What controls the timing of earthquakes? 何が地震が起こるときを決めているか？

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# What controls the timing of earthquakes? 何が地震が起こるときを決めているか？ - PowerPoint PPT Presentation

What controls the timing of earthquakes? 何が地震が起こるときを決めているか？.

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What controls the timing of earthquakes?何が地震が起こるときを決めているか？

Earthquake Cycle　地震のサイクル（繰り返し) time-predictable model　時間が予測できるモデル slip-predictable model　　すべり量が予測できるモデルCoulomb failure function 　クーロン破壊関数Rate and State friction 　速度および状態依存性摩擦Plate coupling　プレートのカップリングBack-slip modeling　バックスリップによるモデル Slow earthquakes 　ゆっくり地震GPS

Earthquake Cycle

Tohoku

Parkfield, California

Periodic Time-predicatable Slip-predicatable

等間隔　　　　　地震の時刻が予測できる　地震のすべり量が予測できる

Shimazaki and Nakata, 1980

Shimazaki and Nakata, 1980

To understand (predict) occurrence of earthquakes in earthquake cycle地震の繰り返しの中で地震の起こるときを知る（予測する）には1. Stress level that earthquakes occur地震が起こる応力の値2. Current level of stress accumulation現在既に蓄積している応力の値

Coulomb Failure Criterionクーロン破壊基準（Navier-Coulomb, Coulomb-Mohr)

Coulomb Fracture Criterion

クーロン破壊基準

Change of Coulomb Fracture Criterion

クーロン破壊基準の変化

Rate and State Friction Law

Dieterich, 1979, Ruina, 1983

‘a-b’

a-b usually < 0

a-b > 0 → stable sliding

Dc

Vo

Dc

Dc

Friction Laws　摩擦則

Slip weakening　すべり弱化

Rate Dependent　速度依存

Rate and State Dependent　速度および状態依存

Ohnaka　大中

Coulombクーロン

Rate and State Friction速度および状態依存摩擦

Coulomb Criterion

クーロン基準

Rate and State

Toda et al., 2002

Global Positioning System - GPS- Measure displacement field 変位場を測定する → strain field → stress fieldひずみ場　　　　　　応力場- Detect Slow Slip Events (Silent Earthquakes)ゆっくり地震（サイレンス地震）をみつける

GPS 24 satellite configuration

http://scign.jpl.nasa.gov/learn/gps1.htm

Satellite Position人工衛星の位置

• Range領域
• >4 Satellites → Receiver Postion
• ４つ以上の衛星で、受信機の位置がわかる

Continuous GPS Stations

GeoNet

(GSI)

993 sta.

ひずみ速度

Dilatational Strain Rate

1996 - 2002

‘Coupling’　　　　　　　　　　　　　　カップリングCoupling = seismic slip/ plate rateカップリング＝地震によるすべり量/プレートの相対移動量

‘Coupling’カップリングCoupling = seismic slip/ plate rateカップリング＝地震によるすべり量/プレートの相対移動量Nankai 南海　~ 100% Tohoku 東北　~ 60-70% Kyushu 九州　~ 10-20% (?)

‘Back-slip’ or ‘Slip Deficit’

バックスリップ　すべり欠損

Matsu-ura and

Sato, 1989

Tokai Slow Slip

2000 - present

Mo = μ(slip)(area)

Mw = (log(Mo) –16.1)/1.5

Slip modeling by Nagoya Univ.

What controls the timing of earthquakes?何が地震の起こるときを決めているか？- Build-up of stress (earthquake cycle)応力の蓄積（地震の繰り返し)- Level of stress depends on the plate (strain) rate and the seismic coupling応力値はプレートの（ひずみ）速度と　　それが地震の発生に関与する割合（カップリング）- Earthquakes occur at some critical stress level (e.g. Coulomb failure, Rate and State) 地震はある臨界状態で起こる（例えばクーロン破壊や速度および状態依存摩擦）But, there are probably other types of triggering effectsしかし、たぶん、他の要素でも地震の発生は誘発されている

References

Dieterich, J.H., Modeling of rock friction, 1. Experimental results and constitutive equations,

J. Geophys. Res., 84, 2161-2168, 1979.

King, G.C.P., R.S. Stein, J. Lin, Static stress changes and triggering of earthquakes, Bull.

Seismol. Soc. Am., 935-953, 1994.

Matsu-ura. M. and T. Sato, Dislocation model for the earthquake cycle at convergent

Plate boundaries, Geophys. J. Int., 96, 23-32, 1989.

Ruina, A.L., Slip instability and state-variable friction laws, J. Geophys. Res., 86,

10,359-10,370, 1983.

Sagiya, T., Interplate coupling in the Tokai District, central Japan, deduced from continuous

GPS Data, Geophys. Res. Lett., 26, 2315-2318, 1999

Scholz, C.H., The mechanics of earthquakes and faulting, 2nd Edition, Cambridge Univ. Press,

2002.

Shimazaki, K. and T. Nagata, Time predictable recurrence model for large earthquakes,

Geophys. Res. Lett., 7, 279-282, 1980.

Toda, S. R. S. Stein, T. Sagiya, Evidence from the AD2000 Izu Islands earthquake swarm that

Stress rates govern seismicity, Nature, 419, 58-61, 2002.