Why AI can’t replace air traffic controllers



Control towers at airports are only the most visible parts of the complex national air traffic control system. Saul Loeb/AFP via Getty Images

THE CONVERSATION
Published: January 30, 2024 

After hours of routine operations, an air traffic controller gets a radio call from a small aircraft whose cockpit indicators can’t confirm that the plane’s landing gear is extended for landing. The controller arranges for the pilot to fly low by the tower so the controller can visually check the plane’s landing gear. All appears well. “It looks like your gear is down,” the controller tells the pilot.

The controller calls for the airport fire trucks to be ready just in case, and the aircraft circles back to land safely. Scenarios like this play out regularly. In the air traffic control system, everything must meet the highest levels of safety, but not everything goes according to plan.

Contrast this with the still science-fiction vision of future artificial intelligence “pilots” flying autonomous aircraft, complete with an autonomous air traffic control system handling aircraft as easily as routers shuttling data packets on the internet.

I’m an aerospace engineer who led a National Academies study ordered by Congress about air traffic controller staffing. Researchers are continually working on new technologies that automate elements of the air traffic control system, but technology can execute only those functions that are planned for during its design and so can’t modify standard procedures. As the scenario above illustrates, humans are likely to remain a necessary central component of air traffic control for a long time to come.

What air traffic controllers do

The Federal Aviation Administration’s fundamental guidance for the responsibility of air traffic controllers states: “The primary purpose of the air traffic control system is to prevent a collision involving aircraft.” Air traffic controllers are also charged with providing “a safe, orderly and expeditious flow of air traffic” and other services supporting safety, such as helping pilots avoid mountains and other hazardous terrain and hazardous weather, to the extent they can.

Air traffic controllers’ jobs vary. Tower controllers provide the local control that clears aircraft to take off and land, making sure that they are spaced safely apart. They also provide ground control, directing aircraft to taxi and notifying pilots of flight plans and potential safety concerns on that day before flight. Tower controllers are aided by some displays but mostly look outside from the towers and talk with pilots via radio. At larger airports staffed by FAA controllers, surface surveillance displays show controllers the aircraft and other vehicles on the ground on the airfield.

This FAA animation explains the three basic components of the U.S. air traffic control system.

Approach and en route controllers, on the other hand, sit in front of large displays in dark and quiet rooms. They communicate with pilots via radio. Their displays show aircraft locations on a map view with key features of the airspace boundaries and routes.

The 21 en route control centers in the U.S. manage traffic that is between and above airports and thus typically flying at higher speeds and altitudes.

Controllers at approach control facilities transition departing aircraft from local control after takeoff up and into en route airspace. They similarly take arriving aircraft from en route airspace, line them up with the landing approach and hand them off to tower controllers.

A controller at each display manages all the traffic within a sector. Sectors can vary in size from a few cubic miles, focused on sequencing aircraft landing at a busy airport, to en route sectors spanning more than 30,000 cubic miles (125,045 cubic km) where and when there are few aircraft flying. If a sector gets busy, a second and even third controller might assist, or the sector might be split into two, with another display and controller team managing the second.

How technology can help

Air traffic controllers have a stressful job and are subject to fatigue and information overload. Public concern about a growing number of close calls have put a spotlight on aging technology and staffing shortages that have led to air traffic controllers working mandatory overtime. New technologies can help alleviate those issues.

The air traffic control system is incorporating new technologies in several ways. The FAA’s NextGen air transportation system initiative is providing controllers with more – and more accurate – information.



Controllers’ displays originally showed only radar tracking. They now can tap into all the data known about each flight within the en route automation modernization system. This system integrates radar, automatic position reports from aircraft via automatic dependent surveillance-broadcast, weather reports, flight plans and flight histories.

Systems help alert controllers to potential conflicts between aircraft, or aircraft that are too close to high ground or structures, and provide suggestions to controllers to sequence aircraft into smooth traffic flows. In testimony to the U.S. Senate on Nov. 9, 2023, about airport safety, FAA Chief Operating Officer Timothy Arel said that the administration is developing or improving several air traffic control systems.

