Innovative handheld mineral analyzer — ‘the first of its kind’

This is Dr. Graeme Hansford of the University of Leicester Space Research Centre. -  University of Leicester
This is Dr. Graeme Hansford of the University of Leicester Space Research Centre. – University of Leicester

Dr Graeme Hansford from the University of Leicester’s Space Research Centre (SRC) has recently started a collaborative project with Bruker Elemental to develop a handheld mineral analyser for mining applications – the first of its kind.

The analyser will allow rapid mineral identification and quantification in the field through a combination of X-ray diffraction (XRD) and X-ray fluorescence (XRF). The novel X-ray diffraction method was invented at the University of Leicester and has been developed at the Space Research Centre. The addition of XRD capability represents an evolution of current handheld XRF instruments which sell 1000s of units each year globally.

The handheld instrument is expected to weigh just 1.5 kg, will be capable of analysing mining samples for mineral content within 1 – 2 minutes, and requires no sample preparation. This would be a world first. The analyser is unique due to the insensitivity of the technique to the shape of the sample, which enables the direct analysis of samples without any form of preparation – something currently inconceivable using conventional XRD equipment.

Dr Hansford said: “It’s very fulfilling for me to see the development of this novel XRD technique from initial conception through theoretical calculations and modelling to experimental demonstration.

“The next step is to develop the commercial potential and I’m very excited to be working with Bruker Elemental on the development of a handheld instrument.”

Bruker Elemental is a global leader in handheld XRF instrumentation, with the mining sector a key customer. Bruker therefore brings essential commercial expertise to the project. The two partners have complementary expertise, and are uniquely placed to successfully deliver this knowledge exchange project.

Alexander Seyfarth, senior product manager at Bruker Elemental, said: “Bruker is excited to be involved in this project as it will bring new measurement capabilities to our handheld equipment. In many cases this system will provide information on the crystallography of the sample in addition to the elemental analysis.”

Dr Hansford originally conceived of the XRD technique in early 2010, when trying to work out how to apply XRD for space applications – for example on the surface of Mars or an asteroid – without the need for any sample preparation.

The next stage of the project will focus on developing and testing the methodology using samples which are representative of real-world problems encountered in mining, such as determining the relative amounts of iron oxide minerals in ore samples. In the second part of the project, a prototype handheld device will be developed at the SRC in conjunction with Bruker to demonstrate efficacy of the technology in the field. A key advantage is that the hardware requirements of the technique are very similar to existing handheld XRF devices, facilitating both rapid development and customer acceptance.

Acid mine drainage reduces radioactivity in fracking waste

Much of the naturally occurring radioactivity in fracking wastewater might be removed by blending it with another wastewater from acid mine drainage, according to a Duke University-led study.

“Fracking wastewater and acid mine drainage each pose well-documented environmental and public health risks. But in laboratory tests, we found that by blending them in the right proportions we can bind some of the fracking contaminants into solids that can be removed before the water is discharged back into streams and rivers,” said Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School of the Environment.

“This could be an effective way to treat Marcellus Shale hydraulic fracturing wastewater, while providing a beneficial use for acid mine drainage that currently is contaminating waterways in much of the northeastern United States,” Vengosh said. “It’s a win-win for the industry and the environment.”

Blending fracking wastewater with acid mine drainage also could help reduce the depletion of local freshwater resources by giving drillers a source of usable recycled water for the hydraulic fracturing process, he added.

“Scarcity of fresh water in dry regions or during periods of drought can severely limit shale gas development in many areas of the United States and in other regions of the world where fracking is about to begin,” Vengosh said. “Using acid mine drainage or other sources of recycled or marginal water may help solve this problem and prevent freshwater depletion.”

The peer-reviewed study was published in late December 2013 in the journal Environmental Science & Technology.

