The Cascadia Subduction Zone is a massive geologic fault that last ruptured in January 1700. But while this fault has stayed quiet for centuries, it regularly generates small tremors that accompany gradual, nondisruptive movement along the fault.

The tiny tremor events and slow slippage are known collectively as “.” Seismic waves associated with these tremor events are recorded and tracked by the UW’s Pacific Northwest Seismic Network. Other groups track the associated slow motion of the plates using GPS measurements. These paired types of events occur regularly and seem to fluctuate with tidal cycles, but they originate deep underground and their cause has been mysterious.

A pair of papers published Jan. 29 provides new confirmation of speculations about a cause of these events. Taken together, the papers show that fluids deep underground create fractures in the rock, and that this creates rumblings that match what we observe at the surface.

, an assistant professor of Earth and space sciences at the UW, and , an affiliate associate professor at the UW who is based with the U.S. Geological Survey, are co-authors on the about the experimental findings.

Denolle began advising lead author Congcong Yuan as a faculty member at Harvard before joining the UW faculty in 2022. Denolle and Gomberg sat down with UW News to answer some questions about the study, and what it means for the Cascadia region.

UW News: What are slow slip earthquakes? And how are slow slip events related to larger, more damaging earthquakes?

Joan Gomberg: When cracks form really quickly, that’s an earthquake. When the rock beneath the surface breaks and moves really fast, and that sends out these big loud vibrations that travel as waves and can knock down buildings. So you care about that a lot.

But sometimes the same thing happens really slowly. So slowly that it doesn’t send out big waves. And it makes these little, tiny little rumblings and shaking, but nothing gets knocked down.

Marine Denolle: The slow earthquakes in Cascadia are a bit more predictable and tractable than large earthquakes. Slow events are accompanied by the “pops” that we detect as tremor at the surface every 12 to 15 months, so they are semi-periodic. These tremor signals, or the “pops” are tracked by the Pacific Northwest Seismic Network — not the larger-scale, slow, absolute fault displacement.

JG: These pops, even though they don’t hurt anything, are really just telling you that something is happening. They’re telltale evidence that yes, something is moving, something is going on. In seismology we call it a passive marker. It’s just a little something chattering, saying: ‘Hi, I’m here, I’m moving!’

Can you describe this experiment that forms the basis of the new AGU Advances paper?

MD: At Harvard we had the apparatus to 3-D print materials, inject high pressure fluid in it, and have a high-speed camera to observe how hydrofracturing cracks the material. What we wanted to do is listen to the sound of the fracture and find the source of the acoustic emissions — sound waves — or vibrations, to map the geometrical expansion of the fracture. We can’t see through rocks, so we wanted to make this experiment with a transparent sample, where we have the ground-truth between acoustic emissions and visualization of the fracture growth.

Because we could see through the sample this slow-growing fracture that has all these pops, we realized that this looks like what we’d see in nature for slow-slip earthquakes, except that we had to invoke the use of fluids to drive the fracture.

Our results show a potential model for slow earthquakes. They are related to the faster earthquakes, in the sense that they relieve stress and they may load stress nearby for future earthquakes. Understanding the behavior at all scales and at all speeds is part of understanding earthquakes that eventually will matter for damaging ground motion.

Your research found that hydraulically driven fractures are causing the seismic signals we observe at the surface. Deep in the Earth, where is the fluid coming from?

JG: Most rocks are in solid form but they have H2O bound up inside of them. It’s not fluid, but it’s got hydrogen and oxygen, and under certain conditions deep in the Earth, when the temperatures and pressures get large enough, that actually does get released. It isn’t melting. It’s just with sufficient pressure and temperature the water is released from of the minerals.

Two papers are being published at the same time. Can you explain how they relate to one another, and to the seismology we observe in nature?

MD: The paper by our colleagues is about the mechanics of these fractures. And our paper in is about how can we provide an analogy, or a model, to the natural world. How can this mechanistic model provide an explanation for the observations that we see in the Earth?

One similarity we observed between the experimental and natural systems was how much seismic energy was released for events of different size. And the other one was the intermittency of the fracture’s growth. When there is a little bit of viscosity in the fluid, the fracture sticks for a while and then pops a little bit before it progresses. Sticks for a while, then pops. And these irregular pops are what has been observed in the natural system.

The evolution of the rupture, the slow-moving, fracturing in the lab was as intermittent and as irregular as what we would see in nature. So it looks like the overall evolution style was similar.

JG: This result shows that it’s all about the role of water — fracturing rock and squishing water into it. If you look at these rocks, it’s very clear that they’re full of veins. Many times there’s a black rock but it has all these white squiggly lines through it that very likely formed as fluids squirted into opening fractures.

This study connects those fluid-filled veins to the observed seismicity. They always say that invoking fluids is a geophysicist’s last resort: If you don’t know how to explain something, say, ‘Oh, it must have been the fluids.’ And so I was skeptical. But this makes me a bigger believer in fluids.

