High-frequency P and S velocity anomalies in the upper mantle beneath Asia from inversion of worldwide traveltime data

A model of seismic P and S anomalies in the upper mantle beneath Asia (in limits of 35 degrees E-140 degrees E, 12 degrees N-57 degrees N) was constructed based on the tomographic inversion of traveltime data from the revised ISC catalog for the years 1964-2004. The inversions were performed independently in 32 overlapping circular windows that cover the entire study area. The free inversion parameters in each window were defined individually depending on the available data based on synthetic modeling. Such adaptive tuning of parameters enables more optimal usage of the input data in areas with inhomogeneous ray coverage compared to global inversions. This approach resolves high-frequency patterns but is less sensitive to large anomalies with sizes comparable to the window diameter. Thus, this approach is somewhat similar to high-frequency filtration of the velocity distribution. The resolution capacity of the model was tested using checkerboard tests with various pattern sizes. To assess the role of random noise, independent test inversions of two data subsets (with odd and even numbers of events) were performed. Clear reconstructions of known structures, such as subducting plates beneath the Japan and Ryukyu arcs whose locations and shapes have been constrained by other studies, further indicate the reliability of the model. The 3-D models of P and S anomalies presented in horizontal and vertical sections show complex interactions of the lithospheric segments beneath the Alpine-Himalayan orogenic belts. Particular attention is focused on the collisional areas of Iran, Pamir-Hindukush, Tien-Shan, and Burma. The digital version of the 3-D P and S models is available at http://www.ivan-art.com/science/REGIONAL.