Small Earthquake Swarm at Mt. Hood, Oregon

I just noticed the earthquake activity at Mt. Hood over the past few hours. According to the PNSN Mount Hood page, there have been 17 small quakes just south of the volcano in the past 6 hours. The largest was a Mag 1.7. The depths average around 6km.
We should keep an eye on it and see what develops.



ETA: Although historically, over the past 40 years, Mt. Hood averages zero earthquakes per month, the seismologists at the Pacific Northwest Seismic Network say this activity is not unusual. Read their blog concerning this afternoon's swarm Here.

Sooo...doesn't sound like this is anything to be alarmed about. But if you would like to monitor the mountain, I find these stations good: TIMB, HOOD, and TDH. You can find them on the this page.



It looks like at least 4 more quakes have rumbled since the last PNSN update, 2 of which look to be near Mag 1.0 size. Tiny.
Mr. Malone, from PNSN, studied the swarms from the 1990s, and feels they are most likely from regional tectonic stresses; not volcanics--but they're watching closely.

Yes small earthquakes are coming up especially the Mega quakes, just earth changes nothing to be afraid of but it would be good to be AWARE.

Nice catch, Olivine.

I was lucky enough to have been informed from somewhere else about this.

I have been over heli data with spectrograph for HOOD, TIMB, VLL, VFP and TDH- and while there is this bit of seismicity, there doesn't appear to have been any tremor of any kind that I can see for all those stations back to 2-22.

But a swarm on Hood is always something to keep an eye on, so glad you posted it.

reply to post by TrueAmerican


I'm glad to have your eyes on this TA. Thanks. After reading the summary of the swarm from 1999, it seems these are probably tectonic in nature.

I just have to say, that zworld brought this to my attention, with his last post in the West Coast thread.

@ Zworld, I blew it. I was excited to start my first thread, and I really should have asked you to do the honors.
Please forgive my cloddish newbie ways.

Yeah sure, Oli, always happy to help.

Although after reading Steve Malone's "boring" assessment of these quakes, I do wonder why he would state that station TDH is the closest station to either Mt. Hood, or to the recent seismicity on the south flank. Because that is incorrect. HOOD is the closest to seismicity, TIMB is closer to seismicity and closest to peak, and TDH is well, aways away.

Just thought we'd clear that up.

And please, check me on that. Cause I did check.

Right after you posted, I too kept checking for information and could find none, However, at 8:36, here in the valley I felt rumbles and watched my glass of water shake a little. It was really mild but definitely obvious.
I found this article of interest, describing how by comparison, Oregon has not been able to get as much funding for locating and studying fault lines as California, so there is much unknown here in our state when it comes to knowing all the fault lines.
www.oregonlive.com...

Peace,
spec

reply to post by Olivine


This has me worried, why? Because I grew up in Portland Oregon, and had a great view of Mt. Hood from our living room. Anyway, back in 1980 when Mt. St. Helens blew her top/side, geologist were predicting that Mt. Hood had a 70% chance of blowing in the next 30-35 yrs. Well, guess what, that is now.

I've climb to the top of Mt. Hood, and near the top is what is called the "hogs back." It is a ridge that runs along a deep crevasse that smokes sometimes, and you get a lot of sulfur smell (from H2S) from it. So I always knew that Mt. Hood was not dormant. Will have to keep an eye on it.

Look at that animation and you will see how many quakes are occurring each hour off the coast of California and up in Alaska. To me that seems to be where the tension is being relieved in small doses. Off the coast of Oregon and British Columbia there aren't as many and to me that's where the tension is at it's worst right now.

reply to post by speculativeoptimist

Hi speculativeoptimist. Thanks for linking that article. It's really a darn shame that they have to scrounge for funding when lives are at stake. Especially disconcerting was the mention of hydroelectric dams. If one fails, that will be catastrophic for everyone down stream.

ETA: Your avatar is a hoot! Cute pup.


reply to post by fastfred

Thanks for posting your firsthand knowledge of the volcano fastfred. I had read that there are fumeroles on the mountain, but I didn't realize that the sulfur smell was so strong. Really interesting--I'm definitely going to do some more reading.
In Mt. Hood Earthquake Activity: Tectonic or Volcanic Origins? found here, the authors state that the very last known volcanic activity was between 1859-1865, when early settlers reporting seeing a glow from the summit.


reply to post by mark1167

Sweet .gif mark1167. Did you make that, or is it hidden on USGS and I just never noticed?


After reading the article linked above, the PNSN scientists are fairly certain these quakes are from normal mechanism faulting--the farthest north such Basin and Range type extensional faulting. But, (there always seems to be a "but") they hold out saying so with absolute certainty for a few reasons:

The 2002 swarm had a mainshock, followed by smaller aftershocks, indicating just your run-of the-mill fault rupture. Earlier swarms from the 1980's and 1990's (as well as this latest swarm) do not follow this pattern.

And, proximity to a historically active volcano.

