The Qinghai-Tibetan plateau, with an average altitude of about 5^{}000m, is one of the most intense regions of intraplate deformation in the globe during the Quaternary. However, the very weak field investigation of active faults and incomplete historical earthquake data in the northern Qinghai-Tibet Plateau limit the in-depth understanding of the deformation mechanism of active tectonics and the characteristics of related strong earthquakes in the Qinghai-Tibetan plateau. Based on the comprehensive geological, remote sensing, and seismic data, the active faults in northern Ngari are interpreted in detail, and the Quaternary activity of the normal faults along the western boundary of Kunchuke Co graben in the southern section of the Aru Co graben system, the newly discovered co-seismic surface ruptures, its magnitude and seismogenic time are analyzed. The newly active fault images show that high-density active fault system dominated by the near east-west extension deformation was developed in the north Ngari. The Quaternary active fault system mainly includes near north-south normal faults and the conjugated strike-slip faults composed of the NW and NE strike-slip faults. The density of the normal faults is significantly higher than that of the strike-slip faults in the region. Based on the comprehensive analysis of the Aruko graben system and the latest co-seismic surface rupture along the western boundary of Kunchuke Co Graben. We present two main conclusions. 1)The Aru Co graben system, with a total length of 210 to 220km, is one of the largest extensional fault depression structures in northern Ngari. The graben system contains four secondary graben and half-graben distributed in left-step echelon distribution from south to north and shows obvious segmented activity characteristics. Meima Co-Aru Co graben is the most intense extensional deformation section along the Aru Co graben system during the Quaternary period. The left echelon pattern of the secondary graben in the graben system indicates that there is a right-lateral shear deformation component along the NW-trending graben system in the region. 2)The newly discovered co-seismic surface ruptures along the boundary fault of the western margin of Kunchuke Co Graben in the southern section of the Aru Co graben are typical normal fault-type ruptures. The surface rupture is distributed along the NNW-trending, with an outcrop length of nearly 400m, a maximum vertical displacement of about 0.8m, and an average vertical displacement of about 0.30.4m. Comprehensive historical earthquake records, the freshness of co-seismic surface ruptures, and the magnitude results based on the classic “surface displacement and magnitude” statistical formula, we concluded that the Kunchuke Co surface rupture should be a result of the 1955 M_W6.5 earthquake event, which epicenter of the instrument was located in eastern Nawu Co of Gègyai county, with a focal depth of 35km and small length and displacement. The deep focal depth is a major cause of lead to the co-seismic surface rupture is obviously small-scale. This small-scale surface rupture event on active faults suggests that irregular or random local fault rupture behavior should be paid attention to in the study of the earthquake recurrence model of active faults.

The collision of the Indian plate with Eurasia in the early Cenozoic era drove the emergence of the Tibetan plateau. At the same time, the subduction of the western Pacific plate towards Eurasia resulted in the stretching and thinning of the lithosphere in eastern Asia, leading to a series of faulted basins and marginal seas. The macro-geomorphic pattern of East Asia was finally established under the control of these two tectonic domains. In this case, the Yellow River, which originated from the Tibetan plateau and flowed through the Loess Plateau and the North China Plain, carried a huge amount of detrital material into the Bohai Sea, which played an important role in the regional geochemical cycle, environmental change, sedimentary flux and the diffusion of detrital material in the shelf sea. Therefore, tracing sediment sources in the Yellow River Basin is of great importance for understanding the coupling relationship between uplift and denudation in the northeastern Tibetan plateau, East Asian monsoon evolution, and detrital material accumulation. However, the Yellow River Basin spans multiple climatic and tectonic zones with different provenance areas, so it is particularly critical to select appropriate provenance tracing methods.

