CHARACTERISTICS OF QUATERNARY ACTIVITIES OF THE GARZÊ-YUSHU FAULT ZONE

The Garzê-Yushu fault zone,lying at the southern end of the Xijir Ulan LakeYushu fault zone,is the northwestward extension of the Xianshuihe fault sensu lato and the northern boundary of the eastward extrusion of the Sichuan-Yunnan rhombic block of the Qinghai-Tibet Plateau.Its structure is complicated.According to the difference in character of its activities,it is divided into three segments.The south segment is composed of a set of echelon sinistral faults and the fault activity gave rise to the Garzê pull-apart basin.The seismic activity is strong at the Yanqiao area.The central segment is mainly characterized by strong strike-slip movement and a number of downfaulted basins occur at the north side of the fault.There has been no earthquake record until now.The north segment,which turns north from Dengke,consists of the principal fault and a number of feather faults that intersect the main faults obliquely,with sinistral strike-slip faults predominating.The downfaulted basins related to the fault are located at the western side of the fault.The seismic activities are scattered and weak.The fault valley of the Yushu-Zhuqing segment of the fault zone is the only way for the water diversion line from the Jinsha River to Yarlung River in the west line of the south-north water diversion project,where strong fault activities and resulting wide fracture zone will cause great difficulty to the operations of the project.