Watching Juan de Fuca Plate

The Juan de Fuca/North American plates are showing some energy build-up-

www.thenewstribune.com...

Some scientists think this could create an even stronger tsunami than they first expected. There is debate about whether it's locked together and would snap by a mega thrust earthquake. This would also cause inner continental damage around Seattle/Tacoma that hadn't been calculated.

I flagged this thread because I believe that any sign of energy build-up is crucial to developing an early warning for tsunami's.

So I will be watching, also!

Did I miss something in that article? It says that tremors occur every 15 months or so. I should think that is a good thing -- releasing energy gradually here and there.
If they didn't happen then the energy would build up; increasing the likelihood of a big earthquake at some point to release it all at once.
No?

reply to post by wayno


The instruments are detecting an inch or two of movement — known as “episodic tremor and slip” — as the Juan de Fuca plate grinds and sinks beneath the North American plate. Closer to the surface, the two plates are locked together.

This is a different kind of tremor happening under the surface. Hopefully they are continuing to slide in a way that is releasing energy.

i read this last week, dureing my weekly search for updates on YS .


so yeah i gave ya both for posting it before i did.

The new swarm at Yellowstone is keeping me interested in how this could effect Juan de Fuca. I had been noticing a few tremors on TWC, except the last few days.

The Haitian earthquake will have the eventual effect of putting extra pressure on the San Andreas and that, in turn will build up the pressure on the Juan De fuca. Everything is tied together here, imo.

Important thread.

S&F

edit to add... yes, small incremental movements would be nice, but the Juan De Fuca is a special sort of situation. It has to do with the NA plate moving onto the Pacific plate and raising the coastline. Major tsunami threat.



[edit on 22/1/10 by masqua]

Originally posted by wayno
Did I miss something in that article? It says that tremors occur every 15 months or so. I should think that is a good thing -- releasing energy gradually here and there.
If they didn't happen then the energy would build up; increasing the likelihood of a big earthquake at some point to release it all at once.
No?

Small earthquakes don't always release pressure, they can cause the opposite sometimes also.

It was long thought that small earthquakes were good because then you would avoid big ones but as you can see by monitoring quakes it doesn't work that way.

Originally posted by winotka

 

Closer to the surface, the two plates are locked together.

Isnt this what happened in Haiti the epicentre was only 6 miles below the surface.

A 'shallow' quake causes more destruction from what I can remember, is that right?

reply to post by _selectThis_
[more

usgs.gov-Shallow earthquakes are between 0 and 70 km deep

scign.jpl.nasa.gov... link discusses different types of earthquakes. For example the geologic make-up around the New Madrid Fault is different from around the San Andreas Fault. The triggering around these faults will result in different consequences. The ground around New Madrid will liquify when there's a moderate to strong eq.

I've personally theorized that since they(Haiti) would've built more to withstand hurricanes, that an earthquake is a totally different kind of destruction.

this produced a tsunami around 1702 or so. thanks to the japanese and their great record keeping, we know this. that they are well acquainted with quakes and the waves after them, when something unusual happens, they take note. around this time on one of the northern islands, a tsunami struck. what was unusual, was there was no quake. they call this a ghost tsunami. there is a stretch on the washington coast that has a forest of dead trees. they were killed when this section dropped a couple of feet in elevation. geologists found evidence of a massive quake in the strata and dirt around this time. sea water then finished up. local natives, tell of an angry spirit that shook the earth with great thunder.
my source for this is a very good show on one of these channels. t.l.c., disc., or the history. this plate is very much like the one in indonesia and can and has produced quakes this size.

There was a huge earthquake in Chile this morning that caused a tsunami. Let's hope it doesn't have any effect on JDF. With this being a different kind of fault, we may not get much warning.

reply to post by blackthorne

Hi Blackthorne,

Yes, as you say, the last mega-quake on the Cascadia fault zone at the junction between the Juan de Fuca and Nth American plates produced a tsunami that was recorded in Japan the next day. To be precise, it shows that this quake occurred on Jan 26, 1700.

