Xinkaidian Faults were observed during the field investigations. No surface ruptures were found in the field work. GPS data indicate that the fault on which this earthquake occurred is a fault east of or near the Lushan county and the earthquake also triggered slip on the fault west of the Lushan county. Field observations,GPS data,focal fault plane,focal depth,and distribution of the aftershocks suggest, that the seismogenic structure associated with the M_S 7.0 Lushan earthquake is the décollement beneath the folds of the eastern Longmen Shan. Slip along this decollement generated the earthquake,and also triggered the slip along the Dachuan-Shuangshi and Xinkaidian Faults.

On April 20,2013,a strong earthquake of M_S 7.0 struck the Lushan County,Sichuan Province of China. In this paper,basic information of the April 20,2013 Lushan earthquake,historical earthquakes in the Lushan earthquake struck area and associated historical earthquake-triggered landslides were introduced firstly. We delineated the probable spatial distribution boundary of landslides triggered by the Lushan earthquake based on correlations between the 2008 Wenchuan earthquake-triggered landslides and associated peak ground acceleration(PGA).According to earthquake-triggered landslides classification principles,landslides triggered by the earthquake are divided into three main categories: disrupted landslides,coherent landslides,and flow landslides. The first main category includes five types: rock falls,disrupted rock slides,rock avalanches,soil falls,and disrupted soil slides. The second main category includes two types of soil slumps and slow earth flows. The type of flow landslides is mainly rapid flow slides. Three disrupted landslides,including rock falls,disrupted rock slides,and soil falls are the most common types of landslides triggered by the earthquake. We preliminary mapped 3883 landslides based on available high-resolution aerial photographs taken soon after the earthquake. In addition,the effect of aftershocks on the landslides,comparisons of landslides triggered by the Lushan earthquake with landslides triggered by other earthquake events,and guidance for subsequent landslides detailed interpretation based on high-resolution remote sensing images were discussed respectively. In conclusion,based on quick field investigations to the Lushan earthquake,the classifications,morphology of source area,motion and accumulation area of many earthquake-triggered landslides were recorded before the landslide might be reconstructed by human factors,aftershocks,and rainfall etc. It has important significance to earthquake-triggered landslide hazard mitigation in earthquake struck area and the scientific research of subsequent landslides related to the Lushan earthquake.

Field investigations on the 2008 surface rupture north to Shikan village show that the surface rupture is still significant in this section.The surface rupture changes its strike at the north of the town of Shikan and does not follow the previously mapped thrust which was initially considered the location the rupture traversed.Nevertheless,clear morphological expressions suggest repeated coseismic displacements along the fault trace the 2008 earthquake rupture followed.Contrast to the previous work,another 12-km-long rupture was found.It runs between Shikan town and Woqian village,trends 15°～45°,and shows thrusting with dextral slipping.The relatively large vertical and dextral strike-slip displacements of 2.1m and 3.0m respectively at Kuangpingzi do not suggest that co-seismic slip diminished gradually from a high value to a low one.The increased component of strike slip may suggest that the rupture ended as a strike-slip mode.Field observations suggest that the rupture terminates at the southwest of the Donghekou village about 20km north to Woqian village.

Based on the field work and seismic reflection profiling data,the paper investigates the deformation characteristics of the Longquanshan Fault zone.The main thrust fault of the Longquanshan Fault belt lies in the west of the Longquanshan anticline and has different properties from northeast to southwest.In the north segment and south segment of the Longquanshan Fault,the plane of fault dips to northwest and is uncontinuous,but in the middle segment,the plane of fault dips to southeast and is continuous.Therefore,the middle part of the fault is the main segment of the Longquanshan Fault.Structural geometries of the middle segment of the fault suggest classical fault-propagation folding and the fault ruptured along different axial directions.Historical earthquakes and geomorphological response to activity of the Longquanshan Fault indicate that the fault was active from the early Pleistocene to late Pleistocene,and its activity is weak since the late Pleistocene,and gradually decreases from south to north.

