# Dictionary:Depth rule

A rule relating the depth of a body to a feature of anomaly shape. Depth rules apply to specific anomaly source-body shapes; see Figure D-10. **1**. Rules used in gravity interpretation include (**a**) **half-width rules** (the half-width being half the width at half the anomaly amplitude): for point masses: depth=1.3 half-width, and for horizontal line masses: depth=half-width. (**b**) For thin semi-infinite slabs and faults: half the width between points where the anomaly is one-quarter and three-quarters amplitude (see Figure H-1). **2**. Rules used in magnetic interpretation include (**a**) the *straight-slope-measurement rule* (q.v.); (**b**) the **Peters’ rule** for dikes: depth=5/8 of the horizontal distance between points where the slope is half the maximum slope; (**c**) the **Tiburg rule** for magnetic poles: depth=2/3 of the horizontal distance at half the maximum amplitude; (**d**) the **Hannel rule** for magnetic poles: depth=half of the horizontal distance at a third the maximum amplitude; (**e**) the **Thalen rule**: the depth of a magnetic source is 0.7 the horizontal distance between maxima and minima; and other such rules. See also *automated depth estimation* and *radial power spectrum*.