资源环境科技发展态势分析平台

On 4 and 6 July 2019, two large strike-slip earthquakes with W-phase moment magnitudes M-WW 6.5 (foreshock) and M-WW 7.1 (mainshock) struck the Eastern California Shear Zone, northeast of Ridgecrest. The faulting geometry and kinematic coseismic slip distribution of both events are determined by jointly inverting seismological and geodetic observations guided by aftershock and surface rupture locations. The foreshock ruptured two orthogonal faults with a prominent L-shaped geometry with maximum slip of similar to 1.1 m on the NE-SW segment. The mainshock faulting extended NW-SE along several primary fault segments that straddle the foreshock slip. The surface rupture and slip model indicate mostly near-horizontal strike-slip motion with maximum slip of similar to 3.7 m, but there is a localized vertical dip-slip motion. Both the foreshock and mainshock ruptures terminate in regions of complex surface offsets. High aftershock productivity and low rupture velocity may be the result of rupture of a relatively immature fault system.

Plain Language Summary Two large earthquakes on 4 July 2019 (magnitude 6.5) and 6 July 2019 (magnitude 7.1) struck northeast of Ridgecrest, California. Earthquakes such as the 1995 Ridgecrest earthquake have occurred previously in this broad region, called the Eastern California Shear Zone, but the deformation is not concentrated into a dominant single fault. The first rupture involved slip on two perpendicular faults, one aligned NE-SW and the other NW-SE, with slip and aftershocks forming an Lshaped pattern. Most slip was on the NE-SW fault. The mainshock ruptured a sequence of NW-SE trending faults, with slip extending across the short NW-SE segment ruptured in the foreshock. Both ruptures were delimited by zones of multiple surface fractures. The rupture for the mainshock expanded relatively slowly with low radiated energy, and a large number of aftershocks occurred, suggesting rupture of an immature segmented fault system.