Deforming Earths Crust Deforming the Earths Crust Deformation

Deforming Earth’s Crust

Deforming the Earth’s Crust Deformation is the process of changing the shape of rock because of stress. Stress - A force that acts on rock to change its shape or volume ► Layers of rock bend when enough stress is applied to them. ► They can eventually reach their elastic limit and break.

There are 3 types of stress: 1. 2. 3. Compression Tension Shearing

1) Compression occurs when two tectonic plates collide or are squeezed together. ►When compression occurs at convergent boundaries, large mountain ranges can form.

2. ) Tension occurs when forces act to stretch on object. § This occurs at divergent boundaries.

3. ) Shearing: Stress that pushes a mass of a rock in opposite, horizontal directions. ► This occurs at transform boundaries

Some rocks break when stress is applied to them. ► The surface along which rocks break and slide past each other is called Fault. ► A fault is classified as a hanging wall or foot wall when it is not vertical. ► A hanging wall is the block of rock above the fault. A foot wall is the block below the fault.

3 Types of Faults ► Reverse ► Normal ► Strike-slip

2. ) Reverse Faults • A type of fault where the hanging wall slides up • Compression forces cause reverse faults

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2. ) Normal Faults • A type of fault where the hanging wall slides downward • Tension forces cause normal faults

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3. Strike-Slip Faults ►A type of fault where rocks on either side move past each other sideways with little up -or down motion. ► Shearing causes these types of faults

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Summary: Why do faults form and where do they occur? ► Faults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the crust so much that the crust breaks

Checkpoint: What are three types of fault? What force of deformation produces each? (tension, compression or shearing? ) ► Strike-slip faults ►Produced ► Normal by shearing faults ►Produced ► Reverse by tension faults ►Produced by compression

What is friction? ►A force that opposes the motion of one surface as it moves across another surface ► Friction exists because… surfaces are not perfectly smooth.

What occurs when the friction along a fault line is low? ► The rocks on both sides of the fault slide by each other without much sticking What occurs when the friction along a fault line is moderate? ► The sides of the fault jam together ► From time to time they jerk free ► Small earthquakes occur

What occurs when the friction along a fault line is high? ► Both sides of the fault lock together and do not move ► The stress increases until it is strong enough to overcome the force of friction ► Larger and/or more frequent earthquakes will occur

Checkpoint: The San Andreas fault in California is a transform boundary that contains _? __ stress. § high