Chapter 34
Countermeasures Against Great Earthquakes
and Tsunamis in the Near Future
Field of expertise: Seismology

Yo Fukushima
Summary
After the Great East Japan earthquake disaster, the policy of the Japanese government fordisaster risk reduction against great earthquakes and tsunamis changed to be able to cope withthe maximum-size earthquakes in each region. One of the pillars of such countermeasures is theevacuation from tsunamis. The Japanese government is developing monitoring systems forearthquakes and tsunamis and a scheme for disseminating information. The stakeholders insociety should work together to build an effective evacuation framework using such information.
Keywords: countermeasures against maximum-size earthquakes, monitoring system, iInformation
dissemination, uncertainty

Introduction
Great earthquakes along the plate interface bring about damage by generating strong
ground motions and large tsunamis. To make the society strong against intense shaking,significant nation-wide efforts constructing earthquake-proof buildings and seismically retrofitting
the existing ones have been conducted. As a result, a high level of safety of the buildings has been
attained as a whole, if not perfect, and the roadmap to further improvements is clear. On the otherhand, a lack of countermeasures against tsunamis were highlighted by the Great East Japanearthquake, which led to a major policy change.

1: Problems Revealed by the Great East Japan Earthquake
What happened?
It was believed before the Tohoku disaster that the forecast of the approximate location andsize, or the evaluation of the seismic potentials of earthquakes in different regions in Japan had
been accomplished, in spite of the long-standing difficulty in predicting earthquakes. However, theearthquake that actually struck Tohoku ruptured a 500 kilometer long and 200 kilometer wide area
along the plate interface to result in magnitude (M) 9.0, way above what was anticipated.

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The reality of the damage
The “exceedingly unexpected” height and current of the tsunami from the M9 event causeddevastating damage. The protective facilities such as the coastal embankments could noteffectively stop the tsunami inundation. In many areas, evacuation was delayed for various
reasons including the underestimation of the tsunami height in the initial warning, lack of
information updates due to power outage, and the over-reliance on the protective facilities. TheFukushima Daiichi Nuclear Power Plant was no exception; a huge tsunami simultaneously
destroyed layers of protective and safety equipment, leading to a fatal accident.

2: Paradigms Destroyed by the Earthquake
Conventional wisdom and necessary responses
The Headquarters of the Earthquake Research Promotion of Japan (HERP), founded in
1995 after the Great Hanshin-Awaji Earthquake, conducted a long-term evaluation of earthquakes
such as calculation of a 30-year probability of earthquake occurrence for different areas in Japan.
HERP valued what we could learn from past earthquakes and assumed that the same kind ofearthquakes would occur in the future. As for the area off the coast of the Tohoku region, ahistorical earthquake significantly larger than an M8 had been found a few years before the 2011
M9 event. This initiated a movement of re-evaluation of earthquakes in the Tohoku region, but not
to the degree where the evaluation was updated and reflected in the reinforcement of thecountermeasures.
As noted before, many residents living near the coast could not take appropriate action forevacuation from the tsunami due to the communication breakdown after the initial underestimatedwarning and other reasons. Considering that the time between the detection of the earthquake andthe arrival of the tsunami was around 30 minutes or more, the degree of damage due to thetsunami should have been much smaller if accurate information on the tsunami forecast hadreached residents in a timely manner.

3: A New Approach
The Central Disaster Management Council (CDMC) of the Japanese government revised
the policy of earthquake disaster risk reduction. Specifically, CDMC made clear that the groundmotion and tsunami from the maximum-possible earthquakes should be considered in their
published report (Cabinet Office, 2011). Complying with this policy change, fault models of M9earthquakes and their associated tsunami heights were published for the areas of the Nankai
Trough subduction in southwest Japan and that of the Japan trench to Kuril trench in northern
Japan. The aforementioned report indicated that two levels of tsunamis should be anticipated andprepared for: The first level (L1) corresponds to the tsunamis caused by earthquakes that occur
once in several decades to a hundred years or slightly more (large earthquakes, considered typicalfor the region), and the second level (L2) corresponds to the maximum-possible tsunamis causedby extremely rare earthquakes that occur every several hundred to a thousand years (CabinetOffice, 2011). Given the distinctions, the report also provided the basic concept such that a holistic
approach including both hard (i.e., relying on man-made structures) and soft (i.e., not relying on
man-made structures, evacuation for example) countermeasures are to be taken (Figure 34-1).

