Previous studies of gas hydrate in the Dongsha area mainly focused on the deep-seated gas hydrates that have a high energy potential, but cared little about the shallow gas hydrates occurrences. Shallow gas hydrates have been confirmed by drill cores at three sites (GMGS2 08, GMGS2 09 and GMGS2 16) during the GMGS2 cruise, which occur as veins, blocky nodules or massive layers, at 8–30 m below the seafloor. Gas chimneys and faults observed on the seismic sections are the two main fluid migration pathways. The deep-seated gas hydrate and the shallow hydrate-bearing sediments are two main seals for the migrating gas. The occurrences of shallow gas hydrates are mainly controlled by the migration of fluid along shallow faults and the presence of deep-seated gas hydrates. Active gas leakage is taking place at a relatively high-flux state through the vent structures identified on the geophysical data at the seafloor, although without resulting in gas plumes easily detectable by acoustic methods. The presence of strong reflections on the high-resolution seismic profiles and dim or chaotic layers in the sub-bottom profiles are most likely good indicators of shallow gas hydrates in the Dongsha area. Active cold seeps, indicated by either gas plume or seepage vent, can also be used as indicators for neighboring shallow gas hydrates and the gas hydrate system that is highly dynamic in the Dongsha area.

以前在东沙地区进行的天然气水合物研究主要集中在具有较高能量潜力的深层天然气水合物，而对浅层天然气水合物的发生却很少关心。在GMGS2航行期间，已在三个地点（GMGS2 08，GMGS2 09和GMGS2 16）的钻芯确认了浅层天然气水合物，它们以脉状，块状结节或块状层的形式出现在海床以下8–30 m。在地震剖面上观察到的烟囱和断层是两个主要的流体运移路径。深层天然气水合物和浅层含水合物的沉积物是运气的两个主要密封。浅层天然气水合物的发生主要受流体沿浅层断层的运移和深层天然气水合物的存在控制。通过海底地球物理数据上确定的通风孔结构，活跃的气体泄漏以相对较高的通量状态发生，尽管不会导致通过声学方法容易检测到的气体羽流。在高分辨率地震剖面上以及在下底剖面的暗淡或混沌层上强烈反射的存在最有可能是东沙地区浅层天然气水合物的良好指示。活跃的冷渗漏（由气柱或渗流孔表示）也可以用作邻近浅层天然气水合物和东沙地区高度活跃的天然气水合物系统的指标。在高分辨率地震剖面上以及在下底剖面的暗淡或混沌层上强烈反射的存在最有可能是东沙地区浅层天然气水合物的良好指示。活跃的冷渗漏（由气柱或渗流孔表示）也可以用作邻近浅层天然气水合物和东沙地区高度活跃的天然气水合物系统的指标。在高分辨率地震剖面上以及在下底剖面的暗淡或混沌层上强烈反射的存在最有可能是东沙地区浅层天然气水合物的良好指示。活跃的冷渗漏（由气柱或渗流孔表示）也可以用作邻近浅层天然气水合物和东沙地区高度活跃的天然气水合物系统的指标。