Although K-feldspar is more vulnerable to chemical weathering than zircon, it is a widely distributed rock forming mineral and can best represent the provenance characteristics of a certain area. The non-clay minerals in the Yellow River Basin are mainly composed of quartz and feldspar. At the same time, the Pb isotope ratios(²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb)of K-feldspar in different blocks are much different from those of Nd and Sr isotope systems and are often used to construct regional Pb isotope geochemistry province, continental crust evolution, and reconstruct paleocurrent direction, etc. In recent years, detrital K-feldspar Pb isotopic composition has been successfully used to trace the provenance of the Indus, Yangtze and Mississippi Rivers. But this method has not been carried out in the Yellow River Basin. Therefore, we systematically analyzed the detailed K-feldspar Pb isotopic compositions from the Yellow River Basin, and compared the results with the potential source areas to determine the specific source areas. It also can provide basic comparative data for future studies on the formation age of the Yellow River and material source areas of the Loess Plateau and deserts in the northwestern China.

We analyzed 15 samples from the Yellow River Basin and obtained 967 in-situ Pb isotopic results of K-feldspar grains by laser erosion inductively coupled plasma mass spectrometer(LA-MC-ICP-MS). K-feldspar grains in the samples from the Yellow River are angular, subangular and subcircular, with diameters ranging from 20μm to 300μm. The ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of K-feldspar grains from the source of the Yellow River to Lanzhou city range from 20 to 16 and 42 to 36. However, some ratios of ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb of K-feldspar grains from the Lanzhou city range from 23 to 19 and 40 to 37, respectively. The ²⁰⁶Pb/²⁰⁴Pb ratio of most K-feldspar samples in Bayannur city is greater than 19, and the maximum value is 24.79, while this ratio from Hequ and Hancheng cities located in the middle reaches of the Yellow River is less than 18.5. The ²⁰⁶Pb/²⁰⁴Pb ratios of the Mesozoic sandstone near the Hequ city range from 16 to 15. The ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of K-feldspar grains from the Weihe River, which is the largest tributary of the Yellow River, range from 19 to 17 and 40 to 37. The ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of K-feldspar grains in the Fenhe River, Yiluohe River, Kaifeng and Lijin cities range from 21 to 14 and 42 to 33. The comparison results of ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios show that the Pb isotopic compositions of K-feldspar grains in the upper Yellow River, Daxiahe River and Huangshui River are significantly different from those in the Lanzhou city. The Pb isotopic composition of K-feldspar grains from the Yellow River from the Lanzhou city is consistent with that in the Bayannur city, which is influenced by similar eolian provenance. K-feldspar grains from the Yellow River and Fen River in the Jinshan Gorge are mainly from the Loess Plateau. By contrast, the K-feldspar grains in the Weihe River are mainly derived from the Qinling Mountains. The Pb isotopic compositions of K-feldspar grains in the Kaifeng and Lijin cities of the lower Yellow River are different to those in the upper Yellow River and the North China Plate, but similar to those in the middle reaches of the Yellow River. The Loess Plateau plays a leading role in the source of K-feldspar gains in the middle and lower reaches of the Yellow River.

