Scientists discover layer of liquified molten rock in Earth’s mantle

Marine scientists haul in a successfully recovered marine electromagnetic receiver. -  Kerry Key
Marine scientists haul in a successfully recovered marine electromagnetic receiver. – Kerry Key

Scientists have discovered a layer of liquified molten rock in Earth’s mantle that may be responsible for the sliding motions of the planet’s massive tectonic plates.

The finding may carry far-reaching implications, from understanding basic geologic functions of the planet to new insights into volcanism and earthquakes.

The research was funded by the National Science Foundation (NSF), and is reported in this week’s issue of the journal Nature by Samer Naif, Kerry Key, and Steven Constable of the Scripps Institution of Oceanography (SIO), and Rob Evans of the Woods Hole Oceanographic Institution.

“This new image greatly enhances our understanding of the role that fluids, both seawater and deep subsurface melts, play in controlling tectonic and volcanic processes,” said Bil Haq, program director in NSF’s Division of Ocean Sciences, which funded the work through the NSF Directorate for Geosciences’ MARGINS (now GeoPRISMS) Program.

The scientists discovered the magma layer at the Middle America trench off Nicaragua’s shores.

Using advanced seafloor electromagnetic imaging technology pioneered at SIO, the scientists imaged a 25-kilometer- (15.5-mile-) thick layer of partially melted mantle rock below the edge of the Cocos plate where it moves beneath Central America.

The new images of magma were captured during a 2010 expedition aboard the research vessel Melville.

After deploying a vast array of seafloor instruments that recorded natural electromagnetic signals to map features of the crust and mantle, the scientists realized they had found magma in a surprising place.

“This was completely unexpected,” said Key. “We went out looking to get an idea of how fluids are interacting with plate subduction, but we discovered a melt layer we weren’t expecting to find.”

For decades scientists have debated the forces that allow the planet’s tectonic plates to slide across the Earth’s mantle.

Studies have shown that dissolved water in mantle minerals results in a more ductile mantle that would facilitate tectonic plate motions, but for many years clear images and data required to confirm or deny this idea were lacking.

“Our data tell us that water can’t accommodate the features we are seeing,” said Naif. “The information from the new images confirms the idea that there needs to be some amount of melt in the upper mantle. That’s what’s creating this ductile behavior for plates to slide.”

The marine electromagnetic technology employed in the study was originated by Charles “Chip” Cox, an emeritus oceanographer at SIO, and in recent years further advanced by Constable and Key.

They have been working with the energy industry to apply this technology to map offshore oil and gas reservoirs.

The researchers say their results will help geologists better understand the structure of the tectonic plate boundary and how that affects earthquakes and volcanism.

“One of the longer-term implications of our results is that we are going to understand more about the plate boundary, which could lead to a better understanding of earthquakes,” said Key.

The researchers are now trying to find the source that supplies the magma in the newly discovered layer.

Scientists discover layer of liquified molten rock in Earth’s mantle

Marine scientists haul in a successfully recovered marine electromagnetic receiver. -  Kerry Key
Marine scientists haul in a successfully recovered marine electromagnetic receiver. – Kerry Key

Scientists have discovered a layer of liquified molten rock in Earth’s mantle that may be responsible for the sliding motions of the planet’s massive tectonic plates.

The finding may carry far-reaching implications, from understanding basic geologic functions of the planet to new insights into volcanism and earthquakes.

The research was funded by the National Science Foundation (NSF), and is reported in this week’s issue of the journal Nature by Samer Naif, Kerry Key, and Steven Constable of the Scripps Institution of Oceanography (SIO), and Rob Evans of the Woods Hole Oceanographic Institution.

“This new image greatly enhances our understanding of the role that fluids, both seawater and deep subsurface melts, play in controlling tectonic and volcanic processes,” said Bil Haq, program director in NSF’s Division of Ocean Sciences, which funded the work through the NSF Directorate for Geosciences’ MARGINS (now GeoPRISMS) Program.

The scientists discovered the magma layer at the Middle America trench off Nicaragua’s shores.

Using advanced seafloor electromagnetic imaging technology pioneered at SIO, the scientists imaged a 25-kilometer- (15.5-mile-) thick layer of partially melted mantle rock below the edge of the Cocos plate where it moves beneath Central America.

The new images of magma were captured during a 2010 expedition aboard the research vessel Melville.

After deploying a vast array of seafloor instruments that recorded natural electromagnetic signals to map features of the crust and mantle, the scientists realized they had found magma in a surprising place.

“This was completely unexpected,” said Key. “We went out looking to get an idea of how fluids are interacting with plate subduction, but we discovered a melt layer we weren’t expecting to find.”

For decades scientists have debated the forces that allow the planet’s tectonic plates to slide across the Earth’s mantle.

Studies have shown that dissolved water in mantle minerals results in a more ductile mantle that would facilitate tectonic plate motions, but for many years clear images and data required to confirm or deny this idea were lacking.

“Our data tell us that water can’t accommodate the features we are seeing,” said Naif. “The information from the new images confirms the idea that there needs to be some amount of melt in the upper mantle. That’s what’s creating this ductile behavior for plates to slide.”

