Article,
Gravity and magnetic fields of polygonal prisms and application to magnetic terrain corrections
Geophysics, 41 (4): 727--741 (Aug 1, 1976)
DOI: 10.1190/1.1440645
Abstract
Computer programs based on the exact calculations of the gravity and
magnetic anomalies of polygonal prisms are faster in operation and
more accurate than previous programs based on the numerical integration
of polygonal laminas. The prism programs also are of more general
application than existing computer programs that are based on the
exact gravity and magnetic effects of rectangular prisms. There are
no restrictions on the use of the exact formula for the gravitational
attraction of a polygonal prism, but the formulas for the magnetic
effect are restricted in that demagnetization is not considered,
and a finite answer is not obtained in the unrealistic circumstance
where an observation point coincides with an edge of the prism.Least-squares
methods permit calculation of the gravity or magnetic effect of models
without knowledge of the density or magnetization contrasts, respectively,
by comparison of the observed anomalies with theoretical dimensionless
values to determine contrasts as regression coefficients. The coefficient
of correlation provides a goodness of fit estimate that helps model
evaluation. After calculating a magnetic terrain correction for an
outcrop of Quaternary dacite and andestite near Clear Lake, Calif.,
an improvement of the coefficient of correlation from 88 to the 92
percent level indicates that this volcanic unit probably extends
at least 150 m beneath the surface. Application of a magnetic terrain
correction to disconnected outcrops of Tertiary andesite, eliminates
most of a prominent v-shaped magnetic anomaly south of the San Juan
Mountains, Colo.
