南海北部海底滑坡的特征、灾害评估和研究展望

doi:10.13745/j.esf.sf.2020.9.3

摘要/Abstract

摘要：

海底滑坡及其触发的海啸是海洋地质灾害的重要组成部分。随着海洋工程设施及沿海地区人口及经济的快速增长,海洋地质灾害研究和评估变得越来越重要和紧迫。根据高精度地球物理资料(地震和多波束),在南海北部主要含油气盆地(珠江口盆地和琼东南盆地)中发现大量的海底滑坡。这些海底滑坡形成于上新世至第四纪,它们多以杂乱或空白的地震反射为特征,部分海底滑坡含有大量滑塌块体;这些海底滑坡的规模从数平方千米至上万平方千米不等。本文梳理了南海北部海底滑坡的特征;并对包括西沙隆起在内的海底滑坡所造成的直接灾害和次生灾害(海啸)进行初步评估;最后,指出了南海北部未来海底滑坡研究中需要解决并有望取得突破的主要科学(海底滑坡的成因机制)和实践(潜在海底滑坡及其触发海啸可能性)问题。

关键词: 海底滑坡, 海啸, 地质灾害, 灾害评估, 南海北部

Abstract:

Submarine landslides and the tsunamis they trigger can cause catastrophic damage to the infrastructure, economy, and lives increasingly expanding on the sea and along the coastlines. Therefore, quick technological progress is needed to guard against geohazards triggered by submarine landslides. Submarine landslides are identified by a large amount of geophysical data (seismic and multibeam bathymetrical data) in the petroliferous basins (the Pearl River Mouth Basin and the Qiongdongnan Basin) along the margin of the northern South China Sea. These submarine landslides formed from the Pliocene to Quaternary periods, ranging in size from several to over ten thousand square kilometers. They are mostly characterized by chaotic and blank seismic reflections; some contain a large number of collapse blocks. The seismic characteristics, sizes, origins, and geohazard potentials of these submarine landslides vary greatly because of their different developing environments. In this study, the seismic expression of submarine landslides is characterized, and their direct and indirect geohazard potentials (including those in the Xisha Massif) are evaluated. Finally, the important scientific (formation mechanism of submarine landslide) and practical questions (possible submarine landslides and landslide-generated tsunami) arising from this research are discussed.

Key words: submarine landslide, tsunami, geohazard, geohazard evaluation, northern South China Sea

中图分类号:

孙启良, 解习农, 吴时国. 南海北部海底滑坡的特征、灾害评估和研究展望[J]. 地学前缘, 2021, 28(2): 258-270.

SUN Qiliang, XIE Xinong, WU Shiguo. Submarine landslides in the northern South China Sea: characteristics, geohazard evaluation and perspectives[J]. Earth Science Frontiers, 2021, 28(2): 258-270.

图/表 8

图1 研究区位置图(海底峡谷、红河—越东断裂带及马尼拉海沟分别引自文献[26,27];底图修改自文献[28])

Fig.1 Locations of the study area.Canyons, Red River-East Vietnam faults and Manila Trench are adapted from [26-27], respectively; base map is modified after [28].

图2 珠江口盆地(修改自文献[34,36])和琼东南盆地(修改自文献[37])综合柱状图珠江口盆地和琼东南盆地海底滑坡分别形成于第四纪和上新世—第四纪时期[17,36]。

Fig.2 Schematic stratigraphic columns of the Pearl River Mouth Basin and the Qiongdongnan Basin. Modified after [34,36-37].

图3 白云滑坡三维地形地貌特征白色短虚线为白云滑坡边界,白色长虚线为滑塌物质运动方向。

Fig.3 3D visualization of the Baiyun Submarine Landslide

图4 白云滑坡头部三维地震特征 a—南北向地震剖面展示白云滑坡陡峭的侧壁,正断层发育在陡坎的下部;b—东西向地震剖面展示海底滑坡的头部陡坎,浅层气发育在头部陡坎的下部。白云滑坡(浅蓝色区域)表现为杂乱或空白的地震反射特征。

Fig.4 3D seismic characteristics of the Baiyun Submarine Landslide in its head zone

图5 白云滑坡在中陆坡和洋盆中的地震特征 a—在中陆坡可以清晰识别出白云滑坡的侧壁陡坎,白云滑坡由多期次滑坡事件所组成;b—白云滑坡在洋盆中表现为丘状的沉积体,局部存在侵蚀凹槽。白云滑坡(浅蓝色区域)表现为杂乱或空白的地震反射特征。

Fig.5 Seismic characteristics of the Baiyun Submarine Landslide in the middle slope and ocean basin

图6 琼东南盆地海底滑坡特征 a—三维地震剖面显示琼东南盆地上新世以来地层几乎全部由海底滑坡物质组成,每期海底滑坡直接可以以负相位区分开,线性或者弧形的滑塌块体存在于海底滑坡沉积物中,在海底滑坡界面处也可以观察到浅层气的存在;b—海底滑坡10底界面处的相干体切片,滑塌块体和滑坡体边界清晰可见。

Fig.6 Characteristics of submarine slope failures in the Qiongdongnan Basin

图7 琼东南盆地海底滑坡局部三维图 a—琼东南盆地西部现今海底中陆坡垮塌所形成的滑动(漂移)块体;b—琼东南盆地中部地区陆坡形态特征。

Fig.7 3D visualization of submarine slope failures in the Qiongdongnan Basin

图8 南海北部陆坡区和西沙隆起区域古海底滑坡(已发生)、潜在海底滑坡(可能发生)以及海底滑坡所触发的直接灾害和次生灾害初步评估

Fig.8 Summaries of paleo-submarine landslides, possible submarine landslides and their triggered direct or indirect geohazards in the northern slopes of the South China Sea and the Xisha Massif

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