- WASHINGTON (AP) -- A new system developed by Mexican scientists could give
coastal residents a crucial few extra minutes warning when earthquakes
generate giant killer waves known as tsunamis.
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- Tsunamis, sometimes mistakenly referred
to as tidal waves, have claimed untold lives over the years, including
more than 2,000 victims last summer when one hit Papua New Guinea in the
Pacific.
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- Hawaii, Mexico, South America and Indonesia
are among areas that have been hit hard in the past.
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- The new system "may provide a reliable
tsunami warning very rapidly," said Nikolai Shapiro of the Universidad
National Autonoma in Mexico City.
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- Indeed, warnings could occur as quickly
as five minutes after a quake, compared with the 10 minutes to 20 minutes
now necessary, according to Shapiro's report in today's edition of Geophysical
Research Letters.
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- That could be a life saving difference
in cases when an earthquake generates a tsunami near a populated coastal
area.
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- The university's scientists devised a
seismic ratio that can help determine whether a quake will produce devastating
waves. The system uses data generated by relatively simple and affordable
seismograph stations.
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- A tsunami results from earthquakes, landslides
or volcanoes that occur beneath the ocean. They generate deep waves spreading
out in all directions.
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- The waves may be little noticed at sea,
but when they near shore the rising sea floor causes them to lift up, sometimes
to massive heights that can sweep away entire coastal villages.
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- When the waves must travel long distances,
the Pacific Tsunami Warning Centre in Hawaii can provide alerts. But when
they originate near shore there is often little chance to warn people.
Even a brief warning can give people time to try to move inland or uphill
to safer ground.
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- Shapiro said the warning can be produced
"with the data available from a single broadband (seismograph) station"
and is thus economically and technically viable in many countries.
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- Eddie Bernard, a tsunami expert who heads
the U.S. National Oceanic and Atmospheric Administration's Pacific Marine
Environmental Laboratory in Seattle, called the study "a nice piece
of work."
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- But Bernard cautioned it is based on
only about 20 earthquakes over a decade, too small a sample "to get
too carried away."
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- In studying earthquakes that occur off
Mexico's west coast, Shapiro and colleagues found that those happening
near a subduction trench -- where the plates that make up the Earth's surface
come together -- are more likely to cause tsunami than those that occur
closer to the coast.
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- They also found that the more hazardous
events near trenches produced fewer high frequency vibrations than the
near-shore quakes. The researchers worked out a ratio of seismic waves
that allowed them to tell quickly which quakes were near subduction trenches
and which were near the coast.
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- The main requirement is a broadband seismograph
located within a few hundred kilometres of the quake.
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- In many regions of the world, broadband
seismographs have not been installed yet or were put in only recently,
Shapiro said. Those regions don't have enough data yet to sort out the
dangerous quakes.
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- However, he added, "we believe that
the phenomenon reported in our paper is a fundamental property of (tsunami-causing)
subduction-zone earthquakes. Therefore, we expect that similar observations
can be done in other regions which are located close to subduction zones."
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- Asked if the system could have helped
the residents of New Guinea, Shapiro noted that while there is a broadband
seismic station at Port Moresby, it is too far from the northern coast
where the wave struck.
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- To get a fast tsunami alert, it would
be better to have a broadband station in the island's central part, he
said.
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