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Understanding Earthquakes Caused by Hydraulic Fracturing

Fri, 08/07/2020 - 16:48

Induced seismicity is the process by which human activities trigger an earthquake. Hydraulic fracturing is a technique used by the petroleum industry to create small fractures in rocks with pressurized fluids, allowing for hydrocarbon production. Earthquakes caused by hydraulic fracturing are important to understand because of their impact as a geohazard, especially in areas that were previously seismically quiet. A recent article in Reviews of Geophysics presents the current state of knowledge on hydraulic fracturing induced seismicity. Here, one of the authors gives an overview of earthquakes induced by hydraulic fracturing, and how they are measured and managed.

How does hydraulic fracturing cause earthquakes?

It has been well known for decades that any injection of fluids in the subsurface has the potential to induce earthquakes. That said, hydraulic fracturing has only been recognized as a source of induced earthquakes very recently.

In the simplest conceptual model, fluids injected in a subsurface well must be connected to a fault via some permeable pathway. This allows the fluid pressure inside of the fault to increase during stimulation, hydraulically opening the fault. While hydraulically opened, the reduced ‘clamping’ force on a fault makes it more likely to slip.

The left panel displays a map of a hydraulic fracturing pad, with four wells and sixteen stages. The right panel shows a depth cross-section of one of the wells, with only the rightmost two stages intersecting a fault. Inset shows hydrocarbons entering the well bore, via the newly stimulated fractures. Credit: Ryan Schultz

How widespread, frequent, and large are hydraulic fracturing induced earthquakes?

Typically less than 1 per cent of hydraulically fractured wells cause induced earthquakes.Typically less than 1 per cent of hydraulically fractured wells cause induced earthquakes. This rarity appears to be related to the unlikely scenario of having all the correct geological conditions together in same place: tectonic, geomechanical, and hydrological. In other words, pressurized ‘frack’ fluids may cause earthquakes only if a stage happens to be connected to a susceptible fault.

Hydraulic fracturing induced earthquakes occur most frequently during the hydraulic stimulation processes. The process of stimulating all the stages in a single well/pad can take days or weeks, with only some (or none) of the stages causing earthquakes. If earthquakes do occur, the large majority happen within this timeframe. That said, earthquakes can linger after hydraulic fracturing has been completed – for periods of up to weeks or months. In some cases, the largest earthquakes have occurred after the well has been completed.

The largest earthquake caused by hydraulic fracturing was magnitude 5.7Observationally, the largest earthquake caused by hydraulic fracturing was magnitude 5.7 and occurred in the Sichuan Basin of China on 16 December 2018. Some plays in North America have hosted events larger than magnitude 4.0 as well (for example, Duvernay, Montney, and Eagle Ford).

The left panel displays a map of a hydraulic fracturing induced seismicity cases, with the date and magnitude of the largest earthquake in each region. The right panel shows the number of hydraulic fracturing wells stimulated in each region. Credit: Ryan Schultz

What are the main physical characteristics of hydraulic fracturing induced earthquakes?

The physical characteristics of these earthquakes appear to be no different than their natural counterparts. Hydraulic fracturing induced earthquakes exhibit the same characteristics that are often associated with natural earthquakes related to fluid-flow: swarm-like sequences, temporal correlation with the injection source, spatial proximity to the fluid source, and a linear relationship between injected volume and number of induced earthquakes. Because of that similarity, this type of induced earthquake provides an opportunity to better understand natural earthquakes related to fluid-flow.

How can scientists work effectively with industry to shape regulation and mitigation efforts?

The key to effective regulation and mitigation is transparency. In this regard, scientists can work towards building trusting relationships with industry, and specifically ones that facilitate the sharing of data openly.The key to effective regulation and mitigation is transparency. In this regard, scientists can work towards building trusting relationships with industry, and specifically ones that facilitate the sharing of data openly.

Certainly, the widespread dissemination of seismological data has been an important part of creating more comprehensive catalogues of earthquakes, by using various newly developing techniques. Examination of catalogues in numerous jurisdictions has begun to show some supporting evidence for when and where these types of earthquakes may occur.

This open sharing should also include geophysical, geological, and completion engineering data. Many of the unresolved (and unrecognized) problems with induced seismicity are multidisciplinary and would benefit from multiple perspectives.

What are some of the unresolved questions where additional research, data or modelling is needed?

Some of the important and currently unresolved questions are related to effective management – what sorts of conditions allow these earthquakes to occur and what sorts of operational changes can reduce their hazards? Greater knowledge on how to identify susceptible areas before fracking begins, combined with confidence in management tools when earthquakes occur can build significant trust with the general public. In one example, recent research efforts have been focused on better understanding the exact triggering mechanism responsible for reactivating susceptible faults; while the physical process that governs how faults begin to slip is still debated, fluid-flow along portions these faults appears to be an important factor.

—Ryan Schultz (rjs10@stanford.edu; 0000-0002-1796-9622), Stanford University, USA

Canada’s Rocky Mountain Forests Are on the Move

Fri, 08/07/2020 - 12:04

On an overcast day in 1927, surveyors Morrison Parsons Bridgland and Arthur Oliver Wheeler trekked up from the Owen Creek drainage in what is now Banff National Park to take a series of photos of the mountains along the North Saskatchewan River. They aimed to make the first accurate topographical maps of the region but in the process created something much bigger than they could have imagined.

Outwardly, the black-and-white photographs Bridgland and Wheeler took look like timeless shots of the Canadian Rockies. But new research using these old images is allowing a group of scientists with the Mountain Legacy Project to quantify a century of change in the landscape. Across the Canadian Rockies, forests are on the march.

The most recent results, published in the journal Scientific Reports, found tree lines extending higher and thicker than at the turn of the 20th century. These changes are helping scientists understand how ecosystems will continue to shift in a warming world.

A hilltop in the Crowsnest Forest Reserve, Alberta, Canada, taken in 2008 shows noticeably more trees than its counterpart image in 1931. Credit: Mountain Legacy Project, CC BY-NC 4.0 Onward and Upward

In the late 1990s, scientists rediscovered Bridgland and Wheeler’s glass plate survey images at Library and Archives Canada in Ottawa. The 140,000-plus high-resolution negatives were taken in the late 1800s and early 1900s to precisely map the Canadian Rockies. A century later, they offer a unique time capsule to understanding ecological change.

“[We] kind of immediately recognized what a goldmine this was for science and for ecology, because you have this systematic coverage, during a period of time that we have really few data points.”“[We] kind of immediately recognized what a gold mine this was for science and for ecology, because you have this systematic coverage, during a period of time that we have really few data points,” said Andrew Trant, lead author on the new paper and an ecologist at the University of Waterloo.

On a sunny summer day 89 years after Bridgland and Wheeler lugged their surveying equipment into the mountains along the North Saskatchewan, scientists returned—except this time they reached the 2,590-meter ridgeline by helicopter and brought a modern, high-resolution digital camera. Stepping in the surveyors’ exact footprints, they carefully aligned and shot new photos that precisely replicated originals.

Mountains in the Siffleur Wilderness Area, Alberta, show changes in snow and tree line between 1927 and 2009. Credit: Mountain Legacy Project, CC BY-NC 4.0

Using this technique, known as repeat photography, scientists trekked to summits and vantage points across the Canadian Rockies. They’ve now replicated 8,000 of these images, and comparisons with their counterparts taken a century ago are showing an evolving landscape. Notably, they’re showing a steady upward creep in tree line and forest density.

“Tree lines have long been considered the canary in the coal mine for climate change.”Tree lines—the upper limit in elevation or altitude beyond which trees cannot grow because of weather conditions—serve as visual boundaries of climate. Since tree lines evolve with shifts in weather patterns, they are useful in identifying how species are vulnerable to climate change.

“Tree lines have long been considered the canary in the coal mine for climate change,” said Melanie Harsch, a research affiliate at NOAA Fisheries who was not involved with the new work. “It is clear from the number of sites where trees have shifted from a shrub form to tree form, and tree density has increased, that climate change is impacting the Canadian Rockies.”

In addition to higher trees, the forests were also denser and contained fewer stunted, windswept trees known as krummholz.

Marching to the Beat of Climate Change

The new results agree with previous research documenting how a changing climate will dramatically redistribute the world’s forests. Previous studies have found that climate change will induce forest-thinning droughts in the tropics. Models also predict heat waves at the poles will increase the zone of subalpine forests. Other field studies have found a piecemeal response around the world, with half of the sites surveyed showing advances in tree line.

“Going into it, we sort of expected something similar, where we find some areas that would have been responding and some areas not,” Trant said. “And what we saw was a fairly uniform response.”

The scientists think the difference might stem from fact that this study, although covering a vast area of the Canadian Rockies, isn’t a global analysis that covers diverse ecosystems. However, the difference might also be due to the usage of a longer timeline than other studies.

Although rising tree lines can be good for some forest species, it comes at a price for others. The encroachment of subalpine ecosystems threatens species that have lived in formerly alpine habitats for thousands of years, including trees such as whitebark pine, flowers such as moss campion, and birds such as Clark’s nutcracker.

“There are a lot of species, big charismatic species that we know and love, that depend on the alpine,” Trant said. “Grizzly bears do a lot of their denning in the alpine area, and caribou spend time there in the winter.”

With tens of thousands of images yet to reproduce, the Mountain Legacy Project hopes to continue documenting change across the Rockies in the years to come. Scientists are also using the data set to assess changes due to glacial recession, fire, and human activity. The possible projects that can be done with the images, Trant said, “are endless.”

