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Volcanic eruptions may have spurred first 'whiffs' of oxygen in Earth's atmosphere
Wednesday, August 25, 2021
A new analysis of 2.5-billion-year-old rocks from Australia finds that volcanic eruptions may have stimulated! population surges of marine microorganisms, creating the first puffs of oxygen into the atmosphere. This would change existing stories of Earth's early atmosphere, which assumed that most changes in the early atmosphere were controlled by geologic or chemical processes.
Though focused on Earth's early history, the research also has implications for extraterrestrial life and even climate change. The study led by the University of Washington, the University of Michigan and other institutions was published in August in the Proceedings of the National Academy of Sciences.
"What has started to become obvious in the past few decades is there actually are quite a number of connections between the solid, nonliving Earth and the evolution of life," said first author Jana Me!ixnerov?, a UW doctoral student in Earth and space sciences. "But what are the specific connections that facilitated the evolution of life on Earth as we know it?"
In its earliest days, Earth had no oxygen in its atmosphere and few, if any, oxygen-breathing lifeforms. Earth's atmosphere became permanently oxygen-rich about 2.4 billion years ago, likely after an explosion of lifeforms that photosynthesize, transforming carbon dioxide and water into oxygen.UW News | July 2018: “Oxygen levels on early Earth rose and fell several times before the successful Great Oxidation Event“
But in 2007, co-author Ariel Anbar at Arizona State University analyzed rocks from the Mount McRae Shale in Western Australia, reporting a short-term whiff of oxygen about 50 to 100 million years before it became a permanent fixture in the atmosphere. More recent research has confirmed other, earlier short-term oxygen spikes, but hasn't explained their rise and fall.
In the new study, researchers at the University of Michigan, led by co-corresponding author Joel Blum, analyzed the same ancient rocks for the concentration and number of neutrons in the element mercury, emitted by volcanic eruptions. Large volcanic eruptions blast mercury gas into the upper atmosphere, where today it circulates for a year or two before raining out onto Earth's surface. T!he new analysis shows a spike in mercury a few million years before the temporary rise in oxygen.
"Sure enough, in the rock below the transient spike in oxygen we found evidence of mercury, both in its abundance and isotopes, that would most reasonably be explained by volcanic eruptions into the atmosphere," said co!-author Roger Buick, a UW professor of Earth and Space Sciences.
Where there were volcanic emissions, the authors reason, there must have been lava and volcanic ash fields. And those nutrient-rich rocks would have weathered in the wind and rain, releasing phosphorus into rivers that could fertilize nearby coastal areas, allowing oxygen-producing cyanobacteria and other single-celled lifeforms to flourish.
"There are other nutrients that modulate biological activity on short timescales, but phosphorus is the one that is most important on long timescales," Meixnerov? said.
Today, phosphorus is plentiful in biological material and in agricultural fertilizer. But in very ancient times, weathering of volcanic rocks would have been the main source for this scarce resource.
"During weathering under the Archaean atmosphere, the fresh basaltic rock would have slowly dissolved,! releasing the essential macro-nutrient phosphorus into the rivers. That would have fed microbes that were living in the shallow coastal zones and triggered increased biological productivity that would have created, as a byproduct, an oxygen spike," Meixnerov? said.
The precise location of those volcanoes and lava fields is unknown, but large lava fields of about the right age exist in modern-day India, Canada and elsewhere, Buick said.
"Our study suggests that for these transient whiffs of oxygen, the immediate trigger was an increase in oxygen production, rather than a decrease in oxygen consumption by rocks or other nonliving processes," Buick said. "It's important because the presence of oxygen in the atmosphere is fundamental - it's the biggest driver for the evolution of large, complex life."
Ultimately, researchers say the study suggests how a planet's geology might affect any life evolving on its surface, an understanding that aids in identifying habitab!le exoplanets, or planets outside our solar system, in the search for life in the universe.
Other authors of the paper are co-corresponding author Eva St?eken, a former UW astrobiology graduate student now at the University of St. Andrews in Scotland; Michael Kipp, a former UW graduate student now at the California Institute of Technology; and Marcus Johnson at the University of Michigan. The study was funded by NASA, the NASA-funded UW Virtual Planetary Laboratory team and the MacArthur Profes!sorship to Blum at the University of Michigan.
