Tuesday, April 21, 1998 | 9:44 a.m.
Although Nevada ranks as the third most earthquake-prone state behind California and Alaska, scientists don't know where or when the "Big One" will strike the Las Vegas Valley.
As urban development sprawls into every corner of Southern Nevada, scientists cannot measure when the seven large faults that slice through the Las Vegas Valley last moved or predict when they will again, geologist Burt Slemmons said.
Slemmons, a member of the state's Seismic Safety Council and retired University of Nevada, Reno scientist, has lived in Las Vegas since 1989. "There's so much that has been urbanized, there's not much left to study," he said, noting development on Sunrise Mountain where the Frenchman/Sunrise fault casts its shadow as one example.
The Nevada Bureau of Mines is seeking funds to date rocks and dig trenches along the faults to find out how old they are and when they moved.
Federal, state and local government officials are busy preparing for a major quake on one of 265 known faults in Nevada with up to 20 of them in the Las Vegas Valley.
Gov. Bob Miller declared this week Earthquake Awareness Week since Nevada is the heart of the Great Basin, where the continent is tearing itself apart over geologic time.
The most critical faults scientists pay attention to in Las Vegas include ones near Cashman Field, at Sunrise Mountain, along Decatur Boulevard, Valley View Boulevard, Whitney Mesa in the southeast valley and in the northwest valley along Lone Mountain Road and Cheyenne Avenue.
Other faults run under McCarran International Airport runways, Strip hotels and the downtown area, Slemmons said.
Slemmons believes earthquakes with magnitudes from 6.0 to 7.0 rocked Southern Nevada and formed such features as Whitney Mesa, the Valley View Boulevard fault above water wells owned by the Las Vegas Valley Water District and the Frenchman fault that slices through the old Sunrise Mountain landfill.
While northern Nevada faces more of a risk from earthquakes, the Las Vegas Valley has not been immune.
The earliest recorded quake registering a 4 or more on the local Richter scale was in 1936. Its epicenter was 62 miles from Las Vegas. Since then, only 29 quakes measuring 4 or higher have been recorded here.
But the 7.2 Landers, Calif., temblor shook Las Vegas out of its complacency on June 28, 1993. That was followed the next day by a 5.6 magnitude quake at Little Skull Mountain, about 12 miles from a proposed high-level nuclear waste dump at Yucca Mountain. That shaker caused more than $400,000 damage to Department of Energy facilities.
After the Jan. 17, 1994, Northridge, Calif., quake rattled Las Vegas residents, seismic experts began to focus on Southern Nevada for its earthquake risks.
New buildings and the major hotels have the latest earthquake-proofing, but the Nevada Department of Transportation had to upgrade the bridge at Tropicana Avenue and Interstate 15 as well as Sahara Avenue and Oakey Boulevard.
Quakes first shook the Boulder City area in the 1930s and again in the mid-1980s after the Colorado River flooded and backed up behind Hoover Dam. D.S. Carder of the U.S. Coast and Geodetic Survey published his warnings that man-made structures such as Hoover Dam could create swarms of small quakes.
Over millions of years, the western United States could break away from the rest of the continent, as the Arabian Peninsula did from Africa to form the Red Sea. The result? The Gulf of California becomes a new sea with a coastline extending along the Nevada-Arizona border, through Utah and beyond Yellowstone National Park. That's why the world's continents resemble a giant jigsaw puzzle.
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