CRUSTAL ANISOTROPY BENEATH SOUTH-CENTRAL TIBET REVEALED BY P-TO-S CONVERSIONS FROM THE MOHO

We investigate crustal anisotropy along the Hi-CLIMB seismic array, an approximately N-S oriented broadband seismic profile of about 800-km long along the longitudinal line of 85 E, by using P-to-S converted phases from the Moho. Using the approach of fitting moveout times of the Pms arrivals on the receiver-functions under the assumption of a flat and sharp Moho, the fast polarization orientation and splitting time at 148 stations have been measured. Our results suggest eastward crustal extrusion occurring in central Tibet and southward crustal flow in southern Tibet. Based on the significant changes of the splitting parameters, we propose the following key elements regarding the Himalayan-Tibetan collision configuration: (1) the onset of mid-crustal low velocity zone at north of the Main Boundary Thrust; (2) the potential termination of the Indian upper crust at the Main Central Thrust; (3) the northern limit of the Indian crust at approximate 31 N in central Lhasa Terrain.