3D Reconstruction of Buried Structures from Magnetic, Electromagnetic and ERT Data: Example from the Archaeological Site of Phaistos (Crete, Greece)

Abstract

A multi‐methodological geophysical prospecting was performed in a survey area of the archaeological Phaistos site on the Greek island of Crete, as part of an international research project aimed at investigating the less excavated hills of Phaistos and the underlying plateau. The article provides an assessment of the resolution of the chosen techniques for non‐destructive testing of buried ancient structures in the geological landscape of Phaistos. The magnetic and electromagnetic surveys clearly detected anomalies related to human activity, some of which were subsequently defined in detail by resistivity tomography imaging. In particular, variations of the observed electrical and magnetic parameters perfectly correlate to a wall structure made of calcareous material, which has been brought to light by subsequent excavations that unearthed large sectors of a fortification in a double curtain wall, chronologically consistent with the historical sources about the destruction of Phaistos in 150 bc. Copyright © 2015 John Wiley & Sons, Ltd.

Multi‐methodological Geophysical Exploration for the Interpretation of the Ancient Landscape of Phaistos (Greece)

“…The Profiler can investigate simultaneously at different depths by selecting up to three different frequencies between 1 kHz and 16 kHz, which are chosen according to the specific application. Based on the results of the previous geophysical test, frequencies of 15 kHz, 10 kHz and 5 kHz were selected, which allow for an accurate in‐depth exploration of the first 2 m of subsoil (Di Maio et al ., ).…”

“…To such relatively large‐scale shallow anomaly pattern, resistive or conductive well‐shaped anomalies overlap; their geometry, which is also confirmed by the GPR data (see next subsection), may be correlated to presence of anthropic structures. In particular, the alignments of contiguous resistive nuclei observed in the northern sector of the shallowest slices (dashed black lines in Figure ) suggest the presence of buried walls, probably made of calcareous material according to both the amplitude of the resistivity values and the remains brought to light by the excavation in the test site (Di Maio et al ., ). Moreover, the semicircular geometry in the centre of the survey area, which is well defined in the first two slices (dashed thick black line in Figure ), resembles one of the semicircular shapes identified by previous orthophoto analyses and tentatively attributed to anthropic remains like tumuli (Bredaki et al ., ).…”

“…After a detailed investigation of a test site (red square in Figure b) aimed at assessing the resolution power of several geophysical techniques for the Phaistos’ geological background (Di Maio et al ., ), the study area indicated with a blue rectangle in Figure b has been characterized by the following geophysical surveys: magnetic, frequency domain electromagnetic, ground penetrating radar and electric resistivity.…”

“…The anomaly in the central sector of the survey area, also detected by previous orthophoto analyses, can be instead reproduced by two perpendicular sources (2 m wide by 11 m long and 2 m wide by 10 m long) by using the same magnetization parameters and top depth as before. The choice for the shape, size, depth and magnetic contrast of the hypothesized structures has been constrained by the results from the high‐resolution ERT and GPR surveys and the characteristics of the wall found in the test area, made of calcareous material interspaced with coarse stones and wet soils (Di Maio et al ., ).…”

“…(b) Location of the three archaeological exploration sectors (A, B and C) in the Phaistos site. The blue rectangle in sector B specifies the geophysical survey area, while the red square in sector A indicates the sample area where various geophysical methods were previously tested for assessing their resolution for the considered geological setting (Di Maio et al ., ).…”