back to top
27.8 C
New York
Sunday, October 6, 2024
Home Blog Page 53

Rock scratches hint at future quakes

Jesse leaning against the fresh fault scarp of the Kekerengu fault, next to some of the curved slickenlines. Credit: Professor Tim Little
Jesse leaning against the fresh fault scarp of the Kekerengu fault, next to some of the curved slickenlines. Credit: Professor Tim Little

Curved scratches in rock faces may give clues to where big quakes could strike next, a study led by Victoria University of Wellington Master’s student Jesse Kearse has shown.

These scratches—or ‘slickenlines’—have been observed on fault lines for decades. Through his Master’s research—published last month in the journal Geology—Jesse was able to link the direction of the slickenlines with the direction a fault line ruptures during an earthquake, providing a record of how past earthquakes have moved on New Zealand’s fault lines and hints as to where future earthquake damage could occur.

Jesse’s research began when he was analysing the Kekerengu fault line as part of the Kaikōura Earthquake Surface Rupture Response Team immediately following the Kaikōura earthquake.

“We were mapping the ground ruptures that occurred around the Kekerengu fault as a result of the Kaikōura earthquake, and we found these intriguing curved marks,” Jesse says. “We wanted to uncover the process behind their formation, because we knew this was a field of research that wasn’t well understood.”

Alongside his supervisors Professor Tim Little of Victoria University of Wellington and Russ van Dissen from GNS Science, Jesse spent many weeks in the field, walking the ground ruptures from end to end—a total distance of 30 kilometres—documenting the ground deformation, and recording the slickenlines.

“After completing these observations, we took our data back to the lab for analysis,” Jesse says. “We knew that the rupturing of the Kekerengu fault had caused the ground to shift sideways by up to 12 m during the Kaikoura earthquake. Our analysis of the slickenlines not only confirmed this movement, but also provided further detailed information about how the fault moved—not in a straight line, but along a complicated, curved route.”

With help from seismologist Yoshi Kaneko from GNS, who uses computer programs to model the dynamics of earthquake ruptures, they were able to confirm that curved slickenlines like the ones they observed on the Kekerengu fault are related to the direction an earthquake moves along the fault.

It has long been known that the direction a fault ruptures can strongly affects the distribution of ground shaking and damage resulting from an earthquake, Jesse says.

“In the Kaikōura earthquake, for example, Wellington experienced much stronger shaking than Christchurch, even though the epicentre of the quake was much closer to Christchurch,” Jesse says. “This is because the Kekerengu fault ruptured towards the north, and so the earthquake energy was focused in that direction.”

Now Jesse and his colleagues can analyse the slickenlines in other faults to see how they have ruptured in the past, including prehistoric earthquakes that took place thousands of years ago.

“We might be able to better predict how they will rupture in the future and where the ground shaking and damage from earthquakes on these faults will occur,” Jesse says. “This will help plan for future quakes, including designing more resilient buildings and architecture in areas that could suffer more quake damage.”

Jesse hopes to see this research tested further across the world to confirm their findings and provide a new way for scientists to discover information about earthquakes.

“This research is very new, so while it’s very exciting it still needs to be tested and verified by the global earth science community,” Jesse says. “Hopefully this analysis will prove that these findings are of real benefit to the lives of people living in earthquake prone regions around the world.”

Reference:
Jesse Kearse et al. Curved slickenlines preserve direction of rupture propagation, Geology (2019). DOI: 10.1130/G46563.1

Note: The above post is reprinted from materials provided by Victoria University of Wellington.

Hidden mysteries lie in wait inside Kenya’s fossil treasury

The 23-million-year-old bones of the newly-discovered giant, Simbakubwa kutokaafrika, had been left for nearly 40 years in a drawer
The 23-million-year-old bones of the newly-discovered giant, Simbakubwa kutokaafrika, had been left for nearly 40 years in a drawer

The only hint that something extraordinary lay inside the plain wooden drawer in an unassuming office behind Nairobi National Museum was a handwritten note stuck to the front: “Pull Carefully”.

Inside, a monstrous jawbone with colossal fangs grinned from a bed of tattered foam—the only known remains of a prehistoric mega-carnivore, larger than a polar bear, that researchers only this year declared a new species.

“This is one-of-a-kind,” said Kenyan paleontologist Job Kibii, holding up the 23-million-year-old bones of the newly-discovered giant, Simbakubwa kutokaafrika, whose unveiling made headlines around the world.

But the remarkable fossils were not unearthed this year, or even this decade. They weren’t even found this century.

For nearly 40 years, the specimens—proof of the existence of Africa’s largest-ever predator, a 1,500 kilogram (3,300-pound) meat eater that dwarfed later hunters like lions—lived in a nondescript drawer in downtown Nairobi.

Museum staff knew the bones were something special—they just didn’t know what exactly. A source of intrigue, dusted off on occasion for guests, Simbakubwa lay in wait, largely forgotten.

How did these fossils, first excavated on a dig in western Kenya in the early 1980s, go unrecognised for so long?

Kibii—who presides over the National Museums of Kenya’s paleontology department, a collection unrivalled in East Africa and one of the world’s great fossil treasuries—has a pretty good idea.

“We have tonnes and tonnes of specimens… that haven’t been analysed,” he told AFP.

“Definitely there are things waiting to be discovered.”

Out of space

The main wing has changed little since legendary paleoanthropologist Louis Leakey first started stockpiling his finds there in the early 1960s.

A card-based filing system is still used to find a specific fossil among the trove, the entries written by hand.

But the collection has grown exponentially, faster than Kibii and his team can keep up.

“We’ve run out of space,” said Kibii, pausing between dusty archival shelves crammed floor to ceiling with finds, dating back more than half a century.

“In this section alone, we have more than a million specimens.”

Gigantic skulls of ancient crocodiles compete for space with a bygone species of horned giraffe.

Nearby, the behemoth tusks of an early African elephant take up valuable real estate.

Even the windowsills are littered with the petrified remains of all manner of weird and wonderful creatures.

Between 7,000 and 10,000 new fossils arrive at the lab every year, Kibii says, overwhelming his 15 staff who must painstakingly clean and log each specimen.

By law, fossils uncovered in Kenya must go to the museum for “accessioning”—the process of labelling, recording and storing for future generations.

The backlog is enormous.

Chipping away

In a dark room, a lone staffer in a protective mask blasts away rock from fossil using an air-powered brush, as Kenyan pop tunes crackle through an old radio.

Outside the door, metal chests sent from dig sites filled to the brim await his magic touch—literally years of work stretching before him.

If a specific expert is not on hand to identify a specimen, things can get wrongly categorised or waylaid.

In some cases, they’re sent to the dreaded “waiting area”, where faded cardboard boxes, sagging with unknown and abandoned fossils, gather dust.

“We have fossils from the 1980s that have not been accessioned,” said collections manager Francis Muchemi, chipping away at a giant elephant molar.

‘Cradle of humanity’

Simbakubwa met a similar fate.

Thought to be a type of hyena, it was filed away in a backroom and unstudied for decades, until stumbled upon by American researchers.

Specific finds unearthed at one of Kenya’s many digs by researchers writing academic papers are given priority and fast-tracked for assessment by the museum.

Even today though, the museum lacks specialists and resources.

Kibii is one of just seven paleontologists in Kenya. He trained in South Africa because there was no course available at home.

“It’s important because Kenya is the cradle of human evolution,” said Muchemi, who learned his skills on the job.

“We have very few Kenyans doing this job. Ninety-nine percent of the people who work here are foreign.”

Kibii said paleontology was considered a lower priority than conserving Africa’s endangered wildlife.

“This one has been in the ground for millions of years. What are you saving it from?” he said, of the prevailing attitude to the science.

He hopes to acquire collapsable shelves to create space in the collection.

Even better, a micro-CT scanner—a powerful tool driving breakthroughs in the world of paleontology—would allow a fresh look at the museum’s most-forgotten corners.

“I always wonder what lies in there on some of these shelves,” Kibii said.

“Simbakubwa is telling a new story. What if, among these thousands, we have 10, 20, new stories that are lying, waiting to be told? That’s always the mystery.”

Note: The above post is reprinted from materials provided by AFP .

Ancient drop of water rewrites Earth’s history

A diagrammatic representation of the Earth in the Archaean showing subducted ocean floor carrying its chemical signature into the deep mantle. The signature which includes water and chlorine is preserved in melt inclusions contained within olivine and carried back up to surface within komatiite lava flows.
A diagrammatic representation of the Earth in the Archaean showing subducted ocean floor carrying its chemical signature into the deep mantle. The signature which includes water and chlorine is preserved in melt inclusions contained within olivine and carried back up to surface within komatiite lava flows.

The remains of a microscopic drop of ancient seawater has assisted in rewriting the history of Earth’s evolution when it was used to re-establish the time that plate tectonics started on the planet.

Plate tectonics is Earth’s vital — and unique — continuous recycling process that directly or indirectly controls almost every function of the planet, including atmospheric conditions, mountain building (forming of continents), natural hazards such as volcanoes and earthquakes, formation of mineral deposits and the maintenance of our oceans. It is the process where the large continental plates of the planet continuously move, and the top layers of the Earth (crust) are recycled into the mantle and replaced by new layers through processes such as volcanic activity.