Researchers are using machine learning to analyze and predict aspects of air traffic and air traffic control, including air traffic flow between cities and air traffic controller behavior.

How technology can complicate matters

New technology can also cause profound changes to air traffic control in the form of new types of aircraft. For example, current regulations mostly limit uncrewed aircraft to fly lower than 400 feet (122 meters) above ground and away from airports. These are drones used by first responders, news organizations, surveyors, delivery services and hobbyists.

NASA and the FAA are leading the development of a traffic control system for drones and other uncrewed aircraft.

However, some emerging uncrewed aircraft companies are proposing to fly in controlled airspace. Some plan to have their aircraft fly regular flight routes and interact normally with air traffic controllers via voice radio. These include Reliable Robotics and Xwing, which are separately working to automate the Cessna Caravan, a small cargo airplane.

Others are targeting new business models, such as advanced air mobility, the concept of small, highly automated electric aircraft – electric air taxis, for example. These would require dramatically different routes and procedures for handling air traffic.

Expect the unexpected

An air traffic controller’s routine can be disrupted by an aircraft that requires special handling. This could range from an emergency to priority handling of medical flights or Air Force One. Controllers are given the responsibility and the flexibility to adapt how they manage their airspace.

The requirements for the front line of air traffic control are a poor match for AI’s capabilities. People expect air traffic to continue to be the safest complex, high-technology system ever. It achieves this standard by adhering to procedures when practical, which is something AI can do, and by adapting and exercising good judgment whenever something unplanned occurs or a new operation is implemented – a notable weakness of today’s AI.

Indeed, it is when conditions are the worst – when controllers figure out how to handle aircraft with severe problems, airport crises or widespread airspace closures due to security concerns or infrastructure failures – that controllers’ contributions to safety are the greatest.

Also, controllers don’t fly the aircraft. They communicate and interact with others to guide the aircraft, and so their responsibility is fundamentally to serve as part of a team – another notable weakness of AI.

As an engineer and designer, I’m most excited about the potential for AI to analyze the big data records of past air traffic operations in pursuit of, for example, more efficient routes of flight. However, as a pilot, I’m glad to hear a controller’s calm voice on the radio helping me land quickly and safely should I have a problem.

Author

Amy Pritchett
Professor of Aerospace Engineering, Penn State
Disclosure statement
Amy Pritchett receives funding from the National Science Foundation through the Center for Advanced Aerial Mobility and Sensors (CAAMS) on the topic of in-flight autonomy capable of resolving faults and failures in on-board systems, and is finishing up a project sponsored by NASA examining human-autonomy teaming in advanced aerial mobility.

 

Soil fungi and teabags respond to loud sounds

Credit: Andreas Häuslbetz / Getty Images

January 31, 2024

Ellen Phiddian

Ellen Phiddian is a science journalist at Cosmos. She has a BSc (Honours) in chemistry and science communication, and an MSc in science communication, both from the Australian National University.

The soils are alive with the sounds of music. Want your soil health to improve? Try making it noisier, say Australian scientists.

The researchers have found that playing soundscapes can make friendly soil fungi grow faster. The discovery could help restore microbial health to the worlds soils, 75% of which are substantially degraded.

Sounds played at volumes of 70-90 decibels, and a pitch of 8KHz, encouraged things to decompose more quickly than ambient background noise at 30 decibels.

“This was informed by previous research that suggested 8 kilohertz at around 80 decibels increases the activity of E. coli bacteria,” says Dr Jake Robinson, a microbial ecologist at Flinders University and lead author on a pre-print (not peer-reviewed) paper.

The researchers first tested the soundness of their theory by playing Youtube soundscapes to teabags.

“The humble teabag is often used in ecological studies to get information about soil decomposition,” Robinson tells Cosmos.

