More Quake-Forecasting Devices Needed on Sea Floor
The 11 March Tohoku-Oki earthquake and tsunami in Japan was a shock for citizens and researchers alike. The disaster is just the latest confirmation of why more ground-deformation monitors are desperately needed at sea, says Andrew Newman in a comment piece in Nature this week.
Newman says the past 20 years have seen great strides in understanding earthquake faults, mainly through improved and expanded tracking of ground deformation. Most devices monitoring ground deformation are land-based because offshore monitoring is more complex — and costly.
This is a problem, says Newman, as “the real action happens” offshore. Most big quakes are generated underwater, and tsunami potential can’t be assessed from land measurements. “Progress has been only partial,” he says.
Ground-deformation monitors use Global Positioning System (GPS) signals to track deformations in the Earth’s surface. The deformations occur over ‘locked’ patches, where tectonic plates get stuck along faultlines. When strain energy is suddenly released from a patch, an earthquake is generated. By keeping an eye on locked patches, researchers can predict the size and timing of quakes.
But the monitors can’t ‘see’ the GPS satellites through water, so when placed offshore they must be used in tandem with ships and sonar transponders. The cost of one survey can be as much as US$500,000.
Newman notes, however, that this must be set against the clean-up costs of giant quakes and tsunamis — a projected $300 billion for the Tohoku-Oki event alone. Offshore monitoring needs to ramp up, he says. “It is vital that all subduction boundaries – particularly those with the capacity for causing massive damage to nearby cities — be densely measured routinely enough to capture the extent of locking,” he writes in Nature. Newman calls on scientists to develop cheaper tools, and on agencies such as the United Nations Educational, Scientific and Cultural Organization and the World Bank to get involved.