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Education by Earthquake
April 24, 2008 - 2:52pm

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When I was very little, my mom took me down to the Mississippi to see a river barge that had broken loose from its tug in a recent flood. It was stranded on the bank, overflowing with coal, and we walked down to the thing and touched its hull. It looked to me like a rusted building stuck awkwardly in the mud. The forces involved were terrifying.

Views of the sublime produce new and lasting awareness. One of my first memories is the Southern Illinois earthquake of 1968. It was the biggest recorded in Illinois: 5.4 magnitude but Intensity VII, felt over 580,000 square miles, or 23 states, and into southern Ontario. In nearby Galatia, Illinois, postmaster Eugene Wallace wrote:

At the time of the earthquake, I was in the city cemetery 1 mile east of town. The earth trembled and tombstones shook and I thought the dead were coming forth, and that this was it...I came back into town and everyone was scared, chimneys were torn down, dishes fell out of cabinets and off tables and some refrigerator doors were even jarred open...

My mom just thought the house was coming down, so we ran out in the front yard. It lasted long enough that even as I lay down in the sun to keep from falling over, the earth kicked the breath out of me. It felt like betrayal.

We’ve had 31 quakes here in five days, starting with a 5.2 magnitude on April 18. The epicenters for most of them have been down near West Salem, Illinois, 130 miles south, but due to the soils over the bedrock throughout the Midwest, we feel temblors more strongly across greater distances than, say, Californians do, even though they have many more. [See map at right for relative intensities of quakes of similar magnitudes.] Ha, ha! Suck it, California! We’re number one! Oh, wait.

The big one everybody here still talks about (actually a series of three massive earthquakes and up to 1,800 of lesser intensity) took place in the New Madrid seismic zone in 1811 and 1812. According to The Center for Earthquake Research and Information (CERI), at The University of Memphis, “The fault system extends 150 miles southward from Cairo, Illinois through New Madrid and Caruthersville, Missouri, down through Blytheville, Arkansas to Marked Tree, Arkansas. It dips into Kentucky near Fulton and into Tennessee near Reelfoot Lake, and extends southeast to Dyersburg, Tennessee. It crosses five state lines, and crosses the Mississippi River in at least three places.”

The first earthquake there in 1811 was one of the biggest on record in what’s now the continental U.S., and a second one, two months later, was about as large. It made church bells on the East Coast ring themselves and woke the residents of Washington, D.C., some of whom got up to see who’d broken into their houses. In Columbia, South Carolina, the college rocked on its foundation and plaster fell, “which so alarmed the students, that they left the chambers without their clothes.” In Kentucky, John James Audubon was staying with friends and wrote:

Morning was fast approaching, when the rumbling noise that precedes the earthquake began so loudly, as to waken and alarm the whole party…. Every person, old and young…rushed wildly out to the grass enclosure fronting the building. […] On the grassplat we all met…huddled together in a state of almost perfect nudity. The earth waved like a field of corn before the breeze: the birds left their perches, and flew about not knowing whither; and the Doctor, recollecting the danger of his gallipots, ran to his shop-room, to prevent their dancing off the shelves to the floor [and] spreading his arms, jumped about the front of the cases, pushing back here and there the falling jars; with so little success, however, that before the shock was over, he had lost nearly all he possessed.

A woman who was closer to the epicenter later wrote:

… we were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder… followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness. The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do—the cries of the fowls and beasts of every species—the cracking of trees falling, and the roaring of the Mississippi… formed a scene truly horrible. […] At first the Mississippi seemed to recede from its banks, and its waters gathering up like a mountain, leaving for the moment many boats, which were here on their way to New Orleans, on bare sand, in which time the poor sailors made their escape from them. It then rising fifteen to twenty feet perpendicularly, and expanding, as it were, at the same moment, the banks were overflowed with the retrograde current, rapid as a torrent—the boats which before had been left on the sand were now torn from their moorings, and suddenly driven up a little creek, at the mouth of which they laid, to the distance in some instances, of nearly a quarter of a mile. The river…receded in its banks again with such violence, that it took with it whole groves of young cotton-wood trees…. The river was literally covered with the wrecks of boats….

Another contemporary account by one George Heinrich Crist:

What are we gonna do? You cannot fight it cause you do not know how. […] The earth quake or what ever it is come again today. It was as bad or worse than the one in December. We lost our Amandy Jane in this one—a log fell on her. We will bury her upon the hill under a clump of trees where Besys Ma and Pa is buried. A lot of people thinks that the devil has come here. Some thinks that this is the beginning of the world coming to a end.

A couple of months later he added:

If we do not get away from here the ground is going to eat us alive. We had another one of them earth quakes yesterdy and today the ground still shakes at times. We are all about to go crazy—from pain and fright. We can not do anything until we can find our animals or get some more. We have not found enough to pull the wagons.

