- (Reuters) -- The massive earthquake that triggered the
Asian tsunami wobbled the Earth on its axis, forced cartographers back
to the drawing board and changed time by a fraction. But there's no need
to adjust your clocks.
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- Six weeks after the tsunami that may have killed 300,000
people on the shores of the Indian Ocean, scientists are discovering more
about the changes wrought by the magnitude 9 quake, the fourth-largest
in the past century.
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- It caused upheaval on the sea floor near its epicentre
off the northwest coast of the Indonesian island of Sumatra and moved several
other islands.
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- But scientists say any movement of land mass can be measured
in centimetres rather than tens of metres.
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- Dr Chen Ji, a seismologist at the California Institute
of Technology, says he found movement along the fault line of about 10
metres laterally and four or five metres vertically.
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- But reports that the entire island of Sumatra, 1700 kilometres
long and 400 kilometres wide, moved 35 metres or more are wildly inaccurate,
scientists say.
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- "We know we have movements of over a metre, perhaps
a couple of metres," says Dr Ken Hudnut, a California-based geophysicist
with the US Geological Survey. "But the idea that Sumatra has moved
[30 metres] is just wrong."
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- Scientists are working on precise measurements by comparing
geographic points whose locations were known before the quake with their
new positions using the global positioning system, which reads exact locations
by satellite.
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- High-tech UK and US ships are investigating changes to
the sea bed and local authorities are measuring depths in critical shipping
channels.
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- Shorter day
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- NASA scientists say the 26 December quake, the largest
to rattle Earth since 1964 in Alaska, disrupted the planet's rotation and
shaved 2.68 microseconds, or millionths of a second, from the length of
a day.
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- NASA scientists Dr Benjamin Fong Chao and Dr Richard
Gross calculated it shifted Earth's mean north pole about 2.5 centimetres
and made the planet slightly less oblate, or flattened at the poles.
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- "Physically, this is analogous to a spinning skater
drawing arms closer to the body, resulting in a faster spin," they
write in an article in Eos, a publication of the American Geophysical Union.
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- But they say these changes are based on calculations
rather than measurements. The changes are so small they are either difficult
to measure or too small to detect.
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- Many earthquakes shake the planet's axis and affect its
rotation, scientists add, but their impact is too small to measure.
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- But environmental damage from the tsunami was vast. The
killer waves gouged beaches, crushed coral reefs, smashed thousands of
hectares of mangrove forests and refashioned coastlines from Thailand to
Somalia.
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- A preliminary survey by Indonesia's government and the
United Nations Environmental Programme (UNEP) estimated the economic cost
to the environment at US$675 million (A$882 million) in Indonesia alone.
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- The survey says 25,000 hectares of mangroves and 29,000
hectares of coral reefs were damaged.
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- Reefs, mangroves
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- Some coral reefs were crushed by the waves. Corals grow
slowly, some only a few centimetres a year, so their recovery could take
decades.
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- John Pernetta, a UNEP official in Bangkok, says the extent
of damage to some of the coral reefs around Thailand was up to 80% in some
places. Their recovery is uncertain.
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- Mangroves torn out by the waves will fare better, he
says, as they leave behind roots and seeds that will help them regenerate.
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- "Long-term damage to mangroves by hurricanes or
tsunamis doesn't really happen," Pernetta says. "After five to
10 years you don't even know anything has happened."
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- Vast stretches of Sumatra's west coast were turned brown
by the tsunami as rice paddies and other vegetation were swamped by salt
water. It could take two or three rainy seasons to wash the salt from the
saturated land, experts say.
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- The tsunami waves ate away beaches and coastal areas
in Thailand, Indonesia and Sri Lanka, radically changing maps.
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- The waves also carried sediment ashore, says Professor
Phil Liu, a Cornell University wave researcher who led a scientific team
to Sri Lanka in mid-January.
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- "There is evidence that a lot of sediment was being
brought onshore," he says. "A post office on the east coast was
found with sediment deposits on the roof."
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- But it remains to be seen whether such sediment is good
for the land or a bane because of its high salt content.
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- ©2005 ABC
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- http://www.abc.net.au/science/news/stories/s1299077.htm
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