as the land above subsides due to gaps in the soil underneath due to tectonic activity, the area above that sinks to a lower level, requires soil to cover that horizontal hole.
as soil is pulled in to this location, it has to come from somewhere and it comes from the nearby land mass, whilst covering that sink-hole made by this one gap underneath, the land mass splits on other parts where the extra soil came from, causing the fissure.
so the fissure is made from the extra soil used to cover the sink-hole, whilst covering the sink-hole made by the underneath gap, making another gap on the surface above, and that is what the fissure ends up as.
in a sense, the gap underneath kinda tranferred to above at the surface.