FOR IMMEDIATE RELEASE
5/1/2003
CONTACT: Richard M. Allen, (608) 262-7513,
rallen@geology.wisc.edu
NOTE TO GRAPHICS EDITORS: To download a graphic to accompany this
story, visit http://www.news.wisc.edu/newsphotos/earthquake.html
EARTHQUAKE ALARM SYSTEM MAY EASE RISK FOR SOUTHERN CALIFORNIANS
MADISON - Capitalizing on the low-energy waves that invariably
precede major earthquakes, scientists have designed and demonstrated
the feasibility of an early-warning system that promises southern
Californians as much as 40 seconds of advanced notice of major
temblors.
The system, described in the Friday, May 2 issue of the journal
Science, could help mitigate disaster by giving people a few moments
to take shelter under solid furniture, evacuate buildings, divert
aircraft, stop trains, shut down pipelines and computer networks and
distance themselves from dangerous machinery and chemicals.
The system is based on TriNet, a dense network of modern seismic
stations deployed in southern California.
"An early warning system is the next generation of seismic
information," says Richard M. Allen, a University of
Wisconsin-Madison professor of geology and geophysics and the lead
author of the paper that describes a prototype earthquake alarm.
"There is a capability now of detecting earthquake parameters within
a matter of seconds" and transmitting that information in a way that
could provide some early warning to the densely populated,
earthquake-prone region.
The earthquake alarm system, developed by Allen in collaboration
with Hiroo Kanamori of the California Institute of Technology's
Seismological Laboratory, is designed to use a network of 155
seismic stations now in place in southern California. It utilizes
what seismologists call P-waves, low-amplitude waves of energy that
are the first to emanate from the underground source of an
earthquake. These low-energy waves, which usually cause little
damage, travel at greater speeds than the ground-rollicking S-waves
that are the biggest threat of any earthquake to life and property.
"The system estimates how serious the danger is and how much
warning time there is," says Allen.
Seismic stations can sense the P-wave and - given the advent of
technology that permits near-instantaneous data processing and
transmission - send signals to trigger alarms to warn the public,
Allen says.
The system, known as ElarmS, is capable of quickly determining
the location, origin, time and magnitude of an earthquake before
there is any significant ground motion. The amount of warning time
people would receive depends on their proximity to the epicenter of
the earthquake; the farther from the origin of the event, the more
warning time is available.
"People who need warning the most will have less time, but at
least the system can give people a chance to react," Allen says. "In
an earthquake, every second counts."
A few seconds is enough time to take shelter under a desk or in
another protected area. As the amount of warning time increases,
people can take other steps to protect themselves, mitigate property
damage and danger to others.
For example, with 15 to 20 seconds of warning, air traffic
controllers can wave off inbound aircraft, factories can stop
production lines, traffic can be prevented from entering freeways,
gas pipelines can be shut off, and trains can be stopped. With that
much time, people can also evacuate some buildings and schools can
take steps to protect children.
One concern, however, is the relative infrequency of large
earthquakes. Given their infrequent occurrence, people may not
respond to an early warning, says Kanamori: "The most exciting and
effective applications of early warning systems would be to include
them in automated control systems for buildings and structures."
With ElarmS, the outside warning time would be about 40 seconds
for people at some distance from the epicenter.
For some large earthquake events, there may even be more warning
time available as they tend to occur deeper within the earth.
In Japan, an early warning system employing P-waves, known as
UrEDAS, has been used to maintain safe operation of bullet trains
during large earthquakes. The new system devised for southern
California, combines P-wave information from several stations of
TriNet to get rapid and accurate magnitude estimates.
Other earthquake-prone countries such as Mexico and Taiwan have
developed early warning systems based on measurements of peak ground
motion the instant the ground-shaking S-wave is detected by a
seismic station. The advantage of the new system, says Allen, is
that it uses the low-energy P-waves, providing precious seconds to
react before the damaging S-waves arrive.
Some early warning systems, such as the one that serves Mexico
City, capitalize on the distance between a seismologically active
area and the densely populated region the system is intended to
warn. Such a luxury is not available to southern California, almost
all of which is densely populated and which is laced with many
active faults, some of which are unknown.
With this system, "we don't need any knowledge about the
distribution of faults," Allen says.
Among the drawbacks to the new system described in Science, is
that it would require a massive campaign of public education, and
there is a potential for false and missed alarms, Allen says.
For the 'Big One,' the anticipated major earthquake that would
rupture a significant portion of a big fault, the new system would
continually update its estimate of earthquake magnitude, perhaps
initially suggesting a smaller earthquake, but increasing the
magnitude and hazard estimate as the event evolves, Allen says.
However, most earthquakes, including those that take life and do
significant damage to property, tend to be more isolated events that
would lend themselves to early detection, according to the Wisconsin
seismologist.
The advantage of the system is that, from a technical and
infrastructure perspective, nearly everything is already in place.
Southern California has hundreds of state-of-the-art seismic
stations that could be harnessed to such an alarm system, Allen
notes.
"The seismic infrastructure to do this has only been installed in
the last five years," Allen says. "Ten years ago, we didn't have the
technology to do this."
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-- Terry Devitt, 608-262-8282,
trdevitt@faacstaff.wisc.edu