Are Seismicity Rate Changes in the Midcontinent Natural or Manmade?
ELLSWORTH, W. L., US Geological Survey, Menlo Park, CA, ; HICKMAN, S. H.=
, US Geological Survey, Menlo Park, CA, ; LLEONS, A. L., US Geological S=
urvey, Menlo Park, CA, ; MCGARR, A., US Geological Survey, Menlo Park, C=
A, ; MICHAEL, A. J., US Geological Survey, Menlo Park, CA, ; RUBINSTEIN,=
 J. L., US Geological Survey, Menlo Park, CA
A remarkable increase in the rate of M 3 and greater earthquakes is curr=
ently in progress in the US midcontinent. The average number of M >=3D 3=
 earthquakes/year increased starting in 2001, culminating in a six-fold =
increase over 20th century levels in 2001. Is this increase natural or m=
anmade? To address this question, we take a regional approach to explore=
 changes in the rate of earthquake occurrence in the midcontinent (defin=
ed here as 85=B0 to 108=B0 West, 25=B0 to 50=B0 North) using the USGS Pr=
eliminary Determination of Epicenters and National Seismic Hazard Map ca=
talogs. These catalogs appear to be complete for M >=3D 3 since 1970. Fr=
om 1970 through 2000, the rate of M >=3D 3 events averaged 21 +- 7.6/yea=
r in the entire region. This rate increased to 29 +- 3.5 from 2001 throu=
gh 2008. In 2009, 2010 and 2011, 50, 87 and 134 events occurred, respect=
ively. The modest increase that began in 2001 is due to increased seismi=
city in the coal bed methane field of the Raton Basin along the Colorado=
-New Mexico border west of Trinidad, CO. The acceleration in activity th=
at began in 2009 appears to involve a combination of source regions of o=
il and gas production, including the Guy, Arkansas region, and in centra=
l and southern Oklahoma. Horton, et al. (2012) provided strong evidence =
linking the Guy, AK activity to deep waste water injection wells. In Okl=
ahoma, the rate of M >=3D 3 events abruptly increased in 2009 from 1.2/y=
ear in the previous half-century to over 25/year. This rate increase is =
exclusive of the November 2011 M 5.6 earthquake and its aftershocks. A n=
aturally-occurring rate change of this magnitude is unprecedented outsid=
e of volcanic settings or in the absence of a main shock, of which there=
 were neither in this region. While the seismicity rate changes describe=
d here are almost certainly manmade, it remains to be determined how the=
y are related to either changes in extraction methodologies or the rate =
of oil and gas production.
Wednesday, April 18th / 3:45 PM Oral / Pacific Salon 4 & 5 =




Jim O'Donnell BC-Geophysics =

Geophysical Consultant/Contractor
Geotechnical/Geothermal/Oil & Gas/Mining Applications
Seismic Surveys- Passive Surface Waves, Refraction-Tomography =

Ground Penetrating Radar, Resistivity, Magnetic, & VLF-EM Surveys
Geophysics@..........  702.293.5664  702.281.9081 cell   =

Boulder City, NV 89005  =

Are Seismicit=
y Rate Changes in the Midcontinent Natural or Manmade?
ELLSWORTH, W. L., US Geological Survey, Menlo =
Park, CA, ; HICKMAN, S. H., US Geological Survey, Menlo Park, CA, ; LLEO=
NS, A. L., US Geological Survey, Menlo Park, CA, ; MCGARR, A., US Geolog=
ical Survey, Menlo Park, CA, ; MICHAEL, A. J., US Geological Survey, Men=
lo Park, CA, ; RUBINSTEIN, J. L., US Geological Survey, Menlo Park, CA

=
A remarkable increase in the rate of M 3 and greater earthquakes is c=
urrently in progress in the US midcontinent. The average number of M >=
;=3D 3 earthquakes/year increased starting in 2001, culminating in a six=
-fold increase over 20th century levels in 2001. Is this increase natura=
l or manmade? To address this question, we take a regional approach to e=
xplore changes in the rate of earthquake occurrence in the midcontinent =
(defined here as 85=B0 to 108=B0 West, 25=B0 to 50=B0 North) using the U=
SGS Preliminary Determination of Epicenters and National Seismic Hazard =
Map catalogs. These catalogs appear to be complete for M >=3D 3 since=
 1970. From 1970 through 2000, the rate of M >=3D 3 events averaged 2=
1 +- 7.6/year in the entire region. This rate increased to 29 +- 3.5 fro=
m 2001 through 2008. In 2009, 2010 and 2011, 50, 87 and 134 events occur=
red, respectively. The modest increase that began in 2001 is due to incr=
eased seismicity in the coal bed methane field of the Raton Basin along =
the Colorado-New Mexico border west of Trinidad, CO. The acceleration in=
 activity that began in 2009 appears to involve a combination of source =
regions of oil and gas production, including the Guy, Arkansas region, a=
nd in central and southern Oklahoma. Horton, et al. (2012) provided stro=
ng evidence linking the Guy, AK activity to deep waste water injection w=
ells. In Oklahoma, the rate of M >=3D 3 events abruptly increased in =
2009 from 1.2/year in the previous half-century to over 25/year. This ra=
te increase is exclusive of the November 2011 M 5.6 earthquake and its a=
ftershocks. A naturally-occurring rate change of this magnitude is unpre=
cedented outside of volcanic settings or in the absence of a main shock,=
 of which there were neither in this region. While the seismicity rate c=
hanges described here are almost certainly manmade, it remains to be det=
ermined how they are related to either changes in extraction methodologi=
es or the rate of oil and gas production.



Wednesday, April 18th / 3:45 PM Oral / Pac=
ific Salon 4 & 5 



Ji=
m O'Donnell BC-Geophysics 
Geophysical Consultant/Co=
ntractor
Geotechnical/Geothermal/Oil & Gas/Mining ApplicationsSeismic Surveys- Passive Surface Waves, Refraction-Tomography 
=
Ground Penetrating Radar, Resistivity, Magnetic, & VLF-EM SurveysGeophysics@..........  702.293.5664  702.281.9081 cell  =
 
Boulder City, NV 89005