But Why?
Helping adults answer children’s nature questions
From the September/October 2011 issue of Iowa Outdoors magazine
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For most of us living in Iowa, we’re much more familiar with snowstorms and tornadoes. What we do know about earthquakes we’ve likely learned from movies or textbooks, but earthquakes do occasionally rumble in our state.
When two blocks of the earth quickly slip past each other underground, it lets out built-up energy that shakes the ground and buildings above the surface. Most earthquakes happen along fault lines, or tears in the earth’s crust where stresses build. Iowa doesn’t have any major fault lines, but we have had at least 13 earthquakes with epicenters within our borders since European settlement.
The epicenter is the point on the Earth’s surface directly above where the fault lines moved. The largest Iowa earthquake shook Davenport in 1934, and Iowans felt the most recent quake southwest of Shenandoah in 2004.
Iowa was one of only four states that did not have an earthquake between 1975 and 1995.
However, just because an earthquake doesn’t originate here doesn’t mean we can’t feel it. Large earthquakes in southeast Missouri in 1811 and 1812 were the first earthquakes that Iowa settlers reported. More recently, quakes in Illinois and Oklahoma have shaken the ground enough for some Iowans to take note, but did little damage here.
In the Midwest, the Earth’s crust is older, thicker, cooler and more brittle, which allows shockwaves to travel further and faster than they do in the western part of the U.S.
So while earthquakes aren’t common here, they do happen.