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Tuesday, 30 May 2017 01:00

New early warning system could have saved lives during the 2011 Japan tsunami

Natori, Japan after the tsunami that followed the 2011 Tohoku earthquake Natori, Japan after the tsunami that followed the 2011 Tohoku earthquake. Credits: CBC News

Simulations assessing how the system would have responded to the 2011 Tohoku earthquake show that a tsunami alarm would have been raised in 7 minutes or less, thus might had saved many of the 22,000 killed by the massive tsunami that followed the earthquake.

Back then, it took 30 minutes for the alarms to sound after the earthquake struck, so the new early warning system would have provided an extra 23 minutes, according to Yuichiro Tanioka of Hokkaido University, who presented the research results at the annual meeting of the European Geosciences Union in Vienna, Austria, last month. In such situations of emergency, when every minute counts, this could have made a difference.

The evaluated system is based on a network of cable-connected seismic and pressure sensors placed on the seabed along quake-prone faults. It is already installed 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 km 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 the 2011 earthquake.

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 predict 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.

The sensor system would simulate likely flooding based on the incoming seismic and pressure data, and activate the alarm automatically if a tsunami was imminent, without the need of any information on the earthquake. According to Tanioka, the accuracy of the system still needs to be further improved, but he is confident it will provide a faster way to raise the alarm wherever it's installed.

Costas Synolakis of the Tsunami Research Center at the University of Southern California states that the presented sensor system could work well in Japan, where tsunamis strike rapidly because they often originate close to the coast. However, in the US, existing early warning systems based on deep buoys already work well because most of the tsunamis that arrive there come from far away regions, such as Chile or Japan, thus allowing much more time for reaction.

Source: New Scientist

Read 1185 times Last modified on Tuesday, 30 May 2017 13:45

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