We are all deeply saddened by the loss of life and property associated with the
horrific attacks on the U.S. by terrorists yesterday. One unique perspective which
those who follow this board may find interesting is to view the seismograms
from LaMont Doherty Seismic Observatory of the sequence of events. These are
some of the largest traces I have seen on these on-line seismograms.
You will want to adjust the seismograms you see. At the bottom of the page
select ALL stations, and hit previous day two times to get to 11 September, then
click on SELECT.
There are two events which appear to relate to the tower collapse that I
can see - the first is at 13:59 UT - a vertical line on all seismograms and the
second at 14:28 UT (10:28 EDT - Eastern Daylight Time is four hours earlier
than UT). The second tower collapsed at approximately 10:30 EDT - could this
have been a precursory signal that the tower was about to collapse. Likewise,
the first collapse occurred at 10:09, but the signal is at 9:59 a.m. (13:59 UT).
It is also interesting to look for other major events in the sequence - I can't
find any signs of the planes colliding with the towers, for example. This
happened at about 8:50 EDT and 9:00 EDT.

• Seismograms from New York City area