> The pyramids aren't rectangular box buildings, of course. I
> could imagine a severe earthquake causing a vertical wall to
> fail, but not an inclined wall which has an inward tilt.
> How much shaking would be required to displace 17 ton blocks
> which have an inward lean and are set at almost 40 degrees off
> the vertical?
You're right of course that a block composing part of a cladding that slopes at 52 degrees is far far less susceptible to falling than a stone in a vertical wall. But in an earthquake it's the entire earth that's moving; it's the very ground on which each block sits. To a large extent each block will move in the same direction relative one another but there are interferance patterns and other effects which will cause even adjacent stones to move in significantly different directions. Since there is relatively internal damage or core stone damage visible on any of these it's very unlikely that an earthquake could have caused the cladding to fail catastrophically except in small regions.
I'm picturing hundreds of stones lying at the base of the pyramid and the entire cladding "loosened". Damage at the corners would be particularly severe because corner stones are required tohold stones on either side but are supported only above, below and two adjacent sides. Other stones are supported and kept from moving on three sides including opposite sides.
Apparently the pyramid was still structurally sound in 400 BC when Herodotus reported that most gaps between stones were invisible but there might have been some deterioration caused by heat stress (expansion) and other processes by the time of the earthquake about 1256 AD.
I believe it was the destruction at the corners that even allowed men to get up here and work methodically and safely to strip the stone. If the cladding stone was intact it would have been too costly in terms of human life to remove. The stone recyclers couldn't have made ramps to get to the top any more than builders could have. If they had made such a means to get up then they'd have gone all the way to the top of G2 rather than near the top.
There are a very limited number of ways to remove this cladding and I agree any earthquake sufficient to cause a collapse would have collapsed the entire structure. But the earthquake that leveled Cairo probably made it possible to remove the cladding to rebuild it.