The shale bedrock underlying Celbridge is only half the story. Along the Liffey valley, pockets of soft alluvium and glacial till create sharp impedance contrasts that can amplify ground motion—even at moderate magnitudes. For a recent school extension near the Hazelhatch Road, the desk study flagged uniform limestone, but the borehole logs told a different tale: three metres of loose silty sand over weathered rock. That single layer shifted the site class from B to C under IS EN 1998-1:2005, pushing the design spectrum up by nearly forty percent. When we carry out seismic microzonation in Celbridge, we go beyond the desktop maps. We run downhole seismic and surface-wave testing to build a measured Vs30 profile, then model 1D site response with actual strain-compatible shear modulus degradation curves. The output is a practical, site-specific elastic response spectrum that feeds directly into the structural engineer's model—no generic assumptions, no unnecessary conservatism.
A measured Vs30 profile and site response analysis can drop the design spectrum by forty percent compared to the default ground type—without compromising safety.
