GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 2.1 319 earthquake forecast models and of declustering models based on the tectonic environment under consideration. As regards the background seismicity, it is usually modeled as a Poisson process that is stationary in time, since independent earthquakes are generally assumed to occur at a constant temporal rate (as the result of a constant tectonic loading of plate motions). In this work, we evaluate whether the two components of seismicity (background and triggered) are affected by the tectonic regime of the studied regions through a comprehensive statistical analysis of several features of the seismicity recorded in different instrumental catalogs. Method. We investigate on the existence of possible differences in the earthquake clustering process in three areas related to distinct crustal tectonic regimes: Italy, Southern California and (onshore) Japan. Since the deformation style is not the sole discriminating factor to characterize the tectonic regime (any tectonic zone can include different fault types), we also consider subsets of the three catalogs that represent regions with homogeneous deformation styles: (1) extensional tectonics for Italy; (2) strike-slip tectonics for Southern California; (3) compressional tectonics for Japan (see Fig. 1 for details). This enables us to also perform a higher-resolution analysis, which only addresses the effect of faulting type (i.e., deformation style) on seismic clustering properties. We separate triggered and background events within each catalog by implementing the Fig. 2 - Clusters identified for the three main seismic sequences occurred in central Italy in the last two decades: the 1997 Umbria Marche, the 2009 l’Aquila earthquake and the 2016 Norcia-Amatrice sequences. Yellow stars represent the main events within each cluster.