On the use of seismic detectors as monitoring and warning systems for debris flows

Debris flows constitute a major threat for several urban settlements located on the fans of mountain catchments and for other infrastructures that interact with these fans, particularly highways and motorways. Often structural measures such as the construction and maintenance of deposition basins, check dams, channel linings are both too expensive and not capable of completely guaranteeing the safety for inhabitants of villages and users of infrastructures affected by debris flows. Therefore the search of functional, reliable and possibly not expensive warning systems should be pursued to increase the available tools to face this often devastating kind of phenomenon. In this paper the use of seismic detectors for the determination of a debris flow occurrence in a torrent before its arrival on the fan will be discussed, together with their potential use as monitoring and warning systems. In 1995 a set of four seismic detectors was placed at a distance of about one hundred meters from each other along a straight channel reach of a debris flow prone torrent located on the Eastern Italian Alps. The purpose, in a first phase of the research, was mainly to verify which information could be obtained through this type of device on the occasion of a debris flow occurrence. On 5 July 1995, 22 June and 8 July 1996 three debris flows were recorded by this seismic network: the data that have been collected will be presented and conveniently processed for their interpretation. The results that have been obtained show that the passage of a debris flow in a torrent can be clearly identified using seismic devices placed at a safe distance from the channel bed and that in some cases a velocity estimation of the flowing mass is also possible through the processing of the seismic data.