Tilted and folded sedimentary beds exposed at The Settlands coast.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Equal geometric scales. coloured beds mark relative ages.

Upright anticline. Fold amplitude 400 m; shortening 10%, with bed volume preserved.

How to read these results

Play or scrub Process to deform the section. Explode separates beds or blocks for inspection; the gap is not a real canyon. Geometry demonstrates structure, not stress, strain history or earthquake timing.

Folds and faults

Compare the rock deformation caused by compression, tension and sideways motion, using folds and faults as evidence.

Drag to rotate. Hold Ctrl and scroll to zoom, or pinch on a touch screen.

Why it happens

Rock layers may bend into folds or break and move along faults. Layer age, orientation and relative movement help distinguish structures that can look similar from one viewing angle.

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Folded strata at The Settlands, Wales. Trace a bed through the exposure to see deformation recorded in solid rock.

Try a comparison

Choose Normal fault and name hanging wall before playing. Reverse the sense of slip with Reverse fault, then compare lateral displacement in Strike-slip.

Reading the result

The deformation is prescribed to reveal structure; it does not solve rock failure or the stresses at a particular site.

A common misunderstanding

The hanging wall is always the side of a fault that moves down.

The hanging wall is defined by its position above an inclined fault plane. It moves down relative to the footwall in a normal fault and up in a reverse fault. Identify the plane and blocks before using their displacement to name the fault type.

Cases

Exam language

Anticline

A fold with the oldest rocks in its core. In a simple upright anticline, the layers arch upwards and dip away from the centre; overturned folds can have different geometry.

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Folded strata at The Settlands, Wales. Trace a bed through the exposure to see deformation recorded in solid rock.

Syncline

A fold with the youngest rocks in its core. In a simple upright syncline, layers dip towards the centre; erosion can leave either a ridge or valley above it.

Normal fault

A fault on which the hanging wall moves down relative to the footwall. It commonly forms where the crust is being extended. Determine movement from displaced layers rather than the present height of the land surface alone.

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Almannagjá, Þingvellir: faults accommodate extension within Iceland's broad North American–Eurasian plate boundary zone.

Reverse fault

A fault on which the hanging wall moves up relative to the footwall, commonly under compression. A low-angle reverse fault is called a thrust. Displaced rock layers help identify motion even after erosion changes the surface.

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Reverse fault in layered igneous rock from Montana's Stillwater Complex. Trace matching layers across the break: the hanging wall moved up relative to the footwall.

Strike-slip

Fault movement that is mainly horizontal and parallel to the fault's strike. Some strike-slip faults form plate-transform boundaries; others lie within plates.

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San Andreas Fault in California's Sierra Madre Mountains. The fault accommodates mainly horizontal motion between the Pacific and North American plates.

Hanging wall

The block above an inclined fault plane. In a normal fault it moves downward relative to the footwall, while in a reverse fault it moves upward. The names describe position relative to the plane, not present elevation.

Footwall

The block of rock below an inclined fault plane. Identify it from the geometry of the plane before describing movement. In a normal fault the hanging wall moves down relative to the footwall; reverse motion is the opposite.

Inversion

In structural geology, the uplift and shortening of a previously subsiding basin. A temperature inversion in meteorology is a different use of the word.

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Chalk cliffs on the Purbeck coast, within the region affected by inversion of the Wessex Basin. The photograph shows the present outcrop; reconstructing earlier subsidence and later compression requires regional geological evidence.

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