pects of earthquake behavior that are completely resistant to theoretical manipulation and manual calculations. These new research capabilities are transforming the field from a haphazard collection of disciplinary activities to a more coordinated “system-level” science—one that seeks to describe seismic activity not just in terms of individual events, but as an evolutionary process involving dynamic interactions within networks of faults.

The scientific challenge is to leverage these advances into an understanding of earthquake phenomena that is both profound and practical. The research needed to move toward these objectives is the focus of this report. The National Earthquake Hazard Reduction Program, the mainstay for federal earthquake research over the past 25 years (Appendix A), has opened many areas of fruitful inquiry. New possibilities are arising from the system-level approach that now organizes the study of active faulting and crustal deformation. In appraising research opportunities, the Committee on the Science of Earthquakes has sought to keep in focus the rationale for future earthquake research from four complementary perspectives: (1) the need to improve seismic safety and performance of the built environment, especially in highly exposed urban areas; (2) the requirements for disseminating information rapidly during earthquake crises; (3) the fresh opportunities for exciting basic science, particularly in the context of current research on complex natural systems; and (4) the responsibility for educating people at all levels of society about the active Earth on which they live. These perspectives are summarized below.

Earthquakes are hazards primarily because strong ground shaking destroys things that people have constructed—buildings, transportation lifelines, and communication systems (Figure 1.1). Earthquakes are also responsible for secondary, though often very damaging, effects such as soil liquefaction, landslides, tsunamis, and fires. Over the last century, earthquakes have caused an average of 10,000 deaths per year worldwide and hundreds of billions of dollars in economic losses. The United States has seen less seismic devastation than many other countries, primarily owing to its lower population density and superior building construction (2). Nevertheless, the annualized long-term loss due to U.S. earthquakes is currently estimated at $4.4 billion per year (3), and this figure appears to be rising rapidly, despite continuing improvements in building codes and structural design (Figure 1.2). California leads with the highest risk, but the problem is truly national: 38 other states face substantial earthquake hazards, including 46 million people in metropolitan areas at moderate to high risk outside of California (Figure 1.3).