Some of California’s biggest earthquakes have occurred on lesser-known fault areas, including both the Ridgecrest quake and the magnitude 6.7 Northridge quake in 1994. And in the Bay Area, geologists have identified the Hayward Fault in the East Bay and the Rodgers Creek Fault in Sonoma County as having the potential to produce major quakes.

Scientists are uncovering a hidden and surprisingly complex earthquake zone beneath Northern California by tracking swarms of tiny earthquakes that are far too weak to feel. These faint tremors are revealing what lies beneath the surface where the San Andreas fault meets the Cascadia subduction zone,

By tracking swarms of very small earthquakes, seismologists are getting a new picture of the complex region where the San Andreas fault meets the Cascadia subduction zone, an area that could give rise to devastating major earthquakes.

The USGS reported that, over the past several days, a sequence of at least five earthquakes shook California, with magnitudes ranging from 2.5 to 3.3. The most recent, a 3.3 magnitude quake, struck near Tres Pinos in San Benito County Saturday morning at a depth of 4 miles.

At this junction, the Pacific Plate moves northwest against the North American Plate, forming the San Andreas Fault, while the Gorda Plate subducts beneath the North American Plate. However, the geological interactions here are far more intricate than a simple three-plate model suggests.

A small town in California was hit by earthquakes once every 22 years for over a century, setting the stage for a major seismic experiment in the 1980s and 90s. But the quake ended up being 11 years late.