Xiongpo anticline locates in Chengdu Basin,to the southeast of Longmenshan tectonic zone.It is an important deformation area where the Longmenshan thrust-nappe structure intrudes into the Chengdu Basin.The Pujiang-Xinjin Fault is an associated fault to Xiongpo anticline.The deformation mode between the fault and anticline fold is in concordance obviously.The geologic section across the anticline indicates that the south segment of Xiongpo anticline is an asymmetric fold and the northeast segment is symmetric,wide and gentle relatively.The fold includes Mesozoic and pre-Mesozoic strata.The topographical investigation reveals that the faulting is always associated with folding.At the northeast part of fold,the fold axial direction is parallel to the fault strike.Near the fault,the strata dips are remarkably different and the height difference of topography is large.The investigation of the Pujiang-Xinjin Fault did not reveal any obvious fault profiles and new activity characteristics.The Pujiang-Xinjin Fault has no influence on the gullies and T1 terraces widely developed in this area,but it controls the pluvial terrace which corresponds to T4 terrace of Nanhe river(the first-order branch of Minjiang River).The OSL age of the pluvial terrace is older than 130ka.All above indicates that the activity age of the Pujiang-Xinjin Fault is at the early-Quaternary.By the late-Quaternary,the faulting weakened or was nearly inactive.So in the area,the major tectonic character is faulting associated with fold deformation,which is also the major deformation mode of Xiongpo anticline.

On 12 May 2008,a magnitude 8.0 earthquake occurred beneath the steep eastern margin of Tibetan plateau in Sichuan,China.Rupture occurred over a length of～240km along the central Longmenshan Fault(Beichuan-Yinxiu Fault)and ～72km along the Longmenshan piedmont fault(Guanxian-Jiangyou Fault).In order to know clearly the activity of the middle segment of Longmenshan Fault,we surveyed the earthquake rupture and excavated 5 trenches in the north part of the central Longmenshan Fault.Four of the five trenches have revealed the deformation of the Wenchuan earthquake and the characteristics of strong earthquake activity on this segment.The 4 trenches are briefly described as follows.The Fenghuang village trench locates on T₂ terrace or T₃ terrace of Pingtong River.The trench logs show that there is another earthquake event except the Wenchuan earthquake.As a tectonic deformation character,the thrust fault is exposed on the surface,the underground soils were thrust over the cultivated surface soil,forming thrust nappe and extrusion wedge.The bedrock near the fault has been compressed and fractured seriously,which is represented by overlap of some old scarps with new ones on the ground surface.The trench on T₁ terrace at Pingtong Panxuanlu records the zigzag deflections of marker bed.According to the recovery of marker bed,it is possible that there was an earlier earthquake event whose magnitude is equivalent to the present Wenchuan earthquake,because the footwall is higher than the hanging wall after the marker bed flattened,and the Wenchuan earthquake scarp on flood plain and T1 terrace is much lower than the scarp at the trench site.The scarp with a length of～20m and height of～2.7m is revealed by the trench excavated near the Da′ai School,but we can't see obvious signs of fault and faulting.Perhaps the fault displacement is represented by slightly folding of each deposit layer,which is one of the surface deformation models of thrust faulting.On T₁ terrace at Miaoziwan village,Nanba town,the trench displays that the vertical displacement of arc-deflection on marker bed is equal to the earthquake scarp height,indicating that this phenomenon is caused by the present earthquake event alone.Now,there are no results of dating samples,so we obtained the topographical age by comparing the adjacent surfaces.According to the dating results of terrace,the forming time of T₁ terrace is about 3000～5000a and T₂ terrace about 12000～20000a.It is revealed that the recurrence interval of strong earthquake on the northern segment of central Longmenshan Fault is more than 3000a.

