【摘要】 地震波在地下传播时能量呈指数衰减,因此常规黏声逆时偏移(Q-RTM)的解析解随频率呈指数增长,造成频率域波场补偿不稳定,甚至使有效波场被高频噪声覆盖,导致偏移失败。为此,基于前人认识,提出了起伏地表频率域稳定Q-RTM方法。通过对频率域波动方程增加一个稳定因子,推导了稳定的频率域Q-RTM波动方程,其中稳定因子只改变有效频带外高频的计算符号,不增加额外的计算量。具体实现流程为:(1)生成贴体网格以及建立物理空间与计算空间的映射关系;(2)在计算空间计算频率域黏声正、反向传播波场,利用反傅里叶变换(IFFT)得到相应的时间域波场;(3)利用建立的映射关系的逆映射得到物理空间正、反向传播波场;(4)利用互相关成像条件对时间域波场成像,并输出成像结果。模型测试和实际资料应用表明,所提方法能补偿由衰减引起的振幅和高频成分损失,从而显著提高地震分辨率,改善浅表层的成像品质。更多还原

【Abstract】 The energy of seismic wave decreases exponentially as it propagates underground.This results in the analytical solution of conventional viscoacoustic reverse time migration(Q-RTM)increasing exponentially with frequency,and consequently instable wave field compensation,and even failed migration due to the effective wave field covered by high-frequency noise.Based on available knowledge,a stable Q-RTM method in frequency domain for undulated shallow surface is proposed.To restrain the growth of high-frequency components,a stable factor is added to the frequency domain viscoacoustic equation,and its corresponding stable expression for Q-RTM is derived.The stable factor only changes the computing sign of the high frequency outside the effective frequency band,but not bringing additional calculation.The specific process is as follows:(1)Establish body-fitted grids and mapping the relationship between physical space and computational space;(2)In the computational space,calculate the forward and backward wave fields with Qin frequency domain and obtain corresponding wave fields in time domain through IFFT;(3)Obtain the forward and backward wave fields in physical space by the mapping relationship;(4) Migrate according to the cross-correlation imaging conditions for every time step.Models and raw data have demonstrated that the proposed method can compensate amplitude and high frequencies caused by attenuation,and significantly improve seismic resolution and imaging quality of shallow surface.更多还原