Lake Superior Crust

I came across an article in Geological Society of American, Memoir 156 (1982) published by Henry Halls on the thickness of the crust in the Lake Superior region. In the article, crustal thicknesses (apparent) at various locations in and around Lake Superior had been compiled from a variety of seismic data sources (primarily Project Early Rise and the Lake Superior Experiment). The data indicated a significant thickening of the earth's crust under and around Lake Superior.