Sewanee, Tenn. – Sunday morning at about 2:30 the United States Geological Survey (USGS) reported a 3.1 magnitude earthquake and then about a minute later registered a smaller 2.8 quake immediately east of the initial quake which could have reportedly affected Marion and Grundy County.
There are no reports of damage from the pair of quakes that were center a few thousand feet west of State Road 156 and just South of Myers Point at Sewanee. There have not been any quakes indicating any aftershock activity. Both of the quakes were more than five miles below the surface and there appeared no change in the landscape surrounding the center point.
When a fault ruptures, seismic waves are propagated in all directions, causing the ground to vibrate at frequencies ranging from about 0.1 to 30 Hertz. Buildings vibrate as a consequence of the ground shaking; damage takes place if the building cannot withstand these vibrations. Compressional waves and shear waves mainly cause high-frequency (greater than 1 Hertz) vibrations which are more efficient than low-frequency waves in causing low buildings to vibrate. Rayleigh and Love waves mainly cause low-frequency vibrations which are more efficient than high-frequency waves in causing tall buildings to vibrate. Because amplitudes of low-frequency vibrations decay less rapidly than high-frequency vibrations as the distance from the fault increases, tall buildings located at relatively great distances (60 miles) from a fault are sometimes damaged.
However, given the relatively low seismic measure for these quakes, there was no dramatic surface activity.