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best practices for mitigating induced seismicity risk in Chapter 6. Chapter 7 contains the report’s findings, conclusions, proposed actions, and research recommendations, including identification of information and knowledge gaps and research and monitoring needs. The remainder of this chapter briefly reviews earthquakes and their measurement, introduces the four energy technologies that are the subject of this report, and presents several historical examples of induced seismic activity related to energy development.

The significance of understanding and mitigating the effects of induced seismicity related to energy technologies has been recognized by other groups as well, both internationally and domestically. The International Partnership for Geothermal Technology Working Group on Induced Seismicity6 under the auspices of the International Energy Agency, for example, has been addressing the issue as it relates specifically to geothermal energy development. International professional societies such as the Society of Petroleum Engineers and the Society of Exploration Geophysicists are coordinating a public technical workshop on the topic.7 Within the United States, government agencies such as the Department of Energy and U.S. Geological Survey have also been engaged in explicit efforts to understand and address induced seismicity in technology development. The Environmental Protection Agency has been facilitating a National Technical Working Group on Injection Induced Seismicity8 since mid-2011 and anticipates releasing a report that will contain technical recommendations directed toward minimizing or managing injection-induced seismicity.

EARTHQUAKES AND THEIR MEASUREMENT

The process of earthquake generation is analogous to a rubber band stretched to the breaking point that suddenly snaps and releases the energy stored in the elastic band. Earthquakes result from slip along faults that release tectonic stresses that have grown high enough to exceed a fault’s breaking strength. Strain energy is released by the Earth’s crust during an earthquake in the form of seismic waves, friction on the causative fault, and, for some earthquakes, crustal elevation changes. Seismic waves can travel great distances; for large earthquakes they can travel around the globe. Ground motions observed at any location are a manifestation of these seismic waves. Seismic waves can be measured in different ways: earthquake magnitude is a measure of the size of an earthquake or the amount of energy released at the earthquake source, while earthquake intensity is a measure of the level of ground shaking at a specific location. The distinction between earthquake magnitude and intensity is important because intensity of ground shaking determines what

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6 See http://internationalgeothermal.org/; http://www.iea-gia.org/documents/Switzerland_Inducedseismicity_IPGT_IEA_201105031.pdf

7 See http://www.spe.org/events/12aden/documents/12ADEN_Brochure.pdf

8 See http://www.gwpc.org/meetings/uic/2012/proceedings/09McKenzie_Susie.pdf; P. Dellinger, presentation to the committee, September 2011.



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