APPLICATION OF SECOND VERTICAL DERIVATIVE ANALYTICAL METHOD TO BOUGUER DATA FOR THE PURPOSE OF DELINEATION OF LITHOLOGICAL BOUNDARIES

Abstract

Formulation by means of which the second vertical derivative (SVD) of
gravity field may be computed at any point of gravity observation was
carried out. In order to calculate the second vertical derivative of the
gravity data, Fast Fourier Transform (FFT) was applied to the gravity data
of Gusau area,North West, Nigeria. The second vertical derivative was
computed by multiplying the Bouguer gravity value of each station by its
weighting coefficient and using the upward continuation technique as a
noise-filter to reduce the noise in the data. The resultant SVD gravity map
forms elongated zero contours which correspond to the edges of local
geologically anomalous density distributions features. The zero milliGal per
metre square (0 mgal/m2) quantity coincides remarkably well with most
lithological boundaries when compared with the major geologic contacts.
Thus a properly designed second vertical derivative map, in addition to
enhancing weaker local anomalies, can be a supplement to geologic
mapping in the identification of lithological units.