We may see more earthquakes in coming years, if oil companies begin a controversial drilling method in Virginia.
The head of Virginia Tech’s Seismological Observatory says the cause of last month’s earthquake in Mineral was a lot of stress centered in an area with several favorable faults. Martin Chapman says seismologists have long predicted an earthquake would occur there but they just didn’t expect it to be as large as a 5.8. Since 2004, oil companies have been using the latest practice of hydraulic fracturing: injecting a high pressure water, sand, and chemical solution horizontally into the earth’s crust to split apart rock and release oil and gas deposits. The practice isn’t used in Virginia, but some environmentalists warn of more frequent earthquakes in areas of the U. S. where “fracking” occurs, such as with the Marcellus shale deposits in West Virginia, Pennsylvania, and New York. Chapman agrees. He says the practice puts pressure on the faults already in an area.
“And the hydrofracking process for gas recovery or hydrocarbon recovery– what the purpose of that is to increase the porosity and permeability of the rock by fracturing it. And that generates small earthquakes. In some cases you can trigger larger earthquakes on pre-existing faults that are already near the critical stress level. So it’s basically provides the straw that causes the fault to happen.”
He says fracking at each injection well covers a small area so there’s no chance a well in a neighboring state could have triggered the Mineral earthquake. Oil companies monitor seismic activity during the fracking process.
“It usually happens when the process is being done. Usually you don’t have a long-term seismic issue there. It usually is during the time the fluids are being injected or disposed of.”
Chapman says that as hydrofracking becomes more common, especially in the Appalachian region, there may be an increase in the number of earthquakes in Virginia and surrounding areas.
–by Beverly Amsler
Virginia Public Radio 