Abstract

In the evening on October 30, 1982, the residents of Columbus, Georgia, experienced two small earthquakes. The first occurred at 11:07 PM EDT (03:07:36.72±0.4 UTC, October 31, 1982). The second event followed in about four minutes (03:12:12.24±0.4 UTC, October 31, 1982). These were the first earthquakes reported from the Columbus, Georgia, area. The mean duration magnitude of the second was mb (Dur) = 3.1. The first was 0.2 magnitude units smaller, mb (Dur) = 2.9. Numerous aftershocks were heard or felt near the epicenter. Because this behavior is typical of shallow events in the Piedmont, particularly near reservoirs, the depth was presumed to be shallow. Thirteen aftershocks were recorded on portable microearthquake seismographs and these data were used to constrain the location to 10 km north of Columbus (32°35.87′N, 84°56.73′W ± 1.0 km). A strike slip focal mechanism implying east-west compression was determined from first motion data and the ratio of P-wave to S-wave amplitudes. The fact that the fault planes were compatible with joint sets in a nearby quarry (N36°W, N40°E) and the fact that the events were presumed shallow focus, support the hypothesis that these events occurred along these shallow joints.

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