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Afterslip of the Mw8.3 2015 Illapel earthquake imaged through a time-dependent inversion of continuous and survey GNSS data
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  • Roxane Tissandier,
  • Jean-Mathieu Nocquet,
  • Emilie Klein,
  • Christophe Vigny,
  • Javier Ojeda,
  • Sergio Ruiz
Roxane Tissandier
Institut de physique du globe de Paris, Université de Paris

Corresponding Author:tissandier@ipgp.fr

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Jean-Mathieu Nocquet
Institut de physique du globe de Paris, Université de Paris & Université Côte d'Azur
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Emilie Klein
Scripps Institution of Oceanography, UCSD
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Christophe Vigny
Ecole Normale Superieure
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Javier Ojeda
Institut de physique du globe de Paris, Université de Paris & Departamento de Geofısica, Universidad de Chile
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Sergio Ruiz
Universidad de Chile
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We use continuous and survey GNSS data to image the spatial and temporal evolution of afterslip during the two-months following the Mw8.3 Illapel earthquake. Our approach solves for the incremental daily slip on the subduction interface using non-negative least-squares and spatial/temporal minimum Laplacian constraints. We find that afterslip developed at three specific areas at the megathrust, surrounding the coseismic rupture. The largest patch takes place at shallow depth north of the coseismic rupture. Smaller patches occur at greater depth north and south of the rupture, but no afterslip is found downdip. In addition, well resolved afterslip also occurs within the coseismic area that experienced 3-5 meters of seismic slip. Our afterslip model shows striking correlations with the spatial distribution of aftershocks and repeating earthquakes. A Mw6.8 aftershock occur on November 7 at the deep patch of enhanced afterslip and our inversion captures the triggered afterslip. Two Mw6.9 events occurred 100 km north of the rupture 55 days after the mainshock. The enhanced shallow afterslip developing northward possibly triggered these remote and delayed events. Enhanced afterslip spatially correlates with areas having experienced regular seismic swarms observed during the years prior to the Illapel earthquake. This correlation supports the view of localized fluid high-pore pressure areas behaving aseismically and surrounding a highly locked asperity, preventing the seismic rupture to propagate into them. The similarity with the behavior observed for the Mw7.8 2016 Ecuador and Mw7.6 2012 Costa Rica, suggests a common behaviour for heterogeneous subduction interfaces.