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Thread: Cascadia Episodic Tremor and Slip

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    Cascadia Episodic Tremor and Slip

    Although this is far from beign official yet. It's on! (Ok so I am hyping it up a little here)

    The Juan-de-Fuca plate is once again in motion and actively sliding under the North American plate.

    Map of all the deep trmors from Feb 8 through Mar 8th. Blue is olders to red Newest.



    It will be consider a full slip when/if the activity from the Potland/Salem area roughly reaches Roseberg. I checked the tremor map for todays activity and it's Just under Corvalis right now, with new activity starting up around Eugene.

    Source article link. http://www.pnsn.org/blog/2013/03/08/...ch-of-cascadia

    Interactive Tremor Page link. http://www.pnsn.org/tremor
    Last edited by dgavin; 2013-Mar-15 at 08:05 PM. Reason: Spelling

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    It will be easier to search if you spell it "Juan," which is the correct spelling. Thank you for the information, but that misspelling of yours always bothers me!
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    Gillian

    "Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

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    I know, but when you are dyslextic Jaun and Juan look exactly the same. And it's random which way I type it at any given time.

    Words ending in 'ing' I have the same issue with. Soemtimes it's right sometimes its not, ing and ign come across the same when reading for my own mistakes.

    I fixed the post

    Remember Dyslexia is finally recognized as a real disability (albeit a learnign disability), and 10% of the population has it in one form or another. Try not to let spelling issues get to you too much, there is no sense is stressing yourself or others, when 10% of the population can't do anything about it.

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    My father was dyslexic. My favourite of my mother's siblings is dyslexic. My younger sister is so severely dyslexic that we once had to wait for her to get home from camp to tell us what her letter said--and she got her high school textbooks on audio from the Braille Institute. Graham is dyslexic. I get dyslexia, and I do consider it a real issue. However, I disagree that ten percent of the population can't do anything about it. Even my sister was eventually able to send legible letters home from camp. I'll also point out that you once asked a mod to change the spelling of a thread title--to the incorrect spelling.
    _____________________________________________
    Gillian

    "Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

    "You can't erase icing."

    "I can't believe it doesn't work! I found it on the internet, man!"

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    Yes I don't mind correcting mistakes at all even my dyslexic ones.

    I'm just a bit sensitive about it is all. Grew up with a Teacher for a mom, 2 brothers of strait A caiber, another an artist, and a botanist for a Father. They didn't understand my issues at all until it was far to late to take some of the remedial education. Had to fix my issues best i can on my own.

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    Well Gillian, I just installed IE 10 on win 7, and it has a built in spell checker. finally. So some of my issues should be caught in future posts!

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    Hooray!

    In all seriousness, I am grateful for the posts, especially those--like this one--that have a chance of affecting me directly. Though I didn't feel any of the tremors in my area. They must be small and deep.
    _____________________________________________
    Gillian

    "Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

    "You can't erase icing."

    "I can't believe it doesn't work! I found it on the internet, man!"

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    Gillianred,

    They are small, deep (40 - 70km) though they arn't tremors in the sense of volcanic tremors. They actualy have a signature somewhat similar to the quakes at the Newberry hydrothermal drilling site. Makes sense if you think about it, at Newberry they are injecting liquids between fault zones, and these deep tremors, are from two plates sliding while producing thier own fluid (magma) beween them. Different causes, but a similar resulting effect.

    As of today the activity center is west of Portland. It was about half way between Eugene and Roseberg a few days ago, but it never made it further south. So it's still uncertain if this is a full slip event or not.

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    I really, really hope not. A full slip event on this fault would be . . . devastating. We are so ridiculously unprepared for it around here. After the Nisqually quake, I asked the housing office at my alma mater (I was living in the dorms at the time) what their emergency plan was, and they might as well have not even had one.
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    Gillian

    "Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

    "You can't erase icing."

    "I can't believe it doesn't work! I found it on the internet, man!"

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    Ahh!

    You can ease your mind a little. Full Slip in this case, just means thats the entire Juan-de-Fuca plate is able to slip under the north american plate, instead of parts of it still being locked up and not in motion. There is about a 1.5 yearly cycle to these (best estimate by USGS). It is not a megathrust pre-cursor.

    If you look at the map image I'm attaching, you can see that there is a large area between Eugene and Medford that hasn't shown any motion slip activity yet. Like wise a larger area in the north. If one of those two area's starts showing tremors, then it will be considered a full slip.


