Albuquerque sits on the deep sediments of the Rio Grande rift, a tectonic basin filled with hundreds of meters of unconsolidated sands and gravels interbedded with finer silts. This depositional environment creates sharp impedance contrasts that influence how seismic waves propagate from the surface down to the bedrock, which can be quite deep in the valley. In our experience across Bernalillo County, a standard SPT blow count alone often misses the amplification effects that occur when shear waves travel through these interlayered basin deposits, making a direct measurement of shear wave velocity the most reliable path to a defensible site class. We run active and passive [MASW](masw) surveys from the West Mesa terraces to the foothills of the Sandias, tailoring the array geometry to the available space on each lot. Because the water table here can be shallow near the river, we frequently pair the velocity profile with [in-situ permeability](in-situ-permeability) testing when the project requires both seismic and drainage parameters for foundation design.
A single MASW line can reveal a 20% drop in VS30 across a building footprint in the Albuquerque basin, a detail that code-based correlations simply cannot predict.
Process and scope
Area-specific notes
One pattern we see repeatedly in Albuquerque is the misclassification that happens when a site is assigned Class C based on blow counts alone, while the MASW survey later shows a VS30 below 180 m/s in the upper 10 meters, placing the site firmly in Class D. The consequence shows up as an under-designed lateral system: the base shear jumps by 30% or more when the correct site coefficient is applied, and fixing that after the structural drawings are issued costs time that a fast-track project simply does not have. Another local hazard is the presence of shallow groundwater in the North Valley and Barelas neighborhoods, which can lower the shear wave velocity of the near-surface sands below the threshold the geotechnical report assumed. We also flag the potential for liquefaction in loose, saturated lenses; combining MASW with a CPT-based [liquefaction](liquefaction) screening gives the most complete picture when the groundwater is within 10 meters of the bottom of the footing.
Video overview
Relevant standards
ASCE/SEI 7-22 Minimum Design Loads and Associated Criteria for Buildings and Other Structures, IBC 2024 Section 1613 Earthquake Loads, ASTM D4428/D4428M-14 Standard Test Methods for Crosshole Seismic Testing (adapted for surface-wave analysis), NEHRP Recommended Seismic Provisions for New Buildings
Linked services
VS30 Site Classification Survey
Rapid active-source MASW line delivering the average shear wave velocity in the upper 100 feet and the corresponding ASCE 7 site class, typically completed in half a day on a standard lot.
Passive-array deep profiling
When the bedrock is expected beyond 30 meters, we deploy circular or linear passive arrays recording ambient noise to resolve the velocity structure down to 60 meters or more.
Combined geophysical and geotechnical package
MASW survey synchronized with SPT borings and laboratory index tests, producing a unified report that satisfies both the geotechnical and structural review requirements of the City of Albuquerque.
Site-specific ground motion analysis
For essential facilities and Risk Category IV structures, we use the measured VS profile to run equivalent-linear or non-linear site response analyses, delivering surface response spectra tailored to the basin stratigraphy.
Typical parameters
Common questions
How much does a MASW/VS30 survey cost for a typical Albuquerque lot?
For a single-family or small commercial parcel within the city, our MASW survey generally runs between US$1,620 and US$3,230. The final price depends on the array length needed and whether passive recording is required to reach the 30-meter target depth.
Does the City of Albuquerque require a measured VS30 or can I use correlations?
The city accepts both, but the structural peer review often asks for a measured VS30 when the site is underlain by Santa Fe Group sediments deeper than 15 meters. A measured value removes the uncertainty in the site coefficient and frequently results in a more favorable design spectrum.
How long does the field work take?
An active MASW line on a cleared lot takes about 90 minutes of recording time, plus setup and calibration. We can typically complete one to two sites per day, and the preliminary VS30 value is available within 48 business hours.
Can you perform the survey on a site with existing pavement or concrete?
Yes, we can couple geophones to asphalt or concrete using mounting plates and a gypsum bond, though the high-frequency energy attenuation through pavement limits the resolution of the shallowest 2-3 meters. We often supplement with a short refraction line or a hand-auger hole to constrain that layer.
What is the difference between MASW and seismic refraction for site class?
Seismic refraction measures P-wave velocity and can infer VS only through assumed Poisson ratios, which is unreliable in the variable saturated soils of the Rio Grande valley. MASW directly measures shear wave velocity and is the preferred method for VS30 determination under NEHRP guidelines. More info.