Relocation of earthquakes in northeastern region of Qinghai-Xizang plateau and characteristics of earthquake activity

The northeastern region of Qinghai-Xizang plateau is the junction part of the Qinghai-Xizang block, Alxa block and Ordos block. To explore tectonic feature of this region 4 study profiles are selected by taking geological background into consideration. The M _L≥3.0 earthquakes located within 40 km on both sides of the selected profiles and M _L≥4.0 earthquakes in the studied region have been relocated. Of the 388 relocated earthquakes, 36% shift their previously determined epicenters by more than 5 km. The amount of relocated earthquake with focal depth determination increases 50% more than that before relocation. In this quasi-trijunction region of the northeastern of Qinghai-Xizang plateau three M≥8 earthquakes occurred historically and microearthquakes are quite active at present, implying a strong tectonic activity persists here to the present day. Foundation item: State Natural Science Foundation (49732095) and National Key Research Development Project (Mechanism and Prediction of Strong Continental Earthquakes) Contribution No. 00FE2013, Institute of Geophysics, China Seismological Bureau.