Unlike fragmental rockfall runout assessments, there are only few
robust methods to quantify rock-mass-failure susceptibilities at
regional scale. A detailed slope angle analysis of recent Digital
Elevation Models (DEM) can be used to detect potential rockfall source
areas, thanks to the Slope Angle Distribution procedure. However,
this method does not provide any information on block-release frequencies
inside identified areas. The present paper adds to the Slope Angle
Distribution of cliffs unit its normalized cumulative distribution
function. This improvement is assimilated to a quantitative weighting
of slope angles, introducing rock-mass-failure susceptibilities inside
rockfall source areas previously detected. Then rockfall runout assessment
is performed using the GIS- and process-based software Flow-R, providing
relative frequencies for runout. Thus, taking into consideration
both susceptibility results, this approach can be used to establish,
after calibration, hazard and risk maps at regional scale. As an
example, a risk analysis of vehicle traffic exposed to rockfalls
is performed along the main roads of the Swiss alpine valley of Bagnes.