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Static stress changes--Coulomb. Coulomb theory. Hypothesis: Faults interact by the transfer of stress. WINCH. SPRING. BRICK. EARTHQUAKE! (only if stick-slip). Force Balance – Brick will not move until : Force on spring Force resisting motion - PowerPoint PPT Presentation
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Static stress changes--Coulomb
SPRING BRICKWINCH
Force Balance – Brick will not move until:
Force on spring Force resisting motion(its length change x its stiffness) (the weight of the brick x friction on surface)
Modeled after Ross Stein’s Coulomb Training I
Hypothesis: Faults interact by the transfer of stress
EARTHQUAKE! (only if stick-slip)
-Lisa Walsh
SPRING BRICKWINCH
Modeled after Ross Stein’s Coulomb Training I
BRICKSPRING
• Add another spring & brick• If you start cranking winch, PURPLE will move first. Then tension on spring will move GREEN.
EARTHQUAKE! EARTHQUAKE!
Source fault Receiver fault
= shear stress change + (coefficient of friction x normal stress change)
ΔCFS = Δτs+μ' Δσn
Coulomb stress calculationCoulomb
stress change
+ ΔCFS = closer to failure- ΔCFS = farther from failure
-Lisa Walsh
Key concepts:•Source faults•Receiver faults•Optimally oriented faults•Assume receiver faults are close to failure•Triggering lag time is a problem
Change of coulomb stress on faults of specified orientation
Can change spatiallyRemote: Sremote
Induced: Sinduced
Total:Sremote+Sinduced
Can change spatially
From King et al (BSSA, 1994)
From King et al (BSSA, 1994)
From King et al (BSSA, 1994)
Change of coulomb stress on faults of optimal orientation
from Todal et al (JGR, 2005)
from Todal et al (JGR, 2005)
from Todal et al (JGR, 2005)
from Todal et al (JGR, 2005)
Stress changes are permanent but seismicity is not
from Todal et al (JGR, 2005)
LosAngelesLosAngeles
Big Bear M = 6.5 (2nd - 3 hrs later)
Big Bear M = 6.5 (2nd - 3 hrs later)
Landers M = 7.3Landers M = 7.3(1(1stst))
First 3 hr of Landers
aftershocks
plotted
First 3 hr of Landers
aftershocks
plottedfrom Stein (Nature, 2003)
1992 - Landers earthquake triggered Big Bear earthquake 3 hrs later!
Stress trigger zone
Stress Shado
w
LosAngelesLosAngeles
Hector Mine Hector Mine
First 7 yr of
aftershocksplotted
First 7 yr of
aftershocksplotted
…and promotes the M=7.1 Hector Mine shock 7 years later (1999).
from Stein (Nature, 2003)
from Lin & Stein (JGR, 2004)
from Lin & Stein (JGR, 2004)
from Lin & Stein (JGR, 2004)
from Lin & Stein (JGR, 2004)
from Lin & Stein (JGR, 2004)
from Lin & Stein (JGR,
2004)
from Lin & Stein (JGR,
2004)
from Lin & Stein (JGR,
2004)
http://quake.usgs.gov/research/deformation/modeling/animations/index.html
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