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Stalagmites May Predict Next 'Big One' Along New Madrid Seismic Zone-UPDATES

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Author Topic: Stalagmites May Predict Next 'Big One' Along New Madrid Seismic Zone-UPDATES  (Read 2024 times)
Bianca
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« on: May 20, 2009, 08:22:24 am »








Small white stalagmites.

Insert:
one stalagmite cut vertically in half, showing generations of growth with the white one on top.



(Credit:
Courtesy of
K. Hackley)
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« Reply #1 on: May 20, 2009, 08:27:12 am »









                 Stalagmites May Predict Next 'Big One' Along The New Madrid Seismic Zone






ScienceDaily
(Sep. 30, 2008)

— Small white stalagmites lining caves in the Midwest may help scientists chronicle the history of the New Madrid Seismic Zone (NMSZ) – and even predict when the next big earthquake may strike, say researchers at the Illinois State Geological Survey and the University of Illinois at Urbana-Champaign.

While the 1811-12, magnitude 8 New Madrid earthquake altered the course of the Mississippi River and rung church bells in major cities along the East Coast, records of the seismic zone’s previous movements are scarce. Thick layers of sediment have buried the trace of the NMSZ and scientists must search for rare sand blows and liquefaction features, small mounds of liquefied sand that squirt to the surface through fractures during earthquakes, to record past events. That’s where the stalagmites come in.

The sand blows are few and far between, said Keith Hackley, an isotope geochemist with the Illinois State Geological Survey. In contrast, caves throughout the region are lined with abundant stalagmites, which could provide a better record of past quakes. “We’re trying to see if the initiation of these stalagmites might be fault-induced, recording very large earthquakes that have occurred along the NMSZ,” he said.

Hackley and co-workers used U-Th dating techniques to determine the age of stalagmites from Illinois Caverns and Fogelpole Cave in southwestern Illinois. They discovered that some of the young stalagmites began to form at the time of the 1811-12 earthquake.

Hackley is scheduled to present preliminary results of the study in a poster at the 2008 Joint Meeting of the Geological Society of America (GSA), Soil Science Society of America (SSSA), American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and Gulf Coast Association of Geological Societies (GCAGS), in Houston, Texas, USA.*

Water slowly trickles through crevices in the ceiling of a cave and drips onto the floor. Each calcium carbonate-loaded drip falls on the last, and a stalagmite slowly grows from the bottom up. Time is typically recorded in alternating light and dark layers – each pair represents a year.

When a large earthquake shakes the ground, old cracks may seal and new ones open. As a result, some groundwater seeping through the cave ceiling traces a new pattern of drips – and, eventually, stalagmites – on the cave floor. Thus it is possible that each new generation of stalagmites records the latest earthquake.

The scientists use fine drills, much like those used by dentists, to burrow into the stalagmites to collect material for dating. In addition to the 1811-12 earthquake, their investigation has recorded seven historic earthquakes dating as far back as almost 18,000 years before the present. Understanding the NMSZ’s past, including whether quakes recur with any regularity, will help the scientists predict the potential timing of future quakes.

In coming months, Hackley and his colleagues plan to expand the study, collecting stalagmites from caves across Indiana, Missouri and Kentucky. They hope that the new data will help to fill in more of the missing history of the NMSZ.

*On 5 October  the Paper 147-8: “Paleo-Seismic Activity from the New Madrid Seismic Zone Recorded in Stalagmites. A New Tool for Paleo-Seismic History”will be presented at the Joint Meeting.


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Adapted from materials provided by Soil Science Society of America.
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 MLA Soil Science Society of America (2008, September 30). Stalagmites May Predict Next Big One Along The New Madrid Seismic Zone. ScienceDaily. Retrieved May 20, 2009, from



http://www.sciencedaily.com­ /releases/2008/09/080924185742.htm
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« Reply #2 on: May 20, 2009, 08:30:30 am »








                                   What Constitutes Acceptable Earthquake Risk?






