Stress III

1. Stress III • The domino effect • Stress transfer and the Coulomb Failure Function • Aftershocks • Dynamic triggering • Volcano-seismic coupling

2. Stress III: The domino effect Example from California: Figure from www.earthquakecountry.info

3. Stress III: The domino effect Example from the North Anatolia Fault (NAF): Figure from Stein et al., 1997

4. Stress III: The Coulomb Failure Function Slip on faults modifies the stress field: Animation from the USGS site

5. Stress III: The effect of a stress step Stresses in the crust may change slowly due to the steady plate motion, and may change abruptly due to earthquakes, volcanic activity and other more. steady plate motion stress abrupt perturbations time

6. Stress III: The effect of a stress step The effect of a stress perturbation is to modify the timing of the failure according to: That means that the amount of time advance (or delay) is independent of when in the cycle the stress is applied.

7. Stress III: The Coulomb Failure Function A function that measures the enhancement of the failure on a given plane due to a stress perturbation is the Coulomb Failure Function (CFF): where: S is the shear stress (- positive in the direction of slip) N is the normal stress (- positive in compression) M is the coefficient of friction Failure on the plane in question is enhanced if CFF is positive, and is delayed if it is negative.

8. Stress III: The Coulomb Failure Function The figures above show the change in the fault-parallel shear stress and fault-perpendicular normal stress, due to right-lateral slip along a dislocation embedded in an infinite elastic medium

9. Stress III: The Coulomb Failure Function

10. Stress III: The Coulomb Failure Function The area affected by the stress perturbation scales with the rupture dimensions. The change in CFF due to the eight largest earthquakes of the 20th century. Alaska, 1964, Mw9.2 Chile, 1969, Mw9.5 Figure from: legacy.ingv.it/~roma/attivita/fisicainterno/modelli/struttureattive

11. Stress III: The Coulomb Failure Function Example from NAF Animations from the USGS site

12. Stress III: Stress shadows The 1906 Great California stress shadow: Stein, 2002 So the CFF concept works not only for positive, but also for negative stress change.

13. Stress III: Multiple stress transfers - The Landers and Hector Mine example Maps of static stress changes suggest that the Landers earthquake did not increase the static stress at the site of the Hector Mine rupture, and that Hector Mine ruptured within a “stress shadow”. Kilb, 2003

14. Stress III: Multiple stress transfers - The Landers and Hector Mine example This map shows the change in CFF caused by the Landers quake on optimally oriented planes at 6km depth. The arrows point to the northern and southern ends of the mapped surface rupture. Figure downloaded from www.seismo.unr.edu/htdocs/WGB/Recent.old/HectorMine

15. Stress III: Multiple stress transfers - The Landers and Hector Mine example • Most Landers aftershocks in the rupture region of the Hector Mine were not directly triggered by the Landers quake, but are secondary aftershocks triggered by the M 5.4 Pisgah aftershock. • The Hector Mine quake is, therefore, likely to be an aftershock of the Pisgah aftershock and its aftershocks. Felzer et al., 2002

16. Stress III: Aftershock triggering Maps of CFF calculated following major earthquakes show a strong tendency for aftershocks to occur in regions of positive CFF. The Landers earthquake (CA): King and Cocco (2000); Stein et al., 1992.

17. Stress III: Aftershock triggering The Homestead earthquake (CA): King and Cocco (2000).

18. Stress III: Remote aftershock triggering Ziv, 2006

19. Stress III: Remote aftershock triggering The Mw7.4 Izmit (Turkey): Mw5.8 Two weeks later

20. Stress III: Remote aftershock triggering The decay of M7.4 Izmit aftershocks throughout Greece is very similar to the decay of M5.8 Athens aftershocks in Athens area (just multiply the vertical axis by 2).

21. Stress III: Dynamic triggering • The magnitude of static stress changes decay as disatnce-3. • The magnitude of the peak dynamic stress changes decay as distance-1. • At great distances from the rupture, the peak dynamic stresses are much larger than the static stresss. Figure from Kilb et al., 2000

22. Stress III: Dynamic triggering Instantaneous triggering No triggering Stress Time Time

23. Stress III: Dynamic triggering Indeed, distant aftershocks are observed during the passage of the seismic waves emitted from the mainshock rupture. Izmit aftershocks in Greece. Brodsky et al., 2000

24. Stress III: Dynamic triggering • Dynamic stress changes trigger aftershocks that rupture during the passage of the seismic waves. • But the vast majority aftershocks occur during the days, weeks and months after the mainshock. • Dynamic stress changes cannot trigger “delayed aftershocks”, i.e. those aftreshocks that rupture long after the passage of the seismic waves emitted by the mainshock. • It is, therefore, unclear what gives rise to delayed aftershocks in regions that are located very far from the mainshock.

25. Stress III: Volcano-seismic coupling - the Apennines and Vesuvius example How normal faulting in the Apennines may promote diking and volcanic eruptions in the Vesuvius magmatic system, and vice versa. Nostro et al. (1998)

26. Stress on a dike striking parallel to the Apennines Stress on a dike striking Perpendicular to the Apennines Pressure change on a spherical magma chamber Stress III: Volcano-seismic coupling - the Apennines and Vesuvius example Coulomb Failure Function calculations Nostro et al. (1998)

27. Stress III: Volcano-seismic coupling - the Apennines and Vesuvius example Volcano-seismic coupling? Nostro et al. (1998)

28. Further reading: • Scholz, C. H., The mechanics of earthquakes and faulting, New-York: Cambridge Univ. Press., 439 p., 1990. • Harris, R. A., Introduction to special section: Stress triggers, stress shadows, and implications for seismic hazard, J. Geophys. Res., 103, 24,347-24,358, 1998. • Freed, A. M., Earthquake triggering by static, dynamic and postseismic stress transfer, Annu. Rev. Earth Planet. Sci., 33, 335-367, 2005.