南海西沙地块岛屿地震观测和海陆联测初步结果  

Preliminary results of the earthquake observation and the onshore-offshore seismic experiments on Xisha Block

作　　者：黄海波[1] 丘学林[1] 徐辉龙[1] 赵明辉[1] 郝天姚[2] 胥颐[2] 李家彪[3] 

机构地区：[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,广州510301 [2]中国科学院油气资源研究重点实验室,中国科学院地质与地球物理研究所,北京100029 [3]国家海洋局海底科学重点实验室,国家海洋局第二海洋研究所,杭州310012

出　　处：《地球物理学报》2011年第12期3161-3170,共10页Chinese Journal of Geophysics

基　　金：国家重点基础研究发展计划(973计划)(2007CB411701);国家自然科学基金(41074066,U0933006,41074058);中国地质调查局项目(GZH200900504)联合资助

摘　　要：为了研究南海西沙地块下方的地壳结构,我们在岛屿区架设了流动地震台站进行天然地震观测和海底地震仪的人工地震探测.本文利用远震接收函数方法和射线追踪方法对琛航台的远震数据和海陆联测数据进行了初步处理和分析,建立了琛航岛下方的一维横波速度模型以及横穿琛航岛的二维地壳结构模型.琛航岛顶部存在2 km厚的新生代低速沉积层,下地壳存在明显低速层,横波速度只有3.5 km/s,莫霍面埋深24～26 km,岛屿两侧地壳厚度向外逐渐变薄,其西北侧地壳结构表现为裂谷特征,可能为西沙海槽在该地区的延伸表现.地幔热活动和区域拉张应力作用引起的上地幔物质的韧性流变构造和各向异性排列可能是产生下地壳低速层的主要原因.Temporary earthquake stations were installed on islands of Xisha Block and onshoreoffshore deep seismic experiment was carried out in order to study the crustal structure beneath Xisha Block. The seismic data were analyzed and processed. A 1-D shear wave velocity model beneath Chenhang island（CHH） was constructed by applying receiver function method to the teleseismic data. A 2-D P-wave velocity crustal structure was modeled by ray-tracing and traveltime simulation. A 2 km-thick low-velocity sediment exists on the top of CHH which is attributed to Cenozoic deposition. In the lower crust, there exists a prominent Low-Velocity Layer （LVL）with average shear wave velocity of 3, 5 km/s; Moho interface lies at the depth of 24~26 km right beneath CHH. The crustal thickness gradually decreases outward along the onshore- offshore seismic line. The crustal structure has the typical characteristics of rift valley in the NW side of CHH, which belongs to the extension of Xisha Trough. The presence o（ anisotropy of upper mantle minerals and the ductile theological structure arising from hot mantle activities may result in the generation of the LVL in lower crust.

关 键 词：西沙地块 接收函数 海陆联测 射线追踪 

分 类 号：P315[天文地球—地震学]