NASA: NNX16AI37G, 80NSSC18K0829Read More
A visit to Mt. Baker’s Easton Glacier
Friday, July 30, 2021
This week, a few members of our UW News team joined glaciologists from the UW Department of Earth & Space Sciences on a trip to Mt. Baker. Students that came along got a pop quiz on glaciology from their professor on the hike up, and we learned about how the recent heat wave impacted the snow melt on the ice. Taryn Black, a PhD candidate in the department, led the hike and is featured in this video. Read More
Edge of Pine Island Glacier's ice shelf is ripping apart, causing key Antarctic glacier to gain speed
Monday, June 14, 2021
The ice shelf on Antarctica's Pine Island Glacier lost about one-fifth of its area from 2017 to 2020, mostly in three dramatic breaks. The timelapse video incorporates satellite images from January 2015 to March 2020. For most of the first two years, the satellite took high-resolution images every 12 days; then for more than three years it captured images of the ice shelf every six days. Images are from the Copernicus Sentinel-1 satellites operated by the European Space Agency on behalf of the European Union.
Credit: Joughin et al./Science Advances
For decades, the ice shelf helping to hold back one of the fastest-moving glaciers in Antarctica has gradually thinned. Analysis of satellite images reveals a more dramatic process in recent years: From 2017 to 2020, large icebergs at the ice shelf's edge broke off, and the glacier sped up.
Since floating ice shelves help to hold back the larger grounded mass of the glacier, the recent speedup due to the weakening edge could shorten the timeline for Pine Island Glacier's eventual collapse into the sea. The study from researchers at the University of Washington and British Antarctic Survey was published June 11 in the open-access journal Science Advances.
"We may not have the luxury of waiting for slow changes on Pine Island; things could actually go much quicker than expected," said lead author Ian Joughin, a glaciologist at the UW Applied Physics Laboratory. "The processes we'd been studying in this region were leading to an irreversible collapse, but at a fairly measured pace. Things could be much more abrupt if we lose the rest of that ice shelf."
Pine Island Glacier contains approximately 180 trillion tons of ice --equivalent to 0.5 meters, or 1.6 feet, of global sea level rise. It is already responsible for much of Antarctica's contribution to sea-level rise, causing about one-sixth of a millimeter of sea level rise each year, or about two-thirds of an inch per century, a rate that's expected to increase. If it and neighboring Thwaites Glacier speed up and flow completely into the ocean, releasing their hold on the larger West Antarctic Ice Sheet, global seas could rise by several feet over the next few centuries.
These glaciers have attracted attention in recent decades as their ice shelves thinned because warmer ocean currents melted the ice's underside. From the 1990s to 2009, Pine Island Glacier's motion toward the sea accelerated from 2.5 kilometers per year to 4 kilometers per year (1.5 miles per year to 2.5 miles per year). The glacier's speed then stabilized for almost a decade.
Results show that what's happened more recently is a different process, Joughin said, related tointernal forces on the glacier.
From 2017 to 2020, Pine Island's ice shelf lost one-fifth of its area in a few dramatic breaks that were captured by the Copernicus Sentinel-1 satellites, operated by the European Space Agency on behalf of the European Union. The researchers analyzed images from January 2015 to March 2020 and found that the recent changes on the ice shelf were not caused by processes directly related to ocean melting.
"The ice shelf appears to be ripping itself apart due to the glacier's acceleration in the past decade or two," Joughin said.
Two points on the glacier's surface that were analyzed in the paper sped up by 12% between 2017 and 2020. The authors used an ice flow model developed at UW to confirm that the loss of the ice shelf caused the observed speedup.
"The recent changes in speed are not due to melt-driven thinning; instead they’re due to the loss of the outer part of the ice shelf," Joughin said. "The glacier'sspeedupis not catastrophic at this point. But if the rest of that ice shelf breaks up and goes away then this glacier could speed up quite a lot."
