Focal mechanism of the induced earthquake of 2015-06-13 (Alberta, Canada), based on waveform inversion

Abstract

Understanding the source mechanisms of induced earthquakes is important to distinguish them from natural earthquakes. The main objective of our study consists in finding out which parameters of the source mechanism can be used most effectively to identify the induced earthquakes. A possibility is also being explored whether they can be retrieved from data of a limited number of stations or even just one. We calculate versions of the seismic moment tensor and the corresponding focal mechanisms of the induced event of 2015-06-13 (t0=23:57:53.00 UTC, φ=54.233˚N, λ=-116.627˚E, hs=4 km, ML4.4) near Fox Creek, Alberta, Canada, by inversion of only direct waves recorded at one, two, three and seven stations. The versions turned out to be practically identical, which indicates the advantage of using only direct waves and the very possibility of determining the focal mechanism from the records at the limited number of seismic stations, which may be especially valuable in areas with a sparse seismic network. The versions also turned out to be very similar to the one obtained in [Wang, 2018], which can be considered an additional proof of the reliability of our method. The source time function of the Alberta event had a longer duration (~4 s) than is typical for tectonic earthquakes of similar size. We assume that this very feature may be specific to induced earthquakes and used in combination with others to distinguish them from tectonic earthquakes.