This might help answer your question GB. Watch the 2 short videos first and you will distinctly hear the blasts as the building is coming down. Just as these fire fighters saw, heard and explainedI agree wholeheartedly.
However, is it possible, that since the basement was so deep, that they just needed to detonate the lowest floor or floors, the explosions for which were not discernible on video?
As you said, I don't see the bottom floors collapsing in tandem with the top floors like you see in controlled-demolition videos.
I just see top few floors crashing down on all the rest.
https://www.youtube.com/watch?v=Iya_s7J7K6Y
https://www.youtube.com/watch?v=XiIT4HInWjY
The audio evidence clearly and distinctly denotes 23 "BOOMS" and NOT 80-100-some punch-press "KLANGS" which would be what a "pancake collapse" would sound like.
The twin towers were brought down by a self-righting helical-cut 5 storey wedge-frame internal steel frame "corkscrew" wedge demolition plan.
1st: Bedrock supported core columns above the basements (below the lobbies) are cut and explosively have wedge cut sections blown out of them in the parking and mechanical levels (3-4 stories up). These preperatory support-removing early morning blasts timed to go off as the planes hit, pre-load the entire vertical structural weight of the core columns and inside floors against the concrete core instead dropping the lobby cores and pulling in the weight of the inner structure against the outer "steel core can" of the building, guaranteeing a concentric "footprint" demolition implosion.

3 story high bedrock base-core beam 3 feet X 5 feet solid steel (top not photographable nor viewable)
The towers were three 32 floor buildings with separate fire-sealed containment so no jet fuel could "leak" from the 80th floor to any point below the 68th floor (2nd Sky Lobby) under any circumstance.
2nd: Diagonal wedge-cut 5 story high core frame sections were thermate®-heat trimmed into sequential North-West-South-East "wedges". This guarantees they will remain righted on top each other as they slide over into themselves, battering each other from above while "coring" the concrete core-can and inside steel and concrete floors as cutter-edge-expanded floor and cross-brace battering rams.

remaining inner section of a corkscrewed core frame wedge
3rd: 23 massive RDX or HTC bombings are necessary while the pre-cut cut steel is still white hot in sequential
Top-down North-East-South-West concrete sides of the inner core to outer floor connections to allow the 5 story battering rams to pull in
the upper floors connected to each at the top while wedging through the floors below as a giant core corkscrew demolishing the internals while still held upright by the outer core frames as they drive down.

Note the extensive internal cross bracing of core steel frames before floors are attached and concrete core walls are poured
THIS IS WHY YOU HEAR 23 BOOMS
If there was a "pancake collapse" of just the floors you'd have ended up with 68 floors of steel core still standing and at least 80-100 KLANGS.