Signature of transition to supershear rupture speed in the coseismic off-fault damage zone
Most earthquake ruptures propagate at speeds below the shear wave velocity within the crust, but in some rare cases, ruptures reach supershear speeds. The physics underlying the transition of natural subshear earthquakes to supershear ones is currently not fully understood. Most observational studies of supershear earthquakes have focused on determining which fault segments sustain fully grown supershear ruptures. Experimentally cross-validated numerical models have identified some of the key ingredients required to trigger a transition to supershear speed. However, the conditions for such a transition in nature are still unclear, including the precise location of this transition. In this work, we provide theoretical and numerical insights to identify the precise location of such a transition in nature. We use fracture mechanics arguments with multiple numerical models to identify the signature of supershear transition in coseismic off-fault damage. We then cross-validate this signature with high-resolution observations of fault zone width and early aftershock distributions. We confirm that the location of the transition from subshear to supershear speed is characterized by a decrease in the width of the coseismic off-fault damage zone. We thus help refine the precise location of such a transition for natural supershear earthquakes.
© 2021 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. Manuscript received 03/05/2021; Manuscript accepted 21/10/2021; Published online 17/11/2021; Published in print 24/11/2021. H.S.B. acknowledges the European Research Council grant PERSISMO (grant no. 865411) for partial support of this work. J.J. and R.J. acknowledge the funding of the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 758210, project Geo4D). L.B. thanks the funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement no. PCOFUND-GA-GA-2013-609102, through the PRESTIGE programme coordinated by Campus France. S.A. and Y.K. are partly supported by the ANR project DISRUPT (ANR-18-CE31-0012). R.J. acknowledges funding from the Institut Universitaire de France. Portions of this research were obtained using resources provided by the Los Alamos National Laboratory Institutional Computing Program, which is supported by the U.S. Department of Energy National Nuclear Security Administration under contract no. 89233218CNA000001. This publication was approved for unlimited release under LA-UR-21-24016. SPOT images are from the ISIS programme from CNES. Data accessibility: All the catalogues and numerical simulation results employed in this work have been obtained from published works, cited in the main text and electronic supplementary material. Authors' contributions: H.S.B. conceived of and designed the study. H.S.B. developed the LEFM solution. M.Y.T. conducted damage mechanics-based numerical modelling and K.O. performed FDEM-based numerical modelling. S.A. conducted the image correlation analysis. J.J. analysed the aftershock catalogue with inputs from M.Y.T. and H.S.B. J.J. and L.B. drafted the first version of this manuscript, which was subsequently modified with inputs from H.S.B., M.Y.T., K.O., S.A., Y.K., A.J.R. and R.J. All authors read and approved the manuscript. We declare we have no competing interests.
Published - rspa.2021.0364.pdf
Submitted - 1909.12672.pdf
Supplemental Material - rspa20210364_si_001.pdf