URBAN EARTHQUAKE HAZARD MAPPING IN THE CENTRAL U.S

The U.S. Geological Survey and its partners in State Geological Surveys, universities, private consulting, and non-profit groups are nearing completion of a large-scale urban seismic hazard mapping project in Memphis, TN., and embarking on similar efforts elsewhere. These include the metropolitan areas of St. Louis in Missouri and Illinois, and of Evansville in Indiana and Kentucky. Damaging earthquakes are only moderately likely in these areas, but the consequences of one may be very high. The Memphis, St. Louis, and Evansville urban areas are typical of the central and eastern U.S., having a paucity of seismically engineered buildings and infrastructure and relatively low regional attenuation. They differ from each other in terms of their near-surface geology, the earthquake sources most likely to affect them, and the amount of existing data available. The properties of the near-surface sediments significantly affect the way the ground shakes during earthquakes. Thus, among the products from each mapping project will be a compilation of surface geology, and subsurface geological and geotechnical databases. Final products include liquefaction and (possibly) landslide susceptibility maps, and ground motion maps that include the effects of near-surface materials. Both scenario and probabilistic maps will be produced. All products will be accessible electronically. The planning and execution of the maps is done in consultation with advisory groups that include engineers, emergency managers, government, and the private sector. Although the Memphis mapping effort was motivated by the production of hazard assessments useful to the public, it also led to focused scientific research and a better understanding of earthquake recurrence, attenuation, and site effects. We expect the same to result from the St. Louis and Evansville projects. In addition, all of the projects will serve as focal points for community outreach and for mitigation activities.