舟山群岛岱衢洋海床的活动性研究及其工程意义

A study on sea bed activity and its engineering implications at the Daiqu Sea in Zhoushan Archipelago

浙江舟山群岛北部岱衢洋为一双槽型峡道,由北部潮流冲刷槽、中部海底平原、南部潮流沙脊和冲刷槽等四个地貌单元构成。应用浅地层剖面、侧扫声呐、回声测深、沉积物取样等地质地球物理调查手段,对峡道内海床活动性进行了综合研究,结果表明近年来北部潮流冲刷槽无明显变化,中南部海底平原冲刷沟微地貌进一步发育,南部潮流沙脊向陡翼一侧移动并造成相邻冲刷槽略微淤积。冲刷沟微地貌发育区与浅层气浅埋/出露区基本重合,含气地层浅埋(<5m)或出露海底可能促进了冲刷沟微地貌的发育。在研究区内曾发生因海床冲刷造成输油管道悬空断裂的溢油事故,可见,海底平原区并非是绝对安全区,今后应加强此类灾害地质环境研究和工程后的长期监测跟进。研究结果对舟山海域及其它类似海洋环境的工程设计、施工和维护都具有借鉴意义。

The Daiqu Sea, located in the northern part of the Zhoushan Archipelago, China, is a strait between two islands with tidal current scour troughs along the both banks. The seafloor can be subdivided into four morphologic units, including the North Tidal Current Scour Trough, Middle Plain, South Tidal Current Ridge and South Tidal Current Scour Trough. Just a few years ago a subsea buried oil pipeline across the sea was broken due to tidal souring and resulting in oil pollution. This paper studies on the sea bed activities of the study area, based on the data of sub-bottom profiling, side scan sonar, echo sounding and sea bottom sediment sampling. The results show that from 2003 to 2008, the North Tidal Current Scour Trough was relatively stable, tidal gullies in the Middle Plain were undergoing relatively rapid evolution, and the South Tidal Current Ridge migrated slightly southward. The tidal-gully developing area is just superposed with where the shallow buried gas is highly elevated or even leaked directly to the seafloor. The shallow buried gas, typically with a buried depth less than 5m, might have triggered the development of tidal gullies. The results are useful for strait engineering planning, implementation, and maintenance in the similar marine environments.