Where it was previously thought that plate tectonics started about 2.7 billion years ago, a team of international scientists used the microscopic leftovers of a drop of water that was transported into the Earth’s deep mantle — through plate tectonics — to show that this process started 600 million years before that. An article on their research that proves plate tectonics started on Earth 3.3 billion years ago was published in the high impact academic journal, Nature, on 16 July.

“Plate tectonics constantly recycles the planet’s matter, and without it the planet would look like Mars,” says Professor Allan Wilson from the Wits School of Geosciences, who was part of the research team.

“Our research showing that plate tectonics started 3.3 billion years ago now coincides with the period that life started on Earth. It tells us where the planet came from and how it evolved.”

Earth is the only planet in our solar system that is shaped by plate tectonics and without it the planet would be uninhabitable.

For their research, the team analysed a piece of rock melt, called komatiite — named after the type occurrence in the Komati river near Barberton in Mpumalanga — that are the leftovers from the hottest magma ever produced in the first quarter of Earth’s existence (the Archaean). While most of the komatiites were obscured by later alteration and exposure to the atmosphere, small droplets of the molten rock were preserved in a mineral called olivine. This allowed the team to study a perfectly preserved piece of ancient lava.

“We examined a piece of melt that was 10 microns (0.01mm) in diameter, and analysed its chemical indicators such as H2O content, chlorine and deuterium/hydrogen ratio, and found that Earth’s recycling process started about 600 million years earlier than originally thought,” says Wilson. “We found that seawater was transported deep into the mantle and then re-emerged through volcanic plumes from the core-mantle boundary.”

The research allows insight into the first stages of plate tectonics and the start of stable continental crust.

“What is exciting is that this discovery comes at the 50th anniversary of the discovery of komatiites in the Barberton Mountain Land by Wits Professors, the brothers Morris and Richard Viljoen,” says Wilson.

Reference:
Alexander V. Sobolev, Evgeny V. Asafov, Andrey A. Gurenko, Nicholas T. Arndt, Valentina G. Batanova, Maxim V. Portnyagin, Dieter Garbe-Schönberg, Allan H. Wilson, Gary R. Byerly. Deep hydrous mantle reservoir provides evidence for crustal recycling before 3.3 billion years ago. Nature, 2019; 571 (7766): 555 DOI: 10.1038/s41586-019-1399-5

Note: The above post is reprinted from materials provided by University of the Witwatersrand.

Synchronization of ice cores using volcanic ash layers

An electron scanning microscope picture of an ash sample from a 55,500 years old ash layer in the NGRIP ice core. The ash shards are the larger pieces that look like broken glass. The colours are not true. The white bar at the bottom left represents 1/10 mm. Credit: University of Copenhagen
An electron scanning microscope picture of an ash sample from a 55,500 years old ash layer in the NGRIP ice core. The ash shards are the larger pieces that look like broken glass. The colours are not true. The white bar at the bottom left represents 1/10 mm. Credit: University of Copenhagen

Thin, brownish layers of a thickness of about a millimeter or two are sometimes observed in the whitish/transparent ice cores. These brown layers consist of material originating from volcanic eruptions.

During a volcanic eruption, gases, lava, rocks, and tiny ash particles are being ejected into the atmosphere. The smallest particles are carried by the wind and transported with the air masses, until the particles drop out and cover the land or ice surface with a thin blanket of volcanic material. Ash that landed on the ice sheet of Greenland thousands of years ago are buried under huge amounts of ice today and can only be retrieved by drilling long ice cores.

Many of the ash particles in the ice cores are too small to be visible to the naked eye. Most often the particles are only one tenth or one hundredth of a millimeter. Only when a huge amount of ash particles is present in a layer, the layer will be visible in the ice core as a thin brown band, but most of the volcanic layers in ice cores are invisible because of the small amount of ash shards. Searching for these ash layers in a three kilometer long ice core may seem like an impossible task. Nevertheless, this is what researchers at the Centre for Ice and Climate do.

The volcanic ash layers can be used as important reference horizons that can link different ice cores and other archives of past climate. The volcanic ash also contains a chemical fingerprint which makes it possible to trace which volcano the ash originates from, and sometimes also which eruption of a particular volcano was the source. It is this property that encourages the researchers to look for the tiny ash particles that are hidden in the long ice cores.

Identification and analysis of volcanic ash

It may seem like an impossible task to find the invisible ash layers in a three kilometer long ice core, consisting of about 20 tonnes of ice. Luckily, some help is at hand. Following a volcanic eruption, the precipitation is often slightly acidic due to the presence of sulphuric acid that comes from conversion of the volcanic sulphuric gases in the atmosphere. The relatively high acid concentrations lead to high electrical conductivity of the ice. It is fast and relatively easy to measure the electrical conductivity of the ice, and the acid peaks in the measured profile can be used as guides for where the tiny ash particles are hiding. Ice samples will usually be cut around where acid peaks are found, but unfortunately there is no guarantee that ash is present, so the samples have to be analyzed very carefully.

The ice samples are melted and centrifuged in order to pour off the water and keep the small amount of impurity particles from the ice. Most of the material is wind-blown dust or fine-grained sand, often coming all the way from deserts in Asia. If ash shards are present, these can be identified visually in a normal light microscope or in an electron scanning microscope.

An ash shard can often be identified by its glassy and shiny look, its particular shape and its transparency. The particles are normally either colorless or light pinkish or brownish, depending on the chemical composition.

After identification of an ash layer, the chemical analysis can start using an electron microprobe. This instrument works by shooting an electron beam at the ash particle investigated. The chemical composition of the shards can be inferred from the wavelengths of the X-rays that are emitted from the sample. Chemical results of good quality require that the samples are prepared well before analysis. This process is very laborious. All the shards to be analyzed need to have a flat and smooth surface and should be at the same level relative to the electron gun in the microprobe. One way to do this is to mount the shards in a resin (epoxy) on a glass slide and then polish the sample with fine-grained diamond dust. The surface of the sample is slowly being removed and polished by the hard diamond dust. Care is taken not to polish away all the precious shards. During the polishing, a microscope is used to check if the surface of the shard is flat and smooth.

When the chemical composition of the shards has been determined, the results are compared with results from analysis of similar shards in other ice or sediment cores or with the composition of ashes found in situ at the volcano responsible for the eruption.

Reference:
Brad S. Singer et al. Synchronizing volcanic, sedimentary, and ice core records of Earth’s last magnetic polarity reversal, Science Advances (2019). DOI: 10.1126/sciadv.aaw4621

Note: The above post is reprinted from materials provided by University of Copenhagen.

Sex appeal helped dinosaurs take flight

A flightless dinosaur called Similicaudipteryx uses its feathers in a mating display. U of A researchers looked at how such displays may have helped dinosaurs evolve feathers that eventually allowed them to fly. Credit: Sydney Mohr
A flightless dinosaur called Similicaudipteryx uses its feathers in a mating display. U of A researchers looked at how such displays may have helped dinosaurs evolve feathers that eventually allowed them to fly. Credit: Sydney Mohr

Attracting mates with showy displays may have helped dinosaurs develop feathers that let them take flight, according to new research by University of Alberta paleontologists.

“The first complex wing feathers show up in tiny raptor dinosaurs that could parachute and glide flying-squirrel-style through the prehistoric treetops,” said Scott Persons, who led the study while he was a post-doctoral researcher at the U of A.

“In this study, we explored how dinosaurs went from staying warm with simple hairy feathers to gliding on complicated wing feathers.”

The study makes the case that larger, stiffer, flatter feathers gradually evolved as showy fans on the arms and tails of dinosaurs to be waved and waggled in courtship displays, leading eventually to the evolution of birds—an interpretation supported by a growing fossil record of early feathers.

“Sexual display remains an important function of complex feathers in some birds to this day,” said Persons, who is now at the College of Charleston. “Think of the feather fans of turkeys and peacocks or the head crest of a cockatoo.”

A missing link

Persons said the feathers on a bird’s wing each have a central hollow shaft called a rachis whereas fossil feathers on many dinosaurs were covered only in simple hair-like feathers that nothing to do with flight. They served as insulation to keep dinosaurs warm.

“Going from simple hairy feathers to sophisticated flight feathers is a big jump. Evolution doesn’t normally work in big jumps. It’s gradual,” explained Persons. “Recognizing the intermediate function of sexual display explains a gradual way for simple feathers to have grown in complexity.”

Though the study offers clues about the evolutionary steps leading from dinosaurs to birds, there are still rich paleontological mysteries to explore concerning fossil feathers, Persons noted.

“We are still missing clear examples of sexually dimorphic feathers in dinosaurs. Today, it’s easy to tell the sexes of many birds apart based on their feathers,” he said. “Male birds tend to have larger, gaudier and brighter feathers because they are the ones doing the displaying.

“This was very likely true of feathered dinosaurs, but we haven’t found a definitive example … yet.”

The study, “Feather Evolution Exemplifies Sexually Selected Bridges Across the Adaptive Landscape,” was published in Evolution.

Reference:
W. Scott Persons et al. Feather evolution exemplifies sexually selected bridges across the adaptive landscape, Evolution (2019). DOI: 10.1111/evo.13795

Note: The above post is reprinted from materials provided by University of Alberta.

