Surface Displacement Distributions for the July 2019 Ridgecrest, California, Earthquake Ruptures

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 M-w 6.4 foreshock and dominantly right-lateral and northwest-striking rupture in the M-w 7.1 mainshock. We present > 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 M-w 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 M-w 6.4 displacement distribution shows that the majority of displacement occurred southwest of the intersection with the M-w 7.1 rupture. The M-w 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 M-w 7.1 displacement distributions demonstrate that maximum displacement occurred along a 12-km-long portion of the fault near the M-w 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 M-w 7.1 rupture. The steepest gradients (similar to 1-3 m/km) flank the 12-km-long region of maximum displacement. In contrast, gradients for the 1992 M-w 7.3 Landers and 1999 M-w 7.1 Hector Mine earthquakes are <0.6 m/km. Our displacement distributions are important for understanding the influence of cross-fault rupture on M-w 6.4 and 7.1 rupture length and displacement and will facilitate comparisons with distributions generated remotely and at broader scales.