The marvellous mechanics of the subduction zone

I'm trying out calligraphy with Inkscape. You can add mass, tremor and other neato stuff to mask your normal horrible strokes! I'm still improving, but already I'm better than Brittney in an MTV concert!

Lots of earthquakes lately in subduction zones. I get some questions (none, here, unfortunately), mainly: Why all these earthquakes now? -- Why not? is the correct answer. :) Also, why do these earthquakes have to be so much bigger to get the same shaking destruction as other types of earthquakes. (I made that up myself!)

To answer that question, we have to look at the mechanics, which is slightly different than the other articles I have written. First, I poo-poo the notion that the oceanic crust is pushed down. All oceanic crust eventually gets cold, old, and tired (like me!). It eventually sinks under its own weight, like elephants going to their grave site. Even New York City will (one day) have its own subduction zone!

As show in my great figure, this slab tends to fall at an angle, and rub up against the island arc complex. Mechanically, this slab is really goopy, full of water and sea-shit (see my Carbon Cycle articles), and has different properties than regular earthquake rock. Once in a while, the descending slab gets hung up on the upper rock, and slippery bathtub feet engage (from Fault Mechanics).

All the normal mechanisms for earthquakes now apply, but the dynamic friction drop may (or may not!) be greater because of all the goop. The important thing is that this is an 'upside down' thrust fault, with the moving element being the slab. As such, the rupture, and the high velocity pulse goes downward.

This reduces the impact of the shaking, but things are not so happy for the inhabitants of the ocean shore. The combination of the rapid slip downward, and the attendant push upward on upper crust, makes for some dramatic ocean wave mechanics. It's like suddenly getting up in your bathtub! If we are lucky (like this last one), most of the oceanic energy gets beamed down to the penguins, who can take care of themselves.

As in my beautiful drawing, the oceanic crust eventually gets a nice warm, peaceful death, and the water-carbon gets pooped out at the top, to cause some other problems for the locals....

Of course, the island arc actually gets pushed by all this, and on the other side we get the juicy high-speed thrust earthquakes that cause so much trouble, for their size (as in the Japanese nuclear earthquake).

Gregory Smith lands on his feet

It's all right everybody! We don't have to worry about The Gregory molderizing on the fishing dock. The former OPG 'new nuclear man' is down in bayou country, providing electricity to all those pumps in New Orleans.

Final thing on water laser

There's an election going on here in Ontario. I know that because they're putting up the signs today. You won't hear much about nuclear power for a while, since OPG will stay low until the shooting stops.

In a Candu plant, they put all these compressible fuel bundles into a long pressure tube, and there's a whole bunch (I can't remember how many!) of these in a reactor (lots of sites explain the Candu system).


You can see the fuel bundle fits very snuggly into the pressure tube. Through this, they squirt a lot of heavy water. As they approach a critical water velocity, the compressed fuel pellet tubes start to bulge.

Here's when the fun comes. Any slight pressure pulse in the water hits the first fuel bundle and compressed it a little bit more, which causes resistance to the flow. A compression wave starts down the fuel bundle chain, driven by the water flow. When it hits the bottom, it reflects back as tensile pulse (that's what waves do!). A bit of tension has less resistance to the flow.

We have now set up our water laser! The fuel bundles pump up any little chop in the water flow. They will keep pumping up to tremendous levels! The amazing thing about this arrangement is that it tunes to the input, much like the unstable air flow in an organ pipe. Around the fuel bundles are many sections of pipe (headers and feeders) that would love to resonate at certain frequencies, as well as the primary pump itself. The tubes are probably happiest at their fundamental frequency (everything pumping up and down at the lowest frequency), but higher frequencies are possible.

It is this 'positive feedback' mechanism with the tubes that allows the water laser to pump up to such high energies. Now, once on Wikipedia, everybody poo-pooed this, as being totally useless. They said that the simple 2 cent rotary water chopper in a water pressure cleaner, did the same thing! They obviously didn't appreciate the magnificence of a multi-million dollar setup doing the same as a 2 cent part!

The water laser can be tuned to different frequencies! It produces a perfect sinusoid water pulse, instead of square waves! It can be used to destroy fuel bundles! Such a sad waste that this magnificent discovery will forever go unacknowledged, until they make another one in the next Candu plant!

Water laser - II

I shall continue my story, even though my ad account remains at a pristine zero! After all, I think I'm writing for my own soul, to boost my serotonin levels!

When the Big Company fired up Darlington, something horrible happened. There were tremendous vibrations, and fuel bundles were coming out shattered. I looked at the photos of these things, and was amazed at the stresses that would be involved to do this. On some bundles, the serial number of the adjacent bundle was imprinted perfectly, implying almost explosive shock-like impact!

For some reason, I was enjoying one of my high cycles in the company, and was thrown into the investigation, because of my experience in dynamics, and they were fond of shit-disturbers! They thought there was some sort of resonance involved, and switched the main pumps from a 5 blade impeller, to 7 blades. This had the effect of a dramatic decrease in vibrations, and broken fuel bundles. The whole case was closed.

