Some New Understandings on the Deep Structure in Yellow Sea and East China Sea

This paper integrates the results of seismic tomography as well as gravity and magnetic data inversion in a region within 26°N~36°N and 120°E~130°E to study the deep structure of the Yellow Sea and East China sea and discuss its relation with surrounding geologic units. Density structure inversion is accomplished along two profiles. The result indicates that the crustal thickness in the East China Sea continental shelf is not obviously different from the land area. The crust thins remarkably in the Okinawa Trough where the middle crust disappears. Beneath the Ryukyu island arc the thickness of crust, especially the upper crust, increases again, which is probably caused by subduction and the difference of motion rates between the plate and the upper mantle near the subduction zone. The longitudinal belts of geophysical anomalies are manifestation of crustal structure change from west to east in the Yellow Sea and East China Sea. However, with the increase of depth, a lithospheric structure pattern dominantly in nearly‐EW direction appears in the study region. It is inferred that the deep nearly‐EW anomalies were caused by collision and compression between northern and southern plates in the Triassic, whereas the shallow NE‐trending anomaly belts were the tectonic effect of shallow lithospheric structures in the later stage. There is an inconsistency between the shallow and deep structural trends of the lithosphere in the Yellow Sea and East China Sea. The result of seismic tomography confirms the existence of the East Margin Fault of the southern Yellow Sea, and also delineates the Shaoxin‐Shiwandashan collision zone appearing as a high velocity zone dipping at about 40° towards NW. Another high velocity zone with similar dip is the reflection of the boundary between the northern and southern Yangtze blocks at depth.