Why use a 3-D printed model for a process that occurs in the Earth?

JG: In the Earth you can measure the seismic waves at the surface, even though they’re being generated way down. But you can never see the crack. These processes occur many, many miles beneath the surface, and you’ll just never see them. The only time you actually see this environment is that sometimes these rocks that are buried miles down just naturally rise up to the surface over millions of years. This is what the geologists call “exhumed.” And you can see they have all these little fractures in them that have been filled with water and minerals and other stuff. But it’s long after the fact — you didn’t see them form, you only see the aftermath.

The experiment in the lab was a way to try to simulate this, so that you could see everything as it was happening. This allowed us to see the cracks form and connect that to the seismic signals we detect at the surface.

What do you think is most exciting about this result?

MD: It’s exciting to see a new demonstration of how the tectonic tremors we observe at the surface could be deep hydraulic fractures in which cracks form and open due to pressurized fluids. As geophysicists, we just assume that the tectonic movements are shear, or sliding motion between two solid objects. But we show experimentally that hydraulic fracture is consistent with the geological record.

For more information contact Denolle at mdenolle@uw.edu and Gomberg at gomberg@usgs.gov.

Unlike the Pacific Northwest, the Atacama Desert in Chile experiences very little rain. But the two regions are both seismically active. Faults in the Atacama Desert are slowly sliding past each other in a way similar to the Seattle Fault in Puget Sound and the San Andreas Fault in California. The Atacama Desert’s lack of rain makes it easier to see how those gradual movements shape the landscape over time.

Alison Duvall, a ����Ӱ�Ӵ�ý associate professor of Earth and space sciences, and doctoral student will travel to Chile this month to study landscapes developed along these types of faults. Duvall has previously studied historic landslides at the site of the rainfall-triggered Oso mudslide and how rainfall, earthquake and landslide risks combine in Oregon.

UW News asked the two geophysicists about their upcoming trip as part of a new series, “In the Field,” highlighting UW field research.

Where are you going, and when?

Tamara Ará�Բ��ܾ���-�鲹����: We will visit the , in the hyper-arid, or dry, core of the Atacama Desert in Northern Chile. The Salar is a dry lakebed that contains economic resources, in the form of salt, that is extracted from the basin and then exported around the world. We’ll be there Nov. 19-25.

We’re interested in this area because it’s extremely dry and has active faults slicing through it. Only a few places on Earth register such low rates of precipitation, offering a landscape that stores climate and tectonic variations from the past 50 million years. At our field site, there are places that haven’t seen a drop of rain in 500 years!

As a result, this is one of the best places on Earth to study how landscapes respond to earthquakes and plate tectonics under hyper-arid conditions. Dry conditions slow down erosion and help preserve landscape form and enable us to observe processes, like tectonic processes, that modify the surface from deeper down.

Have you visited this field site before?

TA: I visited this site last fall with , another doctoral student in the Department of Earth & Space Sciences.

Alison Duvall: This will be my first time to this site, to Chile and to South America.

What do you hope to learn there?

AD: We want to learn more about the dynamics of slow faults that move laterally — strike-slip faults, similar to the San Andreas Fault in California — and how these dynamics control the shape of the landscape. In wet places, it’s hard to isolate faults’ effects on the landscape since water is the main agent driving erosion. What we observe on the surface in other places is a combination of tectonics and surface processes. However, thanks to the aridity of this place, it is easier to be confident about what is changing the landscape.

We’re also interested in how this landscape has shifted with a changing climate. This place was wetter in the past, and there is evidence of climate change happening to make the region hyper-arid. So we are also studying how the landscape has adapted to that change.��

What’s something that you enjoy about this field work — especially something that might not occur to most people?

TA: There is a really special feeling when you’re in the driest place on Earth. It almost feels like you’re on a different planet. You don’t see any signs of life — no water, no animals, no plants — but it’s just amazing to feel that nothingness.

Changes in the landscape are so slow that when you visit the site, you know that each step you make, or any perturbation we make to collect our samples, can be one of the biggest modifications to the landscape in hundreds of years.

Anything you’d like to add?

AD: I’m super excited to get to this incredible field site and spend time with Tamara studying it. We have done field work together in New Zealand, and I have done decades’ worth of field work in many different geomorphic settings, but never in a hyper-arid landscape like this one. I can’t wait to see what we find!

The ����Ӱ�Ӵ�ý is a lead partner on a new multi-institution earthquake research center based at the University of Oregon that the National Science Foundation announced Sept. 8 will receive $15 million over five years to study the Cascadia subduction zone and bolster earthquake preparedness in the Pacific Northwest and beyond.

The Cascadia Region Earthquake Science Center, or CRESCENT, will be the first center of its kind in the nation focused on earthquakes at subduction zones, where one tectonic plate slides beneath another.

