A PALEOSTRESS FIELD FOR PENNSYLVANIA FROM A LINEAMENT ANALYSIS

Paleostress is most easily determined through tectonic features such as faults and fractures. These features may exert a strong control on topographic patterns as they create pathways for weathering and erosion. Among tectonic features, those that may strongly influence topographic patterns include folds, faults, large fracture systems, and joints. Using digital imagery, we highlight topographic lineaments and evaluate the potential control of tectonic induced deformation on topography for the state of Pennsylvania. Several physiographic regions exist within Pennsylvania, most of which extend in curved bands from east to west and are associated with Appalachian tectonics: coastal plains, piedmonts, plateaus, and mountains (parallel ridges and valleys). Past orogenic events have worked to develop many of these regions, and stresses associated with these orogenic events have also deformed the rocks with folds, faults, fractures, and joints. We conducted a statewide lineament analysis on a digital elevation model (DEM) processed as hill-shades at 45° azimuthal increments with a sun-angle of 45° to better highlight topographic changes. Lineaments were manually picked to avoid the selection of man-made structures. The orientation of lineaments and their frequency for cells within a grid over the entire state were compared to structural data and dominant trends were associated with known tectonic features. This proves the tectonic source of dominant lineament trends. Results from the lineament analysis – in conjunction with focal mechanism data – were used to interpret maximum compressive horizontal paleostress orientations within each cell. We present the resulting paleostress field for the state of Pennsylvania, to not only better our understanding of the larger kinematics associated with Appalachian tectonics, but to also identify complexities at a smaller scale.