HR: 09:00h
AN: S31C-05    [Abstracts]
TI: Seismic Hazard and Risk Assessment and Public Policy in the Central United States
AU: * Wang, Z
EM: zmwang@uky.edu
AF: University of Kentucky, Kentucky Geological Survey 228 Mining and Mineral Resources Building, Lexington, KY 40506, United States
AB: Making a public policy on seismic hazard mitigation is not an easy task because it not only depends on seismic hazard itself, but also on seismic risk and other related social and economic issues. Seismic hazard and risk is the basis, however. Although seismic hazard and seismic risk are two fundamentally different concepts, they have been used interchangeably. Seismic hazard describes natural phenomena, such as surface rupture, ground motion, ground-motion amplification, liquefaction, and induced landslides, generated by earthquakes that have potential to cause harm. Seismic risk, on the other hand, describes the probability of experiencing a specified level of seismic hazard in a given time exposure. Seismic hazard occurs naturally and can be evaluated from instrumental, historical, and geological observations. Seismic risk depends not only on the hazard and exposure, but also on models (i.e., time-independent [Poisson] and time-dependent ones) used to describe the occurrence of earthquakes. High seismic hazard does not necessarily mean high seismic risk, and vice versa. In the central Unite States, large earthquakes (M7.0-8.0), similar in magnitude to the 1811-1812 New Madrid events, are of safety concern. Geologic evidences indicate that these large earthquakes have occurred several times in the past few thousand years with a recurrence interval of about 500 to 1,000 years. Consequently, the ground motions from these large earthquakes have the same recurrence interval (about 500 to 1,000 years). The risk posed by these large earthquakes is about 5 to 10 percent probability of exceedance in 50 years. Similarly, the risk posed by the ground motion generated by these earthquakes at a site is also about 5 to 10 percent in 50 years. The ground motion with 2,500-year return period (hazard) or ground motion with 2 percent probability of exceedance in 50 years (risk) has been generated from the same earthquakes and recommended for policy consideration in the central United States, however. This inconsistency is caused by the methodology being used for seismic hazard and risk assessment: probabilistic seismic hazard analysis (PSHA). Although PSHA is the most widely used method for seismic hazard and risk assessment, it contains a mathematical error in the formulation: incorrectly treating the ground-motion uncertainty as an independent random variable. The ground-motion uncertainty is an explicit or implicit dependent variable as it is modeled in the ground-motion attenuation relationship. The mathematical error results in difficulty in understanding and applying PSHA. PSHA mixes temporal measurement (occurrence of an earthquake and its consequence [ground motion] at a site) with spatial measurement (ground-motion variability due to the source, path, and site effects). Thus, use of PSHA in seismic hazard and risk assessment is problematic for policy consideration.
DE: 6309 Decision making under uncertainty
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: 2007 Joint Assembly