Abstract

A sequence of four Mw > 6 earthquakes, including the 1992 Mw = 7.3 Landers and Mw = 7.1 Hector Mine earthquakes, occurred in the Mojave Desert in the 1990s in close proximity to the southern San Andreas fault, inducing stress changes on several of its segments. We calculate that coseismic slip combined with postseismic relaxation of viscous lower crust and/or upper mantle has led to a Coulomb stress increase of 2.3–3.5 bar on the San Bernardino Mountain segment of the southern San Andreas fault between 1992 and 2001, with a projected increase of 3.6–4.9 bar by the year 2020. In comparison, the calculated coseismic stress increase is 1.8 bar for this segment. This accelerated buildup of stresses is predicted to bring the San Bernardino Mountain segment, which last ruptured more than 190 yr ago, closer to a potentially major rupture. Meanwhile we project a net stress decrease of as much as −3.5 bar between 1992 and 2020 for the western Coachella Valley segment if the fault is governed by low effective friction, or an increase of 1.5 bar if the fault is governed by high effective friction. Coulomb stresses are calculated to decrease on the Mojave segment by as much as −1 bar between 1992 and 2020. Accelerated stress buildup is also predicted to occur on parts of the San Jacinto, Elsinore, and Calico faults. The pattern of the observed post-Landers aftershock clustering and the calculated Coulomb stress buildup on the Calico fault is similar to that noted in the Hector Mine region prior to the 1999 Mw = 7.1 earthquake. These results imply that the stress changes caused by an earthquake may still play a role in triggering future quakes in neighboring crust many years later through viscoelastic processes.

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