WEBVTT

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[music]

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Memphis, Tennessee. On the far
side of the Mississippi River,

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the land smooth\'s out in a broad level
plane. Below this veneer of rich farmland,

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one of the planet\'s most powerful
earthquake zones lies hidden.

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In recent history, the Earth is trembled
off from here but really enough to cause

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serious damage. So there hasn\'t
been much concern for earthquakes.

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The population has grown to over 10 million people
in the region, and most development took place

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with no regard for earthquake safety.
The earthquake zone lies buried

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in the heart of America. It trends along the
Mississippi River between Marked tree, Arkansas

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and Cairo, Illinois. Scientists call
it the New Madrid Seismic Zone,

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named after a small town in Southern Missouri.
This is not the original town we see here.

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The first one vanished in 1812 when
the strongest series of earthquakes

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ever known on earth tore the region apart.

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That was a longtime ago, but scientific evidence
shows that the New Madrid earthquake zone

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is still very much alive.

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On a clear winter night, the sky above the earthquake
zone lit up with what looked like lightning.

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Below, a massive temblor with a magnitude
of eight or higher struck near Marked Tree.

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A month later, another jolt as strong
as the first struck near New Madrid.

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Incredibly, a third great
quake, the strongest yet,

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rocked the area just 15 days later. Between
these shocks and for months afterward,

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the earth trembled constantly. \"Earthquakes
were so frequent\", an observer wrote,

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\"The earth was in continual agitation,
visibly waving as a gentle sea.\"

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The Mississippi River was profoundly
disrupted by the earthquakes.

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There are stories in the 1811 earthquake that the
very calm Mississippi River suddenly had rapids

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in several areas along it. If a
(inaudible) crossing the river moves,

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if it throws up part of the river floor, you will have rapids, you
will… And there were also stories that the river ran backwards

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in a few points. The eyewitness
accounts from 1811 and 12

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indicate that the river was essentially
unnavigable. There were vast amounts of

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down trees and debris floating in
the river, the banks had caved,

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sandbars that used to be in one location, perhaps, sunk and others
rose in other areas so that the entire character of the river

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was fundamentally different.

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The quakes caused large tracks of land to
warp upward while other tracks sank down.

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Reelfoot Lake near New Madrid was created when
the land heaved up and dammed a running creek.

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When it was all over, an
area the size of Tennessee

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bore the effects of the earthquakes, buildings
were damaged over an area as vast as

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the state of Texas.
Eyewitness accounts span

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the entire nation east of the
Mississippi River. St. Louis, Missouri,

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125 miles from New Madrid reported severe
shaking, badly cracked stone building,

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and hundreds of chimneys thrown down.
Similar reports came

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from the more distant city of
Cincinnati, Ohio, 300 miles away.

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The quake seismic waves traveled right through
the Appalachian Mountains to the East.

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They arrived forcefully on the Atlantic
Coast, 600 miles from New Madrid.

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In Charleston, South Carolina, cracks
opened in the mortar of stone buildings.

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The bells of St. Philip\'s Church rang out
for a short time. Clock stopped working

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in the coastal city of Savannah, Georgia
where four large shocks were felt.

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Furniture was tossed about in people\'s
homes. Further yet from New Madrid,

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moving furniture woke residents of Washington
DC who thought they were being robbed.

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Shaking interrupted an early morning meeting
of Congress. The earthquakes were felt sharply

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as far south as New Orleans. The local
newspapers reported little damage in the city.

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There was even a report of shaking
from the state of Florida.

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To the North, at least, eight shocks were distinctly
felt in Montreal, Canada, 1200 miles away.

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All in all, 2 million square miles,
well over a half the United States

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was shaken by the New Madrid earthquakes.
This is the largest area

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ever known to be affected by any
earthquake anywhere on earth.

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[sil.]

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The great San Francisco earthquake in 1906 matched
the power of the strongest New Madrid shock.

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It had a Richter magnitude of 8.3,
enough to devastate San Francisco.

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Beyond the city, the quake had a
damage area of 12,000 square miles.

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That\'s 20 times smaller than the area of
damage for the New Madrid earthquakes.

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Earthquakes are normally seen
as a California concern.

