Source Characteristics and Their Implications for Seismic Hazard Assessment in the Central United States

The central United States is located in the stable plate interior, more than 1,000 km away from the active plate boundaries. Recent studies show that the seismic sources in the central United States are different from those in the plate boundaries. For example, one study showed that New Madrid seismic zone is a relaxing weak zone that was initially generated by upswelling magma or a hotspot and was perturbed by glaciation or other recent changes in the regional stress field. The seismicity in the central United States is also different from that of the plate boundaries. Historical data have recorded only minor to moderate earthquakes (M5.5 or less) in the past 200 years. Great earthquakes (M7.0 or above) have occurred only rarely and evidence for these great ones is in the geological records (paleoliquefaction). Strong and damaging earthquakes (M6.0-7.0) were missing. Also, there are significant differences among the current ground motion attenuation relationships, the result of a lack of strong-motion records for the central United States. To perform seismic hazard analysis (either probabilistic seismic hazard analysis or deterministic seismic hazard analysis), three data sets, the seismic source, earthquake magnitude distribution, and ground motion attenuation relationship, are needed. Source, magnitude distribution, and attenuation relationship are extremely variable throughout the central United States, and must be carefully considered when determining the input data sets for seismic hazard analysis. Otherwise, seismic hazard could be overestimated or underestimated.