Observations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep excavation walls in earthquakes are rare even if the structures were not designed for the actual intensity of the earthquake loading. While some failures have been observed, there is no evidence of a systemic problem with traditional static retaining wall design even under quite severe loading conditions. No significant damage or failures of retaining structures occurred in the recent earthquakes such as Wenchuan earthquake in China (2008) and, or the large subduction zone earthquakes in Chile (2010) and Japan (2011). Therefore, this experimental and analytical study was undertaken to develop a better understanding of the distribution and magnitude of seismic earth pressures on cantilever retaining structures. This report covers a portion of the study focused on structures with cohesionless soil backfill which included centrifuge model experiments and numerical simulations of the experiments using FLAC2D. The results of these experiments and analyses show that the Monobe-Okabe method traditionally used to estimate seismic earth pressures on retaining structures becomes overly conservative at design accelerations in excess of 0.4 g. Consequently, recommendation is made for the use of reduced values based on the Seed and Whitman (1970) approximation as the upper limit of expected seismically induced earth pressures for fixed base walls. Even greater reductions in seismic earth pressures are indicated for free standing, cantilever retaining structures.