| The greater St. Louis area of Missouri and Illinois, one of the largest population centers in the Midwest, is located within 200 miles of one of the most seismically active regions in the United States. Since the destructive New Madrid earthquakes of 1811 and 1812, there have been 13 other earthquakes of Modified Mercalli Intensity VII or greater in the area. In addition to the active seismic record of the area, other geologic factors exist to add to the potential for damage from earthquakes. Central United States earthquakes characteristically have larger areas of perceptibility of ground motion and greater duration and amplitude than West Coast earthquakes. The potential for damage is compounded since urban expansion has extended onto the thick lucustrine and alluvial deposits along the Mississippi and Missouri Rivers, as well as onto deep loess deposits on the bluffs above the river valleys. These deep deposits of unconsolidated materials tend to amplify earthquake ground motion, resulting in greater intensities and damage at the surface.; This dissertation presents seismic hazard mapping procedures based on the dynamic response of the local soil deposits. As a result of this concept, a simple and rational method to assess the relative levels of individual seismic hazards was developed. This method was then applied to the Creve Coeur Quadrangle, Missouri. The hazard analysis has been based on state-of-the-art engineering procedures for analysis of ground motion, liquefaction, and slope stability, and the results presented as computer-generated earthquake hazards maps. The maps delineate areas of potential slope failure, liquefaction, and relative damage potential to structures from ground motion, in the event the maximum predicted earthquake were to occur. The hazards maps are intended for use by engineers, architects, and others involved in land-use planning. |
