f COMPARING SHEAR WAVE VELOCITY MEASUREMENTS FROM MASW AND DOWNHOLE SEISMIC METHODS

Seismic shear wave velocity profiles were acquired from 10 boreholes in central Illinois and compared to shear wave velocity profiles generated from the multichannel analysis of surface wave (MASW) data acquired at the borehole locations. The main objective was to determine if the shear wave velocity measurements from the MASW are reliable and can be used to characterize the glacial geology in central Illinois. The boreholes penetrated through glacial sediment consisting of multiple units of till, sandy silt, sand and gravel, and silty clay. The downhole data were acquired in PVC-cased holes drilled to depths ranging from 30 to 60 m using a three-component downhole geophone and a surface source. Travel times of the first-arrival seismic waves were analyzed using the direct and interval methods to generate 1-D seismic velocity profiles. The MASW profiles were acquired using 24-channel engineering seismograph with 1.5 m geophone spacing. The data were analyzed to generate 1-D velocity profile at each borehole location. Correlating the velocity profiles from both methods shows that the velocity values compare fairly well and demonstrate that the MASW is a reliable method to measure shear wave velocity of the subsurface materials.