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Southeastern Section - 63rd Annual Meeting (10–11 April 2014)

Paper No. 7
Presentation Time: 10:15 AM

TOMOGRAPHY AND BACK-PROJECTION IMAGING OF AFTERSHOCKS RECORDED BY THE DENSE AIDA ARRAY DEPLOYED AFTER THE 2011 VIRGINIA EARTHQUAKE


HOLE, John A.1, WANG, Kai1, DAVENPORT, Kathy K.1, CHAPMAN, Martin C.1, QUIROS, Diego A.2, BROWN, Larry D.2, BESKARDES, G. Didem1 and MOONEY, Walter D.3, (1)Geosciences, Virginia Tech, Blacksburg, VA 24061, (2)Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14853, (3)Earthquake Hazards, U. S. Geological Survey, Menlo Park, CA 94025-3591, hole@vt.edu

Aftershock Imaging with Dense Arrays (AIDA) recorded 12 days of seismic data following the 23 August 2011 magnitude 5.8 earthquake in central Virginia. AIDA utilized short-period, vertical-component seismographs at 201 locations at 200-400 m spacing to reduce spatial aliasing. Inter-station correlation enabled a detection threshold between magnitude –1.5 and –2.

Local earthquake tomography with ~1 km resolution detected no three-dimensional variation in seismic velocity, consistent with the aftershocks occurring within a single crystalline-rock terrane. The upper crust has a P-wave velocity of 6.2 km/s and an S-wave velocity of 3.6 km/s. The hypocenters define a fault zone that is weakly concave upwards in depth and along strike. The zone of seismicity is >1 km wide, much larger than the ~100 m hypocenter accuracy.

Reverse time migration was applied to several of the aftershocks to back-project recorded seismic energy to the source. Events as tiny as magnitude –2 and with signal smaller than noise were successfully imaged as point sources with ~200 m resolution. The propagation of energy release as a function of time and space was observed for events of magnitude 2.5 to 3.7. Synthetic data tests show that resolution was primarily limited by the temporal sampling rate. Improved temporal and spatial sampling could produce images with sharper resolution.

Session No. 3

T7. Lessons Learned from the 2011 Virginia Earthquake
Thursday, 10 April 2014: 8:00 AM-12:00 PM
Assembly Hall (Inn and Conference Center at Virginia Tech)
Geological Society of America Abstracts with Programs. Vol. 46, No. 3, p.4
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