geology · structural
Fault Throw, Heave & Net Slip
Net slip = √(throw² + heave²); fault dip = atan2(throw, heave)
click formula to derive ↑
Inputs
ft
ft
Description
Resolves fault throw and heave — the vertical and horizontal components of displacement seen on a fault-perpendicular cross-section — into the net (dip-slip) displacement vector and the recovered dip of the fault plane itself. Throw, heave, vertical separation, and horizontal separation are frequently confused terms in practice; this calculator makes the throw/heave-to-net-slip geometry explicit.
Variables
| Symbol | Unit | Description |
|---|---|---|
| s | ft | Net Slip (Dip-Slip Displacement) |
| δf | ° | Fault Dip (Recovered from Throw/Heave) |
| T | ft | The vertical component of displacement across the fault, measured on a vertical section drawn perpendicular to fault strike — the vertical distance between a marker and its offset counterpart on the other side of the fault. |
| H | ft | The horizontal component of displacement across the fault, measured on the same fault-perpendicular vertical section as the throw. |
Assumptions
- The fault is a pure dip-slip structure with no strike-slip component — net slip computed here is the dip-slip displacement only.
- Throw and heave were both measured on the same vertical cross-section, drawn perpendicular to fault strike.
- The stratigraphic marker used to measure throw and heave is the same correlative surface on both sides of the fault (no facies-change ambiguity).
Limitations
- Cannot detect or account for a strike-slip component — if the fault has oblique-slip motion, the true net slip exceeds the dip-slip value computed here.
- If the cross-section used to read off throw and heave was not truly perpendicular to fault strike, the input values are already vertical/horizontal separation (not throw/heave), and both this calc's inputs and its fault-dip output will be distorted accordingly.
- These throw/heave/net-slip relationships are corroborated across multiple independent secondary structural-geology sources, but Tearpock & Bischke's *Applied Subsurface Geological Mapping*, 2nd ed. (2003) — the textbook they are attributed to — was not directly page-accessed this session. Treat the formulas as secondary-source-corroborated, not a page-checked citation from Tearpock & Bischke directly.
Use Cases
- → Recovering fault dip from a well-constrained throw/heave pair: When throw and heave are both known from cross-section construction or well correlation but the fault plane's own dip was not independently logged or measured, recover it from their ratio.
- → Quality-checking cross-section fault displacement: Verify that a mapped fault's throw, heave, and implied dip are mutually consistent before using the displacement in a reserves or seal-risk calculation.
Related Calculations
Region Notes
Global
Always confirm whether a reported throw/heave pair comes from a strike-perpendicular section — normal-fault-dominated extensional basins (e.g., Gulf of Mexico, North Sea) and listric growth faults in particular often have throw/heave values reported from along-dip sections that are not perpendicular to local fault strike.
References
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