USING LIDAR AND GEOLOGIC MAPPING TO LOOK AT BRITTLE AND DUCTILE FAULT ZONES - NEW AND OLD TOOLS TO AUGMENT SITE INVESTIGATIONS

Digital elevation models (DEMs) derived from airborne Light Detecting And Ranging (LiDAR) are relatively new tools that can be integrated with geologic mapping using a Geographic Information System (GIS) to augment site investigations. Two projects within the Blue Ridge geologic province of western North Carolina are summarized where shaded relief, topographic contour, and slope maps derived from LiDAR DEMs were used to help map and interpret geologic features. LiDAR imagery was used mainly to identify topographic lineaments, and geomorphologic features interpreted as debris fans and other colluvial deposits to be targeted for field evaluation. In both project areas earlier ductile faulting followed by WNW-trending brittle faulting produced deformation fabrics that influence slope stability and potentially groundwater flow.

As part of the landslide hazard mapping in Watauga County we evaluated a 14km x 0.5km zone of existing and potential rock slope instability near Boone. This zone encompasses WNW-trending topographic features where 14 active and past-active rock slides occur mainly in rocks of the Grandfather Mountain Window along the Linville Falls fault. Mapped WNW-trending lineaments are expressions of a regionally extensive area of fractures and faults coincident with this zone. Existing geologic mapping was compiled and supplemented with lineament mapping and kinematic analyses of site specific rock slope data to characterize and delineate the zone of rock slope instability.

We completed 1:6,000-scale geologic mapping of a 3.5-km² area near Skyland, in Buncombe County to establish a geologic framework to support groundwater studies. Rocks are within the Ashe Metamorphic Suite-Tallulah Falls Formation, a highly deformed heterogeneous package of metasedimentary and mafic metaigneous rocks. A >100m wide brittle fault zone was identified by the presence of gouge, breccias and the realignment of older ductile fabrics. Locally the fault is in contact with unconsolidated colluvial(?) deposits. The fault zone trends WNW and is aligned with lineaments identified in LiDAR imagery. Fault and fracture data are consistent with a transtensional-flower structure model interpreted to be Mesozoic or younger in age. LiDAR imagery was also used as an aid to map colluvial deposits associated with the fault zone.