Stress-testing the Cascadia Subduction Zone reveals variability that could impact how earthquakes spread
Our take
A recent study examining 13 years of ground motion data from sites near the Cascadia Subduction Zone has shed new light on the seismic behavior of this critical geological area. Researchers have discovered that the fault may not be as tightly locked as previously believed, suggesting that our understanding of when and how a significant earthquake might impact the Pacific Northwest needs reevaluation. This revelation is particularly timely, considering the ongoing discussions around emergency preparedness and environmental stability in our region. It brings to mind the recent court ruling regarding Texas State, which emphasizes the importance of academic freedom in discussing pressing societal issues, and the lawsuit by Kentucky State University students and alumni aimed at blocking a new state law that affects educational governance. Both highlight the need for communities to remain informed and engaged about the decisions that shape their environments.
The implications of the Cascadia Subduction Zone findings are profound. For residents of the Pacific Northwest, this could mean reassessing personal safety measures and community preparedness plans. A less tightly locked fault may lead to a variety of earthquake scenarios, potentially altering not only the frequency and intensity of earthquakes but also their geographical reach. This uncertainty can be unsettling, but it also presents an opportunity for communities to come together, pooling resources and knowledge to create more resilient infrastructures. By openly discussing these findings, local governments and organizations can foster a culture of preparedness that empowers residents and encourages proactive measures.
Moreover, the study underscores the importance of integrating scientific research into public policy and community planning. As we navigate the complexities of our environment, especially with climate change and other natural hazards, understanding geological dynamics becomes crucial. The research community's role in translating complex data into digestible insights for the public cannot be overstated. It’s vital for citizens to grasp not just the risks associated with earthquakes but also the tangible steps they can take to mitigate those risks. This aligns with ongoing efforts, such as the work of UW researchers deciphering beluga calls, which highlight the interconnectedness of environmental and societal health.
As we reflect on these findings, it’s essential to consider how they might shape our future. What does it mean for the next generation of Cougs, who will inherit not just the physical legacy of our landscapes but also the knowledge and strategies necessary to navigate them? Will we rise to the challenge and transform this new understanding of the Cascadia Subduction Zone into actionable change? Engaging in conversations about preparedness, fostering community resilience, and advocating for informed policy are crucial steps we must take. The road ahead may be uncertain, but by embracing these challenges collectively, we can ensure that our community not only survives but thrives in the face of potential seismic shifts.
The Cascadia Subduction Zone is unusually quiet for a megathrust fault. Spanning more than 600 miles from Canada to California, the fault marks the convergence of the Juan de Fuca and North American plates. While other subduction zones produce sporadic rumblings as the plates scrape past each other, Cascadia shows very little seismic activity, fueling assumptions that the plates are locked together by friction.
The subduction zone — miles offshore and deep underwater — is difficult to observe. Most data collection is based onshore, which limits the breadth and quality of results. The lack of earthquakes further complicates efforts to understand its behavior and structure.
In a new study, the first to monitor strain offshore for an extended period of time, University of Washington researchers report that the plates may not be fully locked. Based on 13 years of ground motion data from sensors in different regions, the study shows the northern portion of the fault is locked and quiet, but the central region appears to be more active. There, researchers observed signs of a shallow, slow-motion earthquake and detected pulses of fluid flowing through subterranean channels, which may relieve pressure from the fault.
The findings, published Feb. 27 in Science Advances, may alter expectations of how this area will respond to a large earthquake. Similar features in other places have stopped a rupture that might have otherwise continued along the entire fault line.
“It’s preliminary, but we think that variable fluid pathways in Cascadia will change the behavior of large earthquakes on the fault,” said co-author Marine Denolle, a UW associate professor of Earth and space science.
The Juan de Fuca plate is advancing toward the North American plate at a rate of approximately 4 centimeters a year. But because the plates are stuck together, that motion generates pressure. Eventually, the building tension will exceed what the plates can tolerate. When they eventually slip free, an earthquake will spread along the boundary.
Megathrust earthquakes, which occur at boundaries where one plate slides beneath another, rock the Pacific Northwest every 500 or so years. Researchers dated the last one to 1700, and estimates suggest a 10 to 15% chance that the entire fault will rupture, producing an earthquake that could exceed magnitude 9, within the next fifty years. The results from this study do not alter those odds, but the dynamics captured might influence the severity of the eventual earthquake.
A recent survey of the seafloor found that the fault can be separated into at least four geologically distinct segments. Each one may be insulated from a rupture in another region. In this study, the researchers took a closer look at two of the regions by analyzing data from three monitoring stations, one near Vancouver Island and two off the coast of Oregon.
“We wanted to understand strain changes in different regions offshore,” said lead author Maleen Kidiwela, a UW doctoral student of oceanography. “We used the seismometers to measure how the seismic velocity varies underneath each station.”
Seismic velocity is a term used to describe the rate at which ambient noise travels through a material. Because the speed of sound depends on what it is moving through, tracking seismic velocity can give researchers a window into processes occurring beneath the ocean floor.
“When you compact something, you can expect the sound waves to move through it faster,” said Kidiwela.
The steady increase in seismic velocity observed at the northern site told the researchers the rock was compacting, which supports the theory that the two plates are locked in place.
The central region displayed a different pattern. For two months in 2016, seismic velocity decreased. The researchers attribute this drop to a slow-motion earthquake on the shallow edge of the oceanic plate that relieved some of the pressure at the fault.
Other drops in seismic velocity, recorded between 2017 and 2022, were linked to fluid dynamics. Subduction squeezes liquid out of rocks and pushes it toward the surface. The study found that other faults, running perpendicular to the subduction zone, may act as pathways for letting trapped fluid out.
“During a megathrust rupture, one of the ways that an earthquake propagates is through fluid pressure. If you have a way to release these fluids, it could help improve the stability of the fault, and potentially impact how the region behaves during a large earthquake,” Kidiwela said.
Pulling data from just three sites, the researchers observed complex dynamics that may have gone overlooked. Future work will greatly expand this effort. UW researchers received $10.6 million in 2023 to build an underwater observatory in the Cascadia Subduction Zone.
“Finding this link between fluids coming to the shallow subduction zone is pretty unique, as is the evidence that the fault is not completely locked,” said co-author William Wilcock, a UW professor of oceanography and one of the scientists involved with the observatory. “It suggests that we need more instruments there, because there may be more going on than people have been able to figure out before.”
Additional co-authors include Kuan-Fu Feng from the University of Utah.
This study was funded by the Jerome M. Paros Endowed Chair in Sensor Networks at the University of Washington and the National Science Foundation.
For more information, contact Kidiwela at seismic@uw.edu.
Read on the original site
Open the publisher's page for the full experience