琼东南盆地陵水研究区海底地质灾害类型、分布和成因机制

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

琼东南盆地陵水研究区位于西沙海槽北部的陆架边缘和陆坡区,地质灾害广泛分布。利用三维反射地震数据,在琼东南盆地陵水研究区识别了海底滑坡、麻坑、丘状体、流体管道、天然气水合物(BSRs)、活动断层等海底地质灾害体,并分析了各类地质灾害体的地震反射特征和分布规律。结合区域构造和沉积演化过程,分析了地质灾害体的成因机制。研究表明,灾害体的分布面积总计超过2000km^2,各类灾害体相互叠置。构造断层活动、充足物源供给和海平面变化是导致该地区海底地质灾害广泛分布的重要原因。第四纪晚期高沉积速率导致陆架边缘和陆坡区沉积了较厚地层,有机质丰富,为水合物成藏提供了潜在气源。陆坡区的滑坡主要分布在加积层序较发育的陡坡区。在陆架边缘和滑坡不太发育的陆坡缓坡区,超压流体释放形成流体管道、丘状体和麻坑。高沉积速率、埋藏的古滑坡和区域的构造不稳定性是诱发超压流体释放的重要因素。

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.