There has been a lot of worry recently about hydraulic fracturing in the hunt for natural gas and the idea that it causes earthquakes. A lot of geologists have been writing on this topic and since they have done a far better job than I can, I am going to refer you to some good reading on the topic. Because the short answer is I am not sure how to answer this question!
What the frack is causing those earthquakes!?
(Earthquake is defined by the dictionary of geologic terms as: a sudden motion or trembling in the earth caused by the abrupt release of slowly accumulated strain.)
To start off I recommend a post written for the volcanocast blog titled “No Fracking Earthquakes” I like the explanation of the basics in this one. Also read the comments!
The next post that I would recommend is “A short FAQ on earthquakes and fracking” from the Highly Allochthonous blog. The question/answer I want you to focus on is “They’re certainly a lot bigger…”
Ok now for some other reading:
First I want to point your attention to a USGS Study titled “Examination of Possibly Induced Seismicity from Hydraulic Fracturing in the Eola Field, Garvin County, Oklahoma” [PDF]
one last on topic blog post from the dynamic earth “Frickin’ Fracking“
If in this reading you want something clarified or explained leave a comment or email me!