Nine To Noon EQs much more damaging to basin edge in Wellington - study
Mar 11, 2026
Tim Stern, emeritus professor and geophysicist who led gravity-modelling of the Wellington Basin. He explains how soft basin sediments slow and amplify seismic waves. He describes gravity and seismic surveys that revealed a deeper, sharper basin edge. He points to localized edge amplification in parts of central Wellington and notes similar risks for other basin-built NZ cities.
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Basin Trapping Amplifies Wellington Shaking
- Wellington's sedimentary basin traps seismic waves and amplifies shaking compared to bedrock.
- Victoria University modelling shows basin geometry and softer sediments cause resonance and longer duration shaking in the city.
Wellington Basin Is Deeper And Has A Sharp Edge
- The Wellington Basin is about 500 metres deep, roughly twice previous estimates, increasing low‑frequency amplification.
- A sharp basin edge runs from Lambton Quay past the stadium toward the ferry terminal, producing strong edge effects.
Edge Effect Triples Shaking At Basin Margin
- A basin edge effect can triple wave intensity at the basin margin compared with surrounding areas.
- Stern likens it to waves slopping over a pool edge, where geometry focuses and amplifies motion at the boundary.