A Research on Deducing the East China Sea Shelf Basin by Jointing Gravity-magnetic and Seismic Data

Abstract:

At present, China's ocean regional geological survey mainly depends on gravity and magnetic prospecting, and 2D seismic prospecting is an important auxiliary. In the research, we give full play to the characteristics of seismic, gravity and magnetic data, complementing each other's advantages. 3D tectonic framework of the East China Sea shelf is inverted by the three data, and then we can slove problems such as the distribution of faults, the regional stratigraphy and the basement structure, etc.

Using the 2D seismic interpretation results, the initial geological geophysical model for interface inversion is established, and the seismic section can determine the shape of the shallow density interface accurately. The weights are modified to different values on deep and shallow density interface layers during the joint inversion. The multi solution of gravity and density interface inversion is greatly reduced with the constraint of seismic data. On the basis of the joint inversion, the refined 2.5 dimensional gravity, magnetic and seismic interpretation of seismic section has been done, abundant geological section maps and the 3D structural features of the study area has been obtained. In the seismic section, the faults can be well identified. Thus, the seismic breakpoints are projected to the gravity and magnetic anomaly map, the faults are combined along the anomalies gradient zone and other gravity-magnetic anomaly maps. Finally, different levels grades and stages of the fracture are obtained, and the fracture of the study area is fully recognized. The identification method of igneous rock is similar to the fault.

A series of new knowledge has been obtained. The three interfaces include the bottom of Pliocene series, Miocene series and sedimentary base by inversion. The dividing line between north and south block of haijiao salient should be shorter in the west and east direction, and the salient area is larger than previously known; The basement of yushan salient in the south can be composed of Mesozoic igneous rocks; The formations of xihu sag were completely developed, the thickness and the subsidence amplitude of Cenozoic sedimentary is big, and the basement base is about 11794 meters. It is proved that the interpretation method by jointing gravity and seismic data is an effective technique, and can be used to other area.