Common questions
How much does a MASW / Vs30 survey cost for a typical Santa Ana commercial lot?
For a standard commercial parcel in Santa Ana — roughly 0.5 to 2 acres — the MASW survey with a single array line, dispersion processing, and the signed Vs30 report runs between US$1,860 and US$3,550. The spread depends on site access, the number of array setups required to cover the building footprint, and whether we're coordinating with concurrent drilling or CPT work. A constrained-access site with limited line length will push toward the upper end because it forces multiple short arrays with lower signal-to-noise ratio.
Does the City of Santa Ana accept MASW in lieu of downhole seismic for site classification?
Yes — the Santa Ana Building Division and most Orange County plan-check reviewers accept active MASW per ASTM D7400 as a valid method for determining Vs30 and NEHRP Site Class, provided the report includes the dispersion curves, inversion parameters, and a clear correlation to any available borehole logs. We've submitted dozens of MASW-based site classification packages in the city, and as long as the metadata is transparent, they move through review without pushback.
How deep does the MASW array need to reach for a reliable Vs30 measurement?
To compute Vs30 per ASCE 7-22, we need a Vs profile to at least 30 meters (100 feet). A 24-channel array with 3-meter geophone spacing typically resolves to 25–35 meters, depending on the stiffness of the shallow layers. In Santa Ana's softer alluvium, we often get clean dispersion down to 35 meters with a sledge source. If the site is particularly stiff — say, on the older terrace deposits near the eastern edge of the city — we'll switch to a weight-drop source or extend the array length to push the investigation depth past 40 meters.
What's the difference between Vs30 from MASW and Vs30 estimated from SPT N-values?
SPT-based Vs estimates use empirical correlations that carry significant scatter — typically a coefficient of variation of 25% to 40% in the silty sands common across Santa Ana. MASW measures Vs directly from surface-wave dispersion, so it's not relying on a proxy. In our experience across Orange County, the SPT correlation can misclassify a site by one full class, especially when thin soft layers are hidden between denser strata. The IBC commentary explicitly favors measured Vs over correlated values, and structural engineers increasingly require it for performance-based designs.
How long does the field work and reporting take for a Santa Ana MASW survey?
Field acquisition for a single MASW line takes about 2 to 3 hours on site, assuming reasonable access and no major buried utilities that require extra clearance. The data processing — picking the dispersion curve, running the inversion, and generating the 1D Vs profile — is another 2 to 3 days in the office. The final signed report, including the Vs30 calculation, site class letter, and the processed field records, is typically delivered within 5 business days from the field date.
