ABSTRACT
One of the functions of the Cartographic and Geological Institute of Catalonia (ICGC) is to “study and assess geological hazards, including avalanches, to propose measures to develop hazard forecast, prevention and mitigation and to give support to other agencies competent in land and urban planning, and in emergency management”. To accomplish these functions, the ICGC began the Geological Hazard Prevention Map of Catalonia (MPRG25M) in 2007. The MPRG25M is designed as a multi-hazard map, indicating the overlapping of different hazard zones in the same area. This article presents the methodology developed for assessing the rockfall hazard. The analysis includes two steps: (a) estimating the magnitude-frequency relationship of the events and (b) estimating the travel distance, based on the angle of reach. The evaluation is done in areas previously identified as susceptible. Susceptibility is defined by the combination of lithology with slope angle. Rockfall frequency and magnitude is obtained by field work with rockfall inventory, activity features, activity evidence and the identification of favorable terrain morphologies. The subsequent processing of these data includes the angle of reach analysis, which determines the area affected by the rock fall trajectories and the degree of hazard. This analysis is systematic and uniform for the whole of the territory to obtain comparable results.