“We basically played sound to these tea bags in the soil to see if it had an effect on the decomposition rate or the fungal biomass. Teabags that received the sound treatment significantly increased in biomass compared to the control group.”

Jake Robinson with his 2023 book.

Specifically, the researchers used green tea and rooibos tea, which Robinson says are used because they have very different consistencies.

“Green tea bags are more leafy, and the rooibos is more woody. [We wanted] to see if that had different effects on the decomposition rate, because you’d expect woody stuff to decompose slightly slower.”

After seeing the sound-treated teabags decompose faster, the researchers turned to a common soil fungus – Trichoderma harzianum – to see if sound had the same effect.

“This fungal species is known to be beneficial for plants. We cultured it in petri dishes, and then did the same thing: we applied sound to the petri dishes, and we found that it significantly increased growth rate.”

The researchers aren’t sure why sounds help the fungi to grow, although they have a few ideas.

“It might be that microbes, including fungi, can convert the soundwave energy into an electrical charge, which stimulates their activity,” says co-author Christian Cando-Dumancela, a research assistant at Flinders University.

Robinson says that the study is a progression of ecoacoustics: studying ecology via listening to soundscapes.

“We’ve developed special microphones that you can put in the soil and listen to the sounds of the little animals in the soil. And that gives you an indication of soil health,” he says.

“But this is actually applying sound.”

The researchers are keen to investigate their soundscape technique further, to see if it can work at a larger scale. Other research recently published by the team has highlighted the threat to microbial communities in degrading soil, and their importance in keeping soil healthy.

“Can we use sound in a positive way? And also, can we kind of prevent the negative sounds that might be damaging our ecosystems?” says Robinson, adding that global noise pollution may also be having a negative effect.

This isn’t a brand-new idea – sound has been proposed to control botrytis fungi in grapes, points out Robinson – but there is still much research to be done before they can establish what will help and hinder the soil.

“We don’t know too much about it yet. The next step is trying to understand the mechanisms, and where we can select for different sounds to promote different communities in the soil,” says Robinson.

New Dutch group reinforces efforts to replace animal testing

By Christoph Schwaiger | EURACTIV


Three Dutch research institutions have teamed up to create a steering group to collaborate more intensively in the field of animal research and animal-free innovations.

While the Netherlands is one of the highest users of animals for scientific purposes in the EU, 77% of its citizens believe more should be done to accelerate the full replacement of animal experiments, according to a poll released last year.

Animal testing in the EU has been on the decline, from 8.8 million animals in 2018 to 7.9 million in 2020. Nevertheless, the expectation that global chemical production will double by 2030 has different stakeholders urging the EU to move faster on replacing animal testing.

Now, a new Dutch steering group, Amsterdam 4R, established in November, wants to join in these efforts while going an extra step to emphasise the reproducibility of stem-cell-derived models.

“We added a fourth R to emphasise that it is essential to reproduce the main features of a specific cell, tissue or organ in stem-cell-derived models,” Amsterdam 4R chairperson Jolanda van der Velden told Euractiv.

The European Partnership for Alternative Approaches to Animal Testing (EPAA), for example, works towards the replacement, reduction, and refinement of animal testing methods. This is known as the 3R principle. Amsterdam 4R, as its name implies, added another principle to this list – reproducibility.

Van der Velden said that while stem cell research advances quickly, the group felt that reproducibility of stem-cell-derived models is an often overlooked aspect in the field of animal-free medical innovations.

According to the professor, if reproducibility is not taken into account properly, new animal-free models will not provide the essential information that is needed for testing toxicity and drug effectiveness. Further funding is needed to perform such research and secure the reproducibility of newly developed innovative stem-cell-derived models.

Van der Velden is also a professor of physiology at the Amsterdam University Medical Center, which joined forces with the Vrije Universiteit Amsterdam and the Academic Centre for Dentistry in Amsterdam (ACTA) to create the Amsterdam 4R steering group.

The group was launched last November to allow for more intensive collaboration in the field of animal research and animal-free innovations.

