Back-analysis of the January 2017 earthquake-avalanche cycle in the Central Apennines

On January 18th, 2017, a sequence of relevant seismic shocks affecterd the Centra Italian Apennines, with twelve shocks having a Magnitude Mw>4and four a magnitude Mw>5,these latter all recorded during the morning, between 9:25 and 13:33 UTC (local time: UTC+1). The 181h of January 2017 was also the day in which a persistent heavy snowfall episode over the central Apennines, which started on the 151h of January and lasted up to the 191h of January, reached its daily maximum amounts. Nevertheless, the 181h of January 2017 is known to be an extraordinary avalanche day for the Abruzzo Region, either in terms of the number of avalanche events that occurred or in terms of damages and victims of avalanches. The deadliest avalanche event of this day happened a few minutes before 17:00 local time in the Farindola Municipality, at the locality of Rigopiano, about 40-45 km away from the epicenter of main seismic shocks; it literally bulldozed the building of the Hotel Rigopiano, killing 29 people and injuring 11. In this work, we analyzed all the available seismic, snow, and avalanche data related to this interesting combined seismic-avalanche cycle, to derive some general insight into the possible relationship between seismicity and avalanche activity. As an outcome of this analysis, we concluded that for earthquakes with a magnitude around 5, seismic triggering of avalanches at a dis- tance higher than 30 km, as for the case of the Rigopiano avalanche, is rather unlikely. Even if the seismic triggering of the Rigopiano avalanche cannot be proven or excluded, the analysis of the avail- able data leads to consider the January 2017 exceptional snow conditions over the Central Italian Ap- ennines as the most reasonable cause of this avalanche.