In hydraulic fracturing – or fracking, as it is sometimes called – millions of tons of water are injected at high pressure down wells to crack open shale deposits buried deep underground and extract natural gas trapped within the rock. Some of the water flows back up through the well, along with natural brines and the natural gas. This “flowback fluid” typically contains high levels of salts, naturally occurring radioactive materials such as radium, and metals such as barium and strontium.

A study last year by the Duke team showed that standard treatment processes only partially remove these potentially harmful contaminants from Marcellus Shale wastewater before it is discharged back into streams and waterways, causing radioactivity to accumulate in stream sediments near the disposal site.

Acid mine drainage flows out of abandoned coal mines into many streams in the Appalachian Basin. It can be highly toxic to animals, plants and humans, and affects the quality of hundreds of waterways in Pennsylvania and West Virginia.

Because much of the current Marcellus shale gas development is taking place in regions where large amounts of historic coal mining occurred, some experts have suggested that acid mine drainage could be used to frack shale gas wells in place of fresh water.

To test that hypothesis, Vengosh and his team blended different mixtures of Marcellus Shale fracking wastewater and acid mine drainage, all of which were collected from sites in western Pennsylvania and provided to the scientists by the industry.

After 48 hours, the scientists examined the chemical and radiological contents of 26 different mixtures. Geochemical modeling was used to simulate the chemical and physical reactions that had occurred after the blending; the results of the modeling were then verified using x-ray diffraction and by measuring the radioactivity of the newly formed solids.

“Our analysis suggested that several ions, including sulfate, iron, barium and strontium, as well as between 60 and 100 percent of the radium, had precipitated within the first 10 hours into newly formed solids composed mainly of strontium barite,” Vengosh said. These radioactive solids could be removed from the mixtures and safely disposed of at licensed hazardous-waste facilities, he said. The overall salinity of the blended fluids was also reduced, making the treated water suitable for re-use at fracking sites.

“The next step is to test this in the field. While our laboratory tests show that is it technically possible to generate recycled, treated water suitable for hydraulic fracturing, field-scale tests are still necessary to confirm its feasibility under operational conditions,” Vengosh said.

Mega-landslide in giant Utah copper mine may have triggered earthquakes

This is Figure 1 from K.L. Pankow et al. of megalandslide at the Bingham Canyon Mine, Utah. Landslide image copyright Kennecott Utah Copper. -  Seismic/Infrasound image by K.L. Pankow et al. Landslide image copyright Kennecott Utah Copper.
This is Figure 1 from K.L. Pankow et al. of megalandslide at the Bingham Canyon Mine, Utah. Landslide image copyright Kennecott Utah Copper. – Seismic/Infrasound image by K.L. Pankow et al. Landslide image copyright Kennecott Utah Copper.

Landslides are one of the most hazardous aspects of our planet, causing billions of dollars in damage and thousands of deaths each year. Most large landslides strike with little warning — and thus geologists do not often have the ability to collect important data that can be used to better understand the behavior of these dangerous events. The 10 April 2013 collapse at Kennecott’s Bingham Canyon open-pit copper mine in Utah is an important exception.

Careful and constant monitoring of the conditions of the Bingham Canyon mine identified slow ground displacement prior to the landslide. This allowed the successful evacuation of the mine area prior to the landslide and also alerted geologists at the University of Utah to enable them to successfully monitor and study this unique event.

The landslide — the largest non-volcanic landslide in the recorded history of North America — took place during two episodes of collapse, each lasting less than two minutes. During these events about 65 million cubic meters of rock — with a total mass of 165 million tons — collapsed and slid nearly 3 km (1.8 miles) into the open pit floor.

In the January 2014 issue of GSA Today, University of Utah geologists, led by Dr. Kristine Pankow, report the initial findings of their study of the seismic and sound-waves generated by this massive mega-landslide. Pankow and her colleagues found that the landslide generated seismic waves that were recorded by both nearby seismic instruments, but also instruments located over 400 km from the mine. Examining the details of these seismic signals, they found that each of the two landslide events produced seismic waves equivalent to a magnitude 2 to 3 earthquake.