—Mara Johnson-Groh (marakjg@gmail.com), Science Writer

This Week: Thirsty Rice, Engaged Investors, and a Bulky Starship

Fri, 08/07/2020 - 12:02

India’s Food Bowl Heads Toward Desertification. This was an interesting (and alarming) read on the dangerous and long-term effects groundwater extraction could have on the state of Punjab, India. The continuous decline in groundwater levels could change not only the agricultural landscape but the economic landscape as well if drastic measures aren’t taken. —Anaise Aristide, Production and Analytics Specialist

 

Investors Launch Climate Plan to Get to Net Zero Emissions by 2050. A new framework offering guidance on climate-friendly investing sounds like a promising step toward decarbonizing the global economy. —Timothy Oleson, Science Editor

 

COVID-19 Lockdown Reduces Forest Fires in the Western Himalayas.

A massive forest fire in 2016 spreads across the hills of Nainital in Uttarakhand, India. Credit: Anup Sah/Barcroft Media/Getty Images

Here is another intriguing connection between COVID-19 lockdowns and our planet. Fewer forest fires occurred between March and May in India because people stayed home. I liked hearing the backstory of how scientists found this connection, and it makes me wonder whether this signal showed up in other countries too. —Jenessa Duncombe, Staff Writer

 

An Early Version of Starship Takes Its First Tentative Steps off Earth.

Amazing footage of the #Starship SN5 prototype making a 150-meter hop. The footage of the tiny tiny landing legs deploying is particularly fantastic. Credit: #SpaceX pic.twitter.com/xFf22DFdVP

— Rocket Rundown (@RocketRundown) August 5, 2020

I’m not quiet about the fact that I’m not a fan of SpaceX or its CEO, but I can recognize that this is a big achievement. Starship will eventually be the rocket that SpaceX uses to get to Mars, and this little hop was its baby steps in that direction. As Eric Berger put it, “Mars remains a long way away. But it seems closer tonight.” —Kimberly Cartier, Staff Writer

 

Thinking Zinc: Mitigating Uranium Exposure on Navajo Land.

Mallery Quetawki’s paintings utilize an Indigenous lens to communicate scientific findings to Native communities. Here her artwork depicts DNA damage through the Indigenous perspective of broken turquoise beads. Credit: Mallery Quetawki

This is just a great example of how the concept of geohealth incorporates both traditional Western science and Indigenous Knowledge. And art! —Caryl-Sue, Managing Editor

All Hands on Deck to Catch Ion Cyclotron Waves

Fri, 08/07/2020 - 11:30

A long-standing question about electromagnetic ion cyclotron waves (EMIC) in the Earth’s magnetosphere is the energies and rates at which they interact with the energetic electrons. A related question is how this interaction drives the precipitation of the energetic electrons into the upper atmosphere. Both questions are due to our lack of precise knowledge on the spatial scale size of EMIC activity regions.

Hendry et al. [2020] effectively turn the combination of two orbiting satellites (the NASA Van Allen Probe B and the Japanese Arase) and a ground sub-ionospheric Very-Low-Frequency (VLF) network into a powerful “magnetosphere-ionosphere observatory”.

By combining the observations from the different space- and ground-based platforms, the authors successfully determine the longitudinal extent of the EMIC source region. In the process, the combination demonstrates the growing power of such “heliospheric observatories” for tackling long-standing questions of the Sun-Earth system.

Citation: Hendry, A. T., Santolik, O., Miyoshi, Y., Matsuoka, A., Rodger, C. J., Clilverd, M. A., et al. [2020]. A multi‐instrument approach to determining the source‐region extent of EEP‐driving EMIC waves. Geophysical Research Letters, 47, e2019GL086599. https://doi.org/10.1029/2019GL086599

—Andrew Yau, Editor, Geophysical Research Letters

Will Ethiopia’s Disputed Dam Collapse?

Thu, 08/06/2020 - 12:32

Located downstream from the headwaters of the Abay, or Blue Nile, River in the Ethiopian Highlands, the Grand Ethiopian Renaissance Dam (GERD) is set to become Africa’s largest hydroelectric power plant. Still under construction, it is eventually expected to be able to generate more than 6,000 megawatts of electricity, which will provide power for about half of Ethiopia’s population and also allow the country to export electricity to neighboring nations. Ethiopia has argued it needs the dam’s electricity to modernize and grow.

The dam would affect the flow of the Nile to downstream residents in Sudan and Egypt and has become a major point of contention over water rights along the river. Scientists and engineers have also voiced concerns over the dam’s structural integrity because of its location in a mountainous terrain in an active tectonic region.

As satellite imagery shows the dam’s reservoir beginning to fill, Ethiopia, Sudan, and Egypt are negotiating to reach a political consensus on safe operational management to ensure health and sustainability in the region.

Damming Water in an Unstable Terrane?

The dam will ultimately create a reservoir with a capacity of 74 billion cubic meters of water. Since construction began in 2011, the project has been contentious among Ethiopia, Sudan, and Egypt, as 74 billion cubic meters of water is coincidentally what Sudan and Egypt negotiated in the 1959 Nile Waters Agreement. (That agreement’s allotment includes the flows of both the Blue Nile and the White Nile, which meet at a confluence near Khartoum, Sudan. The northward flow of the White Nile from Lake Victoria, a much lower volume than the Blue Nile, remains largely unimpeded.)

Studies have suggested that the dam is vulnerable to environmental hazards that may cause its collapse, not the least of which is seismicity.Some engineers have cited research suggesting that the dam is vulnerable to environmental hazards that may cause it to collapse. Seismicity is not the least of these concerns, as the project abuts one of the largest rift zones on Earth: the Great Rift Valley.

“Ethiopia is the most seismically active African country,” said Abbas Sharaky, a professor of geology at Cairo University. In the past 5 years, Ethiopia has had at least five earthquakes measuring from M4.0 to M5.3. “The dam itself and its reservoir are located on a fault.…[Part of the dam] is arched so that the concave side faces the lake, making it weak and vulnerable to collapse.”

Roger Bilham, a professor of geological sciences at the University of Colorado Boulder, mitigates some of these concerns. He said that the dam lies about 500 kilometers to the west of the Afar Triple Junction, a divergent plate boundary where the Nubian, Somali, and Arabian tectonic plates interact. Major earthquakes are rare beyond a distance of about 200 kilometers, Bilham said.

“Earthquakes are frequent along [plate] boundaries, but they tend to be rather small (less than M5) because the Earth’s crust is warmer and thinner than elsewhere and is therefore unable to sustain large damaging earthquakes,” Bilham added.

However, Hesham El-Askary explained, because the dam’s location is tectonically active, an excessive amount of pressure can cause the faults to slip. El-Askary is a professor of remote sensing and Earth system sciences at Chapman University in Orange, Calif. He is currently on leave with the Department of Environmental Sciences at Alexandria University, Egypt, where he is conducting research on natural hazards and the geology of the Grand Ethiopian Renaissance Dam.

“If you are constructing a huge water body like the reservoir of GERD, this causes a massive amount of pressure on the Earth’s crust,” leading to fault slippage and earthquakes, El-Askary said.

Bilham tentatively agreed. “I consider it very probable that earthquakes will indeed be induced by the GERD project, as for example occurred when the Kariba and Aswan dams were first filled.”

Representatives from the Grand Ethiopian Renaissance Dam and the Italian company Pietrangeli, which is implementing the project, did not respond to multiple calls for comment.

Other Risks

Landslides and flooding present other risks to the dam, according to published reports. The source of the Blue Nile is Lake Tana, which sits 1,788 meters above sea level in the Ethiopian Highlands. The river moves across steep and sometimes unstable slopes as it approaches the dam. Sharaky pointed out that “water falls heavily during the rainy season in July, August, and September, and the average of daily water flow is over 600 million cubic meters.”

Flash floods or unexpected water inflows from heavy rainfall—expected to increase with climate change—could raise water to levels the dam might not be able to handle, and trapped silt may make it even more vulnerable to collapse or spillover, researchers have noted. Over the past 40 years, existing dams in Sudan and Ethiopia have lost around half their capacity to siltation.

More Water, More Words

Concerns about the structural integrity of the Grand Ethiopian Renaissance Dam have become more urgent this summer as recent satellite imagery showed the reservoir behind the dam beginning to swell.

Water fills behind the Grand Ethiopian Renaissance Dam on 20 July 2020. Credit: Hailefida, CC BY-SA 4.0

The Ethiopian government denied purposely filling the reservoir, instead attributing rising water to heavy rains in the region. Earlier, Ethiopia’s water minister Seleshi Bekele had attributed rising water levels to the construction process of the dam, although not confirming whether the process involved testing the dam or actually storing water in the reservoir.

“The [Ethiopian] government has not stated explicitly whether the water backing up behind the dam is due to the remaining outlets being closed, or whether it is simply water accumulating behind the almost complete structure during the rainy season,” William Davison, an analyst with International Crisis Group, told the South China Morning Post.

In June and July, representatives from Egypt, Sudan, and Ethiopia engaged in two rounds of full negotiations surrounding the dam’s operation, one chaired by the United Nations and the other sponsored by the African Union. The African Union talks included a “minisummit” video conference hosted by African Union chair and South African president Cyril Ramaphosa and attended by leaders from the three countries, as well as officials from the Democratic Republic of the Congo, Kenya, and Mali.

At the minisummit, leaders agreed to resume full talks at an unspecified later date, focused on forming a legally binding agreement on the filling and operation of the dam.

—Mohammed El-Said (@MOHAMMED2SAID), Science Writer

6 August 2020: This article has been updated to clarify the expertise of Hesham El-Askary.

Fragrances in an Ice Core Tell a Story of Human Activity

Thu, 08/06/2020 - 12:16

Scented chemicals do more than perfume bodies. They often show up in sundry places such as soaps and other cleaning products to add a pleasant scent or mask unwelcome odors. A new study finds that these fragrant molecules can catch a ride on the wind to pile up in the ice of high, remote places.