New species of early dinosaur described from South Africa

Ngwevu intloko skull. Credit: Kimberley Chapelle
Ngwevu intloko skull. Credit: Kimberley Chapelle

A new dinosaur species has been discovered after laying misidentified in a museum collection for 30 years.

Prof Paul Barrett, a dinosaur researcher at the Natural History Museum, is part of a team that reassessed the specimen, which is held at the University of Witwatersrand, Johannesburg. Along with his colleagues in South Africa, and led by Paul’s Ph.D. student Kimberley Chapelle, they recognised it not only as a new species of sauropodomorph, but an entirely new genus. The specimen has now been named Ngwevu intloko which means “grey skull” in the Xhosa language, chosen to honour South Africa’s heritage.

Prof Barrett explains, “This is a new dinosaur that has been hiding in plain sight. “The specimen has been in the collections in Johannesburg for about 30 years, and lots of other scientists have already looked at it. But they all thought that it was simply an odd example of Massospondylus.”

Massospondylus was one of the first dinosaurs to reign at the start of the Jurassic period. Regularly found throughout southern Africa, these animals belonged to a group called the sauropodomorphs and eventually gave rise to the sauropods, a group containing the Natural History Museum’s iconic dinosaur cast Dippy. Researchers are now starting to look closer at many of the supposed Massospondylus specimens, believing there to be much more variation than first thought.

Kimberley Chapelle explains why the team were able to confirm that this specimen was a new species, “In order to be certain that a fossil belongs to a new species, it is crucial to rule out the possibility that it is a younger or older version of an already existing species. This is a difficult task to accomplish with fossils because it is rare to have a complete age series of fossils from a single species. Luckily, the most common South African dinosaur Massospondylus has specimens ranging from embryo to adult! Based on this, we were able to rule out age as a possible explanation for the differences we observed in the specimen now named Ngwevu intloko.”

The new dinosaur has been described from a single fairly complete specimen with a remarkably well-preserved skull. The new dinosaur was bipedal with a fairly chunky body, a long slender neck and a small, boxy head. It would have measured three metres from the tip of its snout to the end of its tail and was likely an omnivore, feeding on both plants and small animals.

The findings will help scientists better understand the transition between the Triassic and Jurassic period, around 200 million years ago. Known as a time of mass extinction it now seems that more complex ecosystems were flourishing in the earliest Jurassic than previously thought.

“This new species is interesting,” says Prof Barrett, ‘because we thought previously that there was really only one type of sauropodomorph living in South Africa at this time. We now know there were actually six or seven of these dinosaurs in this area, as well as variety of other dinosaurs from less common groups. It means that their ecology was much more complex than we used to think. Some of these other sauropodomorphs were like Massospondylus, but a few were close to the origins of true sauropods, if not true sauropods themselves.”

This work shows the value of revisiting specimens in museum collections, as many news species are probably sitting unnoticed in cabinets around the world.

The new paper “Ngwevu intloko: a new early sauropodomorph dinosaur from the Lower Jurassic Elliot Formation of South Africa and comments on cranial ontogeny in Massospondylus carinatus” is published in the journal PeerJ.

Reference:
Kimberley E.J. Chapelle et al. Ngwevu intloko: a new early sauropodomorph dinosaur from the Lower Jurassic Elliot Formation of South Africa and comments on cranial ontogeny in Massospondylus carinatus, PeerJ (2019). DOI: 10.7717/peerj.7240

Note: The above post is reprinted from materials provided by Natural History Museum.

Newly discovered Labrador fossils give clues about ancient climate

This fossilized tree leaf, is the first of their kind to have been found in the area. Alexandre Demers-Potvin, used the samples he collected to establish that Eastern Canada would have had a warm temperate and fully humid climate during the middle of Cretaceous period. Credit: Alexandre Demers-Potvin
This fossilized tree leaf, is the first of their kind to have been found in the area. Alexandre Demers-Potvin, used the samples he collected to establish that Eastern Canada would have had a warm temperate and fully humid climate during the middle of Cretaceous period. Credit: Alexandre Demers-Potvin

The discovery of fossilized plants in Labrador, Canada, by a team of McGill directed paleontologists provides the first quantitative estimate of the area’s climate during the Cretaceous period, a time when the earth was dominated by dinosaurs.

The specimens were found in the Redmond no.1 mine, in a remote area of Labrador near Schefferville, in August 2018. Together with specimens collected in previous expeditions, they are now at the core of a recent study published in Palaeontology.

Some of the specimens, are the first of their kind to have been found in the area. Alexandre Demers-Potvin, a graduate student under the supervision of Professor Hans Larsson, Canada Research Chair in Vertebrate Palaeontology at McGill University, used the samples he collected to establish that Eastern Canada would have had a warm temperate and fully humid climate during the middle of Cretaceous period.

Fossilized leaves and insects, known to be very similar to communities that today live further south, had been found at the Redmond No. 1 mine in the late 1950s had led paleontologists to hypothesize that the cretaceous climate of Quebec and Labrador was far warmer than it is today.

With the new samples they found, Demers-Potvin and his colleagues were able to confirm this using the Climate Leaf Analysis Multivariate Program. This tool is used to predict a variety of climate statistics for a given fossil flora, such as temperature and precipitation variables, based on the shape and size of its tree leaves. Their findings put the area’s mean annual temperature around 15°C. Summers were hot — with temperatures of over 20 degrees Celsius — and year-round precipitations relatively high.

Alexandre Demers-Potvin, who is also the study’s first author, said the new work provides insight into how the climate of Eastern Canada evolved over time, useful information to study today’s changing climate.

“The fossils from the Redmond mine show that an area that is now covered by boreal forest and tundra used to be covered in warm temperate forests in the middle of the Cretaceous, one of our planet’s ‘hothouse’ episodes, Demers-Potvin said. These are new pieces of evidence that can help improve projections of the global average temperature against global CO2 levels throughout the Earth’s history.”

Alexandre Demers-Potvin and his collaborators are now undertaking a description of the new fossilized insects discovered at the Redmond site. Demers-Potvin will return to Schefferville in the hopes of finding more insect specimens and fossilized vertebrates that could be hiding in the rubble of the abandoned mine.

Note: The above post is reprinted from materials provided by McGill University.

Predicting the strength of earthquakes

Marine Denolle (right) and her team, including Jiuxun Yin (left) and Brad Lipovsky, created numerical models to predict an earthquake’s final magnitude 10 to 15 seconds faster than today’s best algorithms. Credit: Stephanie Mitchell/Harvard Staff Photographer
Marine Denolle (right) and her team, including Jiuxun Yin (left) and Brad Lipovsky, created numerical models to predict an earthquake’s final magnitude 10 to 15 seconds faster than today’s best algorithms. Credit: Stephanie Mitchell/Harvard Staff Photographer

Scientists will be able to predict earthquake magnitudes earlier than ever before thanks to new research by Marine Denolle, assistant professor in the Department of Earth and Planetary Sciences (EPS).

“For large-strike slip earthquakes like those that occur on the San Andreas Fault, which are likely to rupture for about 50 seconds, we would be able to predict the final magnitudes 2 to 5 seconds after getting the first seismic wave,” said Denolle, senior author of the study that appeared recently in Geophysical Research Letters.

Denolle shares authorship with Philippe Danré, the first author and former EPS visiting master’s student; Jiuxun Yin, a Ph.D. candidate in the Graduate School of Arts and Sciences; and Brad Lipovsky, an EPS researcher. The team also proved that the activity of earthquakes is actually organized, not chaotic as scientists had previously believed.

“Our research, which is technically rather simple, provides answers relevant not only to earthquake dynamics, but to prediction of earthquake behavior before the earthquake ends,” said Denolle. While there is still no way to predict quakes before they begin, current detection systems consist of a series of sensors that transmit signals to determine the location and magnitude once rapid shaking occurs.

Denolle and her team used data products and created numerical models to predict an earthquake’s final magnitude 10 to 15 seconds faster than today’s best algorithms—seconds that could provide enough time for people to exit a building or for officials to stop traffic before shaking starts.

The team began by examining patterns of seismic signals—transient waveforms that radiate from the first rupture in a fault, a thin seam of crushed rock separating two blocks of the earth’s crust. An earthquake occurs when the blocks break free. Scientists read these waves using an underground instrument called a seismometer that translates motions into a graph called a seismogram. “Seismograms give us information about what happened on the fault at the place where the earthquake occurred,” said Denolle.

Denolle and her team combined previous seismograms, which recorded changes in the waves over time as they traveled between the seismometer and the fault. This data product, known as “source time function,” provides a more accurate read on the waves from the source over long distances.

Denolle and her team examined a catalog of source time functions from earthquakes around the globe between 1990 and 2017. They discovered that large earthquakes are actually composed of a series of subevents, smaller events whose size is nearly proportional to the size of the main one. The team concluded that they could predict the final size of an earthquake based on the size of the first few subevents.

“The self-organization of earthquake ruptures is well-explained by heterogeneity on the fault, and our current knowledge of earthquake physics can explain our observations,” said Denolle.

The researchers hope their work will continue to evolve and can one day help improve the algorithms for early warnings of earthquake. To do this, they will work on extracting more accurate high-frequency signals from earthquakes to understand more about their dynamics.

