Quakes 'can move faster than thought'
Pastor Dale Morgan
*Quakes 'can move faster than thought'*
From correspondents in London
August 17, 2007 05:24am
Article from: Reuters
EARTHQUAKES on long, straight faults can rupture faster than previously
thought and trigger powerful shock waves that make quick-moving quakes
even more destructive, according to a new study published overnight.
The findings could help researchers pinpoint the most dangerous faults
in the world and better predict areas potentially at risk of greater
damage from earthquakes, said Shamita Das, who led the study.
"Given the potential for increased destruction, we must take such
information into account when planning earthquake-resistant construction
worldwide," Ms Das, a seismologist at Oxford University, wrote in the
journal Science.
Earthquakes generally move, or rupture, at a pace of about 2.5km to 3km
per second, a speed many researchers for a long time believed quakes
could not exceed, Ms Das said.
But this study bolsters theories that they can, in fact, move much
faster than that, she said.
Using more powerful computers, higher quality seismograms and new
imaging techniques, the researchers showed that a 2001 earthquake in
Central Tibet along the Kunlun fault line moved at about 5km per second.
That quake was a magnitude 7.8.
The study also found that long, straight fault lines create the
opportunity for these fast-moving quakes in an effect Ms Das compared to
driving in a car on a straight road where it is possible to build up a
lot of speed.
"If the road bends you have to slow down, or if you have a bump you have
to slow down," she said. "Earthquakes behave in a similar way."
After showing that quakes could move much faster, Das turned her
attention to California's San Andreas fault and found that many parts of
it run in the kind of long, straight lines that make it prone to these
quick quakes.
The fault - which triggered the 1906 San Francisco quake and deadly
fires that followed - runs from the Southern California desert to
northern California and marks the boundary of the Pacific and North
American tectonic plates.
"We know there are going to be more earthquakes on the San Andreas
Fault," she said. "If the next one behaves this way, there would be a
greater potential for damage than previously believed."
These highly destructive quakes which can generate powerful shock waves
- similar to the sonic boom from a supersonic aircraft - are also most
likely to hit in so-called strike-slip quakes in which two sides of the
fault slide past one another horizontally, she said.
She said that thrust-fault earthquakes where plates go underneath each
other - like the one that struck Peru on Wednesday and killed hundreds
of people - would probably not produce such shock waves.
But many other earthquakes probably have and the next step is to
identify faults around the world that could in the future fuel these
more powerful quakes, Ms Das said.