Scientists have analyzed an ice core from Mount Elbrus in Russia for fragrances that settled on its snow during the 71 years from 1934 to 2005. Concentrations of fragrances in the later years were about 10 times higher than in the earliest years analyzed, according to research published in Scientific Reports. Trends in these scent molecules also carried a whiff of economic trends and crises.

The study makes a shift from “just checking if some place is polluted…to reconstructing the story of this pollution,” said Marco Vecchiato, an analytical chemist at the Institute of Polar Sciences in Venice, Italy. Vecchiato and his team analyzed the ice core for 17 fragrances and 17 polycyclic aromatic hydrocarbons, called PAHs for short. Released by combustion and industrial manufacturing, PAHs can provide an indication of human activity. Over the 7 decades analyzed, total concentrations of both PAHs and fragrances followed roughly the same pattern.

In the samples from the 1930s and 1940s, fragrance concentrations hovered around the lowest detected levels, which the scientists interpreted as background levels. Although this time period corresponds to World War II (a time when fragrance use may have dropped in Europe), these low levels may occur naturally, as flowers and plants make some of these fragrance molecules. Starting in the 1950s, the fragrance concentrations in samples began to grow and increased drastically starting around the year 2000.

That’s “clearly the Great Acceleration,” Vecchiato said, referring to the drastic increase in human impacts across Earth beginning in 1950.

Mount Elbrus, Europe’s highest peak, receives regular deposits from not only nearby central Europe and Russia but also the Middle East and the Mediterranean, Vecchiato said. The perfume haul may reflect the Anthropocene, a term that describes our current geologic era, dominated by human activity, the authors suggested.

As the Wind Blows

The scientists extracted the fragrances and PAHs from the ice core using a method that separates chemicals on the basis of their tendency to vaporize.

In all the samples, upward of 80% of the perfume belonged to one of three salicylates, chemicals that provide sweet, floral aromas. Humans use a lot of these chemicals for products such as soaps, shampoos, and fabric softeners. They’re fairly inexpensive to produce, Vecchiato noted. He said his team chose to analyze fragrances with a strong smell that can last for weeks or months.

But environmental chemist Staci Simonich, who was not involved with the work, suggests there were fragrances that last longer in the environment the team could have monitored. “There were some fragrance materials I’m surprised they didn’t look for,” she said, pointing to polycyclic musks, a class of fragrances used in personal care products, air fresheners, and detergents that would persist longer in the environment. Simonich works at Oregon State University in Corvallis and was not involved with the study.

The fragrances used in the study have relatively short lifetimes in the atmosphere, Simonich said. If you look at the trajectories of air masses around Elbrus, these fragrances likely come more from regional than global sources, she noted.

Taking the Pulse of Pollution

The Elbrus ice core may present a decades-long diary of fragrance use for the region, mirroring the ups and downs of what was once the Soviet Union.Still, the Elbrus ice core may present a decades-long diary of fragrance use for the region, mirroring the ups and downs of what was once the Soviet Union.

“It’s unusual to see such a clear indication of human output,” said Kimberley Miner, a climate scientist who has studied pollutants and chemicals in the Arctic and in snow. Miner, a scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and a professor at the University of Maine in Orono, was not part of this study.

Between 1964 and 1982, the Union of Soviet Socialist Republics (USSR) experienced what was called the Era of Stagnation. Economic growth didn’t stall entirely but was very slow. Perfume concentrations increased slightly from the 1930s baseline, but levels dipped during the economic slowdown.

Later, between 1989 and 1991, the Soviet Union collapsed, sending many into poverty. Lean times continued through the 1990s in former Soviet republics, including Russia. Both fragrance and PAH levels in the Elbrus ice core mirror these hard years before taking off in the 2000s. “You see this abrupt development…after the fall of the USSR,” Miner said, “so it provides a really beautiful case study.”

Miner wondered whether other contaminants, such as microplastics and certain flame retardants, follow this pattern in the region. This study provides yet another example, she said, “that everything that we use in our daily lives, everything that we use in our industrial processes, finds its way into the wider environment.”

—Carolyn Wilke (@CarolynMWilke), Science Writer

A New Perspective on a Classic Climate Conundrum

Thu, 08/06/2020 - 11:30

In the present-day climate, the Atlantic is saltier than the Pacific because more freshwater is exported from the Atlantic to the Pacific than the other way around. The difference in salinity between the two ocean basins shapes the deep overturning circulation of the ocean, which is associated with differences in buoyancy, or density, determined by temperature and salinity.

Because the Atlantic is saltier, deep convective sinking occurs in the North Atlantic, and the loop described as a “conveyor belt” is closed by slow upwelling in the North Pacific. Previous studies highlighted the tropical pathway for freshwater transport from the Atlantic to the Pacific: easterly winds, that is, winds blowing humidity from the east across Central America. However, using a Lagrangian model, Dey and Döös [2020] show that westerly winds, which prevail in mid-latitudes and blow across Eurasia, actually contribute about 60 percent of transport, significantly more than previously thought.

Citation: Dey, D., & Döös, K. [2020]. Atmospheric freshwater transport from the Atlantic to the Pacific Ocean: A Lagrangian analysis. Geophysical Research Letters, 47, e2019GL086176. https://doi.org/10.1029/2019GL086176

—Alessandra Giannini, Editor, Geophysical Research Letters

“Mushballs” May Drive Ammonia Transport on Jupiter

Wed, 08/05/2020 - 17:56

Observations made by NASA’s Jupiter-orbiting Juno spacecraft have revealed substantial and unexpected depletions of ammonia in the planet’s atmosphere. Although some evidence for this anomaly can be seen from telescopes on Earth, Juno’s close-up microwave measurements show that the depletion of ammonia—a trace, but important, cloud-forming component in Jupiter’s skies—extends far deeper than previously known, down to a hundred kilometers below the clouds, and exhibits a striking dependence on latitude.

Radial profiles produced near Jupiter’s equator show ammonia levels of about 360 parts per million regardless of depth in the atmosphere, whereas profiles made at Jupiter’s midlatitudes reveal upper atmospheric abundances as low as 120 parts per million that increase only slowly with depth. Previously proposed mechanisms, such as direct transport of ammonia by updrafts and circulation in Jupiter’s famous atmospheric bands, do not explain this variance.

In a pair of new papers, Guillot et al. postulate a new transport mechanism—water-ammonia hail—and show that it explains Juno’s microwave data and is linked to the presence of large storms. Water is relatively scarce near Jupiter’s cloud tops, but previous research has suggested that powerful storms can uplift substantial amounts in the form of micrometer-sized ice crystals. The authors calculate that as these crystals rise, they absorb gaseous ammonia, increasing in mass and density and partially liquifying to become the slush-like cores of hail particles. (In an accompanying study of Juno data in Nature, Becker et al. report detections of lightning—and thus confirm the presence of liquid—in the region of the atmosphere where these slushy “mushballs” are thought to form.)

Continuing their ascent, the mushball cores can accumulate additional layers of ice, growing to millimeter and centimeter sizes. Once they become too heavy to remain aloft, the hail balls—now up to 10 centimeters in diameter—reverse course, losing outer layers to evaporation as they fall. But the cores, now denser and cooler than when they first formed, can penetrate far deeper into the atmosphere than where the ice crystals and ammonia gas originated. Because fully grown hail balls can contain up to 30% ammonia, the result is efficient transport of ammonia that may explain Juno’s observations.

Unlike Earth, Jupiter has no solid surface, so these hail particles continue falling until they either fully evaporate or reach neutral buoyancy in the surrounding gas. The combination of the cores’ composition and the depth they ultimately reach may thus help scientists untangle details of Jupiter’s internal structure. (Journal of Geophysical Research: Planets, https://doi.org/10.1029/2020JE006403 and https://doi.org/10.1029/2020JE006404, 2020)

J. Casey Moore (1945–2020)

Wed, 08/05/2020 - 13:33

Casey Moore, cocreator and leader in the field of subduction zone science, passed away in March. Casey was recognized internationally for his contributions to the geology of subduction zones and in understanding the evolution of sediments as they become rocks in the seismogenic zone, where earthquakes originate. He was awarded fellowships from AGU (2013) and the Geological Society of America (1984), and he received the Francis P. Shepard Medal for Marine Geology, awarded for “excellence in marine geology,” from the Society for Sedimentary Geology in 2013. The Geological Society of Japan recognized his outstanding contributions with its International Prize in 2011.

Arriving at the Cusp of a Revolution

Casey’s findings supported the hypothesis of plate tectonics and provided new insights on the growth of continents.Casey spent his youth enjoying the beaches of Southern California. He arrived at Princeton for graduate work in 1968—just as Harry Hess, Jason Morgan, and Fred Vine, all at Princeton, were developing and refining the theory of plate tectonics. He completed nearly 90 days of fieldwork in the summer of 1970 on Sanak and Shumagin Islands, which sit on the seaward edge of Alaska’s Aleutian Arc, where the Pacific plate subducts beneath the North American plate. As a result of this fieldwork, Casey confirmed that deep-sea sediments from the subducting oceanic plate had been deformed and added to the upper plate.

These findings supported the hypothesis of plate tectonics and provided new insights on the growth of continents. The results were published a year after Casey graduated from Princeton in 1971, as he was starting his teaching career at the University of California, Santa Cruz (UCSC), setting the stage for 5 decades of research on modern and ancient subduction zones.