ScienceDaily
(Feb. 21, 2006)

— Earthquakes are a common part of life in California. Towns are prepared for major seismic events and most residents consider earthquake safety an important issue. But in the Midwest, people rarely think of the large New Madrid fault zone underneath their feet.

According to seismologists, major New Madrid earthquakes are rare. When one eventually occurs, however, it can be catastrophic. So how do small towns that line the New Madrid fault zone improve earthquake preparedness when immediate risk and awareness are low and town budgets are stretched?

"Unfortunately earthquake safety in the Midwest is event driven -- most people will not begin to care about the risk until an earthquake happens," says David Gillespie, Ph.D., disaster preparedness expert and professor of social work at Washington University in St. Louis. "Town leaders need to think long-term -- 25 or 50 years out -- about incremental improvements in safety measures that can be sustained. This is a different kind of planning, but it is necessary to be ready for the eventual catastrophic quake that will strike."

Gillespie presented the paper, "Dyanmics of Earthquake Safety and Economic Development," on Feb. 20 at the annual meeting of the American Association for the Advancement science, held Feb. 16-20 in St. Louis.

In his study, Gillespie and colleagues examined 15 years of data from a small Southern Illinois town to see whether it was possible to promote both earthquake safety and economic development.

"We used the Applied Technology Council's ATC-21 measure of seismic building safety to compare earthquake safety to the town's economic development," Gillespie says.

"We looked at the fraction of safe buildings and the fraction of new and retrofitted buildings in the town. Using conflict theory, we hypothesized that competing goals would fight for resources. After looking at the baseline data, we found that, as predicted, the concern for earthquake safety decreased as the push for economic development increased."

Using the same measures, Gillespie and colleagues simulated the comparison for the next 30 years, from 2004-2034.

"Interestingly, the inverse relationship found in the first 15 years disappeared within the first few years of the simulation. Both the push for economic development and earthquake safety ended up decreasing by the end of the simulation," he says.

Gillespie and his colleagues began looking for policy parameters to reverse this trend. They found that the town could increase safety for the community by encouraging the tearing down of old buildings as new buildings were constructed. In addition, by making other policy adjustments such as adding a few hundred acres of land to the town, the researchers found it was possible to spur both earthquake safety and economic development.

This study is important for small towns in the Midwest because it shows that community safety tends to deteriorate with typical short-term, event driven planning, but also because it shows that economic development and safety are not necessarily competing goals. Improving community safety is good for economic development.



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Adapted from materials provided by Washington University in St. Louis, via EurekAlert!, a service of AAAS.
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 MLA Washington University in St. Louis (2006, February 21). What Constitutes Acceptable Earthquake Risk?. ScienceDaily. Retrieved May 20, 2009, from



http://www.sciencedaily.com­ /releases/2006/02/060221084113.htm
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« Reply #3 on: May 20, 2009, 08:34:24 am »









                                  Unearthing Explanations For New Madrid Earthquakes






ScienceDaily
(Feb. 22, 2006)

— On Dec. 16, 1811, residents of New Madrid, Mo., were wrested from sleep by violent shaking and a deafening roar. A short time later, church bells hundreds of miles away in Boston began to ring. It was the first of three massive earthquakes that rocked the central United States between December 1811 and February 1812, even changing the course of the Mississippi River in their aftermath.

"A big earthquake in the same region as the 1811-1812 earthquakes would have devastating consequences should they recur today because of the population centers in St. Louis and Memphis," Stanford University geophysicist Mark Zoback told an audience Feb. 20 at the annual meeting of the American Association for the Advancement of Science in St. Louis, Mo.

vWe simply need to know more about how these systems work in order to serve the public," added Zoback, the Benjamin M. Page Professor in Earth Sciences.

