Ray bending due to strong velocity anomalies

Abstract

Tomographic methods may be useful in determining localized changes in rock masses if accurate methods of inverting the data can be found. However, in the presence of strong localized anomalies, the underlying assumptions of many tomographic inversion methods break down, In fact, velocity contrasts as low as 15 percent can produce quite distorted raypaths. Even though the raypaths are distorted, the traveltimes on these paths are quite close to those which would arise from the straight‐ray assumption. The longer path length is compensated for by higher velocity. As a consequence, blind application of tomographic inversion to data obtained in the presence of strong anomalies can result in an incorrect and distorted but consistent solution.