Static stress changes-Coulomb
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
(its length change x its stiffness)
-Lisa Walsh
Force resisting motion
(the weight of the brick x friction on surface)
Modeled after Ross Stein’s Coulomb Training I
Modeled after Ross Stein’s Coulomb Training I
Source fault
WINCH
SPRING
BRICK
Receiver fault
SPRING
EARTHQUAKE!
• Add another spring & brick
• If you start cranking winch, PURPLE will move first.
Then tension on spring will move GREEN.
BRICK
EARTHQUAKE!
+ ΔCFS = closer to failure
- ΔCFS = farther from failure
Coulomb stress calculation
Coulomb
= shear stress change + (coefficient of friction x normal stress change)
stress change
-Lisa Walsh
ΔCFS = Δτs+μ' Δσn
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 spatially
Remote: 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)
Stress
Shadow
Big Bear M = 6.5
(2nd - 3 hrs later)
Los
Angeles
from Stein
(Nature, 2003)
Stress
trigger
zone
Landers M = 7.3
(1st)
First 3 hr of
Landers
aftershocks
plotted
1992 - Landers earthquake triggered Big Bear earthquake 3 hrs later!
Hector
Mine
Los
Angeles
from Stein
(Nature, 2003)
First 7 yr of
aftershocks
plotted
…and promotes the M=7.1 Hector Mine shock 7 years later (1999).
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