Strain accumulation and release rate in Canada: Implications for
long-term crustal deformation and earthquake hazards
Abstract
To advance the understanding of crustal deformation and earthquake
hazards in Canada, we analyze seismic and geodetic datasets and robustly
estimate the crust strain accumulation and release rate by earthquakes.
We find that less than 20% of the accumulated strain is released by
earthquakes across the study area providing evidence for large-scale
aseismic deformation. We attribute this to Glacial Isostatic Adjustment
(GIA) in eastern Canada, where predictions from the GIA model accounts
for most of the observed discrepancy between the seismic and the
geodetic moment rates. In western Canada, only a small percentage
(< 20%) of the discrepancy can be attributed to GIA-related
deformation. We suspect that this may reflect the inaccuracy of the GIA
model to account for heterogeneity in Earth structure or indicate that
the present-day effect of GIA in western Canada is limited due to the
fast response of the upper mantle to the de-glaciation of the Cordillera
Ice Sheet. At locations of previously identified seismic source zones,
we speculate that the unreleased strain is been stored cumulatively in
the crust and will be released as earthquakes in the future. The
Gutenberg-Richter (GR) model predicts, however, that the recurrence
interval can vary significantly in Canada, ranging from decades near
plate boundary zones in the west to thousands of years in the stable
continental interior. Our attempt to quantify the GIA-induced
deformation provides the necessary first step for the integration of
geodetic strain rates in seismic hazard analysis in Canada.