Abstract: Based on the digital waveforms of ChinArray-Himalaya and Qinghai Seismic Network, we obtained focal mechanism of the Qilian 5.2 earthquake by generalized ploarity and ampliutde technique, and determined locations of its sequence with the reversal-time imaging technique. We analyzed the characteristics of focal mechanisms and source position of Qilian 5.2 earthquake, and spatial distribution of its 64 aftershocks to determine the seismogenic structure. The results show that the origin time of Qilian 5.2 earthquake was at 05:02:38.93s on Nov.23, 2015 and rupture initiation point was at 37.95°N,100.46°E, and depth was 12.4 km. The nodal plane parameters of focal mechanism are strike 108°, dip 44°, rake 40°,and strike 347°, dip 63°, rake 126°, respectively.The parameters of nodal plane Ⅰare close to Tuolaishan fault which is sinistral strike-slip accompanyed by a minor thrust component, and also close to occurrence imaged by aftershocks which dips to SW and dip angle is 48°. The nodal plane Ⅰis earthquake fault plane and Tuolaishan fault is the seismogenic structure of the Qilian 5.2 earthquake.

Key words: Qilian M5.2 earthquake, Time-reversal imaging technique, Generalized polarity and amplitude technique, Seismogenic structure