I just saw an interview with Lindsay Tisch MP dismissing concerns about fracking. Most people don't realise (including Mr. Tisch it seems) that the fracturing of the rock strata is not only achieved by hydraulic pressure but by detonation.
When the hole is bored and the casing is in place, a ‘perf gun' is lowered to the end of the bore hole. This fires detonation charges in all direction which go through the casing (perforating it) into the surrounding rock. As this only fractures a small area, the detonations are repeated over and again as the perf gun is slowly withdrawn.
And this is done in boreholes throughout the target area. Only then is the toxic fluid pumped in under high pressure to further fracture the strata and release hydrocarbons into the well pipe through the perforations.. 'Frack out” is an industry term for an unintentional zone of fracturing from the target area, all the way up to the surface.
It is evidenced by sink holes, contamination of the aquifer and hydrocarbons escaping through the surface. We are led to believe that this can never happen, so they don't need a term for it, do they?

Christopher Martin, Ohauiti.