WASHINGTON -- The controversial practice of hydraulic fracturing to extract natural gas does not pose a high risk for triggering earthquakes large enough to feel, but other types of energy-related drilling can make the ground noticeably shake, a government science report concludes.
Even those man-made tremors large enough to be an issue are rare, according to a special report by the National Research Council. In more than 90 years of monitoring, human activity has been shown to trigger only 154 quakes, most of them moderate or small. That's compared with a global average of about 14,450 earthquakes of magnitude-4.0 or greater every year, the report, released Friday, said.
Most of the quakes are caused by gas and oil drilling the conventional way. Only two worldwide instances of shaking -- a magnitude-2.8 tremor in Oklahoma and a magnitude-2.3 shaking in England -- can be attributed to hydraulic fracturing, which is sometimes called "fracking," "Is it a huge problem? The report says basically no," said report chairman Murray Hitzman, a professor of economic geology at the Colorado School of Mines. "Is it something we should look at and think about? Yes."
The report makes sense as far as it goes, said U.S. Geological Survey seismologist William Ellsworth, but since the research council started its study, government geologists have noticed an increase in earthquakes that seem man-made. At a professional seismology conference in April, Ellsworth presented a USGS report on a six-fold increase in man-made quakes. He pointed to induced quakes of magnitude-4.0 or larger in the past year in Texas, Oklahoma, Arkansas, Colorado, New Mexico and Ohio but said much of this happened too late for the research council to include in its study.
Hitzman said it's too early to tell whether those recent quakes would have changed the report's conclusions.
