Static stress changes and the triggering of earthquakes

TLDR

The Coulomb failure criterion links brittle rock failure to shear and confining stresses, while Coulomb stress changes on a fault depend on fault geometry, slip sense, and friction coefficient, independent of regional stress. The study aims to determine whether the 1992 Landers earthquake altered failure proximity on the San Andreas fault system and to investigate how Coulomb stress changes from one earthquake can trigger subsequent events. The authors apply a Coulomb failure criterion that identifies optimally oriented faults for aftershocks and use it to resolve stress changes on the San Andreas and San Jacinto faults caused by the Landers sequence. Aftershocks clustered where Coulomb stress increased by more than 0.5 bar and were sparse where it decreased, and the Landers and subsequent moderate events raised stress at future epicenters by up to several bars, advancing the Landers event by 1–3 centuries and hastening the next great San Bernardino‑segment earthquake by roughly a decade.

Abstract

Abstract To understand whether the 1992 M = 7.4 Landers earthquake changed the proximity to failure on the San Andreas fault system, we examine the general problem of how one earthquake might trigger another. The tendency of rocks to fail in a brittle manner is thought to be a function of both shear and confining stresses, commonly formulated as the Coulomb failure criterion. Here we explore how changes in Coulomb conditions associated with one or more earthquakes may trigger subsequent events. We first consider a Coulomb criterion appropriate for the production of aftershocks, where faults most likely to slip are those optimally orientated for failure as a result of the prevailing regional stress field and the stress change caused by the mainshock. We find that the distribution of aftershocks for the Landers earthquake, as well as for several other moderate events in its vicinity, can be explained by the Coulomb criterion as follows: aftershocks are abundant where the Coulomb stress on optimally orientated faults rose by more than one-half bar, and aftershocks are sparse where the Coulomb stress dropped by a similar amount. Further, we find that several moderate shocks raised the stress at the future Landers epicenter and along much of the Landers rupture zone by about a bar, advancing the Landers shock by 1 to 3 centuries. The Landers rupture, in turn, raised the stress at site of the future M = 6.5 Big Bear aftershock site by 3 bars. The Coulomb stress change on a specified fault is independent of regional stress but depends on the fault geometry, sense of slip, and the coefficient of friction. We use this method to resolve stress changes on the San Andreas and San Jacinto faults imposed by the Landers sequence. Together the Landers and Big Bear earthquakes raised the stress along the San Bernardino segment of the southern San Andreas fault by 2 to 6 bars, hastening the next great earthquake there by about a decade.