EXAMPLE OF LANDSLIDE HAZARD ASSESSMENT AND PREPARATION OF LANDSLIDE SUSCEPTIBILITY MAPS :
AN EXAMPLE FROM KINGSTON METROPOLITAN AREA (KMA), JAMAICA:

The concepts and methodology used are based on Varnes (1984) and DeGraff (1987, 1991).
The losses from landslides are termed vulnerability. This is one component in determining landslide risk. The other component is landslide hazard.
Landslides are not currently amenable to risk assessment since there is no basis to determine the probability of landslides occurring within a given time period.
Hazard assessments are possible and can be used in place of risk assessments.
Hazard assessments are estimations of an area's susceptibility to landslides based on three inherent physical factors :
... (a) distribution of past landslides,
... (b) slope steepness, - and
... (c) type and structure of bedrock .
We have mapped these three factors for KMA during 1996 to 1998.
The degree of hazard is considered relative since it represents the expectation of future landslide occurrence based on the physical conditions of that particular area.
Compilation of landslide hazard zonation maps is based on three principles (Varnes, 1984). First, the past and present are keys to the future (Chamberlin);
second, the main conditions that cause landsliding can be identified, - and
third, degrees of hazard can be estimated.
We employ the landslide susceptibility matrix technique (DeGraff and Romesburg, 1980) to identify areas with high susceptibility for future slope failure.
This technique (often termed the "DeGraff method") relies on an inventory map of past landslides, and man-made factors that may contribute to landsliding.
Basically, the various factor maps are overlaid to create a mosaic of small areas that contain distinct combinations of slope angle, aspect, geology, vegetation, landuse, etc.
The landslide inventory map is then overlaid on this mosaic map, and those distinct combinations of factors that are associated with each landslide are tabulated and ranked.
This ranking in turn is used to classify the entire study area into landslide susceptibility zones.
Unfailed areas that share many common factors with failed areas are placed in the highest susceptibility class.