基于互相关成像条件的隧道地震波逆时偏移处理

Reverse time migration based on cross-correlation imaging condition for tunnel seismic reflecting wave prediction

目前关于隧道地震反射波超前预报的研究主要集中于波场正演数值模拟或单程波的波动方程偏移,基于双程波波动方程的逆时偏移算法有更高的分辨率和更好的成像效果。将逆时偏移应用于隧道地震反射波成像,通过建立理论的断层、低速夹层、不同倾角地质界面等地质模型进行数值模拟,研究隧道地震超前预报问题。基于声波方程,进行波场逆时延拓的偏移成像,采用交错网格有限差分法,利用互相关成像条件并压制噪音干扰,实现了二维隧道逆时偏移成像。通过建立模型进行偏移的数值试算分析结果表明:采用相关时间成像条件,并对逆时延拓过程中反射波采用特征值法压制,对比激励时间成像条件效果更好,基于交错网格高阶有限差分法的逆时偏移应用于隧道地质超前预报能够对地质界面进行精确成像。

Most researches on nunerical sinulation of tunnel seisnic reflecting wave prediction focus on forward nodeling of wave field or nigration of one - way wave equation;however reverse tine nigration based on two - way wave equation has better resolution and inaging effects. Reverse tine nigration algorithn is applied to tunnel seisnic reflection wave inaging by establis-hing several geological nodels for fault,weak interlayer and tilted interfaces. Migration inaging is realized by reverse tine exten-sion for wave field based on acoustic wave equation. By the staggered grid finite - difference algorithn and using cross - correla-tion inaging condition to avoid the unwanted artifacts,we realize 2D reverse tine nigration inaging for a tunnel. Nunerical ex-anples show that the eigenvalue is useful in suppressing artifacts in reflected wave and the nore accurate inage can be obtained by cross - correlation inaging condition,conpared with excitation tine inaging. In tunnel advanced geological forecast,reverse tine nigration based on staggered grid finite - difference algorithn can produce fine inages for geological interface.