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And while quakes are not as common
in the New Madrid earthquake zone,

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their enormous damage areas put millions of
people at risk in the Central United States.

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Damage areas are so large
partly because of the zones

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relation to global plate tectonics.
The zone lies at the core of

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the North American tectonic plate, one of 12 major
plates that form the outer skin of our planet.

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The plates are floating on molten material
below forcing them to crash together

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or pull apart at the edges. Over
90% of all earthquakes occur

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where plates meet. But the plate\'s cores
or cratons have remained relatively stable

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for billions of years. They have
become rigid. When earthquake strike,

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seismic waves travel great distances
through this dense solid rock.

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At the edge of many crustal
plates, the landscape reflects

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the violence of rocks grinding together.
California straddles the boundary

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between the North American and Pacific plates.
The rugged landscape is geologically very young

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and seismic waves break up quickly in
the broken landscape they created.

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But there are exceptions.

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October 17th, 1909,

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San Francisco\'s Marina District was heavily
damaged by the Loma Prieta earthquake,

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but the quake\'s epicenter was over 60 miles
away. In between the heavily populated bay area

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suffered relatively little damage.
The Marina District was hard hit

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because it is built on
very soft sand and mud,

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ironically part of it was once a lagoon, which was
filled in with sand and rubble from the 1906 earthquake.

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Seismic waves spread away from the Loma Prieta
quake\'s epicenter through hard bedrock below.

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But nearing the Marina, they slowed
down in the loose surface materials.

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This caused the waves to grow into
destructive surges at ground level.

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The New Madrid earthquake zone

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lies buried in the Mississippi River valley.
Connecting with the river is a vast network of

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more rivers, streams, and lakes, all draining
the wet climate of the mid-continent.

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These waterways eroded the land and
left valleys of loose sediment

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over hard crustal rocks below,
a dangerous combination.

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Seismic waves travel great distances through the rigid crust
then build to violent force in soft river valleys sediments.

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By coincidence, this is
where most people live.

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[music]

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[music]

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[music]

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[music]

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[music]

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[music]

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The face of the New Madrid earthquake
zone has changed dramatically

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since the great quakes of 1811 and 12.
The region has become

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a major agricultural and industrial producer. The
busiest transportation corridor in the nation,

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the Mississippi River, winds its way
through. Crowded interstate highways

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and the dense web of railroads
crisscross the earthquake zone.

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Belowground, natural gas and oil pipelines connect
refineries in the South with customers in the Northeast

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where one quarter of the
nation\'s energy is consumed.

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In Memphis, Elvis Presley\'s Graceland attracts
more visitors than any other home in America,

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except the White House. And Memphis airport serves as distribution
headquarters for the world\'s biggest freight carrier.

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The wilderness of 1811 and 12

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is indeed gone. And as the
works of people replaced it,

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the New Madrid earthquake zone remains
silent. So the area grew up unarmed

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against the fury of earthquakes. When an
earthquake does happen in Central Eastern US,

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the damage areas are gonna be a
lot bigger and it\'s gonna be

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a higher density of damage then you would see
for similar sized earthquake in California.

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Most of the buildings in the
Central Eastern United States

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are constructed from unreinforced masonry
which has virtually no resistance

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to strong ground shaking. In
fact, the last major earthquake

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that happened in Central
Eastern US was in 1895,

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when we developed this whole new infrastructure.
Since then, it hasn\'t been tested

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by a strong damaging earthquake. The same
way that California seems to get tested

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every 10 or 20 years, there\'s a strong
earthquake that knocks down buildings,

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they put up new ones, they\'re designed to
withstand, resist those forces better.

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But we haven\'t had the benefit of that
kind of testing in the Central Eastern US.

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So when one finally does happen, the
other projections and damage is gonna be

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a lot more serious. Suzanne, can you
come look at this, please? Sure. Yeah.

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When will the next large earthquake strike?
What will it do to the Central United States?

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For decades, scientists have
been searching for the answers,

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but the earthquake zone does not reveal its secrets
easily. The Mississippi River running chocolate brown

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with silt buried the zone
under 3,000 feet of mud.

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Advanced earthquake studies developed in California
do not work well here. We have to sample everything

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from the surface because the seismicity
is between 5 and 15 kilometers deep.

