舟山六横岛海域浅部地层结构 与水下滑坡分布特征

舟山群岛海域峡道密布,峡道边坡失稳现象普遍发育,规模不一。多发的水下滑坡对海底光缆、港口码头等海岸工程设施都有较大威胁。2012年12月,使用浅地层剖面仪对六横岛周边峡道区进行探测,划分出3个主要声学反射界面以及4个地层单元,上部3个地层为全新世沉积层。发现6处水下滑坡,分布于六横岛沿岸边坡及毗邻的潮流深槽边坡。滑坡结构均为整体性滑坡,部分具多级性。从滑坡体规模看,滑坡体体积介于1.6×10⁵~2.7×10⁷ m³之间,其中超大型滑坡2处、大型滑坡3处、中型滑坡1处。根据界面与滑坡体的相关性,推测水下滑坡均发生在距今2.5 ka以来的全新世晚期。

Distribution characteristics of subaqueous landslides in the sea area of Liuheng Island,Zhoushan

The strait channels are densely covered in the sea area of Zhoushan Islands, and the instability of the slopes of the strait channels is generally developed and varied in scale. The frequent subaqueous landslides pose a greater threat to coastal engineering facilities such as submarine cables and port terminals. In December 2012, the sub-bottom profiles were detected in the sea area of Liuheng Island. Three main acoustic reflection interfaces and four formation units were divided, and the upper three formations were Holocene sedimentary layers. Six subaqueous landslides were found, which were scattered along the coast of Liuheng Island or adjacent to the strait channel slope. The landslides structure were whole landslide, and some of them were multi-step. From the scale of the subaqueous landslides, the volumes were between 1.6×10⁵ to 2.7×10⁷ m³, with 2 super-large landslides, 3 large landslides and 1 medium landslide. According to the correlation between the interface and the landslide body, it was speculated that the subaqueous landslides occurred in the late Holocene since 2.5 ka.