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Earthquake Triggering

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Previous Studies

Earthquake triggering is the process by which an earthquake on one fault can cause an increase in stress on neighboring faults, resulting in earthquake sequences. Understanding the manner in which faults communicate to each other through stress changes can be used to identify regions of elevated seismic hazard (see our review article on the subject: Freed, Annual Reviews, 2005). Our group was the first to show that postseismic relaxation of a viscous mantle can induce a time-dependent transfer stress that may explain the time-delay in earthquake sequences, such as the triggering of the 1999 M7.1 Hector Mine earthquake following the 1992 Landers earthquake (Freed and Lin, Nature, 2001). A similar study shows that diffusion of stress following these earthquakes is currently building stress on faults close to the Los Angeles region (Freed and Lin, Geology, 2004). Postseismic relaxation may explain the triggering of the 2002 M7.9 Denali earthquake following the great 1964 M9.2 Alaska earthquake (Ali and Freed, GJI, 2010), and may explain why seismic activity appears to toggle between the two major strike-slip fault systems in Haiti (Ali et al., GJI, 2008). In a broad study of southern California earthquakes over the past 200 years, we determined that consideration of stress changes associated with postseismic relaxation is a significant factor in the triggering of earthquakes (Freed et al., GJI, 2007).

Current Studies

With the finding that the 2010 Haitian earthquake occurred on the previously unmapped Léogâne Fault, we are now addressed the question of what this means for the potential of an earthquake to occur on the Enriquillo Fault that passes through the heavily populated Port-au-Prince region. We are also working to understand a sequence of earthquakes in the northern Baja region of Mexico, culminating in the 2010 El Major earthquake. If we can interpret the stress communication between the faults that has led to this sequence, we may better understand how these earthquakes have influences faults within nearby southern California.

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