https://www.washington.edu/news/2023/04/10/warm-liquid-spewing-from-oregon-seafloor-comes-from-cascadia-fault-could-offer-clues-to-earthquake-hazards/
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* Warm liquid spewing from Oregon seafloor comes from Cascadia
fault, could offer clues to earthquake hazards
Environment | News releases | Research | Science
April 10, 2023
Warm liquid spewing from Oregon seafloor comes from Cascadia fault,
could offer clues to earthquake hazards
Hannah Hickey
UW News
green seafloor with five bubble columns
This sonar image of the Pythias Oasis site shows bubbles rising from
the seafloor about two-thirds of a mile deep and 50 miles off
Newport, Oregon. These bubbles are a byproduct of a unique site where
warm, chemically distinct fluid gushes from the seafloor. Researchers
believe this fluid comes directly from the Cascadia megathrust zone,
or plate boundary, and helps control stress buildup between the two
plates.Philip et al./Science Advances
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 University of Washington discovered seeps of warm,
chemically distinct liquid shooting up from the seafloor about 50
miles off Newport, Oregon. The paper, published Jan. 25 in Science
Advances, describes the unique underwater spring the researchers
named Pythia's Oasis. 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 Evan Solomon, a UW
associate professor of oceanography who studies seafloor geology.
The feature was discovered by first author Brendan Philip, who did
the work as a UW graduate 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 nearby
seafloor observatory 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 Deborah Kelley, 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 monitor sub-seafloor
fluids 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 Theresa Whorley, 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 Trehu and Robert Collier at Oregon State
University.
For more information, contact Solomon at esolomn@uw.edu or Kelley at
dskelley@uw.edu.
Tag(s): College of the Environment * Deborah Kelley * earthquakes &
seismology * Evan Solomon * geology * School of Oceanography
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