I challenge NIST Answers to FAQ - Supplement (December 14, 2007)

wtc.nist.gov...

I would like to ask especially Valhall, Griff and bsbray11 to have a look at it, I see a few very short answers to very long questions we all had, at the bottom. Any other engineers are of course also invited to the discussion, and everybody else who offers a solid contribution.


Further on, I would like to have you ALL pay attention to my postings in the Conspiracy forum group, especially this post in this thread, titled ""Seismic Data, explosives and 911 revisited"" :
PROVE ME WRONG! IF YOU CAN'T, IT WILL HOUND AND HURT YOU FOREVER - BECAUSE I PROVED 9/11 WAS AN INSIDE JOB!

I invite and challenge everyone willing, to prove me wrong on my thesis (which is not a hypothesis) that the LDEO seismic record of the WTC 7 collapse, compared to the NIST-report timestamped Nicholas Cianca photo which shows the first sign of structural global collapse, clearly shows an additional huge energy input, taking place many seconds before that global collapse initiation, and that seismic energy input was bigger (had a greater amplitude) than the whole seismic input from the WTC 7 building collapsing down to the ground.

Nicholas Cianca photo :
WTC7 Collapse Final.pdf
Page 23 from 42 Observed Fires, north face.
Page 42 from 42 Visual Observations for WTC 7

WTC 7 seismic chart by LDEO in my full thesis :
www.studyof911.com...

Read the whole thread, I am still curious why some people can't or won't see that energy input, and why such a irrefutable undeniable proof of official conspiracy, deserves only ONE star for that thread.....

Of course, if you are used all these years to the official explanations (lies by liars), why we went to war in Iraq and Afghanistan, and why and how 9/11 took place, this revelation will shatter your believe system.
Some people will never want to admit that their government is evil.

If you admit that I am right, then all the NIST reports, and all other official reports like the FEMA report, the 9/11 Commission report and LDEO conclusions must be regarded as written with a secret agenda, namely to hide to the public that factions of the military and politics were the perpetrators of 9/11, and not solely some "terrorist patsies".

Who exactly offered the contract to them, for 9/11, will be an interesting next revelation.

[edit on 15/12/07 by LaBTop]

I see a few very short answers to very long questions we all had, at the bottom. Any other engineers are of course also invited to the discussion, and everybody else who offers a solid contribution.

If I may be the first to dive in here, this is something I noted when I was first made aware of this FAQ when writing my initial, but less eloquently written analysis of part of the NIST report, which LaBTop presented magnificently in his thesis.

From NIST FAQ:

10. Why didn’t NIST fully model the collapse initiation and propagation of WTC Towers?

The first objective of the NIST Investigation included determining why and how WTC 1 and WTC 2 collapsed following the initial impacts of the aircraft (NIST NCSTAR 1). Determining the sequence of events leading up to collapse initiation was critical to fulfilling this objective. Once the collapse had begun, the propagation of the collapse was readily explained without the same complexity of modeling, as shown in the response to question #1 above.

The answer to Question 1 (referred to above) is copied below for convenience:

1. Was there enough gravitational energy present in the World Trade Center Towers to cause the collapse of the intact floors below the impact floors? Why was the collapse of WTC 1 and 2 not arrested by the intact structure below the floors where columns first began to buckle?

Yes, there was more than enough gravitational load to cause the collapse of the floors below the level of collapse initiation in both WTC Towers. The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load was applied gradually and 6 additional floors if the load was applied suddenly (as was the case). Since the number of floors above the approximate floor of collapse initiation exceeded six in each WTC Tower (12 and 29 floors, respectively), the floors below the level of collapse initiation were unable to resist the suddenly applied gravitational load from the upper floors of the buildings. Details of this finding are provided below:

