S-wave velocity structure of the crust and upper mantle under southeastern China by surface wave dispersion analysis

Group velocity dispersion data of fundamental-mode Rayleigh and Love waves for 12 wave paths within southeastern China have been measured by applying the multiple-filter technique to the properly rotated three-component digital seismograms from two Seismic Research Observatory stations, TATO and CHTO. The generalized surface wave inversion technique was applied to these group velocity dispersion data to determine the S-wave velocity structures of the crust and upper mantle for various regions of southeastern China. The results clearly demonstrate that the crust and upper mantle under southeastern China are laterally heterogeneous. The southern China region south of 25 degrees N and the eastern China region both have a crustal thickness of 30 km. The eastern Tibet plateau along the 100 degrees E meridian has a crustal thickness of 60 km. Central China, consisting mainly of the Yangtze and Sino-Korean platforms, has a crustal thickness of 40 km. A distinct S-wave low-velocity layer at 10-20 km depth in the middle crust was found under wave paths in southeastern China. On the other hand, no such crustal low-velocity layer is evident under the eastern Tibet plateau. This low-velocity layer in the middle crust appears to reflect the presence of a sialic low-velocity layer perhaps consisting of intruded granitic laccoliths, or possibly the remnant of the source zone of widespread magmatic activities known to have taken place in these regions since the late Carboniferous. (C) 2000 Elsevier Science Ltd. All rights reserved.