On the Use of Seismic Detectors as Monitoring and Warning Systems for Debris Flows

Debris flows constitute a major threat forseveral urban settlements located on the fans ofmountain catchments and for other infrastructures thatinteract with these fans, particularly highways andmotorways. Often structural measures such as theconstruction and maintenance of deposition basins,check dams, channel linings are both too expensive andnot capable of completely guaranteeing the safety forinhabitants of villages and users of infrastructuresaffected by debris flows. Therefore the search offunctional, reliable and possibly not expensivewarning systems should be pursued to increase theavailable tools to face this often devastating kind ofphenomenon. In this paper the use of seismic detectorsfor the determination of a debris flow occurrence ina torrent before its arrival on the fan will bediscussed, together with their potential use asmonitoring and warning systems. In 1995 a set of fourseismic detectors was placed at a distance of aboutone hundred meters from each other along a straightchannel reach of a debris flow prone torrent locatedon the Eastern Italian Alps. The purpose, in a firstphase of the research, was mainly to verify whichinformation could be obtained through this type ofdevice on the occasion of a debris flow occurrence. On5 July 1995, 22 June and 8 July 1996 three debrisflows were recorded by this seismic network: the datathat have been collected will be presented andconveniently processed for their interpretation. Theresults that have been obtained show that the passageof a debris flow in a torrent can be clearlyidentified using seismic devices placed at a safedistance from the channel bed and that in some casesa velocity estimation of the flowing mass is alsopossible through the processing of the seismic data.