基于Scholte波频散特性的深海海底横波速度反演

Shear wave velocity inversion of marine sediments using deep-water OBS Scholte-wave data

深海环境下海水的声波速度是非匀速的,变速的海水会影响海底Scholte波的频散特性,为了提高利用Scholte波频散特性反演海底横波速度的精度,需建立速度连续变化的水平分层海水-分层海底(HLSLS)模型。本文基于波动理论推导HLSLS模型Scholte波频散方程和振幅深度方程。然后,基于南海海水声速剖面和实际海底弹性介质参数,分析深海环境海水速度变化对Scholte波频散特性的影响。最后,将方法用于南海深水OBS地震数据反演得到一条二维海底横波速度剖面,反演结果很好的指示了海底天然气水合物储层的分布。结果表明:深海环境下,利用海底OBS数据中的Scholte波反演海底浅层横波速度结构是可行的,南海实际深水OBS数据应用进一步验证了方法的准确性和实用性。

Acoustic velocity varies in deep-water environments,and the variable-velocity seawater can affect the dispersion characteristics of Scholte wave.To improve the accuracy of inversion,a horizontal layered-seawater and layered-seabed(HLSLS)model is established with continuously varying velocities for seabed S-wave velocity inversion using Scholte wave.First,we deduced the Scholte wave dispersion equation and the amplitude-depth equation of the HLSLS model based on wave theory.Then,with the real acoustic velocity of the seawater and submarine sediments parameters of the Shenhu area in the South China Sea,we analyzed the influence of variable-velocity seawater on the dispersion characteristics of Scholte wave.Finally,we performed two-dimensional(2D)S-wave velocity inversion on the field OBS multi-component data in the South China Sea.The results showed that the variation of seawater acoustic velocity had a certain influence on the dispersion characteristics of Scholte wave in deep water.The accuracy and practicality of our method were verified through numerical and filed data experiments.