3-Year hybrid microgravity measurements at Etna Volcano encompassing the 2008-2009 eruption

Since 1986, we have been intensively monitoring the gravity field on Mt Etna to detect underground mass movements due to the volcanic activity, which could trigger a pre-eruptive state. Time-dependent gravity observations are generally carried out at Etna using a combination of discrete and continuous measurements. Recently, with the aim to extend the potential of gravity measurements for surveying the Etna volcanic area, we carried out hybrid microgravity measurements employing both absolute and relative gravimeters. The hybrid approach permit of optimizing techniques and strategies of the microgravity measurements on the Etna’s network, ensuring an improvement in the quality of the data and allowing to investigate also on gravity variations with relatively low-amplitude ever considered at Etna volcano. Three measurements of the free-fall acceleration, g, have been performed in five sites at Etna between 2007 and 2009 using the new version of the IMGC-02 absolute gravimeter. Furthermore, in 2009 also the Microg LaCoste FG5 n° 238 absolute gravimeter was employed in 9 sites around the volcano edifice, two of which in the same points measured by the IMGC-02 absolute gravimeter. We present the results of hybrid measurements, which were done just one year before, only two months after the onset, and at the end of the Etna 2008-2009 eruption.