Las Vegas Valley’s faults different from China’s

An earthquake of the caliber that rocked China this week causing catastrophic loss of life and widespread damage is unlikely to occur on less powerful faults in the Las Vegas Valley, but the valley is not immune to strong shaking from faults capable of producing a magnitude-7.9 quake in California, local experts said Tuesday.

"There is some chance, because some faults in eastern California are capable of that in the Death Valley fault system," said Wanda Taylor, professor of the Geoscience Department at the University of Nevada, Las Vegas.

Her comments and those of Barbara Luke, associate professor of Civil and Environmental Engineering at UNLV, followed their presentation on faults and earthquake hazards in the valley to a meeting of the Southwestern Section of the Association of Environmental and Engineering Geologists.

Taylor said at least 11 faults that either cross the valley's floor or are located outside of it are capable of a substantial jolt.

The California Wash Fault, 50 miles northeast of Las Vegas, near Valley of Fire State Park, could deliver a magnitude-7 earthquake and was one of the faults that Hoover Dam was designed to withstand.

But a more problematic fault within the Las Vegas Valley, the Frenchman Mountain Fault, would cause considerable damage and loss of life if it slipped, releasing tremendous energy through the basin's shallow sediments.

Luke cited a computer model by the Nevada Bureau of Mines and Geology that showed what would happen if a magnitude-6.6 quake struck on the Frenchman Mountain Fault.

In that scenario, there would be 200 to 800 fatalities, 3,000 to 11,000 people would need shelter and there would be major damage to 30,000 buildings in and around the Las Vegas Valley.

The projected economic loss would be between $4.4 billion and $17.7 billion.

"And we have old buildings," Luke said, noting that unlike in China, most structures of newer construction in Las Vegas are reinforced to meet earthquake building codes.

Taylor added, however, that, "We don't have a big retrofitting program in progress like Salt Lake City."

In her presentation, Luke referred to a seismic hazard chart for the Las Vegas Valley that showed there is a 10 percent to 20 percent probability of a magnitude-6 or greater earthquake to occur within 50 years and 50 kilometers of the city.

Las Vegas would be particularly vulnerable, because the valley's shallow soils have a strong effect on ground shaking, she said.

There would be stronger shaking in the lower parts of the valley, where the fine grain sediments are located.

There is no known link between the valley's faults and those in Northern Nevada that have generated recent earthquakes near Reno and Wells.

But a large earthquake there of magnitude-7 or greater could have a "triggering" effect that causes faults in Southern Nevada to move, or release strain.

What geoscientists are trying to determine about the Las Vegas Valley's faults is how often they move.

Taylor said the Eglington Fault, on the valley's north side, produced an earthquake 2,245 years ago, based on mesquite charcoal that was found below the surface.

The Black Hills Fault, southwest of Boulder City, produced at least two earthquakes since about 12,000 years ago and as many as five since 21,000 years ago.

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