Active faults and earthquake around Yushu in eastern Tibetan Plateau

Yushu area in Qinghai Province is located in the typical historical strong earthquake zone of the southwest border of Bayan Har block in eastern Tibetan Plateau. Recent remote sensing images interpretation and surface survey of regional active faults show that there are four NW-trending left strike-slip active fault belts, i.e., Qingshuihe fault zone, Yushu fault zone, Abuduo fault and Zadoi fault from north to south. The Yushu fault zone is a lithospheric fault, which constitutes the end structure of Yushu-Xianshuihe-Xiaojiang fault system, and its activity was the most significant among four belts during Quaternary. Yushu fault is a typical Z-shaped sinistral shear deformation belt which is composed of three en echelon major strong active fault zones, i.e., Dangjiang fault, Jiegu-Jielong fault and Sangka-Chawukou fault from northwest to southeast, and many secondary weak active faults. The sinistral strike-slip rate of Yushu fault has been steady at about 4.0~5.4mm/a since Pliocene and late Quaternary, and adjusted the most rotation and extrusion deformation of Qiangtang-Qamdo block on the south side of Bayan Har block. So Yushu fault also forms the main seismogenic structure which controls the activity of large earthquakes (Mw≥6.8) in Yushu area. The analytical results of historical earthquake and paleo-earthquake study reveal that at least eleven large earthquake events, including the 2010 Yushu earthquake, have occurred along Jielong-Chawukou segment of Yushu fault zone since about 14530a BP. The in situ average occurrence interval is about millennium, and the maximum interval is up to ca. 3000a. However, after the 1738 earthquake that occurred in northwestern Yushu, the large earthquake event migrated at low frequency along major different segments of Yushu-Garzê fault zone at 50~100a cycle from southeast to northwest. Comprehensive earthquake geological analysis yielded a preliminary result of seismic hazard assessment on Yushu fault zone, which suggests that there are at least six seismic gaps in Yushu fault zone, which obviously make up potential large earthquake hazard in recent future of about one hundred years, and the potential earthquake magnitude is about Mw6.6~7.3. Among six seismic gaps, the relatively higher hazard sections are Dangjiang-Laze segment of Dangjiang fault and Jielong-Yekanuo segment of Jiegu-Jielong fault zone.