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January 17, 2021 Mount Hood Earthquake Swarm

January 17, 2021

An earthquake swarm at Mount Hood is ongoing. The earthquakes are associated with regional faulting and are not a sign of changes in volcanic activity.

Since noon local time on January 17, there have been over 100 individual earthquakes in an area south of the summit of Mount Hood. At the time of this statement, the PNSN has located several 10's of these earthquakes with a maximum magnitude of M2.7 and depths mostly around 5 km (3 mi) below sea level. Swarms at Mount Hood are common and account for most of the seismicity at the volcano; they can last hours to days. The location of the earthquakes is similar to other swarms in this area that occurred in 2009, 2012, 2014 and 2020.

Mount Hood earthquakes since 2010 map and cross section
Top: Map View of earthquakes at Mount Hood since 2010 (black circles) and the current swarm (red circles), both sized by magnitude. Blue triangles are current seismic stations. Dark lines are highways around the volcano. Bottom: Cross section from line between A and A' above. Dark line is outline of volcano. Earthquakes marked as above.
Earthquakes at Mount Hood, plot
Top: Event rate per week of earthquakes around Mount Hood since 2010. Each spike represents a swarm of earthquakes at the volcano. The current swarm is at the right margin of the plot. Bottom: Depth of earthquakes plotted in time since 2010. The time axis is the same as the top plot.

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