ST. LOUIS REGIONAL
SHEAR WAVE VELOCITY SITE CHARACTERIZATION FOR URBAN SEISMIC HAZARD MAPPING
USING MASW (MULTI-CHANNEL ANALYSIS OF SURFACE WAVES)
HOFFMAN, D., ANDERSON, N.L., and ISMAIL, A.M.A., University of Missouri-Rolla, Rolla, MO 65409, USA, dhoffman@umr.edu, nanders@umr.edu,
St. Louis is a bi-state major urban area and a focus of the current USGS Earthquake Hazard Program in the CEUS. Shear wave velocity (Vs) data is a critical need of this plan to produce urban earthquake hazard maps and risk evaluations. Very little Vs data is currently available for the area. The Multi-Channel Analysis of Surface Waves (MASW) geophysical technique was used to acquire 80 Vs vertical profiles of surficial materials and/or bedrock to a depth of 30 meters. The efficiency and relatively low cost of the MASW technique has permitted acquiring the large number of Vs profile test data needed. The non-invasive nature and the very limited footprint of the MASW technique also make it ideal for the complexities and test site limitations of a major urban area. The acquired data covers 6 of the 29 USGS 7.5' quadrangles that encompass the St. Louis urban study area and 3 of the 4 first year priority quadrangles. An average of about 13 sites per quadrangle were selected and tested to characterize the surficial materials units shown on existing maps. The Vs testing locations were targeted based on mapped surficial geology unit distributions and trying to maintain a relatively uniform coverage. These Vs data are needed to characterize the earthquake ground motion amplification potential of the surficial materials. Coordination with other investigators collecting Vs data in the St. Louis area is being done so no unintended duplication of test sites occur and to maximize test data coverage.