Thursday, January 14, 2010

360 In-Depth: Super Quake - U.S. East, Midwest Are Vulnerable

As you watch the pictures flow in on television and in print this week - terrible, gut-wrenching scenes of rubble and destruction entombing tens of thousands of fellow human beings - try to grasp the fact that such pictures could just as easily be coming from an American city, and not necessarily Los Angeles.

Certainly San Francisco is also a likely candidate for such destruction, as is Salt Lake City, and now even the cities of the Pacific Northwest. The Seattle/Tacoma and Portland areas are, we have just discovered, subject to 9.2 subduction-zone earthquakes equal in magnitude to the monster that mauled Alaska in 1964.

Yet the most physically vulnerable American communities of all lie to the east of the Rocky Mountains. Atlanta, Boston, New York, Charleston, Memphis, St. Louis, Chicago and many other metropolitan hubs sit naked and exposed before the certainty that major earthquakes will soon shake the eastern half of the United States.

Indeed, Dr. Robert Ketter, director of the National Center for Earthquake Engineering Research in Buffalo, N.Y., made that point a few years ago, warning that we will almost certainly have a large Eastern quake - a quake targeted on cities filled with people and political leaders who refuse to believe the existence of the problem.

Of all those communities, only Boston has provisions in its building codes to require some physical resistance to quakes (and those are inadequate). Through the rest of the Midwestern and Eastern United States runs an unbroken horror story: hundreds of thousands of unreinforced-masonry buildings of cinder block and brick, used for homes, offices and high-rise apartments. And laced throughout the region are undependable dams, aging bridges barely attached at each end, questionably sited nuclear-power plants, vulnerable gas, electric, water and sewer lifelines and hazardous chemical-storage facilities sitting tenuously on potentially shaky ground. Stephen King could hardly set up a more terrifying scenario.

Los Angeles can expect to be mightily damaged by movement on the San Andreas Fault, or the Newport-Inglewood or other neighboring faults, most probably within the next 25 years. But the Eastern and Midwestern states also face ground-shaking of colossal proportions, repetitions of such known upheavals as the 1886 Charleston, S.C., quake, the 1755 Boston quake, the Jamaica Bay quake hundreds of years ago on New York's Long Island.

There is no doubt that great quakes roiled the American wilderness before recorded history. Today that wilderness is home to hundreds of thousands of occupied buildings held together only by the grace of undisturbed gravity, brittle constructions based on 100 years of erroneous assumptions that America's heartland cannot shake, rattle or roll.

Throughout the East and Midwest there are cracks in the bedrock that we can't see, under strains that we can't calculate. Exactly when they will produce cataclysmic earth-shaking cannot yet be predicted. But because it could happen as soon as next year or next decade, we should at least alter the standards by which we construct new buildings. (A process of applying well-understood engineering techniques would add, on the average, less than 10% to building costs.) If we live and work in properly designed buildings, our ability to withstand large quakes and emerge with our businesses, our economy, our families and ourselves intact can be boosted from the dubious to the realm of near-certainty.

The New Madrid Fault and the Quakes of the 1800s

The New Madrid Seismic Zone, sometimes called the New Madrid Fault Line, (pronounced New MAD-rid) is a major seismic zone and a prolific source of intraplate earthquakes (earthquakes within a tectonic plate) in the Southern and Midwestern United States stretching to the southwest from New Madrid, Missouri (hence the name). Other intraplate earthquakes include those not only New Madrid, Missouri (1811-1812), but also at Cape Ann, Massachusetts (1755).. Earthquakes occurring along boundaries of plates (e.g., San Francisco, 1906) are well understood in terms of plate tectonics, but those occurring within plates are not similarly understood. This problem still is being studied more than 100 years after the earthquake.

The granddaddy of them all was the1811-12 series of three great quakes on the New Madrid Fault (halfway between St. Louis and Memphis beneath the Mississippi), which shook the entire United States. The next time the New Madrid Fault produces such a quake, it is estimated that 60% of Memphis will be devastated, leaving $50 billion in damage and thousands of dead in its wake. Memphis, you see - like Armenia or Haiti - has looked down the barrel of a cocked and loaded seismic gun for decades, but has done virtually nothing to move out of the crosshairs.

Since the New Madrid fault system was responsible for the 1811–12 New Madrid Earthquakes, it may have the potential to produce large earthquakes in the future. Since 1812 frequent smaller earthquakes were recorded for the area.

Earthquakes that occur there potentially threaten parts of nine U.S. states: Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee, Alabama, Mississippi and Georgia.

...a serious earthquake in the New Madrid

Seismic Zone could result in

"the highest economic losses due

to a natural disaster in the United States,"

further predicting "widespread and catastrophic"

damage across Alabama, Arkansas, Georgia,

Illinois, Indiana, Kentucky, Mississippi, Missouri

and particularly Tennessee...

- November 2008 FEMA Report

The zone had four of the largest North American earthquakes in recorded history, with moment magnitudes estimated to be greater than 8.0, all occurring within a 3 month period between December of 1811 and February of 1812. Many of the published accounts describe the cumulative effects of all the earthquakes (known as the New Madrid Sequence); thus finding the individual effects of each quake can be difficult. Magnitude estimates and epicenters are based on interpretations of historical accounts and may vary.

