A bomb placed at the base of the slab could certainly lead to a directional debris field. The stone closest to it gets ejected directly away from where it was placed which makes sense. The rest of the stone (at the upper part of the slab) collapses downwards as the bottom got blown out). The power of the explosion dissipates really really fast the farther away you get (its probably not a very powerful bomb) meaning the other stones are largely unaffected.