Mine landslide triggered quakes

The April 10, 2013, landslide at Rio Tinto-Kennecott Utah Copper's Bingham Canyon mine contains enough debris to bury New York City's Central Park 66 feet deep, according to a new University of Utah study. The slide happened in the form of two rock avalanches 95 minutes apart. The first rock avalanche included grayer bedrock material seen around the margins of the lower half of the slide. The second rock avalanche is orange in color, both from bedrock and from waste rock from mining. The new study found the landslide triggered 16 small quakes. Such triggering has not been noted previously. The slide likely was the largest nonvolcanic landslide in North America's modern history. -  Kennecott Utah Copper.
The April 10, 2013, landslide at Rio Tinto-Kennecott Utah Copper’s Bingham Canyon mine contains enough debris to bury New York City’s Central Park 66 feet deep, according to a new University of Utah study. The slide happened in the form of two rock avalanches 95 minutes apart. The first rock avalanche included grayer bedrock material seen around the margins of the lower half of the slide. The second rock avalanche is orange in color, both from bedrock and from waste rock from mining. The new study found the landslide triggered 16 small quakes. Such triggering has not been noted previously. The slide likely was the largest nonvolcanic landslide in North America’s modern history. – Kennecott Utah Copper.

Last year’s gigantic landslide at a Utah copper mine probably was the biggest nonvolcanic slide in North America’s modern history, and included two rock avalanches that happened 90 minutes apart and surprisingly triggered 16 small earthquakes, University of Utah scientists discovered.

The landslide – which moved at an average of almost 70 mph and reached estimated speeds of at least 100 mph – left a deposit so large it “would cover New York’s Central Park with about 20 meters (66 feet) of debris,” the researchers report in the January 2014 cover study in the Geological Society of America magazine GSA Today.

While earthquakes regularly trigger landslides, the gigantic landslide the night of April 10, 2013, is the first known to have triggered quakes. The slide occurred in the form of two huge rock avalanches at 9:30 p.m. and 11:05 p.m. MDT at Rio Tinto-Kennecott Utah Copper’s open-pit Bingham Canyon Mine, 20 miles southwest of downtown Salt Lake City. Each rock avalanche lasted about 90 seconds.

While the slides were not quakes, they were measured by seismic scales as having magnitudes up to 5.1 and 4.9, respectively. The subsequent real quakes were smaller.

Kennecott officials closely monitor movements in the 107-year-old mine – which produces 25 percent of the copper used in the United States – and they recognized signs of increasing instability in the months before the slide, closing and removing a visitor center on the south edge of the 2.8-mile-wide, 3,182-foot-deep open pit, which the company claims is the world’s largest manmade excavation.

Landslides – including those at open-pit mines but excluding quake-triggered slides – killed more than 32,000 people during 2004-2011, the researchers say. But no one was hurt or died in the Bingham Canyon slide. The slide damaged or destroyed 14 haul trucks and three shovels and closed the mine’s main access ramp until November.

“This is really a geotechnical monitoring success story,” says the new study’s first author, Kris Pankow, associate director of the University of Utah Seismograph Stations and a research associate professor of geology and geophysics. “No one was killed, and yet now we have this rich dataset to learn more about landslides.”

There have been much bigger human-caused landslides on other continents, and much bigger prehistoric slides in North America, including one about five times larger than Bingham Canyon some 8,000 years ago at the mouth of Utah’s Zion Canyon.

But the Bingham Canyon Mine slide “is probably the largest nonvolcanic landslide in modern North American history,” said study co-author Jeff Moore, an assistant professor of geology and geophysics at the University of Utah.

There have been numerous larger, mostly prehistoric slides – some hundreds of times larger. Even the landslide portion of the 1980 Mount St. Helens eruption was 57 times larger than the Bingham Canyon slide.

News reports initially put the landslide cost at close to $1 billion, but that may end up lower because Kennecott has gotten the mine back in operation faster than expected.

Until now, the most expensive U.S. landslide was the 1983 Thistle slide in Utah, which cost an estimated $460 million to $940 million because the town of Thistle was abandoned, train tracks and highways were relocated and a drainage tunnel built.

