池田菜穂

The Tokyo Conference on International Study for Disaster Risk Reduction and Resilience
14 – 16 January 2015, TokyoA New Proposal for Tsunami Hazard Map Explicitly Indicating Uncertainty of Tsunami Hazard Assessment
Yo Fukutani, Suppasri Anawat, Fumihiko Imamura (International Research Institute of Disaster Science, Tohoku University)

Research Background
Since the tsunami hazard assessment includes large uncertainty, we cannot properly understand the uncertainty when using the only results of thedeterministic hazard assessment.

ObjectiveThe objective of this study is:- to clarify the uncertainty of tsunami hazard assessment.
- to visualize the evaluated uncertainty on the tsunami hazard map.
By doing this, for example, local residents who utilize tsunami
hazard map can properly understand the uncertainty of thetsunami hazard assessment, resulting that it might make a good
impact on their decision-making for disaster prevention.

Study area

Tsunami hazard curve at off the Soma port
-After statistical treatment of the resultsof logic tree calculation, we can obtain
fractile tsunami hazard curves (5%fractile, 50% fractile and 95% fractile)and Simple average curve.
-We can evaluate uncertainty oftsunami height from these curves.
-For example, average tsunami heightwith return period of about 845 years is3.73 m.
-5% fractile wave is 1.21m, 50%
fractile wave is 2.69m, 95% fractile
wave is 7.08m.
-Tsunami heights with even one return
period basically have a high level ofuncertainty.

Soma port(Fukushima prefecture)

Target earthquake zones-We selected elevenearthquake zones including
Tohoku earthquake fault
along the Japan trench forstochastic tsunami hazard
assessment.
-We used a portion ofearthquake zones, which areused in probabilistic seismic
hazard map by HERP* inJapan.
-Based on the earthquake
information, we implemented
a lot of tsunami numericalsimulations.
-We constructed logic trees corresponding to eachearthquake zone.
-Below is an example of logic tree for the off Sanriku
Earthquake

Annual Exceedance Probability-Moment Magnitude（Mw）：Set deviation of 0.1 from themoment magnitude determined by HERP
-Asperity Position： Set three branches for each earthquake-Average Return Period： Set three branches in the logic
trees for the average return period, which is determined byHERP, considering confidence interval. Average return
period of the earthquake is estimated by assuming thePoisson distribution-Lognormal standard
Tsunami Hazard Curvedeviation and truncatedvalue： values of Annaka(2007)’s study-Numbers of all branches
in the logic trees are 1800.
N=1800-Therefore, we can obtain
1800 hazard curves.
Tsunami Height (m)Tsunami hazard map explicitly indicating uncertainty-The below map is tsunami hazard map explicitly indicating uncertainty of tsunami
hazard assessment.
-The blue area is inundation area due to 0.05 fractile wave, the yellow one is for
Average wave and the red one is for 0.95 fractile wave.
-The black line is the inundation area due to the Tohoku earthquake.
-At least in theory, the return period of these inundation area is about 845 years.
-As shown in the map, there exists a high level of uncertainty in the tsunami hazard
assessment.

-We tend to focus on inundation area with one return period, but it is very
important to evaluate, quantify and visualize the uncertainty of the assessment!!
References
Annaka, T., Satake, K., Sakakiyama, T., Yanagisawa, K., and N. Shuto (2007), Logic-tree approach for probabilistic tsunami hazard
analysis and its applications to the Japanese coasts, Pure Appl. Geophys., 164, 577–592.
Fukutani, Y., Suppasri, A., and F. Imamura (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.
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)