珠江口外伶仃洋海底含气沉积物声波反射及衰减特征

Acoustic reflection and attenuation characteristics of gas-containing sediment in the outer Lingding Bay of the Zhujiang Estuary in China

高分辨率地震剖面显示,在珠江口外伶仃洋海底有大面积含气沉积物。根据含气沉积物地震反射特征将其分为声学空白、声学幕、声学扰动、不规则强反射顶部和相位下拉等类型。对含气沉积物声波衰减初步分析表明约在3.3 kHz附近有一衰减峰值,将实际资料与理论模型计算进行对比,认为此峰值频率对应于等效半径约6 mm的气泡的特征振荡频率,此等效半径气泡的阻尼振荡是引起声波衰减的主要原因。

High-resolution seismic profiles indicate that there is a large area of seafloor gas-containing sediment in the outer Lingding Bay of the Zhujiang Estuary. According to the seismic reflection characteristics of gas-containing sediment, the seismic features of shallow gas are divided into five types： an acoustic blanket, an acoustic curtain, acoustic turbidity, an irregular strong top reflection boundary, and a reflection phase pull-down. The acoustic attenuation of gas-containing sediment is primarily analyzed. The result indicates that there is an attenuation peak near the frequency of 3.3 kHz. According to the comparison between surveying data and model results, it is demonstrated that the attenuation peak frequency corresponds to the fundamental resonance frequency of bubbles with 6 mm equivalent radium. The primary conclusion is drawn that the acoustic attenuation is mainly caused by the damping resonance of bubbles with the 6 mm equivalent radium.