Previous seismic studies of crustal structure using short-period P-coda recorded in the vicinity of Leduc in central Alberta have indicated that serious discrepancies exist between the experimental observations and those based on a horizontally layered model of the crust in both the time and frequency domains.Using vertical-radial spectral ratios and synthetic seismograms, a modified crustal model has been derived which gives better agreement between experimental and theoretical results. This model involves the insertion of a layer several kilometers thick having large velocity contrast with respect to the surrounding media at the base of the Precambrian basement (12 km deep). The new crustal model is discussed in the light of evidence for a low velocity zone in the upper crust in certain continental regions.

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