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| 24 April 2012 by Jeff Hecht |
Super-precise sensor networks promise to deliver almost instant warnings when strong earthquakes hit, and assess their magnitude more accurately
WHEN a magnitude-8.6 quake struck in the Indian Ocean last week, millions of people were forced to play an awful waiting game. With memories of the tsunami that devastated the region in 2004 still fresh, residents fled from the coasts, not knowing whether waves were on their way.
A system of super-accurate GPS sensors
being tested in several earthquake and tsunami-prone areas may change all that. Instead of passing tense minutes and hours waiting for deadly waves to make landfall, the system promises to be able to deliver warnings almost instantly, saving lives and possessions.
Current global seismographic networks detect seismic waves rippling through the planet, but they can saturate for quakes larger than magnitude 7, leading to underestimates of quake strength that can have dire consequences.
To complement seismometers, several groups of researchers are assembling networks of real-time GPS sensors that measure their locations every second within 5 to 10 millimetres, far more accurate than consumer GPS. When a quake strikes, the sensors can detect precisely how much the crust has moved. "If we see large static displacement, we know it is a big quake," says Richard Allen, director of the seismology laboratory at the University of California, Berkeley.
Pilot projects of such networks are now in place in the US states of California, Oregon and Washington. They combine GPS sensor data with seismometer readings to rapidly assess quake magnitude. "The goal is to be able to use these for early warning of earthquakes, and also for determining areas that are affected by earthquakes," says Yehuda Bock of the Scripps Institution of Oceanography in La Jolla, California.
In California, such a network might be able to identify intense quakes and give surrounding areas a few seconds of warning, allowing people to seek cover before the seismic waves hit.
Washington and Oregon lie next to the offshore Cascadia subduction zone, which can cause quakes greater than magnitude 9 and trigger tsunamis. Here and in other tsunami-prone regions, the system may be able to provide more advanced warning before a tsunami reaches shore.
The long-term goal is to integrate GPS with seismic stations to create a system that within a couple of minutes could measure earthquake magnitude, locate the fault that failed and determine whether a tsunami was imminent. That would be a big improvement over the warnings issued after last year's Tohoku quake, which Japanese officials initially put at magnitude 8. "It took them about 20 minutes to realise they had a magnitude 9", about 30 times more powerful, says Bock. That meant that the initial tsunami warning underestimated the danger.
