Extracting changes in wave velocity from chaotic data

Abstract

Using seismic interferometry it is possible to extract the Green’s function from recorded measurements of noise or other incoherent signals, it is a way of creating order out off chaos. Since the noise is present at all times, this provides a way to measure seismic velocity changes over time. The seismic velocity in the subsurface, and in buildings, is not constant in time. I will present measurements taken during, and after, the 2011 Tohoku-Oki earthquake to show that deconvolution interferometry can be used to monitor the seismic velocity in the near surface, with a great temporal resolution. The recovery of the seismic velocity typically varies as log-time, which can be related to a spectrum of relaxation processes in the earth.