Pankow and Moore conducted the study with several colleagues from the university’s College of Mines and Earth Sciences: J. Mark Hale, an information specialist at the Seismograph Stations; Keith Koper, director of the Seismograph Stations; Tex Kubacki, a graduate student in mining engineering; Katherine Whidden, a research seismologist; and Michael K. McCarter, professor of mining engineering.

The study was funded by state of Utah support of the University of Utah Seismograph Stations and by the U.S. Geological Survey.

Rockslides Measured up to 5.1 and 4.9 in Magnitude, but Felt Smaller

The University of Utah researchers say the Bingham Canyon slide was among the best-recorded in history, making it a treasure trove of data for studying slides.

Kennecott has estimated the landslide weighed 165 million tons. The new study estimated the slide came from a volume of rock roughly 55 million cubic meters (1.9 billion cubic feet). Rock in a landslide breaks up and expands, so Moore estimated the landslide deposit had a volume of 65 million cubic meters (2.3 billion cubic feet).

Moore calculated that not only would bury Central Park 66 feet deep, but also is equivalent to the amount of material in 21 of Egypt’s great pyramids of Giza.

The landslide’s two rock avalanches were not earthquakes but, like mine collapses and nuclear explosions, they were recorded on seismographs and had magnitudes that were calculated on three different scales:

  • The first slide at 9:30 p.m. MDT measured 5.1 in surface-wave magnitude, 2.5 in local or Richter magnitude, and 4.2 in duration or “coda” magnitude.

  • The second slide at 11:05 p.m. MDT measured 4.9 in surface-wave magnitude, 2.4 in Richter magnitude and 3.5 in coda magnitude.

Pankow says the larger magnitudes more accurately reflect the energy released by the rock avalanches, but the smaller Richter magnitudes better reflect what people felt – or didn’t feel, since the Seismograph Stations didn’t receive any such reports. That’s because the larger surface-wave magnitudes record low-frequency energy, while Richter and coda magnitudes are based on high-frequency seismic waves that people usually feel during real quakes.

So in terms of ground movements people might feel, the rock avalanches “felt like 2.5,” Pankow says. “If this was a normal tectonic earthquake of magnitude 5, all three magnitude scales would give us similar answers.”

The slides were detected throughout the Utah seismic network, including its most distant station some 250 miles south on the Utah-Arizona border, Pankow says.

The Landslide Triggered 16 Tremors

The second rock avalanche was followed immediately by a real earthquake measuring 2.5 in Richter magnitude and 3.0 in coda magnitude, then three smaller quakes – all less than one-half mile below the bottom of the mine pit.

The Utah researchers sped up recorded seismic data by 30 times to create an audio file in which the second part of the slide is heard as a deep rumbling, followed by sharp gunshot-like bangs from three of the subsequent quakes.

Later analysis revealed another 12 tiny quakes – measuring from 0.5 to minus 0.8 Richter magnitude. (A minus 1 magnitude has one-tenth the power of a hand grenade.) Six of these tiny tremors occurred between the two parts of the landslide, five happened during the two days after the slide, and one was detected 10 days later, on April 20. No quakes were detected during the 10 days before the double landslide.

“We don’t know of any case until now where landslides have been shown to trigger earthquakes,” Moore says. “It’s quite commonly the reverse.”

A Long, Fast Landslide Runout

The landslide, from top to bottom, fell 2,790 vertical feet, but its runout – the distance the slide traveled – was almost 10,072 feet, or just less than two miles.

“It was a bedrock landslide that had a characteristically fast and long runout – much longer than we would see for smaller rockfalls and rockslides,” Moore says.

While no one was present to measure the speed, rock avalanches typically move about 70 mph to 110 mph, while the fastest moved a quickly as 220 mph.

So at Bingham Canyon, “we can safely say the material was probably traveling at least 100 mph as it fell down the steepest part of the slope,” Moore says.

The researchers don’t know why the slide happened as two rock avalanches instead of one, but Moore says, “A huge volume like this can fail in one episode or in 10 episodes over hours.”

The Seismograph Stations also recorded infrasound waves from the landslide, which Pankow says are “sound waves traveling through the atmosphere that we don’t hear” because their frequencies are so low.

Both seismic and infrasound recordings detected differences between the landslide’s two rock avalanches. For example, the first avalanche had stronger peak energy at the end that was lacking in the second slide, Pankow says.

