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24 October 2007 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,

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Presentation on theme: "24 October 2007 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,"— Presentation transcript:

1 24 October 2007 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)

2 24 October 2007 > 2 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

3 24 October 2007 > 3 略歴 > BRGM (仏・地質調査所): H. Modaressi 博士 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) > IRSN (仏・放射線防護原子力安全研究所): C. Berge-Thierry 博士 地震ハザード研究への応用 Aki & Richards 翻訳 > ENS Paris (パリ高等師範学校): R. Madariaga 教 授 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 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 地震活動のフラクタル解析

4 24 October 2007 > 4 対象となった論文 (a)Cruz-Atienza, V., J. Virieux and H. Aochi, 3D Finite-Difference Dynamic-Rupture Modelling Along Non- Planar Fault, Geophysics, 72, SM123-SM137, (b)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 /s , (c)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, , (d)Aochi, H., O. Scotti, and C. Berge-Thierry, 3D dynamic rupture propagation along complex segments with different mechanisms, Geophys. Res. Lett., 32, L21304, doi: /2005GL024158, (e)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, , (f)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, , (g)Aochi, H. and E. Fukuyama and R. Madariaga, Constraints of Fault Constitutive Parameters Inferred from Non-planar Fault Modeling, Geichemistry, Geophysics, Geosystems, 4(2), /2001GC000207, (h)Aochi, H., R. Madariaga and E. Fukuyama, Effect of Normal Stress During Rupture Propagation along Non-planar Fault, J. Geophys. Res., 107, /2001JB000500, (i)Aochi, H. and E. Fukuyama, Three-dimensional nonplanar simulation of the 1992 Landers earthquake, J. Geophys. Res., 107, /2000JB000061, (j)Aochi, H., E. Fukuyama and M. Matsu'ura, Selectivity of spontaneous rupture propagation on a branched fault, Geophys. Res. Lett., 27, , (k)Aochi, H., E. Fukuyama and M. Matsu'ura, Spontaneous Rupture Propagation on a Non-planar Fault in 3D Elastic Medium, Pure appl. Geophys., 157, , 2000.

5 24 October 2007 > 5 Cartography / Seismic Hazard Historical Earthquake Catalogue Seismic Hazard Map

6 24 October 2007 > 6 Objectives Understand geological phenomena, develop new methodologies and techniques, and produce and disseminate pertinent, high-quality data Provide public authorities with the necessary tools for drawing up policies for surface, subsurface and resource management, prevent natural risks and pollution, and regional development and planning Three roles Technological research and development and innovation Policy-marketing support and informing the public International cooperation and assistance in development Eight thematic areas Mineral resources Water Development planning and natural risks Contaminated land and waste management Environmental metrology Mapping and geoinformation Geothermal energy and geological storage of CO2 Digital information systems BRGM France's leading public institution involved in geoscience

7 24 October 2007 > 7 King and Nabelek (1985) 破壊の開始・停止 =地震のサイズ 屈曲・セグメント化 断層形状と地震破壊

8 24 October 2007 > 8 差分法 Harris and Day (1991, 93, 99) Kase and Kuge (1998, 2001) Magistrale and Day (1999) Cruz-Atienza et al. (2007) Harris and Day (1999) 境界条件の入れ方(断層形 状)が限られる。 数値研究例

9 24 October 2007 > 9 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) 境界積分法

10 24 October 2007 > Initial Condition Fault Geometry Tectonic Stress Rupture Criterion 2. Dynamic Rupture Propagation (BIEM) 3. Seismic wave Propagation (FDM) 4. Accelerogram Strategy of dynamic simulation Aochi and Fukuyama (JGR, 2002), Aochi et al. (G-cubed, 2003) The 1992 Landers, CA (M7.3) Aochi et al. (Pageoph, 2000)

11 24 October 2007 > Initial Condition Geometry, Stress, Friction, etc. 2. Dynamic Rupture 3. Wave Propagation Modelling Strategy Landers 1992 (M7.2) Eq. 4. Site Effect 5. Structure Response BIEM, FDM, FEM According to the objectives

12 24 October 2007 > 12 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。 1992年ランダース地震

13 24 October 2007 > 13 深さに依存する ‘Slip-weakning’ 構成則 すべり 剪断応力 Sibson (1982, 1984) Scholz (1988) Ohnaka (1992) Ide and Takeo (1997) 断層構成則(境界条件)

14 24 October 2007 > 14 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 テクトニクス(初期条件)

