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Earthquake Alarm System May Ease Risk for Southern CaliforniansBy Ascribe, 5/2/2003 13:27The 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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