The southern Alashan margin fault bundle is composed of 5 faults which strike EW, converge westward and splay eastward. Each fault of the fault bundle extends more than the 100km, controls the distribution of EW-trending Quaternary basins, and is featured with sinistral slip since the late Quaternary. The western part of the fault bundle-the Jintananshan Fault, tends to meet with the Kuantanshan Fault-the east part of the Altun Fault and has some relations to the Wenzhushan uplift in the transformation. According the spatial correlation, it is believed that the Jintananshan Fault as well as the whole fault bundle is the eastward-extending part of the Altun Fault. The special modality of the fault bundle, which spreads out eastwards, is in favor of decomposing and absorbing the slip movement, which is normal at a strike-slip fault's ends. The sinistral strike-slip movement of the fault bundle is the result of the Altun Fault extending further eastward, which might have begun between the end of the early Pleistocene and the beginning of the middle Pleistocene.

The Toupo Fault,located in the southern Anhui Province,strikes N60°～70°E in a linear route that is clear on satellite image. It plays an important role in controlling the tectonics,topography and distribution of Mesozoic-Cenozoic basins and strata. Detailed field investigation was carried out along the Toupo Fault about its activity. Profiles as well as a trench excavated reveal that the Quaternary superstratum above the fault has not been offset. The stratum was sampled and dated with TL methods to be the Mid-Pleistocene time,implying that the fault has been no longer active since then. Three stages can be divided since the fault was formed,namely,the first stage (late Yanshan Movement),when the fault movement was of reversal left-lateral strike-slipping and the tracks formed then are still clear today; the second stage (early Himalayan Movement-the late Cretaceous-early Tertiary),when the fault movement turned to be normal faulting and the southern wall became a tensile basin and received clastic sediments; and the third stage (since the late Tertiary),when the tectonic movement was very week. No late Tertiary sediments were formed and the Quaternary sediment is only as thick as tens meters. The topography also suggests an old-age form. Neither vertical nor horizontal displacement was evident along Toupo Fault during this stage,though fault gouge dating suggests the Toupo Fault might have been active during the Middle Pleistocene.

As the northern boundary of the Tibet Plateau,the Altun Fault runs more than 1500km from Lazhuglung,Tibet Autonomous Region to Kuantanshan,Gansu Province,separating the Tibet Plateau from the Tarim Basin.The fault is one of the longest strike-slip faults in China,and the research of it may provide important information about the formation and evolution processes of the Tibet Plateau. The displacement and slip-rate of the Altun Fault is a topic full of disputation.Because of its significance to the formation and evolution of the Tibet Plateau,different estimates of slip-rates and displacement on the Altun Fault have been proposed in various models of the evolution of the Tibet Plateau. This paper focuses on the late Quaternary slip-rate on the Altun Fault west to the Qarqan River.On the basis of the analysis of SPOT images of this region,three typical sites including Koramlik,Aqqan pasture and Dalakuansayi were chosen for field investigation.To calculate the slip-rate of the fault,displacement of terraces were measured on SPOT satellite images or in-situ during the fieldwork,and the ages were dated by thermo-luminescence method.To get the ages of terraces,samples of sand were collected from the uppermost sand beds just beneath the loess.The method of calculating the slip-rate of a fault is to divide the displacement of a ridge lies between two neighboring terraces of one river by the age of the lower terrace.The displacements of rivers are not considered in this study because of its uncertainty. At Koramlik,the slip-rate of the Altun Fault since6.02?0.47ka BP is11.6?2.6mm/yr,and since15.76?1.19ka BP is9.6?2.6mm/yr. At Aqqan pasture about30km to the west of Koramlik,the slip-rate of the fault since2.06?0.16ka BP is12.1?1.9mm/yr. At Dalakuansayi,the slip-rate of the fault since4.91?0.39ka BP is12.2?3.0mm/yr. The average slip-rate of all above is11.4?2.5mm/yr,which is the average slip-rate of the western segment of the Altun Fault since Holocene.This result is close to the latest results from GPS research.