In the interior of the Tibetan Plateau, the active tectonics are primarily marked by conjugate strike slip faults and north-trending rifts, which represent the E-W extension since late Cenozoic of the plateau. The conjugate faults are mainly composed of NE-trending left-lateral strike-slip faults in Qiangtang terrane and NW-trending right-lateral strike-slip faults in Lhasa terrane. While, the rifts mainly strike N, NNW and NNE within southern Tibet. However, it is still a debate on the deformational style and specific adjustment mechanism of E-W extension. One of key reasons causing this debate is the lack of detailed investigation of these active faults, especially within the northwestern plateau. Recently, we found a 20km long, NNW-trending active fault at Bero Zeco in northwestern Tibet. This fault is presented as fault sag ponds, channel offsets and fault scarps. Displacement of channels and geomorphic features suggested that the Bero Zeco Fault(BZF)is a dextral strike-slip fault with a small amount of normal slip component, which may result from the E-W extensional deformation in the interior of Tibet. BZF strikes N330°~340°W, as shown on the satellite image. The main Quaternary strata in the studied area are two stages alluvial fans around the Bero Zeco. From the satellite images, the old alluvial fans were cut by the lake shoreline leaving many of lake terraces. And the young fans cut across the lake terraces and the old fans. By contrasting to the "Paleo-Qiangtang Huge Lake" since late Quaternary, these old alluvial fans could be late Pleistocene with age ranging from 40ka to 50ka. And the young fans could be Holocene. The sag ponds along the BZF are distributed in the late Pleistocene alluvial fans. Also, the BZF displaced the late Pleistocene fans without traces within Holocene fans, suggesting that the BZF is a late Pleistocene active fault. The fault scarps are gentler with the slope angle of around 10° and the vertical offset is about 2m by field measurement. Reconstruction of the offset of channels suggested that the accumulated dextral offset could be about 44m on the late Pleistocene alluvial fans. Therefore, we infer that the dextral slip-rate could be around 1mm/a showing a low-rate deformation characteristic. The angle between the strike of BZF and principal compressive stress axis(σ₁)is around 30°, which is significantly different to the other faults within the conjugate strike-slip fault zones that is 60°~75°. Now, the deformation mechanisms on these conjugate faults are mainly proposed in the studies of obtuse angle between the faults and σ₁, which is likely not applicable for the BZF. We infer that the BZF could be the northward prolongation of the north-trending rifts based on the geometry. This difference suggests that the conjugate strike-slip faults may be formed by two different groups:one is obtuse angle, which is related to block extrusion or shear zones in Lhasa and Qiangtang terranes possibly; the other is acute angle, which may represent the characteristics of new-born fractures. And more studies are needed on their deformation mechanisms.

It is crucial to reveal the surface traces and activity of active faults by obtaining high-precision microtopography and three-dimensional shallow geometry. However, limited by the traditional geological investigation methods in the field and geological condition factors, the measurement method on microtopography and shallow geometry of active fault is badly insufficient. In this study, the TLS and GPR are firstly used comprehensively to delineate the microtopography and shallow geometry of the normal fault scarp on the north margin of Maoyaba Basin in Litang. Firstly, the vertical displacements of two landforms produced by the latest two periods of normal faulting and the two-dimensional GPR profiles are obtained separately. Secondly, the three-dimensional measurement method of active fault based on TLS and GPR is preliminarily established. On this basis, three-dimensional model of fault scarp and three-dimensional images of subsurface geometry are also obtained. These data all reveal a graben structure at normal fault scarps. Thirdly, the fusion and interpretation of three-dimensional data from the surface and subsurface are realized. The study results show:1)the vertical displacements of the T₁ and T₂ terraces by the normal fault movement is 1.4m and 5.7m, the GPR profile shows a typical fault structure and indicates the existence of small graben structure with a maximum width of about 40m in the shallow layer, which further proves that it is a normal fault. 2)the shallow geometry of the normal fault scarp can be more graphically displayed by the three-dimensional radar images, and it also makes the geometry structure of the fault more comprehensive. The precise location and strike of faults F₁ and F₂ on the horizontal surface are also determined in the three-dimensional radar images, which further proves the existence of small graben structure, indicating the extensional deformation characteristics in the subsurface of the fault scarps. Furthermore, the distribution of small graben structure on the surface and subsurface is defined more precisely. 3)the integrated display of microgeomorphology and shallow geometry of normal fault scarp is realized based on the three-dimensional point cloud and GPR data. The fusion of the point cloud and GPR data has obvious advantages, for the spatial structure, morphological and spectral features from the point cloud can improve the recognition and interpretation accuracy of GPR images. The interpreted results of the GPR profiles could minimize the transformation of the surface topography by the external environment at the most extent, restore the original geomorphology, relocate the position and trend of faults on the surface and constrain the width of deformation zones under the surface, the geological structure, and the fault dislocation, etc.
