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

Ground-penetrating radar (GPR) experiments were conducted on a Quaternary sedimentary (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 tested in a water saturated alluvial deposits (mostly sand and gravel). The 100 MHz antennae provided adequate penetration depth and allowed better lateral continuity and resolution of the subsurface targets than the 50 MHz antennae. Results show that most of GPR data are contaminated by strong diffraction hyperbolae caused by above-ground objects near the survey line. Therefore, it is very important to recognize the diffractions through air and not to confuse them with the reflections from underground geologic features. Despite the air diffraction problem, the GPR data allow us to prospect subsurface sedimentary and tectonic structures. Water table, channels and meander 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 reserved.