The theory of coda wave interferometry
Pure and Applied Geophysics, 163 (2):
455--473 (Mar 13, 2006)DOI: 10.1007/s00024-005-0026-6
Abstract
Coda waves are sensitive to changes in the subsurface because the
strong scattering that generates these waves causes them to repeatedly
sample a limited region of space. Coda wave interferometry is a technique
that exploits this sensitivity to estimate slight changes in the
medium from a comparison of the coda waves before and after the perturbation.
For spatially localized changes in the velocity, or for changes in
the source location, the travel-time perturbation may be different
for different scattering paths. The coda waves that arrive within
a certain time window are therefore subject to a distribution of
travel-time perturbations. Here I present the general theory of coda
wave interferometry, and show how the time-shifted correlation coefficient
can be used to estimate the mean and variance of the distribution
of travel-time perturbations. I show how this general theory can
be used to estimate changes in the wave velocity, in the location
of scatterer positions, and in the source location.