Scientists capture slow-motion earthquake in action
University of Texas at Austin
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Sensors and observation instruments being lowered into a borehole off the coast of Japan nearly 1,500 feet below the seafloor during an International Ocean Discovery Program mission in 2016. Sensors like these transmit data in real time to researchers in Japan and at the University of Texas Institute for Geophysics, and enabled researchers to detect and describe a slow slip earthquake in motion in a new study in Science.
view moreCredit: Photo courtesy of Dick Peterse - ScienceMedia.nl
Scientists for the first time have detected a slow slip earthquake in motion during the act of releasing tectonic pressure on a major fault zone at the bottom of the ocean.
The slow earthquake was recorded spreading along the tsunami-generating portion of the fault off the coast of Japan, behaving like a tectonic shock absorber. Researchers from The University of Texas at Austin described the event as the slow unzipping of the fault line between two of the Earth’s tectonic plates.
Their results were published in Science.
“It's like a ripple moving across the plate interface,” said Josh Edgington, who conducted the work as a doctoral student at the University of Texas Institute for Geophysics (UTIG) at UT Austin’s Jackson School of Geosciences. Slow slip earthquakes are a type of slow-motion seismic event that take days or weeks to unfold. They are relatively new to science and are thought to be an important process for accumulating and releasing stress as part of the earthquake cycle. The new measurements, made along Japan’s Nankai Fault, appear to confirm that.
This breakthrough research was made possible by borehole sensors that were placed in the critical region far offshore, where the fault lies closest to the seafloor at the ocean trench. Sensors installed in boreholes can detect even the slightest motions – as small as a few millimeters, said UTIG Director Demian Saffer, who led the study. Such movement on the shallow fault is all but invisible to land-based monitoring systems such as GPS networks.
The slow slip earthquake, captured by the team’s sensors in fall of 2015, travelled along the tail of the fault — the region close to the seafloor where shallow earthquakes can generate tsunamis — easing tectonic pressure at a potentially hazardous location. A second slow tremor in 2020 followed the same path.
Although the Nankai Fault is known to generate large earthquakes and tsunamis, the discovery suggests that this part of the fault does not contribute energy to these events – acting more like a shock absorber. The results will help researchers home in on the behavior of subduction zone faults across the Pacific Ring of Fire, the tectonic belt that spawns the planet’s largest earthquakes and tsunamis
The two events, which have only now successfully been analyzed in detail, appear as ripples of deformation traveling through Earth’s crust. Originating about 30 miles off the coast of Japan, borehole sensors tracked this unzipping motion along the fault as it moved out to sea before dissipating at the edge of the continental margin.
Each event took several weeks to travel 20 miles along the fault, and each one happened in places where geologic fluid pressures were higher than normal. The finding is important because it is strong evidence that fluids are a key ingredient for slow earthquakes. This is an idea widely circulated in the scientific community, but finding a direct connection has been elusive until now.
The last time Japan’s Nankai Fault produced a significant earthquake was in 1946. The magnitude 8 earthquake destroyed 36,000 homes and killed over 1,300 people. Although another large earthquake is expected in the future, the observations suggest the fault releases at least some of its pent-up energy harmlessly in regular, re-occurring slow slip earthquakes. The location is also important, because it shows that the part of the fault nearest the surface releases tectonic pressure independently of the rest of the fault.
Armed with that knowledge, scientists can begin to probe other regions of the fault to better understand the overall hazard it poses. The knowledge is also vital for understanding other faults, Saffer said.
For instance, Cascadia, a massive earthquake fault facing the Pacific Northwest, appears to lack Nankai’s natural shock absorber. Although some slow slip has been detected at Cascadia, none has been detected at the tsunami-generating, tail end of the fault, which suggests that it may be strongly locked to the trench, Saffer said.
“This is a place that we know has hosted magnitude 9 earthquakes and can spawn deadly tsunamis,” Saffer said. “Are there creaks and groans that indicate the release of accumulated strain, or is fault near the trench deadly silent? Cascadia is a clear top-priority area for the kind of high-precision monitoring approach that we’ve demonstrated is so valuable at Nankai.”
The borehole observatories used in the Japan study were installed by the Integrated Ocean Drilling Program and funded by the U.S. National Science Foundation. Other data were supplied by ocean floor cable observatories operated by Japan Agency for Marine-Earth Science and Technology (JAMSTEC).
