Imaging of Shallow Underwater Ancient Ruins with ERT and Seismic Methods

Abstract

The present geophysical research aims in evaluating the applicability of the Electrical Resistivity Tomography (ERT) and seismic (Multichannel Analysis of Surface Waves - MASW and refraction) methods on mapping shallow underwater ancient remnants. The preliminary results from a single seismic line and its corresponding ERT section (surveyed at the site of Agioi Theodoroi area located 10 km eastern of Heraklion, Crete, Greece) are presented. This work demonstrates that ERT as well as MASW are very promising geophysical methods for the delineation of underwater antiquities. High resistivity anomalies were attributed to building walls and are in accordance with some of their mapped outcrops. Furthermore, MASW method exhibits significant correspondence with ERT showing lateral S-wave velocity variations at the positions where the high resistivity anomalies exist. Surface waves traveling through the shallow sediments (Scholte-waves) demonstrate relatively low velocity values. This makes them suitable for the detection of relatively large (> 0.5 m) underwater manmade structures, providing the use of a high frequency source and thus, the creation of relatively short wavelengths (< 2 m). These preliminary results show the potential in employing modern tomographic techniques in the revealing the cultural dynamics in shallow off-shore archaeological sites.