Sue Ogrocki/Associated Press
Workers inspected earthquake damage at St. Gregory's University in Shawnee, Okla., in 2011.
Researchers have known for years that disposing of waste water from oil and gas production by injecting it into deep wells can lead to earthquakes. Now scientists at Lamont-Doherty Earth Observatory, a part of Columbia University, have discovered the actual trigger for some of those quakes: the passing seismic waves from much larger, far-off earthquakes.
In a study published online Thursday by the journal Science, Nicholas J. van der Elst and colleagues show a link between quakes near injection wells in Oklahoma, Texas and Colorado, and distant magnitude 8 or higher temblors, including those that struck Chile in 2010 and Japan in 2011. Most of the triggered quakes were minor.
When waste water is injected into rock formations, it increases pressure enough that long-dormant faults are primed to slip once again, shaking the earth. Dr. van der Elst suggested that small stresses from the passing seismic waves in effect "squeezed" the rocks at the injection sites, raising the pressure past the tipping point so that the faults slip and the earth shakes.
Some of these areas had even stronger quakes months later — notably Prague, Okla., where a 5.7 quake occurred in 2011 — a further indication that the faults had reached a tipping point.
At the sites studied, injection had been going on for years, or even decades. Some newer injection wells, including one in Ohio that handled waste water from the gas production process known as hydrofracking, have had small earthquakes, but the researchers found no evidence that these quakes were remotely triggered. Because these sites are newer, the stresses in the rock formation would appear to be higher, and adding a small amount of stress from a passing seismic wave would have little impact.
This article has been revised to reflect the following correction:
Correction: July 11, 2013
An earlier version of this article referred imprecisely to the magnitude of the earthquakes at injection well site that were triggered by distant earthquakes. While some of the areas had strong quakes months after far-off earthquake events, it is not the case that the distant earthquakes triggered earthquakes as large as magnitude 5.7.
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