Surface volume and gravity changes due to significant earthquakes occurred in central Italy from 2009 to 2016

We have modelled the surface volume and gravity changes caused by four seismic events: three mainshocks (moment magnitude
Mw 6.0, 5.9, 6.5) occurred during the last seismic period started on 2016, August 24 in central Italy, and the 2009, April
6 L’Aquila Earthquake (Mw 6.3). Our calculations start from the source parameters estimated by the inversion of the largest
dataset of Interferometric Synthetic Aperture Radar (InSAR) and global positioning system observations ever managed in
Italy after earthquake occurrences, based on the half-space elastic dislocation theory. The vertical displacements modelled
after the 2016 events allow to infer a substantial unbalance between the subsided and uplifted volumes. In particular, we
detected ~ 106 × 106 m3 of hangingwall subsidence against ~ 37 × 106 m3 of footwall uplift, that accounts for ~ 74% of the
total volume mobilization. From the ratio between the footwall and total deformed volumes, we have computed an average
fault dip of ~ 47°, in line with the values retrieved by seismological methods. The total gravity variations which affected the
study area are of the order of ~ 1 μGal (1 μGal = 10−8 ms−2) in the far field, and ~ 170 μGal in the near field. The area affected
within a gravity change of 1 μGal is ~ 140 km long and ~ 57 km wide, parallel to the Apennines mountain chain. The larger
contribution is given by positive variations which account for the tensional style of deformation and larger subsided area.
The significant gravity variations modelled from the coseismic deformations point out the need to update our knowledge
about the absolute gravity field in Italy carrying out extensive measurements, and to align Italy to the recent international
standards about national gravity and height networks (International Association of Geodesy, IAG Report, Commission 2—
gravity field,