Currently, accurate tsunami warnings are not possible until the waves are recorded by buoys. The new system detects shifts in the seafloor, the quake-induced "paddles" that can spawn a tsunami.

Tsunami potential could be determined in 15 minutes.

"We'll always need seismology as the first level of alert for large earthquakes, and we'll need ocean buoys to actually sense the tsunami waves," said Geoffrey Blewitt of the Nevada Bureau of Mines and Geology and the University of Nevada, Reno. "The advantage of including GPS in warning systems is that it quickly tells how much the ocean floor moved, and that information can directly set tsunami models into motion."

Blewitt lead a team that tested the concept, reporting their results this month in Geophysical Research Letters, published by the American Geophysical Union.

The 2004 Indonesian tsunami was a classic example of what can happen if officials are slow to recognize tsunami danger.

"Tsunami warning is a race against time," said Seth Stein of Northwestern University in Evanston, Illinois, a co-author of the paper. "Tsunamis travel at jet speed, so warning centers must accurately decide, within minutes, whether to issue alerts. This has to be done fast enough for the warning to be distributed to authorities in impacted areas so they can implement response plans. Together with seismometer and ocean buoy data, GPS adds another tool that can improve future tsunami danger assessments."

The new technology, called GPS displacement, was developed by NASA's Jet Propulsion Laboratory (JPL). It measures when radio signals from GPS satellites arrive at ground stations. From these data, scientists can calculate how far the stations moved because of the quake, and then derive the quake's true size, called its "moment magnitude."

This magnitude is directly related to a quake's tsunami-generation potential, the scientists say.

To test the approach, the scientists used JPL's satellite positioning data processing software to analyze data from 38 GPS stations located at varying distances from the 2004 Sumatra quake's epicenter. The software pinpoints a station's location to within a third of an inch (seven millimeters). Only data that were available within 15 minutes of the earthquake were used. The analysis inferred a magnitude of 9.0, very near the earthquake's final calculated size.

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