MAPPING BRITTLE STRUCTURES IN WESTERN CONNECTICUT USING LIDAR-BASED DEM DATA

A complex pattern of brittle structures in western Connecticut is revealed by hillshade models constructed from LiDAR-based DEM data (horizontal resolution of 10 feet, and a vertical resolution of 1 foot). The structures include linear to curvilinear fractures and faults with typical lengths of 100s of meters, and occasionally several kilometers. The structures are mapped in areas where bedrock is not covered by glacial deposits, although some structures may be discerned through thin layers of till or are extensive enough as to be traceable between till covered areas. The brittle structures, as well as foliation, are commonly enhanced by glacial scouring which made them deeper and wider. Only brittle structures that cut foliation at an angle were considered during mapping, although some structures may be parallel to foliation, they could not be differentiated from scoured foliation. Most structures are interpreted to be fractures, although some may be faults that have not been recognized in previous mapping efforts. Several of the structures do relate to mapped brittle faults such as the Mixville fault north of New Haven, and unnamed faults south of Danbury, but most are not associated with any mapped features.

In this study, three areas were chosen to illustrate the potential of using the LiDAR data for mapping brittle structures. The first area is in the southeastern portion of the Litchfield quadrangle where a series of 270° – 290° trending, 250 – 700 meter long fractures that are spaced at 150 – 200 meters cut across a NE striking foliation in the Hartland Formation. The second area, south of Danbury, shows several previously-mapped faults that cut Proterozoic and Paleozoic metamorphic rocks. In addition, numerous 300-1000 meter long fractures are revealed that are parallel to the mapped faults. In the third area north of Greenwich and Stamford, previously-mapped faults may be extended 100s of meters using the LiDAR data, and numerous additional brittle structures are revealed. Several of these structures extend multiple kilometers trend 005° to 020°.

Delineating these structures is important for understanding groundwater flow, potential movement of subsurface contaminants, and geotechnical planning. Further field work will be done to confirm the origin of these features and their relationship to regional tectonics.