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Recent Mount Hood earthquake swarm typical for this Oregon volcano.

May 16, 2016

At Mount Hood, a swarm of small earthquakes was detected May 15-16, 2016. Studies of past swarms have concluded that they likely are occurring on pre-existing regional faults and are best thought of as "tectonic" earthquakes rather than earthquakes directly linked to magmatic processes.

The earthquakes in this swarm are located 2-3 miles south of the summit of Mount Hood at depths of 2-3 miles below sea level. The largest event was a magnitude 1.8. Earthquake rates reached as many as 20 earthquakes per hour, peaking between 6-7 am on May 16 before decreasing later in the day. The Pacific Northwest Seismic Network (PNSN) located nearly 60 earthquakes; many more events occurred that were too small to be located. This swarm is very typical for Mount Hood because it is located several miles away from the summit vent – it is rare to see swarms occur directly beneath the summit.

Swarms are not uncommon in the Mount Hood area, which typically experiences one or two swarms per year that last for several days to weeks. The most energetic swarm recorded to-date occurred in June-July of 2002, which included a magnitude 4.5 that was broadly felt in the Government Camp area. The current swarm is much, much smaller than the 2002 swarm, both in terms of earthquake size and in number. A paper published in 2005 by J. Jones and S.D. Malone studied Mount Hood swarms in great detail; read more in a PNSN 2012 blog.

For more information, see Mount Hood Monitoring and the Cascade Volcano Observatory Weekly Update.