In a talk titled vTremors in the Heartland: The Puzzle of Mid-Continent Earthquakes," Zoback discussed what is presently known about the New Madrid seismic zone and his work creating geodynamic models of the region. Zoback began his career studying New Madrid. In 1976, shortly after receiving his doctoral degree, he participated in the first seismic work to identify the causative faults. In an article published in the February 2001 issue of Geology, Zoback and former graduate student Balz Grollimund presented a theory explaining why earthquakes occur in this area.

The New Madrid seismic zone, which is roughly at the juncture of Missouri, Kentucky, Arkansas and Tennessee near the Mississippi River, is unusual because most earthquakes occur at the edges of rigid tectonic plates that essentially float on the fluid-like interior of the Earth. The plates produce earthquakes when they move over, under or beside each other. In California, earthquakes occur along the San Andreas Fault because the Pacific plate moves horizontally past the North American plate, like two bumper cars brushing up against each other.

Understanding why earthquakes occur in the New Madrid zone, on the other hand, has proven more elusive. The zone is in the middle of the North American plate, thousands of miles from the edges where all the action usually occurs.

"What makes New Madrid unique are elements of the structure and properties of the Earth's crust and mantle that it inherited over long periods of geologic time," Zoback said. "It's sort of a legacy effect."

He explained that tens of thousands of years ago, the Laurentide ice sheet covered most of Canada and ran as far south as the middle of Illinois. According to Zoback, this massive glacier did not cover the New Madrid zone but was large enough to affect the Earth hundreds of miles to the south-in effect, the ice sheet was so heavy it pressed into the Earth's surface. Think of squeezing a rubber ball with your finger.

As the climate warmed, melting the ice, the ground was freed of the heavy pressure of the ice sheet. It is the constant release of this pressure that causes earthquakes in New Madrid, he explained. Zoback's model predicts that earthquakes could continue to occur in the region for the next few thousand years.

Because a major earthquake could strike the area, Zoback said the science community must help regional officials prepare for such an event.

"What the scientific community must do is continue the fundamental research trying to understand why these earthquakes occur," he said. "At the applied level, scientists need to work with state and local officials to make sure the importance of earthquake hazards are considered in the development of building codes and critical structures such as bridges, schools and hospitals."

Zoback also cautioned that local communities must understand that seismic events, such as those in 1811 and 1812, aren't simply history but are warnings of the potential for future earthquakes.

"It's one thing to know it was a part of your past," he said. "It's another to be prepared for it to be part of your future."

John B. Stafford is a science-writing intern at Stanford News Service.

###
RELEVANT WEB URLS:

MARK ZOBACK WEBSITE http://pangea.stanford.edu/~zoback

USGS NEW MADRID WEBSITE http://neic.usgs.gov/neis/eq_depot/usa/1811-1812.html



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http://www.sciencedaily.com­ /releases/2006/02/060221084236.htm
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« Reply #4 on: May 20, 2009, 08:36:05 am »








Researchers looked at data used in the new edition of the Geothermal Map of North America (American Association of Petroleum Geologists, 2004), which shows all the measurements of the heat coming to the Earth's surface (heat flow) taken from boreholes.

They found that thermally New Madrid is surprisingly similar to other areas of the eastern United States.



(Image courtesy of
Northwestern University)
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« Reply #5 on: May 20, 2009, 08:39:27 am »









                     New Madrid Seismic Zone May Be Cold And Dying, New Evidence Shows






ScienceDaily
(Dec. 29, 2006)

— New results about the temperatures of rock deep below the New Madrid Seismic Zone in the central United States shed light on the puzzling questions of why large earthquakes happened there in 1811 and 1812 and when they may happen again.

Scientists from Northwestern University, the U.S. Army Engineer Research and Development Center and the University of Illinois at Chicago have found that New Madrid appears to be cold and dying. They presented their findings Dec. 13 at the annual meeting of the American Geophysical Union (AGU) in San Francisco.

"Hot rocks are weak," says Seth A. Stein, William Deering Professor of Geological Sciences in the Weinberg College of Arts and Sciences at Northwestern and a coauthor of the study. "So people suggested that the reason large earthquakes occur in the New Madrid area rather than in the many similar geologic settings in other parts of the eastern United States is that the New Madrid rocks are hotter."