The center will unite scientists studying the possible impacts of a major earthquake along the Cascadia subduction zone, an offshore tectonic plate boundary that stretches more than 600 miles (1,000 kilometers) from southern British Columbia to Northern California. The center will advance earthquake research, foster community partnerships, and diversify and train the next generation geosciences work force.

“The main goal of the center is to bring together the large group of geoscientists working in Cascadia to march together to the beat of a singular drum,” said center director at the University of Oregon. “The center organizes us, focuses collaboration and identifies key priorities, rather than these institutions competing.”

CRESCENT includes researchers from 16 institutions around the United States in the Pacific Northwest and beyond. The leadership team includes investigators from the UW, Oregon State University and Central Washington University.

The Cascadia subduction zone has a long history of spurring large earthquakes, but scientists have only started to realize its power within the last few decades. Research shows that the fault is capable of producing an earthquake of magnitude-9.0 or greater — and communities along the U.S. West Coast are ill-prepared for a quake this powerful.

Such an event would set off a cascade of deadly natural hazards in the Cascadia region, from tsunamis to landslides. It could cause buildings and bridges to collapse, disrupt power and gas lines, and leave water supplies inaccessible for months.

CRESCENT’s work can help mitigate that damage. Scientists will use the latest technology — including high-performance computing and artificial intelligence — to understand the complex dynamics of a major subduction zone earthquake. They will gather data and develop tools to better forecast specific local and regional impacts from a quake. That knowledge will help communities to better prepare, by improving infrastructure and nailing down more informed emergency plans.

Valerie Sahakian and Amanda Thomas are co-lead investigators at the University of Oregon.

“Modeling the shaking from California to Canada is a gigantic endeavor,” Sahakian said. “The center enables us to make bigger strides in models, products, and lines of research, to work with engineers to create better building codes and actionable societal outcomes.”

Subduction zones in the U.S. are understudied compared to other kinds of faults, and create distinctive earthquake dynamics that still aren’t fully understood, Melgar said. So the lessons learned from CRESCENT’s work could also be applied to subduction zones in Alaska, the Caribbean and around the world.

Community collaboration will be a major part of the center’s work. The CRESCENT team will work with communities impacted by hazards, regularly soliciting their input to guide research priorities. And they’ll build connections with public agencies, tribal groups, and private industry, so that scientific advances from the center will get translated into community action and policy.

The center will also work to increase diversity in geosciences and train the next generation of geoscientists in the latest technologies. For example, it will engage with minority-serving and tribal high schools to raise interest in and create pathways to geoscience careers, and provide fieldwork stipends and year-round paid research assistantships to support undergraduate students.

, a professor of Earth and space sciences at the UW and director of the Pacific Northwest Seismic Network, leads the effort at the UW.

“This NSF Center will be a game-changer for earthquake research in the Pacific Northwest; it will have direct, real-world public safety consequences for policy and planning,” said Tobin, who holds the Paros Endowed Chair in Seismology and Geohazards and serves as Washington’s state seismologist.

“Initial CRESCENT efforts include identifying key faults — both on land and under the sea — that present earthquake and tsunami hazard, measuring and modeling movements of the crust that could show us where earthquake strain is building, and much more.”

, a research assistant professor of Earth and space sciences at the UW, will lead the working group studying seismic activity and , the more gradual movements along a fault.

“The end goal is to have a community-driven model that describes all of the tectonic structures of Cascadia,” Crowell said. “The objective of CRESCENT is about creating systematic and foundational community science, adapting the best techniques and methods available for use by the seismic community in our region. It will change the process of how we do this science.”

Also initially involved from the UW are , an assistant professor of Earth and space sciences; , a UW professor of Earth and space sciences; and , a professor of oceanography who holds the Jerome M. Paros Endowed Chair in Sensor Networks.

The center will include staff at the U.S. Geological Survey, including affiliate UW faculty members , and , and members of the UW-based Pacific Northwest Seismic Network, which will continue to perform real-time monitoring and communication of seismic risks in the region.

For more information, contact Tobin at htobin@uw.edu or 206-543-6790, Crowell at crowellb@uw.edu and Melgar at dmelgarm@uoregon.edu or 541-346-3488.

Adapted from a University of Oregon press release.

Other CRESCENT participating institutions are:

Cal Poly Humboldt

Cedar Lake Research Group

EarthScope Consortium

Portland State University

Purdue University

Smith College

Stanford University

University of California – San Diego’s Scripps Institution of Oceanography

University of North Carolina-Wilmington

Virginia Tech

Washington State University

Western Washington University

[Updated 4/18/2023 for clarification:

• Scientists are not alarmed at discovering this geologic feature, which does not trigger earthquakes but may regulate friction in the fault zone
• This discovery does not change the current risk of a large earthquake on the Cascadia Subduction Zone]

The field of plate tectonics is not that old, and scientists continue to learn the details of earthquake-producing geologic faults. The Cascadia Subduction Zone — the eerily quiet offshore fault that threatens to unleash a magnitude-9 earthquake in the Pacific Northwest — still holds many mysteries.