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    That's a great relief. I just know that the fault is due for a pretty serious quake--several, possibly, and possibly overdue. A friend who was in the UK during the Nisqually quake sent me a cheerful e-mail saying how pleased she was that she'd missed Washington's "Big One." I told her that it wasn't even close to either of the two prospective Big One scenarios I'd heard, and she was shocked. Despite having lived in this state her whole life.
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    Gillian

    "Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

    "You can't erase icing."

    "I can't believe it doesn't work! I found it on the internet, man!"

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    In case you wondering the yellow lines are the plate junctions, the left most 20km depth, to the right most 40km depth. Almost all of the tremors are happening along the 40km zone, with a noticeable jog towards the 30km zone below the Portland/Salem areas. That might (stress might) mean there is more magma lubricating the plates to the east of that area.

    No surprise there, that's where they used to teach about a suspected 'ball bearing' like pool of magma might be, when I was a kid.

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    Quote Originally Posted by dgavin View Post
    Ahh!

    You can ease your mind a little. Full Slip in this case, just means thats the entire Juan-de-Fuca plate is able to slip under the north american plate, instead of parts of it still being locked up and not in motion. There is about a 1.5 yearly cycle to these (best estimate by USGS). It is not a megathrust pre-cursor.

    If you look at the map image I'm attaching, you can see that there is a large area between Eugene and Medford that hasn't shown any motion slip activity yet. Like wise a larger area in the north. If one of those two area's starts showing tremors, then it will be considered a full slip.
    You've eased my mind a bit as well. That dark blue area at the top is WAY too close to home. As I'm reading it, this activity is a good thing, allowing movement to take place and releasing the tension without having a major earthquake. Is that more or less correct?

    What's the effect of this on the local volcanoes? Wake them up a little? Calm them down a little? Nothing?
    Last edited by Trebuchet; 2013-Mar-20 at 03:54 PM. Reason: Deleted image to save someone a little bandwidth!
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

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    Quote Originally Posted by Trebuchet View Post
    You've eased my mind a bit as well. That dark blue area at the top is WAY too close to home. As I'm reading it, this activity is a good thing, allowing movement to take place and releasing the tension without having a major earthquake. Is that more or less correct?

    What's the effect of this on the local volcanoes? Wake them up a little? Calm them down a little? Nothing?
    Monitoring what is called ETS (Episodic Tremor and Slip) is a relatively new addition to sceince, starting about 12 (+ - a few) years ago. It wasn't until USGS's post recently I heard they had a name for it, or have the 1.5 year cycle figured out. I don't think any other subduction region has this sort of monitoring happening yet, though I suspect Japan will be jumping on this sceince after thier recent activit some years ago.

    What is known:

    Bulk Plate movements (subduction) happen in episodic spurts of activity, and is not constant. There are period of months to years when plates are locked, and periods where they are not locked. During a unlocked phase plate movement can be tracked by deep low level swarms of earth quake activity that occures at the plate juntions as they move past each other.

    What is suspected: It may be possible that the Eposodic plate motions will completly stop, some years to decades before any megathrust event. The real answer here will have to wait for a megathrust alonge the cascadia zone, as it's the only place where full ETS monitoring is currently active. It's still an unkown and until ETS is tracked through a Megathrust event, we won't really know if there are correlations.

    So in answer to one question, yes, it's likely that ETS events are a good sign, but the science is just too new to say for sure.

    What is unknown: Do megathrust quakes happen anyway, by plate locking in the in the 0-30km regions of subduction zones where ETS activity isn't the normal? Or are they alway preceeded be a compltere plate lockign against movement at the 30-60km zones as well. This answer, with the lack of frequncy of megathrust events, and that 3 recent ones were missed, will probably take 200-1000 years to wait for the next series of megatrust quakes.

    Do they affect volcanoes. Definately, the more the plate is moving, the more active volcanoes will be, as there is more melting occuring during those times. However there is like not a direct increase in activity, it would be delayed by the time it takes the magma to perculate up to primary volcanic pools, and thats on the order of decades. So an increase in activity in a primary pool (infusion of magma) could be coming form a ETS yesrs, or decades before. It's still to new of a science to make any concreate correlations to volcanic infusion in primary pools and ETS.

    Saying that, I will take a look at GPS -anyway- around these zones in the up coming months though to see if there is any changes to uplift/subsidence cycles thats noticable.

