critical facilities such as large bridges and nuclear power plants. Together they have quantified the long-term expectations for potentially destructive shaking in the form of seismic hazard maps, and they are striving to improve these forecasts by understanding how past earthquakes influence the likelihood of future events. Consideration of slip models along faults is now leading to predictions of site-specific ground motions, needed by engineers for the design of large urban structures that can withstand seismic shaking.

The second reason for seeking a predictive understanding is epistemological and generic to fundamental research on a variety of geosystems, be they localized—like volcanoes, petroleum reservoirs, and groundwater systems—or global—like the oceans and atmosphere. These geosystems are so complex and their underlying physical and chemical processes are so difficult to characterize that the traditional reductionist approach, based on the elucidation of fundamental laws, is incomplete as an investigative method. In the face of such complexity, the ability to routinely extrapolate observable behavior becomes an essential measure of how well a system is understood. Model-based prediction plays an integral role in this type of empiricism as the first step in an iterated cycle of data gathering and analysis, hypothesis testing, and model improvement.

1.6 ORGANIZATION OF THE REPORT

This report summarizes progress in earthquake science and assesses the opportunities for advancement. Although not intended to be exhaustive, the report documents major scientific achievements through extensive references and technical notes. Chapter 2 charts the rise of earthquake science and engineering, introducing the technical concepts and terminology in their historical context. Chapter 3 gives the current view of seismic hazards on a national and global scale and shows how an improved characterization of these hazards can reduce earthquake losses by lessening risk and speeding response. Chapter 4 describes the observational activities and research methods in four major disciplines—seismology, tectonic geodesy, earthquake geology, and rock mechanics—and discusses the advanced technologies being employed to gather new information on the detailed workings of active fault systems. The integration of this information into a predictive, physics-based framework is the subject of Chapter 5, which lays out key scientific questions in five areas of interdisciplinary research—fault systems, fault-zone processes, rupture dynamics, wave propagation, and seismic hazard analysis. Chapter 6 examines the goals of earthquake research over the next decade and the resources and technological investments needed to achieve these goals in



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