7 earthquakes hit off Oregon coast in less than a day

SALEM, Ore. — Scientists say seven earthquakes that shook off the coast of Oregon are considered an "earthquake swarm," but they are not a signal that a bigger quake is about to happen.

QUICK FACTS:

● Seventh earthquake off Oregon coast occurred Monday night
● No tsunami threat.
● Seventh earthquake in 24-hour period
● Monday afternoon quake was largest at magnitude 5.9
● Magnitude 7 usually quake usually needed for a tsunami

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The biggest quake of the day hit around 1:11 p.m.

A series of sizeable earthquakes struck off the coast of Oregon on Monday morning, but officials say no tsunamis were triggered.

Quake times and recorded magnitude

• 11:52 p.m. Sunday: 5.8M
• After midnight Monday: 4.3M
• 4:46 a.m. Monday: 5.5M
• 7:46 a.m. Monday: 4.4M
• 1:11 p.m. Monday: 5.9M
• 7:50 p.m. Monday: 3.9M
• 8:11 p.m. Monday: 4.2M

Paul Caruso, with the U.S. Geological Survey, says both quakes hit a fault that's west of the Oregon and Washington coast. They were about 330 miles west of Salem.

Click here to see photos of major earthquakes in Seattle (1949, 1965 and 2001).

Caruso said the Oregon coast quakes were not big enough to trigger tsunamis. He says it usually takes a magnitude 7 for that to happen.

Both were about six miles deep, which is relatively shallow, Caruso said.

The deeper the quake, the less likely people will feel it.

For example, the magnitude 7.8 quake that recently struck Japan did little damage because it was 420 miles deep.

Related: Details about an earthquake warning system for Seattle

Related: Seattle has taken steps to make bridges earthquake-proof

A USGS Seismologist tells KOIN that Monday's offshore quakes are not on the same fault line that will produce "the big one."

The "big one's" fault is much closer to the coast and two plates are struck, getting unstruck causes the big quake. Monday's quakes are on an unrelated fault farther our to sea.

KIRO