Earth's Crust Earth's Crust in Motionin Motion

Earthquakes

• So….• What is an Earthquake?• And…• What are some things that can cause them?

Stress in the Crust

1. An earthquake is the shaking that results from the movement of rock beneath Earth's surface.

– This is a super powerful force!!!

– These forces are examples of stress.

2. Stress is a force that acts on rock to change its shape or volume.

Types of Stress3. There are three different kinds of stress

that occur in the Earth’s crust…– Shearing– Tension– Compression

• All of this stress works over millions of years to change the shape of rock.

4. So…Any change in the shape of Earth's crust is called deformation.

Shearing 5. Stress that pushes a mass of rock in two

opposite directions is called shearing.

• Shearing can cause two slabs of rock to slip past each other like the picture below.

• What feature in California is an example of this?

Tension 6. Tension is a stress that pulls on the crust,

stretching rock so that it becomes thinner in the middle.

• Tension occurs where two plates are moving apart.

• Think of pulling a Milky Way candy bar apart.

• What ocean feature is this an example of?

Compression 7. Compression is a stress force that

squeezes rock until it folds or breaks.

• One plate pushing against another plate can compress rock easily….

• Almost like Mr. Wise’s strength!!!

Kinds of Faults• When enough stress builds up in rock, the rock

can break, creating a fault.

8.A fault is a break in the crust where two slabs of crust slip past each other.

• The rocks on both sides of a fault can either move up or down or sideways.

• Faults usually occur along plate boundaries

9.There are three main types of faults: • Strike-slip faults• Normal faults• Reverse faults

Strike-Slip Faults   10.Shearing creates strike-slip faults.

11. In a strike-slip fault, the rocks on either side of the fault slip past each other sideways

• A strike-slip fault that forms the boundary between two plates is called a transform boundary.

• What fault in California is an example of this?

Normal Faults   12. Tension forces in Earth's crust

cause normal faults.

13. In a normal fault, the fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault.

• Tension forces create normal faults where plates diverge, or pull apart.

• What ocean feature is an example of this?

Normal Faults

Reverse Faults   14.Compression forces produce

reverse faults.

15. A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

• What geologic feature is an example created by compression?

Reverse Faults

Mountain Building• The forces of plate movement can build up Earth's surface.

• Over millions of years, fault movement can change a flat

plain into a towering mountain range

Mountains Formed by Faulting 16.When normal faults uplift a block

of rock, a fault-block mountain forms.

Mountains Formed by Folding • Under certain conditions, plate movement can

cause crust to fold.

17.Folds are bends in rock that form when compression shortens and thickens part of Earth's crust.

• The collisions of two plates can cause compression and folding of the crust.

• Some of the world's largest mountain ranges, such as the Himalayas and the Alps, formed when pieces of the crust folded during the collision of two plates.

• Such plate collisions also lead to earthquakes!

Mountains Formed by Folding

Anticlines and Synclines   18.A fold in rock that bends upward into an arch is an

anticline.

19.A fold in rock that bends downward in the middle to form a bowl is a syncline.

• Anticlines and synclines are found on many parts of Earth's

surface where compression forces have folded the crust.