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A simplified procedure for estimating seismic shear-induced permanent displacements in subduction earthquake zones is presented. It may be applied to assess the seismic performance of an earth/rockfill dam, natural slope, heap leach pads, or solid-waste landfill. The new procedure uses the framework of the widely used Bray and Travasarou [1] simplified method (BT07). 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 1620 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 model separates the probability of “zero” displacement (ie,< 1 cm) from the distribution of “nonzero” displacement, so that low values of calculated seismic displacement do not bias the results. The new seismic displacement model better captures the unique seismic setting of subduction earthquakes. The BT07 procedure, which was developed using only shallow crustal earthquake records, tends to overestimate seismic displacements (if applied to subduction settings) relative to the new model which was developed using subduction zone earthquake records. Reasons for the differences in the two models are discussed. The proposed model can be implemented rigorously within a fully …