Sequential Fault Reactivation and Secondary Triggering in the March 2019 Red Deer Induced Earthquake Swarm

Abstract

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.

Insights on Controlling Factors of Hydraulically Induced Seismicity in the Duvernay East Shale Basin

“… Spatial and temporal view of events and HF treatments. (a–d) Spatial view of event epicenters, colored by time and scaled by magnitude (J. Wang et al., 2020). The dashed black line in (b) indicates the lineament distribution of induced events.…”

“…The induced seismicity catalog in Figure 1 is obtained from the Composite Alberta Seismicity Catalog (http://www.inducedseismicity.ca/catalogues, last accessed on 2020/08/27). The induced seismicity catalog and focal mechanisms are available through J. Wang et al., 2020 (chrome‐extension://oemmndcbldboiebfnladdacbdfmadadm/https://agupubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1029/2020GL090219%26file=grl61461-sup-0001-2020GL090219-SI.pdf).…”

“…The fracturing operations were monitored by the regional seismology networks (red triangles in Figures 2a) and 417 induced earthquakes were detected (Schultz & Wang, 2020; J. Wang et al., 2020). In this study, 38 events with the resolved focal mechanisms were selected and shown in Figure 2.…”

“…The light blue line denotes the trajectory of associated horizontal wells. The colored triangles are regional seismic monitoring stations (J. Wang et al., 2020).…”

“…Very few events were observed in the Red Deer area before March 2019; these were nontectonic events with M L < 2. However, on March 4, 2019, an M L 4.18‐magnitude earthquake was triggered during fracturing stimulations of two horizontal wells (Schultz & Wang, 2020; J. Wang et al., 2020). This red‐light event (earthquakes with M L > 4.0) was also felt by nearby residents and hence received public concerns for fracturing‐induced seismicity.…”