Earthquake interaction • The domino effect • Stress transfer and the Coulomb Failure Function • Aftershocks • Dynamic triggering • Volcano-seismic coupling
Earthquake interaction: The domino effect Example from California: Figure from www.earthquakecountry.info
Earthquake interaction: The domino effect Example from the North Anatolia Fault (NAF): Figure from Stein et al., 1997
Earthquake interaction: The Coulomb Failure Function Slip on faults modifies the stress field: Animation from the USGS site
Earthquake interaction: 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.
Earthquake interaction: 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
Earthquake interaction: 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
Earthquake interaction: The Coulomb Failure Function Example from NAF Animations from the USGS site
Earthquake interaction: 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.
Earthquake interaction: 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
Earthquake interaction: 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
Earthquake interaction: 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
Earthquake interaction: 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.
Earthquake interaction: Aftershock triggering The Homestead earthquake (CA): King and Cocco (2000).
Earthquake interaction: Remote aftershock triggering The Mw7.4 Izmit (Turkey): Mw5.8 Two weeks later
Earthquake interaction: 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).
Earthquake interaction: 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
Earthquake interaction: Dynamic triggering Instantaneous triggering No triggering Stress Time Time
Earthquake interaction: 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
Earthquake interaction: 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.
Earthquake interaction: 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)
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 Earthquake interaction: Volcano-seismic coupling - the Apennines and Vesuvius example Coulomb Failure Function calculations Nostro et al. (1998)
Earthquake interaction: Volcano-seismic coupling - the Apennines and Vesuvius example Volcano-seismic coupling? Nostro et al. (1998)
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.