earth's crust in motion. earthquakes so…. what is an earthquake? and… what are some things...
TRANSCRIPT
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Earth's Crust Earth's Crust in Motionin Motion
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Earthquakes
• So….• What is an Earthquake?• And…• What are some things that can cause them?
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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.
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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.
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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?
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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?
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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!!!
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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
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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?
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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?
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Normal Faults
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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?
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Reverse Faults
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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
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Mountains Formed by Faulting 16.When normal faults uplift a block
of rock, a fault-block mountain forms.
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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!
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Mountains Formed by Folding
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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.