The United States Geological Survey recorded a Magnitude 2.8 Earthquake at a depth of 7.7 km, roughly 4 km to the west of the city of Malden in Dunklin County, southeast Missouri, slightly after 8.40 am local time (slightly after 1.40 pm GMT) on Friday 4 July 2014. This was a small event, highly unlikely to have caused any damage or casualties, though people have reported feeling it locally.
The approximate location of the 4 July 2014 Dunklin County Earthquake. Google Maps.
Southeast Missouri lies within an area known as the New Madrid Fault Zone, an seismically active area which lies over the deeply buried Reelfoot Rift, an area of tectonic expansion associated with the breakup of the ancient supercontinent of Rodinia about 750 million years ago. This is no longer an active rift, but it is an area of weakness within the North American Plate which is more prone to movement in response to other tectonic stresses, such as the compression of the plate by expansion beneath the Atlantic and Pacific Oceans.
The Reelfoot Rift is overlain by a deep layer of poorly consolidated tertiary sediments. These sediments are prone to liquefaction during tremors. When this occurs the sediments behave as a liquid, rather than a solid, with often devastating consequences for man made structures such as buildings and roads on the surface.
The structures underlying the New Madrid Fault Zone. Geological Survey of Alabama.
The New Madrid Fault Zone gets its name from the New Madrid Earthquakes of 1811-12, which were felt over much of the central United States, entirely destroying the city of New Madrid, Missouri, and causing damage to buildings as far away as St Louis, Missouri and Memphis Tennessee as well as diverting the course of the Mississippi River.
Witness reports can help Geologists understand Earthquake events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the United States Geological Survey here.
See also...
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On Tuesday 2 April 2013, at about 10.20 pm local time (3.20 am on Wednesday 3 April, GMT), the United States Geological Survey recorded a Magnitude 2.7 Earthquake at a depth of 13.4 km beneath southeastern Missouri, close to the border with Tennessee. Such small quakes rarely cause any damage or injuries, an quite often go completely unnoticed, though this one was felt as far away as Union...
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