Absolute gravity and deformation measurements for a multi-disciplinary study in Central Italy

Bologna, Italy

Since 2018, INGV funded 3 projects aimed to detect ground deformations and gravity variations over different timescale in the area where the recent seismic events of L’Aquila (2009, Mw 6.3) and Amatrice-Norcia (2016, Mw 6.1 and 6.5) took place. The consequent static deformation field reached several centimetres and the modelled impact of such events could have modified the gravity field up to 170 μGal. Furthermore, the medium-long-term gravity and ground deformation variations related to post-seismic relaxation are expected as consequence of vertical deformation of the Earth surface and/or of the internal boundaries separating layers at depth with different densities. In addition, the L’Aquila area is affected by deformations induced by ground water level changes in the aquifers. Therefore, a multidisciplinary approach carrying out joint measurements of deformation and gravity is fundamental to understand the role of each geophysical process.
To this aim, a network of 3 (Terni, Popoli, Sant’Angelo Romano) new non-permanent GNSS stations was realized outside the buildings hosting the absolute gravity stations. At L’Aquila, a permanent GNSS station managed by the Italian Space Agency (AQUI) is continuously working on the rooftop terrace of the Science Faculty, and positioned vertically with respect to the gravimetric station (AQUIg), which is located 4 floors below. Since 4 absolute gravimetric sites are located indoor, the precise coordinates of the gravity benchmark have been obtained by classical topographic surveys, connecting the indoor site to the outdoor GNSS reference point. Here we present the gravity and ground deformation variations observed in the period 2018-2022 after five measurement campaigns.