Abstract:

With the Pwave arrival times from Chinese and ISC stations, we conducted the tomographic inversion for the 3D velocity structure in the crust and mantle beneath the northeastern South China Sea (SCS) and surrounding regions by using spherical finite difference technique. We analyzed the tectonic differences and deep geodynamic characteristics based on the tomographic results, which show high velocity anomalies at the uppermost mantle beneath the northeast SCS, and depict the lithospheric mantle extension from South China continent to marginal sea. Because of the low temperature and thick lithosphere beneath the northeast SCS, it seems no magma intruded from mantle, so we inferred that the rift may only occur in the crust rather than extend to the upper mantle, which shows the nature of nonvolcanic continental margin. The low velocity anomalies at the central subbasin suggest the uplift of hot materials in the mantle. The high velocities at South China continent and Taiwan region, and the low velocities at Okinawa Trough depict the different tectonics of the crust: the former ones belong to the normal crust of Eurasia continent or thickened crust caused by the collision between Philippine Sea Plate and Eurasia Plate, while the latter one belongs to the thinned crust caused by backarc spreading. Between the high velocities of South China continent and northeast SCS, the Binhai fault belt depicts the suture of South China block and SCS block, and the low velocities at upper mantle suggest the deepdriven magma process beneath the marine of South China continent. The velocity anomalies at Luzon, Manila Trench and East Luzon Trench relate to their tectonics natures. The low velocities at the upper mantle from southern Taiwan to northern Luzon depict two volcanic chains: western volcanic chain (WVC) and eastern volcanic chain (EVC). The high velocity belt at north Luzon ridge depicts the subducted continental slab.
Key words: Northeastern South China Sea; P wave velocity structure; lithospheric mantle; seismic tomography

Key words:

关键词：南海东北部;P波速度结构;岩石层地幔;层析成像