Early geophysical papers of the Early geophysical papers of the Society of Exploration Geophysicists earlygeophysical00soci Year: 1947 36 EUGENE McDERMOTT depth determinations opposite it on the cross section. The two re- flections, Pecan Gap and basal Austin member, are marked on the records and the datum values shown. These datum values are shown to scale on the cross section. Due to the greater depth of the Austin, the reflection from it should be smaller in amplitude than that from the Pecan Gap. For a reasonably large Pecan Gap reflection the Austin reflection amplitude NtV&DOO COUNTY- T
Early geophysical papers of the Early geophysical papers of the Society of Exploration Geophysicists earlygeophysical00soci Year: 1947 36 EUGENE McDERMOTT depth determinations opposite it on the cross section. The two re- flections, Pecan Gap and basal Austin member, are marked on the records and the datum values shown. These datum values are shown to scale on the cross section. Due to the greater depth of the Austin, the reflection from it should be smaller in amplitude than that from the Pecan Gap. For a reasonably large Pecan Gap reflection the Austin reflection amplitude NtV&DOO COUNTY- TEXAS Fig. i.—Typical reflection record showing relation of reflections to geologic section. is almost too small to use. It is, therefore, general practice to take several records with different dynamite charges. In this way both large- and small-amplitude records are obtained for the two reflec- tions. The small-amplitude Austin reflections shown in Figure 4 have been further substantiated by larger amplitude records. Attention is called to the absence of the Austin reflection on record It so happens that the normal reflection point on the Austin falls in the Austin fault plane. In view of the extraneous disturbance in this record at the time of normal occurrence of the Austin reflec- 366
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