Seismic Records of the Twin Towers' Destruction:
Clarifying the Relationship Between Seismic Evidence
and Controlled Demolition Theories
Version 0.9, Oct. 31, 2006
The total destruction of each of the Twin Towers produced seismic signals
that were recorded by at least 5 seismic observatories
within 60 miles of lower Manhattan.
The published charts from the
Lamont-Doherty Earth Observatory in Palisades, New York,
have been cited as evidence supporting the following two claims:
- Each Tower fell completely in 10 seconds or less
- The largest seismic spikes preceded the fall of each Tower
Both of these claims can be found in a large cross-section of literature
challenging the official story.
The first claim is also accepted by many defenders of official collapse
theories, and is even found in the
9/11 Commission Report
In this essay I will examine these widely-repeated claims
and show that,
despite their popularity,
they both lack supporting evidence
and are contradicted by verifiable evidence.
I will, however, also show that the seismic records
do support the case for controlled demolition,
but in a way that has been overlooked.
I have previously addressed both claims on these pages:
In this essay I will provide a more focused and complete exposition
of these issues.
Do Seismic Records Really Show that the Towers Fell in Ten Seconds?
Because the claim that the Towers fell in ten seconds
has historically been uncritically repeated
by defenders and detractors of the official story alike,
most newer researchers have not taken the time to closely examine its validity.
The idea that seismic records from distant recording stations
could be used to establish the duration
of a building collapse or demolition is highly questionable on its
face given the complexities inherent in interpreting seismic data,
such as the indirect relationship between ground movement
at a source and and at an observatory miles away.
the assertion that seismic records from observatories
such as that in Palisades
establish that each Tower collapsed within ten seconds is widespread.
Origin of Claim that Towers Fell in Ten Seconds or Less
The assertion that both Towers fell in ten seconds or less apparently
originated with proponents of the collapse theory less
than a month after the attack.
An article in the Journal of the
The Minerals, Metals & Materials Society
contains the following:
This started the domino effect that caused the buildings to collapse
within ten seconds, hitting bottom with an estimated speed of 200 km per hour.
If it had been free fall, with no restraint, the collapse would have
only taken eight seconds and would have impacted at 300 km/h.
Table 1.1 from Chapter 1 of FEMA's WTC Building Performance Study.
The statement cites reference 1, which is listed as
"1. Presentation on WTC Collapse, Civil Engineering Department,
MIT, Cambridge, MA (October 3, 2001)."
Most of the more contemporary references to the ten-second collapse times
appear to have originated with FEMA's
Building Performance Study.
Although the Report makes no claim about how long it took the Towers to
it includes the chart on the right describing the duration
of seismic signals.
That chart gives 10 and 8 seconds for the durations of the signals
corresponding to the South and North Tower "collapses", respectively.
Apparently, the only official report that gives a duration
for either of the "collapses"
is the 9/11 Commission Report,
which states that the South Tower collapsed in ten seconds in
Chapter 9, Section 2:
At 9:58:59, the South Tower collapsed in ten seconds,
killing all civilians and emergency personnel inside,
as well a number of individuals-both first responders and civilians
-- in the concourse, in the Marriott, and on neighboring streets.
The building collapsed into itself,
causing a ferocious windstorm and creating a massive debris cloud.
This passage cites reference 156, which is listed as
'Progress Report on the Federal Building and Fire Safety Investigation
of the WTC,'
June 18, 2004, appendix H, p. 40."
However, wtc.nist.gov lists no publication dated June 18, 2004, and
NIST-SP 1000-5 June 2004
Progress Report on the Federal Building and Fire Safety Investigation
of the World Trade Center
does not appear to provide any estimate of either Tower's collapse duration.
Video Records Show 15-Second+ Durations
Unlike seismic records,
video recordings of the Towers' destruction
allow the conclusive determination of
lower bounds for the durations of each event,
and those are much greater than ten seconds.
Several live television broadcasts showed these events from their
precipitous onsets to their explosive dust-shrouded conclusions.
In each case, portions of the Tower below the exploding rubble clouds
are visible up to at least the 12 second mark.
The North Tower at about 10 seconds into its destruction.
About two-thirds of the Tower is still standing.
Lacking access to the uncut original broadcasts,
timelines for each Tower
using multiple video clips.
These timelines clearly show that,
in the case of each Tower,
the process of destruction lasted a minimum of 15 seconds,
not counting the persistence of fragments of core structures.
This is true even accounting for uncertainties in precise times of onsets,
greater uncertainties in the times of completions,
and margins of error in the compositing of the timelines.
The onsets of the events are different in the two Towers.