These earthquakes were felt in cities as far away as New York and Boston, where ground motion caused church bells to ring.

Hundreds of aftershocks followed over a period of several years. Aftershocks strong enough to be felt occurred until the year 1817. The largest earthquakes to have occurred since then were on January 4, 1843, and October 31, 1895, with magnitude estimates of 6.0 and 6.2 respectively.

This series of earthquakes caused permanent changes in the course of the Mississippi River, giving the illusion that it was flowing backward.

Charleston, South Carolina
September 1, 1886, 2:51 am (local August 31)
Magnitude 7.3

This is the most damaging earthquake to occur in the Southeast United States and one of the largest historic shocks in Eastern North America. It damaged or destroyed many buildings in the old city of Charleston and killed 60 people. Hardly a structure there was undamaged, and only a few escaped serious damage. Property damage was estimated at $5-$6 million. Structural damage was reported several hundred kilometers from Charleston (including Georgia, central Alabama, central Ohio, eastern Kentucky, southern Virginia, and western West Virginia), and long-period effects were observed at distances exceeding 1,000 kilometers.

Effects in the epicentral region included about 80 kilometers of severely damaged railroad track and more than 1,300 square kilometers of extensive cratering and fissuring. Damage to railroad tracks, about 6 kilometers northwest of Charleston, included lateral and vertical displacement of tracks, formation of S-shaped curves and longitudinal movement.

The formation of sand craterlets and the ejection of sand were widespread in the epicentral area, but surface faulting was not observed. Many acres of ground were overflowed with sand, and craterlets as much as 6.4 meters across were formed. In a few locations, water from the craterlets spouted to heights of about 4.5 to 6 meters. Fissures 1 meter wide extended parallel to canal and stream banks. A series of wide cracks opened parallel to the Ashley River, and several large trees were uprooted when the bank slid into the river.

At Summerville, a small town of 2,000 population, 25 kilometers northwest of Charleston, many houses settled in an inclined position or were displaced as much as 5 centimeters. Chimneys constructed independently of the houses commonly had the part above the roofline thrown to the ground. Many chimneys were crushed at their bases, allowing the whole chimney to sink down through the floors. The absence of overturning in piered structures and the nature of the damage to chimneys have been interpreted as evidence that the predominant motion was vertical.

The meizoseismal area of MM intensity X effects is an elliptical area, roughly 35 by 50 kilometers, trending northeast between Charleston and Jedburg and including Summerville. Middleton Place, about in the center of this ellipse, is at the southeast end of a zone (perhaps 15 kilometers long) of microearthquake activity that still continues today. This seismic activity may be a continuation of the 1886 aftershock series.

The intraplate epicenter of this major shock is not unique for large earthquakes in the Eastern and Central United States. This earthquake was reported from distant places such as Boston, Massachusetts; Milwaukee, Wisconsin, Chicago, Illinois; Cuba and Bermuda.

Today and Beyond

In a report filed in November 2008, The U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in "the highest economic losses due to a natural disaster in the United States," further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Georgia, Illinois, Indiana, Kentucky, Mississippi, Missouri and particularly Tennessee, where a 7.7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation system and other vital infrastructure.

The potential for the recurrence of large earthquakes and their impact today on densely populated cities in and around the seismic zone has generated much research devoted to understanding in the New Madrid Seismic Zone. By studying evidence of past quakes and closely monitoring ground motion and current earthquake activity, scientists attempt to understand their causes and recurrence intervals.

However, as recent as last year, a study showed something different. ScienceDaily in their May 20, 2009 edition reported the New Madrid fault system does not behave as earthquake hazard models assume and may be in the process of shutting down. A team from Purdue and Northwestern universities analyzed the fault motion for eight years using global positioning system measurements and found that it is much less than expected given the 500- to 1,000-year repeat cycle for major earthquakes on that fault. They say last large earthquakes in the New Madrid seismic zone were magnitude 7-7.5 events in 1811 and 1812.

Estimating an accurate earthquake threat for the area, which includes parts of Illinois, Indiana, Tennessee, Arkansas and Kentucky, is crucial for the communities potentially affected, said Eric Calais, the Purdue researcher who led the study.

However, eight years doesn't seem to be enough time to make such a prediction of a fault zone that has been active (and acting up) for thousands, if not millions of years.


We know that Americans take a back seat to no one when it comes to finger-pointing after a disaster. We know exactly what the national outcry will be if one of our communities suffers a seismic catastrophe next week or next year, especially on the East Coast: Why were building codes inadequate? Why did the dams, the bridges, the apartments collapse? Why were so many killed and maimed? Why didn't Washington protect us when the resulting national financial catastrophe was so predictable? Why weren't we prepared? Doesn't it make more sense to ask those questions - and find the answers - now?

Links: 1886 Charleston, S.C. Quake photos

Sources: USGS Earthquake data;; John J. Nance - On Shaky Ground, an Invitation to Disaster; Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.

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