The Cardston Earthquake Swarm and Hydraulic Fracturing of the Exshaw Formation (Alberta Bakken Play) by Ryan Schultz,Shilong Mei, Dinu Pană, Virginia Stern, Yu Jeffrey Gu, Ahyi Kim, and David Eaton, November 5, 2015, Bulletin of the Seismological Society of America
Abstract
More than 60 small earthquakes (ML 0.7–3.0) were detected from December 2011 to March 2012 north of Cardston, Alberta, an area with little evidence for previous seismic activity. The timing of these events closely correlates (>99.7% confidence) with hydraulic fracturing completions of the Devonian–Mississippian-age Exshaw Formation at a nearby horizontal well. Unanimous waveform multiplicity within the swarm suggests that the events share a similar origin and source mechanism. This observation is corroborated by the point-like collocation of hypocenters within the crystalline basement during robust, double-difference relocations. Furthermore, the presence of a pre-existing fault is confirmed via formation-top offset mapping and interpreted to be a Late Cretaceous extensional fault. The confirmation of this fault at depth provides a plausible pathway for rapid hydraulic communication from the fracturing interval into the crystalline basement. Consistent with structural interpretations and available stress information, moment tensor inversion of the largest magnitude event (Mw 3.0) indicates reactivation of a basement fault with normal slip. We conclude that the genesis of this earthquake swarm was likely caused by increased pore pressure, within the basement fault, as a result of fracturing stimulation.
Seismic event in southern Alberta: could it be an earthquake? by Mike McKinnon, November 6, 2012, Global News
Earthquakes are generally a natural disaster we don’t have to think about in Alberta, but a Cardston man’s curiosity led to discovery of recent activity in southern Alberta. “I thought I’d zoom in and see what was going on,” said Vernon J. Chiefmoon, who made the discovery. “I noticed in the last week we’ve had four earthquakes in southern Alberta.”
The United States Geological Survey listed the activity at between 2.4 and 2.7 magnitude, beginning on October 27 and ending on November 1. A 7.7-magnitude earthquake struck British Columbia’s north-central coast late on the 27th, but the first tremor in Alberta registered earlier that day. Experts say there is a slim chance that ‘quake had any effect on what happened almost 2,000 kilometres away. “Between the earthquake off the BC coast and Cardston, there are any number of formations, as well as the rocky mountains,” said Darin Barter, a spokesperson for the Enercy Resources Conservation Board. “It’s unlikely, but possible.”
The Alberta Geological Survey said it was more likely industrial activity, rather than seismic. Staff there are looking into whether hydraulic fracturing or mining activity may have caused the readings.
Chiefmoon wonders if the level of activity in our region could have shook southern Albertans. “We’re accustomed to the high winds, so if you feel the ground shaking, you’d think it’s just the wind,” said Chiefmoon.
“It’s pretty unlikely these events would have been felt at the surface,” said Barter. “If anything, it would have been close to a rumble under your feet, like a truck driving by.” [He’s moved on to the National Energy Board. Contact information copied below]
Monitoring the site has been Chiefmoon’s hobby for awhile now, but to his eye, activity around these parts is sporadic. “One every one-to-two years, maybe, and very small,” he said. “Not in terms of a cluster of four that we’ve had lately.” Provincial experts say activity at the magnitude registered in southern Alberta would not cause any surface damage or water well issues. [More lies and frac fraud by Alberta’s quake “experts?’ Refer to: Fracking Industry Has Changed Earthquake Patterns in Northeast BC] [Emphasis added]
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Darin Barter
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National Energy Board
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