Stratigraphic structure and fault interpretation of the foreland basin system in the middle Taiwan Strait

A: A left-lateral strike-slip fault initiated perpendicular to the rifting zones between two rifted basins in the early Eocene due to South China Sea opening (56-47Ma). B: In the late Miocene after rifting (12–7 Ma), change of the stress setting induced by the westward compression from Philippine Sea Plate, reactivating the old left-lateral strike-slip fault and forming a positive strike-slip flower structure. • The initiation, reactivation and changing direction of the left-lateral strike-slip faults in the middle Taiwan Strait have been found. • The left-lateral strike-slip faults in the middle Taiwan Strait were induced by the westward compression from the Philippine Sea Plate. • The right-lateral strike-slip faults near Fujian were induced by the plate motion of the South China Sea with respect to the Philippine Sea Plate Since 2017, we have conducted several surveys to collect multi-channel seismic (MCS) and ocean-bottom seismometer (OBS) data in the middle Taiwan Strait. From the MCS data analysis, the fault distribution in the middle Taiwan Strait is mainly characterized by the normal faults. However, west of the Changyun Ridge, the fault distribution based on depth migrated sections is dominated by the strike-slip faults characterized by flower structures. The strike-slip faults were initiated between two rifted basins and reactivated after rifting. Based on the focal mechanisms and the striking direction of the faults, the strike-slip faults west of the Changyun Ridge are recognized to be left lateral. Additionally, several east–west trending left-lateral strike-slip faults were found in the middle Taiwan Strait. Based on the MCS data, we found that the changing direction of the strike-slip faults occurred in the middle Taiwan Strait before the formation of Taiwan, and was directly subject to the westward compression from the Philippine Sea Plate and the relative plate motion of the South China Sea with respect to the Philippine Sea Plate. Several 2.5 km-deep P-wave velocity models in the middle Taiwan Strait were imaged through inversion of refracted and reflected arrivals picked from the OBS data. At the boundary between the forebulge and foredeep, as well as within the sediment layers beneath the BU, a significant velocity gradient of approximately 2 s −1 was observed in both the lateral and vertical directions. Additionally, a fault-induced offset of about 0.2 km was identified in the sedimentary interfaces.