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A Note on the Goochland County, Virginia, Earthquake of March 15, 1991
Tsoflias, Georgios P.
Tsoflias, Georgios P.
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Abstract
The Goochland county, Virginia, earthquake of March 15, 1991 (mb (Lg) = 3.8), was the largest earthquake recorded in the central Virginia seismic zone (CVSZ) since the Cunningham, Virginia, earthquake of 1984 (mb(Lg) = 4.2). The 1991 event was felt over 23,000 km2 with a maximum MM V epicentral intensity. The preferred depth of focus was 12.5 km as determined graphically from the T2 vs X2 plot, whereas the computer program HYPOELLIPSE gave a more model-sensitive depth of 15 km. The average focal depth for shocks in this zone is 8.6 km, and the 90% quantile depth is 13.3 km. This earthquake is important because it is the largest shock that has occurred near the base of the CVSZ since network recording begun in 1978.
P wave first motions and (SV/P)Z amplitude ratios define a focal mechanism exhibiting primarily strike-slip faulting with a north-south or east-west strike. The P axis trends northwest, similar to deeper focus earthquakes (>8 km) in the CVSZ. P wave spectral analyses indicate a corner frequency at 8 Hz and a low stress drop level of under 100 bars.
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This is the publisher's version, also available electronically from "http://srl.geoscienceworld.org".
Date
1991-07-01
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Seismological Society of America
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Tsoflias, G. (1991). A Note on the Goochland County, Virginia, Earthquake of March 15, 1991. Seismological Research Letters, 32(3), 225-231. http://www.dx.doi.org/10.1785/gssrl.62.3-4.225