Nucleation of Laboratory Earthquakes: Quantitative Analysis and Scalings

Marty, S.; Schubnel, A.; Bhat, H. S.; Aubry, J.; Fukuyama, E.; Latour, S.; Nielsen, S.; Madariaga, R.

Abstract

In this study we use the precursory acoustic emission (AE) activity during the nucleation of stick-slip instability as a proxy to investigate foreshock occurrence prior to natural earthquakes. We report on three stick-slip experiments performed on cylindrical samples of Indian metagabbro under upper crustal stress conditions (30–60 MPa). AEs were continuously recorded by eight calibrated acoustic sensors during the experiments. Seismological parameters (moment magnitude, corner frequency and stress-drop) 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 toward failure and is driven by along fault slip velocity. The stacked AE foreshock sequences follow an inverse Omori type law, with a characteristic Omori time c inversely proportional to normal stress. AEs moment magnitudes increase toward failure, as manifested by a decrease in b-value from ∼1 to ∼0.5 at the end of the nucleation process. During nucleation, foreshocks migrate toward the mainshock epicenter location, and stabilize at a distance from the latter compatible with the predicted Rate-and-State nucleation size. Importantly, the nucleation characteristic timescale also scales inversely with applied normal stress and the expected nucleation size. Finally, we infer that foreshocks are the byproducts of the nucleation phase which is an almost fully aseismic process. Nevertheless, the seismic/aseismic energy release ratio continuously increases during nucleation, highlighting that, the nucleation process starts as a fully aseismic process, and evolves toward a cascading process at the onset of dynamic rupture.

Citation

Marty, S., Schubnel, A., Bhat, H. S., Aubry, J., Fukuyama, E., Latour, S., …Madariaga, R. (2023). Nucleation of Laboratory Earthquakes: Quantitative Analysis and Scalings. Journal of Geophysical Research. Solid Earth, 128(3), Article e2022JB026294. https://doi.org/10.1029/2022jb026294

• Journal Article Type: Article
• Acceptance Date: Mar 15, 2023
• Online Publication Date: Mar 21, 2023
• Publication Date: Mar 27, 2023
• Deposit Date: Aug 2, 2023
• Publicly Available Date: Sep 22, 2023
• Journal: Journal of Geophysical Research: Solid Earth
• Print ISSN: 2169-9313
• Electronic ISSN: 2169-9356
• Publisher: American Geophysical Union
• Peer Reviewed: Peer Reviewed
• Volume: 128
• Issue: 3
• Article Number: e2022JB026294
• DOI: https://doi.org/10.1029/2022jb026294
• Keywords: Space and Planetary Science; Earth and Planetary Sciences (miscellaneous); Geochemistry and Petrology; Geophysics
• Public URL: https://durham-repository.worktribe.com/output/1709933
• Additional Information: Received: 2023-01-09; Accepted: 2023-03-15; Published: 2023-03-27