Interestingly, while there were no measurable seismic events prior to the start of the landslide, the team did measure up to 16 different seismic events with characteristics very much like normal “tectonic” earthquakes beneath the mine. These small (magnitude less than 2) earthquakes happened over a span of 10 days following the massive landslide and appear to be a rare case of seismic activity triggered by a landslide, rather than the more common case where an earthquake serves as the trigger to the landslide.

Later studies of both the seismic and sound waves produced by this landslide will allow Pankow and her team to characterize the failure and displacement of the landslide material in much more detail.

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.

Atlas Mountains in Morocco are buoyed up by superhot rock, study finds

<IMG SRC="/Images/187660813.jpg" WIDTH="350" HEIGHT="206" BORDER="0" ALT="This is a profile depicting the height and depth of the Atlas Mountains. The blue bars indicate the boundary between the crust and the superhot rock below, about 15 km shallower than predicted by previous models. – Figure 2 from the Geology paper, courtesy of Meghan Miller and Thorsten Becker”>
This is a profile depicting the height and depth of the Atlas Mountains. The blue bars indicate the boundary between the crust and the superhot rock below, about 15 km shallower than predicted by previous models. – Figure 2 from the Geology paper, courtesy of Meghan Miller and Thorsten Becker

The Atlas Mountains defy the standard model for mountain structure in which high topography must have deep roots for support, according to a new study from Earth scientists at USC.

In a new model, the researchers show that the mountains are floating on a layer of hot molten rock that flows beneath the region’s lithosphere, perhaps all the way from the volcanic Canary Islands, just offshore northwestern Africa.

“Our findings confirm that mountain structures and their formation are far more complex than previously believed,” said lead author Meghan Miller, assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences.

The study, coauthored by Thorsten Becker, professor of Earth sciences at USC Dornsife, was published by Geology on Jan. 1, 2014 and highlighted by Nature Geoscience.

A well-established model for the Earth’s lithosphere suggests that the height of the Earth’s crust must be supported by a commensurate depth, much like how a tall iceberg doesn’t simply float on the surface of the water but instead rests on a large submerged mass of ice. This property is known as “istostacy.”

“The Atlas Mountains are at present out of balance, likely due to a confluence of existing lithospheric strength anomalies and deep mantle dynamics,” Becker said.

Miller and Becker used seismometers to measure the thickness of the lithosphere – that is, the Earth’s rigid outermost layer – beneath the Altas Mountains in Morocco. By analyzing 67 distant seismic events with 15 seismometers, the team was able to use the Earth’s vibrations to “see” into the deep subsurface.

They found that the crust beneath the Atlas Mountains, which rise to an elevation of more than 4,000 meters, reaches a depth of only about 35 km – about 15 km shy of what the traditional model predicts.

“This study shows that deformation can be observed through the entire lithosphere and contributes to mountain building even far away from plate boundaries” Miller said.

Miller’s lab is currently conducting further research into the timing and effects of the mountain building on other geological processes.

Earthquake lights linked to rift environments, subvertical faults

Earthquake lights from Tagish Lake, Yukon-Alaska border region, around the 1st of July, probably 1972 or 1973 (exact date unknown). Estimated size: 1m diameter. Closest orbs slowly drifted up the mountain to join the more distant ones. -  Photo credit: Jim Conacher, used with permission
Earthquake lights from Tagish Lake, Yukon-Alaska border region, around the 1st of July, probably 1972 or 1973 (exact date unknown). Estimated size: 1m diameter. Closest orbs slowly drifted up the mountain to join the more distant ones. – Photo credit: Jim Conacher, used with permission

Rare earthquake lights are more likely to occur on or near rift environments, where subvertical faults allow stress-induced electrical currents to flow rapidly to the surface, according to a new study published in the Jan./Feb. issue of Seismological Research Letters.

