Estimation of velocity change using repeating earthquakes with different locations and focal mechanisms

Abstract

[1] Codas of repeating earthquakes carry information about the time-lapse changes in the subsurface or reservoirs. Some of the changes within a reservoir change the seismic velocity, and thereby, the seismic signals that travel through the reservoir. We investigate, both theoretically and numerically, the impact of the perturbations in seismic source properties of used repeating earthquakes on time-lapse velocity estimation. We derive a criterion for selecting seismic events that can be used in velocity analysis. This criterion depends on the dominant frequency of the signals, the centertime of the used time window in a signal, and the estimated relative velocity change. The criterion provides a consistent framework for monitoring changes in subsurface velocities using microseismic events and the ability to assess the accuracy of the velocity estimations.