The marine electromagnetic technology employed in the study was originated by Charles “Chip” Cox, an emeritus oceanographer at SIO, and in recent years further advanced by Constable and Key.

They have been working with the energy industry to apply this technology to map offshore oil and gas reservoirs.

The researchers say their results will help geologists better understand the structure of the tectonic plate boundary and how that affects earthquakes and volcanism.

“One of the longer-term implications of our results is that we are going to understand more about the plate boundary, which could lead to a better understanding of earthquakes,” said Key.

The researchers are now trying to find the source that supplies the magma in the newly discovered layer.

Huge and widespread volcanic eruptions triggered the end-Triassic extinction

More than 200 million years ago, a massive extinction decimated 76 percent of marine and terrestrial species, marking the end of the Triassic period and the onset of the Jurassic. This devastating event cleared the way for dinosaurs to dominate Earth for the next 135 million years, taking over ecological niches formerly occupied by other marine and terrestrial species.

It’s not entirely clear what caused the end-Triassic extinction, although most scientists agree on a likely scenario: Over a relatively short period of time, massive volcanic eruptions from a large region known as the Central Atlantic Magmatic Province (CAMP) spewed forth huge amounts of lava and gas, including carbon dioxide, sulfur and methane. This sudden release of gases into the atmosphere may have created intense global warming and acidification of the oceans that ultimately killed off thousands of plant and animal species.

Now researchers at MIT, Columbia University and elsewhere have determined that these eruptions occurred precisely when the extinction began, providing strong evidence that volcanic activity did indeed trigger the end-Triassic extinction. Their results are published in the journal Science.

The team determined the age of basaltic lavas and other features found along the East Coast of the United States, as well as in Morocco – now-disparate regions that, 200 million years ago, were part of the supercontinent Pangaea. The rift that ultimately separated these landmasses was also the site of CAMP’s volcanic activity. Today, the geology of both regions includes igneous rocks from the CAMP eruptions as well as sedimentary rocks that accumulated in an enormous lake; the researchers used a combination of techniques to date the rocks and to pinpoint CAMP’s beginning and duration.

From its measurements, the team reconstructed the region’s volcanic activity 201 million years ago, discovering that the eruption of magma – along with carbon dioxide, sulfur and methane – occurred in repeated bursts over a period of 40,000 years, a relatively short span in geologic time.

“This extinction happened at a geological instant in time,” says Sam Bowring, the Robert R. Shrock Professor of Geology in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “There’s no question the extinction occurred at the same time as the first eruption.”

The paper’s co-authors are Terrence Blackburn (who led the project as part of his PhD research) and Noah McLean of MIT; Paul Olsen and Dennis Kent of Columbia; John Puffer of Rutgers University; Greg McHone, an independent researcher from New Brunswick; E. Troy Rasbury of Stony Brook University; and Mohammed Et-Touhami of the Université Mohammed Premier Oujda in Morocco.

More than a coincidence


The end-Triassic extinction is one of five major mass extinctions in the last 540 million years of Earth’s history. For several of these events, scientists have noted that large igneous provinces, which provide evidence of widespread volcanic activity, arose at about the same time. But, as Bowring points out, “Just because they happen to approximately coincide doesn’t mean there’s cause and effect.” For example, while massive lava flows overlapped with the extinction that wiped out the dinosaurs, scientists have linked that extinction to an asteroid collision.

“If you really want to make the case that an eruption caused an extinction, you have to be able to show at the highest possible precision that the eruption of the basalt and the extinction occurred at exactly the same time,” Bowring says.

In the case of the end-Triassic, Bowring says researchers have dated volcanic activity to right around the time fossils disappear from the geologic record, providing evidence that CAMP may have triggered the extinction. But these estimates have a margin of error of 1 million to 2 million years. “A million years is forever when you’re trying to make that link,” Bowring says.

For example, it’s thought that CAMP emitted a total of more than 2 million cubic kilometers of lava. If that amount of lava were spewed over a period of 1 million to 2 million years, it wouldn’t have nearly the impact it would if it were emitted over tens of thousands of years. “The timescale over which the eruption occurred has a big effect,” Bowring says.

Tilting toward extinction


To determine how long the volcanic eruptions lasted, the group combined two dating techniques: astrochronology and geochronology. The former is a technique that links sedimentary layers in rocks to changes in the tilt of the Earth: For decades, scientists have observed that the Earth’s orientation changes in regular cycles as a result of gravitational forces exerted by neighboring planets. For example, the Earth’s axis tilts at regular cycles, returning to its original tilt every 26,000 years. Such orbital variations change the amount of solar radiation reaching the Earth’s surface, which in turn has an effect on the planet’s climate, known as Milankovich cycles. The result of the climatic change can be preserved in the cyclicity of sediments deposited in the Earth’s crust.

Scientists can determine a rock’s age by first identifying cyclical variations in deposition of sediments in quiet bodies of water, such as deep oceans or large lakes. A cycle of sediment corresponds with a cycle of the Earth’s tilt, established as a known period of years. By seeing where a rock lies in those sedimentary layers, scientists can get a good idea of how old it is. To get precise estimates, scientists have developed mathematical models to determine the Earth’s tilt over millions of years.

