Rake (Pitch) of Fault

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Rake of a Fault

1. What is Rake?

Rake is the angle between the fault slip direction and the horizontal strike line of the fault plane. It measures how a fault moves along its plane.


2. Why is Rake Important?

  • Helps geologists classify fault movement (normal, reverse, or strike-slip).
  • Crucial for understanding earthquake mechanisms and tectonic stress.
  • Used in focal mechanism solutions to describe fault behavior.

3. How is Rake Measured?

  • Measured within the fault plane, ranging from -180° to +180°.
  • A rake of 0° or ±180° indicates pure strike-slip motion.
  • A rake of 90° or -90° indicates pure dip-slip motion (normal or reverse fault).
  • Intermediate values (e.g., 30°, 45°, 60°) indicate oblique-slip movement.

4. Rake Values and Fault Types

Example:

If a fault has a strike of 320° and a slip direction of 40°, the rake would be measured as 40° from the horizontal strike line within the fault plane.


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