Intermittent Criticality and the Gutenberg-Richter Distribution

In recent years there has been renewed interest in observations of accelerating moment release before large earthquakes, as well as theoretical descriptions of seismicity in terms of statistical physics. Most aspects of these works are encompassed by a concept called intermittent criticality in which a region alternately approaches and retreats from a critical -point. From this perspective, the evolution of seismicity in a region is described in terms of the growth and destruction of correlation in the stress field over the course of the seismic cycle. In this paper we test the concept of intermittent criticality by investigating the temporal evolution of the Gutenberg-Richter distribution before and after two successive M ‡ 5.0 earthquakes in western Washington State. The largest event in this distribution, Mmax, is observed to systematically increase before each event, producing accelerating moment release, and then to subsequently decrease. Associated variations in the b-value are minimal. This is the predicted result ifMmax is a measure of the correlation length of the regional stress field.