Enviroprobe recently conducted an underground void locating survey at a traveling center in New Jersey. MASW instead of electrical resistivity tomography (ERT) was used due to reinforced concrete in the survey areas. MASW is one of the seismic survey methods evaluating the elastic condition of subsurface materials. MASW measures seismic surface waves generated from a seismic source, analyzes the propagation velocities of those surface waves, and then finally deduces shear-wave velocity (Vs) variations of subsurface materials.
For each survey area, survey lines were laid out in a grid pattern. A 2 dimensional (2D) MASW survey was conducted along each line. A sledge hammer was used to strike a steel plate on the ground to generate seismic waves and a seismograph was used to record the seismic data.
For each survey line, the seismic data was processed to generate a Vs profile. The profiles of each survey area were then combined and interpolated for 3 dimensional (3D) visualization.
A depth slice from the 3D visualization for a survey area at depth about 10 feet: