JMA seismicity at several remote sites during March 7-13 reveals seismicity rate jumps followed by decays at many sites up to 3 km from the M=9. mainshock rupture 5 3 1 1 M 1 JMA catalog rev March 7 - March 13 11.17 11.18 11.19 11. M 15 39 Cumulative number of earthquakes 1 5 11.17 5 35 3 5 15 1 3 11.18 11.19 11. M 38 37 36 35 1 M8. (M9.) 5 11.17 11.18 11.19 11. 3 3 M 33 15 1 5 136 137 138 139 1 11 1 13 1 11.17 11.18 11.19 11. Time (year) Shinji Toda (DPRI, Kyoto University) 16 March 11
Coulomb stress imparted by the 11 March 11 Off-Tohoku Earthquake to Northern Honshu by regional tectonic setting: Many fault groups are brought closer to failure friction μ Coulomb Stress Change (ΔCFF) A 38 36 3 B D C E A F 136 138 1 1 1 Stress calculated at 1.5 km depth, Yagi Yuji source model v.
The 11 Mar 11 M=9. Off-Tohoku rupture and its aftershock stresses many major faults and portinos of megathrusts friction μ =. friction μ =.8 (km) 5 1 15 6 Coulomb stress change -1.. 1. bar M 9. km) 5 1 15 Coulomb stress change -1.. 1. bar M 9. Yagi Yuji s source model v. M 7.9 6 M 7.9 6 5 3 1 1 3 km 6 km 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.5-1. bar closer to failure (orange-red) Shinji Toda (DPRI, Kyoto Univ.), Ross Stein & Volkan Sevilgen (USGS), 18 Mar 11 :3 PM PDT
Coulomb stress imparted by the M=9. Off-Tohoku rupture and its aftershock to Japan Trench, Sagami Trough and Kanto Fragment 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 Remote M=6.6 aftershock (11 Mar 196 UTC) Increased hazard Decreased hazard 1..8.6.. bar...6.8 1. Suruga trough megathrust ( Tokai gap ) Kanto fragment Z (km) 5 1 15 M=9. Unruptured megathrust 3 Sagami trough megathrust Southern edge of rupture 3 5 Yuji Yagi s source version assumed fault friction =. Fault rake vectors are blue 1 km 1 3 3 1 km 1 Animation of and reference for the Kanto fragment: Toda, Stein, Kirby & Bozkurt, Nature Geoscience, 8 http://www.usgsprojects.org/fragment/ Ross Stein & Volkan Sevilgen (USGS) and Shinji Toda (DPRI, Kyoto Univ.) 18 Mar 11 :15 PM PDT
Vertical dikes presumed to feed active volcanoes are strongly unclamped 3 1 39 Unclamping stress on vertical dikes striking (bars) 1 8 6 6 8 1 38 37 36 Volcanoes 35 3 Coulomb 3..1 16 Mar 11 19:1:1 yagi_m79_ashock.inp Specified planes: strike=, Dip=9 Depth: 15. km 33 136 137 138 139 1 11 1 13 1 15 Ross Stein & Volkan Sevilgen (USGS), Shinji Toda (Kyoto Univ.) rstein@usgs.gov 16 Mar 11 8:3 PM PDT
Spherical magma chambers beneath active volcanoes are strongly dilated 3 Dilatation (x 1 5) 1..8.6 1..... 39.6.8 38 1. 37 36 Volcanoes 35 3 Coulomb 3..1 16 Mar 11 19:7:1 yagi_m79_ashock.inp Strain calc. Depth: 15. km 33 136 137 138 139 1 11 1 13 1 15 Ross Stein & Volkan Sevilgen (USGS), Shinji Toda (Kyoto Univ.) rstein@usgs.gov 16 Mar 11 8:3 PM PDT
Testing the Coulomb hypothesis and earthquake source model on nodal planes of the CMT aftershocks during 11-16 March 11 67% of nodal planes were brought closer to failure by the M=9. mainshock and its aftershock (compared to 53% of 1977-11 pre-mainshock CMTs, the control population) Nodal plane 1 Nodal plane Hashinohe Hashinohe M=9. M=9. Mito Iwaki Outer rise normal mechanisms Mito Iwaki Outer rise normal mechanisms Note: The nodal plane numbering is arbitrary; either could be the fault Yagi Yuji s v. source model used CMT_aftershocks_to_11316.ndk PDE locations of Global CMTs used Coulomb stress change (bar) on earthqake nodal planes Ross Stein & Volkan Sevilgen (USGS), Meredith Nettles (Columbia Univ.), and Shinji Toda (Kyoto Univ.) rstein@usgs.gov 18 Mar 11 :3 PM PDT
This is the control test of Coulomb stress enhancement of the 3 aftershocks with CMT solutions The control population consists of 66 CMT events from 1977 until just before the M=9. earthquake 53% of nodal planes were brought closer to failure by the M=9. mainshock and its aftershock (compared to about 67% after the mainshshock) Nodal plane 1 Nodal plane Hashinohe Hashinohe M=9. M=9. Iwaki Iwaki Mito Mito Note: The nodal plane numbering is arbitrary; either could be the fault Yagi Yuji s v. source model used CMT_events_to_1131.ndk PDE locations of Global CMTs used Color scale (bar) for earthqake dots Volkan Sevilgen & Ross Stein (USGS), Meredith Nettles (Columbia Univ.), and Shinji Toda (Kyoto Univ.) rstein@usgs.gov 18 Mar 11 6:5 PM PDT
Here we used earthquake focal mechanisms during the preceding decade as proxies for active faults One sees that despite a nominal stress shadow cast over northern Honshu, the faulting is so diverse that many faults are likely brought closer to failure μ