Bowring says the technique is good for directly dating rocks up to 35 million years old, but beyond that, it’s unclear how reliable the technique can be. His team used astrochronology to estimate the age of the sedimentary rocks and then tested those estimates against high-precision dates from 200-million-year-old rocks in North America and Morocco.

The researchers broke rock samples apart to isolate tiny crystals known as zircons, which they then analyzed to determine the ratio of uranium to lead. The painstaking technique enabled the team to date the rocks to within approximately 30,000 years – an incredibly precise measurement in geologic terms.

Taken together, the geochronology and astrochronology techniques gave the team precise estimates for the onset of volcanism 200 million years ago, and revealed three bursts of magmatic activity over 40,000 years – an exceptionally short period of time during which massive amounts of carbon dioxide and other gas emissions may have drastically altered Earth’s climate, killing off thousands of plant and animal species.

While the team’s evidence is the strongest thus far to link volcanic activity with the end-Triassic extinction, Bowring says more work can be done.

“The CAMP province extends from Nova Scotia all the way down to Brazil and West Africa,” Bowring says. “I’m dying to know whether those are exactly the same age or not. We don’t know.”

Huge and widespread volcanic eruptions triggered the end-Triassic extinction

More than 200 million years ago, a massive extinction decimated 76 percent of marine and terrestrial species, marking the end of the Triassic period and the onset of the Jurassic. This devastating event cleared the way for dinosaurs to dominate Earth for the next 135 million years, taking over ecological niches formerly occupied by other marine and terrestrial species.

It’s not entirely clear what caused the end-Triassic extinction, although most scientists agree on a likely scenario: Over a relatively short period of time, massive volcanic eruptions from a large region known as the Central Atlantic Magmatic Province (CAMP) spewed forth huge amounts of lava and gas, including carbon dioxide, sulfur and methane. This sudden release of gases into the atmosphere may have created intense global warming and acidification of the oceans that ultimately killed off thousands of plant and animal species.

Now researchers at MIT, Columbia University and elsewhere have determined that these eruptions occurred precisely when the extinction began, providing strong evidence that volcanic activity did indeed trigger the end-Triassic extinction. Their results are published in the journal Science.

The team determined the age of basaltic lavas and other features found along the East Coast of the United States, as well as in Morocco – now-disparate regions that, 200 million years ago, were part of the supercontinent Pangaea. The rift that ultimately separated these landmasses was also the site of CAMP’s volcanic activity. Today, the geology of both regions includes igneous rocks from the CAMP eruptions as well as sedimentary rocks that accumulated in an enormous lake; the researchers used a combination of techniques to date the rocks and to pinpoint CAMP’s beginning and duration.

From its measurements, the team reconstructed the region’s volcanic activity 201 million years ago, discovering that the eruption of magma – along with carbon dioxide, sulfur and methane – occurred in repeated bursts over a period of 40,000 years, a relatively short span in geologic time.

“This extinction happened at a geological instant in time,” says Sam Bowring, the Robert R. Shrock Professor of Geology in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “There’s no question the extinction occurred at the same time as the first eruption.”

The paper’s co-authors are Terrence Blackburn (who led the project as part of his PhD research) and Noah McLean of MIT; Paul Olsen and Dennis Kent of Columbia; John Puffer of Rutgers University; Greg McHone, an independent researcher from New Brunswick; E. Troy Rasbury of Stony Brook University; and Mohammed Et-Touhami of the Université Mohammed Premier Oujda in Morocco.

More than a coincidence


The end-Triassic extinction is one of five major mass extinctions in the last 540 million years of Earth’s history. For several of these events, scientists have noted that large igneous provinces, which provide evidence of widespread volcanic activity, arose at about the same time. But, as Bowring points out, “Just because they happen to approximately coincide doesn’t mean there’s cause and effect.” For example, while massive lava flows overlapped with the extinction that wiped out the dinosaurs, scientists have linked that extinction to an asteroid collision.

“If you really want to make the case that an eruption caused an extinction, you have to be able to show at the highest possible precision that the eruption of the basalt and the extinction occurred at exactly the same time,” Bowring says.

In the case of the end-Triassic, Bowring says researchers have dated volcanic activity to right around the time fossils disappear from the geologic record, providing evidence that CAMP may have triggered the extinction. But these estimates have a margin of error of 1 million to 2 million years. “A million years is forever when you’re trying to make that link,” Bowring says.

For example, it’s thought that CAMP emitted a total of more than 2 million cubic kilometers of lava. If that amount of lava were spewed over a period of 1 million to 2 million years, it wouldn’t have nearly the impact it would if it were emitted over tens of thousands of years. “The timescale over which the eruption occurred has a big effect,” Bowring says.

Tilting toward extinction


To determine how long the volcanic eruptions lasted, the group combined two dating techniques: astrochronology and geochronology. The former is a technique that links sedimentary layers in rocks to changes in the tilt of the Earth: For decades, scientists have observed that the Earth’s orientation changes in regular cycles as a result of gravitational forces exerted by neighboring planets. For example, the Earth’s axis tilts at regular cycles, returning to its original tilt every 26,000 years. Such orbital variations change the amount of solar radiation reaching the Earth’s surface, which in turn has an effect on the planet’s climate, known as Milankovich cycles. The result of the climatic change can be preserved in the cyclicity of sediments deposited in the Earth’s crust.

