The co-seismic rupture is one of the important contents in active tectonic mapping.As the late Quaternary landform is a basic recording medium for the recent deformation of active fault,such as the co-seismic rupture,it is quite useful to acquire the activity information of the active fault from various landforms.We implemented a field work along the southeastern segment of the Xianshuihe Fault,mapped the rupture and excavated some trenches.The preservation characteristics of the surface rupture of the 1786 Moxi earthquake were discussed for the glacial area of the Tibetan plateau,the fluvial and flooding area and seriously eroded area at the margin of the Tibetan plateau,respectively.The cracks and offsets were preserved continuously in the glacial landforms such as the moraines and glacial outwashes along Kangding to Yajiageng segment.As the landforms in the fluvial and flooding area were unstable under strong erosion and rapid deposition,the surface rupture can be discovered in the trenches excavated in Yuejinping village and Ertaizi village with gaps for some previous earthquakes.There was no deposition from the erosion landform to record the surface rupture.We can only infer the earthquake effected area and the ruptured fault from the indirect relationship between landslides and the earthquake strong motion or the fault rupturing.Based on the integrated analysis with the geometry and tectonic setting of the southeastern segment of the Xianshuihe Fault,the Kangding-Tianwan segment of the Xianshuihe Fault was taken as the seismogenic fault of the 1786 Moxi earthquake,and the total length of the rupture is about 80 kilometers.

No earthquake greater than M6 has been documented on the Yilan-Yitong Fault,and no trace of activity since the late pleistocene has been seen either at the northeastern section of the famed Tanlu grand fault zone in eastern China.Thus this fault is recognized active in the early Quaternary and capable of generating moderate quakes.By analyzing high-resolution satellite images and field work,a 70km-long geomorphic scarp in Tonghe County of Heilongjiang Province and a 10km-long geomorphic scarp in Shulan County of Jilin Province were discovered.The scarps are 1～2m high and offset the young terraces.Subsequently,the trench at Tonghe County revealed fault displacement which almost reaches the surface.The uppermost stratum dislocated by the fault is dated to be 1730±40 years B.P.Analysis of geomorphic feature of the fault scarp and the trench profile suggests that an M≥7 paleoearthquake occurred along the fault since 1730±40 B.P.The trench at Shulan County reveals the faulted late Pleistocene stratum covered by stratum dated to be 2360±40 years B.P.All these data suggest that some segments of Yilan-Yitong Fault are active since Holocene and M7 earthquake occurred.So,further detailed research will be necessary to determine the range of the latest activity of this fault,the time of the rupture and recurrence intervals of major earthquakes.These data will be of great significance for earthquake zonation and assessment of seismic risk in this region.

The slip rate decreased at Subei,Shibaocheng and Shulehe regions on the eastern segment of Altyn Fault,the regions called as "singularity points". Subei is one of "singularity points" on the eastern segment of Altyn Fault,and the north of Yemahe Fault in the northeast of Subei is the fault we study in this paper. The fault is located in the northeast of Yemahe Basin. It starts at Erdaogou gully in the east and ends at Niujuan gully,extending along the Yema mountain front and parallel to the Altyn Fault in the direction of NEE on the whole. It separates Sinian from Quaternary gravel layer. There are plenty of left-lateral slip-strike and thrusting geomorphologic phenomena and exposed stratigraphic sections on the sides of gullies. Ridges and gullies are dislocated synchronously.Through more than one month investigation,we obtained the distribution and the geological and geomorphologic characteristics of the fault,measured a series of left-lateral slip gullies,ridges and thrust scarps and got the relevant data. Some samples are also collected. The left-lateral slip of gullies is distributed from 1.3m to 175m,and the height of thrust scarps is from 0.95m to 8.53m. The horizontal averaged slip rate of the fault is calculated to be 1.27?0.18mm/a,and the averaged thrusting rate is 0.4?0.07mm/a. This fault,together with the Danghenanshan thrust fault at its south,resolved part of the movement components of the eastern segment of Altyn Fault.

Haiyuan active fault zone is a main active fault in the northeast boundary of Qing-hai-Xizang plateau. Geologically, mapping of 1:50,000 has been made along the fault zone. The results show that Haiyuan active fault zone, 237km long, striking WNW in its west segment and striking NW in the east segment, has been a strike-slip fault sense since middle-late early Pleistoncene. The horizontal offset is 12-14.5km from middle-late early Pleistocene, with the slip rate of 11.7-19.2mm/a. The strong activity has been going on since the begining of the Holocene, with the sinistral strike slip rate of 6-10mm/a.Haiyuan strike slip fault zone consists of 11 secondary shear faults, mostly left stepping pinnate, partly right stepping pinnate. 8 pull-apart basins and 2 pushed-up blocks were formed along the fault zone. Pull-apart basins showing 2 types of romb and elongated, big ones began to develop in middle Pleistocene, small ones in late Pleistocene. The largest thickness of sediments is greater than 750m. A tensile-shear fault with the sinistral strike-slip was formed in some pull-apart basins.The tensile-shear fault links up two secondary shear faults which control pull-apart basin, intersecting them with low angle. After the formation of this kind fault, pull-apart process of the basin decreased and pull-apart basin gradually became feeble and die. The thrust faults intersecting the secondary shear faults with high angle was formed in the pushing area, appeared as an uplift in topography.A great earthquake of magnitude 8.6 occurred in Haiyuan, in December 16, 1920. The surface ruptures of earthquake can be divided as 15 fracture segments, which developed along secondary shear faults, tensile shear faults on pull-apart basin and boundary normal fault at both ends of pull-apart basin. The horizonal dislocation of 268 values have been measured. The maximum displacement of left-lateral strike-slip is 10-11m.At the southeast end of Haiyuan strike slip fault, a rare end compressional area, which consists of thrust fault zone of east pediment of Liupan Mountain, Madong Mountain fold zone and Xiaoguan Mountain thrust fault zone, striking nearly NS, was formed. The detail mapping and studying have been made on the deformation features of these compressional structure belts and calculation on the amount of crust shortening have been made, and the value is about 12.4-16.7km, which is about equal to the sinistral offset amount of Haiyuan active fault zone.

On the basis of field tectonic mapping and measurement of the water setting displacement, we concluded in this paper that the Xiangshan-Tianjingshan arc fracture zone experienced two different active stages in the Cretaceous, i. e. strongly compression in the beginning and left-lateral strike-slip with compression at the end. The time boundary and cause of transition were analyzed and discussed. The appearance and range of the seismic deformation zone of the 1709 south of Zhongwei M = 7¹/₂ earthquake is also described.