DECOUPLED ANALYSIS

A modification of traditional Newmark analysis that does not require the potential landslide mass to behave as a rigid block but rather models it with an elastic dynamic response. The most commonly used of such analyses was developed by Makdisi and Seed (1978) and estimates the effect of dynamic response on permanent slip in a two-step procedure: (1) Perform a dynamic analysis of the slope (using programs such as QUAD4 or SHAKE) assuming no failure surface; estimate acceleration time histories at several points within the slope and develop an average acceleration time history for the slope mass above the potential failure surface. (2) Use this average time history as the input in a rigid-block analysis and estimate the permanent displacement. This approach is commonly referred to as a decoupled analysis because the computation of the dynamic response and the plastic slip are performed independently. Decoupled analysis thus does not take into account the effects of permanent block movement on ground motion.