Hi,
I have found some evidence for explosion at the South Tower happening several seconds before the start of the collapse.
Quote from the official 9/11 Commission Report: "At 9:58:59, the South Tower collapsed in ten seconds". See Chapter 9.2 SEPTEMBER 11,2001:
Seismograms recorded by LCSN Station PAL:
See:
The seismic recording shows the time for a seismic event related to the collapse of the South Tower: 9:59:04. Notice here that this is the time for the recording at the PAL station. It takes about 17 seconds *) for the seismic wave to reach the PAL center from the source at WTC. Therefore the time for the seismic event at the source was: 9:58:47.
The time difference between the start of the collapse 9:58:59 and the recorded seismic event at the source 9:58:47 for the South Tower is 12 seconds. This indicates that an explosion happened at the WTC about 12 seconds before the start of the collapse of the South Tower.
I have seen claims that the time scale on the x-axis of each seismogram shows the time at the source, not at the PAL station where they were recorded. But the diagram says: "East-West component of motion at PAL". Indicating the time at the source wouldn't make sense for a seismogram, and if the time indicated was at the source then we get an inconsistency between the time stated in the official 9/11 Commission Report and the time recorded at the PAL station. This cannot be blamed on low signal-to-noise errors in time measurement at the PAL station since this was a huge seismic spike.
*) "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." -- From:
http://911research.wtc7.net/wtc/analysi ... efall.html