Rupture Process of the 2019 Ridgecrest, California $Mw$ 6.4 Foreshock and $Mw$ 7.1 Earthquake Constrained by Seismic and Geodetic Data

The 2019 Ridgecrest earthquake sequence culminated in the largest seismic event in California since the 1999 $Mw$ 7.1 Hector Mine earthquake. Here, we combine geodetic and seismic data to study the rupture process of both the 4 July $Mw$ 6.4 foreshock and the 6 July $Mw$ 7.1 mainshock. The results show that the $Mw$ 6.4 foreshock rupture started on a northwest‐striking right‐lateral fault, and then continued on a southwest‐striking fault with mainly left‐lateral slip. Although most moment release during the $Mw$ 6.4 foreshock was along the southwest‐striking fault, slip on the northwest‐striking fault seems to have played a more important role in triggering the $Mw$ 7.1 mainshock that happened $∼34hr$ later. Rupture of the $Mw$ 7.1 mainshock was characterized by dominantly right‐lateral slip on a series of overall northwest‐striking fault strands, including the one that had already been activated during the nucleation of the $Mw$ 6.4 foreshock. The maximum slip of the 2019 Ridgecrest earthquake was $∼5m$⁠, located at a depth range of 3–8 km near the $Mw$ 7.1 epicenter, corresponding to a shallow slip deficit of $∼20%–30%$⁠. Both the foreshock and mainshock had a relatively low‐rupture velocity of $∼2km/s$⁠, which is possibly related to the geometric complexity and immaturity of the eastern California shear zone faults. The 2019 Ridgecrest earthquake produced significant stress perturbations on nearby fault networks, especially along the Garlock fault segment immediately southwest of the 2019 Ridgecrest rupture, in which the coulomb stress increase was up to $∼0.5MPa$⁠. Despite the good coverage of both geodetic and seismic observations, published coseismic slip models of the 2019 Ridgecrest earthquake sequence show large variations, which highlight the uncertainty of routinely performed earthquake rupture inversions and their interpretation for underlying rupture processes.