In a word, the TLS and GPR can quickly and efficiently provide the spatial data with multi-level and multi-visual for non-destructive inspection of the microgeomorphology and shallow structure for the active fault in a wide range, and for the detection of active fault in the complex geological environments, and it is helpful to improve the accuracy and understanding of the investigation and research on microtopography and shallow geometry of active faults. What's more, it also offers important data and method for more comprehensive identification and understanding of the distribution, deformation features, the behaviors of active faults and multi-period paleoseismicity. Therefore, to continuously explore and improve this method will significantly enhance and expand the practicability and application prospects of the method in the quantitative and elaborate studies of active faults.

In 2010, the M_S7.1 earthquake in Yushu, Qinghai Provence caused an obvious phenomenon of earthquake-generated rockfall in many places along the seismogenic fault zone. In the course of surface investigation, it was found that in several typical development areas of latest earthquake-generated rockfall, there are entirely multi-period in-situ recurrent earthquake-generated rockfalls with most typical characteristics. It is so common with thin calcareous coats on the surface of earthquake-generated rock fall. On the basis of systematic sampling for the calcareous coats, which are on the surface of earthquake-generated rock fall in several typical distribution areas near the Yushu active fault belt, the author made an attempt on U-series dating analysis for calcareous coats of the earthquake-generated rock fall, by applying dilute acid leaching method. The ages are mainly distributed in the range of about 69 980a BP, 36 300a BP, 14 900~12 700a BP, 6 030a BP, 4 720a BP, 3 560~3 530a BP, 2 010~1 090a BP, about 760a BP and 230 a BP. This result tallies basically with the multi-period characteristic of earthquake-generated rock fall by surface observation, and primarily with the seismic events reflected from paleo-earthquake trench and paleo-earthquake landslide. It is preliminary confirmed that the development of rock fall near the Yushu Fault zone is of obvious multi-period, and the multi-period rock fall is in close genetic relationship with paleo-earthquake activities. In addition, combined with results of field investigation and the data of paleo-seismic research, it can be judged that the phenomenon of several extensive earthquake-generated rock falls is mainly a reflection of larger intensity of paleo-earthquake events since the late of Q³_p period, of which the paleo-earthquake events occurring in about 3 560~3 530a BP and 14 900~12 700a BP may be the biggest. The exploratory research on U series dating method for calcareous coats in Yushu earthquake-generated rock fall may provide a new way for the future study of paleo-earthquake activity in active tectonic region.

Detailed mapping shows that there are two segments of co-seismic surface ruptures on the Litang-Dewu left-lateral strike-slip fault. The north segment is about 25km long, with a strike about 135°NE. The maximum horizontal left-lateral displacement on the north one is~1.8m and located at the high floodplains on the north side of the Wuliang River near Cun'ge village, offsetting the linear ridges that were left behind by human activity. The south segment is about 41km, striking generally about 146°NE. The maximum horizontal left-lateral displacement is located at the piedmont near the north side of the Rongjia mountain pass and the river floodplain scarp here is offset about 3.2m. There is a surface rupture gap about 11km between these two co-seismic surface rupture segments. The distribution of the co-seismic surface ruptures acquired by detailed mapping in the field survey, the earthquake event revealed by the trench, the AMS-¹⁴C dating result, the historical records of earthquakes at least since AD 1729 in the study area and the visiting on the local people, show consistently that the northern co-seismic surface rupture segment is most possibly produced by the 1729 Litang earthquake. The 1948 Litang earthquake was only responsible for the southern surface rupture segment. However, if only according to the 2 sigma calendar calibrated results of ¹⁴C dating, it cannot be excluded the possibility that the north segment maybe was produced by some older large earthquake occurring at some time during the AD 1420 to AD 1690. The moment magnitude(M_W)of the 1729 earthquake is about 6.7 and that of the 1948 earthquake is about 7.0 calculated from the empirical relations between the earthquake magnitude and the rupture length.

