CHARACTER OF LATE QUATERNARY ACTIVITY OF THE EAST SEGMENT OF THE FRONT-EDGE FAULTS OF KALPINTAG

Based on a lot of outcrop geological surveys, we discussed the thrust fault belt in the front of the east section of Kalpintag in Kalpin area and found many evidences, including the fault incising the surface of diluvium and fluvial channel sediments and terraces, and also the fracture and subsection character of the faults. The evidences indicate that the frontal fault of the Kalpintag is an active thrust-fault of low angle. According to the interpretation and analysis of the satellite image and field investigation, we analyzed the geometry structure of the fault. Many samples in several trenches are used to date the diluvium and fluvial channel sediments and terraces and the sections of the fault scarps at 7 observation points in the field were measured too. Using these data we estimated the slip rate of the fault. The research results implicate that the front edge fault of the east section of kalpintag is divided into two arc segments: from west to east, the first segment is from Bachulinkuang to Sanchakou, and the other segment is from Sanchakou to east of Qionggemandaoban. The Wudaoban, Sanjianfang and Dashankoudaoban are at the crest of the arc of the fault which incises the surface of T_1 and T_2 dilu￣vium and terraces, the horizontal averaged shortening rate of the fault is 0.35～0.44mm/a since Holo￣cene and 0.16～0.30mm/a in the late Pleistocene to Holocene. The neotectonic movement at these sites is strong. Whereas the fault only incises T_3 diluvium at such sites as Bachulinkuang, the north of Sanchakou and Dashankou which are not at the crest of the arc of the fault. The horizontal averaged shortening rate in these areas is 0.05～0.07mm/a since late Pleistocene, being smaller than that of other sites.