A Leak on Pacific Ocean Floor May Be Source of Earthquake, Scientists Say

'The megathrust fault zone is like an air hockey table'

This image taken by underwater robot in 2015 shows Pythia’s Oasis, a warm, high-discharge, water-dominated seafloor seep on the Central Oregon margin of the United States. (University of Washington)

A seafloor hole shooting up warm, mineral-rich liquid into the Pacific Ocean near Oregon’s central coastal might not be a good sign for earthquake activity in the region, scientists say.

The hole, named “Pythia’s Oasis” after the ancient Greek high priestess who speaks the prophecies while inhaling the vapor rising from a hot spring, is described as a “warm, high-discharge, water-dominated seafloor seep” located about 50 miles off Newport, Oregon. It also sits on top of the 600-mile Cascadia Subduction Zone fault, a source of major earthquake events up to magnitude 9.0 or greater.

In their latest study to explain the vent’s nature, researchers at the University of Washington (UW) suggest that the liquid leaking out of it may be acting as a lubricant between the oceanic and continental plates, and that less lubricant means more pressure accumulated to produce a devastating earthquake.

“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,” Evan Solomon, the study’s co-author and an oceanography professor at UW, said in an April 10 press release.

“The megathrust fault zone is like an air hockey table,” the professor explained. “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,” he added. “That’s when stress can build up.”

According to the study, published on Jan. 25 in Science Advances, Pythia’s Oasis was first discovered in 2014, when the sonar on a UW research ship detected unexpected bubble plumes during a routine transit. Using an underwater robot, the UW team revealed that the bubbles coming from 0.75 miles below the water surface were actually a part of a “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,” Solomon said.

Later expeditions to the spring revealed that the fluid shooting out of it is 9 degrees Celsius (16 degrees Fahrenheit) warmer than surrounding seawater. According to the team’s calculations, the fluid appears to come straight from the Cascadia megathrust fault, where temperatures are an estimated 150 to 250 degrees Celsius (300 to 500 degrees Fahrenheit).

The last earthquake that occurred in this fault was in 1700, with an estimated 9.0 magnitude. The impact of this event was felt by those living on both sides of the Pacific, with Japanese historical records indicating that a destructive distantly-produced tsunami struck their coast on Jan. 26 of that year.

Detailed map showing the tectonic plates in the north Pacific with their movement vectors. (Professor Peter Bird/Leonard G/Eric Gaba/NGDC World Coast Line data/CC BY-SA 2.5 [https://creativecommons.org/licenses/by-sa/2.5] via Wikimedia Commons)

The Cascadia Subduction Zone has not produced an earthquake since 1700, although it is building up pressure where the Juan de Fuca Plate is locked against the North American plate.

According to the government of Oregon, researchers are predicting that there is about a 37 percent chance that a megathrust earthquake of 7.1+ magnitude in this fault zone will occur in the next 50 years.