Seismicity Triggered by Human ActivitiesEarthquakes resulting from human activities are called induced earthquakes or induced seismicity. In Alberta, there are three main human activities causing induced earthquakes: mining, producing oil or gas, and injecting fluids underground. Our experts examine earthquake characteristics to determine if earthquakes are natural or induced. This work supports the Alberta Energy Regulator’s regulatory efforts to reduce the hazards associated with induced earthquakes. Recent induced earthquake events in Alberta include events near Fox Creek, Cardston, and Rocky Mountain House.
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Earthquakes caused by human activities are induced seismic events or induced earthquakes. The human activities causing induced earthquakes in Alberta include mining, producing oil or gas, and injecting fluids underground. Alberta has a long history of induced earthquakes dating back to the 1970s. Earthquakes between the 1970s and 2010 were primarily related to conventional oil and gas activities. In 2011, the frequency of earthquakes in Alberta suddenly increased, mainly due to increasing unconventional oil and gas activities, in particular, hydraulic fracturing (injecting fluids to fracture rock) of the Duvernay Formation near Fox Creek, northwestern Alberta. Other noteworthy cases of induced earthquakes include the hydraulic fracturing of the Duvernay Formation near Red Deer and wastewater disposal activities east of Musreau Lake, northwestern Alberta.
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The most recent increases of induced earthquakes in Alberta are related to injecting fluids into the ground for various reasons including fluid disposal and hydraulic fracturing. During fluid disposal, operators inject fluids into the subsurface to dispose of wastewater and other fluids in an environmentally friendly way. During hydraulic fracturing, operators inject fluids (and possibly other components) into a well to fracture the rocks, improving oil and gas recovery or for producing geothermal energy. The following unusual set of conditions are required for fluid-injection activities to cause an earthquake:
- A pre-existing fault must be near the injection well.
- The fault must be in a state of stress that is close to failure (critically stressed).
- There must be a means for the fluids to change the stresses/forces along the fault to cause the fault to slip.
Two main processes contribute to changing the stress/forces on the fault to trigger earthquakes.
- High-pressure fluids injected into the ground may enter a critically stressed fault. The increase of fluid pressure along this fault reduces the friction, allowing rock to slip along the fault causing an earthquake.
- Fluid injected into the ground changes the mass and volume of the rocks surrounding the well. Transmission of this change in stresses/forces through the rock may change the stresses/forces on a nearby fault, allowing it to slip.
The movement of rocks along the fault (slipping) causes the earthquake.
Seismologists examine several characteristics of an earthquake sequence to determine whether or not it was an induced earthquake. There are several questions we ask when determining if an earthquake is induced; if the answer to all of these questions is yes, it is likely the earthquake is induced:
- Are these earthquakes in an area that has not commonly experienced earthquakes?
- Is there an increase in the rate of earthquakes in this area?
- Are the earthquakes occurring at the same time as the suspected human activity?
- Are the earthquakes within a reasonable distance from the suspected human activity?
- Are the human-caused changes in stress/forces on a fault large enough to explain the seismicity?
In 2013, we used these criteria to determine the cause of earthquakes west of Fox Creek, northwestern Alberta. Our results showed hydraulic fracturing operations in the Fox Creek area induced the nearby earthquakes.
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Rocky Mountain House
Earthquakes first started ~30 km southwest of Rocky Mountain House, west-central Alberta, in the 1970s and peaked in 1988 (up to local magnitude (ML) 4.0). Studies linked these earthquakes to gas extraction from the Strachan sour gas reservoir in the Leduc Formation.
Cordel Oil Field
Earthquakes in the Brazeau area, 30 km north of Nordegg, west-central Alberta, started in the 1990s, peaked in the early 2000s (up to ML 4.0), and then started declining. Studies linked these earthquakes to wastewater disposal in the Rundle Group.
Between December 2011 and March 2012, more than 60 small earthquakes (up to ML 3.0) occurred north of Cardston, southwestern Alberta. The cause was hydraulic fracturing in a nearby well. The earthquakes occurred directly below this well, in the crystalline basement rock.
Low magnitude earthquakes first started in the Fox Creek area, northwestern Alberta, in December 2013. We associated them with nearby hydraulic fracturing operations in the Duvernay Formation. Due to concerns after an event was felt by nearby residents and workers in January 2015 (ML 4.6), the Alberta Energy Regulator implemented a traffic light protocol, requiring operators to monitor seismicity and either modify or stop operations when seismic events reach specific magnitudes.
Duvernay East Shale Basin
In early 2018, a sequence of induced events occurred near the city of Red Deer, central Alberta. We linked these induced seismic events to hydraulic fracturing activities at the Duvernay East Shale Basin. In March 2019, a ML 4.24 event in this area led to the Alberta Energy Regulator implementing another traffic light protocol.
A cluster of events started in January 2018 in an area approximately 5 km east of Musreau Lake, northwestern Alberta. To date, the largest event recorded has a ML of 3.94 (December 2019). Our analysis suggests a strong correlation between the seismicity and wastewater disposal activities nearby.
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Alberta Energy Regulator’s Traffic Light Protocol for Fox Creek
Alberta Energy Regulator’s Traffic Light Protocol for Red Deer
Alberta Energy Regulator’s Traffic Light Protocol for Brazeau
Preliminary Overview of the 2018 and 2019 Earthquakes Near Red Deer
The Alberta Energy Regulator implemented multiple measures for reducing hazards associated with seismic events induced by oil and gas development activities:
- Under Subsurface Order Number 2 (SSO No. 2), operators conducting hydraulic fracturing in the Duvernay Formation, near Fox Creek in northwestern Alberta, must monitor neighbouring seismicity during operations and follow the traffic light protocol (TLP). Under the TLP, operators must inform the regulator of any event with a ML >2 (yellow-light event) and apply mitigation strategies to avoid larger events. If an event with a ML >4 occurs (red-light event), the operator must stop operations immediately.
- The Subsurface Order Number 6 (SSO No. 6) stipulates hydraulic fracturing activities are not allowed within 3 km of the Brazeau Dam (west-central Alberta) and outside that area, to a 5 km radius, activities are not allowed in the Duvernay Formation or below. Operators must also follow a TLP, with ML >1.0 events as the yellow-light threshold and ML >2.5 events as the red-light threshold.
- The Subsurface Order Number 7 (SSO No. 7) does not allow hydraulic fracturing activities in the Duvernay Formation or below within 5 km of the Dickson Dam, near Red Deer, central Alberta. Operators performing hydraulic fracturing in the Duvernay Formation in the broader Red Deer area, must follow a TLP with ML >1.0 events as the yellow-light threshold and ML >3.0 events as the red-light threshold.
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