RENO, Nev. (AP) - A day after a magnitude 4.7 earthquake struck northern Nevada's largest city, scientists urged residents to prepare for a larger temblor as the area continued to rumble on Saturday.

More than 100 aftershocks were recorded on the western edge of Reno after the earthquake hit Friday night, the most powerful in a two-month-long series of quakes and the strongest around the city since one in 1953 that measured 5.2, scientists at the University of Nevada, Reno, said.

The latest quake swept store shelves clean, cracked walls in homes and dislodged rocks on hillsides, but there were no reports of injuries or major damage.

Seismologists said the recent activity was unusual because the quakes started out small and had built in strength.

"A magnitude 6 quake wouldn't be a scientific surprise," said John Anderson, director of the seismological laboratory at the University of Nevada. "We certainly hope residents are taking the threat seriously."

But Mr. Anderson said that there was no way to predict what would happen and that the sequence of quakes could end without a major one.

A rock slide set off by the Friday night quake was blamed for causing a 125-foot breach in a wooden flume that carries water to one of the two water treatment plants in Reno, a city of about 210,000.

A backup pump was used to divert water to the plant, and the breach was not expected to cause water shortages, said Aaron Kenneston, the emergency management officer in Washoe County, which includes Reno.

The United States Geological Survey said the earthquake's epicenter was near Mogul, just west of Reno. The upscale area, along the eastern Sierra Nevada, had been rattled by more than 100 quakes on Thursday. The strongest, with a magnitude of 4.2, caused high-rise casinos to sway in downtown Reno.

The strongest aftershock, recorded early Saturday, measured 3.7.

Mike Lentini of Reno said the quake on Friday night 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?" Mr. Lentini said on Saturday. "And when stuff starts falling off the shelves, it's a whole other ballgame."

Hundreds of mostly minor earthquakes have occurred along one or more faults since the sequence began on Feb. 28, said Ken Smith, a seismologist at the Reno laboratory. The quakes have occurred along an area about two 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," Mr. Smith said. "People need to prepare for ground shaking, because there's no way to say how this will play out."

Nevada is the third most seismically active state behind California and Alaska. A magnitude 6 quake on Feb. 21 near the Utah border was the 15th of at least that magnitude in the state's 143-year history.

A magnitude 7.4 quake south of Winnemucca in 1915 is the most powerful in state history.