But the researchers discovered this is not the case. They looked at data used in the new edition of the Geothermal Map of North America (American Association of Petroleum Geologists, 2004), which shows all the measurements of the heat coming to the Earth's surface (heat flow) taken from boreholes. They found that thermally New Madrid is surprisingly similar to other areas of the eastern United States.

"The New Madrid data are essentially no different from other sites in the eastern United States," explains coauthor Jason R. McKenna from the U.S. Army Engineer Research and Development Center. "Although we'd like to have more measurements to be sure, at this point, there's no reason to believe New Madrid rocks are hotter and therefore weaker than rock in other parts of the eastern United States."

One of the most difficult aspects of assessing the earthquake hazard is deciding whether New Madrid is a special place or simply where central U.S. earthquakes have occurred in the past few thousand years. "When we look at things like geology, gravity or the magnetic field, there's no obvious difference between New Madrid and similar places in the eastern United States that haven't had large earthquakes recently," McKenna notes. "Now we see the same for heat flow."

The new heat flow results fit into a growing idea that earthquakes can migrate among similar faults, some of which -- such as the Meers fault in Oklahoma -- appear to have been active about 10,000 years ago but show no activity today. Geological studies find that New Madrid earthquakes comparable to those of 1811-1812 occurred about 1450 and 900 AD. However, because this fault system has not generated significant topography, it is likely to have "turned on" relatively recently, perhaps within the past few thousand years.

With this view, say the researchers, prior earthquakes were concentrated on other faults, and future earthquakes will occur somewhere else when the New Madrid system "shuts down." Once this happens, it may be a very long time -- thousands of years or longer -- before New Madrid becomes active again.

"Although we don't know when the New Madrid fault system will shut down, it may be dying today," says Stein. "The recent cluster of earthquakes may be coming to an end."

Migrating earthquakes also occur in the interior of other continents, such as Australia. This is very different from the way earthquakes occur on boundaries between plates, like the San Andreas fault along the boundary between the Pacific and North American plates. Because the plates keep moving, earthquakes continue to occur on the boundaries in the same places.

Precise measurements taken by Stein, coworkers and other investigators using the Global Positioning System (GPS) show that motion across the New Madrid Seismic Zone currently is either very slow or at zero. Because this motion has to accumulate for many years to cause a large earthquake, it will be at least hundreds of years, and perhaps much longer, before another large earthquake happens.

"Until recently about all we could say was that future earthquakes might occur in places where past ones had," says Stein. "Now we can actually test that idea by looking at the motion accumulating for possible future earthquakes. Although we can't be sure yet, the longer the GPS data continue to show essentially no motion, the more likely it seems that the fault is shutting down and won't cause large earthquakes for a very long time. It's time to start thinking about this possibility and to use what we're learning to improve estimates of the hazard from future earthquakes."

The possibility of the fault shutting down is important for assessing the earthquake hazard in the central United States. Large earthquakes (magnitude 7) occurred in 1811 and 1812, causing shaking across much of the area. Houses collapsed in the tiny Mississippi river town of New Madrid, Mo., and minor damage occurred in St. Louis, Louisville and Nashville. The smaller earthquakes that continue in the area today are typically more of a nuisance than a catastrophe, say the researchers. The largest in the past century, the 1968 southern Illinois earthquake (magnitude 5.5), was widely felt and caused some damage but no fatalities. However, if large earthquakes like those of 1811-12 occurred again, they would be very destructive.

The third coauthor of the study, "No thermal weakening under the New Madrid Seismic Zone," is Carol A. Stein, professor of Earth and environmental sciences at the University of Illinois at Chicago.



