More than 100 people around central Tennessee used the USGS “Did you feel it?” tool on their website to report they felt a shaking sensation today as a mild earthquake rocked the state; it was one of two that hit today. The first earthquake, a magnitude 2.2 event, struck this morning at 1:45 am near Palmer, Tennessee; the second struck at 1:31 pm this afternoon just southwest of Knoxville in Farragut and that magnitude 2.5 event brought 125 people to the USGS website to report what they felt.
Today’s earthquakes struck in an area between two active seismic zones: the very active New Madrid Seismic Zone is off to the west, while the Eastern Tennessee Seismic Zone is to the east.
While today’s earthquakes were quite mild, it adds to the number of earthquakes that have struck Tennessee within recent weeks. Several dozen earthquakes have hit Tennessee since mid August.
Most of the earthquakes over the last 30 days have been located in the western part of the state, where there has been considerable seismic activity in recent weeks. Western Tennessee is located within the New Madrid Seismic Zone, an area famous for a catastrophic series of earthquakes in 1811-1812 that were centered near New Madrid County, Missouri. The New Madrid Seismic Zone is also known as NMSZ for short.
According to the Missouri Department of Public Safety, the New Madrid Seismic Zone is active and averages about 200 measured events per year (magnitude 1.0 or greater). Tremors large enough to be felt (magnitude 2.5 – 3.0) occur annually. On average every 18 months, the fault releases a shock of magnitude 4.0 or greater, which is capable of local minor damage. A magnitude 5.0 or greater occurs about once per decade, can cause significant damage and be felt in several states.
According to USGS, earthquake volume in the NMSZ is running about 300% above normal this summer. While the volume has been high, the intensity has been low with no earthquake creating any damage or injuries.
While eastern Tennessee isn’t part of the NMSZ, they too get quakes from time to time. USGS says western Tennessee has a higher frequency of damaging earthquake shaking, the risk isn’t that low in eastern Tennessee. In the eastern part of the state, USGS says its likely this area would see 50-100 damaging earthquakes over 10,000 years. While this number is low, it is much higher than it is elsewhere in the eastern half of the United States, where it’s likely to have 10 or less earthquakes over the same period.