Seismic Tomography (Refraction/Reflection) in Lexington, KY

For a standard single-family or small commercial lot (0.25 to 0.5 acres) in Fayette County, a seismic refraction tomography survey with 3 to 4 profile lines typically runs US$2,930 to US$4,200. Larger commercial sites or surveys requiring both refraction and reflection coverage run US$4,500 to US$6,000, depending on line length, geophone spacing, and the number of shots. The price includes field acquisition, processing, interpretation, and a stamped report with CAD-ready depth grids.

With a 240-foot spread and a sledgehammer source, we consistently image to 60 to 80 feet depth in the Bluegrass residual soil profile. An accelerated weight drop pushes that to 100 feet or more. Refraction depth equals roughly one-quarter to one-third the spread length. For deeper targets — mapping the contact between the Lexington Limestone and the underlying Tyrone Limestone at 150 to 200 feet — we use reflection acquisition with longer offsets and a higher-energy source. The seismic velocity contrast between the stiff clay (1,800–3,500 ft/s) and fresh limestone (9,000–15,000 ft/s) produces a strong first arrival and a clean tomogram.

Yes, that is one of its strongest applications in Fayette County. Air-filled or sediment-filled karst features produce a marked velocity drop relative to intact limestone. A refraction tomogram shows these as localized low-velocity zones — typically below 4,000 ft/s in a background of 9,000+ ft/s rock. The method resolves features larger than about half the geophone spacing, so with 5-foot spacing we reliably detect voids and grikes 3 feet wide or larger. It does not directly image the void boundary the way a reflection profile does; for that, we recommend supplementing with a resistivity survey, which responds strongly to air-filled versus water-filled cavities. The combination of velocity and resistivity gives a very complete picture of the karst hazard.

Most of Lexington's developed areas fall into ASCE 7 Site Class C (very dense soil and soft rock, Vs30 between 1,200 and 2,500 ft/s), though the downtown core over shallow limestone can reach Site Class B. We determine site class by measuring the time-averaged shear-wave velocity in the upper 100 feet (Vs30). The seismic tomography spread acquires both P-wave refraction data and surface-wave data simultaneously. Processing the surface-wave component with MASW or MAM yields a 1D shear-wave velocity profile directly beneath the array. The Vs30 calculation follows the procedure in ASCE 7-22 Section 20.4, and the result goes into the geotechnical report for the structural engineer's seismic design parameters.