“We didn’t know we were going to go out to record a main shock,” said Holland, a seismologist for the Oklahoma Geological Survey.
The surprise of having such a large quake in Oklahoma, considered geologically stable by most, has not been lost on the public; the substantial seismic event garnered media attention worldwide.
Although some surmised that natural gas exploration may be related to the recent earthquakes, others stated the shake-ups were millions of years in the making.
Whole lotta shakin’
The first earthquake in the recent series was recorded around 2:12 a.m. on Nov. 5, centered in Lincoln County with a magnitude of 4.8, followed over the course of the next few hours by about 15 quakes ranging in magnitude from 2.2 to 3.6, according to the OGS.
That same day, at 10:53 p.m., the big one struck. Measuring 5.6, the quake — also originating in Lincoln County, northwest of Prague and southeast of Sparks — was the largest recorded in the state, breaking the record of an estimated 5.5 near El Reno in 1952. (However, because no seismographs existed in-state at that time, its exact magnitude is uncertain, Holland said.)
The main shock, which was felt as far away as Wisconsin, was followed by dozens of aftershocks over the next few weeks, the largest being a 5.0 on Nov. 8, according to OGS data.
The state Department of Health reported two minor injuries: one in Lincoln County, when a man hit his head while fleeing his home, and another in Pottawatomie County, when a woman cut her foot on broken glass.
In addition, the main shock caused damage to several homes and buildings in Central Oklahoma, as well as to the spires on Benedictine Hall at St. Gregory’s University in Shawnee, several media outlets reported.
The fault where the quakes originated is known as the Wilzetta fault line, Holland said, and while not much was known about it by the general public prior to the quakes, geologists and seismologists have known about it for years.
In fact, Wilzetta was the reason for a 4.3-magnitude earthquake in February 2010, he said.
“That fault is aligned within the regional stress field such that it is more likely to have earthquakes than if it was orientated in a different direction,” Holland said. “The stresses build up over hundreds to tens of thousands of years to generate earthquakes here in Oklahoma.”
The fault is one in a series formed around 300 million years ago, during the intraplate deformation known as the Ancestral Rocky Mountains mountain-building episode.
The Wilzetta fault is what is known as a strike-slip fault, Holland said, similar to California’s San Andreas fault, although on a smaller scale. In a strike-slip, movement is like two bricks lined up side by side, and sliding past each other.
Prior to the most recent quake, the Meers fault in south-central Oklahoma was considered the greatest threat to the state, Holland said. It is the only fault that has produced surface-rupturing earthquakes in the past 3,000 years, he said.
“I certainly knew this (Wilzetta) fault was capable of having earthquakes,” Holland said. “I wasn’t expecting a magnitude 5.6.”
What’s goin’ on?
So what caused the quakes? That’s exactly what Holland and a team of geologists from the University of Oklahoma and Oklahoma State University hope to find out.
The team is currently investigating, and will be studying it for years. However, an early report likely will be out in the beginning of 2012, Holland said, noting there is no evidence to suggest the quake was caused by anything other than natural occurrences.
working hypothesis going into the study is that it was caused by
natural forces, although all possibilities will be thoroughly examined.
right, Damage in the metro was minimal, like a fireplace pulled from a wall in this Edmond home.
“It’s going to take time before we can make any determinations like that,” Holland said. “It’s an important issue for Oklahoma. We have all the right conditions to have a naturally occurring earthquake. … We have them in the geologic record, in the historic record, before man was doing his activities in the area.”
According to the U.S. Geological Survey, seismic activity in Oklahoma has increased in the past few years. From 1972 through 2007, between two to six earthquakes a year were recorded in Oklahoma, but in 2008, more than a dozen earthquakes were recorded, according to the USGS. The number of quakes climbed to around 50 in 2009 and the trend continued in 2010.
Some have pointed to injection wells and hydraulic fracturing: energy-industry techniques used to create cracks in gas- and oil-bearing rock by injecting a high-pressure mixture of water, sand and chemicals into rock formations. Both are used to increase recovery of fossil fuels.
There are approximately 200 injection wells in Lincoln County, said Oklahoma Corporation Commission spokesman Matt Skinner.
But can human activity actually cause earthquakes?
Some research suggests such a link. In 1967, the U.S. Army Corps of Engineers and the USGS determined that a deep, hazardous-waste disposal well at the Rocky Mountain Arsenal near Denver was causing “significant seismic events,” according to an Environmental Protection Agency report on injection wells.
Also, a recent report commissioned by drilling company Cuadrilla Resources confirmed that it was “highly probable” that hydraulic fracking in northwest England had caused a series of small earthquakes there.
Holland wrote a report published early this year on a series of small earthquakes in Garvin County, stating that a resident reported about 43 quakes occurring within three and a half miles of a hydraulic-fracturing project, beginning about seven hours after the first and deepest fracking project started.
“The strong correlation in time and space, as well as a reasonable fit to a physical model, suggest that there is a possibility these earthquakes were induced by hydraulic fracturing,” the report stated. “However, the uncertainties in the data make it impossible to say with a high degree of certainty whether or not these earthquakes were triggered by natural means or by the nearby hydraulic-fracturing operation.”
Natural gas proponents state there is very little to link the two, and that the recent earthquake was not caused by natural gas exploration.During a Nov. 14 forum by the U.S. House Energy and Commerce Committee, Oklahoma City-based Devon Energy executive chairman Larry Nichols told members of Congress that he has serious doubts about whether drilling could cause such a large earthquake.
“It reminds me when the Russians put the Sputnik up in the late ’50s, and the Sputnik was blamed for every evil known to man: earthquakes tornadoes, whatever,” Nichols said.
Cody Bannister, director of communications for the Oklahoma Independent Petroleum Association, said hundreds of wells have been drilled in the state over its history, and it’s impossible to link the recent earthquake, a single instance, to something that has been happening for decades.
“I can confidently say Oklahoma’s earthquakes have no relation to drilling activity,” Bannister said. “If it was the oil and gas industry causing earthquakes, we’d be having one every day.”