GNSS and absolute gravity measurements for a multi-disciplinary study of natural risks in Central Italy

Abstract

Crustal deformations are widely studied in Italy by analyzing data from GNSS permanent networks. However, deformations can be generated by very different geophysical processes related to tectonics but also to fluid circulation and density variations. Therefore, it is very important to understand if the detected deformations are connected to gravity variations (Greco et al., 2021a). 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 (Riguzzi et al., 2019). 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 (Devoti et al., 2018). 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 (Greco et al., 2021b). 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 (Fortunato et al., 2020). 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. In the poster we describe the procedure and results followed to achieve the coordinates of both the GNSS and the absolute gravimetric sites. Furthermore, we also present the results over the short and the medium-long-term obtained by repetitive combined GNSS and integrated absolute and relative gravity measurements.