Washington: By using global positioning systems (GPS) to measure ground deformation caused by a large underwater earthquake, researchers have shown that they can provide accurate warning of the resulting tsunami in just a few minutes after the earthquake onset.
For the devastating Japan 2011 event, the team reveals that the analysis of the GPS data and issue of a detailed tsunami alert would have taken no more than three minutes.
Most tsunamis, including those in offshore Sumatra, Indonesia in 2004 and Japan in 2011, occur following underwater ground motion in subduction zones, locations where a tectonic plate slips under another causing a large earthquake. To a lesser extent, the resulting uplift of the sea floor also affects coastal regions.
There, researchers can measure the small ground deformation along the coast with GPS and use this to determine tsunami information.
"High-precision real-time processing and inversion of these data enable reconstruction of the earthquake source, described as slip at the subduction interface," lead-author Andreas Hoechner from the German Research Centre for Geosciences (GFZ) said.
"This can be used to calculate the uplift of the sea floor, which in turn is used as initial condition for a tsunami model to predict arrival times and maximum wave heights at the coast," he said.
In the new Natural Hazards and Earth System Sciences paper, the researchers use the Japan 2011 tsunami, which hit the country`s northeast coast in less than half an hour and caused significant damage, as a case study.
They show that their method could have provided detailed tsunami alert as soon as three minutes after the beginning of the earthquake that generated it.
The scientists used raw data from the Japanese GPS Earth Observation Network (GEONET) recorded a day before to a day after the 2011 earthquake.
To shorten the time needed to provide a tsunami alert, they only used data from 50 GPS stations on the northeast coast of Japan, out of about 1200 GEONET stations available in the country.
At present, tsunami warning is based on seismological methods.
However, within the time limit of 5 to 10 minutes, these traditional techniques tend to underestimate the earthquake magnitude of large events.
Furthermore, they provide only limited information on the geometry of the tsunami source (see note).
Both factors can lead to underprediction of wave heights and tsunami coastal impact.
Hoechner and his team said their method does not suffer from the same problems and can provide fast, detailed and accurate tsunami alerts.
The research is published in Natural Hazards and Earth System Sciences, an open access journal of the European Geosciences Union (EGU).