Hicks, S.R. 1982 Wainuiomata water reserve seismic refraction surveys of damsites 2, 3 and 4. : . Report / Geophysics Division 145 41 p.
Abstract: Seismic refraction surveys have been conducted at three potential damsites in the Wellington Regional Water Board's Wainuiomata Reserve. At Damsite 2, above the existing Morton Dam, the basement greywacke profile is asymmetric, reaching a maximum depth below ground level of about 38 m at the foot of the western valley wall. At Damsites 3 and 4, below the Morton Dam, there is a buried ridge of basement rock running along the valley, separating two buried channels in the valley floor (maximum depth about 33 m). This ridge may be either a fault scarp or simply an erosional feature. Attempts to trace a shear zone (exposed in a nearby greywacke cutting) by seismic means were unsuccessful. At all three sites surveyed, the greywacke basement has a seismic P-wave velocity of about 3.0 km/s, which is low for Mesozoic greywacke. The Young's Modulus of this greywacke (measured at zero stress) is therefore apparently about half of most near-surface greywacke, probably as a result of fracturing of the rock. (auth)
