南海南北陆缘地壳结构的纵横波联合反演

The comparison between P-wave and S-wave velocity structure of the North and South continental margin of the South China Sea (SCS) is of fundamental significance for the recognition of the tectonic attribute and the rifting process of the conjugate margin. While the previous studies which used the different periods’ OBS data to compare the crustal structure are not optimal. Especially, the S-wave data have not been applied in the south continental margin，thereby lack of compare results of the S-wave velocity structure in the conjugate margin. This new proposed project intends to process the profile OBS2006-1 in the north continent margin and the profile OBS2009-2 in the south continental margin again in high accuracy to obtain more detailed P-wave velocity models by ray tracing, and then to carry out the S-wave velocity structures. The results will reveal the P-wave and S-wave velocity structures，depths of moho，Poisson’s ratio and lithology property of the conjugate margin. In addition, we will compare the differences of results, which will provide evidences to understand the tectonic attribute and conjugate point for the north and south continental margin and improve our knowledge of the rifting and dynamics characteristics of the SCS.

对比研究南海南北陆缘纵、横波速度结构对认识其构造属性、理解共轭陆缘的张裂演化过程有着重要的作用。但南海已有的研究是将不同期的纵波速度结构进行对比，导致结果比较粗糙；同时，南部陆缘尚未开展横波速度结构模拟，缺乏南北陆缘横波速度结构对比结果。本项目通过对位于南海北部陆缘的OBS2006-1测线和南部陆缘的OBS2009-2测线的三分量数据重新处理，经过震相识别，射线追踪和走时模拟，获得相应测线精细的纵波速度结构，并以此为基础，开展横波结构模拟。联合纵、横波速度结果，揭示南海南北陆缘深部地壳结构特征，莫霍面起伏形态，地壳物质的泊松比分布信息及岩石学性质；并对比以上结果的异同，为研究南北陆缘的构造属性和共轭点提供依据，进而揭示其张裂变形特性和形成演化的深部动力学特征。

开展南海南北陆缘纵、横波速度结构对比研究对于认识南北陆缘的构造属性、理解共轭陆缘的张裂过程有着重要的作用。本课题利用位于南海南部陆缘礼乐滩的OBS2009-1测线、北部陆缘西北次海盆和中沙地块的OBS2006-1测线，采用射线追踪方法开展纵、横波速度结构成像，为认识南、北陆缘的构造属性和海盆扩张过程中的陆缘共轭关系提供信息。课题至今完成了两条测线的速度结构模拟，获得了相应测线的纵、横波速度结构和波速比结构，从地壳厚度和速度、波速比、莫霍面埋深及形态变化来认识陆缘构造属性和理解陆缘共轭关系。结果揭示在陆缘的下地壳没有发现高速体的存在；波速比为1.73-1.79，推测岩性介于长英质和铁镁质之间，和非火山性的扬马延海岭相近，我们认为南海北部陆缘西侧和南部陆缘为非火山型大陆边缘；结合北部陆缘东侧OBS2006-1测线的模型结果，对比三条测线深部结构的岩性等信息，发现南部陆缘礼乐滩地壳中的岩性和南海北部陆缘东侧东沙的结果不同，而与北部陆缘西侧的中沙地壳的岩性相似，结合纵波速度揭示速度特征、莫霍面形态和重磁结果，推测礼乐滩和中沙共轭。