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Digital Filtering of Deep Crustal Seismic Reflections

1972; NRC Research Press; Volume: 9; Issue: 4 Linguagem: Inglês

10.1139/e72-035

1480-3313

R. M. Clowes, E. R. Kanasewich,

Seismology and Earthquake Studies

Seismic reflections at near-vertical incidence from within the lower crust were recorded along a 90 km continuous profile in southern Alberta. The digitized seismograms were filtered as a means of improving signal-to-noise ratios. Zero-phase bandpass filtering improves the quality of the records but also introduces a disadvantage; the narrow pass bands cause the filtered seismograms to become more oscillatory and exclusion of the higher frequencies destroys some of the record character which is useful in phase correlation. Velocity filtering is shown to be a more effective means of delineating individual reflection events, particularly if their apparent velocities vary widely. A record section compiled from such filtered data indicates a considerable number of reflecting horizons at various depths in the lower crust. When the reflections are migrated and a "wiggle" structure section compiled, the complexity of the lower crust in southern Alberta is revealed. Vertical relief reaches as much as 9 km over a horizontal distance of 40 km and lateral changes in the layered system can be noted.