Field investigation on the surface ruptures of the M_S8.0 Wenchuan earthquake along the segment between Beichuan and Qingchuan shows that there is one surface rupture zone developed on this segment,which extends generally along the Beichuan-Qingchuan Fault zone.Observation at Huangjiaba Chenjiaba,Guixi,Pingtong,Nanba,and Shikan suggests that the surface ruptures on this segment spread continuously along the trend of the fault,with single structure and a length of 60～90km.The surface rupture has not reached Guanzhuang of Qingchuan county.The observable rupture zone is about 62km,between Beichuan and Shikan,trending 20°～55° in general,dipping NW with an angle of 70°,showing mainly thrusting with dextral strike-slipping.The most distinct feature of the surface ruptures of this earthquake is the vertical surface bending,which indicates the thrusting of the deep fault.Its horizontal motion on this segment displays as dextral strike slipping,without sinistral slipping component.The value of the vertical coseismic displacements decreases gradually from 3m at Huangjiaba to about 1.5m at Nanba and Shikan;The amount of the dextral displacements does not change evidently,generally between 1.5m and 2.0m.Features of the surface rupture show that the causative tectonics of this M_S8.0 Wenchuan earthquake is the Yingxiu-Beichuan-Qingchuan Fault,whose movement is characterized mainly by thrusting,with a dextral slipping component,and the thrusting direction is from west to east.

Slip rates along major active faults are important components of quantitative studies of active tectonics. Slip rates can be directly used to seismic potential evaluation of active faults and seismic safety assessments of major engineering. In principle,dividing total displacement by its initial time yields slip rate along the fault. But,accurate determination of slip rate along a particular fault is not a simple task in practices for which the rates may deviate as much as 3 times among different researches and different methods. We argue that offset terrace risers that are protected by topography upstream of them are more closely dated by the age of the upper terrace than by that of the lower terrace. In some cases,valleys upstream of the fault have been incised into bedrock,and few if any terrace risers can be seen within the valleys. Such streams debouch onto alluviated floodplains or fans that become incised,presumably during climate changes,to create terrace risers. The terrace risers are then displaced so that they lie downslope from bedrock ridges on the upstream side of the fault,and thus the risers become protected from further incision. In such cases,dates of upper terraces should more closely approximate the ages of the risers than those of lower terraces. As noted above,whether the age of the upper or of the lower terrace more closely approximates the age of the riser will depend upon how the stream flowing over the flood plain that becomes the lower terrace alters the riser,and therefore at least in part on whether the offset riser moves into the path of the active stream or becomes shielded from it. Of cause,the age of the riser should be neither greater than the age of the upper terrace nor smaller than the age of the lower terrace. In an ideal situation,the ages of both would be sufficiently similar that they would place nearly equal upper and lower bounds on the slip rate. In many regions,however,the ages of the two terraces are so different that the bounds that they place on the slip rate are too large to be useful. We propose three methods to determine slip rate based on offsets of terrace risers. The first is to use both upper and lower terraces to constrain the maximum and minimum age of the offset of the riser. The second is to use the abandonment age of upper terrace as the initial age of the offset on the side of stream moving away from the river course. The third is to use the inception of sedimentary deposition on the lower strath terrace as the initial age of terrace riser offset. We use these methods to study slip rates along the Haiyuan Fault and the Altun Fault. The results show consistency of slip rates among different time scales,and are also consistent with other independent studies.

The urban area in the eastern China region is mostly covered by the relatively thick loose Quaternary deposits,below which,in many cities,there exist many considerably large buried faults.In these thick-Quaternary-covering areas,does the date of the upper layers dislocated by the buried faults represent the latest faulting? In this paper,based on the integrated analysis on the data of geology,geophysics and earthquakes of cities in the east of China,including Xingtai and Tangshan,we discussed the relation between the upper offset point and the latest activity times of the buried faults in these areas covered by thick Quaternary.Our study shows,in the area with very thick recent deposits in East China,one should not determine the latest faulting of one fault fully according to the younger layers displaced by the fault.To a fault running through the area covered with thick young deposits,its latest active period should be determined comprehensively by the tectonic settings,the controlling of the fault to the young strata,the youngest layer displaced by the fault,the thickness of the young deposits,seismicity and modern tectonic stress field,etc.

Migration of strong earthquakes(M≥7) along the North-South Seismic Belt since 1500 AD shows three patterns: roughly similar time and distance interval migration from N to S, multi-pattern migration from S to N and clusters of strong earthquakes occurring in some periods within the whole seismic belt. Based on analysis of strong earthquakes in the past hundred years, the activity of the North-South Seismic Belt is related to the strong earthquake activity of the South Asia Seismic Belt elongating from Burma to Sumatra, Indonesia. Strong earthquakes along the former belt often occur several months or years after the quakes on the later belt. The above-mentioned migration characteristic of strong earthquakes is likely caused by the northward collision and subduction of the India Plate as well as coaction between the Qinghai-Tibet Plateau and the stable and hard Ordos and Alashan Massif at the northeastern margin of the Plateau. The South-to-North migration of strong earthquakes with different time intervals and different migrating rates may directly reflect the uneven, irregular pushing of the northeastern corner of the India plate, and the gradually northward transmitting and expanding of the related stress as it accumulates and strengthens. While the North-to-South migration of strong earthquakes with long time intervals and uniform rate may relate to the movement of the further deeper materials, or to the interaction between the strongly-deformed Qinghai-Tibet Plateau and the northern hard massif. Perhaps it results from the successive, north-to-south, lateral-slipping and rotational-twisting movement of the strip massifs constituting the Qinghai-Tibet Plateau. As for the phenomenon that strong earthquake clusters occur constantly in a certain time on the North-South Seismic Belt, it may imply that the deformation induced by India Plate indenting strongly into Eurasia continent on the eastern margin of the Qinghai-Tibet Plateau has been strengthened. And the clustering of strong earthquakes on North-South Seismic Belt and South Asia Seismic Belt also confirms that the northern collision zone and the eastern subduction zone of India Plate, as a whole, have impact on the activity of the earthquakes on the Chinese North-South Seismic Belt and Burma, Andaman till Sumatra.

The western Qinling Fault zone is one of the main left-lateral strike-slip active faults in northeastern Tibet. At site of Huangxianggou, the behavior of the fault zone shows typical strike-slip movement. Detailed analysis on the amounts of the offset of the late Quaternary landforms and geologic bodies along the fault shows that at Huangxianggou the maximum horizontal displacement since the late of late-Pleistocene is about 40～60m, and the minimum is 6～8m which is possibly the amount of one principal slip associated with one large earthquake event. And it is also inferred that the amounts of the displacement along the fault can be grouped, and between the groups there is a stable increment of 6～8m. The grouping and the increment of amounts of the offsets suggest that this fault segment displays an activity associated with characteristic earthquakes, and the 7 groups of the displacement values represent 7 characteristic events on the fault. Analysis on the microgeomorphology related to the faulting, such as periodic sag-ponding and deformed pluvial fans, also suggests the corresponding events. Thus it can be inferred, the activity of the fault zone has been dominated by several strong movements since late Late-Pleistocene.

The Xiaodianzi-Maobu segment is part of the Anqiu-Juzian Fault in the Tancheng-Lujiang Fault zone. It starts from northeast of Xiaodianzi village, Juxian County in the north and terminates at Maobu, Juxian County in the south. The fault segment has a general strike of 10°～20°, dipping northwest or southeast at an angle of 60°, and has a length of about 30km. The segment can further be divided into 5 sub-segments: the Xiaodianzi-Qijiazhuang, Yuanhe, Kushan-Xilianci, Qingfengling and Sanzhuang-Zhaike sub-segments from north to south successively. These 5 sub-segments are aligned in right or left-step en-echelon, appearing as a brush structure converging to the north and diverging to the south. The fault segment appears as distinct lineation on satellite image or aerial photo, and geomorphically, as distinct bedrock scarp. According to field observation on natural exposures or trench logs, as well as dating results of samples collected from the fault segment, it can be deduced that the latest faulting event occurred in early Holocene and was dominated by right-lateral strike-slip with compressional reverse faulting component. The distinct horizontal fault striate is well developed along the fault plane and the drainage system crossing the fault segment is right-laterally distorted. This corroborates the right-lateral strike-slip of the fault segment. Field measurement of displacement and dating of the relevant samples have indicated that the displacement amount of the fault is 64～73m, and the displacement rate is 0.91～1.04mm/a in the past 70ka, while in the past 11ka, the displacement is 5.5～7.8m and displacement rate is 0.46～0.65mm/a. The reverse faulting along the fault segment can also be recognized in exposures or trench logs. It can be observed that the Cretaceous or Paleocene system is thrusted over the Quaternary system, making a distinct fault scarp landform. Field measurement of fault scarp and laboratory dating of relevant samples have revealed that in the past 11ka the vertical displacement along the fault segment is 2.3～3.8m and the displacement rate is 0.17～0.32mm/a. In the same period, the right-lateral displacement is 2～3 times as large as the vertical displacement.

