来自海底高速层径向波的理论地震图研究

本文利用各向异性反射率技术计算理论地震图，提出海底高速薄层会产生沿高速层水平传播的波（简称径向波），这种波在水层中作为P波，在固液界面激发下行横波，该均匀横波以临界角入射高速薄层，在层内作为超临界角的非均匀横波水平传播，再以临界角转换为上行传播的均匀横波，最终在固液界面上行透射转换为水层中P波.高速薄层传播的径向波不同于界面折射波，也不同于具有频散的面波和通道波.理论地震图的研究表明，径向波具有线性时距，能与海底强反射具有同等振幅水平；径向波有其振幅、时距位置和斜率这些观测记录参数，分别对应高速层的厚度、深度和近似的横波速度；径向波可以克服折射波解释中遇到的振幅强弱和高速层速度等困难.径向波可作为探测海底高速薄层的有力工具，对于研究高速层屏蔽、海底反射类型的多样性和相应的资料处理解释有重要意义.

A study of the synthetic seismograms for radial waves recorded at seafloor in the presence of a high-speed layer

In this paper, we use the anisotropic reflectivity technique to calculate the theoretical seismogram. It is proposed that the high-speed thin layer of the seabed will produce the waves propagating horizontally inside the high-velocity layer named radial wave. This kind of wave propagates as P-wave in the water layer and stimulates the downward-spreading S-wave in the solid-liquid interface, then the homogeneous S-wave is incident into the high-speed thin layer at the critical angle, changing into the inhomogeneous S-wave which propagates horizontally inside the layer. This wave is then converted into the upward homogeneous S-wave at the critical angle, and finally turns into the P-wave through the solid-liquid interface in the water layer. The radial wave propagating in high speed thin layer is neither similar to the interface refracted wave nor to the surface wave and channel wave with frequency dispersion. The study of the theoretical seismogram shows that the radial wave has a linear time-distance curve and could have the same amplitude level as the strong reflection wave at the seabed. The radial wave has its own amplitude, time-distance position, slope and other observational parameters, which is controlled by the thickness, depth and the approximate S-wave velocity of the high-speed layer. The study of radial wave can overcome the difficulty of the amplitude intensity and the velocity of high-speed layer encountered in the interpretation of the refraction wave. Radial wave can be used as a powerful tool for detecting high-speed thin layers at seabed, which is of great significance for studying high-speed layer shielding, diversity of submarine reflection types and corresponding data processing.