Chapter 4
Development of Tsunami Engineering
Field of expertise: Tsunami Engineering

Anawat Suppasri, Fumihiko Imamura, and Shuji Seto
Translated by Catherine Sachi Kikuchi

Summary
Let us review the role of tsunami engineering in the Great East Japan Earthquake, its challenges,
and its progress in the past 10 years. Why was there a huge tsunami? What was the status of theobservation and warning systems at the time? What was the actual damage of this huge tsunami?
How can we reduce damage and how can we predict tsunamis in the future? We would like tointroduce the creation of a new academic field to reduce human casualty.
Keywords: tsunami engineering, numerical analysis, cascading disaster, comprehensive disasterprevention measures

Introduction
The experience of the 1933 Sanriku tsunami and the 1960 Chilean tsunami led to thedevelopment of tsunami observation and warning systems as well as structural facilities, whichhave since contributed to tsunami disaster prevention. However, the Great East Japan Earthquake
revealed a number of problems, and a new fusion of humanities and sciences started in tsunami
engineering in order to mitigate future damage.

1: Problems Revealed by the Great East Japan Earthquake
The Tohoku region has been experiencing various types of tsunamis for a long time. The869 Jogan Tsunami recorded about 1,000 victims. The 1611 Keicho-Oshu Tsunami hit from
Hokkaido to the Kanto region and caused great damage in the Tohoku region. The 1896 Meiji
Sanriku tsunami caused more than 20,000 casualties, despite the fact that only small tremors werecaused by the "tsunami earthquake." The 1960 Chilean tsunami was an earthquake on the otherside of the world and was not felt in Japan, yet a tsunami arrived in the Sanriku region 23 hours
later, claiming about 140 lives. In our research field, we have assessed the risk of tsunamis in thepast using geological methods, cooperated with governments to estimate tsunami inundation areasusing numerical analysis techniques, promoted tsunami disaster prevention in local communities,
and conducted evacuation drills and educational support activities. However, the Great East Japan
Earthquake had an impact never experienced before. The magnitude of the earthquake was 9, anumber that had never been predicted or assumed in Japan. The earthquake ruptured a wide
range of faults from off the coast of Aomori Prefecture to off the coast of Ibaraki Prefecture.
Because of this, tsunamis reached a height of more than 10 meters in the Sendai Plain and up toabout 40 meters in the Sanriku area. In addition to the ground shaking and liquefaction caused by
the massive earthquake, the tsunami caused damage to structures and buildings. There was a
massive amount of land subsidence, debris, and fires. Long-term health damage, environmentaldamage, ecological impact, and damage caused by the accident at the Fukushima Daiichi Nuclear
Power Plant occured as well. We believe that all of the currently conceivable damage occurred in
one chain. The direct damage and indirect damage (including harmful rumors) were catastrophic.

2: Paradigms Destroyed by the Earthquake
In the past, structural measures such as seawalls were used to prevent tsunami damage,and non-structural measures such as tsunami warnings, evacuation systems, and hazard maps
were also created. After the 1933 Sanriku Tsunami, the tsunami warning system was put into
operation in 1941, and it has been improved with each subsequent tsunami disaster. At the time of
the Great East Japan Earthquake, the first warning was issued about 3 minutes after theearthquake occurred. The system was designed to build a database of the numerical analysis
results of tsunamis caused by earthquakes. When an earthquake occurs, the database is used toretrieve the expected tsunami height and arrival time based on the magnitude of the earthquake.
However, this could not be applied to the Great East Japan Earthquake. Previously, we did not
expect to experience earthquakes with a magnitude of 9, and because of this, the system
underestimated the expected height of the tsunami. Some offshore stations confirmed a massive
tsunami and the warning level was raised, warnings were issued, but the first wave of the tsunami
had already reached the coast by this time. The scale of this tsunami was larger than what wasassumed at the time the hazard map was created, and the failure to evacuate appropriately was
one of the reasons for the large number of casualties, in addition to the issues mentioned about thetsunami warning and observation system.
Structural measures such as seawalls, breakwaters, and floodgates have been developed
mainly in the Sanriku region since the 1960 Chilean tsunami, and this mitigated damage caused by
the 2003 Tokachi-oki tsunami and other tsunamis. However, the huge tsunami of the Great East
Japan Earthquake was much larger than the height of these structures and this caused significant
damage. On the other side of these structures, the tsunami flow velocity increased and scouring
occurred, which caused significant damage to the structures as well. In addition to this, not all of
the structure openings (land locks) were remotely operated or automatically controlled, and there
were reports of casualties among firefighters who tried to close them manually.

3: A New ApproachThis section introduces a new approach based on the experiences and lessons learned
from the Great East Japan Earthquake.
1. Offshore observation and warning systems after a huge tsunami
At the time of the Great East Japan Earthquake, a limited number of GPS wave stations(Figure 4-1) were used, but in addition, about 200 submarine tsunami sensors were installed by theSeafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench (S-net). The1

Japan Meteorological Agency (JMA) can observe tsunamis offshore in real time before they reachthe coast, and this information is useful for sending quick tsunami warnings, updates, andcancellations of these warnings. In addition, the JMA is also developing a new method (Tsunami
Forecasting based on Inversion for Initial Sea-Surface Height, or tFISH) to predict coastal tsunamis
by estimating their location and magnitude based on the waveform data observed offshore.
In our research field, we are focusing on the optimal use of observation networks using
genetic algorithms, and are investigating ways to improve the efficiency of this method. In the caseof tsunami warnings, when there is a suspicion of a huge earthquake, the first tsunami warning isissued using the maximum magnitude expected in the area. However, when the maximum
magnitude expected is used, qualitative expressions such as "huge" are used instead of numericalexpressions until the exact magnitude of the earthquake is determined. In addition, the levels toexpress expected tsunami height were changed from 8 levels to 5, and we now announce thehigher level to the public.

