CORRELATION BETWEEN LINEAMENTS, OUTCROP FRACTURES, AND BOREHOLE FRACTURES IN THE FRACTURED AMPHIBOLITES OF NORTHWESTERN NORTH CAROLINA

Correlations between well and outcrop fracture orientation data and lineaments are not well-documented in the literature. In an effort to test for potential correlations, we present a study in which we compare (1) lineaments, (2) measured fracture sets at the outcrop scale, and (3) fracture sets delineated from optical televiewer (OTV) logs. We confine our study to the amphibolite rocks of northwestern North Carolina. This region contains a monitoring well in which borehole logging methods have been employed as well as many outcrops for direct measurement of fracture sets. We employed two methods of lineament analysis in ArcGIS and ArcView using orthophotos and digital elevation models (DEM). We created lineament shapefiles in ArcGIS and exported them for analysis in ArcView by applying a script to determine (1) count, (2) length, and (3) azimuthal direction of the lineament picks. We then generated histograms and rose diagrams representing weighted length measurements by azimuthal direction. We obtained other fracture orientations from outcrops and a deep monitoring well within the lineament study area. Lineaments constructed in ArcGIS using orthophotos yielded a high concentration of east-west and north-south trends, though other azimuthal directions are also represented. Lineaments constructed with the DEM (with contours added) produced the same relative east-west lineament orientations, but fewer north-south lineament orientations. Outcrop and borehole fracture data roughly verify the orientations presented by the lineament analyses. Outcrop and well data suggest that foliation is responsible for the high occurrence of north-south orientations. East-west trends correlate with (1) several long valleys in the study region, and (2) the primary hydraulically-conductive fracture zone intersecting the monitoring well.