November 1999 -
Mississippi River Valley cities such as St. Louis and Memphis are in grave danger of being hit by a severe earthquake, geologists said Thursday. They found faults, similar to those responsible for the 1994 Northridge quake that badly damaged the Los Angeles area, all along the New Madrid fault region that extends through Arkansas, Missouri, Kentucky, Illinois and Tennessee.
That region was hit by three big quakes with magnitudes greater than 7.0 on the open-ended Richter scale in 1811 and 1812 -- quakes so strong they reportedly caused church bells to ring all the way to Boston.
Writing in the journal Science, a team at the University of Colorado at Boulder and the University of Arkansas said they had found evidence that explains just why the quake threat there is so serious.
"Our evidence shows the New Madrid seismic zone is indeed a threat, which contradicts a recent study of the seismic hazard of the region taken with satellite data," Karl Mueller, who led the study, said in a statement.
"For the first time we can see how fast the earthquake engine is running and how long it takes to build up energy for a quake."
Not only would any quake be strong, but because the valley is made up of layers of silt, the shaking would turn much of the land to jelly in a process known as liquefaction.
"New Madrid is the world's most spectacular example of liquefaction," Mueller said in a telephone interview. "When you take a fine-grained, saturated sediment like mud or silt and you shake it during an earthquake, it turns to the consistency of jello," Mueller said.
"If you have a building that is sitting on top of jello, the building falls down. The scary part about New Madrid is that ... we see liquefaction all over the place there."
Midwest debate over earthquakes growing in magnitude - May 1999 -
By STEPHANIE SIMON -
Los Angeles Times
The New Madrid fault, which cuts through five states along the Mississippi River, ruptured into three of the most monstrous earthquakes ever during the winter of 1811-12. Legend has it the ground shook so violently that the Mississippi ran backward and folks as far off as Canada trembled.So Midwesterners have to wonder: Will it ever happen again?
Seismologists long have warned that the New Madrid seems prone to tremendous tremors once every 500 years or so. The Midwest, in fact, is at bigger risk of a supersized quake than Los Angeles or San Francisco, according to the U.S. Geological Survey.But using new data that show ground along the fault barely moving, a team of scientists asserted last month that New Madrid's threat has been way overstated. ``There's a reasonable chance that earthquakes like those that happened in 1811 and 1812 will never happen again,'' said Seth Stein, a professor of geological sciences at Northwestern University.
What's more, Stein says that the 1811-12 quakes may have been exaggerated. The Midwest was still pioneer territory then, with few people and fewer still reliable historians. Most likely, he says, the biggest of the quakes was just a magnitude 7. Most scientists had pegged the New Madrid temblors at about 8. Stein's conclusions would seem a great relief to most Midwesterners. But no one, least of all other seismologists, knows whether they are correct. When Stein and his colleagues published their research in the journal Science, they touched off a major controversy. Leading seismologists called the conclusions ``irresponsible'' and ``misleading.'' They insisted the New Madrid fault remains extremely dangerous and called on the public to keep pushing lawmakers for tougher seismic building standards.
``We have been accused of being alarmist, Chicken Little, the sky is falling, but we don't want to minimize what we see as a legitimate long-term hazard,'' said Arch Johnston, director of the Earthquake Hazards Program at the University of Memphis. The dispute stems from the basic problem that no one understands why the Midwest has earthquakes. Most quake zones, such as California, are volatile because they perch on or near the intersection of two tectonic plates. When the plates bang against or slide on top of one another, the earth shakes. But the New Madrid region sits square in the middle of a plate. Yet scientists know from the geological record that very big quakes rocked New Madrid in the years 500, 900, 1530 and 1811-12.Eugene Schweig of the Geological Survey is convinced it will happen again -- in the next few hundred years.
Stein and his colleagues disagree. They point to measurements showing that over the last six years, the ground around New Madrid has barely moved -- less than one-tenth of an inch a year. (California's San Andreas fault is shifting up to 2 inches a year.) At that rate of slippage, they figured it could take as many as 10,000 years before New Madrid erupts in another major quake.But critics point out that the New Madrid fault is buried deep, under 3,000 feet of sediment in places. So the movement of ground on the surface may not be particularly telling. In addition, because the New Madrid is located in the center of a plate, comparisons with the San Andreas may be meaningless. The Midwest's fault may have a logic all its own.
Stein acknowledges that the New Madrid still can generate dangerous quakes, especially in the magnitude-6 range. Since the Midwest is poorly prepared, many buildings are not reinforced to even the most basic seismic safety standards -- ``there is a very realistic chance of major damage and loss of life during the next 50 years due to earthquakes at the New Madrid fault,'' said Joe Engeln, a University of Missouri professor who worked with Stein.
March 1999
A devastating series of earthquakes estimated up to magnitude 8 ripped through the Mississippi River valley in 1811-12. A less-severe magnitude 6.6 earthquake rocked the region in 1895. Fissures split the earth, rocks flew through the air and the Mississippi River ran backwards. Scientists have long believed that magnitude-8s could occur again in 500-800 years. A magnitude-7 could occur even sooner. Seismic maps released in 1996 forecast a greater earthquake hazard than previously in the midcontinent region.
Geologist Arch Johnston, who heads an earthquake center at the University of Memphis, has predicted that a magnitude 8 earthquake could occur in the New Madrid zone every 550-1,000 years. Because of shock effects, such a quake could cause tens of billions of dollars worth of damage from Mississippi to Michigan, leveling Memphis and seriously damaging St. Louis. A magnitude 7 earthquake could occur within 50-100 years, and one registering magnitude 6 could occur at any time, according to Johnston's forecasts. The Geological Survey hasn't made specific forecasts, but its hazard assessments are similar to Johnston's.
But Northwestern geologist Seth Stein, lead scientist on the new study, said six years of satellite monitoring of ground movement in the New Madrid zone indicates that, at most, the Midwest should experience a magnitude 8 earthquake every 2,500-10,000 years or a magnitude 7 earthquake every 1,000 years. Their measurements found that movement of the ground was extremely slow. Having blown the pressure in the 1800's the area may have settled down for good and there may never be a quake here again.
Officials at the national survey and the Ohio Geological Survey reacted angrily yesterday to Stein's report, which was funded by the National Aeronautics and Space Administration. Eugene Schweig, central region coordinator for the U.S. Geological Survey's Earthquake Hazards Program, said the conclusions of Stein and his colleagues are premature and are based on inadequate data. We don't understand at all what causes earthquakes in areas like this that are flat and are not on a techtonic plate boundary.
