Purpose: Proposed landfill construction at the site required knowledge of the bedrock surface topography.  A seismic refraction survey was performed to map the bedrock surface.

Results: The interpreted bedrock depths closely matched existing boring information in the area.  The survey was able to provide bedrock depths along the entire traverse, filling in information between and beyond the borings.

Discussion: A seismic refraction investigation is performed by measuring the time it takes a seismic pulse to travel from the shot point location to geophones spaced out along the traverse.  These arrival times are plotted against shot-geophone distance as shown in the upper figure.  This information is used to calculate the thickness and seismic velocity of each layer present beneath the traverse.  The seismic velocities are used to interpret the nature of each layer.  The lower figure is the interpretation of the data shown in the upper figure.  The borings shown in the figure stopped at the bedrock surface.