Alaska earthquake 5.7 - near Anchorage

[FrenchieGirl]

Re: Alaska earthquake 5.7 - near Anchorage

Here's the USGS map link on Google: http://maps.google.com/maps?q=61.93...l=61.9374,-150.5125&spn=2.719063,7.075195&z=7

 

[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

neat map, Frenchie.

One reason we shook so much, is that the valley is filled with aluvial till - old glacial debris deposited as glaciers receeded - sand, gravel, small rocks. So we rarely feel the hard shocks you'd feel if you were sitting on an area close to bedrock. It was all rock'n roll.

The only potential for serious damage, might be some pipelines that go from underwater oil/gas wells in the inlet and over to land, where they go to gathering areas. But the system that feeds the Drift River terminal was shut down because of the recent volcanic eruptions.

it must have been interesting to be in the top of some of the tall hotels in Anchorage.

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[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

I just felt/saw the second aftershock that shook my computer & plants. But no noises.........pheeew.

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[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

aftershocks so far:

MAP 3.0 2009/06/22 19:46:52 61.931 -150.674 18.6 SOUTHERN ALASKA
MAP 2.8 2009/06/22 19:40:12 61.970 -150.881 36.2 SOUTHERN ALASKA
MAP 3.2 2009/06/22 19:35:45 61.949 -150.629 42.9 SOUTHERN ALASKA
MAP 5.7 2009/06/22 19:28:05 61.944 -150.519 56.5 SOUTHERN ALASKA

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[FrenchieGirl]

Re: Alaska earthquake 5.7 - near Anchorage

If you want to map distances between your home and the epicenter, you could use this: Mapping and Distance Tools

 

[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

BREAKING NEWS

5.3 quake rocks Southcentral
Updated: June 22, 2009 11:43 AM
An earthquake rocked Southcentral at about 11:30 a.m. Monday. The 5.3 magnitude quake occurred about 30 miles southwest of Talkeetna, according to preliminary data from the National Oceanic and Atmospheric Administration. There is no tsunami expected, NOAA said.

http://www.ktuu.com/

local radio is reporting there is minor damage in Houston, AK.

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[Lizw]

Re: Alaska earthquake 5.7 - near Anchorage

neat map, Frenchie.

One reason we shook so much, is that the valley is filled with aluvial till - old glacial debris deposited as glaciers receeded - sand, gravel, small rocks. So we rarely feel the hard shocks you'd feel if you were sitting on an area close to bedrock. It was all rock'n roll.

Glad you're okay. My niece lives in Wasilla, so we're waiting to hear from her. My uncle used to be in Houston, but they're up in Delta Junction now, quite a long distance. Hope the aftershocks are over with.

 

[wotan]

Re: Alaska earthquake 5.7 - near Anchorage

I'm showing M5.4 32km E of Skwentna, Z=52KM. Without reviewing the local tectonics (and assuming this is not related to magma movement) the depth seems to indicate an earthquake occcuring within the subducting slab of the Pacific Plate.

 

[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

If you want to map distances between your home and the epicenter, you could use this: Mapping and Distance Tools

I tried, but since the epicenter area has no street addresses, it's difficult. When I put in lat longs, it came back with 6 miles which I know is wrong. Based on data from the USGS, I'd say I'm 19 miles away from the epicenter.

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[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

Glad you're okay. My niece lives in Wasilla, so we're waiting to hear from her. My uncle used to be in Houston, but they're up in Delta Junction now, quite a long distance. Hope the aftershocks are over with.

I'm sure your niece got a good shaking.

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[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

.........assuming this is not related to magma movement) the depth seems to indicate an earthquake occcuring within the subducting slab of the Pacific Plate.

Plate subduction makes sense, however, many of those quakes are far deeper. There are several east-west faults across the valley, which may be the source. A far as magma events, it wouldn't be related to Redoubt, however there are other volcanoes nearby that have erupted in recent years. Infact, 2 eruptions ago of Redoubt, Mt. Spurr (closer to the quakes epicenter) was erupting during part of the same period as Redoubt. Can you image two volcanoes erupting withing sight of Anchorage? I believe, those early volcano quakes are far more shallow than this one. This magnitude is common for this area.

