Cluster of earthquakes in Puget Sound considered 'normal', earthquake researchers say

SEATTLE - Another small earthquake rattled the eastside of Washington state on Tuesday. The Pacific Northwest Seismic Network (PNSN) reported a 3.1 magnitude earthquake was reported in Carnation. Just 18 hours earlier, a reported 2.2 magnitude earthquake also shook in the same area. A 2.9 magnitude earthquake was felt near Monroe on Monday. 

In Oregon, a 5.7 magnitude quake shook 127 miles west of Bandon, off the coast also on Monday. Then on December 15th-19th, a small cluster of earthquakes were reported in Bremerton. No damages or injuries have been reported. 

It does, however, beg the question, is this a precursor for a larger earthquake? Not so, according to earthquake experts.

"I would call all of this background normal activity," said Harold Tobin, Director of the Pacific Northwest Seismic Network at the University of Washington. "You see them happen in clusters. Of course random doesn't mean things happen evenly spaced in time. So, sometimes we see them in little clusters like this."

Even the larger earthquake off the coast of Oregon is considered "normal" according to Tobin because it happened in an area known as the Blanco Transform Fault Zone which is near the Cascadia Subduction Zone. It's known to have earthquakes.

"We've actually had a pretty quiet six months or so. Once we have one, we tend to have a few more. Even smaller earthquakes and aftershocks it turns out," said Tobin.  

And while it's considered "normal" it doesn't mean that we need to be complacent. Despite the challenges of the pandemic, researchers at PNSN continue to keep an eye on earthquakes. 

And soon, the Shake Alert early earthquake warning system will be available to people living in Oregon and Washington, said Tobin.

"We're adding stations along Washington and Oregon all of the time. We have built up our capacity to where we can reliably detect potentially damaging earthquakes as things get started," said Tobin. 

He believes Shake Alert will be available to the public in the first half of 2021.

In terms of tracking the "big one", what Tobin believes will really help is an offshore early warning detection system, similar to what Japan has now. The system is comprised of several underwater fiber optic cables that run along the ocean floor. These cables transmit data to stations along the coast, which then transmits movement information to stations on land along the coast. Those stations would then be connected to the main system where notifications could be sent out to the public. The goal would be to run the cables along the Cascadia Subduction Zone. 

According to Tobin, the U.S. is several years away from that becoming reality. More funding is needed. 

"There has been some push in Congress to add funding for those programs. So far money hasn't been appropriated to build an offshore sensor network system," he said. 

Tobin, along with other earthquake researchers, traveled to Japan in late 2019 to study their subduction zone earthquakes. It required studying onboard a ship for weeks, examing core samples taken from underneath the ocean. Since that time, researchers have learned some similarities to our subduction zone. 

"The work in Japan is telling us that the plates have very small scale, almost imperceptible motions almost all of the time and they're doing things in between earthquakes," he said. 

Until a system like that is built, Tobin reminds people that Washington is in an earthquake zone and to always be prepared for the next earthquake.