Engineers find value in using simplified procedures to estimate seismically induced permanent displacements in their preliminary assessments of the seismic performance of earth structures and buildings. This research develops new, robust simplified procedures to estimate shear-induced displacements of earth and waste structures and natural slopes and to estimate shear-induced settlement of structures founded atop liquefiable soils. Most simplified procedures for estimating seismic slope displacements are based on variations of the Newmark (1965) sliding block analyses. These procedures were developed largely using earthquake ground motions from shallow crustal earthquakes along active plate margins (e.g., California earthquakes). These semi-empirical procedures should not be applied directly to other seismo-tectonic settings, such as subduction earthquake zones, without evaluating their applicability for tectonic settings for which they were not originally developed. In this study, a simplified procedure for estimating seismic shear-induced permanent displacements in slopes located in subduction earthquake zones is developed. The primary source of uncertainty in assessing the likely performance of an earth slope or system during an earthquake is the input ground motion. Hence, a comprehensive database containing 810 recorded ground motions from subduction zone interface earthquakes was developed and used to compute seismic slope displacements. The proposed seismic slope displacement model captures the primary influence of the system's yield coefficient ky, its initial fundamental period Ts, and the ground motion's spectral acceleration at a degraded period of the slope taken as 1.5 Ts. The new procedure uses the framework of the widely used Bray and Travasarou (2007) method developed for shallow crustal settings. The model separates the probability of "zero" displacement (i.e.,