Aftershock imaging using a dense seismometer array (AIDA) after the 2011 Mineral, Virginia, earthquake
Kathy K. Davenport, John A. Hole, Diego A. Quiros, Larry D. Brown, Martin C. Chapman, Liang Han, Walter D. Mooney, 2015. "Aftershock imaging using a dense seismometer array (AIDA) after the 2011 Mineral, Virginia, earthquake", The 2011 Mineral, Virginia, Earthquake, and Its Significance for Seismic Hazards in Eastern North America, J. Wright Horton, Jr., Martin C. Chapman, Russell A. Green
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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. Interstation 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, consistent 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 comparable to those used in controlled-source seismology can be successfully applied to aftershock sequences, and that dense array data can produce high-resolution information about earthquake rupture zones.