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Russian Geology and Geophysics

2014 year, number 10

3D MANTLE STRUCTURE OF CENTRAL ASIA FROM RAYLEIGH WAVE GROUP VELOCITY DISPERSION

V.M. Kozhevnikov, A.I. Seredkina, O.A. Solovei
Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Волны Рэлея, групповые скорости, поверхностно-волновая томография, строение мантии, Rayleigh waves, group velocities, surface-wave tomography, mantle structure

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 40º N to 60º N and 80º E to 132º E. The velocities were processed by the frequency-time analysis at periods from 10 to 250 s to obtain their dispersion curves. Then group velocity maps were computed separately for each period, at different sampling intervals: at every 5 s for the short periods from 10 to 30 s, at 10 s for periods between 30 and 100 s, and at 25 s for the longest periods of 100 to 250 s. 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 700 km 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.

DOI: http://dx.doi.org/10.1016/j.rgg.2014.09.010