Earthquake Event Reports

Seismic Summary Briefings

Special Reports

"Though the Earth Be Moved" - The 1964 Great Alaska Earthquake

Anatomy of a Mega-Quake - The Great Tohoku Earthquake of 2011

World Trade Center Disaster Seismic Signatures

Earthquake Weather - Fact or Fiction?

The World's Largest Recorded Earthquake

The Seismic Signature of Tornadoes

Earthquakes in North Alabama - North and North-Central Alabama Seismicity

World Trade Center Disaster Seismic Signatures

The terrorist attacks against the United States and the World Trade Center (WTC) in New York City on the morning
of September 11, 2001 not only created shock waves in the political and social fabric of the United States, but also formed a
tragic backdrop to a most interesting seismic study of artificially-generated seismic signals and how these compare to the
seismic signatures from earthquakes. Ground vibrations associated with the collapse of the World Trade Center buildings were
recorded across five states, and as far away as 428 km (265 miles) from New York City. The terrorist attacks produced a complex
array of signals generated both from the initial impact of the airplanes, to the collapse of the WTC Towers and subsequent
collapses of neighboring buildings. As will be shown, the North Tower collapse produced a
seismic signature equivalent to a magnitude 2.3 earthquake.

WTC Bombing

Actually, several seismic stations in the greater New York City area recorded signatures of ground vibrations from the terrorist attacks
that morning in lower Manhattan (see Figure 1). The closest was the Lamont-Doherty Cooperative Seismic Network (LCSN)
station PAL located at Palisades, NY. Lamont-Doherty operates 34 seismograph stations in seven Mid-Atlantic and New England
states. The network has been in operation since the early 1970s.

NYC Seismic Stations

Figure 1
Seismic Stations Near Greater New York City
Numerous seismic signals were recorded at station PAL, first a smaller signature when the airplanes impacted the WTC towers,
and then much larger indications as the towers collapsed. The timeline for the two building impacts and subsequent three collapses
of the North and South Towers and the smaller WTC Building 7 begins at approximately 12:46:26 UTC (8:46:26 EDT) and shows
Richter Scale Magnitudes from 0.9 to 2.3

WTC Bombing Times
WTC Impacts and Collapse Times and Richter Scale Magnitudes
The seismogram from station PAL shows that the WTC North Tower collapse was the largest seismic source and had a local
magnitude ML 2.3 (see Figure 3). The seismogram begins at 12:40 UTC and each trace in the seismogram is 30 minutes long.
The North Tower was subject to the first impact (8:46 EDT) and the second collapse (10:28 EDT, magnitude 2.3), while the
South Tower saw the second impact at 9:02 EDT and collapsed first at 9:59 EDT (magnitude 2.1).

WTC Bombing Seismograms
Figure 3
PAL Seismogram from WTC Impacts and Collapses, 11 Sept 2013

Overall, six stations within the greater Metropolitan New York region (Fig. 4) recorded the two tower collapses. Unfortunately, no
seismic recordings of ground motion are currently known to exist at or very close to the WTC complex. Figure 3 shows the North
Tower collapse signature at stations PAL, BRNJ, TBR, MANY, and ARNY, indicating the different times (in seconds) after
the collapse at which the seismic signals were detected at the several stations.