Lots of misinformation on this topic from both sides of the issue. Until the facts are properly gathered, the right public decisions cannot be made.

The injection of waste water to the boundary between the bedrock and sedimentary basin is a likely a source of some earthquakes. The extra pressure does not dissipate easily. So it keeps building as more fluid is pumped. Something eventually has to give. Or the pumping has to stop.

The waste water disposal is a fairly new technology, maybe 30 years old. Its disadvantages were made known maybe a decade later.

Because fracking a well is usually one-off operation, the extra pressure is easily dissipated. For sure when the well is turned into production whatever pressure is built up gets released through the wellbore.

Fracking has been around since the 1950's. In these times, the fracks were deeper and well spaced out apart. It was hard for pressure to build up to induce earthquakes. However not all fracks were successful. Ideally, the frack should travel into the formation away from the wellbore. However if the well is not constructed properly, the frack can travel up the side of the well. This creates a flow channel from the wellbore to the higher acquifers. There has been many cases of a water well producing good water for years but bad water a year after an oil well has been fracked. The petroleum industry could cover itself by taking samples of all water wells before they frack, but they don't. But this "wild frack" is not a common occurrence. Maybe 1-2%.

The notoriety from fracking started about 25 years ago with development of oil/gas shales. This technology required horizontal drilling into the formation. Then that horizontal well is fracked in several places, maybe 50 meters apart. So the possibility is there for excess local pressure to induce local tectonic activity. But again, the pressure is soon relieved after the frack.

The real danger with the new fracking is the chemicals used. For some reason, the oil/gas shales require powerful chemicals whereas traditional fracking was mostly water with fairly benign chemicals. The nature of these chemicals is kept under great secrecy supposedly so that competing companies cannot reverse engineer a similar chemical. But I suspect that the petroleum industry does not want a strange chemical found in ground water to be traced to a fracked oil well. The contamination of ground water is more likely with the oil/gas shale technology than with traditional fracking.

There are ways for the petroleum industry to prove that fracking is not as harmful as the environmentalists claim. But the industry is not making the right steps to get that proof.

And by using cheap excuses to vilify the petroleum industry, the environment movement is not creating the right regulations to handle this technology. This leaves the industry to wait for political conditions to change that allow more such oil/gas shale development. So any ban on fracking is only temporary. The petroleum industry is both patient and clever.

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This issue is extremely polarized. Both sides are propagandizing rather presenting facts. Maybe one day a journalist will appear who can really tell the right story. Then we'll get the right regulations in place.