Static stress changes--Coulomb

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## Static stress changes--Coulomb

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1. Static stress changes--Coulomb

2. 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 springForce 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 -Lisa Walsh

3. Coulomb theory Modeled after Ross Stein’s Coulomb Training I Source fault Receiver fault WINCH SPRING BRICK SPRING BRICK EARTHQUAKE! EARTHQUAKE! • Add another spring & brick • If you start cranking winch, PURPLEwill move first. • Then tension on spring will move GREEN. + ΔCFS = closer to failure - ΔCFS = farther from failure Coulomb stress calculation Coulomb stress change = shear stress change + (coefficient of friction x normal stress change) ΔCFS = Δτs+μ' Δσn -Lisa Walsh

4. Key concepts: • Source faults • Receiver faults • Optimally oriented faults • Assume receiver faults are close to failure • Triggering lag time is a problem

5. Change of coulomb stress on faults of specified orientation Can change spatially Remote: Sremote Induced: Sinduced Total:Sremote+Sinduced Can change spatially

6. From King et al (BSSA, 1994)

7. From King et al (BSSA, 1994)

8. From King et al (BSSA, 1994)

9. Change of coulomb stress on faults of optimal orientation

10. from Todal et al (JGR, 2005)

11. from Todal et al (JGR, 2005)

12. from Todal et al (JGR, 2005)

13. from Todal et al (JGR, 2005)

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

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

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

17. from Lin & Stein (JGR, 2004)

18. from Lin & Stein (JGR, 2004)

19. from Lin & Stein (JGR, 2004)

20. from Lin & Stein (JGR, 2004)

21. from Lin & Stein (JGR, 2004)

22. from Lin & Stein (JGR, 2004)

23. from Lin & Stein (JGR, 2004)

24. from Lin & Stein (JGR, 2004)

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