Tsunami Risk Researches-Development of evaluation method for tsunami risk
using lessons learned from the March 11 Tohoku TsunamiYo Fukutani(E-mail: fukutani@irides.tohoku.ac.jp)
International Research Institute of Disaster Science, Tohoku University

What was the lessons learned from the Tohoku Tsunami?
◆Huge tsunamis (Max inundation height 40.1m) associated with the mega earthquakethat was not included in earthquake hazard assessment generated.
◆These earthquakes and tsunamis caused a vast amounts of damages.
⇒How should we assess tsunami hazard before the earthquake?
◆The excess regions assumed in tsunami hazard map was inundated.
◆This influenced on the tsunami evacuation action by residents.
⇒How should we visualize tsunami hazard assessment?

Example of handling methods for assumed tsunami hazard◆To consider maximum scale of earthquake that have not occurred in the past, but ispossible to occur geophysically in the future (The Cabinet Office, Kyusyu Electric Power
Co. Ltd., Hokkaido Prefecture) (Fig.1, Fig.2)◆To consider few kinds of slip distributions that is possible to occur (Fig.3)◆To consider few kinds of moment magnitude◆To set the level 1 tsunamis and the level 2 tsunamis (Japan Society of Civil Engineering)◆By conducting tsunami simulation considering few kinds of cases as shown left below, we canestimate uncertainty of tsunami wave height (Probabilistic tsunami hazard assessment (Fig.4)).
◆Assumed tsunami heights before earthquakes are not deterministic values.
◆Theoretically, we can confirm frequency distributions of tsunami height with once in athousands (Fig.5).
Small uncertainty
Large uncertainty(a)(b)

Fig.4：Relationships between tsunami height and generation Fig.5： Probable frequency of tsunami height with once inprobability (Japan Society for Civil Engineering(2012)) thousands (a) off Iwate, (b) off Fukushima(Fukutani et al.(2014))

Dealing with the problem oftsunami hazard maps

Quantification of tsunami risk using theresults of probabilistic assessment◆By integrating information for probabilistic
tsunami hazard and fragility assessment, we candevelop tsunami risk curve. (Fig.7 left)◆Expected value of tsunami risk is equivalent
to area below tsunami risk curve. (Fig.7 right)

Fig.1：Nankai Trough Mega Earthquake(The Cabinet Office, 2012)

Fig.2：Ryukyu subduction zone Mega Earthquake(Kyusyu Electric Power Company)

Fig.6：Probabilistic tsunami hazard map (Fukutani et al.(2014))

Fig.7：Tsunami risk curve (left) and expected value of tsunami risk (right)

参考文献

Fig.3：Few kids of slip distribution for the Tohoku Earthquake (Fukutani et al. (2014))

Japan Society for Civil Engineering (2012), A method for probabilistic tsunami hazard assessment,
http://committees.jsce.or.jp/ceofnp/system/files/PTHA20111209_0.pdf (accessed on 19 January, 2015)
The Cabinet Office (2012), Mega earthquake model conference for the Nankai trough, http://www.bousai.go.jp/jishin/nankai/model/(accessed on 19 January, 2015)
Fukutani, Y., Suppasri, A., and Imamura, F (2014), Stochastic analysis and uncertainty assessment of tsunami wave height using arandom source parameter model that targets a Tohoku-type earthquake fault, Stochastic Environmental Research and Risk
Assessment, doi 10.1007/s00477-014-0966-4. (published online)
Fukutani, Y., Suppasri, A., Abe, Y., and F. Imamura (2014), Stochastic evaluation of tsunami inundation and quantitative estimatingtsunami risk, Journal of Japan Society of Civil Engineers, Ser. B2(Coastal Engineering), 70(2), I_1381-I-1385. (in Japanese)2