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
Seismic magnitude scales times. As originally defined by m was based on the maximum amplitude of waves in the first 10 seconds or more. However, the length of the period influences the magnitude obtained. Early USGS/NEIC practice was to measure on the first second (just the first few P-waves), but since 1978 they measure the first twenty seconds. The modern practice is to measure short-period scale at less than three seconds, while the broadband scale is measured at periods of up to 30 seconds. The regional mb scale – also denoted mb_Lg, mbLg, MLg (USGS), Mn, and m – was developed by for