We have this big roiling Earth, and what does that have to do with earthquakes? Simply that the earth has gone with the most efficient method of heat removal which is convection, and transfers that heat to the radiator fins of the ocean crust. It's an operating air conditioner. The upper convection is in the mantle, just below the solid crust, and is responsible for our earthquakes. There may be lower convection cells that give us our magnetic field, and the Earth's core may be a nuclear reactor. :)
Who cares about deeper convection, it's the mantle that does all the interesting stuff to us on the surface. Because of the convection all our continents move around like floating scum, and the oceanic crust gets recycled. The whole thing is called Plate Tectonics, which is a rather surface-oriented expression. I'd rather call it Convection Collision.
You can read all about Plate Tectonics without once thinking about the whole 3-d mechanism. This would be rather shallow of you. :) As I have said, this would be all quiet grinding if it were not for the interaction of quartz and water. That gives us earthquakes, and nobody would care about them if we could all live on high rock.
All the details of Convection Collision (my new theory) are horribly boring. There's subduction, spreading, transform faults, etc. The only thing interesting are the formation of diamonds as the big chunks go down.
Bye for now.
Thursday, August 27, 2015
Earthquake Primers - The Big Bad Earth - Part 1
I'm writing this primer series for all my fans who are making their way in first-class containers to Canada, with Internet. We welcome you all, as long as you are willing to open up good restaurants in our horrible monoglot places such as Flin Flon or Montreal. :) I used to do illustrations, but it was too much work. You can see many of my illustrations on Wikipedia, from when I was in a more productive phase.
The Big Bad Earth has a problem. In the deep infra-red it glows like a lightbulb in space, even if we turned off the Sun for a while. That's the heat from our natural radioactivity, and it's a huge amount of energy. If the Earth were an onion, our atmosphere and oceans would be a molecular layer of graphene on top. Forget global warming, this is the big stuff!
So every day the Earth must radiate this heat out into space. On the surface, standing in your garden, it doesn't seem like much, but once you dig more than a metre or two you start getting into the Earth's heat flow. If you covered the planet with very thick insulating foam, the whole thing would probably melt in a few hundred million years. :)
But the Earth's been happy for a few billion years, and in all that time we've had oceans and continents, in the exact same ratio as we see today. Obviously things have settled down to equilibrium where enough heat has been shed to keep us in a shirtsleeve environment (suitable for life).
The continents are always growing, and you can see that in huge accretion bands, such as the megathrusts that enrich the earthquakes of Oklahoma. That's because the deep hot rock is always producing silicate 'scum' that floats to the surface. By now we should be just one big continent, but it hasn't happened. That's because our continents are the big foam insulator, and the Earth just can't have that.
So even if the Gorists are right and we become a big waterless desert, we will still have ocean basins. That's where we have the main heat flow radiating out into space. Now I hope that all of you in the far reaches have had your Grade 8 physics, which our climate-teests somehow slept through. There are three types of heat transfer: conduction, convection, and radiation. Convection is orders of magnitude above the others, so we make insulating foam with super-tiny air cells that eliminate convection. The foam is also non-transparent to stop radiation. The Gorries envision CO2 as acting like a big foam blanket on the Earth, they have forgotten about convection.
In our thought experiment, we turn off the Sun again, and mop up all the water. Then we look at the Earth with a thermal camera. All the heat is radiating out ocean basins, with some tiny bright spots for volcanoes. The ocean basins are our radiator fins!
-to be continued
The Big Bad Earth has a problem. In the deep infra-red it glows like a lightbulb in space, even if we turned off the Sun for a while. That's the heat from our natural radioactivity, and it's a huge amount of energy. If the Earth were an onion, our atmosphere and oceans would be a molecular layer of graphene on top. Forget global warming, this is the big stuff!
So every day the Earth must radiate this heat out into space. On the surface, standing in your garden, it doesn't seem like much, but once you dig more than a metre or two you start getting into the Earth's heat flow. If you covered the planet with very thick insulating foam, the whole thing would probably melt in a few hundred million years. :)
But the Earth's been happy for a few billion years, and in all that time we've had oceans and continents, in the exact same ratio as we see today. Obviously things have settled down to equilibrium where enough heat has been shed to keep us in a shirtsleeve environment (suitable for life).
The continents are always growing, and you can see that in huge accretion bands, such as the megathrusts that enrich the earthquakes of Oklahoma. That's because the deep hot rock is always producing silicate 'scum' that floats to the surface. By now we should be just one big continent, but it hasn't happened. That's because our continents are the big foam insulator, and the Earth just can't have that.
So even if the Gorists are right and we become a big waterless desert, we will still have ocean basins. That's where we have the main heat flow radiating out into space. Now I hope that all of you in the far reaches have had your Grade 8 physics, which our climate-teests somehow slept through. There are three types of heat transfer: conduction, convection, and radiation. Convection is orders of magnitude above the others, so we make insulating foam with super-tiny air cells that eliminate convection. The foam is also non-transparent to stop radiation. The Gorries envision CO2 as acting like a big foam blanket on the Earth, they have forgotten about convection.
In our thought experiment, we turn off the Sun again, and mop up all the water. Then we look at the Earth with a thermal camera. All the heat is radiating out ocean basins, with some tiny bright spots for volcanoes. The ocean basins are our radiator fins!
-to be continued
Wednesday, August 26, 2015
Earthquake Primers - What kills you - Part 2
Here's where I make a bold statement: Plop down your house anywhere in the world, on solid rock, and your seismic risk of death is zero. Said with 95% confidence, a reasonable house, and 'solid rock' defined by Canadian standards, not Callie.
The statement is backed up by an extensive study I once made at work on ground motions for rock and soil. Once I had this study, I went into the physics. This was to support a nuclear waste facility. It's fun to note that everything I recommended has been ignored for the Bruce Black Hole, and I suspect, as well, that it will the same for the big repository.
The PGV on rock is directly related to the induced strain within the rock mass. On the large scale (the wavelength) rock can take only a very little strain before cracking or fluid flow. Thus, seismic motion is divided into the static motions (near-field) and the propagating component. There is no limit on what can happen right on top of a fault, but seismic waves can only propagate if the rock acts in a linear manner.
