Nearly Simultaneous Pairs and Triplets of Historical Destructive Earthquakes with Distant Epicenters in the Italian Apennines

Abstract

Historical seismic catalogs of Italy record several instances of pairs or triplets of large earthquakes (Mw>6.7) along the Apennine chain, occurring on the same date or within a short time frame (days or weeks). Some of these events have mesoseismic areas tens of kilometers apart and/or seismogenic structures located more than 1–3 times the fault length away. Although in the case of aligned and/or contiguous faults, their cascading activation can be explained by variations in static Coulomb stress, in the case of distant faults, this mechanism could sometimes be replaced by what is known as dynamic triggering, which is caused by the passage of seismic waves generated by a remote source. In this study, I analyze three significant ancient seismic sequences that occurred in the south-central Apennines, suggesting that the extent of the destructive effects of these earthquakes can be attributed to remote dynamic triggering, causing the activation of different and unrelated seismogenic structures within a specific time frame.