From the early days of seismology, the luminous phenomena associated with some earthquakes have intrigued scholars. Earthquake lights (EQL) appear before or during earthquakes, but rarely after.

EQL take a variety of forms, including spheres of light floating through the air. Seconds before the 2009 L’Aquila, Italy earthquake struck, pedestrians saw 10-centimeter high flames of light flickering above the stone-paved Francesco Crispi Avenue in the town’s historical city center. On Nov. 12, 1988, a bright purple-pink globe of light moved through the sky along the St. Lawrence River near the city of Quebec, 11 days before a powerful quake. And in 1906, about 100 km northwest of San Francisco, a couple saw streams of light running along the ground two nights preceding that region’s great earthquake.

Continental rift environments now appear to be the common factor associated with EQL. In a detailed study of 65 documented EQL cases since 1600 A.D., 85 percent appeared spatially on or near rifts, and 97 percent appeared adjacent to subvertical faults (a rift, a graben, strike-slip or transform fault). Intraplate faults are associated with just 5 percent of Earth’s seismic activity, but 97 percent of documented cases of earthquake lights.

“The numbers are striking and unexpected,” said Robert Thériault, a geologist with the Ministère des Ressources Naturelles of Québec, who, along with colleagues, culled centuries of literature references, limiting the cases in this study to 65 of the best-documented events in the Americas and Europe.

“We don’t know quite yet why more earthquake light events are related to rift environments than other types of faults,” said Thériault, “but unlike other faults that may dip at a 30-35 degree angle, such as in subduction zones, subvertical faults characterize the rift environments in these cases.”

Two of the 65 EQL events are associated with subduction zones, but Thériault suggests there may be an unknown subvertical fault present. “We may not know the fault distribution beneath the ground,” said Thériault. “We have some idea of surface structures, but sedimentary layers or water may obscure the underlying fault structure.”

While the 65 earthquakes ranged in magnitude, from M 3.6 to 9.2, 80 percent were greater than M 5.0. The EQL varied in shape and extent, though most commonly appeared as globular luminous masses, either stationary or moving, as atmospheric illuminations or as flame-like luminosities issuing from the ground.

Timing and distance to the epicenter vary widely. Most EQL are seen before and/or during an earthquake, but rarely after, suggesting to the authors that the processes responsible for EQL formation are related to a rapid build-up of stress prior to fault rupture and rapid local stress changes during the propagation of the seismic waves. Stress-activated mobile electronic charge carriers, termed positive holes, flow swiftly along stress gradients. Upon reaching the surface, they ionize air molecules and generate the observed luminosities.

Eyewitness reports and security cameras captured a large number of light flashes during the 2007 Pisco, Peru M 8.0 earthquake. Together with seismic records obtained on a local university campus, the automatic security camera records allow for an exact timing and location of light flashes that illuminated a large portion of the night sky. The light flashes identified as EQL coincided with the passage of the seismic waves.

Thériault likes the account of a local L’Aquila resident, who, after seeing flashes of light from inside his home two hours before the main shock, rushed his family outside to safety.

“It’s one of the very few documented accounts of someone acting on the presence of earthquake lights,” said Thériault. “Earthquake lights as a pre-earthquake phenomenon, in combination with other types of parameters that vary prior to seismic activity, may one day help forecast the approach of a major quake,” said Thériault.

Longmanshen fault zone still hazardous, suggest new reports

The 60-kilometer segment of the fault northeast of the 2013 Lushan rupture is the place in the region to watch for the next major earthquake, according to research published in Seismological Research Letters (SRL). Research papers published in this special section of SRL suggest the 2008 Wenchuan earthquake triggered the magnitude 6.6 Lushan quake.

Guest edited by Huajian Yao, professor of geophysics at the University of Science and Technology of China, the special section includes eight articles that present current data, description and preliminary analysis of the Lushan event and discuss the potential of future earthquakes in the region.

