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利用中德合作在南海西沙海槽首次获得的海底地震仪探测数据 ,通过震相分析和走时模拟 ,研究了该区的纵波速度模型和地壳结构特征。结果显示 ,新生代沉积层厚 1— 4km ,其下的地壳纵波速度从 5.5km·s- 1 向下逐渐增加到 6.8km·s- 1 ,下地壳未见有明显的高速层 ,地壳厚度在剖面两侧为 2 5km ,向中部逐渐减薄至 8km ,莫霍面在剖面中部上隆 ,其速度反差强烈 ,从地壳底部的 6.8km·s- 1 跳跃到上地幔顶部的 8.0km·s- 1 。这一地壳结构反映出新生代拉张裂谷的特征 ,海槽两侧地壳结构相似 ,南北呈对称分布 ,没有或很少下地壳底侵 ,与南海北部陆缘的东段有很大差别。
Based on the seabed seismograph data acquired by Sino-German cooperation for the first time in the Xisha trough of the South China Sea, the P-wave velocity model and crustal structure characteristics of the area are studied by seismic facies analysis and traveltime simulation. The results show that the Cenozoic sedimentary layer is 1 to 4 km thick and its crustal P-wave velocity increases gradually from 5.5 km · s-1 to 6.8 km · s-1. There is no obvious high-velocity layer in the lower crust, The two sides of the section are 25km, and gradually thinned to 8km to the middle. The Moho rises in the middle of the section and contrasts strongly in velocity, jumping from 6.8km · s-1 at the bottom of the crust to 8.0km · s- 1 . The crustal structure reflects the characteristics of the Cenozoic extensional rift. The crustal structures on both sides of the trough are similar in structure, and are symmetrically distributed in the north and south with little or no crustal underplating, which is quite different from the eastern part of the continental margin in the northern South China Sea.