Crustal seismic anisotropy in central Tibet: Implications for deformational style and flow in the crust

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2004-12-01
[ 1] Receiver functions obtained at INDEPTH III stations located near the Bangong-Nujiang suture in central Tibet display a weak Moho signal and strong P to S conversions within the first 5 s that vary systematically with back-azimuth. A single station with representative azimuthal variations located at the sharp onset of strong SKS splitting, is modeled for both dipping layers and seismic anisotropy by using a global minimization technique. Inversion results indicate strong anisotropy (> 10%) near the surface and in the middle crust separated by a south-dipping (-25degrees) layer, possibly related to the earlier phase of crustal shortening. Near-surface anisotropy has a fabric dipping steeply southward and trending WNW-ESE that correlates with the suture and younger strike-slip faults. In contrast, midcrustal anisotropy occurs in a low-velocity zone and has a fabric dipping gently (-18degrees) northward that might be related to a well-developed near-horizontal rock fabric induced by crustal flow.