How is stress stored between tectonic plates?
Animation shows the buildup of stress along the margin of two stuck plates that are trying to slide past one another. They eventually rupture along the fault. The rock is deformed as it builds up strain in the plates; stress increases along the contact. Rock is deformed as it builds up strain in the plates at locked plate boundaries. Stress and strain increase along the contact until the friction is overcome and rock breaks. Actual video footage of a grove of oak trees taken by a USGS camera on Sep. 28, 2004. The camera, stationed along the San Andreas Fault, is part of a monitoring effort to increase our understanding of earthquake behavior. This camera records a snapshot image every 5 minutes until ground motion triggers the video camera to record continuously. About 6 seconds into the clip the M6.0 Parkfield earthquake shakes the ground.
Left-lateral fault strike slip fault with little or no friction along fault contact. There is no deformation of the rock adjacent to contact. If the block opposite an observer looking across the fault moves to the left, the motion is termed left lateral.
Left-lateral fault strike slip fault with low friction along fault contact. There is no deformation of the rock adjacent to contact. If the block opposite an observer looking across the fault moves to the left, the motion is termed left lateral. Example: the San Andreas Fault of California
In a strike-slip fault, the movement of blocks along a fault is horizontal. The fault motion of a strike-slip fault is caused by shearing forces. Other names: transcurrent fault, lateral fault, tear fault or wrench fault. Examples: San Andreas Fault, California; Anatolian Fault, Turkey.
A transform fault is a type of strike-slip fault wherein the relative horizontal slip is accommodating the movement between two ocean ridges or other tectonic boundaries. They are connected on both ends to other faults.
An asperity is an area on a fault that is stuck or locked. Scientists study areas along long fault zones that have not had earthquakes in a long time in order to determine where the next earthquake may occur. As long faults move, all areas of it will, at some point, become "unstuck" causing an earthquake relative to the the size of the asperity that finally breaks.
View looking into a fault zone with a single asperity. Regional right lateral strain puts stress on the fault zone. A single asperity resists movement of the green line which deforms before finally rupturing.
This demonstration, squeezing uncooked spaghetti noodles in a wood template set in a vise, effectively shows how asperities (stuck patches) on a fault rupture at different times.
How can I demonstrate plate tectonic principles in the classroom?
Video lecture demonstrates the use of foam faults to demonstrate faults, and a deck of cards to demonstrate folds and fabrics in rock layers. Different types of faults include: normal (extensional) faults; reverse or thrust (compressional) faults; and strike-slip (shearing) faults.
Using a block-and-sandpaper model, students collaborate in small groups to investigate how energy is stored elastically in rocks and released suddenly as an earthquake (the earthquake cycle). This activity emphasizes the role of mechanical models in understanding and testing ideas in science.
