Ground-penetrating radar detection of small-scale channels, joints and faults in the unconsolidated sediments of the Atlantic Coastal Plain

The geological characterization of the shallow subsurface in the unconsolidated sediments of the Atlantic Coastal Plain, and other unconsolidated sediment regimes, may involve jointing, faulting, and channeling not readily detectable by conventional drilling and mapping. A knowledge of these features is required in environmental, geotechnical, and geomorphological studies. Ground-penetrating radar (GPR) may be used to routinely map these structures. Three principal shallow subsurface features are readily detectable using GPR: paleochannels, joints or fractures, and faults. The detection of paleochannels Is dependent on the scale of the GPR survey and the attitude of the channel within the survey area. Channel morphological features such as scour surfaces, point bars, arid thalwegs are observable. Joints and fractures are more difficult to detect depending upon size, patterns, orientation, and fill material. Vertical joints may not be visible to radar unless they are wider than the sampling interval or are filled with radar-opaque materials such as limonite. Angled joints or fractures may be distinguished by an apparent continuous reflector on the radar profile. Faulting on radar profiles may be observed by the offset of reflectors, the image of the fault plane, or the coherent interpretation of a fault system.