In Carl Sagan’s 1985 sci-fi novel Contact, a radio astronomer battles naysayers and funding setbacks to persist in her audacious plan — scanning the skies for signals from aliens. Sagan had real-life inspiration for his book (and the 1997 movie of the same name): astronomer Jill Tarter, who spearheaded the search for extraterrestrial intelligence, or SETI, for decades.

In Sagan’s story, the protagonist, Ellie Arroway, detects mysterious chatter from the cosmos. Tarter had no such luck. But her story, told by journalist Sarah Scoles in Making Contact, still provides insights into what it means to be human in a vast universe potentially harboring other life.
Tarter began her career as a typical radio astronomer, studying mainstream topics like stars and galaxies as a Ph.D. student. But after graduating in 1975, she began to focus on SETI, poring over data from radio telescopes, searching for unnatural blips that could be a sign of an intelligent civilization. SETI researchers typically focus on radio waves because those long wavelengths can travel through our galaxy’s dust without being absorbed.
Writings about SETI are prone to dreamy romanticism, but Making Contact admirably steers clear of excessive sentimentality. As a child gaping at the stars, Tarter wondered if creatures in the heavens were looking in our direction. Of course, Scoles notes, plenty of kids have wondered the same thing. Though Tarter’s childhood musings might seem special in retrospect, they aren’t what make her stand out.

Instead, Scoles — who has clear affection for her subject — highlights Tarter’s tenacity. In the face of numerous obstacles, Tarter pushed the field forward, seemingly by force of will.

In a detailed portrait of how the science sausage gets made, the book follows Tarter as she faced numerous funding woes. The field of SETI, which has at various points in its history received money through NASA, is an easy target for funding cuts, with some politicians deriding it as a wasteful hunt for “little green men.” Tarter, like the fictional Arroway, fought with Congress for taxpayer dollars SETI received, then scrambled for cash from other sources to keep telescopes and other equipment in operation. Wealthy donors kept SETI afloat — and still do. To maximize their ability to accept funding, Tarter and other SETI pioneers founded the nonprofit SETI Institute, in Mountain View, Calif., in 1984.
Throughout, Tarter somehow managed to maintain her passion for a long shot search.

Although it’s a compelling story, the book stumbles in a few places, mainly minor sloppiness with physics facts, which may bother the most astute readers. (Scoles writes, for example, “Light is the only way we can learn about the universe,” neglecting gravitational waves and neutrinos, both of which have revealed secrets of cosmic objects.)

Now retired, Tarter has lost her chance to follow in Arroway’s fictional footsteps — she will never find any alien communiqués. But even if astronomers never hear from E.T., Tarter sees benefits in the search: SETI is an opportunity to make humankind less selfish. Just the thought that other creatures might inhabit the universe can make human squabbles seem less significant.

Nearly 1 in 5 adolescents has suffered at least one concussion, according to a survey of U.S. teens. And 5.5 percent reported two or more concussions diagnosed in their lifetimes, researchers report in the Sept. 26 JAMA.

About 13,000 eighth-, 10th- and 12th-graders participated in the 2016 Monitoring the Future survey, an annual national questionnaire of adolescent behavior and health given in schools. Among other questions, teens were asked whether they had ever had a head injury that was diagnosed as a concussion — 19.5 percent replied “yes.” Those teens were more likely than others to play competitive sports and be male, white and in a higher grade.

Previous studies have found that kids taking part in contact sports are at higher risk of suffering a concussion. These new data on actual prevalence of concussions, though self-reported, are important, say the authors, for crafting prevention efforts that protect teens from injuries.

Gene-editing tools heralded as hope for fighting invader rats, malarial mosquitoes and other scourges may be too powerful to use in their current form, two new papers warn.

Standard forms of CRISPR gene drives, as the tools are called, can make tweaked DNA race through a population so easily that a small number of stray animals or plants could spread it to new territory, predicts a computer simulation released November 16 at bioRxiv.org. Such an event would have unknown, potentially damaging, ramifications, says a PLOS Biology paper released the same day.
“We need to get out of the ivory tower and have this discussion in the open, because ecological engineering will affect everyone living in the area,” says Kevin Esvelt of MIT, a coauthor of both papers who studies genetic solutions to ecological problems. What’s a pest in one place may be valued in another, so getting consent to use a gene drive could mean consulting people across a species’s whole range, be it several nations or continents.

