A double branching model for earthquake occurrence

Abstract

The purpose of this work is to put forward a double branching model to describe the spatio-temporal earthquake occurrence. The model, applied to two worldwide catalog in different time-magnitude windows, shows a good fit to the data, and its earthquake forecasting performances are superiors to what obtained by ETAS (first-step branching model) and by Poisson model. The results obtained provide also interesting insights about the physics of the earthquake generation process, and the time evolution of seismicity. In particular, the so-called background seismicity, i.e., the catalog after removing short-time clustered events, is described by a further (second-step model) branching characterized by a longer time-space clustering maybe due to long-term seismic interaction. Notably, this branching highlights a long-term temporal evolution of the seismicity that is never taken into account in seismic hazard assessment, or to define reference seismicity models for large earthquakes occurrence. Another interesting issue is related to the parameters of the short-term clustering that appear constant in different magnitude window, supporting some sort of universality for the generating process.