起伏海面条件下的反射地震响应

Undulating sea surface influence on reflection seismic responses

为了更真实地模拟起伏海面的影响,利用兼顾精度与计算效率的有限差分法,采用基于鬼点外推的不等距差分格式,采用文圣常等提出的海浪谱计算模型建立了有效波高为2m的适度平静海面起伏模型,以此研究中国海域内起伏海面条件下的反射地震响应。通过对简单的层状模型和Marmousi模型的数值模拟,得到以下认识:①受起伏海面影响,鬼波与一次反射发生不规则的干涉而产生不同的反射地震响应;②由起伏海面产生的地震反射同相轴"抖动"现象在所有时刻都存在,且与海面的起伏形态相关;③由于二次反射的不均匀照明及其与一次反射的不规则干涉,造成地震反射能量的空间分布不均匀现象,影响直达波和反射波的走时、波形、振幅、频谱、相位和带宽等,造成鬼波压制效果不佳、成像信噪比低、分辨率低、局部反演结果不收敛等一系列实际问题。

In order to truly simulate undulating sea surface influence on reflection seismic responses,a moderate calm sea surface undulation model(2 m wave height)is built with the wave spectrum calculation model proposed by Wen Shengchang et al.Considering both accuracy and computational efficiency,we use the unequal distance difference scheme based on the ghost point extrapolation.Through the numerical simulation of simple layered model and Marmousi model,the following conclusions are obtained:(1)The ghost wave and the primary reflection interferes irregularly under the influence of the undulating sea surface,resulting in different reflection seismic responses;(2)The phenomenon of "jitter"of seismic reflection from the undulating sea surface occurs at all times,and is related to the undulating shape of the sea surface;(3)Due to uneven illuminations of secondary reflection and irregular interferences of primary reflection,an uneven spatial distribution of seismic reflection energy affects greatly travel time,waveform,amplitude,spectrum,phase and bandwidth of direct and reflected waves,and causes a series of practical problems,such as poor ghost suppression,low signal-to-noise ratio,low resolution and local inversion non-convergence.