A NASA-led research team may have come one step closer to accurately predicting the size of earthquake-induced tsunamis. 

Tsunamis are generated when an earthquake or underwater landslide displaces a large amount of water; only when that displaced water reaches shore does it turn into large waves. When an 8.8-magnitude earthquake struck off the coast of Chile on Feb. 27, scientists predicted that waves as high as 12 feet could hit Hawaiian shores; only 12-inch waves actually materialized. "Magnitude is just a proxy for how big [an earthquake] is," says Brian Shiro, a geophysicist at NOAA's Pacific Tsunami Warning Center. "It's tough to say how that translates to movement on the seafloor." 

Because of the sheer size of the earthquake, Shiro says, a Pacific-wide warning was issued right away, before the typical models that predict the size of a tsunami—which use combined readings from deep ocean monitoring buoys and shore-based sea-level gauges—could even be run. (Hawaii residents completely evacuated to higher ground.) The first models predicted the 12-foot waves; a second model, obtained when more data became available, was right on at 12 inches, Shiro says. 

A prototype detection system developed by scientists at NASA's Jet Propulsion Laboratory more accurately predicted the size of the tsunami much more quickly, without the need for buoy feedback. The system used data from JPL's Global Differential GPS (GDGPS) network, which measures the ground movements—down to a few centimeters—of hundreds of regional and local GPS sites every second. The method allows scientists to estimate the amount of energy an undersea earthquake transfers to the ocean to create a tsunami. 

The ground motion of the Feb. 27 quake was captured by a GDGPS station 146 miles from the quake's epicenter. Based on the GPS data—provided to scientists within minutes of the quake—the system predicted that a moderate local tsunami would be generated by the quake, with minimal effects in the Pacific; the result was confirmed using sea surface height measurements from altimetry satellites. 

"This successful test demonstrates that coastal GPS systems can effectively be used to predict the size of tsunamis," team leader Y. Tony Song said in a press release. "This could allow responsible agencies to issue better warnings that can save lives and reduce false alarms that can unnecessarily disturb the lives of coastal residents." 

Yoaz Bar-Sever, manager of the GDGPS system, says that scientists were fortunate to have a station close to the epicenter, which helped them get accurate results quickly. "Broad international collaboration is required to densify the GPS tracking network," he said, "so that it adequately covers all the fault zones that can give rise to large earthquakes around the world."