“Eventually, we would hope that the study can provide some guidelines for proper modeling of large earthquakes, and serve as a tool for earthquake early warning, especially for regions expecting large earthquakes, like the Pacific Coast and Japan,” said Denolle.

Reference:
Philippe Danré et al. Earthquakes Within Earthquakes: Patterns in Rupture Complexity, Geophysical Research Letters (2019). DOI: 10.1029/2019GL083093

Note: The above post is reprinted from materials provided by Harvard University.

Scientists uncover deep-rooted plumbing system beneath ocean volcanoes

Volcano magma chamber. Credit: Cardiff University
Volcano magma chamber. Credit: Cardiff University

Cardiff University scientists have revealed the true extent of the internal ‘plumbing system’ that drives volcanic activity around the world.

An examination of pockets of magma contained within crystals has revealed that the large chambers of molten rock which feed volcanoes can extend to over 16 km beneath the Earth’s surface.

The new study, published today in Nature, has challenged our understanding of the structure of ocean volcanoes, with previous estimates suggesting that magma chambers were located up to 6 km below the surface.

Interconnected magma chambers and reservoirs are the key driver of the dynamics of volcanic systems around the world, so understanding their nature is an important step towards understanding how volcanoes are supplied with magma, and, ultimately, how they erupt.

Mid-ocean ridges in particular make up the most significant volcanic system on our planet, forming a roughly 80,000 km-long network of undersea mountains along which 75 percent of Earth’s volcanism occurs.

However, because these volcanoes are located under thousands of metres of water, and sometimes permanent sea ice, we are only just starting to understand what the subsurface architecture of these volcanoes look like.

It is known that magma plumbing systems exist below the Earth’s surface, which can be thought of as a series of interconnected magma conduits and reservoirs, much like the pipes and tanks that make up plumbing systems in a house, instead at mid-ocean ridges the tap is a volcano.

In their study, the team analysed common minerals such as olivine and plagioclase which grew deep within the volcanoes and were subsequently erupted from the Gakkel Ridge located beneath the Arctic Ocean between Greenland and Siberia.

These minerals act as tape recorders from which changes in the physical and chemical conditions of the environment within which they grew can be measured. Critically, the team were able to record what processes occurred and at what depths these minerals began to crystallise in magma reservoirs.

Lead author of the study, Ph.D. student Emma Bennett, from the School of Earth and Ocean Sciences, said: “To calculate the depths of magma reservoirs we used melt inclusions, which are small pockets of magma that become trapped within growing crystals at different depths in the magmatic system. These pockets of melt contain dissolved CO2 and H2O.

“Because the melt cannot dissolve as much CO2 at shallow pressure as it can at high pressure, we can determine what pressure the melt inclusion was trapped, and in turn work out the depth at which crystallisation occurred, by measuring the amount of CO2 in the melt inclusions.

“Put simply, crystal growth in a magmatic environment can be likened to the growth rings on a tree; for example, a change in the chemical environment will result in the growth of a new layer with a different crystal composition.

“By analysing multiple melt inclusions we can start to reconstruct the architecture of the magmatic system.”

The study was the first to use the mineral plagioclase as a proxy for the depth of magma reservoirs, with previous studies using the mineral olivine.

The results showed that magma plumbing systems at mid-ocean ridges extend to much greater depths than previously thought. Oceanic crust is normally only around 6 km thick, and conventionally magma chambers were thought of as being located here.

Yet the new data has shown that the plumbing system extends to at least 16 km depth, which means that the magma chambers that fed the Gakkel Ridge volcanoes are located much deeper down in the mantle.

Reference:
Emma N. Bennett et al. Deep roots for mid-ocean-ridge volcanoes revealed by plagioclase-hosted melt inclusions, Nature (2019). DOI: 10.1038/s41586-019-1448-0

Note: The above post is reprinted from materials provided by Cardiff University.

Researchers uncover 2.5 billion years of Earth’s continents breaking up and getting back together

Continents breaking up and getting back together. Image credit: Naeblys / Getty Images
Continents breaking up and getting back together. Image credit: Naeblys / Getty Images

A new study of rocks that formed billions of years ago lends fresh insight into how Earth’s plate tectonics, or the movement of large pieces of Earth’s outer shell, evolved over the planet’s 4.56-billion-year history.

A report of the findings, published August 7 in Nature, reveals that, contrary to previous studies that say plate tectonics has operated throughout Earth’s history or that it emerged only 0.7 billion years ago, plate tectonics actually evolved over the last 2.5 billion years. This new timeline impacts researchers’ models for understanding how Earth has changed.

“One of the key ways to understand how Earth has evolved to become the planet that we know is plate tectonics,” says Robert Holder, a Postdoctoral Fellow in Earth and Planetary Sciences at Johns Hopkins University and the paper’s first author.

Plate tectonics dictates how continents drift apart and come back together, helps explain where volcanoes and earthquakes occur, predicts cycles of erosion and ocean circulation, and how life on Earth has evolved.

In a bid to resolve the mystery of how and when plate tectonics emerged on Earth, Holder and the research team examined a global compilation of metamorphic rocks that formed over the past 3 billion years at 564 sites. Metamorphic rocks are rocks that, through the process of being buried and heated deep in the Earth’s crust, have transformed into a new type of rock. Scientists can measure the depth and temperatures at which metamorphic rocks form, and thereby constrain heat flow at different places in Earth’s crust. Because plate tectonics strongly influences heat flow, ancient metamorphic rocks can be used to study plate tectonics in Earth’s past.

The research team compiled data on the temperatures and depths at which the metamorphic rocks formed and then evaluated how these conditions have changed systematically through geological time. From this, the team found that plate tectonics, as we see it today, developed gradually over the last 2.5 billion years.

“The framework for much of our understanding of the world and its geological processes relies on plate tectonics,” says Holder. “Knowing when plate tectonics began and how it changed impacts that framework.”

Clarity on when plate tectonics began and whether it was different in Earth’s past can help scientists better understand why we find certain rocks and minerals where we do and how they formed, says Holder.

Other authors on this paper include Daniel Viete of the Johns Hopkins University; Michael Brown of the University of Maryland, College Park; and Tim Johnson of Curtin University

Reference:
Robert M. Holder, Daniel R. Viete, Michael Brown & Tim E. Johnson. Metamorphism and the evolution of plate tectonics. Nature, 2019 DOI: 10.1038/s41586-019-1462-2

Note: The above post is reprinted from materials provided by Johns Hopkins University.

Earth’s last magnetic field reversal took far longer than once thought

Study co-author Rob Coe and Trevor Duarte orienting cores from a lava flow site recording the Matuyama-Brunhes magnetic polarity reversal in Haleakala National Park, Hawaii, in 2015
Study co-author Rob Coe and Trevor Duarte orienting cores from a lava flow site recording the Matuyama-Brunhes magnetic polarity reversal in Haleakala National Park, Hawaii, in 2015. Credit: Brad Singer

Earth’s magnetic field seems steady and true — reliable enough to navigate by.

Yet, largely hidden from daily life, the field drifts, waxes and wanes. The magnetic North Pole is currently careening toward Siberia, which recently forced the Global Positioning System that underlies modern navigation to update its software sooner than expected to account for the shift.

And every several hundred thousand years or so, the magnetic field dramatically shifts and reverses its polarity: Magnetic north shifts to the geographic South Pole and, eventually, back again. This reversal has happened countless times over the Earth’s history, but scientists have only a limited understanding of why the field reverses and how it happens.

New work from University of Wisconsin-Madison geologist Brad Singer and his colleagues finds that the most recent field reversal, some 770,000 years ago, took at least 22,000 years to complete. That’s several times longer than previously thought, and the results further call into question controversial findings that some reversals could occur within a human lifetime.

The new analysis — based on advances in measurement capabilities and a global survey of lava flows, ocean sediments and Antarctic ice cores — provides a detailed look at a turbulent time for Earth’s magnetic field. Over millennia, the field weakened, partially shifted, stabilized again and then finally reversed for good to the orientation we know today.

The results provide a clearer and more nuanced picture of reversals at a time when some scientists believe we may be experiencing the early stages of a reversal as the field weakens and moves. Other researchers dispute the notion of a present-day reversal, which would likely affect our heavily electronic world in unusual ways.

Singer published his work Aug. 7 in the journal Science Advances. He collaborated with researchers at Kumamoto University in Japan and the University of California, Santa Cruz.

“Reversals are generated in the deepest parts of the Earth’s interior, but the effects manifest themselves all the way through the Earth and especially at the Earth’s surface and in the atmosphere,” explains Singer. “Unless you have a complete, accurate and high-resolution record of what a field reversal really is like at the surface of the Earth, it’s difficult to even discuss what the mechanics of generating a reversal are.”

Earth’s magnetic field is produced by the planet’s liquid iron outer core as it spins around the solid inner core. This dynamo action creates a field that is most stable going through roughly the geographic North and South poles, but the field shifts and weakens significantly during reversals.

As new rocks form — typically either as volcanic lava flows or sediments being deposited on the sea floor — they record the magnetic field at the time they were created. Geologists like Singer can survey this global record to piece together the history of magnetic fields going back millions of years. The record is clearest for the most recent reversal, named Matuyama-Brunhes after the researchers who first described reversals.

For the current analysis, Singer and his team focused on lava flows from Chile, Tahiti, Hawaii, the Caribbean and the Canary Islands. The team collected samples from these lava flows over several field seasons.