So, you've got to believe me that the PGV on rock is very low a reasonable distance from the fault (a few fault lengths). If you are right on the hammer zone (hanging wall) of a shallow thrust, then rocks will fly into the air. Not a good place to be.
If you are on solid rock during a big earthquake, you will only wake up to the screams, or the sound of transformers exploding on the deep soil basin beside you. Soil basins amplify PGV by a factor of 10 to 100. I suspect that this is even greater if there are standing waves. There is only one way for your house to survive on a soil basin, and that is to have piles that go down to something solid.
You can see that 'seismic risk of death' SRD, varies more by foundation than location. Construction method adds very little difference. A historic brick house will survive very well on rock, but is usually hopeless elsewhere. We have seen very strong buildings tip over on soil. Adding dampers gives you a factor of two in seismic capacity, but this is nothing compared to the soil amplification.
Anyway, that's it for now. If there has been a large regional earthquake and you didn't feel it, you are golden. Sure, you're left out of all that Twitter conversation, but be happy.
The statement is backed up by an extensive study I once made at work on ground motions for rock and soil. Once I had this study, I went into the physics. This was to support a nuclear waste facility. It's fun to note that everything I recommended has been ignored for the Bruce Black Hole, and I suspect, as well, that it will the same for the big repository.
The PGV on rock is directly related to the induced strain within the rock mass. On the large scale (the wavelength) rock can take only a very little strain before cracking or fluid flow. Thus, seismic motion is divided into the static motions (near-field) and the propagating component. There is no limit on what can happen right on top of a fault, but seismic waves can only propagate if the rock acts in a linear manner.
So, you've got to believe me that the PGV on rock is very low a reasonable distance from the fault (a few fault lengths). If you are right on the hammer zone (hanging wall) of a shallow thrust, then rocks will fly into the air. Not a good place to be.
If you are on solid rock during a big earthquake, you will only wake up to the screams, or the sound of transformers exploding on the deep soil basin beside you. Soil basins amplify PGV by a factor of 10 to 100. I suspect that this is even greater if there are standing waves. There is only one way for your house to survive on a soil basin, and that is to have piles that go down to something solid.
You can see that 'seismic risk of death' SRD, varies more by foundation than location. Construction method adds very little difference. A historic brick house will survive very well on rock, but is usually hopeless elsewhere. We have seen very strong buildings tip over on soil. Adding dampers gives you a factor of two in seismic capacity, but this is nothing compared to the soil amplification.
Anyway, that's it for now. If there has been a large regional earthquake and you didn't feel it, you are golden. Sure, you're left out of all that Twitter conversation, but be happy.
Earthquake Primers - What kills you - Part 1
Barring a great big wall of water (tsunami), what will kill you is something falling on your head. The odds of getting killed in an earthquake are probably below that of getting hit by a bus, while drinking coffee in Starbucks.
Any given structure is designed to get live loads, such as wind, people dancing, etc. Buildings collapse all the time without earthquakes, from corrosion or foundation problems. Ground shaking will induce dynamic strains, and it is a question of whether the building has enough margin to take it. I would call this the 'seismic capacity'.
A house of cards has no seismic capacity. You can build the equivalent by piling up rocks in arches, such as the old Italian buildings. It is human nature that all building styles seem to settle for a 1 in 500 chance per year of being destroyed by an earthquake. In areas of frequent earthquakes they build stronger because everybody remembers the last disaster.
Our lovely stone building will collapse one day because of ground motion, and I only use peak ground velocity (PGV) to define it. You'll find that other crazy people use peak ground acceleration. This is the motion defined right at the surface of the dirt where you are building. It is best measured directly by a good instrument, or in third world countries like Oklahoma, derived by looking at the damage.
Most people are generally confused by what the dying newspapers report about the earthquake. This is always the magnitude and the location, which are the cheapest things to wring out of recorded data. Thus, one would think a larger magnitude is worse, but not necessarily. It all depends on the type of earthquake, and how far it is away from buildings. A larger earthquake far away produces the exact same PGV as a smaller earthquake right under you.
So, when you are calculating the odds of a brick falling on your head, you must think of the seismic capacity, and the chance of the PGV exceeding that. This is the seismic risk of death. There is one more thing, that I think is the most important of all -- your foundation.
-to be continued.
Any given structure is designed to get live loads, such as wind, people dancing, etc. Buildings collapse all the time without earthquakes, from corrosion or foundation problems. Ground shaking will induce dynamic strains, and it is a question of whether the building has enough margin to take it. I would call this the 'seismic capacity'.
A house of cards has no seismic capacity. You can build the equivalent by piling up rocks in arches, such as the old Italian buildings. It is human nature that all building styles seem to settle for a 1 in 500 chance per year of being destroyed by an earthquake. In areas of frequent earthquakes they build stronger because everybody remembers the last disaster.
Our lovely stone building will collapse one day because of ground motion, and I only use peak ground velocity (PGV) to define it. You'll find that other crazy people use peak ground acceleration. This is the motion defined right at the surface of the dirt where you are building. It is best measured directly by a good instrument, or in third world countries like Oklahoma, derived by looking at the damage.
Most people are generally confused by what the dying newspapers report about the earthquake. This is always the magnitude and the location, which are the cheapest things to wring out of recorded data. Thus, one would think a larger magnitude is worse, but not necessarily. It all depends on the type of earthquake, and how far it is away from buildings. A larger earthquake far away produces the exact same PGV as a smaller earthquake right under you.
So, when you are calculating the odds of a brick falling on your head, you must think of the seismic capacity, and the chance of the PGV exceeding that. This is the seismic risk of death. There is one more thing, that I think is the most important of all -- your foundation.
-to be continued.
Monday, August 24, 2015
Earthquake Primer - Part 2
I'm only giving a broad brush here, and you know I love to get into the details of stick-slip, but not today.
The second major mechanism but we have a relatively strong fault in even stronger rock under high stress. That's the situation of our Eastern North America earthquakes and totally unknown to the Callies until they recently waded into the muck of Oklahoma.
