SEISMICITY AT LAKE CAPRI, ROCKDALE COUNTY, GEORGIA, AUGUST 2000

PAMELA J. W. GORE, Department of Geology, Georgia Perimeter College, 555 North Indian Creek Drive, Clarkston, GA 30021, pgore@gpc.peachnet.edu, and LELAND TIMOTHY LONG, School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 221 Bobby Dodd Way, Atlanta, GA 30332-0340

On Sunday August 27, 2000 at 6:04 pm, a magnitude 2.0 earthquake occurred near Lake Capri in Rockdale County, Georgia approximately 20 miles east of Atlanta. Residents experienced a loud sound resembling an explosion, and felt a short vibration. The event was preceded by a foreshock on August 26 at about 9:11 pm. Aftershocks were also noted two days later on Tuesday morning, August 29. The community lies within about a mile of a rock quarry and is accustomed to blasts. The earthquake was described as "short and sharp" (perhaps 1 - 2 seconds), and was distinctly different from quarry blasting, which is accompanied by 6-7 seconds of rumbling. The Lake Capri earthquakes are probably an example of reservoir-induced seismicity. The area has experienced a drought over the past year and a half, but had several inches of rain just prior to the main event on August 27. Earthquakes are rare in Georgia, but these tremors were felt by some residents who had also experienced the summer 1993 earthquake swarm at Norris Lake, GA, approximately 3 miles to the north. A similar earthquake swarm also occurred near Dacula, GA in fall 1995 and winter 1996, about 20 miles NE of Lake Capri. Students in Physical Geology classes at Georgia Perimeter College assisted with collection of earthquake intensity data for each of these seismic events (Norris Lake, Dacula, and Lake Capri) by interviewing residents. For the Lake Capri earthquakes, students utilized a "reverse lookup" feature of a web-based phone directory service to find names and phone numbers of residents of selected streets near the epicenter.