Published Friday, Feb. 27, 2009 | 8:11 a.m.
Updated Friday, Feb. 27, 2009 | 5:43 p.m.
Beyond the Sun
An earthquake that rattled an area north of the Las Vegas Valley has been upgraded to a 3.0 magnitude temblor by a state seismological laboratory.
The University of Nevada, Reno Seismological Laboratory in northern Nevada has upgraded the quake from a 2.7 magnitude to a 3.0 magnitude.
The earthquake shook an area north of Las Vegas at 7:10 a.m. today, the U.S. Geological Survey says.
While this morning’s quake was minor, the Las Vegas Basin is capable of shuddering from a 7.0 magnitude and would be susceptible to damage from quakes 150 miles away, said Catherine Snelson, an adjunct professor at UNLV and assistant professor of geophysics at New Mexico Institute of Mining and Technology.
Geologic evidence shows a major earthquake struck the valley about 7,000 to 10,000 years ago.
“It’s a big concern. The good thing is that we don’t have big earthquakes very often,” she said. “We haven’t had a large earthquake since people have been living in the valley. That could mean that we’re overdue or it could mean that the reoccurrence interval between these earthquakes is very long.”
Snelson is part of a group of UNLV scientists mapping Southern Nevada faults and the potential damage they could inflict on populated areas.
There are at least seven active faults in the valley known as normal faults because one side of the fault wall drops relative to another side. The side that falls down commonly becomes a valley and the side that remains or is uplifted slightly is a highland or mountain.
Single family homes and tall buildings would be the least affected but buildings in the range of four to nine stories would sustain the most damage according to simulations, Snelson said.
Faults outside the valley also could be problematic. With mountains all around, the valley is a basin and the shape causes seismic vibrations to remain even after the initial earthquake ends.
“Think of the valley as a bowl of Jell-O,” Snelson said. “When there’s a big earthquake in the surrounding area, that’s going to shake that bowl of Jell-O and that bowl is going to keep shaking. So the shaking will seem much more intense than it would if you weren’t in that valley.”
The USGS reported it heard from five people who posted a notice that they felt the quake -- four responses came from North Las Vegas and a fifth from Nellis Air Force Base -- at the time of the temblor in the Aliante area.
The earthquake appears to have struck along the Arrow Canyon Range fault that runs northeast along the northwestern side of Interstate 15 and into Nellis Air Force Base, according to Burt Slemmons, professor emeritus of geoscience at the University of Nevada, Reno. Slemmons retired to Las Vegas and continues to study earthquake faults in the Las Vegas Valley. Slemmons led efforts to identify the eight faults in the valley and show that they were capable of producing large quakes.
Wanda Taylor, a UNLV professor in the Geosciences Department, said the quake would not be widely felt. Taylor is studying the faults in northeastern Las Vegas Valley and beyond and said the Arrow Canyon fault may be linked to the Wildcat Wash fault.
"If an earthquake ruptured both faults, it could produce a magnitude of 7.0, almost," Taylor said, but such an event is unlikely.
The USGS Earthquake Hazards Program site reported that the quake struck an area 14 miles north-northeast of downtown Las Vegas.
Most earthquakes below 3.0 magnitude are not felt by people, but the rocks and soil can magnify earthquake motion, according to the U.S. Geological Survey Web site. The earthquake was located at the base of the Sheep Mountain Range north of Las Vegas.
Aliante resident Gina Marie Croci said she felt the trembler while sitting at the computer in her bedroom.
She described the quake as a rumbling and rolling motion that lasted about five seconds.
“Being from back east, I’d never gone through anything like this in my life,” Croci said. “I was dumbfounded.”
Her father, who was having breakfast at the time, said he didn’t feel it.
“It was very strange,” Croci said. “I thought I was crazy, but I went back to my computer and found the information on the Internet.”
Ken Smith, a seismologist at the Nevada Seismological Laboratory in Reno, said Las Vegas has had few high-magnitude quakes because the area undergoes little geologic strain, at least compared to the Sierra Nevada range.
“So the faults have a much longer reoccurrence interval and much lower slip rates over long periods of times,” he said.
Southern Nevada has had a number of magnitude 3.0 earthquakes since December but they occurred north of Lake Mead, where fewer people would have felt them, Smith said.
The North Las Vegas Fire Department said it had received no notification of the quake.
Metro police and North Las Vegas police said they had received no calls about the small earthquake.
In the past 150 years, there have been 62 quakes with potentially destructive magnitudes of 5.5 or greater making Nevada the third most active state, according to a publication from eight state and federal seismology and disaster organizations.
Nevada experiences thousands of quakes each year that are too small to feel and hundreds that might be felt, the Nevada Seismological Laboratory reports.
An earthquake that is strong enough to be damaging occurs about every three years in this region.
Earthquakes certainly are not uncommon in Nevada. A 6.0 magnitude rocked Wells a year ago destroying much of the town’s historic buildings. The epicenter was about 11 miles southeast of Wells.
Between Feb. 28 and June 3 last year, a swarm of 1,090 quakes rocked Reno, the largest being 4.7 magnitude. The shocks disturbed shelves but caused no major damage.