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Publication date: 15 July 2026

Source: Earth and Planetary Science Letters, Volume 686

Author(s): Xin Wang, Duo Li, Jun Zhu, Xiaohua Xu, Zefeng Li, David Sandwell, Dengcheng Hao, Chengli liu, Rongxin Fang

Publication date: 15 July 2026

Source: Earth and Planetary Science Letters, Volume 686

Author(s): Max Hellers, Jonas Tusch, Carina Gerritzen, Eric Hasenstab-Dübler, Mario Fischer-Gödde, Andreas R.A. Schneider, Chris S. Marien, Josua J. Pakulla, R. Hugh Smithies, Martin J. Van Kranendonk, Dieter Garbe-Schönberg, Carsten Münker

Publication date: 15 July 2026

Source: Earth and Planetary Science Letters, Volume 686

Author(s): Daniel W.J. Lee, Terry Plank, Shuo Ding, Euan J.F. Mutch, Yves Moussallam, Jamshid Moshrefzadeh, Nathan Graham, Jessica Larsen

Publication date: 15 July 2026

Source: Earth and Planetary Science Letters, Volume 686

Author(s): Qi Chen, Craig Lundstrom, Yanchong Li, Young Jay Ryu, Tony Yu, Stella Chariton, Dongzhou Zhang, Vitali Prakapenka, Yanbin Wang

Publication date: 15 July 2026

Source: Earth and Planetary Science Letters, Volume 686

Author(s): Matthew Gleeson, Mark Richards, Cinzia G. Farnetani, Kaj Hoernle, Sally Gibson

Publication date: 15 July 2026

Source: Earth and Planetary Science Letters, Volume 686

Author(s): Xudong Zhao, Yifei Li, Huiping Zhang, Richard O. Lease, Ying Wang, Yuqi Hao, Zifa Ma, Hao Xie, Huan Kang, Jianguo Xiong, Peizhen Zhang

Publication date: 15 July 2026

Source: Earth and Planetary Science Letters, Volume 686

Author(s): Shengchao Yang, Thomas J. Algeo, Thomas Servais, Ronald E. Martin, David A.T. Harper, Charles R. Marshall, Yiying Deng, Zongyuan Sun, Zhengbo Lu, Jian Cao, Chao Li, Shu-zhong Shen, Isabel P. Montañez, Junxuan Fan

Publication date: 15 July 2026

Source: Earth and Planetary Science Letters, Volume 686

Author(s): Jie Wu, Shane J. Cronin, Marco Brenna, Joali Paredes-Mariño, Sung-Hyun Park, Mila Huebsch, Alessio Pontesilli, Chris Firth, David Adams, Teresa Ubide, Kyle Hamilton, Alice MacDonald, Enrico Califano, James D.L. White, Terry Plank, Marta Ribó, Ingrid Ukstins, Frank Ramos, Silvio Mollo, Jihyuk Kim

body {background-color: #D2D1D5;} Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.

Sand is the most exploited solid natural resource on Earth. It has been integrated into how we build homes, roads, buildings, and bridges as well as how we protect coastal infrastructure from rising seas. Sand underpins nearly every aspect of modern infrastructure and economics, plays crucial roles in supporting ecosystem biodiversity, and literally shores up rivers and coasts.

A new report from the United Nations Environment Programme (UNEP) found that we are using 50 billion metric tons (50 trillion kilograms) of sand per year. As global development and industrialization expand, demand for sand in the building sector is expected to rise 45% by the year 2060, outpacing current efforts to sustainably harvest it. The report’s authors urge countries to establish sand as a strategic national asset and develop policies for sustainable extraction.

“Sand is sometimes referred as the unrecognized hero of development, but its essential role in sustaining the natural services on which we depend is even more overlooked,” Pascal Peduzzi, director of the UNEP Global Resource Information Database Geneva, said in a press release about the report. “Sand is our first line of defence against sea level rise, storm surges, and salination of coastal aquifers—all hazards exacerbated by climate change.”

