The granite city presents a deceptive picture of geological stability, yet Aberdeen's seismic hazard profile is shaped by more than just its famously hard bedrock. The fault systems running through the North Sea and the varying thickness of glacial till across the city create a patchwork of site response characteristics that demand precise investigation. A standard desktop assumption simply won't cut it when you're developing critical infrastructure in areas like Altens or the harbour expansion zone. Our approach to seismic microzonation in Aberdeen combines shear wave velocity profiling with detailed borehole logs, mapping how the transition from granitic basement to the overlying silts and clays modifies ground motion. The weathered granite interface itself can amplify certain frequencies, a phenomenon we've documented consistently across sites from Kingswells to Bridge of Don. For deeper profiling where bedrock topography is irregular, we often run MASW surveys alongside downhole testing to capture the full velocity contrast without blind spots.
Aberdeen's weathered granite interface can produce site amplification at frequencies crucial for mid-rise structures, a detail generic national maps simply miss.
Our approach and scope
Site-specific factors
The field kit for a proper microzonation campaign in Aberdeen has to earn its keep. We typically mobilise a tracked CPT rig to push through the softer alluvial pockets near the harbour, but the moment you hit that granitic saprolite, it's game over for cone penetration. That's where the rotary coring rig takes over, extracting samples through the weathered zone so the lab can run cyclic triaxial tests on the transitional material. Skipping this transitional zone characterisation means missing a critical impedance contrast that can trap seismic energy. The biggest technical risk here isn't liquefaction in the classic sense, though saturated lenses in the Dee estuary merit careful NCEER-based analysis. It's the misclassification of a stiff till site as rock, which leads to an unconservative design spectrum and a structure with a fundamental period accidentally tuned to the amplified ground motion. Our reporting explicitly maps the coefficient of variation in Vs across each unit so the design team knows exactly where the uncertainty lies, not just the mean values.
Explanatory video
Regulatory framework
BS EN 1998-1:2004 + UK National Annex, BS 5930:2015+A1:2020, BS 1377/D4428M-14 (crosshole seismic), BS 1377 (resonant column), NCEER 1997 (liquefaction triggering)
Complementary services
Site-Specific Ground Response Analysis
One-dimensional equivalent linear or non-linear analysis using DEEPSOIL or similar, with input motions selected and scaled to match the UK North Sea seismic source model. Output includes surface response spectra, amplification functions, and time histories for structural analysis.
Vs30 Profiling and Site Class Determination
Direct measurement of shear wave velocity through the upper 30 metres using crosshole and downhole seismic methods. We correlate results with geotechnical borehole logs to produce a defensible EC8 site class for each structure footprint, not just a single averaged value for the plot.
Liquefaction Potential and Seismic Hazard Mapping
Evaluation of cyclic resistance ratio versus cyclic stress ratio for loose saturated deposits, particularly in the Lower Dee floodplain and harbour reclamation areas. We deliver factor of safety contours and post-liquefaction settlement estimates integrated with the wider microzonation framework.
Typical parameters
Common questions
Why does Aberdeen need seismic microzonation when the UK has low seismicity?
While UK seismicity is moderate, BS EN 1998-1 still applies and the UK National Annex defines a design ground acceleration of 0.70 m/s² for a 475-year return period. More critically, Aberdeen's highly variable Quaternary cover over hard granite creates sharp site class transitions across short distances. A structure designed to a generic rock assumption may experience amplified motion if founded on a few metres of stiff till over shallow bedrock, something microzonation directly quantifies.
What field tests are essential for a credible microzonation study in Aberdeen?
Crosshole seismic testing per BS 1377 is our standard for direct Vs measurement, supplemented by downhole methods in deeper profiles. We pair this with rotary-cored boreholes to log the weathered granite interface precisely. SPT data from cable percussion provides density and consistency, but shear wave velocity is the primary parameter for site classification. For critical sites, we also run suspension logging where borehole stability allows.
How much does a seismic microzonation study cost in Aberdeen?
For a site-specific study covering a single structure footprint, costs typically range from £3,480 to £13,250 depending on the investigation depth, number of boreholes, and whether dynamic laboratory testing such as resonant column or cyclic triaxial is required. A broader microzonation covering multiple hectares for a development masterplan will be at the upper end due to the geophysical grid density needed.
What's the difference between a national seismic hazard map and a local microzonation?
National maps, including the BGS seismic hazard products, operate at a regional scale and cannot capture site effects caused by local geology. A microzonation study measures the actual soil profile at your specific location, quantifies the impedance contrast between layers, and computes the modification of bedrock motion as it travels upward through those layers. In Aberdeen, the granite-saprolite-till sequence creates amplification patterns that a regional map simply smooths out.