SAN FRANCISCO - A 4.1 magnitude earthquake shook wine country north of San Francisco on Thursday night, the US Geological Survey said, recalling a major temblor that rocked the area last summer and caused millions of dollars in damage.The quake was centered about nine miles (14 km) north of Napa. There were no immediate reports of serious damage or injuries, but the quake spooked residents."It was enough to shake all my bottles and I ran out from under the bar," Cassie Gesiakowski, bartender at a restaurant in nearby Yountville, told the Los Angeles Times. "Nothing broke, just some rumbling and people holding onto their chairs."August's temblor, the biggest in the region in 25 years, injured more than 100 people, damaged historic buildings, set some homes on fire and caused power outages around the picturesque town of Napa, seat of a major wine-growing region.California, which sits along a series of seismic faults, is forecast to experience a much more powerful earthquake at some point, but scientists do not know when it might come or how strong it would measure.