Crustal and upper mantle structure beneath the South China Sea and Indonesia

A three-dimensional (3-D) S-velocity model for the crust and upper mantle beneath the South China Sea and Indonesia is presented, determined by means of Rayleigh wave analysis, in the depth range from 0 km to 400 km. The crustal and lithospheric mantle structure of this study area was previously investigated using several methods and databases. Due to their low resolution, a 3-D structure for this area has not been previously determined. The determination of such a 3-D S-velocity model is the goal of the present study. The most conspicuous features of the crust and upper mantle structure include the S-velocity difference between the Java Sea and the Banda Sea regions and a transitional boundary between these two regions. This model confirms the principal structural features revealed in previous studies: an oceanic crust structure in the center of the South China Sea, crustal thinning from the northern continental margin of the South China Sea to this oceanic crust, and the existence of a high-velocity layer in the lower crust of the northern continental margin. This study concludes that the north of the South China Sea is a nonvolcanic-type continental margin, solving the open question of whether the continental margin of the northern South China Sea is volcanic or nonvolcanic. A new map of the asthenosphere’s base is also presented.