Scientists can determine a rock’s age by first identifying cyclical variations in deposition of sediments in quiet bodies of water, such as deep oceans or large lakes. A cycle of sediment corresponds with a cycle of the Earth’s tilt, established as a known period of years. By seeing where a rock lies in those sedimentary layers, scientists can get a good idea of how old it is. To get precise estimates, scientists have developed mathematical models to determine the Earth’s tilt over millions of years.

Bowring says the technique is good for directly dating rocks up to 35 million years old, but beyond that, it’s unclear how reliable the technique can be. His team used astrochronology to estimate the age of the sedimentary rocks and then tested those estimates against high-precision dates from 200-million-year-old rocks in North America and Morocco.

The researchers broke rock samples apart to isolate tiny crystals known as zircons, which they then analyzed to determine the ratio of uranium to lead. The painstaking technique enabled the team to date the rocks to within approximately 30,000 years – an incredibly precise measurement in geologic terms.

Taken together, the geochronology and astrochronology techniques gave the team precise estimates for the onset of volcanism 200 million years ago, and revealed three bursts of magmatic activity over 40,000 years – an exceptionally short period of time during which massive amounts of carbon dioxide and other gas emissions may have drastically altered Earth’s climate, killing off thousands of plant and animal species.

While the team’s evidence is the strongest thus far to link volcanic activity with the end-Triassic extinction, Bowring says more work can be done.

“The CAMP province extends from Nova Scotia all the way down to Brazil and West Africa,” Bowring says. “I’m dying to know whether those are exactly the same age or not. We don’t know.”

A tiny grain helps reveal the history of a rock

'We can identify the rock from which the rutile originates, even if we only have a tiny grain of rutile,' says researcher Thomas Zack, University of Gothenburg. -  Photographer: Fred Kruijen
‘We can identify the rock from which the rutile originates, even if we only have a tiny grain of rutile,’ says researcher Thomas Zack, University of Gothenburg. – Photographer: Fred Kruijen

Rutile is used in ceramics and paints, but is particularly useful for finding out about the history of a rock.

Where mineral deposits are found, rutile is often also present. The new methods therefore bring opportunities for strategies to find other mineral deposits, such as gold.

Until now, rutile has been a relatively unknown mineral, despite not being rare. For example, rutile can be found on most sandy beaches around the world, including in Sweden.

“It’s incredible to see how little attention was paid to rutile until around five years ago,” says geologist and researcher Thomas Zack, from the University of Gothenburg’s Department of Earth Sciences, who has devoted much of his scientific career to studying the mineral.

Now, geologists can identify rock types containing rutile and follow the changes in temperature and pressure that they have been exposed to throughout its history, even if rutile is barely visible to the naked eye. Previously, researchers had to investigate considerably more rutile-bearing samples in order to carry out analyses.

“But now we can identify the rock from which the rutile originates, even if we only have a tiny grain of rutile,” adds Thomas.

The new method is called “Laser Ablation ICP-MS”, and produces results much faster than previous methods.

“In analytical terms, this is one of the most important analytical instruments at the Department of Earth Sciences here in Gothenburg,” concludes Thomas Zack.

A tiny grain helps reveal the history of a rock

'We can identify the rock from which the rutile originates, even if we only have a tiny grain of rutile,' says researcher Thomas Zack, University of Gothenburg. -  Photographer: Fred Kruijen
‘We can identify the rock from which the rutile originates, even if we only have a tiny grain of rutile,’ says researcher Thomas Zack, University of Gothenburg. – Photographer: Fred Kruijen

Rutile is used in ceramics and paints, but is particularly useful for finding out about the history of a rock.

Where mineral deposits are found, rutile is often also present. The new methods therefore bring opportunities for strategies to find other mineral deposits, such as gold.

Until now, rutile has been a relatively unknown mineral, despite not being rare. For example, rutile can be found on most sandy beaches around the world, including in Sweden.

“It’s incredible to see how little attention was paid to rutile until around five years ago,” says geologist and researcher Thomas Zack, from the University of Gothenburg’s Department of Earth Sciences, who has devoted much of his scientific career to studying the mineral.

Now, geologists can identify rock types containing rutile and follow the changes in temperature and pressure that they have been exposed to throughout its history, even if rutile is barely visible to the naked eye. Previously, researchers had to investigate considerably more rutile-bearing samples in order to carry out analyses.

“But now we can identify the rock from which the rutile originates, even if we only have a tiny grain of rutile,” adds Thomas.

The new method is called “Laser Ablation ICP-MS”, and produces results much faster than previous methods.

“In analytical terms, this is one of the most important analytical instruments at the Department of Earth Sciences here in Gothenburg,” concludes Thomas Zack.

