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: 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
Reverse Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
2.) Normal Faults A type of fault where the hanging wall slides downward Tension forces cause normal faults
Normal Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
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
Strike-Slip Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en
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 the three types of fault Checkpoint: What are the three types of fault? What force of deformation produces each? (tension, compression or shearing?) Strike-slip faults Produced by shearing Normal faults Produced by tension Reverse 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