UPPER MANTLE ANISOTROPY BENEATH THE ASIAN CONTINENT FROM GROUP VELOCITIES OF RAYLEIGH AND LOVE WAVES
T.B. Yanovskaya and V.M. Kozhevnikov*
St. Petersburg State University, Institute of Physics,
1 ul. Ul'yanovskaya, St. Petersburg, Petrodvorets, Russia
* Institute of the Earth's Crust, Siberian Branch of the RAS,
128 ul. Lermontova, 664 033, Irkutsk, Russia
Keywords: Surface waves, group velocity, upper mantle, Asia, anisotropy
Pages: 618-625
Abstract
Upper mantle anisotropy in Asia was investigated by inversion of Love and Rayleigh wave group velocity dispersion curves obtained by the FTAN procedure at periods between 10 and 150 s along paths that traverse Central Asia and Siberia. Our data were supplemented with data from the Center for Imaging the Earth's Interior (Boulder, Colorado), and 2500 to 4000 paths, depending on period, were used altogether. Locally averaged group velocity dispersion curves for Love and Rayleigh waves obtained by 2D seismic tomography for different periods were inverted to velocity-depth profiles, jointly and separately for SV (Rayleigh) and SH (Love) waves. SH waves have higher velocities than SV waves in the crust and upper mantle to a depth of ~300 km. The velocity profiles were used to estimate the mean anisotropy coefficient over depth intervals from the Moho to 100 km, from 100 to 200 km, and from 200 to 300 km. Anisotropy is the most prominent between 100 and 200 km, i.e., in the asthenosphere, and in anticorrelation with asthenospheric velocity: the lower the velocity the higher the anisotropy coefficient. Anisotropy is the greatest beneath active deforming regions of orogeny and vanishing in stable cratonic areas.
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