DISCUSSION ON THE SEISMOGENIC STRUCTURE OF THE 2016 MENYUAN M6.4 EARTHQUAKE IN MENYUAN,QINGHAI

On January 21, 2016, a M6.4 earthquake occurred in Menyuan county, Qinghai Province. Its epicenter is located in the Qilian-Hexi Zoulang tectonic zone, which records several moderate-large historical earthquakes. Previous studies on this event are based on geology, remote sensing data and focal mechanism solutions, lacking analysis on its seismogenic structure. In order to study seismogenic fault plane and seismoteconic style of the earthquake, this work uses data of seismic intensity, aftershocks, and geology to address this issue. Furthermore, we calculate Coulomb stress changes imposed by the 1927 Gulang M8 and 1986 Menyuan M6.4 earthquake on the fault plane of the 2016 Menyuan M6.4 earthquake. The results indicate the early two events have posed distinct impacts on two nodal planes:loading or triggering on nodal plane Ⅰ, and unloading or delay on Ⅱ. In some cases such triggering stress is approaching or up to the threshold value of 0.01 MPa. Combining isoseismals, aftershock distribution, geological structure and different Coulomb stress changes aforementioned, the nodal plane Ⅱ of the source model is considered the seismogenic feature. In conjunction with geophysical data, we establish the seismogenic model of the Menyuan earthquake, which is a positive flower structure in a profile, gentle in the upper and steep in the lower, characterized by thrusting in a strike slipping fault system. This is a possible model for thrusting earthquakes generated by strike-slip faults in a compressional tectonic regime.