Peak horizontal vibrations from GPS response spectra In the epicentral areas of the 2016 earthquake in central Italy

Global Positioning System (GPS) measurements recorded at active sites in central Italy during the seismic events of greatest magnitude (24 August, 26 and 30 October 2016) were processed in kinematic mode according to the Precise Point Positioning (PPP) technique. The resulting data were the displacements and, by derivation with respect to time, the velocities and instantaneous horizontal accelerations. The elastic response spectra along the orthogonal walls of the site (if the GPS antenna was fixed to a building) or along the geographical directions (if the antenna was fixed to the ground) were obtained from the derived accelerations. The maximum amplitudes, i.e. the “peak vibrations”, were then extracted from the response spectra. These peaks, unlike the co-seismic movements, represent the maximum instantaneous vibrations recorded at the sites following the “shock” produced by the seismic waves and thus are representative of both the discomfort perceived by the populations and the structural damage. This study shows that GPS is becoming an increasingly important tool to measure and monitor the dynamic responses of a structure. The results also provide a complete picture of the displacements induced by the seismic sequences in the areas affected by the earthquake, leaving unresolved some questions concerning the localization of the phenomena and the causes of the structural deformations.