• Stress Modeling and Eq Occurrence • Coulomb Failure Function Modeling (also written as ∆ CFF) o A reduction in the failure function means it has been brought further from failure o Amazingly successful at predicting the location of aftershocks o At least part of the answer if we have an eq on the SAF, if we will have another one on the fault or the San Jocinto • 1987 M 5.9 Elmore Ranch Eq o Southern part of the San Jocinto fault just to the west of the Salton trough o NE trending Left-Lateral fault o 12 hours later, Superstition Hills Eq M W 6.5 (triggered earthquake) • Calculating the Coulomb Stress Change o Red = rise in stress o Blue = drop in stress o Change in Shear Stress + (Friction Coefficient x Change in Normal Stress) = Change in Coulomb Failure Stress o ∆τ S + μ ’ ( ∆σ ) = ∆σ f o Big Bear was early example of success of explaining where aftershocks are going to occur o Stresses don’t go away unless they’re relieved by something, i.e. an eq • Relationship between the December 2004 Sumatra and March 2005 Nias Eqs
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fault Bay Area Eq, Eq Occurrence Coulomb, Coulomb Stress Change