“We’d like to be able to use data like this to understand the physics of these large landslides,” Moore says.

The seismic and infrasound recordings suggest the two rock avalanches were similar in volume, but photos indicate the first slide contained more bedrock, while the second slide contained a higher proportion of mined waste rock – although both avalanches were predominantly bedrock.

World’s largest subwoofer: Earthquakes ‘pump’ ground to produce infrasound

Earthquakes sway buildings, buckle terrain, and rumble – both audibly and in infrasound, frequencies below the threshold of human hearing. New computer modeling by a team of researchers indicates that most of the low-frequency infrasound comes from an unexpected source: the actual “pumping” of the Earth’s surface. The researchers confirmed their models by studying data from an actual earthquake.

“It’s basically like a loudspeaker,” said Stephen Arrowsmith, a researcher with the Geophysics Group at Los Alamos National Laboratory in Santa Fe, N.M., who presents his team’s findings at the 164th meeting of the Acoustical Society of America (ASA), held Oct. 22 – 26 in Kansas City, Missouri. “In much the same way that a subwoofer vibrates air to create deep and thunderous base notes, earthquakes pump and vibrate the atmosphere producing sounds below the threshold of human hearing.”

Infrasound can reveal important details about an earthquake. In particular, it may be used to measure the amount of ground shaking in the immediate region above the source, which would normally require an array of many seismometers to measure. There is therefore potential to use infrasound to assess damage in the immediate aftermath of an earthquake.

To better understand the relationship between earthquakes and infrasound, the researchers used the basic idea that the Earth’s surface above the earthquake pumps the atmosphere like a piston. They were then able to apply the same modeling approach used on loudspeaker dynamics.

The researchers tested their model by comparing its predictions to actual data collected from a magnitude 4.6-earthquake that occurred on January 3, 2011, in Circleville, Utah. The University of Utah maintains seismograph stations across the state supplemented with infrasound sensors, which recorded the infrasound produced during that event. Their predictions were in good agreement with the actual data, suggesting that earthquakes generate most of their sound by pumping the atmosphere like a loudspeaker.

“This was very exciting because it is the first such clear agreement in infrasound predictions from an earthquake,” said Arrowsmith. “Predicting infrasound is complex because winds can distort the signal and our results also suggest we are getting better at correcting for wind effects.”

Until now, seismologists have not understood the relative importance of the simple pumping of the ground versus other mechanisms for generating infrasound.

Additional members of the research team include Relu Burlacu and Kristine Pankow, University of Utah; Brian Stump and Chris Haward, Southern Methodist University; and Richard Stead and Rod Whitaker, Los Alamos National Laboratory.

Volcano monitoring will target hazard threat to Marianas, US military and commercial jets

Mariana Islands at map-right, east of the Philippine Sea, and just west of the Mariana Trench in the ocean floor.
Mariana Islands at map-right, east of the Philippine Sea, and just west of the Mariana Trench in the ocean floor.

Technology designed to detect nuclear explosions and enforce the world’s nuclear test-ban treaty now will be pioneered to monitor active volcanoes in the Northern Mariana Islands near Guam. The island of Guam soon will be the primary base for forward deployment of U.S. military forces in the Western Pacific.

The two-year, $250,000 project of the U.S. Geological Survey and Southern Methodist University in Dallas will use infrasound – in addition to more conventional seismic monitoring – to “listen” for signs a volcano is about to blow. The plan is to beef up monitoring of lava and ash hazards in the Northern Mariana Islands, a U.S. commonwealth.

The archipelago’s active volcanoes threaten not only residents of the island chain and the U.S. military, but also passenger airlines and cargo ships. The USGS project calls for installing infrasound devices alongside more traditional volcano monitoring equipment – seismometers and global positioning systems.

Scientists at SMU, which the USGS named the prime cooperator on the project, will install the equipment and then monitor the output via remote sensing. The project is a scientific partnership of the USGS, SMU and the Marianas government.

Infrasound hasn’t been widely used to monitor volcanoes, according to noted volcano expert and SMU geology professor James E. Quick, who is project chief. Infrasound can’t replace seismometers but may help scientists interpret volcanic signals, Quick said.

