Simple rules to minimize exposure to coseismic landslide hazard.

Landslides constitute a hazard to life and infrastructure, and their risk is mitigated primarily by reducing exposure. This requires information on landslide hazard at a scale that can enable informed decisions about how to respond to that hazard. Such information is often unavailable to, or not easily interpreted by, those who might need it most (e.g., householders, local government, and NGOs). To address this shortcoming, we develop simple rules to identify landslide hazard that are understandable, communicable, and memorable, and that require no prior knowledge, skills, or equipment to evaluate. We examine rules based on two common metrics of landslide hazard, local slope and upslope contributing area as a proxy for hillslope location, and we introduce and test two new metrics: the maximum angle to the skyline and the hazard area, defined as the upslope area with slope >39° that reaches a location without passing over a slope of <10°. We then test the skill with which each metric can identify landslide hazard - the probability of being hit by a landslide - using inventories of landslides triggered by six recent earthquakes. We find that the maximum skyline angle and hazard area provide the most skilful predictions, and these results form the basis for two simple rules: minimize your maximum angle to the skyline and avoid steep (>10°) channels with many steep (>39°) areas that are upslope. Because local slope alone is a skilful predictor of landslide hazard, we can formulate a third rule as minimise local slope, especially on steep slopes and even at the expense of increasing upslope contributing area, but not at the expense of increasing skyline angle or hazard area. Upslope contributing area, by contrast, has a weaker and more complex relationship to hazard than the other predictors. Our simple rules complement, but do not replace, detailed site-specific investigation; they can be used for initial estimation of landslide hazard or guide decision-making in the absence of any other information. [ABSTRACT FROM AUTHOR]