Continuous monitoring of surface wave velocity at the Montevecchio earthflow (Forlì-Cesena Province, Northern Apennines)

The Montevecchio landslide is an active earthflow in the province of Forlì-Cesena (Northern Apennines of Italy). In the last few years, this landslide reactivated several times. In order to investigate the landslide dynamics, two monitoring systems were installed by combining 3 permanent GPS stations (to measure landslide movement) and 4 geophones (to evaluate surface-wave velocity). In this paper we present the monitoring data collected during the last reactivation of the landslide (24th - 25th of May 2015). The geophones data show a clear relationship between surface-wave velocity (Vr) and displacement rate. In particular, a decrease of Vr value was observed just before an increase of velocity, while higher Vr values were detected when the landslide was slowing down. Moreover, a pressure sensor, buried at low depth beside the geophones, showed an increase in pore water pressure before the failure in correspondence of the critical rainfall event, and while the displacement rate increased the pore water pressure had a positive value (above the ground level), probably due to the undrained compression of the landslide material.