Youshun Sun, M. Nafi Toksoz, Pei Shunping, and F. Dale Morgan
The layered shear-wave velocity structure of the crust and uppermost mantle in China
Bulletin of the Seismological Society of America (April 2008), 98(2):746-755

Abstract:
We present a layered shear-wave velocity structure of the crust and uppermost mantle of China and the surrounding area. We apply an adaptive moving window (Sun, Li, et al., 2004) to construct the S-wave velocity model from high-quality body-wave phase data extracted from the Annual Bulletin of Chinese Earthquakes (ABCE). More than 350,000 S-wave arrivals are used, spanning from 1990 to 2004. The study area is represented by a 1 degrees geographic grid consisting of 2338 points. At each point, 1D S-velocity-depth profiles are determined independently from the surface to the uppermost mantle; this is accomplished by performing a Monte Carlo random search of optimum layer parameters (thickness and velocity) via minimizing travel-time misfits for fixed earthquake locations. Each profile contains a four-layer crust and a one-layer uppermost mantle. A final 3D model is obtained by combining and smoothing the 1D models. The obtained S-wave model has a good correlation with the previously published P-wave model using the same method (Sun, Li, et al., 2004) and reveals key tectonic features such as the low velocity crust beneath Tibet. Our S-wave model is generally consistent with the existing regional/local models constructed from body-wave travel-time tomography, and provides more detailed structure in both horizontal and vertical directions compared with the model derived from surface wave inversion. Based on our P- and S-wave models, the generated synthetic seismograms fit well with the observed seismograms recorded at broadband stations.