海底地震仪(OBS)主动源转换横波的应用
The Application of Converted S-Waves from the Active-Source Ocean Bottom Seismometer Experiment

横波(S波)为偏振波，具有不同于纵波(P波)的特性，对于地震探测具有特殊的意义.在被动源地震探测中已得到广泛的应用，如接收函数、S波分裂等.在主动源(气枪)海底地震(OBS)探测中，震源在水中，S波为地层转换波，其应用还不多.本文在介绍转换S波的产生、模式、处理和识别的基础上，以实例为切入点简述其具体应用.这些应用主要是基于1D/2D转换S波，用于揭示海底岩石类型、推断地壳性质、共轭陆缘问题、判定地幔蛇纹石化、估算天然气水合物的饱和度和预测流体等.目前在南海已获得了大量的2D和3D的OBS转换S波数据，可将转换S波的研究逐步从2D发展到3D研究，同时结合其他地球物理资料进行共同分析.利用转换S波的研究，有利于揭示南海扩张停止后形成的海山下不同地层的岩性和判定上地幔低速的性质等.
Shear waves are polarized waves showing different characteristics from compressional waves, which are specially important to the seismic exploration. They have been widely used in the passive-source seismic studies, such as the receiver functions and shear wave splitting. However the application of shear waves is still limited in the active-source ocean bottom seismometer exploration. Shear waves are converted waves for the underwater seismic source. In this paper, we firstly summarize the conversion, mode type, processes and identification of shear waves. And we also use real examples to introduce different applications in different oceans. The studies of converted shear waves are mainly used to reveal the submarine rock property, infer the crustal type, discuss the conjugate relationship of the continental margin, identify the mantle serpentinization, infer gas hydrate saturation and predict the fluids based on 1D/2D converted shear waves. Numerous 2D/3D OBS data have been collected in the South China Sea, hence we can gradually change the studies of converted shear waves from 2D to 3D and conduct analysis in combination with other geophysical data . Using those data will help to reveal the composition of seamounts and identify the porosity of the low-velocity upper mantle in the South China Sea