Wastewater injection spurred biggest earthquake yet, says study

A 2011 magnitude 5.7 quake near Prague, Okla., apparently triggered by wastewater injection, buckled US Highway 62. -  (ohn Leeman
A 2011 magnitude 5.7 quake near Prague, Okla., apparently triggered by wastewater injection, buckled US Highway 62. – (ohn Leeman

A new study in the journal Geology is the latest to tie a string of unusual earthquakes, in this case, in central Oklahoma, to the injection of wastewater deep underground. Researchers now say that the magnitude 5.7 earthquake near Prague, Okla., on Nov. 6, 2011, may also be the largest ever linked to wastewater injection. Felt as far off as Milwaukee, more than 800 miles away, the quake-the biggest ever recorded in Oklahoma–destroyed 14 homes, buckled a federal highway and left two people injured. Small earthquakes continue to be recorded in the area. The study appeared today in the journal’s early online edition.

The recent boom in U.S. energy production has produced massive amounts of wastewater. The water is used both in hydrofracking, which cracks open rocks to release natural gas, and in coaxing petroleum out of conventional oil wells. In both cases, the brine and chemical-laced water has to be disposed of, often by injecting it back underground elsewhere, where it has the potential to trigger earthquakes. The water linked to the Prague quakes was a byproduct of oil extraction at one set of oil wells, and was pumped into another set of depleted oil wells targeted for waste storage.

Scientists have linked a rising number of quakes in normally calm parts of Arkansas, Texas, Ohio and Colorado to below-ground injection. In the last four years, the number of quakes in the middle of the United States jumped 11-fold from the three decades prior, the authors of the Geology study estimate. Last year, a group at the U.S. Geological Survey also attributed a remarkable rise in small- to mid-size quakes in the region to humans. The risk is serious enough that the National Academy of Sciences, in a report last year called for further research to “understand, limit and respond” to induced seismic events. Despite these studies, wastewater injection continues near the Oklahoma earthquakes.

The magnitude 5.7 quake near Prague was preceded by a 5.0 shock and followed by thousands of aftershocks. What made the swarm unusual is that wastewater had been pumped into abandoned oil wells nearby for 17 years without incident. In the study, researchers hypothesize that as wastewater replenished compartments once filled with oil, the pressure to keep the fluid going down had to be ratcheted up. As pressure built up, a known fault-known to geologists as the Wilzetta fault–jumped. “When you overpressure the fault, you reduce the stress that’s pinning the fault into place and that’s when earthquakes happen,” said study coauthor Heather Savage, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory.

The amount of wastewater injected into the well was relatively small, yet it triggered a cascading series of tremors that led to the main shock, said study co-author Geoffrey Abers, also a seismologist at Lamont-Doherty. “There’s something important about getting unexpectedly large earthquakes out of small systems that we have discovered here,” he said. The observations mean that “the risk of humans inducing large earthquakes from even small injection activities is probably higher” than previously thought, he said.

Hours after the first magnitude 5.0 quake on Nov. 5, 2011, University of Oklahoma seismologist Katie Keranen rushed to install the first three of several dozen seismographs to record aftershocks. That night, on Nov. 6, the magnitude 5.7 main shock hit and Keranen watched as her house began to shake for what she said felt like 20 seconds. “It was clearly a significant event,” said Keranen, the Geology study’s lead author. “I gathered more equipment, more students, and headed to the field the next morning to deploy more stations.”

Keranen’s recordings of the magnitude 5.7 quake, and the aftershocks that followed, showed that the first Wilzetta fault rupture was no more than 650 feet from active injection wells and perhaps much closer, in the same sedimentary rocks, the study says. Further, wellhead records showed that after 13 years of pumping at zero to low pressure, injection pressure rose more than 10-fold from 2001 to 2006, the study says.

The Oklahoma Geological Survey has yet to issue an official account of the sequence, and wastewater injection at the site continues. In a statement responding to the paper, Survey seismologist Austin Holland said the study showed the earthquake sequence could have been triggered by the injections. But, he said, “it is still the opinion of those at the Oklahoma Geological Survey that these earthquakes could be naturally occurring. There remain many open questions, and more scientific investigations are underway on this sequence of earthquakes and many others within the state of Oklahoma.”

The risk of setting off earthquakes by injecting fluid underground has been known since at least the 1960s, when injection at the Rocky Mountain Arsenal near Denver was suspended after a quake estimated at magnitude 4.8 or greater struck nearby-the largest tied to wastewater disposal until the one near Prague, Okla. A series of similar incidents have emerged recently. University of Memphis seismologist Stephen Horton in a study last year linked a rise in earthquakes in north-central Arkansas to nearby injection wells. University of Texas, Austin, seismologist Cliff Frohlich in a 2011 study tied earthquake swarms at the Dallas-Fort Worth Airport to a brine disposal well a third of a mile away. In Ohio, Lamont-Doherty seismologists Won-Young Kim and John Armbruster traced a series of 2011 earthquakes near Youngstown to a nearby disposal well. That well has since been shut down, and Ohio has tightened its waste-injection rules.

