Investigating alluvial and tectonic features with ground-penetrating radarand analyzing diffractions patterns

Ground-penetrating radar (GPR) experiments were conducted on a Quaternary s edimentary (made up of gravel: sand and loess) site to image the structures and tectonic features. Two sets of antennae, 50 and 100 MHz, have been tes ted in a water saturated alluvial deposits (mostly sand and gravel). The 10 0 MHz antennae provided adequate penetration depth and allowed better later al continuity and resolution of the subsurface targets than the 50 MHz ante nnae. Results show that most of GPR data are contaminated by strong diffrac tion hyperbolae caused by above-ground objects near the survey line. Theref ore, it is very important to recognize the diffractions through air and not to confuse them with the reflections from underground geologic features. D espite the air diffraction problem, the GPR data allow us to prospect subsu rface sedimentary and tectonic structures. Water table, channels and meande r bars are observed on GPR data. Most of these observations are correlated with borehole and trench data. (C) 2000 Elsevier Science B.V. All rights re served.