速度模型的光滑处理分析

Analysis of Velocity Model Smoothing

针对速度模型光滑处理对地震波走时、射线路径以及振幅信息的影响问题,从射线追踪方程组成立的前提条件、射线理论成立的高频近似理论以及菲涅尔带的角度着手,分析了速度模型光滑的理论基础。通过对同一模型光滑前后射线路径的计算表明,在不额外增加射线初始角度的前提下,模型的光滑处理可以有效地提高射线追踪的覆盖率;通过对不同速度模型光滑前后的走时计算及误差分析表明,选取合理的光滑次数,在保证射线追踪可行性和覆盖率的前提下,可以使走时的误差达到最小(横纵向各光滑50次时,Marmousi模型同一横坐标z方向上所有点的走时误差不超过5%;纵向光滑50次时,起伏层状模型同一横坐标z方向上所有点的走时误差不超过1%),而不影响偏移成像的质量。

In view of the impact of velocity model smoothing on wave traveltime,ray path and the amplitude information,we analyzed the theoretical basis of velocity model smoothing from prerequisite establishment of ray tracing equations,the ray theory of high-frequency approximation and Fresnel zone.Ray paths calculation before and after velocity smoothing for a same model showed that the smoothing of model can effectively improve the coverage of ray tracing without additional initial angle.Ray paths calculation and error analysis of before and after velocity smoothing for different model showed that selecting a reasonable number of smoothing under the premise of ensuring the viability of ray tracing and coverage,travel time can minimize errors（50 times smoothing in horizontal and vertical,the maximum relative error less than 5% on marmousi model and 50 times smoothing in vertical,the maximum relative error less than 1% on undulating layered model at the same abscissa of all points in z direction） without affecting the quality of migration.