MASW & VS30 Shear Wave Velocity Testing in Rochester, NY

A 24-channel seismograph with 4.5 Hz geophones laid out in a linear array — that is the setup you will see on a Rochester site when we run a Multichannel Analysis of Surface Waves survey. The equipment captures Rayleigh wave dispersion across frequencies from 2 to 30 Hz, resolving shear wave velocity profiles to depths of 30 meters without a single borehole. In a city underlain by glacial Lake Iroquois silts and the weathered shale of the Irondequoit Formation, knowing your site's VS30 value is not optional; ASCE 7 Chapter 20 ties it directly to your Seismic Site Class and the design spectral accelerations. We pair active-source MASW shots with passive microtremor recordings when ambient noise from East Avenue traffic or I-490 demands it. For deeper bedrock mapping, we often run seismic refraction on the same spread to pick the top of competent rock where the till cover is thin.

A VS30 value derived from MASW is the single most cost-effective parameter for IBC seismic site classification on Rochester's glacial terrain.

Our approach and scope

Rochester's variable overburden creates a distinct geophysical contrast that MASW resolves efficiently. The lake plain clays north of Ridge Road exhibit VS30 values often below 180 m/s, which pushes sites into Site Class E and triggers amplification factors that foundation engineers must account for in the structural model. South of the escarpment, dense glacial till overlying Lockport dolostone produces VS30 readings above 450 m/s — a much stiffer response. We collect 12 to 24 shot gathers per spread, stack the dispersion images, and invert the fundamental mode curve using a least-squares algorithm to produce a 1D shear wave velocity column. When the near-surface stratigraphy includes interbedded sand lenses that could liquefy under the Rochester area's design earthquake (typically a 2,475-year return period), we combine the MASW profile with liquefaction analysis based on SPT blow counts. For sites where a single 30-meter profile is insufficient to capture lateral variability, a CPT test provides continuous tip resistance and pore pressure data that we correlate with the VS profile to refine the ground model.

Local ground factors

A five-story mixed-use project on University Avenue proceeded to foundation design using generic Site Class D assumptions without site-specific shear wave data. The developer assumed the dense till found on neighboring lots would extend across the parcel. Our MASW survey revealed a 12-meter-thick lens of glaciolacustrine silt with VS30 of 165 m/s directly beneath the proposed footprint — Site Class E, not D. The design spectral acceleration at 1.0-second period jumped by nearly 40 percent under ASCE 7, requiring a complete redesign of the lateral force-resisting system. The cost of the MASW survey was less than the structural engineering change order by two orders of magnitude. In Rochester's post-glacial environment, where buried channels of the ancestral Genesee River cut through the till and are now filled with soft organic silts, assuming uniform subsurface conditions is the fastest path to a non-conforming structure.

Technical data

Parameter	Typical value
Test standard	ASTM D7400 / IBC Section 1613
Geophone frequency	4.5 Hz (vertical component)
Number of channels	24 (expandable to 48)
Maximum investigation depth	30 to 45 meters
Acquisition mode	Active MASW + passive MAM
Output	1D VS profile, VS30, Site Class (A-F)
Typical site area	0.1 to 5 acres

Associated technical services

VS30 Site Classification

Single-point or multi-point MASW surveys to determine the average shear wave velocity in the upper 30 meters and assign IBC Site Class A through F for new buildings and additions.

2D Shear Wave Velocity Profiling

Multiple MASW spreads along a transect to map lateral velocity variations across the site, useful for large-footprint structures where a single VS30 value may misrepresent conditions at opposite corners.

Passive Microtremor (MAM)

Ambient noise recording with circular or linear arrays to extend the investigation depth beyond 30 meters and constrain the fundamental mode dispersion curve at low frequencies in noisy urban settings.

Combined Geophysical & Geotechnical Integration

MASW data correlated with SPT borings, CPT soundings, and laboratory resonant column tests to produce a unified ground model for seismic response analysis and soil-structure interaction studies.

Questions and answers

What does a MASW test cost in Rochester, NY?

A standard single-point MASW survey with VS30 reporting for IBC site classification in the Rochester area typically ranges from US$1,490 to US$3,620, depending on the number of spreads, the need for passive microtremor recording, and site accessibility. Multi-line 2D profiles or surveys requiring traffic control on busy corridors like Monroe Avenue or Lake Avenue will fall toward the upper end. We provide a firm quote after reviewing the site plan and understanding the foundation engineer's specific seismic design requirements.

How long does a MASW survey take on site?

Field acquisition for a single MASW spread with 24 geophones takes approximately 45 to 90 minutes, including array layout, multiple active shots, and passive noise recording if required. A typical residential or commercial lot in Rochester with two to three spreads is completed in half a day. Data processing, dispersion analysis, inversion, and the final VS30 report are delivered within three to five business days.

Is MASW accepted by the City of Rochester Building Department?

Yes. MASW-derived VS30 values are accepted for seismic site classification under the New York State Building Code, which adopts IBC 2021 with ASCE 7-22. The method is recognized by NYSDOT, the USGS, and geotechnical peer reviewers across Monroe County. Our reports include the raw dispersion images and inversion parameters so the reviewing engineer can verify the classified Site Class independently.