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« Reply #6 on: May 20, 2009, 08:44:52 am »









                             New Hazard Estimates Could Downplay Earthquake Dangers






ScienceDaily
(Apr. 17, 2008)

— The dangers posed by a major earthquake in the New Madrid and Charleston, South Carolina zones
in the Midwestern and Southern parts of the United States may be noticeably lower than current estimates if seismologists adjust one of the major assumptions that go into calculating seismic hazard, according to a study presented at the Seismological Society of America.

The study revolves around this question: is it unlikely that one major earthquake will follow directly on the heels of a big quake, or are other major earthquakes equally likely to occur any time after a major quake? Hazard estimates for a seismic zone depend on which scenario seismologists choose to plug into their hazard calculations.

The present hazard maps for New Madrid and Charleston use the second assumption. However when seismologist Seth Stein of Northwestern University and Northwestern senior James Hebden chose the first scenario--that a quake is unlikely to occur right after another quake, but that the likelihood of a new quake increases over time--they found that the seismic hazard maps of the New Madrid and Charleston areas looked a lot less dire than current predictions for the regions.

Their "time-dependent" model suggests that the likelihood of another earthquake is relatively low for the first two-thirds of the predicted average interval between earthquakes, after which the likelihood of another quake begins to climb.

The New Madrid and Charleston zones are still in the early years of their earthquake cycle, so the hazard may not be as great as suggested by the prevailing "time-independent" models that assume another quake is equally likely to occur at any moment, according to the researchers.

Stein says the idea behind the study is not to dismiss the risk of a major earthquake in the two regions, but to shed light on the assumptions that go into making hazard maps, which ultimately affect a region's building codes and other costly preparations.

"We want to know how well we can predict that shaking. If we overpredict, communities could be spending enormous amounts of money [on earthquake preparation] that they could be spending on other things," Stein said. "We look at it as whether you're going to spend money putting steel in your schools that might be better spent hiring teachers."

"What we're saying is that this may be nowhere as serious a problem as you've been told, and you don't need to prepare in St. Louis the way we do in Los Angeles, because that may be doing more harm than good," he added.

The desire to prepare is understandable, given the devastation caused by the last major earthquakes in the New Madrid zone in 1811 and 1812, and in Charleston in 1886. The 1811-1812 New Madrid earthquakes uprooted entire forests and changed the course of the Mississippi River. The Charleston earthquake killed more than 60 people and caused damage to nearly every structure in the city, traces of which can still be seen today.

To prepare for the potential dangers of similar severe quakes in the future, seismologists construct hazard maps, which predict the extent of earthquake shaking that has a certain probability of occurring in a geographical area. The hazard maps take into account the possible magnitude of the next earthquake, the likely ground shaking, the time window in which the next quake is likely to occur, and whether earthquakes are time-dependent or time-independent processes.

It's an admittedly "squishy" calculation, Stein says, even in places like California's San Andreas zone that have experienced many more earthquakes in recent years and have been monitored by a blanket of instruments.

Stein and his colleagues have tested each of these variables, from magnitude to timing, to explore which factors may have the greatest effect on hazard mapping for the central U.S.. But he says that the question of time-dependent or time-independent earthquakes is "the meatiest scientific question" among the mapping variables.

The question goes to the heart of how earthquakes work. For instance, most seismologists think there is a buildup of elastic strain in the earth before a quake occurs, and that the strain is relieved for a time by the quake. Under this scenario, a time-dependent model of earthquakes might make more sense to use in hazard maps. But it's far from clear that the popular strain buildup model completely describes the physics of earthquakes, Stein says.

"It's actually kind of embarrassing that we don't know the answer to this," Stein jokes. "But when you do this kind of thing, you want to have a healthy humility in the face of the complexities of nature."

"Time-Dependent Seismic Hazard Maps for the New Madrid Seismic Zone and Charleston, South Carolina Areas" Hebden, J.S. and Stein, S., Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208


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« Reply #7 on: May 20, 2009, 08:46:23 am »




USGS ShakeMap, showing seismic instrumental intensity, of the April 18, 2008 event in Illinois.

