Direct Surface Wave Radial Anisotropy Tomography the Crust of the Eastern Himalayan Syntaxis

A novel method is implemented to invert Rayleigh and Love wave dispersion curves of all paths jointly for 3-D shear wave velocity and radial anisotropy simultaneously without intermediate steps. We use the method to derive high-precision crustal shear wave velocity and radial anisotropy models around the eastern Himalayan syntaxis using ambient noise dispersion data (5-40 s). Results show that the crust can be divided into several subregions with different rigidity and preferred mineral alignment orientation depth-dependently. In the middle crust, combined with other geophysical observations, 3-D geometry of two continuous branches of eastward channelized weak zones is outlined in detail. Both branches of the weak zone are blocked by the high velocity zone with radial anisotropy of V-sh > V-sv at around 96-97 degrees E. In the upper crust, the radial anisotropy model depicts a complex pattern, which is associated with the ongoing surface uplifting and shear strain rate distribution.