gation and management must be based on the integration of these three components. These elements—described in more detail in the following sections—provide the basis for evaluating the prospective benefits and projected costs of seismic monitoring in specific regions of the country.

RISK ASSESSMENT: THE ROLE OF MONITORING IN DEFINING RISK AND REDUCING UNCERTAINTY

Assessing the risk of earthquake damage to structures requires information concerning the

  • type of structure and its response to strong ground motion and other seismic hazards,

  • location of the structure in relation to earthquake faults,

  • type of faulting, and

  • overall distribution of strong ground shaking and its local modification by specific site geology.

Quantitative estimates of seismic risk are important for judging whether earthquakes represent a substantial threat at any location; they enable objective weighting of earthquake risk relative to other natural hazards and other priorities for making design and retrofit decisions (NRC, 1996). Earthquake risk assessment encompasses the range of studies required to estimate the likelihood and potential consequences of a specific set of earthquakes of different magnitudes and intensities. Scientists and engineers are asked to provide the key decision-makers—those who will use earthquake risk assessment data—with a description of the nature of the earthquake risk in specific regions as well as the degree of uncertainty surrounding such estimates.

The essential role of seismic information is to reduce the uncertainty in risk assessment over time and thereby increase its usefulness for emergency preparedness, loss avoidance regulation, private risk financing and insurance, and/or earthquake prediction. As improved monitoring provides increasing amounts of information, a more complete understanding of geophysical processes, more realistic models, and better-informed risk assessments will become possible. As the Advanced National Seismic System (ANSS) produces improved information, it will be possible to design better safety and regulatory programs, to generate improved ShakeMaps after earthquake events, and to improve earthquake prediction capabilities.

Within the range of geological and geophysical investigations conducted under the auspices of the National Earthquake Hazard Reduction Program (NEHRP), seismic monitoring plays a key role in the definition



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