Atlanta sits at 1,050 feet elevation on the Eastern Continental Divide, but what matters for seismic design isn't altitude — it's what lies beneath. The weathered Piedmont residual soils that cover most of the metro area hide a complex transition from saprolite to partially weathered rock, and that interface controls site amplification. We run MASW surveys across Fulton, DeKalb, Cobb, and Gwinnett counties to pin down VS30 values that determine whether your site lands in Site Class C or D under ASCE 7. A half-class jump can swing the seismic design category and add six figures to your structural costs. The seismic microzonation work we've done around the Chattahoochee River corridor shows VS30 can vary by 200 m/s within a single block. We don't guess — we measure.
VS30 is a 30-meter average, but the top 10 meters dominate the result. In Atlanta's residual soils, those top 10 meters are everything.
Technical details of the service in Atlanta
Typical technical challenges in Atlanta
We've seen too many Atlanta projects where the geotech report assumed Site Class D based on a single SPT boring, and nobody caught it until the structural engineer ran the numbers. The problem: saprolite can look like soft rock to a drill rig but transmit shear waves at 500 m/s, which might push you into Site Class C. That's a good thing — lower base shear, lighter framing — but only if you prove it. MASW gives you that proof. On the flip side, a site near a buried stream channel or old fill can come back with VS30 under 180 m/s and trigger Site Class E requirements. We map the velocity across the entire building footprint, not just one point. The IBC lets you use two measurement points to classify a site, but we recommend at least three survey lines for anything over 10,000 square feet. Spatial variability in the Piedmont is real.
Our services
Our Atlanta MASW work feeds directly into structural design decisions. We deliver results within 48 hours of field acquisition.
Standard VS30 Site Classification Survey
Single or dual-line MASW survey for IBC/ASCE 7 site class determination. Includes dispersion curve, shear wave velocity profile, VS30 calculation, and a signed report with NEHRP site factors. Typical turnaround: 2 business days.
Multi-Line Footprint Mapping
Three to five survey lines across the building pad to map VS30 spatial variability. We interpolate velocity contours so the structural team can assign site class by column line if needed. Common for mid-rise steel and concrete projects in Midtown and Buckhead.
Combined MASW + SPT Calibration Package
MASW survey paired with one or two SPT borings at the same location. We use the blow count profile to constrain the inversion model, reducing uncertainty in the VS30 estimate. Ideal for sites near the Class C/D boundary where precision matters.
Common questions
How much does a MASW/VS30 survey cost in Atlanta?
A standard single-line MASW survey for site classification in the Atlanta metro area runs between US$1,810 and US$3,370 depending on site access, array length, and whether we need to clear vegetation or work around existing structures. Multi-line surveys scale linearly with the number of spreads. We provide a firm quote after reviewing your site plan.
How long does a MASW survey take on site?
A single spread takes about 45 to 90 minutes once the crew is set up. Most of the time goes into laying out the geophone cable straight and level, and checking coupling on each sensor. A two-person crew can complete a standard two-line survey in half a day, assuming reasonable site access and no major obstructions.
Does MASW replace the need for a soil boring?
No — MASW measures shear wave velocity, not soil type, strength, or groundwater. It complements a boring program but does not replace it. The IBC requires both VS30 and soil profile information for site classification. We typically recommend at least one boring to confirm stratigraphy, with MASW providing the velocity data across the rest of the site.