Using data from nodal geophones and broadband seismometers, this study investigates the seismicity near Red Deer, Alberta, a region with increasing cases of hydraulic fracturing (HF)-induced earthquakes. A cluster of 417 events was detected, and their spatial distribution and focal mechanisms reveal a NE trending rupture area with two strike-slip fault planes. Reactivation of preexisting faults by pore pressure diffusion is likely responsible for the occurrence of the earthquake sequence following the M L 4.18 mainshock. The temporal sequence of reactivated fault orientations suggests apparent changes in the local stress field following the mainshock, which is also responsible for a remotely triggered cluster observed 1 month after the mainshock. This secondary triggering process enhances our understanding of the trailing effect of HF-induced seismicity. Plain Language Summary Since 2018, the Red Deer region in Alberta, Canada, has experienced an increasing number of earthquakes, most of which are associated with nearby hydraulic fracturing operations. In this study, we analyze data from a dense array of seismic sensors and regional seismometers to detect and locate events surrounding a hydraulic fracturing site near Red Deer from 4 March to 10 April 2019. The spatial distribution of the earthquakes defines a complex fault system that was activated at two different times. The results in this study signify stress changes in the shallow crust in connection with the 4.18 magnitude earthquake on 4 March 2019. Modifications to the regional stress regime are relatively long-lived, as suggested by the continued occurrences of smaller earthquakes 1 month after the mainshock.
Although hydraulic fracturing-induced earthquakes have been widely reported in Alberta, Canada, only one seismic cluster (the Cordel Field) has thus far been linked to wastewater disposal (WD). In this study, we report a statistically significant spatiotemporal correlation between recent earthquakes and nearby WD wells near Musreau Lake—the second disposal-induced earthquake swarm in Alberta. This newly occurred swarm contains five events with local magnitudes ML>3 from January 2018 to March 2020, forming into three tightly spaced clusters. The refined locations and focal mechanisms suggest a ∼10 km long northwest–southeast-trending rupture along the northern Rocky Mountains that developed over time, during which both poroelastic effects and static stress transfer played key roles. Through a statistical analysis of all reported induced earthquake clusters in the western Canada sedimentary basin (WCSB), we propose a linear predictive relationship (i.e., the “Interpolated Strike Orientation” model) between fault rupture direction and fault distance to the Rocky Mountains. This observation-based model, which is supported by both the focal mechanisms of the natural earthquakes and the nearby northwest-striking geological faults, is a new and useful reference for future assessments of seismic hazard in the WCSB.
We analyze the temporal evolution of the induced seismicity related to hydraulic fracturing activities in the Duvernay Formation, near Fox Creek, Alberta, Canada. For this analysis, we estimate annual Gutenberg‐Richter parameters, a(t) $a(t)$‐ and b(t) $b(t)$‐ values, and then calculate the annual likelihood of earthquakes greater than magnitude M>4 $M > 4$ from 2014 to 2020. The seismic hazard near Fox Creek has consistently decreased since 2015, from a 95% probability of an earthquake greater than magnitude M>4 $M > 4$ in 2015 to 4% in 2019 and less than 1% probability in 2020. The induced seismicity in Fox Creek is characterized by two actively seismic regions with distinctive features: (a) an Eastern region (∼220 events M>2 $M > 2$) with lower b‐values and higher hazard; (b) a Western region (∼210 events M>2 $M > 2$) with higher b‐values and lower seismic hazard. In contrast, extensive regions where hydraulic fracturing is performed, particularly East of the seismic cluster, remain non‐seismogenic. The overall decreasing seismic hazard, which contrasts with increasing operator activity, can be associated with (a) the intensification of hydraulic fracturing operations toward areas less susceptible to induced seismicity and (b) the reduction of seismic activity in the Eastern region, which exhibits the highest seismic hazard. We also find evidence of a minimum annual injection volume required to trigger induced seismicity in both the Western and Eastern regions. The minimum injection threshold increases over the years, implying increasingly successful mitigation strategies, likely due to regulatory implementations in the area, which has led the operators to exercise precaution in regions with significant seismic hazard and adapt treatment strategies to avoid triggering moderate magnitude size events during hydraulic fracturing stimulations.
We generate short‐term seismic hazard maps for the province of Alberta, Canada, from 2011 through 2020. First, we describe the required adaptations to probabilistic seismic hazard analysis to generate short‐term seismic hazard maps, following the Monte Carlo simulation approach. Second, we identify the natural and induced seismic source areas in Alberta and estimate their earthquake recurrence parameters revealing considerable spatio‐temporal variations in the a $a$‐ and b $b$‐values in the different seismic clusters in the province. Areas with the highest short‐term seismic hazard during the last decade in Alberta are related to cases of induced seismicity, including hydraulic fracturing activities in the Duvernay Fm., near Fox Creek, and waste‐water disposal activities near the Musreau Lake. These maps provide a valuable tool to quantify the short‐term evolution in the seismic hazard, which is particularly important considering past and emerging cases of induced seismicity related to the energy sector in Alberta. Furthermore, using parameters from the previous year, we make a seismic hazard forecast for the year 2021. Our analysis provides a baseline of expected short‐term seismic hazard, with inheren uncertainty due to the assumption of unchanged recurrence parameters from the previous year; yet our study reveals pertinent seismicity patterns in line with changing human activities.
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