No Dip or Low Dip?

James D. Morse

How does one distinguish between zero homoclinal dip (no dip) and low homoclinal dip (low dip) using just the dipmeter tadpole plot? Because of scatter, no-dip and low-dip settings both involve dip angles near zero that cannot be distinguished on tadpole plots on the basis of dip alone. They can, however, be distinguished on the basis of azimuth: on the A plot (azimuth vs. depth plot), no-dip settings show completely random azimuth distributions, whereas low-dip settings show subtle concentrations of data at the true azimuth. Once we have chosen, on the basis of the A-plot pattern, one of the two settings, SCAT permits tests of this initial interpretation. No-dip and low-dip patterns are usually different on DVA (dip vs. azimuth) and tangent plots; they are almost always ifferent on azimuth-frequency histograms and on plots of apparent dip vs. depth. Therefore, we can test our initial interpretation by examining the actual patterns on these plots, with special emphasis on the last two. This ability to test interpretations is made possible by SCAT's multiple-display approach, an invaluable strength. In low-dip settings, the tadpole plot does not clearly show the preferred azimuth that the A-plot reveals. Moreover, the tadpole-plot approach provides no way to test interpretations. Therefore, zero dip cannot confidently be distinguished from low dip using the tadpole plot.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.