AFTERSHOCK IMAGING WITH DENSE ARRAYS (AIDA): LESSONS FROM VIRGINIA AND MAINE

Aftershocks from the magnitude Mw 5.8 August 23, 2011, central Virginia earthquake were recorded using an unusually dense array 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 of this event to a) more precisely determine hypocentral locations and source properties of the aftershocks to ultra-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. Key results from the AIDA Virginia experiment related to hypocenter location, rupture characteristics and 3D structural imaging are described in other presentations in this session. Here we use the AIDA VA results, along with those from a similar experiment in Maine following the Mw4.0 Waterboro, Maine earthquake of October 16, 2012, to illustrate the even greater potential of dense, true 3D recording (in contrast to the 2.5 D nature of the AIDA pilot studies) to image, monitor and understand subsurface tectonics with unprecedented resolution and at nominal cost. The hardware to carry out much more ambitious, true 3D surveys already exists in the form of the large N recording systems now in routine use by the oil exploration industry.