Ambient noise Rayleigh wave tomography in western Sichuan and eastern Tibet

We perform Rayleigh wave tomography in western Sichuan and eastern Tibet by applying the ambient noise method to broadband data recorded at 49 stations from the Sichuan digital seismic network. Cross-correlations of vertical-component ambient noise data are computed in one-hour segments and stacked over 7 months from June to December 2007. Then Rayleigh wave group dispersion curves from 6 to 48 s were measured using the multiple-filter analysis method. Group velocity maps at periods from 8 to 44 s were inverted. The resulting group velocity maps generally show good correlations with tectonic features. The Sichuan Basin is clearly resolved with lower group velocities at the short periods (8 to 20 s) due to thick sedimentary layers, and a prominent low-velocity zone exhibits in the middle crust beneath the eastern margin of the Tibetan Plateau. The Longmen Shan thrust belt marks not only the rapid lateral velocity variation between the topographically high Tibetan Plateau and low-elevation Sichuan Basin, but also the transition from the thick crust beneath the Tibetan Plateau to the normal continental crust beneath the Sichuan Basin.