Consider a typical floor immediately below the level of collapse initiation and conservatively assume that the floor is still supported on all columns (i.e., the columns below the intact floor did not buckle or peel-off due to the failure of the columns above). Consider further the truss seat connections between the primary floor trusses and the exterior wall columns or core columns. The individual connection capacities ranged from 94,000 lb to 395,000 lb, with a total vertical load capacity for the connections on a typical floor of 29,000,000 lb (See Section 5.2.4 of NIST NCSTAR 1-6C). The total floor area outside the core was approximately 31,000 ft2, and the average load on a floor under service conditions on September 11, 2001 was 80 lb/ft2. Thus, the total vertical load on a floor outside the core can be estimated by multiplying the floor area (31,000 ft2) by the gravitational load (80 lb/ft2), which yields 2,500,000 lb (this is a conservative load estimate since it ignores the weight contribution of the heavier mechanical floors at the top of each WTC Tower). By dividing the total vertical connection capacity (29,000,000 lb) of a floor by the total vertical load applied to the connections (2,500,000 lb), the number of floors that can be supported by an intact floor is calculated to be a total of 12 floors or 11 additional floors.

This simplified and conservative analysis indicates that the floor connections could have carried only a maximum of about 11 additional floors if the load from these floors were applied statically. Even this number is (conservatively) high, since the load from above the collapsing floor is being applied suddenly. Since the dynamic amplification factor for a suddenly applied load is 2, an intact floor below the level of collapse initiation could not have supported more than six floors. Since the number of floors above the level where the collapse initiated, exceeded 6 for both towers (12 for WTC 1 and 29 for WTC 2), neither tower could have arrested the progression of collapse once collapse initiated. In reality, the highest intact floor was about three (WTC 2) to six (WTC 1) floors below the level of collapse initiation. Thus, more than the 12 to 29 floors reported above actually loaded the intact floor suddenly.

Why didn’t NIST fully model the collapse initiation and propagation of WTC Towers?

In short, because this would have exposed the lie of the cause of the collapse. As LaBTop wrote in his thesis (and I fully support), due to the design of the WTC, it wouldn't be possible for a collapse as was witnessed on 9/11 to occur naturally.

Starting with a building that, although slightly damaged from an aircraft collision, is still effectively in one piece, I'll run through my thoughts the best I can:

Post-impact

* As we know, most of the fuel burned up outside the building. What was inside would have burned up in the next few minutes. This would have started office fires.

* Whilst the aircraft obviously hit, and went into the building, due to the angles at which they were flying, they missed the central core. In one instance, it is clear the aircraft was at a large angle, with the aircraft re-emerging out the corner of the building, closely followed by a fireball.

What does this tell us? It tells us that most of the kinetic energy of the aircraft was NOT absorbed by the building, as it had sufficient energy to break out the other side, and keep going at high velocity.

* During this period, the building was reconfiguring the loading to account for the now damaged external structure. We know this was a success as the building remained standing.

* Fire proofing. The explanation given for the melting of the steel was because in part, the fire proofing was "blown off" by the impact of the aircraft. Now, assuming for a moment none of the steel was covered in a fire protection coating, I still can not see how this could lead to a failure, and collapse of the building, in just 57 minutes, when you consider the steel was rated to 3000 °F for SIX HOURS.

Further, considering the aircraft only affected a couple of floors, on ONE SIDE of the building, this further restricts the potential for damage.

Finally, when you also consider there are no less than 47 steel columns making the central core that supports the building, These too would have to be seriously compromised for the building to collapse. In fact, one of the WTC developers is on record as saying that you could take almost 1/2 of them away (both core and exterior), and the building would still stand, such was the nature of the redundancy in the building.

When you also consider the lattice structure of the core, it is evident that this can withstand lateral loading. Something that was overlooked in the report was that the buildings were designed to survive the "100 years storm" with winds of up to 150 MPH.

Considering the mass of the buildings, the swaying motion of the building would be greater than a static building that has had to reconfigure the loading across the structure. In a wind, the building will gently oscillate, constantly pulling in one direction then another, whereas on 9/11, part of the supporting wall was removed, which would cause a slight increase in lateral loading of the columns, but nothing that would compare to the swaying in a gale force wind.