Wastewater injection is not the only way that people can touch off quakes. Evidence suggests that geothermal drilling, impoundment of water behind dams, enhanced oil recovery, solution salt mining and rock quarrying also can trigger seismic events. (Hydrofracking itself is not implicated in significant earthquakes; the amount of water used is usually not enough to produce substantial shaking.) The largest known earthquakes attributed to humans may be the two magnitude 7.0 events that shook the Gazli gas fields of Soviet Uzbekistan in 1976, followed by a third magnitude 7.0 quake eight years later. In a 1985 study in the Bulletin of the Seismological Society of America, Lamont-Doherty researchers David Simpson and William Leith hypothesized that the quakes were human-induced but noted that a lack of information prevented them from linking the events to gas production or other triggers. In 2009, a geothermal energy project in Basel, Switzerland, was canceled after development activities apparently led to a series of quakes of up to magnitude 3.4 that caused some $8 million in damage to surrounding properties.

In many of the wastewater injection cases documented so far, earthquakes followed within days or months of fluid injection starting. In contrast, the Oklahoma swarm happened years after injection began, similar to swarms at the Cogdell oil field in West Texas and the Fort St. John area of British Columbia.

The Wilzetta fault system remains under stress, the study’s authors say, yet regulators continue to allow injection into nearby wells. Ideally, injection should be kept away from known faults and companies should be required to provide detailed records of how much fluid they are pumping underground and at what pressure, said Keranen. The study authors also recommend sub-surface monitoring of fluid pressure for earthquake warning signs. Further research is needed but at a minimum, “there should be careful monitoring in regions where you have injection wells and protocols for stopping pumping even when small earthquakes are detected,” said Abers. In a recent op-ed in the Albany (N.Y.) Times Union, Abers argued that New York should consider the risk of induced earthquakes from fluid injection in weighing whether to allow hydraulic fracturing to extract the state’s shale gas reserves.

Wastewater injection spurred biggest earthquake yet, says study

A 2011 magnitude 5.7 quake near Prague, Okla., apparently triggered by wastewater injection, buckled US Highway 62. -  (ohn Leeman
A 2011 magnitude 5.7 quake near Prague, Okla., apparently triggered by wastewater injection, buckled US Highway 62. – (ohn Leeman

A new study in the journal Geology is the latest to tie a string of unusual earthquakes, in this case, in central Oklahoma, to the injection of wastewater deep underground. Researchers now say that the magnitude 5.7 earthquake near Prague, Okla., on Nov. 6, 2011, may also be the largest ever linked to wastewater injection. Felt as far off as Milwaukee, more than 800 miles away, the quake-the biggest ever recorded in Oklahoma–destroyed 14 homes, buckled a federal highway and left two people injured. Small earthquakes continue to be recorded in the area. The study appeared today in the journal’s early online edition.

The recent boom in U.S. energy production has produced massive amounts of wastewater. The water is used both in hydrofracking, which cracks open rocks to release natural gas, and in coaxing petroleum out of conventional oil wells. In both cases, the brine and chemical-laced water has to be disposed of, often by injecting it back underground elsewhere, where it has the potential to trigger earthquakes. The water linked to the Prague quakes was a byproduct of oil extraction at one set of oil wells, and was pumped into another set of depleted oil wells targeted for waste storage.

Scientists have linked a rising number of quakes in normally calm parts of Arkansas, Texas, Ohio and Colorado to below-ground injection. In the last four years, the number of quakes in the middle of the United States jumped 11-fold from the three decades prior, the authors of the Geology study estimate. Last year, a group at the U.S. Geological Survey also attributed a remarkable rise in small- to mid-size quakes in the region to humans. The risk is serious enough that the National Academy of Sciences, in a report last year called for further research to “understand, limit and respond” to induced seismic events. Despite these studies, wastewater injection continues near the Oklahoma earthquakes.

The magnitude 5.7 quake near Prague was preceded by a 5.0 shock and followed by thousands of aftershocks. What made the swarm unusual is that wastewater had been pumped into abandoned oil wells nearby for 17 years without incident. In the study, researchers hypothesize that as wastewater replenished compartments once filled with oil, the pressure to keep the fluid going down had to be ratcheted up. As pressure built up, a known fault-known to geologists as the Wilzetta fault–jumped. “When you overpressure the fault, you reduce the stress that’s pinning the fault into place and that’s when earthquakes happen,” said study coauthor Heather Savage, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory.

The amount of wastewater injected into the well was relatively small, yet it triggered a cascading series of tremors that led to the main shock, said study co-author Geoffrey Abers, also a seismologist at Lamont-Doherty. “There’s something important about getting unexpectedly large earthquakes out of small systems that we have discovered here,” he said. The observations mean that “the risk of humans inducing large earthquakes from even small injection activities is probably higher” than previously thought, he said.

Hours after the first magnitude 5.0 quake on Nov. 5, 2011, University of Oklahoma seismologist Katie Keranen rushed to install the first three of several dozen seismographs to record aftershocks. That night, on Nov. 6, the magnitude 5.7 main shock hit and Keranen watched as her house began to shake for what she said felt like 20 seconds. “It was clearly a significant event,” said Keranen, the Geology study’s lead author. “I gathered more equipment, more students, and headed to the field the next morning to deploy more stations.”

