Amplitude Analysis of Repetitive GPR Reflections on A Lake Bonneville Delta, Utah

Several recent theoretical studies have documented the sensitivities of the amplitude and waveform of a ground penetrating radar (GPR) reflection to the contrast in electromagnetic properties across the reflecting contact. Here we show that, in a setting with repetitive layering, it is possible to place constraints on conductivity and variations in permittivity within layers and across layer boundaries. The data set consists of 50 MHz, 100 MHz and 200 MHz profiles that image subparallel dipping bedding planes in a gravelly deltaic forest facies on a Lake Bonneville delta, Utah, USA. Strongly reflecting horizons with 1–2 m spacings bound packages with finer internal layering. From finite-difference time-domain (FDTD) simulations of radarwave propagation through such strata, constraints are placed on the variations in permittivity across larger-scale and finer-scale layering. Modelling the relative amplitudes of reflections demonstrates that the finer-scale permittivity contrasts are ∼0.4–0.8 times that of the 1–2 m layering. Amplitude v. offset (AVO) analysis yields an upper bound of ∼3.5 for the contrast in permittivity at the larger-scale layer boundaries. Overall signal attenuation requires the average conductivity to be in the range of 0.7–0.8 mS/m