Saturday, April 19, 2008

Wabash Fault Zone

Many friends that I asked didn't feel the second earthquake that we experienced yesterday because they were either walking or riding in a car at that time.

My young Grandson and his classmates felt it because they were sitting at their desk but their teacher was standing and moving around and didn't feel it. They alerted him and he told them that they could lie down on the floor if they wanted to, so they could feel the vibrations.

I heard on the radio that this was indeed a second earthquake and not an aftershock. This second shaking started as soft vibrations that built up to a 4.5 magnitude quake for only a couple of seconds and then returned to just soft vibrations that lasted quite a while. It hit at 11:14 a.m. according to the United States Geological Service.

The article below gives information about the area that we live in. We are a part of the Wabash Fault Zone, they don't know if this is related to the New Madrid Fault or not. The Wabash Fault runs almost parallel to the Wabash River in Southern Illinois and Indiana and could be a northern extension of the New Madrid Zone but that seems up for debate.

The article says that the reason the quakes in this area are so far reaching is because of our old bedrock that they compare to a bell that carries the seismic waves like sound for a longer distance than the California quakes reach.

California's bedrock is young and fractured, the waves do not carry as far, like a cracked bell wouldn't carry the sound waves as far. So California Earthquakes are more localized. Our bedrock carries these waves well over a thousand miles because of its age and rigidness.

The strongest quake produced by the Wabash Fault was a magnitude 5.3 in southern Illinois in 1968. The New Madrid fault zone produced quakes in 1811 and 1812 that reached an estimated magnitude of 7.0. The Wabash faults have the potential to do the same. Some experts say that the Wabash could produce a quake that could devastate the region.

Scientists say Midwest quakes poorly understood - Yahoo! News

A map of the area where yesterday's quakes were felt:
Yahoo Map Image

Lots of maps of the New Madrid and Wabash Valley seismic zones:
New Madrid and Wabash Valley seismic zones
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