My previous point is that the leading floor of your collapse front (OOS sw front) seems to arrive at floors 77, 75 at the exact same time we see the emergence of the point ejections from those same floors.
If this were true, ....well....that would be incredible. Why? Because it confirms that there are pairs of floors which become overpressurized at a rate which cannot compare to the floors either above or below.
The destruction wave in the south might have initially started with the collapse of 98fl south perimeter (earliest possibility). That destruction wave looks much like some very fast "pancaking" (4.8m/s²) and reaches the lower dust jets 56/55 and 41/43 in time.
Nevertheless, there is no way for that front to reach the floors of the dust jets 85/87 and 75/77.
Hi Res diagram: http://img52.imageshack.us/img52/3508/snapc.jpg
In the above diagram you see the start times of all the jets 55 and above (as visible in a lot of different videos). The fat red curve represents a 4.8m/s² acceleration beginning at the 98th floor at a time 0.7 seconds prior
to the onset of the tilting. I have chosen that moment because it is the end of a 0.7 seconds pause in the seismic records. Pause? Yes - imo something either lost connection or stopped to move - something like that. If the floors collapsed at this time and prior to the tilting then the front would reach the 55th floor in the moment of the dust jet as observed. These collapses are much to slow to reach all the above dust jets. It seems to be impossible that the destruction of the south side started earlier. Videos of the west and south west showing no sign of a collapse prior to the tilting and the huge dust clouds immediately after.
But the situation gets worst. Even free fall acceleration (inside the shafts) cannot reach these dust jet-start times and elevations (thin red curve). As you can see in the gives I posted the 75/77 jets match the hallways BUT there is one floor between left out (same for all pairs). In the Lethin photos it appears that the west jets came from the floor above but these photos where shot from the north and from below. Hence, we are looking upwards.
Furthermore, not all jets came from the hallways e.g. the 44W jet occurs opposite to a wall (columns). The position of the 85 jets makes no "logical" sense too (other than the columns).
Finally the piston theory is highly questionable. The 85 jets emerged while the south collapse (invisible and away from the perimeter) was still in the impact zone. The 3psi fuel-air explosion and subsequent fires had taken everything out of the way of the pressure: windows, elevator doors... The collapse itself was still "slow" (less than 2 seconds after the north face collapse.)
Nevertheless dust jet 75/77 emerged prior to the fireball from floor 92. The pressure - if there was any significant pressure at that time - cannot have passed the opened windows on 93 and 92 and generate extreme and ongoing overpressure 70 meters below. It wasn't just some shock wave but it seemingly started with a shock wave.http://www.youtube.com/watch?v=acTcwA_YHuA
In this video you can see that something really big was shot between the columns at 77W. A short time later the same window was hit by that overpressure and a lot of dust was blown far out. That big sticking thing was finally blown out too.
And back to the theme of this thread: The 77W dust jet looks exactly like the 55W dust jet. The 55W dust jet emerged on a floor in the very same moment that floor was hit by a fast and violent destruction wave in the south (no visible sign in the north but a dust jet). 77 was not hit by a destruction wave. 85 neither. But it looks like a shockwave followed by the same jets that apparently are connected to the destruction front. Either they aren't or there is an invisible collapse going on at the lower escalator 77 and the lower MER floors.
"there are pairs of floors which become overpressurized at a rate which cannot compare to the floors either above or below." Exactly!