Moment tensors, state of stress and their relation to post-glacial rebound in northeastern Canada

• Published in: Geophysical Journal International
• Main Authors: Steffen, Rebekka, Eaton, David W., Wu, Patrick
• Format: Text
• Language: English
• Published: Oxford University Press 2012
• Subjects: Seismology; Canada; Hudson; Hudson Bay
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/189/3/1741; https://doi.org/10.1111/j.1365-246X.2012.05452.x

In the stable craton of northeastern Canada moderate seismicity as well as glacial isostatic adjustment (GIA) has been observed. We investigate five earthquakes with moment magnitudes between 3.6 and 4.1 that have occurred in northern Hudson Bay since 2007, which may be triggered by GIA. Focal mechanisms of the earthquakes are determined using a waveform-fitting procedure for surface waves, in which the best double-couple mechanism is obtained through a grid search over strike, dip, and rake. All events exhibit a thrust-fault mechanism, in general agreement with mechanisms of previously analysed earthquakes in that area. Stress-inversion results incorporating our new mechanisms as well as previously published results exhibit significant differences from previously calculated stresses from GIA models. For the first time, maximum horizontal stress direction S Hmax is compared to the modelled stress values for northeastern Canada. We find that the maximum horizontal stress direction strikes roughly NNW–SSE, in contrast to previously inferred NE-SW orientation of S Hmax . Our results indicate that the local stress field in northern Hudson Bay deviates from regional stresses resulting from the existence of a roughly E–W oriented zone of faulting, which is not included in existing GIA models.