“Lava flows are ideal recorders of the magnetic field. They have a lot of iron-bearing minerals, and when they cool, they lock in the direction of the field,” says Singer. “But it’s a spotty record. No volcanoes are erupting continuously. So we’re relying on careful field work to identify the right records.”

The researchers combined magnetic readings and radioisotope dating of samples from seven lava flow sequences to recreate the magnetic field over a span of about 70,000 years centered on the Matuyama-Brunhes reversal. They relied on upgraded methods developed in Singer’s WiscAr geochronology lab to more accurately date the lava flows by measuring the argon produced from radioactive decay of potassium in the rocks.

They found that the final reversal was quick by geological standards, less than 4,000 years. But it was preceded by an extended period of instability that included two excursions — temporary, partial reversals — stretching back another 18,000 years. That span is more than twice as long as suggested by recent proposals that all reversals wrap up within 9,000 years.

The lava flow data was corroborated by magnetic readings from the seafloor, which provides a more continuous but less precise source of data than lava rocks. The researchers also used Antarctic ice cores to track the deposition of beryllium, which is produced by cosmic radiation colliding with the atmosphere. When the magnetic field is reversing, it weakens and allows more radiation to strike the atmosphere, producing more beryllium.

Since humanity began recording the strength of the magnetic field, it has decreased in strength about five percent each century. As records like Singer’s show, a weakening field seems to be a precursor to an eventual reversal, although it’s far from clear that a reversal is imminent.

A reversing field might significantly affect navigation and satellite and terrestrial communication. But the current study suggests that society would have generations to adapt to a lengthy period of magnetic instability.

“I’ve been working on this problem for 25 years,” says Singer, who stumbled into paleomagnetism when he realized the volcanoes he was studying served as a good record of Earth’s magnetic fields. “And now we have a richer record and better-dated record of this last reversal than ever before.”

This study was supported by National Science Foundation grant EAR-1250446.

Reference:
Brad S. Singer, Brian R. Jicha, Nobutatsu Mochizuki, Robert S. Coe. Synchronizing volcanic, sedimentary, and ice core records of Earth’s last magnetic polarity reversal. Science Advances, 2019; 5 (8): eaaw4621 DOI: 10.1126/sciadv.aaw4621

Note: The above post is reprinted from materials provided by University of Wisconsin-Madison. Original written by Eric Hamilton.

A voracious Cambrian predator, Cambroraster, is a new species from the Burgess Shale

Reconstruction by Lars Fields. Credit: Lars Fields Royal Ontario Museum
Reconstruction by Lars Fields. Credit: Lars Fields Royal Ontario Museum

Palaeontologists at the Royal Ontario Museum and University of Toronto have uncovered fossils of a large new predatory species in half-a-billion-year-old rocks from Kootenay National Park in the Canadian Rockies. This new species has rake-like claws and a pineapple-slice-shaped mouth at the front of an enormous head, and it sheds light on the diversity of the earliest relatives of insects, crabs, spiders, and their kin. The findings were announced July 31, 2019, in a study published in Proceedings of the Royal Society B.

Reaching up to a foot in length, the new species, named Cambroraster falcatus, comes from the famous 506-million-year-old Burgess Shale. “Its size would have been even more impressive at the time it was alive, as most animals living during the Cambrian Period were smaller than your little finger,” said Joe Moysiuk, a graduate student based at the Royal Ontario Museum who led the study as part of his Ph.D. research in Ecology & Evolutionary Biology at the University of Toronto. Cambroraster was a distant cousin of the iconic Anomalocaris, the top predator living in the seas at that time, but it seems to have been feeding in a radically different way,” continued Moysiuk.

The name Cambroraster refers to the remarkable claws of this animal, which bear a parallel series of outgrowths, looking like forward-directed rakes. “We think Cambroraster may have used these claws to sift through sediment, trapping buried prey in the net-like array of hooked spines,” added Jean-Bernard Caron, Moysiuk’s supervisor and the Richard M. Ivey Curator of Invertebrate Palaeontology at the Royal Ontario Museum.

With the interspace between the spines on the claws at typically less than a millimeter, this would have enabled Cambroraster to feed on very small organisms, although larger prey could also likely be captured, and ingested into the circular tooth-lined mouth. This specialized mouth apparatus is the namesake of the extinct group Radiodonta, which includes both Cambroraster and Anomalocaris. Radiodonta is considered to be one of the earliest offshoots of the arthropod lineage (today including all animals with an exoskeleton, a segmented body and jointed limbs).

The second part of the species name falcatus was given in tribute to another of Cambroraster’s distinctive features: the large shield-like carapace covering its head, which is shaped like the Millennium Falcon spaceship from the Star Wars films. “With its broad head carapace with deep notches accommodating the upward facing eyes, Cambroraster resembles modern living bottom-dwelling animals like horseshoe crabs. This represents a remarkable case of evolutionary convergence in these radiodonts,” Moysiuk explained. Such convergence is likely reflective of a similar environment and mode of life—like modern horseshoe crabs, Cambroraster may have used its carapace to plough through sediment as it fed.

Perhaps even more astonishing is the large number of specimens recovered. “The sheer abundance of this animal is extraordinary,” added Dr. Caron, who is also an Assistant Professor in Ecology & Evolutionary Biology and Earth Sciences at the University of Toronto, and the leader of the field expeditions that unearthed the new fossils. “Over the past few summers we found hundreds of specimens, sometimes with dozens of individuals covering single rock slabs.”

Based on over a hundred exceptionally well-preserved fossils now housed at the Museum, researchers were able to reconstruct Cambroraster in unprecedented detail, revealing characteristics that had not been seen before in related species.

“The radiodont fossil record is very sparse; typically, we only find scattered bits and pieces. The large number of parts and unusually complete fossils preserved at the same place are a real coup, as they help us to better understand what these animals looked like and how they lived,” said Dr. Caron. “We are really excited about this discovery. Cambroraster clearly illustrates that predation was a big deal at that time with many kinds of surprising morphological adaptations.”

Fossils from the Cambrian period, particularly from sites like the Burgess Shale, record a dramatic “explosion” of biodiversity at this time, culminating in the evolution of most of the major groups of animals that survive today. But, the story has far more intricacy than a straight line leading from simple ancestors to the vast diversity of modern species. “Far from being primitive, radiodonts show us that at the very outset of complex ecosystems on Earth, early representatives of the arthropod lineage rapidly radiated to play a wide array of ecological roles,” remarked Moysiuk.

The fossils were found at several sites in the Marble Canyon area in Kootenay National Park, British Columbia, which have been discovered by ROM-led field teams since 2012, with some of the key specimens unearthed just last summer. These sites are about 40 kilometers away from the original Burgess Shale fossil site in Yoho National Park that was first discovered in 1909. What is also exciting for researchers is the realization that there is a large new area in northern Kootenay National Park worth scientific exploration, holding the potential for the discovery of many more new species.

The Burgess Shale fossil sites are located within Yoho and Kootenay National Parks and are managed by Parks Canada. Parks Canada is proud to work with leading scientific researchers to expand our knowledge and understanding of this key period of earth history and to share these sites with the world through award-winning guided hikes. The Burgess Shale was designated a UNESCO World Heritage Site in 1980 due to its outstanding universal value, and is now part of the larger Canadian Rocky Mountain Parks World Heritage Site.

Reference:
A new hurdiid radiodont from the Burgess Shale evinces the exploitation of Cambrian infaunal food sources, Proceedings of the Royal Society B, rspb.royalsocietypublishing.or … .1098/rspb.2019.1079

Note: The above post is reprinted from materials provided by Royal Ontario Museum .

Colossal dinosaur bone find in France thrills scientists

Scientists say the femur might have belonged to a gigantic sauropod. Credit: AFP / GEORGES GOBET
Scientists say the femur might have belonged to a gigantic sauropod. Credit: AFP / GEORGES GOBET

Scientists have unearthed a huge two-metre (6.5-foot) dinosaur bone in a winegrowing village in southwestern France dubbed a “national treasure” for its prehistoric gems.

The 140-million-year-old thigh bone, which weighs 400 kilogrammes (880 pounds), is the latest discovery at the vast Angeac-Charente palaeontological site near Bordeaux, where experts and volunteers have dug up thousands of bones over the past decade.

But thanks to its remarkably good condition, the femur—which scientists say probably belonged to a gigantic sauropod—could help piece together an incomplete set of bones which the latest find resembles.

“We were wondering how big it was. We kept saying, ‘Oh, there’s more!'” said Maxime Lasseron, the doctoral student who made the gigantic discovery.

The largest land animals ever to roam the Earth, sauropods were massive plant-eating dinosaurs with a long neck and tail, towering up to 18 metres (59 feet) tall.

“It cost me a bit of money, because I had promised to bring champagne if it was complete,” said Jean-Francois Tournepiche, the operations coordinator at what he calls “one of Europe’s biggest dinosaur sites”.

Tests will now compare the femur to another thigh bone discovered in 2010 to find out if they belonged to the same type of sauropod or even the same creature.

The bone’s “preservation and perfect fossilisation makes it really unique”, said Ronan Allain, a paleontologist at the French Museum of Natural History in Paris.

