UTILIZING BARE EARTH LIDAR TO IDENTIFY LATE QUATERNARY TECTONIC ACTIVITY IN HEAVILY VEGETATED LANDSCAPES, NORTH-CENTRAL COLORADO

In densely treed areas, airborne light detection and ranging (LiDAR) data greatly enhance our ability to identify geomorphic features (e.g., lineaments, scarps) that may have formed from Quaternary fault surface rupture. LiDAR data also aid in distinguishing possible tectonic geomorphic features from similar features with a nontectonic origin (e.g., landslides, moraine crests). Our study of potential Quaternary tectonic features along the east flank of the Gore Range is an example of utilizing LiDAR data. Although aerial photographs had been examined, many potential late Quaternary tectonic features were not recognized until LiDAR data were available; fault scarps and lineaments that cannot be detected on stereo aerial photographs can be readily visible using bare earth LiDAR data.

The LiDAR survey completed for our study covered about 620 km² of densely vegetated mixed terrain, including steep slopes, and produced data for all returns, including bare earth. The average point spacing was 1.57 m, average point density was 0.41/m², and area/point was 2.47 m². Hillshade images of the data were created in ArcGIS, and hillshades with various sun azimuths and altitudes were used by themselves and superimposed to highlight and define geomorphic features with various orientations.

The goal of our study is to evaluate evidence for late Quaternary tectonic activity on the northwest-striking, 45-km-long Gore Range frontal fault, located on the eastern flank of the Gore Range. To do this, we used bare earth LiDAR data to: 1) map the surficial geology, including glacial landforms and landslides, in the Gore Range adjacent to the fault; and 2) identify lineaments and scarps that could indicate late Quaternary fault surface rupture.

Using LiDAR imagery, we identified at least 9 areas with possible fault scarps that cut glacial deposits of possibly two ages. These scarps, which are being examined during ground surveys, could have been produced during the late Quaternary, and may include some with post-Pinedale displacement (within the last ~10,000-12,000 years). The identified scarps are currently being investigated in the field using qualitative and quantitative dating, geomorphic interpretations, and scarp profile measurement.