PEOPLE in Taiwan should soon have up to 25 seconds warning before an earthquake hits, thanks to a computerised early-warning system. It would give automated emergency systems enough time to stop trains, shut down gas lines, or tell surgeons to stop their work. 鈥淭his could be a 911 emergency call for earthquakes,鈥� says Ta-Liang Teng of the Southern California Earthquake Center at the University of Southern California.
When an earthquake hits, shock waves radiate out from the epicentre at between 3 and 6 kilometres per second. Large quakes can do serious damage up to 160 kilometres away, giving a 40-second window to warn people on the outskirts of the quake zone of a coming shock wave.
Many earthquake-prone areas, such as California and Japan, already have networks of seismographs in place to relay information from the epicentre of a quake out to surrounding areas. But these systems are slow because they have a limited number of detectors. In California, the network is designed to distribute information within about a minute after the quake, helping emergency teams send help to where it鈥檚 needed most.
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Taiwan has one of the densest networks of seismographs on the planet 鈥� it would cost $200 million to equip California with a comparable network, says Teng. But ironically, it produces so much information that computers can鈥檛 analyse it fast enough to get a warning out in time. So Teng and colleague Yih-Min Wu have devised a program that automatically picks out a dozen key seismograph stations within 60 kilometres of a quake鈥檚 epicentre. Analysing only the data from those detectors dramatically reduces the processing time, often enough to scrape in under the 40-second limit.
In a trial run, the researchers analysed 54 quakes that had occurred between December 2000 and June 2001, and found they would have been able to send out a warning about them within an average of 22 seconds (Bulletin of the Seismological Society of America, vol 92, p 2008). If the system had been in place during the 1999 Chi-Chi quake, which killed more than 2000 people, they say it could have provided the capital city of Taipei with more than 20 seconds warning (see Graphic).
Taipei was 145 kilometres away from the centre of the quake, but even so, more than 400 homes were destroyed and 134 lives were lost. The system won鈥檛 help people within about 50 kilometres of the epicentre, however, since within that zone the quake will always arrive before the warning call.
Bill Ellsworth, head of the United States Geological Survey鈥檚 earthquake hazards team, points out that because most damage happens inside that blind spot, these early warnings are of limited use. 鈥淏eing prepared for the shaking by designing buildings and roads properly is the most important thing,鈥� he says, 鈥渁nd then being able to direct emergency services as soon as possible.鈥� Nevertheless, he鈥檚 keen to see how useful Teng鈥檚 system will be.