Resolve fault displacement before interpreting map offset

1. Define the evidence and convention

A fault is a fracture or zone across which relative displacement has occurred. For an inclined plane, the hanging wall lies above the plane and the footwall below it. Normal and reverse components refer to downward and upward hanging-wall movement relative to the footwall, not simply to which present ground surface is higher.

2. Connect mechanism and model

The original plane dips east at δ and carries a 10 m hanging-wall displacement. Rake λ is measured in the plane from positive strike toward down-dip. Along-strike motion is 10cosλ, eastward horizontal motion is 10sinλ cosδ, and upward vertical motion is −10sinλ sinδ. These three orthogonal components reconstruct the same 10 m magnitude.

A positive rake in this convention produces a normal dip-slip component, negative rake a reverse component and zero rake pure strike-slip. Oblique slip combines components. The convention must be written down: switching the positive strike direction or the block being described can reverse signs without changing the physical event.

Throw is a vertical component, not net slip. Offset of a particular marker on a map also depends on the marker’s orientation and the ground surface. Fault striations, matching piercing points and multiple mapped relationships can discriminate displacement hypotheses; one apparent map separation cannot generally recover a full slip vector.

3. Reconstruct the worked packet

At dip 45° and rake 45°, strike component is 7.07107 m, east component 5 m and vertical component −5 m. Their squared sum is 100 m². This is oblique normal motion, not a 5 m total slip.

4. Predict and investigate

Predict first: Can two faults with the same net slip have different vertical throws?

Vary dip at fixed rake and then rake at fixed dip. Retain all signed components and reconstruct their vector magnitude. Explain why a marker offset may differ from the full displacement.

5. Test a changed case

Apply the evidence to a changed case

At dip 30° and rake −90°, find strike, east and upward components and classify the dip-slip component.

Retain the evidence frame, calculations and assumptions before opening public feedback.

Compare a worked response

Strike is zero, east is −8.66025 m and upward is +5 m. The hanging wall moves up-dip with a reverse component; net slip remains 10 m.

6. Retain a defensible evidence notebook

Preserve first predictions, map orientation, intermediate calculations, units, assumptions and alternatives. These maps, numerical packets and diagrams are original invented instructional cases, not surveyed sites or current hazard forecasts. Independent practical review and genuinely unfamiliar evidence remain separate learner gates.

Mechanism reference, checked 30 October 2026. Original prose, diagrams and numerical exercises. No physical loading, pressurization or field hazard exposure is requested.