The events of 9/11 weren’t only captured with cameras: a group of seismic monitoring stations also recorded both the plane impacts, and collapses of the WTC towers. And in both cases, it’s been reported that they indicate the use of explosives.
The Journal of 9/11 Studies paper “Seismic Proof - 9/11 Was An Inside Job”, for instance, points out that the seismic records for both impacts gives one set of times, while the 9/11 Commission use another method, producing impact times that are as much as 17 seconds later. Does this prove there were massive explosions before the planes hit? Here are our thoughts.
And an older story explains that there were large spikes at the beginning of the collapse of each tower, indicating that explosives were used to bring them down. More here.