Las Vegas’ earthquake risks exaggerated in urban myths

Major faults run up the entire Las Vegas Valley, and it’s only a matter of time until a big earthquake hits, flattening nearly every building here. The Strip is built on sandy soil that will be subject to soil liquefaction, which would result in all the casinos sinking straight down into the earth.

Well, actually, the truth is quite a bit better than that, but that doesn’t stop the doomsday scenario from being a popular local urban myth.

There are some significant faults in the valley. Seismologists list seven distinct faults, moving in three directions, but none is particularly long. The magnitude of an earthquake is limited by the length of the fault it occurs on, and according to Barbara Luke, a professor in civil and environmental engineering at the University of Nevada, Las Vegas, and director of the university’s Applied Geophysics Center, the valley couldn’t have an earthquake much greater than magnitude 7.0.

"There’s a 100 percent chance that we will get an earthquake as high as 7," Luke said, "but it may not happen in our lifetime."

A study by the Nevada Bureau of Mines and Geology determined that the probability of a magnitude 6.0 earthquake occurring within 50 kilometers, or a little over 30 miles, of Las Vegas within the next 50 years is approximately 12 percent. Those are long odds, but the damage a 6.0 earthquake would cause is substantial.

The results of the study were published in an online publication titled "Earthquake Hazards in Clark County," which is available on the Nevada Bureau of Mines and Geology website, www.nbmg.unr.edu.

It estimates that there would be 280 fatalities, 1,100 hospitalized and 3,600 people needing shelter. An estimated 15,000 buildings would suffer major damage, with an economic loss of $7.2 billion.

A 5.4 magnitude earthquake in Chino Hills near Los Angeles on July 29, 2008, was felt so strongly by some in Las Vegas that a judge cleared a courtroom on the 15th floor of the Regional Justice Center.

Luke said the effects of an earthquake rely on a wide range of variables, including geometry of bedrock, the direction of the motion and the type of soil involved. Faults in Death Valley, which has more frequent earthquakes, could affect tall buildings here, where a closer earthquake is more likely to affect smaller buildings.

"The damage isn’t necessarily greater a half-mile from the fault than three miles," Luke said. "Finer-grain soils amplify motion more than coarse-grain soils. It’s a very complicated problem."

Luke believes buildings are relatively safe here, having been built to withstand quite a bit of shaking. Some older buildings with unreinforced masonry are problematic, but codes are met for newer ones.

Much of preparing for an earthquake is the same as any other disaster. You need to have a plan and a disaster preparedness kit. For more information, visit http://earthquakes.unlv.edu.

There are some things you can do to make your house safer and reduce damage to people and property. Some furniture, particularly bookshelves, can be attached to walls to prevent them from tipping over. Likewise, heavy electronics, such as computers and televisions, can be secured.

During an earthquake, Luke recommends that people drop, cover and hold on, a simple way of saying get down to avoid falling down, find cover such as a sturdy table to get under and hold onto that object. Regardless of whether they’ve been secured, stay clear of bookshelves or heavy objects that might fall on you. The kitchen is usually the most dangerous room in the house during an earthquake.

If you’re in a large, public place when an earthquake hits, don’t panic and rush for the doorway. If you can get out without having to fight your way through a crowd, do so, but remember that a human stampede can be just as deadly as an earthquake. Try to keep away from anything heavy that might fall and crouch on the floor and protect your head and neck with your arms.

If you’re driving when an earthquake hits, simply pull over, set the brake and wait it out. In a car or out of one, keep away from power lines, bridges or anything that might fall on you.

As for soil liquefaction, it is a genuine earthquake phenomenon in which seemingly solid ground acts more like a liquid, but only a few small areas of the valley are likely to be subject to it.

"It would be limited here, although because of development, watering lawns and runoff, we may have liquefaction in areas we never had it in before," Luke said. "The groundwater is deep here, and I think the caliche would work in our favor."

At 10:20 a.m. Oct. 20, many groups in the valley plan to participate in the Great Nevada ShakeOut, an earthquake preparedness drill. For more information, visit shakeout.org/nevada.

Contact Sunrise/Whitney View reporter F. Andrew Taylor at ataylor@viewnews.com or 380-4532.