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Geological hazards in Lingshui region of Qiongdongnan Basin: type, distribution and origin

WANG Junqin;ZHANG Guangxu;CHEN Duanxin;WANG Xiujuan;WANG Zhenzhen;DONG Dongdong;ZHUANG Lihua;HUANG Jie;ZHU Yousheng;LUO Jinhua;CNOOC Research Institute;Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences;Center for Ocean Mega-Science,Chinese Academy of Sciences;Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology;Laboratory for Marine Geology,Qingdao National Laboratory for Marine Science and Technology;Zhanjiang Branch,CNOOC China Limited;China Oilfield Services Limited;  
The Lingshui slope region( LS hereafter) of the Qiongdongnan basin in the South China Sea is located in the shelf edge and slope zone to the north of Xisha Trough. Various types of geohazards occur pervasively. With 3 D seismic data in the LS region, various geohazards, such as submarine landslides, fault, fluid pipes, pockmarks and mounds in addition to BSRs of gas hydrates are recognized. Seismic features and distribution patterns of the geohazards are analyzed in the paper, and the origins of these geohazards are discussed in association of regional tectonics and sedimentation. The geohazards are widely distributed in an area over 2000 km~2. Basement faults, enormous sediment supply and relatively high sea level are the dominating factors to control the occurrence and distribution of geohazards. Especially, the high sedimentation rate in late Quaternary may lead to the deposition of thick sediments and accumulation of natural gas on shelf margin and upper slope, which was prone to form over-pressured layers for the formation of gas hydrate. In the steep slope region, landslide deposits are often observed, in particular in the aggradational phase. However, on the shelf margin and upper gentle slope where landslides rarely appeared, overpressured fluid may erupt to form fluid pipes, mounds and pockmarks. Burial landslides and regionally tectonic activities are believed to be the major factors to trigger the release of overpressured fluid. This study is proved useful to deepwater engineering, such as site selection, drilling and pipeline construction.
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