Massive Earthquake Shakes Aleutian Islands

Jun 24, 2014 Full story: Bad Astronomy Blog

Days earlier, the area around a remote Aleutian volcano was rattled by dozens of smaller quakes, prompting fears of a possible eruption The magnitude 7.9 earthquake that struck Alaska today occurred 15 miles southeast of Little Sitkin Island in the Aleutian chain.

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adeline chacon

Tucson, AZ

#1 Jun 24, 2014
interested in background before dating

“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#3 Jun 25, 2014
This one was a fun article.

The interesting bit was the depth ~109Km or thereabouts. The location (arc graben @ region near Little Sitkin) is in the base of the crust of the overriding plate, rather than the subducting plate which is about 125Km or thereabouts @ that depth.

The moment tensor of the event indicates a transform compression event with the E side (Semisopochnoi & forearc) moving SE, and the W sidr (little Sitkin-Adak) moving NW, and compressing the forearc against the arc graben.

A note about the water leaving Adak harbour indicates that Adak may have gone up in the world as a result. The aftershock footprint shows a lot of events in the forearc S. of little Sitkin (best seen on the NEIC map zoomed in on the Aleutians) indicating that the bulk of the movement was on the W side of the transform with semisopochnoi (a bit grumpy @ present) remaining uncompressed. Semisopochnoi may be aseismic as a result of a magma squeeze out, so be a good idea to keep watching that space.

Also of interest is a transform event of 6.3 in the arc graben E. of Buldir which appears to have come out in sympathy as a result of the recompression of the arc in the main event.

The area is also the footprint of the 1965 megathrust crustal relaxation event (8.7) with an arc runout of about 10m & tsunami in 1965.

By now the arc magma injected into the base of the crust by the 1965 event in fractures perpendicular to the runout should be popping up @ the volcanoes (Buldir-Semisopochnoi).

Will keep watching that space.

Have a nice day: Ag

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