A study led by the ����Ӱ�Ӵ�ý discovered seeps of warm, chemically distinct liquid shooting up from the seafloor about 50 miles off Newport, Oregon. The , published Jan. 25 in Science Advances, describes the unique underwater spring the researchers named . Observations suggest the spring is sourced from water 2.5 miles beneath the seafloor at the plate boundary, regulating stress on the offshore fault.

The team made the discovery during a weather-related delay for a cruise aboard the RV Thomas G. Thompson. The ship’s sonar showed unexpected plumes of bubbles about three-quarters of a mile beneath the ocean’s surface. Further exploration using an underwater robot revealed the bubbles were just a minor component of warm, chemically distinct fluid gushing from the seafloor sediment.

“They explored in that direction and what they saw was not just methane bubbles, but water coming out of the seafloor like a firehose. That’s something that I’ve never seen, and to my knowledge has not been observed before,” said co-author , a UW associate professor of oceanography who studies seafloor geology.

The feature was discovered by first author , who made the discovery as a UW undergraduate student and now works as a White House policy advisor.

Observations from later cruises show the fluid leaving the seafloor is 9 degrees Celsius (16 degrees Fahrenheit) warmer than the surrounding seawater. Calculations suggest the fluid is coming straight from the Cascadia megathrust, where temperatures are an estimated 150 to 250 degrees Celsius (300 to 500 degrees Fahrenheit).

The new seeps aren’t related to geologic activity at the that the cruise was heading toward, Solomon said. Instead, they occur near vertical faults that crosshatch the massive Cascadia Subduction Zone. These strike-slip faults, where sections of ocean crust and sediment slide past each other, exist because the ocean plate hits the continental plate at an angle, placing stress on the overlying continental plate.

Loss of fluid from the offshore megathrust interface through these strike-slip faults is important because it lowers the fluid pressure between the sediment particles and hence increases the friction between the oceanic and continental plates.

“The megathrust fault zone is like an air hockey table,” Solomon said. “If the fluid pressure is high, it’s like the air is turned on, meaning there’s less friction and the two plates can slip. If the fluid pressure is lower, the two plates will lock – that’s when stress can build up.”

Fluid released from the fault zone is like leaking lubricant, Solomon said. That’s bad news for earthquake hazards: Less lubricant means stress can build to create a damaging quake.

This is the first known site of its kind, Solomon said. Similar fluid seep sites may exist nearby, he added, though they are hard to detect from the ocean’s surface. A significant fluid leak off central Oregon could explain why the northern portion of the Cascadia Subduction Zone, off the coast of Washington, is believed to be more strongly locked, or coupled, than the southern section off the coast of Oregon.

“Pythias Oasis provides a rare window into processes acting deep in the seafloor, and its chemistry suggests this fluid comes from near the plate boundary,” said co-author , a UW professor of oceanography. “This suggests that the nearby faults regulate fluid pressure and megathrust slip behavior along the central Cascadia Subduction Zone.”

Solomon just returned from an expedition to off the northeast coast of New Zealand. The Hikurangi Subduction Zone is similar to the Cascadia Subduction Zone but generates more frequent, smaller earthquakes that make it easier to study. But it has a different sub-seafloor structure meaning it’s unlikely to have fluid seeps like those discovered in the new study, Solomon said.

The research off Oregon was funded by the National Science Foundation. Other co-authors are , who did the work as a UW doctoral student and now works as an environmental consultant in Seattle; Emily Roland, a former UW faculty member now at Western Washington University; Masako Tominaga at Woods Hole Oceanographic Institution; and Anne Tréhu and Robert Collier at Oregon State University.

For more information, contact Solomon at esolomn@uw.edu or Kelley at dskelley@uw.edu.

Volcanoes draw plenty of attention when they erupt. But new research shows that volcanoes leak a surprisingly high amount of their atmosphere- and climate-changing gases in their quiet phases. A Greenland ice core shows that volcanoes quietly release at least three times as much sulfur into the Arctic atmosphere than estimated by current climate models.

The , led by the ����Ӱ�Ӵ�ý and published Jan. 2 in Geophysical Research Letters, has implications for better understanding Earth’s atmosphere and its relationship with climate and air quality.

“We found that on longer timescales the amount of sulfate aerosols released during passive degassing is much higher than during eruptions,” said first author , a UW doctoral student in atmospheric sciences. “Passive degassing releases at least 10 times more sulfur into the atmosphere, on decadal timescales, than eruptions, and it could be as much as 30 times more.”

The international team analyzed layers of an ice core from central Greenland to calculate levels of sulfate aerosols between the years 1200 and 1850. The authors wanted to look at the sulfur emitted by marine phytoplankton, which were previously believed to be the biggest source of atmospheric sulfate in pre-industrial times.

“We don’t know what the natural, pristine atmosphere looks like, in terms of aerosols,” said senior author , a UW professor of atmospheric sciences. “Knowing that is a first step to better understanding how humans have influenced our atmosphere.”

