Master degree fieldwork: The electric response of clay’s deposits in the geothermal area of Saturnia (Italy, Grosseto)

The activity done in this fieldwork aimed to execute a geo-electric tomographic survey (to calculate the resistivity values across the depths and along specific hangings) in the geothermal area of Saturnia (Figure 1). To be more specific, the focus of the study were on the clay’s deposits and then be able to extract from them both qualitative (areal distribution/thickness) and quantitative (resistivity values analysis) information.

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Figure 1: Area of the fieldwork

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The clay’s deposits are important because knowing their extension and volumes permit to model the entire geothermal aquifer/hydro-geology of the area. This is very relevant especially for businesses that use such natural thermal source as can be considered the SATURNIA SPA (Figure 2). In fact, SATURNIA SPA commissioned this work to understand how their water caption can be affected negatively and then act in time to avoid surprises in the near future.

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Figure 2: SATURNIA SPA

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The area of study was characterised by both compressional and extensional tectonic events. The extensional events are responsible to create wide sedimentary basins. Starting from Pleistocene these basins were filled by both continental and marine deposits (Figure 3).

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Figure 3: tectonic evolution post-collisional happened during Miocene. (L), Unità liguri; (FT), Unità della falda toscana; (CV), Evaporiti triassiche; (B) Basamento, (Mn) Depositi del Miocene medio; (MS) Depositi del Miocene superiore (da Bonciani et alii, 2005).

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I divided then the study area in smaller geographical regions (Figure 4) based mainly on the geomorphological/geological characteristics. In fact, the position of all the tomographic lines are the result of a very accurate look to all the geomorphological and geological evidences (Figure 5) that allowed me to strategically acquire, at the best of the possibilities, data regarding the clay’s deposits to hight accuracy and precision.

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Figure 4: Position of the different geo-electric tomographic lines divided in zones (indicated by the different colours).

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Figure 5: Geomorphology 3D model of the study area. Delimited with a black line the area interested by the geo-electric survey.

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With the elaboration/interpretation of the geo-electric tomographic lines I have quantified the volumes of clay’s deposit across all the study area (qualitative type of study, Figure 6).

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Figure 6: Example or a geo-electric tomographic line with the use of two different colour scales with the aim to highlight the clay’s deposits.

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As final steps I tried to divide the clay’s deposit in groups based on their resistivity values (quantitative type of study, Figure 7).

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Figure 7: The different class of resistivity obtained in the different sub-areas

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The softwares used were:

Microsoft office

Res2inv (software to process the data acquired by the geo-electric survey)

ArcGis mapping&analysis software by ESDRI (to the generation of maps and creation of a geo-database)

The technical instrument used were:

Geo-resistivimeter ABEM-Terrameter LS (to acquire the resistivity measurement in function of depths)


Livella di Abney (to acquire data relative to the topography along each tomographic lines)


USB Dongle GPS (to record the start and end point of each tomographic line)