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Published October 2020 | Supplemental Material
Journal Article Open

Slip-rate-dependent friction as a universal mechanism for slow slip events

Abstract

A growing body of observations worldwide has documented fault slip transients that radiate little or no seismic energy. The mechanisms that govern these slow slip events (SSEs) and their wide range of depths, slip rates, durations, stress drops and recurrence intervals remain poorly known. Here we show that slow slip can be explained by a transition from rate-weakening frictional sliding at low slip rates towards rate-neutral or rate-strengthening behaviour at higher slip rates, as has been observed experimentally. We use numerical simulations to illustrate that this rate-dependent transition quantitatively explains the experimental data for natural fault rocks representative of materials in the source regions of SSEs. With a standard constant-parameter rate-and-state friction law, SSEs arise only near the threshold for slip instability. The inclusion of velocity-dependent friction parameters substantially broadens the range of conditions for slow slip occurrence, and produces a wide range of event characteristics, which include stress drop, duration and recurrence, as observed in nature. Upscaled numerical simulations that incorporate parameters consistent with laboratory measurements can reproduce geodetic observations of repeating SSEs on tectonic faults. We conclude that slip-rate-dependent friction explains the ubiquitous occurrence of SSEs in a broad range of geological environments.

Additional Information

© 2020 Nature Publishing Group. Received 23 December 2019; Accepted 28 July 2020; Published 07 September 2020. We thank to J. Leeman, S. Michel and A. Gualandi for sharing data. This study was supported by NSF EAR-1821853 to J.-P.A., NSF EAR-1616664 and OCE-1334436 to D.S. and NSF EAR-1763305 and EAR-1520760 to C.M. Data availability: GPS data for Hikurangi and Ryuku are publicly available at the Nevada Geodetic Laboratory (http://geodesy.unr.edu/NGLStationPages/stations/GISB.sta and http://geodesy.unr.edu/NGLStationPages/stations/J750.sta). Mexico GPS data35 and Cascadia inversion data33 are available at the Caltech data repository47 (https://doi.org/10.22002/D1.1286). Source data are provided with this paper. Code availability: Simulation codes are available at Caltech data repository (https://doi.org/10.22002/D1.1286). Author Contributions: K.I. led the numerical modelling effort and writing of the manuscript. All the authors contributed to the interpretation of modelling results and writing the manuscript. D.S. and C.M. initiated the study and contributed to experimental data analysis. K.I. and J.-P.A. led the GPS data analysis. The authors declare no competing interests.

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Additional details

Created:
September 22, 2023
Modified:
October 23, 2023