New computer software can detect the onset of an earthquake and
sound a warning before a quake's most destructive shaking arrives,
scientists are reporting today.
If the system is put into effect, the warning will be short --
tens of seconds at most -- but it may give workers and students time
to duck under desks, air-traffic controllers the chance to wave off
landing planes and officers a few seconds to raise barriers to keep
cars off bridges and overpasses.
For now, though, experts are unsure just how they will use the
warnings and acknowledge that false alarms may create problems.
``Just ringing a bell can cause a lot of panic,'' said Richard
Allen, a professor of geology and geophysics at the University of
Wisconsin.
Writing in today's issue of the journal Science, Allen and Hiroo
Kanamori, a professor of geophysics at the California Institute of
Technology in Pasadena, describe a computer algorithm that analyzes
seismic data gathered from 150 sensors already deployed around
Southern California and continuously sent to a computer at
Caltech.
Other systems possible
Similar systems could also be put in place in other
earthquake-prone areas. Allen said he and Kanamori were researching
whether a sparser and less-expensive network of sensors would still
provide useful warning.
``If we can do that, we can go to the regions that don't have the
resources,'' Allen said. ``I would argue these kinds of systems
could be very useful in places like Turkey.''
Earthquakes shake rocks in two different ways. The warning system
focuses on one kind of seismic wave that moves quickly -- 3.5 miles
a second -- but causes little damage, resembling the waves that
travel along a Slinky toy when one end is pushed and pulled quickly.
The slower, more destructive waves resemble the waves when a Slinky
is shaken side to side.
The computer program, running on the computer at Caltech, detects
the onset of an earthquake in the faster-moving seismic waves, and
within seconds, calculates the epicenter and estimates the
magnitude. A warning can then be issued. A location 35 miles from
the epicenter will get about 15 seconds' warning before the slower,
damaging seismic waves arrive.
The technology appears to be arriving before emergency officials
have had time to think through how warnings should be issued and who
should receive them. Also unresolved are questions like who would
issue the warnings.
``When you start thinking about the next step, it really is a
quagmire,'' said Dr. David Wald, a seismologist with the U.S.
Geological Survey. ``Most people don't know what to do with that
information. We're not ready for it.''
The researchers are considering a system that will send out the
warnings via the Internet.
Ready by autumn
Patrick Small, the computer programmer installing Allen and
Kanamori's algorithms, said he hoped to finish a prototype of
software by the end of the summer that would run on personal
computers and receive and display earthquake warnings from the
Caltech computer.
Small is also working to speed up his computer program. Zooming
in on the epicenter now takes 15 to 40 seconds. ``I think we can get
it down to about five seconds,'' he said.
The researchers will begin a test phase to evaluate the accuracy
and effectiveness of the warnings.
``What I'm working on is definitely not for the public,'' Small
said.
While the technology is unfinished but progressing quickly, the
policy decisions have hardly begun.
``We've thought about it,'' said Dr. John Filson, manager of the
earthquake-hazard program at the Geological Survey. ``And it's a
difficult issue. To turn it into an operational system is going to
take some thoughtful planning with the local emergency-response
officials.''
At first, the warnings may be most easily used in controlled
environments like schools and hospitals, where false alarms will
probably not be more than a nuisance.
Earthquake-warning systems already exist in a few areas,
including Mexico City. There, the system is simpler, because the
earthquake originates from faults nearly 200 miles to the west of
the city and seismometers can easily detect the rumblings before
they reach Mexico City.
The system has generated some false alarms.
In the Los Angeles area, faults crisscross the populated areas.
Even with a fully functioning system, people at the epicenter would
receive no warning. Those farther away would receive more warning,
but suffer less
damage.