Antithetic Surface Deformation on Nearby Faults from the Ridgecrest Earthquakes: Compliant Faults Zones or Triggered Slip?
Session: Crustal Stress and Strain and Implications for Fault Interaction and Slip
Type: Oral
Date: 4/28/2020
Time: 11:15 AM
Room: 240
Description:
We analyzed repeat-pass Sentinel-1 and ALOS-2 synthetic aperture radar images to measure broad-area surface deformation as well as high-resolution surface rupturing from the combined July 4-5 2019 Ridgecrest earthquake sequence. Sentinel-1 stacked phase gradient maps were constructed to illuminate the fine details of the main rupture as well as triggered slip on the near-by faults. We find several areas where the strike-slip displacement across surface fractures is opposed to (antithetic) the prevailing regional tectonic stress. Are these antithetic displacements due to triggered slip or do they reflect the elastic response of a compliant fault zone to changes in Coulomb stress? To investigate the compliant fault model, we first performed a source inversion of the primary faults using the InSAR line-of-sight and GNSS data and then computed static Coulomb stress change for a suite of receiver fault orientations consistent with those exhibiting surface deformations. We then measured the amplitude and width of the deformation across over 300 surface fractures. Using the Coulomb stress and the fault width measurements, we find that though the width and amplitude of the deformation does not show a clear pattern related to prograding or retrograding fracturing, the shear modulus contrast does indicate a reasonable decrease (0.4-0.8) inside the damage zone for the retrograding compliant faults. We can explain all the observations with a model where the crust for the entire region is critically stressed prior to the major earthquakes. The increase in Coulomb stress causes the forward slipping faults to undergo true triggered slip across narrow deformation zones. In contrast, a decrease in Coulomb stress causes the antithetic faults to undergo a purely elastic deformation across a wider compliant damage zone.
Presenting Author: Xiaohua Xu
Authors
Xiaohua Xu xix016@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States Presenting Author
Corresponding Author
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Lauren Ward laward@hawaii.edu University of Hawaiʻi at Mānoa, Honolulu, Hawaii, United States |
Bridget Smith-Konter brkonter@hawaii.edu University of Hawaiʻi at Mānoa, Honolulu, Hawaii, United States |
Christopher W D Milliner christopher.milliner@jpl.nasa.gov Jet Propulsion Laboratory, Caltech, Pasadena, California, United States |
Yehuda Bock ybock@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States |
Peng Fang pfang@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States |
David Sandwell dsandwell@ucsd.edu Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, United States |
Antithetic Surface Deformation on Nearby Faults from the Ridgecrest Earthquakes: Compliant Faults Zones or Triggered Slip?
Category
Crustal Stress and Strain and Implications for Fault Interaction and Slip