Post-Seismic Deformation Related to the 2016 Central Italy Seismic
Sequence from GPS Displacement Time-Series
Abstract
The 2016-2017 Central Italy earthquake sequence struck the central
Apennines between August 2016 and October 2016 with Mw ∈ [5.9;
6.5], plus four earthquakes occurring in January 2017 with Mw ∈
[5.0; 5.5]. Here we study Global Positioning System (GPS) stations
active during the post-seismic phase including near and far-field
domains. We separate the post-seismic deformation from other, mainly
seasonal, hydrological deformation signals present in ground
displacement time-series via a variational Bayesian Independent
Component Analysis technique. For each component, realistic
uncertainties are provided to the related ICA-reconstructed displacement
field. We study the distribution of afterslip on the main structures
surrounding the mainshock, and we highlight the role played by
structures that were not activated during the co-seismic phase in
accommodating the post-seismic deformation. In particular, we report
aseismic deformation occurring on the Paganica fault, which hosted the
Mw 6.1 2009 L’Aquila earthquake, and is located further south of the
2016-2017 epicenters; and on a 〜2-3 km thick subhorizontal
shear-zone, clearly illuminated by seismicity, which bounds at depth the
west-dipping normal faults where the mainshocks nucleated. Since
afterslip alone underestimates the displacement in the far-field
domain, we consider the possibility that the shear zone marks the
brittle-ductile transition, assuming the viscoelastic relaxation of the
lower crust as a mechanism contributing to the post-seismic
displacement. Our results suggest that multiple deformation processes
are active in the first two years after the mainshocks.