Seismic waves were detected at seismograph stations in New York and four neighboring states on September 11, 2001, during the period when WTC 1 and 2 (the North and South Towers) were struck by airliners and collapsed. Scientists at the Lamont Doherty-Earth Observatory (LDEO) at Columbia University published analyses of the seismographic data from the WTC, based on raw data from the Palisades, NY, station. The Federal Emergency Management Agency (FEMA) and the National Institute of Standards and Technology (NIST) relied upon the LDEO analysis in their publications on the events at the World Trade Center. [1] The 9/11 Commission Report also cited the LDEO analysis, [2] although it did not confirm LDEO’s analysis of plane-impact times, basing its own conclusions on ground radar data instead of seismic wave data.

But independent analyses have disputed LDEO’s conclusions and thereby the conclusions reached by FEMA and NIST. These independent analyses dispute even more the conclusions of the 9/11 Commission.

The seismic waves were caused by the airplane impacts into the Twin Towers and the resulting collapses of the buildings. [3] The magnitudes of the airplane impact shocks at WTC 2 and WTC 1, respectively, were 0.7 and 0.9. The collapse of WTC 2 caused a shock of magnitude 2.1; the collapse of WTC 1 caused a shock of magnitude 2.3. [4] The signals were used to determine accurately when the plane impacts and collapses occurred. [5]

The results of independent research conflict with the conclusions by LDEO (Lamont Doherty-Earth Observatory) that the waves were caused by airplane impacts and resulting building collapses.

In 2006, engineers Craig Furlong and Gordon Ross showed that the plane impacts could not have caused the seismic signals attributed to them by LDEO, because they originated several seconds before the 9/11 Commission’s radar-based times of impact.

The seismic events, therefore, must have resulted from causes of a different type. The best (and probably only plausible) candidate for these causes would seemingly be explosions in the basements of the Twin Towers, for which there is abundant physical and testimonial evidence. [6]

Although the present Point deals only with the seismic evidence, much of the physical and testimonial evidence is documented in Point TT-8: “Why Did the Twin Towers Collapse? The Physical and Testimonial Evidence.” [7]

The conclusion of Furlong and Ross – that seismic evidence does not fit the official story (in any of its versions) – was reinforced in 2012 by a French geophysicist, Dr. André Rousseau, who reanalyzed the seismic wave data. [8] Rousseau concluded that the LDEO report is flawed in three significant respects:

• The radar-based timing of the airplane impacts does not match the origin-times of the seismic waves (as indicated by the data);
• The lack of explanation of why, although the two towers were destroyed in essentially the same way, the data show large differences between them in terms of released energy;
• The frequencies of the waves are much too low to have been caused by plane impacts and building collapses (although they match those of underground explosions, evidence for which is documented in Point TT-8).

The Timing of the Wave Origins: LDEO in 2001 published a report giving the times at which four wave signals began. [9] It correlated these times with the two airplane impacts and the two collapses. The LDEO researchers stated that they derived these times by calculation from the times the signals were received at the Palisades station. The 9/11 Commission Report, however, published very different impact times, based on ground radar data, which tracked the airplanes’ approaches to, and collisions with, the buildings. The differences are greatest with regard to WTC 1 (which was first): Rousseau, like Furlong and Ross, pointed out thatthe radar-based times, being approximately 15 seconds later than the times that could be plausibly inferred from the Palisades data, do not support the correlation of the seismic wave-forms with the plane impacts. [10]

Event Magnitudes: “[I]t is strange that identical events … at the same location,” said Rousseau, “would have generated seismic sources of different magnitudes.” [11] This discrepancy occurred both for the plane impacts and the building collapses. For the two waves attributed by LDEO to the impacts, the magnitudes of the signals [12] are different (0.9 for WTC 1, 0.7 for WTC 2), despite the similarity of the two plane crashes into the virtually identical buildings. The signals assigned to the collapses of the Twin Towers also display significant differences (magnitudes 2.1 for WTC-2 and 2.3 for WTC-1), again despite the similarity of the events resulting in the disintegrations of the two essentially identical buildings. Although the difference between 2.1 and 2.3 might seem minor, the unique (logarithmic) way in which seismic events are measured means that a shock that registers a magnitude of 2.3 releases twice as much energy as a magnitude 2.1 event, so the discrepancy is too large to have been due to an error. [13] Rousseau concluded that the waves had to have been caused by something else (which, given the evidence provided in Point TT-8, points to explosives). [14]

Wave Frequencies: The frequencies of waves caused by plane impacts, reported Rousseau, are typically much greater – one to two orders of magnitude higher – than the frequencies of the waves that were, according to LDEO, caused by the plane impacts into WTC 1 and 2. That is, the frequencies of waves typically caused by plane impacts range from (roughly) 10 to 100 Hertz (Hz), whereas the waves that were said by LDEO to be caused by the plane strikes are on the order of only 1 Hz. The idea that the seismic waves in question were caused by plane impacts was, therefore, highly unlikely. Furthermore, the recording equipment at Palisades had a range of only 0.6-5 Hz, so it was incapable of recording waves generated by typical plane impacts. [15]

The discrepancies described above indicate that the LDEO conclusions about the nature of the events that generated the signals recorded at Palisades cannot be correct. Most strikingly, the ground radar data, which is very precise, showed WTC 1 to have been struck 15 seconds later than the Palisades-recorded seismic activity, which LDEO scientists attributed to an airplane impact. The radar also shows WTC 2 to have been struck later than the seismic activity attributed to it. The seismic activity, therefore, must have been produced by something other than the crashes of the airliners into the two buildings.

Rousseau, like Furlong and Ross, provided reasons to conclude that the signals that the official story attributed to airplane impacts had actually been caused by something else – which, as evidence documented in Point TT-8 suggests, was shocks, explosive in nature, that had occurred at the bases of the buildings. Rousseau further demonstrated that the wave details themselves were characteristic of such explosions, not of plane impacts or building collapses.