The Cona-Oiga rift zone is N10～12°E trending,about 220km long,and is the only rift located at the east of Yadong-Gulu rift in southern Tibet. It is located around 92°E and between 27°40'N and 29°40'N and cuts the south Tibet Detachment into High Himalaya block to the south and strides across Yarlung Tsangpo Fault(or Great Counter Thrust fault)into eastern Gangdese batholith zone to the north. There are 3 independent grabens contained in the rift. They are Oiga graben,Qungdo'gyang graben and Cona graben from north to south. The earthquake activity is very prominent along the rift. There are two large earthquakes of M7.5 and M7.0 occurring at northern Cona in 1806 and southern Oiga in 1915, respectively. In the rift,late Quaternary tills and fluvioglacial deposits may be divided into 4 sets corresponding to the so-called Nyanyxungla Ice Age,Jilongshi Ice Age,Ronbushi Ice Age and Holocene glaciations respectively from oldest to youngest. Their TL and U-series ages show that the first(or the oldest)tills formed before marine isotope stage(MIS)6,the second tills formed during about 200～140ka BP,the third and fourth tills formed during the last Glacial maximum(about 28～15ka BP)and Holocene glaciations respectively.The Oiga graben is located at the north of Yarlung Tsangpo Fault. It is about 50km long and widens from 3～5km in the south to 15～18km in the north. The graben is limited to the east and west by two N 18±1°E-trending boundary normal faults of opposite dips, indicating that the extension direction is 108±1° in the region. Field survey shows that the master boundary fault is the eastern margin fault of Oiga Basin which has been active from Quaternary or Pliocene to Holocene. The boundary fault shows obvious activity during late Pleistocene. Based on measurement of fault scarp,the vertical displacements are 50～90m, (24.0±1.5)m, (16.0±1.0)m or (13.7±0.5)m and (3.7±0.4)m since MIS6,24～18ka BP and 15～11ka BP since middle-late Holocene, respectively. Given such displacements and ages of fault scarps,the average throw rates are limited between 0.4～0.9mm/a since MIS6,and about (1.2±0.3)mm/a since MIS2. The Qungdo'gyang graben is a N18°E-trending and 11～20km-wide basin. It cuts across the eastern segment of Yala Xiangbo gneiss dome and is a half-graben limited by the west boundary fault which is a N 18±1°E-trending,east dipping and about 40km long normal fault. It has been active since Pliocene. Based on measurement of late Quaternary fault scarp,the vertical displacements are (29.8±1.0)m and (12.0±0.5)m since about 28～15ka BP, (4.6±0.4)m and (7.0±0.7)m since middle-late Holocene, respectively,and the most probably values of throw rates of main boundary fault aren't less than about 0.5mm/a,and the average throw rate is about 1.0～1.5mm/a since MIS2. The Cona graben is a north-trending basin,about 80km long and 1～10km wide. Its main boundary fault is located on the western margin of basin. It is a N-trending and east dipping normal fault, about 110km long. Based on measurement of fault scarp offset tills and fluviaoglacial terraces,the displacements are 44～80m, (27±1)m and (15.5±0.5)m since MIS6,24～18kaBP and 15～11kaBP, respectively. The average vertical throw rates are between 0.3～0.8mm/a and about (1.3±0.3)mm/a since MIS6 and MIS2 respectively. The late Quaternary throw rates show consistency and constrain the uniform long-term slip rate along Cona-Oiga rift. The obvious increase of throw rate during Holocene most probably results from earthquake cluster in Holocene along the rift.This new observation on Cona-Oiga rift shows that the extension direction of rifts is strictly limited to 100° in southern Tibet,and is parallel with Yadong-Gulu rift. The long-term and short-term slip rates of main bounding normal faults of Cona-Oiga rift are also distinctly similar to the throw rates of Yadong-Gulu graben system. The strict geometry pattern,pronounced similar and consistent to the active magnitude and trend of bounding normal faults in southern Tibet suggests that the N-trending rifts most probably result from the uniform extension deformation controlled by middle-lower crust lateral flow or extension parallel to orogen caused by India lithosphere insert under south Tibet.

