UNLV testing shakes up valley

Jennifer Knight

Tuesday, Aug. 12, 2003 | 11:08 a.m.

UNLV geologists set off a series of underground explosions early this morning to mimic seismic activity and will now begin the six-month process of interpreting the information to determine the potential for a major earthquake in Las Vegas.

Nine detonations occurred between midnight and 2 a.m. as part of the efforts by University of Nevada, Las Vegas, geologists to map fault lines in the valley. City and county fire officials said they received no complaint calls from residents about the blasts.

"It went really well," said Cathy Snelson, an assistant professor of crustal geophysics at UNLV. "All of our (detonations) went off. At my (location) basically all you really felt was a thump."

Las Vegas residents had expressed concern that the explosives, set 150 feet beneath the earth, might trigger an earthquake or damage the foundations of buildings near the areas of the explosions, but Snelson said the blasts only generated slight movement and a sound similar to a firecracker.

The construction company that handled the work carried a $5 million insurance policy to cover UNLV just in case the blast damaged anything, the company's operations manager said.

Using 825 seismic instruments buried in the ground throughout Las Vegas to measure shaking caused by explosives, the experiment was designed to provide a picture of the Las Vegas basin's subsurface.

The findings could end up shaping the way emergency workers respond to an earthquake. They could also force changes in building codes and in the cost of earthquake insurance.

"It does unfortunately mean increased costs down the line, but it also means that buildings will be less likely to collapse during an earthquake," said Snelson, the coordinator of the experiment.

Nevada is the third-most seismically active state in the nation, and earthquakes of up to magnitude 7.0 are possible in the state, Snelson said. The problem is that not much is known about the seismic history of the region or when another earthquake may be due.

Snelson said Monday's experiment will attempt to answer some of those questions by taking what amounts to a CAT scan of the Las Vegas basin.

Cast boosters, which are explosives slightly stronger than dynamite, were used for the detonations, construction workers who set up the blasts said.

"(Dynamite) doesn't have the right density for the project," said Joe Dodd, operations manager for Sanders Construction in Henderson. "They are actually looking for something with a little more power to it."

The holes into which the explosives had been lowered were plugged with gravel and clay.

Instruments sensitive to the slightest ground movement then recorded any movement, helping scientists deduce how large the fault lines are, where they are, what areas would be the most affected and which way a quake would likely shake -- vertically or horizontally.

According to Dodd, UNLV set the following charges at nine areas throughout the valley:

Results of the experiment will take between three and six months to analyze. From that analysis, so-called shake maps will be drawn up and an emergency response plan will be formulated.

"We'll know more after the instruments get picked up," Snelson said. "Hopefully, we'll actually get to see some of the data today."