More than 87,000 people were killed or went missing as a result of the 2008 magnitude 7.9 Wenchuan earthquake in China’s Sichuan province, the largest quake to hit China since 1950. In 2013, the Lushan quake occurred ~90 km to the south and caused 203 deaths, injured 11,492 and affected more than 1.5 million people.

“After the 2008 magnitude 7.9 Wenchuan earthquake along the Longmenshan fault zone in western Sichuan of China, researchers in China and elsewhere have paid particular attention to this region, seeking to understand how the seismic hazard potential changed in the southern segment of the fault and nearby faults,” said Yao. “Yet the occurrence of this magnitude 6.6 Lushan event surprised many. The challenge of understanding where and when the next big quake will occur after a devastating seismic event continues after this Lushan event, although we now have gained much more information about this area.”

Preliminary rupture details

The southern part of the Longmenshan fault zone is complex and still only moderately understood. Similar to the central segment where the 2008 Wenchuan event occurred, the southern segment, which generated the Lushan rupture, includes the Wenchuan-Maoxian fault, Beichuan-Yingxiu fault, the Pengxian-Guanxian fault and Dayi faults, a series of sub-parallel secondary faults.

Although the Lushan earthquake’s mainshock did not break to the surface, the strong shaking still caused significant damage and casualties in the epicentral region. Three papers detail the rupture process of the Lushan quake. Libo Han from the China Earthquake Administration and colleagues provide a preliminary analysis of the Lushan mainshock and two large aftershocks, which appear to have occurred in the upper crust and terminated at a depth of approximately 8 km. While the Lushan earthquake cannot be associated with any identified surface faults, Han and colleagues suggest the quake may have occurred on a blind thrust fault subparallel to the Dayi fault, which lies at and partly defines the edge of the Chengdu basin. Based on observations from extensive trenching and mapping of fault activity after both the Wenchuan and Lushan earthquakes, Chen Lichun and colleagues from the China Earthquake Administration suggest the Lushan quake spread in a “piggyback fashion” toward the Sichuan basin, but with weaker activity and lower seismogenic potential than the Wenchuan quake. And Junju Xie, from the China Earthquake Administration and Beijing University of Technology, and colleagues examined the vertical and horizontal near-source strong motion from the Mw 6.8 Lushan earthquake. The vertical ground motion is relatively weak for this event, likely due to the fact that seismic energy dissipated at the depth of 12-25 km and the rupture did not break through the ground surface.

Possible link between Lushan and Wenchuan earthquakes

Were the Lushan and Wenchuan earthquakes related? And if so, what is the relationship? Some researchers consider the Lushan quake to be a strong aftershock of the Wenchuan quake, while others see them as independent events. In this special section, researchers tackled the question from various perspectives.

To discover whether the Lushan earthquake was truly independent from the Wenchuan quake, researchers need to have an accurate picture of where the Lushan quake originated. Yong Zhang from the GFZ German Research Centre for Geosciences and the China Earthquake Administration and colleagues begin this process by confirming a new hypocenter for Lushan. To find this place where the fault first began to rupture, the researchers analyze near-fault strong-motion data (movements that took place at a distance of up to a few tens of kilometers away from the fault) as well as long distance (thousands of kilometers ) teleseismic data.

Using their newly calculated location for the hypocenter, Zhang and colleagues now agree with earlier studies that suggest the initial Lushan rupture was a circular rupture event with no predominant direction. But they note that their calculations place the major slip area in the Lushan quake about 40 to 50 kilometers apart from the southwest end of the Wenchuan quake fault. This “gap” between the two faults may hold increased seismic hazards, caution Zhang and colleagues.

Ke Jia of Beijing University and colleagues explore the relationship of the two quakes with a statistical analysis of aftershocks in the region as well as the evolution of shear stress in the lower crust and upper mantle in the broader quake region. Their analyses suggest that the Wenchuan quake did affect the Lushan quake in an immediate sense by changing the overall background seismicity in the region. If these changes in background seismicity are taken into account, the researchers calculate a 62 percent probability that Lushan is a strong aftershock of Wenchuan.

