This study is determining the relationships between glacial rebound and tectonic strain in southern Alaska. Very high uplift rates (25-30 mm/yr based on GPS) are reported in the region where the Queen Charlotte-Fairweather fault system ends. High horizontal velocities are associated with this transform system and the area has experienced rapid deglaciation since the Little Ice Age. Numerical isostatic rebound models are being used to generate three-dimensional predictions of deformation, which will be constrained by the extensive data set that has already been acquired. This existing data set is the product of an interdisciplinary effort to determine the timing, magnitude and history of uplift and ice load changes in southeast Alaska. The observations consist of a regional Global Positioning System (GPS) crustal deformation array of 76 sites, sea level rates at 18 tide gauge sites, raised shoreline measurements of total uplift, and onset of uplift at 27 sites. These data characterize the regional pattern of uplift on centennial, decadal, and annual time scales, and portray the current regional pattern of three-dimensional crustal deformation. The research team is: 1) refining current glacial isostatic rebound models using an improved GPS and raised shoreline database; 2) developing numerical rebound models that generate three-dimensional predictions of deformation; 3) using model predictions of three-dimensional deformation to remove the horizontal component of isostatically induced motion from horizontal velocity observations to obtain the tectonic deformation of the region; 4) evaluating the resulting tectonic velocity and strain fields in terms of regional crustal dynamics and processes with specific emphasis on the implications for formation of the Fairweather and St. Elias Ranges, genesis of the Denali fault, and dynamics of the Yakutat Block collision; 5) evaluating seismic potential specifically induced by unloading, as well as effects of unloading on tectonic seismic potential. Using numerical models to quantify glacial isostatic rebound, crustal and mantle viscoelastic properties will be resolved using the vertical deformation signal, and thereby provide a means to separate tectonic and isostatic signals in the horizontal deformation field.