Prehistoric ecosystem

Now known for its cognac vineyards, Angeac-Charente was home to a vast ecosystem of dinosaurs, invertebrates and vegetation thanks to its humid, subtropical climate millions of years ago.

“There was a river and large coniferous trees,” Allain said.

“Amphibians, crocodiles and fish lived in the swamp, and on dry land, small and large dinosaurs. It was full of life”.

The discovery coincides with the 10th annual dig at the site, which stretches over 750 square metres (nearly 8,100 square feet).

But with more discoveries expected on the horizon, the site’s owners have given diggers the go-ahead to excavate in another 4,000 square metres of land.

“Another surprise for our 10-year anniversary,” Tournepiche said. “At this rate, we’ll be busy for the next 30 years!”

Note: The above post is reprinted from materials provided by AFP.

Predicting earthquake hazards from wastewater injection

Wells drilled into Oklahoma's Arbuckle formation inject wastewater (1) which then disperses through the rock. As it spreads, the wastewater can trigger earthquakes in fault zones (2), but their size depends on the amount injected and the rock's properties. The new model can predict quake probabilities by the quantity of wastewater injected.
Wells drilled into Oklahoma’s Arbuckle formation inject wastewater (1) which then disperses through the rock. As it spreads, the wastewater can trigger earthquakes in fault zones (2), but their size depends on the amount injected and the rock’s properties. The new model can predict quake probabilities by the quantity of wastewater injected. Credit: Guang Zhai, Manoochehr Shirzaei/ASU

A byproduct of oil and gas production is a large quantity of toxic wastewater called brine. Well-drillers dispose of brine by injecting it into deep rock formations, where its injection can cause earthquakes. Most quakes are relatively small, but some of them have been large and damaging.

Yet predicting the amount of seismic activity from wastewater injection is difficult because it involves numerous variables. These include the quantity of brine injected, how easily brine can move through the rock, the presence of existing geological faults, and the regional stresses on those faults.

Now a team of Arizona State University-led geoscientists, working under a Department of Energy grant, has developed a method to predict seismic activity from wastewater disposal. The team’s study area is in Oklahoma, a state where much fracking activity has been carried out with a lot of wastewater injection, and where there have been several induced earthquakes producing damage.

The team’s paper reporting their findings appeared in the Proceedings of the National Academy of Sciences on July 29, 2019.

“Overall, earthquake hazards increase with background seismic activity, and that results from changes in the crustal stress,” says Guang Zhai, a postdoctoral research scientist in ASU’s School of Earth and Space Exploration and a visiting assistant researcher at the University of California, Berkeley. “Our focus has been to model the physics of such changes that result from wastewater injection.”

Zhai is lead author for the paper, and the other scientists are Manoochehr Shirzaei, associate professor in the School, plus Michael Manga, of UC Berkeley, and Xiaowei Chen, of the University of Oklahoma.

“Seismic activity soared in one area for several years after wastewater injection was greatly reduced,” says Shirzaei. “That told us that existing prediction methods were inadequate.”

Back to basics

To address the problem, his team went back to basics, looking at how varying amounts of injected brine perturbed the crustal stresses and how these lead to earthquakes on a given fault.

“Fluids such as brine (and natural groundwater) can both be stored and move through rocks that are porous,” says Zhai.

The key was building a physics-based model that combined the rock’s ability to transport injected brine, and the rock’s elastic response to fluid pressure. Explains Shirzaei, “Our model includes the records collected for the past 23 years of brine injected at more than 700 Oklahoma wells into the Arbuckle formation.”

He adds that to make the scenario realistic, the model also includes the mechanical properties of the rocks in Oklahoma. The result was that the model successfully predicted changes in the crustal stress that come from brine injection.

For the final step, Shirzaei says, “We used a well-established physical model of how earthquakes begin so we could relate stress perturbations to the number and size of earthquakes.”

The team found that the physics-based framework does a good job of reproducing the distribution of actual earthquakes by frequency, magnitude, and time.

“An interesting finding,” says Zhai, “was that a tiny change in the rocks’ elastic response to changes in fluid pressure can amplify the number of earthquakes by several times. It’s a very sensitive factor.”

Making production safer

While wastewater injection can cause earthquakes, all major oil and gas production creates a large amount of wastewater that needs to be disposed of, and injection is the method the industry uses.

“So to make this safer in the future,” says Shirzaei, “our approach offers a way to forecast injection-caused earthquakes. This provides the industry with a tool for managing the injection of brine after fracking operations.”

Knowing the volume of brine to be injected and the location of the disposal well, authorities can estimate the probability that an earthquake of given size will result. Such probabilities can be used for short-term earthquake hazard assessment.

Alternatively, the team says, given the probability that an earthquake of certain size will happen, oil and gas operators can manage the injected brine volume to keep the probability of large earthquakes below a chosen value.

The end result, says Zhai, “is that this process will allow a safer practice, benefiting both the general public and the energy industry.”

Reference:
Guang Zhai, Manoochehr Shirzaei, Michael Manga, Xiaowei Chen. Pore-pressure diffusion, enhanced by poroelastic stresses, controls induced seismicity in Oklahoma. Proceedings of the National Academy of Sciences, 2019; 201819225 DOI: 10.1073/pnas.1819225116

Note: The above post is reprinted from materials provided by Arizona State University.

How to recognise where a volcano will erupt

Multiple volcanic craters cover the 'Campi Flegrei' near Naples, Italy. A new method aims at forecasting where new vents will occur.
Multiple volcanic craters cover the ‘Campi Flegrei’ near Naples, Italy. A new method aims at forecasting where new vents will occur. Credit: Mauro Antonio di Vito / INGV

On television, the eruption of volcano shoots magma right out of the top. However, it is not so uncommon that magma erupts from the volcano’s flank rather than its summit. After leaving the underground magma chamber, the magma forces its way sideways by fracturing rock, sometimes for tens of kilometres. Then, when it breaches the Earth’s surface, it forms one or more vents from which it spills out, sometimes explosively. This, for example, occurred at Bardarbunga in Iceland in August 2014, and Kilauea in Hawaii in August 2018.

It is a big challenge for volcanologists to guess where magma is heading and where it will breach the surface. A lot of effort is spent on this task, as it could minimize the risk for villages and cities endangered by eruptions. Now, Eleonora Rivalta and her team from the GFZ German Research Centre for Geosciences in Potsdam and institutional collaborators have devised a new method to generate vent location forecasts. The study is published in the journal Science Advances.

“Previous methods were based on the statistics of the locations of past eruptions,” says Eleonora Rivalta. “Our method combines physics and statistics: We calculate the paths of least resistance for ascending magma and tune the model based on statistics.” The researchers successfully tested the new approach with data from the Campi Flegrei caldera in Italy, one of the Earth’s highest-risk volcanoes.

“Calderas often look like a lawn covered in molehills”

Vents opened at the flank of a volcano are often used by just one eruption. All volcanoes may produce such one-time vents, but some do more than others. Their flanks are punctured by tens of vents whose alignment marks the locations where subsurface magma pathways have intersected the Earth’s surface.

At calderas, that is large cauldron-like hollows that form shortly after the emptying of a magma chamber in a volcanic eruption, vents may also open inside and on its rim. That is because they lack a summit to focus eruptions. “Calderas often look like a lawn covered in molehills,” says GFZ’s Eleonora Rivalta.

Most vents at calderas have only been used once. The resulting scattered, sometimes seemingly random spatial vent distribution threatens wide areas, presenting a challenge to volcanologists who draw forecast maps for the location of future eruptions. Such maps are also necessary for accurate forecasts of lava and pyroclastic flows or the expansion of ash plumes.

Vent forecast maps have so far been mainly based on the spatial distribution of past vents: “Volcanologists often assume that the volcano will behave like it did in the past,” says Eleonora Rivalta. “The problem is that often only a few tens of vents are visible on the volcano surface as major eruptive episodes tend to cover or obliterate past eruptive patterns. Hence, as mathematically sophisticated as the procedure can be, sparse data lead to coarse maps with large uncertainties. Moreover, the dynamics of a volcano may change with time, so that vent locations will shift.”

Succesful tests at the Campi Flegrei

Rivalta, a trained physicist, and a team of geologists and statisticians used volcano physics to improve the forecasts. “We employ the most up-to-date physical understanding of how magma fractures rock to move underground and combine it with a statistical procedure and knowledge of the volcano structure and history. We tune the parameters of the physical model until they match previous eruptive patterns. Then, we have a working model and can use it to forecast future eruption locations,” says Eleonora Rivalta.

The new approach was applied in southern Italy to the Campi Flegrei, a caldera close to Naples, which has a population of nearly one million. In the more than ten kilometres wide caldera, about eighty vents have fed explosive eruptions in the last 15,000 years. The approach performs well in retrospective tests, that is correctly forecasting the location of vents that were not used to tune the model, the researchers report.

“The most difficult part was to formulate the method in a way that works for all volcanoes and not just one—to generalize it,” Rivalta explains. “We will now perform more tests. If our method works well on other volcanoes too, it may help planning land usage in volcanic areas and forecasting the location of future eruptions with a higher certainty than previously possible.”

Reference:
E. Rivalta el al., “Stress inversions to forecast magma pathways and eruptive vent location,” Science Advances (2019). DOI: 10.1126/sciadv.aau9784

Note: The above post is reprinted from materials provided by Helmholtz Association of German Research Centres.

