An earthquake occurred this morning at 4:37 am with a magnitude of 5.4 that was felt throughout Central Illinois. I was up then watching, what else, Doctor Who on the Sci-Fi channel when the house began to shake. I literally felt the walls shake, and when it began, I just sat on the sofa, sort of frozen in time, wondering what the deuce was happening. The desk that our computer is on is a large vertical structure that squeaked during the shaking which lasted about 15 seconds. We have a small fish bowl with a small fish on the top shelf of the desk, which amazingly, survived without spilling any water from the bowl. At first, I thought it was a low flying jet since the airport is about 4 miles southwest of us and planes flying in from Chicago sometimes fly directly over. However, the shaking continued for what seemed like minutes. What was a bit frightening was the sound, the house did not shake quietly, and once I realized it was not a plane, I started moving around checking things out as best I could. I’ll go out after sunrise and check the outside of the house, but everything seems to be fine.

Apparently the quake was centered within 6 miles of West Salem, Illinois which is around 66 miles from Evansville, Indiana. The quake was felt in Chicago’s Loop district, Indianapolis, Cincinnati and St. Louis.

The quake measured in at 5.4 on the Richter scale, which is a measure of the seismic energy of an earthquake. While we’ve had earthquakes in the past, I don’t remember anything of this scale before. At 5.4, the earthquake would be classified as moderate in scale. This is comparatively minor when you think of Californian earthquakes which can be in the upper 6 to lower 7 range. Each whole number increase in the scale is a ten-fold increase in the measured amplitude, so that a 6.4 would be ten times stronger than a 5.4 quake. Each whole number also represents 31.6 times the amount of energy released. It puts some perspective to what the folks in California go through from time to time.

The only experience we’ve had with earthquakes of this size generally relate to the New Madrid fault in southern Missouri, near the Kentucky and Tennessee borders. Even then when we feel the effects of it moving, which are rare events, they don’t last long; certainly not 15 seconds as the one this morning did. These events at this magnitude are not rare, still it spiced up the day thus far. I’m sure it will be a topic of conversation for a while.

Earthquake Location Maps

The United States Geological Survey (USGS) has data on the quake at this link: http://earthquakes.usgs.gov/eqcenter/eqinthenews/2008/us2008qza6/ .

Also, the USGS has revised the magnitude of the quake from 5.4 to 5.2. The earlier figure was a preliminary estimate by USGS.

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