基于AUV观测数据的南海东沙北部浅表层精细地质特征及其灾害因素分析

Analysis of shallow surface fine geological characteristics and hazard factors of the seabed in the northern part of Dongsha,South China Sea based on AUV data

全面认识海底浅表层地质特征是识别和评价浅层海洋地质灾害的基础,对海洋资源开发、海洋工程建设等有重要意义。南海东沙北部有多个油气田正在勘探开发,但目前缺少对东沙北部海底浅表层精细地质特征的系统分析。针对南海东沙北部水深100~400m区域,综合利用AUV(autonomous underwater vehicle)多波束、AUV浅地层剖面、二维地震、沉积物测试等数据,识别了浅表层地质灾害因素,并对其风险性进行了评估。调查发现,研究区海底表层沉积物总体相对稳定,发育有沙波、陡坎、冲沟等海底微地貌;海底以下浅层未见浅层气,多处发育埋藏古河道。海底沙波的形态和分布特征具有显著的空间差异,波高大于1m的沙波主要分布于水深134~143m、168~187m、205m以深区域,并且能够在现代动力条件下发生移动,观测结果显示海底沙波的发育与内波过程相关。陡坎坡度超过20°,本文认为这与贯穿浅层的断层有关。

A comprehensive understanding of the geological characteristics of shallow strata of seabed is the basis for identifying and evaluating shallow marine geological hazards,which is of great significance to the development of marine resources and marine engineering construction.Multiple oil and gas fields are being explored and developed in northern Dongsha,South China Sea.However,there is a lack of systematic analysis of the fine geological characteristics of the shallow strata in this place.Based on the diverse data of AUV(autonomous underwater vehicle),multi-beam,AUV shallow stratum profile,2D seismic data and sediment test,the factors of shallow strata geological hazards were identified and their risks were evaluated in the area of 100~400m water depth in northern Dongsha,South China Sea.The survey found that the seabed surface sediments in the study area were generally relatively stable,and several micro-geomorphologies of the seabed,such as sand waves,steep steps and gullies developed.Shallow gas below the seabed was not observed,and numerous paleovalleys are developed.Significant spatial differences are featured in the shape and distribution characteristics of seabed sand waves.The sand waves with wave height greater than 1m are mainly distributed in the depths of 134~143m,168~187m and 205m,they can move positions under modern dynamic conditions.The observation results show that the development of seabed sand waves is related to the process of internal waves.The steep steps are more than 20°,which is considered to be related to the faults running through the shallow strata.