West Coast USA: Pay Attention, Cascadia May Be Ready to Rupture

reply to post by geotrician


I should have read whole post - the second part remain controversial. Fluids may play a role, just as they might in regular earthquakes, but that role is only poorly (or not) understood.

i would still like to know why the whole world is rocking....i mean really rocking,and ive been following it since 2008.....but Canada west coast has nothing.

not good...not good at all

Originally posted by JohnVidale
reply to post by geotrician

 

I should have read whole post - the second part remain controversial. Fluids may play a role, just as they might in regular earthquakes, but that role is only poorly (or not) understood.

Well, I guess most (including me) have adopted the view expressed in the paper by Houston et. al. 2011 (ref. below) that:
_______________________________________________________________________________________
"rapid reversals of tremor patterns propagate backwards for tens of kilometers at speeds that are 20 to 40 times faster than the relatively slow, steady advance of episodic tremor and slip. Our observations suggest that once the plate interface is weakened by the initial advance of episodic tremor and slip, it allows stresses to induce slip more easily or fluid pressure waves to migrate more rapidly, generating rapid tremor reversals." End quote by Houston et. al.
____________________________________________________________________________________
I strongly believe in the role of fluid pressures on the plate interface as both controlling the location of slip initiation (along with known asperities) and the subsequent pattern of tremor. And I also believe that totally understanding these dynamics may lead to an accurate prediction of the approximate timing of the next major subduction zone event.

Ref:
Houston, Heidi, Brent G. Delbridge, Aaron G. Wech and Kenneth C. Creager, 2011, Rapid tremor reversals in Cascadia generated by a weakened plate interface: Nature Geoscience, 4, p. 404-409. Article can be viewed online at
nature.com...

reply to post by geotrician


Heidi Houston, that's my wife. I'm well aware of her views.

Actually Abhijit Ghosh and I wrote up a fluid hose sort of pressure fluctuation model, and it was in one of our papers on streaking tremor. It's the only time I've had multiple people come up to me after several talks to tell me I should drop that part to avoid embarrassing myself. A large part of the community does not believe fluid pressure pulses can move as fast as the tremor streaks, 50km/hr. It does sound fast, but the possible pressure differentials are huge and the fluid fraction and connectivity is unknown.

I guess it still strikes me that the role of fluids, if any, is not well known. Perhaps unknown is too strong.

Originally posted by JohnVidale
reply to post by geotrician

 

Heidi Houston, that's my wife. I'm well aware of her views.

Actually Abhijit Ghosh and I wrote up a fluid hose sort of pressure fluctuation model, and it was in one of our papers on streaking tremor. It's the only time I've had multiple people come up to me after several talks to tell me I should drop that part to avoid embarrassing myself. A large part of the community does not believe fluid pressure pulses can move as fast as the tremor streaks, 50km/hr. It does sound fast, but the possible pressure differentials are huge and the fluid fraction and connectivity is unknown.

I guess it still strikes me that the role of fluids, if any, is not well known. Perhaps unknown is too strong.

Well, congrats on having such a smart wife. And I don't have a fixed view. It seems to me though that the rapid reversals of tremor direction must include a fluid role. I don't think that there has to be a regionally propagating fluid pressure wave (fire hose?), but that the observed signal is a discrete local pressure change that reflects the readjustment of regional stress after a slip event. I am guessing that the extent and timing of tremor reversals have a multivariate connection that include 1)rocking of the oceanic plate after a slip event, 2)exhaustion of the extent of higher fluid pressure zones, and 3) tracking beyond the boundaries of a given asperity involved in the overall slip event. Interesting stuff, however, and seemingly unique in its rich detail to Cascadia and the excellent data set developed by researchers involved.

reply to post by geotrician


"unique in its rich detail to Cascadia and the excellent data set developed by researchers involved."

Japan has a better permanent seismic network, Hi-NET is fabulous, but we've had denser deployments of portable instruments so far, and strong slow slip tremor directly under the Olympic peninsula to image.

All this observational power, however, has still left plenty of mysteries, fortunately for us researchers.

Oh nice, so I see another pro has joined the fray. And if I had to guess, that's probably Paul, or one of the employees at PNSN.

Great, now we can all just shut up, and watch you two talk. I am enjoying it already, so please, have it.

Cause me, I have a volcano to watch.

www.abovetopsecret.com...

Originally posted by JohnVidale
reply to post by geotrician

 

but we've had denser deployments of portable instruments so far, and strong slow slip tremor directly under the Olympic peninsula to image.

There you go, right there is the key.

Originally posted by TrueAmerican
Oh nice, so I see another pro has joined the fray. And if I had to guess, that's probably Paul, or one of the employees at PNSN.

Great, now we can all just shut up, and watch you two talk. I am enjoying it already, so please, have it.

Cause me, I have a volcano to watch.

www.abovetopsecret.com...

