地震初至波射线路径的追踪

RAYTRACING FOR SEISMIC FIRST ARRIVALS

本文给出了一种不同于常规射线法的精确、高效的射线追踪方法,适用于地震初至波层析成像反演的射线追踪计算.在求解程函方程中使用了可变网格步长的差分格式,再按波前扩展理论计算出任意速度变化模型中离散网格点上的精确时间场分布.在此基础上,根据Fermat原理求出任意点到震源点的射线路径.本方法同样适用于三维问题,并可用于叠前偏移、速度分析及转换波处理.

A new raytracing algorithm which is concise, efficient and distinct from conventional methods is presented here. It is applicable for computing raypath of seismic first arrivals in s cismic tomography. Finite difference scheme with variable grid intervals is used while sotuing cikonal equations. The next is to calculate travel time for each discrete grid point in arbitraryvariablc velocity model based upon the wavcfront spcading theory. With the calculated travel time distribution, we are able to define a raypath from any point to the source point by Fermat 's principle. The alogrithm can be extended to 3-D problem without difficulty, and it is a useful tool in prcstack migration, velocity analysis and converted wave (p-sv) studies.