TIME: Almanac 1993/TIME Almanac 1993.iso/time/082492/0824301.000

Text File | 1993-04-08 | 3.8 KB | 82 lines

                                                                                SCIENCE, Page 56

WARNING: You Have 30 Seconds . . .


    It's one thing to warn people that the Big One is coming --
someday soon. Engineers can design stronger bridges and sounder
buildings; city planners can guide development in ways that
reduce hazards. It's quite another thing to sound the alarm for
an earthquake less than a minute away. Such early-warning
systems are technically feasible, though there is debate about
whether they would save lives or promote panic.

     Convinced that every extra second is of value, Japan has
invested mightily in these systems. Originally such devices were
not tripped until the ground began to shudder -- scant notice
indeed, though enough to prevent the derailment of a speeding
bullet train. Such simple motion-detecting systems are now used
throughout Japan and in parts of California to halt subway
trains and nudge elevators to the nearest floor when ground
motion exceeds a certain threshold. The Alaska pipeline is
similarly equipped for instant shutdown.

     But today more sophisticated systems can alert people as
much as a minute before a city starts to shake. "This is
possible," explains Massachusetts Institute of Technology
geophysicist M. Nafi Toksoz, "because seismic waves propagate
through the earth's crust relatively slowly, 5 to 8 km/sec. With
an extensive network of sensors, we can locate the epicenter and
determine the magnitude of an earthquake. This gives us the
opportunity to warn people in outlying areas." How long a
warning depends on the distance from the epicenter. Had such a
system been in place in Mexico, for example, residents of Mexico
City would have had nearly a minute to brace themselves for the
two offshore quakes that killed more than 7,000 people inland
in 1985.

     For California, an effective system could require
thousands of sensors along various high-risk faults, linked by
sophisticated systems for transmitting data. It would all have
to run automatically by computer, says Hiroo Kanamori of
Caltech's Seismological Laboratory: "There is no room for human
uncertainty or hesitation." Toksoz believes a comprehensive
system could be developed over a five-year period for $100
million. A 1991 report produced for the National Academy of
Sciences recommended that the Federal Government build a
prototype system, but so far, nothing has been implemented.

     Would it be worth it? "It's not a solution to all
earthquake problems, but there are a lot of practical
applications," says Allan Lindh of the U.S. Geological Survey.
"To have 30 seconds' warning would sound like a helluva idea to
me if I worked near a sulfuric acid vat." Japan has already
built advanced systems to shut down nuclear power plants, cut
the gas flow from public utilities and issue tsunami alerts.
Similar systems could divert incoming aircraft, warn rescue
workers of aftershocks and minimize damage to computer,
telecommunication and financial data networks.

     For ordinary citizens, a 30-second warning might be of
limited use unless they had rehearsed what to do. Where it might
be most helpful, according to sociologist Dennis Mi leti, a
warning expert at Colorado State University, "is in schools and
offices where people can practice responding to bells." Here too
Japan has led the way. Its communities regularly conduct
earthquake warning drills, while in California such drills are
done only sporadically in some schools and workplaces. Still,
most Californians know that when the ground starts to rumble,
they must get away from the windows, duck beneath a sturdy
table, stand under a doorframe, or pull over if they're in a
car. History shows they don't always have time for even these
simple measures. But what a difference 30 seconds could make.

     By David Bjerklie