Viscoelastic stress-triggering of the 1999 Hector Mine earthquake by the 1992 Landers earthquake

The 1999 Mw 7.1 Hector Mine earthquake occurred only 20 km from the 1992 Mw 7.3 Landers earthquake fault. The close spacing between the two earthquake s suggests that the Landers earthquake trigger the Hector Mine event. Based on an elastic half-space model, scientists from the USGS, SCEC and CDMG (2 000) have found a negative Coulomb stress change at the Hector Mine hypocen ter due to Landers. This negative stress change is inconsistent with the hy pothesis of static stress triggering. In this paper, I show evidence of str ess triggering of the Hector Mine earthquake by Landers, due to a process g overned by viscoelastic flow in the lower crust. This visoelastic flow has produced broad-scale postseismic rebound observed by GPS and InSAR measurem ents. The result of this study is that viscoelastic flow has significantly modified the regional stress field in the Mojave Desert after the Landers e arthquake. The evolving stress field, including viscoelastic flow, has grad ually moved the Coulomb stress change at the Hector Mine hypocenter to a po sitive level. The increase in Coulomb stress exceeded 1 bar right before th e Hector Mine earthquake, bringing the Hector Mine ruptures to the proximit y of catastrophic failure.