It's not clear whether the shelf will continue to crumble. Other factors, like the slope of the land below the glacier's receding edge, will come into play, Joughin said. But the results change the timeline for when Pine Island's ice shelf might disappear and how fast the glacier might move, boosting its contribution to rising seas.
"The loss of Pine Island's ice shelf now looks like it possibly could occur in the next decade or two, as opposed to the melt-driven subsurface change playing out over 100 or more years," said co-author Pierre Dutrieux, an ocean physicist at British Antarctic Survey. "So it’s a potentially much more rapid and abrupt change."
Pine Island's shelf is important because it's helping to hold back this relatively unstable West Antarctic glacier, the way the curved buttresses on Notre Dame cathedral hold up the cathedral's mass. Once those buttresses are removed, the slow-moving glacier can flow more quickly downward to the ocean, contributing to rising seas.
"Sediment records in front of and beneath the Pine Island ice shelf indicate that the glacier front has remained relatively stable over a few thousand years," Dutrieux added. "Regular advance and break-ups happened at approximately the same location until 2017, and then successively worsened each year until 2020."
Other co-authors are Daniel Shapero and Ben Smith at the UW; and Mark Barham at British Antarctic Survey. The study was funded by the U.S. National Science Foundation, NASA and the U.K. Natural Environment Research Council.
NSF: OPP-1643285, NASA grant: NNX17AG54GRead More
The College of the Environment has created a CoEnv COVID-19 Resources page.
Thursday, June 10, 2021
The College of the Environment has created a CoEnv COVID-19 Resources page for faculty, staff, graduate, and undergraduate students. Read More
South Pole and East Antarctica warmer than previously thought during last ice age, two studies show
Thursday, June 3, 2021
The South Pole and the rest of East Antarctica is cold now and was even more frigid during the most recent ice age around 20,000 years ago -- but not quite as cold as previously believed.
University of Washington glaciologists are co-authors on two papers that analyzed Antarctic ice cores to understand the continent's air temperatures during the most recent glacial period. The results help understand how the region behaves during a major climate transition.
In one paper, an international team of researchers, including three at the UW, analyzed seven ice cores from across West and East Antarctica. The results published June 3 in Science show warmer ice age temperatures in the eastern part of the continent.
The team included authors from the U.S., Japan, the U.K., France, Switzerland, Denmark, Italy, South Korea and Russia.
"The international collaboration was critical to answering this question because it involved so many different measurements and methods from ice cores all across Antarctica," said second author T.J. Fudge, a UW assistant research professor of Earth and space sciences.
Antarctica, the coldest place on Earth today, was even colder during the last ice age. For decades, the leading science suggested ice age temperatures in Antarctica were onaverageas much as 9 degrees Celsius cooler than the modern era. By comparison, temperatures globally at that time averaged 5 to 6 degrees cooler than today.
Previous work showed that West Antarctica was as cold as 11 degrees C below current temperatures. The new paper in Science shows that temperatures at some locations in East Antarctica were only 4 to 5 degrees cooler, about half previous estimates.
"This is the first conclusive and consistent answer we have for all of Antarctica," said lead author Christo Buizert, an assistant professor at Oregon State University. "The surprising finding is that the amount of cooling is very different depending on where you are in Antarctica. This pattern of cooling is likely due to changes in the ice sheet elevation that happened between the ice age and today."
The findings are important because they better match results of global climate models, supporting the models' ability to reproduce major shifts in the Earth's climate.
Another paper, accepted in June in the Journal of Geophysical Research: Atmospheres and led by the UW, focuses on data from the recently completed South Pole ice core, which finished drilling in 2016. The Science paper also incorporates these results.
"With its distinct high and dry climate, East Antarctica was certainty colder than West Antarctica, but the key question was: How much did the temperature change in each region as the climate warmed?" said lead author Emma Kahle, who recently completed a UW doctorate in Earth and space sciences.
That paper, focusing on the South Pole ice core, found that ice age temperatures at the southern pole, near the Antarctic continental divide, were about 6.7 degree Celsius colder than today. The Science paper finds that across East Antarctica, ice age temperatures were on average 6.1 degrees Celsius colder than today, showing that the South Pole is representative of the region.
