San Francisco Oakland Bay Bridge
A woman takes a self portrait beneath an umbrella near the San Francisco Oakland Bay Bridge during a light rain in San Francisco, California June 10, 2015. More than one-third, or 39 percent, of likely California voters surveyed by the Public Policy Institute of California named water shortages and the drought, now in its fourth year, as the state's most pressing issue. Reuters/Robert Galbraith

A magnitude 4.0 earthquake shook San Francisco, California in the U.S. on Monday morning. The quake hit the north of Piedmont, California, around 6.49 a.m. PDT.

The Geological Survey of the United States reported that the initial magnitude of the earthquake was 4.2 but it was later lowered and adjusted to 4.0. Piedmont, the area hit most severely, is located in the East Bay, 13 miles towards San Francisco east, four miles from Oakland downtown and five miles southeast of Berkeley.

The Bay Area Rapid Transit halted transportation for a short period, but trains resumed operation by 7.25 a.m. PDT [12.25 a.m. AEST], according to BART’s statement on Twitter. The Piedmont police reported that there was no indication of damages, although the USGS stated that there were at least six aftershocks of 2.5 magnitudes observed near Piedmont.

The epicentre of the earthquake was about 21 km towards the east of San Francisco on the Hayward Fault. No injuries were reported by the authorities.

On its Twitter page, the city updated “#earthquake tremors felt in #San Francisco. Always be prepared!”

AFP’s Alameda-based correspondent, who was around the bay near the epicentre, said he was awakened by the little rumbling with a sharp jolt of around five seconds towards the end. He added that the photo frames on the walls and dishes started to rattle without any major destruction.

Meanwhile, the Bay Area Rapid Transport system was prepared for medical emergencies and warned the public of delayed travels.

The earthquake in San Francisco followed the hit that struck Napa Valley, California almost one year ago. With a 6.0 magnitude, the Napa Valley earthquake is recorded as one of the strongest strikes to the region in a quarter of a century.

Even then, no deaths were reported but around 130 people sought medical care because of injuries caused by the quake.

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