彥格格的沏茶手記

On the government’s map of relative risk of damaging earthquakes, a Midwest hot spot stands out. (Excerpted from U.S.G.S. image.)

People don’t often think of Illinois and California as two peas in a pod, whether culturally, politically, economically or demographically. But a rattling reminder came early this morning that deep down below the surface (say, six miles deep), they do have something big in common geologically: Both states are earthquake country.

At 4:36 a.m. Central daylight time, a quake of magnitude 5.2 (revised from an initial 5.4) struck the southeastern part of the state, centered five miles from Bellmont, a tiny farm town close to the Wabash River, which marks the border with Indiana.

For a quake that has not so far yielded any reports of injury or significant damage, it sure was felt far and wide: The Associated Press says it was felt as far away as Milwaukee and Cincinnati, and that skyscrapers in Chicago and Indianapolis were set to shimmying (that’s good news, compared to cracking and crumbling). An early morning radio host all the way over in Des Moines reported feeling her desk chair roll and shake beneath her. Even Grand Rapids, Mich., noticed the rumble.

The epicenter lies near the edge of a mid-American hot spot for earthquake activity stretching down the Mississippi valley from southern Illinois to northeast Arkansas. The zone doesn’t produce nearly as many noticeable earthquakes as the fault complex running down the West Coast, and in the popular mind, California has owned the Earthquake Country brand at least since San Francisco famously crashed and burned in 1906. (Odd coincidence: That one was on April 18, too.)

But the tectonic forces grinding and snapping away deep in the planet’s crust tend to do their thing without much reference to the public relations implications, and once in a while bring the unwary up short. A quake only one notch stronger in magnitude — a 5.3 — toppled chimneys, cracked plaster and broke windows across southern Illinois in 1968.

And a Big One is hardly out of the question: The fault running up the Wabash Valley that scientists are initially thinking may have been responsible for this morning’s temblor is part of the same system that produced two of the three strongest earthquakes ever recorded in the Lower 48: The New Madrid, Mo., quakes of December 1811 and February 1812, each thought to have been magnitude 8 or greater. (The strongest was a magnitude-9 whopper in the Pacific Northwest in January 1700, known mainly by the tsunami it created that lashed Japan.)