Azimuthally anisotropic seismic ambient noise tomography of South China block

Abstract

Situated in the far southeastern corner of the Eurasian plate, the South China block is traditionally considered to be created by the collision/amalgamation of the Yangtze craton and Cathaysia terrane. In this study, we use the continuous seismic ambient noise, recorded by dense permanent seismic stations deployed across South China, to image the isotropic and azimuthal anisotropic crustal structure of the South China block. In the short period (5–10s), which is most sensitive to the upper crustal structure, the lateral changes in the isotropic crustal structure show good agreement with surface geology, with lower velocities being associated with major sedimentary basins. More details about the tectonic evolution of the South China block are revealed by the lateral and vertical variations in azimuthal anisotropy. Spatial variations in isotropic model and model with azimuthal anisotropy have been observed across the Jiangshan-Shaoxing fault, related to the crustal suture zone between the Yangtze craton and Cathaysia terrane. The azimuthal anisotropy at short periods (5–10 s) shows a fast-propagation direction broadly parallel to the suture zone. This might reflect folding, thrusting, metamorphism structures, and basin-mountain foreland deformation system created by the intense crustal deformation due to the Yangtze craton colliding with Cathaysia terrane and following multiphase tectonic activities.