Sand Wanted: Dead or Alive

Dead sand, or sand that has been extracted from its natural environment, is a key component in building materials like concrete and asphalt. Communities around the world use sand in water filtration systems, providing clean water for drinking and agricultural use. And although a transition to clean energy sources is necessary to curb the effects of climate change, many of those sources also depend on sand: solar panels require glass made from high-purity silica sand, and wind turbines, hydroelectric dams, and nuclear power plants all require concrete.

Mangroves, one of the most important coastal trees, can grow in sand. Credit: Diego Parra

Sand also plays a critical role in natural ecosystems. It is home to a wide array of critters from crabs, sharks, and turtles to microorganisms like bacteria and fungi. It supports the growth of corals, mangroves, and seagrasses that in turn support even more marine creatures. It is a key component of healthy soil and aids in surface drainage. It guides river evolution and acts as flood buffer and storm barrier. It also provides local economic benefits via tourism.

These are among the values of sand when it is left alone and unused, called “alive” sand. The UN report notes that these benefits are typically of greater value over time than if sand is dredged and used. But because these benefits are hard to see, they are often overlooked when nations calculate the value of their sand resources.

A Sustainable Sand Future

Despite sand’s importance whether dead or alive, the report notes that few countries have established sand as a strategic national asset or have developed strategies for sustainable extraction. At the current pace, humans are extracting sand from the natural environment at a faster pace than it is being replenished by geologic processes.

 
Related

•  Read the Report: Sand and Sustainability: An Essential Resource for Nature and Development
•  Track Global Sand Dredging: Marine Sand Watch
•  Dig Into the Details: Grains of Sand: Too Much and Never Enough
 

What’s more, the UNEP’s Marine Sand Watch tool shows that about half of sand dredging companies are operating within marine protected areas, accounting for about 15% of the volume of dredged sand. This practice, the report notes, is potentially trading in sand’s long-term benefits for short-term gains.

The UN report recommends a few actions to protect the long-term availability of sand as a natural resource, including:

• Recognizing sand as strategic national asset, establishing national inventories, and creating long-term regional planning groups that consider sand as an essential resource for resilience;
• Establishing circularity and recycling of building materials, especially in areas of conflict and natural disasters;
• Strengthening environmental protection practices, and codifying international frameworks to strengthen accountability along the supply chain, including increased transparency about extraction; and
• Integrating sand-related biodiversity and social risks into financial decisionmaking and governance.

“Over-reliance on short-term economic metrics risks obscuring, and further impacting, the geological and ecological processes that take centuries to form and may not be restored once critical thresholds are crossed,” the report states. “What is hardest to measure may be precisely what sustains both nature and human societies over the long term. The challenge ahead is not only to manage extraction, but to recognise and balance the full spectrum of sand’s values.”

—Kimberly M. S. Cartier (@astrokimcartier.bsky.social), Staff Writer

These updates are made possible through information from the scientific community. Do you have a story about science or scientists? Send us a tip at eos@agu.org. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

As the climate warms, tree lines are generally understood to move up, because regions that were previously too cold for trees to survive now have higher, more tree friendly temperatures.

A tree line is clearly visible in the Swiss National Park, in Graubünden, Switzerland. Credit: Sabine Rumpf, University of Basel

This migration can be seen in these images of Canada’s Waterton Lakes National Park…

Rising tree lines are visible in Canada’s Waterton Lakes National Park, seen here in 1913 (left) and 2007 (right). Credit: Mountain Legacy Project

…and of Jackson Glacier in Montana’s Glacier National Park, for example.

Jackson Glacier, in Montana’s Glacier National Park, is seen here in 1912 and 2009. As the climate has warmed, the glacier has receded significantly, and tree lines have risen. Credit: MJ Elrod, U of M Library–9/3/2009, L McKeon, USGS

But new research, published in the International Journal of Applied Earth Observation and Geoinformation, paints a more complicated picture: Between 2000 and 2020, 42% of tree lines shifted up, true. But 25% of them actually moved downhill.

