Glacial Isostatic Adjustment Workshop 2025
Date:
GIA on the Queen Charlotte Fault over the Last Deglaciation
Along major plate boundaries, tectonic loading is usually the first-order driver of earthquake activity and structural evolution. However, Glacial Isostatic Adjustment (GIA) induced by the unloading of major continental ice sheets can perturb the state of stress on plate boundary faults over glacial-interglacial periods. The strike-slip Fairweather-Queen Charlotte Fault (QCF) is located between the Pacific and North American plates, offshore of southeastern Alaska and western British Columbia, in the vicinity of the former Cordilleran Ice Sheet. Recent studies suggest that crustal stress change due to GIA since the Little Ice Age promoted over half of instrumentally-recorded earthquakes on the QCF, but the role of GIA on longer timescales, when ice-mass changes were of greater magnitude, remains unknown. In this study, we assess how GIA modulates stress on the QCF over the last deglaciation (26 to 0 ka), and whether these effects influence seismicity and fault zone structures. We project crustal stress changes onto the fault system using various ice histories and a 1-D spherically symmetrical viscoelastic Earth model. We search for correlations between these stress perturbations and submarine tectonic geomorphic features that indicate zones of transpression or transtension, which correspond to along-strike variations in obliquity on the fault. This approach enables us to evaluate the role of GIA-induced stress changes on earthquake rupture geometry over ice-age timescales, potentially revealing the role of GIA in shaping fault geometry and contributing to earthquake hazards in Alaska.