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You can\'t dig a hole that deep and look for something. We don\'t
quite have that technology. And in San Andreas like situation,

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you can see the fault. You can walk out and
you can find the trace of it, you can see it

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in the dramatic topography that creates
San Andreas Lake. But in New Madrid,

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it\'s not right there for us to say.
It\'s not right there for us to map.

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Borrowing methods used for oil exploration,
scientists looked through the surface layer of mud

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and probed the rocks below. In the
early 19070s, they discovered

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a buried swath of fractured twisted rocks
about 200 miles long and 40 miles wide.

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The structure was named the Reelfoot Rift.

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The late Dr. (inaudible), a geophysicist at
St. Louis University, used newspaper reports

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to locate earthquakes in the rift. His
results have stood the test of time

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despite the reliability of old news stories. Modern
instruments corrected the reliability problem.

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Up until 1974,

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we just knew that earthquakes were
occurring down in the Bootheel, Missouri.

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1974, St. Louis University was
able to establish a modern, dense,

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regional size and graphic network.
As soon as that was installed

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and earthquakes were recorded,
very strong patterns emerged

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uh… showing where the earthquakes
occurred in the region.

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We with our seismic networks can record

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umm… and locate an earthquake about every two
days, and there will be an earthquake about

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92 (inaudible) to 2.5. And certainly
that level of activity, number magnitude

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five earthquakes that we have seen in the last
30 years is much larger than anywhere else

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in the Eastern United States.
So relative to, you know,

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other areas of the Eastern United
States, New Madrid is a hotspot.

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The earthquakes trace out a zigzag pattern when plotted
on a map, but their epicenters are actually located

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2 to 10 miles below the surface, along
deep faults in the earth\'s crust.

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[music]

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These cubes represent earthquakes
along deeply buried faults,

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swinging below New Madrid, seismicity
picks up then dies out farther north.

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To learn what causes these quakes, we must
journey back in time half a billion years.

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At that time, the continent began to
slowly pull apart. Molten magma swelled up

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from below causing the crust to bulge
and crack open up the surface.

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Extreme heat and pressure continued splitting
the rigid crust allowing magma to shoot up

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through fissures and erupt on the surface
forming volcanoes. The Reelfoot Rift

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was tearing the continent in half.
Now this is a fairly common

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umm… geologic process worldwide.

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And when it happens on a large global
scale, it can form new oceans,

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new ocean is opening up right now
in the Red Sea area for instance.

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So but many rifts are not successful,
they fail, they never make it

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to the stage of actual splitting a
continent and creating new oceanic crust.

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And Reelfoot rift was
one of the (inaudible).

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Over the next 300 million years, the
volcanoes and the doomed rift went extinct.

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The thin fractured crust cooled back down collapsing
under its own weight to form a long wide valley.

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Ancient oceans then flooded much of
North America from millions of years.

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They left behind thousands of feet of sediment
which collected in the sunken Reelfoot rift.

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Through the eons, the rift made several
weak attempts to pull apart again.

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Magma started up old fractures
but never reached the surface.

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Sixty million years ago, rifting stopped.
The crust sank down once again.

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And natural erosion filled the rift
with another layer of sediments.

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The Mississippi River began flowing down the rift
valley after the last ice age about 10,000 years ago.

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But down below, the shattered
rifted rocks remained.

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We\'ve got a much weaker overall crust
than you would out in the crater.

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And that\'s where we find larger quarts

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and the stable continental areas.
So we feel that

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umm… as the… as the ancient faults
of the Reelfoot rift system,

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they\'re regenerating earthquakes today.
The ancient faults are kept alive

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by subtle tectonic forces. Stress in the
earth\'s crust is squeezing the rift

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from the east and west. When stress is great enough,
the old faults which are at an angle to the pressure,

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slips suddenly causing earthquakes.

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The southern end of Reelfoot rift near
Memphis is currently under the most stress.

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With a tendency for big earthquakes to strike
at the ends of faults, this is a good candidate

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for the zones next big quake.
The question is when.

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I would not be surprised to witness a greater than
magnitude six earthquake in my lifetime out here.

