Archaeological and paleoenvironmental interpretation through tomographic model classification and geophysical mapping ; Ostia Antica (Rome, Italy) case study

Abstract

The Ostia Antica site, the ancient port of Rome remarkably well preserved, constitutes a privileged study area to trace the geomorphological and environmental evolution of the region. It also offers an ideal framework to test and develop non-destructive investigation methods, in an interdisciplinary approach combining archaeology, geophysics, hydrogeology and geotechnics. Numerous geophysical campaigns have already been conducted there by different research groups to better understand the area. This master thesis is therefore part of the continuation of these investigations and aims to contribute to the interpretation of the geoarchaeology and paleoenvironment of the Ostia Antica region. To this end, two geophysical methods were implemented in the field: electrical resistivity tomography (ERT) and seismics. In addition, part of the magnetic induction survey carried out by Ghent University was also processed. The interpretation of the geophysical data was divided into two parts. Indeed, some profiles, carried out near the Tiber, were processed and interpreted separately from the rest of the profiles. The analysis of the second group of profiles raised several challenges, notably the presence of deep anomalies in some of them, for which it was necessary to determine whether they were related to the inversion process or not. Indeed, a certain ambiguity persists in the inversion, as multiple models can equivalently reproduce the observed data. To address this issue, constrained inversions, based on geostatistical or geotechnical data, were performed in addition to classical isotropic inversions. Finally, part of the inverted profiles was analysed using a probabilistic approach applying Bayes’ rule to classify the inversion results to assign a lithology or a type of deposits to each area. This study relies on data collected by other researchers, which are used to establish the a priori information for the classification. The overall data processing allowed the delimitation of the archeosphere, characterised by higher resistivities, as well as the interface between freshwater-saturated deposits (more resistive) and saltwater-saturated deposits (more conductive). The different inversions suggest that the anomalies observed at depth are probably real, but their interpretation remains difficult to date. It would therefore be relevant to carry out additional profiles with high vertical resolution to study these anomalies. Deep boreholes could also provide complementary information.