Sioux Falls grew from the cascades of the Big Sioux River, but beneath the surface lies a geological contrast that shapes every foundation: dense Sioux Quartzite bedrock overlain by glacial till and alluvial deposits. The vertical transition from stiff clays to shallow, high-velocity rock can mislead a standard boring log. When a project triggers IBC Chapter 16, measuring shear wave velocity directly with a seismic site classification approach becomes essential. Our MASW survey provides continuous VS30 profiles that capture the true impedance contrast, replacing guesswork with a measured Site Class for structural design. For the new mixed-use blocks east of downtown and the industrial expansions near the I-29 corridor, that measurement carries direct dollar implications in base shear calculations.
A five-foot error in bedrock depth can shift a Sioux Falls site from Site Class C to D, doubling seismic design forces.
How we work
Local ground factors
The most frequent mistake we see in Sioux Falls is using default Site Class D for structural design when a quick MASW survey would prove Class C conditions. That assumption inflates the seismic design category and the structural steel budget unnecessarily. On the flip side, assuming shallow bedrock guarantees Class B without measuring velocity can be equally risky: weathered quartzite can fracture and read low, trapping the project in a non-conservative classification. The IBC explicitly permits measured Vs30 to override default assumptions, and the cost of a one-day MASW deployment is trivial compared to redesign or over-engineering a lateral system. On sites near the Big Sioux River floodplain, where alluvial silts mask the bedrock interface, we have documented Vs30 differences of 400 ft/s within 100 lateral feet.
Video resource
Relevant standards
ASCE 7-22 Chapter 20 (Site Classification Procedure), IBC 2021 Section 1613 (Seismic Design Category), ASTM D7400 (Standard Test Methods for Downhole Seismic Testing, referenced for cross-verification)
Other technical services
Standard VS30 Site Classification
Single-line MASW survey with full dispersion analysis, 1D Vs profile, and signed report assigning IBC Site Class A through F. Suitable for commercial pads and multi-family buildings on routine sites.
2D Shear Wave Velocity Cross-Section
Multiple parallel MASW lines to map lateral velocity variation across a site. Used where glacial till thickness varies sharply or where buried paleochannels may create differential stiffness under large-footprint structures.
MASW + Downhole Verification Package
Combined active MASW and downhole seismic in a single boring for sites near the Class C/D threshold. Provides redundancy for peer review and plan check approval on essential facilities.
Typical parameters
Common questions
What does a MASW survey cost for a typical Sioux Falls commercial lot?
For a standard single-line MASW survey on a half-acre to two-acre commercial lot in Sioux Falls, project costs typically range from US$1,810 to US$3,030. The final figure depends on site access, array length needed to reach 30-meter depth, and whether we need to clear vegetation or coordinate with ongoing grading operations.
How does the shallow Sioux Quartzite bedrock affect MASW results?
Shallow bedrock produces a very clear, high-velocity fundamental-mode dispersion curve, which is actually an advantage for MASW processing. The challenge is resolving the exact depth to refusal: we shorten the geophone spacing and increase the source energy to capture the velocity contrast within the upper 20 feet. The resulting Vs30 value is strongly weighted by that high-velocity half-space, often pushing the site into Class C or B territory.
Can MASW replace a boring for IBC site classification?
No. MASW measures shear wave velocity directly, which the IBC uses to assign Site Class, but it does not provide soil type, blow counts, or groundwater data. A proper geotechnical investigation combines MASW with at least one boring logged by a geologist, so you have both the velocity profile and the material description needed for a complete seismic hazard analysis.