Earthquake waveforms and cross-correlation results are promising enough that the next step is to perform surface wave tomography for various time windows. For reservoir monitoring, using surface waves generated by passive seismic interferometry appears to be a better option than using surface waves generated by earthquakes. We are interested in the relatively higher frequencies, which seismic interferometry and ambient noise tomography is better equipped to handle. Passive seismic interferometry is also better for reservoir monitoring because signal is continuously available and is not dependent on random events like earthquakes. Therefore, time-lapse images at the reservoir scale may be possible with passive seismic interferometry.