Seismic hazard mapping and mitigation policy development in the central USA and western China

Communities need sound seismic hazard maps for formulating policies such as engineering design for buildings and other structures to reduce potential earthquake losses. However, developing scientifically sound seismic hazard maps is challenging because there are large inherent uncertainties and many unknowns (or even sheer ignorance). It is critical for any seismic hazard mapping that these uncertainties be quantified and communicated clearly to engineers, policy makers, and the public. Although probabilistic seismic hazard analysis (PSHA) has been the most widely used method for seismic hazard mapping, the hazard maps produced from PSHA are artifacts and difficult, even impossible, to understand because PSHA is a pure computer model without a sound earth science (physics) basis and its mathematics is simply wrong. The use of PSHA hazard maps has led to overly stringent engineering design and mitigation policies in the central USA, and unsafe engineering design and other mitigation policies in western China. On the other hand, the hazard maps derived from deterministic seismic hazard analysis (DSHA) or Neo-DSHA have a clear physical and statistical meaning and are easy to understand. Deterministic (or scenario) hazard maps have been proven to be effective. Thus, deterministic hazard maps are more appropriate for engineering design and other mitigation policy considerations in the central USA and western China, as well as other areas in the world.