作　　者： ; ;

机构地区： 自然资源部海底矿产资源重点实验室广州510075

出　　处： 《海洋地质前沿》 2019年第7期54-61,共8页

摘　　要： 浅表层水合物对于理解冷泉系统以及水合物对环境变化的响应非常重要。由于赋存位置较浅,且赋存的范围一般较小,目前尚缺乏探测浅表层水合物的系统方法。以南海珠江口盆地东部海域GMGS2-08站位为例,综合利用多个不同频率的数据刻画浅表层水合物的赋存。所用的数据包括多道地震数据(主频65Hz)、初次高频浅剖(22kHz)以及二次低频浅剖数据(4kHz)。多道地震上似海底反射(BSR)以不连续的方式出现,表明局部地层受到向上运移流体的扰动。在浅剖剖面上,识别出声空白、增强反射以及弱振幅海底等冷泉系统相关的特征。多道地震剖面上海底反射表现为两个非常接近的强反射轴(相距约16ms),这与正常的海底反射特征不一致。计算表明,海底反射中第2个强反射轴对应的界面深度大约在海底以下12m处。二次低频浅剖剖面上,气烟囱的顶部出现在海底以下大约13.5m处。考虑到计算中存在的误差,认为气烟囱的顶部对应了海底反射中第2个同相轴。此外,根据地震以及浅剖数据识别出的界面与浅表层水合物样品的深度(海底以下9~22m)以及声波测井曲线上高速异常的深度(海底以下9~22m)是一致的。综合利用多频率数据成像能够有效的刻画浅表层水合物的赋存,并能对其形成过程推测。 A large amount of methane may migrate upward to the seafloor and then form shallow gas hydrates deposits there.This type of gas hydrates helps understand how cold seeps and gas hydrates respond to the change of environments.Approaches for detecting the shallow gas hydrate as such has not been well established so far since the shallow gas hydrates occur too close to the seafloor and often in small scale.Taking the GMGS-08 site as an example,we use multi-frequency method to characterize the shallow gas hydrates.The data used includes multi-channel seismic data(~65 Hz),primary high frequency(22 kHz)and secondary low frequency(4 kHz)sub-bottom profiler data.On the seismic data,BSR occurs in a discontinuous way,suggesting perturbations due to the ascent of fluid.On the sub-bottom profiler,acoustic blanking,enhanced amplitude and weak seafloor amplitude are observed and related to cold seep systems.In addition,on the seismic data,the seafloor is characterized by two close strong event(time distance of^16 ms),rather than a single one and this is different from the normal seafloor reflection.Calculation shows that the interface corresponding to the second event lies^12 mbelow the seafloor.On the secondary low frequency profile,the top of the gas chimney lies^13.5 mbelow the seafloor.Accounting the errors during the calculation,we infer that the top of the gas chimney correspond to the second event of the seafloor reflection.Moreover,these two depths are consistent with the interval where shallow gas hydrates are recovered and high velocity anomaly observed.The latter depths are 9-22 mbelow the seafloor.Our results show that multi-frequency imaging is effective in charactering the shallow gas hydrate and is useful in speculating the formation process.

关 键 词： 浅表层水合物 珠江口盆地东部海域 多频率成像 冷泉

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