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[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

local earthquakes just this year...



http://neic.usgs.gov/neis/recent/ak00109810_h.html

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[wotan]

Re: Alaska earthquake 5.7 - near Anchorage

The line of intermediate depth (70-150KM) seems to follow the subduction zone. The pattern would tend to rule out a steeply dipping subduction zone (again, I haven't reviewed the regional tectonics )

Disregard what I said earlier about being intra-slab, I was unconsciously adding a zero to the depth. The intermediate depth would make sense for being a subduction zone earthquake depending on the angle of subduction (lateral offset from the trench). I don't think there's any evidense of any kind of back-arc spreading going on behind the subduction zone, so I think I can rule out normal faulting. Seems too deep to be related directly to orogenesis (mountain building). Also seems a tad too deep to be related to any kind of strike-slip faulting which would likely be in the upper 10-15 km. From the graphic I don't see anything deeper than the 70-150km range, which would definitely help define the location of the subduction zone at depth.

 

[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

During the earthquake, my son and his wife were in a movie theatre in Anchorage. He said it shook the building fairly well. Everyone was a little apprehensive. It was one of those multiple-theatre buildings.

Also, the epicenter was 20+ miles north of a known major east-west fault - the CastleMountain fault. It has produced magnitude 7 earthquakes in the past.

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[wotan]

Re: Alaska earthquake 5.7 - near Anchorage

http://www.castlemountaincoalition.org/castle_mountain_fault.htm

A study by the USGS shows the Castle Mountain fault may be ready to produce a strong magnitude 6 to 7 earthquake.
Peter Haeusseler said his research demonstrated that major earthquakes occurred on this fault on average every 700 years or so in the last 2,700 years, and that the last significant earthquake along the fault occurred about 650 years ago.

I saw a reference to there being transpressional stresses on this fault. That makes sense if the Pacific Plate is striking the North American Plate obluiquely. Still, it seems that fault seems too shallow.

 

[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

This epicenter was well outside the rift zone of the Castle Mountain fault. But I know that some horizontal faults can have related activity on a 45 degree side fault. There are other small faults in the valley - I'll go looking.

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[colormyquilt]

Re: Alaska earthquake 5.7 - near Anchorage

Take care, up there, AlaskaDenise.

 

[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

About 3 years ago this area was proposed for coal bed methane extraction with related deep reinjection wells. They wanted to inject toxic-laden water into the area of the Castle Mountain fault rift zone.

I testified against the proposal and one of my major points was that nobody knew for certain what would happen if a normally active fault, like CastleMountain was "well lubricated" by the wells. Remember the earthquakes outside of Denver in an area with NO seismic history, that were caused by injection wells? same thing for CBM injection wells in Utah.

My very-public question to the industry reps was "if this area normally produces magnitude 5 or 6 earthquakes and injection wells have been known to cause magnitude 4+ earthquakes in non-seismic areas, can they be certain these active faults won't then produce even greater earthquakes, with potential to cause considerable damage to a popualated area?" Their answer: "we don't know"! Local government officials looked rather concerned at those prospects. They voted against the project for a wide variety of reasons.

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[wotan]

Re: Alaska earthquake 5.7 - near Anchorage

In the opposite extreme they stopped pumping ground water, oil, and gas out of the Great Houston area in part because of the concern that the removal of fluids was causing increased activity on our local fault systems (did you know we have them here?), leading to increased subsidence.

 

[AlaskaDenise]

Re: Alaska earthquake 5.7 - near Anchorage

Here's the map with the local major earthquake faults:




http://www.aeic.alaska.edu/Seis/recent/sub/quakes/2009174_evid110007/evid110007.html

The long red line below the epicenter (yellow square) is the Castle Mountain fault.


Also on that page they give distances to nearby volcanoes:

Redoubt - 124 miles (currently active)

Spurr - 70 miles (frequently active - once while Redoubt was also active)

Hayes - 65 miles (not sure of activity, but not in the last 30+ years)

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