They attributed the whole thing to acoustic-type stub resonance, which is the amplification you get with the chamber of an acoustic guitar, perhaps a factor of 2. They actually called it organ pipe resonance, without understanding the physics of an organ pipe! After the pump change, vibrations continued to plague the station, and they fooled around with the end fittings to change the perceived stub resonance. As of this date, they've had to do modifications in the heat exchangers for the vibrations, and I fear the place is shaking apart!

The biggest mistake they made was attributing organ pipe amplification to passive resonance. In reality, there is a feedback mechanism with the air stream, which flows chaotically up against a knife edge. A tiny change in pressure makes the air stream flow into the pipe, compressing the air, while a change the other way, causes the air to flow outward, creating lower pressure. The air stream starts as white noise, and the organ tube selectively filters the resonant frequency. This sets up a wave train of acoustic waves going up and down the pipe. When a compression pulse hits the air stream, it pushes it out, creating low pressure, which adds to the open reflection pulse. This builds up into a tremendous sound!

The combination of the fuel bundles, the water flow, and the pressure tubes, created something much more powerful than an organ pipe, and we'll go into this next time, when I feel like it...

Geology of Bruce, Ontario

Since the cash has started to fly, I would open up the session by telling what I know about the site. I won't cite references because there aren't any! This is the most unstudied area I know. All information is safely hidden in-house.

I first became aware of the site, when I first joined the big company, 28 years ago. At the time, they were building a water intake tunnel, which was so leaky you had to wear a heavy raincoat to go into it. I was terrified, and never took up the opportunity to visit. To dig that tunnel, they had to use trainloads of grout, and they still ran into a huge cavern. Now there's a dog-leg in the tunnel, in order to go around it.

At the time I was taking stress measurements all over Ontario, and I always found high stresses and solid, tight rock. I could not believe there could be such an area where the rock was so bad, so I made a study of it. I wrote some of the results in Paleocollapse.

As such, I formed a hypothesis, which was testable:

Hypothesis One: The paleocollapse was caused by the dissolution of the deep salt beds under the limestones. There should be standard, solid limestone under the former salt beds.

Over 28 years, I learned a lot, so now there is this:

Hypothesis Two: The salt beds and carbonates were laid on the soft hanging wall of the Grenville Front (megathrust). This eventually resulted in extensive fracturing, and the dissolution of the salts.

Both hypotheses can be tested by drilling a deep hole, which is now being done in-house. I just worry that all the results will be spun towards #1. They have to proceed, no matter what, because they have left no alternative. They hearings will conclude that they should proceed, on the proviso that if they find something politcally unacceptable, they will stop. No scientific criteria will be set.

For interest, look at the Google picture. All of the paleocollapse is below a cliff that runs NE, parallel to the Grenville Front. The area NE of the plant shows the sinkholes, and is exactly like an air photo I once saw that was done before the plant was built.

Deep Geology Thingie dishes out the cash

This article is what I've been waiting for! 100 thousand loonies have been handed out to people, to make the OJ-hearings a bit more exciting. I hope they do a good job!

As we all know, the Deep Geology Waste Respository (DGR, whatever!) is a big plan to spend all that money which has been building up, from the nuclear plants (a percentage is set aside for the garbage). This is generally a good thing, and I'm all for nuclear power, but technocrats are in charge of this money.

These people actually hate to be open, and face the public, so they'll have their lawyers do everything. The people getting the money will have more lawyers. The lawyers will get fancy sports cars. All the money, for and against, will go into the Bruce area, so they'll get new cars, as well.

Will there be any open, and worthwhile science? You can figure this out for yourselves!

Carbon and Water Cycles II - boring!

Well, I just took my middle guy to Queens. What a zoo moving day is! I didn't like the low-life Queens engineers insulting the parents, they can insult the frosh all they want. Well, they have to compensate for being inferior to UofT Engineering!! :)

Summer is practically over, and it's time for me to look for some tiny bit of work. I sure hope they take their thumbs out and actually start building a nuclear plant! OPG's top guy already bailed, perhaps because he saw all the political (and union!) interference. I like to think that he presented my ideas for a nuclear plant in my lifetime, to the Big Board, and they tossed him out on his ear! :)

Back to our little thought experiment. Like I said, we have two dials on the world, one for water and one for carbon. More water is injected water vapour, and less water means it has been sucked away down deep. More carbon is injected carbon dioxide, and less carbon means that it, too, has been sucked down deep.

The most fun is with the water dial. We can turn it way down and watch what happens. The oceans shrink. There is much less rain in the world. Large mountain ranges continue to rise, but are never eroded, like some ranges in South America. The ice sheets evaporate, but the world gets colder, like when you are camping and it's a clear night, and you know you are going to freeze! Lots of plants die. We have a cold, dry earth, suitable for tiny mammals that live in the desert.

Enough of that, now let's turn it up! We have lots of water, and oceans rise. There is lots of rain everywhere. The mountain ranges rapidly erode, causing carbon-poor sediments. The plants start growing, but become limited by the lack of carbon dioxide, just like my aquarium plants. The earth becomes very warm, because water vapour is the most effective greenhouse gas of all. We have a very wet, warm world, with limited vegetation.

