2009 Chi-Chi Conference in TaipeiStrong ground motion and Tsunami Simulation for the
Nankai-Trough Mega-thrust Earthquake Using Supercomputers
Takashi FURUMURA 古村 孝志CIDIR/ERI, The University of Tokyo
東京大学 情報学環総合防災情報研究中心 / 地震研究所
Kuril Trench
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Nankai Trough
Hokkaido
Honshu
Shikoku
KyushuNankai 南海
EartuqiakeTokai
東海
Earthquak
e
Nanse
i-Sho
to
Troug
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Nankai-Trough Earthquakes
2-4cm/year
To Taiwan
Strong Ground motion from the 1944 Tonankai earthquake
500 km
The earthquake generate firstly strong ground motions with JMA intensity of 6-7 occur widely along the source region of 300- 500 km long.
Seismic Energy x 200-500
1854 Ansei Edo(M8.4)安政東海地震
Old JMA Intensity (max 6)
Shizuoka
Coseismic surface deformation due to the earthquake
Photos, Courtesy from Prof. Okamura, Kochi Univ.
After 1946 Nankai Earthquake
Downtown Kochi 高知 City Today
Continental Plate
SubsidenceUplift
Then, just after the earthquake coseismic surface deformation upheaves or subsides coastal lines more than 1-2m along the source zone.
Subsidence
Uplift
1946 Nankai Earthquake
Philippine-sea Plate
Kochi
Amplification and long-time prolongation of tsunami
Finally, tall tsunami more than 1-5 m attack wide area along the coast, and it is lasting more than several hours.
Tide-gouge record at Tosashimizu 土佐清水 during the 1946 Nankai Earthquake
5 hours1 m
Photo: JMA Tokushima
An Integrated Ground Motion, Coseismic Deformation, and
Tsunami Simulation
Integrated Ground motion and Tsunami Simulation
(1) Ground Motion and Coseismic Deformation
(2) Tsunami Generation and Propagation Simulation
3D FDM simulation of Equation of Motion 3D FDM simulation of Navier-Stokes Equation
Input
Furumura and Saito (2009) - 1896 Meiji Sanriku Earthquake
SeafloorDeformation
D (x,y,t)
uuu 2 guuuu p
Ground motion (Vertical, Displacement) Seasurface elevation (Tsunami)
Integrated Ground motion and Tsunami Simulation
Saito and Furumura (2009)
(a) Short Rise Time (Ts=10s)
(b) Long Rise Time (Ts=120s)
D=4m, W=20km, h=8000m
Very slow-rupture earthquakes occurring below deep sea cannot generate tall tsunami because tsunami propagating quickly away from the source region
8000m
8000m
slow event
normal event
Integrated Ground motion and Tsunami SimulationDispersion of Tsunami propagating in
deep sea cause elongating and complex tsunami waveform. Such effect is naturally taking into accounted in present simulation.
(b) Linear Long Wave Model
(a) Navier-Stokes Model
OBS
2004 Off Kii-Pen. Earthquake (M7.4)
After JAMSTEC
Tsunami waveform, off Cape Muroto 室戸岬沖
Cape Muroto
Furumura and Saito (2009)
(b) Half-space Model(a) 3D Model
Integrated Ground motion and Tsunami Simulation(2) Tsunami Simulation
米良
内浦
松坂
土佐清水
Uplift
Subsidence
(1) Ground motion Simulation
Tsunami Waveform 3D/1D
Source-rupture Scenario for futureNankai-Trough Earthquake
Nankai-trough mega-thrust earthquake scenarioQuestion: The Hoei 宝永 Earthquake in 1707 was the largest model?
Tsunami Height
Seismic Intensity
Coseismic Deformation
Source Model: An’naka (2003)Uplift
Subsidence
-2 m
2 m
Recently Tsunami deposits during the 1707 Hoei Earthquake was observed at Ryujin pond (龍神池) by e.g. Okamura et al. (2004), indicating extension of source-rupture area to west.
Re-evaluation of the 1707 Hoei Earthquake Model
Uplift
Subsidence-2 m
2 m 津波池Tsunami Pond
写真
Photo: Courtesy from Prof. Okamura
龍神池
1707 Hoei1854 Ansei1896 Nankai
1361 Shohei684 Hakuho
Okamura (2008)
Re-evaluation of the 1707 Hoei Earthquake Model
1707 Hoei Earthquake model
龍神池
日向灘の固着
地震発生帯(固着域)の深さ
Hguga-nada Segment (M7.5)
Back-slip model from GPS data Nishimura et al. (1999)
Philippine-sea Plate Model Nakajima and Hasegawa (2007 ) We assume an additional
fault segment at Huganada based on new geological and seismological findings in order to explain crustal deformation and tsunami in eastern Kyushu
Geological TracingTsunami Depositse.g. Okamura (2008)
Kyushu
Re-evaluation of the 1707 Hoei Earthquake Model
(1) NEW Hoei model Tsunami Simulation
Height of tsunami at the Ryujim Pond from the new source model is 2 - 4 m which is twice larger than that for the previous Hoei source model. Moreover delayed rupture in the segment of Hguga-nada cause increase tsunami height over 6 m.
(1) NEW Hoei model with delayed rupture (14min)
Ground motion simulation for new Hoei Source Model
NEW Hoei Model (N5: Hyuga-nada)
1707 Hoei Model (An’naka, 2003)
20 cm/s
10 cm/s
50 cm/s
PGV
PGV
Simulated Ground Motion
20 cm/s
10 cm/s
50 cm/s
Miyazaki
New model (Hyuga-nada segment)
1707 Hoei Model
Simulation for the Nankai-trough Earthquake SUMMARY(1) Integrated simulation of ground motion and tsunami
- We developed an integrated simulation model for evaluatingstrong ground motions, coseismic deformations, and tsunami by combining FDM simulation of 3D equation of motions and 3D Navier-stokes equations.
- The new simulation model offers direct means for total understanding of complicated disasters due to the occurrence of the Nankai-trough earthquake consistently and accurately.
(2) Nankai-trough earthquake scenario
-We revised the source model for the 1707 Hoei earthquake to cover the rupture area to Hyuga-nada in order to explain coseismic deformation and tsunami deposits at Tsunami ponds at Kyushu.
-Expected tsunami and strong ground motion in eastern seaboard of Kyushu is 1.5-2 times larger than that we expected from the previous model.
Re-evaluation of the 1707 Hoei Earthquake Model
Tsunami propagation from the new Hoei model
Height of tsunami along the coast of Hyuga-nada using the new source model is about 2-4 m which is twice larger than the previous source model.