Researchers have constructed this kind of drive in yeast, a fruit fly and several mosquitoes, but none of the tools have been deployed yet in the wild (SN: 12/12/15, p. 16). Meanwhile, some researchers are already working to add brakes or off-switches into a new generation of gene drives.

The major concern is that current gene drives “are probably too powerful for us to seriously consider deploying in conservation,” says geneticist Neil Gemmell of the University of Otago in Dunedin, New Zealand. Gemmell is a coauthor of the PLOS Biology paper.
This opinion could prove especially controversial in New Zealand. In 2016, the government resolved to protect the nation’s imperiled biodiversity by exterminating invader rats, stoats and possums that are wreaking havoc on native species. Gene drives just might make that possible.

Though warning of perils, the researchers also propose some solutions. A weaker system, which Esvelt calls a daisy drive, splits up components of the drive called guide RNAs. These guide RNAs direct the gene-editing machinery to its DNA target, where molecular scissors then snip and swap genetic material. As genes get inherited or not in the chancy jumbling of sexual reproduction, descendants in later generations become less likely to inherit all the spaced-apart pieces needed to operate the gene drive.

Esvelt’s lab is working to create a daisy drive in two kinds of nematode worms and is looking at other species as well. Other labs are now working on tamer gene drives, too.

Anthony A. James of the University of California, Irvine says that the disease-carrying Anopheles mosquito species that he and his colleagues have equipped with gene drives are self-limiting. When females end up with two of the genes he’s inserting, they don’t “survive very well after they have fed on blood.” Researchers are now raising these mosquitoes to see whether the genes spread and then dwindle away. “We don’t need our genes to last forever,” James says, “only long enough to contribute to getting rid of malaria.”

Another lab’s current version of disease-fighter mosquitoes already has a touch of the daisy. Aedes aegypti mosquitoes engineered with some built-in parts of the gene editor have their guide RNA split into two parts and put on different chromosomes, says molecular biologist Omar Akbari of the University of California, San Diego. Pictures of many weird mosquitoes created this way — all yellow or with three eyes or forked wings — attest to the fact that the drive system works. Akbari’s research appears November 14 in the Proceedings of the National Academy of Sciences.

Akbari is not very worried about the risk of accidentally wiping out disease-carrying mosquitoes. “A thousand children die every day,” he says. It would be unethical not to use a tool that could lessen the loss, he says.

He does recognize that the case for caution could be different for other species. “A lot of pet owners would be sad,” he says, if a gene drive went wrong and escaped worldwide during some future attempt to rid, say, Australia of its terribly destructive feral cats.

Hard-boiled eggs are a dish best served cold.

When quickly reheated in a microwave and then pierced, the picnic staple can explode with a loud bang in a shower of hot, rubbery shrapnel. But this blast is far more likely to make a hot mess than hurt your hearing, according to research presented December 6 at the Acoustical Society of America meeting in New Orleans.

That distinction isn’t as odd as it might sound. In a lawsuit, a man claimed to have suffered burns and hearing damage after a microwaved, hard-boiled egg exploded in his mouth at a restaurant. Researchers from Charles M. Salter Associates, Inc. in San Francisco called as expert witnesses couldn’t find scientific papers backing up the claim that an egg could burst with enough vigor to cause hearing loss — just a lot of YouTube videos documenting eggsplosions.
So the researchers microwaved peeled hard-boiled eggs in water on high power for three minutes.

The eggs were “uncooperative,” study coauthor Anthony Nash said in a news conference. Some exploded in the microwave, while others wouldn’t explode at all. But of nearly 100 eggs tested, 28 exploded outside of the microwave after being poked with a meat thermometer. From 30 centimeters away, the sound pressure from those explosions ranged from 86 to 133 decibels.

The median sound pressure level recorded, 108 decibels, is about the same as that at an average rock concert. Continuous exposure to that noise level could damage hair cells inside ears that respond to sound. The National Institute for Occupational Safety and Health sets recommended exposure limits for sound pressures above 85 decibels, says William Murphy, a researcher at NIOSH who wasn’t part of the study. But those limits are based on daily exposure over years, he says.
A burst egg’s boom, on the other hand, lasts just milliseconds — not long enough to do much harm. “The likelihood for hearing damage from a single exploding egg was very low,” Nash said.

The lawsuit was settled out of court before Nash and his colleagues conducted the second phase of the study – considering how sound hits your ears when it’s coming from inside your mouth. An in-mouth explosion might send slightly more sound pressure to the ears, Nash says, but still probably not enough to cause lasting damage as a one-time accident.

