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MASW & VS30 Shear Wave Velocity in Dublin

Site investigations you can build on.

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Dublin's building stock is a palimpsest of over a thousand years of construction, from Viking wattle to Georgian brick and modern glass towers. Each era placed foundations on the city's complex glacial drift without the seismic knowledge we apply today. Though Ireland sits on a stable intraplate region, the adoption of Eurocode 8 requires seismic site classification for critical structures. Brighter winds and tighter deadlines push the building industry forward. We measure shear wave velocity directly with MASW techniques on sites from the Liffey quays to the M50 corridor. This gives engineers the VS30 value needed to confirm ground type and spectral response. In our experience, Dublin's boulder clay over limestone bedrock creates sharp velocity contrasts that only a continuous MASW profile can capture properly, especially when paired with seismic refraction for bedrock topography.

VS30 is not just a number for a report cover. It defines the entire seismic coefficient used in foundation design.

Process overview

Dublin lies largely on a bowl of Carboniferous limestone, blanketed by glacial till deposited during the last ice age. The till is dense and stony, often with lenses of sand and gravel, which creates local velocity inversions that single-point downhole tests miss. We run active MASW arrays using 24 geophones with a sledgehammer source. The resulting dispersion curve is inverted to produce a 1D shear wave velocity profile. From that profile we calculate VS30 according to the travel-time method defined in ASTM D4428. The value is straightforward: the average velocity of the top 30 metres dictates whether the site is Class B, C, or D under Table 3.1 of IS EN 1998-1:2005. In Dublin, we often see VS30 from 280 m/s to over 500 m/s, depending on how shallow the bedrock sits. For deep soft alluvium near the coast, the CPT test adds complementary cone resistance data when we need to characterise cyclic behaviour beyond what velocity alone reveals.
MASW & VS30 Shear Wave Velocity in Dublin
Technical reference — Dublin

Local context

A mid-rise apartment block near the Grand Canal docks was designed assuming Site Class B based on a nearby borehole log. The developer needed to break ground quickly. We ran a single MASW line across the footprint and found a buried channel of softer alluvium with VS30 dropping to 210 m/s, which reclassified the site to Class C. The structural engineer had to revise the base shear by nearly 15%. In Dublin, the risk is not high seismicity but misclassification. A site wrongly assumed as Class B when it is actually Class C or D leads to under-designed lateral resistance. The fix is not expensive if caught early. If discovered during construction, it can delay the programme by weeks. The seismic microzonation approach across larger masterplans helps catch these transitions before the first foundation is poured.

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Reference standards


ASTM D4428 – Crosshole and Surface Seismic Testing, IS EN 1998-1:2005 (Eurocode 8) – Seismic design, NEHRP site classification (VS30 thresholds)

Technical data

ParameterTypical value
StandardASTM D4428 / IS EN 1998-1:2005
Array length24 or 48 channel, 1–2 m spacing
Source typeSledgehammer or weight drop on steel plate
Depth of investigationTypically 30 m (VS30), up to 50 m feasible
OutputVs profile, VS30, site class A–E
Site class B thresholdVS30 > 360 m/s but < 800 m/s
Typical Dublin VS30280–520 m/s (till over limestone)
Report turnaround3–5 working days with processed curves

Common questions


How much does a MASW survey cost in Dublin?

For a single MASW line with VS30 calculation and a signed report, budget between €1,690 and €2,620 depending on array length, site access, and number of lines. We provide a fixed quote after reviewing the site plan.

What is the difference between MASW and a downhole seismic test?

Downhole requires a borehole and measures Vs point by point with a borehole geophone. MASW is non-invasive and uses surface waves, giving a continuous Vs profile without drilling. MASW is faster for site classification; downhole provides better resolution at depth when a borehole already exists.

Do I need a site class for a single house extension in Dublin?

Most domestic extensions fall outside the mandatory scope of Eurocode 8 for seismic design. However, if the building control officer or the engineer requires it for a structural submission, we can run a short MASW line. The test is quick and non-destructive.

How long does the field test take and what access do you need?

A single MASW line with 24 geophones takes about 45 minutes on site. We need a clear strip roughly 50 metres long, free of heavy traffic. The sledgehammer source is loud but causes no vibration damage to adjacent structures.

Location and service area

We serve projects across Dublin and surrounding areas.

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