Subsurface Expression of the Lambton Fault and Potential for the Basin Edge Effect in the Wellington Central Business District

This study focuses on the subsurface structure of the Wellington basin and an assessment of the shaking potential due to the basin edge‐effect at its western margin. Seismic reflection surveys combined with gravity modelling provide data for a structural model from which to base our shaking analysis. Sediment thickness estimates include a maximum of about 500 m close to Sky Stadium, 200 m throughout much of Thorndon and 150 m to 200 m beneath Waitangi Park, adjacent to Te Papa Museum. An important and new outcome of the most recent gravity survey is that it highlights the dominance of the subsurface expression of the Lambton fault. This fault strikes northeast beneath the railyards and dips steeply to the southeast to form the effective geophysical edge of the Wellington basin. Both a parametric analysis and direct 3D wave‐equation modelling show that localised amplification of shaking by a factor of three is predicted to occur along a narrow corridor just inboard, or east of the Lambton fault.