"The risk of man-made earthquakes has been known for decades, and fracking poses far less risk than other technologies..." writes John Kemp about the various causes of induced earthquakes.
http://uk.mobile.reuters.com/article/idUKL5E8N59DQ20121205?irpc=932. The piece is thorough and well worth reading in full.
Kemp reminds that it has been understood and confirmed for decades that the injection of water under pressure can cause seismic events. He further states that geothermal energy has been associated with 25 low level earthquakes, hydroelectric reservoirs with 44, conventional oil and gas development with 38, and waste water injection with 11.
By comparison, Kemp asserts that fracking itself has caused at most 2 low level earthquakes--one near Blackpool, England and possibly in Oklahoma. My understanding is that the Blackpool earthquake is well documented as being caused by fracking itself but the Oklahoma event is not. On this basis, Kemp concludes that the act of fracking a well has the lowest level of seismic risk when compared to many other energy extraction or waste disposal activities.
Induced seismicity or man-caused earthquakes is another long-standing reality of the modern world that drew next to no attention, until fracking captivated public attention. And paying attention to the various causes of induced earthquakes is a good thing, as these risks exist and can be lowered by better planning and siting.
And reducing the risks of induced seismic activity should be required no matter whether the activity involves shale gas production or not.