The earthquake was detected south of Portland, in an area that has a relatively small population.
The National Oceanic and Atmospheric Administration's Tsunami Warning Centre did not immediately issue a tsunami warning for the area after the earthquake was detected.
The tremor comes just after the Pacific Northwest Seismic Network reported detecting more than 4,500 small earthquakes over a two week span, deep underneath the Olympic Peninsula and outer Vancouver Island. The areas impacted by those tremors also included an area spanning from near Eugene, Oregon — close to where the Thursday earthquake was seen — down to the Siskiyou Mountains in northern California.
Those earthquakes were part of a phenomenon known to scientists as "episodic tremor and slip" or "slow slip", which apparently happens on a regular basis along Cascadia's tectonic plate boundary.
The earthquake, while large, is unlikely to cause much harm, as the closest population centres are likely too far to be significantly impacted.
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