The North Georgia Earthquake of October 9, 1984

In the early morning of October 9, 1984, northwestern Georgia was shaken by a magnitude m_b = 3.5 earthquake. This event is typical of the general seismicity experienced in northwestern Georgia and southeastern Tennessee. Intensity IV effects were felt over 6000 km². The total felt area was 12,000 km². The depth of focus was 10 ± 5 km, which places the earthquake focus below the Paleozoic sediments. First motion and relative amplitude data indicate a strike-slip focal mechanism with the preferred fault plane having right-lateral slip on a north-trending near-vertical plane. Spectral data give an equivalent fault radius of 0.6 km, a stress drop of 40 bars and a moment of 2.5 × 10²² dyne-cm. During an aftershock survey of nearly two weeks duration, only one significant (m_b = 2.0) aftershock was recorded. It occurred on October 15, 1984, six days after the main event.