This is my favourite type of earthquake, since it is so bizarre. Basically, the rock is stressed to its limit by plate tectonics. For our continent, the whole thing has settled into a cold zone, resulting in high horizontal stresses. These stresses don't change on our pitiful time scale, so we get an earthquake when the fault weakens for some reason.
The only thing that weakens such a fault in strong granite is water. But not any old water. There are oceans of water in that ancient water, going down 30 km to the bottom of the crust. This water could unclog your sink drain, and kill your dog, but it doesn't do anything to the rock, because it has been there for millions of years.
For reasons unknown to most Callies, there is fluid flow in this rock, and sometimes new water gets introduced to the deep granite. It eats away at the quartz points and boom! We have an earthquake. This can happen naturally, or can be induced by man.
You can't see the strain accumulate with GPS because the regional strain rate is something like 10-6. That has great confused most Callies. Nevertheless, these earthquakes happen and they can be huge. They also transmit much farther than Callie because it is real rock, not that chewed up crap. Funny enough, this only matters to people on soil basins. You can be on granite and never wake up for the largest Eastern earthquake.
The second major mechanism but we have a relatively strong fault in even stronger rock under high stress. That's the situation of our Eastern North America earthquakes and totally unknown to the Callies until they recently waded into the muck of Oklahoma.
This is my favourite type of earthquake, since it is so bizarre. Basically, the rock is stressed to its limit by plate tectonics. For our continent, the whole thing has settled into a cold zone, resulting in high horizontal stresses. These stresses don't change on our pitiful time scale, so we get an earthquake when the fault weakens for some reason.
The only thing that weakens such a fault in strong granite is water. But not any old water. There are oceans of water in that ancient water, going down 30 km to the bottom of the crust. This water could unclog your sink drain, and kill your dog, but it doesn't do anything to the rock, because it has been there for millions of years.
For reasons unknown to most Callies, there is fluid flow in this rock, and sometimes new water gets introduced to the deep granite. It eats away at the quartz points and boom! We have an earthquake. This can happen naturally, or can be induced by man.
You can't see the strain accumulate with GPS because the regional strain rate is something like 10-6. That has great confused most Callies. Nevertheless, these earthquakes happen and they can be huge. They also transmit much farther than Callie because it is real rock, not that chewed up crap. Funny enough, this only matters to people on soil basins. You can be on granite and never wake up for the largest Eastern earthquake.
Earthquake Primer - Part 1
Wow, my 'rehash' articles are doing well. I've got a huge number of new people from Asia and the Pacific Ring of Fire, who are trying out their English skills. As I've said, if you are a bright person, get out of the trap of where you were born, and learn English with a passion. Then the Internet can lift you up.
Although you can't tell this to a person whose house has fallen on him, earthquakes are essential to life on Earth. Actually, they aren't really, but they are intimately linked to plate tectonics, and the properties of quartz and water. As we know, if the Cosmic Creators had fiddled with any one of these physical properties, we wouldn't be here to discuss them
We all know our Plate Tectonics, turn that off and we become a dead planet, like Mars. My readers on the Rim are aware of all the volcanoes, earthquakes, and tsunamis, and they live with them. Every year they may kill 20,000 people out of billions. I think my drive to the cottage has a greater risk of my shuffling off this mortal coil. I'm going down to Guatemala this year to stare at the active volcanoes. Yeah!
So, there are two distinct mechanisms for earthquakes in this world, although my buddies in the busgus only acknowledge this first one. That's where there is a zone of tremendous weakness, and all the strain concentrates there. These fault zones have rock strengths of orders of magnitude weaker than the surrounding rock. If you go to Callie extreme, you can say that these zones 'cause' earthquakes.
But really, they are only responding to the surrounding strain energy. There are countless sub-categories of the 'weak' zones, such as subduction zones, transform faults, thrust zones such as Nepal, etc.
The basic mechanism is that this fault has a finite shear strength (or shear strain limit) and it accumulates the strain of the region, whether it is compression, tension or shear. The regional strain change is huge, perhaps 10-4 (no units) per year, and can be easily measured with GPS. The weak zones take it all, and when the limit is reached, they slip. If we didn't have any quartz or water, the fault zones would just creep and the only people who got hurt would be those that built on a creeping fault zone.
But unfortunately, the quartz-water combination brings on stick-slip, and we have big earthquakes.
-to be continued
Although you can't tell this to a person whose house has fallen on him, earthquakes are essential to life on Earth. Actually, they aren't really, but they are intimately linked to plate tectonics, and the properties of quartz and water. As we know, if the Cosmic Creators had fiddled with any one of these physical properties, we wouldn't be here to discuss them
We all know our Plate Tectonics, turn that off and we become a dead planet, like Mars. My readers on the Rim are aware of all the volcanoes, earthquakes, and tsunamis, and they live with them. Every year they may kill 20,000 people out of billions. I think my drive to the cottage has a greater risk of my shuffling off this mortal coil. I'm going down to Guatemala this year to stare at the active volcanoes. Yeah!
So, there are two distinct mechanisms for earthquakes in this world, although my buddies in the busgus only acknowledge this first one. That's where there is a zone of tremendous weakness, and all the strain concentrates there. These fault zones have rock strengths of orders of magnitude weaker than the surrounding rock. If you go to Callie extreme, you can say that these zones 'cause' earthquakes.
But really, they are only responding to the surrounding strain energy. There are countless sub-categories of the 'weak' zones, such as subduction zones, transform faults, thrust zones such as Nepal, etc.
The basic mechanism is that this fault has a finite shear strength (or shear strain limit) and it accumulates the strain of the region, whether it is compression, tension or shear. The regional strain change is huge, perhaps 10-4 (no units) per year, and can be easily measured with GPS. The weak zones take it all, and when the limit is reached, they slip. If we didn't have any quartz or water, the fault zones would just creep and the only people who got hurt would be those that built on a creeping fault zone.
But unfortunately, the quartz-water combination brings on stick-slip, and we have big earthquakes.
-to be continued
Sunday, August 23, 2015
Oklahoma earthquakes rehash
Just a little summary for those of you who don't want to trudge through all my stuff. It's like digging up the potatoes, which I did this weekend, you go through a lot of dirt before something good pops up.