A peeled egg probably explodes when pockets of water trapped in the yolk become superheated — hotter than the boiling temperature of water without actually bubbling, Nash suggested. When disrupted, say by a fork or a tooth, the water pockets spontaneously boil, bursting through the squishy egg white and sending bits flying. (It’s the same phenomenon that can occasionally make microwaved coffee spurt out of the mug onto your clean work clothes.)

A bigger risk than the noise might be the heat. Nash and his colleagues measured the temperature of yolks in eggs that didn’t burst. Those temperatures were, on average, 12 degrees Celsius above the surrounding water bath, which was often close to boiling.

This year, gene therapy finally became a clinical reality. The U.S. Food and Drug Administration approved two personalized treatments that engineer a patient’s own immune system to hunt down and kill cancer cells. The treatments, the first gene therapies ever approved by the FDA, work in people with certain blood cancers, even patients whose cancers haven’t responded to other treatments.

Called CAR-T cell immunotherapy (for chimeric antigen receptor T cell), one is for kids and young adults with B cell acute lymphoblastic leukemia, or ALL, approved in August (SN Online: 8/30/17). The other is for adults with non-Hodgkin lymphoma, approved in October. Other CAR-T cell therapies are in testing, including a treatment for multiple myeloma.
“It’s a completely different way of treating cancer,” says pediatric oncologist Stephan Grupp, who directs the Cancer Immunotherapy Program at the Children’s Hospital of Philadelphia. Grupp spearheaded the clinical trials of the newly approved ALL therapy, called Kymriah.

Researchers are developing many different versions of CAR-T cell therapies, but the basic premise is the same: Doctors remove a patient’s T cells (immune system cells that attack invaders) from a blood sample and genetically modify them to produce artificial proteins on their surfaces. Those proteins, called chimeric antigen receptors, recognize the cancer cells in the patient’s body. After the modified T cells make many copies of themselves in the lab, they’re unleashed in the patient’s bloodstream to find and kill cancer cells.
CAR-T cell therapy is particularly exciting because it works well in people whose cancers haven’t responded to other available treatments, says Renier Brentjens, an oncologist at Memorial Sloan Kettering Cancer Center in New York City. Of the 63 kids and young adults treated in a clinical trial of Kymriah, 83 percent had their cancers go into remission within three months.
Now that these therapies have been clinically approved, there’s been an “explosion of interest” in the approach, says Dario Campano, an immunopathologist at the National University Cancer Institute in Singapore. Going forward, he expects to see even more rapid progress in the technology. Fifteen years ago, Campana helped develop the chimeric antigen receptor that’s used in Kymriah today. For now, the treatments are approved for use only when other treatments have failed, but someday CAR-T cell therapy could be the first treatment doctors try, he says.

One drawback is the price. Kymriah costs $475,000 for a onetime treatment, according to Novartis, which makes Kymriah. The non-Hodgkin lymphoma treatment made by Gilead Sciences, called Yescarta, is listed at $373,000. The total price tag for treatment could be higher when the costs of dealing with side effects and complications are factored in.

The approach is approved only for blood cancers. Using CAR-T cell therapy on solid tumors will require finding ways to get the T cells past additional cellular roadblocks, Grupp says.

Have you fallen behind on your reading this year? Or maybe you’ve plowed through your must-reads and are ready for more. Science News has got you covered. Here are the staff’s picks for some of the best science books of 2017. Find detailed reviews from previous issues in the links below or in our Editors pick: Favorite books of 2017.

Against the Grain
James C. Scott

Armed with the latest archaeological research, a political anthropologist argues that the rise of civilization came at a big cost. The initial switch from hunting and gathering to agricultural states brought poor diets, labor-intensive work, outbreaks of infectious diseases and other hardships (SN: 10/14/17, p. 28). Yale Univ., $26

The Great Quake
Henry Fountain

Historical records and interviews with survivors flesh out this tale of how a massive earthquake in Alaska in 1964 provided geologists with key evidence needed to verify the theory of plate tectonics (SN: 9/16/17, p. 32). Crown, $28

Eclipse
Frank Close

More than just a primer on the science of solar eclipses, this memoir chronicles a physicist’s lifetime fascination with the celestial phenomenon and introduces readers to the quirky world of eclipse chasers (SN: 5/13/17, p. 28). Oxford Univ., $21.95

