Research geophysicist Tom Brocher with the U.S. Geological Survey in Menlo Park, Calif., said Bay Area residents should be prepared for a major quake “any day now” because the 4.0-magnitude quake that struck Tuesday occurred on a known fault line that is overdue for a large temblor.
“The past five major earthquakes on the fault have been about 140 years apart, and now we’re 147 years from that 1868 earthquake, so we definitely feel that could happen any time,” Brocher said, according to CBS in San Francisco.
The 1868 quake that struck on the Hayward fault near the city of Hayward had an estimated magnitude of 6.8, and killed 30 and caused extensive property damage in the East Bay.
But a similar earthquake today can be expected to be far more dangerous, since the population in 2015 is 100 times greater.
“The population is now 100 times bigger in the East Bay, so we have many more people that will be impacted,” Brocher said.
Tuesday’s earthquake, which struck at 2:41 a.m. on the border of Fremont and Union City, caused no major damage but did delay the start of BART regional train service while crews checked the tracks for possible damage. None was found.
At least 13 aftershocks have been reported, but none stronger than 2.7 magnitude, CBS said.
The Hayward fault extends north from Fremont through heavily populated cities in the East Bay — including Berkeley and Oakland — through to San Pablo Bay.
“We keep a close eye on the Hayward Fault because it does sit in the heart of the Bay Area and when we do get a big earthquake on it, it’s going to have a big impact on the entire Bay Area,” Brocher said.
Tuesday’s shaker was felt as far south as Santa Cruz and as far east as Livermore, but was strongest in the East Bay and South Bay, the USGS said.
Brocher urged residents to ensure they are prepared for a major quake, including having secure supplies of emergency water and food easily available.
Authorities regularly advise area residents that it could be days before power is restored and rescue workers reach everyone after a major quake.