“This is an experiment to see how much information we can coax out of the infrasound signal,” he said. “My hope is that we’ll see some distinctive signals in the infrasound that will allow us to discriminate the different kinds of eruptive styles – from effusive events that produce lava flows, or small explosive events we call vulcanian eruptions, to the large ‘Plinian’ events of particular concern to aviation. They are certain to have some characteristic sonic signature.”

SMU geologists in recent decades pioneered the use of infrasound to monitor nuclear test-ban compliance, and they continue to advance the technology. For the USGS project, they’ll install equipment on three of the Marianas’ 15 islands. In the event magma begins forcing its way upward, breaking rocks underground and ultimately erupting, seismometers will measure ground vibrations throughout the process, while GPS will capture any subtle changes or deformities in the surface of the Earth, and infrasound devices will record sound waves at frequencies too low to be heard by humans. Infrasound waves move slower than the speed of light but can travel for hundreds of miles and easily penetrate the earth as well as other material objects.

Nine Mariana Islands have active volcanoes. On average, the archipelago experiences about one eruption every five years, said Quick, who was previously program coordinator of the USGS Volcano Hazards Program. Most recently a volcano erupted in 2005 on the island of Anatahan, the largest historical eruption of that volcano, according to the USGS. It expelled some 50 million cubic meters of ash, the USGS reported, noting at the time that the volcanic plume was “widespread over the western Philippine Sea, more than 1300 nautical miles west of Anatahan.” A volcano that erupted on the island of Pagan in 1981 has been showing many signs of unrest, Quick said.

Besides the USGS volcano project, SMU has been active in the Marianas through a memorandum of agreement to help the local government search for alternative energy sources, in particular geothermal.

The Marianas volcano project is part of a larger USGS program that is investing $15.2 million of American Recovery and Reinvestment Act funds to boost existing monitoring of high-risk volcanic areas in partnership with universities and state agencies nationwide.

In targeting the Marianas, the USGS cited the evacuation of residents from the northern islands after the 1981 eruption on Pagan, as well as the threat to the main island of Saipan and to nearby Guam. A U.S. territory, Guam is expected to be home to about 40,000 U.S. military and support personnel by 2014, including 20,000 Marines and dependents redeployed from Okinawa. The Marines will use the island as a rapid-response platform for both military and humanitarian operations. The military also has proposed using the Northern Marianas for military exercises.

The USGS cited also the threat of volcanic ash plumes to commercial and military planes. Air routes connect Saipan and Guam to Asia and the rest of the Pacific Rim, as well as Northeast Asia to Australia, Indonesia, the Philippines and New Zealand.

Worldwide from 1970 to 2000 more than 90 commercial jets have flown into clouds of volcanic ash, causing damage to those aircraft, most notably engine failure, according to airplane maker Boeing.

Volcanic ash plumes can rise to cruise altitudes in a matter of minutes after an eruption, Quick said. Winds carry plumes thousands of miles from the volcanoes, he explained, and then the plumes are difficult or impossible to distinguish from normal atmospheric clouds.

Monitoring by remote sensing allows USGS scientists to alert the International Civil Aviation Organization’s nine Volcanic Ash Advisory Centers as part of ICAO’s International Airways Volcano Watch program. The centers then can issue early warnings of volcanic ash clouds to pilots.

“Monitoring on the ground gives early warning when an eruption begins, as well as an indication that an eruption might be imminent,” Quick said. “The contribution by the USGS and its university partners for volcano monitoring is to provide that earliest warning – or even a pre-eruption indication – that a volcano is approaching eruption so that the volcanic ash advisory centers can get the word out and alerts can be issued.”

The USGS objective is for infrasound on Saipan, four seismometers on Anatahan, which currently has only one functioning seismometer, two seismometers on Sarigan, and GPS on Anatahan, Sarigan and Saipan.

Improved monitoring, Quick said, even might allow evacuated islanders to return to their homes – especially understandable for the island of Pagan, given its freshwater lakes, lush forests, black and white sand beaches and abundant fishing.

“A lot of people would like to move back, but it’s considered unsafe absent monitoring,” he said. “If we can establish monitoring networks on these islands, then I think it becomes more practical for people to think about returning. Properly monitored, one should be able to give adequate warning so that people could evacuate.”