图书馆知识库

We investigate the seismic anisotropy of the crust and upper mantle beneath western Tibet at 31 stations from the temporary Y2 experiment operated from 2007 to 2011 using teleseismic shear wave splitting measurements. Assuming a single-layer anisotropic model, we obtain 803 pairs of SKS splitting parameters represented by fast polarization directions and delay times. Our observations exhibit either an ENE-WSW or nearly E-W trend of stacking fast polarization directions with average delay times from 0.4 to 1.43 s except for those close to similar to 82 degrees E, which present the N-S oriented fast polarization directions with delay times of about 1.0 s. The ENE-WSW or nearly E-W trending fast polarization directions found along the Karakoram fault and the Bangong-Nujiang suture are compatible with other seismic anisotropy observations beneath western Tibet, and could have resulted from the mantle flow in the asthenosphere. The nearly N-S trending fast orientation directions in the southeastern part of the array, just above the underlying fast shear wave anomaly beneath the Indus-Yarlung suture, can be explained by C-type olivine fabric from the underthrusting Indian mantle lithosphere and/or sub-ILM orientated asthenospheric flow. Our measurements suggest decoupling between the crust and mantle lithosphere below western Tibet and the changing behaviour of the Indian lithospheric mantle from slab-like underthrusting beneath the Karakoram fault to underplating at similar to 82 degrees E.