Similarly, Yanzhao Wang from the China Earthquake Administration and colleagues quantified the stress loading of area faults due to the Wenchuan quake and suggest the change in stress may have caused the Lushan quake to rupture approximately 28.4 to 59.3 years earlier than expected. They conclude that the Lushan earthquake is at least 85 percent of a delayed aftershock of the Wenchuan earthquake, rather than due solely to long-term tectonic loading.

After the Wenchuan quake, researchers immediately began calculating stress changes on the major faults surrounding the rupture zone, in part to identify where dangerous aftershocks might occur and to test how well these stress change calculations might work to predict new earthquakes. As part of these analyses, Tom Parsons of the U.S. Geological Survey and Margarita Segou of GeoAzur compared data collected from the Wenchuan and Lushan quakes with data on aftershocks and stress change in four other major earthquakes, including the M 7.4 Landers and Izmit quakes in California and Turkey, respectively, and the M 7.9 Denali quake in Alaska and the M 7.1 Canterbury quake in New Zealand.

Their comparisons reveal that strong aftershocks similar to Lushan are likely to occur where there is highest overall aftershock activity, where stress change is the greatest and on well-developed fault zones. But they also note that by these criteria, the Lushan quake would only have been predicted by stress changes, and not the clustering of aftershocks following the 2008 Wenchuan event.

Future earthquakes in this region

After Wenchuan and Lushan, where should seismologists and other look for the next big quake in the region? After the 2008 Wenchuan quake, seismologists were primed with data to help predict where and when the next rupture might be in the region. The data suggested that the Wenchuan event would increase seismic stress in the southern Longmenshan fault that was the site of the 2013 Lushan quake. But that information alone could not predict that the southern Longmenshan fault would be the next to rupture after Wenchuan, say Mian Liu of the University of Missouri and colleagues, because the Wenchuan earthquake also increased the stress on numerous others faults in the region

Additional insights can be gained from seismic moment studies, according to Liu and colleagues. Moment balancing compares how much seismic strain energy is accumulated along a fault over a certain period with the amount of strain energy released over the same period. In the case of the Longmenshan fault, there had been a slow accumulation of strain energy without release by a major seismic event for more than a millennium. After the Wenchuan quake, the southern part of the Longmenshan fault became the fault with the greatest potential for a quake. And now, after Lushan, Liu and colleagues say that the 60 kilometer-long segment of the fault northeast of the Lushan rupture is the place in the region to watch for the next major earthquake.

Ground-breaking work sheds new light on volcanic activity

Factors determining the frequency and magnitude of volcanic phenomena have been uncovered by an international team of researchers.

Experts from the Universities of Geneva, Bristol and Savoie carried out over 1.2 million simulations to establish the conditions in which volcanic eruptions of different sizes occur.

The team used numerical modelling and statistical techniques to identify the circumstances that control the frequency of volcanic activity and the amount of magma that will be released.

The researchers, including Professor Jon Blundy and Dr Catherine Annen from Bristol University’s School of Earth Sciences, showed how different size eruptions have different causes. Small, frequent eruptions are known to be triggered by a process called magma replenishment, which stresses the walls around a magma chamber to breaking point. However, the new research shows that larger, less frequent eruptions are caused by a different phenomenon known as magma buoyancy, driven by slow accumulation of low-density magma beneath a volcano.

Predictions of the scale of the largest possible volcanic eruption on earth have been made using this new insight. This is the first time scientists have been able to establish a physical link between the frequency and magnitude of volcanic eruptions and their findings will be published today in the journal Nature Geoscience.

