Swarm of 7 earthquakes hit off Oregon coast

The wall of earthquake monitors at the USGS monitoring station in Vancouver, June 1, 2015

SALEM, Ore. (KOIN) — A series of earthquakes struck off the Oregon coast early Monday, but scientists said they weren't strong enough to trigger tsunamis.

The first came at magnitude 5.8. It struck about midnight Sunday and was followed by three quakes early Monday. They were of magnitude 4.3, 5 and 4.4. A fifth struck around 1:13 p.m. and registered at a 5.9 magnitude.

At 7:50 p.m., a 3.9 magnitude earthquake was recorded off the Oregon coast. Then at 8:11 p.m., a 4.2 magnitude trembler was felt.

A ground motion sensor near Mt. Hood picked up all of the ocean quake activity, highlighted by red indicators on screens at the U.S. Geological Survey offices in Vancouver.

They struck at a fault nearly 300 miles west of Coos Bay, Oregon. They were relatively shallow, at 6 miles deep.

KOIN 6 News wanted to know if these quakes could mean we're closer to a big offshore quake, like the one that rattled the region more than 300 years ago.

"These earthquakes are happening in a totally different part of the system and aren't really relevant in a physical way," USGS seismologist Seth Moran said.

According to Moran, Monday's quakes are on a fault line farther out to sea than the much more dangerous fault line right off the Oregon coast. That closer fault line — the Cascadia-Subduction Zone — has caused huge quakes in the past and is currently building up pressure.

"The area where it's stuck is roughly like this and if that entire patch were to go all at once, that's the magnitude 9," Moran said. "It's a long fault, it's a wide fault."

Scientists at the U.S. Geological Survey said it usually takes an earthquake of magnitude 7 or better to trigger a tsunami.

They say the fault that produced them generates frequent earthquakes, but it isn't the type of fault that produces the most violent quakes.

Scientists told KOIN 6 News the action off the coast is an "earthquake swarm," but they are not connected to the fault line that worries experts.