扬子与华夏块体缝合带区域的Rayleigh及Love波相速度层析成像

The South China Craton consists of the amalgamated Yangtze and Cathaysia Blocks, but the NE-SW striking suture of these blocks is not well defined. Improving the definition of the boundary between these two blocks will help further characterize the regional tectonic framework and geologic history. We obtained the 2D phase velocity of Rayleigh and Love waves at periods of 4 similar to 25 s using records of seismic ambient noise observed at 457 stations in South China from 2014 to 2016. The phase velocity maps at periods of 4 similar to 12 s are consistent with geological structures like basins and folds in the upper crust. In the phase velocity maps, at periods of 16 similar to 25 s, the eastern region mainly displays high-velocity anomalies related to its thinner crustal thickness. In the southwestern region, Rayleigh waves identify high-velocity anomalies, and Love waves identify significant low-velocity anomalies. This velocity anomaly difference implies the existence of radial anisotropy in these regions. The phase velocity maps show significant differences in the Yangtze and Cathaysia Blocks. With the constraints of previous geological and geophysical studies, we infer that the Cathaysia Block subducted beneath the Yangtze Block and sutured along the line of Shaoxing-Jiangshan-Pingxiang-Yongzhou-Hechi in the shallow crust. The suture zone, now buried in the deep crust, should extend from Shitai-Jiujiang-Changsha to Yongzhou-Hechi.