Journal
Science
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Migrating shallow slow slip on the Nankai Trough megathrust captured by borehole observatories
Article Publication Date
26-Jun-2025
Review: New framework needed to assess complex “cascading” natural hazards
Summary author: Walter Beckwith
In a Review, Brian Yanites and colleagues argue the need for a unified, interdisciplinary approach to studying cascading land surface hazards. Earth’s surface is continually shaped by a range of natural processes, from slow erosion to sudden disasters like earthquakes and floods. Notably, one hazardous event can trigger a series of subsequent, interrelated disasters, or ”cascading hazards,” that unfold over timescales ranging from seconds to centuries. However, despite their growing impact on human populations, a comprehensive mechanistic framework from which to understand, predict, and manage these interconnected threats remains lacking. Here, Yanites et al. review current research on how Earth systems and the resulting land surface processes can interact in complex, sequential ways that intensify hazard risk. Unlike compound hazards, where multiple events occur independently but simultaneously, cascading hazards involve a direct causal link – one event alters the physical state of the landscape in a way that increases the likelihood of subsequent hazards. For example, earthquakes can destabilize hillslopes, raising landslide risk for years, while wildfires can transform vegetation and soil properties, amplifying the potential for debris flows during post-fire storms. According to the authors, the dynamic nature of these hazards challenges current risk assessment tools. To address this critical gap, Yanites et al. present a collaborative, cross-disciplinary framework that leverages recent technological advances and brings together atmospheric scientists, geologists, geomorphologists, engineers, and others to refine theory, models, and hazard monitoring. The authors argue that the development of a cascading hazards index could offer a promising tool by serving as an integrative, location-specific metric that synthesizes process-based models, observational data, and knowledge of hazard evolution to help communities assess these chains of evolving, interlinked hazards.
Journal
Science
Article Title
Cascading land surface hazards as a nexus in the Earth system
Article Publication Date
26-Jun-2025
New research aims to better predict and understand cascading land surface hazards
Indiana University
BLOOMINGTON, Ind. – When an extreme weather event occurs, the probability or risk of other events can often increase, leading to what researchers call “cascading” hazards.
For example, the danger of landslides or debris flows following wildfires in California, recent flash floods in West Virginia or when historic flooding occurred in North Carolina as Hurricane Helene made its way inland. Such occurrences leave lasting imprints on the landscape that can prime the Earth’s surface for subsequent events.
As part of a collaboration by dozens of researchers across the country, a new paper published in Science, "Cascading land surface hazards as a nexus in the Earth’s system,” outlines a framework to better predict, understand and forecast the cascade (or chain reaction) of these hazards across the landscape.
“There is a scientific need for improving our understanding of these cascading hazards,” said Brian Yanites, lead author and associate professor of earth and atmospheric sciences in The College of Arts and Sciences at Indiana University. “If we want to better prepare for events like hurricanes, we need to also understand a hurricane’s connection to other hazards.”
"How does a hurricane or an earthquake impact the landscape and change the risk for future landslides or floods? How do landslides change river systems’ flooding potential downstream because they suddenly have extra sediment? And how does the Earth’s biosphere, including the microbes converting rock to moveable sediment and tree roots holding soil in place, impact these cascades?”
The paper is the result of a two-year grant from the National Science Foundation, which supported the creation of the Center for Land Surface Hazards Catalyst, or CLaSH. Led by Marin Clark of the University of Michigan, the center catalyst brought together experts from across the country to analyze existing research gaps to better understand connections between Earth systems and processes that change as a consequence of Earth’s shifting surface.
"It's really been work that's come forward in just the last 10 years, following some major events—fires, earthquakes, hurricanes," said Clark, co-author and professor of earth and environmental science at the University of Michigan. "These have given rise to data sets and the thinking about how we can piece together these processes to predict future hazard conditions."
In real time
“It's a vivid memory for me – the Tuesday before Hurricane Helene,” said Yanites. “I emailed the research team that's been working on this new National Center, and I said, ‘This is going to be bad for southern Appalachia.’ We started monitoring it that night, knowing that there were going to be landslides and flooding. But we don't really have the scientific tools to go and say, 'How many landslides? Where are they going to be? What are the consequences for downstream processes and impacts?’”
Researchers say this new framework could also help with disaster response to build societal resilience after natural hazards.
"The federal government and state agencies are charged with reducing losses related to disasters, but we really lack an academic research community in the U.S. focused on primary basic research," said Clark. "That underpins disaster response and enables training a future workforce capable of meeting the urgent and growing need for resilience to natural hazards. This resilience is essential for both safety and economic growth."
Yanites added that this could also help the insurance industry better understand potential hazards.
"In California, we’re seeing a number of major insurance companies that aren’t offering new homeowner insurance in areas because of cascading hazards, such as a debris flow that happens five years after a wildfire,” said Yanites. “They don’t understand how to price cascading hazards into their models.”
Researchers hope to use this future framework to provide a path toward developing actionable plans for communities to prepare for cascading hazards. They also hope to create a “cascading hazards index” to give local communities context for potential cascading events.
For reporters: More information, including a copy of the paper, can be found online at the Science press package.
Journal
Science
Method of Research
Meta-analysis
Subject of Research
Not applicable
Article Title
Cascading land surface hazards as a nexus in the Earth system
Article Publication Date
26-Jun-2025
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