Also interesting, during the number crunching of the 2002 swarm, they discovered a weak low-velocity zone at 4 km depth. (low-velocity zones can indicate an area of warm, possible molten rock)
I'm hoping they will analyze this latest swarm to see if the weak, slow zone is still there.

reply to post by Olivine


If you go to their main page on the left hand column about three quarter's of the way down you'll see the option: "Earthquake animation". You'll find lots of really cool real time animation from all over the world . It's neat because you can see the way some earthquakes swarm in lines or almost semi circular formations in certain area's.

reply to post by mark1167


Awesome! I love it.
Thank you

It looks as if a new tiny earthquake swarm has begun at Mt. Hood. It started yesterday 8 March 2012 @ 06:03:31UTC with a Mag 0.6 and has produced 13 more small quakes since then, the largest being Mag 1.7.

Mag Time (Local) (UTC) Depth (Km) (Miles)
1.7 2012/03/09 15:59:02 4.2
0.5 2012/03/09 09:08:59 2.8
0.6 2012/03/09 07:05:41 2.1
1.3 2012/03/09 06:38:06 5.1
0.8 2012/03/09 06:37:23 5.9
1.7 2012/03/09 06:36:58 3.9
0.0 2012/03/08 21:26:35 3.4
0.2 2012/03/08 20:44:11 3.5
0.3 2012/03/08 19:42:00 3.4
0.1 2012/03/08 19:40:40 2.8
0.6 2012/03/08 10:59:01 2.6
0.4 2012/03/08 10:49:04 2.2
0.2 2012/03/08 08:18:38 3.4
0.6 2012/03/08 06:03:31 3.4

Source--PNSN
This latest swarm looks to be on a parallel line to the west of the February cluster. I'll keep watching--if it picks up in size and/or intensity I'll report back.




ETA: I'm not sure why the link doesn't work, but once on the page, click Mt Hood from the column on the left

Yet another swarm today. I noticed that the last swarm was on March 9, this one on April 9. Suspicious? Ha ha...
peace


17 quakes this time, the largest being a 2.7. Started yesterday around 8am my time (edt), so I guess 3 UTC? ...can't remember if it is plus or minus 5 for where I live.

Thanks for posting LobeDethFaurt.

Map of swarm found on this page

This swarm is really curious.
It is 20 km south of Mt. Hood, which makes this activity too far away from the volcano to be associated with it, according to John Vidale, director PNSN. PNSN facebook link
Also noted on the FB discussion, was how little seismic activity is recorded in the PNSN catalog for this area.

I was just checking on GPS velocities in the Oregon area, to see if there was any movement possibly connected with the current ETS event SW of Eugene, when I noticed something odd at Mt. Hood.
Take a look at the Pacific Northwest Network velocity map. (the east-pointing arrow, just above the much longer NE arrow from South Sister)

This is Station P791 located low on the SE flank of the volcano.
Notice the spikes beginning after March 1st? (approximately--if I'm reading the hash marks properly)
This says it is experiencing 23.5mm/year movement. The swarms were located West of this station.

Just a short-term instrument malfunction, or something interesting? It looks to be returning to normal.

It looks like Mt. Hood is becoming a bit fidgety--4 very small quakes over 20 minutes. Depths are from 2.6 to 6.3 km.



Source (you have to click "Mt. Hood", otherwise the link doesn't work for some reason)

This is station UW.TDH..SHZ old-style webicorder:


Here is the newer style webicorder found here


Edit before my 2 hours is up, lol. The total is up to 8 little quakes, with the depths now ranging between the 0 and 6.3km deep.

reply to post by Olivine


Yep, thanks for the update.

And notice how those were relocated. I've had "eyes" on it since I saw your post, and I saw a couple more- but it appears to have subsided for now. Apparently these are common at Hood, and also they think they are tectonic in nature- not volcanic- even that shallow and directly under the mountain. The more I read the more I realize that tectonics play a critical part in the formation of volcanoes- and it's another reason why it's a specialty to be able to distinguish the different kinds of quakes from the calculated focal mechanisms.

Easy to get Hoodwinked at Hood.

Originally posted by TrueAmerican
reply to post by Olivine

 

And notice how those were relocated.

It looks as if they have fine-tuned the locations and depths one more time.



Total of 10 microquakes, depths ranging from 3.2 to 5.7 km.
Glad to have you watching.

It has been a while, but a new small swarm has emerged near Mt. Hood again. As in the past, it could be tectonic in nature, but since it is so near the volcano, it's good to keep an eye on such events.


image from PNSN

Here is the spectrogram of the largest earthquake in this series (so far) a mag 2.3, 7.1 kms deep.


PNSN spectro

And finally, this is a link to a nearby seismograph station, TDH.UW.EHZ

Mount Hood had a tiny burst of confirmed volcanic earthquakes 9 days ago.

four shallow volcanic earthquakes at Mount Hood occurred on October 8 between 8:39 - 9:18 am local (PDT) with magnitudes 1.6, 0.3, 1.4, and 2.0.

CVO
(I had to remove the (< 2 kms) portion from the quote, because it wouldn't code correctly)

The 3 largest were listed at less than 2.0 kms deep. Here is the link to the associated spectrograms, between 15:39 and 16:10 UTC.