Sorry about that - it looked OK before I left it and pressed enter. There has been a few occasions lately where spurious resizes have crept in, usually a small size difference, this time to the smallest legally possible. Redone the right size.
Quote from the link - "Magnitudes of the earthquakes during hydraulic fracture stimulation in reservoirs such as the Barnett Shale are typically less than 1 ML. This suggests that the earthquake activity observed at Preese Hall is rather unusual."
So, the fact that test fracks produce bigger quakes than expected, what was expected was larger than an "allowable maximum", and production fracking must, by its nature, be more active, is not a worry?
The production companies do not have a good environmental reputation without very solid regulation in place, and there isn't any at the moment. The powers that be, sitting in comfort well away from the everyday reality of most of us, will be telling the local planning authorities what to approve, but these authorities will, at the moment, have no power to check on what is actually happening until well after the event, and even then, the burden of proof is no longer with the company, but with the injured parties.
Quite apart from inducing tremors, there is the bigger question of the toxic slurry which is going to be produced. Worldwide, there are plenty of recorded instances of groundwater being polluted and rendered unfit for irrigation of crops or the use of livestock. Contrary to common belief, our food does not originate on supermarket shelves, it comes from crops and livestock. Anybody bought any Knott End cockles lately? Of course not, those beds were poisoned by outflow from the Hillhouse PVC plant many years ago, and it's likely to be another 20 years before the mercury works its way out of that bit of the ecosystem. The answer to that was to truck the contaminated slurry over to the salt mines and pump it back down there, forming a closed cycle. If the same were to happen with fracking slurry, there is doubt that, if the trucks were to run on methane, there would be any left over for sale.