Using ground-penetrating radar to investigate the internal structure of Puente del Inca, Mendoza, Argentina

Abstract

We performed ground-penetrating radar measurements to study the internal structure of Puente del Inca (Inca Bridge). This natural structure is located in Mendoza, Argentina, and its formation is associated with deposition of travertine caused by geobiological processes created by hot mineral springs. The 200-MHz ground-penetrating radar measurements performed on the surface of the bridge allowed us to relate the behaviour of the electromagnetic signal with the presence or absence of hot spring activity. We also made ground-penetrating radar measurements at 20 MHz to estimate the propagation velocity and study the bridge's internal structure. In order to validate the groundpenetrating radar results, we used a soil dielectric sensor to obtain the attenuation and the velocity of the medium. The results showed similar propagation velocities (0.0222 m/ns on average) between field observation (ground-penetrating radar) and independent sensor data, as well as significant attenuation due to the hot spring water, which is the primary element controlling the response of the electromagnetic signals. As checked through dielectric sensor measurements, the unusually low electromagnetic wave velocity is due to polarisation mechanisms related to thermal water, which cause a very high permittivity value (178.1). However, the medium is not sufficiently dispersive (conductivity=27.7 mS/m; attenuation=3.5 dB/m) to condition the results of ground-penetrating radar measurements if low-frequency antennas (20 MHz) are used.