Interdisciplinary Project Launched to Better Cope with Special Information on the Nankai Trough Earthquake for Disaster Risk Reduction in Society


In January 2019, a project was launched at IRIDeS, tiled “Development of a supporting package for effective countermeasure planning against the rinji jōhō (special information)1) on the Nankai Trough earthquake.” The aim of this project is to contribute to the disaster risk reduction of the society by helping key players such as municipalities and enterprises so that society as a whole can act wisely. Supported by Secom Science and Technology Foundation, an interdisciplinary group composed of thirteen IRIDeS researchers, whose expertise include natural, social and human sciences, is leading this project.

Special Information on the Nankai Trough Earthquake2)

The Nankai Trough earthquake refers to giant earthquakes of M8 class or larger along the plate interface that extends from the Suruga Bay to the Sea of Hyuga. Historically, such earthquakes have occurred approximately every 100–150 years. The probability of the next Nankai Trough earthquake occurrence in the next 30 years is estimated at 70–80%. Such an earthquake would cause extensive damages and impacts over a wide area due to the ground shaking and associated tsunami, and thus the earthquake is often described as a “national crisis.”
With our current knowledge, we cannot predict earthquakes. What we know about the Nankai Trough earthquakes instead is that there have been multiple cases of successive occurrence. For example, an earthquake occurred along the eastern portion of the plate interface in 1944, followed by another one along the western portion in 1946. Furthermore, the latest studies in earthquake science suggest that slow slips can trigger an earthquake, though not always. These findings imply that if some types of geophysical signatures were observed, we can consider that the probability of having a Nankai Trough earthquake has increased. Based on such an idea, a new information system has recently been adopted in Japan that, when the likelihood of a Nankai Trough earthquake has become higher than normal, the Japan Meteorological Agency will announce special information on the Nankai Trough earthquake.3) Threre are two levels of information: a higher level alert (keikai) and a lower level alert (chūi). In 2019, the Cabinet of Japan announced guidelines for municipalities and companies in the anticipated disaster areas, who need to plan the countermeasures in response to the special information.4)

The new project: How can we use uncertain disaster forecast Information more effectively?

The government is pursuing disaster risk reduction, urging society to prepare for and react to a major earthquake before it occurs, through the new information system. However, such proactive countermeasures based on uncertain disaster forecast information is a challenge with no precedent worldwide. Key organizations and the general public—those who receive and try to use this information—could be perplexed by the fact that a giant earthquake may strike but the chance of having one soon is much smaller than not having one.
To address this issue, the IRIDeS research group has decided to conduct an in-depth examination of the special information on the Nankai Trough earthquake from a variety of research fields. The research group thinks that providing a “second opinion” should be useful for the stakeholders to view the problem in different perspectives. The group also thinks that since the guidelines published by the Cabinet office are inevitably limited to general descriptions, providing more detailed and specific recommended solutions can complement the guidelines well. The research group is divided into three teams: the Hazard Assessment Team, the Countermeasures Team, and the Social Effects Team. The teams started examining the special information in each specialized field with inter-team discussions. The initial year of the whole research period of three years has just finished, focusing on Kochi Prefecture as a model area.

Primarily from the natural science and engineering perspectives, the Hazard Assessment Team aims at visualizing the diversity of scenarios that could happen after observation of a large earthquake or an anomalous slow slip, in which case the special information would be announced. Their research outcomes will facilitate the key organizations to overview the wide spectrum of possible scenarios and to better prepare. The team also plans to visualize the tsunami risk maps in the period of alert which is one or two weeks.

The Countermeasures Team will deliver recipes of recommended actions customized to different types of organizations so that they can create effective response plans in case of special information announcement. The team has been in collaboration with stakeholders in Kochi so that the recipes are effective in practical situations. They are currently focusing on the most challenging situation of a giant earthquake having struck on the farther side (that is, not much direct damage) and another one anticipated on the nearer side (which could cause tremendous damage). The team is seeking to promote the implementation of such recommendations through its integration with the general business continuity plans against Nankai Trough earthquakes. The team members are taking as important issues not covered by the government guidelines, such as sold-out stocks at local stores or traffic jams.


From engineering, neuroscience, and scientific communication perspectives, the Social Effects Team is exploring the interactions between the key organizations and society. The actions taken by the organizations have influence on society (other organizations and public) and the response of the society would inversely influence the actions of organizations. The team also focuses on the communication of the uncertain disaster risk information with the public. In the case of the Great East Japan Earthquake in 2011, gaps were observed between the public behavior anticipated bythe key organizations and actual public behavior. Insights can be obtained from such past cases for wiser actions on the future Nankai Trough earthquakes. The final goal of the team is to explore realistic and effective actions of key organizations and effective communication with the public.

About the future

The research group seeks to regularly share their provisional outputs with collaborating organizations, rather than presenting the final outputs at the end of the project period. An interim meeting was held in Kochi on February 19, 2020, where a range of useful discussion has taken place between the research group and the stakeholders in Kochi including Kochi prefectural government as well as other organizations. This interdisciplinary project may serve as a model for IRIDeS to conduct “practical research for disaster reduction.” Assoc. Prof. Yo Fukushima, the project’s principal investigator, remarks, “Multi-disciplinary (among different disciplines) and trans-disciplinary (academia and society) close collaborations are generally difficult. Through this project, however, I have become convinced that conscientious dialogues among different people can open up new possibilities. While aiming at practically useful results, we would like to pursue new approaches which can also promote advancement of each discipline.”

1) There seems no authorized English translation of rinji jōhō at this time. “Special information” is a tentative translation proposed by the project members.
2) The following is a concise explanation of this topic (in Japanese): Fukushima, Y. (2019), “Nankai torafu jishin rinji jōhō: okoru ‘kamoshirenai’ kyodai jishin e no taiō” [Special information on the Nankai Trough earthquake: responding to a mega earthquake that “might” happen], Naifuru no. 119, pp. 4–5,
3) Kishōchō, “Nankai torafu jishin ni kanrensuru jōhō no shurui to happyō jōken” [Types of information related to the Nankai Trough earthquake and conditions for their announcement], (accessed 01/20/2020).
4) Naikakufu (2019), “Nankai torafu jishin no tayōna hassei keitai ni sonaeta bōsai taiō kentō gaidorain dai ichi ban” [Disaster risk reduction response guidelines preparing for diverse possibilities of Nankai Trough earthquake occurrences: version 1]


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