2,000 Earthquakes in a Day Hammer Fault Line Off Pacific Coast

Deep beneath the north Pacific Ocean, a slumbering giant awoke. A volcano submerged under 4,800 meters of water off the coast of British Columbia set off 2,000 earthquakes in a single day earlier this month. Surprisingy, it raised no alarm.

The site, called the Endeavour, is a string of hydrothermal vents along the Juan de Fuca Ridge. About 240 kilometers west of Vancouver, it makes for especially thin crust on the ocean floor. When 800˚C magma bubbled up to the surface, it sent seismographs reeling.

submerged columns of solidified material

The sea floor at the Endeavour segment of the Juan de Fuca Ridge. Photo: Ocean Network Canada/Ocean Exploration Trust


The March 6 tremors were light-duty. Even though they jolted the fault line over 200 times per hour, they posed no threat to humans. Ocean Networks Canada (ONC) measured the strongest events at around 4.1 on the Richter scale. However, they noted the magma is likely adding new material to the ocean floor.

“The vast majority are less than magnitude one. They’re these little pops,” said Zoe Krauss, a doctoral candidate at the University of Washington studying the earthquakes, told LiveScience. “But it’s pretty cool because it allows us to track where things are happening, where things are breaking, and where things are moving around.”

(a) Map of the Juan de Fuca Plate showing the Endeavour segment of the Juan de Fuca Ridge. (b) Bathymetric map of the Endeavour Segment showing the five high-temperature vent fields. Image: Brian Kristall et al


As the crust thins, magma shoots out

It’s a process familiar to many casual geology students. The Juan de Fuca and Pacific plates are pulling apart at the fault line along the Endeavour site. As the segments pull apart, the margins of each plate thin toward the mantle below. Once they separate far enough, cracks form and superheated liquid rock rushes through.

The magma cools right away in the frigid seawater, and new ocean floor is born. At the Endeavour site, this breaking point occurs at only about a meter of separation.

The site hasn’t reached this threshold yet, but it’s the most seismic activity recorded since 2005. It’s a cycle that takes place in bursts, and this year, it’s right on schedule. ONC expects it to occur there roughly every 20 years. 

The group now settles in to track the impact on the subterranean hydrothermal vents and the diverse Endeavour ecosystem. Hot smoking chimneys support deep-sea tubeworms, crabs, and a wide range of bacteria.

“Underwater earthquakes can not only topple existing sulfide towers but also alter the way fluids travel beneath vent systems, changing the chemistry and temperature of the vent. This can lead to communities being displaced and reorganized,” ONC commented.

Fortunately not human ones.

Sam Anderson

Sam Anderson takes any writing assignments he can talk his way into while intermittently traveling the American West and Mexico in search of margaritas — er, adventure. He parlayed a decade of roving trade work into a life of fair-weather rock climbing and truck dwelling before (to his parents’ evident relief) finding a way to put his BA in English to use. Sam loves animals, sleeping outdoors, campfire refreshments and a good story.