In a statement announcing the group’s establishment, van der Velden said that while the partners still think it’s important to show the outside world why animal research is still necessary, it’s equally important to show society the latest developments and innovations in animal-free research.

She expects that such a partnership will allow for more effective and efficient collaboration between the different stakeholders.
New drugs can be tested on cultured heart tissue

The individuals involved in this new collaboration have already started making progress in the field, including van der Velden herself, who is testing the culturing of patients’ heart muscle tissue removed during surgery.

Van der Velden told Euractiv that the tissue slices can be kept in culture for many weeks and allow researchers to study the effectiveness of newly developed drugs to repair cardiac function, such as ones that target the metabolism of heart muscle cells.

Additionally, the toxicity of cancer medication can also be defined in these human cardiac tissue slices.

“We thereby make optimal use of [excess human material collected during surgery], and at the same time reduce the need for such experiments in animals,” van der Velden said.

The steering group also aims to increase the visibility of all 3R-related activities in Amsterdam. It also wants to be transparent about the research performed on animals and train the next generation of scientists in this area.

In previous years, many scientists in Amsterdam have developed experimental models, both animal- and stem-cell-derived, that better reflect human pathophysiology, and they developed models to reduce and refine research in animals.
Still years away from completely replacing animals

However, these initiatives were very much at an individual and departmental level, according to van der Velden.

Thanks to Amsterdam 4R, an overview of all initiatives in the Dutch capital can be formed, allowing researchers and students to discover the state-of-the-art expertise that’s available. As the next generation of scientists is nurtured, current university courses can be expanded and optimised.

One hurdle researchers still face is the complexity of certain diseases, which could involve more than just a single organ. Other factors such as hormones, the immune system, and a person’s diet could also come into play, which all make it more challenging to model complex human diseases.

“While major advancements have been made, we emphasise that it will still take many years and a lot of money to build reproducible experimental models that can replace the research in animals,” van der Velden said.

[By Christoph Schwaiger, Edited by Vasiliki Angouridi/Zoran Radosavljevic | Euractiv.com]

 

Spider webs collect DNA that reveals the species living nearby

DNA analysis of spider webs from two locations in Australia identified dozens of vertebrate species, suggesting a new approach to wildlife monitoring

By James Woodford

30 January 2024

Spider webs capture airborne DNA

Vechterova Valeria/Shutterstock

Elephants, giraffes and rhinos can all be caught in spider webs – or at least their DNA can.

Read more

Spiders think with their webs, challenging our ideas of intelligence

Josh Newton at Curtin University in Western Australia and his colleagues have found that spider webs capture the DNA of creatures living nearby, providing researchers with a novel method of surveying wildlife in difficult environments.

The researchers studied 49 spider webs from two locations in Western Australia – Perth Zoo and Karakamia wildlife sanctuary, a 268-hectare area of bushland some 50 kilometres east of Perth.

Their analysis yielded nearly 2.5 million DNA sequences, which were processed in part with polymerase chain reaction (PCR) technology, the same that is used in covid-19 tests. This technique generates millions or billions of copies of DNA sequences, making it possible to study samples that contained only tiny amounts. Just over 1 million sequences were identified as human and excluded from the analysis.

The team members detected non-human vertebrate DNA in all the web samples they tested. The webs from Perth Zoo yielded a total of 61 vertebrate species, including 33 mammals, 21 birds, five reptiles and two amphibians.

For two of the zoo’s largest species – Asian elephants and northern giraffes – the team found DNA nearly 200 metres away from the animals’ enclosures.

In Karakamia wildlife sanctuary, the scientists detected 32 vertebrate species, including native animals such as western grey kangaroos and motorbike frogs, as well as three invasive species: the red fox, house mouse and black rat.

DNA from cows, sheep and pigs, which aren’t known to live within the sanctuary but are farmed throughout the region, was also found in the samples.

“The DNA is shed from the animals in the environment and becomes airborne,” says Newton. “It may be free-floating DNA or still within cells like hair and skin cells. It’s also likely to be attached to something else, like dust particles.”