Subduction at Sea

Casey distinguished himself as an exceptional field geologist as well as a major leader in ship-based research. He led or participated in dozens of field-based expeditions to exhumed accretionary prisms—wedges of sedimentary material that accumulate at the interface between two colliding tectonic plates—around the world. He was a cochief or science party member on more than 20 research cruises in Barbados, Cascadia, Sumatra, Alaska, Japan, the Indian Ocean, and the Gulf of Mexico.

Casey Moore (right) and Tim Byrne on Kodiak Island, Alaska, in 1983. Photo: Sarah Roeske

His participation and leadership in ocean drilling were integral in ushering in a new era of scientific drilling to study subduction zones, beginning with Legs 25 and 31 of the Deep Sea Drilling Program in 1972 and 1973. Casey was also reportedly the first person to hold a Brunton compass with clinometer to the window of the Alvin submersible so that he could measure the dip of the thrust faults revealed in submarine canyons offshore Oregon.

Casey had the rare talent of being able to seamlessly integrate shipboard data, core descriptions, and geophysics with field observations.Casey had the rare talent of being able to seamlessly integrate shipboard data, core descriptions, and geophysics with field observations from exhumed rocks. He contributed formative concepts on the interaction of fluids and clays during deformation; these concepts underpin our understanding of fault strength in shallow subduction zones. His research was the first to demonstrate the importance of rapid effective burial of subducting sediments in controlling pore pressure and changes in rock strength. He also developed or adapted methods of studying stress, strain, volume change, and the formation of penetrative fabrics in rocks (patterns of mineral orientation that form when the sediments or rocks are deformed) to the unexplored, water-rich settings of shallow subduction zones.

Casey even applied his interest in fault fluids and deformation in his own backyard, where he characterized the deformation of sediments saturated with water and hydrocarbons along the San Gregorio Fault in California. Combining insights from subduction and strike-slip plate boundary faults, Casey’s understanding that the sedimentology and structural evolution of trench sediments were intrinsically coupled and needed to be studied as integrated processes is still influential and relevant today.

A Thirst for Knowledge

Casey’s leadership was exemplified by what he did not do as much as by what he did. It was never Casey’s style to promote himself or to patrol his scientific turf. He enjoyed a healthy discussion and would marshal evidence from geology, hydrogeology, geophysics, and geochemistry to support his positions, always good-naturedly.

Casey Moore (right), Christie Rowe (left), and Francesca Meneghini on Kodiak Island, Alaska, in 2006. Photo: Asuka Yamaguchi

Throughout his career, he kept adding to his breadth of abilities. He regularly dug in deep to learn new methods and techniques so he could add new sources of data to his lifelong synthesis of subduction processes. He did so with remarkable humility, studying appendixes of methodological details and consulting experts, including graduate students astounded that he had approached them for help. He never became entrenched in his past interpretations, and he took joy in seeing them overturned by new insights from his own or others’ work.

His excitement for discoveries and enthusiasm for fieldwork inspired many young scientists. He routinely turned over his best project ideas to his advisees and gave his students complete creative control. He avoided recognition until he couldn’t find an escape, at which point he accepted it graciously. He always focused on the importance and fun of understanding tectonic processes through observations of all kinds.

By example, he taught his students to value interdisciplinarity, talk to everyone, and listen carefully to all ideas. Casey’s legacy shines through the successes of his advisees in a broad range of fields. His students and postdocs are found in the leadership of the International Ocean Discovery Program, heading major research institutes and geoscience departments, winning teaching awards at undergraduate-serving institutions, and starting their own companies.

A Lasting Legacy Casey Moore aboard the drilling vessel Chikyu during the Integrated Ocean Drilling Program’s Expedition 314 and the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) in the fall of 2007. Photo: Harold Tobin

Casey spent his entire academic career at UCSC, where he served as chairman of the Earth Sciences Board from 1984 to 1986. He was a distinguished lecturer for the Joint Oceanographic Institutions/U.S. Science Advisory Committee (JOI/USSAC, 1992–1993) and NSF MARGINS (2006–2008), and he served on the Chikyu +10 Steering Committee and the Chikyu IODP Board for the Integrated Ocean Drilling Program (now the International Ocean Discovery Program) and the Japanese deep-sea drilling vessel Chikyu. He served as associate editor for Tectonics and the Geological Society of America Bulletin. He was also an editorial board member for Geology, Geofluids, and Progress in Earth and Planetary Sciences. In 1999, he was recognized as an Outstanding Alumnus by the Department of Geological Sciences at the University of California, Santa Barbara, his undergraduate alma mater.

Casey died of complications related to non-Alzheimer’s dementia. He spent his last few weeks in the hands of Westwind Memory Care in Santa Cruz. His passing sent waves of love and sadness around the globe, as former students and colleagues reached out to each other with memories and photos. We authors, who were among his first and last Ph.D. students, appreciated the opportunity to honor Casey’s contributions to science and to the community at the AGU Fall Meeting 2019 with a “Giants of Tectonophysics” presentation, attended by members of his family.

Casey will be greatly missed, but his honesty and generosity, and his deep enthusiasm for geology, for science, and for understanding, will live on through his family, friends, and former students.

—Christie Rowe, Department of Earth and Planetary Sciences, McGill University, Montreal; and Tim Byrne (tim.byrne@uconn.edu), Department of Geosciences, University of Connecticut, Storrs

Measuring, Monitoring, and Modeling Ecosystem Cycling

Wed, 08/05/2020 - 11:38

The terrestrial biosphere—the regions of Earth’s land surface that support life—continuously exchanges carbon and water with the atmosphere. Plants capture atmospheric carbon dioxide (CO2) through valves in their leaves, converting the gas into compounds for growth through photosynthesis and respiration. Meanwhile, water moves from the ground through plant roots and stems to leaves, where it is gradually released, or transpired, back into the atmosphere.

Changing climate conditions may shift the balance of ecosystem carbon and water cycles by altering plant processes like photosynthesis, transpiration, and respiration.Globally, the biosphere removes about 30% of the CO2 emitted by human activities from the atmosphere and returns almost 40% of the rainfall it receives back to the atmosphere through transpiration. However, changing climate conditions may shift the balance of ecosystem carbon and water cycles by altering plant processes like photosynthesis, transpiration, and respiration.

Each ecosystem responds uniquely to warmer temperatures, altered precipitation patterns, and higher atmospheric CO2 [Baldocchi et al., 2018]. For example, one black spruce forest in Alaska that once removed carbon from the atmosphere has become a net carbon source. As autumn temperatures have warmed and the rate of decomposition has increased (thereby increasing respiration, which releases CO2), the forest now releases enough carbon to the atmosphere to outpace an increase in photosynthesis (which takes up CO2) [Ueyama et al., 2014]. In contrast, forests in the U.S. Midwest and Northeast increased their removal of carbon from the atmosphere relative to the amount of water they lost through transpiration, thanks to increasing levels of atmospheric CO2, which allow plants to capture carbon more efficiently [Keenan et al., 2013].

The View from Three Perspectives

To detect these trends and identify their biophysical and environmental drivers, scientists measure and monitor ecosystem carbon and water exchanges, or fluxes, in diverse ecosystems around the world. One source of data in the Western Hemisphere, the AmeriFlux network, consists of tower-based sensors that collect in situ eddy covariance measurements of the turbulent exchange of gases between Earth’s surface and the atmosphere. This network started out with just 15 sites in 1996. Through grassroots efforts by individual scientists, the network has grown to comprise more than 300 stations located in every major ecosystem of North, South, and Central America [Novick et al., 2018]. Many of these measurement sites have recorded data for more than 2 decades, enabling scientists to leverage this resource to examine how ecosystems are changing over time [Baldocchi, 2020].

The combination of long measurement records, new remote sensing products, and advances in ecosystem modeling has enabled researchers to investigate previously intractable questions.The ground-based measurements from AmeriFlux are complemented by airborne and satellite remote sensing products, which monitor larger areas and expand the spatial coverage afforded by the monitoring network. Scaling up ground station measurements helps bridge the spatial discrepancy between site observations and models that simulate ecosystem processes at much coarser resolutions.

These ecosystem models represent the scientific community’s collective understanding of ecosystem functioning developed over decades of discovery [e.g., Lawrence et al., 2019; Zhu et al., 2019]. They are useful tools for testing hypotheses and refining our understanding of ecosystem functioning. Ecosystem models can be used to disentangle the ways that different components of the ecosystem are responding to changing environmental conditions and to project how those changes may modify carbon and water cycling under future climate conditions.

The combination of long measurement records, new remote sensing products, and advances in ecosystem modeling has enabled researchers to investigate previously intractable questions and to identify important processes driving observed ecosystem responses to changing environmental conditions. Four key areas of research emerged from discussions at a workshop held last October at the Lawrence Berkeley National Laboratory in Berkeley, Calif., and organized by the RUBISCO-AmeriFlux Working Group. Reducing Uncertainty in Biogeochemical Interactions through Synthesis and Computation (RUBISCO) is a U.S. Department of Energy–sponsored project focusing on analysis of carbon-climate interactions. Here we highlight each of the four areas.

Ecosystem Trend Spotting 

As of 2019, the AmeriFlux network included 63 sites that have been operating for more than 10 years (Figure 1). As AmeriFlux and similar sensor networks continue to collect data, the length of ecosystem carbon and water flux records grows. With these records, scientists are beginning to detect trends in ecosystem metabolism and to disentangle the multifaceted responses of ecosystems to elevated CO2, climate change, and human disturbances [Baldocchi, 2020].

Fig. 1. Histograms showing the distribution of the length of records for AmeriFlux sites in 2000, 2010, and 2019. Data are from AmeriFlux.

