Picture the geophone spread: 24 vertical-component receivers, 4.5 Hz natural frequency, lined up across a weed-choked lot in Gentilly or a warehouse slab in Elmwood. Our crew connects them to a 24-channel seismograph, sets the sledgehammer source offset at 5 meters, and calls for quiet on the site. Three hits stacked, then we scroll through the shot gather to check for near-field effects before moving to the next spread. Down here in New Orleans, the contrast between the stiff Pleistocene terrace deposits and the overlying soft Holocene clays is exactly what makes MASW so effective at resolving the velocity profile. We run a minimum of two spreads per site, often splicing overlapping records to get resolution past 30 meters depth, then invert the dispersion curve using a fundamental-mode Rayleigh wave approach. The result is a 1D Vs profile that feeds directly into the VS30 calculation—the number that determines your Seismic Design Category under ASCE 7-22.
In New Orleans alluvial basins, a 15-meter VS30 difference can shift site class and foundation demand—MASW resolves that gradient without a single borehole.
Methodology applied in New Orleans
Typical technical challenges in New Orleans
In New Orleans, we often see foundation reports that default to Site Class D without measured VS30—just a generic assumption based on SPT blow counts in the upper 10 meters. That shortcut can backfire on deep soft clay sites where the true Vs profile places you in Site Class E, triggering a higher seismic design category and different base shear coefficients. The IBC is clear: VS30 from geophysical measurement trumps correlated values when available. We've tested sites in eastern New Orleans where the top 15 meters of fat clay and peat registered Vs below 150 m/s—firmly Class E—even though the SPT N-values in the upper 3 meters suggested otherwise. If the structural model was sized for Class D, the shortfall in lateral capacity could be significant. Running a single MASW line before finalizing foundation design eliminates that uncertainty. The cost of the survey is trivial next to the cost of redesigning pile caps or adding shear walls after the geotechnical baseline shifts late in the project.
Our services
Our MASW work in New Orleans covers the full range from pre-purchase site screening to detailed VS30 reports for permitting. Each survey includes raw shot gathers, processed dispersion curves, inverted Vs profiles, and a signed report with the site class determination.
VS30 Site Classification Survey
A complete active-source MASW survey with two or more spreads, dispersion analysis, 1D Vs inversion, and VS30 calculation. Delivered with a stamped report citing your site class per ASCE 7-22 and IBC 2024. Suitable for commercial, industrial, and residential projects across Orleans, Jefferson, and St. Bernard Parishes.
Combined MASW + SPT Stratigraphic Package
Surface wave profiling synchronized with standard penetration testing at one or more borehole locations. We correlate Vs with N-values, confirm layer boundaries, and provide a site-specific Vs-N relationship that improves the reliability of liquefaction triggering analyses and seismic settlement estimates in the New Orleans soft soil environment.
Questions and answers
How much does a MASW/VS30 survey cost in New Orleans?
For a standard active-source MASW survey with two spreads and a signed VS30 report, the cost typically runs between US$1,550 and US$2,980 in the New Orleans metro area. The final number depends on site access, the number of spreads needed to reach 30 meters depth, and whether we combine passive-source recording for deeper profiles. Sites with heavy vegetation or restricted access in neighborhoods like the French Quarter or the Garden District may require additional time for geophone layout.
Is MASW accepted by the City of New Orleans for building permit seismic classification?
Yes. The City of New Orleans Department of Safety and Permits recognizes VS30 from surface wave methods under IBC 2024 and ASCE 7-22. Our reports include the raw dispersion curves, the inverted Vs profile, and the calculated VS30 value with site class determination. We've submitted MASW-based site classifications for projects ranging from single-family raised foundations to mid-rise commercial structures in the CBD. The key is presenting the data with full traceability from acquisition through inversion so the plan reviewer can verify every step.
What depth of investigation does MASW provide in New Orleans soils?
With a 46-meter active-source spread and 4.5 Hz geophones, we reliably resolve Vs to approximately 30 meters depth in the soft alluvial soils of New Orleans. That covers the full 30-meter column required for VS30 calculation. When the project requires deeper profiling—for example, a deep excavation or a pile-supported structure where we need Vs to 60 or 100 meters—we supplement with passive-source recording using ambient noise and the Refraction Microtremor technique. The combination gives us a continuous velocity profile from the ground surface to the target depth. More info.