A magnitude 4.4 earthquake on the Hayward Fault jolted Bay Area residents out of bed early Thursday, but it appears to have done little damage.
The temblor, initially reported as magnitude 4.5, struck at 2:39 a.m. two miles east of Berkeley and had a depth of eight miles, according to the U.S. Geological Survey. According to the USGS website, people reported feeling the quake 40 miles south in San Jose.
No injuries or accidents were reported.
At a press conference, USGS officials said there was a small probability that this earthquake was a fore shock and will be followed by a big earthquake: "Looking historically ... about 5% of the time earthquakes are followed by larger earthquakes," said USGS Earthquake Science Center Deputy Director Keith Knudson.
The USGS also said that the agency would not be issuing alerts for the 4.4 magnitude earthquake because quakes of that size "tend not to do that much damage."
The USGS acknowledged though that the earthquake was relatively deep for a Hayward Fault earthquake. The earthquake serves as an important reminder that the "Hayward Fault is ready to go," Knudson said.
There hasn't been a major earthquake on the Hayward Fault in over 100 years. A magnitude 6.8 earthquake occurred on Oct. 21, 1868, and was known at the time as the "Great San Francisco Earthquake." It killed 30 people, caused widespread destruction and was one of the most destructive in California history.
Knudson said the USGS had learned earthquakes, at least on the southern part of the Hayward Fault, occur every 140, 150 to 160 years.
"The last big earthquake on the Hayward fault happened about 150 years ago, in 1868. In fact, the 150th anniversary is coming up, we think that earthquake was a magnitude 6.8 or so,"Knudson said.
NBC Bay Area Chief Meteorologist Jeff Ranieri reported Thursday's quake lasted about 10 seconds, had a bit of rolling and a sharp jolt and was felt across the region in San Francisco and in parts of the East and South Bay.
The California Governor's Office of Emergency Services said there were no reports of damages from the region at this time. But a video posted to Twitter showed products that had fallen from the shelves of a San Leandro Safeway store. There was also a photo of a ceiling panel on the floor.
USGS officials said that usually older structures suffer more damage in earthquakes.
Bay Area Rapid Transit said on Twitter that, while no damage was reported to the system, the first trains this morning were delayed while maintenance crews inspect tracks and structures throughout the BART system. Normal service later resumed.
In the South Bay, the VTA also reported delays due to routine inspections.
Reactions poured into social media immediately after the tremor, with people reporting everything from a jolt, to a roll to a rumble.