The effects on the local native people in the BC/Washington region were horrendous. Whole communities were washed away, areas of land rose or fell, and according to oral histories, the shaking lasted many hours.

For some more data, maps and animated simulations of this event, go to this page on the UCSC website.

If you’d like more data just send me a u2u and I’ll post some references.

reply to post by winotka

Hi winotka and thank you for the thread. (S&F)

The Chile quake occurred due to subduction of the Nazca plate under the Sth American plate, so it’s quite similar to what happened in the mega-thrust quake of 1700 on the Juan de Fuca/Nth American plate subduction zone on the Cascadia fault.

You’re right that we may not get much warning. Just as in Chile, the off-coast Oregon/Washington/BC region gets smaller quakes quite often, but rarely much over a mag of mid-5. The last seriously big one was an 8.1 on 22 August 1949, on Queen Charlotte Island, BC (just north of Vancouver Island). Luckily it was a sparsely populated area and relatively speaking, it didn’t do a great deal of harm.

Problem is, even this big quake 60 years ago has probably not done a lot to alleviate the next really big one. There’ve been mag 8 quakes on the Cascadia fault before but they didn’t stop the mag 9’s. (More on this aspect below.)

Someone commented that small quakes can help relieve the pressure and prevent bigger quakes. Yes, it would help -- if the total amount of energy released by the smaller quakes used up a significant amount of the energy that would otherwise be released by a single big one. Well, while that sounds good and actually even seems pretty logical, it’s not really the case in reality, because quakes are measured on a logarithmic scale, not a linear scale.

Don’t want to bore members to tears, so in simple terms it just means that if you hear of a quake that’s a magnitude 5.0, for example, then another that’s a magnitude 6.0, it means that the 6.0 released 32 times the energy of the 5.0, and had about ten times the amount of shaking. The same applies if they are not exactly whole numbers. A 7.2 is about 32x32* times as powerful as a 5.2, and an 8.2 is 32x32x32 times more powerful, and so on up and down the scale.

[* For the technically minded, the number 32 is an approximation derived from the formula M2 = 10^3/2 .M1, where M2 is the next whole number on the logarithmic scale above M1. In the formula, M1’s energy is taken as a base value of “10”, which is then treated with the fractional exponent 3/2 to derive the value of M2. So, we solve 10^3 (giving us 1000) and then solve its square root, which gives approx 31.6.]

We’ve probably all heard or read recent news reports that compared the Chile quake to the Haiti quake, in terms of energy release. The Chile quake was many hundreds of times more powerful, so even if there’d been a mag 7 in Chile shortly before their latest big one, it wouldn’t have made even a one percent difference to its effects.

Here’s an interesting statistic to really put this into perspective: scientists calculated that the mag 9.5 Chile quake in 1960 released about 25% as much energy as all the other earthquakes of the 20th century combined. And nearly all that energy was released in just a few minutes…

So, getting back to the Pacific Northwest: even if we had a couple of hundred mag 5-range quakes along the Cascadia fault zone in a shorter time (like a few months or weeks, even), it would not make any noticeable difference to a subsequent mega-thrust mag 9 quake. In fact, although that part of the PNW typically gets plenty of micro-quakes and small quakes every year (mag 1’s, 2’s and 3’s), it only averages a dozen or so over mag 5. Two dozen at the outside. So their total energy release will have almost no effect whatsoever on a future mega-thrust event.

