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Midwest Quakes Are Faint Echoes, Not Warning Signs
Produced by Gabriel Spitzer on Wednesday, November 04, 2009
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Tremors felt in the Midwest might not foreshadow a big earthquake in the future. Instead, they may be faint echoes from centuries-old events.
The conventional wisdom has been that little quakes are the earth’s warning signs of big things to come. But Northwestern University’s Seth Stein is finding that in the middle of continents, that may not be the case.
STEIN: Now you realize that probably you’ve got it backwards, that the small earthquakes we see today are actually aftershocks of things that happened hundreds of years ago.
Stein is a professor of earth sciences He says the old model may overestimate the risk in recently active zones, and underestimate it in quiet areas.
He says faults in the middle of continents move much more slowly than big faults on the coasts. So in California, aftershocks might go on for about ten years before the fault reloads for a big one. In Illinois, they could go on for centuries.
In the case of the New Madrid fault, which covers southern Illinois, the main shock came back in 1811. Stein’s findings are out today in the journal, Nature.
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