Question

Method for measuring Dip & Strike

Answer 1

If we had to designate one set of measurements that is fundamental to all geology, it would have to be Dip and Strike. These simple measures define uniquely the orientation (compass bearings and angles) of a planar surface – any plane: bedding, faults, axial planes, mineralized veins, dykes and sills. Armed with dips and strikes, a geologist can project planes and the rocks they encompass across valleys, through mountains and deep beneath the Earth’s surface. They are fundamental to deciphering Earth structures.

Strike: The compass bearing of an imagined horizontal line across the plane. If the plane is flat there is an infinite number of strike lines, all having the same bearing. If the plane is curved (e.g. a plunging fold) the bearing may change systematically over the fold.

Azimuth, or compass bearing is recorded as either (for example) 035o or N35E, or its counterpart 215o and S35W.

Dip: Dip is the angle of inclination measured from a horizontal line at right angles to strike. The angle is measured by placing a compass on the line of dip and rotating the inclinometer to the point where a spirit level indicates horizontal. The direction of dip need not be measured (it can be calculated directly from the strike bearing), but an approximate direction should always be recorded to avoid ambiguity, as in 48oNW.

The inclination measured at right angles to strike is the true dip. Inclinations measured at other angles on the plane will always be less than true dip – these are called apparent dips.