TESTING THE RELIABILITY OF V(P)/V(S) ANOMALIES IN TRAVEL-TIME TOMOGRAPHY

In traveltime tomography, V(P)/V(S) 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 V(P)/V(S) 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 V(P)/V(S) model about a preselected average value and to minimize the insurgence of fictitious V(P)/V(S) 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 V(P)/V(S) 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.