Shear Wave Splitting In The West Nanling Area

Based on enough reading and study about shear-wave splitting,we research of anisotropy in western Nanling.The western Nanling is an important part of southwestern Qin-Hang Metallogenic belt and its adjacent area.It almost converges all the controversial earth science problem.For example,(1)where is the accurate collision belt of the Cathaysia and Yangtze blocks;(2)How to make it clear that the geodynamic model of geotectonic evolution in southwestern Qin-Hang Metallogenic belt,etc.The seismograms we used in this research were recorded by 63 broadband seismic stations located in western Nanling.The time span of the events were between the October of 2014 and the October of 2016.According to the USGS earthquake catalogue,we picked out 388 events that contain high S/N ratio and clear phases by the Seis Man,a seismic processing system compile by the Guilin University of Tecnology.And then,we used the Splitlab,which was developed by Wustefeld,to calculate the shear-wave splitting parameters' spatial characteristics of the study area.Finally,based on the temporal variation of polarization directions in the study area,we find the delay time of the slow shear-waves is between 0.5s and 0.9s.And the polarization direction of the fast shear-waves at stations located at the west region is nearly complex,and is NWW-SEE at the southeast of Yunkai area,and it shows NW-SE mostly in the Xiang-Gui sunken area.The delay time shows that the anisotropy in the western Nanling likely be the result of mineral grains' alignment under the crust and mantle.Part of stations' fast shear-waves directions is paralleled by the fault under stations,it indicates that the fault could affect the stations' fast shear-waves directions.Combined with the anisotropic character and the Tectonic stress and evolution in the study area,we can partly conclude that there existed a deep fracture between the Beihai and Guilin;the fast shear-waves directions is distinctly different in the both sides of the fault,so it should be the collision belt of the Cathaysia and Yangtze blocks.