A state research seismologist threw cold water yesterday on the idea that drilling activities have caused a spike in earthquakes in Oklahoma.
Austin Holland of the Oklahoma Geological Survey said he doesn't dispute that earthquakes can be caused by drilling-related actions, such as deep injection of wastewater.
"But no changes in oil and gas activities are immediately apparent that explain the increase in the number of earthquakes in Oklahoma," Holland said at a news briefing that was telecast as part of the American Geophysical Union fall meeting this week in San Francisco.
Oklahoma was a key part of a U.S. Geological Survey report earlier this year finding that the middle of the country is experiencing a "remarkable" surge of earthquakes.
The rate of earthquakes in Oklahoma greater than magnitude 3.0 "abruptly increased" from an average of 1.2 quakes a year for the previous half-century to more than 25 in 2009, USGS said. It said the surge appeared to be related to oil and gas activity in the area.
The study did not include a magnitude-5.7 earthquake in November 2011 that injured two and caused extensive damage in central Oklahoma. But another study being presented at the AGU conference says it was "likely triggered by fluid injection" (EnergyWire, Dec. 3).
A senior USGS official who was on the panel with Holland said his team stands by its findings.
"The job of USGS is to assess seismic hazards," said Arthur McGarr, chief of USGS's Branch of Earthquake Geology and Geophysics, based in Menlo Park, Calif. "This is contributing to the earthquake hazard, particularly in the middle of the continent."
Holland and other Oklahoma officials have been the leading skeptics of the idea that drilling activities have caused earthquakes in the state. The state is continuing to allow injection near the active fault at the center of the November 2011 quake (EnergyWire, July 25).
Holland illustrated his point yesterday with graphs showing that the areas with the biggest increases in earthquakes have some of the fewest new producing wells and the fewest new injection wells.
Even scientists who see a strong link between injection and earthquakes note that it is difficult to tie any one particular quake to injection.
"It's like smoking," said Cliff Frohlich, senior research scientist at the University of Texas' Institute for Geophysics. "You can't say that smoking caused one particular person to get cancer. But if you look at the statistics, it's clear that smoking causes cancer."
At the conference, Frohlich is presenting his findings that injection of oil and gas wastewater appears to be causing more earthquakes than previously thought in the Barnett Shale region around Dallas-Fort Worth (EnergyWire, Aug. 7).
He said more surveys like his, in which researchers monitored seismic activity around wells rather than responding to quakes, is what policymakers will need to decide how to regulate on the issue.