Shear Wave Velocity Noise Tomography Of The Upper And Middle Crust Of Eastern Himalayan Syntaxis

The Eastern Himalayan syntaxis is located in the southeastern part of the Qinghai-Tibet Plateau and the northeastern corner of the Indian continent.It is the southern margin of the compression and collision between the Eurasian plate and the Indian Ocean plate,also known as the Namche Barwa syntaxis.Because the traditional body wave and surface wave tomography method are influenced by the location of the earthquake,earthquake location accuracy and the station distribution,the resolution of the velocity structure obtained is often low,especially for shallow crust;and the receiver function method can only get the crust and upper mantle structure just below the station location.The cross-correlation method of ambient seismic noise emerged in recent years is able to extract the surface wave empirical Green function;ambient seismic noise tomography can overcome the disadvantages mentioned above and by which high resolution information on the velocity structure for shallow crust is obtainable.Therefore,the empirical Green's function is obtained by using the interstation Cross-correlation functions of ambient seismic noise of continuous vertical component of motion of the 51 digital stations located in the northeastern margin of the Himalayan tectonic area laid out by Lihai University in the United States are obtained.The waveform cross-correlation and superposition of these continuous broadband data are carried out,from which the Rayleigh surface wave empirical Green's functions between two pairs of stations are obtained.According to the direct inversion method of surface wave dispersion of three-dimensional shallow crustal structure proposed by Fang Hongjian et al.in 2015,inversion calculation is carried out.The inversion results show that there is a 20 km thick low velocity layer in the middle and upper crust of the Eastern Syntaxis,which is caused by the friction and collision heat of the collision plate on the interface of MHT.Based on this,it is found that there are more strong folds in the EW direction of MHT and local tearing;and this phenomenon is explained;in addition;In addition,we propose a new viewpoint of the North-South uplift of Namche Barwa.