Scientists warn of quake risks in Southern Nevada

Monday, Feb. 26, 2001 | 10:58 a.m.

More information about earthquakes is available from the seismic laboratory at the University of Nevada, Reno, website (seismo.unr.edu)

A major earthquake in the Las Vegas Valley could kill 300 people and cost more than $10 billion to repair the damage, according to preliminary studies of risk.

A temblor of magnitude 7 might not seem like much of a concern in Southern Nevada, where historically the biggest shakes have come from nuclear bombs being set off at the Nevada Test Site.

But members of the Nevada Earthquake Safety Council, meeting in Las Vegas, were told Friday that the state, the third most seismically active in the nation, had the fifth greatest risk of major damage from earthquake in a recently released study by the Federal Emergency Management Agency.

The FEMA study, released in September, relied on 1990 Census figures, but the Las Vegas Valley's population has more than doubled since then.

Of 40 cities Las Vegas ranked 23rd for anticipated economic losses in the FEMA study and Reno, 28th. Los Angeles was first, with an estimated potential loss of $3 billion.

And recent research makes the possibility of a Big One in Nevada less remote.

The conventional wisdom among geologists who say that the roughly seven major faults in the Las Vegas Valley last erupted 6 million to 12 million years ago is wrong, said Burt Slemmons, professor emeritus of seismology at University of Nevada, Reno, who lives in Las Vegas.

Faults southeast of the valley around Lake Mead and northwest of the valley, in an area called the Las Vegas Shear Zone, are not resting, Slemmons said.

"They are active, but at lower rates than in the past," he said. The seven obvious faults may be connected to a much larger system beneath the valley.

Although the greatest risk for a quake of 7 magnitude or higher appears in the northwestern section of the state, a temblor of 6.8 is possible in the Las Vegas Valley, Craig dePolo, a research geologist for the Bureau of Mines and Geology, said.

The valley got a wakeup call on Feb. 3, the scientists agreed. A quake reaching 3.5 magnitude ruptured a fault about nine miles beneath the western valley's surface, moving a chunk of rock about the size of four football fields roughly 1 1/2 inches.

Municipalities in the Las Vegas Valley and Clark County are considering adopting stricter standards for buildings so they hold up better in a quake, Ron Lynn, chairman of the safety council and assistant director of the county's Building Department, said.

"There are just too many high rises to allow for lower standards," Lynn said during a break in the seven-hour meeting. "We have to ensure that people survive."

The safety council is teaching schoolchildren how to "duck, cover and hold" during an earthquake, as well as endorsing tougher building code standards, Lynn said.

Jim Walker of the emergency management division said the council can help set priorities for taking action after a quake. In the past 150 years there have been 40,000 recorded quakes in Nevada, most of them noted since 1980. Unfortunately, few quake monitors have been available in Nevada, especially in the south.

"It's going to happen some day," Walker said of a major quake in Nevada. "It's just a matter of when."