Investigating GIA-driven intraplate deformation in Eastern Canada with GNSS clustering and 3D strain rate analysis

Intraplate seismicity in Eastern Canada is characterised by spatially clustered earthquakes within the relatively stable continental interior. This seismicity poses significant seismic hazards to urban centres like Ottawa, Montreal, and Quebec City. Deciphering the mechanisms driving the spatiotemporal distribution of intraplate seismicity in eastern Canada has proven elusive with previous work suggesting a complex interplay of far-field tectonic and glacial isostatic adjustment (GIA) processes acting on older geologic structures. We explore the application of a microplate tectonic framework and strain rate analysis based on Global Navigation Satellite System (GNSS) velocities to better understand the physical processes driving the distribution of seismicity and deformation in this region. We test the application of the microplate model in eastern Canada by analysing horizontal GNSS velocities using an established machine learning cluster analysis approach and comparing results with the distribution of GIA signals. The machine learning-based clustering does not reveal distinct microplate boundaries; however, we identify zones of different styles of deformation that align well with zones of uplift and subsidence associated with GIA. For the strain rate analysis, we test the influence of deformation due to GIA by including vertical GNSS velocities in our strain rate calculations assuming volume conservation. In eastern Canada, we quantify volumetric strain rates due to vertical deformation ranging from -1.16 × 10 -9 /yr to 4.12 × 10 -9 /yr and suggest these values may be sufficient to reactivate ancient faults. This work contributes to our understanding of seismic risks associated with GIA by highlighting regions where future seismicity may occur and quantifying volumetric strain rate values that may be sufficient to reactivate preexisting structures.