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Pacific Tsunami Museum
The
next big earthquake… : Information about earthquakes and tsunamis
from the University of Alaska - Fairbanks
Tsunami
Community: This web site, funded by the US National Science Foundation,
represents the breadth of research and knowledge in the tsunami community
for scientists, policy makers, and disaster managers.
The WWW Tsunami Information Resource
It's a disaster that can kill thousands of people without warning.
But as this ScienCentral News video reports, researchers studying the movement
of water are now creating better ways to predict where and how tsunamis can
affect us.
Modeling Waves
In movies like Paramount’s
“Deep Impact” and MGM’s
“Meteor”, a huge wave caused by a comet or meteor crashing into
the ocean wipes out entire cities and kills millions of people. But is such
a wave possible?
In real life, a wave like that might be called a tsunami. Tsunamis (pronounced:
"SOO-nah-MEEs") are usually caused
by earthquakes, explains Stephan
Grilli, a hydrodynamicist in the Department
of Ocean Engineering at the University of Rhode Island. Grilli, who studies
the movement of water, says, “Earthquakes shake the ocean bottom—move
it up and down—and that produces waves on the surface. But earthquakes
can also produce underwater landslides by shaking sediment—loosening up
sediment…. Those underwater landslides can produce waves on the surface,
and those waves, if they occur very close to shore, can be even more damaging"
than waves caused by earthquakes.
The word “tsunami” is Japanese for “harbor wave”, because
of the devastating effects of these waves on low-lying Japanese coastal areas.
But because tsunamis occur most often in earthquake-prone regions, many areas
other than Japan are also at risk. For instance, tsunamis occur in the Pacific
Ocean, along the coasts of Asia, Japan, and North and South America. “These
are regions with very frequent earthquakes, and therefore very frequent tsunamis,”
says Grilli.
Not only are many areas at risk for tsunamis, but the waves occur far more
frequently than one might think. According to Grilli, “Many small tsunamis
are occurring on any given day, but very few of those will be damaging.”
In order to forecast the effects of future tsunamis, Grilli created a computer
program that predicts what a landslide-generated tsunami would look like in
particular conditions. He says, “The computer model actually gives us
numbers that correspond to the motion, the speed, the elevation of a tsunami.”
The computer model, which took many years to develop, can be used to study
both past and future tsunamis. “A computer model can help us simulate
tsunamis in many situations," he says. "So we can actually reproduce
historical tsunamis, as well as [simulate] future tsunamis that could happen
in an area where the potential for a landslide has been identified.”
But how does Grilli know his computer model is accurate? He uses real data
from two different sources: One is a wave tank, and the other is history.
“The wave tank is like a large pool in which we can produce all sorts
of waves,” says Grilli. In fact, he created a scale model of a landslide—a
device that he calls the “flying saucer”—that slides down
a slope in his wave tank. That sliding motion produces waves on the surface
that look and act just like a miniature tsunami. By measuring these small
tsunamis and comparing those numbers to his computer data, he verifies the
predictions of his computer model.
Grilli’s use of historical accounts of tsunamis also helps verify his
computer predictions—and at the same time helps him investigate how they
occurred. For example, he and some of his colleagues have studied a tragic tsunami
that occurred in Papua New Guinea in 1998. In that event, about 15 minutes after
an average size earthquake occurred, very large waves hit the country’s
northern coast. This tsunami killed more than 2000 people, destroyed three villages,
damaged 4 others, and left 12,000 people homeless. The waves were much bigger
and they occurred later than what was expected for such an earthquake. So what
caused the tsunami? Researchers have been searching for the answer for many
years.
Grilli says, “Looking at waves, we can tell by experience where the source
was likely to be located, and it was about 40 miles offshore.” Additionally,
underwater sound recordings taken during that time revealed some rumblings
that could have been caused by a landslide. So some of Grilli's colleagues
created sonar images of the ocean bottom in that area and found evidence of
a landslide. Using that data, soil samples, and his computer model, Grilli
and his colleagues were able to piece together what happened. Grilli says
the earthquake “produced a sizable landslide about 40 miles off the
coast, and about 15 minutes later, very large waves reached the shore, and
those were about 50 feet tall.”
How did this help Grilli verify the accuracy of his model? Grilli’s simulation
of the tsunami matched the actual data—the size of the waves, the direction
that they traveled, and the timing between the landslide and the waves hitting
the coast—better than other computer models.
Grilli hopes that in the future he and others can use his computer model to
help prevent such loss of life or the destruction of property that occurs. He
has made his computer
program available to the public via the Internet so others can use it to
assess the risk from landslide-generated tsunamis in different areas. Grilli
hopes the information can be used to warn people, and perhaps help prevent destruction
from tsunamis. For example, offshore barriers could be built that could block
or break up an incoming tsunami before it reaches shore; or underwater sensors
could be used in an advanced warning system.
Grilli’s research is funded by the National
Science Foundation.