Identifying correctly the segmentation of an active fault is very important for the evaluation of earthquake hazard on this fault. In a fault system, earthquake rupture occur on different segments of the fault, resulting in the segmentation of the fault system. The segmentation of a fault, therefore, may reflect the propagation process of earthquake rupture, and may provide an insight into the development process and seismic behavior of the fault. The segmentation of a fault system can be identified through different methods, among which the most practical one is to identify the segments by using surface ruptures, which is the direct product of earthquake faulting. This paper deals mainly with the segmentation of the surface rupture on the eastern segment of the Altyn Tagh Fault zone. The Altyn Tagh Fault is one of the major east west trending strike slip faults in China. It is the northern boundary of the Qinghai Tibet Plateau, and its linear character is very conspicuous on satellite images. Basing on the offset landforms observed during fieldwork and spot images analysis of the eastern Altyn Tagh Fault, we divide the eastern Altyn Tagh Fault into three segments from west to east according to its surface ruptures: (1) Qingyazi-Lucaowan segment. The extension of the fault on this segment is simple and its sinistral strike slip motion can be recognized from the offsets of streams, alluvial fans and terrace ridges. Here the youngest terraces of 5.24?0.40ka B.P. in age are offset by the fault, indicating that the latest earthquake on the segment is younger than 5.24?0.40ka B.P. (2) Lucaowan-northern Qilianshan segment. The length of this segment is about 250km. By analyzing the offset landforms and combining with the previous results of paleoearthquake research, we find that the youngest terraces here are not offset by the fault, and we conclude that the latest earthquake on the segment occurred at about 7.080?0.57ka B.P. (3) East of the north Qilianshan segment. The displacement of the fault on this segment is much smaller than those on the other segments, and the fault trace disappears gradually eastward. Here the youngest terraces are offset by the fault, and we estimate that the age of the last earthquake on this segment is younger than 5ka B.P.

On 14 November 2001, an extraordinarily large earthquake occurred on the Hoh Sai Hu segment of the Eastern Kunlun Fault, northern Tibetan Plateau. This event, named as Hoh Sai Hu (Kunlanshan) Earthquake, is the largest earthquake occurred in China continent for the past 50 years. The moment magnitude of this earthquake reaches 7.7 to 7.9 (USGS National Earthquake Information Center, 2001; Harvard CMT Catalog, 2001) and the surface wave magnitude reaches 8.1 (China Digital Seismic Network, 2001). Field investigation indicates that the surface rupture zone produced by this earthquake is striking N80°±10°W with a length of 350 km, which initiates from 91°E in the west nearby the east of Buka Daban Feng, a snow-capped summit with an altitude of 6 800m, extends eastwards along the fault traces of the Hoh Sai Hu segment, and terminates at the 94.8°E in the east. The surface ruptures of this earthquake consist of shear fractures, transtensional fractures, tension gashes and mole tracks arranged in en echelon. The shear fractures are N80°～90°W trending and dominated by left-lateral slip. Transtenssional fractures are several to tens meters long, the strike of which varies from N62°E to N65°E or from N70°E to N75°E, and are dominated by left-lateral slip with a component of tensile opening, the width of which decreases with depth. The shear and/or transtensional fractures are arranged in left-stepping or right-stepping to form releasing or restraining steps, on which tension gashes or mole tracks are developed. Tension gashes strike N45°～50°E and are developed at a releasing step to connect with the boundary shear or transtensional fractures which constrain the step in most cases. The tension gashes may also be arranged in en echelon pattern along the surface rupture zone, and especially at the termination of the surface ruptures. The mole tracks of 1.5 to 3 m height are trending 295°to 330°, which are well developed at the right-steps of the shear and/or transtensional fractures of different scales along the surface rupture zone. This surface rupture pattern appears to be purely strike-slip characterized by several meters of left-lateral offset. The maximum left-lateral offset we observed reaches 6 m at a site (93°05.384’E, 35°47.623’N), where a shallow channel bed was left-laterally offset by a single pure shear fracture. The macroscopic epicenter of the Hoh Sai Hu (Kunlunshan) earthquake is then inferred to be located at the piedmont area to the northeast of Hoh Sai Hu Lake, about 80 to 90km west of Kunlunshan Pass, in terms of the features of surface ruptures. It is postulated that this earthquake may trigger the occurrence of future large earthquake on the Dongdatan-Xidatan segment to the east of the Hoh Sai Hu segment of the Eastern Kunlunshan Fault,reflecting the eastward motion or flowing of the Tibetan Plateau along the fault.