Earthquakes in the U.S. Mid-continent

A year or so ago I speculated on the possibility of a large earthquake in Ohio. My amateur speculation was based on a spatial pattern of historical earthquakes in the eastern United States and Canada.

Last fall I go an email from Dave, recommending a book written by Seth Stein called “Disaster Deferred – How New Science Is Changing Our View of Earthquake Hazards in the Midwest”. His recommendation was conveniently given before Christmas and I subsequently received the book as a gift from my older son.

Stein’s book is an excellent read. He is a real geophysicist, not a journalist or writer, so he speaks with more authority than someone else who might have written a book on this subject. The basic theme of the book is that the earthquake hazard in and around the New Madrid Seismic Zone has been exaggerated. In the process of making that argument he gives excellent explanations of earthquakes, both causes and effects, plate tectonics, scientific models and the real-world messiness they describe, and the interplay between science, government, the news media, and the general public along the way.  The earthquake hazard assessment is important in developing disaster response and mediation plans, building and construction codes, and public awareness.  Not getting it right in either direction will be costly.

Stein doesn’t discount the fact of large historical earthquakes in the midwest, although he may disagree with the high end of the estimated magnitudes. Instead he explains what is and isn’t understood about mid-continent earthquakes. The new science alluded to in the title is based on the careful measurement of relative ground motion in and around the New Madrid Seismic Zone. Unlike seismic zones along the edges of tectonic plates where the plates move relative to each other actively increasing the stress on the earthquake faults, virtually no motion is measured in the New Madrid zone. He describes the model of mid-continent earthquakes as resulting from remnants of ancient tectonic processes. I visualize this as residual, unrelieved stresses along ancient faults. The stress along the fault is no longer building as it would be along the edge of a plate but is “locked and loaded” waiting for a trigger to release it. Stein describes an analogy to the the Parker Brothers game called “Booby Trap” that was popular back in the mid-1960s. If you have ever played the game you know that removing a game piece might cause no motion, very slight movement, or cause the whole thing to fly apart and that you can’t really predict the outcome ahead of time.  Of course this is all more complex than I can describe in a paragraph or than Stein can describe in his book.  Many questions remain unanswered.

So did the book change my thinking on the possibility of a large earthquake in Ohio? Not really. In fact, the basic tenants of my original post are supported by the book, although with a lot more authority than I could give. As I said, “I don’t expect a large earthquake in Ohio during my lifetime but I won’t be surprised if there is one.”

Read the book. It’s a good one…

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