Insights into fluid circulation across the Pernicana Fault (Mt. Etna, Italy) and implications for flank instability

We conducted geophysical–geochemical measurements on a ∼2 kmN–S profile cutting across the Pernicana
Fault, one of the most active tectonic features on the NE flank of Mt. Etna. The profile passes from the
unstable E flank of the volcano (to the south) to the stable N flank and significant fluctuations in electrical
resistivity, self-potential, and soil gas emissions (CO2, Rn and Th) are found. The detailed multidisciplinary
analysis reveals a complex interplay between the structural setting, uprising hydrothermal fluids, meteoric
fluids percolating downwards, ground permeability, and surface topography. In particular, the recovered
fluid circulation model highlights that the southern sector is heavily fractured and faulted, allowing the
formation of convective hydrothermal cells. Although the existence of a hydrothermal system in a volcanic
area does not surprise, these results have great implications in terms of flank dynamics at Mt. Etna. Indeed,
the hydrothermal activity, interacting with the Pernicana Fault activity, could enhance the flank instability.
Our approach should be further extended along the full extent of the boundary between the stable and
unstable sectors of Etna for a better evaluation of the geohazard in this active tectonic area.

This work was partly financed by the DPC-INGV FLANK and LAVA
Projects.

Aizawa, K., 2008. Classification of self-potential anomalies on volcanoes and possible
interpretations for their subsurface structure. J. Volcanol. Geotherm. Res. 175,
253–268. doi:10.1016/j.jvolgeores.2008.03.011.
Aizawa, K., Ogawa, Y., Ishido, T., 2009. Groundwater flow and hydrothermal systems
within volcanic edifices: delineation by electric self-potential and magnetotellurics.
J. Geophys. Res. 114, B01208. doi:10.1029/2008JB005910.
Allard, P., Behncke, B., D'Amico, S., Neri, M., Gambino, S., 2006. Mount Etna 1993–2005:
anatomy of an evolving eruptive cycle. Earth-Sci. Rev. 78, 85–114. doi:10.1016/j.
earscirev.2006.04.002.
Baubron, J.-C., Rigo, A., Toutain, J.-P., 2002. Soil gas profiles as a tool to characterise
active tectonic areas: the Jaut Pass example (Pyrenees, France). Earth Planet. Sci.
Lett. 196, 69–81.
Cecchi, E., Wyk, Van, de Vries, B., Lavest, J.-M., 2005. Flank spreading and collapse of
weak-cored volcanoes. Bull. Volcanol. 67, 72–91.
Bonforte, A., Puglisi, G., 2006. Dynamics of the eastern flank of Mt. Etna volcano (Italy)
investigated by a dense GPS network. J. Volcanol. Geotherm. Res. 153, 357–369.
doi:10.1016/j.jvolgeores.2005.12.005.
Chiodini, G., Cioni, R., Guidi, M., Raco, B., Marini, L., 1998. Soil CO2 flux measurements in
volcanic and geothermal areas. Appl. Geochem. 13 (5), 543–552.
Conner, C., Hill, B., LaFemina, P., Navarro, M., Conway, M., 1996. Soil 222Rn pulse during
the initial phase of the June–August 1995 eruption of Cerro Negro, Nicaragua. J.
Volcanol. Geotherm. Res. 73, 119–127.
Corwin, R.F., Hoover, D.B., 1979. The self-potential method in geothermal exploration.
Geophysics 44–2, 226–245.
Dahlin, T., Zhou, B., 2004. A numerical comparison of 2D resistivity imaging with 10
electrode arrays. Geophys. Prospect. 52, 379–398.
Diaferia, I., Barchi, M., Loddo, M., Schiavone, D., Siniscalchi, A., 2006. Detailed imaging of
