Seismic activity in country's center sparks debate
After California quakes, attention turns to New Madrid zone
By KC Wildmoon
CNN



Wednesday, June 22, 2005 Posted: 1951 GMT (0351 HKT)

Earthquakes on the West Coast have prompted fresh speculation about
"the big one" -- a quake that could dump a huge section of California
into the sea.

A few have been large enough to shake the faith of skeptics -- a
magnitude 7.2 quake on June 15, followed two days later by a magnitude
6.7, both off the coast near the California-Oregon border.

Doomsayers have warned about the Pacific Coast for years. But only a
few have raised concerns about an area with the potential to be more
dangerous than California -- the New Madrid seismic zone in the center
of the country.

It's a 120-mile-long system of three to five faults stretching from 40
miles northwest of Memphis to southern Illinois, near Cairo.

"The system is capable of producing a quake near 4.0 magnitude every
three years," said Gary Patterson, a geologist and information services
director for the Center for Earthquake and Research Information in
Memphis, Tennessee. "And they'll cause minimal damage."

But New Madrid already has spawned four earthquakes this year of
similar size, along with nearly 100 smaller quakes. Patterson said such
activity may or may not be the precursor to a much larger quake.

The recent activity is an anomaly, he said.

"It's unusual, and we don't have any reason to believe there is
increased risk," Patterson said. "But any time you have this kind of
activity in an area that has a 25 [percent] to 40 percent chance of a
6.0 or greater in the next 50 years, it will draw attention."

And the region is ill-prepared for a strong quake, he added.

Under pressure
Scientists know little about how the New Madrid seismic zone works, but
in the early 19th century, it was the source of the most violent series
of earthquakes known in North American history.

The zone, named for the town of New Madrid, Missouri, is hundreds of
miles from a tectonic plate boundary, which Patterson said defies the
logic of coastal earthquake science.

"Plate tectonic theory can account for large quakes on the edges of
plate boundaries, but plate boundary theory assumes a rigid continental
plate," he said. "Madrid is in the middle of a continental plate, not
on the boundaries."

Three large quakes happened in the winter of 1811-1812, and strong
rumbles hit several times until near the end of the 19th century.

These quakes were felt keenly over more than 2 million square miles --
people in Boston, Massachusetts, felt one or more of the three main
quakes, the first of which struck in three shocks on the morning of
December 16, 1811.

Two more large shocks struck the area -- on January 23, 1812, and the
largest and most devastating of all hit February 7, 1812, destroying
the town of New Madrid.

By contrast, the 1906 earthquake in San Francisco, California, was felt
over 60,000 square miles.

Patterson said the incredible distance the quakes reached was largely
due to the cold, solid rocks "that make this continent float," a
different environment from the plate boundaries on the coast.

"On the boundaries, the rock is hot, molten and broken up," he said.
The solid rock carries the movement farther from the epicenter.

Earthquake researcher Otto Nuttli estimated 200 moderate to large
earthquakes on the New Madrid fault between December 16, 1811, and
March 15, 1812, and about 1,800 earthquakes of slightly lesser
strength.

The stronger quakes lifted parts of the land high or dropped them down,
and drew the Mississippi's waters in and threw them back far over the
river banks. In some areas, the upheaval beneath the surface was so
violent that it caused the mighty river to flow backward.

Whole islands in the river -- and entire towns -- disappeared.

The strongest quake in the area since 1895 was a magnitude 5.5 in 1968.
New Madrid is "a sleeping giant we don't understand very well,"
Patterson said.

"But we realize the need to understand is very important," he added.
"It's a challenge. If we understand this question, then we've really
put in a piece of how the Earth works as a system."

Trouble for Memphis, other cities?
Patterson said he saw no reason for a "high level of concern" at the
moment but added that so little is known about New Madrid that it's
even more unpredictable than its coastal cousins.

The area isn't prepared for an earthquake of magnitude 6 or higher,
specialists said. Damage from such quakes would be significant over a
multistate area, Patterson said, with the likelihood of significant
infrastructure disruption and damage to population centers and
municipalities that would have huge economic impact.

Memphis, and to a slightly lesser degree, St. Louis, Missouri, could be
seriously hurt by a strong quake, "especially when you have old
infrastructure and a lot of buildings that predate 1940, when
unreinforced masonry was a typical style," Patterson said.

"Our building inventory is very vulnerable and has not been shaken
significantly," he said. "It's potentially a large disaster even from a
magnitude 6."

Ted Ilsley, manager of the plan review section of Shelby County,
Tennessee's building code enforcement division, said the building code
is adequate for an earthquake the size of the 1811-1812 ones. This code
has been in effect since 1989 in the county where Memphis is located.

The county is preparing to adopt an amended version of the
International Building Code, a requirement to receive funding from the
U.S. Department of Homeland Security.

The city of Memphis also likely will adopt something similar to Shelby
County. Calls to the city's code enforcement division were not
returned.

Although strong earthquakes strike the West Coast more frequently, New
Madrid is "an active seismic zone," Patterson said, and population
centers in the area should be concerned -- not with the frequency --
but with the consequences if one does strike.

"It does not take the big one to do a lot of damage," he said. "The
most damaging quake in the United States, in 1994 [the Northridge quake
in Southern California], causing $30 billion, some say $40 billion in
damage, was a 6.7 in a place that's prepared generally for
earthquakes."

There's no doubt that the New Madrid seismic zone has the potential to
spawn catastrophic earthquakes. The question, as with most fault areas,
is when it will occur.

Whenever it occurs, the quake likely will be felt far from its
epicenter. The one in 1968, centered in southeastern Illinois near the
confluence of the Tennessee and Ohio rivers, caused moderate damage,
but it was felt across 23 states -- as far as the Carolinas -- and into
Canada.

CNN researcher Anne Pifko contributed to this report.

Seismic activity in country's center sparks debate
After California quakes, attention turns to New Madrid zone
By KC Wildmoon
CNN



Wednesday, June 22, 2005 Posted: 1951 GMT (0351 HKT)

Earthquakes on the West Coast have prompted fresh speculation about
"the big one" -- a quake that could dump a huge section of California
into the sea.

A few have been large enough to shake the faith of skeptics -- a
magnitude 7.2 quake on June 15, followed two days later by a magnitude
6.7, both off the coast near the California-Oregon border.

Doomsayers have warned about the Pacific Coast for years. But only a
few have raised concerns about an area with the potential to be more
dangerous than California -- the New Madrid seismic zone in the center
of the country.