A series of quakes that began Tuesday evening in and around San Ramon continued through the day Wednesday and into Thursday morning according to the US Geological Survey. This morning has already played host to two earthquakes in the area, with a 3.4-magnitude quake striking at 6:10 a.m. one mile north of San Ramon, and a 3.0-magnitude quake striking the same area two hours later at 8:14 a.m.
The quakes have hit along the Calaveras Fault, which is a branch of the San Andreas Fault that runs under the far East Bay, east of the Hayward Fault.
This is all happening just in time for the annual Great Shakeout (it's at 10:15 a.m. today), a statewide earthquake drill encouraging people to practice the "drop, cover, and hold on" approach to taking shelter during a quake. The 20+ earthquakes to hit the area in the last 72 hours constitute a fully fledged "earthquake swarm" — a term that in no way is meant to evoke some Lovecraftian image of horror and end times.
And no, this swarm is in no way related to Tuesday's warm weather (you made it to the beach, right?), because "earthquake weather" is not a thing. At least according to most smart people, as well as fashionable weather anchor Roberta Gonzales of CBS SF.
I simply do not believe in earthquake weather because weather can not penetrate the earth’s surface and affect plates miles underground. [...] Earthquakes happen miles underground and happen in every type of weather. The USGS estimates there are millions of earthquakes each year, but many go undetected because they happen in remote areas.
So, now that that's settled, what could possibly be behind the earthquake swarm? Well, as a study last year in the Bulletin of the Seismological Society of America kindly reminded us, there are at least four separate fault lines in the Bay Area "locked and loaded."
Maybe now's yet another good time to put together that earthquake kit.