Surface Wave Tomographic Study of Central Asia Tectonic Regimes

Abstract

The detailed study of intermediate period surface wave propagation across Central and Southern Asia is presented. Broadband waveform data from about 600 events from 1988 - 1995 recorded at 83 stations from global and regional networks have produced about 9,000 paths for which individual dispersion curves have been estimated. The combination of measurements on global and regional scales helps to optimize path coverage and azimuthal distribution which together determine resolution. The tomographic technique is used to estimate group velocity maps at different periods between 10 and 40 s for Rayleigh and Love waves. 'Checker-board' tests show that resolutions across most of the studied region are about 4 degrees-5 degrees at 20 s and above, but degrade at shorter periods. Resolution is far from uniform spatially, and is generally worst in Western and Southern Iran and in India. Comparison of the estimated group velocity maps with those predicted by the recent global model CRUST-5.1/S16B30 is qualitatively very good, but, because of the coarseness of its grid, CRUST-5.1 misses some of the smaller sedimentary basins and the geometry of crustal thickening in Central Asia cannot be well represented by any gridded 5 degrees model.