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Environmental and Engineering Geoscience

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Finding the Mean and 95 Percent Confidence Interval of a Set of Strike-and-Dip or Lineation Data

¹ Department of Geology, Baylor University, One Bear Place #97354, Waco, TX 76798-7354

Quantitative observational data should be reported with appropriate uncertainty estimates. Statistical methods developed by Fisher (1953) to analyze paleomagnetic data are also useful for determining the 95 percent confidence interval associated with site mean strike and dip from three or more observations (at least seven observations preferred) of the orientation of geologic surfaces that are approximately homoclinal or of lineations that are subparallel. The uncertainty in the strike of a surface is a function of the uncertainty and inclination of the dip vector and is greater than the dip uncertainty. For example, surfaces with measured orientations (strike and dip) of 310° 38°NE, 319° 45°NE, and 322° 30°NE at a given site have a site mean orientation of 317 ± 18° and 38 ± 14°NE at a 95 percent confidence interval.

Key Words: Field Methods • Uncertainty • Fisher Statistics • Spherical Data