PROBABILISTIC EVALUATION OF EARTHQUAKE-INDUCED SLOPE FAILURE

When there is an estimate of the probability of static failure for a s et of slopes, based on historical records, maps, and subjective judgme nt, it is often necessary to estimate the additional hazard presented by earthquakes. Combining the procedures of reliability analysis with conventional recurrence relations for horizontal earthquake accelerati ons leads to a simple formulation that is easily implemented on a spre adsheet. For simple failure modes the dynamic factor of safety is a si mple function of the static factor of safety, the amplified accelerati on the slope of the failure surface, and the friction angle. Applicati on of the technique to the slopes of the Montes de Caneja in Puerto Ri co indicates that the additional risk due to earthquakes is about one tenth of the static probability of failure, but other sets of input pa rameters can give probabilities of failure during earthquakes that are comparable to the static values.