Destruction caused by P-Waves

[HRS]

Quick seismology question: What properties make P-waves, specifically, destructive? Is it a combination of frequency, speed or amplitude? Or is one factor of P-waves specifically destructive to buildings?

 

I realize that S-waves are particularly destructive because the waves move perpendicular to the direction but right now I am interested in P-waves

[studiot]

S waves cause actual differential movement of parts of a structure.

If this cannot be accomodated by the structure, it will fail.

 

P waves alter the characteristics of the foundation earth material, due to the accelerations involved in the wave.

This has two effects.

 

Firstly it can cause the foundation material to loose some bearing capacity, and therefore the ability to support all or part of a structure.

 

Secondly all loaded foundations have failure planes and other surfaces (eg the slip circle) which are loaded by the earth above and any structure on that superficial earth.

The acceleration of this material increases the force on it, because force = mass x acceleration. This can take it outside the support range of the plane or circle (in shear), causing failure of the earth.

This applies in particular to cutting sides and embankments.

[HRS]

So, to selectively take out a small part of your explanation, the cause of destruction by the P-waves is more a factor of the force of the wave colliding with the buildings than it is any other factor? Perhaps it has more to do with impulse then, and less with the actual mechanics of the wave (except velocity)?

[studiot]

 

So, to selectively take out a small part of your explanation, the cause of destruction by the P-waves is more a factor of the force of the wave colliding with the buildings than it is any other factor? Perhaps it has more to do with impulse then, and less with the actual mechanics of the wave (except velocity)?

 

 

I didn't say any of that, read it again.

 

The P wave affect the foundation earth material. rather than the building.

 

PS do you understand that 'foundation' refers to the earth or ground supporting the structure, not the structure itself?

[HRS]

Ah I see where I made my mistake thanks.

[studiot]

 

Ah I see where I made my mistake thanks

 

Sure thing, I am happy to discuss further if you wish.

[HRS]

Great. So I understand that the P-waves race ahead and shake the foundations of buildings, causing in some destruction based on flaws in the materials and construction being exposed by resonating energy from the waves. Also, if the oscillation of energy is correct in frequency, it can result in "resonance disaster." Am I correct in these assumptions? If not please correct me.

[studiot]

 

Great. So I understand that the P-waves race ahead and shake the foundations of buildings, causing in some destruction based on flaws in the materials and construction being exposed by resonating energy from the waves. Also, if the oscillation of energy is correct in frequency, it can result in "resonance disaster." Am I correct in these assumptions? If not please correct me.

 

Sorry but I didn't say that either.

 

What happens when you shake a bottle of tomato ketchup?

 

[HRS]

I get the analogy: The contents inside shake with it. Analogies often work so much better. Sorry if I seem to bypass your points but I suppose I'm making deductions from somewhere I need not.

[studiot]

I'm trying to be as explicit as I can.

 

If the P wave 'shakes up' the soil then it may loose it's strength, like the ketchup.

 

This was only condition 1 on my list.

 

Condition 2 is different again.

 

The weight of soil (as with anything ) is w =mg. That is the mass times the acceleration due to gravity.

 

Usually this is the only force acting on the soil.

 

But if there is an acceleration due to the P wave then a second force is applied. This may be sufficient to make a previously stable bank of soil unstable.

Edited April 27, 2014 by studiot

[HRS]

Ah, I suppose I needed to be talked to like an child to get it. Thank you.

[studiot]

 

Ah, I suppose I needed to be talked to like an child to get it.

 

Not really.

 

soil mechanics is quite a specialist (and technical) subject.

 

I can do the fancy maths if you prefer.

 

[michel123456]

I don't know much about P and S waves but i know about construction and destruction caused by earthquakes.

One should know that a building is not an self-supporting thing. if you take your car, or an airplane, upside-down, it will not fall apart, it will hold together. that is not true for a building. If you hang a building upside-down, it will fall apart. If you hang it at 90 degrees angle, it will crumble. A building is made to resist gravity, a vertical force oriented from up to down.

What happens with earthquakes is that all of a sudden, the building is shaked and must resist forces that are not oriented from up to down, but from down to up (as if it was hung upside-down) or from the side (as if it was at 90 degrees).

Edited April 27, 2014 by michel123456

[studiot]

 

What happens with earthquakes is that all of a sudden, the building is shaked and must resist forces that are not oriented from up to down, but from down to up (as if it was hung upside-down) or from the side (as if it was at 90 degrees).

 

 

Earthquake effects do not work like this.

 

The Quake is a travelling wave.

This means that is has a wavefront.

This is a sharply defined section.

One side of the wave is doing one thing (perhaps going up)

The other side is doing something else (perhaps going down)

 

This is called differential movement.

 

So as the wavefront passes through the building, different parts of the structure can be moving in opposite directions.

This snaps floor slabs, pushes up sidewalls and detaches them and much more.

 

Unless the building is very tiny ( and therefore probably safe) the quake wave does not affect the whole building at once.

That is the point.

Edited April 27, 2014 by studiot

[michel123456]

 

Earthquake effects do not work like this.

 

The Quake is a travelling wave.

This means that is has a wavefront.

This is a sharply defined section.

One side of the wave is doing one thing (perhaps going up)

The other side is doing something else (perhaps going down)

 

This is called differential movement.

 

So as the wavefornt passes through the building, differnt parts of the structure can be moving in opposite directions.

This snaps floor slabs, pushes up sidewalls and detaches them and much more.

 

Unless the building is very tiny ( and therefore probably safe) the quake wave does not affect the whole building at once.

That is the point.

I don'\t disagree.

 

But again, if your car is the subject of such movements, it will not fall apart. That was my point.

[studiot]

 

But again, if your car is the subject of such movements, it will not fall apart. That was my point

 

Sure, but it makes a good movie eh?

 

[Endy0816]

What if your car is a 100 foot limo?