MASW & VS30 Testing in Tralee – Shear Wave Velocity Profiles

Tralee sits in a complex geological setting where glacial tills, peat deposits, and limestone bedrock create highly variable subsurface conditions. The River Lee basin and underlying Namurian shales influence the stiffness profile significantly. We run multichannel analysis of surface waves directly on your site to measure VS30. This value determines the seismic site class per I.S. EN 1998-1:2005. A wrong class assumption triggers costly overdesign or dangerous underestimation of seismic loads. Our team deploys 24-channel geophone arrays with active and passive sources to reach depths between 30 and 40 metres. The data feeds directly into structural models. For deeper bedrock mapping beyond 40 metres, the seismic refraction method complements the shear wave profile with compressional wave stratigraphy.

VS30 is not a number you guess from a geology map. We measure it on your plot with a 24-channel array and deliver a defensible site class.

Our approach and scope

In Tralee many sites show a thin layer of stiff glacial till over soft alluvial silts. That contrast fools simpler techniques. We capture the full dispersion curve down to the fundamental mode. Processing uses the phase-shift method with manual picking of the fundamental mode. Then we invert the curve into a 1D shear wave velocity profile. The inversion is non-unique. We constrain it with borehole logs or CPT data when available. Results include VS30 calculation per I.S. EN 1998-1 Section 3.1.2. We also provide VS,avg for the top 10 m and 20 m for liquefaction screening. Deliverables come with raw seismograms, dispersion images, inversion fits, and a final profile ready for the structural engineer. Site class A through E gets assigned without ambiguity.

Local considerations

The array is a straight line of 24 geophones planted firmly in the ground. A 10 kg sledgehammer hits an aluminium plate at multiple offsets. The surface waves travel horizontally. The geophones record the vertical component. In Tralee the main risk is high background noise from traffic on the N21 or N69 near urban sites. We solve it by stacking multiple shots and running passive recordings with linear or L-shaped arrays. Peat layers attenuate high-frequency energy. That limits resolution in the top 2 metres. We flag it in the report. Soft clay under stiff crust produces inverse dispersion. Mode misinterpretation is the number one error in MASW. Our processing includes full dispersion spectrum analysis to separate fundamental from higher modes before inversion.

Technical data

Parameter	Typical value
Array length	46 m to 92 m active, 100 m+ passive
Geophone frequency	4.5 Hz vertical component
Depth of investigation	30 m to 45 m typical
Source type	10 kg sledgehammer or weight drop
Sampling rate	0.5 ms to 1 ms
Recording time	2 s active, 30 s passive
VS30 calculation	I.S. EN 1998-1 §3.1.2, travel-time method
Output	1D Vs profile, dispersion image, site class letter

Related services

Active MASW for VS30

Standard 24-channel survey with sledgehammer source. Covers one array position. Delivers VS30 and site class for a single building footprint or small development. Depth reach 30 m typical.

Passive MASW (Microtremor Array)

Uses ambient noise with L-shaped or circular arrays. Reaches 50 m+ depth. Ideal when active sources cannot penetrate stiff layers near Tralee's limestone outcrops.

Combined Active-Passive Survey

Merges high-frequency active data with low-frequency passive data. Produces a broadband dispersion curve. Best for sites with deep soft sediments over bedrock.

2D MASW Profile

Multiple array positions along a line. Generates a cross-section of shear wave velocity. Useful for pipeline routes, embankments, or mapping lateral variability in the Tralee basin.

Frequently asked questions

What does a MASW survey in Tralee typically cost?

A standard active MASW survey for one array position ranges from €1.340 to €2.860 depending on site access, array length, and whether passive recordings are added. Urban sites with restricted space or high noise often need extra processing time, which moves the cost toward the upper end.

How long does the field work take?

One array position with active source takes about 45 to 60 minutes on site. A combined active-passive survey for one location runs roughly 90 minutes. Reporting and inversion processing add two to three working days.

Do you need borehole data to calibrate the MASW results?

Not mandatory. The inversion works without borehole calibration. However, if a borehole log or CPT profile exists nearby, we use it to constrain the layer thicknesses in the inversion model. That reduces the non-uniqueness and tightens the VS30 value.