Rise of the Necrofauna
Britt Wray

Resurrecting woolly mammoths, passenger pigeons and other extinct creatures isn’t just a technological problem, as this book explains. “De-extinction” is also rife with ethical dilemmas (SN: 10/28/17, p. 28). Greystone Books, $26.95

Big Chicken
Maryn McKenna

Antibiotics transformed chicken farming, to the detriment of the birds and of human health, a journalist contends. Widespread use of the drugs fueled the industrialization of poultry production and the rise of antibiotic-resistant bacteria (SN: 9/30/17, p. 30). National Geographic, $27

Inferior
Angela Saini

A science writer makes a persuasive case that centuries of biased thinking and flawed scientific research have reinforced sexist stereotypes about women (SN: 9/2/17, p. 27). Beacon Press, $25.95

Caesar’s Last Breath
Sam Kean

Through fun historical anecdotes and lesser-known backstories of scientific greats, this entertaining book profiles the chemical elements that make up the air we breathe and traces the history of Earth’s atmosphere (SN: 7/8/17 & 7/22/17, p. 38). Little, Brown and Co., $28

Cannibalism
Bill Schutt

The grisly practice of eating your own kind turns out to be widespread in the animal kingdom, a zoologist explains in this captivating look at cannibalism (SN: 2/18/17, p. 29). Algonquin Books, $26.95

The Lost City of the Monkey God
Douglas Preston

A journalist tags along on an archaeological expedition to search for the real-life remains of a mythological city in this rainforest adventure tale that morphs into a medical mystery (SN: 2/4/17, p. 28). Grand Central Publishing, $28

The Death and Life of the Great Lakes
Dan Egan

Invasive species, urbanization and other threats have wreaked havoc on the Great Lakes, but this book still finds some glimmers of hope in the scientists who are making headway in resuscitating the ecosystem (SN: 3/18/17, p. 30). W.W. Norton & Co., $27.95

How to Tame a Fox
Lee Alan Dugatkin and Lyudmila Trut

An experiment to replay animal domestication by selectively breeding wild silver foxes is lovingly retold, including by the researcher who has kept the project alive for nearly 60 years (SN: 5/13/17, p. 29). Univ. of Chicago, $26

Making Contact
Sarah Scoles

In the face of numerous obstacles, Jill Tarter still managed to spearhead the search for extraterrestrial intelligence for decades, as this biography recounts (SN: 8/5/17, p. 26). Pegasus Books, $27.95

A Crack in Creation
Jennifer A. Doudna and Samuel H. Sternberg

Two experts, including one of the pioneers of CRISPR/Cas9, discuss the science and ethics of gene editing. Houghton Mifflin Harcourt, $28

These book reviews contain links to Amazon.com. Science News is a participant in the Amazon Services LLC Associates Program. Please see our FAQ for more details.

Life expectancy in the United States has decreased for the second year in a row, the first back-to-back drops in more than 50 years, the U.S. Centers for Disease Control and Prevention reports.

In 2016, life expectancy at birth was 78.6 years for the U.S. population as a whole. That’s 0.1 year less than in 2015. For men, life expectancy decreased from 76.3 years in 2015 to 76.1 years in 2016, while in women it remained the same, at 81.1 years. The new data, from CDC’s National Center for Health Statistics, are published online December 21.
Heart disease was the leading cause of death for 2016, followed by cancer, unintentional injuries such as drug overdoses and car crashes, chronic lower respiratory diseases including asthma, and stroke. Rounding out the top 10 causes of death were Alzheimer’s disease, diabetes, influenza and pneumonia, kidney disease and suicide.

The overall drop in life expectancy is largely a result of an uptick in the age-adjusted death rates for unintentional injuries, Alzheimer’s disease and suicide, the report’s authors say.

The driving force behind Yellowstone’s long and explosive volcanic history may not be as deep as once thought. A new study suggests that instead of a plume of hot mantle that extends down to Earth’s core, the real culprit is a subducting tectonic plate that began sinking beneath North America hundreds of millions of years ago.

Computer simulations show that movement of broken-up remnants of the ancient Farallon Plate could be stirring the mantle in a way that fuels Yellowstone, researchers report December 18 in Nature Geoscience. “The fit is so good,” says study coauthor Lijun Liu, a geodynamicist at the University of Illinois at Urbana-Champaign.
The giant supervolcano now beneath Yellowstone National Park, located mostly in Wyoming, has a 17-million-year history — much of it on the move. In that time, the locus of volcanism has moved northeastward from southwestern Idaho to its current location, where it most recently explosively erupted about 640,000 years ago. These shifting eruptions have created a track of volcanic craters resembling those created by the hot spot that formed the Hawaiian island chain. As a result, scientists have long suspected that a deep plume of magma originating from the core-mantle boundary, similar to the one that fuels Hawaii’s volcanoes, is the source of Yellowstone’s fury.