In terms of vertical loading, we know there was approximately 50% redundancy in the building, allowing for 1/2 of all the columns to be removed, and have the building remain standing. On 9/11 part of one side was removed, with less being removed on the opposite side as the aircraft flew through, then left, the building again. This still left the floors supported on either side, and in the center, in addition to a few columns on the

impact and exit sides of the building, putting the building inside of the 50% redundancy for loading. We know the building handled this fine, as it remained standing for 57 minutes.

Whilst parts of the floors were unsupported this shouldn't have been an issue as the structure was designed to reload in the event of multiple truss failures.

* Fire. Assuming for a moment that there was no fire proof covering on the steel in the WTC, the fire was distributed such that the heat would be concentrated under a small area of the floor. In addition, the central core couldn't be exposed to 3000 °F for 6 hours due to the fact that they are aligned vertically, and present a small area to any fire that would occur next to them. If that isn't enough, the rest of the column would act as a huge heat sink, so the steel columns making up the core couldn't get thoroughly heated up enough in order to melt in the first instance.

We know that after the initial fireball, very little fuel was left in the building. Of that, and the office fires that were started as a result, we also know that they were starved of oxygen. Billowing black smoke is a sign of incomplete combustion and a cool burning fire (in this instance cool = ~800 °F - far short of the 3000 °F the steel was rated to).

The implication is that the steel simply couldn't have got hot enough for long enough, in order to weaken, and thus collapse due to the forces acting upon it.

THERE IS ALSO A FUNDAMENTAL OVERSIGHT HERE.

The vertical columns are under COMPRESSION, taking the loads.

The trusses supporting the floors, adn primarily under TENSION, as the outside walls attempt to bow outwards. The trusses attach the outer wall to the core, preventing this from occurring. There is vertical loading on them, putting them under STRAIN (if memory serves correctly), but they will have been pre-stressed for this. The majority of the load would be transferred to the core column, and the rest to the external columns.

What does this mean in the event of the steel weakening? In the case of the floor trusses, they would have a tendency to PUSH the columns OUTWARDS.

As they bow, the floor might shift a bit. NOTE THAT CONCRETE WILL NOT SAG! I'm not sure if it would break under its own weight into multiple pieces???? Need a concrete expert here.

Assuming the floor "broke its back" as it is now only being supported at the edges (at the central core, and the outer wall), it will be resting on the truss in the center. This will put the truss into TENSION, as well as STRAIN. At the same time, this will put the central core into STRAIN, as well as the outer wall. Note that the structure was already designed to be put under this type of load. In a wind, these loads increase. On 9/11, apart from an increased static loading due to missing exterior columns, and the fact that there was only a light wind, and as far as I can tell, the building would still be inside of its design limits.

Collapse Initiation

* Incremental truss failure. The first points of failure would have to be trusses. This is where any natural loading would have to come from. As trusses fail, this puts the loading onto a smaller number of trusses, adn into more concentrated areas of the exterior and internal columns. There will be a point of criticality where the exterior and/or interior columns can not take the load, The exterior wall will start to pull inwards, whilst the core pulls outwards, then across its lattice structure, against the opposite trusses, and against the opposite wall.

If the opposite trusses have failed however, this is going to produce unequal loads on the core. It might even result in a slight twisting action at that point in the structure.

If we assume the trusses are still failing, we require a Super Truss to remain intact, or multiple trusses to fail simultaneously, with the weight of the floor on them, in order to pull in the external columns sufficiently to cause a collapse due to failure. As this can't happen simultaneously naturally, there will be an instant tilt as a result of partial failure. At this exact moment, kinetic energy will be added to the system, resulting in eventual failure of the trusses ON THAT SIDE. The killer blow to the Official Story is that the core can't bend easily. Assuming at this moment, on one side (as was witnessed in the videos) the exterior wall collapses, it will break the trusses on that side. The floor won't have anything to support it, and that part of the floor will break off with a rotational action. This can be seen in the first 1 second of the collapse of the North Tower. The KE will build up, and it will fall.

