Small Stress Change Triggering a Big Earthquake: a Test of theCritical Point Hypothesis for Earthquakes

Abstract

Whether or not a small stress change can trigger a big earthquake is oneof the most important problems related to the critical point hypothesisfor earthquakes. We investigate global earthquakes with different focalmechanisms which have different levels of ambient shear stress. Thisambient stress level is the stress level required by the earthquakes fortheir occurrence. Earthquake pairs are studied to see whether theoccurrence of the preceding event encourages the occurrence of thesucceeding one in terms of the Coulomb stress triggering. It is observedthat the stress triggering effect produced by the change of Coulombfailure stress in the same order of magnitudes, about 10-2MPa, isdistinctly different for different focal mechanisms, and thus fordifferent ambient stress levels. For non-strike-slip earthquakes with arelatively low ambient stress level, the triggering effect is moreevident, while for strike-slip earthquakes with a relatively highambient stress level, there is no evident triggering effect. This waterlevel test provides an observational support to the critical pointhypothesis for earthquakes.