La Cabrera Sierra is a granitic paleozoic zone homogeneous in lithology and morphology 5 km long and 60 km from Madrid with rockfall problems. Most of the maps used in common practice, are mainly maps of susceptibility to instability or failure. When rockfall takes place, the main problem for the exposed elements at risk is the block reach due to high mobility of rock-blocks, thus the susceptibility to take into account must be the reach susceptibility, being the run-out, the key parameter for mapping. Several kinds of reach susceptibility maps have been developed for landuse planning in this case according with the susceptibility philosophy, an approach to the complex problem of slope movements from field observations. The Map of Maximum Run-out represents the susceptible zone as the one between the top of scarp and the maximum reach achieved by most mobile fallen blocks. The Map of Maximum Absolute Run-out represents the susceptible zone as the one between the top of scar and the maximum run-out achieved by any block extended to all the area. TheMap ofMinimum Reach Angle, an index used for mobility characterization of slope movements, represents the absolute minimum value achieved by a block extended to the entire zone. The Map of Reach Susceptibility by Dynamic Analysis is a geotechnical map, representing reach susceptibility for the maximum block size (maximum severity) computed with dynamic software. All maps have been performed with the aid of a GIS, taking into account the discussions about the optimal use of these systems. The legends have been carefully designed for the exploitation of possibilities, due to working with large scales for safer land use planning. Comparisons among these types of maps from the point of view of feasibility-risk analysis-economy are performed, and also reflections about the limits of GIS in these cases as well as conceptual problems.
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