Every minute counts Sadatsugu Tomizawa/Jiji Press/AFP/Getty

A new tsunami warning system could have saved many of the 22,000 people killed by the massive tsunami following the 2011 Tohoku earthquake in Japan, had it been in place there at the time.

That’s the message from simulations assessing how the system – now installed elsewhere in Japan – would have responded to the Tohoku quake itself.

They show that the system, based on a network of cable-connected seismic and pressure sensors placed on the seabed along quake-prone faults, would have raised the alarm in 7 minutes or less. Following the quake, it actually took 30 minutes for alarms to be sounded.


“It would have provided an extra 23 minutes,” says Yuichiro Tanioka of Hokkaido University, who presented the results last week at the annual meeting of the European Geosciences Union in Vienna, Austria.

Extra time

The earlier warning would have given residents along the Sanriku coast of north-east Japan precious extra time to reach high buildings and other shelters before the tsunami swept over. “Thousands had already been evacuated because of heavy foreshocks, but many of those who remained might have escaped,” says Tanioka.

The system he evaluated is already in operation off the south-eastern coast of Japan, monitoring the quake-prone Nankai trough parallel to the coastline. Japan’s National Institute of Disaster Prevention is now installing a network of 125 sensors 30 kilometres apart on the Japan trench that gave rise to the Tohoku quake, so Tanioka used data from the Nankai system to predict how the new one would have performed in 2011.

By combining pressure and seismic readings from the sensors with existing data on typical tsunami waveforms, quake-induced sea floor deformations detected by satellites, and data from previous large quakes, Tanioka devised an algorithm to instantly work out the likely tsunami size, which sections of the coastline would be flooded, and how soon.

First, he showed that within minutes, the algorithm very accurately predicted the pattern of flooding seen following tsunamis tracked by the Nankai system.

Then, using input from that “test run”, he simulated how the new, 125-sensor “S-NET” system being installed on the Japan trench would have reacted to the Tohoku quake. He found that it accurately predicted, again within minutes, the scale and location of actual flooding. “The time to predict the tsunami inundation is about 2 to 4 minutes after the tsunami is generated,” he says.

Automatic alarm

To issue swift, accurate warnings, “we wouldn’t need any information on the earthquake”, he says. Instead, the sensor system would simulate likely flooding based on its incoming seismic and pressure data, and activate the alarm automatically if a tsunami was imminent.

Tanioka says that the accuracy of the system needs to be improved further still, but is confident it will provide a faster way to raise the alarm wherever it’s installed. “It could save thousands of lives in the future,” he told New Scientist.

“When you evacuate, every minute counts, and even 5 minutes can be crucial,” says Costas Synolakis of the Tsunami Research Center at the University of Southern California, who heard Tanioka’s presentation.

Synolakis says that the new sensor systems could work well in Japan where tsunamis strike rapidly because they often originate close to the coast. In the US, however, existing warning systems based on deep buoys already work well because most of the tsunamis that arrive there come from far away, such as Chile or Japan, giving much more time to react.

Synolakis also questions whether earlier warnings would have saved many more lives after Tohoku, because evacuation centres had been built to cope with magnitude 7.5 incidents rather than the magnitude 8.9 quake. “Even if with a faster warning, if the planning is wrong, many will die,” he says.