Fig. 13

Spectrograms showing the vertical seismogram signals over a 10-h duration following the 23 August 2017 Pizzo Cengalo rockfall. Vertical channels from station CH.VDL, at 26 km and MN.TUE, at 29 km are shown, both are located towards the North West. The main rockfall event occurs at 07:30, characterised by a high amplitude very broadband signal that is followed by more narrow band energy from 1 to 15 Hz lasting about 10 min—the signal of the mudflow. Additional secondary rockfall and mudflow signals continue to be observed over the next few hours