SEISMIC HAZARD ASSESSMENT AND COMMUNICATION: KEY ELEMENTS FOR HAZARD MITIGATION IN THE CENTRAL UNITED STATES

Ground motions with 2, 5, and 10 percent probability of exceedance (PE) in 50 years have been the basis for seismic design of buildings, bridges, and other facilities in the United States. For example, ground motion with 2 percent PE in 50 years, produced by the U.S. Geological Survey, has been selected as the basis for seismic design for new buildings and other structures (i.e., the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures). The use of this ground motion has resulted in extremely high design ground motion (1.0g PGA or higher) for the New Madrid region of the central United States. Many communities in the New Madrid region, such as Memphis, Tenn., and Paducah, Ky., had difficulty adopting and implementing mitigation policies based on this ground motion.

Development of a policy for seismic hazard mitigation is complicated, and involves not only seismologists and engineers, but also elected officials, the public, and other stakeholders; but seismic hazard assessment is the basis. Difficulty in the development and adaptation of seismic mitigation policies in the central United States has been found to be the result of a misunderstanding of the seismic hazard assessment - probabilistic seismic hazard analysis (PSHA). Although PSHA has been the most commonly used approach for seismic hazard assessment in the United States, it is not consistent with modern earthquake science, and its results such as the ground motion with 2, 5, and 10 percent PE in 50 years are difficult, even impossible, to understand and explain.

It is time to develop new approaches or to use others for seismic hazard assessment that can be easily understood and are scientifically consistent.