Posted on 06/22/2005 3:02:56 PM PDT by QQQQQ
A 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.
An earthquake East of the rockies is felt across a wider area. SOURCE: USGS
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 1800s.
Strange movement
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 whatÕs going on.
Unlike California, the slow shift around New Madrid is not driven by the collision between major plates of EarthÕs crust.
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"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 Nature.
Sooner or later ...
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."
South Carolina had a HUGE quake in the 1800's......at least a 7
"The Charleston quake damaged water wells as far away as northwest Georgia."
I can believ it. I've been looking hard for a source on my post about the granite domes being exposed, and have come across a few interesting things. The people of Charleston were cut off from the world for several days and thought that the rest of the world had been destroyed. The rest of the country thought that a huge earthquake and tidal wave had destroyed Charleston and that Florida had broken off and sunk in the Atlantic.
A 6 to 7 quake is about 90 percent certain, however, and they would be devastating enough if close enough to a city considering poor building codes.
Also, though the article doesn't say, obviously there would be a 50-60 percent chance of a quake slightly higher than 7, and that would be pretty dang bad if that happened.
The risk then quickly would taper off to 10 percent max for the 8. It is pure guesswork on my part, but a 7.5 would maybe be a 30 percent chance.
Tremor In Western Kentucky Felt In Four States
(CLINTON, Ky.) June 20, 2005, 10:25 AM -- The National Earthquake Center reports an earth tremor this morning measuring three-point-nine was centered at Clinton in Hickman County. It was the second earthquake within 10 hours to be centered in Hickman County, but both were of minor intensity. Last night's tremor occurred at 10 p.m. eastern time and was measured at 3.0.
A 4.0 tremor was felt across northwest Tennessee and southeast Kentucky last Thursday, but caused little damage.
Geophysicist John Minch at the National Earthquake Center in Golden, Colorado says it is not certain today's quake was on the New Madrid fault, but seismologists in Memphis think it was.
The quake at 8:21:41 a.m. was centered 10 miles southeast of Cairo, Illinois or 30 miles west southwest of Paducah. Minch says no damage reports have been received this morning.
The Long Point Fault crosses Memorial between Kirkwood and Wilcrest. It causes about a three- or four-foot elevation change at that point. It used to be visible where it crossed Dairy Ashford further west, but the repaving of Dairy Ashford some years ago made it hard to detect.
The fault crosses Wilcrest between Memorial and I-10 with another obvious elevation change, crosses I-10 a few blocks east of Wilcrest, and crosses Beltway 8 a block or two north of I-10. It then proceeds east, crossing Gessner just south of Westview. It then follows Westview for miles, switching from one side to the other. There are, or used to be, some spectacularly damaged houses near Westview that had been built on the fault -- they have tilted windows and doors, crooked rooflines, broken driveways, etc. The fault travels eventually crosses Long Point.
I mapped the fault once based on broken pavement, elevation changes, damaged houses, etc. It makes a fun project tracking it through neighborhoods. When the points are connected on an accurate map, such as a USGS map, you'll find that the fault generally runs in connected straight line segments.
The Long Point Fault is not the only active fault in Houston, but it is probably the best known.
Any elevation change in Houston is fairly remarkable. I obviously haven't been paying attention.
I don't doubt that there may have been some landslides in the Blue Ridge that were a result from the Charlston quake but I seriously doubt that those slides exposed the open rock faces and domes to any major extent in the S.W. counties.
My understanding of the rock faces/domes is that they are the caused by concentric exfoliation. The granite/gniess is fractured along concentric lines and eroded over time the mountain basically peels like an onion.
Also, had the quake created slides of the magnitude required to expose dome/rock faces, the resulting debris piles would still exist in situ at the foot of the faces. I've been all over those mountains and never encountered a debris pile of that magnitude.
Where did you hear this theory?
"Where did you hear this theory?"
It's not so much a theory as it was the lore and history of High Hampton. Everyone there "knew" this regarding the huge dome, looming over the lake and the old chestnut-bark sided lodge on the other side of the lake there. I've had no reason to doubt it until you challenged me on it. I'll admit, I've been looking for a source and have found nothing.
You can drive almost any road in the Houston area and drive across a fault. It is literally that bad. If you hit a bump, and notice it was formed by a linear crack across the road, chances are, you just passed over a fault.
Link to a decent photo of the face of this particular dome:
http://www.historichotels.org/Page/HotelPhotos/Hotel/High_Hampton_Inn.htm
I've never heard of that one. Is it close to the San Andreas?
If you visit Charleston, you can see huge iron bolts running through the buildings from one end to the other. They held the buildings together during quakes.
I remember reading about the 1812 quakes this article talks about. For about a year, the people in some states slept outside their homes. They felled trees perpendicular to the chasms that tended to open up, and built platforms on them for beds. There was one account of a steamboat being pushed upstream almost the length of the Mississippi.
Back in the '60s there was a fairly strong earthquake in Illinois. My mom was at a meeting in Decatur that day when the building began to shake and roll like crazy. Mom said you could see the floors pull away from walls. I don't remember though how much damage there was.
I didn't realize until this thread that we were still experiencing it at the surface level around here.
"If you visit Charleston, you can see huge iron bolts running through the buildings from one end to the other. They held the buildings together during quakes."
I thought those were installed afterwards to prevent the buildings from collapsing in a future earthquake? In any event, you can see them in the older parts of many southern cities as a result... look for a series of distinctive star shapes in black cast iron, higher up on the walls of masonry buildings.
Oh yea, some of them were moving an inch a year back in the late '70's. That is a lot when you are 30' above sea level!
Well over a million dollars in oil and gas royalties are at stake.
The land has dropped over seven feet in elevation during that time.
We're slipping into the sea, I tell ya....
If that ever changes.......we're doomed! DOOOOOMED!!!
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