The rate of earthquakes in Oklahoma has increased by about 50% since October 2013, significantly increasing the chance for a damaging quake in central Oklahoma, the US Geological Survey and Oklahoma Geological Survey jointly said on May 5.
They reported that 183 earthquakes of magnitude 3.0 or greater occurred in the Sooner State from October 2013 through Apr. 14. This compares with a long-term average during 1978-2008 of only two magnitude 3.0 or larger earthquakes per year, they said.
As a result of the increased number of small and moderate shocks, the likelihood of future, damaging earthquakes has increased for central and north-central Oklahoma, the two geologic surveys warned in their joint statement.
"We hope that this new advisory of increased hazard will become a crucial consideration in earthquake preparedness for residents, schools, and businesses in the central Oklahoma area," said Bill Leith, USGS's senior science advisor for earthquakes and geologic hazards.
A likely contributing factor to the increase in earthquakes is wastewater disposal by injection into deep geologic formations, the joint statement indicated. The water injection can increase underground pressures, lubricate faults, and cause earthquakes through a process known as injection-induced seismicity, it said.
"Much of this wastewater is a byproduct of oil and gas production and is routinely disposed of by injection into wells specifically designed and approved for this purpose," the statement continued. "The recent earthquake rate changes are not due to typical, random fluctuations in natural seismicity rates."
'Why now?'
Oil and gas wastewater has been disposed of in Oklahoma for 60-70 years, OGS Staff Seismologist Austin Holland said on May 12. Most of it is produced water, not water from hydraulic fracturing, he told OGJ. "One of the biggest questions we have is why the quakes are happening now," he said. "We've had this sort of activity for a long time."
OGS tries not to overstate the science because it doesn't want oil and gas activity to be shut down without good reason, Holland continued. "But we're also seeing effects in the way the Corporation Commission is looking at new permits and sometimes existing permits as well," he added.
"We think it's important to put the hazard in perspective," Holland said. "The chance of a large, more significant earthquake has increased, but it's still less than damage from a tornado. We face a real hazard from those."
The Interstate Oil & Gas Compact Commission also announced on Apr. 29 that state oil and gas regulators and geological surveys have formed a working group to examine whether a relationship exists between injection wells and seismic events in several states.
