VALIDATION OF THE RELATION BETWEEN PATTERNS IN THE STRUCTURE OF FRACTURED BEDROCK AND STRUCTURAL INFORMATION INTERPRETED FROM TWO-DIMENSIONAL VARIOGRAM MAPS OF VARIOGRAM MAPS

A surprising result was obtained in analyses of the yields of domestic water wells drilled into fractured crystalline bedrock in New Hampshire and Virginia—the patterns on two-dimensional variogram maps can be correlated with the structure of the bedrock. Therefore, variography is useful in decoding the structural control of yields of water wells in areas underlain by poorly-exposed fractured crystalline bedrock. Long-range anisotropies in the variograms are associated with the regional structural and topographic grain, whereas short range anisotropies are interpreted to be the result of local variations in the topography. The variation in the intensity and orientation of horizontal and high-angle fractures in outcrops along a major antiform were correlated with the patterns in the variogram maps. In four small study areas in Loudoun County, Virginia, we successfully verified predictions for variogram patterns by using the known distribution of Mesoproterozoic bedrock units, Mesoproterozoic and Paleozoic foliation, and fracture data.