"Both studies show much warmer temperatures for East Antarctica during the last ice age than previous work -- the most recent 'textbook' number was 9 degrees Celsius colder than present," said Eric Steig, a UW professor of Earth and space sciences who is a co-author on both papers. "This is important because climate models tend to get warmer temperatures, so the data and models are now in better agreement."
"The findings agree well with climate model results for that time period, and thus strengthen our confidence in the ability of models to simulate Earth's climate," Kahle said.
Previous studies used water molecules contained in the layers of ice, which essentially act like a thermometer, to reconstruct past temperatures. But this method needs independent calibration against other techniques.
The new papers employ two techniques that provide the necessary calibration. The first method, borehole thermometry, takes temperatures at various depths inside the hole left by the ice drill, measuring changes through the thickness of the ice sheet. The Antarctic ice sheet is so thick that it keeps a memory of earlier, colder ice age temperatures that can be measured and reconstructed, Fudge said.
The second method examines the properties of the snowpack as it builds up and slowly transforms into ice. In East Antarctica, the snowpack can range from 50 to 120 meters (165 to 400 feet) thick, including snow from thousands of years which gradually compacts in a process that is very sensitive to the temperature.
"As we drill more Antarctic ice cores and do more research, the picture of past environmental change comes into sharper focus, which helps us better understand the whole of Earth's climate system," Fudge said.
Fudge, Steig and Kahle are among 40 authors on the Science paper. Other co-authors on the JGR: Atmospheres paper are Michelle Koutnik, Andrew Schauer, C. Max Stevens, Howard Conway and Edwin Waddington at the UW; Tyler Jones, Valerie Morris, Bruce Vaughn and James White at the University of Colorado, Boulder; and Buizert and Jenna Epifanio at Oregon State University.
Both papers were supported by the U.S. National Science Foundation. Both papers made use of the South Pole ice core, a project that in 2016 completed a 1.75 kilometer (1.09 mile) deep ice core at the South Pole. That project was funded by the NSF and co-led by Steig and Fudge with colleagues at the University of California, Irvine, and the University of New Hampshire.
Part of this articlewere adapted from an OSU press release.Read More
The last glacial maximum in Antarctica wasn't quite so cold.
Tuesday, June 1, 2021
New paper led by recent ESS graduate student Emma Kahle, Eric Steig, TJ Fudge, et al. shows it was ~6.5°C colder at South Pole 20 kyr ago. This new result is is better agreement with climate models. The new paper, in Journal of Geophysical Research, also provides a coprehensive analysis of the history of temperature, snowfall, and ice dynamics at the South Pole, as part of the SPICEcore project led by Steig and Fudge, with colleagues at UC-Irvine and the University of New Hampshire. See http://spicecore.org Read More
The weather is getting weirder at our poles
Wednesday, May 26, 2021
Using ground observations of precipitation in the Antarctic, as well as thunderstorm and lightning data in the Arctic (from 'Lighting in the Arctic, by Prof. Holzworth and his ESS colleagues (https://dx.doi.org/10.1029/2020GL091366 ), the Advanced Science News article discusses the great changes in local climates near the poles. Read More
Earthquake early warnings launch in Washington, completing West Coast-wide ShakeAlert system
Monday, May 3, 2021
When the Big One hits, the first thing Washington residents notice may not be the ground shaking, but their phone issuing a warning. The U.S. Geological Survey, the University of Washington-based Pacific Northwest Seismic Network and the Washington Emergency Management Division on Tuesday, May 4, will activate the system that sends earthquake early warnings throughout Washington state. This completes the tri-state rollout of ShakeAlert, an automated system that gives people living in Washington, Oregon and California advance warning of incoming earthquakes.
"For the first time, advance warning of imminent earthquake shaking will be a reality in our region. Even just seconds, up to a minute of warning is enough to prepare yourself and take cover -- actions that may spare you from injury or even save your life," said Harold Tobin, a UW professor of Earth and space sciences and director of the PNSN, which operates the seismic monitoring in Washington and Oregon.
A team from the UW-based Pacific Northwest Seismic Network installs a new solar panel array at a seismic monitoring site in Enumclaw, Washington, on April 20, 2021. The seismometer, one of hundreds that provide data for ShakeAlert, is in the hole in the foreground. A trench brings cables to the newly installed solar panels, on the right, that power the system, and an aluminum box containing electronics that digitize and transmit the seismic data.
