Abstract
Observations in tectonically active areas increasingly reveal sets of high-angle conjugate faults (‘cross-faults’) that apparently contradict theories of faulting based on experimental data. Possible explanations include a low in situ coefficient of friction, dominant control of ductile shear zones in the lower crust, and tectonic rotation. Discrimination between these mechanisms has been hindered by uncertainties in the state of stress, deformation history and fault geometry at seismogenic depths. Here we use a combination of seismic, geodetic and geologic data to demonstrate that ubiquitous cross-faults in the Ridgecrest (California) area, including those ruptured in the sequence of strong earthquakes in 2019, result from rotation from an initially optimal orientation consistent with experimental data. The inferred rotation pattern can be explained by the geodetically measured velocity field. Our model suggests that the observed asymmetric rotation of faults in the Eastern California Shear Zone can result from simple shear. The same mechanism can be responsible for high-angle conjugate faults observed in other tectonic settings.
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Data availability
All data used in this study are open access. The first motion focal mechanism of the 2019 Mw 7.1 mainshock is available at https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/focal-mechanism. The seismic moment of the 2019 Mw 7.1 mainshock is available at https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/moment-tensor. The seismic moment of the 2019 Mw 6.4 foreshock is available at https://earthquake.usgs.gov/earthquakes/eventpage/ci38443183/moment-tensor. The waveform-relocated earthquake catalog for southern California from ref. 47 is available at https://scedc.caltech.edu/research-tools/alt-2011-dd-hauksson-yang-shearer.html. The GNSS position time series from the PBO is available at https://doi.org/10.7283/P2HT0Z. The coseismic displacement data and fault slip models from ref. 28 are available at https://doi.org/10.5281/zenodo.4646321.
Code availability
MATLAB codes used to generate results presented in this study are available at https://doi.org/10.5281/zenodo.4646292
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Acknowledgements
We thank O. Zielke and M.-H. Huang for their comments. This study was supported by NSF (grants EAR-1841273 and EAR-1945760) and NASA (grant 80NSSC18K0466). Figures were produced using Generic Mapping Tools50 and MATLAB.
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Y.F. performed the data analysis and wrote the manuscript. Z.J. provided a finite fault model of the 2019 Ridgecrest earthquakes and contributed to the graphics design.
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Peer review information Nature Geoscience thanks Olaf Zielke and Mong-Han Huang for their contribution to the peer review of this work. Primary Handling Editor: Stefan Lachowycz.
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Supplementary methods, Figs. 1–9 and references.
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Fialko, Y., Jin, Z. Simple shear origin of the cross-faults ruptured in the 2019 Ridgecrest earthquake sequence. Nat. Geosci. 14, 513–518 (2021). https://doi.org/10.1038/s41561-021-00758-5
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DOI: https://doi.org/10.1038/s41561-021-00758-5
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