So, the mid-west states had been injecting excess water from oil production for a zillion years, and never got an earthquake. If they found a Precambrian megathrust, they could inject till the cows came home. It was a reverse gusher. Nobody bothered to map these things and the busgus stayed in Callie.
Then fracking came along and they used fresh water. This was mixed in with the usual saltwater in deep wells, and we got earthquakes. Ohio and then Arkansas. They quickly shut down the operations.
Every time Texas decided to make a bit more money they had huge earthquakes. They were slipping in the fracking waste on the sly. As soon as people screamed enough, all the earthquakes stopped. Texans could turn earthquakes off and on like a beer tap, but never told anyone their secret.
That left Oklahoma who would do anything for a buck. The fresh water acts as an acid on the deep quartz holding the faults together. It all starts to unzip, just like New Madrid started thousands of years ago. But OK gets to do it a thousand times faster. The earthquakes keep getting bigger and bigger. A New Madrid M7 would level the place. Would anyone notice?
You can read this and realize there is a simple cure. Will never happen. These things must go to a big disaster. It's human nature.
So, the mid-west states had been injecting excess water from oil production for a zillion years, and never got an earthquake. If they found a Precambrian megathrust, they could inject till the cows came home. It was a reverse gusher. Nobody bothered to map these things and the busgus stayed in Callie.
Then fracking came along and they used fresh water. This was mixed in with the usual saltwater in deep wells, and we got earthquakes. Ohio and then Arkansas. They quickly shut down the operations.
Every time Texas decided to make a bit more money they had huge earthquakes. They were slipping in the fracking waste on the sly. As soon as people screamed enough, all the earthquakes stopped. Texans could turn earthquakes off and on like a beer tap, but never told anyone their secret.
That left Oklahoma who would do anything for a buck. The fresh water acts as an acid on the deep quartz holding the faults together. It all starts to unzip, just like New Madrid started thousands of years ago. But OK gets to do it a thousand times faster. The earthquakes keep getting bigger and bigger. A New Madrid M7 would level the place. Would anyone notice?
You can read this and realize there is a simple cure. Will never happen. These things must go to a big disaster. It's human nature.
Wednesday, August 19, 2015
The ensuing tsunami just cleans things up
Reference
I was interesting in this, since the postulated earthquake would be so destructive that nobody would be around to surf the tsunami. Think of something like the Armenia earthquake and then add the tsunami. And I don't even think this would be a big one, since the faulting is strike-slip. I think this is a waste of thinking. I got one word for you "Who cares?"
Subduction tsunamis matter since they are huge and the seismic shaking is low. Therefore it becomes the predominant hazard and you can plan for it. This whole thing is just ugly, but I wouldn't want to be there. :)
Addition: Everybody plans for the 1 in 100 per year earthquake, but the 1 in 500 gobsmacks them. An M7.7 with tsunami is 1 in 1000 or rarer. This is in the area of beach terrace-raising M9 which probably happens every 1000 years or so in California.
I was interesting in this, since the postulated earthquake would be so destructive that nobody would be around to surf the tsunami. Think of something like the Armenia earthquake and then add the tsunami. And I don't even think this would be a big one, since the faulting is strike-slip. I think this is a waste of thinking. I got one word for you "Who cares?"
Subduction tsunamis matter since they are huge and the seismic shaking is low. Therefore it becomes the predominant hazard and you can plan for it. This whole thing is just ugly, but I wouldn't want to be there. :)
Addition: Everybody plans for the 1 in 100 per year earthquake, but the 1 in 500 gobsmacks them. An M7.7 with tsunami is 1 in 1000 or rarer. This is in the area of beach terrace-raising M9 which probably happens every 1000 years or so in California.
GPS didn't do much for early warning
Reference
The one hope I had for a seismic early warning system (actually, it wasn't much hope) would be that a real-time GPS network would catch the pre-slip of a large fault system.
For a large fault, you never know at the beginning if the rupture will continue, or how far. Thus, you have to wait for it to finish. That's a critical 60 seconds. These GPS things are slow creatures, sampling at 5 times a second, so it takes another while for them to report.
All faults need to pre-slip to the 'critical displacement'. Had this signal been caught, you would know that was going to be large. Then you get more time, for whatever good that would do. You also want to get the fact that the rupture was travelling towards the city which ups the PGV by a factor of two at least (directivity).
All in all, another nail in the coffin of early warning. :)
The one hope I had for a seismic early warning system (actually, it wasn't much hope) would be that a real-time GPS network would catch the pre-slip of a large fault system.
For a large fault, you never know at the beginning if the rupture will continue, or how far. Thus, you have to wait for it to finish. That's a critical 60 seconds. These GPS things are slow creatures, sampling at 5 times a second, so it takes another while for them to report.
All faults need to pre-slip to the 'critical displacement'. Had this signal been caught, you would know that was going to be large. Then you get more time, for whatever good that would do. You also want to get the fact that the rupture was travelling towards the city which ups the PGV by a factor of two at least (directivity).
All in all, another nail in the coffin of early warning. :)
Tuesday, August 18, 2015
Energy dampers for buildings
Reference
This is just one of many schemes that come from shake tables. All tall buildings have viscous dampers for wind sway, otherwise secretaries would be barfing in their wastebaskets during wind storms. You put in these things and shake table results show that induced shear strain (scales with PGV) will be cut down by half.
But they are going to plunk this thing down on a large soil basin in California. 50% is nothing when we expect natural variation of a factor of 100. They'll be so happy with a couple of these expensive dampers that they'll cheap out on steel and foundation piles. It's just not enough, you want more than a factor of 10 reduction in PGV which is what you would get with deep piles. The same goes for base isolation, and a thousand other such schemes. We shall see what we shall see. :)
This is just one of many schemes that come from shake tables. All tall buildings have viscous dampers for wind sway, otherwise secretaries would be barfing in their wastebaskets during wind storms. You put in these things and shake table results show that induced shear strain (scales with PGV) will be cut down by half.
