Deep crustal seismic reflections at near-vertical incidence

Abstract

Abstract Seismic reflections from discontinuities deep within the crust (reflection times 8-16 sec) have been recorded along four lines over a widespread area in southern Alberta for a total of 90 km of near-vertical-incidence profiling. Along one profile an expanding spread was utilized and a strong reflection at 11.6 sec was continuously correlated over nearly 25 km. A least-squares analysis of the X 2 , T 2 plot gives an average vertical velocity of 6.2 kmps to a depth of 34 km. Continuous profiling along a line 40 km long resulted in a seismic cross section which shows structural relief of 8 km over a distance of 25 km. These results indicate that the reflection technique with its high resolving power may be used to map complicated structures which even a detailed refraction survey may fail to delineate. It is probable that many continental areas have similar crustal complexities undetected by the refraction method.