“We estimate that a magma chamber can contain a maximum of 35,000 km3 of eruptible magma. Of this, around 10 per cent is released during a super-eruption, which means that the largest eruption could release approximately 3,500 km3 of magma”, explained lead researcher Luca Caricchi, assistant professor at the Section of Earth and Environmental Sciences at the University of Geneva and ex-research fellow at the University of Bristol.

Volcanic eruptions may be frequent yet their size is notoriously hard to predict. For example, the Stromboli volcano in Italy ejects magma every ten minutes and would take two days to fill an Olympic swimming pool. However, the last super-eruption of a volcano, which occurred over 70,000 years ago, spewed out enough magma to fill a billion swimming pools.

This new research identifies the main physical factors involved in determining the frequency and size of eruptions and is essential to understanding phenomena that effect human life, such as the 2010 ash cloud caused by the eruption of Eyjafallajökull in Iceland.

Professor Jon Blundy said: “Some volcanoes ooze modest quantities of magma at regular intervals, whereas others blow their tops in infrequent super-eruptions. Understanding what controls these different types of behaviour is a fundamental geological question.

“Our work shows that this behaviour results from interplay between the rate at which magma is supplied to the shallow crust underneath a volcano and the strength of the crust itself. Very large eruptions require just the right (or wrong!) combination of magma supply and crustal strength.”

Earth’s crust was unstable in the Archean eon and dripped down into the mantle

Earth’s mantle temperatures during the Archean eon, which commenced some 4 billion years ago, were significantly higher than they are today. According to recent model calculations, the Archean crust that formed under these conditions was so dense that large portions of it were recycled back into the mantle. This is the conclusion reached by Dr. Tim Johnson who is currently studying the evolution of the Earth’s crust as a member of the research team led by Professor Richard White of the Institute of Geosciences at Johannes Gutenberg University Mainz (JGU). According to the calculations, this dense primary crust would have descended vertically in drip form. In contrast, the movements of today’s tectonic plates involve largely lateral movements with oceanic lithosphere recycled in subduction zones. The findings add to our understanding of how cratons and plate tectonics, and thus also the Earth’s current continents, came into being.

Because mantle temperatures were higher during the Archean eon, the Earth’s primary crust that formed at the time must have been very thick and also very rich in magnesium. However, as Johnson and his co-authors explain in their article recently published in Nature Geoscience, very little of this original crust is preserved, indicating that most must have been recycled into the Earth’s mantle. Moreover, the Archean crust that has survived in some areas such as, for example, Northwest Scotland and Greenland, is largely made of tonalite-trondhjemite-granodiorite complexes and these are likely to have originated from a hydrated, low-magnesium basalt source. The conclusion is that these pieces of crust cannot be the direct products of an originally magnesium-rich primary crust. These TTG complexes are among the oldest features of our Earth’s crust. They are most commonly present in cratons, the oldest and most stable cores of the current continents.

With the help of thermodynamic calculations, Dr. Tim Johnson and his collaborators at the US-American universities of Maryland, Southern California, and Yale have established that the mineral assemblages that formed at the base of a 45-kilometer-thick magnesium-rich crust were denser than the underlying mantle layer. In order to better explore the physics of this process, Professor Boris Kaus of the Geophysics work group at Mainz University developed new computer models that simulate the conditions when the Earth was still relatively young and take into account Johnson’s calculations.

These geodynamic computer models show that the base of a magmatically over-thickened and magnesium-rich crust would have been gravitationally unstable at mantle temperatures greater than 1,500 to 1,550 degrees Celsius and this would have caused it to sink in a process called ‘delamination’. The dense crust would have dripped down into the mantle, triggering a return flow of mantle material from the asthenosphere that would have melted to form new primary crust. Continued melting of over-thickened and dripping magnesium-rich crust, combined with fractionation of primary magmas, may have produced the hydrated magnesium-poor basalts necessary to provide a source of the tonalite-trondhjemite-granodiorite complexes. The dense residues of these processes, which would have a high content of mafic minerals, must now reside in the mantle.