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This concept was later legally authorized by the Act on Regional Development for Tsunami
Disaster Prevention (taken into force in December 2011).
The new concept for disaster risk reduction requires that timely and reliable information forevacuation is disseminated and that appropriate responsive actions are taken. In the new tsunami
warning system of the Japan Meteorological Agency introduced after the disaster, the initialtsunami warning for earthquakes greater than M8, whose accurate size cannot be estimatedinstantly, automatically assumes the maximum-level tsunami. However, repeatedly disseminatingsuch uncertain and possibly over-predicted information would reduce the reliability of the tsunami
warning, and further hampers residents’ evacuation (so-called crying-wolf syndrome). Prompt andaccurate estimation of the tsunami height thus leads to appropriate evacuation actions.
After the disaster, a new sea-cable observation system called S-net was deployed off theshore of north and northeastern Japan along the Japan and Kuril trenches, enabling early
detection of earthquakes and tsunamis. The extension and upgrade of the DONET observation
system, another sea-cable observation system installed along the Nankai Trough in south westernJapan, also took place. Research on the near real-time estimation of fault models and tsunami
predictions using data from these observation networks and from the GNSS Earth Observation
Network System (GEONET) on land has been actively conducte (Ohta et al., 2018). Timely
integration of this type of analysis into the alert system is highly expected. It makes effective
evacuation, saving lives and important properties of the residents, into a reality.

Figure 34-1. A conceptual figure showing the policy on the earthquake and tsunami disastermitigation in Japan after the 2011 disaster. Compared to typical large earthquakes that occur once
every several decades to one hundred years or slightly more (L1), the goal is to prevent damage
mainly by relying on hard measures. Compared to the maximum-level earthquakes that occur
much less frequently (L2), the goal is to minimize the damage in a holistic approach including not
only through hard measures but also soft measures including tide forests and raised roaddevelopments for dissipating the tsunami energy in order to facilitate evacuation.

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4: Achievements and the Future
A new approach to disaster science
In November 2017, JMA started a service to release warning information when theprobability of having a great earthquake (larger than or equal to M8) along the Nankai Troughsubduction is evaluated to have become higher than normal (Cabinet Office, 2019). The highestlevel alert, as of the timing of writing, is issued for the cases where an M8-class earthquake
occurred along the Nankai Trough and vigilance for another M8 or larger earthquake in the vicinity
needs to be evoked. We can never be certain about the occurrence of a severe earthquake, butscience can provide potentially useful information, such as the areas of elevated risk by using thedata from the observation networks being deployed and extended. This new warning system has
the potential to drastically decrease the number of victims by urging early evacuation fromtsunamis.

Conclusion - from the author
One of the key factors for tsunami disaster mitigation is to appropriately react to theforecast and outlook of the future occurrence of earthquakes and associated tsunamis. The newwarning system for great earthquakes along the Nankai Trough is not an easy information for thesociety to digest because it necessarily entails uncertainty, but if the stake-holders, including
researchers, administrations, residents, and media, can discuss and work together consistently,
future disaster risk reduction can surely be realized. I hope that the stake-holders from different
sectors will be proactively involved in creating an effective warning system for anticipateddisasters.

References
Cabinet Office. (2011). Report of the Committee for Technical Investigation on
Countermeasures for Earthquakes and Tsunamis Based on the Lessons
Learned from the “2011 off the Pacific coast of Tohoku Earthquake”. Government of Japan.
General Disaster Management Council.
http://www.bousai.go.jp/kaigirep/chousakai/tohokukyokun/pdf/Report.pdf
Cabinet Office. (2019). White Paper on Disaster Management 2019 [White paper]. Government ofJapan. Director General for Disaster Management.
http://www.bousai.go.jp/en/documentation/white_paper/2019.html
Ohta, Y., Inoue,T.,Koshimura, S., Kawamoto, S., Hino, R. (2018). Role of Real-Time GNSS in
Near-Field Tsunami Forecasting. Journal of Disaster Research, 13(3), 453-459.
https://doi.org/10.20965/jdr.2018.p0453

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