Earthquake Static Stress Transfer
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The document discusses the Coulomb stress hypothesis which proposes that earthquakes interact by transferring stress. It uses an example of a spring, brick, and winch to model how adding stress to one fault can cause it to fail and transfer stress to trigger a nearby fault. The key concept is that changes in Coulomb stress can bring optimally oriented receiver faults closer to or further from failure. Several earthquake examples from California are presented showing how one earthquake appears to have triggered subsequent quakes by elevating stress in certain areas.
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Earthquake Static Stress Transfer
- 1. Static stress changes-- Coulomb
- 2. 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 (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. Source fault Receiver fault WINCH SPRING BRICK Modeled after Ross Stein’s Coulomb Training I SPRING BRICK EARTHQUAKE! EARTHQUAKE! • Add another spring & brick • If you start cranking winch, PURPLE will move first. Then tension on spring will move GREEN. Coulomb stress calculation = shear stress change + (coefficient of friction x normal stress change) ΔCFS = Δτs+μ' Δσn Coulomb stress change + ΔCFS = closer to failure - ΔCFS = farther from failure -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. Los Angeles Big Bear M = 6.5 (2nd - 3 hrs later) LLaannddeerrss MM == 77..33 ((11sstt)) First 3 hr of Landers aftershocks from Stein (Nature, 2003) plotted 1992 - Landers earthquake triggered Big Bear earthquake 3 hrs later! Stress trigger zone Stress Shadow
- 16. Los Angeles Hector Mine 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)
Editor's Notes
- Coulomb theory is based on the hypothesis that faults interact by the transfer of stress. This can be understood simply by thinking about stress transferred between a brick and spring. If you have a winch winding up the spring, the brick will not move until it exceeds the “force balance” or equilibrium between the force on the spring (its length change x its stiffness) and the force resisting motion (the weight of the brick x friction on the surface). Once the force of the spring is great enough, the brick will zip forward, spring will relax. This is like what happens when we have an earthquake! Then you just have to wait another couple 100 years for the winch to keep winding, stress to accumulate and another earthquake to occur. Until we get to force balance, brick will just sit there. Once we get to equilibrium (or just past) brick will zip forward, spring will relax, causing an earthquake! Then we will wait another couple 100 years for winch to keep winding, stress to accumulate and another earthquake to happen again.
- If you add another spring and brick and start cranking the winch, the BLUE brick will move first, then tension will move the red brick. This is like the what happens with stress is transferred from one fault to another. For example, you could think of a long strike slip system as a series of adjacent bricks and springs. Transfer of Coulomb stress from one fault to another Release of stress from fault plane with earthquake will transfer stress to another fault Example: Long strike slip fault system = series of adjacent bricks and springs This is as complex as Coulomb thinking gets!
- Stresses affect very little of the area
- Stresses affect very little of the area
- Trigger lobes are large & continuous, but you’ve seen that seismicity is blotchy (aftershocks do not fill red zones): why?
- Stress changes are permanent but seismic response is not. How do we go from stress change to seismicity?
- STEIN quake prediction in magazine- MAGNITUDE 7.3 SHOCK in the southern California desert near Landers in 1992 increased the expected rate of earthquakes to the southwest, where the magnitude 6.5 Big Bear shock struck three hours later (top). Stresses imparted by the combination of the Landers and Big Bear events coincided with the regions where the vast majority of tremors occurred over the next seven years, culminating with the magnitude 7.1 Hector Mine quake in 1999 (bottom).
- Figure 5 (a) The Landers and Joshua Tree earthquakes increased Coulomb stress (red regions) where the Big Bear earthquake occurred three hours later. Coulomb stress calculations in (a) are for left-lateral strike-slip faults aligned with the Big Bear rupture surface. (b) Stress changes induced by the Joshua Tree, Landers, and Big Bear earthquakes increased Coulomb stress in regions where the vast majority of aftershocks occurred over the next seven years, culminating in the 1999 Hector Mine earthquake. Coulomb stress calculations in (b) are for right-lateral strike-slip faults aligned with the Hector Mine rupture surface (also reasonable for most aftershocks in the region).