Set the old water back at neutral, and play with the carbon dial! We turn it right down to almost no carbon. The atmospheric carbon dioxide gets quickly used up by plants and erosion, and little sea creatures. The world most likely gets a lot colder (if you believe all those carbon-people!). We have ice sheets, and maybe an ice-age, if the Sun turns down a little, as well. The plants aren't too happy and mostly refuse to grow.

Let's turn it up now. Remember, this dial is infinitely more powerful than the smokestacks of pitiful humans! We flood the place with carbon dioxide, and the oceans go acidic, we dissolve mountains faster, and most likely the world warms up. The plants are limited by the available water.

I think that's generally boring. The big fun comes from twiddling the dials to their extremes. First, we knock down the water, and the carbon. Nothing much happens from the water alone, except the plants are even more dead, and the world is much colder (Iceball Earth!).

Keeping down the water and jacking up the carbon, probably just results in a big mess!

The one I'm more interested in is jacking up the water and the carbon. Then we have a totally different Earth! The mountains are eroded faster, massive carbonate sediments are laid. The earth is very warm, and all the land is filled with swamps, which have tremendous plant growth. The growth of the plants fill the air with oxygen, and the air is thick. All the mammals get fur-rot, and the place fills with dinosaurs. The carbon is so thick, it gets laid down in beds of pure carbon (coal).

These things have actually happened, and we'll look at the geology in the next episode, after I recover from paying the tuition!

Solid as a Rock

I would think that if we are all to be roasted alive by Global Gorming, then the guy would be decent enough to throw in some nice hot cottage summers! Here it is, another cold rainy day in July, and no fishing!

I've always been a rock lover. I guess it comes from the cottage. We have this steep vertical cliff, where the ravens like to have nests, and you can just tell that the rock is anchored down to the Moho. There's something about anchored rock. Most rock isn't truly connected to the earth, even the surface granite. When you put seismometers on it, you can tell that it is delaminated, somewhat detached. True solid rock has a feel to it. If I were to ascribe scientific terms (rather than mystical!), I would think that it has something to do with the general noise field that we can feel with our eyes closed. Solid rock does not echo and resonate with a hollow sound. As well, the rock has thermal conductivity (no gaps) so you can feel that it is cooler with your facial infra-red sensors.

The ancient Incas knew and revered 'true' rock. I was down in Peru, when I saw the most amazing Inca rock wall. Made of pure basalt, it was known to have no mortar, and perfect joints. I felt that I was up against true rock! Those guys knew what they were doing!

I've seen a lot of crap rock! Those of us in rock mechanics wouldn't have a job without it. The most crappy rock I ever saw was up at the Bruce. We put a tunnel through it, and used (literally) trainloads of grout. Even that wasn't enough when we hit a giant cavern! We backed off the tunnel and cut a dogleg to go around it. It's a good thing that water intake tunnel never had to be waterproof!

Deep Geology Thingie

I just have to be the only blog in the world to mention this.

Deep Geology Thingie Saves a Bundle

The DGT has the skids greased to go, as they go straight to a panel of old guys. This will save them lots of unnecessary trouble, such as explaining why the heck they went there in the first place! Anybody with any brains will stay away from this whole affair, and watch it from a dock, with a beer in one hand and a rod in the other!

Sorry for actually putting in a news item. I truly thought I could be the one blog that never does that....

Messy Ice

I've mentioned The Cliff, and it's glacially scoured surface, but the glaciers did more than make pretty lakes for fishing. I used to do a lot of computer analysis for a deep geological nuclear waste repository, and I became amazed at how deep glacial damage can go.

It's not just that they pile up a great weight of ice, but they do it unevenly, building up shear stress. As well, they can pack a lot of water pressure, since most temperate glaciers have a high-pressure melted zone underneath them.

What I found is that I would expect sub-horizontal open fracture zones extending to about a kilometer in depth, provided the surface was clean rock. This is exactly what they found when they were drilling and doing some excavation. It makes the Great North somewhat difficult for a waste repository. Below this fracture zone, in the Manitoba test site, they found rock at extremely high stress, so much so that it was almost impossible to excavate without the rock blowing up in your face!

Here is a picture of some possible glacial rock damage (maybe, maybe not, but a nice picture nevertheless!)

NOAA

This damage is done over clean, permeable rock. As you get down to Toronto, a totally different type of damage is done. My analysis showed that if you cut off the water injection, there was almost no damage to the rock. This was shown with our deep holes drilled along the lake. I was not expecting, however, another type of significant damage.

We were happily running nuclear plants in the mid-90's when all of a sudden, the newspaper headlines were filled with "Big Fault under Pickering". Naturally, it caught our attention. The tricksy Rouge River had cut right through a fault and exposed it for all to see.

I had a look at it, and sure enough, it looked like a classic San Andreas. And this was on top of my lovely rock which I had said was not disturbed because of all the wonderful stress it held. I was stumped, and our feet were held to the fire!

(to be continued) (......ain't that just plain nasty??)