Mixture distributions - an alternative approach for estimating maximum magnitude earthquake occurrence

Summary. Gumbel's theory of extreme value has been employed in the statistical forecasting of maximum-magnitude earthquake occurrence. The basic working hypothesis behind this method assumes that observations follow either Gumbel type I or type III asymptotic distributions. In certain cases, however, it is found that neither type of distribution fits the data well enough to produce accurate parameter-estimates, particularly in the larger earthquake range. This article proposes an alternative approach based on finite-mixture distributions whereby a more realistic prediction of upper earthquake magnitudes (at given return periods) is expected using a combined analysis of both Gumbel types I and III extremal distributions.