[Science] Earthquake risk to central U.S

[vincent]

colossal earthquake that caused damage from South Carolina to Washington D.C. and temporarily reversed the course of the Mississippi River nearly two centuries ago could be repeated within the next 50 years, scientists said today.

Strain is building on a fault near Memphis, Tennessee that was the site of a magnitude 8.1 earthquake in 1812, according to new observations that settle a debate on the risk of another huge quake

The odds of another 8.0 event within 50 years are between 7 and 10 percent, geologists said today. The assessment, based on new data from a recently installed array of sensors, puts to rest a 1990s claim that strain was not increasing.

Such a strong earthquake would rock the entire eastern half of the country and prove devastating to the local region. A lesser but still damaging quake of magnitude 6 or greater has a 90 percent chance of striking in the next five decades. The new study, detailed in the June 23 issue of the journal Nature, reveals a vexing characteristic of the fault that traverses the region. The ground moves more near the fault, creeping a few millimeters every year, than it does farther from it.? "I can't explain how the movement is driven," said study team member Michael Ellis, a geologist at the University of Memphis. That lack of understanding makes the task of pinpointing when the next quake might hit even more challenging.

Repeating history>

In a three-month period in 1811-12, three major earthquakes rattled a broad expanse of the United States, causing damage as far away as Charleston, South Carolina and even rattling nerves in Boston. The quakes triggered landslides into the Mississippi River and, according to some boaters who were not drowned, sent part of the river running the other direction for a time.

The earthquakes were centered around New Madrid, Missouri.? They measured 8.1, 8.0 and 7.8 and represent three of the four strongest earthquakes ever recorded in the lower 48 states.

Over the past 12 years, geologists have found evidence for other prehistoric calamities along the New Madrid fault. Sandy soil in some areas became liquefied in past events, leaving telltale "sandblows" when the material was squished to the surface. This tendency for soil east of the Rockies to liquefy, along with other differences in geology, means earthquakes there pack more potential for damage and are felt over a much wider region than western temblors.

http://www.livescience.com/images/050210_newmadrid_wide_03.gif[/imgAn earthquake East of the rockies is felt across a wider area. SOURCE: USGSb>

The sandblows indicate that three or possibly four earthquakes of magnitude 7.6 or better struck the region in the past 2,000 years, in addition to the incredible series of three in the early 1800sStrange movementb>

The new data show the ground indeed moves a few millimeters each year near the fault, as most geologists had expected. But away from the fault, the movement was discovered to be less. Ellis and his colleagues, including study leader Bob Smalley, speculate that well below the surface, the fault was displaced by the 1811-12 events and that shift is still, slowly, propagating upward.

Ellis cautioned, however, that more data is needed to figure out what?s going on.

Unlike California, the slow shift around New Madrid is not driven by the collision between major plates of Earth's crust.

Ultimately the movement is driven by plate tectonics, with the North American plate moving generally westward," says Martitia Tuttle, a geologist at M. Tuttle & Associates who was not involved in the new research.

Most scientists think the New Madrid fault is part of an ancient system of rifts embedded in the plate.

"The old rift system is a zone of weakness and therefore is more prone to failure, resulting in earthquakes, than surrounding regions," Tuttle told LiveScience.

The new study provides "scientific justification for the adoption of stricter earthquake provisions in the building codes for Memphis and other cities in the central United States," Tuttle said.

The results, and an analysis by Tuttle, are published in the June 23 issue of the journal NatureSooner or later .../b>

The findings contradict a study in the 1990s, based on less data, that concluded the ground was not shifting and so strain buildup was minimal. Since that controversial work, scientists have debated the prevailing view that more major earthquakes are likely.

"Our results confirm the current status of seismic hazard ... that says that the likelihood of another 1811-12 earthquake in the next 50 years is between 7 and 10 percent," Ellis said in an email interview.

The chances of a smaller but still devastating temblor are higher.

"Strong earthquakes in the New Madrid seismic zone are certain to occur in the future," states a fact sheet from the U.S. Geological Survey. "There is a 9-in-10 chance of a magnitude 6 to 7 temblor occurring in the New Madrid Seismic Zone within the next 50 years."

