Wellington airport runway extensions, Evans Bay : engineering geological investigations

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Riddolls, B.W.; Lewis, K.B. 1979 Wellington airport runway extensions, Evans Bay : engineering geological investigations. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 324 27 p.

Abstract: Sub-surface investigations comprising three cored drillholes and a detailed seismic reflection survey have indicated the thickness and variability of sediments in the southern part of Evans Bay and clarified the implications for runway extension of a scarp on the sea floor. The drillholes demonstrated that particle-size varies both laterally and vertically. In general, the upper sediments are finer in an offshore direction, changing from predominantly sand to silt. The converse applies to the lower sediments, which also include gravel at depth. Weathered bedrock was penetrated in two drillholes, but continuous coring was not achieved to these depths. The seismic reflection profiles across the bay indicate that a trough was eroded in the bedrock prior to deposition of younger sediments. Its location may have been partly controlled by shattering associated with the presumed Evans Bay Fault, which is considered to be inactive. West of the infilled trough, a low (0.5 metre) scarp is present on the sea floor. The available evidence suggests that this dislocation is not an active fault, but ground damage caused by an earthquake elsewhere. These findings will be of relevance in the design of the maximum runway embankment. A shorter extension would not intersect the scarp.