Record Number of Oklahoma Tremors Raises Possibility of Damaging Earthquakes

http://earthquake.usgs.gov/contactus/golden/newsrelease_05022014.php[1/22/2015 4:06:59 PM]

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Record Number of Oklahoma Tremors Raises Possibility of Damaging

Earthquakes

Updated USGS-Oklahoma Geological Survey Joint Statement on Oklahoma Earthquakes

Originally Released: 10/22/2013 1:07:59 PM; Updated May 2, 2014

The rate of earthquakes in

Oklahoma has increased

remarkably since October

2013 – by about 50

percent – significantly

increasing the chance for a

damaging magnitude 5.5

or greater quake in central

Oklahoma.

View map of Oklahoma

seismicity.

View animation of

Oklahoma Seismicity.

A new U.S. Geological

Survey and Oklahoma

Geological Survey analysis

found that 145 earthquakes

of magnitude 3.0 or greater

occurred in Oklahoma from

January 2014 (through May 2; see accompanying graphic). The previous annual record, set in 2013, was 109 earthquakes, while the

long-term average earthquake rate, from 1978 to 2008, was just two magnitude 3.0 or larger earthquakes per year. Important to

people living in central and north-central Oklahoma is that the likelihood of future, damaging earthquakes has increased as a result

of the increased number of small and moderate shocks.

Oklahoma’s heightened earthquake activity since 2009 includes 20 magnitude 4.0 to 4.8 quakes, plus the largest earthquake in

Oklahoma’s history – a magnitude 5.6 earthquake that occurred near Prague on Nov. 5, 2011. The 2011 Prague earthquake

damaged a number of homes and the historic Benedictine Hall at St. Gregory's University in Shawnee. Prior to the 2011 Prague

earthquake, the largest earthquake of Oklahoma’s history was a magnitude 5.5 earthquake that occurred in 1952 near El Reno and

damaged state buildings in Oklahoma City.

“While it’s been known for decades that Oklahoma is ‘earthquake country’, we hope that this new advisory of increased hazard will

become a crucial consideration in earthquake preparedness for residents, schools and businesses in the area,” said Dr. Bill Leith,

Senior Science Advisor for Earthquakes and Geologic Hazards at USGS. “Building owners and government officials should have a

special concern for older, unreinforced brick structures, which are vulnerable to serious damage during sufficient shaking.”

USGS statistically analyzed the recent earthquake rate changes and found that they do not seem to be due to typical, random

fluctuations in natural seismicity rates. Significant changes in both the background rate of events and earthquake triggers needed to

have occurred in order to explain the increases in seismicity, which is not typically observed when modeling natural earthquakes.

The analysis suggests that a likely contributing factor to the increase in earthquakes is triggering by wastewater injected into deep

geologic formations. This phenomenon is known as injection-induced seismicity, which has been documented for nearly half a

century, with new cases identified recently in Arkansas, Ohio, Texas and Colorado. A recent publication by the USGS suggests that

a magnitude 5.0 foreshock to the 2011 Prague, Okla., earthquake was human-induced by fluid injection; that earthquake may have

then triggered the mainshock and its aftershocks. OGS studies also indicate that some of the earthquakes in Oklahoma are due to

fluid injection. The OGS and USGS continue to study the Prague earthquake sequence in relation to nearby injection activities.

Collaborative USGS and OGS research to understand earthquake rate increase in the central Oklahoma area includes quantifying

the changes in earthquake rate, assessing the implications of the increased small and moderate earthquake activity for large

earthquake hazards, and evaluating possible links between these earthquakes and wastewater disposal from oil and gas production

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EARTHQUAKES HAZARDS DATA & PRODUCTS LEARN MONITORING RESEARCH
Record Number of Oklahoma Tremors Raises Possibility of Damaging Earthquakes

http://earthquake.usgs.gov/contactus/golden/newsrelease_05022014.php[1/22/2015 4:06:59 PM]

activities. The OGS is also focused on seismicity in north-central Oklahoma.

To more accurately determine the locations and magnitudes of earthquakes in Oklahoma, the OGS has increased the number of

monitoring stations and now operates a seismograph network of 15 permanent stations and 17 temporary stations, many of which are

on loan from the USGS. There are also three permanent seismic stations operated by the USGS and the Incorporated Research

Institutions for Seismology. Data from this network are shared in real-time with the USGS National Earthquake Information Center,

which provides 24x7 reporting on earthquakes worldwide.

Information about earthquake preparedness can be found at the following websites:

Ready.gov

Central US ShakeOut

U.S. Department of the Interior | U.S. Geological Survey

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