Probabilistic Tsunami Hazard Assessment addressing the uncertainty of tsunami source Pacific Rim Forum 2017 January 23, 2017 Yuta Abe, ITOCHU Techno-Solutions Corporation, Japan Copyright (c)2017 ITOCHU Techno-Solutions Corporation
Overview 1. Introduction 2. Tsunami Source Model 3. Calculation Method 4. Tsunami Hazard Curve 5. Summary 1
Introduction The purpose of this presentation is to review the following two papers: H. Sugino, Y. Iwabuchi, N. Hashimoto, K. Matsusue, K. Ebisawa, H. Kameda and F. Imamura : The characterizing model for tsunami source regarding the inter-plate earthquake tsunami., Journal of JAEE, Vol.15, No.13, 2015. (original Japanese paper published: November, 2014) H. Sugino, Y. Iwabuchi, Y. Abe and F. Imamura : Effects of the model for scenario tsunami on the probabilistic tsunami hazard assessment., Journal of JAEE, Vol.16, No.7, 2016. (original Japanese paper published: August, 2015) 2
Introduction Background Estimation of the tsunami design level of Nuclear Power Plant (NPP) Based on the largest magnitude of earthquakes in the past Establish basic models to reproduce the past tsunamis Addressing the uncertainty of possible tsunamis in future Change the model parameters (positions, strikes, dips,...) of basic models Select the model with the greatest in a water level at the target facility Exceeded by 2011 Tohoku Tsunami at Fukushima Daiichi NPP Advancement of the Probabilistic Tsunami Hazard Assecement (PTHA) Revision of the maximum magnitude Characterization of the models for scenario tsunamis Take into account heterogeneous slip distributions in faults Revision of the occurrence probabilities of earthquakes Comparing between the old and new PTHA at Fukushima 3
Introduction Outline of PTHA procedure Sugino et al., 2015 4
Tsunami Source Model Old PTHA Reference to the long-term evaluation reports by the Earthquake Research Committee (2009) Target seismogenic zone is the plate boundary along the Japan Trench The seismogenic zone is divided into 8 segments Simultaneous rupture is considered only for the segments C and D Homogenic slip distribution G F A B C D E H Region Magnitude of Long-term evaluation Magnitude of Scenario source model Earthquake Type A Around M8.0 Mw 8.2, 8.3, 8.4 Reverse fault B No evaluation - - C Around M7.7 Mw 7.9, 8.0, 8.1 Reverse fault D Around M7.5 Mw 7.7, 7.8, 7.9 Reverse fault C+D Around M8.0 Mw 8.2, 8.3, 8.4 Simultaneous rapture E Around M7.4 Mw 7.6, 7.7, 7.8 Reverse fault F M6.7~M7.2 Mw 7.0, 7.3, 7.5 Reverse fault G No evaluation - - H Around Mt8.2 Mw 8.1, 8.2, 8.3 Tsunami earthquake H Around M8.2 Mw 8.4, 8.5, 8.6 Normal fault *Different two types of earthquake are set at Region H 5
Tsunami Source Model New PTHA Target seismogenic zone is the plate boundary along the Kuril - Japan Trench The seismogenic zone is divided into 22 segments By combining the 22 segments, 93 source areas with Mw ranging from 7.9 to 9.6 are produced Spatially heterogenic slip distribution More than one slip pattern for each source area Along the Kuril Trench 6
Tsunami Source Model Slip heterogeneity in New PTHA Specifying method of slip distributions Sugino et al., 2014 7
Tsunami Source Model Slip heterogeneity in New PTHA Example of spatially heterogeneous slip distributions A1 A2 A3 A4 A5 B1 B2 B3 B4 B5 C1 C2 C3 C4 C5 Sugino et al., 2015 8
Tsunami Source Model Occurrence Probabilities when past seismic activities are known Apply the occurrence probabilities calculated by the long-term evaluation The renewal process BPT model or the Poisson process are assumed when past seismic activities are unknown Calculated by an empirical equation G-R law or its extrapolation The regression analysis for the G-R law is based on the data of earthquakes observed in the seismogenic zone from Jan/1/1980 to Feb/28/2011 Sugino et al., 2015 9
Tsunami Source Model Comparizon between the old and new old model new model Target seismogenic zone along the Japan Trench along the Kuril-Japan Trench Simultaneous rupture of multiple segments combine the segments C and D combine the 22 segments Magnitude range Mw 7.0 Mw 8.6 Mw 7.9 Mw 9.6 Slip distribution homogenic (one source model for one source area) heterogeneous for lage earthquake (more than one source model for one source area) Occurrence probability based on the long-term evaluation report based on the long-term evaluation report or extrapolated by G-R law 10
Calculation Method Tsunami Source Model Initial Tsunami Profile Crustal Deformation Analysis By the method of Mansinha and Smylie (1971). Assume a seafloor deformation as a initial tsunami profile. Tsunami Propagation Analysis Based on the non-lieanr long-wave theory. Duration time for simulation is 6 hours after tsunami generation. Simulated Tsunami Wave Relative maximum tsunami height calculated by subtracting crustal deformation from tsunami height (T.P. 0m) 11
Calculation Method In order to remove effects of coastal structures, evaluation base point is set at a point on a depth contour of 150m off the east coast of Fukushima Prefecture Effects of coastal structures will be taken into account in fragility assessments Evaluation Base Point Sugino et al., 2015 12
Tsunami Hazard Curve Old PTHA Evaluation base point A B C D E H F G Dominant earthquake type is Simultaneous rupture type (Region C+D, Mw8.2~8.4) for AEF 10-3 ~10-4 Normal fault earthquake type (Region H) for AEF 10-5 ~10-6 13
Tsunami Hazard Curve New PTHA Along the Kuril Trench Evaluation base point Dominant earthquake type is earthquakes occur along Japan Trench for AEF 10-3 earthquakes occur along Kuril-Japan Trench for AEF 10-4 ~10-6 14
Tsunami Hazard Curve reproduced analysis of the 2011 Tohoku Tsunami 6.9m reproduced analysis of the 2011 Tohoku Tsunami 6.9m 2 5 times larger tsunami heights at the same AEF AEF at the tsunami height 6.9m estimated by the reproduced analysis of the 2011 Tohoku Tsunami (Sugino et al., 2014) is Old PTHA : less than 10-6 New PTHA : 10-3 ~ 10-4 15
Tsunami Hazard Curve Frequency Tsunami height relation in Kuril-Japan Trench earthquakes Frequency 70 60 50 40 30 20 10 Tsunami source model having large magnitude and extra-large slip zone placed near the evaluation point 0 0 2 4 6 8 10 12 14 16 18 20 22 24 Relative Max. Tsunami Height (m) Tsunami source model having small magnitude or extra-large slip zone placed far from the evaluation point 16
Summary The PTHA based on new models for scenario tsunami taking into account of the experience from the 2011 Tohoku Tsunami is condacted. By comparison wtih the old PTHA, The new PTHA resulted in a 2 to 5 times larger tsunami height. The AEF at the tsunami height of the 2011 Tohoku Tsunami was roughly 10-3 times greater. The large difference in the tsunami hazard curve is mainly caused by The maximum value of magnitude which is greater than the largest magnitude in the past Considering simultaneous ruptures of Kuril and Japan Trench segments The new tsunami source models with heterogeneous slip distributions 17