An early warning system being tested at the University of Washington and in Oregon and California located the quake within about 27 seconds, and nailed down its magnitude a few second later.
The magnitude 6.5 earthquake off the coast of Northern California Thursday morning occurred on a fault called the Mendocino Transform, not the more dangerous Cascadia Subduction Zone.
But seismologists are keeping a close watch on the tectonically complex area, especially in light of two smaller quakes off the Oregon coast last week.
“They’re probably unrelated,” said John Vidale, director of the Pacific Northwest Seismic Network. “We’ll just keep an eye out.”
The Thursday quake, which struck at 6:50 a.m., originated about 100 miles west of Ferndale, near an area called the Mendocino Triple Junction, where three tectonic plates meet. It’s also near the terminuses of both the Cascadia Subduction Zone and the San Andreas Fault.
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The quake, which probably moved the seafloor about 3 to 6 feet, could have bumped up the stress on the Cascadia Subduction Zone slightly, Vidale said. But there’s little chance it would be enough to trigger a more powerful subduction zone quake.
“The odds probably have gone up for a little while, but just a little,” Vidale said. “It’s probably not enough that we will see any earthquakes as a result.”
There was no tsunami threat or reports of damage, but the quake was felt along the coasts of Oregon and Northern California.
Bonnie Brower, owner of the Ferndale Pie Company, says she was grabbing something from the refrigerator in the restaurant’s kitchen when the quake happened. It felt like a “big jolt.”
“I just felt this very huge jerk and I didn’t know what it was,” she said.
Afterward, she said it felt like the ground was rolling, “like you were on a boat.”
Dennis Gorton, who owns the Francis Creek Inn in Ferndale, said there was no damage and none of the guests panicked.
“It was just kind of a roller,” he said. “Nothing was thrown off the shelves or anything like that.”
In January 2010, a 6.5 magnitude quake in the Pacific caused about $34 million in property losses in and around the nearby city of Eureka, including partial damage to at least nine buildings.
The area experienced a magnitude 7.2 earthquake in 1992 that injured 95 people and caused millions of dollars in damage, according to the U.S. Geological Survey. That earthquake was felt as far south as San Francisco.
A prototype earthquake early warning system being tested at the University of Washington and in Oregon and California performed well, Vidale said. Sensors located the quake within about 27 seconds, and nailed down its magnitude a few second later. If the system had been operational, it would have provided coastal communities about 20 seconds of warning before the ground shaking started, Vidale said.
Scientists hope to roll out an operational system within the next several years that would send warnings electronically and via cellphone, giving industries and trains time to shut down and allowing people to take cover before the ground starts moving.