Shear-Wave Reflection Imaging of Glacial-Deposit Aquifers in Northern Illinois

Abstract

Geologically-complex glacial sediment present challenges in mapping shallow aquifers with the conventionally-used electrical and electromagnetic geophysical methods. Horizontally-polarized seismic shear (SH)-wave reflection aided by water well information is presented in this study as an effective alternative for mapping aquifers within these sediment. SH-waves cannot be directly used to locate groundwater, however, when combined with borehole data from nearby wells, the sand and gravel potential aquifer units can be delineated. In this study, eight SH-wave seismic profiles with a total length of 17 kilometers were processed and interpreted in an attempt to delineate different glacial aquifers in the study area. The seismic data were correlated with adjacent well logs (gamma ray, conductivity, Vp, Vs) and lithologic descriptions from the available boreholes. Several logs were close enough to the seismic profile to be correlated and this proved to be very useful to register the seismic horizons to their corresponding lithological units in the borehole. The correlated data was interpreted and several individual units were mapped as potential groundwater aquifers along the seismic profiles including three main aquifers and several smaller potential aquifers. The extent and thickness of these unit aquifers were interpreted along the seismic profiles. Though, the SH-wave seismic proved to be effective in this study, the rapid variation in sediment types over short distances, necessitates drilling more wells and acquiring more closely-spaced seismic profiles in order to gain complete understanding of the geology and aquifers in the area.