The team deliberately avoided any major volcanic eruptions and focused on the pre-industrial period, when it’s easier to distinguish the volcanic and marine sources.

“We were planning to calculate the amount of sulfate coming out of volcanoes, subtract it, and move on to study marine phytoplankton,” Jongebloed said. “But when I first calculated the amount from volcanoes, we decided that we needed to stop and address that.”

The location of the ice core at the center of the Greenland Ice Sheet records emissions from sources over a wide swath of North America, Europe and surrounding oceans. While this result applies only to geologic sources within that area, including volcanoes in Iceland, the authors expect it would apply elsewhere.

“Our results suggest that volcanoes, even in the absence of major eruptions, are twice as important as marine phytoplankton,” Jongebloed said.

The discovery that non-erupting volcanoes leak sulfur at up to three times the rate previously believed is important for efforts to model past, present and future climate. Aerosol particles, whether from volcanoes, vehicle tailpipes or factory chimneys, block some solar energy. If the natural levels of aerosols are higher, that means the rise and fall of human emissions — peaking with the acid rain of the 1970s and then dropping with the Clean Air Act and increasingly strict air quality standards — have had less of an effect on temperature than previously believed.

“There’s sort of a ‘diminishing returns’ effect of sulfate aerosols, the more that you have, the less the effect of additional sulfates,” Jongebloed said. “When we increase volcanic emissions, which increases the baseline of sulfate aerosols, we decrease the effect that the human-made aerosols have on the climate by up to a factor of two.”

That means Arctic warming in recent decades is showing more the full effects of rising heat-trapping greenhouse gases, which is by far the main control on Earth’s average temperature.

“It’s not good news or bad news for climate,” Jongebloed said of the result. “But if we want to understand how much the climate will warm in the future, it helps to have better estimates for aerosols.”

Better estimates for aerosols can improve global climate models.

“We think that the missing emissions from volcanoes are from hydrogen sulfide,” said Alexander, referring to the gas that smells like rotten eggs. “We think that the best ways to improve these estimates of volcanic emissions is to really think about the hydrogen sulfide emissions.”

The study was funded by the U.S. National Science Foundation, NASA and the National Natural Science Foundation of China. Other UW co-authors are undergraduate students Sara Salimi and Shana Edouard, doctoral student Shuting Zhai, research scientist Andrew Schauer, and professor Robert Wood. Other co-authors are Lei Geng, a former UW postdoctoral researcher now at the University of Science and Technology of China; Jihong Cole-Dai and Carleigh Larrick at South Dakota State University; Tobias Fischer at the University of New Mexico; and Simon Carn at Michigan Technological University.

For more information, contact Jongebloed at ujongebl@uw.edu or Alexander at beckya@uw.edu.

Research from the ����Ӱ�Ӵ�ý shows that signals from the upper atmosphere could improve tsunami forecasting and, someday, help track ash plumes and other impacts after a volcanic eruption.

A new study analyzed the Hunga Tonga-Hunga Ha’apai eruption in the South Pacific earlier this year. The Jan. 15, 2022, volcanic eruption was the . Ash blanketed the region. A tsunami wave caused damage and killed at least three people on the island of Tonga. It also had unexpected distant effects.

No volcanic eruption in more than a century has produced a global-scale tsunami. The from the underwater eruption was first predicted as only a regional hazard. Instead, the wave reached as far as Peru, where two people .

Results of the new , published this fall in Geophysical Research Letters, uses evidence from the ionosphere to help explain why the tsunami wave grew larger and traveled faster than models predicted.

“This was the most powerful volcanic eruption since the 1883 eruption of Krakatau, and a lot of aspects of it were unexpected,” said lead author , a UW doctoral student in Earth and space sciences. “We used a new monitoring technique to understand what happened here and learn how we could monitor future natural hazards.”

She will present the work in a Wednesday, Dec. 14, at the American Geophysical Union annual meeting in Chicago and she will the work at the meeting that afternoon.

Tsunamis are rare enough occurrences that forecast models, relying on a limited number of tide gauges and ocean sensors, are still being perfected. This study is part of an emerging area of research exploring the use of GPS signals traveling through the atmosphere to track events on the ground.

A big earthquake, or in this case a huge volcanic eruption, generates pressure waves in the atmosphere. As these pressure waves pass through the zone from about 50 to 400 miles altitude where electrons and ions float freely, known as the , the particles are disturbed. GPS satellites beaming coordinates back down to Earth transmit a slightly altered radio signal that tracks the disturbance.

“Other groups have been looking at the ionosphere to monitor tsunamis. We are interested in applying it for volcanology,” said co-author , a UW research scientist in Earth and space sciences. “This Tonga eruption kicked our research into overdrive. There was a big volcanic eruption and a tsunami — normally you’d study one or the other.”

