Early geophysical papers of the Society of Exploration Geophysicists earlygeophysical00soci Year: 1947 GEOLOGICAL APPLICATION OF SEISMOGRAPH]' 1327 or This relation of time of arrival is the principal criterion for the identification of reflections. The differences in arrival time of any other type of wave are considerably greater. For example, the incre- ment of time for the directly transmitted wave is approximately second. For refractions from shallow beds to be confused with the re- flections would require exorbitantly high velocities in these shallow beds. Beds showing
Early geophysical papers of the Society of Exploration Geophysicists earlygeophysical00soci Year: 1947 GEOLOGICAL APPLICATION OF SEISMOGRAPH]' 1327 or This relation of time of arrival is the principal criterion for the identification of reflections. The differences in arrival time of any other type of wave are considerably greater. For example, the incre- ment of time for the directly transmitted wave is approximately second. For refractions from shallow beds to be confused with the re- flections would require exorbitantly high velocities in these shallow beds. Beds showing such velocities do not exist. As a matter of fact there is no great difficulty in identifying reflec- tions on the record. Any difficulties that may present themselves are ordinarily those caused by the presence of too many reflecting strata too close together and the consequent appearance on the record of too many reflections. This, of course, can not be altered without altering the sub- shot RECORDERS Fig. 10.— sloping surface. 45
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