Quote:
The time it took the towers to fall may be one of the most important pieces of evidence in determining their mode of destruction.
It is widely accepted that both towers completely fell (nearly everything but the dust reached the ground) in around ten seconds. This estimate appears to be based mainly on seismic data. However, video evidence of the North Tower collapse suggests that it took close to 15 seconds for the destruction to reach the ground. Establishing a precise time of duration for each fall may not be possible, but there are measurements that can be made. Video records show that each tower's top began its fall precipitously, and show the falling tops for a few seconds before they disappeared into the exploding dust clouds. It is also possible to track other features of the waves of destruction that traveled down each tower. In both collapses dust clouds, exhibiting the behavior of pyroclastic flows associated with volcanoes, rapidly grew as they fell. 1 Each cloud consumed its tower's top in a few seconds, then continued to descend, remaining centered around the tower's axis. Each cloud had a fairly well-defined top and bottom, whose descent can be timed using video records.
Unfortunately, detailed studies of collapse times based on the compositing of photographic, video and seismic evidence are lacking. Instead, seismic signal durations have been treated as synonymous with collapse times by many, and the statements that the towers fell in eight and ten seconds have been repeated by both proponents and detractors from the official explanation.
Meaning of the Seismic Records
Seismic records of the Twin Tower collapses show a large signal for each collapse lasting just under 10 seconds. The durations of the large signals are widely equated with the durations of the collapses themselves. However, the signals may correspond to only parts of the collapse events, such as the rubble reaching the ground.
Consider the seismic records of the closest seismic recording station, at Palisades, N.Y. (PAL). They show a very similar pattern for the leveling of WTC 1 and 2. In both cases there is about five seconds of high-amplitude movement, followed by about three seconds of movement at less than half that amplitude, and then by about 15 seconds of much weaker movement. In addition there is some still weaker movement starting about 12 seconds before the onsets of the high-amplitude movement. The main difference is that for WTC 1 the initial high-amplitude phase builds in intensity to a much higher spike than any seen for WTC 2.
The fact that the largest movement is followed by smaller movement has been cited as evidence that bombs, detonated at the starts of the collapses, generated the large movement, and that the debris impacting the ground contributed to the smaller subsequent movement. However, bombs, if detonated underground, would have generated strong P waves in addition to S waves. The fact that only strong S waves were reported is consistent with the theory that the largest movement was caused by building remains hitting the ground.
Tracking the Tops
The time of onset of collapse is clear in the North Tower, which initiates its telescoping collapse in an instant. The case of the South Tower is complicated by the fact that the top leans for a few seconds before beginning its vertical descent. Although determining the onset of vertical collapse in the South Tower is more difficult, its top is visible for longer and offers a longer span through which to time the rate of fall.
The South Tower
The following analysis is based on the NBC video taken from the east of the towers.
For the South Tower we define onset of collapse as the moment downward movement of the highest point of the roof starts. Unfortunately this time is difficult to determine since the roofline is obscured by smoke when the fall begins. The fall is preceded by a leaning movement that begins around the time the movie begins and accelerates for about three seconds. At somewhere between two and three seconds the top starts to fall. Once the top starts to lean, the highest point of the roof is the northwest edge. 2.5 seconds may be a good estimate for the time that starts to fall. A good marker for this is a small white squib that emerges from the level of the impact zone about three-quarters of the way back on the right face. That immediately precedes the first large ejections from the southeast face.
Using that marker it is possible to time the fall of the South Tower's top up to the moment it gets swallowed up by the dust cloud. At that point the dust cloud rises only slightly above the level of the 78th-floor sky lobby visible as a two-story band on the adjacent North Tower. A small extrapolation gives a good estimate of the time of fall of the South Tower's roof to the level of the 78th floor of five seconds. That distance is about 384 feet (12 feet per story times 32 stories).
The North Tower
The top of the North Tower began to suddenly telescope about a fourth of a second after the radio tower started to fall. In views from the north the top is swallowed up in about two seconds. The CNN live video clip shows the mushrooming dust cloud reaching the ground at about 13 seconds. As the descending pyroclastic dust cloud drops below Building 7, the rising smoke plume shifts to the east revealing the empty space except for the short-lived spire. The first glimpse of empty space where the building stood is at about 13 seconds.
A Timeline for the North Tower
It would be useful if collapse events evident in videos could be associated with seismic signal features. Since some news broadcasts have real-time clocks on their banners, it may be possible to match visual events with features of the seismic signals.
Consider the North Tower, whose entire collapse was recorded by the above-mentioned CNN live feed, which has a clock on its banner. That clock does not have a second counter, but its minute counter flips to 10:29 37 seconds after collapse starts, which places the collapse start, according to the CNN clock, at 10:28:23.
Various pages on columbia.edu put the origin time of the signal at the source at 10:28:31, plus or minus one second. This is based on an estimate of 2 km/s travel speed for the S waves, which, given the PAL station's distance of 34 KM from the WTC, gives a travel time of 17 seconds.
The CNN video suggests that it takes about ten seconds for the bottom of the mushrooming dust cloud to reach the ground, and another seven or so for the top to reach the ground. The following composite timeline combines timing estimates of collapse events from the CNN video and the PAL seismic record. It assumes rubble hitting the ground caused the large ground movement, and thus that the crumbling of the tower prior to that caused only minor ground movement. Given that, the times from these pieces of evidence match up remarkably well.
10:28:23 North Tower starts to crumble
10:28:31 Rubble starts to hit the ground (start of big signal)
10:28:36 The heaviest rubble hits the ground (peak of big signal)
10:28:39 Most heavy rubble has reached the ground (end of big signal)
|
Here are numerous video clips (most are raw footage) of all three buildings collapsing. WTC 7 is the most interesting however, IMHO. If getting a 47 story rectangle to fall symetrically into it's own basement could be achieved by simply exploding deisel fuel in the basement... why do we need folks like Controlled Demolition Inc to charge millions to bring down the buildings that they do? Every single aspect of it's collapse is consistent with a contrlled demolition, from the sagging at the center just prior to collapse, to the symetrical fall, to the shock wave observed by numerous eye wtinesses traveling through the building seconds before collapse, to the numerous squibs seen popping as the building fell.
The owner of the buildings (who btw, took out terrorist insurance for the first time mere weeks before the attacks) explained that he had told the authorities to "pull the buildings" and minutes later (coincidence?) the tower collapsed. Years later his spokesteam attempted to clarify that he meant pull the responders out of the building. Problem is, no responder had been near the building since before noon.
In addition to all of this, 30-60 ton girders from the core are seen traveling slightly upwards then out away from the collapse to a maximum distance of 100 yards. How does this happen without explosive force many times that of anything caused by the collapse? Violating every principle of gravity that we know (remember the only thing supposedly working on the collapse is gravity) there is much solid debris seen ARCING upwards and out.
As with the previous "Eyewitness" video this one also goes into much more detail than this short clip presents. This is just a primer...
Physics demonstration of the WTC 2 Collapse. Again, this is just a small portion of the analysis.
In fact I would suggest skipping the primer and watch the more in depth ananysis.
"Eyestiness" "Detailed Analysis" Approx 33 minutes And yes... I know... the end is very, very cheesy... not my fault LOL.