MASW / VS30 Shear Wave Velocity Testing in Eugene, Oregon

The investigation depth depends on the survey line length and the site's stiffness. In typical Eugene soils—medium-stiff silts over gravel—a 115-foot spread with 5-foot geophone spacing reliably resolves Vs down to 80 to 100 feet. For sites where the depth requirement is marginal, we extend the spread to 150 feet or use a heavier impact source to generate lower-frequency surface waves that sample deeper. The processed Vs profile includes the depth of investigation estimate so the geotechnical engineer can confirm the 100-foot target is met.

Yes, within limits. We have run successful surveys on lots as narrow as 45 feet using 3-foot receiver spacing and a 12-channel acquisition setup. The trade-off is reduced maximum investigation depth—typically 40 to 50 feet on a short line. For shallow bedrock sites common in the south Eugene hills, this is often sufficient. When the 100-foot depth is mandatory but space is tight, we discuss combining MASW with a downhole seismic test in a single borehole to satisfy the building department.

We run MASW surveys year-round in Eugene, including during the wet months from November through March. Saturated near-surface soils actually improve geophone coupling and source repeatability. The main adjustment is operational: we avoid surveying during active heavy rain to protect the seismograph, and we may need to clear standing water from the shot-point area. The data quality is generally better in wet conditions because the higher soil density improves surface-wave generation. Our reports note the moisture conditions so the reviewer understands the seasonal context of the Vs30 value.

For a standard commercial lot in Eugene with one or two survey lines, the cost ranges from US$1,700 to US$2,830 depending on the number of spreads, the line length, and whether the site requires vegetation clearing or traffic control. The price includes field acquisition, dispersion analysis, inversion processing, and the signed report with Vs30 and ASCE 7 site classification.

Yes. The Eugene building department, following the 2024 Oregon Structural Specialty Code, accepts MASW-derived Vs30 values for seismic site classification under ASCE 7-22 Chapter 20. The key requirements are that the survey reaches the 100-foot depth or demonstrates rock at a shallower depth, that the dispersion curve is documented, and that the report is stamped by a licensed geotechnical engineer or engineering geologist. We coordinate with the engineer of record to ensure the submittal package meets the city's review checklist.