Abstract
The degree to which glaciation-deglaciation can influence earthquake activity in eastern Canada depends on how weakened features in structures created by tectonic activity react to glacially-induced stress and strain. There are several regions where current (upper crustal) seismic activity appears to have been reactivated by the recent glacial episode. Seismicity along the Boothia Uplift — Bell Arch, which is a positive basement trend across the Canadian Shield, was probably rejuvenated by glacial loading centres that flanked both sides of this curvilinear trend. The forebulges produced by each load would reinforce each other and thereby generate an extensional stress component, which could reactivate weakened faults in this tectonic structure. At the north end of the Boothia Uplift, differential uplift of raised beaches across seismically-active Peel Sound suggests that adjacent blocks have sometimes moved independently with the differential motions amounting to as much as 100 m. Along northeastern periphery of the Canadian Shield, seismicity, steep gradients in free-air gravity anomaly, and steep gradients in postglacial uplift (since 8000 YBP) coincide, implying a causal correlation between seismicity, postglacial rebound and lateral variations in crustal structure in this region. However, in other regions of the craton where the gradient in uplift rate is small, the current level of seismicity cannot be clearly related to postglacial rebound. Satellite imagery of the southeast periphery of the craton shows pronounced faults or linears that could be boundaries of partially decoupled blocks. Different modes of tilt, rotation or uplift between adjacent blocks could modify the stress field and hence produce a different level of seismic activity. More geodetic and geophysical measurements are required to test this hypothesis and to differentiate between the contributions from postglacial rebound, which current measurements tend to support, and local neotectonic processes.
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Hasegawa, H.S., Basham, P.W. (1989). Spatial Correlation between Seismicity and Postglacial Rebound in Eastern Canada. In: Earthquakes at North-Atlantic Passive Margins: Neotectonics and Postglacial Rebound. NATO ASI Series, vol 266. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-2311-9_28
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DOI: https://doi.org/10.1007/978-94-009-2311-9_28
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