Rockfall hazard zoning is usually achieved using a qualitative estimate
of hazard, and not an absolute scale. In Switzerland, danger maps,
which correspond to a hazard zoning depending on the intensity of
the considered phenomenon (e.g. kinetic energy for rockfalls), are
replacing hazard maps. Basically, the danger grows with the mean
frequency and with the intensity of the rockfall. This principle
based on intensity thresholds may also be applied to other intensity
threshold values than those used in Switzerland for rockfall hazard
zoning method, i.e. danger mapping.
In this paper, we explore the effect of slope geometry and rockfall
frequency on the rockfall hazard zoning. First, the transition from
2D zoning to 3D zoning based on rockfall trajectory simulation is
examined; then, its dependency on slope geometry is emphasized. The
spatial extent of hazard zones is examined, showing that limits may
vary widely depending on the rockfall frequency. This approach is
especially dedicated to highly populated regions, because the hazard
zoning has to be very fine in order to delineate the greatest possible
territory containing acceptable risks.