Gas extraction in the Groningen Province in the Netherlands has caused seismicity. A method was needed for probabilistic assessments of the seismic performance of the levees that protect low-lying polders against flooding. By combining the First Order Reliability Method with response surfaces it proved possible to strongly reduce the required number of simulations with advanced numerical models to obtain reliable failure probability estimates. To illustrate the workings of the method, an application to a levee cross-section along the Eemscanal with a sheet pile wall is presented. The probabilistic method can be used for probabilistic assessments and the probability-based calibration of partial factors, and it could serve as a starting point for quantitative risk analyses for levee systems in earthquake prone regions.