design, risk evaluation, and emergency management need to be educated about the capabilities and implementations of research results. In particular, the procedures described above can be applied in near real time immediately following an earthquake to improve the ground-motion maps now available (Figure 1.5) for guiding emergency response.

6.7 SEISMIC HAZARD ANALYSIS

Seismic hazard analysis provides the methodology for combining all information on seismic hazards into probabilistic and scenario-based predictions of the ground motions. This input is critical to earthquake engineering and design, as well as to the predictions of human casualties, damage to the built environment, and economic losses that can be expected from future earthquakes. Much applied research is still needed to improve the earthquake forecasts, attenuation relations, and site-response factors needed to apply seismic hazard analysis techniques. The methodology of seismic hazard analysis is now fairly mature, but it is highly empirical, based on many simplifications and approximations. Current attenuation relationships fail to capture much of the variance observed in the ground motions from actual earthquakes (Section 5.6). A recent study by the Southern California Earthquake Center concluded that “any model that attempts to predict ground motion with only a few parameters will have substantial intrinsic variability. Our best hope for reducing such uncertainties is via waveform modeling based on the first principles of physics” (4). The time is right to integrate physics-based models of earthquake processes into an improved scientific framework for seismic hazard analysis and risk management that explicitly considers the time dependence of seismic phenomena.

Goal: Incorporate time dependence into the framework of seismic hazard analysis in two ways: (1) by using rupture dynamics and wave propagation in realistic geological structures to predict strong-motion seismograms (time histories) for anticipated earthquakes, and (2) by using fault-system dynamics to forecast the time-dependent perturbations to average earthquake probabilities.

Seismic hazard analysis employs many of the data sets described under the other major science issues. These databases should be available as part of the community modeling framework, since alternative earthquake source models cannot be compared rigorously unless they are based on common sets of data such as earthquake catalogs, GPS velocity vectors, and fault geometries and slip rates. Similar requirements exist for the



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