Ex-NTS scientists stay on alert for quakes

Friday, Aug. 20, 1999 | 4:10 a.m.

With Congress considering a $200 million boost to improve U.S. earthquake studies, two retired Nevada Test Site seismologists have volunteered to improve local sensors to tune into earthquakes in the Las Vegas Valley.

U.S. Department of Energy scientists like James O'Donnell and Garry Vines recorded the rumbles on monitors known as strong sensors.

The state has been without equipment that can accurately detect earthquakes in Southern Nevada since 1993, after the DOE stopped experimenting with nuclear weapons at the Nevada Test Site and removed its seismic monitors.

A seismograph at UNLV hasn't been able to fill the gap. It can detect temblors as far away as Australia, but could not record recent shakers in the Las Vegas Valley because of a lack of sensors in the valley. With surplus equipment available from the DOE, however, Southern Nevada will be once again wired for tremors.

"Although the potential for seismicity is greater in Northern Nevada and the Reno area compared to Southern Nevada, the Las Vegas area can be considered a high-risk area also, because it has lower building code standards than Reno," O'Donnell said. Since Las Vegas is considered at lower risk for quakes, the building code standards are not as high. New construction in Southern Nevada, however, meets ever-changing and always stricter standards.

Until recently all the seismic attention has gone to California, even though Nevada is the third most earthquake-prone state behind its coastal neighbor and Alaska. Scientists ignored Southern Nevada because it was considered at low risk for a major quake.

But Southern Nevada's continued growth and a couple of Southern California earthquakes that were followed by aftershocks in Nevada have rekindled scientific interest in taking the Earth's pulse on this side of the border.

In 1992 Landers, Calif., rocked with a 7.2 magnitude quake on June 28, followed the next day by a 5.6 magnitude quake 12 miles southeast of a proposed high-level nuclear waste repository at Yucca Mountain under a mountain known as Little Skull.

The Little Skull Mountain quake was the largest ever recorded in Southern Nevada.

Then the Northridge, Calif., quake shook the West on Jan. 17, 1994, with a magnitude of 6.7.

On Aug. 1 another 5.6 magnitude temblor rattled Southern Nevada 40 miles north of Little Skull Mountain.

O'Donnell, who lives 35 miles southeast of Las Vegas in Boulder City, noticed minor rumblings in his home town. The quakes were small, magnitude 3.0 or less, but it caught his interest.

"I built a home-made quake detector in my backyard," O'Donnell said. "It's on the patio." He was eight hours shy of having the gadget ready for the Aug. 1 quake.

Likelihood of The Big One

Most recorded earthquakes in Nevada have occurred in the northern part of the state or in sparsely populated areas.

Such earthquakes in the Las Vegas Valley could result in greater injuries and damages, seismologists point out.

And they are not out of the question.

A major quake scenario in Southern Nevada done by Clark County emergency planners in 1992 estimated that an earthquake is always possible on the 20 or more suspected faults in and around the Las Vegas Valley.

An emergency exercise simulating the collapse of the Spaghetti Bowl -- where U.S. 95 intersects Interstate 15 -- demonstrated just how unprepared local officials are for such a disruptive incident. Emergency teams had never imagined that the structure could collapse and they scrambled to deal with the make-believe disaster.

None of the local faults have been studied enough to measure their movements or dated to see how long ago they moved.

Scientists expect a major quake -- The Big One -- to occur every 10,000 years or so in this area.

However, since 1936, when the first earthquake was recorded in Southern Nevada at 4.0 magnitude, only 29 quakes measuring 4 or higher have been recorded in the valley.

A major earthquake generally measures a magnitude 6.0 or more. The earthquake in Turkey on Tuesday that killed more than 10,000 people was 7.8. Every 1.0 increase in the measurement represents 10 times greater magnitude.

In the Las Vegas Valley the area with the greatest chance for a big jolt is Frenchman Fault near Sunrise Mountain.

Other faults needing further study include one running north and east of Cashman Complex at Las Vegas Boulevard North and Washington Avenue and another under Whitney Mesa in the southeast valley.

Measuring shakers

For 30 years, from 1963 to 1993, the federal government tracked earthquakes and ground motion from underground nuclear weapons experiments at the Test Site, 65 miles northwest of Las Vegas, through 20 sensors around Southern Nevada.

When the DOE stopped experimenting with nuclear weapons in 1992, O'Donnell and Vines retired and local quakes were left unrecorded. The DOE's strong sensor network shut down in 1993.

A Lehman seismograph installed in 1979 at UNLV could pick up temblors as far away as Australia, but could not record the 5.6 magnitude shaker on Aug. 1 about 40 miles northwest of the Las Vegas Valley.

So O'Donnell and Vines offered to link unused surplus monitoring equipment from the nuclear weapons testing days to a computer in UNLV's Lily Fong Geoscience Building.

This summer they began wiring five different devices to listen for earthquakes.

There are three orange-colored S-13s, which pick up ground motion, O'Donnell explained recently in the glassed-in room that serves to protect the equipment and computer link. Two L-4 geophones "listen" for trembles in the earth.

The three S-13s, also known as seismometers, will be placed at sites in Red Rock Canyon National Conservation Area, where they will send signals to the Seismology Laboratory at the University of Nevada, Reno.

It is crucial to install the sensors in Red Rock so scientists in the northern Nevada lab can locate the earthquakes in Las Vegas as well, O'Donnell said.

The University of Nevada, Reno has already installed two matching stations -- one in the Sheep Mountains north of Las Vegas and the other at Nelson, about 50 miles southeast of the valley. They easily recorded a magnitude 2.5 quake in Boulder City on May 6 at 5:51 a.m.

But a third station will allow scientists to pinpoint the epicenters using geometrical calculations based on the triangle of sensors.

O'Donnell wants to link the trio of local sensors to a computer at UNLV as well. That would not only make the information more easily analyzed, but also allow students to read detailed, real-time information from the quaking earth on a TV screen at the geoscience lab.

More equipment?

If Congress approves $200 million in funds to improve U.S. seismic stations, UNLV could benefit even further.

The modern digital program proposed by this year's congressional bills is called the Advance Seismic Research and Monitoring System. The upgrade would allow digital devices to collect more detailed information and smaller quakes of 3.0 to 4.0 magnitudes, the size that have rumbled beneath the Las Vegas Valley and Boulder City during the 1990s.

The U.S. Geological Survey has recommended that 200 strong motion sites be installed in the Reno area and 100 sites in the Las Vegas area, part of $170 million earmarked for the USGS.

The bill also authorizes the National Science Foundation to spend almost $82 million for a five-year project to build a computer network to connect earthquake research centers across the nation. It is up to joint congressional budget committees to complete the legislation.

According to some estimates, earthquake damages cost the U.S. economy about $4.4 billion each year. The 1994 Northridge quake cost an estimated $40 billion in damages.