>southern Central Valley, CA
The pattern is a perfect diagonal with where the San Andreas Fault enters the central valley. Lots of monitoring stations, laser reflectors, gps stations and more.
DOD overwatch, looking out for The Big One.
https://www.latimes.com/california/story/2020-08-10/swarm-of-earthquakes-shakes-salton-sea-area-raising-worry-about-the-san-andreas