Modeling Asperities on a Strike-slip Fault with Spaghetti

10min Novice

• Overview
Optional Files 1

An asperity (is an area on a fault that is stuck or locked. In the Earth, tectonic earthquakes are caused by slip along a fault Earthquake Resources movement involves slip on one or more asperities, or “stuck patches” where the friction is highest. Most of the energy that is released by earthquakes comes from the patches that become “unstuck.

Scrap lumber, raw spaghetti, and a ratcheting bar-clamp can be combined to create a physical model of asperities on a fault. In the model the wood represents the fault, the spaghetti represent asperities or stuck patches on the fault, and squeezing the clamp represents tectonic forces. As you slowly apply stress with the clamp, a few spaghetti strands may break (foreshocks) a few seconds prior to many strands breaking in rapid succession (mainshock). This event may be followed by a few remaining strands breaking (aftershocks).

Objectives:

Students will be able to:

• Use the asperity vice to demonstrate and explain asperities on a fault
• Explain the concepts foreshock, mainshock, and aftershock

Related Animations

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.

Animation Novice

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.

Animation Novice

Animation shows the buildup of stress along the margin of two stuck plates that are trying to slide past one another. Stress and strain increase along the contact until the friction is overcome and rock breaks.

Animation Novice

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.

Animation Novice

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

Animation Novice

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.

Animation Novice

Related Lessons

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.

Lesson Novice

Through a demonstration lead by the teacher, the discrepant concept of rocks exhibiting elastic behavior is physically illustrated with an easily obtained, inexpensive model.

Lesson Novice

We encourage the reuse and dissemination of the material on this site as long as attribution is retained. To this end the material on this site, unless otherwise noted, is offered under Creative Commons Attribution (CC BY 4.0) license