By John Kemp
DUBAI, April 17 Recent government reports have
concluded hydraulic fracturing and other fluid injection
activities associated with oil and gas production were
responsible for a series of small tremors in northern England
last year, and they have also been blamed for a six-fold
increase in the number of tremors in the midcontinent of the
United States since 2001.
But the uptick in seismic activity is unlikely to stop the
spread of fracking. The tremors are small and no worse than
those traditionally associated with mining for coal, salt and
other minerals. They pose little or no threat to structures or
In the United States, President Barack Obama's decision to
issue an executive order on April 13 "Supporting Safe and
Responsible Development of Unconventional Domestic Natural Gas
Resources" is a clear sign policymakers are prepared to override
concerns about the risk linked to small earth tremors in order
to boost domestic energy production.
In Britain, the government has launched a six-week
consultation. But it too is clearly preparing to endorse the
practice, albeit with heightened safeguards.
The chief scientific adviser to the Department of Energy and
Climate Change (DECC) launched the review by suggesting it
contained "a set of robust measures to make sure future seismic
risks are minimised, not just as this location but at any other
potential sites across the United Kingdom."
Hydraulic fracturing at the Preese Hall well near Blackpool
in northern England "induced" a number of earthquakes in April
and May 2011, the largest of which had a local magnitude of 2.3,
according to the findings of an official government review
published this week ("Preese Hall shale gas fracturing: review
and recommendations for induced seismic mitigation" April 2012).
It was not the pressure pumping itself which caused the
tremors but the accidental injection of fluids into an adjacent
fault. The largest quakes occurred approximately ten hours after
the start of the injection, when the well was shut in under high
The potential for man-made activities to trigger small
earthquakes is well known. Underground mining, deep artificial
water reservoirs, oil and gas extraction, geothermal power
generation and waste disposal have all resulted in cases of
induced seismicity, according to the report's authors, who
included scientists from the British Geological Survey and Keele
In 2001, pressure maintenance injections at the North Sea's
Ekofisk oil field induced an earthquake with a surprisingly
large magnitude of 4.1. But most tremors are much smaller and
are barely perceptible or measured only with sensitive
Half of the seismic activity experienced in the United
Kingdom in the last century was caused by coal-mining, according
to a government briefing note. Despite the widespread shut down
of most coal mines, traditional mining areas still experience
occasional tremors linked to mine flooding and the restoration
of water levels ("Induced seismicity in the UK and its relevance
to hydraulic stimulation for exploration for shale gas" April
Post-mining tremors range from those only detectable very
close to the source with sensitive instruments up to a maximum
of magnitude 3.2 for one quake in Scotland's Midlothian region.
But most tremors are below 3.0.
In the United States, researchers for the U.S. Geological
Survey (USGS) have found a remarkable increase in the number of
earthquakes occurring each year of magnitude 3.0 or greater,
concentrated along the border of Colorado and New Mexico, and
more recently in Arkansas and Oklahoma.
Between 1970 and 2000, the entire midcontinent region, of
which these areas form a part, averaged 21 +/- 8 events at
magnitude 3.0 or greater. From 2001 to 2008, this increased
slightly to 29 +/- 3.5 events at 3.0 or greater. But then in
2009, 2010 and 2011, the number surged to 50, 87 and 134 events
In Oklahoma, the rate of magnitude 3.0 or higher events has
surged from 1.2 per year in the previous half century to over 25
per year since 2009. This number excludes one strong earthquake
of 5.6 in November 2011 and its aftershocks.
"The modest increase that began in 2001 is due to increased
seismicity in the coal bed methane field of the Raton Basin
along the Colorado-New Mexico border," according to USGS. "The
acceleration in activity that began in 2009 appears to involve a
combination of source regions of oil and gas production,
including the Guy, Arkansas region, and in central and southern
USGS cites research by other scientists linking the Arkansas
earthquakes to deep waste water injection wells.
QUAKES OR TREMORS
Fracking opponents have already begun to characterise these
findings as "fracking causes quakes" but the reality is more
First it is not the fracking itself which seems to be
causing increased seismic activity. Any mining or oil/gas
production activity involving fluid injection into underground
formations can set off small earthquakes.
Tremors have been associated with coal production and
coal-bed methane, and they may be caused by underground
injection of waste water produced from conventional oil and gas
wells just as much as the pressure pumping used to fracture
If carbon capture and storage (CCS) programmes eventually
inject large volumes of liquid CO2 into saline aquifers,
un-mineable coal seams and other rock formations, that too will
cause tremors, which is one reason many environmental groups
have been careful not to oppose injection and pressure pumping
Second, most of these "earthquakes" are very small.
Earthquake is an emotive word associated with mass destruction
of buildings and loss of life. There is no suggestion tremors
caused by fracking and other mining processes have caused any
damage remotely like this.
"To our knowledge, hydrofracturing ... rarely creates
unwanted induced seismicity large enough to be detected on the
surface with very sensitive sensors, let alone be a hazard or
annoyance," wrote researchers at the Earth Sciences Division at
Lawrence Berkeley National Laboratory.
While an earthquake of magnitude 2.3 or even 3.0 sounds
serious, the surface shaking and amount of energy released is
tiny. The surface shaking generated by the worst quake at
Blackpool (2.3) was 10,000 times smaller than in the earthquake
which devastated large parts of Christchurch, New Zealand, in
February 2011. The amount of energy released was 1 million times
There is no simple relationship between the magnitude of a
tremor and the intensity with which it is felt by local
inhabitants. Small, but shallow, earthquakes can be felt quite
strongly while deep but large earthquakes may not be felt as
But USGS suggests an earthquake with a magnitude of 1.0-3.0
would only be felt by a few persons (it would register just 1 on
the 12-point Modified Mercalli Scale). An earthquake of 3.0-3.9,
which is similar to the worst associated with mineral
extraction, would be felt as a weak or noticeable vibration
indoors especially on the upper floors of buildings (it would
register at 2-3 on the Modified Mercalli Scale).
Vibrations would be similar to the passing of a heavy truck
and many people would not recognise it as an earthquake.
The UK government review suggests 3.0 is probably the worst
that could be expected from fracking, based on previous
experience from coal mining. But to create a margin of safety,
it recommended operations should be halted and remedial action
instituted immediately if events of magnitude 0.5 or above are
It also recommends the main frack should be preceded by a
smaller pre-injection and monitoring stage, and future
operations should include effective real-time monitoring of the
locations and magnitudes of seismic events to provide an early
warning of trouble.
Based on the scientific studies so far, however, fracking
will not cause homes and other buildings to collapse or suffer
significant damage. With appropriate safeguards, it is a safe
procedure that poses no more risk than coal mining or developing
geothermal, both of which are seen as perfectly acceptable