The United States Geological Survey says a 6.3 magnitude earthquake has struck roughly 170 miles off the coast of Oregon, in the western United States.

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.

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