Several aspects of ecosystem functioning are essential to changes in terrestrial carbon, water, and energy budgets: water use efficiency, light use efficiency, net ecosystem exchange, and evapotranspiration (ET). To quantify trends in these ecosystem functions, we used the newly available standardized version of the AmeriFlux data set processed using the Open Network-Enabled Flux (ONEFlux) pipeline, a code package compatible with the global FLUXNET2015 data set [Pastorello et al., 2017]. The resulting ONEFlux data set was developed to remove a bottleneck that has long hindered the syntheses of AmeriFlux data derived from multiple sites [Novick et al., 2018], and it contains more site-years and up-to-date observations in the Americas than the widely used global FLUXNET2015 data set.

Scientists with expertise in in situ measurements, partitioning evaporation and transpiration, and land modeling are collaborating to quantify trends in ET, attribute environmental drivers of the observed trends, and model projected future changes. Having diverse perspectives within the team helps advance novel approaches and build collaborations among scientists at different career stages.

Ecosystem Responses to Extreme Events

To understand how ecosystems may respond to changing climate conditions, we can look at how these ecosystems fared under extreme weather conditions in the past. If models accurately simulate how ecosystems responded to past heat waves, dry spells, and flooding events, then these models can be used to project how future climate conditions may affect ecosystems and alter carbon and water exchanges. Long-running AmeriFlux measurements have captured decades of weather events, providing a valuable test bed for evaluating model performance.

Improving model representations of ecosystem carbon and water cycling during extreme weather events improves model projections of future ecosystem vulnerabilities, which can inform conservation efforts.Prior to the workshop, researchers from nine modeling centers around the country performed simulations at AmeriFlux sites using observed local weather and site characteristics. We compared model simulations to observed measurements from a wide range of ecosystems, including a piñon-juniper forest in New Mexico, a maple-poplar forest in Indiana, and an oak savanna in California. Overall, various ecosystems had diverse responses to extreme weather events. The maple-poplar forest slowed photosynthesis to conserve water during a severe drought event in 2012. On the other hand, the New Mexican piñon-juniper forest used up available soil moisture for photosynthesis quickly after summer rain events, as is typical for ecosystems that must take full advantage of infrequent rainstorms.

Some models captured ecosystem responses better than others; by comparing the mathematical representations of plant processes in models that perform well, researchers aim to improve our understanding of plant functioning. Improving model representations of ecosystem carbon and water cycling during extreme weather events improves model projections of future ecosystem vulnerabilities, which can inform conservation efforts.

Untangling Contributions to Carbon Exchange

Two main components influence the net exchange of carbon between ecosystems and the atmosphere: gross primary productivity (GPP) via photosynthesis and ecosystem respiration (Reco). The net ecosystem exchange (NEE) measured at the AmeriFlux sites is partitioned into GPP and Reco components by extrapolating statistical relationships either between nighttime NEE and temperature or between daytime NEE and light. Daytime and nighttime partitioning methods may yield different results, both of which are equally plausible. Without independent complementary measurements, it is challenging to evaluate the partitioning of GPP and Reco from these two methods. When such complementary measurements are integrated with eddy covariance observations, they increase confidence in the AmeriFlux GPP and Reco estimates (Figure 2).

Fig. 2. Estimates of the contribution of gross primary production (GPP) to net ecosystem exchange (NEE) of carbon can be evaluated and improved by incorporating complementary measurements such as soil respiration (Rs), incoming shortwave radiation (SWIN), and vegetation indexes (VI) like the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), near-infrared reflectance of vegetation (NIRv), and solar-induced fluorescence (SIF).

Soil respiration measurements such as those from the continuous soil respiration database (COSORE) serve as one source of measurements to complement eddy covariance data. Reco is composed of autotrophic respiration (Ra) by plants making their own food and heterotrophic respiration (Rh) by microbes gathering food from plant or animal matter. Soil respiration (Rs) is composed of Rh and the belowground (root) fraction of Ra. Soil respiration can be used to estimate GPP by constraining the belowground fraction of Ra and the autotrophic fraction of Rs.

Another complementary data source, satellite-derived vegetation indexes, serves as a proxy for light interception by the tree canopy. These indexes appear to be promising alternatives to direct flux measurements for GPP estimation [Huang et al., 2019]. Additionally, solar-induced chlorophyll fluorescence, a measure of energy flux emitted from plants, can track the seasonality of GPP at high spatial and temporal resolution [Magney et al., 2019]. Together, GPP and Reco estimated from multiple data sources will improve partitioning methods and make estimates more robust.

Scaling Up from Sites to Ecosystems

Eddy covariance flux observations collected across AmeriFlux sites provide valuable data for confronting, diagnosing, and constraining the representation of ecosystem carbon, water, and energy cycle processes in terrestrial ecosystem models. However, these site-based observations are not representative of the entire ecosystem where they are located. The spatial mismatch with regional-scale models complicates model benchmarking and improvement [Metzger, 2018]. Spatial scaling of site-based flux observations to regional landscapes using multiscale observations is critical to reducing uncertainties in flux estimates and constraining models.

The Sun sets behind an AmeriFlux eddy covariance observational station located at Lost Creek in Wisconsin. Credit: AmeriFlux

At the workshop, scientists combined bottom-up and top-down approaches for scaling fluxes across space. In the bottom-up approach, a recently developed environmental response function technique involving a data assimilation system is applied [Metzger, 2018]. The complementary top-down approach uses airborne measurements from NASA’s Atmospheric Carbon and Transport (ACT)–America campaign, which measured atmospheric carbon and water concentrations during five campaigns over three regions in the United States between 2016 and 2019. ACT-America took spatially sparse, but frequent, airborne measurements that provide regional-scale constraints on carbon and water exchange rates [Schuh et al., 2019]. The proposed combination of bottom-up and top-down approaches provides spatially explicit observations enabling regional-scale evaluation of carbon, water, and energy cycles in ecosystem models.

A Collaborative Working Session

Last October’s workshop inverted the standard meeting format: Rather than coming together to present results, attendees met virtually prior to the workshop to determine the most pressing questions and assemble tools and expertise. By the time the workshop kicked off, scientists were ready to start tackling the questions together.

This workshop format was a highly effective model for advancing collective objectives in a diverse research community, bringing together scientists from a wide range of disciplines, career stages, and perspectives. By pooling resources, they made rapid progress toward identifying and advancing some of the most pressing questions in the field. And working together in person helped integrate early-career scientists into the community and form lasting collaborations.

Downhill from Here: Landscape Positions and Greenhouse Emissions

Wed, 08/05/2020 - 11:30

Permafrost environments are under threat from warming. As permafrost thaws, microbial activity leads to significant production of greenhouse gases. Understanding the scales at which the production of these gases varies in permafrost environments is an important piece of understanding the future of global carbon stocks, as a third of Earth’s carbon is in Arctic soils.

Philben et al. [2020] compare landscape positions using a fusion of field measurements and controlled laboratory experiments. Measuring carbon dioxide (CO2) and methane (CH4) production, at varied pH and nutrient availability, the authors find that toeslope positions are associated with significantly more production of these greenhouse gases. A combination of higher pH from mineral leaching and more abundant nutrients for microbial growth, were found to drive the increased production.

These findings demonstrate the link between landscape position and production of greenhouse gases, and as such, should be considered when trying to understand the impacts of future permafrost thawing.

Citation: Philben, M., Taş, N., Chen, H., Wullschleger, S.D., Kholodov, A., Graham, D.E. and Gu, B. [2020], Influences of Hillslope Biogeochemistry on Anaerobic Soil Organic Matter Decomposition in a Tundra Watershed. Journal of Geophysical Research: Biogeosciences, 125, e2019JG005512. https://doi.org/10.1029/2019JG005512

—William M. Hammond, Associate Editor, JGR: Biogeosciences

Solar Mandates in Sacred Groves

Tue, 08/04/2020 - 11:54

India has an ambitious target to generate 175 gigawatts of renewable energy by 2022. Lands chosen to generate the solar component of this energy goal include the Thar Desert, a huge ecosystem in northwest India mostly located in the state of Rajasthan.

Like many deserts, the Thar is often inaccurately described as “barren” or a “wasteland” instead of a productive ecosystem with thriving niches. Among other habitats, the Thar is dotted by orans, small patches of forested landscape.

For generations, local communities have considered orans sacred groves. Orans usually host temples with local deities and are also used as grazing lands, especially during the dry months between April and June and October and December.

Earlier this summer, demolition and construction equipment was brought in to cut down trees and make way for high-tension power transmission lines in a 9,634-hectare oran in a village called Sanwtha.

There are about eight villages around the oran, each with about 50–60 people, most of whom are herders. Locals have honored the oran as sacred for at least 600 years, and during this time, they have never cut any trees or tilled the land, only allowing their herds to graze. Today, an estimated 5,000 camels and more than 200,000 goats and sheep depend on the oran for grazing.

These five camels are a tiny fraction of the 5,000 that Rajasthani herders maintain in orans in the Thar. Credit: Sumer Singh

The power lines will connect to a 700-megawatt grid service station (GSS) located just a few meters outside the oran. The station already supports windmills installed in the area, explained Parth Jagani of the Ecology, Rural Development and Sustainability (ERDS) Foundation, a Rajasthan-based conservation organization.

The GSS will also support a large solar park. Although the park will be installed outside the oran, many residents worry it is still a threat.

“Even today they are cutting down trees and plants to install power lines in a few areas inside the oran,” explained Sumer Singh, a herder from Sanwtha.