Keranen’s recordings of the magnitude 5.7 quake, and the aftershocks that followed, showed that the first Wilzetta fault rupture was no more than 650 feet from active injection wells and perhaps much closer, in the same sedimentary rocks, the study says. Further, wellhead records showed that after 13 years of pumping at zero to low pressure, injection pressure rose more than 10-fold from 2001 to 2006, the study says.

The Oklahoma Geological Survey has yet to issue an official account of the sequence, and wastewater injection at the site continues. In a statement responding to the paper, Survey seismologist Austin Holland said the study showed the earthquake sequence could have been triggered by the injections. But, he said, “it is still the opinion of those at the Oklahoma Geological Survey that these earthquakes could be naturally occurring. There remain many open questions, and more scientific investigations are underway on this sequence of earthquakes and many others within the state of Oklahoma.”

The risk of setting off earthquakes by injecting fluid underground has been known since at least the 1960s, when injection at the Rocky Mountain Arsenal near Denver was suspended after a quake estimated at magnitude 4.8 or greater struck nearby-the largest tied to wastewater disposal until the one near Prague, Okla. A series of similar incidents have emerged recently. University of Memphis seismologist Stephen Horton in a study last year linked a rise in earthquakes in north-central Arkansas to nearby injection wells. University of Texas, Austin, seismologist Cliff Frohlich in a 2011 study tied earthquake swarms at the Dallas-Fort Worth Airport to a brine disposal well a third of a mile away. In Ohio, Lamont-Doherty seismologists Won-Young Kim and John Armbruster traced a series of 2011 earthquakes near Youngstown to a nearby disposal well. That well has since been shut down, and Ohio has tightened its waste-injection rules.

Wastewater injection is not the only way that people can touch off quakes. Evidence suggests that geothermal drilling, impoundment of water behind dams, enhanced oil recovery, solution salt mining and rock quarrying also can trigger seismic events. (Hydrofracking itself is not implicated in significant earthquakes; the amount of water used is usually not enough to produce substantial shaking.) The largest known earthquakes attributed to humans may be the two magnitude 7.0 events that shook the Gazli gas fields of Soviet Uzbekistan in 1976, followed by a third magnitude 7.0 quake eight years later. In a 1985 study in the Bulletin of the Seismological Society of America, Lamont-Doherty researchers David Simpson and William Leith hypothesized that the quakes were human-induced but noted that a lack of information prevented them from linking the events to gas production or other triggers. In 2009, a geothermal energy project in Basel, Switzerland, was canceled after development activities apparently led to a series of quakes of up to magnitude 3.4 that caused some $8 million in damage to surrounding properties.

In many of the wastewater injection cases documented so far, earthquakes followed within days or months of fluid injection starting. In contrast, the Oklahoma swarm happened years after injection began, similar to swarms at the Cogdell oil field in West Texas and the Fort St. John area of British Columbia.

The Wilzetta fault system remains under stress, the study’s authors say, yet regulators continue to allow injection into nearby wells. Ideally, injection should be kept away from known faults and companies should be required to provide detailed records of how much fluid they are pumping underground and at what pressure, said Keranen. The study authors also recommend sub-surface monitoring of fluid pressure for earthquake warning signs. Further research is needed but at a minimum, “there should be careful monitoring in regions where you have injection wells and protocols for stopping pumping even when small earthquakes are detected,” said Abers. In a recent op-ed in the Albany (N.Y.) Times Union, Abers argued that New York should consider the risk of induced earthquakes from fluid injection in weighing whether to allow hydraulic fracturing to extract the state’s shale gas reserves.

How can basin rocks recorded formation of Dabie orogen?

This is a simplified map showing the spatial distribution of the representative end member or eclogite gravels, high-Si phengites, and Triassic zircons that were exhumated in the source area. This map was organized according to provenance analysis results of stratigraphic sections in the Hefei basin, which demonstrate the depth of exhumation increasing from west to east, the unroofing ages of the UHP and HP metamorphic rocks changing from Early Jurassic to Late Jurassic westward, and eastward increasing exhumation rate in the Dabie orogen during the Jurassic. -  ©Science China Press
This is a simplified map showing the spatial distribution of the representative end member or eclogite gravels, high-Si phengites, and Triassic zircons that were exhumated in the source area. This map was organized according to provenance analysis results of stratigraphic sections in the Hefei basin, which demonstrate the depth of exhumation increasing from west to east, the unroofing ages of the UHP and HP metamorphic rocks changing from Early Jurassic to Late Jurassic westward, and eastward increasing exhumation rate in the Dabie orogen during the Jurassic. – ©Science China Press

Deep subduction of continental crust and rapid exhumation of ultrahigh-pressure metamorphic rocks, and its mechanism have been one of the most important issues of the world’s attention in the Dabie orogen. Professor LIU Shaofeng from State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing) and his co-author set out to tackle this problem. Their study results fully demonstrated that basin sediments recorded Dabie formation process and supplied important trails for Dabie uplifting and exhumation. Their work, entitled “Mesozoic basin development and its indication of collisional orogeny in the Dabie orogen”, was published in CHINESE SCIENCE BULLETIN. 2013, 58.

