Transcript File
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 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 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 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? 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