Source Parameters Of The January 21,2016 Menyuan,Qinghai Earthquake

On January 21 2016,an Ms 6.4 earthquake occurred in Menyuan County,Qinghai Province.A large number of houses were damaged and the earthquake caused numerous economic losses.Studying the seismogenic mechanism of this earthquake helps improve the seismic assessment of the epicentral region and explore the spatial damage distribution of moderate thrust earthquakes in further.This paper has carried out a series of studies on the point source and rupture parameters of the Menyuan earthquake.First we collected seismic waveform data recorded by Qinghai,Gansu seismic network and some temporary stations in Qinghai Province,and picked the Pg,Pn,Sg phases manually.Then,we used the HYPOINVERSE-2000 and the Pn/Pg relative location method to determine the relative location between the mainshock and the Ms 4.7 August 13,2016 aftershock.We obtained the relative centroid depths and time-shift information during the CAP inversion.The along-strike rupture directivity of the mainshock was resolved by fitting the waveform time shift with the least-square method.The along-dip rupture directivity of the mainshock was solved by comparing the centroid depth and the hypocenter depth.The results show that the epicenter of the source earthquake is(37.68°N,101.66°E),the focal mechanism solution of nodal plane I is 145°/43°/84°,and the nodal plane II is 334°/47°/96°.The along-strike rupture length is 9.6km,suggesting unilateral rupture in northwest direction.The centroid depth and initial rupture depth of the mainshock are 9km and 10km,respectively,implying that the mainshock ruptured bilaterally along-dip.Combined with the focal mechanism solution of the earthquake,the nature of fault and the regional geological structure,the seismogenic structure of the Menyuan earthquake is considered to be the fault on the north side of the Lenglongling,and the fault tends to be in the southwest direction.We infer that the Menyuan earthquake occurred as the result of long-term stress accumulation via the collision between the Indian plate and the Eurasian plate and the blocking of Ordos and Alxa rigid block.