海床浅表层硬质薄层的声学识别

由沉溺珊瑚礁、各类胶结砂以及胶结的珊瑚石或贝壳碎屑等组成的硬质薄层通常呈零散状分布，地质取样难以准确确定它们是如何分布的，这给海底管线施工带来极大的困难和风险。本文以南海北部为例，基于多种物探资料并结合正演模拟，分析、总结了海底以及海底之下硬质薄层的声学特征，在研究区综合识别出23个硬质薄层分布区。研究认为，硬质薄层与松散沉积物物理性质的差异可用于声学探测数据识别和定位。在浅地层剖面上，硬质薄层表现为强反射薄层，并对其下方地层的地震反射信号有一定的屏蔽作用，这一现象有助于确定硬质薄层是否存在以及其埋深和位置。在侧扫声呐影像和后向散射强度图上，硬质薄层通常表现为具有不规则形状的明暗变化阴影，阴影的边界指示了硬质薄层的分布范围。当硬质薄层出露于海底时，侧扫影像、反向散射强度结合浅地层剖面可以有效地识别并确定硬质薄层的范围；而当硬质薄层位于海床浅部（埋深数米到十几米）时，浅地层剖面可能是识别硬质薄层的唯一且最有效的方法。

Identification of hard-thin layers on the seabed or shallow sediments using geophysical data: A case study in the Liwan pipeline route,northern South China Sea

The hard-thin layers (HTLs) are usually composed of submerged coral reefs, various cemented sands, cemented coral stones or shell fragments and their locations are difficult to be determined by geological sampling due to their sporadic distribution. They bring great challenges and risks to the construction of submarine pipelines. In this paper, taking the northern shelf of the South China Sea as an example, we summarized the acoustic characteristics of the HTLs on the seabed and in the shallow sediments based on a variety of high-resolution geophysical data combined with forward simulation analysis. Twenty-three areas with HTLs in the study area were determined. Our study suggests that differences in the physical properties of HTLs and loose sediments help identify and locate them using high-resolution geophysical data. On the sub-bottom profiles, the HTLs are characterized by reflective interfaces with high-amplitude, beneath of which the low-amplitude reflections usually occur. These reflection features help to determine the HTLs, their depths and locations. The HTLs usually display the alternating light and dark zones with irregular boundaries on the side scan sonar and backscatter intensity images. When the HTLs are located on the seafloor, the comprehensive interpretation of the side-scan images, backscatter intensity images and the sub-bottom profiles is effective to identify and locate them. For those THLs several meters to ten meters below the seafloor, high-resolution sub-bottom profiles may be the only and most effective way to identify and locate them.