南海北部海陆过渡带地壳平均速度及莫霍面深度分析

doi:10.11978/j.issn.1009-5470.2010.04.063

Abstract

Abstract:

In order to study the crustal structure beneath the onshore-offshore transitional zone in the northern South China Sea, we carried out an onshore-offshore seismic experiment offshore of Hong Kong in 2004. Based on the data recorded by the permanent seismic stations in Guangdong Province and Hong Kong and by portable seismic stations on the Dangan Islands, we obtained a series of laterally homogeneous 2-D models using Pg and PmP phases for every station, determined the crustal average velocity, and constrained variations of Moho depth. The results show that the crustal average velocity is generally about 6.2km·s−1, which is lower than the global crustal average velocity of 6.45km·s−1. It suggests that a low velocity layer in the middle crust has developed the beneath onshore-offshore transitional zone in the northern South China Sea. However, the average crustal velocity of 6.7km·s−1 in the eastern part of the study area was higher than the global average velocity (6.45km·s−1) according to the data at the SHW station, which could imply magma underplating and a high velocity layer in the lower crust. The Moho depth was about 26−35km and gradually thinned from northwest to southeast. These results indicate the onshore-offshore transitional zone is the transitional boundary between the northern South China Sea and South China. By modeling and analyzing these data, we have obtained some new knowledge: a low velocity layer of middle crust was generally detected and no high velocity body of lower crust was found on land, while the opposite occurred at sea, namely high velocity body of lower crust was detected and no low velocity layer of middle crust was found; and the thickness of crust thinned from land to sea. These results have improved our understanding on crustal structure and tectonics of South China and the northern South China Sea.

Key words: onshore-offshore transitional zone, northern South China Sea, crustal average velocity, onshore-offshore seismic experiment, Moho

XIA Shao-hong,QIU Xue-lin,ZHAO Ming-hui,XU Hui-long,SHI Xiao-bin. Analysis of crustal average velocity and Moho depth beneath the onshore-offshore transitional zone in the northern South China Sea[J].Journal of Tropical Oceanography, 2010, 29(4): 63-70.

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Analysis of crustal average velocity and Moho depth beneath the onshore-offshore transitional zone in the northern South China Sea

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