Twenty seconds' warning could be the difference between life and death in the California Bay Area's next big quake. That's enough time to dive under your desk or move away from that heavy bookcase or wall mirror.
Japan and Taiwan already use a warning system triggered once an earthquake starts. The system alerts people far from the quake's epicenter before strong shaking hits. It stops trains, shuts down power plants and alerts emergency responders.
"In any significant damaging earthquake in the Bay Area, even if there isn't any warning for the city closest to the earthquake, there would still be a useful warning for many people in cities further away," said UC Berkeley seismologist Richard Allen, who has developed a computer program to drive such a system.
When an earthquake hits, two sets of seismic waves race away from the epicenter at different speeds. The first wave is almost twice as fast and far more gentle than the second, which delivers the real damaging punch.
Allen's program takes advantage of the lag time between the two waves. Using information from the first wave when it hits seismic stations, the program can estimate the size and location of the earthquake, as well as which areas are about to get hit with strong shaking.
All of this takes less than 10 seconds, after which an automated warning could be sent out electronically, or perhaps wirelessly. This leaves some time to warn people at a distance -- maybe just 10 seconds, but possibly as much as a minute or more for really big earthquakes that affect a broad region.
"Every second counts in this business," said David Oppenheimer, a seismologist at the U.S. Geological Survey (USGS) in Menlo Park, Calif.
The USGS has just embarked on a three-year study to test several computer algorithms, including Allen's, to see how a warning system would do in the Bay Area. They will check the programs against past earthquakes and quakes in real time.
The Bay Area's dense sprawl, coupled with its underlying network of long, active faults, make it a good candidate for this kind of warning system, Allen said. And with earthquake prediction barely a glimmer in the eyes of a few scientists, a warning system could be the next best thing.
Nearly all of the deaths from the magnitude 6.9 Loma Prieta earthquake in 1989 occurred in Oakland and San Francisco, more than 50 miles from the epicenter. Allen estimates those cities could have had 20 seconds notice.
The USGS estimates there is a 62 percent chance an earthquake of magnitude 6.7 or greater will strike the Bay Area in the next 30 years. The most likely candidate is the East Bay's Hayward fault and its northern extension, the Rogers Creek fault running from San Pablo Bay to Santa Rosa.
Major earthquakes can travel long distances along a fault, sending seismic waves out as they go. This means that even a few hundred miles from where it started, there can still be very intense ground shaking as the rupture passes by.
If a major quake hits the Hayward fault near Oakland, there won't be time to warn that city, Allen said. "But if the rupture starts up at the northern end of the Rogers Creek fault, then that's when the warning time would be the greatest."
Similarly, much of the East Bay could be warned of a San Andreas quake. For some big quakes, Allen calculated that East Bay cities such as Walnut Creek, Martinez and Richmond could have up to a minute
or more of warning. The research appears in the journal Seismological Research Letters this month.
"Every extra second would help us prepare for an earthquake," said Linton Johnson, a spokesman for the regional transit system. "We could stop our trains."
Twenty seconds is enough for a train traveling at the average speed of 35 miles per hour to stop, Johnson said. A slow or stopped train is less likely to derail or cross damaged tracks in a quake. And some trains could be stopped from entering the transbay tube or the Berkeley Hills Tunnel.
Early warning systems, unlikely to be used in private homes at first, could warn surgeons, shut down utilities and give emergency responders a head start on planning before communications fail. A heads-up to schools and businesses would allow students and employees to take cover under desks.
If the USGS decides a warning system will work in the Bay Area, officials will then have to figure out how to send out alerts, possibly over the Internet or wireless networks, Johnson said.
There are approximately 140 seismic stations in the region that could work within a warning system. The core of the Bay Area is relatively well covered, but not its outskirts. A dozen or so new stations are installed each year, but Oppenheimer hopes the potential for a warning system could speed up that pace.
(c) 2006, Contra Costa Times (Walnut Creek, Calif.). Distributed by Knight Ridder/Tribune Information Services via Newscom. Photo
