Induced seismicity? Recent spike of earthquakes in the central and eastern U.S. may be linked to human activity

The number of earthquakes has increased dramatically over the past few years within the central and eastern United States. More than 300 earthquakes above a magnitude 3.0 occurred in the three years from 2010-2012, compared with an average rate of 21 events per year observed from 1967-2000. This increase in earthquakes prompts two important questions: Are they natural, or human-made? And what should be done in the future as we address the causes and consequences of these events to reduce associated risks? U.S. Geological Survey scientists have been analyzing the changes in the rate of earthquakes as well as the likely causes, and they have some answers.
Source: http://www.sciencedaily.com/releases/2013/07/130712095205.htm