Wrong about any associations. I am a outdoors guy, unemployed, who likes to visit dirt bike and gun forums. But I just get pretty involved and technical and luv geology, so sorry if that offends anybody. Now on to a discussion about KTM dirt bikes and Marlin rifles. Wanna know which gun powder to use in a .308 benchrest rifle.

To better understand the Cascadian megathrust, here are some arguments why we need seafloor instruments.


Scientists have yearned for years to plaster the seafloor around subduction zones with seismometers and every other kind of sensor imaginable. So far, most instruments are dropped from ships, then recovered to sift through the data months later. But driven by new initiatives that emplace permanent cables to carry down power and carry back data, such as John Delaney's OOI cable surveying the Cascadia offshore, better monitoring is possible.

We'll review the reasons offshore instrument have great value.

...

pnsn.org...

I don't know, but it seems like the recent discussion has skeered off TrueAmerican. He is either monitoring his data link to Illiama or visiting with Sheriff Arpaio about how to unseat Obama. Too bad, maybe he could have predicted the eruption of Illiama, got Obama out of office, and prevented the next big Cascadia earthquake in one weekend. Pardon me for funning, but I love these type of threads for a diversion from more serious matters like whether to buy generic peanut butter or brand name and whether to make sure that each has enough 3-Omega in it.

I noticed that many of the little quakes listed on the USGS located inland Washington & Vancouver all say, "a probable quarry explosion". Are these large mining areas?

Also, I recall somewhere on the thread or somewhere that there have been lava flows off the shore of Oregon. I swear the pictures shown were recent. Has that been tied into the recent activity that has been happening along the fault lines?



goetrician- Off topic... stay away from the KTM's nothing but money pits.

reply to post by AuntB


There are a lot of mines, but maybe there are everywhere. We just choose to show them on our earthquake maps because people can feel them, and may wonder why the Earth shook. Most networks record them but do not plot them.

The earthquake this morning was just off shore, while the likely volcanic sequence last year was way out by the ridge-transform system, so the two are likely unrelated.

reply to post by JohnVidale
I know that the quake today was off the shore but where was the lava flow from last year? I have never seen a map as to the location. We did have some activity last month on the more Eastern Fault line and I was curious as to where the lava flow is in relation. From re-reading the article it seemed like it was unexpected and the OSU people are expecting another eruption in 2014.

www.kptv.com... o-erupted-off-oregon-coast-earlier-this-year

The volcano, named Axial Seamount, last erupted in 1998, and the team of OSU scientists forecasted it would erupt again before 2014. Oregon State scientists say this marks the first-ever successful forecast of an undersea volcano. The new eruption was discovered July 28 when scientists used a robot to find a new lava flow on the seafloor that was not present a year ago. Because only a handful of the earthquakes were detected from land, scientists did not initially believe there was an eruption.

I guess my bottom line question is: Is the activity we were seeing last month connected to Axial Seamount?

Originally posted by TrueAmerican
Oh nice, so I see another pro has joined the fray. And if I had to guess, that's probably Paul, or one of the employees at PNSN.

Great, now we can all just shut up, and watch you two talk. I am enjoying it already, so please, have it.

Cause me, I have a volcano to watch.

www.abovetopsecret.com...

TA, no offense meant, but it seems that you would prefer this on-going discussion had its own home.

I have been finding my own need for a dedicated thread for all the latest scientific info/articles/discussion on the CSZ. There seems to be a lot of it out there right now and with Mr. Vidale joining us here, I think it's a great opportunity to expand our data and knowledge.

SO....I began a thread just for that. I would like to invite our newest members interested in contributing to join me there.

A Serious Discussion On The Cascadia Subduction Zone and Latest Studies

reply to post by westcoast

Good on you.

My sons live in the Seattle area, so I am genuinely interested in decifering all the data and see if they are in danger from the next megaquake. I shall visit you on your thread.

reply to post by JohnVidale


Informative blog post, Mr. Vidale. Thank you.

I caught this little shake a few minutes ago, on station PB.B046..EHZ, Petrolia, CA.

Here it is zoomed into.
(click on images to enlarge)

This station's background amplitude normally runs in the +/-100 nm/sec range. I realize that +4/-6 microns/sec is still very small, and I'm still learning to decipher real seismic events versus manmade. Be gentle.
Are these types of events too small to merit listing, or too difficult to locate because of distance offshore, or in the case of this particular "burble"--both?

@geotrician--Welcome to the forum

reply to post by Olivine


I don't see the quake on the Northern California map, and it does clearly look like an earthquake. Those borehole stations are very sensitive, and and S-P difference of just 2 seconds means it was less than 20 km away. There may be only one or two stations that see it, making it hard to locate. I'd guess it is about M1, tiny.

So here is a good question for all concerning preliminary signals of an impending megaquake:
Should we be worrying about earthquakes that are significant (>M4.0) and near the spreading center, similar size events that are along the coastline and near the junction in N. California, or earthquakes of such size that are within or just on top of the subducting ocean plate and well inboard of the margin?