南黄海OBS数据转换横波分析及其地质意义

摘要

多分量地震勘探在减小地球物理反演问题多解性的同时提供了更丰富的地下信息,可以从量化的意义上真正实现岩性勘探.由于地壳结构的复杂性及转换横波的特殊性,南黄海地壳结构研究中基本未涉及横波.本文使用南黄海OBS数据,在不同剖面上对比分析纵横波走时、视速度以及质点运动轨迹,基于纵波理论模型对转换横波震相进行射线追踪和走时试算,识别并拟合了来自不同地层的转换横波震相.研究表明,北部坳陷中主要发生了PPS转换,转换界面为陆相沉积层底界面.千里岩隆起区除了发生转换界面为陆相沉积底界面的PPS转换还有转换界面为海底的PSS转换.断层活动引起岩石破碎,高波速比特征的断层边界为胶莱盆地在海上部分的边界圈定再添证据.千里岩地区高速地层成分含有花岗岩,其纵横波速比为1.67～1.68;推测北部坳陷中的海相沉积北-南地层不同,依次为碳酸盐岩及砂岩两类地层.%Multi-component seismic exploration can reduce the multi-solutions of geophysical inversion.Meanwhile it is able to reveal more abundant underground information.Multicomponent seismic exploration can realize lithologic exploration from a quantitative perspective.S-waves are rarely involved in the study of crust structure in the South Yellow Sea (SYS) for the complexity of the crust structure and the particularity of converted shear waves.With analysis of travel time of OBS data from SYS,this work did ray tracing and fitting to apparent velocity and particle trajectory between P-component and inline component,the transformation phases from crust and sediments based on the known P-wave velocity model.The results show that only PPS mode,whose surface is the continental deposit bottom interface,appears in the North Depression (ND) of the SYS.Both PPS mode and PSS modes are present in the Qianliyan Uplift (QU) and have significant differences in velocity.High VP/VS ratios caused by rock breaking as a result of the fault activity are another piece of evidence regarding to the boundary of the Jiaolai Basin in theSYS.The high velocity layer in the QU mainly comprise metamorphic granite with probable rich silicon,whose ratios range from 1.67～1.68.The VP/VS ratios of the marine sedimentary layer display the characteristics of carbonate rock in the ND.However,the sediment beneath the continental deposit layer is most likely composed of sandstone in the southeast of the ND.