As it falls, it will contact the floors below it. Now remembering for a moment that the central core won't have collapsed in totality or at the same time, the floors below will still be intact. This will have the effect of causing the falling floor to hit it, bend it downwards suddenly and thus cause a failure of that floor. It will likely break off at the central core again due to the design of the core and the fact that it is this lattice. As it does so, it will deflect the falling floors, which already with a large amount of KE, will be rotating in the direction they fell. As it collapses, this should keep rolling, eventually getting to a point where it misses the lower part of the building completely, before crashing to the ground.

I would still expect the majority of the building to still be standing.

As we know however, this did not occur (although the first 2 seconds show what should have continued).

What happened next could not have occurred naturally, and is why NIST did not investigate the actual collapse. The reason is that multiple, simultaneous failure of all the core columns would have to occur for the collapse, as we actually saw it on 9/11, to occur.

If it wasn't a natural collapse, it had to be man-made. If it was man-made, something more than a couple of aircraft had to do it. We know they didn't strike the core; the angle they went in and came out is testament to that.

If that isn't enough, the second killer blow to the Official Story is in the fact the buildings collapsed totally to the ground. Given the approximate physics as I described above in a natural collapse, a total collapse just wouldn't occur. 50% of the building (i.e. the building away from the side on which the building started to collapse towards) would actually be free of any damage. This side would be put initially under tension, then under compression, as the floors on the opposite side were hit. I would expect the floors to fail before either the core or the opposite exterior columns failed due to transient loads caused by the collapse on one side.

Whilst I'm not in a position to be able to put figures to the description of what I reasonably think would occur, I don't expect to be too far off the mark, either.

In summary, given the seismic recordings of the collapse, and of the above, it is inconceivable that the building would have just naturally collapsed as per the official story. I think NIST knows this, and were either told not to investigate, or started to and discovered the truth, and were told to stop investigating. I doubt we will ever know.

There are two posts due to post-length limitations.

Thanks for reading! I look forward to any comments.

[edit on 15-12-2007 by mirageofdeceit]

Wrongo.

The design of the WTC was to support additional mass - NOT impact. There is a difference between the two. Loss of structural support is the cause for collapse. No building larger than a few stories has the structural integrity to survive a collapse once it has been initiated - period. The concept behind the WTC construction is to allow for massive amounts of support to be lost over distributed regions (as in a fire - due to the weakening of steel in a fire) of the structure - or some concentrated regions of damage while routing the stress through more distant supports.

However, because this is a steel-mesh structure, once a collapse of any part of the supporting structure is initiated - the process is terminal and irrecoverable. The tensile strength of steel is superior to its compression and torsion strength - while steel may buckle underneath the immediate collapsing mass, lateral latices will be pulled down with the rest of the mass. This combined tensile strength and robust steel exoskeleton force the collapse to remain contained within the relative confines of the structure (as opposed to falling all over the place). The strength of the steel beams ensures that they are torn down with any supports caught in the main debris pile (which, because the structure was designed to act as one contiguous piece of metal... that means every piece of metal is going to be ripped down).

Each floor will have 1/2[%mass%]x[%velocity%]^2 (yes, I realize I goofed on a previous post in another threat - will fix it) inertial force upon impact with the floor below it (upon initial collapse - subsequent collapses will only accelerate). Given the nature of the structure, it is highly unlikely that only a single floor will be collapsing upon top of another floor - so it is safe to say that the collapse, once it has begun, is terminal (as in - for the structure - it's dead).

Given that the structure was bolted and bracketed together, which goes contrary to the original design plans (which called for a welded structure) - and the bolt sized was reduced due to bean-counter mentality.... it's safe to say that the building would not perform up to its original design specifications.

The fact that this structure had been exposed to a few decades of wind and structural stress (to include a bomb detonation) - which only served to generate what is known as "loose play" in the joints of the structure only further degrades the performance. Then, figure that the steel used in the brackets and bolts is likely of lower hardness and thermal resistance than that of the beams (just the nature of the beast) (steel can have quite a few different properties, you know, depending upon how much carbon and chromium you put in there) - the likelihood that fire, coupled with structural damage caused by an airliner impact, could very well cause at least a portion of the structure collapse - thus initiating a complete structural failure.

Can you prove me wrong?

