Multiple-scale study of fracture indicators at eight sites across the Appalachian orogen in Pennsylvania: Summary of results

Four scales of remote sensing were used to investigate fracture indicators (lineaments and fracture traces) at 8 study areas: (1) 1:500,000 Landsat 5 Thematic Mapper; (2) 1:250,000 Side-Looking Airborne Radar mosaics; (3) 1:80,000 National High-Altitude Program aerial photographs; and (4) 1:20,000 Agricultural Stabilization and Conservation Service aerial photographs. To allow for inter-comparison of results, two traverses of four study areas were arranged across the four major physiographic regions in the Appalachian orogen, (1) Plateau, (2) Ridge and Valley, (3) Great Valley; and (4) Piedmont. The remote sensing results for the Plateau and Ridge and Valley areas indicate that observed orientations are concentrated in the NW to NNW. Orientation peaks for the areas are less well defined but tend to be parallel and perpendicular to Mesozoic features. These findings indicate that causal relationships exist between bedrock paleo-stress trajectories and observed fracture indicator maxima. The results of the geomorphic parameter studies indicate that these features are complexly controlled by factors other than bedrock fracture fabric, most notably bedrock strike. Other findings of this study may generally characterize relationships between classes of fracture indicators. As imagery scale number increases: the average degree of expression of lineament features decreases; lineament frequency over each studymore » area decreases in a decay curve; plots of average lineament length show a positive trend for the three larger scales; and total lineament length over the study area shows a decay curve. Other results define potentially useful relationships between feature length, type, and degree of expression.« less