南海珠江口盆地东部海域含似海底反射沉积层纵波速度结构：反射波旅行时反演结果

摘要

文章利用2012年广州海洋地质调查局在南海珠江口盆地东部海域采集的多道地震(MCS)，通过反射波旅行时反演了含似海底反射(BSR)沉积层的纵波速度结构。从反演的速度结构上，我们发现BSR上方附近速度在横向上变化较大，存在一个明显的相对高速区域(1800~2200m×s-1)以及一个相对低速的区域(1500~1700m×s-1)。结合多道地震成像的结果，我们把相对高速区域解释为含水合物层，而相对低速区域可能不含水合物或者仅含少量的水合物。BSR 一般认为是水合物稳定存在区域的底界面，反演的速度结构结果表明水合物在稳定带内分布不稳定、不连续。相对低速区域的存在可能表明该低速区域下的BSR与水合物的赋存无关，仅仅反映了正常沉积地层与下伏游离气层的界面。%This paper reports the velocity structure of bottom simulating reflector (BSR) -bearing sediment layers from the reflection travel time inversion, using the data acquired in 2012 by Guangzhou marine geological survey in the eastern Pearl River Mouth Basin of the South China Sea. The results show great lateral variation in velocity, namely, there exist a relatively high velocity zone (1800~2200m×s-1) and a relatively low velocity zone. Combed with the Multi-channel seismic (MCS) image, we interpret the relatively high velocity zone as gas hydrate-bearing sediments, and the relatively low velocity zone as sediments with no gas hydrate or little gas hydrate. BSR is often considered as the base of gas hydrate stability zone (GHSZ), and our results suggest that gas hydrate has irregular distribution in the stability zone. The relatively low velocity zone indicates that the BSR below may not be associated with gas hydrate, only reflecting the boundary between the normal sediments above and the free gas-bearing sediments below.