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I\'m comfortable that we know roughly

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where in the broad sense, somewhere in
the current very active seismic zones,

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there will be a magnitude six or greater
earthquake certainly in my lifetime,

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but we still have a lot more to learn. We don\'t
know when the magnitude eights will occur,

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probably not in my lifetime but possibly.
We just don\'t know.

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With few defenses against earthquakes,
even a magnitude six to seven earthquake

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could inflict heavy losses in this region.
Damage will be concentrated

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where geologic conditions are most hazardous.
A fascinating phenomenon called liquefaction

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will be widespread along rivers
and streams. It\'s a phenomenon

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where earthquake waves start
shaking the sand. Soft wet sand

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will start compacting together, like when
you take a box of corn flakes and shake it

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and the corn flakes in the box settle. That happens
with the sand. And as the sand starts to settle,

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the water that\'s between the grains of sand
tries to get out from between the grains.

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And if there\'s something solid on top of the
stand like a layer of clay, the pressure breaks

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the surface layer of clay and sand
will come erupting onto the surface

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in sort of a liquefied form, so we call it
liquefaction. And what this often causes is,

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first of all, the ground to break up.
The ground also loses

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all capacity to hold up objects such as
building, so buildings will settle, sink,

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or tilt during liquefaction. And many
earthquakes, there are things called

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sand blows which form. The upper layer of clay will
crack and the sand will come erupting to the surface

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in sort of a volcano and form a
circular patch of sand maybe 20-40 feet

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across of the crater in the middle. That\'s very
typical. We see it in almost any earthquake

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over magnitude six anywhere in the world.
What I\'m going to do is

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walk on this pristine sand
that can bear my weight.

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And once I start bouncing up and down, you\'ll
see that as the sand starts to compact

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and the water comes out of its pores,
the sand liquefies losing all ability

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to bare my weight. And if we watch
afterwards, we will see that

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water erupting in the surface
in miniature sand boils.

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This is a small sand filled
fissure caused by liquefaction

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during the 1811 and 12 earthquakes. From the air,
huge light-colored patches of liquefied sand

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from those quakes are plainly
visible in farmers\' fields today.

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Liquefaction during the 1811 and 12 quakes
devastated a 1,400-square-mile area

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along the Mississippi River.
Today, this same area

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is covered with thousands of farms and
many communities. Highway 55 traverses

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the entire liquefaction zone. A modern
well build interstate, it is defenseless

00:20:10.000 --> 00:20:14.999
against a liquid-like foundation. The earth
levees along the river are also vulnerable,

00:20:15.000 --> 00:20:19.999
especially during high flood stage.
The river\'s natural banks

00:20:20.000 --> 00:20:24.999
now lined with petroleum storage tanks,
grain-loading facilities, original power plant,

00:20:25.000 --> 00:20:29.999
and long-bridge approaches are especially
vulnerable. Failure of these kind of riverbanks

00:20:30.000 --> 00:20:34.999
normally occurs by a process
that we call lateral spreading

00:20:35.000 --> 00:20:39.999
which occurs when liquefied sand and water
layers beneath the surface of the ground

00:20:40.000 --> 00:20:44.999
are shaken repeatedly over a long period
of time during a major earthquake.

00:20:45.000 --> 00:20:49.999
But the eyewitness accounts from the 1811 and 12
earthquakes indicate that even those low riverbanks

00:20:50.000 --> 00:20:54.999
experienced massive failure.
Transportation may be disrupted for years

00:20:55.000 --> 00:20:59.999
by liquefaction alone, but other earthquake
effects will add to the problem.

00:21:00.000 --> 00:21:04.999
In a future, major earthquake,
there\'s very little doubt

00:21:05.000 --> 00:21:09.999
that there will be major landsliding from bluff such as this
as well as bluffs that are farther away from the river.

00:21:10.000 --> 00:21:14.999
Large amounts of this land will
simply flow towards the river

00:21:15.000 --> 00:21:19.999
and trees and farmland and the ground
itself will simply be precipitated

00:21:20.000 --> 00:21:24.999
into the river. When we think ahead to future
possible earthquakes in the midcontinent,

00:21:25.000 --> 00:21:29.999
navigation is probably one of the issues
that we ought to deal with most seriously

00:21:30.000 --> 00:21:34.999
because obviously, a large
amount of barge traffic

00:21:35.000 --> 00:21:39.999
goes up and down the Mississippi River, and after a major
earthquake, it is likely that the river would be unnavigable

00:21:40.000 --> 00:21:44.999
for quite some period of time,
maybe weeks or even months.

