Book excerpt: Recent earthquakes around the world show a pattern of steadily increasing damages and losses that are due primarily to two factors: (1) significant growth in earthquake-prone urban areas and (2) vulnerability of the older building stock, including buildings constructed within the past 20 years. In the United States, earthquake risk has grown substantially with development while the earthquake hazard has remained relatively constant. Understanding the hazard requires studying earthquake characteristics and locales in which they occur while understanding the risk requires an assessment of the potential damage to the built environment and to the welfare of people - especially in high risk areas. Estimating the varying degree of earthquake risk throughout the United States is useful for informed decision-making on mitigation policies, priorities, strategies, and funding levels in the public and private sectors. For example, potential losses to new buildings may be reduced by applying seismic design codes and using specialized construction techniques. However, decisions to spend money on either of those solutions require evidence of risk. In the absence of a nationally accepted criterion and methodology for comparing seismic risk across regions, a consensus on optimal mitigation approaches has been difficult to reach. While there is a good understanding of high risk areas such as Los Angeles, there is also growing recognition that other regions such as New York City and Boston have a low earthquake hazard but are still at high risk of significant damage and loss. This high risk level reflects the dense concentrations of buildings and infrastructure in these areas constructed without the benefit of modern seismic design provisions. In addition, mitigation policies and practices may not have been adopted because the earthquake risk was not clearly demonstrated and the value of using mitigation measures in reducing that risk may not have been understood. This study highlights the impacts of both high risk and high exposure on losses caused by earthquakes. It is based on loss estimates generated by HAZUS(R)-MH, a geographic information system (GIS)-based earthquake loss estimation tool developed by the Federal Emergency Management Agency (FEMA) in cooperation with the National Institute of Building Sciences (NIBS). The HAZUS tool provides a method for quantifying future earthquake losses. It is national in scope, uniform in application, and comprehensive in its coverage of the built environment.