Discovery leads UW scientists to better understand earthquake threat

Warm liquid seeping from the ocean floor off Oregon is offering University of Washington scientists more information about the threat of a major earthquake in the northwest.

The UW-led team made the discovery during a weather-related delay for a cruise aboard a research vessel. The ship’s sonar showed unexpected plumes of bubbles about three-quarters of a mile beneath the ocean’s surface.

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,” Evan Solomon, UW associate professor of oceanography, said. “That’s something that I’ve never seen, and to my knowledge has not been observed before.”

Scientists named the unique underwater spring Pythia’s Oasis. The spring is believed to come from water 2.5 miles beneath the seafloor at the plate boundary, regulating stress on the offshore fault.

The Cascadia Subduction Zone includes a “megathrust” fault that stretches from Northern Vancouver Island to Cape Mendocino, California. It is a major earthquake concern for scientists.

“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.”

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A study in the journal Science Advances outlined the discovery of warm, chemically distinct liquid shooting up from the seafloor about 50 miles off Newport, Oregon. It was discovered by former UW Chief Scientist Brendan Philip, now a White House environmental advisor.

Calculations suggest the fluid is coming straight from the Cascadia megathrust, where temperatures are estimated at between 300 to 500 degrees Fahrenheit.

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.

Fluid released from the fault zone is like leaking lubricant, Solomon said. That’s bad news and could cause more earthquake hazards as less lubricant means stress can build, creating a more potentially damaging quake.

This is the first known site of its kind, though similar fluid seep sites may exist nearby, Solomon added, 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.