Surface Wave Group Velocity Measurements Across Eurasia,

Earthquake and nuclear explosion data recorded by the GSN, GEOSCOPE, CDSN, and MEDNET broadband networks and the IRISKyrghyz regional network KNET during 1988-1995 have been used to study the characteristics of surface wave propagation across Eurasia. More than 3500 three-component records for different epicenter - station pairs have been processed. Group and phase velocity dispersion curves, spectral amplitude curves, as well as frequency - dependent azimuthal particle - motion anomalies for fundamental Rayleigh and Love waves in the range of periods between about 20 and 300 s have been obtained by means of frequency-time analysis and floating filtering. Data on group velocities have been used to obtain preliminary group velocity maps of the region under study for a broad set of periods. Spatial resolution of these maps depends on the ray coverage, and appears to vary from 600 to 1000 km. Significant lateral variations of Rayleigh and Love group velocities seen on the maps indicate drastic changes of lithospheric shear velocity structure across the region. The Tibetan Plateau, the mountain regions of Central Asia, the Siberian Platform, the Indian Shield, as well as some smaller tectonic features, appear on maps as regions of relatively high or low group velocities. The 2D-inversion of all data into group velocity maps and 3D-inversion for the lithospheric structure of the region is in progress.