Seismic Anisotropy Beneath The Four Fixed Station In The Northeast Of Tibet By Receiver Functions

The northeastern margin of the Tibetan Plateau is a large boundary deformationzone, located in the junction of Qinghai-Tibet block, South China block, Ordos blockand Alxa block. It is an active geological units, Its internal developed a number oflarge-scale faults: Altun fault, Qilian fault, Haiyuan fault and so on. Driven bycrashing, extrusion and continuous drifting of Indian plate in the south, andsynchronously prevented by Russian-Siberia platform in the north, the Qinghai-Tibetplateau, on the one hand, absorbs the north-south strong compression through thecrust thickening and shortening, so that it forms complicated structure in the northeastof Qinghai-Tibet plateau. On the other hand, the plateau materials escape to east andwest respectively. However, no matter what the escape way they are, theSichuan-Yunnan regions in the south-eastern Tibetan plateau are the domains wherethe tectonic escape and lower crust flow pass through. Investigating the crust andmantle anisotropy and deformation mechanisms, will be helpful to know the deepstructure, the characteristic of deformation field, the stress-strain field and tectonicprocess and so on. Furthermore, it is very important to make acquaintance of themechanism of the plateau uplift and the escaping of the deep materials.The tele-sesimc events we used in this research were recorded by broadbandseimic stations which are located in Gansu, Shanxi province. We investigate thecrustal thickness and averaged poisson’s ratios beneath the study area of the gridstacking search method of receiver functions. Our inverstion results show that: thecrustal thickness varies from50km to60km, We have extracte the whole crustalseismic anisotropy parameter of4stations near the northeastern margin of the TibetanPlateau by using Receiver Function.The result of fast shear-waves polarization direction are consistent to the trend offault. It suggests that the fault mainly control the anisotropy feature of this area. Thedelay time between fast and slow wave are long. Each station has a delay time longerthan0.3seconds, it means that the degree of crustal seismic anisotropy is high.Composed by the multi-layered crust anisotropy, anisotropy at various depths showed differences. Mantle and crustal anisotropy is different too. Although we only have theresults of four stations, but at least it shows that the crust anisotropy beneath thesestations is significant and cannot be ignored in the whole crust-mantle anisotropy. Wecompare our result with surface wave split result and SKS wave split result and foundthat our result are more consistent with surface wave split result. Preliminarily weconsider the crust and mantle anisotropy formation mechanism may be different in thenortheastern margin of the Tibetan Plateau.