(Credit:
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« Reply #8 on: May 20, 2009, 08:49:34 am »










                                            Illinois Earthquake Is A Wake-Up Call






ScienceDaily
(Apr. 18, 2008)

— Today's early morning earthquake that jolted many in the central U.S. is a reminder that seismic events do occur in areas not normally thought of as "earthquake country." It is also a lesson that earthquakes east of the Mississippi River are felt more widely than those in the west. This event was felt as far west as Kansas, as far north as Upper Michigan, and as far south as Georgia.

"Earthquakes of comparable size are felt over greater distances in the East than those occurring in the West," said Harley Benz, seismologist for the USGS. "Earthquakes in the central U.S. are infrequent, but not unexpected."

The preliminary magnitude 5.2 earthquake occurred at 4:37 am Central Daylight Time and was centered about 38 miles north-northwest of Evansville, IN or 128 miles east of St. Louis, MO. It occurred in an area known seismically as the Wabash Valley Seismic Zone. Today's event is the strongest earthquake in southern Illinois since November 1968, when a 5.4 earthquake occurred.

On Monday, April 21, the USGS will be issuing updated earthquake hazard assessment maps for the entire U.S. The information on these maps is used to update building codes.

Classified as "moderate," today's event caused some damage and was followed by aftershocks, the largest a M4.6 that occurred at 10:15 am Central Daylight Time. Of much greater concern, however, is the potential for the adjacent New Madrid seismic zone to generate severe earthquakes. During the winter of 1811-1812, a series of three very large earthquakes — the strongest earthquakes to strike the lower 48 states during historic times — devastated the area and were felt throughout most of the nation. Occurring only a few weeks apart on Dec. 16, Jan. 13, and Feb. 7, they generated hundreds of aftershocks, some severely damaging by themselves, which continued for years.

Building codes used in the region incorporate a significant degree of risk from earthquakes, but many buildings constructed before these codes were in place or updated have not been adequately retrofitted.

USGS research into ground shaking is used by building officials to update building codes based on the most up-to-date information. As new buildings replace older, more dangerous structures, death tolls from earthquakes have been significantly reduced in the U.S.

Did you feel this earthquake? You can report your experiences on: http://earthquake.usgs.gov/eqcenter/dyfi/

More information on this event and the history of the region is found on: http://earthquake.usgs.gov/eqcenter/recenteqsus/Quakes/us2008qza6.php


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« Reply #9 on: May 20, 2009, 08:51:03 am »








Map of the region surrounding Memphis, TN.

Darker orange area is covered by think sediments called the Mississippi embayment, that affect how the ground shakes during earthquakes.

White lines indicate likely locations of faults, and black dots show the locations of earthquakes since the mid-1970s.


(Credit:
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« Reply #10 on: May 20, 2009, 08:54:04 am »









                                Earthquake In Illinois Could Portend An Emerging Threat






ScienceDaily
(Apr. 25, 2008)

— To the surprise of many, the earthquake on April 18, 2008, about 120 miles east of St. Louis, originated in the Wabash Valley Fault and not the better-known and more-dreaded New Madrid Fault in Missouri's bootheel.

The concern of Douglas Wiens, Ph.D., and Michael Wysession, Ph.D., seismologists at Washington University in St. Louis, is that the New Madrid Fault may have seen its day and the Wabash Fault is the new kid on the block.

The earthquake registered 5.2 on the Richter scale and hit at 4:40 a.m. with a strong aftershock occurring at approximately 10:15 a.m. that morning, followed by lesser ones in subsequent days. The initial earthquake was felt in parts of 16 states.

"I think everyone's interested in the Wabash Valley Fault because a lot of the attention has been on the New Madrid Fault, but the Wabash Valley Fault could be the more dangerous one, at least for St. Louis and Illinois," said Wiens, professor of earth and planetary sciences in Arts & Sciences. "The strongest earthquakes in the last few years have come from the Wabash Valley Fault, which needs more investigation."

