近地表散射体波场特征分析及成像

Wave field analysis and imaging of near-surface scatterings

研究近地表散射波基本特征,确定散射体的位置,有助于地震成像,进而进行勘测规划,避免地质灾害。为研究近地表异质体波场特征,利用高阶有限差分数值模拟技术和扰动理论方法,模拟了浅地表散射体的波场记录,分析了近地表散射波基本特征;通过引入逆时偏移成像技术利用散射波场作为外推波场,定位了近地表散射体。数值计算结果表明:面波散射能量强于体波散射,正向散射波能量强于逆向散射;散射波逆时偏移对近地表散射体可精确成像,近地表散射体可看作为一个二次震源,增加了近地表照明。利用散射波场可提高近地表速度反演精度和地震成像精度。

Studying the basic characteristics of near-surface scattering waves and determining the location of near-surface heterogeneities help seismic imaging,survey planning,and avoiding geological disasters.In order to study the wave fields characteristics of near-surface heterogeneous bodies,the authors used the high-order finite difference numerical simulation technique and perturbation theory method to simulate the wave field records of shallow surface scatters and analyze the basic characteristics of near-surface scattering waves.The near surface heterogeneity was located by introducing of reverse time migration imaging technology with the scattering wave field as an extrapolated wave field. The numerical results indicate that surface-wave scatterings are usually stronger than those bodywave scatterings and that forward scatterings are also stronger than backward scatterings.Moreover,near-surface scatters can be precisely imaged by the elastic wave reverse time migration.The near-surface scatters can be regarded as a secondary source,which increases the near-surface illumination.Using the scattered wave field can improve the accuracy of near-surface velocity inversion and seismic imaging.