Local Features
(2010-06-11)
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Image: USGS
The Wabash Seismic Zone was the source of the 2008 magnitude 5.2 quake in this region.
Dr. Susan Hough is a seismologist with the U.S. Geological Survey based in Pasadena, California. She is the lead author in the paper, "Wagon Loads of Sand Blows in White County, Illinois" published in 2005 in Seismological Research Letters. She is also author of the new book Predicting the Unpredictable: The Tumultuous Science of Earthquake Prediction.
TRANSCRIPT
News outlets all through the mid-continent played the story. We even aired it from our own station earlier this week. It went something like this: "New research by U.S. Geological Survey scientists is casting doubt on the long-held idea the New Madrid Fault Zone in Missouri's Bootheel unleashed a series of devastating earthquakes in 1811 and 1812. In a new study, the researchers say the culprit may have instead been the Wabash Valley Fault Line that runs through southern Illinois."
It was a report that came down "from the wire," as we call it. And it turned out to be grossly misleading. Granted, some of the stories proceeded to hit on the facts, but the teaser did the damage.
"The Devil is in the details."
This is Dr. Susan Hough, a seismologist with the U.S. Geological Survey based in Pasadena, California. To her surprise, her name popped up in some of the aforementioned news reports. Hough is the lead author on a 2005 article in Seismological Research Letters. The article introduces evidence that the smallest of the three New Madrid earthquakes might have come from the Wabash Valley zone of Southern Illinois and Indiana.
"...which would sort of make it a triggered earthquake, triggered by the New Madrid activity. But there's no question that the sequence was overwhelmingly in the New Madrid seismic zone. So the idea that, Oh we were wrong and the activity was in Illinois, that's just not what the study ever said."
How a theory that introduces the question of one quake being the result of a trigger becomes a treatise that revises the entire location of a major earthquake sequence is a testament to the power of rumor.
But it's that nugget of truth that fascinates scientists.
"That's one of the relatively newer ideas, that it might be remotely triggered." This is Professor Lynne Leasure, a western Kentucky native and a geologist who recently retired from Murray State University's department of geosciences.
"There was possibility that one of the earthquakes in this series might have occurred in Southern Illinois. They do have surface evidence of sandblows. And the sandblows are very common in southeast Missouri from this event."
Sandblows, in this context basically result from the ejection of fluidized sand in water-saturated sediments during an earthquake. They're associated with liquefaction, in layperson's terms, when land takes on a liquefied state.
Dr. Hough says the trigger theory could also explain the shocks felt in the Louisville area at the time of the New Madrid series.
"There's actually very compelling evidence that there were triggered earthquakes near Louisville, Kentucky. A couple of them, I think you can identify from these accounts. And so this fits in with our new recognition that you do get triggered earthquakes, or you can get them after you have a big main shock."
One such earthquake account, she says came from a young Zachary Taylor, the future president and then-Army officer in Louisville.
"...and he described one of the earthquakes and this tumultuous shaking, and one of his buddies jumped out of a window and hurt his leg, and chimneys were toppling."
Dr. Hough says, at the end of the day, scientists are still looking into these questions.
"The January main shock... I can present evidence for why the Wabash valley is a plausible source. But the truth is that we really can't constrain the location of that event. It could have been in Western Kentucky. It could have been in New Madrid. But the observations just aren't as strong."
Dr. Hough's more recent research proposes that the New Madrid tremors weren't as huge as people thought, with magnitudes closer to 7 than to 8.
For WKMS News, I'm Jacque Day
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