Imagine this: a mag 6 is equal to 32 mag five’s, and it takes 32 mag 6 quakes to equal one mag 7, and 32 of them to add up to the energy of a single mag 8. And it takes about 32 mag 8’s to equal the energy of just one mag 9. So, to have enough relatively harmless offshore mag 5’s to even reduce a mag 9 down to a still highly-dangerous mag 8, we’d need a total energy release equivalent to 32 mag 8’s -- and in a fairly short space of time. And that means we’d need about 32x32x32x32 mag 5’s. Around one million mag 5 quakes, in other words. (A few thousand either way doesn’t really matter.) That’s just to reduce one mag 9 quake down to a mag 8. And a mag 8 is still big enough to do a heck of a lot of damage, especially to coastal areas around Vancouver and down to Seattle.

This “million-mag-five-quake” thing just doesn’t happen. As far as we know, it never has. And the reason is simple: these mega-thrust quakes are so called because when they thrust, the results are mega. The quake of Jan 26, 1700 involved a rupture and thrust along about 1,000 km (600 miles) of coastline. The chunk of real estate involved was about 150 km (90 miles) wide. The average movement -- thrust in one direction -- was about 15 metres. That’s nearly 50 feet -- and most likely, the majority of that movement occurred in just a few minutes.

If the plates move over or against each other fairly smoothly and gradually, all relatively good. But these mega-thrust quakes happen where the plates don’t let go gradually. That’s what happened in Sumatra off Banda Aceh, and it’s what happened in Chile. They occurred because a huge chunk of a plate got stuck, and the pressure on it built and built over many years. Then, when the stuck region can take no more, it lets go like an avalanche. The longer it takes before it lets go, the bigger the thrust and the more powerful the quake. Not even a few thousand smaller quakes will make much difference to that power. And as far as we know, a big chunk of the Juan de Fuca plate is stuck.

Mike

There was a tremor in the last 2 days-

www.pnsn.org...

It was only a 2.1.

reply to post by winotka

Yep, just a tiny quake. They get lots of them -- Sth Cal gets even more, in the range of hundreds every week. (Members can refer to the Southern California Earthquake Data Center for more info. For example, the near-real-time Recent Quakes Map for California-Nevada is showing 773 quakes right now -- and that is nothing out of the ordinary!) These micro and small quakes do help a little to alleviate stresses, but as I said, if there's a big one building up they won't make a lot of difference to it.

Actually it's hardly worth taking much note of very small quakes like these most of the time. You'd go nuts just trying to keep track of them all. But it's a different matter entirely if they come in swarms within one area. Then they are worth studying further, because they can indicate either seismic activity or possibly volcanics. There have been some swarms of small quakes in the middle region of the Juan de Fuca plate over the years, and for one of the last major ones, scientists were so interested in it that they sent a research ship out to study it "on location", so to speak.

For a brief report about the research of the above swarm and its results, go to this page from Oregon State University.

It turns out that while the seven previously studied swarms were volcanic in nature, this one occurred due to activity within a previously unknown series of faults within the plate (and not at its boundaries). As a marine geologist involved in the research said:

“This pattern of earthquakes demonstrates that the Juan de Fuca plate is continually moving and converging with North America at the Cascadia Subduction Zone,” Dziak said. “It isn’t clear if the swarms that occurred in 2008 represent normal stress release within the plate, or if they are from deformation related to the Cascadia Subduction Zone. We simply don’t yet know.”

In other words, not even the scientists fully understand what's going there. I have no problems with that; it's a complex system, after all. But the key thing is that the plate is not only still moving, it's still undergoing changes within itself as well. What that might lead to we have no idea. So, because this Cascadia fault zone is a major threat, we need to keep a close eye on any swarms on the Juan de Fuca. They might be the only major warning that we'll get -- if we recognize what it means.

Increased activity in the volcanoes on land in that near coastal region could also be indicators, though, because much of their energy (heat and magma) comes from the subducted plate. So, if those volcanoes start acting up, keep an eye on the plate zone for any uptick in activity.

Mike




[edit on 5/3/10 by JustMike]

I see there was a tremor off the coast-

www.weather.com...

I don't have time or presence of mind to dig any deeper at present. There was just a death in the family.