Fault Throw, Heave, and Net Slip Calculator

Fault displacement is one of those topics where the vocabulary trips people up more than the actual geometry does. Throw, heave, dip-slip, net slip, rake, they all describe pieces of the same picture, but if you’ve only ever seen one or two of these terms, the rest can feel like a separate language. Once you see how they all connect through a couple of right triangles and one vector equation, it clicks fast.

The calculator on this page handles both halves of the problem. Enter any one known value, throw, heave, or the net dip-slip displacement along the fault plane, and it solves for the rest using the dip angle. Then, if the fault also moved sideways along strike rather than purely up or down the dip, you can add that strike-slip component and get the true net slip vector in three dimensions.

Throw, Heave, and Dip-Slip: The Basic Right Triangle

Picture a fault plane tilted at some angle from horizontal. A marker bed on one side of the fault has been offset from its matching position on the other side. That offset breaks down into two components.

Throw is the vertical component, the difference in elevation of the marker on either side of the fault.

Heave is the horizontal component, the offset measured perpendicular to the fault’s strike.

Net dip-slip is the true displacement measured directly along the fault surface itself, in the down-dip direction. It’s the hypotenuse of the right triangle formed by throw and heave, with the fault’s dip angle sitting between the hypotenuse and the heave side.

That right triangle relationship gives you three clean equations: throw equals dip-slip times the sine of the dip angle, heave equals dip-slip times the cosine of the dip angle, and dip-slip equals the square root of throw squared plus heave squared. Know the dip angle and any one of the three, and the other two follow immediately.

A Worked Example

Say you’ve mapped a fault with a dip of 60 degrees, and drilling on either side shows a marker bed offset with 50 meters of throw.

Dip-slip equals throw divided by the sine of the dip angle. Sine of 60 degrees is about 0.866, so 50 divided by 0.866 gives a net dip-slip of roughly 57.7 meters.

Heave equals throw divided by the tangent of the dip angle. Tangent of 60 degrees is about 1.732, so 50 divided by 1.732 gives a heave of roughly 28.9 meters.

Notice that a steeper fault (higher dip angle) produces less heave for the same amount of throw, since the displacement is more vertical to begin with. A shallow, low angle fault with the same 50 meters of throw would produce a much larger heave, since more of its total displacement runs horizontal.

When Faults Move Sideways Too: Oblique Slip

Pure dip-slip faults, ones that move straight up or down the dip direction with no sideways component, are actually somewhat rare in nature. Most faults show at least some oblique motion, a combination of dip-slip and strike-slip movement happening together. This is where the second half of the calculator comes in.

If you know the size of the dip-slip component and the size of the strike-slip component separately, along with the fault’s strike and dip, you can find the true net slip vector, meaning its actual magnitude and its actual direction in three dimensional space, not just along the fault’s dip line.

The way this works mathematically: the strike direction and the down-dip direction are two directions that both lie within the fault plane, and they happen to be perpendicular to each other. Treat each as a vector, scale them by however much slip happened in each direction, and add them together. The result is the true net slip vector, and from it you can extract the net slip magnitude, its trend and plunge (the compass direction it points and the angle it dips below horizontal), and its rake, the angle it makes with the strike line as measured within the fault plane itself.

Understanding Rake

Rake, sometimes called pitch, is the angle between the net slip vector and the strike line, measured within the fault plane. It’s a single number that tells you the character of the fault’s motion at a glance.

A rake near 90 degrees (or negative 90) means the fault moved almost purely up or down the dip, a classic dip-slip fault, normal or reverse depending on direction.

A rake near 0 or 180 degrees means the fault moved almost purely sideways along strike, a strike-slip fault.

Anything in between describes oblique motion, some mix of the two, and the closer the rake sits to 45 degrees, the more evenly split the dip-slip and strike-slip components are.

This single number is exactly why rake shows up constantly in earthquake focal mechanism solutions and fault slip data. It compresses a full 3D motion into one comparable value.

Why the Sign of Each Component Matters

In the calculator, a positive dip-slip component means normal sense motion, meaning the hanging wall (the block above the fault surface) moved down relative to the footwall. A negative value means reverse sense, the hanging wall moved up and over. Getting this sign right matters, since normal and reverse faults imply completely different stress regimes, extension for normal faults, compression for reverse faults, so mixing up the sense isn’t a minor detail.

Similarly, the strike-slip component’s sign tells you which of the two possible lateral directions the motion happened in, relative to whichever strike azimuth you entered. Since strike can technically be described in either of two opposite directions (a fault striking 045 could equally be described as striking 225), staying consistent about which direction you’re calling positive matters for getting a trend that actually matches what you observed in the field.

Common Mistakes

Mixing up throw with the total dip-slip displacement. Throw is only the vertical piece, not the full displacement along the fault surface, and treating them as the same thing understates the true amount of slip, sometimes significantly on a low angle fault.

Forgetting that heave depends heavily on dip angle. Two faults with identical throw can have very different heave values if their dip angles differ, which matters a lot when you’re trying to reconstruct offset across a fault in map view.

Ignoring the strike-slip component entirely on a fault that’s genuinely oblique. If field evidence like slickenlines suggests oblique motion but you only calculate dip-slip, you’ll underestimate the true net slip and get the wrong trend for it.

Who Uses This

Structural geologists reconstructing fault offset from throw and heave measured in cross section or from well data.

Students working through fault kinematics problems for the first time and wanting to check their trigonometry.

Seismologists and engineering geologists working with rake and net slip data from fault studies or focal mechanism solutions.

Anyone reconciling stratigraphic offset seen in adjacent boreholes with the geometry of a fault that likely caused it.

Try It Above

Start with the dip-slip section if you’re working with a straightforward normal or reverse fault and know one of throw, heave, or dip-slip. If there’s a lateral component too, move to the second section, add your strike and strike-slip value, and get the full net slip vector along with its rake.

Related Calculators and Reference

• Apparent and True Dip Converter, because throw and heave depend on the true dip, not the apparent one.
• Three Point Problem Calculator, to get a plane from three points before measuring offset on it.
• Cross Section Maker for Boreholes, to draw the offset section the numbers describe.
• Well Log Correlation Panel, when the offset is picked from correlated logs rather than mapped.
• USGS Mineral Resources Program, published structural and resource mapping data.