Sabine Rumpf, an ecologist at the University of Basel in Switzerland, said many studies of tree line shifts tend to be concentrated in limited geographic areas. A preponderance are based primarily on data from North America, Europe, and the Himalayas, where researchers are more likely to have funding to head to the field to take measurements themselves.

“But that also means that a large proportion of the surface of our planet is so understudied,” Rumpf said. “And [to remedy] that, remote sensing data [are] really amazing because you can get a truly global picture, even though there’s nobody, or too few people, observing things in the field.”

Tree Lines Aren’t Living up to Their Potential

So the team set out to take a more global look. They used a world mountain map, developed in 2018, with a 250-meter resolution. They did exclude some regions from their analysis: cells with less than 10% high-mountain coverage (which have so few trees that they don’t have much of a tree line) and cells more than 95% covered with trees (which have so many trees that they don’t have much of a tree line). For their purposes, the team defined the “observed tree line” as the upper limit of trees that stand 3 meters or taller.

Then, said Rumpf, they used a model to calculate the potential tree lines for each area, because, thanks to human effects on the environment, “where these trees could be surviving is almost always higher than where the trees are currently.” The model looked at the growing season length and mean growing season temperature for each cell in the map’s grid. The researchers determined that if a cell had a growing season length of 94 days or longer, and an average growing season temperature of 6.4°C or higher, it could potentially host trees. Cells that didn’t meet both criteria were considered unable to be covered in forest, and thus above the potential tree line.

With this model, “you can calculate based on climatic data where trees could potentially occur or not occur, even though they might not be there in the field,” Rumpf said. “It’s actually super simple. And that’s the beauty of it.”

Credit: Sabine Rumpf, University of Basel

Jordon Tourville, a terrestrial ecologist with the Appalachian Mountain Club, said the overall findings are not surprising, because other studies have shown seemingly “paradoxical downslope shifts in some cases.” But he noted that whereas this study estimated potential tree lines based on temperature constraints, some scientists have suggested that factors such as nutrient availability and wind exposure are also important in determining tree line position.

Unsurprising, on Second Thought

In areas with more human disturbance, the upward spread of trees is suppressed, or even reversed.

Armed with this information about observed versus potential tree lines, the researchers hypothesized that areas with the smallest deviation between the two were mostly responding to climatic factors. In contrast, they speculated, areas with a greater difference between observed and potential tree lines were likely experiencing more anthropogenic disturbance, such as logging, agriculture, and infrastructure development.

Their hypothesis held up. In areas with less human disturbance, tree lines were moving upward more quickly (the researchers noted, though, that the upward migration of tree lines lagged behind the rate of climate change). In areas with more human disturbance, the upward spread of trees is suppressed, or even reversed.

Fire played a big role in tree line shifts as well: The researchers found that 38% of the downslope shifts were linked to fire events. Wildfires played a particularly big role in western North America and Alaska.

Wildfires played a particularly large role in the downward shift of tree lines in western North America. Here, a tree line is visible in California’s Little Lakes Valley. Credit: mlhradio/Flickr, CC BY-NC 2.0

Rumpf and several of her colleagues are located in the Alps, where glaciers are retreating, tree lines are climbing, and towns are generally more threatened by mudslides than by wildfires.

Some of the study’s findings, like a quarter of tree lines shifting down, or such a clear signal from wildfires in some areas, were at first unexpected. But after some reflection, Rumpf realized the diversity of data was a perfect example of why global-scale research is important.

“A lot of scientific funding is based in North America and Europe,” Rumpf said, which means many studies return similar results. “Then we do something global and we are surprised that things are different somewhere else on the globe?… I mean, well, duh.”

—Emily Gardner (@emfurd.bsky.social), Associate Editor

This news article is included in our ENGAGE resource for educators seeking science news for their classroom lessons. Browse all ENGAGE articles, and share with your fellow educators how you integrated the article into an activity in the comments section below.

