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Published March 31, 2020 | Submitted
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Continuum of earthquake rupture speeds enabled by oblique slip


Earthquake rupture speed can affect ground shaking and thus seismic hazard. Seismological observations show that large earthquakes span a continuum of rupture speeds, from slower than Rayleigh waves up to P wave speed, and include speeds that are predicted to be unstable by 2D theory. This discrepancy between observations and theory has not yet been reconciled by a quantitative model. Here we present numerical simulations that show that long ruptures with oblique slip (both strike-slip and dip-slip components) can propagate steadily at various speeds, including those previously suggested to be unstable. The obliqueness of slip and the ratio of fracture energy to static energy release rate primarily control the propagation speed of long ruptures. We find that the effects of these controls on rupture speed can be predicted by extending the 3D theory of fracture mechanics to long ruptures with oblique slip. We propose that this model provides a quantitative framework to interpret supershear earthquakes, to constrain the energy ratio of faults based on observed rupture speed and rake angle, and to relate the potential rupture speed and size of future earthquakes to the observed slip deficit along faults.

Additional Information

License: GNU Lesser General Public License (LGPL) 2.1. Submitted: March 30, 2020; Last edited: July 29, 2020. The open-source software SPECFEM3D used in our 3-D dynamic rupture simulations is available from the Computational Infrastructure for Geodynamics at https://geodynamics.org/cig/software/specfem3d/. This work was supported by the French government through the Investments in the Future project UCAJEDI (ANR-15-IDEX-01) managed by the French National Research Agency (ANR). We thank Diego Molina for providing the central Andes coupling model in digital form. Author contributions: H.W. designed and carried out the numerical experiments, and analysed the numerical results. H.W. and J.-P.A. developed the theoretical model, interpreted the results, and wrote the paper. Competing Interests: The authors declare that they have no competing interests.

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