Big quakes trigger tremors at US oil and gas sites

Kerry Sheridan: Large earthquakes around the world have been found to trigger tremors at US sites where waste water from gas drilling operations is injected into the ground, a US study said Thursday.

For instance, the massive 9.0 magnitude earthquake in Japan in 2011 set off a swarm of earthquakes in the western Texas town of Snyder near the Cogdell oil field, culminating in a 4.5 magnitude quake there about six months later, said the research in the journal Science. Similarly, small to mid-sized quakes were observed near active injection wells in Prague, Oklahoma following an 8.8 magnitude quake in Chile in 2010.

Uncommon seismic activity stirred that region 16 hours after the Chile quake with a 4.1 magnitude tremor, and it continued until a 5.7 magnitude quake in November 2011, said researchers at Columbia University's Lamont-Doherty Earth Observatory. The 2010 Chile quake also led to heightened seismic activity in Trinidad, Colorado, including a 5.3 magnitude quake in August 2011, in an area where methane is extracted from the coal bed and waste water is re-injected into the Earth.

"We weren't really confident until we found the same pattern of little bursts of seismicity following the passage of seismic waves from several of these big earthquakes," lead author Nicholas van der Elst of Columbia University told AFP.

"Any individual case could be a coincidence but once you start observing it systematically, then you can have more confidence that you are really looking at a physical relationship."

The study helps explain a surge in earthquakes in the central United States, which in recent years has seen a more than six-fold increase in earthquakes over 20th century levels.

An accompanying study in Science said there were 300 3.0-magnitude or higher earthquakes in the central United States from 2010 to 2012, after an average of 21 such quakes per year from 1967 to 2000.

The change coincides with a growing natural gas boom that is based on using large amounts of fluids to crack open rocks for natural gas, known as hydro-fracturing or fracking.

Then, once gas and oil have been extracted from deep within the Earth, companies often inject the wastewater back below the surface.

The US Department of the Interior last year also acknowledged an uptick in seismic activity -- predominantly in Texas, Colorado, Arkansas, Oklahoma and Ohio -- where disposal of waste water through injection wells has "increased significantly," it said. AFP. Theindependent