Citation: Gardner, E. (2026), Tree lines are migrating. Some up, some down., Eos, 107, https://doi.org/10.1029/2026EO260146. Published on 12 May 2026. Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

For roughly 45 million years, the eastern section of the African continental plate has been slowly pulling apart. Like a giant zipper extending from the Red Sea to Mozambique, the East African Rift System will likely be home to new oceanic crust that will well up from the widening split in Earth’s surface. While most of the rifts in that system are still zipped shut, the Afar region in northern Ethiopia has already partially unzipped and may be starting to create a future ocean basin.

Most models of this rift system suggest that it should continue to unzip sequentially from north to south. However, new research suggests that a region in the middle of the zipper is on the verge of splitting open.

High-resolution seismic reflection data show that the crust near Kenya’s Lake Turkana is only 13 kilometers thick. This suggests that the region has entered the second stage of rifting, called necking, and is one step closer to breaking apart. It is the only rift zone on Earth currently undergoing this short-lived tectonic process.

The Lothagam site in the Turkana Rift Zone contains tilted sediments from the late Miocene (about 7 million years ago), just before the necking phase of rifting commenced. Credit: Christian Rowan Breaking Up Is Hard to Do

Just like mid-ocean ridges on the seafloor, sections of Earth’s crust on land also stretch apart as tectonic plates separate. This process, called rifting, takes place in three stages. First, the crust stretches, creating tension. Then it rapidly thins like pulled taffy—this is the necking stage. Finally, magma wells up from the lithospheric mantle, which creates new seafloor and breaks the continental plate apart.

“This is one of the unique places on Earth where you can see a continental rift.”

Not every rift makes it that far. Some remain stuck in the stretching phase with crust more than 20 kilometers thick. But northern sections of the East African Rift System (EARS), specifically the Afar Rift and the Red Sea, are already undergoing the final stage, oceanization.

“This is one of the unique places on Earth where you can see a continental rift,” said Anne Bécel, a geophysicist at Lamont-Doherty Earth Observatory of Columbia University in Palisades, N.Y., and coauthor of new research published in Nature Communications in April. “The East African Rift System has been studied for a very long time by geologists to really learn about our planet and how continents break apart, and then transpose that to mid-ocean ridges where oceanic plates spread apart.”

The team suspected that the Turkana Rift Zone, located at a critical triple junction in northern Kenya, was behaving differently from other areas of the rift system. It is home to an unusually large and continuous hominin fossil record dating back about 4 million years. Past research has also shown that the bottom of the crust, called the Moho, is unusually shallow in the Turkana Basin, just 20 kilometers deep compared with the average depth of 39 kilometers farther away from the rift.

During several field expeditions to Lake Turkana in partnership with local industries, the team mapped the top of the continental crust using borehole measurements and seismic reflection—sending seismic waves into the ground and measuring how the waves bounce back, like sonar. They combined those measurements with past research into Moho depths to calculate the crustal thickness near Lake Turkana.

That map showed that far away from the rift, the crust is more than 35 kilometers thick, but in the Turkana Rift Zone it is a mere 13 kilometers thick, below the threshold for necking.

“If you look at the modern day topography, the whole East African Rift is in this really low, broad land between two big plateaus, one to the north in Ethiopia and one towards the south,” said lead researcher Christian Rowan, a geologist and doctoral candidate at Columbia University. “It’s this very strange topographic feature, and part of that low-lying topography is actually how thin the crust is there.”

“The oldest rocks that record the initiation of the East Africa Rift System are also in the Turkana Rift,” said coauthor Folarin Kolawole, a Columbia University geologist. Geochemical analysis of those rocks suggests that necking in the Turkana Rift Zone began about 4 million years ago.

Christian Rowan measures a fault in the Turkana Rift. Credit: Christian Rowan About to Break?

“Any time you have a place on the planet that is rare in the modern but seen in the past, it is compelling,” said Erik Klemetti Gonzalez, a volcanologist at Denison University in Granville, Ohio, who was not involved with this research. “The data does show that the Turkana Rift is the home of anomalously thin continental crust, so if you are looking for a location that meets criteria for necking, it seems to be the case.”

