SEISMIC SHAPE FEATURES AND DISTRIBUTION OF SHALLOW GAS IN THE SEA AREA OFF THE YANGTZE RIVER ESTUARY

There are various kinds of shallow gas seismic reflections in shape in the region off the Yangtze River estuary. They can be classified into following categories:(1)According to general shape:the curtain-like reflection, the column-like reflection and the gas chimney-like reflection; (2)According to the shape of the top interface:shallow gas with irregular top interface and shallow gas with regular top interface; (3)According to the shape features on lateral:upright and protruded shallow gases; (4)According to the combined shape features:shallow gas with multiple-layer strong reflection in vertical direction, with reflection interrupted on lateral and with reflection varying in vertical direction. Based on the above mentioned shallow gas shape features, we mapped and summarized the distribution pattern of shallow gas in the region, and discussed the relationship between the strong reflections and the migration pathway.