南中國海位於歐亞大陸的東南方、屬於歐亞大陸板塊的一部分。近十幾年來，成為研究海底擴張過程的一個天然場所。在南海北部有一系列多頻道震測以及反射震測探勘，但由於地震測深局限於某些特定點以及剖面，不能大範圍的確定南海海域的深部地殼結構。然而重力數據具有可以反演大範圍大尺度構造的優點。在地球物理研究上可以與地震磁力等數據相結合而取得一個良好的效果。 本研究利用了南海周圍船測重力資料以及衛星重力資料。經過資料整理之後得到南海地區的重力異常，之後消除海水層、沉積層及海底地形造成的重力效應，得到南海區域布蓋重力異常。代入Parker-Oldenburg關係式計算莫荷面深度，得到南海區域的莫荷面深度起伏。在南海海盆西北方及中沙群島，莫荷面深度約為15至24公里，為一個大陸邊緣的大陸性地殼特徵。在南海海盆內部的莫荷面深度為10公里，其重力異常特性及莫荷面深度都顯示其為一個已達均衡的海洋性地殼，在南海擴張中心周圍的地殼厚度由中心向外的地殼厚度逐漸增厚。呈現一個厚-薄-厚的走向。在南海海盆內部的海底火山處，因為火成作用的影響，其局部地區會有地殼增厚的現象。 The South China Sea (SCS) is a part of the western Pacific Ocean, bounded by Eurasian Plate in the west and Indo-Australian Plate and Pacific Plate in the east. In the past, several surveys with multi-channel seismic were investigated in SCS. But the seismic data are limited by some specific points or profiles. And then, Gravity study provides useful geophysical information in the shallow depths and large regional area. It’s can be helpful to investigate the analysis. In this study, the gravity data is used marine and satellite of free-air anomalies, bathymetric model and sediment thickness data from NGDC in South China Sea area. Removing gravity effects generated by the water, sediment layer and seafloor topography, the regional Bouguer gravity anomaly is obtained. Moho depth is computed by the Parker-Oldenburg method from the when regional Bouguer gravity data set. In results, it indicates that the Moho depth beneath in SCS is about 10 km. The characteristic of gravity anomaly and Moho depth indicated the oceanic crust with Isostasy. The Moho depth is 15~24 km in the northwest SCS and Zhongsha Islands. It’s thin continental crust. It suggested that it exist two crust types including the thin continental and oceanic crust in South China Sea area. Moho depth is relatively shallower in spread axis in the central basin and thickens toward both sides of the spread axis.