He says it is also possible that the DNA of larger animals has been picked up by flies or other insects, which later become trapped in the webs.

Spider webs could be a valuable way to sample environmental DNA such as this and monitor wildlife, says Newton. “With species in decline globally, monitoring them is becoming increasingly important,” he says. “This new technology is in the early stage of application in terrestrial systems, and while it’s not a silver bullet and traditional survey methods will always be needed, it does allow us to rapidly monitor ecosystems beyond what we are able to easily see and hear.”

Journal reference:

iScience DOI: 10.1016/j.isci.2024.108904

Hubble Spies a Spinning Spiral


This new NASA Hubble Space Telescope image features the face-on spiral and Seyfert galaxy, ESO 420-G013.

NASA/ESA/A. Evans (University of Virginia)/Processing: Gladys Kober (NASA/Catholic University of America)

Looking like a baseball lobbed into the depths of the universe, ESO 420-G013 is a face-on spiral galaxy and a Seyfert galaxy. Dark lanes of dust are visible against the background glow of the galaxy’s many stars.

About 10 percent of all the galaxies in the universe are thought to be Seyfert galaxies. They are typically spiral galaxies and have very bright nuclei, the result of supermassive black holes at their centers accreting material that releases vast amounts of radiation. The cores of these “active galaxies” are brightest when observing light outside the visible spectrum. Often galaxies with these kinds of active galactic nuclei are so bright that the host galaxy itself cannot be seen, washed out by the glow of its nuclei, but Seyfert galaxies are distinctive because the galaxy itself is also visible. In the case of ESO 420-G013, we can enjoy the galaxy’s almost perfectly round disk, brighter core, and whirled filaments of dark dust.

NASA’s Hubble Space Telescope observed ESO 420-G013 as part of a study of Luminous Infrared Galaxies, or LIRGs, which are known to be extremely bright in the infrared part of the spectrum. Galactic interactions trigger new regions of star formation in LIRGs, causing them to be highly luminous in infrared light.

NASA Hubble Mission Team
Goddard Space Flight Center
JAN 30, 2024

Iranian companies dredging Russia’s Volga river: PMO chief


TEHRAN, Jan. 30 (MNA) – The chief executive of the Iranian Ports and Maritime Organization (MPO) said Iranian companies are implementing dredging operations in Russia’s Volga River.

Ali Akbar Safaei also described the construction operation of the gantry crane as one of the strategic port equipment in the country and noted that the revenues of the organization will witness a significant hike in the current year (started March 21, 2023) compared to a year earlier.

Regarding the latest situation of talks with India on a long-term investment contract at Chabahar Port, the deputy minister of roads said India’s ports and shipping minister will soon visit Iran to clinch a contract for the development of the port.

India’s high-ranking officials are determined to play a key role in the development of Chabahar Port, Safaei underlined.

Elsewhere in his remarks, the deputy roads minister pointed to the port equipment and machinery needed to be imported to the Chabahar Port by India and added, “Under the contract, the gantry crane will be imported by the Indian side into Chabahar Port.”

Meanwhile, construction of the strategic port equipment by the Iranian manufacturers is under the finalization stage, he said, adding that giant investment has been made in the administration of President Ebrahim Raisi in the field of supplying relevant port equipment, according to which, the capacity of ports has so far increased from 270 tons to 290 tons.”

SD/TSN

 

European Parliament proposal to ban patenting of gene edited plants divides opinion

30 Jan 2024 | 

MEPs have approved plans to loosen regulations around crop plants that are improved using gene editing, but a move to ban patenting of plants that are modified using these techniques could stand in the way of a final agreement

By Martin Greenacre

Brassica shoot regeneration – part of the gene editing process. Photo: John Innes Centre / Flickr

Genetically manipulated crop plants have long been a divisive issue, but the European Parliament’s food safety committee ENVI has now managed to unite industry and environmentalists in opposition to its proposal to ban patenting of plants that are modified using new genomic techniques (NGTs).

