In November 2011, an historic 5.6-magniute earthquake with an epicenter near Prague caused damage and rattled the nerves of Oklahomans.
That quake damaged homes and businesses, including the turrets at Benedictine Hall at St. Gregory's University in Shawnee.
Since then, smaller earthquakes have become more of a common occurrence in many parts of the state. In fact, state geologists reported that earthquake activity in Oklahoma in 2013 was 70 times greater than it was before 2008.
The increased activity prompted scientists to study the causes and implications of what was being called an “earthquake swarm.”
Now, more than three years later, scientists, with evidence from many studies, seem certain that oil and gas drilling has been causing earthquakes across Oklahoma and the U.S.
On Thursday, the U.S. Geological Survey released the first comprehensive maps pinpointing more than a dozen areas in the central and eastern U.S. that have been jolted by quakes that the researchers said were triggered by drilling.
The report said man-made quakes tied to industry operations have been on the rise.
USGS scientists identified 17 areas within eight states with increased rates of induced seismicity — Alabama, Arkansas, Colorado, Kansas, New Mexico, Ohio, Oklahoma, and Texas.
Since 2000, the reports shows several of these areas have experienced high levels of seismicity, with substantial increases since 2009 that continue today.
Scientists have mainly attributed the spike to the injection of wastewater deep underground, a practice they say can activate dormant faults. Only a few cases of shaking have been blamed on fracking, in which large volumes of water, sand and chemicals are pumped into rock formations to crack them open and free oil or gas.
"The picture is very clear" that wastewater injection can cause faults to move, said USGS geophysicist William Ellsworth.
The USGS report outlines a preliminary set of models to forecast how hazardous ground shaking could be in the areas where sharp increases in seismicity have been recorded. The models ultimately aim to calculate how often earthquakes are expected to occur in the next year and how hard the ground will likely shake as a result. This report looked at the central and eastern United States; future research will incorporate data from the western states as well.
This report also identifies issues that must be resolved to develop a final hazard model, which is scheduled for release at the end of the year after the preliminary models are further examined. These preliminary models should be considered experimental in nature and should not be used for decision-making.
“This new report describes for the first time how injection-induced earthquakes can be incorporated into U.S. seismic hazard maps,” said Mark Petersen, Chief of the USGS National Seismic Hazard Modeling Project. “These earthquakes are occurring at a higher rate than ever before and pose a much greater risk to people living nearby. The USGS is developing methods that overcome the challenges in assessing seismic hazards in these regions in order to support decisions that help keep communities safe from ground shaking.”
Page 2 of 2 - These new methods and products result in part from a workshop hosted by the USGS and the Oklahoma Geological Survey. The workshop, described in the new report, brought together a broad group of experts from government, industry and academic communities to discuss the hazards from induced earthquakes.
The Oklahoma Geological Survey also acknowledged earlier this week that it is "very likely" that recent seismic activity was caused by the injection of wastewater into disposal wells.
The largest jolt linked to wastewater injection was the 5.6-magnitude that hit Prague in 2011.
To learn more about earthquakes, go to www.usgs.gov or www.ogs.ou.edu.
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The Associated Press contributed to this report.
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