Seismic Hazard Analysis and Probabilistic Ground Motions in the Upper Mississippi Embayment

The evaluation of the seismic hazard for a particular site involves the estimation of ground motions associated with potentially damaging earthquakes. Typically the seismic hazard is first computed at the bedrock level. To obtain the seismic hazard at the soil surface, the mean rock hazard is usually multiplied either by a mean amplification function or by a set of average site amplification factors. In this type of approach the variability in the site response is often lost or is not coupled appropriately with the variability associated with the rock hazard. Recent studies have proposed methods to account for the site response in probabilistic seismic hazard analyses using a probabilistic approach. Although these more refined procedures take into account the uncertainty in the entire earthquake process, the most accurate approach to develop site-specific ground motions is the use of site-specific soil attenuation relationships in the probabilistic seismic hazard calculations. Ground motion attenuation relationships were developed for soil sites in the Upper Mississippi Embayment that incorporate uncertainties in the earthquake source, path, and site processes. These attenuation relationships have been used for deterministic and probabilistic seismic hazard analyses for the region. Suites of probabilistic ground motions have been generated for selected cities within the Upper Mississippi Embayment.