Stress drop estimates and hypocenter relocations of induced seismicity near Crooked Lake, Alberta

We use a sequence of induced earthquakes near Crooked Lake, Alberta, to investigate the physical differences between induced and tectonic earthquakes. Starting with the Natural Resources Canada earthquake catalogue, we use a spectral ratio method to calculate the static stress drops of a group of relocated earthquakes ranging from December 2013 to June 2015. We find that stress drops fall within the high side of the typical reported range of tectonic events and show no correlation with earthquake magnitude, depth, or distance from the well. The stress drops appear roughly constant for events with M-w 3 to 4. Relocated hypocenters cluster both spatially and temporally around corresponding injection wells and appear to migrate deeper with increasing time from injection. Fine-scale lineations apparent in relocated hypocenters could indicate the presence and orientation of fault planes, consistent with the published focal mechanism solutions of M 4+ events in the area.