Improved Seismicity Forecast with Spatially Varying Magnitude Distribution

In this article, we present a time-independent earthquake rate forecast for California. Our model features spatial variations of the Gutenberg-Richter b-value using the method of Kamer and Hiemer (2015). We account for lessons learned from the outcome of the Regional Earthquake Likelihood Models (RELM) experiment and use RELM's framework to investigate different concepts for modeling the spatial distribution of seismicity. Our resulting forecast shows a significant information gain with respect to all first-generation RELM mainshock forecasts. Our findings indicate that large-scale b-value variations are a considerable feature for increasing the skill of Californian seismicity forecasts. We underline the importance of statistical rigor when implementing earthquake occurrence hypotheses. Our results have implications for seismic hazard studies, in which the b-value is either chosen as a regional constant or varies spatially between local zones. Future improvements of our model may serve as a basis for choosing either of these approaches.