STRUCTURAL SIGNIFICANCE OF LINEAMENTS INFERRED FROM HIGH-RESOLUTION LIDAR DIGITAL ELEVATION MODELS IN AREAS WITH HEAVY VEGETATION OR SOIL COVER

The structural interpretation of lineaments inferred from high resolution lidar topographic data can be straightforward in areas of sparse vegetation and minimal soil cover. When bedrock is obscured by thick surficial deposits or heavy forest cover, however, interpretation may become more difficult and ambiguous. This can be because the lineaments are muted expressions of actual bedrock structures or because they are surficial guide structures that indirectly reflect subsurface deformation and underlying structures, or some combination of the two. In two areas for which both airborne lidar coverage and outcrop measurements of structures were available—one underlain by flat lying and largely undeformed bedrock along the Ohio River valley and the other underlain by highly deformed metamorphic rock adjacent to the Skagit River valley in the North Cascades of Washington—orientations from lidar-based lineament maps agree well with with the strikes of steeply dipping bedrock joints. Indications of gently dipping foliation and formational contacts, however, are absent (although they might be inferred by other means, for example tracing persistent slope angle breaks). In the first example, bedrock structures also appear to exert significant influence on landslide size on steep slopes along the river valley. In two other cases for which independent outcrop measurements are not available, lineament maps produced from statewide 2-m lidar coverage appear to show secondary shear deformation above the buried Suffield fault in northeastern Ohio (a structure that is weakly seismogenic and truncates regionally important petroleum reservoirs) and the coincidence of producing Marcellus Shale wells with areas of high lineament density in southeastern Ohio. Thus, it appears that high resolution lidar data may help to elucidate geologic structures (fracture zones in particular) in areas of poor bedrock exposure.