The crustal anisotropy and its geodynamical significance of the strong basin-range interaction zone beneath the east margin of Qinghai-Tibet plateau

Abstract

Based on the data of a dense linear array of a passive seismic experiment crossing the Longmenshan Fault in the east margin of Qinghai-Tibet Plateau,we measured the splitting parameters of Moho-converted Ps phases(Pms)for 147 teleseismic events recorded by 28 stations,and then analyzed the crustal anisotropy of this strong basin-range interaction zone.The results demonstrate that the crustal anisotropy of study area has significantly different characteristics in different subregions.On the whole,the splitting time averaged over the Songpan-Ganzi Block is greater than that in Sichuan Basin(～0.28 s vs.～0.16 s).The fast polarization direction(FPD)in Aba Sub-block is nearly consistent with that in Sichuan Basin,but there is a trend of clockwise rotation from the Aba Sub-block in the northwest to the Longmenshan Fault in the southeast.It changes from NNW(-24°)to NNE(13°)till nearly parallel to the strike of Longmenshan Fault.The azimuthal variation of FPD in different blocks indicates that the crustal deformation is accommodated or controlled by the major boundary faults between the blocks.