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    I'd rather, as I said, that the megathrust event took its time.
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    Gillian

    "Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"

    "You can't erase icing."

    "I can't believe it doesn't work! I found it on the internet, man!"

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    Although USGS hasn't announced it yet, according to their definition the plate is in full slip motion now. Some tremor activity getting close to Roseburg, and there was a good swarm of tremors up around Nanaimo on Vancouver Island. So the two large gaps without activity are starting to show slip.

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    Tremors up to 26.5 per hour the last three days, still no official word if they will call this a full motion plate slip, but it's looking like it is from thier definition a few weeks ago.

    A bulk of the tremor activity this week was below the PDX/Hood/Salem/Silver Falls regions.

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    "Too close to home," Treb says. His home wasn't mentioned by name. Naming Silver Falls disturbs me a bit more because I grew up in Silverton, just north of the state park.

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    Quote Originally Posted by dgavin View Post
    Do they affect volcanoes. Definately, the more the plate is moving, the more active volcanoes will be, as there is more melting occuring during those times. However there is like not a direct increase in activity, it would be delayed by the time it takes the magma to perculate up to primary volcanic pools, and thats on the order of decades. So an increase in activity in a primary pool (infusion of magma) could be coming form a ETS yesrs, or decades before. It's still to new of a science to make any concreate correlations to volcanic infusion in primary pools and ETS.
    I would think that ETS seismic activity would also have the effect of causing some existing magma pools to release magma that might have been temporarily hung up, thus increasing volcanic activity in a shorter time frame.

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    Quote Originally Posted by geonuc View Post
    I would think that ETS seismic activity would also have the effect of causing some existing magma pools to release magma that might have been temporarily hung up, thus increasing volcanic activity in a shorter time frame.
    The tremors are too deep and week to have a direct impact on volcano's magma pools. Also they are from lubricated/slip motion as opposed to strike/slip motion.

    Primary volcanic pools are usually from 2-8km depth below a mountain. With episodic volcanoes (like St. Helens), it's assumed they have larger secondary pool around 12-20km depth. The Magma melt zone pools from the plates are around 30-60km depth. The Transfer from melt zone to pool happens along fault zones, or existing channels, that are not very large, and often succumb to being blocked at times by crystallization between the magma and the channels themselves.

    So again, there should be no direct affect from increased plate slip or when slip is frozen.

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    Tremors have slowed down to about 3.2 per hour the last two days. Still appears to be in a full slip mode, with a quiet spot between Salem and Roseberg over the last week. There was pretty much tremor activity along all the rest of the subduction zone otherwise, even if it seems to be slowing down in frequency of events.
    Last edited by dgavin; 2013-Apr-08 at 07:58 PM.

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    Ok the ETS event was pronounced officially over on the 4th, though there are still some bouts of tremors. Some of the statistic indicate that the region around Portland/Salem/Eugene had reached a tremor rate of 300 per hour. The rest of the Cascadia zone only reached 200 per hour. With the notable exception of the region around Roseburg to Medford, which only had reached few brief swarms of maybe 20 per hour. While the rest of the subduction zone seems to be slipping at a good rate, the lack of slip in this region does seem to indicate some plate locking there, which does add some reinforcement to other research that the Coos Bay area is where the next major quake would likely start.

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    Was the fault slipping from depth to the surface in the segments where it was slipping? Has anyone detected changes in GPS readings in survey points? I was just wondering if this movement may be shifting loads to other parts of the fault, if that makes any sense.
    Et tu BAUT? Quantum mutatus ab illo.

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    Not to dampen your enthusiasm, dgavin, but it's been official for more than a decade (probably much much longer than that but I don't want to look it up).

    And there's another recent thread, Slow Slip where I've posted some recent links of mine.

    Of course we all know if there is anything new at all, Swift will post it first. Do not be discouraged.


    For the record, recent 7.+ mag quakes on the Cascadia fault are anything but reassuring. But they seem to have quieted down now, the slip is preceding normally, and 7.+ quakes have occurred before. The Cascadia fault has a mega-quake every 300-500 years or so and the last one was precisely in 1700. I do have earthquake insurance on my house, for what it's worth.
    Last edited by beskeptical; 2013-Apr-11 at 05:16 AM.