But they are going to plunk this thing down on a large soil basin in California. 50% is nothing when we expect natural variation of a factor of 100. They'll be so happy with a couple of these expensive dampers that they'll cheap out on steel and foundation piles. It's just not enough, you want more than a factor of 10 reduction in PGV which is what you would get with deep piles. The same goes for base isolation, and a thousand other such schemes. We shall see what we shall see. :)
Monday, August 17, 2015
Minor earthquake stupidities
I'm finished with my big list. These are stupidities that could easily be fixed, and will be fixed only after the next big earthquake. For now we stuck with them. I write all this in the hope that it might help a bright young thing sometime down the road. One day he (she) will be sitting in response spectra class and will want to scream "THIS IS SO STUPID!". But he better not and listen to the professor if he wants to pass. For that guy has tenure and will still be lecturing when the student is dead and gone, since they will just animate his corpse. :)
That is the rate of progress in this field, and we need a big earthquake in Boston or New York to shock us out of our complacency. Till then, have fun. :)
ps. I forgot the title again. There are so many minor stupidities that they slip by me. Oh well.
That is the rate of progress in this field, and we need a big earthquake in Boston or New York to shock us out of our complacency. Till then, have fun. :)
ps. I forgot the title again. There are so many minor stupidities that they slip by me. Oh well.
Earthquake Stupidity #4 -- Shake Tables
As an early warning system is to a seismologist, so a shake table is to an engineer. In fact, there is holy war on shake tables, getting bigger and bigger ones. It's not enough that they can get an entire house on one, we look forward to entire towns!
So, why are we all into shake tables? A long time ago there was an earthquake in Venezuela that affected some really bad buildings on soft soil, but as usual, the PGA wasn't that high. Ergo, the fault was not in the bad soil, but rather that the buildings had resonated like a porch swing. Engineers went nuts with this resonance thing, introducing modal analysis and response spectra. They could fling model buildings on shake tables and make them do the shimmy-shake. It was obvious that resonance was the worst thing ever.
Never mind that PGV on soft basins is amplified a 100 times, they applied response spectra to every building. I remember those days, seismic analysis used up most of the computing power of the corporation. It was magnificent.
And it was all make-believe. People studied hundreds of earthquakes with structures on average soil, and there was never any sign of resonance. It never existed. But when you bolted a springy structural model onto a solid steel slab, you could vary the frequencies on your shake table and get lots of resonance.
If you do a real analysis of a reasonable building on a reasonable foundation, you find the seismic energy goes in and then goes out again. I used finite-difference computer models with realistic time histories and it was always the same. There is no resonance. There's a factor of two for the top, but that's the same for the free surface, and the building is on a foundation that has a lower initial PGV.
To get on my top stupidity list, you have to kill people in the next earthquake. This is linked with PGA because they scale the shake tables based on PGA. Buildings do not pancake any more, they tip over, thanks to shake table analysis. All such buildings should have a sign: "Designed on a shake table and built proudly on soft soil.". Then all your furniture should be made of foam. No books, and not too much booze in glass bottles. Appliances should all be built-in, then you are good to go! You can survive a tip-over.
So, why are we all into shake tables? A long time ago there was an earthquake in Venezuela that affected some really bad buildings on soft soil, but as usual, the PGA wasn't that high. Ergo, the fault was not in the bad soil, but rather that the buildings had resonated like a porch swing. Engineers went nuts with this resonance thing, introducing modal analysis and response spectra. They could fling model buildings on shake tables and make them do the shimmy-shake. It was obvious that resonance was the worst thing ever.
Never mind that PGV on soft basins is amplified a 100 times, they applied response spectra to every building. I remember those days, seismic analysis used up most of the computing power of the corporation. It was magnificent.
And it was all make-believe. People studied hundreds of earthquakes with structures on average soil, and there was never any sign of resonance. It never existed. But when you bolted a springy structural model onto a solid steel slab, you could vary the frequencies on your shake table and get lots of resonance.
If you do a real analysis of a reasonable building on a reasonable foundation, you find the seismic energy goes in and then goes out again. I used finite-difference computer models with realistic time histories and it was always the same. There is no resonance. There's a factor of two for the top, but that's the same for the free surface, and the building is on a foundation that has a lower initial PGV.
To get on my top stupidity list, you have to kill people in the next earthquake. This is linked with PGA because they scale the shake tables based on PGA. Buildings do not pancake any more, they tip over, thanks to shake table analysis. All such buildings should have a sign: "Designed on a shake table and built proudly on soft soil.". Then all your furniture should be made of foam. No books, and not too much booze in glass bottles. Appliances should all be built-in, then you are good to go! You can survive a tip-over.
Friday, August 14, 2015
Earthquake Stupidity #3 -- Using PGA instead of PGV
Okay, we all know how an earthquake knocks us down. We are standing there, admiring the birdies, when there is a big lurch to the left, and we fall down. We feel that we have experienced a lateral acceleration, which can be measured as a percentage of the actual downward acceleration (force) that is gravity. We can probably take 30% g lateral and keep standing. Any more and we fall.
The early seismologists noted this and designed instruments to measure it. They were mostly pendulums and masses on springs. These were incredibly crude, and needed a lot of motion to get them to work. That chance happened with the famous El Centro earthquake, right in the middle of a huge soil basin.
This was the single biggest thing to happen to earthquake engineering. Everybody+dog used this ground motion for design. Problem was they applied it everywhere to any area and foundation. Applying that to some situations would be the equivalent of crushing all the surrounding rock to powder. Waves only propagate if the stress disturbance stays within the linear zone. It's like watching those stupid huge wake boats churning up huge breaking waves and thinking they will smash your dock. They don't, they turn into something that will propagate.
PGA only works for the very low frequencies of soil basins. Stupidity piled onto stupidity when they took this stuff east for nuclear plants. As well, they considered seismic motion as infinite sinusoids which was more horrible. This combined to make rock sites horrible, and soft soil sites good.
If the frequency starts to go above 1 Hz, then PGA has no more link with standard physics. At high frequencies, instruments record a high PGA which makes solid rock sites terrible. In actuality they have a low PGV and are good what ails you. I remember the high PGA for the east had all the dams sliding into the ocean, in their dreamworld of phoney analysis.
