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USA – Earthquake swarms – are they a sign of ‘the big one’? (VIDEO)

Parts of the American Northwest are experiencing earthquake swarms – with some places recording dozens of shakes around 3.0 on the richter scale every week.

Geologists have been studying the causes and effects of such swarms, which begs the question – could the next ‘big one’ be just around the corner?

CNN’s Dan Simon explains what they are, and what they mean.



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