An improved ground motion seismic hazard model for use in performance based earthquake engineering is presented. The model is an improved approximation of the so-called 'power law' model, which is linear in log-log space. The mathematics of the model and uncertainty incorporation is briefly discussed. Various means of fitting the approximation to 'exact' hazard curves developed by seismologists are discussed, including the limitations of the model. Based on 'exact' hazard data for major centers in New Zealand, the parameters for the proposed model are calibrated. To illustrate the significance of the proposed model, a simplified performance-based assessment is conducted on a typical bridge pier. The new hazard model is compared to the current power law relationship to illustrate its effects on the loss estimation assessment. The propagation of seismic hazard uncertainty to drift hazard is also considered.