[CEUS-earthquake-hazards] Recent NPR story: New Madrid Quakes: USGS Scientist Dispels Errant Report

[Oliver Boyd]

New Madrid Quakes: USGS Scientist Dispels Errant Report
NPR-WKMS
Jacque Day (2010-06-11)
http://www.publicbroadcasting.net/wkms/news.newsmain/article/1/0/1662035/Loc
al.Features/USGS.Scientist.New.Madrid.IS.the.Seismic.Zone.of.Origin

NEW MADRID, MO. (wkms) - A little information, out of context, can be
dangerous. That's what we found out this week. A story suggesting that the
New Madrid earthquakes of 1811-12 originated in Southern Illinois gained
some traction in news outlets across the mid-continent. But as our
correspondent Jacque Day reports, that wasn't the whole story. Here, she
looks into the facts versus the fiction.

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 the U.S. Geological Survey casts doubt on the long-held
idea that the New Madrid fault zone in Missouri's Bootheel unleashed a
series of devastating earthquakes in 1811 and 1812. The new study suggests
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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