南沙东北部海域地震速度岩性分析应用  

APPLICATION OF SEISMIC VELOCITY TO THE AREA OF NORTHEASTERN NANSHA WATERS

作　　者：樊奇[1] 田继军[1] 成赛男[1] 张杰[2] 姚永坚[3] 张江勇[3] 赵利[3] 

机构地区：[1]新疆大学地质与矿业工程学院,乌鲁木齐830047 [2]成都理工大学地球科学学院,成都610059 [3]国土资源部广州海洋地质调查局,广州510760

出　　处：《海洋地质前沿》2015年第12期42-51,共10页Marine Geology Frontiers

基　　金：国家重大专项"天然气水合物资源勘查与试采工程"(2011-2020)子课题

摘　　要：南沙海域油气等矿产资源丰富,但受客观因素所限,该区地质调查工作仅限于二维地震勘探和表层取样,而对沉积盆地古地理特征的了解近乎空白。因此,利用地震速度资料求取速度场分布特征、建立速度岩性关系并恢复地层分布特征,成为了南沙区域地质调查工作中十分重要的工作手段。以二维地震资料为基础,利用速度谱解释和层速度计算、制作时深转换尺和砂泥岩性量板、绘制砂比指数平面图,并开展探讨及相关分析。研究表明:埋深和岩性是影响速度的主要因素,通过速度岩性量板的建立,可以有效识别研究区岩性分布规律、判断物源及沉积变化;南沙东北部物源方向及沉积特征的变化与南沙地块新生代裂谷期、漂移期、前陆期的构造演化相互关联,其物源分别来自华南古陆块、内生物源及菲律宾岛弧,借此可以初步认识南沙东北部海域沉积分布。研究发现,对能量团速度的理解差异导致了海底起算时间在不同运算步骤中的不同结果,而这种差异表现应该引起重视。上述工作有助于为该区地质调查工作提供参考。The Eastern Nansha Waters are rich in resources such as oil and gas, gas hydrate and poly- metallic nodules. However, geological survey is only limited to 2D seismics, gravity, magnetism, surface sampling due to technical limitations and other reasons. The understanding of the structural geology and stratigraphy of the sedimentary basins in the Nansha is almost blank. In this regard, seis- mic velocity data has become the only mean to explore the regional pattern of the seismic velocity field, to establish the relationship between speed and lithology and to reconstruct palaeofacies. Based on 2D seismic data, we made seismic stratigraphic calibration and structural interpretation, velocity spectrum interpretation and velocity calculations, time-depth conversion, the envelope template of sand and shale, and compilation of maps of sand distribution. Results show that, depth and lithology are the main factors controlling the difference in velocity, the envelope template of sand and shale can be used to identify the distribution pattern of lithology and the evolution of depositional provenance. It is recognized that the Cenozoic sediments of the region could be grouped into 3 super sequences, i.e. the pre-rifting, drifting and foreland sequences. As to the provenance, sediments are mainly from the Huanan paleoland, endogenic deposition and Philippine arc. It is also found that difference in under- standing of energy group velocity formula has lead to different results of velocity calculation, and at- tentions should be paid to every step of the performance. The above work will help clarifying the structural and stratigraphic pattern of the area and be effective for further geological survey in the Nansha Waters.

关 键 词：地震速度 岩性 时深转换 新生代 南沙海域 

分 类 号：P315[天文地球—地震学]