The most persistent mistake we see in Adelaide is treating base isolation as a simple product selection rather than a site-specific seismic design exercise. Teams order generic isolators from a catalogue, bolt them under the structure, and assume the building will ride out an earthquake. That approach ignores the stiff Pleistocene clays and the variable depth to bedrock across the Adelaide Plains. The city sits on a thin sediment veneer over Proterozoic basement, with the Para Fault and Eden-Burnside Fault still active enough to generate magnitude 5 to 6 events roughly every few thousand years. A proper base isolation seismic design here must reconcile the short-period spectral demand with the long-period displacement capacity of the isolators, all while accounting for the shrink-swell behaviour that defines Adelaide’s reactive soil profile. When the isolator period is tuned without factoring in the site-specific response spectrum from AS 1170.4, the structure may amplify ground motion rather than filter it. We often pair early-stage seismic microzonation with seismic microzonation studies to map the basin-edge effects that complicate isolation design in the eastern suburbs.
In Adelaide, the design displacement of an isolation system is governed less by the design earthquake magnitude and more by the stiffness contrast between the shallow reactive clays and the basement rock beneath.