The team suspects that Turkana might have been primed to split apart more easily because another rifting event took place there a mere 17 million years before the present rift began. The Turkana Basin inherited a weaker section of crust that didn’t have time to fully heal in the (geologically) short time between rifting events. There was also an extended period of magmatic activity throughout much of the past 45 million years.

“Magmatism is well known to be a significant weakening factor in rifting,” Rowan said. “I think the two compounding effects of this inheritance and then magnetism is why the Turkana rift is so much more mature than other segments.”

“I would hope that more collaboration with African geoscientists could create the ability to collect data from places that have been more inaccessible over the past half century.”

“There are many ‘failed rifts’ in the geologic record, so the question of whether the EARS is actually leading to a continental break up, albeit a small one, is still very much up in the air,” Klemetti Gonzalez said. These new results tip the scales toward breakup, but he noted that more of the rift system still needs to be mapped to really understand the fate of this region.

“I would hope that more collaboration with African geoscientists could create the ability to collect data from places that have been more inaccessible over the past half century,” he added.

Rowan and his team are working toward that end by continuing to map crustal thicknesses in other nearby rift zones.

“This was the only known rift that was undergoing necking along the entire East African Rift System, or in the world,” said Kolawole. “But based on ongoing work, there is evidence that there are other segments that are at the onset of necking in the East African Rift System.”

—Kimberly M. S. Cartier (@astrokimcartier.bsky.social), Staff Writer

Citation: Cartier, K. M. S. (2026), Eastern Africa is splitting apart, but not where we expected, Eos, 107, https://doi.org/10.1029/2026EO260148. Published on 12 May 2026. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Author(s): L. N. A. Amaral, J. D. Szezech, and I. L. Caldas

We introduce a simple symmetric Hamiltonian map that models the magnetic field lines of a double-null diverted tokamak and compare its behavior with the corresponding symmetric single-null map. The phase-space structure of both models is characterized using the finite-time Lyapunov exponent and the …

[Phys. Rev. E 113, 055207] Published Tue May 12, 2026

Author(s): I. Dukanov, E. Yushkov, P. Frick, and D. Sokoloff

Based on the data recorded during the Parker Solar Probe mission, it can be suggested that there is no balance between kinetic and magnetic energy in the vicinity of the Sun. The spectra collected at different radial distances show an energy transfer from one component to another, followed by a chan…

[Phys. Rev. E 113, 055208] Published Tue May 12, 2026

Author(s): Eran Daniel, Gilad Hurvitz, Yuri Ralchenko, Ariel Shaham, Moshe Fraenkel, Yosi Ehrlich, Izhak Levi, Yair Ferber, Galit Strum, Yacov Carmiel, and Ehud Behar

A wide variety of spectroscopic methods are used for the diagnostics of laser-produced plasma. One particularly powerful diagnostic is high-resolution emission line spectroscopy, in conjunction with atomic calculations and radiation hydrodynamic simulations. In this work, we present line-resolved sp…

[Phys. Rev. E 113, 055209] Published Tue May 12, 2026

body {background-color: #D2D1D5;} Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.

As the midpoint of the year approaches, several climate records have already been broken. Arctic winter sea ice extent reached a record low. Several countries saw record-breaking winter heat waves. And more than 150 million hectares have already burned globally in wildfires. 

The increasingly likely emergence of an El Niño this summer will likely continue the year’s record-breaking weather trends and could lead to “an unprecedented year of global fire,” according to a statement from World Weather Attribution, a climate research collaboration. 

“In modern human history, we’ve never experienced a strong or very strong El Niño event amid pre-existing conditions that were this warm globally.”

NOAA’s Climate Prediction Center predicts there is a 61% chance of El Niño—a natural climate pattern that involves warming waters in the Pacific Ocean—emerging by July 2026 and persisting through the end of the year. El Niño typically temporarily boosts global temperatures. 

At a press briefing on 11 May hosted by World Weather Attribution, climate scientists outlined the potential risks of this emerging El Niño against the backdrop of human-caused climate change, including intensifying wildfire seasons, extreme heat waves, and worsening droughts.

