| NEW YORK, July 11
NEW YORK, July 11 Powerful earthquakes thousands
of miles (km) away can trigger swarms of minor quakes near
wastewater-injection wells like those used in oil and gas
recovery, scientists reported on Thursday, sometimes followed
months later by quakes big enough to destroy buildings.
The discovery, published in the journal Science by one of
the world's leading seismology labs, threatens to make hydraulic
fracturing, or "fracking," which involves injecting fluid deep
underground, even more controversial.
It comes as the U.S. Environmental Protection Agency
conducts a study of the effects of fracking, particularly the
disposal of wastewater, which could form the basis of
regulations on oil and gas drilling.
Geologists have known for 50 years that injecting fluid
underground can increase pressure on seismic faults and make
them more likely to slip. The result is called an "induced"
A recent surge in U.S. oil and gas production - much of it
using vast amounts of water to crack open rocks and release
natural gas, as in fracking, or to bring up oil and gas from
standard wells - has been linked to an increase in small to
moderate induced earthquakes in Oklahoma, Arkansas, Ohio, Texas
Now seismologists at Columbia University say they have
identified three quakes - in Oklahoma, Colorado and Texas - that
were triggered at injection-well sites by a major earthquake a
long distance away.
"The fluids (in wastewater injection wells) are driving the
faults to their tipping point," said Nicholas van der Elst of
Columbia's Lamont-Doherty Earth Observatory in Palisades, New
York, who led the study. It was funded by the National Science
Foundation and the U.S. Geological Survey.
Fracking opponents' main concern is that it will release
toxic chemicals into water supplies, said John Armstrong, a
spokesman for New Yorkers Against Fracking, an advocacy group.
But "when you tell people the process is linked to
earthquakes, the reaction is, 'what? They're doing something
that can cause earthquakes?' This really should be a stark
warning," he said.
Fracking proponents reacted cautiously to the study.
"More fact-based research ... aimed at further reducing the
very rare occurrence of seismicity associated with underground
injection wells is welcomed, and will certainly help enable more
responsible natural gas development," said Kathryn Klaber, chief
executive of the Marcellus Shale Coalition.
Quakes with a magnitude of 2 or lower, which can hardly be
felt, are routinely produced in fracking, said geologist William
Ellsworth of the U.S. Geological Survey, an expert on
human-induced earthquakes who was not involved in the study.
The largest fracking-induced earthquake "was magnitude 3.6,
which is too small to pose a serious risk," he wrote in Science.
But van der Elst and colleagues found evidence that
injection wells can set the stage for more dangerous quakes.
Because pressure from wastewater wells stresses nearby faults,
if seismic waves speeding across Earth's surface hit the fault
it can rupture and, months later, produce an earthquake stronger
than magnitude 5.
What seems to happen is that wastewater injection leaves
local faults "critically loaded," or on the verge of rupture.
Even weak seismic waves arriving from faraway quakes are
therefore enough to set off a swarm of small quakes in a process
called "dynamic triggering."
Once these quakes stop, the danger is not necessarily over.
The swarm of quakes, said Heather Savage of Lamont-Doherty and a
co-author of the study, "could indicate that faults are becoming
critically stressed and might soon host a larger earthquake."
For instance, seismic waves from an 8.8 quake in Maule,
Chile, in February 2010 rippled across the planet and triggered
a 4.1 quake in Prague, Oklahoma - site of the Wilzetta oil field
- some 16 hours later.
That was followed by months of smaller tremors in Oklahoma,
and then the largest quake yet associated with waste injection,
a 5.7 temblor in Prague on Nov. 6, 2011.
That quake destroyed 14 homes, buckled a highway and injured
The Prague quake is "not only one of the largest earthquakes
to be associated with wastewater disposal, but also one of the
largest linked to a remote triggering event," said van der Elst.
The Chile quake also caused a swarm of small temblors in
Trinidad, Colorado, near wells where wastewater used to extract
methane from coal beds had been injected.
On Aug. 22, 2011, a magnitude 5.3 quake hit Trinidad,
damaging dozens of buildings.
The 9.1 earthquake in Japan in March 2011, which caused a
devastating tsunami, triggered a swarm of small quakes in
Snyder, Texas - site of the Cogdell oil field. That autumn,
Snyder experienced a 4.5 quake.
The presence of injection wells does not mean an area is
doomed to have a swarm of earthquakes as a result of seismic
activity half a world away, and a swarm of induced quakes does
not necessarily portend a big one.
Guy, Arkansas; Jones, Oklahoma; and Youngstown, Ohio, have
all experienced moderate induced quakes due to fluid injection
from oil or gas drilling. But none has had a quake triggered by
a distant temblor.
Long-distance triggering is most likely where wastewater
wells have been operating for decades and where there is little
history of earthquake activity, the researchers write.
Before the advent of injection wells, triggered earthquakes
were a purely natural phenomenon. A 7.3 quake in California's
Mojave Desert in 1992 set off a series of tiny quakes north of
Yellowstone National Park in Wyoming, for instance.
Now, according to the Science paper, triggered quakes can
occur where human activity has weakened faults.
Current federal and state regulations for wastewater
disposal wells focus on protecting drinking water sources from
contamination, not on earthquake hazards.
(Reporting by Sharon Begley; Additional reporting by Edward
McAllister; Editing by Michele Gershberg and Xavier Briand)