Mark Harms 10/31/081 Stick-Slip Activity Intro Exploring an earthquake model

Mark Harms 10/31/082 += ?

3 What is Stick-Slip? The jerking motion that often occurs when two surfaces are sliding over each other. –The surfaces alternate between sticking and slipping –Common examples Music from a violin (bow across string) Sound of noisy brakes on a car Screeching car tires Glass Harp (wet finger around the rim of a wine glass)

Mark Harms 10/31/084 What is Required for Stick-Slip? The force required to “un-stick” the surfaces is greater than the force required to keep the surfaces moving. –The static coefficient of friction must be higher than the kinetic coefficient of friction A force that varies with displacement is also required. –An elastic (“springy”) material stores elastic energy as it deforms and could supply such a force. Rigid materials are elastic to some degree – even rock!

Mark Harms 10/31/085 The Stick-Slip Cycle One cycle of stick-slip: 1.Surfaces are stuck 2.An external shear force is applied (continuously) 3.Elastic material deforms, storing elastic energy 4.Surfaces remain stuck, since the force delivered to the contact area is less than the force needed to overcome static friction 5.Eventually the force at the contact area overcomes static friction – the surfaces begin to slide 6.Stored energy in the elastic material is released, causing the surfaces to accelerate as they slide past each other 7.As the elastic material returns to its previous shape (elastic rebound) the force delivered to the surfaces decreases until it can no longer overcome kinetic friction and the surfaces stop moving 8.The surfaces are stuck again

Mark Harms 10/31/086 “Stick” “Slip” Stick-Slip on an Earthquake Fault

Mark Harms 10/31/087 += Friction along fault segment Deformed rocks store elastic potential energy Elastic energy released! EARTHQUAKE!

Mark Harms 10/31/088 Earthquake Slip Activity Demo Workshop Activity

Mark Harms 10/31/089 Vocabulary Creep: Slow, steady fault movement. Deformation: The change in shape of an object as a result of the application of stress to it. Elasticity: The property of returning to an initial form following deformation. Elastic rebound: As plates move, elastic strain energy builds along edges, until rocks rupture and return to their undeformed shapes. Strain: deformation of the earth. Static friction: The force between two objects that are not moving relative to each other. Friction that keeps things from moving. Stress: A force applied over an area. Stick-slip: Adjacent surfaces alternating between sticking to each other and sliding past each other.