Upper crustal structure beneath the northern South Yellow Sea revealed by wide-angle seismic tomography and joint interpretation of geophysical data

Mapping the crustal structure beneath the South Yellow Sea (SYS), which includes the collision zone between the North China Block and the South China Block, will help to reveal the geologic history and relationship between these geologic blocks. Previous interpretations of the crustal structure of the SYS did not use detailed seismic velocity structure as a constraint. We produced an upper crustal velocity model of the northern SYS using a new wide-angle seismic dataset. Velocity anomalies resolved by our models correlate well with known features such as sedimentary basins and the tectonic uplifts in the SYS as low- and high-velocity anomalies, respectively. As might be expected, not only major faults and/or lithologic boundaries were found to be associated with large velocity gradients, but also our models exhibited resolvable deeply penetrating vertical low-velocity anomalies associated with the locations of strike-slip faults that were poorly resolved in an older seismic reflection profile. Our interpretations of the locations of major faults were based on the stacked seismic reflection profile and velocity modelling of wide-angle seismic array data and were extended to neighbouring regions by following trends in gravity, magnetic and earthquake location data. Faults traversing the North Basin of the SYS converged with the onshore Jia-Xiang Fault (JXF), suggesting that the branching of the JXF fault system controlled the formation of the North Basin. The distribution of the strike-slip faults resolved by our modelling of the JXF leads us to propose a model for the North Basin as a strike-slip stress regime that is consistent with the known tectonic framework. These models will be useful for future analysis of the regional tectonic evolution of the SYS region.