Abstract:

Multiply scattered waves are extremely sensitive to small changes of the medium through which these waves have propagated. Coda Wave Interferometry [Science 295, 2253--2255 (2002)] is a new technique that utilizes multiply scattered waves in the time domain to monitor small changes in media. This is applied to ultrasonic waves that were recorded in a granite sample that was subjected to a change in temperature. Velocity perturbations of about 0.1% can be detected with this technique with an accuracy of about 0.02%. A multiply scattered wave in an elastic medium has traveled part of its trajectory as a P-wave and part as an S-wave. A model for the equilibration of P- and S-waves is presented. This model is used to extend the theory of coda wave interferometry to include elastic wave propagation. [Work was partially supported by the NSF (EAR-0106668 and EAR-0111804), by the U.S. Army Research Office (DAAG55-98-1-0070), and by the sponsors of the Consortium Project on Seismic Inverse Methods for Complex Structures at the Center for Wave Phenomena.]