MASW & VS30 Testing: Shear Wave Velocity for Seismic Site Class

For a single-family or small commercial parcel within the Oklahoma City metro, a complete active-source MASW survey with 1D VS profile, VS30 calculation, and signed engineering report typically falls between US$1,830 and US$3,190. The range depends on line length, number of spreads, and whether we need to trim vegetation or work around buried utilities. Sites in the alluvial corridor near the North Canadian River sometimes require longer spreads to reach the 30-meter target depth, which nudges the cost toward the upper end.

Downhole testing places a triaxial geophone in a borehole and measures direct arrival times, giving a high-resolution VS log at the cost of drilling a cased hole. MASW uses surface waves and inverts a dispersion curve to obtain a layered VS model without drilling. The trade-off is vertical resolution: downhole detects thin soft layers better, while MASW averages over a thickness of roughly one-half to one-third the wavelength. For most IBC site classification purposes, the VS30 from both methods agrees within 5 to 10 percent when the subsurface is laterally uniform, which is typical across the Hennessey Shale and Garber Sandstone formations that underlie most of Oklahoma County.

A single MASW spread with 24 geophones and a sledge source takes 45 to 90 minutes of active acquisition, plus setup and line layout. The crew works at ground level with no drilling mud, no casing, and no heavy equipment beyond a handheld hammer and a seismograph. We can work around light site traffic as long as the geophone line stays undisturbed during the stacking sequence. The raw data goes through dispersion analysis and inversion in the office, with the engineering report typically delivered within three to five business days after field completion.