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Panel 6. Puig Ciutat: Geophysical prospecting

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What is geophysics and why is it applied in Puig Ciutat?

Geophysics is the science that applies non-invasive systems for exploring the subsoil. It was applied right from the start of the project as a tool that could help manage the excavations. Puig Ciutat is also an experimental site that enables us to test equipment and develop working methods. In addition to the surveys carried out in the early years, which are presented here, a systematic survey of each new area to be excavated is carried out at the beginning of each dig.

We are able to systematically apply geophysical techniques at Puig Ciutat thanks to the participation of the company SOT Prospecció Arqueològica.

Magnetic prospecting

What does it consist of? This measures local variations in the Earth’s magnetic field.

What does it enable us to do? It is useful for identifying kilns, hearths, burned areas, metals, filled trenches, as well as for delimiting sites.

Magnetic gradient map: burnt areas and possible metals are indicated in red, possible streets or ditches in white (data from SOT Propsecció Arqueológica)
Magnetic gradient map: burnt areas and possible metals are indicated in red, possible streets or ditches in white (data from SOT Propsecció Arqueológica)

Ground-penetrating radar (GPR) prospecting

What does it consist of? This measures variations in humidity by emitting an electromagnetic pulse, the echoes of which are subsequently received at the surface

What does it enable us to do? It is useful for detecting built structures, and allows us to visualise what structures are like at depth.

GPR reflectivity map: the built elements and bedrock are represented in black (data: SOT Propsecció Arqueológica)
GPR reflectivity map: the built elements and bedrock are represented in black (data: SOT Propsecció Arqueológica)

Electromagnetic prospecting

What does it consist of? This measures variations in conductivity and magnetic susceptibility by analysing the way the subsoil responds to an electromagnetic field applied from the surface.

What does it enable us to do? It is useful for characterising substrate composition and indirectly defining parameters like salinity, permeability, and porosity.

Electrical conductivity map: the black areas were interpreted as either the limey marl bedrock or construction material from the site; the white areas are clayey marls of the upper levels (data: Ghent University, Belgium)
Electrical conductivity map: the black areas were interpreted as either the limey marl bedrock or construction material from the site; the white areas are clayey marls of the upper levels (data: Ghent University, Belgium)

Interpretation of results

What does it consist of? This gives archaeological meaning to variations in the physical properties of the subsoil.

What does it enable us to do? This allows us to extract the archaeologically most significant elements from the geophysical images

Interpretation of the results: synthesis of the results and classification according to archaeological significance
Interpretation of the results: synthesis of the results and classification according to archaeological significance

Aerial and relief images: www.icgc.cat