The use of PGA will be deadly in the next earthquake for buildings that have been 'designed'. PGA has no amplification on soft soil. PGV is physically linked to the induced shear strain and has meaning related to damage on all soil types and in all areas of the world. It links smoothly to the Modified Mercalli intensity scale. You need a PGV of about 50 cm/s for structural damage. 10-20 cm/s will knock down the ceiling tiles and bonk you on the head.
The old company designed nuclear plants using El Centro on solid rock. Everything failed testing and analysis, when we looked back on it. But somehow everything passed. (We could never figure out how) They are using the same methodology for the retrofit. I hope they know the secret techniques of the Ancients. :)
*PGA stands for peak ground acceleration. It represents the maximum swing of a pendulum.
*PGV is peak ground velocity. It is derived from the integration of the time series of acceleration. Thanks to the chip revolution and the necessity to have accelerometers in your phone, it is becoming quite easy to measure these things.
The early seismologists noted this and designed instruments to measure it. They were mostly pendulums and masses on springs. These were incredibly crude, and needed a lot of motion to get them to work. That chance happened with the famous El Centro earthquake, right in the middle of a huge soil basin.
This was the single biggest thing to happen to earthquake engineering. Everybody+dog used this ground motion for design. Problem was they applied it everywhere to any area and foundation. Applying that to some situations would be the equivalent of crushing all the surrounding rock to powder. Waves only propagate if the stress disturbance stays within the linear zone. It's like watching those stupid huge wake boats churning up huge breaking waves and thinking they will smash your dock. They don't, they turn into something that will propagate.
PGA only works for the very low frequencies of soil basins. Stupidity piled onto stupidity when they took this stuff east for nuclear plants. As well, they considered seismic motion as infinite sinusoids which was more horrible. This combined to make rock sites horrible, and soft soil sites good.
If the frequency starts to go above 1 Hz, then PGA has no more link with standard physics. At high frequencies, instruments record a high PGA which makes solid rock sites terrible. In actuality they have a low PGV and are good what ails you. I remember the high PGA for the east had all the dams sliding into the ocean, in their dreamworld of phoney analysis.
The use of PGA will be deadly in the next earthquake for buildings that have been 'designed'. PGA has no amplification on soft soil. PGV is physically linked to the induced shear strain and has meaning related to damage on all soil types and in all areas of the world. It links smoothly to the Modified Mercalli intensity scale. You need a PGV of about 50 cm/s for structural damage. 10-20 cm/s will knock down the ceiling tiles and bonk you on the head.
The old company designed nuclear plants using El Centro on solid rock. Everything failed testing and analysis, when we looked back on it. But somehow everything passed. (We could never figure out how) They are using the same methodology for the retrofit. I hope they know the secret techniques of the Ancients. :)
*PGA stands for peak ground acceleration. It represents the maximum swing of a pendulum.
*PGV is peak ground velocity. It is derived from the integration of the time series of acceleration. Thanks to the chip revolution and the necessity to have accelerometers in your phone, it is becoming quite easy to measure these things.
Earthquake Stupidity #2 -- Early warning systems
Early warning systems are a seismologist's wet dream. Remember that these guys can't do math, and have no concept how shaking damages things. All they know is that these systems bring in lots of money, and they lobby the politicians relentlessly. Any money for this is taken out of strong ground motion recording.
They work like this: In an ideal world, you have a tiny fault rupture, at a pinpoint. It emits seismic waves, and is detected by seismometers, hopefully underwater for the Cascades. Your super-smart hardware, programmed by super-smart seismologists instantly characterizes the earthquake, giving the PGV at given distances. If it is going to cause damage to bullet trains and such, it gives a warning to all and their dogs, allowing them to totally save themselves before the actual shear body waves hit. This miracle is achieved through the magic of physics, in that the seismic waves are slower than the Internet.
Perhaps some of you smart ones begin to perceive the holes in this logic, but if you were that smart you wouldn't be reading this, you'd be writing it. :)
The system has an open-ended cost. You can be super-cheap for a few million, or you can go full-hog. For maximum efficiency you have to predict the exact earthquake you wish to catch.
Now, here's where physics starts to interfere with dreams. First of all, none of these people know about PGV, it's all PGA. That's the first horrendous mistake. But we must look at the grandaddy of such systems - Mexico City, where I have planned my stopover for my next trip, because I didn't want to stop at an American City, where people walk down the streets with assault rifles. Those big Mexican drug kings don't shoot where they eat. :)
Those smart Mexicans have planned for the exact same earthquake that hit them before. It was an M8 on the subduction zone far, far away from the city. There is no chance for any other type of earthquake -- maybe. That earthquake produced 20 cm/s on the shore and didn't damage any steam plants. By the time it hit the city, it was about 5 cm/s on rock. The whole city is on a really weird basin that not only focusses seismic waves for the rock, but then jiggles like jello on the soft soil. If you just consider PGV, it amplifies by a factor of 100.
It knocked down a lot of cheap government pancake concrete buildings, but didn't touch the bank towers. They now have an early warning system that nobody can access, but many are working on that. Let's assume that soon everybody+dog gets the warning "You're about to die!". What do they do?
So, we got that problem, but what goes into the 'Die!' message? The seismometers have to pick up the motions, which is difficult because they clip for large earthquakes. Then they must determine the size. For a regular earthquake, this takes a long time, since you must get information from around the world, and the seismic waves take a while to get there. Unless you predict 'exactly' what the fault rupture is going to do, you can't do it. Fault ruptures are horribly complex things, starting, stopping, putting out little motion, and then a lot.
So that means a lot of false alarms. Think of the guy on the Portland beach. He gets the 'Die Sucka' warning. He phones his wife "Sorry, take care of my two other mistresses, and my bastard children." Boy is he going to be mad if it's a false alarm!
Think of cell phones when this message goes out. The first few people are instantly going to phone other people, the whole system will die before the earthquake even hits. Wow.
Well, there's whole bunch of other things, and there is no real benefit. You don't think trains can't take a lateral hit? Is it worth turning off the power grid? And there's the fact that the next earthquake won't be exactly as predicted, it's all useless for the one right under the basin.
This is also a stupidity that will get a lot of people killed because it instils a moral hazard. Why do anything else when you are protected by a warning system? Japan fell into that one for Kobe.
That's enough, I'm getting depressed....
