热带海洋学报 ›› 2010, Vol. 29 ›› Issue (4): 63-70.doi: 10.11978/j.issn.1009-5470.2010.04.063

• 海洋地球物理学 • 上一篇    下一篇

南海北部海陆过渡带地壳平均速度及莫霍面深度分析

夏少红, 丘学林, 赵明辉, 徐辉龙, 施小斌   

  1. 中国科学院边缘海地质重点实验室, 中国科学院南海海洋研究所, 广东 广州 510301
  • 收稿日期:2009-05-08 修回日期:2009-08-13 出版日期:2010-07-31 发布日期:2010-07-29
  • 作者简介:夏少红(1981—), 男, 湖北省监利县人, 博士, 现为中国科学院南海海洋研究所助理研究员, 主要从事海洋地球物理与层析 成像结构研究。
  • 基金资助:

    中国科学院海洋地质与环境重点实验室基金(MGE2009KG09); 国家自然科学基金(U0933006); 科技部“973”项目(2007CB
    411701); 中国科学院边缘海地质重点实验室基金(MSGL0704)

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

XIA Shao-hong, QIU Xue-lin, ZHAO Ming-hui, XU Hui-long, SHI Xiao-bin   

  1. Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, CAS, Guangzhou 510301, China
  • Received:2009-05-08 Revised:2009-08-13 Online:2010-07-31 Published:2010-07-29
  • About author:夏少红(1981—), 男, 湖北省监利县人, 博士, 现为中国科学院南海海洋研究所助理研究员, 主要从事海洋地球物理与层析 成像结构研究。
  • Supported by:

    中国科学院海洋地质与环境重点实验室基金(MGE2009KG09); 国家自然科学基金(U0933006); 科技部“973”项目(2007CB
    411701); 中国科学院边缘海地质重点实验室基金(MSGL0704)

摘要:

南海北部海陆过渡带是一条深地震探测的空白带, 其地壳结构研究不仅可以揭示华南沿海地区地震活动规律和构造活动特征, 而且可以将以往在海上和陆上使用深地震探测所获得的地壳结构模型进行有效的衔接。鉴于南海北部海陆过渡带地壳结构的重要性, 2004年我们在香港外海域进行了一次海陆地震联测实验。本文以此次实验中广东和香港地区固定地震台网以及担杆岛流动台所获得的数据为基础, 对各台站接收到的Pg和PmP震相进行了近似横向均一的二维结构模拟, 获得了各台站对应的地壳平均速度和PmP反射点处的莫霍面深度值。其结果显示研究区地壳平均速度普遍为6.2km·s−1左右, 比全球地壳平均速度6.45km·s−1要低, 这可能与普遍发育于华南沿海地带的中地壳低速层有关。研究区东边的SHW台所获得的地壳平均速度为6.7km·s−1左右, 要明显高于全球地壳平均速度, 它可能是由于局部异常结构所造成的, 其与地幔岩浆的侵入作用可能存在一定联系。研究区莫霍面深度在26—35km左右, 变化趋势较为明显, 从北西向南东方向逐渐变浅, 属于地壳减薄型结构, 推测其可能与南海北部边缘的形成演化有密切联系。研究表明南海北部海陆过渡带是一个明显的转换地带, 它的深部地壳结  构特征应该与南海的扩张演化有密切联系, 这些认识推进了华南地区和南海北部陆缘地壳结构和构造属性的深入研究。

关键词: 南海北部海陆过渡带, 地壳平均速度, 海陆地震联测, 莫霍面

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