If you can't, you must accept an official conspiracy, by the US government.

DECORUM.

Not a sign of it in that rant. Capped it off with an insult bordering on life threatening.
Lucky for you , you have no idea who you are talking to.
One of the build-in safeguards of the Internet.

By the way, when are you going to counter my arguments?
In a civil manner.

Originally posted by Aim64C
The tensile strength of steel is superior to its compression and torsion strength - while steel may buckle underneath the immediate collapsing mass, lateral latices will be pulled down with the rest of the mass.

Can you tell me exactly what type of deformation you're referring to, when you talk about a "buckle" that pulls down 'the rest of the mass' (referring to the "lateral latices")?

In other words, what type of failure allows a column to just move straight down, when below it, there is just more steel column that is solidly and continuously welded in three-floor sections at a time, all braced laterally at every floor? That is what is referred to as a "telescoping" motion, if you get the reference. Is that what you're implying? Or would you like to clarify your geometry here for us?

[edit on 17-12-2007 by bsbray11]

Nice work Labtop.. good job dude..

First off great post LabTop, where are all the de-bunkers now?

Originally posted by Aim64C
No building larger than a few stories has the structural integrity to survive a collapse once it has been initiated - period.

Well first you have to prove this as fact. It is a myth perpetuated by NIST that global collapse was inevitable once initiated to cover their asses. If they could convince people of this, which obviously they did, then their research wouldn't have to explain how the building actually collapsed; only what they want you to believe initiated it, plane impacts and fires. See how their thinking is? They rely on you not knowing enough to see through the smoke screen they set up.

Now what initiated the collapse is in question first off, yet to be proved it was fire or plane impacts, so they have to answer that before they get to the collapse itself. We don't believe it was office fires or the impact damage for reasons you should know.
Then they have to explain the global collapse with no resistance, that they have convinced some was inevitable when science tells us that's just not true. They have yet to do that. Why? Well they can't, so they rely on folks to believe their little misrepresentation of events.

Where is the precedence that a building, however tall, is liable to global collapse once initiated? I say it's a stupid baseless claim, prove me wrong.

(BTW didn't the Windsor tower partially collapse? So where was the inevitable global collapse that we should have expected once that started?)

[edit on 17/12/2007 by ANOK]

The implications of what LaBTop has come up with are huge. If you look at some of the eyewitness testimony combined with this then you are driven to one conclusion.

The following link is some of the eyewitness testimony prior to the collapse of the South Tower

whatreallyhappened.com...

The Ground Shake Preceding
the Collapse of WTC 2

"We felt the ground shake. You could see the towers sway and then it just came down and I never looked back once I started running." [Lonnie Penn, E.M.T. (E.M.S.)]

"...all of a sudden the ground just started shaking. It felt like a train was running under my feet. ... The next thing we know, we look up and the tower is collapsing." [Paul Curran, Firefighter (F.D.N.Y.)]

"At around 9:50 AM, Michael and his colleague were only a block and a half a way from the WTC, when there was an ominous rumbling that grew into a roar, shaking the ground "like a thousand trains." It took them a moment to realize that the South Tower was starting to fall." [backroadsofvermont]

"Shortly before the first tower came down I remember feeling the ground shaking. I heard a terrible noise, and then debris just started flying everywhere. People started running...." [Bradley Mann, Lieutenant (E.M.S.)]

Originally posted by ANOK
First off great post LabTop, where are all the de-bunkers now?

Even though I wasn't debunking LabTop, we were having a conversation. Maybe you can tell me where my 2 posts in this thread from yesterday migrated to.

First off great post LabTop, where are all the de-bunkers now?

Hmm... I just can't imagine.

Now... seeing as I was so rudely interrupted....

(oh, I'm a masochist... I will re-type my point a million times because I like the pain it brings my soul).

Pressure waves, also called Primary waves or P-waves, travel at the greatest velocity within solids and are therefore the first waves to appear on a seismogram. P-waves are fundamentally pressure disturbances that propagate through a material by alternately compressing and expanding (dialating) the medium, where particle motion is parallel to the direction of wave propagation. For a visual example of this movement, try laying a coil (like a Slinky) on a flat surface. Tap lightly on one end, and you will see the coil compress and then expand along the whole length of the coil. This is a P-wave-like phenomenon.

