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

Bulletin of the Seismological Society of America
By: , and 

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Abstract

The 2019 Ridgecrest, California earthquake sequence generated surface fault rupture along two orthogonal cross faults, including the dominantly left-lateral and northeast-striking Mw6.4 rupture and dominantly right-lateral and northwest-striking Mw7.1 rupture. We present >650 field-based surface-displacement observations for these ruptures, calculate displacement curves, and synthesize our results into cumulative along-strike displacement distributions. Using these data, we calculate displacement gradients and compare our results with historical ruptures in the Eastern California Shear Zone. For the M6.4 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 0.30.5 m and maximum of 0.71.6 m. Net mean vertical displacement based on the difference of down-to-the-west and down-to-the-east displacement curves is close to zero (0.02 m down-to-the-west). The M6.4 displacement distribution shows that the majority of displacement occurred southwest of the intersection with the M7.1 rupture. The M7.1 rupture is northwest-striking and 50 km long based on 576 field measurements. Displacement curves indicate a mean right-lateral displacement of 1.21.7 m and a maximum of 4.37.0 m. Net vertical displacement in the rupture averages 0.3 m down-to-the-west. The M7.1 displacement distributions demonstrate that maximum displacement occurred ~23 km SE of the M7.1 epicenter, releasing 66% of the geologically based seismic moment along 12 km, or 24% of the total rupture length. Using our displacement distributions, we calculate kilometer-scale displacement gradients for the M7.1 rupture. The steepest gradients flank the 12-km-long region of maximum displacement and are ~13 m/km. In contrast, gradients for the 1992 M7.3 Landers and 1999 M7.1 Hector Mine earthquakes are <0.6 m/km. Our displacement distributions are important for understanding the influence of cross-fault rupture on M6.4 and M7.1 rupture length and displacement and will facilitate comparisons with distributions generated remotely and at broader scales.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Surface displacement distributions for the July 2019 Ridgecrest, California earthquake ruptures
Series title Bulletin of the Seismological Society of America
DOI 10.1785/0120200058
Edition Online First
Year Published 2020
Language English
Publisher Seismological Society of America
Contributing office(s) Earthquake Science Center, Geologic Hazards Science Center, Geology, Minerals, Energy, and Geophysics Science Center
Country United States
State California
Other Geospatial Ridgecrest
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