As if pulled from a B-tier dystopian movie, a series of sizable earthquakes struck San Ramon this weekend, sending shockwaves that could be felt as far away as Fremont.
The United States Geological Survey (USGS) recorded three proper tremors this weekend that were registered in San Ramon, about 34 miles west of San Francisco. The first of the three quakes was the largest, a 3.9 magnitude tremor recorded Saturday evening, created aftershocks on Sunday capable of being felt in the South Bay, registering 3.0 magnitude and 2.8 magnitude in strength, respectively and chronologically. These tremors, however, only created “light” shaking that could be felt about 15 miles away from each one’s epicenter.
Notable quake, preliminary info: M 3.9 – 5 km SE of San Ramon, CA https://t.co/Jp28brqg9q
— USGS Earthquakes (@USGS_Quakes) December 21, 2025
All of these earthquakes occurred within 2km, roughly a mile, of each other. A sequence of tremors occurred on the Calaveras Fault — one of Northern California’s most active and potentially dangerous fault systems — earlier this month, as well.
Seismologists suggest the Calaveras Fault has an 11% chance of producing the SF Bay Area’s next “big one” within the next 30 years, creating an earthquake of 6.7 magnitude or higher; the Hayward-Rodgers Creek Fault system, however, remains the region’s largest seismic threat, with experts assigning it an over 33% chance of rattling the Bay Area with a life-changing quake within the next 25 years.
The largest quake to occur on this fault in recent history was the 1984 Morgan Hill earthquake. Registering a magnitude of 6.2, geologists suggest it’s the largest (or thereabout) size quake the fault system can produce, given its nominal creep rate and nearly locked behavior.
Between today’s earthquakes and the thousands still plunged into darkness after yesterday’s history-making blackout in San Francisco, it’s an eerie series of events that gives us an uncanny glimpse as to how the region might look after the next “big one.”