tectonic structures by multiscale Earth resistivity tomographies: the Colfiorito
normal faults (central Italy). Geophys. Res. Lett. 33, L09305. doi:10.1029/
2006GL025828.
Finizola, A., Lénat, J.F., Macedo, O., Ramos, D., Thouret, J.C., Sortino, F., 2004. Fluid
circulation and structural discontinuities inside Misti volcano (Peru) inferred from
self-potential measurements. J. Volcanol. Geotherm. Res. 135, 343–360.
doi:10.1016/j.jvolgeores.2004. 03.009.
Giammanco, S., Gurrieri, S., Valenza, M., 1999. Geochemical investigations applied to
active fault detection in a volcanic area: the NE Rift on Mt. Etna (Sicily, Italy).
Geophys. Res. Lett. 26, 2005–2008.
Giammanco, S., Immè, G., Mangano, G., Morelli, D., Neri, M., 2009. Comparison between
different methodologies for detecting Radon in soil along an active fault: the case of
the Pernicana Fault system. Mt. Etna. Applied Radiation and Isotopes 67, 178–185.
doi:10.1016/j.apradiso.2008.09.007.
Lentini, F., 1982. The geology of the Mt. Etna basement. Mem. Soc. Geol. It. 23, 7–25.
Loke, M.H., Barker, R.D., 1996. Rapid least-squares inversion of apparent resistivity
pseudosections by a quasi-Newton method. Geophys. Prospect. 44, 131–152.
Neri, M., Rossi, M., 2002. Geometria e volume dell'apparato vulcanico etneo: il
contributo offerto dall'uso di mappe digitali. Quaderni di Geofisica 20 (1–16),
1590–2595.
Neri, M., Behncke, B., Burton, M., Giammanco, S., Pecora, E., Privitera, E., Reitano, D.,
2006. Continuous soil radon monitoring during the July 2006 Etna eruption.
Geophys. Res. Lett. 33, L24316. doi:10.1029/2006GL028394.
Neri, M., Mazzarini, F., Tarquini, S., Bisson, M., Isola, I., Behncke, B., Pareschi, M.T., 2008.
The changing face of Mount Etna's summit area documented with Lidar technology.
Geophys. Res. Lett. 35, L09305. doi:10.1029/2008GL033740.
Neri, M., Casu, F., Acocella, V., Solaro, G., Pepe, S., Berardino, P., Sansosti, E., Caltabiano,
T., Lundgren, P., Lanari, R., 2009. Deformation and eruptions at Mt. Etna (Italy): a
lesson from 15 years of observations. Geophys. Res. Lett. 36, L02309. doi:10.1029/
2008GL036151.
Revil, A., Finizola, A., Piscitelli, S., Rizzo, E., Ricci, T., Crespy, A., Angeletti, B., Balasco, M.,
Barde Cabusson, S., Bennati, L., Bolève, A., Byrdina, S., Carzaniga, N., Di Gangi, F.,
Morin, J., Perrone, A., Rossi, M., Roulleau, E., Suski, B., 2008. Inner structure of La
Fossa di Vulcano (Vulcano Island, southern Tyrrhenian Sea, Italy) revealed by high
resolution electric resistivity tomography coupled with self-potential, temperature,
and CO2 diffuse degassing measurements. J. Geophys. Res. 113 (B07207).
doi:10.1029/2007JB005394.
Rice, J.R., 2006. Heating and weakening of faults during earthquake slip. J. Geophys.
Res.-Solid Earth 111, B05311.
Rust, D., Behncke, B., Neri, M., Ciocanel, A., 2005. Nested zones of instability in the
Mount Etna volcanic edifice, Sicily. J. Volcanol. Geotherm. Res. 144, 137–153.
doi:10.1016/j.jvolgeores.2004.11.021.
Stummer, P., Maurer, H., Green, A.G., 2004. Experimental design: electrical resistivity
data sets that provide optimum subsurface information. Geophysics 69, 120–139.
Zlotnicki, J., Nishida, Y., 2004. Review of morphological insights of self-potential
anomalies on volcanoes. Surv. Geophys. 291–338 Kluwer Acad., Norwell, Mass.