MASW and VS30 Shear Wave Velocity Testing in Minneapolis

A standard active-source MASW survey for VS30 in the Twin Cities area typically runs between US$1,800 and US$3,220, depending on the number of array positions, passive array requirements, and travel distance. A combined active-passive survey for deeper profiles falls at the upper end of that range. Each quote includes field time, dispersion processing, inversion modeling, and the signed engineering report.

MASW gives you the shear wave velocity profile directly, which is what the IBC uses for site class, but the Minneapolis building department still wants at least one boring to tie the velocity profile to material type. We typically run MASW adjacent to an SPT boring so the Vs and N-value correlate through the same stratigraphic column. The two methods together satisfy ASCE 7-22 and local Chapter 13 requirements.

Active MASW uses a controlled source (sledgehammer or weight drop) and gives high-resolution data in the upper 15 to 20 meters, but low-frequency energy is limited. Passive MASW uses ambient noise—traffic, wind, industrial vibrations—to extract surface-wave energy down to 50 meters or more. In Minneapolis, we often run both and merge the dispersion curves because the glacial till surface can be deep and the active source alone may not resolve the velocity below 25 meters.

Field acquisition takes about two to three hours per array position, including setup, shot stacking, and passive recording if specified. Data processing and inversion modeling require an additional two to three business days. Most Minneapolis projects receive the final signed report within four to five business days from the field date.

The USGS Vs30 proxy map for Minneapolis is based on topographic slope and has significant uncertainty in areas with complex glacial stratigraphy—especially near the Mississippi River bluffs and along the chain of lakes. The city accepts site-specific MASW data as the preferred method under IBC Section 1613.3.2, and our experience is that site-measured VS30 often differs by one full site class from the proxy value.