Faint foreshocks foretell California quakes

Earthquakes run in packs, but you can hear them coming, as noted in research from Los Alamos National Laboratory and California Institute of Technology.
Earthquakes run in packs, but you can hear them coming, as noted in research from Los Alamos National Laboratory and California Institute of Technology.

New research mining data from a catalog of more than 1.8 million southern California earthquakes found that nearly three-fourths of the time, foreshocks signalled a quake’s readiness to strike from days to weeks before the the mainshock hit, a revelation that could advance earthquake forecasting.

“We are progressing toward statistical forecasts, though not actual yes or no predictions, of earthquakes,” said Daniel Trugman, a seismologist at Los Alamos National Laboratory and coauthor of a paper out today in the journal Geophysical Research Letters. “It’s a little like the history of weather forecasting, where it has taken hundreds of years of steady progress to get where we are today.”

The paper, titled “Pervasive foreshock activity across southern Californa,” notes foreshocks preceded nearly 72 percent of the “mainshocks” studied (the largest quakes in a particular sequence), a percentage that is significantly higher than was previously understood.

Many of these foreshocks are so small, with magnitudes less than 1, that they are difficult to spot through visual analysis of seismic waveforms. To detect such small events requires advanced signal processing techniques and is a huge, data-intensive problem. Significant computing capabilities were key to extracting these new insights from the southern California Quake Template Matching Catalog, recently produced by Trugman and coauthor Zachary Ross, an assistant professor in seismology at Caltech. The template matching took approximately 300,000 GPU-hours on an array of 200 NVIDIA-P100 GPUs, involving 3-4 weeks of computing time for the final run. GPUs are special types of computers, optimal for massively parallel problems, as each GPU has thousands of cores, and each core is capable of handling its own computational thread. For perspective, a standard laptop has either 2 or 4 cores.The earthquake catalog is archived by the Southern California Earthquake Data Center.

The small foreshocks may be too difficult to discern in real time to be of use in earthquake forecasting. Another important issue is that quakes run in packs: they cluster in both space and time, so sorting the foreshocks of a particular quake out from the family of preliminary, main and aftershock rumbles of its fellow earth adjustments is no simple task.

An earthquake prediction tool is still far off, Trugman explains, and for humans who like a yes or no answer, a statistical analysis that suggests a quake’s probability is frustrating. But the potential insights and early warnings are improving, quake by quake.

Reference:
Daniel T. Trugman et al, Pervasive foreshock activity across southern California, Geophysical Research Letters (2019). DOI: 10.1029/2019GL083725

Note: The above post is reprinted from materials provided by Los Alamos National Laboratory.

Predicting seismic activity at fracking sites to prevent earthquakes

Aerial view of the hydraulic fracturing rig at Cuadrilla’s Preston New Road site. Credit: Matthew Hampson, Cuadrilla Resources Ltd
Aerial view of the hydraulic fracturing rig at Cuadrilla’s Preston New Road site. Credit: Matthew Hampson, Cuadrilla Resources Ltd

Scientists from the University of Bristol have found a more effective way to predict seismic activity at hydraulic fracturing sites, ensuring that potential earthquake activity remains within safe levels.

Hydraulic fracturing, or fracking, is a technique designed to recover gas and oil from shale rock by drilling down into the earth and injecting a mixture of water and sand at high-pressure, creating fractures that allow the gas or oil to flow out.

Like many other industries, such as coal mining, hydro-electricity and geothermal energy, fracking has in some cases been known to cause earthquakes.

In 2011 test operations near Blackpool had to be suspended after tremors of 1.5 and 2.2 magnitude were detected.

Investigations carried out after this concluded that it was highly probable that the drilling had caused the tremors and new ‘traffic light’ regulations were introduced at fracking sites across the country.

If earthquake magnitudes are below a certain level, then the injection can proceed as normal. If the earthquakes exceed a certain amber light magnitude, then the operator must proceed with caution by, for example, reducing the injection rate, pressure or volume. If the magnitude exceeds the red light magnitude, then the injection must pause.

Currently, there is little scientific basis for how the amber and red-light thresholds should be decided.

Lead author, Dr. James Verdon from the University’s School of Earth Sciences, said: “Many industries can create induced earthquakes, including both longstanding ones like coal mining and hydroelectricity, and newer ones like geothermal and hydraulic fracturing for shale gas.

“Our goal is to manage induced seismicity, ensuring that these industries conduct their activities in a safe manner, without posing a risk to nearby buildings and infrastructure.”

The Bristol-led research, published today in the journal Seismological Research Letters,shows that using microseismic data to make forecasts about expected seismicity can provide a far more effective approach than the simple traffic light scheme (TLS) system which is currently used.

Dr. Verdon added: “The TLS is a retroactive method. This means that the red-light threshold must be set far below the actual level we need to avoid, otherwise the operator would only stop after larger earthquakes have occurred.

“This is a problem because on the one hand operators may be required to stop their work even though everything is actually at a safe level. However, on the other hand if they set the red-light level too high then they may allow damaging events to occur.

“Our work is about developing and testing a model that can take the observations we have at an early stage in the operation and make predictions that are robust and accurate about what will happen as the injection proceeds, thus allowing an operator to make decisions while ensuring that any earthquakes remain within a safe level.”

All subsurface industries (for example, oil production, mining and geothermal) produce very small magnitude “microseismic events”—these are far too small to be detected even by sensitive instruments at the surface.

Instead, recording instruments called geophones are installed in monitoring boreholes that are within a few 100 meters of the injection point.

This allows them to pick up the pops and cracks of the rock as the fluid is injected. To give an idea of scale, a typical microseismic event might consist of a fracture the size of a dinner plate moving by less than a millimeter.

Dr. Verdon said: “These microseismic events can give us clues about whether the injection might be about to reactivate a larger fault and give us larger events, and it can give us clues as to what magnitude that event might be.

“So, our aim is to use the microseismic data, which is far too small to be felt by people at the surface and make models and predictions of whether the injection might be about to give us a larger event, and therefore should be stopped.”

The team developed a statistical model that takes the small-magnitude microseismic data and makes predictions about what magnitude the tremors might reach as injection continues.

Previously they tested their approach using past data from older sites. However, in this case they were analyzing live data from the Preston New Road site in Lancashire, and providing the operator, Cuadrilla, with their results, which they used to inform real-time decisions about how to proceed.

Dr. Verdon said: “Importantly, our modeling approach was successful—the magnitudes that actually occurred were in line with the magnitudes that we predicted from our model. This gives us confidence that our approach is robust and can be used for decision making at future injection sites.

“This approach has implications not only for today’s shale gas industry, but for future industries like geothermal energy and carbon capture and storage that are being planned in the UK.

Reference:
Huw Clarke, et al. Real-Time Imaging, Forecasting, and Management of Human-Induced Seismicity at Preston New Road, Lancashire, England. Seismological Research Letters, 19.06.2019.

Note: The above post is reprinted from materials provided by University of Bristol.

World’s smallest fossil monkey found in Amazon jungle

These fossil-rich sediments along the Alto Madre de Dios River in southern Peru have yielded hundreds of fossil teeth and bones, clues to what life in the Amazon was like 18 million years ago.
These fossil-rich sediments along the Alto Madre de Dios River in southern Peru have yielded hundreds of fossil teeth and bones, clues to what life in the Amazon was like 18 million years ago. Credit: Wout Salenbien, Duke University

A team of Peruvian and American scientists have uncovered the 18-million-year-old remains of the smallest fossil monkey ever found.

A fossilized tooth found in Peru’s Amazon jungle has been identified as belonging to a new species of tiny monkey no heavier than a hamster.

The specimen is important because it helps bridge a 15-million-year gap in the fossil record for New World monkeys, says a team led by Duke University and the National University of Piura in Peru.

The new fossil was unearthed from an exposed river bank along the Río Alto Madre de Dios in southeastern Peru. There, researchers dug up chunks of sandstone and gravel, put them in bags, and hauled them away to be soaked in water and then strained through sieves to filter out the fossilized teeth, jaws, and bone fragments buried within.

The team searched through some 2,000 pounds of sediment containing hundreds of fossils of rodents, bats and other animals before they spotted the lone monkey tooth.

“Primate fossils are as rare as hen’s teeth,” said first author Richard Kay, a professor of evolutionary anthropology at Duke who has been doing paleontological research in South America for nearly four decades.

A single upper molar, the specimen was just “double the size of the head of a pin” and “could fall through a window screen,” Kay said.

Paleontologists can tell a lot from monkey teeth, particularly molars. Based on the tooth’s relative size and shape, the researchers think the animal likely dined on energy-rich fruits and insects, and weighed in at less than half a pound—only slightly heavier than a baseball. Some of South America’s larger monkeys, such as howlers and muriquis, can grow to 50 times that heft.

“It’s by far the smallest fossil monkey that’s ever been found worldwide,” Kay said. Only one monkey species alive today, the teacup-sized pygmy marmoset, is smaller, “but barely,” Kay said.

In a paper published online July 23 in the Journal of Human Evolution, the team dubbed the animal Parvimico materdei, or “tiny monkey from the Mother of God River.”

Now stored in the permanent collections of the Institute of Paleontology at Peru’s National University of Piura, the find is important because it’s one of the few clues scientists have from a key missing chapter in monkey evolution.