They work like this: In an ideal world, you have a tiny fault rupture, at a pinpoint. It emits seismic waves, and is detected by seismometers, hopefully underwater for the Cascades. Your super-smart hardware, programmed by super-smart seismologists instantly characterizes the earthquake, giving the PGV at given distances. If it is going to cause damage to bullet trains and such, it gives a warning to all and their dogs, allowing them to totally save themselves before the actual shear body waves hit. This miracle is achieved through the magic of physics, in that the seismic waves are slower than the Internet.
Perhaps some of you smart ones begin to perceive the holes in this logic, but if you were that smart you wouldn't be reading this, you'd be writing it. :)
The system has an open-ended cost. You can be super-cheap for a few million, or you can go full-hog. For maximum efficiency you have to predict the exact earthquake you wish to catch.
Now, here's where physics starts to interfere with dreams. First of all, none of these people know about PGV, it's all PGA. That's the first horrendous mistake. But we must look at the grandaddy of such systems - Mexico City, where I have planned my stopover for my next trip, because I didn't want to stop at an American City, where people walk down the streets with assault rifles. Those big Mexican drug kings don't shoot where they eat. :)
Those smart Mexicans have planned for the exact same earthquake that hit them before. It was an M8 on the subduction zone far, far away from the city. There is no chance for any other type of earthquake -- maybe. That earthquake produced 20 cm/s on the shore and didn't damage any steam plants. By the time it hit the city, it was about 5 cm/s on rock. The whole city is on a really weird basin that not only focusses seismic waves for the rock, but then jiggles like jello on the soft soil. If you just consider PGV, it amplifies by a factor of 100.
It knocked down a lot of cheap government pancake concrete buildings, but didn't touch the bank towers. They now have an early warning system that nobody can access, but many are working on that. Let's assume that soon everybody+dog gets the warning "You're about to die!". What do they do?
So, we got that problem, but what goes into the 'Die!' message? The seismometers have to pick up the motions, which is difficult because they clip for large earthquakes. Then they must determine the size. For a regular earthquake, this takes a long time, since you must get information from around the world, and the seismic waves take a while to get there. Unless you predict 'exactly' what the fault rupture is going to do, you can't do it. Fault ruptures are horribly complex things, starting, stopping, putting out little motion, and then a lot.
So that means a lot of false alarms. Think of the guy on the Portland beach. He gets the 'Die Sucka' warning. He phones his wife "Sorry, take care of my two other mistresses, and my bastard children." Boy is he going to be mad if it's a false alarm!
Think of cell phones when this message goes out. The first few people are instantly going to phone other people, the whole system will die before the earthquake even hits. Wow.
Well, there's whole bunch of other things, and there is no real benefit. You don't think trains can't take a lateral hit? Is it worth turning off the power grid? And there's the fact that the next earthquake won't be exactly as predicted, it's all useless for the one right under the basin.
This is also a stupidity that will get a lot of people killed because it instils a moral hazard. Why do anything else when you are protected by a warning system? Japan fell into that one for Kobe.
That's enough, I'm getting depressed....
Earthquake Stupidity #1 -- Evacuation of High Rises
This is my new series on major earthquake stupidities.
Every little earthquake rumble sends all the occupants of high rises onto the streets. This is an immediate, near panic evacuation. As well, the fire alarms go off, and for larger earthquakes, the main power is lost. This is right after duck and cover, but most people don't do that.
In most cities, like Tokyo and New York, there isn't enough room for everybody. It's bad enough they evacuate for tiny M6's and 5's, but a real earthquake would loosen glass, and out it flies on a windy day. A crowd has not yet been decapitated by a giant pane of glass, but it will happen one day.
For New York, the most likely scenario is a Grand Banks-type shelf earthquake. That should not bother the high rises on rock, but will send a horrendous tsunami. Is this the time to pack the streets, ferries, and subways?
All high rises should be instrumented for PGV at the base (at the very least). Then, there should an 'earthquake override' for the fire alarm. Then there should be an automatic PA announcement:
"You have probably noticed already that we are experiencing an earthquake. Our instruments have noted that there is no chance of strucural damage to this building, and the fire alarm has been overridden. Do not evacuate at this time. Please tend to your neighbour if there are minor injuries from falling objects. The whole city is now in this situation, and we await further information."
As I have mentioned with the other stupidities, there is no chance of this being implemented anywhere. We have to wait for unnecessary deaths. :(
Along with this goes the next stupidity -- Stupid early warning systems that give seismologists lots of money.
Every little earthquake rumble sends all the occupants of high rises onto the streets. This is an immediate, near panic evacuation. As well, the fire alarms go off, and for larger earthquakes, the main power is lost. This is right after duck and cover, but most people don't do that.
In most cities, like Tokyo and New York, there isn't enough room for everybody. It's bad enough they evacuate for tiny M6's and 5's, but a real earthquake would loosen glass, and out it flies on a windy day. A crowd has not yet been decapitated by a giant pane of glass, but it will happen one day.
For New York, the most likely scenario is a Grand Banks-type shelf earthquake. That should not bother the high rises on rock, but will send a horrendous tsunami. Is this the time to pack the streets, ferries, and subways?
All high rises should be instrumented for PGV at the base (at the very least). Then, there should an 'earthquake override' for the fire alarm. Then there should be an automatic PA announcement:
"You have probably noticed already that we are experiencing an earthquake. Our instruments have noted that there is no chance of strucural damage to this building, and the fire alarm has been overridden. Do not evacuate at this time. Please tend to your neighbour if there are minor injuries from falling objects. The whole city is now in this situation, and we await further information."
As I have mentioned with the other stupidities, there is no chance of this being implemented anywhere. We have to wait for unnecessary deaths. :(
Along with this goes the next stupidity -- Stupid early warning systems that give seismologists lots of money.
Thursday, August 13, 2015
Stupidity in Earthquakes
I've learned not to rail against mass stupidity. It never does any good, and you get depressed. It's a useless activity for us old men. Instead I laugh at it. I love these earthquake articles written by people who don't know the first thing about earthquakes. They line up their talking heads, but take things out of context.