The M_S 5.6 earthquake occurred in Amdo county of central Tibet on March 7,2004.The epicenter is 31.68°N,91.31°E and 31.64°N,91.24°E from CENC(China Earthquake Netwosks Center)and NEIC(National Earthquake Information Center of America)respectively(Fig.1).It is the maximum magnitude earthquake near Golmud-Lhasa railway after the 2001 M_S 8.1 Kunlun earthquake.Based on field intensity susveying,the iso-seismal contours map of the earthquake was drawn.The map shows that iso-seismal lines for the earthquake are NNE-trending and the area of the same intensity is larger to north and west than to south and east(Fig.2).Its maximum intensity is Ⅶ and lies between Gongbatang and Jianong at the east of Dung Co Lake(Photo 1,2),so this earthquake is called the 2004 M_S 5.6 Dung Co earthquake.The intensity survey results suggest that the macroscopic epicenter is 31.70°N,91.26°E,which approximately coincides with the epicenter located based on instrument monitoring.The distribution of intensity indicates the earthquake probably results from faulting of NNE-trending fault zone along the eastern margin of the Dung Co basin.The results of active faults survey confirm that the fault zone controlling the earthquake is a main boundary normal fault zone of the Dung Co basin and called the eastern boundary fault zone of the NNE-trending Dung Co basin,which is a half graben about 10～15km wide and 40km long,connecting with the NNE-trending Peng Co basin to the south and adjacent to the NE-trending Tsona-Amdo graben to the north.The boundary fault zone of Dung Co graben is NNE-trending,about 40km long and composed of three minor normal faults,all dipping to west and forming a right-stepped en echelon array indicating the left lateral strike-slip component of the fault zone(Fig.3).Surface observation along the faults shows that the fault underwent prominent normal faulting during late Quaternary.The severe faulting is expressed by the prominent northwest facing triangular facets along mountain front and multiple generations of fault scarps in late Quaternary sediments(Photo 5～7).The results of in-suit measurement with level instrument and tape show that there are three sets of fluvial terrace surfaces and a piedmont slope that were vertically offset by 1～1.2m(terrace 0～1 and 0～2),2～3m(terrace 1)and 13～19m(or piedmont slope)along the northern segment of the fault zone,respectively;and there are three sets of fluvial terrace surfaces which were vertically offset by 0.5～0.7m(terrace 1),2～3m(terrace 2)and 12～15m(terrace 3)along the central segment of the fault zone,respectively.The offset of terraces all took place during late Pleistocene and Holocene,implying that the normal faulting has continued and the average rate of vertical displacement is estimated as 0.2±0.1mm/a and about 0.06mm/a on the northern and central segment respectively since late Pleistocene based on the relationship between the terraces evolution and climate change during late Quaternary and comparing the distributions of similar terraces in the adjacent areas of Dung Co.Along the northern segment of fault zone,a ～6km long surface rupture,which offset the terrace 0～1 and terrace 0～2 of late Holocene,was discovered,indicating the latest paleo-earthquake event since late Holocene.The vertical displacement is 1.0～1.2m across the surface rupture,which represents the minimum offset during the last paleo-earthquake event on the northern segment(Photo 6).In space,the central segment of the eastern margin fault zone of Dung Co graben coincides with the maximum intensity area of the 2004 M_S 5.6 Dung Co earthquake.It indicates that the earthquake results from the normal faulting along the central section of the fault zone.The results of field survey are in agreement with the fault plane solution from CENC,but are inconsistent with the focal mechanism solution from HRV.It suggests the results from CENC are reasonable for explaining the 2004 M_S 5.6 Dung Co earthquake.Studies on regional tectonics and distribution features of earthquake suggest that the NNE-trending Peng Co basin,Dung Co graben,and Amdo-Tsona basin make up apparently of a regular left-lateral en echelon distributed rift system trending N35°～45°E from south to north,about 120 long(Fig.1).This rift zone constitutes a NNE-trending seismic zone called Dung Co-Amdo earthquake zone.The magnitude of late Quaternary faulting varies remarkably along different segments of Dung Co-Amdo seismic zone.Based on field survey,the vertical slip rates on the northern segment of Dung Co fault zone and the western segment of northern boundary fault zone of Amdo-Tsona graben are much faster than that of the central-southern segment of Dung Co fault and eastern segment of Amdo-Tsona northern boundary fault,and there are records about paleo-earthquakes of late Holocene along the two fault segments,but recent earthquakes(M_S≥3)since 1971 are almost distributed around the central-southern segment of Dung Co basin and eastern segment of Amdo-Tsona graben.The prominent differences indicate that the southern segment of Dung Co fault zone and the eastern segment of northern boundary fault zone of Amdo-Tsona graben are the sites where future earthquake will possibly occur because the strain accumulating time is longer at these areas.

