Wednesday, 3 April 2013

Earthquake in southeast Missouri.

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 City in Tennessee.

Areas where shaking from the 2 April Earthquake was felt. USGS.

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 New Madrid Earthquakes of 1811-12 was felt over mush of the central United States, entirely destroying the city of New Madrid, Missouri, caused damage to buildings as far away as St Louis, Missouri and Memphis Tennessee and diverted the course of the Mississippi River.

The structures underlying the New Madrid Fault Zone. University of Arizona.

 Witness reports can help Geologists understand Earthquake events and the underlying structures that cause them. If you felt this quake you can report it to the United States Geological Survey here.

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