Efficient generation of traveltime tables for complex velocity models

Abstract

The present invention provides a method for rapidly and efficiently generating traveltime tables from complex velocity models for application in depth migration. Initially, a velocity model is received which may include a plurality of velocities with various subsurface reflectors or boundaries. The model is plotted with the boundaries defining closed area cells within the model, with the cells having given velocity structures. The outside of each cell, or the cell wall, is made up of a series of segments. In the first basic step, traveltimes are computed from a preselected source location to each sample point on each segment. In this step, the order of processing all the cells is important. Therefore, the present method proceeds from those cells that are closest to the source location first to those cells that are further away in an expanding wave front from the source location. In the second basic step, the model is plotted on a two dimensional grid and the traveltime to each grid point inside each cell is generated using traveltime values from the segments surrounding the cell. The sample points on the surrounding segments are used as secondary sources and traveltimes are determined from these secondary sources to each grid point within the cell. In this step, the order of processing cells is arbitrary.