MEPs voted through an amendment to the Commission’s proposal to update EU rules to reflect the greater precision of new gene editing techniques such as CRISPR on 24 January.

NGTs are tools used to modify an organism’s genetic make-up without inserting foreign genetic material, or by inserting genetic material from organisms that can cross in nature. These are being used to develop plant varieties with improved properties, such as drought resistance or salt tolerance, or which require fewer pesticides and fertilisers.

Breeders and farmers fear that patents will extend not just to the processes used to obtain certain traits, but to the traits and the plants themselves. NGTs may speed things up, but these traits could also be introduced via conventional breading methods.

If traceability and labelling requirements are removed for NGT-modified plants, breeders and farmers are worried they will be forced to sign licencing agreements with large companies to use seeds that naturally contain the genetic trait in question, or which are the result of conventional breading.

The MEPs’ move to ban patenting is a “fake solution”, because revising the EU directive on biotech patents would take several years, says Eric Gall, deputy director of the lobby group IFOAM Organics Europe. The European Patent Convention would also need to be amended, he added.

Rather than banning patents on NGT-modified plants, there should be a legal modification to “make it clear that in no case should genetic material and traits that can be obtained by conventional breeding, or in nature, be subject to a patent,” Gall said. “Patents which are more and more applied to conventional seeds are a threat to the European model of innovation in breeding.”

IFOAM is calling for the plenary vote on the Parliament’s position, currently scheduled for early February, to be delayed so that these concerns can be addressed.

Consensus across industry

The proposed ban on patents requires “a lot more differentiation”, between patents on technology and on traits and plants obtained with that technology, said Garlich von Essen, secretary general of seed industry association Euroseeds.

He said there is “a consensus across a vast majority of the industry” that small companies should continue being able to use the varieties of their competitors, but that firms which develop technologies and traits for companies to use in their breeding programmes do require intellectual property (IP) protection.

Von Essen agrees that an amendment to the NGT regulation is not the right arena in which to strike this balance. “It will not be done with two or three trilogue meetings,” he said.

Instead, the EU should push ahead with the NGT file, and shelve the patenting issue until the Commission publishes its report assessing the impact of patents on breeders’ access to genetic material and techniques, the availability of seeds to farmers, and the competitiveness of European biotech. This is due for 2026, but MEPs want it brought forward to 2025.

“Any company that wants a product on the market will need to put it through the regular variety registering system, which takes three or four years. We can use that time to sort out the IP issue,” von Essen said.

“Patents are an important incentive to drive innovation and related investments,” but they are not the only incentive, said Gabino Sanchez, business development director at Netherlands-based gene editing company Hudson River Biotechnology.

Using traditional methods, it usually takes 12 years to bring a new crop variety to market, making patents essential to safeguard the investment in R&D investments. But gene editing techniques can reduce that to three years.

Discussions will need to take place with stakeholders around patents and other ways to capture value. Those talks should begin now, Sanchez argues, so that once the Commission’s report is published, a new regulatory framework can follow.

Worries that big companies will increase their dominance through patents have “nothing to do with gene editing”, but these techniques exacerbate those fears, as they allow more varieties to be brought to the market much more quickly.

While awaiting that longer-term fix, Sanchez does not expect the proposed patenting ban to hinder innovation, as the R&D process takes several years. The real barrier to innovation would be failing to update the NGT regulation, he said.

Companies is related sectors will be keeping a close eye on the file. EuropaBio, trade association that represents health and industrial biotech companies, worries that decisions here will set a precedent for other sectors, even though agriculture covers just a small percentage of biotech patents. NGTs are used not just in plants, but also in microorganisms, and the first gene edited drug was approved recently.

“Any discussion should be done within the context of the Biopatent Directive. It should be holistic, and not only focus on one sector,” said Anne-Gaëlle Collot, industrial biotechnology director at EuropaBio, Any changes should come after the Commission has published its report.