An upgraded Pacific Northwest Seismic Network monitoring station in Enumclaw, Washington, on April 20, 2021. The newly installed solar panels provide power for the system that detects the first signs of an earthquake.
An upgraded Pacific Northwest Seismic Network monitoring station in Enumclaw, Washington, on April 20, 2021. The newly installed solar panels provide power for the system that detects the first signs of an earthquake.
As of late April 2021, more than 230 stations contributed to the ShakeAlert network in Washington state, with more stations going online every week.
Once the system goes live on May 4, the first signs of an earthquake above a magnitude 4.5 or 5, about when the shaking becomes noticeable indoors, will trigger an alert and a reminder to drop, cover and hold on. Warning times range from a few seconds to tens of seconds depending on your distance to the epicenter. The launch will be silent -- there will be no test on May 4.
The 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, someof them on the UW campus, that quickly calculate the size and location of the event.
People connected to the Wireless Emergency Alert system (the same system that produces AMBER alerts), will now get earthquake alerts for events of magnitude 5 or greater, using a similar interface. Alerts for events of magnitude 4.5 or above will be integrated into Android devices, where screens will also show the earthquake's approximate magnitude and location. When people get an alert, they should use the brief warning to seek immediate protection, following this safety advice. No downloads are required - find out how to get alerts.
The ShakeAlert system, similar to existing early warning systems in Mexico and Japan, began sending alerts in California in 2019 and in Oregon in March 2021. With the addition of Washington state, the system will now issue warnings to millions more people at risk from the largest possible earthquake in the lower 48 states -- a rupture of the offshore Cascadia Subduction Zone, a 700-mile fault that runs from California's Cape Mendocino to the tip of Canada's Vancouver Island (discovered in part through UW research). The alerts will also warn of potentially damaging earthquakes that are more likely to occur sooner, on one of two dozen crustal faults in the Puget Sound region alone, or deeper slips on the underlying ocean plate. The system works by detecting the first signs of an earthquake before the slower-moving but more damaging ground-shaking waves arrive.
- PNSN will host an event on the science of ShakeAlert 6:30-7:30 p.m., May 4
- USGS: "ShakeAlert earthquake early warning delivery for the Pacific Northwest"
- Washington Emergency Management: "ShakeAlert comes to Washington"
- Reporters: Download b-roll and photos of PNSN sites
- More on how the system works and how to get alerts from the PNSN
- Q&A with Harold Tobin about the launch of ShakeAlert in Oregon and Washington
- Read past UW News articles on the system’s development
The PNSN began testing the ShakeAlert system with select Washington and Oregon businesses, utilities and organizations in 2015. Besides the individual alerts on phones, the system will be available for organizations or businesses to incorporate into their emergency plans -- for instance, to close water valves, slow trains to prevent derailment, halt surgeries or pause sensitive equipment before the shaking starts.
"Business in the pilot program have used these alerts to close valves for water and natural gas, stop rotating equipment and alert employees. We have also partnered with Stanwood Elementary School, which has connected the system to its PA system so students can do earthquake drills that use ShakeAlert," said PNSN communications manager Bill Steele, who has coordinated the regional test users.
Scientists at the PNSN are continuing to improve the system. About 65% of the planned seismic stations in the network are complete in Washington state. PNSN field teams will install more seismometers through late 2025 in places like the Olympic Peninsula and Eastern Washington.
"The network is successfully detecting earthquakes now, but that doesn't mean we can't make it even better. We're continuing to install seismometers and improve algorithms to make the alerts faster and more reliable, to give people more warning time and lower the chance of any missed events or false alarms," Tobin said.
Initial development of the earthquake alert system by three West Coast universities, including the UW, began a decade ago and was funded by the Gordon and Betty Moore Foundation. The buildout of the system was funded by Congress, with major grants administered by the USGS in 2015 and 2019, and completed by federal and state agencies working with a consortium of four West Coast universities: the UW; the University of Oregon; the University of California, Berkeley; and the California Institute of Technology.
