Kentucky and surrounding states were shaken by an earth tremor of magnitude 4.3 (M4.3) on Saturday 10 November, 2012.
The quake, which occurred at a depth of around 24 km, was located in the south east of the state close to the border with Virginia and Tennessee.
Although no damage was known at the time of writing, Fox News reported that the tremor was felt in Virginia, West Virginia and Tennessee.
Without detailed seismological information, it’s impossible to be specific about the fault on which the earthquake occurred.
A look at a geological map produced by the Kentucky Geological Survey, however, suggests that it is most likely to be associated with the faulting along the western flank of the Appalachians.
Here a major thrust fault, the Pine Mountain fault, runs ne-sw close to the earthquake’s epicentre.
Earthquakes in the Eastern United States
The eastern United States is generally regarded as geologically stable, being located far from the tectonic plate boundaries which are the focus of most of the planet’s seismic activity (both in terms of number and magnitude of tremors). Deeply-buried faults within the rock, however, are nevertheless capable of significant movement and earthquakes, though not generally large are not uncommon: in 2011, for example, the state of Virginia was the location of a tremor of M5.8.
Typically, however, tremors in the eastern USA are felt over a wider region that those along the west coast, where the boundary between the Pacific and North American tectonic plates is the location of regular tremors. In the west the crust tends to be newer and therefore (relatively) warmer. The energy from a seismic event is therefore dissipated more rapidly than in the older, colder crust further east and the seismic waves are felt over a lesser distance.
Seismic History of the Region
The November 2012 earthquake is not the largest to hit the state – that distinction belongs to an M5.2 which struck near Maysville in 1980. Neighbouring states have also experienced larger tremors – in Virginia the largest on record is M5.9, in Tennessee M5.0 and in West Virginia M4.9. Indiana has experienced tremors of up to M5.1 and Ohio M5.4.
Most notable of all, however, is the series of major tremors which struck in the New Madrid area of Missouri in 1811-1812, causing significant damage. Although no modern magnitude reading is available, they are estimated to have been as large as M7.7, putting them among the USA’s largest earthquakes.
Kentucky Quake and Eastern U.S.
It’s clear, therefore, that though the eastern U.S. is not associated with major seismic zones, buried faults within the bedrock mean that it is not immune to earthquake activity, though mostly at a low level.
Fox News. Magnitude 4.3 earthquake strikes eastern Kentucky. (2012). Accessed November 10, 2012.
Kentucky Geological Survey. Geology of Kentucky. (2006). Accessed November 10, 2012.
USGS. M4.3 – 13km W of Whitesburg, Kentucky. (2012). Accessed November 10, 2012.