In the press briefing, Frederike Otto, a climate scientist at World Weather Attribution and Imperial College London, emphasized that climate change will likely play a larger role in the rest of this year’s extreme weather events than El Niño will, pointing to more than 100 analyses done by World Weather Attribution that have controlled for the effects of the El Niño Southern Oscillation (ENSO), the broader climate phenomenon that produces El Niño and its sister condition, La Niña. 

 
Related

•  Read About the 2024 El Niño: Record-Breaking Temperatures Likely as El Niño Persists
 

“We find that human-induced climate change has a much greater influence on the likelihood and intensity of extreme weather events than ENSO,” she said. 

Still, El Niño could push average global temperatures to extremes. The effects of El Niño will “be amplified considerably by the now nearly 1.5°C [(2.7°F)] of global warming experienced as of 2026,” Daniel Swain, a climate scientist at the University of California, Los Angeles and the California Institute for Water Resources, said in a statement. “In modern human history, we’ve never experienced a strong or very strong El Niño event amid pre-existing conditions that were this warm globally.”

The global fire season has “got off to a very fast start,” particularly in the African savanna, Southeast Asia, and northeastern China, Theodore Keeping, who studies extreme weather and wildfires at Imperial College London and World Weather Attribution, said in the briefing. Though El Niño may have mixed effects on the U.S. wildfire season, much of the U.S. is expected to face elevated wildfire risk, and a strong El Niño could worsen wildfires elsewhere in the world, particularly in the Amazon rainforest and Australia, Keeping said. 

More than 150 million hectares have burned in wildfires so far this year. Credit: Our World in Data, CC BY

“This rapid start [to the wildfire season], in combination with the forecast El Niño, means that we’re looking at a particularly severe year materializing,” Keeping said. “The likelihood of harmful, extreme fires potentially could be the highest we’ve seen in recent history.”

—Grace van Deelen (@gvd.bsky.social), Staff Writer

These updates are made possible through information from the scientific community. Do you have a story about science or scientists? Send us a tip at eos@agu.org. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Isotope analysis of gas from geothermal springs in Zambia could show that a new continental rift is forming, scientists say. Unexpectedly high helium isotope ratios indicate that a weakness in Earth's crust has broken through to reach the mantle beneath. This rift could eventually become a new tectonic plate boundary. In the meantime, opportunities for geothermal energy could boost local economies.

SummaryThe collision between the European plate and the Adria microplate during the Cenozoic led to the formation and uplift of key mountain belts, including the Alps, Apennines, and Dinarides. This convergence also resulted in a highly complex assemblage of tectonic units, each characterized by distinct geological and geophysical properties within the accreted crustal domains. A comprehensive understanding of the geodynamic evolution of this region requires integrated imaging of both the crust and upper mantle. To achieve this goal, we apply Teleseismic Full Waveform Inversion (TFWI) to P-wave seismic data recorded by permanent European broadband stations, supplemented by the dense temporary deployments of the AlpArray initiative, SWATH-D, and CIFALPS-2 projects. Leveraging this unprecedented seismological coverage, our study aims to design a suitable TFWI workflow to develop a multiparameter model defined by P- and S-wave velocities and density of the Alpine orogen down to 500-km depth. The critical importance of high-quality data for ensuring the reliability of TFWI results first prompts us to develop a semi-automated workflow for data selection and quality control, from which we select 84 teleseismic events for inversion. The seismograms were filtered within the 5-to-25-s period band, and a 30-s time window from the first arrival was used for inversion. Other critical aspects are the assessment of the resolution power of TFWI provided by the field acquisition geometry, as well as potential sources of artefacts. We review the key theoretical factors controlling resolution and imaging artefacts, and further illustrate these issues with numerical experiments designed with the field acquisition geometry to provide the necessary guidelines for sound geological interpretation of the TFWI models. The reconstructed TFWI models effectively capture key crustal features, including low-velocity sedimentary basins, high-velocity anomalies like the Ivrea Body, deep mountain roots beneath the Alpine and Apennine chains, and the signature of the continental subduction. The TFWI models also reveal small-scale anomalies previously identified by local tomography studies. Then, we extend the analysis at upper-mantle depths by comparing the footprint of the subducting slabs in the P and S velocity TFWI models with previous ones obtained by surface wave tomography and teleseismic body-wave traveltime tomography. These comparative analyses highlight the incomparable power of TFWI to resolve multiparameter models of the Earth’s interior from the surface down to the upper mantle. From this first critical analysis of the TFWI results, a comprehensive geological survey of the reconstructed structures will be presented in a companion paper.