“For us, bio patents are crucial.” They safeguard investment in research from large firms, and support access to finance for smaller companies, she said.

French microbiologist Emmanuelle Charpentier, co-inventor of CRISPR technology, won the Nobel prize in 2020, but gene edited crops are yet to be introduced in the EU, and policymakers fear the bloc will fall even further behind if the rules are not adapted.

In 2018, the Court of Justice of the EU ruled that NGTs must be subject to the same strict rules as all genetically modified organisms. Yet NGTs did not exist in 2001 when the EU legislation on GMOs was adopted.

The new legislative proposal separates NGT plants into two categories. Category 1, considered to be equivalent to conventionally-bred plants and having undergone fewer than 20 modifications, will be exempted from the requirements in the GMO legislation, unlike Category 2 plants which are more heavily modified.

Industry welcomed the move, although environmental organisations such as Greenpeace have warned that weakening rules on safety checks and labelling requirements would infringe on the rights of farmers and consumers.

MEPs agreed that all NGT-modified plants should remain prohibited in organic production, as this will require further consideration.

The Parliament and Council may yet reach a final agreement on the text before this summer’s EU elections, but the issue of patents could be a stumbling block.

The Council is yet to agree on its position. “We have a majority in Council, just not a qualified majority,” said von Essen. Intellectual property rights are one of the issues currently dividing member states.

Scientists Model What’s Moving Beneath Earth’s Surface

A 3D printed model of a fault served as the setting for a hydrofracturing experiment exploring the mechanisms behind slow earthquakes.

By Aaron Sidder

30 January 2024

The presence of multiple rock veins like these ones, found in an exhumed metasedimentary unit in the Arosa Zone, Switzerland, is evidence of tectonic tremors. Recent laboratory experiments have improved understanding of the underlying mechanisms and behaviors of these tremors, offering new insights into slow earthquakes. 

Credit: Condit and French, 2022, https://doi.org/10.1029/2022GL098862, CC BY 4.0

Source: AGU Advances

Earthquakes that cause conspicuous surface shaking and infrastructure damage are the result of fast ruptures and slippage along faults. But they aren’t the only types of movements occurring in Earth’s crust.

Fast earthquakes last just a few seconds or minutes and emit large, easily observed seismic waves. In contrast, slow earthquakes, mostly aseismic, can last days to years and generate tiny waves called tremors. These tremors are observed primarily through highly sensitive networks of seismic sensors. Although slow earthquakes, whose waves proceed 3 to 4 orders of magnitude more slowly than those of fast rupturing quakes, occur often and relieve stresses in Earth, the mechanisms that cause them remain largely unknown.

Yuan et al. developed a laboratory experiment to observe drawn-out fractures and better understand how slow earthquakes form. The authors 3D printed a small cylinder (about the size of a bagel) out of a stiff and transparent plastic called polymethylmethacrylate and then injected the model with pressurized viscous fluid to create a fracture. Using high-speed photography and acoustic sensors, the authors watched and listened to the breaks and cracks caused by the expansion of the fluid. The so-called hydrofracturing experiment replicated tectonic tremors and aseismic slips in the ground.

The results showed slow cracks radiating from the initial fracture in a bursty, or intermittent, pattern and that their spread was influenced by the viscosity and pressure of the injected fluid. The fractures matched observed patterns of slow earthquakes and tremors in Cascadia, a tectonically active region stretching from Northern California to British Columbia.

The results offer insights into the generation of the slow slips and tectonic tremors that comprise slow earthquakes. Additionally, the study provides clear experimental evidence that fluids and hydrofracturing contribute to these events and that radiated seismic energy can serve as a measure of slow earthquake rupture area or size. (AGU Advances, https://doi.org/10.1029/2023AV001002, 2024)

—Aaron Sidder, Science Writer
Citation: Sidder, A. (2024), Scientists model what’s moving beneath Earth’s surface, Eos, 105, https://doi.org/10.1029/2024EO240026. Published on 30 January 2024.