Asian Quake Moved Islands, Shortened
Days
By Jim Loney - Reuters 2-9-5
-- 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.
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.
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.
But scientists say any movement of land mass can be measured in
centimetres rather than tens of metres.
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.
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.
"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."
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.
High-tech UK and US ships are investigating changes to the sea bed
and local authorities are measuring depths in critical shipping
channels.
Shorter day
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.
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.
"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.
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.
Many earthquakes shake the planet's axis and affect its rotation,
scientists add, but their impact is too small to measure.
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.
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.
The survey says 25,000 hectares of mangroves and 29,000 hectares
of coral reefs were damaged.
Reefs, mangroves
Some coral reefs were crushed by the waves. Corals grow slowly,
some only a few centimetres a year, so their recovery could take
decades.
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.
Mangroves torn out by the waves will fare better, he says, as they
leave behind roots and seeds that will help them regenerate.
"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."
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.
The tsunami waves ate away beaches and coastal areas in Thailand,
Indonesia and Sri Lanka, radically changing maps.
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.
"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."
But it remains to be seen whether such sediment is good for the
land or a bane because of its high salt content.
©2005 ABC
http://www.abc.net.au/science/news/stories/s1299077.htm
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