The US Geological Survey said Friday night's quake was centered around Mogul, just west of Reno. The area of upscale homes along the eastern Sierra was rattled by more than 100 quakes the day before, the strongest a magnitude 4.2 that caused high-rise casinos to sway in downtown Reno.
The strongest aftershock measured 3.7 and was recorded early Saturday.
Mike Lentini of Reno said Friday night's quake felt "like a big truck hit the building" and awakened his family.
"It's the unknown. It's shaking, and when's it going to stop?" he said Saturday. "And when stuff starts falling off the shelves it's a whole other ballgame."
Jars of mayonnaise and bottles of ketchup and shampoo fell from shelves at a Wal-Mart store in northwest Reno. Overhead televisions swayed at a sports bar in neighboring Sparks, 11 miles east, where bartender Shawn Jones said the rumble was significantly stronger than Thursday's event.
"The bottles were shaking, so I sent everybody outside," he said.
Hundreds of mostly minor quakes have occurred along one or possibly more faults since the sequence began Feb. 28, said Ken Smith, a seismologist at the Reno laboratory. The quakes have occurred along an area about 2 miles long and a half-mile wide.
"We can't put a number on it, but the probability of a major earthquake has increased with this sequence," Smith said Saturday. "People need to prepare for ground shaking because there's no way to say how this will play out."
Among other things, scientists urged residents to stock up on water and food, to learn how to turn off water and gas, and to strap down bookshelves, televisions and computers.
"It's getting a little bit frightening," Daryl DiBitonto of Reno told the Reno Gazette-Journal. "I'm very concerned about this increase in not only activity, but also in magnitude."
The quakes around Reno began a week after a magnitude 6 temblor in the northern Nevada town of Wells, near the Utah border. The Feb. 21 quake caused an estimated $778,000 in damage to homes, schools and historic downtown buildings, dePolo said.
Scientists said they're unsure whether the seismic activity at opposite sides of Nevada is related.
Nevada is the third most seismically active state in the US behind California and Alaska. The Wells quake was the 15th of at least magnitude 6 in the state's 143-year history.
A magnitude-7.4 quake south of Winnemucca in 1915 is the most powerful in state history.