A series of chemical explosions in Hudson Bay in 1965 has been studied using array techniques on the recordings at the Yellowknife seismic array. An upper mantle velocity model valid for the Churchill Province of the Canadian Shield has been derived, using the Wiechert-Herglotz method for the upper layers. A strong velocity gradient is required for the first 150km under the Mohorovicic discontinuity, underlain by a weak P-wave low velocity layer. Comparison with array results from the 1966 Early Rise shots in Lake Superior strongly suggests significant Pvelocity differences in the upper mantle under the different provinces of the Canadian Precambrian Shield.