The South Tower's top leans for about two seconds before
the roof starts to plunge downwards,
whereas the North Tower's roof begins its plunge about a half second
after its radio antenna begins to drop.
In both cases I used the first evident motion --
the rotation of the South Tower's top, and the drop of the North Tower's antenna --
to set the timeline origin.
Using these timelines, it is clear that large portions of each Tower
below the descending debris clouds remained intact at the 10-second mark.
Reasonable estimates for the duration of these events are around 17 seconds.
Did Seismic Spikes Really Precede Collapses?
The claim that seismic "spikes"
preceded the collapse of each Tower
has been uncritically reported by numerous
websites, books, and videos challenging the official collapse story,
Loose Change, and
The claim is that the greatest ground shaking,
whose estimated local magnitude was 2.1 and 2.3 on the Richter scale,
occurred before or at the beginning of the destruction of each Tower,
not at the end as the falling rubble was impacting the ground.
Origin of Claim that Spikes Preceded Collapses
The claim that the largest seismic signal marked the beginning
of the destruction of each Tower apparently originated with
reporter Christopher Bollyn,
who published in August 28, 2002 the article
"Seismic Evidence Points to Underground Explosions Causing WTC Collapse"
in the American Free Press,
the sister publication of the Hitler-lionizing Barnes Review.
That article, commented on
includes the following:
Seismographs at Columbia University's
Lamont-Doherty Earth Observatory in Palisades, New York,
21 miles north of the WTC, recorded strange seismic activity
on September 11 that has still not been explained.
While the aircraft crashes caused minimal earth shaking,
significant earthquakes with unusual spikes occurred at the beginning
of each collapse.
The Palisades seismic data recorded a 2.1 magnitude earthquake
during the 10-second collapse of the South Tower at 9:59:04
and a 2.3 quake during the 8-second collapse of the North Tower at 10:28:31.
The Palisades seismic record shows that -- as the collapses began --
a huge seismic "spike" marked the moment the greatest energy
went into the ground.
The strongest jolts were all registered at the beginning of the collapses,
well before the falling debris struck the earth. These unexplained "spikes"
in the seismic data lend credence to the theory that massive explosions
at the base of the towers caused the collapses.
-- Christopher Bollyn, American Free Press
The article mixes facts about the
Lamont-Doherty Earth Observatory's charts
with unfounded assertions.
While it's true that the station recorded 2.1 and 2.3 magnitude quakes,
Bollyn provides no evidence that the spikes occurred at the beginning
of each "collapse".
This story was reproduced by numerous websites, and continues to be cited
even by scholars who apparently have failed to check the validity
of its claims.
After first providing some background on seismology,
I will provide three lines of analysis showing that the
largest seismic signals correspond
to the times that the rubble was reaching the ground,
not to times at or before the onsets of the Tower's destruction:
Interpreting the data from seismographs
is not as straightforward as implied by the article
"Seismic Evidence Points to Underground Explosions Causing WTC Collapse".
Seismology is a science typically practiced by scientists
with graduate degrees in seismology or geophysics.
Correctly interpreting the data from seismometers
includes considering such factors as:
- Different response characteristics of different seismometers
- The various types of seismic waves and their propagation characteristics
- Different rates of propagation of a given type of seismic wave through
different types of soil and rock
The first factor is typically dealt with by processing the instrument data
with various functions such as convolution filters.
The graphs presented on this page have already been massaged in some way.
The second factor arises from there being four distinct types of seismic waves,
which belong to two categories:
body waves, which can propagate deep underground,
and surface waves, which propagate near the surface.
Body waves come in two types:
P or pressure waves, which oscillate in the direction of propagation, and
S or shear waves, which oscillate perpendicular to the direction of propagation.
Surface waves also come in two types:
Rayleigh waves, which cause the ground to move laterally, and
Love waves, which cause it to undulate vertically.
Each of these waves has different propagation rates,
which are similar for the two types of surface waves.
Figure 3: Vertical components of the North Tower event
recorded by seismometers at five different observatories
According to the article
Seismic Waves Generated by Aircraft Impacts and Building Collapses
at World Trade Center, New York City
by scientists at the Lamont-Doherty Earth Observatory of Colombia University,
seismometers at the various observatories recorded
only surface waves arising from events in lower Manhattan on 9/11/01.
The third factor can result in different observatories producing
very different seismograms for the same event,
because of the differing ground structure between the source
and the different observatories.
Consider Figure 3, which shows recordings
of the North Tower destruction made at five different observatories.
The graphs are arranged in order of the distance
of their respective observatories from the World Trade Center,
with the Palisades chart being the first.
The length of the high-amplitude signal varies from about six seconds
for the observatories labeled TBR and ARNY
to about 18 seconds for the one labeled MANY.