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    Quote Originally Posted by Ara Pacis View Post
    Was the fault slipping from depth to the surface in the segments where it was slipping? Has anyone detected changes in GPS readings in survey points? I was just wondering if this movement may be shifting loads to other parts of the fault, if that makes any sense.
    The slow slip occurs on a regular basis ~ every 15-18 months and has for many years. It was also detected that the ground raises up on the Olympic Peninsula and then slips back down like an inchworm but I'm having trouble locating that data. I know it's there though. Living in the Cascadia Fault area, I've read voraciously about this phenomena over the years.

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    Quote Originally Posted by dgavin View Post
    Although this is far from beign official yet. It's on! (Ok so I am hyping it up a little here)

    The Juan-de-Fuca plate is once again in motion and actively sliding under the North American plate.

    Map of all the deep trmors from Feb 8 through Mar 8th. Blue is olders to red Newest.



    It will be consider a full slip when/if the activity from the Potland/Salem area roughly reaches Roseberg. I checked the tremor map for todays activity and it's Just under Corvalis right now, with new activity starting up around Eugene.

    Source article link. http://www.pnsn.org/blog/2013/03/08/...ch-of-cascadia

    Interactive Tremor Page link. http://www.pnsn.org/tremor
    This is great stuff. Thanks for the update. I always hate it when they say stuff like, "bares watching".
    The central Oregon batch bares watching. This is the part of Cascadia for which full ETS episodes are fairly rare (from 18 to 23 months between them compared to 12 to 15 months for northern Washington ones and 9 to 12 months for northern Californa ones). If the current central Oregon activity is the beginning of a full ETS then it should last for another few weeks and extend south to the Roseburg area. The last major ETS in this region was in June, 2011, so one is about due.

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    Quote Originally Posted by beskeptical View Post
    This is great stuff. Thanks for the update. I always hate it when they say stuff like, "bares watching".
    Do you hate it because of the sentiment, or because they confused "bears" with one of its homophones?
    Et tu BAUT? Quantum mutatus ab illo.

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    beskeptical - the it's official wording I was using was for meant this particular ETS episode. Also while ETS is considered similar to slow slip isn't exactly the same. Slow slip can happen along normal fault zones, and doesn't exhibit cyclic behavior often. Where as from reading some of your sources (Good info that!) ETS seems limited to subduction zones and is almost always cyclic. I think I caught one paragraph in your sources that it also might happen in hotspot volcanic regions.

    USGS seem to have two terms for ETS, partial slip and full slip. Even though the slip reached Roseberg, USGS never indicated that it was a full slip, though it met their conditions for it.

    The Olympic peninsula is indeed rising with each ETS episode, where as, death valley in California is spreading and sinking at a fairly constant rate. After watching a geology show last night on death valley, I found out it's crustal area is only 12 miles thick (and getting thinner slowly) compared to the surrounding 20mile think or so continental crust.

    It dawned on me that Death Valley might be an early precursor to rifting.

    Anyway, yes ETS been known about for a while, but before that seismology blog, I never found out about them in time to post one as it happened like this one.

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    Quote Originally Posted by dgavin View Post
    beskeptical - the it's official wording I was using was for meant this particular ETS episode. Also while ETS is considered similar to slow slip isn't exactly the same. Slow slip can happen along normal fault zones, and doesn't exhibit cyclic behavior often. Where as from reading some of your sources (Good info that!) ETS seems limited to subduction zones and is almost always cyclic. I think I caught one paragraph in your sources that it also might happen in hotspot volcanic regions.

    USGS seem to have two terms for ETS, partial slip and full slip. Even though the slip reached Roseberg, USGS never indicated that it was a full slip, though it met their conditions for it.

    The Olympic peninsula is indeed rising with each ETS episode, where as, death valley in California is spreading and sinking at a fairly constant rate. After watching a geology show last night on death valley, I found out it's crustal area is only 12 miles thick (and getting thinner slowly) compared to the surrounding 20mile think or so continental crust.

    It dawned on me that Death Valley might be an early precursor to rifting.

    Anyway, yes ETS been known about for a while, but before that seismology blog, I never found out about them in time to post one as it happened like this one.
    Don't mind my hasty wording. There was a duplicate thread I had just posted in and I was reading about the Olympics recent ETS because there was a 7.+ quake on the Cascadia fault ~6 months ago.

    This event was "official" months back. Unless you are saying the section in OR and CA are now official.

    But, who cares, the point is this is fascinating stuff and I appreciated your update.


    Re bears vs bares, whew, at least it was their error and not mine.

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