The north-south-trending Wenquan graben is located to the north of Tanggula Mountains in central Qinghai-Tibet Plateau,having a length of about 40km and a width of 8～12km. The graben is filled with Quaternary moraine,fluvioglacial deposits and alluvia. An east-dipping boundary normal fault of about 45km length is developed along the western margin of the graben,where the relief is dramatically varied. The fault offsets vertically the bedrock,alluvial fan,river terraces and travertine platform. On the upthrown side of the fault,there are 4 prominent fault facets,which are ～600m,～400m,～200m,and ～80m above the surface of piedmont plain,respectively. At the base of fault facets,sustained faulting has given rise to the formation of east-facing fault scarps and surface ruptures that cut the terraces,alluvial fans and travertine platform. Leveling survey and in-situ measurement with tape measure show that the 6 sets of fault scarps are about 0 3～0.6m,4～5m,8±1m,15±3m,24±4m and 45±5m in height,respectively,and that the higher the scarp,the older the strata cut by the scarp. Among them,the 0.3～0.6m high fault scarp might be associated with M_S6～7 earthquake of middle-late Holocene,the 4～5m and 8±1m fault scarps offset separately the terraces Ⅰ and Ⅱ,while the 15±3m,24±4m and 45±5m high fault scarps offset separately the terrace Ⅲ,Ⅳ,Ⅴ and travertine platform. U-series dating results indicate that the fault scarp that offsets the terracesⅠand Ⅱ was formed 11～7ka BP,the scarp that offsets the terraces Ⅲ was formed 21～25ka BP,and the scarps that offset the terrace Ⅳ and Ⅴ and the correlated travertine platform were formed 45 2～53 6ka BP and 103～127ka BP,respectively. The 80～200m high scarps might be formed since 324～521ka BP. Moreover,the dating results suggest also that the average vertical slip rate along the normal fault on the western side of the Wenquan graben is 0.45mm/a with the maximum value of less than 1.2mm/a. The relief across the normal fault indicates that the minimum cumulative displacement on the fault is about 2.1km. The maximum cumulative throws on the fault is about 8.2km. The trenching across the fault revealed that at least 3 paleoseismic events have occurred along the fault since late Pleistocene. The magnitude of those events can be estimated to be M_S6～7 and the approximate recurrence interval to be from about 400 to 3000yr. The slip rate on normal fault from Wenquan graben implies that the east-west extension rate absorbed by a single graben in central Tibet is significantly lower than that of the grabens in southern Tibet,but this does not imply that the east-west extension rate in central Tibet must be significantly lower than that in southern Tibet. This is because that the east-west extension in central Tibet might be accommodated by a larger number of normal and strike-slip faults distributed in this area. On the basis of the total cumulative throws and the average vertical slip rate on the fault,it is inferred that the initiation time of the normal faulting to be at about 18 2～1 8Ma BP. The broad similarities in the magnitude of slip,the direction of extension and the initiation time of normal faulting in both central and southern Qinghai-Tibet Pateau imply that the east-west extension within the Qinghai-Tibet Plateau has occurred synchronously,and that the crustal thickness in central and southern Tibet Plateau has reached its maximum value since Miocene,while the whole Plateau has reached its present elevation.