The Washington system also got state funding in the 2020-21 budget. Private support for Washington's system has also come from the M.J. Murdock Charitable Trust, Amazon, Puget Sound Energy and individual donors.
UW launches GeoHazards Initiative; names Paros Chair in Seismology and GeoHazards
Thursday, April 29, 2021
Leveraging the tectonic laboratory of the Cascadia subduction zone, the University of Washington today announced a new effort to best understand how to studyand live with the threats of earthquakes, tsunamis, volcanos, landslides and other seismic hazards. Dubbed the GeoHazards Initiative, the interdisciplinary work aims to develop and promote the adoption of early detection systems both on land and at sea to help prevent the loss of human life and property.
"The vision ultimately is for an integrated initiative that will span geohazards and their impact on society," said Harold Tobin, the newly named Paros Endowed Chair in Seismology and Geohazards. "A big goal of this new effort is to bring together the strengths of different pieces of the UW research community to tackle all these problems in a truly novel way that can help us make progress on understanding all of those hazardous events and how to mitigate their damaging effects."
The initiative's starting place will be focused on sensors, both on land and at sea, that can help scientists better understand seismic events and how to detect them as they begin, and even to determine times and places where risk may be heightened.
"We need to be able to detect movement deep beneath the ground both on land and under the ocean equally, in order to take this to the next level," Tobin said, who already is the Washington state seismologist, directs the Pacific Northwest Seismic Network, and is a professor in the Department of Earth & Space Sciences. "And that’s traditionally been two different realms here at the university. But really it's all an Earth process and we need to work together."
Tobin will initially partner with researchers in the UW School of Oceanography and the UW Applied Physics Lab, with hopes to bring other parts of the university in as the research progresses.
The work is fueled by a $2 million gift from Jerome "Jerry" M. Paros to fund the named chair. Additionally, UW will match that gift with $2 million to be used over 20 years to launch and support the initiative.
"The UW is uniquely positioned to be a leader in understanding how geohazards impact our lives," said Paros, a leader in the field of geophysical measurements. He is the founder, president and chairman of Paroscientific, Inc., Quartz Seismic Sensors, Inc. and related companies that use the quartz crystal resonator technology he developed to measure pressure, acceleration, temperature, weight and other parameters. "We just now are beginning to have better detection systems on land and at sea. This effort knits these resources together under Harold's direction. We couldn't be better positioned to push this work forward, ideally protecting property and saving lives."
Paros has supported science and education with philanthropic endowments at universities and organizations across the country. His prior contributions to the UW include the endowment of the Jerome M. Paros Chair in Sensor Networks and the Cascade Sensor Network Fund. These gifts support the research, development and deployment of new instrumentation and measurement systems that will advance cross-disciplinary knowledge in the oceanic, atmospheric and Earth sciences. In addition, Paros established the Paros Fund for Brain Research at the Institute for Learning & Brain Sciences.
With the Paros Endowed Chair in Seismology and Geohazards, Tobin now has a platform from which to launch the development of new sensing systems on land and under the sea, build coalitions of public and private stakeholders in the Pacific Northwest and beyond, and engage policymakers at the state and federal levels.
The initiative will launch new research to design, build and deploy arrays of ocean sensors to detect earthquakes, tsunamis and seafloor motion, and to provide data transmission that connects onshore and offshore observations to effectively detect emerging geohazards and mitigate against disasters.
Technological options for the array could include sensors connected to cables on the seafloor, attached to both dedicated research cables and existing commercial telecom cables. Arrays could also include offshore boreholes, standalone stations on the seafloor that store their data, and mobile platforms like drones or buoys.
"Offshore sensors can help provide early warning for earthquakes and tsunamis, and help advance scientific understanding of what's happening under the ocean in the Cascadia subduction zone," said William Wilcock, the Jerome M. Paros Endowed Chair in Sensor Networks and professor in the School of Oceanography, who will also work on the GeoHazards Initiative.
"We already have systems on land that can provide early warnings of seismic events, but we now are developing technologies that can help us better understand earthquakes under the ocean and the tsunamis they produce," Wilcock said.
