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Abstract:
Although most wells in Alberta have no correlation with induced earthquakes, the Rocky Mountain House Seismogenic Zone (RMHSZ) defies this trend. The RMHSZ is a long-lived (1970’s to present) cluster of induced earthquakes located in west-central Alberta, Canada that has attracted attention following a stark increase in the regional seismicity rate after 2014. Seismicity in the RMHSZ has historically been linked to two mechanisms: poroelastic effects from gas production from the Strachan D3-A pool, a fractured Devonian reef; and natural earthquakes related to thrust faulting. The recent resurgence of seismicity brings the previously accepted poroelastic model into question, as gas production from the gas pool has ceased; new evidence suggests a nearby brine disposal scheme may be the culprit. This region is predisposed to favor induced seismicity from fluid injection based on overall sedimentology, diagenetic history, and complex structure, leading to increased seismic risk. Publicly available fluid injection data provided by geoSCOUTTM reveals the operator of the injector wells switched to a stratigraphically higher dolomitic zone, the Devonian Wabamun Group, in 2013; this timing coincides with the increase in seismicity. We investigated the strength and nature of the relationship between recent seismicity and the production and injection history of nearby wells in the RMHSZ by applying a cross-correlation algorithm to injection volumes and earthquake counts. We found that recent seismicity does correlate with brine disposal in space and time; this method can be applied to other retroactive seismicity studies. On-site earthquake monitoring at RMHSZ should be undertaken in the future.
