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 (⁠∼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 M_w 6.4 and 7.1 rupture length and displacement and will facilitate comparisons with distributions generated remotely and at broader scales.