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ERROR: 'Seismic Spikes Preceded the Towers' Collapses'

The leveling of the Twin Towers generated seismic disturbances that were recorded by a half-dozen seismic recording stations within a 20-mile radius of Manhattan. Numerous websites have repeated an erroneous interpretation of the seismic recordings as evidence that bombs in the basements of the Towers severed the core columns at the onsets of the collapses. One source of this error is an article by American Free Press reporter Christopher Bollyn, reprinted in Serendipity.li.

e x c e r p t
title: Seismic Evidence Points to Underground Explosions Causing WTC Collapse
authors: Christopher Bollyn

CENTRAL COLUMNS SEVERED

Videos of the North Tower collapse show its communication mast falling first, indicating that the central support columns must have failed at the very beginning of the collapse. Loizeaux told AFP, "Everything went simultaneously."

"At 10:29 the entire top section of the North Tower had been severed from the base and began falling down," Hufschmid writes. "If the first event was the falling of a floor, how did that progress to the severing of hundreds of columns?"

Asked if the vertical support columns gave way before the connections between the floors and the columns, Ron Hamburger, a structural engineer with the FEMA assessment team said, "That's the $64,000 question."

Loizeaux said, "If I were to bring the towers down, I would put explosives in the basement to get the weight of the building to help collapse the structure."

SEISMIC "SPIKES"

Seismographs at Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York, 21 miles north of the WTC, recorded strange seismic activity on September 11 that has still not been explained.

While the aircraft crashes caused minimal earth shaking, significant earthquakes with unusual spikes occurred at the beginning of each collapse. The Palisades seismic data recorded a 2.1 magnitude earthquake during the 10-second collapse of the South Tower at 9:59:04 and a 2.3 quake during the 8-second collapse of the North Tower at 10:28:31.

The Palisades seismic record shows that -- as the collapses began -- a huge seismic "spike" marked the moment the greatest energy went into the ground. The strongest jolts were all registered at the beginning of the collapses, well before the falling debris struck the earth. These unexplained "spikes" in the seismic data lend credence to the theory that massive explosions at the base of the towers caused the collapses.

A "sharp spike of short duration" is how seismologist Thorne Lay of Univ. of California at Santa Cruz told AFP an underground nuclear explosion appears on a seismograph.

The two unexplained spikes are more than twenty times the amplitude of the other seismic waves associated with the collapses and occurred in the East-West seismic recording as the buildings began to fall.

Lerner-Lam told AFP that a 10-fold increase in wave amplitude indicates a 100-fold increase in energy released. These "short-period surface waves," reflect "the interaction between the ground and the building foundation," according to a report from Columbia Earth Institute.

"The seismic effects of the collapses are comparable to the explosions at a gasoline tank farm near Newark on January 7, 1983," the Palisades Seismology Group reported on Sept. 14, 2001.

One of the seismologists, Won-Young Kim, told AFP that the Palisades seismographs register daily underground explosions from a quarry 20 miles away. These blasts are caused by 80,000 lbs. of ammonium nitrate and cause local earthquakes between Magnitude 1 and 2. Kim said the 1993 truck-bomb at the WTC did not register on the seismographs because it was "not coupled" to the ground.

Experts cannot explain why the seismic waves peaked before the towers hit the ground. Asked about these spikes seismologist Arthur Lerner-Lam, director of Columbia University's Center for Hazards and Risk Research told AFP, "This is an element of current research and discussion. It is still being investigated."

"Only a small fraction of the energy from the collapsing towers was converted into ground motion," Lerner-Lam said. "The ground shaking that resulted from the collapse of the towers was extremely small."

Last November, Lerner-Lam said, "During the collapse, most of the energy of the falling debris was absorbed by the towers and the neighboring structures, converting them into rubble and dust or causing other damage -- but not causing significant ground shaking,"

Evidently, the energy source that shook the ground beneath the towers was many times more powerful than the total potential energy released by the falling mass of the huge towers.

Bollyn's assertions that "seismic waves peaked before the towers hit the ground" and that the ground-shaking energy was "many times more powerful" than the Towers' stored gravitational energy, though interwoven with quotations of scientists, are neither supported by those scientists nor an examination of the events. Consider first the sequence of the waves recorded by the Palisades station.

As the video and photographic evidence shows, the Towers exploded into expanding clouds of rubble that were about 400 feet from top to bottom by the time they reached the ground. Those rubble clouds contained virtually all of the mass of the Towers -- thousands of tons of rubble falling from as high as 1000 feet. That could certainly be expected to produce pronounced seismic waves.

In fact the seismic evidence from the Palisades station comports well with the sequence of destruction evident in photographs and videos: each Tower was consumed by a wave of destruction that started near the crash zone and moved downward as it generated an expanding cloud of rubble. It took about ten seconds for the bottom of this cloud to reach the ground and another eight seconds for its top to reach the ground. Likewise the seismic records show small disturbances lasting for about ten seconds, followed by large spikes lasting for about eight seconds.

There appears to be no basis for the claim that the large spikes preceded the "collapses", nor that the energy indicated by those spikes was more than could be accounted for by the approximately 110 megawatt-hours of gravitational energy stored in the elevated mass of each Tower. And there is strong evidence contradicting the idea that the seismic spikes indicated underground explosions including:

  • There is no support in the large body of photographic and video collapse evidence for the idea of powerful explosions in the Towers' basements at the onset of the collapses. Instead the evidence shows waves of destruction proceeding methodically downward from the crash zones to the ground.
  • Underground explosions would have produced strong P waves, but the seismic stations registered only strong S waves. P waves oscillate horizontally -- parallel to the direction of travel; whereas S waves oscillate vertically -- perpendicular to the direction of travel.

An analysis of the timeline of the North Tower collapse on the 9-11Research site corroborates the idea that the large seismic spikes were produced by rubble reaching the ground.

e x c e r p t
title: Speed of Fall: The Towers' Tops Fell Virtually Unimpeded
authors: 9-11 Research

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 abovementioned 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 1 second. This is based on an estimate of 2KM/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 10 seconds for the bottom of the mushrooming dust cloud to reach the ground, and another 7 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)

That the larger spikes of the seismic signatures of the Tower collapses were produced by falling rubble does not preclude that the Towers were destroyed with explosives. In a typical demolition, numerous small explosives are used to shatter the columns supporting the building. Unless the explosives are detonated simultaneously, they are unlikely to produce detectable seismic signatures. If explosives were responsible for the Towers' destruction, they were numerous and were detonated in a synchronized but progressive manner, contributing little to the recorded seismic disturbance.


page last modified: 2010-12-18
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Seismic chart of South Tower collapse (LEDO)
Seismic chart of North Tower collapse (LEDO)