Sunday 11 November 2012

Earthquake in eastern Kentucky.

On Saturday 10 November 2012, slightly before 12.10 pm local time (slightly before 5.10 pm, GMT), the United States Geological Survey recorded a Magnitude 4.3 Earthquake 19.9 km beneath eastern Kentucky. This is not a particularly large quake, and is in a fairly sparsely populated area, but the United States Geological Survey estimate there is a 24% chance of a quake of this size in this area causing at least one fatality. This quake does not appear to have caused any damage or casualties, but it was felt up to 240 km away by residents of seven states. 

Location of the 10 November 2012 quake. Google Maps.

The American Midwest is not an area generally associated with Earthquakes, but has in fact suffered some of North Americas largest and most destructive events. This is due to the New Madrid Fault Zone, and ancient area of tectonic activity dating back to the breakup of the Rodinian Supercontinent in the Neoproterozoic, about 750 million years ago. The area is underlain by the Reelfoot Rift, a potential ocean that started to open during the Rodinian breakup but never developed. The rocks of the fault zone were drawn apart over an area that runs from Illinois to Mississippi, and suffered a number of volcanic intrusions. 750 million years later these structures are deeply buried by more modern sediments, but are also prone to movement again. North America is being squeezed by the expansion of the Atlantic Ocean to the east and the subduction of parts of the ancient Farallon Plate to the west. This necessitates some movement within the continent to relieve the stress, and the New Madrid Fault Zone provides an area of pre-existing weakness where this can happen.

The ancient rift structure beneath the New Madrid Fault Zone. Geological Survey of Alabama.

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