GEOPHYSICAL SURVEY IN EASTERN CHINA SEAS AND THE CHARACTERISTICS OF GRAVITY AND MAGNETIC FIELDS

Marine geophysical investigation in China started from 50's of the last century. It could be roughly divided into the starting-up stage, early stage, developing stage, rapid developing stage and accelerated developing stage. A large number of high-resolution geological and geophysical data have been acquired by the surveys in the past years. With regard to the magnetic data, the background of magnetic anomalies is ±200 nT, with some anomalies higher than ±500 nT occurring in some local areas. Most of the anomalies extend in NE or NNE direction in a band pattern. However, some anomalies vary in both types and distribution patterns. Free air and Bouguer gravity anomalies are also showing a NE distribution pattern. In a general view, negative anomalies prevail in land, whereas the sea is dominated by positive anomalies. The intensity of free air gravity anomalies normally vary in the range of -45 and +100 mGal, with some of anomalies higher than +200 mGal in local areas. The intensity of Bouguer gravity anomalies change between -140 and +440 mGal. According to the intensity of gravity and magnetic anomalies, in combination with the characteristics of geomorphology, we may divide the region into nine areas, such as the North China-Bohai magnetic anomaly area and Shandong peninsula-north Yellow Sea anomaly area. The distribution pattern of "zoning in east-west direction and blocking in north-south direction" is rather obvious.