Radial anisotropy in the crust of SE Tibet and SW China from ambient noise interferometry

Abstract

We use Rayleigh and Love wave Green's functions estimated from ambient seismic noise to study crustal structure and radial anisotropy in the tectonically complex and seismically active region west of the Sichuan Basin and around the Eastern Himalaya Syntaxis. In agreement with previous studies, low velocity zones are ubiquitous in the mid-lower crust, with substantial variations both laterally and vertically. Discrepancies between 3-D shear velocity from either Rayleigh (V[subscript SV]) or Love (V[subscript SH]) waves are examined both in view of non-uniqueness of tomographic solutions and radial anisotropy. Low shear wave speed and radial anisotropy with V[subscript SH] > V[subscript SV] are most prominent in mid-lower crust in area northwest to the Lijiang-Muli fault and around the Red River and Xiaojiang faults. This anisotropy could be caused by sub-horizontal mica fabric and its association with low velocity zones suggests mica alignment due to flow in deep crustal zones of relatively low mechanical strength.