## Earthquake Machine: Demonstration of the 2-block Model

### How can we model differential friction along a fault?

THE two-block "Earthquake Machine" model uses two blocks with different grit sandpaper to model interactions between adjacent patches on a fault. The two-block model demonstrates how motion on one area of a fault can increase stress on an adjacent area, bringing it closer to failure in an earthquake. The yellow line plots the steady displacement of the hand. The red line shows the strain on the rubber band between the hand and the red block. The strain drops suddenly to a lower level each time the red block slips (earthquake slip). There is low friction between the red block and the surface, so "earthquakes" tend to be more frequent and smaller. The blue line shows the strain on the rubber band between the blocks. The blue block has higher friction with the surface, so it tends to slip in larger "earthquakes."

#### Keypoints:

• Block-and-sandpaper model can be used to teach the concept of elastic rebound and how energy is stored and released.
• Physics concepts: sliding and static friction, conversion of energy from one form to another; the elastic properties of materials.
• Motion on one area of a fault can increase stress on an adjacent area
• Strain is released during “earthquakes”

Level: Intermediate

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