Geologist: Nevada at risk for major quake

J. Craig Anderson

Friday, Sept. 23, 2005 | 10:27 a.m.

Floods, tremors, volcanoes and radioactivity may terrify the average citizen, but to a group of geologists meeting this week in Las Vegas for a conference, they are the spice of life.

"Nevada has gold, earthquakes, water and nuclear waste -- what more could you want?" Nevada State Geologist Jonathan Price said jokingly to an audience of about 150 during Wednesday's opening session of the 48th annual Conference of the Association of Engineering Geologists, which runs through Monday at the Flamingo.

Price began the conference with an overview of the state's various geologic hazards before he launched into a detailed explanation of the proposed nuclear waste dump at Yucca Mountain and how conditions under the earth's surface there could cause radioactive contamination to escape.

Of all the state's geologic hazards, earthquakes pose the greatest risk to residents, with seismic hazard data pointing to the south and west as the most unstable regions.

Carson City is comparable to Los Angeles or San Francisco when it comes to the likelihood of earthquakes, he said.

The Las Vegas area is less prone to earth-shattering seismic activity, but the cost in human lives could be far greater than in Carson City if a major quake does occur.

"The risk might be higher because there's a lot more population at risk," Price said.

A Federal Emergency Management Agency study based on 2000 census data indicates a 10 to 20 percent chance that a major earthquake -- 5.9 or greater on the Richter scale -- will hit within striking distance of Las Vegas during the next 50 years.

A conservative estimate of the economic damage is $3 billion to $8 billion, based on the FEMA study. A stronger earthquake of 6.9 on the Richter scale or more could do as much as $25 billion in damage. Price said because the area's population has grown so rapidly during the past five years, the FEMA estimates may not be high enough.

It is difficult to predict how some hotels would hold up during a serious earthquake because of their unusual designs, he said. Still, Price wasn't sure if the FEMA estimates specifically took into consideration the valley's abundance of casino resorts.

The reason Nevada is so prone to earthquakes is that two tectonic plates -- slowly shifting land masses that make up the continents -- are sliding in different directions along the state's western border.

The plates don't slide smoothly. They tend to lock into place until enough pressure builds to snap them apart, thus causing an earthquake.

Nevada is actually moving away from Utah, "and not just philosophically," Price said, adding that the movement adds about 1 1/2 new acres of land to the Silver State each year.

Price then turned to the subject of Yucca Mountain, the site chosen by Congress in 1987 as the future repository for the nation's most radioactive nuclear waste.

Federally mandated research on the location "really brings to bear quite a bit of geological issues," he said, such as fracturing of the earth that could result from nearby fault lines.

Price said there is evidence that, over thousands of years, rainwater could seep down to the storage area. The containers that hold the waste will corrode eventually, and contaminated water could find its way back into natural springs and wells from which people drink.

"The concern is how much groundwater will flow through those faults," he said.

A string of small, relatively young volcanoes in the region also could have an impact on the containment of nuclear waste by facilitating shifts in the underground rock, Price added.

Price said social and political factors tend to outweigh geotechnical ones when it comes to the placement of waste dump sites because geologists face so many uncertainties when it comes to predicting the odds of a disaster.

"Our job as scientists often becomes narrowing down the uncertainties so that rational decisions can be made," he said.

Scott Ball, chairman of the association's Southwest section, said the conference's purpose is to give engineering geologists -- who often do consulting on large construction projects such as tunnels, pipelines and dams -- new ideas, investigative techniques and approaches.

He said Nevada's geology is a good subject for such a conference.

"It's a great place," Ball said. "There's a lot of things here that other people don't necessarily run into."