Reply #63: You are right about the 17 seconds disparity (not 15)...

[quicknthedead]

but to say seismic data is inferred, well, maybe a better way to say it is there must be enough "strong" data recorded to get an accurate time of origin.

Read Kim here about the Pentagon crash and how this relates to this question we are discussing:

(1st paragraph--1st page)
http://www.mgs.md.gov/esic/publications/download/911pentagon.pdf

Good seismic data depends has many variables, all of which can help to accurately compute origin times. Origin times are computed from data collected from station proximity, type of bedrock, number of stations, depth of signal, etc.

With good data, accuracy is precise, and has been for years; it was back on 9/11/01. The Lamont-Doherty planes "impact" data was very reliable, tracked from Palisades 21 miles away with origin times computed with a high confidence level to plus or minus 1 second for AA Flt 11 and plus or minus 2 seconds for UA Flt 175.

As Dr. Kim wrote, Palisades was "only about 34 km away from the WTC."

Did I mention that LDEO is also on the world atomic clock, just like the FAA and the radar they use?