A three-dimensional Vp, Vs, and Vp/Vs crustal structure in Fujian, Southeast China, from active- and passive-source experiments

Fujian, Southeastern China, has experienced multistage tectonic activities since the Neoproterozoic Era and is currently influenced by collision between the Eurasian and Philippine Sea plates. Topography, fault zones, and patterns of seismicity are the imprints of tectonic evolution. Historically, there have been several catastrophic earthquakes in the southeastern part of Fujian. To understand the crustal structure related to the fault zones, we performed Vp, Vs, and Vp/Vs travel-time tomography using joint inversion of active and passive sources. A total of 75,827 and 31,044 arrivals of P and S waves, respectively, from 33 explosions and 2543 earthquakes are used in our study. As a result, seismicity has indicated that two NE strike seismogenic zones, the Zhenghe-Dapu and Changle-Zhaoan fault zones, are currently active. Low Vp/Vs ratios in inland Fujian imply that the crust is mainly composed of felsic rocks as part of the Eurasian continental crust, which is consistent with geological observations at the surface. Based on Vp tomography, the thickness of the crust along the coastline is shallower than that on land, which is related to higher heat flow and the Bouguer anomaly. This shallow crust phenomenon near the coastline could be related to the regional extensional stress: the remaining structure of the back-arc extension that stretched the continental crust during the Mesozoic Era or/and the Cenozoic extension due to South China sea opening in Taiwan Strait.