Baluncore
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The wall shown is blocky, not slick or scarred, so it looks like it failed in tension, not as the surface expression of a vertical shear fault.dlgoff said:This image ... blows my mind:
What appears to have happened is a solid landslip. A large block of sedimentary rock on a hillside with a similar slope to the bedding, slid down-slope on an incompetent mudstone layer, leaving that precipice as the headwall.
The rock slide event was triggered by the earthquake. The foot of the rock slide is not shown. If the block was wedge shape, then the foot of the slide may be insignificant.