136 137 138 139 140 141 142 143 144 33 34 35 36 37 38 39 40 41 42 東北地域太平洋沖地震 謝辞：3/15に気象庁HPから暫定震源リストを使用させていただきました．
東北地方太平洋沖地震にともなって地震活動が活発化した可能性がある地域の例
2011年３月16日 京都大学防災研究所 遠田晋次1
1
2
2
4
4
3
3
JMA catalog rev
March 07 - March 13
0 10 20 30 40 50 50 100 150 200 0 0 0 2011.17 2011.17 2011.18 2011.19 2011.20 2011.18 2011.19 2011.20 2011.17 2011.18 2011.19 2011.20 2011.17 2011.18 Time (year) 2011.19 2011.20 50 100 150 200 250 300 350 400 450 50 100 150 200 累積地震数 累積地震数M8.4
(M9.0)
M 0 2 4 M 0 2 4 M 0 2 4 M 0 2 4JMA seismicity at several remote sites during March 7-13 reveals seismicity rate jumps
followed by decays at many sites up to 300 km from the M=9.0 mainshock rupture
Shinji Toda (DPRI, Kyoto University) 16 March 2011
Receievr faults 0°/45°/90°
A
A
F
B
C
D
E
136°
138°
140°
142°
144°
34°
36°
38°
40°
42°
Coulomb Stress
Change (ΔCFF)
1.0 bar MPa 0.0 -1.0 0.1 0.0 -0.1 レシーバ断層 （応力を計算する 断層面とすべりの向き） Okada (1992)の半無限弾性体 ポアソン比: 0.25剛性率: 3.2E5 bar (32GPa) 計算深度： 12.5 km friction μ =0.4
Assumed fault geometry (strike range/dip/rake) 地域：走向/傾斜/レイク A: 356°-35°/40°-55°/90° 165°-215°/40°-55°/90° B: 50°-65°/90°/180° 120°-160°/90°/0° C: 300°-330°/40°-55°/120° 120°-150°/40°-55°/120° D: 15°-60°/30°-45°/90° 195°-240°/30°-45°/90° E: 355°-25°/90°/0° 95°-125°/90°/180° F: 0°-35°/45°-60°/-90° (outer rise normal faults) 上記範囲の計算において 最大値をピックアップ
Stress calculated at 12.5 km depth, Yagi Yuji source model v. 2
Coulomb stress imparted by the 11 March 2011 Off-Tohoku Earthquake to Northern
Honshu by regional tectonic setting: Many fault groups are brought closer to failure
震源断層
モ
デ
ル
八木
（
2011, ver
.2
）
震源断層
モ
デ
ル
八木
（
2011, ver
.2
）
東北地方太平洋沖地震にともなう周辺地殻浅部（12.5km）に分布する断層へのクーロン応力変化
灰色実線により地域を区分した．それぞれの地域で不確定性を考慮して複数パターンを計算し，最大値を表示．
A：北海道・東北・信越地域の逆断層，B：中部地域の横ずれ断層，C：西関東∼房総の斜めずれ断層，D：東海地
域の逆断層，E：伊豆半島∼伊豆諸島の横ずれ断層，F：太平洋プレート内の正断層（アウターライズ型）．緑線は
活断層分布（活断層研究会，1991），灰色線は地域区分境界を示す．
謝辞：つくば大学八木勇治准教授には同地震の震源断層モデルを提供いただいた． 2011年３月16日 京都大学防災研究所 遠田晋次−600 −500 −400 −300 −200 −100 0 100 200 300 km −400 −200 0 200 400 600 150 100 50 0 深さ (km) Depth (km) −600 −400 −200 0 km 200 −400 −200 0 200 400 600 150 100 50 0
ISTL
Suruga TroughM 9.0
M 7.9M 9.0
M 7.9 東海 東南海 南海 相模トラフ 上町断層 糸静線 中央構造線 八木（2011） 震源断層モデル Tokyo Sendaifriction
μ
’=0.8
friction
μ
’=0.4
The 11 Mar 2011 M=9.0 Off-Tohoku rupture and its M=7.9 aftershock stresses many major faults and portinos of megathrusts
Shinji Toda (DPRI, Kyoto Univ.), Ross Stein & Volkan Sevilgen (USGS), 18 Mar 2011 4:30 PM PDT
Yagi Yuji’s source model v.2
Coulomb stress change
1.0 bar 0.0
-1.0
応力変化
Most Tohoku-Chubu district reverse faults fall under a stress shadow (blue), but many major faults in southwest Japan,
including the Itoigawa-Shizuoka Tectonic Line (ISTL), are brought 0.5-1.0 bar closer to failure (orange-red)
Coulomb stress change
0.0 1.0 bar−400 −300 −200 −100 100 200 300 −400 −300 −200 −100 0 km 0 km 100 200 300 400 500 −150 −100 −50 0 Z (km)
Tokyo
Kanto fragment Sagami trough megathrust Suruga trough megathrust (’Tokai gap’) Remote M=6.6 aftershock (11 Mar 1946 UTC) Unruptur ed mega thrust Southern edge of ruptur eCoulomb stress imparted by the M=9.0 Off-Tohoku rupture and its M=7.9 aftershock to Japan Trench, Sagami Trough and Kanto Fragment
