POTENTIAL VALUE OF LANDSLIDE INVENTORY MAPS FROM AN INSURANCE PERSPECTIVE

Landslide damage is excluded from essentially all types of private property insurance. This lack of availability of insurance coverage for landslide risk probably results from a combination of factors, such as insurance companies not being able to develop accurate models of landslide hazard (location, magnitude and frequency of occurrence) or extent of damage to buildings sitting on landslides that move (potential loss). Landslide maps, to actually portray hazard, must show the probability of landslides occurring in a given area within a time interval or with a specific frequency. Maps showing the locations of old landslides may document past instability and thereby be used to imply potential future instability. However, without the magnitude and frequency components, inventory maps are not hazard maps. Landslide inventory maps that incorporate probabilities of processes that can trigger movements, such as rainfall thresholds or levels of earthquake shaking, imply frequency but omitting magnitude. Furthermore, not all storms or earthquakes trigger slope movements, and a factor-of-safety approach defines even the slightest amount of movement as 'failure'.

Landslide inventory maps showing boundaries of past landslides are analogous to maps of automobile-accident locations: X marks the spot of the accident, but without additional details (e.g., characteristics of vehicles and drivers) such maps cannot be used by insurance actuaries to define risks or set prices for automobile insurance policies. Reliable landslide inventory maps would be useful for defining areas free of past landslides or unstable slopes where insurance companies could offer landslide coverage as part of general all-peril policies. In other landslide areas, whether insurance would be offered would depend on the magnitude and frequency components of landslide hazard maps. Landslide inventory maps also may have insurance value to private and public agency owners of buried utilities (e.g., water and sewer) that could initiate landslides or exacerbate damage if they leaked. Surveillance and maintenance activities could be conducted more frequently in areas shown on inventory maps to have landslides. Emergency management agencies may plan for improved disaster response in known landslide areas thereby potentially reducing some risks.