The researchers said they plan to investigate the fault systems onshore and offshore using geophysical imaging and direct measurements for groundtruthing to gain insight into the geohazard sources and processes.
"These activities will build a strategic alliance across the university to position UW as the foremost hub of subduction hazard research, positioning us to compete for emerging national and international opportunities," Tobin said.
He said it was an honor to receive this new endowed chair in Paros' name, a man who has personally been a driving force in the development of geophysical sensors that are in use across the world.
"I feel a responsibility to really make this initiative be effective and serve as a platform to work on these problems at a larger scale," Tobin said. "We in Western Washington literally inhabit the subduction zone -- the place where two plates meet -- that is this perfect place to study all these processes from within them. And the University of Washington has the kind of critical mass of expertise and people, and the forward-looking science and technology, to really take concrete steps to leap forward our understanding not just for Washington but for the world."
For more information, reach Tobin at email@example.com.
Deep earthquakes within the Juan de Fuca plate produce few aftershocks
Tuesday, April 13, 2021
In the Cascadia subduction zone, medium- and large-sized "intraslab" earthquakes, in which the slip happens within the oceanic plate and below the continental plate, will likely produce only a few detectable aftershocks, according to a new study from the University of Washington and the U.S. Geological Survey.
The findings, published April 13 in the Bulletin of the Seismological Society of America, could help seismologists better forecast aftershocks in the Pacific Northwest.
Seismologists currently make aftershock forecasts based in part on data from other subduction zones around the world. But new research shows that Cascadia intraslab earthquakes, slips that occur within the subducting Juan de Fuca tectonic plate, produce fewer aftershocks compared to similar quakes in other subduction zones. The study shows that in Cascadia, the number of aftershocks for a given magnitude event are less than half the global average for this type of earthquake.
Joan Gomberg, a UW affiliate professor of Earth and space sciences and researcher at the U.S. Geological Survey in Seattle, and Paul Bodin, a UW research professor of Earth and space sciences, decided to study the phenomenon after recent intraslab earthquakes in Mexico and Alaska produced dozens of aftershocks, including some big jolts.
"This was startling, because the lore in Cascadia was that intraslab earthquakes had puny aftershock sequences," said Gomberg, who led the study. The Cascadia region experienced three magnitude-6.5 to magnitude-6.8 intraslab earthquakes, in 1949, 1965 and 2001, that produced few to no aftershocks.
"Additionally, the USGS has begun to generate quantitatively estimated aftershock forecasts based initially on global patterns," Gomberg said. "Given these contrasting regional experiences, it seemed time to generate some objective numbers to base Cascadia’s forecasts on."
The researchers analyzed catalogs of earthquakes between 1985 and 2018 from the UW-based Pacific Northwest Seismic Network and the Geological Survey of Canada. Earthquakes that took place in the upper plate produced the most aftershocks, they found. Aftershock rates were the lowest for intraplate earthquakes in the Puget Lowlands portion of the subduction zone, which contains the Seattle metropolitan area, while aftershock rates varied at the northern end of the zone, near Vancouver Island, and at the southern edge, near Cape Mendocino in northern California.
The tectonic environment at each end of the subductionzone could help explain why aftershock production is higher at the edges, the researchers said. Multiple tectonic plate boundaries meet in these areas, which could "concentrate stress, so more faults exist and are closer to failure than in other areas," they noted.
Why Cascadia produces so few aftershocks is still unclear, but "one strong possibility would seem to be that temperature for the deeper slab earthquakes is a dominant controlling parameter," Bodin said. In Cascadia, "the young, hot Juan de Fuca plate is being jammed beneath North America."
The deeper the earthquake, the higher the temperatures, and the researchers found that aftershock activity decreases with depth. "However, this is not so different than southern Mexico, where, as we noted, recent intraslab mainshocks have supported vigorous aftershock sequences," Bodin said.
The analysis was limited by Cascadia's low seismicity rates, and sparse data to pinpoint the location and depth of most earthquakes in the region. Methods that help researchers detect and locate smaller earthquakes could provide a better sense of overall aftershock rates and the physical processes that control them, the authors argue in the paper.
Adapted from a press release by the Seismological Society of America.Read More