南沙海域海底浅层第四系地震地层结构与地质意义

摘要

科技进步使得地震采集数据量及其精度实现质的飞跃,南沙海域的地震调查,采用国际先进水平的等离子震源,获得地震剖面精度优于3 m局部甚至可在1 m之内,为科学研究、工程、浅层资源、地质灾害预警等研究奠定基础.在南沙第四系识别出了七个地震反射界面,确定500 ms至海底沉积区间内地震层序与三期海平面升降并与冰期、间冰期对应,典型地震剖面展示第四纪至少有三套完整的具有三角洲顶积层、前积层、底积层的地震相证据,与全球的第四纪海平面的变化一致.精细的浅层地震结构表明:南沙的地质现象丰富,浅层断层非常发育,下切河谷、泥石流、滑坡等地质遗迹的形成的地震相清晰,是地质活动频繁的地区.%Technological progress helps scientists obtain more accurate seismic data.Seismic survey around the Nansha Islands,which adopted the plasma source for the first time,acquired seismic sections with 3 m accuracy and in some areas even achieved 1 m accuracy.This seismic survey provides new data for scientific research,engineering,shallow resources investigation,geological disaster warning and others.Seven seismic reflection interfaces of Quaternary strata around Nansha are identified in this paper.Within the seismic sequence from 500 ms to seabed sediments,three phases of sea level change are recognized.Whether the phase of sea level change was in glacial or interglacial periods is discussed.Typical seismic profiles indicate that there are at least three integrated seismic facies including delta topset,foreset bed and bottomset bed,which correspond to the Quaternary global sea level change.The high-resolution Quaternary seismic structure around Nansha indicates numerous geological phenomena of Nansha,such as shallow faults,incised valleys and landslides which created sharp seismic phases,representing frequent geological activities in this region.