The story...

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...

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.
http://www.serendipity.li/wot/bollyn2.htm

Our take...

This story uses the following chart to make its point.



And indeed, it does look like the spikes occur early on, but that's mostly because the chart is so compressed. If you look at the actual spikes for each collapse ( as recorded at http://www.ldeo.columbia.edu/LCSN/Eq/WTC_20010911.html ) then the results are very different.


Here’s the first collapse, for instance...


And this is the second.


The original story tells us that “the strongest jolts were all registered at the beginning of the collapses”, but it doesn ‘t look that way here, does it? What we have, in both cases, is a noticeable build-up lasting a number of seconds, showing a gradual start to the collapse. The strongest jolts are not at the beginning; the claim is simply incorrect.

Do we have the qualifications to interpret these correctly, though? Nope, none whatsoever. Arthur Lerner-Lam, a seismologist at the University that recorded these readings does, though, and his statement to Popular Mechanics doesn’t leave much room for interpretation.

"There is no scientific basis for the conclusion that explosions brought down the towers," Lerner-Lam tells PM. "That representation of our work is categorically incorrect and not in context."
http://www.popularmechanics.com/science/defense/1227842.html?page=5&c=y

Geophysicist Terry Wallace concurs.

"How can geologists catch a terrorist? With their instruments, explains Terry Wallace, a geophysicist at the University of Arizona. There are about 16,000 seismometers installed around the world, many of which offer data on freely accessible Web sites. Seismometers detect motion in the Earth, which can be triggered by an earthquake, or possibly explosions.

By learning how to read these signals, Wallace hopes scientists might catch on to suspicious activity.

"We can study these signals and begin to develop a portfolio of different kinds of signatures of explosions," says Wallace. "It will be like have a set of fingerprints."

Geophysicists have already contributed critical data to terrorist investigations. It was geologists who determined there were no secondary explosions at the base of the World Trade Center towers — but only the impact of the airplanes and subsequent fires — that contributed to the towers' collapse on Sept. 11".
http://www.globalsecurity.org/org/news/2002/020527-secure.htm

Not much support for “bombs in the basement” here.