Seismic surveys at Blackburn, Buller coalfields, New Zealand

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Paintin, I.K.; Stern, T.A. 1985 Seismic surveys at Blackburn, Buller coalfields, New Zealand. [s.l.]: [s.n.]. Report / Geophysics Division 202 34 p.

Abstract: Seismic reflection and refraction methods were used to investigate the basement structure in the Blackburn-Seddonville area of the Buller coal fields. This is a remote area with the only vehicular access being to the Seddonville seismic line site. The other five seismic lines were conducted from a field camp that was transported from site to site by helicopter. The remoteness, combined with the pakihi swamp conditions and the thick bush, produced some special problems associated with the seismic survey. Near Seddonville, basement was found at a depth of 50- 150 m beneath Kaiata Formation sediments - the Kaiata Formation being a Tertiary marine mudstone. Because of the shallowness of basement at this site a refraction analysis was adequate to define the depth and attitude of basement. At the other sites, where the basement surface is considerably deeper, reflections of varying quality were used to calculate the depth to basement. At the Base Swamp site good quality reflections gave a depth of 500+/-50 m to basement. Kaiata Formation sediments with a RMS velocity of 2.9+/-0.1 km/s overlie basement. At the Blackburn pakihi swamp site the reflection events were not as pronounced as those at Base Swamp. Nevertheless an estimate of 190+/-20 m for depth to basement is made; this is in good agreement with the 180 m depth to altered granite basement found in drillhole 1353 that was put down subsequent to this survey. One site in the Ngakawau River bed and two in the St George Stream bed were tried. Satisfactory reflections were obtained from the St George Stream sites, however, at the Ngakawau River site no clear reflections could be confidently identified. (auth.)