Scientists Explain Origin Of South Asia's
Deadly Tsunami
The earthquake that
triggered massive tsunamis in South Asia
Dec. 26, killing more than 100,000 people
and leaving millions more homeless, was
centered deep under the Indian Ocean off the
coast of Indonesia. As relief workers
struggle to help survivors, scientists are
working to better understand the forces that
unleashed such devastation.
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The most powerful earthquake in 40 years --
measuring 9.0 on the Richter scale --
occurred approximately four miles below the
Indian Ocean near the Indonesian Island of
Sumatra.
Scientists say this happened when two of the
major plates that make up the Earth's crust,
the India plate and the Burma plate,
collided and created a tsunami, or extremely
powerful waves.
"[The earthquake] causes large-scale
immediate uplifting of the terrain under the
water that creates a massive wave. That wave
travels very efficiently across the ocean.
And so it shows up hundreds and even
thousands of miles away with much of the
same energy that it started with," said Jim
Devine, a senior science adviser to the
director of the U.S. Geological Survey, the
government agency in charge of monitoring
earthquakes.
These large wave swells, some of which
traveled 3,000 miles to the African coast of
Somalia, caused the majority of the death
and destruction throughout Sri Lanka, India,
Indonesia, Thailand and Malaysia.
"I myself was out swimming in the sea with
my husband when all of a sudden we heard
screams from the beach to return to the
shore. We had no idea why. I started to
return to the beach and as soon as I got
there, I turned my back again and to see
what I can only describe as a wall of water
approaching," said Di Ridley, a television
news producer on her honeymoon in Thailand.
Tsunamis
The term tsunami, which is often
incorrectly referred to as a tidal wave, was
officially adopted for general use in 1963
during an international scientific
conference. It is a Japanese word
represented by two characters: "tsu" which
means harbour and "nami" which means wave.
Most waves that hit the typical beach are
wind generated. Smaller and less powerful
than other waves, wind-generated waves have
a period -- the time between two successful
waves -- of five to twenty seconds. Their
wavelength -- the distance between two
successful waves -- is usually about 50 to
600 feet.
Tsunamis, on the other hand, can have
periods between ten minutes and one hour and
a wavelength in excess of 430 miles.
With an underwater disturbance like an
earthquake, millions of gallons of seawater
are suddenly and violently displaced. The
waves they create radiate in all directions
from the epicenter of the quake, moving at
the speed of a commercial jet. As they get
closer to a shoreline or coast the front of
the tsunami wave slows due to friction. The
waves behind stack up onto each other
creating a pile of waves that can reach 30
feet, hitting land with enough force to
flatten buildings and trees and carry boats
and ships miles inland.
Why weren't people warned?
Unfortunately, scientists say, the
earthquakes that cause such massive tsunamis
are notoriously hard to predict. They may be
able to predict where large quakes are
likely to occur but not exactly when.
There are systems to warn people that a
tsunami is approaching, but the system of
sensors can cost countries an enormous
amount.
"A system to record, identify and get the
word out to all the countries is expensive.
And for something that only happens once
every 100 years or so, it is very difficult
to justify having such a system. We only put
one in place in the Pacific Ocean in 1967
after the 1964 earthquake, which killed many
people in Hawaii and even in California,"
Devine said.
Because earthquakes of this magnitude are
rare in the Indian Ocean, warning systems
like those in the Pacific had not been put
into place.
But, following the destruction of December's
tsunamis, India has announced that it will
install an early tsunami warning system to
predict the lethal waves in the future. The
$27 million project should take two and a
half years to implement, according to
India's Science and Technology Minister
Kapil Sibal.
The existing international warning system,
which attempts to predict tsunamis in
Pacific-Rim countries, did record the giant
earthquake that created the deadly tsunami.
But without ocean sensors in the region they
were unable to determine the size of the
waves or their direction.
The human toll of the earthquake and deadly
tsunamis will not be fully known for weeks,
as doctors, relief workers and government
officials struggle to help those injured and
in need.
But scientists in all the heavily affected
nations have already set to work to try and
improve the prediction and tracking of these
deadly waves in hopes that the horrifying
death and destruction won't be repeated in
the future.
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