Abstract

The Arctic seismic program of 1964 and 1965 comprised two refraction profiles between Prince Patrick Island and Melville Island, and one refraction profile extending 192 km onto the ocean northwest of Brock Island. Numerous intermediate layer (P1) and upper mantle (Pn) events were also recorded on paths not confined to the profiles, thus allowing a "time-term" analysis for these events.High-velocity layers within the sedimentary section cause a velocity inversion problem, whereby the lower velocity and depth of the underlying basement complex is not revealed by the seismic refraction method. The bottom of the basement complex is marked by the intermediate layer having a compressional wave velocity of about 6.25 km/s and depths near 10 km.Velocity of Pn events is 8.18 km/s and these were recorded near the critical distance at one station, providing an estimate of the time-term to depth conversion factor of 9.56 km/s. Pn events traversing Eglinton Island and the west coast of Melville Island show excess times of 0.6 s to 3 s. This region of apparently low mantle velocity may be related to the geomagnetic variation anomaly reported near by.The average time-term of 3.67 s represents an average crustal thickness of 35 km. Some variation in crustal time-terms is caused by differing thicknesses of low velocity sediments rather than undulations on the crust–mantle interface. The time-term of 3.07 s for the most distant shot on the ocean profile does not, by itself, suggest a thinner crust than similar values among the islands; this is shown to be a possible interpretation problem.A negative correlation between crustal time-terms and Bouguer gravity values is noted to be partly due to the effect of varying proportions of low-velocity – low-density rocks and high-velocity – high-density rocks within a few km of depth.

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