3-D Crustal Shear-Wave Velocity Structure of the Taiwan Strait and Fujian, SE China, Revealed by Ambient Noise Tomography

The Taiwan Strait, along with the southeastern continental margin of the Eurasian plate, Fujian in SE China, is not far from the convergent boundary between the Eurasian plate and the Philippine Sea plate. Although this region is considered tectonically relatively inactive, many small earthquakes still occur, and normal faults are well developed in the strait. To better understand the geological processes in this region, we use 2 years of ambient noise data from more than 100 stations in Fujian and Taiwan to obtain a 3-D crustal shear-wave velocity model using a direct surface-wave inversion method. Our results show that the low-velocity zone beneath the Zhenghe-Dapu suture zone plays an important role in the tectonic evolution of the Fujian area. The relatively high velocity in the eastern part of the suture zone and low velocity in the west correspond to the Mesozoic magmatic zone and the Wuyi-Yunkai orogenic belt in Fujian, respectively. The coastline of Fujian presents a high-velocity anomaly in the upper crust, which is related to the Mesozoic Pingtan-Dongshan metamorphic belt. The long strip-like high-velocity zone through the rift basins in the strait is interpreted as igneous rocks due to extension of the lithosphere in the Cenozoic. Two-stage extension with different extensive centers in the strait may be the reason for the high- and low-velocity anomalies in the middle to lower crust and uppermost mantle of the strait.