Transcript BRGM, France

３次元複雑断層系における地震発生過程の理論的研究
Theoretical study on earthquake generation process
in a 3D complex fault system
青地秀雄（仏・地質調査所）
Hideo Aochi (BRGM, France)
24 October 2007
本日の目次
> 簡単な紹介
> 問題設定とシミュレーション手法
> １９９２年ランダース地震
> 中部デュロンス断層帯（仏南東部）におけるシ
ナリオ地震
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略歴
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2004- BRGM （仏・地質調査所）：H. Modaressi博士
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力学的計算に基づく地震ハザード・リスク研究（有限要素法）
2003-2004 IRSN（仏・放射線防護原子力安全研究所）：C. BergeThierry 博士
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地震ハザード研究への応用
Aki & Richards 翻訳
2000-2003 ENS Paris （パリ高等師範学校）：R. Madariaga教授
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相互作用のある断層系における地震破壊過程の数値的研究
近地地震動の計算（差分法）
2000 東大院理（博士）:松浦充宏教授
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３次元複雑断層系における地震破壊過程の理論的研究（境界積分法）
断層構成則の研究
1995 東北大理（学士）：大竹政和・佐藤春夫教授
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地震活動のフラクタル解析
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対象となった論文
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Cruz-Atienza, V., J. Virieux and H. Aochi, 3D Finite-Difference Dynamic-Rupture Modelling Along NonPlanar Fault, Geophysics, 72, SM123-SM137, 2007.
Aochi, H. and J. Douglas, Testing the validity of simulated strong ground motion from the dynamic
rupture of a fault system, by using empirical equations, Bull. Earthq. Engineering, DOI
10.1007/s10518-006-0001-3, 2006.
Aochi, H., M. Cushing, O. Scotti, and C. Berge-Thierry, Estimating rupture scenario likelihood based
on dynamic rupture simulations: the example of the segmented Middle Durance fault, southeastern
France, Geophys. J. Int.,165, 436-446, 2006.
Aochi, H., O. Scotti, and C. Berge-Thierry, 3D dynamic rupture propagation along complex segments
with different mechanisms, Geophys. Res. Lett., 32, L21304, doi:10.1029/2005GL024158, 2005.
Aochi, H. and K. B. Olsen, On the effects of non-planar geometry for blind thrust faults on strong
ground motion, Pure appl. Geophys., 161, 2139-2153, 2004.
Aochi, H. and R. Madariaga, The 1999 Izmit, Turkey, earthquake: Non-planar fault structure, dynamic
rupture process and strong ground motion, Bull. Seism. Soc. Am., 93, 1249-1266, 2003.
Aochi, H. and E. Fukuyama and R. Madariaga, Constraints of Fault Constitutive Parameters Inferred
from Non-planar Fault Modeling, Geichemistry, Geophysics, Geosystems, 4(2),
10.1029/2001GC000207, 2003.
Aochi, H., R. Madariaga and E. Fukuyama, Effect of Normal Stress During Rupture Propagation along
Non-planar Fault, J. Geophys. Res., 107, 10.1029/2001JB000500, 2002.
Aochi, H. and E. Fukuyama, Three-dimensional nonplanar simulation of the 1992 Landers earthquake,
J. Geophys. Res., 107, 10.1029/2000JB000061, 2002.
Aochi, H., E. Fukuyama and M. Matsu'ura, Selectivity of spontaneous rupture propagation on a
branched fault, Geophys. Res. Lett., 27, 3635-3638, 2000.
Aochi, H., E. Fukuyama and M. Matsu'ura, Spontaneous Rupture Propagation on a Non-planar Fault
in 3D Elastic Medium, Pure appl. Geophys., 157, 2003-2027, 2000.
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断層形状と地震破壊
屈曲・セグメント化
破壊の開始・停止
＝地震のサイズ
King and Nabelek (1985)
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数値研究例
差分法
• Harris and Day (1991, 93, 99)
• Kase and Kuge (1998, 2001)
• Magistrale and Day (1999)
• Cruz-Atienza et al. (2007)
境界条件の入れ方（断層形状）
が限られる。
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Harris and Day (1999)
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境界積分法
• 無限均質弾性媒質のグリーン関数（解析解）
• 仮想反射震源をおくことにより自由表面を近似
• 解の精度
• 計算量がべき乗で増える
• 歴史
•2D anti-plaine …Cochard and Madariaga (1994)
•3D plaine … Fukuyama and Madariaga (1995)
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Strategy of dynamic simulation
1. Initial Condition
Fault Geometry
Tectonic Stress
Rupture Criterion
The 1992 Landers, CA (M7.3)
2. Dynamic Rupture Propagation (BIEM)
Aochi et al. (Pageoph, 2000)
3. Seismic wave Propagation (FDM)
4. Accelerogram
Aochi and Fukuyama (JGR, 2002), Aochi et al. (G-cubed, 2003)
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Modelling Strategy
1. Initial Condition
Geometry, Stress, Friction, etc.
Landers 1992 (M7.2) Eq.
BIEM, FDM, FEM
According to the objectives
2. Dynamic Rupture
3. Wave Propagation
4. Site Effect
5. Structure Response
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１９９２年ランダース地震
地表断層トレース
(Hart et al., 1993)
古地震の研究
(Rockwell et al., 2000)
• Kickapoo 小断層は過去に存
在した。
• 同時代に各断層が前回破壊
した。
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断層構成則（境界条件）
深さに依存する‘Slip-weakning’ 構成則
Sibson (1982, 1984)
Scholz (1988)
Ohnaka (1992)
Ide and Takeo (1997)
剪断応力
p
0
r
Dc
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すべり
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テクトニクス（初期条件）
テクトニクスモデル
Unruh et al. (1994)
テクトニクス応力のシステム
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動的破壊シミュレーション（境界積分法）
Example 1
Tectonic stress
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Example 2
Tectonic stress + heterogeneity
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地震動計算（波数積分法）
Fréquence
0.07-0.5Hz
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中部Durance断層（フランス南東部）
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Characteristic Features
1. Moderate Seismicity
2. Repeated Historical Earthquake
(M5-5.3, since 1509 every 100y)
3. Paleoseismological large earthquake (M=7)
One of the most important region for seismic risk
assessment in France
What are Possible Earthquake Scenarios?
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Compilation of Stress Field
(geology, seismicity, in-situ measurements, …)
After M. Rocher
(IRSN/BERSSIN)
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Durance
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Segmented Fault Model
5 Segments with different mechanisms
Seg
1
2
3
4
5
Length
10 km
15 km
18 km
12 km
10 km
Width
8 km
8 km
8 km
8 km
8 km
Strike
225°
200°
215°
230°
230°
Dip
90°
80°
60°
45°
45°
BIEM Param
(infinite/homogeneous)
Tectonic Stress (uni-axiale)
s1 = N160°E  a
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Rigidity m
P-wave velocity
S-wave velocity
Grid size Ds
Time step Dt
29.6 GPa
5.8 km/s
3.35 km/s
500 m
0.04 sec
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Stress and Rupture Criterion
Fixed param.

