# Static stress changes-- Coulomb. SPRINGBRICKWINCH Force Balance – Brick will not move until: Force on spring Force resisting motion (its length change.

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Static stress changes-- Coulomb

SPRINGBRICKWINCH 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

SPRINGBRICKWINCH 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! Source fault Receiver fault = shear stress change + (coefficient of friction x normal stress change) ΔCFS = Δτ s +μ' Δσ n Coulomb stress calculation Coulomb 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 spatially Remote: Sremote Induced: Sinduced Total:Sremote+Sinduced Can change spatially

From King et al (BSSA, 1994)

Change of coulomb stress on faults of optimal orientation

from Todal et al (JGR, 2005)

Stress changes are permanent but seismicity is not from Todal et al (JGR, 2005)

Los Angeles Los Angeles Big Bear M = 6.5 (2 nd - 3 hrs later) Landers M = 7.3 Landers M = 7.3 (1 st ) First 3 hr of Landers aftershocks plotted First 3 hr of Landers aftershocks plotted from Stein (Nature, 2003) 1992 - Landers earthquake triggered Big Bear earthquake 3 hrs later! Stress trigger zone Stress Shadow

Los Angeles Los Angeles Hector Mine First 7 yr of aftershocks plotted First 7 yr of aftershocks plotted …and promotes the M=7.1 Hector Mine shock 7 years later (1999). from Stein (Nature, 2003)

from Lin & Stein (JGR, 2004)

http://quake.usgs.gov/research/deformation/modeling/animations/index.html

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