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Seismic slope stability is performed using a reliability-based analysis. In this approach, a log-spiral failure mechanism of the limit analysis is adopted. The study is carried using two deterministic models of earthquake loadings: The first model uses the seismic coefficient concept to identify the quasi-static representation of earthquake effects. In the reliability analysis, the performance function is based on the safety factor of the slope obtained by the strength reduction method. The second model uses Newmark method to calculate the permanent displacement at the toe of the slope as a result of the application of a time-history acceleration earthquake record at the base of the slope. The performance function is then defined with respect to the permanent displacement of the toe. For the assessment of the slope reliability, the Hasofer-Lind reliability index is considered. Therefore, the random variables are the cohesion and the angle of internal friction of the soil. Results show that the pseudostatic approach produces more conservative results than the Newmark sliding block analysis. The optimal slope height for a target reliability index is identified based on a reliability design procedure. Finally, the analysis is applied with the use of a case study of typical Lebanese slope to illustrate the above approaches.