Checking the gPhone-054 spring gravimeter after several years under intense seismo-volcanic activity conditions

The spring gravimeter gPhone # 054, belonging to the Spanish National Geographic Institute (IGN), is used as part of the volcano monitoring network deployed on El Hierro (Canary Island) since the last eruption on 2011-2012. Due to the extreme measuring conditions for more than 3 years, which led to several problems with the acquisition system and the power supply, in 2015 it was removed and installed at the gravity pavilion of the ‘Centro de Desarrollos Tecnológicos de Yebes’, in the centre of the Iberian Peninsula. There, several tests have been performed in order to check its behavior.

We present a detailed comparison between the tidal model obtained from the superconducting gravimeter SG064 record and the corresponding obtained using the gPhone054. This comparison is additionally sustained by four absolute gravity measurements obtained with the FG5#211 ballistic gravimeter. These absolute measurements are used both to control the respective drift behavior and to calibrate the gravity sensor. Finally, aiming to evaluate the instrument behavior during the different seismo-volcanic processes monitored at El Hierro from 2011 to 2014, we compare this new calibration with the one which was carried out at J9 superconducting gravity station in Strasbourg (France) for more than 300 days between 2008 and 2009. Through it, we evaluate also the time stability of the calibration factor.