Abstract

Record sections from partially reversed refraction lines in northern British Columbia show that the amplitudes of upper mantle arrivals vary smoothly with distance, while the pattern of crustal arrival amplitudes is not smooth. Normalization of the seismograms to remove the effects of varying shot size and instrument response show that Pn amplitudes are largely site-independent.Models derived from ray theory indicate a crust which thins from about 40 km in the Omineca Crystalline Belt to about 25 km in the Insular Trough. The average Pn velocity is 8.06 km s−1, and the average crustal velocity is 6.4 km s−1. The secondary energy indicates that the models are greatly simplified.A time–term profile between the Omineca Crystalline Belt and the Coast Mountains suggests a Mohorovičić transition which is characterized by two significant topographic wavelengths. The shorter (200 km) wavelength correlates roughly with the Cordilleran structural elements of Wheeler and Gabrielse (1972). The larger (800 km) wavelength may have tectonic significance.

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