Nevada has had quakes of magnitude 7 or more

Thursday, March 1, 2001 | 9:55 a.m.

Nevada has had its share of magnitude 7 or greater temblors -- about once every 30 years, seismologists around the state said Wednesday after Seattle's 6.8 magnitude event.

While Northern Nevada has more potential for large earthquakes, the Las Vegas area is criss-crossed with faults that could trigger a 6.0 magnitude or larger temblor. Scientists say they have not studied the Las Vegas Valley enough to predict how much of a threat local faults pose.

"Seattle's event occurred exactly where it is supposed to," UNLV geology professor David Weide said. "This is why Seattle is a prime earthquake zone and Las Vegas isn't."

The last major earthquake in Nevada was a magnitude 7.2 in 1954 at Fairview Peak, about 100 miles southeast of Reno.

The largest earthquake recorded in Nevada was estimated between 7.3 and 7.8 magnitude in 1915 about 35 miles south of Winnemucca in Pleasant Valley.

Larger earthquakes in Nevada have occurred in areas now crowded with homes and businesses. Within the past 3,000 years two quakes rattled the Genoa fault, which extends from northeastern California into Carson City, scientists say. The magnitudes are estimated between 7.2 and 7.5.

There are 30 faults likely to produce damage in the Carson City-Reno area and at least another seven in the Las Vegas Valley area.

The biggest difference between Seattle's shaker on Wednesday and earth movements in Nevada are the depth and types of faults, research seismologist Ken Smith at the University of Nevada, Reno, said.

The Seattle quake was at least 30 miles deep in an area known as the Cascadia subduction zone, a site where two plates meet. "We don't have these deeper subduction zones," Smith said.

The plate near Seattle bent during Wednesday's quake, said Robert Karlin, who came to the University of Nevada, Reno, from the University of Washington. Because the temblor was so deep, aftershocks may not be such a problem as they would be if it had occurred in the shallower crust, he said.

The Great Basin, which includes all of Nevada, is being pulled apart by the stress built up between the Pacific plate and the continent.

Both UNLV and UNR seismographs recorded the Seattle quake.

No one in Reno, 800 miles away from Seattle, reported feeling the temblor, retired Seismic Laboratory Director James Bruin, said. People in high-rise buildings in Salt Lake City reported feeling the shaking 700 miles away.

"The big worry is, is it a precursor to a larger quake on the subduction zone?" Bruin said.

To prepare for an earthquake, seismologists recommend securing home hot water heaters, bookshelves and sensitive equipment such as TVs and VCRs. After an earthquake, they recommend staying off the telephone and tuning into local radio or television stations if they are available.