For the new study, the researchers analyzed 818 ground stations in the Global Navigation Satellite System, the global network that include GPS and other satellites, around the South Pacific to measure the atmospheric disturbance in the hours following the eruption. Results support the hypothesis that the sonic boom generated by the volcanic explosion made the . The ocean wave got an extra push from the atmospheric pressure wave created by the eruption. This extra push wasn’t included in the initial tsunami forecasts, researchers said, because volcano-triggered tsunamis are so rare.

“Tsunamis typically can travel in the open ocean at 220 meters per second, or 500 miles per hour. Based on our data, this tsunami wave was moving at 310 meters per second, or 700 miles per hour,” Ghent said.

The authors were able to separate out different aspects of the eruption – the acoustic sound wave, the ocean wave and other types of pressure waves – and check their accuracy against ground-based observation stations.

“The separation of these signals, from the acoustic sound wave to the tsunami, was what we had set out to find,” Ghent said. “From a hazards-monitoring perspective, it validates our hope for what we can use the ionosphere for. This unusual event gives us confidence that we might someday use the ionosphere to monitor hazards in real time.”

While the Tonga eruption didn’t eject much ash for the size of the event, Ghent and Crowell say the Global Navigation Satellite System signals could be used in other ways to accurately track volcanic ash plumes.

Looking upward to monitor volcanoes and tsunamis is appealing because ground-based monitoring has challenges in the Pacific Northwest and other areas. Sensors must be maintained and repaired, snow and ice can block signals or cause damage, accessing the monitoring stations may be difficult.

What’s more, “the wild mountain goats can eat the cables of the ground instruments because the goats like salt,” Ghent said.

“If you have a way to monitor an area without actually being there, you’re really opening the door to being able to monitor it all year long and help keep people safe around the world.”

This research was funded by NASA and the National Science Foundation.

For more information, contact Ghent at jghent@uw.edu and Crowell at crowellb@uw.edu.

Scientists who drilled deeper into an undersea earthquake fault than ever before have found that the tectonic stress in Japan’s Nankai subduction zone is less than expected.

The results of the led by the ����Ӱ�Ӵ�ý and the University of Texas at Austin, published Sept. 5 in Geology, are a puzzle, since the fault produces a great earthquake almost every century and was thought to be building for another big one.

Although the Nankai fault has been stuck for decades, the findings reveal that it is not yet showing major signs of pent-up tectonic stress. Authors say the result doesn’t alter the long-term outlook for the fault, which last ruptured in 1946, when it caused a tsunami that killed thousands, and is expected to do so again during the next 50 years.

The findings will help scientists home in on the link between tectonic forces and the earthquake cycle. This could potentially lead to better earthquake forecasts, both at Nankai and other megathrust faults, like the Cascadia subduction zone off the coast of Washington and Oregon.

“Right now, we have no way of knowing if the big one for Cascadia — a magnitude-9 scale earthquake and tsunami — will happen this afternoon or 200 years from now,” said lead author , a UW professor of Earth and space sciences and co-chief scientist on the drilling expedition. “But I have some optimism that with more and more direct observations like this one from Japan we can start to recognize when something anomalous is occurring and that the risk of an earthquake is heightened in a way that could help people prepare.

“We learn how these faults work by studying them all over the world, and that knowledge will directly translate into insight into the Cascadia hazard as well.”

Megathrust faults such as Nankai and Cascadia, and the tsunamis they generate, are among the most powerful and damaging on the globe. Scientists say they currently have no reliable way of knowing when and where the next big one will hit.

The hope is that by directly measuring the force felt between tectonic plates pushing on each other — tectonic stress — scientists can learn when a great earthquake is ready to happen.

“This is the heart of the subduction zone, right above where the fault is locked, where the expectation was that the system should be storing energy between earthquakes,” said co-author at University of Texas at Austin, who also co-led the scientific drilling expedition. “It changes the way we’re thinking about stress in these systems.”

The nature of tectonics means that the great earthquake faults are found in deep ocean, miles under the seafloor, making them incredibly challenging to measure directly. Tobin and Saffer’s drilling expedition is the closest scientists have come.

Their aboard a Japanese scientific drilling ship, the Chikyu, which drilled almost 2 miles, or just over 3 kilometers, into the tectonic plate before the borehole got too unstable to continue — 1 mile short of the fault.

Nevertheless, the researchers gathered invaluable data about subsurface conditions near the fault, including stress. To do that, they measured how much the borehole changed shape as the Earth squeezed it from the sides, then pumped water to see what it took to force its walls back out. That told them the direction and strength of horizontal stress felt by the plate pushing on the fault.

Contrary to predictions, the horizontal stress expected to have built up since the most recent great earthquake was close to zero, as if the system had already released its pent-up energy.

The researchers suggested several explanations: It could be that the fault simply needs less pent-up energy than thought to slip in a big earthquake, or that the stresses are lurking nearer to the fault than the drilling reached. Or it could be that the tectonic push will come suddenly in the coming years. Either way, the researchers said the drilling showed the need for further investigation and long-term monitoring of the fault.