Singh noted that many such power lines crisscross the landscape and, in addition to destroying grazing grounds, there have been numerous instances when wildlife, birds in particular, have come in contact with the lines and have either died or been injured. “Just 15 days ago, a tawny eagle was electrocuted and injured,” he said.

In addition to tawny eagles, the Sanwtha oran is host to a variety of wildlife, including the critically endangered great Indian bustard, of which there are only about 250 mature adults left in the world. Numerous migratory birds, including Siberian species that fly over during winter, are frequent visitors. The habitat is also home to the chinkara (Indian gazelle), desert fox, and nilgai (huge Asian antelope also known as blue bulls), among dozens of species endemic to the Thar.

When asked about the ill effects of high-power transmission lines on local wildlife, Tulasa Ram, a tehsildar (administrative official) of the Fategarh area that comprises Sanwtha, dismissed such concerns. He said “[power] lines have to be placed if electricity has to be produced…accidents happen on roads too…animals die but we cannot stop developmental work because of this.”

Power Struggle

Currently, Bhadla Solar Park near Jodhpur, Rajasthan, is India’s largest solar facility, with an installed capacity of 2.25 gigawatts. “What will come up near [the Sanwtha oran] is very likely bigger than [Bhadla],” explained Sumit Dookia, a wildlife biologist at Guru Gobind Singh Indraprastha University in New Delhi and scientific adviser to the ERDS Foundation.

The dilemma faced by Indian villages over solar power echoes a similar conflict over wind power.The dilemma faced by Indian villages over solar power echoes a similar conflict over wind power. Dookia noted that when the state government started building wind energy parks back in 2001, villagers started demanding that their lands be saved.

Jagani agreed. “In 2004, about 23,000 bighas [3,690 hectares] of the land were recorded as orans in governmental records,” he said. When the government designated land as an oran, it was recognized as a sacred space in the form of village commons.

In response to queries about how the government has the authority to indulge in work on land that belongs to the community, Ram denied claims that the community holds rights over these lands. “All of the land belongs to the government,” he said.

But that statement is false. Governmental records show almost 3,700 hectares (23,000 bighas) have, in fact, been recorded in the name of the local deity. Such an ownership is unique in the sense that “deities cannot sell the land and the local community has grazing rights and the right to respect the land,” Dookia explained.

In 2018, the Supreme Court of India ordered that sacred groves of Rajasthan are to be treated as “deemed forests.” Deemed forests, which account for about 1% of land in India, are tracts of land (which may include deserts and grasslands) that have not been officially recognized as federally or municipally protected forests in historic records. Designating the orans as deemed forests “is like the second layer of protection to the land,” Dookia noted.

Nevertheless, power lines still cut through the orans. Additionally, nearby orans still held by the government “are being allotted to energy companies which are felling age-old trees, engaging in construction work, and damaging local ecology,” Dookia said.

Villagers around the Sanwtha oran fear a similar outcome. “We want the land to be given back to us,” Singh said.

—Rishika Pardikar (@rishpardikar), Science Writer

A GOLDen Way to Study Space Weather

Tue, 08/04/2020 - 11:48

One of NASA’s newest missions, called Global-scale Observations of the Limb and Disk (GOLD), is revealing how the upper fringes of Earth’s atmosphere affect space weather by observing atmospheric airglow in unprecedented detail. In a new study, Eastes et al. report early data from the mission, including observations of how neutral gases in the thermosphere interact with charged particles in Earth’s ionosphere and how these interactions respond to disturbances in Earth’s magnetic field caused by solar storms hazardous to critical infrastructure.

GOLD was launched into geostationary orbit in 2018 aboard a communications satellite and began making routine observations in October of that year. The instrument measures wavelengths of ultraviolet light emitted by excited atoms and molecules at altitudes of 100 kilometers or higher when they relax to lower energy levels. These emissions phenomena include aurora as well as much fainter yet steady airglow across the night sky.

From its vantage over the western Atlantic, GOLD observes airglow across the full disk of Earth every 30 minutes, as well as in the thin ribbon of atmosphere, called the limb, surrounding it. Occasionally, when a star passes behind Earth, the instrument takes advantage of the starlight passing through the atmosphere to measure the density of oxygen in the air at different altitudes based on the light it absorbs. GOLD also collects valuable temperature readings and observations of the ratio of oxygen to molecular nitrogen, as well as of how these characteristics change during geomagnetic storms.

Early observations of Earth’s nightside from the mission have yielded surprising discoveries about airglow over the equatorial region, where large, continent-spanning stripes of emissions tend to form. This “equatorial anomaly” is far more dynamic than expected, with its brightness and appearance changing rapidly even during quiet periods between geomagnetic storms.

The authors suggest that all told, GOLD’s observations should help scientists develop better models of the thermosphere-ionosphere system and advance our understanding of space weather effects on Earth. (Journal of Geophysical Research: Space Physics, https://doi.org/10.1029/2020JA027823, 2020)

—Mark Zastrow, Science Writer

Super Dense Array Measurement Magnifies Seismic Wavefields

Tue, 08/04/2020 - 11:30

Earthquake ground motions vary depending on the subsurface soil conditions and surface topography. However, ground motion can only be recorded where there are seismic stations, so it is difficult to measure variations in ground motion changes within a small area.

To study more localized variability, Johnson et al. [2020] used about one thousand geophones spaced 10 to 20 meters apart atop the San Jacinto Fault in Southern California. This is a much denser array of apparatus than usual seismic observations. Their observations of Peak Ground Velocity (PGV) within the 0.36 km2 study area over a period of one month revealed variations in ground motion of up to 22% across the array. They also observed that the recorded measurements of PGV depends not only on the site locations, but also on the directivity of seismic waves. Variations in amplification are much larger if the earthquake occurs within the San Jacinto fault zone.

The variability of site characteristics is important for the development of nonergodic ground-motion prediction equations (GMPE) and has thus implications for probabilistic seismic hazard analysis. This study should be useful for a range of scientists from engineering seismology to earthquake physics.

Citation: Johnson, C. W., Kilb, D., Baltay, A., & Vernon, F. [2020]. Peak ground velocity spatial variability revealed by dense seismic array in Southern California. Journal of Geophysical Research: Solid Earth, 125, e2019JB019157. https://doi.org/10.1029/2019JB019157

—Masumi Yamada, Associate Editor, JGR: Solid Earth

Deep-Sea Mining May Have Deep Economic, Environmental Impacts

Mon, 08/03/2020 - 12:17

Advocates of deep-sea mining claim the process is important for providing metals for renewable energy technologies. One of the strongest arguments against offshore mining is that the environmental risks are too high, given that deep-sea ecosystems are among the most undiscovered places on Earth.

A less reported issue is the impact that deep-sea mining would have on developing economies that rely on land-based mining of those same metals. That is the subject of a recent report commissioned by the International Seabed Authority (ISA).

The global seabed area is beyond any national jurisdiction, but ISA regulates mining. To carry out exploratory missions, state-backed companies must obtain an ISA license, which grants exclusive access to seabed areas of up to 150,000 square kilometers. To date, 30 licenses have been issued, with China holding the most, with five. The United States is not eligible for licenses, as it is not an ISA member state, but U.S. defense firm Lockheed Martin has a license through its U.K. subsidiary.

The report names 13 nations, the majority in Africa, as being most vulnerable to additional metal supplies entering the market. Each identified country currently generates at least 10% of its export earnings from one or more of the key metals targeted by deep-sea mining: copper, cobalt, nickel, and manganese.

The report identifies Zambia, Democratic Republic of Congo, Eritrea, Chile, Lao People’s Democratic Republic, Mongolia, and Peru as vulnerable to a market influx of offshore copper supplies. Copper plays an important role in renewables due to its ability to conduct electricity and heat. Almost all cobalt (used in batteries) is a by-product of copper production, so it could also affect these countries.

The economies of Madagascar and Zimbabwe will be affected by new supplies of nickel, which is expected to play a key role in electric vehicles and high-capacity batteries. Gabon will be affected by new manganese supplies, used in the production of high-grade steel. Mauritania, Namibia, and Papua New Guinea are at risk because of the cumulative effect of all of the specified metals.

Assistance Fund

One of ISA’s key recommendations is that these nations should be compensated if deep-sea mining does commence, which the report predicts will happen in 2027. The requirement for this economic support is linked with the United Nations Convention on the Law of the Sea, which became effective in 1994.

“This support will be in the form of an economic assistance fund created from a portion of the proceeds from deep-sea mining.”“This support will be in the form of an economic assistance fund created from a portion of the proceeds from deep-sea mining,” said Michael Lodge, ISA secretary-general. Lodge said that the report is based on long-term economic projections and so should be unaffected by the COVID-19 pandemic.

But the proposal already has its critics. Among them is Bramley Murton, who leads the marine mineral research team at the National Oceanography Centre in the United Kingdom. He argues that deep-sea mining will be viable only if the commodity price is high enough as a result of increasing demand. “[Offshore] production costs are always likely to be greater than a well-resourced and efficient on-land mine,” he said.

As the global seabed is not a part of any one nation’s exclusive economic zone, Murton thinks it is unfair that only selected countries should benefit from ocean-mining royalties.

Andy Whitmore of the Deep Sea Mining Campaign is in favor of economic support for developing nations that rely on mining, but he questions the quantity of money that would be available from ISA’s proposed fund. “The amounts that are likely to be paid would likely be very low, unless the scale of deep-sea mining was so widespread, with so many exploitation licenses issued, that there would be significant impact on the seabed in international waters,” he said.

