Activity identification of the buried segment of Liangshan south margin fault in the west of Hanzhong basin

Hanzhong basin is a Cenozoic faulted basin located in the differential uplift region among Qinghai--Xizang plateau, Qinling mountain and Dabashan--Longmenshan. It is a connection hub among them. Based on the analysis of ground geological survey, shallow seismic prospecting and composite drilling geologic profile carried out recently in active fault surveying of Hanzhong, we recognized that there is an active fault in Hanzhong basin, namely the Liangshan south margin fault. Shallow seismic investigation data indicate that this fault cuts many sets of Quaternary strata in Hanzhong city and the offsets are reduced gradually from bottom up. Composite drilling geologic profiles show that this fault breaks sand and gravel strata of the middle and late period of Late Pleistocene. The offset is about six meters. These phenomena show the latest activity age and nature of the Liangshan south margin fault in Hanzhong for the first time.