“Findings like this can seem like they muddy the picture, because things aren’t as simple as our theory or models predicted they were,” Tobin said. “But that just means we’re gaining more understanding of how the real world works, and the real world is messy and complicated.”

The research was funded by the Integrated Ocean Drilling Program and the Japan Agency for Marine-Earth Science and Technology, or JAMSTEC. Other co-authors are Takehiro Hirose at JAMSTEC and David Castillo at Insight GeoMechanics in Australia.

###

For more information, contact Tobin at htobin@uw.edu or Saffer at demian@ig.utexas.edu.

Adapted from an by the University of Texas at Austin.

Watch: Researchers Brad Lipovsky and Marine Denolle explain how fiber-optic cables can be used to sense ground motion. Credit: Kiyomi Taguchi/UW

The fiber-optic cables that travel underground, along the seafloor and into our homes have potential besides transmitting videos, emails and tweets. These signals can also record ground vibrations as small as a nanometer anywhere the cable touches the ground. This unintended use for fiber-optic cables was discovered decades ago and has had limited use in military and commercial applications.

A ����Ӱ�Ӵ�ý pilot project is exploring the use of fiber-optic sensing for seismology, glaciology, and even urban monitoring. Funded in part with a $473,000 grant from the M.J. Murdock Charitable Trust, a nonprofit based in Vancouver, Washington, the new UW Photonic Sensing Facility has three decoder machines, or “interrogators,” that use photons traveling through a fiber-optic cable to detect ground motions as small as 1 nanometer.

“Fiber-optic sensing is the biggest advance in ground-based geophysics since the field went digital in the 1970s,” said principal investigator , a UW assistant professor of Earth and space sciences. “The UW Photonic Sensing Facility and its partners will explore this technology’s potential across scientific fields — including seismology, glaciology, oceanography and monitoring hydrology and infrastructure.”

The new center — the largest in the United States and the first of its kind in the Pacific Northwest — is among a handful of research hubs around the world that are beginning to explore fiber optics for sensing ground motion. This approach to monitoring could expand the amount of seismic data by thousands of times.

For now, one of the three UW interrogator machines is hooked up to a “dark fiber,” or unused cable, that runs between the UW campuses in Seattle and Bothell. The researchers will soon also connect to a similar underwater cable across Alaska’s Cook Inlet to sense volcanic, oceanic, glacial and tectonic systems there. The other equipment will be used for temporary deployments.

When the ground vibrates — due to a heavy truck, construction work, or an earthquake — the seismic waves travel out from the source like ripples on a pond. When a seismic wave reaches the fiber-optic cable, the cable stretches very slightly, and that disrupts photons that are naturally reflected back to the source. The researchers can detect this disruption in the returning light waves and determine where the cable was disturbed.

The technique is known as “distributed acoustic sensing,” or DAS, because the system is spread out and can be used to monitor both sound waves and ground motion.

The same technology can also record more gradual motions. Lipovsky, who studies glaciers, and UW graduate student carried equipment up to Easton Glacier on Mount Baker to monitor the rate of surface melt. The team installed a cable and used an interrogator to see how much snow was melting on the glacier.

In other pilot projects, UW researchers with the Pacific Northwest Seismic Network are exploring uses for seismology, including earthquakes, volcanoes and landslides. UW oceanographers will use fiber-optic cables connecting to a seafloor observatory to monitor ocean faults and even eavesdrop on whales. UW civil engineers will study whether this technology could monitor traffic collisions or building and bridge infrastructure.

The facility will include semi-permanent observatories in Seattle and other unused “dark” fibers, including a cable that runs to Whidbey Island. The team also plans to lay cables for temporary field deployments at Mt. Rainier and is exploring projects farther afield at a fjord in Greenland and at McMurdo Station in Antarctica.

“We’re getting to the ‘smart Earth’ concept, where we can listen to the Earth,” said , a UW assistant professor of Earth and space sciences. “This technology allows seismic sensing to go to places you could not go before — where it was too hard, or too expensive, to deploy sensors. The other aspect that’s new is a density of sensors beyond what we had before.”

Today’s seismometers record ground motion at a single point, whereas fiber-optic cables take measurements at many points along the cable — the test cable has 15,000 data channels. Denolle will use computing and machine learning to make sense of this new mountain of seismic data.

“In seismology, our data used to be just wiggles,” Denolle said. “This is the first time we can get 2D images, and even videos, of data streaming in.”

The grant was awarded in late 2021. Researchers have used the funds to hook up and test the equipment last spring, and a data-visualization room on campus is coming soon.

“Thanks to the M.J. Murdock Charitable Trust’s support, the UW is the first university to acquire so much equipment for this technique,” Lipovsky said. “This is in the pilot experiment stage, and we are excited to see where it goes.”

Other funders are the UW and the UW-based Pacific Northwest Seismic Network.

