A new computer method was developed to derive values of dip and vertical extent, as well as location, for the truncated face of a horizontal‐plate model. The method is based on lateral offsets of the zero‐crossover point of the second horizontal derivative of an upward‐continued gravity profile. Application requires that the distance to the upper surface of the model be known. Numerical tests indicate useful results are obtained when both the length of the gravity profile, and the finite‐strike length of a model are at least three times the maximum depth extent of the model. Gaussian noise with a standard deviation of 1 mGal can be tolerated given an anomaly amplitude of 70 mGal. An example from the Trans‐Hudson Orogen of central Manitoba, Canada, indicates that the Kisseynew metasedimentary gneisses extend over a vertical distance of 16–18 km, and are separated from the Baldock batholith to the north by a near‐vertical boundary.

Dip and depth extent of density boundaries using horizontal derivatives of upward‐continued gravity data

A method for analysing gravity anomalies due to a geologic contact by Fourier transform

A case study of forward calculations of the gravity anomaly by spectral method for a three-dimensional parameterised fault model

Spectral characteristics of the gravity and magnetic profile data over a geological contact

The application of the method of the Fourier transform in interpreting gravity anomalies of faults has so far been based upon the Fourier transform of the gravity anomaly due to a single semi‐infinite block cut by a vertical fault. A general expression for the Fourier transform of the fault anomaly is here derived which is valid for an arbitrary angle of inclination of the fault plane. For deriving the general expression, the gravity anomaly of the fault is first separated into a constant and a variable term. The transforms of the two terms are calculated separately and then added to give the general expression for the Fourier transform of the fault anomaly.

Bijon Sharma

Papers

A general expression for the Fourier transform of the gravity anomaly due to a fault