GIS-Based Virtual Geotechnical Database for the St. Louis Metro Area

The St. Louis metropolitan area is the focus of the U.S. Geological Survey's Earthquake Hazard Program's plan for assessing the likely risks of an earthquake emanating from the New Madrid Seismic Zone or the Wabash Valley Seismic Zone, which are the most active seismic zones recognized in the Midwestern United States. The St. Louis metro area includes portions of eight counties located both in Missouri and Illinois that abut the state boundary formed by the Mississippi River. The Illinois and Missouri geological surveys have prepared geologic maps and data sets that employ dissimilar geodata information, differing map units, map scales, and storage formats, with geodata stored in analog or digital formats. This research sought to combine the dissimilar geodata sets and to integrate them into a single Virtual Geotechnical Database within an accepted geographic information system (ArcGIS), which could be manipulated to retrieve subsurface data and to perform an array of spatial analyses. The geodatabase is intended to promote standardization of geologic interpretations between Missouri and Illinois and will be available to other researchers. The existing body of data was manipulated to extract useful information on the surficial geology, loess thickness, bedrock geology, well locations, and measured values of shear wave velocity, which could be conjoined to create stand-alone GIS information layers. "Depth-to-bedrock'' refers to the lithologic contact with early Paleozoic-age strata recognized by formational assignments across the two states. Depth-to-bedrock and groundwater table elevations underling the study area were interpolated using geostatistical methods of ordinary kriging and cokriging, respectively.