S-waves, also called Shear waves or secondary waves, are transverse waves that travel more slowly than P-waves and thus appear later than P-waves on a seismogram. Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids such as air or water.

Surface waves travel more slowly than P-waves and S-waves, however, because they are guided by the surface of the Earth, and their energy is trapped near the Earth's surface, they can be much larger in amplitude than body waves, and can be the largest signals seen in earthquake seismograms. They are particularly strongly excited when the seismic source is close to the surface of the Earth.

That's from Wikipedia. It seems to coincide with everything I was taught in science class - so I doubt it is fundamentally inaccurate.

The same type of evidence presented in this thread was used to attempt to prove that there was 'another bomb' in the Oklahoma City bombing.

However, upon some testing and observation done by a third party - it was found that a single bomb (or impact) could generate two separate spikes on a seismograph.

Taking this into account with the evidence presented... there is your explanation.

"But wait! Where is the second peak!?"

Well, seeing as you would still be receiving the rumbling from the collapse, it would likely be obscured amongst all of that noise.

"But what about the bombs!?"

What bombs? You do realize that a bomb used to destroy a steel beam, in comparison to a large, heavy building collapsing would be like comparing a hand grenade to a dump-truck hitting the ground at Mach 1, right?

And, if there were a bomb present that could have even been noticed in-amongst the collapse of the WTC - you would have seen it on video, clearly. It wouldn't have been a puff of smoke or a single glass window breaking - it would have blown the living hell out of that building and made the plane crash look like some sad pyrotechnics display.

Aim64 : The same type of evidence presented in this thread was used to attempt to prove that there was 'another bomb' in the Oklahoma City bombing.

However, upon some testing and observation done by a third party - it was found that a single bomb (or impact) could generate two separate spikes on a seismograph.

Taking this into account with the evidence presented... there is your explanation.

Have a look at the forums and essays at StudyOf911.
I and others have posted extensively on the Oklahoma City bombing subject.
The Pentagon published a secret report that 5 bombs were in fact responsible for the damage seen at the Murrah building.
General Partin was the first real demolition expert on the scene, and he went public with his lectures, that the damage observed could not at all have been caused by one single Anfo bomb in a Ryder truck.

There were many witness statements about distinct explosions, separated clearly from each other.
There were witnesses reporting that bomb squads found several unexploded ordnances. One witness of that, who saw it with his own eyes, was murdered afterwards.
It is a whole can of worms in itself.

The "two separate spikes on a seismograph" were noted when a, hired by the government, demolition team, demolitioned the still standing remains of the building, weeks later.
It was a specific feature of that specific piece of soil between the explosions and the seismograph used.
Not to be compared with 34 km of upper NY crust on 9/11.
Where the specific signals (pictured in my posted specific seismograms) travelled through with a speed of 2 km/hr.
Have a look at LDEO's website what type of waves, they say, travel with a speed of 2 km/hr.
And what waves travel faster, thus arrive earlier on the seismograms we are discussing here, and what type of waves travel slower, thus arrive later.
They have a seismogram up there, with all those waves in them (from various seismic posts), but that is NOT the type of seismograms (from f.ex. WTC 7), we discuss here.

*yawn*

I am referring to an actual reenactment (or as good as you can get without rebuilding the building and blow it up again), measuring the force exerted on one of the suspect columns, using the arrangement described in the "official lies". The measured force was that which was published in the official report, which was sufficient enough to cause the collapse of the structure.

Also, seismic readings showed the two distinct spikes that I mentioned earlier.

This was done by a third party team of investigators - and, interestingly enough, a televised event on the Discovery Channel (or the Science Channel, I forget which).

Eyewitness accounts of the Oklahoma City incident aside, unless you are going to somehow provide some sort of evidence to prove that this spike is something other than the first-arrival of a P-wave ... then I think I just met the qualifications in your original post. Can I have a cookie, now?