The new monitoring system around the New Madrid fault should eventually allow geologists to refine their predictions.

"Folks out west, California in particular, are much further ahead than are we," Ellis said. "They have more data, more instrumentation, and a simpler tectonic environment.? Our results though will begin to constrain the set of reasonable theoretical models for the generation of midplate earthquakes, and that's the beginning of making better forecasts."

Source

[Koolslacker]

Thanks for the info. I'll try to avoid moving in central US ;)

[Julius Caro]

I thought earthquakes were not predictable.

[gigapixels Veteran]

I thought earthquakes were not predictable.

586128678[/snapback]

Nobody's predicting exactly when, they simply said that it very well could happen sometime within the next 50 years. A prediction would be a much smaller range of time... 50 years is too long to be definitive enough to be considered a prediction.

[Toolage]

we have been have quakes ranging from 2-3 here in the southern il, ky, tn area for the last few weeks. We had a 3.0 today just a few miles away so activity has most definitely increased over the last few weeks here.

[James Rose]

I thought earthquakes were not predictable.

586128678[/snapback]

Correct, of a sort. Earthquakes are not predictable becuase there are too many parameters to calculate. When you see an article such as this, they are not stating in the next 50 years that a quake WILL happen, they are stating based on past events, therefor a PROBABILITY of an event happening. Meaning a sizable event has happened, historically, every X years, and since it has been X +20 years geologists are estimating that a quake is due or overdue based on past events. However, it is important to know that you can rarely plan future events on past events. (ooh, a little phylosophy mixed in with geology today! ;)

I lived 30+ years in San Francsico, and the only major quake while I was there was in 1989 (barely notied it myself, but I was on Potrero Hill, which is one big rock) but now I live in NYC on 43rd Ave, and there is a small fault line on 42nd street (out my window) It is more likely that a quake in CA will cause damage in my lifetime than in NYC, but again, the parameters to this equation are quite large and many of the variables are unpredictable.

[gdodson]

I thought these quakes were results of Atlantic Floor Spreading and a "weaker" point in the central US formed millions of years ago when North America merged into one landmass. The weaker point is where the merge between old landmasses would have been, kind of like a poor weld. At least this is what I learned in geology and I remember an article saying there was no true fault in central US anymore. Lies my teacher/textbook told me?

[TheNay]

Interesting images and article, thanks for the read ;)

[James Rose]

I thought these quakes were results of Atlantic Floor Spreading and a "weaker" point in the central US formed millions of years ago when North America merged into one landmass. The weaker point is where the merge between old landmasses would have been, kind of like a poor weld. At least this is what I learned in geology and I remember  an article saying there was no true fault in central US anymore. Lies my teacher/textbook told me?

586128740[/snapback]

Not realy lies. Yes the faults in the middle of the country are from the colliding of the contient. (see also The Rockies) but the faults there remain, and movement still happens areas outside of The Ring of Fire (US West coast, Japan, etc) but it is more rare than within areas that are not on active technonic plates.

Also, North America did not collide with aonther continent, it was just a chunk of Pangea (sp?) the super continent that driffted apart over the millenia

[Hupp]

w00t for central us...we got tornados and possible huge earth quakes...yay

[Boffa Jones Veteran]

lol, hardly a prediction. 'There is a 7 to 10 percent chance that within the next 50 years there may be an earthquake....' Not exactly something that you would want to bet on.

[LOC Veteran]

lol, hardly a prediction. 'There is a 7 to 10 percent chance that within the next 50 years there may be an earthquake....' Not exactly something that you would want to bet on.

586130623[/snapback]

Oh but it is something you can bet on. Scientists are to modest when it comes to -predictions like this, and it is well known that the New Madrid faultline will cause a major quake, perhaps not in the next 10 years, but certainly within the next 25-50 years.

[Rob2687]

There's a chance a lot of things could happen but hey...we don't need to go through another y2k fiasco again.

[Alex Suraci]

Oh snap, I live in Indiana. Northern, but still, I'm in the yellow. But I'm sure I'll move away by the time I'm 64 anyway..unless it's tomorrow. Eek.

[Hum]

Posted on June 23rd:

https://www.neowin.net/forum/index.php?showtopic=335650