For more information contact Lipovsky at bpl7@uw.edu and Denolle at mdenolle@uw.edu.

The Pacific Northwest’s last magnitude-9 event from the offshore subduction zone was in 1700. Only a few clues remain about how it unfolded. But with the earthquake early warning system being built out and improved, seismologists want to know how ShakeAlert would do if the really big one were to happen today.

A research project by the ����Ӱ�Ӵ�ý and the U.S. Geological Survey uses simulations of different magnitude-9 slips on the Cascadia fault to evaluate how the ShakeAlert system would perform in 30 possible scenarios. Results show the alerts generally work well, but suggests ways the system could be improved for some of these highest-risk events.

The will be presented Dec. 13 as an online poster at the American Geophysical Union’s annual fall meeting, being held as a hybrid event based in New Orleans.

“I’ve experienced both the Loma Prieta and the Nisqually earthquakes, and both times my first thought was: ‘Is this really happening?’” said lead author , a UW doctoral student in Earth and space sciences. “An early warning system gives people a moment to collect their thoughts and prepare to react. That’s especially important for a major earthquake.”

The work used detailed computer simulations of magnitude-9 earthquakes created for a previous study looking at how a big offshore event would play out, depending on where and how deep the Cascadia tectonic fault slipped. Thompson played those simulations through an off-line version of the ShakeAlert system and calculated the alerts that would go out across the region.

“The alerts are generally doing well, but they’re not perfect,” said co-author ,�� manager at the UW-based Pacific Northwest Seismic Network. “This project is trying to understand the system’s limitations so that we can make recommendations for future alerting strategies.”

The alerts performed well even though big offshore earthquakes are harder for the system to detect and locate. But there were cases in which a warning arrived too late to some areas.

For instance, when the simulated rupture started at the southern end of the fault, the initial estimate for places far away, like Seattle, were sometimes below the shaking intensity level 5 threshold to generate an immediate alert. As the slip moved northward the shaking increased, but at this point the alerts arrived too late in Seattle to give ample warning time for level-5 and higher levels of shaking in that area.

“Magnitude-9 events are challenging because the alerts are being generated as the seismic event continues to unfold,” Thompson said. “The Nisqually earthquake was a magnitude-6.8 and lasted only about six seconds. But a magnitude-9 earthquake could take more than five minutes for the whole rupture to occur.”

One solution for this uncertainty, which Hartog says is in some ways unavoidable, might be for users to lower their threshold for alerts to shaking intensity 3 or 4. Users might get alerts for some minor events, but they would also have better odds of being alerted to a magnitude-9 earthquake – even if the slipping started far away.

“For the scenario that starts in Northern California, if the threshold is set to shaking intensity-3 then everyone in the West Coast ShakeAlert region is alerted, and some people can get warning times of up to one minute,” Thompson said. “But if you use a higher intensity-5 threshold, you’ll see smaller alerting regions that will have missed alerts on the outer edges.”

In the case of a rupture starting in southern Oregon or Northern California, the entire Seattle-Tacoma region would miss alerts at the higher threshold. Apps, expected to arrive soon in Washington state, will allow users to set their own alert thresholds.

“What is the cost of taking action when it is not necessary, versus not taking action when it is necessary? It just depends on each individual situation, and that’s how people should decide how to set the threshold,” Hartog said.

Installing seismic sensors on the seafloor directly over the offshore fault would be another way to improve the alerts, especially for coastal communities.

Final results will be analyzed and shared with the full West Coast ShakeAlert community to determine whether and how to adjust the system’s warning algorithms.

“The ShakeAlert system is constantly evolving. The algorithms are being tuned, our networks are still being built out,” Hartog said. “It’s not a static system, it’s still actively being improved.”

Also involved in this work is , a research scientist at the U.S. Geological Survey and a UW affiliate faculty member in Earth and space sciences. The research was funded by the U.S. Geological Survey.

For more information, contact Thompson at usherm42@uw.edu or Hartog at jrhartog@uw.edu.

Download the simulation video for a southern Oregon epicenter quake , or other earthquake simulations .

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On May 4, 2021, the U.S. Geological Survey, the ����Ӱ�Ӵ�ý-based and the Washington Emergency Management Division activated a system called ShakeAlert that sends earthquake early warnings throughout Washington state directly to people’s cell phones.

PNSN operates a growing network of about 230 seismic stations in Washington and some 155 stations in Oregon that provide data for ShakeAlert. When four or more of these instruments detect unusual shaking, that motion is analyzed by computers on the UW campus that quickly calculate the size and location of the seismic event.

The UW is part of a consortium of universities that developed the earthquake early warning system in partnership with the USGS. Seismologists are continuing to build out and improve the system, even as public alerting has been activated.

Read full story:��/news/2021/05/03/earthquake-early-warnings-launch-in-washington-completing-west-coast-wide-shakealert-system/

For more information, contact Kiyomi Taguchi at ktaguchi@uw.edu or 206-685-2716.