Characterizing the Recent Increasing Seismicity near Musreau Lake, Alberta

Abstract:

Recently, emerging cases of seismicity in the Duvernay East Shale Basin have garnered major public attention and scientific interest in academia and industry. From December 2019, an M~3.9 earthquake and its numerous aftershocks were detected near Musreau Lake in west-central Alberta. The sudden rise in seismicity in a relatively short time and the correlation between the timing of earthquake activity and fluid disposal in this region suggest that these events are potentially induced. In this study, we utilize regional broadband stations to investigate the spatiotemporal variations of the Musreau Lake earthquake sequence from January 2019 to March 2020. Using three-component raw time series data and a 16-layer velocity model, we construct a refined earthquake catalog with more accurate event locations. A machine-learning phase-picker (PhaseNet) was used to re-identify P and S arrivals with confidence levels. The reported hypocenter locations were then refined by a least-square location method and further improved using a double-difference relocation algorithm. Our relocated catalog contains three tightly spaced clusters of events, with an apparent spatial migration towards southeast over time along the Rocky Mountains. The determined source parameters of a subset of M>1.5 earthquakes demonstrate NNW-SSE left-lateral strike-slip mechanisms. A detailed comparison of Musreau Lake earthquake swarm against other induced earthquakes in Fort St. John, Fox Creek, and Red Deer in western Alberta suggests a strong spatial change in the fault orientations from NW to NE along the Rocky Mountains foothills. The strike angles of the four induced earthquake clusters linearly correlate with event distances to the Rocky Mountain foothills, which may be attributed by the two components: (1) the pre-existing NW-SE trending and (2) the NE-SW regional stress. In summary, these results offer new insights into both the spatiotemporal variations in earthquake location and the focal mechanism associated with induced earthquakes in western Alberta.