Abstract

We provide a close look at the source mechanism of hydraulically fractured induced earthquakes and the in situ stress field within the southern Montney unconventional play in the northeast British Columbia, Canada. P‐wave first‐motion focal mechanisms were obtained for 66 earthquakes with magnitudes between 1.5 and 4.6. Results show that strike‐slip movement is the prevailing source mechanism for the events in this area, although reverse faulting is also observed for a few earthquakes. The best‐fitting nodal plane mostly strikes at N60°E, with most events having dip angles of >60°. Using the Martinez‐Garzon et al. (2014) stress inversion module, we obtained the orientation of the three principal compressive stress (S1>S2>S3) and the relative intermediate principal stress magnitude (R) in five clusters. Assuming the best‐fitting nodal plane to be the causative fault, R values are mostly between 0.8 and 0.9 suggesting that the magnitude of S2 and S3 are similar, which is consistent with strike‐slip or reverse‐faulting regimes. The plunge of S1 varies between 1° and 3°, with its trend varying between N21°E and N34°E. On the other hand, the plunge of S3 varies between 22° and 50°, with its trend varies between N68°W and N58°W. Following Lund and Townend (2007), we calculated the trend of maximum horizontal stress to vary from N22°E to N33°E, in comparison with the average trend of N41°E from the World Stress Map (Heidbach et al., 2016). Through analysis of the Coulomb failure criterion and Mohr diagrams, we estimated the amount of pore‐pressure increase necessary to initiate shear slip to range between 4 and 29 MPa (average of 14±8  MPa) in the study area.

You do not currently have access to this article.