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

Abstract

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.

Upper Mantle Shear Wave Velocity Structure of Southeastern China: Seismic Evidence for Magma Activities in the Late Mesozoic to the Cenozoic

“…However, the first extension lasted longer and spread wider, which may lead to the lowest anomaly in the north of the strait (Figure 10). The upper mantle shear wave velocity structure confirms and promotes the conclusion that the strait has two stages of extension in the Cenozoic with different centers, which has also been proposed based on the shallow crustal structure (Zhang et al, 2018).…”

“…There are many normal faults in the strait that serve as the dividing line between the extensional basin and the uplifts formed in the Cenozoic (Gao & Huang, 1995) (Figure 1). Rifting with lithospheric extension in the early and late Cenozoic with variable centers are responsible for most features in the strait, including the formation of the relatively thick sediments (Lin et al, 2003;Zhang et al, 2018). In the Taiwan area, the Central Range has a thickened mountain root due to the collision.…”

“…Rayleigh wave phase dispersion curves were extracted using the ambient noise cross-correlation (NCC) method within the period range of 2-40 s (Zhang et al, 2018). For the traditional two-station (TS) method (Yao et al, 2006(Yao et al, , 2008, we used continuous waveform data recorded by stations of the Earthquake Administration of Fujian Province (EAFP) (Data Management Center of China National Seismic Network, 2007;Zheng et al, 2010) and the Broadband Array in Taiwan for Seismology (BATS) (Institute of Earth Sciences, Academia Sinica, Taiwan, 1996) from 2014 to 2015.…”

“…We also used the direct surface wave tomography method (Fang et al, 2015) and selected the optimal inversion parameters as we have done on the crustal structure of the same region (Zhang et al, 2018). This study mainly focuses on the structural characteristics of the upper mantle.…”

“…The complex crustal structure, however, can greatly affect the final inversion results. To eliminate the crustal influence, the velocity model (0-120 km) inverted from the NCC dispersion data (Zhang et al, 2018) was used for the shallow part in our initial model, and a 1-D ak135 model (Kennett et al, 1995) was added for the deeper part. Different initial models were also tested to evaluate the dependence of the inversion results on the initial model using the same inversion parameters (supporting information Figures S1 and S2).…”