Optimum acquisition and processing parameters for multichannel analysis of surface waves using 3 D electrical resistivity tomography as control.

摘要

Multichannel Analysis of Surface Waves (MASW) and Electrical Resistivity Tomography (ERT) data were acquired in the Newburg, Missouri with the goal of determining optimum MASW acquisition parameters. Users of the MASW tool generally state that greater geophone intervals and greater shot-to-receiver offsets provide for more accurate results. The objective was to determine if this "rule of thumb" applies in karst terrain.;ERT data were acquired along four traverses with eighty-four (84) electrodes at five feet spacing with SuperSting R8 Resistivity System using dipole- dipole array. The data were processed using Earth Imager to generate 2-D resistivity inversion and thereafter, Voxler software was used to collate the 2-D ERT data into a 3-D resistivity model. MASW data on the other hand, were acquired along the same ERT traverses on the same locations using a suite of different geophone intervals (1-ft, 2.5-ft, 5-ft, 7.5-ft, and 10-ft) and shot-to-receiver spacings (0-ft, 10-ft, 20-ft, 30-ft, 40-ft, and 50-ft) with a 20lb sledge hammer as the source. The data were processed using Surfseis software to generate the dispersion curves and 1-D shear wave velocity profiles of the area.;On the basis of the comparative analyses of the ERT and MASW data, it was determined that 2.5-ft and 5-ft geophone gave generated depth of bedrock that was consistent with ERT data. With 5-ft geophone spacing it is possible to image the subsurface to greater depth, but with the 7.5-ft and 10-ft, unidentifiable dispersion curves would be generated. Therefore, in this study area, on the basis of data that were acquired it is recommended that 2.5ft spacing be used if depth of investigation is about 40ft, but if the depth of investigation is about 80-ft, using a sledge hammer source then 5-ft geophone spacing at 20-ft shot-receiver offset distance is recommended.