People claimed to see the Mississippi run backward. Entire islands disappeared, and coal and sand were spit high and wide from cracks in the earth. Lake St. Francis, in eastern Arkansas, 64 kilometers long by 1 kilometer wide, was formed by subsidence. Just before the quake, the crew of the first steamboat coming down to New Orleans under the twilight of the Great Comet witnessed “tens of thousands” of squirrels “in a deep and solid phalanx” drowning themselves in the Ohio River. Within days the crew were caught on the river near the epicenter of the quake. It was perceptible over five million square kilometers.

If a quake of this magnitude happened here now, of course, with current population densities and bigger and more buildings in cities such as St. Louis and Memphis, and with modern infrastructure across the landscape, it would be disastrous. (U.S. Geological Survey Circular 1066 [1990] estimates potential losses to dwellings alone at $50 billion, in 1980 dollars.) I thought it would be nice to talk to somebody who knows what’s going on, and I was lucky enough to track down Dr. Buddy Schweig in his car and ask him a few questions by phone.

Dr. Schweig is Chief Scientist, Earth Surface Processes Team, U.S. Geological Survey, and recent Adjunct Professor and USGS scientist at The Center for Earthquake Research and Information (CERI), at The University of Memphis.

Q: What’s the difference between the magnitude and the intensity of an earthquake?

A: Magnitude—we don’t usually call it the Richter scale anymore—is the size of the earthquake, the energy released. Intensity is the shaking felt at a spot in the affected area.

Q: So loose soils, like we have in the Midwest, magnify the effect?

A: Yes. Imagine the waves of the earthquake traveling through rock like cars doing 60. Suddenly they hit a traffic jam—the different density of the strata—and pile up because they have to move so much more slowly. That piled-up energy can cause more damage.

Q: My house was built in 1871. If there’s a big quake, should I run outside waving my hands in the air?

A: Don’t run outside! More people are injured by things falling off buildings than are injured inside them. Most houses in the Midwest can withstand earthquakes well, especially since they tend to be wood-framed. I don’t know about your house….

Q: My house is three courses of brick. No matter. The reading I’ve been doing on Midwest fault lines says it’s a mystery why there’s so much seismic activity so far from the edges of the tectonic plates. Any new thinking there?

A: It is a mystery, but there are lots of theories. For instance, the continent is thickest in the middle, so if you can imagine the tectonic plates sailing through the asthenosphere in the process of continental drift, that thickness acts like a keel would on a boat, and there’s going to be drag forces at work.

Q: I’m suspicious: Is there any connection between the paths of the two big rivers here and the regional faults?

A: I’m not sure there is, at least not in the sense of one causing the other. There have been rivers flowing where the Mississippi is for 80 million years, so you could say there’s naturally a low spot there. Question is, why? Maybe a weakness in the earth’s crust, or it’s a place where the continent tried but failed to rip apart. There’s certainly a relationship. We’re just not clear on what it is. The water doesn’t cause earthquakes, and the earthquakes don’t bring on the water.

Q: Are the New Madrid (in Missouri) and Wabash (in Illinois) seismic zones one and the same?

A: If you look at them on a map, they seem to connect, but the respective ages aren’t the same. The earthquakes in each have taken place historically at different times. There’s no evidence they affect each other in major ways.

Q: Do these frequent temblors we’re having relieve seismic pressure, so to speak, reducing the possibility of a major event?

A: That would be nice, but I’m afraid not. One unit on the Richter scale releases 32 times the energy of the one below it. So a magnitude 6.0 releases 32 times more energy than a magnitude 5.0, and about one thousand times more energy than a magnitude 4.0. Little quakes do nothing to make a difference. It would take a million magnitude 2.0 earthquakes to release the energy of one magnitude 6.0 quake.

Q: I see. I assume that the USGS, like most governmental agencies, could use more cash, and suddenly I wish you had a bunch of it. How would you use it?

A: The Advanced National Seismic System has been authorized but never fully appropriated. The Wabash Valley, for instance, where the recent Illinois quakes occurred, is hugely under-instrumented. Until we get more sensors around it, we can’t get a good picture of what’s going on. Even smaller earthquakes add to our knowledge before bigger ones occur.

Q: Any chance the earth’s crust will crack open and the citizens of West Salem, Illinois, will find a volcano in their backyards? I have hopes of growing fair-trade coffee for Starbucks.

A: I’m afraid not. I can’t think of any place in the world less likely for that to happen. The crust is very thick and very cold.

Q: What will the folks at The Center for Earthquake Research and Information do when the rumbling quiets down?

A: There are always earthquakes going on. CERI’s scientists also study the prehistoric record, go all over the world to do research. Others do education and outreach. The charter is to study the causes and consequences of earthquakes, and it keeps a staff of 60, including grad students, quite busy.

My thanks to Dr. Schweig. For more info, see theUSGS fact sheet“Earthquake Hazard in the Heart of the Homeland.”

 

 

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