Rancho Cucamonga’s transformation from a vineyard-dotted agricultural outpost into a sprawling logistics and residential hub has placed unprecedented demand on its subsurface. What was once sandy loam under citrus groves now supports tilt-up distribution centers, and the geotechnical conversation has shifted from simple bearing capacity to dynamic soil response. In our experience profiling sites from the Etiwanda alluvial fan up toward the foothills of the San Gabriels, we consistently encounter abrupt velocity contrasts that can amplify ground motion during a rupture on the nearby Cucamonga Fault. A well-executed MASW survey maps these transitions without the depth limitations of a standard boring, providing a continuous Vs profile that feeds directly into ASCE 7 site class determination. For deeper targets or bedrock mapping, the data pairs naturally with seismic refraction to resolve velocity inversions that surface-wave methods alone might miss.
A single MASW line often reveals velocity shifts that twenty borings would never detect — and those shifts can change the entire seismic design category of a structure.
Scope of work
Area-specific notes
ASCE 7-22 and the current IBC explicitly require site classification based on the average shear wave velocity in the upper 100 feet, and Rancho Cucamonga’s position straddling the Cucamonga Fault Zone makes this requirement more than a paperwork exercise. The fault, part of the larger San Andreas system, is capable of producing a magnitude 6.5+ event with rupture directivity effects that disproportionately impact stiff-over-soft soil profiles — exactly the kind of profile that only a continuous Vs sounding can characterize. Ignoring the velocity structure beneath a warehouse or school invites a design error where the code-prescribed site coefficient is simply wrong for the actual conditions. Our team has worked on multiple re-classification efforts where a developer inherited a conservative Class D assumption, only to find through MASW that the site qualified as Class C, unlocking significant structural savings while still meeting life-safety objectives. The data also feeds into liquefaction triggering analyses, where Vs-based procedures from Andrus & Stokoe provide an alternative to SPT-based correlations.
Standards used
ASTM D4428/D4428M — Standard Test Methods for Crosshole Seismic Testing (adapted for surface-wave MASW), ASCE 7-22 Chapter 20 — Site Classification Procedure for Seismic Design, IBC 2024 Section 1613 — Earthquake Loads and Site Ground Motion, FHWA-NHI-05-037 — Geotechnical Engineering Circular No. 5: Ground Motion Parameters
Linked services
VS30 Site Classification Surveys
Active MASW lines configured to deliver a code-compliant Vs30 value and NEHRP site class letter for IBC submittal. Typical survey completes in one field day, with preliminary site class available within 48 hours.
2D Vs Cross-Sections & Seismic Microzonation
Multiple parallel MASW lines or combined active-passive arrays to map lateral velocity variations across large footprints. Used for campus-scale projects, solar fields, and warehouse parks where uniform site class cannot be assumed.
Typical parameters
Common questions
What does a MASW survey typically cost for a single-family residential lot in Rancho Cucamonga?
For a standard residential parcel requiring one or two MASW lines to 100-foot depth, the survey typically falls between US$1,630 and US$3,310 depending on site access, surface conditions, and whether passive array recordings are needed to supplement the active data. Commercial sites with larger footprints or difficult terrain fall toward the upper end of that range.
Can MASW replace soil borings for site classification?
MASW provides the shear wave velocity profile needed for ASCE 7 site class determination, but it does not replace soil borings for strength, consolidation, or groundwater data. The most solid approach combines MASW with at least one boring or CPT sounding to correlate velocity with soil type and to confirm that no velocity inversions are present.
How does the Cucamonga Fault influence VS30 requirements?
The Cucamonga Fault is a near-source hazard for much of Rancho Cucamonga, meaning that short-period ground motion amplification is especially critical. A site-specific Vs30 value allows the structural engineer to use the correct site coefficients rather than defaulting to conservative assumptions that may overstate — or in some stiff-soil cases understate — the design spectral acceleration.
How long does a MASW survey take and what access do you need?
A single MASW line for Vs30 determination usually takes two to four hours of field time, including setup and teardown. We need a roughly straight 150-foot run with a relatively flat surface; asphalt, compacted gravel, and short grass are all acceptable. Heavy traffic areas or sites with buried utilities close to the surface may require additional coordination.