Geologist Burt Slemmons, of Las Vegas, who is professor emeritus at the University of Nevada, Reno, said older, brick-type masonry buildings that aren't steel-reinforced would be damaged the most by local earthquakes where faults are capable of generating 6.5 to 7.0 magnitude temblors.

"I think there would be quite a bit of damage scattered through the town," Slemmons said. "Bookcases and China cabinets would likely be toppled. Except for the occasional buildings that are poorly built, most would hold up very well.

Unfortunately, most construction up until two decades ago "did not have uniformly good earthquake designs because faults were thought to be not earthquake-related," he said. "Now, every geologist regards the faults in the Las Vegas Valley as earthquake-generating, or tectonic."

Exactly when a strong earthquake could strike in the valley is anybody's guess. The Frenchman Fault on the valley's eastern edge, for example, has produced 3-foot offsets in caliche from 125,000 years ago, meaning the fault is capable of magnitude-6.75 to magnitude-7.0.

Slemmons guesses that one of those quakes happen about every 10,000 years when stresses that build up over that period are released. Without knowing when the last one occurred, a strong earthquake could happen there tomorrow, or 100 or 9,000 years in the future.

With every increase in magnitude, the size of the seismic waves that travel through the crust increase by a factor of 10. In terms of energy released, that translates to a 30-fold increase, which means a magnitude 6.7 earthquake sends out 900 times more energy than a 4.7 earthquake.

A database kept by the Nevada Seismological Laboratory dating back to 1868 lists 201 earthquakes of magnitude-5 or greater, including 31 that were 6 or greater and three that were at least magnitude-7.

The last of the big events occurred Dec. 16, 1954 near Fallon and was two earthquakes that occurred minutes apart at Fairview Peak (7.1) and Dixie Valley (6.8), Slemmons said.

A magnitude-7.2 earthquake on Dec. 12, 1932 struck Cedar Mountain near Gabbs, about 110 miles east-southeast of Reno.

The most powerful earthquake in the Nevada database is the Oct. 3, 1915 Pleasant Valley event with a magnitude listed as 7.8. But Slemmons said newer studies based on surface rupture have reduced the magnitude to 7.3.

The magnitude-6.2 Clover Mountain earthquake on Sept. 22, 1966 near Caliente was the last one in Southern Nevada that was on par with Thursday's earthquake near Wells.

In what Anderson described as "ironic timing," the seismological laboratory issued a news release Tuesday that says 2007 "was one of the quietest on record" for seismic activity in Nevada with the third-lowest events on record.

"It is difficult to forecast what is in store for 2008," the release reads.

After Thursday's earthquake, Anderson said, "Indeed shall we call ourselves prophets."

Contact reporter Keith Rogers at krogers@ reviewjournal.com or (702) 383-0308.