Distribution of geological materials in Lower Hutt and Porirua, New Zealand: a component of a ground shaking hazard assessment

Geological materials in the Lower Hutt, Eastbourne, Wainuiomata, and Porirua urban areas are mapped and described as part of a multi-disciplinary assessment of seismic ground shaking hazards. Emphasis is mainly on the flat-lying parts of these areas which are underlain by variable Quaternary-age sediments that overlie Permian-Mesozoic age «greywacke» bedrock. Within the Quaternary-age sediments, the two material types recognised on strength characteristics are: 1) Soft sediments, typically composed of normally consolidated, fine-grained materials (sand, silt and clay), with typical standard penetration values (SPT) of < 20 blows/300 mm; and 2) Loose to compact coarser-grained materials (sand, gravel), with SPT values of 20 blows/ 300 mm