Classification of Faults

Summary

This lesson explores how geologists classify and characterize faults, using key terms like dip, strike, hanging wall, and footwall. The video covers different fault types, including normal, reverse, and strike-slip faults, explaining how these are formed by tension, compression, or horizontal motion. Viewers are introduced to the concepts of dip-slip and strike-slip faults, along with the classifications of right-lateral and left-lateral strike-slip faults. Through visual examples and hands-on demonstrations, learners are encouraged to identify and label various fault types, deepening their understanding of fault dynamics and their real-world applications.

Takeaways

• 😀 Earthquakes occur as a result of movements on faults, and understanding fault classification helps predict seismic events.
• 😀 Dip refers to the slope or inclination of a geological surface relative to horizontal, with a steeper slope having a larger dip angle.
• 😀 Strike is a horizontal line drawn on a sloping surface, and it is perpendicular to the dip.
• 😀 Examples of dip and strike include brick mortar joints, where the dip and strike are parallel, and inclined signs and panels.
• 😀 The hanging wall is the block above an inclined fault surface, and the footwall is the block below it. To identify them, move your finger upward along the fault.
• 😀 In vertical faults, there is no hanging or footwall since neither block can be considered above or below the other.
• 😀 Dip-slip faults are classified into normal and reverse faults based on the movement of the hanging wall relative to the footwall.
• 😀 Normal faults occur under tension, with the hanging wall moving downward, and are commonly found at divergent plate boundaries (e.g., oceanic ridges).
• 😀 Reverse faults occur under compression, with the hanging wall moving upward, and are typically found at convergent plate boundaries.
• 😀 Strike-slip faults involve horizontal displacement with minimal vertical movement, often occurring along transform plate boundaries.
• 😀 Strike-slip faults are classified as either right-lateral or left-lateral based on the direction of displacement when observing across the fault.
• 😀 The San Andreas Fault is an example of a right-lateral strike-slip fault, where features on opposite sides of the fault appear displaced to the right.

Q & A

What is the definition of 'dip' in geology?

Dip refers to the slope or inclination of a geological surface, measured relative to horizontal. The steeper the slope, the larger the dip angle.

How is 'strike' defined in geology?

Strike is any horizontal line drawn or inscribed on a sloping surface. It is perpendicular to the dip and represents the direction of the line that intersects the sloped surface.

How do dip and strike relate to each other?

Dip and strike are perpendicular to each other, meaning they are at a 90-degree angle. While dip refers to the inclination of the surface, strike refers to the horizontal line on the surface.

What are 'hanging wall' and 'footwall' in fault terminology?

The hanging wall is the block of rock above an inclined fault surface, while the footwall is the block below the fault surface. These terms help identify the relative positions of blocks during fault movements.

What is a 'dip-slip fault'?

A dip-slip fault occurs when the hanging wall moves up or down the fault surface parallel to the dip direction. There are two types: normal faults (hanging wall moves down) and reverse faults (hanging wall moves up).

What is the difference between normal and reverse faults?

In normal faults, the hanging wall moves down relative to the footwall, typically under tension. In reverse faults, the hanging wall moves up relative to the footwall, usually formed under compression.

How do tension and compression affect fault formation?

Tension causes rocks to move apart or diverge, forming normal faults, while compression causes rocks to move together, leading to reverse faults.

What is a 'strike-slip fault'?

A strike-slip fault is a type of fault where rocks move horizontally with little to no vertical displacement. It occurs primarily at transform plate boundaries.

How can you classify a strike-slip fault as 'right lateral' or 'left lateral'?

A strike-slip fault is classified as right lateral if, when standing on one side of the fault, you must look to the right to match features across the fault. It is left lateral if you must look to the left.

Can you identify the type of fault based on the movement of trees or streams?

Yes, by observing the offset of trees, streams, or other natural features across the fault line, you can determine whether the fault is right lateral or left lateral. For example, if a feature moves to the right, it's a right lateral fault; if it moves to the left, it's a left lateral fault.