PNNL

Abstract

We performed the first large-scale 3D tomography of the electrical conductivity of Stromboli volcano (Aeolian Islands, Italy) using 2D acquisition lines and a total of 18,880 measurements and 2402 unique electrode locations. This dataset was inverted in 3D by minimizing the L2 norm of the data misfit using a Gauss-Newton algorithm, parallel processing on an unstructured tetrahedral mesh containing 678,420 finite-element nodes, and 3,580,145 elements to accurately model the rough topography of the volcanic edifice. The 3D tomogram shows a conductive body (10-2–1 S m-1) consistent with the position of temperature and CO2 anomalies observed at the ground surface. It is interpreted as the hydrothermal system with high electrical conductivity potentially associated with alteration. In order to confirm this interpretation, a 2.5D large-scale induced polarization tomography was performed crossing the volcano. The joint interpretation of the conductivity and normalized chargeability is done with a petrophysical model previously tested and verified at both shield- and strato-volcanoes. This model implies that alteration (through the effect of the cation exchange capacity associated with clay minerals and zeolites) plays a strong role in both controlling the electrical conductivity and normalized chargeability at Stromboli volcano. A temperature tomogram, derived from the geoelectrical measurements, is consistent with surface temperature anomalies and the Very Long Period seismicity related to the mild-explosive activity. This survey displays at 600 m a.s.l. a lateral shift in the highest temperature location, also corresponding to the source of Very Long Period seismicity. Structural boundaries such as NeoStromboli crater, Pizzo crater and SW active crater seem to have a major role in the hottest hydrothermal fluids rising below the active crater terrace of Stromboli volcano.