There have been 4 more microquakes since the 3.7 aftershock to yesterday’s 4.1 Calaveras Fault temblor. I did not know this, but that fault is a branch of the San Andreas, veering off around shaky Hollister and running parallel and to the east of the ready-to-go Hayward fault. This week’s quakes occurred at the point where the Hayward and Calaveras faults diverge. Now they think the Calaveras and Hayward faults are connected way down below, and if so, this would have implications for the potential of a quake on the Hayward fault. Hayward is the one people are mostly concerned with in the Bay Area, because it runs directly beneath major population centers and significant transportation, water, and energy infrastructure, and it’s capable of a magnitude 7 quake.
Another fun fact: Calaveras means “skulls” in Spanish. Nice.