Key Takeaways
- Central California experiences third consecutive day of earthquake swarms
- Multiple tremors detected south of San Jose, including magnitude 3.4, 2.6, and 2.5 quakes
- All activity occurring along fault networks connected to the San Andreas Fault system
- No injuries or property damage reported so far
Central California has been rocked by earthquake swarms for the third straight day, raising concerns that the feared ‘Big One’ might be approaching. The latest tremors struck south of San Jose on Friday morning, adding to the seismic activity that has been building throughout the week.
Friday’s Earthquake Activity
Three minor earthquakes were detected less than 30 miles south of San Jose Friday morning, striking within three minutes of each other between 10.40 and 10.43am ET. The US Geological Survey (USGS) reported the first tremor registered as magnitude 3.4, followed by magnitude 2.6 and 2.5 quakes.
No injuries or damage to local property has been reported. Earthquakes between 2.5 and 5.4 magnitude are typically felt for several miles but usually cause only minor effects like objects falling from shelves.
Expanding Seismic Pattern
Friday’s swarm follows significant activity from previous days. Just a day earlier, at least 13 tremors ranging from magnitude 1.0 to 3.7 were reported near The Geysers geothermal field in Northern California. Another swarm of three more powerful earthquakes struck in nearly the same location south of San Jose on Wednesday.
The Friday morning swarm near San Juan Bautista marked the second event in the area within 24 hours. Earlier, a group of three earthquakes including a magnitude 4.0 seismic event occurred between 3pm and 4pm on Thanksgiving.
Fault System Connections
All six earthquakes detected in the Central California Coast area were centered on or near the Calaveras Fault, a major branch of the San Andreas Fault system. The San Andreas, an 800-mile plate boundary responsible for much of California’s seismic activity, doesn’t operate alone.
It connects to multiple parallel and branching faults, including the Calaveras, which distributes plate motion and spreads earthquake risk across the entire region. In Northern California, Thursday’s earthquake swarms near The Geysers occurred along a network of faults including the Bartlett Springs Fault Zone and the Healdsburg-Maacama Fault system.
Both these fault systems branch out from the San Andreas, which runs directly through the San Francisco Bay Area and into the Pacific Ocean, creating ongoing seismic concerns for the region.
