SEISMIC HAZARDS, RISK ASSESSMENT, AND POLICY IMPLICATIONS

Seismic hazards, especially ground-motion hazard, can be assessed using geologic information. The hazard information, in turn, can be used to assess seismic risk. The Federal Emergency Management Agency (FEMA) has used the national seismic hazard maps produced by the U.S. Geological Survey (USGS) in 1996 to estimate economic losses. These loss estimates are staggering: $4.4 billion per year nationally, $0.19 billion per year in the central United States, and $18.7 million per year in Kentucky.

One of the goals of seismic risk assessment is to promote earthquake policy development. But, seismic risk assessment has a significant amount of uncertainty, especially the uncertainty inherent in the seismic hazard assessment. This makes it difficult for policy-makers to develop reasonable mitigation regulations; moreover, the uncertainty often misleads the policy-makers.

We compared several seismic hazard scenarios for Kentucky, and also assesses the risk for these scenarios using HAZUS99 software and its default building database. The seismic hazard scenarios were: (1) ground-motion with 10 percent probability of exceedance in 50 years (500-year recurrence interval), (2) ground-motion with 5 percent probability of exceedance in 50 years (1,000-year recurrence interval), (3) ground-motion with 2 percent probability of exceedance in 50 years (2,500-year recurrence interval), (4) an M8.5 earthquake occurring in the New Madrid Seismic Zone.

Not surprisingly, the various hazard scenarios resulted in different loss estimates. Consequently, we, as geoscientists, are challenged to decide which seismic hazard scenario should be used for policy-making, because of the insufficient understanding of geology and lack of ground motion data in Kentucky and the central US. Geoscientists need to convey the hazard information, especially the uncertainty, more clearly to the policy-makers and the general public.