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Surface displacement distributions for the July 2019 Ridgecrest, California earthquake ruptures

June 23, 2020

Surface rupture in the 2019 Ridgecrest, California, earthquake sequence occurred along two orthogonal cross faults and includes dominantly left‐lateral and northeast‐striking rupture in the Mw">Mw 6.4 foreshock and dominantly right‐lateral and northwest‐striking rupture in the Mw">Mw 7.1 mainshock. We present >650">>650 field‐based, surface‐displacement observations for these ruptures and synthesize our results into cumulative along‐strike displacement distributions. Using these data, we calculate displacement gradients and compare our results with historical strike‐slip ruptures in the eastern California shear zone. For the Mw">Mw 6.4 rupture, we report 96 displacements measured along 18 km of northeast‐striking rupture. Cumulative displacement curves for the rupture yield a mean left‐lateral displacement of 0.3–0.5 m and maximum of 0.7–1.6 m. Net mean vertical displacement based on the difference of down‐to‐the‐west (DTW) and down‐to‐the‐east (DTE) displacement curves is close to zero (0.02 m DTW). The Mw">Mw 6.4 displacement distribution shows that the majority of displacement occurred southwest of the intersection with the Mw">Mw 7.1 rupture. The Mw">Mw 7.1 rupture is northwest‐striking and 50 km long based on 576 field measurements. Displacement curves indicate a mean right‐lateral displacement of 1.2–1.7 m and a maximum of 4.3–7.0 m. Net vertical displacement in the rupture averages 0.3 m DTW. The Mw">Mw 7.1 displacement distributions demonstrate that maximum displacement occurred along a 12‐km‐long portion of the fault near the Mw">Mw 7.1 epicenter, releasing 66% of the geologically based seismic moment along 24% of the total rupture length. Using our displacement distributions, we calculate kilometer‐scale displacement gradients for the Mw">Mw 7.1 rupture. The steepest gradients (⁠∼1–3  m/km">∼1–3  m/km⁠) flank the 12‐km‐long region of maximum displacement. In contrast, gradients for the 1992 Mw">Mw 7.3 Landers and 1999 Mw">Mw 7.1 Hector Mine earthquakes are <0.6  m/km"><0.6  m/km. Our displacement distributions are important for understanding the influence of cross‐fault rupture on Mw">Mw 6.4 and 7.1 rupture length and displacement and will facilitate comparisons with distributions generated remotely and at broader scales.

Publication Year 2020
Title Surface displacement distributions for the July 2019 Ridgecrest, California earthquake ruptures
DOI 10.1785/0120200058
Authors Christopher DuRoss, Ryan D. Gold, Timothy E. Dawson, Katherine Scharer, Katherine J. Kendrick, Sinan Akciz, Stephen J. Angster, Jeffery Bachhuber, Steven Bacon, Scott E. K. Bennett, Luke Blair, Benjamin A. Brooks, Thomas Bullard, W. Paul Burgess, Colin Chupik, Michael DeFrisco, Jaime Delano, James D. Dolan, Erik Frost, Nick Graehl, Elizabeth Haddon, Alexandra Elise Hatem, Janis Hernandez, Christopher S. Hitchcock, Kennth Hudnut, Jessica Thompson Jobe, Richard D Koehler, Ozgur Kozaci, Tyler C. Ladinsky, Christopher Madugo, Devin McPhillips, Christopher Milliner, Alexander Morelan, Brian Olson, Jason Patton, Belle E. Philibosian, Alexandra J. Pickering, Ian Pierce, Daniel J. Ponti, Gordon G. Seitz, Eleanor Spangler, Brian J. Swanson, Kate Thomas, Jerome Treiman, Francesca Valencia, Alana Williams, Robert Zinke
Publication Type Article
Publication Subtype Journal Article
Series Title Bulletin of the Seismological Society of America
Index ID 70210864
Record Source USGS Publications Warehouse
USGS Organization Earthquake Science Center; Geologic Hazards Science Center; Geology, Minerals, Energy, and Geophysics Science Center