World Trade Center Disaster

Here is a summary of seismic observations of the
two impacts and the three collapses:

DateOrigin
Time (UTC)		Magnitude
(Richter scale)		Time
(EDT)		 Dominant
Period		Signal
Duration		Remark
09/11/200112:46:26±1 0.908:46:260.8 sec12 secondsfirst impact
09/11/200113:02:54±2 0.709:02:540.6 sec 6 secondssecond impact
09/11/200113:59:04±1 2.109:59:040.8 sec10 secondsfirst collapse
09/11/200114:28:31±1 2.310:28:310.9 sec 8 secondssecond collapse
09/11/200121:20:33±2 0.617:20:330.7 sec18 secondsBuilding 7 collapse

Location of the World Trade Center is 40.71°N and 74.01°W.

Seismograms recorded by LCSN Station PAL (Palisades, NY)


Four seismogram traces showing the two hours of seismogram recorded at Palisades (PAL), New York. Each trace is 30 minutes long. The first trace starts at 08:40 (EDT), second trace starts at 09:10 (EDT), third at 09:40 and the last trace starts at 10:10 (EDT; 14:10 UTC). Notice the seismic signals from the first impact at 08:46 EDT, second impact at 09:03 (very small), two large signals due to collapse of the World Trade Center buildings at 09:59 and 10:28 (EDT). We understand from news reports, that the first impact (0846 EDT) resulted in the second collapse (1028 EDT), and the second impact (0903 EDT) resulted in the first collapse (0959 EDT).


Lynn Sykes, Paul Richards, Won-Young Kim, Jeremiah Armitage, Klaus Jacob and Art Lerner-Lam
at Lamont-Doherty Earth Observatory of Columbia University
contributed to this note and seismogram images.