Defining:
Induced Seismicity
What is Induced Seismicity?
What is the Link to Hydraulic Fracturing?
Seismicity is a recorded earthquake caused primarily
by fault movement, typically referring to events greater
than a 0.5 magnitude. Induced seismicity is an event
resulting from human activity, and can be caused by
industries such as mining and natural gas development.
Induced seismicity is seldom felt at the surface and
in British Columbia events have been recorded at low
magnitudes.
Hydraulic fracturing is the process of injecting fluid
(usually water) at high pressures to create fractures or
open existing fractures in hydrocarbon-bearing rocks
deep underground. A hard granular substance (called a
proppant and usually sand) mixed with the fluid holds the
cracks open once the pressure is lowered. The purpose
of hydraulic fracturing is to enable the natural gas to flow
from the formation to the wellbore. As hydraulic fracturing
fluid is injected, thousands of micro-seismic events are
created as the rock is fractured. In some cases, where
there is a pre-existing fault, fault movement can be
triggered.
Studies
How is Seismic Activity Monitored?
Seismic activity in British Columbia is monitored by
the Natural Resources Canada (NRCan) regional
seismograph stations and more specialized seismic
arrays. The BC Oil and Gas Commission (Commission)
routinely reviews this data to monitor for potential
occurrences of induced seismicity.
The 2012 Observed Seismicity in the Horn River and
the 2014 Observed Seismicity in the Montney Trend
reports concluded seismic activity in areas of the Horn
River Basin (between 2009 and 2011) and the Montney
Trend (2013 to 2014) were triggered by fluid injection
during hydraulic fracturing. All seismic events were low
magnitude.
The 2014 Montney report showed 231 seismic events
within the Montney Trend were recorded by NRCan
during the Aug. 2013 to Oct. 2014 study period. The
report concluded 193 of these events were triggered by
hydraulic fracturing, or 2.6 per cent of the 7,400 hydraulic
fracturing stages. Only about 0.15 per cent of these
events were felt at surface.
For Further Information
Email [email protected] or call 250-794-5200
24 Hour Incident Reporting for Industry 1-800-663-3456
This information is published by the BC Oil and Gas Commission and available online at www.bcogc.ca
rev. Nov. 2015
What Did We do with the Recommendations?
Recommendations from the 2012 and 2014 reports called for
enhanced seismicity monitoring, including an increase in the
number of seismic monitoring stations. Recommendations were
implemented after each study. This has led to more accurate data
sharing with researchers, and regulatory clarity and mitigation
measures. Specific updates include:
Nine new seismograph stations were installed in the
Canadian National Seismograph Network in northeast
B.C., greatly increasing the ability to monitor for seismicity
in the region. In addition, 13 localized seismograph arrays
have been installed by operators to provide more detailed
seismological data.
New regulations were implemented that require
the immediate suspension of hydraulic fracturing if a
magnitude 4.0 or greater event is triggered, as well as the
mandatory reporting of felt events. Operations can only
be resumed with the implementation of a Commissionapproved mitigation plan.
The requirement for risk assessments of disposal
wells, which operate under strict volume and pressure
restrictions.
Implementation of buffer zones, prohibiting hydraulic
fracturing operations around the Peace and Bennett
Dams.
Scientific studies with the University of British Columbia
to further understand induced seismicity.
Proactively Regulating
The diverse expertise and experience of Commission staff provides
critical insight at every level of natural gas and oil production. This
cumulative knowledge base provides perspective through scientific
evidence, guidance, best practices, reports, tools and analysis.
Commission staff are able to clearly show how natural gas and
oil activities relate to the environment and consistently reviews
regulations and policies to ensure they are in the best interest of
British Columbians.
Measuring Earthquakes
The Commission uses the Richter magnitude scale
(ML) in reporting seismic events, which can occur
as both positive and negative numbers. The Richter
scale was originally calibrated to a seismograph
in 1935. At that time, zero on the scale was set
as an event that would cause a one-micrometre
displacement on a seismogram 100 kilometres from
an epicentre. Instrument sensitivity has improved
with time and modern seismographs are capable
of detecting earthquakes that fall below the original
zero value set by Richter. Negative Richter values
account for this enhanced sensitivity.