15 24 October 2007 > 15 Example 1 Tectonic stress 動的破壊シミュレーション(境界積分 法) Example 2 Tectonic stress + heterogeneity

16 24 October 2007 > 16 Fréquence Hz 地震動計算(波数積分法)

17 24 October 2007 > 17 1999年イズミット地震の断層モデル A: Seismic (Bouchon et al., 2002) B: GPS (Wright et al., 2001) C: SPOT images (Michel and Avouac, 2002) D: FDM simulation (Harris et al., 2002) E: Geological after Barka et al. Aochi & Madariaga (BSSA, 2003)

18 24 October 2007 > 18 Spontaneous Rupture Propagation The 1999 Izmit Earthquake Geometry simple Complex System embeded in uniform stress field so that hypocenter location is favorable Depth dependent slip-weakening law stable – unstable (brittle) – stable (ductile) Hydro-static confining pressure

19 24 October 2007 > 19 Source Parameters (simulations vs. inversions) Heterogeneity on fault Lateral = fault strike x local principal stress Vertical = depth-dependent friction law (absolute stress level) x free surface

20 24 October 2007 > 20 Seismic Wave Propagation during the 1999 Izmit Earthquake Rupture scenarios embedded in the FD simulation in the same 1D structure as Bouchon et al.(2002). From West to East Low-pass up to 1 Hz

21 24 October 2007 > 21 Geological Parameter (Surface Breaks) Watch « Tendance » & « Absolute Value »

22 24 October 2007 > 22 Remarks : which model is better? > Geometrical irregularities (bend/jog/step) localize fault slip and makes the rupture more complex (from Model A to D). > Near-field seismograms indicate a rapid and uniform rupture propagation in the eastern direction (smooth fault model, A & B), but a more complex process in the western direction (segmented somehow, B & C). > Geological traces match with segemented fault model (E) > Thus, in real, fault structure should be …

23 24 October 2007 > 23 中部 Durance 断層(フランス南東部)

24 24 October 2007 > 24 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 Characteristic Features What are Possible Earthquake Scenarios?

25 24 October 2007 > 25 After M. Rocher (IRSN/BERSSIN) Durance Compilation of Stress Field (geology, seismicity, in-situ measurements, …)

26 24 October 2007 > 26 Segmented Fault Model 5 Segments with different mechanisms SegLengthWidthStrikeDip 110 km8 km225°90° 215 km8 km200°80° 318 km8 km215°60° 412 km8 km230°45° 510 km8 km230°45° Tectonic Stress (uni-axiale)  1 = N160°E   Rigidity  29.6 GPa P-wave velocity5.8 km/s S-wave velocity3.35 km/s Grid size  s 500 m Time step  t 0.04 sec BIEM Param (infinite/homogeneous)

27 24 October 2007 > 27 Stress and Rupture Criterion Fixed param. Variable param. O  slip Shear stress =50cm cf. Aochi et al. (JGR, 2002)

28 24 October 2007 > 28 Probabilistic Approach Focal Mechanism (Baroux et al., 2001) Hypothesis (unknown)

29 24 October 2007 > 29 Simulations Results Condition 1.Tectonic Stress=N180E. 2.Low Absolute Stress. 3.Hypocenter on Seg 3. Probability=0.17% Results Ruptured Seg=4. Rupture Length=55km. Rupture Mode=bilateral Mw=6.92. rake=0° 4° 19° 40°

30 24 October 2007 > 30 Simulations Results Condition 1.Tectonic Stress=N160E. 2.Low Absolute Stress. 3.Hypocenter on Seg 4. Probability=4.55% Results Ruptured Seg=3. Rupture Length=45km. Rupture Mode=uni-lateral Mw=6.80. rake=8° 36° 63°

31 24 October 2007 > 31 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. rake=63°

32 24 October 2007 > 32 Results of Earthquake Scenarios Ruptured Seg Numbe r Freq.Prob. 500% 432% 31126% 231% 12044% 01326% Maximum event: 4 segment rupture Mw6.9 High possibility: Independent rupture on each segment, or 3 segment SN striking rupture

33 24 October 2007 > 33 Comparison between Segments Easiest segment to be ruptured Note: Initial stress is always the same on Seg 4 and 5.

34 24 October 2007 > 34 Rupture Directivity Note: No propagation between Seg 5 and the others is found. More favorable

35 24 October 2007 > 35 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。

36 24 October 2007 > 36 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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