Dabie orogen was formed by collision between the South China and North China plates. During and after collision periods, sedimentary basins were developed beside and within the mountains, in which the sediments sourced from Dabie were filled. These sedimentary strata, like “historical book”, recorded the geological processes of subduction of the South China plate under the North China plate and then rapid uplift and unroofing of the subducted South China plate. Therefore, it is effective to probe into Dabie Mountains formation based on basin sedimentary stratigraphic analysis.

These newly studies have shown a fundamental progress. The Dabie orogen records gradual transition from overall shortening and thrusting to dominantly extension and rift basin formation expanded from its core to its margins, although these shortening and extension overlapped in time from the Jurassic through Early Cretaceous at crustal levels. The unroofing ages of the ultra-high pressure metamorphic rocks subducted into hundreds kilometers deep in the Dabie orogen change from Early Jurassic to Late Jurassic westward. The depth of exhumation increases eastwards (Fig. 1). The sediment sources for the basin in the north are mostly composed of the deeply exhumed, axial Dabie metamorphic complex, and the sediment sources for the basin in the south are mostly from cover strata in the southern orogen and related strata with subjacent (i.e. subsequently overthrusted) plate suture belt.

Geodynamic analysis represents that continental collision between the North China Block and the South China Block along the plate sutures, subsequently northwestward progradation of the Jiangnan fold and thrust belt, and the underthrusting of the North China Block along the Northern Boundary Fault of Qinling Range led to crustal thickening, gravitational spreading and balanced rebound of the resultant thick crustal welt, and multi-episodic exhumation of the HP/UHP metamorphic rocks.

This work will be a valued reference of probing into how sedimentary basins record tectonic evolution of the orogenic belt which underwent deep continental subduction, rapid exhumation, and the huge amount of erosion. Furthermore, it will be significant to reveal the evolution of basin/mountain system and geodynamics.

How can basin rocks recorded formation of Dabie orogen?

This is a simplified map showing the spatial distribution of the representative end member or eclogite gravels, high-Si phengites, and Triassic zircons that were exhumated in the source area. This map was organized according to provenance analysis results of stratigraphic sections in the Hefei basin, which demonstrate the depth of exhumation increasing from west to east, the unroofing ages of the UHP and HP metamorphic rocks changing from Early Jurassic to Late Jurassic westward, and eastward increasing exhumation rate in the Dabie orogen during the Jurassic. -  ©Science China Press
This is a simplified map showing the spatial distribution of the representative end member or eclogite gravels, high-Si phengites, and Triassic zircons that were exhumated in the source area. This map was organized according to provenance analysis results of stratigraphic sections in the Hefei basin, which demonstrate the depth of exhumation increasing from west to east, the unroofing ages of the UHP and HP metamorphic rocks changing from Early Jurassic to Late Jurassic westward, and eastward increasing exhumation rate in the Dabie orogen during the Jurassic. – ©Science China Press

Deep subduction of continental crust and rapid exhumation of ultrahigh-pressure metamorphic rocks, and its mechanism have been one of the most important issues of the world’s attention in the Dabie orogen. Professor LIU Shaofeng from State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing) and his co-author set out to tackle this problem. Their study results fully demonstrated that basin sediments recorded Dabie formation process and supplied important trails for Dabie uplifting and exhumation. Their work, entitled “Mesozoic basin development and its indication of collisional orogeny in the Dabie orogen”, was published in CHINESE SCIENCE BULLETIN. 2013, 58.

Dabie orogen was formed by collision between the South China and North China plates. During and after collision periods, sedimentary basins were developed beside and within the mountains, in which the sediments sourced from Dabie were filled. These sedimentary strata, like “historical book”, recorded the geological processes of subduction of the South China plate under the North China plate and then rapid uplift and unroofing of the subducted South China plate. Therefore, it is effective to probe into Dabie Mountains formation based on basin sedimentary stratigraphic analysis.

These newly studies have shown a fundamental progress. The Dabie orogen records gradual transition from overall shortening and thrusting to dominantly extension and rift basin formation expanded from its core to its margins, although these shortening and extension overlapped in time from the Jurassic through Early Cretaceous at crustal levels. The unroofing ages of the ultra-high pressure metamorphic rocks subducted into hundreds kilometers deep in the Dabie orogen change from Early Jurassic to Late Jurassic westward. The depth of exhumation increases eastwards (Fig. 1). The sediment sources for the basin in the north are mostly composed of the deeply exhumed, axial Dabie metamorphic complex, and the sediment sources for the basin in the south are mostly from cover strata in the southern orogen and related strata with subjacent (i.e. subsequently overthrusted) plate suture belt.

Geodynamic analysis represents that continental collision between the North China Block and the South China Block along the plate sutures, subsequently northwestward progradation of the Jiangnan fold and thrust belt, and the underthrusting of the North China Block along the Northern Boundary Fault of Qinling Range led to crustal thickening, gravitational spreading and balanced rebound of the resultant thick crustal welt, and multi-episodic exhumation of the HP/UHP metamorphic rocks.

This work will be a valued reference of probing into how sedimentary basins record tectonic evolution of the orogenic belt which underwent deep continental subduction, rapid exhumation, and the huge amount of erosion. Furthermore, it will be significant to reveal the evolution of basin/mountain system and geodynamics.