A collapse scenario for WTC 7 --- The FEMA report on the collapse of WTC 7 appears to require 47 seconds from start to finish, much longer than the 18 seconds for the preliminary estimated time from the LDEO seismograph record. While the beginning of the collapse might not cause ground shocks, surely the final event, the collapse of the north wall, did. So this collapse scenario is just long enough to account for the 18 seconds of ground shocks. You may add more 'collapse' at the beginning if you wish. The events to be discussed occurred in the following order, with the stated times, taken from the previously posted video:

unobserved............................... 4 seconds
east penthouse sinks............... 5 seconds (first 3 to disappear)
west penthouse sinks.............. 2 seconds
north wall falls........................... 7 seconds
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total time................................. 18 seconds

Unobserved: The collapse is believed to initiate about floor 5--7. Some accounts state that floor 5 was burning most fiercely, others than it was floor 7. In either case, the fire was strongest in the eastern portion of the building, with flames coming out the windows in the east side. My choice of moment 0.0 is when enough of the lower portion of the east part of WTC 7 collapsed onto the ConEd station below to begin producing the seismograph trace of the entire event. Perhaps by this time up through floor 12, another floor with observed fires, had fallen. The east side continues to fall, from the bottom towards the top. The east curtain wall largely falls in, to the west. The east portion of the south curtain wall falls partly to the south, onto the street to the south.

East penthouse sinks: The east penthouse slowly sinks below the parapet of the north wall, developing a kink in the middle where the collapse of the penthouse and the roof is most pronounced. (The kink is not the 'kink' mentioned in the FEMA report. That one I will call a 'crease' and is not yet observed.) The east and south curtain walls continue as before; the north and west curtain walls are unaffected as yet. After the east penthouse has completely disappeared, it is possible to see daylight through at least one upper story window in the north wall toward the east end. This indicates that entire inner structure has fallen for the eastern approximately 1/3 of the building.

West penthouse sinks: This penthouse is about twice as long, east to west, as the other. It sinks out of sight behind the parapet of the north wall as the internal structure below it falls apart. At this stage the western portion of the south wall is falling as well. Again some goodly portion of it falls into the street to the south and some of the southwesterly-most portions actually end up on top of WTC 6 across the street to the south. Both the north and the west curtain walls continue to stand as the west penthouse disappears.

North wall falls: The north and west walls are now completely free of any connections except for the posts and beams of the curtain walls themselves. Also, the last remaining bracing below the curtain walls now fails. The north and west walls, largely in one piece at the beginning of the fall, fall freely. A substantial portion of the west curtain wall falls to the west of the WTC 7 site. The north wall, however, falls somewhat southerly, hence ending up draped over the WTC rubble pile. After these walls have fallen about 10 stories, a crease appears in the upper left hand corner of the north wall. This crease rapidly races, as a growing line, across the face of the north wall, both down and to the right. This approximately 30 degree crease indicates that the segments of the north wall have lost all internal structural integrity as the wall falls freely.

So: the scenario agrees with the debris field, the videos, the seismograph records, the firemen's reports on Firehouse.com, and --- to an extent --- various descriptions such as the FEMA report and (perhaps) what various NIST investigators have said. I haven't restated all of that evidence here, but I am now ready for comments, complaints, and interpretations.

Elevators were locked and could only  be opened from the elevator roof. The people trained to open the elevators were ordered to leave.