Tanlu Fault zone is one of the most important active faults in east China. Yishu Fault,the middle section of the Tanlu Fault zone,presents a graben system consisting of two grabens and four main boundary faults. The eastern graben between Weifang and Jiashan is the most active segment of the Tanlu fault zone,along which developed a 360km long Holocene active fault zone (F₅). The F₅ fault zone has been defined as what consists of all Holocene faults in the eastern graben. The Anqiu earthquake of AD 70 and the Tancheng earthquake of 1668 occurred along the northern and middle segments of the Holocene active fault,respectively. We found a 7km long surface rupture between the main boundary faults of the eastern graben in Juxian County,when we made an investigation on the Yishu Fault in 2003. As an active fault,it should belong to the F₅ fault zone. The carbon date of the un-faulted deposit covering the newly-found surface rupture shows that no earthquake has occurred along this rupture since 2 140?190 yr BP. Therefore,we infer that this newly-found surface rupture is independent of the surface rupture of 1668 Tancheng earthquake,although it is necessary to make a further research to verify this inference.

The Youjiang Fault zone is located in the Guixi (Western Guangxi) fault block region. Since the beginning of seismic records,22 earthquakes of magnitude 4.0～6 occurred in this region,among which the largest one is the magnitude 6/2 earthquake occurred in the area between Leye,Guangxi Autonomous Region and Luodian,Guizhou Province in 1875. Of these events,15 earthquakes of magnitude 4.0～5.0 occurred on the Youjiang Fault zone. The Tianlin Bagui M5.0 earthquake of 1962 and the Pingguo M5.0 earthquake of 1977 had caused certain damages of basic installations in the regions. Obviously,the Guixi region is an active region of moderate earthquake,and the Youjiang Fault zone is an active belt of moderate earthquake,which plays an important role in the seismicity in Guixi fault block region and in the territory of the Guangxi Autonomous Region. Based on the interpretation and analysis of satellite images,aerophotos,and large-scale topographic maps,as well as field investigation,a line of geologic geomorphic evidence of late Pleistocene activity of the Youjiang Fault zone have been obtained,and the left-lateral displacements on the fault zone have been measured. This paper presents all these results and provides the horizontal and vertical slip rates of the fault zone since mid-late Pleistocene. The Youjiang Fault zone can be divided into 3 segments. They are the west of Bose,Bose-Silin and Silin-Tanluo segments,each of which can be subdivided into several sub-segments. The offset of late Pleistocene terrace deposit and talus can be observed along each segment of the fault zone. The ages of the deposits have been dated to be (3.28±0.25)×10⁴a BP～(10.16±0.79)×10⁴a BP. Geomorphically,the fault zone controlled the development of the Bose-Tiandong late Quaternary basin. A series of fault valleys,troughs,and scarps were developed along the fault strand,while the drainage system crossing the fault zone was left-laterally offset. According to the comparison of the amplitudes of vertical and horizontal displacements on the fault zone,it is inferred that the activity since late Pleistocene of the fault zone has been dominated by left-lateral strike-slipping accompanied by extensional differential motion. The horizontal displacement rate since late Pleistocene on the fault zone has been determined to be 1.47～1.98 mm/a,the vertical displacement rate since middle Pleistocene is 0.74～0.76 mm/a,and the vertical displacement rate since late Pleistoce is 0.1～0.35mm/a. All these values are significantly lower than those on the fault zones surrounding or within the Chuandian fault block. The recent results of GPS observation support also this conclusion.

