Baking,
The stacks are constrained, by the configuration: the top attached to the PIG and the base attached to the SIS, to straighten and therefore to compress: more it is vertical (relative to the PIG) and more the distance between the base and the top is small.
If it is the last point of strong shear, then the game is done.
Concerning the fact of controlling in detail what happens in the ZD I notice that even with Sentinel2 is not a small matter, a small animation is not enough to show the force fields, in reality we risk to see what we want to see => demonstration value 0.
Indeed currently there are no more big blocks for which we can observe the deformations more easily: formation of the bulges, measure the shortening due to compression, deduce the direction of the compression, make precise diagrams of their possible movements and see the stresses and measure them, as we have done in some moments for the Cork. This is even more difficult with Sentinel1. As you can judge what happens between two blocks by looking at the white spot that separates it? And there are too few fractures to evaluate the forces in action.
It's like predicting the future by looking in the back of the coffee, it's a waste of time.
On the other hand, it might be interesting to see if an a posteriori analysis of what happened this winter, a real analysis, not two, three arrows drawn on a picture. It should be possible, but his request for time...
As regards cR1, this rift was born as an extension of mR1 beyond a point of resistance (a ridge), but, at least for me, and since the calving corresponding to the complete opening of mR1, it has become a central rift and it lives its life as a central rift under the constraints of a central rift.