The Bouguer Gravity Anomaly And Tectonic Interpretation Of Taiwan Strait

The Taiwan Strait is the transition area between the East Sea and the South Sea of China. It’s rich in oil and gas resources. At present, the exploration degree of oil and gas resource in the western plain area of Taiwan Island is high. But the development degree of oil and gas resources in western strait is relatively low, and the geological study of ocean basin basement is less especially.Gravity method is the main tool to study the basement structure and crust structure. During the process of the ocean bouguer gravity anomaly’s computation, people will not do the land terrain correction normally, even sometimes ignore the seabed terrain correction. This will generate considerable error to the offshore gravity anomaly. With the improvement of the accuracy of exploration, people have recognized the importance and necessity of terrain corrections in marine areas. This paper uses the gravity data to study the base or the other deep structures of Taiwan strait. The selected scope of study area is 117～125’E、21.5～26’N. First, we do the land and seabed terrain correction to the free-air gravity data of the study area, then we can get the complete bouguer gravity anomaly. And terrain correction divides near area、 middle area and far area, adopts different terrain correction models, and the radius of terrain correction is 166.7 km.Using the wavelet transform and multi-scale analysis method to deal with gravity anomaly, after the comparison and analysis, we get the conclusion that the four-step wavelet approximation of the bouguer gravity anomaly reflects the moho interface, and three-step wavelet details of the residual gravity anomaly reflects the basement interface, and we can get the anomaly value corresponding to the interfaces of moho and basement respectively. Then we take the known geological and geophysical data as constraints, and use the Parker-Oldenburg’s inversion method to obtain the moho interface and basement interface of the Taiwan Strait. Fracture structures reveal the evolution and causes of geological tectonic, and they are the major divided basis of tectonic units. Horizontal derivation maximum often corresponds to the fracture’s distribution. We use the horizontal derivation maximum to determine basement faults of the study area and divide the study area into three primary tectonic units, three second-grade tectonic units and six third-grade tectonic units.Through this research, we obtain the Taiwan strait’s complete bouguer gravity anomaly, the buried depth and morphology of the moho interface and basement interface, fracture structures and partition of tectonic units, etc., to provide reference for the study of geological structure and the exploration of oil and gas of the Taiwan strait.