The signal recorded by the observatory at Palisades (labeled PAL)
has an intermediate length of about 10 seconds.
According to the Colombia University scientists,
the differing durations of the signals recorded by the different stations
was a function of paths the wave packets took from their source to
the various stations.
Whereas waves followed relatively simple paths
to the TBR, ARNY, and BRNJ stations,
their traversal to the MANY and PAL stations up the Hudson was complicated
by different strata of rock with different traversal speeds.
The scientists concluded that the source event
was about 5-6 seconds in duration,
meaning that the signal at PAL was spread out by about 4 seconds.
The 'Large Spikes' Were Preceded by Smaller Signals
With the benefit of this background information let's look
at a PAL seismogram in Figure 4, below.
which represents horizontal ground displacement
produced by the North Tower's destruction.
At about 5 seconds into the graph we see a transition from background noise
to a distinct signal with a period of about 0.8 seconds.
That signal continues up until the onset of the large signal
at about 17 seconds,
becoming slightly stronger at about 9 seconds.
The first signal thus starts about 12 seconds before the large signal.
Since the spread of about 4 seconds would affect the small and large
the arrival of the first signal about 12 seconds before the large signal at PAL
indicates the onset of an event generating a smaller disturbance
about 12 seconds before an event generating the large disturbance
at the source.
A similar pattern is evident in the seismic records
from the other observatories.
Figure 4: East-West component of the North Tower event recorded at PAL
If we now review the video timeline of the North Tower,
we see that the rubble begins to reach the ground about 12 seconds after
the roof begins to drop.
Thus, the PAL chart, and those of the other observatories,
show a pattern of seismic activity that fits the following interpretation
of the North Tower's destruction.
As the Tower breaks up from top to bottom,
it generates a seismic disturbance of relatively consistent magnitude
lasting as long as it takes the destruction to reach the ground --
about 17 seconds.
At about 12 seconds into this event,
this signal is eclipsed by the much larger disturbance of thousands of tons
of material impacting the ground.
Correlating Seismic and Video Records of the North Tower
Frames from CNN's live broadcast at 2 second intervals
In my earlier
analysis of the Towers' speed of fall
I attempted to establish a correspondence between
the CNN live broadcast of the North Tower's destruction
and a seismogram from PAL showing that event.
Correlating the timelines of these two pieces of evidence is possible
because the CNN broadcast shows a real-time clock,
the seismic records include precise time coordinates,
and the travel time of seismic waves between the source
and seismic observatory can be estimated.
The CNN live broadcast of the North Tower destruction,
which is excerpted by this
has a real-time clock on its banner which displays hours and minutes.
The minute counter flips from 28 to 29 about 37 seconds after
the roof starts to drop.
On that basis,
I estimated, in 2003, that the North Tower's destruction started at 10:28:23.
That is one second from the time NIST assigned to the event in its 2004
Draft Report on the Twin Towers: 10:28:22.
Reports published on colombia.edu
estimate that the start of the large signal originated at
The large spikes began to reach the PAL seismometers starting at around
Since Colombia scientists estimated that the surface waves traveled
at about 2 km/s, and the station is 24 km from the World Trade Center,
they placed the time of the onset of the large signal at the source at
17 seconds before the signal arrived at the observatory.
10:28:31 -- the estimated start of the large signal --
is 9 seconds after
10:28:22 -- the estimated start of the North Tower's destruction.
Video recordings show that the rubble started to reach the ground about
12 seconds after the start of the destruction.
These times fit the interpretation that the large signal corresponded
to rubble hitting the ground,
modulo an error of about 3 seconds.
That error can be explained by the spread in arrival of wave packets
To summarize, the video and seismic data support the following
approximate timeline for the North Tower's destruction:
||North Tower roof starts to drop (small signal starts)|
||Rubble starts to hit the ground (large signal starts)|
||The heaviest rubble hits the ground (large signal peaks)|
||The Tower is completely down,
except for fragments of the core|
Rubble Ground Impact Energy Explains Large Signal
that first claimed that
a "huge seismic 'spike'" marked the beginning of each "collapse",
also asserted that the signals were "strange", "unusual", "unexplained",
and support a theory that
"massive explosions at the base of the towers caused the collapses."
However, none of these assertions are supported by the scientists
at Lamont-Doherty Earth Observatory that Bollyn interviewed.
Those scientists reported that the seismic energy
represented only a fraction of the gravitational potential energy
released when the Towers came down:
The gravitational potential energy associated with the collapse of each tower
is at least 1011 J. The energy propagated as seismic waves
for ML 2.3
is about 106 to 107 J.
