Are Large Earthquakes Preferentially Triggered by Other Large Events?

Fundamentally related to the ultraviolet (UV) divergence problem in physics, conventional wisdom in statistical seismology is that the smallest earthquakes, which are numerous and often go undetected, dominate the triggering of major earthquakes, making accurate forecasting of the latter difficult if not inherently impossible. Using the general class of epidemic type aftershock sequence (ETAS) models and rigorous pseudo-prospective experiments, we show that ETAS models featuring a specific magnitude correlation between triggered and triggering earthquakes and a magnitude-dependent Omori kernel significantly outperform simpler ETAS models, in which these features are absent. Using the best forecasting model, we then show that large events preferentially trigger large earthquakes. These findings have far-reaching implications for short-term and medium-term seismic risk assessment and the development of a deeper theory without UV cut-off that is locally self-similar.