RENO, Nev. (AP) - More than 50 aftershocks were recorded on the
west edge of Reno after the largest earthquake in a two-month-long
swarm of temblors dumped cans off shelves, knocked pictures off
walls and pushed rocks off hillsides along the Sierra Nevada.
There were no immediate reports of injuries or major damage early Saturday, but the magnitude 4.7 quake that hit at 11:40 p.m. Friday cracked walls in northwest residential areas, broke lawn watering lines and damaged a wooden flume built along the Truckee River in the late 1800s to carry lumber from Lake Tahoe down the mountain to Reno.
It was the strongest quake to shake the city in a series of much smaller events in the area since the end of February.
The U.S. Geological Survey said Friday night's temblor was centered six miles west of Reno near Mogul, where a swarm of more than 100 quakes rattled the area the day before. The strongest of those was a magnitude 4.2 that caused high-rise hotels to sway in the downtown casino district.
"The earthquake was strongly felt in west Reno and felt throughout the Reno metropolitan area," the University of Nevada, Reno's seismology lab said in a statement early Saturday.
The 4.7 quake originally was estimated to be 4.9, the USGS said, but revised downward after more details were available. Of the more than 50 aftershocks, only eight were bigger than 2.0, including a 3.7 aftershock that was recorded at 12:29 a.m. Saturday.
The initial quake was felt 30 miles north in Portola, Calif., and at least 45 miles south near Stateline, Nev., on Lake Tahoe's south shore.
"This one has been so active, it is so interesting," said Glenn Biasi, a seismologist at UNR's lab.
"They have swarms in California, but to my knowledge I'm unaware of one that each evening makes the evening news and is bigger than the one before."
Jars of mayonnaise, bottles of ketchup and shampoo fell from shelves at a Wal-Mart store in northwest Reno late Friday night. It caused the overhead televisions to sway 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.
Scientists said earlier Friday that Reno faces a "small increase" in the chance of a major earthquake in the aftermath of the seismic activity.
"The persistence of this particular earthquake sequence slightly increases the probability for a significant earthquake in west Reno," the UNR lab said. "However, the occurrence of additional earthquake activity in the Mogul area cannot be predicted or forecast."
Ken Smith, a seismologist at the university lab, said the recent activity around Reno is unusual in that the quakes started out small and continue to build in strength. The normal pattern is for a main quake followed by smaller aftershocks, such as the Feb. 21 quake in the northern Nevada town of Wells.
The magnitude 6 temblor in Wells, 350 miles east of Reno, has been followed by hundreds of smaller aftershocks.
"If the pattern continues we may be looking at a larger event" in the Reno area, Smith said Friday. "We wouldn't be surprised to see it (swarm) end at any time and it also wouldn't be surprising to see a large earthquake. The bottom line is we don't know what will happen."
Reno's last major quake occurred at 12:34 a.m. on April 24, 1914. The 6.1 temblor awakened people as far away as Sacramento, Calif., prompted people to rush out of Reno saloons and hotel lobbies into streets and toppled chimneys, said Craig dePolo, research geologist with Nevada Bureau of Mines and Geology.
On the Net:
U.S. Geological Survey: http://www.usgs.gov
University of Nevada, Reno, seismology lab: www.seismo.unr.educ
(Copyright 2008 by The Associated Press. All Rights Reserved.)