Smoothed Seismicity Models for the 2016 Italian Probabilistic Seismic Hazard Map

For the first time, the 2016 Italian Probabilistic Seismic Hazard maps will incorporate smoothed seismicity models as a part of the earthquake rate forecast. In this study we report progress on the comparison of smoothed seismicity models developed using fixed and adaptive smoothing algorithms, and investigate the sensitivity of seismic hazard to the models. Recent developments in adaptive smoothing methods and statistical tests for evaluating and comparing rate models prompt us to investigate the appropriateness of adaptive smoothing methods for the Italian Hazard Maps. The approach of using spatially-smoothed historical seismicity is different from the one used previously by Working Group MSP04 (2004), and Slejko et al. (1998) for Italy, in which source zones were drawn around the seismicity and the tectonic provinces and is the first to be used for the new probabilistic seismic hazard maps for Italy. We develop two different smoothed seismicity models using fixed (Frankel 1995) and adaptive smoothing methods (Helmstetter et al., 2007) and compare the resulting models (Werner et al., 2011; Moschetti, 2014) by calculating and evaluating the joint likelihood test. The smoothed seismicity models are constructed from the new, historical CPTI15 and instrumental Italian earthquake catalogues and associated completeness levels to produce a space-time forecast of future Italian seismicity. We follow guidance from previous studies to optimize the neighbor number (n-value) by comparing model likelihood values, which estimate the likelihood that the observed earthquake epicenters from the recent catalog are derived from the smoothed rate models. We compare likelihood values from all rate models to rank the smoothing methods. We also compare these two models with the Italian CSEP experiment models, to check their relative performances.