LINKING GEOPHYSICAL SIGNATURES TO SEDIMENT PROPERTIES IN LUCAS COUNTY, OHIO

Geophysical measurements are becoming an important method for mapping Quaternary-aged sediments in Lucas County, OH. Geophysical signatures must be linked to sediment properties to enhance confidence in geophysical interpretations. Developing this linkage requires sediment sampling and analysis in conjunction with geophysical measurements. Sampling and sample analysis protocols were developed for consistency. The geophysical signatures measured are seismic (compression and shear) wave velocities and electrical resistivity. The Mastersizer particle size analyzer is used to determine grain-size properties of samples. Because geophysical signatures are influenced by water, fluid conductivity was measured where possible. Geophysical data and sediment properties are cataloged and mapped in a GIS. Future geophysical investigations in the region will benefit from this classification of geophysical signatures to quickly identify sediment types. One example involves concurrent research at a closed landfill, where the presence of silt (rather of clay) under several meters of surficial sand was identified because its electrical resistivity is too high. Another survey infers a hard, stony till buried where geophysical measurements characterize a clay-rich layer that hand augers, vibracore tubes and even a light track mounted coring unit could not penetrate.