Seismic reflection profiling in very cShallow waters in the upper Waitemata Harbour, New Zealand

Publisher Website
Google Scholar
Abstract
A marine seismic reflection survey was conducted in the upper Waitemata Harbour, using a high-resolution acoustic prafiling system. The depths to the identified seismic reflectors agree dosely with the measured strata depths from borehole data, the differences between the two sets having a standard deviation of ± O-9 m. This is despite the paar signal-to-noise ratio resulting hecause the water depth was at tirnes less than 2 m. The structure of the area is complex, but three principal stratifications have been identified. Waitemata Formation sandstones of the Miocene Period are overlain by Pleistocene materials (days and silts, with mucl- fine sand), which vary in thickness fram 0 to more than 30 m. Most of the area is covered with up to 18 rn of Recent marine deposits, typically a very soft, silty day. Each zone, especially the Pleistocene, exhibits internal structure. The two rnajor boundaries have been contoured. Two anomalous features were recorded in the Recent marine sedirnents : astrang reflector which has not been related to any change in physical praperties of the sediments, and localised acoustically opaque zones which are probably a result of gas bubbles occurring within the sediments.