Satellites Use Ripples in Space to Detect Tsunamis

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Tsunamis are born in the violent interaction of two simple ingredients: rock and water. Outer space would seem like the last place to put an instrument designed to detect one of these potentially devastating waves.

But a new study proposes to do just that, using global positioning system (GPS) satellites already in orbit.

According to Lucie Rolland of the Institute of Geophysics of Paris (IPGP) in France and a team of researchers, tsunamis produce "internal gravity waves" in the atmosphere — waves of energy that ripple up through the sky. High above the Earth in the ionosphere, these waves jostle electrons and charged particles in a distinct pattern that GPS satellites can pick up.

As a rule, the strong quakes required to generate trans-ocean tsunamis like the ones we saw in the Indian Ocean in 2004 and in the Pacific Ocean earlier this year are rare. But when they do happen, getting a speedy, accurate warning out can save thousands of lives.

The research team looked at the 2004 tsunami, one generated off Peru following a magnitude 8.2 quake in 2001, and the Chilean tsunami in February. For each wave, satellites measured a discernible gravity wave signature in the ionosphere within a couple of hours of tsunami formation.

With a dense network of GPS satellites over the Pacific, the team believes they've found a useful new way to issue tsunami warnings. Current warning systems include mid-ocean buoys, sea floor pressure gauges, and land-based measurements of seismic activity. Together they do a very good job of identifying whether a wave has been generated, and how big it is.

But there is always room to get better, and the use of this and other experimental new techniques (tsunamis are even thought to generate their own underwater electrical currents that could be used to improve warnings, for example) could one day change tsunamis from disasters than can kill hundreds of thousands of people to waves that we worry about, but know how to elude.

Image: NOAA