The Longmenshan Fault zone is an important thrust fault on the eastern margin of the Qinghai-Tibet Plateau.The Cenozoic activity of the fault zone has attracted great attention of many scientists at home and abroad.The Longmenshan Fault zone consists of the Back-range,the Central and the Front-range Faults,which differ from each other in size and activity.Meanwhile,the activity of the whole fault zone is characterized by segmentation.Previous studies on the middle and southern segments of the fault zone showed that these two segments have been active since late Pleistocene.However,little work had been done on the activity of the northern segment of the fault zone so far.In this study,we made a detailed field investigation on the northern segment of the fault Fault and collected many samples from the strata covering the fault or from fault zone materials for TL and ESR dating.According to the observation of the northern segment of the Longmenshan Fault zone and dating results,it can be concluded that the Back-range Fault had once been active in early-mid Quaternary,but has been inactive since late Pleistocene,the Central Fault was active during early Quaternary or pre-Quaternary,and the Front-range Fault was active during pre-Quaternary.They all have been inactive since late Pleistocene.However,the middle and southern segments of the Longmenshan Fault zone have been active since late Quaternary,controlling the development of late-Quaternary basin,and many strong earthquakes occurred in history along these two segments.What has caused the different activities of the different segments of the Longmenshan fault? The main reason might be the change of the construction of the block boundaries due to the variation of the regional stress field in this region.Since mid-Pleistocene,affected by the southeastward moving of the Tibet Plateau,the stress field of the region where the Longmenshan fault zone is located was changed,causing the change of the boundary faults that bound the active blocks.At present,the northern segment of the Longmenshan Fault zone is no longer the boundary fault of the active block,while the uplifting of the Minshan Mountains acts as a protective wall hampering the movement of the Longmenshan fault zone.All these factors have caused the weakening of the activity of the northern segment of the Longmenshan Fault zone.However,the southern and middle segments of the Longmenshan Fault zone,together with the Minshan uplift tectonic zone constitute the eastern border of the compressional system,controlling the development of present topography and strong earthquakes in this region.This recognition may provide useful information for the study of the geodynamics of the Qinghai-Tibet Plateau.

In consideration of the disturbances of the Datong Basin reach of the Sanggan River during late Quaternary time caused by external variables,such as the emplacement of basalts,along-valley faulting processes and climate changes,a conceptual model is developed for distinguishing fluvial incision induced by faulting from that induced by climate.Provided that lava blocking causes the rise of base-level of a river reach,so that stream flow of the reach has sufficient power to incise vertically at an amount equal to the base-level rise,then the bed altitude of the reach will decrease and consequently the gradient of the reach relative to the next upstream reach will also be reduced.Therefore,a supply of flowwith sufficient energy over a long period of time is of great importance to maintain the vertical incision of the reach with rising base-level.Under the prevailing warmer and wetter climate condition during the late Quaternary period in the study area,the establishment of backwater condition in the next upstream reach due to basalt blocking resulted in quick fluvial incision in the lava dam reach;on the other hand,fluvial incision induced by along-valley faulting led the lava dam upstream reach to attaining and maintaining over a long period of time a graded profile,which was able to provide the flowwith sufficient discharges but relatively less sediments for sustaining vertical incision in the lava dam downstream reach.The distinction between the fluvial incision induced by faulting and by climate was made both in quantity and in event.Equilibrium profile analyses prove that displacement produced by along-valley faulting is equal to fluvial incision induced by faulting,allowing us to distinguish fluvial incision induced by faulting from that induced by climate in quantity.Meanwhile,the fluvial incision events caused by faulting and by climate were further distinguished in terms of the reconstruction of the stream operation history recorded by stream terraces.The results indicate that the post-basalt fluvial incision induced by faulting is slightly predominant in the lava dam upstream reach;in contrary,the post-basalt fluvial incision induced by climate plays a leading role in the lava dam reach.It is suggested that the synchronous landforms eventually produced by long-term effects of the adjustment of stream operation in response to the disturbances caused by external variables,can be apparently regarded as the basis for correlating the fluvial incision with aggradation events and for reconstructing the evolutionary history of the stream longitudinal profile in the studied reach.The principal erosion processes in the lava dam reach might have been implemented by knickpoint migration as well as quarrying and abrasion of basalt controlled by structural properties,such as the frequency and orientation of joint and the thickness of basalt bed.

