The Tohoku earthquake of 11 March 2011 (UTC) devastated huge regions, causing the Great East Japan Earthquake Disaster (Cabinet of Japan, 2011) together with large aftershocks and triggered earthquakes. This disaster resulted in 16,019 fatalities, 3,805 missing, 6,121 injured, and 118,621 house collapses as of 11 October 2011 (Fire and Disaster Management Agency of Japan, 2011). Since more than 90% of the fatalities were from drowning (Kyodo News, 2011), and the number of injured people was relatively small, the disaster is featured by severe tsunami damage rather than moderate ground motion damage.
The national seismic hazard assessment program, initiated by the Japanese government after the 1995 Kobe earthquake, was unable to foresee this earthquake. Geller (2011) indicated that since 1979, earthquakes that caused 10 or more fatalities in Japan, including the Tohoku earthquake, have actually occurred in places assigned a relatively low probability by the national seismic hazard assessment. He also declared “this discrepancy strongly suggests that the hazard map and the methods used to produce it are flawed”. However, we think the discrepancy does not imply a flaw of the method or seismology that the method is based on, but a limitation of seismology.
“Earthquake” is a complex system, and it is impossible to perform a real-scale experiment for this phenomenon. The frequency of its occurrence is extremely low, so that data for this phenomenon are very limited. Therefore, future earthquakes, which were foreseen for the hazard assessment by using the limited data and a probabilistic method, include great ambiguity. It is not surprising that damaging earthquakes in the last thirty years occurred in low probability regions. In other words, the method and seismology are not flawed but the results include large limitations. A real problem is that the Japanese government has not clearly stated these limitations of the seismic hazard assessment to the public. Such risk of communication is a kind of negative campaign on the usefulness of hazard assessment, but we think it is indispensable for science communication related to be to natural disaster.
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Risk communication under the limitations of science
The case of seismology and 2011 Tohoku earthquake

Kazuki Koketsu   Earthquake Research Institute, the University of Tokyo

Satoko Oki   Earthquake Research Institute, the University of Tokyo

Hiroo Kanamori   Seismological Laboratory, California Institute of Technology

The Tohoku earthquake of 11 March 2011 (UTC) devastated huge regions, causing the Great East Japan Earthquake Disaster (Cabinet of Japan, 2011) together with large aftershocks and triggered earthquakes. This disaster resulted in 16,019 fatalities, 3,805 missing, 6,121 injured, and 118,621 house collapses as of 11 October 2011 (Fire and Disaster Management Agency of Japan, 2011). Since more than 90% of the fatalities were from drowning (Kyodo News, 2011), and the number of injured people was relatively small, the disaster is featured by severe tsunami damage rather than moderate ground motion damage.
The national seismic hazard assessment program, initiated by the Japanese government after the 1995 Kobe earthquake, was unable to foresee this earthquake. Geller (2011) indicated that since 1979, earthquakes that caused 10 or more fatalities in Japan, including the Tohoku earthquake, have actually occurred in places assigned a relatively low probability by the national seismic hazard assessment. He also declared “this discrepancy strongly suggests that the hazard map and the methods used to produce it are flawed”. However, we think the discrepancy does not imply a flaw of the method or seismology that the method is based on, but a limitation of seismology.
“Earthquake” is a complex system, and it is impossible to perform a real-scale experiment for this phenomenon. The frequency of its occurrence is extremely low, so that data for this phenomenon are very limited. Therefore, future earthquakes, which were foreseen for the hazard assessment by using the limited data and a probabilistic method, include great ambiguity. It is not surprising that damaging earthquakes in the last thirty years occurred in low probability regions. In other words, the method and seismology are not flawed but the results include large limitations. A real problem is that the Japanese government has not clearly stated these limitations of the seismic hazard assessment to the public. Such risk of communication is a kind of negative campaign on the usefulness of hazard assessment, but we think it is indispensable for science communication related to be to natural disaster.

A copy of the full paper has not yet been submitted.

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