00:21:45.000 --> 00:21:49.999
[sil.]

00:21:50.000 --> 00:21:54.999
Landslides and liquefaction are triggered
by strong shaking during earthquakes.

00:21:55.000 --> 00:21:59.999
By itself, shaking is a serious threat to weak
structures. Most vulnerable are old bridges

00:22:00.000 --> 00:22:04.999
and unreinforced masonry
buildings built on lose ground.

00:22:05.000 --> 00:22:09.999
Unfortunately, many historic ornate buildings around the
New Madrid earthquake zone fall under this category.

00:22:10.000 --> 00:22:14.999
When most of us think of earthquakes,

00:22:15.000 --> 00:22:19.999
we pictured gaping fissures like this one.
This is indeed a common scene

00:22:20.000 --> 00:22:24.999
when a quake strikes California. The
Landers quake in 1992 opened fissure

00:22:25.000 --> 00:22:29.999
50 miles long across the floor of the Mojave Desert.
But the faults of the New Madrid quick zone

00:22:30.000 --> 00:22:34.999
are too deeply buried to rupture the
ground except in massive quakes.

00:22:35.000 --> 00:22:39.999
Liquefaction, shaking, and landslides are the
main effects of earthquakes in this region.

00:22:40.000 --> 00:22:44.999
And the city most threatened by earthquakes is
the Blues music capital of the world Memphis.

00:22:45.000 --> 00:22:53.000
[music]

00:22:55.000 --> 00:22:59.999
As musicians play on Beale Street,
scientists from Memphis State University

00:23:00.000 --> 00:23:04.999
are evaluating Shelby County\'s public
buildings and bridges for earthquake safety.

00:23:05.000 --> 00:23:09.999
Preliminary results are sobering. One out of four
hospitals are in the highest seismic risk category,

00:23:10.000 --> 00:23:14.999
25% of the public schools,
and 15% of the fire stations

00:23:15.000 --> 00:23:19.999
also fall in this category. A
sampling of the county\'s 900 bridges

00:23:20.000 --> 00:23:24.999
showed that one out of four are
at the highest level of risk.

00:23:25.000 --> 00:23:29.999
Seismic evaluation of public utilities and
other critical lifelines is also underway.

00:23:30.000 --> 00:23:34.999
These studies will guide the strengthening of
only the most dangerous and critical structures.

00:23:35.000 --> 00:23:39.999
Retrofitting is expensive and there are
a great number of weak facilities.

00:23:40.000 --> 00:23:44.999
On the other hand, building new buildings to
be earthquake safe raises construction costs

00:23:45.000 --> 00:23:49.999
only 10% on average. But earthquake
codes are weak to non-existent

00:23:50.000 --> 00:23:54.999
in the New Madrid quake zone. The
state of Kentucky is an exception.

00:23:55.000 --> 00:23:59.999
They adopted modern earthquake codes in
1981. And recently, surrounding states

00:24:00.000 --> 00:24:04.999
are taking earthquakes more seriously. Researchers
found new evidence of one or more massive quakes

00:24:05.000 --> 00:24:09.999
near Vincennes, Indiana. The large
cities of Indianapolis and Evansville

00:24:10.000 --> 00:24:14.999
are less than 100 miles away. Chicago, Illinois
built on a veneer of very loose lake muds

00:24:15.000 --> 00:24:19.999
is 200 miles away. Skyscrapers
are in danger of excessive swing

00:24:20.000 --> 00:24:24.999
from low-frequency
high-amplitude seismic waves.

00:24:25.000 --> 00:24:33.000
[music]

00:24:40.000 --> 00:24:44.999
There\'s another way to view this scenario. Earthquakes
are at the very root of this region\'s prosperity.

00:24:45.000 --> 00:24:49.999
The Mississippi River flows through here
because rifting opened a natural pathway

00:24:50.000 --> 00:24:54.999
to the sea. Earthquakes
literally shaped this rich land

00:24:55.000 --> 00:25:00.000
and will continue to do so.