Etna: Self-potential, geoelectric and magnetotelluric measurements

We present the results of electrical and electromagnetic studies in the Etnean area during 1993-95, devoted both to volcanic hazard evaluation and to geologic and volcanic structural modeling. As it regards the first objective, we have performed on April 26, 1993, just a few days after the end of the last eruptive event started in December 1991, a further self-potential (SP) survey along a profile located at about 1600 m of height a.s.l. on the SP92 road and crossing the fracture system opened in 1989. The SP measurements was also repeated on November 28, 1995. These last SP profiles followed a group of 17 identical surveys, performed from October 23, 1989 to October 13, 1992, and constitute the experimental basis for the SP tomographic modeling. Moreover, we have carried out in 1994 a dipolar geoelectric (DG) tomography of about 2 km of length, along the same profile (1.32 km long), where we have performed, since 1989, the 19 SP surveys. The aim was essentially obtaining the electric structural scheme with which compare the results of the SP tomographic model. Finally, we present the interpretation of the couple of dipolar geoelectric (DG) and magnetotelluric (MT) soundings, performed at about 2500 m of height a.s.l. very close to the eruptive vent of the last effusive manifestation, and of 17 MT soundings carried out in the southern-eastern part of the Etnean area. These last MT measurements were aimed at studying the resistivity deep distribution in this sector of the volcano. Due to the proximity of the MT sites to known highly conductive structures, namely the sea water body and the Caltanissetta basin at the eastern and western sides of the surveyed area, respectively, we have also made a theoretical 2D modeling, in order to study the degree of distortion of the MT curves caused by the above mentioned lateral effects.