Deep crustal seismic reflections at near‐vertical incidence

TLDR: In this paper, a system of geophone and hole patterns was designed to form an effective filter against long period surface waves, which were recorded on FM analog magnetic tape and the results were digitized in order to apply digital processing techniques.

Abstract: Seismic reflections from discontinuities deep within the crust (reflection times of 8 to 16 sec) have been recorded along four different lines over a widespread area in southern Alberta, resulting in a total of 90 km of near‐vertical‐incidence profiling. Systems of geophone and hole patterns were designed to form an effective filter against long period surface waves. The data were recorded on FM analog magnetic tape and the results were digitized in order to apply digital processing techniques. Power‐spectra calculations indicate that the energy of the reflected wavelets is concentrated in the range 5 to 15 Hz. Synthetic seismograms were made for comparison with field recordings and they suggest that velocity transition zones within the deep crust are less than one kilometer in vertical extent. 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 X2, T2 plot gives an average vertical velocity o...