南黄海西部地区浅层气地震特征

通过近年来南黄海西部地区的浅层地震调查,发现该地区浅层气地震特征丰富而多变,特别是多处海底面、海水层中的浅层气地震记录,揭示本区存在较多浅层气,且部分浅层气由海底逸出,释放到海水层中。该区的浅层气地震特征按空间位置分为3大类:(1)地层中的特征:声学空白、声学幕、声学扰动、不规则强反射顶界面、两侧相位下拉;(2)海底面的特征:海底麻坑、大型塌陷坑;(3)海水层中的特征:声学羽流、云状扰动、点划线反射。选择相应特征的典型浅层气地震记录,进行了声学成因解释,讨论了大型塌陷坑的浅层气成因、海水层中声学反射与浅层气体的成因关系以及浅层气地震特征的气体浓度指示作用。根据南黄海西部地区浅层气地震特征,绘制了该区的浅层气分布图。

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.