Why epicenter of 3.9 earthquake between Hayward, Calaveras fault lines is significant
DUBLIN, Calif. (KGO) -- From Napa to Santa Cruz, many Bay Area residents say they felt the big jolt of a 3.9 earthquake on the Calaveras fault in the East Bay.
It struck at 7:46 p.m. Monday night in Dublin in the hills just north of Interstate 580.
The Calaveras fault branches off from the Hayward fault in the South Bay and runs up to Danville, generally on the west of Interstate 680 when you get between Sunol and San Ramon.
RELATED: Magnitude 3.9 earthquake strikes near Dublin, USGS says
It is connected at the surface and deep in the earth to the Hayward fault.
"An interesting thing about this earthquake, we were talking about with our department today is, it's actually west of the Calaveras fault and kind of in between the Hayward and Calaveras fault, so this is maybe joining the two faults and accommodating some of the stress between these two faults," said UC Berkeley seismologist Angie Lux.
"There have been I think 19, 18 other earthquakes that have happened since that magnitude 3.9 earthquake and that's very normal and most people won't feel them. There is a small chance this could be a foreshock to a larger earthquake, but we will never know until that larger one happens, if it ever does," she said.
Across the East Bay, people were still talking about it with one San Ramon resident saying her whole house was shaking.
"I did personally feel the earthquake. It was a quick jolt with a slow roll afterwards. There were no reports of damage. There were no calls for service," said Battalion Chief Stephen Lund with the Livermore-Pleasanton Fire Department.
The San Francisco Public Utilities Commission completed work on the New Calaveras Dam back in 2019 in the East Bay and it was unaffected.
It was built to withstand a 7.25 magnitude earthquake on the Calaveras fault.
Seismologists still say the biggest concern for a 7.0 plus quake is still on the Hayward fault. Another reminder to be prepared.
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