Hence, only a very small portion of the potential energy was converted
into seismic waves.
Visual records of the events themselves and their aftermath clearly show
that most of the mass of the Towers fell outside their footprints.
Tens of thousands of tons of steel assemblies fell through the air --
some of it from a height of more than a thousand feet --
before hitting the ground.
It is difficult to imagine that any events
prior to the rubble hitting the ground
could have produced anywhere near as much ground shaking.
Even the detonation of large bombs in the building
would have been dwarfed by comparison.
According to the same scientists, the 1993 basement bombing did not
produce detectable seismic signals:
A truck bomb at the WTC in 1993, in which approximately 0.5 tons of explosive
were detonated, was not detected seismically,
even at a station only 16 km away.
The 1993 explosion was so intense it blew a cavity about 5 stories high
in the parking garage, constructed of steel-reinforced-concrete.
Being in the basement, it was presumably well-coupled to the ground.
Cutter charges needed to sever the Towers' core columns
would be tiny by comparison.
The claim of "massive explosions at the base of the towers"
at the onsets of the Towers' destruction
is echoed by the 2005 film
and other productions.
None of these produce credible evidence to support this idea,
which is contradicted by the visual records including
most credible and extensive body of eyewitness accounts.
The Seismic Records as Evidence of Controlled Demolition
Although the seismic records from the
Doherty Earth Observatory and other recording stations
don't support the theory of controlled demolition put forth by
Christopher Bollyn and other proponents of
basement bomb scenarios,
they nonetheless do support the case for controlled demolition,
albeit in an indirect sense.
The term controlled demolition has a broader meaning
than many people appreciate.
It does not require that a building be destroyed from the ground up,
Answers to Frequently Asked Questions
It simply means the destruction of a building in a controlled,
or engineered, manner.
In the case of the Twin Towers' top-down destruction,
it is the only alternative to the premise of the official story
that the Towers collapsed due to impact and fire damage.
Hence a disproof of this premise
would constitute a proof of controlled demolition.
A disproof of a particular theory satisfying that premise
would not prove controlled demolition since another theory,
perhaps yet undiscovered, might explain the collapses.
However, it is clear that a substantial number of experts have
put a great deal of effort in coming up
with the most plausible collapse mechanism that money can buy.
To disprove the explanation endorsed by NIST
-- the agency that has put more than $20 million into researching the issue --
would be strong evidence for controlled demolition.
A number of different theories of the Towers' collapse have been advanced
by proponents of the official story,
with the two most extensive government reports endorsing
mutually contradictory theories.
NIST's theory of
"column instability" leading to "global collapse"
has replaced FEMA's theory of
floor pancaking leading to the buckling of "unsupported columns"
as the explanation favored by most informed supporters of the official story.
NIST's theory is essentially a
in which the top of the Tower smashes the intact portion of the building
to oblivion, from the crash zones downward.
NIST hides the fact that it depends on this theory by
failing to acknowledge the progressive nature of the event.
Once the upper building section began to move downwards,
the weakened structure in the impact and fire zone was not able to absorb
the tremendous energy of the falling building section
and global collapse ensued.
-- Final Report of the National Construction Safety Team
on the Collapses of the World Trade Center Towers
The pile-driver, AKA sledgehammer,
theory explains the destruction of the intact portion of the Tower
by the smashing action of the falling block.
NIST hasn't described the scenario, but Professor Bazant did in a paper
published in the
Journal of Engineering Mechanics ASCE:
At that moment, the upper part has acquired an enormous kinetic energy
and a significant downward velocity.
The part of building lying beneath is then impacted again
by an even larger mass falling with a greater velocity,
and the series of impacts and failures then proceeds all the way down.
It seems intuitively obvious that a smashing action sufficient
to destroy the building would generate intense shaking.
shows that the large signal is about 24 times the magnitude of
the small signal that precedes it for about 12 seconds.
Assuming that displacement magnitude is proportional to power,
it follows that there was about 24 times as much energy being released
at the peak of rubble hitting the ground
than was being released at any one time
in the 12 seconds before the rubble started to reach the ground.
Since the Tower was mostly destroyed by the time the large signal started,
the small signal has to account for the vibrational energy transferred
through the columns to the ground
from all of the smashing and crushing that was required to destroy
the 95 floors of intact steel and concrete below the impact zone.
Yet that energy was dwarfed
by the energy released by the rubble hitting the ground.
Most expositions of collapse theories invoke the "tremendous energy"
of falling mass impacting the floors below
to explain the thorough destruction of the Towers.
Yet the seismic records clearly show that the vast majority of this mass
did not participate in the destruction of the Towers
since it evidently did not encounter substantial resistance to its
descent until it reached the ground.