Fault Friction Derived From Fault Bend Influence on Coseismic Slip During the 2019 Ridgecrest M_w 7.1 Mainshock
The variation of stress on faults is important for our understanding of fault friction and the dynamics of earthquake ruptures. However, we still have little observational constraints on their absolute magnitude, or their variations in space and in time over the seismic cycle. Here we use a new geodetic imaging technique to measure the 3D coseismic slip vectors along the 2019 Ridgecrest surface ruptures and invert them for the coseismic stress state. We find that the coseismic stresses show an eastward rotation that becomes increasingly transtensional from south-to-north along the rupture, that matches the known background stress state. We find that the main fault near the M_w 7.1 mainshock hypocenter was critically stressed. Coseismic slip was maximum there and decreased gradually along strike as the fault became less optimally oriented due its curved geometry. The variations of slip and stress along the curved faults are used to infer the static and dynamic fault friction assuming Mohr-Coulomb failure. We find shear stresses of 4–9 MPa in the shallow crust (∼1.3 km depth) and that fault friction drops from a static, Byerlee-type, value of 0.61 ± 0.14 to a dynamic value of 0.29 ± 0.04 during seismic slip. These values explain quantitatively the slip variations along a transpressional fault bend.
© 2022. American Geophysical Union. We thank Jeanne Hardebeck, Xin Wang, Egill Hauksson and Shuzhong Sheng for making their stress results available. We thank Kim Olson, the editor Isabelle Manighetti, the associate editor and two anonymous reviewers for their comments and suggestions which helped strengthen the manuscript. We thank the NASA NGA commercial archive data service for access to the WorldView imagery (https://cad4nasa.gsfc.nasa.gov/index.php) which is provided under the NextView license agreement. This research was supported by the NASA Earth Surface and Interior focus area and performed at the Jet Propulsion Laboratory, California Institute of Technology (80NM0018D0004). Satellite imagery for this project were also purchased under SCEC Grant 19222. The authors declare no conflicts of interest relevant to this study. Data Availability Statement Optical Images were made available through NASA NGA commercial archive data service (https://cad4nasa.gsfc.nasa.gov/index.php), which is provided under the NextView license agreement. Maps were made using Generic Mapping Tools (https://www.generic-mapping-tools.org/). The COSI-Corr image correlation software can be accessed from (http://www.tectonics.caltech.edu/slip_history/spot_coseis/download_software.html). The measurements of the coseismic fault slip vectors, the 3D displacement maps and the MATLAB scripts to invert the coseismic slip vectors for the deviatoric stress tensor can be found from the Zenodo open repository https://doi.org/10.5281/zenodo.7162335.
In the originally published version of this article, the equation at the end of Section 3.3 contained typographical errors. The sentence should read: "This gives a stress drop at the failure point of 4.04 ± 0.49 MPa." The "A" that appeared in the middle of the originally published version of the equation should have been deleted in the PDF version. In addition, a paragraph break should be introduced before the start of the following sentence in the last paragraph of Section 3.3: "Following our quasi-static assumption (Equation 12) we inverted the coseismic slip (D) for friction for both the central and southern zones (the northern zone lacks a sufficient range of slip magnitude to obtain robust values)." The errors have been corrected, and this may be considered the authoritative version of the record.
Supplemental Material - 2022jb024519-sup-0001-supporting_information_si-s01.pdf
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