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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gasa

war

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Nankai Trough

Hokkaido

Honshu

Shikoku

KyushuNankai 南海

EartuqiakeTokai

東海

Earthquak

e

Nanse

i-Sho

to　

Troug

h

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.