Radial anisotropy in the crust beneath Fujian and the Taiwan strait from direct surface-wave tomography

• Published in: Tectonophysics 2022-03, Vol.827, p.229270, Article 229270
• Main Authors: Zhang, Yayun, Yao, Huajian, Xu, Min, Liu, Bin
• Format: Article
• Language: English
• Subjects: Ambient noise; Anisotropy; Cenozoic; Cross correlation; Deformation; Direct inversion; Fractures; Fujian-Taiwan Strait; Geological processes; Geological structures; Geology; Horizontal polarization; Love waves; Metamorphism; Radial anisotropy; Shear wave velocities; Stress distribution; Surface wave tomography; Tectonics; Tomography; Underground structures; Velocity; Vertical polarization; Wave dispersion; Wave velocity; Waveforms
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2022.229270

The Fujian-Taiwan Strait-Taiwan area has undergone multiple periods of alternate compressional and extensional tectonic events, forming a complex geological structure. The underground structure and deformation characteristics, reflected by three-dimensional velocity structure and anisotropy, are the basis for analyzing the influences of different geological processes. In this study, utilizing 2 years of continuous waveform data from more than 100 permanent stations in Fujian and Taiwan, we extracted Rayleigh and Love wave dispersion data based on the cross-correlation of vertical and tangential components. A direct inversion method was employed to obtain the 3-D shear wave velocity and radial anisotropy structure of the crust. Vertical and horizontal polarized shear wave velocity structures were also inverted separately, and then used to calculate another radially anisotropic velocity model for comparison. The results show that the middle and lower crust of Fujian and the Taiwan Strait are dominated by positive radial anisotropy attributed to the near-horizontal alignment of minerals caused by extension. Although in an extension environment, most of the shallow crust exhibits weak anisotropy due to the vertical cutting of fractures and fissures, except for the strait area covered by horizontal sedimentary layers leading to strong positive radial anisotropy. In addition to the influence of faults and other shallow structures, the stress distribution caused by metamorphism also plays an important role; thus, the upper crust of the marine metamorphic belt shows negative radial anisotropy. Different from the strong positive anisotropy in other parts of the lower crust, relatively weak anisotropy appears beneath the Penghu area, which is related to two-stage Cenozoic extension. •A direct inversion method was adopted to obtain the crustal radial anisotropy beneath Fujian and the Taiwan Strait.•Most of the study region is dominated by positive radial anisotropy due to Mesozoic to Cenozoic extension.•The marine metamorphic belt shows negative anisotropy and may be affected by Mesozoic metamorphism.