A Study on Velocity Distribution in Upper Crust and Tectonics of Basement and Cover in South China

Abstract

AbstractFive representative wide‐angle seismic profiles in South China are analyzed to study the fine velocity structure. The interpolation was made by fitting the travel times of first arrive Pg waves, and combining with other geophysical data and geological data, the synthesis explanations for the tectonics of basement and cover are performed. It is proved that some fault basins infilled with Mesozoic volcanic rock above the basement are distributed in the eastern region of Zhejiang, Fujian, and Guangdong provinces and the thickness of the volcanic rock layer is 1 000–4 000 m. In the region of western Zhejiang, southern Anhui, Hunan, and Jiangxi Provinces, the basement surges obviously and the cover is mainly Palaeozoic group, and some Mesozoic Cretaceous smaller basins controlled by boundary faults develop there. The Chuxiong basin in western South China is a deep depression with complex structure, in which the thickness of Jurassic‐Cretaceous systems is over 10km. This basin is divided into two parts of eastern ascent and western depression, and the western depression is farther divided by a center uplift into two smaller deep depressions. Some Main faults in the researched region are reflected clearly in the contour velocity diagrams. Jiangshan‐Shaoxing fault, Lianhuashan fault and Wuchuan‐Sihui fault in the eastern region, and Chenghai fault, Luzhijiang fault in the western region are all the important tectonic boundaries, also flock basement faults are primarily the boundaries of the basins and the uplifts.