Friday, May 02, 2003
Copyright © Las Vegas Review-Journal

Study increases damage estimate for major quake

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WASHINGTON -- A major earthquake in Southern Nevada would cause much more damage than previously thought because the basin of the Las Vegas Valley would shake more than twice as much as prior research indicated, according to a study released this week by a UNLV professor.

Catherine Snelson, an assistant geophysics professor at the University of Nevada, Las Vegas, said new research suggests a major earthquake would result in a substantial increase in previous estimates of 400 deaths, 10,000 injuries, and $11 billion in economic losses.

Snelson said she does not know how many more deaths might be caused because that issue was not part of the new study.

The damage estimates Snelson relied upon in making her comparison were included in a 2001 report prepared by seismologists John Perry and Jim O'Donnell for an international conference of engineers and seismologists at UNLV. That study was based on an earthquake of magnitude 6.9 striking the valley.

"The valley is surrounded by a big, deep-faulted basin that would shake like a bowl of Jell-O if struck by a major earthquake and would continue to shake until the energy dissipates," Snelson said.

Snelson cautioned her research does not suggest there is a greater likelihood of a major earthquake occurring in Southern Nevada.

"The likelihood of a large earthquake occurring is unknown at this time," Snelson said. "It could happen tomorrow or 100 years from now or 1,000 years from now."

Snelson noted there has not been a major earthquake in the valley since settlers began moving there in the middle of the 19th century.

"We don't know when the last earthquake occurred, so we can't predict when to expect the next one," Snelson said. "We're hoping to have that information after we complete our study next year."

Southern Nevada residents need to be better prepared for a major earthquake, Snelson said.

"With all the new evidence that the valley is in an active earthquake zone, we think the building codes need to be increased," Snelson said. "We are lower than Reno and California."

Snelson is a member of the Las Vegas Seismic Response project, a group of about 10 seismologists and engineers who have been studying the basin for about a year. She released a report on the preliminary findings Wednesday in San Juan, Puerto Rico, at the annual meeting of the Seismological Society of America.

John Louie, a University of Nevada, Reno, seismology professor who is also a member of the research group, said the findings should be a wake-up call for Southern Nevada.

"What this tells us is that earthquake preparedness is important for everybody in Nevada, and Las Vegas is not immune from having to worry about it," Louie said.

But like Snelson, Louie said Southern Nevada residents should not panic. "The likelihood of a major earthquake in the Las Vegas Valley is low," Louie said.

Most of the damage from a major earthquake would occur in the northeast section of the Las Vegas Valley, Snelson said. The deepest part of the basin is more than 3 miles long and is located directly under Nellis Air Force Base.

"Our basin has a very funny shape that is really deep on the northeast side and shallow on the southwest side," Snelson said.

The two-year study began about a year ago after the Department of Energy laboratory at Livermore, Calif., provided $150,000 for the group to determine how the Las Vegas Valley would be impacted if underground nuclear tests resumed at the Nevada Test Site, 65 miles northwest of Las Vegas. The group also obtained a $100,000 grant from the U.S. Geological Survey.

"The study showed that if nuclear testing resumed, it would not cause significant ground motion that would affect structures or residents in the Las Vegas Valley," Snelson said.

But other research showed an earthquake of magnitude 6.5 to 7.0 would shake the basin more than twice as much as previously anticipated. This data was collected by more than 400 seismic recorders that measured the effects of dynamite blasts from rock quarries in the valley and the test site.

There are eight faults in the Las Vegas Valley. The most hazardous fault is widely considered to be the Frenchman Mountain fault east of Las Vegas, said Craig dePolo, a research geologist for the Nevada Bureau of Mines and Geology.

In August, the research group plans to place 900 seismic sensors about six miles apart from each other to monitor ground motion from underground chemical explosions. The explosions will occur in holes drilled 150 feet deep, Snelson said.

"We hope to take a CAT scan of the subsurface of the Las Vegas Valley to determine where most of the shaking is likely to occur," Snelson said.