CLASSIFYING GEOLOGICAL FAULTS

classify geological faults according to the angle of the fault plane and direction of slip;

What is a geological fault?

A geological fault is a fracture in Earth’s crust where rocks on either side move relative to each other due to tectonic forces.

What determines the classification of a fault?

Faults are classified based on:

1. Angle of the fault plane, and

2. Direction of slip (movement) of the rock blocks.

What is the fault plane?

The fault plane is the flat or sloping surface along which rocks move during a faulting event.

Define “hanging wall” and “footwall.”

• Hanging wall: The block of rock above the fault plane.

• Footwall: The block of rock below the fault plane.

What is a normal fault?

A normal fault occurs when the hanging wall moves downward relative to the footwall due to tensional forces (pulling apart).

What is the angle of the fault plane in a normal fault?

Normal faults typically have a steep angle where the hanging wall drops downward along the fault plane.

What is a reverse fault?

A reverse fault occurs when the hanging wall moves upward relative to the footwall due to compressional forces (pushing together).

What is the angle of the fault plane in a reverse fault?

Reverse faults usually have a steep fault plane, similar to normal faults, but movement is upward.

What is a thrust fault?

A thrust fault is a type of reverse fault with a shallow, low-angle fault plane (< 45°) where the hanging wall moves up and over the footwall.

What is a strike-slip fault?

A strike-slip fault involves horizontal movement of rock blocks where the fault plane is nearly vertical and the slip is side-to-side.

Distinguish left-lateral and right-lateral strike-slip faults.

• Left-lateral: The block across the fault moves to the left.

• Right-lateral: The block across the fault moves to the right.

Which types of faults are most common in the Philippines?

The Philippines commonly experiences:

• Reverse and thrust faults (due to convergent boundaries)

• Strike-slip faults, especially along the Philippine Fault Zone (PFZ)
  QR Suggestion: PHIVOLCS map showing fault systems.