SummaryThe complexity of earthquake rupture dynamics and the diversity of observed seismic behaviors are fundamentally governed by the frictional properties of faults and their response to tectonic stress. Grounded in the rate-and-state constitutive law derived from laboratory experiments on rock friction at slow slip velocities, we employ a fully dynamic model to investigate how frictional conditions give rise to a diverse range of rupture modes and influence their propagation dynamics. Under uniform background stress and nucleation conditions, the rupture type, whether supershear, sub‑Rayleigh, self‑arresting or slow self‑arresting rupture (SSAR), is governed by the relative contributions of the direct effect and the evolution effect, expressed as $R = 1 - \frac{a}{b}$, together with the normalized characteristic slip distance D. Their respective regimes are summarized in a phase diagram. We demonstrate that the friction parameters R and D significantly influence the rupture process, with R primarily enhancing stress release and slip during rupture, while D predominantly controls the rupture speed. For varying values of R, there exists an optimal intermediate D that maximizes rupture velocity. Furthermore, simulations suggest that when frictional parameters approach the boundaries between different rupture types regimes, the earthquake may not be confined to a single mode. Instead, a single rupture event can exhibit complex, continuous, yet rapid transitions between distinct types under a single triggering without interruption. These transitions can occur smoothly among various rupture types, including transitions from SSAR to sub-Rayleigh rupture and subsequently to supershear rupture. This study indicates the key role of frictional properties in governing rupture dynamics, offering new perspectives on the inherent complexity of earthquake processes.

SummaryThe Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission continues the legacy of satellite gravimetry in monitoring Earth’s mass redistribution. Equipped with dual-frequency Global Positioning System (GPS) receivers and a K-Band Ranging (KBR) system, it enables precise orbit determination and high-resolution gravity field recovery. While integer ambiguity resolution (IAR) has proven effective for GPS-based orbit determination, its impact on time-variable gravity field recovery remains unclear. Here we develop a dynamic framework that jointly estimates GRACE-FO satellite orbits and monthly gravity fields by integrating GPS and KBR observations, in which single-differenced integer ambiguities are fixed and constrained into the normal equations as pseudo-observations with micrometer-level constraint precision. Using GRACE-FO onboard data from July to December 2019, we compare ambiguity-fixed and ambiguity-float solutions in terms of post-fit residuals, orbit accuracy, and gravity field quality. IAR improves three-dimensional orbit precision to ∼1.2 cm RMS, with along- and cross-track components enhanced by up to 52 per cent and 71 per cent, respectively. Satellite Laser Ranging validation confirms ∼1.2 cm agreement. Gravity field solutions from float ambiguities agree closely with official Science Data System (SDS) RL06.1 models up to degree 96, whereas IAR-based solutions maintain consistency only to about degree 40 and exhibit irregular oscillations beyond this range, particularly near orbital resonance conditions around order 45. At higher degrees, these oscillations are accompanied by intensified north–south striping in equivalent water height maps. Covariance diagnostics reveal increased off-diagonal correlations between spherical harmonic coefficients under IAR, indicating weakened spectral orthogonality and potential leakage of high-degree noise. These results indicate that ambiguity-fixed gravity solutions do not consistently outperform float-based solutions beyond spherical harmonic degree 40 in the near-polar orbiting GRACE-FO constellation.

Researchers have cautioned that well-intended suggested changes to carbon markets risk worsening climate impacts if core safeguards are weakened. Climate change, biodiversity loss and human rights are deeply interconnected challenges, often sharing solutions that can deliver shared benefits.