A MODEL FOR THE CREATION OF A DISASTER-RESISTANT COMMUNITY

On June 10, 1987, while staff of the Indiana Geological Survey (IGS) were preparing to celebrate the agency's sesquicentennial of service to the state, a magnitude 5.1 earthquake shook the lower Wabash Valley. The temblor produced only minor damage in Indiana, but it provided the impetus necessary to gain public and governmental support for meaningful seismic hazards research in southwestern Indiana. The City of Evansville sought help from the IGS to evaluate the seismic hazard for their community. Our research efforts began with a public survey of the physical effects of the earthquake that was published in the Evansville newspapers shortly after. The survey results provided a rough approximation of site response to ground shaking as perceived by the public. This began a series of collaborative efforts with the City of Evansville, the Indiana Fire and Building Services agency, Indiana Emergency Management Agency, and the U.S. Geological Survey STATEMAP program to assess geologic conditions and subsequent response to ground shaking in the greater Evansville area. Downhole shear wave velocity information was collected from IGS bore holes, and from existing water wells. Boreholes were logged for natural gamma radiation, which is a method of measuring the natural radiation of earth materials. Used in combination with geologic terrain maps, this information helps illustrate the relationship between geologic materials and the amplification of ground shaking and to calculate soil periods specific localities. Soil period data are particularly useful for evaluating potential damage to structures, each of which has its own period of oscillation that is dependent mainly on building height. This research helped lead to upgraded seismic codes for Evansville structures, a greatly enhanced seismic-response plan, and far reaching multi-hazard planning for all of Vanderburgh County. The Evansville business community also supported these efforts and Sandia National Laboratory aided development of an overarching proposal for Evansville as a disaster-resistant community. The local, state, federal and private sector cooperation that was spawned by the June 10, 1987 earthquake culminated in the selection of Evansville as one of the nation's premier Disaster-Resistant Communities.