The weathered Boone Formation limestone that underlies much of Fayetteville creates a subsurface where rock rippability and soil stiffness can shift abruptly over short distances. On the University of Arkansas campus expansion projects alone, we have seen shear wave velocities jump from 350 m/s in residual clay to over 800 m/s in pinnacled bedrock within a single survey line. That kind of contrast makes the MASW method particularly valuable here, because it averages these lateral heterogeneities into a shear wave velocity profile that the IBC and ASCE 7 can actually use. The 36th parallel latitude puts Fayetteville in a region where the New Madrid Seismic Zone still generates long-period ground motion, even at a distance of roughly 300 miles, so site classification based on VS30 is not just a paperwork exercise. When the karst voids are suspected, we often pair the surface wave data with a targeted resistivity survey to identify air-filled cavities before interpreting the velocity model.

A VS30 measurement is not just a number for the permit drawing; it is the parameter that decides whether your Fayetteville site sees a 10% or a 70% increase in design base shear under ASCE 7.

Scope of work in Fayetteville Arkansas

Fayetteville sits at an elevation of about 1,400 feet on the Springfield Plateau, where the Boone-St. Joe limestone sequence controls much of the near-surface geotechnical response. Our field crews use a 24-channel seismograph with 4.5 Hz geophones, deploying spreads of 46 to 92 meters depending on the target depth, and generate active-source energy with a 10 kg sledgehammer on an aluminum plate. The dispersion curve extraction follows the phase-shift method, and inversion is constrained by borehole logs when available. For sites along the West Fork of the White River, where alluvium thickness can exceed 15 meters, the low-frequency fundamental mode often dominates, and we extend the array length to capture it. One parameter that surprises many designers is the NEHRP site class — in Fayetteville, most naturally occurring soil profiles fall into Site Class C or D, but a thin stiff clay over karst can produce a site period below 0.15 seconds that classifies as C even when the blow counts suggest otherwise. When the stratigraphy includes chert rubble, we find that the seismic refraction tomogram helps separate the weathered zone from competent rock, improving the starting model for the MASW inversion.

MASW & VS30 Shear Wave Velocity Testing in Fayetteville, Arkansas

Parameter	Typical value
Method standard	ASTM D4428/D4428M-14 (crosshole/seismic), adapted for surface wave MASW
Typical array length	46 m to 92 m, with 2 m geophone spacing for 24-channel acquisition
Depth of investigation	15 m to 30 m below grade, depending on array geometry and site stiffness
VS30 calculation	Average shear wave velocity to 30 m depth per ASCE 7-22 Section 20.4
NEHRP site classes encountered	C (very dense soil/soft rock), D (stiff soil profile), occasional B (rock)
Source type	Active: 10 kg sledgehammer; passive MAM available for deeper profiles
Data deliverables	1D VS profile, 2D VS cross-section, dispersion curves, site class letter, signed engineer's report

Critical ground factors in Fayetteville Arkansas

ASCE 7-22 Section 11.4.3 requires a site-specific ground motion analysis when Site Class F is present, and in Fayetteville the karstic limestone with potential for subsidence can push a site into that category quickly. The risk is not just regulatory delay — a misclassified Site D instead of C adds a short-period site coefficient of 1.3 instead of 1.0, potentially adding five figures in unnecessary foundation steel. Liquefaction is rarely the driver here, but the deep alluvium along the White River tributaries can amplify long-period motion, and the VS30 profile is the first line of evidence for a liquefaction screening when the groundwater table is shallow. Our team has reviewed enough Ozark borehole logs to know that a single N-value from an SPT spoon can be misleading in cherty ground, which is why the geophysical average from MASW often saves the structural engineer from designing to a worst-case assumption that the subsurface does not actually deliver.

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Applicable standards: ASCE/SEI 7-22 Minimum Design Loads and Associated Criteria for Buildings and Other Structures, IBC 2021 Section 1613 Earthquake Loads — Site Classification, ASTM D4428/D4428M-14 Standard Test Methods for Crosshole Seismic Testing (adapted principles for MASW), NEHRP Recommended Seismic Provisions for New Buildings and Other Structures (FEMA P-2082)

Our services

Our Fayetteville geophysics group provides the MASW service as part of a broader site characterization package, and the three configurations below cover the most common requests from structural engineers and architects working in Northwest Arkansas.

VS30 Site Classification Package

One MASW line with passive roadside MAM extension, processed to deliver a signed VS30 value, NEHRP site class letter, and the 1D shear wave velocity profile. Accepted by City of Fayetteville Building Safety for IBC compliance.

2D Shear Wave Cross-Section

Two or more parallel MASW spreads gridded across the building footprint, inverted jointly to produce a 2D VS cross-section. Useful for irregular foundations and sites where bedrock depth varies by more than 5 meters from corner to corner.

Combined Seismic Refraction and MASW

Shared spread acquisition where P-wave tomography from refraction constrains the MASW starting model. Recommended for Boone Formation sites with suspected pinnacles or buried chert float, where the velocity contrast between soil and rock is extreme.

Common questions

How long does a MASW survey take on a typical Fayetteville lot?

A single-line active MASW acquisition with 24 geophones takes about 90 minutes of field time. Adding passive MAM for deeper coverage extends the session by roughly 45 minutes. Data processing and the signed report are typically delivered within three business days.

What does MASW testing cost for a residential or small commercial site in Fayetteville?

Can MASW work on steep slopes common in the Ozark foothills around Fayetteville?

Yes, but the array must be laid along a contour line rather than up the fall line to avoid topographic effects on the dispersion curve. For slopes steeper than 15 degrees, we apply a topographic correction during processing and document the geometry in the report so the engineer can judge the uncertainty.

Does the City of Fayetteville require a VS30 measurement for new construction?

The city adopts the IBC with Arkansas-specific amendments, so any structure assigned to Seismic Design Category C or higher triggers the site classification requirements of ASCE 7 Chapter 20. In practice, most commercial, institutional, and multi-family projects in Fayetteville must provide a VS30 or equivalent site class determination as part of the building permit submittal.