A Historic and Citizen Science Observation-Based Seismic Hazard Map of the United States (1900—2012)

Abstract:

Macroseismic intensities — site-specific numerical representations of shaking assigned on the basis of observed earthquake effects without the aid of seismographs —have been used to express the shaking due to earthquakes for almost two centuries. Shaking intensities can be assigned retroactively to earthquakes for which descriptions of earthquake effects are available. Macroseismic intensities constitute a consistent set of earthquake observations for many land areas, which are often the longest-period of earthquake records and most spatially-dense reports for each earthquake. Since 1998, macroseismic intensities assigned by the U.S. Geological Survey (USGS) have been determined using data contributed by the public through the “Did You Feel It?” web-site (http://earthquake.usgs.gov/earthquakes/dyfi/.) In this study, we use the USGS ShakeMap methodology as a consistent strategy to combine earthquake source parameters, instrumental ground motion measurements and macroseismic intensity observations to create an interpolated map of individual earthquakes occurring from 1900 to 2012. Compositing the individual ShakeMaps, we produce summary maps of specific attributes of strong ground-motion such as peak intensity, peak ground acceleration, and occurrence rates of a particular intensity. Products of this study include: (1) an aggregate database of reported felt earthquakes and their observed intensities across the U.S. for 1900—2012; (2) a database of ShakeMaps for the same events; (3) database summaries such as peak intensity and peak ground motion maps for the entire U.S.; and (4) observed frequency of shaking occurrence and derived hazard curves for selected cities. Our peak intensity and frequency maps are representations of seismic hazard that complement probabilistic seismic-hazard maps.