Uncertainties in Seismic Hazard Maps for the New Madrid Seismic Zone and Implications for Seismic Hazard Communication

Abstract

Earthquake risk assessment has been described as “a game of chance of which we still don't know all the rules” (Lomnitz, 1989). This challenge is illustrated by attempts to estimate the seismic hazard for parts of the central U.S. due to earthquakes in the New Madrid Seismic Zone (NMSZ). The U.S. Geological Survey National Seismic Hazard Maps predict that the seismic hazard in the area is surprisingly high, in some ways exceeding that in California. These predictions reflect crucial parameter assumptions, many of which have considerable uncertainty due to the absence of instrumental data from any but small earthquakes. Hence we explore the coupled questions of how the predicted hazard depends on various assumptions and how the uncertainties in estimates of hazard might be communicated to scientists, engineers, policy-makers, and others facing the challenge of deciding on seismic safety strategies that balance costs and benefits. At present, most seismic hazard assessment is done using the probabilistic seismic hazard analysis (PSHA) approach developed by Cornell (1968) and widely applied in engineering design ( e.g., Reiter, 1990; McGuire, 1995). An informative and entertaining overview of PSHA is given by Hanks and Cornell (1994). Major studies of seismic hazard in the central and eastern United States, including the NMSZ, were conducted in the 1980's by Lawrence Livermore National Laboratory (Bernreuter et al., 1985) and the Electric Power Research Institute (EPRI, 1986) for application to nuclear power plant licensing. A detailed study of the NMSZ was also carried out for the U.S. Department of Energy for the Gaseous Diffusion Plant in Paducah, Kentucky (Risk Engineering, 1999). Based on these and related efforts, and motivated bythe design and licensing needs of critical facilities, detailed consensus recommendations have been developed for conducting PSHA (SSHAC, 1997). It has become common to apply the PSHA method to …