0 p
r
Shear stress
p
0
r
Variable param.

O
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D c =50cm slip
cf.
Aochi et al. (JGR, 2002)
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Probabilistic Approach
Hypothesis (unknown)
Focal Mechanism (Baroux et al., 2001)
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Simulations Results
Condition
1. Tectonic Stress=N180E.
2. Low Absolute Stress.
3. Hypocenter on Seg 3.
Probability=0.17%
rake=0°
4°
Results
• Ruptured Seg=4.
• Rupture Length=55km.
• Rupture Mode=bilateral
• Mw=6.92.
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19°
40°
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Simulations Results
Condition
1. Tectonic Stress=N160E.
2. Low Absolute Stress.
3. Hypocenter on Seg 4.
Probability=4.55%
rake=8°
Results
• Ruptured Seg=3.
• Rupture Length=45km.
• Rupture Mode=uni-lateral
• Mw=6.80.
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36°
63°
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Simulations Results
Condition
1. Tectonic Stress=N180E.
2. Low Absolute Stress.
3. Hypocenter on Seg 5.
Probability=4.55%
Results
• Ruptured Seg=1.
• Rupture Length=10km.
• Rupture Mode=single
• Mw=6.32.
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rake=63°
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Results of Earthquake Scenarios
Ruptured
Seg
Numbe
r
5
4
3
2
1
0
Freq.
Prob.
0
3
11
3
20
13
0%
2%
26%
1%
44%
26%
Maximum event:
4 segment rupture
Mw6.9
High possibility:
Independent rupture
on each segment, or
3 segment SN striking
rupture
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Comparison between Segments
Easiest segment to be ruptured
Note: Initial stress
is always the same
on Seg 4 and 5.
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Rupture Directivity
More favorable
Note: No propagation
between Seg 5 and
the others is found.
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まとめ
> 断層構造の複雑さをシミュレーションし、地震破壊
過程を３次元で議論することに成功した。
> マクロな断層構造が、破壊の進行方向、アスペリテ
ィーを支配することを実際の地震のシミュレーション
から明らかにした。
> これらの知見は地震ハザード研究へ応用される。
> より一層、実際に近い状況（周辺構造の複雑さ）で
モデル化されることが望まれる。
> より一層の実際の地震の例を検証する必要がある。
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謝辞
> Thanks for the director of my theses, all my
colleagues and friends I met.
> Thanks for all the professional opportunities I
got mainly in Japan and France.
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