DETROIT – A 3.2 magnitude earthquake occurred in Michigan at 11:42 AM today, centered seven miles northeast of Union City (fourteen miles south-southeast of Battle Creek).
This is just above the threshold that people start noticing any shaking, and is likely associated with the same seismic activity that caused the 4.2 magnitude quake near there in May. And by the way, keep in mind that the earthquake magnitude scale we use is a log rhythmic scale, which means that a one-point increase is a ten times greater release of energy. So, today's quake was 10 times weaker than the one in May.
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A lot of people ask me about earthquake history here in Michigan, so here's a little background.
First of all, earthquakes are caused by the movement of giant rocky "plates" below the earth's surface. Imagine a jigsaw puzzle, only with bigger pieces, all put together -- and you start pushing on one side of the puzzle. At first, the pieces would hold together. As you pushed harder, the edges between those pieces would start straining and, at some point, pieces would move. That's what's happening below our planet's crust...those pieces, or plates, push against each other (the edges between them are called "faults"), which builds up tremendous potential energy. At some point, a plate slips and either slides laterally, or pushes above or below the other plate it's up against. That's an earthquake.
Here in Michigan, we don't sit above any major faults. While the occasional quake actually occurs here, most of the time we feel quakes that happened elsewhere. For example, the massive New Madrid fault quakes (southeast Missouri) of 1811 and 1812 -- where I traveled to in the early 1990s and reported on -- was felt not only here in Michigan, but all the way to New England.
The great Charleston earthquake of 1886 (where I also have traveled to and learned about), was also felt here.
There are a number of instances of quakes being felt here throughout Michigan's history but, more recently, some of you may remember the 1987 magnitude 5.1 Illinois quake that we felt, or the 1998 magnitude quake in Pennsylvania just east of Cleveland that was felt here, the 2000 magnitude 5.4 quake in Quebec (Chuck Gaidica and I missed that one -- we were flying back from a live shot in a helicopter when it happened!), or the 2008 magnitude 5.4 quake in southeast Illinois that a lot of people in Detroit felt.
