Geology · Year 12 · Geological Structures and Maps · 4.º Período

Faults and Folds

Classify different types of faults (normal, reverse, strike-slip) and folds (anticlines, synclines). Understand the tectonic regimes that produce these geological structures.

TL;DR:Faults and folds are the visible scars of tectonic movement. In this topic, students learn to classify these structures with precision, distinguishing between normal, reverse, and strike-slip faults, as well as anticlines and synclines. This is a fundamental skill for the OCR A-level, requiring students to link specific geometries to the tectonic regimes that produced them (e.g., extension vs. compression).

• National Curriculum Attainment Targets
• OCR Geology AS/A-level: 4.2.1 Fault classification
• OCR Geology AS/A-level: 4.2.2 Fold geometry

About This Topic

Faults and folds are the visible scars of tectonic movement. In this topic, students learn to classify these structures with precision, distinguishing between normal, reverse, and strike-slip faults, as well as anticlines and synclines. This is a fundamental skill for the OCR A-level, requiring students to link specific geometries to the tectonic regimes that produced them (e.g., extension vs. compression).

Students will move beyond simple identification to understand the 3D orientation of these features, using terms like dip, strike, and axial plane. They will also explore how these structures influence the landscape and the location of natural resources. This unit is highly visual and spatial, forming the basis for map interpretation and field geology.

Students grasp this concept faster through structured discussion and peer explanation, where they must use 3D models to demonstrate how a fault moves or how a fold is oriented in space.

Key Questions

1. How are normal and reverse faults distinguished?
2. What tectonic forces create anticlines and synclines?
3. How can fault movement be measured in the field?

Watch Out for These Misconceptions

Common Misconception

An anticline is always a hill and a syncline is always a valley.

What to Teach Instead

Folds refer to the 'age' and 'dip' of the rock layers, not the surface topography. Erosion can turn an anticline into a valley (an anticlinal valley). Comparing a structural map to a topographic map helps students see the difference.

Common Misconception

The 'hanging wall' is always the one that moves.

What to Teach Instead

Both sides of a fault move relative to each other. The terms 'hanging wall' and 'footwall' are just names based on the geometry of the fault plane. Using a 'tunnel' analogy (where you walk on the footwall and hang a lamp on the hanging wall) clarifies the naming convention.

Active Learning Ideas

Simulation Game

Fault Blocks

Using 'fault blocks' (wooden or foam blocks cut at angles), students model different fault types. They must move the blocks to show tensional and compressional movement and identify the 'hanging wall' and 'footwall' for each.

30 min·Pairs

Gallery Walk

Fold Geometry

Stations show photos and diagrams of various folds (symmetrical, asymmetrical, recumbent). Students move between stations to identify the axial plane and limb dip, and then sketch how these would look on a flat map.

40 min·Small Groups

Inquiry Circle

Tectonic Reconstruction

Groups are given a map with several faults and folds. They must work backwards to determine the sequence of tectonic forces (e.g., 'first it was squeezed, then it was pulled apart') that created the complex pattern.

50 min·Small Groups

Frequently Asked Questions

How do I tell the difference between a normal and reverse fault?

Look at the hanging wall (the block above the fault plane). In a normal fault, the hanging wall moves down relative to the footwall, caused by tension. In a reverse fault, the hanging wall moves up, caused by compression.

What is the difference between an anticline and a syncline?

An anticline is an arch-like fold where the oldest rocks are in the centre (the core). A syncline is a trough-like fold where the youngest rocks are in the centre. In an anticline, the layers dip away from the centre; in a syncline, they dip towards it.

What are the best hands-on strategies for teaching faults and folds?

Physical 3D models are the most effective tool. Having students build their own 'paper models' of faults or use 'folding boxes' with layers of sand allows them to see the relationship between the internal structure and the surface expression. This bridges the gap between a 2D diagram and a 3D geological reality.

What is a strike-slip fault?

A strike-slip fault is a structure where the dominant displacement is horizontal, parallel to the strike of the fault. These are caused by shear stress. A famous example is the San Andreas Fault in California.