Integration between microgravity observations routinely performed on Etna and absolute measurements acquired by the IMGC-02 transportable absolute gravimeter

Temporal gravity changes in volcanic zones are related to sub-surface mass-redistrubutions or to elevation changes in response to a magmatic activity and vary according to the size, depth and rate of evolution (e.g. degassing) of the magma bodies involved. The associated gravity anomalies can thus change significantly in both space (wavelengths ranging from hundreds of meters to tens of kilometers) and time (periods ranging from minutes to years). The choice of monitoring strategy (i.e. spacing between network stations, rate at which campaigns are accomplished, etc.) is, therefore, 551 GNGTS 2007 SESSIONE 3.3 crucial for correctly assessing geophysical parameters. Discrete and continuous microgravity observations have been routinely performed at Mt. Etna since 1986 and 1998, respectively, by using L&R spring gravimeters. These instruments are affected by meteorological parameters (mainly temperature but also humidity and, to a less extent, pressure) and suffer strong instrumental drift. During the summer of 2007, in co-operation between the INGV-CT and the INRiM–Torino, a measurement experiment using the new IMGC-02 transportable absolute gravimeter was performed with the aim of compare relative microgravity measurements acquired on Etna with absolute gravity observations. The IMGC-02 transportable instrument adopts the absolute ballistic method, which has been recognized at international level (Comité International des Poids et Mesures - CIPM) as primary method of measurement of the acceleration due to gravity. To assure the measurement compatibility the IMGC-02 participates regularly to the International Comparisons of Absolute Gravimeters (ICAGs) organized by the Bureau International des Poids et Mesures (BIPM).