Abstract: Techniques and Uses of Slope Mapping

W. E. Dole, N. F. Jordan

"Slope" mapping is a technique for visual presentation of the gradient of geologic and geophysical surfaces. This presentation method shifts emphasis from the highs and lows of the original data to the steep-gradient zones. The shift in emphasis often provides new insight into edges, alignments, or discontinuities which were hidden or obscured on the original map presentation. Slope maps of bathymetry and structure have suggested the positions of geologic alignments and discontinuities. Slope maps of gravity and magnetic data have helped locate regional alignments or discontinuities associated with possible crustal disruptions.

Slope maps produce a quantitative expression of the slope--the rate of vertical change in the original data over some horizontal distance. Mathematically, the slope could be described as the maximum positive first-horizontal derivative at a given point. The highest slope values are in the steepest gradient zones on the original map.

Three different techniques were developed to make slope maps. A manual slope-mapping technique uses hand measurement and contouring to produce reasonably accurate results over large areas. A computer slope-mapping technique uses digital processing to produce highly detailed slope maps over local areas. A commercially available analog device, the Datacolor machine, can be used to produce instantaneous and reasonably accurate colored slope maps over local or regional areas.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA