GPS system can accurately predict post-quake tsunami, study finds

When the magnitude 9 earthquake struck Japan more than two years ago, there were 1,200 global positioning system stations recording ocean floor movement in real time.

None was linked to that nation’s tsunami warning system, which underestimated the full impact of the inundation that killed more than 18,000 people, left at least 350,000 homeless and caused meltdowns in three nuclear reactors.

Data from those GPS stations could have produced a more accurate warning within three minutes, including a better estimate of wave sizes and tremor magnitude, a team of European researchers has found.

Authorities in Japan did issue a warning within three minutes of the March 11, 2011, quake, but only for three nearby prefectures.

“Japan has a very dense network of GPS stations, but these were not being used for tsunami early warning as of 2011. Certainly this is going to change soon,” states Hoechner.

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“Japan has a very dense network of GPS stations, but these were not being used for tsunami early warning as of 2011. Certainly this is going to change soon,” said lead author Andreas Hoechner from the German Research Center for Geosciences.

A “GPS shield” that could warn populations of tsunami threats has been the dream of disaster preparedness at least since the 2004 Indian Ocean tsunami that killed about 230,000 people over a vast region.

The research team already proved that such a system was feasible. But the Japan quake, the most carefully measured seismic event in history, gave the researchers a wealth of data with which to test their system.

The researchers used 50 of the GPS stations closest to the quake’s epicenter, and produced a warning that closely correlates with actual measurements from the event. Their work is published in the journal Natural Hazards and Earth System Sciences, a publication of the European Geosciences Union.

Tsunami warning systems linked to conventional seismographs can issue general warnings based on finding the quake’s hypocenter, but their early magnitude readings are preliminary and often aren’t corrected for hours. The seismic systems also essentially treat the earthquake as a “point source,” and don’t account for massive ruptures that can occur over many miles. In the Japanese quake, tectonic plates broke along nearly 250 miles. In the 2004 quake off Indonesia that triggered the Indian Ocean tsunami, that rupture was more than 900 miles.

GPS systems can detect those ruptures and other deformations of the crust.

Researchers said they hoped their results would lead Japanese authorities to develop a GPS shield system. Some GPS sites have been installed in Indonesia, but there are not enough of them to provide a workable shield, the researchers said.