南海北部新生界地层的远偏移距折射波速度特征

Far offset refractive velocity properties of the Cenozoic strata in the northern South China Sea

南海北部为张裂大陆边缘,在新生代时期经历了复杂的地质演化,具有良好油气勘探前景.本文首次利用南海北部某区域长排列地震数据的远偏移距折射波速度计算方法获得南海北部地层层速度,并进行了分析,此外,还提出了非初至折射波的概念.本方法在共偏移距剖面上识别、拾取折射波层位,得到折射波走时的横向连续变化数据,利用不同共偏移距同一折射波层位的到达时差计算该折射层位的速度结构.该方法在南海北部陆坡某区域地震资料的应用,揭示了新生界地层层速度的整体结构,反映了新生代不同时代地层的速度变化特征,为进一步利用折射层速度资料探讨南海新生代地质演化提供了新的视角.研究表明,与常规初至折射波法相比,远偏移距折射波能够提供更多的地质信息;该方法的初步应用能够对远偏移距折射波的研究提供进一步的视角.

The northern South China Sea is a rifted continental margin. It has experienced complicated geological evolution and has been proved to have the prospect of oil and natural gas. In this paper, the velocity structures of strata in the northern South China Sea are obtained and analyzed by the velocity structure calculation of far offset refractive wave method using the long cable multi-channel seismic data collected in a northern region of South China Sea and in addition, the conception of non first-arrival refractive wave is proposed. In this method, refractive horizons are recognized; travel times of the same horizon in different common offset sections and different horizons in the same common offset section are collected. The velocity structure of the same horizon is calculated by the difference of travel-time in different common offset sections. The application of this method in a northern region of South China Sea reveals the whole velocity structure and the velocity change prosperities of the Cenozoic strata of different ages. The application provides a fresh sight using far offset refractive velocity structure to study the Cenozoic geological evolution of South China Sea. The results show that far offset refractive wave method supplies more geological information compared with the conventional first-arrival refractive wave method~ the preliminary application provides a new insight for the research of far offset refractive wave method.