Preprints
https://doi.org/10.5194/se-2021-6
https://doi.org/10.5194/se-2021-6

  05 Feb 2021

05 Feb 2021

Review status: this preprint is currently under review for the journal SE.

Very early identification of a bimodal frictional behavior during the post-seismic phase of the 2015 Mw8.3 Illapel, Chile, earthquake

Cedric Twardzik1,a, Mathilde Vergnolle1, Anthony Sladen1, and Louisa L. H. Tsang1,b Cedric Twardzik et al.
  • 1Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, IRD, Geoazur, UMR 7329, Valbonne, France
  • anow at: Institut de Physique du Globe de Strasbourg, UMR 7516, Université de Strasbourg, EOST, CNRS, Strasbourg, France
  • bnow at: University of Surrey, International Study Centre, Guildford, United Kingdom

Abstract. It is well-established that the post-seismic slip results from the combined contribution of seismic slip and aseismic slip. However, the partitioning between these two modes of slip remains unclear due to the difficulty to infer detailed and robust descriptions of how both evolve in space and time. This is particularly true just after a mainshock when both processes are expected to be the strongest. Using state-of-the-art sub-daily processing of GNSS data, along with dense catalogs of aftershocks obtained from template-matching techniques, we unravel the spatiotemporal evolution of post-seismic slip and aftershocks over the first 12 hours following the 2015 Mw8.3 Illapel, Chile, earthquake. We show that the very early post-seismic activity occurs over two regions with distinct behaviors. To the north, post-seismic slip appears to be purely aseismic and precedes the occurrence of late aftershocks. To the south, aftershocks are the primary cause of the post-seismic slip. We suggest that this difference in behavior could be inferred only few hours after the mainshock, and thus could contribute to a more data-driven forecasts of long-term aftershocks.

Cedric Twardzik et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on se-2021-6', Sylvain Barbot, 11 Feb 2021
  • RC1: 'Comment on se-2021-6', Bernd Schurr, 04 Mar 2021
  • CC2: 'Comment on se-2021-6', Dietrich Lange, 22 Mar 2021
  • RC2: 'Comment on se-2021-6', Mathilde Radiguet, 11 May 2021

Cedric Twardzik et al.

Data sets

30s Position Time Series for the 2015 Illapel earthquake Cedric Twardzik https://doi.org/10.5281/zenodo.4498200

Model code and software

Python Code for sidereal filtering Cedric Twardzik https://doi.org/10.5281/zenodo.4498160

Cedric Twardzik et al.

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Short summary
After an earthquake, the fault continues to slip for days to months. Yet, little is know about the very early part of this phase (i.e., minutes to hours). So, we have looked at what happens just after an earthquake in Chile from 2015. We find that the fault responds in two ways: south of the rupture zone it slips seismically in the form of aftershocks, while north of the rupture zone it slips slowly. Early inference of such bimodal behavior could prove to be useful for forecasting aftershocks.