@ingalls

Just going to pop in here (as a former SoCal resident - grew up there) and as a former geology minor at uni) to drop a screenshot showing the "Mendocino Transform" transverse fault which pretty much lies under that east-west trending series of epicenters trending out to the Big One

Transform faults define the boundaries of transform plates, where lateral movement is accommodated along long linear fault lines like the San Andreas, and often connect one plate to another: here, the North American Plate to the Juan de Fuca plate out west of the Pacific Northwest

The third plate here (labeled by an orphaned word) is the Pacific Plate to the south and west

See, here: https://www.nps.gov/subjects/geology/plate-tectonics-transform-plate-boundaries.htm

ALT