Environmental Threats

Researchers are only beginning to learn how deep-sea mining may affect benthic organisms. For this reason, many organizations are calling for a moratorium on deep-sea mining until environmental impacts are more fully understood. In 2019, the prime minister of Fiji joined these calls with the backing of several other Pacific island nations. The European Parliament adopted a resolution in 2018 urging its member states to stop sponsoring deep-sea mining and to invest in more sustainable consumption of materials.

Sediment plumes are considered the greatest ecological threat posed by deep-sea mining, appearing to cause lasting damage to microbial life. If mining operations scale up, noise could increasingly affect whales and other animals that rely on echolocation, while light pollution could affect animals that use bioluminescence.

“We’re only beginning to scratch the surface of what’s down there. The loss of biodiversity due to mining activities will be inevitable and permanent on a human scale, as nodules take millions of years to form.”The short- and long-term effects on specific regions are unknown. More than half of the current licenses for deep-sea mining, for instance, relate to the Clarion-Clipperton Zone (CCZ), a fracture region in the Pacific Ocean covering 4.5 million square kilometers, roughly half the size of the continental United States. For the CCZ, the greatest commercial interest is polymetallic nodules, compacted mineral-rich cements resembling blackened cauliflower florets.

Surveys of the CCZ have revealed that it also contains an abundance and diversity of life. Some species, including sponges and anemones, attach themselves to the nodules for feeding. Other species rely on the nodules indirectly, such as the recently discovered octopus nicknamed “Casper” that attaches its eggs to the stalks of dead sponges. A 2016 study published in Scientific Reports suggested that roughly half of the megafauna in the CCZ depend on the nodules as a hard substrate habitat.

“We’re only beginning to scratch the surface of what’s down there. The loss of biodiversity due to mining activities will be inevitable and permanent on a human scale, as nodules take millions of years to form,” said Matthew Gianni, cofounder of the Deep Sea Conservation Coalition.

—James Dacey (@JamesDacey), Science Writer

Arsenic Pollution in Bangladesh is Catching Up with Deeper Wells

Mon, 08/03/2020 - 11:30

In an effort to get people to stop drinking dirty surface water, development organizations worked with the Bangladeshi government to promote the use of shallow, hand-pumped wells. However, it turned out that arsenic levels in the shallow aquifers were too high, leading to arsenic poisoning. As a result, new deeper wells have been dug to tap the underlying arsenic-free aquifers.

Mozumder et al. [2020] use a smart combination of groundwater dating, geochemical analysis, and groundwater modeling to show that pumping from such aquifers may not actually be safe in the long run. They explain that massive pumping from a deeper arsenic-free aquifer below the city of Dhaka reduces its pressure and induces flow of arsenic- and carbon-rich groundwater from the overlying aquifer. This causes the deeper aquifer to be slowly contaminated with arsenic as well.

Citation: Mozumder, M. R. H., Michael, H. A., Mihajlov, I., Khan, M. R., Knappett, P. S. K., Bostick, B. C., et al. [2020]. Origin of groundwater arsenic in a rural Pleistocene aquifer in Bangladesh depressurized by distal municipal pumping. Water Resources Research, 55, e2020WR027178. https://doi.org/10.1029/2020WR027178

—Marc F. P. Bierkens, Editor, Water Resources Research

Megaripple Migration Offers Insights into Martian Atmosphere

Fri, 07/31/2020 - 14:05

Scientists show for the first time that large sand ripples known as megaripples are migrating on Mars, according to a new study. The findings suggest Mars’s dusty surface might be much more active than previously suspected, offering clues about the Red Planet’s poorly understood atmosphere.

Sand dunes and ripples are typical features of deserts on both Earth and Mars. Megaripples are distinguished from smaller ripples by the coarser sand grains that gather at their crests, as well as by their larger size: Megaripples range from 30 centimeters (1 foot) to tens of meters across. Megaripples develop taller crests and migrate more slowly because their coarser grains are more difficult for wind to move.

Until now, scientists thought megaripples were relics of Mars’s more geologically active past. Many thought it was impossible for the Red Planet’s thin atmosphere—100 times less dense than Earth’s—to conjure up winds powerful enough to move the coarser crests. But the new study by Silvestro et al. shows that wind can blow hard enough to move megaripples, suggesting the Martian atmosphere is more dynamic than previously thought.

“The implications are global in terms of climate,” said Simone Silvestro, lead author of the new study and a staff research scientist at the National Institute for Astrophysics in Naples, Italy. “If you see these features are moving now, it means you don’t need the past climate to explain them.”

Studying Ripple Movement

Megaripples are apparent in high-resolution images of Mars’s surface, but researchers considered them a now-static fixture formed long ago when the planet’s atmosphere was thicker.

Scientists had once thought the same of even small ripples in the sand, Silvestro said. “Since the 80s and 90s, Mars was considered kind of dead from a geological point of view,” he said.

Ten years ago, Silvestro and his colleagues used high-resolution images of Mars’s surface to prove that wind was moving the planet’s smaller ripples, publishing the findings in Geophysical Research Letters. Silvestro’s ripples study showed dynamic winds did exist on Mars, capable of changing the patterns of sand on the planet’s surface.



For his latest study, Silvestro and his colleagues looked at images of megaripples from HiRISE, the High Resolution Imaging Science Experiment camera on the Mars Reconnaissance Orbiter that has been taking pictures of the planet’s surface since 2006. They focused on two dune-associated locations, Nili Fossae and McLaughlin Crater, comparing images of megaripples at each site that were taken 5 Martian years apart. The team found that the megaripples moved an average of 1.2 meters (4 feet) at Nili Fossae and 0.9 meter (3 feet) at McLaughlin Crater over the roughly 5-year period.

“Now, 10 years later, we are seeing also the megaripples are moving,” Silvestro said. They are “the last thing you would expect to see moving, [but] they are also moving.”

Ripples Bright and Dark

The researchers noted that a previously known trait of Martian megaripples could also hold clues about the Martian atmosphere: Their crests are bright toned. Most of the sand covering Mars’s surface comes from basaltic rocks, giving dunes a dark color in HiRISE images, but megaripples buck this trend.

There are a couple of potential reasons for the megaripples’ crests’ lighter color scheme, Silvestro said. They are bright either because their slow movement relative to the dunes allows fine dust from the atmosphere to settle and accumulate or because the coarse sand that makes up the crests is itself composed of a different material. Either possibility could tell researchers more about the dynamics of the Martian atmosphere.

The research is a reminder that as scientists strive to learn more about the Red Planet, sometimes the answers can be found closer to home.“If you want to understand the climate of Mars and the geology of Mars—present and past—and if you want to continue exploration by sending robots and one day sending humans, we want to know much more about the circulation of Mars and how the winds interact with the surface material,” Silvestro said.

Interest in megaripples on Mars has sparked renewed interest in the phenomenon back on Earth. Past studies on Earth megaripples and research grants Silvestro received to study megaripples in Morocco provided crucial information for his Mars megaripple research. It’s a reminder that as scientists strive to learn more about the Red Planet, sometimes the answers can be found closer to home, he said.

“These waves in sand have been studied for 150 years,” Silvestro said of terrestrial megaripples. “They probably thought that they were studying stuff that nobody would be interested in. But actually, many years later, we are using them to wonder how the atmosphere could work on other planets.” (Journal of Geophysical Research: Planets, https://doi.org/10.1029/2020JE006446, 2020)

—Rachel Fritts (@rachel_fritts), Science Writer

This Week: Mars in 4K and Silence on Earth

Fri, 07/31/2020 - 14:04

Bringing Mars Rocks to Earth: Our Greatest Interplanetary Circus Act. With the latest Mars missions heading toward their destination, there is growing anticipation about what all this new robotic instrumentation might soon reveal of the Red Planet. Of course, planetary scientists and engineers have also long had the goal of bringing bits of Mars back to Earth for much closer, hands-on investigations. The complex plan taking shape to do that has a certain “Are you kidding me?” feel to it yet also sounds just plausible enough to inspire optimism (in this observer at least). It’s reminiscent of the rescue effort in The Martian, but just replace Matt Damon with a soccer ball filled with rocks and dust. —Timothy Oleson, Science Editor

 

The Seismic Hush of the Coronavirus. By now we’ve all seen photos of eerily empty streets and public spaces during regional shutdowns, and earlier this year the media covered the pandemic’s effect on air quality. But who would have thought that a decrease in human activity would register on seismometers around the world? Well, every seismologist and a lot of other scientists, I’m sure, but it hadn’t occurred to me. Of particular note, data collected during the pandemic could help scientists distinguish human-caused tremors from natural ones, and seismic monitoring could also be used to monitor human activity during this pandemic and in the future. —Faith Ishii, Production Manager

 

Astro(wildlife)biology.

Today’s astronomy tales:

“Astro(wildlife)biology”

Observatories are spectacular and meticulously-engineered hubs of scientific research. They also work best when we maroon them in the MIDDLE OF NOWHERE

“Nowhere” sometimes gives us some interesting observing companions… pic.twitter.com/sw6pakhLAz

— astrotweeps: Emily (@starstuffwilson) (@astrotweeps) July 22, 2020

Just a fun thread of the various critters your everyday astronomer might encounter while studying the universe. My wildlife encounters include moths, spiders, roadrunners, cats and dogs, and *shudder* ladybugs. —Kimberly Cartier, Staff Writer

 

Revealed: Oil Giants Help Fund Powerful Police Groups in Top U.S. Cities. In an investigation by the Public Accountability Initiative, researchers found that big oil and gas companies like Chevron and Shell are funding private police foundations in U.S. cities. The police foundations support local policing groups with “training, weapons, equipment, and surveillance technology” and face less oversight than publicly funded organizations. These companies have also been accused of producing toxic pollution that disproportionately hurts communities of color. As Black Lives Matter protests renounce state-sanctioned violence and anti-Black racism, it is important to look at the ties between environmental and racial justice. —Jenessa Duncombe, Staff Writer

 

Trump Administration Says Massive Alaska Gold Mine Won’t Cause Major Environmental Harm, Reversing Obama. Controversy about Alaska’s proposed Pebble Mine has churned for decades. The site sits in the headwaters of the world’s most productive salmon fishery. There are concerns about faults under the site of a 500-foot (152-meter) earthen dam required to contain the billions of tons of rock expected to be removed during the mine’s operation. The mining company is angling for approval of a smaller footprint, with the option to expand (to where most of the gold is) later. Locals, who don’t see the big payouts from mining that oil offers and are unlikely to be hired by the mining company, are lukewarm on the project. Opponents have complained that the Army Corps of Engineers’ environmental impact statement is not scientifically rigorous. Lawsuits expected! —Liza Lester, Staff Writer

 

Mars In 4K.

