Wednesday, August 8, 2012

Large And Shallow Earthquake Swarm Near Aniakchak Volcano

Aniakchak volcano in Alaska is one of the largest, and most active volcanoes in the Aleutian arc. The volcano contains a 10km wide caldera, with multiple cinder cones occupying the ~3400 year old caldera floor. The last eruption of Aniakchak occurred in 1931, which marked the only known historical eruption of the volcano.

A large earthquake swarm struck approximately 25 miles NE of Aniakchak on August 3-5, centered between Aniakchak volcano and the lesser-known Yantari volcano (which apparently had a very Mt. St. Helens like eruption in pre-history). The largest quake was a 4.7 magnitude quake at a depth of around half a kilometer (which is very shallow). Many other shallow quakes, some with similar magnitudes have occurred (see the below image) since.

Google Earth plugin with USGS real-time overlay enabled showing the location of the quake swarm

The depths of most quakes in the area are usually some hundreds of KM deep, as this is a subduction zone where one plate slides underneath the other. Occasionally this process generates a magma vein, that results in dike intrusions and the birth of most of the world's stratovolcanoes.

This quake swarm is curious due to its location and the very shallow depths. New volcanoes have been born in Alaska in the past, sometimes with disastrous results such as the eruption of Novarupta, the largest eruption of a US volcano in recorded history. While it is likely that this is a magma dike intrustion into the crust, it is impossible to say what might occur if the swarm does not return, or no new magma is injected into the crust. Most dike intrusions do not result in an immediate eruption, and some times they never do.

In any case, I will be keeping a close eye on this, and possibly email AVO about the swarm and see if they were aware of it (which I am sure they were) and whether they might be able to shed some light on it for our readers. Stay tuned!

*****UPDATE 8/9/2012*****

Another single quake at a depth of 5km measuring 2.5 occurred today in the area. This is the first aftershock/tremor in a few days. I have contacted AVO requesting information on the current swarm, and hopefully will hear back from them soon!

*****UPDATE 8/10/2012*****

AVO responded to my email with the following response:

"They're regional tectonic earthquakes. We have no indication that these earthquakes have anything to do with volcanism.This series of earthquakes, at this time, is not alarming to us."

So it appears that there may be several faults criss-crossing the Aleutians that occasionally have these shallow types of quakes occur, even very near active volcanoes.

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