1 The Geological Society of America Special Paper 509 2015 Aftershock imaging using a dense seismometer array (AIDA) after the 2011 Mineral, Virginia, earthquake Kathy K. Davenport John A. Hole Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, Virginia 24061-0001, USA Diego A. Quiros Larry D. Brown Department of Earth and Atmospheric Sciences, Cornell University, 3120 Snee Hall, Ithaca, New York 14853-1504, USA Martin C. Chapman Liang Han Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall, Blacksburg, Virginia 24061-0001, USA Walter D. Mooney U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA ABSTRACT The Aftershock Imaging with Dense Arrays (AIDA) project recorded 12 days of high-density seismic array data following the 23 August 2011 Mineral, Virginia (USA), earthquake. AIDA utilized short-period, vertical-component seismographs at 201 locations to record closely spaced data that would reduce spatial aliasing. Inter- station correlation enabled a detection threshold between magnitude –1.5 and –2. A joint hypocenter and velocity inversion algorithm was applied to compressional and shear wave arrival times for 300 of the larger events. Traveltime misfits were minimized using a constant velocity of Vp = 6.2–6.25 and Vs = 3.61–3.63. Hypocenter location error estimates for this range of velocities are ~100 m. Little to no three- dimensional variation exists in the seismic velocity of the upper crust, consistent with the aftershock zone being within a single crystalline rock terrane. The hypocenter locations define a 1–2-km-wide cloud with a strike of ~029° and dip of ~53°E, consis- tent with the focal mechanism of the main shock. The cloud bends ~5° along strike and has a slightly shallower dip angle below ~6 km depth, indicating a broad, complex fault zone with a slightly concave shape. This study shows that seismic arrays com- parable to those used in controlled-source seismology can be successfully applied to aftershock sequences, and that dense array data can produce high-resolution infor- mation about earthquake rupture zones. Davenport, K.K., Hole, J.A., Quiros, D.A., Brown, L.D., Chapman, M.C., Han, L., and Mooney, W.D., 2015, Aftershock imaging using a dense seismometer array (AIDA) after the 2011 Mineral, Virginia, earthquake, in Horton, J.W., Jr., Chapman, M.C., and Green, R.A., eds., The 2011 Mineral, Virginia, Earthquake, and Its Significance for Seismic Hazards in Eastern North America: Geological Society of America Special Paper 509, p. 1–283, doi:10.1130/2015.2509(15). For permis- sion to copy, contact editing@geosociety.org. © 2014 The Geological Society of America. All rights reserved. on August 31, 2015 specialpapers.gsapubs.org Downloaded from