Large Repeating Gorda Intraplate Earthquakes Occurring Along an Inherited Weak Zone near the Mendocino Triple Junction

Abstract On 22 December 2022, a destructive earthquake with a magnitude Mw 6.4 ruptured the oceanic lithosphere emplaced beneath Northern California. This event was a repeat of an earthquake that occurred 47 yr earlier, on 7 June 1975, with a magnitude of MD 5.7. Both earthquakes caused significant damage during 10–16 s of strong shaking, primarily in the town of Rio Dell, with Fortuna and Ferndale also affected. Evidence indicates that the hypocenters of these two ruinous earthquakes occurred along the same fault within the downgoing Gorda plate, with the hypocenters located on opposite ends of the slip patch determined for the 2022 event. This pattern of recurring destructive intraplate earthquakes along inherited weak zones throughout the offshore Gorda basin is likely not unique to this sequence.