Testing the reliability of Vp/Vs anomalies in traveltime tomography

Abstract

In traveltime tomography, Vp/Vs models calculated as ratio between the resolved P and S models are affected by the different ray coverages and phase‐onset reading accuracies of P and S waves. the result of this is that the computed Vp/Vs models can display large fluctuations which are unrelated to the true structure. Introduction of some P‐S coupling (e.g. proportionality, correlation) as a priori data permits us to stabilize the resulting Vp/Vs model about a preselected average value and to minimize the insurgence of fictitious Vp/Vs anomalies. In general, addition of P‐S coupling trades off with data misfit and adoption of this technique is suggested for robustness tests of resolved Vp/Vs features. the technique is applied to a synthetic data set generated using an idealized fault structure and the source‐receiver geometry existing at Parkfield, California. Copyright © 1993, Wiley Blackwell. All rights reserved