|Micro-earthquake monitoring with sparsely-sampled data|
The interferometric imaging condition used in conjunction with time-reverse imaging reduces the artifacts caused by random velocity fluctuations that are unaccounted-for in imaging and by the sparse wavefield sampling on the acquisition array. The images produced by this procedure are crisper and support automatic picking of micro-earthquake locations. Imaging with sparse arrays allows increased aperture for identical acquisition cost with that of a narrower but denser array. At the same time, a larger aperture improves focusing of the events, thus facilitating automatic event identification. The interferometric imaging procedure has a similar structure to conventional imaging and the moderate cost increase is proportional to the size of the windows used by the pseudo Wigner distribution functions. The source positions obtained using this procedure can be used to monitor fluid injection or for studies of naturally occurring earthquakes in fault zones.