GPS monitoring of the Ancona landslide

The northern slope of Montagnolo Mount, Ancona District, Italy, is a sliding area. This area and also the nearest zones are involved in a fault system direct N-W / S-E. The area has been hit by some catastrophic events, such as the 1972 earthquake and the 1982 landslide. Because of the first event, in order to monitoring the dynamic of the seismicity, a geodetic network has been set up; afterwords for the control of the slide two different geodetic networks have been estabilished, the first one in 1976, and the second one 1983. Serious problems derived from the difficulty in finding near "stable" areas to be regarded as reference and from the difficulty in estabilishing good planimetric networks because of the topography of the zone. A Global Positioning System network has been set up, consisting in seven points; four points are in the sliding and seismic area and the other three are in the hilly "stable" areas in the surroundings. Such net allows the determination of the crustal deformations getting rid of the need of reciprocal visibility, from zones completely stable, due to the fact that it is possible to carry out measurements from very long distances, with very high accuracy achievable in short time; it leeds to homogeneity of the different nets, and finally to the unification and integration of the height and planimetric networks: the GPS satellite points are characterized by almost equivalent accuracy in the three coordinates and therefore there isn't distinction between the height network and the planimetric one. In other words GPS network should overcome all the limits of the previous nets, integrating them in only one network more general and valid for more than one purpose.