Calculation of Travel Times and Ray Paths for Lateral Inhomogeneous Media

Abstract

This article describes a ray-tracing method for two-dimensional inhomogeneous media. This method was first developed for near-surface sedimentary structures with discontinuous distributions of velocity. The subsoil models consist of layers with constant velocity or constant velocity gradient of arbitrary direction. Their boundaries are polygons with any kind of topography; even outcrops and pillow-formed structures are possible. Thus, diverse models of the subsoil can easily be constructed. As applications of the method show, satisfactorily exact approximations of continuous velocity distributions are possible. Furthermore, the simple basic structure of the models allows a very quick calculation of ray-paths and travel times by the ALGOL computer program. The method is demonstrated by the model of a salt dome in northern Germany. As examples of application models derived from refraction-seismic measurements at the northern margin of the Eastern Alps are shown. The most important structure of these models is a layer of about 7 km maximum thickness underlying the Northern Calcareous Alps up to at least 15 km southward of their northern margin, probably containing younger sediments.