M. Arattano and G. Lollino (CNR-IRPI, Strada delle Cacce 73, 10135 Torino, Italy)

Debris flows constitute a major threat for several urban settlements located on the fans of mountain catchments. 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 of the inhabitants. Therefore the individuation 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. The use of geophones for the determination of the size and velocity of a debris flow wave before its arrival on the fan will be discussed. In 1995 a set of four geophones was placed at a distance of about one hundred meters from each other along a straight channel reach of a debris flow torrent on the Eastern Italian Alps. The goal was to verify which information could be obtained through this type of device on the occasion of a debris flow occurrence. On July 5, 1995, June 22 and July 8, 1996 three debris flows occurred that were recorded by the four seismic sensors. The results will be presented together with a comparison with the information regarding the events obtained through other types of devices (ultrasonic sensors and video cameras).