Jan. 5, 2010: A quake registering 2.6 magnitude rattled LaFayette, Ga., about 7:20 a.m.
May 23, 2010: A 1.5-magnitude quake hit the outskirts of Dalton.
June 23, 2008: A 2.8-magnitude quake was centered about 13 miles northeast of Dalton.
The East Tennessee Seismic Zone's largest recorded earthquake is a 4.6 that occurred in Fort Payne, Ala., in 2003.
Source: U.S. Geological Survey
Earthquake magnitudes are measures of earthquake size calculated from ground motion recorded on seismographs.
* A quake of magnitude 2.5 to 3 is the smallest generally felt by people.
* A magnitude 4 quake can cause moderate damage.
* A magnitude 5 quake can cause considerable damage.
* A magnitude 6 quake can cause severe damage.
* A magnitude 7 is a major quake capable of widespread, heavy damage.
* A magnitude 8 and above quake is capable of tremendous damage.
Source: The Associated Press
An earthquake expert said the 2.7 magnitude earthquake that hit Dalton, Ga., Wednesday and a 2.5 tremor in Dyersburg, Tenn., point up a need for further quake research in the East Tennessee Seismic Zone.
"At the end of the day, it's the second-most-active seismic zone in the eastern United States, but we just don't know a lot about it," said Gary Patterson, director of education and outreach for the Center for Earthquake Research and Information at the University of Memphis.
Experts say the Dalton quake, reported by Whitfield and Catoosa county residents at 11:45 a.m. EST, was centered a mile west and southwest of the city and about three miles underground. It was felt from Dayton, Tenn., to Atlanta and from Gainesville, Ga., into Alabama.
No damage was reported, but Whitfield officials evacuated the county courthouse for a brief time.
Patterson said scientists use the times and movements shown on quake instruments and look at quake trends over time to try to map fault lines and estimate the maximum credible magnitude in a seismic zone.
In the East Tennessee Seismic Zone, he said, experts know that one very large or several parallel faults stretch nearly 200 miles from Virginia to Northeast Alabama and are responsible for about 80 small earthquakes a year.
But there hasn't been enough research to investigate fully the depth of the fault or faults, a key factor in understanding possible risks, he said.
"If you're going to put nuclear facilities and sludge-holding ponds on top of these seismic zones, then it's important to know what the maximum credible event is," Patterson said.
Crystal Paulk-Buchanan, spokeswoman for the Georgia Emergency Management Agency, said authorities first thought the Dalton tremors might be mild aftershocks from the Dyersburg temblor, which occurred at 6:35 a.m. CST about 76 miles northeast of Memphis.
But reports and data proved the Dalton temblor to be a separate and more-powerful earthquake, she said.
The Georgia and West Tennessee shakes follow reports of more than two dozen earthquakes in Oklahoma so far this month.
Dozens of people in the Dalton area reported feeling the quake and hearing its noise.
Danny Green, who works at the Dalton Print Shop downtown, said the noise sounded like a Dumpster crashing while it was being emptied. Green said the shaking vibrations lasted "for a split second."
Gary Brown, director of Whitfield County's Building and Grounds Department, said county officials received calls from people concerned about the noise from as far south as Cartersville and as far east as Murray County.
Staff writer Mariann Martin contributed to this story.