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THE USE OF AMPLITUDES IN REFRACTION SHOOTING – A CASE HISTORY *
Author(s) -
O'BRIEN P. N. S.
Publication year - 1960
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1960.tb01725.x
Subject(s) - refraction , geology , amplitude , overburden , seismology , attenuation , reflection (computer programming) , arrival time , refracting telescope , seismic refraction , geodesy , gemology , optics , geotechnical engineering , engineering geology , physics , tectonics , engineering , computer science , transport engineering , programming language , volcanism
A bstract On a group of seismic refraction records there occurs a late arrival with the same apparent velocity as an earlier arrival. It was first thought that the late arrival travelled along the same refractor as the earlier one but had been delayed in the overburden either by multiple reflection or by P‐S (dilatation to shear) conversion. Either of these two mechanisms could be made to fit the time‐distance data. A study of the ratio of the amplitudes of the two events showed that the observed ratio was about ten times that to be expected on either of these hypotheses. Also, the rate of attenuation of the earlier arrival (3.7 ± 1.0 db/1000 ft) was appropriate to a thin layer while the rate for the later arrival (0.74 ± 0.30 db/1000 ft) was appropriate to a thick layer. Accordingly, the later arrival was identified as a refraction from a deeper layer. The subsequent depth section agreed very well with that found by drilling.