Scaling of induced seismicity, implications for the role of geological setting on seismic hazard

In this study we present conflicting stress drop estimates of injection-induced events in two regions of the Western Canadian Sedimentary Basin. Horn River Basin events show lower stress drops than Duvernay Basin events by a factor of 10 to 20. We propose that the observed stress drop differences are caused by different regional stress characteristics, assuming the seismic events are generated during similar injection programs. A potential difference the Fox Creek region is characterized by the presence of reefs in the Leduc formation that cross-cut the Duvernay shale formations which form drapes over the reef-off reef facies (Stoakes, 1980). We suggest that differences in stress drops reflect differences in the regional stress state with events occurring in more stressed regions having higher stress drops, that is, being able to release larger quantities of stored elastic strain. Higher stress drop earthquakes have a significant role in seismic hazard as they generate higher frequency strong ground motions which can potentially cause more damages.