ABSTRACT
The development of small-scale, national, probabilistic earthquake ground motion hazard maps suggests paradigms for landslide maps. National maps of landslide incidence already exist for the United States. Maximum landslide “intensity” maps await a suitable definition of intensity. Spatial generalization of such maps is viable where the causes act over an area, as with rainfall or earthquake shaking, or where similar geology and topography are widespread. Probabilistic landslide intensity maps await functions connecting landslide intensity with variation in causes (magnitude and distance for earthquake-induced slides, rainfall amount or rate for rain-induced slides). However, as an interim product, useful probabilistic maps of landslide “opportunity” are feasible for earthquake-induced slides ąnd rainfall-induced slides for a standard site condition, independent of variations in susceptibility. For the former, one needs a locus defining the maximum distance at which a given magnitude earthquake can produce landslides. For the latter, one needs a threshold value of rainfall amount or rate sufficient to cause landsliding. Combined with a geographic description of the time rate of earthquake magnitude or rainfall amount or rate, a map showing the probability of getting threshold landsliding can be produced. Likelihood adjustment to other site conditions ought to be possible using logistic regression, thus accounting for variations in susceptibility.
