Seismic Records of the Twin Towers' Destruction on 9/11/01

Seismic Records of the Twin Towers' Destruction:
Clarifying the Relationship Between Seismic Evidence and Controlled Demolition Theories
by
Jim Hoffman
Version 0.9, Oct. 31, 2006
911research.wtc7.net/essays/demolition/seismic.html

(excerpt)

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, as NIST's Answers to Frequently Asked Questions or Protec's Critical Analysis imply. 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 buckling "unsupported columns" as the explanation favored by most informed supporters of the official story. NIST's theory is essentially a pile-driver theory, 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.
Why Did the World Trade Center Collapse?-Simple Analysis,

It seems intuitively obvious that a smashing action sufficient to destroy the building would generate intense shaking. Figure 4 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.