Investigating the effects of smoothing on the performance of earthquake hazard maps

Abstract

We explore whether less detailed probabilistic hazard maps might perform better by assessing how smoothing Japan's national earthquake hazard maps affects their fit to a 510-year record of shaking. As measured by the fractional exceedance metric implicit in such probabilistic hazard maps, simple smoothing over progressively larger areas improves the maps' performance such that in the limit a uniform map performs best. However, using the squared misfit between maximum observed shaking and that predicted as a metric, map performance improves up to a ~75-150 km smoothing window, and then decreases with further smoothing. This result suggests that the probabilistic hazard models and the resulting maps may be over-parameterized, in that including too high a level of detail to describe past and future earthquakes may lower the maps' ability to predict future shaking.