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.
This study analyzes earthquake recordings from four near‐source (<10 km) stations near Fox Creek, Alberta, a region known for hydraulic fracturing‐induced seismicity. We examine the spatiotemporal variations of focal mechanisms and seismic anisotropy in the sedimentary strata. The focal mechanisms of surrounding earthquake swarms are generally consistent with the strike‐slip mechanism of the ML 4.6 earthquake, favoring a flower type of fault structure. The NE‐SW‐orientated fast splitting direction, determined from the shear wave splitting measurements, reflects the combined effects of (1) N‐S faults and (2) NE‐SW time‐dependent hydraulically stimulated fractures. The latter effect dominates the apparent anisotropy during the days leading to the mainshock, while its contributions are reduced by 60–70% after the mainshock. Loss of fluid into the fault damage zone, which causes the closure of fractures, is responsible for the observed spatiotemporal variation of seismic anisotropy near the hydraulic fracturing well.
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.
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