The hoops that Cuadrilla had to jump through were many and onerous in order to secure permission to drill and frack.
Quite why the levels at which fracking would stop were chosen, I do not know. BUT they are extremely low and as soon as they are broached, works cease, athat is true.
However, these tremors have been detected by nothing other than the machines designed and set to do so.
Stargazer's OP is about tremors/earthquakes and not about chemicals, etc., if you now want to argue those points, you'll nedd to go to another question.