A 4.0 magnitude earthquake struck at 2:41 a.m. near Fremont, according to the United States Geological Survey.
The USGS site shows that the epicenter was located near Mission Boulevard and Mayhews Road in the city's Niles District. USGS scientists said the epicenter was on the Hayward Fault, two miles northeast of Fremont, about 5.5 to 6 miles below the surface.
Thirteen additional quakes followed the first earthquake, with the two strongest being magnitude 2.7 and 2.6 at 2:56 a.m. and 3:07 a.m. respectively, the USGS said.
Fremont police and fire departments in Oakland and San Jose said residents reported feeling the temblor but no injuries or damage were caused. Meanwhile, BART reported a systemwide delay due to the earthquake, but said that tracks have been inspected and trains were running at normal speeds.
The Hayward Fault is the most densely populated fault in California, with an estimated 2 million people living on it, and scientists say the fault has been very active the last 15 years. Tuesday’s quake is “an indication the stress level is high and the plates are getting tweaked,” said Dr. David Schwartz, a USGS senior research geologist.
The last major earthquake on the Hayward Fault was a 6.8 shaker back in 1868. Scientists have calculated that there’s a 31 percent chance another big one will strike on the Hayward Fault in the next 30 years.
“It could happen in the next 30, 40 or 50 years,” Schwartz said, “but we know sometime soon the Hayward Fault is going to pop.”
Tuesday's earthquake comes nearly a year after a 6.0 magnitude struck Napa, toppling buildings, injuring people and killing one person.
BART recovering: 10 min delay system wide due to an earthquake. all tracks have been inspected and trains are running at normal speeds.— SFBARTalert (@SFBARTalert) July 21, 2015