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Showing papers by "Geophysical Survey published in 1969"


Journal ArticleDOI
W. I. Reilly1
TL;DR: In this article, a digital plotter given values at points on a square grid is achieved by two-way polynomial interpolation so that the interpolated values fit exactly at the grid points.
Abstract: Contouring gravity anomalies by digital plotter given values at points on a square grid is achieved by two-way polynomial interpolation so that the interpolated values fit exactly at the grid points. Contours are drawn for one grid square at a time using the 2n × 2n array of grid values surrounding the square. The method of polynomial interpolation is designed to ensure continuity in the gradients of the contours across the boundaries of each square.

7 citations


Journal ArticleDOI
R. A. Garrick1
TL;DR: In this article, the authors compared the differences in tectonic environment between New Zealand and North America and made comparisons of New Zealand seismic measurements and North American oil-well data.
Abstract: Examination of the density variations found in cores taken from wildcat wells highlights the differences in Tertiary sedimentation on the east and west coasts of the North Island of New Zealand. A number of measurements of density, magnetic susceptibility, and longitudinal wave velocity have been made on East Coast rock outcrops. The results, although far from comprehensive, reveal some new and interesting trends. Comparisons of New Zealand seismic measurements and North American oil-well data throw new light on the rock-forming processes of diagenesis and burial metamorphism and allow comparisons to be made of the differences in tectonic environment between New Zealand and North America.

6 citations


Journal ArticleDOI
W. I. Reilly1
TL;DR: In this paper, the Fourier-Bessel integral expansion of the gravity anomaly field is used as a low-pass filter to transform gravity anomalies observed at randomly distributed points into a continuous harmonic function on a level surface.
Abstract: Numerical methods are examined whereby gravity anomalies observed at randomly distributed points may be transformed into a continuous harmonic function on a level surface. The interpolated value at a height z at the origin is found from the observed values gi at distances heights ζi and representing areas ai by a linear summation The weighting functions fi are derived from the Fourier-Bessel integral expansion of the gravity anomaly field, and are designed to act as low pass filters. Two cases are considered: the first is a sharp cut-off filter, where the frequency v has an upper limit ω, so that the frequency response is 1 for 0 ⩽ v ≪ ω and 0 for v > > and the second is an exponential filter of theoretical frequency response exp(−v 2/ω2) for which Differentiation of these formulae with respect to z yields the higher vertical derivatives directly from the observed anomalies. The methods include allowance for local variations in the density of observation points, and are designed to prepare data f...

5 citations