3D mantle structure of Central Asia from Rayleigh wave group velocity dispersion

Abstract

The mantle structure in Central Asia was investigated by surface-wave tomography from dispersion of the fundamental mode of the Rayleigh wave group velocities along more than 3200 earthquake-station paths within 40° N to 60° N and 80° E to 132° E. The velocities were processed by the frequency-time analysis at periods from 10 to 250s to obtain their dispersion curves. Then group velocity maps were computed separately for each period, at different sampling intervals: at every 5s for the short periods from 10 to 30s, at 10s for periods between 30 and 100s, and at 25s for the longest periods of 100 to 250s. Resolution was estimated according to the effective averaging radius (R) and presented likewise in the form of maps. To estimate the depths of the revealed inhomogeneties, locally averaged dispersion curves were calculated using the group velocity maps, with reference to the radius R, and were then inverted to S-wave velocity-depth profiles. The resulting three-dimensional S-wave velocity structure to depths of about 700km revealed large lateral inhomogeneties through the entire depth range. This pattern may be due to the history of the major tectonic structures, as well as to ongoing processes in the mantle.