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. The 9/11 Commission Report also cited the LDEO analysis,  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 Official Account
The seismic waves were caused by the airplane impacts into the Twin Towers and the resulting collapses of the buildings.  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.  The signals were used to determine accurately when the plane impacts and collapses occurred. 
The Best Evidence
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. 
Although the present Point deals only with the seismic evidence, much of the physical and testimonial evidence is documented in TT Point 8: “Why Did the Twin Towers Collapse? The Physical and Testimonial Evidence.” 
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.  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 TT Point 8.
The Timing of the Wave Origins: LDEO in 2001 published a report giving the times at which four wave signals began.  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 that the 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. 
Event Magnitudes: “[I]t is strange that identical events … at the same location,” said Rousseau, “would have generated seismic sources of different magnitudes.”  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  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.  Rousseau concluded that the waves had to have been caused by something else (which, given the evidence provided in TT Point 8, points to explosives). 
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. 
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 TT Point 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.
References for Twin Towers Point 7
- World Trade Center Building Performance Study: Data Collection, Preliminary Observations, and Recommendations (FEMA, 2002: 1-10); William Pitts, et al., Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Visual Evidence, Damage Estimates, and Timeline Analysis (NIST NCSTAR 1-5A, 22-23, pdf: 118-9).
- The 9/11 Commission Report, 2004, Note 168, 461
- “[We] recorded numerous seismic signals from two plane impacts and building collapses from the two World Trade Center (WTC) towers. … Collapses of the two WTC towers generated large seismic waves, observed in five states and up to 428 km away. … The collapse of 7 WTC at 17:20:33 EDT was recorded [as well]. … The two largest signals were generated by collapses of Towers 1 and 2.” Won-Young Kim et al., “Seismic Waves Generated by Aircraft Impacts and Building Collapses at World Trade Center, New York City,” EOS, Transactions American Geophysical Union, November 20, 2001 (82/47): 565, 570-71.
- “For collapses 1 and 2, values of ML [local magnitude] determined from E-W components are 2.1 and 2.3. … The seismic energy of a ML 0.7 to 0.9 [was] computed for the impacts … ” (Ibid., 1, 5).
- “Scientists at Lamont-Doherty Earth Observatory … were able to determine accurate times of the plane impacts and building collapses using the seismic signals recorded at numerous seismographic stations in the Northeastern United States,” Won-Young Kim and Gerald R. Baum, “Seismic Observations during September 11, 2001 Terrorist Attack,” Maryland Geological Survey Earth Science Information Center Publications.
- Craig T. Furlong and Gordon Ross, “Seismic Proof – 9/11 Was An Inside Job (Updated Version II).”
- Point TT-8: “Why Did the Twin Towers Collapse? The Physical and Testimonial Evidence”
- André Rousseau, “Were Explosives the Source of the Seismic Signals Emitted from New York on September 11, 2001?” Journal of 9/11 Studies, vol. 34, November 2012. This peer-reviewed published article has not been challenged in the scientific literature.
- Kim et al., “Seismic Waves Generated by Aircraft Impacts and Building Collapses at World Trade Center, New York City.” The report also treated the collapse of WTC7, but it is not relevant here.
- The problem of the ‘displacements’ between the times of origin of the seismic waves and the times at which the planes crashed into the Towers, particularly that for WTC 1, is certainly a key question and one that is emblematic of all the contradictions of the official version of September 11, 2001, as already pointed out by Furlong and Ross in 2006. Rousseau also wrote: “There is a hiatus of 15 seconds between the plausible time of the origin of the Rayleigh wave based on the Palisades data and the time – afterwards – of the crash of the plane into WTC1 based on the ground radar data. … A similar discrepancy exists in the data for the seismic wave and impact times for WTC2,” Rousseau, “Were Explosives the Source of the Seismic Signals Emitted from New York on September 11, 2001?” p. 6.
- Rousseau, “Were Explosives the Source of the Seismic Signals Emitted from New York on September 11, 2001?” Abstract, p. 1.
- As indicated by wave amplitudes.
- A 2.1 magnitude shock releases 89 MJ (mega Joules), while a 2.3 event releases 178 MJ. These values are equivalent to 21 and 42 kilograms of TNT. One can check this on this calculator of energy released by magnitudes.
- Rousseau, “Were Explosives the Source of the Seismic Signals Emitted from New York on September 11, 2001?”
- “Three minutes of continuous data shown starting at 09:36:30 EDT (13:36:30 UTC). Data were sampled at 40 times/s and passband filtered from 0.6 to 5 Hz,” Kim and Baum, “Seismic Observations during September 11, 2001 Terrorist Attack;” Rousseau, “Were Explosives the Source of the Seismic Signals Emitted from New York on September 11, 2001?” p. 4.