The National Seismic Hazard Model (NSHM), which is regularly updated by the USGS for all U.S. territories, is the basic source of seismological information used by decision-makers at the local, state, and federal levels for earthquake risk assessment, seismic safety engineering, and disaster preparedness. The NSHM is currently limited by uncertainties in long-term earthquake rupture forecasts, the paucity of near-field recordings of large earthquakes, and the variability arising from fault rupture complexity and wave propagation through highly heterogeneous crustal structures. In this presentation, Thomas H. Jordan, Center Director, Southern California Earthquake Center (SCEC), will describe how large-scale, physics-based simulations of earthquakes can improve seismic hazard mapping by addressing these limitations.