An inverse ray method for computing geologic structures from seismic reflections—Zero‐offset case

Abstract

Seismic interpretation of structures usually involves identifying and mapping marker reflections in the time domain; however, forward modeling has shown that it can be difficult to map the complex reflection images arising from geologic structures. Inverse modeling by ray techniques offers the potential of computing a structure in the depth domain where it is comparatively easy to evaluate a structural target. An interactive algorithm is presented which has its basis in the eikonal equation and results in a practical procedure to compute models with complex geometries and inhomogeneous layers. Input consists of interpreted reflection times from a CDP‐stacked section and spatial velocity functions determined externally to the algorithm. Output is a two‐dimensional (2-D) model having curvilinear reflectors that can terminate within the model, at faults, and at unconformities. Benefits of structural inverse modeling are realized in the rapid construction of models that have velocity fields defined in the depth domain, explicitly accounting for ray curvature and ray kinking. To illustrate the inverse technique, examples of a complex synthetic thrust fault model and a field‐recorded growth fault model are included. The capability to inverse model steeply dipping structures is of particular interest because it completes a full modeling cycle of (1) theoretical prediction that steep‐dip reflections should be observable, (2) processing of field‐recorded CDP trace data to produce interpretable steep‐dip reflections, and finally (3) computation of steep‐dip reflector positions in the depth domain. An interesting benefit is the application of this algorithm to computing image rays on complex structures and the subsequent implications about time migration of CDP‐stacked sections.