But the nature of the Yellowstone plume has been the subject of debate. “Usually with plumes, we can trace them to the core-mantle boundary,” says Robert Porritt, a seismologist at the University of Texas at Austin, who was not involved in the new work. To “see” Earth’s structure, seismologists use a technique called seismic tomography, which maps the interior using seismic waves generated by earthquakes. Particularly hot or liquid parts of the mantle slow some seismic waves known as shear waves. Tomographic images of mantle plumes such as the one beneath Hawaii show a low-velocity region that extends all the way down to the boundary between mantle and core, about 2,900 kilometers below Earth’s surface. Such deep plumes are thought to be necessary to provide sufficient heat for the volcanism.

“But at Yellowstone, we don’t have that large low-shear velocity thing at the core-mantle boundary,” Porritt says. Current images suggest a region of low-velocity material extending at least 1,000 kilometers deep — but whether there is a deeper plume is uncertain.

And the region is tectonically complex. About 200 million years ago, a tectonic plate to the west, known as the Farallon Plate, began to slide eastward beneath the North American Plate. The current Juan de Fuca Plate off the Pacific Northwest coast, one of the last remnants of the Farallon Plate, continues to slide beneath the western United States. Some researchers have suggested that, instead of a deep mantle plume, the flexing and melting of the subducting Juan de Fuca Plate are responsible for Yellowstone’s volcanism.
Liu and his colleagues have yet another idea. In 2016, Liu published research suggesting that the sinking ancient Farallon slab was acting like a lid on a deep mantle plume, preventing the plume from rising to the surface (SN Online: 2/3/16). “But we kept in mind that the problem was not solved,” Liu says. “The heat source [for Yellowstone] was still missing.”

The researchers created a sophisticated, supercomputer-driven series of simulations to try to find the best scenario that matches the three known knowns: the current tomographic images of the subsurface beneath the western United States; the volcanic history at Yellowstone as well as in the nearby Basin and Range regions; and the movements of the subducting slab since about 20 million years ago.

Yellowstone’s volcanism is linked not just to the currently subducting young Juan de Fuca Plate, but also to the remnants of its older incarnation, the Farallon Plate, the simulations suggest. Those remnants have continued to slide deeper and now lie beneath the eastern United States. This downward dive dragged hot mantle eastward along with it. As the Juan de Fuca Plate began to break up beneath the western United States, the hot mantle rose through the cracks. Some of that hot mantle circulated back to the west across the top of the Juan de Fuca Plate, fueling volcanism in the Basin and Range region. And some of it flowed eastward, adding heat to Yellowstone’s fire. The study doesn’t rule out the presence of a deep magma plume, but it suggests that such a plume plays little role in Yellowstone’s volcanism.

Porritt says he’s intrigued by the idea that the sinking Farallon slab beneath the central and eastern United States could be driving mantle circulation on such a large scale. However, he says, he isn’t convinced that the authors have truly solved the larger mystery of Yellowstone’s volcanism — or that a yet-to-be-found deep plume still isn’t playing a major role. “It’s an interesting debate that’s going to be raging, hopefully for decades.”

Magnetic poles are seemingly inseparable: Slice a magnet in half, and you get two smaller magnets, each with its own north and south poles. But exotic magnetic particles that flout this rule may be lurking undetected, some physicists suspect.

The hunt is in full swing for these hypothetical particles known as magnetic monopoles — which possess a lone north or south pole. Now, two groups of researchers have further winnowed down the particles’ possible masses and characteristics, using data from particle accelerators and the corpses of stars.
There’s good reason to suspect magnetic monopoles are out there, some physicists suggest. The particles’ existence would explain why electric charge is quantized — why it always seems to come in integer multiples of the charge of an electron instead of a continuous range of values. As a result, magnetic monopoles are popular. “A lot of people think they should exist,” says James Pinfold, a particle physicist at the University of Alberta in Edmonton, Canada.

If even a single magnetic monopole were detected, the discovery would rejigger the foundations of physics. The equations governing electricity and magnetism are mirror images of one another, but there’s one major difference between the two phenomena. Protons and electrons carry positive and negative electric charges, respectively, but no known particle has a magnetic charge. A magnetic monopole would be the first, and if one were discovered, electricity and magnetism would finally be on equal footing.

