Geographic area covered: Lower Hutt and Porirua areas within the Wellington region. 

This report presents a detailed assessment of ground shaking hazards in the Lower Hutt and Porirua areas, prepared as part of the Wellington Regional Council’s Natural Disaster Reduction Plan. The study identifies zones of varying seismic risk based on geological, geotechnical, and seismic data, including drillhole logs, microearthquake recordings, strong motion records, and penetrometer tests. The region is divided into hazard zones ranging from Zone 1 (least shaking) to Zone 5 (most shaking), with Porirua having three zones and Lower Hutt having four. Two earthquake scenarios are considered: a large distant earthquake and a local rupture of the Wellington Fault. Zone 5 areas, underlain by soft sediments, are expected to experience the strongest ground motion, with high amplification and longer duration of shaking. Zone 1 areas, typically bedrock, are expected to experience minimal amplification. The report quantifies expected Modified Mercalli intensities, peak ground accelerations, duration of shaking, and spectral amplification for each zone. It highlights the importance of local geological conditions in influencing seismic response and recommends site-specific studies for critical infrastructure. Limitations include uncertainties in shear wave velocities, topographic effects, and near-source ground motion data. The findings support land use planning, engineering design, and civil defence preparedness by identifying areas of increased seismic risk and guiding mitigation strategies.