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Evidence of an aseismic slip continuously driving the 2017 Valparaiso earthquake sequence
  • +2
  • Luc Moutote,
  • Yuji Itoh,
  • Olivier Lengliné,
  • Zacharie Duputel,
  • Anne Socquet
Luc Moutote
Institut Terre et Environnement de Strasbourg, UMR7063, Université de Strasbourg/EOST, CNRS, Strasbourg, France

Corresponding Author:lmoutote@unistra.fr

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Yuji Itoh
Universite Grenoble Alpes
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Olivier Lengliné
Université de Strasbourg, IPGS, CNRS
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Zacharie Duputel
Institut de Physique du Globe de Strasbourg, UMR7516, Université de Strasbourg/EOST, CNRS
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Anne Socquet
Université Grenoble Alpes
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Following laboratory experiments and friction theory, slow slip events and seismicity rate accelerations observed before mainshock are often interpreted as evidence of a nucleation phase. However, such precursory observations still remain scarce and are associated with different time and length scales, raising doubts about their actual preparatory nature. We study the 2017 Valparaiso Mw= 6.9 earthquake, which was preceded by aseismic slip accompanied by an intense seismicity both suspected to reflect its nucleation phase. We complement previous observations, which have focused only on precursory activity, with a continuous investigation of seismic and aseismic processes from the foreshock sequence to the post-mainshock phase. By building a high-resolution seismicity catalog and searching for anomalous seismicity rate increases compared to aftershock triggering models, we highlight an over-productive seismicity starting within the foreshock sequence and persisting several days after the mainshock. Using repeating earthquakes and high-rate GPS observations, we highlight a transient aseismic perturbation starting just before the first foreshock and extending continuously after the mainshock. The estimated slip rate is lightly impacted by large magnitude earthquakes and does not accelerate towards the mainshock. Therefore, the unusual seismic and aseismic activity observed during the 2017 Valparaiso sequence might be interpreted as the result of a slow slip event starting before the mainshock and extending beyond it. Rather than pointing to a possible nucleation phase of the 2017 Valparaiso mainshock, the identified slow slip event acts as an aseismic loading of nearby faults, increasing the seismic activity, and thus the likelihood of a large rupture.
28 Feb 2023Submitted to ESS Open Archive
01 Mar 2023Published in ESS Open Archive