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First seconds of a quake can show its size
-study
09 Nov 2005 17:59:52
GMT
Source: Reuters
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By Jeremy Lovell
LONDON, Nov 9 (Reuters) - With the devastation of last
month's Pakistan earthquake still fresh in the mind, scientists said
on Wednesday they have developed a way of predicting the size of a
tremor even as it starts.
Seismologists have tried and failed for years to predict
where and when quakes will happen and how big will they be.
Now there is a glimmer of light on the horizon -- at least
for the latter goal, according to scientists at the University of
California, Berkeley.
"We can determine the magnitude within a couple of seconds of
initiation of rupture and predict the ground motion from seconds to
tens of seconds before it is felt," said lead researcher Richard
Allen.
Although that time frame would be far too short for people to
react and evacuate, it could be enough to tell local emergency
services almost instantaneously the scale of the disaster they are
likely to be facing when the dust settles.
It could also set off alarm bells in far flung centres who
could begin to mobilise support earlier.
Up to now, the cascade theory of earthquakes that portrays
them as acting like a row of dominoes with one action triggering
another in sequence, has meant it has been impossible to gauge the
scale of the quake until it has ended.
By that time, communications could well have been destroyed
leaving local emergency services in an information black hole.
But the study led by Allen and co-author Erik Olson,
published in Thursday's edition of Nature science journal, uses a
different theory.
It suggests that the size, type and depth of the first break
on the fault line -- that can be measured as it happens -- gives a
very good indication of the earthquake's eventual reach.
"Most seismologists are surprised, and frequently skeptical,
that you can predict the magnitude of an earthquake before it has
ended," Allen said in a statement from Berkeley.
"But this is telling us that there is something very
different from what we thought about the physics of the processes
involved in the rupture," he added.
In a commentary on the research also published in Nature,
Rachel Abercrombie of Boston University said the new theory had
crucial implications but that more work was needed.
"We are far from understanding how onset, propagation and
state of stress of the surrounding fault interact to determine the
final size of a seismic event," she wrote.
"Olson and Allen's study advances that understanding and thus
our ability to predict an earthquake's size before it reaches its
peak," she added.
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