GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 ___ GNGTS 2023 The value of the frequency exponent c is approximately equal to 0.3, except in the shallower part of the model between x = 25 and 75 m, where higher values ​ are observed (~ 0.4), likely due to an increase of the silty-clayey-peaty fraction in agreement with the model. σ '' The results of the inversion of MASW data were limited to a maximum depth of 20 m to make a comparison with the ERT/TDIP models. The vs model highlights a strong impedance contrast at a depth of approx. 2 m, likely due to a transition between a soft layer (peat, clays, silt) to a stiffer (sandy silt) one, as already shown by the conductivity models. The transition from sandy silts to the sand formation at approx. 7 m depth is characterized by a lower impedance contrast. Finally, the permeability section (Fig. 2d) resulting from the prediction after Weller et al. (2015), shows values ​ between 10-10 and 10-11 m2 for sandy lithotypes (deep layer and left side at x = 0-25 m of the shallow layer), while k is ~ 10-11-10-12 m2 for the intermediate sandy silts and for the shallow zone between x = 25-75 m, with the lowest values ​ ( k < 10-12 m2) where clay or peat are likely located. The prediction of k for the aforementioned zone at x = 80-100 m, likely affected by the massive presence of anthropogenic features, is not reliable. Conclusions In this work we presented an example (on a selected line) of the application of ERT and TDIP methods, integrated by MASW data and validated by borehole measurements, for the characterization (layering and permeability) of a shallow coastal aquifer located within the Circeo National Park (LT). The integration of the multi-parameter model resulting from the full-decay inversion of TDIP data and with the vs model retrieved through the inversion of MASW data can help to reduce the residual ambiguities arising when i.e. ERT is applied standalone. In fact, we were able to discern between changes in parameters due to saturation and/or to a near-surface increase of the clay/silt fraction. This approach allows a first approximation prediction of the permeability, to be used for rapid hydro-geophysical screening of the coastal areas. However, the application of the presented procedure for extremely conductive coastal environments, where the signal/noise ratio is generally very low, is only limited to the shallower portion of the subsurface Acknowledgements Francesco Pugliese (“Sapienza” University of Rome) is thanked for his technical support to the on-site geophysical measurements. References