Wiens said that seismologist Robert Hermann of Saint Louis University, Gary Pavils of Indiana University, and several geologists including Steven Obermeir of the U.S. Geological Survey (USGS), have made studies of the Wabash Valley Fault. Pavils also has run a dense local array of stations and recorded many very small earthquakes at the Wabash Valley Fault. Hermann has studied the 1968 magnitude 5.5 earthquake, the largest ever recorded there. Obermeir and others have found disturbed sediments from previous earthquakes along the fault with estimated magnitudes of about 7 on the Richter scale over the past several thousand years.

According to Wysession, there are 200,000 earthquakes recorded every year, with a magnitude 6 earthquake happening every three days somewhere in the world.

"There hasn't been a magnitude 6 earthquake on the New Madrid zone in more than 100 years, yet in 20 years there have been three magnitude 5 or better earthquakes on the Wabash Valley Fault," said Wyssession, associate professor of earth and planetary sciences. "There is evidence that sometime in the past the Wabash Valley Fault has produced as strong as magnitude 7 earthquakes. On the other hand, the New Madrid Fault has been very quiet for a long time now. Clearly, the Wabash Valley Fault has gotten our deserved attention."

Wysession said a recent re-analysis of data by USGS shows that the New Madrid fault risk is much less than was thought three decades ago. The three notable earthquakes that occurred at the end of 1811 and the beginning of 1812 were not magnitude 8s, rather magnitude 7s. A magnitude 8 is 30 times more energetic than a magnitude 7.

"The damage to the region by those earthquakes has been exaggerated," Wysession said. "St. Louis was here at the time, and all that happened was some chimneys fell in East St. Louis. The little village of St. Genevieve, closer to the fault zone, had no damage at all. But, let's face it, St. Louis is the biggest city in the region of both faults, and the Wabash Valley Fault is closer to us. If the big one does occur, it's looking more like it will come out of Illinois."

Wysession said that the North American Earth's crust is filled with cracks and faults, and that an earthquake can occur anywhere on the continent. Many of the faults are undetected.

"As the continents bang into each other, sometimes they pull apart, and the crust cracks and ruptures, causing earthquakes," he explained. "This whole region of New Madrid and the Wabash Valley seismic zone became a rift zone about 750 million years ago when the continent almost broke apart. There was a lot of volcanic activity, a lot of seismic activity. The crust got stretched and thinned. By looking at seismometers, we can actually see many of these faults in the thinning of crusts underground."

Wysession said that an earthquake in the Midwest will be felt ten times farther away than one occurring in the western United States because the crust beneath the Midwest is very old, stiff and cold. The rock is about 1.7 billion years old and the seismic waves can travel very long distances through this type of crust. It can be felt hundreds of miles away, even if it was a smaller earthquake. In the western United States, the rock is hotter, and thus it dampens the shock waves and they are not felt as far away.

Despite the fact that most seismologists, including Wysession and Wiens, don't think it likely that earthquakes ever will be predicted — which inevitably dredges up memories of the 1990 Midwest earthquake scare sparked by Iben Browning — Wysession says that there are some precursory phenomena that have been observed right before some earthquakes. Radon or helium gas may leak out of the ground as the ground cracks. Sometimes water well pressure changes, or there's a change in the magnetic field. Electrical resistivity changes have been noted, too.

"These are changes we can measure with instruments, but we can't sense them as humans," he said. "Many people think that animals sense atmospheric changes. You always get stories about Rover going bananas right before an earthquake. But until Rover learns to tell us what he's barking about, we won't be able to employ animals in any predictive way. "


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Adapted from materials provided by Washington University in St. Louis.
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 MLA Washington University in St. Louis (2008, April 25). Earthquake In Illinois Could Portend An Emerging Threat. ScienceDaily. Retrieved May 20, 2009, from



http://www.sciencedaily.com­ /releases/2008/04/080424171350.htm
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