For instance, here they are dissing poor old Richter. I've read his original papers and they are beautiful. He did what he had to do, just like the first qwerty keyboard. Is this the stupidest thing in the whole earthquake biz? Not by a long shot.
I'm not listing the entire realm of stupidities, god knows I've written enough about it. All will be clarified during the next big earthquake in a modern country. Then we'll change stupid assumptions as we always have. Too bad for you losers!
ps. San Francisco high rises on the solid rock of Telegraph Hill have nothing to worry about, except the stupid bit about evacuation to the mucked up street. Now, that's a stupidity!
Clarification: By 'modern' I mean Southern California. Nothing that happens in other countries gets into code and design. I've learned a lot from Taiwan and Chile. Nothing ever comes out of Japan. Loma Prieta only did something for bridges. Right now everything is based on Imperial Valley, San Fernando, and a bit of Northridge.
Tuesday, August 11, 2015
The Bipolar Attitude of Nuclear Plants and Earthquakes
Reference
So, a pitiful Japanese nuclear reactor got hit by a 1 in 500 seismic event. Big mess. The reactor beside it wasn't bothered. Now they are restarting, and this probably puts less lives at risk than burning coal or oil
They had numerous earthquake incidents before to warn them, but ignored everything. It's all the little things that bring down a plant. We have the same thing here with the ancient Pickering plant. It's no use going into details because all our newspapers are dead, and everybody accepts the Bland Face of Nothing. As with earthquake engineering, it always takes a disaster to close the barn door. :)
The title refers to the practice of putting everything into the heavy systems that will never fail in an earthquake, and totally ignoring all the rest.
So, a pitiful Japanese nuclear reactor got hit by a 1 in 500 seismic event. Big mess. The reactor beside it wasn't bothered. Now they are restarting, and this probably puts less lives at risk than burning coal or oil
They had numerous earthquake incidents before to warn them, but ignored everything. It's all the little things that bring down a plant. We have the same thing here with the ancient Pickering plant. It's no use going into details because all our newspapers are dead, and everybody accepts the Bland Face of Nothing. As with earthquake engineering, it always takes a disaster to close the barn door. :)
The title refers to the practice of putting everything into the heavy systems that will never fail in an earthquake, and totally ignoring all the rest.
Sunday, August 9, 2015
The New Tilting Buildings
In the 60's we had our tilting buildings for earthquakes when there was extreme liquefaction. That's when the loose sand turned to soup. Many years of study and finally people understood not put buildings on loose sand. No tilting buildings for decades. Just a lot of pancaking. Then that was fixed by putting a bit more steel in the concrete. Now we have the new tilting buildings. One of my pictures from the Nepal earthquake shows a building on its side, composed of a lot of glass. Not one pane broken. And Chile had a tall building tilt over with nothing broken. A triumph of engineering? No. You won't survive this under a desk if the grand piano slides over.
These buildings are tilting on average soil. It's from relying too much on shake tables. When you set up one of those things you bolt the model to a big steel slab and shake the heck out of it. But in the real world, you are on a foundation. These guys just pour a slab and stick the building on top. If they want to make it worse, they put in soft stories, which are somehow ok on shake tables. We are now entering a stage of false seismic engineering, as good as the time when we built on loose sand. I can't wait for the next big earthquake.
These buildings are tilting on average soil. It's from relying too much on shake tables. When you set up one of those things you bolt the model to a big steel slab and shake the heck out of it. But in the real world, you are on a foundation. These guys just pour a slab and stick the building on top. If they want to make it worse, they put in soft stories, which are somehow ok on shake tables. We are now entering a stage of false seismic engineering, as good as the time when we built on loose sand. I can't wait for the next big earthquake.
Friday, August 7, 2015
Big Guy launches his start-up
My California son has started.
This the web site.
Throw your money at it! I've spent enough money on the education. If it is successful, maybe I get some travel out of it, if my son is generous. :)
The modus operandi of Silicon Valley startups is to attack the margin of monopolists, such as taxi cabs. This venture is a shot at the whole mortgage industry including the banks. Soon, bank presidents will in the streets, demanding that John Tory save them. :)
This is good for the States, but in Canada, there is that horrible thing about 'joint and severally liable', which nailed me several years ago. We are also due for a massive housing correction, and it might be best to let the banks take that hit.
The nugget buried in here is the new system for landlords to take care of the property. I think this was the original core, but it's better if everybody becomes a landlord.
This the web site.
Throw your money at it! I've spent enough money on the education. If it is successful, maybe I get some travel out of it, if my son is generous. :)
The modus operandi of Silicon Valley startups is to attack the margin of monopolists, such as taxi cabs. This venture is a shot at the whole mortgage industry including the banks. Soon, bank presidents will in the streets, demanding that John Tory save them. :)
This is good for the States, but in Canada, there is that horrible thing about 'joint and severally liable', which nailed me several years ago. We are also due for a massive housing correction, and it might be best to let the banks take that hit.
The nugget buried in here is the new system for landlords to take care of the property. I think this was the original core, but it's better if everybody becomes a landlord.
Wednesday, August 5, 2015
The Physics of Balancing Rocks
I've read these papers for years. It's amazing how people can study these without a speck of physics. They tried to estimate PGA for gawd sake! These things are sensitive to PGV, as are all structures. The PGV is related to induced shear strain, which is just the thing to knock these over.
Now what's the thing that reduces PGV to a very small value? That's right, solid rock. These rocks have been standing for thousands of years, and we know from the beach terraces that California gets one of those massive state-ripping M9'+'s every thousand years or so. So, it doesn't really matter that the rupture 'jumps', these things shouldn't stand, following busgus philosphy. They wouldn't know physics if it hit them on the head.
These things stand because they are on a piece of incredible rock. This could be easily confirmed by a seismic survey. You know that by the narrow foundations, you can easily estimate the strength, and the fact that it does not settle one micro-inch. In Callie, there is no solid rock for the most part, but this rock is Yosemite-grade granite. We can't have these in Canada because the frost would work to tip them.
Since Callie is a big mush bowl, you can have the biggest earthquakes, and the PGV on solid rock won't exceed a few cm/s. That's not enough to even wake you up if you were sleeping right under one of these things. :)
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