Large-scale, dense, continuously recording areal arrays are now commonplace in oil and gas exploration. This new equipment represents a transformative technology for the imaging and monitoring of deep structure and tectonic processes. Here we illustrate the potential of this technology with results from pilot studies of aftershocks from the magnitude Mw 5.8, August 23, 2011, earthquake in central Virginia. Aftershocks were recorded using unusually dense profiles of seismometers in what has been termed an AIDA (Aftershock Imaging with Dense Arrays) deployment. Over 200 recorders were set out in the epicentral area, most at a station spacing of 200m. Goals were to: a) more precisely determine hypocentral locations and source properties of the aftershocks to very low magnitudes, b) more accurately define velocity structure in the aftershock zone, c) image geologic structures in the hypocentral volume using reflection techniques with the aftershocks serving as illumination sources, d) characterize regional propagation characteristics and e) assess the potential of seismic interferometry for subsurface imaging using both body and surface waves from aftershocks and ambient noise. Here we review what worked, what didn't work and lessons for future deployments of dense (large N) arrays for the study of natural processes.
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