Figure 4-1. Current tsunami observation points (Japan Meteorological Agency, 2022)
2. Disaster prevention facilities to prevent or reduce inundation by a huge tsunami
Level 1 and Level 2 tsunami countermeasures were discussed and proposed by the Japan
Society of Civil Engineers (JSCE) and other organizations. Level 1 tsunamis are the largest inmodern times (with a probability of occurring once in 100 years). It is a structural measure ofdisaster prevention, and is expected to protect not only human life, but also property and economicactivities. On the other hand, Level 2 tsunamis are the largest (with a probability of occurring about
once in 1,000 years). It is a comprehensive measure that is expected to protect human lives,
reduce economic loss, prevent major secondary disasters, and enable early recovery. The conceptof tsunami disaster prevention facility design has changed accordingly. In the past, disasterprevention measures were based on a single design level and they were considered unbreakable.
Today, disaster prevention and mitigation measures have features for multiple design levels, astable performance, as well as functions and stability performance that change depending onpriority.

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As a result, it has become necessary to improve the technical standards of tsunami disasterprevention facilities and promote technology development. For example, the damage patterns ofdisaster prevention facilities were identified and through research and development, the damaged
areas will be repaired so that they become resilient structuresFigure 4-2. Example of a resilient structure (Suppasri, et al., 2016)
3. Predicting damage from a huge tsunami
After the Great East Japan Earthquake, data from more than 250,000 damaged buildings
were collected, including the type of structures, number of floors, building function, etc. to analyze
damage (indicating the relationship between the external force of the tsunami and damage tobuildings, etc.). In addition to buildings, we have also developed a wide range of tsunami damage
analysis for fishing boats, coastal embankments, road bridges, and aquaculture facilities toimprove the prediction of more complex tsunami damage. In recent years, advanced computational
science and personal computers have made it possible to reproduce detailed tsunami flows anddrifts, and to perform detailed structural analysis, thus improving the accuracy of tsunami damage
prediction.
4. New research on science of human survival from disasterNew research to protect human lives from various natural hazards that are likely to occur inthe future has started. Our institute has received information from the Miyagi Prefectural Police
Headquarters on approximately 9,000 victims who died in the tsunami that followed the Great East
Japan Earthquake, and we are currently analyzing this information. In this analysis, forensic
medicine, disaster medicine, tsunami engineering, fluid mechanics, and others are collaborating toreorganize the causes of death in tsunami disasters and to clarify the actual damage andcharacteristics in each region. In the future, the results of these studies will be linked to rescue andevacuation methods, so that people can survive even if they are caught in a tsunami. This is thefirst research to utilize the vast amount of information on the victims of the Great East Japan
Earthquake, and it is expected to make a significant contribution to the mitigation of humansuffering.
5. Newly established organizations
New initiatives have begun worldwide. The Sendai Framework for Disaster Risk Reduction
2015-2030, the resulting document of the Third UN World Conference on Disaster Risk Reductionof 2015, is the successor to the Hyogo Framework for Action of 2005, and as a guideline for3international disaster reduction efforts. Based on the Sendai Framework for Disaster RiskReduction, other countries around the world have begun making changes as well. The Global
Centre for Disaster Statistics (GCDS) was established at the same time, mainly in collaboration
with the United Nations Development Program (UNDP) and other disaster reduction-relatedorganizations, to provide support for improving disaster reduction capacity in developing countries
through the collection, analysis, and utilization of disaster damage statistics, including those on
tsunamis.

4: Achievements and Future Prospects
Even now, the offshore observation stations are giving us useful reference data forconfirming tsunami generation and issuing tsunami warnings immediately after an earthquake.
Before a tsunami arrives on land, it is possible to determine the fault parameters of an earthquake
in real time, calculate and visualize the tsunami inundation area, and announce the expected
inundation map and damage prediction through analysis. As for the construction of survival science
as a discipline to fundamentally reduce human casualty, the cause of death in the Great East
Japan Earthquake was classified in detail, including address, place where the body was found,regional characteristics, leading to the relationship between these factors and the cause of death(drowning, unknown, burning, hypothermia) being found. In addition to the external forces of thetsunami, we would like to make proposals to protect lives through detailed studies. Finally, thenewly established international organizations are in the process of data collection and analysis,
and we can look forward to international guidelines based on the results.

Conclusion - From the authors
In the future, the basic principles of tsunami risk assessment, observation and prediction,
damage estimation and mitigation, as well as community development, including tsunami disasterprevention culture, will remain unchanged. Tsunami engineering aims to provide technologies that
contribute to practical damage reduction, but its development is based on the fusion of academic
fields and basic science, and we will continue to move forward through collaboration.

References
Japan Meteorological Agency. (n.d.). Tsunami observation points (All Japan).
https://www.data.jma.go.jp/svd/eqev/data/tsunamimap/index.html [accessed August 2, 2022]. (InJapanese).
Seto, S. and Imamura, F. (2020). Classification of tsunami deaths by modifying ICD-10 categories
in the 2011 Tohoku earthquake tsunami - A case study in Miyagi prefecture. International Journalof Disaster Risk Reduction, 50, Article 101743. https://doi.org/10.1016/j.ijdrr.2020.101743
Suppasri, A., et al. (2016). Improvement of tsunami countermeasures based on lessons from the2011 great east japan earthquake and tsunami -Situation after five years
Earthquake and tsunami -Situation after five years-. Coastal Engineering Journal. 58(4): 1640011.
https://doi.org/10.1142/S0578563416400118

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