Shear‐Wave Velocity Structure beneath Southeast Coastal Areas of China from the F-J Multimodal Ambient Noise Tomography

Abstract

The Southeast Coastal Areas of China (SCAC) is part of the Cathaysia block, the convergence area of the Eurasian, Pacific and India-Australian plates. The Cathaysia and the Yangtze blocks collided and merged into the South China block in the Neoproterozoic. These areas have experienced complex geological evolution and multiple periods of intense magmatic events since the Paleozoic, mainly manifested as a large number of Paleozoic and Mesozoic granitic rocks and Cenozoic mafic magmatism. Large-scale structural deformation caused by emplacements is very strong to the stratum reconstruction, forming a series of faults with different scales and directions. The development of large-scale fault systems has led to the potential risk of strong earthquake disasters in the region. In addition, the urban agglomeration with its dense population, is located in SCAC. Thus, seismic risk assessment and seismic research are very urgent and critical. The high-resolution crustal structure model is especially necessary for understanding the geological processes and seismic hazards in and around the areas. We collected ambient noise data from fixed and temporary seismic stations in the SCAC, and used the frequency-Bessel transform (F-J) method to extract Rayleigh wave dispersion curves and performed multimodal ambient noise dispersion curves inversion. We constructed a 3D high-resolution S-wave velocity model for this area. Specifically, we extracted reliable multimodal dispersion curves (up to the 8th higher-order in some sub-areas) with a broad frequency band range (0.03Hz-0.65Hz). Preliminary results show a widespread mid-crustal low-velocity zone, and we will further discuss the crustal structural anomalies and their related tectonic implications and evolution mechanisms.