Mars never looked so good, but it’s the voice-over that makes this a classic. In a (red) world…. —Caryl-Sue, Managing Editor

Curiosity Solves the Mystery of Gale Crater’s Hematite Ridge

Fri, 07/31/2020 - 14:01

It was the ultimate ground truth. Standing out for its unique spectral characteristics from orbit, Vera Rubin ridge (VRR) is located near the base of Mount Sharp in Gale crater, Mars. This 200-meter wide and 6½ kilometer long ridge was the primary subject of investigation by the Curiosity rover for more than an Earth year. Through a carefully coordinated science campaign, the rover used a combination of imaging, spectral remote sensing, contact science, and drilled sample analysis to understand the origin of VRR and its distinctive characteristics.

A new special issue in JGR: Planets describes the findings from the VRR campaign, and details clear evidence for multiple episodes of aqueous activity at Gale crater, including later groundwaters that helped to form VRR. We asked science campaign leader Dr. Abigail Fraeman about the major findings at VRR and about the potential implications for ancient habitable environments at Gale crater.

Why was Vera Rubin ridge (VRR) of interest to the science team, prior to arrival?

The Curiosity Mars rover is studying the habitability of ancient Mars. Curiosity’s landing site, Mount Sharp, is an ideal place to do this because the strata that make up the approximately five-kilometer tall mound preserve a record of Mars’ changing ancient environments that the rover can access.

One of the key environmental markers identified prior to landing was a prominent ridge near the base of Mount Sharp. Orbital spectral data showed hematite, an iron oxide mineral, was present in the ridge. This discovery excited the team because it suggested the ridge might preserve a site where iron oxidation occurred in the past. On Earth, iron oxidation/reduction at redox interfaces is often catalyzed by microbes, and therefore the ridge was a prime location to explore habitability.

Orbital view of Curiosity’s traverse and Vera Rubin ridge from a gray scale 25 cm/pixel High Resolution Imaging Science Experiment (HiRISE) camera. Spectral data showing absorptions at 860 nm attributed to Fe3+ in hematite are overlain in red. Credit: NASA/JPL-Caltech/Univ. of Arizona

How did Vera Rubin ridge get its name?

In practice with naming key regions Curiosity explores after famous scientists, the Curiosity science team informally named the ridge “Vera Rubin ridge” (VRR) in honor of the pioneering American astronomer Vera Cooper Rubin (1928–2016). Dr. Rubin’s precise measurements of the rotation rates of galaxies revealed the existence of dark matter. She was also a fierce advocate for the equal treatment of women in science.

The south side of Vera Rubin ridge towering over the Glen Torridon region from a Mastcam right camera mosaic collected on sol 2299, sequence ID mcam12272. Credit:NASA/JPL-Caltech/MSSS

What were some of the hypotheses about VRR’s geologic history, prior to the investigations with the Curiosity rover?

Based on similar orientation of the ridge’s strata and the rest of Mount Sharp in orbital data, we hypothesized that the rocks in VRR formed during the same time Mount Sharp was being built. We also hypothesized that VRR’s high relief relative to its surroundings was due to change grain size or increased cementation.

As for the strong hematite signal, we initially thought VRR was a uniquely hematite-bearing interval, and proposed that the hematite formed either when iron-bearing, oxygen-poor fluids encountered an oxidizing environment and precipitated insoluble iron-bearing minerals, or by localized in-place oxidative weathering of other minerals.

However, we began to question these hypotheses when Curiosity’s instruments found hematite in the several hundred meters of strata below VRR. New questions emerged, such as How does the hematite in VRR relate to units stratigraphically below? and Why is the spectral signature of hematite so strong at VRR in orbital data?

What were the major findings regarding the origin and geologic history of VRR? What was the biggest surprise to the science team?

ChemCam Remote Mast Imager (RMI) mosaic of a lacustrine VRR rock, target informally named “Mount Coe” from sol 1812. The numbered red crosses indicate locations of Laser Induced Breakdown Spectroscopy (LIBS) shots. Credit: NASA/JPL-Caltech/CNES/CNRS/LANL/IRAP/IAS/LPGN

We found that most rocks in the ridge were fine grained with parallel bedding, and they were lain down in an ancient lake, just as were most of the strata below the ridge.

Hematite was present in the ridge as predicted from orbit, but somewhat surprisingly, there wasn’t significantly more hematite in the ridge than the strata below.

We discovered the strong hematite spectral signature seen from orbit along VRR was due in part to less sand and dust obscuring the ridge, but mostly because small changes in the hematite mineral grain size deepened the hematite spectral absorptions in the bedrock.

Another surprising finding was isolated “patches” of gray bedrock that were almost identical in composition to the red bedrock that made up the majority of VRR.

The team concluded the rocks were gray because they had “gray hematite,” which has larger mineral grain sizes than red hematite. The gray patches cross-cut primary bedding, so they formed sometime after the strata on the ridge were laid down. On Earth, gray hematite is most commonly found in hydrothermal settings, so its presence on the top of the ridge is puzzling.

Mars Hand Lens Imager (MAHLI) images of red and gray rocks on VRR acquired at a 25 cm standoff distance on sols 2005 and 1934. Yellow circles show where the rover brushed away ubiquitous red Martian dust to reveal bedrock color. Credit: NASA/JPL-Caltech/MSSS/Deirdra Fey

Overall, the data Curiosity collected at VRR suggest that the ridge formed from late-stage fluids that hardened and recrystallized a band of pre-existing rocks in Mount Sharp. These rocks later became a ridge as millions or even billions of years of wind erosion worked to lower the level of the softer rocks on either side of VRR.

How did the VRR findings change the current framework of understanding for the geologic history of Mt. Sharp and/or habitability of Gale crater in general?

VRR is a new example of how groundwater shaped the Martian rock record on a scale that is visible from orbit. The finding that the rocks in the ridge were initially deposited in a lake, similar to the approximately 300 meters of strata below the ridge, demonstrates that these environments persisted for a very long time, likely tens of millions of years.

While VRR does not represent a redox interface that would have marked a new kind of habitable environment, the evidence for at least one, and more likely multiple, late-stage interactions with fluids at VRR further expands the period of time when liquid waters would have been present at Gale crater, likely in the shallow or deep subsurface. The presence of coarse-grained gray hematite on the ridge top might indicate waters were warm and/or long-lived, which could have provided favorable environments in the shallow subsurface sheltered from surface radiation and temperature variations. Combined, these results suggest habitable environments may have been preserved late into the Hesperian, first at the surface and later in the subsurface.

A portion of a 360˚ mosaic taken using Curiosity Navcam as the rover ascended Vera Rubin ridge on sol 1812. Credit: NASA/JPL-Caltech

As the Curiosity rover continues its traverse of Mt. Sharp, what are the lessons learned from the VRR investigation that may be applied to future investigations?

Curiosity’s exploration of VRR adds to a list of examples that demonstrate the power of coordinated orbital and rover investigations for Mars exploration. Curiosity confirmed the orbital detection of hematite at VRR, but wheels on the ground were needed to reveal the full geologic context of this detection and provide critical clues to unravel the ridge’s history.

—A. Deanne Rogers, Editor, JGR: Planets; Mariek Schmid, Associate Editor, JGR: Planets; and Abigail Fraeman (abigail.a.fraeman@jpl.nasa.gov;  0000-0003-4017-5158), NASA Jet Propulsion Laboratory

Real-time Ground Motion Estimation for Large Earthquakes

Fri, 07/31/2020 - 11:30

Large earthquakes can generate long-period (LP) ground motions, surface waves that can travel large distances and cause significant damage to buildings and infrastructure many hundreds of kilometers from the epicenter.

One place where this is particularly pertinent is Japan. The Nankai Trough subduction zone off the southwest coast of Japan has been the source of a number of large earthquakes over recent centuries and the next one is expected in the coming decades. This poses a tremendous threat to large urban populations and physical infrastructure, including the greater Tokyo region.

Oba et al. [2020] carried out numerical tests using motion records from a past earthquake (the 2004 Off Kii Peninsula earthquake) together with simulated seismograms of potential large earthquake scenarios in the Nankai Trough. Their approach is a major advance because it combines direct assimilation of observed data with full accounting for the important effects of 3D basin structure.

This method, making use of advanced high-performance computing technology, has the potential to provide advance warning of ground shaking in real time, thereby buying valuable time for damage mitigation actions.

Citation: Oba, A., Furumura, T., & Maeda, T. [2020]. Data assimilation‐based early forecasting of long‐period ground motions for large earthquakes along the Nankai Trough. Journal of Geophysical Research: Solid Earth, 125, e2019JB019047. https://doi.org/10.1029/2019JB019047

—Masumi Yamada, Associate Editor, JGR: Solid Earth

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