Ross Stein & Volkan Sevilgen (USGS) and Shinji Toda (DPRI, Kyoto Univ.) 18 Mar 2011 4:15 PM PDT
Most of Sagami trough is brought farther from failure, but basal surface of Kanto
fragment—possible source of 1855 M~7.3 Ansei-Edo quake—is stressed
−1.0 −0.8 −0.6 −0.4 −0.2 0 bar 0.2 0.4 0.6 0.8 1.0 Increased hazard Decreased hazard
Yuji Yagi’s source version 2
assumed fault friction = 0.4
Fault rake vectors are blue
Animation of and
reference for the Kanto
fragment: Toda, Stein, Kirby &
Bozkurt, Nature Geoscience, 2008
http://www.usgsprojects.org/fragment/
Sendai
M=9.0
M=7.9
Coulomb 3.2.01 16−Mar−2011 19:21:14 yagi2_M79_ashock.inp Specified planes: strike=20, Dip=90 Depth: 15.00 km
136 137 138 139 140 141 142 143 144 145 33 34 35 36 37 38 39 40 41 42 43
Unclamping stress
on vertical dikes
striking 20°
(bars)
−10
−8
−6
−4
−2
0
2
4
6
8
10
Vertical dikes presumed to feed active volcanoes are strongly unclamped
Ross Stein & Volkan Sevilgen (USGS), Shinji Toda (Kyoto Univ.) [email protected] 16 Mar 2011 8:30 PM PDT
Coulomb 3.2.01 16−Mar−2011 19:27:21 yagi2_M79_ashock.inp Strain calc. Depth: 15.00 km
136 137 138 139 140 141 142 143 144 145 33 34 35 36 37 38 39 40 41 42 43
−1.0
−0.8
−0.6
−0.4
−0.2
0.0
0.2
0.4
0.6
0.8
1.0
Dilatation (x 10 )
−5
Spherical magma chambers beneath active volcanoes are strongly dilated
Volcanoes
67% of nodal planes were brought closer to failure by the M=9.0 mainshock and its M=7.9 aftershock (compared to 53% of 1977-2011 pre-mainshock CMTs, the control population)
Nodal plane 1
Note: The nodal plane numbering is arbitrary; either could be the fault
Nodal plane 2
M=7.9
M=7.9
M=9.0
M=9.0
Testing the Coulomb hypothesis and earthquake source model on nodal planes of the 44 CMT aftershocks during 11-16 March 2011
Ross Stein & Volkan Sevilgen (USGS), Meredith Nettles (Columbia Univ.), and Shinji Toda (Kyoto Univ.) [email protected] 18 Mar 2011 4:30 PM PDT
Tokyo
Tokyo
Sendai Mito Iwaki Hashinohe Hashinohe Iwaki Mito Sendai Outer rise normal mechanisms Outer rise normal mechanismsYagi Yuji’s v. 2 source model used CMT_aftershocks_to_20110316.ndk PDE locations of Global CMTs used
53% of nodal planes were brought closer to failure by the M=9.0 mainshock and its M=7.9 aftershock (compared to about 67% after the mainshshock)
Nodal plane 1
Note: The nodal plane numbering is arbitrary; either could be the fault
Nodal plane 2
M=7.9
M=7.9
M=9.0
M=9.0
This is the control test of Coulomb stress enhancement of the 43 aftershocks with CMT solutions
The control population consists of 626 CMT events from 1977 until just before the M=9.0 earthquake
Volkan Sevilgen & Ross Stein (USGS), Meredith Nettles (Columbia Univ.), and Shinji Toda (Kyoto Univ.) [email protected] 18 Mar 2011 6:05 PM PDT
Tokyo
Tokyo
Sendai Mito Iwaki Hashinohe Hashinohe Iwaki Mito SendaiYagi Yuji’s v. 2 source model used CMT_events_to_20110310.ndk PDE locations of Global CMTs used
