复杂介质地震初至波数值模拟

发展了一种地震初至波(first break)数值模拟的旅行时插值波前追踪方法.将复杂变速介质剖分成匀速的矩形或多边形单元,在单元边界上设置一些对波前旅行时采样的节点.首先从震源开始计算波前到达所有节点的旅行时,然后从接收点开始反向确定震源与接收点之间的射线路径.其中,到达任意一点的波前旅行时和射线是通过对该点所在单元其它两两相邻的已算节点旅行时的插值和Fermat原理求极小而获得的.该算法对介质的复杂程度、单元形状和震源与接收点的位置没有限制,能模拟直达波、临界折射波和绕射波以及盲区射线等,具有较强的适应性和较高的精度.用该方法对一些典型近地表模型的初至波进行了数值计算,清晰地显示出这些模型的波前形态和射线路径.

Numerical Modeling of Seismic First Break in Complex Media

A traveltime interpolation wavefront tracing method for numerical modeling of seismic wave in complex media is developed.It is based on an earth model consisting of uniform-velocity rectangular or polygonal cells with nodes placed at vertices and along cell edges.The wavefronts are propagated away from source throughout the entire model and sampled at the nodes,in which the first arrival time at a node is calculated by the interpolation of two previously computed traveltimes at all pair of adjacent nodes within a cell and minimization of traveltimes in the light of Fermat's principle. Once the wavefront traveltimes are sampled throughout the model, the minimal traveltime and raypaths from the source to receivers are easily obtained using the same technique as above.This method is regardless of model complexity,cell's shape and the positions of source and receivers.It can model all types of first arrival wave,such as direct waves,critical refractions and diffractions,and can trace entirely minimum traveltime paths.So it has a good flexibility and a high precision.At last,the method is applied to first arrival wave modeling of some typical near-surface models,the wavefront shapes and raypaths of which are shown explicitly.