Earthquake!!!

It would be a crime not to write something about this. In southern Illinois, some 250 miles south of Chicago, an earthquake of magnitude 5.2 on the Richter scale struck West Salem, Illinois at about 4:30 AM on Friday, April 18th . Reports were that skyscrapers swayed downtown in the loop, Indianapolis, and St. Louis and that the earthquake was felt hundreds of miles away, as far as Detroit and Cincinatti. After shocks were reported as strong as 4.6 later that morning.

There was moderate damage to some buildings near the quake, but nothing much happened in Chicago. A chunk of re-rod in the Edens Expressway in northwest Chicago was said to have been broken and exposed by the earthquake, causing damage to passing cars.

We felt nothing in our building. Keren and I slept soundly. In the U.S., the U.S.Geological Survey usually compiles information on these earthquakes. In fact, we're encouraged to report our experiences here. I don't know how they weed spam out of this, but there you have it.

Earthquakes are not completely unknown to this part of the country (see picture at right); we sit near the New Madrid Seismic Zone. It's not a normal seismic zone like those found near the intersection of plates (e.g. San Andreas in California, Dead Sea Fault in Israel -- see next map of earthquakes since 1963, where most fall along major fault lines). Rather, it's part of a Midcontinent Rift System, specifically the so-called "Reelfoot Rift".

The strongest recorded earthquake in Illinois was in 1968, at magnitude 5.4. However, a legendary earthquake in neighboring Missouri, the New Madrid earthquake, is said to have actually diverted the flow of the Mississippi River on Feb 7, 1812 (Chicago didn't exist yet). Geologists estimate the earthquake to have reached 8.0 on the Richter scale (recall that a one unit increase on the Richter scale is a factor of 10 higher in intensity). If true, this is 100's of times stronger than what we experienced yesterday. For reference, the devastating Great Sumatra-Andaman Earthquake, which killed hundreds (due to tsunami) on Dec 26, 2004, measured a 9.1.

I don't want to say in this high rise we live in long enough to find out if an earthquake will ever damage Chicago. The city hasn't even been here 200 years, short on geological time scales, so it doesn't seem impossible that we might get a real scare someday. If another 8.0 quake should strike within a few hundred miles of here, the last place I want to be is on the 9th floor of any building.