Monday, Feb. 5, 2001 | 11:07 a.m.
Seismologist Burt Slemmons heard the earthquake about 7:30 p.m. Saturday, before he felt the ground move beneath his feet. Neither Slemmons nor anyone else in Las Vegas noticed a 1.4 magnitude quake in Boulder City an hour and a half later.
Slemmons, who moved to Las Vegas in 1991 after retiring from the University of Nevada, Reno, lives in The Lakes subdivision in western Las Vegas.
"It was just boom," Slemmons said of the 3.4 magnitude earthquake that struck about 10 miles west of downtown Las Vegas. "We felt it very distinctly and very strongly."
The fault, part of the relatively new West Charleston system, probably slipped, one side going up, one dropping, less than five miles underneath the surface of the desert, Slemmons said.
Saturday's quake was the strongest recorded in the fault system. Most are about 2.0 to 2.5, which generally cannot be felt.
Some neighbors thought Saturday's temblor was a sonic boom from Nellis Air Force Base training exercises earlier in the day, Slemmons said.
The fault system was first spotted two years ago, in aerial photos shot before new homes and golf courses had sprung up in the area, he said. It extends from south of Sahara Avenue north to Fort Apache, then dives northeast and crosses U.S. 95.
There are some 20 known faults in the Las Vegas Valley, some of them capable of producing a magnitude 6.0 earthquake, Slemmons said. Generally, it takes a temblor above a 4 to cause damage.
The second quake occurred at 9 p.m. in Boulder City, seismologist Jim O'Donnell of Boulder City said. That one was felt only by monitors at O'Donnell's Boulder City home and at UNLV.
O'Donnell is helping UNLV set up seismographs throughout the Las Vegas Valley, so that geologists can begin to record large and small temblors in Southern Nevada, an area neglected by earthquake hunters as developers bulldozed and paved over surface features that provide scientific clues to active faults.
Only in the past 11 years have Southern Nevada residents realized that Las Vegas shakes. Nevada is the third most seismically active state behind Alaska and California.
On Dec. 14, 1998, a 2.7 magnitude temblor shook northwest Las Vegas residents, the first jolt that people felt from the valley floor in 14 years.
The Big One -- a quake measuring over 6.0 magnitude -- rattling either Reno or Las Vegas could happen once in 500 years, and some seismologists believe Southern Nevada is overdue, O'Donnell said. "But we never know when a quake will occur," he said.
A 7.5 magnitude quake in Landers, Calif., in 1992 triggered a 5.6 magnitude temblor at Little Skull Mountain, less than 12 miles away from the proposed high-level nuclear waste repository site at Yucca Mountain. The Department of Energy reported some surface damage.