For decades, scientists have searched fruitlessly for magnetic monopoles. Recent work at the Large Hadron Collider, located at the particle physics lab CERN in Geneva, has reinvigorated the search. Magnetic monopoles might be produced there as protons slam together at record-high energies of 13 trillion electron volts.

Unfortunately, the latest search by Pinfold and collaborators with the Monopole and Exotics Detector at the LHC, or MoEDAL (pronounced “medal”), found no magnetic monopoles, despite analyzing six times the data as the project’s previous pursuits. Still, the new research has set some of the most stringent constraints yet on how easily the hypothetical particles may interact with matter, the MoEDAL collaboration reports December 28 at arXiv.org.
Magnetic monopoles may also dwell where magnetic fields are extraordinarily strong and temperatures are high. Under these conditions, pairs of monopoles might form spontaneously. Such extreme environments can be found around a special kind of dead star known as a magnetar, and in the aftermath of collisions of heavy atomic nuclei in particle accelerators. By studying these two scenarios, physicists Arttu Rajantie and Oliver Gould, both of Imperial College London, put new constraints on monopoles’ masses, the researchers report in the Dec. 15 Physical Review Letters.

If magnetic monopoles had relatively small masses, the particles would sap the strength of magnetars’ magnetic fields. That fact suggests that the particles must be more massive than about 0.3 billion electron volts — about a third the mass of a proton — the researchers calculate. That estimate depends on another unknown property of monopoles, the strength of their magnetic charge. The particles have a minimum possible magnetic charge. A magnetic charge larger than this baseline value would correspond to a minimum mass greater than 0.3 billion electron volts.

For a monopole with twice the minimum charge, Rajantie and Gould determined that magnetic monopoles must be more massive than about 10 billion electron volts, going by data from collisions of lead nuclei in the Super Proton Synchrotron, a smaller accelerator at CERN. Studying similar collisions of lead nuclei in the LHC could improve this estimate, due to the LHC’s higher collision energies.

While other experiments have set higher monopole mass limits than the new estimates, those analyses relied on questionable theoretical assumptions, Rajantie says. “These are currently the strongest bounds on the masses of magnetic monopoles that don’t rely on assumptions” about how the particles are created, he says.

The results are “very exciting,” says theoretical physicist Kimball Milton of the University of Oklahoma in Norman, who was not involved with the research. Of course, he adds, it’s “not as exciting as if somebody actually found a magnetic monopole.”

Even if monopoles do exist, the particles might be so heavy that they can’t be produced by accelerators or cosmic processes. The only magnetic monopoles in the universe might be remnants of the Big Bang. A future incarnation of MoEDAL, located on a mountaintop instead of in an accelerator’s cavern, could look for such magnetic monopoles that sprinkle down on Earth from space, Pinfold says.

Fracking wells should not go to 11. Instead, turning down the volume — that is, of water pumped underground to help retrieve oil and gas — may reduce the number of earthquakes related to hydraulic fracturing.

The amount of water pumped into fracking wells is the No. 1 factor related to earthquake occurrence at Fox Creek, a large oil and gas production site in central Canada, researchers report January 19 in Science. An injection of 10,000 cubic meters of fluid or more at a well appears to trigger a quake.
Fox Creek sits atop the Duvernay Formation, a sedimentary layer rich in oil and gas. Before December 2013, the area was earthquake-free. Since then, hundreds of earthquakes have shaken the region; most were below magnitude 4, but a magnitude 4.8 quake in 2016 temporarily shut down operations.

Previous investigations revealed that fracking well injections at the site were triggering earthquakes on an underlying fault system. But mysteries remained: For example, why didn’t the quakes didn’t start until almost three years after fracking activities began in 2010?

Ryan Schultz of the Alberta Geological Survey in Edmonton and his colleagues compared the timing and location of the earthquakes with fracking activity at 300 wells in the region.

An analysis of rates of injection, fluid pressure and fluid volume for the wells closest in proximity to the quakes revealed that, at this site, only volume was linked to the quakes. A previous study has linked the rate of wastewater disposal injections to seismic slip (SN: 7/11/15, p. 10).
As for the three-year delay, the authors say, fracking well injections tend to increase in volume over time as operations mature. So once the injection volumes reached that 10,000-cubic- meter threshold, the earthquakes began.