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Nucleation of laboratory earthquakes: quantitative analysis and scalings
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  • samson marty,
  • Alexandre Schubnel,
  • Harsha S Bhat,
  • Jérôme Aubry,
  • Fukuyama Eiichi,
  • Soumaya latour,
  • Stefan Nielsen,
  • Raul Madariaga
samson marty
Rock and Sediment mechanics laboratory - PSU

Corresponding Author:sam92son@gmail.com

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Alexandre Schubnel
CNRS - Ecole Normale Supérieure, Paris
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Harsha S Bhat
Laboratoire de Geologie - ENS
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Jérôme Aubry
École Normale Supérieure
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Fukuyama Eiichi
National Research Institute for Earth Science and Disaster Prevention (NIED)
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Soumaya latour
Université Toulouse 3 - Paul Sabatier
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Stefan Nielsen
Durham University
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Raul Madariaga
Ecole Normale Superieure
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Decades of seismological observations have highlighted the variability of foreshock occurrence prior to natural earthquakes, making thus difficult to track how earthquakes start. Here, we report on three stick-slip experiments performed on cylindrical samples of Indian metagabbro under upper crustal stress conditions (30-60 MPa). Acoustic emissions (AEs) were continuously recorded by 8 calibrated acoustic sensors during the experiments. Seismological parameters of the detected AEs (-8.8 <= Mw <= -7 ) follow the scaling law between moment magnitude and corner frequency that characterizes natural earthquakes. AE activity always increases towards failure and is found to be driven by along fault slip velocity. The stacked AE foreshock sequences follow an inverse power-law of the time to failure (inverse Omori), with a characteristic Omori time c inversely proportional to normal stress and nucleation length. AEs moment magnitudes increase towards failure, as manifested by a decrease in b-value from ~ 1 to ~ 0.5 at the end of the nucleation process. During nucleation, the averaged distance of foreshocks to mainshock continuously decreases, highlighting the fast migration of foreshocks towards the mainshock epicenter location, and stabilizing at a distance from the latter compatible with the predicted Rate-and-State nucleation size. Finally, the seismic component of the nucleation phase is orders of magnitude smaller than that of its aseismic component, which suggests that foreshocks are the byproducts of a process almost fully aseismic. Seismic/aseismic energy release ratio continuously increases during nucleation, which starts as a fully aseismic process and evolves towards a cascading process.
18 Jan 2023Submitted to ESS Open Archive
20 Jan 2023Published in ESS Open Archive