GNGTS 2019 - Atti del 38° Convegno Nazionale

576 GNGTS 2019 S essione 3.1 the Tuscan Nappe. From 2 to 5 km of depth in the central part of the 2D model a large body of about 1000 Ωm was identified. This body is coherent with the previous model of Manzella et al. (2006) except that it does not result laterally continuous. This may suggest new insights into the K-horizon, the deep reflector whose discontinuity has been recently demonstrated in Larderello (Bertani et al. , 2018). We have confidence that more implications will be inferred thanks to the 3D characterization we are currently working on. Conclusion. The PSO algorithm was adopted for the 2D stochastic inverse modelling of an MT field data set located in the Larderello-Travale geothermal area (Italy). The investigated profile was composed of 11 sites and was interpreted with a metaheuristic method for the first time. The outcome was in line with results of previous research, with the advantage that the modelling was not initially biased by the external starting model derived from geology. Another contribution of this work is that our method has proven to be a valid tool for the investigation of a very complex electrical structure. A possible direction of future work will be the adoption of the models resulting from PSO to initially constrain the 3D MT inversion. The inclusion of part of this data set in a 3D inversion modelling is already underway. Aknowledgements. Computational resources provided by hpc@polito (http://hpc.polito.it) . References Bertani, R., Büsing, H., Buske, S., Dini, A., Hjelstuen, M., Luchini, M., ... and Serniotti, L.; 2018: The first results of the Descramble project . Proceedings from the 43 rd workshop on geothermal reservoir engineering, Stanford University, Stanford, California. Caldwell, T.G., Bibby, H.M. and Brown C.; 2004: The magnetotelluric phase tensor . Geophysical Journal International, 158 , 457–469. Ledo, J.; 2005: 2-D versus 3-D Magnetotelluric data interpretation . Surveys in Geophysics, 26 , 511–543. Manzella, A., Spichak, V., Pushkarev, P., Sileva, D., Oskooi, B., Ruggieri, G. and Sizov, Y.; 2006: Deep fluid circulation in the Travale geothermal area and its relation with tectonic structure investigated by a magnetotelluric survey. Proceedings from the 31 st Workshop on Geothermal Reservoir Engineering. Stanford, California, January 30- Feb 1, 2006, pp. 1-6. Marti, A., Queralt, P. and Ledo, J.; 2009: WALDIM: A code for the dimensionality analysis of magnetotelluric data using the rotational invariants of the magnetotelluric tensor. Computers and Geosciences, 35 (12), 2295-2303. Pace, F., Santilano, A. and Godio, A.; 2019: Particle Swarm Optimization of 2D Magnetotelluric data. Geophysics, 84 (3), E125-E141. Fig. 2 - The resistivity model of the Travale MT profile resulting from stochastic inverse modeling (PSO) after 4000 iterations and without a priori starting model.