Geoscience Reference
In-Depth Information
Induced Seismicity and
Energy Technologies
INTRODUCTION TO INDUCED SEISMICITY AND STUDY BACKGROUND
An earthquake is a shaking of the ground caused by a sudden release of energy within
the Earth. Most earthquakes occur because of a natural and rapid shift (or slip) of rocks
along geologic faults that release energy built up by relatively slow movements of parts of
the Earth's crust. The numerous, sometimes large earthquakes felt historically in California
and the earthquake that was felt along much of the East Coast in August 2011 are examples
of naturally occurring earthquakes related to Earth's movements along regional faults (see
also the section Earthquakes and Their Measurement, this chapter). An average of ~14,450
earthquakes with magnitudes above 4.0 (
M >
4.0)
1
are measured globally every year. This
number increases dramatically—to more than 1.4 million earthquakes annually—when
small earthquakes (those with greater than
M
2.0) are included.
2
Although the vast majority of earthquakes have natural causes, some earthquakes may
also be related to human activities and are called induced seismic events.
3
Induced seismic
events are usually small in both magnitude and intensity of shaking (see the section on
Earthquakes and Their Measurement later in this chapter). For example, underground
nuclear tests, controlled explosions in connection with mining or construction, and the im-
poundment of large reservoirs behind dams can each result in induced seismicity (Box 1.1).
Energy technologies that involve injection or withdrawal of fluids from the subsurface also
have the potential to induce seismic events that can be measured and felt (see Kerr, 2012).
The earliest and probably most familiar documented example of an induced seismic
event related to fluid injection is the activity that occurred in the Denver, Colorado, area
in the 1960s in connection with liquid waste disposal at the Rocky Mountain Arsenal. An
injection well at the Arsenal pumping into relatively impermeable crystalline basement
1
M
represents magnitude on the moment-magnitude scale, which is described in the section Earthquakes and Their
Measurement, this chapter.
2
See earthquake.usgs.gov/learn/faq/?faqID=69.
3
Some researchers (e.g., McGarr et al., 2002) draw a distinction between “induced” seismicity and “triggered” seismicity.
Under this distinction, induced seismicity results from human-caused stress changes in the Earth's crust that are on the same
order as the ambient stress on a fault that causes slip. Triggered seismicity results from stress changes that are a small fraction
of the ambient stress on a fault that causes slip. Anthropogenic processes cannot “induce” large and potentially damaging
earthquakes, but anthropogenic processes could potentially “trigger” such events. In this report we do not distinguish between
the two and use the term “induced seismicity” to cover both categories.
