Dynamic Rupture Simulations of the M6.4 and M7.1 July 2019 Ridgecrest, California, Earthquakes.

The largest earthquakes of the 2019 Ridgecrest, California, sequence were a M6.4 left‐lateral rupture followed 34 hr later by a M7.1 on a perpendicular right‐lateral fault. We use dynamic rupture modeling to address the questions of why the first earthquake did not propagate through the right‐lateral fault in one larger event, whether stress changes from the M6.4 were necessary for the M7.1 to occur, and how the Ridgecrest earthquakes affected the nearby Garlock Fault. We find that dynamic clamping and shear stress reduction confined surface rupture in the M6.4 to the left‐lateral fault. We also find that stress changes from the M6.4 were not necessary to allow a M7.1 on the right‐lateral fault but that they affected the slip and likely accelerated the timing of the M7.1. Lastly, we find that the Ridgecrest earthquakes may have brought the central Garlock Fault closer to failure. Plain Language Summary: The M6.4 and M7.1 Ridgecrest, California, earthquakes of July 2019 occurred 34 hr apart, on two faults that cross each other. We used physics‐based computer simulations of the earthquake process to investigate why both faults did not move together in one bigger earthquake and whether the second earthquake only happened due to effects from the first. We found that the fault movement in the first earthquake compressed the second fault, which prevented it from moving at the same time. We also found that the second fault could have had a M7.1 earthquake on its own, without the influence of the M6.4 on the previous day but that the first earthquake affected the details of the second and likely made the second one happen sooner than it would have otherwise. This has meaning both for understanding why the Ridgecrest earthquakes happened this way and also for understanding possible earthquake behaviors on other crossing faults. We also looked at whether the Ridgecrest earthquakes brought the nearby Garlock Fault, which is capable of a M8 earthquake, closer to having a big earthquake, and we found that this is possible but not certain. Key Points: Dynamic stress changes from the first Ridgecrest earthquake were insufficient to immediately trigger the second earthquakeAlthough the first earthquake did not create the conditions necessary for the second to occur, it affected the slip distribution and timingStress changes from the Ridgecrest ruptures explain the location of creep on the Garlock Fault and may have brought it closer to failure [ABSTRACT FROM AUTHOR]