Firstly LaBToP, I want to congratulate you on the amount of work and study you've put into this - it sets a very high standard for others to try and match.

Just a couple of questions:

Given the omnidirectional nature of seismic vibrations, was WTC7 the only detectable source of activity in that area at that point in time (pre-collapse)?

Apart from the mechanism involved in a total failure of the truss over the 5 story high substation within the building, could an internal collapse of a major part of the core of the building into the substation have been the cause of the precollapse signal?

I'm not out to debunk your data. If enough possibilities can be clearly eliminated hopefully what we'll be left with is what really happened.

reply to post by jthomas


jthomas, I have a feeling you mix up two threads now, this one started by me, and "Seismic Data, explosives and 911 revisited", started by Damocles.
www.abovetopsecret.com...
You were posting 2 posts in that page 6 :
www.abovetopsecret.com...
www.abovetopsecret.com...

and I answered them extensively. Have a look, if you lost track of that thread :
www.abovetopsecret.com...

Aim64C : unless you are going to somehow provide some sort of evidence to prove that this spike is something other than the first-arrival of a P-wave ... then I think I just met the qualifications in your original post. Can I have a cookie, now?

According to the article : Seismic Waves Generated by Aircraft Impacts and Building Collapses at World Trade Center, New York City :
911research.wtc7.net...
by scientists at the Lamont-Doherty Earth Observatory of Colombia University, seismometers at the various observatories recorded only surface waves (Rg, Rayleigh) arising from events in lower Manhattan on 9/11/01.

Surface waves were the largest seismic waves observed at various stations. The presence of seismic body waves is questionable even at Palisades for the two largest collapses; they are not observed at other stations.

That means no P or S waves.
No cookie.

To answer another question I see coming :

No, these huge pre-collapse spikes on the WTC 7 graph are not P or S waves, since these are much smaller in amplitude than Rg waves, the surface ones mainly received by LDEO on 9/11.

And you also can't propose that that first pack of biggest peaks were spread-out main collapse signals.
If the main collapse would have been shown in the WTC 7 collapse graph as a spread-out signal packet from a real time event which was seconds shorter in duration, like in another type of seismogram from LDEO, then it would still be totally impossible for the spread-out graph, to have bigger than collapse signals in front of the collapse signals.

Imagine a copper coil of one foot with a double cone shape.
If you spread this coil out to two feet, still the amplitude of the two cones of the coil will never become any bigger, only the length of the coil will be spread out over the horizontal axis, but in the vertical axis nothing changes.

reply to post by Pilgrum

Given the omni directional nature of seismic vibrations, was WTC7 the only detectable source of activity in that area at that point in time (pre-collapse)?

See for other activity that day, the same link as in my answer to Aim64C above, to LDEO's dr Kim's essay for the only other significant seismic events recorded after the North tower WTC 1 collapse, and before the WTC 7 collapse :

Computed origin times and seismic magnitudes are listed in Figure 1.

Origin times with an uncertainty of 2 s were calculated from the arrival times of Rg waves at PAL using a velocity of 2 km/s. The collapse of 7 WTC at
17:20:33 EDT was recorded but is not shown.
Three other small signals shown in Figure 1 and ones at 12:07:38 and 12:10:03 EDT may have been generated by additional collapses.

These are the only other seismic signals LDEO refers to except the WTC 7 collapse.
So we can rule out another late partial collapse from one of the other WTC buildings, interfering exactly at that moment in the WTC 7 graph, just before global collapse.
That would be stretching reality far above its natural occurrence.

Apart from the mechanism involved in a total failure of the truss over the 5 story high substation within the building, could an internal collapse of a major part of the core of the building into the substation have been the cause of the pre-collapse signal?

Everyone should seriously ask them self, if they could believe that the total collapse of a whole building would cause LESS seismic signals than the failure of ONE or a few columns INSIDE that building.
That event inside, would be about equal in seismic effect, as the energy of all the columns breaking, divided by the energy of that one column breaking.
No chance at all it could be bigger than all columns breaking.