Monkeys are thought to have arrived in South America from Africa some 40 million years ago, quickly diversifying into the 150-plus New World species we know today, most of which inhabit the Amazon rainforest. Yet exactly how that process unfolded is a bit of a mystery, in large part because of a gap in the monkey fossil record between 13 and 31 million years ago with only a few fragments.

In that gap lies Parvimico. The new fossil dates back 17 to 19 million years, which puts it “smack dab in the time and place when we would have expected diversification to have occurred in the New World monkeys,” Kay said.

The team is currently on another fossil collecting expedition in the Peruvian Amazon that will wrap up in August, concentrating their efforts in remote river sites with 30-million-year-old sediments.

“If we find a primate there, that would really be pay dirt,” Kay said.

Reference:
Richard F. Kay et al, Parvimico materdei gen. et sp. nov.: A new platyrrhine from the Early Miocene of the Amazon Basin, Peru, Journal of Human Evolution (2019). DOI: 10.1016/j.jhevol.2019.05.016

Note: The above post is reprinted from materials provided by Duke University.

Careful analysis of volcano’s plumbing system may give tips on pending eruptions

Pressure changes in the summit reservoirs of Kīlauea may help explain the number of earthquakes — or seismicity — in the volcano’s upper East Rift Zone.
Pressure changes in the summit reservoirs of Kīlauea may help explain the number of earthquakes — or seismicity — in the volcano’s upper East Rift Zone. Credit: USGS

A volcano will not send out an official invitation when it’s ready to erupt, but a team of researchers suggest that scientists who listen and watch carefully may be able to pick up signs that an eruption is about to happen.

In a study of Hawaii’s Kīlauea volcano, the researchers reported that pressure changes in the volcano’s summit reservoirs helped explain the number of earthquakes—or seismicity—in the upper East Rift Zone. This zone is a highly active region where several eruptions have occurred over the last few decades, including a spectacular one in 2018.

“We are interested in looking at the mechanisms that trigger seismicity at a very active and dynamic volcano, like Kīlauea Volcano in Hawaii,” said Christelle Wauthier, assistant professor of geosciences and Institute for CyberScience co-hire, Penn State. “There are several physical processes that can drive seismicity and, in this study, we were trying to find out which one was the most likely.”

According to Wauthier, the pressure changes that occur in the summit reservoir—an underground chamber hosting hot magma—causes stresses in the rocks and ground that surround the magma, even not at its immediate proximity. These stress changes can trigger small magnitude volcano-tectonic earthquakes, most of the time imperceptible to humans but that are picked up by the sensitive seismic equipment that monitor the volcano. This seismic activity, then, may better predict magma movements and resulting eruptions.

The researcher’s work challenges a previous theory that suggested the seismic activity in the rift zone was being triggered by the volcano’s gradual slip toward the sea. The southern flank of Kīlauea is gradually moving toward the ocean at about six centimeters a year.

While most people picture volcanoes violently erupting at their summits, Kīlauea is different because its sprawling system of underground tunnels and chambers where magma flows results in eruptions that can happen at various points miles from its summit. When magma travels out of these chambers and onto the Earth’s surface, it is called lava.

“Underneath, there is a conduit system that is extremely long—we’re talking 20 miles or so,” said Wauthier. “And it’s just like the plumbing in a house. A volcano’s plumbing system can be plugged up or blocked and that just might lead to an eruption.”

By better understanding the forces that are triggering seismicity, scientists monitoring seismic activity at other volcanoes could predict future eruptions more accurately, according to the researchers, who reported their findings in a recent issue of Geology. Because Kīlauea is one of the world’s most closely and densely monitored volcanic systems, it serves as a living laboratory to study volcanic activity that can be applied to study other volcanoes, added Wauthier, who worked with Diana C. Roman, staff scientist, Carnegie Institution for Science, and Michael P. Poland, scientist-in-charge, Yellowstone Volcano Laboratory, U.S. Geological Survey.

“While there are only a few volcanoes that are as highly instrumented as Kīlauea, which has a super-dense seismic network and GPS, so it’s very well-monitored, but other volcanoes are not monitored like that,” said Wauthier. “However, for volcanoes that have good seismic networks—and there are many of them—you can apply the exact same approach as this one to look if your volcano-tectonic seismicity—these small earthquakes—are due to magma being injected into a magma reservoir, or due to something else.”

The team used both seismic and satellite imagery data from mid- to late-2007 for the study. Seismic analysis was conducted with data collected on the upper East Rift Zone from the U.S. Geological Survey Hawaiian Volcano Observatory (HVO). Using information from global positioning satellites, also collected by HVO, the researchers were also able to analyze physical changes to the mountain’s shape and paying particular attention to ground surface deformations at the summit. They then looked at how these factors correlated with models of the stress changes caused by inflations and deflations of the summit reservoir.

By carefully analyzing movements to a volcano’s summit reservoir, researchers may be able to better predict when and where eruptions are likely to occur, then, according to the researchers. However, more work needs to be done, said Wauthier. Future research plans include looking at seismic activity and ground deformation data from other time periods of the volcano.

“We’ve been looking at the period in 2007, but that’s just a subset,” said Wauthier. “We could imagine just looking at a longer time period where we have other inflation-deflation events happening and see if we still conclude that same thing that it’s magma reservoir inflating that triggers the seismicity. It is likely that over the course of a long-term eruption like the 1983-2008 one, things are changing.”

Reference:
Christelle Wauthier et al. Modulation of seismic activity in Kīlauea’s upper East Rift Zone (Hawaiʻi) by summit pressurization, Geology (2019). DOI: 10.1130/G46000.1

Note: The above post is reprinted from materials provided by Pennsylvania State University.

Research could protect cities in active earthquake zones

U of T's Jeremy Rimando sets up Differential Global Positioning System (DGPS) survey equipment to measure the amount of displacement on the Las Chacras Fault in San Juan, Argentina.
U of T’s Jeremy Rimando sets up Differential Global Positioning System (DGPS) survey equipment to measure the amount of displacement on the Las Chacras Fault in San Juan, Argentina. Credit: Cesar Distante

A study from the University of Toronto Mississauga reveals new clues about an earthquake that rocked Argentina’s San Juan province in the 1950s. The results add important data about one of the Earth’s most active thrust zones and could help to protect cities in the region from earthquake damage in the future.

Jeremy Rimando, the lead author of the study and a Ph.D. candidate in the lab of study co-author Lindsay Schoenbohm, an associate professor in the department of chemical and physical sciences. Their study, published in the journal Tectonics, focuses on the La Rinconada Fault in the western central area of Argentina.

“This region is seismically active and is bound by many thrust faults where one block of land moves over top of another,” says Rimando, who has conducted field research at several sites in the area. “It’s an area that experiences frequent earthquakes.”

The 30-kilometre-long La Rinconada Fault line marks a tectonic transition zone where the thin-skinned crust of the Eastern Precordillera meets the thick-skinned crust of Sierras Pampeanas in the Andes mountain range. The area is arid and rocky, with steep gravel-strewn hills and terraces that reveal the displacement of the Earth’s surface as the land shifts and slips along the fault line.

San Juan, with a population of 500,000, lies 15 kilometres to the north in an area bounded by several faults, including La Rinconada. A 1944 earthquake devastated the city and killed 10,000 people. Eight years later, San Juan experienced another severe earthquake with a recorded magnitude of 6.8. Rimando’s data points to the La Rinconada Fault as a potential generator of the second quake.

To determine if La Rinconada might be connected to the 1952 quake, Rimando calculated the slip rate—how fast two sides of the fault are moving relative to one another—which can provide clues about how often an earthquake might occur.

“We looked at features that were displaced by the fault line,” he says. “A low slip rate is usually associated with a long recurrence interval.”

Long recurrence intervals can mean that earthquakes may not happen often, but when they do, they can be big because of the strain that has built up over time. “If the slip rate is moving slowly, it can eventually build up a large amount of strain, resulting in big earthquakes that take place on a less frequent basis,” he says.

“Our data shows that La Rinconada is moving slowly at 0.4 mm per year,” Rimando says. He notes that the La Rinconada slip rate is associated with earthquakes ranging in magnitude from 6.6 to 7.2. “This is within the range of the 1952 earthquake.”

“Further investigation is required to determine the timing and recurrence interval on this fault, but knowing the very specific likely magnitude is helpful for planners,” says Schoenbohm. “Buildings shake at different frequencies depending on the earthquake, so the most likely magnitude is more important to know than the maximum magnitude. Narrowing that range as much as possible is really useful.

He adds that researchers “can’t definitively say that this was the fault, but we have added to possible proof that it could be because of the similarity in magnitude of the 1952 earthquake and the possible earthquake magnitudes that this fault caused. This information could impact building locations, zoning requirements and engineering infrastructure.”

Reference:
Jeremy M. Rimando et al. Late Quaternary Activity of the La Rinconada Fault Zone, San Juan, Argentina, Tectonics (2019). DOI: 10.1029/2018TC005321

Note: The above post is reprinted from materials provided by University of Toronto.

1...525354...333Page 53 of 333

Related Articles

All
Facebook Instagram Linkedin TikTok Twitter Youtube
© © 2011-2024. All Rights Reserved.