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]. We study Global Positioning System time series including near‐ and far‐field domains. We use a variational Bayesian independent component analysis technique to separate the post‐seismic deformation from signals caused by variation of the water content in aquifers at hundreds of meters of depth and of the soil moisture. For each independent component, realistic uncertainties and a plausible physical explanation are provided. We focus on the study of afterslip on the main structures surrounding the mainshock, highlighting the role played by faults that were not activated during the co‐seismic phase in accommodating the post‐seismic deformation. We report aseismic deformation occurring on the Paganica fault, which hosted the Mw 6.1 2009 L'Aquila earthquake, suggesting that static stress transfer and aseismic slip influence the recurrence time of nearby (∼50 km further south of the mainshocks) segments. 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, also shows aseismic slip. 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 2 years after the mainshocks.

The Unlocking Process Leading to the 2016 Central Italy Seismic Sequence

“…Aftershocks distribution shows the geometry of the shallow SW‐dipping normal fault segments hosting the mainshocks of the sequence, confined at depth by a sub‐horizontal, approximately 2–3 km thick, shear zone (SZ) active between 7 and 12 km (SZ; Chiaraluce et al., 2017; Waldhauser et al., 2021); a discontinuity interpreted as a litho‐structural feature or as the limit of the brittle‐ductile transition, contributing differently to pre‐ co‐ and post‐seismic displacement (respectively Barchi et al., 2021 and Mandler et al., 2021).…”

Searching for Transient Slow Slips Along the San Andreas Fault Near Parkfield Using Independent Component Analysis

“…We estimate the uncertainties of the event detection based on IC1. To do so, similarly to Mandler et al (2021), we build 100 perturbed displacement time series by adding to each position at each time step a random realization of a Gaussian noise based on the data uncertainties. For each of the 100 time series, we apply our decomposition, inversion of the dominant IC and detection methods.…”

Postseismic Deformation in the Northern Antarctic Peninsula Following the 2003 and 2013 Scotia Sea Earthquakes

“…This problem is non‐trivial. It may be possible to separate the various spatial‐temporal processes using principal or independent component analysis, or other data separation approaches such as those based on machine learning (Dong et al., 2006; Gao et al., 2022; Liu et al., 2018; Mandler et al., 2021). A viscoelastic model that includes both earthquake‐related slip and a changing ice load would also be a step forward in modeling Antarctic deformation in a consistent way.…”