Quakes, injection disposal of fracking water linked

http://www.sfgate.com/science/article/Quakes-injection-disposal-of-fracking-water-4663183.php

America’s boom in oil and natural gas production may have triggered an unwelcome side effect – earthquakes.

A new study in the journal Science finds that the number of temblors shaking the central and eastern United States has soared in recent years, even as the controversial practice of hydraulic fracturing has opened up those regions to oil and gas drilling.

More than 300 earthquakes stronger than magnitude 3 struck in the last three years, according to the study. In the past, the central and eastern states experienced an average of 21 similarly sized quakes each year.

The problem does not appear to be hydraulic fracturing – or fracking – itself. Instead, many of the quakes erupt near wells where the dirty water left over from fracking, or other oil and gas operations, is injected deep underground for permanent disposal.

“The people in the industry I’ve talked to, they’re very cognizant of this problem, and they’re concerned about it,” said study author William Ellsworth, a geophysicist with the U.S. Geological Survey.

The use of fracking is on the rise in seismically active California. If the practice takes off, it could lead to more deep injection wells. California regulations do not prevent companies from drilling injection wells near faults, although the rules do limit injection pressure.

The state already has about 2,300 injection wells, according to Ellsworth’s study. But few of them are in areas with high seismicity. The potential link he sees between wells and quakes in states such as Arkansas and Oklahoma doesn’t seem to be happening here.