Things are rocking and rolling in Youngstown OH due to the 4.3 magnitude earthquake that struck today, December 31st, just in time for New Years. My family did not feel the quake in New Castle PA, but my nephew in Youngstown did. He is a chef in one of the upscale restaurants. When I asked him about it he said that "It felt like a bomb went off". I asked him for pictures, expecting perhaps, a few broken plates. He sent me a picture of an oven door that opened up during the quake, don't laugh my Californian friends, a 4.0+ earthquake is a big deal in this part of the country.
Some have been quick to blame the spat of recent earthquakes (today's being the largest) on shale-related drilling and a fluid-injection well in the area. While evidence indicates a relationship, a history lesson points out the earthquakes are not new to the region. A 1986, 4.8 magnitude earthquake should put to rest any conjecture that shale gas is the sole cause of any earthquake that occurs.
All of this reminds me of an earthquake prediction paper that I wrote as a Penn State University college freshman. There have been very, very few examples of man being able to cause an earthquake, but they are not unheard of. From the USGS:
Earthquakes induced by human activity have been documented in a few locations in the United States, Japan, and Canada. The cause was injection of fluids into deep wells for waste disposal and secondary recovery of oil, and the use of reservoirs for water supplies. Most of these earthquakes were minor. The largest and most widely known resulted from fluid injection at the Rocky Mountain Arsenal near Denver, Colorado. In 1967, an earthquake of magnitude 5.5 followed a series of smaller earthquakes. Injection had been discontinued at the site in the previous year once the link between the fluid injection and the earlier series of earthquakes was established. (Nicholson, Craig and Wesson, R.L., 1990, Earthquake Hazard Associated with Deep Well Injection–A Report to the U.S. Environmental Protection Agency: U.S. Geological Survey Bulletin 1951, 74 p.)
I recommend that we we not jump to the conclusion that every earthquake in an area where there are injection wells must be the result of that injection activity. Earthquakes are not uncommon and they will continue with or without injection wells. Some areas may indeed be more prone to injection well activity causing a release of stress along fault planes beneath the surface of the earth. In addition, it is important to understand that the "potential energy" is already there. Rock structures on either side of an active fault are already under stress and will fail or slip at some point. Are injection wells inducing slip that would have been more severe if nature stored up even more potential energy before a natural release? Or are injection wells inducing slip all at once as opposed to nature releasing the energy more slowly over time? More study needs to be done and the answer likely varies from location to location.