Governmental Roles and Responsibilities Related to Underground Injection and Induced Seismicity - Induced Seismicity Potential in Energy Technologies - page 110

BOX 4.3 Continued
cooperating state geological surveys and regional seismic networks to address specific local seismic monitoring
issues. NEIC's acquisition and processing system allows them to automatically integrate near-real-time and
non-real-time waveform and source parameter data from regional seismic networks and portable seismic
stations to develop complete seismic catalogs of earthquake sequences. As an example, NEIC is presently
integrating its existing seismic bulletin for the 2011 M 5.8 Virginia earthquake with other non-real-time data
from more than 40 stations deployed by multiple universities and/or state and federal agencies.
a See earthquake.usgs.gov/regional/neic/.
BOX 4.4
The 2010-2011 Guy Greenbrier, Arkansas, Earthquake Swarm
and Arkansas Class II Injection Well Moratorium Area
A group of Class II wastewater disposal wells started operation April 2009 in central Arkansas, near
the towns of Guy and Greenbrier, Arkansas. The wells were used to dispose of wastewater associated with
gas development from the Fayetteville shale. A swarm of earthquakes ( M ≤ 4.7) started in September 2010
between the towns of Guy and Greenbrier (Figure 1). The close spatial and temporal correlation between
the seismicity and the wastewater injection wells suggests a link between injection and seismicity. All but
2 percent of the earthquake activity occurred in the vicinity of about a 6-km (3.7-mile) radius of three specific
injection wells (labeled wells 1, 2, and 5 in Figure 1) (Horton, 2012). One injection well, number 5, appears
to intersect a known fault, the Enders, which may allow fluid to travel down into deeper crustal structures
(Horton, 2012).
Central Arkansas commonly experiences diffuse swarm seismicity, which is thought to be associated with
the New Madrid Seismic Zone (NMSZ), the largest seismic zone east of the Rocky Mountains. The NMSZ is
located on the northeastern part of Arkansas, southeast Missouri, and northwest Tennessee (Figure 1). The
Guy-Greenbrier area has a history of seismic activity, a series of earthquakes referred to as the Enola swarms,
which occurred in the 1980s and in 2001, east-southeast of Greenbrier (Figure 2). The Enola swarms were
not well located due to poor instrumentation; however, the activity tended to form elongated east-west trends
from 3 to 7 km (9850-23,000 feet) in depth (Chui et al., 1984; Rabak et al., 2010).
The AOGC approved a moratorium for any new or additional Class II disposal on January 26, 2011.
The injection moratorium area is approximately 5 miles surrounding the Guy-Greenbrier and Enola seismically
active area and covers an area of over 1,150 square miles (AOGC, 2011). a Operators with existing Class II
wells are required to report daily injection pressures and volumes to the AOGC director. The moratorium
Box continues