Fault structures are well developed in the Zhujiang Delta area. They can be classified into NW-, NE- and E-W-trending groups, most of which display distinct features of vertical differential movement. Since most of the faults are buried and their activities are relatively weak, the evidence of vertical dislocation are difficult to be identified directly in the field, and hence the amount of displacement along the faults can not be measured. Fortunately, a large number of drill holes have been drilled during the construction of the Zhujiang Delta, and a lot of data concerning the present altitudes above sea level of late Quaternary deposits and their ages have been measured and determined. Basing on the analysis of the formation and evolution of the Zhujiang Delta, we have selected a pair or some pairs of bore holes, which are close in position and may reveal the deposition time and environment of the same strata for comparative analysis. Then the vertical displacements along the faults can be determined according to the differences between the present altitudes above sea level of the same strata on both sides of the faults, and hence the dislocation rates can be calculated based upon the age data. We have calculated the late Quaternary vertical dislocation rates for 5 faults. The results show that the dislocation rates are within the range of 0.14～0.47mm/a. Among them, the vertical dislocation rate of the Xijiang Fault in the past 29,400 years is 0.44mm/a. The vertical dislocation rate of the Baini-Shawan Fault in the past 15,000 years is 0.39mm/a, while that in the past 11,400 years is 0.38mm/a. The vertical dislocation rate of the Gulao-Conghua Fault in the past 29,530 years is 0.47mm/a. The vertical dislocation rate of the Wuguishan north piedmont fault in the past 6,390 years is 0.19mm/a. The vertical dislocation rate of the Shougouling Fault in the past 29,800 years is 0.14mm/a, and that in the past 17,480 years is 0.19～0.21mm/a. All these results are of great importance to the project of detecting the active faults in major cities that will be carried out in the near future.

The Western Jiuquan (Jiuxi) Basin is located in the westernmost part of the Hexi Corridor. The basin is bounded by the Qilian Mountain fault on the south, by Alytn Taugh fault on the north, and by Jiayuguan fault on the east, respectively. The Hexi Corridor is one of the seismically active regions in western China. According to historical records, a large number of strong earthquakes had occurred in this area. Recently, we have discovered three Holocene active faults through the interpretation of aerial photos and field investigation in the Jiuxi basin. These three faults are called Xinminpu, Yinwashan and Yumen faults, respectively. The Xinminpu fault is a Holocene thrust fault, which is 17km in length, striking 315°and dipping southwest, located in the northern part of the basin. A fault scarp of 14m height was developed on the hanging wall of the fault, and it is superposed by the newly formed fault scarp with free surface. The rate of vertical motion along the fault is determined to be 0.24mm/yr. The Yinwashan fault is a Holocene thrust fault located on the alluvial fan at the eastern piedmont of the Yinwashan Mountain, striking 315°with a length of 17km and dipping southwest. The rate of vertical motion along the fault is determined to be 0.18mm/yr. Two Holocene paleoearthquake events have been identified through trenching on the fault. The first event occurred 10.64±0.83ka B.P., while the second event occurred between 4.09±0.31ka B.P. and 8.22±0.63ka B.P. The Yumen fault is also a Holocene thrust fault, which is nearly EW-striking and south dipping, located on the alluvial fan at the northern piedmont of the Qilianshan Mountain. A fault scarp of less than 2m height was developed along the fault. The fault scarp was perhaps produced by a historical earthquake. The rate of vertical motion along the fault is determined to be 0.25mm/yr. Two Holocene paleoearthquakes were revealed by trenching on the fault. The first earthquake occurred at 3.05±0.24 ～3.20±0.25ka B.P. The second occurred after 3.05±0.24ka B.P. As mentioned above, all the three Holocene faults belong to thrust fault, and thus no obvious horizontal displacement can be observed along the fault. This may indicate that this area is dominated by compressional deformation. According to historical records, the Jiuquan earthquake of 756 A.D. is the latest historical earthquake occurred in this area. It is postulated that the Xinminpu fault or Yumen fault would be ruptured during this earthquake, but currently we are unable to determine which fault was ruptured by this earthquake on the basis of available dating data. The ages of paleoearthquakes and the characters of surface ruptures along the three faults suggested that the three faults were activated independently or sometimes in cluster.