Randolph, Tennessee in the area since 1974 occurred on August 19, 1994 – the temblor was measured 3.2 on the Richter scale with an epicenter at coordinates , ca. west of Randolph, at a depth of . On January 16, 2009 at 3:09 p.m. local time (21:09 UTC), "a small earthquake shook portions of Tipton County". The earthquake was measured at a magnitude 2.8 on the Richter scale. According to the Center for Earthquake Research and Information (CERI), the epicenter of the temblor was reported to be at coordinates at a depth of . There were no reports of damage caused by
Richter magnitude scale used by astronomers. Second, he wanted a magnitude of zero to be around the limit of human perceptibility. Third, he specified the Wood-Anderson seismograph as the standard instrument for producing seismograms. Magnitude was then defined as "the logarithm of the maximum trace amplitude, expressed in microns", measured at a distance of 100 km. The scale was calibrated by defining a magnitude 3 shock as one that produces (at a distance of 100 km) a maximum amplitude of 1 micron (1 µm, or 0.001 millimeters) on a seismogram recorded by a Wood-Anderson torsion seismograph. Finally, Richter calculated a table of distance