Faults and Earthquakes

• A fault is a break or fracture between two blocks of rocks due to stress.
• One block moves relative to the other.
• The fault plane is the surface along which the blocks move.

Relationship of Fault and Earthquake

• Faulting causes earthquakes.
• Earthquakes can occur when rocks are initially broken to create a fault, or when an already existing fault is moved or re-activated.

Fault Movement & Earthquakes

• An earthquake is caused by a sudden slip on a fault.
• Tectonic plates move slowly but get stuck because of friction.
• When the stress overcomes the friction, an earthquake occurs, releasing energy that travels through the earth's crust, causing shaking.
• The focus is where the slip happens below ground.
• The epicenter is where the shaking is first felt above ground, directly above the focus.

Three Types of Stress

• Tension: Rocks stretch and break to produce a fault.
• Compression: Rocks fold and break to produce a fault.
• Shear: Forces producing shear strain result in a fault.

Terminology

• Strike: A horizontal line along the direction of a fault plane.
• Dip: The angle between the fault plane and the horizontal.
• Hanging wall: The block above the fault plane.
• Foot wall: The block below the fault plane.

Normal Fault

• The hanging wall moves down in relation to the foot wall.
• Caused by tensional stress.

Reverse Fault

• The hanging wall moves up relative to the foot wall.
• Caused by compressional stress.

Strike-Slip Fault

• Exists between two pieces of crust.
• Horizontal movement, where the sides slide past each other.