Wednesday, May 16, 2012

Anchorage Gets Jolted Just After 7am (4.6)

Some quakes you wonder about - "Was that a quake?"

Not this one.  The room jerked hard as if startled.  And then it was over, maybe a few seconds.  No damage here, but it definitely got our attention.

[I changed the title from 4.8 to 4.6.  The original USGS maps - below - said 4.8.]

UPDATE 7:23am  From the US Geological Survey Earthquake Page

Map from USGS


Map from USGS
The 3:02 UTC is 7:02 Anchorage time. It felt much stronger than what I associate with 4.8 [4.6] but that's probably because it was very close - it says (12km - 7miles) south of Anchorage.  That begs the question - where do the measure "Anchorage" at?  Downtown?  The airport? 


To put this into context, here's a list of earthquakes today in Anchorage from the Alaska Earthquake Information Center at the University of Alaska Fairbanks.  The give the 7:02 quake a 4.6. 


Screen shot at 8:20am 5/16/2012









Magnitude and Age Legend for Earthquakes




157 Earthquakes Shown on This Page:




Local Time




Magnitude




Region
07:56 AM AKDT Wednesday May 16th, 2012 1.28 ML in the central region of Alaska
07:42 AM AKDT Wednesday May 16th, 2012 1.96 ML in the Kenai Peninsula region of Alaska
07:22 AM AKDT Wednesday May 16th, 2012 Unknown in the central region of Alaska
07:12 AM AKDT Wednesday May 16th, 2012 1.44 ML in the central region of Alaska
07:02 AM AKDT Wednesday May 16th, 2012 4.61 ML in the Cook Inlet region of Alaska
05:21 AM AKDT Wednesday May 16th, 2012 1.84 ML in the Cook Inlet region of Alaska
05:13 AM AKDT Wednesday May 16th, 2012 1.72 ML in the Cook Inlet region of Alaska
04:57 AM AKDT Wednesday May 16th, 2012 1.28 ML in the central region of Alaska
04:44 AM AKDT Wednesday May 16th, 2012 2.13 ML in the central region of Alaska
03:20 AM AKDT Wednesday May 16th, 2012 Unknown in the central region of Alaska
03:06 AM AKDT Wednesday May 16th, 2012 2.59 ML in the Cook Inlet region of Alaska
02:29 AM AKDT Wednesday May 16th, 2012 3.07 ML in the Kenai Peninsula region of Alaska
02:21 AM AKDT Wednesday May 16th, 2012 0.82 ML in the central region of Alaska
01:49 AM AKDT Wednesday May 16th, 2012 1.07 ML in the central region of Alaska
01:35 AM AKDT Wednesday May 16th, 2012 0.50 ML in the central region of Alaska









This historic summary is from the same page as the second map.
Tectonic Summary Seismotectonics of the Aleutian Arc The Aleutian arc extends about 3,000 km from the Gulf of Alaska to the Kamchatka Peninsula. It marks the region where the Pacific plate subducts into the mantle beneath the North America plate. This subduction is responsible for the generation of the Aleutian Islands and the deep offshore Aleutian Trench. Relative to a fixed North America plate, the Pacific plate is moving northwest at a rate that increases from about 55 mm per year at the arc's eastern edge to 75 mm per year near its western terminus. In the east, the convergence of the plates is nearly perpendicular to the plate boundary. However, because of the boundary's curvature, as one travels westward along the arc, the subduction becomes more and more oblique to the boundary until the relative plate motion becomes parallel to the arc at the Near Islands near its western edge. Subduction zones such as the Aleutian arc are geologically complex and produce numerous earthquakes from multiple sources. Deformation of the overriding North America plate generates shallow crustal earthquakes, whereas slip at the interface of the plates generates interplate earthquakes that extend from near the base of the trench to depths of 40 to 60 km. At greater depths, Aleutian arc earthquakes occur within the subducting Pacific plate and can reach depths of 300 km. Since 1900, six great earthquakes (M8.3 or larger) have occurred along the Aleutian Trench, Alaska Peninsula, and Gulf of Alaska: M8.4 1906 Rat Islands; M 8.6 1938 Shumagin Islands; M8.6 1946 Unimak Island; M8.6 1957 Andreanof Islands; M 9.2 1964 Prince William Sound; and M8.7 1965 Rat Islands.

2 comments:

  1. There is a great map on the adn.com site. The epicenter is off Klatt, between Toby's house and mine. I heard a rumbling sound first, sort of like heavy equipment in the street, and was walking toward the window to check on it when I felt the sharp jolt.

    I watched Hacking Democracy last night. Wow! This was a real eye-opener. Everyone who trusts the security of our elections should see this. Thanks for putting up the link (in your May 13 Suppose Someone Found a Body post).

    ReplyDelete

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