SEISMIC FEATURES OF SHALLOW GAS IN THE WESTERN AREA OF THE YELLOW SEA

According to the shallow seismic survey we carried out in the west area of the Yellow Sea in recent years,we find that there are various kinds of shallow gas seismic features in the region, and the seismic records of shallow gas in the seabed and in the water column indicate that the area is rich in shallow gas and some of them is seeping from seabed and releasing into seawater column.According to their space position,the seismic features of shallow gas in this region can be divided into three groups:(1)features in the stratum:acoustic blanket,acoustic curtains,acoustic turbidity,irregular strong top reflection boundary,and phase pull-down in both flanks;(2)features of the seabed:seabed pockmark and giant sunken pit;(3)features in the seawater column:acoustic plumes,cloudy turbidity and point-line-type reflection.Selecting typical seismic record with related features in the area,we explained their acoustic causes and discussed (1)the origin relation between shallow gas and acoustic reflection in seawater column,(2)shallow gas causing the giant sunken pit, and (3)concentration indications of the shallow gas seismic features.Based on the shallow gas seismic features,we mapped the distribution of shallow gas in this region.