When major shocks occur at the Earth's surface or at depth, waves of different types, magnitudes and speeds may move out from the source location. Such waves can be detected by seismometers located at recording stations, and the data from the recordings can be analyzed to learn many details of the source events. Seismic signals were recorded at stations in New York and four neighboring states on September 11, 2001 during the period when the North and South Towers (WTC1 and WTC2, respectively) were struck by airliners and collapsed, as well as during the collapse of Building 7 of the WTC, which had not been hit by a plane.
Data from the Palisades, NY recording station, located 34 km north-north-east of Manhattan, published by the Lamont-Doherty Earth Observatory of Columbia University (LDEO), provide the most detailed seismic waveforms for analysis, particularly for the determination of the locations (aerial, surface, or subsurface) and timing of the events that created the seismic waves.
Seismologists have been puzzled in their analysis of signals recorded for the events at the World Trade Center, as the contradictions are significant. They are particularly intrigued by the presence of seismic "peaks" before the collapses. This text focuses on the study of the seismic signals from Palisades. The new interpretation presented here renders the assertions of the seismic analysis of the events at the WTC, presented by the government, null and void.
Five waveforms will be analyzed below. They are attributed by the LDEO team to specific causes, as follows:
1. the signals that, according to LDEO, match the moment when the planes hit WTC1 and WTC2, respectively, shown in figures 1a and 1b;
2. the signals that match the collapses of WTC1 and WTC2, respectively, shown in figures 2a and 2b; and
3. the signal that shows the collapse of WTC7, shown in Figure 2c.
The analysis presented here will question LDEO's identifications of the causes of the waveforms.........
The waveforms that the LDEO team attributes to the impacts of the airliners into the Twin Towers are shown in figures 1a and 1b. Although the waveforms look somewhat similar, they are sufficiently different to raise questions about LDEO's analysis. Although the cause of the two signals is similar -- the crashing of a plane, according to LDEO -- the magnitude (reflected by the amplitudes, or distribution on the vertical axis) of the two signals is different. Further, the waves generated by the two events do not have the same apparent velocity. The calculation of the propagation speeds, as shown in the graphs of Figures 1a and 1b, where the origin was fixed according to the corresponding crash, indicates 2900 m/s for WTC1 and 2150 m/s for WTC2.
A more serious difficulty with LDEO's attribution of the waveforms to plane impacts at the Twin Towers is that even if the impacts had been considerably more energetic, these signals could not have been generated by such impacts. The actual waves generated by the crashes had to have been deadened before hitting the ground. Frequencies of waves generated by explosions are on the order of 1 Hertz (1 Hz, or one cycle per second) -- which is the case with the Rayleigh waves shown in figures 1a and 1b -- while those of crash impacts are above 10 Hz and are often around 100 Hz. Furthermore, the range of the recording instruments (0.6-5 Hz) cited does not allow for the recording of the high-frequency waves that would be created by plane impacts. As to the theory of the oscillation of the Towers to explain these signals, as defended by Irvine (2001), it is inadequate because in such a case we would have had a "square" signal of long duration and a constant amplitude, while in actuality we observe a "bell-like" signal, representing a strong and brief explosion, which is particularly evident in the case of WTC2.
Given that it is geophysically impossible to have two different propagation speeds for two waves of the same type at the same frequency travelling the same path only a few minutes apart, one must bow to the evidence that the supposed origins of the recorded waves are incorrect, and that they are not linked to the plane crashes but to another origin. The waveform data, far from suggesting the conclusion of LDEO that they were caused by plane impacts into the Towers, suggest instead two explosions with different time displacements from the moments of plane impact at each building. Further, the difference in the magnitude of the two signals can only be linked to differences in the volume of explosives and/or their distance from the surface.........
At the times of the planes' impacts into the Twin Towers and during their collapses, as well as during the collapse of WTC7, seismic waves were generated. To the degree that (1) seismic waves are only created by brief impulses and (2) that low frequencies are associated with an energy (magnitude) that is comparable to a seismic event, the waves recorded at Palisades and analyzed by LDEO undeniably have an explosive origin. Even if the planes' impacts and the fall of the debris from the Towers onto the ground could have generated seismic waves, their magnitude would have been insufficient to be recorded 34 km away and should have been very similar to one another. As we have shown, they were not.
The types and magnitudes of the seismic signals show significant differences. The greatest differences occur in their propagation speeds, even though their paths were essentially identical under identical conditions. This difference is physically unexplained in the interpretation of the events offered by the LDEO researchers, the 9/11 Commission and NIST. Therefore, we must question their calculations of wave propagation speeds based on their assumption that the wave origins are shown on the video images of impacts and collapses. We can only conclude that the wave sources were independently detonated explosives at other times, thus accounting for the variable discrepancies for each wave origin in relation to the videos.
The composition of the waves is revealing both in terms of the location of the source and the magnitude of the energy transmitted to the ground. The subterranean origin of the waves emitted when WTC1 collapsed is attested by the presence of the P and S body waves along with the Rayleigh surface waves, which are present in all five explosions. The placement of the source locations of the four other explosions is subaerial, attested by the unique presence of Rayleigh waves. The aerial explosions visible on the videos of the upper floors of the Twin Towers do not produce seismic waves 34 km from the source.
There is a factor of ten between the power of the explosions at the time of the plane impacts on the Twin Towers (as well as at the time of the collapse of WTC7) and the strength of those more powerful explosions at the times of their collapses, the subterranean explosion under WTC1 being the one that transmitted the most energy to the ground.
Note as well the degree to which the surface waves are dispersive (i.e., their speed depends upon their frequency). The duration of the recorded signal is not representative of the duration of the signal at the source.
Finally, controlled demolition of the three towers, suggested by the visual and audio witness testimony as well as by observations of video recordings of their collapses, is thus confirmed and demonstrated by analysis of the seismic waves emitted at the moments of the plane impacts and at the moments of the collapses.