A predictive penetrative fracture mapping method from regional potential field and geologic datasets, southwest Colorado Plateau, U.S.A.

M.e Gettings ,Mark W Bultman

doi:10.1186/bf03351850

Abstract

Abstract Some aquifers of the southwest Colorado Plateau, U.S.A., are deeply buried and overlain by several impermeable units, and thus recharge to the aquifer is probably mainly by seepage down penetrative fracture systems. This purpose of this study was to develop a method to map the location of candidate deep penetrative fractures over a 120,000 km2 area using gravity and aeromagnetic anomaly data together with surficial fracture data. The resulting database constitutes a spatially registered estimate of recharge location. Candidate deep fractures were obtained by spatial correlation of horizontal gradient and analytic signal maxima of gravity and magnetic anomalies vertically with major surficial lineaments obtained from geologic, topographic, side-looking airborne radar, and satellite imagery. The maps define a sub-set of possible penetrative fractures because of limitations of data coverage and the analysis technique. The data and techniques employed do not yield any indication as to whether fractures are open or closed. Correlations were carried out using image processing software in such a way that every pixel on the resulting grids was coded to uniquely identify which datasets correlated. The technique correctly identified known deep fracture systems and many new ones. Maps of the correlations also define in detail the tectonic fabrics of the southwestern Colorado Plateau.

Highlights

The Colorado Plateau south of the Colorado River and west of the Little Colorado River (Fig. 1) is the source area for ground water recharge to the deep aquifers feeding the springs and seeps on the south side of the Grand Canyon (Robson and Banta, 1995)
Candidate deep fractures were obtained by spatial correlation of horizontal gradient and analytic signal maxima of gravity and magnetic anomalies vertically with major surficial lineaments obtained from geologic, topographic, side-looking airborne radar, and satellite imagery
The objective of this study was to produce a set of maps of candidate deep fractures for the southwestern Colorado Plateau derived from vertical spatial correlation of surficial fractures with the lineaments of deep structure derived from analysis of gravity and aeromagnetic data (Gettings, 2003, 2003a)

Summary

Introduction

The Colorado Plateau south of the Colorado River and west of the Little Colorado River (Fig. 1) is the source area for ground water recharge to the deep aquifers feeding the springs and seeps on the south side of the Grand Canyon (Robson and Banta, 1995). The Mississippian Redwall Limestone, with its fracturing and karsts, is an important deep aquifer. This part of the Plateau is sparsely populated and relatively undeveloped with few deep boreholes, and little is known of its geology and hydrology except at a regional scale. On the maps of candidate deep fracture locations, areas of high density or spatial frequency of correlations provide an estimate of where recharge potential is more favorable

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Discussion

Conclusion