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Charles Lord, left, senior hydrologist, explains the mapping procedure used by the Corporation Commission to chart fault lines, earthquakes and disposal wells, as Jim Marlatt, right, Oil & Gas Specialist, looks on from his desk, in Oklahoma City on Nov. 30, 2015. State regulators have taken steps to try and curb the number of quakes, working with disposal well operators in the area to have them reduce the volume in disposal wells or shut them down entirely.(Photo: Sue Ogrocki, AP)
While the earth continues to shudder more frequently than seven years<span style="color: Red;">*</span>ago<span style="color: Red;">*</span>beneath Oklahomans feet, the rate of earthquakes in the state<span style="color: Red;">*</span>in 2016 is down from last year.
The state has been shaken by 448 magnitude-3.0 and greater quakes so far this year, down from the 558 it experienced in the same time frame in 2015, according to data from the U.S. Geological Survey.
Increased regulation on wastewater disposal related to oil and gas extraction could be one reason behind the decline, said<span style="color: Red;">*</span>Robert Williams, a geophysicist at the United States Geological Survey. Wastewater disposal is<span style="color: Red;">*</span>linked to quakes in Oklahoma and other states.
Regulators this year increased restrictions limiting<span style="color: Red;">*</span>wastewater disposal and expanded the area in the state those constraints cover, Williams said. At the same time, a<span style="color: Red;">*</span>decrease in oil and gas activity<span style="color: Red;">*</span>led to a smaller volume of water being disposed of,<span style="color: Red;">*</span>also potentially<span style="color: Red;">*</span>contributing to fewer quakes, he added.
The extraction of oil and gas in hydraulic fracturing<span style="color: Red;">*</span>— also known as fracking<span style="color: Red;">*</span>—<span style="color: Red;">*</span>likely does not contribute to a rise in earthquakes, but<span style="color: Red;">*</span>wastewater disposal associated with the activity<span style="color: Red;">*</span>does, said<span style="color: Red;">*</span>Jefferson Chang, a geophysicist for the Oklahoma Geological Survey at the University of Oklahoma.
That's because during the disposal process, briny wastewater is injected at high pressures into rock formations underground. And that process takes place at greater depths underground than fracking does,<span style="color: Red;">*</span>Chang said.
While the overall rate of earthquakes is down, the temblors are still happening regularly in Oklahoma.<span style="color: Red;">*</span>In the past 30 days, 26<span style="color: Red;">*</span>earthquakes with a magnitude-3.0 or greater<span style="color: Red;">*</span>have hit the state, according to<span style="color: Red;">*</span>USGS data.<span style="color: Red;">*</span>A magnitude-4.0 rocked an area just outside Oklahoma City early Wednesday.
“The people around here have felt this before, but that was probably a pretty good shock,” Williams said of Wednesday's quake.
Much of the seismic activity also takes place in clusters in parts of the state. In<span style="color: Red;">*</span>January, 70 small earthquakes shook Oklahoma in just one week, mainly in northwestern Oklahoma.
At a magnitude-3.0, the ground is moving enough that people actually begin to feel it, Chang said.
USA TODAY
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In March, a USGS report linked activities related to oil and gas extraction, notably wastewater disposal, to seismic activity.<span style="color: Red;">*</span>The report found that Oklahoma along with five other states —<span style="color: Red;">*</span>Kansas, Texas, Colorado, New Mexico and Arkansas —<span style="color: Red;">*</span>faced the highest potential for earthquake hazards.
Since 2009, more than 2,000 magnitude-3.0 or greater earthquake have shaken Oklahoma. That's far above the one or two per year the state experience before that year, a change Williams called unprecedented.
In 2008,<span style="color: Red;">*</span>only two<span style="color: Red;">*</span>magnitude-3.0<span style="color: Red;">*</span>earthquakes<span style="color: Red;">*</span>were registered in Oklahoma, according to the USGS. By 2015, that number climbed to 890.
There is no one clear answer why Oklahoma experiences more earthquakes than other states, but Williams thinks the location of many of the wastewater disposal sites, which lay<span style="color: Red;">*</span>on top of ancient seismic fault lines, contributes to the trend.
USA TODAY
'Reawakened' faults could trigger big Okla. earthquakes
While scientists cannot link all quakes<span style="color: Red;">*</span>to wastewater disposal, one of<span style="color: Red;">*</span>the largest Oklahoma experienced<span style="color: Red;">*</span>in recent years, magnitude-5.6 in 2011, was induced by that activity, Williams said.
Katie Brown, a spokesperson for Energy In Depth, told USA TODAY in March after the USGS report was released<span style="color: Red;">*</span>that only a small percentage of wells are associated with the quakes.<span style="color: Red;">*</span>Energy In Depth is<span style="color: Red;">*</span>a program of the Independent Petroleum Association of America, a trade group.
However,<span style="color: Red;">*</span>Chang said monitoring earthquakes in Oklahoma has been difficult, and no study has conclusively surveyed the state. As a result, he said, these days, “it’s really hard to quantify what is episodic and what is ‘normal.’ ”
USA TODAY
Oklahoma hit with 70 quakes in a week
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